Scipedia: Documents published in 2021

Geomechanical Modeling Using Variable Order Spectral Element Method at Non-Conformal Meshes

Scipedia content — Thu, 11 Mar 2021 16:59:11 +0100

The paper considers an overview of the problems of mathematical modeling of geomechanical processes occurring in rocks during the geological exploration and development of reservoirs and well boring process. The mathematical formulation is based on the theory of repeated superposition of large deformations. A numerical discretization of the posed boundary problems of interacting solids is performed using a discontinuous spectral element method and multi-point constraints at non-matching mesh interfaces between interacting solid rock structures. Several industrial applications of the developed approach are considered. Seismic wave propagation in the heterogeneous media with initial geomechanical stresses is considered. A modelling of an induced anisotropy is performed by the superposition of dynamic deformations onto initial generally finite strains. Use of variable order spectral elements at non-conformal meshes allows one to simplify the process of unstructured mesh generation for the discretization of complex geological models and to set the local spatial order of the SEM discretization depending on the speed of seismic waves in geological structures, which significantly reduces the computational costs when conducting numerical modeling and lowers the requirements to the model preprocessing and mesh quality. The considered approach allows predicting in more detail the behavior of the rock during reservoir development, taking into account different stages of the field deformations. In particular, the redistribution of accumulated deformations during multistep loading and / or changes in the structure (topology) of the loaded body, as well as contact conditions of adhesion / sliding at the interlayer boundaries and bonded contacts are taken into account. These problems were solved using CAE Fidesys software, which allows solving static and dynamic problems of geomechanics and geophysics using finite (FEM) and spectral (SEM) element methods of a variable approximation order in space at non-conformal unstructured meshes.

SPH-DEM Coupling for Debris Flows

Scipedia content — Thu, 11 Mar 2021 16:59:02 +0100

Debris flows are natural events with a high potential of damage due to the materials, volume, and velocity they can reach once the flows were triggered. Mathematical models and numerical schemes constitute a transcendental way to get a deeper comprehension of these natural phenomena. Thus, the coupling of numerical methods is becoming more relevant to describe the behaviour of debris flows. The coupling of Smooth Particle Hydrodynamics (SPH) and Discrete Element Method (DEM) is presented in this work to show the capability to represent the interaction of several materials simultaneously. SPH is employed to represent the fluid and soil by using different constitutive models, from a continuum approach. On the other hand, DEM describes immersed objects to represent large boulders and unmoveable boundary conditions. Thus, it is possible to couple the behaviour occurring at very different scales, fines and water through the continuum approach, and boulders with the discrete one. A hypothetical case here presented shows the potential of our coupling method for simulating debris flows.

Robust and Efficient Large Deformation Analysis of Kirchhoff–love Shells: Locking, Patch Coupling and Iterative Solution

Scipedia content — Thu, 11 Mar 2021 16:58:53 +0100

Isogeometric Kirchhoff-Love elements have received an increasing attention in geometrically nonlinear analysis of thin walled structures. They make it possible to meet the C1requirement in the interior of surface patches, to avoid the use of finite rotations and to reduce the number of unknowns compared to shear flexible models. Locking elimination, patch coupling and iterative solution are crucial points for a robust and efficient nonlinear analysis and represent the main focus of this work. Patch-wise reduced integrations are investigated to deal with locking in large deformation problems discretized via a standard displacement-based formulation. An optimal integration scheme for third order C2NURBS, in terms of accuracy and efficiency, is identified, allowing to avoid locking without resorting to a mixed formulation. The Newton method with mixed integration points (MIP) is used for the solution of the discrete nonlinear equations with a great reduction of the iterative burden and a superior robustness with respect to the standard Newton scheme. A simple penalty approach for coupling adjacent patches, applicable to either smooth or non-smooth interfaces, is proposed. An accurate coupling, also for a nonmatching discretization, is obtained using an interface-wise reduced integration while the MIP iterative scheme allows for a robust and efficient solution also with very high values of the penalty parameter.

Chance Constraint Optimization of a Complex System: Application to the Fatigue Design of a Floating Offshore Wind Turbine Mooring System

Scipedia content — Thu, 11 Mar 2021 16:58:45 +0100

In this paper, we seek to minimize the cost of the anchoring system of a floating offshore wind turbine under reliability constraints. Taking into account the uncertainties on the model, on the resistance threshold and on the environmental conditions implies constraints expressed as probabilities depending on random vectors and a piecewise stationary Gaussian process. The main difficulty of the studied problem is to compute these probabilities since reliability methods require many calls to the simulator of the system. We propose in this paper a two-step methodology allowing to solve the optimization problem with a reasonable number of calls to the simulator. First, we exploit the properties of the problem to reformulate the constraints into easier to compute ones. Then we propose a new approach based on adaptive kriging well suited to the reformulated problem: AK-ECO.

Accuracy of Neural Networks for Surrogate Modelling of the Sag of Hanging Cables

Scipedia content — Thu, 11 Mar 2021 16:58:38 +0100

The creation of surrogate models is a classical problem in Machine Learning. The present paper is a case study of training a surrogate model for a real-life engineering problem: the computation of the sag of a cable hanging between two pylons. Neural networks have been trained using samples of the solution for several physical parameters. A parametric study of the role of three hyperparameters (the number of training samples, the size of the network and the initialization of gradient descent) is presented.

Characterization of the Viscoelastic Behaviour of Gears Oils by EHL Simulation

Scipedia content — Thu, 11 Mar 2021 16:58:31 +0100

Within the scope of this work, the friction in the lubricating gap between elliptical contact of two surfaces operating under full-film lubrication was experimentally and simulatively investigated. The experimental examination of fluid friction was carried out on a twin-disc-machine by varying the load and slide-to-roll-ratio at constant hydrodynamic velocity and oil inlet temperature. As results, traction curves are obtained which show the change of the coefficient of friction or the shear stress respectively as a function of the slide-to-roll-ratio. From measurements, the maximum shear stress is obtained, which is used for the numerical determination of traction curves. To this end, the EHL theorieis is used, taking into account the pseudoplastic and the viscoelastic behaviour of the lubricant. In this work, two gear oils based on polyalkylene glycol were used as examples of lubricants used in modern worm gearboxes.

A Simplified Blade Model for Reliable Seismic Assessments of Wind Turbines

Scipedia content — Thu, 11 Mar 2021 16:58:24 +0100

Wind turbines are dynamically complex structures. They entail slender towers, flexible foundations, and heavy rotor-nacelle-assembly (RNA). In the context of earthquake analysis, the RNA is often simplified as a rigid point mass which can suppress the modal contribution of blades from the global system dynamics and may further affect the reliability of seismic response of wind turbines. Other high-fidelity finite element (FE) blade models are difficult to implement due to the complex layup of composite materials and reduced computational efficiency. Thus, there is a need for an intermediate solution that allows the realistic and accurate consideration of blades in the seismic assessment of wind turbines. This study presents a meta-heuristic, problem-independent optimisation method, known as the genetic algorithm (GA), to identify simplified material and cross-sectional properties of a typical wind turbine blade. The properties are used to construct a simplified FE blade model that can be implemented in global wind turbine models. The optimised design solutions are examined with regards to the mechanical and dynamic response of a reference 5MW wind turbine having 61.5 m long blades. The accuracy of the modal behaviour validates the presented optimisation and simplified blade modelling approach and signifies the potential of its application in seismic assessments of wind turbines.

Reversible Order-Disorder Transition in Ettringite-Metaettringite Conversion

Scipedia content — Thu, 11 Mar 2021 16:58:16 +0100

The stability of ettringite under sorption and the conversion into metaettringite are studied using hybrid Grand Canonical Monte Carlo (GCMC) and (classical) Molecular Dynamics (MD) simulations sampling the osmotic ensemble. The desorption branch obtained from simulation and the associated volume changes are in agreement with the experimental evidence. We pay special attention to the structural changes at low RH, which is associated with metaettringite conversion, which is recognized as a disordered polymorph of ettringite with an unknown structure to date. We show that the conversion of ettringite into metaettringite is associated with an increase in entropy. The adsorption branch obtained from simulations is reversible in the ettringite domain in agreement with experiments. The reversibility in the conversion of metaettringite into ettringite, which is observed experimentally, is not captured by the simulation approach adopted. The large deformations associated with ettringite desorption make it difficult to capture reversibility with a direct sampling of the osmotic ensemble. Further, we discuss the role of hydrogen bonds on the hysteresis observed in sorption cycles in ettringite.

DNS of Near Wall Dynamics of Premixed CH4/Air Flames

Scipedia content — Thu, 11 Mar 2021 16:58:06 +0100

This work presents a numerical study on the effect of flame-wall interaction (FWI) from the viewpoint of flame dynamics. For that purpose, direct numerical simulations (DNS) employing detailed calculations of reaction rates and transport coefficients have been applied to a 2D premixed methane/air flame under atmospheric condition. Free flame (FF) and side-wall quenching (SWQ) configurations are realized by defining one lateral boundary as either a symmetry plane for the FF or a cold wall with fixed temperature at 20 oC for the SWQ case. Different components of flame stretch and Markstein number regarding tangential, normal (due to curvature) and total stretch, Kas , Kac and Katot = Kas + Kac, as well as their correlations with respect to the local flame consumption speed SL have been evaluated. It has been shown that the FWI zone is dominated by negative flame stretch. In addition, SL decreases with decreasing normal stretch due to curvature Kac while approaching the cold wall. However, SL increases with decreasing Kac while approaching the symmetry boundary for the free flame case, leading to an inversion of the Markstein number Matot based on Katot from positive in the free flame case to negative in the SWQ case. The quenching distance evaluated based on wall-normal profiles of SL has been found to be approximately equal to the unstretched laminar flame thickness, which compares quantitatively well with measured data from literature. The flame speed has been confirmed to scale quasi-linearly with the stretch in the FWI zone. The results reveal a distinct correlation during transition between FWI and FF regarding flame dynamics, which brings a new perspective for modeling FWI phenomena by means of flame stretch and Markstein number. To do this, the quenching effect of the wall may be reproduced by a reversed sign of the Markstein number from positive to negative in the FWI zone and by applying the general linear Markstein correlation (SL/SL,0 = 1− Ma ·Ka), leading to a decrease of the flame speed or the reaction rate in the near-wall region.

Open Issues on the EAS Method and Mesh Distortion Insensitive Locking-Free Low-Order Unsymmetric EAS Elements

Scipedia content — Thu, 11 Mar 2021 16:57:59 +0100

One of the most popular mixed finite elements is the enhanced assumed strain (EAS) approach. However, despite numerous advantages there are still some open issues. Three of the most important, namely robustness in nonlinear simulations, hourglassing instabilities and sensitivity to mesh distortion, are discussed in the present contribution. Furthermore, we propose a novel Petrov-Galerkin based EAS method. It is shown that three conditions have to be fulfilled to construct elements that are exact for a specific displacement mode regardless of mesh distortion. The so constructed novel element is lockingfree, exact for bending problems, insensitive to mesh distortion and has improved coarse mesh accuracy.

A P1/P1 Finite Element Framework for Taking Into Account Capillary Effects in Biphasic Flow Simulations

Scipedia content — Thu, 11 Mar 2021 16:57:50 +0100

This work describes a computational strategy, based on a stabilised finite element method, to simulate bifluid flow with capillary effects in a fibrous microstructure. In this framework, triple junction equilibrium is imposed as a natural condition in the weak formulation of the Stokes problem. Two types of 2D microstructures are then considered, hexagonal and random, and studied in terms of numerical permeability and capillary pressure.

Time Steps V.S Cohesion in Non-Smooth Contact Dynamics Algorithm

Scipedia content — Thu, 11 Mar 2021 16:57:43 +0100

We present the equations obeyed by contacts forces in a granular system solved by the Contact Dynamics algorithm. We consider their resolution in a very simple case of cohesive interaction, i.e.for a straightforward two-body 2D normal collision. The equations predict that increasing time steps should coincide with an increase of the effective cohesion of the systems. Numerical simulations are performed to verify the predictions, in the case of cohesive granular piles falling in the gravity field. A discussion on how a seemingly purely numerical quantity may end up being a non-trivial ingredient in the physics of the simulated system ensues.

LDG Method with P-Adaptivity Applied to LES of Blade-Vortex Interaction

Scipedia content — Thu, 11 Mar 2021 16:57:35 +0100

In the present work the Local Discontinuous Galerkin (LDG) method with polynomial adaptivity is applied to the Large Eddy Simulation (LES) of the parallel blade-vortex interaction (BVI). The BVI phenomenon occurs on helicopter and drone rotors in manoeuvring conditions and it produces impulsive changes in the pressure distributions, vibrations and noise. To deeply understand the mechanism of load generation related to the pressure field and three dimensional perturbations growth, to focus on the interaction between the vortex and the three dimensional structures in boundary layer and wake, accurate 3D unsteady numerical simulations of turbulent flows are necessary. For this reason, it is very important the use of a numerical code based on high order schemes such as LDG. Moreover, in the LDG approach, the numerical resolution can be varied on each element and in time, adapting to the requirement of the simulated flow and saving a large amount of computing resources. In the used numerical code the criterion for variation of the polynomial order is based on a refinement indicator especially suited for LES and based on the structure function. The local polynomial representation directly provides a means to separate large from small scale modes, thus providing the starting point for the definition of the subgrid scale models. In the present simulations, the subgrid scales contribution is represented with a sophisticated dynamic anisotropic subgrid model, suitable and well tested for wall resolved LES and complex separated turbulent flows. The BVI is simulated highlighting the effect of the vortex on the pressure distributions, on the boundary layer separation and on the resulting forces.

Comparing Principal Component Analysis (PCA) and -Variational Autoencoder (ß-VAE) for Anomaly Detection in Selective Laser Melting (SLM) Process Data

Scipedia content — Thu, 11 Mar 2021 16:57:28 +0100

The usability of machine learning approaches for the development of in-situ process monitoring, automated anomaly detection and quality assurance for the selective laser melting (SLM) process receives currently increasing attention. For a given set of real machine data we compare two established methods, principal component analysis (PCA) and -variational autoencoder (ß-VAE), for their applicability in exploratory data analysis and anomaly detection. We introduce a PCA-based unsupervised feature extraction algorithm, which allows for root cause analysis of process anomalies. The ß-VAE enables a slightly more compact dimensionality reduction; we consider it an option for automated process monitoring systems.

Optimization Loop Algorithm for Adsorbed Natural Gas Storage Systems

Scipedia content — Thu, 11 Mar 2021 16:57:19 +0100

In the past few years, the development of inverse design and optimization methods has opened up new possibilities. The so-called Adjoint method is of great significance in that context, since it permits high fidelity to flow-physics at comparatively low computational costs. The present work is a sequel of a previous one presented in WCCM2018, called 'On the use of the Adjoint Method to evaluate sensitivities in adsorbed natural gas storage systems'. where one have developed and validated an Adjoint based approach to computing sensitivity derivatives for adsorbed natural gas (ANG) storage systems. The main goal of this work is to, by using the approach to compute sensitivities presented before, obtain and validate a basic structure of an optimization loop algorithm (OLA) for optimization of natural gas storage systems. Both flow and Adjoint solvers, which were previously developed, are assembled in FREEFEM++ platform. The OLA consists on solving sequential problems to achieve an optimal configuration of parameters that maximize/minimize an objective functional. It starts by solving the primal problem (flow solver), which consists in a physics flow solution, followed by the dual problem, based on the Adjoint Method. With both solutions, the OLA receives the sensitivity derivatives with respect to parameters and, if the configuration is not the optimal, a new values of parameters is obtained and the cycle restarts. To validate the OLA, we make use of the inverse design optimization, defining the objective functional as the mean square error, MSE, of the actual density of adsorption distribution q, with respect to an user--defined target distribution, qt. The strategy is generated a target distribution with a known filling flow curve and the OLA, starting the optimization cycles with other flow curve, minimizing the functional, finding the same curve as we use to generate qt. The results of the several tests showed that the OLA have the capacity to regenerate the original curves, proving the consistency of the source code. The next step for the future researchers is the application for the engineering purposes, by using operational requirements to optimize the process.

Eulerian Multi-Fluid Model for Polydisperse Flows

Scipedia content — Thu, 11 Mar 2021 16:57:11 +0100

This work restricts the term multiphase only to disperse flows, where one of the phases is present in the form of particles, droplets or bubbles, which are suspended within the continuous phase. The dispersed elements can vary in size. The proposed method uses the classes method in the Euler-Euler framework to handle the flow's polydisperse nature. With this approach, every droplet/bubble/particle class is treated like a different phase in the calculation, i.e. every size class has its continuity and momentum equation. However, the pressure is shared among all phases. The derived model is tested for various polydisperse flows, which display the developed model's capability to predict such complex dynamic behaviour. These test cases include complex bubbly flows and dense spray (where droplet sizes vary significantly).

A stable variational formulation for non-ordinary state-based peridynamics

Scipedia content — Thu, 11 Mar 2021 16:57:03 +0100

The paper builds a stable variational formulation for the non-ordinary state-based peridynamics (NOSB-PD). Firstly, a new force state vector is reformulated by introducing the first Piola-Kirchhoff stress in continuum mechanics. The consistency of the new governing equation of the proposed pridynamic model and classical continuum mechanics is proved. Secondly, a stable variational formulation of non-ordinary state based peridynamics is developed to unify the boundary conditions in peridynamcis and continuum mechanics. The zero mode oscillations of non-ordinary state based peridynamics is also eliminated by penalty method in numerical implementation. Numerical examples are illustrated to validate the proposed method. Numerical solutions obtained by the proposed method also indicate that the proposed method can well capture the general nonlinear behavior of solid materials.

The Simulation of Rockfill in a Characteristic of Three-Dimensional Strength

Scipedia content — Thu, 11 Mar 2021 16:56:55 +0100

To study the three-dimensional strength characteristics of rockfill material under an anisotropic state, the anisotropic state variables were introduced into the Mohr-Coulomb failure criterion, and the failure criterion describing the three-dimensional strength of rockfill which was obtained in linear form in this paper. The anisotropic state variables were established with the fabric of rockfill particles. Based on the experimental results of a large triaxial consolidated drained test, fractal dimension theory was introduced to study the relationship between strength and deformation characteristics under different gradation and confining pressures. The experimental results and simulation have shown that: (1) The fractal theory can be used to quantitatively describe the rockfill particles crushing with all kinds of grades under different stress levels. (2) The fabric of rockfill particles was closely related to the three-dimensional strength characteristics. (3) The anisotropic state variables can describe the three-dimensional strength characteristics of rockfill well from a microscopic perspective.

Numerical Simulation of Temperature-Driven Free Surface Flows, with Application to Laser Surface Melting

Scipedia content — Thu, 11 Mar 2021 16:56:48 +0100

A mathematical model coupling the heat and fluid flow with solidification and free surfaces is presented. The numerical method relies on an operator splitting strategy, and a two-grid method. The free surfaces are tracked with a volume-of-fluid approach. A special emphasis is laid on the modeling of surface tension forces on the free surface. A comparison between approaches is highlighted, and a mesh convergence analysis is presented. Finally, the model is validated with the simulation of a static laser melting process.

Encoding Priors with Group Sparsity for Model Learning From Limited and Noisy Biological Data

Scipedia content — Thu, 11 Mar 2021 16:56:40 +0100

Numerical methods for approximately solving partial differential equations (PDE) are at the core of scientific computing. Often, this requires high-resolution or adaptive discretization grids to capture relevant spatio-temporal features in the PDE solution, e.g., in applications like turbulence, combustion, and shock propagation. Numerical approximation also requires knowing the PDE in order to construct problem-specific discretizations. Systematically deriving such solution-adaptive discrete operators, however, is a current challenge. Here we present an artificial neural network architecture for data-driven learning of problemand resolution-specific local discretizations of nonlinear PDEs. Our proposed method achieves numerically stable discretization of the operators in an unknown nonlinear PDE by spatially and temporally adaptive parametric pooling on regular Cartesian grids, and by incorporating knowledge about discrete time integration. Knowing the actual PDE is not necessary, as solution data is sufficient to train the network to learn the discrete operators. A once-trained neural architecture model can be used to predict solutions of the PDE on larger spatial domains and for longer times than it was trained for, hence addressing the problem of PDE-constrained extrapolation from data. We present demonstrative examples on long-term forecasting of hard numerical problems including equation-free forecasting of non-linear dynamics of forced Burgers problem on coarse spatio-temporal grids.

Numerical Simulation of a Separating Laminar Boundary Layer Exposed to Ambient Turbulence

Scipedia content — Thu, 11 Mar 2021 16:56:33 +0100

Laminar separation on wings exposed to flow of a low Reynolds number is a very common phenomenon already at low angles of attack. It is extremely sensitive to turbulence in the freestream as is can affect the boundary layer upstream of the separation, the transition into turbulence and at very large length scales also locally change the angle of attack. Hybrid RANS/LES simulations of laminar separation haven been performed with parametric variations of both intensity and length scale of the ambient turbulence. The boundary layer has then been analyzed in order to demonstrate the effect of eddies impinging the laminar boundary layer upstream of the separation leading to stabilizing and destabilizing effects, which both have been identified and visualized.

Global stability failure of a 3D composite structure accompanied by unavoidable polymorphic uncertainties

Scipedia content — Thu, 11 Mar 2021 16:56:26 +0100

In this study, a non-linear stability analysis of a carbon fiber reinforced plastic (CFRP) considering unavoidable polymorphic uncertainties is conducted. For the realistic incorporation of the uncertainties in the finite element model, thickness variations and geometrical inaccuracies have been detected in advance by non-destructive testing. For that, a structure made of CFRP has been designed. Additionally, the material parameters have been defined as dependent stochastic variables based on reference studies in the literature. The distinction in aleatory and epistemic uncertainties leads to different uncertainty models and to a computationally costly fuzzy-stochastic analysis. Strains and displacements have been measured in a symmetric three-point bending test and compared to the numerical predictions. In addition to the present uncertain parameters, a case study shows that the fiber volume content and a small pre-deformation should be taken into account to minimize the deviation from the experimental results.

Efficient Characterization and Modelling of the Nonlinear Behaviour of LFT for Crash Simulations

Scipedia content — Thu, 11 Mar 2021 16:56:16 +0100

Modeling the nonlinear material behaviour of long fiber reinforced thermoplastics (LFT) presents a challenging task since local inhomogeneities and nonlinear effects must be taken into account also on the microscale. We present a computational method with which we can predict the nonlinear material response of a composite material using only standard DMA measurements on the pure polymer matrix material. The material models considered include plasticity, damage, viscoelasticity, and viscoplasticity as described in [1]. These models can be combined similar to the model from [2] and extended to the composite by assigning linear elastic properties to the fibers. The mechanical response of the composite is computed using an FFT-based technique [3]. The geometry of the composite, in particular the fiber orientation, can be characterized using injection molding simulations or micro CT scans. We create virtual models of the composite using the algorithm of [4]. We show that with this method, the material behaviour of the composite can be predicted while the experimental complexity needed for the material characterization is low.

A Residual-Based HP-Mesh Optimization Technique for Petrov-Galerkin Schemes with Optimal Test Functions

Scipedia content — Thu, 11 Mar 2021 16:56:08 +0100

In recent times, Petrov-Galerkin schemes with optimal test function framework have presented themselves as a stable and robust technique for solving partial differential equations. These schemes are also accompanied by an inbuilt error estimator, which makes them an ideal candidate for mesh adaptation. In this paper, we present a metric-based mesh adaptation strategy utilizing this inbuilt error estimator to generate optimal hp meshes.

A Diffused Interface Immersed Boundary-Lattice Boltzmann Method for Simulation of Channel Flow

Scipedia content — Thu, 11 Mar 2021 16:56:00 +0100

The immersed boundary method has attracted growing interest in CFD research community due to its simplicity in dealing with moving boundaries. In the diffused interface immersed boundary method, a discrete delta function is introduced to account for the boundary effects on the fluid, which causes the diffusion of the boundary interface. Therefore, the diffused interface immersed boundary method requires higher grid resolution in the vicinity of the immersed boundaries to get a better representation of the boundary. A strategy for the application of diffused interface immersed boundary-lattice Boltzmann method is introduced in the simulation of stenosis. The developed numerical method has been examined in the simulation of stenosis. Results show that the current solver is able to accurately predict the velocity profile within the stenosis.

Diffraction Imaging and Image Processing – Tools for Localization and Characterization of Fractured Zones by Seismic Data

Scipedia content — Thu, 11 Mar 2021 16:55:53 +0100

The paper presents a technique for the localization and characterization of fractured zones by seismic data. The developed approach combines the diffraction imaging and topological analysis of diffraction images. The testing results for realistic synthetic models and real seismic data demonstrate the possibility of a reliable restoration of the fractured zones' statistical characteristics.

Uncertainty and Sensitivity Analysis in Turbulent Pipe Flow Simulation

Scipedia content — Thu, 11 Mar 2021 16:55:46 +0100

In this study, we would like to evaluate and improve the performance of Wall-Modeled LargeEddy Simulation (WMLES) on the modeling of a pipe flow for which Direct Numerical Simulation (DNS) data is available [1] and considered as a reference for further comparisons. Models used in WMLES may raise problems of accuracy which come from the uncertain values of model parameters and model simplifications. In this study, we focus firstly on the impact of the model parameter uncertainties on the simulation results, and then on the reduction of these uncertainties via data calibration. These studies using sampling-based approaches can be unaffordable when coupled with a high-fidelity simulation that requires several CPU hours for a single execution. To reduce the computational cost while maintaining a target accuracy, we propose to build surrogate models based on Gaussian Processes for simulations outputs, and replace the simulator for evaluating the large size sampled sets. For this study, a CFD-UQ methodology is developed which couples our internal UQ tool and a CFD solver. It has been applied on a turbulent pipe flow case that allows us to validate its implementation.

A Hierarchical Coupled Multi-Scale Model for Short Fiber Composites

Scipedia content — Thu, 11 Mar 2021 16:55:37 +0100

Short Fiber Reinforced Composites (SFRCs) are being increasingly used in a variety of applications due to their interesting mechanical properties and ease of processing. For SFRCs, different micro-structural parameters (in addition to the constitutive behaviour of the matrix and reinforcement fibers), such as fiber orientation distribution, fiber aspect ratio and fiber/matrix interface strength play important roles in the macroscopic mechanical behaviour. Hence, to have an accurate and reliable modelling approach, using multi-scale models is a natural choice. In this study, a coupled multi-scale model is proposed using a recently developed micromechanical model and the Finite Element Method. The proposed model enables analysis of macroscopic specimens considering micro-structural properties.

Simulation Project Management by Modified Gaussian S-Curve

Scipedia content — Thu, 11 Mar 2021 16:55:29 +0100

Contemporary project management rises to the level of various associative groups, going beyond project management (PM) in a specific, defined activity. Processes not directly related to one activity are becoming more important. Planning a process group by cash-flow methods or S-curve defines the given process

Two Dimensional Topology Optimization of Heat Exchangers with the Density and Level-Set Methods

Scipedia content — Thu, 11 Mar 2021 16:55:22 +0100

We design heat exchangers using two topology optimization approaches: the density, i.e. volume fraction and level set methods. Our goal is to maximize the heat exchange between two fluids in separate channels while constraining the pressure drop across each channel. The heat exchanger is modeled with a coupled thermal-flow formulation. The flow is governed by an isothermal and incompressible Stokes-Brinkman equation and the heat transfer is governed by a convection-diffusion equation with high Peclet number. We solve one set of Stokes-Brinkman equations per fluid. Each Brinkman term in the flow equation serves to model the other phase as a solid, thereby preventing mixing. We first represent the solid and fluid phases using a volume fraction variable and apply a SIMP-like penalization in the Brinkman term to drive the optimization to a discrete design. The cost and constraint function derivatives are automatically calculated with the library pyadjoint and the optimization is performed by the Method of Moving Asymptotes. In a second optimization formulation, we use the level set approach to define the interface that separates the two fluids. Pyadjoint calculates the shape derivatives of the cost and constraint functions and the Hamilton-Jacobi advects the interface, allowing for topological changes. We present results in two dimensions and discuss the advantages and disadvantages of each approach.

Finite Element Simulation of 3d-Printed SMA-SMP Composite Actuators

Scipedia content — Thu, 11 Mar 2021 16:55:14 +0100

The shape memory alloy-shape memory polymer (SMA-SMP) composite actuators are the novel smart actuator designs which capable of large recoverable actuation deformation as well as retaining shape in the actuated state without consuming extra energy. This is particularly doable because of the recent progresses in additive manufacturing technologies. The 4D printed actuators designed in the previous study [7] are fabricated by multi-material inkjet 3D printing and is able to deposit various range of digital materials with different elastic stiffness in micro-scale. In this study, we have developed the numerical simulation of the 4D-printed composite actuator hinges to determine important actuation parameters and develop a design tool for future applications. The three-dimensional finite element models were conducted in ABAQUS and the nonlinear temperature dependence behaviour of shape memory alloy (SMA) and shape memory polymer (SMP) materials are incorporated through the user material subroutines (UMATs). The finite element results then have been compared with the experimental measurements and illustrate the accuracy of our numerical analysis. Therefore, the validated computational framework could be used for further development of actuators that could generate complex deformations.

Design Optimization, Cost and Risk Analysis of CNG Vessels Transportation

Scipedia content — Thu, 11 Mar 2021 16:55:06 +0100

The GASVESSEL Project, financed by the EU under H2020, aims to prove the technoeconomic feasibility of a new CNG (Compressed Natural Gas) transport concept, enabled by
a novel patented Pressure Vessel manufacturing technology and a new conceptual ship design
including safe on- and off-loading solution.
In this paper we illustrate how the process automation and web-based collaboration software
from ESTECO have been used by the partners in the different phases of the Project for the
design of the system.
In function of each different geographical scenarios (which includes East Mediterranean,
Barents Sea and Black Sea) and gas demand, parameters such as ship size and number,
storage and facilities units at the ports have been optimized in order to reduce the
transportation costs and therefore gas tariff.
Components of the gas vessels, in particular material and type of the fibers that wraps the
liner, have been then optimized to minimize weights while respecting high value of safety
factors.
Finally, a CFD study is performed to analyze the risks related to gas leakages and explosions

Design of an Artificial Neural Network for the Analysis of Stellar Spectra

Scipedia content — Thu, 11 Mar 2021 16:54:59 +0100

We have developed an artificial neural network, whose purpose is to automatically find in a database of synthetic stellar spectra the one which best reproduces an observed spectrum. Using the equivalent widths of selected spectral lines, the network fits a set of lines related to the physical parameters in the stellar atmosphere (i.e., temperature, gravity and mass loss rate). The main advantage of this approach is its scalability.

Simulating Powder Bed Based Additive Manufacturing Processes: From DEM Calibration to Experimental Validation

Scipedia content — Thu, 11 Mar 2021 16:54:50 +0100

Powder flowability is a critical parameter for additive manufacturing techniques involving powders. In order to obtain thin and homogenous powder layers, a compromise between grain size and flowability has to be found. Unfortunately, when the grain size decreases, the cohesiveness increases and the flowability decreases. Too often, both the powder spreadability assessment and the optimization of printing parameters are costly empiric processes. In this paper, we describe an original method associating GranuDrum powder flow characterization instrument and DEM numerical simulations to asses the process-ability of powders and to optimize printing parameters like recoater speed, layer thickness or recoater geometry. The powder characterization allows to calibrate the simulation parameters and in particular to quantify the inter-grain cohesiveness. Then, the recoating process is simulated with the calibrated simulations to predict the behaviour of the powder inside the printer. In parallel, the results are validated by testing the powder in a printer equipped with an in-situ powder layer homogeneity tester based on image analysis.

Multiscale isogeometric optimization for cellular structure with multiple prototypes

Scipedia content — Thu, 11 Mar 2021 16:54:41 +0100

This paper presents a multiscale concurrent isogeometric design method for the cellular structure composed of the multiple prototype microstructures. Based on the unified-skeleton modeling scheme, the graded microstructures obtained from a same prototype have similar topology and good connectivity between each other. For the different prototypes, the configurations are rearranged and added the thin-wall material in common interfaces. Thus, the geometric features as well as the structural skeletons can have a smooth transition. Through combining the numerical homogenization method with the interpolation technique, the effective properties of graded microstructures can be estimated efficiently. For the multiscale scheme, the allocation of microstructures is optimized by a material distribution-based method while the configurations of prototypes are designed by the isogeometric parameterized level set method. The proposed method inherits the high accuracy and high efficiency of isogeometric analysis and the smooth boundaries and distinct interfaces of level set method. The cellular structure can be freely customized with favorable connectivity.

Using a Smart Recognition Framework for the Automated Transfer of Structural Whole Engine Models

Scipedia content — Thu, 11 Mar 2021 16:54:34 +0100

The development of adequate simulation models from geometric CAD assemblies is one of the most important tasks in early design phases. With this step requiring a lot of manual effort, the desire for a process efficiency improvement via an automated solution rises. In order to derive information about the assembly to build Finite-Element (FE) models, various different steps have to be taken which require visual assessment and engineering evaluation, knowledge and judgement. The approach described in this research mimics the engineer's logic and way of thinking to automate these steps. Thereof, the recognition of entities plays a fundamental role for further processing. To achieve the desired recognition, methods have been developed to retrieve criteria like form, function, context and positioning from the available geometry data. The developed recognition framework supports and provides a component categorization so that specifically optimized process chains for each category can be implemented, depicting a more robust and reasonable overall process.

Turbulence Model Extension for Vortex Dominated Flows and Optimization with Experimental Data

Scipedia content — Thu, 11 Mar 2021 16:54:26 +0100

This document provides information and instructions for preparing a Full Paper to be included in the Proceedings of 14th WCCM ECCOMAS CONGRESS 2020.

Symplectic Time Integration Methods for the Material Point Method, Experiments, Analysis and Order Reduction

Scipedia content — Thu, 11 Mar 2021 16:54:19 +0100

The provision of appropriate time integration methods for the Material Point Method (MPM) involves considering stability, accuracy and energy conservation. A class of methods that addresses many of these issues are the widely-used symplectic time integration methods. Such methods have good conservation properties and have the potential to achieve high accuracy. In this work we build on the work in [5] and consider high order methods for the time integration of the Material Point Method. The results of practical experiments show that while high order methods in both space and time have good accuracy initially, unless the problem has relatively little particle movement then the accuracy of the methods for later time is closer to that of low order methods. A theoretical analysis explains these results as being similar to the stage error found in Runge Kutta methods, though in this case the stage error arises from the MPM differentiations and interpolations from particles to grid and back again, particularly in cases in which there are many grid crossings.

Simulation of Adhesive Frictional Contact of Soft Materials by Bi-Potential Method

Scipedia content — Thu, 11 Mar 2021 16:43:10 +0100

We propose a numerical formulation for the simulation of frictional contact with interfacial adhesion between soft bodies. In this work, the adhesive interface behaviour derives from a free surface energy and a pseudo-potential of the surface dissipation, which describe both the de-bonding process of the adhesive links due to tangential and normal interface deformation. Subsequently, a complete contact and friction law with the account for interface adhesion is formulated. Then the local contact nonlinear equations are solved using a Newton-like algorithm within the bi-potential framework. Numerical examples are performed to demonstrate the capacity of the proposed approach.

DNS of Turbulent Heat Transfer in Impinging Jets at Different Reynolds and Prandtl Numbers

Scipedia content — Thu, 11 Mar 2021 16:43:02 +0100

The heat transfer between an impinging circular jet and a flat plate is studied by means of direct numerical simulations (DNS) for different Prandtl numbers of the fluid. The thermal field is resolved for Pr= 1, 0.72, 0.025, and 0.01. The flow is incompressible and the temperature is treated as a passive scalar field. The jet originates from a fully developed turbulent pipe flow and impinges perpendicularly on a smooth solid heated plate placed at two pipe diameters distance from the jet exit section. The values of Reynolds numbers based on the pipe diameter and bulk mean velocity in the pipe are set to Re= 5300 and Re= 10000. Inflow boundary conditions are enforced using a precursor simulation. Heat transfer at the wall is addressed through the Nusselt number distribution and main flow field statistics. At fixed Reynolds number it is shown that the Prandtl number influences the intensity of the Nusselt number at a given radial location, and that the Nusselt number distribution along the plate exhibit similar features at different Prandtl numbers. The characteristic secondary peak in the Nusselt number distribution is found for both Reynolds numbers for Pr= 0.025 and Pr = 0.01. All the simulations presented in this study were performed with the high order spectral element code Nek5000. Generated flow field statistics are available in the open access repository KITOpen.

An IB-LBM for FSI Problems Involving Viscoelastic Fluids and Complex Geometries

Scipedia content — Thu, 11 Mar 2021 16:42:54 +0100

An immersed boundary-lattice Boltzmann method (IB-LBM) for fluid-structure interaction (FSI) problems involving viscoelastic fluids and complex geometries with a few validation cases is presented in this paper. In this method, the lattice Boltzmann method is used to solve the fluid dynamics and the constitutive equations of viscoelastic fluids. An artificial damping is introduced to enhance numerical stability in solving the constitutive equations. A hybrid of the finite difference method (2D and 3D rigid particles) and the finite element method (3D capsule) is employed to solve the structural dynamics. The interaction between the solid structure and the fluid is achieved by an immersed boundary method. The present method and models are validated by several cases including 2D Oldroyd-B channel flow, 2D lid-driven cavity flow, 2D Oldroyd-B flow over a confined cylinder, a 2D rigid particle migration in an Oldryod-B Couette flow, a spherical particle rotation in an Oldroyd-B shear flow, a spherical particle settling in a Newtonian fluid, and the deformation of a spherical capsule in a long channel filled with a Newtonian fluid.

Coupling 3D Geomechanics to Classical Petroleum System Simulation

Scipedia content — Thu, 11 Mar 2021 16:42:45 +0100

Geomechanical models of classical petroleum system simulators are limited to 1D phenomenological laws relating porosity to vertical effective stress. In order to overcome this limitation, a 3D poromechanical model is integrated in the sedimentary basin simulation by applying an iterative coupling scheme between a conventional basin code and a mechanical finite element code. This paper presents the porous material constitutive law specifically devised to deal with basin modeling, together with essential aspects of the mechanical code implementation and explicit coupling workflow. The numerical procedure is first verified according to a semi-analytical solution and then compared to an implicit academic code. Finally, a 3D synthetic case demonstrates the importance of incorporating 3D geomechanics to basin simulation. The results show that tectonic compression may significantly contribute to overpressure development and natural fracturing of seal rocks, contrary to the standard procedures of petroleum system simulation which are unable to capture such effect.

Investigating Model-Data Inconsistency in Data-Informed Turbulence Closure Terms

Scipedia content — Thu, 11 Mar 2021 16:42:37 +0100

In the present work, we investigate the stability of turbulence closure predictions from neural network models and highlight the role of model-data-inconsistency during inference. We quantify this inconsistency by applying the Mahalanobis distance and demonstrate that the instability of the model predictions in practical large eddy simulations (LES) correlates with a deviation of the input data between the training dataset and actual simulation data. Moreover, the method of 'stability training' is applied to increase the robustness of recurrent artificial neural networks (ANN) against small perturbations in the input, which are typically unavoidable in any practical scenario. We show that this method can increase the stability of simulations with ANN-based closure term predictions significantly. The models also achieve good accuracy on the blind testing set in comparison to the baseline model trained without stability training. The work presented here can thus be seen as a building block towards long-term stable data-driven models for dynamical systems and highlights methods to detect and counter model-data-inconsistencies.

Physics-Aware, Deep Probabilistic Modeling of Multiscale Dynamics in the Small Data Regime

Scipedia content — Thu, 11 Mar 2021 16:42:29 +0100

The data-based discovery of effective, coarse-grained (CG) models of high-dimensional dynamical systems presents a unique challenge in computational physics and particularly in the context of multiscale problems. The present paper offers a probabilistic perspective that simultaneously identifies predictive, lower-dimensional coarse-grained (CG) variables as well as their dynamics. We make use of the expressive ability of deep neural networks in order to represent the right-hand side of the CG evolution law. Furthermore, we demonstrate how domain knowledge that is very often available in the form of physical constraints (e.g. conservation laws) can be incorporated with the novel concept of virtual observables. Such constraints, apart from leading to physically realistic predictions, can significantly reduce the requisite amount of training data which enables reducing the amount of required, computationally expensive multiscale simulations (Small Data regime). The proposed state-space model is trained using probabilistic inference tools and, in contrast to several other techniques, does not require the prescription of a fine-to-coarse (restriction) projection nor time-derivatives of the state variables. The formulation adopted is capable of quantifying the predictive uncertainty as well as of reconstructing the evolution of the full, fine-scale system which allows to select the quantities of interest a posteriori. We demonstrate the efficacy of the proposed framework in a high-dimensional system of moving particles.

2D Self-Organized Gradient Percolation Model for Numerical Simulation of Impregnation in Porous Media

Scipedia content — Thu, 11 Mar 2021 16:42:21 +0100

Reactive impregnation concerns many science and engineering areas, such as corrosion in the steel-making industry and chemical engineering. Furthermore, reactive impregnation can become dangerous in some applications. Simulating non-reactive impregnation with classical methods is the first step before computing reactive impreg++nation. However, existing numerical methods present problems such as high computational cost and spurious oscillation. To avoid these computational difficulties, we propose the Self-organized Gradient Percolation model. It is a numerical model based on probabilistic approaches and, in particular, on percolation methods. This work aims to present a 2D model based on the 1D developed model. The first results are free from spurious oscillation and drastically reduced the computational cost compared with the classical methods.

An improved bond-based peridynamic model based on Timoshenko beam theory

Scipedia content — Thu, 11 Mar 2021 16:42:12 +0100

An improved constitutive model based on Timoshenko beam theory is proposed for bond-based peridynamics. The motion and force governing equations of the bond are established by introducing Timoshenko beam element to simulate the interaction between the particles including the bond tension-rotation-shear coupling effects. Since the axial displacement, transverse displacement and relative rotation angle of the bond are considered in the model, it can overcome the limitation of Poisson’s ratio in the classical bond-based peridynamics model. Three kinds of peridynamic parameters, corresponding to the compressive, shear and bending stiffness of the bond, are introduced to keep the consistence between the strain energy of the peridynamic model and that of the continuum mechanics under arbitrary deformation field. Moreover, an energy-based failure criterion, involving the maximum stretch, shear strain and rotation angle limits of the bond, is proposed to capture the progressive failure of general quasi-brittle materials. The validation of the proposed model is verified by comparing the simulation results to the experiment observations and analytical solution. Numerical results show that this improved model can be widely used to predict the nonlinear deformation, crack propagation and progressive failure of materials with variable Poisson’s ratio under complex loading conditions.

A General-Purpose AMG Linear Solver for High Performance Computing

Scipedia content — Thu, 11 Mar 2021 16:42:04 +0100

The numerical simulation of modern engineering problems via finite elements requires the solution of sparse linear systems of millions or even billions of unknowns. The algebraic multigrid (AMG) methods are the most common choice as linear solvers because of their fast convergence even for large-size problems. In this communication, we propose Chronos, a massively parallel implementation of a novel AMG framework, specifically designed to address complex problems by adapting its components, from the smoother, to the coarse grid correction and prolongation to the problem at hand. This work demonstrates not only the numerical performance of the proposed library, but also its robustness and adaptability to very challenging matrices, arising from different fields of application.

How One Can Arrange the Multibody System Dynamics Computer Model

Scipedia content — Thu, 11 Mar 2021 16:41:57 +0100

The symplest computer models for mechanical systems can be organized using Cauchy normal form. Further complicating the mechanical model is able to bring us to application the implicit functions of next complexity level. Process of the multibody system computer models development is of special difficulty. There exist different ways for organizing such a models. Mainly these ways are reduced to the model transformation to the form of differential-algebraic equations (DAEs). These latter ones correspond to Lagrange equations of the first kind. Note that usually differential equations of DAEs mentioned correspond to dynamical and kinematical equations of mechanics, while the algebraic equations are generated by constraints. Computational experience makes it possible to classify objects of the multibody system dynamics [1]. Such a model includes two classes of objects. They correspond to notions of 'body' and 'constraint'. Let us also remark that these two classes of objects define the structure of the undirected graph such that 'bodies' play a role of the graph vertices, while 'constraints' play the role of edges. There exists yet another graph interpretation using the bi-chromatic bipartite graph. In this case both bodies and constraints are interpreted as vertices. Objects of bodies compose a partition and are coloured by one colour while objects of constraints compose the complement partition of the whole graph and are coloured by another colour. Edges connecting vertices of partitions for the graph are arranged in a way such that for any vertex of constraint there exist exactly two vertices of class 'body' thus implementing participation in the constraint. Two ways for the multibody system dynamics computer model graph composition mentioned above define ways for constructing the visual model of such a system thus defining ports interconnection structure. Different cases of the multibody system dynamics computer model implementation were analysed as an examples. Models under construction are the following ones: (a) Rattleback; (b) Snakeboard; (c) Skateboard; (d) Tippe-Top; (e) Ball Bearing; (f) Spur Involute Gear; (g) OmniVehicle.

Interfacial Element for Finite Element Modal Analysis of Bolted Joints

Scipedia content — Thu, 11 Mar 2021 16:41:49 +0100

Multi-material structures are going to be a main scheme to construct automobiles. For the construction of multi-material structures, techniques to join dissimilar materials are required. The major joining techniques are classified into welding, adhesion and mechanical fastening such as bolted joints and riveting. Especially, bolted joints enable joining of metallic materials (steel and aluminium alloy, etc.) and non-metallic materials (CFRP, etc.) with high joint strength. However, the total stiffness of structures with bolted joints is relatively low because interfaces in bolted joints just contact each other, and its interfacial stiffness is lower than elastic modulus of base materials. Moreover, interfacial stiffness of bolted joints depends on clamping force of bolt and nut. This study has proposed an interfacial element for finite element modal analysis of bolted joints. The interfacial element simulates interfacial stiffness of bolted joints. Contact of interfaces is assumed to be the Hertzian contact of elastic asperities whose peak heights obey the Gaussian distribution. Based on this assumption, the stiffness of the interfacial element is derived from the compressive stress and the surface texture of the interfaces. By using the finite element model with the interfacial element, the modal analysis computes the natural frequency and the vibration mode. Finite element simulations and hammering tests have been conducted with several bolted joints. In general, the natural frequency of the bolted joints in the hammering tests increases with the increase in the clamping force, but it is lower than the calculation results in which the stiffness reduction of the jointed interfaces is ignored. The calculation results by using the proposed interfacial element agree with the hammering tests. Therefore, the proposed interfacial element contributes to improvement of modal analysis of bolted joints by mathematically modelling stiffness reduction of jointed interfaces based on tribology.

Computational Modelling of Thermomechanical Behaviour of Cast Irons: Effect of Boundary Conditions

Scipedia content — Thu, 11 Mar 2021 16:41:41 +0100

In this work, a microstructure-based modelling approach is employed to investigate the performance of cast irons under thermal loading. Cast irons have a complex microstructure with graphite particles of different shapes, sizes and orientations embedded in an iron matrix. As a result of the mismatch in coefficients of thermal expansion of constituents, even a purely thermal load can cause failure. To evaluate this behaviour, representative volume elements of cast-iron microstructures are studied using finite-element simulations. Specific inputs in the models are provided based on statistical analysis of SEM micrographs. Further, the influence of boundary conditions is discussed. The obtained results demonstrate that the failure in the examined unit cells is sensitive to the adopted modelling assumptions, as well as the boundary conditions.

Numerical Prediction of Stresses at High Temperature of 3rd Generation Advanced High Strength Steels During Resistance Spot Welding - Liquid Metal Embrittlement Risk Assessment. Methodology to Create and Validate a Reliable and Robust Numerical Material Card

Scipedia content — Thu, 11 Mar 2021 16:41:33 +0100

The prediction of stress level during Resistance Spot Welding at high temperature is
very useful to reduce and/or avoid Liquid Metal Embrittlement phenomenon. However, the
experimental estimation of stress level into metal sheets during a Resistance Spot Welding
process is impractical. Therefore, a numerical methodology to predict mechanical stresses,
using more accessible experiments, is proposed in this work.

Imperfections Sensitivity Analysis of Stainless Steel Equal-Legs Angle Subjected to Compression

Scipedia content — Thu, 11 Mar 2021 16:41:24 +0100

This paper presents a numerical analysis of initial geometrical imperfections sensitivity in fixed-end hot-rolled stainless steel 304 equal-leg angle columns under flexuraltorsional buckling. Experimental measurements evidenced that equal-leg angle columns exhibit three initial geometrical imperfections types, specifically: minor-axis bending (dm), major-axis bending (dM), and cross-section torsional rotation (β). Therefore, using the numerical finite element model in Ansys software, validated with the experimental results, analyses were performed to investigate the influence of the initial geometrical imperfections on the ultimate loads of fixed-end columns failing by flexural-torsional buckling.

Moisture Transport In Polyamide (PA6) and Its Effect On the Mechanical Behaviour

Scipedia content — Thu, 11 Mar 2021 16:41:16 +0100

Polyamide exhibits hygroscopic nature and can absorb up to 10 % of moisture relative to its weight. The absorbed moisture increases the mobility of the molecular chains and causes a reduction in the glass transition temperature. Thus, depending on the moisture distribution, a polyamide component can show different stiffness and relaxation times. The moisture distribution also depends on the mechanical loading of the material. However, it was noticed that the diffusion process remains unaffected when the process is compared for a loaded and an unloaded material. It is postulated that the moisture redistribution is due to an external force that takes place as a result of the pressure acting on the moisture. The diffusion process is unaffected by preloading of the dry material as the pressure is applied purely on the material and not on the absorbed moisture. However, when a saturated specimen is loaded, the pressure is exerted on the moisture too which causes its redistribution. In this work, the distribution of the absorbed moisture is simulated by a non-linear diffusion model. It is coupled with the viscoelastic behaviour of PA6. The stiffness of the viscoelastic model changes and the relaxation time reduces with increasing moisture concentration. The coupling of diffusion to mechanical loading is achieved with the recalculation of the moisture concentration caused due to the redistribution of volume. It is assumed that there is no transport of moisture, but the transport of volume and the change in volume creates a change in concentration in the specimen. This strongly coupled model has been implemented using the finite element method. The model results are compared to experiments for validation. A strongly coupled model was thus created which could reproduce the experimental results with reasonable accuracy.

Two States Analysis for Granular Material in Infinite High Tubes

Scipedia content — Thu, 11 Mar 2021 16:41:09 +0100

A displacement field a pressure field and a velocity field describe the behavior of hybrid materials that is not covered by a single solid or liquid state approach. A primary analysis that is represented by a functional and its associated principle is based on a two states analysis consisting of a solid part and a pressure part. The pressure part is related to a velocity field in a secondary analysis. With respect to granulates the interaction at the walls is directed towards the avoidance of tension. Equilibrium is achieved separately for area and boundary. The distribution of the specific weight on solid and liquid parts depends on the first stress invariants.

A Decomposition of the Raviart-Thomas Finite Element into a Scalar and an Orientation-Preserving Part

Scipedia content — Thu, 11 Mar 2021 16:41:02 +0100

This contribution considers the conforming finite element discretizations the vector-valued function space H(div,Ω) in 2 and 3 dimensions. A new set of basis functions on simplices is introduced, using a decomposition into an orientation setting part with the edgewise constant normal flux as a degree of freedom and an orientation preserving higher-order part. As a simple combination of lowest-order Raviart-Thomas elements and higher order Lagrange-elements, the basis is suited for fast assembling strategies.

An Analytical Validation of the Localized Collocation Meshless Method Formulation for Transdermal Drug Delivery

Scipedia content — Thu, 11 Mar 2021 16:40:54 +0100

The Localized Collocation Meshless Method (LCMM) is applied to the solution of a set of partial differential equations describing the diffusive transport of a dermally injected compound. This efficient and accurate numerical technique then provides the framework for the estimation of pharmacokinetic (PK) parameters by the comparison of two models, both containing information derived from experimental results, using the iterative Golden Section search algorithm. This comparison is quantified using a norm between the two solution spaces. While this method does provide an estimate of the effective-diffusion coefficient, it ultimately demonstrates that a simple, free-diffusion model is inadequate for quantifying the spatial and temporal distribution of a dermally-injected compound if elimination effects are not accounted for properly.

Supra-Conservative Finite-Volume Methods for the Simulation of Subsonic Flow

Scipedia content — Thu, 11 Mar 2021 16:40:47 +0100

It is demonstrated how finite-volume methods can be designed such that, next to the primary invariants (mass, momentum and internal energy), they also conserve secondary invariants (kinetic energy), i.e., they are supra-conservative. Key ingredient is a consistency between the discrete divergence terms in the constituting equations and the discrete pressure gradient. The requirements hold for any discretization method with a volume-consistent scaling.

Effect of Vehicle-Bridge-Interaction on the Vibration of the Bridge

Scipedia content — Thu, 11 Mar 2021 16:40:40 +0100

This paper studies the effect of vehicle-bridge interaction (VBI) on the vibration of the supporting bridge, and subsequently proposes a decoupled analysis scheme for the VBI problem with reference to high-speed railway systems. The study examines the VBI problem analytically and reveals the main coupling parameters between vehicles and bridges. It proves that, except for the stiffness ratio, the impedance ratio, defined as the ratio of the vehicle's damping and bridge's mechanical impedance, is also a dominant coupling parameter between vehicles and bridges. Following, the study shows that VBI alters the mechanical system of the bridge via an additional damping, an additional stiffness and a modified loading term. The coupling terms (i.e., the vehicle response) appear solely in the modified loading term. Assuming small stiffness ratio, which is realistic for practical train-bridge systems, the proposed decoupling scheme eliminates the vehicle response from the bridge's equation of motion in a systematic manner. With respect to the fully coupled system, the proposed method returns more accurate results compared to well-known decoupling methodologies, such as the moving load approximation.

On the Adjoint Equation in Fluid-Structure Interaction

Scipedia content — Thu, 11 Mar 2021 16:37:28 +0100

In this contribution, we revisit adjoint formulations for stationary and nonstationary spacetime fluid-structure interaction. The adjoints serve for two purposes: goal-oriented a posteriori error estimation with the dual-weighted residual method and gradient-based numerical optimization. Our developments are substantiated with comments on numerical simulations in some other published studies.

A Discontinuum Finite Element Modelling Approach for Reproducing the Structural Behaviour of Masonry Walls

Scipedia content — Thu, 11 Mar 2021 16:31:10 +0100

This paper defines an innovative approach for modelling masonry walls when the structural behaviour of new or existing buildings, subjected to vertical and lateral load, has to be evaluated. Such an approach aims to provide a calculation tool that allows to model the non-linear behaviour of masonry structures with a reduced numerical effort, but, nonetheless, without jeopardizing the accuracy of obtained results. The proposed model is a typical D-FEM (Discontinuum Finite Element Model) that, differently by the most common methodologies, is composed by deformable blocks separated by interface elements arranged along pre-established surfaces of potential cracks. To this aim, the 'Combined Cracking-Shearing-Crushing' model, proposed by Lourenco for the FEM analysis with the so called simplified micro-models, is used. Some experimental tests taken by litterature are described. Such tests are used as reference for setting up a non-linear model with the 'simplified micro-modelling' approach, which considers the presence of blocks, of the same geometry of the stone units, separated by interface elements. Once that this modelling approach is validated, it is used to obtain the nonlinear response of 65 masonry panels which differ in terms of geometry, vertical loads, as well as in terms of the most significant mechanical parameters. The obtained responses for the 65 panels are taken into account for the calibration of the here proposed model. In detail, a proper variation of the coefficients contributing to the 'Combined Cracking-Shearing-Crushing' formulation is implemented through a trial and error procedure, which ends when a satisfying comparison between the results provided by the two different methods of modelling is achieved; this for taking into consideration the constraints imposed on the development of cracking surfaces. The outcomes obtained with the here proposed modelling approach are then elaborated in order to develop suitable closed form equations, which provide the necessary coefficients that have to be used for implementing the modified 'Combined Cracking-Shearing-Crushing' when a generic masonry panel has to be modelled.

On the Importance of Cross-Sectional Distortions and their Inclusion in an Efficient GBT-Formulation

Scipedia content — Thu, 11 Mar 2021 16:31:02 +0100

This proceeding proposes an efficient generalized beam theory formulation, which accounts for cross-sectional deformations in slender prismatic structures. It was shown by the authors in a recent publication [1] that in-plane distortional deformations and accompanied out of plane warping deformations of the cross-section influence the accuracy of results in beam dynamics especially if thin-walled cross-sections are applied. The GBT formulation proposed in [1] overcomes the inaccuracies of classical beam mechanics, however, requires a two-dimensional plane discretization of the cross-section. The computational complexity can be reduced vastly, if the thin-walled cross-sections can be discretized with one-dimensional elements. Consequently, this proceeding discusses a corresponding derivation, where the line mesh which discretizes the cross-section has six degrees of freedom at each node. The membrane part consists of mass-less micro-polar rotations (drilling rotations) and can be derived independently from the bending part, where a shear elastic formulation is selected.

Modeling One and Two Passive Scalar Mixing in Turbulent Jets Using One-Dimensional Turbulence

Scipedia content — Thu, 11 Mar 2021 16:30:53 +0100

Turbulent mixing of two passive scalars is investigated in a constant-property jets using stochastic one-dimensional turbulence (ODT). Scalars are separately injected by a central round and a surrounding annular jet that issue into a uniform co-flow of low velocity. These scalars are transported downstream and dispersed in radial direction by turbulent advection and molecular diffusion. The jet as well as the turbulent inflow are numerically simulated with ODT as stand-alone tool using a temporal (T-ODT) and spatial (S-ODT) formulation. We show that ODT captures key properties of the turbulent mixing for one scalar by performing individual scalar statistics and for two scalars by computation of joint probabilities. Some limitations of the one-dimensional modeling approach are also discussed.

Parameter Identification of a Friction Model in Metal Cutting Simulations with GPU-Accelerated Meshfree Methods

Scipedia content — Thu, 11 Mar 2021 16:30:45 +0100

A modular computational framework for the identification of friction parameters in metal machining applications is presented. Numerical simulation of such processes using mesh-based techniques (usually) necessitates the re-meshing procedure, which is time-consuming and hard to parallelize. Therefore, the present framework synthesizes the advantages of mesh-free methods with GPU parallel computing, offering an efficient tool for the optimization procedures in thermomechanical modeling of cutting problems. The proposed approach employs an inverse method to determine the unknown coefficients of a temperature-dependent friction model in high-speed metal cutting. We found good agreement between the numerical results and experimental data through a quantitative-qualitative comparison.

Learning Computable Models From Data

Scipedia content — Thu, 11 Mar 2021 16:30:37 +0100

Numerical methods for approximately solving partial differential equations (PDE) are at the core of scientific computing. Often, this requires high-resolution or adaptive discretization grids to capture relevant spatio-temporal features in the PDE solution, e.g., in applications like turbulence, combustion, and shock propagation. Numerical approximation also requires knowing the PDE in order to construct problem-specific discretizations. Systematically deriving solution-adaptive discrete operators, however, is a current challenge. Here we present an artificial neural network architecture for data-driven learning of problemand resolution-specific local discretizations of nonlinear PDEs. Our proposed method achieves numerically stable discretization of the operators in an unknown nonlinear PDE by spatially and temporally adaptive parametric pooling on regular Cartesian grids, and by incorporating knowledge about discrete time integration. Knowing the actual PDE is not necessary, as solution data is sufficient to train the network to learn the discrete operators. A once-trained network can be used to predict solutions of the PDE on larger spatial domains and for longer times than it was trained for, addressing the problem of PDE-constrained extrapolation from data. We present examples on long-term forecasting of hard numerical problems including equation-free forecasting of the nonlinear dynamics of the forced Burgers problem on coarse spatio-temporal grids.

Multiscale FE-MD Coupling: Influence of the Chain Length on the Mechanical Behavior of Coarse-Grained Polystyrene

Scipedia content — Thu, 11 Mar 2021 16:30:27 +0100

Polymers have become increasingly essential to cope with modern engineering challenges. To better understand their microstructure's influence, multi-scale approaches that couple molecular dynamics and continuum mechanics are emerging progressively. However, these simulation techniques require detailed knowledge of the material behavior, which is commonly derived from molecular dynamics simulations. Reducing the degrees of freedom by coarse graining enables the investigation of sufficiently large samples and thus we focus on coarse-grained (CG) polystyrene as a model material. The goal of this contribution is two-fold: Firstly, we identify the minimum sample size necessary to analyze the mechanical properties. Secondly, we quantify the influence of chain length on the material behavior of polystyrene. To this end, we investigate density, end-to-end distance, stress-strain behavior, Young's modulus, and Poisson's ratio. In conclusion, we were able to verify that we can use significantly smaller samples for our investigations without affecting their structure or mechanical behavior. The chain length has a drastic influence on the mechanical properties, with a loss of stiffness in the range of 15 % for very short-chain specimens.

Virtual Method for the Investigation of Dynamic Emission Formation for Gasoline Engines

Scipedia content — Thu, 11 Mar 2021 16:30:18 +0100

Significantly reduced development times of today's powertrains as well as steadily increasing requirements regarding fuel consumption and pollutant emissions require a continuous refinement of the development methods for internal combustion engines. The presented simulation method focuses on the new and tightened approval cycles for passenger car engines; more particularly on the start-up phase as well as on sharp load changes, which lead to increased engine out emissions. The aim of this study is to create a simulation tool for the investigation and the evaluation of the emissions during the dynamic engine operation. Established simulation methods, such as Computational Fluid Dynamics (CFD), are bundled in such a way that transient processes can be simulated within a reasonable calculation time without significant loss of information. The tool is based on a 1D gas exchange simulation software. Herein, detailed reaction kinetics are used to simulate the combustion process, which also takes the thermal boundary conditions (wall temperatures) and the quality of the mixture formation into account. For this purpose, the gas exchange model is extended with a thermal network and the mixture formation process is assessed with CFD. Suitable test bench data serve to validate the whole process chain. In addition to the improvement of the CAE-based assessment for the development of virtual engines, the simulation tool should provide an understanding of the phenomena leading to emission formation under the transient engine operation. Furthermore, using such a tool can contribute to the development of alternative driving concepts like plug-in hybrid electric vehicles (PHEV) and exhaust aftertreatment systems.

The Hybrid Capriccio Method: A 1D Study for Further Advancement

Scipedia content — Thu, 11 Mar 2021 16:30:10 +0100

Polymers and, in particular, polymer composites are known for the enormous adjustability of their mechanical, chemical, and thermal behavior. Multiscale methods are increasingly employed to unravel the polymer microstructure's impact on the material properties. These methods combine the accuracy of particle-based techniques with the efficiency of continuum mechanical approaches. Amorphous polymers pose a special challenge since their microstructure does not continue periodically, and therefore special attention needs to be paid to the particle domain boundary. In this study, we introduce a coupling via an interface between the continuum and the particle domain. Padding atoms as particle representations of the continuum, which serve as interaction partners for the atoms in the particle region, allow for the transfer of displacements and forces between the domains. We present a straightforward 1D example with simple interactions, evaluate the scheme's performance, discuss the resulting energy contributions, and identify an optimal set of coupling parameters. Eventually, this forms the basis for future 3D implementations.

Numerical Simulation of Load Transfer in Mooring Anchor Systems

Scipedia content — Thu, 11 Mar 2021 16:30:02 +0100

A numerical model for the load transfer mechanism in mooring anchor systems, commonly used in offshore petroleum industry, is presented in this work. Special attention is paid to the mechanical modelling of the contact interaction of the two medium components, namely the soil and the embedded mooring line. Resorting to the 'embedded element concept' [1], a mixed 3D-1D finite element formulation is developed in the context of finite elastoplasticity. A Tresca-like model is used to describe the nonlinear material behaviour of the surrounding soil under undrained conditions, whereas the embedded mooring line regarded as curvilinear bar-like inclusion is assumed to behave elastically with account for geometric nonlinearities. The Mohr-Coulomb model is employed to define the bond-stress and bond-slip relationships at the interface. Nonlinear static and dynamic analyses are performed with a corotational kinematic description in order to include large deformation in the problem [2]. Preliminary results indicate that the main frequencies of the dynamic load applied to the mooring line-soil system are much lower than those of the system itself, thus the overall system may be evaluated disregarding inertial effects. Further simulations based on parametric studies by varying relevant problem parameters are needed to corroborate this result. Moreover, the average load attenuation induced by friction along the soil/mooring line interface for the studied cases is around 25%. Formulation of the interface constitutive behaviour in the context of large strain to address large relative movements between embedded inclusion and surrounding soil is an ongoing task [3]. Parallel implementation of the finite element model with specific data structure storage and iterative solver is currently addressed to handle large 3D computational models.

Semantic interoperability Based on the European Materials and Modelling Ontology and its Ontological Paradigm: Mereosemiotics

Scipedia content — Thu, 11 Mar 2021 16:29:18 +0100

The European Materials and Modelling Ontology (EMMO) has recently been advanced in the computational molecular engineering and multiscale modelling communities as a top-level ontology, aiming to support semantic interoperability and data integration solutions, e.g., for research data infrastructures. The present work explores how top-level ontologies that are based on the same paradigm the same set of fundamental postulates as the EMMO can be applied to models of physical systems and their use in computational engineering practice. This paradigm, which combines mereology (in its extension as mereotopology) and semiotics (following Peirce's approach), is here referred to as mereosemiotics. Multiple conceivable ways of implementing mereosemiotics are compared, and the design space consisting of the possible types of top-level ontologies following this paradigm is characterized.

Modeling and Simulation of Suction Blow Molding Process for Producing Curved Ducts

Scipedia content — Wed, 10 Mar 2021 15:11:44 +0100

During suction blow molding process, the extruded parison undergoes twisting deformation within the mold cavity, as the air drawing flow around the deforming parison exerts non-uniform shear stresses on its surface. This research is devoted in developing a fluid-structure interaction model for predicting parison deformation during suction blow molding process, with a specific emphasis on the suction stage. A fluid flow model, based on Hele-Shaw approximations, is formulated to simulate the air drag force exerted on the parison surface. The rheology of the polymer during suction is assumed to obey the K-BKZ integral viscoelastic model. The numerical results of this study allowed identifying a clear correlation between the twisting deformation undergone by the parison during the suction stage, also observed experimentally and the design parameters, namely, the air suction speed, the geometry of the duct mold cavity, and the parison/mold eccentricity.

Review of PSE (Problem-Solving Environment) in Computing Science

Scipedia content — Wed, 10 Mar 2021 15:11:16 +0100

In this paper a review is presented on the PSE (Problem Solving Environment) concept in computing science. PSE is an emerging scientific and technological active area in computing science. In the PSE concept, human concentrates on target problems and works on solutions, and a part of application of solutions, which can be solved mechanically, is performed by computers or machines or software. PSE provides integrated human friendly innovative computational services and facilities for easy incorporation of novel solution methods to solve a target class of problems. PSE is an innovative concept to enrich our e-Science, eLife, eEngineering, e-Production, e-Commerce, e-Home, etc. The PSE-relating studies were started in 1970's to provide a higher-level programming language than Fortran, etc. in scientific computations [Trans. Jpn. Soc. Comput. Eng. and Science, 20171001, (2017)]. The trend at that time was natural to deliver more humanfriendly programming environment, and was resulting in PSE, CAE (Computer Assisted Engineering), libraries, etc. At present PSE covers a rather wide area, for example, program generation support PSEs ['Enabling Technologies for Computational Science', Kluwer Academic Pub., 291, (2000)], education support PSEs, CAE software learning support PSEs, Grid/Cloud computing support PSEs, job execution support PSEs, e-Learning support PSEs, etc. This review paper includes the PSE definition, a brief history of PSE, example PSE study activities, uncertainty management PSE and future research directions in PSE.

A Multiscale Approach to Friction On Surfaces of Polymeric Solids and in Bulk Polymeric Materials

Scipedia content — Wed, 10 Mar 2021 15:11:07 +0100

Friction models of polymers must be considered in terms of specific microstructures, specific friction mechanisms and different scales on external surfaces of polymeric solids and inside the polymeric materials. Presented friction models take into account: evolution of surface microstructures, friction anisotropy and heterogeneity on surfaces of polymeric solids, micromechanical models of macromolecules, friction anisotropy in bulk polymeric materials

Advanced Computational Aided Development of Autonomous Inflow Control Device (AICD)

Scipedia content — Wed, 10 Mar 2021 15:10:58 +0100

Autonomous inflow control devices (AICDs) represent a successful technology utilized in maximizing reservoir sweep and increased oil recovery. They are an evolutionary enhancement over the passive inflow control device (ICD) such as a nozzle or helix type, which have a choke that is fixed for the lifetime of the well. This paper discusses a technique which accelerated the AICD development from defining the operational parameters to delivering a fully functional product, while considering the various mechanical and hydraulic loads that are critical in providing robustness during operations. Due to limited space availability between the AICD sub-assembly, basepipe dimensions, and complex loading conditions, iterative designs were established to meet the operational parameters. Simulations using finite element analysis (FEA) facilitated the development via performance evaluation of each design under various load conditions. The FEA simulation results provided the direction to refine, optimize and finalize the design. Mechanical loads evaluated in the simulations included: tension, torque, bending, and impact shock, while hydraulic loads included: collapse, burst, and injection pressure. On finalizing the design, the simulation results were validated with prototype testing. The final design met the operational parameters through FEA, that enabled the successful development of the product, saving more than 50% of a typical development cycle time. The FEA simulations provided stress information of each feature, modelling the anticipated loading during the service life, which contributed to the improved robustness and complex features reliability. Prototype test samples were manufactured based on the final design. A full range of validation tests were conducted to validate the final design of the simulation model and to establish appropriate operational limitations of the AICD assembly when subjected to various loads. A leak test was performed before and after the applicable tests to verify that a leak path had not developed. At the conclusion of every test, each AICD element (manufactured from tungsten carbide) was inspected for damage to verify the device had not failed. The test results proved the final design could achieve or exceed the minimum requirements under various load conditions using the simulation technique that accelerated the development process. This design has been used as the basis for various other sizes, with a similar mounting system, which have been successfully deployed in field applications. The use of this technique significantly accelerated the development process. It involved several design iterations and FEA simulations to evaluate various designs throughout the development cycle. FEA has been applied as a value adding tool to guide design optimization, which has been verified by testing, to successfully anticipate the loadings as per operational parameters. In addition to the shortened development process, the validation test development
cost was significantly minimized, using FEA, and a robust product was delivered. The validation test results aligned with the FEA predictions.

Numerical Studies of Different Mixed Phase-Field Fracture Models for Simulating Crack Propagation in Punctured EPDM Strips

Scipedia content — Wed, 10 Mar 2021 15:10:50 +0100

We consider a monolithic phase-field description for fractures in nearly incompressible materials, i.e., carbon black filled ethylene propylene diene monomer rubber (EPDM). A quasi-static phasefield fracture problem is formulated in mixed form based on three different energy functionals (AT2, AT1 and Wu’s model) combined with two different stress splitting approaches (according to Miehe and Amor). It leads to six different phase-field fracture formulations in mixed form. The coupled variational inequality systems are solved in a quasi-monolithic manner with the help of a primal-dual active set method handling the inequality constraint. Further, adaptive mesh refinement is used to get a sharper crack zone. Numerical results based on the six different problem setups are validated on crack propagation experiments of punctured EPDM strips with five different test configurations. As a quantity of interest, the crack paths of experiments and numerical computations are discussed.

A Finite Elements Penalized Direct Forcing Method to Take Into Account Infinitely Thin Immersed Boundaries in a Dilatable Flow

Scipedia content — Wed, 10 Mar 2021 15:10:10 +0100

In the framework of the new passive safety systems developed by the French Atomic Energy Commission (CEA) for the second and third generations of nuclear reactors, a numerical simulation tool capable of modeling thin inflow obstacles is needed [1]. Considering its future use in shape optimization and thermalhydraulics safety studies, the tool must be the fastest, the most accurate and the most robust possible. The aforementioned context has lead to the Computational Fluid Dynamics (CFD) modeling we are currently developing. For now, it involves a projection scheme to solve the dilatable Navier-Stokes equations and, to take into account obstacles, an adaptation of the Penalized Direct Forcing (PDF) method [2] a technique whose characteristics inherit from both penalty [3] and Immersed Boundary Method (IBM) [4] to a Finite Element (FE) formulation. This first modeling offers two variants : one in which the velocity imposed at the vicinity of an obstacle is constant and another in which it is linearly interpolated using properties of the considered immersed boundary (normal vector, barycenter, characteristic function) and the FE basis functions. The results obtained via those two variants, for laminar flow, are in good agreement with analytical and experimental data. However, when compared to each other, it appears that the interpolation of the velocity imposed at the vicinity of the immersed boundary increases the mesh convergence order which is very interesting, in term of accuracy/computation time ratio. Some enhancements of the tool are also considered, mainly related to turbulence modeling. Indeed, the interpolating process, instead of being linear, could follow a turbulent wall law.

Energy-Momentum Scheme with Drilling Degrees of Freedom for Composites with Curvature-Twist Stiffness

Scipedia content — Wed, 10 Mar 2021 15:09:57 +0100

This paper is motivated by the increasing application of 3D fiber-reinforced composites in rotating systems [1]. In 2D fiber-reinforced composites, single fibers with a diameter in the range of micrometers are embedded in a matrix material. But, these composites are prone to delamination damage, wherefore the development of 3D composites has been undertaken. Here, fiber bundles are woven, knitted, braided or stitched, in order to fix the fibers before they are surrounded by a matrix material. From a material modelling point of view, these two kind of composites make a huge difference, because a fiber bundle has to be considered as a beam-like structure with curvature-twist (bending as well as twisting) stiffness, in addition to the usual stretching stiffness (cf. [2]). The former is then responsible for the increasing strength-to-weight ratio of 3D fiber-reinforced composites for thin-walled lightweight structures. Therefore, 3D fiber-reinforced composites demand for a bespoke simulation technique. We have to consider a representative volume element, in which secondary effects as a micro inertia and a curvature-twist stiffness must be taken into account. We introduce these secondary effects in a continuum formulation by means of independent drilling degrees of freedom (cf. [3]). The resulting nonisothermal constrained micropolar continuum is derived by a mixed principle of virtual power (cf. [4]). This variational principle simultaneously generates in the discrete setting a mixed B-bar method and a Galerkin-based energy-momentum scheme of higher order. We also take into account viscoelastic material behaviour, which arises from a mixture of organic and inorganic fibers in a polymeric matrix material. Representative numerical examples demonstrate the twisting and bending stiffness of the fiber bundles.

Computational Modeling of the Experimental Response of Microscale Bistable Tensegrity Structures

Scipedia content — Wed, 10 Mar 2021 15:09:22 +0100

We report about the analysis, design, and experimental testing of modular structures composed of bistable units derived from the classic triangular tensegrity prism. Tensegrity structures are pinconnected frameworks, composed by bars and cables, possessing internal mechanisms and self-stress states, and featuring a variety of structural responses depending on their prestress, edge connectivity, and geometry. When a tensegrity system has only one internal mechanism and one self-stress state, as in the triangular prism case, it is possible to associate to it a corresponding bistable unit, by replacing all cables with bars and changing their edge-lengths slightly. After presenting experimental results of compression tests carried out on microscale specimens fabricated through multiphoton lithography, we compare them with the numerical predictions obtained by our computational model.

Computational Modeling of The Mechanics of Energy Harvesters Based On Tensegrity Solar Façades

Scipedia content — Wed, 10 Mar 2021 15:08:38 +0100

This work is focused on the computational design of tensegrity shading systems of energy efficient buildings which mitigate air conditioning consumption and optimize the energy performance of the building. It is concerned with the design of active solar façade screens based on lightweight tensegrity units, which are easily integrated with energy harvesting piezoelectric cables. The unit cells of the analyzed screens are controlled by tensioning and releasing selected cables of the structure. A numerical procedure simulates the dynamics of the analyzed tensegrity façades, by considering the opening and closure motions of the screens, and the vibrations produced by the action of dynamic wind forces. The energy harvesting ability of the proposed façade is numerically estimated.

Computational Modeling of the Seismic Response of Tensegrity Dissipative Devices Incorporating Shape Memory Alloys

Scipedia content — Wed, 10 Mar 2021 15:07:20 +0100

Infrastructures and buildings must have sufficient protection for design level earthquake excitations while minimizing major damage to comply with existing seismic design criteria. This paper explores the computational modeling of a tensegrity based brace, which helps dissipate energy while preventing inter-story drifts. The proposed brace integrates a D-bar tensegrity structure, shaped like a rhombus, with Shape-Memory Alloy (SMA) cables or tendons. These tendons grow austenitic-martensiticaustenetic (solid to solid) transformations, which make them more susceptible to mechanical stress when taking strain, and amplifying the stress into broad superelastic hysteresis, even after repeated mechanical cycles that require strains of up to 6% 8%. In addition in this article two special classes of the tensegrities are discussed namely 2D and 3D braces. 3D braces have been proven more efficient because of an enhaced capacity of energy dissipation, and also due to their improved safety against buckling. The effectiveness of the planned bracing paves the way to the development of innovative systems of seismic energy dissipation that combine tensegrity concepts with superelasticity.

A review of deterministic and data-driven methods to quantify energy efficiency savings and to predict retrofitting scenarios in buildings

Benedetto Grillone — Tue, 09 Mar 2021 11:41:02 +0100

Increasing the energy efficiency of the built environment has become a priority worldwide and especially in Europe. Because of the relatively low turnover rate of the existing built environment, energy efficiency retrofitting appears to be a fundamental step in reducing its energy consumption. Last experiences have shown that there is a vast energy efficiency potential lying in the building stock, and it is mainly untapped. One of the reasons is a lack of robust methodologies able to evaluate the effect of applied energy efficiency measures and inform about the expected impact of potential retrofitting strategies. Nowadays, dynamic measured data coming from automated metering infrastructure provides valuable information to evaluate the effect of energy conservation strategies. For this reason, energy performance modeling and assessment methods based on this data are starting to play a major role. In this paper, several methodologies for the measurement and verification of energy savings, and for the prediction and recommendation of energy retrofitting strategies, are analysed in detail. Practitioners looking at different options for these two processes, will find in this review a thorough and detailed overview of the different methods that can be used. Guidance is also provided to determine which method could work best depending on the specific case under analysis. The reviewed approaches include statistical learning models, machine learning models, Bayesian methods, deterministic approaches, and hybrid techniques that combine deterministic and data-driven modeling. Existing research gaps are identified and prospects for future investigation are presented within the main conclusions of this research work.

Integration of Marine Wave Energy Converters into Seaports: A Case Study in the Port of Valencia

Raúl Cascajo — Tue, 09 Mar 2021 08:49:02 +0100

feasibility study for the installation of Wave Energy Converters (WEC) in a Spanish Mediterranean port is evaluated in this paper. The final aim is to evaluate the possibility of building a new infrastructure which combines a breakwater and a WEC able to provide energy to the commercial port of Valencia. An estimation of the wave power potential is made according to existing databases from different sources. A review of the existing WEC types is carried out in order to choose the most suitable technology for its installation in a port environment. The authors discuss the main advantages and issues of the integration of WEC in port breakwaters. A prospective study for the Port of Valencia is made, considering the port energy demand evolution, historical data on wave energy potential and the port expansion plans. We conclude that Overtopping Devices (OTDs) are the most suitable ones to allow the good integration with the new breakwater needed for the expansion of the Port of Valencia and we give an estimation on the power available from the resource in our case study.

Método de Newton para búsquedas en Línea en el espacio de Hilbert (L^2)^3.

JORGE LOPEZ LOPEZ — Tue, 09 Mar 2021 03:26:06 +0100

Este trabajo trata sobre la aplicación del método de Newton para resolver un problema de búsqueda en línea asociado con la minimización de un funcional definido en el espacio de Hilbert (L^{2}(0,T))^3, con T un tiempo final dado. El funcional es parte de un problema de control de un circuito de 3 juntas de Josephson modelado por un sistema de tres ecuaciones diferenciales ordinarias no lineales dependientes del tiempo. El problema de control se puede resolver con el método de gradiente conjugado, dentro del cual se deben resolver problemas de búsqueda en línea como el descrito en este trabajo. Se describe tanto el caso continuo como su versión discreta para lo cual, las funciones en (L^{2}(0,T)) se aproximan por funciones lineales por pedazos y los sistemas diferenciales ordinarios se resuelven con el método de Euler Explícito.

Simulation of Surface Flow Through the Lattice Boltzmann Method Using Sub-basin Junction

Vanderlei Galina — Sat, 06 Mar 2021 22:20:07 +0100

The watershed surface runoff was investigated through the one-dimensional numerical simulation using the Lattice Boltzmann Method (LBM). A computational model was developed where the watershed is represented by the junction of nine sub-basins. For this, two equilibrium distribution functions were established through the Chapman-Enskog Expansion on a D1Q5 lattice, one suitable for flow on the basin surface and another for the main channel, obtaining the water depth on the basin surface and the channels cross-sectional area. In addition, the boundary condition was established in the flow passage from one sub-basin to another, taking into account the mass conservation and, in order to obtain a simulation closer to reality, it was considered an initial river flow (baseflow) of each channel stretch. The numerical results obtained by the LBM were compared with data measured in field.

A Study on the Effect of Time Duration by Vibrating or Tamping Fresh Concrete on the Compressive Strength of C-25 Concrete

Emer T. Quezon — Sat, 06 Mar 2021 17:01:03 +0100

Many years ago, consolidation accomplished by laborers wielding a variety of spades, tampers, and similar tools. In Ethiopia, there is no enough knowledge by the laborers, while the site engineers ignored the correct application due to some constraints. The agreement of acceptable vibration level in fresh concrete to which tamping time duration is optimum is an issue to obtain the desired specific compressive strength. This research study aims to evaluate the maximum time length and techniques used to Vibrating or Tamping fresh concrete and its effect on the compressive strength of C-25 Concrete through internal Rodding. Therefore, to study the effects of the period by vibrating or tamping, the needle-type internal vibrator was used to test new concrete cubes based on ACI309R-96. The quality of concrete is important to make physical tests on materials used before any actual experiments to perform. The fresh concrete samples tested by using internal vibration methods and techniques of compaction with different time duration of 1sec, 2sec, 3sec, 4sec, and 5sec. These tests performed by using steel rod in fresh concrete to know the Optimum time of compaction by internal vibration on the cube test of new concrete. Laboratory experiments had been conducted to check the methods and techniques applied to construction sites, as well as site observation on the effects of the vibration time of fresh concrete on the compressive strength and flexural strength of C-25 Concrete with varying vibration time duration and steel rod tamping. Based on the results of cube tests of compressive strength of Concrete Samples have been checked on the 3rd day, 7th day, and 28th day. This research study found out that the Optimum period of compaction was 3sec to produce an acceptable right quality of the concrete mix. Likewise, the flexural strength of the Concrete Sample, when it tested in the laboratory on the 7th day and 28th day, results revealed that the flexural strength improved when vibration time increased, but the amount of water has to be reduced to obtain the desired strength. Finally, Tamping is needed to place fresh concrete in the mold correctly. Furthermore, new concrete produced should match the properties and avoid improper tamping or vibration applications. This situation must not cause differences in the compressive strength of concrete.

Influence of Subsurface Courses Materials On Pavement Performance: A Case Study in Yebu-Agaro Road

Emer T. Quezon — Sat, 06 Mar 2021 16:56:02 +0100

The properties of subsurface materials would vary from place to place while it is true the performance of pavement along the route also differs. The research study had been undertaken at the Yebu-Agaro road section with the main objective to determine the Influence of Subgrade Soil on pavement performance. In order to realize the desired objective, a systematic methodology was adopted which includes field investigation, field test, and laboratory tests. While the purposive sampling method was used to extract soil samples from the road section that are severely damaged showing different failure types and non-distress surfaces. Those severe types of failures observed along the road section are reflective crack, pothole, rutting, alligator crack, and block crack. From these failure types, five representative samples were extracted at different locations along the failures section and one non-distress pavement of the road section using a manual hand auger. The analyses of soil samples were carried out based on the Geotechnical properties such as wash gradation, Atterberg limit, and Modified proctor test, California Bearing Ratio (CBR) and field test, as well as Axle load analysis. It was found out that the liquid limit of subgrade soil varies from 33% -60.5% and the plasticity index from 20.3% -30.1% while there was a significant increase in moisture content at the field and observed beyond the OMC in the laboratory result due to the distress of pavement affected by water infiltration through cracks, that tend to reduce the dry density. The recorded soaked CBR values of subgrade soil materials range between 8% -13%, which was below the 15% minimum value specified by the ERA manual. However, the existing CBR values of the subgrade soils indicate a poor material used for pavement structures. According to ASSHTO, the soil is classified as A-2-6 and A-7-6 category which means the existing soils are fair to poor as a sub-grade material while USCS classification shows that the soil falls into the SC group. In addition, the failures that are frequently observed on the road surface were significantly influenced by subgrade soil. For the sub-base layer materials, it was noted to have satisfied the minimum requirements as compared with standard specification, except deficiency of its thickness. For the base course materials, inferior qualities of material were used in some sections. The overall results showed that heavy vehicles or traffic loads are one of the major causes of road failure along the study road section. Hence, the influence of other factors such as poor drainage courses, level of groundwater table, variety of geologic materials along the road route, and poor construction materials should be thoroughly addressed before the start of the rehabilitation of the road section in the future. Finally, a possible remedial measure is recommended for every observed failure or distress on the pavement condition of the study area in order to sustain the design life of the pavement.

Investigation of Traffic Accident Prone Areas Related to Existing Road Condition and Driver’s Behavior along Menagesha- Ambo Road Section

Emer T. Quezon — Sat, 06 Mar 2021 16:48:02 +0100

Traffic accidents worldwide are increasing due to pragmatic vehicle ownership, acquisition, which necessitates daily activities. The primary objective of this research work was to identify the most hazardous location and provide countermeasures that will minimize traffic accident at the designated sites. The scope of the study was limited to Ambo-Ginchi- Addis Ababa road, a total length of the study road section of 87kms. The traffic accident data collected from each Wededa Police station covering the period of 2012-2015. It was analyzed using a Priority value formula for EjereWereda and Holota town, and accident frequency for Ambo wereda, Dendiwereda, and Welmeraweredato rank the traffic accident areas. Based on the results of the analysis, thirteen locations of the road stretch were found to be accident-prone areas. Out of these sites, three of them are in Ambo Wereda, two in Ejerewereda, one in Welmerawereda, and seven in Holota town. The time when most of the accidents occurred from 3:00 PM-6: 00 PM. The primary causes of the accidents were overspeeding, driving without attention, and some unknown reasons. Also, it showed that the drivers’ age group who caused most of the accidents composed of 25-34 years old. Based on the findings of the study, it is concluded that there was a significant increase in the number of crashes in the afternoon. Young drivers are believed to cause more accidents than older ones due to aggressiveness. To minimize the occurrence of accidents along the study road section, it is recommended that provision of speed limit signboards and warning signs at the strategic locations where traffic accident areas are identified to forewarn the overspeeding drivers. It is also recommended that the road agency should have to undertake to widen the lane width of the road, provision of sufficient climbing lane, installation of roadside Delineator, conduct roadside improvements, and repaint faded pavement markings.

Engineering Properties of Mechanically Stabilized Subbase Material Using Natural Gravel around Jimma Quarry Sites for Unpaved Road Construction

Emer T. Quezon — Sat, 06 Mar 2021 16:41:02 +0100

Unpaved roads are designed with a small input and are constructed from the nearest available materials as possible. It requires routine and periodic maintenance, and its condition can be significantly affected by a period of excessive traffic volumes or inclement weather conditions. The accurate estimation of maintenance cost is difficult. Many problems occur in the economic analysis of unpaved roads in comparison with paved roads. D effects that may affect unpaved roads are dusty, potholes, stoneness, corrugations, and rutting. Hence, it needs to apply a sufficient stabilization method to strengthen and increase the durability of the unpaved road. Mechanical stabilization is an important application in engineering for different types of construction to improve the performance of road construction materials. The objective of this research was to determine the Engineering properties of natural gravel materials by mechanical stabilization method to be used in subbase material for the unpaved road. The methodology carried out in this research study includes: (a) field visual inspection and sampling of natural gravel materials from three quarry sites around the Jimma area; and (b) laboratory tests to identify the physical and mechanical properties of natural gravel. Based on the laboratory test results, natural gravel materials from the Seka quarry site has an excellent Abrasion resistance of 35.26%, Plasticity Index of 13% a little bit above the upper limit, and good gradation (coarser and less subtle or binder materials), right CBR value. While the Jiren quarry site has a little Abrasion resistance of 52.09%, medium plasticity index, poor gradation (moderate fine material), CBR value of 28.90% which was below 30% minimum requirement, but had good MDD. On the other hand, the Merewa quarry site comprised of a very poor Abrasion resistance of 78.3 4%, Plasticity Index of 2 3.90% which was beyond the upper limit plasticity index of 1 2%, and poor gradation (more fine materials), poor CBR value and poor MDD. Therefore, it is concluded that the natural gravel from the Seka quarry site is suitable for the subbase course. But since road construction around Jimma is booming, the natural gravel from this quarry site would be soon depleted. About this, mechanical stabilization is recommended by blending the natural gravel from the Seka quarry site with 54% by weight with Jiren natural gravel of 46% by weight to meet the minimum requirements for subbase materials.

EFFECTS OF MECHANICALLY STABILIZED GRADED ASSORTED COARSE-GRAINED SOILS IN THE PERFORMANCE OF UNPAVED ROAD: A CASE STUDY IN GOFFA ZONE, SAWLA AREA

Emer T. Quezon — Sat, 06 Mar 2021 16:28:03 +0100

Road network development in Ethiopia is booming, radiating from Addis Ababa towards NorthSouth directions, and East-West directions, due to the good economic growth of the country. However, there are challenges always facing by the pavement designers, and materials engineers for every road project, specifically the unpaved roads in Goffa Zone. It was because, most parts of the existing unpaved road sections within the study area are heavily damaged, and lack proper maintenance. The source of good quality sub-base course materials limited and becoming depleted. It is for this reason that the research study focused on the investigation of the effects of mechanically stabilized graded assorted coarse-grained soils. Disturbed and undisturbed samples from different quarry sites were considered and tested in the laboratory. Laboratory tests for each location performed, and the results served as control values of the engineering properties of natural soils. The Disturbed samples tested for Gradation, Atterberg's Liquid Limit Tests, and Compaction, while, the undisturbed sample tested for the CBR strength, using the ASTM manual. The results of the assorted materials for the sub-base course were analyzed and compared with the AASHTO and ERA Standard Specifications.

Identification of Road Traffic Accident Blackspot locations and its countermeasures in Oromia Region, East Wollega Zone

Emer T. Quezon — Sat, 06 Mar 2021 16:07:02 +0100

One of the inputs for the economic development of a country is the expansion of the road network, which is important for the transportation of people and freights from place to place. With this expansion, the occurrences of a road traffic accident is increasing in all parts of the world from time to time, killing the lives of many peoples and damage to properties. This problem is growing with the highest rate in sub-Saharan African countries like Ethiopia. The general objective of this study is to identify the hazardous locations of road traffic accidents and suggest countermeasures to mitigate the occurrence of road accidents. The study area was conducted in the East Wollega Zone of the Southwestern part of Ethiopia in the Oromia Region. Districts exposed to high traffic volume are sampled using the purposive sampling method. Those sampled districts include Digga, Sibbu Sire, Nekemte town, Wayyu Tuka, Guto Gidda, Gobbu Sayyo, Leka Dullacha, and Jimma Arjo. Road accident data are collected from all administrative districts from September 2012 to June 2015 (2005 -2007 E.C), and it was used for the analysis. In addition, a field survey was made to observe the existing geometry, an environment of the roadside, traffic flow regulators, and markings of the road sections. To rank each of the sample districts, evaluation of Priority value had been used consisting of a number of deaths, minor and major injuries that occurred for three years. Based on these parameters, each of the districts was listed from highest to lowest (i.e. Digga, Nekemte town, Sibbu Sire, Wayyu Tuka, Guto Gidda, and Gobbu Sayyo) out of the whole sample districts. This research study had found out that there was a significant increase in terms of the number of deaths occurring due to road traffic accidents as a result of the increase in the coverage of road crashes and their consequences. The major causes of road accidents include over-speeding, ignoring warning posts, road geometry, deterioration of pavement, and roadside environment. In order to minimize the frequency of road traffic accidents at the identified hazardous road locations, countermeasures are recommended, addressing to the concerned agency which includes speed breakers, installation of guardrails at curvatures, installation of hazard light to minimize night-time road accidents, removing roadside obstructions, repair, and maintenance of pavement defects to restore to as-is good condition and building additional facilities for pedestrians in an urban area.

Investigation on the Suitability of Waste Plastic Bottle as Partial Replacement of Sand in a Cement Tile Production

Emer T. Quezon — Sat, 06 Mar 2021 15:51:03 +0100

The rapid growth of the world's construction industry is profoundly affecting the cost of construction materials, as well as the natural resources required to produce the materials and environment. Besides, waste plastic bottles are also becoming another challenge in our surroundings due to their presence in large amounts and their nonbiodegradability property. Even if various methods were attempted to manage this waste, applying it as the partial replacement for different construction materials seems feasible concerning solving the above-stated problems. The objective of this research was to investigate the competency of waste plastic bottles as partial replacement of sand in a cement tile production through conducting workability, dry density, water absorption, and compressive strength test on it at the particular 7th and 21st days of curing. Experimental laboratory method used in this research design for testing some physical and mechanical properties of cement tiles. Other than this comparative method was also applied to compare different properties of controlled cement tile with cement tile made with just 3%-33% ground waste plastic bottle as sand at 3% incremental ratio and also cement tile produced by sodium hypochlorite treated plastic sand. The result showed an increment in the workability of the fresh concrete of the cement tile, decrement in compressive strength, reduction in dry density, and declined water absorption result. Finally, the study concluded the possibility of partial plastic replacement of sand in a cement tile production up to 32.11% replacement ratio for 21st day curing ages and even if the replacement above 32.11% had an adverse effect on the compressive strength and workability of cement tile, it also got an advantage with respect to dry density and water absorption. Also, the study revealed the power of sodium hypochlorite solution in improving the high physical and mechanical properties of cement tile. It recommended for the responsible parties to apply this technology in the real production process of cement tile.

Assessment of Factors Affecting Labor Productivity on Road Construction Projects in Oromia Region, Bale Zone

Emer T. Quezon — Sat, 06 Mar 2021 15:44:02 +0100

Road construction in Ethiopia is booming and radiating from Addis Ababa towards North-East and East-West directions to fulfill its long-term development program. Transportation is a prime mover to all sectors in the country to uplift the economic activities of the populace in the locality. In most countries, experience and related literature have revealed that road construction labor costs accounted for 30-60% of the total cost of a project, depending on the terrain and source of materials, labor, and equipment to be utilized. Therefore, construction labor productivity plays a vital role in the performance and profitability of road construction projects. Road sector construction projects in Ethiopia are means through which development strategies are achieved. This research study gives insight on the assessment of the factors affecting labor productivity in road construction projects through a structured questionnaire survey of 83 respondents working on construction road projects in Oromia Region, Bale Zone. Respondents were required to rate how the 61 factors affecting labor productivity with respect to the importance and frequency of occurrence. Understanding these factors is helpful for the construction professionals who work on the initial phase of construction planning in order to efficiently deliver the project plan and to solve poor labor productivity. The results of this survey were then analyzed using the Relative Importance Index (RII) and ranked. The reliability of these 61 factors for assessing the effect on labor productivity was tested by Chronbach’s alpha measurement, and the results indicated that the 30 factors tested are reliable (α= 0.973), and checked by SPSS. The result of this analysis showed that there are 11 groups that have significant impacts on the labor productivity ranked as Material and Equipment Factor with RII=0.819, Manpower and WorkForce Factor with RII=0.764, Management Factor with RII=0.737, Quality Factors with RII=0.720, Supervision Factor with RII=0.699, Safety Factor with RII=0.691, Motivation Factor with RII=0.682, Schedule Factor with RII=0.647, Political Factor with RII=0.620, Natural and environmental Factor with RII=0.566 and Cultural and Religious Factor with RII=0.541. Based on the results of this research study, the top factors that affect labor productivity includes Lack of experience of labor, Material construction shortage, Lack of labor skills, Accident, Tools and Equipment shortage, Labor’s bad habit, Poor site management, Lack of Labor surveillance, Payment delay and Ignore safety precautions. Therefore, this research study suggests that the contractors should assign project managers and construction supervisors with sufficient managerial skills in road construction projects so that when there are any problems which may arise, it would be acted and solved immediately at the project site. On the other hand, the role of the Ethiopian government in project implementation is very significant, which requires proper attention to the productivity issue to enforce hard and fast laws and regulation which help to obtain productive workforce in the road construction industry.

Analysis of Road Traffic Accident Related of Geometric Design Parameters in Alamata-Mehoni- Hewane Section

Emer T. Quezon — Sat, 06 Mar 2021 15:34:02 +0100

Geometric design deficiencies on existing roads would lead to a potential accident, such as an accident that happens at the sharp curves, layered pavement conditions, and slippery pavement surface. A road traffic accident has been increasing in the Southern Region of Tigray, of which this area was shown to have alarming rates. According to the Southern Tigray Regional Police, a high figure of road traffic accidents was recorded in Alamata, Mehoni, and Hewane districts. This research study focused on the analysis of traffic accidents related to geometric design parameters of the existing asphalt road. While the data for the analysis covered route data, traffic accident reports from the police station containing some injuries, crashes, and damage to properties, as well as interviews and questionnaire surveys to people who are directly involved in road travels, are considered. The primary data have mainly covered the geometry of the road which was measured during the site survey, road safety audit using the checklist, interview, and questionnaire survey. On the other hand, the secondary data collected from the traffic management office in the district offices. On this, the results presented in the form of line graphs, pie charts, figures for road traffic accidents, and sketches for the suggested improvement in the road design problem. Based on the results of the study in the year 2010 to the year 2015, it found out that there were 866 Road Traffic Accidents have been occurring in the vicinity of the survey road sections. From this figure, the road traffic accident and damage to properties expressed as an equivalent amount of about 33,565,122.00 Birr. It revealed that the primary cause of road traffic accidents in the study area emanated from the road design elements due to some geometric deficiencies in the traffic accident-prone areas. Therefore, this study concluded that the frequency of occurrence of road traffic accidents and the figure of casualties is significantly increasing. This road accident would persist if the concerned agencies do not adequately address the malady.

Comparative Study on Compressive Strength of Locally Produced Fired Clay Bricks and Stabilized Clay Bricks with Cement and Lime

Emer T. Quezon — Sat, 06 Mar 2021 15:27:03 +0100

The local fired brick production technique is the known method of brick making, especially in Jimma Town. Firing of bricks in local brick production method is conducted by burning of much amount of woods. But this method of firing bricks by burning of woods will affect the environment. The locale firing technique is difficult to control the firing temperature, which will result in non-uniform burnt bricks. The major objective of this experimental study was to compare the compressive strengths of locally fired clay bricks and the local unfired cement and lime stabilized clay bricks. Specifically, the index properties of soil used for brick production, the compressive strength of locally fired clay bricks, and stabilized clay bricks had been determined and compare with the standard specifications. This study, it was used contents of the stabilizer for cement and lime of 10%, 12%, and 14%, respectively. The mix ratio applied 1:9, 1:7, and 1:6 by volume of clay with stabilizer 10%, 12%, and 14%. Based on the result on the 28th day, the mean compressive strength test, the 10%, 12%, and 14% cement Stabilized clay bricks have compressive strengths of 2.91Mpa, 3.28Mpa, and 3.79Mpa respectively, which are better than the mean compressive strength of the locally fired clay bricks which is 2.73Mpa. On the other hand, the 28th day means compressive strengths of the lime stabilized clay bricks were 2.19Mpa, 2.51Mpa, and 2.69Mpa, respectively. Therefore, these results showed that the Fired Clay Brick fails the minimum mean compressive strength requirement based on the ES, ASTM, and IS standards. But the Stabilized Clay Bricks fulfill the minimum compressive strength requirements of IS standard for stabilized bricks. Among these three methods, the cement stabilized clay bricks indicated better quality than both locally fired and lime stabilized bricks.

Evaluation on the Operational Characteristics of Gerji-Imperial Roundabout: A Case Study in Addis Ababa

Emer T. Quezon — Sat, 06 Mar 2021 15:20:02 +0100

Highly congested roundabouts are usually considered as the critical points within the urban road network and the evaluation of their performance provides valuable understanding and useful indication about the performance of the city road network system. Roundabouts should be designed to operate at no more than 85 percent of their estimated capacity. Beyond this threshold, delay and queues vary significantly from their mean values. The roundabout approach is dependent on the conflicting circulating flow and the roundabout’s geometric elements. In Addis Ababa, most of the intersections are congested and operate in poor LOS. During peak hours, it is common to see congestion, long queues, and delay at junctions. Accordingly, the objective of the study was to evaluate the operational characteristics of the selected roundabout in Addis Ababa. This research focused on the capacity and evaluation of the level of service at Gerji Imperial Roundabout and addressed the most important element of operational characteristics. The methodology employed for this study was the quantitative descriptive research design method. The necessary geometric data for the analysis (average entry width, circulatory road width, number of entry and circulatory lanes, and island diameter), traffic movement data with vehicle characteristics, and pedestrian volume were collected from the study area. The capacity analysis was done based on the gap – acceptance method that is adopted by the SIDRA Software program. Based on the results, the degree of congestion of the roundabout found out to have 1.749 which is far beyond the recommended values for a satisfactory level of service. Therefore, this indicates that the Gerji-Imperial roundabout is serving in a poor level of service. It is recommended to construct a road overpass or underpass at the most problematic approach to improve the operational capacity of the intersection.

EXPERIMENTAL STUDY OF STABILIZED EXPANSIVE SOIL USING PUMICE MIXED WITH LIME FOR SUBGRADE ROAD CONSTRUCTION

Emer T. Quezon — Sat, 06 Mar 2021 15:14:02 +0100

Unsuitable soil materials along the alignment of road projects have a significant influence on planning, design, construction, and maintenance. Expansive soils are susceptible to considerable volume changes due to seasonal variations and moisture content. Most soils found in Jimma and Ambo Zones composed of plastic clay soil, causing severe damage at the intermittent of pavement sections. This research study conducted laboratory investigation considering combinations of materials blended to stabilize the expansive soil for subgrade construction. An experimental type of study performed started by collecting specimens. Two clayey soil specimens considered to test the free swell index obtained from a depth of 1.5m to remove the organic impurities. Results indicated the chemical analysis of pumice contained 82.68%, while its physical properties of the test of fineness specific surface and residue on 45 microns showed 3770 cm2/gm and 30%, respectively. As the lime content increased, the CBR strength also increased. But, if the percent content of lime decreased with an increasing pumice content, the CBR value did not show any significant increase. Both the chemical and physical properties satisfied the requirements according to ASTM C-618. Hence, this experiment obtained 7% lime + 3% pumice as an optimum mix ratio to stabilize expansive soils.

Traffic Safety Evaluation on Urban Road Un-signalized Intersection using Proactive Approach: A Case Study in Adama City

Emer T. Quezon — Sat, 06 Mar 2021 15:10:03 +0100

Deaths and injuries as a result of road accidents are a recognized global problem and authorities are aware of the consequences this global phenomenon might lead to. Because of the rapid development of urbanization and motorization in developing and transitional countries, like Ethiopia, actions to improve traffic safety conditions are urgently needed. Highway intersections are among the greatest safety challenges because they are some of the most common highway features. Improving the safety level of the urban intersection is an important way to increase safety. Safety evaluations can help to develop effective safety countermeasures to lower crash rates and reduce crash severity. So how to diagnose safety problems and improve urban road intersection safety effectively becomes an important issue. Now, there have been quite a number of safety analysis methods and theories in the city intersection, but these methods and theories are formed on the basis of traffic accidents. However, the data on traffic accidents is not accurate enough, these theories are not appropriate for our country. Also, it is impractical and unethical to wait for accidents to occur before being able to draw statistically sound conclusions regarding safety improvement. Hence there is a need to develop a proactive approach, a non-accident-based approach, to evaluate urban road Unsignalized intersection safety performance. A proactive approach (indirect and non-accident based approach) was attempted to that of traditional reactive approach (direct and accident based approach) which is purely based on the existing conditions that have direct relationships or impacts to traffic safety such as the geometric, traffic control & engineering, road Surface and environment characteristics. The non-accident-based approach is based on field surveys under the conditions mentioned previously, summarizes the intersection safety diagnosis in a safety index to indicate the safety performance of the intersection. The study indicates that the proposed methodology and intersection safety diagnosis technique can be used to perform an evaluation of traffic safety and improvement at an intersection even when there are few resources available. Also, the use of intersection safety diagnosis is a more resource-efficient and ethically appealing alternative for fast, reliable, and effective safety assessment.

Effects of Varying Dosage Replacement of Cement Content by Animal Bone Powder in Normal Concrete Mix Production

Emer T. Quezon — Sat, 06 Mar 2021 15:01:02 +0100

Cement being the main constituent of concrete plays a vital role in concrete production. In Ethiopia, cement consumption has grown well with a growth rate of about 16.1% per year. Hence, an alternative material to partially replace cement was initiated to reflect the needs of the local community in the study area. The waste quantity of animal bones has impacted the environment which is unusual to see in other Non-African countries. The primary aim of the research is to investigate the effects of varying dosage replacement of cement by animal bone powder (ABP) in normal concrete production. The bone samples collected from the Seka Waste Disposal Site of Jimma town, approximately 10km from the bus station where a quantity of waste animal bones can be found. After cleaning and drying, the bone samples burned in the Furnace. The average required energy to burn the animal bone obtained at a temperature of 340°C. The burnt bone was allowed to cool before grinding in a hammer mill and sieving. There were six proportions prepared to start from 0% (as control specimen), 5%, 10%, 15%, 20%, and 25% dosage increment by weight of bone powder, and evaluated the normal concrete strengths of C-25 grade concrete. The laboratory test results indicated the chemical analyses of a bone powder composed of similar compounds of oxide in cement but slightly lesser in content based on ASTM C-150. Likewise, the effects of replacing animal bone on the properties of cement such as consistency and setting time remained within the acceptable limits of the Standard Specifications. On the other hand, the results of compressive, flexural tensile, and split tensile strengths significantly declined from the control specimen during the dosage increment of the replacement made. Therefore, the optimum dosage of the bone powder indicated 10% by weight to replace cement content in normal concrete mix production.

Suitability of Ambo Sandstone Fine Aggregate as an Alternative River Sand Replacement in Normal Concrete Production

Emer T. Quezon — Sat, 06 Mar 2021 14:32:03 +0100

Technical experts in construction industries are trying to improve the quality, ease of using materials in different forms, and increasing structure performance. However, in the changing cost of each item, quality of works could be sacrificed. In Ethiopia, the practice of using alternative ingredients to produce materials was observed weak in some scenarios. It was because ignoring the right procedures to perform the required material requirements for construction materials. It is known that Ambo area has a scarcity of natural sand or rivers sand which can be extracted from the river bed. Notably, if available, the quality is not good due to the presence of silt and clay. Once it used, it adversely affects the structural integrity of concrete structures. The primary objective of the research is to evaluate the suitability of Ambo Sandstone Fine Aggregate (ASFA) as an alternative replacement of river sand in normal concrete production. Samples extracted from Senkele and Aleltu quarry sites of Ambo Area. Results showed that fine aggregates from Senkele quarry site indicated 14.28% silt content, while from the Aleltu quarry site indicated 12.28% silt content, all of which exceeded 6% based on Ethiopian Standard Specification. It means the samples must be rejected or appropriately washed before use as a part of a concrete mix. After performing the procedure to remove silt content, it found out that the silt content reduced to 5.3%, less than the allowable maximum of 6%. Hence, Ambo Sandstone Fine Aggregates (ASFA) are suitable for concrete mix production and strength determination. There were nine samples of concrete cubes prepared and tested at 7th, 14th, and 28th days for concrete compressive strength with a mix ratio of 1:2:3 and water to cement ratio of 0.50. Based on the laboratory test results with full replacement of river sand by Ambo Sandstone Fine Aggregate (ASFA), the mean compressive strengths at 7th day was 16.61 MPa, while at the 14th day was 19.62MPa, and at 28th day was 25.59 MPa. It means at 28th day; it satisfied the minimum requirement for C-25 grade concrete. Likewise, the cost of production of the fine aggregate of the Ambo Sandstone quarry site is 140 ETB per cubic meter, while the price of river sand from Legeher Market is 300 ETB-400 ETB per cubic meter. Therefore, Ambo Sandstone Fine Aggregate (ASFA) is cheaper than the river sand. However, it must be given emphasis that the Ambo Sandstone Fine Aggregates must wash thoroughly before use in construction projects.

Factors Affecting the Performance in the Implementation of Government Building Construction Projects: A Case Study in Bole SubCity of Addis Ababa

Emer T. Quezon — Sat, 06 Mar 2021 14:29:03 +0100

Building project implementation has so many issues and complex performance, such as time, cost, quality, and safety. This study identified and assessed the essential factors influencing the implementation of public building projects, particularly in the Bole Sub-city of Addis Ababa. There were 46 factors identified, validated, and divided into 9 categories. Questionnaires are distributed to 120 respondents, of which 8 for owners, 25 for consultants, 86 for contractors, and one head of the office. The key factors decided upon were: liquidity of the organization, improved availability of commodity prices for people with high experience and expertise, and the quality of equipment and raw materials in the project. The agreement between the parties on the ranking of factors was calculated based on their Relative Importance Index. Besides, the value of the Cronbach’s Alpha for variables calculated above 0.7, which means the data and scale are reliable and accepted for further analysis to correlate the different groups of factors. Results showed that cost, time, quality, productivity, and customer satisfaction are the top five essential factors affecting the performance of the government public building in the study area.

Experimental Study on the Use of Reclaimed Asphalt Pavement as Base Course Materials through Blending with Crushed Stone Aggregates

Emer T. Quezon — Sat, 06 Mar 2021 14:18:02 +0100

Overlay and maintenance resolve medium distress, but reconstruction may feasible and economical while Asphalt pavement are badly deteriorated with time and traffic. This requires the removal of existing pavement surfaces. Recycling such construction waste has benefited from economic to sustainability point of view and reduce the exploitation of natural resources. The shortage of virgin aggregate supplies along with the increase in processing and hauling cost have encouraged the use of reclaimed material from the old structure as base course construction materials, and involved in regular practice in various countries around the world. Unfortunately, using Reclaimed asphalt pavement (RAP) is to take off in Ethiopia despite the current ambitions of road building program ongoing. However, RAP material may be not conventional road making materials and need for improvement. This study was aimed to investigation the Engineering properties effect of using RAPs and CSA in their natural state by conducting common laboratory tests in first phase, and Second phase of the study was intended to analysis the strength and interpret the optimum allowable percentage as partial replacement of CSA blended with 10/90, 20/80, 30/70, 40/60, 50/50 proportions by total weights from the two quarries site in Jimma town for RAP as compared results with specification for highly trafficked road (GB1) materials. According to the AASHTO soil classification system the natural and blends of RAP-CSA were classified under A-1-a. The mechanical and physical properties test results for neat natural blended Jimma-Sokoru with Jimma-Agaro roads RAP aggregate gives ACV, AIV, LAA, SG, CBR and Water absorption of 7.9%, 9.5%, 7.8%, 2.31, 42.1% and 0.98% respectively. Also the mechanical blending of 30% RAP aggregate and 70% CSA test results were 15.7%, 12.8%, 16.5%, 107.63%, 2.67 and 1.24% for ACV, AIV, LAA, CBR, SG, Water absorption values respectively with 143KN and 114KN when soaked and unsoaked in water for TFV results. The results obtained from Gradation, Atterberg’s limits, SG and water absorption ACV, AIV, LAA, Compaction and CBR results indicate that Mixes containing 30% RAP contents were successful replaced CSA in highly trafficked unbound road base course layer of Asphalt concretes.