Scipedia: Documents published in 2023

Improving asphalt discrete numerical modelling with realistic particle shapes

Jesús Sánchez Pinedo — Thu, 23 Nov 2023 13:37:18 +0100

Micromechanical modelling based on the Discrete Element Method (DEM) has been widely used to investigate asphalt behaviour due to its ability to represent an irregular microstructure with variable-sized aggregates, bitumen and voids. The 3D rigid particle models with randomly distributed spherical particles and adopting elastic and/or simple viscoelastic models at the contacts are the standard approach, however, in recent years, a significant research effort is noted to incorporate real particle morphologies in the numerical models. In this study, a previously developed 3D DEM model of asphalt employing a generalised Kelvin contact model formulation for the viscoelastic contacts is further improved with realistic particle shapes representing the coarse aggregates. A digital library of aggregate shapes was created from the X-ray computed tomography (CT) scan of an asphalt specimen, using an adaptive image-processing method to separate the aggregates in the CT images and the Delaunay triangulation method to define the aggregate 3D surface model. Several virtual aggregates with different sizes were selected from the library to represent the coarse aggregate gradation of the modelled 3D DEM asphalt specimen. Each virtual aggregate is discretized with smaller spherical particles and its deformability is taken into account through the inner particle contacts. The numerical asphalt specimens with realistic particle shapes were submitted to uniaxial tension-compression cyclic tests to determine the stiffness properties, and the results were compared with those of the numerical specimens with all constituents represented by single spherical rigid particles. As shown, the proposed methodology greatly enhances the 3D DEM model's ability to simulate the asphalt behaviour.

Investigation of Dynamic Characteristics of Rolling-Ball Dampers

Jesús Sánchez Pinedo — Thu, 23 Nov 2023 13:37:03 +0100

Tuned mass dampers, consisting of a mass, spring, and damper, are widely used for vibration suppression in structures. Despite being small and lightweight, these dampers exhibit excellent damping effectiveness. However, there are issues such as performance degradation due to the aging of the spring and damper, as well as the need for frequent maintenance. Therefore, as an alternative vibration control device that does not rely on these components, a rolling-ball damper is proposed. This damper consists of a container with a lid and multiple enclosed particles on its curved surface. By utilizing the contact between particles and the friction between particles and the container, the rolling-ball damper can absorb and suppress the vibration energy imposed on the structure to which the container is attached. In this study, we investigated the characteristics of the rolling-ball damper in a horizontal vibration system. We experimentally verified the effects of the size and number of enclosed particles on damping performance. Furthermore, numerical simulations were conducted by the discrete element method using EDEM® software and the multibody dynamics simulation method using MotionSolve® software. A comparison between experimental and numerical simulation results demonstrated the effectiveness of numerical calculations in predicting the amplitude response

Experimental and Numerical Studies on the Efficiency of Damping upon Horizontal Stirring of Granular Materials

Jesús Sánchez Pinedo — Thu, 23 Nov 2023 13:36:46 +0100

In this study, the damping torque exerted on a horizontally rotating blade in granular materials under gravity was investigated. To capture the stirring behaviour of the granular materials in detail, a mechanical stirring apparatus was fabricated. The rotating blade was driven sinusoidally by a shaker through a ball screw mechanism. It was found that energy dissipation depends on various parameters such as particle material and particle size. Energy dissipation was also calculated using the EDEM® software based on the discrete element method. To verify the validity of the numerical simulation model, numerical simulation results were compared with experimental results.

Fast Point-To-Mesh Distance Computation Technique Based On Cell Linked List For Polygon-Wall Boundary In Moving Particle Semi-Implicit Method

Jesús Sánchez Pinedo — Thu, 23 Nov 2023 13:36:27 +0100

The simulation of fluid-structure interaction (FSI) problems usually involves many degrees of freedom, and a considerable number of particles is generally required to model both fluid and solid domains. In relation to the modeling of solid walls by particles, the use of triangular meshes provides more efficient and smoother representation of complex-shaped solid surfaces as well as the straight coupling between particle and mesh-based methods, which is suitable for FSI applications. However, in the particle-based simulations with solid boundaries modeled by mesh, the computation of the particle-mesh distances is a critical time-consuming task, and a fast technique is of major importance. Taking advantage of the cell linked list structure widely adopted for fixed-radius neighborhood search algorithms in particle methods, we proposed a Fast Point-to-mesh Distance computation technique based on Cell linked list (FPDC). Alongside this new technique, a particle-polygon wall contact model was introduced to enable simulations of the collision between the surface of the moving bodies and fixed wall represented, respectively, by particles and mesh. The results show that the proposed technique provides a significant processing time speedup and can be used for practical large-scale problems.

A coupled DEM-CFD model to study the physical behavior of loose armor revetments in maritime waterways

Jesús Sánchez Pinedo — Thu, 23 Nov 2023 13:18:39 +0100

Revetments serve to protect a canal or river bank against erosion caused by natural and ship-induced waves and currents. A profound understanding of loads and resistances acting on revetments is indispensable for an economic and sustainable, but also safe revetment design. This paper presents a coupled CFD-DEM model (Computational Fluid Dynamics and Discrete Element Method) to study the physical behavior of loose armor stone revetments in maritime waterways. The waves and currents are modelled with a CFD add-on for the particle-based DEM software PFC3D. The DEM approach allows to simulate the shape, size and mass distribution and displacement of the individual armor stones realistically. DEM and CFD are coupled to capture the response of the armor stones to the hydraulic loads. In this paper, the model calibration and validation are presented using data derived from a full-scale flume experiment. The numerical model is compared to the flume tests where a slope is subjected to flow at different velocities. It can be shown that the implementation of revetment and hydraulic loads provides results that are consistent with the experimental data. Both flow velocities and armor stone displacements agree well between the physical and the numerical model. The herein presented study thus provides the basis for the application of the numerical model to more advanced stability analyses of revetments that are, e. g., subjected to wave and current attack.

Elastic Behaviour of Linear Structures Using Modal Superposition and Lagrangian Differencing Dynamics

Jesús Sánchez Pinedo — Thu, 23 Nov 2023 13:18:11 +0100

Elastic deformation and dynamics response of the linear structures due to fluid loads are studied to understand the Fluid Structure Interaction (FSI). A modal coupling solver is developed by solving dynamic equation of motion with external loads, using the mode superposition method with the help of relevant mode shapes and natural frequencies associated with the structure. Natural frequencies and mode shapes have been pre-calculated and provided as input for the simulation. Modal coupling is integrated into the Lagrangian Differencing Dynamics (LDD) method, utilizes finite differences within the framework of Lagrangian context, and strong and implicit formulation of Navier Stokes equations to model the incompressible free-surface fluid. Elastic deformation of the structure due to fluid force obtained from the flow solver is calculated in the modal coupling algorithm using direct numerical integration. Then the elastic deformation is imposed in the flow solver to account for change of the geometry and obtain new flow pressure and velocity fields. The two-way coupling of fluid and structure is successfully validated by simulating dam-break through an elastic gate. Since the LDD method works directly on surface meshes, the simulation is quickly setup and direct coupling of structural deformation eliminated the usual step of mapping of fluid results on the structural mesh and vice-versa

A DEM-FEM Coupling Framework Applied to Railroad Infrastructure Simulations

Jesús Sánchez Pinedo — Thu, 23 Nov 2023 13:17:48 +0100

Swedish and other European governments invest significant resources in railroad infrastructure, including maintenance and construction. The degradation of track ballast layers is one of the most critical maintenance issues. Hence, it is of significant interest for infrastructure owners to find novel solutions to mitigate the problem by improving design and maintenance operations. However, established tools for the simulation of railroad systems typically consider the ballast as a solid continuum structure, while in practice, the discrete nature of the particle assembly has to be accurately represented in the model. The sleepers and rails must be modelled as solid structures, which results in the complex coupled problem of combining particulate and structural analysis models. In this paper, the simulation of railroad infrastructure with the example of a transition zone is performed with an explicit surface coupling algorithm of the Discrete Element Method (DEM) and the Finite Element Method (FEM). The ballast layer is represented by individual particles in DEM, where the computations are performed on the GPU. This study focuses on the comparison between a convex and a non-convex particle shape. The rail system with sleepers and the subground with varying stiffness is modelled with solid structures in FEM. Properties of the ballast bed, such as the particle shape, are found to have a significant impact on the stiffness within the bed and the deflection of the sleepers and rails. Furthermore, the sudden transition from low to high stiffness causes a peak in tensile stress in the subground. The results show that accurate particle shape representation and high computational performance are critical aspects of achieving predictions on a relevant scale. Studying the ballast layer as a particulate system provides a new perspective on dynamics in tracked ballast structures.

Computational Modeling of Cold Spray Process Using Particle-based Methods

Jesús Sánchez Pinedo — Thu, 23 Nov 2023 10:58:20 +0100

Cold gas dynamic spraying (CGDS), as a high strain rate shearing and innovative solid-state technique enables to rapidly develop additive manufacturing and coating for metal deposition. This paper investigates the development and evolution of various interfacial bonding characteristics during high strain rate shearing process through Multiphysics numerical simulations of single particle impact. Two different particle-based modeling strategies such as smoothed particle hydrodynamics (SPH), molecular dynamics (MD) are investigated using commercial software ABAQUS/Explicit and LAMMPS, respectively. To separate the difficulties related to complex metallurgy of alloys, our first investigations focus on pure aluminum. The Johnson-Cook (J-C) constitutive model is used to describe the high strain rate self-consolidation process in SPH modeling. Embedded Atom Method (EAM) is used to describe the interactions between Aluminum atoms in MD modeling. The predictions from the different particle-based models are compared with each other and with experimental results. Through the investigations, SPH numerical approach has strong advantage in capturing the phenomena that occur during the cold spray process. It is able to describe the complex features of particle and substrate, especially in the interface vicinity. At the same time, MD numerical approach gives the fundamental understanding of the deposition behavior at the atomistic level. The key finding is the strong relationship between the un-uniform distribution of shear strain and jet formation during high-speed collision. Plastic strain along with an increase of temperature lead to thermal softening of pure Aluminum resulting in metallurgical bonding at the interface.

Particle-based Flow Simulation of Molten Aluminum Alloy Through Casting Filters

Jesús Sánchez Pinedo — Thu, 23 Nov 2023 10:58:02 +0100

Casting defects can be predicted in advance of practice and countermeasures can be taken to improve casting quality and increase productivity. Applying the casting filters is a method of improvement methods for defects caused by unsuitable molten metal flow. Casting filters have the effect of removing inclusions in molten metal and rectifying the flow. However, specific conditions such as the type, pore size, and setting position of the casting filter are not clear. Casting filter conditions are determined by conventional empirical rules that are not theoretical. In the other view, the use of casting CAE is essential to realize front-loading for the process design process, in which casting defects are predicted in advance of practice and countermeasures are taken. In the previous study, K. Taki et al. performed direct observation of mold filling and flow simulations passing through the casting filter. The particle-based COMINA CAE software was used for the flow simulation of molten metal in complex interior geometries in the filter. The calculations used a model of the filter that was reproduced on an X-ray CT system. To inspect the filter performance it was necessary to make a small and simplified filter model, which is called the 1/4 model of filter. In the present study, the flow dynamics through the filter are investigated using various 1/4 models. The 1/4 model maintains permeability on the surface and porosity of volume while halving the dimensions. As a result, we succeed in reproducing the flow behaviour of molten metal when it passed through the filter by setting the particle size of molten metal to 1/16 of the filter’s pore diameter. Further, we try to evaluate the performance of the filter by extending the calculation target from only the area around the filter to the entire mold. If mold filling behavior for the mold with filter could be simulated, it wouldbe used effectively in casting geometry design and defect countermeasure.

Examination of Variable Tilting Speed on Flow Behaviour during Ladle Pouring in Die Casting using SPH Simulation

Jesús Sánchez Pinedo — Thu, 23 Nov 2023 10:57:42 +0100

Disturbance of the molten metal flow during ladle pouring before the plunger advancing in the aluminium alloy die casting process can cause entrapment defects of air and oxide film. Slow pouring to control the turbulence of the flow front reduces productivity due to increased cycle time. Further, the risk of cold flake formation increases caused by large temperature drops in accordance with the long cycle time. On the other hand, rapid pouring is desired to improve productivity, but the risk of air entrapment increases. Therefore, quick and quiet pouring is desired in the ladle pouring process. In the present study, we focus on variable tilting speed as a method to achieve good ladle pouring. The effects of variable ladle tilting speed and switching time on the wave behavior of molten metal are investigated in visualization experiments and simulations. The flow behaviours in ladle pouring are simulated using ”COLMINA CAE”, which is the casting analysis software by particle-based SPH method. Furthermore, the plunger advancing process is also examined. From the simulation results, the variable tilting speed from fast to low can suppress the rise of the maximum wave height of molten aluminium alloy. However, the pouring completion time is longer. Further, the falling position of molten metal poured from the ladle varied with changing tilting speed. And then, the wave height is influenced not only by ladle pouring but also by the plunger advancing process. These trends of wave behaviour obtained in the simulation are similar to that of the actual phenomenon. Therefore, the present simulation method can accurately estimate the ladle pouring process and plunger advancing process. So, casting CAE is an effective tool for exploring die casting conditions.

Comparison of Incompressible and Weakly-Compressible SPH for the Simulation of Laser Beam Welding

Jesús Sánchez Pinedo — Thu, 23 Nov 2023 10:57:25 +0100

The process of laser beam welding is simulated using the Weakly-Compressible Smoothed Particle Hydrodynamics (WCSPH) and the Incompressible SPH (ISPH) methods. The presented models consider significant physical effects such as heat conduction, temperature-dependent surface tension with wetting, the phase transitions melting and solidification, and an evaporation-induced recoil pressure. Here, particular emphasis is placed on the modeling differences between the WCSPH and ISPH methods. Then, both methods are evaluated in terms of their accuracy and performance in the simulation of deep penetration laser beam welding with oscillating laser power.

Calibration of AM powders for Optimization of Recoating Applications using DEM

Jesús Sánchez Pinedo — Thu, 23 Nov 2023 10:57:04 +0100

Additive Manufacturing (AM) has been a subject of significant attention from both industrial manufacturers and research communities. However, several challenges hinder the widespread implementation of this technology in the industry. Powder recoating is a crucial step in powder-bed AM process that involves achieving a uniformly packed bed of powder particles that are later melted by an energy source, such as a laser or electron beam. One of the main challenges is calibrating the contact model parameters accurately to match the flowability and spreadability of specific powder alloys. This paper proposes a Discrete Element Method (DEM) model calibration framework based on surrogate model optimisation. The study utilises a Revolution Powder Analyser (RPA) as the experimental reference system. The proposed method is demonstrated with two AM powder samples, Ti64 and Inconel 718. The results indicate that particle-particle friction, rolling resistance, and van der Waals (vdW) surface energy significantly affect the system responses. Furthermore, the validation results show good correspondence between the simulation with calibrated parameters and experimental data. Overall, proposed calibration framework has the potential to optimise powder recoating and to improve the accuracy and effectiveness of the additive manufacturing.

How the Packing Density and Penetration Resistance is Influenced by Particle Shape: DEM Modelling of Plate Penetration in Granular Media

Jesús Sánchez Pinedo — Thu, 23 Nov 2023 10:44:35 +0100

Granular materials play a crucial role in various geotechnical, mining, and bulk handling applications. Understanding their mechanical properties is essential for optimal use in these industries. Traditional experimental methods like Cone Penetration Test (CPT) and open pile testing have limitations on their repeatability and offer little insight into the contact mechanics. The Discrete Element Method (DEM) is a powerful tool for investigating and simulating granular material behaviour at the element scale and provides deeper understanding in geometry-material interactions. However, due to computational costs, spherical particles are often preferred, though they may not always capture realistic particle interactions. In the current study, the packing density and the penetration resistance of particle beds with different particle shapes, including sphere, multi-spheres and polyhedrons, are compared using a plate penetration test modelled in DEM. Sensitivity analyses are performed for sliding friction, consolidation pressure, and Particle Size Distribution (PSD). Results indicate that polyhedral shapes show lower penetration resistance compared to spherical and multi-spherical shapes. Sliding friction has the most significant impact on resistance, while consolidation pressure has minimal effect on porosity. The study highlights the importance of particle shape in granular media modelling and emphasizes the need for further research in this area.

ISPH with a Geometric Multigrid Preconditioning Solver using Background Cells in GPU environment

Jesús Sánchez Pinedo — Thu, 23 Nov 2023 10:44:16 +0100

Incompressible fluid analysis using the ISPH or MPS methods requires the solution of the pressure Poisson equation, which takes up most of the overall computation time. In addition, the iteration number for solving pressure Poisson equations may increase as the simulation model scale increases. This is a common problem in particle methods and the other implicit time integration solvers. In different methods, FEM, etc., good quality preconditioning, such as multigrid preconditioning, can significantly improve the convergence of iterative solution methods. There are two types of multigrid preconditioners, algebraic multigrid and geometric multigrid methods, but there are few examples of their application in particle methods. In this study, we attempted to develop a framework for a geometric multigrid preconditioner for solving the pressure Poisson equation in the ISPH. First, we focused on the geometric multigrid preconditioner using background cells, which are used for neighboring particle search, and implemented it on a GPU environment. Through a simple dam-break problem, we compared the computation time between the Conjugate gradient (CG) solver with a traditional preconditioner and the CG solver with a geometric multigrid preconditioner. We confirmed that the background cell-based geometric multigrid preconditioner is practical for the ISPH method.

A Macro-Meso-Microscale Meshless Model for Multiphysics Particle-Laden Flows

Jesús Sánchez Pinedo — Thu, 23 Nov 2023 10:33:09 +0100

This work extends a multi-phase mixing model framework designed for a Smoothed Particle Hydrodynamics context. Specifically, we propose a higher-order variation using the first-order accurate Generalised Finite Difference differential operators to construct an incompressible scheme for simulating fluid-solid coupled systems resolved via a continuum mixture model. The proposed scheme incorporates inter-phase shear between phases and the viscosity dependency of the solid phase concentration. The scheme is verified by simulating a modified lid-driven cavity case at Re = 1000. In this simulation, our method was capable of treating initially discontinuous concentration fields with a maximum solid volume concentration of 0.5 and a solid-to-fluid density ratio of 4.

Discrete Element Method to simulate the thermo-mechanical behavior of plasma-sprayed thermal barrier coatings during a thermal cycle

Jesús Sánchez Pinedo — Thu, 23 Nov 2023 10:32:51 +0100

Thermal Barrier Coatings (TBCs) are multilayer systems used in Ni-based superalloy components for gas turbine blades submitted to high temperatures resulting in the development of high thermal stresses. The intricacy of their microstructure coupled to severe environmental conditions lead to their premature failure according to complex mechanisms involving notably creep and Coefficient of Thermal Expansion (CTE) mismatch effects. This work aims to investigate the development of thermal residual stress within TBCs during a heating step using a numerical model based on Discrete Element Method (DEM). The suitability of such an approach is investigated in terms of stress field distribution in comparison to Finite Element Method (FEM). Results reveal the capability of the proposed DEM approach to simulate creep phenomenon in a TBC system under thermal loading and predict accurately thermal stresses leading to failure.

Particle-based Semi-resolved Coupling Model for the Simulation of Internal Erosion in soil structures

Jesús Sánchez Pinedo — Thu, 23 Nov 2023 10:32:31 +0100

Internal erosion, caused by seepage flow inside the soil, accelerates soil failure during a natural disaster. Numerical simulation can be an effective tool to quantitatively evaluate the relationship between internal erosion and the instability of the ground as a whole. Internal erosion and multiphase flow simulation of fluid and granular materials with a particle size distribution require coupling simulations that can represent the interaction between particles and pore water and the movement of particles. There are two main types of coupling models: ”Resolved coupling model,” which can calculate detailed flow and fluid forces, and ”Unresolved coupling model,” which is based on empirical drag and seepage flow models. Previous studies have indicated that both models should be judged appropriately based on the ratio of particle-fluid spatial resolution. However, applying a resolved coupling model to the vast number of soil particles that make up the ground is impractical from a computational cost perspective, and empirical unresolved coupling model has difficulty in representing localized failures such as internal erosion. Therefore, developing a new coupling model that satisfies both computational accuracy and efficiency is desirable. In this study, we applied ISPH (Incompressible Smoothed Particle Hydrodynamics) for fluid analysis and DEM (Discrete Element Method) for soil particles to develop a fluid-soil coupling simulation model that can directly represent the movement of soil particles during the internal erosion process. Through numerical experiments using a particle layer with the vertical upward flow, we understand the limitations of the conventional coupling model and propose a new hybrid type of semi-resolved coupling model that combines these two models appropriately.

PUBLIC HEALTH IN GERMANY BEFORE 1848: PRACTICE AND THEORY

Elisaveta Grebennikova — Tue, 21 Nov 2023 13:06:04 +0100

The rise of public health care in Germany was part of a modernization process, the first product of which was the state. As part of the cameralist policy of encouraging population productivity, the dignitaries of Prussia and other German states began to establish special authorities responsible for the health and well-being of the population as early as the late seventeenth century. The 18th century saw a bureaucratization of health management methods, with district doctors (Kreisphysickus) as representatives in the field. They were entrusted with a wide range of administrative responsibilities, but their social status remained low. Some of the district doctors became known as the authors of treatises on medical police, presenting their views on the development of public health. Their theories, however, were far removed from actual practice. The situation began to change only after 1848, when political events in Germany prompted a new generation of physicians to vigorously demand political, social and medical reforms.

PROBLEMS OF READINESS OF THE SECONDARY VOCATIONAL EDUCATION SYSTEM FOR THE GROWTH OF THE INCOMING POPULATION

Elisaveta Grebennikova — Tue, 21 Nov 2023 12:51:03 +0100

Introduction. The relevance of the study of this problem is due to the growing burden on the secondary vocational education system, namely the increase in the number of graduates of 9th and 11th grades who choose this level of education after school. The purpose of the article was to study the problems, consequences and risks of the growth of the number of entrants to the secondary vocational education system. Methodology. The leading method of research was the analysis of statistical data in the field of vocational education, as well as a sociological study conducted by the Center for the Economics of Continuing Education of the RANEPA in August 2020 among 903 graduates of educational organizations of the secondary vocational education system, which revealed the main motives for young people to choose the next stage of education. The Results of the study are the conclusions that the secondary vocational education system is not currently ready for increased interest on the part of young people. The growing number of middle-level and skilled personnel entering training programmes is constrained by limited resources for secondary vocational education, which forces young people to enter professional educational organizations on a paid basis or choose other regions for admission. The author considered the factors limiting the possibility of the secondary vocational education system to the tendency to increase the number of people wishing to enter professional educational organizations and the associated risks. Conclusion. The materials presented in the article can be used by the executive authorities of the constituent entities of the Russian Federation to assess the dynamics of development indicators and evaluate the performance of the secondary vocational education system and educational organizations.

NUMERICAL SIMULATION OF A LABORATORY-SCALE FREE FALL CONE PENETROMETER TEST IN MARINE CLAY WITH THE MATERIAL POINT METHOD

Debasis Mohapatra — Mon, 20 Nov 2023 19:19:02 +0100

This paper shows a numerical replication of a laboratory-scale free fall cone penetrometer test of marine clay. The numerical simulation involves large deformations and considers the destructuration of clay, strain rate effects, and non-linear material behaviour. The numerical simulation well replicates the laboratory experiment captured on a high-speed camera. The penetration process is replicated accurately in time, and the depth of the penetration corresponds to that obtained in an experiment. The simulation results indicate that the numerical framework implemented in Uintah software, consisting of an advanced soil model and the Generalized Interpolation Material Point Method, is well-suited for replication of the dynamic penetration process in soft and sensitive marine clay.

Design of Graphical Symbols for Shape Transformations of 4D Printed Parts

Jesús Sánchez Pinedo — Thu, 16 Nov 2023 13:13:14 +0100

The term “4D Printing” (4DP) is defined as the ability for a part produced using an additive manufacture process to change its shape when activated by or exposed to one or more stimuli over time. This emerging technology offers unique advantages over conventional Additive Manufacturing (AM) by extending the three dimensions of space into the fourth dimension of time. 4DP parts can be programmed to actuate passively without the need for an external power source such as an electromechanical or other active system, thereby reducing the probability of failure and the complexity of components. This work attempts to address some of the challenges faced by the design engineer in a project team when producing technical documentation to specify the desired shape transformation of a 4DP part with a structured graphical representation at an appropriate level of abstraction. In this paper the requirements for a shape transforming 4DP part are represented as the allowable variation in dimensional size and tolerance in geometric form of the functionally critical features on the part for each function that the transformed shape serves. In this paper, the authors describe how the proposed standard to specify the desired shape transformations of a 4DP part could use graphical symbols in a structured specification by means of a Transformation Control Frame (TCF) to define the rules of transforming between shapes and a Bill of Transformations (BoT) to enumerate all the Transformation Control Frames (TCF) necessary to describe the intended sequence of shape transformations. To illustrate how the graphical symbols could be applied, a SMA actuated gripper is presented as a use-case.

Thermal model for laser-based powder bed fusion of metal process: modelling, calibration, and experimental validation

Jesús Sánchez Pinedo — Thu, 16 Nov 2023 13:13:03 +0100

In the present contribution, we propose an effective numerical thermal modeling solution for melt pool simulations in Laser-based Powder Bed Fusion of Metals processes. The proposed model employs an anisotropic conductivity to represent melt pool dynamics effectsin a homogeneous material model. The numerical implementation of the proposed physical model is first experimentally calibrated and then validated with respect to a series of melt pool measurements as acquired by using a short-wave infrared (SWIR) camera monitoring system.

Cellular Automata Simulation of Fully Equiaxed Microstructure Formation in Scalmalloy® during Additive Manufacturing with Adjustable Ring Mode Laser

Jesús Sánchez Pinedo — Thu, 16 Nov 2023 13:12:50 +0100

We utilized an Adjustable Ring-Mode (ARM) laser to achieve an almost fully equiaxed microstructure in powder bed Fusion-laser beam Scalmalloy®. ARM laser-built specimens exhibited over 90% fine-grained material, while circular laser-built specimens yielded less than 50% fine-grained material, using the same laser power, speed, and hatch spacing. To gain insights into these interesting results, we employed a Cellular Automata (CA) solidification simulation, incorporating the nucleation role of L12 Al3(ScxZr1-x) precipitates through a particle-based nucleation model. The simulation was coupled with the corresponding temperature field derived from finite difference analyses of the circular and ARM laser beams. The simulation results revealed a significantly thicker precipitation zone (equiaxed grains) under the ARM laser compared to the circular beam, primarily attributed to reduced temperature and cooling rates. The excellent correlation between simulation and experimental results demonstrates promising potential for the predictive application of the developed model. It can be effectively utilized to optimize heat source modulation and process parameters, thereby enabling the adaptation of microstructure and mechanical properties

The Effect of Geometrical Imperfections on the Mechanical Properties of Lattice Structures Produced by the Powder Bed Fusion (PBF) Process

Jesús Sánchez Pinedo — Thu, 16 Nov 2023 13:12:30 +0100

In this paper, the effects of geometrical imperfections observed in a lattice structure fabricated by metal 3D printer on the compressive response were investigated by using FE simulation. Geometrical imperfections which are due to excessive heat transfer and the melting of unnecessary metal powder during the fabrication process was observed using a 3D X-Ray microscope (XRM) machine. Based on the observation, two types of geometrical imperfections (strut diameter deviation and the center-axis offset) were measured, and the quantities of these imperfections on the mechanical properties of lattice block were discussed. By introducing imperfections to the FE model, a likelihood of reduced mechanical properties can be potentially adverted. In addition, by comparing the amount of geometrical imperfections, the initial stiffness and plastic collapse strength in the models based on different strut diameters, we proposed appropriate manufacturing conditions for the lattice blocks that would minimize the reduction of their mechanical properties.

Numerical Investigation of Vibration Properties of Chiral Structures with Artifical Structural Anisotropy

Jesús Sánchez Pinedo — Thu, 16 Nov 2023 13:12:16 +0100

The dynamic vibration response of sandwich beams with an anti-tetra-chiral lattice as a lightweight sandwiched core have been studied by using a nonlinear finite element analysis (FEA). Since the anti-tetra-chiral structure has a weak shear stiffness, its vibration response is strongly affected by the shear deformation. In our calculation, a 3-point bending flexural test was conducted for calculating the effective shear stiffness as well as the effective Young’s modulus of the chiral core. The natural frequency of the sandwich beam has been calculated by FEA, and predicted by using the Rayleigh-Ritz method, assuming that the sandwich beam is composed of composite continuum materials with equivalent Young’s modulus and shear modulus. Moreover, the natural frequency and damping ration of the sandwich beam produced by a 3D printer bas been measured through a vibration test, and compared with numerical results in order to clarify the effectiveness of the chiral sandwich beam as a mechanical component.

Towards neuronal network enhanced finite element simulations in additive manufacturing

Jesús Sánchez Pinedo — Thu, 16 Nov 2023 13:12:04 +0100

Parametric Study of Directed Energy Deposition Of Duplex Stainless Steels To Optimize Ferrite-Austenite Phase Ratio And Residual Stresses

Jesús Sánchez Pinedo — Thu, 16 Nov 2023 13:11:53 +0100

Optimal material properties of duplex stainless steels generally require near 50-50 ferrite-austenite microstructures. The development of additive manufacturing of duplex steels is hindered by difficulty in controlling cooling conditions to ensure a balanced phase ratio. In addition, non-uniform phase distribution is usually observed. Thus, sufficiently fast part scale process simulations are interesting to optimize process parameters to better predict and control the temperature history during fabrication and therefore solid-state phase transitions. Furthermore, stresses should also be taken into account in the optimization of the phase field in order to avoid cracking, buckling or excessive distortions. Numerical results obtained from a fast modeling of directed energy deposition including thermal analysis, diffusion of alloying element to account for phase transitions, and stress computation are analyzed. On this basis, we investigate the effect on stresses of an optimized fabrication strategy designed to target uniform and balanced ferrite-austenite ratio with respect to a reference printing strategy

Closed-walled topology optimization of an additively manufactured motor bracket for an unmanned cargo aerial vehicle

Jesús Sánchez Pinedo — Thu, 16 Nov 2023 13:11:38 +0100

Compared to conventional intuition-based design, topology optimization (TO) provides considerable mass savings by clearing excess material from lightly loaded regions of a structural part. The remaining material may be distributed in a purely truss-like fashion, or in the form of a closed-walled design consisting of flat plates or curved shells with variable thickness. Unless buckling is of critical concern, closed-walled designs are in general more efficient than trusses which makes them particularly interesting for challenging applications in lightweight design. However, closed-walled designs obtained by topology optimization are still the exception rather than the rule. This paper investigates the applicability of the recently developed selective penalization approach to the design of a motor bracket for an unmanned aerial vehicle (UAV) to deliver defibrillators which is currently being developed by the HORYZN student initiative at the Technical University of Munich. The optimization results are closed walled designs as desired. A comparison to a truss-like design as well as to a conventional off-the-shelf motor bracket reveals that the closed-walled design even outperforms the topology optimized truss-like design by additional 3% in terms of stiffness-to-weight ratio. Moreover, it provides a streamlined housing protecting the motor cables and contributing to the reduction of aerodynamic drag at cruise speed. Another key finding of this case study is: Depending on the specific optimization problem, and a suitable build orientation provided, closed-walled designs may lower the amount of necessary sacrificial support structures or may even be almost self-supporting. For the closed-walled motor bracket design we found a reduction by more than 25% compared to the truss-like design. This did not require limiting the freedom of design by imposing any additional constraints. The motor bracket was successfully manufactured from aluminium alloy using laser powder bed fusion (LPBF) followed by removal of support structures and CNC machining of functional surfaces.

Incremental Viscoelasticity for 3D Concrete Printing: Finite Strain Modeling and Parametric Studies

Jesús Sánchez Pinedo — Thu, 16 Nov 2023 13:11:20 +0100

Within a 3D concrete printing process, concrete is still fresh and possible collapse may occur due to its own weight and lack of formwork. On the other hand, the mechanical characteristics of the material are continuously evolving due to hydration during curing. Withina predictive theory, the constitutive relation of the early age concrete is to be defined in rate form. In this contribution, and due to the soft nature of the problem at hand, a finite strainincremental viscoelastic modeling is adopted. A generalized Maxwell rheological model is used together with a Saint-Venant-like incremental elasticity. A parametric study is conducted on simulated slump-tests to highlight the abilities of the present framework. Clearly, the early age rheology and mechanical properties have a great impact on the buildability of the fresh concrete. A set of simulations is then given for the purpose of demonstration.

Effect of Residual Stresses on the Mechanical Properties of TPMS Lattice Structures Manufactured Using 316L Stainless Steel

Jesús Sánchez Pinedo — Thu, 16 Nov 2023 13:10:58 +0100

In recent years, the use of Triply Periodic Minimal Surface (TPMS) lattice structures has gained popularity due to their advantages like high surface to volume ratio and their lightweight potential. Nowadays, TPMS lattice structures can be seen in many fields, including aerospace and medical applications, which can be fabricated using AM methods like Laser Powder Bed Fusion (PBF-LB/M) process. During the PBF-LB/M process, the transient emperature change is caused by the cyclic nature of the thermal load resulting in the accumulation of residual stresses (RS). These RS can cause dimensional inaccuracies, warpageand have a severe impact on the loading capacity and quality of the PBF-LB/M part. In this paper, the effect of RS on the mechanical properties of primitive and gyroid TPMS lattice structures of volume fraction 20%, 30% and 40% undergoing compression testing is studied using Finite Element Analysis (FEA) and experiments. The sequentially coupled thermomechanical finite element model is used to account for the RS accumulation and its effect on Young’s modulus, yield strength and Specific Energy Absorption (SEA).

SAMPLE3D: A Versatile Numerical Tool for Investigating Texture and Grain Structure of Materials Processed by PBF Processes

Jesús Sánchez Pinedo — Thu, 16 Nov 2023 13:10:37 +0100

Powder Bed Fusion (PBF) not only enables the fabrication of metal parts with complex geometries in near-net-shape, but also offers the potential to tailor the microstructure and, consequently, the mechanical properties of the final product. In this contribution, we present our in-house developed simulation software SAMPLE3D (Simulation of Additive Manufacturing on the Powder scale using a Laser or Electron beam in 3D), which is designed specifically for simulating grain structure evolution during PBF processes. The core of SAMPLE3D is composed of a finite difference model and a cellular automaton model. The finite difference model is used to obtain the temperature field caused by an electron or laser beam. This temperature field is further used in the cellular automaton model to simulate grain structure development where grain selection as well as nucleation is considered. A range of information can be extracted from the simulation results, such as texture, grain morphology, and grain boundary arrangement. SAMPLE3D provides a way to get insight into the relationship between PBF process strategies and microstructures. SAMPLE3D has been employed to investigate the texture and grain structure evolution of various materials in different research projects.

Multi-Scale Topology Optimization of Bodies with TPMS-based Lattice Structures and Mortar Contact Interfaces

Jesús Sánchez Pinedo — Thu, 16 Nov 2023 13:10:23 +0100

The combination of topology optimization, lattice structures and 3D printing has quickly emerged as a potential alternative for the design and manufacturing of lightweight components. However, the size of the building chamber restricts the size of this kind of lightweight designs. A possibility to overcome this limitation is to design assemblies of 3D printed lightweight components put together with contact interfaces. To design such an optimal lightweight assembly, the components should not be optimized separately, but the wholeassembly should be optimized simultaneously with all components including their unilateralcontact interfaces. This is the topic of the following work. In this paper, a framework formulti-scale topology optimization of assemblies of bodies with triply periodic minimal surfaces(TPMS)-based lattice structures and unilateral contact interfaces is developed and implementedin 3D. The contact interfaces are formulated for finite element bodies with non-matching meshesusing the mortar approach which in turn is solved by the augmented Lagrangian formulationand Newton’s method. The multi-scale topology optimization formulation, suggested in [1],is set up by defining two density variables for each finite element: one macro density variablegoverned by RAMP (Rational Approximation of Material Properties), and a micro densityvariable governed by representative orthotropic elastic properties obtained by numerical finiteelement homogenization of representative volume elements of the TPMS-based lattice structure. Thus, the macro density variable defines if an element should be treated as a void or be filled with lattice structure, and the micro density variable sets the local grading of the lattice. The potential energy of the system is maximized with respect to the design variables, in such manner no extra adjoint equation is needed for the sensitivity analysis. Both density variables are treated with a density filter, and the macro density variable is also passed a Heaviside filter. The final optimal assembly design is realized by transforming the optimal density fields to implicit surface-based geometries using a support vector machine and Shepard’s interpolation method, which then can be 3D printed as the corresponding stl-file obtained by applying the marching cube algorithm. The implemented framework is demonstrated for three-dimensional benchmark problems.

Fluid Flow-Based Topology Optimization of Internal Channels of a LPBF-Manufactured Calibrator Side Lath

Jesús Sánchez Pinedo — Thu, 16 Nov 2023 13:10:06 +0100

In this study, a method is presented to design embedded cooling channels in an additively manufactured metal part. A fluid flow-based Topology Optimization (TO) methodology was applied on a specific industrial case study with thermal objectives and constraints. The resulting design was 3D-printed and assessed numerically. In addition, the cooling efficiency is compared against that of the original design, which is machined. This work was performed using commercial software tools Simcenter STAR-CCM+ to perform the thermal and fluid flow optimization and simulations; NX to generate a final geometry from optimization results and 3DXpert to assess part printability.

Thermal and Mechanical calibration of multi-material DED AM process simulations on part-scale

Jesús Sánchez Pinedo — Thu, 16 Nov 2023 13:09:48 +0100

Additive Manufacturing (AM) processes, such as Directed Energy Deposition (DED), offer great potential for producing complex and customized components. To optimize these processes, accurate simulations and numerical modeling techniques are essential. This paper presents a study on the thermal and mechanical calibration of DED AM process simulations on a part-scale. The research aims to develop a comprehensive finite element model that incorporates the multi-physics nature of the DED process, accurately predicting thermal behavior, internal stresses, and distortion of manufactured components. The calibration process involves experimental measurements and simulations using Abaqus software. The thermal calibration involves calibrating parameters such as emissivity, absorptivity, and convection coefficients, while the mechanical calibration focuses on plastic strain properties. Additionally, the study explores the simulation of multi-material prints and functionally graded materials. The results demonstrate that the models can accurately represent thermal and mechanical phenomena, with calibration of material properties playing a crucial role. The paper concludes with recommendations for further validation, including demonstrator prints and investigations into simulation parameters. This research contributes to advancing the understanding and application of DED AM simulations, enabling more accurate and reliable predictions for industrial applications.

Simulation-Based Process Optimization Towards Homogeneous Ti6Al4V L-PBF Components

Jesús Sánchez Pinedo — Thu, 16 Nov 2023 13:09:30 +0100

In this study, macro-scale thermal simulation of the laser powder bed fusion (LPBF) process is employed to predict and limit geometry-induced overheating of complex Ti6Al4V components. First, the overheating effect is reproduced in tensile specimens. Overheating is found to increase the local oxygen content by almost 80% and lower the elongation at break by over 70% in overheated regions. By employing macro-scale thermal simulations, an automated routine is developed to efficiently optimize the L-PBF process to prevent local overheating. Variable interlayer wait times are numerically optimized to allow cooling of the material without adding manufacturing time where this is not required. In this way, local overheating can successfully be prevented resulting in a more homogeneous temperature distribution during the L-PBF process. This method was found to fully restore the mechanical properties in geometries prone to overheating, resulting in more homogeneous and predictable Ti6Al4V components.

Numerical model for the laser metal deposition additive manufacturing process: Multiphysics modeling and experimental validation

Jesús Sánchez Pinedo — Thu, 16 Nov 2023 13:09:17 +0100

Metallic Additive Manufacturing (AdM) technologies (3D printing) is rapidly spreading to a variety of industrial applications. In recent years, advances in AdM have gradually transformed the way in which manufactured products are designed and produced. It enables easy manufacturing of complex shaped parts with high performance, less material waste and short development cycle. Laser Metal Deposition (LMD) is one of the processes in this growing field. This process can produce high performance parts by the injection of powders into a melt-pool created by a laser heat source. However, the LMD is complex and several defects may appear during the printing process. In this context, numerical simulation could be a helpful tool to describe the involved physical phenomena and then to predict the impact of process parameters on the material state. Such numerical tool can predict the heat exchanges and the fluid flow within the molten pool enabling defect prediction and process optimization. In this work, a multi-physics numerical model of the LMD process, at a mesoscopic scale, (i.e. at the layer thickness scale) is developed to predict thermal cycles during fabrication, as well as the complex relationships between part construction and operating parameters. For this purpose, the finite element code COMSOL Multiphysics is used. The developed model takes into account fluid flow and heat transfer in the different phases (gas, substrate and melt pool). As a key feature, the developed model simulates the growth of the track using the generation of droplets when the powder flow is intercepted by the laser beam. Material addition, interface tracking, and strong topological changes are handled using the level set technique. The numerical results are compared to the experimental results for validation purposes. This validation includes the comparison between the predicted molten pool cross-section and measurements from macrographs and high-speed videos.

Multiphysical modeling of soft-tissue stent interaction (Plenary Lecture)

Jesús Sánchez Pinedo — Thu, 16 Nov 2023 10:42:57 +0100

The efficacy of cardiological interventions, including the implantation of prostheses, is highly dependent on patient-specific immunohistology and can be enhanced with computational predictive tools. Therefore, an in silico replication of neointimal hyperplasia shall provide the necessary insights about the biochemical and cellular interactions within the vessel wall, and eventually address the risks of in-stent restenosis in a patient-specific manner. In this context, we set up a multiphysics framework considering key mediators of restenosis and couple them to a continuum mechanical vessel wall model. The governing set of coupled partial PDEs for the underlying mechanobiological system is solved via the finite element method and the results are compared to those obtained using a deep learning framework employing physics-informed neural networks (PINNs). Another interesting cardiological intervention-related problem is the maturation of tissue-engineered cardiovascular implants wherein the evolution of the collagen density affects the tissue’s mechanical behavior. The model we present allows us to predict the evolution of collagen density within textile-reinforced heart valves.

A coupled model for the formation of Atherosclerosis due to inflammation processes

Jesús Sánchez Pinedo — Thu, 16 Nov 2023 10:36:02 +0100

Atherosclerosis is a disease in blood vessels that often results in plaque formation and lumen narrowing. It is an inflammatory response of the tissue caused by disruptions in the vessel wall nourishment. Blood vessels are nourished by nutrients originating from the blood of the lumen. In medium-sized and larger vessels, nutrients are additionally provided from outside through a network of capillaries called vasa vasorum. It has recently been hypothesized [1] that the root of atherosclerotic diseases is the malfunction of the vasa vasorum. This, so called outside-in-theory, is supported by a recently developed numerical model [2] accounting for the inflammation initiation in the adventitial layer of the blood vessel. Building on the previous findings, this presentation proposes an extended material model for atherosclerosis formation that is based on the outside-in-theory. Beside the description of growth kinematics and nutrient diffusion, the roles of monocytes, macrophages, foam cells, smooth muscle cells and collagen are accounted for in a nonlinear continuum mechanics setting. Cells are activated due to a lack of vessel wall nourishment and proliferate, migrate, differentiate and synthesize collagen, leading to the formation of a plaque. Numerical studies show that the onset of atherosclerosis can qualitatively be reproduced. Thus, the in silico model backs the new theory.

Reduced-Order Models in Bayesian solvers for inverse problems

Jesús Sánchez Pinedo — Thu, 16 Nov 2023 10:33:31 +0100

Challenging inverse problems aim at identifying large sets of parameters using data from different sources and diverse accuracy. This is the case of data assimilation for geophysical crust dynamics, were the number of parameters to identify amounts to thousands. In this context, Bayesian inverse solvers combined with Markov-Chain Monte Carlo (MCMC) strategies are an affordable strategy, accounting for the uncertainty of the input data and quantifying also uncertainty of the output. Despite the efficiency of the MCMC approach, the direct problem has to be evaluated an extremely large number of times, many (after the burn-in phase) with the input parameters lying in a narrow range. This is the ideal situation for Reduced-Order Models (ROM): many repeated queries to the model corresponding to parameters lying in a limited manifold. Thus, we aim at applying ROM to large-dimensional parametric forward problems. In this case, it is important optimising the dimensionality reduction technique inherent to the ROM strategy. For instance, Proper Orthogonal Decomposition (POD) is associated with a linear Principal Component Analysis (PCA). PCA is linear in the sense that assumes the reduceddimension manifold to be Euclidean. We explore using kernel PCA (kPCA) to further reduce the dimension, thus devising a kPOD approach. Different options to select physically inspired kernels, based on the knowledge of the problem under consideration, are discussed. Moreover, the computational strategy to explore the feature space (the reduced-dimensional space) is also discussed.

Model Order Reduction in the Parametrized Multi-Scale and Coupled Setting

Jesús Sánchez Pinedo — Thu, 16 Nov 2023 10:29:32 +0100

A New Paradigm for Multiphysics Simulation: Its Initial Application to Fluid-Structure Interaction

Jesús Sánchez Pinedo — Thu, 16 Nov 2023 10:15:58 +0100

A new paradigm for simulating mulitipysics systems is presented with initial focus on FluidStructure Interaction (FSI). For each single-field governing equations adopting Lagrangian frame, a projection operator couples the coupled field without invoking interface Lagrange multipliers. For FSI problems where fluids are modeled by employing ALE kinematics, a physics-based interface equations are formulated as an independent set of third-field equations. This approach facilitates the connection of non-matching meshes and provides consistent dynamic equations of motion for the interface that can be integrated in parallel. The proposed simulation paradigm adopts stand-alone software modules for the fluid and the structure, which is coupled through a third interface system treating their interaction, which preserves the modularity of the singlediscipline software modules. The new FSI simulation paradigm is demonstrated as applied to several FSI benchmark examples, demonstrating its efficiency and accuracy. Extension of the proposed new multiphysics simulation paradigm to treat other multiplhysics problems are suggested.

Efficient Algorithm for Exponentiation of Imaginary Number

Hassan Raza Khan — Wed, 15 Nov 2023 17:55:03 +0100

The real number integer exponents of the imaginary unit, 'i' has 4 possible values—i, -1, -i, -1. Traditional method to find such values without the use of computational devices, such as calculators and computers, require splitting the exponent to simpler numbers, which can be quite burdensome if the exponent is of very large value, like 38127938127. This paper presents a simple three-step algorithm for quickly computing large exponents of the imaginary unit 'i,' explained in a way that even the non-mathematicians will be able to understand it. This method simplifies complex number exponentiation, turning minutes of hard calculation into seconds with minimal effort, and can serve as an extremely effective tool in mental mathematical calculations. The algorithm combines the real/imaginary determination, division by 2 (and subtraction by 1 if odd) and sign determination, using only last two digits of the exponent. We further prove our method using modular arithmetic and demonstrate it using examples.

CECM: A continuous empirical cubature method with application to the dimensional hyperreduction of parameterized finite element models

Jesús Sánchez Pinedo — Tue, 14 Nov 2023 13:17:03 +0100

We propose a method for finding optimal quadrature/cubature rules with positive weights for parameterized functions in 1D, 2D or 3D spatial domains. The method takes as starting point the values of the functions at the Gauss points of a finite element (FE) mesh of the spatial domain for a representative sample of input parameters, and then construct an elementwise continuous orthogonal basis for such functions using the truncated Singular Value Decomposition (SVD) along with element polynomial fitting. To avoid possible memory bottlenecks in computing the SVD, we propose a Sequential Randomized SVD (SRSVD) in which the matrix is provided in a column-partitioned format, and which uses randomization to accelerate the processing of each individual block. After computing the basis functions, the method determines an exact integration rule for such functions, featuring as many points as functions, and in which the points are selected among the Gauss points of the FE mesh. Finally, the desired optimal rule is obtained by an sparsification process in which the algorithm zeroes one weight at a time while readjusting the positions and weights of the remaining points so that the constraints of the problem are satisfied. We apply this methodology to multivariate polynomials in cartesian domains to demonstrate that the method is indeed able to produce optimal rules – i.e., Gauss product rules –, and to a 2-parameters, 3D sinusoidal–exponential function to illustrate the use of the SRSVD in scenarios in which the standard SVD cannot handle the operation because of memory limitations. Lastly, the fact that the method does not require the analytical expression of the integrand functions – just their values at the FE Gauss points – makes it suitable for dealing with the so-called hyperreduction of parameterized finite element models. We exemplify this by showing its performance in the derivation of low-dimensional surrogate models in the context of the multiscale FE method. The Matlab source codes of both the CECM and the SRSVD, along with the scripts for launching the numerical tests, are openly accessible in the public repositoryhttps://github.com/Rbravo555/CECM-continuous-empirical-cubature-method.

Empirical Interscale Finite Element Method (EIFEM) for modeling heterogeneous structures via localized hyperreduction

Jesús Sánchez Pinedo — Tue, 14 Nov 2023 13:13:16 +0100

This work proposes a special type of Finite Element (FE) technology – the Empirical Interscale FE method – for modeling heterogeneous structures in the small strain regime, for both dynamic and static analyses. The method combines a domain decomposition framework, where interface conditions are established through “fictitious” frames, with dimensional hyperreduction at subdomain level. Similar to other multiscale FE methods, the structure is assumed to be partitioned into coarse-scale elements, each of these elements is equipped with a fine-scale subgrid, and the displacements of the boundaries of the coarse-scale elements are described by standard polynomial FE shape functions. The distinguishing feature of the proposed method is the employed “interscale” variational formulation, which directly relates coarse-scale nodal internal forces with fine-scale stresses, thereby avoiding the typical nested local/global problems that appear, in the nonlinear regime, in other multiscale methods. This distinctive feature, along with hyperreduction schemes for nodal internal and external body forces , greatly facilitate the implementation of the proposed formulation in existing FE codes for solid elements. Indeed, one only has to change the location and weights of the integration points, and to replace a few polynomial-based FE matrices with “empirical” operators, i.e., derived from the information obtained in appropriately chosen computational experiments. We demonstrate that the elements resulting from this formulation are not afflicted by volumetric locking when dealing with nearly-incompressible materials, and that they can handle non-matching fine-scale grids as well as curved structures. Last but not least, we show that, for periodic structures, this method converges upon mesh refinement to the solution delivered by classical first-order computational homogenization. Thus, although the method does not presuppose scale separation, it can represent solutions in this limiting case by taking sufficiently small coarse-scale elements.

Experiment and SHM on the membrane structure of Shanghai Kunshan Football Stadium

Jesús Sánchez Pinedo — Mon, 13 Nov 2023 14:48:58 +0100

Form-finding of lightweight tension-compression structures with equilibrium-based graphical methods

Jesús Sánchez Pinedo — Mon, 13 Nov 2023 14:48:45 +0100

50 Years of Form Finding by the Force Density Method

Jesús Sánchez Pinedo — Mon, 13 Nov 2023 14:48:33 +0100

Thinking to close the loop in membrane architecture

Jesús Sánchez Pinedo — Mon, 13 Nov 2023 14:48:23 +0100

The Evolution in the Design Tools for Membrane Structures

Jesús Sánchez Pinedo — Mon, 13 Nov 2023 14:48:11 +0100

Progressive Damage in thin 2D Woven CFRP Laminates due to Stress Concentrations at Free Edges and Notches

Jesús Sánchez Pinedo — Thu, 09 Nov 2023 14:30:36 +0100

Stress concentrations are present at cut-outs, notches, and generally at free edges in woven CFRP structures. Under cyclic loading, damage initiates from these stress raisers and progresses into the laminate, leading to strength reduction and structural failure. The present contribution provides a literature review summarizing analytical, experimental and numerical investigations regarding damage initiation and propagation in the presence of free edges and at notches in thin plain-woven 2D CFRP laminates. For free edges, initiation of damage is given as interlaminar matrix cracking. Modelling approaches for the progression by cohesive zone models or linear-elastic fracture mechanics are summarized. Recent advances using image correlation and numerical modelling are presented. In terms of notches, a brief survey of relevant literature is given, followed by a more detailed treatment of the damage progression originating from a circular hole. Additionally, the shortcomings of standard specimens with holes for fatigue damage progression investigations are addressed, since both mechanisms, damage from the free edge and the hole, interact. Latest research to uniquely identify the damage emanating from the hole is presented

Investigation into the Manufacture of Hybrid Wear Resistant Forging Tools using Tailored Forming Technology

Jesús Sánchez Pinedo — Thu, 09 Nov 2023 14:30:21 +0100

Forging tools that are subject to high thermo-mechanical loads require a correspondingly high heat resistance, hardness and ductility to prevent undesirable failure patterns due to wear, plastic deformation and crack formation. These properties are mainly required in the layer of the tool engraving close to the surface, as this area is exposed to the highest loads due to the contact with the hot workpiece. With the heat transfer from the workpiece to the tool, a cyclic tempering process of the tool material often occurs in this area, resulting in a decrease in wear resistance. Diffusion treatments of the tool surface, such as additional nitriding, cannot provide sufficient protection in thermally highly stressed tool areas, as the heat-affected zone in these areas extends beyond the surface modification. As a result, a tempered layer forms under the nitrided layer, on which it can slide off or break as a result of the high process loads and the wear protection is lost. The use of nickel-based alloys promises an improvement in service life due to their high specific heat. However, these alloys are much more expensive than hot-work tool steels and are more difficult to machine, which has a negative effect on the economic use as a die material. Furthermore, nickel-based alloys do not have the high strength of steel that is often required in the base material that is subject to low thermal loads. To reduce the material usage of nickel-based alloys, but to fully take advantage of their positive properties, the suitability of the Tailored Forming concept in thermo-mechanically highly stressed areas were investigated within the scope of this research. For this reason, hybrid forging tool inserts with a base material of hot-work tool steel and a protective nickel-based alloy surface layer were produced. The hybrid tools are manufactured through a process combination of rotatory friction welding and die forging. The surface enlargement as a result of the forming process is to be used specifically to protect the relevant tool areas with a layer of nickel-based alloy and at the same time minimize the use of the expensive material. The effects of the thermo mechanical treatments occurring in the joining zone were examined and the potential of the technology was investigated

Evaluation of Bend-Twist Coupling in Shape Memory Alloy Integrated Fiber Rubber Composites

Jesús Sánchez Pinedo — Thu, 09 Nov 2023 14:30:01 +0100

Advancements in textile technologies such as the integration of wire shaped Shape Memory Alloys (SMAs) on to the fabric with the help of Tailored-Fiber-Placement (TFP) method, and weft insertion of SMAs during manufacturing of textiles using knitting machines are helping to create composites capable of bending deformations without any external loads. These advancements laid the foundations for versatile applications especially in soft robotics. One such application is Interactive Fiber Rubber Composites (IFRC). The aim of this project is to evaluate the bend-twist coupling in the IFRC. The SMA reinforced composite is made of polydimethylsiloxane (PDMS) and has two layers of glass fibers stacked upon one another and joined with the help of TFP machine. This work focuses on the simulation of this approach in ANSYS with the Woodworth & Kaliske material model for SMA. The important feature of this model is that the shape memory effect can be achieved for different profiles of SMA, thus eliminating the necessity for a pre-stretch in contrast to the built-in model. The experimental values are evaluated from Multi-DIC technique, which is capable of determining deformations with respect to all directions. A comparative study with simulation and experimental results of the deformation and twisting angles is carried out. The derived conclusions will be helpful in obtaining and evaluating 3D spatial movements in IFRC structures with multiple joints in the future projects

Analysis of Cure Behaviour Uncertainties in Thermoset Composite Parts using Particle Filter

Jesús Sánchez Pinedo — Thu, 09 Nov 2023 14:29:39 +0100

Process-induced deformations result from internal residual stress caused by the anisotropic properties of thermoset composite parts. The study’s focus is diagnosing the polymerization process, or curing, and considering how uncertainties in boundary conditions affect cure kinetics. This is achieved through a Particle Filter approach, utilizing a Bayesian framework. This framework recursively estimates the evolving cure state’s posterior distribution based on observed measurements from Differential Calorimetry Scanning tests and thermocouples. The algorithm simultaneously estimates the cure state parameters and predicts part temperature and process-induced deformations, which are closely tied to cure behaviour. This is accomplished using diffusion cure kinetics and analytical deformation models. Furthermore, it introduces an augmented cure state formulation to address uncertainties in cure boundary conditions, which conventional models overlook. The developed stochastic approach adeptly captures uncertainties related to cure evolution while providing comparable deformation predictions with minimal computational costs and memory usage. Experimental measurements of process-induced deformations in C-shaped thermosetting parts, made of unidirectional 8552/AS4 fibres and cured following the Manufacturing Recommended Curing Cycle, are validated using the developed algorithm. After validation, the proposed model is employed to predict outcomes, which are then utilized to determine the optimal curing cycle using a Genetic Algorithm.

Numerical Simulation of the Fatigue Damage Growth in Unidirectional Composites based on Fibre-Matrix Debonding

Jesús Sánchez Pinedo — Thu, 09 Nov 2023 14:29:04 +0100

A methodology for investigating the micromechanical fatigue behaviour of unidirectional composites based on fibre-matrix debonding is developed. The fatigue damage mechanism is based on the progressive failure of fibres caused by debond crack tip stress fields resulting from fibre breaks in previous load cycles. The methodology combines an analytical model to describe the debond crack initiation and growth with a numerical finite element model to calculate resulting stresses. The methodology is applied on a two-fibre model composite. It can qualitatively predict the stress development within the simulation domain as well as the mechanism of a debond crack tip stress field triggering a break in a neighbouring fibre. Both is consistent with microscale observations in the literature.

Micromechanical Homogenization Methods of Short Glass Fiber-reinforced Injection-molded Bio-based Composite Material

Jesús Sánchez Pinedo — Thu, 09 Nov 2023 14:28:44 +0100

Herein, microscale approaches were explored to determine the homogenized properties of short fibre reinforced polymer material. The analytical homogenization follows the shear lag principle to approximate elastic modulus in the case of longitudinally oriented short fibres. For the finite element-based homogenization, a periodic 3D representative volume element of the composite is constructed to apply forward numerical homogenization. This unit cell is discretized by tetrahedral 3D finite elements resulting in a periodic mesh. An effective spring element method was further developed to homogenize the properties of short fibre-reinforced material. The reduced order spring method predicted the elastic properties almost equally to the finite element-based homogenization. A novel bio-based polyamide matrix with 40% glass fibre content and a traditional polyamide with 30% glass fibre reinforcement serve for the application and validation of the developed micromechanical methods. An additional effectivity parameter must be considered to capture the manufacturing imperfections of the injection molding process. This parameter can be calibrated based on experimental data from tensile testing. The developed numerical frameworks show good potential for extensions to more advanced modelling of the composite, such as nonlinear behaviour or failure mechanism.

Impact damage modelling in composite laminates – numerical implementation of a strain rate dependent damage model

Jesús Sánchez Pinedo — Thu, 09 Nov 2023 14:28:29 +0100

In this work, a numerical methodology for simulation of impact damage in laminated CFRP structures has been developed and implemented into the Abaqus/Explicit software. The methodology is based on the recent insights into the mechanical behaviour of CFRP materials at various strain rates. Failure initiation is modelled using the failure theory that was introduced in Coles et al. (2019). This approach has been modified to include the strain rate effects according to work presented in Raimondo et al. (2012) and to account for the mesh objectivity of the damage process in this work. The model has been implemented into Abaqus/Explicit using the user material subroutine VUMAT and details of the implementation are discussed in the work. The model has been applied to the simulation of two impact simulations demonstrating that the damage modes of the composite plate, as well as damage scope and displacement fields, have been simulated accurately. The methodology has been previously developed for application in unidirectional composite plates, whereas this work and current research phase focus on woven composites. Additionally, only the in-plane failure modes are currently considered whereas the out-of-plane damage modes will be investigated in the future research.

SHM system for bonding line monitoring of composite wing box skin-spar cap during manufacturing

Jesús Sánchez Pinedo — Thu, 09 Nov 2023 14:28:10 +0100

The CFRP wing box section under investigation is a stringer less wing-box (develop within the OPTICOMS research project) and consists of two portions: an upper part, made of co-cured spars and a top skin panel, and a bottom cured skin panel. The two portions are joined with a bonding process, giving rise to the final wing-box. During that final assembly step, distributed fibre optics were embedded between the spar caps and the bottom skin panel along the bonding lines. The embedded FO consists of six distributed fibres running within the bonding layer for about 1 m along the span direction. An irregular damage map was defined, by simulating the presence of manufacturing bonding defects by the intersection of teflon patches, different for width and length, to check an SHM system capabilities in detecting such flaws. The SHM system was tested after the final bonding process, by exploring the info contained within the “residual strains” data of the unloaded structure. Results obtained by post processing data for each fibre optic, are reported. The damage index associated to the eligible sensors is provided. Based on the available data, the SHM algorithm appeared to be sensible enough to hundreds of microstrain signals. Concerning faults detection, sensor density seems a key. Errors in the estimate of the damage extension can be assessed to be around 25%

Application of Model-based Design Approach on Dynamic Tensile Testing of Carbon/Epoxy Composites at Intermediate Strain Rates

Jesús Sánchez Pinedo — Thu, 09 Nov 2023 14:27:52 +0100

The reliable strain rate-dependent material properties at intermediate strain rate levels (1-200 s-1 ) are crucial for an accurate crashworthy design of fibre-reinforced polymer (FRP) composite structures. However, the presence of unacceptable oscillations in measured force signals hinders the precise identification of the dynamic mechanical response of materials. The current work reports the results of gained in an initial study using a novel numerical model developed through a Model-based Design (MBD) approach. A multi-degree of-freedom (MDOF) mass-spring-damper model is employed to investigate the dynamic characteristics of a whole experimental test setup to gain insights into the dynamic interaction between the test machine and the test specimen. The developed model was calibrated by the results from dynamic tension testing of Aluminium Alloy 2024-T3. Then, the model parameters were optimised using a genetic algorithm (GA). Subsequently, the adaptability of the developed model to carbon/epoxy composites, IM7/8552, was examined. The proposed model is promising to identify the influence of the test setup on the measurements and effectively distinguish excessive oscillations caused by its inertial effect at intermediate strain rate levels. The model will offer a robust solution to identify oscillations and, therefore, expand the testing capabilities to a broader range of strain rates.

Tensile Testing of Pinned Hybrid CFRP/Titanium Joints and Damage Monitoring with Electrical Resistance Measurements

Jesús Sánchez Pinedo — Thu, 09 Nov 2023 14:05:09 +0100

This contribution presents a new evaluation approach for Structural Health Monitoring of a pinned hybrid CFRP/titanium single-lap shear joint with the help of direct current electrical resistance measurements. The result is a dimensionless, load-independent damage indicator that is similar to an already developed evaluation approach by the authors but is simpler and more robust in comparison. Readily published test data is re-evaluated with the new evaluation approach and compared with the existing structural as well as the electrical resistance results. Finally, further test setup improvements for future tests are discussed.

Effect of Ply Thickness on Dynamic Damage Progression in Cross-ply Laminates Under Low-velocity Impact

Jesús Sánchez Pinedo — Thu, 09 Nov 2023 14:03:59 +0100

: In this study, we have conducted in-situ LVI experiments on cross-ply CFRP beams having stacking layups [04/904/02]s and [02/902/02/902/02]s. The progression of damage is observed through high-speed photography. In addition to LVI, quasi-static indentation (QSI) experiments are performed to reduce challenges in monitoring damage progression during the short impact loading interval. QSI experiments provide magnified in-situ observations on the free edge of the beam using a traveling digital microscope. Numerical simulations of these experiments are carried out using the finite element method in ABAQUS/Explicit. The orthotropic constitutive material model, predicting fiber and matrix damage initiation and evolution, is implemented through a VUMAT subroutine. The comparison between numerical simulations and experimental observations allowed us to investigate the influence of ply clustering on the LVI-induced damage mechanisms.

Investigation of Several Impact Angles for Predicting Bird-Strike Damage in a Riveted eVTOL Composite Wing

Jesús Sánchez Pinedo — Thu, 09 Nov 2023 14:02:36 +0100

A 3D Damage Model for Simulating Damage Modes in Fibre Metal Laminates

Jesús Sánchez Pinedo — Thu, 09 Nov 2023 14:02:19 +0100

This paper presents a 3D damage model utilized for studying the failure characteristics of GLARE. The current damage model adopted the 3D forms of Hashin’s and Puck’s failure criteria for predicting the onset of failure of fibres and matrix in the composite plies. Whilst the damage evolution is modelled based on the dissipation of fracture energy. In addition, a ductile damage model was employed to study the failure of metal layers and the delamination was assessed via a cohesive interface model. The current damage model was adopted to predict the failure modes and the blunt notch strength of GLARE; where various failure modes were observed, such as Fibre breakage, matrix cracking, delamination and plastic damage of aluminium layers. The model showed strong agreement with experimental results.

Virtual manufacturing of thick composite beams, investigating cure cycle and shrinkage induced stress

Jesús Sánchez Pinedo — Thu, 09 Nov 2023 14:01:14 +0100

Investigating cure shrinkage-induced stress in thick composite beams by virtual manufacturing is the focus of this study. The research aims to understand the behaviour of thick-walled composite structures, particularly in relation to curing shrinkage-induced damages. The curing process of resin is simulated thermally and mechanically to investigate the residual cure-induced stress. The study utilizes a finite element model in Abaqus, considering material properties, mesh, boundary conditions, and user subroutines. Ten different cure cycles are investigated, showing improvements in reducing internal stresses after curing compared to the manufacturer's cycle of about 20%. However, during curing, the investigated cycles provide marginal improvements. This study demonstrates the potential for optimizing cure cycles to reduce internal stresses in thick-walled applications. It is important to note that the proposed method is not experimentally validated and requires accurate measurements for validation.

Free Vibration Analysis of Thermally Prestressed Constant and Variable Stiffness Laminated Beams using Strong Unified Formulation

Jesús Sánchez Pinedo — Thu, 09 Nov 2023 14:00:51 +0100

Free vibration analysis is an essential requirement to capture the behaviour of composite structures subject to dynamic loading environment. To enhance the vibratory behaviour of composite structures, variable stiffness (VS) concept offers increased design flexibilities to tailor the structural response to meet a wide range of applications. Mechanically, the increased design space created by VS techniques leads to complexities of non-classical stiffness couplings which necessitate robust computational frameworks with enriched kinematics to predict the dynamic response accurately and efficiently. In this regard, this study proposes an enhanced differential quadrature based Strong Unified Formulation (SUF) to investigate the free vibration behaviour of thermally prestressed constant and variable stiffness composite beams. The proposed SUF model exploits the flexible kinematical description of the Theory of Unified Formulation to combine a hierarchical serendipity Lagrange-based 2D finite element (FE) with 1D differential quadrature method beam element for efficient free vibration characterisation of composite beams induced with prestress at different temperatures. The proposed SUF free vibration solutions of constant stiffness and VS beams demonstrate satisfactory accuracy and achieved improved efficiency with up to 99.9% computational savings when benchmarked against ABAQUS 3D FE solutions. Finally, a numerical study reveals that the effects of thermal prestress significantly contribute to the free vibration response of constant stiffness and VS laminated beams underscoring the importance of the study.

On the Importance of Fibre Direction Mesh Alignment for Artificial Lightning Strike Simulations

Jesús Sánchez Pinedo — Thu, 09 Nov 2023 14:00:36 +0100

Composite materials, used in primary aircraft structures, produce weight reduction and improved fuel efficiency over legacy metal airframes but are more susceptible to lightning strike damage. Therefore, research into lightning strike damage and protection systems, through experiments and simulations, is an important research topic. For any FE simulation appropriate representation of the material behaviour, the loading and boundary conditions are key to accurate predictions. In addition, an aspect which has been under reported in many studies is the meshing strategy. Fibre direction mesh alignment has been reported to yield more accurate results in the modelling of mechanical damage (intralaminar damage initiation and propagation) in unidirectional fibre reinforced composite structures. However, this model meshing strategy has not found wide application and has not been used for the modelling of thermal damage events, e.g. lightning strike direct effect simulation. Instead, authors have typically refined the mesh around the arc attachment area. This paper, for the first time, examines the influence of fibre direction mesh alignment for artificial lightning strike simulations and the prediction of thermal damage. Initially, the mesh alignment is introduced partially in the central region of the specimen. The paper uses a mature modelling approach with a transient, fully coupled, thermal-electric step in ABAQUS with a lightning test Waveform A (40 kA, 4/20 µs) applied to the specimen. Specimen boundary conditions match those typically used in experiments and a mesh convergence study is undertaken to ensure no element size influence on the results. The use of this meshing strategy has been shown to significantly improve the prediction of both moderate and severe thermal damage profiles, when compared with the standard meshes used in previous research. The predicted moderate (2659 mm2 vs 2833 mm2 ) and severe (1059 mm2 vs 1061 mm2 ) damage areas were improved to within 4% and 1% of experimental results, respectively, using this meshing strategy.

Coupled problems in bio-inspired robotics

Jesús Sánchez Pinedo — Thu, 09 Nov 2023 11:48:39 +0100

Determinants of invoice currency selection by Russian exporters

Elisaveta Grebennikova — Tue, 07 Nov 2023 10:02:04 +0100

The presented paper empirically accesses the determinants of invoice currency choice by Russian exporters. The relevance of the work is dictated by the sanctions imposed against Russia, which, among other things, make international settlements in the dominant currencies difficult and facilitate the transition of Russian exporters and importers to settlements in other currencies. The existing economic literature considers the invoice currency as one of the most important factors of the magnitude of the exchange rate passthrough into prices and quantities. The basic assumption of such models is short-term price rigidity in terms of invoice currency, which is in line with the data. The dominant view is that the choice of contract currency made by exporters based on the desired medium-term exchange rate pass-through, which in turn depends on company’s share in the market and the intensity of imported components using. In this paper using the detailed data of customs statistics of the Russian Federation it is show that key determinants of the Russian exporter’s contract currency choice are the competitor’s choice of the contract currency, the firm’s market share, the invoice currency import structure and firm productivity, as well as the degree of differentiation of the exported product. The main conclusion is that the currency structure of export payments will change due to changes in the currency structure of imports, and in many product markets the short-term stability of the share of Russian exporters will suffer, including due to difficulties in using the US dollar as the currency for nominating exports.

Import Price Reaction to the Ruble Exchange Rate and Leaving the Russian market by Foreign Suppliers

Elisaveta Grebennikova — Tue, 07 Nov 2023 09:46:03 +0100

The aim of the work is an empirical analysis of the ruble exchange rate pass-through into prices under reorientation of imports to suppliers from neutral countries due to the withdrawal of some suppliers from the Russian market. The motivation is related to the structural transformation of Russian foreign trade and the continued volatility of the ruble exchange rate. I collected a database of Russian imports based on statistics of the main trading partners. The data shows three periods since February 2022: a drop of import flows from all countries in February-April 2022; a period of reorientation (increase) of imports from neutral countries in May – December; and following general stabilization of trade. The result of econometric analysis at commodity-group level consistent with the hypothesis of reorientation of imports: the average growth rates of import prices from 'unfriendly' countries during the considered period significantly exceed the rate of price growth in the pre-crisis period. The difference is from 1.9 to 4.9 percentage points in a year basis. At the same time, there is no evidence in favor of the hypothesis of an increase in the growth rate of import prices from neutral countries during the crisis period. The main conclusion is that, by the end of 2022, the ruble exchange rate pass-through into import prices returned to the characteristic values of previous periods. This suggests that the current weakening of the ruble will affect import prices and lead to a reduction of imports volumes. The period of turbulence and reorientation of Russian imports has ended. Its result was a multiple drop in imports from 'unfriendly' countries and a higher increase in the prices of imports from them.

FEM Simulations for Nonlinear Multifield Coupled Problems: Application to thixoviscoplastic flow

Jesús Sánchez Pinedo — Thu, 02 Nov 2023 14:09:31 +0100

In this note, we are concerned with the solvability of multifield coupled problems with different, often conflictual types of non-linearities. We bring into focus the challenges of getting EFM numerical solutions. As for instance, we share our investigations of the solvability of thixoviscoplastic flow problems in FEM settings. On one hand, nonlinear multifield coupled problems are often lacking unified FEM analysis due to the presence of different nonlinearities. Thus, the importance of treating auxiliary subproblems with different analysis tools to guarantee existence of solutions. Moreover, the nonlinear multifield problems are extremely sensitive to the coupling. On other hand, monolithic Newton-multigrid FEM solver shows a great success in getting numerical solutions for multifield coupled problems. Thixoviscoplastic flow problem is a perfect example in this regard. It is a two field coupled problem, by means of microstructure dependent plastic-viscosity as well as microstructure dependent yield stress, and microstructure and shear rate dependent buildup and breakdown functions. We adapt different numerical techniques to show the solvability of the problem, and expose the accuracy of FEM numerical solutions via the simulations of thixoviscoplastic flow problems in channel configuration.

Modified Kirsch Problem Incorporating Surface Stresses under Plane Stress

Jesús Sánchez Pinedo — Thu, 02 Nov 2023 14:09:14 +0100

We consider the Kirsch problem, taking into account the surface stresses at the boundary of the circular hole and on the front surfaces of the plate, in the framework of the original Gurtin–Murdoch model. The boundary conditions on the cylindrical surface of a circular hole in a nanoplate are derived in terms of a complex variable in the case of the plane stress state. The solution of the two-dimensional problem for an infinite plane with a circular hole under remote loading is explicitly obtained. Based on the analytical solution, we investigated the dependence of the elastic stress field on the nanosised plate thickness and dimension of the hole. Numerical examples are given in the paper to illustrate quantitatively the effect of the plate thickness at the nanoscale on the stress field at and near the cylindrical surface. The results are presented graphically as the dependence of the components of the stress tensor on the polar angle.

On Numerical Simulation of Fluid - Structure- Acoustic Interactions Related to Human Phonation Process

Jesús Sánchez Pinedo — Thu, 02 Nov 2023 14:06:02 +0100

This paper focus on mathematical modelling and numerical simulation of human phonation process. The mathematical FSI model is presented consisting of the description of the structural model, the flow model and the coupling conditions. In order to treat the VFs contact, the problem of the glottis closure is addressed. To this end several ingredients are used including the use of suitable boundary conditions, modification of the flow model and robust mesh deformation algorithm. The FSI model is extended to FSAI problem by inclusion of the Lighthill model of aeroacoustics. The numerical approximation of the problem is presented and several numerical results are shown.

X-Mesh: A new approach for the simulation of two-phase flow with sharp interface

Jesús Sánchez Pinedo — Thu, 02 Nov 2023 14:04:59 +0100

Sound Insulation Optimization of a Roller Shutter Box

Jesús Sánchez Pinedo — Thu, 02 Nov 2023 14:04:38 +0100

This research aims to develop an advanced numerical model to accurately predict and optimize the acoustic insulation performance of roller shutter boxes, which are important for thermal and acoustic insulation in building facades. Traditional laboratory tests for evaluating sound transmission can be expensive and lack repeatability, particularly at low frequencies. To overcome these limitations, the proposed numerical approach utilizes the finite element method to model solid and fluid domains within the roller shutter box structure. Poroelastic layers are accounted for using a mixed displacement-pressure formulation of the Biot poroelasticity equations. Excitation and sound radiation are simulated using a diffuse field of plane waves with random phases and directions, employing the infinite elements method. The numerical model is validated by comparing its results with laboratory tests, which are described in detail. The practical application of this numerical method includes investigating factors such as assembly conditions, positioning of poroelastic layers, and the inclusion of heavy masses on the acoustic behavior of roller shutter boxes.

Global sensitivity analysis of sound transmission loss of double-wall with porous layers

Jesús Sánchez Pinedo — Thu, 02 Nov 2023 14:04:10 +0100

This study examines the acoustic performance of a double-wall system with a porous layer and conducts a global sensitivity analysis of sound transmission loss. The authors use the transfer matrix method to predict sound transmission, which provides cost-effective modeling of complex acoustic interactions and detailed high-frequency information. The method employs transfer matrices to represent sound wave propagation in each layer, considers material characteristics and layer thickness, and incorporates interface matrices for boundary conditions. The poroelastic layer is modeled using the Biot-Allard approach with nine parameters. Morris and Sobol methods are applied for global sensitivity analysis, identifying significant parameters. The investigation focuses on eleven parameters, including foam properties and layer thicknesses. The findings indicate the impact of geometric parameters at lower frequencies and foam properties at higher frequencies. This study is the first to optimize sound transmission in double-wall systems with porous layers using sensitivity analysis methods, offering insights for system behavior and design

Coupled Simulations of Extreme Fluid-Structure Dynamics

Jesús Sánchez Pinedo — Thu, 02 Nov 2023 14:03:37 +0100

This work presents ongoing research on the influence of fluid-structure interaction (FSI) effects on the ductile crack growth in blast-loaded steel plates. Thin steel plates with Xshaped, pre-formed defects are used to allow for large, inelastic strains and ductile fracture. FSI effects were studied by comparing the numerical predictions of the uncoupled and the coupled FSI approach, where experimental data served as a backdrop to evaluate the accuracy of the numerical simulations. Numerical simulations are conducted in the EUROPLEXUS software. The clear conclusion from this study is that ductile fracture and crack propagation are influenced by FSI effects during the dynamic response of the plate. That is, the crack growth was very sensitive to the actual loading on the plate. Moreover, because the increase in CPU cost may be significant when uniformly refining the mesh, adaptive mesh refinement (AMR) was found very promising in reducing the CPU cost and maintaining the solution’s accuracy. The performance of AMR is an interesting finding in the view of numerical simulations of coarsely meshed (prior to AMR) shell structures exposed to blast loading

Layered Model of Fluid-Structure Interaction in Dry Wire Drawing with Coupled Axial Velocity

Jesús Sánchez Pinedo — Thu, 02 Nov 2023 14:03:16 +0100

An innovative 2D axisymmetric fluid-structure interaction model of wire drawing is developed to numerically investigate the interaction between the thin lubricant film and the plastically deforming steel wire. The deformation of the wire is obtained from the linear momentum balance and the lubricant film has been calculated by the Navier-Stokes equations. Moreover, the coupling between wire and lubricant is performed by the IQN-ILS technique and a no-slip condition is imposed on the sliding fluid-structure interaction interface. In order to reduce the computational cost, a layering technique is implemented in the axially moving structure domain. This results on the one hand in monitoring the stresses and displacements of the structure and on the other hand in an observation of the hydrodynamic pressure build-up and wall shear stresses in the lubricant. Additionally, the evolution of the fluid film thickness is presented.

Implicit Schur complement iterative modal solvers for multiphysics model order reduction

Jesús Sánchez Pinedo — Thu, 02 Nov 2023 13:58:12 +0100

In this work, we propose iterative modal solvers to generate multiphysics finite element reduced order models. We consider the strongly coupled problems defined through differential-algebraic equations with sparse discrete operators. Piezoelectric models are common examples of such problems. The approach we propose is based on the Model Order Reduction (MOR) after Implicit Schur method [1] which is used for the Krylov subspace reduction of piezoelectric devices. While their work uses the knowledge of the loading applied to the model to generate a Krylov subspace reduction basis, we propose to build a reduction basis with a priori unknown loading by modal synthesis. The basis is built from the eigenvectors of the problem after the static condensation by Schur complement of one of the physics. Typically, the Schur complement matrix is computed explicitly and it leads to dense operators [2] which limit the problem scales that can be studied due to large memory requirements and costly computations for the eigensolver used afterward. For Krylov-based eigensolvers, the most computationally difficult step is to obtain a basis spanning the eigenspace of the problem on the considered eigenvalue range. By generalizing the MOR after Implicit Schur method, this basis can be constructed by an iterative procedure using the original sparse operators instead of the dense condensed operators. The original model may be significantly larger compared to the condensed model for typical cases. However, keeping the sparsity is a critical computational advantage for the considered problems. This method is minimally intrusive for the eigensolvers that only require the implementation of a matrix-vector product. Comparing this implicit Schur complement approach to the explicit Schur complement approach shows large computational cost reductions. It also underlines the problem scale limitations of the explicit approach even on high performance computing hardware.

Time adaptive Waveform-Relaxation methods for Fluid Structure Interaction

Jesús Sánchez Pinedo — Thu, 02 Nov 2023 13:50:36 +0100

We consider waveform iterations for dynamic coupled problems with respect to the role of time window length. We review existing theoretical results about the error of waveform iterations and the role of the time window length. Furthermore, we present numerical results for waveform iterations with both time adaptive sub solvers and with fixed time steps. This way, we are able to give a recommendation on the choice of the time window. The use of time windows can lead to an increase in efficiency. For fixed time grids, we can reliably achieve a small performance increase. For time adaptive solvers, more research is needed.

The effect of the number of subproblem iterations in partitioned fluid-structure interaction simulation

Jesús Sánchez Pinedo — Thu, 02 Nov 2023 13:50:16 +0100

In a partitioned fluid-structure interaction simulation separate flow and structure solvers, each with their own spatial domain, are coupled by exchanging data on the common interface. Its computational cost is dominated by the execution of these solvers, and the cost associated with the coupling algorithm and communication are often deemed negligible. From this point of view, the computational cost is in literature typically expressed by the number of required coupling iterations per time step or equivalently the number of solver executions. However, this reasoning implicitly assumes a constant solver cost and ignores the varying number of internal subproblem iterations, i.e., solver iterations in the nonlinear solvers. This work addresses this shortcoming and shows that the computational cost of a partitioned fluid-structure interaction simulation is significantly impacted by the number of subproblem iterations performed in each solver call. Specifically, it is demonstrated that performing subproblem iterations until the solver is fully converged in each call does typically minimize the number of coupling iterations, but does not lead to minimal computational time. Instead, under the assumption of constant subproblem iteration cost, the optimum is found by minimizing a weighted sum of both coupling and subproblem iterations. The weighting factors are determined by the problem itself as well as the computer architecture.

Introducing a cloud-based framework for creating, visualising, testing and automating complex simulation workflows

Jesús Sánchez Pinedo — Thu, 02 Nov 2023 13:44:19 +0100

Engineers increasingly need tools that help them automate complex simulation workflows. Besides performance, robustness and usability requirements, tools should also be easily accessible. To fulfil these requirements, Dapta Ltd is developing a cloud-based framework, which is designed to be an all-in-one solution to create, visualise, test and automate simulation workflows. Here we demonstrate the use of the dapta platform with open-source software libraries, focusing on an FSI multiphysics example.

Multistep interface coupling for high-order adaptive black-box multiphysics simulations

Jesús Sánchez Pinedo — Thu, 02 Nov 2023 13:43:57 +0100

Many multiphysics problem can be described by the coupling of several models through physical surfaces. Relying on existing model-specific solvers is very desirable, however they must be coupled in a way that ensures an accurate and stable coupled simulation. In this contribution, we present a multistep coupling scheme which relies on the history of the exchanged quantities to enable a high-order accurate coupling with time adaptation. Explicit and implicit variants are discussed in details. Numerical experiments conducted with an opensource demonstrator on a conjugate heat transfer problem show that high-order convergence is attained, and that stability is favourable compared to other classical approaches.

Partitioned MPM-FEM Coupling Approach for Advanced Numerical Simulation of Mass-Movement Hazards Impacting Flexible Protective Structures

Jesús Sánchez Pinedo — Thu, 02 Nov 2023 13:37:58 +0100

The intensity and frequency of natural hazards such as landslides, debris flow, and mud flows have increased significantly over the last years due to climate change and global warming. These catastrophic events are responsible for numerous destructions of infrastructures and landscapes and often even claim human lives. Therefore, in addition to the prediction, the design and installation of protective structures are of tremendous importance. In recent decades, highly flexible protective structures have been favored due to their enormous energy absorption capacity while adapting well to the environment. However, dimensioning such protective structures is a very complex task requiring advanced numerical simulation techniques. To capture the behavior of such natural hazards on the one hand and the highly flexible protection structures, including complex elements such as sliding cables or brakes on the other hand, a partitioned coupling approach is proposed in this work. This way, the most appropriate solvers, treated as black-box solvers, can be selected for each physics involved while the interaction is shifted to the shared interface.

Partitioned MPM-FEM Coupling Approach for Advanced Numerical Simulation of Mass-Movement Hazards Impacting Flexible Protective Structures

Jesús Sánchez Pinedo — Thu, 02 Nov 2023 13:37:40 +0100

A certified wavelet-based physics-informed neural network for the solution of parameterized partial differential equations

Jesús Sánchez Pinedo — Thu, 02 Nov 2023 13:28:58 +0100

Physics Informed Neural Networks (PINNs) have frequently been used for the numerical approximation of Partial Differential Equations (PDEs). The goal of this paper is to construct PINNs along with a computable upper bound of the error, which is particularly relevant for model reduction of Parameterized PDEs (PPDEs). To this end, we suggest to use a weighted sum of expansion coefficients of the residual in terms of an adaptive wavelet expansion both for the loss function and an error bound. This approach is shown here for elliptic PPDEs using both the standard variational and an optimally stable ultra-weak formulation. Numerical examples show a very good quantitative effectivity of the wavelet-based error bound.

Multiphysical Modeling of Soft Tissue-Stent Interaction

Jesús Sánchez Pinedo — Thu, 02 Nov 2023 13:21:13 +0100

The prevalence of in-stent restenosis after percutaneous coronary intervention necessitates the development of computational tools to derive pathophysiological inferences and finetune interventional procedures patient-specifically. In this context, a multiphysics framework is presented herein that captures the chemo-mechano-biological interaction involved. Strategies that could potentially accelerate the computations as well as add versatility to them are shortly discussed. We hence take a minute step towards enabling computer-assisted clinical practices.

On the 2D-1D Coupling in Numerical Simulations of Simplified Air Flow Model in Human Airways

Jesús Sánchez Pinedo — Thu, 02 Nov 2023 13:20:56 +0100

This paper presents selected results regarding the implementation, validation and testing of a simple 2D-1D coupled model designed to capture some essential features of the oscillatory air flow in human respiratory system. The model relies on a 2D flow model solved by a simple finite-difference scheme in the immersed boundary setting. The incompressible fluid flow from this model is coupled to a simplified 1D fluid-structure-interaction model simulating the flow in a tube with elastic walls. Some first results obtained using the coupled 2D-1D model in an oscillating (Womersley-like) type of flow are presented and discussed in detail. The influence of model parameters is explored for a range of physically relevant settings.

Assessing Scaling and Kinematic Errors in a Coupled Experimental-Computational Infant Musculoskeletal Model

Jesús Sánchez Pinedo — Thu, 02 Nov 2023 13:20:33 +0100

Musculoskeletal models are valuable tools that enable the study and quantification of biomechanical parameters, allowing researchers to better understand the mechanisms influencing or contributing to human movement. Furthermore, musculoskeletal models have the potential to serve as diagnostic tools for identifying pathologies and disorders, such as developmental dysplasia of the hip. However, current musculoskeletal models are developed using adult subjects, with only a few studies focusing on infant populations, despite the greatest growth rate being in early infancy. Therefore, the objective of this study was to evaluate the impact of multiple linear scaling approaches of increasing complexity on the development of an infant musculoskeletal model. Motion capture technology was used to collect data from the spontaneous kicking movement of a 2.4-month-old infant lying supine. The experimental motion capture data and anthropometric measurements were used to scale the generic gait2392 OpenSim model. Four linear scaling methods of increasing complexity were used: uniform (Uni), nonuniform (Non), nonuniform with knee and ankle joint centers (NAKJCs), and nonuniform with knee, ankle, and regression-derived hip joint centers (NHJCs). Results suggest that the maximum marker errors decreased with the increasing complexity of the scaling approach. The Uni scaling approach resulted in the largest scaling and kinematic errors, with maximum marker errors of 4.92 cm and 5.30 cm, respectively. The NHJCs scaling approach had the lowest maximum marker errors, with errors of 4.17 cm and 4.36 cm, respectively. The scaling method used to develop infant musculoskeletal models should be considered carefully, especially when using linearly scaling generic models developed using adult cadaveric data.

A Novel Musculoskeletal-driven Exoskeleton Framework for Spina Bifida Rehabilitation in Infants

Jesús Sánchez Pinedo — Thu, 02 Nov 2023 13:20:10 +0100

Soft exoskeletons are lightweight robotic devices currently used for physical therapy and rehabilitation. Most of the current research on soft exoskeletons has focused on the adult population, providing limited options for infant physical therapy and rehabilitation. Spina bifida, a condition affecting the infant’s brain and spinal cord, requires muscle movement treatment through physical therapy. Coupling physiological infant movement with soft robotics can provide solutions for rehabilitation and physical therapy. This study couples joint kinematics from a novel musculoskeletal model with a soft-robotic exoskeleton that uses vacuum-powered artificial muscles. The accuracy of the exoskeleton is assessed when replicating physiological infant kicks. Knee joint kinematics from the musculoskeletal model during infant movement were used to drive the soft exoskeleton. Preliminary results showed that the robotic system replicated infant kicks with lower frequency and small ranges of motion (RMS < 2 degrees) more accurately than those with higher frequency and large ranges of motion (RMS > 6 degrees). The proposed framework has the potential to replicate physiological infant kicks that could be used for infant physical therapy and rehabilitation.

A mechanobiological bone remodelling model coupling bone physiology and systemic calcium and phosphorus homeostasis

Jesús Sánchez Pinedo — Thu, 02 Nov 2023 13:19:50 +0100

In this work we couple a physiologically based mathematical model of integrated calcium and phosphorus homeostasis to a cell population bone remodelling model and to a pharmacokinetics (PK) - pharmacodynamics (PD) model of denosumab (Dmab), an antiresorptive drug administered to combat osteoporosis (OP). The model of Ca and P homeostasis allows to incorporate the effect of factors such as Ca dietary changes, vitamin D supplementation, concurrence of renal deficiency or hyperparathyroidism into the study of OP and its treatment.

An HPC Multi-Physics Framework for Next-Generation Industrial Aircraft Simulations

Jesús Sánchez Pinedo — Thu, 02 Nov 2023 12:55:51 +0100

The aerodynamic performance of industrial aircraft is strongly coupled with the structural deformation under aerodynamic load. Consequently, multi-physics simulations represent an important asset during the design and optimization phases. Most of the Fluid-Structure Interaction (FSI) coupling approaches adopted by researchers and engineers can be divided into monolithic and partitioned techniques. The monolithic coupling, which consists of a unique system of equations for the coupled problem, is usually characterized by higher robustness and easier scalability. However, this approach is inherently customized for specific applications and requires a significant development effort. The partitioned coupling links existing software on a higher level, benefitting from higher flexibility and lower time-to-solution. As the computational world marches towards the exascale, black-box coupling libraries such as preCICE [2] aim to combine the flexibility and user-friendliness of partitioned approaches with complete and efficient usage of the available computational power. This paper focuses on aeroelasticity analyses currently performed at the Leonardo Labs facilities, exploiting the recently installed davinci-1 supercomputer [14]. Open-source CFD and structural dynamics software applications are coupled using preCICE to conduct fully threedimensional FSI analyses of aeroelastic test cases of industrial interest. The activities are part of a broader Digital Innovation industrial strategy centred on Digital Twins combining high-fidelity, highly scalable numerical simulations with data-driven AI models.

Hemodynamic evaluation of aortic aneurysms using FSI simulations

Jesús Sánchez Pinedo — Thu, 02 Nov 2023 12:55:31 +0100

The work focuses on understanding aortic blood flow dynamics and emphasize the importance of considering the flexible aortic wall model in assessing cardiovascular health and identifying potential risk factors for aneurysm and related conditions. In this paper, a fluidstructure interaction (FSI) study of vascular blood flow based on the partitioned approach using open-source software tools, OpenFOAM for Computational Fluid Dynamics (CFD) and CalculiX for Computational Structural Mechanics (CSM), coupled through the preCICE tool is presented. The FSI simulations were performed on raw and simplified (based on area of interest) patient-specific models of aneurysmatic blood vessels, considering Newtonian fluid and laminar flow assumptions. The arterial wall was modeled using the CalculiX’s isotropic linear elastic model and the communication of data is handled by preCICE. The biomedical metrics such as the Time-Averaged Wall Shear Stress (TAWSS) and the Oscillatory Shear Index (OSI) in correlation with cardiac cycles were quantified to predict rupture prone regions.

Data-Parallel Radial-Basis Function Interpolation in preCICE

Jesús Sánchez Pinedo — Thu, 02 Nov 2023 12:55:13 +0100

We present data-parallel approaches to solve radial-basis function interpolation problems in the context of partitioned multi-physics simulations, where interpolation methods are required to transfer coupling data between non-matching vertex clouds. Data-parallel approaches are a key component for the efficient use of accelerator cards and thus for performance portability on modern compute platforms. The presented approach is integrated into the open-source coupling library preCICE.

After discussing different implementation strategies, we introduce a solution based on thelinear algebra library Ginkgo, which provides a common abstraction layer for cross-platform performance with focus on solving sparse linear systems. The new implementation exploits accelerator cards for both, matrix assembly as well as solving the resulting linear system. The capability of the presented approach is compared to already existing implementations in preCICE using a turbine blade geometry

Implementation and Formulation of a Multi-Region, Electromagnetic Solver for Discontinuous Media

Jesús Sánchez Pinedo — Thu, 02 Nov 2023 12:54:54 +0100

The formulation and implementation of a finite-volume, multi-region, electromagnetic solver into OpenFOAM, and coupled using preCICE is presented, to enable the solution of electromagnetic problems with large material discontinuities.

Partitioned Flow Simulations with preCICE and OpenFOAM

Jesús Sánchez Pinedo — Thu, 02 Nov 2023 12:54:33 +0100

Large and heterogeneous flow simulations could benefit from partitioning, where each subdomain is solved by an individual, dedicated code. In this paper, we investigate and validate the fluid-fluid module of the preCICE-OpenFOAM adapter by coupling two incompressible OpenFOAM fluid solvers via a surface Dirichlet-Neumann coupling approach. The results of various simple test cases are compared to monolithic OpenFOAM simulations. By utilizing a special pressure boundary condition, the coupled results show only a small error around the coupling interface. The magnitude of this error depends on the velocity gradient, the mesh width, as well as the cell orthogonality. Looking into the OpenFOAM source code reveals that higher accuracy is only possible by manipulating the solvers themselves and thereby violating the black-box approach of preCICE. The fluid-fluid module is extended to couple temperature with sufficient accuracy for one validation case. Furthermore, support for multiphase flow solvers is added to the adapter. Lastly, custom inlet-outlet boundary conditions are implemented for pressure and velocity, which switch their behavior dynamically, depending on the flow direction. The results shown in this presentation provide a basis for future fluid-fluid coupling applications with preCICE.

Towards Computational Efficient Fully Coupled Aeroelastic Simulations of Turbomachinery Blades with TRACE and CalculiX

Jesús Sánchez Pinedo — Thu, 02 Nov 2023 12:54:17 +0100

In the industrial design of turbomachinery blades their aeroelastic behaviour is most commonly investigated by methods, that use linearization or rely on unidirectional coupling. To circumvent the limitations of those methods a new fully coupled simulation in the time domain with the structural solver CalculiX and the turbomachinery CFD solver TRACE is currently developed and presented in this paper. The coupling library preCICE is chosen to couple the mentioned elaborated single physics solvers due to its focus on high performance computing applications. Within this work the preCICE adapter for CalculiX has recently been enabled to work with a special CalculiX method, that allows to investigate dedicated eigenforms of the blades or other structural objects. It is furthermore shown that the use of this CalculiX method can lead to a massive speedup for use cases, where the structural dynamics response can be well described by a piece-wise linear approximation within each increment. On the other hand a completely new preCICE adapter for TRACE has been developed and is introduced here. The preCICE-coupled system of CalculiX and TRACE is successfully validated against a TRACE-internal coupling approach by investigating a simple testcase with a NACA profile blade that shows good agreement.

Implementing a Comprehensive Hydromechanical Model for Sedimentary Basins by Coupling a 3D Mechanical Code to a Classic Basin Fluid Flow Code with the PreCICE Library

Jesús Sánchez Pinedo — Thu, 02 Nov 2023 12:53:57 +0100

In this paper, we present a coupling strategy for the implementation of a comprehensive hydromechanical model for sedimentary basins [1]. The preCICE framework [2] has been used to efficiently implement an iterative coupling scheme between ArcTem, a sedimentary basin fluid flow code, and Code Aster [20], a finite element general purpose mechanical code. We discuss several issues related to different domain partitions used by the parallel codes, to the time evolutivity of the 3D meshes and to the different time stepping used by each code. We have used the preCICE framework communication system to efficiently exchange data between the codes and to interpolate fields between usually non-matching meshes. The iterative coupling scheme is managed by means of the functionalities provided by preCICE. We validate our coupled code on a real sedimentary basin study [19]. We evaluate the flexibility of the preCICE framework to efficiently implement advanced iterative coupling algorithms. We compare the performance of our solution to a standard approach based on a centralized supervisor controlling the coupling flow and using files to exchange data between the codes.

Ensemble Kalman Inversion for reduced Multi-scale Model via Deep-learning

Jesús Sánchez Pinedo — Thu, 02 Nov 2023 11:09:37 +0100

In the context of nonlinear multi-scale problems, the inverse estimation of macroscopic distribution of some microscopic parameters based on macroscopic measurements poses significant challenges. These challenges arise from (1) the high computational cost to solve the complex forward problem, and (2) the need for derivatives of the complex multi-scale forward model, which combines macro-scale and micro-scale simulations, both of which are typically nonlinear. To address these challenges, we propose a novel approach that combines ensemble Kalman inversion for derivative-free inverse estimation and a physics-informed deep learningbased model order reduction (DL-MOR) to accelerate the micro-scale simulation. We evaluate the performance of our method using a non-linear hyper-elastic model. The results demonstrate the effectiveness of DL-MOR in significantly speeding up the micro-scale simulation and enabling relatively accurate estimation of the microscopic parameter using only macro-scale boundary measurements.

Non-Intrusive Model Order Reduction for Sintering Applications

Jesús Sánchez Pinedo — Thu, 02 Nov 2023 11:09:20 +0100

We are interested in thermo-mechanical problems arising in the context of a practically relevant manufacturing process called sintering. These models can be defined using a non-linear material model, namely the Skorohod-Olevsky Viscous Sintering (SOVS) constitutive model. This SOVS model is used to predict macroscopic sintering behavior, such as shrinkage and density evolution. Also, it relies on material properties such as temperature-dependent viscosity and surface tension. However, high-fidelity simulations of coupled, macroscopic, thermo-mechanical models are computationally intensive. Furthermore, developing reducedorder models addressing the non-linearities is challenging due to the history dependence and presence of internal variables. Performing parametric studies, optimization, real-time control, or parameter estimation for such problems, thus, becomes infeasible. In order to accelerate sintering simulations for such multi-query scenarios, a surrogate model is vital. Here, we present a non-intrusive reduced-order modelling framework based on proper orthogonal decomposition and Gaussian process regression. Furthermore, we discuss the performance of such a surrogate model using different metrics for the two-parameter Arrhenius-type viscosity function

Component-based model order reduction procedure for large scales Thermo-Hydro-Mechanical systems

Jesús Sánchez Pinedo — Thu, 02 Nov 2023 11:09:03 +0100

In this work we develop a component-based model order reduction (CB-pMOR) procedure for a class of problems in nonlinear mechanics with internal variables. The work is motivated by applications to thermo-hydro-mechanical (THM) systems for radioactive waste disposal. The THM system is coupled, time-dependent, and highly nonlinear; furthermore, the solution to the problem depends on several parameters, which might be related to the geometric configuration (e.g. the number of repositories, their distance or their size) or the material properties of the medium. We investigate the effectiveness of the proposed method in terms of accuracy and computational costs for a two-dimensional THM system in the case of overlapping partitions

A Comparison Of Direct Solvers In FROSch Applied To Chemo-Mechanics

Jesús Sánchez Pinedo — Thu, 02 Nov 2023 11:03:55 +0100

Sparse direct linear solvers are at the computational core of domain decomposition preconditioners and therefore have a strong impact on their performance. In this paper, we consider the Fast and Robust Overlapping Schwarz (FROSch) solver framework of the Trilinos software library, which contains a parallel implementations of the GDSW domain decomposition preconditioner. We compare three different sparse direct solvers used to solve the subdomain problems in FROSch. The preconditioner is applied to different model problems; linear elasticity and more complex fully-coupled deformation diffusion-boundary value problems from chemomechanics. We employ FROSch in fully algebraic mode, and therefore, we do not expect numerical scalability. Strong scalability is studied from 64 to 4 096 cores, where good scaling results are obtained up to 1 728 cores. The increasing size of the coarse problem increases the solution time for all sparse direct solvers.