Scipedia: Documents published in 2024

Hyper-dimensional gap finite elements for the enforcement of interfacial constraints

Jesús Sánchez Pinedo — Mon, 01 Jul 2024 13:27:35 +0200

In the classical theory of two-body contact, a single shared contact interface is considered between two continuum bodies, and is further discretized as such in the finite element setting. In general, however, the finite element mesh topology of two contacting bodies will be non-conforming at this shared interface, requiring the definition of a preferred or intermediate surface over which integral constraints may be evaluated. The specification of this interface is deemed to be somewhat arbitrary, but in practice the numerical solution of contact problems may exhibit sensitivity to the particular choice of intermediate surface. A further complication concerns the need to establish projective mappings between the discretized finite element surfaces and the chosen intermediate surface, particularly for the sake of evaluating the contact gap function between pairs of points on each of the two bodies. In this work, a new methodology for the enforcement of contact constraints in the context of finite element analyses is proposed. The method entails an alternative representation of contact surface integrals by equivalently integrating over the interstitial – albeit degenerate gap volume between two contacting bodies. An auxiliary indicator field is defined on each body, and is used to represent the degenerate interstitial volume as a non-degenerate hyper-dimensional gap volume. Over this domain, the gradient of the continuously interpolated displacement field with respect to the indicator field yields the oriented displacement gap, which may be used in the formulation of contact inequality constraints. Discretization of the hyper-dimensional gap volume into conforming finite elements is explored, and is observed to offer several advantages over existing contact discretization methods: the proposed method does not require the computation of geometric intersections or projections; it exploits conventional Gaussian quadrature schemes to integrate the hyper-dimensional gap integrals with a sufficient degree of accuracy; and may be naturally and efficiently extended to represent contact between higher-order surfaces. The efficacy of the method is demonstrated on several benchmark problems. Continuing and future work is also discussed, with a focus on intended applications and extensions of the method.

Development of a Mixed Reality visualization system using a location-based method for the underwater objects

Jesús Sánchez Pinedo — Mon, 01 Jul 2024 13:26:09 +0200

This paper presents a development of a hybrid Mixed Reality visualization system using location-based and marker-based methods. The Microsoft Hololens 2 is employed for the MR device. In open-sky environment, location-based method was used for the superimposition method. To obtain location information, GNSS (Global Navigation Satellite System) receivers are used, which can obtain highly accurate location information by network RTK positioning at open-sky environment. The system is capable of superimposed 3D models into real space accurately and automatically. Also, by allowing the switch to marker-based method, this system can be applied to non-open-sky environment. The present system is applied to the visualization of underwater objects in order to check the validity and effectiveness.

Development of a land use classification model based on semantic segmentation using aerial photographs and its application to Tsunami simulation

Jesús Sánchez Pinedo — Mon, 01 Jul 2024 13:25:50 +0200

This paper presents a development of land use classification model based on semantic segmentation using aerial photographs and its contribution to the efficiency of 2D tsunami inundation simulations. The proposed method uses Artificial Intelligence(AI)-based image classification to generate a roughness coefficient mesh, which is then applied to a 2-D tsunami run-up simulation using the finite element method on real geometry. Numerical results are compared to evaluate the improvement in simulation efficiency, and the potential benefits of the proposed method are discussed by analyzing the differences in simulation results.

Research on heat distribution design of carbon ceramic brake discs and shape optimization of rib for high-speed train

Jesús Sánchez Pinedo — Mon, 01 Jul 2024 13:24:03 +0200

High speed and lightweight are the development trends of high-speed trains in the world. Air braking technology is the last line of defense to ensure the safety and reliability of trains. The complex working environment and huge braking power put forward higher requirements for brake disc configuration and material. Carbon-ceramic composite materials have the characteristics of large specific heat capacity, thermal shock resistance, lightweight and high temperature resistance, and are considered to be high-performance friction materials. By imitating the distribution of animal and plant nutrients transportation pipelines, a carbon-ceramic composite brake disc structure with #-shaped heat dissipation ribs was designed that take into account the anisotropy of the thermal conductivity of carbon-ceramic composite materials. The branched rib structure realizes rapid heat transmission in the disc material, thereby achieving high efficiency and uniform temperature distribution, prevents the concentration of heat generated by friction, which can reduce the maximum temperature value under braking conditions. Then combined with the shape optimization and size optimization design of the local heat dissipation ribs of the brake disc. Further research on the uniform temperature performance and heat dissipation under emergency braking conditions of 400km/h was carried out. The LSR model was used to analyze the different outlet angle, inlet angle and number of the cooling ribs in the same reference flow field. By comprehensively considering parameters as the average maximum temperature, convection heat transfer coefficient, an optimal design that balances cooling efficiency and aerodynamic loss is obtained.

Pratt truss characteristics for optimal weight

Jesús Sánchez Pinedo — Mon, 01 Jul 2024 13:23:48 +0200

This paper presents a study on the characteristics of Pratt trusses under conditions of optimal or near-optimal weight. Trusses with varying numbers of panels, spans, and heights are selected for analysis. Several characteristics describing truss geometry and internal forces are examined. Four dimensioning approaches are developed to perform calculations and obtain data for analysis. A parametric model of truss geometry is developed and integrated with a finite element calculation algorithm in the Rhino8/Grasshopper software. The data are processed and analyzed using the machine learning software Weka and the statistical analysis software RStudio. Results show correlations between various truss characteristics. This study focuses on truss weight and height-span ratio to find the optimal weight. Based on truss height at optimal weight for each span, other characteristics are analyzed. It is observed that a larger number of panels increases the truss weight but also makes the results more consistent and predictable. The objective of this work is to better understand Pratt truss performance, which can be used to reduce the size of optimization tasks.

Finite element-based simulation of large wind turbines wake using the actuator line method

Jesús Sánchez Pinedo — Mon, 01 Jul 2024 13:19:05 +0200

The numerical simulation of wind turbines and wind farms aerodynamics represents an open challenge in computational mechanics. It involves multi-physics and multi-scale phenomena, turbulent flows at very large Reynolds numbers, atmospheric boundary layer features, and rotor machinery flow features and dynamics. The geometrically resolved Computational Fluid Dynamics (CFD) is recognized as the highest-fidelity approach for wind turbine simulations but it has still a too high computational cost if employed for wind farm flow analysis. For this application, several reduced-order models have been formulated to obtain reliable results at a sustainable computational effort. Among the others, Large Eddy Simulations (LES) with Actuator Line Model (ALM) represents a valid middle-fidelity alternative for accurately simulating the wind turbine wakes dynamics and its interaction with the atmospheric boundary layer turbulence. Most implementations of the ALM are derived for volume-based CFD solvers. In this work we present the implementation of this model in a Finite Element Method (FEM) framework, which allows the use of a Residual Based Variational Multiscale (RBVMS) method to model the turbulent flow field, instead of the standard LES formulation. The ALM-VMS formulation is applied to study a 5MW and a 15MW wind turbine rotors, comparing the results with data available in literature in terms of aerodynamic variables of main interest, such as rotor loads and aerodynamics and near and far wake features.

Compressive stocking optimization for lymphedema treatment at lower-limb

Jesús Sánchez Pinedo — Mon, 01 Jul 2024 13:18:36 +0200

Lymphedema is a chronic disease that causes swelling in the soft tissues, mostly taking place in the extremities. This research focuses on the treatment of lymphedema through compression, which is widely applied to reduce the volume of edemas. Although effective at a clinical level, the use of off-the-shelf stockings with predefined sizes, reduces the efficiency at the patient-specific level. With the long-term goal of designing patient-specific stockings, this study aims to develop a real-time simulation tool, able to predict the efficiency of a given compression stocking for a given patient. For such purpose, the use of standard Finite Element Method (FEM) falls short due to high computational cost. Therefore, a solution based on Reduced Order Modeling (ROM) is developed to compute, in real-time, the hydrostatic pressure distribution at the location of the lymphatic dysfunction. It is assumed that hydrostatic pressure improves lymph circulation and increase the drainage capacity. This method enables to design the most efficient compressive stockings considering the particularities of each patient.

Study of the dynamic behavior of cellular structures for the absorption of mechanical vibrations

Jesús Sánchez Pinedo — Mon, 01 Jul 2024 13:18:19 +0200

Vibration is a prevalent issue in structural engineering, encompassing a wide array of problems that, if left unaddressed, can lead to severe consequences. These consequences can vary from causing discomfort for pedestrians traversing a perceptibly moving bridge to inducing premature fatigue in aeronautical structural components, ultimately resulting in catastrophic failures and loss of human life. Various sources can induce vibration in structural components, such as misalignment of rotating systems, seismic excitations, road loads on vehicles, and aerodynamic loads. To address these phenomena, in addition to appropriate structural design, various mechanisms, which can operate actively or passively, are used to attenuate oscillatory effects and minimize their impact. Active systems use electronic controllers to generate a response via actuators, reducing the signal transmissibility level based on specific oscillatory signals. Passive systems, on the other hand, mainly rely on viscoelastic polymeric materials, utilizing the reduction of the natural frequency associated with their use and a characteristic phenomenon of these materials for energy dissipation, hysteresis [1]. Hysteresis is a phenomenon where mechanical deformation energy is dissipated in the form of heat. In other words, part of the energy that would be transmitted to the structure is dissipated, thereby increasing the system's damping. Active systems are extremely efficient in their purpose, as they can isolate vibrations across a wide frequency spectrum and can be applied to structures of different magnitudes, from small and lightweight systems using piezoelectric actuators to large structures using hydraulic actuators, such as in active stabilization systems for reducing vibrations caused by seismic activities in buildings. However, they tend to be quite costly and imply an additional layer of systems, which, if not properly designed, can reduce the structure's reliability [2].

Investigating the domain of attraction of SDRE applied to a CubeSat attitude control system during launch orbit phase based on cold gas thrusters

Jesús Sánchez Pinedo — Mon, 01 Jul 2024 13:18:01 +0200

The precision of controlling the attitude of a CubeSat during the injection phase in orbit is of fundamental importance for the success of the mission. In general, the CubeSat starts this phase with high angular velocity, and then the controller needs to maneuver the CubeSat to its nominal mode of operation, which is characterized by an attitude of small angles. One way to achieve such a transition between these two modes is by using cold gas thrusters. In this paper, we investigate the region of attraction (ROA) of the State-Dependent Riccati Equation (SDRE) applied to the Attitude Control System (ACS) algorithm during the Launch and Early Orbit Phase which has nonlinear dynamics due to the high angular velocities and perturbations. The SDRE controller is based on cold gas thruster torques to reduce the high angular velocities. The main result of this investigation is the approach to numerically approximate the ROA.

Minimization of vibrations in aeronautical wing spars under flutter situation

Jesús Sánchez Pinedo — Mon, 01 Jul 2024 13:17:42 +0200

This research project aims to investigate the mitigation of vibrations in the spars of aeronautical wings during flutter occurrences. The study will delve into aeroelastic phenomena, particularly focusing on flutter, defined as the self-excited interaction of vibration modes within a modified system, which can potentially lead to catastrophic failures. An analytical method has been developed to compute the flutter velocity, considering the stiffness and mass matrices, and the utilization of a Tuned Mass Damper (TMD) has been proposed to enhance the flutter velocity, thereby extending the aircraft's operational range. Suggestions for future research directions have been provided.

Evaluation of effectiveness of traffic jam absorption driving using computer simulation

Jesús Sánchez Pinedo — Mon, 01 Jul 2024 13:17:24 +0200

Traffic congestion absorbing driving is a method of driving at low speed with a larger inter-vehicle distance than surrounding vehicles. This makes it possible to reduce excessive acceleration and deceleration, which is effective in alleviating traffic congestion. The traffic simulation in the sag section confirmed that the traffic congestion absorption driving is effective for traffic congestion mitigation. It was shown that it is possible to increase the average speed in congested sections by means of congestion absorption driving.

Enhanced mechanical behavior of nickel-coated graphene graphene reinforced CoCrFeMnNi nanolayered composites

Jesús Sánchez Pinedo — Mon, 01 Jul 2024 13:12:28 +0200

High entropy alloys (HEAs) especially CoCrFeMnNi HEAs have drawn more and more attention due to their excellent combination performance. However, the mechanical properties of CoCrFeMnNi HEAs still remain to be improved due to the single-phase FCC crystal structure. Although many efforts have been made on strengthening methods by grain refinement or nitriding the improvement of the mechanical properties is still unsatisfactory. To improve the mechanical properties of CoCrFeMnNi HEAs and broaden their application fields, we proposed that adding functionalized graphene in CoCrFeMnNi HEAs and investigated nanoscale mechanical properties and the strengthening mechanism using molecular dynamics (MD) simulation in this paper. The mechanical properties of pristine single-layer graphene nanoplatelets (GNPs) and double-side nickel-coated GNP (Ni-GNP-Ni) reinforced CoCrFeMnNi composites (Ni-GNP-Ni/CoCrFeMnNi) are studied under uniaxial tension by molecular dynamics (MD) simulations. The simulated results show that the mechanical properties of Ni-GNP-Ni/CoCrFeMnNi composites are improved significantly by the addition of Ni coated GNPs. The mechanical properties of Ni-GNP-Ni/CoCrFeMnNi composites exhibit temperature softening and strain rate strengthening effect, and their tensile mechanical properties such as the tensile strength, fracture strain decrease with increasing temperature and enhance with increasing strain rate. It is concluded that the main strengthening mechanisms for Ni-GNP-Ni/CoCrFeMnNi composites are strong interface bonding, effective load transfer from the CoCrFeMnNi matrix to the Ni-GNP-Ni and dislocation/twin strengthening by analysis of the evolution of atomic structure.

Modeling the effect of backbone instabilities and guest occupancies on interfacial and structural processes and dynamics of sII gas hydrate systems using molecular dynamics

Jesús Sánchez Pinedo — Mon, 01 Jul 2024 13:12:10 +0200

Gas hydrates are inclusion compounds that form in conditions of low temperature and high-pressure systems with water and gaseous molecules. Their potential use in carbon capture and storage, energy exploitation, and flue gas extraction makes them prime candidates for various engineering applications and climate change mitigation technologies. However, their nucleation is poorly understood and the effect of guest molecule interactions with the host on macroscale properties has yet to be elucidated. Herein we study the optimal positions of a point mass, linear molecule, and planar triangular guest molecule using a distance minimization technique that can replicate preliminary density functional theory results. The linear molecule shows strong alignment to hexagonal phases of cages, while the triangular guest molecule shows very distinct positions. These positions indicate a lower number of degrees of freedom, which in turn affect the molecules’ ability to move and vibrate in heat absorption, for example. Additionally, it shows that hydrate formation may only be possible when the guest is oriented a certain way, providing an avenue to control nucleation by adjusting guest molecule position with external fields.

Beyond lubrication flow for thin-film manufacturing

Jesús Sánchez Pinedo — Mon, 01 Jul 2024 13:09:05 +0200

Reynolds’ hydrodynamic lubrication theory has been used extensively to analyze and quantify thin film manufacturing1 . Applications span liquid flows in bearings, coatings, and molds, and gas flows between rigid or elastic surfaces. To enable further applications of efficient, reduced-order modelling, we pursue streamlined algorithms for non-Newtonian liquids in marginally “thin” geometries with multiple phases and capillarity. The goal is expanded use of “modified”, non-traditional lubrication methods to bring physics-based knowledge to bear in process design, optimization, and control methods.

Towards a multiscale computational framework for simulating flow-mediated crystallization based on phase-field crystal formalisms

Jesús Sánchez Pinedo — Mon, 01 Jul 2024 13:08:46 +0200

We lay the foundation and framework for a multiscale approach for studying crystallization in the presence of flow by coupling the Structural Phase Field Crystal (XPFC) formalism with the Navier-Stokes equations. We discuss the numerical techniques and verify the formalism against previous attempts with the vanilla Phase Field Crystal (PFC) formalism. Moreover, with this new Hydrodynamically coupled Structural Phase Field Crystal (HXPFC) method, we discuss unreported global and local crystal microstructural transformation induced by the flow. The HXPFC method establishes a framework to predict more complex crystal structures while incorporating physics relevant to film coating flows.

Design of in-mold decoration mold for complex thin-walled parts

Jesús Sánchez Pinedo — Mon, 01 Jul 2024 13:08:28 +0200

In order to address the issues of warping deformation and long-term production of complex thin-walled parts during In-Mold Decoration (IMD) production, the structure design of the IMD mold was carried out with the humidifier top cover as the production object. To ensure the flow characteristics of molten plastic in the mold during the injection molding process, based on the technical contradiction analysis of TRIZ theory, the hot runner mold is improved to mix cold and hot runner, that is, the sprue is set as a hot runner, the branch runner is set as a cold runner, and use a multi-point injection cold gate solution. And construct a complex structure numbering method to arrange and design various complex structure undercut-forming side insert mechanism, design of special structure lifters along the same direction of motion the two inverted buckle at the same time undercut-forming. The lifter mechanisms are used to complete the molding, parting, demolding and ejection of plastic parts, multiple uses for one mechanism. In order to optimize product quality and improve production efficiency, providing theoretical and empirical support for the production of complex thin walled parts with IMD molds. Then design the cooling system and demolding mechanism separately. Finally, based on Moldflow software, the final flow of plastic part warpage analyzed. The maximum warping deformation of the product is 0.7055mm, while the maximum warping deformation of the traditional cold runner mold is 0.8519mm, reducing the warping deformation of the humidifier top cover.

Numerical simulations of origami-based folded carbon-reinforced concrete shells

Jesús Sánchez Pinedo — Mon, 01 Jul 2024 13:04:05 +0200

The advantages of carbon-reinforced concrete (CRC) over traditional concrete elements reinforced with steel, including high strength, low weight, and corrosion resistance, make it a promising material for thin, efficient, and more sustainable designs. As the demand for less CO2-intensive materials such as concrete grows, a shift from simple massive elements to thin-walled elements with complex geometries is becoming increasingly necessary. However, to seek optimal design variants, efficient nonlinear numerical calculations that provide reasonable predictions of the structural behavior, including the stress-redistribution process and the failure mechanisms are essential. This paper presents FEM simulations of origami-based folded CRC shells that were experimentally investigated in a previous study. Two FEM modeling approaches were used, employing a smeared and a discrete representation of the carbon reinforcement. For both approaches a damage plasticity model for the concrete has been used. The load-deflection response from the discrete approach closely matches the experimentally obtained curves. Despite an overestimation of the load capacity, the computationally less expensive smeared FEM model qualitatively reproduces the structural response and the correct failure mechanism. Therefore, the quality of the results obtained from the smeared model is sufficient to determine preferable design variants in a typical design scenario. This is necessary to provide a deeper understanding of the structural behavior of these folded elements and to facilitate the sustainable design and application of thin-walled CRC elements in the future.

Development of a design methodology for slender carbon-reinforced concrete columns in axial compression based on EC3

Jesús Sánchez Pinedo — Mon, 01 Jul 2024 13:03:05 +0200

Advancements in concrete construction, such as carbon-reinforced and ultra-high performance concretes, enable the creation of slender, high-capacity structures, enhancing resource efficiency and reducing CO2 emissions. Despite the clear advantages of such innovative material composites, challenging load-bearing and deformation behavior emerges in slender carbon-reinforced concrete components, indicating potential stability issues. To address this concern, current research is dedicated to experimental and analytical investigations of the structural behavior and failure of slender components in compression made of carbon reinforced concrete, aiming to enhance our understanding of stability-related aspects.

Possibilities for numerical model validation through computed tomography generated data

Jesús Sánchez Pinedo — Mon, 01 Jul 2024 13:02:41 +0200

In order to make accurate predictions of the structural behaviour of non-metallic reinforced concrete elements, one of the key problems in the development of this type of new material system is the capacity of modelling the load transfer mechanisms between the concrete matrix and the reinforcement elements. To predict the load-deflection response up to ultimate limit state conditions, a wide range of numerical simulation approaches, with capability of modelling the bond behaviour between the different materials has been proposed over the years and compared to experimental results. This research work presents new possibilities for comparing numerical finite elements models with laboratory data generated by computed tomography, namely in the context of three-point bending tests performed on carbon-reinforced concrete specimens. The aim is to present the potential of in situ computed tomography for validation of numerical simulations. Examples of computed tomography generated quantitative results and data visualisation are shown, which focus on generated displacement fields and crack patterns.

Examples of analysis methods for ultrasonic vibration-assisted machining

Jesús Sánchez Pinedo — Mon, 01 Jul 2024 13:02:26 +0200

Ultrasonic vibration has been applied to many machining processes. It has been reported that the application of ultrasonic vibration to machining has improved machining efficiency and accuracy. In this report, ultrasonic vibration is applied to welding, drilling, and knurling, and its effects are shown through experiments and analyses. In welding, it is shown that ultrasonic vibration can reduce tensile residual stress. In addition, the simulation method using a simple model showed that residual stress is reduced by the plastic deformation caused by ultrasonic vibration. In the drilling process, it was found that the surface roughness of the machined surface was improved when ultrasonic vibration was used. The conditions under which the surface roughness is improved by the impulse due to cutting resistance were also determined. In knurling, it was found that the pressing and friction forces were reduced by the use of ultrasonic vibration. It was also shown that the reduction in pressing force is expressed as the product of the equivalent mass and the amplitude of ultrasonic vibration

Coupled twin conical funnels or conical hoses: an internal process of dynamic flow distribution

Jesús Sánchez Pinedo — Mon, 01 Jul 2024 13:02:12 +0200

The first objective of this study is to revisit an analytical test by the author that helps now for a prediction and explanation for the likely physical existence of twin funnels in the fluid crossed by shock wave, under certain conditions. These funnels function like a conical hose within shock waves traveling through matter. In terms of the laws of continuity, momentum, and energy the classical shock wave model is empowered with a not widespread actual function that explains a nonlocal physical phenomenon of matter distribution. The second objective is the recognition and application of two almost new analytical boundary conditions V1S = −V1 and 1 1 M S = iM , provided in the recent past that open the theory to the, at least, analytical existence of hoses or coupled twin funnels. Finally, given that supersonic and hypersonic solid cones are related to theoretical, experimental, natural, aeronautical, astronautical, geophysical and industrial interests, among others, certain analytical regions derived from this recently characterized formulation are shown and hoses or twin funnels located among them. These regions can be visualized on the plot of cone angle, shock angle, and free-stream Mach number for analogy, comparison, and prediction.

Determination of high-order frequency response of nonlinear systems using the arc-length method

Jesús Sánchez Pinedo — Mon, 01 Jul 2024 13:01:57 +0200

While linear systems have been extensively studied in the past few decades, systems with strong nonlinearities are not as widely investigated. One of the reasons why these are less applied in engineering is due to the fact that solving nonlinear equations usually demands a steep increase in processing capacity and time when compared to their linear counterparts. As computers become more powerful, significantly more advanced nonlinear systems can be studied and analyzed, providing solutions that are more accurate for real-world applications. When it comes to frequency analysis, it is possible that nonlinear frequency response shows the phenomena of hardening or softening. In this case, the resonance peaks of the frequency response are tilted to the right or left, respectively, in comparison with linear frequency response. The consequences of these phenomena might prove essential to safety assessment of real-life structures as the resonance peak might greatly differ from those obtained in a linear analysis. In this study, the high-order frequency response of the Helmholtz-Duffing oscillator is analyzed in order to evaluate its influence on the system. The oscillator exhibits Duffing nonlinearities represented by cubic springs and Helmholtz nonlinearities represented by quadratic springs. The high-order harmonic balance method was used to determine the dynamic equation in the frequency domain. The nonlinearities were numerically integrated based on the coefficients of the Fourier series. Originally used to find the solution path of nonlinear static structural analyses, the arc-length method was adapted to determine the nonlinear frequency response

Hybrid structure health monitoring technique for enhancing modal parameter identification accuracy

Jesús Sánchez Pinedo — Mon, 01 Jul 2024 13:01:04 +0200

SHM relies on the possibility of estimating structural modal parameters, such as mode shapes, natural frequencies, and damping, from the structure’s measured data. Nevertheless, modal parameter estimation still faces accuracy problems. The identification of bridge and/or vehicle system parameters and vibration characteristics have been studied both numerically and experimentally. The knowledge of bridge vibration characteristics and vehicle system parameters is crucial to the maintenance of bridges. The issue is that the techniques used to identify bridge and vehicle system parameters usually work very well with numerical simulation but present accuracy issues with experimental data due to environmental noise. Traditionally, measured data were obtained by instrumenting bridges with connected sensor systems, which had issues such as high cost, maintenance problems, safety concerns, and traffic disruption. More recently, indirect SHM (iSHM) methods, such as drive-by using passing instrumented vehicles, have been researched[1,2]. However, these methods still struggle with the accuracy of modal parameter identification, particularly for higher vibration modes sensitive to localized bridge damage, limiting the widespread adoption of iSHM methodologies[1,3]. A combination of indirect and direct monitoring methods is proposed to address these limitations. This approach aims to improve modal parameter identification, including higher vibration modes, for localized damage detection and structural assessment. The proposed method uses GPS-time synchronized sensors for simultaneous measurement of vehicle and bridge vibration data and is verified through numerical simulation assuming multiple runs over the same bridge. The study highlights the potential of this hybrid SHM technique to significantly improve the accuracy of indirect structural health monitoring, providing more reliable and precise modal parameter estimates, especially for higher vibration modes, allowing for the identification of localized bridge damage.

An explicit time-marching procedure for elastodynamic analyses based on adaptive time-integration parameters and time-step values

Jesús Sánchez Pinedo — Mon, 01 Jul 2024 13:00:18 +0200

This study discusses an explicit time-marching procedure that is designed for the time-domain resolution of elastodynamic models considering their physical properties and adopted spatial discretizations. The technique is entirely automated and proves itself to be highly effective, featuring second-order accuracy, adaptive algorithmic dissipation and extended stability limits. Additionally, the discussed methodology is truly explicit, truly selfstarting, and it incorporates automated subdomain/sub-cycling splitting procedures to enhance its overall performance. Thus, the algorithm automatically divides the domain of the problem into different subdomains, adjusting their time-step values according to the properties of the discretized model, which allows improving the efficiency and the accuracy of the analysis, while ensuring stability. Locally-defined adaptive time-integration parameters are also considered, establishing an entirely self-adjustable formulation. In this case, expressions for the timeintegration parameters are provided based on the local features of the discrete model, allowing to create a further link between the adopted temporal and spatial discretization procedures, better counterbalancing their errors. These parameters are locally formulated to nullify the bifurcation spectral radius of the method at pre-established sampling frequencies, providing maximal numerical damping at the highest sampling frequency of the elements of the adopted spatial discretization. This design optimizes the formulation to mitigate the influence of spurious high-frequency modes on the computed responses, allowing for enhanced analyses. In fact, the primary goal of introducing numerical damping is to eliminate non-physical spurious oscillations that may arise from the excitation of spatially unresolved modes. Therefore, the methodology not only tracks down the frequency range of the discretized model, but also it is designed to adaptively enforce significantly low values (close to zero) for the spectral radius of the method at the highest frequencies of the model, as well as it aims to provide relatively high spectral radius values (close to one, considering physically undamped models) in the important low-frequency range. Benchmark analyses are conducted at the end of this study to demonstrate the technique's effectiveness taking into account theoretical problems and complex models that are representative of real-world applications in the OIL & GAS industry.

An enhanced fully-adaptive explicit-implicit time-marching formulation for elastodynamics

Jesús Sánchez Pinedo — Mon, 01 Jul 2024 12:59:55 +0200

In this work, an explicit-implicit time-marching formulation, which adapts to the model's properties, its adopted spatial and temporal discretizations, and its computed responses, is studied for elastodynamic analyses. Explicit-implicit approaches have become referred to as effective time-domain solution methodologies since they allow to combine the advantageous features of both explicit and implicit formulations, such as reduced solver efforts and guaranteed stability, providing very attractive techniques.

Non-destructive stress wave amplitude testing for interface bonding strength of 3D printable concrete

Jesús Sánchez Pinedo — Mon, 01 Jul 2024 12:59:37 +0200

The aim of this study is to investigate the impact of interface bonding properties of 3D printable concrete (3DPC) on non-destructive testing. By fabricating concrete specimens with varying numbers of layers and employing ultrasonic devices for non-destructive testing, it was observed that the presence of interface layers results in 3DPC exhibiting smaller wave amplitudes compared to conventionally cast concrete. Moreover, with an increase in printing layers, there is a trend of initial growth followed by a decline in interface bonding strength, accompanied by changes in amplitude attenuation. Through the use of non-destructive testing methods and by observing the pattern of amplitude decay, the interface bonding properties of 3DPC were investigated. The results indicate that, compared to conventionally cast concrete, 3DPC prepared using additive manufacturing techniques significantly affects the propagation of stress waves due to interface layers, and there exists a linear relationship between interface bonding strength and wave amplitude loss. This may also be a fundamental factor contributing to differences in non-destructive testing outcomes.

Estimation of grinding contact stiffness and damping parameters from dynamic output only using Hunt-Crossley force model and Unscented Kalman filter

Jesús Sánchez Pinedo — Mon, 01 Jul 2024 12:59:17 +0200

. This paper introduces a novel approach that combines the Unscented Kalman Filter with the Hunt-Crossley force model to accurately estimate the stiffness and damping characteristics at the contact point of a grinding process conducted by a flexible manipulator. The Hunt-Crossley force model is proposed for the force contact considering the flexibility of the manipulator structure and is written in a state form as functions of the contact stiffness and damping. Leveraging the Unscented Transform to linearize the nonlinear measurement functions, the Unscented Kalman Filter effectively estimates and updates the stiffness and damping parameters based on the state model. This method is put into practice in a real grinding scenario employing a flexible manipulator. Its practicality and convenience make it a promising technique for estimating operational machining parameters and developing an efficient vibration control strategy for machining applications.

A study on the structural systems with tapered hardening-type hysteresis devices

Jesús Sánchez Pinedo — Mon, 01 Jul 2024 12:58:58 +0200

The Japanese seismic design code allows for formation of plastic hinges at beam ends during large earthquakes. However, in cases in which seismic motion exceeds anticipated levels, seismic energy surpassing the structure’s absorption capacity may result in partial destruction, ultimately leading to the collapse of the whole building. Unexpected damage to buildings may also occur if they are subjected to long-period ground motions. To prevent such damage, we propose a displacement control device with hardening-type hysteresis. We performed experiments and analysis to verify the performance.

Dynamic displacement recognition of frame structures based on computer vision

Jesús Sánchez Pinedo — Mon, 01 Jul 2024 12:57:57 +0200

Displacement induced by external forces is one of the most intuitive variables for assessing structural safety. Traditional contact methods, such as deploying displacement sensors on structures, are often limited by objective factors. Non-contact methods, such as utilizing computer vision algorithms like optical flow estimation and feature matching, offer the advantages of rapid and accurate structural displacement acquisition, unaffected by the structure itself and quick deployment. However, enhancing the accuracy of displacement monitoring based on computer vision remains a focal point in this field of study. In this paper, based on experimental data from a vibration table testing a four-layer reinforced concrete framework under three different conditions, we propose a method for processing dynamic displacement data that combines non-contact and contact approaches. This method integrates dynamically recognized structural displacements based on computer vision technology with data recorded by acceleration sensors on the structure to enhance displacement monitoring accuracy. The research results demonstrate that our method can obtain structural dynamic displacements based on computer vision information, confirming the effectiveness and reliability of our approach.

Study of wind-induced vibrations on a trellis pylon controlled through an active mass damper system

Jesús Sánchez Pinedo — Mon, 01 Jul 2024 12:56:56 +0200

The rapid expansion of telecommunications infrastructure, driven by the deployment of the 5G network, necessitates innovative engineering solutions to ensure the reliability and stability of these critical structures. Steel trellis pylons, designed for hosting several telecommunication antennas, are particularly susceptible to wind-induced vibrations due to their slender profiles, high equivalent area exposed to wind loads and low structural damping. Such vibrations can lead to structural deterioration, signal disturbance, and, in severe cases, total structural failure. In this context, the need for effective vibration control measures is becoming more and more relevant. This paper underscores the complex challenge of windinduced vibrations in telecommunications pylons and the promising potential of AMD systems as a mitigation strategy. This study aims at advancing the state of the art by integrating experimental wind load measurements, modal analysis, and the application of AMD technology to a 50-meter-high steel trellis pylon. Through comprehensive analysis and numerical simulation, the effectiveness of AMD systems in enhancing structural performance and resilience under wind loading conditions is validated.

Mathematical and experimental modeling of a Stockbridge damper used to suppress Aeolian vibration of transmission line conductors

Jesús Sánchez Pinedo — Mon, 01 Jul 2024 12:55:54 +0200

The asymmetric Stockbridge vibration damper is commonly employed in overhead power cables to mitigate Aeolian vibration, which is the oscillation of conductor cables within the 3–150 Hz frequency range. The damper's effectiveness is determined by its resonant frequencies, which increase power dissipation to exceed the wind-induced power input. While the basic symmetric Stockbridge damper has two resonant frequencies, the asymmetric version can exhibit up to four. Previous studies have shown that changes in the counterweight's geometry can increase the natural frequencies. This paper presents experiments on a modified asymmetric damper and uses an analytical model from Vaja et al. (2018), to confirm their findings. employed in overhead transmission lines to mitigate Aeolian vibration

Weight reduction in dynamically loaded systems through the effect of damping in bolted joints

Jesús Sánchez Pinedo — Mon, 01 Jul 2024 12:54:54 +0200

In order to reduce vibration amplitudes, the MFPA Weimar is investigating joint damping. The effect is based on the relative displacement between two components between which a surface pressure acts. In this case, the surface pressure is applied by a bolted connection. The damping behavior is dependent on normal force and amplitude. Decay tests clearly show that it is not possible to approximate the curves due to the viscous behavior (exponential decay function). The superposition with Coloumb's friction leads to a new damping model, especially in the initial range. The aim is to set up a numerical model in order to be able to take the local damping effects into account in the development of components. For this purpose, zero thickness elements (ZTE) are introduced into the joint in the FE simulation and provided with a constitutive model that can represent the energy dissipation. The ZTEs are parameterized as a function of material, surface pressure and surface roughness. The amplitude reduction, which is often achieved by a frequency shift of the natural frequencies via tuned mass dampers, is replaced and thus contributes to lightweight construction.

Modeling of an oblique incident P-wave within a water saturated soil with the wave based method

Jesús Sánchez Pinedo — Mon, 01 Jul 2024 12:53:52 +0200

In this contribution, a coupling approach between the Wave Based Method and an oblique incident P1-wave is presented. The approach is used to model a poroelastic halfspace with an empty canyon by applying Biot’s theory for low frequencies. The system’s response is compared with a reference solution from literature. Moreover, a second coupling approach is introduced to permit the modeling of a filled canyon. In the special case of a canyon filled with the material of the surrounding soil, the simulation results are compared with the underlying analytical solution

Stochastic FE-BE method for homogenization analysis of 2D diffusion problems considering uncertainties of inclusion shape

Jesús Sánchez Pinedo — Mon, 01 Jul 2024 12:53:38 +0200

The stochastic method for homogenization analysis of diffusion problems considering uncertainties of inclusion shape is developed using a microscopic spectral stochastic BEM and a macroscopic FEM. The spatial variation of inclusion shape is modeled using KarhunenLoeve expansion with exponential-type covariance kernels. The characteristic function on a 2-D unit cell and the homogenized diffusion tensor are calculated using the spectral stochastic BEM. The macroscale diffusion problems are solved using the stochastic FEM with the polynomial chaos (PC) expansion. Through numerical tests, the expected value and the standard deviation of the concentration in macroscale problems and their distribution are investigated.

Optimal design of graphene-reinforced composites using shunted piezoelectric systems for optimal vibration attenuation

Jesús Sánchez Pinedo — Mon, 01 Jul 2024 12:53:20 +0200

. Smart structures exploit the synergy between several coupled physical phenomena to produce materials and structures with enhanced properties. Such structures incorporate integrated sensors and actuators, mechanical and electronic components and control. The design of smart structures is a multidisciplinary challenge, which is of high importance for viability and resilience of industry. Usage of piezocomposites with integrated nonlinear shunted circuits for vibration suppression improves effectiveness and accuracy of many high-value products. The finite element method is widely used to simulate the mechanical response of composite materials and multi-physics problems. In this work a numerical investigation is conducted on small scale beams aiming to improve their vibration response by applying piezoelectric shunted circuits. Finite element models are developed in MATLAB, simulating graphene-reinforced nanocomposite piezoelectric beams with shunted circuits under vibration excitations. Piezoelectric materials are applied to the beams to allow for the interaction between electric charge and mechanical deformation. In addition, shunted circuits, which are paired with piezoelectric elements, are used to provide damping (vibration suppression) of one or more critical eigenfrequencies. To derive the optimal vibration response, a particle swarm optimization (PSO) algorithm is adopted. Optimization is then aimed to minimize the vibration amplitude as well as optimize the mechanical and electrical parameters of the investigated system.

Nonlinear interaction in composites using physics informed neural networks

Jesús Sánchez Pinedo — Mon, 01 Jul 2024 12:53:02 +0200

Modelling of composites requires the consideration of various components that work together and interact in a linear and nonlinear way. Linear and nonlinear modelling in view of demanding needs, like representative volume element calculations within numerical homogenization and the advent of new tools, like physics informed neural networks, are reviewed in this article. In particular, a concept is proposed towards the implementation of a unilateral contact mechanics law within physics-informed neural networks. The theoretical framework and related applications are presented. Results indicate that the proposed deep learning approach can further be applied towards solving contact mechanics problems, considering the mechanical interactions between the constituents of composites.

A nonoverlapping domain decomposition method for extreme learning machines solving elliptic partial differential equations

Jesús Sánchez Pinedo — Mon, 01 Jul 2024 12:52:43 +0200

Extreme learning machine (ELM) is a methodology for solving partial differential equations (PDEs) using a single hidden layer feed-forward neural network. It presets the weight/bias coefficients in the hidden layer with random values, which remain fixed throughout the computation, and uses a linear least squares method for training the parameters of the output layer of the neural network. It is known to be much faster than Physics Informed Neural Networks. However, classical ELM is still computationally expensive when a high level of representation is desired in the solution as this requires solving a large least squares system. In this paper, we propose a nonoverlapping domain decomposition method (DDM) for ELMs that not only reduces the training time of ELMs, but is also suitable for parallel computation. In numerical analysis, DDMs have been widely studied to reduce the time to obtain finite element solutions for elliptic PDEs through parallel computation. Among these approaches, nonoverlapping DDMs are attracting the most attention. Motivated by these methods, we introduce local neural networks, which are valid only at corresponding subdomains, and an auxiliary variable at the interface. We construct a system on the variable and the parameters of local neural networks. A Schur complement system on the interface can be derived by eliminating the parameters of the output layer. The auxiliary variable is then directly obtained by solving the reduced system after which the parameters for each local neural network are solved in parallel. An initialization method suitable for high approximation quality in large systems is also proposed. Numerical results that verify the acceleration performance of the proposed method with respect to the number of subdomains are presented.

A performance analysis procedure based on corrected displacements to evaluate the seismic response of steel 2D frames

Jesús Sánchez Pinedo — Mon, 01 Jul 2024 12:52:26 +0200

In the proposed methodology, a load pattern is applied in a non-adaptive fashion to obtain the seismic response of two-dimensional steel moment resisting frames. The proposed methodology is based on the structural dynamics theory and consists of a single run nonlinear analysis. This invariant load pattern is formulated by considering higher mode effects with the use of an effective modal mass contribution factor. Also, part of the proposed procedure, a corrective factor is employed to adjust the displacements obtained from the nonlinear analysis ensuring that the drift values obtained from the corrected displacements are adequate. The procedure allows the analysis of the structural response, i.e, story displacement and story drifts. To evaluate the methodology a nine-story steel moment frame is analyzed. Material and geometric non linearities are considered for all the cases. The results are compared with the ones obtained by the Nonlinear time history analysis.

Adaptivity and uncertainty of multi-fidelity surrogate models for shape optimization

Jesús Sánchez Pinedo — Mon, 01 Jul 2024 11:13:14 +0200

Engineering design optimization based on expensive simulation is increasingly performed with surrogate models [1], i.e. approximate models fitted through a small dataset of simulation results. To build surrogates within the lowest possible computational budget, modern approaches use multi-fidelity data (combinations of cheap low-fidelity and expensive high-fidelity simulation results) and adaptive sampling strategies, which add simulation points one by one where they are most likely to discover the optimum [2]. Uncertainty estimation of the surrogate model is crucial for efficient adaptive sampling, since it guides the choice of new sampling points. Thus, underestimation of the uncertainty may lead to sampling in suboptimal regions, missing the true optimum. Existing surrogate models such as Gaussian process regression [3] and Stochastic Radial Basis Functions (SRBF) [4], provide uncertainty estimations, which are often used. Nevertheless, uncertainty estimation is so important for a successful surrogate model, that a more thorough investigation seems warranted. This is the main objective of this paper. This paper studies three issues with uncertainty estimation, in the context of multifidelity SRBF. First, most existing techniques rely on knowledge about the global behavior of the data, such as spatial correlations. However, the number of training points can be too small to reconstruct this global information from the data. We argue that in this situation, user-provided estimation of the function behavior is a better choice (section 3). Furthermore, the dataset may contain noise, i.e. random errors without spatial correlation (section 4). Surrogate models can filter out this noise, usually by modeling it as belonging to a normal distribution with zero mean, but this introduces two separate uncertainties: the optimum amount of noise filtering is unknown, and for a small dataset the local mean of the noisy data may not correspond to the true simulation response. Finally, in multi-fidelity models, the low-fidelity data are corrected by high-fidelity results, which could reduce the amount of uncertainty they introduce.

A PROBABILISTIC GRAPHICAL MODEL APPROACH TO INTERPRET, VERIFY, AND DECOUPLE MULTI-PHYSICS SYSTEMS

Jesús Sánchez Pinedo — Mon, 01 Jul 2024 11:12:55 +0200

Multi-physics scientific codes, like those used in weather prediction and spacecraft simulation, often involve the coupling of many subdomain models. The resulting models are generally expensive to run. These costs, along with the model’s complexity, make downstream tasks like model calibration and uncertainty quantification especially difficult. In this work, we simplify structure in multi-physics models by learning an undirected graphical model corresponding to the system state variables, where the edges in the learned graph represent conditional dependence between variables. Depending on the application of interest, the resulting graph may (1) reveal the probabilistic structure of the joint distribution; (2) identify the most important coupling variables (those that must be shared between subdomain models), and those which may be safely neglected; (3) identify candidate variables for first-pass verification tasks; or (4) decouple parts of a model, while maintaining accuracy in the model predictions. We illustrate these possibilities through two multi-physics numerical models, the Multiple Prediction Across Scales-Atmosphere (MPAS-A) code base and a fire detection satellite model

A mesoscopic domain decomposition approach composed with preconditioned conjugate gradient for modeling concrete

Jesús Sánchez Pinedo — Mon, 01 Jul 2024 11:12:36 +0200

Concrete structure is widely used in civil engineering. Numerical Simulation in mesoscale could provide a powerful analysis tool, which is based on the Total Finite Element Tearing and Interconnecting (TFETI) method. However, the unneglectable computational resource consumption limited the implementation of the meso-modeling method in engineering. This study investigated an efficient solution for concrete structure simulation, which was programmed using Python. A cantilever beam model with dimensions of 100mm × 50mm was simulated and studied. Then, a comparison with the ABAQUS model was given to demonstrate the accuracy and efficiency of the TFETI. Furthermore, a reliability analysis of a 300mm × 300mm concrete sample under the axial compression was performed. The results showed that the TFETI method achieved the same level of accuracy as ABAQUS. Moreover, the TFETI model solving required less computational source for the same number of elements as the one on the ABAQUS. In the reliability analysis of the axially loaded model, TFETI demonstrated superior solution speed. In conclusion, the TFETI exhibits excellent solution efficiency in finite element analysis of concrete structures, offering valuable insights and references for computational analysis of large-dimension civil engineering structures.

A kinematically-exact reduced-order rod model for elastoplastic failure in thin-walled members

Jesús Sánchez Pinedo — Mon, 01 Jul 2024 11:03:17 +0200

This work profits from a weakly coupled multiscale approach to derive a 7-DOF kinematically-exact reduced-order rod model for thin-walled members (starting from [1]) with a plastic hardening constitutive equation (based on [2]-[3]) that emulates the coupling between local buckling effects and hardening plasticity at material level. The model is implemented in an in-house finite element program for flexible thin structures and shall be validated against reference solutions. The novelty as compared to [2]-[3] is the extension to the fully 3D context, including torsion-warping degrees-of-freedom and arbitrary (plastic) failure mode capabilities, allowing for the modelling of complex structural problems involving thin-walled rod members. Although kinematically-exact rod models are able to detect critical loads and represent postcritical configurations in many common scenarios, issues are bound to emerge when local effects (such as buckling of web and/or flanges) are relevant, especially when they are coupled with plastic deformations. For rod models, the combination of those factors can be satisfactorily represented in a phenomenological way by embedding them on a stress-resultant/crosssectional strains hardening plastic model, instead of enriching the model´s kinematics and related material law. One can employ weakly coupled multiscale modelling to generate constitutive relationships among the different strain and stress in a pre-processing stage. Information about plasticity, loss of geometrical stiffness and local buckling are passed to the macro-scale rod model without increasing the amount of global degrees-of-freedom. Incremental steps of the numerical solution are solved with the split operator, whereby local variables are solved in an element-wise fashion and thus not introduced in the global system. Quadratic convergence of the overall solution procedure is achieved. The coupling among geometrical and hardening effects limits the load bearing capacity of the structural members and determinates the failure load.

A finite deformation micropolar peridynamic theory and its application to metamaterials

Jesús Sánchez Pinedo — Mon, 01 Jul 2024 11:03:02 +0200

Metamaterials with engineered microstructures exhibit exceptional properties such as negative Poisson’s ratio, energy absorption, and bandgap. These materials can prevent propagation of elastic waves in certain range of frequency called bandgap. The microstructure of these materials affects the overall response of the structures. Microstructures may undergo significant rotations and their rotary inertia needs to be considered along with deformation. As the metamaterials in the study involve cracks, we develop a finite deformation micropolar peridynamics (PD) theory. The proposed PD micropolar theory is validated by comparing the results obtained from the boundary element solutions of plate with a hole. The response of metamaterials with periodic arrangement of holes and cracks is studied under static and dynamic loads and the results are compared with the nonpolar PD theory.

Generative model to predict the deformation field of CFRP laminates with geometric deviations in wing assembly

Jesús Sánchez Pinedo — Mon, 01 Jul 2024 11:02:04 +0200

Thin-walled structure of CFRP laminates is widely utilized in the assembly of aircraft wings. The deformation field generated during the assembly process can impact the assembly performance of the structure, thereby influencing the product quality and operational performance of the wings. The geometric deviations on the critical mating surfaces of the laminate and physical parameters are key factors influencing the deformation fields during the assembly process. Analyzing the mapping relationship between fusion assembly data and deformation field plays a crucial role for assessing the assembly results. The traditional analysis methods only consider the impact of simple directional deviations on assembly results and do not comprehensively account for the multi-source input. This paper proposes a multi-source assembly input -deformation analysis framework for CFRP bolted joints in aircraft wing assembly. Taking the parameters representing the geometric deviations and physical parameters as input and deformation field as output, a conditional generative model is employed to learn the influence pattern of the geometric deviations on the deformation field. The framework establishes a prediction model from the deviation field to the deformation field and introduces specific accuracy metrics. Corresponding simulations demonstrate that the proposed method can predict assembly deformation field more efficiently than traditional numerical methods.

A fast prediction method for bearing strength of aircraft composite bolted structures considering initial assembly deviation

Jesús Sánchez Pinedo — Mon, 01 Jul 2024 11:01:04 +0200

Bearing limitation is a key performance indicator for composite bolted joints. Assembly process parameters such as washer structural parameters, interfacial friction coefficients and tightening process parameters have a significant effect on the bearing limitation. In the actual production process, there are inevitably deviations between the assembly process parameters and their design values. The accumulation of assembly process deviations leads to an obvious dispersion of the bearing limitation, which makes it difficult for composite bolted joints to be reliably in service. In this paper, the dispersion of assembly process parameters is experimentally tested to quantitatively characterize its uncertainty. Then, based on the high fidelity finite element analysis method, a data set of bearing limitation under different assembly process parameters is prepared. A data-driven algorithm is used to establish a fast prediction model for bearing limitation. The fast prediction model is used to realize the uncertainty analysis and the reliability evaluation for the bearing limitation. The established analysis method and the obtained conclusions can provide a reference for the reliability design and analysis of composite bolted joints.

Hybrid quantum algorithm for the Lattice-Boltzmann method

Jesús Sánchez Pinedo — Mon, 01 Jul 2024 11:00:28 +0200

We present a quantum algorithm for computational fluid dynamics based on the Lattice-Boltzmann method. Our approach involves a novel encoding strategy and a modified collision operator, assuming full relaxation to the local equilibrium within a single time step. Our quantum algorithm enables the computation of multiple time steps in the linearized case, specifically for solving the advection-diffusion equation, before necessitating a full state measurement. Moreover, our formulation can be extended to compute the non-linear equilibrium distribution function for a single time step prior to measurement, utilizing the measurement as an essential algorithmic step. However, in the non-linear case, a classical postprocessing step is necessary for computing the moments of the distribution function. We validate our algorithm by solving the one dimensional advection-diffusion of a Gaussian hill. Our results demonstrate that our quantum algorithm captures non-linearity.

On the iterative solution of saddle point problems using a symmetric positive definite preconditioner

Jesús Sánchez Pinedo — Mon, 01 Jul 2024 11:00:09 +0200

Saddle point problems frequently appear in many mathematical and engineering applications. Most systems of partial differential equations with constraints give rise to saddle point linear systems. Typical examples include mixed finite element formulations to solve fluid flows and/or elasticity problems under full incompressibility. The inversion of saddle point problems is challenging due to inherent numerical instability in the direct inversion methods. Many direct and iterative methods have been proposed to overcome this challenges, such as the Schur complement and the Uzawa’s method. In the context of mixed finite element for incompressible flows using stable H(div)-L2 spaces for velocity and pressure, we propose an iterative method that can effectively solve a saddle point problem iteratively by summing a small compressibility to the original matrix. The preconditioning matrix is symmetric positive definite, which allows the usage of Cholesky decomposition and/or CG-like iterative solvers to compute the incremental solution for the velocities unknowns. A procedure to compute the average pressure of each element of the incompressible problem is developed using the unbalanced fluxes caused by the compressibility perturbation. The average is updated during the iterative process as a function of the velocity increment at each iteration.

Effect of the capillary force on the repose angle of granular materials

Jesús Sánchez Pinedo — Mon, 01 Jul 2024 10:59:53 +0200

The angle of repose does affect the behavior of granular materials and has a wide range of applications. The addition of a small amount of liquid can dramatically change the properties of granular media, leading to an increase in the repose angle. This change is mainly attributed to the capillary force resulting from the liquid bridge when the small amount of water was introduced. The capillary force as an attractive force increases the interaction between particles and becomes a dominant factor affecting the angle of repose because it is usually stronger than gravity. In this paper, a new discrete element method (DEM) model was developed in which the capillary force was calculated by the liquid bridge model based on toroidal approximation. The developed DEM model linked the microscopic liquid bridge volume to the macroscopic water content and it also considered the effect of liquid bridge breakage and formation on capillary force. The numerical model was first validated by comparing the experimental and numerical results. Then, the effects of surface tension, volume of the liquid bridge, and the contact angle are studied numerically. Finally, the empirical equation between water content and angle of repose is given under the present simulation conditions. This work will provide a deep understanding for the effect of capillary on the angle of repose.

Model-based design approach finding optimal liquid cooling flow path for electric vehicle battery

Jesús Sánchez Pinedo — Mon, 01 Jul 2024 10:59:37 +0200

Today many electronic devices that generate significant heat are required to be equipped with liquid cooling systems to reduce their temperature. Since the liquid flow path in the cooling system affects cooling performance, determining flow path in the early development phase can improve the efficiency of the downstream development process and reduce the total cost. In this paper, we propose a model-based analysis system for thermo-fluid phenomena based on CFD results and demonstrate the parametric optimization of flow path.

Input-output reduced order modeling for public health intervention evaluation

Jesús Sánchez Pinedo — Mon, 01 Jul 2024 10:59:21 +0200

In recent years, mathematical models have become an indispensable tool in the planning, evaluation, and implementation of public health interventions. Models must often provide detailed information for many levels of population stratification. Such detail comes at a price: in addition to the computational costs, the number of considered input parameters can be large, making effective study design difficult. To address these difficulties, we propose a novel technique to reduce the dimension of the model input space to simplify model-informed intervention planning. The method works by first applying a dimension reduction technique on the model output space. We then develop a method which allows us to map each reduced output to a corresponding vector in the input space, thereby reducing its dimension. We apply the method to the HIV Optimization and Prevention Economics (HOPE) model, to validate the approach and establish proof of concept.

Computational model for local buckling of compressively loaded omega-stringer-stiffened panels

Jesús Sánchez Pinedo — Mon, 01 Jul 2024 10:59:06 +0200

Thin-walled composite structures are used in applications such as aircraft and spacecraft due to their low weight and corresponding high stiffness properties. To optimize the potential of these structures to the fullest extent, a complete understanding of their stability behavior is required. Thereby, uniaxial compression describes an important load case that is investigated. A closed-form analytical method based on the energy method for determining the local buckling load of omega-stringer-stiffened panels is presented. The stiffened panel under consideration consists of the skin plate with eccentrically attached stringer feet along the longitudinal sides of the panel, while the remaining part of the omega-stringer is modeled by corresponding elastically restrained edges. Due to the applied stringer feet, stiffness discontinuities occur in the stiffened panel. This is covered by the presented method, whereas in comparable studies in the literature, a homogeneous stiffness is often assumed across the entire panel. To evaluate the new analysis method, a comparison with the numerical solution of the corresponding Levy-type ´solution and the finite element analysis is being drawn.

Developments in the use of the Bonded Particle Model to study ore fracture

Jesús Sánchez Pinedo — Mon, 01 Jul 2024 10:58:50 +0200

In mineral processing, ore fracture is an essential first step for which the objective is to increase the exposed surface area of the valuable mineral, thereby increasing the likelihood of liberation in subsequent separation stages. This process is well known to be energy-intensive, and increasing scrutiny around sustainable practices has heightened the need to examine the efficiency of current industry approaches. Factors such as mineralogical structure and inherent weakening in the form of micro cracks are known to affect ore breakage mechanisms. However, isolating and investigating individual factors under experimental conditions is challenging and typically impractical. Numerical techniques such as the Bonded Particle Model-Discrete Element Method (BPM-DEM) have been developed as a means of investigating in isolation, the effects of different factors on ore breakage behaviour under closely controlled breakage conditions. In this work, the robustness of the BPM-DEM in predicting fracture characteristics during SILC impact breakage is evaluated. Thereafter, the BPM-DEM is used to analyse the internal mechanical response of a simulated rock specimen under impact loading commensurate with that of the SILC. The method is shown to be an insightful opportunity to study intrinsic and extrinsic rock properties during dynamic loading and breakage

Effect of particle-size-scaling on particle interactions in DEM-simulations of sand in the context of air pluviation

Jesús Sánchez Pinedo — Mon, 01 Jul 2024 10:58:34 +0200

DEM (discrete element method) is a widely used numerical simulation method, which models the behaviour of a bulk substrate based on the individual interactions of many particles. One of its possible applications is the modelling of sand behaviour in different laboratory tests, e.g., cone penetration tests [1] or direct shear tests [2]. Furthermore, DEM is specifically of interest as a modelling method for investigating air pluviation, because it models the individual inter-particle and particle-environment interactions, both friction and collisions, which determine the compaction and homogeneity of the created samples. However, one disadvantage of DEM is the relatively long computational time [3] especially with decreasing particle sizes. This makes larger particle sizes compared to reality more interesting, especially for large scale or repeating simulations. On the other hand, if the size of the chosen particles is too large, certain interactions, such as interactions with other materials and equipment, may not be simulated in a way that properly represents real behaviour. This would lead to preferring smaller sized particles, which again would lead to longer computational times. Therefore, the chosen particle size as an important aspect of DEM simulations will be discussed, as well as the effects on different simulation aspects. This includes necessary parameter calibrations, the resulting inter-particle and particle-environment interactions as well as the achieved simulation results and accuracies. Of specific interest is the largest particle size, at which accurate and realistic results concerning real-world particle interactions can be achieved. Further, the effects of graded particle sizes to better represent the sand during the pluviation process will be discussed.

Full waveform modeling in seismic exploration based on a digital geological model using spectral element method on GPU

Jesús Sánchez Pinedo — Mon, 01 Jul 2024 10:58:16 +0200

The paper considers the solution of a three-dimensional problem of modeling of all types of seismic waves propagating in real geological media. The numerical algorithm based on the spectral element method (SEM). The main advantages of SEM (high order space discretization, explicit time integration scheme) are presented in comparison with the classical approach based on the finite element method (FEM). The features of the massively parallel implementation of the algorithm on modern MultiGPU systems (based on A100 GPU) using CUDA technology are considered. The efficiency of parallelization on hybrid systems with different SEM orders and parameters of the numerical time integration scheme is analyzed. The results of solving a three-dimensional problem of modeling the propagation of seismic waves in a heterogeneous geological media with faults and sharply varying properties of layers are presented. Analysis of the numerical convergence of SEM for dispersive waves of the Rayleigh type is performed. Local and non-local non-reflective boundary conditions on the artificial boundary of the computational region are considered. The 3D computational model is constructed using a detailed digital geological model built for one of the Arctic regions. It was converted to an unstructured hexahedral mesh to perform SEM calculations using CAE FIDESYS software. The model is further generalized for typical seismic-geological conditions of Western Siberia, so that on the basis of such modeling it is possible to conduct a wide range of studies on the possibilities of seismic exploration to study the main oil and gas reservoirs in this region. The solution was sought on a hexahedral mesh consisting of 5.5 mln spectral elements of the 5th order with a total number of SEM nodes 1.2 billion. The output results of full-wave modeling are stored in the SEG-Y format, suitable for all types of industrial seismic processing. The analysis of the obtained model seismograms and wave fields is carried out. The conclusion is made about the practical significance of the conducted research.

The method of boundary integral equations in the boundary value problems of dynamics of fluids and gases

Jesús Sánchez Pinedo — Mon, 01 Jul 2024 10:58:01 +0200

Based on the created generalized apparatus of vector-tensor analysis, integral representations of the main dynamic and kinematic characteristics of the problem of viscous gas flow around force systems of arbitrary spatial shape are constructed. The boundary value problem of the interaction of such systems with a viscous gas flow is reduced to a system of linear, conditioned by physical boundary conditions, boundary integral equations regarding the kinematic and dynamic characteristics of the problem. It is proven that all the obtained characteristics depend on the newly obtained irrotational vector potential of the momentum, which significantly simplifies the integral representations of solutions and their numerical implementation. On the basis of the created generalized apparatus of vector-tensor analysis, integral representations of the main dynamic and kinematic characteristics of the problem of the flow of a viscous gas flow around supporting systems of satisfactory spatial form have been constructed. The boundary value problem of the interaction of such systems with a viscous gas flow is reduced to a system of linear, conditioned by physical boundary conditions, boundary integral equations regarding the kinematic and dynamic characteristics of the problem. It is proven that all the obtained characteristics depend on the newly obtained, vortex-free vector potential of the momentum, which significantly simplifies the integral representations of the solutions and their numerical implementation.

Landslide run-out simulations with depth-averaged models and integration with 3D impact analysis using the Material Point Method

Jesús Sánchez Pinedo — Mon, 01 Jul 2024 10:35:04 +0200

Landslides pose a significant threat to human safety and the well-being of communities, making them one of the most challenging natural phenomena. Their potential for catastrophic consequences, both in terms of human lives and economic impact, is a major concern. Additionally, their inherent unpredictability adds to the complexity of managing the risks associated with landslides. It is crucial to continuously monitor areas susceptible to landslides. In situ detection systems like piezometers and strain gauges play a vital role in accurately monitoring internal pressures and surface movements in the targeted areas. Simultaneously, satellite surveys contribute by offering detailed topographic and elevation data for the study area. However, relying solely on empirical monitoring is insufficient for ensuring effective management of hazardous situations, especially in terms of preventive measures. This study provides advanced simulations of mudflows and fast landslides using particle depth-averaged methods, specifically employing the Material Point Method adapted for shallow water (Depth Averaged Material Point Method). The numerical method has been parallelized and validated through benchmark tests and real-world cases. Furthermore, the investigation extends to coupling the depth-averaged formulation with a three-dimensional one in order to have a detailed description of the impact phase of the sliding material on barriers and membranes. The multidimensional approach and its validation on real cases provide a robust foundation for a more profound and accurate understanding of the behavior of mudflows and fast landslides

Numerical simulation investigation on nonlinear flow characteristics of rough single fractures with different contact areas

Jesús Sánchez Pinedo — Mon, 01 Jul 2024 10:34:04 +0200

To comprehensively understand the influence of the contact area on the flow characteristics of rough single fractures, a rough fracture surface is initially constructed using a spatial frequency domain approach. Subsequently, rough single fractures with varying contact ratios are derived by translating and displacing the fracture surface. The Navier- Stokes equation and Mass-conservation equation are solved by utilizing the laminar flow module integrated within the COMSOL software. The simulation results show that the nonlinear correlation between fluid flow velocity and pressure gradient can be described by using Forchheimer equation. Under the same flow velocity, a higher contact rate will exacerbate the nonlinear characteristics of fluid flow. In contrast to non-contact fractures, the streamlines within contact fractures exhibit increased tortuosity, accompanied by an elongation of flow pathways. Furthermore, with an expanding contact area, the complexity of the streamline pattern amplifies. The overall pressure field distinctly exhibits non-uniform characteristics, with larger pressure gradient observed within localized contact regions, consequently facilitating an increase in flow velocity.

Numerical study of fractal-tree-generated turbulence

Jesús Sánchez Pinedo — Mon, 01 Jul 2024 10:33:04 +0200

We study the aerodynamics of fractal trees by using a simulation based on the Lattice Boltzmann Method with a cumulant collision term. We have applied L-system rules to construct self-similar fractal tree models in aerodynamic computations. We found that the drag coefficient closely matches that of previous literature at high tree-height-based Reynolds numbers (ReH ≥ 60 000). A normalization process capable of collapsing turbulence intensity for various tree models is made. This process reveals that, at the same Reynolds number, different tree models exhibit the same behaviour in the turbulence intensity of their wake region. Our assessment of global and local isotropy in the turbulence generated by fractal trees reveals that the distant wake can be considered nearly locally isotropic at a high Reynolds number (ReH ≥ 60 000). Finally, the present numerical results confirm the non-equilibrium dissipation behaviour previously observed in the case of space-filling fractal square grids[2]. In the wake region, the non-dimensional dissipation rate Cϵ = constant is not valid. Instead, it is inversely proportional to the local Taylor-microscale-based Reynolds number, Cϵ ∝ 1/Reλ.

Physics-informed neural network vs finite element method for modeling coupled water and solute flow in unsaturated soils

Jesús Sánchez Pinedo — Mon, 01 Jul 2024 10:32:04 +0200

Accurate modeling of water infiltration and solute transport in unsaturated soils is critical for various applications. These include optimizing irrigation practices to conserve water and minimize environmental impact, as well as predicting the fate of contaminants in soil and groundwater. This study explores the application of the vanilla physics informed neural network (PINN) approach for modeling the coupled system of water flow and solute transport in unsaturated soils. We compare the performance of PINN with the Galerkin finite element method (FEM) to evaluate their effectiveness. Various techniques are implemented to improve the PINN solver, including adaptive activation functions. Numerical tests were carried out to evaluate the efficiency of the PINN solver in comparison to the FEM. The findings reveal that PINN can achieve accuracy comparable to FEM, albeit at a significantly higher computational cost during training, while maintaining fast inference times.

A predictor-corrector second-order time-stepping schemes for solving water flow and solute transport in unsaturated porous media

Jesús Sánchez Pinedo — Mon, 01 Jul 2024 10:31:33 +0200

The objective of this study is to numerically solve the coupled system of water flow and solute transport in unsaturated porous media using a noniterative predictor-corrector temporal scheme for the Richards equation and a semi-implicit temporal scheme for the advection dispersion equation (ADE). The standard and non-standard Galerkin finite element methods are used for spatial discretization. Three different techniques are proposed to calculate the pressure head in the Levrett equation. These techniques are different in terms of the chosen shape functions in the finite element space. The proposed schemes offer distinct advantages due to the linear nature of the resulting system, facilitating easy implementation and avoiding the issues associated with the divergence of iterative schemes. We evaluated the robustness and efficacy of the suggested methods using a computational experiment to simulate soil salinity and water flow in loamy soil. We compared it with data found in the literature. The results provide compelling evidence confirming the proposed methods’ effectiveness and stability.

Incompressible viscous fluid analysis around complex shapes using Isogeometric Analysis

Jesús Sánchez Pinedo — Mon, 01 Jul 2024 10:31:05 +0200

This paper aims to apply the Isogeometric Analysis(IGA) to fluid-structure interaction problem in the civil engineering field. Recently, IGA has attracted much attention as an analysis method to structure with arbitrary surfaces. In this paper, IGA is applied to a twodimensional incompressible viscous flow problem as a basic study for the fluid-structure interaction analysis using IGA. The vortex induced vibration of a circular cylinder is investigated as a numerical example, and the effectiveness and validity of the coupled analysis using IGA are discussed.

Development of traffic noise evaluation system using finite element method

Jesús Sánchez Pinedo — Mon, 01 Jul 2024 10:30:38 +0200

This paper presents a traffic noise evaluation system based on acoustic theory. The finite element method is employed for unsteady wave equations, which is suitable for arbitrary shapes and has excellent applicability to non-uniform materials. The 3D wave equation is employed for the governing equation and the Perfectly Matched Layer (PML) method is utilized as a treatment method for boundary condition. In order to consider multiple moving sound sources such as a traffic noise, a time-variant convolution method is introduced. The auralization method based on VR technology is also introduced to understand the noise level intuitively

Effect of long-term sea water exposure on dielectric materials

Jesús Sánchez Pinedo — Mon, 01 Jul 2024 10:14:04 +0200

Dielectric materials, which are commonly used in capacitors, could increase energy storage density on a per volume basis in film capacitors compared to current technologies accommodating ever-increasing power demands. Recent work in this area has brought about dramatic increases in the dielectric permittivity and moderate increases in dielectric loss, leading to increased material performance on a per volume basis. However, little is known about the aging and breakdown of these materials, which could decrease the performance of these films over time due to decaying dielectric loss and energy storage density. A basic study of the aging of two different state-of-the-art dielectric materials, 3M's Very High Bond (VHB) 4910, commonly used in actuator applications, and bi-axially oriented polypropylene (BOPP), commonly used in large wound film capacitators, is completed. Accelerated life tests using distilled water are conducted to simulate the aging of these materials in a marine environment. An acceleration factor is determined by diffusion studies of distilled water into the materials. Aminabhavi’s and Crank’s methods are used and compared to compute the diffusion coefficient. The two methods produce identical activation energies and, in turn, acceleration factors. The success of this work could actively exhibit the promise of these materials in microelectronic uses.

Coupling multiple resonances for enhancing sound transmission loss of acoustic metamaterials

Jesús Sánchez Pinedo — Mon, 01 Jul 2024 10:13:18 +0200

Recent developments in acoustic metamaterials have been focused on broadening the attenuating bandwidth features towards lower frequency ranges, well below 1000 Hz, as well as tackling manufacturing issues. In this context, a multi-resonant layered acoustic metamaterial (MLAM) was proposed as a practical realization for addressing both challenges. The MLAM’s layered-based design makes it amenable to large-scale manufacturing and the periodic features of each layer enable the application of computational homogenization models to characterize the sound transmission loss (STL) response. Combining these models with optimization techniques allows to determine realistic MLAM designs that trigger multiple resonances in broad frequency ranges. By exploiting coupling mechanisms these resonances translate into multiple STL peaks that produce a broadband continuous frequency range of attenuation, i.e., without transmission peaks in-between. In this work, the proposed computational homogenization model is presented and applied to the design of different MLAM configurations. The goal is to assess the influence of the number of coupled resonating layers in the STL response of the whole MLAM panel, in terms of increasing the attenuation intensity and the effective frequency bandwidth. The results demonstrate the STL enhancements features obtained from exploiting coupling mechanisms, compared to other acoustic metamaterial configurations based on local resonance phenomena. In this context, the proposed MLAM technology exhibits a great potential to provide an efficient, easy-to-manufacture solution to the sound insulation problem at low frequency ranges

Application of the Harmonic Balance Method to predict wave propagation in one-dimensional nonlinear metamaterial excited harmonically

Jesús Sánchez Pinedo — Mon, 01 Jul 2024 10:12:53 +0200

This work exposes a computational procedure designed to aid in modeling mechanical systems featuring stiffness nonlinearity. The basis of the procedure is the Harmonic Balance Method, which is combined with a numerical continuation technique. To present the efficacy of the approach, a one-dimensional nonlinear metamaterial is analyzed. The aim is to demonstrate the suitability of the procedure to extract information regarding higher harmonic generation and the influence of the amplitude of excitation on the system dynamic response.

Ritter-Križaić iteracion method of truss constructions

Jesús Sánchez Pinedo — Mon, 01 Jul 2024 10:12:21 +0200

The optimization of the dimensioning of constructive designs is constantly evolving. FEM, evolutionary, and other various methods are being developed, which are implemented with algorithms in computer simulations of building models. The problem with these methods is solving large differential equations, which is inconceivable without computers and large memories. The Ritter-Križaić (RK) iteration method works for both straight and oblique networks with one side, and it can even be used instead of trigonometric and FEM equations. It does this by adding the geometric properties of the networks and outside actions to the directional equations. By creating straightforward monograms of RK-FEM technology with straightforward differential or subspace equations that are simple to calculate by hand or draw with Mathcad tools, the RK-FEM loop enables COD to define various types of trusses and even other supports. RK-FEM COD is therefore used to create simulation games that explain many logical phenomena in the design of external and internal actions of beam supports, which can be compared to a spider thread or an ice plate structure as an RK string and even to the moon

Influence evaluation of flow diverter stent parent vessel coverage on cerebral aneurysm through the CFD-DEM coupling simulation

Jesús Sánchez Pinedo — Fri, 28 Jun 2024 13:20:21 +0200

Cerebral aneurysms are a type of cerebrovascular disorder where a balloon-like bulge forms in part of an artery in the brain. One of the developed treatments for large cerebral aneurysms is the Flow-diverter Stent (FDS) placement technique. Effective treatment outcomes in cerebral aneurysm treatment using FDS require proper placement of the device. Improper placement can lead to increased blood flow velocity and Wall Shear Stress (WSS) within the aneurysm, as well as increased pressure, which suggests a potential risk of rupture in large aneurysms. Considering these circumstances, this study evaluates the impact of FDS positioning on cerebral aneurysms by creating multiple FDS placement models with the device positioned proximally and distally to the aneurysm. Subsequently, we conducted fluid-structure interaction simulation analyses using the Particle Finite Element Method-Second Generation (PFEM-2) for the non-Newtonian fluid model of blood and the Discrete Element Method (DEM) for the FDS. This study reports the results of comparing blood behavior, WSS, and pressure inside the cerebral aneurysm based on the FDS placement position.

Delta-P1 model implementation for numerical simulation of photothermal cancer therapy in three-dimensional heterogeneous tissues

Jesús Sánchez Pinedo — Fri, 28 Jun 2024 13:19:58 +0200

Photothermal therapy (PTT) stands as a promising avenue for cancer treatment. Metallic nanoparticles (NPs) absorb near-infrared light, inducing localized heating for tumor cell apoptosis. Predicting spatial temperature information in preclinical models is crucial due to cell death sensitivity to temperature changes. Heat transfer models, rely on the radiative transport equation (RTE), where its approximation is essential for this purpose. Existing models for the radiative transport equation, such as the Beer-Lambert law, the diffusion approximation, the discrete ordinates method, and Monte Carlo (MC) simulations, are widely used in the context of PTT. However, each of them has limitations. This study focuses on the δP1 model, wich is an extension of the diffusion approximation. Unlike standard diffusion approximation (SDA), the δP1 model treats forward and scattered light independently, preserving accuracy over a wider range of optical properties, including media with plasmonic NPs. The δP1 model equations are discretized and solved by the Finite Element Method (FEM) . Its numerical results for fluence rate in a heterogeneous geometry with nanoshells is compared to MC simulations and the standard diffusion approximation. This study validates and applies the model to the simulation of light transport in photothermal therapy in general two-dimensional geometries. Results demonstrate the δP1 shows a significant improvement over the SDA in heat transfer simulations in heterogeneous tissues geometries. This underscores its potential as a valuable tool for optimizing photothermal therapy preclinical models.

Optimum design method for artificial ear ossicles based on a high-precision vibration analysis model

Jesús Sánchez Pinedo — Fri, 28 Jun 2024 13:19:17 +0200

In this study, we propose a topology optimization approach aimed at designing an optimal artificial auditory ossicle to enhance hearing restoration in the sound conduction reconstruction of a damaged human middle ear. The primary objective of our design is to maximize the vibration displacement of the stapes footplate by employing the concept of mutual mean compliance. Using this method, we can determine the optimal topology configurations of the artificial component based on topology sensitivity, which we theoretically derive in this paper. To demonstrate the effectiveness and practical utility of our proposed approach, we present a design example of artificial auditory ossicles utilized in tympanoplasty procedures.

Markov chain Monte Carlo capabilities in Dakota

Jesús Sánchez Pinedo — Fri, 28 Jun 2024 13:15:11 +0200

We give an overview of MCMC capabilities in the Dakota software package from Sandia National Laboratories, and present some Bayesian calibration results.

Modelling and simulation of a fully electric hybrid propulsion system for passenger ships using AVL Cruise-M software

Jesús Sánchez Pinedo — Fri, 28 Jun 2024 13:14:50 +0200

The maritime industry's pursuit of sustainability drives the exploration of alternative fuels, with hydrogen emerging as a promising solution. This paper presents a comprehensive study on a fully electric hybrid propulsion system for passenger ships, utilizing hydrogen as the primary power source. Multi-physics simulation using AVL Cruise-M software enables detailed analysis of system dynamics and performance. Results from a full acceleration test reveal the intricate interplay between the fuel cell and battery system, crucial for meeting power demands during transient phases. Examination of material flows highlights the importance of maintaining optimal water balance for system efficiency and durability. Temperature and pressure variations significantly influence FC efficiency, showcasing improvements over time, stabilizing at approximately 56% efficiency after 2.6 minutes. These findings underscore the value of comprehensive simulations and temporal analysis in optimizing hybrid propulsion systems, suggesting strategies for further enhancement, such as precise temperature and mass flow control.

Understanding the solidification and heat treatment characteristics in the CoCrNiSix medium-entropy alloy by experimentally verifiable multiscale thermodynamic and kinetic computational techniques

Jesús Sánchez Pinedo — Fri, 28 Jun 2024 13:14:30 +0200

CoCrNi medium-entropy alloy (MEA) possesses an FCC crystal structure with multiple slip systems and low stacking fault energy [1]; a substantial amount of nanoscale deformation twins can be generated under low-temperature and high-speed deformation. Adding a proper amount of Si can not only reduce the manufacturing cost and mass density but also enhance ballistic resistance by further lowering the stacking fault energy. Previous studies [2] utilized small-scale vacuum arc remelting techniques to investigate the solid solution or secondary phase strengthening of CoCrNi-based MEAs with Al or Si additions. However, to extend the application of lightweight, high-entropy alloys to industrial-grade impact-resistant plate manufacturing, especially for low-temperature environments, it is necessary to study the solidification and heat treatment characteristics of CoCrNiSix castings. This study employs finite element analysis at the macroscopic scale to investigate the solidification phase transformation and heat transfer characteristics of CoCrNiSix under precision-cast conditions. Additionally, at the mesoscopic scale, the phase-field method [3] is used to simulate the dendritic solidification microstructure and element segregation of CoCrNiSix. Thermodynamic parameters required for simulations are calculated using Thermo-Calc high-entropy alloy databases TCHEA6 and MOBHEA2. This research also utilizes electron microscopy to analyze the microstructures of chemically complex CoCrNiSix ingots, focusing on measuring the secondary dendrite arm spacing and elemental segregation profiles. Collecting these microstructure-related features allows us to reasonably infer the cooling rate corresponding to the investment casting process of CoCrNiSix and design rational parameter combinations for homogenization heat treatment of the cast ingots in terms of temperature and isothermal holding time. By validating macroscopic and mesoscopic simulation results through CoCrNiSix microstructure analysis experiments, the multiscale kinetic computational techniques included in this study can be further applied to cost-saving and process optimization practices in the manufacturing of various lightweight high-entropy alloys

Space-time Galerkin finite element discretization and error control for coupled problems

Jesús Sánchez Pinedo — Fri, 28 Jun 2024 13:14:04 +0200

In this work, we consider one key component, namely the wave equation, of a recently proposed space-time variational material model. The overall model is derived from a thermodynamically consistent Hamilton functional in the space-time cylinder in which mechanics, temperature and internal variables couple. Through the derivation, rather unusual end time conditions for the second-order in time wave equation arise. In order to understand their behavior better, we solely focus on the wave equation (neglecting temperature and internal variables) and formulate a Galerkin finite element discretization in time and space. Based on this discretization and the corresponding implementation, some numerical simulations are conducted. Therein, both traditional initial conditions for the displacements and the velocities are considered, as well as our newly proposed conditions for initial time and final time acting on the velocity variable only

Goal oriented error estimation for space-time adaptivity in phase-field fracture

Jesús Sánchez Pinedo — Fri, 28 Jun 2024 13:13:40 +0200

This work focuses on temporal adaptivity for phase-field fracture problems. The methodology requires a space-time formulation and utilizes a space-time Galerkin finite element discretization for the governing phase-field equations. Then, goal functionals (i.e., quantities of interest) are introduced. The computational implementation of goal-oriented error control employs the dual-weighted residual method in which an adjoint problem must be solved. As the analysis is quasi-static, without a temporal derivative, the adjoint problem of the quasistatic primal problem decouples in time. Nonetheless, time-averaged goal functionals can also be considered. The temporal errors are localized using a partition of unity, which allows one to adaptively refine and coarsen the time intervals in the space-time cylinder. Numerical tests are performed on a single edge notched tensile test to investigate the quality of the proposed error estimator.

Assessment of flow-induced stresses in spiral weld pipes with bends

Jesús Sánchez Pinedo — Fri, 28 Jun 2024 13:13:18 +0200

This study numerically investigates flow-induced stresses and displacements in bent pipes at varying angles (20◦ ≤ θb ≤ 80◦ ) using Solids4Foam at Reynolds number of 20,000. The results indicate that increasing θb enhances the formation of symmetric vortex structures, which coincide with enhanced non-uniformity in pressure distribution and wall shear stresses. Additionally, maximum equivalent stresses (σeq) for the solid shell occur near the inlet. The pipes with higher θb also depict a reduced displacement magnitude(D), which hints at the strong role of fixed displacement boundary condition assigned at the pipe inlet and outlet. These findings provide essential insights for performing numerical investigation of pipeline reliability and structural integrity in oil transportation.

Computational interpretation of shape memory epoxy: processing and its operation

Jesús Sánchez Pinedo — Fri, 28 Jun 2024 13:12:56 +0200

The shape forming and restoration mechanisms of shape memory epoxy originate from the molecular-scale dynamics that epoxy molecules undergo during thermomechanical processes. In this study, the microstructural changes that occur at the molecular scale caused by heat and load during the programming and operation of the epoxy network were investigated using molecular dynamics simulations. The mechanical behaviors of each molecule were analyzed by classifying it into translation, rotation, and deformation based on the classical kinematic framework. Specifically, depending on its structural properties, each molecular component was rearranged to different levels, forming local residual stresses. The principle leading to shape recovery as the subsequent thermal load breaks the equilibrium of residual stresses and resulting changes in the mechanical anisotropy of entire epoxy network were also analyzed through a subcontinuum perspective. This study has the potential to be extended to a method for designing epoxy resins that satisfy desired physical properties and shape recovery performance

An improved flux vector splitting method for characteristic-wise WENO schemes of the Euler equations

Jesús Sánchez Pinedo — Fri, 28 Jun 2024 13:10:37 +0200

Steger-Warming (SW) [1] and Lax-Friedrich-type (LF) [2] flux vector splitting methods are used extensively by shock capturing WENO schemes in varieties of compressible flow simulations. Due to the less dissipation, the SW method is preferred in flow calculations that require fine scale structures such as direct numerical simulation of turbulence. However, this paper shows that, even if the characteristic-wise WENO scheme is used, the SW method may still exhibit some oscillations near contact discontinuities, while the LF method does not. Analysis similar to the reference [3] shows that, using the SW method may make the characteristic-wise WENO scheme become close the component-wise WENO scheme near subsonic contact discontinuities. Based on that, an improved flux vector splitting method, which adjusts the eigenvalues of the flux vector splitting in the characteristic-wise WENO procedure, is proposed to obtain the low-dissipation property and prevent contact discontinuity oscillations at the same time. Numerical experiments are performed to validate and evaluate the new method. Numerical results show that the proposed method keeps the non-oscillatory flow field near discontinuities as LF method and also avoids smearing out other flow regions, similar to the SW method.

Modeling the enhanced geothermal systems using the extended–FEM and an equivalent continuum model

Jesús Sánchez Pinedo — Fri, 28 Jun 2024 13:10:16 +0200

. In this paper, a computational technique is presented for Thermo-Hydro-Mechanical (THM) simulation of Enhanced Geothermal Systems (EGS) based on the eXtended Finite Element Method (XFEM) and Equivalent Continuum Method (ECM) in the framework of Local Thermal Non-Equilibrium (LTNE). Heat extraction from Enhanced Geothermal Systems involves several multi-physics coupling processes, including the seepage through the fractured porous media, the thermal exchange between the working fluid and the matrix, and the deformation of fractured porous media that play essential roles in exploiting the geothermal energy contained in hot dry rocks. The ECM provides the equivalent tensors for the fluid permeability and solid compliance, which is an essential feature for the coupled Thermo-Hydro Mechanical simulation of fracture networks. In the model, the XFEM is employed for large scale fractures to capture the mass and heat transfer between the fracture and matrix more accurately, while the ECM is applied on the network of small-scale fractures. Hence, the proposed model benefits from the advantages of both methods, and it allows for managing between accuracy and cost. The set of THM equations is solved with both Local Thermal Equilibrium (LTE) and Local Thermal Non-Equilibrium (LTNE) assumptions to find out the impact of each method on the production temperature. The capability of the proposed computational model is demonstrated for the diagonal arrangement of the injection and production wells with different fracture orientations in-between. The simultaneous effects of fracture connectivity and inclination are investigated between the two injection and production wells. It is observed that the temperature difference between the two cases is higher in the middle of the domain by comparing the results of LTE and LTNE assumptions. Moreover, it is concluded that the LTE model overestimates the fluid temperature in comparison to the LTNE model in cold water injection problems. The results show the proposed computational model is a promising tool for estimation of the heat mining performance of EGS

Stabilization of mixed displacement-pressure finite elements at finite strains using polyhedral formulations and Voronoi meshing

Jesús Sánchez Pinedo — Fri, 28 Jun 2024 13:09:55 +0200

The hexahedral mixed displacement-pressure finite element of the lowest order (H1/P0) has shown to be simple and effective during both linear and nonlinear analysis of incompressible solids. While the discrete displacement field is generally considered to be sufficiently accurate, the discrete pressure field can sometimes be heavily polluted by spurious pressure modes. This results from the fact that the element does not fulfill the inf-sup condition. While postprocessing techniques, such as pressure filtering or smoothing, exist to remove the spurious pressure modes from the solution, this contribution aims on the exclusion of spurious pressure modes from the solution a priori due to the element geometry. By employing polyhedral finite element formulations on Voronoi tessellations in three dimensions, we show that the discrete kernel of the linearized mixed bilinear form only consists of the hydrostatic pressure mode. A spurious pressure mode is automatically suppressed due to the vertex-to-volume ratio in the finite element mesh. These considerations hold for any arbitrary physically admissible displacement state that can occur within a Newton-Raphson framework. A nonlinear numerical example shows that spurious pressure modes are indeed suppressed if the type of tessellation is changed from hexahedral to Voronoi.

A coupled SPH-FDM method for simulations of unsteady flows

Jesús Sánchez Pinedo — Fri, 28 Jun 2024 13:08:56 +0200

The fluid-flexible-structure interaction (FFSI) is characterized by the large deformation, the thin structure, and the complex of the flow field. Accurately simulating FFSI poses three challenges, which are the reproduction of thin structure, the capture of moving interface, and the numerical stability of multi-physics field coupling, respectively. In this study, the FFSI is simulated by the smoothed particle hydrodynamics (SPH) because of its natural advantage in dealing with the moving interface. The shell model with single-layer particles[1] is introduced into SPH to simulate the thin flexible structure. The truncation error caused by the single-layer boundary is modified by the normal flux approach[2]. κ-ε turbulence model is introduced into SPH to enhance the numerical stability and capture complex flow details. In addition, other techniques or models that ensure the efficiency and stability of the calculation are used in this study, including PST (particle shifting technique), δ-SPH method, and GPU (graphics processing unit). The flows around the single filament are simulated to verify the accuracy and stability of the current FFSI algorithm based on the SPH method.

A computationally efficient method for considering a large number of nonlinear multi-point constraints within the finite element method

Jesús Sánchez Pinedo — Fri, 28 Jun 2024 13:07:54 +0200

Nonlinear constraints are crucial in modeling various problems in computational mechanics. Among other things, they can be used for the subsequent consideration of rigid inclusions in a body originally modeled as deformable, without requiring a remeshing of the considered domain and thus contributing to a rapid modeling building. Unlike Lagrange multipliers and the penalty method, the master-slave elimination reduces the problem dimension but is limited to linear constraints. We introduce a new master-slave elimination method for arbitrary nonlinear multi-point constraints. It is compared to existing methods through analysis of the resulting equations and numerical examples. Results indicate that the method is as accurate, robust, and flexible as Lagrange multipliers, with improved efficiency due to reduced degrees of freedom, which is particularly advantageous when a large number of constraints have to be considered.

Geometric formulation of three-temperature radiation hydrodynamics

Jesús Sánchez Pinedo — Fri, 28 Jun 2024 13:06:57 +0200

Three-temperature (3T) radiation hydrodynamics models high energy-density plasma of nonlinearly coupled electron, ion, and radiation fields, finding applications in astrophysics and inertial confinement fusion. We present a geometric formulation of three-temperature radiation hydrodynamics. This is done utilizing an irreverisble portHamiltonian framework in the entropy representation. This geometric formulation separates the advection, interaction, and diffusion processes occuring into separate operators and establishes the energy-preserving interconnections between them. Structural properties such as mass, momentum and energy conservation as well as entropy production arise naturally from the geometric formulation. As an application, we briefly discuss a framework for the energy control of the 3T system within the port-Hamiltonian framework.

The Picard-Newton iteration for the Boussinesq equations

Jesús Sánchez Pinedo — Fri, 28 Jun 2024 13:06:08 +0200

We consider the Picard-Newton and Anderson accelerated Picard-Newton solvers applied to the Boussinesq equations, nonlinear Helmholtz equations and Liouville equation, for the purpose of accelerating convergence and improving robustness with respect to problem parameters. In all cases, we show the proposed solvers improve efficiency over the commonly used solvers and are able to find solutions for a much larger set of problem parameters.

A new concept for embedding sub-structures via level-sets

Jesús Sánchez Pinedo — Fri, 28 Jun 2024 13:05:47 +0200

A framework is presented to continuously embed sub-structures such as fibres and membranes into otherwise homogeneous, isotropic bulk materials. The bulk material is modeled with classical finite strain theory. The sub-structures are geometrically defined via all level sets of a scalar function over the bulk domain. A mechanical model that is simultaneously applicable to all level sets is given and coupled to the bulk material. This results in a new concept for anisotropic materials with possible applications in biological tissues, layered rocks, composites, and textiles. For the numerical analysis, the bulk domain is discretized possibly using higher-order finite elements which do not conform to the level sets implying the shapes of the embedded sub-structures. Numerical results confirm the success of the proposed embedded sub-structure models in different contexts

On triangular self-stabilized virtual elements for Kirchhoff-Love shells

Jesús Sánchez Pinedo — Fri, 28 Jun 2024 13:05:26 +0200

This work presents a self-stabilized triangular virtual element for linear Kirchhoff–Love shells. The domain decomposition by flat triangles directly approximates the shell geometry without resorting to a curvilinear coordinate system or an initial mapping approach. The problem is discretized by the lowest-order conventional virtual element method for the membrane, in which stabilization is needless, and by a stabilization-free virtual element procedure for the plate. Numerical examples of static problems show the potential of the formulation as a prelude for the evolution of self-stabilized Kirchhoff–Love shell virtual elements.

Projector assembly: bridging Poisson and elasticity formulations

Jesús Sánchez Pinedo — Fri, 28 Jun 2024 13:05:05 +0200

Virtual element methods define their shape functions implicitly (tailored to each element’s geometry), foregoing the typical reference element and transformation scheme usually employed by the finite element method. The formulation leverages the use of polynomial projections supplied by heuristic stabilizations when necessary. These projections are represented by projector matrices, which require the solution of a local system. Elasticity formulations usually employ an ð¿ 2 -projection from a displacement multifield onto a strain multifield, requiring the solution of a considerably larger system than a typical Poisson problem would require, with dense matrices and lots of zeroes. This work presents a way to obtain the projections for elasticity formulation by assembling from the ð¿ 2 -projection for each derivative of the one-field a Poisson formulation, resulting in smaller local systems being solved and more efficient storage. This approach is based on the linearity of both projections and derivatives, and is shown in the examples to preserve the convergence rate of the method.

Mixed partition of unity methods and stochastic Gillespie algorithms for Transport-Reaction equations

Jesús Sánchez Pinedo — Fri, 28 Jun 2024 13:04:48 +0200

We introduce a new type of model framework which is part stochastic and part deterministic. The starting point is a finite size particle system within a single reaction volume, with type exchanges modelled by a contact process. Inside the reaction volume, each particle can interact with every other particle with the same probability. This is the setting of a classical reaction system simulated with a Gillespie algorithm. Such systems can be used to describe other than chemistry type exchanges, like an infection process, and therefore are already very versatile. Their advantage is that they are able to be used where small size effects can play a role, like extinction events, which are impossible to model with differential equations, including stochastic differential equations. However finite size and single reaction volume settings for reaction systems are too restrictive in other ways. We might like to add internal or external states to the particles. These states are coordinates in a position space. An example of an internal position/state space is age (since entering the system), an example for an external position/state space is geographical location. The particles then can also change their positions in these state spaces, according to some probability distribution which evolution is modelled deterministically. The classical example for a transport process is a partial differential equation like the heat equation, or more general parabolic advection-diffusion equations. We assume that the distribution of the particles in position space is not influencing the evolution of the probability distribution driving in turn the evolution of the particles’ positions. The model framework with its finite-size particle population approach can very accurately model situations where finite-size effects take place, however provides in addition detailed descriptions of both internal and external particle state spaces where needed. The framework can therefore be used in addition to traditional established models, like transport PDEs or internally structured population models, when the computation of the statistics of finite-size effects is important.

Immersed-boundary approach based on integrated RBFs and smooth extension for solving PDEs in complex domains

Jesús Sánchez Pinedo — Fri, 28 Jun 2024 13:04:27 +0200

We propose an immersed-boundary approach, based on point collocation, five-point integrated radial basis function stencils, rectangular Cartesian grids and smooth extension of the solution, for solving the two-dimensional elliptic partial differential equation in a geometrically complex domain.

pyMesoscale: A friendly python library for generating 3D concrete mesoscale models based on the local background grid method

Jesús Sánchez Pinedo — Fri, 28 Jun 2024 11:58:53 +0200

Mesoscale modeling of concrete and its composites has attracted a lot of researchers over the years with the promise of establishing an accurate relationship between the mesoscopic model and the macroscopic mechanical properties of concrete. The primary constraints inhibiting the widespread application of mesoscale modeling include (i) achieving high packing density with control over aggregate shape and gradation, (ii) high computational cost, (iii) accomplishing realistic interfacial transition zone, and (iv) implementing efficient aggregate intrusion detection. Besides these constraints, one major challenge is the lack of open program codes for algorithms implemented in published research papers. For example, improving, upgrading, and repurposing an existing algorithm by other researchers requires the open availability of the codes. The unavailability of these codes and the common absence of subtle implementation details in published papers hinder research progress on mesoscale modeling of concrete composites. This paper presents pyMesoscale, a Python library for generating 3D mesoscale models for concrete like composites. pyMesoscale implements the local background method, a highly effective mesoscale generation algorithm that offers a much better aggregate intrusion detection system and a high aggregate volume fraction. Developed with Python due to its smoother learning curve and beginner friendliness, pyMesoscale reduces implementation complexity for ease of use by both new and experienced researchers in the field. This paper offers the mathematical formulars and the detailed steps required to implement the generation of mesoscale geometric model of concrete and its derived mesoscale finite element model covering aggregate gradation and shape, random aggregate translation and aggregate intrusion detection.

Modeling the quasi-brittle fracture of structural materials using a mixed stabilized two-field finite element formulation

Jesús Sánchez Pinedo — Fri, 28 Jun 2024 11:58:01 +0200

The fracture process zone (FPZ) is typically characterized as a small region around a crack where non-linear phenomena occur, such as plasticity. In brittle materials, this zone is small and can be safely neglected. However, in quasi-brittle materials, which exhibit a combination of brittle and ductile behavior rather than a clear manifestation of either, the material within the FPZ tends to damage and displays a softening curve after reaching peak load. This behavior is frequently observed in structural materials like concrete and timber, and it can be challenging to model. Traditionally, displacement-based irreducible finite element (FE) formulations have been widely used for simulating structural materials. However, this approach comes with significant drawbacks, such as mesh dependence and convergence problems, when applied to certain phenomena like softening, localization, and fracture. To address these challenges, various techniques have been employed, including extended FE methods and phase-field modeling. In this work, the utilization of a mixed FE formulation in which both displacement and strain serve as primary unknowns within the system, is proposed. To ensure satisfaction of the inf-sup condition, which is associated with saddle point stability in mixed formulations, we employ the variational multiscale method to introduce stabilizing terms into the system. The implementation is conducted using FEniCS, an open-source FE software that offers a high-level programming interface written in Python. The implementation is validated by comparing the obtained results with those reported in the literature for bending test in notched specimens. The results demonstrate remarkably good performance in terms of maximum load, softening curve, and structural size effect in various specimens, exhibiting minimal mesh dependence even when using low-order interpolation elements

Calibration of damage parameters of super high-rise frame-core structural subsystem under torsional ground motion

Jesús Sánchez Pinedo — Fri, 28 Jun 2024 11:57:39 +0200

To clarify the dynamic characteristics of the structure under torsional seismic excitation, a macroscopic dynamic model of the structure and simplified hysteretic models of each sub-system were established through theoretical derivation, and the accuracy of the models was verified using finite element models. To determine the design parameters of the hysteretic models for each sub-system, a multi-objective seismic optimization approach considering both structural cost and overall torsional damage was proposed. Through multi-objective optimization based on torsional overturning analysis, the design parameters of each sub-system were successfully determined. The results indicate that the outrigger truss sub-system plays a significant role in controlling the overall torsional behavior of the structure.

Synergistic effects of environmental deterioration on fatigue and flexure properties of glass fiber reinforced polymeric (GFRP) composites : a multiscale and multiphysics model.

Jesús Sánchez Pinedo — Fri, 28 Jun 2024 11:57:18 +0200

This study aims to simulate synergistic UV & moisture deterioration and demonstrate its role in changing the residual fatigue and flexure strength in architectural GFRP composite material. This study develops an experimentally validated 3D Multiphysics model at a structural level and gets this homogenization-based model to identify the degradation mechanisms observed in the experimental data. Sensitivity analyses are conducted to investigate the effect of mesh density on the accuracy of functions homogenized from micromechanical models. In addition, this macroscale model also quantifies how these degradation mechanisms weaken the strength and durability of environmentally aged composite materials. The aging-fatigue-bend macroscale model assumes that the degradation-induced damage field is concentrated within a depth to the plate surface. According to the computational results, the degradation process caused by the combined effect of UV and moisture exposure involves the removal of polymeric matter from the exposed surface. In other words, the degradation mechanism of UV exposure involves both the chemical alteration and mechanical damage of polymeric matter, primarily located at the exposed surface. This model can be incorporated into many commercial finite element codes for a sustainability study of composite structures/systems. In future work, the models developed in this study will be combined with life cycle assessment (LCA) tools to support better sustainability-focused new material design, thus reducing costs and environmental impacts in the built environment.

Algebraic Flux Correction for Equi-dimensional Transport Problems in Porous Fractured Media

Jesús Sánchez Pinedo — Fri, 28 Jun 2024 11:56:56 +0200

We present a simple finite element framework which enables numerical simulations of transport problems in fractured porous media based on equi-dimensional models, i.e., models where fractures are considered heterogeneities of the same geometrical dimension as the embedding background. The two main ingredients of the proposed framework are an adaptive mesh refinement strategy, and an algebraic flux correction stabilization. The proposed finite-element method for equi-dimensional models is inherently simple and can be easily implemented in any common simulation software, as it does not require the complicated management of different meshes and discretizations, which are necessary for numerical simulations based on hybrid-dimensional models, i.e., models where fractures are considered as heterogeneities of a lower geometrical dimension than the embedding background. Actually, our equi-dimensional approach provides a strategy to validate hybrid-dimensional models. Our adaptive approach is inherently conservative and naturally reduces the discretization error which, for problems with heterogeneities, is concentrated at the interfaces.

Computational modeling of cutting disc-rock interaction in mixed ground conditions

Jesús Sánchez Pinedo — Fri, 28 Jun 2024 11:55:54 +0200

This paper presents the performance of a simulation tool based on state-based peridynamic theory, developed to model the interaction between cutting discs of a Tunnel Boring Machine (TBM) and the ground being excavated. Compared to existing TBM performance prediction models, the current computational approach accounts for mixed ground conditions, different TBM and disc designs, as well as the direct coupling with wear models. The developed peridynamic model is thoroughly validated using several benchmarks, including indentation tests on sandstone specimens. Additionally, a full-scale Linear Cutting Machine (LCM) test conducted on Colorado Red granite is simulated, where cutting forces obtained from the computational model at various disc spacings are compared against experimental data. Excavation in mixed ground conditions, which can lead to excessive tool wear or failure due to rapidly changing cutting forces, was examined through an LCM experiment. Scaled-down peridynamic simulations show cutting force trends consistent with the LCM experiment results. Finally, to predict the influence of these varying cutting forces on tool life, an abrasive wear model is implemented in the peridynamic simulation framework.

An improved hybrid computational mechanics framework for composite damage modelling and simulation

Jesús Sánchez Pinedo — Fri, 28 Jun 2024 11:55:33 +0200

In this study, an integrated modeling framework is proposed, combining continuum damage modeling (CDM), the extended finite element method (X-FEM), and the cohesive zone modeling (CZM) techniques, to model the progressive failure of fibre-reinforced composite laminates. This modeling framework has the capability to efficiently capture fibre failure, matrix cracking, and interlaminar delamination. The Schapery theory (to address polymer matrix viscoelastic behavior) is also incorporated to accurately simulate the pre-peak nonlinearity of the load-bearing response due to matrix microcracking. The proposed hybrid model is developed and implemented using Abaqus with user-defined subroutines. A multidirectional composite laminate with an open-hole notch configuration under tension (OHT) is examined as a case study. The simulation results are compared with the physical experiments in the open literature. The proposed framework represents a practical paradigm, which not only drastically reduces the pre-processing workload to build a physics-based highfidelity damage model, but also largely decreases the computational cost

Multiscale modeling of hydrogen transport in steels and its resulting embrittlement effect

Jesús Sánchez Pinedo — Fri, 28 Jun 2024 11:55:12 +0200

A multiscale modeling approach is adopted in this study to understand the hydrogen embrittlement (HE) mechanisms and to predict failure of engineering components under the influence of hydrogen environment. Molecular dynamics simulations of the bodycentered cubic (BCC) iron are conducted to examine the theories of hydrogen enhanced localized plasticity (HELP) and hydrogen enhanced decohesion (HEDE). It is shown that hydrogen aggregation at the crack tip and along grain boundary (GB) reduces the surface energy for creating new crack surfaces, leading to changes in fracture modes caused by preemptive crack propagation. At the continuum level, a numerical framework is developed, which incorporates hydrogen transport in steels and the resulting HELP and HEDE mechanisms into a finite element phase field model to predict crack initiation and propagation in engineering components. As an example, a compact tension (CT) specimen made of a pipeline steel is analyzed. The numerical model captures the phenomenon of hydrogen aggregation occurring proximal to the crack tip driven by the high gradient of hydrostatic stress and large plastic deformation in this region. The resultant hydrogen concentration elicits an interplay of HELP and HEDE effects and reduces the specimen’s load carrying capacity. With properly chosen model parameters, the numerical model has the potential of serving as tool for predicting crack propagation and ductile to brittle transition due to the presence of hydrogen.

Critical planes analysis of the impact of porosities on the fatigue of metal solids

Jesús Sánchez Pinedo — Fri, 28 Jun 2024 11:54:52 +0200

In this work, we take interest in the impact of defects present in metal solids manufactured by material fusion or by additive manufacturing on their fatigue life during cyclic loading. Indeed, we observe a more or less strong local plasticity around the defects even if the stresses remain below the elastic limit, which can strongly impact the fatigue life of such solids. In the case of a part obtained by steel casting, it is the retassures that make the part most vulnerable. In the case of solids obtained by additive manufacturing, the most damaging defects are surface roughness and porosities linked to a lack of fusion. In order to estimate the fatigue life of such solids, it is necessary to observe the states of stress and strain around the defects during a cycle. As stress levels can be relatively high locally, critical plane type criteria are relevant for estimating the fatigue life of such solids. In order to carry out a fatigue analysis of a part obtained by steel casting or by additive manufacturing, we propose to model it by finite elements, with a refinement of the elements around the porosities, then to calculate the local stress and strain states, and finally to implement a critical plane type criterion, like the Fatemi-Socie criterion. The critical planes are the planes on which the maximal shear strain amplitudes occur. The local stress and strain states can be highly multi-axial. So the determination of the critical planes can be very computationally and storage consuming. In the present work, an analysis in the space of deviators of the deformation tensor makes possible determination of such planes in each of the numerous nodes of the mesh. These three steps of calculation, correlated with experimental tests, makes it possible to envisage obtaining fatigue life laws for numerous metallic materials presenting defects.

Semi-analytical failure prediction of adhesive joints by Finite Fracture Mechanics

Jesús Sánchez Pinedo — Fri, 28 Jun 2024 11:53:55 +0200

The current contribution suggests a semi-analytical structural model for an adhesive joint with a closed-form higher-order description of the adhesive layer and the potential occurrence of a debonding crack. This enables a highly efficient failure prediction by the concept of Finite Fracture Mechanics, employing a coupled failure criterion that consists of a stress and an energy subcriterion. The comparison with accompanying finite element calculations and experimental findings demonstrates the high predictive quality of this approach

Fatigue crack propagation behavior analysis of 15MnTi steel based on cyclic cohesion model

Jesús Sánchez Pinedo — Fri, 28 Jun 2024 11:52:58 +0200

15MnTi steel is widely used in high load structures such as bridges, pressure vessels, ships, and vehicles due to its excellent mechanical properties. In the course of service, the failure of steel structure is mostly caused by fatigue fracture. In order to investigate the crack growth of 15MnTi steel under fatigue load, the cohesive zone model (CZM) was used to simulate the crack growth. The CZM can simulate brittle and plastic fracture behavior by using the function of crack interface opening force and opening displacement to avoid the stress singularity of crack tip. On this basis, a cyclic cohesive zone model (CCZM) was established to study the fatigue crack propagation behavior. This model effectively links damage, tractive force, and cumulative displacement while incorporating the process of fatigue crack growth to accurately simulate material damage evolution under fatigue load. Experimental studies on crack growth in 15MnTi steel at three stress ratios reveal a linear relationship between crack growth rate and stress intensity factor range for different stress ratios. The parameters of Paris formula were calculated using crack growth rate and stress intensity factor range, which provided reference for the selection of model parameters. By utilizing the user element subroutine (UEL) in Abaqus and compiling the CCZM using Fortran language specifically for 15MnTi steel, simulations were conducted to analyze the evolution of crack tip state under various stress ratios and discuss the corresponding crack growth behavior based on experimental observations. The results demonstrate that the fatigue crack propagation rate varies linearly with both stress ratio range and stress intensity factor range, consistent with experimental findings. The results of the opening and closing evolution of the crack tip are consistent with the law of crack propagation, which indicates that the plastic behavior of the crack tip can be effectively characterized by the CCZM. Furthermore, parameters obtained from the cyclic cohesive zone model's Paris formula closely match experimental data, thus validating its accuracy and feasibility in simulating fatigue crack propagation behavior.

Numerical simulation of the swelling and deswelling process of gel

Jesús Sánchez Pinedo — Fri, 28 Jun 2024 11:52:41 +0200

It is well known that the entropy elasticity of rubberlike materials and Brownian motion are described by formally analogous equations as both originated from thermal fluctuations. In rubberlike materials, the shear modulus is conventionally considered to be proportional to the absolute temperature and the proportionality factor is the number density of polymer chains for an affine polymer chains’ network model. On the other hand, the self-diffusion coefficient of Brownian motion is described as the product of the mobility and the absolute temperature. However, for the polymer chains’ network in a solvent, the interaction between the polymer chains and the solvent molecules occurs and the collective diffusion coefficient of the solvent molecules should be different to the self-diffusion coefficient of Brownian motion. Moreover, the shear modulus of the resultant polymer gel should be dependent on the swelling ratio due to the nonaffine movement of polymer chains. Therefore, to verify the analogy of the equations for the shear modulus of the nonaffine polymer chains’ network model and the collective diffusion coefficient of the solvent molecules, in this study, the swelling and deswelling process of the polymer gel is investigated by the numerical simulations.