Remeshing Technique Research Articles

Modelling diffusive phase transformations in multiphase systems using the Voronoi implicit interface method

Abstract This paper presents a general level set framework for modelling diffusive solid-state phase transformation processes in binary systems comprising several grains and phases. Notably, it is demonstrated how the Voronoi implicit interface method (VIIM) can be used to simulate microstructure evolution in polycrystals driven by diffusion. The key advantage of VIIM is that a single level set function can be utilized to describe the evolution of the microstructure. Thus, the computational cost is significantly reduced compared to more traditional approaches, in which each grain in the microstructure is assigned a separate level set function. Moreover, VIIM facilitates the reconstruction of a fully compatible grain boundary network without the presence of any void regions or grain overlaps. The reconstruction procedure does not require any special handling of junctions and can be easily extended to higher dimensions. Moreover, the reconstruction step enables an adaptive remeshing technique to be employed such that the mesh nodes conform with the location of the grain boundaries. Hence, the diffusion problem can be solved in distinct phase domains, demarcated by sharp interfaces. The kinetics of the phase interfaces are described by the amount of flux towards the interface in accordance with the theory of diffusion-controlled phase transformations. To examine the capabilities of the proposed model, both single-phase and multiphase problems are examined. For the single-phase problem, it is shown that the model behaves in accordance with analytical solutions and maintains mass conservation. For the multiphase problems, two model cases of polycrystals that share the same initial geometry but exhibit different phase distributions are investigated, as well as a representative microstructure example. The evolution of the microstructures towards an equilibrium state is in agreement with the expected phase fractions and demonstrates that the model produces reliable results. The error in mass conservation of the considered multiphase examples is within a margin of ±5%.

Joint Optimization-Based Texture and Geometry Enhancement Method for Single-Image-Based 3D Content Creation

Recent studies have explored the generation of three-dimensional (3D) meshes from single images. A key challenge in this area is the difficulty of improving both the generalization and detail simultaneously in 3D mesh generation. To address this issue, existing methods utilize fixed-resolution mesh features to train networks for generalization. This approach is capable of generating the overall 3D shape without limitations on object categories. However, the generated shape often exhibits a blurred surface and suffers from suboptimal texture resolution due to the fixed-resolution mesh features. In this study, we propose a joint optimization method that enhances geometry and texture by integrating generalized 3D mesh generation with adjustable mesh resolution. Specifically, we apply an inverse-rendering-based remeshing technique that enables the estimation of complex-shaped mesh estimations without relying on fixed-resolution structures. After remeshing, we enhance the texture to improve the detailed quality of the remeshed mesh via a texture enhancement diffusion model. By separating the tasks of generalization, detailed geometry estimation, and texture enhancement and adapting different target features for each specific network, the proposed joint optimization method effectively addresses the characteristics of individual objects, resulting in increased surface detail and the generation of high-quality textures. Experimental results on the Google Scanned Objects and ShapeNet datasets demonstrate that the proposed method significantly improves the accuracy of 3D geometry and texture estimation, as evaluated by the PSNR, SSIM, LPIPS, and CD metrics.

Treatment of inelastic material models within a dynamic ALE formulation for structures subjected to moving loads

AbstractThis article showcases the development of a dynamic Arbitrary Lagrangian Eulerian (ALE) formulation to account for inelastic material models within a finite element framework. Such a formulation is commonly utilized in research domains like fluid mechanics, fluid‐structure interaction, quasi static remeshing techniques, and quasi static load movement. The work at hand describes the application of the ALE formulation to efficiently analyse structures subjected to moving loads in the field of transient inelastic solid mechanics. In particular, structures such as pavements, gantry crane girders etc., which are subjected to moving loads, can be numerically simulated, and their transient response in the relevant region around the load can be obtained without relying on moving loads. The focus of this article is to facilitate the treatment of history variables stemming from inelastic material models. Of particular interest is the advection procedure required to transport the history variables through the mesh, as the material appears to flow through it. The mathematical framework necessary to treat this advection process is described in detail, considering a nonlinear viscoelastic material model on a neo‐Hookean base at finite deformations. Then, four methods for numerically achieving the advection are implemented within a transient finite element ALE formulation. These methods are compared against each other, and additionally with the conventional Lagrangian method for validation. The results demonstrate satisfactory agreement with conventional simulation methods, while offering a significant improvement in terms of computation speed. With the work at hand, the dynamic response of inelastic materials subjected to moving loads can be numerically simulated in a computationally efficient manner.

Finite element analysis of sliding wear on the borided AISI 316L stainless steel

This work implements a 3D finite element to analyze wear in borided AISI 316 L stainless steel. The 3D model was validated through sliding wear test under a ball-on-flat configuration, following the ASTM G133 standard procedures. ABAQUS software was used with an Arbitrary Lagrangian-Eulerian (ALE) remeshing technique alongside the UMESHMOTION subroutine to apply an elemental level Archard’s equation. The artificial roughening of the worn surfaces due to discretization in finite element sizes was controlled by relating the maximum increment time on each wear step to the element size and the stroke. The study also described the evolution of the stress field and the behavior of the contact area. The maximum stress was estimated after the first indentation, decreasing as the contact area increased, reaching a minimum at the last wear step. The results revealed a good correlation between the experimental and modeled data, with a maximum error of 8.34% in the contact stress and a maximum error of 22% in the wear depth.

Particle Virtual Element Method (PVEM): an agglomeration technique for mesh optimization in explicit Lagrangian free-surface fluid modelling

Explicit solvers are commonly used for simulating fast dynamic and highly nonlinear engineering problems. However, these solvers are only conditionally stable, requiring very small time-step increments determined by the characteristic length of the smallest, and often most distorted, element in the mesh. In the Lagrangian description of fluid motion, the computational mesh quickly deteriorates. To circumvent this problem, the Particle Finite Element Method (PFEM) creates a new mesh (e.g., through a Delaunay tessellation, based on node positions) when the current one becomes overly distorted. A fast and efficient remeshing technique is therefore of pivotal importance for an effective PFEM implementation in explicit dynamics. Unfortunately, the 3D Delaunay tessellation does not guarantee well-shaped elements, often generating zero- or near-zero-volume elements (slivers), which drastically reduce the stable time-step size. Available mesh optimization techniques have limited applicability due to their high computational cost when runtime remeshing is required. An innovative possibility to overcome this problem is the use of the Virtual Element Method (VEM), a variant of the finite element method that can make use of polyhedral elements of arbitrary shapes and number of nodes. This paper presents the formulation of a 3D first-order Particle Virtual Element Method (PVEM) for weakly compressible flows. Starting from a tetrahedral mesh, poorly shaped elements, such as slivers, are agglomerated to form polyhedral Virtual Elements (VEs) with a controlled characteristic length. This approach ensures full control over the minimum time-step size in explicit dynamics simulations, maintaining stability throughout the entire analysis.

Exploratory research on the multi-life stages mesh-type model of Caenorhabditis elegans in radiation ecology

To address the lack of effective dose quantification methods for the model organism Caenorhabditis elegans (C. elegans) in radiation ecology research, this study employs remeshing techniques to develop a comprehensive mesh-type model covering multi-life stages, from embryonic to larval (L1, L2, L3, L4) and adulthood. Using these models, Dose Coefficients (DC) for C. elegans in a soil environment under different exposure conditions (external and internal), material settings, and radioactive nuclides (³H, ⁶⁰Co, ⁹⁰Sr, 12⁹I, 1³1I, 1³⁴Cs, 1³⁷Cs) were calculated with the Monte Carlo toolkit Geant4. The results show that the difference in DC, when C. elegans material is set as either biological material or water, is within 5%. Under external exposure conditions, the impact of life stages on the population's average DC is minimal (with a maximum deviation not exceeding 10%). However, the distribution within the population varied significantly across life stages (under external exposure to 137Cs, the dispersion was 12.02% for adults and a considerably higher 60.30% for larvae). The earlier the life stage, the greater the variability in DC distribution within the C. elegans population. Furthermore, correlation analysis indicates a strong relationship between DC and life stages under internal exposure scenarios. The mesh-type model of C. elegans established in this study provides a valuable tool for radiation ecology research and has potential applications in broader research fields.

Coupled thermomechanical finite element analysis of ultrasonic hot embossing process

Ultrasonic Hot Embossing of polymers is one of the most attractive manufacturing methods of high-quality and complex microparts needed for biological and chemical processes. A little simulation work has been done to study the deformation mechanism and the required load in the Ultrasonic Hot Embossing of polymethyl methacrylate (PMMA). This paper developed a 2D coupled thermo-mechanical finite element model to simulate the forming behavior of the ultrasonic embossing process of PMMA, optimize the mold microfeature corner, and predict the embossing load as well. VDISP ABAQUS subroutine has been used to describe the downward motion of the mold assisted with ultrasonic vibration. The Arbitrary Eulerian-Lagrangian re-meshing technique has been implemented to refine the deformation zone during simulation to avoid divergence due to localized excessive deformation. Embossing load, temperature, stresses, strains, and energy dissipation have been recorded and analyzed. Simulation results revealed that the coupled thermo-mechanical FE Model efficiently captures the deformation behavior and Embossing load. It also proved that a Mold microfeature corner of 20 μm filet radius is recommended to adequately fill out the area around the mold and maintain uniform temperature and strain distributions.

High-resolution simulating of grain substructure in cold rolling and its effects on primary recrystallization in annealing of ferritic stainless steel

In this study, an integrated crystal plasticity and cellular automaton (CA) model has been developed and employed to investigate the processes of cold rolling and annealing in ferritic stainless steel. Crystal plasticity simulates the deformation microstructure, deformation texture and corresponding dislocation density distribution in the cold rolled ferritic stainless steel. Meanwhile, CA predicts the microstructural evolution originating from nucleation and growth. The resolution of the crystal plasticity model has been improved using a newly developed remeshing technique, which allows for the capture of the grain substructure in the deformation microstructure. The developed model has been validated by experimental measurements with electron backscatter diffraction (EBSD) in terms of comparing the orientation distribution functions (ODFs), misorientation, local substructures, and grain size. The good agreement between simulations and experiments indicates that the developed crystal plasticity with CA model is reliable and efficient for predicting the microstructure and texture evolutions during cold rolling and subsequent annealing.

M-Voronoi and other random open and closed-cell elasto-plastic cellular materials: Geometry generation and numerical study at small and large strains

The present study deals with a numerical design strategy of a novel class of three-dimensional random Voronoi-type geometries, called M-Voronoi. These materials comprise random, non-quadratic convex void shapes and non-uniform intervoid ligament thicknesses, and can span high-to-low relative densities. The starting point for their generation is a random adsorption algorithm (RSA) construction with spherical voids embedded in an incompressible, nonlinear elastic matrix phase. The initial RSA geometry is subjected to large elastic volume changes by prescribing Dirichlet boundary conditions. Due to the incompressibility of the matrix phase, the externally imposed volume changes lead to significant void growth. The numerical growth process may be stopped at any desired porosity. The proposed M-Voronoi process is general and allows the formation of isotropic (or anisotropic) designs. As a byproduct of the developed approach, we also present a novel remeshing technique allowing to read arbitrary geometries of one or multiple phases. The elasto-plastic properties of the M-Voronoi porous materials are numerically investigated at small strains as well as large compressive and shear loads. Their response is assessed by comparison with other well-known random and periodic porous geometries such as polydisperse porous materials with spherical voids (RSA), classical TPMS Gyroid geometries and random Spinodoid topologies. The results show that M-Voronoi and RSA (with spherical voids) geometries exhibit the stiffest elastic and highest flow stress response compared to the other two geometries. This study shows unambiguously that randomness may or may not lead to enhanced mechanical response such as higher stiffness or flow stress.

Prediction of fatigue lives for steel beams and steel reinforced concrete beams

With the wide application of steel reinforced concrete (SRC) beams, the problem of fatigue has become increasingly prominent. To deeply understand the fatigue performance of SRC beams, a finite element analysis (FEA) about fatigue failure process of SRC beams was performed. The internal H-steel inside SRC beam (SRCH-steel) was shown to possess similar fatigue failure characteristics to steel beam and exert a deciding influence on the fatigue resistance of SRC beam in previous experiments. Therefore, FEA of fatigue crack growth (FCG) was conducted using a fully-automated remeshing technique for steel beam first. Comparisons were made and a good agreement was found between predicted and experimental fatigue lives. The average value of ratio between predicted and experimental fatigue lives for the five steel beams is 1.149, which verifies the accuracy of FEA model. Then, based on the FEA model of steel beam, rebars and external concrete were included to simulate fatigue failure process of SRC beams. The results suggest that the average value of ratio between predicted and experimental fatigue lives for SRCH-steels inside the thirty-nine SRC beams is 1.191, and the average value for tensile rebars is 1.212, which indicates that the numerical model is accurate and reliable. At last, further analysis about influences of critical parameters on fatigue performance of SRC beams was conducted, such as nominal stress range, steel ratio of SRCH-steel, steel ratio of tensile rebars, fatigue strength of tensile rebars, shear span-to-depth ratio, concrete strength grade and stirrup ratio.

Stability of chemical reaction fronts in solids: Analytical and numerical approaches

Localized chemical reactions in deformable solids are considered. A chemical transformation is accompanied by the transformation strain and emerging mechanical stresses, which affect the kinetics of the chemical reaction front to the reaction arrest. A chemo-mechanical coupling via the chemical affinity tensor is used, in which the stresses affect the reaction rate. The emphasis is made on the stability of the propagating reaction front in the vicinity of the blocked state. There are two major novel contributions. First, it is shown that for a planar reaction front, the diffusion of the gaseous-type reactant does not influence the stability of the reaction front – the stability is governed only by the mechanical properties of solid reactants and stresses induced by the transformation strain and the external loading, which corresponds to the mathematically analogous phase transition problem. Second, the comparison of two computational approaches to model the reaction front propagation is performed – the standard finite-element method with a remeshing technique to resolve the moving interface is compared to the cut-finite-element-based approach, which allows the interface to cut through the elements and to move independently of the finite-element mesh. For stability problems considered in the present paper, the previously-developed implementation of the cut-element approach has been extended with the additional post-processing procedure that obtains more accurate stresses and strains, relying on the fact that the structured grid is used in the implementation. The approaches are compared using a range of chemo-mechanical problems with stable and unstable reaction fronts.

Thermomechanical behavior and microstructural characteristics of 7055 aluminum alloy during friction stirring welding

This study employed a viscoplastic finite element model and re-meshing technique to investigate the thermomechanical response of 7055 aluminum alloy during friction stir welding (FSW). The stirring pin rotates at 800–1200 rpm and moves at 80–120 mm/min (i.e., welding speed) during the FSW process. The temperature field and viscoplastic flow were mathematically modeled based on a computational solid mechanics method and predicted by a three-dimensional coupled thermomechanical numerical simulation. To validate the simulation results, real-time temperature measurements at the welded joint were acquired via thermocouples embedded in the plate prior to the welding process. Additionally, optical microscopy and electron backscatter diffraction techniques were used to examine the metallographic structure and grain orientation of the welds, respectively. The results revealed a temperature difference of 5–10 ℃ between the advancing and retreating sides of the plate. The material on the advancing side was extruded upward in a circular motion and eventually reached the surface. Meanwhile, the material on the retreating side moved half a revolution around the pin and remained at the original depth of the plate. Complete dynamic recrystallization occurred in the weld nugget, resulting in the formation of fine equiaxed grains with random orientation. In the thermomechanically affected zone, the proximity to the weld nugget was associated with an increased proportion of high-angle grain boundaries and recrystallized structures. Simultaneously, the intensity of the deformation texture decreased, while the recrystallized texture showed an initial strengthening followed by a subsequent weakening. This comprehensive investigation contributes to a deeper understanding of the thermomechanical behavior and metallographic characterization of 7055 aluminum alloy during the FSW process.

Development of a Numerical Approach for the CFD Simulation of a Gear Pump under Actual Operating Conditions

The geometric complexity and high-pressure gradients that characterize the design of the flow field of gear pumps make it very difficult to obtain an accurate CFD simulation of the component. Usually, assumptions are made both in terms of geometrical features and physics being included in the analysis. The contact between the teeth, which is a key factor for the correct functioning of these pumps, represents a critical challenge in 3D CFD simulations, mainly due to the intrinsic limits of the dynamic meshing techniques that can hardly effectively manage a zero or close to zero gap point forming during gear rotation. The geometric complexity and high-pressure gradients that characterize the gear pump flow field make a CFD analysis quite difficult, and the contact between the gear teeth is usually avoided, thus being an extremely important feature. In this paper, a gear pump composed of inlet and outlet pipes was considered, and the contact between the gear’s teeth was modeled in two different ways, one where it is effectively implemented and one where it is avoided using distancing and a proper casing modification. Herein, a new methodology is proposed for the application of the dynamic mesh method in the Simcenter STAR-CCM+ environment using an adaptive remeshing technique. The proposed methodology is compared with the alternative overset meshing method available in the software. The new meshing method is implemented using a user-routing that reproduces the real geometry of the gears while rotating during the pump operation, with teeth contact included. The routine is optimized in order to limit the additional computation and time needed for the remeshing process. The results that can be obtained using the two meshing approaches for the gear pump are compared in terms of computational effort and the accuracy of the results. The two methods showed opposite results in almost all the reported results, with the overset being more precise in the radial pressure evaluation and the dynamic being more reliable in the cavitation/aeration extension cloud.

Nanite as a Disruptive Technology for the Interactive Visualisation of Cultural Heritage 3D Models: A Case Study

The use of digital models of cultural heritage objects obtained from 3D scanning or photogrammetry requires the development of strategies in order to optimise computational resources and enhance the user experience when they are used in interactive applications or virtual museums. Through a case study, this work compares an original photogrammetric model with its optimised version using traditional remeshing techniques and an improved version using Nanite technology, developed by Epic Games. A self-contained executable is created in Unreal® 5.1 game engine to test the performance of the three models measured in frames per second (FPS). As a result, it was demonstrated that, although there is no substantial difference in the FPS rate, the Nanite technology avoids the need to perform the mesh and texture editing processes that lead to the construction of the optimised model. This saves considerable time and specialised effort, as the photogrammetric model can be converted to a Nanite object automatically. This would be a great advantage in the case of virtualisations of large collections of heritage objects, which is a common case in virtual museums.

Accelerating surface remeshing through GPU-based computation of the restricted tangent face

High-quality mesh surfaces are crucial for geometric processing in a variety of applications. To generate these meshes, polyhedral remeshing techniques truncate Voronoi cells of the original surface and yield precise intersections, but the calculation is complicated. Some methods apply auxiliary points to construct Voronoi diagrams to simplify these techniques, thereby extracting co-planar facets to approximate the original surface. However, extracting these approximate facets from the constructed Voronoi diagram makes it inefficient and non-parallelizable. To this end, we propose an efficient GPU method for manifold surface remeshing, where the restricted tangent face (RTF) is utilized to approximate the original surface. By intersecting the pre-clipped Voronoi cell with the tangent plane, this method directly calculates the RTF of each point without any auxiliary points or traversing Voronoi cells. Moreover, to restrict the movement of points, we introduce a projection method based on the KNN strategy, where each point is projected onto the triangular facet in the original surface. Owing to the independence and non-interference of the RTF computation and projection of each point, our method is implemented in parallel on the GPU. Experimental results on various mesh surfaces demonstrate the superior performance of our method in the viability, effectiveness, and efficiency.

Comprehensive modeling strategy for thermomechanical tribological behavior analysis of railway vehicle disc brake system

A comprehensive modeling strategy for studying the thermomechanical tribological behaviors is proposed in this work. The wear degradation considering the influence of temperature (T) is predicted by Archard wear model with the help of the UMESHMOTION subroutine and arbitrary Lagrangian–Eulerian (ALE) remeshing technique. Adopting the proposed method, the thermomechanical tribological behaviors of railway vehicle disc brake system composed of forged steel brake disc and Cu-based powder metallurgy (PM) friction block are studied systematically. The effectiveness of the proposed methodology is validated by experimental test on a self-designed scaled brake test bench from the perspectives of interface temperature, wear degradation, friction noise and vibration, and contact status evolution. This work can provide an effective way for the investigation of thermomechanical tribological behaviors in the engineering field.

Multi-Physical Field Simulation of Cracking during Crystal Growth by Bridgman Method.

Crystal materials are prone to cracking during growth, which is a key problem leading to slow growth and difficulty in forming large-size crystals. In this study, based on the commercial finite element software COMSOL Multiphysics, the transient finite element simulation of the multi-physical field, including fluid heat transfer-phase transition-solid equilibrium-damage coupling behaviors, is performed. The phase-transition material properties and maximum tensile strain damage variables are customized. Using the re-meshing technique, the crystal growth and damage are captured. The results show the following: The convection channel at the bottom of the Bridgman furnace greatly influences the temperature field inside the furnace, and the temperature gradient field significantly influences the solidification and cracking behaviors during crystal growth. The crystal solidifies faster when it enters the higher-temperature gradient region and is prone to cracking. The temperature field inside the furnace needs to be properly adjusted so that the crystal temperature decreases relatively uniformly and slowly during the growth process to avoid crack formation. In addition, the crystal growth orientation also significantly affects the nucleation and growth direction of cracks. Crystals grown along the a-axis tend to form long cracks starting from the bottom and growing vertically, while crystals grown along the c-axis induce the laminar cracks from the bottom in a horizontal direction. The numerical simulation framework of the damage during crystal growth, which can accurately simulate the process of crystal growth and crack evolution and can be used to optimize the temperature field and crystal growth orientation in the Bridgman furnace cavity, is a reliable method to solve the crystal cracking problem.

Numerical simulation for the control rod assembly drop time evaluation in a LFR

During scram, the Control Rod Assembly (CRA) is quickly dropped into the core and as well, if any of the operating limits are exceeded, the CRA is dropped into the core within a stipulated time to shut down the reactor power as soon as possible. In this study, the Computational Fluid Dynamics (CFD) approach was used to investigate the CRA drop dynamics of a lead-based research reactor. To simulate the flow field around the CRA in the guide tube, a 3-dimensional model of the CRA in the LBE-filled guide tube was developed and discretized; and the averaged Navier-Stokes equations coupled with the dynamic mesh method were adopted. Considering the large mesh deformation in the LBE coolant domain while the CRA drops, the recently developed FSI method in the CFX code, namely the rigid body approach, was adopted, which falls under the monolithic method. In this method, the translational CRA wall, which is partially immersed in the LBE, was set as a rigid body. It has the advantage of updating and improving the mesh quality through the mesh and re-meshing technique during the process of computation. Compared with the results of the work done in the available literature, the CFD model proved to be applicable and reliable. From the results, the inherent high density among the LBE flow characteristics had the most influence on the drop time. The mass of the CRA impacts its driving force so that the drop time reduces when the CRA mass is increased. In conclusion, the method used in this study can be applied to compute and predict significant parameters which can serve as a reference for a suitable design of the CRA and its drive mechanism in the case of modification for safety.

Bimaterial interface crack analysis using an extended consecutive-interpolation quadrilateral element

A very important problem in the research of layer structures is the modeling of cracks on the material interface. Due to the complex physical and mechanical properties of this structure, the simulation of discontinuities such as cracks and material interface by traditional finite element methods requires a very fine mesh density. Furthermore, mesh smoothing requires a really large amount of computational resources. Therefore, the extended algorithm which does not require the remeshing technique was born to solve the crack problems. In this paper, the extended consecutive-interpolation finite element method (XCFEM) is employed to modeling the mix-mode interface cracks between two dissimilar isotropic materials. The XCFEM using 4-node consecutive-interpolation quadrilateral element (XCQ4) provides continuity of nodal gradient due to the concept of “consecutive-interpolation” so that the stress and strain fields derived from XCQ4 is smoother than that obtained by the classical FEM element. The accuracy and effectiveness of the method are demonstrated via various numerical examples and compared with other researches.

Fracture propagation based on meshless method and energy release rate criterion extended to the Double Cantilever Beam adhesive joint test

In this work, a numerical methodology based on a meshless technique is proposed to predict the fracture propagation in Double Cantilever Beam (DCB) adhesive joints. The Radial Point Interpolation Method (RPIM) is used to approximate the field variable at each crack increment step. The meshless method permits a flexible discretization of the problem domain in a set of unstructured field nodes and eases the implementation of the geometric crack propagation algorithm. Regarding the fracture propagation algorithm, a recent adaptative remeshing technique is used combined with the RPIM. The crack tip is explicitly propagated by locally remeshing the field nodes and triangular integration cells in the crack tip vicinity. To predict the crack initiation, a fracture mechanics criterion based on the energy release rate in DCB is implemented. The proposed numerical methodology is validated with experimental data.