Remeshing Technique Research Articles

QEx

The most popular and actively researched class of quad remeshing techniques is the family of parametrization based quad meshing methods . They all strive to generate an integer-grid map , i.e. a parametrization of the input surface into R 2 such that the canonical grid of integer iso-lines forms a quad mesh when mapped back onto the surface in R 3 . An essential, albeit broadly neglected aspect of these methods is the quad extraction step, i.e. the materialization of an actual quad mesh from the mere "quad texture". Quad (mesh) extraction is often believed to be a trivial matter but quite the opposite is true: numerous special cases, ambiguities induced by numerical inaccuracies and limited solver precision, as well as imperfections in the maps produced by most methods (unless costly countermeasures are taken) pose significant challenges to the quad extractor. We present a method to sanitize a provided parametrization such that it becomes numerically consistent even in a limited precision floating point representation. Based on this we are able to provide a comprehensive and sound description of how to perform quad extraction robustly and without the need for any complex tolerance thresholds or disambiguation rules. On top of that we develop a novel strategy to cope with common local fold-overs in the parametrization. This allows our method, dubbed QEx , to generate all-quadrilateral meshes where otherwise holes, non-quad polygons or no output at all would have been produced. We thus enable the practical use of an entire class of maps that was previously considered defective. Since state of the art quad meshing methods spend a significant share of their run time solely to prevent local fold-overs, using our method it is now possible to obtain quad meshes significantly quicker than before. We also provide libQEx, an open source C++ reference implementation of our method and thus significantly lower the bar to enter the field of quad meshing.

Crack growth simulation for arbitrarily shaped cracks based on the virtual crack closure technique

In this paper, crack growth simulation for arbitrarily shaped cracks was investigated based on the virtual crack closure technique. During simulations, the crack front was represented by an approximated zigzag line which had the same general shape as the given crack. For this approximated zigzag crack front, a modified approach was developed to determine the required nodal forces, virtually closed area and displacement opening. After the strain energy release rate G was calculated, crack growth was governed by the fracture criterion G/GC = 1 at all the crack tip nodes. The important features of the proposed approach are that (i) a simple stationary finite element mesh can be used for arbitrarily shaped cracks and (ii) adaptive re-meshing technique is avoided in studying crack growth. Three cases having different initial crack shapes are presented to assess the validity of this approach and to evaluate the ease of use in tracking crack growth. Reasonable agreement between the present study and other approaches are obtained. The shape changes during crack propagation can also be tracked with ease.

Simulation of Thermal and Mechanical Response of (Zr,W)B<sub>2 </sub>Ceramic after Oxidation

This study relates to a micromechanics based finite element model of the effect of oxidation on heat transfer and mechanical behavior of a (Zr,W)B2ceramic at high temperature. An adaptive remeshing technique is employed in both heat transfer and thermal stress analysis models. A global-local modeling technique is used to combine finite elements with infinite elements for thermal stress analysis. Temperature and thermal stress distributions in the ceramic and the oxides are presented.

XFEM investigation of a crack path in residual stresses resulting from quenching

The aim of this work is the numerical study of a crack path in a residual stress field resulting from a manufacturing process such as quenching. An XFEM technique is proposed to that end and the example illustrating the quenching of a large thick plate is considered so as to demonstrate the capability of the method proposed. Indeed, during the quenching of steels, metallurgical transformations can occur, leading to high residual stresses at room temperature. From the practical point of view, the thick plate must be sawn after quenching. But it is experimentally observed that, under certain quenching conditions, the crack initiated by the sawing, suddenly propagates through the thickness of the plate and then rotates through an angle of about 90°. The numerical simulation of quenching is detailed and the results obtained under two operating conditions are given. Then the XFEM technique applied to the crack propagation in a residual stress field is presented and the cracking path obtained on the quenched plate is compared to that obtained using the FEM coupled with a remeshing technique. It is shown that the computed crack path justifies experimental observations.

5th International Conference OTEH 2012 - defense technology (Proceedings review)

This article gives an overview of all papers and events at the Fifth International ScientificConference on Defense Technologies OTEH 2012 held in Belgrade, in the Military Technical Institute (VTI), from 18 th to 19 th September 2012. The paper review presents the Conference Sections by subjects and guest-lectureres as well as the institutions of all authors who actively participated at the Conference. About the Conference The Fifth International Scientific Conference on Defense Technologies OTEH 2012 was held in Belgrade in the Military Technical Institute in Žarkovo, from 18 th to 19 th September 2012.. The Conference program was organized in two plenary sessions and a working part which took place in four halls. In the plenary session, two key lectures were held by eminent experts from abroad. The first lecture entitled „An adaptive remeshing technique for 3D crack growth simulations”, was given by Dr Vincent Chiaruttini (ONERA Institute, Paris, France). The second one, „New Technologies for Advanced Defence Systems”, was held by Dr Filippo Neri (Virtualabs Company, Rome, Italy). Fifteen sessions were organised at the Conference. The authors presented their works in open discussions answering questions from the audience. The average number of attendees at each session was about 40. The papers were sorted by topic areas: Aerodynamics and flight dynamics: 12 papers Aircraft: 23 papers Weapon systems, ammunition, energy materials, combat vehicles: 29 papers Integrated sensor systems and robotic systems: 16 papers Telecommunication and information systems: 18 papers Materials and technologies: 34 papers Quality, standardization, metrology, maintenance and exploitation: 11 papers Out of 163 submitted papers for this Conference, 145 papers were accepted and distributed in an electronic form on CDs to the present authors, co-authors, guests and invitees to the Conference. The number of participants with authors and co-authors was impressive - 243. The authors (either of their own or plenary papers) from 15 countries were present at the Conference. It should be noted that at this conference, unlike the previous one also held in the VTI, Belgrade, in 2011, there was a significantly higher number of younger researchers. There was a general impression that many reseach results communicated at the Conference deserved to be published in reference journals on the SCR list. A number of papers from this Conference will be considered for publication in the Scientific Technical Review. It should be noted that the MO-VTI organizing committee largely contributed to the Conference to be evaluated as a well-organized event. From a total number of papers (145), there were 32 (or 22.06% ) from abroad. Once again, the Conference justified the purpose of this type of conferences. The other works of authors and co-authors were from the following institutions in Serbia: The Ministry of Education and Science and Technological Development, Military Technical Institute (VTI), Military Academy (MA), the Army of Serbia (SAF), the Ministry of Defence (MOD), Department of Defense Technology (MDT), University of Defence (UD) Military Institution Dedinje, Military Archives, Technical Test Center (TTC), Technical Overhaul Institute Cacak (TRZ), the Central Logistics Base, Institute of Strategic Studies, Criminal Police College, GOSA Institute, Institute of Engineering, Faculties of Mathematics, Mechanical Engineering, Electrical Engineering, Metropolitan University, Faculty of Technology and metallurgy, College of Project Management, UTVA Aircraft Industry Pancevo, Intel Communications, IHATEM, Vlata com, Iritel, Peripolis-Electronics, Computer Engineering, Thermo Electric, HK Krusik Valjevo. Conclusion The Conference had a truly international character. As in previous years, the participation of the Army of Serbia in this important event is fully justified, and the goal is reached. In addition to the communication of the research results, there was a fruitful discussion in which the problems were reviewed, opinions and experiences exchanged and possibilities to solve presented problems discussed. It was again confirmed that communicating work at such events with the participation of scientists and relevant institutions from the country and abroad certainly has a positive impact on the scientific and professional level of work in the Army. It also has a positive impact on professional and scientific training of researchers in experimental centers and institutes as well as teachers, thus raising the quality of teaching in undergraduate and postgraduate studies at the Military Academy. It can be concluded that the cooperation of the Army with the members of other institutions in solving and researching problems of organizations and scientific-technical approach confirms the openness of the Army for the involvement of other individuals and institutions in solving problems in the field of defense as well as the willingness and ability of the members of the defense system to engage in solving problems in civil institutions.

Failure Analysis of a Sheet Metal Blanking Process Based on Damage Coupling Model

In this paper, a blanking process of sheet metal is studied by the methods of numerical simulation and experimental observation. The effects of varying technological parameters related to the quality of products are investigated. An elastoplastic constitutive equation accounting for isotropic ductile damage is implemented into the finite element code ABAQUS with a user-defined material subroutine UMAT. The simulations of the damage evolution and ductile fracture in a sheet metal blanking process have been carried out by the FEM. In order to guarantee computation accuracy and avoid numerical divergence during large plastic deformation, a specified remeshing technique is successively applied when severe element distortion occurs. In the simulation, the evolutions of damage at different stage of the blanking process have been evaluated and the distributions of damage obtained from simulation are in proper agreement with the experimental results.

Dramatic Speed-Up in FEM Simulations of Various Incremental Forming Processes Thanks to Multi-Mesh Implementation in Forge®

Improvements in parallel computing and adaptive remeshing have permitted to simulate a wide range of metal forming processes within few hours or days on modern multi-core workstations. However, they do not tackle the issues encountered in incremental forming processes, making them very challenging. Multi-mesh methods opens very interesting doors in this domain, making possible to take advantage of adaptive remeshing techniques (optimizing the ratio precision/cost) without its usual drawbacks (loss of information and diffusion issues).We present in this article a fully parallel Dual-Mesh implementation in the commercial FEA software FORGE®, compatible with a wide range of other FEM facilities. Speed-up larger than 4 are common for incremental forming simulations, and speed-up larger than 10 can be reached in favorable cases. Parallel efficiency is the same than for our standard computations (>80% for more than 2000 nodes per core).

Modelling cohesive crack growth in concrete beams using scaled boundary finite element method based on super-element remeshing technique

A super-element remeshing technique is developed to model cohesive crack growth based on the linear asymptotic superposition assumption. The remeshing operation only occurs along the crack path. Mesh size is refined merely at the crack-tip super-element. The stress intensity factors are solved semi-analytically by the scaled boundary finite element method, sufficient accuracy can be ensured. The cohesive tractions are treated as side-face forces, and the induced displacement field can be sought as a particular solution to the governing differential equations. Numerical examples validate the efficiency and accuracy of the proposed approach.

Dynamic crack propagation simulation with scaled boundary polygon elements and automatic remeshing technique

An efficient methodology for automatic dynamic crack propagation simulations using polygon elements is developed in this study. The polygon mesh is automatically generated from a Delaunay triangulated mesh. The formulation of an arbitrary n-sided polygon element is based on the scaled boundary finite element method (SBFEM). All kind of singular stress fields can be described by the matrix power function solution of a cracked polygon. Generalised dynamic stress intensity factors are evaluated using standard finite element stress recovery procedures. This technique does not require local mesh refinement around the crack tip, special purpose elements or nodal enrichment functions. An automatic local remeshing algorithm that can be applied to any polygon mesh is developed in this study to accommodate crack propagation. Each remeshing operation involves only a small patch of polygons around the crack tip, resulting in only minimal change to the global mesh structure. The increase of the number of degrees-of-freedom caused by crack propagation is moderate. The method is validated using four dynamic crack propagation benchmarks. The predicted dynamic fracture parameters show good agreement with experiment observations and numerical simulations reported in the literature.

Study on the Effect of Tool Geometrical Parameters on Cutting Forces Based on Finite Element Method

Based on finite element software DEFORM-3D, a three-dimensional oblique cutting model for aerospace aluminum alloy was built. The material’s flow stress behavior was described with Johnson-Cook constitutive equation. The separation of the chips with the workpiece was realized by the combination of adaptive remeshing technique and separation criterion. The material’s failure was defined by adopting Cockcroft & Latham fracture criterion. The tool-chip friction model was the combination of a Coulomb friction model and shear (sticking) friction model. To validate the finite element model, cutting tests were conducted. The effects of tool geometrical parameters such as flank wear, cutting edge inclination and corner radius on cutting forces were analyzed by three-dimensional oblique finite element model.

Finite element simulation of dynamic crack propagation process using an arbitrary Lagrangian Eulerian formulation

ABSTRACTIn this paper, the arbitrary Lagrangian Eulerian formulation is employed for finite element modelling of dynamic crack propagation problem. The application phase simulation of computational dynamic fracture is applied to model by which the crack propagation history and variation of crack velocity are predicted using the material dynamic fracture toughness. The dynamic solution of problem is accomplished using the implicit time integration method. The convective terms due to mesh‐material motion are taken into account via the convection equation. A robust and efficient mesh motion technique, that its equations need not to be solved at every time step, is employed in Eulerian phase. The mesh connectivity is preserved during the analysis. So, the successive remeshing of model is eliminated. When the dynamic fracture criterion is satisfied for crack growth, the presented algorithm allows the crack to advance by splitting the material particle at the crack tip. The dynamic energy release rate is calculated at each time step to determine dynamic stress intensity factor. The predicted results are compared with those obtained through the experimental study and remeshing technique cited in the literature. The proposed computational algorithm leads to an accurate and efficient simulation of dynamic crack propagation process.

Development of Thermal Elastic-plastic FEM for Line Heating with Remeshing Technique

In order to predict deformation during line heating accurately, thermal elastic-plastic FEM with remeshing technique is developed. The model is represented by a fine mesh near the heat source and much coarser mesh around the fine area. Mesh of the model is updated with the movement of heat source, and solution variables are mapping from the old mesh to the new mesh. The analysis procedure after each remeshing step is the same as conventional method. Results of a typical line heating example show that the remeshing technique ensures the accuracy and accelerates computing speed greatly. Ship hull is formed by many plates with complex geometrical shape which are usually made by skillful workers with line heating. The decrease of these people and lack of new workers specializing in this area will be a problem for shipbuilding. Research on computer aided process dates back to the last decade of 20th century and automation system for line heating has now been employed in some shipbuilding companies. It is recognized to be a much more efficient way compared with that operated by human hand. So it is necessary to predict the distortion quantitatively before performing line heating. Inherent strain method proposed by Ueda and Murakawa is employed currently for analysis of plate distortion under line heating 1) . Stretching strain component and bending strain component are firstly computed based on the initial surface and target surface. And then heating paths can be determined by the distribution of the strain components. Since inherent strain method is an elastic FEM and there are usually some iterative procedures required to obtain the final target shape. Thermal elastic-plastic finite element method (TEP-FEM) is a

Advanced Algorithms for Etching Simulation of 3D MEMS-Tunable Lasers

 Abstract—The integrated circuits (ICs) industry uses a number of technology computer aided design (TCAD) software tools to simulate the manufacturing and the operation of many ICs at different levels. At very low level, the simulation tools are used to simulate the device fabrication and design. These simulation tools are based on solving mathematical equations that describe the physics of doping diffusion, silicon oxidation, etching, deposition, lithography, implantation, and metallization. The simulation of physical etching solves etching equations to calculate the etching rate. And this rate is used to move the geometry of the device. The simulation of non-physical (geometrical) etching is based on geometrical Boolean operations. In this paper, we are proposing new and advanced geometrical etching algorithms for the process simulation of three dimensional (3D) micro electro mechanical systems (MEMS) and MEMS-tunable vertical cavity semiconductor optical amplifiers (VCSOAs). These algorithms are based on advanced domain decomposition methods, Delaunay meshing algorithms, and surface re-meshing and smoothing techniques. These algorithms are simple, robust, and significantly reduce the overall run time of the process simulation of 3D MEMS and MEMS-tunable laser devices. The description of the proposed etching algorithms will be presented. Numerical simulation results showing the performances of these algorithms will be given and analyzed for realistic 3D MEMS and MEMS-tunable laser devices.

An Unstructured Moving Grid Scheme for Shock Impacting on Material Interface

An unstructured moving grid scheme is applied to track the real-time motion state of the material interface with large-scale deformation induced by shock in the compressible multi-material flow. The material interface is denoted as a special internal boundary which is made up of unstructured grid edges, and on both sides of that there exist grids used for the two different materials. Riemann problem is solved in order to track the motion of the grid points on the material interface, and the local re-meshing technique is also applied to cope with the large-scale deformation of the moving grids near the interface, especially for the case of strong shocks existing in the multi-material flows. Simultaneously, the material interface is also defined as a kind of grid-deforming boundary in case grid volumes are negative. To obtain the resolution of the whole multi-material flow domain, the arbitrary Lagrangian-Eulerian (ALE) is discretized using Harten-Lax-van Leer-Contact (HLLC) scheme. Several numerical calculations from shock-interface examples demonstrate that this moving grid technique is feasible and effective in tracking the real-time motion state of the material interface.

Three-Dimensional Finite Element Analysis on Heavy Cutting for High Strength Steel

The finite element modeling and experimental validation of three-dimensional heavy cutting of high strength steel (2.25Cr-1Mo-0.25V) are presented. The commercial software Deform 3D applied for the finite element modeling is studied the effect of feed rate on the principal cutting forces and the temperature fields. The friction between the tool and the chip is assumed to follow a shear model and the local adaptive remeshing technique is used for the formation of chip. The feed rate significantly affects the cutting forces, but slightly influences the maximum temperature of the chip. The simulation results are compared with experimental data and found to be in good agreement.

A level-set and anisotropic adaptive remeshing strategy for the modeling of void growth under large plastic strain

A numerical model based on the use of a level set framework coupled with an anisotropic re-meshing technique is presented in order to describe the void growth process for 2D and 3D configurations. Interfaces of inclusions and voids are described implicitly using level set functions. An anisotropic meshing – remeshing strategy is employed to track interfaces and ensure the accuracy of finite element calculations. The matrix and inclusions are elastic–plastic materials. The numerical methodology is adopted to study the effect of different parameters such as void or inclusion orientation and domain size. A good agreement is found with available experimental data and those found in the literature. The proposed method is shown to be an efficient promising technique to study ductile damage stages as void nucleation and growth. A demonstration of the method potential is illustrated by studying void growth for a 2D real complex microstructure and for a simple 3D microstructure.

Finite Element Simulation of Large H-Beam in X-H Rolling Process

In order to research the hot rolling process of large H-beam, the thermal-mechanical coupling analysis and big distortion theory are used to simulate the whole X-H rolling process of HN900x300 by ABAQUS, in which the re-meshing technique is taken into simulation to increase the accuracy. Based on the simulation results, the stress and deflection of the roller as well as the metal flowing law and temperature field of workpiece are discussed emphatically. The results clearly show that the roller is subjected to alternating shear force and compressive stresses of three directions, and the metal of flange tends to flow from outside to inside. The simulation results are compared with the measuring results, which proves the correctness of simulation.

Predictions of tool forces in friction stir welding of AZ91 magnesium alloy

Adaptive remeshing technique based finite element model of friction stir welding was used for the investigation of tool forces in the welding processes. Results indicate that the maximum tool forces occur at the initial time in the translational stage. In the tool forces in the three directions, the axial force is the maximum. The tool force in the direction perpendicular to the welding line is the minimum. The tool forces in the three directions are all increased with the increase in transverse speed and decreased with the increase in angular velocity.

An Analysis of the Flow around a Wind Propeller Using the Finite Element Method

To analyze the wind flow around a wind propeller is important in wind engineering. The wind tunnel experiment has issue of cost and time. Additionally, because the shape of a wind propeller influences energy efficiency, wind tunnel experiments must be performed many times. The finite element method is one of the effective numerical approach to simulate wind propeller. But, it is necessary to generate the finite element mesh. To generate the 3-dimensional finite element mesh is almost impossible by hand. Generating any complicated 3-dimensional mesh automatically is very important. In this study, automatic 3-dimensional mesh generation is performed. Additionally, it is fluid-structure interaction analysis. In the finite element method, it is necessary to consider the moving boundaries. The purpose of this study, to generate the complicated 3-dimensional models and to analyze moving boundary problems. In this study, a re-meshing technique for moving boundaries is introduced, and to generate finite element mesh, the Delaunay method is applied. The character of this method is generating mesh from arbitrary nodal distribution of nodal points.

Thermal fatigue life estimation and delamination mechanics studies of multilayered MEMS structures

This paper is concerned with the application of a Physics of Failure (PoF) methodology to assessing the reliability of Micro-Electro-Mechanical-System (MEMS) switches. Numerical simulations, based on the finite element method (FEM) using a sub-domain approach, were performed to examine the damage onset (e.g. yielding) due to temperature variations and to simulated the crack propagation arising after thermal fatigue. In this work remeshing techniques were employed in order to develop a damage tolerance approach based on the assumption that initial flaws exist in the multi-layered structure due, for instance, to manufacturing processes and/or are originates after thermal fatigue, as preliminary experimental tests has shown.