Automatic Mesh Generation Research Articles

Finite Element Simulation Based on Soil Mesostructures Extracted from Digital Image

This paper presents a finite element method based on digital image processing for the two-dimensional mechanical analysis of soil stabilized by cement mortar by actually taking into account the soil inhomogeneities and mesostructures. Digital image techniques are used to acquire the inhomogeneous distributions of soil particles and voids in digital format. Then, the digital image is transferred as a vectorization image including the geometric structure and sub-regions of particles and voids. Next, the vectorization image is used to as inputs for finite element mesh generations using automatic mesh generation techniques. Lastly, the finite element method is employed to carry out the computation and analysis of the soil mechanical problems under the unlimited compression test by taking into account the actual internal inhomogeneity of the soil. The numerical results show that the actual distributions of the internal stress and displacement are different from the analysis results based on the continuum mechanics theory and the soil mesostructures have significant effects on the compaction stress and displacement distribution along the loading.

Acceleration of Dynamic Bubble Mesh Generation for Large-Scale Model

An automatic mesh generation method employing a dynamic bubble system can provide a high-quality mesh for electromagnetic finite element analysis. However, it takes a very long time to compute bubbles' movement when a mesh with a large number of elements is generated. The bubbles move according to a force among them, such as the van der Waals force. However, the force received from bubbles of very far distance can be ignored. Therefore, it is unnecessary to calculate the force from all the bubbles. In this paper, we propose a subdivided dynamic bubble system in order to shorten the computation time. The proposed method considers the analysis region to be divided into some tetrahedral subdivisions, and then the bubbles move independently in the tetrahedral subdivisions. As a result, acceleration of the computation time is achieved.

Efficient inversion of three-dimensional finite element models of volcano deformation

Numerical techniques, as such as finite element method, allow for the inclusion of features, such as topography and/or mechanical heterogeneities, for the interpretation of volcanic deformation. However, models based on these numerical techniques usually are not suitable to be included in non-linear estimations of source parameters based on explorative optimization schemes because they require a calculation of the numerical approach for every evaluation of the misfit function. We present a procedure for finite element (FE) models that can be combined with explorative inversion schemes. The methodology is based on including a body force term representing an infinitesimal source in the model formulation that is responsible for pressure (volume) changes in the medium. This provides significant savings in both the time required for mesh generation and actual computational time of the numerical approach. Furthermore, we develop an inversion algorithm to estimate those parameters that characterize the changes in location and pressure (volume) of deformation sources. Both provide FE inversions in a single step, avoiding remeshing and assembly of the linear system of algebraic equations that define the numerical approach and/or the automatic mesh generation. After providing the theoretical basis for the model, the numerical approach and the algorithm for the inversions, we test the methodology using a synthetic example in a stratovolcano. Our results suggest that the FE inversion methodology can be considered suitable for efficiently save time in quantitative interpretations of volcano deformation.

Quadrilateral Mesh Generation with Deferred Constraint Insertion

In this paper, we present a new method for quadrilateral mesh generation in complex 2D domains, based on deferred constraint insertion. Our method is especially designed to handle complex geological cross-sections and multi-fractured media. We first introduce a new algorithm for triangular mesh generation: starting with a initial mesh, in general simple and regular, we adaptively modify it in order to accommodate each constraint, despite its complexity. We then propose a set of heuristics to convert the achieved triangular mesh into a quadrilateral one, pursuing the alignment of elements along constraints. As a result, we achieve a very stable, efficient, good-quality, and automated mesh generator. We demonstrate the robustness of our proposal by showing resulting triangular and quadrilateral meshes for a set of geological domains with complex line constraints.

Automatic Curvilinear Quality Mesh Generation Driven by Smooth Boundary and Guaranteed Fidelity

The development of robust high-order finite element methods requires the construction of valid high-order meshes for complex geometries without user intervention. This paper presents a novel approach for automatically generating a high-order mesh with two main features: first, the boundary of the mesh is globally smooth; second, the mesh boundary satisfies a required fidelity tolerance. Invalid elements are eliminated. Example meshes demonstrate the features of the algorithm.

接触を考慮した繰り返しねじり荷重下の弾塑性き裂進展解析

Crack growth under the elastic-plastic fracture is an important issue of the structural integrity, because seismic wave causes low cycle fatigue in the engineering structure. We developed automated FEM analysis framework for elastic-plastic crack growth simulation. The framework consists of 4 major modules. In this work, we employ crack opening angle (COA) and displacement (COD) which are the angle between crack surfaces and the displacement vector to be defined near the crack tip. The present work is applied to the cyclic loading analysis of a pipe with a single notch. The work shows automated mesh generation capability and fracture mechanics parameters to evaluate crack growth criterion.

Least squares finite element method with high continuity NURBS basis for incompressible Navier–Stokes equations

Modern least squares finite element method (LSFEM) has advantage over mixed finite element method for non-self-adjoint problem like Navier–Stokes equations, but has problem to be norm equivalent and mass conservative when using C0 type basis. In this paper, LSFEM with non-uniform B-splines (NURBS) is proposed for Navier–Stokes equations. High order continuity NURBS is used to construct the finite-dimensional spaces for both velocity and pressure. Variational form is derived from the governing equations with primitive variables and the DOFs due to additional variables are not necessary. There is a novel k-refinement which has spectral convergence of least squares functional. The method also has same advantages as isogeometric analysis like automatic mesh generation and exact geometry representation. Several benchmark problems are solved using the proposed method. The results agree well with the benchmark solutions available in literature. The results also show good performance in mass conservation.

Complex fluid simulations with the parallel tree-based Lattice Boltzmann solver Musubi

We present the open source Lattice Boltzmann solver Musubi. It is part of the parallel simulation framework APES, which utilizes octrees to represent sparse meshes and provides tools from automatic mesh generation to post-processing. The octree mesh representation enables the handling of arbitrarily complex simulation domains, even on massively parallel systems. Local grid refinement is implemented by several interpolation schemes in Musubi. Various kernels provide different physical models based on stream-collide algorithms. These models can be computed concurrently and can be coupled with each other. This paper explains our approach to provide a flexible yet scalable simulation environment and elaborates its design principles and implementation details. The efficiency of our approach is demonstrated with a performance evaluation on two supercomputers and a comparison to the widely used Lattice Boltzmann solver Palabos.

Towards the Integration of Topology Optimization into the CAD Process

This paper presents a contribution to the automation and integration of topology optimization methods (TOM) with CAD, in the context of the design of statically loaded mechanical structures and parts. Starting from an initial CAD model with relevant engineering data, the goal is automatically generating an optimized CAD model with respect to engineering objectives and constrains. Though many optimization methods are now available, their complete and efficient integration into the design process faces several problems. After introducing the basic steps involved in the whole process and identifying the challenges inherent to this integration, this paper presents our contribution in addressing these challenges. The paper is focused on the specification of design and non-design sub-domains, on automatic mesh generation problems induced and on the adaptation of TO concepts in the context of 3D unstructured meshes. TO itself is adapted from a SIMP scheme, which is an arbitrary choice as any other optimization m...

Multi-Constrained Quadrilateral Mesh Generation for Ship Assembly

The assembly of ship blocks is achieved through welding. To get a high level of closure accuracy, finite element analysis (FEA) is always needed to predict the welding deformation. However, the fast automatic mesh generation technique during the finite element method (FEM) for the ship assembly is not mature enough yet. Due to the complex ship architecture, during FEA, the model must be built up manually in most cases. This process is complicated and the errors are easy to occur. Consequently, the efficiency of FEA during the ship assembly is highly affected. Automatic mesh generation is a key factor restricting the development of FEM, since the quality and speed of the mesh generation directly influence the accuracy of calculation and the efficiency of analysis. In the field of marine engineering and aerospace engineering, the mesh elements are required to be quadrilateral. However, the technique of the quadrilateral mesh generation is still more difficult and less mature than that of the triangular mesh generation. This work proposed a hybrid mesh generation algorithm, borrowing the advantages from both the quad-morphing algorithm and the paving algorithm as well as considering the factor of multi-constraints. An example case is also given to illustrate the result of this proposed algorithm.

Optimizing polycube domain construction for hexahedral remeshing

Polycube mapping can provide regular and global parametric representations for general solid models. Automatically constructing effective polycube domains, however, is challenging. We present an algorithm for polycube construction and volumetric parameterization. The algorithm has three steps: pre-deformation, polycube construction and optimization, and mapping computation. Compared with existing polycube mapping methods, our algorithm can robustly generate desirable polycube domain shape and low-distortion volumetric parameterization. It can be used for automatic high-quality hexahedral mesh generation.

Automatic mesh generation and transformation for topology optimization methods

This paper presents automatic tools aimed at the generation and adaptation of unstructured tetrahedral meshes in the context of composite or heterogeneous geometry. These tools are primarily intended for applications in the domain of topology optimization methods but the approach introduced presents great potential in a wider context. Indeed, various fields of application can be foreseen for which meshing heterogeneous geometry is required, such as finite element simulations (in the case of heterogeneous materials and assemblies, for example), animation and visualization (medical imaging, for example). Using B-Rep concepts as well as specific adaptations of advancing front mesh generation algorithms, the mesh generation approach presented guarantees, in a simple and natural way, mesh continuity and conformity across interior boundaries when trying to mesh a composite domain. When applied in the context of topology optimization methods, this approach guarantees that design and non-design sub-domains are meshed so that finite elements are tagged as design and non-design elements and so that continuity and conformity are guaranteed at the interface between design and non-design sub-domains. The paper also presents how mesh transformation and mesh smoothing tools can be successfully used when trying to derive a functional shape from raw topology optimization results.

Generalizing the advancing front method to composite surfaces in the context of meshing constraints topology

Being able to automatically mesh composite geometry is an important issue in the context of CAD–FEA integration. In some specific contexts of this integration, such as using virtual topology or meshing constraints topology (MCT), it is even a key requirement. In this paper, we present a new approach to automatic mesh generation over composite geometry. The proposed mesh generation approach is based on a generalization of the advancing front method (AFM) over curved surfaces. The adaptation of the AFM to composite faces (composed of multiple boundary representation (B-Rep) faces) involves the computation of complex paths along these B-Rep faces, on which progression of the advancing front is based. Each mesh segment or mesh triangle generated through this progression on composite geometry is likely to lie on multiple B-Rep faces and consequently, it is likely to be associated with a composite definition across multiple parametric spaces. Collision tests between new front segments and existing mesh elements also require specific and significant adaptations of the AFM, since a given front segment is also likely to lie on multiple B-Rep faces. This new mesh generation approach is presented in the context of MCT, which requires being able to handle composite geometry along with non-manifold boundary configurations, such as edges and vertices lying in the interior domain of B-Rep faces.

해상 풍력 타워에 관한 자동요소 생성법

The more accurate numerical analysis is needed, The more important to arrange nodes and elements properly on the structures wanted to be analyzed. In this study, automatic mesh generation method is developed for triangular mesh modeling in wind tower and substructure formed in circular sections especially, which have structural and economical benefits in shallow water area. It can consider variety conditions by inputting the detail data such as height and types. Also, this study includes the comparison and verification with the mesh generation by Delaunay triangular technique on 3 dimensional space and the examples of mesh generation for proposed tower and substructure. The result of this study will be widely applied to analyze the existing and proposed models for wind turbines.

An Improved Paving Method of Automatic Quadrilateral Mesh Generation

This article describes an improved paving method of automatic quadrilateral mesh generation. Paving, which was first proposed by Blacker and Stephenson [1], is a kind of direct method for generating a quadrilateral mesh and has been widely used since it was presented. This article aims to improve some weaknesses of the traditional paving method by generating high-quality quadrilateral grids without employment of a background mesh. Through efficient intersection resolution and other optimization measures, the improved paving method can generate well-aligned rows of quadrilateral elements almost parallel to the boundary of the domain, automatically and quickly.

Adaptive Arithmetic of Rock and Concrete’s Crack Propagation

A numerical implement to simulate the crack propagating process in arch dam and rock base has been put forward. A new remeshing strategy of FEM meshing grid was presented for improving the calculation accuracy and efficiency. In the period of dividing the dam structure and the foundation rock into an appropriate number of discrete subregion (finite elements), the adaptive element was used to divide the original 3-D element into 8 son-elements analogical to its father-elements entirely. Of course the 2-D element was divided into 4 son-elements analogical to its father-elements entirely using the same method. The element shape function was used to solve suspend nodal point. The arithmetic and shape function’s formulation also were put forward. To satisfy the engineering accurate result, the adaptive element was used to divide the son-element or the grandson-element again. In the calculating processor, the arithmetic of adaptive load step was presented. Only one element failures in a load step. So the cracking processor can be found with automatic mesh generation. An arch dam has been as example to validate the method is right and stability. The arithmetic has important theory and utility value.

The Parallelized Automatic Mesh Generation Using Dynamic Bubble System With GPGPU

An automatic mesh generation method employing a dynamic bubble system can provide a high-quality mesh for electromagnetic finite-element analysis. However, there is a problem in that it takes a very long time to compute the bubbles' movement when a mesh with a large number of elements is produced. It is possible to independently and simultaneously compute the bubbles' movement; therefore, the computation of the bubbles' movement is suitable for parallel computing. In order to shorten the computation time, the computation of the bubbles' movement is parallelized with the graphics-processing unit (GPU). We propose a dynamic bubble system parallelized with GPU. As a result, a reduction in computation time was achieved.

Three-dimensional modeling and highly refined mesh generation of the aorta artery and its tunics

This paper describes strategies and techniques to perform modeling and automatic mesh generation of the aorta artery and its tunics (adventitia, media and intima walls), using open source codes. The models were constructed in the Blender package and Python scripts were used to export the data necessary for the mesh generation in TetGen. The strategies proposed are able to provide meshes of complicated and irregular volumes, with a large number of mesh elements involved (12,000,000 tetrahedrons approximately). These meshes can be used to perform computational simulations by Finite Element Method (FEM).

Large Eddy Simulations of 2D and Open-tip Airfoils Using Voxel Meshes

This paper presents Large Eddy simulations of flow and acoustic computations around 2D and 3D airfoils using a novel type of mesh called voxel mesh. Voxel mesh refers to the mesh that has different number of nodes in the neighbouring cell layers. Voxel mesh has many advantages such as creating cells with minimum skewness, automatic mesh generation and uniformity in cell shapes and sizes. The voxel meshes aren’t yet validated in boundary layer computations. In this paper we validate the use of voxel meshes in boundary layer computations in 2D and 3D airfoils. Six cases were tried out in the research three 2D meshes and three 3D cases were tried out. Each case was simulated at Reynolds number 2.83×105 and attack angle of 90. Flow field computation was done by FrontFlowBlue-7.2 software the acoustic computation was done by using FrontFlowBlue-Acoustic2.2 software. The results obtained from the simulations were compared with the experimental values. The use of voxel meshes to resolve the boundary layer in turbulent fluid flows could be validated using 2D airfoils. Therefore voxel meshes were used in 3D airfoil flow computations. After successful flow computations the source fluctuations in the flow was used for the acoustic computations. The sound pressure levels computed from the acoustic computations were compared with the experimental values. Some oscillation in the pressure could be observed due to the step like structure at the surface of voxel mesh but these variations were less apparent in meshes that had smaller cells.

OS1541 自動メッシュ生成技術を援用した三次元き裂の完全自動パラメトリック/進展解析

When crack analyses are performed for the structural integrity evaluations, the hexahedral elements are adopted in generally. It is very time consuming to build the finite element mesh using the hexahedral elements. Therefore, automated mesh generation by using the tetrahedral elements is adopted in present software system. Automated parametric analysis system from the meshing to the stress intensity factor computation can eliminate the manual operations completely. In this paper, automated parametric system is briefly described and a numerical example is presented.