Automatic three‐dimensional mesh generation by the modified‐octree technique

Recently developed solid modelling systems for the design of complex physical solids using interactive computer graphics offer the exciting possibility of an integrated design/analysis system. Called geometric modellers, these systems build complex solids from primitive solids (cubes, cylinders, spheres, solid patches, etc.) and macro solids (combination of primitives)3, 4, 8, 16, 18, 25, 38. To provide an effective structural analysis capability for these systems, methods must be devised to ease the burden of discretizing the solid geometry into a user controlled (usually locally graded) finite element mesh. The purpose of this paper is to describe an interactive solid mesh generation system capable of generating valid meshes of well‐proportional tetrahedral finite elements for the decomposition of multiply connected solid structures. The system uses a semi‐automatic node insertion procedure to locate element node points within and on the surface of a structure. An independent automatic three‐dimensional triangulator then accepts these nodes as input and connects them to form a valid finite element mesh oftetrahedral elements. Although this report makes use of a modeller based on a constructive solid geometry representation (a so‐called CSG modeller), the mesh generation strategy elaborated herein is completely general and makes no particular use of the CSG representation.

For electrical impedance tomography (EIT) of brain, the use of anatomically accurate and patient-specific finite element (FE) mesh has been shown to confer significant improvements in the quality of image reconstruction. But, given the lack of a rapid method to achieve the accurate anatomic geometry of the head, the generation of patient-specifc mesh is time-comsuming. In this paper, a m odified fuzzy c-means algorithm based on no n-local means method is performed to implement the segmentation of different layers in the head based on head CT images. This algorithm showed a better effect, especially an accurate recognition of the ventricles and a suitable performance dealing with noise. And the FE mesh established according to the segmentation results is valid ated in computational simulation. So a rapid practicable method can be provided for the generation of patient-specific FE mesh of the human head that is suitable for brain EIT. Keyword: Computerized tomography, image segmentation, mesh generation, electrical impedance tomography

In the past few years there has been a lot of interest and excitement generated by solid modeling. Numerous papers have been presented on the value and benefits of this technology. Many talented individuals have contributed to the state of the art. Solid modeling has played a larger role at SIGGRAPH in the past three years, with tutorials, panel discussions and technical papers. All this material has been presented for the most part by academics, researchers and developers of solid modeling systems. The users of solid modeling systems have yet to be heard from. The reason is that there have been very few of them out there in the past. However, that situation is slowly changing. Now that several CAD/CAM vendors are marketing solid modeling systems, a small cadre of users does exist. This panel will be composed primarily of users of solid modeling systems. They will discuss topics of interest to potential users (and also developers) of solid modelers. Questions to be addressed include: What is the status of solid modeling systems from a user standpoint? Can the present solid modelers be used in a production environment today? Should a solid modeling system replace the present wire frame and surface systems or be integrated with them? What are the problems associated with using a solid modeling system? How good is the user interface? Does the necessary application software exist? The primary intent of this Panel discussion is to give the potential user some idea as to whether the available solid modeling systems are useful for his applications. It is beginning to look like the next generation CAD/CAM system for mechanical design will be a solid modeler. The big question is “when will this occur?”

Parametric 3D finite-element mesh generation

In many cases, the overriding difficulty associated with finite element analyses of complex structures is the generation of error-free finite element meshes. In view of this situation, a number of mesh generation schemes for planar (e.g., [1], [2]) and shell (e.g., [3], [4]) structures have recently been proposed (see [5] for an extensive bibliography). At one extreme are the fully automatic methods in which the computer is used to determine regions of high and low element densities and then create a finite element mesh accordingly. At the other extreme are methods which require the analyst to completely define the element mesh, while the mesh generating algorithm itself performs only minor clerical tasks such as checking for consistency and error detection. While the fully automatic methods tend to be somewhat inflexible and frequently time consuming to implement, the simplest schemes fail to relieve the user of enough of the tedium accompanying manual decomposition of the structure.

Model and mesh generation of cracked tubular Y-joints

An ANN-based element extraction method for automatic mesh generation

Fatigue crack growth behaviour of pressure vessel steels and submerged arc weldments in a high-temperature pressurized water environment: Liaw, P. K., Logsdon, W. A. and Begley, J. A.Metall. Trans. A Oct. 1989 20A, (10), 2069–2085

A mesh generator for the production of high-quality finite-element meshes is being proposed. The mesh generator uses an artificial neural network, which grows during the training process in order to adapt itself to a prespecified probability distribution. The initial mesh is a constrained Delaunay triangulation of the domain to be triangulated. Two new algorithms to accelerate the location of the best matching unit are introduced. The mesh generator has been found able to produce meshes of high quality in a number of classic cases examined and is highly suited for problems where the mesh density vector can be calculated in advance.

Volume discretization into tetrahedra—II. 3D triangulation by advancing front approach

This study implemented a large scale model for transient flow problems through the vadose zone derived using the stochastic approach to account for spatial variability of soil properties. The heterogeneity of natural soil formations were included in the effective hydraulic conductivity and specific moisture capacity. The set of stochastic differential equations was solved using a finite element formulation. A computer code was developed to implement the stochastic finite element formulation and a mesh generator was also developed to create the finite element mesh. Numerical simulations were performed for different scenarios using real data and the results for pressure head and volumetric water content distribution profiles at different times were compared to analytical and deterministic solutions, and experimental results. The stochastic perturbation approach showed to have the great advantage of being computationally much less expensive than the Monte Carlo method. The stochastic approach predicted significantly slower vertical movement and faster horizontal movement of the wetting front compared to the deterministic approach. The results agreed with field observations. The difference between stochastic and deterministic head pressure and volumetric moisture content profiles was significant and should not be discarded.

Sensitivity analysis with the modified Heaviside function for the optimal layout design of multi-component systems

Numerical evaluation of 3-D SIF for arbitrary finite element meshes

Automatic generation of quadrilateral finite element meshes

Four local error estimators used for a posteriori h-type adaptive finite-element mesh generation are presented and compared in the solution of several steady-state multiconductor eddy-current problems, encountered in electrical power transmission and distribution systems. The proposed technique combines four different criteria with the concept of Delaunay triangulation to provide finite-element triangular meshes, adaptive to the characteristics of each problem. By refining the elements with the largest errors and recomputing the solution iteratively, finite-element meshes having a uniform error density are obtained. The problems examined lead to quantitative results concerning the performance of each estimator in the accuracy of the solution, in terms of both convergence rate and quality of electromagnetic field lines.