Mesh generation for voxel -based objects

A new physically-based approach to unstructured mesh generation via Monte-Carlo simulation is proposed. Geometrical objects to be meshed are represented by systems of interacting particles with a given interaction potential. A new way of distributing nodes in complex domains is proposed based on a concept of dynamic equilibrium ensemble, which represents a liquid state of matter. The algorithm is simple, numerically stable and produces uniform node distributions in domains of complex geometries and different dimensions. Well-shaped triangles or tetrahedra can be created by connecting a set of uniformly-spaced nodes. The proposed method has many advantages and potential applications.;The new method is applied to the problem of meshing of voxel-based objects. By customizing system potential energy function to reflect surface features, particles can be distributed into desired locations, such as sharp corners and edges. Feature-preserved surface mesh can then be constructed by connecting the node set.;A heuristic algorithm using an advancing front approach is proposed to generate triangulated surface meshes on voxel-based objects. The resultant surface meshes do not inherit the anisotropy of the underlying hexagonal grid. However, the important surface features, such as edges and corners may not be preserved in the mesh.;To overcome this problem, surface features such as edges, corners need to be detected. A new approach of edge capturing is proposed and demonstrated. The approach is based on a Laplace solver with incomplete Jacobi iterations, and as such is very simple and efficient. This edge capturing approach combined with the mesh generation methods above forms a simple and robust technique of unstructured mesh generation on voxel-based objects.;A graphical user interface (GUI) capable of complex geometric design and remote simulation control was implemented. The GUI was used in simulations of large fuel-cell stacks. It enables one to setup, run and monitor simulations remotely through secure shell (SSH2) connections. A voxel-based 3D geometrical modeling module is built along with the GUI. The flexibility of voxel-based geometry representation enables one to use this technique for both geometric design and visualization of volume data

Large-scale Geometric Data Decomposition, Processing and Structured Mesh Generation

Mesh generation is a fundamental and critical problem in geometric data modeling and processing. In most scientific and engineering tasks that involve numerical computations and simulations on 2D/3D regions or on curved geometric objects, discretizing or approximating the geometric data using a polygonal or polyhedral meshes is always the first step of the procedure. The quality of this tessellation often dictates the subsequent computation accuracy, efficiency, and numerical stability. When compared with unstructured meshes, the structured meshes are favored in many scientific/engineering tasks due to their good properties. However, generating high-quality structured mesh remains challenging, especially for complex or large-scale geometric data. In industrial Computer-aided Design/Engineering (CAD/CAE) pipelines, the geometry processing to create a desirable structural mesh of the complex model is the most costly step. This step is semi-manual, and often takes up to several weeks to finish. Several technical challenges remains unsolved in existing structured mesh generation techniques. This dissertation studies the effective generation of structural mesh on large and complex geometric data. We study a general geometric computation paradigm to solve this problem via model partitioning and divide-and-conquer. To apply effective divide-and-conquer, we study two key technical components: the shape decomposition in the divide stage, and the structured meshing in the conquer stage. We test our algorithm on vairous data set, the results demonstrate the efficiency and effectiveness of our framework. The comparisons also show our algorithm outperforms existing partitioning methods in final meshing quality. We also show our pipeline scales up efficiently on HPC environment

Shaken Baby Syndrome: Retinal Hemorrhaging. A Biomechanical Approach to Understanding the Mechanism of Causation

Shaken Baby Syndrome (SBS) is a form of abuse where typically an infant, age six months or less, is held and shaken. There may or may not be direct impact associated with this action. Further, there is very little agreement on the actual mechanism of SBS. Clinical studies are limited in showing the exact mechanism of injury and only offer postulations and qualitative descriptions. SBS has received much attention in the media, has resulted in a great deal of litigation and can be the source of unfounded accusations. Therefore, it is necessary to try to quantify the forces that may cause injury due to SBS. The physiology of infants makes injury due to SBS more likely. Infants have relatively large heads supported by weak necks that simply act as tethers (Prange et al., 2003). Therefore, there is minimal resistance to shaking. In addition, the cerebrospinal fluid (CSF) layer surrounding the infant\u27s brain is up to 10 mm thick as opposed to 1–2 mm in older children and adults (Morison, 2002). This thick layer reduces the resistance in rotation of the brain and can cause shearing injuries to the brain tissue. In addition, retinal hemorrhaging has been reported in SBS. The infant\u27s eyes have a vitreous that is typically more gelatinous and with a higher viscosity than in adult eyes. In addition, this vitreous is firmly attached to the retina and is difficult to remove (Levin, 2000). A preliminary parametric model of an infant eye will be presented so that resultant nodal retinal force of the posterior retina can be investigated and compared with a documented shaking frequency and a documented impact pulse. Retinal forces are then compared with various studies that investigate retinal detachment or adhesive strength. This eye model is built using a variety of material properties that have been reported for the sclero-cornea shell, choroids, retina, vitreous, aqueous, lens, ciliary, optic nerve, tendons, extra ocular muscles, optic nerve, and orbital fatty tissue. The geometry of the eye has been carefully optimized for this parametric model based on scaling to an infant from an adult using idealized eye globe geometry and transverse slice tracings of The Visible Human Project. This model shows promise in investigating the forces and kinematics of the infant eye exposed to harmonic shaking and further bolsters some of the few biomechanical studies investigating SBS. However, improvements are necessary to complete the eye model presented. Specifically, improvements on the mechanical properties for the components of the eye and especially the infant eye are needed. There is currently a deficit of biomechanical studies of the materials needed for the infant eye that is specifically geared for use in an explicit finite element code package. Conversions and adaptations of available materials are used in this first version of the infant eye model presented here and are in fair agreement with some of the clinical studies concerning SBS