Bharat K. Soni

Parallel unstructured mesh generation by an advancing front method

Mesh generation is a critical step in high fidelity computational simulations. High-quality and high-density meshes are required to accurately capture the complex physical phenomena. A robust approach for a parallel framework has been developed to generate large-scale meshes in a short period of time. A coarse tetrahedral mesh is generated first to provide the basis of block interfaces and then is partitioned into a number of sub-domains using METIS partitioning algorithms. A volume mesh is generated on each sub-domain in parallel using an advancing front method. Dynamic load balancing is achieved by evenly distributing work among the processors. All the sub-domains are combined to create a single volume mesh. The combined volume mesh can be smoothed to remove the artifacts in the interfaces between sub-domains. A void region is defined inside each sub-domain to reduce the data points during the smoothing operation. The scalability of the parallel mesh generation is evaluated to quantify the improvement on shared- and distributed-memory computer systems.

An Approach to Generate High Quality Unstructured Hybrid Meshes

This paper describes the method to generate hybrid meshes comprised of triangular prisms, pyramids, hexahedra and tetrahedra for viscous computational fluid dynamics (CFD) simulations. Surface triangulation is performed using a direct advancing front method or a modified mesh-decimation method. From a surface mesh, a near-field mesh is generated using an advancing layer approach. To generate high quality meshes and to mesh around singular points, multiple marching directions are prepared from nodes on sharp convex corners. Tetrahedral meshing is then performed to fill the rest of the domain using an advancing front method. The hybrid mesh generation method is applied to several models to demonstrate its capability.

Finite element model development of a child pelvis with optimization-based material identification

A finite element (FE) model of a 10-years-old child pelvis was developed and validated against experimental data from lateral impacts of pediatric pelves. The pelvic bone geometry was reconstructed from a set of computed tomography images, and a hexahedral mesh was generated using a new octree-based hexahedral meshing technique. Lateral impacts to the greater trochanter and iliac wing of the seated pelvis were simulated. Sensitivity analysis was conducted to identify material parameters that substantially affected the model response. An optimization-based material identification method was developed to obtain the most favorable material property set by minimizing differences in biomechanical responses between experimental and simulation results. This study represents a pilot effort in the development and validation of age-dependent musculoskeletal FE models for children, which may ultimately serve to evaluate injury mechanisms and means of protection for the pediatric population.

Childhood obesity as a risk factor for bone fracture: A mechanistic study

To investigate the risk of bone fracture sustained by obese children exposed to falls. The bone fracture risk of obese children would be greater than that of their nonobese counterparts was hypothesized.

Original articles: Patient-specific geometry modeling and mesh generation for simulating Obstructive Sleep Apnea Syndrome cases by Maxillomandibular Advancement

The objective of this paper is the reconstruction of upper airway geometric models as hybrid meshes from clinically used Computed Tomography (CT) data sets in order to understand the dynamics and behaviors of the pre- and postoperative upper airway systems of Obstructive Sleep Apnea Syndrome (OSAS) patients by viscous Computational Fluid Dynamics (CFD) simulations. The selection criteria for OSAS cases studied are discussed because two reasonable pre- and postoperative upper airway models for CFD simulations may not be created for every case without a special protocol for CT scanning. The geometry extraction and manipulation methods are presented with technical barriers that must be overcome so that they can be used along with computational simulation software as a daily clinical evaluation tool. Eight cases are presented in this paper, and each case consists of pre- and postoperative configurations. The results of computational simulations of two cases are included in this paper as demonstration.

Moving-body simulations using overset framework with rigid body dynamics

The simulation of flow past bodies in relative motion is a challenging task due to the presence of complex flow features, moving grids, and rigid body movements under the action of external forces and moments. A generalized grid-based overset framework is presented for the simulation of this class of problems. The equations that govern the fluid flows are cast in an integral form and are solved using a cell-centered finite volume upwind scheme. The rigid body dynamics equations are formulated using quaternion and are solved using fourth-order Runge-Kutta (RK) time integration. The overset framework and the six degree of freedom (6-DOF) rigid body dynamics simulators are developed in a library form for easy incorporation into existing flow solvers. The details of the flow solver, the 6-DOF library, and the overset framework are presented in this paper along with the validation results of the developed system.

Validation and verification of Courant number insensitive CE/SE method for transient viscous flow simulations

In this paper, we report an extension of the space-time conservation element-solution element (CE/SE) framework-based viscous flow solver. With the accuracy of solution obtained through the use of a CE/SE-based solver closely related to the CFL number disparity across the mesh, a new formulation to make the solution insensitive to CFL number disparity is herein presented. The capability of the developed solver is then validated through simulation of 2D problems such as driven cavity, external flow over a flat plate, laminar flow over a square cylinder, etc. Investigations are also conducted to verify the sensitivity of results to grid spacing and mesh structure.

A Hole-filling Algorithm Using Non-uniform Rational B-splines

A three-dimensional (3D) geometric model obtained from a 3D device or other approaches is not necessarily watertight due to the presence of geometric deficiencies. These inadequacies must be repaired to create a valid surface mesh on the model as a pre-process of computational engineering analyses. This procedure has been a tedious and labor-intensive step, as there are many kinds of deficiencies that can make the geometry to be nonwatertight, such as gaps and holes. It is still challenging to repair discrete surface models based on available geometric information. The focus of this paper is to develop a new automated method for patching holes on the surface models in order to achieve watertightness. It describes a numerical algorithm utilizing Non-Uniform Rational B-Splines (NURBS) surfaces to generate smooth triangulated surface patches for topologically simple holes on discrete surface models. The Delaunay criterion for point insertion and edge swapping is used in this algorithm to improve the outcome. Surface patches are generated based on existing points surrounding the holes without altering them. The watertight geometry produced can be used in a wide range of engineering applications in the field of computational engineering simulation studies.

Computational science simulations based on web services

We describe the software architecture of a system for doing multiphysics simulation of a coupled fluid, thermal, and mechanical fracture problem. The system is organized as a collection of geographically-distributed software components in which each component provides a web service, and uses standard web-service protocols to interact with other components. The resulting system incorporates many features such as componentization and geographical distribution which we believe are vital to adaptive and dynamic data-driven application systems (DDDAS).

Development of an efficient aerodynamic shape optimization framework

Although many efforts have been made to develop an aerodynamic shape optimization (ASO) framework, iterative grid generation of the complex configuration within the optimization loop has still been a critical barrier. In this paper, an efficient ASO framework is developed by integrating a parametric grid generator, an optimization toolkit, and a flow solver. A geometry-grid template toolkit is developed to address the need to produce a large number of grids in a timely manner for the parametric design study. An object-oriented optimization toolkit that allows a flexible and extensible interfacing with user-specific codes is used. An in-house full Navier-Stokes flow solver is developed and used in the framework. Code integration is achieved using a black-box interface with script files. Two ASO applications and their optimum solutions are presented to demonstrate the success of this framework.