Preprocessing General Head Models for BEM-FMM Modeling Pertinent to Brain Stimulation

Introduction: Transcranial magnetic stimulation (TMS) is a major noninvasive neurostimulation method in which a coil placed near the head employs electromagnetic induction to produce electric fields and currents within the brain. To predict the actual site of stimulation, numerical simulation of the electric fields within the head using high-resolution subject-specific head models is required. A TMS modeling software toolkit has been developed based on the boundary element fast multipole method (BEM-FMM), which has several advantages over conventional finite element method (FEM) solvers.Objective: To extend the applicability of the BEM-FMM TMS simulation toolkit to head models whose meshing scheme produces a single mesh for every unique tissue instead of producing a single mesh for every unique tissue/tissue boundary.Method: The MIDA model of the IT’IS Foundation, Switzerland, comprises 115 high-resolution tissue models in the form that the BEM-FMM toolkit is modified to accept. The updated BEM-FMM toolkit is tested using this head model.Results: The BEM-FMM toolkit has been successfully modified to accept head models consisting of one unique mesh per unique tissue while still supporting its initial model format of one unique mesh per boundary between two specific tissues. Performance impacts occur in the preprocessing phase only, meaning that the charge computation method performs equally well regardless of model format.

Hybrid Compliant Mechanism Design Using a Mixed Mesh of Flexure Hinge Elements and Beam Elements Through Topology Optimization

This paper proposes a topology optimization framework to design compliant mechanisms with a mixed mesh of both beams and flexure hinges for the design domain. Further, a new type of finite element, i.e., super flexure hinge element, was developed to model flexure hinges. Then, an investigation into the effects of the location and size of a flexure hinge in a compliant lever explains why the point-flexure problem often occurs in the resulting design via topology optimization. Two design examples were presented to verify the proposed technique. The effects of link widths and hinge radii were also investigated. The results demonstrated that the proposed meshing scheme and topology optimization technique facilitate the rational decision on the locations and sizes of beams and flexure hinges in compliant mechanisms.

A Time-Domain Boundary Elements Method Applied to Multi-Body Simulations With Large Relative Displacements

This paper presents a time domain boundary elements method that accounts for relative displacements between two bodies subjected to incoming waves. The numerical method solves the boundary value problem together with a re-meshing scheme that defines new free surface panel meshes as the bodies displace from their original positions and a higher order interpolation algorithm used to determine the wave elevation and the velocity potential distribution on new free surface collocation points. Numerical solutions of exciting forces and wave elevations are compared to data obtained in a fundamental experimental text carried out with two identical circular section cylinders, in which one was attached to a load cell and the other was forced to move horizontally with a large amplitude oscillatory motion under different velocities. The comparison of numerical and experimental result presents a good agreement.

A Quadrilateral Meshing Method for Shear-Wall Structures

In this paper, a meshing scheme for shear-wall structures is developed based on the paving method and associated with the mapping and geometry decomposition method. The present method would combine the advantages of free mesh, such as strong generality for complicated structures, and mapping mesh, such as outstanding efficiency for some specific geometries, and result in the following four merits: (1) theoretically suitable for arbitrary shear wall and slab; (2) the mesh is compatible, i.e., the adjacent boundary of the shear-wall and slab has identical nodes; (3) all or most of the elements are quadrilateral which is important for finite element analysis; (4) the mesh is uniform and homogeneous, and the transition between different mesh size would be automatically smoothed. Finally, some meshing examples for complicated building structures are presented to illustrate the validity of this meshing scheme.