202 research outputs found
On the development of an efficient truly meshless discretization procedure in computational mechanics
No full textSupervised by Mandayam A. Srinivasan and Klaus-Jurgen Bathe.Also issued as Thesis (Sc.D.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2001.Includes bibliographical references (leaves 157-163).by Suvranu De
Modeling of the Lap-Band® for Laparoscopic Adjustable Gastric Banding Operation
No full textThis paper presents a physics-based model of the Lap-bands (Inamed Health) system for simulation of laparoscopic gastric banding (LAGB) operation. The Lap-band (R) has different mechanical properties along the centerline due to different thickness and curvature which makes the task of simulating its dynamics in a stable manner within a multimodal virtual environment rather challenging. A hybrid modeling technique is adopted with a mass-spring model being used for the less stiff portion and a quasi-static articulated rigid link model for the stiffer and relatively more inextensible portion. To allow the trainee for interactive bimanual manipulation of the Lap-band (R) with two graspers, we propose an efficient method to compute exact constraint forces based on velocity constraint in the quasi-static articulated rigid link systems. The performance of the proposed method is compared with the penalty force approach. The virtual Lap-band (R) model has been implemented into a complete graphics-haptics-physics-based system with two PHANToM Omni devices (from Sensible Technologies) being used for real-time bimanual interaction with force feedback
On the development of an efficient truly meshless discretization procedure in computational mechanics
No full textThesis (Sc.D.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2001.Includes bibliographical references (leaves 157-163).The objective of this thesis is to present an efficient and reliable meshless computational technique - the method of finite spheres - for the solution of boundary value problems on complex domains. This method is truly meshless in the sense that the approximation spaces are generated and the numerical integration is performed without a mesh. While the theory behind meshless techniques is rather straightforward, the generation of a computationally efficient scheme is quite difficult. Computational efficiency may be achieved by proper choice of the interpolation functions, effective ways of incorporating the essential boundary conditions and efficient and specialized numerical integration rules. The pure displacement formulation is observed to exhibit volumetric "locking" during incompressible (or nearly incompressible) analysis. A displacement/pressure mixed formulation is developed to overcome this problem. The stability and optimality of the mixed formulation are tested using numerical inf-sup tests for a variety of discretization schemes. Solutions to several example problems are presented showing the application of the method of finite spheres to problems in solid and fluid mechanics. A very specialized application of the technique to physically based real time medical simulations in multimodal virtual environments is also presented. In the current form of implementation, the method of finite spheres is about five times slower than the finite element techniques for problems in two-dimensional elastostatics.by Suvranu De.Sc.D
An efficient coarse-grained parallel algorithm for global-local multiscale computations on massively parallel systems
No full textMay 2009School of EngineeringM
On the Development of a Fast Fourier Transform (FFT)-Accelerated Stokes Flow Solver for Drag Computation on MEMS Devices
No full textSome experiences in developing a Virtual Basic Laparoscopic Skill Trainer (VBLaST™)
No full textAugust 2009School of EngineeringM
Enrichment of the method of finite spheres using geometry-independent localized scalable bubbles
No full text
Multiscale modeling of irradiated polycrystalline FCC metals
No full textAbstractWe propose a set of models for the post-irradiation deformation response of polycrystalline FCC metals. First, a defect- and dislocation-density based evolution model is developed to capture the features of irradiation-induced hardening as well as intra-granular softening. The proposed hardening model is incorporated within a rate-independent single crystal plasticity model. The result is a non-homogeneous deformation model that accounts for defect absorption on the active slip planes during plastic loading. The macroscopic non-linear constitutive response of the polycrystalline aggregate of the single crystal grains is then obtained using a micro–macro transition scheme, which is realized within a Jacobian-free multiscale method (JFMM). The Jacobian-free approach circumvents explicit computation of the tangent matrix at the macroscale by using a Newton–Krylov process. This has a major advantage in terms of storage requirements and computational cost over existing approaches based on homogenized material coefficients in which explicit Jacobian computation is required at every Newton step. The mechanical response of neutron-irradiated single and polycrystalline OFHC copper is studied and it is shown to capture experimentally observed grain-level phenomena
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