published_or_final_version / Mechanical Engineering / Master / Master of Philosophy

published_or_final_version / Civil and Structural Engineering / Master / Master of Philosophy

published_or_final_version / Civil and Structural Engineering / Master / Master of Philosophy

published_or_final_version / Mechanical Engineering / Doctoral / Doctor of Philosophy

A biomechanical model of the human tongue was constructed, based upon a detailed anatomical study of an actual cadaver. Data from the Visible Human Project were segmented to create a volumetric representation of the tongue and its constituent muscles. The volumetric representation was converted to a smooth NURBS-bounded solid model--for compatibility with meshing algorithms--by lofting between splines, the vertices of which were defined by the coordinates of a smoothed triangular mesh representation. Using a hyperelastic constitutive model that allowed for the addition of active stress, the model deforms in response to user-specified muscle activation patterns. A series of meshes was created to perform a mesh validation study; in the validation tests performed, a 245,223-element mesh was found to be sufficient to model tongue behavior.Systematic samples of the behavior of the model were collected. Principal component analyses were performed on the samples to discover low-dimensional representations of tongue postures. Statistical models (linear regression models and neural networks) were fit to predict tongue posture from muscle activation, and vice versa. In all tests, it was found that a relatively small sample of tongue postures can be used to successfully generalize to larger data sets.Finally, a variety of specific tests were performed, based on claims and predictions found in previous literature. Of these, the claims of the muscular hydrostat theory of tongue movement were best supported. Simulations were also run that simulated lingual hemiplegia. It was found that substantially different muscular activation patterns were required to achieve equivalent postures in a hemiplegic tongue, relative to a normal tongue.

The primary objective of the dissertation research is to establish the seismic demands of precast concrete floor diaphragms designed with an emerging design methodology. To accomplish this, three-dimensional (3D) finite element (FE) models of diaphragm-sensitive precast concrete structures have been developed by extending two-dimensional (2D) diaphragm model developed previously for nonlinear static "pushover" analyses. Using these models, diaphragm seismic demands under expected hazard are evaluated through the nonlinear transient dynamic analyses (NLTDA).The research work is composed of four major parts:(1) Developing 3D NLTDA analytical model for diaphragm-sensitive precast concrete structures: The 3D structure model is extended from a 2D FE diaphragm model developed by a previous researcher. This process involves properly handling comparability conditions in 3D, incorporating proper hysteresis behavior for the diaphragm reinforcement, and developing appropriate lateral force resisting system (LFRS) models. A sensitivity analysis is performed for 3D NLTDA modeling to assist in creating an appropriate model.(2) Application of the model in integrated analysis-driven physical testing: These experiments occurred at Lehigh University (LU) with project collaborators. The loading in these tests were controlled by NLTDA of the 3D analytical model. The tests were used to examine the seismic response of key joints (critical flexure and shear joints) in the diaphragm under realistic demands and to further calibrate the analytical model.(3) Analytical modeling in support of shake table testing: The shake table test was performed at University of California San Diego (UCSD). The test involved a half scale three-story diaphragm-sensitive precast concrete structure. NLTDA using the 3D analytical model is used to assist in design and performance prediction of the test specimen. The test results are being used to calibrate/verify the analytical model.(4) Calibrating design factors for the emerging diaphragm design methodology: In the last research step, the 3D analytical model is used to calibrate trial design factors for the emerging diaphragm design methodology. These factors are established based on a parametric study of NLDTA at different seismic hazard levels using simple structure configurations. These factors will be evaluated on models of realistic structures to determine design factors for the final design procedure.

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