SUMMARYA new methodology is introduced in this work to simulate normal walking using a spatial digital human model. The proposed methodology is based on an optimization formulation that minimizes the dynamic effort of people during walking while considering associated physical and kinematical constraints. Normal walking is formulated as a symmetric and cyclic motion. Recursive Lagrangian dynamics with analytical gradients for all the constraints and objective function are incorporated in the optimization process. Dynamic balance of the model is enforced by direct use of the equations of motion. In addition, the ground reaction forces are calculated using a new algorithm that enforces overall equilibrium of the human skeletal model. External loads on the human body, such as backpacks, are also included in the formulation. Simulation results with the present methodology show good correlation with the experimental data obtained from human subjects and the existing literature.
A node-based design variable implementation for continuum structural topology optimization in a finite element framework is presented and its properties are explored in the context of solving a number of different design examples. Since the implementation ensures C 0 continuity of design variables, it is immune to elementwise checkerboarding instabilities that are a concern with element-based design variables. Nevertheless, in a subset of design examples considered, especially those involving compliance minimization with coarse meshes, the implementation is found to introduce a new phenomenon that takes the form of "layering" or "islanding" in the material layout design. In the examples studied, this phenomenon disappears with mesh refinement or the enforcement of sufficiently restrictive design perimeter constraints, the latter sometimes being necessary in design problems involving bending to ensure convergence with mesh refinement. Based on its demonstrated performance characteristics, the authors conclude that the proposed nodebased implementation is viable for continued usage in continuum topology optimization.
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