Vehicle collisions frequently happen at a low speed. Insurance companies and the Research Council for Automobile Repairs both require reduction of repair costs and improvement in occupant safety in a low-speed crash. In order to reduce repair costs, an energy absorbing device such as the crash box is usually installed. The crash box is a thin-walled structure attached between the vehicle bumper structure and the side rail. The determination of the crash box geometry is quite important to absorb the impact energy, since the installation space of the crash box is not very large. In this research, a design procedure to determine the cross-sectional dimensions is proposed to enhance the energy absorption capability of the crash box. The proposed process has two steps. In the first step, the cross-sectional dimensions for the conceptual design are determined in two ways. One is a parameter study using discrete design with an orthogonal array. The cross-sectional dimensions of the crash box are selected among the available cross-sections, such as a circle or a polygon. The cross-sectional dimensions are determined by the analysis of the mean from the discrete design with an orthogonal array. The other is topology optimization, which is performed to determine the cross-section of the crash box to maximize the absorbed strain energy based on the Research Council for Automobile Repairs test conditions. The equivalent static loads method for non linear static response structural optimization is employed to solve the formulated topology optimization problems. The cross sections of the crash box are determined from the results of the conceptual design. In the second step, the detailed design processes are performed by using discrete design with an orthogonal array for the models that are selected in the first step. The detailed shapes of the new crash boxes are determined from the detailed design. The optimization problem for the crash box is formulated considering the geometric constraints of fitting into the given space for the crash box. Three new types of crash box are suggested, with detailed shapes from the proposed design procedure.
The eccentric check butterfly valve is a butterfly valve that has an eccentric rotating axis. It is not only used as a butterfly valve to control the flowrate or pressure, but also as a check valve to prevent backward flow. A new design process is proposed for designing the valve. First, an optimization problem with a characteristic function is formulated to determine the amount of eccentricity. The characteristic function to be minimized is defined for the flow characteristics. Second, the waterhammer pressure of the valve disc is calculated by waterhammer analysis when the flow stops suddenly. Structural analysis is carried out to evaluate the waterhammer pressure of the valve disc and structural safety. Structural optimization is performed considering the structural safety and the flow characteristics. The process of structural optimization has two steps: topology optimization and shape optimization. Mass distribution of the disc housing is determined using topology optimization. Since topology optimization does not give the final dimensions, shape optimization is utilized to determine the details based on the results of topology optimization. A light design is derived to satisfy the structural safety and the flow characteristics.
Engineering structures consist of various components, and the components interact with each other through contact. Engineers tend to consider the interaction in analysis and design. Interactions of the components have nonlinearity because of the friction force and boundary conditions. Nonlinear analysis has been developed to accommodate the contact condition. However, structural optimization using nonlinear analysis is fairly expensive, and sensitivity information is difficult to calculate. Therefore, an efficient optimization method using nonlinear analysis is needed to consider the contact condition in design. Nonlinear Response Optimization using Equivalent Loads (NROEL) has been proposed for nonlinear response structural optimization. The method was originally developed for optimization problems considering geometric/material nonlinearities. The method is modified to consider the contact nonlinearity in this research. Equivalent loads are defined as the loads for linear analysis, which generate the same response field as that of nonlinear analysis. A nonlinear response optimization problem is converted to linear response optimization with equivalent loads. The modified NROEL is verified through three examples with contact conditions. Three structural examples using the finite element method are demonstrated. They are shape optimization with stress constraints, size optimization with stress/displacement constraints and topology optimization. Reasonable results are obtained in the optimization process.
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