Itsurou Kajiwara

Optimum design of structures by sensitivity analysis

Abstract A series of researches by the authors on structural optimum design by sensitivity analysis is introduced. First, the sensitivity of the anti-resonance frequency is defined, and an approach to eliminate the resonance peak from the frequency response function is proposed using this sensitivity. Next, an experimental approach for structural optimization based on a vibration test is introduced. An approach for optimum design combined with a substructure synthesis method is proposed, in which the objective function is an impulse response function. The proposed methods are illustrated by some examples.

Simultaneous optimum design of structure and control systems by sensitivity analysis

Abstract An approach is proposed for simultaneous optimum design of a structure and feedback control system by sensitivity analysis, for the following two purposes. One is to decrease both the response and the control force of the system under a white noise disturbance force. The other is to modify the gain, the pole and the zero-point to the desirable values. The weighting constant of the feedback control system, and the mass, stiffness, shape, dimensions, etc. of the structure, are adopted simultaneously as the design variables. The proposed method is verified by a model simulation.

Modelling and Optimum Design of the Control System based on the Identification of Spatial Matrices.

The authors propose a method to design the optimum control system toward flexible structural systems. The mechanical structural system can be modelled by identifying the spatial matrices from experimental frequency response functions. The optimum control system is easily designed by applying the optimum control theory to the identified system. However, the stability of the control system is not always guaranteed because the mechanical system is generally identified with small degrees of freedom ignoring high-order modes. This report proposes an optimization method of the control system which guarantees the stability of the actual system which is also an identified system with high degrees of freedom. The characteristics of both the identified and actual system are simultaneously optimized by the proposed method based on sensitivity analysis and nonlinear programming. An experimental example verifies the effectiveness of the proposed method.

H.INF. Robust Vibration Control of Continuous Structures using Modal Analysis.

In this paper, we consider a robust vibration control of a continuous body structure, such as plate structure. Modeling of a complex structure composed by a continuous body is difficult. FEM is usually used for direct modeling of an actual structure. However, FEM model has originally structural errors and FEM model has so large degree-of-freedom (DOF) that a vibration control system can hardly be designed. This model is reduced to modal coordinate in order to decrease DOF of FEM model. However, the control system becomes unstable frequently because of structural errors and ignored high order modes. We show a design method of a robust vibration control system based on H∞ control theory. The robustness against structural errors and ignored high order modes can be realized by H∞ control. Both the control performance and the robustness of the closed loop system can be improved by applying adequate weighting functions of H∞ control. The effectiveness of the method is verified by the results of both analysis and experiment.