A Study on New Approaches for Developing Process of Vibrational Characteristic Improvement by using Transmissibility: Boundary Identification and Relative Sensitivity Analysis

Abstract

When analyzing the components assembled compactly in a system for setting the shaker or measuring an impact force exerted on the component correctly, the measurement errors caused by an incorrectly measured force could be increased. Transmissibility includes only response data, unlike FRFs that include force measurements. In this thesis, new approaches for developing process of vibrational characteristic improvement that consider boundary properteis and sensitivity of responses are presented. Transmissibility concepts is adopted to identify the boundary properties and to suggest indices for relative sensitivity analysis. A new method for identifying boundary properties are proposed. Equation for estimating boundary properties is derived by investigating the difference in transmissibilities between a component under the coupled condition and under the free condition. Discrete multiple degrees of freedom system with single boundary and multiple boundary conditions are used to verify of the method. The method is also applied to a beam which is the simplest structural form of continuous system to investigate whether the method still usable in practical condition. Good agreement is achieved when estimated properties are compared with exact properties. Further, Error equation using measurement noise is developed to assess the robustness of the method for application under practical conditions. In addition, indices based on the transmissibility are suggested to analyze relative sensitivity of responses. Relative senstivity of responses with respect to variables should be analyzed to make small design modifications for improving the vibrational charactertistics of a system. Two types of indices with respect to variables are developed for indicating an appropriate position where the design variable could be modified and indicating an effect of the specific design variable on the responses. Discrete multiple degrees of freedom system and two numerical beam models are used to investigate whether the proposed indices reflect the relative changes in response to small design modifications. It has been found that the proposed indices exactly represent the sensitivity characteristics of the system by showing that the indices agreed well with the indicators for all frequency ranges.