Detection of Nonlinearity Using a Fourth Moment

Existence of any nonlinearity in responses of a nonlinear system is tested using a kurtosis or a fourth moment which has been widely used to characterize signal patterns. By inputting a harmonic signal to a system and investigating the distortions of an output signal from a harmonic pattern, which are due to violations of proportionality between the input and the output, it is judged whether the output is generated from a nonlinear system or not. Through applying the method presented in this work to simulation studies on detections of nonlinearities of a single degree of freedom system, in which three kinds of nonlinearities are treated as restoring force terms, feasibilities of the method are shown and the range of both frequency and input amplitude, in which the system generates nonlinear responses, is determined

Development of a Multi-Input Modal Analysis System Using a PC

본 연구에서는 비교적 저가인 소형 컴퓨터(IBM-AT급) 및 주변 장치를 이용하 는 다점가진 모우드해석 시스템의 개발과 관련된 신호 수집, 다차원 스펙트럼 해석법 에 의한 주파수 응답함수 행렬의 계산, 곡선 피팅에 의한 후처리 문제등을 소개하고, 모의실험(simulation) 및 실제 가진실험을 통하여 개발된 시스템의 실용화 가능성을 검토하였다. A multi-input/multi-output modal analysis system is developed using a PC and its peripheral devices to estimate dynamic properties of a mechanical structure. Theoretical backgrounds for the calculation of frequency response function matrices and for the extraction of modal Parameters are introduced. Some problems occurring at the stages of data acquisition and determinations of modal parameters are presented, and their treatments are proposed. Subsequently, the feasibility of the developed system is demonstrated through applications to a simulated 3-DOF system and an engine lathe

Estimation of Sensitivity Axis Offset of an Accelerometer for Accurate Measurement of the 6 DOF Human Head Motion

Motion sickness is well known to be caused by long time exposure to the very low frequency motion in the multiple axes of human body. Since the vestibular system for the perception of low frequency motion is located in the head, accurate measurement of 6 degree of freedom head motion is of great importance. In this study, the measurement system consisting of a safety helmet and 9 translational accelerometers was constructed for the estimation of 3 translational and 3 rotational motions of human head. Since estimation errors of 3 rotational components can be significantly magnified even by small offset of the sensitivity axis from the geometric center of an accelerometer, accurate measurement of sensitivity axis must be preceded. The method for accurate estimation of the offset was proposed, and the effect of offset on the estimation of angular acceleration was investigated

Experimental modal analysis by multi-excitation

학위논문(석사) - 한국과학기술원 : 생산공학과, 1989.2, [ [v], 67 p. ]한국과학기술원 : 생산공학과