플렉시블 조인트를 갖는 배기계 진동특성에 관한 연구

Abstract

A systematic approach to verify effectiveness of the modal analysis for the exhaust system of a passenger vehicle including a flexible joint has been considered in this thesis. The modal analysis refers to experimental or analytical methods applied in vibration analysis to describe the dynamic behavior of a structure with general terminologies such a natural frequencies, damping ratios and mode shapes.

It should be recognized that frequency responses of the system containing non-linear characteristics have been used to evaluate dynamic performance in the framework of linear system analysis under the assumption that agitation of non-linearity did not exceed a certain limit. Considering that easiness of getting frequency response between measurement and excitation points, impact hammering and sine sweep. With these techniques, the dynamical behavior of non-linear can be assessed with those terms often used in the linear system analysis. Moreover, the results are than compared to those obtained from in-car measurements.

The nonlinear characteristic caused by the flexible joint, such as dry friction and stiffness hysteresis, have been investigated to find an optimum input magnitude to excite the system properly. Depending on the level of exhaust system movement, the nonlinearities are behaving differently. It is therefore very important to decide the magnitude of a right input to excite the system to the level corresponding to actual measurement results. For the experimental modal analysis on the rig to see modal behaviors of the exhaust system, the excitation through sine sweep has shown a reliable similarity compared to impact hammering.

In conclusion, the liner system analysis tools can be easily extended to dynamic analysis of a non-linear system, especially, like the exhaust system of a passenger vehicle possessing a relatively less degree of non-linearity, if the input magnitude was properly chosen.