Quantification and Implementation of Structural Damping in MBS Flexible Bodies

University essay from Lunds universitet/Mekanik

Author: Anton Flink; [2015]

Keywords: Technology and Engineering;

Abstract: In multi body simulation (MBS) using flexible bodies, damping is an important model input to be able to predict the response of a structure with sufficient precision. The purpose of this thesis has been to estimate the structural damping of an experimental setup and implement the estimated damping into MBS-models of the setup. In this thesis the modal properties in terms of natural frequencies, mode shapes and modal damping of a chassis frame with a number of attached components are identified through physical testing. The experimental setup is modeled in the MBS software MSC Adams using both flexible and rigid bodies coupled together, a total of three different models are created. Two with different modeling of the bolted joints in the setup and one where components are modeled as separate flexible bodies and coupled with joints. The modal properties of the models are compared to the identified modal properties of the setup. The simplification in modeling of the bolted joints results in small differences in modal properties of the model compared to more detailed modeling of the bolted joints. Modeling of components as separate flexible bodies results in lesser consistency compared to identified modal parameters, making it more difficult to mimic the damping of the experimental setup. For each of the models a damping function is suggested and implemented,based on the identified modal damping of the physical system. Simulation is then performed, comparing the different models ability to predict the pseudo damage relative to the physical system. The suggested damping functions shows improved ability to predict pseudo damage for Components attached to the chassis frame. The prediction of pseudo damage on the frame side members and cross members is less sensitive to the choice of damping in the MBS-model. Parts of the modeling procedure as well as the implementation of identified damping shows room for improvement and further studies are recommended.

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