Identification of damping in joints using dynamic substructuring techniques

Abstract

Predicting and characterizing damping in joints and connections is a bottleneck in many design processes. New analysis techniques can be used to advance the engineering practice. These techniques would for example be useful to make a better estimation of the coupled dynamics of an engine-generator set (gen-set) on a ship. Large ships are commonly equipped with a gen-set to provide power to the vessels and to the electrical consumers on board. In some cases the engine vibration levels are too high to satisfy vibration guideline limits. In order to get insight in the system dynamics and to propose useful structural modifications an accurate system description of the total system is needed. In the Msc. project, research has been done on the identification of the dynamic behaviour of joints. Joints can significantly influence the dynamics of the entire system. The identification will be done by using Dynamic Substructuring (DS) techniques. The joint will be modelled and treated as a subsystem and the properties will be iteratively obtained. An often encountered problem in practice is the absence of crucial response measurements on the interface due to tight packaging of the system. A method is proposed to describe the unmeasured interface Degrees of Freedom (DoF), which are needed for compatibility of motions on the interface, in terms of measured DoF. Measurements are done on a base-upright test structure which is tested in different support conditions. It is shown that DS techniques can be used to identify properties of joints. The proposed method for describing unmeasured DoF has been validated with simulated experiments. Further investigation is needed to use this method with measured data.