Identification of external force acting on machines or structures (Improvement method by additional mass and truncated singular values)

Abstract

The identification of external force acting on a machine or a structure is important for diagnosis. One of the force identification methods is based on the frequency response function (FRF). The method is very useful although it requires the information of the location of acting force. In this study, an identification method is proposed for the case of unknown excitation points. In the method, the inverse problem of force identification is solved by increase the number of FRF by adding a mass on the target structure and truncated singular values. The optimum identification condition is determined by the combined objective function of the reconstruction accuracy of measured data and the variation of the identified external force. The identification method proposed is checked using the actual measured data. A beam structure elastically supported at both ends is considered. The beam is excited by using an electromagnet. This excitation method is non-contact way so the magnitude of the external force cannot be directly measured by the load cell. The external force is identified using the measured data with an excitation frequency. It was shown that the identified external force was feasible using the proposed method. Then the numerical simulation, which was almost similar situation of the experiment, was carried out and the adequate result could be obtained. As the result, it was concluded that the force identification method was very useful for the actual application.

Keywords

• force identification
• modal analysis
• singular value decomposition
• truncation
• reconstruction of response