Extracting method of structural modification area using mutual modal kinetic energy distribution and effect of vibration reduction by tuned natural frequency

Abstract

Computer-aided engineering is widely used in mechanical engineering to analyze the noise- and vibration-related performances of components and assemblies. Recently, extremely fine meshes of the body structure and large number of degree-of-freedom (DOF), in a finite element model (FE model) with increased CPU power, have been used to run simulations in high-frequency regions and to improve the accuracy of the simulations. This FE model is better suited for studying the effects of changing physical parameters, such as material stiffness and structural details, thereby facilitating a detailed analysis of the vibration behavior. Moreover, with an FE model, it is difficult to develop effective countermeasures against noise and vibration because of the increasing number of modes in unit intervals of frequency. For this type of problem in high modal density regions, earlier studies have explored several mode-grouping methods based on similarity of mode shapes. The overall mode shapes are similar in groups but dissimilar in parts. On comparison of two mode shapes, it is observed that the vibration behavior of dissimilar parts is similar to that of a mass damper. If the structure parts that behave like a mass damper can be extracted, we can use the design theory of tuned mass damper for designing structures. This study presents extraction of structure parts that behave like a mass damper. This proposed method uses mutual modal kinetic energy distribution and extracts anti-phase area by two different modes. The main system is defined as the in-phase element, the subsystem is defined as the anti-phase element. In the case that the natural frequency of the subsystem is very close to that of the main system, it is found that the height of the resonance peak decreases.

Keywords

• modal analysis
• vibration reduction
• high modal density
• tuned mass damper