Structural modification and evaluation using finite element reconciliation method

Abstract

Structural dynamic modification (SDM) techniques are important in structural optimisation of the system to modify the dynamics behaviour of the structure. It can be implemented by utilising the dynamic test data to alters the dynamic behaviour of the structure. However, there are some concern in the design process in which the undesirable mode shapes movement of structure are occurred along side with desired natural frequencies. Therefore, the SDM technique can be used as to varying the predicted dynamic behaviour of structure to solve noise, vibration and harshness problems (NVH). In order to be well predicted the modified dynamic behaviour of structure, the optimisation method via finite element (FE) model updating is used to obtain a reliable and accurate unmodified FE model. The main goal of this research is to change or altered the mode shapes movement of the mild steel bar structure due to the mass modification without shifting the natural frequencies away from unmodified value. In this research, the FE model of the mild steel bar structure was constructed using MSC software and the predicted dynamic behaviour were compared with the experimental modal analysis (EMA) data. The measured data was obtained using an impact hammer testing and roving accelerometers under free-free boundary conditions with data were extracted from LMS SCADAS software. Then, reconciliation process via FE model updating method is carried out in order to reduce the inaccuracy of initial FE model based on the measured data where the initial error has been reduced from 24.81 percent to 7.71 percent. Finally, the updated FE model was used for SDM technique using mass modification. The results reveal that the mode shapes of the structure can be change by manipulating the mass. It is agreed that by adding a reasonable mass with a right position to the structure the mode shapes can be change without shifting the natural frequencies away from unmodified values.