Effects of Extensional Wave propagating through Shell Structure on Vibration Energy Flow

Shell structures are often employed in mechanical structures from viewpoints of light weight and high rigidity. Typical vibration countermeasures in mechanical structures are a direct damping of the vibration energy source and cutting off transmission paths of the main vibration energy. It is necessary to identify vibration transmission paths in either case of them. The Vibration Intensity (VI or Structure Intensity: SI) method is one of the techniques to visualize vibration transmission paths. In the vibration transmission in curved shells, the extensional wave occurs in addition to the flexural wave, which directly affects the noise from the shell. Previous researches reported that the extensional wave little affects the noise but interacts with the flexural wave in the curved shell and shows complicated transmission paths of the vibration energy. However, there are still unknown characteristics of vibration transmission paths in the curved shell. The purpose of this research is to elucidate the characteristics of vibration transmission paths in curved shells by VI method. The finite element method analysis was conducted for L-shaped shells consisting of two flat parts I and II and a curved part between the flat parts. The curvature radius ranged from 20 to 100 mm. The flat part I was excited in the out-plane direction by a sine wave with the amplitude of 1 N. The excitation frequency was varied from 10 to 3000 Hz. The results of the flexural VI and extensional VI show that effects of extensional wave propagating in Curve part on vibration energy flow is lager for smaller curvature radius.