Experimental study on load characteristics of vehicle during high-speed water entry

During the process of high-speed water entry, the vehicle will bear large loads. Obtaining and analysing the time-frequency characteristics of loads is of great engineering significance for the protection of shell and equipment. The high-speed camera is used to capture the evolution of cavity and the accelerometer is used to collect the acceleration of model during water entry. The time-frequency characteristics of acceleration are obtained based on the short-time Fourier transform and discrete wavelet transform. The results indicate that the cavity exhibits an asymmetric shape and shrinks near free surface during the oblique high-speed water entry. When the cavity undergoes closure and collapse, the collapsing order of the upper and lower parts is opposite. Through the short time Fourier transform, it was found that the loads contain components of different frequency at different periods. When the model collides with free surface, the frequency contained in acceleration are more complex, reflecting the complexity of mechanical environment. The discrete wavelet transform is used to extract the components with more time-resolution and obtain the relative energy of each component. It is found that the relative energy of low-frequency components increases with the increase of water entry speed.