An experimental study on the water entry mechanism of a cylinder with foam cap

The impact force experienced by a vehicle entering water at high speed across media can threaten its structural safety and the stability of its entry trajectory. In order to explore the influence of water entry impact on the structure, the cylinder with a foam head cap was taken as the experimental research object to explore the water entry impact load characteristics of different foam head caps under different water entry speeds and angles. In the experiment, high speed camera technology was used to capture the shape characteristics of the water inlet bubbles of the cylinder with a leading cap, and the bubble features were analyzed based on the Canny edge detection algorithm. At the same time, the water impact load was obtained through the built in accelerometer, and the complementary ensemble empirical mode decomposition method was used for filtering load analysis. By analyzing the images and sensor measurement results of the experimental process, the evolution characteristics of bubbles and the variation rules of acceleration in water entering different speeds, angles, and head shaped cylinders were obtained, and the reasons for these changes were compared. The load reduction effects of different load reduction methods were also compared. The experimental results show that the load on the cylinder entering the water increases linearly with the square of the velocity; the head shape has the most obvious buffering effect on the low speed water entry load of the cylinder. The load reduction effect of the head cap with conical shape reaches 86. 8%, and the load reduction and buffering effect of the conical foam head cap reaches 97%. In addition, the experiment also shows the phenomenon of the tail bubbles gradually falling off after the deep closure of the water entering bubbles of the cylinder, which forms a gradually decreasing pulse load on the cylinder. A polymethacrylimide foam head cap will not change the shape of water entering cavitation, but will make the cavitation wall rough and fuzzy. © 2024 Chinese Vibration Engineering Society. All rights reserved.