Experimental Study on the Vibration Transfer Function of a Small Autonomous Underwater Vehicle

Abstract

This paper presents the experimental results about vibration characteristics of a small autonomous underwater vehicle (AUV) named OKPO 300. The autonomy of AUVs leads to the increased use of AUVs in scientific, military, and commercial areas because their autonomy makes it possible for AUVs to be utilized instead of humans in hazardous missions such as mine countermeasure missions (MCMs). It is impossible to use devices with electro-magnetic waves for gathering information in an underwater environment. Only sonar systems that use sound waves can be utilized underwater, and the performance of sonar can strongly affect the autonomy of AUVs. Since a thruster system that combines a motor and propeller in a single structure is widely used as the propulsion system of an AUV and is mounted on the outside of the AUV’s stern, the vibration generated by the thruster system can be transferred throughout the shell of the AUV from the stern to the bow. The transferred vibration can affect the performance of various sonar systems that are installed in the AUV such as side-scan sonar or forward-looking sonar. Therefore, it is necessary to identify the effect of the transferred vibration of the AUV on the sonar systems. Even if various numerical methods were used to analyze the vibration problem of surface ships, it would be hard to apply numerical methods of the surface ships to identify the vibration phenomena of an AUV because of the underwater environment. In this work, an experimental study with OKPO 300 and an impact hammer was carried out to analyze vibration features of an actual small AUV in the air. Based on the experimental results, the frequency response function of vibration is presented. Based on the experimental results of this study, the natural frequency of OKPO 300 was confirmed, and the possibility of estimating the vibration characteristics of AUV using the transfer function method was shown.