# Frequency Sensitivity and Mode Characteristics of Body Structure for a Piezoelectric-Based UUV
## 1 Introduction  
Unmanned underwater vehicles (UUVs) have been widely used in areas such as oceanographic surveys, underwater detection, undersea rescue, etc. [1; 2; 3]. Significant research progress has been made by researchers from all over the world in the investigation of UUVs. A Manta Test Vehicle (MTV) was built as the prototype of a new class of UUVs. This unit had complete nonlinear dynamics and control systems [4]. To support undersea mine hunting, a UUV named REDERMOR has been proposed to test different concepts of mine hunting. Meanwhile, the REDERMOR II is able to execute missions lasting several hours in autonomous mode [5]. In addition, a design methodology and a software module have been proposed for application to the design and manufacture of a stiffened pressure vessel, which can be mounted on a 6000 m class deep-sea unmanned underwater vehicle [6]. [PERSON] et al. [7] have presented the details for an automatic vision-based system for UUV station keeping. The station keeping system is based on a feature-based motion detection algorithm, which exploits standard correlation and explicit textural analysis to solve the correspondence problem. The following year, [PERSON] et al. [8] proposed an intelligent navigation system for a UUV powered by renewable energy. This vehicle was designed for shadow water inspection during missions of a long duration. The proposed vehicle is a useful tool for monitoring large areas of the sea, and it has been used to monitor the Mar Menor lagoon. The same year, [PERSON] et al. [9] designed a bio-robotic unmanned underwater vehicle, and a new accurate model for calculating the fluid dynamics of flap-ping hydrofoil was used to simulate the motion of this vehicle. The results indicated that the bio-robotic UUV has excellent maneuverability at low velocity. The purpose of this vehicle is for navigation over longperiods and large distances. To address the energy demands of long continuous operations, a rocking energy generation device based on wave energy is proposed [10]. Recently, significant advances in the development of UUV have been achieved. [PERSON] et al. [11] developed a method for a robust H-infinity control of a UUV based on the interpolation of the solution of the Riccati equation. The results showed that the controllers were feasible, effective, and robust for managing the control of the UUV. To address the navigation accuracy problems of multi-unmanned Underwater Vehicles (multi-UUVs) in the polar region, a polar cooperative navigation algorithm for multi-UUVs was proposed, which took communication delays into consideration. The results demonstrated that this proposed polar cooperative navigation algorithm can effectively navigate multi-UUVs in the polar region [12]. In addition, [PERSON] et al. [13] gave a comparative experimental evaluation of one model-free proportional-derivative (PD) three degree-of-freedom (DOF) controller and two model-based three-DOF controllers, that were designed to facilitate low-speed, neutral buoyancy, and fully actuated underwater vehicles capable of performing trajectory tracking in the X, Y directions to heading DOFs. The investigation on the UUV produced numerous valuable results. However, large amounts of wave energy are typically wasted during the operation of these vehicles. Hence, a novel piezoelectric-based UUV is proposed in this report that can facilitate piezoelectric energy harvesting as well as piezoelectric vibration reduction. Although the piezoelectric-based UUV has not been investigated as yet, the piezoelectric energy harvesting has been investigated and utilized by several researchers. [PERSON] et al. [14] developed a bimorph cantilever piezoelectric energy harvester. Experimental validation of the single-mode coupled voltage output and vibration response expressions is presented for a bimorph cantilever with a tip mass. [PERSON] et al. [15] proposed an analytical approach to derive the closed-form mechanical and electrical response expressions of multiple piezo-patch energy harvesters. [PERSON] et al.