Study On The Motion Control For Underwater Gliders Of Variable Buoyancy Process In The Vertical Plane

As a new type of underwater vehicle,the underwater glider is widely used in marine environment observation,military reconnaissance and other fields due to its advantages of low power consumption and long-range.However,due to the complexity of marine environment and nonlinearity of UG’s dynamic model,it is difficult to establish an accurate model to demonstrate various motion behaviors of the underwater glider currently.To address this problem,the paper develops an accurate dynamic model for the Petrel-II underwater glider,which was developed by Tianjin University.The novel dynamic model decreases the errors between simulated results with sea trial data.Based on that,a control policy with numerical simulation analysis is proved to improve the motion performance of the underwater glider.The main research work and results of this paper are as follows:Based on the motion characteristics of the Petrel-II and the variation of sea water density and pressure at different depths,an accurate dynamic model of underwater glider power is established.This model takes the seawater quality of the front and rear deflector and other water-immersible parts of the underwater glider as part of the quality of the underwater glider itself,and uses the oil out-in movement of the underwater glider as a mass-changing process to change the depth of the seawater.The process of its buoyancy variation is analyzed as a variable buoyancy process,the traditional modeling method is improved,thus a more accurate dynamic model is established.To make the simulation results of underwater glider’s motion more consistent with that working in actual sea test,and to obtain more accurate motion parameters during the simulation process,the paper introduces the ocean current model to improve and modify the underwater glider’s kinematic model.In addition,the displacement of forward and backward movement of the battery pack is used as the input control variable,and the pitch angle is used as the output variable for numerical simulation of the model to verify its effectiveness.Combined with the sea test data,the comparison results show that the simulation test results are in good agreement with the actual test results,which verifies the model’s efficiency.Furthermore,based on the kinematic model simulation considered the influence of the ocean current,the velocity pole diagram curve of the underwater glider is obtained.Combined with the steady-state analysis of the vertical plane of the underwater glider,the graphical method is used to obtain the underwater glider’s control parameters such as optimal gliding angle,pitch angle and pitch rudder displacement in each depth range under the influence of ocean currents.Finally,taking the obtained optimal gliding angle as the control reference variable,and the pitch rudder value as the initial typical rudder value,the PID controller is used to track the pitch angle for motion simulation.The results show that the optimized control strategy can significantly improve the performance of the underwater glider.The single-profile distance and other motion performance verifies the accuracy of each control parameter.