Design of the Depth Controller for a Floating Ocean Seismograph

Haocai Huang,Weiwei Ding,Xinke Zhu,Chenyun Zhang,Guiqing Sun,Hangzhou Wang

doi:10.3390/jmse8030166

Abstract

Floating ocean seismograph (FOS) is a vertical underwater vehicle used to detect ocean earthquakes by observing P waves at teleseismic distances in the oceans. With the requirements of rising to the surface and transmitting data to the satellite in real time and diving to the desired depth and recording signals, the depth control of FOS needs to be zero overshoot and accurate with fast response. So far, it remains challenging to implement such depth control due to the variation of buoyancy caused by the seawater density varying with the depth. The deeper the water is, the greater the impacts on buoyancy are. To tackle it, a fuzzy sliding mode controller considering the influence of seawater density change is proposed and simulated in MATLAB/SIMULINK based on the variable buoyancy system and state space function of FOS. Compared with proportional-integral-derivative (PID) controller, fuzzy PID controller and sliding mode controller, the simulation results indicate that the proposed controller shows its superiority regardless of the disturbing force. Its advantages include smaller steady-state error, faster response time, smaller system chatter, and well robustness. This proves that the designed fuzzy sliding mode controller is able to meet the working requirements and thus, lays a foundation for FOS application.

Highlights

With the development of human science and technology, the exploration process of the ocean is gradually expanding to include deeper depths and more remote locations, and the research on the structure and the internal dynamics of the deep earth has become critical
Its velocity is more stable than the Sliding Mode Controller (SMC) method, which greatly saves its energy consumption. These indicate that in the depth control of floating ocean seismographs (FOS), the performance of fuzzy PID controller and fuzzy sliding mode controller is significantly better than pure PID controller and SMC controller
For the depth control of FOS, its mathematical model has been obtained based on the hydrodynamic equation and on the characteristic parameters of the buoyancy control device with considering the variation of seawater density with depth

Summary

Introduction

With the development of human science and technology, the exploration process of the ocean is gradually expanding to include deeper depths and more remote locations, and the research on the structure and the internal dynamics of the deep earth has become critical. The formation of the ocean seismograph network is of great significance and value to scientific research [5], and floating ocean seismographs (FOS) can exactly realize such value [6]. It is a vertical underwater vehicle used to observe P waves (primary waves, the first signal from an earthquake) in ocean earthquakes [7,8]. Eng. 2020, 8, 166 controller (F-PID) [20,21] and fuzzy sliding mode controller (F-SMC) [22,23]. Lower accuracy and worse quality with simple fuzzy information, have steady-state errors

Dynamic Models

Coordinate Systems and Forces

Depth Controller Design

Simulation ResultsInapnudt vAarniaablleysis

Conclusions