Underwater Glider Modelling And Analysis For Variable Control Parameters

Underwater glider is a type of autonomous underwater vehicle that can glide by controlling their buoyancy and attitude using internal actuators. By changing the vehicle’s buoyancy intermittently, forward motion can be achieved. Deriving the mathematical model directly from the system can be too complicated due to time constraints in prototyping development processes. This thesis presents the early development of the USM underwater glider platform consist of prototype development involves vehicle concept design using SolidworksTM, vehicle simulations by Computational Fluid Dynamics (CFD) and alternative way of modelling known as system identification in order to obtain the underwater glider system model. The appropriate control parameters for underwater glider control were determined by selecting the ballast rate as the input. Three aspects of the dynamics of a glider will be observed, i.e. net buoyancy, depth of the glider and pitching angle. The best three parametric models that are able to estimate the system correctly are chosen, and the fit between measured and estimated outputs is presented in order to get an optimal underwater glider vehicle model for USM underwater glider platform

Modeling And Identification Of An Underwater Glider.

Underwater gliders are type of autonomous underwater vehicle that glide by controlling their buoyancy and attitude using internal actuators

Nonlinear robust integral sliding super-twisting sliding mode control application in autonomous underwater glider

1016-1027The design of a robust controller is a challenging task due to nonlinear behaviour of the glider and surround environment. This paper presents design and simulation of nonlinear robust integral super-twisting sliding mode control for controlling the longitudinal plane of an autonomous underwater glider (AUG). The controller is designed for trajectory tracking problem in existence of external disturbance and parameter variations for pitching angle and net buoyancy of the longitudinal plane of an AUG. The algorithm is designed based on integral sliding mode control and super-twisting sliding mode control. The performance of the proposed controller is compared to original integral sliding mode and original super-twisting algorithm. The simulation results have shown that the proposed controller demonstrates satisfactory performance and also reduces the chattering effect and control effort

DEVELOPMENT AND MODELLING OF UNMANNED UNDERWATER GLIDER USING THE SYSTEM IDENTIFICATION METHOD

This paper describes a comparison study for the modelling of the unmanned Underwater Glider (UG) using system identification techniques based on two experimental set up. The experimental data obtained from lab tank test and pool test to infer model using a MATLAB System Identification toolbox. The experimental testing of UG only considered the horizontal movement or called as auto-heading. The modeling obtained will be used to design the suitable controller for heading control. The UG will be tested on an open loop system to obtain measured input-output signals. Input and output signals from the system are recorded and analyzed to infer a model using a System Identification MATLAB toolbox. Two models obtained based on data tabulated and verify using mathematical modelling of UG. The parameter of UG come up from the real model of UG and Solidworks software. The Underwater Lab Tank model has better performance which has faster rise time and settling time than swimming pool model and mathematical model

A New Roll and Pitch Control Mechanism for an Underwater Glider

In this paper, a new roll and pitch control mechanism for an underwater glider is described. The mechanism controls the glider’s pitch and roll without the use of a conventional buoyancy engine or movable mass. It uses water as trim mass, with a high flow rate water pump to shift water from water bladders located at the front, rear, left, and right of the glider. By shifting water between the left and right water bladder, a roll moment is induced. Similarly, pitch is achieved by shifting water between the front and rear water bladders. The water bladders act not only as a means for roll and pitch control but as a buoyancy engine as well. This eliminates the use of a dedicated mechanism for pitch and roll, thereby improving gliding efficiency and energy consumption, as the glider's overall size is decreased since the hardware required is reduced. The dynamics of the system were derived and simulated, as well as validated experimentally. The glider is able to move in a sawtooth pattern with a maximum pitch angle of 43.5˚, as well as a maximum roll angle of 43.6˚ with pitch and roll rates increase with increasing pump rate

Design and MATLAB Simulation of Pitch Motion System Controller for Underwater Vehicle

Underwater vehicle is an important machine nowadays. It can perform multiple underwater complex tasks. For example, pipelines detection or mapping, underwater terrain exploration and underwater inspections. Due to rotation of the thruster at back of most underwater vehicle, it causes disturbances of fluid around the vehicle and affect the stability of the vehicle. Thus, a control system for the motion of the vehicle should be designed to compensate the instability. However, in this project the focus is directed to design a PID controller for one degree of vehicle’s motion which is pitch motion. The study is based on NPS AUV II which is an underwater vehicle. Recently, there are many researches related to underwater vehicle’s motion controller

Development and Modelling of Unmaned Underwater Glider using the System Identification Method

This paper describes a comparison study for the modelling of the unmanned Underwater Glider (UG) using system identification techniques based on two experimental set up. The experimental data obtained from lab tank test and pool test to infer model using a MATLAB System Identification toolbox. The experimental testing of UG only considered the horizontal movement or called as auto-heading. The modeling obtained will be used to design the suitable controller for heading control. The UG will be tested on an open loop system to obtain measured input-output signals. Input and output signals from the system are recorded and analyzed to infer a model using a System Identification MATLAB toolbox. Two models obtained based on data tabulated and verify using mathematical modelling of UG. The parameter of UG come up from the real model of UG and Solidworks software. The Underwater Lab Tank model has better performance which has faster rise time and settling time than swimming pool model and mathematical model.

Fault-Tolerant Control For A Remotely Operated Vehicle (Rov) Propulsion System

Remotely Operated Vehicle (ROV) propulsions system is frequently exposed to harsh operating and underwater environments. Faults and undesired working conditions contribute to performance degradation thus repair actions are required. Stop of operation causes operational cost to increase. Therefore, a Fault-Tolerant Control System (FTCS) is introduced to deal with this situation. This method aims to ensure reliability, sustainability and safety of a dynamical system. This thesis presents a fault-tolerant control specifically designed for ROV electric propulsion system with brushed DC motor thrusters. There are two components in FTCS which are the Fault Detection and Diagnosis (FDD) and Controller Re-Design (CRD). The FDD is done by monitoring two thruster parameters i.e. armature voltage and current load and compare between actual and reference process parameters. Via statistical design of experiment techniques, an offline experiment is performed to simulate possible event of faults. Analysis of variance (ANOVA) methods such as two-factor factorial design and Tukey’s Kramer rule are used to analyze the faults and provides the reference model to implement the controller re-design i.e. fault accommodation. A Takagi-Sugeno (T-S) fuzzy system is used to design the fault accommodation and ROV motion controller. The FTCS method has been tested in fresh water pool and proved to be fast in handling the thruster faults. It takes about 500 ms for a fault in a single thruster to be detected, isolated and new thruster command to be initiated. The FTCS method causes the ROV degree of freedom (DOF) to be reduced to a minimum but the ROV still able to continue the operation

Observer Design For Underwater Glider

Underwater gliders have numerous advantages over the conventional underwater vehicles in oceanographic applications. Gliders offered long duration and long range missions with low energy consumption. Internal actuation design protected actuators from ocean environment and have higher durability. Autonomous control strategies and path planning have been proposed by researchers. Controller for glider system required information from the system sensed outputs to perform closed-loop system. However some of the system states are difficult and unable to be measured during underwater and they are needed to be estimated. Presently the glider states estimation are based on assumption of constant angle of attack, pitch angle and so on. But this states estimation technique is lack of accuracy. To overcome this, linear observer has been proposed to estimate the unmeasured states and improved the estimation accuracy. However the states estimation by linear observer is only accurate for observation on linear model with motion close to equilibrium glide. For states estimation on nonlinear dynamic and all glide path aspect, nonlinear glider model based observer design is desired

Study on Structural and Hydrodynamics of Autonomous Underwater Gliders

Underwater gliders are autonomous underwater vehicles that use buoyancy to convert horizontal to vertical displacement to propel underwater. The most famous and common AUGs in the market are Slocum, Seaglider, Spray, and LiberdadeXray. All these gliders serve at different operating depth and payload. However, external forces and hydrodynamic forces are important to define the operational capacity of an AUG. Experimentally, it is expensive and difficult to determine the behaviour of structural and hydrodynamic forces. Therefore simulation is used to optimize the structural and hydrodynamics of the AUGs. There are two types of analysis proposed to compare both Slocum and Seaglider which are structural FEA and hydrodynamic CFD analysis. For structural FEA analysis, CATIA Dessault software is used meanwhile ANSYS FLUENT is used to analysis hydrodynamic performance of these AUGs. For the structural analysis, FEA modelling has been used to test the Von Mises stress and buckling of three types of materials on the AUGs hull body. On the other hand, hydrodynamic performance of the AUGs are tested to interpret the coefficient of lift, coefficient of drag and lift to drag ratio generated on Slocum and Seaglider at different angle of attacks (-15° − +15°). For this project, these findings are to be compared between the chosen gliders based on structural and hydrodynamic performance. From structural perspective, it is found that Seaglider has better hull body performance compared to Slocum because Seaglider is designed at thicker hull thickness and higher buckling resistance compare to Slocum. Based on hydrodynamic performance, Seaglider also has higher performance than Slocum because Seaglider produced less drag and higher lifted when simulated at different angles of attacks. This is because an AUG shape greatly influences its hydrodynamic performance. Seaglider has shape more closely to NACA airfoil design which performs to have less drag and higher lift