Sensitivity Analysis of the Turning Motion of an Underwater Glider on the Viscous Hydrodynamic Coefficients

Autonomous underwater gliders (AUG) are a class of underwater vehicles that move using a buoyancy engine and forces from wings. Gliders execute turning motion with the help of a rudder or an internal roll control mechanism and the trajectory of the turn is a spiral. This paper analyses the sensitivity of the characteristics of spiral manoeuvre on the hydrodynamic coefficients of the glider. Based on the dynamics model of a gliding fish whose turn is enabled by a rudder, the effect of hydrodynamic coefficients of the hull and the rudder on the spiral motion are quantified. Local sensitivity analysis is undertaken using the indirect method. The order of importance of hydrodynamic coefficients is evaluated. It is observed that the spiral path parameters are most sensitive to the side force created by the rudder and the effect of the drag coefficient is predominant to that of the lift coefficients. This study will aid in quantifying the effect of change of geometry on the manoeuvrability of AUGs

Effect of water current on underwater glider velocity and range

An autonomous underwater glider speed and range is influenced by water currents. This is compounded by a weak actuation system for controlling its movement. In this work, the effects of water currents on the speed and range of an underwater glider at steady state glide conditions are investigated. Extensive numerical simulations have been performed to determine the speed and range of a glider with and without water current at different net buoyancies. The results show that the effect of water current on the glider speed and range depends on the current relative motion and direction. In the presence of water current, for a given glide angle, glide speed can be increased by increasing the net buoyancy of the glider

Numerical investigation on the hydrodynamic characteristics of an autonomous underwater glider with different wing layouts

An autonomous underwater glider is a self-propelled underwater vehicle which is designed primarily for oceanography. It moves with low speed in saw-tooth pattern and has long endurance. The vertical motion of the glider is controlled by changing its buoyancy and its wings convert this vertical motion into horizontal motion. The hydrodynamic coefficients of glider will dictate its performance and possible applications. In this paper, the impact of rectangular and tapered wings on the hydrodynamics coefficient of a glider and the corresponding glide velocity was investigated using ANSYS Computational Fluid Dynamics (CFD) turbulence model and FLUENT flow solver. The lift force of a rectangular wing is higher with less drag force compared to tapered wings. A glider with tapered wings glider will have a larger glide angle and is therefore suitable of deep ocean applications

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

Numerical Study of the Effect of Wing Position on Autonomous Underwater Glider

 Autonomous underwater gliders are a class of underwater vehicles that transit without the help of a conventional propeller. The vehicle uses a buoyancy engine to vary its buoyancy and with the help of the wings attached executes its motion. The hydrodynamic characteristics of the vehicle affect the longitudinal and turning motion. This paper discusses the effect of the wing’s position on the vehicle’s lift and drag characteristics. Computational fluid dynamics (CFD) tool is used to estimate the lift, drag, and pitching moment coefficients of the vehicle. The numerical methodology is validated using flow over NACA0012 wing results for low Reynolds numbers, and the results of CFD are discussed for possible application in estimation of glider motion

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

Effect of wing form on the hydrodynamic characteristics and dynamic stability of an underwater glider

We are developing a prototype underwater glider for subsea payload delivery. The idea is to use a glider to deliver payloads for subsea installations. In this type of application, the hydrodynamic forces and dynamic stability of the glider is of particular importance, as it has implications on the glider's endurance and operation. In this work, the effect of two different wing forms, rectangular and tapered, on the hydrodynamic characteristics and dynamic stability of the glider were investigated, to determine the optimal wing form. To determine the hydrodynamic characteristics, tow tank resistance tests were carried out using a model fitted alternately with a rectangular wing and tapered wing. Steady-state CFD analysis was conducted using the hydrodynamic coefficients obtained from the tests, to obtain the lift, drag and hydrodynamic derivatives at different angular velocities. The results show that the rectangular wing provides larger lift forces but with a reduced stability envelope. Conversely, the tapered wing exhibits lower lift force but improved dynamic stability

Variable Gain Super Twisting Sliding Mode Control (VGSTW) application in longitudinal plane of Autonomous Underwater Glider (AUG)

This paper presents a robust control design using variable gain super twisting sliding mode control application in Autonomous Underwater Glider (AUG). AUGs are known as underactuated systems and very nonlinear in nature make difficult to control. The controller is designed for longitudinal plane of an AUG that tracks the pitching angle and net buoyancy of a ballast pump for nominal system, system in existence of external disturbance and parameter variations in hydrodynamic coefficients. The Lyapunov stability theorem has proved that the proposed control law is satisfied the stability sufficient condition. The simulation results have shown that the proposed controller has improved the transient response, reduced steady error and chattering effects in control input and sliding surface in all cases

Variable Gain Super Twisting Sliding Mode Control (VGSTW) application in longitudinal plane of Autonomous Underwater Glider (AUG)

904-913This paper presents a robust control design using variable gain super twisting sliding mode control application in Autonomous Underwater Glider (AUG). AUGs are known as underactuated systems and very nonlinear in nature make difficult to control. The controller is designed for longitudinal plane of an AUG that tracks the pitching angle and net buoyancy of a ballast pump for nominal system, system in existence of external disturbance and parameter variations in hydrodynamic coefficients. The Lyapunov stability theorem has proved that the proposed control law is satisfied the stability sufficient condition. The simulation results have shown that the proposed controller has improved the transient response, reduced steady error and chattering effects in control input and sliding surface in all cases

Justification for the Body Construction Selection of the Unmanned Uninhabited Underwater Apparatus

The paper explores the possibility of creating an underwater apparatus in the form of a body of rotation. The form of the device will allow to effectively examine the found underwater objects, the bottom topography, measurement of other parameters of the underwater environment or objects. The devices of a different streamlined body form are considered. The apparatus in the form of a rotation body is proposed. The geometric shape of the proposed apparatus, the system of motion and control are investigated. Methods for calculating the motion parameters, methods for the vehicle positioning in the flow and the underwater vehicle movement in the vertical plane are proposed. The study confirms the ability of the underwater vehicle to move under water in a horizontal and vertical directions. The study confirms that the device possess stability at rectilinear motion, good turning ability and at the same time it is able to position itself during the flow