Toward an improved understanding of thruster dynamics for underwater vehicles

Abstract

IntroductionThis paper proposes a novel approach to As the use of Remotely Operated modeling the four quadrant dynamic response Underwater Vehicles becomes more of thrusters as used for the motion control of widespread and their tasking more complex ROV and AUV underwater vehicles. The in deeper waters, there is a need to free the significance is that these vehicles are small in vehicle from the power and signal tether, and size and respond quickly to commands.to increase both the level of control autonomy Precision in motion control will require and the maneuvering precision of these further understanding of thruster performance underwater robots. In a recent paper, Yoerger than is currently available. The model et. al. (1990) point out that Underwater includes a four quadrant mapping of the Vehicle thrusters must be properly modeled if propeller blades lift and drag forces and is good results are to be obtained for the vehicle coupled with motor and fluid system motion control. Thrusters are comprised of dynamics. A series of experiments is propellers driven by a motor -the usual way described for both long and short period in which ships have been propelled through triangular, as well as square wave inputs.the seaway since the days of commercial The model is compared favorably with sailing ships. However, while there is a long experimental data for a variety of differing history of theoretical research, experimental conditions and predicts that force overshoots validation and practical experiential are observed under conditions of rapid knowledge concerning the performance of command changes. Use of the model will ships propellers, the issues relating to the improve the control of dynamic thrust on control of Remotely Operated Vehicles these vehicles.(ROVs) and Autonomous Underwater Yoerger et. al. [I], developed a lumped parameter model of the dynamic response of an ROV thruster that went beyond the popular notion that, for a given unit with fixed pitch blading, thrust and input torque are related to the modified square of the propeller rotational rate and the angle of advance.They introduced the idea that fluid momentum considerations in the thruster shrouding area gives rise to a time lag in the response of thrust to stepwise inputs of motor torque. Experimental results under steady state conditions for single quadrant operation certainly verified the well known square law relationship between thrust and propeller rotational speed, and it did appear that the thrust response had long lag times at low thrust levels. However, little details were provided of the actual experimental thrust data under varied experimental conditions. For instance, dynamic energy balance arguments were applied but dynamic momentum arguments were ignored in the formulation of the thrust equation. Also, an instantaneous relationship between propeller rotational rate and the lumped parameter measure of flowrate was used which cannot be supported in reality.We believe that such a model is still insufficient to understand th...

Modelling Tunnel Thrusters for Autonomous Underwater Vehicles

“…The authors tested the performance of the thruster in three different operating modes, namely, forward travel, low speed manoeuvring, and high speed turning. The basis model used was similar to that developed in (1) (Healey et al, 1995). It was found that the dynamic performance of the thruster was not significantly altered by the operating mode of the vehicle, however the steady state performance was affected.…”

“…These relationships are combined with a model of the motor and blade element relations such that an example model can be summarised as (Healey et al, 1995):…”

Dynamic Positioning of Underwater Robotic Vehicles with Thruster Dynamics Compensation

“…In later works [2,10,12], more accurate models employing lift and drag curves, and that also incorporate some However, considering recent experimental results, marine thrusters may also exhibit non-smooth nonlinearities such as dead-zones. A dead-zone is a hard nonlinearity, frequently encountered in many industrial actuators, and its presence can drastically reduce control system performance and lead to limit cycles in a closed-loop system.…”

“…Many of these works [12,[25][26][27] address the problem of the influence of thruster dynamics on overall vehicle behaviour, and the importance of considering this effect in the dynamic positioning system. Traditionally, some mathematical models of the thruster are used directly to estimate, in a feed-forward manner, the required voltage (or current) to produce the desired thrust force.…”

Preliminary Simulation Studies of a New Four-Quadrant Propeller Thrust Controller Applied to Underwater Vehicles

“…The precision and complexity of the required tasks need an increase of the maneuvering accuracy and the propulsion system plays a key role in the achievement of the missions. Thruster modeling and control has been subject to a growing interest in the last years (Yoerger et al 1990), (Healey et al 1995), (Whitcomb and Yoerger 1995), (Fossen and Blanke 2000), (Bachmayer et al 2000), (Smogeli 2006) and (Pivano et al 2007). The primary objective of low level thruster control is to obtain the desired thrust from the propeller regardless the environmental state.…”