Luca Pivano

A Four-Quadrant Thrust Estimation Scheme for Marine Propellers: Theory and Experiments

A thrust estimation scheme for marine propellers that can operate in the full four-quadrant range of the propeller shaft speed and the vessel speed has been developed. The scheme is formed by a nonlinear observer to estimate the propeller torque and the propeller shaft speed and by a mapping to compute the thrust from the observer estimates. The mapping includes the estimation of the propeller advance ratio. The advance speed is assumed to be unknown, and only measurements of shaft speed and motor torque have been used. The robustness of the scheme is demonstrated by Lyapunov theory. The proposed method is experimentally tested on an electrically driven fixed pitch propeller in open-water conditions, in waves and with a wake screen that scales the local flow down in order to simulate one of the effects of the interaction between the propeller and the vessel hull.

Nonlinear Thrust Controller for Marine Propellers in Four-Quadrant Operations

In this paper a nonlinear thrust controller for a marine propeller in four-quadrant operations is presented. It is a shaft speed controller where the desired velocity is computed based on the desired propeller thrust and on the torque losses, estimated with a nonlinear observer. Experimental results are provided to demonstrate the effectiveness of the controller. The proposed scheme shows improved performance in thrust production when compared to traditional shaft speed and torque control.

Marine Propeller Thrust Estimation in Four-Quadrant Operations

This paper proposes a scheme for thrust estimation of a marine propeller over the full four-quadrant range of propeller shaft speed and vessel speed. Based on shaft speed and motor torque measurements, the scheme involves a nonlinear observer for the propeller torque that shows stability and robustness for hounded modeling and measurement errors. The propeller thrust is computed as a static function of the propeller torque. The performance has been demonstrated in experimental tests

NONLINEAR MODEL IDENTIFICATION OF A MARINE PROPELLER OVER FOUR-QUADRANT OPERATIONS

Abstract This paper proposes a nonlinear dynamics model for a marine propeller able to reproduce the propeller thrust over the full four-quadrant range of propeller shaft speed and vessel speed. A two-state model has been identified from experimental data. The model includes a state equation for the propeller shaft speed and one that describes the dynamics of the axial flow velocity. The model reproduces accurately propeller thrust and torque over a wide range of operation.

A Four-Quadrant Thrust Controller for Marine Propellers with Loss Estimation and Anti-Spin

In this paper a nonlinear thrust controller for fixed pitch marine propellers with torque loss estimation and an antispin strategy is presented. The controller, designed to operate in the four-quadrant plane composed by the shaft speed and the vessel speed, is a combination of a thrust controller developed for calm/moderate sea states and an anti-spin strategy to reduce power peaks and wear-and-tear in extreme sea conditions. The thrust controller aims at producing the demanded thrust independently from the propeller losses. The anti-spin algorithm lowers the shaft speed once large torque losses are detected and increases the shaft speed to normal when the loss situation is considered over. The torque losses are estimated with a nonlinear observer. The performance of the proposed controller is validated by experiments carried out in a towing tank.

AN EFFICIENCY OPTIMIZING PROPELLER SPEED CONTROL FOR SHIPS IN MODERATE SEAS - MODEL EXPERIMENTS AND SIMULATION

Abstract Ships in moderate sea experience time-varying thrust and torque load on the shaft of their prime mover. The reason is the varying inflow velocity to the propeller during the passage of a wave. This variation has been considered a nuisance to the main engine control where the induced fluctuations in torque, shaft speed and power have been suppressed by some control schemes and ignored in others. This paper shows how the fluctuation in inflow velocity can be utilized to increase the average efficiency of propulsion in waves without reducing the vessel speed. A nonlinear controller is proposed that is shown to theoretically enhance the propulsion efficiency. Model tests determine dynamic characteristics of propellers in waves and a simulation is employed to validate the novel control scheme.

A MODEL-BASED OCEAN CURRENT OBSERVER FOR 6DOF UNDERWATER VEHICLES

Abstract The problem of ocean current estimation for 6DOF underwater vehicles is considered in this paper. A model-based observer for ocean current estimation is proposed and it is shown how the performance of underwater vehicles can be improved by incorporating the ocean current estimates in the controller. The results are illustrated with a simulation case study with the HUGIN AUV.

INTEGRATOR RESET ANTI-SPIN FOR MARINE THRUSTERS OPERATING IN FOUR-QUADRANTS AND EXTREME SEA CONDITIONS

Abstract Transient regimes arise when the propeller of a ship is operating in extreme seas, where ventilation and in-and-out of water effects results in loss of propeller thrust. By introducing Lyapunov based controller state reset, the performance in transient regimes may be increased without influencing the performance in calm seas. Improvements have been presented previously for dynamically positioned (DP) vessels. Transit operations, however, introduces additional losses due to variations in the propeller advance velocity. The controller in this paper combines an existing shaft speed reference generator that uses an estimate of the propeller torque losses with a PI shaft speed control law with integrator reset. Moreover, an anti-spin strategy is included to be able to operate also in extreme seas. The method is experimentally validated in a towing tank.

PRELIMINARY SIMULATION STUDIES OF A NEW FOUR-QUADRANT PROPELLER THRUST CONTROLLER APPLIED TO UNDERWATER VEHICLES

Abstract In this paper a recently reported four-quadrant nonlinear thrust controller for marine propellers is applied to the velocity control of an underwater vehicle. The controller, designed for fixed pitch electrically driven propellers, is based on a shaft speed control and employs an estimate of the propeller torque loss. A simulation study is performed in order to compare the presented approach with the conventional shaft speed and torque propeller controllers.