Session: 06-05-04 Marine Hydrodynamics IV

Paper Number: 80816

80816 - Investigating Hull Blockage and Thruster-Hull Effects on an ASD Tug 

The interactions between a vessel’s hull and its propulsor are important to consider, from a design and engineering perspective. The presence of a hull can lead to alterations in flow fields around a propulsor, and may result in significant changes to its propulsive output. For vessels equipped with azimuthing propulsors, these interactions may be compounded due to the ability of such propulsors to direct thrust over a wider sector, even into its own hull. In this study, we examine the interactions between a pair of thrusters and the hull of an azimuthing stern drive (ASD) tug. The coupled thruster and hull interactions can be branched into two categories: hull-on-thruster (or hull-thruster, for short) interactions, and thruster-hull interactions. The former materialises as changes in thruster-inflow properties due to hull-wake effects. The latter is a result of the hull impeding flow from a thruster’s slipstream. This effect is known as blockage and occurs when thruster jets are directed close to or into hull surfaces. For ASD tugs, this could happen when the vessel is reversing or braking, when thruster jets are blowing towards the bow. Thruster-hull effects can also be a result of alterations in flow fields around the hull due to flows emanating from a thruster. An example is when thruster jets accelerate flow behind the stern of a vessel. This further reduces the low pressure around a transom during forward motion, and can result in increase in hull resistance.

In this study, we focus on quantifying thruster-hull effects on the propulsive performance of an ASD tug. A series of model tests were conducted to evaluate these effects using static and dynamic captive tests, in both bare hull and appended hull configurations. The difference in the summated hull and propulsion forces between bare and appended hull tests indicates the degree of thruster-hull interactions. Further, we apply computational fluid dynamics (CFD) to simulate a subset of cases. By doing so we are able to visualise flow fields to better attribute these effects to specific physical phenomena. Results from this study give further insight into physical mechanisms affecting thruster performances in different thruster, hull and flow conditions.

Presenting Author: Lucas Yiew Technology Centre for Offshore and Marine, Singapore

Authors:

Lucas Yiew Technology Centre for Offshore and Marine, Singapore
Bhushan Taskar Technology Centre for Offshore and Marine, Singapore
Yingying Zheng Technology Centre for Offshore and Marine, Singapore
Allan Magee Technology Centre for Offshore and Marine, Singapore