Hydrodynamics of Wind-Assisted Ships

Abstract

With fuel oil the main driver for operational expenses, increasingly stringent regulations on emissions of ships and a growing environmental awareness throughout the industry, the concept of Wind-Assisted Ship Propulsion (WASP) presents itself as a means to reduce fuel consumption. Though a promising concept, the performance prediction of a wind-assisted vessel is a complex task involving many physical interactions. As part of a larger research plan on WASP at the Delft University of Technology, this thesis focusses on the hydrodynamic forces on bare hull models at drift angles resulting from the wind-assisted operating conditions. The aim of this study is firstly to show the adequacy of RANS CFD as a numerical tool to estimate the hydrodynamic forces (resistance, side force and yaw moment) for vessels sailing at a drift angle. Secondly, the aim is to deliver a database of hydrodynamic forces for a series of hull forms. This database will ultimately aid in modelling a wind-assisted vessel in a Performance Prediction Programme (PPP). A systematic series of bare hull forms based on one parent hull is constructed by varying draught T, prismatic coefficient Cp and midship section area coefficient Cm. The numerical tool is used to obtain the hydrodynamic forces of all models while three selected models are tested in a towing tank for validation. On the simulation results, regression analysis is performed to arrive at formulations expressing the dependency of these forces on the bare hull form parameters. The validation study shows that the numerical tool captures most hydrodynamic forces sufficiently accurate for use in a PPP tool. With side force most poorly resolved, there is room for improvement however. Using a different turbulence model could provide improvement in this area, albeit at the cost of increased computational time. The formulations obtained by regression show satisfactory robustness for vessels having hydrostatic parameters both within and outside the range of the Delft Systematic Wind-Assisted Series (DSWAS). Unfortunately, the lack of precision of the side force formulation can lead to erroneous results when applied in a PPP.