Hydrodynamic Forces on Wind Assisted Ships using CFD

Hydrodynamic Forces on Wind Assisted Ships using CFD

Settels, J.W.

Van Terwisga, T.J.C. (mentor)

Mechanical, Maritime and Materials Engineering

Maritime Technology

Ship Hydromechanics

2015-06-26

With the fluctuating fuel oil prices and increasing environmental awareness more and more attention is given to durable ways of shipping cargo around the world. Reducing fuel consumption by using wind as a source of auxiliary propulsion is one way to achieve that goals. Different projects utilising Wind Assisted Ship Propulsion (WASP) have been investigated and/or realised in the past years. Since these devices often don’t exert the propulsive force in line with the sailed course a leeway angle is introduced, which influences the hydrodynamic forces. This thesis focusses on predicting the sail induced hydrodynamic forces on a coastal cargo vessel under stationary leeway angleswith the RANS solver ReFRESCOat model scale. The ship was modelled in three distinct modelling steps: The bare hull without appendages and propeller, the appended hull without propeller and the appended hull with propeller, implemented through a RANS-BEM coupling. All configurations were calculated for a range of (small) leeway angles in a double body set up, neglecting free surface effects. The appended configurations were calculated with different rudder angles and different thrust ratios relative to the thrust required at the self propulsion point of the model. Furthermore a grid refinement study was performed for the bare hull configuration to estimate the numerical uncertainty of the obtained results. The bare hull configuration and the appended configuration with implemented propeller were compared to available model test data obtained from available towing tank test results. From the grid refinement study on the bare hull a high numerical uncertainty became apparent for the lateral force and yawing moment. Visualisation of the calculated flow around the hull revealed an increase in vortex intensity and a change in location of the shed vortices for grids with increasing cell density. The bare hull longitudinal force was not validated. The lateral force and yawing moment were validated with a high validation uncertainty. The calculated bare hull forces on the grid with highest cell density show an under prediction prediction of the longitudinal force, which can be explained by the omission of wavemaking drag in the calculations due to the double body set-up. The lateral force is under predicted while the yawing moment is over predicted. The lift and drag due to leeway shows good agreement with the results up to six degrees of leeway but are under estimated for leeway angles of nine degrees. This indicates that asymmetric wave profiles due to leeway contribute to these forces and cannot be captured by a double body set-up. The lateral centre of effort is predicted too far forward but the trend with respect to leeway was captured. For the appended condition with implemented propeller good agreement between the calculated and measured values for the lift due to leeway was found with comparison error for higher rudder angles. The drag due to leeway showed good agreement with the measured results with higher comparison errors for lower thrust ratios. All calculations showed an over prediction of the longitudinal position of the centre of effort of the lateral force. Higher thrust ratios and higher rudder angles showed greater under prediction of lateral force and over prediction of the yawing moment, which was likely caused by the incapability of the model to calculate the increased turbulence in the propeller wake, influencing the forces on the aft part of the hull and rudder. The rudder force in longitudinal direction showed values of up to the same magnitude of the force generated by the hull for higher angles of attack on the rudder. The lateral force produced by the propeller due to leeway was found to be negligibly small in comparison to the lateral force produced by the hull and rudder.

CFD
RANS
sail-assisted
leeway

http://resolver.tudelft.nl/uuid:b8276e19-acf7-4c29-8203-d09d6922e1ad

2020-05-26

Student theses

master thesis

(c) 2015 Settels, J.W.