1. Causes of added resistance in waves Unfavourable shifts in buoyancy forces causing heaving and pitching. This absorbs energy both from the waves themselves but also from the ships momentum causing speed loss. Reflection of incident waves at the bow Disturbances of the flow around the hull causing boundary layer distortion and poor propeller performance Background Predicting the power needed to achieve the designed service speed in the actual conditions experienced on the intended route has always been an issue for ship designers. The subject is complex and there has been no conclusive study able to give a solution to the above issue Designers therefore tend to use prescriptive percentage additions to the calculated still water resistance based on experience, e.g. +25% for North Atlantic trades, +15% for coastal operations. Older studies by Maruo [1], Gerritsma & Beukelmann [2] and Faltinsen[3] have successfully described the global phenomena giving rise to added resistance and is able to predict it well for certain sea states. No method however is able to predict it over a wide range of sea states. Because the limit of what can be done analytically to model the whole phenomenon of added resistance seem to have been reached, later studies have focused more on more detailed apects. However, there is a strong indication that coupling between different phenomena plays a major role in understanding why some methods work and others don’t in certain conditions. With developments in computing power and open source RANS-based CFD software it is possible to use large scale CFD simulations to study the behaviour of ships in waves with a high level of detail. The influence of surface waves on the added resistance of merchant ships Björn Windén - b.winden@soton.ac.uk-, Supervised by D.A. Hudson and S.R. Turnock Fluid Structure Interactions Research Group Acknowledgement This project is supported by funds from the Lloyd’s Register Educational Trust, through the Lloyd’s Register University Technology Centre FSI Away Day 2012 References 1.Maruo H, The excess resistance of a ship in rough seas, International shipbuilding progress, vol 4, No 35, 1957 2.Gerritsma J & Beukelman W, Analysis of the resistance increase in waves of a fast cargo ship, International shipbuilding progress, vol 19, No 217, 1972 3.Faltinsen O.M, Minsaas K.J Liapis N & Skjordal S.O, Prediction of resistance and propulsion of a ship in a seaway, Proc. 13th symposium of naval hydrodynamics, 1980 Experimental study Has shown that there might be an effect of viscous phenomena on added resistance something that has not yet been confirmed in the literature. Figure 1 (a) shows the added resistance at three different periods of encounter and at different forward speeds. In Figure 1 (a) When T e =0.7 the resistance grows with speed due to resonance. The decrease in added resistance for higher speeds at other T e could be explained by increased viscous damping. This is supported by a measured increase of the decay rate in heave with speed for the same hull (b). A large amount of data in regular and irregular waves has been gathered for CFD validation. Aims To validate the open source CFD-package OpenFOAM © for predictions of added resistance in waves. To conduct new towing tank experiments focusing on areas not previously addressed to support this validation. To use results from OpenFOAM © and the experiments to highlight important phenomena giving rise to added resistance. To use this information to test how new bow designs could reduce added resistance in waves. Figure 1a b CFD study Has started with a validation study against a fixed Wigley hull in waves to evaluate how the phase and amplitude of the added forces are predicted. This has proven to be problematic in previous studies. Has investigated how best to design the mesh to capture wave propagation and ship-wave interaction without using excessive numbers of cells. Has created modified multiphase solvers to deal with wave damping at domain outlet. Future focus To continue to add complexity to the CFD model and monitor the errors arising from each step to get a better understanding of how best to model ships in waves. Improve the experiments with more uncertainty analysis and repeated tests to be able to give a confident new contribution to the knowledgebase regarding added resistance. Use acquired knowledge and models to test how the bow shape influences the highlighted aspects of added resistance.