Wave pattern resistance determined by using a surface-patch of free surface deformations

Ship resistance is the force needed to move a ship at a desired speed in still water. Nowadays, this force is generally provided by diesel engines or turbines and converted into thrust by propellers or water-jets. These engines and turbines need fuel to create this force. In the present days, the amount of used fuel is so important. For this reason, ship's force needs on critical velocities, such as service speed, must be known for a first design phase. Therefore, main engine or turbine, should be selected to provide maximum efficiency. Ship total resistance is generally devided into two parts. One of the resistance component comes from viscous effects and it is known as viscous resistance. The second one is the wave making resistance which is related to energy that is carried by the wave pattern created by ship. Wave-making resistance could be determined mainly by means of two diffrent ways. One way is based on the integration of pressure distribution on the wetted surface of the ship hull. Second one is based on determination of energy carried by ship's wave pattern. Transverse cut method and longitudinal cut methods are the well-known examples of these second kind methods. The idea in these methods is to calculate the energy which passes through a selected control surface – located either in in longitudinal or transverse direction. Both of them have disadvanteges. In order to eliminate these disanvantages, a surface-patch method was proposed by Çalışal et al. (2009). Thus, the aim of the present study is to investigate the surface-patch method in full detail by a series of case studies. In this method, wave resistance term was derived from wave slope data instead of wave heights. Wave slopes of the wave system converge to zero quicker relatively as compared to wave hights. For this reason, it is possible to calculate the wave resistance with relatively smaller x (longitudinal) distances. Surface-patch method has this advantage. In the present study, surface-patch method was employed to calculate the wave-making resistance. Firstly, wave hights within a selected surface patch of the wave pattern around the ship must be determined for resistance calculations. For this purpose, the flow around the DTMB-5415 model ship, KCS container ship and DTC container ship were solved using Star CCM+ CFD software in inviscid mode and accordingly wave heights were determined. Subsequently, wave resistance coefficient was calculated by the surface-patch method using the wave calculated. These calculated values were compared with model test resistance data, which are obtained from open literature, for validation. Around 1 percent accuracy was attained, but to get this accuracy; location and dimensions of surface patch must be selected carefully. Consequently, in order to figure out the sensitivity of the dimensions of the surface patch to the Froude number, a search was carried out by testing the effect of several y1 (first location on y direction of surface patch) locations on the wave resistance. The search showed that y1 values are required to be increased as the Froude number increases for the DTMB-5415 model ship. When considering calculated values of KCS and DTMB 5415 at the similar Froude number, we observed that the results point out almost the same y1 value but DTC value stays away from these values. This discrepancy shows some doubt about surface-patch method. A deeper study is necessary to arrive at a sound conclusion.