A Study Of Viscous Pressure Resistance Of Trimaran Hulls

As a new type of hull form, Trimaran in recent years, with its superior performance has got more and more attention. In the process of trimaran new ship form development, resistance prediction is a very important process.Tests show that viscous pressure resistance is the resistance prediction of part can not be ignored. However academia usually adopt the method of empirical formula, through conversion to determine the shape factor, and then estimated pressure resistance. This method is the deficiency of the froude number in the range of0.1～0.2, but at a high speed period of accuracy is not enough.In the graduation thesis, combination of numerical simulation and model test is used. Through the changes of outtrigers’ position, and compared with mono-hull ship, a trimaran’s viscous pressure is studied.Wave making resistance coefficients have been calculated based on the slender body theory. Slender body theory method has the advantage of less computing time step values, simple meshing, operation time saving but accurate the results at the same time. Considering the characteristic that the high-speed trimaran’s navigation attitude changes significantly when it is sailing, the sinkage and trimming on the influence of the wave making resistance should be considered when calculating the results. The outtriger’s location relative to the mainhull can be different, this is called a configuration of trimaran. The total resistance of different configurations of the trimaran in static water has been measured by a series of model resistance experiments. According to the measured total resistance, the empirical formula is used to calculate the frictional resistance coefficient. Residual resistance coefficient is calculated using Two dimensional scaling method. Sketching the curves of residual resistance coefficient and the wave-making resistance coefficient on a diagram and it has been found that in each configuration’s process of sailing, there always exists a D-value between the residual resistance coefficient and the wave-making resistance coefficient. According to the division of resistance by Hughes, it is viscous pressure resistance due to the viscosity of water exists in the high-speed, transom trimaran. Through the three dimensional (1+K) conversion viscous pressure resistance coefficient are obtained. Through the analysis of the results found that different locations of outtriger will affect the change of viscosity pressure resistance. It’s also be found that different configuration of trimaran’s viscous pressure resistance in the range of0.5×10-3to1.4×10-3, and peak at about Fr=0.2. This can be speculated that in practice if you know the location of the three body side body, you can estimate the curves of viscous pressure resistance, and simply estimate trimaran’s viscous pressure resistance coefficient at a certain speed.In order to compare with trimaran’s viscous pressure resistance,the second half of this paper studied the mono-hull ship’s viscous pressure resistance. Studies have found that single ship viscous pressure resistance is unimodal, compared with the trimaran, mono-hull ships’ viscous pressure resistance are more regular.The study shows that the in ship sailing process, viscous pressure resistance can not be ignored. The interaction between main hull and the outtriger would affect the trimaran’s viscous pressure resistance. Trimaran’s viscous pressure resistance coefficient is not only relation with hull shape but also with outtriger’s positions. Through the judgment of trimaran’s ship type, the viscous pressure resistance coefficient under a certain speed could be simply estimated.