Experimental and numerical investigation of the effect of aft deformation using wedge and step on the performance and stability of hard chine mono-hull high-speed craft and their optimization using Taguchi statistical method

Abstract

Speed and stability play crucial roles in the performance of high-speed crafts. In the present paper, a two-stepped model is tested in towing tank and compared with stepless and wedge-mounted models, which have previously been tested by the authors. This study is conducted to compare the stability and performance of the mentioned models in the displacement, semi-planing, and planing regimes. The length and width of these models are 2.64 meters and 0.55 meters, respectively. The measured parameters include trim, rise-up, and resistance. The whisker sprays of the models are also depicted at different speeds. the performance of stepped boats is not suitable prior to the planing regime. But wedged model can perform well in this area. One of the features of this type of model is having a chine. So far, no comparison has been made between the chined models. Further, the whisker spray edge approaches to the keel line by increasing speed in all considered models. These tests are conducted in three series at speeds of 2,4,6 and 8 m/s within the mentioned motion regimes. Based on the experimental findings, it is observed that tested models are stable in displacement and semi-displacement regimes. The bare hull which has no transverse step or wedge, is longitudinally unstable in planning regime. However, the vessels with two transverse steps exhibit longitudinal stability and have less drag than the bare-hull model in all motion regimes. On the other hand, the trim and rise-up in stepped as well as wedged vessel are less than those in the bare-hull model in all motion regimes. Meanwhile, the drag of the two-step model at high speeds is determined to be less than the other two models. Ultimately, using the Taguchi design method, different wedge-mounted and two-stepped vessels are selected to conduct numerical studies. These simulations are done via STAR-CCM + commercial code. The calculated results show that at speeds higher than 8 m/s, the resistance could be reduced by optimizing the step location. As the first step gets farther from the stern, the resistance of the vessel reduces. However, increasing the distance between the second step and the stern leads to a drag penalty for the vessel.