High-Speed Simulation in Towing Tank for Dynamic Lifting Vessels

Abstract

This paper presents a new testing technique developed for the simulation of high-speed dynamically lifted vessels. The complexity of the testing technique arises out of the need to test relatively small models in the towing tank in comparison with tests for normal displacement vessels. In order to simulate high Froude numbers much in excess of the threshold limit of 0.8 for planing, there are several challenges in designing the experiment. The challenges presented are due to small size model, necessity for giving the freedom to trim significantly and sink or emerge with reference to the static water level, lack of knowledge of the location of the point of trim, weight control of the model and delicate measurement system for the drag. Finally yet importantly, there is the caution that in the event of longitudinal plane instability there can be sometimes catastrophic damage and loss of transducers and even the model itself. The object of towing tank test for dynamically lifted crafts is to not only assess the drag and therefore power requirement, but also equally importantly verify that the hull form lifts clean at the transition-planing region, the bow wave formation and spray are not excessive, and there is no instability such as porpoising. Model tests also demonstrate the influence of loading, effect of centre of gravity location and the effect of chine lines and spray rails. Hence, model tests with dynamically lifting crafts are vital for verifying or improving the performance of the hull. This paper presents the development of a unique test set-up developed here to prepare and handle small-scale rapid-prototyped, precision models of high-speed planing hull forms. The new features incorporate an important counter-balancing mechanism, a sliding trim position control, vertical displacement guide system with delicate load cell-based data acquisition system. The newly developed system has been demonstrated in successfully simulating high speeds in the range of 25–30 knots with faithful capture of the entire kinematics, which include the trim, emergence and the wave pattern. This paper also presents some of the CFD simulation results for comparisons with the scenario recorded in the towing tank during experiments.