Shallow water effects on circular motion tests using an efficient and robust approach

Abstract

This paper presented an efficient and robust numerical approach for conducting circular motion tests (CMTs) with fully appended ship under deep and shallow water conditions. A 135 m long benchmark inland waterway ship was selected for systematic investigations. By comparing predictions obtained from the widely applied moving grid and rotating reference frame approaches for CMTs, the proposed rotating flow approach attained predictions equally as accurate as the moving grid approach, but computationally significantly more efficient. By coupling the rotating flow approach with the free surface, the ship’s trim and sinkage were also accounted for. Grid independence study and comparison with physical CMTs carried out at HSVA validated the proposed approach. The influence of the free surface and the action of the propellers on hydrodynamic forces and moments was demonstrated by performing CMTs at water depth to draft ratios of 8.0 and 1.2. Effects of the free surface and the propellers were more pronounced in shallow water. In the end, systematic CMTs were carried out with the free surface and operating propellers across four different water depths, employing water depth to draft ratios of 1.2, 1.5, 2.0, and 3.0, and demonstrated the influence of shallow water on maneuvering forces and on the associated turning ability of the investigated ship.