Influence of propeller on brash ice loads and pressure fluctuation for a reversing polar ship

Abstract

When a polar ship is stuck in ice-covered waters, reversing operation is an effective way for it to escape from ice. During this operation, rotational propeller will affect flow field and motion of brash ice, thus affecting ice loads and pressure fluctuation. In this paper, a new coupling model using Computational Fluid Dynamics (CFD) and Discrete Element Method (DEM) is proposed to investigate characteristics of brash ice loads and pressure fluctuation for a polar ship reversing in a brash ice channel. The present method is well validated by model tests of a towing polar ship in brash ice channel. The simulation results show that in reversing process, brash ice blocks collide with the stern and two sides of ship, where ice blocks accumulate. When the reversing speed is low, the pumping action and acceleration effect of the propeller on the brash ice are obvious. The pumping action reduces the average value of the longitudinal and vertical ice loads, and the acceleration effect makes ice loads occur multiple peaks. The increase in reversing speed worsens the performance of propeller, weakening the pumping action and acceleration effect. The pressure fluctuation period is consistent with propeller rotation period, which decreases for poor propeller propulsion caused by higher reversing speed. It is necessary to strengthen the stern structure in reversing process, especially at low speed, for pumping action and acceleration effect of propeller.