Modelling of Hull Lift and Cross Flow Drag Forces in Large Waves in a Computationally Efficient Dynamic Stability Prediction Tool

Abstract

The US Navy is developing a new computationally efficient simulation tool to predict the responses of a ship operating in severe sea states. The tool computes the total force on the ship as the summation of component forces. An important component to the total force on the ship is the force from hull lift and cross-flow separation. These forces are predicted in calm water by maneuvering simulation tools but are often ignored by traditional seakeeping simulation tools. As viscous effects are important in the prediction of these forces, most maneuvering simulations are based on empirical data from calm water maneuvering tests. While these methods are valid in calm water the wetted shape of the hull changes significantly in large waves having significant influences on the hull lift and cross flow drag forces. In the present method a hull lift and cross flow drag force model is presented that accounts for the varying wetted geometry of the hull in waves. The method uses calm water maneuvering data from model tests and RANS calculations to calibrate the model. Proper modeling of the hull lift and cross flow drag force in large waves is very important for the prediction of some dynamic stability events such as broaching and broaching leading to capsize.