An Efficient Method for Computing the Pressure Field of a Ship in Unsteady Maneuvers

摘要

An efficient method was developed to compute the pressure field induced on the seafloor by a ship performing maneuvers such as acceleration, deceleration, and turning. Linear, potential flow theory with transient, finite-depth Green function is used to formulate the solution for the velocity potential. To reduce run time, thin-ship approximation is made, and the Green function is evaluated using Chebyshev polynomials instead of numerical integration. A systematic asymptotic expansion of the derived equation for the potential is carried out in terms of the small beam to length ratio ε to obtain the thin-ship approximation where both sources and dipoles are used to represent the flow field. Sample calculations are presented for a Wigley ship undergoing acceleration and deceleration. Comparing the results with the steady pressure at equivalent speed, the effects of acceleration and deceleration are seen to be most severe when the ship crosses the critical depth Froude number of one. The pressure pattern changes significantly across the critical Froude number, and the changes linger for quite some time before settling into the new steady state.