A displacement-hull wave-frequency vessel motion model.



Executive Summary

Shipsim is a general-purpose six degree-of-freedom wave-frequency vessel motions program specifically enhanced for displacement-hull vessels with relatively large block coefficients. Vessels in this category include drillships, barges and tankers. Shipsim utilizes an efficient algorithm for calculating wave-frequency forces and moments which permits accurate modeling using as input only gross hydrostatic and mass properties (metacentric heights, displacements, overall dimensions, centers of gravity, gyradii, etc.), eliminating the need for tedious and error-prone input of vessel lines details. This typically permits comprehensive executions to be completed in one hour or less. Non-linear effects, particularly in the roll degree of freedom, are fully modeled, leading to realistic roll response predictions which depend on details of bilge geometry. A wide range of environmental conditions is accommodated, including extensive built-in wave spectral types, azimuthal spreading of wave directions and an optional independent background swell. Accelerations, velocities and displacements at any point on the vessel can be computed. Effects of finite water depth are fully modeled and either English or metric units may be selected for vessel specification and data output. Output is in the form of amplitude and phase of vessel Response Amplitude Operators (RAOs) and/or statistical characterizations of vessel response to irregular wave conditions. Execution is carried out in the frequency domain, resulting in short run times and unambiguous predictions of statistical response values.

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