Wave Drift Forces' Calculation on Two Floating Bodies Based on the Boundary Element Method—Attempt for Improvement of the Constant Panel Method

An improved constant panel method for more accurate evaluation of wave drift forces and moment is proposed. The boundary element method (BEM) of solving boundary integral equations is used to calculate velocity potentials of floating bodies. The equations are discretized by either the higher-order boundary element method or the constant panel method. Though calculating the velocity potential via the constant panel method is simple, the results are unable to accurately evaluate wave drift forces and moment. An improved constant panel method is introduced to address these issues. The improved constant panel method can, without difficulty, employ the near-field method to evaluate wave drift forces and moment, especially for multiple floating bodies. Results of the new evaluation method will be compared with other evaluation method. Additionally, hydrodynamic interaction between multiple floating bodies will be assessed.

Reduced-Order Time-Domain Simulation of Floating Bodies for Efficient Design Analysis

This paper describes the development and implementation of a reduced-order model to represent the hydrodynamic forces acting on a ship using Impulse-Response Functions (IRF). The approach will be conducted using Aegir, a timedomain seakeeping program that uses an advanced, Non-Rational Uniform B-Spline (NURBS) based, high-order boundary element method. The Cummins equation is slightly modified such that the memory function is decomposed into two terms: one for the impulsive velocity and the other term for the impulsive displacement. The present approach also further develops a method to simulate interactions between multiple floating bodies. The IRF convolutions for the free surface memory effect significantly reduce the computational effort compared to direct simulation. This will be demonstrated for both single and multi-body forward-speed, seakeeping simulations.

Resonant Motion of Liquid Confined between Floating Structures

Many applications occur in the field of marine hydrodynamics where two or more vessels are in sufficiently close proximity to experience significant wave action. The motion of such floating bodies in waves is frequency dependent. In the case of multiple floating bodies, when resonance occurs, the effect of confined liquid between the bodies has some serious implications on the safety and operation of the offloading system. The main objective of the work is to determine the hydrodynamic behaviour of two bodies freely floating in water. A frequency domain method is adopted for the prediction of the resonant frequency. 3D linear diffraction radiation analysis is used to solve the problem. Structures are modelled in ANSYS AQWA and analysed in selected range of frequency with different spacing. As the spacing increases the resonant frequency in roll is found to be decreasing for both ship and tugboat and the frequency shift between the two is increasing. The wave elevation pattern within the spacing has been observed and the result has been shown for different spacings.

A Numerical Investigation on Hydrodynamics of Multiple Floating Bodies in Offshore Installation Engineering

There are many applications in marine engineering where two or more floating vessels are in close proximity. Probably the most significant one is related to the offshore installation engineering. On the background of the upper module installation operation of spar platform, this paper investigates the hydrodynamic interaction effects of multiple floating bodies in offshore installation engineering. The numerical simulation bases on the 3-D frequency domain linear potential theory. The calculations are carried out for the crane ship, the transport ship and the spar platform. Finally the best environmental parameters and the relative position of floating bodies are selected, which can provide good advice on installation operation scheme design.