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SummaryModel test is an effective way to verify numerical dynamic analysis of floating system. The diffraction and radiation analysis is carried out in frequency domain based on potential theory to predict motion response of rigid platform. The quasi static and dynamic methods are usually adopted to simulate mooring system, which determines if the whole system is coupled within the analysis. Here model tests are performed to indicate the accuracy of potential theory and quasi static and dynamic methods for the whole system. A FPSO is tested under regular waves to find its RAO. The FPSO with internal turret mooring system under irregular wave, wind and current are also studied in the deepwater basin of Harbin Engineering University. The results are compared between the model test and numerical models, which show the model test results agree well with the coupled numerical model, while the maximum mooring tensions are under estimated in quasi static analysis.

SummaryIn this paper, a numerical model was proposed to simulate the parametric rolling of ships in head seas. The method was developed in time-domain based on strip theory, in which a consistent way of estimating the radiation forces was applied using impulse response function method. To take the coupling effect into account, the heave and pitch motions were solved together with the rolling motion. Also, the Froude-Krylov forces and hydrostatic forces were evaluated on the instantaneously wetted surface of the ship, in order to model the time varied restoring rolling moment in waves. Based on the developed numerical model, the parametrically roll motions of C11 containership was simulated. The influence of roll damping was investigated using two different methods, and the numerical results were compared with model tests. The comparative study shows that results obtained by the proposed method generally agree well with experimental data. Discussions and possible improvements of the current numerical model were also presented in this paper, with regard to the numerical deviation between the numerical and experimental results when the wave steepness was larger than 0.04.

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Parametric resonance can lead to dangerously large rolling motions, endangering the ship, cargo and crew. The QR-factorization method for calculating (LCEs) Lyapunov Characteristic Exponents was introduced; parametric resonance stability of ships in longitudinal waves was then analyzed using LCEs. Then the safe and unsafe regions of target ships were then identified. The results showed that this method can be used to analyze ship stability and to accurately identify safe and unsafe operating conditions for a ship in longitudinal waves.