Datta, R., Rodrigues, J.M. and Guedes Soares, C. (2018), “Prediction of motions and wave induced loads on a container ship using non linear 3D time domain panel method”, 4th International Conference in Ocean Engineering (ICOE 2018), 18-21 February, Normandy, Northern France

Prediction of motions or wave induced load in extreme sea conditions for a vessel is extremely challenging task. For large amplitude motion problems, the classical linear theory may not produce results within engineering accuracy and perhaps non linear theories are more adequate. Specially the ship with larger flare, even hydrostatic forces are no longer act like linear restoring forces and proper non linear model is required to develop in such cases. Within the framework of potential theory, several non linear theories are developed for last couple of decades. In this paper, a relatively simplified non linear method based on 3D time domain panel method is used to predict the motions and vertical bending moment of a container ship with and without forward speed. The numerical formulation is based on on transient free surface Green's function. Nonlinearities arising from the large-amplitude incident waves are considered in the computations of FroudeKrylov and hydrostatic restoring forces for which a suitable algorithm is developed that can find the exact wetted surface under the incident wave profile. In case of estimation of radiated diffracted forces, a modified form of the body-kinematic condition is applied.The methodology is validated for a simplified structure such as Wigley hull, rectangular barge etc. In the present paper, a realistic container ship ( S175 ) is taken for the analysis. Heave, pitch motions and vertical bending moments are computed and compared with experimental results for head sea condition. The comparison shows present methodology is efficient and robust enough to predict the wave induced motion and loads. Once the method is validated, to check the effect of non linearity, the motions and force results are computed for different steepness. Results shows beyond a steepness factor of 0.08, non linear effects are significant.

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