PREDICTION METHOD FOR NON-GAUSSIAN BEHAVIOR AND ITS EXTREMUM OF A MOORED FLOATING BODY IN NON-GAUSSIAN MULTI-DIRECTIONAL IRREGULAR OCEAN WAVES

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The prediction method of extremum for motion responses or waves loads in severe sea conditions have not been developed yet, since the responses are non-Gaussian. And there have been many marine facilities or bulk-carriers which suffered structural damages, sank and lost many lives. There have reported several examples which shows that the Rayleigh method was not hold for non-Gaussian cases. That is the reason why wer start to develop the practical prediction method of extremum for non-Gaussian process.We first tried to predict extremum of low frequency motions of a catenary moored floating structures in multi-directional waves. If only external wave excitations are non-linear and the other terms, radiation hydrodynamic forces and damping term and restoring term are all linear, then the method developed by Naess or Kato-Kinoshita works well, however, if we introduce non-linear terms in the left hand side of the equation of motion, the analytical method based on Naess or Kato-Kinoshta does not function. Then we conclude that the only practical prediction method for full non-linear, non-Gaussian process is the time domain simulation method which is applicable to so called simulation based design.We then developed the time domain simulation code for ship motions, waves loads and unsteady pressures on a ship hull with advanced speed and in multi-directional waves. Moreover we introduce non-linear terms to this time domain simulation.