Abstract

The recent trends in pipeline installation analyses are using irregular wave spectra because it produces more realistic results, especially when fatigue analyses are required. Although, by adopting irregular wave model analyses will consume more time to produce results than regular wave model. However, with current available computing technology, the required computing time is just becoming lesser and no longer a limitation issue.

Irregular Wave Analyses will require Wave realization which relies on wave Seeds selection. Wave Seed is a random number where every seed number will give different maximum wave rise, maximum wave fall and also the time windows when the peak is occurred in the 3hrs simulations.

The key question is about, How to choose the "correct" wave Seed number? There are few suggestions to address this subject. It is either to pick up several seeds randomly, and choose the average of those results; or choose several random Seeds, up to 20 seeds in fitting those results to Gumbel Distribution to get the extreme maxima, or fitting those results to Weibull distribution to compute the extreme maxima.

This paper will discuss about the effect of wave seed selection base on irregular wave analyses (i.e. maximum wave extreme rise and fall), vessel motions (i.e. Maximum/Minimum Vessel heave, Pitch, Roll at Motion, velocity and acceleration) and also during Pipeline installation analyses. The result discussion is focused on J-lay Installation analyses using reel-lay vessel. On each of the analyses (Wave, Motions and Pipeline Installation) 3hrs simulation is carried out. In the conclusion, Time windows from the motion analyses and Installation Analyses will be compared to show which motion characteristic will influence the Pipelay parameters the most. And based on those time windows, Short simulation analyses will be performed to verify the accuracy of the selected time windows.

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