ANALYSIS OF TOWED SUBSEA PIPELINES IN RANDOM SEA

Offshore pipelines are conventionally installed using either lay barges or reel barges. In the first case, prefabricated pipeline segments of around 12 m in length are welded together on the bargeas the pipeline is being laid. In the second case, up to 25 km of prefabricated pipeline is woundon a large diameter reel and the laying operation consists of unwinding the reel and straighteningthe `pipe. The reel barge method avoids the need for large scale offshore welding operations buthas the disadvantage of being applicable only to relatively small diameter pipelines. A third approach, which is applicable to pipelines of arbitrary diameter, is to fabricate the pipeline on shore and then tow the resulting lines to the offshore site.In planning a pipeline tow, care must be taken to ensure that the pipeline will not be damaged by either wave action or the manoeuvring which occurs at the launch and final installation stages. In this paper, the response of a long towed pipeline to random spreading seas is considered. Adynamic model was used according to the type of Tow method and nonlinear response of thepipeline is carried out in both time and frequency domains. Distribution of bending stress thatmade with random waves and related to wave excitation was shown to analyze the motion of the pipeline. The responses of the pipeline mooring system related to wave excitation was done to analyze the motion of the unit with its mooring system.

Keywords:

Pipe laying , Sensitivity Analysis , Towing , Jonswap , Random wave