Dynamisk bevegelse av et stigerør som henger mellom to skip.

Abstract

In this assignment we've been looking at the problem of transporting oil, gass and water from an FPSO-Floating Production, Storage and Offloading system, to a tankship. The possibility of doing this with a pipe from one ship to the other has been studied. The problem has been studied analythically and numerically and the results have been compared. Analytically, the pipe has been described both as a catenary and as a parabola. The numerical program used for the analysis is RIFLEX.

A pipe between two ships will be exposed to dynamical exitation from the movements of the ships.This exitation will lead to stress in the pipe. The stress in the pipe has been described for different load cases.

To be abel to describe the ships' movements, a dynamical analysis of the ships has been carried out by using Wadam. The results from Wadam were in the frequency domain and they were converted using an inverse Fourier transformation to the time domain. The ships' movements were then described as time series. These time series were then used to described the displacements of the pipe.

The results of the stress analysis showed that the pipe was exposed to large stresses, bendigstress being the dominant part. In the analytical analysis the problem was analysed without taking bendingstress into account. The only stress in the pipe when the bendingstress is neglected will arise from stress caused by the tension force. This will not give a good indication of the total stress in a pipe with bendingstiffness. To describe the displacements of the pipe, the analytical methods used without bendingstifness gave much better results.