Multibody Dynamic Analysis of the Lift Off Operation: A Time Domain Approach

Multibody Dynamic Analysis of the Lift Off Operation: A Time Domain Approach

Wang, S.

Metrikine, A.V. (mentor)

Mechanical, Maritime and Materials Engineering

Hydraulic Engineering

Offshore and Dredging Engineering

2015-06-19

In the coming decades, the offshore decommissioning industry is becoming a quickly growing market, especially at the North Sea, where most offshore platforms have operated for more than twenty years. There is little room for the mistake in the offshore decommissioning operation, therefore the motion response analysis is essential to avoid the risks. It is common practice to use frequency domain analysis to simulate the dynamic behavior of floating structures in waves for linear system. However, offshore operations generally involve various nonlinearities such as nonlinear mooring system, wave-induced impacts during lift-off operation, and viscous forces. The frequency domain analysis is not capable of dealing with these nonlinearities, so the time domain analysis is pursued in this study. The Cummins equation provides an attractive way of analyzing the dynamics response of offshore structures in time domain, in which a convolution term is introduced to describe the uid memory effect. Neither the frequency domain analysis, nor the time domain convolution integral is convenient for time domain simulation. To facilitate the efficiency of time domain simulation, a state space model is introduced to replace the convolution term leading to a constant parameter time domain model. At the same time, the physical properties of the convolution term can be enforced into the state space model using convex optimization. The proposed time domain approach has been validated by comparing with the frequency domain analysis results for a linear system in the regular and irregular wave conditions. The topside removal concept proposed by Mammoet consists of a twin barges, in order to eliminate the problem caused by the moment-induced by the topside, as well as wave-induced motion, two linkages are incorporated into this concept. The time domain analysis proves that the purpose of these linkages are achieved that the relative sway and roll are successfully restricted. Finally, different load transfer stages are studied to obtain the dynamic response and its interaction forces between the topside and barges.

Multibody
System Identification
Time Domain Approach

http://resolver.tudelft.nl/uuid:50d72ee9-e2a7-4a5a-8b61-a79075668d4f

Student theses

master thesis

(c) 2015 Wang, S.