Partly submerged crane suspended jacket

Partly submerged crane suspended jacket

Eijgenraam, Koen (TU Delft Mechanical, Maritime and Materials Engineering)

Miedema, Sape (mentor)
Schreier, Sebastian (graduation committee)
Duinkerken, Mark (graduation committee)
Bokhorst, Job (mentor)
Samudero, Pandu (mentor)

Delft University of Technology

Offshore and Dredging Engineering

2020-06-03

This study is focused on the decommissioning of a jacket with a heavy lift vessel. During the transport the crane suspended jacket hanging in air can start swinging due to swell waves. This can result in undesired risks such as a collision between the jacket and the vessel. To prevent this undesired risks from occurring a solution must be sought. A possible contingency scenario to prevent this risks from occurring is to (partly) submerge the jacket. The aim of this study is to investigate in which way the jacket motion response changes if it would be in the water. A research methodology will be derived to investigate this. This will be done by investigating the a jacket transport with the Thialf. As a starting point, and for later comparison, the behaviour of the a jacket in air, while it is free hanging from the cranes of the Thialf, will be investigated in a frequency domain solver Liftdyn. The resulting modes and response between the model and measurements indicate a good starting point. Thereafter the jacket will be lowered in to the water and the resulting forces will be determined. The forces on the jacket will be determined using the linearised Morison equation. For the damping two approaches are investigated, i.e. the absolute velocity approach and the relative velocity approach. Subsequently different submerged depths are investigated and the effect of adding tugger winches is investigated. The operability for the different scenarios is derived and compared. It is observed that by submerging the jacket the pitch mode is limiting the operability for wind waves. This mode can be damped by adding tugger winches. By submerging the jacket deeper the operability improves. For swell waves the operability is improved when the jacket is submerged. It is concluded that submerging the jacket can be used as a contingency scenario for a swell train, but it is crucial to know the behaviour of the jacket. Because submerging it at the wrong depth could lead to large resonant responses. And by understanding the behaviour of the jacket tugger winches can be used to damp out a specific modes.

Frequency Domain
Morison
Decommissioning

http://resolver.tudelft.nl/uuid:de0b07ca-ac3b-4a6a-b0bc-aa764d5831e3

Student theses

master thesis

© 2020 Koen Eijgenraam