Nonlinear coupling problems between the multiple bodies or between the
mooring/riser and the offshore platform are incorporated in the CHARM3D-MultiBody,
a fully coupled time domain analysis program for multiple bodies with moorings and
risers. The nonlinear spring connection module and the three dimensional beam module
are added to appropriately solve the structural connection problem. The nonlinear spring
connection module includes the hydro-pneumatic tensioner module with the friction &
stick/slip implementation, the tendon/mooring disconnection (breakage/unlatch) module
with the tendon down-stroke check, and the contact spring with the initial gap with the
friction force implemented.
The nonlinear coupling may happen in many places for the offshore floating
structures, such as hydro-pneumatic tensioner, tendon of TLP down stroke at the bottom
joint, stick-slip phenomena at the tie down of the derrick and most of the fender-to-steel
or steel-to-steel contact problem with initial gap during the installation. The mooring/tendon broken and unlatch can be a nonlinear connection problem once the
transient mode is taken into account.
Nonlinearity of the stiffness and friction characteristics of the tensioner
combined with stick-slip behavior of riser keel joint is investigated. The relationship
between tensions and strokes for hydro-pneumatic tensioner is based on the ideal gas
equation where the isotropic gas constant can be varied to achieve an optimum stroke
design based on tensioner stiffness.
A transient effect of tendon down-stroke and disconnection on global
performance of ETLP for harsh environmental condition is also investigated by
incorporating the nonlinear boundary condition of the FE tendon model in CHARM3D.
The program is made to be capable of modeling the tendon disconnection both at the top
and the bottom connection as well as the down stroke behavior for the pinned bottom
joint.
The performance of the tie-down clamp of derrick is also investigated by using
six degrees of freedom spring model and the three(3) dimensional FE beam model. The
coupling of the TLP motion with the reaction force at the tie-down clamp is considered
by using exact nonlinear dynamic equations of the motion with the reaction forces
modeled with the spring or FE beam model. The method reduces too much conservatism
when we design the tie-down system by the conventional method, in which all the
environmental forces are combined without the phase lag effect between them. The FE beam model is also applied to the connectors between the
semisubmersible and the truss for the pre-service and in-place conditions to be verified
with the model test results, which shows good agreements.
| Identifer | oai:union.ndltd.org:tamu.edu/oai:repository.tamu.edu:1969.1/ETD-TAMU-2009-05-779 |
| Date | 2009 May 1900 |
| Creators | Yang, Chan K. |
| Contributors | Kim, Moo-Hyun |
| Source Sets | Texas A and M University |
| Language | English |
| Detected Language | English |
| Type | Book, Thesis, Electronic Dissertation, text |
| Format | application/pdf |
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