A time-domain global hydrodynamic analysis of a TLP in 1830 m water depth is carried out. Extreme metocean conditions in the Gulf of Mexico are simulated, including waves, current and wind in noncollinear configurations. 3-hours storms are analyzed. Wave loads on the hull are modeled by use of second-order diffraction analysis (WAMIT), including low-frequency (LF), wave-frequency (WF) as well as high-frequency (HF, springing) excitation. In addition, viscous drag forces on the hull due to relative motions in waves and current are included through a distributed slender-body load model, and wind loads are included through wind coefficients. The vessel motions are dynamically coupled in the time domain to the top-end tether and riser tensions, through detailed FEM (Finite-Element-Modeling) assuming slender-body hydrodynamics of this part of the system. The RIFLEX-C software is used. Using the SIMO software, de-coupled analyses are performed for comparison. Observed coupling effects are analyzed and discussed. The results are compared to data from 1:87 scaled model tests. Irregular wave and wind records from the actual experiments are used as input in the simulations, making direct comparison of time series and spectra possible. The capability of the numerical model to reproduce observed effects in vessel motions as well as in tether and riser tensions is evaluated, including LF-, WF- and HF contributions. Based on the comparison, hydrodynamic parameters of the numerical model are adjusted to match the measurements. Large damping contributions from the deep-water risers and tensions are identified.


The need for advanced numerical computer tools for the global analysis of deepwater floating systems is growing as the oil industry is going into deeper and deeper waters. This has several reasons. First, the deep water itself represents new technical challenges and phenomena to be explored and taken into account in the system design.

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