In this research, a software package specifically conceived for educational/research purpose was developed for deep water offshore tension leg platforms (TLPs). Emphasis was placed on user interfaces, automatic data generation and graphical display of results in an effort to minimize the need for cumbersome and time consuming data preparation and lengthy output that are normally found in commercial/research programs. A state-of-the-art workstation approach was developed with emphasis on procedural programming languages, interface languages and graphical display. The TLP program is easy to use — yet it is capable of producing real graphical simulation of structural response of TLPs in deep water.
Comprehensive case studies for a sustained wave indicate that effects of nonlinearities in the forcing function are more significant than those of the structure. Either of the three structural options (i.e., constant axial stiffness, variable axial stiffness or large displacement theory) yield similar result. The forcing function, however, differs significantly depending on whether Morison forces are evaluated in the original or deformed geometry. In the initial stages, the predicted response is influenced by the assumed at rest conditions and the starting position of the wave; however, the steady state response is independent of the staring conditions. With respect to the initial conditions, the pontoons play an important role in damping out unwanted heave motions that would otherwise propagate throughout the solution. In addition, it has been found that the pitch has a small effect in the Morison calculation. Perhaps the most significant observation is the necessity for a fully coupled analysis of the hull and tendons, showing that it is not reasonable to neglect the hydrodynamic forces on the tendons.
General considerations for the software package as well as theory is presented. Three numerical examples for a deep water TLP at an ocean depth of 5,000 feet are presented to demonstrate the program’s versatility.
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