The Motion Responses Of The Deep Sea Offshore Platforms Induced By Internal Waves

Stratified fluids are very common in the ocean owning to the variation of the temperature and salinity with depth. In such stratified fluids, internal waves will be generated if the fluid is stably stratified and there are existing disturbances. The amplitudes of internal waves are often much larger than the ones of surface waves, which offen carrys enormous energies, so that strong underwater current can been generated. The effect of the strong current on the floating offshore structures cannot be neglected. The serious problems have caught the offshore oil's great attention, but at present we have no solution in practical engineering application. Therefore, the investigation on the motion responses of the deep sea offshore platform induced by internal waves in a strarified fluid is not only academically important, but is of considerable importance in practical engineering application.On the basis of reviewing and summarizing the recent research progress of this subject, the motion responses of the deep sea offshore platforms in a two-layer fluid are considered. The research in the following aspects has been carried out:In Chapterâ…¡, The motion responses of the Spar platform induced by internal waves in a two-layer fluid are investigated. A numerical method for computing the motion response and mooring line tension characteristics of the Spar platform induced by internal waves is presented. The effects of the interface location of the two-layer fluid, the wave lengths of the incident internal waves and the initial forces of the mooring line on the motion response and mooring line tension characteristics of the Spar platform induced by internal waves are numerically analyzed. Numerical results show that the effects of the internal waves on the pitch motion response of the Spar platform is small, but the surge and heave motion responses, as well as the mooring line tensions of the Spar platform induced by internal waves are considerably important for its application.In Chapterâ…¢, The motion responses of the TLP induced by internal waves in a two-layer fluid are considered. According The Newton's second law, we can abtain the equantions of the six components of the TLP motions. By using the modified Morison equation, we can get the hydrodynamic forces acting on the TLP. We also deduce the hydrostatic forces and the tesions in tendon. From the above deduction, we can kown that the external forces and moments are all nonlinear of the resposes of the TLP. The motion equation of the TLP is the couple nonlinear differential equation. By using the classic fourth-order Runge-Kutta method, we can solve the nonlinear equation in time domain. The effects of the interface location of the two-layer fluid, the wave lengths and the heights of the internal waves on the motion responses of the TLP induced by internal waves are numerically analyzed.