Response behavior of TLP under hydro-dynamic loading is nonlinear due to large structural displacements and fluid-structure interaction. This study focuses on influence of two imperative parameters namely inertia coefficient and wave directionality on its geometry. Paper develops a mathematical formulation for non-linear variation of hydrodynamic inertia coefficient (Cm) along the water depth to yield optimum force on TLPs as well as influence of wave directionality on their geometric configuration while discussing the method of solution. Responses are obtained for two configuration of TLPs namely square and equivalent triangular TLP with total initial pretension same as that of square.
Offshore TLPs are vertically moored compliant structures built for petroleum extraction in deep sea. Their compliant mechanism extends high degree of mobility to alleviate destructive loads, enabling early oil production and reduced field installation costs. Inertia forces become predominant when they are dynamically excited. Researchers (Chandrasekaran et al., 2002b) studied the complexities arising from various nonlinearities namely:
change in tether tension;
buoyancy; as well as
hydrodynamic drag forces and discussed appropriate solution procedures.
They showed that calculation of wave forces on displaced position of the platform introduces a steady offset component in structural response. Water particle kinematics based on Navier- Stokes' equation is nonlinear with respect to the transverse velocity (see for example, Drobyshevski, 2004). Therefore influence of hydrodynamic coefficients on response behavior of compliant structures like TLPs showed the importance of including first order terms while computing the wave forces. (Sabuncu and Sander, 1981); however, these variations do not influence heave response much. (see for example, Spyros 2005). Chaplin & Subbiah (1994) presented results for probability distribution of peak forces and Morison coefficients based on experimental investigation on a rigid vertical cylinder under multidirectional waves.
