This paper deals with an advanced stochastic analysis for deep water offshore structures under wave-current and structure-fluid interactions. Having described the random sea and transfer functions of water velocities and accelerations in a wave-current field, wave forces, hydrodynamic damping ratios and added masses are calculated on the base of using the Morison's equation. The drag force term of the Morison's equation is linearized by using an equivalent second-moment criterion and the relative water velocity concept. Then, attention is paid on the structural response analysis. It is emphasized that a proper and correct analysis can be fulfilled by considering the wave-current and fluid-structure interactions.
Wave-current and fluid-structure interactions are important subjects to be considered in the analysis of offshore structures. Since the process of wave loads in an ocean environment is stochastic, spectral methods are usually applied to calculate response statistical characteristics of structures. In this calculation, the effect of current is reflected on response results in two ways as a) the existence of current alters the sea spectrum, b) wave loadings and damping ratios are dependent on the current velocity so that loading and structural transfer functions are also affected by the current. In" general, wave-current interaction is a complicated and difficult subject. Under certain conditions which will be mentioned later, spectral description of sea states in a wave-current field can be obtained in terms of sea spectra in a quiescent area. Since the non-linear drag force term of the Morison's equation is dependent on the total water velocity, the linearized form of this term contains two components as being timeinvariant (assuming that current is not a function of time) and stochastic. The time invariant component results in mean value responses.