Structural response to extreme events or fatigue loading and structural integrity are major criteria to be quantified in a rational process of reassessment for offshore structures. It is now well established that the probabilistic mechanics approach gives an efficient means for measuring the relative changing in safety level compared to a predefined requirement. This paper proposes a probabilistic modelling of marine growth effects based on both Response Surface Methodology and the panel of available tests in laboratory. This method is here suggested to condition hydrodynamics coefficient to particle kinematics field randomness.
The proposed paper takes place in the actual challenge for the reassessment of existing offshore structures where some uncertainties are to be quantified on the basis of inspection reports analysis. When studying the mechanical behaviour of structures placed in severe environmental conditions as offshore platforms, the structural reliability analysis offers, after decades of developments, a set of robust tools and methods. It leads to state the importance of uncertainty and sensitivity analysis especially in view to characterise the stochastic structure of the loading acting on the platforms. One must consider the intrinsic randomness of waves and the uncertainty on the modelling of fluidstructure interaction in their relative contribution to the response i.e. the load on the structure. Particularly, one must take into account the natural cluster of organisms i.e. the marine growth fouling (kelps, mussel beds …) versus a probabilistic modelling. In fact, this settlement of the structure includes the major uncertainty source in term of diameter increment and hydrodynamic coefficients level. Its corresponding uncertainty evolves upon several factors (seasons, depth, …) and during the life of the structures and is greater at the design step when no inspection reports are available. Only effects on these platforms are considered here.
