Mooring system reliability analysis of an ORE device using general Polynomial Chaos

We demonstrate the use of general Polynomial Chaos (gPC) in determining the reliability of a mooring system designed for an offshore renewable energy (ORE) device. General Polynomial Chaos is used to forward propagate uncertainties in two design variables, and to obtain the probability density function of the Most Probable Maximum tension in the most loaded line. Then, the probability of failure is estimated using the First Order Reliability Method. For this case study, we obtain a probability of failure of 3.4×10 -6 for the mooring system, around 10 times lower than required by DNV-OS-E301. The most interesting result, however, is that by applying gPC, we can build a probability density function for the tension running only 36 simulations using the deterministic numerical model, instead of hundreds or thousands as would be required by using a Monte-Carlo method. This reduces the computational effort required for probabilistic design and analysis of floating structures, enabling the shift from conservative Partial Safety Factor based design, to Reliability and Risk based design.