Probabilistic assessment of parametric instability of a top tensioned riser in irregular waves

A reliability analysis was used to investigate the parametric instability of a top tensioned riser (TTR) operating under irregular sea conditions. In practical applications, the parametric instability evaluation of a riser is a very difficult task, owing to uncertainty of various parameters such as the environmental conditions of the load, the structural geometric parameters, and material properties. Considering the uncertainties of these parameters, it is vital to adopt a probabilistic approach in evaluating the instability. In this work, the Hill equation of a TTR operating under real sea conditions is first derived, and the corresponding stochastic external excitation is obtained using the Pierson-Moskowitz wave spectrum. The effects of various random variables on the parametric instability are studied by a sensitivity analysis. A surrogate model is used to construct the response surface for assessing the reliability of the parametric instability of the riser. The distribution regularity of parametrically unstable cases is examined using the contour of the parametrically excited responses. The effect of three significant uncertain factors on the probability of the parametric stability is investigated using the surrogate model. The proposed approach is demonstrated to be efficient for evaluating the reliability of the parametric instability of a TTR.