Dynamic response of platform-riser coupling system with hydro-pneumatic tensioner

A mathematical model of direct-acting tensioner system was developed to analyze the effect of internal friction of tensioner cylinder on the tensioner performance. The platform-tensioner-riser coupling system was established by implementing the tensioner model into ANSYS-AQWA through user subroutines written in PYTHON scripts. The overall coupling dynamic response under different wave conditions was investigated. The results from current analyses considering the effect of internal friction of hydraulic cylinder show that the relationship between tension and piston stroke of tensioner under the cyclic displacement is not simple nonlinear relationship but hysteretic loop relationship. Based on the results of the dynamic response under same wave conditions, it found that the variation of vertical relative displacement between platform and riser obtained with the hysteretic tensioner model is similar to that with the nonlinear tensioner model. Whereas the tension obtained with the hysteretic tensioner model has greater scope when compared to that with the nonlinear tensioner model. Moreover, the tension from the hysteretic tensioner model would change suddenly several times in relatively short period under irregular waves, due to the existence of high-frequency component, which resultantly exerts great impact on the fatigue life of the riser and tensioner.