Modelling and Control of Flow Induced Vibration of Top–Tensioned Marine Risers Using Analytical Methods

Abstract

For a riser array in deep waters, interference between individual risers in strong ocean current is of operational concern and thereby a key design issue. The lateral deflection is likely to be large, and the risers may experience collision with fatigue or coating damage as a consequence. In this paper, active control of flexible marine riser angle and the reduction of flow induced (forced) vibration under a time varying distributed load were considered using boundary control approach. A torque actuator was introduced in the upper riser package and a boundary control was designed to generate the required signal for riser angle control and vibration reduction with guaranteed closed-loop stability. The design is based on the partial differential equations of the system, which are developed using energy principle. Analytical method of solution was deployed with the aid of a program, developed within the framework of MATLAB, to predict the riser's behaviour by top tensioning. A sensitivity analysis for different values of the control variables was carried out. The results of this work showed that active control of flexible marine riser by top-tensioning reduced flow induced vibration.