Monte Carlo Simulation of a Partially Submerged Compliant Structure

Abstract

The response of a single-tendon tension leg platform subjected to stochastic wave and current loading is presented with a planar motion assumption. The tension leg platform will oscillate about its vertical position due to ocean waves. Current will cause a tension leg platform to oscillate about an offset position rather than its vertical position. This offset in the surge direction has a corresponding set down, the lowering of the hull in the heave direction, which increases the buoyancy forces. This results in a higher tension in the tendons than if the tendon and hull were in a vertical position. In prior papers the equations of motion and forcing functions were fully developed. The tendon and hull are both assumed to be cylindrical and therefore Morison’s equation was applied. In this paper, a Monte Carlo simulation was performed on the drag and inertia coefficients in Morison’s equation. A uniform random distribution of coefficients was selected from 0.6 to 2.0 for each coefficient. Twenty computer simulations were implemented for each coefficient. The response showed that the offset position and the amplitude are both dependent on the drag coefficient. The surge of the hull shows a maximum offset approximately three times greater for the coefficient that resulted in the maximum displacement than the minimum. The response did not show a significant dependence on the inertia co-efficient, however, this is not necessarily true for unsteady current, large hull and tendon diameters, ocean wave frequencies greater than 1 radian/second, and low current velocity.