Experimental and numerical analysis of a deepwater mini-TLP

Abstract

As the quest for oil and gas resources drives the industry to ever deeper waters, model testing still represents an essential step after numerical modeling when designing offshore platforms in these hostile environments. In an attempt to better understand the overall response behavior of a small-size deepwater tension leg platform (TLP) designed by the offshore industry, an experimental campaign was led at the Offshore Technology Research Center (OTRC) in cooperation with Statoil. Time-domain statistics and dimensionless ratios are used to characterize the environmental design sea conditions. Similar methods are utilized to examine the critical issues of the clearance between the wave train crests and the underside of the platform's deck, and the wave run-up on the TLP columns. Rough estimations of the wave forces applied on the hull are given by a Morison's equation modified to fit the TLP geometrical complexity. These predictions are compared with WAMIT numerical simulations and the experimental results. The structure's natural periods of vibration and damping coefficients are computed by fitting free-decay tests and by analyzing the motion spectral responses. The time-domain analysis provides estimates of extreme surge offset and maximum yaw angle. The low-frequency, wave-frequency and high-frequency components of the response signals are identified through the spectral density analysis of the platform's motions and tendon tensions.