Ringing response of offshore triceratops

Abstract

Triceratops is a new generation offshore platform, proposed for oil and gas exploration in ultra-deep waters. Deck is supported by buoyant legs, but isolated from each other by ball joints. Buoyant legs are taut-moored to the seabed using tethers with high initial pretension. The presence of ball joints makes the platform less sensitive to the encountered environmental loads. The present study investigates transient response of triceratops under distinctly high sea waves through numerical studies. Spectral analysis is carried out to estimate the ringing response, which is highly nonlinear. While ringing waves are simulated with parametric variation, JONSWAP spectrum is used to simulate the time series of large irregular waves causing ringing response on triceratops. Based on the numerical studies carried out, a gradual decay is seen in the response of buoyant legs looking similar to that of a beat phenomenon. Deck response shows a significant reduction in rotational degrees-of-freedom than that of the buoyant legs due to the presence of ball joints, which aids the platform to remain operational even under high sea states. Statistical analyses on tether tension variation show that ringing caused by strong asymmetric waves is responsible for causing impact load on the platform.