A Preliminary Analysis on the Statistics of about One-Year Air Gap Measurement for a Semi-submersible in South China Sea

Air gap performance has been a key issue in the design of semisubmersible platform. In this paper, a comprehensive study on air-gap is carried out based on the field measurement data of a semisubmersible in South China Sea using statistical analysis. The analysis shows that the energy extremes of air gap mainly appear in the wave frequency range. By fitting the probability density and cumulative probability distribution curve, the air gap extreme can be predicted. And the air gap performance of the platform is relatively stable in different months because the curves in different months appear very close. Moreover, the correlation between air gap and vertical motion of the platform is analyzed, which indicates that parts of the lowfrequency data are unreliable, and a method to evaluate the reliability of the field measurements is proposed.