Research On Specific Environmental Load Of The Self-elevating Platform Locating On The Beibu Gulf

Calculating the wind and wave load of the self-elevating platform in the operating situation is the key item of the design and assessment of the platform. The paper chose the self-elevating platform(Super M2) locating on the Beibu Gulf in the South China Sea as the researching object of the wind and wave load. Specifically, the environmental parameters including the wind speed and significant wave height were updated, and the definition and recommended value of the fluid dynamic parameters in the assessment were reconsidered. Lastly, the difference of the displacement response of the platform under dangerous wind direction caused by modified parameters was analyzed. The work and conclusion were as follows:(1) The data of environmental long-term variable in the Beibu Gulf was obtained from ECMWF database and four samples were conducted according to the data. Then the samples were fitted by three common 1D extreme-value distributions and four classical parameter-estimating methods. The environmental parameters were calculated based on the unique factor. The results showed that Gumbel distribution is the best one, and Log-normal distribution is the second, while the Weibull distribution is the worst one. The best parameter-estimating method of the Gumbel distribution is least-square method. Lastly, according to the approach of predicting the environmental parameters, the unique factor method, the wind speed is 24.7608 m/s and the significant wave height is 5.6640 m.(2) The correlation analysis of the two samples(sample A: dominant wind and following wave, sample B: dominant wave and following wind) was finished. Consequently, the samples were fitted by three 2D extreme-value distribution including BMGD, BGLD, bivariate Log-normal distribution and three kinds of Copula distribution. The environmental parameters were calculated based on the conditional probability density function. The results showed that beside of the Gumbel Copula, the others perform well in the fitness of the samples. For sample A, the Frank Copula is the best one. However the Clayton Copula is the most appropriate one for sample B. The environmental parameters are more conventional than the above mentioned one and the mean value of conditional function is more conventional than the maximum value of it.(3) The definition of the wind resistance coefficient respect of wind load and the stable simulating method of wind load were given. Based on the mentioned theory, the influence of wind direction on wind load and its corresponding resistance coefficient is researched. The results showed that the drag coefficient is varied from 1.15 to 1.44. Under the direction of 90°and 45°, it reaches to the maximum value, 1.43, and the minimum, 1.15. Except of the direction of 90°, the drag coefficient keeps low level, approximately, 1.2. The mentioned parameters can be interpreted by the simulating air-field.(4) The definition of the drag coefficient of the chord and the dynamical simulating method of current load were given. Based on the mentioned theory, the influence of the roughness of the chord and water direction on wave drag coefficient is researched. The results showed that under the water direction of 0°, the drag coefficient linear with the logarithmic term of the roughness and the recommended value in the standard agree well with the simulating one. When the water direction ranging from 0 ° to 45 °, the recommended value coincide to the simulating one under the roughness of R3~R7. However, when the water direction angle is ranging from 45° to 75°, the simulating is bigger than the recommended one obviously. At last, the simulating coefficient is returned to the recommended value.(5) The effects of the different groups involved environmental parameters and fluid dynamic parameters on displacement response of self-elevating platform were researched. The results showed that the major index of displacement calculated from the unique factor method is higher than the one from the conditional probability density function method. The effect of the modified fluid dynamic parameters on the index is not obvious, while the effect of wind resistance coefficient is sharper than the drag coefficient.