The long-term prediction of extreme wave height and wind speed plays an important role in the maritime structure design. Based on the hindcast data, a Poisson Bivariate Logistic Distribution (PBLD) is proposed to calculate the joint probability of extreme wind speed and wave height simultaneously occurred during the storm processes. Compared with the single variable frequency analysis method, the joint design criteria of environmental loads calculated by the proposed bivariate distribution, are recommended to offshore structure design in the Bohai Bay. The calculated results show that the proposed bivariable statistical model fits the design of ocean engineering, which frequently suffers from storm attacks, especially in the exploitation of the marginal fields.
In last two decades, more than a half oil-gas fields in China discovered by China National Offshore Oil Corporation are marginal fields.
According to the traditional method, the design force of most platforms is dominated by waves. A wave height of 50 or 100 years return period is the commonly used design criterion, which was extended by employing the combination of the 100-year wave with the 100-year wind. The latter approach will lead to over-estimated results since the largest wave and wind of 100-year return period very rarely occur simultaneously. Wen and Banon (1991) showed that applying simultaneously 100yr wave height, 100yr wind speed, and 100yr current speed did over-predict the design overturning moment on a platform in the Gulf of Mexico by 17-21%. In order to reasonably decrease present design criteria for maritime structure design, much more researchers have concentrated on the study of multidimensional statistical analysis (Forristall et al, 1991; Wen and Banon, 1991; Coles and Tawn, 1994; API, 1995; Liu et al, 1995, 1996; Morton and Bowers, 1996; Zachary et al, 1998; Liu et al, 2000, 2002; Dong et al, 2003b, 2004).