On the basis of 21 years hindcasted data in the Bohai Sea, a Trivariate Nested Logistic Distribution model is utilized to calculate the joint probability of extreme environmental conditions, such as wind speed, significant wave height, and current velocity, which simultaneously occur during storm processes. Statistical analysis shows that this approach is simple in mathematical form, explicit in its expression, and can be easily applied to parameter estimation. It involves hierarchical dependence and can be applied to a wider field than the symmetric Logistic model. The ocean environmental contours in three demensions are created rather than the usual two. The contours as slices through return periods of wind speed is displayed to find the mode of wave height and current velocity. Based on the multivariate extreme value distribution theory, the determination of environmental parameter values will be objective and reasonable in engineering design.

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