The parameters of principal and directional extrema in a marine environment are important in marine engineering design,especially for appropriate construction of oceanic platforms and other structures.When designing wave walls and break water structures,the orientation of the breakwater or seawall depends mainly on the direction of the strongest waves.However,the strength of the breakwater and the elevation of the seawall depend on the magnitude of the biggest wave height of the strongest waves.Thus,identification of directional extrema plays an important role in the design of wave factors.When calculating the directional extremum,different materials may require different specific computational methods,yet few theoretical studies have been conducted in this field of research.Based on multivariate extremum statistical theory,this paper utilizes a discrete random variable to build a joint probability model compounded by a discrete random variable and a multivariate continuous random variable.Furthermore,this paper provides the first investigation on the theories and methodologies to deduce wave directional extrema.The results provide tools for both creating the calculation method of the directional extremum value and providing the rational directional extremum parameters for marine engineering design.
Significant wave height is an important criterion in designing coastal and offshore structures.Based on the orthogonality principle, the linear mean square estimation method is applied to calculate significant wave height in this paper.Twenty-eight-year time series of wave data collected from three ocean buoys near San Francisco along the California coast are analyzed.It is proved theoretically that the computation error will be reduced by using as many measured data as possible for the calculation of significant wave height.Measured significant wave height at one buoy location is compared with the calculated value based on the data from two other adjacent buoys.The results indicate that the linear mean square estimation method can be well applied to the calculation and prediction of significant wave height in coastal regions.
A new compound distribution model for extreme wave heights of typhoon-affected sea areas is proposed on the basis of the maximum-entropy principle.The new model is formed by nesting a discrete distribution in a continuous one,having eight parameters which can be determined in terms of observed data of typhoon occurrence-frequency and extreme wave heights by numerically solving two sets of equations derived in this paper.The model is examined by using it to predict the N-year return-period wave height at two hydrology stations in the Yellow Sea,and the predicted results are compared with those predicted by use of some other compound distribution models.Examinations and comparisons show that the model has some advantages for predicting the N-year return-period wave height in typhoon-affected sea areas.
