Combinatorial Analysis Of Extreme Design Water Level In Coastal Engineering

Reasonably determining the return values of extreme water level is an important part to design disaster-prevention structures in coastal engineering. Traditional univariate frequency analysis method generally ignores the combined action of multi-loads on marine structures. Although joint probability method of astronomical tide and storm surges considers each element as independent event, the marginal distribution of each variable can not be selected as its best fitted distribution due to the restrict of bivariate theoretical distribution. And there are still less practical bivariate theoretical models. Let both probability and probability density of marginal distribution be equal to those of a normal distribution, an equivalent bivariate distribution will be established by means of bivariate normal distribution. The type of this joint distribution can be classified according to the type of its marginal distribution. Considering the correlation between astronomical tides and storm surges, this paper sets up an equivalent bivariate distribution to estimate the joint probability of extreme wave height and wind speed. Extreme design water levels of a certain coastal engineering are given out with several methods for reference of the corresponding government department. The main content of this paper is as follows:1. To summrize the existing univariate and bivariate statistical distribution model in coastal engineering.2. To propose a set of equivalent bivariate distribution models, such as: equivalent bivariate Pearson-â…¢distribution model, equivalent Pearson-â…¢and log-normal mixed bivariate distribution, et al.3. Data samples are selected from 29-year observed extreme wind speed and significant wave height at Weizhoudao Hydrologic Station. Equivalent bivariate Pearson-â…¢distribution is presented to calculate the joint return values of wind and wave with several different methods. Calculation results are given for ocean engineering design.4. Data samples are selected from 25-year observed data of astronomical tide and storm surges at Laizhou Hydrologic Station. Equivalent bivariate Pearson-â…¢distribution and equivalent bivariate Pearson-â…¢and Log-normal mixed distribution are put forward to calculate the joint return values of astronomical tide and storm surges with several different methods. Calculation results are given as decision-making references for departments of government, planning and design.