Short-term Forecast And Investigation On Probabilistic Characteristics Of Wave Loads To Ship

In this paper, based on the response to wave loads, studies how todetermine the bulk carriers and oil tankers at any given time to run to the actual seaconditions change characteristics of wave loads by theoretical calculations. Waveloads forecast are based on theoretical calculations of wave loads on the applicationof stochastic process theory.Direct calculations of the short-term wave induced loads are carried out for theactual ships of6bulk carriers,6oil tanks by WALCS software. The laws of thevertical mid-ship bending moment, the vertical shear fore at L/4（L is ship length）andthe vertical shear force at3L/4are analyzed for the two types of ships at the situationof0speed in head sea and uniform full loads or interval cabin full loads. Accordingto these laws, a set of empirical formula for short-term forecast of ships’ verticalwave loads are given in this paper.Application of extreme value theory and DNV (note30.4) method,forecasting the boat amidships vertical bending moments of six bulk carriersand ten oil tankers in different loading conditions, different time periods.After comparing vertical wave bending moment value of extreme valuetheory with vertical wave bending moment value of DNV method of six bulkcarriers and ten oil tankers under all significant wave heights, it’s found thatDNV approach larger than the extreme value theory between10%-15%. Bulkcarriers’ vertical wave bending moment values of loading conditions ofuniform load are larger than loading conditions of bulkhead full, bulkcarriers’ vertical wave bending moment values of loading conditions of lightballast to the port are smaller than loading conditions of light ballastdeparture, bulk carriers’ vertical wave bending moment values of loadingconditions of heavy ballast to the port are smaller than loading conditions ofheavy ballast departure. Oil tankers’ vertical wave bending moment values ofloading conditions of uniform load are larger than loading conditions ofbulkhead full, oil tankers’ vertical wave bending moment values of loading conditions of ballast to the port are smaller than loading conditions of ballastdeparture.Finally, short term wave loads of6bulk carriers and10oil tankers areforecast by WALCS software. Also based on extreme value theory, forecastthe short term wave bending moment of16ships, and the two kinds of resultswere compared. Meanwhile two parameters and their expectations andvariance of extreme type I distribution can be identified.