Intensity Change Trend Of Typhoons Occurred In Nearshore Area Of China And Their Return Wind Speeds Estimation

In recent years, there is a tremendous development of the trade between Chinaand other countries, and marine transport plays a crucial role in this progress. Soports、breakwaters、sea dikes and other offshore structures increase quickly, and theybecome more and more important. Offshore oil drilling platforms in the coastal watersof China become more and more common as the further mining of marine petroleum.So it must be related to the safety of these marine structures. This Safety andeconomics are contradicted when the offshore engineering is designed, which dependon the cognition of the ocean environmental conditions. Throughout the world，typhoon occurred more frequently in China, especially in the South China Sea andEast China Sea. And the position whereat China typhoons reached their maximumstrength had a trend to move northwards during its life. Historically, the occurrencesof major natural disasters in coastal waters of China almost have relations with thetyphoons. The climate is growing warming in the recent years, and risingtemperatures would make typhoon stronger in turn. These dynamic changes putforward a new challenge to the accurate calculations of hydrology extremes in thedesign of marine structures. Better estimations of return values for hydrologicalelements would result in the safer application of marine engineering structures.The main works are as follows:1. The moving average method is adopted to analyze the trend of the frequencies,strengths and annual extreme strengths of the typhoons which affected China in thepast58years. And the Spearman rank correlation method is adopted to conduct thesignificance tests. Then forecast the future trends of frequencies, strengths and theannual extreme strengths of typhoons by Rescaled Range Analysis based on fractaltheory. The results show that the frequencies, strengths and annual extreme strengthsof typhoons which will affect China increase and become stronger. And there is a positive relation between annual frequencies and strengths of typhoons.2. The maximum entropy distribution consists of almost all the common extremevalue distributions, and it is the general formula of these distributions. The furtherstudies have obvious theoretical and practical significance. The maximum likelihoodmethod is used to calculate the parameter estimations of maximum entropydistribution. And the34years annual maximum wave height data observed inWeizhou hydrological station are applied to test the maximum likelihood method, andthe result shows that it’s a good complement to curve fitting method, and the returnvalues calculated satisfy the design need of the local marine structures. Maximumlikelihood method is also introduced into the Poisson maximum entropy distribution,and calculate the return values of the hydrology extremes in the typhoon-prone waters.And typhoon data of Taiwan’s Hualien Port, for example, to verify the applicability ofthe Poisson-maximum entropy distribution of the maximum entropy maximumlikelihood method parameters.3. Marine engineering design should pay more attention to climate warming. Theclimate is warming still. The rising temperature of ocean can increase the frequencyand intensity of typhoons. We should consider these aspects in marine engineeringdesign. At last, a correction formula of return values for hydrological elements in thetyphoon-prone waters is given.