Maximum Entropy Estimation of n-Year Extreme Waveheights

A new method for estimating the n (50 or 100) -year return-period waveheight, namely, the extreme waveheight expected to occur in n years, is presented on the basis of the maximum entropy principle. The main points of the method are as follows: (1) based on the Hamiltonian principle, a maximum entropy probability density function for the extreme waveheight H, f(H)=αHγ e -βH4 is derived from a Lagrangian function subject to some necessary and rational constraints; (2) the parameters α, β, and γ in the function are expressed in terms of the mean , variance V= (H-)2 and bias B= (H-)3 ; and (3) with , V and B estimated from observed data, the n -year return-period wave height H n is computed in accordance with the formula 11-F(H n)=n , where F(H n) is defined as F(H n)=∫ H n 0f(H) d H. Examples of estimating the 50 and 100-year return period waveheights by the present method and by some currently used method from observed data acquired from two hydrographic stations are given. A comparison of the estimated results shows that the present method is superior to the others.

THE EFFECTS OF RADIATION STRESS ON WAVE HEIGHTS AND SEA LEVEL IN THE INTERACTION OF COUPLED WAVE-TIDE-SURGE IN THE COASTAL AREA

Based on coastal high-resolution (2′X2′) coupled wave-tide-surgeinteraction numerical model, the effects of radiation stress on wave heights and sea level in thecoastal area of Huanghe Delta were studied. By comparisons of simulated and measured wave heightsand sea level for two mediately strong weather cases, it is demonstrated that the results simulatedby coupled wave-tide-surge model are closer to the measured and particularly in excellent agreementin the extreme values of the wave heights and set-up. This study shows that the radiation stress canincrease the wave heights maximally to 67cm and sea level to 40cm. It is also found that there areareas of over 50cm wave height increase and an area of over 20cm sea level increase in the HuangheDelta coastal area, and this find may be very important in engineering. For this reason, it issuggested that in the practical engineering application, the coupled wave-tide-surge interactionnumerical model should be prefered.

Experimental Determination of Significant Waveheight by OSMAR071: Comparison with Results from Buoy

OSMAR071 is the latest product of the OSMAR （ocean state monitor and analysis radar） series of high frequency surface wave radar （HFSWR）, which was developed by the Radiowave Propagation Laboratory of Wuhan University. It adopts a modified Barrick waveheight inversion model. The modifications are introduced to improve the model＇s performances under the effect of noises and interferences and in the case of broad beam radar detection. The two unknown coefficients in the modified model are figured out by fitting the HFSWR significant waveheight results to those output from a wave buoy located in the radiating coverage of the radar site. The model is applied to inverse the waveheights from radar data for the duration from Dec. 1st, 2008 to Feb. 25th, 2009, and then the radar waveheights are compared with the buoy measurements. Results show that the rms difference between radar-derived significant waveheights and those from the buoy is 0.38 m and the correlation coefficient between the two series is 0.66. This study describes OSMAR071 observation of significant waveheight with relatively satisfactory accuracy during about three months.