Standardization Of Wind Speed Measurements At Near Ground Level From Isolated Islands And Associated Applications

Due to the merits of easy availibity and low costs,in-situ measurements of wind at near ground levels have been widely used in the field of wind engineering for both theoretical studies and engineering practices,such as the wind resistance design of high-rise buildings,the site selection of wind power plants and the evaluation of wind energy.In recent years,with the fast development of coastal and maritime activities,field measurements of surface wind from offshore islands have received increasing concerns.However,the above data are usually affected by the influences of island topography and the variation of marine with approaching wind strength.Direct use of these data without corresponding correction may cause great errors for subsequent applications.Therefore,it is necessary to correct the measurement data into their counterparts that correspond to a standard height?e.g,10 m?above a reference terrain?terrain roughness z₀=0.03 m?and associated with a reference average duration?e.g.,10 min?.At present,existing theoretical method for correcting field measurements of surface wind is generally only applicable for the cases with an open flat terrain.Meanwhile,most studies on the standardization of near-surface wind speed data from offshore islands only consider the influence of topographic effects.Based on the above situation,this study presents a systematic study on the standardization of wind speed measurements at near ground level from isolated islands by a combined consideration of the topographic effects and the speed-dependence of marine roughness.A standardization scheme has been proposed to eliminate the above effects effectively.The proposed standardization method is then applied in conjunction with varied statistical models to evaluate the extreme-wind climate feature and wind energy around an offshore island.The standardization scheme is established with the aid of an atmospheric boundary layer wind tunnel laboratory.Rough elements,whose heights can be adjusted through remote control,are adopted to generate a series of approaching winf flied with varied roughness length for simulating the speed-dependence of marine roughness.A topographic model of an isolated island is then tested in the wind tunnel under the context of a series of approaching wind fields with varied z0.Values of correction factor?CF?to eliminate combined topographic/terrain effects are obtained through wind tunnel tests and theoretical analysis.Then,the measurement records of surface wind speed from the island are standarizaed by using the CFs.The correction results are further compared with those from peers.It is found that the CF values from previous studies,which only account for a fixed marine roughness setup,are all reasonably located in the range of CFs obtained in this study,which reflects the validity of the standardization method proposed in this thesis.Based on the proposed standardizaton method,field measurements of surface wind from an isolated island is corrected to their potential values associated with a reference condition.The corrected measurement data are then used to asssess the regional extreme-wind climat characteristics and wind energy.In the thesis,the extreme wind dominated by typhoon in the50-year recurrence period is analyzed.The wind speed data recorded by waglan island meteorological station for 61 years are modified by the method of correcting the double effects of topography and sea surface roughness.Moment method,Gumbel method,Excess over Threshold method,Lieblein BLUE method and XIMIS method were used as the parameter estimation methods of extreme type I distribution to study the extreme wind analysis of wind speed data before and after standardization.The results of the modified terrain and sea surface roughness in this study were compared with the results of extreme wind calculated by the same method which larger about 2m/s.Furthermore,the measured wind speed data required in the assessment of offshore wind energy before the location of the far offshore wind farm is modified by the method of standardization proposed in this thesis.Then the statistical method and Weibull method are used to evaluate the wind speed data before and after standardization.The results show that the regional extreme winds obtained from the wind speed data before and after standardization are quite different.The wind energy density obtained by using the revised wind speed data is more concentrated and the effective wind speed frequency increases.This thesis proposed a systematic standardization scheme to eliminate the combined influenc of togogaphic effects and effects due to speed-dependence of marine roughness on field masurements from isolated islands,based on which some application studies have been conducted.In consideration of the fast developments of offshore civil structures and offshore wind energy,results from this study are expected to cater for the increasing requirements about high-quality in-situ measurements of offshore wind and more ciredible assessment results.