In confirming whether the guarantee speed of ship is satisfied or not,the effect of estimation result of ship's air resistance due to wind isconsiderably high. The air resistance could be generally determinedfrom the wind tunnel test, data set of similar vessels or empiricalmethods according to ISO15016:2015. The wind tunnel test for a shipis performed by using a model-ship less than 2 meters in length due tovery sensitive blockage effect. Wind speed in tunnel is not high enoughto meet the Reynolds number of full scale ship. However the turbulenceintensity and wind profile in test section are simulated for similarity ofactual ocean wind. Data set of similar vessels and empirical formulasare used as economic options but these are less accurate because it isdifficult to take into account the exact geometrical characteristics of thetarget ship. Alternatively, full scale CFD can be applied to determinethe air resistance of a ship for geometrical and physical similarity. Inthis paper, full scale CFD results of two general cargo ships for airresistance are compared with Fujiwara formula and the data set ofISO15016:2015. In case of CFD computation, atmospheric boundarylayer is functionally simulated based on Frøya wind profile for winddirections of 0 to 180. Comparative analysis between model and fullscale is also carried out to examine the scale effect. Finally, thedifference of resistance increase due to wind is based on ISO15016 isinvestigated according to the results of CFD, data-set and empiricalformulas for air resistance. The difference of air resistance results byeach method shows that the uncertainty can be increased in the shipspeed-power correction. This study confirms that the application ofmore accurate data for air resistance is an important factor in theverification of ship guarantee speed.
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