حساسيت ارتفاع پيش بيني شده امواج نسبت به زمان تداوم باد

SENSIBILITY OF PREDICTED WAVE HEIGHT TO WIND DURATION

In order to predict wave height from wind data, information on fetch, wind velocity direction and duration is necessary. Due to complexity and difficulty of wind duration determination for a large amount of data, say some years of available -hours wind data, and the amount of time and money needed for doing this, Engineers usually consider a constant wind duration of ror f hours in their analysis. On the other hand, the expense of marine projects dramatically increases with increase in wave height and thus, we are obliged to predict wave characteristics as accurate as possible. Therefore, it is necessary to investigate the effects of above-mentioned assumption about wind duration on predicted wave heights. In this paper, more than -years wind and wave data recorded in Bushehr coastal area is used to investigate the sensibility of predicted wave height to wind duration. Constant r and f hours wind durations together with observed wind velocities and calculated fetch lengths are used in prediction method introduced in shore protection manual (SPM) to predict wave height. Comparisons between the results and the measured wave heights at the same wind conditions reveal that consideration of constant rand ,c hours wind duration give rise to inaccurate prediction results for wave height. To provide simple but more accurate estimations of wind duration, the observed wave heights, wind velocities, and calculated fetches are used to give a prediction formulation for wind duration in Bushehr area only as a function of wind velocity. Using the proposed formula and resulted value for wind duration, wave height is expected to be predicted more accurately in Bushehr coastal area.