A simple model for wave generation under varying wind condition

Sammanfattning: The Hanson Larson evolution model assumes that wave height grows or decays from an initial condition towards an equilibrium wave height through a simple exponential growth. The model uses wind input data, fetch length and depth measurements. Using this input parameters, it both determines the wave height and period values, thus predicts wave climate. The model is developed using deep water conditions where group velocity is assumed be constant. The model is validated using measured wave data from the Baltic Sea. The wave and input wind data are retrieved from the Swedish meteorological and hydraulic institute’s (SMHI) data base. The wind stations used in the analysis have a correlation coefficient of 0.72. The wind inputs were also checked for their reliability to represent the wind condition at the wave buoy. This was done by comparing the wind speed and wind direction measured at the wind stations. Whenever the difference between speeds was less than 5 m/s and wind direction difference less than 45 degrees, the wind input was taken as reliable. The wave heights calculated were in a fair agreement with observed values for most of the trial runs, except when wind direction was abruptly changing. The error observed was more for wave periods as compared to wave height, but the growth and decay pattern calculated by the model was similar as the observed pattern. Other two more models based on wave energy analysis are also tested as to predict wave height and wave period, from wind input data. In comparison to the Hanson Larson evolution model, these models resulted in more disagreement between calculated and observed values, rendering them less useful.