Characteristic Variables In Wind Wave Interaction

The study is made on surface roughness and wind speed scaling by analyzing wind and wave data in an experiment made in wind wave channel.In the past several decades, extensive studies have been made on the roughness. Observations in recent years showed that the roughness decreases with wave age. However, considerable scatter exists in some of the results. This indicates that surface roughness may depend on some other factors in wind wave fields. The experiment was made in the wind wave channel in the Laboratory of Physical Oceanography in Ocean University of China. The wave surface displacements and the vertical wind profile over the wave field were measured at ten fetches in the channel. By studying the relation between roughness and wave steepness, it is found that the roughness increases with spectral width. For waves with broad spectrum the roughness is remarkably higher than waves with narrow spectral width. For narrow spectrum, the roughness decreases with the decreasing wave steepness. For broad spectrum the roughness may be high even for low wave steepness and high wave age. This indicates that spectral width is important in determining the roughness.The wind speed distribution over the wave surface is studied by analyzing the data in the experiment. The concept of entropy is applied in studying the distribution. It is found that the entropy of the distribution of wind speed increases with the increasing wave steepness and the spectral width. The distribution of wind speed deviates from the normal distribution.In analyzing the data in the wind wave channel, it is found that the friction velocity scaling greatly reduces the scatter in the scaling using wind speed at 10m height. The friction velocity scaling has much less scatter than the scaling using other wind speeds. The friction velocity seems to play a distinctive role in wave growth. The result is important in the applications of the similarity theory and in wave modeling. In theory it gives an insight into the mechanism of wind wave interaction.