A laboratory investigation of effects of long waves on statistical properties of short waves

The statistical properties of short wind waves under the influence of long waves are investigated based on wave data from a laboratory experiment carried out in the large Marseille-Luminy wind wave tank. The wind waves are generated with various fetches and speeds. The long wave is mechanically generated by a submerge paddle and propagates in the wind direction. Surface wave elevations are measured by an array of capacitance wave gauges aligned in the wind direction. The long wave effects are examined based on the statistical parameters derived from the probability distribution and zero-up-crossing wave height and wave period of wind waves. In the absence of long waves, the skewness of the probability distributions, an index of wave nonlinearity, shows a clear dependence to the increase of the significant slopes of wind waves. The presence of long waves significantly decreases the skewness and the dependence to the wave slopes. The wind waves riding on the crest of long waves show a larger mean wave height and shorter mean wave period than those riding in the trough of long waves