Experimental Investigation of Breaking Criteria of Wind-Generated Deepwater Waves

In a wind wave flume, waves were generated using three different wind speeds and measured at two locations to obtain wave trains of no, intermittent, or frequent breaking. Water particle movement and free surface elevation were measured simultaneously using a PIV system and a wave gauge, respectively. For wind waves, not all the waves measured at a fixed location are breaking waves, and the breaking of a larger wave is not guaranteed. However, the larger the wave height, the larger the probability of breaking. In order to take as many breaking waves as possible for the cases of frequent breaking, we used the waves whose heights were close to the highest one-tenth wave height. The experimental results showed that the geometric or kinematic breaking criteria could not explain the occurrence of breaking of wind waves. On the other hand, the vertical acceleration beneath the wave crest was close to the previously suggested limit value, -0.5 g, when frequent breaking of large waves occurred, indicating that the dynamic breaking criterion would be good for predicting wave breaking of deepwater wind waves.