Numerical Simulation Of Waves In Bohai Sea And Research On The Influence Of Swells On Wind Waves

Waves play an important role in ocean dynamic environment and air-sea interactions. And the numerical simulation of waves is a key part in the study of ocean waves. There are many controversies in the affect by swell to wind wave. By means of the third-generation ocean wave model SWAN, the wave in the Bohai Sea is numerically modeled. Parameter settings are improved for the application of SWAN to the waves in the Bohai Sea. Laboratorial and field measurements of waves are conducted to study the affects by swells to the growth of wind waves.The mixed wind data of QuickSCAT/NCEP are used as the input wind field of SWAN in the modeling of waves in the Bohai Sea. And the measured data is from the field observation in the oil platform in the Bohai Sea. The numerical test shows that there is no effective influence on the calculation by the computational grid. And the numerical test also shows that the term of dissipation due to whitecapping is important and greatly influence the calculation.There are 6 schemes in SWAN, involving 3 kinds of wind input schemes and 4 kinds of whitecapping dissipation. These schemes are tested respectively to find if the default indexes of SWAN fits the Bohai Sea well. Results show that the default modeling of wave height and period are less than the measurement. So the indexes of whitecapping dissipation in each scheme are revised, in order to find the most suitable indexes. From the results, to modeling of waves in the Bohai Sea, the expressions of wind input and whitecapping dissipation from Komen and the saturation based model are found to be more suitable.The swells'influence to wind waves in laboratory and open ocean are studied respectively. Experiments are conducted in wave tanks to measure the displacement of wind waves with or without long waves which are mechanically made to represent swells. The ratio of zeroth-order spectral moments could indicate the energy of wind waves with or without swells then indicate the influence of swells to the energy of wind waves. In most case, swell suppresses the growth of wind waves. And the results shows that the suppression by swell of wind-wave energy increases with the steepness of swell ( S ), reverse wave age ( u / C) and ratio ( f s /fwp)of the spectral peak frequency of the swell to the wind wave frequency. The ratios correlated with wave energy can be described by its relationship with the dimensionless parameter . Additionally, the swell will increase the growth of wind waves in some special cases.In the open ocean, the results of some numerical experiment shows that the swell moves with or opposite to the wind waves would enhance the growth of wind waves in the default expression of SWAN, while in the saturation based model, there is no effect of swell on wind waves. Farther more, wave spectrum with normal wind inputs and of pure wind waves are modeled with field measurements. The results indicate that the opposite swell could low the peak frequency of wind waves, while the following swell would not effect the growth of wind waves.