The Study On The Evolution Characteristics Of Breaking Waves Based On PIV And BIV Coupling

Wave-breaking is a common phenomenon in the activities of Ocean.When the wave propagates to shallow water,its wave steepness increases,then the wave-breaking occur.The deep-water waves,for example,the wind waves,can break on a certain condition.Wave-breaking plays an important role in the movement of sea-air interface and Marine environment.In addition,wave-breaking will dissipate a lot of wave energy,and it will have a great impact force on the structures.To learn more about the characteristics and mechanism of wave-breaking,it is necessary to study the wave breaking flow field more carefully,however,due to the limitation of traditional measurement methods,more comprehensive information of the crushing flow field cannot be obtained.At present PIV technology and BIV technology can effectively solve the defects of traditional contact method or single point method in wave breaking measurement.The measurement methods of laboratory wave-breaking using PIV technology and BIV technology and the flow field of laboratory wave-breaking need to be further explored.Aiming at the above problems,this paper discusses the characteristics of wave breaking flow field and the verification and improvement of PIV and BIV techniques in wave breaking measurement based on experiments.The main research contents and results are as follows:(1)Build PIV and BIV systems for laboratory measurement of breaking waves and verify them.According to the basic principles of PIV and BIV and the summary of previous literature,a PIV and BIV system suitable for breaking wave measurement is built in the laboratory.According to the existing equipment in the laboratory,a series of verification tests are carried out on the PIV and BIV system,which proves the accuracy of measurement of the system.(2)It is proved that two new illumination scheme can be used for BIV measurement,one of which can be used for both BIV and PIV measurement.By classifying lighting of BIV measurement,set up 10 different illumination scheme,measurement result is compared with general BIV illumination scheme,it is found the 7W laser with the back lights,4W laser with the front lights can be used as a general BIV lighting solution alternatives,and 7W laser with the back lights can be further used for BIV and PIV simultaneously measurement.(3)Through PIV and BIV coupling measurement,the global flow field of the breaking wave is obtained.Through the window partition,calibration and stitching of the breaking area and the processing of the overlapping area of adjacent windows and PIV-BIV,the global flow field of the breaking wave is finally obtained.The velocity field,structural characteristics and vorticity field of the selected working conditions are analyzed.(4)It is found that the maximum horizontal velocity in the bubble region of the plunging wave is about 1.66 times of the phase velocity,and the spilling wave was about 1.44 times.The breaking waves in different working conditions are set and measured in the bubble region.Among them,the ratio of the maximum velocity in the bubble region to the phase velocity calculated by the spectral peak frequency was 1.65~1.69 times,while that of the spilling wave is 1.44 times.