The 12th International Conference on Hydrodynamics
18 – 23 september 2016, Egmond aan Zee, The Netherlands
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EVOLUTION CHARACTERISTICS OF WAVE PERIODS FOR DEEP-WATER BREAKING WAVES


Go-down ichd2016 Tracking Number 116

Presentation:
Session: Linear and-linear waves III
Room: Room 1
Session start: 10:30 Wed 21 Sep 2016

Shuxiu Liang   sxliang@dlut.edu.cn
Affifliation: Dalian University of Technology

Yonghong Rao   121361968@qq.com
Affifliation: Navy Engineering Design and Research Institute

Xiaoning Tang   tang_xn@163.com
Affifliation: Navy Engineering Design and Research Institute

Yanling Chang   1174714244@qq.com
Affifliation:


Topics: - Linear and non-linear waves and current

Abstract:

Wave factors(wave height, period) are the important environmental conditions for the ocean engineering design. At present, general numerical wave models, such as SWAN、WAVEWATCH can directly calculate out the significant wave height and spectral averaging periods .While there are many factors ignored in the simulation and little research on factors affecting the wave periods. The evolution characteristics of the wave period of deep-water extreme breaking waves common in the ocean are mainly analyzed based on an experiment. Deep-water breaking waves are generated by the energy focusing method in a 2-D wave flume and the breaking strength that range from gently spilling to plunging is greater by increasing the input wave steepness. The spectral averaging periods T0,1、T0,2、T0,-1、T0,-2 are computed by a fast Fourier transform (FFT) and the average period T and significant period TH1/3 are computed using Zero-up crossing method based on surface elevations. Experimental results show that whether waves break or not, the four kinds of spectral averaging periods are all stable before and after focusing area. T0,-2 is the most stable among them. And changes of spectral averaging periods in the focusing area are irregular. The average period T and significant period TH1/3 in upstream focusing area are rather unstable. Due to the fewer wave components, they could not reach the statistical requirements for Zero-up crossing method. For smaller input wave steepness, waves focus at the focal point with non-breaking. Wave periods have no significant change after the focal point because of the weak nonlinear interaction of wave components outside the focusing area. While breaking causes wave periods increasing and the increment of wave periods are more appreciable as the wave breaking is stronger. Especially the wave period T0,2 changes most obviously and it increases 7% after breaking for plunging breaker, which are determined by the definition of the spectral averaging periods and the evolution characteristics of the wave energy spectrum. It’s concluded that T0,2 is the most suited to express the characteristics of the wave period of extreme breaking waves through comprehensive analysis from the stability and evolution characteristics of the wave energy spectrum in focusing and breaking process.