The object of present study is to investigate the bed shear stress on a slope under regular breaking waves by a novel instrument named Micro-Electro-Mechanical System （MEMS） flexible hot-film shear stress sensor. Th...The object of present study is to investigate the bed shear stress on a slope under regular breaking waves by a novel instrument named Micro-Electro-Mechanical System （MEMS） flexible hot-film shear stress sensor. The sensors were calibrated before application, and then a wave flume experiment was conducted to study the bed shear stress for the case of regular waves spilling and plunging on a 1 ： 15 smooth PVC slope. The experiment shows that the sensor is feasible for the measurement of the bed shear stress under breaking waves. For regular incident waves, the bed shear stress is mainly periodic in both outside and inside the breaking point. The fluctuations of the bed shear stress increase significantly after waves breaking due to the turbulence and vortexes generated by breaking waves. For plunging breaker, the extreme value of the mean maximum bed shear stress appears after the plunging point, and the more violent the wave breaks, the more dramatic increase of the maximum bed shear stress will occur. For spilling breaker, the increase of the maximum bed shear stress along the slope is gradual compared with the plunging breaker. At last, an empirical equation about the relationship between the maximum bed shear stress and the surf similarity parameter is given, which can be used to estimate the maximum bed shear stress under breaking waves in practice.展开更多
As wave propagates into shallow water, the shoaling effect leads to increaseof wave height, and at a certain position, the wave will be breaking. The breaking wave is powerfulagents for generating turbulence, which pl...As wave propagates into shallow water, the shoaling effect leads to increaseof wave height, and at a certain position, the wave will be breaking. The breaking wave is powerfulagents for generating turbulence, which plays an important role in most of the fluid dynamicalprocesses in the surf zone, so a proper numerical model for describing the turbulent effect isneeded urgently. A numerical model is set up to simulate the wave breaking process, which consistsof a free surface model using the surface marker method and the vertical two-dimensional model thatsolves the flow equations. The turbulence is described by Large Eddy Simulation (LES) method wherethe larger turbulent features are simulated by solving the flow equations, and the small-scaleturbulence that is represented by a sub-grid model. A dynamic eddy viscosity sub-grid scale stressmodel has been used for the present simulation. The large eddy simulation model, which we presentedin this paper, can be used to study the propagation of a solitary wave in constant water depth andthe shoaling of a non-breaking solitary wave on a beach. To track free-surface movements, The TUMMACmethod is employed. By applying the model to wave breaking problem in the surf zone, we found thatthese model results compared very well with experimental data. In addition, this model is able toreproduce the complicated flow phenomena, especially the plunging breaker.展开更多
Free surface elevation time series of breaking water waves were measured in a laboratory flume. This was done in order to analyze changes in wave characteristics as the waves propagated from deep water to the shore. A...Free surface elevation time series of breaking water waves were measured in a laboratory flume. This was done in order to analyze changes in wave characteristics as the waves propagated from deep water to the shore. A pair of parallel- wire capacitive wave gages was used to simultaneously measure free surface elevations at different positions along the flume. One gage was kept fixed near the wave generator to provide a reference while the other was moved in steps of 0.1 m in the vicinity of the break point. Data from these two wave gages measured at the same time constitute station-to-station free surface elevation time series. Fast Fourier Transform (FFT) based cross-correlation techniques were employed to determine the time lag between each pair of the time series. The time lag was used to compute the phase shift between the reference wave gage and that at various points along the flume. Phase differences between two points spaced 0.1 m apart were used to calculate local mean wave phase velocity for a point that lies in the middle. Results show that moving from deep water to shallow water, the measured mean phase velocity decreases almost linearly from about 1.75 m/s to about 1.50 m/s at the break point. Just after the break point, wave phase velocity abruptly increases to a maximum value of 1.87 m/s observed at a position 30 cm downstream of the break point. Thereafter, the phase velocity decreases, reaching a minimum of about 1.30 m/s.展开更多
基金supported by the National Key Scientific Instrument and Equipment Development Project(Grant No.2013YQ04091108)the National Natural Science Foundation of China(Grant No.51309158)
文摘The object of present study is to investigate the bed shear stress on a slope under regular breaking waves by a novel instrument named Micro-Electro-Mechanical System （MEMS） flexible hot-film shear stress sensor. The sensors were calibrated before application, and then a wave flume experiment was conducted to study the bed shear stress for the case of regular waves spilling and plunging on a 1 ： 15 smooth PVC slope. The experiment shows that the sensor is feasible for the measurement of the bed shear stress under breaking waves. For regular incident waves, the bed shear stress is mainly periodic in both outside and inside the breaking point. The fluctuations of the bed shear stress increase significantly after waves breaking due to the turbulence and vortexes generated by breaking waves. For plunging breaker, the extreme value of the mean maximum bed shear stress appears after the plunging point, and the more violent the wave breaks, the more dramatic increase of the maximum bed shear stress will occur. For spilling breaker, the increase of the maximum bed shear stress along the slope is gradual compared with the plunging breaker. At last, an empirical equation about the relationship between the maximum bed shear stress and the surf similarity parameter is given, which can be used to estimate the maximum bed shear stress under breaking waves in practice.
文摘As wave propagates into shallow water, the shoaling effect leads to increaseof wave height, and at a certain position, the wave will be breaking. The breaking wave is powerfulagents for generating turbulence, which plays an important role in most of the fluid dynamicalprocesses in the surf zone, so a proper numerical model for describing the turbulent effect isneeded urgently. A numerical model is set up to simulate the wave breaking process, which consistsof a free surface model using the surface marker method and the vertical two-dimensional model thatsolves the flow equations. The turbulence is described by Large Eddy Simulation (LES) method wherethe larger turbulent features are simulated by solving the flow equations, and the small-scaleturbulence that is represented by a sub-grid model. A dynamic eddy viscosity sub-grid scale stressmodel has been used for the present simulation. The large eddy simulation model, which we presentedin this paper, can be used to study the propagation of a solitary wave in constant water depth andthe shoaling of a non-breaking solitary wave on a beach. To track free-surface movements, The TUMMACmethod is employed. By applying the model to wave breaking problem in the surf zone, we found thatthese model results compared very well with experimental data. In addition, this model is able toreproduce the complicated flow phenomena, especially the plunging breaker.
文摘Free surface elevation time series of breaking water waves were measured in a laboratory flume. This was done in order to analyze changes in wave characteristics as the waves propagated from deep water to the shore. A pair of parallel- wire capacitive wave gages was used to simultaneously measure free surface elevations at different positions along the flume. One gage was kept fixed near the wave generator to provide a reference while the other was moved in steps of 0.1 m in the vicinity of the break point. Data from these two wave gages measured at the same time constitute station-to-station free surface elevation time series. Fast Fourier Transform (FFT) based cross-correlation techniques were employed to determine the time lag between each pair of the time series. The time lag was used to compute the phase shift between the reference wave gage and that at various points along the flume. Phase differences between two points spaced 0.1 m apart were used to calculate local mean wave phase velocity for a point that lies in the middle. Results show that moving from deep water to shallow water, the measured mean phase velocity decreases almost linearly from about 1.75 m/s to about 1.50 m/s at the break point. Just after the break point, wave phase velocity abruptly increases to a maximum value of 1.87 m/s observed at a position 30 cm downstream of the break point. Thereafter, the phase velocity decreases, reaching a minimum of about 1.30 m/s.
