An analytical solution for predicting the vertical distribution of streamwise mean velocity in an open channel flow with submerged flexible vegetation is proposed when large bending occurs. The flow regime is separate...An analytical solution for predicting the vertical distribution of streamwise mean velocity in an open channel flow with submerged flexible vegetation is proposed when large bending occurs. The flow regime is separated into two horizontal layers: a vegetation layer and a free water layer. In the vegetation layer, a mechanical analysis for the flexible vegetation is conducted, and an approximately linear relationship between the drag force of bending vegetation and the streamwise mean flow velocity is observed in the case of large deflection, which differes significantly from the case of rigid upright vegetation. Based on the theoretical analysis, a linear streamwise drag force-mean flow velocity expression in the momentum equation is derived, and an analytical solution is obtained. For the free water layer, a new expression is presented, replacing the traditional logarithmic velocity distribution, to obtain a zero velocity gradient at the water surface. Finally, the analytical predictions are compared with published experimental data, and the good agreement demonstrates that this model is effective for the open channel flow through the large deflection flexible vegetation.展开更多
Water waves in coastal areas are generally non- linear, exhibiting asymmetric velocity profiles with different amplitudes of crest and trough. The behaviors of the bound- ary layer under asymmetric waves are of great ...Water waves in coastal areas are generally non- linear, exhibiting asymmetric velocity profiles with different amplitudes of crest and trough. The behaviors of the bound- ary layer under asymmetric waves are of great significance for sediment transport in natural circumstances. While pre- vious studies have mainly focused on linear or symmetric waves, asymmetric wave-induced flows remain unclear, par- ticularly in the flow regime with high Reynolds numbers. Taking cnoidal wave as a typical example of asymmetric waves, we propose to use an infinite immersed plate oscillat- ing cnoidally in its own plane in quiescent water to simulate asymmetric wave boundary layer. A large eddy simulation approach with Smagorinsky subgrid model is adopted to investigate the flow characteristics of the boundary layer. It is verified that the model well reproduces experimental and theoretical results. Then a series of numerical experiments are carried out to study the boundary layer beneath cnoidal waves from laminar to fully developed turbulent regimes at high Reynolds numbers, larger than ever studied before. Results of velocity profile, wall shear stress, friction coeffi- cient, phase lead between velocity and wall shear stress, and the boundary layer thickness are obtained. The dependencies of these boundary layer properties on the asymmetric degree and Reynolds number are discussed in detail.展开更多
With the large-scale density stratified tank and the numerical flume proposed,series of numerical cases in line with the experiments are carried out to investigate the interaction between the tension leg platforms(TLP...With the large-scale density stratified tank and the numerical flume proposed,series of numerical cases in line with the experiments are carried out to investigate the interaction between the tension leg platforms(TLPs)and the internal solitary waves(ISWs).The waveforms,and the loads and the torques on the TLP obtained by the experiments and the simulations agree well with each other.Experimental results show that the amplitudes of the dimensionless horizontal force and torque linearly increase with the dimensionless amplitude,while that of the vertical force increases in a parabolic curve.Besides,the numerical results indicate that the horizontal and vertical forces on the TLP due to the ISWs can be divided into three components,namely,the wave pressure-difference forces,the viscous pressure-difference forces,and the frictional force that is negligible.The wave pressure-difference forces are always the major constituents.However the viscous pressure-difference component is unimportant,it is negligible as compared with the vertical forces.展开更多
The fission of solitary waves propagating over variable topography is investigated.In previous theories,to predict the number and the amplitudes of disintegrated solitons in the wave packet generated from a solitary w...The fission of solitary waves propagating over variable topography is investigated.In previous theories,to predict the number and the amplitudes of disintegrated solitons in the wave packet generated from a solitary wave,the parameters of the water environment and the incident solitary wave are required.However,it is difficult to measure these parameters in the ocean because of their temporal and spatial variations.In this paper,a fission law,in the form of the expressions of the number and the amplitudes of the disintegrated solitons,is derived from the partial information available on the wave packet.Theoretical analysis shows that the law is suitable fbr describing the fission of both surface and internal solitary waves and is also applicable to the cases of wave damping and wave breaking.Comparisons between the model output and the results from laboratory experiments,numerical simulations and field observations available in the literature demonstrate that the fission law can efficiently estimate the number and the amplitudes of solitons in the wave packet generated by a solitary wave.展开更多
基金Project supported by the National Natural Science Foundation of China(Nos.11372232 and 51479007)the Specialized Research Fund for the Doctoral Program of Higher Education(No.20130141110016)the State Water Pollution Control and Management of Major Special Science and Technology(No.2012ZX07205-005-03)
文摘An analytical solution for predicting the vertical distribution of streamwise mean velocity in an open channel flow with submerged flexible vegetation is proposed when large bending occurs. The flow regime is separated into two horizontal layers: a vegetation layer and a free water layer. In the vegetation layer, a mechanical analysis for the flexible vegetation is conducted, and an approximately linear relationship between the drag force of bending vegetation and the streamwise mean flow velocity is observed in the case of large deflection, which differes significantly from the case of rigid upright vegetation. Based on the theoretical analysis, a linear streamwise drag force-mean flow velocity expression in the momentum equation is derived, and an analytical solution is obtained. For the free water layer, a new expression is presented, replacing the traditional logarithmic velocity distribution, to obtain a zero velocity gradient at the water surface. Finally, the analytical predictions are compared with published experimental data, and the good agreement demonstrates that this model is effective for the open channel flow through the large deflection flexible vegetation.
基金financial support to this work from the National Natural Science Foundation of China (Grants 11172307 and11232012)973 Program (2014CB046200)
文摘Water waves in coastal areas are generally non- linear, exhibiting asymmetric velocity profiles with different amplitudes of crest and trough. The behaviors of the bound- ary layer under asymmetric waves are of great significance for sediment transport in natural circumstances. While pre- vious studies have mainly focused on linear or symmetric waves, asymmetric wave-induced flows remain unclear, par- ticularly in the flow regime with high Reynolds numbers. Taking cnoidal wave as a typical example of asymmetric waves, we propose to use an infinite immersed plate oscillat- ing cnoidally in its own plane in quiescent water to simulate asymmetric wave boundary layer. A large eddy simulation approach with Smagorinsky subgrid model is adopted to investigate the flow characteristics of the boundary layer. It is verified that the model well reproduces experimental and theoretical results. Then a series of numerical experiments are carried out to study the boundary layer beneath cnoidal waves from laminar to fully developed turbulent regimes at high Reynolds numbers, larger than ever studied before. Results of velocity profile, wall shear stress, friction coeffi- cient, phase lead between velocity and wall shear stress, and the boundary layer thickness are obtained. The dependencies of these boundary layer properties on the asymmetric degree and Reynolds number are discussed in detail.
基金supported by the National Key Research and Development Program of China(Grant No.2017YFC1404202)the National Natural Science Foundation of China(Grant Nos.11972352,11572332)the Strategic Priority Research Program of the Chinese Academy of Sciences(Grant Nos.XDB22040203,XDA22000000).
文摘With the large-scale density stratified tank and the numerical flume proposed,series of numerical cases in line with the experiments are carried out to investigate the interaction between the tension leg platforms(TLPs)and the internal solitary waves(ISWs).The waveforms,and the loads and the torques on the TLP obtained by the experiments and the simulations agree well with each other.Experimental results show that the amplitudes of the dimensionless horizontal force and torque linearly increase with the dimensionless amplitude,while that of the vertical force increases in a parabolic curve.Besides,the numerical results indicate that the horizontal and vertical forces on the TLP due to the ISWs can be divided into three components,namely,the wave pressure-difference forces,the viscous pressure-difference forces,and the frictional force that is negligible.The wave pressure-difference forces are always the major constituents.However the viscous pressure-difference component is unimportant,it is negligible as compared with the vertical forces.
基金Supported by the National Key Research and Development Program of China(Grant No.2017YFC1404202)the National Natural Science Foundation of China(Grant Nos.11572332,11602274)the Strategic Priority Research Program of the Chinese Academy of Sciences(Grant Nos.XDB22040203,XDA22000000).
文摘The fission of solitary waves propagating over variable topography is investigated.In previous theories,to predict the number and the amplitudes of disintegrated solitons in the wave packet generated from a solitary wave,the parameters of the water environment and the incident solitary wave are required.However,it is difficult to measure these parameters in the ocean because of their temporal and spatial variations.In this paper,a fission law,in the form of the expressions of the number and the amplitudes of the disintegrated solitons,is derived from the partial information available on the wave packet.Theoretical analysis shows that the law is suitable fbr describing the fission of both surface and internal solitary waves and is also applicable to the cases of wave damping and wave breaking.Comparisons between the model output and the results from laboratory experiments,numerical simulations and field observations available in the literature demonstrate that the fission law can efficiently estimate the number and the amplitudes of solitons in the wave packet generated by a solitary wave.