Sea bottom stress is conventionally assumed to be directly proportional to the square of the verticallyaveraged velocity,and the drag coefficient to be dependent on the speed and direction of the wind on the sea surfa...Sea bottom stress is conventionally assumed to be directly proportional to the square of the verticallyaveraged velocity,and the drag coefficient to be dependent on the speed and direction of the wind on the sea surface,the depth and dimension of the sea,the period of the tide and so on. In this paper a three-dimensional numerical model is used to discuss the relation the dragcoefficient and the above-mentioned factors.It can be shown from calculation that the relation, is valid,that the drag coefficient is a constant in a major part of a sea as thought conventionally,andthat there is a small area near the coast where the drag coefficient is far greater.We call it singular area. A number of conclusions on the relation between the drag coefficient and the speed and direction ofthe wind,the sea depth and so on,were obtained.展开更多
This paper presents a high-resolution (2′X2′) numerical model of coastalcoupled wave-current interaction with explicit consideration of the effects of wave-currentinteraction on bottom stress. For two selected storm...This paper presents a high-resolution (2′X2′) numerical model of coastalcoupled wave-current interaction with explicit consideration of the effects of wave-currentinteraction on bottom stress. For two selected storms with measured data in the Yellow River coastalarea of the Bohai Sea, it is shown that the bottom stress calculated by using a coupledwave-current model is increased, as one would expect, compared with the bottom stress computed withan uncoupled current model. Moreover, the current velocity field is also changed, but thecorresponding current directions show less influence in the two simulations. The extents of changesin bottom stress and current velocity vary with storm intensities. The results further imply thatthe coupled wave-current model should be used as the basis for simulating the current velocity andsea level in the near shore region.展开更多
On the basis of the measurement data pertaining to waves, current, and sediment in February 2012 in the mouth bar of the Modaomen Estuary, the Soulsby formulae with an iterative method are applied to calculating botto...On the basis of the measurement data pertaining to waves, current, and sediment in February 2012 in the mouth bar of the Modaomen Estuary, the Soulsby formulae with an iterative method are applied to calculating bottom shear stresses （BSS） and their effect on a sediment resuspension. Swell induced BSS have been found to be the most important part of the BSS. In this study, the correlation coefficient between a wavecurrent shear stress and SSC is 0.86, and that between current shear stresses and SSC is only 0.40. The peaks of the SSC are consistent with the height and the BSS of the swell. The swell is the main mechanism for the sediment re-suspension, and the tidal current effect on sediment re-suspension is small. The peaks of the SSC are centered on the high tidal level, and the flood tide enhances the wave shear stresses and the SSC near the bottom. The critical shear stress for sediment re-suspension at the observation station is between 0.20 and 0.30 N/m2. Tidal currents are too weak to stir up the bottom sediment into the flow, but a WCI （wave-current interaction） is strong enough to re-suspend the coarse sediment.展开更多
When ocean waves propagate over the sea floor,dynamic wave pressures and bottom shear stresses exert on the surface of seabed.The bottom shear stresses provide a horizontal loading in the wave-seabed interaction syste...When ocean waves propagate over the sea floor,dynamic wave pressures and bottom shear stresses exert on the surface of seabed.The bottom shear stresses provide a horizontal loading in the wave-seabed interaction system,while dynamic wave pressures provide a vertical loading in the system.However,the bottom shear stresses have been ignored in most previous studies in the past.In this study,the effects of the bottom shear stresses on the dynamic response in a seabed of finite thickness under wave loading will be examined,based on Biot＇s dynamic poro-elastic theory.In the model,an ＂u-p＂ approximation will be adopted instead of quasi-static model that have been used in most previous studies.Numerical results indicate that the bottom shear stresses has certain influences on the wave-induced seabed dynamic response.Furthermore,wave and soil characteristics have considerable influences on the relative difference of seabed response between the previous model（without shear stresses） and the present model（with shear stresses）.As shown in the parametric study,the relative differences between two models could up to 10% of p0,depending on the amplitude of bottom shear stresses.展开更多
This work presents a new approach for simulating the random waves in viscous fluids and the associated bottom shear stresses. By generating the incident random waves in a numerical wave flume and solving the unsteady ...This work presents a new approach for simulating the random waves in viscous fluids and the associated bottom shear stresses. By generating the incident random waves in a numerical wave flume and solving the unsteady two-dimensional Navier-Stokes equations and the fully nonlinear free surface boundaiy conditions for the fluid flows in the flume, the viscous flows and laminar bottom shear stresses induced by random waves axe determined. The deterministic spectral amplitude method implemented by use of the fast Fourier transform algorithm was adopted to generate the incident random waves. The accuracy of the numerical scheme is confirmed by comparing the predicted wave spectrum with the target spectrum and by comparing the nanlerical transfer function between the shear stress and the surface elevation with the theoretical transfer function. The maximum bottom shear stress caused by random waves, computed by this wave model, is compared with that obtained by Myrhaug＇ s model （1995）. The transfer function method is also employed to determine the maximum shear stress, and is proved accurate.展开更多
文摘Sea bottom stress is conventionally assumed to be directly proportional to the square of the verticallyaveraged velocity,and the drag coefficient to be dependent on the speed and direction of the wind on the sea surface,the depth and dimension of the sea,the period of the tide and so on. In this paper a three-dimensional numerical model is used to discuss the relation the dragcoefficient and the above-mentioned factors.It can be shown from calculation that the relation, is valid,that the drag coefficient is a constant in a major part of a sea as thought conventionally,andthat there is a small area near the coast where the drag coefficient is far greater.We call it singular area. A number of conclusions on the relation between the drag coefficient and the speed and direction ofthe wind,the sea depth and so on,were obtained.
文摘This paper presents a high-resolution (2′X2′) numerical model of coastalcoupled wave-current interaction with explicit consideration of the effects of wave-currentinteraction on bottom stress. For two selected storms with measured data in the Yellow River coastalarea of the Bohai Sea, it is shown that the bottom stress calculated by using a coupledwave-current model is increased, as one would expect, compared with the bottom stress computed withan uncoupled current model. Moreover, the current velocity field is also changed, but thecorresponding current directions show less influence in the two simulations. The extents of changesin bottom stress and current velocity vary with storm intensities. The results further imply thatthe coupled wave-current model should be used as the basis for simulating the current velocity andsea level in the near shore region.
基金The Program of International S&T Cooperation under contract No.2010DFA24470the National Science Foundation of China under contract No.41376101the Guangdong Provincial Science and Technology Planning Project under contract Nos 2012A030200002 and 2011B031100008
文摘On the basis of the measurement data pertaining to waves, current, and sediment in February 2012 in the mouth bar of the Modaomen Estuary, the Soulsby formulae with an iterative method are applied to calculating bottom shear stresses （BSS） and their effect on a sediment resuspension. Swell induced BSS have been found to be the most important part of the BSS. In this study, the correlation coefficient between a wavecurrent shear stress and SSC is 0.86, and that between current shear stresses and SSC is only 0.40. The peaks of the SSC are consistent with the height and the BSS of the swell. The swell is the main mechanism for the sediment re-suspension, and the tidal current effect on sediment re-suspension is small. The peaks of the SSC are centered on the high tidal level, and the flood tide enhances the wave shear stresses and the SSC near the bottom. The critical shear stress for sediment re-suspension at the observation station is between 0.20 and 0.30 N/m2. Tidal currents are too weak to stir up the bottom sediment into the flow, but a WCI （wave-current interaction） is strong enough to re-suspend the coarse sediment.
基金supported by State Key Laboratory of Ocean Engineering Self-Development (GKZD010053-3) and EPSRC (EP/G006482/1)
文摘When ocean waves propagate over the sea floor,dynamic wave pressures and bottom shear stresses exert on the surface of seabed.The bottom shear stresses provide a horizontal loading in the wave-seabed interaction system,while dynamic wave pressures provide a vertical loading in the system.However,the bottom shear stresses have been ignored in most previous studies in the past.In this study,the effects of the bottom shear stresses on the dynamic response in a seabed of finite thickness under wave loading will be examined,based on Biot＇s dynamic poro-elastic theory.In the model,an ＂u-p＂ approximation will be adopted instead of quasi-static model that have been used in most previous studies.Numerical results indicate that the bottom shear stresses has certain influences on the wave-induced seabed dynamic response.Furthermore,wave and soil characteristics have considerable influences on the relative difference of seabed response between the previous model（without shear stresses） and the present model（with shear stresses）.As shown in the parametric study,the relative differences between two models could up to 10% of p0,depending on the amplitude of bottom shear stresses.
基金the Science Council (Grant No. NSC95-2221-E-006-474)
文摘This work presents a new approach for simulating the random waves in viscous fluids and the associated bottom shear stresses. By generating the incident random waves in a numerical wave flume and solving the unsteady two-dimensional Navier-Stokes equations and the fully nonlinear free surface boundaiy conditions for the fluid flows in the flume, the viscous flows and laminar bottom shear stresses induced by random waves axe determined. The deterministic spectral amplitude method implemented by use of the fast Fourier transform algorithm was adopted to generate the incident random waves. The accuracy of the numerical scheme is confirmed by comparing the predicted wave spectrum with the target spectrum and by comparing the nanlerical transfer function between the shear stress and the surface elevation with the theoretical transfer function. The maximum bottom shear stress caused by random waves, computed by this wave model, is compared with that obtained by Myrhaug＇ s model （1995）. The transfer function method is also employed to determine the maximum shear stress, and is proved accurate.
