振荡流层移输沙条件下悬沙层泥沙扩散系数垂向分布特征研究
|
摘要
层移输沙是海岸带泥沙运动的主要形式之一,其垂向悬沙浓度分布规律的研究一直是海岸工程关心的重点。一般情况下,经典的纯扩散模型被用来描述和解释悬沙浓度的试验数据,该模型认为周期平均悬沙浓度主要由参考浓度、泥沙沉速和泥沙扩散系数确定。泥沙扩散系数可以由泥沙沉速和悬沙浓度的垂向梯度反演得到。既往研究大多直接给出泥沙扩散系数的结果,对于不同反演计算方法间结果差别的研究较少。本研究汇总了已有振荡流层移输沙试验数据,采用曲线拟合方法和直接差分方法计算了相应的泥沙扩散系数,研究表明两种方法得到的计算结果在垂向位置z <0.15 m处差异不大,随着垂向位置的升高,差分方法的计算结果略微大于拟合方法。考虑到拟合方法可以得到连续的泥沙扩散系数垂向分布,本研究推荐使用幂函数形式的曲线拟合方法求解悬移泥沙扩散系数。基于此,对比分析了层移输沙悬沙层泥沙扩散系数随泥沙粒径、振荡流周期、均方根流速和振荡流类型等物理参数的变化规律。在纯振荡流层移输沙条件下,泥沙扩散系数随泥沙粒径的增大而增大,而振荡流周期和均方根流速几乎不影响泥沙扩散系数。在振荡流和定常流共同作用下,泥沙扩散系数受振荡流周期和定常流流速的影响,泥沙扩散系数随着振荡流周期的增大或定常流流速的减小而增大。
Sheet flow regime is one of the main sediment movement patterns in coastal zone. Suspended sediment transport plays a significant role in studying the coastal sediment movement. In general,the traditional pure diffusion model is used to describe and interpret the existing experimental data. Accordingly,time-averaged suspended sediment concentration depends on the reference concentration,settling velocity and sediment diffusivity. Consequently,sediment diffusivity can be obtained using the sediment settling velocity and the vertical distribution of time-averaged suspended sediment concentration. However,most of the previous studies directly present the results of the sediment diffusivity,without comparing the differences among various calculation methods. In this study,the difference between the curve-fitting method and the direct-difference method is investigated. It is confirmed that difference between these two methods is trivial when vertical elevation z is smaller than 0.15 m. To obtain a continuous vertical distribution of sediment diffusivity,it is recommended to use the curve-fitting method. In addition,the effects of the grain size,oscillatory flow period,rootmean-squared( RMS) oscillatory flow velocity and oscillatory flow type on the sediment diffusivity are also discussed. Under the pure oscillatory flow condition,the larger the grain size is,the larger the sediment diffusivity is. Nevertheless,both oscillatory flow period and RMS flow velocity hardly affect the sediment diffusivity. Under the combined oscillatory flow and current condition,sediment diffusivity however is affected by the oscillatory flow period and current velocity. The longer the oscillatory flow period or the smaller the current velocity is,the larger the sediment diffusivity is.
Sheet flow regime is one of the main sediment movement patterns in coastal zone. Suspended sediment transport plays a significant role in studying the coastal sediment movement. In general,the traditional pure diffusion model is used to describe and interpret the existing experimental data. Accordingly,time-averaged suspended sediment concentration depends on the reference concentration,settling velocity and sediment diffusivity. Consequently,sediment diffusivity can be obtained using the sediment settling velocity and the vertical distribution of time-averaged suspended sediment concentration. However,most of the previous studies directly present the results of the sediment diffusivity,without comparing the differences among various calculation methods. In this study,the difference between the curve-fitting method and the direct-difference method is investigated. It is confirmed that difference between these two methods is trivial when vertical elevation z is smaller than 0.15 m. To obtain a continuous vertical distribution of sediment diffusivity,it is recommended to use the curve-fitting method. In addition,the effects of the grain size,oscillatory flow period,rootmean-squared( RMS) oscillatory flow velocity and oscillatory flow type on the sediment diffusivity are also discussed. Under the pure oscillatory flow condition,the larger the grain size is,the larger the sediment diffusivity is. Nevertheless,both oscillatory flow period and RMS flow velocity hardly affect the sediment diffusivity. Under the combined oscillatory flow and current condition,sediment diffusivity however is affected by the oscillatory flow period and current velocity. The longer the oscillatory flow period or the smaller the current velocity is,the larger the sediment diffusivity is.
引文
[1] O'DONOGHUE T,WRIGHT S. Flow tunnel measurements of velocities and sand flux in oscillatory sheet flow for well-sorted and graded sands[J]. Coastal Engineering,2004,51(11):1163-1184.
[2] O'DONOGHUE T,WRIGHT S. Concentrations in oscillatory sheet flow for well sorted and graded sands[J]. Coastal Engineering,2004,50(3):117-138.
[3] DOHMEN-JANSSEN C M. Grain size influence on sediment transport in oscillatory sheet flow:Phase lags and mobile-bed effects[D]. Netherlands:University of Twente,1999.
[4] RIBBERINK J S,Al-SALEM A A. Sedimem transport,sediment concentrations and bedforms in simulated asymmetric wave conditions[R]. Delft Hydraulics,Report H840,Part IV,1991.
[5] RIBBERINK J S,CHEN Z. Sediment transport of fine sand under asymmetric oscillatory flow[R]. Delft Hydraulics,Report H840.20,Part VII,1993.
[6] RAMADAN K A H. Time-averaged sediment transport phenomena in combined wave-current flows[R]. Delft Hydraulics,Report H1889.11,Part I,1994.
[7] RIBBERINK J S. Time-averaged sediment transport phenomena in combined wave-current flows[R]. Delft Hydraulics,Report H1889.11,Part II,1995.
[8] RIBBERINK J S,Al-SALEM A A. Sediment transport in oscillatory boundary layers in cases of rippled beds and sheet flow[J].Journal of Geophysical Research:Oceans,1994,99(C6):12707-12727.
[9] RIBBERINK J S,Al-SALEM A A. Sheet flow and suspension of sand in oscillatory boundary layers[J]. Coastal Engineering,1995,25(3-4):205-225.
[10] ROUSE H. Experiments on the mechanics of sediment suspension[C]∥Proceedings of the Fifth International Congress for Applied Mechanics. New York:John Wiley&Sons,1938:550-554.
[11]李延召.挟沙水流紊流模型对泥沙扩散系数的影响研究[D].北京:清华大学,2008.(LI Y Z. Comparing suspended sediment diffusivity formulated with different turbulence models[D]. Beijing:Tsinghua University,2008.(in Chinese))
[12] NIELSEN P. Coastal bottom boundary layers and sediment transport[M]. Singapore:World Scientific Publishing Company,1992:201-262.
[13] ABSI R. Concentration profiles for fine and coarse sediments suspended by waves over ripples:An analytical study with the 1-DV gradient diffusion model[J]. Advances in Water Resources,2010,33(4):411-418.
[14] THORNE P D,WILLIAMS J J,DAVIES A G. Suspended sediments under waves measured in a large-scale flume facility[J].Journal of Geophysical Research,2002,107(C8):10.1029/2001JC000988.
[15] VAN RIJN L C. Principles of sediment transport in rivers,estuaries and coastal seas[M]. Amsterdam:Aqua Publications,1993:8.35-8.57.
[16] COLEMAN N L. Flume studies of the sediment transfer coefficient[J]. Water Resources Research,1970,6(3):801-809.
[17] NIELSEN P,TEAKLE I A L. Turbulent diffusion of momentum and suspended particles:A finite-mixing-length theory[J].Physics of Fluids,2004,16(7):2342-2348.
[18] GRAF W H,CELLINO M. Suspension flows in open channels; experimental study[J]. Journal of Hydraulic Research,2002,40:435-447.
[19]钱宁,万兆慧.泥沙运动力学[M].北京:科学出版社,1983:298-321.(QIAN N,WAN Z H. Mechanics of sediment transport[M]. Beijing:Science Press,1983:298-321.(in Chinese))
[20]张磊,关见朝,王友胜,等.悬移质泥沙输移扩散方程适用条件的讨论[J].水利学报,2018,49(6):694-702.(ZHANG L,GUAN J Z,WANG Y S,et al. Discussion on the application conditions of diffusion equations of suspended sediment transport[J]. Journal of Hydraulic Engineering,2018,49(6):694-702.(in Chinese))
[21]张瑞瑾.河流泥沙动力学[M].北京:中国水利水电出版社,1998:149-159.(ZHANG R J. River sediment transport dynamics[M]. Beijing:China Water&Power Press,1998:149-159.(in Chinese))
[22] CHEN X,NIU X J,YU X P. Near-bed sediment condition in oscillatory sheet flows[J]. Journal of Waterway,Port,Coastal,and Ocean Engineering,2013,139:393-403.
[23] YOU Z J. Eddy viscosities and velocities in combined wave-current flows[J]. Ocean Engineering,1994,21(1):81-97.
[2] O'DONOGHUE T,WRIGHT S. Concentrations in oscillatory sheet flow for well sorted and graded sands[J]. Coastal Engineering,2004,50(3):117-138.
[3] DOHMEN-JANSSEN C M. Grain size influence on sediment transport in oscillatory sheet flow:Phase lags and mobile-bed effects[D]. Netherlands:University of Twente,1999.
[4] RIBBERINK J S,Al-SALEM A A. Sedimem transport,sediment concentrations and bedforms in simulated asymmetric wave conditions[R]. Delft Hydraulics,Report H840,Part IV,1991.
[5] RIBBERINK J S,CHEN Z. Sediment transport of fine sand under asymmetric oscillatory flow[R]. Delft Hydraulics,Report H840.20,Part VII,1993.
[6] RAMADAN K A H. Time-averaged sediment transport phenomena in combined wave-current flows[R]. Delft Hydraulics,Report H1889.11,Part I,1994.
[7] RIBBERINK J S. Time-averaged sediment transport phenomena in combined wave-current flows[R]. Delft Hydraulics,Report H1889.11,Part II,1995.
[8] RIBBERINK J S,Al-SALEM A A. Sediment transport in oscillatory boundary layers in cases of rippled beds and sheet flow[J].Journal of Geophysical Research:Oceans,1994,99(C6):12707-12727.
[9] RIBBERINK J S,Al-SALEM A A. Sheet flow and suspension of sand in oscillatory boundary layers[J]. Coastal Engineering,1995,25(3-4):205-225.
[10] ROUSE H. Experiments on the mechanics of sediment suspension[C]∥Proceedings of the Fifth International Congress for Applied Mechanics. New York:John Wiley&Sons,1938:550-554.
[11]李延召.挟沙水流紊流模型对泥沙扩散系数的影响研究[D].北京:清华大学,2008.(LI Y Z. Comparing suspended sediment diffusivity formulated with different turbulence models[D]. Beijing:Tsinghua University,2008.(in Chinese))
[12] NIELSEN P. Coastal bottom boundary layers and sediment transport[M]. Singapore:World Scientific Publishing Company,1992:201-262.
[13] ABSI R. Concentration profiles for fine and coarse sediments suspended by waves over ripples:An analytical study with the 1-DV gradient diffusion model[J]. Advances in Water Resources,2010,33(4):411-418.
[14] THORNE P D,WILLIAMS J J,DAVIES A G. Suspended sediments under waves measured in a large-scale flume facility[J].Journal of Geophysical Research,2002,107(C8):10.1029/2001JC000988.
[15] VAN RIJN L C. Principles of sediment transport in rivers,estuaries and coastal seas[M]. Amsterdam:Aqua Publications,1993:8.35-8.57.
[16] COLEMAN N L. Flume studies of the sediment transfer coefficient[J]. Water Resources Research,1970,6(3):801-809.
[17] NIELSEN P,TEAKLE I A L. Turbulent diffusion of momentum and suspended particles:A finite-mixing-length theory[J].Physics of Fluids,2004,16(7):2342-2348.
[18] GRAF W H,CELLINO M. Suspension flows in open channels; experimental study[J]. Journal of Hydraulic Research,2002,40:435-447.
[19]钱宁,万兆慧.泥沙运动力学[M].北京:科学出版社,1983:298-321.(QIAN N,WAN Z H. Mechanics of sediment transport[M]. Beijing:Science Press,1983:298-321.(in Chinese))
[20]张磊,关见朝,王友胜,等.悬移质泥沙输移扩散方程适用条件的讨论[J].水利学报,2018,49(6):694-702.(ZHANG L,GUAN J Z,WANG Y S,et al. Discussion on the application conditions of diffusion equations of suspended sediment transport[J]. Journal of Hydraulic Engineering,2018,49(6):694-702.(in Chinese))
[21]张瑞瑾.河流泥沙动力学[M].北京:中国水利水电出版社,1998:149-159.(ZHANG R J. River sediment transport dynamics[M]. Beijing:China Water&Power Press,1998:149-159.(in Chinese))
[22] CHEN X,NIU X J,YU X P. Near-bed sediment condition in oscillatory sheet flows[J]. Journal of Waterway,Port,Coastal,and Ocean Engineering,2013,139:393-403.
[23] YOU Z J. Eddy viscosities and velocities in combined wave-current flows[J]. Ocean Engineering,1994,21(1):81-97.
© 2004-2018 中国地质图书馆版权所有 京ICP备05064691号 京公网安备11010802017129号 地址：北京市海淀区学院路29号 邮编：100083 电话：办公室：(+86 10)66554848；文献借阅、咨询服务、科技查新：66554700 |