刚性植物对波高衰减和水流结构的影响
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摘要
为了研究植物的消浪能力及对水流紊流特性的影响,开展室内水槽试验,用木棒模拟刚性植物,分析了5组植物区布置方案和4组波要素条件下的波高衰减和水流结构。结果表明:植物密度对波高衰减具有显著影响;波浪通过植物区时波高衰减的速率逐渐减小;在同等植物特征条件下,短波比长波衰减幅度更大;植物区内的拖曳力系数CD与低科勒冈-卡朋特(Keulegan-Carpenter)数KC之间存在二次函数关系,CD随着KC的增大而减小,且变化速率呈变缓的趋势;波高和植物密度的增大会引起植物区内部紊动能量ETK的增大;完全淹没植物条件下的ETK大于不完全淹没条件下的ETK;在完全淹没植物的影响下,从底面至水面ETK呈先增大后减小的规律,并在植物冠层处达到最大值。
Flume experiments were carried out to study the effect of vegetation on wave attenuation and turbulence. Wood cylinders were used to simulate the rigid vegetation. Wave height attenuation and flow structures were analyzed for five vegetation configuration types and four kinds of wave conditions. The results show that vegetation density has great influence on wave attenuation. With the wave propagating inside the vegetation zone,the rate of wave attenuation decreases. The attenuation of short waves is larger than that of long waves. The relationship between the drag coefficient of vegetation(CD)and Keulegan-Carpenter number(KC) is fitted with a quadratic function,and CDdecreases with the increase of KCwith a decreasing variation rate. Turbulent kinetic energy(ETK) in the vegetation zone increases with the wave height and vegetation density. ETKinduced by submerged vegetation is larger than that by emerged vegetation. Under the effect of submerged vegetation,ETKincreases from the vegetation bottom to water surface,and the highest ETKoccurs near the top of vegetation canopy.
Flume experiments were carried out to study the effect of vegetation on wave attenuation and turbulence. Wood cylinders were used to simulate the rigid vegetation. Wave height attenuation and flow structures were analyzed for five vegetation configuration types and four kinds of wave conditions. The results show that vegetation density has great influence on wave attenuation. With the wave propagating inside the vegetation zone,the rate of wave attenuation decreases. The attenuation of short waves is larger than that of long waves. The relationship between the drag coefficient of vegetation(CD)and Keulegan-Carpenter number(KC) is fitted with a quadratic function,and CDdecreases with the increase of KCwith a decreasing variation rate. Turbulent kinetic energy(ETK) in the vegetation zone increases with the wave height and vegetation density. ETKinduced by submerged vegetation is larger than that by emerged vegetation. Under the effect of submerged vegetation,ETKincreases from the vegetation bottom to water surface,and the highest ETKoccurs near the top of vegetation canopy.
引文
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[2]杨建民.植物消浪护岸动力机制理论分析与模型实验研究[D].天津:天津大学,2003.
[3]刘达,黄本胜,邱静,等.华南沿海防浪林带种植宽度对消浪效果影响的试验研究[J].水利水电技术,2015,46(9):109-114.(LIU Da,HUANG Bensheng,QIU Jing, et al. Experimental study on impact from planting width of coastal wavebreak forest zone in South China on its wave absorbing effect[J]. Water Resources and Hydropower Engineering,2015,46(9):109-114.(in Chinese))
[4]LUHAR M,INFANTES E,NEPF H. Seagrass blade motion under waves and its impact on wave decay[J].Journal of Geophysical Research Oceans,2017,122(5):3736-3752.
[5] BRADLEY K,HOUSER C. Relative velocity of seagrass blades:implications for wave attenuation in low-energy environments[J]. Journal of Geophysical Research-Earth Surface,2009,114(F1):F01004.
[6]DALRYMPLE R A,KIRBY J T,HWANG P A. Wave diffraction due to areas of energy dissipation[J]. Journal of Waterway, Port, Coastal, and Ocean Engineering,1984,110(1):67-79.
[7]MENDEZ F J,LOSADA I J. An empirical model to estimate the propagation of random breaking and nonbreaking waves over vegetation fields[J]. Coastal Engineering,2004,51(2):103-118.
[8]SUMER B M, FREDSOE J. Hydrodynamics around cylindrical structures[M]. Singapore:World Scientific,1997.
[9]AUGUSTIN L N,IRISH J L,LYNETT P. Laboratory and numerical studies of wave damping by emergent and nearemergent wetland vegetation[J]. Coastal Engineering,2009,56(3):332-340.
[10]NI Y. Drag forces on vegetation due to waves and currents[D]. Delft:Delft University of Technology,2014.
[11] WU W C,COX D T. Effects of wave steepness and relative water depth on wave attenuation by emergent vegetation[J]. Estuarine, Coastal and Shelf Science,2015,164:443-450.
[12]KEULEGAN G,CARPENTER L. Forces on cylinders and plates in an oscillating fluid[J]. Journal of Research of the National Bureau of Standards,1958,60(5):423-440.
[13]PUJOL D,COLOMER J,SERRA T,et al. A model for the effect of submerged aquatic vegetation on turbulence induced by an oscillating grid[J]. Estuarine,Coastal and Shelf Science,2012,114:23-30.
[14] ROS A,COLOMER J,SERRA T,et al. Experimental observations on sediment resuspension within submerged model canopies under oscillatory flow[J]. Continental Shelf Research,2014,91:220-231.
[15] NEPF H M. Drag,turbulence,and diffusion in flow through emergent vegetation[J]. Water Resources Research,1999,35(2):479-489.
[16]张英豪,赖锡军,姜加虎.含苦草水流紊流结构典型剖面的象限分析[J].水动力学研究与进展,2015,30(5):526-532.(ZHANG Yinghao,LAI Xijun,JIANG Jiahu.Quadrant analysis of the typical profile of turbulence structure in flow with Vallisneria natans[J]. Chinese Journal of Hydrodynamics,2015,30(5):526-532.(in Chinese))
[17]张英豪,赖锡军.苦草对水流结构的影响研究[J].水科学进展,2015,26(1):99-106.(ZHANG Yinghao,LAI Xijun. Impact of Vallisneria natans on flow structure[J]. Advances in Water Science,2015,26(1):99-106.(in Chinese))
[18] CAROLLO F G,FERRO V,TERMINI D. Analyzing turbulence intensity in gravel bed channels[J]. Journal of Hydraulic Engineering,2005,131(12):1050-1061.