Experimental And Simulation Research On Roughness Of Grassed Revetment

Ecological revetment engineering can protect the river from water erosion damage,and to ensure the integrity of the rivers of biodiversity and ecosystem,the vegetation ecological engineering measures is often used in ecological revetment engineering.Vegetation can ease the nearshore velocity,and to reinforce the root and the restriction of soil,effectively prevent the erosion of the water of the river.But the plant has changed the original quay wall roughness,increases the flow resistance and affect the flow regime,lead to part of the bank and riverbed sediment deposition,river flow ability of the original.Recently,the mechanism of interaction between vegetation and water,and the influence of the original bank slope roughness is very less,therefore two ways of the physical test method and numerical simulation method to analyze the impact of grassed revetment on drag force characteristics,and the research results will provide a theoretical basis for the design of revetment engineering and technical personnel.The indoor physical tests selected representative plants of festuca arundinacea as the test piece of grass,to scour the turf specimen measurement under the 18 working condition and carry out a systematical analysis.The study found that the grassed revetment roughness value generally range from 0.021 to 0.083,which was mainly related to the flow condition,height of plant cultivation,density of plant cultivation.The test data obtained with mechanical theory,analyzes the influencing factors of grass slope roughness and its variation,the results show that the height of plant grass decreased by 6cm,and the roughness value decrease by 20.5%-28%;the density of plant grass doubled,the roughness value increased by28.2%-36%;when the slope depth and grass height relative height of Dr<0.44,roughness value increases with the depth of the slope;when the slope depth and grass height relative height of 0.44<Dr<1,roughness with the increase of the slope depth value decreases;when the slope depth and grass height relative height of Dr>1,roughness value tends to be stable.By the test of indoor physical test results obtained on bank slope planting grass flow resistance characteristics are simulated,the standard equation three dimension turbulent mathematical model,using computational fluid dynamics for numerical calculation.To track the free surface by VOF method,the grass simplified as porous medium,assumed porous medium model has no effect on the turbulence structure,determine the porosity of the porous medium model by volume drainage method.The numerical simulation results are compared with the measured results,and the results are in good agreement,which proves the feasibility of the physical experiment.