Measuring the geometry of a developing scour hole in clear-water conditions using underwater sonar scanning  

作　　者：Ashley Rogers Costantino Manes Toru Tsuzaki 

机构地区：[1]Faculty of Engineering and the Environment,University of Southampton,University Road,Southampton,SO171BJ,UK [2]Department of Environmental,Land and Infrastructure Engineering,Politecnico di Torino,Corso Duca degli Abruzzi 24,10129 Torino,Italy

出　　处：《International Journal of Sediment Research》2020年第1期105-114,共10页国际泥沙研究（英文版）

基　　金：supported by a joint partnership between Network Rail and the University of Southampton;support of“Compagnia di San Paolo”who partly funded this work through the scheme "Attrarre docenti di qualita tramite Starting Grant"

摘　　要：A novel scanning technique using a rotating-head sonar profiler attached to a slider mechanism is presented as a means to directly measure the complex erosion and deposition features of local scour holes developing in clear-water conditions around vertical cylinders mimicking bridge piers.Extensive validation shows that the method produces high-density elevation surfaces to within y1.5±2 mm accuracy in a quasi-non-invasive manner.This equates to 0.5±0.7%relative to the flow depth which sonar resolution is well known to scale with.Experimental data from three trials using different cylinder diameters indicate that monitoring of the entire scour hole over time(instead of only the maximum depth as is commonly done in laboratory experiments)can reveal important information about local scour evolution.In particular,results show that the scour-hole volume scales with the maximum scour depth cubed(VOL y3s)through three linear regimes.The transition to the third linear regime was found to represent a step change in the scour evolution process.Following the recent theoretical framework proposed by Manes and Brocchini(2015),this change,termed the crossover point,was interpreted as the point where the production of turbulent kinetic energy plateaus which corresponds to a stabilization in the erosive power of the horseshoe vortex.Scour development beyond the crossover point is characterised by a significant reduction in the rate of volumetric scour,relative to the steadily-increasing maximum scour depth.This overall reduction in volume-development is attributed to a balance between erosion from in-front of the pier and deposition around the sides using topography analysis.It is speculated that the existence of the crossover point may help to identify the characteristic length and time scales describing the evolution of local scour,which may be used for modeling purposes.A novel scanning technique using a rotating-head sonar profiler attached to a slider mechanism is presented as a means to directly measure the complex erosion and deposition features of local scour holes developing in clear-water conditions around vertical cylinders mimicking bridge piers.Extensive validation shows that the method produces high-density elevation surfaces to within≌1.5±2 mm accuracy in a quasi-non-invasive manner.This equates to 0.5±0.7% relative to the flow depth which sonar resolution is well known to scale with.Experimental data from three trials using different cylinder diameters indicate that monitoring of the entire scour hole over time（instead of only the maximum depth as is commonly done in laboratory experiments） can reveal important information about local scour evolution.In particular,results show that the scour-hole volume scales with the maximum scour depth cubed(VOL-yS3) through three linear regimes.The transition to the third linear regime was found to represent a step change in the scour evolution process.Following the recent theoretical framework proposed by Manes and Brocchini（2015）,this change,termed the crossover point,was interpreted as the point where the production of turbulent kinetic energy plateaus which corresponds to a stabilization in the erosive power of the horseshoe vortex.Scour development beyond the crossover point is characterised by a significant reduction in the rate of volumetric scour,relative to the steadily-increasing maximum scour depth.This overall reduction in volume-development is attributed to a balance between erosion from in-front of the pier and deposition around the sides using topography analysis.It is speculated that the existence of the crossover point may help to identify the characteristic length and time scales describing the evolution of local scour,which may be used for modeling purposes.

关 键 词：Local SCOUR SCOUR volume CLEAR water SONAR SCOUR hole GEOMETRY SIMILARITY 

分 类 号：TV1[水利工程]