This study presents an innovative theoretical approach to predicting the scour depth around a foundation in large-scale model tests based on small-scale model tests under combined waves and currents.In the present app...This study presents an innovative theoretical approach to predicting the scour depth around a foundation in large-scale model tests based on small-scale model tests under combined waves and currents.In the present approach,the hydrodynamic parameters were designed based on the Froude similitude criteria.To avoid the cohesive behavior,we scaled the sediment size based on the settling velocity similarity,i.e.,the suspended load similarity.Then,a series of different scale model tests was conducted to obtain the scour depth around the pile in combined waves and currents.The fitting formula of scour depth from the small-scale model tests was used to predict the results of large-scale tests.The accuracy of the present approach was validated by comparing the prediction values with experimental data of large-scale tests.Moreover,the correctness and accuracy of the present approach for foundations with complex shapes,e.g.,the tripod foundation,was further checked.The results indicated that the fitting line from small-scale model tests slightly overestimated the experimental data of large-scale model tests,and the errors can be accepted.In general,the present approach was applied to predict the maximum or equilibrium scour depth of the large-scale model tests around single piles and tripods.展开更多
When subway tunnels are routed underneath rivers, riverbed scour may expose the structure, with potentially severe consequences. Thus, it is important to identify the maximum scour depth to ensure that the designed bu...When subway tunnels are routed underneath rivers, riverbed scour may expose the structure, with potentially severe consequences. Thus, it is important to identify the maximum scour depth to ensure that the designed buried depth is adequate. There are a range of methods that may be applied to this problem, including the fluvial process analysis method, geological structure analysis method, scour formula method, scour model experiment method, and numerical simulation method. However, the application ranges and forecasting precision of these methods vary considerably. In order to quantitatively analyze the characteristics of the different methods, a subway tunnel passing underneath a river was selected, and the aforementioned five methods were used to forecast the maximum scour depth. The fluvial process analysis method was used to characterize the river regime and evolution trend, which were the baseline for examination of the scour depth of the riverbed. The results obtained from the scour model experiment and the numerical simulation methods are reliable; these two methods are suitable for application to tunnel projects passing underneath rivers. The scour formula method was less accurate than the scour model experiment method; it is suitable for application to lower risk projects such as pipelines. The results of the geological structure analysis had low precision; the method is suitable for use as a secondary method to assist other research methods. To forecast the maximum scour depth of the riverbed above the subway tunnel, a combination of methods is suggested, and the appropriate analysis method should be chosen with respect to the local conditions.展开更多
This paper outlines the application of the multi-layer perceptron artificial neural network (ANN), ordinary kriging (OK), and inverse distance weighting (IDW) models in the estimation of local scour depth around bridg...This paper outlines the application of the multi-layer perceptron artificial neural network (ANN), ordinary kriging (OK), and inverse distance weighting (IDW) models in the estimation of local scour depth around bridge piers. As part of this study, bridge piers were installed with bed sills at the bed of an experimental flume. Experimental tests were conducted under different flow conditions and varying distances between bridge pier and bed sill. The ANN, OK and IDW models were applied to the experimental data and it was shown that the artificial neural network model predicts local scour depth more accurately than the kriging and inverse distance weighting models. It was found that the ANN with two hidden layers was the optimum model to predict local scour depth. The results from the sixth test case showed that the ANN with one hidden layer and 17 hidden nodes was the best model to predict local scour depth. Whereas the results from the fifth test case found that the ANN with three hidden layers was the best model to predict local scour depth.展开更多
A precise prediction of maximum scour depth around bridge foundations under ice covered condition is crucial for their safe design because underestimation may result in bridge failure and over-estimation will lead to ...A precise prediction of maximum scour depth around bridge foundations under ice covered condition is crucial for their safe design because underestimation may result in bridge failure and over-estimation will lead to unnecessary construction costs. Compared to pier scour depth predictions within an open channel, few studies have attempted to predict the extent of pier scour depth under ice-covered condition. The present work examines scour under ice by using a series of clear-water flume experiments employing two adjacent circular bridge piers in a uniform bed were exposed to open channel and both rough and smooth ice covered channels. The measured scour depths were compared to three commonly used bridge scour equations including Gao’s simplified equation, the HEC-18/Jones equation, and the Froehlich Design Equation. The present study has several advantages as it adds to the understanding of the physics of bridge pier scour under ice cover flow condition, it checks the validity and reliability of commonly used bridge pier equations, and it reveals whether they are valid for the case of scour under ice-covered flow conditions. In addition, it explains how accurately an equation developed for scour under open channel flow can predict scour around bridge piers under ice-covered flow condition.展开更多
Water jet technology is widely used in submerged buried pipes as a non-traditional trenching process,often invol-ving a complex sediment response.An important adjustable and influential engineering variable in this tec...Water jet technology is widely used in submerged buried pipes as a non-traditional trenching process,often invol-ving a complex sediment response.An important adjustable and influential engineering variable in this technol-ogy is represented by the impinging distance.In this study,the FLOW-3D software was used to simulate the jet scouring of sand beds in a submerged environment.In particular,four sets of experimental conditions were con-sidered to discern the relationship between the maximum scour depth and mass and the impinging distance.As shown by the results,a critical impinging distance h0 exists by which the static scour depth can be maximized;the scour mass ratio between dynamic and static conditions decreases as the impinging distance increases.Moreover,the profile contours are similar when the erosion parameter Ec is in the range 0.35<Ec<2.Empirical equations applicable for predicting the jet trenching contour under both dynamic and static scour modes are also provided in this study.展开更多
It is essential to predict the scour depth around bridge piers for hydraulic engineers involved in the economical design of bridge pier foundation. Conventional investigations have long been of the opinion that empiri...It is essential to predict the scour depth around bridge piers for hydraulic engineers involved in the economical design of bridge pier foundation. Conventional investigations have long been of the opinion that empirical scour prediction equations based on laboratory data over predict scour depths. In this article, the Back-Propagation Neural Network (BPN) was applied to predict the scour depth in order to overcome the problem of exclusive and the nonlinear relationships. The observations obtained from thirteen states in USA was verified by the present model. From the comparison with conventional experimental methods, it can be found that the scour depth around bridge piers can be efficiently predicted using the BPN.展开更多
Local scour around bridge piers and abutments is one of the most significant causes of bridge failure.Despite a plethora of studies on scour around individual bridge piers or abutments,few studies have focused on the ...Local scour around bridge piers and abutments is one of the most significant causes of bridge failure.Despite a plethora of studies on scour around individual bridge piers or abutments,few studies have focused on the joint impact of a pier and an abutment in proximity to one another on scour.This study conducted laboratory experiments and flow analyses to examine the interaction of piers and abutments and their effect on clear-water scour.The experiments were conducted in a rectangular laboratory flume.They included 18 main tests(with a combination of different types of piers and abutments)and five control tests(with individual piers or abutments).Three pier types(a rectangular pier with a rounded edge,a group of three cylindrical piers,and a single cylindrical pier)and two abutment types(a wingewall abutment and a semicircular abutment)were used.An acoustic Doppler velocimeter was used to measure the three-dimensional flow velocity for analyses of streamline,velocity magnitude,vertical velocity,and bed shear stress.The results showed that the velocity near the pier and abutment increased by up to 80%.The maximum scour depth around the abutment increased by up to 19%.In contrast,the maximum scour depth around the pier increased significantly by up to l71%.The presence of the pier in the vicinity of the abutment led to an increase in the scour hole volume by up to 87%relative to the case with a solitary abutment.Empirical equations were also derived to accurately estimate the maximum scour depth at the pier adjacent to the abutment.展开更多
Scour depth around bridge piers plays a vital role in the safety and stability of the bridges.The former approaches used in the prediction of scour depth are based on regression models or black box models in which the...Scour depth around bridge piers plays a vital role in the safety and stability of the bridges.The former approaches used in the prediction of scour depth are based on regression models or black box models in which the first one lacks enough accuracy while the later one does not provide a clear mathematical expression to easily employ it for other situations or cases.Therefore,this paper aims to develop new equations using particle swarm optimization as a metaheuristic approach to predict scour depth around bridge piers.To improve the efficiency of the proposed model,individual equations are derived for laboratory and field data.Moreover,sensitivity analysis is conducted to achieve the most effective parameters in the estimation of scour depth for both experimental and filed data sets.Comparing the results of the proposed model with those of existing regression-based equations reveal the superiority of the proposed method in terms of accuracy and uncertainty.Moreover,the ratio of pier width to flow depth and ratio of d50 (mean particle diameter)to flow depth for the laboratory and field data were recognized as the most effective parameters,respectively.The derived equations can be used as a suitable proxy to estimate scour depth in both experimental and prototype scales.展开更多
Scour around a submerged square pile was realized experimentally in a steady flow to study the effects of flow depth on local scour.Flow depth to pile height ratios ranging from 1.5 to 5 in uniform sand and 2 to 5 in ...Scour around a submerged square pile was realized experimentally in a steady flow to study the effects of flow depth on local scour.Flow depth to pile height ratios ranging from 1.5 to 5 in uniform sand and 2 to 5 in non-uniform sand were tested in the approaching flow velocity to critical velocity(larger than which the sediment particle is motivated)ratios of 0.56 and 1.03,respectively.The influences of flow depth were investigated on the basis of analysis of the three-dimensional topography,temporal maximum scour depth,bed profile development,and equilibrium scour depth.Results showed that the maximum scour depth was at the upstream corners of the pile other than at the stagnation point.The evolutions of the maximum scour depth data in non-uniform sand were well fitted with a recent exponential function,which characterized the initial,developing,and equilibrium stages of scour depth.The scour hole slopes upstream of the pile were found to be parallel to each other in the process of each test and were mainly governed by the sediment repose underwater.The equilibrium scour depth varied slightly with flow depth when the submergence ratio was larger than 1 in uniform sand while it was 2 in non-uniform sand.The armoring effects of coarse sediment particles markedly reduced the sediment transport in non-uniform sand despite the 0.34 increment in non-uniformity.展开更多
Unlike the pier scour in bridge waterways,the local scour at offshore monopile foundations should take into account the effect of wave-current combination.Under the condition of wave-current coexistence,the water-soil...Unlike the pier scour in bridge waterways,the local scour at offshore monopile foundations should take into account the effect of wave-current combination.Under the condition of wave-current coexistence,the water-soil interfacial scouring is usually coupled with the pore-pressure dynamics inside of the seabed.The aforementioned wave/current-pile-soil coupling process was physically modeled with a specially designed flow-structure-soil interaction flume.Experimental results indicate that superimposing a current onto the waves obviously changes the pore-pressure and the flow velocity at the bed around the pile.The concomitance of horseshoe vortex and local scour hole around a monopile proves that the horseshoe vortex is one of the main controlling mechanisms for scouring development under the combined waves and current.Based on similarity analyses,an average-velocity based Froude number(Fra)is proposed to correlate with the equilibrium scour depth(S/D)at offshore monopile foundation in the combined waves and current.An empirical expression for the correlation between S/D and Fra is given for predicting equilibrium scour depth,which may provide a guide for offshore engineering practice.展开更多
Drainage canals are engineering structures widely used for debris flow mitigation.When passing through a drainage canal,debris flow usually scours the gully bed at the back of the rib sill of the drainage canal,which ...Drainage canals are engineering structures widely used for debris flow mitigation.When passing through a drainage canal,debris flow usually scours the gully bed at the back of the rib sill of the drainage canal,which leads to failure of the rib sill.Therefore,the scour depth at the back of the rib sill is an important design problem and it is related to the economic benefits of engineering and service years.To explore the law of the depth of the scour pit after debris flow through drainage canal ribs,we first proposed a formula for the calculation of the maximum scour depth at the back of a rib sill based on energy conservation.We then conducted a series of simulation experiments to test the proposed formula.The experimental results show that the scour depth,trench slope and the distance between ribs all increase with a decrease in debris flow density.We then compared the results of experiments and formula calculations.Through the testing analysis,we found that the calculation results of the conductedformula correspond with the experimental results better.Finally,taking Qipan Gully as an example,we designed the ultimate depth of a drainage canal for debris flow using the calculation formula.展开更多
In this article,current research findings of local scour at offshore windfarm monopile foundations are presented.The scour mechanisms and scour depth prediction formulas under different hydrodynamic conditions are sum...In this article,current research findings of local scour at offshore windfarm monopile foundations are presented.The scour mechanisms and scour depth prediction formulas under different hydrodynamic conditions are summarized,including the current-only condition,wave-only condition,combined wave-current condition,and complex dynamic condition.Furthermore,this article analyzes the influencing factors on the basis of classical equations for predicting the equilibrium scour depth under specific conditions.The weakness of existing researches and future prospects are also discussed.It is suggested that future research shall focus on physical experiments under unsteady tidal currents or other complex loadings.The computational fluid dynamics-discrete element method and artificial intelligence technique are suggested being adopted to study the scour at offshore windfarm foundations.展开更多
Local scour around bridge abutments is a widespread problem that can result in structural failure. Collars can be used as a countermeasure to reduce the scour depth. In this study, the temporal scour development aroun...Local scour around bridge abutments is a widespread problem that can result in structural failure. Collars can be used as a countermeasure to reduce the scour depth. In this study, the temporal scour development around a wing-wall abutment was investigated with and without collars. The tests were carried out under clear-water conditions for different abutment lengths, with collars of different sizes placed at the bed level. When no collar was used in the experiments, 70% of the maximum scour depth occurred in less than 2 h. However, when a collar with a width greater than the length of the abutment was used, no scour was observed for up to 200 min from the beginning of the experiments. The results show that an increase in the collar width not only led to a lag time for the onset of scouring but also reduced the maximum scour depth. Moreover, an increased collar width led to a better performance in mitigating scouring around smaller abutments. Generally, the scour depth decreased by 9%-37% with different collar widths.展开更多
基金financially supported by the Fundamental Research Funds for the Central Universities(No.202061027)the National Natural Science Foundation of China(No.41572247)。
文摘This study presents an innovative theoretical approach to predicting the scour depth around a foundation in large-scale model tests based on small-scale model tests under combined waves and currents.In the present approach,the hydrodynamic parameters were designed based on the Froude similitude criteria.To avoid the cohesive behavior,we scaled the sediment size based on the settling velocity similarity,i.e.,the suspended load similarity.Then,a series of different scale model tests was conducted to obtain the scour depth around the pile in combined waves and currents.The fitting formula of scour depth from the small-scale model tests was used to predict the results of large-scale tests.The accuracy of the present approach was validated by comparing the prediction values with experimental data of large-scale tests.Moreover,the correctness and accuracy of the present approach for foundations with complex shapes,e.g.,the tripod foundation,was further checked.The results indicated that the fitting line from small-scale model tests slightly overestimated the experimental data of large-scale model tests,and the errors can be accepted.In general,the present approach was applied to predict the maximum or equilibrium scour depth of the large-scale model tests around single piles and tripods.
基金supported by the National Natural Science Foundation of China (Grants No. 50909037,50879019,and 50879020)the Natural Science Foundation of Hohai University (Grant No. 2008426611),the Foundation for Introducing Talents of Hohai University (Grant No. 20080415)+1 种基金the National Science and Technology Pillar Program during the Eleventh Five-Year Plan Period (Grant No. 2008BAB29B08)the Fundamental Research Funds for the Central Universities (Grant No. 2010B01114)
文摘When subway tunnels are routed underneath rivers, riverbed scour may expose the structure, with potentially severe consequences. Thus, it is important to identify the maximum scour depth to ensure that the designed buried depth is adequate. There are a range of methods that may be applied to this problem, including the fluvial process analysis method, geological structure analysis method, scour formula method, scour model experiment method, and numerical simulation method. However, the application ranges and forecasting precision of these methods vary considerably. In order to quantitatively analyze the characteristics of the different methods, a subway tunnel passing underneath a river was selected, and the aforementioned five methods were used to forecast the maximum scour depth. The fluvial process analysis method was used to characterize the river regime and evolution trend, which were the baseline for examination of the scour depth of the riverbed. The results obtained from the scour model experiment and the numerical simulation methods are reliable; these two methods are suitable for application to tunnel projects passing underneath rivers. The scour formula method was less accurate than the scour model experiment method; it is suitable for application to lower risk projects such as pipelines. The results of the geological structure analysis had low precision; the method is suitable for use as a secondary method to assist other research methods. To forecast the maximum scour depth of the riverbed above the subway tunnel, a combination of methods is suggested, and the appropriate analysis method should be chosen with respect to the local conditions.
基金Foundation item: Supported by the State Key Laboratory of Hydraulic Engineering Simulation and Safety (Grant No. HESS-1401), the National Natural Science Foundation of China (Grant No. 51279124), the Marine Science and Technology Foundation of South China Sea Branch, State Oceanic Administration (Grant No. 1417), and the National High Technology Research and Development Program of China (Grant No. 2008AA09A401). Acknowledgement We wish to thank Prof. Bai YC for stimulating discussions and reviewers for their helpful comments that led to considerable improvements to the paper.
文摘This paper outlines the application of the multi-layer perceptron artificial neural network (ANN), ordinary kriging (OK), and inverse distance weighting (IDW) models in the estimation of local scour depth around bridge piers. As part of this study, bridge piers were installed with bed sills at the bed of an experimental flume. Experimental tests were conducted under different flow conditions and varying distances between bridge pier and bed sill. The ANN, OK and IDW models were applied to the experimental data and it was shown that the artificial neural network model predicts local scour depth more accurately than the kriging and inverse distance weighting models. It was found that the ANN with two hidden layers was the optimum model to predict local scour depth. The results from the sixth test case showed that the ANN with one hidden layer and 17 hidden nodes was the best model to predict local scour depth. Whereas the results from the fifth test case found that the ANN with three hidden layers was the best model to predict local scour depth.
文摘A precise prediction of maximum scour depth around bridge foundations under ice covered condition is crucial for their safe design because underestimation may result in bridge failure and over-estimation will lead to unnecessary construction costs. Compared to pier scour depth predictions within an open channel, few studies have attempted to predict the extent of pier scour depth under ice-covered condition. The present work examines scour under ice by using a series of clear-water flume experiments employing two adjacent circular bridge piers in a uniform bed were exposed to open channel and both rough and smooth ice covered channels. The measured scour depths were compared to three commonly used bridge scour equations including Gao’s simplified equation, the HEC-18/Jones equation, and the Froehlich Design Equation. The present study has several advantages as it adds to the understanding of the physics of bridge pier scour under ice cover flow condition, it checks the validity and reliability of commonly used bridge pier equations, and it reveals whether they are valid for the case of scour under ice-covered flow conditions. In addition, it explains how accurately an equation developed for scour under open channel flow can predict scour around bridge piers under ice-covered flow condition.
基金supported by the Research on the Prediction Mechanism of Corrosion for High Strength Steel in Deep Sea Service Driven by Multi-Scale,High-Dimension and Small-Sample Data(C2301002635)Research on the Influence of Nozzle Structure on the Scouring Effect of Submerged Water Jet(2023R411045)+1 种基金the Zhejiang Ocean University Outstanding Master’s Thesis Cultivation Project(ZJOUYJS20230018)the Scientific Research Project of Zhejiang Graduate Education Society in 2022(2022-021)which was gained by Chen.
文摘Water jet technology is widely used in submerged buried pipes as a non-traditional trenching process,often invol-ving a complex sediment response.An important adjustable and influential engineering variable in this technol-ogy is represented by the impinging distance.In this study,the FLOW-3D software was used to simulate the jet scouring of sand beds in a submerged environment.In particular,four sets of experimental conditions were con-sidered to discern the relationship between the maximum scour depth and mass and the impinging distance.As shown by the results,a critical impinging distance h0 exists by which the static scour depth can be maximized;the scour mass ratio between dynamic and static conditions decreases as the impinging distance increases.Moreover,the profile contours are similar when the erosion parameter Ec is in the range 0.35<Ec<2.Empirical equations applicable for predicting the jet trenching contour under both dynamic and static scour modes are also provided in this study.
文摘It is essential to predict the scour depth around bridge piers for hydraulic engineers involved in the economical design of bridge pier foundation. Conventional investigations have long been of the opinion that empirical scour prediction equations based on laboratory data over predict scour depths. In this article, the Back-Propagation Neural Network (BPN) was applied to predict the scour depth in order to overcome the problem of exclusive and the nonlinear relationships. The observations obtained from thirteen states in USA was verified by the present model. From the comparison with conventional experimental methods, it can be found that the scour depth around bridge piers can be efficiently predicted using the BPN.
文摘Local scour around bridge piers and abutments is one of the most significant causes of bridge failure.Despite a plethora of studies on scour around individual bridge piers or abutments,few studies have focused on the joint impact of a pier and an abutment in proximity to one another on scour.This study conducted laboratory experiments and flow analyses to examine the interaction of piers and abutments and their effect on clear-water scour.The experiments were conducted in a rectangular laboratory flume.They included 18 main tests(with a combination of different types of piers and abutments)and five control tests(with individual piers or abutments).Three pier types(a rectangular pier with a rounded edge,a group of three cylindrical piers,and a single cylindrical pier)and two abutment types(a wingewall abutment and a semicircular abutment)were used.An acoustic Doppler velocimeter was used to measure the three-dimensional flow velocity for analyses of streamline,velocity magnitude,vertical velocity,and bed shear stress.The results showed that the velocity near the pier and abutment increased by up to 80%.The maximum scour depth around the abutment increased by up to 19%.In contrast,the maximum scour depth around the pier increased significantly by up to l71%.The presence of the pier in the vicinity of the abutment led to an increase in the scour hole volume by up to 87%relative to the case with a solitary abutment.Empirical equations were also derived to accurately estimate the maximum scour depth at the pier adjacent to the abutment.
基金This research was supported by the Hungarian State and the European Union under the EFOP-3.6.1-16-2016-00010 project and the 2017-1.3.1-VKE-2017-00025 project.
文摘Scour depth around bridge piers plays a vital role in the safety and stability of the bridges.The former approaches used in the prediction of scour depth are based on regression models or black box models in which the first one lacks enough accuracy while the later one does not provide a clear mathematical expression to easily employ it for other situations or cases.Therefore,this paper aims to develop new equations using particle swarm optimization as a metaheuristic approach to predict scour depth around bridge piers.To improve the efficiency of the proposed model,individual equations are derived for laboratory and field data.Moreover,sensitivity analysis is conducted to achieve the most effective parameters in the estimation of scour depth for both experimental and filed data sets.Comparing the results of the proposed model with those of existing regression-based equations reveal the superiority of the proposed method in terms of accuracy and uncertainty.Moreover,the ratio of pier width to flow depth and ratio of d50 (mean particle diameter)to flow depth for the laboratory and field data were recognized as the most effective parameters,respectively.The derived equations can be used as a suitable proxy to estimate scour depth in both experimental and prototype scales.
基金the support of the National Natural Science Foundation of China(Nos.51679223 and 51739010)the 111 Project(No.B14028),the Shangdong Provincial Key Laboratory of Ocean Engineering(No.kl oe202009)+1 种基金the Ningbo Natural Science Foundation(No.2021J096)a grant from the 7th Generation Ultra-Deepwater Drilling Rig Innovation Project。
文摘Scour around a submerged square pile was realized experimentally in a steady flow to study the effects of flow depth on local scour.Flow depth to pile height ratios ranging from 1.5 to 5 in uniform sand and 2 to 5 in non-uniform sand were tested in the approaching flow velocity to critical velocity(larger than which the sediment particle is motivated)ratios of 0.56 and 1.03,respectively.The influences of flow depth were investigated on the basis of analysis of the three-dimensional topography,temporal maximum scour depth,bed profile development,and equilibrium scour depth.Results showed that the maximum scour depth was at the upstream corners of the pile other than at the stagnation point.The evolutions of the maximum scour depth data in non-uniform sand were well fitted with a recent exponential function,which characterized the initial,developing,and equilibrium stages of scour depth.The scour hole slopes upstream of the pile were found to be parallel to each other in the process of each test and were mainly governed by the sediment repose underwater.The equilibrium scour depth varied slightly with flow depth when the submergence ratio was larger than 1 in uniform sand while it was 2 in non-uniform sand.The armoring effects of coarse sediment particles markedly reduced the sediment transport in non-uniform sand despite the 0.34 increment in non-uniformity.
基金supported by the National Natural Science Foundation of China(Grant Nos.1123201210872198)the National Basic Research Program of China("973"Project)(Grant No.2014CB046204)
文摘Unlike the pier scour in bridge waterways,the local scour at offshore monopile foundations should take into account the effect of wave-current combination.Under the condition of wave-current coexistence,the water-soil interfacial scouring is usually coupled with the pore-pressure dynamics inside of the seabed.The aforementioned wave/current-pile-soil coupling process was physically modeled with a specially designed flow-structure-soil interaction flume.Experimental results indicate that superimposing a current onto the waves obviously changes the pore-pressure and the flow velocity at the bed around the pile.The concomitance of horseshoe vortex and local scour hole around a monopile proves that the horseshoe vortex is one of the main controlling mechanisms for scouring development under the combined waves and current.Based on similarity analyses,an average-velocity based Froude number(Fra)is proposed to correlate with the equilibrium scour depth(S/D)at offshore monopile foundation in the combined waves and current.An empirical expression for the correlation between S/D and Fra is given for predicting equilibrium scour depth,which may provide a guide for offshore engineering practice.
基金financially supported by the key Projects of the Chinese Academy of Sciences (Grant No.KZZD-EW-05-01-04)the National Science and Technology Support Program (Grant No.2012BAC06B02)the sub-program of Science and technology research and development plan from China Railway (Grant No.2014G004-A-5)
文摘Drainage canals are engineering structures widely used for debris flow mitigation.When passing through a drainage canal,debris flow usually scours the gully bed at the back of the rib sill of the drainage canal,which leads to failure of the rib sill.Therefore,the scour depth at the back of the rib sill is an important design problem and it is related to the economic benefits of engineering and service years.To explore the law of the depth of the scour pit after debris flow through drainage canal ribs,we first proposed a formula for the calculation of the maximum scour depth at the back of a rib sill based on energy conservation.We then conducted a series of simulation experiments to test the proposed formula.The experimental results show that the scour depth,trench slope and the distance between ribs all increase with a decrease in debris flow density.We then compared the results of experiments and formula calculations.Through the testing analysis,we found that the calculation results of the conductedformula correspond with the experimental results better.Finally,taking Qipan Gully as an example,we designed the ultimate depth of a drainage canal for debris flow using the calculation formula.
基金supported by the Major International Joint Research Project P0W3M of the National Natural Science Foundation of China(Grant No.51920105013)the General Project of the National Natural Science Foundation of China(Grant No.52071127).
文摘In this article,current research findings of local scour at offshore windfarm monopile foundations are presented.The scour mechanisms and scour depth prediction formulas under different hydrodynamic conditions are summarized,including the current-only condition,wave-only condition,combined wave-current condition,and complex dynamic condition.Furthermore,this article analyzes the influencing factors on the basis of classical equations for predicting the equilibrium scour depth under specific conditions.The weakness of existing researches and future prospects are also discussed.It is suggested that future research shall focus on physical experiments under unsteady tidal currents or other complex loadings.The computational fluid dynamics-discrete element method and artificial intelligence technique are suggested being adopted to study the scour at offshore windfarm foundations.
文摘Local scour around bridge abutments is a widespread problem that can result in structural failure. Collars can be used as a countermeasure to reduce the scour depth. In this study, the temporal scour development around a wing-wall abutment was investigated with and without collars. The tests were carried out under clear-water conditions for different abutment lengths, with collars of different sizes placed at the bed level. When no collar was used in the experiments, 70% of the maximum scour depth occurred in less than 2 h. However, when a collar with a width greater than the length of the abutment was used, no scour was observed for up to 200 min from the beginning of the experiments. The results show that an increase in the collar width not only led to a lag time for the onset of scouring but also reduced the maximum scour depth. Moreover, an increased collar width led to a better performance in mitigating scouring around smaller abutments. Generally, the scour depth decreased by 9%-37% with different collar widths.