Scour around bridge pier foundations is a complex phenomenon that can threaten structural stability.Accurate prediction of scour depth around compound piers remains challenging for bridge engineers.This study investig...Scour around bridge pier foundations is a complex phenomenon that can threaten structural stability.Accurate prediction of scour depth around compound piers remains challenging for bridge engineers.This study investigated the effect of foundation elevation on scour around compound piers and developed reliable scour depth prediction models for economical foundation design.Experiments were conducted under clear-water conditions using two circular piers:(1)a uniform pier(with a diameter of D)and(2)a compound pier consisting of a uniform pier resting on a circular foundation(with a foundation diameter(D_(f))of 2D)positioned at various elevations(Z)relative to the channel bed.Results showed that foundation elevation significantly affected scour depth.Foundations at or below the bed(Z/D≥0)reduced scour,while those projecting into the flow field(Z/D<0)increased scour.The optimal foundation elevation was found to be 0.1D below the bed level,yielding a 57%reduction in scour depth compared to the uniform pier due to its shielding effect against downflow and horseshoe vortices.In addition,regression,artificial neural network(ANN),and M5 model tree models were developed using experimental data from this and previous studies.The M5 model outperformed the traditional HEC-18 equation,regression,and ANN models,with a coefficient of determination greater than 0.85.Sensitivity analysis indicated that flow depth,foundation elevation,and diameter significantly influenced scour depth prediction,whereas sediment size had a lesser impact.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
Scour depth prediction of offshore pipelines is of great significance to the design and construction of the submarine pipeline projects. In this paper, based on the CFD software package FLUENT and User Defined Functi...Scour depth prediction of offshore pipelines is of great significance to the design and construction of the submarine pipeline projects. In this paper, based on the CFD software package FLUENT and User Defined Function （UDF）, an Eulerian two-phase model, which includes an Euler-Euler coupled model for water and sediment phases, and a turbulent model for the fluid phase, is adopted to predict the scour depth around pipelines. The model is verified by observation data obtained from laboratory experiments. On the basis of the simulations, the factors affecting the scour depth, including the effects of incipient velocity, pipe diameter and sediment particle size and so on, were investigated. Meanwhile, according to formulas of incipient velocity of various sediments, approximate calculation on theoretical scour depths is developed for pipelines of seven stations in the South China Sea, where engineering application information is available.展开更多
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
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
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
Local scour is the reduction of original bed level around any hydraulic structure.Bridge failure due to scouring has made researchers study the cause of scouring and predict the scour depth and pattern around bridge p...Local scour is the reduction of original bed level around any hydraulic structure.Bridge failure due to scouring has made researchers study the cause of scouring and predict the scour depth and pattern around bridge piers and foundations.Several investigators have extensively studied local scour around isolated bridge pier,but modern designs of the bridges comprise of wide span and thus group of piers rather than a single pier.The flow and scour pattern around group of piers are different from the case of a single pier due to the interaction effect.The objective of present study is to investigate the effect of mutual interference of bridge piers on local scour experimentally around two piers in non-cohesive bed.Experiments were carried out on model bridge piers of circular cross section in a meandering channel.It was observed that when front and rear piers were placed at an angular displacement ofθ=40°and 80°respectively,maximum depth of scour is maximum.Hereθis the angle the line drawn at the inlet of bend to the line joining the centre of curvature and any point on the outer portion of the bend.展开更多
Offshore wind power plays a crucial role in energy strategies.The results of traditional small-scale physical models may be unreliable when extrapolated to large field scales.This study addressed this limitation by co...Offshore wind power plays a crucial role in energy strategies.The results of traditional small-scale physical models may be unreliable when extrapolated to large field scales.This study addressed this limitation by conducting large-scale(1:13)experiments to investigate the scour hole pattern and equilibrium scour depth around both slender and large monopiles under irregular waves.The experiments adopted KeuleganeCarpenter number(NKC)values from 1.01 to 8.89 and diffraction parameter(D/L,where D is the diameter of the monopile,and L is the wave length)values from 0.016 to 0.056.The results showed that changes in the maximum scour location and scour hole shape around a slender monopile were associated with NKC,with differences observed between irregular and regular waves.Improving the calculation of NKC enhanced the accuracy of existing scour formulae under irregular waves.The maximum scour locations around a large monopile were consistently found on both sides,regardless of NKC and D/L,but the scour hole topography was influenced by both parameters.Notably,the scour range around a large monopile was at least as large as the monopile diameter.展开更多
The composite bucket foundations of offshore wind turbines penetrate minimally into the seabed, making local scour a significant threat to wind turbine stability. This study develops a physical model to examine local ...The composite bucket foundations of offshore wind turbines penetrate minimally into the seabed, making local scour a significant threat to wind turbine stability. This study develops a physical model to examine local scour patterns around a novel mono-column composite bucket foundation(MCCBF) under unidirectional flows. The experiments reveal that under weak-flow conditions, no significant scour pits develop at the front or lateral sides of the MCCBF,while two distinct scour pits form behind the lateral sides. Under strong-flow conditions, substantial scour pits emerge at both frontal and lateral sides of the bucket foundation, with two scour pits extending downstream on either side. The research demonstrates that both the range and depth of local scour increase with higher flow velocity and decreasing water depth, though the mechanisms influencing local scour around the MCCBF prove more complex than those affecting monopiles. The distinctive structural features of the MCCBF necessitate particular consideration of effects related to bucket foundation exposure. The study concludes by proposing an empirical formula for predicting maximum scour depth around the MCCBF.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
The Keulegan-Carpenter(KC)number is the main dimensionless parameter that affects the local scour of offshore wind power monopile foundations.This study conducted large-scale(1:13)physical model tests to study the loc...The Keulegan-Carpenter(KC)number is the main dimensionless parameter that affects the local scour of offshore wind power monopile foundations.This study conducted large-scale(1:13)physical model tests to study the local scour shape,equilibrium scour depth,and local scour volume of offshore wind power monopiles under the action of irregular waves with different KC numbers.Systematic experiments were carried out with the KC number ranging from 1.0 to 13.0.With a small KC number(KC<6),and especially when the KC number was less than 4,the scour mainly occurred on both cross-flow sides of the monopile with a low scour depth.When the KC number exceeded 4,the shape of the scour hole changed from a fan to an ellipse,and the maximum scour depth increased significantly with KC.With a large KC number(KC>6),the proposed method better predicted the equilibrium scour depth when the wave broke.In addition,according to the results of three-dimensional terrain scanning,the relationship between the local equilibrium scour volume of a single offshore wind power monopile and the KC number was derived.This provided a rational method for estimation of the riprap redundancy for monopile protection against scour.展开更多
The evolvement history of modern Huanghe River Delta tidal flat, coastline and underwater terrain were studied based on the analysis of remote sensing images and water depth data. Based on the analysis of seafloor ter...The evolvement history of modern Huanghe River Delta tidal flat, coastline and underwater terrain were studied based on the analysis of remote sensing images and water depth data. Based on the analysis of seafloor terrain evolution on different historical stages, a formula simulating the erosion and deposition evolvement model of subaqueous Huanghe River Delta slope was proposed, and the evolvement trend of the subaqueous delta terrain was predicted. The result shows that the equilibrium transition zone is near the water depth of 12 m with seabed erosion in shallower water and accumulation in deeper water during the first 150 a after the river channel was deserted. In the meantime, the underwater slope became gentler and the coastal erosion rate became slow gradually. Then, the subaqueous delta slope changed to up concave from upper convex, and the shape of subaqueous delta disappeared. The coast type changed to silt-mud coast about 100-150 a after the river course was deserted. The erosion depth in the foot of the seawall is calculated based on the formula.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
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 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
A piggyback pipeline consists of two pipes such that the secondary line rides on the main pipe with a fixed distance between two pipes in length.The novel strategy is utilized in offshore areas instead of a single flo...A piggyback pipeline consists of two pipes such that the secondary line rides on the main pipe with a fixed distance between two pipes in length.The novel strategy is utilized in offshore areas instead of a single flow line.In this regard,there are only a handful of experimental and numerical studies investigating the effect of scour below a piggyback pipeline under steady current.Hence,this study focuses on examining the influential factors on scouring due to steady current including the pipe diameter and the gap between pipes through numerical simulations and experimental tests.Accordingly,at the first phase of the research,a single pipe was established and tested in laboratory to compare the results with those of an empirical equation.After finishing experimental verifications,piggyback pipelines were also assembled to study the scouring under steady current conditions.It was concluded that by increasing the gap distance between the pipes,the maximum scour depth decreases;however,an increase in the small pipe’s diameter results in a larger maximum scour depth.Secondly,numerical simulations were carried out using the FLOW-3D software which was found to be a suitable tool for the numerical investigation of this study.Finally,the numerical results have been compared with the corresponding experimental data and a relatively good agreement was achieved between them.展开更多
Bank erosion of rivers, e.g. Bagmati, Burhi Gandak, Kosi and Kamla-Balan, all originating in the Himalayan hills of Nepal and flowing throughthe alluvial plains of North Bihar, is a chronic and common phenomenon.Cutti...Bank erosion of rivers, e.g. Bagmati, Burhi Gandak, Kosi and Kamla-Balan, all originating in the Himalayan hills of Nepal and flowing throughthe alluvial plains of North Bihar, is a chronic and common phenomenon.Cutting and deposition result in shifting or meandering of the riverendangering the embankment, road, bridge, barrage, and countryside.Anti-erosion and maintenance require huge investment. The river Kamla-Balan faces bank erosion throughout its embanked length, but stretchesat km 37 and 62 are highly unstable and vulnerable. This paper dealswith the problem, presents the hydrological details responsible for thehazard, and demonstrates the effectiveness of supplementary geo-textilewith conventional sand filter pitching to protect the soil and slope of theriverbank. Estimated flood discharge and velocity at 100 years of returnperiod is nearly 2100 cumecs and 0.9 m/sec, respectively. Riverbed andbank material is represented by silt with d50 of 0.018 to 0.05 mm while0.02 mm of silt may get eroded and transported by flow above 0.15 m/s. Launching apron is also required due to local scour. Model study testshows its suitability under various hydraulic conditions. Study reveals theeffectiveness of woven type geo-textile reinforced revetment irrespective ofcost and environmental consideration.展开更多
It is of important significance to study the evolution law of the riverbed near underwater crossing line pipes for ensuring the safe operation of oil and gas pipelines and reducing the risk of damage by waterflood disa...It is of important significance to study the evolution law of the riverbed near underwater crossing line pipes for ensuring the safe operation of oil and gas pipelines and reducing the risk of damage by waterflood disasters.In order to clarify the evolution law of the riverbed near un-derwater crossing line pipes and its negative effects,this paper conductedflume model experiments on underwater crossing line pipes.The physical process of riverbed evolution near pipes was observed and the effect of hydrodynamic conditions on the local pipe scour was studied.What's more,the formation mechanism of local scour at underwater crossing line pipes was revealed.And the following research results were obtained.First,when the waterflow is slow,the riverbed evolution process near underwater crossing line pipes is mainly divided into six stages,including riverbed undercutting,pipe exposure,micro-pore formation,scour hole propagation,pipe suspension and scour equilibrium.Second,vortex and seepageflow are the reasons for the local scour of underwater crossing line pipes.Before pipes are exposed,the silt around the pipes is reduced by vortex.After pipes are exposed,micro-pores occur at the pipe bottom under the joint action of vortex and seepageflow.And thus,local scour is formed.Third,flow velocity and water depth jointly influence the riverbed scour duration of each stage and the maximum scour depth at the pipe bottom.When the Froude number(Fr)is in the range of 0.306e0.808,with the increase of Fr,waterflow gets fast,the maximum scour depth at the pipe bottom increases,the duration for scour equilibrium decreases,the riverbed undercutting depth increases and the riverbed topographically getsflatter.The maximum scour depth at the pipe bottom is 0.9e1.6 times the pipe diameter,and the duration for scour equilibrium is between 1650 min and 2620 min.In conclusion,the experimental results provide important reference for predicting the burial depth of underwater crossing line pipes and ensuring their safe operation.展开更多
Scour is a natural phenomenon that is created by the rivers streams or the flood which brings about transferring or eroding of bed materials. To have accurate and safe erosion control structures design, maximum scour ...Scour is a natural phenomenon that is created by the rivers streams or the flood which brings about transferring or eroding of bed materials. To have accurate and safe erosion control structures design, maximum scour depth in downstream of the structures gains specific significance. In the current study, M5 model tree as remedy data mining approaches is suggested to estimate the scour depth around the abutments. To do this, Kayaturk laboratory data (2005), with different hydraulic conditions, are used. Then, the results of M5 model were also compared with genetic programming (GP) and pervious empirical results to investigate the applicability, ability, and accuracy of these procedures. To examine the accuracy of the results yielded from the M5 and GP procedures, two performance indicators (determination coefficient (R2) and root mean square error (RMSE)) were used. The comparison test of results clearly shows that the implementation of M5 technique sounds satisfactory regarding the performance indicators (R<sup>2</sup> = 0.944 and RMSE = 0.126) with less deviation from the numerical values. In addition, M5 tree model, by presenting relationships based on liner regression, has good capability to estimate the depth of scour abutment for engineers in practical terms.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
文摘Scour around bridge pier foundations is a complex phenomenon that can threaten structural stability.Accurate prediction of scour depth around compound piers remains challenging for bridge engineers.This study investigated the effect of foundation elevation on scour around compound piers and developed reliable scour depth prediction models for economical foundation design.Experiments were conducted under clear-water conditions using two circular piers:(1)a uniform pier(with a diameter of D)and(2)a compound pier consisting of a uniform pier resting on a circular foundation(with a foundation diameter(D_(f))of 2D)positioned at various elevations(Z)relative to the channel bed.Results showed that foundation elevation significantly affected scour depth.Foundations at or below the bed(Z/D≥0)reduced scour,while those projecting into the flow field(Z/D<0)increased scour.The optimal foundation elevation was found to be 0.1D below the bed level,yielding a 57%reduction in scour depth compared to the uniform pier due to its shielding effect against downflow and horseshoe vortices.In addition,regression,artificial neural network(ANN),and M5 model tree models were developed using experimental data from this and previous studies.The M5 model outperformed the traditional HEC-18 equation,regression,and ANN models,with a coefficient of determination greater than 0.85.Sensitivity analysis indicated that flow depth,foundation elevation,and diameter significantly influenced scour depth prediction,whereas sediment size had a lesser impact.
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Scour depth prediction of offshore pipelines is of great significance to the design and construction of the submarine pipeline projects. In this paper, based on the CFD software package FLUENT and User Defined Function （UDF）, an Eulerian two-phase model, which includes an Euler-Euler coupled model for water and sediment phases, and a turbulent model for the fluid phase, is adopted to predict the scour depth around pipelines. The model is verified by observation data obtained from laboratory experiments. On the basis of the simulations, the factors affecting the scour depth, including the effects of incipient velocity, pipe diameter and sediment particle size and so on, were investigated. Meanwhile, according to formulas of incipient velocity of various sediments, approximate calculation on theoretical scour depths is developed for pipelines of seven stations in the South China Sea, where engineering application information is available.
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 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.
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.
文摘Local scour is the reduction of original bed level around any hydraulic structure.Bridge failure due to scouring has made researchers study the cause of scouring and predict the scour depth and pattern around bridge piers and foundations.Several investigators have extensively studied local scour around isolated bridge pier,but modern designs of the bridges comprise of wide span and thus group of piers rather than a single pier.The flow and scour pattern around group of piers are different from the case of a single pier due to the interaction effect.The objective of present study is to investigate the effect of mutual interference of bridge piers on local scour experimentally around two piers in non-cohesive bed.Experiments were carried out on model bridge piers of circular cross section in a meandering channel.It was observed that when front and rear piers were placed at an angular displacement ofθ=40°and 80°respectively,maximum depth of scour is maximum.Hereθis the angle the line drawn at the inlet of bend to the line joining the centre of curvature and any point on the outer portion of the bend.
基金supported by the National Nature Science Foundation of China National Outstanding Youth Science Fund Project(Grant No.52122109)the National Natural Science Foundation of China(Grants No.51861165102 and 52039005).
文摘Offshore wind power plays a crucial role in energy strategies.The results of traditional small-scale physical models may be unreliable when extrapolated to large field scales.This study addressed this limitation by conducting large-scale(1:13)experiments to investigate the scour hole pattern and equilibrium scour depth around both slender and large monopiles under irregular waves.The experiments adopted KeuleganeCarpenter number(NKC)values from 1.01 to 8.89 and diffraction parameter(D/L,where D is the diameter of the monopile,and L is the wave length)values from 0.016 to 0.056.The results showed that changes in the maximum scour location and scour hole shape around a slender monopile were associated with NKC,with differences observed between irregular and regular waves.Improving the calculation of NKC enhanced the accuracy of existing scour formulae under irregular waves.The maximum scour locations around a large monopile were consistently found on both sides,regardless of NKC and D/L,but the scour hole topography was influenced by both parameters.Notably,the scour range around a large monopile was at least as large as the monopile diameter.
基金financially supported by the Scientific Research Foundation of China Three Gorges Corporation (Grant No. 32007095)。
文摘The composite bucket foundations of offshore wind turbines penetrate minimally into the seabed, making local scour a significant threat to wind turbine stability. This study develops a physical model to examine local scour patterns around a novel mono-column composite bucket foundation(MCCBF) under unidirectional flows. The experiments reveal that under weak-flow conditions, no significant scour pits develop at the front or lateral sides of the MCCBF,while two distinct scour pits form behind the lateral sides. Under strong-flow conditions, substantial scour pits emerge at both frontal and lateral sides of the bucket foundation, with two scour pits extending downstream on either side. The research demonstrates that both the range and depth of local scour increase with higher flow velocity and decreasing water depth, though the mechanisms influencing local scour around the MCCBF prove more complex than those affecting monopiles. The distinctive structural features of the MCCBF necessitate particular consideration of effects related to bucket foundation exposure. The study concludes by proposing an empirical formula for predicting maximum scour depth around the MCCBF.
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.
基金supported by the National Natural Science Foundation of China(Grants No.52001149,52039005,and 51861165102)the Research Funds for the Central Universities(Grants No.TKS20210102,TKS20210110,and TKS20210303)the Tianjin Science and Technology Planning Project(Grant No.17PTYPHZ00080).
文摘The Keulegan-Carpenter(KC)number is the main dimensionless parameter that affects the local scour of offshore wind power monopile foundations.This study conducted large-scale(1:13)physical model tests to study the local scour shape,equilibrium scour depth,and local scour volume of offshore wind power monopiles under the action of irregular waves with different KC numbers.Systematic experiments were carried out with the KC number ranging from 1.0 to 13.0.With a small KC number(KC<6),and especially when the KC number was less than 4,the scour mainly occurred on both cross-flow sides of the monopile with a low scour depth.When the KC number exceeded 4,the shape of the scour hole changed from a fan to an ellipse,and the maximum scour depth increased significantly with KC.With a large KC number(KC>6),the proposed method better predicted the equilibrium scour depth when the wave broke.In addition,according to the results of three-dimensional terrain scanning,the relationship between the local equilibrium scour volume of a single offshore wind power monopile and the KC number was derived.This provided a rational method for estimation of the riprap redundancy for monopile protection against scour.
基金The National Basic Research Program of China under contract No. 2005CB422304
文摘The evolvement history of modern Huanghe River Delta tidal flat, coastline and underwater terrain were studied based on the analysis of remote sensing images and water depth data. Based on the analysis of seafloor terrain evolution on different historical stages, a formula simulating the erosion and deposition evolvement model of subaqueous Huanghe River Delta slope was proposed, and the evolvement trend of the subaqueous delta terrain was predicted. The result shows that the equilibrium transition zone is near the water depth of 12 m with seabed erosion in shallower water and accumulation in deeper water during the first 150 a after the river channel was deserted. In the meantime, the underwater slope became gentler and the coastal erosion rate became slow gradually. Then, the subaqueous delta slope changed to up concave from upper convex, and the shape of subaqueous delta disappeared. The coast type changed to silt-mud coast about 100-150 a after the river course was deserted. The erosion depth in the foot of the seawall is calculated based on the formula.
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.
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.
文摘A piggyback pipeline consists of two pipes such that the secondary line rides on the main pipe with a fixed distance between two pipes in length.The novel strategy is utilized in offshore areas instead of a single flow line.In this regard,there are only a handful of experimental and numerical studies investigating the effect of scour below a piggyback pipeline under steady current.Hence,this study focuses on examining the influential factors on scouring due to steady current including the pipe diameter and the gap between pipes through numerical simulations and experimental tests.Accordingly,at the first phase of the research,a single pipe was established and tested in laboratory to compare the results with those of an empirical equation.After finishing experimental verifications,piggyback pipelines were also assembled to study the scouring under steady current conditions.It was concluded that by increasing the gap distance between the pipes,the maximum scour depth decreases;however,an increase in the small pipe’s diameter results in a larger maximum scour depth.Secondly,numerical simulations were carried out using the FLOW-3D software which was found to be a suitable tool for the numerical investigation of this study.Finally,the numerical results have been compared with the corresponding experimental data and a relatively good agreement was achieved between them.
文摘Bank erosion of rivers, e.g. Bagmati, Burhi Gandak, Kosi and Kamla-Balan, all originating in the Himalayan hills of Nepal and flowing throughthe alluvial plains of North Bihar, is a chronic and common phenomenon.Cutting and deposition result in shifting or meandering of the riverendangering the embankment, road, bridge, barrage, and countryside.Anti-erosion and maintenance require huge investment. The river Kamla-Balan faces bank erosion throughout its embanked length, but stretchesat km 37 and 62 are highly unstable and vulnerable. This paper dealswith the problem, presents the hydrological details responsible for thehazard, and demonstrates the effectiveness of supplementary geo-textilewith conventional sand filter pitching to protect the soil and slope of theriverbank. Estimated flood discharge and velocity at 100 years of returnperiod is nearly 2100 cumecs and 0.9 m/sec, respectively. Riverbed andbank material is represented by silt with d50 of 0.018 to 0.05 mm while0.02 mm of silt may get eroded and transported by flow above 0.15 m/s. Launching apron is also required due to local scour. Model study testshows its suitability under various hydraulic conditions. Study reveals theeffectiveness of woven type geo-textile reinforced revetment irrespective ofcost and environmental consideration.
基金supported by the National Natural Science Foundation of China"Soil-pipe-water coupling effect and seismic damage mechanism of buried water pipeline"(No.:51478403)PetroChina Major Science&Technology Project"Sudy and application of key technology for maintaining 30 billion cubic meters of production in Southwest Oil and Gas Field(No:2016E-0610).
文摘It is of important significance to study the evolution law of the riverbed near underwater crossing line pipes for ensuring the safe operation of oil and gas pipelines and reducing the risk of damage by waterflood disasters.In order to clarify the evolution law of the riverbed near un-derwater crossing line pipes and its negative effects,this paper conductedflume model experiments on underwater crossing line pipes.The physical process of riverbed evolution near pipes was observed and the effect of hydrodynamic conditions on the local pipe scour was studied.What's more,the formation mechanism of local scour at underwater crossing line pipes was revealed.And the following research results were obtained.First,when the waterflow is slow,the riverbed evolution process near underwater crossing line pipes is mainly divided into six stages,including riverbed undercutting,pipe exposure,micro-pore formation,scour hole propagation,pipe suspension and scour equilibrium.Second,vortex and seepageflow are the reasons for the local scour of underwater crossing line pipes.Before pipes are exposed,the silt around the pipes is reduced by vortex.After pipes are exposed,micro-pores occur at the pipe bottom under the joint action of vortex and seepageflow.And thus,local scour is formed.Third,flow velocity and water depth jointly influence the riverbed scour duration of each stage and the maximum scour depth at the pipe bottom.When the Froude number(Fr)is in the range of 0.306e0.808,with the increase of Fr,waterflow gets fast,the maximum scour depth at the pipe bottom increases,the duration for scour equilibrium decreases,the riverbed undercutting depth increases and the riverbed topographically getsflatter.The maximum scour depth at the pipe bottom is 0.9e1.6 times the pipe diameter,and the duration for scour equilibrium is between 1650 min and 2620 min.In conclusion,the experimental results provide important reference for predicting the burial depth of underwater crossing line pipes and ensuring their safe operation.
文摘Scour is a natural phenomenon that is created by the rivers streams or the flood which brings about transferring or eroding of bed materials. To have accurate and safe erosion control structures design, maximum scour depth in downstream of the structures gains specific significance. In the current study, M5 model tree as remedy data mining approaches is suggested to estimate the scour depth around the abutments. To do this, Kayaturk laboratory data (2005), with different hydraulic conditions, are used. Then, the results of M5 model were also compared with genetic programming (GP) and pervious empirical results to investigate the applicability, ability, and accuracy of these procedures. To examine the accuracy of the results yielded from the M5 and GP procedures, two performance indicators (determination coefficient (R2) and root mean square error (RMSE)) were used. The comparison test of results clearly shows that the implementation of M5 technique sounds satisfactory regarding the performance indicators (R<sup>2</sup> = 0.944 and RMSE = 0.126) with less deviation from the numerical values. In addition, M5 tree model, by presenting relationships based on liner regression, has good capability to estimate the depth of scour abutment for engineers in practical terms.
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.
