Current Flume Research Articles

Numerical and Experimental Power Output Estimation for a Small-Scale Hinged Wave Energy Converter

Wave energy converters (WECs) integrated into breakwaters present a promising solution for combining coastal protection with renewable energy generation, addressing both energy demands and environmental concerns. Additionally, this integration offers cost-sharing opportunities, making the overall investment more economically viable. This study explores the potential of a hinged point-absorber WEC, specifically designed as a floating hinged half-sphere, by assessing the device’s power output and comparing two different breakwater configurations. To evaluate the device’s performance, a comprehensive numerical and experimental approach was adopted. Numerical simulations were carried out using a radiation-diffraction model, a time domain tool for analyzing wave–structure interactions. These simulations predicted average power outputs of 25 kW for sloped breakwaters and 18 kW for vertical breakwaters located at two strategic sites: the Port of Leixões and the mouth of the Douro River in Portugal. To validate these predictions, a 1:14 scale model of the WEC was constructed and subjected to testing in a wave–current flume, replicating different sea-state conditions. The experimental results closely aligned with the numerical simulations, demonstrating a good match in terms of relative error and relative amplitude operator (RAO). This alignment confirms the reliability of the predictive model. These findings support the potential of integrating WECs into breakwaters, contributing to port energy self-sufficiency and decarbonization.

Experimental investigation on hydrodynamic performance of submerged floating tunnel under the protection of a new floating energy dissipation and anti-vibration device

This study describes an efficient and applicable approach to decrease the hydrodynamic response of a submerged floating tunnel (SFT). A new type of floating energy dissipation and anti-vibration device is proposed, mainly consisting of a floating box superstructure with water and a polyvinyl chloride porous media substructure. The experimental model of an SFT with the present protection device is designed and conducted in a wave–current flume. The wave–current attenuation mechanisms for the present protection device are experimentally investigated. The sensitivity analysis for the key parameters, e.g., structure type and wave–current parameter, is conducted to investigate the hydrodynamic performance of the SFT with the present protection device. The results show that the present protection device has excellent wave–current attenuation capacity, and the transmission coefficients and the current–velocity attenuation coefficient reach 0.2 and 0.15, respectively. The sway, heave, roll, and typical cable tension from the SFT with the protection are, respectively, about 8, 6, 8, and 3 times smaller than that from without the protection. The results show that the SFT with the present protection device has excellent anti-vibration performance, which is beneficial for its safety and stability. This study has important theoretical and practical values to the anti-vibration design of SFTs serviced in complicated ocean environments.

Influence of wakes interaction and upstream turbulence on three tidal turbines behaviour

The current study presents numerical results on three tidal turbine models (two in front, one downstream) interacting in a turbulent upstream flow. The numerical results come from a lifting-line (LL) embedded in a Lagrangian vortex particle (VP) solver: Dorothy LL-VP. The objective is to assess the extent to which this numerical tool is suited to reproduce accurately wakes interaction as well as fluctuating loads perceived by the downstream turbine. To this aim, the numerical set-up reproduces an experimental campaign led at IFREMER’s wave and current flume tank. The downstream turbine is placed at different positions to change the wakes interaction. Two upstream turbulence intensities (TI) experimentally tested are reproduced numerically using the synthetic eddy method (SEM). Favourable comparisons are obtained between numerical and experimental wakes, including velocity profiles. Preliminary results suggest that the downstream turbine performance decrease is numerically well captured. More investigations are needed on the loads fluctuations with longer computation time, and adding an angular velocity controller as well as hub modelling to Dorothy LL-VP.

Development and validation of a lifting‐line code associated with the vortex particle method software Dorothy

AbstractThis paper presents a lifting‐line implementation in the framework of a Lagrangian vortex particle method (LL‐VP). The novelty of the present implementation lies in the fluid particles properties definition and in the particles shedding process. In spite of mimicking a panel method, the LL‐VP needs some peculiar treatments described in the paper. The present implementation converges rapidly and efficiently during the shedding sub‐iteration process. This LL‐VP method shows good accuracy, even with moderate numbers of sections. Compared to its panel or vortex filaments counterparts, more frequently encountered in the literature, the present implementation inherently accounts for the diffusion term of the Navier‐Stokes equations, possibly with a turbulent viscosity model. Additionally, the present implementation can also account for more complex onset flows: upstream ambient turbulence and upstream turbine wakes. After validation on an analytical elliptic wing configuration, the model is tested on the Mexnext‐III wind turbine application, for three reduced velocities. Accurate results are obtained both on the analytical elliptic wing and on the New MEXICO rotor cases in comparison with other similar numerical models. A focus is made on the Mexnext‐III wake analysis. The numerical wake obtained with the present LL‐VP is close to other numerical and experimental results. Finally, a last configuration with three tidal turbines in interaction is considered based on an experimental campaign carried out at the IFREMER wave and current flume tank. Enhanced turbine‐wake interactions are highlighted, with favourable comparisons with the experiment. Hence, such turbine interactions in a farm are accessible with this LL‐VP implementation, be it wind or tidal energy field.

Experimental comparison of the flow-induced loading between a ducted bottom-mounted twin vertical axis tidal turbine at still and an unducted prototype

The FloWatt project aims to demonstrate the efficiency of the HydroQuest’s 2.5 MW-rated turbine for commercial farm deployment. The project is dedicated to develop an innovative design of a turbine for high energetic sites and to deploy seven vertical axis tidal turbines on the Raz Blanchard site, France. This technology has already been successfully developed in a previous project at a smaller scale on the Paimpol-Bréhat test site.
 Along the past three years, an important amount of work has been achieved to widely characterise the behaviour of the 1/20 scale 2-VATT similar to the 1MW-rated demonstrator. The turbine was tested in many different operating conditions in the Ifremer’s wave and current flume tank to reproduce full-scale conditions and turbine response (wide range of operating points and incident velocities, facing aligned and misaligned currents, with and without vertical velocity shear, with and without bathymetry generated turbulence, with and without surface waves following and against the current). Based on that experience, we gain confidence in the design process by comparing those experimental results to numerical and in-situ ones.
 
 After a quick presentation of the industrial development for the deployment of a pilot farm with the manufacture, installation and operation of 7 turbines on the Raz-Blanchard site, we will focus on the scientific development aiming to prepare large-scale deployments of the next generation of turbine. One important step is to compare the flow-induced loading between the 2 kinds of turbine (ducted and unducted) and to analyse environmental loads during survival conditions. To investigate those points, the behaviour of a 1/20 scale 2-VATT similar to the 2.5 MW-rated demonstrator is experimentally studied in a wide range of operating conditions: with and without vertical velocity shear, and with and without surface waves following and against the current. 
 In the paper, we will compare at 1/20 scale the behaviour of the two kinds of turbine: 1 MW-rated and 2.5 MW-rated turbines. The experiments have been done in the same basin, under the same experimental conditions. The databases are being processed before launching a fine physical analysis.

Experimental flow conditions effects on a bottom-mounted ducted twin vertical axis tidal turbine compared to real sea conditions

From 2019 to 2021, HydroQuest tested its 1 MW-rated ducted twin vertical axis tidal turbine (2-VATT) at Paimpol-Bréhat test site, France. At this site, the turbulent intensity is evaluated about 15 % and extreme wave conditions up to 6 m significant wave height with 12 s peak period were observed during the two years of demonstration. In addition, the current vertical velocity profile is sheared with about 20 % velocity difference between the top and the bottom of the turbine, and the average directions of the ebb and flood tides are about 22° asymmetrical. The bottom mounted 2-VATT was instrumented for performance and loads assessment which allowed the certification of the power curve, both in flood and ebb tides, as well as the analysis of the sea state influence on the turbine behaviour. Based on that experience, the company wants to gain confidence in its design process by comparing those results to numerical and lab-scale experiments ones.
 Along the past three years, an important amount of work has been achieved to widely characterise the behaviour of the 1/20 scale 2-VATT similar to the 1MW-rated demonstrator. The turbine was tested in many different operating conditions in the Ifremer’s wave and current flume tank to try to reproduce full-scale conditions and turbine response. Those conditions include a wide range of operating points and incident velocities, facing aligned and misaligned currents, with and without vertical velocity shear, with and without bathymetry generated turbulence, with and without surface waves following and against the current. In this presentation, we propose to synthesise the effects of all these conditions on the 2-VATT response to highlight the most critical ones in the design process of such a device, in comparison to the results obtained at sea.
 To this date, we showed that the lab-scale model behaviour differs between ebb and flood tide current conditions due to the difference of relative counter-rotation of the two columns of rotors and to the base asymmetry. The wake is also significantly different as it recovers 30 % faster in the flood tide configuration compared to the ebb. We also found that the presence of a sheared and misaligned incident current barely affects the ducted 2-VATT average performance. However, it modifies the torque repartition between the rotors leading to an increase of the power fluctuations. Furthermore, when adding bathymetry obstacle upstream, the high flow shear and turbulence also generate strong power fluctuations on the 2-VATT. The load fluctuations are significantly increased, impacting the structure fatigue compared to a flat floor configuration, but the risks of device drifting or toppling are not affected. The waves impact the power and loads fluctuations too while barely affecting the average performance; and the average performance increases with the Reynolds number in the tank. Those two latter points still need investigations to better characterise their effect on the 2-VATT.

USING HYDRODYNAMICS TO IMPROVE SEA STAR FISHERIES IN COASTAL REGIONS

Sea stars (starfish) predate on various shellfish such as mussels and clams, and can have a negative impact on the blue-mussel production and aquaculture. This has encouraged the harvesting of sea stars to protect blue mussels and clams from predation, but they are also targeted commercially, as a valuable protein source used e.g. in animal feed. Towed fishing gears can be used to harvest sea stars in coastal regions, however, little is known scientifically about the hydrodynamics around these gears. To better understand the hydrodynamics around towed fishing gears, an experimental investigation has been carried out in a current flume within the DTU Civil and Mechanical Engineering Hydraulics Laboratory.

Misaligned sheared flow effects on a ducted twin vertical axis tidal turbine

Most tidal turbines experimental tests are carried out in idealised conditions with uniform velocity profiles and without flow misalignment. However, at sea, the velocity profiles are mostly sheared and the flow direction spreads out around the main direction. In this study, we address experimentally the effect of those realistic conditions on the response of a twin counter-rotating vertical axis tidal turbine in Ifremer’s wave and current flume tank. At the whole turbine scale, the current shear hardly affects the drag and the average power coefficient but it leads to a 35 % increase of the power standard deviation. The flow misalignment does not affect the power production but it raises the average drag coefficient by 15 % for a ±15°angle of incidence. At the rotor column scale, both the shear and the misalignment modify the torque distribution with regard to the blades angular position, with a torque asymmetry up to 30 % between the upper and lower rotors, among other effects. Absolute rotor angular position as well as blades local flow visualisation would be needed to explain the complex torque distribution on a rotor column, which must be taken into account in the turbine design. This paper also provides a wide experimental database for the validation of numerical models applied to ducted twin vertical axis tidal turbines.

Experimental performance and wake study of a ducted twin vertical axis turbine in ebb and flood tide currents at a 1/20th scale

While studies on horizontal axis tidal turbines are plentiful, those on ducted twin vertical axis alike HydroQuest’s turbines are lacking. For such a device, both the relative counter-rotation direction of the rotors and the tripod base geometry upstream are different between ebb and flood tide. Consequently, this paper analyses the effect of the two opposed flow directions on the hydrodynamic performance and on the wake of the turbine. The study is based on experimental measurements at a 1/20th scale in Ifremer’s wave and current flume tank. The hydrodynamic performance of the model are characterised over a wide range of operating points with the turbine installed on a tripod and on a monopile base. In addition, the 3D wake of the turbine is thoroughly analysed in the two flow directions using 3-component laser Doppler velocimetry. Overall, the drag and the maximum average power coefficient are not affected by the current direction but the optimal tip speed ratio is 7 % lower during ebb with 1.5 times higher power fluctuations compared to flood tide. Besides, the wake of the two rotor columns interact differently depending on the flow direction, leading to a 30 % faster surface averaged velocity recovery in the flood tide configuration. The observed effect of flow direction provides a better knowledge of twin vertical axis turbine wake interactions and highlights the impact of the gravity base geometry on the development of the overall turbine wake. This paper also provides a wide experimental database for the validation of numerical models applied to ducted twin-vertical axis tidal turbines.

A conceptual basis for surveying fouling communities at exposed and protected sites at sea: Feasible designs with exchangeable test bodies for in-situ biofouling collection

The enhanced inertia load caused by biofouling on device components, such as the foundations of wind turbines or other structures at sea, modifies the hydrodynamic properties, and increases the stress to structures, predominantly in upper water layers with high impact from wave dynamics. This compromises the stability, functioning, operation as well as the durability of these devices especially in exposed environments. A main challenge is the quantification of the impact of hydrodynamic forces on irregular bodies being overgrown by soft- and hard-bodied biofouling organisms. Therefore, test bodies from the upper 1–5 m water depth and thus exposed to the strongest wave actions close to the surface shall be overgrown by biofouling and used in measurement trials in a wave and current flume. These measurements shall shed light on the varying roughness and its influence on the load bearing capacity of foundation piles. Consequently, the main aims of the present work were the development of two independent test stations as holding devices for artificial test bodies for the collection of biofouling organisms during field studies: a carrying unit floating at the surface in an exposed area (System A) and a sampling device with access from a land-based facility (System B). Both systems are relatively easy to access, exhibit straightforward handling, and are reasonable cost-effective. A Test Body Support Unit (TBSU, System A) was designed and mounted on a spare buoy to carry the test bodies (cylinders), which serve as substrate for the fouling. The system was sufficiently robust to withstand several periods of rough sea conditions over the first two years. This system can only be accessed by vessels. System B (MareLift) provided the robustness and functionality needed for areas exhibiting harsh conditions but can be operated from land. The here used test bodies (steel panels) exhibited a sound basis for the monitoring of succession processes in the biofouling development. System B offered the possibility to analyse two habitats (intertidal and subtidal) and revealed clear differences in the composition and development of their fouling communities.Overall, both systems provide advantages in obtaining standardized biofouling samples compared to previous approaches. Such test stations play an important role in the risk management of marine sectors as they could help characterising biofouling communities over different geographical areas. System A and B provide a sound basis for biofouling research but potentially also for other potential research approaches in exposed areas as they provide space for future developments.

Experimental Investigation of the Dynamic Behavior of Submerged Floating Tunnels under Regular Wave Conditions

Submerged floating tunnels (SFTs) are an innovative traffic structure for transportation in deep and long-distance ocean environments. SFTs have the risk of being subjected to wave action in the complex ocean environment. Therefore, in order to ensure the safety and stability of SFTs during their service, the dynamic behavior of an SFT subjected to the action of waves is experimentally investigated in this study. Based on the wave–current flume, a physical scale-model experiment of an SFT for studying the dynamic behavior of an SFT subjected to regular waves interactions is deeply and thoroughly explored. The results show that the wave outputs from the wave-making system are verified to be reliable. The influence of major load parameters on the dynamic behavior of the SFT are deeply and thoroughly explored. The effects of wave height and wave period on acceleration, wave pressure, anchor cable force and displacement in an SFT are discussed. This experimental study has theoretical and practical significant for SFT design and safety.

Drag-related wave–current interaction inside a dense submerged aquatic canopy

The seabed in coastal regions is often covered by a dense submerged canopy formed by benthic organisms. The in-canopy flow is of great interest to coastal researchers. In this study, a semi-analytical model is proposed for the in-canopy current profile under the influence of coexisting waves. The current is driven by a mean shear stress at the canopy top and a mean streamwise pressure gradient. Wave–current interaction arises from the mean canopy drag, which is described by the conventional quadratic law. An algebraic eddy viscosity model, which accounts for the turbulence generated by a canopy-scale vortex and stem-scale wake, is proposed. The model is calibrated against unidirectional flume experiments, and is subsequently validated against a wave–current flume experiment. It is found that the mean canopy drag experienced by the current can be significantly amplified by a co-existing wave-driven oscillatory flow. Under the same current driving force, the current in wave–current flow is reduced from that in a pure-current flow. The reduction increases with canopy density and wave strength. For a wave and current at an angle, veering of the current velocity vector is suggested by the model, which makes the mean canopy drag align with the driving force of the current.

Prediction of the wave–current forces acting on a composite bucket foundation using machine learning method

The prediction of wave–current forces is the critical content in the design of the composite bucket foundation (CBF). Inaccurate calculations of wave–current forces lead to failure for offshore wind power foundation. In this study, experiments for the hydrodynamic forces acting on a CBF with a scale of 1:40 under different wave and current conditions in the wave–current flume were designed and conducted. A machine learning and data mining method called M5′ model tree was used to predict the hydrodynamic forces acting on the foundation. The accuracy of the new formulae was confirmed by the statistical indicators using Pearson correlation coefficient, agreement index, scatter index, and bias. The results show that the M5′ models were effective in predicting the hydrodynamic forces. The scatter parameter and relative cylinder diameter play vital roles in the prediction of the wave forces. In the prediction of the wave–current forces, the relative cylinder diameter is the most important parameter, and the wave–current forces increase with relative cylinder diameter increase. Overall, the results illustrate that the developed formulae can serve as a valuable tools for the prediction of the wave–current forces acting on a CBF.

Scale Model Experiment on Local Scour around Submarine Pipelines under Bidirectional Tidal Currents

In nearshore regions, bidirectional tidal flow is the main hydrodynamic factor, which induces local scour around submarine pipelines. So far, most studies on scour around submarine pipelines only consider the action of unidirectional, steady currents and little attention has been paid to the situation of bidirectional tidal currents. To deeply understand scour characteristics and produce a more accurate prediction method in bidirectional tidal currents for engineering application, a series of laboratory scale experiments were conducted in a bidirectional current flume. The experiments were carried out at a length scale of 1:20 and the tidal currents were scaled with field measurements from Cezhen pipeline in Hangzhou Bay, China. The experimental results showed that under bidirectional tidal currents, the scour depth increased significantly during the first half of the tidal cycle and it only increased slightly when the flow of the tidal velocity was near maximum flood or ebb in the following tidal cycle. Compared with scour under a unidirectional steady current, the scour profile under a bidirectional tidal current was more symmetrical, and the scour depth in a bidirectional tidal current was on average 80% of that under a unidirectional, steady current based on maximum peak velocity. Based on previous research and the present experimental data, a more accurate fitted equation to predict the tidally induced live-bed scour depth around submarine pipelines was proposed and has been verified using field data from the Cezhen pipeline.

New system design for the cultivation of extractive species at exposed sites - Part 2: Experimental modelling in waves and currents

Aquaculture is projected to be a major supplier of marine proteins to large parts of the global population. This includes bivalves, which have a high potential to offset protein deficits, as they are highly adaptable to varying water temperature, salinity, desiccation, and oxygen conditions. This work is part of a two-piece contribution on novel marine aquaculture technology and details physical laboratory tests of a new cultivation system for bivalve farming called “Shellfish Tower”. The tested 1:20 model consists of a rectangular cage (2 × 2 m prototype scale) with a central buoyancy element and a height of 2 – 4 m. Testing was done in a current flume as well as a wave basin for current velocities between 0.4 – 2.2 m/s and wave heights of 1.6 to 5.0 m with periods between 5 to 14 s. The tests were conducted to prove the feasibility and functionality of this aquaculture system, which is usable for the collection and cultivation of mussel spat as well as for the grow-out of oysters, scallops, and seaweed in marine environments. Tests carried out in a current flume revealed that drag coefficients decrease with increasing current velocities, and range from Cd=0.5 to 2.5, while the mooring inclination increases from 12° to 84° with increasing flow velocity, which is highly dependant on the buoyancy related pretension. The examination of the mooring line tensions recorded in a wave basin showed that the largest values of snap-induced tension were up to 10 times that of the semi-static tension. The maximum-recorded tension on the system was 48 kN for a single and 89 kN for a double configuration, compared to non-snap tension values, which were in the range of 6 – 10 kN. The insights gathered in this study will inform the future design of aquaculture systems in high-energy environments and allow for an integration into numerical models.

Wind–Water Experimental Analysis of Small SC-Darrieus Turbine: An Approach for Energy Production in Urban Systems

Smart cities have a significant impact on the future of renewable energies as terms such as sustainability and energy saving steadily become more common. In this regard, both wind and hydrokinetic compact-size turbines can play important roles in urban communities by providing energy to nearby consumption points in an environmentally suitable manner. To evaluate the operation of a Darrieus turbine rotor as a wind or hydro microgenerator, a series of wind tunnel and water current flume tests were performed. Power and characteristic curves were obtained for all test conditions. In the wind tests, all curves seemed to be identical, which means that the turbine rotor works properly under open-field conditions. Two blockage correction equations were applied to the water channel tests that were performed under blockage values ranging from 0.2 to 0.35 to estimate the operational behavior in open water. Finally, it has been demonstrated that, with the condition of maintaining the Reynolds number between experiments in the wind tunnel and water flume, the turbine wind characteristics represents the its operation in open-water conditions.

Analysis on the influence of water concentration on ADCP current measurement

With the objective of improving the measure performance of Acoustic Doppler Current Profiler (ADCP) and promoting the level of marine environmental monitoring, the precision and accuracy of ADCP current measurement have been analyzed in detail based on the current flume with water concentration (0 - 20) kg/m3. The experiments indicated that the precision of ADCP current measurement is enhanced with the uprising of water concentration. The precision of ADCP measurement was significantly influenced by the water concentration when the current was (0.7-0.9) m/s, and it was less affected by the water concentration when the current was 0.3m/s. In addition, with the increase of water concentration, the accuracy of ADCP measurement increased at first and then decreased. The accuracy of current measurement was higher when the concentration was (9-11) kg/m3, and decreased in varying degrees outside this range. When the current was 1.1 m/s, the accuracy of ADCP was greatly affected by the concentration, while it was less affected by the concentration in the case that current is 0.3 m/s. The correlation analysis and conclusion can provide a reference not only for the research and development of ocean observation equipment, but also for marine scientific studies.

Fate and behaviour of weathered oil drifting into sea ice, using a novel wave and current flume

Increased knowledge about the fate and behaviour of weathered oil in different sea ice conditions is essential for our ability to model oil spill trajectories in ice more precisely and for oil spill response decision making in northern and Arctic areas. As part of the 3-year project: “Fate, Behaviour and Response to Oil Drifting into Scattered Ice and Ice Edge in the Marginal Ice Zone”, a novel wave and current flume was built to simulate these processes in the laboratory. This paper discusses some of the findings from this project, which included Marine Gas Oil and four Norwegian crude oils. All crude oils were weathered prior to testing, simulating having drifted on the sea surface for a period (tentatively 1–3 days) before encountering ice. The build-up of oil drifting against an ice barrier and horizontal and vertical migration of oil droplets under solid ice and in frazil ice was studied.

Experimental study of bathymetry generated turbulence on tidal turbine behaviour

In high flow velocity areas like those suitable for tidal applications, turbulence intensity is high and flow variations may have a major impact on tidal turbine behaviour. A three-bladed horizontal axis turbine model (scale 1:20) is positioned in the wake of a square wall-mounted cylinder, representative of specific in situ bathymetric variation, to experimentally study these effects in a current flume tank. Local and global loads are acquired in synchronization with velocity measurements to study the turbine response to flow fluctuations. Velocity measurements need to be obtained close to the turbine, contrary to what is commonly considered, to properly correlate velocity and loads fluctuations. Results show that the loads phase average and their dispersion evolve according to the sheared velocity profile. We conclude that the turbine load fluctuations directly respond to the low frequency velocity fluctuations and are dominated by the turbulent structures shed from the cylinder. It is then possible to compare the effects of large coherent turbulent structures on the turbine behaviour to cases with more classical free stream turbulence commonly studied. These results provide a substantive database in high Reynolds number flows for further fatigue analysis or recommendations for turbine positioning in such flows.

Experimental Investigation of Local Scour Protection for Cylindrical Bridge Piers Using Anti-Scour Collars

Local scour of bridge piers is one of the main threats responsible for bridge damage. Adopting scour countermeasures to protect bridge foundations from scour has become an important issue for the design and maintenance of bridges located in erodible sediment beds. This paper focuses on the protective effect of one active countermeasure named an “anti-scour collar” on local scour around the commonly used cylindrical bridge pier. A cylindrical pier model was set up in a current flume. River sand with a median particle size of 0.324 mm was selected and used as the sediment in the basin. A live-bed scour experimental program was carried out to study the protective effect of an anti-scour collar by comparing the local scour at a cylindrical bridge pier model with and without collar. The effects of three design parameters including collar installation height, collar external diameter and collar protection range, on the scour depth and scour development were investigated parametrically. According to the experimental results, it can be concluded that: the application of an anti-scour collar alleviates the local scour at the pier effectively; and the protection effect decreases with an increase in the collar installation height, but increases with an increase in the collar external diameter and the protection range. Design suggestions for improving the scour protective effect of the anti-scour collar are summarized and of great practical guiding significance to the development of anti-scour collars for bridge piers.