A method and device for scour protection of diversion pile foundations

Abstract

This invention discloses a flow-guiding pile foundation scour protection method and device, relating to the fields of marine engineering and hydraulic engineering. It includes the following steps: S1, flow field analysis to obtain hydrological characteristic data of the sea area; S2, preliminary design of key component dimensions of the protection device based on the hydrological characteristic data; S3, simulation analysis; S4, construction layout; S5, operation and maintenance. The structure includes a main flow guide plate and lateral flow guide plates. This invention utilizes Bernoulli's principle to design a flow-guiding protection device that, through multi-stage flow field regulation, transforms destructive downflow into constructive sediment-carrying flow, weakening scour while inducing sediment deposition in specific areas around the pile. It effectively avoids flow separation caused by abrupt pressure gradient changes when water flows over the surface of the main flow guide plate, helping to guide sediment-laden water smoothly into and out of the protection area, and better controlling the direction of sediment transport.

Description

Technical Field

[0001] This invention relates to the fields of marine engineering and hydraulic engineering, and specifically to a method and device for protecting against scour of a flow-guiding pile foundation. Background Technology

[0002] In marine and estuarine environments, vertical pile structures are subjected to the reciprocating forces of waves and currents. When fluid flows around the piles, the boundary layer separates due to the adverse pressure gradient in front of the piles, forming a high-intensity horseshoe vortex in front of the piles and a Karman vortex street behind them. These large-scale coherent vortex structures violently stir up seabed sediment, resulting in localized scour pits around the piles that are 1.5 to 2.5 times the pile diameter deep, seriously threatening structural safety. Existing protective measures are mainly divided into two categories: passive protection: such as riprap, interlocking concrete blocks, and stabilizing soil. The disadvantages are increased seabed load, susceptibility to secondary scour at the edges, frequent maintenance, and complex and precise construction operations during maintenance. Active protection: such as installing fairings, slotted piles, or deploying sacrificial piles and sand-trapping barriers on the piles. The disadvantages are that some structures are complex, which may increase the wave load on the pile body and affect the safety of the pile foundation structure; at the same time, sacrificial piles or sand retainers can also cause severe scouring in certain areas, which can lead to the failure and destruction of the protective structure, and once damaged, it is difficult to maintain. At present, there is a lack of a protective structure that can reduce pile foundation scouring, achieve a certain degree of "reverse backfilling" of the pile foundation pit through precise control of the movement of sediment at the bottom, and also has the characteristics of convenient maintenance in the later stage. Summary of the Invention

[0003] This invention aims to solve the problems of passive protection being prone to edge scour and active protection structures being complex and difficult to maintain in existing technologies. It proposes a flow-guiding pile foundation scour protection method and device designed using Bernoulli's principle. Through multi-stage flow field regulation, the destructive downflow is transformed into a constructive sediment-carrying flow, thereby weakening scour while inducing sediment deposition in specific areas around the pile.

[0004] The objective of this invention is achieved through the following technical solutions:

[0005] A method for scour protection of diversion pile foundations includes the following steps:

[0006] S1. Flow field analysis: Based on the measured data of the engineering area, obtain the hydrological characteristics of the sea area, including the tidal rose diagram, seabed sedimentity, main direction of tidal current, and maximum tidal velocity.

[0007] S2. Based on hydrological data, conduct preliminary design of the key aggregate dimensions of the protective device. Key aggregate dimensions include: the height of the exposed bed structure in the mainstream area. h and length L1The quantity and length of lateral flow guidance structures, the quantity and length of reverse flow ribs, and the burial depth of protective devices; the main flow area includes two main flow guide plates, and is divided into a front guide section, a middle energy dissipation section, and a rear diffusion zone. The front guide section is streamlined and flared, and this section of the main flow guide plate is above the seabed surface. The length of the front guide section is... The inlet width of the front-end guide section guide channel G2 Set to less than or equal to the pile diameter D The width of the flow channel in the middle energy-consuming section gradually increases, and the height of the mainstream flow guide plate exposed above the bed surface increases. h Similar to the front guide section, the width of the guide channel in the rear diffusion zone gradually increases. The tail of the main guide plate is located on both sides of the central axis of the pile foundation in the side view. Simultaneously, the height of the main guide plate gradually decreases along the water flow direction until it is flush with the seabed. This design weakens the abrupt flow field at the end of the device, solving the problem of "secondary scouring at the edge" inherent in traditional solidification protection measures. Within this section, the water flow gradually decreases in velocity due to the gradually expanding channel cross-section. The reduction in device height further increases the flow cross-section and introduces the mixing effect of the surrounding flow field, causing the sediment carried by the water to gradually move and deposit near the pile foundation, achieving "sediment replenishment." The burial depth of the device can be initially designed to be 0.2D to 0.5D or the actual thickness of the active seabed layer; export the STL file of the preliminary design device entity.

[0008] S3. Simulation Analysis: Based on the maximum tidal flow velocity and the STL file of the preliminary design device, computational fluid dynamics software is used in conjunction with a turbulence model to conduct auxiliary simulations of the scouring and flow field characteristics of the protective device. The stress on the protective device under possible extreme flow velocity conditions, the scouring depth of the pile foundation and the vicinity of the protective device, and the overturning moment of the protective device are analyzed. The configuration of the protective device is optimized through simulation data to ensure that the selected size data can achieve a good protective effect and guarantee the stability of the protective device. If the protective effect is poor or the stability does not meet the requirements, the process can be returned to S2 to redesign the device.

[0009] S4. Construction layout: The protective device is prefabricated in sections at the land prefabrication yard, with pre-reserved hoisting holes and connectors. The seabed around the pile is leveled, and soft floating mud on the surface is removed in advance. The protective device is transported to the preset position near the pile foundation and sinked with the assistance of a hydraulic vibratory hammer to ensure that the cutting depth reaches the design value.

[0010] S5. Operation and Maintenance: Regularly, or after the typhoon season, use multibeam sonar to scan the scour depth near the pile foundation. If the scour depth near the pile foundation or protective device is greater than or equal to 0.3D, initiate a sand replenishment procedure. During sand replenishment, sand and gravel with a particle size gradation slightly smaller than the original seabed soil can be placed in the area of ​​the guide section at the front end of the protective device. This backfill material ensures the stability of the guide device and, under the action of ocean currents, will gradually move towards the pile foundation to achieve natural backfilling. This method significantly reduces the positioning accuracy requirements and diving operation risks in deep-water operations, and significantly reduces the total life-cycle operation and maintenance costs.

[0011] Preferred,

[0012] Step S2 Mainstream guide plate length Take approximately 4.0 times the pile diameter, and calculate as follows:

[0013] Inlet width of the front-end guide section guide channel G2 =0.5D <= G2 <=1.0D; to ensure that a certain volume of fluid enters the main flow channel. The length of the front guide section is... The front guide section will have a portion completely exposed above the bed surface. Based on the characteristics of the horseshoe vortex scale and the range of the downflow in front of the pile, and considering the stress and cost characteristics of the device itself, the height... h It must be able to cover the main vortex core of the horseshoe vortex in front of the pile, if h If the temperature is too low, the high-energy fluid will overflow and create a new downward flow; if... h If the height is too high, the device will be subjected to excessive stress and it will be uneconomical. Based on the distribution scale characteristics of horseshoe vortices before the pile under different water flow intensities, the height h of the mainstream guide plate in the front guide section protruding from the bed surface can be calculated by the following formula:

[0014] ,

[0015] in, For the height coefficient, when the Froude number Fr < 0.2 hour ; Fr > 0.2 hour ;

[0016] The length of the central energy-consuming section is In this section, additional measures can be added to improve the roughness of the channel and further dissipate the energy of the incoming flow. For example, several counter-current turbulence ribs can be alternately arranged on both sides of the guide channel wall of the main flow deflector in the middle energy dissipation section. When the water flows through this area, the overall flow velocity will gradually decrease due to the widening of the channel. At the same time, alternating vortices will be formed when the water flows through the turbulence ribs. These vortices can ensure that the sediment carried from upstream will not be excessively deposited in this section. At the same time, the vortices will gradually interact with each other during the backward convection motion, further dissipating the energy of the incoming water flow.

[0017] The width G1 of the rear diffuser is between 1.5D and 2.5D. The length of the rear diffuser is calculated based on the angle of the rear diffuser and the widths of the inlet and outlet sections. The angle of the rear diffuser is referenced to the angle of the side guide vane channel deviating from the mainstream region. Then the minimum length of the rear diffusion region is:

[0018] .

[0019] This design can reduce the abrupt flow field at the end of the device, solving the problem of "secondary scouring at the edge" in traditional solidification protection measures. Within this end, the water flow gradually decreases in velocity due to the gradually expanding cross-section of the flow channel. Simultaneously, the reduced device height further increases the flow cross-section of the water flow and introduces the mixing effect of the surrounding flow field. This allows the sediment-laden water to gradually accumulate around the pile foundation in the area in front of the pile, achieving "sediment replenishment."

[0020] Preferably, the length of the reverse spoiler rib is calculated using the following formula:

[0021] ,

[0022] in, The local width of the flow channel at its location. This is the critical initiation velocity for sediment. This is a coefficient, which can be taken as 0.1 to 0.2. Typically... The preset value can be 0.2 to 0.3 times the pile diameter. Under strong flow conditions, the upper limit can be used to increase resistance.

[0023] Preferably, the lateral deflector zone includes multiple lateral deflectors, and the number and length of the lateral deflectors are calculated as follows:

[0024] The number of side deflectors is determined by the following formula:

[0025] ,

[0026] In engineering, this can be simplified to:

[0027] ,

[0028] in, To prevent flow separation, the angle of the lateral guide vane channel deviating from the mainstream area is controlled between 7 and 15 degrees. To achieve the maximum tidal current velocity within the design recurrence period, For reference flow velocity, take 1 m / s. The correction factor is set to 1.5 to 2.5, and ceil is the floor function.

[0029] For normal sea states when U < 1.5 m / s, 1 to 2 blocks are arranged on one side; for strong current sea states when U < 2.0 m / s, 3 to 4 blocks are arranged on one side.

[0030] The side deflectors should be arranged in a stepped pattern, with the inner side longer than the outer side. The length of each side deflector stage can be calculated from the length of the main flow deflector, assuming the total length of the main flow deflector is... Counting from the inside out, the length of the i-th stage side deflector is... for:

[0031] ,

[0032] in This is the length reduction factor, with a value ranging from 0.6 to 0.8.

[0033] The number of lateral deflectors depends on the extent of the flow field disturbance, which is related to the Reynolds number ( ). Re = U L p / v , L p This refers to the projected length of the main component in the flow direction. This value is approximately the same as the pile diameter, and can be taken as the pile diameter in the design. D ) and Froude number ( Fr =U / , H (This is related to water depth). The higher the flow velocity, the greater the lateral pressure gradient, and the more stages of lateral guide vanes are needed to gradually smooth the flow velocity.

[0034] Preferably, for sandy seabeds, the burial depth of the protective device is initially calculated using the following formula:

[0035] ,

[0036] ,

[0037] in, A safety factor, such as 1.5 or 2.0, is required for anti-tipping stability. For effective severe cases, The internal friction angle of the soil. The total bending moment under external loads at the bed surface can be obtained through numerical simulation results. This refers to the thickness of the natural interaction layer of the local seabed or the maximum scour depth in numerical simulation calculations.

[0038] This invention also provides a flow-guided pile foundation scour protection device obtained using the above-mentioned flow-guided pile foundation scour protection method. The protection device is streamlined and flared along the central axis of the pile foundation, including a main flow guide plate and lateral flow guide plates. The thickness of the main flow guide plate and the lateral flow guide plates is 0.05-0.15 times the diameter of the pile foundation. The lateral flow guide plates are composed of lateral flow guide plates with a similar configuration to the main flow guide plate but shorter in length. The lateral flow guide plates can further disperse the incoming flow, reduce the impact force on the main flow guide plate, and also assist in the regulation of sediment movement.

[0039] Preferably, the protective device further includes reverse flow ribs, wherein the reverse flow ribs are alternately installed on both sides of the wall of the guide channel in the middle energy consumption section.

[0040] Preferably, the projected shapes of the main flow guide plate and the side flow guide plates on the horizontal plane are designed according to the streamline principle of fluid mechanics. Specifically, the wall curves of the main flow guide plate and the side flow guide plates are constructed using continuous variable curvature curves. This ensures a smooth transition of curvature and avoids discontinuities in the first derivative (i.e., sharp corners). This design effectively avoids flow separation caused by abrupt changes in pressure gradient when water flows over the surface of the main flow guide plate and the side flow guide plates, helping to guide sediment-laden water to smoothly enter and exit the protected area, and better control the direction of sediment transport.

[0041] Preferably, the wall curves of the main guide vane and the side guide vanes are cubic spline curves or higher-order B-spline curves.

[0042] Preferably, the front end of the main flow deflector and the side flow deflector has a semi-circular or parabolic blunt head structure to reduce the local high pressure when the incoming flow impacts; the back end of the main flow deflector and the side flow deflector has a smooth transition structure or a gradually tapering structure to reduce the size of the wake region.

[0043] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0044] This invention utilizes Bernoulli's principle to design a flow-guiding and protective device. Through multi-stage flow field regulation, it transforms destructive downflow into constructive sediment-carrying flow, weakening scouring while inducing sediment deposition in specific areas around the pile. It effectively avoids flow separation caused by abrupt pressure gradient changes when water flows over the surface of the main flow guide plate, helping to guide sediment-laden water smoothly into and out of the protected area and better control the direction of sediment transport. The turbulence ribs create alternating vortices. These vortices ensure that sediment carried from upstream does not excessively deposit in this section, while the vortices gradually mix and dissipate as they move backward, further aggravating the energy consumption of the downstream flow. The design of the rear diffusion zone weakens the abrupt flow field at the end of the device, solving the problem of "secondary scouring at the edge" inherent in traditional solidification protection measures. As the cross-section of the flow channel gradually expands and the flow velocity gradually decreases in this area, the reduction in the height of the device further increases the flow cross-section of the water and introduces the mixing effect of the surrounding flow field. As a result, the water carrying sediment gradually replenishes the sediment particles around the pile foundation in the area in front of the pile. Attached Figure Description

[0045] To more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings used in the following description of the embodiments will be briefly introduced. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0046] Figure 1 This is a top view of the protective device of the present invention;

[0047] Figure 2 This is a side view of the protective device of the present invention;

[0048] Figure 3 This is a three-dimensional rendered stereoscopic view of the protective device of the present invention;

[0049] Figure 4 This is a diagram showing the device layout applicable to different current flows according to the present invention;

[0050] Figure 5 A three-dimensional structural diagram showing the layout of the simulation calculation area in this invention;

[0051] Figure 6 The results are simulations of pile foundation scour without protective devices.

[0052] Figure 7 The results of pile foundation scour simulation when installing protective devices;

[0053] The diagram is labeled as follows: 1 is the main flow guide plate, 2 is the lateral flow guide plate, 3 is the reverse flow rib, and 4 is the pile foundation. Detailed Implementation

[0054] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

[0055] Many specific details are set forth in the following description in order to provide a full understanding of the invention. However, the invention may also be practiced in other ways different from those described herein, and those skilled in the art can make similar extensions without departing from the spirit of the invention. Therefore, the invention is not limited to the specific embodiments disclosed below.

[0056] Secondly, the term "one embodiment" or "embodiment" as used herein refers to a specific feature, structure, or characteristic that may be included in at least one implementation of the present invention. The phrase "in one embodiment" appearing in different places in this specification does not necessarily refer to the same embodiment, nor is it a single or selective embodiment that is mutually exclusive with other embodiments.

[0057] Example 1

[0058] A method for scour protection of diversion pile foundations that is easy to maintain includes the following steps:

[0059] S1. Flow field analysis: Based on the measured data of the engineering area, obtain the hydrological characteristics of the sea area, including the tidal rose diagram, seabed sedimentity, main direction of tidal current, and maximum tidal velocity.

[0060] S2. Based on hydrological data, conduct preliminary design of the key aggregate dimensions of the protective device. Key aggregate dimensions include: the height of the exposed bed structure in the mainstream area. h and length L1 The quantity and length of lateral flow guidance devices, the quantity and length of reverse flow ribs 3, and the burial depth of protective devices; wherein, the mainstream area includes two mainstream flow guide plates 1, the mainstream area is divided into a front flow guide section, a middle energy dissipation section, and a rear diffusion zone, the front flow guide section is streamlined and flared, this section of the mainstream flow guide plate is higher than the seabed surface, and the length of the front flow guide section is The inlet width of the front-end guide section guide channel G2 Set to less than or equal to the pile diameter D The width of the flow channel in the middle energy-consuming section gradually increases, and the height of the mainstream flow guide plate protruding from the bed surface increases. hSimilar to the front guide section, the width of the rear diffusion zone guide channel gradually increases, with its tail located on both sides of the central axis of the pile foundation in the side view. Simultaneously, the height of the main flow guide plate 1 gradually decreases along the water flow direction until it is flush with the seabed. This design weakens the abrupt flow field at the end of the device, solving the problem of "secondary scouring at the edge" inherent in traditional solidification protection measures. Within this end, the water flow gradually decreases in velocity due to the gradually expanding channel cross-section. The reduction in the height of the main flow guide plate 1 further increases the flow cross-section and introduces the mixing effect of the surrounding flow field, causing the sediment carried by the water to gradually move and deposit near the pile foundation, achieving "sediment replenishment." The burial depth of the device can be initially designed to be 0.2D to 0.5D, or based on the measured thickness of the active seabed layer; export the STL file of the preliminary design device entity.

[0061] In this embodiment, the preferred length of the mainstream area guide vane 1 is... Take approximately 4.0 times the pile diameter, and calculate as follows:

[0062] Inlet width of the front-end guide section guide channel G2 =0.5D <= G2 <=1.0D; to ensure that a certain volume of fluid enters the main flow channel. The length of the front guide section is... The main guide plate 1 in the front guide section will have a portion completely exposed above the bed surface. Based on the characteristics of the horseshoe vortex scale and the range of the downflow in front of the pile, and considering the stress and cost characteristics of the device itself, the height of the main guide plate 1 is... h It must be able to cover the main vortex core of the horseshoe vortex in front of the pile, if h If the temperature is too low, the high-energy fluid will overflow and create a new downward flow; if... h If the height is too high, the main flow guide plate 1 will be subjected to excessive force and be uneconomical. Based on the distribution scale characteristics of horseshoe vortices before the pile under different water flow intensities, the height h of the main flow guide plate 1 exposed above the bed surface in the front flow guide section can be calculated by the following formula:

[0063] ,

[0064] in For height coefficient, when Fr < 0.2 hour ; Fr > 0.2 hour ;

[0065] The length of the central energy-consuming section is In this section, additional measures can be added to improve the channel roughness and further dissipate the energy of the incoming flow. For example, several reverse flow ribs 3 can be alternately arranged on both sides of the guide channel wall in the front guide section. When the water flows through this area, the overall flow velocity will gradually decrease due to the widening of the channel. At the same time, alternating vortices will be formed when flowing through the flow ribs 3. These vortices can ensure that the sediment carried upstream will not be excessively deposited in this section. At the same time, the vortices will gradually mix and dissipate as they move backward, further aggravating the energy consumption of the downstream water flow. The reverse flow ribs 3 should not excessively block the channel, and their length can be calculated by the following formula:

[0066] ,

[0067] in, The local width of the flow channel at its location. This is the critical initiation velocity for sediment. This is a coefficient, which can be taken as 0.1 to 0.2. Typically... The preset value can be 0.2 to 0.3 times the pile diameter. Under strong flow conditions, the upper limit can be used to increase resistance.

[0068] The width G1 of the rear diffuser is between 1.5D and 2.5D. The length of the rear diffuser is calculated based on the rear diffuser angle and the widths of the inlet and outlet sections. The rear diffuser angle is referenced to the angle of the side guide vane channel deviating from the main flow guide vane. Then the minimum length of the rear diffusion region is:

[0069] .

[0070] This design can reduce the abrupt flow field at the end of the device, solving the problem of "secondary scouring at the edge" in traditional solidification protection measures. Within this end, the water flow gradually decreases in velocity due to the gradually expanding cross-section of the flow channel. Simultaneously, the reduced device height further increases the flow cross-section of the water flow and introduces the mixing effect of the surrounding flow field. This allows the sediment-laden water to gradually accumulate around the pile foundation in the area in front of the pile, achieving "sediment replenishment."

[0071] In this preferred embodiment, the lateral deflection zone includes multiple lateral deflection plates 2, and the number and length of the lateral deflection plates 2 are calculated as follows:

[0072] The number of side deflectors 2 is determined by the following formula:

[0073] ,

[0074] In engineering, this can be simplified to:

[0075] ,

[0076] in, To prevent flow separation, the angle of the lateral guide vane 2's flow channel deviating from the mainstream area is controlled between 7 and 15 degrees. To achieve the maximum tidal current velocity within the design recurrence period, For reference flow velocity, take 1 m / s. The correction factor is set to 1.5 to 2.5, and ceil is the floor function.

[0077] For normal sea states when U < 1.5 m / s, 1 to 2 blocks are arranged on one side; for strong current sea states when U < 2.0 m / s, 3 to 4 blocks are arranged on one side.

[0078] The side guide vanes 2 should be arranged in a stepped pattern with the inner side longer than the outer side to match the diffusion cone angle of the rear diffuser zone. The length of each stage of the side guide vane 2 can be calculated from the length of the main flow guide vane 1. Let the total length of the main flow guide vane 1 be... Counting from the inside out, the length of the i-th stage side guide vane 2 is... for:

[0079] ,

[0080] in This is the length reduction factor, with a value ranging from 0.6 to 0.8.

[0081] The number of lateral guide vanes 2 depends on the range of flow field disturbance, which is related to the Reynolds number ( Re = U L p / v , L p This refers to the projected length of the main component in the flow direction. This value is approximately the same as the pile diameter, and can be taken as the pile diameter in the design. D ) and Froude number ( Fr =U / , H (This is related to water depth). The higher the flow velocity, the greater the lateral pressure gradient, and the more stages of rectifier blades (lateral guide vanes) are needed to achieve gradual smoothing of the flow velocity.

[0082] In this preferred embodiment, for sandy seabeds, the burial depth of the protective device is initially calculated using the following formula:

[0083] ,

[0084] ,

[0085] in, A safety factor, such as 1.5 or 2.0, is required for anti-tipping stability. For effective severe cases, The internal friction angle of the soil. The total bending moment under external loads at the bed surface can be obtained through numerical simulation results. This refers to the thickness of the natural interaction layer of the local seabed or the maximum scour depth in numerical simulation calculations.

[0086] S3. Simulation Analysis: Based on the maximum tidal flow velocity and the STL file of the preliminary design device, this embodiment uses Flow-3D or OpenFOAM computational fluid dynamics software, combined with turbulence models RNG k-epslion or k-omega, to perform auxiliary simulations of the scour and flow field characteristics of the protective device. The analysis examines the stress on the protective device under possible extreme flow velocity conditions, the scour depth near the pile foundation 4 and the protective device, and the overturning moment of the protective device. The configuration of the protective device is optimized using simulation data to ensure that the selected dimensions provide good protection and stability. If the protection effect is poor or the stability does not meet the requirements, the process can return to S2 for redesign of the device.

[0087] S4. Construction Layout: In the land prefabrication yard, C50 or higher grade marine concrete or anti-corrosion steel is used to prefabricate the protective device in sections, reserving lifting holes and connectors. The seabed around the pile is leveled, and soft, loose mud is removed beforehand. In this embodiment, a GPS-RTK positioning system is used to transport the protective device to a preset position near pile 4. A hydraulic vibratory hammer is used to assist in sinking, ensuring the cutting depth reaches the design value. For areas with strong tidal currents or other reciprocating forces, the device can be arranged along the main current direction, and can also be symmetrically arranged along the main current direction of pile 4 (e.g., ...). Figure 4 (As shown) to control the scouring process of water flow in different directions. At the same time, in other non-mainstream directions, the parts around the pile foundation 4 that also have devices (including those exposed and those not exposed on the bed surface) can also play a role in steep slope protection.

[0088] S5. Operation and Maintenance: Regularly, or after the typhoon season, use multibeam sonar to scan the scour depth near pile foundation 4. If the scour depth near pile foundation 4 or the protective device is greater than or equal to 0.3D, initiate a sand replenishment procedure. During sand replenishment, sand and gravel with a particle size gradation slightly smaller than the original seabed soil can be placed in the area of ​​the guide section at the front end of the protective device. This backfill material ensures the stability of the guide device and, under the action of ocean currents, will gradually move towards pile foundation 4 to achieve natural backfilling. This method significantly reduces the positioning accuracy requirements and diving operation risks in deep-water operations, and significantly reduces the total life-cycle operation and maintenance costs.

[0089] Example 2

[0090] like Figures 1-4As shown, a flow-guiding pile foundation scour protection device obtained using the method of Example 1 is described. The device is streamlined and flared along the central axis of the pile foundation 4, and includes a main flow guide plate 1 and lateral flow guide plates 2. The thickness of the flow guide plates is 0.05-0.15 times the diameter of the pile foundation. The lateral flow guide plates 2 are composed of lateral flow guide plates with a similar configuration to the main flow guide plate 1 but shorter in length. The composition of the lateral flow guide plates 2 can further disperse the incoming flow, reduce the impact force on the main flow guide plate 1, and also assist in the regulation of sediment movement.

[0091] In this preferred embodiment, the protective device further includes a reverse turbulence rib 3, wherein the reverse turbulence rib 3 is alternately installed on both sides of the energy-consuming section guide channel wall in the middle of the main flow guide plate 1;

[0092] In this preferred embodiment, the projected shapes of the main flow guide plate 1 and the side flow guide plate 2 on the horizontal plane both follow the streamline principle of fluid mechanics. Specifically, the wall curves of the main flow guide plate 1 and the side flow guide plate 2 are constructed using continuous variable curvature curves. This ensures a smooth transition of curvature and avoids discontinuities in the first derivative (i.e., sharp corners). This design effectively avoids flow separation caused by abrupt changes in pressure gradient when water flows over the surfaces of the main flow guide plate 1 and the side flow guide plate 2, helping to guide sediment-laden water to smoothly enter and exit the protected area, and better control the direction of sediment transport.

[0093] In this preferred embodiment, the wall curves of the main guide vane 1 and the side guide vane 2 are cubic spline curves or higher-order B-spline curves.

[0094] In this preferred embodiment, the front end of the main flow guide plate 1 and the side flow guide plate 2 is a semi-circular or parabolic blunt-head structure to reduce the local high pressure when the incoming flow impacts; the back end of the main flow guide plate 1 and the side flow guide plate 2 has a smooth transition structure or a gradually tapering structure to reduce the size of the wake region.

[0095] Example 3

[0096] Numerical simulation experiment

[0097] This embodiment utilizes Flow-3D to establish a numerical simulation experiment for the protective device proposed in this invention, in order to analyze the scour protection performance of the device under water flow conditions. The computational domain is arranged as follows: Figure 5 As shown, the length, width, and height of the calculation area are 18m, 6m, and 3m, respectively, and the water depth is 2m. The diameter of pile foundation 4 (red area) is set... D The length is 1m, and pile foundation 4 is located at the center of the calculation area. This embodiment considers the case of steady unidirectional flow and adopts the following... Figure 3The apparatus layout shown has the following characteristics: the left side of the computational domain is the inflow boundary with an inflow velocity of 1 m / s; the right side is the outflow boundary; the front and rear sides are symmetrical boundaries; the bottom is the sediment region (yellow area) with a sediment particle size of 0.65 mm and a critical starting Shields number of 0.03.

[0098] First, a numerical simulation was conducted on the scour process of pile foundation 4 without protective devices. Figure 6 The changes in the local scour pit of pile foundation 4 after scour for 30 minutes are shown. It can be found that the maximum local scour depth of the pile foundation is about 0.85m, and the scour range is mainly concentrated in the local area of ​​pile foundation 1D.

[0099] Based on the simulation results without protective devices, a protective device with the following parameters was installed, including the inlet width of the guide section. G2 It is 0.75 D Width at the end of the diffusion section G1 It is 1.5 D The height of the main area exposed above the bed surface h It is 1.0. D and length L1 It is 4.0 D The reverse turbulence ribs 3 are arranged alternately on both sides of the main structure. Their length is determined according to the calculation formula of the reverse turbulence ribs 3 in the middle energy consumption section. In this embodiment, it is 0.25D and the preset burial depth is 0.5m.

[0100] Figure 7 The changes in the local scour pits of the pile foundation after 30 minutes of scour after the scour device was installed are shown. It can be found that the maximum local scour depth of the pile foundation decreased to 0.2m, and the scour depth decreased by about 75%. In addition, due to the formation of obvious accumulation areas in the diffusion zone of the mainstream area and the rear of the lateral flow zone, the size of the scour pit near pile foundation 4 was also significantly reduced.

[0101] Simultaneously, numerical simulation analysis showed that during the scouring process, the external load bending moment of the hydrodynamic force acting on the main protective structure was approximately 560 Nm. Taking the internal friction angle of the sediment as 31 degrees and the sediment density as 2650 kg / m³, the results were analyzed. 3 According to the formula , The calculated burial depth is approximately 0.38m to 0.42m.

[0102] in, A safety factor, such as 1.5 or 2.0, is required for anti-tipping stability. For effective severe cases, The internal friction angle of the soil. The total bending moment under external loads at the bed surface can be obtained through numerical simulation results. This refers to the thickness of the natural interaction layer of the local seabed or the maximum scour depth in numerical simulation calculations.

[0103] The burial depth set in this simulation initially meets the requirements, but considering the complex sea conditions leading to continuous scouring and other processes, the burial depth can be further increased to 0.6–0.7 m.

[0104] It should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A method of scour protection for a pile foundation, the method comprising: providing a pile foundation; providing a flow guide; and positioning the flow guide around the pile foundation. The method comprises the following steps: S1, obtaining hydrological characteristic data of the sea area according to measured data of the engineering area, wherein the hydrological characteristic data comprises a tidal current rose diagram, seabed sediment properties, a main flow direction of the tidal current, and a maximum tidal current velocity; S2. Based on hydrological data, conduct preliminary design of the key aggregate dimensions of the protective device. Key aggregate dimensions include: the height of the device exposed above the bed surface in the main flow area. h and length L1 The number and length of lateral flow guidance structures, the number and length of reverse flow ribs, and the burial depth of protective devices; the main flow area includes two main flow guide plates, and is divided into a front flow guide section, a middle energy dissipation section, and a rear diffusion zone. The overall structure is streamlined. The front flow guide plate is higher than the seabed surface, and the length of the front flow guide section is... The inlet width of the front-end guide section guide channel G2 Set to less than or equal to the pile diameter D The width of the flow channel in the middle energy-consuming section gradually increases, and the height of the mainstream flow guide plate exposed above the bed surface increases. h Similar to the front guide section, the width of the rear diffusion zone guide channel gradually increases. The tail of the main guide plate is located on both sides of the central axis of the pile foundation in the side view. At the same time, the height of the main guide plate gradually decreases along the water flow direction until it is flush with the seabed. The burial depth of the protective device can be initially designed to be 0.2D to 0.5D or greater than the actual thickness of the active seabed layer. Export the STL file of the preliminary design device entity. S3, simulation analysis, according to the maximum tidal current velocity and an STL file of the preliminary design device, auxiliary simulation of scouring and flow field characteristics of the protection device is performed by using computational fluid dynamics software in combination with a turbulence model, stress of the protection device under possible extreme flow velocity conditions, scouring depth near the pile foundation and the protection device, and overturning moment of the protection device are analyzed, configuration of the protection device is optimized through simulation data, it is ensured that the selected size data can achieve good protection effect and ensure stability of the protection device, if the protection effect is poor or the stability does not meet the requirements, the device can be redesigned again in S2; S4, construction arrangement, the protection device is prefabricated in blocks in a land prefabrication yard, a hoisting hole and a connecting piece are reserved, the seabed around the pile is leveled, surface soft and weak floating mud is removed in advance, the protection device is transported to a preset position near the pile foundation, and is placed by using a hydraulic vibration hammer, so that the cutting depth reaches a design value; S5, operation and maintenance, scouring depth change near the pile foundation device is scanned by using a multi-beam sonar regularly or after a typhoon season, if the scouring depth near the pile foundation or the protection device is greater than or equal to 0.3D, a sand supplement program is started, and sand and stones with a particle size gradation slightly smaller than the original seabed soil are placed in a region where the flow guide section of the protection device is located.

2. The method of erosion protection for a pile foundation according to claim 1, wherein, Step S2 main flow deflector length Take about 4.0 times the diameter of the pile foundation, the calculation method is as follows: The inlet width of the flow guiding passage of the front end flow guiding section G2 0.5D <= G2 1.0D; the length of the front end flow guiding section is The height h of the front end flow guiding section leaking out of the bed surface can be calculated by the following formula: ， wherein is the height coefficient, when the Froude number Fr < 0.2 is ; Fr > 0.2 is ; The length of the middle energy consumption section is ; The width G1 of the rear diffusion zone is 1.5D-2.5D, and the length of the rear diffusion zone is calculated according to the rear diffusion zone angle and the width of the inlet section and the outlet end, wherein the rear diffusion zone angle refers to the angle of the flow channel of the lateral guide vane deviating from the main flow area The minimum length of the rear diffusion zone is: 。 3. The method of scour protection for a pile foundation according to claim 1, wherein, The length of the reverse spoiler rib is calculated as follows: ， wherein, is the local width of the flow passage at its location, is the critical incipient velocity of the sediment, is a coefficient, taken as 0.1-0.2, usually is taken as 0.2-0.3 of the pile diameter, and for high flow conditions, the upper limit is taken to increase resistance.

4. The method of erosion protection for a pile foundation of a guide vane according to claim 1, characterized in that, The lateral flow guide area comprises a plurality of lateral flow guide plates, and the number and length of the lateral flow guide plates are calculated as follows: The number of the lateral flow guide plates is determined by the following formula: ， In the engineering, it can be simplified as: ， wherein, is an angle of the flow passage of the side deflector from the main flow region, controlled at 7 to 15 degrees to prevent flow separation, is the maximum tidal current velocity in the design recurrence period, is a reference velocity, taken as 1 m / s, is a correction coefficient taken as 1.5 to 2.5, and ceil is a rounding-up function. For general sea conditions, when U < 1.5 m / s, 1-2 pieces are arranged on one side; for strong flow sea conditions, when U < 2.0 m / s, 3-4 pieces are arranged on one side; The lateral guide plates should be arranged in an inner long and outer short ladder shape to match the diffusion cone angle of the rear diffusion zone, the length of each stage of lateral guide plates is calculated from the length of the main flow guide plate, and the total length of the main flow guide plate is The length of the i-stage lateral guide plate is ​ ， wherein, is a length decreasing coefficient, taking a value of 0.6-0.

8.

5. The method of erosion protection for a pile foundation according to claim 1, wherein, For sandy seabed, the burial depth of the protection device is initially calculated by the following formula: ， ， wherein, is the safety factor for anti-tilt stability, such as 1.5 or 2.0, is the effective weight, is the internal friction angle of the soil, is the total bending moment of the external load at the bed surface, which can be obtained from the numerical simulation results, is the natural interaction layer thickness of the local seabed or the maximum scour depth in the numerical simulation calculation.

6. A flow directing pile scour protection device obtained by the method of any one of claims 1 to 5, characterized in that, The protection device is in a streamlined flared shape along the central axis of the pile foundation, and comprises a main flow guide plate and a lateral flow guide plate, and the thickness of the main flow guide plate and the lateral flow guide plate is 0.05-0.15 times the diameter of the pile foundation.

7. A flow directing pile foundation scour protection device according to claim 6, characterised in that, The protection device further comprises a reverse spoiler rib, and the reverse spoiler rib is alternately installed on both sides of the wall surface of the middle energy consumption section flow guide channel.

8. A flow directing pile foundation scour protection device according to claim 6, characterised in that, The projection shape of the main flow guide plate and the lateral flow guide plate on the horizontal plane is designed according to the principle of fluid mechanics streamline, specifically, the wall surface curve of the main flow guide plate and the lateral flow guide plate is constructed by using a continuous variable curvature curve.

9. A flow directing pile foundation scour protection device according to claim 6, characterised in that, The wall surface curve of the main flow guide plate and the lateral flow guide plate adopts a cubic spline curve or a high-order B-spline curve.

10. A flow directing pile foundation scour protection device according to claim 6, characterised in that, The flow-attacking end of the main flow guide plate and the lateral flow guide plate is a blunt structure in a semicircular or parabolic shape, and the backflow end of the main flow guide plate and the lateral flow guide plate is a smooth transition structure or a gradually tapered structure.

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