Tidal flow hydrodynamic force numerical simulation method with pile foundation open type breakwater

Abstract

The invention discloses a tidal current hydrodynamic numerical simulation method provided with a pile foundation open-type breakwater, and relates to the technical field of offshore tidal current hydrodynamic simulation, and the method comprises the following steps: S1, determining a target sea area for constructing the pile foundation open-type breakwater, and determining a coastline of the target sea area; s2, setting grid precision, and constructing a tidal current hydrodynamic two-dimensional model of the target sea area by using a structured grid; s3, setting a boundary condition and an initial background field for driving the tidal current hydrodynamic two-dimensional model; s4, working condition simulation is carried out based on the tidal current hydrodynamic two-dimensional model in the S2 and the boundary conditions and the initial background field set in the S3; and S5, working condition simulation is carried out based on the tidal current hydrodynamic two-dimensional model in the S2 and the boundary condition and the initial background field determined in the S4. According to the method, the influence of the pile foundation type breakwater on the hydrodynamic environment field in the tidal current environment can be accurately simulated.

Description

Technical Field

[0001] The invention relates to the technical field of offshore tidal current hydrodynamic simulation, and in particular to a tidal current hydrodynamic numerical simulation method for a pile-foundation hollow breakwater. Background Art

[0002] The use of pile-based permeable breakwaters can block waves while maintaining some water exchange, thereby alleviating ecological damage. However, the piles and perforated plates of the permeable structure still have a significant blocking effect on the water flow, leading to problems such as compression of the water-passing section and abnormal attenuation of local flow velocity, which may cause siltation or retention of pollutants in the water behind the breakwater. It is urgent to accurately quantify the water blocking effect of the breakwater to balance protection and ecological needs.

[0003] The simulation of pile-based hollow breakwaters usually includes tidal hydrodynamic simulation and wave hydrodynamic simulation, among which the tidal hydrodynamic simulation method has significant defects: the traditional numerical model requires the grid of detailed structures such as piles to be encrypted to the centimeter level, resulting in huge consumption of computing resources; at the same time, the existing methods mostly simplify the breakwater into a fixed roughness or impermeable entity, ignoring the characteristics of the dynamic change of the drag coefficient of the hollow structure with parameters such as water flow intensity and opening rate. This over-simplification cannot accurately evaluate the long-term impact of the project on tidal channels and water exchange cycles.

[0004] In view of this, this invention is proposed. Summary of the invention

[0005] The purpose of the present invention is to solve the shortcomings existing in the prior art, and to propose a tidal hydrodynamic numerical simulation method for a pile-foundation hollow breakwater, which can ensure calculation efficiency and take into account the water-blocking characteristics of the pile-foundation breakwater, and can accurately simulate the influence of the pile-foundation breakwater on the hydrodynamic environment field under the tidal environment.

[0006] In order to achieve the above object, the present invention adopts the following technical solutions: A method for numerically simulating tidal current hydrodynamics of a pile-based hollow breakwater comprises the following steps: S1: Determine the target sea area for constructing pile-based open-type breakwaters and the coastline of the target sea area; S2: Set the grid accuracy and use structured grids to construct a two-dimensional tidal hydrodynamic model of the target sea area; S3: Setting boundary conditions and initial background fields for driving the tidal hydrodynamic two-dimensional model; S4: Based on the tidal hydrodynamic two-dimensional model of S2, and the boundary conditions and initial background field set in S3, the working condition simulation is carried out to obtain the simulated data of the target sea area, and the data is compared and verified with the measured data. If the error between the simulated data and the measured data does not meet the accuracy requirements, the boundary conditions and initial background field are adjusted, and the simulation is repeated until the accuracy requirements are met; S5: Based on the tidal hydrodynamic two-dimensional model of S2, the boundary conditions and initial background field determined by S4, the working condition simulation is carried out, and the sub-grid method is used to perform numerical simulation on the target sea area to obtain the tidal spatiotemporal evolution data of the target sea area. In particular, at the location where the pile-based permeable breakwater is to be built, the drag coefficient C is calculated by the following formula D : , In the formula, Fr 0 is the initial Froude number, ε eq is the equivalent porosity of the perforated breakwater in the pile foundation, h * is the equivalent water depth.

[0007] Furthermore, in S1, the nautical chart data of the target sea area and the measured water depth data of each coordinate in the target sea area are obtained, and the coastline of the target sea area is determined.

[0008] Furthermore, in S2, a tidal hydrodynamic two-dimensional model of the target sea area is constructed based on the shallow water equation, and the Boussinesq and hydrostatic pressure assumptions are adopted when constructing the tidal hydrodynamic two-dimensional model of the target sea area.

[0009] Furthermore, in S3, the boundary conditions include: tidal harmonic constants of astronomical tides or water level time series data; the initial background field includes: initial water depth field, initial suspended sediment concentration, initial wind field, initial pressure field, initial roughness and calculation time step.

[0010] Further, in S4, the simulation data includes: tidal water level, tidal flow velocity and flow direction data of the target sea area; the error accuracy conditions are that the average error of the tidal water level is less than 0.1 meter, the average error of the tidal flow velocity is less than 10% and the average error of the flow direction is less than 10°.

[0011] Further, in S4, if the error between the simulated data and the measured data does not meet the accuracy requirement, the boundary conditions and the initial roughness in the initial background field are adjusted, and the simulation is repeated until the accuracy requirement is met.

[0012] Furthermore, in S5, the calculation formula of the initial Froude number is as follows: , In the formula, u is the flow velocity, g is the acceleration of gravity, and h is the water depth in front of the dike; In S5, the calculation formula for the equivalent porosity of the perforated wave-breaking board in the pile-based permeable breakwater is as follows: , In the formula, ε 1 is the porosity of the front opening plate, ε 2 is the porosity of the rear opening plate; In S5, the calculation formula for equivalent water depth is as follows: , In the formula, h is the water depth in front of the dike, h m It is the limit water depth at the connection between the upper pedestal and the lower pile foundation of the pile-based hollow breakwater.

[0013] Furthermore, the range of the initial Froude number is as follows: 0 <1; the porosity range of the open hole wave-breaking plate is as follows: 0.1≤ε≤0.3.

[0014] Compared with the prior art, the present invention has the following beneficial effects: 1. The numerical simulation method of tidal hydrodynamics of pile-foundation hollow breakwaters of the present invention designs an improved drag force coefficient calculation formula, which solves the defect of traditional methods that the hollow structure is simplified into a fixed resistance or solid body, and significantly improves the simulation realism of the interaction between tidal currents and pile-foundation breakwaters.

[0015] 2. The numerical simulation method of tidal hydrodynamics of a pile-based hollow breakwater of the present invention is based on an improved drag force coefficient calculation formula and adopts a sub-grid calculation method to avoid the traditional model's reliance on extremely small-sized grids, thereby greatly reducing computing resource consumption and improving computing efficiency while ensuring accuracy.

[0016] 3. The tidal hydrodynamic numerical simulation method of the pile-foundation hollow breakwater of the present invention can quickly simulate the changes in key parameters such as water level and flow velocity under different wave and tidal conditions, and provide reliable data support for the ecological design (such as porosity optimization) and environmental impact assessment of pile-foundation breakwaters; and through the visualization technology of the hydrodynamic environment field, it can guide the design of pile-foundation breakwaters with both protective performance and ecological benefits, maintain nearshore water exchange while reducing coastal erosion, and promote sustainable development. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 It is a flow chart of a numerical simulation method of tidal current hydrodynamics for setting pile-based hollow breakwater; Figure 2 is a water depth topographic map of the target sea area for simulation, wherein (a) is a computational grid map of the target sea area for simulation, and (b) is a water depth topographic map of the target sea area for simulation; Figure 3 It is a water level verification diagram of the characteristic measuring station simulated by the method of the present invention; Figure 4The flow velocity and flow direction verification diagrams of the characteristic measuring stations simulated by the method of the present invention, wherein (a) is a comparison diagram of the flow velocity and flow direction change process between the measured and simulated flow velocity and flow direction of the measuring station L1, (b) is a comparison diagram of the flow velocity and flow direction change process between the measured and simulated flow velocity and flow direction of the measuring station L2, and (c) is a comparison diagram of the flow velocity and flow direction change process between the measured and simulated flow velocity and flow direction of the measuring station L3; Figure 5 A comparison chart of the drag force coefficient formula prediction data and the physical model test data of the method of the present invention; Figure 6 : is a comparison diagram of simulation results of the method of the present invention and the traditional method, wherein a is the simulation result diagram of model 1, b is the simulation result diagram of model 2, and c is the simulation result diagram of model 3. DETAILED DESCRIPTION

[0018] The technical solutions in the embodiments of the present invention will be described clearly and completely below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all the embodiments.

[0019] Embodiment 1: A numerical simulation method for tidal hydrodynamics of a pile-based hollow breakwater is proposed. Figure 1 As shown, the following steps are included: S1: Determine the target sea area for constructing pile-based open-type breakwaters and the coastline of the target sea area.

[0020] In this embodiment, the pile-foundation hollow breakwater may include supporting piles and a vertical pedestal structure assembled and fixed on the supporting piles; the supporting piles are angular structures, and the supporting piles are divided into two groups, which are arranged front and back along the wave direction, and each group of supporting piles is provided with a perforated plate on the side facing the waves, and the bottom of the perforated plate is suspended, that is, the bottom of the perforated plate is higher than the bottom of the supporting piles, so as to ensure that water can flow through from under the perforated plate; the vertical pedestal structure is a solid impermeable structure to prevent wave crossing, and the cross-section of the vertical pedestal structure 2 is L-shaped.

[0021] S2: Set the grid accuracy and use structured grids to construct a two-dimensional tidal hydrodynamic model of the target sea area.

[0022] S3: Set the boundary conditions and initial background field used to drive the tidal hydrodynamic two-dimensional model.

[0023] S4: Based on the tidal hydrodynamic two-dimensional model of S2, as well as the boundary conditions and initial background field set in S3, the working condition simulation is carried out to obtain the simulated data of the target sea area, and the data is compared and verified with the measured data. If the error between the simulated data and the measured data does not meet the accuracy requirements, the boundary conditions and initial background field are adjusted, and the simulation is repeated until the accuracy requirements are met.

[0024] In this embodiment, the boundary conditions and the initial background field of the two-dimensional model of the tidal current hydrodynamics are verified and determined by the error between the simulated data and the measured data to ensure the accuracy of the simulation calculation.

[0025] S5: Based on the tidal hydrodynamic two-dimensional model of S2, the boundary conditions and initial background field determined by S4, the working condition simulation is carried out, and the sub-grid method is used to perform numerical simulation on the target sea area to obtain the tidal spatiotemporal evolution data of the target sea area. In particular, at the location where the pile-based permeable breakwater is to be built, the drag coefficient C is calculated by the following formula D : , In the formula, Fr 0 is the initial Froude number, ε eq is the equivalent porosity of the perforated breakwater in the pile foundation, h * is the equivalent water depth.

[0026] The numerical simulation method for tidal hydrodynamics of a pile-foundation hollow breakwater in this embodiment designs an improved drag force coefficient calculation formula, which solves the defect of traditional methods that simplifies the hollow structure into a fixed resistance or solid body, and significantly improves the simulation realism of the interaction between tidal currents and pile-foundation breakwaters.

[0027] The numerical simulation method of tidal hydrodynamics of a pile-foundation hollow breakwater in this embodiment is based on an improved drag force coefficient calculation formula and adopts a sub-grid calculation method to avoid the traditional model's reliance on extremely small-sized grids, thereby greatly reducing computing resource consumption and improving computing efficiency while ensuring accuracy.

[0028] In summary, the tidal hydrodynamic numerical simulation method for setting up pile-foundation hollow breakwaters in this embodiment can quickly simulate the changes in key parameters such as water level and flow velocity under different wave and tidal conditions, and provide reliable data support for the ecological design (such as porosity optimization) and environmental impact assessment of pile-foundation breakwaters; and through the visualization technology of hydrodynamic environmental fields, it can guide the design of pile-foundation breakwaters with both protective performance and ecological benefits, maintain nearshore water exchange while reducing coastal erosion, and promote sustainable development.

[0029] In an optional embodiment, in S1, the nautical chart data of the target sea area and the measured water depth data of each coordinate in the target sea area are obtained, and the coastline of the target sea area is determined.

[0030] In an optional embodiment, in S2, a tidal hydrodynamic two-dimensional model of the target sea area is constructed based on the shallow water equation, and the Boussinesq and hydrostatic pressure assumptions are used when constructing the tidal hydrodynamic two-dimensional model of the target sea area.

[0031] In an optional embodiment, in S3, the boundary conditions include: tidal harmonic constants or water level time series data of astronomical tides; the initial background field includes: initial water depth field, initial suspended sediment concentration, initial wind field, initial pressure field, initial roughness and calculation time step.

[0032] In an optional embodiment, in S4, the simulation data includes: tidal water level, tidal flow velocity and flow direction data of the target sea area; the error accuracy conditions are that the average tidal water level error is less than 0.1 meters, the average tidal flow velocity error is less than 10% and the average flow direction error is less than 10°.

[0033] In this optional embodiment, a time series comparison diagram of water level, flow velocity, and flow direction of characteristic sites may be drawn to determine the error between the simulated data and the measured data.

[0034] In an optional embodiment, in S4, if the error between the simulated data and the measured data does not meet the accuracy requirement, the boundary conditions and the initial roughness in the initial background field are adjusted, and the simulation is repeated until the accuracy requirement is met.

[0035] In an optional embodiment, in S5, the calculation formula of the initial Froude number is as follows: , In the formula, u is the flow velocity, g is the acceleration of gravity, and h is the water depth in front of the dike; In S5, the calculation formula for the equivalent porosity of the perforated wave-breaking board in the pile-based permeable breakwater is as follows: , In the formula, ε 1 is the porosity of the front opening plate, ε 2 is the porosity of the rear opening plate; In S5, the calculation formula for equivalent water depth is as follows: , In the formula, h is the water depth in front of the dike, h m It is the limit water depth at the connection between the upper pedestal and the lower pile foundation of the pile-based hollow breakwater. This value can be understood as the vertical height of the supporting pile 1.

[0036] In an optional embodiment, the value range of the initial Froude number is as follows: 0 <1; the porosity range of the open hole wave-breaking plate is as follows: 0.1≤ε≤0.3.

[0037] In order to verify the effectiveness of the numerical simulation method of tidal hydrodynamics for setting a pile-based permeable breakwater in this embodiment, a target sea area for setting a pile-based breakwater model was established. The target sea area is located near the northern area of ​​Rizhao Port, and its water depth, topography and coastline are as follows: Figure 2As shown, the boundary conditions are provided by the French FES2014 high-precision global ocean tidal model.

[0038] Observation stations were set up on both sides of the pile-based hollow breakwater along the tidal direction. The spatial longitude and latitude coordinates of the three observation stations L1-L3 are shown in Table 1. The constructed two-dimensional tidal hydrodynamic basic model was used to simulate the basic working conditions, and the tidal water level, tidal flow velocity and flow direction data of the target sea area were obtained, which were compared and verified with the measured data. Figure 3 The measured and simulated water level changes at station L2 from 9:00 on August 1, 2015 to 11:00 on August 2, 2015 were compared. Figure 4 The flow velocity and flow direction changes of the measured and simulated stations L1-L3 during the same period were compared. During the verification period, the average water level error of the model was less than 0.1 meter, the average flow velocity error was less than 10%, and the flow direction was basically synchronized.

[0039] Table 1 Coordinates of tide and water level observation stations After that, multiple groups of tidal conditions are set for simulation calculation to solve the tidal spatiotemporal evolution data. The following drag force coefficient calculation formula is used in the simulation calculation: , The drag coefficient C calculated by the solution of this embodiment is D and the measured drag coefficient C D For example Figure 5 As shown, the determination coefficient R 2 It is 0.8352, which shows that the scheme implemented in this paper can accurately represent the interaction between the pile-based open-type breakwater and the tidal current.

[0040] In addition, Figure 2 Based on the water depth topography map, this embodiment also simulates and compares the effectiveness of different schemes. The input conditions and model settings of the compared models are shown in Table 2, where Model 1 is a direct simulation, that is, the local water depth topography is modified by setting the grid accuracy at the corresponding position to simulate and set a physical breakwater. Model 2 is a traditional model, that is, a sub-grid physical breakwater model. Model 3 is the scheme of this embodiment. The simulation results are shown in Table 2. Figure 6 shown.

[0041] Table 2 Model input conditions and model settings contrast Figure 6It can be seen that setting up a physical structure identical to the pile-foundation hollow breakwater body by setting the grid precision at the corresponding position cannot effectively simulate the water-blocking effect of the breakwater; using the traditional model for simulation will significantly enhance the water flow velocity at the head of the breakwater, forming a strong flow along the breakwater body, and cannot effectively consider the effect of the breakwater on the water flow; the solution of this embodiment can provide more reliable tidal field prediction results.

[0042] In addition, the simulation calculation time required for models 1, 2, and 3 is shown in Table 3.

[0043] Table 3 Simulation calculation time According to the simulation performance comparison data shown in Table 3, Model 3 of the present embodiment has an advantage in simulation calculation time, which is of great significance for guiding the design of pile-based hollow breakwaters with both protective performance and ecological benefits.

[0044] The above description is only a preferred specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any technician familiar with the technical field can make equivalent replacements or changes according to the technical scheme and inventive concept of the present invention within the technical scope disclosed by the present invention, which should be covered by the protection scope of the present invention.

Claims

1. A method for numerical simulation of tidal current hydrodynamics of a pile-based hollow breakwater, characterized in that: The steps include: S1: Determine the target sea area for constructing pile-based open-type breakwaters and the coastline of the target sea area; S2: Set the grid accuracy and use structured grids to construct a two-dimensional tidal hydrodynamic model of the target sea area; S3: Setting boundary conditions and initial background fields for driving the tidal hydrodynamic two-dimensional model; S4: Based on the tidal hydrodynamic two-dimensional model of S2, and the boundary conditions and initial background field set in S3, the working condition simulation is carried out to obtain the simulated data of the target sea area, and the data is compared and verified with the measured data. If the error between the simulated data and the measured data does not meet the accuracy requirements, the boundary conditions and initial background field are adjusted, and the simulation is repeated until the accuracy requirements are met; S5: Based on the tidal hydrodynamic two-dimensional model of S2, the boundary conditions and initial background field determined by S4, the working condition simulation is carried out, and the sub-grid method is used to perform numerical simulation on the target sea area to obtain the tidal spatiotemporal evolution data of the target sea area. In particular, at the location where the pile-based permeable breakwater is to be built, the drag coefficient C is calculated by the following formula D : ， In the formula, Fr0 is the initial Froude number, ε eq is the equivalent porosity of the perforated breakwater in the pile foundation, h * is the equivalent water depth.

2. The method for numerical simulation of tidal current hydrodynamics of a pile-based hollow breakwater according to claim 1, characterized in that: In S1, the nautical chart data of the target sea area and the measured water depth data of each coordinate in the target sea area are obtained, and the coastline of the target sea area is determined.

3. The method for numerical simulation of tidal current hydrodynamics of a pile-based hollow breakwater according to claim 1, characterized in that: In S2, a tidal hydrodynamic two-dimensional model of the target sea area is constructed based on the shallow water equation, and the Boussinesq and hydrostatic pressure assumptions are adopted when constructing the tidal hydrodynamic two-dimensional model of the target sea area.

4. The method for numerical simulation of tidal current hydrodynamics of a pile-based hollow breakwater according to claim 1, characterized in that: In S3, the boundary conditions include: tidal harmonic constants of astronomical tides or water level time series data; the initial background field includes: initial water depth field, initial suspended sediment concentration, initial wind field, initial pressure field, initial roughness and calculation time step.

5. The method for numerical simulation of tidal current hydrodynamics of a pile-based hollow breakwater according to claim 4, characterized in that: In S4, the simulation data include: tidal water level, tidal velocity and flow direction data of the target sea area; the error accuracy conditions are that the average error of tidal water level is less than 0.1 meter, the average error of tidal velocity is less than 10% and the average error of flow direction is less than 10°.

6. The method for numerical simulation of tidal current hydrodynamics of a pile-based hollow breakwater according to claim 4, characterized in that: In S4, if the error between the simulated data and the measured data does not meet the accuracy requirement, the boundary conditions and the initial roughness in the initial background field are adjusted, and the simulation is repeated until the accuracy requirement is met.

7. The method for numerical simulation of tidal current hydrodynamics of a pile-based hollow breakwater according to claim 1, characterized in that: In S5, the calculation formula of the initial Froude number is as follows: ， In the formula, u is the flow velocity, g is the acceleration of gravity, and h is the water depth in front of the dike; In S5, the calculation formula for the equivalent porosity of the perforated wave-breaking board in the pile-based permeable breakwater is as follows: ， In the formula, ε1 is the porosity of the front perforated plate, and ε2 is the porosity of the rear perforated plate; In S5, the calculation formula for equivalent water depth is as follows: ， In the formula, h is the water depth in front of the dike, h m It is the limit water depth at the connection between the upper pedestal and the lower pile foundation of the pile-based hollow breakwater.

8. The method for numerical simulation of tidal current hydrodynamics of a pile-based hollow breakwater according to claim 7, characterized in that: The value range of the initial Froude number is as follows: Fr0<1; the value range of the porosity of the open-hole wave-breaking plate is as follows: 0.1≤ε≤0.3.

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