A numerical simulation method for tidal current hydrodynamics of a piled-through breakwater

Abstract

The present invention discloses a numerical simulation method for tidal current hydrodynamics of a pile-supported open breakwater, which relates to the technical field of offshore tidal current hydrodynamics simulation and includes the following steps: S1: Determine the target sea area for constructing the pile-supported open breakwater and determine the coastline of the target sea area; S2: Set the grid accuracy and use structured grids to construct a two-dimensional tidal current hydrodynamics model of the target sea area; S3: Set the boundary conditions and initial background field for driving the two-dimensional tidal current hydrodynamics model; S4: Based on the two-dimensional tidal current hydrodynamics model in S2 and the boundary conditions and initial background field set in S3, conduct a working condition simulation; S5: Based on the two-dimensional tidal current hydrodynamics model in S2 and the boundary conditions and initial background field determined in S4, conduct a working condition simulation. The method of the present invention can accurately simulate the influence of the pile-supported breakwater on the hydrodynamic environment field under the tidal current environment.

Description

Technical Field

[0001] The present invention relates to the technical field of offshore tidal current hydrodynamic simulation, and particularly relates to a numerical simulation method for tidal current hydrodynamics with a piled-through breakwater installed. Background Art

[0002] The adoption of a piled-through breakwater can maintain partial water exchange while blocking waves, thereby alleviating ecological damage. However, the piles and perforated plates of the through structure still have a significant blocking effect on the water flow, resulting in problems such as the compression of the water passing section and the abnormal attenuation of the local flow velocity, which may cause siltation in the waters behind the breakwater or the retention of pollutants. It is urgent to accurately quantify the water blocking effect of the breakwater to balance the protection and ecological requirements.

[0003] The simulation of a piled-through breakwater usually includes tidal current hydrodynamic simulation and wave hydrodynamic simulation. Among them, there are significant defects in the tidal current hydrodynamic simulation method: traditional numerical models need to encrypt the detailed structure grids such as piles to the centimeter level, resulting in huge consumption of computing resources; at the same time, existing methods mostly simplify the breakwater as a fixed roughness or impermeable entity, ignoring the characteristics that the drag coefficient of the through structure changes dynamically with parameters such as water flow intensity and opening ratio. This kind of over-simplification cannot accurately evaluate the long-term impact of the project on tidal channels and water exchange cycles.

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

[0005] The purpose of the present invention is to solve the deficiencies existing in the prior art, and to propose a numerical simulation method for tidal current hydrodynamics with a piled-through breakwater installed, which can ensure the calculation efficiency, and takes into account the water blocking characteristics of the piled breakwater, and can accurately simulate the impact of the piled breakwater on the hydrodynamic environment field under the tidal current environment.

[0006] In order to achieve the above purpose, the present invention adopts the following technical solutions:

[0007] A numerical simulation method for tidal current hydrodynamics with a piled-through breakwater installed includes the following steps:

[0008] S1: Determine the target sea area for constructing the piled-through breakwater, and determine the coastline of the target sea area;

[0009] S2: Set the grid accuracy, and use structured grids to construct a two-dimensional tidal current hydrodynamic model of the target sea area;

[0010] S3: Set the boundary conditions and initial background field for driving the two-dimensional tidal current hydrodynamic model;

[0011] S4: Based on the two-dimensional tidal current hydrodynamic model in S2 and the boundary conditions and initial background field set in S3, conduct condition simulations to obtain the simulation data of the target sea area, and compare and verify it with the measured data. If the error between the simulation data and the measured data does not meet the accuracy requirements, adjust the boundary conditions and the initial background field, and re-simulate until the accuracy requirements are met;

[0012] S5: Based on the two-dimensional tidal current hydrodynamic model in S2 and the boundary conditions and initial background field determined in S4, conduct condition simulations, and use the sub-grid method to numerically simulate the target sea area to obtain the tidal current spatio-temporal evolution data of the target sea area. Among them, at the location of the proposed pile-supported open breakwater, calculate the drag coefficient C through the following formula D :

[0013] ,

[0014] In the formula, Fr0 is the initial Froude number, and ε eq is the equivalent porosity of the perforated wave-breaking plate in the pile-supported open breakwater, and h * is the equivalent water depth.

[0015] Furthermore, in S1, obtain the chart data of the target sea area and the measured water depth data of each coordinate in the target sea area, and determine the coastline of the target sea area.

[0016] Furthermore, in S2, based on the shallow water equations, construct a two-dimensional tidal current hydrodynamic model of the target sea area, and adopt the Boussinesq and hydrostatic pressure assumptions when constructing the two-dimensional tidal current hydrodynamic model of the target sea area.

[0017] Furthermore, in S3, the boundary conditions include: the tidal harmonic constants or water level time series data of the astronomical tidal components; the initial background field includes: the initial water depth field, the initial suspended sediment concentration, the initial wind field, the initial pressure field, the initial roughness coefficient, and the calculation time step.

[0018] Furthermore, in S4, the simulation data includes: the tidal water level, tidal current velocity, and flow direction data of the target sea area; the accuracy condition of the error is that the average error of the tidal water level is less than 0.1 m, the average error of the tidal current velocity is less than 10%, and the average error of the flow direction is less than 10°.

[0019] Furthermore, in S4, if the error between the simulation data and the measured data does not meet the accuracy requirements, adjust the boundary conditions and the initial roughness coefficient in the initial background field, and re-simulate until the accuracy requirements are met.

[0020] Furthermore, in S5, the calculation formula for the initial Froude number is as follows:

[0021] ,

[0022] 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;

[0023] In S5, the calculation formula for the equivalent porosity of the perforated wave-breaking board in the pile-based permeable breakwater is as follows:

[0024] ,

[0025] In the formula, ε1 is the porosity of the front perforated plate, and ε2 is the porosity of the rear perforated plate;

[0026] In S5, the calculation formula for equivalent water depth is as follows:

[0027] ,

[0028] 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.

[0029] Furthermore, 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.

[0030] Compared with the prior art, the present invention has the following beneficial effects:

[0031] 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.

[0032] 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.

[0033] 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

[0034] Figure 1 It is a flow chart of a numerical simulation method of tidal current hydrodynamics for setting pile-based hollow breakwater;

[0035] Figure 2 It is a bathymetric topographic map of the target sea area for simulation. Among them, (a) is the computational grid map of the target sea area for simulation, and (b) is the bathymetric topographic map of the target sea area for simulation;

[0036] Figure 3 It is the water level verification map of the characteristic measuring station simulated by the method of the present invention;

[0037] Figure 4 It is the verification map of the flow velocity and direction of the characteristic measuring station simulated by the method of the present invention. Among them, (a) is the comparison diagram of the measured and simulated flow velocity and direction change processes of measuring station L1, (b) is the comparison diagram of the measured and simulated flow velocity and direction change processes of measuring station L2, and (c) is the comparison diagram of the measured and simulated flow velocity and direction change processes of measuring station L3;

[0038] Figure 5 It is the comparison diagram of the predicted data of the drag force coefficient formula and the physical model test data of the method of the present invention;

[0039] Figure 6 It is the comparison diagram of the simulation results of the method of the present invention and the traditional method. Among them, 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 implementation mode

[0040] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments.

[0041] Embodiment 1:

[0042] A numerical simulation method for tidal current hydrodynamics of a piled-through breakwater is as Figure 1 shown, and includes the following steps:

[0043] S1: Determine the target sea area for constructing the piled-through breakwater and determine the coastline of the target sea area.

[0044] In this embodiment, the piled-through breakwater may include support piles and a vertical caisson structure assembled and fixed on the support piles; the support piles are angular structures, there are two groups of support piles, which are arranged front and back along the wave direction, and an opening plate is arranged on each side facing the wave of the two groups of support piles. The bottom of the opening plate is suspended, that is, the bottom of the opening plate is higher than the bottom of the support pile to ensure that the water flow can flow under the opening plate; the vertical caisson structure is a solid impermeable structure to prevent overtopping, and the cross-section of the vertical caisson structure 2 is L-shaped.

[0045] S2: Set the grid accuracy and use structured grids to construct a two-dimensional tidal current hydrodynamic model of the target sea area.

[0046] S3: Set the boundary conditions and initial background field used to drive the tidal hydrodynamic two-dimensional model.

[0047] 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.

[0048] 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.

[0049] 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 :

[0050] ,

[0051] 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.

[0052] 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.

[0053] 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.

[0054] 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.

[0055] 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.

[0056] 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.

[0057] 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.

[0058] 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°.

[0059] 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.

[0060] 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.

[0061] In an optional embodiment, in S5, the calculation formula of the initial Froude number is as follows:

[0062] ,

[0063] 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;

[0064] In S5, the calculation formula for the equivalent porosity of the perforated wave-breaking board in the pile-based permeable breakwater is as follows:

[0065] ,

[0066] In the formula, ε1 is the porosity of the front perforated plate, and ε2 is the porosity of the rear perforated plate;

[0067] In S5, the calculation formula for equivalent water depth is as follows:

[0068] ,

[0069] In the formula, h is the water depth in front of the dike, h mIt is the boundary water depth at the connection between the upper bearing platform and the lower pile foundation of the pile-supported open breakwater, and this value can be understood as the vertical height of the support pile 1.

[0070] In an optional embodiment, the value range of the initial Froude number is as follows: Fr0 < 1; the value range of the porosity of the perforated wave dissipating plate is as follows: 0.1 ≤ ε ≤ 0.3.

[0071] To verify the effectiveness of a numerical simulation method of tidal current hydrodynamics for a pile-supported open breakwater in this embodiment, a target sea area with a pile-supported breakwater model was set up. The geographical location of the target sea area is near the north area of Rizhao Port, and its water depth topography and shoreline are as Figure 2 shown, and the boundary conditions are provided by the high-precision global ocean tide model FES2014 of France.

[0072] Observation stations were set on both sides of the pile-supported open breakwater along the tidal current direction. Table 1 shows the spatial longitude and latitude coordinates of three observation stations L1 - L3. Using the constructed two-dimensional tidal current hydrodynamics basic model to simulate the basic conditions, the tidal water level, tidal current velocity and direction data of the target sea area were obtained and compared with the measured data for verification. Figure 3 The measured and simulated water level change processes at station L2 from 9:00 on August 1, 2015 to 11:00 on August 2, 2015 were compared. Figure 4 The measured and simulated velocity and direction change processes at stations L1 - L3 during the same period were compared. During the verification period, the average error of the water level of the model was less than 0.1 m, the average error of the velocity was less than 10%, and the directions were basically synchronous.

[0073] Table 1 Coordinates of tidal current and water level observation stations

[0074]

[0075] After that, multiple groups of tidal current conditions were set for simulation calculations to solve the spatio-temporal evolution data of the tidal current. The following drag coefficient calculation formula was used during the simulation calculations:

[0076] ,

[0077] The drag coefficient C calculated by the scheme of this embodiment D and the measured drag coefficient C D are compared as Figure 5 shown. The determination coefficient R 2 is 0.8352. It can be seen that the scheme of this embodiment can accurately represent the interaction between the pile-supported open breakwater and the tidal current.

[0078] In addition, in Figure 2Based on the bathymetric map, in this embodiment, the effectiveness of different solutions was also simulated and compared. The input conditions and model settings of the models for comparison are shown in Table 2, where Model 1 is a direct simulation, that is, a solid breakwater is simulated by setting the grid accuracy to modify the local bathymetry at the corresponding position. Model 2 is a traditional model, that is, a sub-grid solid breakwater model. Model 3 is the solution of this embodiment. The simulation results are as Figure 6 shown.

[0079] Table 2 Input conditions and model settings of the models

[0080]

[0081] Comparison Figure 6 It can be seen that setting the grid accuracy at the corresponding position to simulate a solid structure identical to the piled-through breakwater body cannot effectively simulate the water-blocking effect of the breakwater; using the traditional model for simulation will significantly increase the water flow velocity at the head of the breakwater, forming a strong flow along the breakwater body, and the effect of the breakwater on the water flow cannot be effectively considered; the solution of this embodiment can provide more reliable tidal current field prediction results.

[0082] In addition, the simulation calculation time required for Models 1, 2, and 3 is shown in Table 3.

[0083] Table 3 Simulation calculation time

[0084]

[0085] According to the simulation performance comparison data shown in Table 3, Model 3 of the solution of this embodiment has an advantage in the simulation calculation time, which is of great significance for guiding the design of piled-through breakwaters with both protection performance and ecological benefits.

[0086] The above is only a preferred specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Any person skilled in the art within the technical scope disclosed by the present invention, according to the technical solution of the present invention and its inventive concept, makes equivalent substitutions or changes, and 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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