A numerical simulation method of wave hydrodynamics in sea areas with bamboo fences and shrub dams

Abstract

The present invention discloses a wave hydrodynamic numerical simulation method for a sea area with bamboo fence and shrub dam, which relates to the technical field of offshore wave simulation, and comprises the following steps: S1: determining a target sea area, and collecting measured water depth topographic data and sea chart water depth data of the target sea area, wherein the target sea area refers to a salt marsh beach sea area where the bamboo fence and shrub dam is planned to be arranged; S2: setting grid accuracy, and using structured grids to construct a wave hydrodynamic two-dimensional model of the target sea area; S3: setting boundary conditions for driving the wave hydrodynamic two-dimensional model, and setting initial parameters; S4: based on the wave hydrodynamic two-dimensional model constructed in S2, using a sub-grid method to perform numerical simulation on the target sea area, and obtain the characteristic wave height and periodic space-time distribution of the target sea area. The method of the present invention can ensure the calculation efficiency, and takes into account the wave transmission characteristics of the bamboo fence and shrub dam, and can accurately simulate the influence of the construction of the bamboo fence and shrub dam on the wave hydrodynamic environment field.

Description

Technical Field

[0001] The invention relates to the technical field of offshore wave simulation, and in particular to a wave hydrodynamic numerical simulation method for a sea area where bamboo fences and shrub dams are set. Background Art

[0002] Salt marshes provide habitats for biodiversity, mitigate the effects of climate change through carbon sequestration, and effectively reduce soil erosion by increasing surface roughness and dense root networks, and minimize flooding when traditional hard protection measures fail. However, in recent decades, the coastline retreat of salt marshes and tidal flats has become increasingly evident around the world due to the accelerated rate of sea level rise caused by climate change, which has changed the dynamic mechanism of sediment transport. The retreat of salt marshes has increased the pressure on protection measures in major coastal areas and led to the loss of biodiversity in wetland ecosystems.

[0003] When sediment supply is adequate, salt marshes can dynamically adapt to sea level changes under normal sea conditions through vertical deposition and lateral expansion of sediment. In areas with little or no foreshore vegetation, promoting adequate sediment accumulation is essential to ensure optimal coastal zone management. Therefore, revegetation in erosion-prone coastal areas requires support structures such as bamboo shrub dams to mitigate the impacts of the hydrodynamic environment, mainly in terms of wave action reduction and sediment retention.

[0004] Bamboo hedge dams are mainly used to promote the growth and protection of salt marshes. The structural characteristics of bamboo hedge dams include two or more rows of bamboo hedge stakes, with shrubs or shrub-like porous materials filled in the middle. During high tide, suspended sediment is transported to the nearshore waters through the openings of the shrub dam. The presence of the shrub dam reduces the energy of the water flow, which is conducive to the sedimentation of suspended sediments and minimizes the re-suspension process of sediments. The reduction in wave energy promotes the growth of soil stabilizing vegetation, thereby reducing soil erosion. During low tide, the sediment transported to the sea is significantly reduced by the obstruction of the dam body. Compared with other coastal protection measures, bamboo hedge dams have moderate costs, low material technology content, and low environmental impact. They provide the potential to reduce the pressure on major coastal protection measures while adapting more naturally to changing environmental drivers.

[0005] Before the construction of bamboo fence shrub dam, it is necessary to use a wave hydrodynamic model to simulate the changes in the wave hydrodynamic environment field before and after the construction of the project, so as to evaluate the impact of bamboo fence shrub dam construction on the environment and further optimize the design of bamboo fence shrub dam construction. However, there is no systematic simulation study on the impact of bamboo fence shrub dam on the change of wave hydrodynamic environment field. Traditional hydrodynamic numerical simulations mostly add equivalent roughness or generalize to impermeable structures, which requires the grid of the project area to be encrypted to a very small size, and the calculation efficiency is low. In addition, the calculation formulas based on other traditional hydrodynamic numerical simulations are mostly for smooth non-permeable structures or engineering structures composed of blocks of specific sizes, which cannot effectively consider the resistance characteristics and different porosity characteristics of bamboo fence shrub dams. Therefore, considering the wave transmission characteristics of bamboo fence shrub dams, efficiently and accurately simulating the impact of bamboo fence shrub dam construction on the wave hydrodynamic environment field, and then providing more reliable prediction and decision support for engineering design and environmental impact assessment is an urgent problem to be solved.

[0006] In view of this, this invention is proposed. Summary of the invention

[0007] The purpose of the present invention is to solve the shortcomings existing in the prior art, and to propose a wave hydrodynamic numerical simulation method for a sea area with a bamboo fence and shrub dam, which can ensure calculation efficiency, take into account the wave transmission characteristics of the bamboo fence and shrub dam, and can accurately simulate the impact of the bamboo fence and shrub dam construction on the wave hydrodynamic environment field.

[0008] In order to achieve the above object, the present invention adopts the following technical solutions:

[0009] A wave hydrodynamic numerical simulation method for a sea area with bamboo fences and shrub dams, comprising the following steps:

[0010] S1: Determine the target sea area and collect the measured water depth topographic data and chart water depth data of the target sea area, where the target sea area refers to the salt marsh beach sea area where the bamboo fence shrub dam is planned to be arranged;

[0011] S2: Set the grid accuracy and use the structured grid to build a two-dimensional wave hydrodynamic model of the target sea area. When the interaction between the bamboo fence shrub dam and the waves needs to be calculated, the following wave propagation equation is used for calculation:

[0012] ,

[0013] In the formula, K t is the transmission coefficient, R c is the freeboard of the bush dam, H moi is the incident effective wave height, P f is the porosity coefficient, B is the dam crest width, d is the water depth in front of the dam, s 0p is the equivalent wave steepness coefficient;

[0014] S3: Set the boundary conditions for driving the wave hydrodynamic 2D model and set the initial parameters;

[0015] S4: Based on the two-dimensional wave hydrodynamic model constructed in S2, the sub-grid method is used to perform numerical simulation of the target sea area to obtain the characteristic wave height and period spatial and temporal distribution of the target sea area.

[0016] Furthermore, the wave hydrodynamic two-dimensional model in S2 is a wave hydrodynamic two-dimensional model of the target sea area where the bamboo fence and shrub dam is set up, which is constructed based on the spectral density equation.

[0017] Furthermore, a two-dimensional wave hydrodynamic model of the target sea area with bamboo fence and shrub dam is constructed based on the spectral density equation. The spectral density equation used is as follows:

[0018] ,

[0019] In the formula, N is the action density parameter, c x and c y are the propagation velocities in the x and y directions, c σ and c θ are the propagation velocities in the spatial directions σ and θ respectively, S is the source term, and t is the time.

[0020] Further, the P in S2 f and 0p The calculation formula is as follows:

[0021] ,

[0022] ,

[0023] In the formula, n is the volume porosity, L is 0p The wavelength is deep water.

[0024] Furthermore, the value range of n is as follows: 0.4 <n≤0.7;H moi The value range is as follows: 0.3m <H moi <0.8m.

[0025] Further, R c / H moi The value range is as follows, -2.3 <R c / H moi <2.7; H moi The value range is as follows: 0.3m <H moi <0.8m; the value range of B / d is as follows: 0.26

[0026] ​Furthermore, in S3, wave data under normal sea conditions and extreme sea conditions in the target sea area are collected to drive the boundary conditions of the wave hydrodynamic two-dimensional model.

[0027] Furthermore, the boundary conditions driving the wave hydrodynamic two-dimensional model include: the tide and wave conditions of normal sea conditions in the target sea area, and the tide and wave conditions during extreme weather periods.

[0028] Furthermore, in S3, the initial parameters include: initial terrain data and roughness of the target sea area, calculation time step, pressure and wind field temporal and spatial distribution, and wave breaking index.

[0029] Compared with the prior art, the present invention has the following beneficial effects:

[0030] 1. In the constructed two-dimensional wave hydrodynamic model, the improved wave propagation equation is used to calculate the interaction between the bamboo fence shrub dam and the wave, which makes up for the deficiency of the traditional model in simulating the influence of the bamboo fence shrub dam by adding equivalent roughness or generalizing it as an impermeable structure, and reduces the limitation of the traditional model that ignores the permeability and different resistance characteristics of the bamboo fence shrub dam. It can more realistically and accurately reflect the wave propagation, deformation and dissipation process around the bamboo fence shrub dam.

[0031] 2. Due to the improvement of the wave propagation equation, the sub-grid method can be used to perform numerical simulation of the target sea area, avoiding the high-resolution grid requirements of the traditional model, saving computing resources, and thus ensuring computing efficiency.

[0032] 3. When simulating the wave hydrodynamic environment around the bamboo fence shrub dam, it can more quickly and accurately simulate the spatial and temporal distribution of key characteristics of the wave field such as wave height and period under different dynamic conditions, and then more accurately evaluate the impact of the bamboo fence shrub dam on wave propagation in the surrounding sea area, providing more reliable prediction and decision-making support for the design and environmental impact assessment of the silt-promoting ecological bamboo fence shrub dam.

[0033] 4. It has extensive application potential in the fields of marine engineering, coastal protection, and ecological environmental protection. It provides a solid technical guarantee for engineering design, construction, and maintenance. The method of the present invention can use MATLAB to intuitively display the wave hydrodynamic environment field of the bamboo fence shrub dam, provide reliable technical support for engineering design, construction, and maintenance, and thus enhance the wave-proof ability of the bamboo fence shrub dam, effectively alleviate coastal erosion problems, protect the ecological environment, promote the prosperity and development of salt marshes and mangrove areas, and flexibly respond to the environmental challenges of rising sea levels, making positive contributions to the sustainable development of coastal areas. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 This is a flow chart of a numerical simulation method of wave hydrodynamics in a sea area with bamboo fences and shrub dams;

[0035] Figure 2 Bathymetric topographic map of the nearshore area for simulation;

[0036] Figure 3 The figures are comparison diagrams of the simulation results of the method of the present invention and the traditional method, wherein (a) is the comparison diagram of model A, (b) is the comparison diagram of model B, and (c) is the comparison diagram of model C. DETAILED DESCRIPTION

[0037] 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.

[0038] Embodiment 1:

[0039] A numerical simulation method of wave hydrodynamics in a sea area with bamboo fences and shrub dams is proposed. Figure 1 As shown, the following steps are included:

[0040] S1: Determine the target sea area and collect the measured water depth topographic data and chart water depth data of the target sea area, where the target sea area refers to the salt marsh beach sea area where the bamboo fence shrub dam is planned to be arranged;

[0041] S2: Set the grid accuracy and use the structured grid to build a two-dimensional wave hydrodynamic model of the target sea area. When the interaction between the bamboo fence shrub dam and the waves needs to be calculated, the following wave propagation equation is used for calculation:

[0042] ,

[0043] In the formula, K t is the transmission coefficient, R c is the freeboard of the bush dam, H moi is the incident effective wave height, P f is the porosity coefficient, B is the dam crest width, d is the water depth in front of the dam, s 0p is the equivalent wave steepness coefficient;

[0044] S3: Set the boundary conditions for driving the wave hydrodynamic 2D model and set the initial parameters;

[0045] S4: Based on the two-dimensional wave hydrodynamic model constructed in S2, the sub-grid method is used to perform numerical simulation of the target sea area to obtain the characteristic wave height and period spatial and temporal distribution of the target sea area.

[0046] In an optional embodiment, the wave hydrodynamic two-dimensional model in S2 is a wave hydrodynamic two-dimensional model of the target sea area where the bamboo fence and shrub dam is set up, which is constructed based on the spectral density equation.

[0047] In an optional embodiment, a two-dimensional wave hydrodynamic model of a target sea area where a bamboo fence and shrub dam is set is constructed based on a spectral density equation, and the spectral density equation used is as follows:

[0048] ,

[0049] In the formula, N is the action density parameter, c x and c y are the propagation velocities in the x and y directions, c σ and c θ are the propagation velocities in the spatial directions σ and θ respectively, S is the source term, and t is the time.

[0050] In an optional embodiment, the P in S2 f and 0p The calculation formula is as follows:

[0051] ,

[0052] ,

[0053] In the formula, n is the volume porosity, L is 0p The wavelength is deep water.

[0054] In an optional embodiment, the value range of n is as follows: 0.4 <n≤0.7;H moi The value range is as follows: 0.3m <H moi <0.8m.

[0055] In an alternative embodiment, R c / H moi The value range is as follows, -2.3 <R c / H moi <2.7; H moi The value range is as follows: 0.3m <H moi <0.8m; the value range of B / d is as follows: 0.26

[0056] In an optional embodiment, in S3, wave data under normal sea conditions and extreme sea conditions in the target sea area are collected to drive the boundary conditions of the wave hydrodynamic two-dimensional model.

[0057] In an optional embodiment, the boundary conditions driving the wave hydrodynamic two-dimensional model include: the tide level and wave conditions of normal sea conditions in the target sea area, and the tide level and wave conditions during extreme weather periods.

[0058] ​In an optional embodiment, in S3, the initial parameters include: initial terrain data and roughness of the target sea area, calculation time step, pressure and wind field temporal and spatial distribution, and wave breaking index.

[0059] The present embodiment provides a wave hydrodynamic numerical simulation method for a sea area with a bamboo fence and shrub dam. In the constructed two-dimensional wave hydrodynamic model, an improved wave propagation equation is used to calculate the interaction between the bamboo fence and shrub dam and waves, which makes up for the deficiency of the traditional model in simulating the influence of the bamboo fence and shrub dam by adding equivalent roughness or generalizing it to an impermeable structure, reduces the limitation of the traditional model in ignoring the permeability and different resistance characteristics of the bamboo fence and shrub dam, and can more realistically and accurately reflect the wave propagation, deformation and dissipation process around the bamboo fence and shrub dam.

[0060] The present embodiment provides a method for numerically simulating wave hydrodynamics in a sea area with a bamboo fence and shrub dam. Due to the improved wave propagation equation, a sub-grid method can be used to perform numerical simulation on the target sea area, thus avoiding the high-resolution grid requirement of traditional models, saving computing resources, and thus ensuring computing efficiency.

[0061] In summary, the wave hydrodynamic numerical simulation method of the sea area with a bamboo fence and shrub dam in this embodiment can more quickly and accurately simulate the spatiotemporal distribution of key characteristics such as wave height and period of the wave field under different dynamic conditions when simulating the wave hydrodynamic environment around the bamboo fence and shrub dam, and thus more accurately evaluate the wave propagation impact of the bamboo fence and shrub dam on the surrounding sea area, providing more reliable prediction and decision-making support for the design and environmental impact assessment of the silt-promoting ecological bamboo fence and shrub dam.

[0062] On this basis, the wave hydrodynamic numerical simulation method for the sea area with bamboo fence and shrub dam in this embodiment has broad application potential in the fields of marine engineering, coastal protection and ecological environmental protection. It provides a solid technical guarantee for engineering design, construction and maintenance. The wave hydrodynamic numerical simulation method for the sea area with bamboo fence and shrub dam in this embodiment can use matlab to intuitively display the wave hydrodynamic environment field of the bamboo fence and shrub dam, providing reliable technical support for engineering design, construction and maintenance, thereby enhancing the wave-proof ability of the bamboo fence and shrub dam, effectively alleviating coastal erosion problems, protecting the ecological environment, promoting the prosperity and development of salt marshes and mangrove areas, and flexibly responding to the environmental challenges of rising sea levels, making positive contributions to the sustainable development of coastal areas.

[0063] In order to verify the effectiveness of the wave hydrodynamic numerical simulation method for setting bamboo fence and shrub dam in this embodiment, a target sea area for setting bamboo fence and shrub dam was set up, and its terrain is as follows: Figure 2The input conditions and model settings of the model are shown in Table 1, where Model A is a direct simulation, that is, a structure with the same volume as the simulated bamboo fence shrub dam is set at the corresponding position, Model B is a traditional model, and Model C is the solution of this embodiment. The volume porosity adopted is 0.7. The wave height calculated by simulation is shown in Table 2. The simulation results are shown in Figure 3 As shown, for the convenience of display, two observation points O1-O2 are selected on the wave-facing side and the wave-back side of the bamboo fence shrub dam. O1 is located on the wave-facing side of the front edge of the shrub dam, and O2 corresponds to the sheltered area on the wave-back side of the shrub dam.

[0064] Table 1 Model input conditions and model settings

[0065]

[0066] Table 2 Simulation results

[0067]

[0068] In order to compare the validity of the data, under the same conditions, a bamboo fence shrub dam with a volume porosity of 0.7 was set in the actual marine environment to obtain measured data. The effective wave height at O1 was 0.47m, and the effective wave height at O2 was 0.31m. According to the results in Table 2, the effective wave height at O2 is 0.31m, and the effective wave heights at O2 simulated and calculated by Model A, Model B, and Model C are 0.161m, 0.177m, and 0.316m, respectively, with corresponding relative errors of 48%, 43%, and 2%, respectively; since Model A and Model B assume that the structure is impermeable, they will overestimate the effect of the bamboo fence shrub dam on waves, that is, overestimate the attenuation of waves after passing through the bamboo fence shrub dam, and thus make the simulated effective wave height after the dam lower. It can be seen that the two are not conducive to the design of the shrub dam and disaster protection; and the simulation of the effective wave height of Model C in this embodiment is more accurate, which can reflect the permeability of the bamboo fence shrub dam and the different resistance characteristics caused by the complex structure. In addition, according to Figure 3 , Model A and Model B cannot effectively simulate the attenuation mechanism of the bamboo fence shrub dam on the wave-facing side or the wave-back side of the bamboo fence shrub dam, while Model C of this embodiment can provide more reliable prediction results of effective wave height.

[0069] In addition, the simulation calculation time required for Model A, Model B, and Model C is shown in Table 3.

[0070] Table 3. Time required for simulation calculation

[0071]

[0072] According to the data in Table 3, Model C of the embodiment has an advantage in simulation calculation time, which is of great significance for improving the wave protection performance of bamboo fence shrub dams, optimizing the design of engineering structures, reducing coastal erosion, and protecting the ecological environment, and can contribute to the sustainable development of coastal areas.

[0073] 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 numerical simulation method for wave hydrodynamics in a sea area with bamboo fences and shrub dams, characterized in that: The steps include: S1: Determine the target sea area and collect the measured water depth topographic data and chart water depth data of the target sea area, where the target sea area refers to the salt marsh beach sea area where the bamboo fence shrub dam is planned to be arranged; S2: Set the grid accuracy and use the structured grid to build a two-dimensional wave hydrodynamic model of the target sea area. When the interaction between the bamboo fence shrub dam and the waves needs to be calculated, the following wave propagation equation is used for calculation: ， In the formula, K t is the transmission coefficient, R c is the freeboard of the bush dam, H moi is the incident effective wave height, P f is the porosity coefficient, B is the dam crest width, d is the water depth in front of the dam, s 0p is the equivalent wave steepness coefficient; S3: Set the boundary conditions for driving the wave hydrodynamic 2D model and set the initial parameters; S4: Based on the two-dimensional wave hydrodynamic model constructed in S2, the sub-grid method is used to perform numerical simulation of the target sea area to obtain the characteristic wave height and period spatial and temporal distribution of the target sea area.

2. The wave hydrodynamic numerical simulation method for setting bamboo fence and shrub dam in the sea area according to claim 1 is characterized in that: The wave hydrodynamic two-dimensional model in S2 is a wave hydrodynamic two-dimensional model of the target sea area where bamboo fences and shrub dams are set up, which is constructed based on the spectral density equation.

3. The wave hydrodynamic numerical simulation method for setting bamboo fence and shrub dam in the sea area according to claim 2 is characterized in that: The wave hydrodynamic two-dimensional model of the target sea area where the bamboo fence shrub dam is set is constructed based on the spectral density equation. The spectral density equation used is as follows: ， In the formula, N is the action density parameter, c x and c y are the propagation velocities in the x and y directions, c σ and c θ are the propagation velocities in the spatial directions σ and θ respectively, S is the source term, and t is the time.

4. The wave hydrodynamic numerical simulation method for setting bamboo fence and shrub dam in the sea area according to claim 1 is characterized in that: The S2P f and 0p The calculation formula is as follows: ， ， In the formula, n is the volume porosity, L is 0p The wavelength is deep water.

5. The wave hydrodynamic numerical simulation method for setting bamboo fence and shrub dam in the sea area according to claim 4 is characterized in that: The value range of n is as follows: 0.4 <n≤0.7;H moi The value range is as follows: 0.3m <H moi <0.8m.

6. The wave hydrodynamic numerical simulation method for setting bamboo fence and shrub dam in the sea area according to claim 1 is characterized in that: R c / H moi The value range is as follows, -2.3 <R c / H moi <2.7; H moi The value range is as follows: 0.3m <H moi <0.8m; the value range of B / d is as follows: 0.26 <B / d<2.62。 7. The wave hydrodynamic numerical simulation method for setting bamboo fence and shrub dam in the sea area according to claim 1 is characterized in that: In S3, wave data under normal sea conditions and extreme sea conditions in the target sea area are collected to drive the boundary conditions of the wave hydrodynamic two-dimensional model.

8. The wave hydrodynamic numerical simulation method for setting bamboo fence and shrub dam in the sea area according to claim 7 is characterized in that: The boundary conditions driving the two-dimensional wave hydrodynamic model include: the tidal and wave conditions of normal sea conditions in the target sea area, as well as the tidal and wave conditions during extreme weather periods.

9. The wave hydrodynamic numerical simulation method for setting bamboo fence and shrub dam in the sea area according to claim 1 is characterized in that: In S3, the initial parameters include: initial terrain data and roughness of the target sea area, calculation time step, pressure and wind field temporal and spatial distribution, and wave breaking index.

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