An analysis method for simulating evolution of island reef topography under sea level change

Abstract

The application discloses an analysis method for simulating island and reef topography evolution under sea level change, which can be applied to the technical field of marine engineering. The application obtains island physical parameters and island near-sea parameters, constructs a two-dimensional scouring model of the island according to a two-dimensional profile of the island, divides the two-dimensional scouring model in a grid size, sets simulation initial conditions and simulation boundary conditions, determines a sediment transport mode according to island sediment parameters, sets island simulation running time according to the island near-sea parameters, and then simulates island topography change according to the two-dimensional scouring model after the grid division, the simulation initial conditions, the simulation boundary conditions, the sediment transport mode and the island simulation running time, so that the simulation running time is greatly reduced, and then the evolution law of the island under the action of the sea level rise is analyzed, reasonable protection measures for the island to adapt to the future sea level rise are provided, and the safety of the island is improved.

Description

Technical Field

[0001] This invention relates to the field of marine engineering technology, and in particular to an analytical method for simulating the evolution of island and reef morphology under sea level changes. Background Technology

[0002] In related technologies, with the anticipated significant rise in global sea levels, coral reef islands, as gravel or sandy islands deposited on atolls and platform reefs, are among the coastal environments most vulnerable to sea-level rise and changes in wave conditions. Sea-level rise and the increase in super typhoons are expected to undermine the physical stability of islands, potentially rendering them uninhabitable within the next few decades in some extreme cases. However, mounting evidence suggests that islands are geologically resilient and can adapt to changes in sea level and climate. Understanding the evolution of island morphology under sea-level rise can help islands adapt to future environments. Current island morphological dynamics models are relatively slow, resulting in long simulation times. Summary of the Invention

[0003] This invention aims to at least solve one of the technical problems existing in the prior art. To this end, this invention proposes an analytical method for simulating the evolution of island and reef morphology under sea-level changes, which can effectively improve the efficiency of simulation operation.

[0004] This invention provides an analytical method for simulating the evolution of island and reef morphology under sea-level changes, comprising the following steps:

[0005] Acquire island physical parameters and island nearshore parameters. The island physical parameters include two-dimensional profiles of the island and island sediment parameters. The island nearshore parameters include nearshore wave data and tidal data.

[0006] A two-dimensional scour model of the island is constructed based on the two-dimensional cross-sectional view of the island, and the two-dimensional scour model is divided into mesh sizes.

[0007] Set the initial and boundary conditions for the simulation;

[0008] The sediment transport method is determined based on the island sediment parameters;

[0009] Set the island simulation operation time according to the island's nearshore parameters;

[0010] Based on the two-dimensional scour model after grid division, the initial simulation conditions, the boundary conditions, the sediment transport method, and the island simulation running time, the island morphology change is simulated to obtain the island morphology change process.

[0011] In some embodiments, the sediment transport mechanism includes the Nielsen sediment transport equation, the expression of which is as follows:

[0012]

[0013] Where, q s ρ represents the volumetric sediment transport rate, θ represents the Shields parameter, and ρ represents the density of water. s D represents the density of sediment. 50 denoted by , where represents the median sediment grain size, and g represents the gravity constant.

[0014] In some embodiments, the Shields parameter is adjusted using the bed slope effect, and the adjustment process is expressed as follows:

[0015]

[0016] Among them, u * β represents the friction velocity, β represents the riverbed angle, and Φ represents the angle of repose of the sediment.

[0017] In some embodiments, the friction speed includes an approximate friction speed, the calculation expression of which is as follows:

[0018]

[0019] Among them, f s T represents the sediment friction factor. m-1,0 This represents the near-shore spectral period based on the first negative moment of the energy spectrum. The lag angle is represented by u, the water flow velocity is represented by t, and the time is represented by t.

[0020] In some embodiments, the sediment transport mechanism includes the Van Riji sediment transport equation, the expression of which is as follows:

[0021]

[0022] Where, q b The volumetric sediment transport rate is represented by γ, and the calibration coefficient is represented by D. 50 The median sediment grain size is represented by ρ, the density of water is represented by θ. cr τ represents the Shields coefficient for initiating transport, θ′ represents the Shields parameter after correction for riverbed slope; b This represents shear stress, and g represents the gravitational constant. v represents the kinematic viscosity coefficient of water.

[0023] In some embodiments, the formula for expressing the Shields coefficient for initiating transport is as follows:

[0024]

[0025] in,

[0026] In some embodiments, when the climate of the island's location is without obvious seasonality, the calculation steps for the island's simulation running time include:

[0027] Based on the ocean wave data and the tide data, the annual average value of extreme wave height and the annual average time of high tide occurrence in the nearshore waters of the island are obtained.

[0028] The simulated operating time of the island was calculated based on the annual average extreme wave height near the island and the annual average time of high tide near the island.

[0029] In some embodiments, the calculation formula for calculating the island simulation operation time based on the annual average extreme wave height near the island and the annual average time of high tide near the island is as follows:

[0030] t = x% * t0 * n

[0031] Where t0 represents the average annual time of high tide near the island, and t represents the simulated operating time of the island after n years.

[0032] In some embodiments, when the climate of the island's location is characterized by distinct seasonality, the calculation steps for the island's simulation running time include:

[0033] Based on the ocean wave data and the tide data, the annual average value of extreme wave height in the nearshore waters of the islands and the seasonal average time of high tide occurrence in the nearshore waters of the islands are obtained.

[0034] The simulated operating time of the island was calculated based on the annual average extreme wave height near the island and the seasonal average time of high tide near the island.

[0035] In some embodiments, the calculation formula for obtaining the island simulation operation time based on the annual average extreme wave height near the island and the seasonal average time of high tide near the island is as follows:

[0036] t = x% * (t1 + t2 + t3 + t4) * n

[0037] Where t1, t2, t3, and t4 represent the average time of the seasonal high tides, and t represents the simulated operating time of the island after n years.

[0038] The analytical method for simulating the evolution of island and reef morphology under sea-level changes provided by this invention has the following beneficial effects:

[0039] This embodiment acquires island physical parameters, including two-dimensional cross-sectional images and sediment parameters, as well as nearshore parameters, including nearshore wave and tidal data. A two-dimensional scour model of the island is then constructed based on the two-dimensional cross-sectional images. The model is then meshed, and initial and boundary conditions are set. Sediment transport methods are determined based on the sediment parameters, and the simulation run time is set based on the nearshore parameters. Finally, the island's morphological changes are simulated using the meshed two-dimensional scour model, initial and boundary conditions, sediment transport methods, and simulation run time. This process significantly reduces simulation time, facilitating the analysis of island evolution under sea-level rise. This provides assistance in developing reasonable protection measures for islands to adapt to future sea-level rise, thereby improving island safety.

[0040] Additional aspects and advantages of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. Attached Figure Description

[0041] The present invention will be further described below with reference to the accompanying drawings and embodiments, wherein:

[0042] Figure 1 This is a flowchart illustrating an analytical method for simulating the evolution of island and reef morphology under sea-level changes, according to an embodiment of the present invention.

[0043] Figure 2 This is a schematic diagram of a two-dimensional scour model at a first moment according to an embodiment of the present invention;

[0044] Figure 3 This is a schematic diagram of a two-dimensional scour model at a second time step according to an embodiment of the present invention;

[0045] Figure 4 This is a schematic diagram illustrating the change of boundary water level over time according to an embodiment of the present invention. Detailed Implementation

[0046] Embodiments of the present invention are described in detail below. Examples of these embodiments are shown in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain the present invention, and should not be construed as limiting the present invention.

[0047] In the description of this invention, it should be understood that the orientation descriptions, such as up, down, front, back, left, right, etc., are based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limiting this invention.

[0048] In the description of this invention, "several" means one or more, "multiple" means two or more, "greater than," "less than," and "exceeding" are understood to exclude the stated number, while "above," "below," and "within" are understood to include the stated number. The use of "first" and "second" in the description is merely for distinguishing technical features and should not be construed as indicating or implying relative importance, or implicitly indicating the number of indicated technical features, or implicitly indicating the order of the indicated technical features.

[0049] In the description of this invention, unless otherwise explicitly defined, terms such as "set up," "install," and "connect" should be interpreted broadly, and those skilled in the art can reasonably determine the specific meaning of the above terms in this invention in conjunction with the specific content of the technical solution.

[0050] In the description of this invention, the terms "one embodiment," "some embodiments," "illustrative embodiment," "example," "specific example," or "some examples," etc., refer to specific features, structures, materials, or characteristics described in connection with that embodiment or example, which are included in at least one embodiment or example of the invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0051] Reference Figure 1 This invention provides an analytical method for simulating the evolution of island and reef morphology under sea-level changes. This method can be applied to open-source software processors, such as XBeach-G. When simulating and analyzing the evolution of island morphology under sea-level changes, a simulation task is first established within the open-source software. Then, based on this simulation task, the following steps are performed, including but not limited to:

[0052] Step S110: Obtain island physical parameters and island nearshore parameters, wherein the island physical parameters include island two-dimensional profile map and island sediment parameters, and the island nearshore parameters include nearshore wave data and tidal data;

[0053] Step S120: Construct a two-dimensional scour model of the island based on the two-dimensional cross-sectional view of the island, and divide the two-dimensional scour model into mesh sizes;

[0054] Step S130: Set the initial simulation conditions and simulation boundary conditions;

[0055] Step S140: Determine the sediment transport method based on the island sediment parameters;

[0056] Step S150: Set the island simulation operation time according to the island's nearshore parameters;

[0057] Step S160: Based on the two-dimensional scour model after mesh division, the initial simulation conditions, the boundary conditions, the sediment transport method, and the island simulation running time, simulate the island morphology change process to obtain the island morphology change process.

[0058] In this embodiment, the grid size should be appropriate. Specifically, the grid can be divided based on island sediment parameters and nearshore wave data. After grid division, the following can be obtained: Figure 2 The two-dimensional scour model is shown. During mesh generation, an excessively large mesh will lead to non-convergence, while an excessively small mesh will result in excessively long computation times. After simulation analysis over a certain period, the following results can be obtained: Figure 3 The two-dimensional scour model shown is from Figure 3 It is known that changes occur in the island's foreshore due to the erosion of sediments by waves and tides. In this embodiment, the island sediment parameters include the median grain size D of the sediments. 50 Characteristic particle size D 90 Porosity n and hydraulic conductivity (permeability coefficient) K.

[0059] In this embodiment, the JONSWAP wave spectrum can be used as the boundary condition for simulating the island. For example... Figure 4 As shown, this is a schematic diagram of boundary water level changes based on the JONSWAP wave spectrum. The horizontal axis represents time, and the vertical axis represents water level height. The diagram shows that, over a long period of operation, the correlation between water level height and island morphology can be obtained. Specifically, the nearshore wave data includes the enhancement factor Ω and the significant wave height H. s and peak period T p .

[0060] In this embodiment, the sediment transport method is used to control the changes in island morphology during the simulation. The sediment transport method includes the Nielsen sediment transport equation, the expression of which is shown in formula (1):

[0061]

[0062] Where, q s This represents the volumetric sediment transport rate, with units of m³. 3 / s; θ represents the Shields parameter (-); ρ represents the density of water, ρ s This indicates the density of sediment, expressed in kg / m³. 3 ;D 50 The value represents the median sediment grain size in meters (m); g represents the gravitational constant.

[0063] In this embodiment, the Shields parameter can be adjusted by the bed slope effect, and the expression for the adjustment process is shown in formula (2):

[0064]

[0065] Among them, u * The value represents the friction velocity, measured in m / s; β represents the riverbed angle; and Φ represents the angle of repose of sediment (°).

[0066] To account for the expansion and contraction of the boundary layer in the jet, the pressure gradient effect, and the presence of turbulent fronts, the friction velocity can be replaced by an approximate friction velocity. Specifically, the expression for calculating the approximate friction velocity is shown in equation (3):

[0067]

[0068] Among them, f s The value represents the sediment friction factor, with an order of 0.01 (-), typically ranging from 0.01 to 0.05; T m-1,0 This represents the near-shore spectral period based on the first negative moment (s) of the energy spectrum. The phase lag angle is represented by u, the water flow velocity is represented by m / s, and t is represented by time.

[0069] In this embodiment of the application, the sediment transport method may also include the Van Riji sediment transport equation, the expression of which is shown in formula (4):

[0070]

[0071] Where, q b The volumetric sediment transport rate is represented by γ, and the calibration coefficient is represented by D. 50 The median sediment grain size is represented by ρ, the density of water is represented by θ. cr τ represents the Shields coefficient for initiating transport, θ′ represents the Shields parameter after correction for riverbed slope; b Shear stress is expressed in N / m. 2 g represents the gravitational constant. v represents the kinematic viscosity coefficient of water.

[0072] In this embodiment, the Shields coefficient can be calculated using formula (5):

[0073]

[0074] In this embodiment, the Shields coefficient θ is used to define the sediment migration rate, which reflects the ratio of the force that causes the riverbed sediment to move to the force that resists the movement, as shown in formula (6):

[0075]

[0076] Where, Δ i This represents the relative effective weight of the sediment. To account for the effect of cross-bed flow on particle weight, the effective weight of the particles is corrected using formula (7):

[0077]

[0078] Where, ρ s Let represent sediment density, K represent riverbed hydraulic conductivity, α represent an empirical constant relating surface permeability and riverbed permeability, with a value of 0.5, and S represent the exchange rate between groundwater and surface water. To account for the influence of riverbed slope on sediment transport, the Shields coefficient θ′ is corrected using formula (8):

[0079]

[0080] Where β represents the local angle of the riverbed (°), and φ represents the angle of repose of sediment (°).

[0081] In this embodiment, when the climate of the island's location is without obvious seasonality, the island simulation operation time can be calculated by obtaining the annual average extreme wave height and the annual average time of high tide near the island based on wave and tide data; then, the island simulation operation time is calculated based on the annual average extreme wave height and the annual average time of high tide near the island. Specifically, the annual average extreme wave height of the first x% of the island's nearshore area is obtained, and the island simulation operation time is calculated using formula (9):

[0082] t = x%*t0*n Formula (9)

[0083] Where t0 represents the average annual time of high tide near the island, and t represents the simulated operating time of the island after n years.

[0084] In this embodiment of the application, when the climate of the island's location is distinctly seasonal, the island simulation operation time can be calculated by obtaining the annual average extreme wave height and the seasonal average time of high tide near the island based on wave and tide data; then, the island simulation operation time is calculated based on the annual average extreme wave height and the seasonal average time of high tide near the island. Specifically, the annual average extreme wave height of the first x% of the island's nearshore area is obtained, and the island simulation operation time is calculated using formula (10):

[0085] t = x% * (t1 + t2 + t3 + t4) * n Formula (10)

[0086] Where t1, t2, t3, and t4 represent the average time of the seasonal high tides, and t represents the simulated operating time of the island after n years.

[0087] In this embodiment, it is assumed that low to moderate wave hydrodynamic conditions only shape island beaches, and only extreme conditions lead to large-scale changes in island structure. Furthermore, extreme wave heights and high tides are independent events. For example, the specific calculation of the simulation time for an island without obvious seasonal climate is as follows: using nearshore wave and tidal data, the annual average value of the top 2% extreme wave heights and the annual average time of high tides near the island are obtained as 80 hours. Then, using formula (9), the simulation calculation time for the island 100 years later can be calculated as 2% * 80 * 100 = 160 hours. Therefore, this embodiment simplifies the 100-year calculation time to 160 hours, greatly saving simulation time and improving simulation efficiency.

[0088] This invention provides an analysis system for simulating the evolution of island and reef morphology under sea-level changes, comprising:

[0089] The first module is used to acquire island physical parameters and island nearshore parameters. The island physical parameters include island two-dimensional profiles and island sediment parameters, while the island nearshore parameters include nearshore wave data and tidal data.

[0090] The second module is used to construct a two-dimensional scour model of the island based on the two-dimensional cross-sectional view of the island, and to divide the two-dimensional scour model into mesh sizes.

[0091] The third module is used to set the initial and boundary conditions for the simulation.

[0092] The fourth module is used to determine the sediment transport method based on the island's sediment parameters;

[0093] The fifth module is used to set the island simulation operation time based on the island's nearshore parameters;

[0094] The sixth module is used to simulate island morphology changes based on the two-dimensional scour model after meshing, the initial simulation conditions, the simulation boundary conditions, the sediment transport method, and the island simulation running time, so as to obtain the island morphology change process.

[0095] The content of the method embodiments of the present invention is applicable to the system embodiments. The specific functions implemented in the system embodiments are the same as those in the above method embodiments, and the beneficial effects achieved are also the same as those achieved by the above methods.

[0096] This invention provides an analysis system for simulating the evolution of island and reef morphology under sea-level changes, comprising:

[0097] At least one memory for storing programs;

[0098] At least one processor is used to load the program for execution. Figure 1 The method shown is an analytical approach to the evolution of island and reef morphology under simulated sea-level changes.

[0099] The content of the method embodiments of the present invention is applicable to the system embodiments. The specific functions implemented in the system embodiments are the same as those in the above method embodiments, and the beneficial effects achieved are also the same as those achieved by the above methods.

[0100] This invention provides a storage medium storing a computer-executable program, which, when executed by a processor, is used to implement... Figure 1 The method shown is an analytical approach to the evolution of island and reef morphology under simulated sea-level changes.

[0101] The content of the method embodiments of the present invention is applicable to the storage medium embodiments. The specific functions implemented by the storage medium embodiments are the same as those of the above method embodiments, and the beneficial effects achieved are also the same as those achieved by the above methods.

[0102] Furthermore, embodiments of the present invention also provide a computer program product or computer program, which includes computer instructions stored in a computer-readable storage medium. A processor of a computer device can read the computer instructions from the computer-readable storage medium, and the processor executes the computer instructions, causing the computer device to perform... Figure 1 The method shown is an analytical approach to the evolution of island and reef morphology under simulated sea-level changes.

[0103] The embodiments of the present invention have been described in detail above with reference to the accompanying drawings. However, the present invention is not limited to the above embodiments, and various changes can be made within the scope of knowledge possessed by those skilled in the art without departing from the spirit of the present invention. Furthermore, the embodiments of the present invention and the features thereof can be combined with each other unless otherwise specified.

Claims

1. An analytical method for simulating the evolution of island and reef morphology under sea-level changes, characterized in that, Includes the following steps: The island's physical parameters and nearshore parameters are obtained. The island's physical parameters include two-dimensional profiles of the island and sediment parameters. The nearshore parameters include nearshore wave data and tidal data. A two-dimensional scour model of the island is constructed based on the two-dimensional cross-sectional view of the island, and the two-dimensional scour model is divided into mesh sizes. Set the initial and boundary conditions for the simulation; The sediment transport method is determined based on the island sediment parameters; Set the island simulation operation time according to the island's nearshore parameters; Based on the two-dimensional scour model after mesh division, the initial simulation conditions, the simulation boundary conditions, the sediment transport method, and the island simulation running time, the island morphology change is simulated to obtain the island morphology change process; The sediment transport mechanism includes the Nielsen sediment transport equation, the expression of which is as follows: ； in, Indicates volumetric sediment transport rate, This refers to the Shields parameter. This indicates the density of water. Indicates the density of sediment. Indicates the median grain size of sediments. Represents the gravitational constant; The Shields parameters are adjusted using the bed slope effect, and the adjustment process is expressed as follows: ； in, Indicates friction speed, Indicates the angle of the riverbed. Indicates the angle of repose of sediment; The friction speed includes an approximate friction speed, which is calculated using the following expression: ； in, Indicates the friction factor of sediment. This represents the near-shore spectral period based on the first negative moment of the energy spectrum. Indicates the phase lag angle. t represents the water flow velocity, and t represents time.

2. The analytical method for simulating the evolution of island and reef morphology under sea-level changes according to claim 1, characterized in that, The sediment transport mechanism includes the Van Riji sediment transport equation, the expression of which is as follows: ； in, Indicates volumetric sediment transport rate, Indicates the calibration coefficient. Indicates the median grain size of sediments. This indicates the density of water. This represents the Shields coefficient used to initiate transport. This represents the Shields parameters after correction for riverbed slope; Represents shear stress. Represents the gravitational constant. , This represents the kinematic viscosity coefficient of water.

3. The analytical method for simulating the evolution of island and reef morphology under sea-level changes according to claim 2, characterized in that, The formula for expressing the Shields coefficient for initiating transport is as follows: ； in, .

4. The analytical method for simulating the evolution of island and reef morphology under sea-level changes according to claim 1, characterized in that, When the climate of the island's location is without obvious seasonality, the calculation steps for the island's simulation operation time include: Based on the ocean wave data and the tide data, the annual average value of extreme wave heights and the annual average time of high tides in the nearshore waters of the islands are obtained. The simulated operating time of the island was calculated based on the annual average extreme wave height near the island and the annual average time of high tide near the island.

5. The analytical method for simulating the evolution of island and reef morphology under sea-level changes according to claim 4, characterized in that, The formula for calculating the simulated operating time of the island, based on the annual average extreme wave height near the island and the annual average time of high tide near the island, is as follows: ； in, t represents the average annual time of high tide near the island, and t represents the simulated operating time of the island after n years.

6. The analytical method for simulating the evolution of island and reef morphology under sea-level changes according to claim 1, characterized in that, When the climate of the island's location is characterized by distinct seasonality, the calculation steps for the island's simulation operation time include: Based on the ocean wave data and the tide data, the annual average value of extreme wave height in the nearshore waters of the islands and the seasonal average time of high tide occurrence in the nearshore waters of the islands are obtained. The simulated operating time of the island was calculated based on the annual average extreme wave height near the island and the seasonal average time of high tide near the island.

7. The analytical method for simulating the evolution of island and reef morphology under sea-level changes according to claim 6, characterized in that, The formula for calculating the simulated operating time of the island, based on the annual average extreme wave height near the island and the seasonal average time of high tide near the island, is as follows: ； in, , , and t represents the average time of the seasonal high tides, and t represents the simulated operating time of the island after n years.

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