Dynamic value calculation method for predicting seabed erosion and deposition and application

Abstract

The invention discloses a dynamic value calculation method for predicting seabed erosion and deposition. The dynamic value calculation method comprises the following steps: step 1, determining dominant dynamic factors influencing seabed erosion and deposition evolution; 2, determining the critical starting shear stress and the critical deposition shear stress of the sediment; step 3, establishing and verifying a tidal current mathematical model and (or) a wave mathematical model, calculating dynamic elements of the research area, and giving a flow field and (or) a wave field of the research area; 4, calculating a bed surface shear stress field of the research area; step 5, comparing the critical starting shear stress and the critical silting shear stress of the sediment determined in the step 2 with the bed surface shear stress calculated in the step 4, and judging the starting and silting conditions and ranges of the bed surface sediment; and 6, calculating the seabed erosion and deposition amplitude by adopting an erosion and deposition calculation formula, and analyzing the seabed erosion and deposition trend. The method overcomes the defect that the traditional seabed evolution analysis method cannot quantitatively predict the seabed erosion and deposition amplitude, and is simpler and more efficient than a method for predicting the seabed erosion and deposition by adopting a sediment mathematical model.

Description

Technical Field

[0001] The invention belongs to the field of water transport technology and relates to a dynamic numerical calculation method for predicting seabed scouring and silting. Background Art

[0002] The prediction of seabed scouring and silting before and after the implementation of the project has always been a key technical issue in seabed evolution and coastal engineering, and is also the focus of port and waterway engineers. Many scholars at home and abroad have carried out a lot of research on seabed scouring and silting prediction through field observations and model research. The main research methods can be divided into three categories: empirical judgment based on measured data, semi-empirical and semi-theoretical formula prediction, and sediment mathematical model prediction. Since the empirical judgment method based on measured data has not yet reached the quantitative standard, the relevant parameter calibration of the semi-empirical and semi-theoretical formula prediction method is relatively random, the research results have a certain degree of uncertainty, and the sediment mathematical model prediction method is time-consuming and requires a large investment. Therefore, it is objectively necessary to develop a simple and efficient seabed scouring and silting prediction method. Summary of the invention

[0003] The technical problem to be solved by the present invention is to overcome the shortcomings of previous seabed erosion and siltation prediction methods, such as the inability to conduct quantitative analysis, long calculation time and high investment, and to provide a dynamic numerical calculation method for predicting seabed erosion and siltation, whose calculation efficiency and accuracy can meet the needs of seabed evolution analysis and coastal engineering research.

[0004] In order to solve the above technical problems, the present invention adopts the following technical solutions:

[0005] A dynamic numerical calculation method for predicting seabed scouring and silting includes the following steps:

[0006] Step 1: Determine the dominant dynamic factors affecting the evolution of seabed scouring and silting: According to the water depth conditions, hydrodynamic conditions, sediment characteristics, etc. of the study area, determine the dominant dynamic factors affecting the evolution of seabed scouring and silting, which can generally be divided into three situations: tidal current, wave, and wave-current combined action;

[0007] Step 2: Determine the critical starting shear stress and critical deposition shear stress of sediment through sediment hydraulic property tests or literature review;

[0008] Step 3: According to the dominant dynamic factors determined in step 1, establish a mathematical model of tidal current and (or) wave, and verify the model using measured data. The verification results meet the requirements of the Technical Specifications for Simulation Test of Water Transport Engineering.

[0009] (JTS / T 231-2021) requirements, carry out numerical simulation of hydrodynamic elements and give the flow field and (or) wave field in the study area;

[0010] Step 4, substituting the hydrodynamic results calculated in step 3 into the shear stress calculation formula to calculate the bed shear stress in the study area;

[0011] Step 5, comparing the critical starting shear stress and critical siltation shear stress determined in step 2 with the bed shear stress calculated in step 4, to determine the starting and siltation conditions and range of bed sediment; usually: when the bed shear stress is greater than the critical starting shear stress of sediment, sediment starts to move; when the bed shear stress is less than the critical siltation shear stress of sediment, sediment accumulates;

[0012] Step 6, using the scouring and silting calculation formula to calculate the seabed scouring and silting amplitude, and analyze the scouring and silting trend of the bed surface: according to the scouring and silting trend of the seabed determined in step 5, calculate the scouring and silting of the seabed, and analyze the scouring and silting trend of the bed surface.

[0013] The specific process of step 1 is: according to the water depth conditions, hydrodynamic conditions, sediment characteristics, etc. of the study area, determine the dominant dynamic factors affecting the evolution of seabed scouring and silting, which can generally be divided into three situations: tides, waves, and the combined effects of waves and currents.

[0014] The specific process of step 2 is: determining the critical starting shear stress and critical siltation shear stress of the sediment in the study area according to the test results of the hydrodynamic characteristics of the sediment in the study area or the literature review;

[0015] The specific process of step 3 is: determine the dominant dynamic factors affecting the evolution of seabed scouring and silting according to step 1, establish tidal and (or) wave mathematical models respectively, and perform simulation calculations of the aforementioned hydrodynamic elements after calibration and verification.

[0016] (1) In areas where tidal currents are dominant, a mathematical model of water flow is established;

[0017] (2) In areas where wave action is dominant, establish a wave mathematical model;

[0018] (3) In areas where the interaction of waves and currents is dominant, it is necessary to establish mathematical models for water flow and waves respectively.

[0019] The control equations of the mathematical model and the wave mathematical model and their solution methods can adopt the equations and solution methods recommended in the current relevant specifications (Technical Specifications for Simulation Tests of Water Transport Engineering (JTS / T 231-2021)).

[0020] The specific process of step 4 is: substitute the hydrodynamic results calculated in step 3 into the shear stress calculation formula to calculate the bed shear stress in the study area. Bed shear stress τ b The calculation can be done using the empirical formulas in the "Hydraulics" textbook or publicly published literature, or the following calculation formula can be selected based on the dominant dynamic factors in the study area.

[0021] 1) Only tidal current acts, bed shear stress τ b The following formula can be used for calculation:

[0022] τ b =τ c =ρu *c (1)

[0023] Where: τ c is the bed shear stress under the action of water flow, ρ is the density of water, u *c is the friction velocity of the bed surface under the action of water flow, h is the water depth, Δ is the bed roughness height, and when the median particle size of the bed sediment is D 50 ≤0.5mm, Δ=1mm, when D 50 >0.5mm, Δ=2D 50 , is the vertical average flow velocity, calculated by the hydrodynamic mathematical model described in step 3.

[0024] 2) Only wave action, bed shear stress τ b The following formula can be used for calculation:

[0025]

[0026] Where: τ wm is the bed shear stress under wave action, f w is the wave friction coefficient, which generally ranges from 0.005 to 0.02. For muddy seabed, it is generally taken as 0.01. wm is the velocity amplitude of the water particle at the bottom of the water under the action of waves, Where H is the wave height, T is the wave period, k is the wave number, k=2π / L, and L is the wavelength; H, T and L are calculated by the wave mathematical model in step 3.

[0027] 3) Wave and current interact, bed shear stress τ b The following formula can be used for calculation:

[0028]

[0029] Where: It is the average value of bed shear stress within one wave cycle under the combined action of waves and currents.

[0030] The specific process of step 5 is: compare the critical starting shear stress τ of sediment determined in step 2 e , critical sedimentation shear stress τ d The bed shear stress τ calculated in step 4 b , judge the start-up, sedimentation and range of bed sediment. Usually: when the bed shear stress is greater than the critical start-up shear stress of sediment, sediment starts to move; when the bed shear stress is less than the critical sedimentation shear stress of sediment, sediment accumulates.

[0031] (1) If τb >τ e , the bed sediment starts to move into the water body;

[0032] (2) If τ b <τ d , the sediment in the water body falls and precipitates on the bed surface;

[0033] (3) If τ d <τ b <τ c , there is no sediment exchange between the bed surface and the water body.

[0034] by or As a criterion for judging whether the seabed sediment has obviously started to move or silted up, the thickness of seabed scouring or silting is calculated. and It can be judged that the seabed erosion and siltation in the study area is relatively balanced.

[0035] The specific process of step 6 is: using the scouring and silting calculation formula to calculate the seabed scouring and silting amplitude and analyze the seabed scouring and silting trend.

[0036] The thickness of seabed erosion and deposition can be calculated using the empirical formula in the textbook "Seabed Evolution" or in publicly published literature, or the following calculation formula can be used according to the form of sediment movement:

[0037] 1) Areas where sediment mainly moves in the form of suspended load

[0038] (1) When sedimentation occurs on the bed surface, the sedimentation thickness is calculated according to the following formula:

[0039]

[0040] Where: η d is the sedimentation thickness, Δt d is the sedimentation time, k is the probability of sediment deposition, C b is the bottom sediment content, ω is the sediment settling velocity, τ b is the bed shear stress, τ d is the critical sedimentation shear stress of sediment. The sediment deposition probability k in formula (4) can be calculated using the following formula:

[0041]

[0042] is the probability integral function, which can be found in Table 2; ω is the sedimentation velocity, σ is the root mean square of the pulsating flow velocity, v is the average flow velocity of the cross section, g is the gravitational acceleration, and C is the Xie Cai coefficient of the study sea area.

[0043] Table 2 Probability integral function Value table

[0044]

[0045] (2) When scouring occurs on the bed surface, the scouring thickness is calculated according to the properties of the bed surface using the following formula:

[0046] ① If the bulk density is uniformly distributed vertically on the bottom bed,

[0047] ② If the bulk density of the natural dense bed gradually increases from top to bottom,

[0048] Where: η e is the scour thickness, Δt d is the scouring time, M is the bed sediment scouring coefficient, which is related to the sediment properties, α and β are parameters that vary with the sediment structure and density, etc., τ e is the critical starting shear stress of sediment.

[0049] (3) When τ d <τ b <τ c , there is no siltation or scouring on the bed surface, that is, Δη d =Δη e =0.

[0050] (4) Change of bed surface erosion and siltation Δη b =Δη d +Δη e .

[0051] 2) Areas where sediment is mainly transported in the form of bedload

[0052] (1) When sedimentation occurs on the bed surface, the sedimentation thickness is calculated according to the following formula:

[0053] Δη d =Δt d ·ωC b (8)

[0054] (2) When scouring occurs on the bed surface, the scouring thickness is calculated according to the following formula:

[0055]

[0056] Where: s is the specific gravity of sediment, g is the acceleration of gravity, D 50 is the median particle size of sediment, ψ, ψ c are the Shields number under hydrodynamic force and the critical starting Shields number of sediment, ν is the viscosity coefficient of water.

[0057] If the bed surface sediment thickness Δη d≤0.2m or sediment thickness Δη e ≤0.2m, it is judged that the seabed in the study area is relatively stable. On the contrary, if Δη d >0.2m or Δη e >0.2m, it is judged that the seabed activity in the study area is strong, and the calculation results of step 6 are reviewed according to the seabed scouring and silting trend determined in step 5.

[0058] Thus, the whole process of dynamic numerical calculation for predicting seabed erosion and deposition is completed.

[0059] Compared with the prior art, the advantages of the present invention are:

[0060] The present invention discloses a dynamic numerical calculation method for predicting seabed scouring and silting. The method uses measured critical starting shear stress and critical siltation shear stress to compare and analyze with bed shear stress calculated by a mathematical model to predict seabed scouring and silting. The calculation method disclosed in the present invention is concise and efficient, and overcomes the defects of previous predictions of seabed evolution such as the inability to conduct quantitative analysis, the long time consumption and limited accuracy of sediment mathematical models in predicting beach scouring and silting, and enriches the research methods of seabed evolution. BRIEF DESCRIPTION OF THE DRAWINGS

[0061] Figure 1 It is a flow chart of a dynamic numerical calculation method for predicting seabed scouring and silting according to the present invention.

[0062] Figure 2 This is an embodiment of the present invention (Lianyungang and its adjacent sea areas).

[0063] Figure 3 It is the calculation range and grid division diagram of the two-dimensional tidal mathematical model and wave mathematical model of the present invention.

[0064] Figure 4 It is a calculation result diagram of the tidal current mathematical model of the present invention.

[0065] Figure 5 It is a diagram of calculation results of the wave mathematical model of the present invention.

[0066] Figure 6 This is a diagram showing the calculation results of bed shear stress at typical moments during strong winds according to the present invention.

[0067] Figure 7 This is a prediction result diagram of seabed scouring and silting after strong winds according to the present invention. DETAILED DESCRIPTION

[0068] The present invention is described in detail below with reference to an example of Lianyungang and its adjacent sea areas.

[0069] Lianyungang is located in the southwest of Haizhou Bay in the Yellow Sea. Its north and east are open seas. Lianyungang District, Xuwei Port District and a 300,000-ton waterway are currently built in the sea area, and the waterway plane is arranged in a "human" shape. The tidal movement in Lianyungang and nearby waters is controlled by the standing wave system of the South Yellow Sea. It is a rotating flow in the open sea and transitions to a reciprocating flow in the nearshore area. The flow direction is basically consistent with the direction of the coastline; there is no large-scale runoff converging into the sea area, and the flow velocity is generally small. The influence of waves is significant, and the direction of common waves and strong waves are both biased to the NE. Lianyungang and nearby waters are typical muddy coasts, with fine suspended sand particle sizes and bottom sediment particle sizes. The mechanism of sediment movement is "sand lifted by waves and transported by tides."

[0070] Here, a dynamic numerical calculation method for predicting seabed scouring and silting according to the present invention is used, which includes the following steps:

[0071] Step 1, determine the dominant dynamic factors affecting the evolution of seabed scouring and silting: According to the water depth conditions, hydrodynamic conditions, sediment characteristics, etc. of the study area, determine the dominant dynamic factors affecting the evolution of seabed scouring and silting, which can generally be divided into tides, waves, and the combined effects of waves and currents.

[0072] The evolution of the seabed in Lianyungang and its surrounding waters is affected by the combined effects of waves and tides, so it is necessary to calculate the scouring and silting of the seabed caused by the combined effects of the two.

[0073] Step 2: Determine the critical starting shear stress and critical accumulation shear stress of sediment through sediment hydraulic property tests or literature review.

[0074] According to the hydraulic characteristics test results of Tianjin Water Transport Engineering Research Institute of the Ministry of Transport, the critical starting shear stress of sediment in Lianyungang channel under the combined action of waves and tides is 0.44~0.48N / m 2 In this example, the average value is 0.46N / m 2 According to Huang Jianwei's research results on the movement of coastal and estuarine viscous sediments and their application, the initial sand content of Lianyungang silt is 0.4-1.7 kg / m 3 When the critical sedimentation shear stress is 0.044~0.065N / m 2 Considering the high sand content in the Lianyungang Sea area on windy days (during the "Wipha" typhoon in September 2007, the maximum vertical average sand content observed by the bottom frame at 3m and 5m water depths in the Xuwei Sea area was 2.0kg / m 3 So the critical sedimentation shear stress in this example is 0.07N / m 2 .

[0075] Step 3: According to the dominant dynamic factors determined in step 1, a tidal mathematical model and (or) wave mathematical model is established, and the model is verified using measured data. After the verification results meet the requirements of the "Technical Specifications for Simulation Tests of Water Transport Engineering" (JTS / T 231-2021), numerical simulation of hydrodynamic elements is carried out to give the flow field and (or) wave field in the study area.

[0076] This example establishes a two-dimensional tidal mathematical model and wave mathematical model for Lianyungang and its nearby sea areas, and uses unstructured grids to divide the computational domain. For details on the computational domain and grid division, see Figure 3 The tidal mathematical model is verified using the hydrological test data from September 2023. After the verification results of the tide level, flow velocity and flow direction of the measuring point meet the accuracy requirements specified in the Technical Specifications for Simulation Tests of Water Transport Engineering (JTS / T 231-2021), the flow field simulation during the high tide period in this sea area is carried out. The flow field and flow velocity distribution at the time of rapid rise are shown in Figure 4 The wave mathematical model was verified using the wave observation data of the pedestal during the period when Typhoon Wipha affected the Lianyungang waters in September 2007. After the verification results of the wave height, wave period and wave direction of the measuring point met the accuracy requirements specified in the Technical Specifications for Simulation Tests of Water Transport Engineering (JTS / T 231-2021), the wave field simulation under the action of a NE-direction gale of level 10 in this sea area was carried out. The effective wave height distribution at the high water level is shown in Figure 2. Figure 5 .

[0077] Step 4: Substitute the hydrodynamic results calculated in step 3 into the shear stress calculation formula to calculate the bed shear stress field in the study area: Substitute the hydrodynamic elements calculated in step 3 into the corresponding bed shear stress calculation formulas (1) to (3) to calculate the seabed shear stress field in the study area. The wave friction coefficient f in formula (2) is w According to the muddy seabed in Lianyungang, combined with the wave characteristics analysis, the wave friction coefficient f w The value is 0.01;

[0078] Substitute the tidal velocity and water depth calculated by the tidal model in step 3 above, and the wave height, wave period, wavelength and water depth calculated by the wave model into equations (1) and (2) respectively to calculate the bed shear stress under the action of tidal currents and waves, and then use equation (3) to calculate the bed shear stress under the combined action of waves and tidal currents. The distribution of bed shear stress under the combined action of waves and tidal currents at typical moments (high water level moments) during strong winds is shown in Figure 6 .

[0079] Step 5, compare the critical starting shear stress and critical sedimentation shear stress determined in step 2 with the bed shear stress calculated in step 4 to make a judgment.

[0080] Compare the critical starting shear stress τ of Lianyungang sediment determined in step 2 e, critical sedimentation shear stress τ d The bed shear stress τ under the combined action of waves and tidal currents calculated in step 4 on a windy day b , the starting and silting conditions and scope of bed sediment. or It is judged that the bed sediment in this area has obviously started to move or silted up, and the seabed scouring or silting thickness calculation is carried out in step 6; if and It is judged that there will be no obvious erosion and siltation changes in the seabed in this area and the seabed is stable.

[0081] Step 6: Calculate the seabed scouring and silting amplitude using the scouring and silting calculation formula and analyze the seabed scouring and silting trend.

[0082] (1) If sediment deposition in a certain area is obvious, the sediment deposition thickness is calculated using formula (4), where the sediment deposition probability k is calculated using formula (5) and is taken as 0.7 (the sediment deposition probability k is calculated using the calculation formula).

[0083] (2) If the sediment in a certain area starts to move significantly, the scour thickness is calculated using equation (6) or equation (7), where the scour coefficient M of the bed sediment is taken as 0.36×10 -4 kg / m 2 ·s.

[0084] The prediction results of the seabed erosion and siltation amplitude after a force 10 NE gale in Lianyungang and nearby waters are shown in Figure 7 The calculation results of step 6 were reviewed according to the seabed scouring and silting trend determined in step 5. The scouring and silting calculation amplitude was basically consistent with the scouring and silting trend.

[0085] The above description of the embodiments is to facilitate the understanding and use of the present invention by those skilled in the art. It is obvious that those skilled in the art can easily make various modifications to these embodiments and apply the general principles described herein to other embodiments without creative work. Therefore, the present invention is not limited to the above embodiments, and improvements and modifications made by those skilled in the art based on the disclosure of the present invention without departing from the scope of the present invention should be within the protection scope of the present invention.

Claims

1. A dynamic numerical calculation method for predicting seabed scouring and silting, comprising the following steps: Step 1: Determine the dominant dynamic factors affecting the evolution of seabed scouring and silting: Determine the dominant dynamic factors affecting the evolution of seabed scouring and silting based on the water depth conditions, hydrodynamic conditions, and sediment characteristics of the study area; Step 2: Determine the critical starting shear stress and critical deposition shear stress of sediment through sediment hydraulic property tests or literature review; Step 3: According to the dominant dynamic factors determined in step 1, a mathematical model of tidal current and / or wave is established, and the model is verified using measured data. After the verification results meet the requirements of the Technical Specifications for Simulation Tests of Water Transport Engineering (JTS / T231-2021), a hydrodynamic numerical simulation is carried out to give the flow field and / or wave field in the study area; Step 4, substituting the hydrodynamic results calculated in step 3 into the shear stress calculation formula to calculate the bed shear stress in the study area; Step 5, comparing the critical starting shear stress and critical siltation shear stress determined in step 2 with the bed shear stress calculated in step 4, to determine the starting and silting conditions and range of bed surface silt; Step 6: Use the scouring and silting calculation formula to calculate the seabed scouring and silting amplitude and analyze the scouring and silting trend of the seabed surface.

2. The dynamic numerical calculation method for predicting seabed scouring and silting according to claim 1 is characterized by: The dominant dynamic factors described in step 1 are tidal currents, waves, and the combined effects of waves and currents.

3. The dynamic numerical calculation method for predicting seabed scouring and silting according to claim 1 is characterized by: In step 3, the dominant dynamic factors affecting the evolution of seabed scouring and silting are determined according to step 1, and mathematical models of tidal currents and / or waves are established respectively. After calibration and verification, simulation calculations of the aforementioned hydrodynamic elements are performed; (1) In areas where tidal currents are dominant, a mathematical model of water flow is established; (2) In areas where wave action is dominant, establish a wave mathematical model; (3) In areas where the interaction of waves and currents is dominant, it is necessary to establish mathematical models for water flow and waves respectively.

4. The dynamic numerical calculation method for predicting seabed scouring and silting according to claim 1 is characterized by: In step 4, the bed shear stress τ b Calculated using empirical formula.

5. The dynamic numerical calculation method for predicting seabed scouring and silting according to claim 1 is characterized in that: In step 4, only the tidal current acts, and the bed shear stress τ b The calculation is done using the following formula: Where: τ c is the bed shear stress under the action of water flow, ρ is the density of water, u *c is the friction velocity of the bed surface under the action of water flow, h is the water depth, Δ is the bed roughness height, and when the median particle size of the bed sediment is D 50 ≤0.5mm, Δ=1mm, when D 50 >0.5mm, Δ=2D 50 , is the vertical average flow velocity, calculated by the hydrodynamic mathematical model described in step 3.

6. The dynamic numerical calculation method for predicting seabed scouring and silting according to claim 1 is characterized in that: In step 4, only waves act, and the bed shear stress τ b The calculation is done using the following formula: Where: τ wm is the bed shear stress under wave action, f w is the wave friction coefficient, u wm is the velocity amplitude of the water particle at the bottom of the water under the action of waves, Where H is the wave height, T is the wave period, k is the wave number, k=2π / L, and L is the wavelength; H, T and L are calculated by the wave mathematical model in step 3.

7. The dynamic numerical calculation method for predicting seabed scouring and silting according to claim 1 is characterized in that: In step 4, the wave and current work together, and the bed shear stress τ b The calculation is done using the following formula: Where: It is the average value of bed shear stress within one wave cycle under the combined action of waves and currents.

8. The dynamic numerical calculation method for predicting seabed scouring and silting according to claim 6 is characterized by: f w The value range of f is 0.005~0.02; for muddy seabed, f w The value of is 0.

01.

9. The dynamic numerical calculation method for predicting seabed scouring and silting according to claim 1 is characterized by: In step 5, compare the bed shear stress τ calculated in step 4 b The critical starting shear stress τ of sediment determined in step 2 e , critical sedimentation shear stress τ d ; (1) If τ b >τ e , the bed sediment starts to move into the water body; (2) If τ b <τ d , the sediment in the water body falls and precipitates on the bed surface; (3) If τ d <τ b <τ c , there is no sediment exchange between the bed surface and the water body.

10. The dynamic numerical calculation method for predicting seabed scouring and silting according to claim 1 is characterized by: In step 6, according to the analysis results of step 5, or As a criterion for determining whether the seabed sediment has been significantly moved or deposited, the seabed scouring or deposition thickness calculation in step 6 is performed. and It can be judged that the seabed erosion and siltation in the study area is relatively balanced.

11. The dynamic numerical calculation method for predicting seabed scouring and silting according to claim 10 is characterized by: The thickness of bed scouring and silting is calculated using an empirical formula.

12. The dynamic numerical calculation method for predicting seabed scouring and silting according to claim 10 is characterized in that: For areas where the sediment is mainly in the form of suspended load, the bed scouring and silting thickness is calculated using the following formula: (1) When sedimentation occurs on the bed surface, the sedimentation thickness is calculated according to the following formula: Where: η d is the sedimentation thickness, Δt d is the sedimentation time, k is the probability of sediment deposition, C b is the bottom sediment content, ω is the sediment settling velocity, τ b is the bed shear stress, τ d is the critical sedimentation shear stress of sediment; (2) When scouring occurs on the bed surface, the scouring thickness is calculated according to the properties of the bed surface using the following formula: ① If the bulk density is uniformly distributed vertically on the bottom bed, ② If the bulk density of the natural dense bed gradually increases from top to bottom, Where: η e is the scour thickness, Δt d is the scouring time, M is the bed sediment scouring coefficient, which is related to the sediment properties, α and β are parameters that vary with the sediment structure and density, etc., τ e is the critical starting shear stress of sediment; (3) When τ d <τ b <τ c , the bed surface does not accumulate or scour, that is, Δη d =Δη e =0; 4 b =D d +D e 。 13. The dynamic numerical calculation method for predicting seabed scouring and silting according to claim 10 is characterized in that: For areas where sediment is mainly transported in the form of bed load, the following calculation formula is used for bed scouring thickness: (1) When sedimentation occurs on the bed surface, the sedimentation thickness is calculated according to the following formula: See you later. d =Δt d ·ωC b (8) (2) When scouring occurs on the bed surface, the scouring thickness is calculated according to the following formula: Where: s is the specific gravity of sediment, g is the acceleration of gravity, d50 is the median particle size of sediment, ψ, ψ c are the Shields number under hydrodynamic force and the critical starting Shields number of sediment, ν is the viscosity coefficient of water; If the bed surface sediment thickness Δη d ≤0.2m or sediment thickness Δη e ≤0.2m, the seabed in the study area is judged to be relatively stable. d >0.2m or Δη e >0.2m, it is judged that the seabed activity in the study area is relatively strong.

14. The dynamic numerical calculation method for predicting seabed scouring and silting according to claim 12 is characterized by: The probability of sediment deposition k in formula (4) is calculated using the following formula: is the probability integral function, which can be found in Table 1; ω is the sedimentation velocity, σ is the root mean square of the pulsating flow velocity, v is the average flow velocity of the cross section, g is the gravitational acceleration, and C is the Xie Cai coefficient of the study sea area.

15. The dynamic numerical calculation method for predicting seabed scouring and silting according to claim 14 is characterized by: From the table below; Probability integral function Value table 16. The application of the dynamic numerical calculation method for predicting seabed scouring and silting as claimed in claim 1 is characterized by: The methods are respectively used to predict seabed erosion and deposition under the action of tidal currents, wave action, and combined action of wave and current, as well as seabed erosion and deposition when sediment moves mainly in the form of suspended load or sediment moves mainly in the form of bed load.

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