Bidirectional fluid-solid coupling numerical simulation method for simulating rainfall erosion of cemented soil

Abstract

The invention provides a bidirectional fluid-solid coupling numerical simulation method for simulating rainfall erosion of cemented soil, and belongs to the technical field of fluid-solid coupling numerical analysis. The method comprises the following steps: calibrating microcosmic parameters of cemented soil; correcting the cemented soil parallel cementation model based on the relationship between the cementation radius coefficient and the rainfall by using the microcosmic parameters of the cemented soil; based on the cemented soil parallel cementation model, setting grids, fluid density and viscosity and fluid boundary conditions, and generating a cemented soil-rainfall coupling model; and solving the cemented soil-rainfall coupling model based on the Magnus force, the drag force and the buoyancy. According to the method, the cemented soil-rainfall coupling model is constructed by considering the influence of rainfall on the cemented radius coefficient in the cemented soil, so that the simulation accuracy is improved; and the model is solved through multiple angles of Magnus force, drag force and buoyancy, so that the accuracy of the simulation process is further improved.

Description

Technical Field

[0001] The invention relates to the technical field of fluid-solid coupling numerical analysis, and in particular to a bidirectional fluid-solid coupling numerical simulation method for simulating rainfall erosion of cemented soil. Background Art

[0002] For ancient city wall buildings, their rammed earth is often damaged by rainfall erosion. In order to find an effective protection plan, it is necessary to collect a large amount of data on the physical and mechanical changes of the rammed earth during rainfall erosion.

[0003] In the existing technology, rammed earth can be regarded as a kind of cemented soil; and then the erosion process data is collected through the fluid-solid coupling numerical analysis method; however, the existing method only considers the impact of rainfall on soil particles, and does not consider the impact of rainfall on the cementing material in cemented soil and the impact of rainfall on the rotation of soil particles; which affects the accuracy of numerical simulation.

[0004] Therefore, a bidirectional fluid-solid coupling numerical simulation method for simulating rainfall erosion of cemented soil is needed, which takes into account the influence of rainfall on cement. Summary of the invention

[0005] In view of this, the present invention provides a bidirectional fluid-solid coupling numerical simulation method for simulating rainfall erosion of cemented soil, and constructs a cemented soil-rainfall coupling model considering the influence of rainfall on the cementation radius coefficient and thickness in cemented soil to improve the simulation accuracy.

[0006] To this end, the present invention provides the following technical solutions:

[0007] A bidirectional fluid-solid coupling numerical simulation method for simulating rainfall erosion of cemented soil, comprising:

[0008] Calibrate the microscopic parameters of cemented soil;

[0009] The parallel bonding model of cemented soil is modified based on the relationship between bonding radius coefficient and rainfall using microscopic parameters of cemented soil.

[0010] The cemented soil model is prepared based on the modified parallel cemented soil model; the grid, fluid density and viscosity, and fluid boundary conditions are set to generate a cemented soil-rainfall coupling model;

[0011] The constraints of the cemented soil-rainfall coupling model are constructed based on Magnus force, drag force and buoyancy.

[0012] Furthermore, the calibration of microscopic parameters of cemented soil includes:

[0013] The range of microscopic parameters of original cemented soil is determined by scanning electron microscope;

[0014] And through triaxial test, the stress-strain curve of original cemented soil is obtained;

[0015] Based on the value range of microscopic parameters of original cemented soil, prepare cemented soil samples with different microscopic parameters; and stress-strain curves of cemented soil samples;

[0016] By comparing the stress-strain curves of cemented soil samples with those of original cemented soil, a group of microscopic parameters of cemented soil samples were calibrated.

[0017] Furthermore, the microscopic parameters of the cemented soil include:

[0018] Some parameters of particles: particle normal stiffness, tangential stiffness, density, modulus, damping ratio, friction coefficient and element composition of particles;

[0019] Bonding parameters: bond normal stiffness, tangential stiffness, modulus, Poisson's ratio, damping ratio, bond distribution form, bond shape, and bond radius coefficient.

[0020] Furthermore, the parallel bonding model correction part of the cemented soil includes:

[0021] η=0.993-0.006α

[0022] Where η is the cementation radius coefficient and α is the rainfall.

[0023] Furthermore, the fluid boundary conditions include:

[0024] The bottom and sides of the cemented soil-rainfall coupling model are impermeable;

[0025] Rainfall in the upper part of the cemented soil-rainfall coupled model.

[0026] Furthermore, the cemented soil-rainfall coupling model includes:

[0027]

[0028] In the formula, m i is the mass of the ith particle, is the translational velocity vector of the ith particle; is the contact force generated by the jth particle or wall on the i-th particle; is the force exerted by the fluid-particle interaction on the ith particle, including pressure difference force, drag force and Magnus force; is the gravity of the ith particle; I i is the moment of inertia of the ith particle, is the angular velocity of the ith particle, is the contact torque generated by the jth particle or wall on the i-th particle;

[0029] Furthermore, the constraint conditions of the cemented soil-rainfall coupling model based on the Magnus force, the drag force and the buoyancy force include:

[0030] The continuity equation for the fluid within a mesh cell is:

[0031]

[0032] The momentum equation for the fluid within a grid cell is:

[0033]

[0034] Where n is the porosity of the grid unit, ρ is the fluid density, is the average velocity of the grid unit; μ is the dynamic viscosity of the fluid, p is the fluid pressure; f is the particle-fluid interaction force within the grid unit, including buoyancy, drag force and Magnus force; g is the gravitational acceleration.

[0035] Furthermore, the drag force expression is:

[0036]

[0037] Where, d p is the diameter of the particle, C d is the particle-fluid drag coefficient, and χ is the correction factor considering the local porosity.

[0038] Furthermore, the buoyancy expression is:

[0039]

[0040] Furthermore, the Magnus force expression is:

[0041]

[0042] Where C is the resistance coefficient, is the line speed.

[0043] Advantages and positive effects of the present invention:

[0044] The present invention calibrates the particle parameters and cementation parameters in cemented soil by combining electron microscope scanning with stress-strain curve comparison, thereby improving the accuracy of model construction; considers the influence of rainfall on the cementation radius coefficient in cemented soil, and constructs a parallel cementation model including the cementation radius coefficient-rainfall relationship; improves the accuracy of simulating rainfall erosion of cemented soil; and introduces buoyancy, drag force and Magnus force into the fluid-particle interaction force, thereby further improving the accuracy of simulating rainfall erosion of cemented soil. BRIEF DESCRIPTION OF THE DRAWINGS

[0045] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative labor.

[0046] Figure 1 This is a schematic diagram of the principle of the CFD-DEM coupling model in an embodiment of the present invention;

[0047] Figure 2 This is a graph showing the relationship between the bonding radius and rainfall in an embodiment of the present invention. DETAILED DESCRIPTION

[0048] In order to enable those skilled in the art to better understand the scheme of the present invention, the technical scheme in the embodiments of the present invention will be clearly and completely described 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, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work should fall within the scope of protection of the present invention.

[0049] It should be noted that the terms "first", "second", etc. in the specification and claims of the present invention and the above-mentioned drawings are used to distinguish similar objects, and are not necessarily used to describe a specific order or sequence. It should be understood that the data used in this way can be interchanged where appropriate, so that the embodiments of the present invention described herein can be implemented in an order other than those illustrated or described herein. In addition, the terms "including" and "having" and any variations thereof are intended to cover non-exclusive inclusions, for example, a process, method, system, product or device that includes a series of steps or units is not necessarily limited to those steps or units that are clearly listed, but may include other steps or units that are not clearly listed or inherent to these processes, methods, products or devices.

[0050] The invention provides a bidirectional fluid-solid coupling numerical simulation method for simulating rainfall erosion of cemented soil. The method collects particle parameters and cementation parameters in the cemented soil by combining electron microscope scanning and stress-strain curve comparison. The method also considers the influence of rainfall on the cementation radius coefficient in the cemented soil, and constructs a parallel cementation model including the cementation radius coefficient-rainfall relationship. The method also constructs a cemented soil-rainfall coupling model in combination with fluid parameters. The method introduces buoyancy, drag force and Magnus force into the fluid-particle interaction force, and improves the accuracy of simulating rainfall erosion of cemented soil.

[0051] Combination Figure 1 The method of the present invention is further described:

[0052] Step 1: Obtain the original cemented soil, carry out triaxial shear tests under three confining pressure conditions (50 kPa, 100 kPa, 200 kPa), and obtain the stress-strain curves of the original cemented soil under the three confining pressure conditions; carry out electron microscope scanning tests, conduct microscopic observation of the original cemented soil, and obtain the value range of the microscopic parameters of the original cemented soil.

[0053] Step 2: In the DEM module, according to the range of micro-parameter values ​​obtained in step 1, a sample of cemented soil is prepared, and a triaxial shear test under three confining pressure conditions (50 kPa, 100 kPa, and 200 kPa) is simulated. By changing the micro-parameters, the stress-strain curves of the simulated cemented soil under three confining pressure conditions when the micro-parameter values ​​are different are obtained;

[0054] Step 3, comparing the stress-strain curves of the original cemented soil and the simulated cemented soil under different micro-parameter conditions at different confining pressures, and calibrating a set of reasonable micro-parameters of the cemented soil;

[0055] Step 4: Carry out erosion tests on cemented soil under different rainfall conditions to obtain the variation law of cementation radius coefficient with rainfall; and implant the variation law of cementation radius coefficient with rainfall into the DEM micro-model;

[0056] In this embodiment, some experimental results of the change of the bonding radius coefficient with rainfall are shown in Table 1; and the relationship diagram is drawn as shown in Figure 2 shown.

[0057] Table 1

[0058]

[0059] Therefore, in this embodiment, the relationship between the bonding radius coefficient and the rainfall is linear, which can be expressed as:

[0060] χ=0.993-0.006α

[0061] Where χ is the cementation radius coefficient and α is the rainfall.

[0062] Step 5: The relationship between the bonding radius coefficient and rainfall is implanted into the DEM micro-model. Combined with the micro-parameters obtained in steps 3 and 4, the DEM model of the cemented soil is established, and the initial stress field is set.

[0063] Step 6: Develop a CFD-DEM coupling solver based on C++ language, which takes into account the effects of drag force, Magnus force, pressure difference force, and gravity;

[0064] Step 7, read the boundary of the DEM model in the CFD module, divide the grid, set the fluid parameters, boundary conditions, and time step, and select the coupling solver established in step 6 to establish a CFD-DEM coupling model, wherein the bottom and sides of the coupling model are set with impermeable boundary conditions, and the upper part is set with rainfall boundary conditions;

[0065] Step 8, running the coupling model to obtain numerical simulation results;

[0066] Step 9, change the model parameters to obtain rainfall erosion results under different conditions.

[0067] In this embodiment, the parameters for simulating cemented soil in step 3 include: particle part: particle normal and tangential stiffness, density, modulus, damping ratio, friction coefficient;

[0068] Bonding part: bond normal and tangential stiffness, modulus, Poisson's ratio, and damping ratio.

[0069] The micro-contact model selected for the cemented soil in step 5 of this embodiment is a modified parallel cementation model, which takes into account the influence of rainfall conditions on the cementation radius coefficient.

[0070] The correction part includes: η = 0.993-0.006α;

[0071] In this embodiment, step 7, CFD-DEM coupling model, includes:

[0072] The equation of motion for soil particles is:

[0073]

[0074] In the formula, m i is the mass of the ith particle, is the translational velocity vector of the ith particle; is the contact force generated by the jth particle or wall on the i-th particle; is the force exerted by the fluid-particle interaction on the i-th particle, which includes the pressure difference force, drag force and Magnus force; is the gravity of the ith particle; I i is the moment of inertia of the ith particle, is the angular velocity of the ith particle, is the contact torque generated by the jth particle or wall on the ith particle.

[0075] The continuity equation for the fluid within a mesh cell is:

[0076]

[0077] Where n is the porosity of the grid unit, ρ is the fluid density, is the average velocity of the grid cells;

[0078] The momentum equation for the fluid within a grid cell is:

[0079]

[0080] Where μ is the dynamic viscosity of the fluid, p is the fluid pressure, f is the particle-fluid interaction force within the grid unit, including buoyancy, drag force and Magnus force, and g is the gravitational acceleration.

[0081] In this embodiment, the solver takes into account the effects of drag force, Magnus force, pressure difference force, and gravity; the porosity is calculated as follows:

[0082]

[0083] Where V v is the volume of the pores in the grid unit, V t is the total volume of the grid cells.

[0084] The drag force is calculated as:

[0085]

[0086] Where, d p is the diameter of the particle, C d is the particle-fluid drag coefficient, and χ is the correction factor considering the local porosity.

[0087] The buoyancy is calculated as:

[0088]

[0089] The calculation method of Magnus force is:

[0090]

[0091] Where C is the resistance coefficient, is the line speed.

[0092] The fluid-solid coupling (CFD-DEM) numerical simulation method for simulating rainfall erosion of cemented soil provided by the present invention simulates the destruction process of cemented soil induced by rainfall. The present invention takes into account the erosion of soils with different cementation strengths under different rainfall intensities, and is suitable for the analysis and prediction of soils damaged by rainfall, as well as soil protection engineering, providing a basis for the protection and management of such soils.

[0093] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A bidirectional fluid-solid coupling numerical simulation method for simulating rainfall erosion of cemented soil, characterized in that: include: Calibrate the microscopic parameters of cemented soil; The parallel bonding model of cemented soil is modified based on the relationship between bonding radius coefficient and rainfall using microscopic parameters of cemented soil. Prepare cemented soil model based on the modified parallel cemented soil model; The grid, fluid density and viscosity, and fluid boundary conditions are set to generate a cemented soil-rainfall coupling model; The constraints of the cemented soil-rainfall coupling model are constructed based on Magnus force, drag force and buoyancy.

2. A bidirectional fluid-solid coupling numerical simulation method for simulating rainfall erosion of cemented soil according to claim 1, characterized in that: The microscopic parameters of the calibrated cemented soil include: The range of microscopic parameters of original cemented soil is determined by scanning electron microscope; And through triaxial test, the stress-strain curve of original cemented soil is obtained; Based on the value range of microscopic parameters of original cemented soil, prepare cemented soil samples with different microscopic parameters; and stress-strain curves of cemented soil samples; By comparing the stress-strain curves of cemented soil samples with those of original cemented soil, a group of microscopic parameters of cemented soil samples were calibrated.

3. A bidirectional fluid-solid coupling numerical simulation method for simulating rainfall erosion of cemented soil according to claim 2, characterized in that: The microscopic parameters of the cemented soil include: Some parameters of particles: particle normal stiffness, tangential stiffness, density, modulus, damping ratio, friction coefficient and element composition of particles; Bonding parameters: bond normal stiffness, tangential stiffness, modulus, Poisson's ratio, damping ratio, bond distribution form, bond shape, and bond radius coefficient.

4. According to claim 1, a bidirectional fluid-solid coupling numerical simulation method for simulating rainfall erosion of cemented soil is characterized by: The parallel bonding model correction part of the cemented soil includes: η=0.993-0.006α Where η is the cementation radius coefficient and α is the rainfall.

5. The bidirectional fluid-solid coupling numerical simulation method for simulating rainfall erosion of cemented soil according to claim 1, characterized in that: The fluid boundary conditions include: The bottom and sides of the cemented soil-rainfall coupling model are impermeable; Rainfall in the upper part of the cemented soil-rainfall coupled model.

6. The bidirectional fluid-solid coupling numerical simulation method for simulating rainfall erosion of cemented soil according to claim 1, characterized in that: The cemented soil-rainfall coupling model includes: In the formula, m i is the mass of the ith particle, is the translational velocity vector of the ith particle; is the contact force generated by the jth particle or wall on the i-th particle; is the force exerted by the fluid-particle interaction on the ith particle, including pressure difference force, drag force and Magnus force; is the gravity of the ith particle; I i is the moment of inertia of the ith particle, is the angular velocity of the ith particle, is the contact torque generated by the jth particle or wall on the ith particle.

7. The bidirectional fluid-solid coupling numerical simulation method for simulating rainfall erosion of cemented soil according to claim 1, characterized in that: The constraints of the cemented soil-rainfall coupling model based on Magnus force, drag force and buoyancy force include: The continuity equation for the fluid within a mesh cell is: The momentum equation for the fluid within a grid cell is: Where n is the porosity of the grid unit, ρ is the fluid density, is the average velocity of the grid unit; μ is the dynamic viscosity of the fluid, p is the fluid pressure; f is the particle-fluid interaction force within the grid unit, including buoyancy, drag force and Magnus force; g is the gravitational acceleration.

8. A bidirectional fluid-solid coupling numerical simulation method for simulating rainfall erosion of cemented soil according to claim 7, characterized in that: The drag force expression is: Where, d p is the diameter of the particle, C d is the particle-fluid drag coefficient, and χ is the correction factor considering the local porosity.

9. A bidirectional fluid-solid coupling numerical simulation method for simulating rainfall erosion of cemented soil according to claim 7, characterized in that: The buoyancy expression is:

10. The bidirectional fluid-solid coupling numerical simulation method for simulating rainfall erosion of cemented soil according to claim 7, characterized in that: The Magnus force expression is: Where C is the resistance coefficient, is the line speed.

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