Numerical simulation method of calibration and time transformation of seepage parameters considering cross-scale grid characteristics
By calibrating the fluid bulk modulus through laboratory experiments and small-scale models, the correspondence between the seepage calculation step and the actual time was established, which solved the problem of unclear seepage time in engineering-scale coal body models and realized the laboratory verification of seepage parameters and the physical interpretation of numerical simulation.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- INNER MONGOLIA RESEARCH INSTITUTE CHINA UNIVERSITY OF MINING AND TECHNOLOGY (BEIJING)
- Filing Date
- 2026-05-07
- Publication Date
- 2026-07-24
AI Technical Summary
In existing numerical simulation methods for seepage, the seepage calculation results of engineering-scale coal body models lack a clear meaning of seepage time, making it difficult to correspond with actual engineering time. Furthermore, the selection of seepage parameters depends on experience and lacks verification by laboratory tests.
Coal sample seepage data were obtained through laboratory water immersion tests. A small-scale model was established, the fluid bulk modulus was calibrated, and the correspondence between the seepage calculation step and the actual time was established through cross-scale grid features. Numerical simulation was performed using FLAC3D software to achieve parameter calibration and time conversion.
It improves the physical interpretability of numerical simulation results, realizes laboratory test basis for seepage parameters, solves the problem of seepage parameters relying on experience, and enhances the guiding role of numerical simulation in practical engineering.
Smart Images
Figure CN122452149A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the fields of mining engineering, geotechnical engineering, and numerical simulation of coal and rock seepage, specifically to a method for calibrating and converting seepage parameters and time in numerical simulation that considers cross-scale grid characteristics. Background Technology
[0002] Numerical simulation of seepage and fluid-structure interaction numerical simulation are important techniques in mining engineering, geotechnical engineering, and groundwater seepage research. They have been widely applied in fields such as analyzing the long-term water immersion process of coal pillars, evaluating the stability of underground reservoir dams, studying the seepage instability of water-resistant coal pillars, and predicting the hydraulic response of coal and rock masses under mining influence. By establishing engineering-scale coal body models corresponding to actual engineering projects, it is possible to analyze the water migration range, seepage evolution process, and structural stability of coal and rock masses under different seepage conditions. Therefore, they are of great significance in safe coal mining and water hazard prevention.
[0003] However, in existing numerical simulation methods for seepage, the seepage calculation results of engineering-scale coal body models are usually given in the form of seepage calculation steps. These calculation steps are merely discrete iterations in the numerical solution process, lacking a clear meaning of the actual seepage time. It is difficult to determine how long the actual seepage duration corresponds to the current numerical simulation results in actual engineering (for example, if the actual seepage time of the coal body in an engineering project is 5 days, it is unclear in the numerical simulation how many steps the engineering-scale coal body model has calculated to correspond to 5 days of actual coal seepage). Furthermore, in engineering-scale coal body models, the coal body size is large, the seepage path is long, and the calculation scale is high. In actual engineering projects, the coal body size is enormous, making it difficult to comprehensively measure its seepage parameters. Therefore, it is often difficult to directly establish the correspondence between engineering-scale coal body seepage time and numerical model seepage calculation steps through engineering measurements, thus limiting the guiding role of numerical simulation results in time history analysis and state determination in actual engineering projects. In addition, the selection of seepage parameters in existing studies largely relies on experience, analogy, or literature values, lacking quantitative calibration and verification methods based on laboratory experimental processes. Summary of the Invention
[0004] To address the aforementioned technical problems, this invention proposes a numerical simulation method for seepage parameter calibration and time transformation that considers cross-scale grid characteristics, comprising the following steps:
[0005] S1: Obtain coal samples for laboratory testing, conduct water immersion tests, and record the curve of overall coal saturation as a function of seepage time;
[0006] S2: Establish a small-scale coal sample model at a 1:1 scale with the laboratory coal sample, and apply seepage boundary conditions consistent with those of the laboratory coal sample water immersion test; set the fluid bulk modulus as the only parameter to be calibrated; compare the curve of overall coal sample saturation versus seepage time obtained based on the small-scale coal sample model with the curve of overall coal sample saturation versus seepage time obtained from the laboratory coal sample water immersion test, and continuously adjust the fluid bulk modulus to make the two curves match as closely as possible;
[0007] S3: The actual seepage time of the laboratory coal sample to reach the target total saturation is t. sf The seepage calculation steps for a small-scale coal sample model to achieve the same overall target saturation are f. step,sf This allows for the characteristic seepage time t of the small-scale coal sample model. c,s satisfy: ;
[0008] S4: Seepage characteristic length L based on engineering-scale coal body model c,e , seepage characteristic time t c,e The characteristic length L of seepage in a small-scale coal sample model c,s , seepage characteristic time t c,s Based on the relationship, the seepage calculation steps for the engineering-scale coal body model can be obtained. step,e The seepage time t of coal in actual engineering e Relationship satisfies:
[0009] .
[0010] Preferably, in step S1, a standard cylindrical coal sample with a diameter of 50 mm and a height of 100 mm is used.
[0011] Preferably, in step S1, the curve of saturation change with seepage time is plotted with seepage time on the horizontal axis and saturation on the vertical axis.
[0012] Preferably, in step S2, a small-scale coal sample model is established using FLAC3D numerical simulation software.
[0013] Preferably, in step S2, steady-state seepage analysis conditions are selected; and predetermined constant parameters are assigned to the small-scale coal sample model, including the tensile strength and density of the fluid and the permeability coefficient K of the material. p And porosity n.
[0014] Preferably, in step S2, the number of saturated units in the small-scale coal sample model is monitored in real time, and the overall saturation is calculated based on the ratio of the number of saturated units to the total number of units.
[0015] Preferably, in step S3, the seepage characteristic time t of the small-scale coal sample model c,sThat is, the actual coal seepage time corresponding to each calculation step of the small-scale coal sample model.
[0016] Preferably, in step S3, the seepage characteristic length L of the small-scale coal sample model c,s Diffusion rate c and seepage characteristic time t c,s satisfy: Wherein, the diffusivity c is a constant.
[0017] Preferably, in step S4, the seepage characteristic length L of the engineering-scale coal body model c,e Diffusion rate c and seepage characteristic time t c,e satisfy: Based on the fact that the diffusivity c is the same in both the engineering-scale coal body model and the small-scale coal sample model, a cross-scale seepage characteristic time conversion relationship is established: .
[0018] Preferably, step S4 further includes: establishing an engineering-scale coal body model at a 1:1 scale with the actual project, setting seepage conditions, material parameters, and fluid parameters corresponding to the actual project, and performing numerical simulation calculations; based on the required seepage time t of the coal body in the actual project... e Determine the computational steps f required for the engineering-scale coal body model step,e And according to the calculation step f step,e Calculations are performed, and the water seepage situation of the coal body under actual engineering conditions is obtained based on the numerical calculation results.
[0019] Preferably, in step S4, an engineering-scale coal body model is established using FLAC3D numerical simulation software.
[0020] The beneficial effects of this invention are as follows: 1. This invention first transforms the coal permeability characteristics, which are difficult to measure in actual engineering, into laboratory conditions. Based on coal samples taken from actual engineering projects, water immersion tests are conducted on the coal samples in the laboratory. Then, a small-scale coal sample model with the same size as the coal sample is established. Using laboratory coal sample saturation and small-scale coal sample saturation as constraints, a clear correspondence is established between the laboratory coal sample seepage time and the seepage calculation steps of the small-scale coal sample model in numerical simulation. This solves the problem that in engineering-scale coal models, the coal body size is large, the seepage path is long, and the calculation scale is high, while in actual engineering projects, the coal body size is enormous, making it difficult to comprehensively measure its seepage parameters. Subsequently, a conversion relationship between seepage characteristic length and cross-scale seepage characteristic time is introduced to establish a link between the small-scale coal sample model and the engineering-scale coal body model. Through the bridging effect of the small-scale coal sample model, a clear correspondence is established between the laboratory coal sample seepage time and the seepage calculation steps of the engineering-scale coal body model in numerical simulation. Therefore, the actual seepage time can be calculated back from the existing calculation step results of the engineering-scale model, improving the physical interpretability of the numerical simulation results.
[0021] 2. Based on laboratory coal sample water immersion tests, this invention establishes a small-scale coal sample model with the same size as the laboratory coal sample and uses the overall saturation process of the laboratory coal sample as a constraint to invert and calibrate the key seepage parameters in the numerical model. This makes the selection of parameters in the small-scale model have clear experimental basis, which changes the problem in the prior art that seepage parameters mainly rely on empirical values and lack laboratory test verification. Attached Figure Description
[0022] Figure 1 This is a flowchart illustrating the overall process of numerical simulation seepage parameter calibration and time conversion method of the present invention.
[0023] Figure 2 This is a schematic diagram showing the correspondence between the actual seepage time of the laboratory coal sample and the seepage calculation steps of the small-scale model in this invention. Detailed Implementation
[0024] The specific calculation method of the present invention will be described in detail below with reference to the accompanying drawings.
[0025] This invention proposes a numerical simulation method for calibrating seepage parameters and time transformation that considers cross-scale grid characteristics, such as... Figure 1-2 As shown, it includes the following steps:
[0026] S1: Obtain coal samples for laboratory testing in the actual engineering area, conduct water immersion tests on the coal samples in the laboratory, and obtain laboratory coal sample water immersion test data. The laboratory coal sample water immersion test data includes at least the geometric dimensions of the coal sample and the curve of the overall saturation of the coal sample changing with seepage time (with seepage time as the horizontal axis and saturation as the vertical axis). In this embodiment, a standard cylindrical coal sample with a diameter of 50 mm and a height of 100 mm is used.
[0027] S2: Calibration of seepage parameters in small-scale coal samples; including:
[0028] S21: In FLAC3D numerical simulation software, establish a small-scale coal sample model at a 1:1 scale with the laboratory coal sample, and apply seepage boundary conditions consistent with those of the laboratory coal sample water immersion test.
[0029] S22: Select steady-state seepage analysis conditions; assign predetermined constant parameters to the small-scale coal sample model, including the tensile strength and density of the fluid (water in this example), and the permeability coefficient K of the material. p And porosity n (in this example, coal); fluid bulk modulus K f Set as the only parameter to be calibrated; under steady-state seepage analysis conditions, the compressibility of material particles does not need to be considered, only the seepage process of fluid in the material is considered.
[0030] S23: Assign initial fluid bulk modulus K to the small-scale coal sample model fThe seepage calculation was performed. During the seepage calculation, the FISH program was used to monitor the number of saturated units in the small-scale coal sample model in real time, and the overall saturation was calculated based on the ratio of the number of saturated units to the total number of units.
[0031] S24: Compare the overall saturation curve of the coal sample as a function of seepage time obtained based on the small-scale coal sample model with the overall saturation curve of the coal sample as a function of seepage time obtained from laboratory coal sample water immersion tests, and continuously adjust the fluid bulk modulus K. f The two curves should be matched as closely as possible. The curve of the overall saturation of the coal sample with the seepage time includes a rapid growth stage, a slow growth stage, and a stable saturation stage. The consistency of the change characteristics in each stage is used as the basis for judging the match.
[0032] By adjusting the fluid bulk modulus K f The basis for this inversion is that when the porosity n of coal is small, the true fluid bulk modulus K of water is... f The drainage bulk modulus, being much larger than that of coal—a porous medium framework—leads to a significant decrease in the convergence speed of numerical calculations. Simultaneously, dissolved air bubbles in the pore water reduce the equivalent fluid bulk modulus. Therefore, adjusting the fluid bulk modulus K... f It can effectively reflect the actual seepage saturation process.
[0033] S3: Establish the correspondence between the actual seepage time of laboratory coal samples and the seepage calculation steps of small-scale coal sample models, including:
[0034] S31: The actual seepage time of the laboratory coal sample to reach the target total saturation is t. sf In this embodiment, the saturation is complete, approximately 3 days; the seepage calculation steps for a small-scale coal sample model to achieve the same overall target saturation are f. step,sf In this embodiment, the flow is fully saturated, approximately 22590 steps. Therefore, the seepage characteristic time t of the small-scale coal sample model is... c,s (The actual coal seepage time corresponding to each calculation step in the small-scale coal sample model) satisfies:
[0035]
[0036] S32: Characteristic seepage length L of a small-scale coal sample model c,s Diffusion rate c and seepage characteristic time t c,s satisfy:
[0037]
[0038] That is, the characteristic time t of seepage in a small-scale coal sample model c,s Its seepage characteristic length L c,s The diffusivity is directly proportional to the square of the diffusivity; where the diffusivity c is a constant, determined by the permeability coefficient K.p Calculation of the ratio to the water storage coefficient S:
[0039]
[0040] The method for determining the water storage coefficient S is as follows: based on the fluid bulk modulus K. f The Biot modulus M is calculated from the porosity n, and its expression is:
[0041]
[0042] Under saturated seepage mode, the storage coefficient S is calculated based on the Biot modulus M, and its expression is:
[0043]
[0044] In the unsaturated seepage mode, the storage coefficient S is calculated based on the Biot modulus M, and its expression is as follows:
[0045]
[0046] In a fully fluid-structure interaction problem, the storage coefficient S is calculated using the following formula:
[0047]
[0048] In the formula, α is the Biot coefficient, and ρ w Let L be the fluid density, g be the acceleration due to gravity, and L be the acceleration due to gravity. p Where is the characteristic seepage height, K is the bulk modulus of coal, and G is the shear modulus of coal.
[0049] S4: Perform seepage time conversion from small-scale coal sample models to engineering-scale coal body models; including:
[0050] Small-scale coal sample models are small in size, making it easy to calculate to their saturation state using numerical models. However, engineering-scale coal body models are large in scale, making it difficult to calculate to their saturation state. Furthermore, coal bodies in actual engineering projects generally do not reach saturation. Therefore, engineering-scale coal body models do not need to be calculated to saturation or near-saturation. However, it is necessary to correlate the seepage calculation steps of the engineering-scale coal body model with the seepage time of coal bodies in actual engineering projects. This allows for the calculation of the characteristics of coal bodies in actual engineering projects at any seepage time based on the engineering-scale coal body model.
[0051] S41: Seepage characteristic length L of engineering-scale coal body model c,e Diffusion rate c and seepage characteristic time t c,e (The actual seepage time corresponding to each calculation step in the engineering-scale coal body model) satisfies:
[0052]
[0053] S42: Based on the fact that the diffusivity c is the same in engineering-scale coal body models and small-scale coal sample models, establish the time conversion relationship of cross-scale seepage characteristics:
[0054]
[0055] S43: Based on the formulas in step S31 and step S42, the seepage calculation step f for the engineering-scale coal body model can be obtained. step,e The seepage time t of coal in actual engineering e Relationship satisfies:
[0056]
[0057] S44: In FLAC3D numerical simulation software, establish an engineering-scale coal body model at a 1:1 scale with the actual project, set the seepage conditions, material parameters (coal body in this example), and fluid parameters (water in this example) corresponding to the actual project, and perform numerical simulation calculations; determine the required seepage time t of the coal body in the actual project. e The calculation steps required for the engineering-scale coal body model are determined according to the formula in step S43. step,e And according to the calculation step f step,e Calculations are performed to determine the water seepage situation in the coal seam under actual engineering conditions.
[0058] This invention is not limited to the above embodiments. Any modifications or equivalent substitutions made within the spirit and principles of this invention should be included within the scope of protection of this invention.
Claims
1. A numerical simulation method for calibrating seepage parameters and time transformation considering cross-scale grid characteristics, characterized in that, include: S1: Obtain coal samples for laboratory testing, conduct water immersion tests, and record the curve of overall coal saturation as a function of seepage time; S2: Establish a small-scale coal sample model at a 1:1 scale with the laboratory coal sample, and apply seepage boundary conditions consistent with those of the laboratory coal sample water immersion test; set the fluid bulk modulus as the only parameter to be calibrated; compare the curve of overall coal sample saturation versus seepage time obtained based on the small-scale coal sample model with the curve of overall coal sample saturation versus seepage time obtained from the laboratory coal sample water immersion test, and continuously adjust the fluid bulk modulus to make the two curves match as closely as possible; S3: The actual seepage time of the laboratory coal sample to reach the target total saturation is t. sf The seepage calculation steps for a small-scale coal sample model to achieve the same overall target saturation are f. step,sf This allows for the characteristic seepage time t of the small-scale coal sample model. c,s satisfy: ; S4: Seepage characteristic length L based on engineering-scale coal body model c,e , seepage characteristic time t c,e The characteristic length L of seepage in a small-scale coal sample model c,s , seepage characteristic time t c,s Based on the relationship, the seepage calculation steps for the engineering-scale coal body model can be obtained. step,e The seepage time t of coal in actual engineering e Relationship satisfies: 。 2. The numerical simulation seepage parameter calibration and time transformation method considering cross-scale grid characteristics according to claim 1, characterized in that, In step S1, a standard cylindrical coal sample with a diameter of 50 mm and a height of 100 mm is used.
3. The numerical simulation seepage parameter calibration and time transformation method considering cross-scale grid characteristics according to claim 1, characterized in that, In step S1, the curve of saturation change with seepage time is plotted with seepage time on the horizontal axis and saturation on the vertical axis.
4. The numerical simulation seepage parameter calibration and time conversion method considering cross-scale grid characteristics according to claim 1, characterized in that, In step S2, steady-state seepage analysis conditions are selected; predetermined constant parameters are assigned to the small-scale coal sample model, including the tensile strength and density of the fluid, and the permeability coefficient K of the material. p And porosity n.
5. The numerical simulation seepage parameter calibration and time transformation method considering cross-scale grid characteristics according to claim 1, characterized in that, In step S2, the number of saturated units in the small-scale coal sample model is monitored in real time, and the overall saturation is calculated based on the ratio of the number of saturated units to the total number of units.
6. The numerical simulation seepage parameter calibration and time transformation method considering cross-scale grid characteristics according to claim 4, characterized in that, In step S3, the seepage characteristic time t of the small-scale coal sample model c,s That is, the actual coal seepage time corresponding to each calculation step of the small-scale coal sample model.
7. The numerical simulation seepage parameter calibration and time transformation method considering cross-scale grid characteristics according to claim 6, characterized in that, In step S3, the seepage characteristic length L of the small-scale coal sample model c,s Diffusion rate c and seepage characteristic time t c,s satisfy: Wherein, the diffusivity c is a constant.
8. The numerical simulation seepage parameter calibration and time transformation method considering cross-scale grid characteristics according to claim 7, characterized in that, In step S4, the seepage characteristic length L of the engineering-scale coal body model c,e Diffusion rate c and seepage characteristic time t c,e satisfy: Based on the fact that the diffusivity c is the same in both the engineering-scale coal body model and the small-scale coal sample model, a cross-scale seepage characteristic time conversion relationship is established: .
9. The numerical simulation seepage parameter calibration and time transformation method considering cross-scale grid characteristics according to claim 8, characterized in that, Step S4 also includes establishing an engineering-scale coal body model at a 1:1 scale with the actual project, setting seepage conditions, material parameters, and fluid parameters corresponding to the actual project, and performing numerical simulation calculations; based on the required seepage time t of the coal body in the actual project... e Determine the computational steps f required for the engineering-scale coal body model step,e And according to the calculation step f step,e Calculations are performed, and the water seepage situation of the coal body under actual engineering conditions is obtained based on the numerical calculation results.
10. The numerical simulation seepage parameter calibration and time transformation method considering cross-scale grid characteristics according to any one of claims 1-9, characterized in that, In step S2, a small-scale coal sample model is established using FLAC3D numerical simulation software; in step S4, an engineering-scale coal body model is established using FLAC3D numerical simulation software.