Mechanical parameter calibration method for discrete element model of hydrate-containing sediment

Abstract

The invention belongs to the field of mechanical research of natural gas hydrate sediments, and provides a hydrate-containing sediment discrete element model mechanical parameter calibration method, which comprises the following steps: S1, sample preparation and triaxial shear test; s2, respectively constructing discrete element models for the four sediment samples in the step S1; s3, performing staged calibration on mechanical parameters of the sediments with different components; and S4, outputting a discrete element model result. According to the method, four samples are prepared aiming at the muddy silt hydrate-containing sediments, different contact models are adopted according to the mechanical characteristics of different components of the samples, the model complexity is gradually increased from a single component to multiple components through staged calibration, it is ensured that the mechanical behavior of each component can accurately reflect actual experimental data, and the experimental accuracy is improved. Through combination of experiments and numerical simulation, accurate calibration of micromechanical parameters of the muddy silt hydrate-containing sediment discrete element model is realized, and the accuracy of the discrete element model is improved.

Description

Technical Field

[0001] The invention belongs to the field of mechanical research on natural gas hydrate sediments, and in particular relates to a mechanical parameter calibration method of a discrete element model of hydrate-containing sediments based on experiments. Background Art

[0002] Natural gas hydrate is an ice-like crystalline compound formed by water and natural gas under high pressure and low temperature conditions. It usually exists in the form of hydrate-containing sediments in continental shelf permafrost and marine sediments. Due to its abundant reserves, high energy density and low environmental impact, natural gas hydrate is regarded as a potential clean alternative energy source in the future, attracting many countries to carry out field test mining. However, the decomposition of hydrates during the mining process destroys the phase equilibrium between hydrates and sediments, which may cause geomechanical problems in the reservoir. The hydrate reservoir in the Shenhu Sea area of ​​the South my country Sea is typically muddy silt sand type, with the characteristics of undiagenetic and weak cementation, which makes the mechanical properties of the sediments more complex, and thus faces more prominent geomechanical challenges during the mining process. Therefore, in-depth research on the mechanical properties of muddy silt sand hydrate-containing sediments is crucial to solving mining problems. However, due to the high cost and difficulty of mechanical testing of hydrate samples in the laboratory, the application of numerical simulation methods in the study of hydrate sediment mechanics is becoming increasingly important.

[0003] As a numerical simulation tool for effectively analyzing the mechanical behavior of granular materials, the discrete element method can deeply reveal the microscopic mechanism of macroscopic mechanical properties and has been widely used in the mechanical analysis of hydrate-containing sediments. However, the accuracy and reliability of the discrete element model are highly dependent on the precise calibration of micromechanical parameters. Existing calibration methods mostly rely on empirical values ​​or fitting based on the overall mechanical performance of the sample, but have limitations when dealing with complex multiphase and multicomponent particle systems. Hydrate-containing sediments are a multiphase material, mainly composed of sediment phase and hydrate phase. The content and distribution of the hydrate phase will change during the reaction process, resulting in changes in the overall mechanical properties of the hydrate-containing sediment. In muddy silt hydrate sediments, the mechanical behaviors of clay, sand and hydrate are relatively complex. Existing empirical calibration methods often ignore the mechanical differences between these components. The discrete element model will find it difficult to effectively capture the true mechanical behaviors between the components, which will not only cause the simulation results of macroscopic mechanical properties to deviate from the experimental data, but also may cause the overall calculation results to be distorted due to the simplification or neglect of the mechanical differences between the components. Summary of the invention

[0004] In order to effectively improve the accuracy of the discrete element model of hydrate-containing sediments, the present application provides a method for calibrating mechanical parameters of the discrete element model of hydrate-containing sediments to improve the reliability and accuracy of the discrete element model in predicting the mechanical properties of hydrate-containing sediments. The method adopts the following technical scheme: The method for calibrating mechanical parameters of the discrete element model of hydrate-containing sediments includes:

[0005] S1. Sample preparation and triaxial shear test;

[0006] Prepare sandy sediment, sandy hydrate sediment, muddy silt sediment and muddy silt hydrate samples, and conduct triaxial shear tests in stages on all sediment samples;

[0007] S2, constructing discrete element models for the four sediment samples described in step S1 respectively;

[0008] S3, calibrate the mechanical parameters of sediments of different components in stages;

[0009] The first stage is the parameter calibration of a single component of sandy sediments, the second stage is the parameter calibration of two components of sandy hydrate sediments, the third stage is the parameter calibration of two components of muddy silt sand sediments; the fourth stage is the parameter calibration of multiple components of muddy silt sand hydrate sediments;

[0010] S4. Discrete element model result output.

[0011] Furthermore, in step S3: in the first stage, the parameter calibration process of a single component of sandy sediment is carried out by using the anti-rolling

[0012] The dynamic contact model is used to simulate the mechanical behavior of the sand-sand component. The calibration process is as follows:

[0013] S310, adjust the elastic modulus E and use the formula To determine the normal contact stiffness K n , where v is Poisson's ratio; by fitting the stress-strain curve at the initial stage of the experiment, the elastic deformation of the particle contact in the model is ensured to be consistent with the experimental results;

[0014] S311, adjust the stiffness ratio α to control the tangential contact stiffness K s and normal stiffness K n The relationship k s =α·k n , ensuring that the sliding and shearing behavior of the particles is consistent with the experimental data;

[0015] S312, adjusting the friction coefficient μ, based on Coulomb's friction law F=μ·N, where F is the friction force and N is the normal force, by fitting the critical shear strength in the experiment, ensuring that the shear strength of the model is consistent with the experimental results;

[0016] S313, adjust the anti-rolling coefficient η r , through the anti-rolling moment formula M r =η r ·F n d controls the resistance of the particles during rotation and ensures that the strain hardening or softening phenomenon of the model at high strain stage is consistent with the experimental results.

[0017] Furthermore, in step S3: in the second stage parameter calibration process of the two components of the sandy hydrate-containing sediment, the mechanical parameters of the sand-hydrate component and the hydrate-hydrate component are assigned using the parallel bonding contact model, and the mechanical parameters of the sand-sand component use the calibration results of the first stage. The second stage calibration process is as follows:

[0018] S320, adjust the elastic modulus E, through the formula To determine the normal contact stiffness K n , ensuring that the initial stiffness of the model is consistent with the experimental data;

[0019] S321, density ρ, directly use actual data;

[0020] S322, adjust the friction coefficient μ, the calculation formula is τ=σ n μ, by comparing with the shear strength in the experiment, gradually adjust the friction coefficient, and by gradually optimizing the friction coefficient, reduce the shear force deviation in the model to ensure consistency with the experimental results;

[0021] S323, parallel bond tensile strength σ t and shear strength τ s , through the formula and Calibration was performed to ensure that the tensile and shear fracture behaviors between particles were consistent with experimental results;

[0022] S324. Adjust the internal friction angle φ to ensure that the shear strength and slip characteristics are consistent with the experimental data.

[0023] Furthermore, in step S3: in the parameter calibration process of the two components of the muddy silt sediment in the third stage, the linear bonding contact model is used to assign mechanical parameters to the clay-clay component, the clay-sand component and the clay-hydrate component, and the sand-sand component, the sand-hydrate component and the hydrate-hydrate component use the calibration results of the second stage. The calibration process of the third stage is as follows:

[0024] S330, adjust the elastic modulus E, through the formula F n =k n ·δ n Calculate the normal force F n , where δ n is the normal displacement, and K is gradually adjustedn , so that the tensile rupture behavior of the particles is consistent with the experimental data;

[0025] S331, adjust the tangential stiffness k s , which controls the rupture behavior of particles under shear conditions, is given by F s =k s ·δ s , where δ s is the tangential displacement, and k is gradually adjusted s , ensuring that the shear mechanical response is consistent with the experimental data;

[0026] S332, adjust the linear bond tensile strength σ c and shear strength τ c , ensuring that the failure behavior of particles in tensile and shear experiments matches the actual data. By adjusting these parameters, the model can efficiently and accurately reflect the mechanical properties of muddy silt under tensile and shear conditions.

[0027] Further, in step S4: in the fourth stage, the parameter calibration process of the multi-component muddy silt sand hydrate sediment, the sand-sand component, the sand-hydrate component, the hydrate-hydrate, the clay-clay component, and the clay-sand component adopt the calibration results of the third stage, and the fourth stage calibration process is as follows:

[0028] S340, adjust normal stiffness F n To control the rupture behavior of the sample under tensile conditions, the formula F n =k n ·δ n The experimental data were fitted step by step to ensure that the tensile rupture behavior between particles was consistent with the experimental results;

[0029] S341, adjust the tangential stiffness k s , through the formula F s =k s ·δ s , gradually fit the shear test data to ensure that the shear failure is consistent with the experimental data;

[0030] S342, adjust the linear bond tensile strength σ c and linear bond shear strength τ c , through experimental fitting, it is ensured that the fracture behavior of the clay-hydrate component in the model under tension and shear conditions is consistent with the experimental results.

[0031] Compared with the prior art, the advantages and positive effects of the present invention are as follows:

[0032] The present invention aims at muddy silt sand hydrate sediments, prepares four samples of sandy sediments, sandy hydrate sediments, muddy silt sand sediments and muddy silt sand hydrates, adopts different contact models according to the mechanical properties of different components of each sample, and gradually increases the model complexity from a single component to multiple components through staged calibration to ensure that the mechanical behavior of each component can accurately reflect the actual experimental data, and realizes the accurate calibration of the micromechanical parameters of the discrete element model of the muddy silt sand hydrate sediments through the combination of experiments and numerical simulations, thereby improving the accuracy of the discrete element model. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] In order to more clearly illustrate the embodiments of this specification or the technical solutions in the prior art, the following briefly introduces the drawings used in the embodiments. Obviously, the drawings described below are only some embodiments of the present application, and for ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0034] Figure 1 This is a flow chart of mechanical parameter calibration of a discrete element model of muddy silt sand hydrate sediment according to an embodiment of the present invention;

[0035] Figure 2 is a stress-strain curve diagram of a triaxial shear test of samples of different components in an embodiment of the present invention;

[0036] Figure 3 is a triaxial shear stress-strain curve diagram of the indoor and discrete element models of sandy sediments according to an embodiment of the present invention;

[0037] Figure 4 is a triaxial shear stress-strain curve diagram of the experiment and discrete element model of the sandy hydrate-containing sediment in the embodiment of the present invention;

[0038] Figure 5 is a triaxial shear stress-strain curve diagram of the experiment and discrete element model of the muddy silt sand sediment in the embodiment of the present invention;

[0039] Figure 6 It is a triaxial shear stress-strain curve diagram of the experiment and discrete element model of the muddy silt sand hydrate sediment in the embodiment of the present invention. DETAILED DESCRIPTION

[0040] The embodiments of the present application are described in detail below, and examples of the embodiments are shown in the accompanying drawings, wherein the same or similar reference numerals throughout represent the same or similar elements or elements having the same or similar functions. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain the present application, and cannot be understood as limiting the present application.

[0041] refer to Figure 1This embodiment proposes a method for calibrating mechanical parameters of a discrete element model of hydrate-containing sediments, comprising:

[0042] Step 1. Experimental material preparation and triaxial shear test

[0043] In order to fully understand the mechanical properties of different components of sediments and provide benchmark data for subsequent discrete element modeling and parameter calibration, this embodiment prepares four samples: sandy sediments, which are mainly used to study the mechanical properties of sand-sand components; sandy hydrate-containing sediments, focusing on the mechanical properties between sand-hydrate components and hydrate-hydrate components; muddy silt sand sediments, focusing on the mechanical properties between sand-clay components and clay-clay components; muddy silt sand hydrate-containing sediments, which can analyze the mechanical behavior between clay-hydrate. These four samples represent the mechanical properties of different components in the sediments, thereby providing the necessary mechanical data for the model, ensuring a comprehensive analysis of various factors that may affect the mechanical properties of sediments, and laying the foundation for accurate model construction.

[0044] First, quartz sand that meets the reservoir particle grading is selected as the matrix, dried and filled into the mold, and sandy sediment samples are prepared according to the "Standard for Geotechnical Test Methods" (GB / T 50123-2019). Then, the quartz sand matrix is ​​mixed with the water sample to generate a sand-hydrate mixture with a specific hydrate saturation, and hydrates are generated at appropriate temperature and pressure to finally obtain sandy hydrate-containing sediment samples. At the same time, the submarine clay in the Shenhu Sea area of ​​the South China Sea is mixed with quartz sand in proportion, and the same method is used to prepare muddy silt sand and muddy silt sand hydrate sediment samples.

[0045] After the sample preparation is completed, all samples are subjected to staged triaxial shear tests according to the Triaxial Shear Test Method for Hydrate Sediments (T / CAOE 52-2023). During the test, key parameters such as axial stress, axial strain and pore pressure are continuously monitored and recorded until the predetermined strain is reached. After the test, the experimental data are summarized, the stress-strain curve is drawn, and the mechanical properties and deviatoric stress development trend of each sample are deeply analyzed.

[0046] Step 2. Construction of multi-component sediment discrete element model

[0047] First, the discrete element method is used to construct a container consistent with the experiment, and a geometric model consistent with the actual reservoir particle gradation is generated. For sandy sediment samples, particles are generated according to the quartz sand particle size in the experiment and evenly filled into the model container. Consolidation stress is applied to simulate the compaction process to ensure stress balance. For sandy hydrate-containing sediment samples, sandy particles are first generated, and then hydrate particles are generated according to the hydrate saturation, and isotropic consolidation stress is applied. The hydrate saturation S of sandy hydrate-containing sediments is HControlled by particle number.

[0048]

[0049] Among them, V h is the volume of a single hydrate particle, m 3 ;n h is the number of hydrate particles; V b is the sample volume, m 3 ; p is the porosity of the sample.

[0050] The modeling of muddy silt sediment samples generates mixed particles of clay and sand according to the proportions, and is prepared according to the steps of sandy sediment sample preparation. The clay content is achieved by controlling the number of clay particles:

[0051]

[0052] Among them, V c is the volume of a single clay particle, m 3 ;n c is the number of clay particles; V b is the volume of the sample, m 3 ; p is the porosity of the sample.

[0053] For the muddy silt hydrate sediment sample, the same modeling method as the sandy hydrate sediment was used. After generating muddy silt particles, hydrate particles were generated according to the hydrate saturation, and the internal stress balance was ensured through iterative calculation. h The calculation formula is:

[0054]

[0055] In this embodiment, discrete element models are constructed for sandy sediments, sandy hydrate-containing sediments, muddy silt sediments and muddy silt hydrate, respectively, to ensure that the mechanical properties between particles of different components are accurately reflected at the microscopic scale.

[0056] Step 3. Staged calibration of mechanical parameters of different components of combined experiments

[0057] In the process of multi-component discrete element model calibration, it is crucial to use a suitable contact model for the mechanical properties of different components. Through phased calibration, the model complexity is gradually increased from a single component to multiple components to ensure that the mechanical behavior of each component can accurately reflect the actual experimental data. Ultimately, it can ensure that the simulation results are consistent with the actual physical behavior.

[0058] The calibration steps are as follows:

[0059] Phase 1: Calibration of parameters of a single component of sandy sediments

[0060] Natural sand has an irregular shape, and there is rolling friction and interlocking effect between sand particles. This embodiment uses an anti-rolling contact model to simulate the mechanical behavior of sand-sand components. This model can overcome the limitations of the linear bonding model in dealing with nonlinear contact characteristics between particles, and the problem that the parallel bonding model cannot effectively simulate rolling friction and interlocking phenomena between particles. The anti-rolling contact model can more accurately reflect the complex interactions of sand particles under stress conditions, thereby improving the accuracy of the simulation.

[0061] The main mechanical parameters of the anti-rolling model are: elastic modulus E, stiffness ratio α, friction coefficient μ and anti-rolling coefficient η r In the process of parameter calibration, a step-by-step optimization method was adopted. First, the elastic modulus E was adjusted and the formula To determine the normal contact stiffness K n , where v is Poisson's ratio. By fitting the stress-strain curve at the beginning of the experiment, the elastic deformation of the particle contact in the model is ensured to be consistent with the experimental results, thereby eliminating the interference of other variables and improving the calibration efficiency. Next, adjust the stiffness ratio α to control the tangential contact stiffness K s and normal stiffness K n The relationship k s =α·k n , thus ensuring that the sliding and shearing behaviors of the particles are consistent with the experimental data. Then, the friction coefficient μ is adjusted. Based on Coulomb's friction law F = μ·N, where F is the friction force and N is the normal force, the shear strength of the model is ensured to be consistent with the experimental results by fitting the critical shear strength in the experiment. This process enables the model to accurately simulate the sliding friction behavior between particles. Finally, the anti-rolling coefficient η is adjusted r , through the anti-rolling moment formula M r =η r ·F n ·d controls the resistance of the particles during rotation, ensuring that the strain hardening or softening phenomenon of the model in the high strain stage is consistent with the experimental results. The advantage of this calibration method is that it starts with the elastic modulus and gradually optimizes other parameters, which simplifies the calibration steps, reduces the coupling between parameters, significantly improves the calibration efficiency and accuracy, and ensures a high degree of consistency between the model and the experimental data.

[0062] Phase II: Calibration of parameters of two components of sandy hydrate-bearing sediments

[0063] Considering that hydrates have a certain bonding strength, the particles can withstand a certain tensile force and shear force. This embodiment uses a parallel bonding contact model to assign values ​​to the mechanical parameters of sand-hydrate components and hydrate-hydrate components. The parallel bonding model can simulate the bonding effect between hydrate particles. By controlling the parallel bonding tensile strength and shear strength, it can accurately reflect the tensile and shear failure behavior of hydrates when subjected to stress. The mechanical parameters of the sand-sand component adopt the calibration results of stage one. The main mechanical parameters of the parallel bonding contact model include: elastic modulus E, density ρ, friction coefficient μ, parallel bonding tensile strength σ t , parallel bond shear strength τ s , internal friction angle φ.

[0064] First, adjust the elastic modulus E, through the formula To determine the normal contact stiffness K n , ensuring that the initial stiffness of the model is consistent with the experimental data. This can eliminate the interference of other variables in the initial stage, reduce the complexity of subsequent adjustments, and improve the calibration efficiency. Next, the density ρ is the density of the actual sample, which does not need to be adjusted and the actual data is used directly. Then, adjust the friction coefficient μ, which is calculated as τ=σ n ·μ, by comparing with the shear strength in the experiment, the friction coefficient is gradually adjusted to ensure that the model shows a reasonable mechanical response during the shear process. By gradually optimizing the friction coefficient, the shear force deviation in the model can be reduced to ensure a high degree of consistency with the experimental results. Next, the parallel bond tensile strength σ t and shear strength τ s , through the formula and Calibration is performed to ensure that the tensile and shear fracture behaviors between particles are consistent with the experimental results. This step enables the model to accurately reflect the mechanical properties of the material in tensile and shear failure. Finally, the internal friction angle φ is adjusted to ensure that the shear strength and slip characteristics are consistent with the experimental data. Through the gradual optimization of these steps, not only the mutual influence between the parameters is reduced, the calibration process is simplified, but also the efficiency and accuracy of the overall calibration are improved, ensuring the consistency of the model with the experimental data.

[0065] Phase III: Calibration of parameters of two components of muddy silt sediments

[0066] In the calibration process of muddy silt sediments, since clay particles have strong cohesion and plasticity, this means that when subjected to force, clay particles not only show elastic deformation, but also have significant plastic deformation characteristics. This embodiment uses a linear bonding contact model to assign mechanical parameters to clay-clay components, clay-sand components, and clay-hydrate components, which can simulate the cohesion between particles and allow particles to break or slide after reaching a certain tensile or shear force, which is consistent with the failure mode of clay after being subjected to force.

[0067] In this embodiment, the sand-sand component, sand-hydrate component, and hydrate-hydrate component adopt the calibration results of stage 2. The main mechanical parameters of the linear bonding contact model include: elastic modulus E, stiffness ratio α, linear bonding tensile strength σ c , linear bond shear strength τ c First, adjust the elastic modulus E, by controlling the normal stiffness K n , ensuring that the mechanical behavior of the particles under tensile conditions can accurately reflect the experimental results. n =k n ·δ n Calculate the normal force F n , where δ n is the normal displacement. Gradually adjust K n , so that the tensile fracture behavior of the particles is consistent with the experimental data. This approach of optimizing the elastic modulus first can quickly lock the initial stiffness of the model and reduce the complexity of subsequent parameter adjustments. Then, by adjusting the tangential stiffness k s , which controls the rupture behavior of particles under shear conditions, is given by F s =k s ·δ s , where δ s is the tangential displacement. Gradually adjust k s , ensuring that the shear mechanical response is consistent with the experimental data. On this basis, the linear bond tensile strength σ is adjusted c and shear strength τ c , to ensure that the failure behavior of particles in tension and shear experiments matches the actual data. Through these parameter adjustments, the model can efficiently and accurately reflect the mechanical properties of muddy silt under tension and shear conditions.

[0068] Phase 4: Calibration of multi-component parameters of muddy silt hydrate sediments

[0069] The sand-sand component, sand-hydrate component, hydrate-hydrate component, clay-clay component, and clay-sand component use the calibration results of stage 3. First, adjust the normal stiffness F n To control the rupture behavior of the sample under tensile conditions, the formula F n =k n ·δ n The experimental data were fitted step by step to ensure that the tensile fracture behavior between particles was consistent with the experimental results. Next, the tangential stiffness k was adjusted. s , through the formula F s =k s ·δ s , gradually fitting the shear test data to ensure that the shear failure is consistent with the experimental data. Then, adjust the linear bond tensile strength σ cand linear bond shear strength τ c , through experimental fitting, to ensure that the fracture behavior of the clay-hydrate component in the model under tension and shear conditions is consistent with the experimental results. By adjusting these parameters, the model can accurately reflect the effect of the interaction between the clay and hydrate components on the overall mechanical properties.

[0070] Table 1 shows the micromechanical parameters of the contact model of particles with different components

[0071]

[0072] Step 4. Output of discrete element model results

[0073] A complete discrete element model is established using precisely calibrated mechanical parameters. In addition, this embodiment also performs error analysis on the simulation results and experimental results, verifies the correctness of the calibrated parameters by calculating the errors, and ensures that the model can accurately reflect the actual situation. The model can be used for subsequent simulations of multiple conditions and parameter sensitivity analysis to evaluate the mechanical properties of hydrate-containing sediments of different components. The appropriate output file format can be selected according to research requirements to facilitate subsequent data processing and analysis. The results include mechanical data such as stress-strain curves, which can fully reflect the mechanical behavior of the sample under different conditions.

[0074] The specific implementation process is introduced in detail below in combination with specific experiments.

[0075] 1. Experimental material preparation and triaxial shear test

[0076] Quartz sand with the same particle gradation as that in the Shenhu area of ​​the South China Sea was selected as the matrix material. After drying, it was filled into a mold with a diameter of 50 mm and a height of 100 mm, and sandy sediment samples were prepared according to the "Standard for Geotechnical Test Methods" (GB / T 50123-2019). Subsequently, the quartz sand was mixed with water to produce a mixture with a hydrate saturation of 30%, and frozen at -10°C, while applying an initial confining pressure of 0.5 MPa. After freezing, the confining pressure was gradually increased to 3.5 MPa, the pore pressure to 3 MPa, and the temperature was raised to 5°C to generate hydrates, and finally a sandy hydrate-containing sediment sample was prepared. The submarine clay in the Shenhu area of ​​the South China Sea was mixed with quartz sand in a ratio of 15% clay and 85% sand, and muddy silt and muddy silt hydrate samples were prepared in the same way. After the sample preparation was completed, the sample was subjected to a triaxial shear test in accordance with the "Triaxial Shear Test Method for Hydrate-Containing Sediments" (T / CAOE 52-2023). During the test, the effective confining pressure was maintained at 1 MPa, the temperature was controlled at 1°C, and the axial loading was performed at a loading rate of 0.002 mm / s until the axial strain reached 20%. After the test was completed, the experimental data was saved, the stress-strain curve was plotted, and the mechanical properties were analyzed. The test results are as follows Figure 2 shown.

[0077] 2. Construction of phased discrete element model

[0078] When modeling sandy sediment samples, sandy hydrate-containing sediment samples, muddy silt sediment samples, and muddy silt sediment samples containing hydrate, the discrete element method was used to construct the container. To ensure the calculation efficiency, a geometric model with a radius of 3 mm and a height of 6 mm was generated. For sandy sediment samples, particles were generated according to the quartz sand particle size in the experiment, evenly filled into the model container, and an equivalent consolidation stress of 0.5 MPa was applied to simulate the compaction process in the experiment, and stress balance was ensured through cyclic calculation. For sandy hydrate-containing sediment samples, sandy particles were first generated, and then hydrate particles were generated according to the preset hydrate saturation of 30%. Subsequently, isotropic consolidation stress was applied to simulate the effective stress during hydrate generation to ensure the internal stress balance of the sample. The hydrate saturation was controlled by the number of particles.

[0079]

[0080] Among them, V h is the volume of a single hydrate particle, m 3 ;n h is the number of hydrate particles; V b is the sample volume, m 3 ; p is the porosity of the sample.

[0081] When modeling muddy silt sediment samples, clay-sand component mixed particles are generated according to the ratio of 15% clay and 85% sand by volume, and modeling is carried out according to the modeling steps of sandy sediment samples. The clay content is achieved by controlling the number of clay particles:

[0082]

[0083] Among them, V c is the volume of a single clay particle, m 3 ;n c is the number of clay particles; V b is the volume of the sample, m 3 ; p is the porosity of the sample.

[0084] For the modeling of muddy silt sand hydrate sediment samples, in addition to generating muddy silt sand particles, a muddy silt sand hydrate sediment sample with a hydrate saturation of 30% was generated in the same way as the sandy hydrate sediment. The model was constructed for four samples separately to ensure that the mechanical properties between particles of different components are accurately reflected at the microscopic scale. The hydrate saturation calculation formula in the discrete element model of muddy silt sand hydrate sediment is:

[0085]

[0086] 3. Phased calibration of mechanical parameters of different components combined with experiments

[0087] Phase 1: Calibration of parameters of a single component of sandy sediments

[0088] First, adjust the elastic modulus E, which is related to the normal contact stiffness K n The relationship is The Poisson's ratio v is taken as 0.3 based on experience. By fitting the stress-strain curve at the beginning of the experiment, the elastic modulus E is gradually adjusted to ensure that the elastic deformation of the particle contact in the model is consistent with the experimental results, thereby eliminating the interference of other variables and improving the calibration efficiency. Adjust K n Substitute 0.55GPa into the formula: E = k n ×(1-ν 2 )≈0.5GPa The final calibrated elastic modulus is 0.5GPa. Then, the tangential contact stiffness K is controlled by the stiffness ratio α s and normal stiffness K n The relationship between: k s =α·k n The initial value of the stiffness ratio is set between 1.0 and 1.5. By fitting the stress-strain data in the shear experiment, the stiffness ratio α is gradually adjusted to control the slip and shear behavior in the model. By fitting the experimental data, the stiffness ratio α is determined to be 1.20, and the tangential stiffness is: k s =1.20×0.55=0.66GPa, and the final calibrated stiffness ratio is 1.20, thus ensuring that the sliding and shearing behaviors of the particles are consistent with the experimental data. Subsequently, the friction coefficient μ is adjusted, and the friction force is calculated according to Coulomb's friction law, τ=σ n ·μ, where τ is the shear stress between particles and the normal stress is set to 1.83MPa. The initial friction coefficient is set to 0.4 and is gradually adjusted by fitting the critical shear strength in the shear experiment. The friction coefficient finally obtained by fitting is: Ensure that the strength is consistent with the experiment. The average particle diameter d = 8.7 × 10 -5 By fitting the stress-strain data in the high strain stage, the anti-rolling coefficient is gradually adjusted and the final anti-rolling coefficient obtained by fitting is: Ensure that the strain hardening or softening phenomenon of the model at high strain stage is consistent with the experimental results, such as Figure 3 shown.

[0089] Phase II: Calibration of parameters of two components of sandy hydrate-bearing sediments

[0090] The mechanical parameters of the sand-sand component are calibrated using the results of stage 1. First, assuming that the elastic modulus E is 0.5-0.8 GPa, according to the formula By fitting the stress-strain curve at the beginning of the experiment, the elastic modulus was gradually adjusted. At this time, the elastic modulus was 0.6GPa, ensuring that the initial stiffness of the model was consistent with the experimental data. This can eliminate the interference of other variables in the initial stage, reduce the complexity of subsequent adjustments, and improve the calibration efficiency. Density ρ = 2730kg / m 3 , reflecting the density of the actual sample. Then, by adjusting the friction coefficient μ to 0.80, the formula τ=σ n ·μCalculate the sliding resistance to ensure that the shear strength is consistent with the experimental results. Next, adjust the parallel bond tensile strength σ t and shear strength τ s , the tensile strength σ is obtained by fitting the experimental data t =1.5MPa and shear strength τ s =1.0MPa to ensure that the tensile and shear fracture behaviors between particles are consistent with the experimental results. This step enables the model to accurately reflect the mechanical properties of the material in tensile and shear failure. Finally, adjust the internal friction angle φ, initially set to φ = 28°, and use the formula τ = σ n ·tan(φ) calculated shear stress is τ=2.0×tan(28°)=1.07MPa. After gradual adjustment, the internal friction angle is finally calibrated to 30° to ensure that the shear strength and slip characteristics are consistent with the experimental data. When the stress-strain curve consistent with the experimental results is finally obtained, the mechanical parameters of the sand-hydrate and hydrate-hydrate components are calibrated. Figure 4 shown.

[0091] Phase III: Calibration of parameters of two components of muddy silt sediments

[0092] The linear bonding contact model is used to assign mechanical parameters to the clay-clay component, clay-sand component and clay-hydrate component, and the sand-sand component, sand-hydrate component and hydrate-hydrate component use the calibration results of stage 2. First, the initial normal stiffness K is set n is 0.06GPa, and through the formula F n =k n ·δ n The normal stiffness is adjusted step by step to ensure that the tensile failure between particles is consistent with the experimental data. By fitting the experimental results, the elastic modulus E is finally calibrated to 0.06GPa. This method of optimizing the elastic modulus first can quickly lock the initial stiffness of the model and reduce the complexity of subsequent parameter adjustments. Next, the tangential stiffness k is adjusted. s To control the fracture behavior of the sample under shear conditions, the tangential stiffness k sis 0.006GPa, and K is adjusted according to the stiffness ratio α = 0.1 n and k s The relationship k s =α·k n , through the formula F s =k s ·δ s The shear data were fitted step by step to ensure that the shear failure was consistent with the experimental data. Subsequently, the linear bond tensile strength σ was adjusted c and linear bond shear strength τ c , the initial setting is 5MPa. Through experimental fitting, the final calibrated tensile strength is 1MPa and the shear strength is 1MPa. Through repeated optimization, the model results are finally consistent with the experimental results, and the mechanical parameters of clay-clay and clay-sand components are calibrated. Figure 5 shown.

[0093] Phase 4: Calibration of multi-component parameters of muddy silt hydrate sediments

[0094] In the calibration process of muddy silt hydrate sediments, the linear bonding contact model was used to calibrate the clay-hydrate component, and the sand-sand component, sand-hydrate component, hydrate-hydrate component, clay-clay component, and clay-sand component were calibrated using the stage three calibration results. Through experimental fitting, the final parameters obtained were: elastic modulus of 0.08GPa, stiffness ratio of 0.120. Adjust the normal stiffness and tangential stiffness, and use the formula F n =k n ·δ n and F s =k s ·δ s To control the rupture behavior of the sample under tension and shear conditions. By fitting the experimental data, the calibrated linear bond tensile strength σ c is 1.2MPa, linear bond shear strength τ c When the stress-strain curve of the muddy silt sand hydrate sediment matches the experimental results, the mechanical parameters of the clay-hydrate component are calibrated, such as Figure 6 The micromechanical parameters of the muddy silt sand hydrate sediment calibrated through the above steps are shown in Table 2.

[0095] Table 2 Mechanical parameters of the discrete element model of muddy silt hydrate sediment

[0096]

[0097]

[0098] 4. Output of discrete element model experimental results

[0099] After completing the mechanical parameter calibration, a complete discrete element model was established based on the calibrated micromechanical parameters in Table 2. Figure 5 The error analysis of the stress-strain curves of the indoor experiment and the numerical model was carried out. The results showed that the error between the numerical model and the experimental data in the peak deviatoric stress was 2.4%, and the error in the secant modulus was 3.9%, both of which were within a reasonable range. In addition, the stress-strain curves of the numerical model and the indoor experiment showed obvious strain softening after the peak. This shows that the mechanical parameters in the established numerical model can accurately reflect the mechanical properties of the actual sample. The model has been accurately calibrated and can be used for subsequent simulation analysis under various working conditions, and parameter sensitivity analysis can be performed to evaluate the mechanical properties of hydrate-containing sediments of different components. According to the research needs, the appropriate output file format is selected to facilitate subsequent data processing and analysis. The experimental results include mechanical data such as stress-strain curves.

[0100] The above-described embodiments of the present invention do not constitute a limitation on the protection scope of the present invention. Any modification, equivalent substitution and improvement made within the spirit and principle of the present invention shall be included in the protection scope of the claims of the present invention.

Claims

1. A method for calibrating mechanical parameters of a discrete element model of hydrate-containing sediments, characterized in that include: S1. Sample preparation and triaxial shear test; Prepare sandy sediment, sandy hydrate sediment, muddy silt sediment and muddy silt hydrate samples, and conduct triaxial shear tests in stages on all sediment samples; S2, constructing discrete element models for the four sediment samples described in step S1 respectively; S3, calibrate the mechanical parameters of sediments of different components in stages; The first stage is the parameter calibration of a single component of sandy sediments, the second stage is the parameter calibration of two components of sandy hydrate sediments, the third stage is the parameter calibration of two components of muddy silt sand sediments; the fourth stage is the parameter calibration of multiple components of muddy silt sand hydrate sediments; S4. Discrete element model result output.

2. The method for calibrating mechanical parameters of a discrete element model of hydrate-containing sediments according to claim 1, characterized in that: In step S3: in the first stage, the parameter calibration process of a single component of sandy sediment uses an anti-rolling contact model to simulate the mechanical behavior of the sand-sand component. The calibration process is as follows: S310, adjust the elastic modulus E and use the formula To determine the normal contact stiffness K n , where v is Poisson's ratio; by fitting the stress-strain curve at the initial stage of the experiment, the elastic deformation of the particle contact in the model is ensured to be consistent with the experimental results; S311, adjust the stiffness ratio α to control the tangential contact stiffness K s and normal stiffness K n The relationship k s =α·k n , ensuring that the sliding and shearing behavior of the particles is consistent with the experimental data; S312, adjusting the friction coefficient μ, based on Coulomb's friction law F=μ·N, where F is the friction force and N is the normal force, by fitting the critical shear strength in the experiment, ensuring that the shear strength of the model is consistent with the experimental results; S313, adjust the anti-rolling coefficient η r , through the anti-rolling moment formula M r =η r ·F n d controls the resistance of the particles during rotation and ensures that the strain hardening or softening phenomenon of the model at high strain stage is consistent with the experimental results.

3. The method for calibrating mechanical parameters of a discrete element model of hydrate-containing sediments according to claim 1, characterized in that: In step S3: in the second stage parameter calibration process of the two components of the sandy hydrate-containing sediment, the mechanical parameters of the sand-hydrate component and the hydrate-hydrate component are assigned using the parallel bonding contact model. The mechanical parameters of the sand-sand component use the calibration results of the first stage. The second stage calibration process is as follows: S320, adjust the elastic modulus E, through the formula To determine the normal contact stiffness K n , ensuring that the initial stiffness of the model is consistent with the experimental data; S321, density ρ, directly use actual data; S322, adjust the friction coefficient μ, the calculation formula is τ=σ n μ, by comparing with the shear strength in the experiment, gradually adjust the friction coefficient, and by gradually optimizing the friction coefficient, reduce the shear force deviation in the model to ensure consistency with the experimental results; S323, parallel bond tensile strength σ t and shear strength τ s , through the formula and Calibration was performed to ensure that the tensile and shear fracture behaviors between particles were consistent with experimental results; S324. Adjust the internal friction angle φ to ensure that the shear strength and slip characteristics are consistent with the experimental data.

4. The method for calibrating mechanical parameters of a discrete element model of hydrate-containing sediments according to claim 1, characterized in that: In step S3: in the third stage, the parameter calibration process of the two components of the muddy silt sediment uses a linear bonding contact model to assign mechanical parameters to the clay-clay component, the clay-sand component and the clay-hydrate component, and the sand-sand component, the sand-hydrate component and the hydrate-hydrate component use the calibration results of the second stage. The third stage calibration process is as follows: S330, adjust the elastic modulus E, through the formula F n =k n ·δ n Calculate the normal force F n , where δ n is the normal displacement, and K is gradually adjusted n , so that the tensile rupture behavior of the particles is consistent with the experimental data; S331, adjust the tangential stiffness k s , which controls the rupture behavior of particles under shear conditions, is given by F s =k s ·δ s , where δ s is the tangential displacement, and k is gradually adjusted s , ensuring that the shear mechanical response is consistent with the experimental data; S332, adjust the linear bond tensile strength σ c and shear strength τ c , ensuring that the failure behavior of particles in tensile and shear experiments matches the actual data. By adjusting these parameters, the model can efficiently and accurately reflect the mechanical properties of muddy silt under tensile and shear conditions.

5. The method for calibrating mechanical parameters of a discrete element model of hydrate-containing sediments according to claim 1, characterized in that: In step S4: in the fourth stage, the parameter calibration process of the multi-component muddy silt sand hydrate sediment, the sand-sand component, the sand-hydrate component, the hydrate-hydrate, the clay-clay component, and the clay-sand component adopt the calibration results of the third stage. The fourth stage calibration process is as follows: S340, adjust normal stiffness F n To control the rupture behavior of the sample under tensile conditions, the formula F n =k n ·δ n The experimental data were fitted step by step to ensure that the tensile rupture behavior between particles was consistent with the experimental results; S341, adjust the tangential stiffness k s , through the formula F s =k s ·δ s , gradually fit the shear test data to ensure that the shear failure is consistent with the experimental data; S342, adjust the linear bond tensile strength σ c and linear bond shear strength τ c , through experimental fitting, it is ensured that the fracture behavior of the clay-hydrate component in the model under tension and shear conditions is consistent with the experimental results.

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