A rock peridynamic transfer modeling method reflecting real discontinuities

Abstract

The present invention discloses a rock peridynamic transfer modeling method that reflects real discontinuities, relating to the field of geotechnical engineering technology. The rock peridynamic transfer modeling method comprises: obtaining a rock image containing a discontinuity, preprocessing the rock image to obtain a binary image, and obtaining rock characteristic pixel points in the binary image based on edge segmentation technology; constructing a peridynamic model based on material point discrete transfer technology and rock characteristic pixel points, and determining the type of bonds between material points; using numerical simulation technology to evaluate the accuracy of the peridynamic model based on mechanical boundary conditions, and optimizing the peridynamic model based on the evaluation results; pre-configuring force loading and displacement loading boundary conditions based on experimental requirements, and determining rock damage indicators in combination with the optimized peridynamic model. The present invention can realize intelligent modeling and programmed calculation, facilitating the acquisition of mechanical properties and crack evolution characteristics of rocks containing discontinuities.

Description

Technical Field

[0001] The present invention relates to the field of geotechnical engineering technology, and in particular to a rock peridynamic transfer modeling method that reflects a real discontinuity surface. Background Art

[0002] Under tectonic movement, rocks often produce discontinuous structural surfaces such as cracks and joints, which not only destroy the integrity of the rock, but also weaken the strength and stability of the entire rock mass. In geotechnical engineering, the existence of discontinuities makes the stress distribution of the rock uneven under loading, leading to zonal destruction of the rock mass, sliding along the structural surface, etc., and ultimately causing engineering disasters. Therefore, the crack development and evolution process of rocks containing discontinuities is of great significance to engineering safety.

[0003] For example, Chinese patent CN109359416B discloses a particle flow numerical simulation method that reflects the distribution of real engineering soil-rock mixtures. It proposes a method for establishing a PFC model through image processing of a real image of the soil-rock mixture. However, this method is based on discrete elements, and therefore requires many macro- and micro-parameters to be calibrated. In addition, a theoretical formula needs to be established to determine the material of a material point, making the conversion relationship between pixel points and material points complex.

[0004] At the same time, the existing technology usually explores the mechanical properties of rocks containing discontinuities through numerical simulation, but it often uses the method of pre-setting the joint inclination and spacing to establish a numerical model of regular discontinuities. There is a lack of model construction methods based on real rock discontinuities, which makes it difficult to meet the exploration of the mechanical properties of rocks under random discontinuities. In addition, the existing rock mechanics numerical modeling methods are concentrated on finite elements and discrete elements, but the finite element method is based on continuous medium mechanics and cannot solve the singularity problem at the discontinuity. The discrete element method requires more microscopic parameters to be calibrated and cannot accurately describe the initiation and development of cracks.

[0005] Currently, no effective solutions have been proposed for the problems in related technologies. Summary of the Invention

[0006] In response to the problems in the related art, the present invention proposes a rock peridynamic transfer modeling method that reflects the real discontinuity surface to overcome the above-mentioned technical problems existing in the existing related art.

[0007] To this end, the specific technical solutions adopted in the present invention are as follows:

[0008] A rock peridynamic transfer modeling method reflecting a real discontinuity surface, the rock peridynamic transfer modeling method comprising:

[0009] Obtaining a rock image containing discontinuous surfaces, preprocessing the rock image to obtain a binary image, and obtaining rock feature pixel points in the binary image based on edge segmentation technology;

[0010] Based on the discrete transfer technology of material points and rock characteristic pixel points, a peridynamic model is constructed and the bond type between material points is determined. Based on the mechanical boundary conditions, the accuracy of the peridynamic model is evaluated using numerical simulation technology, and the peridynamic model is optimized based on the evaluation results.

[0011] Based on the test requirements, the boundary conditions of force loading and displacement loading are pre-configured, and the rock damage index is determined in combination with the optimized peridynamic model.

[0012] Preferably, obtaining a rock image containing a discontinuous surface, preprocessing the rock image to obtain a binary image, and obtaining rock feature pixel points in the binary image based on an edge segmentation technique include:

[0013] A photographic method is used to obtain a rock image containing a rock discontinuity surface, and after pre-processing the rock image, a binarization process is used to convert the rock image into a binary image;

[0014] Initialize and mark the pixel points corresponding to the binary image as bright filling points, and generate the bright filling matrix corresponding to the pixel points based on the bright filling points;

[0015] Edge detection and global thresholding technology are used to obtain edge pixels and dark filling points on the binary image, and the obtained edge pixels and dark filling points are marked as edge and dark filling point matrices;

[0016] The pixel type corresponding to the binary image is determined based on the detection box of a preset size, and the tag set is determined according to the type result.

[0017] Preferably, edge detection and global thresholding technology are used to perform edge pixel point and dark filling point acquisition operations on the binary image, and the acquired edge pixel points and dark filling points are marked as edge and dark filling point matrices, including:

[0018] Apply Gaussian filtering technology to perform pixel weighted averaging operation on binary images, and calculate the pixel gradient size and direction based on the operation results;

[0019] Screen and retain the maximum value of the gradient of each pixel one by one, mark the pixel corresponding to the maximum value as the edge pixel, and use the global threshold technology to set the strongest threshold and the weakest threshold;

[0020] The gradient value corresponding to the edge pixel point and the difference between the strongest threshold and the weakest threshold are determined to select the dark filling point, and the obtained edge pixel points and dark filling points are marked as the edge and dark filling point matrix.

[0021] Preferably, judging the type of pixels corresponding to the binary image based on a detection frame of a preset size, and determining a tag set according to the type result includes:

[0022] Set the pixel points corresponding to the binary image as the discrimination pixel points, input the discrimination pixel points to the center position of the detection frame of a preset size, and determine the actual number of pixels filled according to the type of the discrimination pixel points;

[0023] The actual number of filled pixels in the detection frame is classified and counted, and the edge pixels, dark filled pixels and bright filled pixels are determined to generate a label set based on the classification results and screening rules.

[0024] Preferably, a peridynamic model is constructed based on the discrete transfer technology of material points and rock characteristic pixel points, and the bond type between material points is determined; based on the mechanical boundary conditions, the accuracy of the peridynamic model is evaluated using numerical simulation technology, and the peridynamic model is optimized according to the evaluation results, including:

[0025] The material is discretized into equally spaced material points to form an approximate dynamic network, and the pixels in the binary image are matched with the material points in the approximate dynamic network. The peridynamic model is established according to the coordinate transfer principle of the same rows and columns and the same horizontal and vertical coordinates.

[0026] Based on the peridynamic model and the tag set, the attribute transfer technology is used to assign attribute parameters to the material points, and the bond type of the material points is determined based on the attribute assignment results and the bond type judgment rules;

[0027] The imprinting accuracy of the peridynamic model is evaluated based on rock characteristic pixel points and screening rules. Mechanical boundary conditions are imposed by combining numerical simulation technology, and the damage index is predicted to verify the accuracy of the peridynamic model.

[0028] Preferably, assigning attribute parameters to material points using attribute transfer technology based on the peridynamic model and the tag set, and determining the bond type of the material points according to the attribute assignment results and the bond type determination rules include:

[0029] The difference between the pixels in the marker set is analyzed using the peridynamic model and material points, and the corresponding discontinuity properties of the rock are obtained based on the difference results.

[0030] According to the principle that the mark corresponds to the material point attribute, the material point attribute sequence corresponding to the mark set is obtained, and the material point attribute sequence is used to assign attribute parameters to the material point;

[0031] The corresponding material properties of the material point are obtained, and the bond type of the adjacent material points of any material point is determined by combining the material point property parameters and the material point property sequence.

[0032] Preferably, the imprinting accuracy of the peridynamic model is evaluated based on rock feature pixels and screening rules, and mechanical boundary conditions are imposed by combining numerical simulation technology to predict the damage index to verify the accuracy of the peridynamic model, including:

[0033] A restoration strategy is formulated based on the label set screening rules, and accurate near-field dynamics and deviation near-field dynamics are generated according to the restoration strategy and binary image respectively;

[0034] The imprinting accuracy evaluation index of the peridynamic model is calculated based on the accurate peridynamics and the deviation peridynamics, and the mechanical boundary conditions are applied to the peridynamic model according to the imprinting accuracy evaluation index.

[0035] Carry out numerical simulation test operations based on mechanical boundary conditions and numerical simulation technology, and obtain the numerical simulation damage index according to the test results;

[0036] The relative error is used as a metric to analyze the accuracy of the predicted damage index corresponding to the numerical simulation, and the accuracy of the peridynamic model is verified based on the accuracy results.

[0037] Preferably, based on the test requirements, the boundary conditions of force loading and displacement loading are pre-configured, and the rock damage indicators are determined in combination with the optimized peridynamic model, including:

[0038] After setting the force loading and displacement loading conditions according to the test requirements, select the near field and determine the volume information and external force density of all material points in the near field.

[0039] The optimized peridynamic model is used to combine the volume information of the material point with the density of the external force to iteratively calculate the state information of the material point;

[0040] The critical elongation of the material point bond force is analyzed based on the state information, and the number of bond fractures is determined according to the critical elongation. The integral of the number of bond fractures within the volume information is used to represent the local damage degree of the rock at the current spatial position and determine the rock damage index.

[0041] Preferably, the state information calculation formula of the material point is:

[0042]

[0043] Where ρ represents the material density, x represents the material point before deformation, represents the acceleration of the material point x at time t, u represents the displacement, x′ represents the material point after deformation, f represents the bond force between x and x′, d represents the distance between the material points, b(x, t) represents the external force density of the material point, V x ′ represents the volume composed of all material points in the near field, and μ represents a scalar function.

[0044] Preferably, the calculation formula of the damage index is:

[0045]

[0046] Where, represents the damage index, x represents the material point before deformation, t represents time, H x represents the selection of the near field, ξ represents the bond length of the material point before deformation, d represents the distance between the material points, V x′ Represents the volume composed of all material points in the near field.

[0047] The beneficial effects of the present invention are:

[0048] 1. The present invention uses photography technology to obtain real images of rocks containing discontinuities, and uses image processing technology to extract discontinuity features and mark pixel points. At the same time, a peridynamic model is constructed based on the pixel point markings to determine the type of bonds between material points and conduct numerical simulations. Its easy implementation can realize intelligent modeling and programmed calculations, making it easy to obtain the mechanical properties and crack evolution characteristics of rocks containing discontinuities.

[0049] 2. Based on edge detection and global threshold technology, the present invention can extract the main discontinuity surface features of rocks, show the destruction characteristics of rocks, and establish a numerical model based on actual images, which can improve the accuracy of modeling. At the same time, it uses spatial integration to describe the internal effects of materials, changes the singularity problem of traditional finite element methods at discontinuities, avoids the problem of too many parameters in discrete element methods, and can simulate the random expansion and evolution of cracks inside materials. It is flexible and convenient in implementation methods. BRIEF DESCRIPTION OF THE DRAWINGS

[0050] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0051] Figure 1 This is a flow chart of a rock peridynamic transfer modeling method reflecting a real discontinuity according to an embodiment of the present invention;

[0052] Figure 2 This is a flow chart of outputting rock images in a rock peridynamic transfer modeling method reflecting a real discontinuity surface according to an embodiment of the present invention;

[0053] Figure 3 1. This is a schematic diagram of the classification of discriminant pixels and filled pixels in a rock peridynamic transfer modeling method reflecting a real discontinuity according to an embodiment of the present invention;

[0054] Figure 4 1. It is a schematic diagram of a process for constructing a peridynamic model in a rock peridynamic transfer modeling method reflecting a real discontinuity according to an embodiment of the present invention;

[0055] Figure 5 is a binary image before processing in a rock peridynamic transfer modeling method reflecting a real discontinuity surface according to an embodiment of the present invention;

[0056] Figure 6 is a binary image processed in a rock peridynamic transfer modeling method reflecting a real discontinuity surface according to an embodiment of the present invention;

[0057] Figure 7 Schematic diagram of a rock peridynamic model containing discontinuities in a rock peridynamic transfer modeling method reflecting real discontinuities according to an embodiment of the present invention;

[0058] Figure 8 3. It is a schematic diagram comparing experimental and numerically simulated stress-strain curves of discontinuous surface rocks in a rock peridynamic transfer modeling method reflecting a real discontinuity surface according to an embodiment of the present invention. DETAILED DESCRIPTION

[0059] To further illustrate each embodiment, the present invention provides drawings, which are part of the disclosure of the present invention. They are mainly used to illustrate the embodiments and can be used in conjunction with the relevant descriptions in the specification to explain the operating principles of the embodiments. By referring to these contents, ordinary technicians in this field should be able to understand other possible implementation methods and the advantages of the present invention.

[0060] According to an embodiment of the present invention, a rock peridynamic transfer modeling method reflecting a real discontinuity is provided.

[0061] The present invention will now be further described with reference to the accompanying drawings and specific embodiments. Figure 1 As shown, according to an embodiment of the present invention, a rock peridynamic transfer modeling method reflecting a real discontinuity surface includes:

[0062] Step S1: obtaining a rock image containing a discontinuous surface, preprocessing the rock image to obtain a binary image, and obtaining rock feature pixel points in the binary image based on edge segmentation technology;

[0063] Step S2: Based on the material point discrete transfer technology and rock characteristic pixel points, a peridynamic model is constructed and the bond type between the material points is determined; based on the mechanical boundary conditions, the accuracy of the peridynamic model is evaluated using numerical simulation technology, and the peridynamic model is optimized based on the evaluation results;

[0064] Step S3: Based on the test requirements, the boundary conditions of force loading and displacement loading are pre-configured, and the rock damage index is determined in combination with the optimized peridynamic model.

[0065] In this embodiment, when obtaining a rock image containing a discontinuous surface, preprocessing the rock image to obtain a binary image, and obtaining rock feature pixel points in the binary image based on edge segmentation technology, a photographic method can be selected to obtain a rock image containing a rock discontinuous surface, and after performing a preprocessing operation on the rock image, a binarization processing technology is used to convert the rock image into a binary image; the pixel points corresponding to the binary image are initialized and marked as bright filling points, and a bright filling matrix corresponding to the pixel points is generated based on the bright filling points; edge pixel point and dark filling point acquisition operations are performed on the binary image using edge detection and global threshold technology, and the acquired edge pixel points and dark filling points are marked as an edge and dark filling point matrix; the type of pixel points corresponding to the binary image is judged based on a detection frame of a preset size, and a label set is determined according to the type result.

[0066] In this embodiment, when edge detection and global thresholding technology are used to perform edge pixel and dark filling point acquisition operations on a binary image, and the acquired edge pixel and dark filling points are marked as an edge and dark filling point matrix, Gaussian filtering technology can be applied to perform a pixel weighted averaging operation on the binary image, and the pixel gradient size and direction are calculated based on the operation results; the maximum value of the gradient of each pixel is screened and retained one by one, the pixel corresponding to the maximum value is marked as an edge pixel, and the global thresholding technology is used to set the strongest threshold and the weakest threshold; the gradient value corresponding to the edge pixel, the difference between the strongest threshold and the weakest threshold are judged to select the dark filling point, and the acquired edge pixel and dark filling point are marked as an edge and dark filling point matrix.

[0067] In this embodiment, when judging the type of pixel points corresponding to a binary image based on a detection frame of a preset size and determining a mark set according to the type result, the pixel points corresponding to the binary image can be set as discrimination pixels, and the discrimination pixels can be input into the center position of the detection frame of a preset size, and the number of actual filled pixels can be determined according to the type of the discrimination pixels; the number of actual filled pixels in the detection frame is classified and counted, and the edge pixels, dark filled pixels and bright filled pixels are determined to generate a mark set based on the classification results and the screening rules.

[0068] In this embodiment, a peridynamic model is constructed based on the discrete transfer technology of material points and rock characteristic pixel points, and the bond type between material points is determined; based on the mechanical boundary conditions, the accuracy of the peridynamic model is evaluated using numerical simulation technology, and when the peridynamic model is optimized according to the evaluation results, the material can be discretized into equally spaced material points to form an approximate dynamic network, and the pixel points in the binary image are corresponded to the material points in the approximate dynamic network, and the peridynamic model is established according to the coordinate transfer principle of the same rows and columns and the same horizontal and vertical coordinates; based on the peridynamic model and the label set, the attribute transfer technology is used to assign attribute parameters to the material points, and the bond type of the material points is determined according to the attribute assignment results and the bond type judgment rules; the imprinting accuracy of the peridynamic model is evaluated based on the rock characteristic pixel points and the screening rules, and the mechanical boundary conditions are imposed in combination with the numerical simulation technology to predict the damage index to verify the accuracy of the peridynamic model.

[0069] In this embodiment, when attribute parameters are assigned to material points using attribute transfer technology based on the peridynamic model and the marker set, and the bond type of the material point is judged according to the attribute assignment results and the bond type judgment rules, the difference between the pixel points between the peridynamic model and the material point analysis marker set can be used, and the discontinuity surface properties corresponding to the rock can be obtained according to the distinction results; according to the principle that the markers correspond to the material point attributes, the attribute sequence of the material points corresponding to the marker set is obtained, and the attribute sequence of the material points is used to assign attribute parameters to the material points; the corresponding material properties of the material points are obtained, and the bond type of the adjacent material points of any material point is determined by combining the attribute parameters of the material points with the attribute sequence of the material points.

[0070] In this embodiment, when evaluating the imprinting accuracy of the peridynamic model based on rock characteristic pixel points and screening rules, and combining numerical simulation technology to impose mechanical boundary conditions and predict the damage index to verify the accuracy of the peridynamic model, a restoration strategy can be formulated based on the label set screening rules, and accurate peridynamics and deviation peridynamics can be generated according to the restoration strategy and the binary image, respectively; the imprinting accuracy evaluation index of the peridynamic model is calculated based on the accurate peridynamics and the deviation peridynamics, and mechanical boundary conditions are imposed on the peridynamic model according to the imprinting accuracy evaluation index; numerical simulation test operations are carried out based on the mechanical boundary conditions and numerical simulation technology, and the damage index of the numerical simulation is obtained according to the test results; the accuracy of the predicted damage index corresponding to the numerical simulation is analyzed using relative error as a measurement standard, and the accuracy of the peridynamic model is verified based on the accuracy results.

[0071] In this embodiment, when the boundary conditions of force loading and displacement loading are pre-configured based on the test requirements and the rock damage index is determined in combination with the optimized near-field dynamics model, the near-field domain can be selected after setting the force loading and displacement loading conditions according to the test requirements, and the volume information of all material points in the near-field domain and the density of the external force they are subjected to can be judged; the state information of the material points can be iteratively solved and calculated using the optimized near-field dynamics model in combination with the volume information of the material points and the density of the external force they are subjected to; the critical elongation of the bond force of the material points is analyzed based on the state information, and the number of bond fractures is judged based on the critical elongation, and the local damage degree of the rock at the current spatial position is represented by the integral of the number of bond fractures in the volume information to determine the rock damage index.

[0072] In order to facilitate understanding of the above technical solutions of the present invention, the working principle or operation mode of the present invention in actual process is described in detail below.

[0073] Step 1: rock image acquisition;

[0074] The rock images containing discontinuities are obtained by taking pictures, which contain real and irregular discontinuities.

[0075] Step 2: rock image processing;

[0076] like Figures 2 to 6 As shown in the figure, the specific purpose of rock image processing is to obtain a binary image after image processing of the rock image, identify the rock features in the binary image and obtain the coordinates of three types of pixel points: bright fill, dark fill, and edge. The specific implementation process is as follows:

[0077] (1) After the image is binarized, all pixels in the image are initialized and marked as bright filling points b, and the matrix marked with b corresponding to the pixel is obtained based on the bright filling points b;

[0078] (2) The canny operator (edge ​​detection) is used to perform edge detection and the detected pixel points are marked as edge e. At the same time, the ostu method (global threshold technology) is used to automatically divide the threshold and mark the darker pixel points detected as dark fill d. For the pixel points marked as edge e and dark fill d at the same time, the pixel point is marked as edge e, and then the matrix marked with b, e, and d corresponding to the pixel point is obtained.

[0079] The basic principle of edge detection using the Canny operator is to find an optimal edge solution or the location where the grayscale intensity changes most strongly in an image. The specific steps are as follows:

[0080] 1. Use Gaussian filtering to denoise, that is, calculate the weighted average of the pixels around the pixel through the filter.

[0081] 2. Calculate the gradient size G and direction θ of each pixel. The calculation formula is as follows:

[0082]

[0083] θ=arctan2(G F ,G Z );

[0084] Where G Z With G F They are expressed as the gradients in the Z direction and the F direction respectively, and the gradient direction perpendicular to the edge is calculated, usually taking 8 directions: horizontal, vertical, and diagonal.

[0085] 3. Filter and retain the maximum value of the gradient intensity at each pixel. That is, after going through the pixels one by one, determine whether the current pixel is the maximum value of the same gradient direction among the surrounding pixels. If it is a local maximum, retain it.

[0086] 4. Use the dual threshold method to determine strong and weak boundaries. That is, set a strong threshold and a weak threshold. If the gradient value of the current edge pixel is greater than or equal to the strong threshold, it is a strong boundary. If the gradient value is between the strong and weak thresholds, it is a weak boundary. The selection of weak boundaries is further determined by hysteresis technology. That is, if the weak boundary is connected to the strong boundary, it is retained; if it is not connected, it is discarded.

[0087] The basic principle of the ostu method to achieve threshold division is to find an applicable threshold. Assuming a threshold TH and dividing the pixels of the entire image into two categories, the division probability and grayscale mean are R1, R2 and W1, W2 respectively, and the grayscale mean of the entire image is W G , then according to the probability relationship:

[0088] R1×W1+R2×W2=W G ;

[0089] R1+R2=1;

[0090] The expression of between-class variance is:

[0091] σ 2 =R1(W1-W G ) 2 +R2(W2-W G ) 2 ;

[0092] In the formula, σ represents the between-class variance, and the threshold TH that takes the maximum value in the probability relationship is what we are looking for.

[0093] (3) The main occurrence of the discontinuous surface is further extracted through the detection frame. A 3×3 detection frame is pre-set, and the binary image pixels are traversed in sequence. Each pixel will be detected as a discriminant pixel. The discriminant pixel is placed in the center of the detection frame. The discriminant pixels can be divided into three types: middle pixels, boundary pixels, and corner pixels, which correspond to eight, five, and three surrounding pixels actually filled in the detection frame, respectively.

[0094] The number of actual filled pixels in the detection frame is classified and counted, so as to further screen the judgment pixel points in the center of the detection frame: if the judgment pixel point is a pixel point with an edge mark (e), whether the actual filled pixels around it have more than or equal to m dark filling marks (d), if so, the pixel point is further identified as a definite edge pixel point (e′); if the judgment pixel point is a pixel point with a dark filling mark (d), whether the actual filled pixels around it have more than or equal to n dark filling marks (d), if so, the pixel point is further identified as a definite dark filling pixel point (d′); the remaining pixels are supplemented as definite bright filling marks (b′), among which m and n can be adjusted according to the recognition requirements and pixel category. If the recognition accuracy requirement is high, the values ​​of m and n can be set to be smaller.

[0095] Step 3: Transfer and construct a peri-field dynamics model;

[0096] like Figure 7 As shown in the figure, the transfer construction of the near-field dynamics model mainly adopts the idea of ​​gridless construction, which can discretize the material into several material points for modeling. The specific construction steps are divided into coordinate transfer, property transfer, bond type judgment, modeling optimization and accuracy evaluation.

[0097] (1) Coordinate transfer: The macroscopic material is discretized into equally spaced material points to form a peridynamic network. At the same time, the pixels in the processed image are matched one-to-one with the material points in the peridynamic network. Based on the principle that “pixel points and material points have the same row and column numbers and the same horizontal and vertical coordinates” in the same coordinate system, a peridynamic model is established. The relationship is as follows:

[0098] Material point spacing d x = actual length / number of pixels;

[0099] horizontal coordinate coord x = -1 / 2 × length + d x / 2+(row number-1)×d x ;

[0100] vertical coordinate coord y = -1 / 2 × width + d x / 2+(column number-1)×d x ;

[0101] (2) Attribute transfer: The near-field dynamics model obtained according to the coordinate transfer step should reflect the difference of pixel labels (e′, d′, b′) through the attributes of the material points, thereby reflecting the properties of the discontinuous surface. At the same time, according to the principle of "pixel matrix labels correspond to material point attributes" in the same coordinate system, different pixel labels (e′, d′, b′) correspond to the values ​​in the attribute sequence matnum (1, 2, 3), thereby giving the material points different attribute parameters, including the density, volume, elastic modulus, critical elongation, etc. of the material points.

[0102] (3) Bond type judgment: According to the different properties of the material points, they are separated by different values ​​(1, 2, 3) in the sequence matnum, and different material critical elongation (S1, S2, S3) and other properties are assigned to judge the type of bond between the material points. When the material properties of both ends of the bond are the same, that is, the matnum value is 1, 2, or 3, it is judged that they are the same type of bond, and the critical elongation S0 of the bond is taken as the critical elongation of the material.

[0103] When the material properties at both ends of a bond are different, it is judged to be a heterogeneous bond. The critical elongation S0 of the bond is taken as υ times the sum of the critical elongations of the materials at both ends, where υ is the weakening coefficient. For example, if the matnum values ​​of the material point properties at both ends of the bond are both 1, then the critical elongation S0 of the bond is S1; if the matnum values ​​of the material point properties at both ends of the bond are 1 and 2, then the critical elongation of the bond is S0=υ(S1+S2).

[0104] (4) Modeling optimization: According to the main occurrence characteristics of the rock discontinuity surface, the accuracy can be adjusted by different m and n values. Therefore, the model accuracy evaluation index P is defined as:

[0105]

[0106] Where X represents the peridynamic model restored one-to-one from the image, i.e., the model established in step 2 with m = 1 and n = 1; Y represents the approximately restored peridynamic model, i.e., the model established in step 2 with m ≠ 1 or n ≠ 1; and |X ∩ Y| represents the pixel overlap between the two models.

[0107] The value of P varies between 0 and 1, where 0 means that the true discontinuity is not restored at all, and 1 means that the true discontinuity is completely restored. The modeling accuracy is evaluated by the P value. If the error is large, the m and n values ​​in step 2 are adjusted cyclically.

[0108] (5) Accuracy evaluation: For stability issues of large-area surrounding rock, such as the stability of the tunnel excavation face, local rock sampling can be carried out after obtaining image information. Indoor uniaxial tests can be carried out on the rock samples, and damage indicators can be obtained using acoustic emission technology. At the same time, modeling is carried out based on the image information, and a near-field dynamic model is established based on the image information. Numerical simulation is carried out under mechanical boundary conditions to obtain the damage index of the numerical simulation. The relative error (Relative Error) is used as the accuracy evaluation indicator to measure the actual damage index (test) and the predicted damage index (numerical simulation).

[0109]

[0110] Where, represents the predicted damage index, Represents the measured damage index. The relative error RE is used to evaluate the overall error of the prediction result. The smaller the RE, the smaller the overall error of the prediction result. The damage accuracy is evaluated by RE. If the error is large, the m and n values ​​in step 2 are adjusted cyclically.

[0111] Therefore, in the process of transferring and constructing the peridynamic model, the pixel points are corresponded to the peridynamic material points through coordinates, and the main discontinuity surface features are obtained by automatic image processing methods. The material points are given attributes through pixel point markings. At the same time, according to the different material properties, the specific attributes and classification of the bonds between adjacent material points are determined. The imprinting accuracy is evaluated, and the modeling is optimized in real time. Based on the damage index evaluation results, the accuracy of the mechanical properties is improved. Finally, the imprinting from the image to the peridynamic model is realized from both coordinates and attributes. The obtained model can not only reflect the size of the rock material and the actual occurrence of the discontinuity surface, but also realize the distinction between the properties of the joints and the rock material, with accuracy guaranteed in both image and mechanical properties.

[0112] Step 4: Simulation analysis;

[0113] like Figure 8 As shown in the figure, according to the test requirements, boundary conditions such as force loading or displacement loading are set, and the state information of the material point is obtained by iteratively solving the peridynamic motion equation:

[0114]

[0115] Where ρ represents the material density, x represents the material point before deformation, represents the acceleration of the material point x at time t, u represents the displacement, x′ represents the material point after deformation, f represents the bond force between x and x′, d represents the distance between the material points, b(x, t) represents the external force density of the material point, V x′ represents the volume composed of all material points in the near field, and μ represents a scalar function.

[0116] Specifically, the bond lengths between the material point x before deformation and the material point x′ after deformation are ξ and ξ+η, respectively. Then S(ξ) is defined as the bond elongation, that is:

[0117]

[0118] μ is a scalar function that determines whether a bond is broken or not, namely:

[0119]

[0120] S0 is the critical elongation of the bond. When the elongation S of the bond between material points is greater than the critical elongation S0 of the bond, the bond breaks and the scalar function μ=0.

[0121] The integral of the number of broken bonds per unit volume represents the local damage degree of the material at the current spatial position. The damage index can be expressed as:

[0122]

[0123] Where, represents the damage index, x represents the material point before deformation, t represents time, H x represents the selection of the near field, ξ represents the bond length of the material point before deformation, d represents the distance between the material points, V x′ Represents the volume composed of all material points in the near field.

[0124] In summary, with the help of the above-mentioned technical solution of the present invention, the present invention uses photography technology to obtain real images of rocks containing discontinuities, and uses image processing technology to extract discontinuity features and mark pixel points. At the same time, a near-field dynamics model is constructed based on the pixel point marking to determine the type of bonds between material points and conduct numerical simulations. Its convenient implementation can realize intelligent modeling and programmed calculations, and facilitate the acquisition of mechanical properties, crack evolution characteristics, etc. of rocks containing discontinuities. Based on edge detection and global threshold technology, the present invention can extract the main discontinuity features of rocks, show the destruction characteristics of rocks, and establish a numerical model based on actual images, which can improve modeling accuracy. At the same time, spatial integration is used to describe the internal effects of materials, changing the singularity problem of traditional finite element methods at discontinuities, avoiding the problem of too many parameters in discrete element methods, and simulating the random expansion and evolution of cracks inside materials. It is flexible and convenient in implementation method.

[0125] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A rock peridynamic transfer modeling method reflecting real discontinuities, characterized by: The rock peridynamic transfer modeling method includes: Obtaining a rock image containing discontinuous surfaces, preprocessing the rock image to obtain a binary image, and obtaining rock feature pixel points in the binary image based on edge segmentation technology; Based on the discrete transfer technology of material points and rock characteristic pixel points, a peridynamic model is constructed and the bond type between material points is determined. Based on the mechanical boundary conditions, the accuracy of the peridynamic model is evaluated using numerical simulation technology, and the peridynamic model is optimized based on the evaluation results. Based on the test requirements, the boundary conditions of force loading and displacement loading are pre-configured, and the rock damage index is determined by combining the optimized peridynamic model; The method of constructing a peridynamic model based on the discrete transfer technology of material points and rock characteristic pixel points and determining the bond type between material points; evaluating the accuracy of the peridynamic model using numerical simulation technology based on mechanical boundary conditions, and optimizing the peridynamic model based on the evaluation results includes: The material is discretized into equally spaced material points to form an approximate dynamic network, and the pixels in the binary image are matched with the material points in the approximate dynamic network. The peridynamic model is established according to the coordinate transfer principle of the same rows and columns and the same horizontal and vertical coordinates. Based on the peridynamic model and the tag set, the attribute transfer technology is used to assign attribute parameters to the material points, and the bond type of the material points is determined based on the attribute assignment results and the bond type judgment rules; The imprinting accuracy of the peridynamic model is evaluated based on rock characteristic pixel points and screening rules. Mechanical boundary conditions are imposed by combining numerical simulation technology, and the damage index is predicted to verify the accuracy of the peridynamic model.

2. The rock peridynamic transfer modeling method reflecting real discontinuities according to claim 1 is characterized in that: The method of obtaining a rock image containing a discontinuous surface, preprocessing the rock image to obtain a binary image, and obtaining rock feature pixel points in the binary image based on an edge segmentation technique includes: A photographic method is used to obtain a rock image containing a rock discontinuity surface, and after pre-processing the rock image, a binarization process is used to convert the rock image into a binary image; Initialize and mark the pixel points corresponding to the binary image as bright filling points, and generate the bright filling matrix corresponding to the pixel points based on the bright filling points; Edge detection and global thresholding technology are used to obtain edge pixels and dark filling points on the binary image, and the obtained edge pixels and dark filling points are marked as edge and dark filling point matrices; The pixel type corresponding to the binary image is determined based on the detection box of a preset size, and the tag set is determined according to the type result.

3. The rock peridynamic transfer modeling method reflecting real discontinuities according to claim 2 is characterized in that: The edge detection and global thresholding technology is used to perform edge pixel point and dark filling point acquisition operations on the binary image, and the acquired edge pixel points and dark filling points are marked as edge and dark filling point matrices, which include: Apply Gaussian filtering technology to perform pixel weighted averaging operation on binary images, and calculate the pixel gradient size and direction based on the operation results; Screen and retain the maximum value of the gradient of each pixel one by one, mark the pixel corresponding to the maximum value as the edge pixel, and use the global threshold technology to set the strongest threshold and the weakest threshold; The gradient value corresponding to the edge pixel point and the difference between the strongest threshold and the weakest threshold are determined to select the dark filling point, and the obtained edge pixel points and dark filling points are marked as the edge and dark filling point matrix.

4. The rock peridynamic transfer modeling method reflecting real discontinuities according to claim 3 is characterized in that: The step of determining the pixel type corresponding to the binary image based on the detection frame of a preset size and determining the tag set according to the type result includes: Set the pixel points corresponding to the binary image as the discrimination pixel points, input the discrimination pixel points to the center position of the detection frame of a preset size, and determine the actual number of pixels filled according to the type of the discrimination pixel points; The actual number of filled pixels in the detection frame is classified and counted, and the edge pixels, dark filled pixels and bright filled pixels are determined to generate a label set based on the classification results and screening rules.

5. The rock peridynamic transfer modeling method reflecting real discontinuities according to claim 1 is characterized in that: The method of assigning attribute parameters to material points using attribute transfer technology based on the peridynamic model and the tag set, and determining the bond type of the material points according to the attribute assignment results and the bond type determination rules includes: The difference between the pixels in the marker set is analyzed using the peridynamic model and material points, and the corresponding discontinuity properties of the rock are obtained based on the difference results. According to the principle that the mark corresponds to the material point attribute, the material point attribute sequence corresponding to the mark set is obtained, and the material point attribute sequence is used to assign attribute parameters to the material point; The corresponding material properties of the material point are obtained, and the bond type of the adjacent material points of any material point is determined by combining the material point property parameters and the material point property sequence.

6. The rock peridynamic transfer modeling method reflecting real discontinuities according to claim 5 is characterized in that: The method of evaluating the imprinting accuracy of the peridynamic model based on rock characteristic pixels and screening rules, and applying mechanical boundary conditions in combination with numerical simulation technology to predict the damage index and verify the accuracy of the peridynamic model includes: A restoration strategy is formulated based on the label set screening rules, and accurate near-field dynamics and deviation near-field dynamics are generated according to the restoration strategy and binary image respectively; The imprinting accuracy evaluation index of the peridynamic model is calculated based on the accurate peridynamics and the deviation peridynamics, and the mechanical boundary conditions are applied to the peridynamic model according to the imprinting accuracy evaluation index. Carry out numerical simulation test operations based on mechanical boundary conditions and numerical simulation technology, and obtain the numerical simulation damage index according to the test results; The relative error is used as a metric to analyze the accuracy of the predicted damage index corresponding to the numerical simulation, and the accuracy of the peridynamic model is verified based on the accuracy results.

7. The rock peridynamic transfer modeling method reflecting real discontinuities according to claim 6, characterized in that: Based on the test requirements, the boundary conditions of force loading and displacement loading are pre-configured, and the rock damage indicators are determined in combination with the optimized peridynamic model, including: After setting the force loading and displacement loading conditions according to the test requirements, select the near field and determine the volume information and external force density of all material points in the near field. The optimized peridynamic model is used to combine the volume information of the material point with the density of the external force to iteratively calculate the state information of the material point; The critical elongation of the material point bond force is analyzed based on the state information, and the number of bond fractures is determined according to the critical elongation. The integral of the number of bond fractures within the volume information is used to represent the local damage degree of the rock at the current spatial position and determine the rock damage index.

8. The rock peridynamic transfer modeling method reflecting real discontinuities according to claim 7 is characterized in that: The calculation formula for the state information of the material point is: Where ρ represents the material density, x represents the material point before deformation, represents the acceleration of the material point x at time t, u represents the displacement, x′ represents the material point after deformation, and f represents the distance between x and x. bond force, d represents the distance between material points, b(x, t) represents the external force density of the material point, V x′ represents the volume composed of all material points in the near field, and μ represents a scalar function.

9. The rock peridynamic transfer modeling method reflecting real discontinuities according to claim 8, characterized in that: The calculation formula of the damage index is: Where, represents the damage index, x represents the material point before deformation, t represents time, H x represents the selection of the near field, ξ represents the bond length of the material point before deformation, d represents the distance between the material points, V x Represents the volume composed of all material points in the near field.

Images