Rock near-field dynamic transfer modeling method for reflecting real discontinuous surface

Abstract

The invention discloses a rock near-field dynamic transfer modeling method capable of reflecting a real discontinuous surface, and relates to the technical field of geotechnical engineering.The rock near-field dynamic transfer modeling method comprises the steps that a rock image containing the discontinuous surface is obtained, the rock image is preprocessed to obtain a binary image, and the binary image is stored in a database; obtaining rock feature pixel points in the binary image based on an edge segmentation technology; on the basis of a material point discrete transfer printing technology and rock characteristic pixel points, constructing a near-field dynamic model, and judging the type of a key between the material points; based on a mechanical boundary condition, performing precision evaluation on the near-field dynamic model by using a numerical simulation technology, and optimizing the near-field dynamic model according to an evaluation result; and based on test requirements, pre-configuring boundary conditions of force loading and displacement loading, and determining rock damage indexes in combination with the optimized near-field dynamic model. According to the method, intelligent modeling and programmed calculation can be realized, and the mechanical property and fracture evolution characteristics of the rock containing the discontinuous surface can be conveniently obtained.

Description

Technical Field

[0001] The invention relates to the technical field of geotechnical engineering, and in particular to a rock peridynamic transfer modeling method reflecting 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 real images of soil-rock mixtures after image processing. However, this method is based on discrete elements, and therefore requires many macro and micro parameters to be calibrated, and requires the establishment of theoretical formulas for material point judgment, which makes the conversion relationship between pixel points and material points complicated.

[0004] At the same time, the existing technology usually explores the mechanical properties of rocks with discontinuities through numerical simulation, but it often uses the method of pre-setting the inclination and spacing of joints 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. 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 discontinuities. The discrete element method requires more calibrated microscopic parameters and cannot accurately describe the initiation and development of cracks.

[0005] Currently, no effective solution has been proposed for the problems in the related technologies. Summary of the invention

[0006] In view of 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 solution adopted by the present invention is 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 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;

[0010] Based on the material point discrete transfer technology 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 by combining 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 discontinuous surface of the rock, and after a pre-processing operation is performed on the rock image, a binarization processing technique 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 a bright filling matrix corresponding to the pixel points based on the bright filling points;

[0015] Using edge detection and global threshold technology to implement edge pixel point and dark filling point acquisition operations on the binary image, the acquired edge pixel points 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 a detection frame of a preset size, and a tag set is determined based on the type result.

[0017] Preferably, edge detection and global threshold technology are used to implement 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 average operation on binary images, and calculate the pixel gradient size and direction based on the operation results;

[0019] The maximum value of the gradient of each pixel point is screened and retained one by one, the pixel point corresponding to the maximum value is marked as an edge pixel point, and the strongest threshold and the weakest threshold are set using the global threshold technology;

[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 edge and dark filling point matrices.

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

[0022] The pixel points corresponding to the binary image are set as the determination pixel points, the determination pixel points are input to the center position of the detection frame of a preset size, and the number of pixels actually filled is determined according to the type of the determination 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, based on the material point discrete transfer technology 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 according to the evaluation results, including:

[0025] The material is discretized into equally spaced material points to form an approximate dynamic network, and the pixel points in the binary image correspond 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;

[0026] Based on the peri-field dynamics model and the marker set, attribute transfer technology is used to assign attribute parameters to material points, and the bond type of material points is determined according to the attribute assignment results and the bond type judgment rules;

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

[0028] Preferably, assigning attribute parameters to material points by 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 result and the bond type determination rule include:

[0029] The pixel points between the marker sets are distinguished by using the peridynamic model and material point analysis, and the discontinuity properties of the rock are obtained according to the distinguishing 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 with the material point property sequence.

[0032] Preferably, the imprinting accuracy of the peridynamic model is evaluated based on rock characteristic pixels and screening rules, and mechanical boundary conditions are applied in combination with 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 rule, and accurate near-field dynamics and deviation near-field dynamics are generated according to the restoration strategy and the 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 damage index of numerical simulation 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 index is 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 and the density of the external force it is subjected to 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 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, and the rock damage index is determined.

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

[0042]

[0043] In the formula, 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] In the formula, represents the damage index, x represents the material point before deformation, t represents the time, H x represents the selection of the near field, ξ represents the connection 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 adopts photographic 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 according to the pixel point marks to judge the type of bonds between material points and carry out numerical simulation. Its implementation is convenient to realize intelligent modeling and programmed calculation, and it is convenient to obtain the mechanical properties of rocks containing discontinuities, crack evolution characteristics, etc.

[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 numerical models based on actual images, which can improve the accuracy of modeling. 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 being able to 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 drawings required for use in the embodiments will be briefly introduced below. 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 creative work.

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

[0052] Figure 2 It 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 This is a schematic diagram of the classification of discriminated pixels and filled pixels in a rock peridynamic transfer modeling method reflecting a real discontinuity surface according to an embodiment of the present invention;

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

[0058] Figure 8 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 and are mainly used to illustrate the embodiments. They can be used in conjunction with the relevant descriptions in the specification to explain the operating principles of the embodiments. With reference to these contents, ordinary technicians in this field should be able to understand other possible implementation methods and 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 is further described with reference to the accompanying drawings and specific embodiments. Figure 1 As shown, according to a rock peridynamic transfer modeling method reflecting a real discontinuity surface according to an embodiment of the present invention, the rock peridynamic transfer modeling method 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 an edge segmentation technique;

[0063] Step S2: construct a peridynamic model based on the material point discrete transfer technology and rock characteristic pixel points, and determine the bond type between material points; based on the mechanical boundary conditions, use numerical simulation technology to evaluate the accuracy of the peridynamic model, and optimize the peridynamic model according to 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 photographing 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 edge and dark filling point matrices; 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 threshold 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 point are marked as an edge and dark filling point matrix, Gaussian filtering technology can be applied to perform a pixel weighted average operation on the binary image, and the pixel gradient size and direction are calculated based on the operation results; the maximum value of each pixel gradient is screened and retained one by one, the pixel corresponding to the maximum value is marked as an edge pixel, and the strongest threshold and the weakest threshold are set using the global threshold technology; 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, the discrimination pixels can be input into the center position of the detection frame of a preset size, and the number of actually filled pixels can be determined according to the type of the discrimination pixels; the number of actually 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 according to the classification results and the screening rules.

[0068] In this embodiment, a peridynamic model is constructed based on the material point discrete transfer technology 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 by 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 marker 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 applied in combination with the numerical simulation technology, and the damage index is predicted 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 peri-field dynamics model and the marker set, and the bond type of the material point is judged according to the attribute assignment result and the bond type judgment rule, the difference between the pixel points between the peri-field dynamics 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 result; according to the principle that the marker and the material point attributes correspond, the attribute sequence of the material point corresponding to the marker set is obtained, and the attribute parameters are assigned to the material point using the material point attribute sequence; 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 attribute parameters with the material point attribute sequence.

[0070] In this embodiment, when evaluating the imprinting accuracy of the peridynamic model based on rock characteristic pixel points and screening rules, and applying mechanical boundary conditions in combination with numerical simulation technology, and predicting 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 are 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 applied to 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, based on the test requirements, the boundary conditions of force loading and displacement loading are pre-configured, and when the rock damage index is determined in combination with the optimized near-field dynamics model, the near-field domain can be selected after the force loading and displacement loading conditions are set 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 are judged; the state information of the material points is calculated by iteratively solving 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 the actual process is described in detail below.

[0073] Step 1: rock image acquisition;

[0074] Rock images containing discontinuities are obtained by taking photos, 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 pixel points: bright filling, dark filling 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 a 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 pixels 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 detected darker pixels as dark fill d. For the pixels marked as edge e and dark fill d at the same time, the pixel is marked as edge e, and then a matrix marked with b, e, and d corresponding to the pixel 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, use the filter to calculate the weighted average of the pixels around the pixel.

[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] In the formula, 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 in eight directions: horizontal, vertical, and diagonal.

[0085] 3. Filter and retain the maximum value of the gradient intensity at each pixel. That is, after traversing 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 double threshold method to determine the strong boundary and the weak boundary, that is, set the strong threshold and the 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, and if the gradient value is between the strong and weak thresholds, it is a weak boundary. The selection of the weak boundary is further determined by the hysteresis technology, that is, if the weak boundary is connected to the strong boundary, it is retained, and 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 want.

[0093] (3) The main occurrence of the discontinuity 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 used as a discriminant pixel for detection. The discriminant pixel is placed in the center of the detection frame. The discriminant pixel can be divided into three types: middle pixel, boundary pixel, and corner pixel, which correspond to eight, five, and three surrounding pixels actually filled in the detection frame, respectively.

[0094] The number of actually filled pixels in the detection frame is classified and counted, so as to further screen the judgment pixel in the center of the detection frame: if the judgment pixel is a pixel with an edge mark (e), whether the actually filled pixels around it have more than or equal to m dark filling marks (d), if so, the pixel is further identified as a definite edge pixel (e′); if the judgment pixel is a pixel with a dark filling mark (d), whether the actually filled pixels around it have more than or equal to n dark filling marks (d), if so, the pixel is further identified as a definite dark filling pixel (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 near-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 "the 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 x =-1 / 2×length+d x / 2+(row number-1)×d x ;

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

[0101] (2) Attribute transfer: The near-field dynamics model obtained in the coordinate transfer step should reflect the differences in pixel labels (e′, d′, b′) through the material point attributes, 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 the bond between the material points. When the material properties of the two ends of the bond are the same, that is, the matnum values ​​are 1, 2, or 3, they are judged to be the same type of bonds, 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 the bond are different, it is judged as 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 rock discontinuities, 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 based on the image, that is, the model established in step 2 when m=1 and n=1, Y represents the approximately restored peridynamic model, that is, the model established in step 2 when m≠1 or n≠1, and |X∩Y| represents the pixel overlap of the two models.

[0107] The value of P varies between 0 and 1, where 0 means that the real discontinuity is not restored at all, and 1 means that the real 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 tunnel excavation faces, 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 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 is used as the accuracy evaluation indicator to measure the actual damage index (test) and the predicted damage index (numerical simulation).

[0109]

[0110] In the formula, 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 point attributes are given by pixel point marking. At the same time, according to the different material properties, the specific properties and classification of the bonds between adjacent material points are determined. The imprinting accuracy is evaluated, the modeling is refined in real time, and 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 two aspects of 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, and has accuracy guarantee 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] In the formula, 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 elongation of the bond, that is:

[0117]

[0118] μ is a scalar function for determining 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 bond breaks 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] In the formula, represents the damage index, x represents the material point before deformation, t represents the time, H x represents the selection of the near field, ξ represents the connection 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 technical solution of the present invention, the present invention uses photographing 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 pixel point marking to judge the type of bonds between material points and carry out numerical simulation. Its implementation is convenient to realize intelligent modeling and programmed calculation, and it is convenient to obtain the mechanical properties and crack evolution characteristics 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 the accuracy of modeling. At the same time, spatial integration is used to describe the internal effects of materials, change the singularity problem of traditional finite element methods at discontinuities, avoid the problem of too many parameters in discrete element methods, and simulate the random expansion evolution of cracks inside materials. It is flexible and convenient in implementation methods.

[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 principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A rock peridynamic transfer modeling method reflecting real discontinuities, characterized in that: The rock peridynamic transfer modeling method includes: 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; Based on the material point discrete transfer technology 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.

2. A rock peridynamic transfer modeling method reflecting a real discontinuity surface according to claim 1, 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 discontinuous surface of the rock, and after a pre-processing operation is performed on the rock image, a binarization processing technique 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 a bright filling matrix corresponding to the pixel points based on the bright filling points; Using edge detection and global threshold technology to implement edge pixel point and dark filling point acquisition operations on the binary image, the acquired edge pixel points 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 a detection frame of a preset size, and a tag set is determined based on the type result.

3. A rock peridynamic transfer modeling method reflecting a real discontinuity surface according to claim 2, characterized in that: The edge detection and global threshold technology is used to implement the edge pixel point and dark filling point acquisition operation on the binary image, and the acquired edge pixel points and dark filling points are marked as edge and dark filling point matrices, which includes: Apply Gaussian filtering technology to perform pixel weighted average operation on binary images, and calculate the pixel gradient size and direction based on the operation results; The maximum value of the gradient of each pixel point is screened and retained one by one, the pixel point corresponding to the maximum value is marked as an edge pixel point, and the strongest threshold and the weakest threshold are set using the global threshold technology; 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 edge and dark filling point matrices.

4. A rock peridynamic transfer modeling method reflecting a real discontinuity surface according to claim 3, characterized in that: The step of judging 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: The pixel points corresponding to the binary image are set as the determination pixel points, the determination pixel points are input to the center position of the detection frame of a preset size, and the number of pixels actually filled is determined according to the type of the determination 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 the real discontinuity surface according to claim 1 is characterized in that: The method is based on the discrete transfer technology of material points and the characteristic pixel points of rocks to build a near-field dynamics model and determine the bond type between material points; Based on the mechanical boundary conditions, the accuracy of the peridynamic model is evaluated by numerical simulation technology, and the peridynamic model is optimized according to the evaluation results, including: The material is discretized into equally spaced material points to form an approximate dynamic network, and the pixel points in the binary image correspond 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 peri-field dynamics model and the marker set, attribute transfer technology is used to assign attribute parameters to material points, and the bond type of 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 rock characteristic pixels and screening rules, and the mechanical boundary conditions are imposed by combining numerical simulation technology to predict the damage index and verify the accuracy of the peridynamic model.

6. A rock peridynamic transfer modeling method reflecting a real discontinuity according to claim 5, characterized in that: The method of assigning attribute parameters to material points by 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 result and the bond type determination rule includes: The pixel points between the marker sets are distinguished by using the peridynamic model and material point analysis, and the discontinuity properties of the rock are obtained according to the distinguishing 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 with the material point property sequence.

7. A rock peridynamic transfer modeling method reflecting a real discontinuity surface according to claim 6, 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 rule, and accurate near-field dynamics and deviation near-field dynamics are 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 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 damage index of numerical simulation 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.

8. A rock peridynamic transfer modeling method reflecting a real discontinuity surface according to claim 7, characterized in that: 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, 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 and the density of the external force it is subjected to 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 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, and the rock damage index is determined.

9. A rock peridynamic transfer modeling method reflecting a real discontinuity surface according to claim 8, characterized in that: The state information calculation formula of the material point is: Where ρ represents the material density, x represents the material point before deformation, ü(x, t) 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, and V x′ represents the volume composed of all material points in the near field, and μ represents a scalar function.

10. A rock peridynamic transfer modeling method reflecting a real discontinuity surface according to claim 9, characterized in that: The calculation formula of the damage index is: In the formula, represents the damage index, x represents the material point before deformation, t represents the time, H x represents the selection of the near field, ξ represents the connection 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