CN108986208B - Reconstruction method for caving form of coal mine goaf - Google Patents

Abstract

The invention provides a method for reconstructing the caving form of a goaf in a coal mine, and relates to the technical field of mine safety. Including: establishing a physical similar model of the initial shape of the goaf in the coal mine, and arranging sensor monitoring parameter data in the model; randomly generating the initial shape of the goaf in the coal mine and forming a three-dimensional grid lattice of the goaf in the coal mine; constructing a genetic algorithm Coal mine goaf chromosome coding; use the lattice Boltzmann method to calculate the parameter data of the randomly generated coal mine goaf simulation model; judge whether the ratio of the absolute error of the calculation result to the monitoring value is less than the threshold; structure. The invention provides a method for reconstructing the caving form of goafs in coal mines, which solves the influence of fracture-cave combination, multi-scale, and large-scale characteristics on the newly-born goafs based on the concept of REV in the past. It has important theoretical significance and practical value to study the prevention and control of natural fire in the goaf of coal mine, gas drainage and management, and to ensure the safe production of coal mine.

Description

A reconstruction method of caving form in coal mine goaf

technical field

The invention relates to the technical field of mine safety, in particular to a method for reconstructing the caving form of a goaf in a coal mine.

Background technique

After the coal seam is mined, the old roof at the back of the coal mining face collapses within the range of the step distance, and the direct roof and the old roof collapse under the action of the mine pressure, and the goaf shows dynamic continuous changes, resulting in a large number of gaps and large cavities of different scales. The interstitial spaces of the rocks form a multi-scale complex medium in which the gaps between rock blocks, the gaps between floating coal fragments, large cavities and the pores of coal remains are overlapped and nested. The goaf within the range of the caving step behind the coal mining face is a high-incidence area of spontaneous combustion, and it is also a sensitive area that affects the gas concentration distribution in the stope. The real flow of fluid inside the goaf is the premise and basis for the study of spontaneous combustion and gas distribution in the goaf, so it is extremely necessary to master the complex geometric structure of the goaf.

In the past, the goaf flow field was treated assuming that the goaf was a continuous medium, which was based on the concept of REV and regarded as the category of porous media. At present, the models describing the structure of porous media mainly include: continuum model, capillary bundle model, network model, spatial periodicity, fractal model, process method model, statistical reconstruction model, and real models using CT, scanning electron microscopy, and slice combination methods. Structural models, etc. The existing 3D reconstruction technology of goafs mainly uses automatic laser scanning The mechanical properties and seepage laws of the overlying strata, Wang Beibei, Liang Bing, etc. used the Menger sponge fractal model to establish the void structure model of the collapsed rock mass in the goaf under the assumption that the rock mass blocks were consistent, and deduced the void ratio and The residual dilation coefficient formula calculates the water storage volume of the collapsed rock mass in the goaf. Reconstruction technology is mostly used for three-dimensional reconstruction of microscopic pores in porous media such as rocks. However, goafs in coal mines fall as they are mined, and the internal space cannot be detected by existing advanced technologies. It is impossible to use advanced technology to scan or slice, so the 3D reconstruction of the new goaf with multi-scale and large-scale features is still blank.

Affected by various factors such as coal and rock physical and mechanical properties, joints, coal mining methods, and mining heights, the shapes of coal and rock fragments are various, and the void space formed is ever-changing. The shape of the void is also dynamically and randomly changed. It can be said that there are no two completely identical hollow forms in new mined-out areas, either in terms of time or space. In addition, there are the following problems: (1) The real cavity structure of the rock block is complex, and the cavities and cracks are distributed across scales and disorderly. Quantitative description, lack of corresponding mathematical and physical description. (2) Using the simplified goaf cavity distribution or using several simple statistical characteristic functions to determine the cavity structure distribution cannot truly express the cavity structure of the goaf, and there must be a gap between the reconstructed goaf cavity and the real goaf. gap. (3) Due to the limitations of test conditions and equipment, there is no reasonable test method to understand the real internal cavity structure of the goaf.

Contents of the invention

Aiming at the problems existing in the prior art, the present invention provides a method for reconstructing the caving form of goafs in coal mines. Genetic algorithms are used to "exhaustively guess" the caving forms of newly mined-out areas, and the lattice Boltzmann method is used to estimate the caving forms of goafs. The cavity flow in the new mined-out area is calculated, and the calculation results are compared with the gas pressure and component gas concentration distribution of the actual goaf flow, so as to obtain the caving form of the internal structure of the new mined-out area.

In order to achieve the above purpose, a method for reconstructing the caving form of a goaf in a coal mine includes the following steps:

Step 1: Establish a physical similarity model of the initial shape of the coal mine goaf by placing solid blocks in the space, and arrange sensors to monitor parameter data in the model, including pressure, velocity and component concentration;

Step 2: Randomly generate the initial shape of the goaf in the coal mine, divide it into a three-dimensional grid to form a three-dimensional grid lattice of the goaf in the coal mine, and fill the three-dimensional grid lattice of the goaf in the coal mine with coal and rock mass The grid is set to 1, and the unfilled gas phase medium is set to 0;

Step 3: Construct the goaf chromosomal code for the newborn coal mine using the genetic algorithm, and randomly generate the 0-1 sequence of the goaf simulation model of the coal mine according to the genetic algorithm;

Step 4: Use the lattice Boltzmann method to calculate the pressure, velocity and component concentration inside the randomly generated coal mine goaf simulation model;

Step 5: Determine whether the ratio of the absolute error of the calculation result of the lattice Boltzmann method to the parameter data monitored by the sensor in the physical similarity model is less than the relative error threshold, and if so, output the 3D reconstruction model of the coal mine goaf, that is, complete the coal mine goaf The reconstruction of the falling form, if not, return to step 3.

Further, the calculation formula of the absolute error of the calculation result of the lattice Boltzmann method in the step 5 is as follows:

Δ=|C-L|;

Among them, Δ is the absolute error of the calculation result of the lattice Boltzmann method, C is the calculation value of the lattice Boltzmann method, and L is the monitoring parameter data of the monitoring points of the physical similarity model.

Further, the relative error threshold in step 5 is specifically set according to the actual situation.

Beneficial effects of the present invention:

The present invention proposes a method for reconstructing the caving form of gobs in coal mines, which overcomes the limitations of traditional techniques in the flow simulation of complex structures, and solves the problems of fracture-cave combinations, multiple The impact of scale and large block characteristics on the new goaf, the present invention reconstructs the movement process, dispersion process and mass transfer and heat transfer process of the gas phase medium in the goaf according to the caving form of the goaf in the new coal mine, and obtains a process that can be compared with the actual situation on site. The state parameters of gas flow field, component gas concentration distribution field and temperature distribution field with consistent conditions have important theoretical significance and practical value for the study of spontaneous combustion prevention, gas drainage and management in goafs of coal mines, and for ensuring safe production in coal mines.

Description of drawings

Fig. 1 is the flow chart of the reconstruction method of the caving form of the coal mine goaf in the embodiment of the present invention;

Fig. 2 is the schematic diagram of the initial form physical similarity model of the coal mine goaf constructed in the embodiment of the present invention;

Fig. 3 is a schematic diagram of the positions of the sensors arranged in the physical similarity model in the embodiment of the present invention;

Fig. 4 is a schematic diagram of the finally reconstructed three-dimensional model of the coal mine goaf in the embodiment of the present invention.

Detailed ways

In order to make the purpose, technical solution and advantages of the present invention clearer, the present invention will be further described in detail below in conjunction with the accompanying drawings and specific embodiments. The specific embodiments described here are only used to explain the present invention, not to limit the present invention.

A method for reconstructing the caving form of gobs in coal mines, the process flow is shown in Figure 1, and the specific methods are as follows:

Step 1: Establish a physical similarity model of the initial form of the coal mine goaf by placing solid blocks in the space, and arrange sensors in the model to monitor parameter data, including pressure, velocity and component concentration.

In this embodiment, the established physical similarity model of the initial shape of the coal mine goaf is shown in Figure 2, and the position of the sensor P is shown in Figure 3, where P1-P12 are 12 sensors arranged.

Step 2: Randomly generate the initial shape of the goaf in the coal mine, divide it into a three-dimensional grid to form a three-dimensional grid lattice of the goaf in the coal mine, and fill the three-dimensional grid lattice of the goaf in the coal mine with coal and rock mass The grid is set to 1, and the unfilled gas phase medium is set to 0.

As shown in FIG. 2 , in this embodiment, the grid is the area filled with coal and rock mass, and the blank grid is the unfilled area.

Step 3: Construct the goaf chromosomal code for the newborn coal mine using the genetic algorithm, and randomly generate a 0-1 sequence simulation model of the goaf in the coal mine according to the genetic algorithm.

In this example, the newly constructed goaf chromosome code for the genetic algorithm is:

Step 4: Use the lattice Boltzmann method to calculate the pressure, velocity and component concentration inside the randomly generated coal mine goaf simulation model.

The Lattice Boltzmann method, referred to as LBM, is a computational fluid dynamics method based on the mesoscopic simulation scale. Compared with other traditional CFD calculation methods, this method has the characteristics of a mesoscopic model between the microscopic molecular dynamics model and the macroscopic continuous model. , so it has the advantages of simple description of fluid interaction, easy setting of complex boundaries, easy parallel computing, and easy implementation of programs, and is an effective means to describe fluid motion.

Step 5: Determine whether the ratio of the absolute error of the calculation result of the lattice Boltzmann method to the parameter data monitored by the sensor in the physical similarity model is less than the relative error threshold, and if so, output the 3D reconstruction model of the coal mine goaf, that is, complete the coal mine goaf The reconstruction of the falling form, if not, return to step 3.

The calculation formula of the absolute error of the calculation result of the lattice Boltzmann method is as shown in formula (1):

Δ＝|C-L| (1)

Among them, Δ is the absolute error of the calculation result of the lattice Boltzmann method, C is the calculation value of the lattice Boltzmann method, and L is the monitoring parameter data of the monitoring points of the physical similarity model.

In this embodiment, the relative error threshold is set to 0.05.

In this embodiment, the monitoring values corresponding to the monitoring positions and the numerical results calculated by using the lattice Boltzmann method are shown in Table 1, and the chromosome code of the finally generated coal mine goaf is:

Table 1 The monitoring values corresponding to the monitoring positions and the numerical results calculated by the lattice Boltzmann method

Calculated by formula (1), the ratio of the absolute error of the calculation result of the lattice Boltzmann method to the parameter data monitored by the sensor in the physical similarity model is less than the relative error threshold, so the final reconstructed 3D model of the coal mine goaf is output, as shown in Figure 4 It shows that the reconstruction of the caving form of the coal mine goaf is completed.

Finally, it should be noted that: the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand; it still can Modifications are made to the technical solutions described in the foregoing embodiments, or equivalent replacements are made to some or all of the technical features; therefore, these modifications or replacements do not make the essence of the corresponding technical solutions depart from the scope defined by the claims of the present invention.

Claims (3)

1. A reconstruction method of the caving form of a coal mine goaf, characterized in that, comprising the following steps: Step 1: Establish a physical similarity model of the initial shape of the coal mine goaf by placing solid blocks in the space, and arrange sensors to monitor parameter data in the model, including pressure, velocity and component concentration; Step 2: Randomly generate the initial shape of the goaf in the coal mine, divide it into a three-dimensional grid to form a three-dimensional grid lattice of the goaf in the coal mine, and fill the three-dimensional grid lattice of the goaf in the coal mine with coal and rock mass The grid of the grid is set to 1, and the unfilled gas phase medium is set to 0, and the chromosome coding of the mined-out area of the nascent coal mine is constructed for the genetic algorithm; Step 3: Construct the goaf chromosomal code for the newborn coal mine using the genetic algorithm, and randomly generate the 0-1 sequence of the goaf simulation model of the coal mine according to the genetic algorithm; Step 4: Using the lattice Boltzmann method to calculate the pressure, velocity and component concentration of the gas inside the coal mine goaf simulation model randomly generated in the step 3; Step 5: Determine whether the ratio of the absolute error of the calculation result of the lattice Boltzmann method in the step 4 to the parameter data monitored by the sensor in the physical similarity model in the step 1 is less than the relative error threshold, and if so, output the three-dimensional coal mine goaf Reconstruct the model, that is, complete the reconstruction of the caving form of the coal mine goaf, if not, return to step 3. 2. the reconstruction method of coal mine goaf caving form according to claim 1, is characterized in that, the calculation formula of the absolute error of lattice Boltzmann method calculation result in the described step 5 is as follows: Δ=|C-L|; Among them, Δ is the absolute error of the calculation result of the lattice Boltzmann method, C is the calculation value of the lattice Boltzmann method, and L is the monitoring parameter data of the monitoring points of the physical similarity model. 3. The method for reconstructing the caving form of coal mine goaf according to claim 1, characterized in that the relative error threshold in step 5 is specifically set according to actual conditions.

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