Research on mine ventilation network solution and collaborative control technology

With the development of intelligent ventilation system in domestic coal mines, the demand for ventilation network solving software is becoming more and more intense. Aiming at the problem that the traditional ventilation network solution algorithm is difficult to meet the increasingly complex ventilation system solution needs of domestic mines, and the lack of functions of the collaborative control of ventilation equipment and facilities, this paper uses theoretical analysis combined with mine reality to study the relevant theories and algorithms in the field of ventilation network solution and collaborative control at home and abroad, and optimizes the network solution and collaborative control related algorithms such as iterative calculation of ventilation network, identification and stability analysis of angle-linked wind network, natural wind pressure calculation, local fan collaborative control, and collaborative control of damper and wind window. Provide theoretical guidance for future network solution software development.


Introduction
In recent years, the intelligent construction of coal mines in China has developed rapidly under the guidance of multiple factors of national policies, industry demand and technological development.In 2022, the National Energy Administration issued the "Intelligent Demonstration Coal Mine Acceptance Management Measures", which puts forward clear requirements for the intelligent construction of coal mine ventilation systems, and ventilation network solution software is in strong demand as the core embodiment of ventilation system intelligence [1][2][3].There are many research results in the field of ventilation network solution of underground coal mines at home and abroad.With the construction of intelligent ventilation system in domestic coal mines, the use of existing ventilation network solution software has exposed the following problems: (1) There are dozens of network solution methods, and the solution results of different methods vary greatly, and for software developers, the choice of solution methods in software development has become a problem; (2) The existing software mostly uses the Scott-Hinsley method for solving, and the traditional algorithm is slow to solve the increasingly complex ventilation system in domestic mines, which is difficult to meet the needs of intelligent construction; (3) Most of the existing software only has network solving functions, and does not have further collaborative control capabilities of ventilation equipment and facilities [4][5].In view of the above problems, this paper deeply analyzes the relevant methods in the field of ventilation solution at home and abroad, summarizes the optimization network solution and collaborative control methods based on the actual use needs of mines, and provides reference for the development of integrated ventilation control software in the future.

Scott-Hinsley Method
The principle of the Scott-Hinsley method is to obtain a nonlinear equation system by taking a set of cotree chord air volume as a variable, and obtaining a system of nonlinear equations from the wind pressure balance equation of each independent loop, using the approximation of a group of roots in the equation to expand the Taylor series of the equation, simplifying it to obtain the calculation formula of the air volume correction value, and then obtaining the approximate true value of the air volume through successive iterative calculations.
First, the equations are established using the law of air volume balance, the law of wind pressure balance and the law of mine ventilation resistance [6][7]: Combining the above equations yields a new wind pressure balance equation： Taking the cosaurine air volume as a variable, the wind pressure balance equation system of each independent circuit is established: Equation ( 5) is expanded by the Taylor series and ignoring the second-order trace amount: Equation ( 6) is obtained by writing it as a matrix and assuming a diagonal advantage: The matrix of equation ( 7) can be expressed as: is a function about   , and the chord air volume is repeatedly iteratively calculated and corrected until the predetermined air volume error is met, the iterative calculation is completed, and the air volume value of each circuit is obtained.

Newton-Raphson Method
In the process of calculating the modified value of the Scott-Hinsley method, the Jacobian matrix is simplified twice, which increases the calculation error, and the principle of the Newton-Raphson method is not to simplify the Jacobian matrix and directly calculate.Its advantage is that the results are more accurate than the Scott-Hinsley method, and the disadvantage is that the calculation process is more complicated, and it is greatly affected by the selected iteration preliminary value, the iteration initial value is selected appropriately, and the convergence is fast, on the contrary, the convergence is very slow or even not convergent, so it is not suitable for the increasingly complex ventilation network solution in China [8].

Kyodai Second Test Method
The first two methods are used to solve the nonlinear wind pressure balance equation.This method first substitutes the air volume balance equation into the ventilation resistance law equation, and then substitutes the air pressure balance equation.Assuming that the branch air volume is a certain value q, the linear equations can be solved, but it also faces the problem that the calculation process is complicated and the convergence speed is not fast enough [9].

Angular ventilation network identification and stability analysis
The core problem of the diagonal wind network is the identification and stability analysis of the diagonal wind path.

Angular ventilation network identification
The identification of diagonal wind path includes directed graph path method, undirected graph path method and node method.The core idea of the directed graph path method and the undirected graph path method is consistent, that is, two paths from the air inlet shaft to the air return shaft are found in advance, and all the remaining branches are analyzed in turn.If the starting and ending nodes are on these two paths respectively, it indicates that this branch is an angular branch, otherwise it is not.These two methods are slow in operation.The main reason is that there are not only two paths from the air inlet shaft to the air return shaft, and the two paths are randomly combined to form a combination.The remaining branches need to be re-identified again, which takes a long time.
The node method adopts reverse thinking, and begins not to find each channel from the inlet shaft to the return shaft, and directly determines whether each branch is a diagonal wind path.The specific discrimination method is as follows: ⊙ is a node, rectangle representing any number of nodes.Z and Z � are the points of separation and confluence, respectively.V i and V j are the common nodes of the left and right pathways, that is, the two nodes of the diagonal wind path.The common nodes V i and V j are used to cut the left and right paths to form a network subgraph, and the path segments between Z → V i and V j → Z � are removed to obtain Figure 1 (b).According to the definition of the path method, if the following conditions are satisfied at this time: Then it is considered that the wind path   belongs to the diagonal wind path.The specific discriminant procedure is as follows: For a known wind path   , it is first assumed that it is a diagonal wind path.If two paths satisfying Eq. ( 9) can be found, it is a diagonal wind path, and vice versa.By definition, there is at least one path   such that Z to   is reachable, that is: To avoid   ∈   , need to follow: itself is the end node of the wind path, so there must be a path   up to  ̅ , let: Combining Eq. (11), we get: The formula (13) can determine one of the two paths of a path satisfying formula (9).At the same time, there is at least one path   such that   can reach  ̅ , which can be obtained by the same method: The simultaneous equations ( 13) and ( 14) obtain: For a certain wind path, if two paths of Satisfying Formula (15) can be found, it can be concluded that this wind path belongs to the diagonal wind path.

Stability analysis of Angular ventilation network
As shown in Figure 1 (c), the wind direction of the diagonal wind path 5 is only related to the wind resistance of the associated branches.The specific calculation method is as follows: It can be seen from Eq. ( 16) that the airflow direction of the diagonal wind path in the simple diagonal wind network depends entirely on the wind resistance ratio of the associated wind path, and has nothing to do with the size of its own wind resistance.The closer the K value is to 1, the more unstable the flow in the diagonal wind path is and the easier it is to reverse.In addition, the diagonal wind network has the following characteristics: (1) The total air pressure of the wind network increases with the increase of the wind resistance of the wind path, and the total air volume of the wind network decreases with the increase of the wind resistance of the wind path.
(2) With the increase of the wind resistance of the diagonal wind path, the air volume of the diagonal wind path decreases, the air volume of the associated wind path with the same wind direction of the diagonal wind path decreases, and the air volume of the associated wind path opposite to the wind direction of the diagonal wind path increases, but the total air intake of the wind network decreases, and the air volume of the associated wind path increases or decreases to a certain value.It tends to be balanced and is no longer affected by the change of the wind resistance of the diagonal wind path.
(3) With the increase of the wind resistance of the associated wind path on the inlet side, the air volume of other wind paths decreases except that of the associated wind path in parallel.After the air volume of the corner coupling air path is reduced to a certain value, the air flow is reversed; however, the decreasing trend of air volume on the return air side will not change with the reverse wind direction of the diagonal wind path, and the total air volume of the diagonal wind network will decrease.The influence of the increase of the wind resistance of the associated air path on the return air side on the air volume of each air path in the diagonal ventilation network shows the same law.

Coordinated control of Mine local ventilator
With the change of the length of the heading face and the change of the gas concentration, the required air volume of the heading face is in a real-time changing state.Local ventilator is the main means of ventilation regulation in the area of underground tunneling working face, and the local ventilator system in coal mine now faces two problems: one is the high energy consumption of local ventilator operation, and the other is that it is difficult to control the air volume according to the gas concentration.This part studies the relationship between the required air volume of the heading face and the length of the working face, and puts forward a reasonable scheme for the cooperative air control of the underground mine local ventilator.

Air volume required for heading face
Based on the number of personnel in the excavation face, the gas concentration and the amount of explosives used, the air demand Q of the excavation face is calculated, and the air demand of the excavation face is the largest of the three values.It is worth mentioning that when the gas emission concentration is used as the basis for calculating the air demand, it is necessary to consider whether the roadway is single-lane excavation or double-lane tunneling, and the main impact of single-roadway or double-roadway excavation on the calculation of air demand is that the gas concentration monitoring value is different, and there is only one  2 sensor for single-lane gas concentration monitoring, and only the average value of this sensor needs to be taken when taking the value; There are two  2 sensors in the double-lane tunneling, and the average value of the monitoring data of these two sensors needs to be taken.The analysis process of air demand of the excavation face is shown in Figure 3.  (3) On-demand air supply control method for local ventilator Considering that the local fan cannot always be in the state of frequency conversion control in the actual use process, this paper puts forward the problem of air leakage of the local ventilator according to the required air volume of the heading face and the change of the length of the working face.This paper proposes a segmented air regulation method, that is, when the required air volume is in a certain range, the local ventilator is adjusted to the corresponding segmented frequency for air supply.The specific process is as follows:

Conclusion
Combined with the analysis of the actual production conditions of domestic coal mines, the Scott-Hinsley method is more suitable for the calculation of ventilation networks in domestic coal mines, and the judgment method of angular air path is further proposed, and the influencing factors of stability are analyzed.Regarding the cooperative control of ventilation equipment and facilities, the analysis algorithm of air demand in the roadway and the technical method of collaborative control of local ventilator were proposed.The specific conclusions are as follows: (1) Scott-Hinsley loop air volume method has the advantages of simple calculation process and fast convergence speed compared with Newton-Raphson method and Peking University second trial method, which is suitable for complex mine ventilation network calculation.
(2) The undirected graph path method and the directed graph path method to identify the diagonal wind path are complex and time-consuming.The node method further reduces the time-consuming on the basis of ensuring the accuracy of identification.The wind direction and stability of the diagonal wind path are independent of the wind resistance of the diagonal wind path itself, and are related to the wind resistance of the associated wind path of the diagonal wind path.
(3) The air supply volume of the local ventilator is related to the length of the heading face, and the sectional adjustment method can be adopted to realize the on-demand air supply.

Figure 1 .
Figure 1.Simple Angular ventilation network schematic diagram Figure 1 (a) The left and right pathways P 1 and P 2 are composed of the inlet side associated pathway P i and the outlet side associated pathway P o of the diagonal wind path P d .⊙ is a node, rectangle representing any number of nodes.Z and Z � are the points of separation and confluence, respectively.V i and V j are the common nodes of the left and right pathways, that is, the two nodes of the diagonal wind

Single-lane excavation Double-lane excavation Figure 2 .
Schematic diagram of single-lane excavation and double-lane tunneling the maximum value of Qp,Qi and Qj as the air demand Qx Take the maximum value of Qp and Qi as the air demand Qx

Figure 3 .
Figure 3. Airflow analysis algorithm 4.2.Mine local ventilator provides air on demand After calculating the required air volume Q of the heading face, it is necessary to consider the change of the length of the heading face and the increase of the air leakage of the air duct, and the change of the air supply volume of the local fan.(1) Calculation method of outlet air volume of local ventilator Head air volume = air duct suction volume (one-hundred meters air leakage rate × air duct length / 100) (2) Calculation method of air leakage of local ventilator duct local ventilator 100 meters air leakage rate = 100 (Duct air volume-Duct air volume) / (Duct length × Duct air volume) (3) On-demand air supply control method for local ventilator

Figure 4 .
Figure 4. Collaborative air control process of local ventilator