The unreasonable design of guide vanes in the axial fan could have negative effects. In order to enhance the performance, the relationship between the air volume flow rate of the selected axial fan and geometric parameters of guide vanes is firstly analysed by DOE and CFD, and optimal parameters are found by the Gaussian Process method. Results show that the number and total chord of guide vanes have a nonlinear effect on the air volume flow, and the total chord of vanes is the main factor in affecting calculation results. For the particular configuration studied here, the optimal design of guide vanes shows that lessening the chord of vanes by 38 mm and increasing the number of the vanes to 18 could produce more airflow under the same rotation speed.

Pore and fracture structure heterogeneity is the basis for coalbed methane production capacity. In this paper, high-pressure mercury intrusion test curves of 16 coal samples from the Taiyuan Formation in the Linxing area are studied. Based on the fractal dimension values of mercury intrusion and retreat curves, the correlation between the two different fractal parameters is studied. Then, the permeability variation of different types of coal samples is studied using overlying pressure pore permeability tests. The correlation between the permeability variation of coal samples and dimension values is explored, and the results are as follows. (1) Based on porosity and mercury removal efficiency, all coal samples can be divided into three types, that is, types A, B, and C. Among them, Type A samples are characterized by lower total pore volume, with pore volume percentages ranging from 1000 to 10,000 nm not exceeding 15%. (2) During the mercury injection stage, both the M-model and S-model can reflect the heterogeneity of seepage pore distribution. In the mercury removal stage, the M-model cannot characterize the heterogeneity of pore size distribution in each stage, which is slightly different from the mercury injection stage. (3) The permeability of Type A samples is most sensitive to pressure, with a permeability loss rate of up to 96%. The original pore and fracture structure of this type of coal sample is relatively developed, resulting in a high initial permeability. (4) There is no significant relationship between compressibility and fractal dimension of mercury injection and mercury removal, which may be due to the comprehensive influence of pore structure on the compressibility of the sample.

Many studies have used fractal theory to characterize pore structure distribution heterogeneity through mercury intake curves. However, there is relatively little research on the fractal model calculation of mercury removal curves. In this study, a high-pressure mercury intrusion test is used to describe the pore and fracture distribution heterogeneity (PFDH). The fractal physical meaning of the mercury removal curve was determined by calculating the change in the curve’s fractal dimension value. The results are as follows. (1) According to mercury removal efficiency and porosity, samples can be divided into types A (mercury removal efficiency above 35%) and B (mercury removal efficiency below 35%). In general, type A sample belongs to micro-pore-developed types, and type B samples belong to the macro-pore-developed type. (2) The Menger model (M) represents the complexity of a specific surface area, while the Sierpinski model (S) represents the roughness of the pore volume. Among all the samples, the lower-pore-volume region controls PFDH. (3) According to the calculation results of the single fractal model, it can be seen that the PFDH of type B is stronger than that of type A, which is similar to the results of mercury intrusion. According to the calculation structure of the multifractal model, it can be seen that the volume distribution heterogeneity of type B under various pores is significantly stronger than that of type A. This is opposite to the result of mercury injection. (4) D_M has a relationship with the pore volume percentage at different stages, so the M model at the mercury inlet stage can better characterize PFDH at the mercury inlet stage.

The direct current resistivity method is a primary technique for detecting water-bearing structures ahead of tunnel and coal mine excavation faces. We propose a dipole array advance detection device based on the DC method, and quantified the advance detection effect and the optimum device parameters using numerical simulation, and then verified it on field application. Firstly, the corresponding methods for data gathering and processing are introduced. Then, according to simulation of several geoelectric models, we optimized the device parameters on the detection effectiveness, such as the current electrode numbers, electrode spacing, the shape and position of the anomalous body. The optimal device parameters are then selected based on these considerations. Using the optimized parameters, we finally conducted a field test to obtain the electrical response characteristics ahead of the tunneling face, and the results were validated with the transient electromagnetic method. The device successfully detects low-resistance anomalies at distances of 20 to 50 meters ahead of the tunnel face, validated by borehole drilling. It illustrates that the dipole array advance detection device can at least detect low-resistance anomalies up to 40 meters ahead of the tunneling face, with an electrode spacing of 4 meters and four current electrodes. The device’s high detection accuracy and construction efficiency significantly reduce manpower and material costs in field applications, offering both theoretical and practical value.

In deep underground engineering applications, such as coal mining, coal–rock masses are frequently subjected to repeated loading and unloading conditions. Understanding the evolution mechanisms of their internal three-dimensional fracture fields has become a critical scientific challenge. This study utilized X-ray Microscopy (XRM) to observe changes in internal fractures of coal samples after each loading–unloading cycle, reconstructing the internal fractures and mineral particles. Scanning Electron Microscopy (SEM) and Energy Dispersive Spectroscopy (EDS) were employed to analyze the surface morphology and mineral composition of coal sample cross-sections. The experimental results revealed that: (1) With an increasing number of loading–unloading cycles, the samples’ volumes initially decreased and then expanded, with the expansion accompanied by rapid propagation of CT-scale fractures; (2) During the linear elastic phase, micro-fractures developed progressively but remained small, while sustained stress caused these fractures to interconnect, eventually leading to macroscopic failure; (3) Hard mineral particles within the coal samples, such as iron ore, acted as barriers to crack propagation. These findings indicate that the evolution characteristics of the internal fracture fields in coal–rock masses are influenced by stress state, pre-existing fractures, and the distribution of mineral particles.

Coal rupture in coal mining is prone to cause rockburst dynamic hazards. To investigate the effect of joint structure characteristics on the mechanical behavior and the fracture mechanism of coal sample. In this study, uniaxial compression numerical simulation experiments were carried out on coal sample with joint spacings (JSs) of 3 mm and 6 mm and joint angles (JAs) of 0°, 30°, 60°, 90°, respectively, by using the discrete element method (DEM) method. The combined effect of JS and JA on the mechanical properties of coal and its damage mechanism is investigated. The results show that: (1) By increasing JA, the uniaxial compressive strength (UCS) of the specimen first decreased and increased, and the UCS was minimized at θ = 60°. The cracks in the coal sample were transformed from “X”-shaped distribution to “V”-shaped distribution and were dominated by shear cracks. (2) The enlargement of JS contributed to increasing the UCS of the coal sample. At the same time, the crack length remarkably expanded, and the crack distribution broadened. (3) A smaller JA favors the development of tensile cracks and the aggregation of tensile chains towards the end of the specimen. The cracking inclination of the coal sample showed an inverse “N”-type movement with the increase in JA. (4) As the increase in JS benefits the forming of tensile cracks, the extension of cracking inclination of coal sample diminishes. The spread range and accumulation level of tensile chain grows.