CO2 deep-hole presplit explosions are an important technology for enhancing gas drainage in low-permeability coal seams. In the process of a CO2 gas explosion, the initial burst crack generated by the shock wave expands the crack tip under the splitting action of high-pressure CO2 gas. To explore the effects of CO2 gas explosions on crack tips, we constructed an analytical model of gas pressure attenuation at different positions based on fluid motion equations, proposed equations for crack opening and growth rates, and inverted the energy field of the whole process of CO2 blasting. We used a test platform for the independent development of CO2 gas explosions under experimental conditions of 1 MPa axial pressure and 2 MPa CO2 gas pressure and a VIC-3D measurement system. We conducted the gas explosion experiments on prefabricated cracked samples with a crack length of 10 mm and width of 0.2 mm to analyze the dynamic response of the crack tip. The results showed that there were three stages in the propagation of a prefabricated crack under the action of a CO2 gas explosion. The first stage, from 0 to 290 ms, included energy storage at the crack tip and a maximum opening rate increment of 0.0043 m/s. The second stage, from 291 to 295 ms, was rapid crack propagation with maximum opening rate increment and propagation rates of 0.1865 and 5.35 m/s, respectively. In the third stage, from 296 to 309 ms, the crack tip propagated slowly, the maximum opening rate increment and growth rates were 0.0969 and 5.81 m/s, respectively, and the crack arrest coordinates were 4.57 and 35.28 mm. The experimental study verified the accuracy of the calculation model, proved that CO2 gas promotes the growth of crack tips, explained the spatiotemporal evolution mechanism of the CO2 explosion process, and provided experimental support for subsequent research related to explosions.
For safety engineering majors, it is very important to cultivate the practical ability of professional talents. Due to the difficulty of conducting experiments in dangerous environments, a virtual simulation experiment teaching platform was established. The platform allowed students to understand the structure of the subway ventilation room, and master the control requirements of the ventilation system in the event of sudden fire, blockage, and failure in the subway. Its construction used technologies such as 3D modeling, human–computer interaction, and VR. To test the teaching effect of the simulation experiment platform, two indexes of operating skills and cognitive load were selected to study and analyze the experimental results of students. The research adopts the method of stratified sampling, 46 boys and 10 girls were selected from the first-year students majoring in safety engineering, and they were randomly divided into experimental group and control group, with 23 boys and 5 girls in each group. The experimental group used the simulation platform for teaching, while the control group used the traditional teaching method. The score of the assessment module in the platform was taken as the index of students’ operating skills, and the cognitive load test was carried out by questionnaire to test the teaching effect. The test module scores showed that the average score of the experimental group was 32.79 points higher than that of the control group, and the results of the cognitive load test questionnaire showed that the experimental group scored 35.14% lower than the control group. The research shows that the virtual simulation experiment has a stronger teaching effect than the field experiment.
The construction of subway tunnels in the coastal section is affected by special soil quality, with complex construction conditions of unstable soil and vulnerability to groundwater corrosion. The design difficulty of subway tunnels is greatly increased, and the safety performance in the event of an earthquake is greatly reduced. To study the changes in shield tunnel lining structure under earthquake and propose damping measures, ANSYS software is used to conduct tunnel soil numerical simulation. Firstly, static analysis and modal analysis are carried out, and it is found that the maximum displacement deformation occurs at 3.8 cm of the arch crown, and the maximum stress occurs at 2.6 × 107 Pa of the left and right wall corners, 8 easily deformed points are obtained at the same time. Input EI_Centro EW forward 19 s seismic wave is used to analyze the displacement, acceleration and stress vibration characteristics of tunnel lining. The upper part of the lining is more vulnerable to earthquake, and the right arch waist is subject to the maximum stress, reaching 1.37 × 10−4 Pa, the maximum displacement deformation point is 3.65 × 10−10 m at the right wall. To reduce the impact of earthquakes on tunnel lining, the damping scheme of adding an isolation layer is adopted. Using foam concrete isolation material can reduce the stress of the arch waist by 74.6%, and rubber isolation material can reduce the stress by 80%. In consideration of groundwater corrosion and subsequent engineering construction, it is recommended to use foam concrete as the material for the isolation layer. This study can provide a theoretical basis for the design of metro tunnels in offshore areas.
As the main component of the tractor gearbox, the box has the functions of shifting operation and carrying the cab, it also carries part of the framework function. If the strength, stiffness, or vibration characteristics of the box do not meet the allowable requirements, large vibration and noise may occur, and even there is the possibility of fracture in some limiting conditions. To solve this problem, according to the structural parameters of a gearbox, the three-dimensional model of the box was established by using the three-dimensional modeling software Creo. According to the dangerous degree of the transmission load when the tractor is working normally, three vehicle working conditions are selected: a round of suspension conditions, farm tool lifting conditions, and emergency turning conditions. In addition, according to the transmission ratio of each gear meshing inside the gearbox, two gear conditions are selected: gear condition one and reverse gear condition one. The forces of the box under these extreme conditions are analyzed. The static analysis and modal analysis of the tractor gearbox are carried out by using the Static Structural module of ANSYS Workbanch. The deformation, equivalent stress distribution, and modal vibration frequency of the gearbox are tested. The topology optimization method is used to improve structural defects and reduce box quality. The results show that the weight of the optimized box reduces by 8.44%, the deformation decreased by 15.89%, and the equivalent stress decreased by 18.34%. The strength and stiffness of the box are improved, the quality is lightweight, the waste of resources is reduced, and the heat dissipation performance and fracture resistance of the box are enhanced.
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