Abstract: In recent years, there have been a number of developments in deep mining research with respect to safety mechanisms and disaster prevention and control. However, it will be difficult to fully resolve the challenges associated with disaster prevention and reduction based on current theories and technologies, and as yet no sound deep mining research approach regarding cataclysm and its control has been established. This paper reviews the literature and discusses problematic research areas associated with deep mining disasters, including in-situ stress measurement and its distribution law, deep rock mechanics and the coupling damage mechanism, dynamic disaster mechanism and prediction, and the water inrush mechanism and early warning, as well as the surrounding rock deformation mechanism and control technologies. This paper analyzes the deficiencies in existing research and identifies key problems that must be solved in deep-mining-induced disasters. Lastly, this paper indicates future prospects in the study of ultra-deep mining disasters.
Abstract: The new support way-square confined concrete (SQCC) arch in complex-condition underground engineering applications has higher supporting strength and post-bearing capacity. The grouting holes become key parts of the arch with local weakening and stress concentration effects and greatly influence the bearing capacity of the whole arch. As such, it is necessary to reinforce this area. In laboratory tests and numerical experiments on SQCC test specimens with grouting holes, the strengthening mechanism was investigated by comparative analysis of the mechanical properties, including the deformation and failure patterns, load displacement curve, and ultimate bearing capacity. To compare the different reinforcing effects, strength and economic indexes were established. The results show the ultimate bearing capacity of a short column with grouting holes to be reduced by 29.9% compared to the SQCC short column. In a case study of the SQCC150×8 short column, the reinforcement method using two-angle steel exhibited better reinforcing effect, improving both the strength and economic indexes of short columns up to 148.7% and 90.8%, respectively. When the length of the reinforcement plate ranges from 180-240 mm and the plate thickness is 8 mm, the reinforcement effect is best, and the economic index also reaches its peak value. Moreover, the angle steel strengthening (ASS) experiments was conducted in a full-scale laboratory test. The application of SQCC arches in roadway supports has a good effect, and these research results provide a basis for the design of confined concrete support.
Abstract: The flotation separation of galena, sphalerite, and pyrrhotite was investigated with CCSL as a depressant. Flotation test results show that galena and sphalerite can float but pyrrhotite can barely float with CCSL as a depressant. The flotation tests also show that galena can be separated efficiently from pyrrhotite, and that sphalerite can be separated on the whole from pyrrhotite, but the separation efficiency of the former is much better. The X-ray photoelectron spectroscopy (XPS), IR spectrum, and Zeta potential analysis results indicate that the interaction of sodium acetate and pyrrhotite is not only physical absorption. The UV spectrum indicates that the decline in floatability of pyrrhotite is due to the hydrophilicity caused by CH3COO- being stronger than that caused by dixanthogen, and the xanthate adsorption on pyrrhotite is not prohibited by CH3COO-. The CH3COO- reacts not only with pyrrhotite, but also with H+ in water as a H-bond, so the pyrrhotite becomes hydrophilic.
Abstract: Two groups of Mn metal fuels with different particle-size distributions were prepared with median diameters of 18.73 and 5.24 μm. The particle-size distribution was measured by a laser particle-size analyzer, the surface morphology was analyzed via scanning electron microscopy (SEM), and energy dispersive spectrometry (EDS) determined the contained elements. For the NaClO3, the NaClO3 and Co3O4 as well as NaClO3, Co3O4, and Mn mixtures were subjected to TGA-DSC combined thermogravimetric analysis. The effects of the Mn metal fuel particle size on the catalytic effect and pyrolysis stability of NaClO3 were investigated by comparing the pyrolysis onset/final temperature and other characteristics. The results show that although Co3O4 has a significant catalytic effect on the pyrolysis of NaClO3, e.g., the onset pyrolysis temperature decreases from 512.3 to 333.0℃, it can lead to instability in NaClO3 pyrolysis, namely the pyrolysis steps from 1 to 3. The Mn metal fuel has a clear catalysis effect on the intermediate products of NaClO3 pyrolysis. With the decrease in particle size, the catalytic effect gradually increases and the pyrolysis final temperature Tf decreases from 419.8 to 351.9℃. Meanwhile, the pyrolysis step of NaClO3 decreases and the temperature range of pyrolysis decreases from 180.6 to 19.4℃, indicating that the pyrolysis process becomes more stable.
Abstract: The solvothermal method was used to prepare Fe3O4@C core-shell microspheres. The structure and morphology of the nanocomposite powders were characterized by X-ray diffraction, transmission electron microscopy, and Fourier transform infrared spectroscopy, and then the particles were used as heterogeneous catalysts in the UV-Fenton removal of VOCs in gas. The results show that the Fe3O4@C core-shell microspheres have a strong adsorption capacity for VOCs due to the outer layer of Fe3O4 being coated with a carbon layer of uniform thickness and pore structure. For sparingly soluble organic gases such as octane, the adsorption of these particles could increase the total concentration of VOCs in the liquid phase. Therefore, the opportunity for the Fenton reagent to be in contact with the VOCs gas increases, causing a significant improvement in the gas removal efficiency. Moreover, the cooperation factor β was introduced to evaluate the synergistic effects in the integrated process of the adsorption-catalytic oxidation by the core-shell structure particles.
Abstract: In-situ research was conducted to illuminate the high-temperature behavior of primary carbide in H13 steel that had been cast in different ways. Experimental observations indicate the obvious segregation of Cr, Mo, V, and C in the interdendrite zone of continuously cast and electroslag remelting (ESR) samples. In the interdendrite zone, primary carbide is composed of Cr, Mo, V, and Ti. A liquid phase was observed to occur around the primary carbide of two as-cast samples cast by continuous casting and ESR processes when heated to 1200℃ and 1250℃, respectively. The temperature at which the liquid phase appears agrees well with theoretical calculations. The liquid-phase region expands as the heating temperature increases and the continuous casting sample shows a larger liquid zone. The emergence of a partial liquid phase accelerates the diffusion of the segregated elements and is an important factor in the high-temperature behavior of primary carbide.
Abstract: Resin transfer molding (RTM) and hot-pressing molding (HPM) were used to prepare phenolic resin matrix composites reinforced by carbon fiber. The tribological properties of the materials were tested using a MS-T3001-type friction and wear tester. A scanning electron microscopy and three-dimensional laser microscopy were used to analyze the superficial microstructure of the friction materials. Furthermore, a comparative analysis was employed to investigate the influences on the tribological properties by two types of material-forming processes. Results indicate that the friction coefficient decreases with increased relative sliding speed and workload. For the RTM friction material, the main form of wear is adhesive wear and fatigue wear, the coefficient of friction is 0.075-0.120, and the wear rate is 7.5×10-8 g·N-1·m-1. In contrast, for the HPM friction material, abrasive wear is the main form of wear, and the friction coefficient and wear rate are 0.085-0.130 and 1.5×10-8 g·N-1·m-1, respectively.
Abstract: To improve the stability of the six-high cold rolling mill, the roll offset method is often used. This paper uses ABAQUS finite element software to establish the rolls-strip coupling model. The study analyzes typical roll systems with different roll offsets to determine the effect of different roll offsets on the shape-control characteristics of the six-high cold rolling mill. Specifically, the results show that when the intermediate roll offset is positive, the bending force of the work rolls has the best control effect on the quadratic crown, as well as great influence on the quartic crown. For the four roll offsets used, the efficiency of the bending force of the intermediate rolls on the quadratic and quartic crowns of the strip is almost the same, ranging from 0-300 kN. When the intermediate roll offset is positive, the bending force of the intermediate rolls has the best control effect on the quadratic crown, ranging from 300-500 kN. When the work roll offset is positive, the bending force of the intermediate rolls also has a great influence on the quartic crown. The controlling tendencies of the shift of the intermediate roll on the quadratic crown are almost the same for different roll offsets, and the efficiency of negative roll shifting on the quadratic crown is better than that of positive roll shifting. Intermediate roll shifting also has a great influence on the quartic crown when the work rolls are offset.
Abstract: To accurately describe the material degradation process from elastoplastic deformation to final rupture, an elastoplastic constitutive model was established to feature damage and crack initiation. A user-defined material subroutine VUMAT was developed, based on the Abaqus/Explicit platform, and its reliability was validated with an example. The damage parameter values were determined in cyclic loading-unloading tensile tests, using the Young's modulus weakening method. To predict the sheared edge quality, a finite element model of rotary blanking coupling with a Lemaitre damage model was built and the numerical results were compared with experimental results. The influences of blanking clearance, die wear and sheet metal thickness on the sheared edge quality, blanking force and torque were investigated. The results show that the sheared edge quality of the leading cutting edge is generally better than that of the trailing cutting edge, but the burnish depth of the leading cutting edge tilts at an angle. The rollover is larger, as is the die clearance. There is an extreme increase in the burr height when the degree of die wear is higher. The highest blanking force and torque values increase as the sheet metal thickness increases.
Abstract: Cutting energy can be transformed into cutting heat, which directly affects the cutting temperature. Therefore, it is important to understand the generation, transfer, and transformation of cutting energy to cutting temperature. In this paper, an innovation design of a new cemented carbide micro-pit turning tool specially cutting 304 stainless steel was taken as an example. Through comparative studying the cutting performance of new micro-pit turning tool and original turning tool, the relationship model between cutting energy and cutting temperature of rake face was established. And the prediction of shear energy and friction energy of the new micro-pit turning tool and experimental verification were carried out. The results show the input energy to be reduced by 8.96%, the shear energy to be decreased by 10.50% and the friction energy to be reduced by 5.32% compared with the original turning tool under dry cutting conditions using the manufacturer's recommended cutting parameters. The cutting surface temperature can be reduced by a decrease in the cutting energy. The cutting energy prediction model can serve as a reference for predicting cutting energies and cutting face temperatures under complex cutting conditions.
Abstract: To investigate the feasibility of speed adjustment of the drum and the influence of speed adjustment on the dynamic performance of the transmission system, a cutting-haulage coupled model of the electromechanical transmission system of the coal shearer was established using MATLAB/Simulink. Then, considering reliable operation and efficient production, four types of speed adjustment schemes were formulated for the overload conditions of the cutting unit. The method of selecting the speed adjustment scheme was proposed according to the target cutting thickness, while the motor current was chosen as a feedback signal to calculate the target cutting thickness. Lastly, the electromechanical dynamic characteristics of the system corresponding to different adjustment schemes were simulated and compared. The results show that when the overload ratio of the cutting motor is small, using the drum speed adjustment scheme can not only reduce the system load, but also enable the coal-mining productivity to not be affected. Conversely, the system reliability can be improved when the haulage speed adjustment scheme is used, and using the haulage-drum sequential speed adjustment scheme can lead to high productivity.
Abstract: The DC-DC converter can adjust and control the voltage and power outputs of renewable energy systems, including fuel cell and photovoltaic cell systems. This study used high-efficiency SiC MOSFETs in a two-phase interleaved boost-type DC-DC converter in fuel cell vehicles. This paper analyze the performance of the converter with the SiC power device, based on calculation, simulation, and experimental results. The results show that the application of new SiC devices in high-power DC-DC converters can improve the power density, converter reliability, and power system efficiency. The results can be used for reference in the application of new power electronic devices and related research in the renewable energy filed.
Abstract: The output voltage computation model of a magnetostrictive displacement sensor was established considering the influence of the hysteresis effect based on the Jiles-Atherton hysteretic model, Wiedemann effect, and piezomagnetic effect. The consistency between the calculated data and experimental data shows the correctness of the output voltage model. The structure of the traditional Fe-Ga magnetostrictive displacement sensor was improved, eliminating displacement measurement hysteresis caused by the hysteresis effect of the magnetostrictive material, thereby reducing the influence of the residual magnetization and the driving pulse current on the output voltage so that the voltage signal-to-noise ratio increased from 14.7 to 27.6 dB. A type of Fe-Ca magnetostrictive displacement sensor was fabricated. The experiments show that the new structure can improve the linearity, repeatability, hysteresis, and precision of the magnetostrictive displacement sensor. Based on this new sensor structure, the research provides a theoretical and experimental basis for optimization and manufacture of magnetostrictive displacement sensors.
Abstract: To overcome the insufficiencies of varying illumination, large displacement estimation, and outlier removal, a motion-adaptive V1-MT (MAV1MT) motion estimation algorithm based on machine learning and a bio-inspired model of sequence image was proposed, starting from the theory of visual cognition. First, a structure-texture decomposition technique based on the Rudin Osher Fatemi (ROF) model was introduced to manage the variation in illumination and color. Then, a pooling stage at the MT level with non-normalization, which combines the afferent V1 responses using the adaptive weights trained by ridge regression, is modeled to obtain the local velocities. Finally, through introducing the coarse-to-fine method and pyramid structure subsampling of the local motion, the MAV1MT model is used on realistic video. Theoretical analysis and experimental results suggest the new algorithm, which is more fitting to information processing features of the human visual system, has universal, effective and robust motion perception performance.
Abstract: Most traditional classification algorithms assume the data set to be well-balanced and focus on achieving overall classification accuracy. However, actual data sets are usually imbalanced, so traditional classification approaches may lead to classification errors in minority class samples. With respect to imbalanced data, there are two main methods for improving classification performance. The first is to improve the data set by increasing the number of minority class samples by over-sampling and decreasing the number of majority class samples by under-sampling. The other method is to improve the algorithm itself. By combining the cluster-based under-sampling method with ensemble classification, in this paper, an approach was proposed for classifying imbalanced data. First, the cluster-based under-sampling method is used to establish a balanced data set in the data processing stage, and then the new data set is trained by the AdaBoost ensemble algorithm. In the integration process, when calculating the error rate of integrated learning, this algorithm uses weights to distinguish minority class data from majority class data. This makes the algorithm focus more on small data classes, thereby improving the classification accuracy of minority class data.
Abstract: Fully connected Boltzmann machine models can be used to provide a comprehensive description of statistical dependencies between sparse coefficients but with high time complexity. To improve the speed and quality of the Boltzmann machine-Bayesian matching pursuit (BM-BMP) method, an improved algorithm was proposed. First, the maximum a posteriori (MAP) estimation of the BM-BMP algorithm is decomposed into its value at the last iteration and an increment; thus, it only needs to calculate the increment in each iteration, which greatly reduces the computational time. Second, by calculating the mean of the significant MAP estimations, an effective approximation is obtained for the minimum mean square error (MMSE) estimation and a smaller reconstruction error is achieved. Compared with the BM-BMP, this method reduces the running time on average by 73.66% while improving the peak signal to noise ratio (PSNR) by 0.57 dB.
Abstract: A brain computer interface (BCI) system was proposed to realize the two-dimensional indoor space target searching for multi-rotor aircraft. This system consists of semi-autonomous navigation and decision subsystems. The semi-autonomous navigation subsystem is employed to provide feasible directions for the decision subsystem and avoid obstacles semi-automatically for multi-rotor aircraft. The decision subsystem utilizes the cross-correlation (CC) and logistic regression (LR) methods to implement motor imagery (MI) electroencephalogram (EEG) feature extraction and classification, respectively. The actual indoor target searching experiment validates the feasibility and effectiveness of this BCI system. Compared to similar methods, the proposed BCI system reduces the burden of the subjects and the control difficulties. The control precision increases by approximately ±10 cm.
Abstract: Existing grouting test devices have difficulty providing sufficient sealing effect and experimental space in multifunctional tests. Due to the limitations of current devices, this paper developed a new comprehensive grouting reinforcement test system. The major advantages of this system include:(1) its moderate size and reasonable structure that offer a large experimental space and good sealing property; (2) its ability to simulate the different groundwater environments and grouting conditions of rock soil media; (3) its ability to obtain a variety of physical information for researching the space-time response law of reinforcement parameters; and (4) its ability to simultaneously test the compressive and shear strengths of the solid and microscopic grouting coupling mechanisms of the slurry-rock interface. An orthogonal grouting reinforcement test was designed for fault breccia using the new device. The study then investigated the grouting reinforcement mechanism of fault breccia with respect to the stress response-transfer characteristics, the growth law of solid strength, and the reinforcement mode. The test results show fault breccia to be mainly reinforced by permeation grouting and the grouting reinforcement model can be divided into three types-substrate, micro-splitting, and significant splitting. The study achieved an increase in the strength of grouting reinforcement bodies by changing the medium connection mode and fitted the empirical formula for the increased strength of solid grouting. It also determined the distribution and transfer mechanism of grouting pressure.
Abstract: The variation of properties of concrete with initial damage under sulfate and wet-dry-cycle environments was experimentally investigated. With increased corrosion time, changes in the parameters of concrete with initial damage were analyzed, including mass, ultrasonic velocity, compressive strength, stress-strain curves, and the activities of acoustic emission under uniaxial compression. A quantitative evaluation and parameter fitting for corrosion damage was made based on damage mechanical theory. Based on the acoustic emission characteristics, a damage model of corroded concrete with initial damage was established and its damage evolution was analyzed. Using environmental scanning electron microscopy (ESEM) and energy-dispersive X-ray analysis (EDX), the damage mechanisms were revealed in observations of the microstructures and element compositions of concretes with initial damage induced by sulfate corrosion. The research results show that with increased erosion time, the mass, ultrasonic velocity, and compressive strength of concrete with different degrees of initial damage first increase and then decrease. Increases in the degree of initial damage may accelerate the degradation of physical and mechanical properties, but a threshold effect exists. Compressive strength and ultrasonic velocity can be regarded as damage variables, and corrosion damage evolution equations and the functional relationship between different damage formulas were established. With increased erosion time, the stress-strain curve of concrete with initial damage is obviously concave-upward and the elastic-stage time period can be comparatively shorter whereas the yield-stage time period increases. An increase in the degree of initial damage results in an obvious attenuation of the acoustic emission activity, which lags behind the time of the obvious acoustic emission response. Based on the acoustic emission characteristics, the damage evolution process of concrete with initial damage can be divided into three stages, including the compaction, stable damage evolution and development, and accelerating damage development stages. With an increase in the degree of initial damage, stronger corrosion reactions and composition changes occur inside the concrete. Compared to undamaged concrete, the expansion and extension of denser and deeper micro-cracks occur in concrete with initial damage under sulfate attack, which accelerates the degradation of the physical and mechanical properties of corroded concrete.
Abstract: Precise calculation of the stress intensity factors at crack tips is of great significance in accurate analysis of a structure's crack initiation and fracture mode. In this research, a three-dimensional printing technique was adopted to manufacture a non-residual stress plate model, where high-precision printed pre-cracks avoid the occurrence of residual stress compared to traditional manufacturing processes. By comprehensively considering the singular and non-singular stresses at the near-crack-tip region, three constant stresses controlled by the far field were adopted. Multiple parameters of the photoelastic method combined with the least-squares method were applied to analyze the stress intensity factors of mode I and mixed modes in three-point bending tests under different loads, and a theoretical solution comparison was conducted. Results show that compared with the theoretical solution, the average calculation error for the mode I stress intensity factor is 6.1% and those for I-Ⅱ mixed modes are 6.4% and 5.5%, respectively. This slight calculation error verifies the reliability and accuracy of the multiple-parameter method and provides a reference for further precise calculations of the stress intensity factors using the photoelastic method.
Monthly, started in 1955 Supervising institution：Ministry of Education Sponsoring Institution：University of Science and Technology Beijing Editorial office：Editorial Department of Chinese Journal of Engineering Publisher：Science Press Chairperson：Ren-shu Yang Editor-in-Chief：Ai-xiang Wu ISSN 2095-9389CN 2095-9389
