Mining Science and Technology (China)最新文献

Permanent magnet synchronous motor (PMSM) is widely used in mining, and there exists chaotic behavior when it runs. In order to dispel its adverse effect on security in mining, the chaotic system of PMSM was analyzed. With noise disturbances, the complex dynamic characteristics of chaos were also analyzed, and proved the objective existence of chaos. As we all know, it is very difficult for conventional PMSM control to meet the design requirements, therefore, in order to ensure the robustness of the system, the chaotic orbits were stabilized to arbitrary chosen fixed points and periodic orbits by means of sliding mode method. Finally MATLAB simulations were presented to confirm the validity of the controller. The results show that the PMSM with the sliding mode control has a good dynamic performance and steady state accuracy.

Level control in flotation columns is an important factor that influences the recovery and the grade of concentrate from the column. A flotation column is a nonlinear, multi-variable problem with changeable parameters that traditional methods have difficulty controlling. We have applied fuzzy control methods to the flotation column and tested the performance of the design by Matlab/Simulink simulation. The simulations show that level control in the flotation column becomes smoother and more rapid with the fuzzy controller. Compared to PID control methods the overshoot in valve position, the adjustment time, and the robustness of the controller are all improved. This indicates that it is suitable to model fuzzy controllers in applications for the study of automatic control of flotation column.

Nowadays, the researches of using Differential Interferometric Synthetic Aperture Radar (D-InSAR) technique to monitor the land subsidence are mainly on how to qualitatively analyze the subsidence areas and values, but the analysis of subsidence process and mechanism are insufficient. In order to resolve these problems, 6 scenes of ERS1/2 images captured during 1995 and 2000 in a certain place of Jiangsu province were selected to obtain the subsidence and velocities in three time segments by “two-pass” D-InSAR method. Then the relationships among distributions of pumping wells, exploitation quantity of groundwater, and confined water levels were studied and the subsidence mechanism was systematically analyzed. The results show that using D-InSAR technique to monitor the deformation of large area can obtain high accuracies, the disadvantages of classical observation methods can be remedied and there is a linear relationship among the velocities of land subsidence, the water level and the exploitation quantity.

Based on radon gas properties and its existing projects applications, we firstly attempted to apply geophysical and chemical properties of radon gas in the field of mining engineering, and imported radioactive measurement method to detect the development process of the overlying strata mining-induced fractures and their contained water quality in underground coal mining, which not only innovates a more simple-fast-reliable detection method, but also further expands the applications of radon gas detection technology in mining field. A 3D simulation design of comprehensive testing system for detecting strata mining-induced fractures on surface with radon gas (CTSR) was carried out by using a large-scale 3D solid model design software Pro/Engineer (Pro/E), which overcame three main disadvantages of “static design thought, 2D planar design and heavy workload for remodification design” on exiting design for mining engineering test systems. Meanwhile, based on the simulation design results of Pro/E software, the stability of the jack-screw pressure bar for the key component in CTSR was checked with a material mechanics theory, which provided a reliable basis for materials selection during the latter machining process.

The similarities and differences in seepage flow evolution laws of CH₄ and CO₂ during complete stress–strain process of samples were comparatively analyzed. The results show that the seepage flow evolution laws of CH₄ and CO₂ are extremely similar during the stress–strain process, showing that the characteristic first decreased and then increased. A mathematical model was also established according to the relationship of seepage velocity and axial strain. However, due to the strong adsorption ability of CO₂, the coal samples generated a more serious “Klinkenberg effect” under the condition of CO₂. Owing to this, the CO₂ seepage flow resulted into occurrence of “stagnation” phenomenon during the late linear elastic stage II. In the strain consolidation stage III, the increment rate of CH₄ seepage velocity was significantly greater than that of CO₂. In the stress descent stage IV, when the axial load reached the peak pressure of coal, the increment rates of CH₄ seepage velocity presented a turning point. But the changing rate of CO₂ seepage velocity still remained slow and a turning point was presented at one time after the peak of the strain pressure, which showed an obvious feature of hysteresis.

One dimensional non-steady, non-Darcy flow of water in a rock stratum was reduced into a system described by six ordinary differential equations involving five controlling parameters. Through response computations and time series analysis, chaotic behavior in the reduced system was discussed in details. Firstly, the dynamical response of the reduced system under a set of parameters was calculated, and the power spectrum of the attractor was obtained through fast Lagrangian transformation; then the phase space was reconstructed by fixing embedding dimension to be 6 and delay time to range from 1 to 20, and the correlation dimension of the attractor was calculated based on the curves under the coordinates of logarithm of correlation integral vs. logarithm of covering radius; and lastly, the Lyapunov indices of the attractor were calculated by using Gram-Schmit’s orthogonalization method. The results show that the power spectrum of the attractor is continuous; the correlation dimension of the attractor is equal to 2.36; among the Lyapunov indices, LE1, LE2, LE3 are positive, LE5, LE6 are negative, and LE4 fluctuates near zero. All the analysis indicates that there may exist chaos in the system of non-steady, non-Darcy flow.

Coals from different mines are feed in the Zirab plant without any control on weight percentage blending of them. Three major coal types of different ranks (Kiasar, Lavidj and Karmozd) were blended in various proportions to find an optimum condition in flotation circuit in Alborz Markazi coal washing plant. Flotation tests were conducted for prepared blended coal samples to assess floatability of various coal samples. In this paper, mixture design as a statistical method was used to optimize coal blend to increase recovery and grade in Zirab coal washing plant. The statistical analysis showed that the weight percent blending of different coals and interaction between Lavidj and Karmozd regions coal had significant effects on the coal recovery. The optimum condition of 95% recovery and 12% ash content could be reached with 10%, 20%, and 70% blending portion of Kiasar, Lavidj and Karmozd regions coal, respectively.

Gas holdup is one of the key parameters in flotation process. Gas holdup as measured by a differential pressure method was investigated and the relative errors compared to the average gas holdup from the volume expansion method. The errors were used to establish optimum measurement positions. The results show that the measurement position should be in the middle of the column and in the region half way from the center to the wall (the half-radius). The gas holdup along the axial direction is lower at the bottom and higher at the top of the floatation column. The gas holdup along the radial direction is lower near the wall and higher near the center of the flotation column. The average gas holdup measurement can be replaced by regional gas holdup values.

The modification of Shenfu coals by a microwave treatment carried out under a hydrogen or a methane atmosphere, and the subsequent maceral separation by flotation, are described in this paper. The surface contact angle and the Zeta potential of the coal macerals were measured both with and without the treatment. The results show that the surface wettability of SFF (Shenfu Fusain) and SFV (Shenfu Vitrain) can be changed by the microwave treatment. An increase in the difference in surface wettability of SFF and SFV causes in a subsequent increase in the enrichment of inertinite and vitrinite. The results of the Zeta potential measurements show that the surface potentials of SFF and SFV are also changed by the treatment.

A mine-scale analysis of Longwall Top Coal Caving (LTCC) is performed using a continuum mechanics finite element solver called COSFLOW. The uniqueness of COSFLOW is that it incorporates Cosserat continuum theory in its formulation for describing the load deformation of bedded rocks. It is shown that such a continuum based code is valuable for assessing the feasibility of introducing LTCC in any mine. Various LTCC parameters, for example chock convergences, top coal failure behavior, strata caving mechanism, abutment stresses and vertical stresses, were evaluated for a mine using COSFLOW.