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Research on mine seal stability under explosion load and ground pressure in underground coal mines

Cheng Jianwei, Song Wanting, Jing Yi, Zhang Xixi, Korzec Marek, Borowski Marek, Wang Yue

Archives of Mining Sciences

2020

Vol. 65, no. 1

71--87

The mine seals in coal mines with a good impact resistance and air tightness are mainly used to isolate abandoned mining areas from active workings. For one thing, it can prevent the leakage of harmful gases, such as toxic gas from abandoned areas. For another, once an underground mine explosion happens, it can effectively block the spread of the explosion between the abandoned mining areas and the active workings. Hence, it is of great significance to study the explosion-proof performance and mechanical properties of the mine seals. First of all, the effect of slotting on the stability of the seals in coal mines under explosion load was explored in this study. By numerical simulations, the mechanical response characteristics of the seals with or without cutting a slot under the explosion load were compared in detail. The results show that slotting improved the stress concentration at the contact surface of surrounding rock by transferring partial impact received by mine seals to the surrounding rocks, thus, to achieve the effect of buffering explosion impact. Besides, such effect will be enhanced with increasing cutting depth into rock, and will stabilize when the depth is 20 cm. On this basis, the mechanical properties and damage of the seals constructed by different materials (standard brick and #C40 concrete) under the explosion load were compared. It was found that once a slot was set, the maximum deformation of the concrete seal was reduced, while the maximum deformation of the brick seal increased. Since the non-deformability of the concrete seal is obviously stronger than that of the brick seal, with the impact resistance stronger than that of the brick seal, the concrete seal is more suitable for slotting. Moreover, the damage of the seals in underground coal mines under the strata ground pressure was studied; the results of which show that the damage state under the ground pressure can be divided into 3 levels, i.e. no damage, minor damage and rapid development of damage. Meanwhile, it was found that the prestressed structure fordem by the ground pressure at the level of no damage can enhance the protective effect of the seals in coal mines. However, when the ground pressure was further developed, the seal itself was destroyed and the protective effect was lost. In addition, the influence of roof to floor moving convergence, a deformation parameter of the roadway, on the seals was also investigated. The results show that the ground pressure and roof-to-floor convergence act on the seals in coal mines in the same way, thus roof to floor moving convergence can replace the ground pressure to analyze other related mechanical properties of the seals in coal mines in the future researches.

Permanent-magnet brushless DC electromotor with tooth coils and self-braking

Afanasiev A., Babak A., Efimov V., Nesterin V., Nikiforov V., Spiridonov A., Chihnyaev V.

Prace Instytutu Elektrotechniki

2006

Z. 229

189-204

The electric drives with synchronous gearmotors are obtained generally in actuating constant velocity devices in electroenergetics, heat-power engineering, pipeline transportation today. But they have not only well-known advantages but also essential disadvantages. The permanent magnet brushless DC motor with weakening from rotor permanent magnets and staror tooth coils may be an alternative to this fixed electromotor. The made optimization of cross geometry of PM brushless DC motor is based on the field mathematical model with Nd-Fe-B plastomagnets and six stator teeth. The rating value of moment is 1 Nm, of rotor speed is 750 rpm. It was calculated the width of interpole nonmagnetic arcs which provides the desired value of cogging torque after the stator coils are currentless. It was appreciated the effect of the width of tangent-magneted interpole arcs to the maximum peaks of the cogging torque and the full load torque. It was analysed the possibility to produce the rotor version of magnet ring without m-metal core.

Napędy elektryczne z synchronicznymi silnikami przekładniowymi są stosowane ogólnie w napędach o stałej prędkości w energetyce, elektrociepłowniach, transporcie rurociągami, ale mają one nie tylko ogólnie znane zalety lecz również istotne wady. Alternatywą może być bezszczotkowy silnik prądu stałego o magnesach trwałych z dodatkowymi uzwojeniami na zębach stojana. Optymalizacja geometrii tego silnika jest oparta na matematycznym modelu pola z magnesami Nd-Fe-B i z sześcioma zębami stojana. Znamionowa wartość momentu wynosi 1 Nm, prędkości obrotowej 750 obr/min. Obliczono szerokość niemagnetycznego łuku między magnesami, która daje żądaną wartość momentu utknięcia, gdy w uzwojeniu statora nie ma prądu. Oceniono wpływ szerokości łuków między biegunami na maksymalną wartość momentu utknięcia i na moment pełnego obciążenia. Przeanalizowano możliwość wykonania wersji pierścienia magnetycznego wirnika bez rdzenia z metalu m.

Comparative comparison and physical and mathematical modelling of magnetoelectric brushless DC motors in slotting and without slotting executions

Afanasyev A., Babak A., Belov V., Nesterin V., Nikiforof V., Nikolaev A., Chichnayev V.

Prace Instytutu Elektrotechniki

2006

Z. 229

205-226

On the basis of field calculation of a magnetic field in an active zone without grooving of the BLDC motor optimization of his cross-section geometry is offered with the purpose of increase in his electromagnetic torque. Characteristics serial slotting BLDC motor and a model sample without slotting BLDC motor, having identical cases are compared. The technique of definition of magnetic losses in the core and neodymium-iron-bor magnets is offered. The technique of analytical calculation (on the first harmonics of voltage and currents) performance data of salient pole BLDC motor with the inverter of a voltage and with magnetoelectric and electromagnetic excitation is offered.

Na podstawie obliczenia pola magnetycznego w strefie czynnej ze żłobkami, proponuje się optymalizację geometrii jego przekroju w celu zwiększenia jego momentu elektromagnetycznego. Porównano charakterystyki seryjnego bezszczotkowego silnika prądu stałego następnie magnetoelektrycznego silnika bezszczotkowego i jego modelu bez żłobków. Podano definicję strat magnetycznych w rdzeniu i magnesach neodym-żelazo-bor. W artykule podano metodę analitycznego obliczania danych silnika bezszczotkowego z biegunami ukrytymi z przekształtnikiem napięcia ze wzbudzeniem magnetoelektrycznym i elektromagnetycznym z uwzględnieniem 1-szej harmonicznej napięcia i prądu.