Last data update: Sep 23, 2024. (Total: 47723 publications since 2009)
Records 1-6 (of 6 Records) |
Query Trace: Mohamed KM [original query] |
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Analysis of global and local stress changes in a longwall gateroad
Tulu IB , Esterhuizen GS , Gearhart D , Klemetti TM , Mohamed KM , Su DWH . Int J Min Sci Technol 2017 28 (1) 127-135 A numerical-model-based approach was recently developed for estimating the changes in both the horizontal and vertical loading conditions induced by an approaching longwall face. In this approach, a systematic procedure is used to estimate the model's inputs. Shearing along the bedding planes is modeled with ubiquitous joint elements and interface elements. Coal is modeled with a newly developed coal mass model. The response of the gob is calibrated with back analysis of subsidence data and the results of previously published laboratory tests on rock fragments. The model results were verified with the subsidence and stress data recently collected from a longwall mine in the eastern United States. |
A practical application of photogrammetry to performing rib characterization measurements in an underground coal mine using a DSLR camera
Slaker BA , Mohamed KM . Int J Min Sci Technol 2016 27 (1) 83-90 Understanding coal mine rib behavior is important for inferring pillar loading conditions as well as ensuring the safety of miners who are regularly exposed to ribs. Due to the variability in the geometry of underground openings and ground behavior, point measurements often fail to capture the true movement of mine workings. Photogrammetry is a potentially fast, cheap, and precise supplemental measurement tool in comparison to extensometers, tape measures, or laser range meters, but its application in underground coal has been limited. The practical use of photogrammetry was tested at the Safety Research Coal Mine, National Institute for Occupational Safety and Health (NIOSH). A commercially available, digital single-lens reflex (DSLR) camera was used to perform the photogrammetric surveys for the experiment. Several experiments were performed using different lighting conditions, distances to subject, camera settings, and photograph overlaps, with results summarized as follows: the lighting method was found to be insignificant if the scene was appropriately illuminated. It was found that the distance to the subject has a minimal impact on result accuracy, and that camera settings have a significant impact on the photogrammetric quality of images. An increasing photograph resolution was preferable when measuring plane orientations; otherwise a high point cloud density would likely be excessive. Focal ratio (F-stop) changes affect the depth of field and image quality in situations where multiple angles are necessary to survey cleat orientations. Photograph overlap is very important to proper three-dimensional reconstruction, and at least 60% overlap between photograph pairs is ideal to avoid unnecessary post-processing. The suggestions and guidelines proposed are designed to increase the quality of photogrammetry inputs and outputs as well as minimize processing time, and serve as a starting point for an underground coal photogrammetry study. |
Analysis of the current rib support practices and techniques in U.S. coal mines
Mohamed KM , Murphy MM , Lawson HE , Klemetti T . Int J Min Sci Technol 2016 26 (1) 77-87 Design of rib support systems in U.S. coal mines is based primarily on local practices and experience. A better understanding of current rib support practices in U.S. coal mines is crucial for developing a sound engineering rib support design tool. The objective of this paper is to analyze the current practices of rib control in U.S. coal mines. Twenty underground coal mines were studied representing various coal basins, coal seams, geology, loading conditions, and rib control strategies. The key findings are: (1) any rib design guideline or tool should take into account external rib support as well as internal bolting; (2) rib bolts on their own cannot contain rib spall, especially in soft ribs subjected to significant load - external rib control devices such as mesh are required in such cases to contain rib sloughing; (3) the majority of the studied mines follow the overburden depth and entry height thresholds recommended by the Program Information Bulletin 11-29 issued by the Mine Safety and Health Administration; (4) potential rib instability occurred when certain geological features prevailed - these include draw slate and/or bone coal near the rib/roof line, claystone partings, and soft coal bench overlain by rock strata; (5) 47% of the studied rib spall was classified as blocky - this could indicate a high potential of rib hazards; and (6) rib injury rates of the studied mines for the last three years emphasize the need for more rib control management for mines operating at overburden depths between 152.4 m and 304.8 m. |
Deflagration-to-detonation transition in natural gas-air mixtures
Zipf Jr RK , Gamezo VN , Mohamed KM , Oran ES , Kessler DA . Combust Flame 2014 161 (8) 2165-2176 The gas explosion test facility (GETF) previously used to study detonability of natural gas (NG)-air mixtures was modified for studies of flame acceleration and deflagration-to-detonation transition (DDT). The 73-m-long by 1.05-m-diameter tube was equipped with 15 baffles of varying blockage ratio (BR) = 0.13, 0.25, or 0.50, placed near the closed end of the tube and spaced 1.52-m apart. The remaining part of the tube was smooth. Experiments used mixtures between 5.1% and 15.0% NG-air. Ignition was achieved in NG-air mixtures over the composition range 6.1-14.1%. After passing the 15 baffles, both flame and pressure wave velocity were more than 300 m/s over this range. Flame velocity was increasing over the range 6.2-12.8% NG-air, and it reached the sound speed in the burned gases (800-1000 m/s) over the composition range 8.0-10.8% NG-air. Pressure wave velocity was increasing over the composition range 6.1-14.1% NG-air and had reached sonic velocity over the composition range 6.2-12.6% NG-air. Shock waves with magnitude greater than 1 MPa were measured in all tests over the composition range 6.5-12.4%. DDT within the baffled section of the tube and sustained detonations beyond the baffles in the smooth part of the tube were observed over the composition range 8.0-10.8% NG-air. The observed run-up length to sonic flame velocity normalized by the tube diameter, Xru/D, ranges from 16 to 23 at BR = 0.13, 10 to 21 for BR = 0.25, and 13 to 21 for BR = 0.50. The observed run-up length to DDT normalized by the tube diameter, XDDT/D, ranges from 19 to 23 at BR = 0.13, and 16 to 23 for BR = 0.25 and 0.50. Coal mine safety regulations in the US require mine seals to resist an explosion pressure-time curve that rises instantaneously to 0.8 MPa and remains at that level for 4 s. Pressure-time curves measured in these experiments show that shock waves with near-instantaneous rise time and magnitude greater than 1 MPa can develop from weak spark ignition after passing 15 turbulence-generating obstacles in test mixtures ranging from 6.5% to 12.4% NG-air. |
Detonability of natural gas-air mixtures
Gamezo VN , Zipf Jr RK , Sapko MJ , Marchewka WP , Mohamed KM , Oran ES , Kessler DA , Weiss ES , Addis JD , Karnack FA , Sellers DD . Combust Flame 2011 159 (2) 870-881 Direct initiation experiments were carried out in a 105 cm diameter tube to study detonation properties and evaluate the detonability limits for mixtures of natural gas (NG) with air. The natural gas was primarily methane with 1.5–1.7% of ethane. A stoichiometric methane–oxygen mixture contained in a large plastic bag was used as a detonation initiator. Self-supporting detonations with velocities and pressures close to theoretical CJ values were observed in NG–air mixtures containing from 5.3% to 15.6% of NG at atmospheric pressure. These detonability limits are wider than previously measured in smaller channels, and close to the flammability limits. Detonation cell patterns recorded near the limits vary from large cells of the size of the tube to spiral traces of spin detonations. Away from the limits, detonation cell sizes decrease to about 20 cm for 10% NG, and are consistent with existing data for methane–air mixtures obtained in smaller channels. Observed cell patterns are very irregular, and contain secondary cell structures inside primary cells and fine structures inside spin traces. |
Methane-air detonation experiments at NIOSH Lake Lynn Laboratory
Zipf Jr RK , Gamezo VN , Sapko MJ , Marchewka WP , Mohamed KM , Oran ES , Kessler DA , Weiss ES , Addis JD , Karnack FA , Sellers DD . J Loss Prev Process Ind 2011 26 (2) 295-301 The methane-air detonation experiments are performed to characterize high pressure explosion processes that may occur in sealed areas of underground coal mines. The detonation tube used for these studies is 73m long, 105cm internal diameter, and closed at one end. The test gas is 97.5% methane with about 1.5% ethane, and the methane-air test mixtures varied between 4% and 19% methane by volume. Detonations were successfully initiated for mixtures containing between 5.3% and 15.5% methane. The detonations propagated with an average velocity between 1512 and 1863m/s. Average overpressures recorded behind the first shock pressure peak varied between 1.2 and 1.7MPa. The measured detonation velocities and pressures are close to their corresponding theoretical Chapman-Jouguet (CJ) detonation velocity (DCJ) and detonation pressure (PCJ). Outside of these detonability limits, failed detonations produced decaying detached shocks and flames propagating with velocities of approximately 1/2 DCJ. Cell patterns on smokefoils during detonations were very irregular and showed secondary cell structures inside primary cells. The measured width of primary cells varied between 20cm near the stoichiometry and 105cm (tube diameter) near the limits. The largest detonation cell (105cm wide and 170cm long) was recorded for the mixture containing 15.3% methane. |
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