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Technology News 416 - MULSIM/NL: a boundary element method program for stress analysis of coal mines.

Denver, CO: U.S. Department of the Interior, Bureau of Mines, TN 416, 1993 Jan; :1-4
Objective: Provide the U.S. mining industry with a user friendly computer program to calculate stresses in underground coal mines in order to improve safety conditions for mine workers. Capabilities of MULSIM/NL: MULSIM/NL (multiple seams, nonlinear) is a three-dimensional boundary-element method (BEM) program developed at the U.S. Bureau of Mines for stress and displacement analysis of coal mines. It can analyze one or two parallel seams that can have any orientation with respect to the Earth's surface. Three main new features distinguish MULSIM/NL from its predecessors: (1) nonlinear material models, (2) multiple mining steps, and (3) energy release and strain energy computations. MULSIM/NL has six material models for the in-seam material: (1) linear elastic for coal, (2) strain softening, (3) elastic plastic, (4) bilinear hardening, (5) strain hardening, and (6) linear elastic for gob. The multiple mining step capability enables the user to efficiently simulate a changing mine geometry. Finally, MULSIM/ NL computes energy release rate due to mining using the most recent concepts advanced by Salamon. The MULSIM/NL package consists of the actual BEM program, along with a preprocessor program called MULPRE/NL and a postprocessor program called MULPLT /NL. The preprocessor helps the user to generate the required input file for the main program MULSIM/NL, and the postprocessor assists the user to examine the calculated stresses in an easy-to-use graphical manner. Figure 1 shows an example MULPLT/NL output of MULSIM/NL stress calculations for a complete longwall face. The slightly angled longwall face moves from left to right. Using a strain-softening material model for the coal, the model can realistically calculate crushing of the small pillar on the headgate side of the face, followed by crushing of the big pillar on the tailgate side. Using MULSIM/NL: MULSIM/NL has many uses in practical coal mine engineering. The stresses and displacements calculated by the program can help an engineer choose pillar sizes based on their calculated loads and their interaction with the surrounding strata. MULSIM/NL allows the user to calculate stresses for very complicated mine geometries such as longwall gate road systems, room-and-pillar layouts, and multiple-seam situations. MULSIM/NL uses a coarse- and fine-mesh modeling grid to approximate the actual in-seam coal mine geometry. Figure 2 shows part of a typical room-and-pillar coal mine geometry and illustrates its connection to a MULSIM/NL grid. In this analysis problem, retreat mining methods will extract the central pillar in this layout. The coarse-mesh blocks cover a large section of the actual mine layout, whereas fine-mesh elements cover a central region of interest where greater computational detail is desired. MULSIM/NL allows up to a 50 by 50 coarse-block array, which has an embedded array of up to 150 by 150 fine-mesh elements. As with most BEM programs, a linear elastic rock mass surrounds the seams; however, MULSIM/NL now permits various nonlinear material models for the in-seam block and element materials. Prior versions of MULSIM permitted linear stress-strain relations only for the in-seam materials, such as coal and gob. As shown in figure 3, MULSIM/NL now has six material models from which to choose. With these material models, MULSIM/NL can account for the effects of fractured rock, the yield zone in coal pillars, and consolidation of the gob. As shown in figure 4, the user assigns to each block and element in the model a letter code that signifies the material model type and the material properties for that block or element. Again, a preprocessor program called MULPRE/NL helps the user generate an input file for MULSIM/NL. After running the main analysis program, a post-processor program called MULPLT /NL helps the user view the results. MULPLT/NL is a menu-driven, graphics program that can display pseudo-three-dimensional plots or two-dimensional cross sections of the stresses and displacements calculated by MULSIM/NL. Figure 1 showing computed stresses around a longwall face and figure 5 showing stresses in a pillar were produced with MULPLT/NL. Computer Hardware Requirements for MULSIM/NL: To make this powerful program readily available to the U.S. mining industry, the Bureau downloaded MULSIM/NL to the personal computer. Minimum hardware requirements include (1) a 386 processor with a 387 math coprocessor, (2) 4 Mb of RAM for the small-memory version and 8 Mb of RAM for the large-memory version, and (3) a VGA or SVGA color monitor. In addition, if hard copies of the color output from the post-processor are desired, software with a screen capture utility and a rasterizing color printer are required.
Mining-industry; Coal-mining; Geology; Computer-models; Computer-software; Room-and-pillar-mining
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Denver, CO: U.S. Department of the Interior, Bureau of Mines, TN 416
Page last reviewed: September 2, 2020
Content source: National Institute for Occupational Safety and Health Education and Information Division