Factors considered for increasing longwall panel width

Longwall mining is the preferred method in coal mining to maximize production and reserve recovery by extracting large blocks of coal that have been outlined with a set of continuous miner development entries. In the US, technological advances and system enhancements have steadily improved productivity more in the longwall retreat process as compared to the improvements in continuous miner gateroad development process. Consequently, longwall extraction rates have outpaced gateroad development mining advancement.;This thesis addresses the factors considered for increasing panel width and the solutions to the technical concerns for increasing the longwall face width from the current accepted industry standard of 1050 feet to 1600 feet (320 m to 488 m). The process of increasing the width of longwall panels, while helping to increase coal production, reducing continuous miner development, and increasing coal reserve recovery, will result in additional design considerations for equipment, roof control, ventilation design, infrastructure, and longwall moves. This thesis will discuss the areas for design considerations and solutions to the technical concerns

Stress distribution at the load introduction point of glass plates subjected to compression

p. 822-830Often a crucial place in glass design is the point of load introduction where a high in-plane compression load is introduced in the glass. In this case, the common hypothesis that glass fails when the tensile stresses reach their tensile strength, seems not to be true. More specifically, at the load introduction point, a complex two-dimensional stress state takes place and the glass failed at tensile stress levels far below its tensile strength. To study these phenomena, laboratory investigations and numerical simulations of glass plates with a low slenderness (to avoid stability problems), subjected to in-plane compressive loads introduced through boreholes by point fixing devices, were conducted. At the load introduction point (contact point), maximal principal compressive stresses occurred. Due to Poisson's effect, perpendicularly to this compressive stresses the maximal principal tensile stresses took place. At a certain distance from the load introduction point, the compressive stresses became constant over the glass width while the tensile stresses disappeared. Parametric investigation studied the influence of boreholes distance on the stress distribution at the contact point. For distances larger than the glass panel width, the stress distribution remained unchanged, while for distances smaller than the panel width, a significant influence was recognised.Mocibob, D.; Belis, J.; Crisinel, M.; Lebet, J. (2010). Stress distribution at the load introduction point of glass plates subjected to compression. Editorial Universitat Politècnica de València. http://hdl.handle.net/10251/694

Application of response surface methodology to stiffened panel optimization

In a multilevel optimization frame, the use of surrogate models to approximate optimization constraints allows great time saving. Among available metamodelling techniques we chose to use Neural Networks to perform regression of static mechanical criteria, namely buckling and collapse reserve factors of a stiffened panel, which are constraints of our subsystem optimization problem. Due to the highly non linear behaviour of these functions with respect to loading and design variables, we encountered some difficulties to obtain an approximation of sufficient quality on the whole design space. In particular, variations of the approximated function can be very different according to the value of loading variables. We show how a prior knowledge of the influence of the variables allows us to build an efficient Mixture of Expert model, leading to a good approximation of constraints. Optimization benchmark processes are computed to measure time saving, effects on optimum feasibility and objective value due to the use of the surrogate models as constraints. Finally we see that, while efficient, this mixture of expert model could be still improved by some additional learning techniques

A method for predicting the panel flutter fatigue life of Saturn 5 panels

Development of method for predicting fatigue life of panels under flutter conditions with application to Saturn 5 launch vehicle structure

Study of rock displacement with the help of equivalent materials using room-and-pillar mining method

Field study made with the help of equivalent materials to determine minimum dimension of interchamber and barrier pillars and limiting chamber span was carried out. Modeling was made for gypsum quarry

Effects of scale in predicting global structural response

Analytical techniques for scale-up effects were reviewed. The advantages and limitations of applying the principles of similitude to composite structures is summarized and illustrated by simple examples. An analytical procedure was formulated to design scale models of an axially compressed composite cylinder. A building-block approach was outlined where each structural detail is analyzed independently and the probable failure sequence of a selected component is predicted, taking into account load redistribution subsequent to first element failure. Details of this building-block approach are under development

Slow and fast motion of cracks in inelastic solids. Part 1: Slow growth of cracks in a rate sensitive tresca solid. Part 2: Dynamic crack represented by the Dugdale model

An extension is proposed of the classical theory of fracture to viscoelastic and elastic-plastic materials in which the plasticity effects are confined to a narrow band encompassing the crack front. It is suggested that the Griffith-Irwin criterion of fracture, which requires that the energy release rate computed for a given boundary value problem equals the critical threshold, ought to be replaced by a differential equation governing the slow growth of a crack prior to the onset of rapid propagation. A new term which enters the equation of motion in the dissipative media is proportional to the energy lost within the end sections of the crack, and thus reflects the extent of inelastic behavior of a solid. A concept of apparent surface energy is introduced to account for the geometry dependent and the rate dependent phenomena which influence toughness of an inelastic solid. Three hypotheses regarding the condition for fracture in the subcritical range of load are compared. These are: (1) constant fracture energy (Cherepanov), (2) constant opening displacement at instability (Morozov) and (3) final stretch criterion (Wnuk)

Applications of simulation and optimization techniques in optimizing room and pillar mining systems

The goal of this research was to apply simulation and optimization techniques in solving mine design and production sequencing problems in room and pillar mines (R&P). The specific objectives were to: (1) apply Discrete Event Simulation (DES) to determine the optimal width of coal R&P panels under specific mining conditions; (2) investigate if the shuttle car fleet size used to mine a particular panel width is optimal in different segments of the panel; (3) test the hypothesis that binary integer linear programming (BILP) can be used to account for mining risk in R&P long range mine production sequencing; and (4) test the hypothesis that heuristic pre-processing can be used to increase the computational efficiency of branch and cut solutions to the BILP problem of R&P mine sequencing. A DES model of an existing R&P mine was built, that is capable of evaluating the effect of variable panel width on the unit cost and productivity of the mining system. For the system and operating conditions evaluated, the result showed that a 17-entry panel is optimal. The result also showed that, for the 17-entry panel studied, four shuttle cars per continuous miner is optimal for 80% of the defined mining segments with three shuttle cars optimal for the other 20%. The research successfully incorporated risk management into the R&P production sequencing problem, modeling the problem as BILP with block aggregation to minimize computational complexity. Three pre-processing algorithms based on generating problem-specific cutting planes were developed and used to investigate whether heuristic pre-processing can increase computational efficiency. Although, in some instances, the implemented pre-processing algorithms improved computational efficiency, the overall computational times were higher due to the high cost of generating the cutting planes --Abstract, page iii