Browsing by Author "Goodman, Gerrit V. R."

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    Development of a remote analysis method for underground ventilation systems using tracer gas and CFD
    Xu, Guang (Virginia Tech, 2013-04-04)
    Following an unexpected event in an underground mine, it is important to know the state of the mine immediately to manage the situation effectively. Particularly when part or the whole mine is inaccessible, remotely and quickly ascertaining the ventilation status is one of the pieces of essential information that can help mine personnel and rescue teams make decisions. This study developed a methodology that uses tracer gas techniques and CFD modeling to analyze underground mine ventilation system status remotely. After an unanticipated event that has damaged ventilation controls, the first step of the methodology is to assess and estimate the level of the damage and the possible ventilation changes based on the available information. Then CFD models will be built to model the normal ventilation status before the event, as well as possible ventilation damage scenarios. At the same time, tracer gas tests will be designed and performed on-site. Tracer gas will be released at a designated location with constant or transient release techniques. Gas samples will be collected at other locations and analyzed using Gas Chromatography (GC). Finally, through comparing the CFD simulated results and the tracer on-site test results, the general characterization of the ventilation system can be determined. A review of CFD applications in mining engineering is provided in the beginning of this dissertation. The basic principles of CFD are reviewed and six turbulence models commonly used are discussed with some examples of their application and guidelines on choosing an appropriate turbulence model. General modeling procedures are also provided with particular emphasis on conducting a mesh independence study and different validation methods, further improving the accuracy of a model. CFD applications in mining engineering research and design areas are reviewed, which illustrate the success of CFD and highlight challenging issues. Experiments were conducted both in the laboratory and on-site. These experiments showed that the developed methodology is feasible for characterizing underground ventilation systems remotely. Limitations of the study are also addressed. For example, the CFD model requires detailed ventilation survey data for an accurate CFD modeling and takes much longer time compared to network modeling. Some common problems encountered when using tracer gases in underground mines are discussed based on previously completed laboratory and field experiments, which include tracer release methods, sampling and analysis techniques. Additionally, the use of CFD to optimize the design of tracer gas experiments is also presented. Finally, guidelines and recommendations are provided on the use of tracer gases in the characterization of underground mine ventilation networks.
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    Flow characteristics of jet fans in mines: experimental and numerical modeling
    Konduri, Indu Mohan (Virginia Tech, 1996-12-05)
    The use of induction fans for face ventilation in room and pillar mines has proved to be an efficient, flexible, and viable technique. In addition to their merits over conventional systems, induction fans enable remote controlled mine operations with low maintenance requirements. Theoretical investigations were conducted initially to verify the potential of free air jets in mine ventilation. A laboratory model using water as the fluid medium was designed to study the flow characteristics of a jet fan in a blind entry. The model was tested in a variety of brattice curtain and nozzle combinations to investigate the ventilating efficiency of jet fans. A jet fan was selected and tested in a full scale model and in a coal mine. Experiments were conducted to evaluate the laboratory flow models. Flow quantities and velocities in the entry were measured using state-of-the-art instrumentation to quantify various parameters. Air velocities near the face were found to be satisfactory to dilute contaminants from the face. A model for the axial velocity profile of the jet was suggested. Beyond 25m distance from the jet fan exit the jet tended to move away from the wall to the opposite wall. Carbon dioxide was used as a tracer gas to measure the effective ventilating air quantity near the face and re-circulation in various tests. The re-circulation involved in the system was found to be less than 40% in all the experiments. It was also found that the use of line curtains in combination with a jet a fan can eliminate any type of re-circulation. Numerical modeling of a jet fan in a typical coal mine heading was conducted to obtain details of the flow. The results of the simulation using computational fluid dynamics were similar to the flow patterns observed in the experiments. It was found that a jet fan can effectively ventilate an entry as deep as 40m. Fan positioning, airway geometry, airway surface properties, and mine layout severely affect its performance. It is therefore necessary to understand the flow mechanics of a jet fan in a mine heading before applying the technique for a particular situation.
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    A mixed integer model for optimizing equipment scheduling and overburden transport in a surface coal mining operation
    Goodman, Gerrit V. R. (Virginia Polytechnic Institute and State University, 1987)
    Recently, competition has increased in the surface coal mining industry, which has necessitated the development of more efficient methods for coal removal. Despite this trend, very little emphasis has been placed on the development of optimization techniques applicable to the surface coal industry. The available methods are inadequate in that they recognize neither the complex equipment interactions present in a surface mining operation nor the interdependence of overburden removal and spoil placement. The lack of available techniques prompted the development of a mixed integer model to optimize the scheduling of equipment and the distribution of overburden in a typical mountaintop removal operation. Using this format, a (0-1) integer model and transportation model were constructed to determine the optimal equipment schedule and optimal overburden distribution, respectively. To solve this mixed integer program, the model was partitioned into its binary and real-valued components. Each problem was successively solved and their values added to form estimates of the value of the mixed integer program. Optimal convergence was indicated when the difference between two successive estimates satisfied some pre-specified accuracy value. The performance of the mixed integer model was tested against actual field data to determine its practical applications. To provide the necessary input information, production data was obtained from a single seam, mountaintop removal operation located in the Appalachian coalfield. As a means of analyzing the resultant equipment schedule, the total idle time was calculated for each machine type and each lift location. Also, the final overburden assignments were analyzed by determining the distribution of spoil material for various overburden removal productivities. Subsequent validation of the mixed integer model was conducted in two distinct areas. The first dealt with changes in algorithmic data and their effects on the optimality of the model. The second area concerned variations in problem structure, specifically those dealing with changes in problem size and other user-inputted values, such as equipment productivities or required reclamation. For each of these optimal schedules and assignments obtained from the model, analyses were conducted in manner similar to that discussed above.