Pillar strength in underground stone mines in the United States Esterhuizen, G.S.; Dolinar, D.R.; Ellenberger, J.L.
International journal of rock mechanics and mining sciences (Oxford, England : 1997),
2011, 2011-1-00, 20110101, Letnik:
48, Številka:
1
Journal Article
Recenzirano
Stone mines in the Eastern and Midwestern United States make use of the room-and-pillar method of mining to extract relatively flat-laying sedimentary formations. A survey of pillar performance was ...carried out to identify potential modes of instability. Pillars were found to have been successful in providing support to the overburden, but a small number of individual failed pillars were observed. Failure of the pillars was observed to be related to spalling of the hard brittle rocks, shearing along pre-existing angular discontinuities or progressive extrusion of soft infill materials on bedding planes. A method of estimating the pillar strength and selecting a safety factor for design was developed based on observations of stable and failed pillars, supplemented by numerical models. The developed pillar strength equation can be used to design stable stone mine pillars provided the rock conditions are similar to those included in the study.
This paper presents the evaluation of saturation and cross-magnetization effects in an interior permanent magnet synchronous motor (IPMSM) over the entire range of direct- and quadrature-axis ...excitations. The conventional two-axis machine model is modified in order to include the influence of saturation and cross-coupling effects on the variation of self- and cross-coupling inductances in the direct and the quadrature axis. The two-axis machine model parameters are evaluated by experiments performed on an IPMSM using a controlled voltage-source inverter and are compared with parameter values evaluated by the finite-element method. The evaluation of two-axis machine model parameters reveals significant saturation and cross-magnetization effects in both axes, especially in the flux-weakening regime.
This paper presents 1-D dynamic magnetization models of non-oriented soft magnetic steel sheets that can be expressed as simple systems of ordinary differential equations. The discussed models take ...into account the dynamic effects on magnetization due to eddy currents and hysteresis inside such sheets and differ in the way the coupled Maxwell equations with hysteresis are solved. The presented modeling approaches include finite-difference schemes of different accuracies, various magnetic equivalent circuits (MECs), including a recent approach to eliminate the deficiencies of classical MECs, and a mesh-free approach. The different modeling approaches are analyzed and compared in terms of mathematical structure, implementation work, spatial discretization, and accuracy, where both voltage- and current-driven versions are investigated.
•Methods for voltage sag source detection are discussed that use only line currents.•Instantaneous current vector is introduced using Clarke’s components.•The proposed method is compared to the ...already known phasor-based method.•Both methods are evaluated by numerical simulations, laboratory and field testing.•The proposed method shows considerably higher effectiveness for transient events.
The presented research reflects those methods for detecting voltage sag sources that only use measurements of line currents. It is shown that the phasor-based method known from the literature is unsatisfactory, especially in the cases of transient voltage sag events. Therefore, a generalised method is proposed that is based on the instantaneous current vector written in Clarke’s components. The phasor-based method and the proposed method for voltage sag source detection were evaluated by applying extensive simulations, laboratory tests, and field testing. The obtained results show considerably higher effectiveness for the proposed method. The correctness of the instantaneous vector-based approach is verified in this way. Moreover, the proposed method that uses only measurements of line currents is just as effective as some other instantaneous vector-based methods that use measurements of line currents and line voltages.
In this paper, parameters of the Jiles-Atherton (J-A) hysteresis model are identified using a stochastic search algorithm called differential evolution (DE). The J-A hysteresis model's parameters are ...identified by DE in such a way, that best possible agreement is obtained between the measured and model calculated hysteresis loops. This agreement is furthermore increased by improving the J-A hysteresis model. The improvement is achieved by replacing a constant pinning parameter in the J-A hysteresis model with a variable one. Here, the variable pinning parameter is written as a function of a magnetic field. By DE identified parameters are used in the J-A hysteresis model, which is included in the dynamic model of a single-phase transformer. The effectiveness of the improved J-A hysteresis model and parameters identification approach is verified with experiments and simulations.
This paper presents a detailed theoretical background of the saturation wave model (SWM), which offers a simplified homogenized solution of the nonlinear diffusion phenomena inside soft magnetic ...steel sheets (SMSSs). The SWM is capable of predicting the complicated dynamic magnetization of SMSS without discretization of the cross section of the SMSSs. Despite its simplicity, the SWM predicts exact solutions of the discussed problems when step-like magnetization curves are assumed and reasonably accurate solutions for real magnetization curves. In this paper, the SWM is analyzed in comparison to the numerical solution of the diffusion phenomena using the parametric magnetodynamic model, where interesting properties of the SWM are discussed and pointed out.
This paper compares two different identification methods of a static rate-independent energy-based hysteresis model with regard to the dynamic hysteresis loop shape prediction when coupled to the ...parametric magnetodynamic lamination model. The values of hysteresis model parameters are determined solely based on the quasi-static major loop. A semiphysical approach identifying the reversible and irreversible field components independently and a purely mathematical scheme using a differential evolution optimization algorithm determining all parameters simultaneously are compared. Both variants of parameter identification are analyzed in terms of hysteresis loop shape prediction for quasi-static as well as dynamic loops.
The performance comparison of three- and single-phase line-start interior permanent magnet synchronous motors (LSIPMSMs) and induction motors (IMs) with equal squirrel-cage design and symmetric ...four-pole stator windings is presented. The finite element method was employed in analysis of steady-state synchronous performance of LSIPMSMs. A magnetically linear lumped parameter model was employed in analysis of line-starting performance of LSIPMSMs, where the electrical and also the mechanical subsystems were considered. The procedure which was used for the LSIPMSM design was validated by comparison of calculation and measurement results. The performance of three- and single-phase LSIPMSMs and IMs with equal squirrel-cage design was directly compared and evaluated, thus emphasizing impacts of the permanent magnet breaking torque and reluctance breaking torque on the LSIPMSM performance in the asynchronous operation region.
This paper discusses methods for voltage-sag source detection, which are based either on energy, current, or impedance criteria. It is shown that methods known from the literature do not work well, ...particularly in cases of asymmetrical voltage sags. Therefore, generalized methods for voltage-sag source detection are proposed, using a vector-space approach. All the discussed methods, both the already known and the proposed ones, were tested by applying extensive simulations, as well as laboratory and field tests. The correctness of the proposed generalized methods was verified in this way. The obtained results show that all the proposed methods are highly effective in all cases of voltage sags, whereas the overall effectiveness of those methods known from literature is mainly unacceptable.
This paper extends the parametric magneto-dynamic model of soft magnetic steel sheets to account for the phase shift between local magnetic flux density and magnetic field strength. This phase shift ...originates from the damped motion of domain walls and is strongly dependent on the microstructure of the material. In this regard, two different approaches to include the rate-dependent effects are investigated: a purely phenomenological, mathematical approach and a physical-based one.
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