Abstract Investigating the stress drop of abutment pressure is the key to a deep quantitative analysis of the discontinuous stress redistribution under mining. In the present study, uniaxial and triaxial compression tests are carried out separately to determine the bulk and shear moduli, the cohesion, and the internal friction angle of the coal samples. By extending the meaning of Mohr’s circle referring to yield stress instead of the maximum principal stress, a yield line is introduced to illustrate the stress drop of Mohr’s circle referring to yield stress instead of the maximum principal stress at the elastoplastic boundary. Furthermore, a theoretical solution of the stress drop as a function of the damage is proposed to investigate how the abutment pressure differs considering the yield line and failure line. In addition, applying the stress drop at the yield line in non-pillar mining, top coal mining, and protective coal mining shows that the damage has a nonlinearly positive influence on the stress drop. The results shows that the bulk modulus and internal friction angle have a more sensitive influence on the stress drop than do the shear modulus and cohesion. Finally, the stress drop is divided into a discontinuous stress drop at the yield line and a structural stress drop at the failure line. The stress drop is effective in describing the discontinuous stress redistribution and shows a clear difference in the movement direction of Mohr’s circle considering the unloading pressure.
In order to solve the collision problem in the process of identifying a large number of monitoring signals when RFID wireless system is applied to the equipment monitoring of mountainous substations, the RFID wireless system architecture for equipment monitoring of mountainous substations is established. On the basis of the traditional frame-time slot ALOHA algorithm, a multi-antenna RFID reader is used to realize the parallel recognition of multi-signals in a single slot. Then the upper envelope of each throughput curve is taken according to the frame length N, and the frame length is adjusted at the intersection point. The signal flow is divided into groups, and the final algorithm flow chart is obtained. The simulation results show that the throughput can be improved up to 97.3% after parallel recognition, but the recognition rate S is limited by frame length N and signal number n; the recognition rate S can be maintained above 90% after frame length adjustment; and the recognition rate S at the tail of envelope can be reduced sharply with the increase of signal number n after periodic grouping. The simulation results show that the improved parallel recognition ALOHA algorithm not only improves the recognition rate, but also keeps a relatively stable recognition rate with the increase of the monitoring signal. The recognition rate is increased from 34% to 90% by the traditional frame-slot ALOHA algorithm, which greatly improves the monitoring signal of substation equipment. The probability of successful identification guarantees the safe and stable operation of mountain substations.
The multigrid-reduction-in-time (MGRIT) technique has proven to be successful in achieving higher run-time speedup by exploiting parallelism in time. The goal of this article is to develop and analyze an MGRIT algorithm, using FCF-relaxation with time-dependent time-grid propagators, to seek the finite element approximations of two-dimensional unsteady fractional Laplacian problems. Motivated by [B. S. Southworth, SIAM J. Matrix Anal. Appl. 40 (2019), pp. 564-608], we provide a new temporal eigenvalue approximation property and then deduce a generalized two-level convergence theory which removes the previous unitary diagonalization assumption on the fine and coarse time-grid propagators. Numerical computations are included to confirm theoretical predictions and demonstrate the sharpness of the derived convergence upper bound.
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