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• The dual vector, dual coupling coefficient operator and dual modal coordinates of flexible modules are derived. • The algebra of dual numbers for rigid-flex combination system is developed. • The relative dynamics between two rigid-flex combination systems is proposed. • The cross-coupling effect of relative equations of motion is analyzed. Dual numbers are applied in this paper to relative dynamics between rigid-flex combination systems. In space cooperative missions, the relative dynamic equations with engineering applicability require description in rotating frame of reference. Taking advantages of dual numbers which can represent spiral movement in a compact form with respect to the rotating frame, the dual vector, dual momentum, dual inertia operator, dual coupling coefficient operator and dual modal coordinates of flexible modules are derived. The algebra of dual numbers for rigid-flex combination system is further developed. On this basis, relative equations of motion between two rigid-flex combination systems in rotating frame of reference are proposed. The behaviors of relative dynamics present complex cross-coupling effects between attitude-orbit coupling and rigid-flex coupling. An on-orbit assembly mission of flexible modules via free flying robots is presented as an exemplary application of the cross-coupling relative dynamics. Ground testing results illustrate the cross-coupling effects on the six degree-of-freedom motion of rigid-flex combination system. Simulation results prove the engineering significance of the cross-coupling relative dynamic model. [ABSTRACT FROM AUTHOR]

This paper analyzes the influence of the overlying extremely thick primary key stratum on the strong mine pressure hazard at the large mining face in Gaojiapu coal mine. The analysis of the distribution characteristics of the primary key stratum in the Gaojiapu coal mine reveals the bow-shaped structural characteristics of the overlying thick primary key stratum. An elastodynamic model was developed using the variational method to calculate and analyze the influence of the movement of the primary key stratum on the stress and energy of the underlying weak rock. The results show that the arch structure of the overlying extremely thick primary key stratum can significantly affect the distribution pattern of stress and strain energy in the coal body, and the stress and strain energy in the coal body are transferred to the middle of the coal column, and the middle region of the coal column enters a high stress state. These results suggest that the change in thickness of the overlying primary key stratum at Gaojiapu in the coal column area is a major factor in the frequent occurrence of impact ground pressure events at the mine. This study explains the causes of frequent impact ground pressure in the lower coal rock mass of the extremely thick primary key stratum, and provides a reference for the prevention and control of impact hazards in the extremely thick primary key stratum. [ABSTRACT FROM AUTHOR]

• The strength of the C-R-A combination is mainly determined by the weak coal seam. • In the case of failure of the C-R-A combination, fractures mainly occur in the coal seam. • The damage and fracturing evolution of the C-R-A structure is most significantly influenced by the rock stratum. • The burst proneness of the C-R-A combination is negatively correlated with the rock stratum. Coal and other mineral resources are also commonly found in bauxite mining. The process of bauxite mining is usually affected by retained ore pillars in other strata, which leads to the formation of combinations composed of different strata. Once these combinations become unstable, they can cause serious disasters that threaten production safety. Aiming at the safe mining of co-associated resources in the overlying coal seams of bauxite mines, in this paper, the strength, fracture development, and energy evolution of the coal-rock-aluminum (C-R-A) combination under varying thickness proportions of coal, rock, and aluminum were studied by means of particle flow code (PFC) numerical simulation, SPSS statistical analysis, and other methods. The results indicate that the strength of the combination is significantly negatively correlated with the thickness of the soft coal seam and remarkably positively correlated with the thickness of the hard aluminum layer. Under the same stress conditions, fractures in the combination mainly occur in the coal seam. As the thickness proportion of the coal seam in the overall structure increases, the number of fractures there grows correspondingly. Under a larger thickness proportion of the rock stratum, the combination releases its elastic energy faster after instability, and the fractures develop more intensely. As the thickness proportion of the rock stratum decreases, the elastic energy index (W ET ) in the C-R-A combination rises, and the burst proneness strengthens. Areas where the thickness proportions of coal, rock, and aluminum lie in the ranges of 30%–60%, 10%–20%, and 30%–60% respectively are considered high-risk zones, and rock burst accidents are most likely to occur when the thickness ratio of coal, rock, and aluminum is 4: 1: 5. These research findings can provide guidance for the safe mining of similar coal and aluminum associated resources. [ABSTRACT FROM AUTHOR]

The technology of flame stabilization on cavity-based scramjet combustor has great significance in the field of future spacecraft. In this paper, a compressible modified FGM model was established based on the idea of the flamelet model, which was adopted to simulate the unsteady combustion process of the hydrogen transverse jet in the upper cavity of the scramjet. The results show that the compressible modified FGM model can accurately reflect the flow field and the propagation process of the flame in the supersonic cavity, and can capture the fine shock structure in the flow field. The coupling effect of shock waves and shear layer cause the shear layer to quickly destabilize, resulting in the turbulence effect, which promotes the mixing of air and fuel. The boundary layer separation at the upper wall of the combustion chamber will reduce the stability of the shear layer. [ABSTRACT FROM AUTHOR]

To address problems associated with mining above gob piles in the Chinese midwest mining area, a mechanic model for a coal pillar was established based on the displacement variation method. Additionally, the effect of critical unfilled zone height in the underlying gob (UZHUG) on the coal pillar was investigated through a 3DEC numerical simulation; fieldwork was conducted with a borehole televiewer to measure the UZHUG in the Yuanbaowan Coal Mine. The results indicated that the shear stress value and distribution layout in the coal pillar were affected by the UZHUG. The larger the UZHUG, the greater the shear stress and the wider the distribution scope, moving from two sides to the middle zone. Moreover, the larger the UZHUG, the smaller the maximum bearing capacity of the coal pillar, and subsequently, the greater the horizontal deformation of the coal pillar and roof convergence. The critical UZHUG is 2 m considering coal pillar deformation and stress transfer characteristics. Field measurements have confirmed that the UZHUG of 2 m ensured safe mining in the No. 6 coal seam. However, a second round of filling is needed when achieving a UZHUG of 4.4 m. This study serves as a reference for safe mining above gob piles. [ABSTRACT FROM AUTHOR]

Disturbances owing to coal mining result in the movement and failure of floor strata. Mining-induced fractures within the floor may propagate to the confined aquifer, thereby causing water inrush disasters. In this study, we propose using strip mining and backfill replacement mining above the confined aquifer to investigate the failure depth of the floor. The problem is simplified as a distributed force model on a half-plane body. First, the stress disturbance of the floor during strip mining is calculated and the results are combined with the von Mises yield criterion. Then, the destruction of the floor after replacing the remaining coal pillars is explored. The results show that the widths of the strip mining face and coal pillars play an important role in affecting the failure depth of the floor: the greater the width, the larger the failure depth. Based on the parametric study results, the mining face and retention coal pillar width of 20 m is sufficient to prevent the occurrence of water inrush accidents. After the replacement of the remaining coal pillars, the failure area of the floor rock mass increases, but the maximum failure depth remains unchanged. Finally, we employed field measurement techniques at the Bucun coal mine to monitor the shear and vertical strains of the floor. The data collected was compared with the predicted results obtained from the proposed theoretical model. Good agreement was found between the monitoring and calculation results, which demonstrate the effectiveness of the proposed method. [ABSTRACT FROM AUTHOR]

Purpose: The purpose of this paper is to propose a pre-defined performance robust control method for pre-assembly configuration establishment of in-space assembly missions, and collision avoidance is considered during the configuration establishment process. Design/methodology/approach: First, six-degrees-of-freedom error kinematic and dynamic models of relative translational and rotational motion between transportation systems are developed. Second, the prescribed transient-state performance bounds of tracking errors are designed. In addition, based on the backstepping, combining the pre-defined performance control method with a robust control method, a pre-defined performance robust controller is designed. Findings: By designing prescribed transient-state performance bounds of tracking errors to guarantee that there is no overshoot, collision-avoidance can be achieved. Combining the pre-defined performance control method with a robust control method, robustness to disturbance is guaranteed. Originality/value: This paper proposed a pre-defined performance robust control method. Simulation results demonstrate that the proposed controller can achieve a pre-assembly configuration establishment with collision avoidance in the existence of external disturbances. [ABSTRACT FROM AUTHOR]

There are two major characteristics of in-space structure assembly missions. First, in order to improve the transport efficiency of assembly robot and reduce the number of structural modules, the size of each structural module is usually designed as large as possible. Second, it is necessary for autonomous assembly robot to quickly transport such large-sized flexible structural modules to the desired locations for integration. However, the coupling effect between the deformation of structural module and large-scale maneuver of robot is inevitably involved during transportation. In this paper, a dynamics modeling method for in-space assembly (ISA) robot with large translational and rotational maneuvers was proposed. The descriptions of dual quaternions were expanded, and a general expression for the dynamics model of rigid-flex system was derived to describe motion of the assembly robot. Innovation of this method is that it considered the complex coupling effect among deformation of structural modules, translational and rotational maneuvers of the assembly robot during transportation in ISA missions. On this basis, the proportional-derivative (PD) controllers were adopted as the in-space structural module assembly method. Finally, taking the ISA of antenna as an example, successful application of the proposed dynamics model and controller to the assembly mission was verified. • A dual quaternion dynamics model for the transportation of ISA mission was proposed. • The model considers coupling effects among deformation, translation and rotation of assembling robot. • A PD controller of relative motion is designed based-on the coupling dynamics model. [ABSTRACT FROM AUTHOR]

Underground mining using the room and pillar method leaves pillars to support the overlying strata. When longwall mining is used to extract a lower coal seam beneath the room and pillar mine, the bending of the interburden strata can induce pillar failure and roof caving. In this study, two physical model experiments with different pillar width/height ratios were performed, and a non-contact displacement measurement technique was used to record and analyse the deformation and failure processes. The failure mechanism of pillars and the roof in a room and pillar mine induced by longwall mining in a lower coal seam was investigated. The results show that, during the longwall retreat, the immediate roof of the longwall panel collapses and the main roof bends resulting in load redistribution among a series of overlying pillars. Eventually pillar failure and unsteady strata movement are induced. Physical model tests indicate the entire deformation and failure process can be divided into two stages, i.e. steady deformation and failure propagation. In addition, it is observed that different width/height ratios of pillars lead to different failure patterns in the second stage. For model #1 with higher pillar width/height ratios, load redistribution is induced by the bending of the main roof of the longwall mine, but most panel pillars remain stable. The unsteady movement of the main roof of the longwall causes an upward failure propagation in the overburden strata. For model #2 with lower pillar width/height ratios, the failure propagates downward and it is triggered by the progressive collapse of the panel pillars during the load redistribution process. [ABSTRACT FROM AUTHOR]

In this paper, we establish a thermochemical ablation model of C/C composite based on the lattice Boltzmann method, in which the flow, diffusion, chemical reaction, heat transfer, and the evolution of solid phase are comprehensively considered. In the model, the flow, mass transport and heat transfer, chemical reaction, and the evolution of solid phase are addressed by the multiple relaxation time model, the single relaxation time model, boundary condition, and the volume of pixel method, respectively. Then, we research the ablation process of carbon fibers based on the pore-scale using this model, and we discuss the effects of temperature field, inlet temperature, inlet velocity, and inlet concentration. Numerical results indicate that H 2 O contributes more ablation than CO 2 . Without temperature source term, increasing inlet temperature, inlet velocity, and inlet concentration can accelerate ablation. [ABSTRACT FROM AUTHOR]

In Shendong coalfield, severe support failure accidents caused by the dynamic pressure occurred frequently when longwall faces extracting the lower coal seam progress below the chamber coal pillars. These incidents largely threaten the personnel safety and regular operations. The rationale of the dynamic pressure has been investigated based on the movement law of the overlying strata. Experimental and numerical simulations of a longwall face in Shigetai coal mine agree well with the qualitative explanations. It is shown that the failure of the chamber coal pillars causes the sudden break and even rotation of the key strata, thereby leading to strong dynamic load that crushes the supports in the longwall face. Several guidelines have been proposed to prevent the occurrence of the dynamic pressure, the capability of which has been demonstrated by in situ practice in two longwall faces in Shendong coalfield. [ABSTRACT FROM AUTHOR]

Large density ratio multiphase flow is a persistent challenge within the field of computational fluid dynamics. This paper investigates improvements to the lattice Boltzmann based large density ratio multicomponent multiphase pseudo-potential model. The improvements include: the multiple-relaxation-time (MRT) collision operator; the exact difference method scheme; the Carnahan-Starling equation of state; and an addition of correction factor k to the equation of state. The improved model can be used for simulating large density ratio (O(1000)) multiphase flow with small spurious current and better numerical stability. The smaller spurious current can be obtained by decreasing k value, and yet interface thickness increases. The density ratio is 1284 for k = 0.1 and the spurious current is reduced to 0.0069, which is much smaller than that of 0.033 in literature. The interfacial tension can be adjusted independently from density ratio by changing k value. A thermal multiphase flow model is developed based on the large density ratio pseudo-potential model. The model is validated by using static heat conduction and dynamic flow simulations. The result of the static heat conduction of the flat interface has smaller error with the theoretical solution than that of droplet. The result of thermocapillary migration is comparable with the theoretical prediction. Finally, the heat conduction melting is simulated by coupling the enthalpy-based method. [ABSTRACT FROM AUTHOR]

In this paper, the solid-liquid phase change problems are investigated by the lattice Boltzmann method. The flow field and the temperature field are solved by the MRT and LBGK collision schemes, respectively. The latent-heat source term is treated by the enthalpy-based method. The natural convection in the square cavity, conduction melting, and 3D lid-driven flow are used for validating the model and code, and the simulation results are in good agreement with the benchmark/analytical solution or experimental data. The 2D and 3D natural convection melting in a square cavity are researched and compared in detail. Numerical results indicate that some discrepancies are presented for 2D and 3D simulation. The melting rate of 2D simulation is faster than that of 3D simulation. The multicellular structure is obtained for 2D cases, yet 3D results show the monocellular structure. The solid-liquid interface shapes and positions obtained from 3D cases are in good agreement with the experimental data, but 2D results have larger discrepancies with the experimental data. For similar problems, 3D effect can not be ignored. [ABSTRACT FROM AUTHOR]

The pier column backfilling method in the goaf of a thin coal seam introduced in this paper is the latest backfilling technology in China, which has the combined advantages of high efficiency and low cost. In order to fully verify the load bearing effect of this backfilling method, a comprehensive evaluation model which combined the actual measurement, numerical simulation and physical simulation is implemented in this paper. First, the stress bearing formula and backfilling volume rate of a pier column backfilling body is obtained by theory analysis. Then, through field monitoring, it was concluded that the bearing capacity when the backfilling body reached a stable state was similar to the results of theoretical calculation, and no obvious deformation occurred by observation the roadway deformation with the site. Finally, based on the drilling columnar and lithological parameters of the site, corresponding physical and numerical models were established and used to study the bearing effect of this backfilling method. It could be found that the stresses and displacements data that resulted from the simulation relatively confirmed data obtained from the site. After comprehension of above researches, it is concluded that the pier column backfilling method in a goaf has good bearing effect and a good economic benefit for mining thin coal seams. [ABSTRACT FROM AUTHOR]

For better film characteristics of the main pump seal (MPS), a theoretical calculation model was proposed based on the Reynolds equation. A case study with defined MPS was carried out, film stiffness was taken as the basic constraint condition, and the cone angle and clearance are two optimization targets. When the film stiffness reaches a maximum, the corresponding cone angle and clearance is the optimal value. The results show that: (1) film stiffness increased and decreased with clearance and cone angle, respectively; (2) the optional clearance was determined to be within a range of 2~8 µm at a cone angle of between 0.1~1.2′; (3) the maximum of film stiffness is inversely proportional to the cone angle (Clearance) approximately under the clearance (Cone angle) is fixed; (4) leakage is directly proportional to the clearance to power three, and the clearance has greater influence on the amount of leakage than the cone angle. These results provide a reliable theoretical justification for MPS-based designs including optimization method. It therefore forms a fundamental base for research and practical application. [ABSTRACT FROM AUTHOR]

When there are multiple key strata in the overburden of a deep coal seam and the surface subsidence coefficient after mining is small, this indicates that the overlying key strata fail to break completely after mining. On this occasion, stress is easily concentrated in the working face, which in turn leads to the occurrence of dynamic disasters such as rock bursts. This study adopted a comprehensive analysis method of field monitoring and numerical simulations to explore the influence of the key stratum on the evolution law of mining-induced stress in the working face. A distributed optical fiber sensor (DOFS) and a surface subsidence GNSS monitoring system were arranged inside and at the mouth of the ground observation borehole, respectively. According to the monitoring results of strain obtained from the DOFS, the height of the broken stratum inside the overlying strata was obtained and according to the monitoring results of surface subsidence, the surface subsidence coefficient was proven to be less than 0.1, indicating that the high key stratum is not broken completely, but enters a state of bending subsidence instead. In order to reveal the influence of the key stratum on the mining-induced stress of the working face, two 3DEC numerical models with and without the key stratum were established for a comparative analysis. As the numerical simulation results show, when there are multiple key strata in the overburden, the stress influence range and the stress concentration coefficient of the coal seam after mining are relatively large. The study revealed the working mechanism of rock burst accidents after large-scale mining and predicted the potential area with a rock burst risk after mining of the working face, which was verified by field investigations. The research results are of great guiding significance for the identification of the working mechanism of rock bursts in deep mining condition and for their prevention and control. [ABSTRACT FROM AUTHOR]

In the present paper, the flow characteristics of dry and wet particles in circulating fluidized bed riser are simulated by using the Euler–Lagrange approach, in which the solid phase is modeled by the discrete element method (DEM) and the gas phase is solved by the Navier–Stokes equations. The forces acting on particles include contact force, friction force, van der Waals force, liquid bridge force, gravitational force, drag force, and pressure gradient force. The flow behaviors of dry and wet particles are compared, and the agglomerate characteristics of wet particles are also analyzed quantitatively. Numerical results indicate that a remarkable heterogeneity is observed from both dry and wet particles in the riser. However, a major difference exists for the flow between dry and wet particles, which shows that the flow structure with a dilute region in the upper zone and a dense region near the bottom is formed for the dry particles and the wet particles show the opposite way. The results show a significant influence of the physical parameters of particles on the formation of particle clusters in the riser. The wet particles move in two forms: the single-particle and agglomerate. The effect of the moisture contents is remarkable on agglomerate characteristics. [ABSTRACT FROM AUTHOR]

Abstract: Cimicomorpha, which consists of 16 families representing more than 19,400 species, is the largest infraorder in Heteroptera, Insecta. We present the first molecular phylogenetic investigation of family relationships of Cimicomorpha, including 46 taxa from 12 of 16 Cimicomorphan families. Three genes, with a total of 3277bp of sequence data (nuclear 18S rDNA: 2022bp, 28S rDNA: 755bp, and mitochondrial 16S rDNA: 498bp) were analyzed. Data partitions were analyzed separately and in combination, by employing ML (maximum likelihood), MP (maximum parsimony), and Bayesian methods. As saturation was detected in substitutions of 16S rDNA, influence of data conflict in combined analyses was further explored by three methods: the incongruence length difference (ILD) test, the partitioned Bremer support (PBS), and the partition addition bootstrap alteration approach (PABA). PBS and PABA approaches suggested that 16S rDNA was not very suitable for addressing relationships at this level in Cimicomorpha. Our results also supported the nabid–cimicoid lineage for Cimicoidea proposed by Schuh and Štys [Schuh, R.T., Štys, P., 1991. Phylogenetic analysis of Cimicomorphan family relationships (Heteroptera). J. NY Entomol. Soc. 99 (3), 298–350]. Data incongruence and the utility of the three genes were briefly discussed. [Copyright &y& Elsevier]

Water outbursts and rock bursts often occur during the mining of coal seams under water-rich sandstone strata with thicknesses exceeding 50 m, otherwise called ultrathick-and-hard strata (UTHS), which are common throughout the mining areas of northwestern China. It is important to understand the behaviors of their movement and the evolution of their internal fractures to inform the formulation of effective disaster prevention. Due to the presence of the Luohe Formation UTHS in the overburden of the Tingnan Coal Mine in the Binchang mining area and the powerful mining-induced pressure (MIP) events that occurred during the excavation of Panel #2, the internal strata movement of the overburden and the evolution of its fractures were monitored in situ by fiber optic and multipoint borehole extensometers (MPBX) during the excavation of Working Face #207. It was found that a large number of ring-shaped fractures were observed at 24.8–81 m above the lower boundary of the Luohe Formation—in areas above the goaf of Working Face #206—before Working Face #207 was mined. When Working Face #207 was mined, the fractures that were originally located in the deep strata of the Luohe Formation started to close and migrate towards shallow strata. Crack closure and migration were also observed during the monitoring of internal strata movement. Furthermore, the final displacements of Y1-1-1#, Y1-2-2#, and Y1-2-3# relative to the surface were 77, 248, and 134 mm, which were very small relative to the surface subsidence of 1380 mm. It was found that mining-induced perturbations caused the Luohe Formation UTHS to subside continuously and no risk of a large and sudden break would occur in the Luohe Formation UTHS during the mining of Working Face #207. The results of this study provide important data for the safety of mining operations at Working Face #207, which were validated by microseismic monitoring during the mining of it. [ABSTRACT FROM AUTHOR]

Underground coal mining causes stress relief and strata/ground movement, threatening the safety of the surface structures. Investigating the movement laws of the strata above the working face ends is important because it determines the deformation level of the surface subsidence trough at the boundary, which is also the zone with the largest deformation degree. This paper presents a study on the movement laws of the overlying strata at the working face ends, and assesses their effects on the surface deformation using field monitoring as well as physical and numerical modelling. The results show that the surface deformation at the subsidence trough boundary is closely related to the movement and rotation of the broken blocks of the primary key stratum (PKS), which control the development of the bed separation and the degree of the surface deformation at the corresponding locations. The numerical modelling results suggest that, the larger the mining height, the greater the rotation angle of the broken blocks and the more severe the surface deformation above the ends of the working face. The results also highlight the role of the thickness of the topsoil. The implications of the results and the limitations of the research are also briefly discussed. [ABSTRACT FROM AUTHOR]

Ground subsidence caused by underground coal mining is one of the challenging environmental issues in mining engineering. This paper presents a field monitoring study of longwall mining-induced ground subsidence in Shendong coalfield, China. The paper includes the subsidence data of four longwall panels, with mining and geological conditions varied. All the longwall faces have a high mining height (4.5-7 m) and extraction speed (9.0–13.3 m/day), but with shallow mining depth (180-210 m). High-frequency field observations allow the dynamic characteristics of the ground subsidence caused by high-intensity longwall mining to be captured and revealed. Results show that, for a longwall panel with a width to depth ratio of 1.35–1.6, the subsidence ratio is generally between 51.1–54.3%, and the maximum subsidence speed can reach 0.4 m/day. Furthermore, the overlying goaf considerably increases the subsidence ratio, and the instability of the boundary coal pillars decreases the ground surface deformation but increases the range of influence. Results also suggest the use of dynamic surface subsidence to infer the breakage and movement laws of the strata in the high-intensity longwall mining condition. Finally, the practical implications of the results and the associated environmental effects are briefly discussed. [ABSTRACT FROM AUTHOR]

• A robust and efficient variant of PISO algorithm is proposed. • The design of this algorithm draws on the conclusions of Fourier analysis and the practices of PRIME algorithm. • The stability and convergence of the proposed algorithm are demonstrated by three test flows. • The proposed algorithm is particularly suitable for simulations where large time-step are needed. An efficient separated method for fluid flows on collocated grid, named EPPL (Error Production and Propagation Limited), has been proposed involving robustness and convergence. The main features of the method include changing the solution procedure according to the matching degree of velocity and pressure dynamically, optimizing the under-relaxation strategy according to the characteristics of momentum interpolation, and enhancing the robustness of pressure equation. In this paper, the basic ideas of the three improvements and the overall solution procedure of the EPPL algorithm are introduced in details. Theoretical support for each improvement is provided by three benchmark compressible/incompressible flow tests, demonstrating the superior performance of the EPPL algorithm. Tests show that the EPPL algorithm achieves significant improvements in both robustness and convergence. In addition, the EPPL algorithm is simple and easy to implement, and the ideas in it are very suitable for porting to existing codes. Finally, the real performance of EPPL for complex case is demonstrated by simulating the interaction of jet and supersonic cross-flow in the background of fuel injection of scramjet. [ABSTRACT FROM AUTHOR]

In petroleum drilling engineering, self-synchronous vibration screen with single-frequency actuation is difficult to implement the scheduled synchronous behavior caused by its invariance and instability of dynamic characteristics, which usually leads to reduction of the production efficiency. Hence, to solve the problem mentioned above, a dual-frequency counter-rotating synchronization control method among three exciters is presented by combining adjacent cross-coupling control (ACCC) structure with global sliding mode control (GSMC) theory. Firstly, motion differential equation of the vibration system in each direction is derived according to mathematical model of the tri-rotor vibration machine. Secondly, considering exponential reaching law and adaptive control algorithm, the adjacent cross-coupling controller and the vector controller of each induction motor are investigated to achieve the stable zero phase difference synchronization between double-frequency rotors. Subsequently, Runge-Kutta method is introduced to establish the electromechanical coupling control model and prove validity of the control theory. Meanwhile, it is also discussed that the rotors cannot obtain an ideal self-synchronization state since velocity of high-frequency motor is not strictly equal to twice that of low-frequency motor. Finally, based on the experimental test scheme, an experimental prototype related to controlled multi-rotor synchronization vibration system is designed independently, which further verifies the validity of theory and computer simulation. Research shows that the desirable synchronous state of the vibration system can be accurately controlled via the designed control strategy, and the control system can implement diversity of the dynamical characteristics, due to the existence of strong robustness. [ABSTRACT FROM AUTHOR]

The deformation and movement characteristics of high-level key stratums in overlying strata are important for estimating ground subsidence and understanding failure characteristics of ultrathick strata during mining. In this study, a distributed optical fiber sensor (DOFS) and multipoint borehole extensometers (MPBXs) were collaboratively employed to monitor the deformation of high-level key stratums in situ during the mining process at working face 130,604 of the Maiduoshan Coal Mine. DOFS monitoring results showed that the distance from advance influence of mining on the ground surface is 219.2 m. The deformation of the shallow stratums were greater and was affected earlier than that of the deep stratums. The deformation in the strata did not occur continuously and the boundary curve of the impact from advance mining was not a straight line with the advancement of the working face. By the MPBX technology, we measured the strata movement and obtained four-stage characteristics of high-level key stratum movement. The subsidence of the primary key stratum and the sub key stratum were monitored to reach 1389 and 1437 mm; their final relative displacement differed by 48 mm. No bed separation was observed in between the strata, and the key stratums tended to sink as a whole with the advancement of the working face. This research guides the analysis the movement of thick high-level key stratums. [ABSTRACT FROM AUTHOR]

Understanding how mining-induced strata movement, fractures, bed separation, and ground subsidence evolve is an area of great importance for the underground coal mining industry, particularly for disaster control and sustainable mining. Based on the rules of mining-induced strata movement and stress evolution, accumulative dilatation of mining-induced unloading rock mass is first proposed in this paper. Triaxial unloading tests and theoretical calculation were used to investigate the influence of elastic dilatation of mining-induced unloading rock mass on the development of bed separation in the context of district No. 102 where a layer of super-thick igneous sill exists in the Haizi colliery. It is shown that the elastic dilatation coefficient of mining-induced unloading hard rocks and coal were 0.9~1.0‰ and 2.63‰ respectively under the axial load of 16 MPa, which increased to 1.30~1.59‰ and 4.88‰ when the axial load was 32 MPa. After successively excavating working faces No. 1022 and No. 1024, the elastic dilatation of unloading rock mass was 157.9 mm, which represented approximately 6.3% of the mining height, indicating the elastic dilatation of mining-induced unloading rock mass has a moderate influence on the development of bed separation. Drill hole detection results after grouting, showed that only 0.33 m of the total grouting filling thickness (1.67 m) was located in the fracture zone and bending zone, which verified the result from previous drill hole detection that only small bed separation developed beneath the igneous sill. Therefore, it was concluded that the influences of elastic dilatation of mining-induced unloading rock mass and bulking of caved rock mass jointly contributed to the small bed separation space beneath the igneous sill. Since the accurate calculation of the unloading dilatation of rock mass is the fundamental basis for quantitative calculation of bed separation and surface subsidence, this paper is expected to be a meaningful beginning point and could provide a useful reference for future, related research. [ABSTRACT FROM AUTHOR]

One task facing by the geotechnical engineers is to protect the workspace in an underground construction/excavation site from various forms of geological disasters, such as the water inrush, rock burst, and collapse of the surrounding rock/soil. In this paper, a combined controlling measure was proposed based on underground mining and water environment: the method of strip mining has been initially proposed as an effective measure against underground workspace floor failure when mining above confined aquifer in the Bucun coal mine, China, and however, its ability to avoid floor water inrush has yet to be demonstrated; in the next step, field trials using caving zone backfill technology to prevent underground workspace floor failure and excavate retained strip coal pillars were implemented based on the theoretical calculation and numerical simulation results. Engineering practice showed that the failure depth of the underlying strata of the workspace had no growth without the possibility of water inrush, and the safety of the underground space was achieved. Thus, this study represents a successful attempt to develop the combined strip mining and caving zone backfilling technique to ensure the safety of the underground workspace and control surface subsidence when excavating the retained strip coal pillars above confined aquifer. The proposed combined technique can also be used in other underground excavation activities with similar problems. [ABSTRACT FROM AUTHOR]

Mining‐induced voids are the main circulation pathways for underground fluids such as water and coalbed methane. The collapse of these voids transmits to the ground surface, resulting in subsidence and building collapse. Accordingly, effective and feasible solutions are needed to control surface subsidence. In this study, a novel technique of void filling in the short‐wall caving zone was proposed to better control surface subsidence in thin coal seam mining. The width of the working face plays a key role in the proposed technique. A maximum surface subsidence value was predicted using numerical simulation and physical simulation experiments with different working face widths. The results indicate that the appropriate working face width should be less than 50 m for the studied coal mine. In this example, the surface subsidence coefficient was less than the standard value for initial damage to rural structures. Both advancing speed and productivity of the working face were achieved using the proposed technique because the filling and mining processes were conducted simultaneously on different faces. The results suggest that surface subsidence during thin coal seam mining could be controlled using the proposed technique. This technique can also help mitigate mining‐induced water inrush and gas leakage disasters by filling voids. [ABSTRACT FROM AUTHOR]

In-situ investigations are the most direct and authentic approach for determining the law of strata movement. In this study, in-situ investigation was carried out to determine the law of fracture and movement of a key stratum. Four-point surface extensometer (FPSE) inside overlying strata and borehole camera observation were used in the overlying strata of a fully mechanized caving face of a super-thick coal seam in the Datong coalfield. The time–space correspondence between the fracture and movement of the key stratum and ground pressure in stopes was established in combination with observations of the ground pressure of the working face. Results show that the primary key stratum of the overlying strata is the main controlling stratum and its fracture and movement are the underlying cause of strong ground pressure behaviours, such as rib spalling, roof fall, and support crushing. The findings suggest that the primary key stratum can be weakened, and the energy release can be decreased by hydraulic fracturing, deep hole blasting, and other measures, thus relieving ground pressure behaviour. The research method of establishing the time–space correspondence between fracture and movement of the key stratum and ground pressure behaviours based on in-situ investigation can provide guidance for mining engineering schemes, such as exploring master control strata with strong ground pressure behaviour under similar conditions and determining a reasonable capacity for the support. [ABSTRACT FROM AUTHOR]

Clear understanding of overburden failure propagation during underground mining is critical in managing safety and environmental issues such as rock burst hazards, groundwater inrush and longwall convergency. This paper presents an in-situ monitoring study of overburden strain dynamics at a kilometre-deep longwall mine using distributed fibre optic sensing technology (DFOS). A deep borehole was drilled from the ground surface to near the mining seam and installed with an optical fibre cable to detect rock deformation in a contiguous fashion. In addition, a Global Navigation Satellite System (GNSS) device was installed at the borehole collar to monitor surface subsidence. The results suggested that strata delamination contiguously extended to 347 m, about 34 times the mining thickness. The remaining 600 m thick strata above this height behaved as the intact zone. Such an overburden deformation pattern resulted in minor surface subsidence of only 0.6 m or 6% of the mining thickness. A step-wise, upward breakage of the optical fibre cable (due to excessive strain) was observed and found to correlate with other ground behaviours, including an increase in the total microseismic energy and periodic weighting on the longwall supports. These observations corroborate that the dynamic deformation of overburden is primarily governed by competent stratum units, i.e., the key strata. The monitoring results have served to develop a reliable mine-scale 3DEC model for predicting stress redistributions in the subsequent longwall panels for preventing dynamic hazards. The study also demonstrates that DFOS-based strain monitoring can be a valuable tool to investigate overburden responses to mining and has significant potential for applications in various mining methods, such as block caving, sub-level caving and open stopping. [ABSTRACT FROM AUTHOR]

Carbon nanomaterial is widely used in structural health monitoring due to the advantage of sensitivity and good mechanical properties. This study presents a novel approach employing carbon nanocomposite materials (CNMs) to characterize deformation and damage evolution in physical modelling. As the primary measurement method, the CNM is used to investigate the deformation characteristics of a 200–400 m thick sandstone bed at a 1 km deep longwall mine. The sandstone unit is identified as an ultra-thick key stratum (UTKS), with its thicknesses varying across different mining panels of the UTKS. The results of CNM monitoring show that the UTKS remains stable even after a consecutive excavation of 900 m in width. This stability impedes the upward propagation of overlying strata failure, leading to minimal surface subsidence. The study demonstrates the huge potential of CNM in the mining area, which can be useful for investigating material damage in physical modelling studies. The findings suggest that the cumulative extraction width in individual mining areas of the mine should be controlled to avoid a sudden collapse of the UTKS, and that special attention should be paid to where the UTKS's thickness changes substantially. The substantial variation in UTKS thickness significantly impacts the pattern of overburden subsidence. [ABSTRACT FROM AUTHOR]

Affected by coal mining activities, the remaining coal pillars are very likely to be destabilized and cause safety accidents. The backfilling of the remaining goaf can maintain the stability of the coal pillar well, but the coal pillar in the unfilled zone may still be unstable. In this paper, the effect of backfilling materials on coal pillars and the reinforcement method are discussed using numerical simulation, statistical mathematics, elastic mechanics, and mechanical test methods. The results show that: backfilling with solid waste materials and reinforcing the coal pillar could maintain the stability of the bottom goaf, where the backfill body height is the main factor in the strength of the coal pillar. The propagation of the confining stress of the backfill body on the pillar in the unfilled zone is the primary way to influence the coal pillar strength. Changing the backfill body height filling can affect the coal pillar strength. By analyzing the propagation law of confining stress in the coal pillar, the minimum backfill body height is determined to be 7 m. Combined with mechanical tests and the Mohr–Coulomb criterion, the minimum confining pressure required to maintain the coal pillar stability under the peak ground pressure is analyzed. The ratio of solid waste materials is determined based on this. Field tests have proved that the coal pillar remains stable when the goaf is not filled, and the cement/fly ash ratio is 1:4, which can ensure product safety. The research has significant value and significance for the governance of the remaining coal pillars and production safety. [ABSTRACT FROM AUTHOR]

The Shendong coalfield is characterized with shallow cover depth and multi coal seams that are closely distributed. A number of longwall (LW) faces are in operation in the second coal seam. Due to the geological disturbances and different deployments of LW panels, a large number of coal pillars were left in the overlying extracted coal seam. Massive LW chock support failure incidents (e.g. sudden closure and hydraulic cylinder damage) occurred when the LW face of the lower coal seam cut across below the coal pillars of the upper coal seam. Through conducting stability analysis of key blocks above coal pillars, the mechanism involved was revealed and the roles that two key factors (depth of cover of the overlying coal pillar, and inter-burden thickness) played in the process were investigated. It is believed that the rotation and motion of the key blocks of roof strata above coal pillar have the potential to make the overlying stress concentrated at coal pillars. The high compressive stress is very likely to be transferred to the inter-burden and LW chocks. Hence redirecting the stress and/or reducing the capability of stress transfer of coal pillars become the primary consideration for developing a solution. A method of pre-advancing a roadway through the upper coal pillar was proposed to induce it to fail prior to LW face exiting the coal pillar. The proposed solution was subsequently applied to LW22303 of the Bulianta coal mine, Shendong coalfield, and achieved substantial benefits. [ABSTRACT FROM AUTHOR]

An overlying 140-m-thick massive igneous sill has adversely affected mining activities considerably in the Haizi Coal Mine, China. A coal and gas outburst disaster occurred during the drivage for a subsequent longwall, after the extraction of two faces in the II102 mining area. The massive sill was determined to be primarily responsible for this outburst owing to the bed separation that occurred below the sill due to the sill׳s large span. This is because such separation meant the massive sill was not supported by the gob, as in a general case, but it was supported by the solid coal instead, resulting in a long load transfer distance that caused the drivage gate to collapse unexpectedly into the abutment. Thus, it was determined that the high abutment pressure primarily triggered the outburst. Such disaster risk would have remained had the drivage in the gate continued, and a wide-area and sudden roof fall could have occurred during the extraction of the next longwall had the igneous sill broken suddenly as the critical span was reached. With these risks in mind, a field trial of a method of grouting into the overburden of the abandoned faces from surface boreholes was conducted for dynamic disaster control. This technique alleviates the abutment pressures and restrains the igneous sill deflection by eliminating fractures and voids in the overburden using grouting. The adoption of this grouting method led to the subsequent drivage and mining of a further 510 m without occurrence of any further dynamic disasters. [ABSTRACT FROM AUTHOR]

A thorough understanding of mining-induced overburden deformation characteristics and the associated stress redistributions are essential to effectively manage complex safety and environmental issues that arise from underground mining. This is particular for mining in deep environments. This paper presents a numerical modelling study on a kilometer-deep longwall coal mine where a thick sandstone aquifer is situated approximately 200 m above the working seam. The mine adopts a special mine layout with narrow and wide pillars between longwalls and areas to manage water inrush and coal burst risks. The modelling results show that overburden deformation stops at a certain height, above which the displacement profile over multiple longwall panels become nearly flat. Increasing panel width and extraction height lead to a greater extent of the fractured zone and a larger magnitude of surface subsidence. An extraction height of more than 7 m may breach the thick aquifer. Stress concentration on the wide pillar can undergo up to 5 times increase in the in-situ stress, posing high risks of coal burst. Adjusting mining parameters such as panel width and extraction height can facilitate an effective strategy to minimize water inrush and coal burst risks in such a mining condition. [ABSTRACT FROM AUTHOR]

Dynamic loading events in the longwall faces under slopes in the Shendong Coalfield, China, seriously limit the safety and efficiency of mining. The slope characteristics, such as direction, height, and angle, determine the load type and the stability of the voussoir beam structure (VBS) formed by fractured blocks of the primary key stratum (PKS). Whether or not dynamic loading events will occur can be directly determined based on the presence or absence of a stable VBS in the PKS. Based on this relationship, six structural mechanical VBS models for different load distributions were established and then the effects of the slope direction, height, and angle on the stability of VBS was analysed. Changes of load type intensified the compression force between the hinged blocks. When the compression force between blocks exceeded the strength of the rock, VBS instability and dynamic loading events occurred. The compression force in the VBS increased with increasing slope angle and height when the slope directions were similar, becoming more pronounced for mining under the uphill sections of the slopes. Therefore, a method of determining the critical slope parameter values indicating a risk of dynamic loading was proposed, enabling such slopes to be recognised in advance. Measures such as slope top cutting or backfilling can then be applied to prevent potential dynamic loading accidents. This study can provide guidelines for safe mining under geological conditions involving widespread slopes and gullies. [ABSTRACT FROM AUTHOR]

Underground coal mining leads to fracture and movement in the overburden and the occurrence of weighting events in stopes. There are certain key strata that play an important role in controlling overburden movements. After the key stratum breaking, the fractured blocks would form the voussoir beam structure. The rotational speed of the voussoir beam structures directly affects the intensity of the ground pressures in a stope. In this study, a mechanical model was constructed to describe the rotational motions of the voussoir beam structures formed by the key strata based on elastomechanical theories. The angular velocity equations for the rotational motions of the voussoir beam structures in the key strata were obtained. Moreover, the manner in which loads and block lengths affect the angular velocity was investigated. The rotational angular velocity of the fractured blocks was found to increase with greater overlying loads on the key strata and shorter block lengths. The main roof has a major influence on strata behavior in stopes, and increases in the angular velocity of its voussoir beam structures increase roof subsidence rates, the yield of powered supports within each coal mining cycle, and the intensity of weighting events in stopes. If one or more of the voussoir beam structures formed by key strata above the main roof have greater rotational speeds than those of their underlying key strata, additional loads are applied to the latter, causing their rotational speeds to increase. If this application of loads is transmitted to the main roof, there is a strong possibility that highly intense weighting events will occur as a result of increases in the rotational speed of the main roof's voussoir beam structures. The research result provided a rational explanation for the significant differences in the weighting events of the No. 52304 working face in the Daliuta Coal Mine, which was covered by thick versus thin Aeolian sands. The results may be greatly significant in evaluating the intensity of weighting events, predicting the scope in which the strata movement affects the weighting events in stopes and determining a reasonable powered support capacity. [ABSTRACT FROM AUTHOR]

Dendritic cells (DCs) and cytokine-induced killer (CIK) cells have both shown activity as immunotherapy in some malignancies. Our aim was to prospective assess the effect of this immunotherapy in patients with stage IV breast cancer. Between Aug 2003 and Dec 2013, we collected 368 patients who met inclusion criteria and divided into immunotherapy group (treatment group: 188 patients) and chemotherapy group (control group: 180 patients). DCs were prepared from the mononuclear cells isolated from patients in the treatment group using IL-2/GM-CSF and were loaded with tumour antigens; CIK cells were prepared by incubating peripheral blood lymphocytes with IL-2, IFN-γ, and CD3 antibodies. After the patients had received low-dose chemotherapy, those in the treatment group also received the DC-CIK therapy, which was repeated four times in a fortnight to form one cycle. At least three cycles of DC-CIK therapy were given. Immune function was measured in treatment group patients' sera. Disease-free survival (DFS) and Overall survival (OS) after the diagnosis of stage IV breast cancer was assessed after a 10-year follow-up. The result demonstrated that immune function is obviously enhanced after DC-CIK therapy. By Cox regression analysis, DC-CIK therapy reduced the risk of disease progression (p < 0.01) with an increased OS (p < 0.01). After low-dose chemotherapy, active immunization with DC-CIK immunotherapy is a potentially effective approach for the control of tumour growth in stage IV breast cancer patients. [ABSTRACT FROM AUTHOR]

Numerous room-and-pillar mining goaf are apparent in western China due to increasing small coal mining activities, which causes the collapse of the overlying coal pillars and the occurrence of strong ground pressure on the longwall face and surface subsidence. In this study, Yuanbao Bay Coal Mine, Shuozhou, Shanxi, was selected to study the collapse of the overlying coal pillars on the longwall face and reveal the mechanism of the pillar collapse and the disaster-causing mechanism caused by strong ground pressure. Results show that the dynamic collapse process of coal pillars is relatively complicated. First, the coal pillars on both sides of the goaf are destroyed and destabilized, followed by the adjacent coal pillars, which eventually cause a large-scale collapse of the coal pillars. This results in a large-scale cut-off movement of the overlying strata, and the large impact load that acts on the longwall face causes an unmovable longwall face support. Moreover, the roof weighting is severe when strong ground pressure occurs on the longwall face, causing local support jammed accidents. Furthermore, the data of each measurement point of the strata movement inside the ground borehole significantly increases, and the position of the borescope peeping error holes in the ground drill hole rise steeply. The range of movement of the overlying strata increases instantaneously, and the entire strata begin to move. Research on the mechanism of strong ground pressure can effectively prevent mine safety accidents and avoid huge economic losses. [ABSTRACT FROM AUTHOR]