Showing papers in "Journal of Central South University in 2015"

Flow of Casson nanofluid with viscous dissipation and convective conditions: A mathematical model

Abstract: The magnetohydrodynamic (MHD) boundary layer flow of Casson fluid in the presence of nanoparticles is investigated. Convective conditions of temperature and nanoparticle concentration are employed in the formulation. The flow is generated due to exponentially stretching surface. The governing boundary layer equations are reduced into the ordinary differential equations. Series solutions are presented to analyze the velocity, temperature and nanoparticle concentration fields. Temperature and nanoparticle concentration fields decrease when the values of Casson parameter enhance. It is found that the Biot numbers arising due to thermal and concentration convective conditions yield an enhancement in the temperature and concentration fields. Further, we observed that both the thermal and nanoparticle concentration boundary layer thicknesses are higher for the larger values of thermophoresis parameter. The effects of Brownian motion parameter on the temperature and nanoparticle concentration are reverse.

Risk evaluation of rock burst through theory of static and dynamic stresses superposition

Abstract: Rock burst is one of the most catastrophic dynamic hazards in coal mining. A static and dynamic stresses superposition-based (SDSS-based) risk evaluation method of rock burst was proposed to pre-evaluate rock burst risk. Theoretical basis of this method is the stress criterion incurring rock burst and rock burst risk is evaluated according to the closeness degree of the total stress (due to the superposition of static stress in the coal and dynamic stress induced by tremors) with the critical stress. In addition, risk evaluation criterion of rock burst was established by defining the “Satisfaction Degree” of static stress. Furthermore, the method was used to pre-evaluate rock burst risk degree and prejudge endangered area of an insular longwall face in Nanshan Coal Mine in China. Results show that rock burst risk is moderate at advance extent of 97 m, strong at advance extent of 97–131 m, and extremely strong (i.e. inevitable to occur) when advance extent exceeds 131 m (mining is prohibited in this case). The section of two gateways whose floor abuts 15-3 coal seam is a susceptible area prone to rock burst. Evaluation results were further compared with rock bursts and tremors detected by microseismic monitoring. Comparison results indicate that evaluation results are consistent with microseismic monitoring, which proves the method’s feasibility.

Shear modulus and damping ratio of sand-granulated rubber mixtures

Abstract: Recycled waste tires when mixed with soil can play an important role as lightweight materials in retaining walls and embankments, machine foundations and railroad track beds in seismic zones Having high damping characteristic, rubbers can be used as either soil alternative or mixed with soil to reduce vibration when seismic loads are of great concern Therefore, the objective of this work was to evaluate the dynamic properties of such mixtures prior to practical applications To this reason, torsional resonant column and dynamic triaxial experiments were carried out and the effect of the important parameters like rubber content and ratio of mean grain size of rubber solids versus soil solids (D 50,r/D 50,s) on dynamic response of mixtures in a range of low to high shearing strain amplitude from about 4×10-4% to 27% were investigated Considering engineering applications, specimens were prepared almost at the maximum dry density and optimum moisture content to model a mixture layer above the ground water table and in low precipitation region The results show that tire inclusion significantly reduces the shear modulus and increases the damping ratio of the mixtures Also decrease in D 50,r/D 50,s causes the mixture to exhibit more rubber-like behavior Finally, normalized shear modulus versus shearing strain amplitude curve was proposed for engineering practice

A novel virtual machine deployment algorithm with energy efficiency in cloud computing

Abstract: In order to improve the energy efficiency of large-scale data centers, a virtual machine (VM) deployment algorithm called three-threshold energy saving algorithm (TESA), which is based on the linear relation between the energy consumption and (processor) resource utilization, is proposed. In TESA, according to load, hosts in data centers are divided into four classes, that is, host with light load, host with proper load, host with middle load and host with heavy load. By defining TESA, VMs on lightly loaded host or VMs on heavily loaded host are migrated to another host with proper load; VMs on properly loaded host or VMs on middling loaded host are kept constant. Then, based on the TESA, five kinds of VM selection policies (minimization of migrations policy based on TESA (MIMT), maximization of migrations policy based on TESA (MAMT), highest potential growth policy based on TESA (HPGT), lowest potential growth policy based on TESA (LPGT) and random choice policy based on TESA (RCT)) are presented, and MIMT is chosen as the representative policy through experimental comparison. Finally, five research directions are put forward on future energy management. The results of simulation indicate that, as compared with single threshold (ST) algorithm and minimization of migrations (MM) algorithm, MIMT significantly improves the energy efficiency in data centers.

Pressure relief and structure stability mechanism of hard roof for gob-side entry retaining

Abstract: In order to explore the pressure relief and structure stability mechanism of lateral cantilever structure in the stope under the direct coverage of thick hard roof and its impact on the gob-side entry retaining, a lateral cantilever fractured structural mechanical model was established on the basis of clarification for the stress environment of gob-side entry retaining, and the equation of roof given deformation and the balance judgment for fracture block were obtained. The optimal cantilever length was proposed based on the comparison of roof structural characteristics and the stress, deformation law of surrounding rocks under six different cantilever lengths by numerical simulation method. Double stress peaks exist on the sides of gob-side entry retaining and the entry located in the low stress area. The pressure of gob-side entry retaining can be relieved by reducing the cantilever length. However, due to the impact of arch structure of rock beam, unduly short cantilever would result in insufficient pressure relief and unduly long cantilever would bring larger roof stress which results in intense deformation. Therefore, there is optimal cantilever length, which was 7-8 m in this project that enables to achieve the minimum deformation and the most stabilized rock structure of entry retaining. An engineering case of gob-side entry retaining with the direct coverage of 10 m thick hard limestone roof was put forward, and the measured data verified the reasonability of conclusion.

Boundary layer flow of third grade nanofluid with Newtonian heating and viscous dissipation

Abstract: Two-dimensional boundary layer flow of an incompressible third grade nanofluid over a stretching surface is investigated. Influence of thermophoresis and Brownian motion is considered in the presence of Newtonian heating and viscous dissipation. Governing nonlinear problems of velocity, temperature and nanoparticle concentration are solved via homotopic procedure. Convergence is examined graphically and numerically. Results of temperature and nanoparticle concentration are plotted and discussed for various values of material parameters, Prandtl number, Lewis number, Newtonian heating parameter, Eckert number and thermophoresis and Brownian motion parameters. Numerical computations are performed. The results show that the change in temperature and nanoparticle concentration distribution functions is similar when we use higher values of material parameters β1 and β2. It is seen that the temperature and thermal boundary layer thickness are increasing functions of Newtonian heating parameter γ. An increase in thermophoresis and Brownian motion parameters tends to an enhancement in the temperature.

Performance of recycling abrasives in rock cutting by abrasive water jet

Abstract: Rock cutting performance of recycling abrasives was investigated in terms of cutting depth, kerf width, kerf taper angle and surface roughness. Gravity separation technique was employed to separate the abrasives and the rock particles. The recycling abrasive particles were then dried and sieved for determination of their disintegration behaviors. Before each cutting with recycling abrasives, the abrasive particles less than 106 μm were screened out. It is revealed that a considerable amount of used abrasives can be effectively reused in the rock cutting. The reusabilities of abrasives are determined as 81.77%, 57.50%, 34.37% and 17.72% after the first, second, third and fourth cuttings, respectively. Additionally, it is determined that recycling must be restricted three times due to the excessive disintegration of abrasives with further recycling. Moreover, it is concluded that cutting depth, kerf width and surface roughness decreases with recycling. No clear trend is found between the kerf taper angle and recycling. Particle size distribution is determined as an important parameter for improving the cutting performance of recycling abrasives.

Decentralized PID neural network control for a quadrotor helicopter subjected to wind disturbance

Abstract: A decentralized PID neural network (PIDNN) control scheme was proposed to a quadrotor helicopter subjected to wind disturbance. First, the dynamic model that considered the effect of wind disturbance was established via Newton-Euler formalism. For quadrotor helicopter flying at low altitude in actual situation, it was more susceptible to be influenced by the turbulent wind field. Therefore, the turbulent wind field was generated according to Dryden model and taken into consideration as the disturbance source of quadrotor helicopter. Then, a nested loop control approach was proposed for the stabilization and navigation problems of the quadrotor subjected to wind disturbance. A decentralized PIDNN controller was designed for the inner loop to stabilize the attitude angle. A conventional PID controller was used for the outer loop in order to generate the reference path to inner loop. Moreover, the connective weights of the PIDNN were trained on-line by error back-propagation method. Furthermore, the initial connective weights were identified according to the principle of PID control theory and the appropriate learning rate was selected by discrete Lyapunov theory in order to ensure the stability. Finally, the simulation results demonstrate that the controller can effectively resist external wind disturbances, and presents good stability, maneuverability and robustness.

Strength and deformation characteristics of carbonated reactive magnesia treated silt soil

Abstract: A series of unconfined compression tests (UCTs) were conducted to investigate the effects of content of reactive magnesia (MgO) and carbonation time on the engineering properties including apparent characteristics, stress-strain relation, and deformation and strength characteristics of reactive MgO treated silt soils. The soils treated with reactive MgO at various contents were subjected to accelerated carbonation for different periods of time and later, UCTs were performed on them. The results demonstrate that the reactive MgO content and carbonation time have remarkable influences on the aforementioned engineering properties of the soils. It is found that with the increase in reactive MgO content, the unconfined compressive strength (q u) increases at a given carbonation time (<10 h), whereas the water content and amounts of crack of the soils decrease. A threshold content of reactive MgO exists at approximately 25% and a critical carbonation time exists at about 10 h for the development of q u. A simple yet practical strength-prediction model, by taking into account two variables of reactive MgO content and carbonation time, is proposed to estimate q u of carbonated reactive MgO treated soils. A comparison of the predicated values of q u with the measured ones indicates that the proposed model has satisfactory accuracy.

Serret-Frenet frame based on path following control for underactuated unmanned surface vehicles with dynamic uncertainties

Abstract: The path following problem for an underactuated unmanned surface vehicle (USV) in the Serret-Frenet frame is addressed. The control system takes account of the uncertain influence induced by model perturbation, external disturbance, etc. By introducing the Serret-Frenet frame and global coordinate transformation, the control problem of underactuated system (a nonlinear system with single-input and ternate-output) is transformed into the control problem of actuated system (a single-input and single-output nonlinear system), which simplifies the controller design. A backstepping adaptive sliding mode controller (BADSMC) is proposed based on backstepping design technique, adaptive method and theory of dynamic slide model control (DSMC). Then, it is proven that the state of closed loop system is globally stabilized to the desired configuration with the proposed controller. Simulation results are presented to illustrate the effectiveness of the proposed controller.

Finite element analysis of deformation characteristics in cold helical rolling of bearing steel-balls

Abstract: Due to the complexity of investigating deformation mechanisms in helical rolling (HR) process with traditional analytical method, it is significant to develop a 3D finite element (FE) model of HR process The key forming conditions of cold HR of bearing steel-balls were detailedly described Then, by taking steel-ball rolling elements of the B7008C angular contact ball bearing as an example, a completed 3D elastic-plastic FE model of cold HR forming process was established under SIMUFACT software environment Furthermore, the deformation characteristics in HR process were discovered, including the forming process, evolution and distribution laws of strain, stress and damage based on Lemaitre relative damage model The results reveal that the central loosening and cavity defects in HR process may have a combined effect of large negative hydrostatic pressure (positive mean stress) caused by multi-dimensional tensile stresses, high level transverse tensile stress, and circular-alternating shear stress in cross section

Design and parametric optimization of thermal management of lithium-ion battery module with reciprocating air-flow

Abstract: Single cell temperature difference of lithium-ion battery (LIB) module will significantly affect the safety and cycle life of the battery. The reciprocating air-flow module created by a periodic reversal of the air flow was investigated in an effort to mitigate the inherent temperature gradient problem of the conventional battery system with a unidirectional coolant flow with computational fluid dynamics (CFD). Orthogonal experiment and optimization design method based on computational fluid dynamics virtual experiments were developed. A set of optimized design factors for the cooling of reciprocating air flow of LIB thermal management was determined. The simulation experiments show that the reciprocating flow can achieve good heat dissipation, reduce the temperature difference, improve the temperature homogeneity and effectively lower the maximal temperature of the modular battery. The reciprocating flow improves the safety, long-term performance and life span of LIB.

Effects of homogeneous-heterogeneous reactions in flow of Powell-Eyring fluid

Abstract: The steady two-dimensional flow of Powell-Eyring fluid is investigated. The flow is caused by a stretching surface with homogeneous-heterogeneous reactions. The governing nonlinear differential equations are reduced to the ordinary differential equations by similarity transformations. The analytic solutions are presented in series forms by homotopy analysis method (HAM). Convergence of the obtained series solutions is explicitly discussed. The physical significance of different parameters on the velocity and concentration profiles is discussed through graphical illustrations. It is noticed that the boundary layer thickness increases by increasing the Powell-Eyring fluid material parameter (e) whereas it decreases by increasing the fluid material parameter (δ). Further, the concentration profile increases when Powell-Eyring fluid material parameters increase. The concentration is also an increasing function of Schmidt number and decreasing function of strength of homogeneous reaction. Also mass transfer rate increases for larger rate of heterogeneous reaction.

Multi-channel electromyography pattern classification using deep belief networks for enhanced user experience

Abstract: An enhanced algorithm is proposed to recognize multi-channel electromyography (EMG) patterns using deep belief networks (DBNs) It is difficult to classify the EMG features because an EMG signal has nonlinear and time-varying characteristics Therefore, in several previous studies, various machine-learning methods have been applied A DBN is a fast, greedy learning algorithm that can find a fairly good set of weights rapidly, even in deep networks with a large number of parameters and many hidden layers To evaluate this model, we acquired EMG signals, extracted their features, and then compared the model with the DBN and other conventional classifiers The accuracy of the DBN is higher than that of the other algorithms The classification performance of the DBN model designed is approximately 8860% It is 755% (p=982×10−12) higher than linear discriminant analysis (LDA) and 289% (p=194×10−5) higher than support vector machine (SVM) Further, the DBN is better than shallow learning algorithms or back propagation (BP), and this model is effective for an EMG-based user-interfaced system

MHD stagnation point flow by a permeable stretching cylinder with Soret-Dufour effects

Abstract: Combined effects of Soret (thermal-diffusion) and Dufour (diffusion-thermo) in MHD stagnation point flow by a permeable stretching cylinder were studied. Analysis was examined in the presence of heat generation/absorption and chemical reaction. The laws of conservation of mass, momentum, energy and concentration are found to lead to the mathematical development of the problem. Suitable transformations were used to convert the nonlinear partial differential equations into the ordinary differential equations. The series solutions of boundary layer equations through momentum, energy and concentration equations were obtained. Convergence of the developed series solutions was discussed via plots and numerical values. The behaviors of different physical parameters on the velocity components, temperature and concentration were obtained. Numerical values of Nusselt number, skin friction and Sherwood number with different parameters were computed and analyzed. It is found that Dufour and Soret numbers result in the enhancement of temperature and concentration distributions, respectively.

Mining pressure monitoring and analysis in fully mechanized backfilling coal mining face-A case study in Zhai Zhen Coal Mine

Abstract: Fully mechanized solid backfill mining (FMSBM) technology adopts dense backfill body to support the roof. Based on the distinguishing characteristics and mine pressure control principle in this technology, the basic principles and methods for mining pressure monitoring were analyzed and established. And the characteristics of overburden strata movement were analyzed by monitoring the support resistance of hydraulic support, the dynamic subsidence of immediate roof, the stress of backfill body, the front abutment pressure, and the mass ratio of cut coal to backfilled materials. On-site strata behavior measurements of 7403W solid backfilling working face in Zhai Zhen Coal Mine show that the backfill body can effectively support the overburden load, obviously control the overburden strata movement, and weaken the strata behaviors distinctly. Specific performances are as follows. The support resistance decreases obviously; the dynamic subsidence of immediate roof keeps consistent to the variation of backfill body stress, and tends to be stable after the face retreating to 120–150 m away from the cut. The peak value of front abutment pressure arises at 5–12 m before the operating face, and mass ratio is greater than the designed value of 1.15, which effectively ensures the control of strata movement. The research results are bases for intensively studying basic theories of solid backfill mining strata behaviors and its control, and provide theoretical guidance for engineering design in FMSBM.

Generalized thermoelastic interaction in functional graded material with fractional order three-phase lag heat transfer

Abstract: The present work is concerned with the solution of a problem on thermoelastic interactions in a functional graded material due to thermal shock in the context of the fractional order three-phase lag model. The governing equations of fractional order generalized thermoelasticity with three-phase lag model for functionally graded materials (FGM) (i.e., material with spatially varying material properties) are established. The analytical solution in the transform domain is obtained by using the eigenvalue approach. The inversion of Laplace transform is done numerically. The graphical results indicate that the fractional parameter has significant effects on all the physical quantities. Thus, we can consider the theory of fractional order generalized thermoelasticity an improvement on studying elastic materials.

An optimal energy management development for various configuration of plug-in and hybrid electric vehicle

Abstract: Due to soaring fuel prices and environmental concerns, hybrid electric vehicle (HEV) technology attracts more attentions in last decade. Energy management system, configuration of HEV and traffic conditions are the main factors which affect HEV’s fuel consumption, emission and performance. Therefore, optimal management of the energy components is a key element for the success of a HEV. An optimal energy management system is developed for HEV based on genetic algorithm. Then, different powertrain system component combinations effects are investigated in various driving cycles. HEV simulation results are compared for default rule-based, fuzzy and GA-fuzzy controllers by using ADVISOR. The results indicate the effectiveness of proposed optimal controller over real world driving cycles. Also, an optimal powertrain configuration to improve fuel consumption and emission efficiency is proposed for each driving condition. Finally, the effects of batteries in initial state of charge and hybridization factor are investigated on HEV performance to evaluate fuel consumption and emissions. Fuel consumption average reduction of about 14% is obtained for optimal configuration data in contrast to default configuration. Also results indicate that proposed controller has reduced emission of about 10% in various traffic conditions.

An experimental study on thermal characteristics of nanofluid with graphene and multi-wall carbon nanotubes

Abstract: High-thermal conductivity enhancement of nanofluid is one of the promising topics of the nanoscience research field. This work reports the experimental study on the preparation of graphene (GN) and multi-walled carbon nanotubes (MWCNTs) based nanofluids with the assistance of sodium dodecyl benzene sulfonate (SDBS) and sodium dodecyl sulfate (SDS) surfactants, and their thermal behaviors. The present work suggests not a solution, but a solution approach and deduces a new conclusion by trying to resolve the agglomeration problem and improve the dispersibility of nanoparticles in the base fluid. The analysis results of FESEM, thermal conductivity, diffusivity, effusivity and heat transfer coefficient enhancement ratio of nanofluid with surfactants SDS and SDBS expose strong evidence of the dispersing effect of surfactant on the making of nanofluid.

Non-pneumatic mechanical elastic wheel natural dynamic characteristics and influencing factors

Abstract: Non-pneumatic tire appears to have advantages over traditional pneumatic tire in terms of flat proof and maintenance free. A mechanical elastic wheel (MEW) with a non-pneumatic elastic outer ring which functions as air of pneumatic tire was presented. The structure of MEW was non-inflatable integrated configuration and the effect of hinges was accounted for only in tension. To establish finite element model of MEW, various nonlinear factors, such as geometrical nonlinearity, material nonlinearity and contact nonlinearity, were considered. Load characteristic test was conducted by tyre dynamic test-bed to obtain force-deflection curve. And the finite element model was validated through load characteristic test. Natural dynamic characteristics of the MEW and its influencing factors were investigated based on the finite element model. Simulation results show that the finite element model closely matched experimental wheel. The results also show that natural frequency is related to ground constraints, material properties, loads and torques. Influencing factors as above obviously affect the amplitude of mode of vibration, but have little effect on mode of vibration shape. The results can provide guidance for experiment research, structural optimization of MEW.

Simulation of crack coalescence mechanism underneath single and double disc cutters by higher order displacement discontinuity method

Abstract: The present research is focused on the numerical crack coalescence analysis of the micro-cracks and cracks produced during the cutting action of TBM disc cutters. The linear elastic fracture mechanics (LEFM) concepts and the maximum tangential stress criterion are used to investigate the micro crack propagation and its direction underneath the excavating discs. A higher order displacement discontinuity method with quadratic displacement discontinuity elements is used to estimate the stress intensity factors near the crack tips. Rock cutting mechanisms under single and double type discs are simulated by the proposed numerical method. The main purposes of the present modeling are to simulate the chip formation process of indented rocks by single and double discs. The effects of specific disc parameters (except speed) on the thrust force F r, the rolling force F r, and the specific energy E S are investigated. It has been shown that the specific energy (energy required to cut through a unit volume of rock) of the double disc is less than that of the single disc. Crack propagation in rocks under disc cutters is numerically modeled and the optimum ratio of disc spacing S to penetration depth P d (i.e. S/P d ratio) of about 10 is obtained, which is in good agreement with the theoretical and experimental results cited in the literature.

Generation of 3D random meso-structure of soil-rock mixture and its meso-structural mechanics based on numerical tests

Abstract: The mesoscopic failure mechanism and the macro-mechanical characteristics of soil-rock mixture (S-RM) under external load are largely controlled by S-RM’s meso-structural features. The objective of this work is to improve the three-dimensional technology for the generation of the random meso-structural models of S-RM, for randomly generating irregular rock blocks in S-RM with different shapes, sizes, and distributions according to the characteristics of the rock blocks’ size distribution. Based on the new improved technology, a software system named as R-SRM3D for generation and visualization of S-RM is developed. Using R-SRM3D, a three-dimensional meso-structural model of S-RM is generated and used to study the meso-mechanical behavior through a series of true-triaxial numerical tests. From the numerical tests, the following conclusions are obtained. The meso-stress field of S-RM is influenced by the distribution of the internal rock blocks, and the macro-mechanical characteristics of S-RM are anisotropic in 3D; the intermediate principal stress and the soil-rock interface properties have significant influence on the macro strength of S-RM.

Phase transformation in suspension roasting of oolitic hematite ore

Abstract: Suspension roasting followed by magnetic separation is a promising method to upgrade oolitic hematite ore. An oolitic hematite ore was roasted using suspension roasting technology at different temperatures. The phase transformation for iron minerals was investigated by XRD and Mossbauer spectrum, and the characteristics of roasted product were analyzed by VSM and SEM-EDS. Results indicate that the magnetic concentrate is of 58.73% Fe with iron recovery of 83.96% at 650 °C. The hematite is rapidly transformed into magnetite during the roasting with transformation ratio of 92.75% at 650 °C. Roasting temperature has a significant influence on the phase transformation of hematite to magnetite. The transformation ratio increases with increased temperature. After roasting, the magnetic susceptibility is significantly improved, while iron ore microstructure is not altered significantly.

Crosswind stability of high-speed trains in special cuts

Abstract: Analysis of the aerodynamic performance of high-speed trains in special cuts would provide references for the critical overturning velocity and complement the operation safety management under strong winds. This work was conducted to investigate the flow structure around trains under different cut depths, slope angles using computational fluid dynamics (CFD). The high-speed train was considered with bogies and inter-carriage gaps. And the accuracy of the numerical method was validated by combining with the experimental data of wind tunnel tests. Then, the variations of aerodynamic forces and surface pressure distribution of the train were mainly analyzed. The results show that the surroundings of cuts along the railway line have a great effect on the crosswind stability of trains. With the slope angle and depth of the cut increasing, the coefficients of aerodynamic forces tend to reduce. An angle of 75° is chosen as the optimum one for the follow-up research. Under different depth conditions, the reasonable cut depth for high-speed trains to run safely is 3 m lower than that of the conventional cut whose slope ratio is 1:1.5. Furthermore, the windward slope angle is more important than the leeward one for the train aerodynamic performance. Due to the shield of appropriate cuts, the train body is in a minor positive pressure environment. Thus, designing a suitable cut can contribute to improving the operation safety of high-speed trains.

Degradation of ethyl xanthate in flotation residues by hydrogen peroxide

Abstract: The degradation behavior of ethyl xanthate (EX) salt was the most widely used collector in sulfide mineral flotation and emission of flotation tailings with residual EX was harmful to environment. In this work, hydrogen peroxide (H2O2) was investigated by UV-visible spectroscopy (UV/Vis) at different pH values from 3 to 12. For pH value from 5 to 12, EX was oxidized into ethyl per xanthate (EPX) by H2O2. Then EPX was further oxidized into thiosulfate (TS) salt rather than ethyl thiocarbonate (ETC) and this step was the reaction-limited step. Then depending on pH values, TS was degraded into sulphate and carbonate salts (pH>7) or elemental sulfur (pH 3.0 during test time.

Layout and support design of a coal roadway in ultra-close multiple-seams

Abstract: A roadway within ultra-close multiple-seams (RUCMSs) is one of the most difficult supported coal roadways to deal with in underground coal mines. This is usually due to the unknown stress distributions, improper roadway layout, and unreasonable support parameters. In order to solve this support problem and effectively save RUCMSs from frequent and abrupt disasters (such as serious deformation of the surrounding rock, roof cave ins, and coal side collapse), a comprehensive method is adopted here which includes theoretical analysis, numerical simulation, and field monitoring. A mechanical model was constructed to determine the stress distribution in the coal pillar after two sides of a longwall panel had been mined. Based on this model, the horizontal, vertical, and tangential stress equations for the plane below the floor of the upper-left coal pillar were deduced. In addition, a typical coal mine (the Jinggonger colliery, located in Shuozhou city, Shanxi province, China) with an average distance between its 9# and 11# coal seams of less than 8.0 was chosen to conduct research on the proper layout and reasonable support required for a typical coal roadway located within coal seam 11#. Using FLAC3D (Fast Lagrangian Analysis of Continua in 3-Dimensions) numerical software, eight schemes were designed with different horizontal distances (d) between the center lines of the coal pillar and the roadway in the lower coal seam (RLCS). The simulations and detailed analysis indicate that the proper distances required are between 22.5 and 27.5 m. A total of 20 simulation schemes were used to investigate the factors influencing the support provided by the key bolts (bolt length, spacing, distance between two rows, installation angle, and pre-tightening force). The results were analyzed and used to determine reasonable values for the support parameters. Field results show that the stability and strength of the RLCS can be effectively safeguarded using a combination of researched stress distribution characteristics, proper layout of the RLCS, and correct support parameters.

Impact of permafrost degradation on embankment deformation of Qinghai-Tibet Highway in permafrost regions

Abstract: Based on long-term monitoring data, the relationships between permafrost degradation and embankment deformation are analyzed along the Qinghai-Tibet Highway (QTH). Due to heat absorbing effect of asphalt pavement and climate warming, permafrost beneath asphalt pavement experienced significant warming and degradation. During the monitoring period, warming amplitude of the soil at depth of 5 m under asphalt ranged from 0.21 °C at the XD1 site to 0.5 °C at the KL1 site. And at depth of 10 m, the increase amplitude of ground temperature ranged from 0.47 °C at the NA1 site to 0.07 °C at the XD1 site. Along with ground temperature increase, permafrost table beneath asphalt pavement decline considerably. Amplitude of permafrost table decline varied from 0.53 m at the KL1 site to 3.51 m at the NA1 site, with mean amplitude of 1.65 m for 8 monitoring sites during the monitoring period. Due to permafrost warming and degradation, the embankment deformation all performed as settlement at these sites. At present, those settlements still develop quickly and are expected to continue to increase in the future. The embankment deformations can be divided into homogeneous deformation and inhomogeneous deformation. Embankment longitudinal inhomogeneous deformation causes the wave deformations and has adverse effects on driving comfort and safety, while lateral inhomogeneous deformation causes longitudinal cracks and has an adverse effect on stability. Corresponding with permafrost degradation processes, embankment settlement can be divided into four stages. For QTH, embankment settlement is mainly comprised of thawing consolidation of ice-rich permafrost and creep of warming permafrost beneath permafrost table.

Three-dimensional analysis of slopes reinforced with piles

Abstract: Based on the upper bound of limit analysis, the plane-strain analysis of the slopes reinforced with a row of piles to the 3D case was extended. A 3D rotational failure mechanism was adopted to yield the upper bound of the factor of safety. Parametric studies were carried out to explore the end effects of the slope failures and the effects of the pile location and diameter on the safety of the reinforced slopes. The results demonstrate that the end effects nearly have no effects on the most suitable location of the installed piles but have significant influence on the safety of the slopes. For a slope constrained to a narrow width, the slope becomes more stable owing to the contribution of the end effects. When the slope is reinforced with a row of piles in small space between piles, the effects of group piles are significant for evaluating the safety of slopes. The presented method is more appropriate for assessing the stability of slopes reinforced with piles and can be also utilized in the design of plies stabilizing the unstable slopes.

A two-stage short-term traffic flow prediction method based on AVL and AKNN techniques

Abstract: Short-term traffic flow prediction is one of the essential issues in intelligent transportation systems (ITS). A new two-stage traffic flow prediction method named AKNN-AVL method is presented, which combines an advanced k-nearest neighbor (AKNN) method and balanced binary tree (AVL) data structure to improve the prediction accuracy. The AKNN method uses pattern recognition two times in the searching process, which considers the previous sequences of traffic flow to forecast the future traffic state. Clustering method and balanced binary tree technique are introduced to build case database to reduce the searching time. To illustrate the effects of these developments, the accuracies performance of AKNN-AVL method, k-nearest neighbor (KNN) method and the auto-regressive and moving average (ARMA) method are compared. These methods are calibrated and evaluated by the real-time data from a freeway traffic detector near North 3rd Ring Road in Beijing under both normal and incident traffic conditions. The comparisons show that the AKNN-AVL method with the optimal neighbor and pattern size outperforms both KNN method and ARMA method under both normal and incident traffic conditions. In addition, the combinations of clustering method and balanced binary tree technique to the prediction method can increase the searching speed and respond rapidly to case database fluctuations.

Acoustic emission characteristics of rock under impact loading

Abstract: Acoustic emission tests were performed using a split Hopkinson pressure bar system (SHPB) on 50-mm-diameter bars of granite, limestone, sandstone and skarn. The results show that the amplitude distribution of hits is not well centralized around 50 dB, and that some hits with large amplitudes, usually larger than 70 dB, occur in the early stages of each test, which is different from the findings from static and low-loading-rate tests. Furthermore, the dominant frequency range of the recorded acoustic emission waveforms is between 300 kHz and 500 kHz, and frequency components higher than 500 kHz are not significant. The hit with the largest values of amplitude, counts, signal strength, and absolute energy in each test, displays a waveform with similar frequency characteristics and greater correlation with the waveform obtained from the elastic input bar of the split Hopkinson pressure bar system compared with the waveforms of the other hits. This indicates that the hit with the largest values of amplitude, counts, signal strength, and absolute energy is generated by elastic wave propagation instead of fracture within the rock specimen.