Journal of Northeastern University(Natural Science)

Memetic Algorithm for Crane Scheduling Problem in Slab Yard with Spatial and Temporal Constraints

WANG Xu， LIU Shi-xin， WANG Jia

2017, 38 (7): 913-917. DOI: 10.12068/j.issn.1005-3026.2017.07.001

Abstract ( 640 )

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Crane scheduling problem was researched for slab yard in steel plant. Considering the time and space as well as the hot rolling， a crane scheduling model for slab yard was established. According to the characters of real-time and non-crossing for the problem， a Memetic algorithm was designed to solve it， including the crane allocation rule based on the priority relation， the decoding rules based on discrete event dynamic simulation(DEDS)， adaptive crossover operator and simulate annealing global search after each crossover and mutation. Simulation experiment was performed with data by crane scheduling for slab out， and the results of simulation experiments showed that the proposed algorithm has high convergence speed and stability， which meets actual production demand.

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Trajectory Compression Method Based on Sort Tree Index

LIN Shu-kuan， ZHANG Pei-he， LIU Xiao-qiang， QIAO Jian-zhong

2017, 38 (7): 918-922. DOI: 10.12068/j.issn.1005-3026.2017.07.002

Abstract ( 556 )

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Raw GPS trajectories are usually long and the data volume is large. The transmission， storage and processing of trajectory data are becoming more and more difficult. So， raw GPS trajectories data need to be compressed. However， those problems still exist in the current DPTC (direction-preserving trajectory compression) methods， such as that error tolerance is difficult to determine， computation cost is high， and compression effect is bad. For these problems， the trajectory compression method based on sort tree index was proposed. With the help of the sort tree index， effective pruning in the trajectory compression process improved the efficiency of trajectory compression. Meanwhile， the segment error was redefined， which played a decisive role in determining whether a trajectory point is preserved in the compressed trajectory or not， and the compression effect was enhanced. The extensive experimental results on real data sets show the effectiveness and efficiency of the proposed method.

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Hemisphere Symmetry Feature Based on Tensor Space and Recognition of Epilepsy

JIANG Hui-yan， LIU Ruo-nan， GAO Fei-fei， MIAO Yu

2017, 38 (7): 923-927. DOI: 10.12068/j.issn.1005-3026.2017.07.003

Abstract ( 616 )

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With brain PET(positron emission tomography) image information， a recognition method based on hemisphere symmetry feature of tensor space was proposed to identify the epilepsy lesions of PET(positron emission tomography) images. Firstly， the SUV(standard uptake value) of each voxel in brain PET images was calculated and the third order tensor based on SUV was constructed. Then， the hemisphere symmetry feature was extracted and the hemisphere symmetry tensor model was built. Next， a multi linear principal component analysis (MPCA) algorithm was used for feature selection of hemisphere symmetry tensor model. Lastly， the support vector machine (SVM) was used to identify the epilepsy. The results show that the epilepsy lesions of the brain PET images can be effectively identified by the proposed algorithm， which can be used as a computer aided diagnosis way to help doctors with epilepsy disease diagnosis.

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Geometric Labeling of Image Regions Based on Combination of Multiple Features

LIU Wei， YU Bing， ZHOU Ting， YUAN Huai

2017, 38 (7): 927-931. DOI: 10.12068/j.issn.1005-3026.2017.07.004

Abstract ( 543 )

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A geometric labeling method of image regions was proposed based on combination of multiple features. First of all， according to the requirement of multi-scale feature information extraction， a novel network structure—multi-scale kernel convolutional network (MSKCN) was proposed. The multi-scale feature information was used for inferring geometric label of pixel. The geometric labeling of super-pixel regions with the image super-pixel segmentation was achieved. Then a feature representation of super-pixel regions was established by combining multi-scale features proposed and traditional features of super-pixel regions. Finally， a CRF(conditional random field) model was constructed for the super-pixel image to infer geometric label of super-pixel regions with the image super-pixel segmentation. The experiments on public database Geometric Context (GC) indicated that the accuracy of geometric labeling was improved by using the proposed method compared with the existing state-of-art.

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Respiratory Rate Estimation from Smartphone-Camera-Acquired Pulse Wave Signal Using Visible Light

CHEN Xing-chi， ZHAO Hai， BI Yuan-guo， YU Yang

2017, 38 (7): 932-935. DOI: 10.12068/j.issn.1005-3026.2017.07.005

Abstract ( 711 )

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To solve the problem of estimating respiratory rate in smartphone platform， a novel fusion respiratory rate estimation (FRRE) method was proposed to calculate respiratory rate via smartphone camera. By combining the red light with the green light from the visible light of flashlight， a fusion pulse wave was computed and then the photo plethysmo graphy signal was extracted from human opisthenar. The instantaneous heart rate was calculated by green pulse wave. Using coherent demodulation to eliminate the heart rate signal from the fusion pulse wave， the respiration signal could be obtained. The respiratory signal was addressed by fast Fourier transform and power spectral density. Then， the respiratory rate was gained. Experimental results show that FRRE has a better accuracy and real-time than traditional VFCDM， FRRE provides an effective respiratory rate estimation method.

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Two-Material Decomposition Algorithm of Dual-Energy CT Based on Gradient Descent Method

TENG Yue-yang， ZHENG Sun-yi， LU Zi-peng， KANG Yan

2017, 38 (7): 936-940. DOI: 10.12068/j.issn.1005-3026.2017.07.006

Abstract ( 809 )

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Basis material decomposition is a very essential step in dual-energy CT (DECT) reconstruction and two-material decomposition is one of the most common model whose key point is to obtain the projections of decomposition coefficient. To improve the speed of it， two-material decomposition algorithms were proposed， which are the dual-energy CT based on the error feedback gradient descent method and the Armijo-Goldstein rule gradient descent method， respectively. These two methods were able to get the projections of decomposition coefficient quickly because of the computed step size in gradient descent. Moreover， the nonlinear problem in dual-energy CT reconstruction was also effectively and efficiently solved by using the proposed methods. Simulation results indicated that compared to the projection matching method， the two proposed methods can get stable convergence and high reconstruction precision with a short span of time， which has an important significance to the clinical application. With the same reconstruction precision， the algorithm based on the Armijo-Goldstein rule gradient descent is faster， using the inexact linear search step size.

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Effect of Asymmetric Hot Rolling on Microstructure and Mechanical Properties in Low Alloy Steel

LI Cheng-ning， YUAN Guo， KANG Jian， WANG Guo-dong

2017, 38 (7): 941-945. DOI: 10.12068/j.issn.1005-3026.2017.07.007

Abstract ( 671 )

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The effects of asymmetric hot rolling on the microstructure and mechanical properties of low alloy steel were investigated when the symmetric hot rolling and asymmetric hot rolling with roll velocity ratio of 1.2 were applied to the steel. The results show that asymmetric hot rolling can promote the austenite/ferrite transformation significantly and improve the microstructure uniformity along thickness direction of the steel strip. After the symmetric hot rolling process， the microstructure at the surface of the steel strip was fine ferrite layer and was coarse bainite at the thickness of 1/4 or 1/2. However， the microstructure through the thickness of the steel was the uniform ferrite after asymmetric hot rolling process. The tensile strength and elongation of the steel after these two rolling processes respectively， were very close， which were about 710~718MPa and 20%. After replacing the symmetric hot rolling process by the asymmetric one， the yield strength of the steel increased from 526MPa to 561MPa. The main reason is that the transformation strengthening is dominant in a symmetric hot-rolled steel， but grain refinement is more prominent for asymmetric hot-rolled steel.

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Effect of Electromagnetic Field on Microstructure of 1100 Aluminum Alloy Sheet During Roll Casting

XU Guang-ming， PAN Jiang-shen

2017, 38 (7): 946-949. DOI: 10.12068/j.issn.1005-3026.2017.07.008

Abstract ( 666 )

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When adding different amount of Al-Ti-B refiner(0.4%， 0.2% and 0.1%) in the 1100 aluminum alloy sheet， the effects of electromagnetic oscillating field on refining microstructure of the sheet during roll casting were investigated. The results show that the refining effects on the microstructure of the roll-casted sheet were significant after applying electromagnetic oscillating field compared with that in the traditional roll-casted one. Also，when the refiner content was within the scope of 0.1% to 0.4%， the refining effect of electromagnetic field was prominent and the refining microstructure was superior to that in the traditional roll-casted one with adding 0.4% refiner. Therefore， the electromagnetic vibration roll casting process can decrease the amount of the refiner greatly， reduce element segregation and improve internal quality in a roll-casted billet.

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Effect of Zn on Microstructure and Mechanical Properties of 5083 Alloy

SHI Jian-chao， LUO Hong-jie， YAO Guang-chun

2017, 38 (7): 950-954. DOI: 10.12068/j.issn.1005-3026.2017.07.009

Abstract ( 773 )

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When 1.5%~5% Zn(mass fraction)element was added into 5083 alloy， the effect of Zn on microstructure and mechanical properties was investigated. The microstructures of as-cast， homogenized and rolled alloys were characterized by SEM and EDS and mechanical property of the rolled alloy was obtained in a tensile test. It was found that the segregation in as-cast alloy increased with the additive of Zn and the second phases were mainly the rich-Mg and rich-Zn phases. After homogenization treatment， the homogenized alloy could be rolled more easily， the volume fraction of the second phase decreased significantly and the unresolved second phases were Mg₂Si and Al₃Fe. The results also showed that the grain size of the rolled alloy decreased obviously to 150nm. With the more additive of Zn， the yield and tensile strength of the rolled alloy increased， while the elongation decreased slightly.

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Effect of Cooling Mode on BN Phase Morphology and Mechanical Properties of CB2 Steel

MA Yu-lin， LIU Yue， GU Jin-tao， LIU Chun-ming

2017, 38 (7): 955-959. DOI: 10.12068/j.issn.1005-3026.2017.07.010

Abstract ( 687 )

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To study the effect of cooling mode on the BN phase morphology and mechanical properties of a new generation ferritic heat resistant steel， the CB2 steel with the B content of 0.012% after 1100℃ austenitizing was carried out by the air-cooling and water-cooling treatment， respectively. The results showed that the size of the BN phase in the austenitized CB2 steel reduced with the increase of cooling rate.A BN phase with 600nm size was observed in the water-cooled CB2 steel sample， associated with the increase of mechanical property.The BN phases were irregular blocks in an air-cooled sample， associated with internal cracks and fracture， while they were compact rectangles in a water-cooled one.Because the growth rate of BN nuclei increased with the increase of cooling rate and the nucleation rate of BN phase increased with the increase of supercooling degree， it was found that the refiner BN phases were dispersed in the CB2.

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Study of Non-isothermal Crystallization Kinetics of Modified Blast Furnace Slag

REN Qian-qian， ZHANG Yu-zhu， LONG Yue， ZOU Zong-shu

2017, 38 (7): 960-965. DOI: 10.12068/j.issn.1005-3026.2017.07.011

Abstract ( 626 )

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The precipitation process of minerals in modified blast furnace slag was simulated with Factsage software. The crystallization process of modified blast furnace slag was studied by using differential scanning calorimeters (DSC)， field emission scanning electron microscope (SEM) and X-ray diffraction(XRD) techniques. Based on the DSC curves， the crystallization activation energy was calculated by using Kissinger equation， Ozawa equation and Augis-Bennett equation. The crystal growth index n was calculated by using Augis-Bennett equations and the crystallization mechanism was also determined. The results show that with the increasing of heating rate， the modified blast furnace slag is changed from three-dimensional volume crystallization to surface crystallization. For the modified blast furnace slag of M_○k=1.3 and 1.4， the main precipitations are gehlenite and akermanite， and the crystallization activation energies are 469kJ/mol， 471kJ/mol (T_p1)， 393kJ/mol (T_p2)， respectively.

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Numerical Simulation of Electromagnetic-Thermal-Hydrodynamic Field in Tundish with Sidewall-Type Induction Heating

LI Yang， LI Liang， CHEN Yuan-yuan， DENG An-yuan

2017, 38 (7): 966-971. DOI: 10.12068/j.issn.1005-3026.2017.07.012

Abstract ( 740 )

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A new induction heating method was proposed for tundish and three kinds of side-type electromagnetic induction heaters were designed. The distribution of electromagnetic force of heaters， and its effects on flow field and temperature distribution in tundish were studied by numerical simulation. The optimal heater and heating power was obtained by analyzing the RTD (residence time distribution) curve. The results show that the flow field and temperature distribution of the molten steel in the tundish are improved by moving electromagnetic induction heater towards the end of the tundish. With the same heating power， the heating effect of the U-type heater is superior to E-type heater， and compared with bilateral and symmetrical distribution of U-type heater， the unilateral U-type heater has a better thermal efficiency. Increasing the induction heating power is beneficial to improve the flow of molten steel and improve the quality of the casting. For a four-strand tundish， the heating power of 800~1000kW is enough to compensate the heat loss.

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Experimental Study on Selective Catalytic Reduction of NO_○x With CO at Low-Temperature

LIU Kai-jie， YU Qing-bo， WANG Kui-ming， WANG Chun-peng

2017, 38 (7): 972-977. DOI: 10.12068/j.issn.1005-3026.2017.07.013

Abstract ( 706 )

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The experiment of selective catalytic reduction of NO_○x with CO in flue gas at low temperature was carried out. The study focused on the effect of action temperature， the load proportion of active metal and the type of active metals on the denitrification efficiency and the conversion of CO. The results show that， within the experimental temperature range， with the rise of reaction temperature， the NO conversion with Cu-Co/Al₂O₃ catalyst increases， the conversion of NO increases at first and then decreases with Cu-Mn/Al₂O₃ catalyst， and the conversion of CO increases. In the experimental conditions， as the load proportion of active metal changes， when the m(Cu)/m(Co) and m(Cu)/m(Mn) is 1.5， the catalyst has the best denitrification efficiency. The overall NO conversion with Cu-Mn/Al₂O₃ is better than that with Cu-Co/Al₂O₃. Comprehensive comparison of the eight catalysts shows that the Cu-Mn/Al₂O₃ catalyst with 1.5 load proportion of active metal has the best denitrification efficiency at 160℃.

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Optimization of Process Parameters for Small Hole Drilling of Carbon Fiber Reinforced Composites

WEN Quan， ZHAO Yue， GONG Ya-dong， ZOU Ping

2017, 38 (7): 978-982. DOI: 10.12068/j.issn.1005-3026.2017.07.014

Abstract ( 761 )

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The carbide twist drill was used for drilling experiments of 3 mm diameter small hole in carbon fiber reinforced resin matrix composites. The effects of process parameter and tool wear on the cutting force and the hole quality were studied. Firstly， the drilling force with different process parameters was measured by drilling test. The relationships between the thrust force， torque， rotational speed and feed speed were obtained by regression analysis. Then， the change curve of flank wear with the number of holes drilled was obtained using tool wear experiment. The relationship between burr area and drilling torque was obtained by measuring and fitting the hole exit burrs. Finally， the maximum material removal rate was regarded as the optimization goal， and drilling without delamination and burr damage meeting the requirements were chosen as the constraint conditions. The optimal rotational speed and feed speed were obtained by establishing the optimization model of drilling process parameters.

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Experimental Study on Influencing Factor of Surface Quality in Micro Side Grinding of Single Crystal Silicon

ZHOU Yun-guang， GONG Ya-dong， GAO Qi， ZHU Zong-xiao

2017, 38 (7): 983-988. DOI: 10.12068/j.issn.1005-3026.2017.07.015

Abstract ( 688 )

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To obtain the microstructure of single crystal silicon with a good surface quality， the single crystal silicon was grinded along the (100) crystal plane with microscale grinding technology by using microgrinding tool with diameter of 0.9 mm. Firstly， the main influence factors on microgrinding surface roughness of single crystal silicon were analyzed by the orthogonal experiment with three factors and five levels. Then， the microgrinding process was optimized to obtain minimum surface roughness. Lastly， the effect of process parameters on the surface roughness (R_○a) of microgrinding single crystal silicon was analyzed through single-factor experiment. The results show that: in the microgrinding process (20000r/min≤v_○s≤60000r/min， 20μm/s≤v_○w≤170μm/s and 3μm≤a_○p≤15μm) along (100) crystal plane of single crystal silicon， the influence of spindle speed on R_○a was maximum; when the spindle speed (v_○s) was 50000r/min， feeding rate (v_○w) was 20μm/s， grinding depth (a_○p) was 3μm， R_○a was minimum; R_○a reduces basically with the increase of v_○s， but if v_○s was too large， the spindle appeared vibration， R_○a showed the tendency of increase. R_○a raises with the increase of v_○w and a_○p.

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Development of Test Bench for Measuring Performance of Magneto-Rheological Fluid Brake

WANG Na， SONG Wan-li， HU Zhi-chao， MA Jin-tao

2017, 38 (7): 989-992. DOI: 10.12068/j.issn.1005-3026.2017.07.016

Abstract ( 574 )

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Theoretically， the quality of a vehicle braking system is mainly determined by the performance of brake. In order to coordinate the development of new magneto-rheological(MR) brake， a specific test system is developed and discussed in detail. The test apparatus system consists of measuring module and load applied module. For the system， it is a crucial problem to realize real-time measurement and display of data. Based on the LabVIEW software， the measuring module， including the speed torque sensor and the data acquisition card (DAQ card)， is ultimately developed. The test system is validated to be reasonable and practical by the successful application of braking performance tests of MRB.

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On the Friction Characteristics of CNC Machine Tool′s Feed Drive System

CHEN Ye， ZHAO Chun-yu， ZHANG Yi-min， WEN Bang-chun

2017, 38 (7): 993-997. DOI: 10.12068/j.issn.1005-3026.2017.07.017

Abstract ( 828 )

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Based on the FOCAS function set for the FANUC numerical control system， a real-time acquisition method of worktable position and servo motor torque current for a feed drive system is proposed. The continuous functions of the worktable position and the servo motor torque current for time are determined by virtue of inserting their discrete data with the cubic spline function， respectively. Then， an algorithm is proposed to identify the friction of the feed system. The characteristics of average value and spectrum for the friction are analyzed by using the experimental data. The results demonstrate that the local average frictions take on a catenary form because the lead screw-nut pair and the bearings at both ends are not concentric. The average friction over the experimental feed length is larger when the feed speed is low， and it decreases rapidly with the increase of the feed speed. However， when the feed speed reaches a certain value， the friction force increases slightly with the increase of the feed speed. In the operating process of the feed drive system， the periodic motion of rolling elements inside the screw groove， screw waviness， balls going in and out of the screw-nut pair and circular rails in the guides can motivate the corresponding fundamental and harmonic frequencies of the friction.

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Quatric-Topology-Optimization Design and Performance Analysis of Vehicle Chassis Structures

GUO Li-xin， ZHOU Hong-yang

2017, 38 (7): 998-1002. DOI: 10.12068/j.issn.1005-3026.2017.07.018

Abstract ( 705 )

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To solve the design problem of heavy commercial vehicle chassis， a global topology optimization method based on multi-load conditions and quatric local-optimization was proposed. A structural topology model was constructed based on the real sizes of commerical vehicle chassis. A preliminary topology structure was obtained based on seven typical loading conditions of the vehicle， and the final chassis optimization structure was obtained with the quatric-topology-optimization method based on different loading conditions. Finally， the finite element validation was given. The results showed that the new chassis mass reduced by nearly 30kg， and its stiffness， intensity and modal quality improved to a certain extent compared to the current one， and the effectiveness of the proposed quatric-topology-optimization method was verified.

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An Analysis Method of Mechanical Structural Reliability Based on the Kriging Model

LIU Kuo， LI Xiao-lei， WANG Jian

2017, 38 (7): 1002-1006. DOI: 10.12068/j.issn.1005-3026.2017.07.019

Abstract ( 576 )

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Based on an analysis of the drawbacks of the existing mechanical structure reliability sampling methods and the main factors influencing the estimation accuracy of failure probability， an analysis method of mechanical structural reliability based on the Kriging model and adaptive sampling strategy is proposed. The proposed sampling strategy combines random sampling and clustering algorithm， and ensures in probability that the new sample points locate themselves in the area that makes significant contribution to failure probability and avoids unnecessary sampling in the unimportant areas. The condition of convergence for the proposed Kriging model is deduced mainly based on the law of large numbers and central limit theorem. Two examples are adopted to illustrate the convergence process， accuracy and stability of the proposed method. The results show that the proposed method can estimate failure probability with high accuracy in the condition that the number of calls to structural performance function is small.

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Influence of Dolomite on Flotation Behavior of Magnesite

LUO Na， WEI De-zhou， LI Ming-yang， ZHANG Cai-e

2017, 38 (7): 1007-1011. DOI: 10.12068/j.issn.1005-3026.2017.07.020

Abstract ( 846 )

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The flotation behaviors of magnesite and dolomite were studied with sodium oleate(NaOL) as collector and sodium hexametaphosphate (SHMP) as depressant and the effect of Ca²⁺ appeared in the flotation pulp of artificial mixed ore containing dolomite and magnesite on flotation behavior of magnesite was explored by means of zeta potential measurements， adsorption tests and SEM-EDS analysis. Flotation results show that SHMP is a good selective depressant in single mineral flotation of magnesite and dolomite， while in the flotation separation of mixed mineral，magnesite and dolomite were both depressed by SHMP， flotation separation of two minerals can not be achieved. Adsorption tests and SEM-EDS analysis show that Ca²⁺ dissolved from dolomite adsorbs on magnesite surface during flotation process. Zeta potential measurements show that the adsorption of Ca²⁺ on magnesite surface makes the two minerals surface property similar， which seriously affects the flotation separation of magnesite and dolomite.

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Effects of Biocathode Construction Methods on Azo Dye Degradation Process

WANG You-zhao， PAN Yuan， XIE Yuan-hua， ZHU Tong

2017, 38 (7): 1012-1016. DOI: 10.12068/j.issn.1005-3026.2017.07.021

Abstract ( 697 )

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The biocathode can enhance the azo dye decolorization process in bioelectrochemical system. Three construction methods for biocathode were analyzed. The experimental results indicated that all the biocathodes formed by those methods could accelerate the azo dye decolorization process and those reactions were mostly dynamical processes. Among those methods， the anode polarity-reversal method showed the maximum catalytic current (0.12mA) and azo dye removal efficiency (85.2%). While the other method，in which the biocathode was formed by anaerobic sludge inoculation，had the advantage in electron recovery efficiency(71.8%). By analyzing the microbial biofilm structure of biocathodes， there were large amount of microbes correlated with functions of electrochemical activity or azo dye decolorization， which indicated that the enhancing effect of biocathodes related closely to the biofilm structures.

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Unsteady Simulation on Biomass Gasification Heating System with Fan & Double-Tube

YAN Fang， XU Kai-li， ZHANG Xiu-min

2017, 38 (7): 1017-1021. DOI: 10.12068/j.issn.1005-3026.2017.07.022

Abstract ( 604 )

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Aimed at solving the antifreezing problem of the wet purification device of biomass gasification station due to the installation of the firewall in winter time of north China， a waste-heat recovery system based on fan & double-tube is proposed. The Fluent and k-ε model is used to simulate the unsteady state of heating. The results indicate that the antifreezing requirement can be met in 90 or 40min when the inlet air velocity is 9 or 13m/s， respectively. Then the feasibility of the technique can be proved. The heating effects of different inlet air velocities of 5， 9， 13m/s at different times are also simulated. It shows that the heating effect can be raised and the time needed to reach the antifreezing requirement can be shortened and the temperature distributed in purification room can be more even by increasing the fan air volume. But the air speed should be restricted according to the corresponding standard and the energy consumption considerations.

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Combustion Characteristics of Diesel Pool Fire with Different Water Ratios in Ventilation Environment

ZHANG Pei-hong， CAO Yu， PAN Long-tao

2017, 38 (7): 1022-1026. DOI: 10.12068/j.issn.1005-3026.2017.07.023

Abstract ( 776 )

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Diesel pool fire experiments on different diesel water ratios were conducted under various ventilation conditions. The flame temperature， the radiation heat flux and the mass loss rate were measured， and the fire splash phenomenon was observed in order to analyze the combustion characteristics and the diesel pool fire spread rules. Results show that the diesel pool fire with 1∶1 diesel water ratio is always in the boilover status and the splash continuously occurs in the fire developed stage under natural ventilation conditions; both the temperature and the radiant heat flux reach the maximum value in the continuous splash. With the decreasing of the diesel water ratio， the flame temperature and the radiant heat flux are reduced and the frequency and the intensity of splashing are reduced either. If the air velocity is increased to 1.0m/s， the combustion is intensified significantly by the ventilation speed and the duration time of the developed stage of fire is increased. When the air velocity is further increased to 1.5m/s， the pool fire is hard to reach the developed stage or only last for a short time， which illustrates the negative impact of ventilation velocity increasing.

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Experimental Research on Timeliness of Promoting Gas Drainage by N₂ Injection in Coal Bed

CHEN Li-wei， YANG Tian-hong， YANG Hong-min， FENG Zhao-yang

2017, 38 (7): 1026-1030. DOI: 10.12068/j.issn.1005-3026.2017.07.024

Abstract ( 615 )

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In order to make clearly the process and features of gas emission by injecting N₂， N₂ displacement coal seam CH₄ tests were performed by using coal bed gas injection displacement experiment device. The results show that N₂ displacement coal bed CH₄ is a time-dependent process with a gradual decay of drained CH₄ concentration， and CH₄ flow increases at first and then decreases. Gas injection pressure has significant impact on the displacement effect， the higher the injection pressure， the faster the drained CH₄ concentration decay， the larger injection gas flow， the more significant the flow rate increases. During the same time， the higher gas injection displacement pressure is， the larger the drained CH₄ volume. According to the theoretical analysis， the mechanisms of injecting N₂ displacement coal bed CH₄ include the gas displacement， the air carrying and the dilution and diffusion of gas flow.

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Optimization of Open Pit Multielement Ore Blending Based on Goal Programming

WANG Li-guan， SONG Hua-qiang， BI Lin， CHEN Xin

2017, 38 (7): 1031-1036. DOI: 10.12068/j.issn.1005-3026.2017.07.025

Abstract ( 692 )

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On account of long-time ore blending with multi elements & ore dropping points， and rough ore blending upon the uneven grade distribution of blast heaps， so an open pit automation ore blending method based on goal programming was put forward. Blasting heap was discretized into a number of cell block， then based on the sampling data of rock powder， the accurate prediction the grade of blasting heaps was realized by use of the geostatistics method. Considering the priority of ore blending and taking the minimum grade deviation as the objective function， the optimization model of the open pit ore blending based on goal programming was established. Using C++ language programming and solving the model by the LPSlove， then output the open pit ore blending optimization scheme and enclose the areas of mining area automatically. The method is applied to a large polymetallic open pit in Inner Mongolia， resulting in a quick ore blending computation time， a good ore blending result within the range of allowable error， and a high-efficiency of ore blending.

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A Reoptimization-Based All-Pairs Shortest Path Algorithm for Large-Scale Network—RASP Algorithm

JIANG Jin-cheng， WU Li-xin， ZHANG Yuan-yuan， LIU Shan-jun

2017, 38 (7): 1037-1042. DOI: 10.12068/j.issn.1005-3026.2017.07.026

Abstract ( 1134 )

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In order to improve the computational performance of searching all-pairs shortest paths in a large-scale network， an exact all-pairs shortest path method—RASP algorithm is proposed based on the reoptimization theory. First， the correlation and difference between the shortest path trees with different sources are analyzed. Second， the efficient conversion from a known single-source shortest path tree to another one with different source is achieved based on the reoptimization-based theory. Furthermore， the reoptimization-based all-pairs shortest path (RASP) algorithm utilizes this conversion method to calculate efficiently all-pairs shortest paths. At last， the time complexity of RASP algorithm is proved to be O(3n²+2nm). The experimental test demonstrates that RASP algorithm gains the advantage over Floyd， n-Dijkstra algorithms and their improved algorithms in both sparse and dense networks.

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Influence of Pore Water Pressure Gradient on Guiding Hydraulic Fracturing in Underground Coal Mine

CHENG Yu-gang， LU Yi-yu， GE Zhao-long， ZHONG Jian-yu

2017, 38 (7): 1043-1048. DOI: 10.12068/j.issn.1005-3026.2017.07.027

Abstract ( 716 )

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Based on the influence of pore water pressure gradient on the stress of hole wall and crack tip， a new crack-guiding method with guiding drilling is proposed. According to research on changing of the effective stress， the calculation model of the fracturing pressure and fracture propagation pressure is established. By using RFPA^3D-Flow fluid solid coupling software， the numerical model of oriented fracturing under pore water pressure gradient field is established. 7 groups of different guiding drilling models are calculated to study the guide fracturing effect of three main factors， viz. arrangement of guide borehole， distance， and water pressure. The results show that the pore pressure gradient can effectively reduce the crack initiation pressure and crack propagation pressure. The pressure of initiation and crack propagation is positively correlated with the control pressure of the guiding hole and inverse correlation between the distance from the guide hole. The variation law of the initial crack pressure calculated by the numerical calculation is consistent with the theoretical prediction. The study demonstrates that the guiding fracturing pressure calculation model is correct and the control method of the fracture orientation is feasible.

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Study on the Corrosion Model of Tunnel Lining Structure in Gypsum Rock

REN Song， LI Zhen-yuan， CHEN Fan， JIANG De-yi

2017, 38 (7): 1049-1054. DOI: 10.12068/j.issn.1005-3026.2017.07.028

Abstract ( 726 )

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In order to study the corrosion of gypsum rock to tunnel lining structure， the mechanism and influence factors of sulfate attacking on concrete were analyzed. The orthogonal test was designed to study the sulfate’s influence on the changing rule of the concrete corrosion coefficient. The results show that there is a quadratic function between the anti-permeability level and the C₃A content and a logarithmic function between the corrosion coefficient， sulfate concentration and time; however， there is a linear relation between the pressure and the corrosion coefficient. The influence weight of each factor was calculated by using the range and AHP. According to the weight of each factor， it can be listed as C₃A content， sulfate concentration， time， anti-permeability level， pressure in order. Considering all the factors， a prediction model on the strength of concrete after concrosion was established based on the BP neural network. This model was applied in the design of Lirang tunnel lining.

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Reliability Analysis of SFRC Beams Under Ultimate Limit States of Long-Term Load

LI Yi， DONG Jin-xia， TAN Kiang Hwee

2017, 38 (7): 1055-1059. DOI: 10.12068/j.issn.1005-3026.2017.07.029

Abstract ( 779 )

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Time-dependent reliability model for the ultimate load-carrying capacity of steel fiber reinforced concrete (SFRC) beams subjected to long-term load is established based on the results obtained from the beams under sustained load ten years.Two series of tested beams are considered: Series I with constantly applied load but varying steel fiber content， and Series II with the same steel fiber content but subjected to different applied loads. The time-dependent reliability indexes are determined and the reliability pattern for 100 years of long-term load is forecasted using the equivalent resistance method and the first-order-second-moment method. The results show that the optimum content of steel fibers is 0.5% in Series I beams; however， for Series II beams with the same steel fiber content， the smaller the applied load is， the larger the reliability index and the flexural capacity are. Also， the reliability indexes are almost the same for similar applied loads. Under service conditions， the reliability indexes increase at first and then decrease with time. An inflection point is observed in the reliability index curves when the steel reinforcement starts to corrosion， leading to an obvious decrease in the flexural capacity.

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Impact of Land Use Changes on Spatial Distribution of Groundwater Level

NIE Si-yu ， SUN Xiao-qing ， BIAN Jian-min

2017, 38 (7): 1060-1064. DOI: 10.12068/j.issn.1005-3026.2017.07.030

Abstract ( 686 )

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In order to study the relationship between land use changes and groundwater level， based on the TM(thematic mapper) image of Da′an city in the west of Jilin province， the transformation matrix of the land use was calculated. By using the groundwater level data observed from monitoring wells and the knowledge of geostatistics， the relationship between the land use changes and the groundwater levels was analyzed. Results show that the changing of groundwater level takes on an obvious spatial characteristic and the influnence of human factors on the changing of groundwater level is gradually increased. The land use of Da′an city is dramatically changed in that if there is a rapid change of groundwater level， there is a rapid change of land use， which indicates there is a positive correlation between the land use and the spatial distribution of groundwater level.

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