28 August 2012, Volume 30 Issue 24

    

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  Theory of Dual-porosity Media in Coal Bed Methane and Its Application

  CAI Qiang;NIU Congcong;LIU Yuewu;LI Haisheng

  . 2012, 30(24): 17-22. https://doi.org/10.3981/j.issn.1000-7857.2012.24.001

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  Considering the effects of both steady and unsteady desorption of Coal Bed Methane(CBM), two kinds of dual-porosity unsteady seepage models are developed, including pseudo-steady cross-flow model and dual-porosity unsteady cross-flow model. The two models are solved by finite volume method and their characteristic curves are analyzed by considering different geological parameters. The calculation results show that both steady desorption and unsteady desorption of CBM delay the propagation of pressure wave; the increase of CBM desorption coefficients makes the pressure draw down slowly in the coalbed, it manifests the increase of boundary distance in pressure and pressure derivative curve. For different coalbeds, when either the cross-flow flow coefficient or the fracture storage coefficient is oversize, the dual-porosity media characters in theoretical curves will be covered up. The fact is consistent with the field test data which are difficult to appear the dual-porosity media characters. Therefore the root of the problem is discovered based on the research, while the field test data is hard to show the dual-porosity media characters.
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  Influencing Factors of Nitrogen Foam Plugging Performance Under Reservoir Condition

  YANG Zhaopeng;GAO Shusheng;WANG Yining;KE Wenqi;LU Yan;WANG Zhongbin

  . 2012, 30(24): 23-27. https://doi.org/10.3981/j.issn.1000-7857.2012.24.002

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  The plugging performance of the foam is strongly affected by the environment pressure. The back pressure is set to 10 MPa to simulate the environment pressure of the foam, in order to study the influencing factors of the plugging performance of the foam under the reservoir pressure. The nitrogen is chosen as the gas phase medium. The influencing factors studied in this paper include the reservoir pressure, the gas liquid ratio, the permeability, the oil saturation and the dip angle. It is shown that the plugging performance of the nitrogen foam is affected by the reservoir pressure. The greater the reservoir pressure is, the smaller the resistance effect will be. Within a certain range, the higher the gas liquid ratio of foam is, the better the plugging performance will be. The pore structure of the reservoir affects the generation of the foam, so that the higher the permeability is, the higher the plugging ability of the foam will be. Under the condition of a low oil saturation, the foam still has a certain plugging effect. But because the plugging period of a valid foam is very short, the nitrogen foam can only have a temporary plugging effect in the low oil saturation reservoir. The nitrogen foam is better distributed in the angle reservoir, where the plugging resistance of the nitrogen foam is higher. In the meantime, it is indicated that the plugging performance of the foam is better in the vertical direction.
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  Adsorption Characteristics of Petroleum Hydrocarbon Pollution in Aquifer Media

  SU Xiaosi;YUAN Wenzhen;SONG Mian;ZHANG Yuling;WANG Wei

  . 2012, 30(24): 28-32. https://doi.org/10.3981/j.issn.1000-7857.2012.24.003

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  Because of the petroleum pipelines corrosion in northeastern China, the groundwater would be polluted by the hydrocarbons and the adsorption by aquifer media would have impact on the transport of hydrocarbons in aquifer. According to the test results of groundwater quality, combining with the hydrogeology conditions, by means of the kinetics and isothermal experiments of adsorption, taking the largest adsorption, absorption rate, and adsorption dynamics constant as quantitative indices, the adsorption characteristics of the aquifer medium to petroleum pollution in the regions are qualitative analyzed. The results show that the adsorption dynamics law involving aquifer medium to petroleum pollution are complied with two class dynamics model, adsorption volume is proportional to the specific surface area of aquifer medium, the major adsorption effect is physical adsorption effect; the isothermal adsorption law of aquifer medium to petroleum pollution is nonlinear isothermal adsorption; based on Langmuir model, by colloids, adsorption quantity and adsorption rate for aquifer medium to petroleum hydrocarbon by the order from large to small are silty, silty sand, and fine sand. The above experimental results provide the reliable scientific basis for the further study on the gas transform rule for petroleum pollutant in aquifer media and relevant repair technology.
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  Dynamic Monitoring and Ecological Effect of Microbial Reclamation on Subsided Land in Area of Shendong Coal Mine Area

  YUE Hui;BI Yinli;LIU Ying

  . 2012, 30(24): 33-37. https://doi.org/10.3981/j.issn.1000-7857.2012.24.004

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  By taking the result of remote sensing on subsided land in the area of Shendong coal mine as an example, the Normalized Difference Vegetation Index (NDVI), vegetation fraction (F_g), and Leaf Area Index (LAI) data from environment and disaster reduction small satellites (HJ-CCD) images were applied to dynamically monitor mining subsidence land reclamation effects of microbial ecological in the area of Shendong mining. The remote sensing data were compared with the sampling experimental data in the same period; they were plant height, ground diameter, and crown width. It is discovered that the microbial reclamation improves vegetation fraction and ground biomass, and recovers the vegetation effectively. The microbe of microbial reclamation in the area of Shendong mining is Arbuscular Mycorrhizal Fungi (AMF) which inoculated in Amorpha fruticosa L. Through rhizosphere sampling experimental analysis, the results show that AMF inoculation could improve the plant micro environment, enlarge the root of the nutrient range, and is able to help on the vegetation restoration and reconstruction of mining area.
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  Experimental Study of Concrete Body Formed by Explosion

  CUI Zhuo;WANG Hailiang

  . 2012, 30(24): 38-41. https://doi.org/10.3981/j.issn.1000-7857.2012.24.005

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  The mechanical properties and microscopic structures of the curing concrete in flowing state are studied under the extreme condition of explosion. The concrete test blocks are formed by different charges of explosive in semi-infinite soil. Using the SHIMADZU universal testing machine AG-X250kN system, the uniaxial compression tests are carried out to study the stress-strain curves of the concretes formed by explosion, the concretes curing under the same condition and those of the standard curing. Using the SEM JSM-6510LV system, the microscopic structure images of concretes are obtained under various conditions. It is shown that the concretes formed by explosion have significantly higher strength than those curing under the same conditions, and also higher than those of the standard curing. The qualitative analysis of the microscopic structure of concretes formed by explosion shows that the microscopic structures are in accordance with the improvement of strength.
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  Optimization of a Partial Projectile Structure of the Penetration Warhead

  WANG Jiangbo;ZHANG Qingming;FENG Chengliang;CHEN Wen;LI Weibing;WANG Heng

  . 2012, 30(24): 42-45. https://doi.org/10.3981/j.issn.1000-7857.2012.24.006

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  The optimization is a key issue for the penetrating projectile. This paper proposes an auto optimization method for a partial projectile structure of the penetration warhead. The preliminary optimization of the projectile structure and the auto optimization of a partial projectile structure are realized. With the DOE debugging method, all material parameters in the simulation model used in the numerical simulation for the projectile penetrating concrete are obtained. The numerical simulation results are compared with the experiment, and it is found that the material parameters have the desired precision. The auto optimization method is used to design the nose section of the projectile, which improves the nose section design, reduces the resistance and the acceleration of the projectile, and increases the residual velocity and the penetration ability.
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  Accident Analysis of Gas Explosion in Constructing Gas Tunnel by Using FTA

  CHEN Yuanjiang;CHENG Gang;XIONG Jianming

  . 2012, 30(24): 46-51. https://doi.org/10.3981/j.issn.1000-7857.2012.24.007

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  The gas tunnel of the road traffic engineering in its construction stage faces the gas explosion risk, with very complex influencing factors. The typical tunnel gas explosions both at home and abroad are analyzed,to explore the sources of the gas explosion hazard. Through the FTA theory, an FAT model of the tunnel gas explosion is built, the minimum cut sets and the minimum path sets of accidents are computed, 380 ways leading to the gas explosion and 2 sets preventing the gas explosion are identified. The FTA important structure is computed, the faulty electromechanical and gas managements are considered as the main issues in considering the prevention of the tunnel gas explosion. Finally the countermeasures to prevent tunnel gas explosion are established. It is shown that in the prevention and control of the gas explosion, the prevention of the gas accumulation should be put in the first place, and the control of the spark origin in the second place, based on the safety construction management of the gas tunnel.
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  Bursting Crack Mechanism of Closure Segment Bottom Slab for the Certain Prestressed Variable Depth Box-section Bridge

  LOU Lilu

  . 2012, 30(24): 52-56. https://doi.org/10.3981/j.issn.1000-7857.2012.24.008

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  Prestressed variable depth box-section bridge has been widely used due to its advantages. In recent years, during the period of construction, some accidents occur, and the bottom slab of these bridges has bursting crack. Up to very recently, the research on the damage causes that could be found in the domestic literatures is only with rough analysis but detailed calculation. The primary reasons are made by these notional studies, however secondary reasons are unclear. In practice, the reason should be considered based on the structure instead of construction errors. With a specified engineering sample, 3D FEM analysis is performed so that the distribution of vertical stress on the section of tendon pipeline in the bottom slab is obtained. Result shows that four main external factors have impact on the vertical stress in bottom slab. They are deadweight of the bottom slab, longitudinal pressure, radial force originated from longitudinal bending prestressed tendon, and additional radial force caused by prestressed pipeline deviating from the design. Therefore, parametric analysis with respect to these four factors is conducted as the base for the discussion of the failure mechanism. Results indicate that the primary reason is the additional radial force produced by the radial force of bending tendon cluster and its position deviation from original design. With the longitudinal pressure is applied to, box beam segment of the cracked bottom beam would eventually burst apart due to instability. Based on the failure mechanism, two solutions are recommended for improving the resistant ability in the bursting crack of the bottom slab. They are setting hooked stirrups, and shortening the distance between the spacer bars of prestressed tendon cluster.
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  A Background Reconstruction Algorithm Based on Neighboring Correlation

  XIAO Mei;ZHANG Lei;KOU Wenyu;LIU Wei;MIAO Yonglu

  . 2012, 30(24): 57-61. https://doi.org/10.3981/j.issn.1000-7857.2012.24.009

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  The background subtraction is an important method for detecting the moving objects, which is widely applied in the video monitor system. When background is occupied by a foreground for a long time, the foreground will be mistakenly regarded as a background. In order to solve the background reconstruction in which background does not always appears with the largest appearance frequency, a new background reconstruction algorithm based on neighboring correlation is proposed. At first, the data is sorted in an ascending or descending order; secondly, the sorted data is classified by the simple method; thirdly, the appearance frequency of classified classes is computed. The definite identity of background is obtained by appearance frequency. The candidate backgrounds are selected for the pixels without definite background; finally, background selection procedure based on neighboring correlation is repeatedly executed to the pixels until the background of all pixels has been obtained. Simulations results show that the algorithm is able to deal with the complex scene in which the background has been covered for a long time. The proposed algorithm is able to reconstruct the background of scene well, and therefore the target could be perfectly extracted and successfully tracked.
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  Influence of Heat Sink and Source Temperature on Operation Reliability of Natural Circulation System

  YU Yu;QIAN Xiaoming;GAO Qinghan;WANG Xiaoxuan

  . 2012, 30(24): 62-65. https://doi.org/10.3981/j.issn.1000-7857.2012.24.010

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  In the Probabilistic Safety Assessment (PSA), Fault Tree (FT) is the approach commonly used for system reliability analysis. And it is the important feature of passive system and the basic difference from the active system that nuclear plant is able to be driven to safe state or shutdown by inherent safety characters of the reactor and physical principles, and is independent of human interfere or the operations of outside equipments, when the reactor is in the abnormal condition. Therefore, the passive system is widely used in new generation Nuclear Power Plant(NPP), such as AP1000 NPPs and high-temperature gas-cooled reactors to improve the safety. At the same time, since the passive system operation is depending on natural force, both the driven force and resistance are influenced by many uncertain factors, physical process failure become one of the significant causes for the system failure, which need to be considered in the system reliability analysis. FT method is not power enough to deal with this condition. For the passive system which is operating based on natural circulation, temperature of heat source and sink are important influence factors on system operation. Monte Carlo (MC) simulation is used to analyze the influence of heat source and sink temperature on system operation. From the result, it could be seen that the less the number of operation train is, the more prominent influence is. And if the safety margin is big enough, the system might not fail even when the system configuration does not satisfy design requirement, that is, the system failure is the integrate result of physical process failure and device failure which are mutually conditional.
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  Genome Shuffling of Rhodobacter Sphaeroides to Improve Coenzyme Q₁₀ Production

  SONG Liya;QIAO Zhixin;LI Weijing;HE Min;YU Qun

  . 2012, 30(24): 66-70. https://doi.org/10.3981/j.issn.1000-7857.2012.24.011

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  Coenzyme Q₁₀(CoQ₁₀ ) is an important electron transfer molecule in the respiratory chain and the indispensable coenzyme in the production of ATP, and it is widely used in therapeutic applications for several diseases such as heart diseases, hepatitis, Parkinson and so on. In order to improve the production of CoQ₁₀, this paper studies the screening of the mutant Rhodobacter Sphaeroides aiming for a higher CoQ₁₀ production by genome shuffling. According to the biosynthetic pathway and its mechanism, various resistance markers are selected, including the roxithromycin, the kanamycin, the p-hydroxy benzcic acid, the vitamin K3 and sodium sulfide(Na₂S). Their concentrations are determined according to the tolerance experiments on Rhodobacter sphaeroides. The improved starting population including nine mutant strains is generated by different resistance markers and different mutagenesis ways, such as the ultraviolet irradiation, the ultraviolet/lithium chloride, the diethyl sulfate, the microwave radiation and the γ Co60. Several high CoQ₁₀-producing colonies, including PN13, are selected from the first shuffled library. The CoQ₁₀ content of the PN13 reaches 2.39mg/g, 2.52 times of that of the wild-type strain.
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  A ZigBee-based Reservation and Exhibition Environment Monitoring System for Special Necessities of Ethnic Minorities

  SUN Yanhui;XU Guokai;ZHANG Junxing;SONG Peng

  . 2012, 30(24): 71-74. https://doi.org/10.3981/j.issn.1000-7857.2012.24.012

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  A reservation and exhibition environment monitoring system for special necessities of ethnic minorities based on the ZigBee net is developed. The system is designed to collect and transmit the environment information in real time; and, whenever an index goes above the standard line, the monitor center will send a demand to switch on a fan on the terminal node to realize the reversion control, and send warning messages by GSM. Users can check and control the state of any node in the net by PCs, embedded handsets or mobiles. The system is stable, low-cost, and with a wide adaption possibility and good portability.
Reviews
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  A Review of Flow Mechanisms in Shale Gas Reservoir

  YU Rongze;BIAN Yanan;ZHANG Xiaowei;YAN Jun;ZHAO Shouyuan;LIN Jun

  . 2012, 30(24): 75-79. https://doi.org/10.3981/j.issn.1000-7857.2012.24.013

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  This paper reviews the studies both at home and abroad of the gas flow mechanisms in shale gas reservoirs. The mathematical description methods, the influencing factors, the applicability and the disadvantages of the desorption, the diffusion and the seepage are analyzed. It is shown that the gas flow in the shale reservoir includes desorption, diffusion and seepage. The Langmuir isothermal adsorption law could describe the shale gas desorption accurately, but further researches are needed for the law to describe multi-component gas desorption. The Fick second diffusion law describes the gas diffusion in the matrix effectively, but the coupling between the diffusion and the seepage needs to be further studied. The gas seepage in the natural fractures follows the generalized Darcy's law with consideration of the slippage effect, and the gas seepage in the artificial fractures follows the Forchheimer equation. The pressure-sensitive effect, the two-phase flow of gas and water, the thermal effects, and the phase transition are the additional flow mechanisms in the shale gas reservoir that need to be further studied.