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    15 September 2004, Volume 25 Issue 9 Previous Issue    Next Issue

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    OriginalPaper
    Global adaptive output tracking control of a class of nonlinear systems
    Wang, Qiang-De (1); Jing, Yuan-Wei (1); Zhang, Si-Ying (1)
    2004, 25 (9):  817-820.  DOI: -
    Abstract ( 184 )   HTML   PDF (2153KB) ( 541 )  
    Focuses on the global adaptive control of a class of uncertain nonlinear systems with uncontrollable unstable linearization and unknown linear parameters. The control object is to design a robust adaptive nonlinear state feedback controller to solve the problem of global output tracking. Based on Lyapunov stability theory and using the modified adaptive power-added integrator as a tool, a nonlinear adaptive smooth-state feedback controller is proposed recursively. The proposed controller can ensure not only output tracking error sufficient small, but also all signals of the closed-loop systems globally bounded. Simulated results show that the controller is feasible and effective.
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    Dual-mode predictive control scheme for nonlinear discrete systems using fuzzy system
    Song, Chong-Hui (1); Wang, Yong-Fu (1); Chai, Tian-You (1)
    2004, 25 (9):  821-824.  DOI: -
    Abstract ( 246 )   HTML   PDF (167KB) ( 441 )  
    A dual-mode predictive controller of discrete nonlinear system is proposed using the fuzzy system as a predictive model. In the neighborhood of the origin, a linear feedback controller designed for the linearizing system generates the control action. If outside this neighborhood, however, a predictive controller based on fuzzy model applies to the real nonlinear system and drives the trajectory of the nonlinear system to the attractive region. The closed-loop stability is guaranteed under some conditions. A simulation is done to exemplify the effectiveness of the scheme proposed.
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    Dissipative chaotic neuron and its time-delay classification
    Yao, Yu (1); Gao, Fu-Xiang (1); Yu, Ge (1)
    2004, 25 (9):  825-828.  DOI: -
    Abstract ( 198 )   HTML   PDF (249KB) ( 525 )  
    The dynamics of a discrete and dissipative nonlinear model neuron is discussed. Numerical simulations demonstrate that the self-inhibitory units with non-zero decay rates exhibit a complex dynamics including period doubling routes to chaos. A BP/CNN hybrid neural network is constructed using the chaotic neuron in the neural network to conduct an after-processing for the output from BP network, with the reverse bifurcation of the chaotic neuron used to implement time-delay classification. The BP/CNN network thus constructed can detect the SYN flooding misuse intrusion featured with typical time-delay behavior. The result shows that these types of hybrid neural network have a capability for flexible time-delay classification so as to extend the computational capability of BP neural network and provide a new type of classifying method. The proposed neural network can be generalized to other time-delay classification.
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    Enhanced inter-domain routing aggregation algorithm based on Internet hierarchical structure
    Wang, Rui-Jun (1); Wang, Hong-Jun (1); Chen, Dong-Ming (1); Gao, Yuan (1)
    2004, 25 (9):  829-832.  DOI: -
    Abstract ( 209 )   HTML   PDF (755KB) ( 525 )  
    An enhanced inter-domain routing aggregation algorithm is proposed to strengthen routing aggregation behavior and constrain route advertising scope, based on the properties of Internet hierarchical structure and the relationship between autonomous systems. A prototype system implementation algorithm is thus provided, in which all the required data will be got from the interior of autonomous systems without global coordination data. The algorithm proposed can efficiently avoid the negative impact of aggregation on load balancing and link redundancy. Testing data statistics and analysis show that this algorithm can evidently reduce the routing table size so as to relax the pressure due to high-speed expansion of routing table at present and enhance the Internet expandability.
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    Video-integrated scheduling for proxy-assisted VOD
    Hu, Yu-Qi (1); Zang, Huai-Quan (2); Gao, Yuan (1)
    2004, 25 (9):  833-836.  DOI: -
    Abstract ( 348 )   HTML   PDF (239KB) ( 697 )  
    Video scheduling and proxy caching were investigated for proxy-assisted VOD (video-on-demand). The existing scheduling schemes were analyzed in a distributive proxy-based VOD system including mainly the client-pull and server-push schemes. In order to improve the utilization rate of bandwidth resources efficiently, a clear distinction between popular and unpopular videos was made taking the visual consumption of system's bandwidth resource as a performance index. A video-integrated scheduling scheme was proposed to configure client-pull and server-push scheduling schemes differing unpopular from popular videos. In addition, an optimal proxy caching algorithm was also proposed in combination with the video-integrated scheduling scheme, thus resulting in an efficient utilization of bandwidth resources. A performance evaluation showed that both algorithms can widen greatly the bandwidth bottleneck.
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    Recrystallization textures and microstructures of aluminium alloy 3004
    Zhang, De-Fen (1); Hu, Zhuo-Chao (1); Zuo, Liang (1); Wang, Fu (1)
    2004, 25 (9):  840-843.  DOI: -
    Abstract ( 275 )   HTML   PDF (274KB) ( 1231 )  
    The effect of temperature on recrystallization texture and microstructure of 3004 aluminium alloy has been investigated by means of orientation distribution function (ODF) and transmission electron microscope (TEM). The results showed that the orientation intensity of recrystallization cube texture |001| (100) is strong in annealed samples and become stronger along with increasing annealing temperature of which the intensity grades are f(g)∼8 and f(g)∼12 after annealing for 120 min at 350°C and 450°C respectively. But, the intensities of recrystallization texture R/S{124}<211>, S{123} <634> and C{112} <111> are weak; TEM images showed that the recovery process of the sample comes to the end after annealing at 250°C for 120 min. If annealed at over 300°C, the recrystallized grains grow increasingly and the 2nd-phase particles are precipitated further to disperse on the subboundaries in grains with dislocations surrounding them along with the increasing annealing temperature. Moreover, the 2nd-phase particles play the role of fostering the nucleation in recrystallization process.
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    Experimental study of Cu-Ag alloy contact wire manufactured through upward-casting process
    Liu, Qiang (1); Cui, Jian-Zhong (1); Xu, Guang-Ming (1); Liu, Xiao-Tao (1)
    2004, 25 (9):  844-847.  DOI: -
    Abstract ( 379 )   HTML   PDF (279KB) ( 681 )  
    The upward-casting process, to manufacture Cu-Ag alloy contact wire, and its product properties were investigated experimentally. The results showed that the electromagnetic stirring effect in the upward-casting process can improve the homogeneity of alloy composition prominently, by which the deviation of Ag mass fraction can be reduced down to 0.01% or only half by other methods. Tests with the samples of Cu-Ag alloy contact wire showed that the main properties of Cu-Ag alloy contact wire are better than those of the pure copper one, i.e., higher breaking load, lower elongation and slightly lower conductivity with the increasing Ag content. Its plasticity decreased notably when Ag mass fraction exceeds 0.12%. As to the softening temperature, the alloy wire is about 100°C higher than that of the pure copper one - it is of far-reaching importance to safe railway running and wire's service life. In view of the wholeness of properties, the Ag mass fraction of Cu-Ag alloy contact wire should be kept from 0.1% to 0.12%.
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    Surface nanocrystallization of 316L stainless steel induced by surface mechanical attrition treatment
    Lu, Ai-Qiang (1); Liu, Chun-Ming (1); Liu, Gang (2)
    2004, 25 (9):  848-850.  DOI: -
    Abstract ( 293 )   HTML   PDF (194KB) ( 1068 )  
    Surface nanocrystallization of 316L stainless steel was successfully realized by means of surface mechanical attrition treatment (SMAT). The microstructural evolution was examined through XRD and TEM, as well as its grain refinement behavior and hardness variation. The experimental results showed that high density dislocations form about 100 μm deep under sample surface, and then the mechanical twins are induced about 50 μm deep with increasing strain value and strain rate. The lamellar twins intercross each other to refine grain. Finally, a nanostructured surface layer about 20 μm thick forms after SMAT process, of which the microstructure consists of a mixture of both martensite and austenite phases with grain size about 10-30 nm. The realization of surface nanocrystallization is considered as resulting from the grain refinement due to dislocation-twin and twin-twin interactions, and its hardness is improved greatly after SMAT.
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    Effect of Si3N4/AlN additives on microstructure and properties of Sialon bonded corundum refractories synthesized once through
    Ru, Hong-Qiang (1); Gong, Gan-Lei (1); Sun, Xu-Dong (1); Xue, Xiang-Xin (1)
    2004, 25 (9):  851-854.  DOI: -
    Abstract ( 250 )   HTML   PDF (227KB) ( 515 )  
    Sialon-corundum multiphase refractories were synthesized once through using silicon powder, aluminum powder and black corundum as raw materials. Effects of Si3N4/AlN additives on N content, modulus of rupture and microstructure of Sialon were investigated. The results showed that the N content in the synthesized material increase and its flexural strength increases then decreases along with the increasing Si3N4/AlN content. N content in the specimen approaches to saturation after nitriding at 1330°C for over 8 hours. The additive may lower greatly the synthesizing temperature of the Sialon phase. In the synthesis process the range from 1230°C to 1280°C is an important initial nitriding phase in which the whole nitriding reaction can be completed by 94.2%. It was proved that nitriding fully Al and Si in early stage is beneficial to the formation and complete grain growth of Sialon phase.
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    Reproducing kernel particle method and its application in metal forming process
    Cui, Qing-Ling (1); Liu, Xiang-Hua (1); Wang, Guo-Dong (1); Xiong, Shang-Wu (1)
    2004, 25 (9):  855-858.  DOI: -
    Abstract ( 238 )   HTML   PDF (313KB) ( 641 )  
    Introduces the principle of the meshless reproducing kernel particle method (RKPM) and its application in metal forming processes. The penalty function is used to satisfy the essential boundary conditions, with a 2D frictionless planar upsetting process simulated for ideal plastic materials. Three kinds of aspect ratio of slab are computed with different compressible factors. Comparing the computation results with the analytic solution results, it is indicated that the geometry of deformed workpiece and its strain have a proper goodness of fit with analytic solution results. The error of the calculated stress might come from the nodal integration. The results obtained from the simulation of upsetting process verified the validity of RKPM.
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    FEM analysis of metal flow behavior during continuous extruding/extending forming in semi-solid state
    Wang, Shun-Cheng (1); Chen, Yan-Bo (1); Liu, Xiang-Hua (1); Wen, Jing-Lin (1)
    2004, 25 (9):  859-862.  DOI: -
    Abstract ( 219 )   HTML   PDF (210KB) ( 528 )  
    How the metal flows in the extending cavity during continuous extruding/extending forming in semi-solid state was simulated by finite element method (FEM) to investigate the metal flow behavior in the moulds designed with different parameters. The calculated results indicate that the highly solidifiable semi-solid alloy fills in the extending mould in form of laminar flow and the flow velocity decreases gradually from the center to all sides in mould. The flow velocity at the outlet of mould becomes more even with increasing extending angle or step length. However, The flow velocity at the outlet of mould becomes more uneven with increasing outlet width. There is a dead zone or vortex flow on both sides of mould when the step is too long. It is proved that the continuous extruding/extending forming can be implemented only if the mould is designed rationally.
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    Research on joint between Bi2223/Ag superconductor tapes
    Guo, Ren-Chun (1); Wang, Jin-Xing (1); Zong, Xi-Hua (1); He, Yan-Fa (1)
    2004, 25 (9):  863-865.  DOI: -
    Abstract ( 238 )   HTML   PDF (536KB) ( 488 )  
    A chemical method of making joints between Bi2223/Ag superconductor tapes was developed. At an end, the silver shield was removed from a Bi2223/Ag tape at one side surface, with that at the other side kept. Two of such tapes were contacted each other with Bi2223 powder filled in the gap to form a joint through proper heat-treatment in a tube furnace. The four-probe method was used to measure the current Ic of specimens. The Ic value of original tape is 40 A and it drops to 28 A after heat-treatment, and the Ic value at joint is 25 A after heat-treatment. Such a result shows that a superconducting joint has been developed. The SEM images of the fracture surface of joint show that its microstructure differs to a certain extent from that of the tape itself, so that the critical current drops at the joint. The testing results of the stress/strain of the joint show that the mechanical properties of the joint is somewhat lower than that of the tapes especially its malleability.
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    Effect of CaO on crystallization behavior of CaO-Al2O3-SiO2 system glass ceramics
    Shi, Pei-Yang (1); Jiang, Mao-Fa (1); Liu, Cheng-Jun (1); Wang, De-Yong (1)
    2004, 25 (9):  866-869.  DOI: -
    Abstract ( 227 )   HTML   PDF (276KB) ( 1921 )  
    Several glass ceramics of CaO-Al2O3-SiO2 system were prepared via sintering process and investigated by means of DTA, XRD and SEM, based on crystallization kinetics. The activation energy E, for the crystallization transform of such glasses are calculated by Kissinger equation, and it is found that the activation energy decreases with increasing CaO content and decreasing crystallization temperature. As a result, an inference is drawn that the system is integrally crystallized if the characteristic parameter n=2. Experimental results reveal that the crystallization phase of such glasses are all of wollastonite, and the increasing CaO content is beneficial to the further crystallization of glass ceramic. But, at the same time, it brings more obvious defects to glass surface, such as pits, outshoots and cracks.
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    Effect of TiC particles on conductivity of CaO-SiO2-MgO-Al2O3-TiO2 quasi-quinary slag
    Xue, Xiang-Xin (1); Zhang, Hui (1); Zhao, Na (2); Wang, Shu-Lan (3)
    2004, 25 (9):  870-872.  DOI: -
    Abstract ( 195 )   HTML   PDF (293KB) ( 847 )  
    The apparent conductivities of the slag CaO-SiO2-MgO-Al2O3-TiO2 containing TiC particles of different sizes and concentrations were measured by A.C. impedance spectrum technique at 1633 K. An equivalent circuit was proposed rationally to simulate the A.C. impedance spectra of the slag, and the apparent activation energies of the slag were estimated from the relationships between the apparent conductivities and the temperature at the range of 1633-1693 K. The results indicated that the apparent activation energy of the slag would increase with increasing content of TiC particles and decreasing particle size. When the mass fraction of TiC is 0.5%, the apparent activation energy would decrease slightly with decreasing TiC particle size. The apparent conductivity of the slag would decrease with increasing TiC content and decreasing TiC particle size at 1633 K. When the mass fraction of TiC is 0.5%, the apparent conductivity of the slag would increase slightly with TiC particle size. In sum, the relationship between the apparent conductivity and temperature of the slags of the same TiC content and particle size at the temperature range 1633-1693 K is in conformity with Arrhenius relationship.
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    Preparation of TiB2 inert cathode by electrodeposition process for aluminum electrolysis
    Xu, Jun-Li (1); Shi, Zhong-Ning (1); Qiu, Zhu-Xian (1)
    2004, 25 (9):  873-875.  DOI: -
    Abstract ( 257 )   HTML   PDF (165KB) ( 618 )  
    The TiB2 as inert cathode material for aluminum electrolysis, was electrodeposited successfully on carbon cathode as a coating by way of molten salts electrolysis at 800°C for 3 hours with a current density 0.3 A/cm2, of which the composition of the electrolyte used is 4.8KC1-55.7KF-15.3 K2TiF6-24.2 KBF4 in % as mass fraction. XRD was used to detect the composition of the coating with the Electron Probe Micro Analyzer (EPM) used for morphology observation. The results showed that the coating is composed of a single compound, i.e., TiB2 without inclusions. The 0.2 mm-thick TiB2 coating is smooth and appears metallic luster, especially it is bonded firmly to the carbon substrate. It is confirmed that Ti and B can be co-deposited to form a TiB2 coating on carbon surface as an inert cathode in this way.
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    Measurement of SnF2 standard gibbs free energy of formation
    Han, Yuan-Shan (1); Wang, Chang-Zhen (1); Tian, Yan-Wen (1); Zhai, Yu-Chun (1)
    2004, 25 (9):  876-879.  DOI: -
    Abstract ( 425 )   HTML   PDF (1094KB) ( 1216 )  
    The work cells introducing LaF3 single crystal (mixed) as solid electrolyte was prepared using Pb-PbF2 reference electrode, Sn-SnF2 work electrode and Ag electrode wire by means of grinding, sieving and mixing Pb, PbF2, Sn and SnF2 together and pressing them into thin piece in a ratio of 4:1. The whole operating process was done in a box filled in with Ar gas. Its composition is (+)Ag|Pb,PbF2|LaF3 single crystal (mixed) |Sn,SnF2|Ag(-). The EMF (electromotive force) of cell was measured in the temperature rang from 293.15 K to 353.15 K. The relationship between SnF2 standard Gibbs free energy of formation and temperature was calculated on the basis of two kinds of PbF2 standard Gibbs free energy of formation. Because the EMF measuring errors are far smaller than that of PbF2 Gibbs free energy and the difference between two expressions of SnF2 standard Gibbs free energy of formation is very small, both the calculated results as above are confirmed reliable.
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    Synthesis and mesomorphic properties of three-armed liquid crystals containing aromatic esters
    Yao, Dan-Shu (1); Zhang, Bao-Yan (1); Sun, Qiu-Ju (1); Dong, Sen (1)
    2004, 25 (9):  880-883.  DOI: -
    Abstract ( 227 )   HTML   PDF (244KB) ( 696 )  
    A series of novel three-armed liquid crystals based on 1,3,5-trihydroxybenzene as a core and tw-[4-(p-alkoxybenzoloxy)phenoxycarbonyl]valeric acid as mesogenic arms were synthesized by aromatic esterification. They are a new kind of liquid crystals differing from conventional rod-like or discotic molecules. Their chemical structures were confirmed by FTIR and 1HNMR spectra and their mesomorphic phase behavior was investigated by differential scanning calorimetry (DSC), polarizing optical microscopy (POM) and thermograrimetric analyzer (TG). The results showed that the three-armed liquid crystals exhibit broad range of liquid crystalline phase at moderate temperature, and the mesomorphic ranges (Δt) broadens with increasing terminal alkyl chains. The temperatures at which the weight loss is up to 5% is higher than 340 t, which revealed that the synthesized three-armed liquid crystals are of high thermal stability. Threadlike texture, typical of nematic phase can be observed in the liquid crystalline state during heating/cooling process.
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    Nonlinear pattern recognition of metal fracture surface images
    Yan, Yun-Hui (1); Yang, Hui-Lin (1); Wang, Cheng-Ming (1)
    2004, 25 (9):  884-886.  DOI: -
    Abstract ( 223 )   HTML   PDF (106KB) ( 507 )  
    Aiming at the characters of pattern recognition of fracture surface images, a character pick-up method by wavelet transform is proposed. Then, based on BP neural network theory, a nonlinear classifier is designed specially for such a pattern recognition, and its network structure was determined by test to give the way to choose parameters involved. Experimental investigations were carried out on computer aiming at several typical metal fracture surface images. The results showed that the average rate of correct recognition achieves 93.75%, even 95% if using the energy as character parameters alone. It means that a nonlinear classifier has a higher and more reliable rate of correct recognition than the linear classifier. The results showed that the nonlinear pattern recognition and classification method based on wavelet transform and BP neural network theory can recognize correctly the images in which the texture is complex, with a better adjustability provided.
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    Reliability model of dependent failure system
    Wang, Xue-Min (1); Xie, Li-Yang (1); Zhou, Jin-Yu (1); Wang, Yun (1)
    2004, 25 (9):  887-890.  DOI: -
    Abstract ( 278 )   HTML   PDF (240KB) ( 866 )  
    Starting from the happening mechanism of common cause failures, a new common cause failure model was developed by using conditional probability. According to the reliability expression of some specific components, the probability that some specific m components were all good was obtained. The model can be used easily and approximates further to the real system. It makes up for the insufficiences of traditional common cause failure models, thus avoiding the NP problem. Several typical systems are given to exemplify how to use the new model, with the calculated results compared to those resulting from β-factor model. The results show that it is highly consistent with qualitative analysis, and the model's correctiveness is thus proved.
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    Development and study on architecture of open numerical control system structure
    Lu, Yan-Jun (1); Lin, Hu (1); Ren, Zhao-Hui (1); Ren, Li-Yi (1)
    2004, 25 (9):  891-894.  DOI: -
    Abstract ( 242 )   HTML   PDF (277KB) ( 791 )  
    Summarizing the characteristics of an open numerical control system, four principal problems are put forward for building the open architecture of numerical control system, i.e., the confirmation of function elements, the system description, the interaction mode of function elements and interface protocol. It follows that it is necessary to discuss how to determine the function elements of the architecture of open numerical control system and the function composition of a controller system architecture. The system characteristics and relation among function elements are explored further in view of the hierarchical control system, control flow in system, data stream and module structure. A definition is given to the interface of servo control function using C++ language from the viewpoint of implementation with the existing insufficiencies in development process summarized.
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    Study on dynamic bio-oxidation of interface between leaching bacterium solution and natural pyrite
    Yang, Hong-Ying (1); Gong, En-Pu (2); Zhao, Yu-Shan (2); Chen, Gang (1)
    2004, 25 (9):  895-898.  DOI: -
    Abstract ( 244 )   HTML   PDF (226KB) ( 601 )  
    The process of oxidizing pyrite by leaching bacterium is such a process that the old chemical bond is broken with new chemical bond formed by leaching bacterium on the pyrite crystal surface. The interfaces between leaching bacterium solution and natural pyrite produce a series of biochemical reactions. Because of the different distribution patterns and densities of Fe2+ and [S2]2- of pyrite on crystal faces (100), (110) and (111), the extensions of their bio-oxidation and corrosion are also different. The process of pyrite bio-oxidation can be divided into three phases according to the dynamic test of bio-oxidation of pyrite (100), (110) and (111). The first is an initial one of pyrite bio-oxidation named as pitting bio-oxidation. The second is of surface bio-oxidation and the third is that the pyrite crystal is seriously oxidized and corroded by bacterium and finally broken. The bio-oxidation intensity of pyrite crystal faces is ranked as (111)>(110)>(100).
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    Numerical test using ring specimen as medium to determine indirect tensile strength of rock
    Zhu, Wan-Cheng (1); Feng, Dan (2); Chau, Kam-Tim (3); Tang, Chun-An (1)
    2004, 25 (9):  899-902.  DOI: -
    Abstract ( 237 )   HTML   PDF (222KB) ( 770 )  
    The RFPA (Rock Failure Process Analysis) code is used to carry out the numerical test using ring specimen as a medium to determine the indirect tensile strength of rock. The effect of diameter of internal hole on failure modes and determined strength of rock specimens is discussed, and the related rock failure mechanisms are clarified. The existing practical problem found in the lab test is also explained according to numerical results. Compared with the test results, both the failure modes and peak loads show in good conformity. Moreover, based on numerical result, a new test scheme is proposed using the cracking load to determine the indirect tensile strength of rock.
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    Forecast to coal/gas outburst area through pattern recognition method
    Nan, Cun-Quan (1); Feng, Xia-Ting (1)
    2004, 25 (9):  903-906.  DOI: -
    Abstract ( 300 )   HTML   PDF (760KB) ( 626 )  
    Based on the coal/gas outburst characteristics of the 13-1 coal seam in Panyi Coal Mine, the outburst mechanism was explored. The erupted or extruded type of the coal seam is regarded as mainly caused by the tectonic stresses. How to forecast the coal/gas outburst area and its practice are discussed from the point of view of various control factors and engineering feasibility. The abnormality of the physical-mechanical properties of the coal and rock supported by roofs and information on gas are the basic characteristics and inevitably the general character causing the hazardous erupted or extruded outburst areas mainly due to tectonic stresses. The area forecast is proposed the way it should be based on sufficient data mining for the exploration and log information in combination with multi-factor pattern recognition approach by using an advanced classification algorithm of the support vector machine. Such a forecast is not only based on a theoretical foundation but provide engineering practicability and operability. The forecast results obtained are in good conformation with the measured data of the 13-1 coal seam in Panyi Coal Mine.
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    Optimal management model for pumping groundwater in Shenyang's urban area planning
    Yang, Wei (1); Wang, En-De (1); Bian, Da-Zhong (2)
    2004, 25 (9):  907-910.  DOI: -
    Abstract ( 272 )   HTML   PDF (163KB) ( 576 )  
    A simulation model of groundwater flow is developed on the basis of analyzing the dynamic data accumulated for many years and the features of reservation/discharge function of groundwater system in Shenyang's urban area planning. The model is disintegrated to find the nonlinear response matrix which is iterated to be a group of linear response matrices, then they are superposed to become a 2-order mixed response matrix. Thus, an optimal management model is developed for effective utilization of groundwater, of which the objectives are to control the continuous drawdown of water table in the area, minimize the extension of drawdown funnel and control the influence of surface water pollution on groundwater to meet the requirement of watersupply for Hunnan New District. The optimization result shows that the exploitable quantity of groundwater can increase by 12.98×104 m3/d. The groundwater resources management is thus optimized and available to support and provide a resonable zonal layout for groundwater exploitation and water table conservation.
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    2004, 25 (9):  911-913.  DOI: -
    Abstract ( 216 )   HTML   PDF (529KB) ( 532 )  
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    2004, 25 (9):  914-917.  DOI: -
    Abstract ( 222 )   HTML   PDF (189KB) ( 721 )  
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