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08 April 2014, Volume 36 Issue 2
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    Review
    2014, 36(2):  137-146.  doi:10.6052/1000-0879-14-023
    Abstract ( 900 )   PDF (3998KB) ( 1283 )  

    This paper discusses the abnormal driving forces induced by highly curved micro/nano matter spaces. It is pointed out that such abnormal driving forces are constructed by two fundamental factors: the bending extent of the space, i.e. the curvatures, and the non-uniform extent of the bending of the space, i.e. the the gradients of the curvatures.

    THE JET INTERACTION EFFECTS OF REACTION CONTROL SYSTEMS IN HYPERSONIC VEHICLES
    XU Chenhao, JIANG Chongwen, GAO Zhenxun, QIAN Zhansen, LI Chunxuan
    2014, 36(2):  147-155,160.  doi:10.6052/1000-0879-13-376
    Abstract ( 727 )   PDF (5298KB) ( 1375 )  
    The reaction control system (RCS) is widely used in hypersonic vehicles and is one of the most important maneuvering apparatuses. When the RCS is activated, a complicated jet interaction flow field caused by the mixture of the jet and the freestream would lead to difficulties in predicting the effectiveness of the RCS. In this paper, the layouts of the RCS are put into 4 categories based on the layout of the RCS in different hypersonic flight vehicles and the local shape characteristics, which are the jet on surfaces with small curvature, the jet on surfaces with large curvature, the jet on the nose and the jet near the wings. Four typical models are used to simulate the flow characteristics of each type of layout, and the state-of-the-art of each typical model is summarized in this paper. In the end, some suggestions for the future research are proposed.
    Applied Research
    2014, 36(2):  156-160.  doi:10.6052/1000-0879-13-357
    Abstract ( 468 )   PDF (1271KB) ( 643 )  

    The flow mechanism in the shale reservoir involves the seepage, the diffusion and the desorption. A productivity formula for the shale gas is obtained under the stable condition with considerations of both the Knudsen diffusion and the desorption. With this formula, a productivity equation for the fractured vertical wells is established by the method of percolating resistance, with consideration both of the desorption and the diffusion. According to the formula derived and the production examples, the influence of the diffusion coefficient, the half-length of fractures and the fracture conductivity on the well gas productivity is studied. It is shown that the gas production increases with the increase of the diffusion efficiency. The greater the fracture conductivity, the larger the gas production will be. When the fracture conductivity adds up to 0.12 μm2·cm, the amplification of the gas production decreases significantly. The contribution of the free gas accounts for 85%~90%. So the free gas has a great contribution on the productivity. The model provides a theoretical basis for the production prediction and the optimization of the development index.

    CORRELATION SPECTRUM ANALYSIS IN THE NEAR WAKE BEHIND A DISK
    ZHONG Wei, YANG Jianzhi, ZHANG Xintai, LIU Quan, LIU Minghou
    2014, 36(2):  161-167.  doi:10.6052/1000-0879-13-340
    Abstract ( 404 )   PDF (3775KB) ( 1004 )  
    A large eddy simulation (LES) is conducted in the near wake behind a circular disk at Re=22 000 with the diameter-thickness ratio D/h=5. Through fast Fourier transformation (FFT) of the fluctuating velocities at x/D=1, 2 and 8, three characteristic frequencies are identified, with corresponding Strouhal numbers being 0.035, 0.123 and 1.3~1.7. It is shown that St2=0.123, is the natural vortex shedding frequency, as in agreement with previous research results; St1=0.035, the smaller one, may be related to the combined action of the recirculation zone's "pump" motion and the azimuthal rotation of the shedding location near the shear layer; St3=1.3~1.7, might result from the instability of the turbulent shear layer. The correlation coefficients, the coherent spectrum and the phase spectrum are calculated between two points with different separation angles in the same axial section of r/D=2.8. Due to the vortex shedding, the correlation coefficients fluctuate between positive and negative values in the intervals of 30 or 45 degrees. This indicates that the position of the vortex shedding is random in the azimuthal direction.
    THREE-DIMENSIONAL MODEL FOR ESTIMATING COAL AND GAS OUTBURST
    CHEN Li, QIAO Jiyan, DING Yansheng
    2014, 36(2):  168-171.  doi:10.6052/1000-0879-13-392
    Abstract ( 323 )   PDF (1216KB) ( 680 )  
    A coupling relationship between the gas pressure and the coal deformation is obtained based on the principle of effective stress. Under joint actions of the crustal stress and the gas pressure, in the coal there will be elastic-brittle damages and layer fractured-powdering damages, accordingly, and the danger of coal and gas outburst is estimated. A three-dimensional model is validated by the numerical simulation result, which is approximately in agreement with the outburst experiment in the coal shockwave tube.
    2014, 36(2):  172-179.  doi:10.6052/1000-0879-13-471
    Abstract ( 470 )   PDF (4479KB) ( 1171 )  
    The method for solving the problem of manned asteroids exploration trajectory optimization based on ephemeris matching method was studied in this paper. The concept of ephemeris matching method was proposed, and then the initial launch window and the candidate optimal probe sequences were given. Time nodes and other parameters were optimized for the specific probe sequences by using genetic algorithm. The final orbit and thrust control laws were optimized by using homotopic method based on the Pontryagin's maximum principle. The results showed that the ephemeris matching method can quickly and accurately find out the optimal initial launch window and the candidate probe sequences, which can greatly improve the efficiency of solving the manned asteroid exploration and other multi-objective rendezvous problems.
    2014, 36(2):  180-184.  doi:10.6052/1000-0879-13-273
    Abstract ( 510 )   PDF (903KB) ( 1012 )  
    This paper studies the lateral supporting mechanism of the prestressed cable for a mega steel frame-cable bracing structure to provide a theoretical basis for determining cable's parameters. Based on the mechanism and by analyzing the prestress, a theoretical equations for cable's lateral stiffness is derived. After the model test and a comparison with the theoretical result and the numerical value, the lateral supporting mechanism of the prestressed cable is finally verified. With the prestressing force offering the axial stiffness and the stability for the cable, the prestressed cable can sustain tension and pressure and provide an elastic restraint support for the mega steel frame-cable bracing structure.
    MODAL ANALYSIS OF PRECISION EQUIPMENT SEMI-TRAILER TRAIN
    KE Yongguo, MA Li, QIAN Jing
    2014, 36(2):  185-189.  doi:10.6052/1000-0879-13-547
    Abstract ( 401 )   PDF (1427KB) ( 840 )  
    By analyzing the vibration of a precision equipment semi-trailer train with suspending-type traction device,a 14-degree-of-freedom dynamical model is established for modal analysis. On this basis, the first six natural frequencies and modes of a typical semi-trailer train are calculated under both the undamped condition and the damped condition,which offer some theoretical references for the design of precision equipment semitrailer trains.
    BOUNCING VIBRATION RESPONSE ANALYSIS OF THE CARGO UNHOOKING OF SINGLE SPAN AERIAL CABLEWAY
    FENG Huirong, ZHOU Chengjun, ZHOU Xinnian, WU Zhilong
    2014, 36(2):  190-194,189.  doi:10.6052/1000-0879-13-349
    Abstract ( 417 )   PDF (14466KB) ( 1766 )  
    Based on the theory of string (rope) vibration, with the overhead skidding single span cableway with full suspension reinforcement as an example,the carrying rope bouncing and the free vibration due to the instant elastic energy release at cargo's unhooking are analyzed.The unhooking vibration model is established and the natural angular frequency, the period, the wavelength, the main vibration mode,the free modal vibration, and the total energy are discussed,and illustrated by 3D graphics.The results provide some guidance for the installation design, the improvement of the technology and the safety code of practice for forestry aerial ropeways.
    2014, 36(2):  195-197,171.  doi:10.6052/1000-0879-13-345
    Abstract ( 483 )   PDF (1267KB) ( 977 )  
    In this paper, a testing method to determine the modulus of elasticity of the wirerope based on random vibration is proposed. The wirerope and the hanging weight are simplified as a mass-spring of a single degree of freedom, the natural frequency of which is measured by the random vibration hammer testing method. Then the modulus of elasticity of the wirerope can be calculated according to the frequency. At the same time, the natural frequency can also be calculated by the longitudinal wave theory of elastomer, and the two natural frequency formulas give the same results. The suggested random vibration testing method is simple and accurate and can be used to test the modulus of elasticity of the wire rope.
    IMPACT LOAD OF ROLLING BEARING UNDER FREE FALLING CONDITION
    LUO Tianyu, SUN Dong, LUO Jiwei
    2014, 36(2):  198-200,167.  doi:10.6052/1000-0879-13-403
    Abstract ( 460 )   PDF (747KB) ( 1016 )  
    The elastic contact deformation energy of a rolling bearing is analyzed firstly. Based on the energy conservation law, the impact loads of the rolling bearing under its free falling condition are calculated. The energy distribution between the spring and the bearing is analyzed according to their rigidity ratio in the damping spring-bearing system. The calculated result shows that it is close to the engineering values and can be used as a reference to determine the impact load of bearings.
    SETTLEMENT PROPERTIES OF PUSHIHE CONCRETE-FACED ROCKFILL DAM
    LI Shouju, ZHANG Jun, JING Jianwei, LIANG Jinquan, TIAN Zerun
    2014, 36(2):  201-206.  doi:10.6052/1000-0879-13-398
    Abstract ( 414 )   PDF (1610KB) ( 993 )  
    The pouring process of the Pushihe concrete-faced rockfill dam is simulated by using the ABAQUS finite element software and the element birth and death procedure. The deformation characteristics of the dam after completion of construction and the stage of full water are investigated. The mathematical models of the dam deformations versus the water level, the environmental temperature and the time-effect are proposed. Based on the in-situ observation data for the dam deformations and the multi-element and nonlinear regression analysis approach, the parameters of the mathematical models are estimated. It is indicated that the vertical deformations are quite regular and the forecasted vertical deformations of the dam are in a good agreement with observations.
    2014, 36(2):  207-209,206.  doi:10.6052/1000-0879-13-323
    Abstract ( 447 )   PDF (708KB) ( 1073 )  
    In order to improve the calculation speed and precision for bending moment distribution method calculation, the process of bending moment distribution was transfered as sequences of geometric series. After the first round of the bending moment distribution and transfer, first item and common ratio of the sequences of geometric series can be found, and by using the geometric series formula, the exact solution can be got simply and accurately. This paper brought up the idea of using bi-direction transmission and geometric series to seek the exact solutions of structures which have three distribution points during the procedure of the bending moment distribution method. The accuracy and the practicality of the proposed method were verified by a computation example, which is a two-span asymmetric frame under asymmetric load. The solutions of both computer analysis and formula method computation were compared.
    ON PATTERNS OF LÜDERS BANDS
    YUAN Xuezhong, LIU Jiemin, SUN Yazhen
    2014, 36(2):  210-211.  doi:10.6052/1000-0879-12-339
    Abstract ( 548 )   PDF (607KB) ( 727 )  
    The Lüders bands can be observed on the surface of one-dimensional tension or compression test samples of some metals such as low-carbon steel. In some textbooks for mechanics of materials the patterns for the Lüders bands of tensile samples are drawn as net-like bands. The Lüders bands in tensile samples are not net-like when yielding. We suggest that the figures in these textbooks should be modified accordingly.
    DISCUSSION OF A TRANSIENT SYSTEM
    XU Chunhui, ZHANG Linnan, QIN Taiyan
    2014, 36(2):  212-215.  doi:10.6052/1000-0879-12-473
    Abstract ( 370 )   PDF (624KB) ( 842 )  
    A transient system is discussed in detail. The concept of equivalent tensile stiffness is introduced according to the result that the vertical load is proportional to the cubic of the dimensionless vertical displace- ment. The value of the equivalent tensile stiffness is exactly equal to the structural stiffness under the horizontal loads. Based on the finite deformation theory, the relation between the vertical load and displacement for asym- metric structures in the Lagrange coordinate system is given. The uniform relationship between the load and displacement can be obtained by ignoring the horizontal displacement.
    2014, 36(2):  216-218,221.  doi:10.6052/1000-0879-12-437
    Abstract ( 626 )   PDF (987KB) ( 1859 )  

    In the first part of paper, we discuss the application of the Saint-Venant's principle of the elasticity to fracture mechanics, pointing out that misusing of the principle may cause extremely large error by using sone examples. In the second part, we discuss methods for determining the shape and size of Tresca and Mises yielding surfaces and make an extension to the description of Mohr-Coulomb and Drucker-Prager yielding surfaces. We present a three-dimensional image showing the shape and size of Tresca and Mises yielding surfaces in the principal stress space to correct the errors in existing textbooks and monographs on elasto-plasticity.

    2014, 36(2):  219-221.  doi:10.6052/1000-0879-13-013
    Abstract ( 641 )   PDF (265KB) ( 782 )  
    Impact calculation problem of dynamic load was studied by using linear vibration theory based on considering the effect of damping. The function expressions for structural dynamical displacement, factor of dynamic load and impact time were derived by using the vibration equation. And the effects of structural damping on dynamic load problem were discussed and analysed.
    AN IMPACT DYNAMIC STRESS EXPERIMENT DESIGN AND RESULT ANALYSIS
    CHEN Chao, HOU Zhende, WANG Zhongbao, XU Jiafu, FU Donghui, WANG Yanqun
    2014, 36(2):  222-225.  doi:10.6052/1000-0879-13-023
    Abstract ( 390 )   PDF (1257KB) ( 923 )  
    In order to understand the error rang of actual result and theory of impact loading problem, based on mechanics of materials principle, we designed an impact loading experimental setup. This setup consists of a cantilever and a falling body, and the impact factors were measured with the falling body striking the cantilever at different heights. For comparison, calculated impact factors were obtained by simulating the experiments using a soft ware ANSYS/LS-DYNA. The relative errors were respectly below 3% between the two group factors and 14%~23% between the tested results and theory results. The experimental and simulated results supported each other, indicating the validity of the experimental results. The results give a deep understanding of the model, theory and error of impact loading problem, which may be helpful to determine the error range in applications.