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08 June 2014, Volume 36 Issue 3
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    Review
    APPLICATION OF COMPUTATIONAL FLUID DYNAMICS IN THE PLANNED DITCHING OF A TRANSPORT AIRPLANE
    LIU Peiqing, QU Qiulin, GUO Baodong, JIN Xin, WU Jiali, ZHANG Kai
    2014, 36(3):  278-284.  doi:10.6052/1000-0879-13-153
    Abstract ( 657 )   PDF (2221KB) ( 2278 )  

    This paper discusses the development and the application of the boundary element method, the finite element method, the smoothed particle hydrodynamics method, the finite volume method, the engineering method and the mixing analysis in the planned ditching of a transport airplane, including their advantages and disadvantages.

    2014, 36(3):  269-277.  doi:10.6052/1000-0879-13-042
    Abstract ( 1071 )   PDF (3060KB) ( 1008 )  

    A Eulerian two-fluid model based on the kinetic theory of granular flow is important for the calculation of large-scale multi-phase flows and reactions. The drag model which describes the interphase interactions is critical with respect to the calculation accuracy. This paper reviews various methods to develop drag models for dense heterogeneous gas-solid flows and discusses their merits and demerits. Based on the energy analysis of multi-phase flows, an energy minimization multi-scale (EMMS) drag model is established. The core of the EMMS model is the conservation equations of mechanical energy and the solution of such equations with the stability condition that the energy for the particle suspension and transport reaches the minimum. This paper discusses the development process of the EMMS model and points out its substantial defects in describing cluster characteristics. New descriptions of cluster characteristics are proposed and verified with experimental data. The predicted drag with the new cluster descriptions agrees well with experimental results, indicating the effectiveness of the model revision. Finally, this paper discusses the EMMS model defects in universal applications and suggests the developing directions.

    Applied Research
    2014, 36(3):  333-336,340.  doi:10.6052/1000-0879-13-140
    Abstract ( 628 )   PDF (832KB) ( 825 )  

    The free vibration of post-buckling beams subjected to non-conservative load is studied. Based on the large deformation theory for the elastic beams, the geometrically nonlinear dynamic equations are established for beams subjected to a distributed tangential follower force along the central axis. By assuming that the amplitude of beam's vibration is small and its response harmonic, a linear version of the vibration problem is deduced. By employing the numerical shooting technique to solve the governing equations for vibration, numerical solutions of the first three natural frequencies against the load parameter are obtained. The results show that the features of the vibration response of the beams subjected to a non-conservative load are evidently different from those subjected to a conservative load.

    2014, 36(3):  330-332.  doi:10.6052/1000-0879-13-427
    Abstract ( 380 )   PDF (7189KB) ( 982 )  

    The applications and the performance test of the slip rings are reviewed. To overcome the diffculties in the measurement of the contact force between the brush wire and the ring in precision satellite slip rings, a measurement scheme based on the cantilever beam theory is proposed and its principle is explained. According to the deformation linearity of the cantilever beam, the unary regression analysis using the least squares method for the measurement data is carried out to obtain the initial loading force. The contact force is finally calculated according to its relationship with the initial loading force.

    2014, 36(3):  323-329.  doi:10.6052/1000-0879-13-429
    Abstract ( 393 )   PDF (7189KB) ( 1039 )  

    The seismic performance of steel frames with reduced beam section connections is evaluated by using the finite element analysis, the modal analysis and the time-history analysis. The vibration period, the dynamic internal force, the dynamic stress and the plastic deformation zone in steel frames are studied in detail; and the results are compared with those of steel frames with ordinary connections. It is shown that the seismic performances of the steel frames with reduced beam section connections are not very satisfactory under weak earthquakes, but they are very good under strong earthquakes, the plastic deformation occurs at the reduced beam, the plastic strain increases, the column base shear and the top displacement of the steel frames are all smaller than those of the steel frames with ordinary connections, so it is suggested that reduced beam section connections should be used in areas with strong earthquakes.

    Review
    2014, 36(3):  253-260.  doi:10.6052/1000-0879-13-204
    Abstract ( 668 )   PDF (1554KB) ( 1184 )  

    The sediment is in a very active movement along the muddy coast. Both the siltation which is directly related to the shoreline changes and the coastal protection become very important in the last few decades. This paper presents a review, which includes the rheological properties of the cohesive sediment, the interaction between wave and cohesive sediment, the wave attenuation as well as the sediment mass transport.

    2014, 36(3):  261-268,277.  doi:10.6052/1000-0879-13-133
    Abstract ( 591 )   PDF (2831KB) ( 1210 )  
    Hypersonic technical project "Hyper-X" not only makes use of the hypersonic flight within the atmosphere and verifies the core principles of supersonic combustion and airframe integrated propulsion design, but also promotes the sustainable development of the worldwide hypersonic technology. This paper analyzes the research progress of Hyper-X in fundamental and applied hypersonic technologies, especially those combining theoretical computations and ground tests with flight tests to solve major aerodynamic problems systematically. The ideas and methods of Hyper-X aerodynamic researches are reviewed on the level of methodology, and the essence of the methodology includes such as the decomposition and integration, the progressive and transition, the knowledge and standards, the verification and validation. Some applications of the methodology in solving key aerodynamic problems arising from hypersonic airbreathing vehicle are also discussed.
    Applied Research
    2014, 36(3):  285-287,293.  doi:10.6052/1000-0879-13-410
    Abstract ( 406 )   PDF (1637KB) ( 521 )  
    Bulk density of substitution method is a common method for slope stability analysis. The equivalence relationship between the water loads taken as face loads and the body loads respectively that act on a circular sliding block under steady-state seepage was analyzed firstly, then based on that equivalence relationship, a modified substitution method for circular sliding slope stability analysis under steady-state seepage is proposed.
    2014, 36(3):  288-293.  doi:10.6052/1000-0879-13-281
    Abstract ( 476 )   PDF (1637KB) ( 884 )  
    The variational multiscale method is applied to a one-dimensional mechanical model of a cable in the paper. With the use of the Green's function, the microscopic shape functions and the theory of residual-free bubbles, the macroscopic finite element model for the cable is established and the solution of the microscopic displacement is obtained. The key problems as well as the shortcomings of the application of the variational multiscale method are revealed. The numerical simulation for the cable model with given boundary conditions and constant rigid modulus is made. By comparing the numerical solution of the macroscopic displacement with the exact solution and the analytical solution of the microscopic displacement with the exact solution, it is demonstrated that the microscopic displacement can be regarded as the posteriori error estimation for the general finite element model. The success of applying the variational multiscale method to a one-dimensional mechanical model shows its practicability to mechanical and engineering problems.
    2014, 36(3):  294-297,307.  doi:10.6052/1000-0879-13-307
    Abstract ( 557 )   PDF (1254KB) ( 1151 )  
    The size optimization for a cantilever I-beam under distributed loads is based on the variational method, and the width distribution of an edge strip under the strength and stiffness constraints is used as an example to demonstrate the use of the variational method. The optimization criterion method and the MIGA (multi-island genetic algorithm) with the FEM (finite element method) are discussed. An engineering cantilever I-beam model of the wing structure is presented to illustrate the three methods. It is shown that the variational method can greatly improve the effciency compared with the other two methods, and also the exact solutions of the optimal size distribution can be obtained, which can be used in the wing structure design during the preliminary design phase.
    2014, 36(3):  298-302.  doi:10.6052/1000-0879-13-465
    Abstract ( 391 )   PDF (1261KB) ( 889 )  
    In order to improve the prediction method of the aerodynamic noise using the acoustic analogy theory based on incompressible flow fields, the characteristics of the disturbance propagation in the incompressible and compressible fluids should be studied firstly. In this paper, the analytical solution for the flow disturbance generated by a sphere oscillating in an incompressible fluid is obtained. The velocity and pressure fields are analyzed, and are compared to the results in a compressible fluid, namely, the acoustic field. It is shown that with respect to the velocity fields the disturbance has components with infinite and finite propagating speeds, while with respect to the pressure only disturbance with infinite propagating speed exists. When the fluid viscosity vanishes or the oscillating frequency becomes infinite, the velocity is identical to the near-field sound generated by the sphere oscillating in the compressible fluid; thus the acoustic near-field disturbance is incompressible, i.e., the pseudo-sound.
    2014, 36(3):  303-307.  doi:10.6052/1000-0879-13-409
    Abstract ( 517 )   PDF (1260KB) ( 778 )  
    Based on Hamilton's principal, the ordinary differential control equations for the transverse nonlinear free vibration and the buckling of a compressive bar on an elastic foundation are obtained by using the method of "assumed-time-mode". With one end fixed and the other end movable simply supported, the numerical results of the first to third order structural frequencies and the first order buckling load are obtained by employing the shooting method.The results show that the structural frequencies decrease with the increase of the axial compressive force. The structural frequencies and the buckling load increase with the increase of the elastic foundation's stiffness. The effect of the stiffness of the elastic foundation on high order structural frequencies is reduced with the increase of the order number of the vibration modes. The effect of different vibration modes on the first order buckling load is negligible as far as a small amplitude is concerned.
    2014, 36(3):  308-312.  doi:10.6052/1000-0879-13-462
    Abstract ( 323 )   PDF (1715KB) ( 1048 )  

    Based on the random vibration theory, the frequency domain calculation method is adopted to analyze the wind-induced response of a monolayer cable net. Some parameters crucial to the response of the wind vibration are highlighted, and different algorithms for the frequency domain calculation and the selected spatial coherence functions are discussed. According to the different algorithms and spatial coherences, three analysis patterns of the monolayer cable net are established to analyze the effect of the parameters. The results show that the coupling effect between different modes is significant; the selected coherence function greatly affects the computation, and the coherence function related to the wind frequency is more reasonable.

    BACK CALCULATION METHODS FOR DEFORMATION MODULUS BASED ON SETTLEMENTS IN DYNAMIC COMPACTION
    LIU Miao, WANG Zhiyin, ZHANG Rumany, YUAN Honghuy, ZHANG Qiweiy
    2014, 36(3):  313-317.  doi:10.6052/1000-0879-13-455
    Abstract ( 423 )   PDF (2504KB) ( 973 )  
    Based on two kinds of consolidating theories, the motion equation method (MEM) and the energy method (EM), the back-calculation equations are established separately so that the foundation's deformation modulus could be calculated using the settlement data of hammer pit, which can easily be obtained in monitoring. According to the dynamic compaction experiment of Beijing Garden EXPO Park, the deformation modulus varies with different compacting times. It is shown that the deformation modulus gradually increases with the number of tamping but the growth diminishes at the same time, and the deformation appears to be stable in the end. The initial deformation modulus is 5~8MPa and it rises to 18~22MPa which is 3~4 times of the initial value after the 7th tamping. Besides, the EM method involves a relatively simple calculating process and can be recommended in similar projects.
    2014, 36(3):  318-322,329.  doi:10.6052/1000-0879-13-361
    Abstract ( 399 )   PDF (7189KB) ( 1005 )  
    In order to study the effect of cavity thickness on the seismic properties of foam core sandwiched wall, model tests and numerical simulations of the in-plane and out-of-plane seismic properties of 20 patches of foam core sandwiched wall and 2 patches of solid wall are carried out, and the validity and the accuracy of the numerical simulations are verified. The numerical simulations of the in-plane and out-plane seismic properties of the foam core sandwiched wall of different cavity thicknesses are carried out. The relative displacement difference is most remarkably affected by the cavity thickness when the foam core sandwiched walls are loaded in-plane; the seismic bearing capacity is most remarkably affected by the cavity thickness when the foam core sandwiched walls are loaded out-plane. In general, the cavity thickness has a greater effect on the in-plane seismic property than on the out-of-plane seismic property. The deformation coordination capacity will be reduced remarkably when the cavity thickness increases. It is therefore recommended that cavity thickness is not greater than 100mm in the buildings of high earthquake intensity regions.
    2014, 36(3):  337-340.  doi:10.6052/1000-0879-13-085
    Abstract ( 549 )   PDF (832KB) ( 522 )  
    The transient response of a hanging chain after an initial impact at the free end, is not only an interesting mathematical problem, but also has a certain engineering application. In the theoretical frame of the Lagrange dynamics differential equation, the dynamic response of a hanging chain under the impact of a horizontal impulse-momentum S is analyzed by using the second kind Lagrange's equations under a generalized impulse-momentum, and a general solution is obtained to compute the angular velocity of each segment. This method can be used conveniently to obtain the transient response of a hanging chain with several segments and in different initial conditions.
    AN APPROXIMATION METHOD FOR THE LARGE DEFLECTION OF CANTILEVER BEAMS
    ZHAO Ze'ang, DENG Zongbai, SONG Anping
    2014, 36(3):  341-344,366.  doi:10.6052/1000-0879-13-124
    Abstract ( 825 )   PDF (728KB) ( 2254 )  
    This paper studies the large deflection of cantilever beams. A simple method to obtain the deflection is developed through numerical and theoretical analyses. How to measure the extent of large deformation is discussed at the same time. The error between the accurate deflection and the approximate deflection, obtained by the approximate deformation equation, can be represented by the square of the ratio of the approximate deflection to the length of the beam. By using this relation, we can have an estimation of the accurate deflection value without complex calculation and numerical methods. This method can be used in practical applications.
    THE DETERMINATION OF BUCKLING POINT AND CRITICAL LOAD OF COMPRESSIVE MEMBER
    WANG Tingwei, HUANG Lihua, LIU Ming, FU Rao
    2014, 36(3):  345-347,360.  doi:10.6052/1000-0879-13-103
    Abstract ( 785 )   PDF (854KB) ( 1781 )  
    In order to analyze the relationship between the critical load and the buckling shape of a pole bar, on the basis of theoretical analysis and experiments, the method of determinating the critical load through looking for the buckling point for a long slender member subjected to axial compressive force is used in this paper. The critical load can be determined by the longitudinal displacement at one end of the compressive member, which is in equilibrium with a small lateral deflection. The critical load with consideration of the longitudinal displacement is compared to that from Euler's formula, and a larger critical load is obtained.
    THE GENERAL SOLUTION OF THE MULTI-ROD JUNCTION PROBLEMS
    CHEN Ping, CHEN Guoliang, YANG Xupu
    2014, 36(3):  348-350,378.  doi:10.6052/1000-0879-13-125
    Abstract ( 360 )   PDF (776KB) ( 854 )  
    The displacement method is used to derive the general solution for multi-rod junctions under a load, which can be used without considering complicated geometric relations. The solution is valid for statically determinate or indeterminate structures.