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10 April 2004, Volume 26 Issue 2
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    Education Study
    2004, 26(2):  0-0.  doi:10.6052/1000-0992-2002-382
    Abstract ( 1490 )   PDF (256KB) ( 604 )  
    In order to decrease the numbers of identification parameters and overcome difficulties in computation, the rank of structure should be reduced at first. In this paper, the rank of structure model is reduced by K-L(Karhunen-Loeve) eigenvalue extracting method. Modal parameters of the reduced model are identified by the least square method. The number of identification parameters and the computing complexity are greatly reduced. A simple girder is analyzed as an example. A three rank model is obtained. The identified inherent frequencies and the ratios of modal damping are close to the analytic result.
    2004, 26(2):  0-0.  doi:10.6052/1000-0992-2002-390
    Abstract ( 1097 )   PDF (507KB) ( 768 )  
    With the development of science and technology, one has to develop new materials and to explore potential of material properties. This paper presents the development of the elasticity theory with different Young's modulus in tension and compression. There are fundamental problems for the finite element method (FEM) and engineering applications. In this paper, Ambartsumyan FEM computational model, Jones' FEM computational model, Zhang's FEM computational model, and Ye's FEM computational model are improved and discussed by an equivalent concept. We find that the error of numerical results is apparent in the stiffness and strength of the materials for engineering structures if uniform Young's modulus is used.
    2004, 26(2):  0-0.  doi:10.6052/1000-0879-2002-426
    Abstract ( 926 )   PDF (236KB) ( 760 )  
    In order to take effective measures to avoid the earlier cracks in welded area of high-pressure steam pipes of the 125MW turbine, the stress analysis under high temperature was put into practice. The paper analyzes the causes of cracks based on the experimental data, which is helpful for finding out protective measures in the design.
    2004, 26(2):  0-0.  doi:10.6052/1000-0992-2002-428
    Abstract ( 1358 )   PDF (256KB) ( 612 )  
    In this paper, the Element-free method (EFM) is used to study the stability of a thin plate. The corresponding geometric stiffness matrix is derived using the moving least-square method and variational principle. Numerical results show that the method posseses a higher accuracy as compared with the finite element method for stability analysis of thin plates.
    2004, 26(2):  0-0.  doi:10.6052/1000-0992-2002-435
    Abstract ( 1903 )   PDF (378KB) ( 867 )  
    In this paper, a computer simulation for the automobile's bumper impact is presented. An improved design is proposed based on the analysis.
    2004, 26(2):  0-0.  doi:10.6052/1000-0992-2003-001
    Abstract ( 981 )   PDF (273KB) ( 531 )  
    The tensile tests are conducted and the void shape is measured using the 3-dimensional SEM (scanning electron microscope) on the tensile test ductile fracture surface by changing the notch radius of tensile test specimens, which is made of the SiC reinforced metal matrix composite material. The effects of void configuration and coalescence under the different stress-triaxiality condition are analyzed. The results show that the average void aspect ratio increases with the average void size. It means that the stress triaxiality and strain constraint play an important role during the damage process. These experimental results could be used to correctly simulate the ductile damage process of the metal matrix material under the multi-dimensional loads, to propose a reasonable strength evaluation method and to reveal the ductile damage mechanism.
    2004, 26(2):  0-0.  doi:10.6052/1000-0992-2003-018
    Abstract ( 1828 )   PDF (243KB) ( 867 )  
    The upwind TVD and finite volume method are employed to solve the supersonic flow field, and the finite element method or finite difference method is employed to solve the solid wall temperature distribution. The two parts work together, each one provides a boundary condition for the other, and exchanges information through the solid wall surface. This technology provides an efficient way for aerothermal problems.
    2004, 26(2):  0-0.  doi:10.6052/1000-0992-2003-022
    Abstract ( 1341 )   PDF (323KB) ( 483 )  
    Abnormal damage of Babbitt Alloy being stripped off and cracking of oil film bearing shortens its service life. By analyzing the backup roller oil film bearing of 2050 rolling mill of BaoShan Steel Co. by 3D-contact BEM, the pressure distribution on bearings is obtained. Contact models of oil film bearing can simulate the actual restricted conditions and external loading. It is observed that unreasonable restriction results in severe non-uniformly distributed load on oil film bearing, and carrying capacity of bearings can be improved through changing restricted conditions. The non-uniformly distributed load is lowered and oil film bearing's service life is prolonged. This result provides a theoretical basis for studying the burnout of oil film bearings and abnormal damage of Babbitt Alloy being stripped off and cracking in the bearing. Owing to the consideration of influence of elastic distortion, this method is advantageous in high precision and convergence speed.
    2004, 26(2):  0-0.  doi:10.6052/1000-0879-2003-027
    Abstract ( 7415 )   PDF (335KB) ( 767 )  
    Four KBKZ integral-type constitutive equations, including Wagner model, PSM model, 2e model and 3r model proposed by the authors, were used in the paper to describe the viscoelastic characteristics of a Boger fluid. The least square approximation was adopted to fit $G'$ and $G''$ to obtain the relaxation spectrum of the fluid, and the nonlinear programming method was employed to fit $N_{1}$ to obtain the parameter values in the damping function of the four models. The results show that the four models can characterize the rheological properties of the Boger fluid precisely. Either Wagner model or PSM model is a good choice for characterizing the viscoelastic properties of Boger fluid, due to its simplicity.
    2004, 26(2):  0-0.  doi:10.6052/1000-0992-2003-040
    Abstract ( 1719 )   PDF (306KB) ( 625 )  
    The chaotic vibrations of a clamped-clamped pipe conveying fluid, excited by the harmonic motions of its supporting base, were investigated theoretically. The nonlinear equations of motion were derived, and the equilibrium and stabilities of the system were analyzed. The expressions of homoclinic orbits of the unperturbed system were calculated. The system parameters for the occurrence of chaotic motions were obtained by means of Melnikov method. Phase portrait and Poinc\'are map were used to simulate the chaotic motions of the original system. Comparison between the results from theoretical analyses and numerical simulations reveals that the critical value of the parameter determined by Melnikov method is slightly lower than that corresponding to the chaotic motion observed first in numerical simulations.
    2004, 26(2):  0-0.  doi:10.6052/1000-0992-2003-058
    Abstract ( 1573 )   PDF (228KB) ( 537 )  
    The mask vibration degrades the color purity in the perfectly flat color picture tube of high resolution television. This paper is concerned with some analytical methods for calculating the natural frequency of the perfectly flat mask. Then applying the basic theories of elasticity, we have established the governing equation for the horizontal oscillation of a thin plate and yielded the natural frequencies and modal shapes of the perfectly flat mask by modal analysis with its four edges simply supported. The results obtained are found to be satisfactory by comparison with experiments. It also shows that the method for determining the natural frequency of the perfectly flat mask is effective, simple and valid. The result provides a basis for optimal designs of structure parameters in order to reduce the perfectly flat mask vibration.
    2004, 26(2):  0-0.  doi:10.6052/1000-0992-2003-087
    Abstract ( 1173 )   PDF (296KB) ( 654 )  
    Under different stress states, the physical mechanisms of the process of fractures can be different. Traction facture occurs when brittle materials are subject to traction, and shearing fracture occurs when they are subject to pressure, which are two kinds of fracture patterns with different physical mechanisms. The Mohr's strength theory uses only one fracture condition, which is questionable. This problem is studied in combining with fracture damage tests of grey cast iron HT200 materials. The results indicate that Mohr's theory can not rationally predict the strength of material fractures in the state of complicated stresses.
    Application study
    2004, 26(2):  0-0.  doi:10.6052/1000-0992-2003-092
    Abstract ( 1183 )   PDF (272KB) ( 532 )  
    Fractal dimension and characteristic lengths of rock masses are obtained by image processing. The edge detection and pixel scanning methods are used to acquire these parameters. From the numerical results, it is shown that when the scanning is fine enough the results are stable. So the method presented here would give reasonable values of the parameters in consideration.
    Education Study
    2004, 26(2):  0-0.  doi:10.6052/1000-0992-2003-119
    Abstract ( 1303 )   PDF (316KB) ( 1163 )  
    This paper discusses how to use HLLC method to treat moving boundary. The explicit finite volume method based on unstructured meshes is employed to solve Eulerian equations. The impulse piston moving backward and forward is simulated to validate the moving boundary treatment. As an example, flows around a static cylinder and around a moving cylinder in a static flow field are calculated. The numerical results indicate that it is feasible to use the HLLC method to treat the moving boundary condition.
    2004, 26(2):  0-0.  doi:10.6052/1000-0992-2003-169
    Abstract ( 916 )   PDF (243KB) ( 588 )  
    In this paper, an identification and transformation method for foundation parameters of airport pavement is proposed. Based on the theory of Winkler foundation plate and the theory of elastic semi-space model, the theoretical deflections of the airport pavement are derived. The least square method is used to identify the resilience modulus of foundation $E_{0}$ and the response modulus $K$ by fitting the testing and theoretical deflections. The transformations from $E_{0}$ to $K$ and from $K$ to $E_{0}$ are also realized by using the equal deflection values of testing points. A testing deflection of an airport pavement is used as a numerical example. Table 2 shows the identification results of $K$ and $E_{0}$. Table 3 and Fig.2 show the high accuracy of the results by comparing the testing deflection with the identification deflection. Table 4 and Table 5 show that we may easily transform $E_{0}$ to $K$ and then transform $K$ to $E_{0}$ of the airport pavement.
    2004, 26(2):  0-0.  doi:10.6052/1000-0992-2003-199
    Abstract ( 1949 )   PDF (256KB) ( 657 )  
    Among various attitude representations of rigid body, the Euler angles, Cardan angles and Euler parameters are applied frequently in engineering. Recently the application of Rodrigues parameters in the attitude control of spacecraft attracts some attention. The Rodrigues parameters have some distinctive advantages of simplicity in representation and their algebraic calculation. In the space flight practice, it is difficult to determine the accurate value of dynamical parameters of a spacecraft in orbit, then the adaptive behavior of attitude control is required to adapt the variation of parameters. In the present paper the dynamical equations of controlled attitude motion of a torque-free gyrostat expressed by Rodrigues parameters are derived, and an adaptive approach based on Rodrigues parameters is proposed to keep a predetermined attitude under the internal disturbance. The Lyapunov theorem is used to prove the asymptotic stability of the controlled motion.
    2004, 26(2):  0-0.  doi:10.6052/1000-0879-2003-245
    Abstract ( 1648 )   PDF (462KB) ( 617 )  
    The grid shape, skin thickness and stiffener size of a stiffened cylinder shell have a dramatical effect on the buckling loads. To achieve the minimum weight in this kind of structural design, a 3-D finite-element model using ABAQUS software is built. Parameterization study is carried out and general conclusions are drawn. The numerical results show that the axial buckling resistance and the buckling failure modes vary as the stiffener size and the skin thickness change. The buckling resistance reaches the maximum at the critical point where the global buckling failure mode transforms to the local buckling failure mode of the stiffened shell. According to this property, an optimal design strategy for orthogrid stiffened cylinder shells is developed. An example of the optimal design of the grid stiffened cylinder shell presented in the paper shows the validity of the present method.
    2004, 26(2):  0-0.  doi:10.6052/1000-0992-2004-022
    Abstract ( 2130 )   PDF (694KB) ( 1215 )  
    The current status of research and development of Micro Air Vehicles (MAV) is reviewed in the present paper. The main technical difficulties in the practical application of MAV are analyzed with emphasis on low Reynolds number aerodynamics, aerodynamic configuration with high lift to drag ratio and intelligent flight control. Based on previous experience and theory it can be said that it is almost impossible to design MAV with good flying performance using conventional design method when MAV's main scale is less than 15\,cm. Biomimatics must be considered for the design. The major issues related to biomimatic design of MAV, such as high lift mechanism, intelligent high maneuverability, resistance to disturbance and energetics, are discussed in the present paper.