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10 June 2004, Volume 26 Issue 3
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    Education Study
    2004, 26(3):  0-0.  doi:10.6052/1000-0992-2003-038
    Abstract ( 1034 )   PDF (384KB) ( 405 )  
    In this paper, some mechanics problems on the design of CRT are discussed. These problems include the FEM analysis of the thermal stress during the manufacturing process of the panel and of the thermal deformation of the mask, and the investigation of the vibration and microphony effect of the mask. Furthermore, by a numerical example, the effectiveness of this analysis is investigated.
    2004, 26(3):  0-0.  doi:10.6052/1000-0992-2003-046
    Abstract ( 1249 )   PDF (353KB) ( 507 )  
    A new type shaped charge warhead was put forward based on the energy concepts and its penetration capability was studied. Then the molding process and the penetration mechanism were discussed with respect to the shaped charge jet and the projectile produced by the new type shaped charge warhead. Based on the above analysis, the static steel target experiments were systematically carried out based on the new type shaped charge warhead in order to find the influence of the key configuration parameters and the match between the small angle liner material and the large angle liner material on the penetration results. The experiment results revealed that at the optimal stand offs of the new type shaped charge warhead and the EFP, the penetration capability of the new type shaped charge warhead could achieve an increase of about 50{\%} from the penetration capability of the EFP with a comparative diameter of their craters under the same charge and casing conditions.
    Application study
    2004, 26(3):  0-0.  doi:10.6052/1000-0992-2003-054
    Abstract ( 1210 )   PDF (231KB) ( 417 )  
    During the trial production of a four-cylinder diesel engine, cracks occurred on a cylinder block. In order to ensure the engine's safe working, the issue must be solved. In this paper, mechanics theory is applied to analyse the issue and it is concluded that the cracks were caused by uneven forces acting on the block. At the same time, the experimental stress anlysis is carried out to study two types of four-cylinder engine blocks, and the effect of cylinder washer on block's stress and cylinder sheath's distortion is found. So a method is given to reduce the block's stress and the cracks have not appeared again. Oil-leak, air-leak and cylinder scratch have not occurred either, and reliability is improved greatly.
    Education Study
    2004, 26(3):  0-0.  doi:10.6052/1000-0992-2003-068
    Abstract ( 1175 )   PDF (391KB) ( 387 )  
    In the paper, the limit load formulae for a thick-walled tube with different strength in tension and compression state are derived based on the twin shear unified strength theory, under the action of an inner pressure and axial force. In these formulae, the results with Tresca criterion, linear approximate Mises criterion and twin shear stress yield criterion can be obtained with different coefficient values reflecting the middle main stress effect, and limit loading curves for different yielding criterions are plotted. Therefore, accurate solutions for limit loads can be obtained with this theory under the three-dimensional state; the limit loading diagram is consistent to yielding curves of twin shear stress, Mises and Tresca criterions; these formulae can be used for the material with differentia strength in tension and compression state.
    2004, 26(3):  0-0.  doi:10.6052/1000-0992-2003-075
    Abstract ( 1083 )   PDF (238KB) ( 427 )  
    Fatigue crack initiation is an important period in the whole fatigue life. The crack initiation period cannot be estimated with fracture mechanics, which is used for large cracks. In this paper, the crack initiation life estimate equation is deduced by using the fatigue damage continuous curve with the basis of experimental data obtained from the crack initiation plastic hysteresis energy as a control parameter.
    2004, 26(3):  0-0.  doi:10.6052/1000-0992-2003-082
    Abstract ( 1092 )   PDF (222KB) ( 413 )  
    The perforated casing is more vulnerable to collapse under external pressure than that without perforates. This paper gives the elastic differential equation of collapse of perforated casing, and a general formula for reduction factor of elastic collapsing by perturbation method. Compared with the exact solution of square holes, the perturbation ones are of high precision for elastic collapsing of perforated casing.
    2004, 26(3):  0-0.  doi:10.6052/1000-0992-2003-084
    Abstract ( 1297 )   PDF (234KB) ( 392 )  
    This paper presents a stochastic analysis of an axially-loaded cantilever bar with the Young's modulus being considered as a random field. For a small variation, the stochastic governing differential equation and the boundary conditions of the problem are first decomposed into two sets of equations and conditions corresponding to a mean value problem and a deviation problem, respectively. According to the similarity between the above two sets of equations and conditions, analytical solutions corresponding to different covariance structures and fluctuation scales are then obtained. On this basis, the sensitivity study of the covariance functions on the structural response is carried out. It is shown that different covariance structures have certain effects on the stochastic results, but have little influence on the solutions when the fluctuation scales are either small or large. The exact solutions obtained in this paper may also be used to verify the validity of other numerical methods.
    2004, 26(3):  0-0.  doi:10.6052/1000-0992-2003-085
    Abstract ( 1125 )   PDF (349KB) ( 541 )  
    In an accident, the front and back of bodywork model can adsorb impact energy on condition that the internal space of it has no distortion. Based on finite element LS-DYNA program, this paper has analyzed the model of additional mass attaching to a single section, the model of additional mass attaching to two sections proportionately, and the model whose front wall thickness is changed. According to the result, the problem is discussed of how to increase the amount of impact energy of space absorbed by the impact energy of front and back, with the internal space unchanged.
    2004, 26(3):  0-0.  doi:10.6052/1000-0992-2003-102
    Abstract ( 999 )   PDF (337KB) ( 541 )  
    Traditional FEM algorithm analysis for a serial processing computer can not satisfy the demand of scientific research and engineering technology development. Parallel processing technology provides a new prospect for solving this kind of problems. Cluster parallel computer uses a very popular parallel processing method at present. Based on the features of FE Method, this paper proposes a parallel finite element algorithm, together with an Object-Oriented FEM program under multi-parallel computers with distributing memory. The calculated examples show that this algorithm improves analyzing efficiency with simple organization.
    2004, 26(3):  0-0.  doi:10.6052/1000-0992-2003-103
    Abstract ( 1105 )   PDF (166KB) ( 524 )  
    A new approximate solution to thickness reduction of plastic bending sheet is presented by considering the characteristics of deformation and stress distribution. The proposed method is based on the incremental theory, and volume invariance and planar cross-section are assumed. As a calculation example, the sheet reduction ratio and the distance from the neutral plane to inner boundary are calculated and compared with published data. A fairly good agreement is obtained between the calculated results and the experimental data.
    2004, 26(3):  0-0.  doi:10.6052/1000-0992-2003-130
    Abstract ( 1245 )   PDF (302KB) ( 457 )  
    To obtain an approximate solution with the method of weighted residuals, the perturbation method with plate center deflection as perturbation parameter is used to turn nonlinear partial differential equations for large deflection of rectangular plate to linear partial differential equations. Then, a solution is obtained with the least square method. In the course of solution, an ascending power trial function family is used, which can be conditioned by the control parameter $f$. The results agree with the experimental ones. Compared with previous researches, the precision of calculation is improved evidently. It is an effective method to obtain a best trial function and a best approximate value.
    2004, 26(3):  0-0.  doi:10.6052/1000-0992-2003-132
    Abstract ( 1150 )   PDF (236KB) ( 442 )  
    The traditional method to draw contours has some disadvantages, such as adjacent contours are not well fitted and contours intersect and overlap each other. In order to overcome them, another simple but highly effective method is proposed in this paper. This method is based on mechanical model of spline function. The principle is that the vertical displacements of elastic lamella grids the elevation of land key points. Consequently we can use the finite element method to draw contours accurately. Through two examples, the practicability of this method is illuminated by using finite element general program ANSYS to draw contour. This method can be widely used in drawing contours of large scale relief maps.
    2004, 26(3):  0-0.  doi:10.6052/1000-0992-2003-163
    Abstract ( 1282 )   PDF (290KB) ( 464 )  
    Local wall-thinning, as a common defect on the surfaces of pipelines, not only reduces the load-carrying capacities, but also causes serious failure accidents of pipelines. In this paper, a computational method for plastic limit loads is adopted. The plastic collapse analysis of defective pipe elbows under internal pressure and bending moment is performed by the proposed algorithm. The defects considered here include part-through spherical, ellipsoidal and rectangular slots. Based on a number of numerical examples, the limit loads of pipe elbows are computed for a range of geometric parameters. The effects of axial, circumferential, small and large area local wall-thinnings with different sizes on load-carrying capacities of pipe elbows under internal pressure and in-plane bending moment are analyzed. Some typical failure modes corresponding to different configurations of slots and loading forms are studied. The computational results can provide theoretical foundations for the safety assessment of defective pipe elbows.
    2004, 26(3):  0-0.  doi:10.6052/1000-0879-2003-195
    Abstract ( 1376 )   PDF (251KB) ( 428 )  
    Using the transport equation for nematic liquid, the orientational motion of fiber spinning flow of liquid crystalline polymer (LC) is studied, including steady and unsteady flows. Using the Lagrange approach, the stability of the fiber spinning flow is investigated. The conclusion is drawn that the fiber spinning flow of LC polymer is stable, which serves as the basis of the nematic mechanism of high strength of the fiber of the LC polymer.
    2004, 26(3):  0-0.  doi:10.6052/1000-0992-2003-235
    Abstract ( 1185 )   PDF (613KB) ( 817 )  
    Underwater weightlessness simulation, developed overseas from the 1960s, is an indispensable training method for astronauts on the ground. Theoretical basis of this method is the dynamics of the underwater weightlessness simulation, which can provide the theoretical direction and the practice support. There are certain inherent problems in this method, such as the water drag, deviation between the center of gravity and the center of buoyance, the change of the buoyance, and so on. Consideration of these factors in the application is necessary to attain a high-fidelity simulation. The theoretical analysis, mathematical simulation and physical test are the useful ways, which can indicate the underlying principles for the underwater weightlessness simulation, answer the theoretical problems in practice and provide effective measures to attain high-fidelity simulation results. This article provides a schematic introduction on the underwater weightlessness simulation, outlines the developing background, basic principles, progresses, advantages and disadvantages of underwater weightlessness simulation, summarises the current research of dynamics of underwater weightlessness simulation both in China and abroad, and finally points out the trends of dynamics research for underwater weightlessness simulation in the future.
    2004, 26(3):  0-0.  doi:10.6052/1000-0992-2003-241
    Abstract ( 920 )   PDF (196KB) ( 407 )  
    Aiming at the cylinder grouting manner, this paper studied repetitive grouting and multiple holes grouting for osmotic grouting, put forward some valuable theoretical equations of grouting in rock mass. It can be used to instruct design and construction of grouting engineering in site.
    2004, 26(3):  0-0.  doi:10.6052/1000-0992-2003-242
    Abstract ( 1242 )   PDF (264KB) ( 497 )  
    In this paper, a three-dimensional finite element for the drilling rig foundation is built for studying the dynamic characteristics and design of the drilling rig foundation. Through analysis of its modes, the dynamic characteristics of the drilling rig foundation are discussed. On the basis of the analysis of the dynamic characteristics for the drilling rig foundation, the effect of basic frame on the dynamic characteristics of the drilling rig foundation is investigated. According to the conclusions drawn from the analysis, the dynamic design or modification of drilling rig foundation structures is made by optimization of frames. The method put forward by the paper can be used in the dynamic design or modification of drilling rig foundation structures.
    2004, 26(3):  0-0.  doi:10.6052/1000-0992-2003-257
    Abstract ( 1230 )   PDF (183KB) ( 427 )  
    In this paper the orthogonal and ortho-laid space grids are assumed as an orthotropic sandwich plate, which is analyzed by the theory of plate with consideration of shear deformation and three generalized displacements. The calculating formulas for internal forces and displacements of double-layer space grids under local loading are given based upon ESPM, and have been validated by the finite element method (ANSYS). In general, the differences between ESPM and FEM are less than 10\% and 5\% for internal forces and displacements, respectively. So this method can be used in the design of double-layer space grids.
    2004, 26(3):  0-0.  doi:10.6052/1000-0992-2003-336
    Abstract ( 1133 )   PDF (364KB) ( 408 )  
    This paper discusses the calculation of plastic limit of bending moment of a workpiece, the determination of motor power matching a stake-flange machine and the choice of geometric shape and dimension of workpiece sections in the process of the machine design. Plasticity theory is applied to solve these problems and a new simplified method based on Tresca yielding's law is presented according to the features of the problems in order to solve the problems mentioned above. The plastic stress and strain distribution of the workpiece and the respective mathematical formulas are obtained. A calculating example from a factory is given.
    2004, 26(3):  0-0.  doi:10.6052/1000-0992-2003-358
    Abstract ( 1300 )   PDF (376KB) ( 498 )  
    The evolutionary structural optimization method has been under continuous development since 1992. Recently a bi-direction evolutionary structural optimization method is developed whereby material can be added and removed. In order to consider the effects of element removing or adding on structural stress constraints, in this paper, a new bi-direction evolutionary structural optimization method is proposed for structures under multiple loads. First, based on an idea that artificial material is added around optimal structural cavities and boundaries, a structural optimization model and a set of stress sensitivity formula are built. Then combining structural stresses and its sensitivities, a set of criteria, for adding and removing finite elements for the topology optimization problem of structures under multiple loads, is established, and a kind of new topology optimization procedure is obtained. Several simulation examples show that the proposed method is valid and effective for structural topology optimization.
    2004, 26(3):  0-0.  doi:10.6052/1000-0992-2004-176
    Abstract ( 1443 )   PDF (865KB) ( 788 )  
    Architectural wind environment study is a cross discipline between aerodynamics and atmospheric science focusing on the interaction of architectures with the urban wind fields. In the study, wind tunnel tests and flow visualization approaches, as consistently used in aerodynamics, are applied for the investigation of the wind field distribution and variation in urban atmospheric boundary layers and around the architectures. The numerical computations and wind tunnel tests are mutually complementary and their combination can improve the experimental studies. In the present paper, the wind environment of Beijing Central Business District (CBD) is studied. The simulation of the urban atmospheric boundary layer in the wind tunnel and the method of the wind field visualization around architectures are described in detail. The experimental results are compared with numerical computations and they are in agreement. Some useful suggestions in the study are made for the improvement of urban planning and urban wind environment in CBD area.