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15 December 2011, Volume 33 Issue 6
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    The discuss about plane hypothesis of torsional deformation
    Min Li Tiancai Tan Qiusheng Ma
    2011, 33(6):  73-74.  doi:10.6052/1000-0879-lxysj2011-026
    Abstract ( 1198 )   PDF (5480KB) ( 585 )  
    By the plane hypothesis meanings of torsional deformation, the stress analysis of torsional deformation of a circular bar is associated with the plane hypothesis. The condition of plane hypothesis is discussed to explain the warp of the rectangle bar. And it could be a didactical supplement part for mechanics of materials
    2011, 33(6):  69-72.  doi:10.6052/1000-0879-lxysj2011-006
    Abstract ( 856 )   PDF (8617KB) ( 317 )  
    The mechanical analysis is carried out for the preliminary design of the pipeline crossing diagonal cable type structure in Mulong River by the finite-element method. The results indicate that the cable with some pre-strain can improve the strength and the stiffness of the structure while it is installed, but if the pre-strain is too large the strength and the stiffness will be declined, so there is an optimum value of pre-strain for the structure, to be influenced by the form of structure and the loads on structure; under the work loads or the water filling loads, the strength of the structure just meets the requirements. Under the ultimate loads, the strength of the structure does not meet the requirements. There are three places where the maximum stress is reached in the structure the left tower top connected with cable, the right tower top connected with cable and the upper limb of the intermediate pipe bridge.
    2011, 33(6):  79-80.  doi:10.6052/1000-0879-lxysj2011-007
    Abstract ( 819 )   PDF (2995KB) ( 428 )  
    As for the state of zero deflection of clamp-clamp Euler beam acted on uniform distributed couple only, the inherent factors to induce this zero deflection can be analyzed by forth order differential equation of deflection of Euler beam that take into the effect of distributed force and couple. Then Euler beam acted on uniform distributed couple with the six kinds of classic boundary condition has been analyzed. The key factor inducing the zero deflection of Euler beam acted on uniform distributed couple only can be found is whether shear force in boundary condition equal to zero.
    2011, 33(6):  81-82.  doi:10.6052/1000-0879-lxysj2011-142
    Abstract ( 763 )   PDF (3548KB) ( 530 )  
    APPLICATION OF GENETIC ALGORITHM TO ANTI-SHOCK ISOLATION
    Shuhao Ban Xiaoyan Li Xuedong Jiang Aiping Hu
    2011, 33(6):  40-44.  doi:10.6052/1000-0879-lxysj2011-140
    Abstract ( 693 )   PDF (18263KB) ( 345 )  
    A nonlinear mathematical model of the first-order approximation is proposed based on Taylor series expansion, the genetic algorithm is adopted for the natural frequency of the system, and the simulation model of the corresponding system is constructed. Simulations of the system of an active hard-disk with a wireless isolator are carried out under the action of a half-sine impulse. From the theoretical analyses and simulated results, it can be seen that the simulation model can be used for different impulse widths, can have the effect of isolation with the permissible maximum of deformations, and effectively inverse the natural frequency of the system with wireless isolators.
    2011, 33(6):  18-22.  doi:10.6052/1000-0879-lxysj2011-211
    Abstract ( 969 )   PDF (9907KB) ( 420 )  
    Based on the fractal theory and the numerical simulation method, the curres of the height of imbibition and the mass of imbibition against time are obtained for a power law liquid in a single tortuous capillary. The results show that the effect of the gravity may be neglected at the initial stage of capillary rise and the effect of the gravity becomes important as time goes on. The maximum equilibrium height of imbibition for a power law liquid in a single tortuous capillary is found to be a function of the capillary diameter $\lambda $ and the density $\rho $ of the power law liquid, and independent of the tortuousity of a single tortuous capillary and the power exponent $n$. Meanwhile, the rise velocity increases with the decrease of the power exponent $n$ at the initial stage of capillary rise. And the larger the tortuousity fractal dimension $D_T $, the more the mass of imbibition at equilibrium will be.
    2011, 33(6):  45-49.  doi:10.6052/1000-0879-lxysj2011-137
    Abstract ( 1134 )   PDF (8666KB) ( 626 )  
    Based on the boundary conditions of transverse vibration of non-uniform beams, second order inexplicit-recursive differential equations with variable coefficients about deflection and bending moment are obtained from the fourth order differential vibration equation with variable coefficients by the method of order reduction. By the method of finite difference, the numerical calculation method and its precision for the natural frequency of the transverse vibration of the simply supported non-uniform beams are studied. Examples of theoretical analysis and orthogonal calculation show that the numerical calculation algorithm is very simple, and its precision depends on the number of calculation steps and the vertical variation rates of the gradually changed cross-section and is independent of width and length of beams; the precision of the numerical calculation can be estimated according to a given length or the number of calculation steps and the reasonable length or the number of calculation steps can be determined by a given precision requirement.
    2011, 33(6):  75-76.  doi:10.6052/1000-0879-lxysj2010-490
    Abstract ( 1359 )   PDF (4885KB) ( 527 )  
    2011, 33(6):  85-87.  doi:10.6052/1000-0879-lxysj2011-036
    Abstract ( 1270 )   PDF (4623KB) ( 411 )  
    In this paper, a simplified method was deduced for calculating the deformation of indeterminate structures with spring supports, according to the regular formula based on the principle of virtual work. The proposed formula, which is briefer, has the same form as the regular deformation formula for structures with rigid supports. Finally, an example was solved by the given formula and its correctness was proved by results of the finite element method.
    2011, 33(6):  88-90.  doi:10.6052/1000-0879-lxysj2010-486
    Abstract ( 919 )   PDF (7636KB) ( 354 )  
    By the comparing the advantages and disadvantages of the traditional teaching model and Problem-Based Learning (PBL), the latter approach is introduced into the engineering graduate course of the finite element analysis. Curriculum design based on PBL is implemented by the renovation of the curriculum structure and knowledge structure, strengthening students’ self-study and research capability, and stimulating their imagination and creativity. The practice of PBL has well balanced the gap between theoretical instruction and engineering application, and the gap between shortage of faculties and large size of students.
    2011, 33(6):  91-93.  doi:10.6052/1000-0879-lxysj2010-484
    Abstract ( 774 )   PDF (6016KB) ( 438 )  
    Abstract: this paper explored and practiced the rational use of the multimedia teaching in structural mechanics, as well as analyzed the advantages and existing problems. Meanwhile, how to maximize favourable factors and minimize unfavourable ones and use multimedia teaching in structural mechanics rationally are discussed emphatically from some aspects, such as, the teaching methods, teaching contents, teaching means, courseware forms and amount of information etc.
    STUDY OF FREE SURFACE FLOW WITH PARTIALLY-SLIP BOUNDARY
    AHMAD Salman Baozeng Yue Xiaojuan Song
    2011, 33(6):  9-12.  doi:10.6052/1000-0879-lxysj2011-231
    Abstract ( 964 )   PDF (6647KB) ( 611 )  
    The researches on sloshing of the free surface flow in containers carrying liquid are of theoretical and practical significance. Numerical solutions often involve some approximations of the boundary condition, when considering the wide-range movement or the nonlinearity of the free surface flow. In this paper, under partial slip boundary conditions, the high-order nonlinear differential equations of a cylinder-shaped partially filled liquid container are numerically solved. The influences of the contact line and the fluid height of liquid and the partial slip boundary conditions on the macroscopic radius of the fluid layer are discussed. The results may serve a reference for treating similar boundary conditions of free surface flow for partially filled liquid carrying containers.
    2011, 33(6):  59-62.  doi:10.6052/1000-0879-lxysj2011-225
    Abstract ( 988 )   PDF (7933KB) ( 338 )  
    To study the underwater explosion shock wave attenuation of the pressure, experiments were carried out with different charge amount of grain, to obtain the underwater explosion pressure curve and the relationship between the charge volume and the peak pressure. The numerical simulation verifies the experiments. In the case of the same charge weight, the attenuation of the radial pressure of a grain of underwater explosion is obtained. The peak pressure at the explosive center is decayed with the increase of the radial distance and the curve fitting formulas are obtained.
    Around the mechanics
    2011, 33(6):  1-8.  doi:10.6052/1000-0879-lxysj2011-352
    Abstract ( 1529 )   PDF (15221KB) ( 4932 )  
    The classical physics and mechanics in flat space are first reviewed. Three typical examples of physics and mechanics in curved space, i.e. the biomembrane mechanics, the shallow shell mechanics and the diffusion dynamics on curved surfaces, are explained. The essential differences between the physics and mechanics in flat space and curved space are discussed. It is shown that there is only one fundamental differential operator in the physics and mechanics in flat space, i.e. the classical gradient. However, there are two fundamental differential operators in the physics and mechanics in curved space, i.e. the classical gradient and the shape gradient.
    2011, 33(6):  13-17.  doi:10.6052/1000-0879-lxysj2011-219
    Abstract ( 704 )   PDF (9398KB) ( 576 )  
    paper took Tacoma Narrow Bridge accident caused by wind vibration for an example, researched mechanism of the bridge vibration on the H-type bridge deck and analyzed flow symmetry breaking and conditions of the bridge vibration induced by the flow around. Based on the actual size of bridge deck, two-dimensional numerical calculation was set up by Fluent software. The results showed that the low pressure area was gradually formed from the middle region, moved down wind and changed alternately and periodically on the upper and lower bridge deck; Secondly, the bigger the wind speed, the smaller the variance period of bridge resistance force and lift force and the rate of period variance; Thirdly, the variance period of lift coefficient was two times of resistance coefficient, and the variance period of lift coefficient was around 31.5s, with the wind velocity is 19m/s.
    2011, 33(6):  23-29.  doi:10.6052/1000-0879-lxysj2011-243
    Abstract ( 923 )   PDF (12391KB) ( 368 )  
    In order to solve the problem of unsteady fluid flow in fractured rock, a new numerical model is proposed. For the calculation of fluid flow in a single fracture, the governing equations are simplified Navier-Stokes equations based on some assumptions, which are numerically solved by the finite difference method and the volume of fluid method. In a fracture network, the fluid flow in intersection places is governed by special equations. The results show that this numerical model could not only improve the computational efficiency of unsteady fluid flow in the fractured rock, but also avoid the influence of isolated fractures. Finally, the applicability of the numerical model is validated by two engineering examples.
    2011, 33(6):  30-34.  doi:10.6052/1000-0879-lxysj2011-326
    Abstract ( 799 )   PDF (9206KB) ( 539 )  
    A more reasonable computational fluid dynamics (CFD) analysis is carried out for the external aerodynamic characteristics of the high-speed car in this paper. The realizable $k$-$\varepsilon $ turbulence two equations model of RNS methods based on the FVM (finite volume method) combined with the enhanced wall treatment method is apllied to simulate the external flow field of a car model with tires, side mirrors and antenna and other protruding parts under vehicle's different speed conditions. The results show that the difference of the vehicle surface pressure along the x-direction leads to the car's aerodynamic drag; with the increased vehicle's speed, the car's aerodynamic drag grows faster than the aerodynamic lift.
    2011, 33(6):  35-39.  doi:10.6052/1000-0879-lxysj2010-178
    Abstract ( 931 )   PDF (9490KB) ( 481 )  
    In view of the mechanical characteristics of the porous hard and brittle materials the existing problems in the measurement of the dynamic mechanical behavior based on the conventional SHPB experimental technique were analyzed on the basis of the two fundamental assumptions in the SHPB experiment. The influencies on experimental results of some factors such as the incident bar, transmission bar, sensors, specimen, incident wave shape and the data processing algorithm were investigated, respectively. According to the results, a modified experimental technique was developed for measuring the compressive stress-strain response of these materials. This paper provides some gaidances the design of SHPB experiments for porous materials or brittle materials.
    SURROUNDING-ROCK RUPTURE MECHANISM AND CONTROL OF EXTRACTION ROADWAY IN HIGH STRESS AREA
    Huaqiang Hou Lianguo Wang Huiying Li Xianwei Li Songtao Xing
    2011, 33(6):  50-54.  doi:10.6052/1000-0879-lxysj2011-323
    Abstract ( 918 )   PDF (8973KB) ( 395 )  
    To study the relation between the rupture risk degree of the surrounding-rock and the engineering geological condition, the stress function of the roadway surrounding rock is obtained by using the complex function theory of elastic-plastic mechanics in this paper, then the rupture mechanism of the high stress roadway is studied. It is shown that the risk degree of the surrounding-rock and the slip distribution when the roadway bursts can be determined by a function of danger, which is a practical control technology of the extraction roadway with advantages of being used widely and calculated simply.
    2011, 33(6):  55-58.  doi:10.6052/1000-0879-lxysj2011-203
    Abstract ( 935 )   PDF (8387KB) ( 318 )  
    In order to study the relative dynamic modulus of elasticity, deteriorated due to the accumulative fatigue damage under the freeze-thaw enviorment, fatigue experiments were carried out for fifteen prestressed or reinforced concrete beams under different cycles of freeze-thawing. With the relative dynamic modulus of elasticity as the damage variable, the influence on the damage of the freeze-thaw and the fatigue load is analyzed through the variance analysis method. It is shown that the freeze-thawing is the main damage factor at the initial stage and then the fatigue damage becomes the main factor in this two-factor experiment, but the fatigue is the major factor of damage in the whole life of test beams. Applying prestress or enhancing prestress extent has an obvious inhibition effect on the damage of test beams and will reduce the period in which the fatigue is the major damage factor in the life time of test beams.
    2011, 33(6):  63-68.  doi:10.6052/1000-0879-lxysj2011-287
    Abstract ( 775 )   PDF (10005KB) ( 512 )  
    A dynamics model of a rod-shaped rotational expansion mechanism with consideration of the flexibility of the center rod is developed for studying the dynamic property in the expanding process. A numerical simulation is carried out under an ideal operating condition. The kinematic parameter in the computed results agree well with the test result. Finally a simulation is carried out with considerations of operation direction, dynamic deflection and mass unbalance. It is shown that the influence of operation direction and mass unbalance is much more important, and that of the dynamic deflection could be ignored in the small angle area.
    Geometry to determine the center of gravity of uniform polygonal thin plate
    Yvcheng Zhao Mingyuan MingLiu Zhiquan Xiang
    2011, 33(6):  77-78.  doi:10.6052/1000-0879-lxysj2010-390
    Abstract ( 1342 )   PDF (4726KB) ( 449 )  
    It is very important for controlling the objects’ balance and stability that to grasp the center of gravity position in many cases. For some of the actual sheet-like structures, how to quickly identify the location of its center of gravity? Analytical method using the coordinates of many points to be determined is time-consuming and labor-intensive; using the test method (suspension method) in many cases is unrealistic; In this paper presents a geometry to quickly determine the center of gravity location of the uniform shin polygon.
    2011, 33(6):  96-97.  doi:10.6052/1000-0879-lxysj2011-346
    Abstract ( 1389 )   PDF (3852KB) ( 460 )  
    2011, 33(6):  100-102.  doi:10.6052/1000-0879-lxysj2011-383
    Abstract ( 964 )   PDF (8184KB) ( 473 )  
    2011, 33(6):  103-104.  doi:10.6052/1000-0879-lxysj2011-472
    Abstract ( 984 )   PDF (3638KB) ( 487 )  
    2011, 33(6):  105-106.  doi:10.6052/1000-0879-lxysj2011-272
    Abstract ( 1310 )   PDF (3547KB) ( 865 )