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08 October 2009, Volume 31 Issue 5
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    Education Study
    2009, 31(5):  69-71.  doi:10.6052/1000-0992-2007-506
    Abstract ( 1326 )   PDF (703KB) ( 684 )  
    The requirement to mode of person with ability training and innovation of higher education is taller with development of present-day science and technology. It is a new challenge for all courses, how to adapt the transformation of new person with ability’s requirement and new training mode. For adapting to new mode of person with ability training and the requirement of engineering technology, in this paper some concrete innovation actions about theoretical mechanics is introduced, in order to be referred by other courses.
    Application study
    2009, 31(5):  35-40.  doi:10.6052/1000-0879-2008-015
    Abstract ( 1180 )   PDF (1320KB) ( 805 )  
    Experimental and numerical investigations were performed on explosive shock wave around the wall and explosive loads on the protective wall. The transducer pressure measurement technology was adopted to measure the pressure distribution around the protective wall. Pressure history on the forward and backside of the protective wall was gained, Based on ALE algorithm and JWL state equation, a numerical simulation was carried out to simulate the above complex phenomenon of mechanics of explosion. Both experimental and numerical results are in good agreement, which show the inherent mechanism of blast wave around the wall and provide a reference for reinforcement mechanism study of the protective wall.
    Around the mechanics
    2009, 31(5):  85-88.  doi:10.6052/1000-0879-2008-125
    Abstract ( 1395 )   PDF (983KB) ( 1681 )  
    In this paper, a lot of natural phenomena are presented to show the universality of the principle of least action. The essence of surface wetting is illustrated by the principle of least action. At the same time, the energy formulation and differential formulation are proved to be equivalent for surface wetting phenomenon. Some physical phenomena are explained by the principle of least action, such as super-hydrophobic state of the lotus leaf, jumping on water of the water strider, directional motion of the liquid drop and capillary adhesion. Some philosophical meanings are also discussed in this paper.
    Education Study
    2009, 31(5):  72-74.  doi:10.6052/1000-0879-2008-145
    Abstract ( 1186 )   PDF (505KB) ( 549 )  
    The curriculum teaching of "Engineering mechanics" in the higher professional education must link up closely with the operation, must carry on the whole to the curriculum the teaching design, thus reforms the teacher “to teach” and the student comprehensively “study”. Through carring on the analysis to the typical work duty,this article takes mechanics knowledge application as a center, takes trains student's ability as the key point, takes the motion as the study process, introduces curriculum teaching design mentality and the concrete procedure of integrate learn with operation on five aspects as the curriculum goal, the curriculum content, the teaching situation, the study resources and autonomous studies, respectively.
    Application study
    2009, 31(5):  26-29.  doi:10.6052/1000-0879-2008-190
    Abstract ( 1196 )   PDF (540KB) ( 671 )  
    On the basis of the theory of thin-walled member, the continuity of warping in analysis of bending shearing flow and warping shearing flow in thin-walled box-girder is studied. With the continuity condition of warping, the formula of warping shearing flow in restrained torsion of thin-walled box-girder is established. The error in relevent references is pointed out and corrected. The warping shearing flow in a cantilever box girder under restrained torsion is calculated.
    2009, 31(5):  30-34.  doi:10.6052/1000-0879-2008-351
    Abstract ( 1341 )   PDF (865KB) ( 789 )  
    A theoretical analysis is carried out for concrete targets subjected to impact of projectiles. According to the vast comminution feature of concrete materials subjected to projectiles high-velocity impact, the materials in the comminuted or plastic region are assumed to obey the Griffith strength theory. A dynamic cavity expansion model is built for projectiles deeply penetrating into concrete targets. An analytical calculation formula is obtained. Predictions are in good agreement with test data.
    THE CT TEST FOR POROUS STRUCTURAL CHANGE UNDER COMPRESSIVE LOAD
    Yang Yong-Ming Song Zhen-Duo Ju Yang Wang Hui-Jie Peng Rui-Dong
    2009, 31(5):  15-20.  doi:10.6052/1000-0879-2008-388
    Abstract ( 1246 )   PDF (2437KB) ( 656 )  
    In order to investigate the influence of pores on mechanical properties of rock, porous physical models were developed, and through the uniaxial compressive and CT scanning tests, the evolution of porous structure with different porosity on rock and the influence of porous structure on macroscopical physical/mechanical properties are studied under various loading conditions. The crack growth law of pore models and the damage law of pores and solid media are obtained for different loads and CT observation scales. The test results indicate that the most of cracks appear after the peak value of tensile strength is reached. The main cracks appear in the place of densely distributed pores with many minor cracks. Before the peak value, a few minor cracks appear around pores.
    2009, 31(5):  45-50.  doi:10.6052/1000-0879-2008-391
    Abstract ( 1510 )   PDF (1322KB) ( 1196 )  
    The peak value of stress response is important when the strength of the structure in broadband random vibrations is considered. Based on the peak value equivalent theory of the random vibration and the sinusoidal vibration, the peak value of stress response in a random vibration can be obtained by the stress response at the resonant frequency of the sinusoidal vibration. The modal analysis, frequency response, prediction for the acceleration response and the peak value of stress response of a selected structure in random vibrations are carried out with MSC.NASTRAN. It is shown that the error of the peak value of stress response between analysis and test results is less than 10{\%}; therefore, the method of stress response prediction in random vibrations is reasonable and practical.
    2009, 31(5):  51-55.  doi:10.6052/1000-0879-2008-436
    Abstract ( 1048 )   PDF (1773KB) ( 785 )  
    An analysis of dynamics with changing topology for the humanoid running robot is carried out. First, a coordinate system is chosen. Then the constraint equation and the Jaccobi matrix are derived and the dynamics equations of the robot in stance phase and in flight phase are obtained. Next, the identification equation in different phases is derived as the condition of the robot from one phase to another phase. In addition, the impact between a foot of the robot and the ground is analyzed when the robot contacts the ground from the air. Finally, a virtual model of the robot is built by the software ADAMS and the validity of the method is verified by the simulation for the virtual model of the robot.
    2009, 31(5):  56-60.  doi:10.6052/1000-0879-2008-440
    Abstract ( 1013 )   PDF (933KB) ( 710 )  
    Integrant modal data are used to update a five-layer steel frame. The comparisons between the efficiencies and precisions of the Genetic Algorithm (GA), Particle Swarm Optimization Algorithm (PSO) and GA-PSO in the model updating processes show that all the four modal frequencies and modal shapes of the updated model can approach the target values with in varying degrees, which proves that these methods can all efficiently update the model. In particular, GA-PSO algorithm uses GA to efficiently search for the global-optical solution at an early stage, and uses PSO to intensively search for the local-optimal solution at a later stage. Comparing with the PSO and GA, GA-PSO algorithm enjoys higher updating efficiency and precision.
    2009, 31(5):  41-44.  doi:10.6052/1000-0879-2008-469
    Abstract ( 1306 )   PDF (1226KB) ( 601 )  
    A floating interval method is proposed for topology optimization problems of continuum structures. The major idea of the present approach is to consider the structure to be optimized as a piece of bone, whose growing process is controlled by an floating interval of reference strain energy density, i.e., the update of each material point in the design domain is determined by its current strain energy density and the reference interval. The update of the reference interval is determined by the active constraint of the optimization problem. Two numerical examples are given to show the validity of the present approach.
    2009, 31(5):  8-14.  doi:10.6052/1000-0879-2008-553
    Abstract ( 1126 )   PDF (1647KB) ( 741 )  
    Under the inlet pressure distortion, the internal 3D viscous flow fields of the transonic axial-flow compressor is numerically analyzed using the full passage method, based on a finite volume method and the Spalart-Allmaras turbulent model. The performance for the compressor and the internal flow structure are analyzed in detail under the inlet distortion condition. Compared with experimental data, good agreements are found, which indicates that the model and the method are practical and reliable.
    2009, 31(5):  21-25.  doi:10.6052/1000-0879-2009-022
    Abstract ( 1033 )   PDF (1288KB) ( 923 )  
    In order to obtain the dynamic properties, for the development of CFRP cable-stayed bridges in China, dynamic tests were carried out with ambient excitation and hammer excitation. Test results obtained under different test conditions are compared and analyzed. It is shown that the corresponding frequency value sees very small difference and vibration modes are similar; the ambient excitation test method is better than hammer excitation test method; with ambient excitation test method, more frequencies can be obtained than the hammer excitation test method.
    Review
    2009, 31(5):  1-7.  doi:10.6052/1000-0879-2009-108
    Abstract ( 1203 )   PDF (1741KB) ( 1218 )  
    The physical mechanisms and R{\&}D (research and development) status of Proton Exchange Membrane Fuel Cells (PEMFC) are reviewed in this paper, including its structural design and related issues of fluid dynamics. The numerical model and software platform for optimization based on computational fluid dynamics (CFD) are also discussed.
    Mechanics History
    2009, 31(5):  92-95.  doi:10.6052/1000-0879-2009-173
    Abstract ( 1390 )   PDF (1133KB) ( 519 )