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15 April 2011, Volume 33 Issue 2
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    2011, 33(2):  114-115.  doi:10.6052/1000-0879-lxysj2009-418
    Abstract ( 1340 )   PDF (401KB) ( 673 )  
    2011, 33(2):  30-34.  doi:10.6052/1000-0879-lxysj2010-235
    Abstract ( 1157 )   PDF (962KB) ( 544 )  
    According to the rheological deformation characteristics of mudstone around an inclined well in Gao Jia Liang mine, this paper proposes a mudstone model with effective support measures for the inclined well. Through mudstone creep loading and unloading tests and based on the model theory of unified rheology, an elastic-viscous-visco elastic-visco elastic-plastic model is established, which can reasonably represent rheological properties of mudstone, and the model parameters are calculated. Through analyzing mudstone mechanical properties obtained by tests and field observation data, and with the bolt-spray-net joint support method, the simulation is carried out by Large-scale finite element software ADINA. It is shown that the support method can effectively control mudstone's deformation, and the bolt-spray-net support method is reasonable and reliable.
    2011, 33(2):  91-92.  doi:10.6052/1000-0879-lxysj2010-261
    Abstract ( 1057 )   PDF (295KB) ( 593 )  
    2011, 33(2):  8-11.  doi:10.6052/1000-0879-lxysj2010-227
    Abstract ( 1190 )   PDF (1649KB) ( 349 )  
    An in-situ observation of the initial nucleation of the colloidal crystal was performed by utilizing a long working distance microscope. The streamlines in the vicinity of the three-phase contact line are calculated by the fluid dynamics software Fluent. The trajectory of the particle indicates that the streamline is bent around short chains. When the particle goes close to a short chain, a horizontal flow pushes the particle to the end of the short chain (flowing-around, FA). The simulation indicates that the particles have the ability of self-adjusting when they are assembled into a colloidal crystal. The FA would inhibit too fast growth in a local area, which would lead to a straight growth front. This study provides an insight into the self-assembling dynamics and the nucleation process for colloidal crystal growth.
    2011, 33(2):  62-66.  doi:10.6052/1000-0879-lxysj2010-287
    Abstract ( 1530 )   PDF (1954KB) ( 666 )  
    crank-rocker flapping mechanism inspired by insects is proposed based on the analysis of the normal flapping mechanism. The parallel crank-rocker is a kind of spatial linkage mechanism, in which due to the two parallel crank-rockers and the wing control mechanism between them, the flapping mechanism can not only keep the symmetry of the left and right wings during the motion, but also provide an accurate control of stroke angle and angle of attack simulation. MATLAB nonlinear optimization toolbox is employed to achieve the motion optimization. A scaled model is developed based the optimization and the reference motion of the model is a hovering flight Hawkmoth. The force measurement results reveal that the flapping mechanism can provide a high unsteady lift force, and the flapping mechanism is shown to be one of a practicable and novel design in flapping Micro Aero Vehicle research.
    2011, 33(2):  24-29.  doi:10.6052/1000-0879-lxysj2010-318
    Abstract ( 1220 )   PDF (3978KB) ( 407 )  
    A micro-mixing method is proposed, by which a secondary flow is produced under electromagnetic forces. Then the Dean eddies appear to produce reciprocation flows in the micro channel. The interface of the fluids is bent and stretched. The efficiency of mixing is greatly improved due to a great increase of the contact area between two mixing fluids. The structures of three cases are discussed. A theoretical model of the micro-mixing is built and numerical simulations are carried out. The fluid mixing process is analyzed and the mixing efficiency is evaluated. Experiments are carried for verification.
    2011, 33(2):  58-61.  doi:10.6052/1000-0879-lxysj2010-336
    Abstract ( 1398 )   PDF (804KB) ( 485 )  
    Three damping identification methods based on time response functions are studied in this paper, including the logarithmic decrement method, the Hilbert transform method and the wavelet transform method. The algorithms of these methods are presented and the ability of these methods to identify close modes is analyzed. The damping estimation accuracy is calculated using noise contaminated response with 5{\%}, 10{\%} and 30{\%} white noises, respectively. Results show that the wavelet transform method is more robust than the logarithmic decrement method and the Hilbert transform method. The wavelet transform method is then used to identify the modal parameters of Runyang suspension bridge using the vibration responses obtained by Structural Health Monitoring System. Modal parameters of six low order modes are identified. The difference of the modal frequency between the second mode and the third mode is only 0.015\,Hz. Therefore, the wavelet transform method can identify modal damping of closely spaced modes from noise contaminated data. The method should be a good choice for engineering applications.
    Around the mechanics
    2011, 33(2):  1-7.  doi:10.6052/1000-0879-lxysj2011-009
    Abstract ( 1638 )   PDF (1657KB) ( 720 )  
    Several key issues in flexible multibody dynamics with contact/impact are presented, including the modeling of the contact region, the models for contact, the kinematics of the flexible body, the numerical methods of constraint. The shortcomings and merits of these methods are discussed. The development trends are pointed out.
    2011, 33(2):  12-17.  doi:10.6052/1000-0879-lxysj2009-391
    Abstract ( 1113 )   PDF (1115KB) ( 423 )  
    Based on the Reynolds-Averaged Navier-Stokes equations with $k$-$\omega$ SST turbulent model and coupled with the motion equations for an elastic supported system, the steady and unsteady flows for airfoils with different incidences are simulated, specially, for high incidences when separated vortices exist. For the given Reynolds numbers and structure parameters considered in this paper, the frequencies of shedding vortex have a complicated relation with the airfoil vibration. The average aerodynamic force may vary for some forced vibrations. For airfoils with thickness larger than 20{\%}, the aeroelastic response can lead to a separated flow field from one balance state to another so that the aerodynamic force changes from one value to another. These results can explain the poor repeatability of experimental results in these regions.
    2011, 33(2):  18-23.  doi:10.6052/1000-0879-lxysj2010-411
    Abstract ( 1350 )   PDF (1136KB) ( 404 )  
    Influences of the curvature radius of the hypersonic leading edge on the evolution of temperature, stress, and deformation are studied in this paper. Firstly, the hypersonic aerodynamic heating model is established to determine the thermal environment of the leading edge made of niobium alloy by the finite volume method. Secondly, the temperature field, stress field, and deformation field of the leading edge with their evolution are obtained by the finite element method. The numerical results reveal that the evolution of the temperature field is closely related to the curvature radius. The stress value of the leading edge during the aerodynamic heating process reaches the maximum when the curvature radius is 1\,mm; the displacement increases with the increase of the curvature radius.
    2011, 33(2):  35-38.  doi:10.6052/1000-0879-lxysj2010-441
    Abstract ( 1168 )   PDF (670KB) ( 561 )  
    According to the characteristic of low-cycle fatigue, the equation of S-N curve of concrete is simplified. A new model of strength degradation and the predictor method of life period for concrete under low-cycle fatigue loading are proposed, and the necessary parameters are obtained by the fatigue test. By comparison with the evolution of the actual strain and the Miner rule, the model and method are shown to reflect the damage of low-cycle fatigue of concrete correctly.
    2011, 33(2):  39-45.  doi:10.6052/1000-0879-lxysj2010-189
    Abstract ( 1018 )   PDF (1885KB) ( 415 )  
    In order to study strata movement and stability where coal-pillar under water, building or railway is replaced by gangue backfills of different compactness, spring principle and elastic-plastic theory are used to analyze the compression mechanism of gangue backfills as supporting bodies, and related formula for the early stage compression is obtained. The compression value and the equivalent mining height for different compactness is obtained based on compaction principle of gangue backfills and rock mechanics. In a engineering example, the theoretical calculation and the numerical simulation are used to analyze strata movement for gangue backfills of different compactness. It is shown that the roof subsidence and the equivalent mining height of quadratic strata movement steadily increase with the decrease of compactness degree of gangue backfills. When the void ratio is about 0.55, the increment speed of equivalent mining height becomes very sensitive and the rising tendency of the maximum side displacement become marked.
    2011, 33(2):  46-51.  doi:10.6052/1000-0879-lxysj2010-428
    Abstract ( 1211 )   PDF (4530KB) ( 390 )  
    Based on the engineering background of Rui-Gan Expressway Xiashan tunnel, for complex stress state of two-hole parallel tunnels with small spacing, the finite element method is used in a small clear distance zone of a deep tunnel under different bias conditions to simulate the step construction scheme. The different excavations before and after the tunnel surrounding rock displacement and support structure and the stress variation are analyzed. On the basis of different tunnel construction processes, and the mechanical behavior of rock, the concept of weak rock is proposed to show clearly the engineering geological conditions of weak rock tunnel control panel folder, achieved good results in actual constructions.
    2011, 33(2):  52-57.  doi:10.6052/1000-0879-lxysj2010-498
    Abstract ( 984 )   PDF (1169KB) ( 435 )  
    In order to determine the relationship between different filter functions in structural topological optimization, the paper focuses on the filter function in the ICM method. For a filter function with the form of power functions, first the homogenization method and the least squares method are adopted to calculate the weight filter function and the stiffness filter function. Then the numerical simulation method is used to study the relationship between the weight filter function and the stiffness filter function. Finally, the concept of exponential coefficients of filter function is proposed, and the relation of the stiffness filter function with the weight filter function is obtained.
    Around the mechanics
    2011, 33(2):  67-70.  doi:10.6052/1000-0879-lxysj2010-504
    Abstract ( 1100 )   PDF (643KB) ( 529 )  
    The first two natural frequencies of transverse vibration of moving vehicles over a smooth road based on a half-vehicle model are numerically simulated. The car's body is modeled as an Euler-Bernoulli beam with free boundary conditions at both ends, and the tires are modeled as two springs with different spring indexes in the half-vehicle model. The governing equation for transverse vibration of the car's body is established. The first two natural frequencies are obtained for the beams via the Galerkin method with both the trial and weight functions chosen as eigenfunctions of a stationary beam under the free boundary condition at both sides. The numerical results illustrate the relation of the first two natural frequencies with the changing speed of vehicle, the flexural stiffness of the car's body and the stiffness of the tires.
    2011, 33(2):  71-74.  doi:10.6052/1000-0879-lxysj2010-326
    Abstract ( 995 )   PDF (734KB) ( 424 )  
    In this paper, the sectional optimization with the lightest weight of the shell structure as the objective function is carried out by using two level optimization methods based on discrete variables and the style of bar group and the effect of different mesh densities on optimal results are mainly considered. In the course of the optimization procedure, integral stability constraints are shown to be good for practical engineering. For K6 type of single-layer shell structure with span of 50\,m and rise-span ratio of 1/5, 42 shell models with six different bar groups and seven different mesh densities were built and optimized. Finally, an new and better choice of bar group and mesh density is obtained.
    2011, 33(2):  75-79.  doi:10.6052/1000-0879-lxysj2010-088
    Abstract ( 1295 )   PDF (753KB) ( 962 )  
    This paper analyzes the loop arc in table tennis using fluid mechanics and theoretical mechanics, and Matlab is used to solve and simulate the arc. The results show that the rotation in table tennis obviously affects the ball's flying route, which is important for the judgment of fake action.
    2011, 33(2):  80-81.  doi:10.6052/1000-0879-lxysj2010-374
    Abstract ( 1112 )   PDF (515KB) ( 365 )  
    2011, 33(2):  82-83.  doi:10.6052/1000-0879-lxysj2010-427
    Abstract ( 1085 )   PDF (658KB) ( 744 )  
    By the stress analysis about pressure vessels, the characters of several structures in mechanics of materials are compared. The application of pressure vessels are brought forth and it could be a didactical supplement part for mechanics of materials
    2011, 33(2):  84-85.  doi:10.6052/1000-0879-lxysj2010-023
    Abstract ( 1090 )   PDF (656KB) ( 417 )  
    The derivation of the relationships between loads, shear forces, and bending moments in beams in current textbooks was not exact. Based on the definition of differential and the L'Hospital rule (or the mean value theorem of integrals), the complete demonstration of above-mentioned relationships was presented in this paper.
    2011, 33(2):  86-88.  doi:10.6052/1000-0879-lxysj2009-440
    Abstract ( 1077 )   PDF (746KB) ( 384 )  
    Building structure mechanical analysis of the structure are calculated based on the calculation diagram, how to establish the calculation diagram will effect calculation model and solution, this paper discusses the Concept of calculation diagram and Calculation model, the principle and the content of establish the calculation diagram .
    2011, 33(2):  89-90.  doi:10.6052/1000-0879-lxysj2009-446
    Abstract ( 2511 )   PDF (295KB) ( 500 )  
    The end displacements or slopes of stepped cantilever beams can be conveniently obtained by making use of the inverse ratio relationship between flexural rigidity and displacement or slope. It’s a independent superposition method.
    2011, 33(2):  93-95.  doi:10.6052/1000-0879-lxysj2010-010
    Abstract ( 1753 )   PDF (615KB) ( 977 )  
    In the existing structural mechanics textbook, the expression of virtual work principle in general can be divided into four categories: Virtual work principle is one type of sufficiency and necessity. It only proves necessity part. It only necessity. It has two applications - virtual displacement principle and virtual force principle. Virtual work principle only is the proposition of necessity, virtual work principle and virtual displacement principle and virtual force principle is the similarities and differences. In the recently published in the "11th Five " plan textbooks, virtual work principle still is part of sufficiency and necessity. Therefor we give the correct exposition and certification of this principle to indicate that is needs distinction for virtual work principle and virtual displacement principle, we also elaborate on the similarities and differences between them.
    2011, 33(2):  100-101.  doi:10.6052/1000-0879-lxysj2011-116
    Abstract ( 1321 )   PDF (208KB) ( 351 )  
    2011, 33(2):  101-102.  doi:10.6052/1000-0879-lxysj2011-115
    Abstract ( 1551 )   PDF (176KB) ( 442 )  
    2011, 33(2):  102-103.  doi:10.6052/1000-0879-lxysj2011-114
    Abstract ( 1235 )   PDF (459KB) ( 377 )  
    2011, 33(2):  103-104.  doi:10.6052/1000-0879-lxysj2011-121
    Abstract ( 1359 )   PDF (692KB) ( 470 )  
    2011, 33(2):  108-110.  doi:10.6052/1000-0879-lxysj2011-128
    Abstract ( 1353 )   PDF (2006KB) ( 448 )  
    2011, 33(2):  111-112.  doi:10.6052/1000-0879-lxysj2011-101
    Abstract ( 1190 )   PDF (635KB) ( 292 )  
    2011, 33(2):  112-113.  doi:10.6052/1000-0879-lxysj2010-470
    Abstract ( 2008 )   PDF (812KB) ( 715 )  
    This paper aims to disclose the secret of Xuankong Temple, which is suspending and seemingly dangerous but in fact absolutely safe. It analyzes the force and deformation of the statically indeterminate beam and gets the relationship between internal force of the column under the beam and the suspending length of the beam.
    2011, 33(2):  116-123.  doi:10.6052/1000-0879-lxysj2010-413
    Abstract ( 1577 )   PDF (1940KB) ( 559 )  
    The 2nd Chinese Deep-Space Trajectory Design Competition is hosted by the Chinese society of theoretical and applied mechanics, the general establishment of space science and application, the Chinese academy of sciences, and the national key laboratory of astronautic dynamics, the China satellite measuring and control center in Xi’an. The competition notice is announced on Jan.1 2010, and we received more than 30 teams for registration. On Mar. 25 2010, the competition problem is disclosed, and the design solution submission is due on May 15 2010. The background of the design problem is multi-task and multi-target deep-space exploration – a spacecraft carrying a lander is to flyby multiple near-earth small bodies and release the lander at a proper date such that the lander can fly to Mars. Finally, we received 15 solutions designed by 15 different teams, and 12 solutions are deemed correct and the ranking of all these solutions is made public. The championship team is from the School of Aerospace, Tsinghua University, and the second and third places are awarded to the teams from the Department of Astronautics and Material Engineering, National University of Defense Technology and the Center for Space Science and Application, the Chinese Academy of Science, respectively. The other teams, such as the Department of Astronomy, Nanjing University and the Purple Mountain Observatory etc, are awarded victory prizes. This summary is to briefly present the competition problem, evaluation standard, design solutions by the 12 teams, and lessons learned from the competition.