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08 February 2009, Volume 31 Issue 1
Application study
2009, 31(1):  52-56.  doi:10.6052/1000-0992-2007-207
Abstract ( 1146 )   PDF (776KB) ( 574 )
This paper derives the formulas for stresses and displacements in a compound and orthotropic shaft and analyzes the stresses and displacements in a compound shaft with two floor concrete liners and a mid-aerated plastic board. If the circumferential elastic modulus is less than the radial elastic modulus of a shaft liner, the maximum shear stress and the radial displacement in an inner liner increase rapidly with the decrease of the circumferential elastic modulus. Consequently, if the shaft is designed based on isotropic calculation, there will be some safety problems. These conclusions have been proved by engineering applications and field observations. The new design methods for the compound shaft are put forward. The reliable calculation formulas and the new consolidation theory are obtained for designing a compound shaft built with the freezing method.
2009, 31(1):  57-60.  doi:10.6052/1000-0879-2007-493
Abstract ( 1507 )   PDF (1129KB) ( 777 )
The effective torsional rigidity is equal to the geometric mean of two principal bending rigidities, as is characteristic of the orthotropic plates with smooth up and down surfaces. According to that characteristic and based on the differential equation of the deformed surface of the orthotropic plate, with one principal direction size fixed, changing another principal direction size linearly, maintaining elasticity coefficient the same as in the first principal direction and Poisson ratio equal to the geometric mean of two principal Poisson ratios, the original orthogonal plate is equivalent to an isotropic plate. Results obtained show that the deflections of the equivalent isotropic plate are the same as the deflections of the original orthotropic plate at the corresponding points, the forces of the correspondent points have simple relations. The method of the paper will be easy to use for engineers and technicians.
2009, 31(1):  61-65.  doi:10.6052/1000-0992-2007-565
Abstract ( 988 )   PDF (1196KB) ( 680 )
Multilayer digital elevation model is simple and effective in building a three-dimensional stratigraphic model. Based on the borehole data of a coal field, different geological layers are identified. The method for gathering and processing the data of the cross-layer and absent-layer is proposed. The elevation contours of the different layers are obtained with the processed elevation data. The Kriging interpolation method is used to get the data of the strata for the three-dimensional stratigraphic model of the mining area. The profile diagrams are drawn from the built three-dimensional stratigraphic model and compared with that of the same sections by manual drawing. The results show that the former model is more reliable than the latter. Finally, the numerical simulation with finite element method is carried out by drawing data from the built three-dimensional stratigraphic model. The simulating results also show that they agree fairly well with the results obtained by geological survey and those gathered in coal mining process and can be used in coal mining design and tectonic prediction.
2009, 31(1):  20-23.  doi:10.6052/1000-0879-2007-597
Abstract ( 1034 )   PDF (686KB) ( 725 )
The translational and rotational dynamics of fibers suspended in a fluid medium are important in many different fields of modem technology. Jeffery derived an equation of motion for a single rigid ellipsoidal particle suspended in Newtonian fluids. Unfortunately, the analytical solutions of Jeffery equation could only be obtained in a simple planar shear flow and a planar elongational flow. The main difficulty in the numerical treatment of Jeffery equation is the singularity due to the term $\cot \theta$. In this paper, a co-rotational coordinate system is proposed, which can completely eliminates this singularity. The validity of the proposed scheme is shown by a comparison between numerical results and the analytical solution. New algorithm can easily be extended to simulate the dynamics of single fiber in complex flow fields.
Education Study
2009, 31(1):  83-85.  doi:10.6052/1000-0879-2008-021
Abstract ( 1151 )   PDF (450KB) ( 615 )
Application study
2009, 31(1):  16-19.  doi:10.6052/1000-0879-2008-026
Abstract ( 1137 )   PDF (741KB) ( 695 )
According to different available conditions, periodic cruise conditions of a hypersonic vehicle are determined by Newton-Raphson's iteration and Genetic Algorithm. The attraction region of fixed points of the periodic cruise is obtained by a cell-to-cell mapping method. The results indicate that the hypersonic vehicle can cruise periodically under certain conditions and initial values of the periodic cruise can be selected in a wide range.
2009, 31(1):  28-33.  doi:10.6052/1000-0879-2008-067
Abstract ( 1321 )   PDF (1512KB) ( 548 )
Numerical model of the wire with defect in the process of multi-drawing is built based on finite element method and fracture mechanics, and the effects of parameters (draft reduction, die angle and cracking) on the wire drawing are analyzed. It is concluded that the effective method to reduce the rate of broken rods is: choose the best parameters in multi-drawing process about the draft reduction and die angle; control the length of crack by using nondestructive examination to improve the quality of the finished product. The results show that values of $J$-integral and COD increase with the increasing length of crack in the same die angle; the best condition diameter increases with the increasing die angle in the same length of crack; the best die angle is in the range of 4$^\circ \sim 8^\circ$. The above findings can be used to improve wire drawing technique and the quality of wire.
2009, 31(1):  66-69.  doi:10.6052/1000-0879-2008-073
Abstract ( 906 )   PDF (802KB) ( 782 )
The load analysis of bulldozer includes the external load, and each component load of work equipment under the external load. The structure of bulldozer's six-oriented shovel is simplified, and the load analysis on its model is carried out. At the same time, the oil jar force, the reaction load of pushing peak frame and the reaction load of each joint point are analyzed. The work not only provides a basis for framework analysis of work device, but also for rigidity tolerance analysis.
2009, 31(1):  34-38.  doi:10.6052/1000-0879-2008-105
Abstract ( 1322 )   PDF (962KB) ( 657 )
Considering the elasticity of bearing and vibration isolating pad, this paper sets up a nonlinear rubbing model for asymmetric support rotor experimental table systems. Based on speed parameters for the bifurcation, by using the numerical integration method, the system response is obtained, and the effects of the vibration isolating pad stiffness on the system bifurcation and chaos are analyzed, through Poincar\'{e} map and auto-correlation function method. The results of system responses show that the effects are significant and the routes to chaos are mainly intermittence chaos and period doubling bifurcation. The simulation results agree well with the experimental results.
2009, 31(1):  39-42.  doi:10.6052/1000-0879-2008-114
Abstract ( 1086 )   PDF (570KB) ( 639 )
The circular underground continuous wall is studied in the paper. The continuous wall is simplified as an elastic thin cylinder. A unit thickness ring is considered as a plane-strain problem. With polar coordinate system the analytic solution is obtained. The calculated values agree well with the actual test values.
Education Study
2009, 31(1):  74-75.  doi:10.6052/1000-0879-2008-120
Abstract ( 1143 )   PDF (614KB) ( 837 )
This paper gives some reviews on the subject system in the textbooks titled "Engineering Mechanics" employed in China, from which some problems existed in the books are presented. It is expacted that the pullulation of excellent and innovative young researchers in China is propoted by the higher education through the advancement of the textbook.
Application study
2009, 31(1):  47-51.  doi:10.6052/1000-0879-2008-146
Abstract ( 1270 )   PDF (795KB) ( 640 )
This paper investigates the far field solution of SH-wave scattered by an interface cylindrical inclusion with a disconnected curve near bi-media material by use of Green's function method and complex function method. First, along the interface of bi-media material, we divide the space into up and down parts. In the down part, a suitable Green's function for the present problem is constructed, which is the essential solution of the displacement field due to the out-plane harmonic line source load at the horizontal surface. Then in the up part, a suitable Green's function is used. Thereby the semicircular disconnected curve can be constructed when the two parts are bonded to be continuous in the interface impacted by SH-wave. And the expressions of the displacement field and the stress field are obtained and the integral equation is set up under this situation. The displacement mode of scattered wave at far field and scattering cross-section is obtained. Numerical results are illustrated and the influence of different parameters at far field is discussed. It is found that the displacement and scattering cross-section can be enlarged by the disconnected curve.
2009, 31(1):  43-46.  doi:10.6052/1000-0879-2008-154
Abstract ( 1382 )   PDF (653KB) ( 824 )
The signal parameter of rock's acoustic emission is of fractal nature. The signal parameters of acoustic emission are obtained in uniaxial compression experiment about griotte and red sandstone at different stress levels. By introducing relevant dimensions functions, the dimension number of signal parameters of rock's acoustic emission in time domain at different stress levels is computed and the relevant dimensions are obtained as a function of stress levels. The results show that the process of AE has less obvious fractal feature with $m$ increasing under same stress level. Under different stress levels, the dimension number is different, the precess of AE have different degree of self-similar and fractal nature. Fractal characteristics of the process parameter of rock's acoustic emission has a certain dimension scope.
2009, 31(1):  24-27.  doi:10.6052/1000-0879-2008-194
Abstract ( 1376 )   PDF (794KB) ( 679 )
A numerical study on mobile bed hydraulics of roll waves with sediment transport and morphological evolution is presented. The governing equations of the model comprise the shallow water hydrodynamics equations closed with the Manning formulation for the boundary resistance. The second-order Total-Variation-Diminishing version of the Weighted-Average-Flux method, along with the HLLC approximate Reimann Solver, is used to solve the governing equations, which can properly capture shock waves and deal with irregular boundaries. Brock's laboratory experiments of roll waves in a fixed-bed channel are reproduced. Numerical simulations show the development and propagation of roll waves over mobile-bed. It is shown that the morphological evolution has a great effect on the roll waves' dynamic characteristics.
Around the mechanics
2009, 31(1):  96-97.  doi:10.6052/1000-0879-2008-270
Abstract ( 1211 )   PDF (855KB) ( 794 )
Different Horologes like sundial, machine clock, quartz clock and atomic clock are analyzed. Evolution of horologes based on from natural phenomena, mechanics, to high frequency vibration is elaborated. The escapement mechanism in Chinese chronometer, a transition between clocks based on the first and second principle, is discussed as a technical preparation for the invention of machine clock.
Review
2009, 31(1):  1-7.  doi:10.6052/1000-0879-2008-412
Abstract ( 1636 )   PDF (2408KB) ( 890 )
This paper introduces the basic principles and applications of electro-spraying and spinning and some important physical mechanisms in them, and reviews the studies on instability of electrified jets in their processes.
2009, 31(1):  8-15.  doi:10.6052/1000-0879-2008-510
Abstract ( 1042 )   PDF (1646KB) ( 519 )
Physical and performance characteristics of power sources including batteries, fuel cells and solar cells from manufacturers' data are collated and a database is built using advanced selection software. A method is subsequently developed for selecting portable power sources based on matching their physical and performance characteristics, such as weight, volume, capacity, voltage and cost, to the requirements of a given task. This allows the construction of performance maps in terms of voltage, maximum current, mass energy density, volume energy density and cost, with a systematic comparison of different kinds of power sources. The use of the method as a preliminary design tool is demonstrated in a case study on the selection of batteries for mobile phones.