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08 August 2009, Volume 31 Issue 4
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    Application study
    2009, 31(4):  59-63.  doi:10.6052/1000-0879-2008-058
    Abstract ( 1408 )   PDF (1070KB) ( 716 )  
    By the classical method of strength of material, the deformation of carbon-tube nanosprings (CTNS), including cylindrical, conical and looped ones, under axial-compression, is analyzed, and a general formula for stiffness of CTNSs is obtained. In order to validate the formula, the stiffness for a cylindrical CTNS is calculated and compared with the corresponding experimental and FE (Finite element) results. It is shown that the present value of the stiffness is very close to both experimental and FE ones.
    2009, 31(4):  24-27.  doi:10.6052/1000-0879-2008-200
    Abstract ( 1076 )   PDF (664KB) ( 569 )  
    The growth process of industrial 8 inch single crystals is simulated by FLUTRAP(fluid flow and transport phenomena program), which is based on non-orthogonal grid and finite-volume method. The results show that the flow field inside the crucible and the pulling rate are oscillating during the growth processes. The pulling rate is fluctuating with a period of about 2 minutes. The fluctuation amplitude of the pulling rate could be reduced by applying a cusp magnetic field.
    2009, 31(4):  64-68.  doi:10.6052/1000-0879-2008-219
    Abstract ( 1239 )   PDF (1067KB) ( 696 )  
    Experiments were conducted to investigate the maximum static friction force on a dragged probing rod in the uniform granular pile contained in a cylindrical vessel. It is observed that the force obtained is greater than that of Jassen Model, when the gap between the wall and the rod is smaller than 50 times of the spheres diameter. When the diameter of vessel is small, the force is related to the shape of the detecting rod. This strange behavior is due to the fact that the scattered granular can not be approximated as a continuum medium when the diameter (D) is small. The force chain in the granular pile plays a major role.
    2009, 31(4):  54-58.  doi:10.6052/1000-0879-2008-241
    Abstract ( 1528 )   PDF (1276KB) ( 825 )  
    In order to improve the shock resistance of shipboard equipment as well as to increase the testing capability of the shock testing system, a novel high-energy hydraulically-actuated anti-shock testing system is proposed. The key techniques to store and release high energy instantly, and to avoid second impacting during shock tests are related with a novel velocity generator. A nonlinear dynamic model of this system is established, which can produce the required shock pulse in a given time duration. Then a numerical simulation about the system is carried out to evaluate the prospective capability of the shock testing machine under different shock velocity inputs. The simulation results show that the shock testing machine proposed in this paper can produce nearly the same shock acceleration waveform as opecified by the new shock resistance standard BV043/85 and MIL-S-901D. Moreover, this shock testing machine can be adjusted conveniently to test different types of equipment and be extended easily to satisfy more severe shock standard and heavier equipment.
    Education Study
    2009, 31(4):  79-80.  doi:10.6052/1000-0879-2008-362
    Abstract ( 1497 )   PDF (451KB) ( 728 )  
    Base on the linear relationship of curvature and moment, adding the moment of unknown reactions to the moment of section of beam ,both the slops and the deflection equations can be obtained by integration, in witch the constants of integration and unknown reactions can be evaluated from boundary conditions and continuity conditions, the slops and deflection equations and equations are also obtained. The working expands the scope of application of traditional integration method. Teaching practice has showed that using integration to calculate the deformation of statically indeterminate beam is good in helping students to learn boundary value problems of solid mechanics.
    Application study
    2009, 31(4):  69-70.  doi:10.6052/1000-0879-2008-365
    Abstract ( 882 )   PDF (387KB) ( 666 )  
    A mechanical shaft model of human body is established to calculate the angular speed and translational speed of the body upon its first collision with a vehicle. The possible moving states of the body collapsing onto the hood at different crashing speeds are then discussed, which is found to agree with the actual circumstances. These results can be used for traffic accident investigations and identifications.
    Review
    2009, 31(4):  12-23.  doi:10.6052/1000-0879-2008-384
    Abstract ( 1329 )   PDF (3820KB) ( 697 )  
    This paper presents an overview of the theoretical and experimental investigations on the liquid flow in a liquid-filled container, including studies on inertial wave and its breaking-down, secondary flow, spin-up flow, critical layer, natural sloshing, large amplitude sloshing, wave breaking, drop ejection, bubble entrainment. As far as cylindrical containers go, the liquid-filled containers can be rotating and non-rotating. Some brief outlines on corresponding numerical methods and their applications are given. Furthermore, from the point of view of systems dynamic simulation, related problems of coupling systems dynamics of liquid-filled containers are discussed.
    Application study
    2009, 31(4):  49-53.  doi:10.6052/1000-0879-2008-419
    Abstract ( 1065 )   PDF (849KB) ( 642 )  
    In order to analyze the dynamic characteristics of an antenna pedestal drive system, a new dynamic model called a rigid-flexible coupled model is proposed. In the new model, the deformation of spinnings and the supporting of bearings are considered. Gear tooth mesh is also taken into account based on an advanced contact model. The traditional multi-body transmission system model is improved, where the deformation of spinnings and the supporting of bearings are neglected. The simulation results reflect the dynamic characteristics of the antenna pedestal drive system, consistent with the theoretical analysis. The dynamic model and results may provide a guidance to engineering design and capability checkout.
    2009, 31(4):  32-36.  doi:10.6052/1000-0879-2008-435
    Abstract ( 1651 )   PDF (1429KB) ( 779 )  
    The numerical difficulties in dealing with dynamic stiffness matrices for continuous Bernoulli-Euler beam and continuous Timoshenko beam are analyzed. The dynamic stiffness matrices of these two beam elements are obtained from their flexural vibration governing partial differential equations. The independent variables of hyperbolic functions in these dynamic stiffness matrices are expressed in several variables. A method for estimating the reasonable lengths of continuous beams is proposed. A cantilever beam is used as a numerical example. It is modeled with a single continuous Bernoulli-Euler beam element and a single continuous Timoshenko beam element, respectively. Dynamic responses of this beam are analyzed. It is found that when the reasonable sizes of continuous beams are adopted, the required natural frequencies of engineering structures may be obtained without numerical problems in dealing with dynamic stiffness matrices for continuous beams. This research may provide a theoretical reference for constructing engineering models by using continuous beam elements.
    2009, 31(4):  41-44.  doi:10.6052/1000-0879-2008-500
    Abstract ( 1306 )   PDF (666KB) ( 598 )  
    A damage detection method for truss structures based on an improved residual force vector method is proposed. The stiffness connectivity matrix of the truss structures is obtained by the sensitivity analysis, and the stiffness matrix perturbation of the damaged structure can be expanded to a diagonal matrix by the stiffness connectivity matrix, then with its substitution into the residual force vector equation, a new residual force vector equation expressed by the stiffness connectivity matrix is obtained, which can be solved directly, so the stiffness perturbation of truss bars is obtained, therefore, the damaged bars and the damage extents can be detected. Because the complete modal shapes are difficult to get by measurement, the complete modal shapes are obtained by modal expansion. At last, a numerical example of a truss structure is given, the effectiveness of the proposed method is verified.
    2009, 31(4):  37-40.  doi:10.6052/1000-0879-2008-523
    Abstract ( 1253 )   PDF (1040KB) ( 555 )  
    In the process of laser aided direct metal deposition (DMD), the control of thermal-induced residual stress is very difficult, because the stress is affected by many parameters including geometrical dimensions, material properties and process parameters. In this paper, dimensional analysis is employed to extract key dimensionless parameters of geometry, heat transfer and thermal deformation. In addition, a 3D transient FEA model is proposed to study the effects of these key dimensionless parameters on the residual stress. It is shown that the residual stress can be controlled by employing materials with relatively small thermal expansion coefficient or small yield stress. Furthermore, the residual stress can be reduced by decreasing heat loss, increasing laser power, especially, by increasing preheat temperature.
    2009, 31(4):  45-48.  doi:10.6052/1000-0879-2008-524
    Abstract ( 1223 )   PDF (637KB) ( 770 )  
    In order to reduce the flexure resistance of a belt conveyor, based on the energy theory of viscoelastic materials under dynamic loading, a theoretical analysis of mechanism of energy consumption of the belt flexure is carried out when the conveyor is running. A approximate formula for the flexure resistance coefficient of the conveyor belt is derived and its validity is checked by experiment. Based on it, the effects of various factors on the flexure resistance are studied by means of the Matlab software with specific technical parameters of the conveyor. The results show that this formula can correctly reflect the effects of various factors on the flexure resistance, and it is primarily the viscoelasticity of the belt that is responsible for the flexure resistance. The rational viscoelastic parameters of a belt can be obtained by using selected mating rubber, so the flexure resistance can be reduced, with some adjustment in structural parameters of the belt and the conveyor.
    Around the mechanics
    2009, 31(4):  93-97.  doi:10.6052/1000-0879-2008-540
    Abstract ( 1242 )   PDF (961KB) ( 608 )  
    Since Aristotle, many well-known scientists theoreticians have researched the falling movement of dynamics but only Galileo finally made a correct conclusion and inspired a new era for modern dynamics. The article, by interpreting the works by Aristotle, Galileo and others, and by analysis and contrast, looks at the deepening process of human research in falling movement and shows that scientific development not only needs the accumulation of knowledge and innovation but also advanced thoughts and scientific methods.
    2009, 31(4):  90-92.  doi:10.6052/1000-0879-2009-055
    Abstract ( 1256 )   PDF (717KB) ( 765 )  
    Analog of human thinking, which is an important way of thinking of innovation in scientific research, is widely used. Through the process of creating quantum mechanics, especially for de Broglie, Schrodinger, Dirac, such as physicist Born in quantum mechanics process of the establishment and perfection of the form, they used analog methods of analysis and research on analog thinking in the scientific innovation in a significant role. To play analog thinking modern educational value to this form of transplantation to innovative thinking in the classroom teaching will be cultivate innovative talents to have a positive impact.
    Review
    2009, 31(4):  1-11.  doi:10.6052/1000-0879-2009-140
    Abstract ( 1327 )   PDF (3094KB) ( 831 )  
    As we know, the regular arterial flow is in the laminar flow regime. The blood flow properties, particularly, the shear stresses along the blood vessel, and the sites where atherosclerosis develops, have attracted tremendous researches in recent decades. It has been well known that the oscillating and low shear stresses play an important role in the development of vascular lesions. Unsteady irregular stress distributions are likely to prevail at the curved and bifurcated vessels with side branches, where, due to complicated geometries, blood flows always contain flow separation or secondary motions difficult to be simulated and understood in fluid mechanics. In this paper, the past studies on the transient multi-dimensional blood flows in arterial stenosis or in arterial geometries relevant in the conditions of atherosclerosis are reviewed. We also make suggestions for the future possible studies of circulatory vascular flows and wish to provide some food for though for further designs of bio-medical devices.
    Application study
    2009, 31(4):  28-31.  doi:10.6052/1000-0879-2009-260
    Abstract ( 1146 )   PDF (563KB) ( 519 )  
    The transfer function matrix of a beam with damping is derived by means of spectral element method (SEM). The analytical solution for a one-dimensional beam is applied in the form of shape functions in continuous form. Compared to the finite element method, the spectral element method can be used to obtain high precision with less degrees of freedom and elements. The proposed transfer function is represented by the transcendental function with geometrical and physical parameters of the beam, and is different from the traditional transfer function, represented by modal parameters. A new method to identify physical parameters of a beam structures based on the genetic algorithm is proposed. Two numerical examples of cantilever beams with varying cross section are given to show the effectiveness of the proposed method.