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Acta Mechanica Sinica
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10 February 2007, Volume 29 Issue 1
DAMAGE IDENTIFICATION AND DIAGNOSIS OF EXISTING STEEL TRUSS BRIDGE
2007, 29(1): 50-52. doi:
Based on the theory of structural dynamics, the damage identification and diagnosis of existing steel truss bridges is studied. With the natural frequency as the characteristic parameter and using method of BP neural network and the MATLAB, the damage identification and diagnosis is analysed and a complete flow chart for the bridge damage identification and diagnose is proposed. With the method, the damage process of a steel truss bridge is numerically stimulated.
DETERMINATION OF PARAMETERS FOR THE CLIPPED GAUSS PROBABILITY DENSITY FUNCTION
2007, 29(1): 64-68. doi:
This paper presents a method to determine the unknown parameters for the clipped Gauss probability density function, used to describe the turbulent fluctuation of a scalar. The algebraic equations for the unknown parameters are properly expressed in a form convenient to solution. The Newton method, Newton downhill method, and damped Newton method are jointly used in the iterative solution for the equations. The initial values for the iteration are chosen properly. The unknown parameters are obtained as different mean values and mean squares values from fluctuating values of the scalar.
THE CRACKING IN THE FOUNDATION OF TIANDUO GARDEN BUILDING
2007, 29(1): 46-49. doi:
This paper studies the initiation of cracks in the large foundation mat of Tianduo Garden Building. With ANSYS finite method software, the authors simulated the temperature field in the construction period, and calculated the stress field and simulated the cracking of the concrete structure, with a model of cracking, crushing and failure for the concrete material, and distributed cracks. Some conclusions were obtained.
STUDIES ON THE MECHANISM OF WATER JET-ASSISTED DRILLING TECHNOLOGY(1)--CAVITATION AND EROSION
2007, 29(1): 29-33. doi:
The dynamics of a single high-speed bubble impacting with a solid target are simulated by MSC.Dytran. The relations between the damage depth or damage width and the initial pressure, velocity, the incident angle of bubbles and drips, and the thickness of target, are presented in curves, and the physical mechanism is discussed. The theory of water jet impacting rock is also discussed.
SCALING ANALYSIS OF UNSTEADY NATURAL CONVECTION FLOW OF A FLUID WITH LOW PRANDTL NUMBER
2007, 29(1): 23-28. doi:
A natural convection flow will be formed adjacent to a vertical plane immersed in a quiescent homogeneous or linearly-stratified fluid after the plate is heated with a uniform thermal flux. The flow will undergo a start-up stage, followed by a transitional stage, before reaching a steady state. The transient behavior of the flow is parameterized by the plate temperature, the thermal boundary-layer thickness, the inner and outer velocity boundary-layer thicknesses, the maximum vertical velocity within the boundary layer, and the time for the boundary layer to reach the steady state. In this paper, a scaling analysis is used to obtain scaling laws for all the parameters at various development stages of unsteady natural convection boundary-layer flow in homogeneous and linearly-stratified fluids with low Prandtl number ($Pr<1$) along a vertical plate heated with a uniform thermal flux.
CABLE-PULLEY ELEMENT IN FINITE ELEMENT ANALYSIS OF CABLEWAY ERECTION SYSTEM
2007, 29(1): 58-63. doi:
In order to model the pulley in structures, a new element is developed for the pulley and its supported cable segment, with the radius of pulley taken into consideration. This new three-node element, which is called the pulley element, takes the center of the pulley as the middle node, and the cable ends at each side of the pulley as the other two nodes. The new element simplifies computations by automatically adjusting the cable on each side of the pulley to maintain equilibrium. The derivation is based on the basic principles of finite element analysis, and the relation of the forces in the element at the equilibrium state is used. The related algorithms are described, and examples confirm their validity. The new element can be incorporated into conventional finite element analysis schemes. The final example shows the effectiveness and simplicity in of using the new element structural analysis of cable structures with pulleys.
THE HARMONIC VIBRATION OF INFINITE PLATE ON TRANSVERSELY ISOTROPIC SATURATED SOIL GROUND
2007, 29(1): 42-45. doi:
This paper studies the dynamic response of an infinite rectangular plate on transversely isotropic saturated soil ground under a harmonic excitation. Based on the general solutions of the 3-d wave motion equations in rectangular coordinates for transversely isotropic saturated soil media presented by the author, the equation for dynamic interaction between the saturated soils and plate is established and solved by using the technique of double Fourier transform. Integral solutions of displacements for the plate excited by a harmonic source are presented. The calculation results indicate an obvious difference of the vibration properties of the infinite plate based on the model of isotropic saturated soils and that based on the transversely isotropic saturated soils.
THE RELATION BETWEEN SEEPAGE VOLUME AND ROCK COVER THICKNESS IN SUBSEA TUNNEL
2007, 29(1): 34-37. doi:
In the subsea tunnel construction, the seepage volume and the minimum rock cover are most important in the drainage design of the tunnel, and in the tunnel route selection. With the hydro-geological model of half infinite space, the seepage water volume is computed both by analytical method and numerical simulation, and the relation between seepage volume and rock cover thickness is analyzed. According to the rock cover thickness determined by the minimum seepage volume, a linear relation between sea depth and rock cover thickness is obtained.
A HIGH PRECISION METHOD TO COMPUTE THE ALE GRID VELOCITY IN LIQUID SLOSHING SIMULATION
2007, 29(1): 14-16. doi:
The computational precision is important for ALE description in liquid sloshing simulation to calculate the grid velocity. On the free surface, the grid velocity is corrected by using the curvature there to improve its description precision. Piecewise smooth functions are used to calculate the grid velocity inside, they are better than a linear relationship applied before for the subdivision of the high quality grid. A 2D problem excited in a rectangular tank is computed and results are compared with experiment, as in the reference. The advantage of using high precision grid velocity is obvious.
EXPERIMENT AND INVERSE ANALYSIS FOR MECHANICAL PROPERTIES OF LARGE DIAMETER PRESTRESSED CONCRETE TUBULAR PILE AT SEAPORT
2007, 29(1): 38-41. doi:
The deformation of the large diameter prestressed concrete tubular pile subjected to external forces is tested on the spot by applying fiber grating sensing technology. Based on test results, the related mechanical parameters of the large diameter prestressed concrete tubular pile were obtained by an inverse analysis. At the same time, the epoxide resin at the joint gap has little effect on the mechanical properties of the large diameter prestressed concrete tubular pile. The reasonable mechanical parameters obtained by the inverse analysis provide useful data for stress analysis and health monitoring of the large diameter prestressed concrete tubular pile under various engineering conditions.
A SIMPLIFIED MODEL FOR LONG TUBULAR PENETRATION INTO OBLIQUE FINITE HOMOGENEOUS TARGET
2007, 29(1): 53-57. doi:
The experiments of long tubular penetration into oblique homogeneous target are carried out. On basis of the penetration mechanism, a simplified model for the long tubular penetration into oblique finite homogeneous target is established. The patterns of the penetration are described. The motions of the long tube and the external forces are analyzed. The cutaway views of the crater are much similar to those of the long rod, but with two obvious ``horns'' in the back and front of the target, respectively. The variations of the residual velocity with the initial velocity are obtained. The theoretical results agree with experimental data well in the limit velocity, which validates the model established for the penetration course.
MODELLING AND MOTION ANALYSIS OF SPACE ELECTRODYNAMIC TETHERED SYSTEMS
2007, 29(1): 17-22. doi:
To study the kinetic characteristics, the motion of the LEO electrodynamic tethered (EDT) propulsion system is modeled, in this paper, from the angle of mechanics and electrodynamics. The numerical solutions under various initial conditions are obtained, based on which the motion of space EDT system is discussed. The effects of Ampere force, the tether's deformation and deflexion, on the orbital plane, as well as on the orbital altitude, are studied. In addition, the efficiency of space EDT system and the effect of the earth's rotation are evaluated.
MODERN THEORY FOR WIND RESISTANT BRIDGE AND ITS APPLICATION
2007, 29(1): 1-13. doi:
This paper presents the theory for wind resistant bridge developed under the support of Natural Science Foundation of China in the 1996-2000 key project (No. 59895410), and the experience gained from its engineering application to long-span bridges in China. Main concerns are placed on the wind environment around the bridge site and its simulation, the methodology of wind-induced problems about bridges, and aerodynamic design and evaluation of long-span bridges. One can see the development in theory and practice about wind resistant bridges in China.
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