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08 October 2008, Volume 30 Issue 5
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    Application study
    2008, 30(5):  90-92.  doi:10.6052/1000-0992-2006-008
    Abstract ( 917 )   PDF (784KB) ( 554 )  
    It is very difficult to get rid of the rubbles in the barometer tube, as the diameter of the barometer tube used for monitoring the dam base water pressure is very small. Through various attempts, a very efficient way is found, which is proved workable in practice. Simulated experiments show its clear dynamical states. By analyzing the pellet's dynamical states, it is shown that the process of the pellet's discharge can be clearly explained.
    2008, 30(5):  86-89.  doi:10.6052/1000-0992-2006-186
    Abstract ( 1046 )   PDF (889KB) ( 727 )  
    Combined with wind tunnel test, the numerical simulation was used to analyze the wind-induced pressure on six low rise and hip roofed buildings, with Reynolds-averaged equations and realizable $k$-$\varepsilon $ turbulence model. The computational domain was divided into tetrahedral elements of good topology. The flow field was numerically discretized to be solved by FLUENT, a famous CFD software. Good agreement was obtained between the computed results and wind-tunnel test results of the single house, and the variation trend of wind pressures on the surface of low-rise building under interference of the other house is discussed.
    2008, 30(5):  70-74.  doi:10.6052/1000-0992-2007-215
    Abstract ( 993 )   PDF (771KB) ( 563 )  
    For heavy rail rolling by universal mill, a simplified 3-dimention theoretical model is built firstly. The kinematically admissible velocity fields of the web, head and base of rail are determined, respectively, and the corresponding strain rate fields and the intensity of shear strain rate are also obtained. Then the plastic deformation power, the friction powers and the powers consumed on the velocity discontinuity surface are obtained. According to the upper-bound principle, the roll force of horizontal roll and two vertical rolls can be obtained. Moreover, the roll force can also be calculated by the formula of slab rolling under the same deformation condition. The roll force from the formula of slab rolling differs greatly from the field data, and the roll force from upper-bound method is somewhat greater than the field data but in general the difference is less than 13 percent. So, it is more reliable to preset and optimize the parameters of rolling technology according to the upper-bound method.
    2008, 30(5):  40-44.  doi:10.6052/1000-0992-2007-267
    Abstract ( 1324 )   PDF (791KB) ( 538 )  
    Rigid finite elements are used to construct a kinematically admissible velocity field. The objective function for determination of earth pressure contains some unknowns, subject to a set of linear constraints derived from the energy-work balance equation, the Mohr-Coulomb failure (yield) criterion, the associated flow rule and a number of boundary conditions. The objective function with constraints leads to a linear programming problem, which can be solved by an interior point algorithm. A classical earth pressure calculation case shows that the presented method is of valid.
    2008, 30(5):  37-39.  doi:10.6052/1000-0992-2007-292
    Abstract ( 897 )   PDF (3362KB) ( 592 )  
    According to the in-situ measurement of damage shape of impacted object and the theory of direct back analysis, the magnitude of the impact load and the dynamic tensile strength for laminar rock plank are identified by taking the similitude-degree between the measured damage shape and the numerical simulated shape as the target function. The analysis method is effective for some ancient architectures, especially when the initial information and measurement data, are scare.
    Review
    2008, 30(5):  9-15.  doi:10.6052/1000-0992-2007-297
    Abstract ( 1318 )   PDF (1571KB) ( 753 )  
    Due to the limit of time and expense, small samples are always used in fatigue experiments of aeronautic structures. The recent studies on fatigue life of small sample experiments based on the historical data are reviewed in this paper. The definition of small sample is given and the methods developed in the recent decade are classified and discussed in cluding distribution determination, parameters estimation and goodness-of-fit test according to the purposes of the researches. Some possible and prospective future research directions are discussed.
    Application study
    2008, 30(5):  32-36.  doi:10.6052/1000-0992-2007-322
    Abstract ( 961 )   PDF (891KB) ( 514 )  
    Taking the structure system as a sandwich composite element, a calculation model is proposed, and the lateral displacement of the structure, shearing force and bending moment of the components are obtained according to deformation compatibility. The calculation analysis shows that shear force distribution of components is only related to with stiffness and width of components, and shear stress in upper internal composite slab is larger than that of lower slab; bending moment distribution coefficient of components decreases as $\lambda $ increases, and whole structure is strengthened, and when $\lambda $ is enough large, mechanical behavior of structure is similar to a cantilever member.
    2008, 30(5):  65-69.  doi:10.6052/1000-0992-2007-390
    Abstract ( 1102 )   PDF (881KB) ( 599 )  
    The stress concentration factor of K-joints subjected axial loads is analyzed using finite element method. 3D solid elements are used to model the entire structure, which is divided into several zones and the mesh of each zone is produced separately. Thereafter, the mesh of the entire structure is obtained by merging the meshes of all the zones. The general software package ABAQUS is used to analyze the stress concentration factor (SCF) along the weld of tubular K-joint subjected to axial compression loads. The effects of different parameters on the SCF of chord and brace of K-joints are investigated. Finally, the detailed effects of the geometrical parameters on the SCF and the place of the SCF of K-joints are obtained from parametric analysis.
    2008, 30(5):  28-31.  doi:10.6052/1000-0992-2007-391
    Abstract ( 883 )   PDF (677KB) ( 636 )  
    Double optimal design variables are reduced into a single optimal design variable, and the optimization design model of pre-stressed concrete filled square steel tubular column is established accordingly. By using penalty function method, the iteration formulas of optimal design variables are derived, and the calculation procedure of the double iterative method is given in this paper. The numerical example shows that it is simple in concept and convenient for solving cross-section optimization design problems of pre-stressed square steel pipe concrete columns, and it provides a better approach for nonlinear programming.
    2008, 30(5):  57-61.  doi:10.6052/1000-0992-2007-403
    Abstract ( 1067 )   PDF (795KB) ( 845 )  
    Based on the study on semi-active hydraulic suspension model of two-degrees of freedom with fuzzy controller, representing a quarter of a vehicle, a parameters-self-tuning fuzzy PID controller is designed for a half-car model of semi-active hydraulic suspension with four-degrees-of-freedom. PID parameters can be adjusted on-line according to the fuzzy control rules. The results of simulation by using MATLAB/Simulink show that, excited by sinusoid road input, pulse road input and analogous Grade C road input, the ride comfort of hydraulic semi-active suspension with fuzzy PID controller is better than that of passive suspension and hydraulic semi-active suspension with fuzzy controller. Parameters-self- tuning fuzzy PID controller enjoys better self-adaptation.
    2008, 30(5):  45-48.  doi:10.6052/1000-0992-2007-405
    Abstract ( 1286 )   PDF (724KB) ( 560 )  
    The stability of one dimensional standard SPH with a cubic B-spline kernel is analyzed by von Neumann stability analysis method, and the effect of perturbation wavelength on the stability of SPH is discussed. The results of theoretical analysis are verified by numerical SPH computations of a one dimensional elastic bar, in which different wavelength perturbation are applied on the SPH particles. The numerical test indicates that the SPH stability is closely related with the perturbation wavelength. The numerical stable domain shape is the same as that of theoretical analysis except an offset of the stable domain boundaries of the numerical test. The SPH method used in this paper is the most unstable at the shortest perturbation wavelength, and it can be stable in tension at other perturbation wavelengths.
    2008, 30(5):  62-64.  doi:10.6052/1000-0992-2007-419
    Abstract ( 1063 )   PDF (979KB) ( 734 )  
    According to the requirement of the pasty propellant rocket engine design and pasty propellant pipe flow experiment, a new type of pasty propellant supply system is proposed. This scheme uses variable frequency motors and frequency transformers as drive forces and screw/ nut, gearbox as drive components. The design can guarantee a accurate flow rate. The pipe flow experiment of HTPB was conducted with established supply platform. The flow rate and pressure drop were obtained. The experiment result was analyzed with Non-Newtonian flow theory. The viscosity data acquired from the results are consistent with those in literature. From the pipe flow experiment, it is concluded that the scheme of the new supply system is feasible and the parameters of the system are correct.
    2008, 30(5):  82-85.  doi:10.6052/1000-0879-2007-420
    Abstract ( 1323 )   PDF (737KB) ( 629 )  
    In this paper, by analyzing the order of magnitude, the flow process of the leaking LPG is simplified into three independent sub-processes, including the process of LPG sedimentation to floor; spreading to other room and diffusing to roof, then a simplified method for forecasting concentration distribution of indoor explosion gas is put forward. The feasibility and simplicity of this method are discussed by applying it to analyzing an actual LPG explosion hazard.
    2008, 30(5):  53-56.  doi:10.6052/1000-0992-2007-470
    Abstract ( 1651 )   PDF (720KB) ( 694 )  
    The study on the dome-roof tank shells with imperfections under the axial compressive and buckling loads shows that the buckling strength of fixed-roof tank shells should be checked during its design and construction stages as well as during the service stage. Based on the stability theory and the numerical analysis of critical buckling strength for cylindrical shell subjected to axially compressive loads, a checking computation method and its mathematical model are established, and then the formula for calculating the buckling loads are obtained by regression analysis. The stability of tanks of several typical sizes with initial geometric imperfections is also studied, and the buckling strength of the tank shells under axial compression is decreased with their volume and shell's increasing initial deflection.
    CALCULATION METHODS FOR ULTIMATE MOMENT CAPACITY OF SRC COLUMNS WITH T-SHAPED STEEL
    [中]王秋维 [英]WANG Qiu-Wei Qing-Xuan SHI
    2008, 30(5):  24-27.  doi:10.6052/1000-0992-2007-485
    Abstract ( 1332 )   PDF (720KB) ( 569 )  
    The calculation method for bearing capacity of concrete columns reinforced with I-shaped steel is modified for SRC columns reinforced with T-shaped steel and their mechanical properties and failure modes are analyzed. Combining with the current national codes, the calculation methods and formulas of ultimate moment capacity of this kind of columns are proposed and heights of the concrete pressured region in two situations are compared. The bearing capacity of one SRC column with T-shaped steel is checked using above formulas and the results agree well with the experimental data, and this numerical example shows that the suggested method has a good precision.
    2008, 30(5):  16-18.  doi:10.6052/1000-0879-2008-036
    Abstract ( 864 )   PDF (570KB) ( 652 )  
    Darcy formula is not valid for flows in low permeability reservoirs, due to the obvious non-linear characteristics of the flows. Based on the experiment data of low permeability core, a non-linear formula with two parameters is proposed in this paper. Combining with the Buckly-Leverett formula, non-linear displacement formula is obtained. From the solution of the displacement formula, is compared with the linear flow, it is seen that the displacement efficiency of non-linear flow is lower, the water cut is higher with the same $s_{\rm w}$, especially, and the pressure gradient is bigger, which means the higher injection/production pressure difference. So, smaller well distance and higher injection/production pressure difference are needed for effectively developing low permeability reservoirs.
    2008, 30(5):  75-78.  doi:10.6052/1000-0879-2008-061
    Abstract ( 1129 )   PDF (1836KB) ( 686 )  
    The ICM (independent continuous mapping) method as a topology optimization methods is used to design the trunnions in transformers. The formulae of the distributed load in the hole are derived. According to the FEM analysis and topological optimization results, two new structures of the trunnion are proposed. The numerical results show that the new structures can meet the requirements of strength and rigidity and the weight of the structures is reduced.
    2008, 30(5):  19-23.  doi:10.6052/1000-0879-2008-086
    Abstract ( 906 )   PDF (980KB) ( 659 )  
    The Hilbert spectra of frequency-time-amplitude can be obtained by HHT and be applied to dynamic analysis of the seismic signal. A quantitative index to evaluate strength of vibration effect by the use of the maximum energy (integral of the time-domain frequency density function) and the crest factor of earthquake wave are put forword, as a preliminary unified criterion of vibration effect, and the feasibility and reliability of the criterion are validated by several instances.
    Education Study
    2008, 30(5):  93-93.  doi:10.6052/1000-0879-2008-087
    Abstract ( 1387 )   PDF (297KB) ( 643 )  
    Review
    2008, 30(5):  1-8.  doi:10.6052/1000-0879-2008-094
    Abstract ( 1009 )   PDF (6083KB) ( 545 )  
    This paper discusses recent progresses of research on the generation of elastic turbulence and its influence on the efficiency of micro-mixing. Flows of elastic and inertial turbulence have similar characteristics, but their mechanisms are different. Inertial turbulence is motivated by Reynolds stress, while elastic turbulence is generated by elastic stress. In the case of micro flow, inertial forces are neglectable, so the mixing of Newtonian fluid is very difficult. In order to help mixing, one can add a very little amount of high molecular weight polymer into the fluid to form a viscoelastic fluid. The elastic turbulence resulted from this viscoelastic fluid can have an enormous effect on increasing the efficiency of mixing.
    Application study
    2008, 30(5):  79-81.  doi:10.6052/1000-0879-2008-095
    Abstract ( 968 )   PDF (542KB) ( 653 )  
    Based on hydraulic pressure theory,and combined with the post-grouting technique of hole pour piles, a calculation model on limiting bearing capacity of single pile is built and the calculation formula is presented. Compared with the experiment data, it's proved that the model and formula can be used for practice .
    Interesting mechanics story
    2008, 30(5):  112-112.  doi:10.6052/1000-0879-2008-220
    Abstract ( 1422 )   PDF (293KB) ( 782 )  
    The golden section 0.618 is a magic number, which has extensive applications in the domains of architecture, painting, sculpture, music, and various aspects of human's life. In this paper some examples of the golden section in mechanics are discussed.
    Around the mechanics
    2008, 30(5):  115-115.  doi:10.6052/1000-0879-2008-274
    Abstract ( 1432 )  
    Interesting mechanics story
    2008, 30(5):  110-111.  doi:10.6052/1000-0879-2008-432
    Abstract ( 1298 )   PDF (1156KB) ( 600 )