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10 August 2005, Volume 27 Issue 4
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    Education Study
    2005, 27(4):  0-0.  doi:10.6052/1000-0992-2004-144
    Abstract ( 1173 )   PDF (608KB) ( 692 )  
    The similarity formulae of model testing in advancing shield tunnels are proposed based on the Goodierian theory. Many practical factors such as the advancing pressure and speed, the soil pressure, the soil discharging and losing ratio, and the infused mud quantities are included in them. The viscosity-elasticity-plasticity property as well as the large deformation of the soft soil are considered in the discussion. The formulae can be used to design the
    2005, 27(4):  0-0.  doi:10.6052/1000-0992-2004-180
    Abstract ( 1161 )   PDF (517KB) ( 592 )  
    In order to establish the relationship between acousto-caustics and stress intensity factor under plane stress condition, a new acoustic-stress coefficient---the ratio between acoustic-path difference and stress is defined. The new coefficient is related not only to the material properties but also to the coupling medium and the acoustic traveling path. The method and the steps to get the new coefficient are described together with the tested results of 6061-T6 aluminum and EPTI steel. It is concluded that the new acousto-stress coefficient can be obtained as soon as the ratio of relative change of ultrasonic longitudinal wave to the sum of the principal stresses under plane stress condition is known.
    2005, 27(4):  0-0.  doi:10.6052/1000-0992-2004-243
    Abstract ( 1028 )   PDF (661KB) ( 452 )  
    A solution of deformation, critical pressure and stress for square pipe under pressure is obtained by using plane bending formula and a transformation from plane stress to plane strain in elasticity. The maximum deformation, critical stress and maximum stress are obtained. The results are compared with those obtained by the finite element software of Msc. Marc.
    2005, 27(4):  0-0.  doi:10.6052/1000-0992-2004-263
    Abstract ( 1177 )   PDF (718KB) ( 620 )  
    The GY902A computerized embroidery machine's beam is studied, and the natural frequency of the beam is abtained by using vibration experiment and finite element analysis. The simulation design using the finite element model is carried out with the beam's natural frequency being increased by 22{\%}, under the same weight of Computerized Embroidery Machine, and the chance of beam's resonance is reduced.
    2005, 27(4):  0-0.  doi:10.6052/1000-0992-2004-296
    Abstract ( 1159 )   PDF (1754KB) ( 510 )  
    In order to reduce the weight of aircraft structures effectively, the skeleton of aircraft is treated in the conceptual design of strengthening frame. By analyzing the concept of `gradient threshold' and pointing out its weakness, the author proposes the concept of `modified gradient threshold' and combines it with the strategy of `constraint compensation' to form a new kind of topology optimization algorithm for structural layout of a strengthening frame. The topology optimization results of several examples show that their layouts are good. We can see that, using the combination of CAD/CAE and topology optimization for aircraft strengthening frame conceptual design is feasible and that the proposed `modified gradient threshold' topology optimization algorithm is effective.
    2005, 27(4):  0-0.  doi:10.6052/1000-0992-2004-345
    Abstract ( 1148 )   PDF (653KB) ( 592 )  
    A soil column with non-uniform section is taken from the infinite subsoil. The vertical displacement of the subsoil is obtained from the one dimensional differential equation of wave propagation. Based on this, the dynamic random response of machine foundation subjected to the exciting force of dynamic machine is computed.
    2005, 27(4):  0-0.  doi:10.6052/1000-0992-2004-357
    Abstract ( 1482 )   PDF (599KB) ( 506 )  
    The relation between shape ratio and depth of fatigue crack on sucker rod is studied using fracture mechanics. The results show that the shape ratio of fatigue cracks with different depth will develop toward a stable value approximatively for whatever initial shape. The crack extension test is carried out to determine the asymptotic shape ratio of the fatigue crack, and specimens made of 20CrMo with circular section are used. A linear fitting line is obtained from the experimental data and the shape ratio of fatigue crack on sucker rod with diameter of 15.9\,mm is determined to be 0.78.
    Application study
    2005, 27(4):  0-0.  doi:10.6052/1000-0992-2004-399
    Abstract ( 1316 )   PDF (785KB) ( 754 )  
    Mass matrix and stiffness matrix of semi-rigid frames for dynamic finite element analysis are deduced.Multistory frames with semi-rigid connections of different initial stiffness are constructed together with the corresponding rigid frame. Finite element analysis software ANSYS is used to perform the numerical analysis. The influence of connection stiffness on natural frequencies of structures is analyzed. The response of different frames according to harmonic loading with different frequencies is studied. Further, by adopting a time--dependent method, structures under excitation of seismic waves are analyzed. Analysis results show that the connection flexibility has a great effect on structure's natural frequencies. The natural frequency decreases with the increase of connection flexibility. It is necessary to consider the connection flexibility in the seismic design of steel structures. Time curves of top point lateral displacement and column base shearing force of semi-rigid frames behave stably during the excitation time. Flexible connections can be used instead of rigid connections in seismic design of steel frames.
    Education Study
    2005, 27(4):  0-0.  doi:10.6052/1000-0992-2004-418
    Abstract ( 1150 )   PDF (820KB) ( 492 )  
    This paper gives a set of calculating formula of the driving force moment that is responsible for the tube-insert self-rotating and automatical cleaning in heat transfer tubes, using the principle of momentum moment and kinematics. It can be used to optimize the structure of the tube-insert with spiral flange. Based on the formula, several tube-inserts of different structure are designed and compared through experiments. The optimal insert (No. D) can be used reliably at low flowing velocity of more than 0.4m/s. The driving force moment and heat transfer coefficient are increased by 141{\%} and 50%, respectively. The flow resistance is in the limit of industrial standards.
    2005, 27(4):  0-0.  doi:10.6052/1000-0992-2004-442
    Abstract ( 1501 )   PDF (902KB) ( 395 )  
    To study the complicated mechanical process of spontaneous combustion of remnant coal in goafs under the conditions of open region nitrogen injection, based on seepage continuous equation, gas dispersion equation and integrated heat transfer equation, a non-steady numerical model of spontaneous combustion of coal in nitrogen injection goaf is established, and these equations are solved by windward finite element method. The spontaneous combustion process in goaf with different flux of nitrogen is computated, and the flow pattern of air leakage and the flow pattern of nitrogen are expressed by graphs, together with the variation of oxygen and carbon monoxide concentration and temperature distribution in goaf. Some influencing factors, such as gas effusion and the advance of working front are taken into account during computation. It is concluded that a high temperature zone usually appears at the inlet air side in goaf spontaneous combustion under open region nitrogen injection, but the shape turns to narrow. The spontaneous combustion period will become long with the increase of nitrogen injection quantity until spontaneous combustion stops. Theoretical simulation result and practical nitrogen injection conditions are in general agreement.
    2005, 27(4):  0-0.  doi:10.6052/1000-0992-2004-471
    Abstract ( 1024 )   PDF (476KB) ( 543 )  
    The slim pipe string in well bore is a special structure in petroleum engineering. In this paper, a dynamical model of rotating pipe string is proposed, with the consideration of the impact contact between rotating pipe string and well bore in any direction and at any point of well depth and well bore circumference. The analysis is carried out using dynamic gap element, space beam element and Newmark method. The application to the B3-4-P31 well shows that the rod string design can guarantee safe operation in well bore and prevent the rod string from failure.
    2005, 27(4):  0-0.  doi:10.6052/1000-0992-2005-082
    Abstract ( 1238 )   PDF (574KB) ( 586 )  
    To investigate the phase changing processes in traffic flow, we simulated a single lane traffic flow using a cellular automation. By extracting the section flux data and using discrete Fourier transform method, we made the power spectrum analysis. From the result we foundthat in the phase of jam, there exists a same period as that of a traffic shockwave resulting from our using the periodic boundary conditions; in the phase of heavy synchronized flow with high road occupancy, there still exists some periodic waves which are very different from the traffic shockwave, and we could not attribute them to the periodic boundary conditions; in the phase of free flow under low road occupancy, no periodic waves exist.
    2005, 27(4):  0-0.  doi:10.6052/1000-0992-2005-121
    Abstract ( 1095 )   PDF (1324KB) ( 571 )  
    Ethylene belongs to intermediate in the pyrolytic processes. The yields of ethylene change with pyrolsis durations which reach the peak at the optimal resident time. While the reaction temperature increases, the peak yields of ethylene is increased and the optimal resident time is sharply shortened. The vertical pipe furnaces in common use in convensional pyrolytic technology are difficult to satisfy the demands for significantly higher yields of ethylene and lower production costs. The advantages and disadvantages of heating by standing shock wave are reviewed and the developing heating method by mixing of opposite jets with high temperature steam flow is described briefly.
    Application study
    2005, 27(4):  0-0.  doi:10.6052/1000-0992-2005-149
    Abstract ( 1219 )   PDF (664KB) ( 669 )  
    rigid bar, the sprocket as a rigid polygon, and the roller between any two links as a revolving joint. The system is a closed kinematic chain of rigid bodies connected by revolving joints. The gear constraint is treated as a variable constraint. When the link meshes with the sprocket, the constraint force between the link and the sprocket is determined by testing. If the force is positive, the constraint is treated as a fixed constraint, otherwise the link leaves the sprocket. Lagrange's equation of motion is solved with Runge-Kutta method. Different driving processes are simulated and analyzed. The phenomenon of locking is explained, and two treatments to avoid locking of the system are proposed and analyzed.
    Education Study
    2005, 27(4):  0-0.  doi:10.6052/1000-0992-2005-295
    Abstract ( 1184 )   PDF (1489KB) ( 1613 )  
    In this paper the historical background of the development of special relativity and the relativistic kinematics and its results are briefly summarized. In particular, it is emphasized that the modifying of Newtonian absolute simultaneity is the key point for constructing special relativity. Furthermore, the relativistic dynamics and its achievements are introduced, which are also tests of special relativity. Finally, direction about developing special relativity in the future is expounded.