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2010 Vol. 42, No. 5

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2010, 42(5): 818-829. doi: 10.6052/0459-1879-2010-5-lxxb2009-230
A Comparative Study on Traffic Flow Models Based on Real Measured Data
Through both the analysis of over 26,000 real measured data collected on Shanghai's Yan'an Viaduct and the comparison with Kerner's classic model, it is found that the flow-density figure shows that non-linear regional characters even exist in the low density section. In addition, a method to quantify the proportion of aggressive drivers is proposed by means of fitting different equilibrium functions to real measured data and then forming a piecewise function composed of the best-fit function in each density section. This piecewise equilibrium function is much closer to China's present traffic conditions. Keywords: Traffic Flow Models; Measured Data; Flow-density Figure; Piecewise Equilibrium Function ;Aggressive Drivers;
2010, 42(5): 848-855. doi: 10.6052/0459-1879-2010-5-lxxb2009-128
Bifurcation of the Curved Panel in Supersonic Air Flow
An investigation on bifurcation of the curved panel in supersonic air flow is performed in this paper. The nonlinear aeroelastic model for a two-dimensional curved panel with constant stream-wise curvature is built in supersonic air flow and elevated temperature environment. The Von-Karman’s large deflection plate theory, the quasi-steady first-order piston theory and the quasi-static temperature distribution are used in the formulation. The Galerkin’s method has been used to reduce the mathematical problem to a set of coupled nonlinear ordinary differential equations. Then the nonlinear ordinary differential equations are studied by using static bifurcation and Hopf bifurcation. The results show that at different combinations of control parameters dynamic pressures, temperature elevation and height-rise of the panel, different static equilibrium positions may coexist. And there are two different mechanisms of the instability onset of curved panel.
2010, 42(5): 863-869. doi: 10.6052/0459-1879-2010-5-lxxb2009-333
2010, 42(5): 880-888. doi: 10.6052/0459-1879-2010-5-lxxb2009-315
A Bridging Scale Method for Multi-scale Analysis of Granular Materials
The bridging scale method (BSM) that couples the discrete particle assembly modeling with discrete element method (DEM) and the Cosserat continuum modeling with finite element method (FEM) in both fine and coarse scales respectively is proposed to study the mechanical behaviors in granular materials. The coarse scale domain, which is modeled with the Cosserat continuum and numerically simulated with the FEM, covers the whole medium concerned. While the fine scale one, which is modeled with the discrete particle assembly and numerically simulated with the DEM, is limited to a localized region, where the material microstructure and discontinuous deformation behaviors and their evolutions are needed to pay particular attentions. The interfacial condition between the two domains is presented and the scheme for its numerical implementation is proposed. By using a proper bridging scale projection operator, two decoupling sets of equations of motion of the combined coarse-fine scale system are allowed to solve with two separate solvers and to use distinct time step sizes, that will greatly enhance the computational efficiency of the BSM. The numerical results for a 2D example problem of the soil foundation illustrate the applicability and performance of the proposed method, and its advantages as compared with the FEM based on the Cosserat continuum modeling and the DEM based on the discrete particle assembly modeling.
2010, 42(5): 889-900. doi: 10.6052/0459-1879-2010-5-lxxb2009-323
ew Features of Positive Time-Delayed Feedbacks in Vibration Control
Compared with negative feedbacks that are used intensively, positive feedbacks have been used relatively few in control theory and control engineering, because positive feedbacks enlarge state variations so that they deteriorate the system stability. This is not the case if a delay involves in the feedback path. On the basis of stability switches and the rightmost characteristic roots that determine the system stability, this paper investigates the control effect of positive feedbacks in stabilizing unstable motion as well as in improving stability of the typical linear vibration system. One of our observations is that a time-delayed positive displacement feedback works more effectively than the corresponding negative feedback as shown in the following three aspects: (1). the delay values that are used for stabilization via positive feedback are smaller than the admissible delays via negative feedbacks; (2). the admissible delay range for stabilization via positive feedback is broader than that via negative feedbacks; (3). in a given range of delay, the minimal value of the real parts of the rightmost characteristic roots of the closed-loop under positive feedback control is much smaller than that for the case of negative feedback, so that with such a delay, the state of the closed-loop under positive feedback approaches to the equilibrium much more quickly than the case of negative feedback, if the states start from the same initial conditions. For the same stabilization problem, however, negative feedback works more effectively than positive feedback if a delayed velocity feedback or a delayed acceleration feedback is performed. In addition, with the same feedback gain, a positive delayed displacement feedback is preferable than a positive delayed velocity feedback or a positive delayed acceleration feedback. Keywords stabilization, vibration control, positive delayed feedback, stability switches, characteristic roots
2010, 42(5): 933-942. doi: 10.6052/0459-1879-2010-5-lxxb2009-313
Biomechanical analysis and numerical calculation of earthworm crawling
Shi Weiping
Earthworm is a typical multi-body segment and soft-bodied animal. In this paper starting from a biomechanical point of view we analysis the tensile stress of the body wall during rest and peristaltic crawling and describes the deformation coupled with a simple friction model during peristaltic crawling. We calculate the body wall stress and crawling velocity for a certain range of mass of earthworms . The dynamic equation of earthworm crawling is presented and calculated numerically. Numerical results show that the mean speed of earthworm crawling for different mass is consistent with experimental value.
2010, 42(5): 951-956. doi: 10.6052/0459-1879-2010-5-lxxb2009-043
Experimental investigation of the excited jet in supersonic mixing
Sheng-Long Gu Chen Lihong
Hartmann-Sprenger(H-S) tube could make flow oscillated with high frequency and high amplitude under JRG mode. This article made the excited jet by putting H-S tube into the traditional jet device to investigate its effects on the supersonic mixing. The CO2 jet excited under three different frequencies was injected into the Mach 2.5 supersonic flow. The planar laser scattering was used to visualize the instantaneous flow while measuring total pressure and sampling the concentration of CO2 were used to obtain the time averaged results. The results showed that the excited jet improved the depth of jet penetration, and made much more large-scale structures ,so that got better mixing in the supersonic flow with less total pressure loss. Keywords: Excited Jet, Supersonic Mixing, Depth of penetration, The large-scale structure
2010, 42(5): 957-961. doi: 10.6052/0459-1879-2010-5-lxxb2009-750
Influence of Phase Transition on Spalling Behavior in FeMnNi alloy
Li Qingzhong
This article obtained the loading and unloading process and phase transition spalling characteristics of FeMnNi alloy through symmetrical and same thickness impact and reverse impact experiments. By means of the modified Boettger model and a non-equilibrium mixture phase model, we explained the physical principle of the shock phase transition and reverse transition and rarefaction shock wave in numerical simulation. We described the spalling mechanism from the interaction process of stress wave. And we found that the phase transition and reverse transition of FeMnNi alloy sample are just about the physical mechanism which leads to spallation.
2010, 42(5): 971-977. doi: 10.6052/0459-1879-2010-5-lxxb2008-448
The Relationship between Random Divergence Mechanisms and Disassortative Mixing Property in Biological Networks
Liu Zengrong
In the theory of biological evolution, duplication and divergence are two intrinsic mechanisms. In this article, we mainly study how divergence mechanisms influence disassortative mixing property in biological networks. We study several kinds of random divergence mechanisms, such as random node deletion divergence mechanism, random edge deletion divergence mechanism, random edge addition divergence mechanism and random edge rewiring divergence mechanism. Our results show that both random node deletion divergence mechanism and random edge deletion divergence mechanism will not impact on disassortative mixing property strongly; while random edge addition divergence mechanism and random edge rewiring divergence mechanism will neutralize disassortative mixing property.
2010, 42(5): 989-994. doi: 10.6052/0459-1879-2010-5-lxxb2009-244