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1.
Tariq Talha 《Journal of Turbulence》2013,14(11):1091-1113
The unsteady turbulent channel flow subject to the temporal acceleration is considered in this study. Large-eddy simulations were performed to study the response of the turbulent flow to the temporal acceleration. The simulations were started with the fully developed turbulent channel flow at an initial Reynolds number of Re0 = 3500 (based on the channel half-height and the bulk-mean velocity), and then a constant temporal acceleration was applied. During the acceleration, the Reynolds number of the channel flow increased linearly from the initial Reynolds number to the final Reynolds number of Re1 = 22,600. The effect of grid resolution, domain size, time step size on the simulation results was assessed in a preliminary study using simulations of the accelerating turbulent flow as well as simulations of the steady turbulent channel flow at various Reynolds numbers. Simulation parameters were carefully chosen from the preliminary study to ascertain the accuracy of the simulation. From the accelerating turbulent flow simulations, the delays in the response of various flow properties to the temporal acceleration were measured. The distinctive features of the delays responsible for turbulence production, energy redistribution, and radial propagation were identified. Detailed turbulence statistics including the wall shear stress response during the acceleration were examined. The results reveal the changes in the near-wall structures during the acceleration. A self-sustaining mechanism of turbulence is proposed to explain the response of the turbulent flow to the temporal acceleration. Although the overall flow characteristics are similar between the channel and pipe flows, some differences were observed between the two flows. 相似文献
2.
利用正向加载和逆向加载相结合的实验方法,实验研究了从低压到高压三种不同压力范围内Fe基α相合金(Fe-85.03wt%,Mn-7.63wt%,Ni-7.01wt%,Al-0.3wt%)的冲击相变和卸载逆相变历程及对应加载状态的层裂行为特征.给出了Fe基α相合金含冲击相变和卸载逆相变的加卸载Hugoniot线,发现冲击相变阈值、逆相变阈值和冲击加载压力共同决定其冲击加卸载历程,冲击相变强烈影响其层裂行为,导致样品发生了"异常"层裂.利用获得的冲击加卸载历程从应力波相互作用的角度解
关键词:
α相合金')" href="#">Fe基α相合金
相变
逆相变
层裂 相似文献
3.
We investigate two models for traffic flow with modified acceleration (‘slow-to-start’) rules. Even in the simplest case vmax = 1 these rules break the ‘particle-hole’ symmetry of the model. We determine the fundamental diagram (flow-density relationship) using the so-called car-oriented mean-field approach (COMF) which yields the exact solution of the basic model with vmax = 1. Here we find that this is no longer true for the models with modified acceleration rules, but the results are still in good agreement with simulations. We also compare the effects of the two different slow-to-start rules and discuss their relevance for real traffic. In addition, in one of these models we find a new phase transition to a completely jammed state. 相似文献
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A. O. Gerasov M. P. Shandura Yu. P. Kovtun A. D. Kachkovsky 《Journal of Physical Organic Chemistry》2008,21(5):419-425
Combined quantum‐chemical and spectral studies of the features of electron transitions and absorption spectra of symmetrical and unsymmetrical polymethine dyes, derivatives of aminocoumarin, have been performed. It was established that the lowest two electron transitions are splitting transitions, involving solitonic level and two low positioned acceptor levels, in contrast to the cationic cyanine dyes, where two lowest transitions are connected with two splitting donor levels and solitonic level. The considerable interaction between two acceptor levels in symmetrical dyes provides an additional decrease of the first transition energy and hence leads to the relatively deep and intensive color, whereas the second transition with its negligible oscillator strength is practically unobserved. The higher electron transitions involve orbitals located mainly at the coumarin residue; the corresponding spectral bands appear in the short‐wavelength region. Introduction of dialkylamino group in coumarin heterocycle shifts bathochromically the long‐wavelength absorption band and considerably increases the intensity of S0 → S1 and S0 → S3 electron transitions. Copyright © 2008 John Wiley & Sons, Ltd. 相似文献
6.
In this paper, we study traffic flow patterns induced by incessant constant disturbances in the full velocity difference car-following model. It is found that intermittent unstable structures may occur in the convectively unstable traffic flow under certain situations. A phenomenological explanation of the phenomenon is given: the incessant constant disturbances mainly function to maintain the stationary oscillating structure while the stationary oscillating structure is not always stable, the intermittent instability of it leads to the intermittent unstable structures. The similarity of the stationary oscillating structure to the transition layer in the local cluster effect is pointed out. The dependence of the phenomenon on the headway of the initially uniform traffic, the safety distance xc, the sensitivity parameters κ and λ, and the noise term is also investigated. 相似文献
7.
Enhancement of measurement accuracy of X‐ray PIV in comparison with the micro‐PIV technique 下载免费PDF全文
Hanwook Park Sung Yong Jung Jun Hong Park Jun Ho Kim Sang Joon Lee 《Journal of synchrotron radiation》2018,25(2):552-559
The X‐ray PIV (particle image velocimetry) technique has been used as a non‐invasive measurement modality to investigate the haemodynamic features of blood flow. However, the extraction of two‐dimensional velocity field data from the three‐dimensional volumetric information contained in X‐ray images is technically unclear. In this study, a new two‐dimensional velocity field extraction technique is proposed to overcome technological limitations. To resolve the problem of finding a correction coefficient, the velocity field information obtained by X‐ray PIV and micro‐PIV techniques for disturbed flow in a concentric stenosis with 50% severity was quantitatively compared. Micro‐PIV experiments were conducted for single‐plane and summation images, which provide similar positional information of particles as X‐ray images. The correction coefficient was obtained by establishing the relationship between velocity data obtained from summation images (VS) and centre‐plane images (VC). The velocity differences between VS and VC along the vertical and horizontal directions were quantitatively analysed as a function of the geometric angle of the test model for applying the present two‐dimensional velocity field extraction technique to a conduit of arbitrary geometry. Finally, the two‐dimensional velocity field information at arbitrary positions could be successfully extracted from X‐ray images by using the correction coefficient and several velocity parameters derived from VS. 相似文献
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The density functional calculations of the energy band structure and density of state for the tetragonal PbO-type phase α-FeSe and hexagonal NiAs-type phase β-FeSe are reported in this paper. The structural phase transition from tetragonal to hexagonal FeSe under high pressure is investigated, it is found that the calculated transition pressure for the α → β phase transformation is 8.5 GPa. Some fluctuations in the transition pressure maybe occurred by different external factors such as temperature and stress condition. There is about 17% volume collapse accompanying the α → β phase transformation. 相似文献
10.
This paper modifies the weighted probabilistic cellular automaton model (Li X L, Kuang H, Song T, et al 2008 Chin. Phys. B 17 2366) which considered a diversity of traffic behaviors under real traffic situations induced by various driving characters and habits. In the new model, the effects of the velocity at the last time step and drivers' desire for acceleration are taken into account. The fundamental diagram, spatial-temporal diagram, and the
time series of one-minute data are analyzed. The results show that this model reproduces synchronized flow. Finally, it simulates the on-ramp system with the proposed model. Some characteristics including the phase diagram are studied. 相似文献
11.
Numerous formulations describing the dynamics and morphology of corrugated flames, including the scenarios of flame acceleration, are based on a “geometrical consideration”, where the wrinkled-to-planar flame velocities ratio, Sw /SL , is evaluated as the scaled flame surface area, while the entire combustion chemistry is immersed into the planar flame speed SL , which is assumed to be constant. However, SL may experience noticeable spatial/temporal variations in practice, in particular, due to pressure/temperature variations as well as non-uniform distribution of the equivalence ratio and/or that of combustible or inert dust impurities. The present work initiates the systematic study of the impact of the local SL -variations on the global flame evolution scenario. The variations are assumed to be imposed externally, in a manner being a free functional of the formulation. Specifically, the linear, parabolic and hyperbolic spatial SL -distributions are incorporated into the formulations of finger flame acceleration in pipes, and they are compared to the case of constant SL . Both two-dimensional channels and cylindrical tubes are considered. The conditions promoting or moderating flame acceleration are identified, and the revisited equations for the flame shape, velocity and acceleration rate are obtained for various SL -distributions. The theoretical findings are validated by the computational simulations of the reacting flow equations, with agreement between the theory and modelling demonstrated. 相似文献
12.
The orientational phase transitions in solid C60 and C70 are accompanied by quite different anomalies in the crystalline strains. In solid C60 the phase transition Fm3m→Pa3 is primarily an orientational effect (antiferro-rotational), which is driven by the condensation of orientational modes belonging to X5 + irreducible representation (irreps) of Fm3m. These modes are the primary order parameters (oops) and their number is equal to the number of irreps of T2g and T1g symmetry within the manifolds under consideration. Taking into account irreps up to the manifold 1=12, we have studied the rotation-rotation-translation (RRT) coupling between the oops and the lattice displacements. We have investigated the resulting lattice contraction and the change of the elastic constant c11 at the phase transition. In solid C70 (fcc-phase) we investigate the bilinear coupling of orientational fluctuations of T2g symmetry to transverse acoustic lattice displacements. This coupling is the driving mechanism for the ferroelastic phase transition Fm3m → R3m. Finally we investigate the transition from the rhombohedral phase to a low temperature monoclinic phase. This transition in antiferro-rotational. 相似文献
13.
使用格子Boltzmann方法对零质量射流激励下液体的相变演化过程进行了数值模拟和分析.首先,提出了此特定零质量射流进出口边界的处理格式.然后,结合Shan和Doolen提出的单组分多相模型,模拟了方腔内液体受到此零质量射流激励而诱发产生空化的过程,着重分析了三个重要射流参数ε/T,T和v out/v in对方腔内液体相变的影响.分析表明:演化过程中方腔内气相节点数量在初始阶段急剧增长,然后经振荡趋于一个稳定值.由于ε/T和v out/v in可以反映射流在出入方腔两个过程间相互转换时的急剧变化,所以能够影响方腔中的液体相变的演化;而改变参数T并不影响射流速度的变化程度,所以T对液体相变的影响较弱.对于本文给定的参数取值,ε/T较小时,方腔内液体相变生成的孤立气泡脱离壁面;较大的ε/T下产生附着于方腔壁面的气泡,并且能够加速液体的相变进程;v out/v in的增加使方腔内相应的孤立气泡所覆盖的范围略有减小.研究结果揭示了零质量射流激励诱发的液体相变过程,为进一步探索液体空化的控制途径奠定了基础. 相似文献
14.
The paper discusses the theory of Couette flow of a nematic liquid crystal. The apparent viscosity, orientation and velocity
profiles are computed forp-azoxyanisole as functions of shear rate and magnetic field for symmetric and asymmetric molecular alignments at the boundaries
and for different relative radii of the cylinders. For symmetric homeotropic boundary condition an azimuthal field exhibits
a threshold analogous to a Freedericksz transition. An expression is also derived for the Freedericksz threshold in the hydrostatic
case. 相似文献
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C. Meis M. Jardino B. Gely M. Desaintfuscien 《Applied physics. B, Lasers and optics》1989,48(1):67-72
RF traps are widely used nowadays in high resolution hyperfine spectroscopy. The spectrum of the microwave hyperfine transition at 40.5 GHz of the fundamental level2
S
1/2 of199Hg+ is phase modulated at the secular frequency of the stored ions and it consists of a narrow central line and lateral bands broadened by the ion trajectory and velocity distribution. The central line itself is shifted by the second-order Doppler effect which is the most important systematic error of stored ions frequency standards. In this paper the relativistic Doppler effect in the case of199Hg+ stored ions is deduced applying a mathematical formalism and using physical parameters that we have measured experimentally. 相似文献
17.
The stability analysis is one of the important problems in the traffic flow theory, since the congestion phenomena can be regarded as the instability and the phase transition of a dynamical system. Theoretically, we analyze the stable conditions of the full velocity and acceleration difference model (FVADM), which is proposed by introducing the acceleration difference term based on the previous car-following models (the optimal velocity model and the full velocity difference model, OVM and FVDM). By numerical simulations, it is found that when the traffic flow is unstable, the traffic jam in the FVADM is weaker than that in the FVDM. Also it is observed that the spreading speed of the jam is slower in the FVADM than that in the FVDM and the fluctuations of vehicles in the FVADM are smaller than those in the FVDM. Therefore, the acceleration difference term has strong effects on traffic dynamics and plays an important role in stabilizing the traffic flow. 相似文献
18.
M. P. Rekalo 《Russian Physics Journal》1983,26(12):1139-1141
Since at the threshold the P-odd amplitude of deuteron photodisintegration (γ + D → P + N) is determined by three independent multipole amplitudes (describing the El →1S0, El →3S1, and M2 →3S1 transitions), at least three different experiments on measuring the P-odd polarization characteristics of the γ + D → P + N process are needed (provided that P-odd threshold amplitudes are known) in order to determine the multipole amplitudes. A P-odd dependence of the threshold cross section on the polarizations of the colliding γ-quantum and deuteron is established and P-odd contributions to the polarization vector of protons formed in the γ + D → P + N process are found. The P-odd characteristics are calculated in terms of P-even and P-odd threshold amplitudes. 相似文献
19.
In this paper, we study the anisotropy parameter and Dzyaloshinskii-Moriya (DM) interaction on negativity and quantum phase transition (QPT) by using the quantum renormalization-group (QRG) method in the spin model. In our model, the anisotropy parameter and DM interaction can influence the phase diagrams. Negativity can develop two different values which separated two phases i.e. Spin-fluid phase and the Néel phase with the number of QRG iterations increased, and can obviously exhibit QPT at the critical point. Then, we find that negativity of particles 1, 3 throughout is less than negativity of particles 1, 2 or particles 2, 3. Because of information between the three particle distributions, please see the conclusion. We find that the negativity difference value (S) can also clearly detect QPT at the critical point. Most importantly, the maximum S max become more and more close to the critical point. So S max can be used as a criterion of the quantum phase transition occurrence when the spin chain is infinity (N → ∞). 相似文献
20.
Abstract Present paper is an overview of our efforts during the past few years to understand complicated corelations of physical phenomena related to pressure in Fe(I1) solid state spin transition systems. Some principal results concerning p, T, λ-experiments are extracted. In the context of correlation of the crystallographic phase transition with simultaneous HS → LS relaxation and LS → HS photopopulation, we show the latest results: Brillouin and magnetic measurements on the crystal [Fe(pt6](BF6)2. 相似文献