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1.
2.
In this study, detonation cell sizes of methanol–oxygen mixtures are experimentally measured at different initial pressures
and compositions. Good agreement is found between the experiment data and predictions based on the chemical length scales
obtained from a detailed chemical kinetic model. To assess the detonation sensitivity in methanol–oxygen mixtures, the results
are compared with those of hydrogen–oxygen and methane–oxygen mixtures. Based on the cell size comparison, it is shown that
methanol–oxygen is more detonation sensitive than methane–oxygen but less sensitive than hydrogen–oxygen. 相似文献
3.
In this paper, we present a novel approach to quantify regular or chaotic dynamics of either smooth or non-smooth dynamical
systems. The introduced method is applied to trace regular and chaotic stick–slip and slip–slip dynamics. Stick–slip and slip–slip
periodic and chaotic trajectories are analyzed (for the investigated parameters, a stick–slip dynamics dominates). Advantages
of the proposed numerical technique are given. 相似文献
4.
Although a fundamental physical parameter, surface tension is difficult to measure. Common tensiometry inaccuracy comes from
failure to control air–liquid–solid contact conditions, or account for liquid meniscus geometry and buoyancy corrections.
This paper describes an in situ tensiometry technique, based on withdrawal of a thin-walled tube from the liquid interface,
that enforces a known air–liquid–solid contact condition. This technique can be pursued at any level of experimental hygiene.
Experimental results for filtered tap water, an alcohol–water solution, and a surfactant–water solution show that results
repeatable to three significant digits are obtained with modest effort for a variety of geometrical parameters.
Received: 7 October 1997/Accepted: 23 April 1998 相似文献
5.
It is known that a transform of Liouville type allows one to pass from an equation of the Korteweg–de Vries (K–dV) hierarchy
to a corresponding equation of the Camassa–Holm (CH) hierarchy (Beals et al., Adv Math 154:229–257, 2000; McKean, Commun Pure
Appl Math 56(7):998–1015, 2003). We give a systematic development of the correspondence between these hierarchies by using
the coefficients of asymptotic expansions of certain Green’s functions. We illustrate our procedure with some examples. 相似文献
6.
Juhi Jang 《Archive for Rational Mechanics and Analysis》2009,194(2):531-584
Inspired by the work (Bastea et al. in J Stat Phys 1011087–1136, 2000) for binary fluids, we study the diffusive expansion
for solutions around Maxwellian equilibrium and in a periodic box to the Vlasov–Maxwell–Boltzmann system, the most fundamental
model for an ensemble of charged particles. Such an expansion yields a set of dissipative new macroscopic PDEs, the incompressible
Vlasov–Navier–Stokes–Fourier system and its higher order corrections for describing a charged fluid, where the self-consistent
electromagnetic field is present. The uniform estimate on the remainders is established via a unified nonlinear energy method
and it guarantees the global in time validity of such an expansion up to any order. 相似文献
7.
The propagation mechanism of high speed turbulent deflagrations 总被引:2,自引:0,他引:2
The propagation regimes of combustion waves in a 30 cm by 30 cm square cross–sectioned tube with an obstacle array of staggered
vertical cylindrical rods (with BR=0.41 and BR=0.19) are investigated. Mixtures of hydrogen, ethylene, propane, and methane with air at ambient conditions over a range
of equivalence ratios are used. In contrast to the previous results obtained in circular cross–sectioned tubes, it is found
that only the quasi–detonation regime and the slow turbulent deflagration regimes are observed for ethylene–air and for propane–air.
The transition from the quasi–detonation regime to the slow turbulent deflagration regime occurs at (where D is the tube “diameter” and is the detonation cell size). When , the quasi–detonation velocities that are observed are similar to those in unobstructed smooth tubes. For hydrogen–air mixtures,
it is found that there is a gradual transition from the quasi–detonation regime to the high speed turbulent deflagration regime.
The high speed turbulent deflagration regime is also observed for methane–air mixtures near stoichiometric composition. This
regime was previously interpreted as the “choking” regime in circular tubes with orifice plate obstacles. Presently, it is
proposed that the propagation mechanism of these high speed turbulent deflagrations is similar to that of Chapman–Jouguet
detonations and quasi-detonations. As well, it is observed that there exists unstable flame propagation at the lean limit
where . The local velocity fluctuates significantly about an averaged velocity for hydrogen–air, ethylene–air, and propane–air mixtures.
Unstable flame propagation is also observed for the entire range of high speed turbulent deflagrations in methane–air mixtures.
It is proposed that these fluctuations are due to quenching of the combustion front due to turbulent mixing. Quenched pockets
of unburned reactants are swept downstream, and the subsequent explosion serves to overdrive the combustion front. The present
study indicates that the dependence on the propagation mechanisms on obstacle geometry can be exploited to elucidate the different
complex mechanisms of supersonic combustion waves.
Received 5 November 2001 / Accepted 12 June 2002 / Published online 4 November 2002
Correspondence to: J. Chao (e-mail: jenny.chao@mail.mcgill.ca)
An abridged version of this paper was presented at the 18th Int. Colloquium on the Dynamics of Explosions and Reactive Systems
at Seattle, USA, from July 29 to August 3, 2001. 相似文献
8.
An experimental study was conducted to identify the effect of viscosity on the characteristics of liquid sheets formed by
a splash plate nozzle. Various mixtures of corn syrup and water are used to obtain viscosities in the range 1–170 mPa.s. Four
different splash plates with nozzle diameters of 0.5, 0.75, 1, and 2 mm, with a constant plate angle of 55° were tested. Liquid
sheets formed under various operating conditions were directly visualized. The sheet atomization process for the range of
parameters studied here is governed by two different mechanisms: Rayleigh–Plateau (R–P) and Rayleigh–Taylor (R–T) instabilities.
R–P occurs at the rim and R–T occurs on the thin sheet. The rim instability can be laminar or turbulent, depending on the
jet Reynolds number. The R–T instability of the sheet is observed at the outer edges of the radially spreading sheet, where
the sheet is the thinnest. It can also occur inside the sheet, due to formation of holes and ruptures. 相似文献
9.
We analyze the Lyapunov stability of impulsive Takagi–Sugeno fuzzy systems. Using the direct Lyapunov method, we establish
sufficient conditions for the stability of these systems. We show that these conditions can be expressed in terms of a system
of linear matrix inequalities. As an example, we consider an impulsive fuzzy control in a two-species “predator–prey” model.
Translated from Neliniini Kolyvannya, Vol. 11, No. 4, pp. 481–494, October–December, 2008. 相似文献
10.
We establish a Navier–Stokes–Fourier limit for solutions of the Boltzmann equation considered over any periodic spatial domain
of dimension two or more. We do this for a broad class of collision kernels that relaxes the Grad small deflection cutoff
condition for hard potentials and includes for the first time the case of soft potentials. Appropriately scaled families of
DiPerna–Lions renormalized solutions are shown to have fluctuations that are compact. Every limit point is governed by a weak
solution of a Navier–Stokes–Fourier system for all time. 相似文献
11.
Yann Brenier 《Archive for Rational Mechanics and Analysis》2009,193(1):1-19
We show that Kruzhkov’s theory of entropy solutions to multidimensional scalar conservation laws (Kruzhkov in Mat Sb (N.S.),
81(123), 228–255, 1970) can be entirely recast in L
2 and fits into the general theory of maximal monotone operators in Hilbert spaces. Our approach is based on a combination
of level-set, kinetic and transport-collapse approximations, in the spirit of previous works by Brenier (in C R Acad Sci Paris
Ser I Math, 292, 563–566, 1981; in J Diff Equ, 50, 375–390, 1983; in SIAM J Numer Anal, 21, 1013–1037; in Methods Appl Anal,
11, 515–532, 2004), Giga and Miyakawa (in Duke Math J, 50, 505–515, 1983), and Tsai et al. (in Math Comp, 72, 159–181, 2003). 相似文献
12.
The effect of temperature on the interfacial tension for PS/PMMA, PS/PE, and PMMA/PE was measured using the imbedded fiber
retraction method. Interfacial tensions for PS/PMMA, PS/PE, and PMMA/PE were measured over temperature ranges of 160–250 °C,
140–220 °C, and 140–220 °C, respectively. The interfacial tension was found to follow a dependence of 3.6–0.013 T dyn/cm, 7.6–0.051 T dyn/cm and 11.8–0.017 T dyn/cm for PS/PMMA, PS/PE, and PMMA/PE, respectively. Comparison of the data with the mean field theory of Helfand and Sapse
were made; however, a simple linear fit to the data described the temperature dependence in the experimental window as well
as the predictions of the mean field theory.
Received: 6 July 1999 Accepted: 23 March 2000 相似文献
13.
Konstantin Pileckas 《Journal of Mathematical Fluid Mechanics》2008,10(2):272-309
The time-dependent Navier–Stokes system is studied in a two-dimensional domain with strip-like outlets to infinity in weighted
Sobolev function spaces. It is proved that under natural compatibility conditions there exists a unique solution with prescribed
fluxes over cross-sections of outlets to infinity which tends in each outlet to the corresponding time-dependent Poiseuille
flow. The obtained results are proved for arbitrary large norms of the data (in particular, for arbitrary fluxes) and globally
in time.
The authors are supported by EC FP6 MC–ToK programme SPADE2, MTKD–CT–2004–014508. 相似文献
14.
15.
C.G. Speziale 《Theoretical and Computational Fluid Dynamics》1999,13(3):161-166
A resent extension of the nonlinear K–ε model is critically discussed from a basic theoretical standpoint. While it was said in the paper that this model was formulated
to incorporate relaxation effects, it will be shown that the model is incapable of describing one of the most basic such turbulent
flows as is obvious but is described for clarity. It will be shown in detail that this generalized nonlinear K–ε model yields erroneous results for the Reynolds stress tensor when the mean strains are set to zero in a turbulent flow
– the return-to-isotropy problem which is one of the most elementary relaxational turbulent flows. It is clear that K–ε type models cannot describe relaxation effects. While their general formalism can describe relaxation effects, the nonlinear
K–ε model – which the paper is centered on – cannot. The deviatoric part of the Reynolds stress tensor is predicted to be zero
when it actually only gradually relaxes to zero. Since this model was formulated by using the extended thermodynamics, it
too will be critically assessed. It will be argued that there is an unsubstantial physical basis for the use of extended thermodynamics
in turbulence. The role of Material Frame-Indifference and the implications for future research in turbulence modeling are
also discussed.
Received 19 February 1998 and accepted 23 October 1998 相似文献
16.
We perform a detailed numerical study of transient Taylor vortices arising from the instability of cylindrical Couette flow
with the exterior cylinder at rest for radius ratio η = 0.5 and variable aspect ratio Γ. The result of Abshagen et al. (J Fluid Mech 476:335–343, 2003) that onset transients apparently evolve on a much smaller
time–scale than decay transients is recovered. It is shown to be an artefact of time scale estimations based on the Stuart–Landau
amplitude equation which assumes frozen space dependence while full space–time dependence embedded in the Ginzburg–Landau
formalism needs to be taken into account to understand transients already at moderate aspect ratio. Sub-critical pattern induction
is shown to explain the apparently anomalous behaviour of the system at onset while decay follows the Stuart–Landau prediction
more closely. The dependence of time scales on boundary effects is studied for a wide range of aspect ratios, including non-integer
ones, showing general agreement with the Ginzburg–Landau picture able to account for solutions modulated by Ekman pumping
at the disks bounding the cylinders.
相似文献
17.
The Galerkin–Bubnov method with global approximations is used to find approximate solutions to initial–boundary-value creep
problems. It is shown that this approach allows obtaining solutions available in the literature. The features of how the solutions
of initial–boundary-value problems for oneand three-dimensional models are found are analyzed. The approximate solutions found
by the Galerkin–Bubnov method with global approximations is shown to be invariant to the form of the equations of the initial–boundary-value
problem. It is established that solutions of initial–boundary-value creep problems can be classified according to the form
of operators in the mathematical problem formulation 相似文献
18.
New sufficient conditions of local regularity for suitable weak solutions to the non-stationary three-dimensional Navier–Stokes
equations are proved. They contain the celebrated Caffarelli–Kohn–Nirenberg theorem as a particular case.
相似文献
19.
Prediction of separation flows around a 6:1 prolate spheroid using RANS/LES hybrid approaches 总被引:2,自引:0,他引:2
Zhixiang Xiao Yufei Zhang Jingbo Huang Haixin Chen Song Fu 《Acta Mechanica Sinica》2007,23(4):369-382
This paper presents hybrid Reynolds-averaged Navier–Stokes (RANS) and large-eddy-simulation (LES) methods for the separated
flows at high angles of attack around a 6:1 prolate spheroid. The RANS/LES hybrid methods studied in this work include the
detached eddy simulation (DES) based on Spalart–Allmaras (S–A), Menter’s k–ω shear-stress-transport (SST) and k–ω with weakly nonlinear eddy viscosity formulation (Wilcox–Durbin+, WD+) models and the zonal-RANS/LES methods based on the
SST and WD+ models. The switch from RANS near the wall to LES in the core flow region is smooth through the implementation
of a flow-dependent blending function for the zonal hybrid method. All the hybrid methods are designed to have a RANS mode
for the attached flows and have a LES behavior for the separated flows. The main objective of this paper is to apply the hybrid
methods for the high Reynolds number separated flows around prolate spheroid at high-incidences. A fourth-order central scheme
with fourth-order artificial viscosity is applied for spatial differencing. The fully implicit lower–upper symmetric-Gauss–Seidel
with pseudo time sub-iteration is taken as the temporal differentiation. Comparisons with available measurements are carried
out for pressure distribution, skin friction, and profiles of velocity, etc. Reasonable agreement with the experiments, accounting
for the effect on grids and fundamental turbulence models, is obtained for the separation flows.
The project supported by the National Natural Science Foundation of China (10502030 and 90505005). 相似文献
20.
The studies on the deformation and short-term damage of physically nonlinear homogeneous and composite materials are systemized.
A single microdamage is modeled by an empty quasispherical pore in place of a microvolume damaged in accordance with the Huber–von
Mises failure criterion. The ultimate microstrength is assumed to be a random function of coordinates. The porosity balance
equation is derived. Together with the macrostress–macrostrain relationship, it constitutes a closed-form system of equations.
The damage–macrostrain relationship and macrostress–macrostrain curves for homogeneous and composite materials are analyzed 相似文献