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1.
The mechanism of precursor ionization ahead of strong shock waves has been studied in a low density shock tube. The experimental
results are illustrated with Arrhenius plots with kink points dividing them into two parts with apparent activation energy
ratio 1:2, namely with the values 7.7 eV and 15.3 eV, and varying with first and third power of the density respectively.
A model is proposed to interpret the facts where the process taking place in the precursor region, is a two step photo ionization
accompanied with the drift flow effect of the gas relative to the shock wave or the ionization recombination effect according
to whether the shock speed and initial density are low enough. The product of the A-A collision excitation cross section coefficientS
* multiplied by the radiation cross sectionQ
* of ArgonS
*×Q
*=1×10−36 (cm4eV−1) and the three body recombination coefficient of Argon at room temperaturek
ra
=1×10−24 (cm−6s−1).
The project supported by the National Natural Science Foundation of China 相似文献
2.
This paper presents the electromagnetic wave propagation characteristics in plasma and the attenuation coefficients of the microwave in terms of the parameters he, v, w, L, wb. The φ800 mm high temperature shock tube has been used to produce a uniform plasma. In order to get the attenuation of the electromagnetic wave through the plasma behind a shock wave, the microwave transmission has been used to measure the relative change of the wave power. The working frequency is f = (2-35)GHz (ω=2πf, wave length A =15cm-8mm). The electron density in the plasma is ne = (3×10^10-1×10^14) cm^-3. The collision frequency v = (1×10^8-6×10^10) Hz. The thickness of the plasma layer L = (2-80)cm. The electron circular frequency ωb=eBo/me, magnetic flux density B0 = (0-0.84)T. The experimental results show that when the plasma layer is thick (such as L/λ≥10), the correlation between the attenuation coefficients of the electromagnetic waves and the parameters ne,v,ω, L determined from the measurements are in good agreement with the theoretical predictions of electromagnetic wave propagations in the uniform infinite plasma. When the plasma layer is thin (such as when both L and A are of the same order), the theoretical results are only in a qualitative agreement with the experimental observations in the present parameter range, but the formula of the electromagnetic wave propagation theory in an uniform infinite plasma can not be used for quantitative computations of the correlation between the attenuation coefficients and the parameters ne,v,ω, L. In fact, if ω<ωp, v^2<<ω^2, the power attenuations K of the electromagnetic waves obtained from the measurements in the thin-layer plasma are much smaller than those of the theoretical predictions. On the other hand, if ω>ωp, v^2<<ω^2 (just v≈f), the measurements are much larger than the theoretical results. Also, we have measured the electromagnetic wave power attenuation value under the magnetic field and without a magnetic field. The result indicates that the value measured under the magnetic field shows a distinct improvement. 相似文献
3.
G. Bazalitski V. Ts. Gurovich A. Fedotov-Gefen S. Efimov Ya. E. Krasik 《Shock Waves》2011,21(4):321-329
Results of one-dimensional numerical simulations of the parameters of the converging strong shock wave generated by electrical
underwater explosions of a cylindrical wire array with different array radii and different deposited energies are presented.
It was shown that for each wire array radius there exists an optimal duration of the energy deposition into the exploding
array, which allows one to maximize the shock wave pressure and temperature in the vicinity of the implosion axis. The simulation
results agree well with the 130-GPa pressure in the vicinity of the implosion axis that was recently obtained, which strongly
indicates the azimuthal symmetry of the converging shock wave at these extreme conditions. Also, simulations showed that using
a pulsed power generator with a stored energy of ~200 kJ, the pressure and temperature at the shock wave front reaches ~220
GPa and 1.7 eV at 0.1 mm from the axis of implosion in the case of a 2.5 mm radius wire array explosion. It was found that,
in spite of the complicated equation of state of water, the maximum pressure at the shock wave front at radius r can be estimated as P ≈ (P*(r*/r)
α
, where P* is the known value of pressure at the shock wave front at radius r* ≥ r and α is a parameter that equals 0.62±0.02. A rough estimate of the implosion parameters of the hydrogen target after the interaction
with the converging strong shock wave is presented as well. 相似文献
4.
V. Zh. Madirbaev A. E. Zarvin 《Journal of Applied Mechanics and Technical Physics》1998,39(6):832-836
Results of an experimental study of the process of quenching of excited states ofHF
+ ions in a hydrofluoride-helium electron-beam plasma are reported. The rate constant of quenching ofA
2∑+(v′=2)HF+ by helium atoms is measured. The ions were excited by activation of the rarefied gas mixture by an electron beam. Diagnostics
of internal states of the ions was performed using the electron-vibration-rotation spectrum of their spontaneous emission.
Novosibirsk State University, Novosibirsk 630090. Translated from Prikladnay Makhanika i Tekhnicheskaya Fizika, Vol. 39, No.
6, pp. 16–20, November–December, 1998 相似文献
5.
S. G. Mironov 《Journal of Applied Mechanics and Technical Physics》1999,40(6):1029-1035
The characteristics of travelling perturbations of density in a hypersonic shock layer on a flat plate for the Mach number
M∞=21 and unit Reynolds numberRe
1=6·105 m−1 were experimentally studied by the method of electron-beam fluorescence. The perturbations were generated by interaction
of the shock layer behind an oblique gas-dynamic whistle and the leading edge of the plate. The cases of unsteady and quasi-steady
interaction were considered. In both cases, vortex disturbances of finite amplitude were generated. The measurements were
performed at the fundamental frequency F=0.6·10−4 and at the harmonic; the streamwise phase velocities, the growth rates of the disturbances, and the angles of wave propagation
were obtained. The measurement results are compared with some experimental data for subsonic flows, some particular results
of the linear stability theory for compressible flows, and the results obtained on the basis of a simple model of the nonlinear
stage of disturbance evolution in a hypersonic boundary layer.
Institute of Theoretical and Applied Mechanics, Siberian Division, Russian Academy of Sciences, Novosibirsk 630090. Translated
from Prikladnaya Mekhanika i Tekhnicheskaya Fizika, Vol. 40, No. 6, pp. 41–47, November–December, 1999. 相似文献
6.
Understanding the radiation embrittlement of reactor pressure vessel (RPV) steels is required to be able to operate safely
a nuclear power plant or to extend its lifetime. The mechanical properties degradation is partly due to the clustering of
solute under irradiation. To gain knowledge about the clustering process, a Fe−1.1 Mn−0.7 Ni (at.%) alloy was irradiated in
a test reactor at two fluxes of 0.15 and 9 ×1017 n
E > 1MeV
.m − 2.s − 1 and at increasing doses from 0.18 to 1.3 ×1024 n
E > 1MeV
.m − 2 at 300°C. Atom probe tomography (APT) experiments revealed that the irradiation promotes the formation in the α iron matrix of Mn/Mn and/or Ni/Ni pair correlations at low dose and Mn–Ni enriched clusters at high dose. These clusters
dissolve partially after a thermal treatment at 400°C. Based on a comparison with thermodynamic calculations, we show that
the solute clustering under irradiation can just result from an induced mechanism. 相似文献
7.
This paper presents an experimental and theoretical investigation of drying of moist slab, cylinder and spherical products
to study dimensionless moisture content distributions and their comparisons. Experimental study includes the measurement of
the moisture content distributions of slab and cylindrical carrot, slab and cylindrical pumpkin and spherical blueberry during
drying at various temperatures (e.g., 30, 40, 50 and 60°C) at specific constant velocity (U = 1 m/s) and the relative humidity φ = 30%. In theoretical analysis, two moisture transfer models are used to determine drying process parameters (e.g., drying
coefficient and lag factor) and moisture transfer parameters (e.g., moisture diffusivity and moisture transfer coefficient),
and to calculate the dimensionless moisture content distributions. The calculated results are then compared with the experimental
moisture data. A considerably high agreement is obtained between the calculations and experimental measurements for the cases
considered. The effective diffusivity values were evaluated between 0.741 × 10−5 and 5.981 × 10−5 m2/h for slab products, 0.818 × 10−5 and 6.287 × 10−5 m2/h for cylindrical products and 1.213 × 10−7 and 7.589 × 10−7 m2/h spherical products using the Model-I and 0.316 × 10−5–5.072 × 10−5 m2/h for slab products, 0.580 × 10−5–9.587 × 10−5 m2/h for cylindrical products and 1.408 × 10−7–13.913 × 10−7 m2/h spherical products using the Model-II. 相似文献
8.
The transition from regular reflection (RR) to Mach reflection (MR) as a plane shock wave diffracts around a triangular mountain of 45° inclination is analysed in this paper, both by optical
measurement in a shock tube and by numerical simulation the numerical method developed by Li Yingfan[1] is of the FLIC type with triangular mesh. The dependence of the critical transition point Lk ofRR→MR on shock Mach numberM
i
is analyzed and the variations of the incidence angle ω
i
of the impinging shock and the reflection angle ω
r
with the distanceL
* are investigated. Our experimental and numerical results agree well with the theoretical results of Iton and Italya. 相似文献
9.
In this paper, we propose a novel method for evaluating the frequency response of shock accelerometers using Davies bar and
interferometry. The method adopts elastic wave pulses propagating in a thin circular bar for the generation of high accelerations.
The accelerometer to be examined is attached to one end of the bar and experiences high accelerations of the order of 103∼105 m/s2. A laser interferometer system is newly designed for the absolute measurement of the bar end motion. It can measure the motion
of a diffuse surface specimen at a speed of 10−3 ∼100 m/s. Uncertainty of the velocity measurement is estimated to be±6×10−4 m/s, proving a high potential for use in the primary calibration of shock accelerometers. Frequency characteristics of the
accelerometer are determined by comparing the accelerometer's output with velocity data of the interferometry in the frequency
domain. Two piezoelectric-type accelerometers are tested in the experiment, and their frequency characteristics are obtained
over a wide frequency range up to several ten kilohertz. It is also shown that the results obtained using strain gages are
consistent with those by this new method.
Paper was presented at the 1992 SEM Spring Conference on Experimental Mechanics held in Las Vegas, NV on June 8–11. 相似文献
10.
Yoshihiro Ueda Tohru Nakamura Shuichi Kawashima 《Archive for Rational Mechanics and Analysis》2010,198(3):735-762
This paper is concerned with the asymptotic stability of degenerate stationary waves for viscous gases in the half space.
We discuss the following two cases: (1) viscous conservation laws and (2) damped wave equations with nonlinear convection.
In each case, we prove that the solution converges to the corresponding degenerate stationary wave at the rate t
−α/4 as t → ∞, provided that the initial perturbation is in the weighted space
L2a=L2(\mathbb R+; (1+x)a dx){L^2_\alpha=L^2({\mathbb R}_+;\,(1+x)^\alpha dx)} . This convergence rate t
−α/4 is weaker than the one for the non-degenerate case and requires the restriction α < α*(q), where α*(q) is the critical value depending only on the degeneracy exponent q. Such a restriction is reasonable because the corresponding linearized operator for viscous conservation laws cannot be dissipative
in L2a{L^2_\alpha} for α > α*(q) with another critical value α*(q). Our stability analysis is based on the space–time weighted energy method in which the spatial weight is chosen as a function
of the degenerate stationary wave. 相似文献
11.
Suppose A,B and C are the bounded linear operators on a Hilbert space H, when A has a generalized inverse A- such that (AA-)*=AA- and B has a generalized inverse B- such that (B-B)*=B-B,the general characteristic forms for the critical points of the map Fp:X→‖AXB-C‖pp(1
p=2. Similarly, the same question has been discussed for several operators. 相似文献
12.
The aim of this work is to carry out an experimental investigation into the generation of airborne microparticles when millimetric
droplets of aqueous solutions impact onto a liquid film. Impact experiments using 3.9 mm diameter droplets were carried out
for Weber numbers between 159 and 808, with a fixed Ohnesorge number of 2 × 10−3 and film parameters S
f (the ratio between the thickness of the liquid film h
film and the diameter of the impacting droplet d
i) between 0.3 and 1. Observed results show that the deposition/splashing threshold is independent of the parameter S
f in agreement with the data in the literature. The aerosol measurement results demonstrate the production of solid particles
from the evaporation of secondary microdroplets with diameters less than 30 μm formed when splash occurs. The median diameter
of these microdroplets is around 20 μm, corresponding to a value of d
50/d
i = 5 × 10−3. Taken together, the results show that the mass and the number of particles emitted increase as the Weber number increases.
Moreover, at a Weber number of 808, the results show that the mass and number of particles emitted increases as the parameter
S
f decreases. In this case, the mean number of microdroplets emitted per impact is equal to 14 for S
f = 1 and equal to 76 for S
f = 0.3. 相似文献
13.
In this paper, the ethylene/oxygen/nitrogen premixed flame instabilities induced by incident and reflected shock wave were
investigated numerically. The effects of grid resolutions and chemical mechanisms on the flame bubble deformation process
are evaluated. In the computational frame, the 2D multi-component Navier–Stokes equations with second-order flux-difference
splitting scheme were used; the stiff chemical source term was integrated using an implicit ordinary differential equations
(ODEs) solver. The two ethylene/oxygen/nitrogen chemical mechanisms, namely 3-step reduced mechanism and 35-step elementary
skeletal mechanism, were used to examine the reliability of chemistry. On the other hand, the different grid sizes, Δx × Δy = 0.25 × 0.5mm and Δx × Δy = 0.15 × 0.2mm, were implemented to examine the accuracy of the grid resolution. The computational results were qualitatively
validated with experimental results of Thomas et al. (Combust Theory Model 5:573–594, 2001). Two chemical mechanisms and two
grid resolutions used in present study can qualitatively reproduce the ethylene spherical flame instability process generated
by an incident shock wave of Mach number 1.7. For the case of interaction between the flame and reflected shock waves, the
35-steps mechanism qualitatively predicts the physical process and is somewhat independent on the grid resolutions, while
the 3-steps mechanism fails to reproduce the instability of ethylene flame for the two selected grid resolutions. It is concluded
that the detailed chemical mechanism, which includes the chain elementary reactions of fuel combustion, describes the flame
instability induced by shock wave, in spite of the fact that the flame thickness (reaction zone) is represented by 1–2 grids
only.
相似文献
14.
In order to evaluate characteristics of the liquid film flow and their influences on heat and mass transfer, measurements
of the instantaneous film thickness using a capacitance method and observation of film breakdown are performed. Experimental
results are reported in the paper. Experiments are carried out at Re = 250–10000, T
in = 20–50°C and three axial positions of vertically falling liquid films for film thickness measurements. Instantaneous surface
waveshapes are given by the interpretation of the test data using the cubic spline method. The correlation of the mean film
thickness versus the film Reynolds number is also given by fitting the test data. It is revealed that the surface wave has
nonlinear behavior. Observation of film breakdown is performed at Re = 1.40 × 103–1.75 × 104 and T
in = 85–95°C. From experimental results, the correlation of the film breakdown criterion can be obtained as follows: Bd = 1.567 × 10−6
Re
1.183 相似文献
15.
The operation of microscopic high-speed liquid-metal jets in vacuum has been investigated. We show that such jets may be produced
with good stability and collimation at higher speeds than previously demonstrated, provided that the nozzle design is appropriate
and that cavitation-induced instabilities are avoided. The experiments with a medium-speed tin jet (u ∼ 60 m/s, Re=1.8×104, Z=2.9×10−3) showed that it operated without any signs of instabilities, whereas the stability of high-speed tin jets (d=30 μm, u=500 m/s, Re=5.6×104, Z=4.7×10−3) has been investigated via dynamic similarity using a water jet. Such a 500-m/s tin jet is required as the anode for high-brightness
operation of a novel electron-impact X-ray source. 相似文献
16.
Laser driven shock wave transit time in thin aluminium targets was experimentally estimated by determining the shock emergence
time at the rear of thin aluminium foils of varying thickness from 5 to 35 μm. A 20 J, 5 ns Nd:glass laser was focused to
produce laser intensity of 1012 to 5 × 1013 W/cm2 on the targets which were placed in vacuum. Target foil movement was measured to an accuracy of 10 μm using optical shadowgraphy
technique. This technique was used to accurately measure the shock transit time by recording the optical shadowgrams at various
instants of time and thus identify the instant at which the foil is just set into motion. Shock transit time measured in foils
of different thickness can give the value of shock velocity at a given laser intensity. Target motion recorded by shadowgraphy
can also give the target foil velocity from which shock pressure can be estimated. Experimental values of shock transit time,
shock velocity and shock pressure were observed to agree well with the values using one-dimensional multi-group radiation
hydrodynamic simulations.
PACS 52.50Jm; 52.50Lp; 52.25
Communicated by K. Takayama 相似文献
17.
M. D. Brodetsky A. M. Kharitonov E. Krause A. A. Pavlov S. B. Nikiforov A. M. Shevchenko 《Experiments in fluids》2000,29(6):592-604
The leeside vortex structures on delta wings with sharp leading edges were studied for supersonic flow at the Institute of
Theoretical and Applied Mechanics of the Russian Academy of Sciences in Novosibirsk. The experiments were carried out with
three wings with sweep angles of χ=68°, 73°, and 78° and parabolic profiles in the 0.6 × 0.6 m2 test section of the blow-down wind tunnel T-313 of the institute. The test conditions were varied from Mach numbers M=2 to 4, unit Reynolds numbers from Re
l=26 × 106 to 56 × 106 m−1, and angles of attack from α=0° to 22°. The results of the investigations revealed that for certain flow conditions shocks
are formed above, below, and between the primary vortices. The experimental data were accurate enough to detect the onset
of secondary and tertiary separation as well as other boundaries. The various flow regimes discussed in the literature were
extended in several cases. The major findings are reported.
Received: 6 September 1999/Accepted: 24 January 2000 相似文献
18.
The interaction of a planar shock wave with a spherical density inhomogeneity is studied experimentally under reshock conditions.
Reshock occurs when the incident shock wave, which has already accelerated the spherical bubble, reflects off the tube end
wall and reaccelerates the inhomogeneity for a second time. These experiments are performed at the Wisconsin Shock Tube Laboratory,
in a 9m-long vertical shock tube with a large square cross section (25.4×25.4 cm2). The bubble is prepared on a pneumatically retracted injector and released into a state of free fall. Planar diagnostic
methods are used to study the bubble morphology after reshock. Data are presented for experiments involving two Atwood numbers
(A = 0.17 and 0.68) and three Mach numbers (1.35 < M < 2.33). For the low Atwood number case, a secondary vortex ring appears immediately after reshock which is not observed
for the larger Atwood number. The post-reshock vortex velocity is shown to be proportional to the incident Mach number, M, the initial Atwood number, A, and the incident shock wave speed, W
i. 相似文献
19.
The flow and heat transfer in an inclined and horizontal rectangular duct with a heated plate longitudinally mounted in the
middle of cross section was experimentally investigated. The heated plate and rectangular duct were both made of highly conductive
materials, and the heated plate was subjected to a uniform heat flux. The heat transfer processes through the test section
were under various operating conditions: Pr ≈ 0.7, inclination angle ϕ = −60° to +60°, Reynolds number Re = 334–1,911, Grashof number Gr = 5.26 × 102–5.78 × 106. The experimental results showed that the average Nusselt number in the entrance region was 1.6–2 times as large as that
in the fully developed region. The average Nusselt numbers and pressure drops increased with the Reynolds number. The average
Nusselt numbers and pressure drops decreased with an increase in the inclination angle from −60° to +60° when the Reynolds
number was less than 1,500. But when the Reynolds number increased to over about 1,800, the heat transfer coefficients and
pressure drops were independent of inclination angles. 相似文献
20.
Tensile impact experiments of EC8.0−24×7 glass fiber bundles at different low temperaturesT(14°C, −40°C and −10°C) and strain rates ɛ were carried out, and complete stress-strain curves were obtained. Within the range
of the experiment temperatures and strain rates, it is found that the initial modulusE, the ultimate strength σmax and the unstable strain ɛ
b
of the glass fiber bundles all increase with ɛ at an identicalT. At an identical ɛ, with the decrease ofT, E and σmax increase; but ɛ
b
increases when 10°C>T>−40°C and decreases when −40°C>T>−100°C. The strain-rate- and temperature-dependent bimodal Weibull statistical constitutive theory was adopted for the statistical
analysis of the experimental results, and the Weibull parameters of single fiber were obtained. The results show that the
bimodal Weibull distribution function is suitable to represent the strength distribution of the glass fiber at low temperature
and different strain rates. The differences in the mechanical properties between EC8.0−24×7 and EC5.5−12 ×14 glass fiber bundles
were also discussed.
Project supported by the National Natural Science Foundation of China (No. 19772058). 相似文献