Interaction of a shaped-charge jet with a target possessing an axial orifice is studied experimentally. For an orifice diameter
approximately equal to 0.2D, where D is the shaped-charge diameter, the shaped-charge penetration depth is found to be substantially reduced owing to
deviation of the shaped-charge jet axis from the shaped charge axis because of imperfections of the manufacturing technology.
A diameter of the target orifice providing unconstrained penetration of the shaped-charge jet is determined.
__________
Translated from Prikladnaya Mekhanika i Tekhnicheskaya Fizika, Vol. 49, No. 6, pp. 13–16, November–December, 2008. 相似文献
We consider transport of a solute obeying linear kinetic sorption under unsteady flow conditions. The study relies on the
vertical unsaturated flow model developed by Indelman et al. [J. Contam. Hydrol. 32 (1998), 77–97] to account for a cycle of infiltration and redistribution. One of the main features of this type of transport,
as compared with the case of a continuous water infiltration, is the finite depth of solute penetration. In the infiltration
stage an analytical solution that generalizes the previous results of Lassey [Water Resour. Res. 24 (1988), 343–350] and Severino and Indelman [J. Contam. Hydrol. 70 (2004), 89–115] is derived. This solution accounts for quite general initial solute distributions in both the mobile and
immobile concentration. When the redistribution is also considered, two timescales become relevant, namely: (i) the desorption
rate k−1, and (ii) the water application time tap. In particular, we have assumed that the quantity ε =(ktap)−1 can be regarded as a small parameter so that a perturbation analytical solution is obtained. At field-scale the concentration
is calculated by means of the column model of Dagan and Bresler [Soil Sci. Soc. Am. J. 43 (1979), 461–467], i.e. as ensemble average over an infinite series of randomly distributed and uncorrelated soil columns.
It is shown that the heterogeneity of hydraulic properties produces an additional spreading of the plume. An unusual phenomenon
of plume contraction is observed at long times of solute propagation during the drying period. The mean solute penetration
depth is studied with special emphasis on the impact of the variability of the saturated conductivity upon attaining the maximum
solute penetration depth. 相似文献
The dependence of the detonation velocity of aNIL-1 low-density sheet explosive on density is found in the range of charge densities0.1–0.3 g/cm3. The equation of state of theNIL-1 detonation products with a linear dependence of the effective isentropic exponent of unloading on the density of an explosive
that is acceptable for applied calculations is proposed. Calculated estimates of the mechanical action of anNIL-1 explosion on obstacles from several powerful explosive compositions are given.
Institute of Experimental Physics, Sarov 607190. Translated from Prikladnaya Mekhanika i Tekhnicheskaya Fizika, Vol. 41, No.
3, pp. 43–47, May–June, 2000. 相似文献
A theoretical study is presented herein on the pen- etration of a semi-infinite target by a spherical-headed long rod for Yp 〉 S, where Yp is the penetrator strength and S is the static target resistance. For Yp 〉 S, depending upon initial impact velocity, there exist three types of penetration, namely, penetration by a rigid long rod, penetration by a deforming non-erosive long rod and penetration by an erosive long rod. If the impact velocity of the penetrator is higher than the hydrodynamic velocity (VH), it will penetrate the target in an erosive mode; if the impact velocity lies between the hydrodynamic velocity (VH) and the rigid body velocity (VR), it will penetrate the target in a deformable mode; if the impact velocity is less than the rigid body velocity (VR), it will penetrate the target in a rigid mode. The critical conditions for the transition among these three penetration modes are proposed. It is demonstrated that the present model predictions correlate well with the experimental observations in terms of depth of penetration (DOP) and the critical transition conditions. 相似文献
The parameters of the Grigoryan soil model are determined using an experimental-computational method previously proposed and
the results of reversed experiments on penetration of projectiles with flat and hemispherical heads at impact velocities of
50–450 m/sec in sandy soil. It is shown that the quasistationary dependences of the resistance force on impact velocity obtained in the
reversed experiment can be used to solve problems of deep penetration of projectile in soil with an error not exceeding the
measurement error. 相似文献
The time and depth of vertical one-dimensional projectile penetration into sandy media in the near shore region are derived.
A precise definition for the physical properties and for the behavior of the sandy medium following the projectile impact
are evaluated. Three separate time intervals following projectile impact are identified. During the first 3 ms of penetration,
the deviatoric friction stress is shown to be negligible and the integrated Mie–Grüneisen equation of state (or, equivalently,
the Hugoniot-adiabat) may be applied to compute the normal penetration resistance force from the sand pressure. In order to
compute sand pressure as a function of the sand density D by the integrated Mie–Grüneisen equation of state, the Mie–Grüneisen
dimensionless constants γ0 and s and the dimensional speed of sound C0 in the sandy medium are required. In order to illustrate the one-dimensional shock wave propagation in both wet and dry sands,
Hugoniot data for wet and dry silica sands are evaluated by a three degrees of freedom algorithm to compute these required
constants. The numerical results demonstrate that the amplitude of the shock wave pressure in the wet silica sand (41% porosity)
is approximately one-third of the shock wave pressure amplitudes in the dry silica sands (22% and 41% porosity). In addition,
the shock wave pressure dampens quicker in the wet sand than in the dry sands. 相似文献
The nonstationary rectilinear motion of an amphibian air-cushion vehicle (AACV) on a water surface covered with finely broken ice is considered for various modes of velocity variation. The influence of
the water depth, flotation parameters, and mode of motion on the wave resistance of the vehicle is analyzed. Maneuvering methods
for increasing or decreasing the wave resistance of AACVs are proposed.
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Translated from Prikladnaya Mekhanika i Tekhnicheskaya Fizika, Vol. 48, No. 1, pp. 97–102, January–February, 2007. 相似文献
Experimental turbulent combustion studies require systems that can simulate the turbulence intensities [u′/U0 ~ 20–30% (Koutmos and McGuirk in Exp Fluids 7(5):344–354, 1989)] and operating conditions of real systems. Furthermore, it is important to have systems where turbulence intensity can be
varied independently of mean flow velocity, as quantities such as turbulent flame speed and turbulent flame brush thickness
exhibit complex and not yet fully understood dependencies upon both U0 and u′. Finally, high pressure operation in a highly pre-heated environment requires systems that can be sealed, withstand high
gas temperatures, and have remotely variable turbulence intensity that does not require system shut down and disassembly.
This paper describes the development and characterization of a variable turbulence generation system for turbulent combustion
studies. The system is capable of a wide range of turbulence intensities (10–30%) and turbulent Reynolds numbers (140–2,200)
over a range of flow velocities. An important aspect of this system is the ability to vary the turbulence intensity remotely,
without changing the mean flow velocity. This system is similar to the turbulence generators described by Videto and Santavicca
(Combust Sci Technol 76(1):159–164, 1991) and Coppola and Gomez (Exp Therm Fluid Sci 33(7):1037–1048, 2009), where variable blockage ratio slots are located upstream of a contoured nozzle. Vortical structures from the slots impinge
on the walls of the contoured nozzle to produce fine-scale turbulence. The flow field was characterized for two nozzle diameters
using three-component Laser Doppler velocimetry (LDV) and hotwire anemometry for mean flow velocities from 4 to 50 m/s. This
paper describes the key design features of the system, as well as the variation of mean and RMS velocity, integral length
scales, and spectra with nozzle diameter, flow velocity, and turbulence generator blockage ratio. 相似文献
An experimental study is presented for water droplet impingement on a liquid surface. The impaction process was recorded
using a high-speed digital camera at 1,000 frames/s. The initial droplet diameter was fixed at 3.1 mm ± 0.1 mm, and all experiments
were performed in atmospheric air. The impact velocity was varied from 0.36 m/s to 2.2 m/s thus varying the impact Weber number
from 5.5 to 206. The impacted liquid surface consisted of two fluids, namely water and methoxy-nonafluorobutane, C4F9OCH3 (HFE7100). The depth of the water and HFE7100 pool was varied from 2 mm to 25 mm. The collision dynamics of water in the
HFE7100 pool was observed to be drastically different from that observed for the water droplet impingement on a water pool.
The critical impact Weber number for jet breakup was found to be independent of liquid depth. Water–HFE7100 impact resulted
in no jet breakup over the range of velocities studied. Therefore, no critical impact Weber number can be defined for water–HFE7100
impact.
Received: 27 June 2001/Accepted: 29 November 2001 相似文献
The penetration of long gas bubble through a viscoelastic fluid in a capillary tube has been studied in order to investigate
the influence of viscoelastic material properties on the hydrodynamic coating thickness and local flow kinematics. Experiments
are conducted for three tailored ideal elastic (Boger) fluids, designed to exhibit similar steady shear properties but substantially
different elastic material functions. This allows for the isolation of elastic and extensional material effects on the bubble
penetration process. The shear and extensional rheology of the fluid is characterized using rotational and filament stretching
rheometers (FSR). The fluids are designed such that the steady-state extensional viscosity measured by the FSR at a Deborah
number (De) greater than 1 differs over three orders of magnitude (Trouton ratio = 103–106). The experiment set up to measure the hydrodynamic coating thickness is designed to provide accurate data over a wide range
of capillary numbers (0.01 < Ca < 100). The results indicate that the coating thickness in this process increases with an
increase in the extensionally thickening nature of the fluid. Experiments are also conducted using several different capillary
tube diameters (0.1 < D < 1 cm), in order to compare responses at similar Ca but different flow De. Suitable scaling methods and nonlinear viscoelastic
constitutive equations are explored to characterize the displacement process for polymeric fluids. Bubble tip shapes at different
De are recorded using a CCD camera, and measured using an edge detection algorithm. The influence of the mixed flow field
on the bubble tip shape is examined. Particle tracking velocimetry experiments are conducted to compare the influence of viscoelastic
properties on the velocity field in the vicinity of the bubble tip. Local shear and extension rates are calculated in the
vicinity of the bubble tip from the velocity data. The results provide quantitative information on the influence of elastic
and extensional properties on the bubble penetration process in gas-assisted injection molding. The bubble shape and velocity
field information provides a basis for evaluating the performance of constitutive equations in mixed flow.
Received: 19 January 1999 Accepted: 30 June 1999 相似文献
An assessment has been made of the potential reduction in calculated fatigue-crack-growth lives when the small-crack effect
is considered. The assessment was based on small-crack and large-crack grwoth-rate data of 2024-T3 aluminum alloy forR=−1 andR=0 constant-amplitude loading and for a fighter-wing spectrum loading (FALSTAFF). The potential impact of the small-crack
effect was assessed by comparing lives computed using only large-crack data to those computed using a combined small- and,
large-crack data based. Based on life calculations, the small-crack effect would have: (1) no impact on life analyses that
assume an initial crack depth large than about 0.3 mm (such as in current airframe damage-tolerance analyses); (2) only a
small impact on life analyses that assume an inital depth of 0.1 mm (such as im some current durability analyses) if the large-crack
thresholds are ignored; but (3) a large impact on life analyses that assume an initial depth of about 0.01 mm (such as in
a total-life analysis).
Paper was presented at the 1988 SEM Spring Conference on Experimental Mechanics held in Portland, OR on June 5–10. 相似文献
A study on the resistance of rigid projectiles penetrating into semi-infinite concrete targets is performed in this paper. Experimental data are analyzed to examine the penetration resistance during various stages of the penetration process. A numerical tool using AUTODYN hydrocode is applied in the study. The numerical results on both deceleration-time history and depth of penetration of projectiles are in good agreement with experimental data, which demonstrate the feasibility of the numerical model in these conditions. Based on the numerical model with a two-staged pre-drilled hole, the rigid projectile penetration in tunneling stage is studied for concrete targets with different strengths in a wide range of impact velocities. The results show that the penetration in tunnel stage can be divided into two different cases in terms of initial impact velocity. In the first case, when the impact velocity is approximately less than 600 m/s, the deceleration depends on initial impact velocity. In the second case, when the impact velocity is greater than 600 m/s, the effect of target inertia becomes apparent, which agrees with commonly used concrete penetration resistance equations based on cavity expansion model.
Graphic abstract
A two-staged pre-drilled hole model was developed and the results show that the depth of entrance stage tends to decrease with the increase of impact velocity. The influence of the inertial term at low velocity range (approximately close to 600 m/s) is inconspicuous. With further increase of the penetration velocity, the effect of the target inertia becomes apparent as proposed by Forrestal. The effect of mass abrasion of projectiles, entrance phase and strain effect of concrete materials on the tendency of deceleration was clarified.
Fluid flow at the interface of a porous medium and an open channel is the governing phenomenon in a number of processes of
industrial importance. Traditionally, this has been modeled by applying the Brinkman’s modification of Darcy’s law to obtain
the velocity profile in terms of an additional parameter known as the “apparent viscosity” or the “slip coefficient”. To test
this ad hoc approach, a detailed experimental investigation of the flow was conducted using Laser Doppler Anemometry (LDA) in the close
vicinity of the permeable boundary of a porous medium. The porous medium used in the experiments consisted of a network of
continuous glass strands woven together in a random fashion.
A Hele–Shaw cell was partially filled with a fibrous preform such that an open channel flow is coupled with the Darcy flow
inside the preform through the permeable interface of the preform. The open channel portion of the Hele–Shaw cell also acts
as an ideal porous medium of known in-plane permeability which is much higher than the permeability of the fibrous porous
medium. A viscous fluid is injected at a constant flow rate through the above arrangement and a saturated and steady flow
is established through the cell. Using LDA, steady state velocity profiles are accurately measured by traversing across the
cell in the direction perpendicular to the flow. A series of experiments were conducted in which fluid viscosity, flow rate,
solid volume fraction of the porous medium and depth of the Hele–Shaw cell were varied. For each and every case in which the
conditions for Hele–Shaw approximation were valid, the depth of the boundary layer zone or the screening length inside the
fibrous preform was found to be of the order of the channel depth. This is much larger as compared to the Brinkman’s prediction
of the screening length which is of the order of √K, where K is the permeability of the fibrous porous medium. Based on this finding, we modified the boundary condition in the Brinkman’s
solution and found that the velocity profile results compared well with the experimental data for the planar geometry and
the fibrous preforms for volume fractions of 7%, 14% and 21% for Hele–Shaw cell depths of 1.6 and 3.175 mm. For a cell depth
of 4.8 cm, in which the Hele–Shaw approximation was not valid, the boundary layer thickness or the screening length was found
to be less than the mold or channel depth but was still much larger than the Brinkman’s prediction.
Received: 10 May 1996 / Accepted: 26 August 1996 相似文献
The existence of capillary-gravitational equilibrium is detected in the problem of the penetration of a nonwetting fluid into
a porous medium from the top. Using a numerical simulation method, three qualitatively feasible regimes of operation of the
system are distinguished: total penetration of the soil; penetration to a finite depth, i.e., starting from a certain moment
of time the gravitational head is weaker than the capillary resistance of the medium; no penetration of the soil. The existence
of these three regimes makes it possible to distinguish critical parameters of the process expressed in terms of the Bond
number.
Moscow. Translated from Izvestiya Rossiiskoi Akademii Nauk, Mekhanika Zhidkosti i Gaza, No. 2, pp. 95–103, March–April, 1998. 相似文献
To better understand mixing by hairpin vortices, time-series particle image velocimetry (PIV) was applied to the wake of
a trapezoidal-shaped passive mixing tab mounted at the bottom of a square turbulent channel (Reh=2,080 based on the tab height). Instantaneous velocity/vorticity fields were obtained in sequences of 10 Hz in the tab wake
in the center plane (x–y) and in a plane (x–z) parallel to the wall. Periodically-shed hairpin vortices were clearly identified and seen to rise as they advected downstream.
Experimental evidence shows that the vortex-induced ejection of the near-wall viscous fluid to the immediate upstream is important
to the dynamics of hairpin vortices. It can increase the strength of the hairpin vortices in the near tab region and cause
generation of secondary hairpin vortices further downstream when the hairpin heads are farther away from the wall. Measurements
also reveal the existence of a type of new secondary vortice with the opposite-sign spanwise vorticity. The distribution of
vortex loci in the x–y plane shows that the hairpin vortices and the reverse vortices are spatially segregated in distinct layers. Turbulence statistics,
including mean velocity profiles, Reynolds stresses, and turbulent kinetic energy dissipation rate distributions, were obtained
from the PIV data. These statistical quantities clearly reveal imprints of the identified vortex structures and provide insight
into mixing effectiveness.
Received: 24 February 2000/Accepted: 24 October 2000 相似文献
Creep experiments with a solution of polystyrene (Mw = 2.6 MDa, 16 vol.%, 25 °C) in diethyl phthalate are reported for stresses between 100 and 2,500 Pa (≈ 3GN0/4). The aim was to look for a flow transition as reported for strongly entangled poly(isobutylene) solutions. The experiments
with the polystyrene solution were repeated for cone angles of 2, 4, and 6° (radius 15 mm) and showed no dependence on cone
angle. The Cox–Merz rule was not fulfilled for stresses beyond about 800 Pa. The tangential observation with a CCD camera
showed that the edge took a concave shape because of the second normal stress difference. Beyond 1,000 Pa, the concave edge
develops into a crevice, thus substantially reducing the effective cross-section. This leads to runaway in a constant torque
experiment. At p21 = 800 Pa, head-on particle tracking confirms that the originally linear velocity profile takes a gooseneck shape, thus revealing
shear banding. When the creep stress is stepped down to 100 Pa, this velocity profile evolves back to a linear one. The conclusion
from this work is that even if nonlinear creep experiments are reproducible and a steady state is reached, this does not mean
that the flow field is homogeneous.
This paper was presented at Annual European Rheology Conference (AERC) held in Hersonisos, Crete, Greece, April 27–29, 2006. 相似文献
We study the flow of yield stress fluids over a rotating surface when both the viscoelastic solid behavior below a critical
deformation (γc) and liquid properties beyond γc can play a significant role. We review the detailed characteristics of the flow in the solid regime in the specific case
of a pure elongational strain (large height to radius ratio). We, in particular, show that there exists a critical rotation
velocity (ωc) associated with the transition from the solid to the liquid regime. We then consider the specific case of lubricational
regime (small height to radius ratio) in the liquid regime. In that case we describe the different possible evolutions of
the equilibrium shape of the material as a function of the rotation velocity (ω), from which we extrapolate the transient shape evolutions as ω increases. We show that for a sufficiently large rotation velocity the sample separates into two parts, one remaining at
rest around the rotation axis, the other going on moving radially. These predictions are then compared with systematic spin-coating
tests under increasing rotation velocity ramps followed by a plateau at ωf with typical yield stress fluids. It appears that there exists a critical velocity below which the material undergoes a limited
elongation and beyond which it starts to spread significantly over the solid surface. For a larger ωf value the sample forms a thick peripheral roll, leaving behind it a thin layer of fluid at rest relatively to the disc. These
characteristics are in qualitative agreement with the theoretical predictions. Beyond a sufficiently large ωf value this roll eventually spreads radially in the form of thin fingers. Moreover, in agreement with the theory in the lubricational
regime, the different curves of deformation vs ω fall along a master curve when the rotation velocity is scaled by ωc for different accelerations, different sample radii, or different material yield stress. The final thickness of the deposit
seems to be mainly governed by the displacement of the roll, the characteristics of which take their origin in the initial
stage of the spreading, including the solid–liquid transition. 相似文献
We investigate the gas-particle dynamics of a device designed for biological pre-clinical experiments. The device uses transonic/supersonic gas flow to accelerate microparticles such that they penetrate the outer skin layers. By using a shock tube coupled to a correctly expanded nozzle, a quasi-one-dimensional, quasi-steady flow (QSF) is produced to uniformly accelerate the microparticles. The system utilises a microparticle “cassette” (a diaphragm sealed container) that incorporates a jet mixing mechanism to stir the particles prior to diaphragm rupture. Pressure measurements reveal that a QSF exit period – suitable for uniformly accelerating microparticles – exists between 155 and 220 mus after diaphragm rupture. Immediately preceding the QSF period, a starting process secondary shock was shown to form with its (x,t) trajectory comparing well to theoretical estimates. To characterise the microparticle, flow particle image velocimetry experiments were conducted at the nozzle exit, using particle payloads with varying diameter (2.7–48 μm), density (600–16,800 kg/m3) and mass (0.25–10 mg). The resultant microparticle velocities were temporally uniform. The experiments also show that the starting process does not significantly influence the microparticle nozzle exit velocities. The velocity distribution across the nozzle exit was also uniform for the majority of microparticle types tested. For payload masses typically used in pre-clinical drug and vaccine applications (≤ 1 mg), it was demonstrated that payload scaling does not affect the microparticle exit velocities. These characteristics show that the microparticle exit conditions are well controlled and are in agreement with ideal theory. These features combined with an attention to the practical requirements of a pre-clinical system make the device suitable for investigating microparticle penetration into the skin for drug delivery. 相似文献