共查询到20条相似文献,搜索用时 15 毫秒
1.
Edwin A. Cowen Russell D. Dudley Qian Liao Evan A. Variano Philip L.-F. Liu 《Experiments in fluids》2010,49(1):77-88
The design, calibration, and testing of a borescopic quantitative imaging profiler (BQuIP) system, suitable for the insitu
measurement of two components of the instantaneous velocity in high sediment concentration flows, are presented. Unlike planar
quantitative imaging techniques, BQuIP has a concentration-dependent field of view, requiring detailed calibration. BQuIP
is demonstrated in unidirectional sheet flow in an open channel flume with a narrow-graded sand with median diameter 0.25 mm.
Acoustic velocity measurements are made in the suspension region above the BQuIP measured region yielding a continuous measurement
of velocity and turbulent stress from the immobile bed to just below the free surface. The temporal history at a point reveals
the sheet flow sediment velocities to be highly intermittent, and the spectra reveal a broad range of temporal scales close
to −5/3 in slope for the streamwise velocity component. At its core BQuIP is a quantitative imaging technique giving it significant
flexibility in terms of both the spatial and temporal analysis parameters (e.g., interrogation subwindow size and Δt, the time between images in a pair to be analyzed), allowing it to have tremendous dynamic range in terms of the velocities
that can be measured. 相似文献
2.
In this paper we present a non intrusive device to detect the inception of sediment transport and to measure bed load in
low-submergence flows. A solid state linear CCD camera provides linear images of the sediment movements across a control section,
located on the bottom of a laboratory flume. These arrays of information are reassembled to provide a raster image of the
bottom of the flume in correspondence of the control section. An on-line operating image processing software counts the number
of grains and evaluates their velocity.
Received: 25 July 1996/Accepted: 3 February 1997 相似文献
3.
Bart Beulen Nathalie Bijnens Marcel Rutten Peter Brands Frans van de Vosse 《Experiments in fluids》2010,49(5):1177-1186
An ultrasound velocity assessment technique was validated, which allows the estimation of velocity components perpendicular
to the ultrasound beam, using a commercially available ultrasound scanner equipped with a linear array probe. This enables
the simultaneous measurement of axial blood velocity and vessel wall position, rendering a viable and accurate flow assessment.
The validation was performed by comparing axial velocity profiles as measured in an experimental setup to analytical and computational
fluid dynamics calculations. Physiologically relevant pulsating flows were considered, employing a blood analog fluid, which
mimics both the acoustic and rheological properties of blood. In the core region (|r|/a < 0.9), an accuracy of 3 cm s−1 was reached. For an accurate estimation of flow, no averaging in time was required, making a beat to beat analysis of pulsating
flows possible. 相似文献
4.
A new cryomechanics measurement technique has been developed to measure fracture-induced dissipated energies as small as 10
nJ (10×10−9 J) at temperatures near 4.2 K. The technique, with much less stringent instrumentation requirements than those used for measurement
of ∼10 nJ energies, was applied to an induced fracture experiment where dissipation energies were of the order of ∼100 μJ.
Fracture of 0.5-mm diameter pencil leads of two different hardnesses gave rise to measured energies of 65 ∼ 110 μJ. A two-dimensional
finite-element analysis was used to interpret the experimental measurements. Based on the analysis, approximately 50 μJ of
65 ∼ 110 μJ measured is estimated to be the dissipated energy associated with crack formation and propagation. 相似文献
5.
Sara Nauri José Nogueira Antonio Lecuona Mathieu Legrand Pedro A. Rodríguez 《Experiments in fluids》2008,45(4):609-621
Particle image velocimetry with local field correction (LFC PIV) has been tested in the past to obtain two components of velocity
in a two dimensional domain (2D2C). When compared to conventional correlation based algorithms, this advanced technique has
shown improvements in three important aspects: robustness, resolution and ability to cope with large displacements gradients.
A further step in the development of PIV algorithms consists in the combination of LFC with the stereo technique, which is
able to obtain three components of velocity in a plane (2D3C PIV). In this work this combination is implemented and its performance
is evaluated carrying out the following two different tasks:
The first task has been achieved using synthetic images. Afterwards the coherence of the results has been checked with real
images. The results show improvement of Stereo-LFC PIV in respect to Stereo-Multigrid PIV enhanced with image distortion.
The performance of Stereo-LFC when only large scales are involved shows an increase of the dynamic range of measurable vorticity.
When small scales are analysed, the magnitude of the error resulting when using Stereo-LFC is about half of the one obtained
for the Stereo-Multigrid measurements. Results with errors below 20% have been achieved for some of the cases with peak vorticities
as large as 1.8 Δt
−1 (in the absence of out-of-plane displacements), out-of-plane loss of particle pairs of 65% (with a low peak vorticity of
0.06 Δt
−1) and peak vorticities as large as 1.5 Δt
−1 with 50% particle pair loss. For the second task most of the information has been obtained using real images. It has been
found that the resolution limit is very dependent on the robustness of the algorithms against image defects and variability.
The results show a remarkable improvement when using the Stereo-LFC PIV processing, although a full quantification and characterization
would need further study because of the variety of noise sources possible in a real image. 相似文献
– | Comparison of robustness and accuracy for large and small scale flow structures. This is carried out using three techniques: the conventional Stereo PIV, the Stereo-LFC PIV and the Stereo-Multigrid PIV enhanced with image distortion. |
– | Insight on the limit of resolvable scales for the Stereo-LFC. This task is relevant because the resolution attainable by this combination is higher than what has been obtained by the rest of the herein used algorithms. |
6.
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
7.
This article describes a pseudo-heterodyne demodulation technique for interferometric fiber optic sensors that has a larger
measurement range than is currently possible with pseudo-heterodyne demodulation. This sensor demodulation technique has a
bandwidth of 30 Hz to 2.5 kHz, is capable of resolving optical phase angles as small as 5×10−4 rad, and has a maximum measurement range of tens of radians in a bandwidth of 30–500 Hz. A comparison between the response
obtained from a resistance strain gage and a fiber optic sensor using this demodulation is favorable. 相似文献
8.
An aluminum alloy1 was tested at quasi-static to dynamic strain-rates (from 10−1 to 5 103 s−1), using a single measuring device, a modified Split Hopkinson Bar. A wave separation technique [Bussac et al., J Mech Phys
Solids 50:321–350, 2002] based on the maximum likelihood method was applied to process the strain and velocity measurements recorded at various points
on each bar. With this method, it is possible to compute the stress, strain, displacement and velocity at any point on the
bar. Since the measurement time is unlimited, the maximum strain measured in a given specimen no longer decreases with the
strain-rate, as occurs with the classical Split Hopkinson Bar method.
1The authors wish to thank the automobile manufacturer who provided samples of the alloy used in this study. For reasons of
commercial and industrial confidentiality, we were not informed about the composition of this alloy. 相似文献
9.
A particle image velocimetry system for microfluidics 总被引:20,自引:0,他引:20
J. G. Santiago S. T. Wereley C. D. Meinhart D. J. Beebe R. J. Adrian 《Experiments in fluids》1998,25(4):316-319
A micron-resolution particle image velocimetry (micro-PIV) system has been developed to measure instantaneous and ensemble-averaged
flow fields in micron-scale fluidic devices. The system utilizes an epifluorescent microscope, 100–300 nm diameter seed particles,
and an intensified CCD camera to record high-resolution particle-image fields. Velocity vector fields can be measured with
spatial resolutions down to 6.9×6.9×1.5 μm. The vector fields are analyzed using a double-frame cross-correlation algorithm.
In this technique, the spatial resolution and the accuracy of the velocity measurements is limited by the diffraction limit
of the recording optics, noise in the particle image field, and the interaction of the fluid with the finite-sized seed particles.
The stochastic influence of Brownian motion plays a significant role in the accuracy of instantaneous velocity measurements.
The micro-PIV technique is applied to measure velocities in a Hele–Shaw flow around a 30 μm (major diameter) elliptical cylinder,
with a bulk velocity of approximately 50 μm s-1.
Received: 26 November 1997/Accepted: 26 February 1998 相似文献
10.
Jiří Neustupa 《Archive for Rational Mechanics and Analysis》2010,198(1):331-348
We prove the existence of a weak solution to the steady Navier–Stokes problem in a three dimensional domain Ω, whose boundary
∂Ω consists of M unbounded components Γ1, . . . , Γ
M
and N − M bounded components Γ
M+1, . . . , Γ
N
. We use the inhomogeneous Dirichlet boundary condition on ∂Ω. The prescribed velocity profile α on ∂Ω is assumed to have an L
3-extension to Ω with the gradient in L
2(Ω)3×3. We assume that the fluxes of α through the bounded components Γ
M+1, . . . , Γ
N
of ∂Ω are “sufficiently small”, but we impose no restriction on the size of fluxes through the unbounded components Γ1, . . . , Γ
M
. 相似文献
11.
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
12.
A hybrid holographic system has been developed for three-dimensional particle image velocimetry. With unique high pass filters,
the system combines advantages of both in-line and off-axis holography without having their draw-backs. It improves the signal
to noise ratio of the reconstructed image, allows use of 3–15 μm particles in water at high population and achieves large
dynamic ranges in both velocity and space. With an automated image acquisition and processing system it has been used for
measuring the velocity distributions in a square duct at Re=1.23×105. The data consists of 97×97×87 vectors (with 50% overlapping of adjacent interrogation windows). The quality of the results
is evaluated using the continuity equation. The deviation from the equation decreases rapidly with increasing control volume
and reaches a level of less than 10%. Mean velocities, r.m.s. velocity fluctuations and turbulence spectra are estimated using
the data.
Received: 16 December 1996/Accepted: 6 March 1997 相似文献
13.
The boundary layer structure of oscillatory shallow open channel flows has been studied in a wide flume. Fluorescence solution
was released at a porous rough bed through a diffuser covered by gravel of 0.5 cm grain size. A planar laser-induced fluorescence
(PLIF) system was used to visualise the dye plumes in both vertical and horizontal planes for a qualitative understanding
of the roles of large-scale flow structures in mass transport. A variety of tests were conducted for a range of oscillatory
periods (30–240 s), water depths (3–16 cm) and velocity amplitudes (0.027–0.325 m/s), which cover a wide range of oscillatory
flows with Reynolds numbers Re
a
varied from 0.3 × 104 (laminar) to 2.1 × 106 (fully turbulent). For quantitative investigation, a novel technique, namely combined laser-induced fluorescence (LIF) and
2D laser Doppler velocimetry (LDV) (LIF/LDV), was developed and used to measure the velocity and solute concentration simultaneously
in a vertical plane over 50 cycles. From the dye plumes revealed by the PLIF in transitional flows, there are different patterns
of flow structure and solute transport with three representative stages of acceleration, deceleration and flow reversal. In
the acceleration stage, turbulence was suppressed with dye layers adhering to the surface with little vertical mass transport.
In the deceleration stage, flame-like turbulent structures occurred when turbulence generation was prominent. This was investigated
quantitatively by recording the percentage occurrence of the adhered smooth layers per cycle. For those smooth bed cases with
Re
a
< 1.8 × 105, the adhered smooth dye layers type of boundary layer occupied 100% of the oscillation period. Over a sufficiently high Re
a
, a rough bed can generate fully turbulent oscillatory flows without the appearance of adhering dye layers. Between these
two extremes, a transitional flow regime occurs in a wide range of flow conditions: Re
a
> 2.7 × 104 over the rough bed and Re
a
> 8.3 × 106 over a smooth bed. 相似文献
14.
M. Hokka J. Kokkonen J. Seidt T. Matrka A. Gilat V.-T. Kuokkala 《Experimental Mechanics》2012,52(2):195-203
Mechanical properties of most metallic materials can be improved by reducing their grain size. One of the methods used to
reduce the grain size even to the nanometer level is the severe plastic deformation processing. Equal Channel Angular Pressing
(ECAP) is one of the most promising severe plastic deformation processes for the nanocrystallization of ductile metals. Nanocrystalline
and ultrafine grained metals usually have significantly higher strength properties but lower tensile ductility compared to
the coarse grained metals. In this work, the torsion properties of ECAP processed ultrafine grained pure 1070 aluminum were
studied in a wide range of strain rates using both servohydraulic materials testing machines and Hopkinson Split Bar techniques.
The material exhibits extremely high ductility in torsion and the specimens did not fail even after 300% of strain. Pronounced
yield point behavior was observed at strain rates 500 s−1 and higher, whereas at lower strain rates the yielding was continuous. The material showed slight strain softening at the
strain rate of 10−4 s−1, almost ideally plastic behavior at strain rates between 10−3 s−1 and 500 s−1, and slight but increasing strain hardening at strain rates higher than that. The tests were monitored using digital cameras,
and the strain distributions on the surface of the specimens were calculated using digital image correlation. The strain in
the specimen localized very rapidly after yielding at all strain rates, and the localization lead to the development of a
shear band. At high strain rates the shear band developed faster than at low strain rates. 相似文献
15.
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
16.
F. Lanza di Scalea 《Experimental Mechanics》1998,38(4):233-241
The measurement of the coefficients of thermal expansion (CTEs) of composite materials using electrical resistance strain
gages is addressed. Analytical expressions for the CTEs of an orthotropic lamina are derived, accounting for the effects of
transverse sensitivity and possible misalignment of the gages. Experiments are performed for the characterization of the thermal
expansion behavior of a fiber-glass-reinforced epoxy unidirectional lamina using an invar specimen as reference material.
Preliminary training cycles are performed for the determination of an optimal heating rate for the measurements, which ensures
thermal equilibrium conditions. Three measurement cycles yield the principal CTEs of the lamina α1, α2 and α12 with repeatability within ±0.34×10−6, ±0.85×10−6 and ±2.8×10−6/°C, respectively. It is noted that inhomogeneity of the specimen and variation in thermomechanical properties of the gages
can cause a noticeable spead in the measurements. 相似文献
17.
The passage of solid spheres through a liquid–liquid interface was experimentally investigated using a high-speed video and
PIV (particle image velocimetry) system. Experiments were conducted in a square Plexiglas column of 0.1 m. The Newtonian Emkarox
(HV45 50 and 65% wt) aqueous solutions were employed for the dense phase, while different silicone oils of different viscosity
ranging from 10 to 100 mPa s were used as light phase. Experimental results quantitatively reveal the effect of the sphere’s
size, interfacial tension and viscosity of both phases on the retaining time and the height of the liquid entrained behind
the sphere. These data were combined with our previous results concerning the passage of a rising bubble through a liquid–liquid
interface in order to propose a general relationship for the interface breakthrough for the wide range of Mo
1/Mo
2 ∈ [2 × 10−5–5 × 104] and Re
1/Re
2 ∈ [2 × 10−3–5 × 102]. 相似文献
18.
Knowledge of the airflow characteristics within the nasal cavity with nasal high flow (NHF) therapy and during unassisted
breathing is essential to understand the treatment’s efficacy. The distribution and velocity of the airflow in the nasal cavity
with and without NHF cannula flow has been investigated using stereoscopic particle image velocimetry at steady peak expiration
and inspiration. In vivo breathing flows were measured and dimensionally scaled to reproduce physiological conditions in vitro.
A scaled model of the complete nasal cavity was constructed in transparent silicone and airflow simulated with an aqueous
glycerine solution. NHF modifies nasal cavity flow patterns significantly, altering the proportion of inspiration and expiration
through each passageway and producing jets with in vivo velocities up to 17.0 ms−1 for 30 l/min cannula flow. Velocity magnitudes differed appreciably between the left and right sides of the nasal cavity.
The importance of using a three-component measurement technique when investigating nasal flows has been highlighted. 相似文献
19.
T. Aihara K. Yamamoto K. Narusawa T. Haraguchi M. Ukaku A. Lasek F. Feuillebois 《Heat and Mass Transfer》1997,33(1-2):109-120
Heat transfer characteristics of a turbulent, dilute air-solids suspension flow in thermally developing/developed regions
were experimentally studied, using a uniformly heated, horizontal 54.5 mm-ID pipe and 43-μm-diameter glass beads. The local
heat transfer was measured at 27 locations from the inlet to 120-dia downstream of the heated section over a range of Reynolds
numbers 3×104−1.2×105 and solids loading ratio 0–3, and the fully developed profiles of air velocity/temperature and particle mass flux were measured
at a location 140-dia downstream of the heated section using specially designed probes, inserted into the suspension flow.
The effects of the Reynolds number, solids loading ratio, and azimuthal/longitudinal locations on the heat transfer characteristics
and their interactions are discussed through comparison of the present results with the data obtained by other investigators.
Received on 14 October 1996 相似文献
20.
Fluctuations of bed load solid discharge and grain size distribution on steep slopes with image analysis 总被引:1,自引:0,他引:1
A new device using image analysis has been designed to measure the grain size distribution and the solid discharge of natural particles downstream of an experimental mobile bed flume. Experiments were performed in a 10 cm wide, 15% steep flume, with both uniform (4–5 mm) and non-uniform materials (3–15 mm). For the uniform material, outgoing solid discharge fluctuations were not significant, whereas they were large for the non-uniform material. The lower solid discharges were coarser than the higher solid discharges; this behavior is associated with the smallest particles playing a major role through building and destroying transient antidune-like bedforms. 相似文献