Performance of digital image velocimetry processing techniques

McKenna, Sean P.; McGillis, Wade R.

doi:10.1007/s003480200011

Cited by 53 publications

(35 citation statements)

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“…DIC operates through the discretisation of an image into multiple interrogation windows, which are correlated with the same features in the following images. Displacement vectors are obtained for the change in position of each interrogation window, allowing strain distributions across the full image to be calculated [40]. DIC allows sub-pixel displacement measurements [41].…”

Section: Finite Element Modelmentioning

confidence: 99%

An Evaluation of the Double Torsion Technique

2011

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Double Torsion (DT) is a powerful testing technique for fracture mechanics characterisation of brittle materials as, in principle, it provides a crack length independent test configuration. However, several corrections have been proposed to address variations of experimental results reported from various laboratories. These correction factors address the validity of the DT configuration and its crack length independent stress intensity. Never the less, there seems to be no consensus in literature on the various corrections and the reason of reported variations. This paper presents firstly a critical review of the DT technique, followed by proposed corrections through an experimental analysis using the proposed corrections, a Finite Element model of the geometry and the use of Digital Image Correlation to measure out-of-plane surface deformations. It focuses on the validity of the constant stress intensity regime and the independence of crack length in a critical evaluation using Polymethylmethacrylate test specimens. Assessment of three un-grooved specimen geometry configurations demonstrated the apparent regime of approximately constant stress intensity, although a small but clear dependence of the stress intensity on crack length was observed in all specimen configurations. This dependence is attributable to significant load-point deflections and out-of plane deformations that are not accounted for in the DT analysis. Revisions of the proposed analysis methodologies show that a crack length independent specimen geometry can be achieved, however at the cost of less accurate data. Reliable and accurate data can be achieved with a DT testing configuration using an optimum specimen configuration.

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Section: Finite Element Modelmentioning

confidence: 99%

An Evaluation of the Double Torsion Technique

2011

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“…The velocity field of the flow is determined by dividing average local displacements of seeding particles in the flow by the time step, ∆t, between the laser pulses. In this work, we used a hybrid DPIV code that performs a quick FFT estimate of sub-window displacements and then refines the estimate to sub-pixel accuracy by local cross-correlation (McKenna and McGillis, 2002). Sub-windows were 32ϫ32 pixels with an overlap of 16 pixels.…”

Section: Flow Visualizationmentioning

confidence: 99%

“…The laser sheet was 1-2·mm thick and the flow was seeded with silver-coated, hollow glass spheres, 10·µm in diameter (DANTEC, Skovlunde, Denmark). The time step, ∆t, between laser pulses was set at 2-10·ms, depending on swimming speed to optimize particle displacements (McKenna and McGillis, 2002). The laser pulse length, or exposure time, was 3-5·ns with an available power of 500·mJ per pulse.…”

Section: Flow Visualizationmentioning

confidence: 99%

Jet flow in steadily swimming adult squid

Anderson

Grosenbaugh

2005

Journal of Experimental Biology

121

154

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SUMMARY Although various hydrodynamic models have been used in past analyses of squid jet propulsion, no previous investigations have definitively determined the fluid structure of the jets of steadily swimming squid. In addition, few accurate measurements of jet velocity and other jet parameters in squid have been reported. We used digital particle imaging velocimetry (DPIV) to visualize the jet flow of adult long-finned squid Loligo pealei(mantle length, Lm=27.1±3.0 cm, mean ± s.d.) swimming in a flume over a wide range of speeds(10.1-59.3 cm s-1, i.e. 0.33-2.06 Lms-1). Qualitatively, squid jets were periodic, steady, and prolonged emissions of fluid that exhibited an elongated core of high speed flow. The development of a leading vortex ring common to jets emitted from pipes into still water often appeared to be diminished and delayed. We were able to mimic this effect in jets produced by a piston and pipe arrangement aligned with a uniform background flow. As in continuous jets, squid jets showed evidence of the growth of instability waves in the jet shear layer followed by the breakup of the jet into packets of vorticity of varying degrees of coherence. These ranged from apparent chains of short-lived vortex rings to turbulent plumes. There was some evidence of the complete roll-up of a handful of shorter jets into single vortex rings, but steady propulsion by individual vortex ring puffs was never observed. Quantitatively, the length of the jet structure in the visualized field of view, Lj, was observed to be 7.2-25.6 cm, and jet plug lengths, L, were estimated to be 4.4-49.4 cm using average jet velocity and jet period. These lengths and an average jet orifice diameter, D, of 0.8 cm were used to calculate the ratios Lj/D and L/D, which ranged from 9.0 to 32.0 and 5.5 to 61.8, respectively. Jets emitted from pipes in the presence of a background flow suggested that the ratio between the background flow velocity and the jet velocity was more important than L/D to predict jet structure. Average jet velocities in steadily swimming squid ranged from 19.9 to 85.8 cm s-1 (0.90-2.98 Lm s-1) and were always greater in magnitude than swimming speed. Maximum instantaneous fluid speeds within squid jets ranged from 25.6 to 136.4 cm s-1. Average jet thrust determined both from jet velocity and from three-dimensional approximations of momentum change in successive jet visualizations showed some differences and ranged from 0.009 to 0.045 N over the range of swimming speeds observed. The fraction by which the average jet velocity exceeded the swimming speed, or `slip',decreased with increasing swimming speed, which reveals higher jet propulsive efficiency at higher swimming speeds. Jet angle, subtended from the horizontal, decreased from approximately 29° to 7° with increasing swimming speed. Jet frequency ranged from 0.6 to 1.3 Hz in the majority of swimming sequences, and the data suggest higher frequencies at the lowest and highest speeds. Jet velocity, angle, period and frequency exhibited increased variability at speeds between 0.6 and 1.4 Lms-1. This suggests that at medium speeds squid enjoy an increased flexibility in the locomotive strategies they use to control their dynamic balance.

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“…Such techniques are used in fluid imaging to estimate dense correlation field, known as Particle Image Velocimetry [40]. The measurement confidence could be also estimated in the Fourier space.…”

Section: Remarks On Computational Complexitymentioning

confidence: 99%

Conditional filters for image sequence-based tracking - application to point tracking

Arnaud

Mémin

Cernuschi-Frias

2005

IEEE Trans. on Image Process.

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Abstract-In this paper, a new conditional formulation of classical filtering methods is proposed. This formulation is dedicated to image sequence based tracking. These conditional filters allow solving systems whose measurements and state equation are estimated from the image data. In particular, the model that is considered for point tracking combines a state equation relying on the optical flow constraint and measurements provided by a matching technique. Based on this, two point trackers are derived. The first one is a linear tracker well-suited to image sequences exhibiting global dominant motion. This filter is determined through the use of a new estimator, called the conditional linear minimum variance estimator. The second one is a nonlinear tracker, implemented from a conditional particle filter. It allows tracking of points whose motion may be only locally described. These conditional trackers significantly improve results in some general situations. In particular, they allow dealing with noisy sequences, abrupt changes of trajectories, occlusions and cluttered background.

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Performance of digital image velocimetry processing techniques

Cited by 53 publications

References 0 publications

An Evaluation of the Double Torsion Technique

An Evaluation of the Double Torsion Technique

Jet flow in steadily swimming adult squid

Conditional filters for image sequence-based tracking - application to point tracking

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