IMAGE PROCESSING METHODS IN APPLIED MECHANICS
May 6 - 8, 1999
Holographic interferometry and digital speckle pattern interferometry as techniques for measuring out-of-plane velocity fields are presented. The feasibility of introducing phase shifting techniques in order to improve the accuracy of holographic interferometry is investigated. The techniques are demonstrated in a Rayleigh-Bénard convective flow.
Book of Abstracts Page # 39
Nonmetallic inclusion-metallic matrix interface structure in refractory compound-based composite materials seriously affects such events as plastic strain and rupture. Boron carbide (Ti-Ni-Mo) binder granule material structure by X-ray phase and microscopic analysis. Study of phase makeup of B4C - metallic binder transition zone revealed existence of two-phase zone consisting of bond and carbon phases.
Book of Abstracts Page # 43
The paper presents the current state of the researches on modern rail car brakes diagnosing and supervising. Our considerations concern the estimation of the brake friction parts wear by measuring friction elements thickness using image processing techniques.
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Modeling solid particle transport in a liquid turbulent flow is a difficult subject due to the equal importance of most of the terms in the particle equation of motion. Experimetal methods, such as particle image velocimetry (PIV), may provide information in complex flow situations that currently may not be obtained by numerical simulations. The goal of the present paper is to measure by DPIV simultaneously the instantaneous velocity field of both phases of a particle-liquid flow.
Book of Abstracts Page # 51
Optical methods or visualizations cannot be performed for granular flows because of the opacity of these materials. Hence, the efficient techniques developed for flows analysis cannot be adapted. This reduces the possibilities to expensive magnetic or radioactive tracking methods or X-rays visualizations. In this paper an optical particle tracking velocimetry is presented for a mixture of oil and glass beads by matching the index refraction of both materials. Lagrangian observations of single colored particle as well as Eulerian statistical fluxes are then possible. The technique is applied on a sedimentation flow in a squared section vertical tunnel.
Book of Abstracts Page # 123
The quaternionic Fourier transform (QFT) is introduced as a modification of the 2D complex Fourier transform. We analyze the symmetry properties of the QFT and find that according to these properties the 2D Hartley transform,the complex Fourier transform and the QFT can be regarded as three levels of a hierarchy of 2D harmonic transforms. Based on the QFT a new definition of the analytic signal in 2D is proposed. Quaternionic Gabor filters are introduced and shown to provide an approximation to the 2D quaternionic analytic signal. The local phase of a real 2D signal is defined as the angular phase of its quaternionic Gabor filter response. We show that there is a close relation between the local intrinsically 2D structure of a signal and its local phase as defined above. Applications to the image processing task of texture segmentation are presented.
Book of Abstracts Page # 65
A conditional PIV acquisition technique and averaging procedure is developed to study coherent structures forming in the interaction between a jet and a cross stream. The experiment is conducted in a water tunnel and the jet is forced by a mechanical device. Sequences of images are acquired synchronized to the external forcing and with a fixed phase. Instantaneous and averaged velocity and vorticity 2D fields are obtained for several flow conditions.
Book of Abstracts Page # 67
Infrared (IR) thermography is a two-dimensional, non-contact technique of temperature measurement which can be usefully exploited in a vast variety of industrial applications as well as research fields [1-9]. The infrared scanning radiometer (IRSR) basically includes a camera which detects the electromagnetic energy radiated in the infrared spectral band by an object (whose surface temperature is to be measured) and converts it into an electronic video signal. This signal corresponds to the object temperature map. In the present work, attention is focused on the capability of IRSR to measure heat transfer coefficients in three different fluid flow configurations; in particular, the heat transfer to a jet centrally impinging on a rotating disk; the complex heat transfer pattern associated with a jet in cross-flow; the heat transfer distribution along a 180deg turn channel.
Book of Abstracts Page # 7
During last decade the experimental flow investigation based on image analysis (PIV and PTV) received a big development due to the improvement of hardware support and acquisition systems (digital cameras and image acquisition cards). PIV technique is based on the detection of the displacement of seeding particles which can represent, for their characteristics, the flow . In PIV the displacement is calculated by analysing images acquired at known times, the images are subdivided in sub-domains and the mean particles displacement is calculated by means of auto or cross-correlation. By using cross-correlation it is possible to increase the dynamical range of measurement but it requires the acquisition of two distinct images. Several techniques were suggested in order to obtain two single-exposed images: - Cross-correlation cameras, which can acquire two digital images, commonly with 1000x1000 pixels. - Digital cameras equipped with narrow-band optical filters and using lasers emitting at different wavelength . - A photo camera, with a laser system emitting two different colour laser beam, acquires a multiexposed colour image. A successive separation into two images utilising the colour information is required in order to apply cross-correlation technique. The present work proposes a method, based on the detection of the principal components of the image, to obtain two single-exposed images from a colour digital PIV image.
Book of Abstracts Page # 71
Automatic quality inspection of ferrite cores is a challenging task. The main difficulties in defect detection stem from the fact that the surface of ferrite cores is relatively dark and in many cases it is covered by a pattern of more or less regular stripes which represent traces of the grinding of some of the walls of the cores. This means that one deals with a very low signal-to-noise ratio. A 2-stage vision system for detection and measurement of crack regions was devised. In the first, detection stage the regions with strong evidence for cracks are detected. The main tool used for crack detection are morphological operations detecting irregular changes of brightness in the image. Subsequently a morphological reconstruction of cracks is carried out. The cracks usually consist of randomly distributed straight line segments, which are detected using the structuring elements in the form of short line segments directed at certain angles to the coordinate axis. Changing the thresholds for the binarization of the gray level map of cracks one obtains the marker and the mask necessary for the reconstruction of the binary map of cracks. The resulting map usually contains most of the information concerning the cracks together with some undesired information on the stripes coming from the grinding. The traces of grinding represent the false positive classification error. The second stage of the described vision system includes a feature-based K-nearest neighbor fuzzy classifier, which analyzes all the pixels indicated by the reconstructed binary map of cracks. The classifier uses reference patterns generated by a preparatory process including reclassification and replacement procedures. The combination of the morphological detector with the K-nearest neighbor classifier gives more precise results in a reasonable time. The detector is fast, but it assigns too many pixels to cracks. The classifier checks the results of the detector and in general reduces the number of pixels assigned to cracks. However, the classifier is much slower, hence the detector is indispensable for reduction of the amount of data processed by the classifier. Experimental results obtained with the described vision system are presented.
Book of Abstracts Page # 151
A number of algorithmic methods have recently been gaining attention which offer the possibility of higher accuracy or more robust PIV measurements. An overview of some of these methods will be presented along with the approach being taken by DLR Goettingen. The suitability of these methods for application to other measurement fields is also considered.
Book of Abstracts Page # 75
The perfection of mechanical experimental techniques and devices is based on the opportunities of the optical-physical measurements. The more promising is the idea of using the speckles, obtained as a result of interaction between the laser radiation and the surface of the object. The proposed report presents the results of the solutions of a number of theoretical and applied problems on speckle-measurements of deformations.
Book of Abstracts Page # 119
An Optical Flow technique based on the use of Dynamic Programming has been applied to Particle Image Velocimetry yielding a significant increase in the accuracy and spatial resolution of the velocity field. We applied this technique to characterize the interaction between a laminar boundary layer and cavities of different shape factor.
The experimental characterisation of the interaction between a boundary layer and a cavity was developed in order to valid a three dimensional computation code based on the L.E.S. method (Large Eddies Simulation). The main application of this work is the study of the pollutant transport and dispersion in a street canyon.
Book of Abstracts Page # 83
Simulation tests of aircraft icing have been usually performed with clouds of supercooled water drops whose median volume diameter was about 20 \mum. For these sizes, drops were assumed to be at the static temperature of the flow. There is a recent interest in simulating freezing drizzle (diameters up to 500 \mum) and it is necessary to measure drop temperatures before impaction on obstacles because the cooling time increases with drops size and may become larger than the transport duration of drops.
There exist some techniques which can be used for droplet temperature measurement, like rainbow angle measurement, dual burst technique or extended phase doppler anemometer . These techniques are applicable only if the refractive index variation of the liquid varies significantly with temperature. However, this is not the case for water from the supercooled state (around -40 o C) up to 50 o C. So, we choose another method based on Laser Induced Fluorescence (LIF) of a dilute organic dye.
Guilbault  has pointed out that fluorescent molecules like rhodamine B are very sensitive to a temperature variation (temperature quenching), and Nakajima et al.  have used this organic dye to measure the temperature of a liquid flow by Planar LIF (PLIF). We show here that LIF could be employed for temperature measurement of a liquid phase dispersed in a gas. A theoretical analysis using quantum mechanics, geometrical optics and generalized Lorenz-Mie Theory (GLMT) yields, for low rhodamine B concentration C and a drop diameter D smaller than the beam diameter w0, the following expression for the intensity of fluorescence emitted by a drop crossing a laser beam at a distance y from the axis :
A validation of equation (1) was performed with a simple experimental setup. A monodisperse injector, filled with a water solution containing 10-4 mol.l-1 of rhodamine B, was placed vertically and produced periodically droplets with a nominal diameter of 92 \mum. The initial temperature of droplets was known and adjustable. Tests on polydisperse sprays were done using the injector in some peculiar modes. Falling drops were illuminated by a 60 mW Ar-ion laser (with \lambda = 514.5 nm) and fluorescent red light was collected on a photomultiplier after passing through a pass band filter centered at 600 nm (maximum peak of rhodamine B fluorescence). Signals were then analyzed on an oscilloscope.
The results confirmed that the equation (1) is correct for temperature above 293 K. Although accuracy is limited here to 0.5 K due to thermal probe uncertainty, the measured value of coefficient \beta indicated that the accuracy on temperature measurement could reach 0.1 K.
Book of Abstracts Page # 105
As an effective method to enhance heat and mass transfer, impinging jets have been used in many industrial applications; the drying process of papers and films, the tempering process of glass, the annealing process of steel, the cooling process of gas turbine system and electronic components, etc. Numerous analytical and experimental studies have been made by many researchers to investigate the basic heat transfer characteristics of jet impingement.
The authors previously focused on the jet orientation to generate large-scale steady vortices and carried out flow and heat transfer experiments for an obliquely discharged jet into crossflow1-2. In the present study, as the next step, the attention was paid to the visualizations of flow and heat transfer fields modified by the interaction between the two jets obliquely discharged into crossflow, and also to the comparison of the heat transfer performance between vertical and oblique jet cases. The temperature of the heat transfer target surface were measured with thermochromic liquid crystal sheets. The colors of the liquid crystal images taken by a CCD camera were transformed accurately and effectively into the temperatures by means of the neural network technique to obtain Nusselt number distributions on the target surface. Fluorescent dyes were added to the jet fluid to visualize also the cross-sectional flow patterns with the light sheet of a laser.
1. Nakabe K., Suzuki K., Inaoka K., Higashio A., Acton J. S. and Chen W.: Generation of Longitudinal Vortices in Internal Flows with an Inclined Impinging Jet and Enhancement of Target Plate Heat Transfer Int. J. Heat and Fluid Flow 19, p.573, 1998.
2. Nakabe K., Yamamoto Y., Fornalik E., Chen W. and Suzuki K.: Visualizations of Obliquely Discharged Jet Flows and Their Heat Transfer Enhancement Regions CD-Rom Proc. 8th Int'l. Symp. on Flow Visual., ISBN 09533991 0 9, Sorrento 1998.
Book of Abstracts Page # 95
Image processing is applied to investigate melting of a subcooled paraffin. Physically, the aim of the work is experimental study of the final, steady state regime when solid-liquid interface reaches a stationary position and convective heat transfer in the liquid is balanced by heat conduction throgh the solid core. In general, the experimental method proposed is to make analysis of the visual information automatically by means of digital processing. The technique was applied: to visualise steady state melt contours strongly influenced by natural convection, to obtain quantitative data such as area of regions occupied by either phase, to detect shape and location of the solid-liquid interface, and finally to obtain volume of the material melted.
Book of Abstracts Page # 99
This paper presents developments realized on photoelastodynamic bench of ENSICA's Department of Mechanical Engineering. In a first step, classical wave, vibrating, shock and rotating parts theories, including several analytical results, were compared with color pictures of isochromic lines obtained with rapid camera and urethane resin specimens. For non-linear shock and large deflection, explicit code LS-DYNA has been used. Then, the facility has been used to analyse dynamic work of gears for power transmission, in comparison with numerical computations performed at ENSICA. In addition, this photostress research development has lead to a demonstration which is now included in engineering first year general courseware, about stress analysis. It is now planned to visualize vibrating eigenwaves in isotropic and orthotropic membrane. Orthotropy will be obtained by inclusion of plasic fibers in resin, and will also provide dynamic information about reinforcement/resin interfaces.
Book of Abstracts Page # 101
Image processing in fluid mechanics, often in conjunction with quantitative flow visualisation, is now an important tool used in experimental studies. The development of inexpensive, powerful image capture and processing hardware is being complemented by imaginative software development, both utilising ideas developed from optical image processing and evolving new concepts based on advances in computation and electronic publication. The present paper reviews these developments with emphasis on computation and electronic presentation.
Book of Abstracts Page # 15
Thermovision cameras, based on pyrovidicon, are widely used in thermal phenomena investigation including applied mechanics. It is known that pyrovidicon target has the effect of charges appearance under machanical influences. As a result, special noises aggravate the quality of thermographic images. Besides external sources of mechanical influences, some influences may be generated by thermovision camera units that ensure action of obturator. The last is the integral part of pyrovidicon camera. Peculiarities of mentioned influence and details of their sources are discussed in the paper. Special processor for these influences decrease is proposed. Image quality enhancement is based on pyrosignal processing by that processor. The nature of influences and results of signal processing are illustrated. The structure of the processor is shown
Book of Abstracts Page # 61
Three-dimensional localization of an arbitrary tool or the particles in flow in 3D scene is developed. It combines three arbitrarily localized cameras and system of calibration points. Least square data fitting is used to solve set of algebraic equations obtained for points localized at three planes of the cameras. At the present stage an accuracy below 1 mm is obtained for a typical 0.2 m3 3D scene. Quasi real-time (10 fps) data evaluation can be achieved using 32-bit frame grabber (AM-STD) and 450 MHz Pentium II processor. The primary application of the system is live tracking of a surgical tool within an operative field and displaying tool's position on a set of diagnostic tomographic images.
Book of Abstracts Page # 107
Theoretical and applied problems of development and use of ultrasonic computer tomographic (USCT) methods and systems for non-destructive evaluation (NDE) of the material state in the product are considered in the report. Results conscern to following questions: USCT in problems of NDE of the material defective state and USCT in problems of NDE of the material predefective state. Accordingly, new USCT technologies and units for analysis of internal defective structure of highly inhomogeneous materials, for material structure analysis, for analysis of inhomogeneous stress-deformed state of material have been presented.
Book of Abstracts Page # 111
Helicopter's blade during its rotation acomplishes a complex spatial movement and deformation. This Blade Deformation Measuring System (BDMS) was developed to measure parameters of the real-scaled blade movement and its bending-twisting deformation. This system operates under videogrammetry principles. The basic principles of registration of video-images and processing of results of measurements are stated. Brief description of the system design is given. This system was tested during experimental investigations of blade deformations of the real upper rotor of Kamov-26 helicopter with radius 6.5 m on the VP-5 rotor test facility in TsAGI's T-101 wind tunnel. The tests have shown opportunity of twist deformation measurements of the blade with a root-mean-square error lower than 3-6 angular minutes and bend deformations measurements with an error of 0.3-0.6 mm. The technique of calibration of Blade Deformation Measurement System and appropriate software had been developed and tested.
Book of Abstracts Page # 57
The videogrammetric system was developed and applied to industrial control of the geometrical parameters of railway wheels.The measuring system uses three videogrammetric channels. Two of them apply the laser light sheet scheme. These channels have a measurement range of 500x500 mm. The measurement errors of each of the two coordinates do not exceed 0.15 mm. The third channel is constructed under a shadowgraphic scheme on base of a light beam of radial rays and provides the measurements of the wheel rolling surface geometry. This channel has a measurement range of 120x180 mm and measurement tolerance of 0.05 mm. The measurement system has been placed in operation on the industrial conveyor at Vyksunsky steel works. It operates in real time with the conveyor.
Book of Abstracts Page # 91
Examples of the image processing methods applied to the several classical problems of two phase flow are given. Images of oscillating droplets are used to obtain quantitative data about material properties, image analysis of growing vapour bubble allows to evaluate the evaporation rate and local interface velocity. Simultaneous measurements of temperature and velocity fields using liquid crystal tracers are exemplified for a solidification problem.
Book of Abstracts Page # 115
In digital holography optically generated Fresnel- or Fraunhofer holograms are recorded by a CCD-array and stored in computer memory. The reconstruction of the real or virtual images is not performed optically by illuminating the hologram with the reference wave but numerically by multiplication of the stored hologram with a numerical model of the reference wave. The diffracted field in the image plane is calculated either by the Fresnel-approximation or by a multiplication of its spectrum with the free-space transfer function followed by an inverse Fourier-transform. Both approaches result in a complex field, from which intensity and phase can be determined, while optically only an intensity distribution can be reconstructed. Thus digital holography differs significantly from ESPI/DSPI, where the object is imaged sharply onto the CCD-target and only intensities are reconstructed by a correlation process.
Digital holography offers a wide range of applications: e. g. holographic interferometry for deformation or contour measurement or holographic particle analysis. A subtraction of the reconstructed phase distributions of the wavefields belonging to two loading states of the object yields the interference phase distribution without sign ambiguity and without the necessity of an interferogram evaluation but with a resulting resolution and accuracy comparable to the phase shifting methods. If series of digital holograms with gradually varied load are recorded and stored, one may decide lateron, which holograms should be compared interferometrically. On the other hand motion components leading to high fringe densities can be compensated numerically during evaluation. Effective image enhancement methods exist which employ the numerical availability of the phase distribution.
In digital holography concepts can be realized numerically which are optically impossible: negative intensities to eliminate the zero-order reference wave overlapping the real or virtual image, or the generation of intensity and phase images oriented along the line of sight. The presentation will outline the ways how to record holograms onto CCD-arrays, will show the different approaches to numerical reconstruction, and will present various applications of the method in holographic interferometric deformation measurement, in contour measurement, and in particle analysis.
Book of Abstracts Page # 19
The recent success in implementation of optical full-field measuring methods into industrial, medical and commercial areas depends on automatic analysis of their output i.e. fringe patterns, FP. The demands for recent modern systems are to retrieve a measurand coded in a fringe pattern faster, more accurate and reliable and more communicative towards other systems such as CAD/CAM, FEM, computer graphics etc. The paper is intended to be a review of fringe pattern analysis methods and their capabilities to analyse extended class of FP. The special emphasis is paid to phase (active) methods which require phase modification of a fringe pattern by introducing alternatively such controlled parameters as: temporal and spatial carrier frequency and phase shifts. More detailed description is given to the most commonly used methods, namely temporal and spatial phase shifting methods, as well as to the hybrid concept of spatio-temporal analysis for multiply and variable in time objects. The fringe pattern analysis process is considered in respect to three main stages: determination of phase modulo 2pi, phase unwrapping and phase scaling. The main trends in development of phase methods and algorithms together with comparison of their capabilities are presented. The methods are illustrated by numerous examples of analysis of fringe patterns delivered by shape, displacement and deformation measuring systems.
Book of Abstracts Page # 23
The motion of a sphere in a viscous liquid is measured with an interferometric technique together with a video system. The laser interferometric technique is used to measure the translational velocity in the vertical direction (direction of gravity) with an excellent precision. The laser beam reflected by the sphere in motion as a cone of light is also used as the input to a system controlling the horizontal motion of the sphere. A video system with associated image analysis software is used to measure the rotational velocity of the sphere together with the translational one. These combined techniques are demonstrated to study the relative motion of two nearby rough particles which come into apparent contact in a surrounding Stokes flow. Hydrodynamic interactions and contact forces combine to give rolling and rolling plus slip regimes.
Book of Abstracts Page # 127
Fully developed turbulent wake flows from two-dimensional rectangular prisms(D/H=1, 2, 3) with several inclined angle of attacks were recorded for PIV analysis by using circular free surface water channel. Reynold number is 20,000. High-resolution CCD camera was adopted for image acquisition on NTSC format. Continuous PIV data were obtained via cross-correlation identification by frame by frame analysis. Animation procedure not relying on commercial post-processor was developed and its details are mentioned. Various animation AVI file images such as velocity vector distribution, vorticity shedding pattern and streaklines were produced and they are displayed directly on PC monitor in real-time sense. Intrinsic understanding of complicated bluff body turbulent flows is easily accessible through this original animation in-line software. And some recent PIV works made by Flow Informatics Lab in Korea Maritime University will be introduced.
Book of Abstracts Page # 131
A new tomographic measurement technique visualises the field of local void fraction in the two phase flow of air and water in the mixing chamber of a two-phase-nozzle. With this measurement technique a high spatial and temporal resolution can be achieved. The measured physical property is the different electric conductivity of the two fluids water and air. In the measurement plane the conductivity is measured between many wires strained in the investigated cross section. The measurement values are proportional to the relative liquid fraction. With an algebraic reconstruction technique (ART) the field of the liquid fraction in the investigated cross-section is calculated from the measurement values. The quality of the reconstruction is increased by a-priori-knowledge.
Book of Abstracts Page # 135
Acquiring high-speed images for motion analysis in a computer has become easy with the new PCI and network-based MotionScope technology. Based on a common platform, images can be captured locally (MotionScope PCI board within the PC) or remotely via the MotionScope e/Cam system and a standard 10/100 Ethernet network. Frame rates range from 50 to 8,000 pictures per second. Up to 4 PCI camera systems and 255 Ethernet camera systems can be supported from a single PC with the application software provided.
Book of Abstracts Page # 215
Comparative study of correlation-based PIV evaluation methods
R. Fei, L. Gui, W. Merzkirch
Lehrstuhl fuer Stroemungslehre, Universitaet Essen,
D-45117 Essen, Germany
The PIV algorithms are compared by applying them to the evaluation of simulated (artificial) PIV recordings, in which the particle images are distributed stochastically and have a Gaussian grey value distribution.
Book of Abstracts Page # 87
In the given work the digital data processing methods are considered with the purpose of pressure field on an aircraft model surface with the help of the PSP method accuracy of definition increase. The methods of the image characteristic allocation are considered, including specially put luminescent markers and local - adaptive filtration of the image by means of anisotropic filter keeping sharp intensity differences, that allows using the additional information to increase accuracy of the measuring and reference images alignment.
Book of Abstracts Page # 139
In the given work the methods of digital data processing are considered with the purpose of aircraft model surface pressure distribution field obtained with the PSP method accuracy increase. The problem consists in correction of luminescent distribution field in places of aircraft elements interface. The methods of elimination of illumination from various aircraft surfaces are considered in view of real geometry. For the first time given problem was delivered in . For modelling of self-illumination the mixed model of diffuse-mirror reflection with trace of beams was chosen. It was shown that by selection of the reflecting sublayer characteristics it is possible to reduce mirror component practically to negligibly small values. The check was carried out by means of account both mixed model, and complete diffuse model.
Book of Abstracts Page # 145
The attempt to develop a method of the three-dimensional solid geometric bone model reconstruction on the bases of the received CT images is made. The end-to-end design technique hip joint prosthesis and the exploration of the interaction of bone-prosthesis system are proposed.
Book of Abstracts Page # 149
The main objective of visualization is to get more insight into complex data sets. The most popular method is a conversion from two-dimensional arrays of numbers to colour table images. We can easily generate an image that represents milion of data values. This is constantly increasing development of the equipment for data acquisition. However, human physiology and psychology of vision reduces our perception to only a few dozen grayscale and a few hundred of colour coded data levels. The problem is how to choose the colours in order to maximize our insight into those numbers? I would like to present a current state of the pseudocolour techniques. I would discuss the rules of colour selection and the most commonly used pseudocolour colour tables such as grayscale, the rainbow, red-white-blue, sharp transition. Additionally I would introduce the fractal colour tables with their distinctive features especially useful when we deal with images representing continuous transitions in experimental data values. Real data sets (bathymetry and fluid flow images) support the presented ideas.
Book of Abstracts Page # 155
New algorithms for the use in particle tracking velocimetry (PTV) have been implemented and tested using several types of particle image in fluid flows. The new algorithms have been introduced in order to improve not only the performance of the particle tracking itself but also that of the individual particles extraction. As regards the particle tracking, the relaxation algorithm is used with some improvement and refinement from the original form. For the extraction of individual particles, there are four algorithms tested in the present work, among which are included two new algorithms: the modified Moravec operator method and the dynamic threshold binarization method
Book of Abstracts Page # 163
For some years a new way of thinking appears with respect to the solution of vision tasks. A paradigm has already arisen, known under the various names Active/Purposive/Animate, etc. ..., Vision. There is an important difference between the active and the classic passive as well as adaptive approach. When we work in passive mode, a set of images is given which have to be processed with the algorithms we are going to develop. On the other hand, when we work in active mode we do not want pre-recorded data since we include the image acquisition as an component of equal importance into the complete evaluation process. And this means far more than making the system adaptive to unfavourable boundary conditions such as a shading correction at unevenly illuminated scene.
Active vision offers a new approach for building intelligent and more flexible systems. In this sense an active system is not only able as just to ßee". It is designed to do something, i.e. to make an action, which is anything that changes the state of the system or the environment. Similar to human perception as an active way to explore a natural scene by changing the view or the focus, the role of the observer and observation system, respectively, is defined as an active component for gathering data. Further on the strategy for solving an image analysis problem is actively influenced by use of controlled feedback loops between the components that capture the optical information and those that evaluate it. In computer vision and optical metrology sometimes the difference between a so called active and passive technique is only made with respect to the way of working with the light, i.e. illumination. For instance in shape measurement the technique shape from shading is classified as an passive technique whereas structured light illumination is called as active. The difference between both approaches is that in the first case the shape is recovered from the brightness at each point of an image usually illuminated by one point light source with the same lighting throughout the surface and in the second case the structure of the lighting is modulated systematically throughout the surface of the object. In my understanding the other way of object illumination by using structured light delivers not more as the possibility to realize the triangulation principle in a field wise manner by addressing each point with a mod 2p phase value. But a lot of problems still remain, especially with respect to the ambiguity of the phase reconstruction. Here the application of more sophisticated procedures such as absolute phase measurement or wavelength scanning is necessary with respect to a unique solution. These methods bring a certain amount of activity into the system since the role of the observer is active by capturing more information as a single view can bring. However, active vision/metrology is not just the use of multiple frames. The modern understanding of being active means that the image acquisition process is controlled and thus constraints that facilitate the recovery of information about the state of the object under test (3D shape, 3D displacement, subsurface defects, etc) are introduced.
The contribution describes the origin of the problems and why only an active approach can be successful in many measurement problems. To explain the different ways of dealing with problems in optical metrology a well known example is used that is quite common for a lot of applications namely the reconstruction of continuous phase distributions from 2D fringe patterns.
Book of Abstracts Page # 29
A non-intrusive Moire interferometry system has been designed to acquire the instantaneous deformation of models during wind tunnel testing. The resulting interferograms are evaluated without manual intervention using a technique based on the Fourier Transform. The system has been installed in the cryogenic European Transonic Wind Tunnel (ETW). The deformation of a model wing (generic model of a transport aircraft with a full span of 1.60 m) has been measured. In a second experiment, the bending angle of a flap of a hypersonic vehicle was measured in order to determine the hinge moment due to aerodynamic loads. The experiment was carried out in the transonic wind tunnel Goettingen (TWG).
Book of Abstracts Page # 167
Inhomogeneous temperature and velocity fields were caused in liquids due to the procedure of pressurizing. To date this effect mostly has been remained unconsidered in high pressure investigations because of the lack of knowledge and adequate measuring technique. On the other hand processes under pressure may be decisively affected by temperature and motion, e. g. in high pressure treatment processes of foods. In previous studies we have shown, that the liquid crystal measuring technique is an adequate means to visualize temperature and velocity fields at high pressure. The change of the reflected wavelength of TLCs due to pressure is inverse to the effect of temperature. However, a high temperature resolution can be achieved at high pressure and the color changes remain reversible. In this study encapsulated TLCs of different start temperatures and bandwidths have been used in order to visualize temperature and velocity fields during pressurizing water in an optical cell up to 700MPa. Therewith the decay times of temperature and motion in the liquid after pressurizing have been investigated. First results of the measured decay times depending on the pressurizing rates and the pressure levels will be presented and discussed. Some additional notes concerning the applicability of the TLC technique in high pressure investigations and the choice of convenient TLCs will be given as well.
Book of Abstracts Page # 171
The ability to make precise X-ray attenuation measurements on a very small volume elements is a developing technology. This technology is known as X-ray microtomography to delineate the method as a form of X-ray microscopy that uses tomographic reconstruction techniques to build three-dimensional images of microstructure. Since the morphological data of a microstructure are usually collected from plane cross sections taken through an opaque material then this necessary step results in a great loss of information regarding spatial features of the dispersion. In order to overcome this difficulty X-ray microtomography is applied to extract the 3-D information that may be used for micromechanical modelling purposes.
Book of Abstracts Page # 175
Georges M. QUÉNOT
CLIPS-IMAG, 385, rue de la Bibliothèque, B.P. 53, 38041 Grenoble Cedex 9, France
Summary This paper presents a quantitative performance evaluation of an Optical Flow technique on the test data of the PIV-STD group of the Visualization Society of Japan. Near the optimal conditions for the method, the accuracy (average velocity error divided by the average velocity module) is below 2 % and it is below 4 % in all other cases except for very high and very low in-plane velocities.
The experimental fluid mechanics technique of Particle Image Velocimetry (PIV) has proven to be a valuable method for quantitative, two-dimensional flow structure evaluation1. It enables the measurement of the instantaneous in-plane velocity vector field within a planar section of the flow field. Nowadays, almost all PIV is done by computer image processing on digital images2 and most methods are based on image intercorrelation. Optical Flow techniques3-4, conventionally developed for detecting motion of large objects in a real world scene, were also recently successfully applied to the PIV problem5. The objective of the present study is to better characterize the performance of the optical flow technique for PIV and how it is influenced by experimental parameters (particle density and size, in-plane and out-of-plane velocities). For convenience and easy comparison of results, a standard PIV test set was used6.
Book of Abstracts Page # 177
The resuspension rate, defined as the ratio between the number of resuspended particles by unit surface and unit time, is the main parameter that characterises the resuspension process. Ziskind and al1 made an exhaustive review of resuspension models and experimental techniques which were developed for small particles (diameter greater than 5 µm and smaller than 50 µm). The experimental techniques developed to characterise resuspension are difficult to employ (particle counting under microscope) and they are not able to describe the characteristic time scale of the resuspension phenomena (<1s). In this study we propose a new technique based on image processing to quantify the particle resuspension process.
Book of Abstracts Page # 181
Physicians often perform diagnoses based on the evolution of lesions, tumours or anatomical structures through time. The objective of this paper is to describe several vector field operators to detect regions with local variations between two 3D images. Those operators are applied to displacement fields obtained after a non-rigid registration between successive 3D temporal images. Because we want to study the deformations between several temporal states, continuum mechanics is well suited for developing such operators.
Book of Abstracts Page # 185
Combinatorial 3-D Sequencing Theory, namely the concept of Three-dimensional Ideal Ring Bundles (3D-IRBs), can be used for finding optimal solutions for wide classes of problems in applied mechanics. 3D-IRBs are cyclic sequences of integer 3D-vectors which form perfect 3D-partitions of a finite 3D-space of vectors. The vector sums of connected sub-sequences of 3D-IRB enumerate the set of integer 3D-vectors exactly k-times. This property makes 3D-IRBs useful in applications which need to partition sets with the smallest possible number of intersections. Applications profiting from Combinatorial 3-D Sequencing Theory are for example synthesis of nonredundant aperture mask systems for holohraphic image, 3D-image coding and compression, pattern recognition and three-dimensional image analysis.
Book of Abstracts Page # 189
The basic source of experimental data for hybrid methods in solid state mechanics are optical full-field methods including moire, holographic and speckle interferometry. The output of these methods are interferograms from which the coded measurand is retrived by automatic fringe pattern analysis methods. The measurand is delivered as the high resolution file with equally sampled values of displacement or strain (eg.512 x 512) within the experimental field of view. These data may be used in hybrid methods by transfering the values of displacement/ strains into the mesh of nodes specified by FEM procedures. The paper describes the methodology of experimental data preprocessing and interpolation of the measurand values into the FEM mesh which usually is not uniformly spaced over the domain and has reduced number of nodes.Additionally the problem of domains mathing between experimental field of view and FEM is discussed. The methodology is presented on the example of hybrid analysis of ceramic-to-metal joint. The specific problems connected with high noise and high strain gradients are presented.
Book of Abstracts Page # 193
A pattern recognition technique for the investigation of large-scale coherent structures, is applied in the turbulent separated flow over a backward facing step (BFS) at a Reynolds number of Reh=5000. The Instantaneous two-dimensional velocity distribution is obtained by means of digital particle image velocimetry (D-PIV). High spatial resolution (delta_r=0.05h) is achieved with the application of an iterative window refinement image processing algorithm. The measurement plane is oriented in order to investigate span-wise aligned vortices footprints. The detection algorithm is based on velocity patterns spatial cross-correlation. An additional isotropy condition is proposed to improve the detection of vortices and shear layer. The structure of the shear layer emanating from the step edge is examined emphasising the role of coherent fluctuations with scale d ranging from 0.25h to 0.65h. Conditional data averaging is also applied to the results and structural properties (coherent velocity and vorticity) are obtained.
Book of Abstracts Page # 197
The presented algorithm provides an approach to fast rendering of medical volume data. It is based on the ray casting algorithm, which is substantially speeded up in terms of voxel addressing and interpolation.
Book of Abstracts Page # 201
Results are presented from theory and experiments carried out to excite and observe a localized nonlinear longitudinal strain wave (soliton) in nonlinearly elastic solid rods. It is shown that such a wave conserves its amplitude and shape during its propagation in a waveguide. The process of soliton reflection from both the free and bounded tips of the rod is studied.
Book of Abstracts Page # 79
Differential interferometry in polarized light using Wollaston prismas is a wellknown technique used for a very long time for flow visualization either with light or with a laser source.
"Shearography" was used more recently but in solid mechanics mainly for non-destrutive testing. A laser source is necessary with this technique.
One argument for using ßhearography" on site for industrial application is its relative insensitivity to environmental industrial conditions, i-e vibrations and air convection. On the other side, ßhearography" is used to visualize vibrations and air flows! I shall comment upon that.
This talk will describe different set-up and applications in both fields of mechanics and will comment upon sensitivity, spatial and temporal coherence, and image processing.
An outlook on the future will be done including new developments on digital interferometry.
Book of Abstracts Page # 31
Commonly used video cameras provide 25 (CCIR) or 30 (EIA) frames per second. Increasing the camera readout speed and reducing its spatial resolution frame rates of some thousand per second can be reached. Higher performances can be obtained only with special systems. An Ultra High-Speed Video Camera System for single, and a High-Speed Video Stroboscope for fast repeatable events, both developed by the authors, are presented. The operation principle and some examples of application are given.
Book of Abstracts Page # 207
Liquid crystals have been employed in heat transfer experiments for years. However, their use has mainly been qualitative until the recent development and wide-spread availability of inexpensive image digitiser has made routine digital image analysis feasible. As known, thermochromic liquid crystals modify incident white light and display colours whose wavelength is a function of temperature. They can be painted or sprayed on a surface or suspended in a fluid and used to visualise temperature fields. Liquid crystal change in appearance is concentrated over a narrow range, typically few Kelvin degrees: this field is called "colour-play interval" and represents the temperature range within they can be used as temperature indicators. The interpretation of colour images displayed by liquid crystals is performed by the true-colour image processing. The image-processing system includes a video-camera to record the image, a frame grabber to digitise it and an appropriate software to convert the colour pattern into the temperature field. This last step can be performed under two distinct procedure: (i) the use of the separate colour component red, blue and green (R,G,B) and either a multiple regression method or a neural network to obtain the correlation equation between colour and temperature; (ii) the conversion of the image, pixel by pixel, from the RGB domain into the HSI (Hue, Saturation, Intensity) domain. In this way, only the Hue parameter can be retained since it is related to temperature through a relationship that can be obtained by a calibration experiment. The hue-temperature relationship depends not only on the liquid crystal compound but also on the experimental conditions, i.e. lighting, angle of view, presence of glasses between the video-camera and the LC layer. Information about saturation and intensity are not useful for the temperature reconstruction and can be abandoned, thus reducing the size of the digitised image and saving memory into the computer. In this work examples of liquid crystals applications to the study of convective heat transfer are illustrated [1-5]. Attention is focused to the use of liquid crystal thermography to the study of compact heat exchangers performance. The complex geometry that often characterises these devices do not generally allow heat transfer investigation by traditional invasive sensors; conversely, optical methods, and in particular the liquid crystal thermography, are useful tools to gain whole-field and real-time information about flow and thermal fields. Three different configurations have been considered: (i) a corrugated-undulated passage, (ii) a rectangular channel roughened by square ribs, and (iii) a rectangular channel finned by staggered or in-line diamond-shaped elements. All these geometry are frequently encountered in compact heat exchangers. Experiments were performed by using pre-packaged liquid crystal films consisting of a liquid crystal layer deposited onto a plastic sheet having a background colour with black paint. The film is glued onto the surface whose temperature distribution is to be detected. Under given conditions of heat transfer at the wall (for instance, uniform heat flux) and of mass flow rate, the distributions of heat-transfer coefficients have been extracted.
 G.Tanda, J.Stasiek and M.W.Collins "Application of holographic interferometry and liquid crystal thermography to forced convection heat transfer from a rib-roughened channel", Proc. of Int. Conf. on Energy and Environment ICEE '95, pp. 434-441, Shanghai, China, 8-10 May 1995.
 G.Tanda, M.Ciofalo, J.Stasiek and M.W.Collins "Experimental and numerical study of forced convection heat transfer in a rib-roughened channel", Proc. of XIII Italian Heat Transfer Conf., pp.243-254, Bologna, 22-23 June 1995.
 G.Tanda, J.Stasiek and M.W.Collins "An experimental study by liquid crystals of forced convection heat transfer from a flat plate with vortex generators", Proc. of IV UK National Conference on Heat Transfer, pp.141-145, Manchester, U.K., 26-27 September 1995.
 Stasiek J., Collins M.W., Ciofalo M., and Chew P. " Investigation of Flow and Heat Transfer in Corrugated Passages. Part I: Experimental Results", Int.J. Heat Mass Transfer, Vol.39, 1996, pp.149-164.
 Stasiek J., "Experimental Study of Heat Transfer and Fluid Flow Across Corrugated-Undulated Heat Exchanger Surfaces", Int.J. Heat Mass Transfer, Vol.41, 1998, pp.899-914.
Book of Abstracts Page # 211
The paper will present an image pattern recognition application based on statistical parameters and Fourier's coefficients and the facility of this application to measure the vibration of ultrasound transducers concerning the acquisition of a sequence of images. The application is developed using Microsoft Visual C++5 software and the MFC libraries.
Book of Abstracts Page # 219
Motion tracking is an important step of the analysis of flow image sequences. However, PIV techniques rarely use tracking methods developed in computer vision, they usually work with FFT and correlation based methods. Two major types of motion estimation algorithms exist: the optical flow and the feature based ones. Promising results have been obtained by applying optical flow techniques to PIV. The applicability of feature based tracking algorithms to PIV images is examined in this article. Two tracking algorithms are considered and preliminary flow visualisation results for standard PIV sequences are presented.
Book of Abstracts Page # 223
To analyse the dynamic of coherent structures and the vortex structures themselves, three dimensional measurements are required. In comparison to the wake of a cylinder, the wake of a sphere is more difficult to investigate due to the complex flow-structures and the strong three-dimensional character of the flow. With PIV ( Particle Image Velocimetry ) we can apply a non introducive method to measure an instantanious two dimensional velocity field but to investigate the behavior and to get information about possible active influence on the flow this is not enough. So the idea of a three dimensional measurement was performed with LIF (Laser Induced Fluorescence ) and a 3-D-PIV system was tested in the wake of a sphere at Reynolds-numbers (Re=U*D/nu) in the range of 100 to 700. The measurement techniques provides interesting and good qualitative and quantitative results on the wake of the sphere at stationary and starting flows, like the dynamic of vortex loop structures, and the description about the vortex loop length.
Book of Abstracts Page # 159
A device, which performs in-vivo measurement of elasto-mechanical properties of human soft tissue is described. The device permits the controlled application of vacuum to small spots of organic tissue and registers the small deformations caused during the whole measurement process. Deformations are measured in two dimensions (via silhouette) with a vision based technique. The images are grabbed at a rate of 25 Hz and processed in real-time to avoid storage problems. Subsequently, several elasto-mechanical properties of the tissue can be determined via inverse finite element method.
Book of Abstracts Page # 227
How do people learn and recognize things? These amazing capabilities have been taken for granted for years. Until recently, when one tries to use computers or machines to do things like recognizing handwritten characters, it becomes clear that such seemingly trivial tasks by human being turn out extremely difficult, if not impossible, by mechanical means such as computers. After decades of rigorous attacks, such research is still as fresh as ever, and such mystery as for how human beings can do it remains largely unknown. In a sense, up to date, ``human brain" is still the ``smartest" or the ``most intelligent" mechanism than any computer can provide. In a way, the study of pattern recognition and artificial intelligence techniques has attracted more and more interests and attention. This talk intends to get some inside views of PR techniques using AI methodologies, and its applications to represent, learn, understand and recognize characters/words, one of the most popular, interesting, complicated and difficult languages in the world.
The speaker intends to conduct an on-line real time demo in this talk, on the internet : http://www.ccs.neu.edu/home/pwang/ObjectRecognition/
Book of Abstracts Page # 37
Electrical capacitance tomography has been used to image a bubble column. Sets of linear back projection tomographs are then analysed to yield gas hold-up values and to determine flow regime in a traditional manner. Further analysis is performed producing a statistic (Heterogeneity Index for Tomograms) that is independent of the average hold-up. This is used to provide an alternative and superior means to determine flow regime.
Book of Abstracts Page # 231
The process of turbulent mixing is encountered in many engineering applications. ...
Book of Abstracts Page # 235
Brief description both mobile and stationary set of optical research equipment created for investigations in wind tunnel are presented. Examples of interferograms and holograms, created during experiments in wind tunnel are produced.
Book of Abstracts Page # 239
We present the image processing techniques suitable for the automation of tribo-diagnostics. Processing of digital microgram displaying the wear particles in the lubricating oil gives a set of separated objects representing the wear particles. The feature vectors of objects input the consequent particle classification and machine condition estimation. Therefore, the precise retrieval of all wear particles (i.e. the application of the optimal processing techniques on the microgram) is the crucial problem of computer aided tribodiagnostics.
Book of Abstracts Page # 243
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