Václav Kopecký

General temperature field measurement by digital holography

This paper presents a digital holographic method for measurement of periodic asymmetric temperature fields. The method is based on a modified Twyman-Green setup having double sensitivity. For measurement only one precisely synchronized and triggered digital camera is used. The periodicity and self-similarity of each cycle of the measured phenomenon combined with the precisely synchronized camera capture allow one to obtain data later used for three-dimensional (3D) measurement. The reconstruction of 3D temperature field is based on tomographic approach.

Frequency Shifted Digital Holography for the Measurement of Vibration with Very Small Amplitudes

A method for measurements of nanometer‐scale vibrations based on frequency shifted time average digital holographic interferometry employing the principle of the phase shifting technique is presented. This approach allows a reduction of noise and results in a higher sensitivity. The method has been applied to study the normalized vibration amplitude and the structure of vibration modes of piezoelectric transformers and actuators. In addition, quantitative information on the vibration amplitudes has been obtained in some cases.

3D form inspection of grinded optical surfaces by digital holography

Paper presents the method for shape measurement by digital holography based on wavelength contouring. The method employs multiple measurements from different illumination directions followed by stitching of the individual measurements by least square method. This approach is promising in measuring of steeper surface slopes more accurately

Local Turbulent Energy Dissipation Rate in an Agitated Vessel: Experimental and Turbulence Scaling

The hydrodynamics and the flow field in an agitated vessel were measured using 2-D time resolved particle image velocimetry (2-D TR PIV). The experiments were carried out in fully baffled cylindrical flat bottom vessels 300 and 400 mm in inner diameter. The 300 mm inner diameter tank was agitated by a Rushton turbine 100 mm in diameter, and the 400 mm inner diameter tank was agitated by a Rushton turbine 133 mm in diameter. Three liquids of different viscosities were used as the agitated liquid: (i) distilled water (ν = 9.35 × 10–7 m2/s), (ii) a 28 vol % aqueous solution of glycol (ν = 2 × 10–6 m2/s), and (iii) a 43 vol % aqueous solution of glycol (ν = 3 × 10–6 m2/s). The velocity fields were measured at an impeller rotation speed in the range from 300 to 850 rpm, which covers the Reynolds number range from 50000 to 189000. This means that fullydeveloped turbulent flow was reached. The experiments were performed to investigate the applicability of the following relations: ε* = ε/(u4/ν) = const, vK/u = const, Λ/ηK = const, τΛ/τK = const, ε* = ε/((Nd)4/ν) = const, Λ/d ∝ Re–1, ηK/d ∝ Re–1, vK/(Nd) = const, NτΛ ∝ R–1, NτK ∝ Re–1, and ε/(Nq) ∝ Re. These formulas were theoretically derived in our previous work, using turbulence theory, in particular, using turbulence spectrum analysis. The correctness of the proposed relations is investigated by statistical hypothesis testing.

Local velocity scaling in an impeller discharge flow in T400 vessel agitated by tooth impeller in a fully turbulent region

Hydrodynamics and flow field were measured in an agitated vessel using 2-D Time Resolved Particle Image Velocimetry (2-D TR PIV). The experiments were carried out in a fully baffled cylindrical flat bottom vessel 400 mm in inner diameter agitated by a tooth impeller 133 mm in diameter. The velocity fields were measured in the impeller discharge flow for impeller rotation speeds from 300 rpm to 700 rpm and three liquids of different viscosities (i.e. (i) distilled water, ii) a 28% vol. aqueous solution of glycol, and iii) a 43% vol. aqueous solution of glycol), corresponding to the impeller Reynolds number in the range 68 000 < Re < 221 000. This Re range secures the fully-developed turbulent flow of agitated liquid. In accordance with the theory of mixing, the dimensionless mean and fluctuation velocities in the measured directions were found to be constant and independent of the impeller Reynolds number. On the basis of the test results the spatial distributions of dimensionless velocities were calculated. The radial turbulence intensity was found to be in the majority in the range from 0.3 to 0.9, which corresponds to the high level of this quantity.

Reconstruction of three-dimensional velocity vector maps from two-dimensional PIV data

In this paper a three-dimensional reconstruction of flow field in a tunnel with the Hump profile is presented. The reconstruction is always performed for pair of 2D vector maps obtained by 3D PIV with two cameras which record measurement area from different locations. Three-dimensional reconstruction can be obtained in various ways. This paper summarizes two: the reconstruction based on the known correspondence between images, and the reconstruction based on the knowledge of intrinsic and extrinsic parameters of cameras. The both methods can be used in the cases when it is impossible to use a calibration pattern or when reconstruction by commercial software fails.

Comparison of digital holographic interferometry and constant temperature anemometry for measurement of temperature field in fluid

The presented paper shows possibility of using digital holographic interferometry (DHI) for temperature field measurement in moving fluids. This method uses a modified Twymann-Green setup having double sensitivity instead of commonly used Mach-Zehnder type of interferometer in order to obtain sufficient phases change of the field. On the other hand this setup is not light efficient as Mach-Zehnder interferometer. For measurement of the fast periodical phenomenon is not necessary to use always the high speed camera. One can consider this field to coherent phenomenon. With employing one digital camera synchronized to periodic field and external triggered one can capture whole period of the phenomenon. However the projections form one viewing direction of asymmetrical temperature field maybe misguided. Hence for sufficient examination of the asymmetrical field one should capture a large number of the phenomenon’s projections from different viewing directions. This projections are later used for 3D tomographic reconstruction of the whole temperature field and its time evolution. One of the commonly used method for temperature field measurement in moving fluids is hot wire method - constant temperature anemometry (CTA). In contrast to whole field measurement of DHI it is an invasive point temperature measurement method. One of the limiting factor of using CTA in moving fluids is frequency of temperature changes. This changes should not exceed 1 kHz. This limitation could be overcome by using of optical methods such as DHI. The results of temperature field measurement achieved by both method are compared in the paper.

Improved holographic method for vibration amplitude measurement from nano to microscale

This paper presents a frequency shifted time average digital holography technique for small mechanical vibration amplitude measurement and a novel single-pixel method for vibration amplitude distribution reconstruction. The reconstruction method is compared with results from common interpolating based technique used in holographic vibration analysis. Further the developed method is used for measurement of vibration amplitudes of a glass window in order to verify its reliability.

Optics and Measurement 2012

The conference focuses on processes and technology connected to optical elements and systems creation. It includes design, manufacturing, measurement and testing. It should help to bring an overview of projects being solved, in the above mentioned field. Its aim is to provide the organizational backup for meeting research workers, industry experts, postgraduates and students of final years at universities who are interested in field of optics manufacturing and measurement technology. The conference should contribute to making closer contacts and sharing experience.