Sanjeeb Prasad Panday

Particle Tracking Velocimetry Using the Genetic Algorithm

A new concept genetic algorithm (GA) has been implemented and tested for the use in the 2-D and 3-D Particle Tracking Velocimetry (PTV). The algorithm is applicable to particle images with larger (greater than 2000) number of particles without losing the excellent accuracy in the particle matching results. This is mainly due to a new fitness function as well as unique genetic operations devised especially for the purpose of particle matching problem. The new fitness function is based on the relaxation of movement of a group of particles and is particularly suited for an increased density of particle images. The unique genetic operations give rise to the concentration of more fit genes in the forward part of the gene strings where the crossover and mutation processes are suppressed. The new algorithm also profits from the new genetic encoding scheme which can deal with the loss-of-pair particles (i.e., those particles which exist in one frame but do not have their matching pair in the other frame), a typical problem in the real image particle tracking velocimetry. In the present study, the new method is tested with 2-D and 3-D synthetic as well as real particle images with a large number of particles.

A SOM based stereo pair matching algorithm for 3-D particle tracking velocimetry

A self-organizing map (SOM) based algorithm has been developed for 3-D particle tracking velocimetry (3-D PTV) in stereoscopic particle pairing process. In this process every particle image in the left-camera frame should be paired with the most probably correct partner in the right-camera frame or vice versa for evaluating the exact coordinate. In the present work, the performance of the stereoscopic particle pairing is improved by applying proposed SOM optimization technique in comparison to a conventional epipolar line analysis. The algorithm is tested with the 3-D PIV standard image of the Visualization Society of Japan (VSJ) and the matching results show that the new algorithm is capable of increasing the recovery rate of correct particle pairs by a factor of 9 to 23 % compared to the conventional epipolar-line nearest-neighbor method.

Particle Tracking Velocimetry using Digital In-Line Holograohy

1 . I n t r o d u c t i o n The use of holography for the diagnostics of small particles can be traced back to late 1960,s i). A l t hough ho lography is potent ia l ly the most power fu l tools for d iagnos ing 3D flows, the convent iona l procedure of film-based holography, wh i ch inc ludes film based recording, wet chemica l processing, a nd optical reconstruction, has severely restricted the user friendliness of the ho lograph ic ima g i n g technique. I n this regard , d i g i t a l ho lography is very p rom is i ng . I t records ho lograms directly to d i g i t a l med i a such as CCD or CMOS sensors and reconstructs the objects numer ica l ly . The numer i ca l ho log ram reconstruction was in i t i a ted i n the ear ly 1980s by Yaros lavskn a nd Merz l yakov 2 ) . Onu r a l a nd Scott 3 》furthe i’ improved this reconstruction a l go r i thm and app l ied to part icle measurements . The advent of charge coupled devices (CCDs) by Schnars and Juptner 4 ) i n 1994 was a b ig step i n the development of direct recording of Fresne l ho lograms. Th is method now enables d i g i t a l recording a nd processing of ho lograms, w i thou t any photographic recording as intermed iate step. The d i g i t a l ho log ram reconstruction, d i g i t a l holography, offers much more possib i l i t ies than convent iona l (optical) processing. Th is pape r presents the numer i ca l reconstruction process of ho lograms i n d i f ferent p lanes a long w i t h in-focus a nd out-of-focus particles based on the two methods name ly the Four i e r t ransform and Convo lut ion schemes. Th is approach to d i g i t a l ho log ram recording and numer i ca l reconstruction enables the use of complex amp l i t ude in fo rmat ion wh i ch w h e n used i n part icle extraction s ign i f icant ly improves part ic le axial-location accuracy compared w i t h other optical reconstruction schemes Further , these methods also al leviate the speckle noise prob lem intr ins ic to d i g i t a l in-l ine ho log raphy as speckles a nd particles can be clearly d i f ferent iated i n complex wave-field obta ined f rom reconstruction. 2. Genera l Pr inc ip les a n d N u m e r i c a l Recons t ruc t ion Fig. l*,a; i l lustrates the concept of d ig i ta l hologram recording. A plane reference wave and the wave reflected from a three dimensional object placed at a distance d from a CCD or CMOS are in ter fer ing at the same surface. The result ing hologram is electronically recorded and stored. I n optical reconstruction as shown in Fig. 1(b), a v i r tua l image appears at the posit ion of the original object and the real image is also formed at a distance d, but in the opposite side from the CCD or CMOS.