Time resolved PIV of the flow field underneath an accelerating meniscus. - In: International Symposium on Particle Image Velocimetry, ISSN 2769-7576, Bd. 1 (2021), 1, insges. 10 S.
We present an experimental analysis of the flow field near an accelerating contact line using time-resolved Particle Image Velocimetry (TR-PIV). Both advancing and receding contact lines are investigated. The analyzed configuration consists of a liquid column that moves along a vertical 2D channel, open to the atmosphere and driven by a controlled pressure head. Large counter-rotating vortices were observed and analyzed in terms of the maximum intensity of the Q-field. To compute smooth spatial derivatives and improve the measurement resolution in the post-processing stage, we propose a combination of Proper Orthogonal Decomposition (POD) and Radial Basis Functions (RBF). The RBFs are used to regress the spatial and temporal structures of the leading POD modes, so that “high-resolution” modes are obtained. These can then be combined to reconstruct high-resolution fields that are smooth and robust against measurement noise and amenable to analytic differentiation. The results show significant differences in the flow topology between the advancing and the receding cases despite velocity and acceleration of contact lines are comparable in absolute values. This suggests that the flow dynamics are tightly linked to the shape of the interface, which significantly differs in the two cases.
https://doi.org/10.18409/ispiv.v1i1.129
Measurement of the acoustic streaming pattern in a standing surface acoustic wave field. - In: International Symposium on Particle Image Velocimetry, ISSN 2769-7576, Bd. 1 (2021), 1, insges. 2 S.
The application of standing surface acoustic waves (sSAW) has enabled the development of many flexible and easily scalable concepts for the fractionation of particle solutions in the field of microfluidic lab-ona-chip devices. In this context, the acoustic radiation force (ARF) is often employed for the targeted manipulation of particle trajectories, whereas acoustically induced flows complicate efficient fractionation in many systems [Sehgal and Kirby (2017)]. Therefore, a characterization of the superimposed fluid motion is essential for the design of such devices. The present work focuses on a structural analysis of the acousticallyexcited flow, both in the center and in the outer regions of the standing wave field. For this, experimental flow measurements were conducted using astigmatism particle tracking velocimetry (APTV) [Cierpka et al. (2010)]. Through multiple approaches, we address the specific challenges for reliable velocity measurements in sSAW due to limited optical access, the influence of the ARF on particle motion, and regions of particle depletion caused by multiple pressure nodes along the channel width and height. Variations in frequency, channel geometry, and electrical power allow for conclusions to be drawn on the formation of a complex, three-dimensional vortex structure at the beginning and end of the sSAW.
https://doi.org/10.18409/ispiv.v1i1.24
On the uncertainty of defocus methods for 3D particle tracking velocimetry. - In: International Symposium on Particle Image Velocimetry, ISSN 2769-7576, Bd. 1 (2021), 1, insges. 2 S.
Defocus methods have become more and more popular for the estimation of the 3D position of particles in flows (Cierpka and Kähler, 2011; Rossi and Kähler, 2014). Typically the depth positions of particles are determined by the defocused particle images using image processing algorithms. As these methods allow the determination of all components of the velocity vector in a volume using only a single optical access and a single camera, they are often used in, but not limited to microfluidics. Since almost no additional equipment is necessary they are low-cost methods that are meanwhile widely applied in different fields. To overcome the ambiguity of perfect optical systems, often a cylindrical lens is introduced in the optical system which enhances the differences of the obtained particle images for different depth positions. However, various methods are emerging and it is difficult for non-experienced users to judge what method might be best suited for a given experimental setup. Therefore, the aim of the presentation is a thorough evaluation of the performance of general advanced methods, including also recently presented neural networks (Franchini and Krevor, 2020; König et al., 2020) based on typical images.
https://doi.org/10.18409/ispiv.v1i1.80
SmartPIV - an app for flow visualization by cross-correlation and optical flow using smartphones. - In: International Symposium on Particle Image Velocimetry, ISSN 2769-7576, Bd. 1 (2021), 1, insges. 2 S.
In recent years smartphones considerably changed our communication and are used on a daily (or even every minute) basis especially by students without any difficulties. Fluid flows also belong to our daily experiences. However, the education of the basic principles of fluid mechanics is sometimes cumbersome due to its non-linear nature. This problem may be tackled in practical sessions applying flow visualization techniques in wind or water tunnels and directly learn from own observations. Nowadays, often optical methods like particle imaging velocimetry (PIV) or particle tracking velocimetry (PTV) are used for these purposes. A typical PIV/PTV setup consists of a (double)pulse laser, a scientific camera and a synchronization device. The costs for this equipment can easily add up to more than 100,000 euros and the installations and set up of the systems requires experiences and is complex. For these reasons Universities often only offer practical courses for a small amount of students and the students may not be allowed to use and set up the systems by their own as the equipment is also needed for scientific research. Due to the COVID-19 pandemic it is also often not allowed to share equipment or even to work in larger groups during practical sessions.
https://doi.org/10.18409/ispiv.v1i1.78
Multi-spectral imaging for Thermochromic Liquid Crystal based Particle Image Thermometry: a proof of concept. - In: International Symposium on Particle Image Velocimetry, ISSN 2769-7576, Bd. 1 (2021), 1, insges. 8 S.
In this contribution, a novel imaging approach for Thermochromic Liquid Crystal (TLC) based Particle Image Thermometry (PIT) is demonstrated. In contrast to state of the art approaches, a multi-spectral camera was used to record the color response of the Thermochromic Liquid Crystals seeding particles. An experiment with a transparent, water-filled, cylindrical cell as the central element was set up to investigate the novel approach. The temperature in the cell can be controlled by adjusting the temperature of the bottom and top plate. Calibration images at eleven different temperatures ranging from 18 ˚C to 21.6 ˚C, as well as images of a stable thermal stratification, were recorded. 90 percent of the calibration data was used to train a neural network (NN) to predict the temperature. The remaining 10 percent of the calibration data and the data of the stable thermal stratification were used to test the NN. The tests show that the deviation between predicted and ground truth temperature is mostly below 0.1 K and that the linear profile of the stable thermal stratification can be predicted with a maximum deviation of ≈ 0.15 K. This shows that multi-spectral imaging with neural networks for data processing is feasible and a promising concept.
https://doi.org/10.18409/ispiv.v1i1.168
Production of individual structures from silicate materials using Wire-Laser Additive Manufacturing :
Herstellung individueller Strukturen aus silikatischen Werkstoffen mittels Wire-Laser Additive Manufacturing. - In: ce/papers, ISSN 2509-7075, Bd. 4 (2021), 1, S. 181-191
Die vorliegende Studie zeigt Grundzüge eines Verfahrens, welches Potentiale zum Ausgleich der Defizite bisheriger additiver Verfahren bezüglich Maßhaltigkeit, Homogenität und Transparenz der Struktur aufweist. Silikatische Gläser werden durch eine CO2-Laserquelle aufgeschmolzen. Ein Dreiachssystem defokussiert den Laserstrahl, um die Intensitäten zum Aufschmelzen unterschiedlicher silikatischer Gläser einzustellen und die Bewegung von Druckstufe und Substrat zu realisieren. Die flexible Zuführung des Zusatzwerkstoffes ermöglicht die kontinuierliche Anpassung des Aufbauprozesses und die Möglichkeit der Geometrieänderung. Erste Versuche verdeutlichen, dass dieser Prozess eine Alternative zu den bisher angewendeten Verfahren darstellt. Production of individual structures from silicate materials using Wire-Laser Additive Manufacturing. This study shows the main features of a method, which has the potential to compensate for the deficits of previous additive methods in terms of dimensional accuracy, homogeneity and transparency of the structure. Silicate glasses are melted by a CO2-laser source. A three-axis system defocuses the laser beam to adjust the intensities for melting different silicate glasses and to realize the movement of pressure stage and substrate. The flexible feeding of the filler material allows the continuous adaptation of the build-up process and the possibility of changing the geometry. Initial tests have shown that this process is an alternative to the methods previously used.
https://doi.org/10.1002/cepa.1252
Physik-geführte NARXnets (PGNARXnets) zur Zeitreihenvorhersage. - In: Proceedings 31. Workshop Computational Intelligence, (2021), S. 235-261
Make some noise: energy-efficient 38 Gbit/s wide-range fully-configurable linear feedback shift register. - In: SMACD / PRIME 2021, (2021), S. 384-387
https://ieeexplore.ieee.org/document/9547997
Every clock counts - 41 GHz wide-range integer-N clock divider. - In: SMACD / PRIME 2021, (2021), S. 388-391
https://ieeexplore.ieee.org/document/9547998
Impact analysis of temperature and humidity effects on polishing. - In: EOS Annual Meeting (EOSAM 2021), (2021), 03011, S. 1-3
The polishing process for optical glass is one with intertwined chemical and mechanical processes. The aim of the present study is to verify whether control of these factors can be used to improve the efficiency of the polishing process.
https://doi.org/10.1051/epjconf/202125503011