The Experts below are selected from a list of 279 Experts worldwide ranked by ideXlab platform
Zheng-zhou Wang - One of the best experts on this subject based on the ideXlab platform.
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an improved Schlieren Method for measurement and automatic reconstruction of the far field focal spot
PLOS ONE, 2017Co-Authors: Zheng-zhou Wang, Qinye YinAbstract:The Schlieren Method of measuring far-field focal spots offers many advantages at the Shenguang III laser facility such as low cost and automatic laser-path collimation. However, current Methods of far-field focal spot measurement often suffer from low precision and efficiency when the final focal spot is merged manually, thereby reducing the accuracy of reconstruction. In this paper, we introduce an improved Schlieren Method to construct the high dynamic-range image of far-field focal spots and improve the reconstruction accuracy and efficiency. First, a detection Method based on weak light beam sampling and magnification imaging was designed; images of the main and side lobes of the focused laser irradiance in the far field were obtained using two scientific CCD cameras. Second, using a self-correlation template matching algorithm, a circle the same size as the Schlieren ball was dug from the main lobe cutting image and used to change the relative region of the main lobe cutting image within a 100×100 pixel region. The position that had the largest correlation coefficient between the side lobe cutting image and the main lobe cutting image when a circle was dug was identified as the best matching point. Finally, the least squares Method was used to fit the center of the side lobe Schlieren small ball, and the error was less than 1 pixel. The experimental results show that this Method enables the accurate, high-dynamic-range measurement of a far-field focal spot and automatic image reconstruction. Because the best matching point is obtained through image processing rather than traditional reconstruction Methods based on manual splicing, this Method is less sensitive to the efficiency of focal-spot reconstruction and thus offers better experimental precision.
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Algorithm of focal spot reconstruction for laser measurement using the Schlieren Method
Optik, 2017Co-Authors: Hui Lin, Da Zhengshang, Shi-kang Cao, Zheng-zhou WangAbstract:Abstract The far-field distribution of lasers is an important parameter for measuring beam quality. To overcome the insufficiencies of the CCD Camera dynamic range when measuring the far-field focal spot, the Schlieren Method was used to measure the focal spot far-field spatial distribution. Focal spot reconstruction was achieved after gray image matching, calculating the center, and image merging of the main lobe and side lobe. In this study, we used an algorithm based on the optimal arc to obtain the center for the side lobe images by fitting the circle center to improve the accuracy of the focal spot reconstruction. The results showed that the Schlieren Method of measuring the focal spot reconstruction algorithm could effectively, accurately and completely obtain the far-field focal spot.
Philipp Rudolf Von Rohr - One of the best experts on this subject based on the ideXlab platform.
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penetration length studies of supercritical water jets submerged in a subcritical water environment using a novel optical Schlieren Method
Journal of Supercritical Fluids, 2011Co-Authors: Tobias Rothenfluh, Martin J Schuler, Philipp Rudolf Von RohrAbstract:Abstract In hydrothermal spallation deep drilling a high-velocity, hot, supercritical water jet is directed towards the rock to induce fragmentation. One major challenge in the realization of this novel technique is the entrainment of comparatively cool, aqueous drilling fluid by the hot water jet, which can lead to significant heat losses before the hot jet's energy can be transferred to the rock. The present work quantifies such entrainment effects by determining penetration lengths of supercritical water jets injected into a cool, subcritical environment using a novel optical Schlieren Method. Penetration lengths of supercritical jets were found to be equal to the injector's nozzle diameter and almost independent of the jet's temperature at the nozzle exit and the jet's mass flow under almost all experimental conditions investigated. A semi-empirical model adapted from steam jet studies confirmed these findings and indicates that heat and mass transfer are primarily controlled by turbulent mixing.
Qinye Yin - One of the best experts on this subject based on the ideXlab platform.
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an improved Schlieren Method for measurement and automatic reconstruction of the far field focal spot
PLOS ONE, 2017Co-Authors: Zheng-zhou Wang, Qinye YinAbstract:The Schlieren Method of measuring far-field focal spots offers many advantages at the Shenguang III laser facility such as low cost and automatic laser-path collimation. However, current Methods of far-field focal spot measurement often suffer from low precision and efficiency when the final focal spot is merged manually, thereby reducing the accuracy of reconstruction. In this paper, we introduce an improved Schlieren Method to construct the high dynamic-range image of far-field focal spots and improve the reconstruction accuracy and efficiency. First, a detection Method based on weak light beam sampling and magnification imaging was designed; images of the main and side lobes of the focused laser irradiance in the far field were obtained using two scientific CCD cameras. Second, using a self-correlation template matching algorithm, a circle the same size as the Schlieren ball was dug from the main lobe cutting image and used to change the relative region of the main lobe cutting image within a 100×100 pixel region. The position that had the largest correlation coefficient between the side lobe cutting image and the main lobe cutting image when a circle was dug was identified as the best matching point. Finally, the least squares Method was used to fit the center of the side lobe Schlieren small ball, and the error was less than 1 pixel. The experimental results show that this Method enables the accurate, high-dynamic-range measurement of a far-field focal spot and automatic image reconstruction. Because the best matching point is obtained through image processing rather than traditional reconstruction Methods based on manual splicing, this Method is less sensitive to the efficiency of focal-spot reconstruction and thus offers better experimental precision.
Jurgen Kompenhans - One of the best experts on this subject based on the ideXlab platform.
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advanced measurement techniques for high reynolds number testing in cryogenic wind tunnels
48th AIAA Aerospace Sciences Meeting Including the New Horizons Forum and Aerospace Exposition, 2010Co-Authors: Uwe Fey, Robert Konrath, Tania Kirmse, Thomas Ahlefeldt, Jurgen Kompenhans, Yasuhiro EgamiAbstract:The present paper addresses the development, qualification trials and application of some non-intrusive measurement techniques suitable for operation in industry-scale, pressurised cryogenic wind tunnels. The application of cryogenic Temperature-Sensitive Paint (cryoTSP) as a tool for transition detection is described as well as the implementation of the Image Pattern Correlation Technique (IPCT) and the Backward Oriented Schlieren Method (BOS) in the European Transonic Windtunnel (ETW). Progress on the development of cryogenic Pressure-Sensitive Paint (cryoPSP) is shown, and considerations for the establishment of a Particle Image Velocimetry system suited for low temperatures (cryoPIV) are presented. Furthermore, the state of adaptation of the microphone array technique
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investigation of the accuracy of the background oriented Schlieren Method
2008Co-Authors: Ekaterina Popova, Jurgen Kompenhans, Nadezhda SkornyakovaAbstract:The aim of this work is to investigate the accuracy of the Background Oriented Schlieren Method and its dependence on the parameters of the experimental setup. For this purpose a plano-convex lens with precisely known parameters is used as test object.
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measurement of the position of rotor blade vortices generated by a helicopter in free flight by means of stereoscopic background oriented Schlieren Method bos
2006Co-Authors: Falk Klinge, Jurgen Kompenhans, Martin Hecklau, Markus Raffel, Uwe GohmannAbstract:During a measurement with a MMB Bo 105 in Braunschweig, the rotor blade tip vortex position was investigated by means of stereoscopic BOS
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investigation of the density and velocity distribution of a wing tip vortex by means of stereoscopic background oriented Schlieren Method bos and stereoscopic particle image velocimetry piv
2004Co-Authors: Falk Klinge, Tania Kirmse, Jurgen KompenhansAbstract:In case of Background Oriented Schlieren Method (BOS) and Particle Image Velocimetry (PIV) the information about the flow can be taken simultaneously in the whole flow field. Coupling these two techniques enables the measurement of the thermodynamic state of the flow. The test in an industrial transonic wind tunnel was carried out to show the feasibility of coupling these two techniques for the investigation of axis-symmetrical flows. The wing tip vortex of a modern large transportation aircraft in the transonic wind tunnel in Gottingen was investigated by means of stereoscopic BOS and stereoscopic PIV. Thus, the density and the velocity distribution of the flow behind the wing tip were observed. Three different flow speeds (Mach = 0.5, 0.6 and 0.7) and four different angles of incidence (-3°, +1°, +2°, +3°) were investigated. Based on investigations about the possibility measuring the local density distribution with BOS accurately, with information on the position of the density variation a further development of the measurement technique was achieved by new post processing algorithms. Further on it was possible to derive criteria for setting up the BOS system in order to obtain reliable quantitative data.
Yasuhiro Oikawa - One of the best experts on this subject based on the ideXlab platform.
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spatio temporal filter bank for visualizing audible sound field by Schlieren Method
Applied Acoustics, 2017Co-Authors: Nachanant Chitanont, Kenji Ishikawa, Kohei Yatabe, Yasuhiro OikawaAbstract:Abstract Visualization of sound field using optical techniques is a powerful tool for understanding acoustical behaviors. It uses light waves to examine the acoustical quantities without disturbing the sound information of the field under investigation. Schlieren imaging is an optical Method that uses a camera to visualize the density of transparent media. As it uses a single shot to capture the information without scanning, it can observe both reproducible and non-reproducible sound field. Conventionally, the Schlieren system is applied to high-pressure ultrasound and shock waves. However, since the density variation of air caused by the audible sound field is very small, this Method was not applicable for visualizing these fields. In this paper, a spatio-temporal filter bank is proposed to overcome this problem. As the sound is a very specific signal, the spatio-temporal spectrum (in two-dimensional space and time) of the audible sound is concentrated in a specific region. The spatio-temporal filter bank is designed for extracting the sound field information in the specific region and removing noise. The results indicate that the visibility of the sound fields is enhanced by using the proposed Method.
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Visualization of sound field by means of Schlieren Method with spatio-temporal filtering
2015 IEEE International Conference on Acoustics Speech and Signal Processing (ICASSP), 2015Co-Authors: Nachanant Chitanont, Kohei Yatabe, Keita Yaginuma, Yasuhiro OikawaAbstract:Visualization of sound field using Schlieren technique provides many advantages. It enables us to investigate the change of the sound field in real-time from every point of the observing region. However, since the density gradient of air caused by the disturbance of acoustic field is very small, it is difficult to observe the audible sound field from the raw Schlieren video. In this paper, to enhance visibility of the audible sound fields from the Schlieren videos, we propose to use spatio-temporal filters for extracting sound information and for noise removal. We have utilized different filtering techniques such as the FIR bandpass filter, the Gaussian filter, the Wiener filter and the 3D Gabor filter, to do this. The results indicate that the data observed after using these signal processing Methods are clearer than the raw Schlieren videos.
