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Particle Image Velocimetry
Published in Rajpal S. Sirohi, Speckle Metrology, 2020
Particle image velocimetry, as we have seen, consists of two steps: the recording of a suitably illuminated configuration of small particles within the flow, usually as a double-, rarely a multiple-exposure record, traditionally on a single photographic frame, and the interrogation of this record to obtain the spatial distribution of the velocity. Multiple-frame techniques are becoming popular with videoelectronic recording but are not typical of PIV. Much experimental skill goes into the production of the double-exposure photograph as explained in Section 6.4. A typical example from a flow is shown in Fig. 6.2; careful examination reveals the double structure of the particle images. Considerable development time has been invested in the processing of such PIV records, devising schemes to extract the desired displacement information from them and optimizing the signal-to-noise ratio. To understand more about these techniques and their limitations, we will proceed with a theoretical analysis of the data stored in the double exposure. To begin with, we assume ideal conditions, i.e., we have obtained undistorted images of the particles, identical over the entire record and in both exposures. Since velocity interests us as a space-dependent quantity, we select a small interrogation area from the record. Let us describe the image within this region.
Experimental Methods in Cardiovascular Mechanics
Published in Michel R. Labrosse, Cardiovascular Mechanics, 2018
Particle image velocimetry is an optical velocity measurement technique that uses a laser, digital cameras, and seeding particles. Two consecutive images of the illuminated particles are taken by the high-speed camera. The images are divided into small interrogation regions, typically between 8 × 8 pixels and 64 × 64 pixels in size. A cross-correlation is then applied on the interrogation regions to identify the direction and displacement of the seeding particles. The timing between the two images, or laser pulses, and the estimated displacement lead to the determination of the velocity vector in each interrogation region (Adrian 1991; Keane and Adrian 1992; Raffel et al. 2013). Particle image velocimetry allows for the determination of time-resolved 2D and 3D velocity fields. More recent techniques, such as tomographic PIV (tomo-PIV), allow for direct time-resolved volumetric measurements (Elsinga et al. 2005; Hasler and Obrist 2016). Because PIV is an optical-based technique requiring a transparent fluid, its application is limited to experimental, in vitro, velocity measurements. Its application to cardiovascular flows includes the investigation of flow characteristics in models of the left and right ventricles, the aorta, the pulmonary artery, the left atrium, the carotid artery, and aneurysms of the abdominal aorta. Particle image velocimetry has also been used to investigate the performance of medical devices and surgical procedures, including various heart valves, left ventricular assist devices, and the total cavopulmonary connection.
Precast segmental bridge construction in seismic zones
Published in Fabio Biondini, Dan M. Frangopol, Bridge Maintenance, Safety, Management, Resilience and Sustainability, 2012
Fabio Biondini, Dan M. Frangopol
The Laser Doppler Velocimeter is a system to measure the velocity of an object using Doppler effects of laser. The laser beam irradiated from the instrument hit the object, and it is reflected as a wave of beam. If the object is parting from the instrument, the wavelength of reflected beam become longer compared with incident beam. On the contrary, if the object is approaching the instrument, the wavelength of reflected beam become shorter compared with incident beam. It is possible to non-contact measurement of speed by measuring this change in wavelength. Figure 1 shows the schematic diagram. Natural frequencies is calculated the by converting velocity obtained from measurements, using the fast Fourier transform. Figure 2 shows a schematic diagram of a method for calculating the natural frequencies.
On the TSD deflection velocity measurements: a revision to the current state of the art and discussion over its applicability for concrete pavement assessment
Published in International Journal of Pavement Engineering, 2022
Martín Scavone, Samer W. Katicha, Gerardo W. Flintsch, Eugene Amarh
The Doppler lasers used by the TSD measure the instantaneous relative velocity of the pavement and the Doppler laser. The velocity measurement of solids or fluids using Doppler lasers is referred to as Laser Doppler velocimetry (or anemometry). This technique was first used by Yeh and Cummins (1964) to measure fluid flow and has been used for a wide range of applications such as vibration measurements (Castellini et al. 2006, Castellini et al. 2013, Rothberg et al. 2017), tissue blood flow measurements (Obeid at al. 1990, Vennemann et al. 2007, Rajan et al. 2009), and measurements of vehicle speeds (Jendzurski and Paulter 2008, Gao et al. 2017, Sung and Majji 2022). The method has been applied in pavement engineering to measure the pavement response under a moving wheel load which led to the development of the Traffic Speed Deflectometer (TSD) (Hildebrand et al. 1999, Hildebrand and Rasmussen 2002).
Numerical and experimental analysis of the flow over sinusoidal hills
Published in International Journal of Ambient Energy, 2021
Pramod Kumar Sharma, Vilas Warudkar, Siraj Ahmed
Particle image velocimetry which is an optical measurement method used to capture velocity fields in fluid volumes. It is carried using a pulsed laser and camera system. There is system inbuilt within the PIV system so that the different levels of complexity can be produced. With the help of two cameras from different viewing angles, 3D velocity fields can be obtained. Stereoscopic PIV was used in the given work. A cylindrical lens directed the laser, so that perpendicular plane to the stream direction could be ilthe luminated. The camera lenses had a 110 mm focal length, to capture a wide range of view resolution of the cameras. Smoke which was derived from condensed DEHS oil was injected into the wind tunnel, before starting the image acquisition process. The procedure of smoke injection was done at the last of the test section so that it can travel through the return of the wind tunnel before approaches the laser plane.
The effects of the height-to-width ratio of the rectangular inlet on the flow field and separation performance by hydrocyclone
Published in International Journal of Coal Preparation and Utilization, 2022
Feng Li, Peikun Liu, Xinghua Yang, Yuekan Zhang, Lanyue Jiang, Hui Wang
Currently, scholars mainly investigated the internal flow field and separation performance of hydrocyclones via experiment or numerical analysis (Boysan et al. 1983; Narasimha, Brennan, and Holtham 2007; Rakesh et al. 2014). The experimental methods mainly include laser doppler velocimetry (LDV), particle image velocimetry (PIV) (Marins et al. 2010) and particle dynamic analysis (PDA). Despite of accurate measurement of inner flow field, the experimental methods are greatly restricted in engineering due to the expensive equipment and limited laboratory condition. Scholars have conducted numerical simulation on the hydrocyclone using multiple physical models in computational fluid dynamics (CFD) in recent years. The high coincidence between the calculation results and the experimental data contributes to the popularity of CFD (Cui, Wang, and Li 2015; Jawarneh et al. 2008). Overall, CFD technology can adopt reasonable model to predict fluid and particle motions. As regard to high turbulence flow field in a hydrocyclone, the commonly used models are the Reynolds Stress model (RSM) and the LES model. The RSM model now has been extensively applied since it takes anisotropic turbulence into account. Multiphase model mainly includes the volume of fluid (VOF) model, the mixture model and the Eulerian-Lagrangian model (CFD-LPT). The VOF model can effectively trace the gas-liquid interface so as to provide convenience for analyzing the formation and variation of air, which can also well predict the flow field in hydrocyclones (Brennan 2006). The mixture model can be simplified as two-fluid model (TFM), it fully considers the collision and shear stress among particles, and can well predict the particle separation performance (Kuang et al. 2012).