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Image-Based Photonic Techniques for Microfluidics
Published in Sushanta K. Mitra, Suman Chakraborty, Fabrication, Implementation, and Applications, 2016
David S. Nobes, Mona Abdolrazaghi, Sushanta K. Mitra
Fluid velocity is a fundamental parameter that is used to derive and define fluid motion and transport. It is difficult to determine the velocity of individual fluid molecules; however, a number of measurement techniques have been developed to measure fluid velocity by monitoring the motion of tracer particles that are seeded into the flow (Sinton, 2004; Lindken et al., 2009; Lee and Seok, 2009). The assumption here is that the seeded particles faithfully follow the flow (Melling, 1997). Laser Doppler velocimetry (Yeh and Cummins, 1964; Durst et al., 1976) is a technique that determines velocity by measuring the Doppler frequency shift of a scattered laser beam at a single point. It was originally developed for macroscale flows (Yeh and Cummins, 1964) and has been used at the microscale (Minor et al., 1997). However, as it is not image based, it is not discussed further here. There are a number of different image-based methods that have been developed in terms of both image acquisition and analysis of data to measure fluid flow velocity. These include particle image velocimetry (PIV), particle tracking velocimetry (PTV), and molecular tagging velocimetry (MTV). The next section is a discussion on the measurement and data processing principle used in each method, with some examples from the literature, and on the parameters that impact the design of the measurement system.
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.
Medicine and Biology
Published in Wen-Jei Yang, Handbook of Flow Visualization, 2018
Laser Doppler velocimetry can be used to determine the dynamic characteristics of blood flow through vessels [7]. The flow of blood is different from ordinary fluid flow in that (1) the blood flow in arteries varies with time, e.g., pulsatile, (2) blood vessels are characterized by a complicated geometry and viscoelastic properties, and (3) blood is a highly concentrated suspension of red blood cells and thus non-Newtonian in rheological property. Hence, studies of blood flow dynamics are quite difficult compared with nonbiological fluid flows. However, recent progress in laser optics has made it possible to apply the Doppler method to determine blood flow dynamics related to the pathogenesis of vascular diseases such as arteriosclerosis or thrombosis.
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).