Journal of microelectromechanical systems, Dec 1, 2018
We report on a flow velocity measurement technique based on snap-through detection of an electros... more We report on a flow velocity measurement technique based on snap-through detection of an electrostatically actuated, bistable micromechanical beam. We show that induced elecrothermal Joule heating and the convective air cooling change the beam curvature and consequently the critical snap-through voltage (VST ). Using single crystal silicon beams, we demonstrate the snap-through voltage to flow velocity sensitivity of dV ST /du ≈ 0.13 V s m -1 with a power consumption of ≈ 360 µW. Our experimental results were in accord with the reduced order, coupled, thermo-electro-mechanical model prediction. We anticipate that electrostatically induced snap-through in curved, micromechanical beams will open new directions for the design and implementation of downscaled flow sensors for autonomous applications and environmental sensors.
Author comment on "A modeling methodology to study the tributary-junction alluvial fan connectivi... more Author comment on "A modeling methodology to study the tributary-junction alluvial fan connectivity during a debris flow event" by Alex Garcés et al., Nat. Hazards Earth Syst.
Ulva is a widespread green algal genus with important ecological roles and promising potential as... more Ulva is a widespread green algal genus with important ecological roles and promising potential as a seagriculture crop. One of the major challenges when cultivating Ulva is sudden biomass disappearance, likely caused by uncontrolled and unpredicted massive sporulation. However, the dynamics of this process are still poorly understood. In this study, we propose a mathematical model describing the biomass accumulation and degradation of Ulva, considering the potential impact of sporulation inhibitors. We developed a differential equation model describing the time evolution of Ulva biomass. Our model simulates biomass in compartments of different Ulva "age" classes, with varying growth and sporulation rates. Coupled with these classes is a differential equation describing the presence of a sporulation inhibitor, produced and secreted by the algae. Our model mimics observed Ulva dynamics. We present Ulva's biomass accumulation under different initial algae population, age distributions and sporulation rates. Furthermore, we simulate water replacement, effectively depleting the sporulation inhibitor, and examine its effects on Ulva's biomass accumulation. The model developed in this work is the first step towards understanding the dynamics of Ulva growth and degradation. Future work refining and expanding our results should prove beneficial to the ecological research and industrial growth of Ulva.
OpenPIV is an open source Particle Image Velocimetry analysis software written in Python, Matlab ... more OpenPIV is an open source Particle Image Velocimetry analysis software written in Python, Matlab and C++
<p>Multi-hot-wire/film probes made from multiple sensors provide three components of veloci... more <p>Multi-hot-wire/film probes made from multiple sensors provide three components of velocity and velocity derivatives in a point. Typically the calibrations are using inverse polynomials to fit the angle dependence of each sensor. This code suggests a use of look-up tables for the task</p
this release fixes two bugs and improves process tests process.py is removed, all pure Python imp... more this release fixes two bugs and improves process tests process.py is removed, all pure Python implementation is in pyprocess.py tests are improved, both Cython and Python versions are compared fixed the bug in Cython due to // fixed the bug in Cython for cases when window_size == search_size == image size, caused range(0,0)
Liberzon, Harrington, Daniel, Gurka, Harari and Zilman "Moth-inspired navigation algorithm i... more Liberzon, Harrington, Daniel, Gurka, Harari and Zilman "Moth-inspired navigation algorithm in a turbulent odor plume from a pulsating source" proposed a novel navigator principle using properties of a turbulent patchy plume, https://journals.plos.org/plosone/article/comments?id=10.1371/journal.pone.0198422 In order to compare this moth-inspired navigator with other navigator types available in the literature, e.g. by Carde and co-workers, we use <code>pompy</code> https://github.com/InsectRobotics/pompy and add these moth-inspiried navigators to its simulation fields. We try to create mean wind with meandering and turbulence and vary odor release parameters to test various navigators' statistics, e.g. success rate, flight time, etc. The main contributors are: @NoamBenelli and @alexlib Note: we use an older version of <code>pompy</code>, included in the repository. In the future, we would be able to update to a newer version of <code>pompy</code> and implement it as a submodule.
OpenPIV is an open source Particle Image Velocimetry analysis software written in Python, Matlab ... more OpenPIV is an open source Particle Image Velocimetry analysis software written in Python, Matlab and C++
extended area search is available in Python version, in addition to the one in Cython (process.py... more extended area search is available in Python version, in addition to the one in Cython (process.pyx) more tests added for shifts
Seedless velocimetry is gaining interest in many industrial and research applications. We report ... more Seedless velocimetry is gaining interest in many industrial and research applications. We report on a comparative study of time-resolved optical velocimetry using traditional, mirror-type knifeedge schlieren optics versus Background-Oriented Schlieren (BOS) of subsonic round turbulent helium jets in air at Red = 5,890 and 11,300. Digital images with 1024 pixels streamwise resolution (0 ≤ x/d ≤ 200) were captured at 6000 frames/s in large ensembles. Velocimetry was performed on these results by digital image correlation (DIC) using OpenPIV software, and by streak-schlieren analysis of x-t diagrams (kymography). Limited PIV data were also collected for verification of the schlieren velocimetry results. Both BOS and traditional schlieren show partial success in measuring the mean-flow helium jet self-similarity in terms of the 1/x decay of centerline velocity, Gaussian-shaped radial velocity profiles, and linear spreading rate of the jet. Visualized turbulent eddies, used as tracers in schlieren velocimetry, are observed to last longer than is necessary for this purpose in the present helium jets. Also, the measured convective velocity appears to be sufficiently robust to sum to the jet mean velocity in some of the results. Kymography yields better overall results than DIC, which we attribute to kymography's spatiotemporal "spectrum" of jet velocities, enabling the discrimination of fast eddies near the jet centerline from slower ones near the jet periphery. DIC and other analysis methods suffer from a path-averaging bias which negatively affects the results. The reduction of kymographic data for velocimetry was done manually and also by a Fourier-transform image-feature-orientation code, both yielding equivalent results.
Experimental Thermal and Fluid Science, Oct 1, 2016
Abstract Three-dimensional Particle Tracking Velocimetry was employed to characterize jets from c... more Abstract Three-dimensional Particle Tracking Velocimetry was employed to characterize jets from circular and semi-circular pipes in the intermediate and far fields. Grid-interpolated velocity were used to validate the measurements, and confirmed the negligible effect of the pipe shape on the mean flow in the intermediate field. Several volumetric regions were defined to get Lagrangian statistical description of the flow from categorized particle trajectories. Probability density functions of the velocity fluctuations, particle acceleration, and curvature of the trajectories revealed common and distinctive features of the jets. The first one showed departure from the Gaussian distribution away from the core, and the acceleration exhibited heavy tails in the two jets; however the curvature pdf revealed distinctive footprint of the pipe shape.
Algal Research-Biomass Biofuels and Bioproducts, Sep 1, 2015
Biorefineries aim to provide sustainable production of food and generation of low carbon energy i... more Biorefineries aim to provide sustainable production of food and generation of low carbon energy in the next decades. Current strategies for biorefinery reply mostly on the classic terrestrial agriculture for biomass production. However, land availability, competition with food crops and total energy balance are challenging limiting factors for terrestrial bioenergy crop production. Off-shore macroalgae production could provide alternative, sustainable feedstocks for biorefineries without competition with food crops. Increasing the yields of off-shore macroalgae cultivation systems could further improve the total energy balance of the marine biorefineries. In this work, based on the fundamental principle of timing differences between light harvesting and carbon fixation in algae, we developed a theoretical framework for increasing the yields of off-shore macroalgae biomass using external mechanical mixing. We show that for a given physiological parameter of macroalgae light harvesting and carbon fixation, mixing could allow for increase of the total energy gain by two orders of magnitude. The overall biorefinery to biofuel efficiency, however, is constrained by drag and macroalgae thallus size.
3D-PTV is a quantitative flow measurement technique that aims to track the Lagrangian paths of a ... more 3D-PTV is a quantitative flow measurement technique that aims to track the Lagrangian paths of a set of particles in three dimensions using stereoscopic recording of image sequences. The basic components, features, constraints and optimization tips of a 3D-PTV topology consisting of a high-speed camera with a four-view splitter are described and discussed in this article. The technique is applied to the intermediate flow field (5 <x/d <25) of a circular jet at Re ≈ 7,000. Lagrangian flow features and turbulence quantities in an Eulerian frame are estimated around ten diameters downstream of the jet origin and at various radial distances from the jet core. Lagrangian properties include trajectory, velocity and acceleration of selected particles as well as curvature of the flow path, which are obtained from the Frenet-Serret equation. Estimation of the 3D velocity and turbulence fields around the jet core axis at a cross-plane located at ten diameters downstream of the jet is compared with literature, and the power spectrum of the large-scale streamwise velocity motions is obtained at various radial distances from the jet core.
The motion of particles through density-stratified interfaces is a common phenomenon in environme... more The motion of particles through density-stratified interfaces is a common phenomenon in environmental and engineering applications. However, the mechanics of particle-stratification interactions in various combinations of particle and fluid properties are not well understood. This study presents a novel machine-learning (ML) approach to experimental data of inertial particles crossing a density-stratified interface. A simplified particle settling experiment was conducted to obtain a large number of particles and expand the parameter range. Using ML, the study explores new correlations that collapse the data gathered in this and in previous work by Verso et al. . The "delay time", which is the time between the particle exiting the interfacial layer and reaching a steady-state velocity, is found to strongly depend on six dimensionless parameters formulated by ML feature selection. The data shows a correlation between the Reynolds and Froude numbers within the range of the experiments, and the best symbolic regression is based on the Froude number only. This experiment provides valuable insights into the behavior of inertial particles in stratified layers and highlights opportunities for future improvement in predicting their motion.
We report on a simple yet efficient approach allowing direct electrothermal excitation of paramet... more We report on a simple yet efficient approach allowing direct electrothermal excitation of parametric resonance (PR) in double-clamped flexible nano-and microscale beams. The application of a time-harmonic voltage between the beam's ends leads to the electric current and Joule's heating of the entire beam, which induces a time-periodic axial stress and results in excitation of the structure lateral vibrations through the PR mechanism. The proposed approach has an advantage, simplifying fabrication and integration and reducing the influence of residual stress, and thermal mismatch, unlike conventional piezoelectric, photothermal, or electrostatic actuation approaches, which require additional piezoelectric layers, light sources, or electrodes in the proximity of a vibrating beam. Single crystal silicon, nominally 500 lm long, 30 lm wide, and 5 lm thick beams were fabricated by deep reactive ion etching and operated at a pressure of %1.9 mTorr. The experimental results, consistent with the reduced order and numerical model predictions, demonstrate the feasibility of the suggested excitation scenario, which could be implemented in resonant sensors, timing devices, signal processing, and micro and nanomechanical logical elements.
We report on a flow velocity measurement technique based on snap-through detection of an electros... more We report on a flow velocity measurement technique based on snap-through detection of an electrostatically actuated, bistable micromechanical beam. We show that induced elecro-thermal Joule heating and the convective air cooling change the beam curvature and consequently the critical snap-through voltage (VST). Using single crystal silicon beams, we demonstrate the snapthrough voltage to flow velocity sensitivity of dV ST /du ≈ 0.13 V s m −1 with a power consumption of ≈ 360 µW. Our experimental results were in accord with the reduced order, coupled, thermo-electro-mechanical model prediction. We anticipate that electrostatically induced snap-through in curved, micromechanical beams will open new directions for the design and implementation of downscaled flow sensors for autonomous applications and environmental sensors.
Journal of microelectromechanical systems, Dec 1, 2018
We report on a flow velocity measurement technique based on snap-through detection of an electros... more We report on a flow velocity measurement technique based on snap-through detection of an electrostatically actuated, bistable micromechanical beam. We show that induced elecrothermal Joule heating and the convective air cooling change the beam curvature and consequently the critical snap-through voltage (VST ). Using single crystal silicon beams, we demonstrate the snap-through voltage to flow velocity sensitivity of dV ST /du ≈ 0.13 V s m -1 with a power consumption of ≈ 360 µW. Our experimental results were in accord with the reduced order, coupled, thermo-electro-mechanical model prediction. We anticipate that electrostatically induced snap-through in curved, micromechanical beams will open new directions for the design and implementation of downscaled flow sensors for autonomous applications and environmental sensors.
Author comment on "A modeling methodology to study the tributary-junction alluvial fan connectivi... more Author comment on "A modeling methodology to study the tributary-junction alluvial fan connectivity during a debris flow event" by Alex Garcés et al., Nat. Hazards Earth Syst.
Ulva is a widespread green algal genus with important ecological roles and promising potential as... more Ulva is a widespread green algal genus with important ecological roles and promising potential as a seagriculture crop. One of the major challenges when cultivating Ulva is sudden biomass disappearance, likely caused by uncontrolled and unpredicted massive sporulation. However, the dynamics of this process are still poorly understood. In this study, we propose a mathematical model describing the biomass accumulation and degradation of Ulva, considering the potential impact of sporulation inhibitors. We developed a differential equation model describing the time evolution of Ulva biomass. Our model simulates biomass in compartments of different Ulva "age" classes, with varying growth and sporulation rates. Coupled with these classes is a differential equation describing the presence of a sporulation inhibitor, produced and secreted by the algae. Our model mimics observed Ulva dynamics. We present Ulva's biomass accumulation under different initial algae population, age distributions and sporulation rates. Furthermore, we simulate water replacement, effectively depleting the sporulation inhibitor, and examine its effects on Ulva's biomass accumulation. The model developed in this work is the first step towards understanding the dynamics of Ulva growth and degradation. Future work refining and expanding our results should prove beneficial to the ecological research and industrial growth of Ulva.
OpenPIV is an open source Particle Image Velocimetry analysis software written in Python, Matlab ... more OpenPIV is an open source Particle Image Velocimetry analysis software written in Python, Matlab and C++
<p>Multi-hot-wire/film probes made from multiple sensors provide three components of veloci... more <p>Multi-hot-wire/film probes made from multiple sensors provide three components of velocity and velocity derivatives in a point. Typically the calibrations are using inverse polynomials to fit the angle dependence of each sensor. This code suggests a use of look-up tables for the task</p
this release fixes two bugs and improves process tests process.py is removed, all pure Python imp... more this release fixes two bugs and improves process tests process.py is removed, all pure Python implementation is in pyprocess.py tests are improved, both Cython and Python versions are compared fixed the bug in Cython due to // fixed the bug in Cython for cases when window_size == search_size == image size, caused range(0,0)
Liberzon, Harrington, Daniel, Gurka, Harari and Zilman "Moth-inspired navigation algorithm i... more Liberzon, Harrington, Daniel, Gurka, Harari and Zilman "Moth-inspired navigation algorithm in a turbulent odor plume from a pulsating source" proposed a novel navigator principle using properties of a turbulent patchy plume, https://journals.plos.org/plosone/article/comments?id=10.1371/journal.pone.0198422 In order to compare this moth-inspired navigator with other navigator types available in the literature, e.g. by Carde and co-workers, we use <code>pompy</code> https://github.com/InsectRobotics/pompy and add these moth-inspiried navigators to its simulation fields. We try to create mean wind with meandering and turbulence and vary odor release parameters to test various navigators' statistics, e.g. success rate, flight time, etc. The main contributors are: @NoamBenelli and @alexlib Note: we use an older version of <code>pompy</code>, included in the repository. In the future, we would be able to update to a newer version of <code>pompy</code> and implement it as a submodule.
OpenPIV is an open source Particle Image Velocimetry analysis software written in Python, Matlab ... more OpenPIV is an open source Particle Image Velocimetry analysis software written in Python, Matlab and C++
extended area search is available in Python version, in addition to the one in Cython (process.py... more extended area search is available in Python version, in addition to the one in Cython (process.pyx) more tests added for shifts
Seedless velocimetry is gaining interest in many industrial and research applications. We report ... more Seedless velocimetry is gaining interest in many industrial and research applications. We report on a comparative study of time-resolved optical velocimetry using traditional, mirror-type knifeedge schlieren optics versus Background-Oriented Schlieren (BOS) of subsonic round turbulent helium jets in air at Red = 5,890 and 11,300. Digital images with 1024 pixels streamwise resolution (0 ≤ x/d ≤ 200) were captured at 6000 frames/s in large ensembles. Velocimetry was performed on these results by digital image correlation (DIC) using OpenPIV software, and by streak-schlieren analysis of x-t diagrams (kymography). Limited PIV data were also collected for verification of the schlieren velocimetry results. Both BOS and traditional schlieren show partial success in measuring the mean-flow helium jet self-similarity in terms of the 1/x decay of centerline velocity, Gaussian-shaped radial velocity profiles, and linear spreading rate of the jet. Visualized turbulent eddies, used as tracers in schlieren velocimetry, are observed to last longer than is necessary for this purpose in the present helium jets. Also, the measured convective velocity appears to be sufficiently robust to sum to the jet mean velocity in some of the results. Kymography yields better overall results than DIC, which we attribute to kymography's spatiotemporal "spectrum" of jet velocities, enabling the discrimination of fast eddies near the jet centerline from slower ones near the jet periphery. DIC and other analysis methods suffer from a path-averaging bias which negatively affects the results. The reduction of kymographic data for velocimetry was done manually and also by a Fourier-transform image-feature-orientation code, both yielding equivalent results.
Experimental Thermal and Fluid Science, Oct 1, 2016
Abstract Three-dimensional Particle Tracking Velocimetry was employed to characterize jets from c... more Abstract Three-dimensional Particle Tracking Velocimetry was employed to characterize jets from circular and semi-circular pipes in the intermediate and far fields. Grid-interpolated velocity were used to validate the measurements, and confirmed the negligible effect of the pipe shape on the mean flow in the intermediate field. Several volumetric regions were defined to get Lagrangian statistical description of the flow from categorized particle trajectories. Probability density functions of the velocity fluctuations, particle acceleration, and curvature of the trajectories revealed common and distinctive features of the jets. The first one showed departure from the Gaussian distribution away from the core, and the acceleration exhibited heavy tails in the two jets; however the curvature pdf revealed distinctive footprint of the pipe shape.
Algal Research-Biomass Biofuels and Bioproducts, Sep 1, 2015
Biorefineries aim to provide sustainable production of food and generation of low carbon energy i... more Biorefineries aim to provide sustainable production of food and generation of low carbon energy in the next decades. Current strategies for biorefinery reply mostly on the classic terrestrial agriculture for biomass production. However, land availability, competition with food crops and total energy balance are challenging limiting factors for terrestrial bioenergy crop production. Off-shore macroalgae production could provide alternative, sustainable feedstocks for biorefineries without competition with food crops. Increasing the yields of off-shore macroalgae cultivation systems could further improve the total energy balance of the marine biorefineries. In this work, based on the fundamental principle of timing differences between light harvesting and carbon fixation in algae, we developed a theoretical framework for increasing the yields of off-shore macroalgae biomass using external mechanical mixing. We show that for a given physiological parameter of macroalgae light harvesting and carbon fixation, mixing could allow for increase of the total energy gain by two orders of magnitude. The overall biorefinery to biofuel efficiency, however, is constrained by drag and macroalgae thallus size.
3D-PTV is a quantitative flow measurement technique that aims to track the Lagrangian paths of a ... more 3D-PTV is a quantitative flow measurement technique that aims to track the Lagrangian paths of a set of particles in three dimensions using stereoscopic recording of image sequences. The basic components, features, constraints and optimization tips of a 3D-PTV topology consisting of a high-speed camera with a four-view splitter are described and discussed in this article. The technique is applied to the intermediate flow field (5 <x/d <25) of a circular jet at Re ≈ 7,000. Lagrangian flow features and turbulence quantities in an Eulerian frame are estimated around ten diameters downstream of the jet origin and at various radial distances from the jet core. Lagrangian properties include trajectory, velocity and acceleration of selected particles as well as curvature of the flow path, which are obtained from the Frenet-Serret equation. Estimation of the 3D velocity and turbulence fields around the jet core axis at a cross-plane located at ten diameters downstream of the jet is compared with literature, and the power spectrum of the large-scale streamwise velocity motions is obtained at various radial distances from the jet core.
The motion of particles through density-stratified interfaces is a common phenomenon in environme... more The motion of particles through density-stratified interfaces is a common phenomenon in environmental and engineering applications. However, the mechanics of particle-stratification interactions in various combinations of particle and fluid properties are not well understood. This study presents a novel machine-learning (ML) approach to experimental data of inertial particles crossing a density-stratified interface. A simplified particle settling experiment was conducted to obtain a large number of particles and expand the parameter range. Using ML, the study explores new correlations that collapse the data gathered in this and in previous work by Verso et al. . The "delay time", which is the time between the particle exiting the interfacial layer and reaching a steady-state velocity, is found to strongly depend on six dimensionless parameters formulated by ML feature selection. The data shows a correlation between the Reynolds and Froude numbers within the range of the experiments, and the best symbolic regression is based on the Froude number only. This experiment provides valuable insights into the behavior of inertial particles in stratified layers and highlights opportunities for future improvement in predicting their motion.
We report on a simple yet efficient approach allowing direct electrothermal excitation of paramet... more We report on a simple yet efficient approach allowing direct electrothermal excitation of parametric resonance (PR) in double-clamped flexible nano-and microscale beams. The application of a time-harmonic voltage between the beam's ends leads to the electric current and Joule's heating of the entire beam, which induces a time-periodic axial stress and results in excitation of the structure lateral vibrations through the PR mechanism. The proposed approach has an advantage, simplifying fabrication and integration and reducing the influence of residual stress, and thermal mismatch, unlike conventional piezoelectric, photothermal, or electrostatic actuation approaches, which require additional piezoelectric layers, light sources, or electrodes in the proximity of a vibrating beam. Single crystal silicon, nominally 500 lm long, 30 lm wide, and 5 lm thick beams were fabricated by deep reactive ion etching and operated at a pressure of %1.9 mTorr. The experimental results, consistent with the reduced order and numerical model predictions, demonstrate the feasibility of the suggested excitation scenario, which could be implemented in resonant sensors, timing devices, signal processing, and micro and nanomechanical logical elements.
We report on a flow velocity measurement technique based on snap-through detection of an electros... more We report on a flow velocity measurement technique based on snap-through detection of an electrostatically actuated, bistable micromechanical beam. We show that induced elecro-thermal Joule heating and the convective air cooling change the beam curvature and consequently the critical snap-through voltage (VST). Using single crystal silicon beams, we demonstrate the snapthrough voltage to flow velocity sensitivity of dV ST /du ≈ 0.13 V s m −1 with a power consumption of ≈ 360 µW. Our experimental results were in accord with the reduced order, coupled, thermo-electro-mechanical model prediction. We anticipate that electrostatically induced snap-through in curved, micromechanical beams will open new directions for the design and implementation of downscaled flow sensors for autonomous applications and environmental sensors.
During diastole, coronary perfusion depends on the pressure gradient between the myocardial tissu... more During diastole, coronary perfusion depends on the pressure gradient between the myocardial tissue and the coronary origin located at the aortic root. This pressure gradient is influenced by the flow field near the closing valve leaflets. Clinical evidence is conclusive that patients with severe aortic stenosis (AS) suffer from diastolic dysfunction during hyperemia, but show increased coronary blood flow during rest. Physiological or pathological factors do not provide an explanation of this effect. Transcatheter aortic valve implantation (TAVI) was shown to decrease the coronary flow along with its main purpose of improving the aortic flow and reducing the risk of heart failure. There is no clear physiological or pathological explanation for the increase of coronary flow due to AS and its decrease immediately after TAVI. In this manuscript, we present a numerical study that examines the impact of AS and valve replacement on the coronary perfusion during rest conditions. The study compares the hemodynamics of five different 2D numerical models: a baseline “healthy valve” case, two AS cases and two TAVI cases. The analysis used time-dependent computational fluid-structure interaction (FSI) simulations of the blood flow in the aortic root including the dynamics of the flexible passive valve leaflets and the varying resistance of the coronary arteries. Despite its simplifications, our 2D model succeeded to capture the major effects that dominant the blood hemodynamics in the aortic root, and to explain the hemodynamic effect that leads to the changes in coronary flow found in other in-vitro and clinical studies. It provides an important insight and emphasizes the need for more comprehensive studies on coronary's hemodynamics after valve replacement. There are numerous variations of TAVI designs and it is very difficult and time consuming to cover all the possible models using complex 3D models. The use of a simple 2D model with FSI and varying coronary resistance can be of great help to demonstrate the main features of the design.
Turbulent resuspension, a process of lifting solid particles from the bottom by turbulent flow, i... more Turbulent resuspension, a process of lifting solid particles from the bottom by turbulent flow, is ubiquitous in environmental and industrial applications. The process is a sequence of events that start with an incipient motion of the particle being dislodged from its place, continue as sliding or rolling on the surface, ending with the particle being detached from the surface and lifted up into the flow. In this study the focus is on the resuspension of solid spherical particles with the density comparable to that of the fluid and the diameter comparable with the Kolmogorov length scale. We track their motion during the lift-off events in an oscillating grid turbulent flow. We measure simultaneously the Lagrangian trajectories both of the particles freely moving along the bottom smooth wall and of the surrounding flow tracers. Different force terms acting on particles were estimated based on particle motion and local flow parameters. The results shown that: i) the lift force is dominant; ii) drag force on freely moving particles is less relevant in this type of resuspension; iii) the Basset (history or viscous-unsteady) force is a non-negligible component and plays an im-*
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Papers by Alex Liberzon
In this manuscript, we present a numerical study that examines the impact of AS and valve replacement on the coronary perfusion during rest conditions. The study compares the hemodynamics of five different 2D numerical models: a baseline “healthy valve” case, two AS cases and two TAVI cases. The analysis used time-dependent computational fluid-structure interaction (FSI) simulations of the blood flow in the aortic root including the dynamics of the flexible passive valve leaflets and the varying resistance of the coronary arteries.
Despite its simplifications, our 2D model succeeded to capture the major effects that dominant the blood hemodynamics in the aortic root, and to explain the hemodynamic effect that leads to the changes in coronary flow found in other in-vitro and clinical studies. It provides an important insight and emphasizes the need for more comprehensive studies on coronary's hemodynamics after valve replacement. There are numerous variations of TAVI designs and it is very difficult and time consuming to cover all the possible models using complex 3D models. The use of a simple 2D model with FSI and varying coronary resistance can be of great help to demonstrate the main features of the design.