Velocity Vector Maps Research Articles

A New Method to Develop Homogeneous and Heterogeneous Porous Micromodels Applicable to Enhanced Oil Recovery and Flow Visualization Experiments

AbstractIn this paper, a new method to fabricate micromodels having homogeneous and heterogeneous porous structures is reported to gain fundamental insight into the flow through porous media. The technique of microparticle image velocimetry (PIV) is used to map the pore-scale velocity field inside the micromodels. A thin perforated metal sheet composed of uniformly distributed circular holes is used as the master pattern, and the replica of the negative of this perforated sheet is transferred to a polydimethylsiloxane (PDMS) substrate using a method similar to the soft lithography. This method allows an efficient fabrication of micromodels having different porosity by adjusting and selecting the perforated sheets of different hole sizes. The prepared micromodels were tested for its applicability and reliability by carrying out the measurements of pore-scale velocity distribution using the micro-PIV technique. The experiments with micromodels with high porosity but different grain arrangements showed qualitative as well as quantitative differences in the velocity field. The pressure drop across the two ends of micromodel is also measured. The variation of pressure difference with the flowrate is found to be nonlinear with a significant effect on the patterns of micropillars. However, at low porosity, the variation of pressure difference with the flowrate is found linear and there is almost no influence of the micropillar patterns. The flow visualization measurements are also conducted with the dual porosity micromodels, and the flow patterns were examined by analyzing the velocity vector maps.

SRflow: Deep learning based super-resolution of 4D-flow MRI data.

Exploiting 4D-flow magnetic resonance imaging (MRI) data to quantify hemodynamics requires an adequate spatio-temporal vector field resolution at a low noise level. To address this challenge, we provide a learned solution to super-resolve in vivo 4D-flow MRI data at a post-processing level. We propose a deep convolutional neural network (CNN) that learns the inter-scale relationship of the velocity vector map and leverages an efficient residual learning scheme to make it computationally feasible. A novel, direction-sensitive, and robust loss function is crucial to learning vector-field data. We present a detailed comparative study between the proposed super-resolution and the conventional cubic B-spline based vector-field super-resolution. Our method improves the peak-velocity to noise ratio of the flow field by 10 and 30% for in vivo cardiovascular and cerebrovascular data, respectively, for 4 × super-resolution over the state-of-the-art cubic B-spline. Significantly, our method offers 10x faster inference over the cubic B-spline. The proposed approach for super-resolution of 4D-flow data would potentially improve the subsequent calculation of hemodynamic quantities.

Joint Deep-Learning-Enabled Impact of Holistic Care on Line Coagulation in Hemodialysis.

In order to investigate the impact of holistic care on line coagulation and safety in hemodialysis and to address limitations of the conventional ultrasound flow vector imaging (VFM) technique, which requires proprietary software to acquire raw Doppler and scatter tracking data, a combined deep-learning-enabled holistic care approach to line coagulation in hemodialysis is proposed. First, velocity along the direction of the sound beam, which is provided by the color Doppler echocardiogram, is obtained as the radial velocity component using a velocity scale. Moreover, the left ventricular wall contour is automatically identified using a U-Net network and the left ventricular wall velocity is calculated as the boundary condition of continuity equation by a retrained PWC-Net model. Likewise, the velocity component of each blood mass in the vertical direction of the sound beam is obtained by solving the continuity equation (i.e. tangential velocity component). Finally, the velocity vector map of cardiac flow field was synthesized and visualized in the flow diagram. For this purpose, sixty patients admitted to receive hemodialysis from February 2019 to June 2020 were randomly divided into two groups of 30 patients where the control group implemented conventional care and the study group implemented all-round care on the basis of conventional care. The nursing effects of both groups were compared. Incidence of pipeline coagulation and complications in the study group were lower than those in the control group and the difference was statistically significant (P < 0.05). The nursing detail score, nursing attitude score, nursing professionalism score, and total satisfaction score in the study group were higher than those in the control group and the difference was statistically significant (P < 0.05). Applying all-round nursing in hemodialysis can effectively reduce the incidence of line coagulation complications and improve the safety of hemodialysis, as well as improve patients' satisfaction with nursing care.

Abstract 14293: Automated Arrhythmia Detection in HiPSC-Derived Cardiac Cell Sheet Models for Drug Testing and Disease Modeling

Introduction: The use of human-induced pluripotent stem cells (hiPSC) derived cardiomyocytes may bring a unique value for drug testing and disease modeling applications. In this project, we developed an automatic and robust arrhythmia detection tool that enables recognition of early-after-depolarizations (EADs) and reentrant activity (spiral waves) in hiPSC-derived cardiac tissue models. Methods and Results: hiPSCs were differentiated into cardiomyocytes, seeded as large-scale hiPSC-derived cardiac cell-sheets (hiPSC-CCSs), loaded with a voltage-sensitive dye, and optically mapped. Arrhythmias were induced either spontaneously, using pacing interventions, or following drug applications. We examined two algorithms to detect spiral wave arrhythmias: optical flow (OF) and dominant frequency (DF). OF enables flow detection through spatial analysis of local velocity vectors (Fig.1 a-d). DF maps depict the frequency with the highest energy in each pixel (Fig.1 e-f). Spiral waves were readily detected by both approaches by the presence of significant diversity in both the frequencies maps (DF) and in the velocity angles (OF). Moreover, in DF maps, the core of the spiral wave (singularity point) could be identified as pixels displaying high dominant frequency as compared to values in other parts of the specimen. (Figure 1). Finally, EADs could be detected using a curve-fitting approach (Fig.1g). Figure 1: (a-d) Consecutive optical map frames (a, c) and velocity vector maps (b, d) of normal (a, b) and a spiral wave (c-d) propagations. (e-f ) DF maps of normal (e) and spiral wave (f) propagations. (g) EAD detection in red. Conclusion: Automatic algorithms were developed to enable robust detection of arrhythmic activity (EADs and spiral waves) in a hiPSC-based cardiac tissue model. This novel approach may bring a unique value to arrhythmia mechanistic studies, high throughput drug screening, and disease modeling.

Düz Kanal İçerisine Yerleştirilmiş Kare Şekilli Silindir Ardındaki Akış Yapısı

Experiments were conducted to investigate the flow topology downstream of a square-shaped cylinder situated in a straight channel. The critical parameters such as the Reynolds number (Re = 500) and the blockage ratio of the square-shaped cylinder (25%) were determined in light of the literature. A Particle image velocimetry (PIV) system was used to obtain the instantaneous velocity vector map. The flow structures, including the time-mean vorticity distribution, &amp;lt;ω&amp;gt; instantaneous and time-mean streamline topology, Ψ, distributions of streamwise velocity fluctuations, urms, turbulent kinetic energy, TKE are presented with Figures.

Automatic Screening of Lung Diseases by 3D Active Contour Method for Inhomogeneous Motion Estimation in CT Image Pairs

Lung diseases are now the third leading cause of death worldwide because of the many risk factors we are exposed to daily, such as air pollution, tobacco use, viruses (such as COVID-19), and bacteria. This work introduces a new approach of the 3D Active Contour Model (3D ACM) to estimate an inhomogeneous motion of lungs, which can be used to analyze lung disease patterns using a hierarchical predictive model. The biophysical model of lungs consists of End Expiratory (EE) and End Inspiratory (EI) models, generated by high-resolution computed tomography images (HRCT). A proposed technique uses the 3D ACM to estimate the velocity vector by using the corresponding points on the parametric surface model of the EE model to the EI model. The external energy from the EI models is the external force that pushes the 3D parametric surface to reach the boundary. The external forces, such as the balloon force and Gradient Vector Flow (GVF), were adjusted adaptively based on the which was calculated from the ratio of the maximum value of EI to EE on the Z axis. Next, the feature representation is studied and evaluated based on the lung structure, separated into five lobes. The stepwise regression, Support Vector Machine (SVM), and Artificial Neural Network (ANN) techniques are applied to classify the lung diseases into normal, obstructive lung, and restrictive lung diseases. In conclusion, the inhomogeneous motion pattern of lungs integrated with medical-based knowledge can be used to analyze lung diseases by differentiating normal and abnormal motion patterns and separating restrictive and obstructive lung diseases. HIGHLIGHTS Inhomogeneous motion analysis from the expanding and shrinking lungs of HRCT pair Adaptive 3D Active Contour Model (ACM) for detecting the shape of the lung by balancing the balloon force with the stopping condition Lung lopes separation using oblique fissure and anatomical location Structure the velocity vector map of lung motion using bag of words of the magnitude Neural Network model for predicting obstructive and restrictive lung diseases GRAPHICAL ABSTRACT

Evaluating flow-field and expelled droplets in the mockup dental clinic during the COVID-19 pandemic.

In the setting of widespread severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) community transmission, reducing the exposure risk on dental professionals and the next patients is the key to reopening dental services in this pandemic environment. The study is motivated by the lack of understanding of the flow-field characteristics and droplet distribution during aerosol-generating procedures. The particle image velocimetry measurements with high temporal and spatial resolutions were performed under ultrasonic scaling in the mockup experimental dental clinic. Compared with other methods focusing on the settled droplet particles, the study focused on the visualization of suspended droplets. From the results of the velocity vector and trajectory map, the high-level contaminated area will be within 1 m from the oral cavity. The vortex structures were identified by the vorticity index. In the surface near the patient's head, a counterclockwise vortex would carry some droplets and contaminate this region. The small droplets circulated in the turbulence cloud and the droplet nuclei generated by dehydration are the two primary sources of suspended particles, which may cause airborne transmission in the dental clinic. About 65%–74% of the droplets in ultrasonic scaling were in the range of 50–180 . The research will provide references to the development of the precaution measures to reduce the SARS-CoV-2 exposure risk of dental professionals.

Focusing of Tsunami Energy at Imwon Port

Lee, K.-J. and Cho, Y.-S., 2020. Focusing of tsunami energy at Imwon Port. In: Malvárez, G. and Navas, F. (eds.), Global Coastal Issues of 2020. Journal of Coastal Research, Special Issue No. 95, pp. 247–251. Coconut Creek (Florida), ISSN 0749-0208.In the last few decades, several catastrophic tsunamis triggered by undersea earthquakes have occurred and struck not only neighboring but also distant coastal communities around the world. These tsunamis have caused a large number of human casualties and severe property damage. In this study, a geographical feature of the Imwon Port located at eastern coast of the Korean Peninsula, is investigated by studying a group of historical and virtual tsunamis caused by 3 historical and 11 virtual undersea earthquakes suggested by KEDO (1999). In addition, the effectiveness of the wave ray model is then examined by estimating tsunami heights at specific positions. Finally, the location of wave energy focusing is predicted by estimating tsunami heights and wave ray tracing, and whether the location is right is reconfirmed by the actual particle velocity vector map. The results of this study shall be used by a civil defense authority to mitigate the tsunami hazards in the case of a real tsunami attack.

Three-Dimensional Reconstruction of Evaporation-Induced Instabilities Using Volumetric Scanning Particle Image Velocimetry

The three-dimensional (3D) flow below the interface of an evaporating liquid at a low pressure is visualized and quantified using scanning particle image velocimetry. The technique presented highlights the use of a single camera and a relatively fast moving laser sheet to image the flow for an application where using more than one camera is difficult. The technique allows collection of the full three-dimensional velocity vector map over the whole liquid volume. The out-of-plane component of the velocity has been determined using two different processing approaches: (i) deriving the full vector from a 3D cross-correlation of the particle volumes and (ii) applying the continuity equation to determine out-of-plane velocities from the calculated in-plane velocity vector fields. The results obtained from both methods showed good agreement with each other. The 3D velocity field reveals the existence of a torus shaped vortex below the evaporating meniscus that was induced by the exposure of the cold liquid to the warmer solid walls. The velocity data also shows that the maximum velocity occurs below the interface, not at the interface which highlights that the observed vortex is not driven by thermocapillary forces that usually govern the flow during evaporation at smaller scales.

Experimental and Numerical Investigations of the Fluid Flow in a Hydroclyclone with an Air Core

Hydrocyclone separators are widely used in various industrial applications in the oil and mining industries to sort, classify, and separate solid particles or liquid droplets within liquid suspensions, which are considered to be multiphase systems. Numerous valuable studies have been conducted in recent years to investigate the flow fields inside hydrocyclones. However, much of the information regarding the performance of cyclones in the literature has limitations and much of it cannot be considered as completely applicable to most real-world applications; many of the studies investigated the flow fields within extremely simplified hydraulic designs that are not representative of the complex geometries or large sizes which are typical in industry. Therefore, in this study, the two-phase flow system inside the actual hydraulic geometry of a milling circuit hydrocyclone is explored with the aid of both computational and experimental techniques (particle image velocimetry (PIV)). More specifically, the flow field with an air core has been investigated. In addition, the air-liquid two phases flow in a hydrocyclone might cause some challenges on both the computational and experimental sides. Two turbulence models are utilized in the numerical calculations: the Reynolds stress model and large eddy simulation. The computational studies are mainly focused on the local flow behavior and the prediction of the dimensions and shape of the air core. Different section planes of hydrocyclone are selected as planes of interest and divided into several fields of view (FOV) for PIV measurements. Two-dimensional experimental velocity vector maps are obtained in each of the fields of view. The computational results are validated globally using pressure and flow rate readings at the boundaries and locally by comparison to the PIV velocity vector maps and profiles.

Experimental and computational study on flow over stepped spillway

The flow over a stepped spillway has complex nature, and its characteristics are remarkably different from other kinds of spillways. This study conducts experimental investigations and numerical simulations on the flow behavior (velocity, concentration profile) and macroscopic features (interface position and self-aeration) of water and neutrally buoyant suspension of non-colloidal particles in a stepped spillway with uniform steps. The development of nappe, transition, and skimming flow regimes is experimentally investigated by using a flow visualization technique. The inception point related to air entrainments is identified in the experimental study. The inception point usually moves downstream and increases the length of the non-aerated region with the increase of flow rate. Results of numerical and experimental studies indicate that a vortex is formed in the triangular cavity below the pseudo-bottom line (imaginary line joining two adjacent step edges) in the stepped channel. This vortex rotates in a clockwise direction for a short time period and returns to the main flow to move downward in the channel. The velocity vector map from numerical simulation predicts the maximum velocity in the middle portion of the spillway, that is, near the pseudo-bottom line. A volume of fluid model coupled with a standard k-e turbulence model is used in the CFD simulations to predict the location of the air-water air-suspension interface. The results are compared with experimental measurements. The calculated interface position agrees well with the experimental measurements. The migration and transport of particles are evaluated based on a diffusive flux model of shear induced particle migration. The contour map for velocity and particle concentration shows a remarkable increase in particle concentration near the air-suspension interface.

Flow characteristics in HyperVapotron elements operating with nanofluids

HyperVapotrons are highly robust and efficient heat exchangers able to transfer high heat fluxes of the order of 10–20 MW/m2. They employ the Vapotron effect, a complex two phase heat transfer mechanism, which is strongly linked to the hydrodynamic structures present in the coolant flow inside the devices. HyperVapotrons are currently tested in the Joined European Torus (JET) and the Mega Amp Spherical Tokamak (MAST) fusion experiments and are considered a strong candidate for the International Thermonuclear Experimental Reactor (ITER). The efficiency of heat transfer and the reliability of the components of a fusion power plant are important factors to ensure its longevity and economical sustainability. Optimisation of the heat transfer performance of these devices by the use of nanofluids is investigated in this paper. Nanofluids are advanced two phase coolants that exhibit heat transfer augmentation phenomena. A cold isothermal nanofluid flow is established inside two HyperVapotron models representing the geometries used at JET and MAST. A hybrid particle image velocimetry (PIV) method is employed to measure the flow and create a dense velocity vector map of a region of interest. The vector spatial resolution is 30 μm. The instantaneous and mean flow structures of a nanofluid are compared to those present during the use of a traditional coolant (water) in order to detect any departure from the hydrodynamic design operational regime of the device. It was discovered that the flow field of the JET model is considerably affected when using nanofluids, while the flow in the MAST geometry does not change significantly by the introduction of nanofluids. Evidence of a shear thinning mechanism is found inside the momentum boundary layer of the nanofluid flows and it might be important to calculating the pumping power losses of a functional nuclear fusion power plant cooling system ran with nanofluids instead of water.

Left heart simulator for evaluation of prosthetic heart valves: behavior of tricuspid bioprosthetic mitral valves during diastole

Abstract The purpose of this work was to know the characteristics of tricuspid bioprosthetic mitral valves in terms of velocity fields and valve aperture areas for some instants concerning the diastole. A left heart simulator was used as an in vitro platform for the bioprostheses. A particle image velocimetry (PIV) system was applied for characterizing instantaneous 2D-velocity fields within the left ventricular model (LVM), and also for detection of mitral bioprostheses aperture areas. The ventricular states were established for 60, 70 and 90 bpm (beats per minute) and a blood analog fluid based on glycerol was employed at 36.5±0.5oC. Two mitral bioprostheses (nominal diameter of 27 and 31 mm) and an aortic bileaflet mechanical valve (27 mm diameter) were used. Instantaneous two-dimensional velocity fields at the upper part of the LVM, for two sections (in the middle of the LVM, and also in a section at 7 mm of distance from that) were obtained. Averaged velocity vector maps (N = 50) were calculated for some instants of interest. According to different heart rates, bioprostheses and sections within the LVM, the velocity fields were presented, as well the bioprostheses aperture areas. In conclusion, the experimental scope including different ventricular states showed how the inflow characteristics of the LVM change according to the chosen variables. This information will aid the validation of a numeric model for the LVM operation, which has been elaborated (some specific methods are presented in the Appendix).

Interaction and propagation characteristics of two counter and co-propagating Mach cones in a dusty plasma

We theoretically investigate the interaction and propagation characteristics of two co/counter propagating Mach cones triggered by two projectile particles moving with supersonic velocities in the same/opposite directions through a dusty plasma medium. The Mach cone solutions are obtained by solving a model set of fluid equations for a heavily charged dust fluid that includes the contributions of the projectile particles in the Poisson equation. The density profiles and velocity vector maps of the Mach wings show interesting structural changes when they interact with each other and form patterns similar to interference fringes. Compared to the co-propagating Mach cones, the wings of counter propagating Mach cones produce a larger number of maxima and minima in the pattern resulting from their mutual interaction. In addition, the time duration of the formation of two maxima or minima at a particular point decreases due to the interactions of Mach cones. Another notable feature is that the spacing between adjacent maxima increases, while the fringe angle decreases with the increase of relative velocity of the counter propagating projectile particles.

Hydrodynamic Study of Single- and Two-Phase Flow in an Advanced-Flow Reactor

The hydrodynamics of the G1 fluidic module of the Corning Advanced-Flow reactor (AFR) was characterized using particle image velocimetry. Two series of experiments, single-phase flow with liquid flow rates of 10–40 mL/min and two-phase flow with an identical overall flow rate range and gas volume transport fractions ranging from 0.125 to 0.50, were performed. From the instantaneous velocity vector maps, the mean and the root-mean-square velocities were computed, which allowed a systematic investigation of the single- and two-phase flow hydrodynamics and transport processes in the AFR. In single-phase flow, the velocity field is symmetric in the heart-shaped cells, and their particular design results in a stagnation zone that limits momentum exchange in each cell. The addition of the gas phase greatly increases the momentum exchange in the heart-shaped cells, which leads to a more uniform distribution of velocity fluctuations and increased transport processes within the AFR.

Investigation of Effect of Boundary Layer on Flow Structure Around a Cylinder with a Strip

In this study, the flow characteristic of the circular cylinder was placed vertically in channel which has dimensions as 8000 mm, 1000 mm, 750 mm, lenght, width and height repectively, was investigated. The cylinder was located in boundary layer with a diameter of 60 mm (D) and a elastic stripwhich has a 1400 N/mm 2 modulus of elasticity vinyl PVC transperent film was attached behind the cylinder. Lenght of the strip (L) was 240 mm L/D=4. The Reynolds number was fixed at Re=7500. The time-averaged and instantaneous velocity vector maps, vorticity contours, Reynold shear and normal stresses, turbulent kinetic energy and frequency of shedding were obtained using the particle image velocimetry (PIV) technique. It was found that the elastic plate which exists behind the cylinder has a slight influence on the flow structure of the wake-boundary layer interaction. Values of turbulent kinetic energy, streamwise Reynold stress, transverse Reynold stresses were decreased by attaching strip.

Comparison of Flow Structures in the Downstream Region of a Cylinder with Flexible Strip

The present study investigates the details of flow structure to downstream of a circular cylinder mounted on a flat surface, in successive plan-view plane both in the boundary layer and up level region. The behavior of the flow in the wake of the bare cylinder and attached a flexible strip which has a 1400 N/mm 2 modulus of elasticity vinyl PVC transperent film. The length of strip 240 mm (L/D=4) is investigated using Particle Image Velocimetry (PIV) technique for Reynolds numbers based on the cylinder diameter of 2500. The flow data downstream of the cylinder are presented using time-averaged velocity vector map, Vavg, streamline patterns, � avg, vorticity contours, � avg, and Reynolds stress correlations, u ' u ' avg, v ' v ' avg, u ' v ' avg and rms velocity values. The locations of the peak values of Reynolds stress correlations and other data are also presented in both bare cylinder and attached body in order to determine the regions under high fluctuations. Another L/D ratios will be investigated in other experiments.

PIV measurements of air-core intake vortices

Particle Image Velocimetry (PIV) measurements were conducted in a large-scale hydraulic model to obtain the horizontal velocity field of intake vortices with considerable air entrainment. Vortex wandering and air-core diameter were determined by object detection using PIV images and velocity vector maps. This allowed for the calculation of ensemble- and azimuthally-averaged velocity fields. The results of the horizontal velocity field around the vortex, whose circulation affects a wide area, confirm the applicability of the analytic solution of the 2D Navier–Stokes equation for a potential (free) vortex. The setup and the improvement of the PIV measurements and their limitations are presented. For example, a completely resolved velocity field close to the air-core did not exist due to reflections at the interface between air and water. Vortex characteristics like vorticity and circulation are derived from the velocity fields and turbulence is shown by representing in-plane Turbulent Kinetic Energy (TKE).

Experimental investigation of flow instabilities in a laminar separation bubble

The present paper reports the results of a detailed experimental study aimed at investigating the dynamics of a laminar separation bubble, from the origin of separation up to the breakdown to turbulence of the large scale coherent structures generated as a consequence of the Kelvin-Helmholtz instability process. Measurements have been performed along a flat plate installed within a double contoured test section, designed to produce an adverse pressure gradient typical of Ultra-High-Lift turbine blade profiles, which induces the formation of a laminar separation bubble at low Reynolds number condition. Measurements have been carried out by means of complementary techniques: hot-wire (HW) anemometry, Laser Doppler Velocimetry (LDV) and Particle Image Velocimetry (PIV). The high accuracy 2-dimensional LDV results allow investigating reverse flow magnitude and both Reynolds normal and shear stress distributions along the separated flow region, while the high frequency response of the HW anemometer allows analyzing the amplification process of flow oscillations induced by instability mechanisms. PIV results complement the flow field analysis providing information on the generation and evolution of the large scale coherent structures shed as a consequence of the separated shear layer roll-up, through instantaneous velocity vector maps. The simultaneous analysis of the data obtained by means of the different measuring techniques allows an in depth view of the instability mechanisms involved in the transition/reattachment processes of the separated shear layer.

The Anatomy of a Pipe Bomb Explosion: Measuring the Mass and Velocity Distributions of Container Fragments

Improvised explosive devices such as pipe bombs are prevalent due to the availability of materials and ease of construction. However, little is known about how these devices actually explode, as few attempts to characterize fragmentation patterns have been attempted. In this study, seven devices composed of various pipe materials (PVC, black steel, and galvanized steel) and two energetic fillers (Pyrodex and Alliant Red Dot) were initiated and the explosions captured using high-speed videography. The video footage was used to calculate fragment velocities, which were represented as particle velocity vector maps. In addition, the fragments were weighed. The results demonstrate a correlation between the type of energetic filler and both the size and velocity of the fragments. Larger fragments were produced by Pyrodex filler indicating a less complete fragmentation, compared with smaller fragments produced by double-base smokeless powder. Additionally, higher fragment velocities were seen with Alliant Red Dot filler.