Particle Image Velocimetry Analysis Research Articles

An automated image analysing routine for estimation of equivalent diameter in high-speed image sequences with high accuracy and its validation

Bubbly flow plays an important role in industrial processes. Obtaining detailed information on the flow is, however, a challenging task. One of the key process parameters is the diameter of the bubbles, which is often determined as equivalent diameter. In this study, an automatic image analysis routine for time-resolved analysis and estimation of equivalent diameter of rising single bubbles in high-speed image sequences with high accuracy is developed using the open source software KNIME. Common estimation techniques for the equivalent diameter, e.g. based on the major/minor axes, are compared to a novel rotation algorithm, where the detected bubble segments are rotated by 180° in 1° steps, for the determination of the Feret diameter. Additionally, the elongation is measured as a morphological parameter and the centroid positions are determined. In combination with the frame rate of the image sequences the ascent rates can be calculated in form of a Bubble Tracking Velocimetry (BTV). The routine was validated using static computer generated geometrical shapes as well as precision grade solid glass spheres with diameters of 0.7–2.5 mm under dynamic (settling) conditions. High-speed image sequences were recorded and analysed with a critical statistical evaluation. It could be shown that the deviation between measured diameter and real diameter of the glass spheres is less than 1.5% when using the rotating Feret diameter algorithm. Settling velocities were determined with a maximum error of 3%. A first test of the analysing routine in a bubbly flow showed that it is unaffected by dirt, small tracer particles or internals in the viewing area, which makes a combined Particle Image Velocimetry (PIV) and Shadowgraphy analysis feasible.

Experimental prediction of multi-nozzle spray characteristics for optimal design in a lead frame etching process

The objective of this paper is to provide quantitative information of uniform impact forces on the sprayed surface in order to optimize the multi-nozzle spray etching system. Spray characteristics obtained from optical non-intrusive measurements using particle image velocimetry (PIV) and particle motion analysis system (PMAS) are measured in single- and twin-nozzle sprays, and then the multi-nozzle spray characteristics is simulated based on those of measurement data. The influences of the multi-nozzle arrangement, nozzle pitch, and pipe pitch on the spray characteristics such as droplets’ velocity, diameter, number density, impact force and their uniformity are properly evaluated. The experimental cases E1 and E2 represent single-spray nozzle A and B, respectively. For twin-spray tests, three nozzle combinations, namely E3 (nozzle A-A), E4 (nozzle A-B) and E5 (nozzle B-B) are considered with different nozzle pitches. The multi-spray simulation cases S1 and S6 represent the multi-spray cases with a homo-nozzle arrays which is consisted in all nozzles of nozzle A or B. For cases from case S2 to S5, the multi-spray cases with a hybrid-nozzle arrays which is consisted in all nozzles of nozzle A and B. The results show that the impact force increases approximately twice as much for changing of experimental test cases from E1 to E5 owing to the differences in nozzle characteristics of single-sprays and the overlap region between two adjacent nozzles. For the multi-nozzle spray simulation, the uniformity of impact force (UI) is increased with increasing the number of nozzle B which has larger orifice diameter and a wider spray angle. The optimum multi-nozzle spray arrangement is case S4 with more than 90 % UI, based on the fact that the UI is quite stable with increasing the nozzle pitch ranging from 90 mm to 145 mm.

Experimental Study of Ground Subsidence Mechanism Caused by Sewer Pipe Cracks

Simultaneous leakage of soil particles and groundwater into underground vacant spaces caused by sewer pipe defects and cracks can cause underground cavities and even ground collapse on the surface. Numerical studies of this problem are limited, and the mechanism of ground subsidence caused by leakage of soil and groundwater into construction sites has yet to be verified. In this study, the factors affecting the mechanism of ground subsidence are verified via physical modelling of a sewer pipe defect. Through visual inspection and particle image velocimetry analysis, it has been found that the groundwater flow direction, hydraulic gradient around the leakage point, and strength of the ground to support itself are the main factors that dominate the mechanism of ground subsidence. These factors can affect ground deformation and cavity expansion direction, ground subsidence development and collapse speed, and occurrence of sudden ground collapse, respectively. It was also found that pore pressure fluctuates when cavity cavern collapse and cavity expansion occur.

Manipulation-free cultures of human iPSC-derived cardiomyocytes offer a novel screening method for cardiotoxicity.

Induced pluripotent stem cell (iPSC)-based cardiac regenerative medicine requires the efficient generation, structural soundness and proper functioning of mature cardiomyocytes, derived from the patient's somatic cells. The most important functional property of cardiomyocytes is the ability to contract. Currently available methods routinely used to test and quantify cardiomyocyte function involve techniques that are labor-intensive, invasive, require sophisticated instruments or can adversely affect cell vitality. We recently developed optical flow imaging method analyses and quantified cardiomyocyte contractile kinetics from video microscopic recordings without compromising cell quality. Specifically, our automated particle image velocimetry (PIV) analysis of phase-contrast video images captured at a high frame rate yields statistical measures characterizing the beating frequency, amplitude, average waveform and beat-to-beat variations. Thus, it can be a powerful assessment tool to monitor cardiomyocyte quality and maturity. Here we demonstrate the ability of our analysis to characterize the chronotropic responses of human iPSC-derived cardiomyocytes to a panel of ion channel modulators and also to doxorubicin, a chemotherapy agent with known cardiotoxic side effects. We conclude that the PIV-derived beat patterns can identify the elongation or shortening of specific phases in the contractility cycle, and the obtained chronotropic responses are in accord with known clinical outcomes. Hence, this system can serve as a powerful tool to screen the new and currently available pharmacological compounds for cardiotoxic effects.

Optimized Time-Resolved Echo Particle Image Velocimetry- Particle Tracking Velocimetry Measurements Elucidate Blood Flow in Patients With Left Ventricular Thrombus.

Contrast ultrasound is a widely used clinical tool to obtain real-time qualitative blood flow assessments in the heart, liver, etc. Echocardiographic particle image velocimetry (echo-PIV) is a technique for obtaining quantitative velocity maps from contrast ultrasound images. However, unlike optical particle image velocimetry (PIV), routine echo images are prone to nonuniform spatiotemporal variations in tracer distribution, making analysis difficult for standard PIV algorithms. This study introduces optimized procedures that integrate image enhancement, PIV, and particle tracking velocimetry (PTV) to obtain reliable time-resolved two-dimensional (2D) velocity distributions. During initial PIV analysis, multiple results are obtained by varying processing parameters. Optimization involving outlier removal and smoothing is used to select the correct vector. These results are used in a multiparameter PTV procedure. To demonstrate their clinical value, the procedures are implemented to obtain velocity and vorticity distributions over multiple cardiac cycles using images acquired from four left ventricular thrombus (LVT) patients. Phase-averaged data elucidate flow structure evolution over the cycle and are used to calculate penetration depth and strength of left ventricular (LV) vortices, as well as apical velocity induced by them. The present data are consistent with previous time-averaged results for the minimum vortex penetration depth associated with LVT occurrence. However, due to decay and fragmentation of LV vortices, as they migrate away from the mitral annulus, in two cases with high penetration, there is still poor washing near the resolved clot throughout the cycle. Hence, direct examination of entire flow evolution may be useful for assessing risk of LVT relapse before prescribing anticoagulants.

Effects of the extensional rheological properties of polymer solutions on vortex shedding and turbulence characteristics in a two-dimensional turbulent flow

An experimental study was performed to investigate the relationship between the extensional rheological properties of polymer solutions and vortex deformation in turbulent flow. Polyethyleneoxide as a flexible polymer and hydroxypropyl cellulose as a rigid polymer are added to two-dimensional (2D) turbulent flow. Specifically, 2D flow is advantageous as it examines the effect of the extensional rheological properties of polymers on the flow. In the study, 2D turbulent flow and vortex shedding in 2D turbulent flow were observed using interference patterns and particle image velocimetry (PIV). Power spectrum of the 2D flow images and 2D turbulence statistics calculated by PIV analysis indicated that there are three flow regimes of vortex shedding in the 2D turbulent flow of the polymer solution. The vortex shedding in the 2D flow was categorized into three types, and this was affected by the relaxation time of the polymer solutions.

The Use of Tactile Sensors and PIV Analysis for Understanding the Bearing Mechanism of Pile Groups.

Model tests were carried out in dry silica sand under pile loading and visualizing observation to investigate the behavior of a pile group. The pile group consisted of nine cylindrical model piles of 40 mm in diameter in most tests or three rectangular parallelepiped model piles in the visualizing observation. Pile spacings of 200 mm and 100 mm between pile centers were used in the models. Tactile sensors were installed to measure the pressure distribution in the ground and colored sand layer with particle image velocimetry (PIV) analysis to reveal the ground deformation in addition to strain gauges inside the model piles to investigate the interaction among group piles. The tests results showed that a narrower spacing between piles resulted in a wider affected area of the ground and the interaction was more significant below the tips.

Experimental study of the face stability of shield tunnel in sands under seepage condition

Understanding of the failure mechanism and limit support pressure of a shield tunnel face under seepage condition is important in engineering design and construction. Nine physical model tests, i.e. three tests in dry sands, three tests in submerged sands under undrained condition, and three tests under seepage condition were carried out. A rigid plate was set in front of the tunnel face to maintain stability at the initial state. By moving the plate backward from the soil, the displacement and earth pressure curve of the tunnel face was obtained. The earth pressure dropped sharply to a constant value which corresponds to the limit support pressure required to stabilize the tunnel face. The limit pressure was found to increase with the cover-to-diameter ratio in a shallow tunnel, and it turned to be irrelevant to cover-to-diameter ratio in a deep tunnel. The ratio of limit pressure and initial earth pressure decreases with the cover-to-diameter ratio, indicating the effect of soil arching in stabilizing tunnel face stability. Under the same water level condition, the limit pressure of tunnel face with seepage is larger than the one without seepage. The limit support pressure under seepage condition is about 70% of the earth pressure at rest; it is about 50% under undrained condition and is about 15% in dry sand. The flow line around the tunnel face was traced by infused pigment, and the distribution was shown to be irrelevant with water level. The image captured by a HD camera during the test was analyzed by PIV (particle image velocimetry) analysis; the soil particle movements and the distribution of shear strain showed the failure mechanism of tunnel face. The failure mode is a combination of a wedge with slip arc and a prism. Comparing with the failure mode in dry sands and in saturated sands below water table undrained condition, the inclination angle of the wedge block under seepage condition is much smaller.

Particle Image Velocimetry (PIV) Analysis of Particle Settling in Narrow Fracture Experiments

Abstract This paper presents the results of an experimental study of dense sand particles’ settling micromechanics in narrow smooth and rough fractures. Particle Image Velocimetry (PIV) is used for the analysis of velocities of individual particles and groups of particles and their relative paths, collisions, and agglomerating in viscous Newtonian fluid. The displacement vectors obtained through PIV analysis show the movements and velocities of individual and groups of particles and the global velocity trends of the observed area. Experiments were conducted in a relatively narrow 2-mm slot compared to the main particle size of 0.66 mm across. Smooth and rough fracture walls are considered, in which acrylic plates and 3-D–printed hydraulic fracture replica were used. The measured results from this experimental study give new insights into the effects of particle and agglomerate size and shape as well as fluid dynamic viscosity on slurry settling velocity. It was found that an increase in fluid dynamic viscosity promotes the formation of larger agglomerated particles of sand, which, in return, affect overall slurry settling velocity. Observations from rough fracture wall experiments yielded significantly different slurry behavior, with increased erratic particle motions and fewer agglomerations compared to the smooth, idealized fracture walls. Experimental results give new insights into slurry settling in narrow fractures, which has applications to proppant settling in fractures for the oil, gas, and geothermal industries.

Soil behaviour around the stub abutment of an integral bridge and buried piles in the contraction state

The change in the deck length under temperature load affects the upper part of integral bridge abutments and causes abutments rotation. The deck contraction makes the abutment move away from the backfill and causes a failure wedge. To prevent the failure wedge, a new method has been proposed. In this method, the inhibition of integral bridges under contraction is done by cables connected from each abutment to the buried piles outside the bridge along the abutments. In the analysis, the behaviour of soil around the abutment and buried piles is an important parameter which has a great influence on the results. In this paper, the soil behaviour around a laterally loaded stub abutment and buried piles was studied on laboratory stub abutment models using the PIV (particle image velocimetry) method. The PIV analysis was carried out to obtain the deformation pattern and shear strains of the soil around the stub abutment and buried piles. The effects of piles number and soil – pile interaction on the soil deformation pattern were investigated. The results showed that the use of buried piles connected by the cable avoided creating a failure wedge in the backfill.

Feature Tracking Velocimetry Applied to Airborne Measurement Data from Murg Creek

A new image feature tracking velocimetry is presented and tested on airborne video data available from a previous study at Murg Creek (Canton Thurgau, Switzerland). Here, the seeded flow scenery had been recorded by an off-the-shelf action camera mounted to a low-cost quadcopter, and video frames were ortho-rectified to sizes of 4482×2240 px2 at a scale of 64 px/m. The new velocimetry approach is as follows: An adaptive Gaussian mixture model is used for video background subtraction. Then, scale-invariant keypoints on each remaining binary foreground image frame are determined by a feature detection algorithm, and corresponding feature points in subsequent frame pairs are matched using the iterative random sample consensus method. The related feature shifts in metric space divided by the video frame rate finally give the velocity vectors. The obtained velocimetry fields are compared with findings from both a particle image velocimetry and particle tracking velocimetry analysis in terms of accuracy and needed computational power. Indication is given that the feature tracking algorithm presents slightly less precise results, but clearly outperforms the other two in relation to computational power. Therefore, the new simplified method provides a high potential tool that may enable a future way to real time surface velocity measurements obtained from unmanned airborne vehicles.

PI(4,5)P2 forms dynamic cortical structures and directs actin distribution as well as polarity in Caenorhabditis elegans embryos.

Asymmetric division is crucial for embryonic development and stem cell lineages. In the one-cell Caenorhabditis elegans embryo, a contractile cortical actomyosin network contributes to asymmetric division by segregating partitioning-defective (PAR) proteins to discrete cortical domains. In the current study, we found that the plasma membrane lipid phosphatidylinositol 4,5-bisphosphate (PIP2) localizes to polarized dynamic structures in C. elegans zygotes, distributing in a PAR-dependent manner along the anterior-posterior (A-P) embryonic axis. PIP2 cortical structures overlap with F-actin, and coincide with the actin regulators RHO-1 and CDC-42, as well as ECT-2. Particle image velocimetry analysis revealed that PIP2 and F-actin cortical movements are coupled, with PIP2 structures moving slightly ahead of F-actin. Importantly, we established that PIP2 cortical structure formation and movement is actin dependent. Moreover, we found that decreasing or increasing the level of PIP2 resulted in severe F-actin disorganization, revealing interdependence between these components. Furthermore, we determined that PIP2 and F-actin regulate the sizing of PAR cortical domains, including during the maintenance phase of polarization. Overall, our work establishes that a lipid membrane component, PIP2, modulates actin organization and cell polarity in C. elegans embryos.

Analysis on River Bed Changes in Weir Downstream by Real-Scale Experiment

Flood damage has aggravated recently owing to artificial structures in high flow rare areas such as small rivers, which can lead to secondary damage. In this regard, studies are required to examine the conventional design criteria formulas to secure the stability of structures such as weirs and drop structures. Although studies on the stability of these structures have been conducted through small-scale experiments, few empirical studies have investigated the hydraulic phenomena occurring near actual artificial structures. In this study, we fabricated real-size models of weir and drop structure at the Andong River Experiment Center and investigated the flow patterns around the structures by applying the particle image velocimetry analysis technique with a flow tracker. We also measured the scour length in the waterspout section when the structures are overflowing, and compared it with the values calculated using the formula. Consequently, as the supply flow increases, the result is different from the value calculated using the formula given in the existing design standard, and it is judged to be inappropriate for a small stream area with high flow rate. Thus, it is necessary to consider the design factors such as energy gradient and the flow amount per unit width into weir and drop structure as well as the existing design factors in designing an apron section for a weir and drop structure.

Experimental observation of dust circulation in unmagnetized cogenerated dusty plasma

The vortex motion of a dust cloud was experimentally observed in unmagnetized cogenerated dusty plasma in different experimental parameters. Particle image velocimetry analysis demonstrated that several vortex zones exist in the dust cloud at relatively low pressures (0.06 mbar (or 6 Pa)–0.08 mbar (or 8 Pa)) and low discharge voltages (peak‐to‐peak voltage 540–560 V), whereas in relatively high pressure (0.4 mbar (or 40 Pa)–0.7 mbar (or 70 Pa)) and high discharge voltage (peak‐to‐peak voltage 690–740 V), dust vortices formed in dense dust cloud with background plasma fluctuation.

Synchrotron speckle-based x-ray phase-contrast imaging for mapping intra-aneurysmal blood flow without contrast agent

Intracranial aneurysms carry risk of rupture with life threatening consequences. Hemodynamic forces are considered to be the key in cerebral aneurysm rupture. Notably, the hemodynamic analysis requires precise characterization of intra-aneurysmal blood velocity field, raising the need to develop novel measurement techniques. This study aims to assess the performance of speckle-based x-ray phase contrast particle imaging velocimetry (PIV) for velocity field mapping of a pulsatile blood flow in a patient specific aneurysm model without contrast agent. Porcine blood was used in a blood circulation loop including the aneurysm model, which was imaged using the synchrotron x-ray phase contrast imaging (PCI) at an optimum phase propagation distance. X-ray images were processed to improve speckle characteristics for PIV analysis. A computational fluid dynamic (CFD) model was developed for simulation of the blood velocity field and compared to the x-ray PCI-PIV measurements. The CFD model and x-ray PCI-PIV measurements showed similar intra-aneurysmal blood flow structures although the velocity magnitudes were generally higher in CFD model. Contrary to CFD model, x-ray PCI-PIV measurements revealed formation of blood cell stagnation at the aneurysm dome at low blood flow rate, cushioning upon the blood flow shear force. Synchrotron x-ray PCI-PIV offers potential for hemodynamic analysis in patient specific cerebral aneurysm models without contrast agent.

Testing steady and transient velocity scalings in a silo

Gravity-driven discharge experiments were performed in a perspex 3D flat bottomed silo which was filled with a granular material, and had a variable discharge orifice size. The granular material used was amaranth seed with an average diameter of 1 mm. Particle Image Velocimetry (PIV) analysis was performed on a high-speed video recording of the discharge, and used to quantify the velocity field within the silo both at steady state and during the development of flow. We verified not only that the steady-state velocity of the granules in the silo scales with the flow rate, but, additionally, the transition to a steady-state regime is also rate-controlled by the volumetric discharge. We present evidence that, away from the discharge orifice, the flow behaves identically, regardless of the orifice diameter, in a scaled time. We discuss these results with reference to the physics and mathematical modelling of granular flows.

PIV Analysis of Particle Behavior in Electrostatic Precipitator

SUMMARYAn electrostatic precipitator (ESP) is a means to collect particulate matter (PM). They are characterized by a high total particle collection efficiency with a low pressure drop. The particle behavior in ESP depends on the particle characteristic, electric field, space charge, and flow pattern. It is important to understand the particle behavior in ESP. Particle image velocimetry (PIV) was used to grasp the particle behavior in ESP. In this paper, results of PIV of the particle flow velocity fields in a wire‐to‐plate type ESP model are presented. The ESP was an acrylic parallelepiped with a wire electrode and plate collecting electrode. The positive and negative dc voltages were applied to the wire electrode, placed at right angles to the main gas flow. The obtained results show that the particle flow velocity was increased with increasing discharge current. This is attributed to increase in ionic wind. The particle velocity right under of the wire electrode was the fastest.

Dynamics of cytoplasm and cleavage divisions correlates with preimplantation embryo development.

In vitro fertilization has become increasingly popular as an infertility treatment. In order to improve efficiency of this procedure, there is a strong need for a refinement of existing embryo assessment methods and development of novel, robust and non-invasive selection protocols. Studies conducted on animal models can be extremely helpful here, as they allow for more extensive research on the potential biomarkers of embryo quality. In the present paper, we subjected mouse embryos to non-invasive time-lapse imaging and combined the Particle Image Velocimetry analysis of cytoplasmic dynamics in freshly fertilized oocytes with the morphokinetic analysis of recordings covering 5 days of preimplantation development. Our results indicate that parameters describing cytoplasmic dynamics and cleavage divisions independently correspond to mouse embryo's capacity to form a high-quality blastocyst. We also showed for the first time that these parameters are associated with the percentage of abnormal embryonic cells with fragmented nuclei and with embryo's ability to form primitive endoderm, one of the cell lineages differentiated during preimplantation development. Finally, we present a model that links selected cytoplasmic and morphokinetic parameters reflecting frequency of fertilization-induced Ca2+-oscillations and timing of 4-cell stage and compaction with viability of the embryo assessed as the total number of cells at the end of its preimplantation development. Our results indicate that a combined analysis of cytoplasmic dynamics and morphokinetics may facilitate the assessment of embryo's ability to form high-quality blastocysts.

Sliding of water–glycerol mixture droplets on hydrophobic solid–liquid bulk composites using Ti plates with a fibrous TiO2 layer

Fibrous TiO2 layer was formed on a metal Ti plate by soaking it in a KOH solution and subsequently firing it in air at 600 °C for 2 h. Hydrophobic solid–liquid bulk composite (SLBC) was prepared by impregnation of a commercial silicone-based oil into the fibrous TiO2 layer after coating with fluoroalkylsilane. Based on the spreading coefficients from interface energies, the topmost solid surface of the SLBC was covered by the oil film when a water–glycerin mixture droplet was placed on the surface. The mixture droplets slid down the SLBC with acceleration. Particle image velocimetry (PIV) analysis revealed rolling and slipping modes in the sliding of the mixture droplets on the SLBC surface. During sliding, the coefficient of the viscous drag force was correlated with the velocity ratio (U total/U slip). Results suggest that the estimation of the internal fluidity of the liquid droplet was feasible to some degree by evaluating the coefficient during droplet sliding with constant acceleration on the SLBC surface.

CFD as an approach to understand flammable dust 20 L standard test: Effect of the ignition time on the fluid flow

A computational study based on the Euler–Lagrange approach was developed for the characterization of flammable dusts in the 20 L sphere standard test. The aim of the study was to analyze some parameters that might affect the experimental data (e.g., cold turbulence and particle size). The turbulence of a wheat starch cloud was described with the Detached Eddy Simulation model. Both the pressure of the system and the RMS velocity were compared with the flow patterns established with a particle image velocimetry analysis. It was concluded that the rebound nozzle forms a cloud that is composed by clumps. This fact implies dissimilarities between the local concentrations and the nominal value. Finally, a granulometric analysis established that the mean diameter of the particle size distribution (PSD) decreased by 69% during the dispersion. Thus, it is suggested to consider the PSD at the ignition zone rather than the PSD of the sample. © 2017 American Institute of Chemical Engineers AIChE J, 63: 42–54, 2018