Local Velocity Measurements Research Articles

4D flow MRI velocity uncertainty quantification.

An automatic method is presented for estimating 4D flow MRI velocity measurement uncertainty in each voxel. The velocity distance (VD) metric, a statistical distance between the measured velocity and local error distribution, is introduced as a novel measure of 4D flow MRI velocity measurement quality. The method uses mass conservation to assess the local velocity error variance and the standardized difference of means (SDM) velocity to estimate the velocity error correlations. VD is evaluated as the Mahalanobis distance between the local velocity measurement and the local error distribution. The uncertainty model is validated synthetically and tested in vitro under different flow resolutions and noise levels. The VD's application is demonstrated on two in vivo thoracic vasculature 4D flow datasets. Synthetic results show the proposed uncertainty quantification method is sensitive to aliased regions across various velocity-to-noise ratios and assesses velocity error correlations in four- and six-point acquisitions with correlation errors at or under 3.2%. In vitro results demonstrate the method's sensitivity to spatial resolution, venc settings, partial volume effects, and phase wrapping error sources. Applying VD to assess in vivo 4D flow MRI in the aorta demonstrates the expected increase in measured velocity quality with contrast administration and systolic flow. The proposed 4D flow MRI uncertainty quantification method assesses velocity measurement error owing to sources including noise, intravoxel phase dispersion, and velocity aliasing. This method enables rigorous comparison of 4D flow MRI datasets obtained in longitudinal studies, across patient populations, and with different MRI systems.

Flow-Mediated Dilatation: Learning Curve Study with a Novice Operator

BackgroundPerforming reproducible flow-mediated dilatation (FMD) measurements can be challenging, especially among inexperienced operators. Our aim was to present the detailed learning curve of a novice operator.MethodsFollowing a one-week basic training period, the operator performed duplicate measurements on 6–8 individuals per week, for six weeks. The operator followed the recommendations of the most recent guideline. Duplex ultrasound was used for the simultaneous and continuous measurement of brachial artery diameter and local blood flow velocity. Following a 1-min recording of baseline diameter (D), FMD was measured after a 5-min period of occlusion of the proximal forearm vessels. Inter-session coefficient of variation (CV) values for D and FMD were calculated for each week.ResultsThe number of volunteers assessed each week were the following: 8, 7, 7, 6, 7, 7 individuals. CV values for both D and FMD exhibited a decreasing trend over the training period, ending at 1.73% for D and 14.24% for FMD at week 6. These CV values are within the range outlined in the most recent FMD guideline for proficiency.ConclusionWithin a reasonable timeframe, and with careful adherence to measurement guidelines, the attainment of sound reproducibility in FMD measurements by a novice operator is feasible.

Global-local state analysis and monitoring-based velocity measurement of oil–gas–water three-phase flow

The mixture fluids of oil–gas–water metamorphose through the change of phase, properties and structure. This poses a challenge to decipher their dynamic entanglement for phase velocity measurement. It is evident that progressively grasp of process states provides valuable prior information for further flow velocity measurement. As a significant flow characteristic, multiscale gives unique inspiration for flow state monitoring and velocity measurement from a global–local view. In this work, empirical wavelet transform-based Hilbert-Huang transform (EWT-based HHT) and multiscale robust empirical permutation entropy (Ms-rePE) are employed for the analysis of CWUD and conductance signals respectively, achieving the joint characterization of oil–gas–water flow structure by acoustic-electrical dual-mode information. On this basis, a data-mechanism dual-driven model for flow velocity measurement is established under a unified multiscale framework. And a novel approach of hypergraph-based global–local structure analysis (HGLSA) is proposed to simultaneously extract global–local information embodied in the complex flow process. The proposed scheme of global–local state monitoring-based flow velocity measurement is verified by the dynamic experiment of oil–gas–water three phase flow.

A frictional soliton controls the resistance law of shear-thickening suspensions in pipes

Pipe flows are commonly found in nature and industry as an effective mean of transporting fluids. They are primarily characterized by their resistance law, which relates the mean flow rate to the driving pressure gradient. Since Poiseuille and Hagen, various flow regimes and fluid rheologies have been investigated, but the behavior of shear-thickening suspensions, which jam above a critical shear stress, remains poorly understood despite important applications (e.g., concrete or food processing). In this study, we build on recent advances in the physics of shear-thickening suspensions to address their flow through pipes and establish their resistance law. We find that for discontinuously shear-thickening suspensions (large particule volume fractions), the flow rate saturates at high driving stress. Local pressure and velocity measurements reveal that this saturation stems from the emergence of a frictional soliton: a unique, localized, superdissipative, and backpropagating flow structure coexisting with the laminar frictionless flow phase observed at low driving stress. We characterize the remarkably steep effective rheology of the frictional soliton and show that it sets the resistance law at the whole pipe scale. These findings offer an unusual perspective on low-Reynolds suspension flows through pipes, intriguingly reminiscent of the transition to turbulence for simple fluids. They also provide a predictive law for the transport of such suspensions in pipe systems, with implications for a wide range of applications.

Simultaneous Measurement of Local Pulse Wave Velocities in Radial Arteries Using a Soft Sensor Based on the Fiber Bragg Grating Technique.

Arterial stiffness has been proved to be an important parameter in the evaluation of cardiovascular diseases, and Pulse Wave Velocity (PWV) is a strong indicator of arterial stiffness. Compared to regional PWV (PWV among different arteries), local PWV (PWV within a single artery) outstands in providing higher precision in indicating arterial properties, as regional PWVs are highly affected by multiple parameters, e.g., variations in blood vessel lengths due to individual differences, and multiple reflection effects on the pulse waveform. However, local PWV is less-developed due to its high dependency on the temporal resolution in synchronized signals with usually low signal-to-noise ratios. This paper presents a method for the noninvasive simultaneous measurement of two local PWVs in both left and right radial arteries based on the Fiber Bragg Grating (FBG) technique via correlation analysis of the pulse pairs at the fossa cubitalis and at the wrist. Based on the measurements of five male volunteers at the ages of 19 to 21 years old, the average left radial PWV ranged from 9.44 m/s to 12.35 m/s and the average right radial PWV ranged from 11.50 m/s to 14.83 m/s. What is worth mentioning is that a stable difference between the left and right radial PWVs was observed for each volunteer, ranging from 2.27 m/s to 3.04 m/s. This method enables the dynamic analysis of local PWVs and analysis of their features among different arteries, which will benefit the diagnosis of early-stage arterial stiffening and may bring more insights into the diagnosis of cardiovascular diseases.

Reconstructive interpolation for pulse wave estimation to improve local PWV measurement of carotid artery.

Ultrasonic transit time (TT)-based local pulse wave velocity (PWV) measurement is defined as the distance between two beam positions on a segment of common carotid artery (CCA) divided by the TT in the pulse wave propagation. However, the arterial wall motions (AWMs) estimated from ultrasonic radio frequency (RF) signals with a limited number of frames using the motion tracking are typically discrete. In this work, we develop a method involving motion tracking combined with reconstructive interpolation (MTRI) to reduce the quantification errors in the estimated PWs, and thereby improve the accuracy of the TT-based local PWV measurement for CCA. For each beam position, normalized cross-correlation functions (NCCFs) between the reference (the first frame) and comparison (the remaining frames) RF signals are calculated. Thereafter, the reconstructive interpolation is performed in the neighborhood of the NCCFs' peak to identify the interpolation-deduced peak locations, which are more exact than the original ones. According to which, the improved AWMs are obtained to calculate their TT along a segment of the CCA. Finally, the local PWV is measured by applying a linear regression fit to the time-distance result. In ultrasound simulations based on the pulse wave propagation models of young, middle-aged, and elderly groups, the MTRI method with different numbers of interpolated samples was used to estimate AWMs and local PWVs. Normalized root mean squared errors (NRMSEs) between the estimated and preset values of the AWMs and local PWVs were calculated and compared with ones without interpolation. The means of the NRMSEs for the AWMs and local PWVs based on the MTRI method with one interpolated sample decrease from 1.14% to 0.60% and 7.48% to 4.61%, respectively. Moreover, Bland-Altman analysis and coefficient of variation were used to validate the performance of the MTRI method based on the measured local PWVs of 30 healthy subjects. In conclusion, the reconstructive interpolation for the pulse wave estimation improves the accuracy and repeatability of the carotid local PWV measurement.

Combining Reinforcement Learning and In Situ Current Velocity Measurements for Efficient UUV Guidance

Conventional guidance algorithms for unmanned underwater vehicles commonly operate on geometric principles that do not directly take into account local environmental conditions. We describe here a deep reinforcement learning (RL) framework that partially addresses this issue by generating energy-minimizing guidance systems. Specifically, the proposed framework outputs trained policy networks (agents) capable of mapping histories of local current velocity measurements to heading and depth commands that yield nearly-optimal, minimum-energy transits through spatially varying current fields. Numerical experiments in three spatial dimensions on realistic ocean currents, where direction and speed vary non-monotonically in depth, demonstrate that trained agents reduce the energy costs of transits when compared against dead-reckoning, a common in-service guidance heuristic. In particular, numerical results suggest that trained agents learn an explore-exploit strategy according to which they initially execute an exploratory dive, followed by a return to a depth with optimally favorable currents, which they exploit for the remainder of the transit.

Hydraulic Effect of Vegetation Zones in Open Channels: An Experimental Study of the Distribution of Turbulence

The development of vegetation in riverbeds is an important part of river engineering, and an in-depth understanding of its hydraulic influence is greatly needed. Our research focuses primarily on common reed (Phragmites australis) in riverbeds. To date, little is known about the hydraulic impact of the Phragmites australis reed and both field and laboratory data are still very scarce. Consequently, the main goal of our study was to evaluate the effect of vegetation zones on the spatial distribution of turbulence. Based on laboratory measurements of local instantaneous velocities, the values of the turbulence intensity (degree) Tu were determined, and its spatial distribution was illustrated. Analysis of the results showed that the relatively dense clusters of plants (reeds) act as “openwork deflectors” of the current and very clearly shape its spatial distribution. This can also be observed in the case of the distribution of the turbulence parameter Tu. For example, in the case of the development of riparian vegetation in the form of quasi-triangular communities of common reed (Phragmites australis) located alternately, there is a channelization of the flow, but also spatial changes in its character that occur. This work only presents results for preliminary hydraulic tests for Phragmites reed. These experiments should also be continued for other species of flexible riparian vegetation such as wicker. In the laboratory, the hydraulic influence of only triangle-shaped vegetation zones has been studied. Therefore, there is also a need for further hydraulic studies on vegetation zones of shapes other than triangular, e.g., rectangular, as well as vegetation zones with irregular shapes The authors see the need for such research and have already planned its continuation. Research on the interactions between vegetation and the structure of water flow in the riverbed is a very important aspect of contemporary trends in river environment management. Conscious, planned, and model-tested locating (or removing) of vegetation in a stream allows for shaping hydraulic and morphological conditions, thus controlling the processes of erosion, transport, and accumulation of debris.

A Pressure Drop and Particle Image Velocimetry Investigation into Depressurized Loss-of-Coolant Accident Parameters Applied to Packed Beds with an Aspect Ratio of D/dp = 4.4

New developments in porous media modeling have allowed for a new opportunity to implement experimental data for validation and verification. This includes velocity measurements using particle image velocimetry and global pressure drop measurements that are used to produce pressure drop correlations. We conducted such experiments on two very similar facilities of packed spheres by the authors of this paper. The results from the measurements are presented in this paper as a complete experimental study of a packed bed of smooth spheres through a two-prong approach. First, a set of global pressure drop correlations are validated with experimental data and presented as a function of porous Reynolds numbers. Second, the local velocity measurements from three depths spanning 2.4 sphere diameters are presented and further analyzed through the use of a normalized probability distribution function of the time-resolved velocity field. The conclusion of this paper is a suggestion for the results to be used in the creation or validation of computational fluid dynamics porous media models in the measured flow regimes for a packed bed of smooth spheres with an aspect ratio between the sphere diameter and the empty column diameter of 4.4.

Distributed parameter identification for the Navier–Stokes equations for obstacle detection

We present a parameter identification problem for a scalar permeability field and the maximum velocity in an inflow, following a reference profile. We utilize a modified version of the Navier–Stokes equations, incorporating a permeability term described by the Brinkman’s Law into the momentum equation. This modification takes into account the presence of obstacles on some parts of the boundary. For the outflow, we implement a directional do-nothing condition as a means of stabilizing the backflow. This work extends our previous research published in (Aguayo et al 2021 Inverse Problems 37 025010), where we considered a similar inverse problem for a linear Oseen model with do-nothing boundary conditions on the outlet and numerical simulations in 2D. Here we consider the more realistic case of Navier–Stokes equations with a backflow correction on the outflow and 3D simulations of the identification of a more realistic tricuspid cardiac valve. From a reference velocity that could have some noise or be obtained in low resolution, we define a suitable quadratic cost functional with some regularization terms. Existence of minimizers and first and second order optimality conditions are derived through the differentiability of the solutions of the Navier–Stokes equations with respect to the permeability and maximum velocity in the inflow. Finally, we present some synthetic numerical test based of recovering a 2D and 3D shape of a cardiac valve from total and local velocity measurements, inspired from 2D and 3D MRI.

Development of an in vitro platform for transesophageal echocardiographic and color Doppler hemodynamic assessments of left atrial appendage occlusion devices

Abstract Introduction Device-related thrombus (DRT) remains a significant complication after left atrial appendage occlusion (LAAO) and is associated with device position. Clinical prospective study of the influence of device position on DRT is cumbersome. Purpose To establish an in vitro bench test platform that allows visual, transesophageal echocardiographic and color Doppler hemodynamic assessments of left atrial appendage occlusion devices. Methods Based on a mock circulatory system, an in vitro platform was developed to create pathophysiological environment and left atrium wall motion under atrial fibrillation condition. Results LAAO devices could be visualized in the left atrium phantom model using transesophageal echocardiography and color Doppler measurement of local blood velocity at LAAO devices were proven to be capable. Deep implantations resulted in uncovered left upper pulmonary vein ridges. In comparison to ostium-fitted device positions, deep implantations were associated with reduced velocity of blood and the local velocity in the "cul-de-sac" remained lower than the critical threshold of 0.2 m/s. Conclusions An in vitro platform was developed that allows transesophageal echocardiographic and color Doppler hemodynamic assessments of left atrial appendage occlusion devices.

Keynote lecture. Towards reliability-management for debris flow risk assessment

Recent progress in data-integrated simulation methods excelled our understanding of debris flows including triggering mechanisms and dynamic run-out behavior. Research groups and geohazard practitioners worldwide successfully integrate advanced simulations into workflows for hazard mapping. However, many challenges remain in predictively applying such tools for accepted decision support. One reason is our lack of a systematic approach to managing the simulations’ reliability. In this contribution, we present results on an investigation to which extent the choice of data used for calibration influences the simulation’s reliability. We start with introducing building blocks of a modular and extendible data-integrated debris flow simulation toolchain developed by our group. Next, we introduce reliability as one quality measure of a holistic debris flow simulation and discuss how it can be assessed. Based on a synthetic example, we then show how different types of observed calibration data, such as impact area, deposit volume or localized velocity measurements impacts on the subsequent forward simulation’s posterior probability distribution, hence the simulation’s reliability. We conclude by discussing how linking a debris flow simulation’s reliability to type, scope and resolution of the calibration data could offer a novel pathway towards reliability management for debris flow risk assessment.

Stabilizing and Maneuvering Angle Rigid Multiagent Formations With Double-Integrator Agent Dynamics

This article studies 2-D formation stabilization and maneuvering of mobile agents governed by double-integrator dynamics. The desired formation is described by a set of triple-agent interior angles. A carefully chosen such set of angle constraints guarantees that the desired formation is angle rigid. To achieve the desired angle rigid formation, a stabilization control law is proposed using only local velocity and direction measurements. We show that the closed-loop dynamics of the formation, when each agent is modeled by a double-integrator, are closely related to the corresponding one in single-integrator agent dynamics. Sufficient conditions are constructed to guarantee the closed-loop stability for identical and distinct velocity damping gains, respectively. To guide an angle rigid formation to move with the desired translational velocity, orientation, and scale, formation maneuvering laws are then proposed. Simulation examples are also provided to validate the results.

Maneuvering Angle Rigid Formations With Global Convergence Guarantees

Angle rigid multi-agent formations can simultaneously undergo translational, rotational, and scaling maneuvering, therefore combining the maneuvering capabilities of both distance and bearing rigid formations. However, maneuvering angle rigid formations in 2D or 3D with global convergence guarantees is shown to be a challenging problem in the existing literature even when relative position measurements are available. Motivated by angle-induced linear equations in 2D triangles and 3D tetrahedra, this paper aims to solve this challenging problem in both 2D and 3D under a leader-follower framework. For the 2D case where the leaders have constant velocities, by using local relative position and velocity measurements, a formation maneuvering law is designed for the followers governed by double-integrator dynamics. When the leaders have time-varying velocities, a sliding mode formation maneuvering law is proposed by using the same measurements. For the 3D case, to establish an angle-induced linear equation for each tetrahedron, we assume that all the followers' coordinate frames share a common <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$Z$</tex> direction. Then, a formation maneuvering law is proposed for the followers to globally maneuver <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$Z$</tex> -weakly angle rigid formations in 3D. The extension to Lagrangian agent dynamics and the construction of the desired rigid formations by using the minimum number of angle constraints are also discussed. Simulation examples are provided to validate the effectiveness of the proposed algorithms.

Image-Free Fast Ultrasound for Measurement of Local Pulse Wave Velocity: In Vitro Validation and In Vivo Feasibility.

Local pulse wave velocity (PWV), a metric of the target artery's stiffness, has been emerging in its clinical value and adoption. State-of-the-art ultrasound technologies used to evaluate local PWV based on pulse waves' features are sophisticated, non-real-time, and are not amenable for field and resource-constrained settings. In this work, we present an image-free ultrasound system to measure local PWV in real-time by employing a pair of ultrasound transducer elements. An in vitro study was performed on the arterial phantom to: 1) characterize the design aspects of the system and 2) validate its accuracy against beat-by-beat (invasive) local PWV measured by a reference dual-element catheter. Furthermore, a repeatability and reproducibility study on 33 subjects (21-52 years) investigated the in vivo measurement feasibility from the carotid artery. With the experimentally deduced optimal design (frame-rate =500 Hz, RF sampling rate =125 MHz, LPF cutoff =14 Hz, and order =4 ), the system yielded repeatable beat-to-beat measurements (variability =1.9 % and over 15 cycles) and achieved a high accuracy (root-mean-square-error =0.19 m/s and absolute-percentage-error =2.4 %) over a wide range of PWVs (2.7-11.4 m/s) from the phantom. Subsequently, on human subjects, the intra- and inter-operator PWV measurements were highly repeatable (intraclass correlation coefficient ). The system does not impose a demand for special processors with high-computational power while offering real-time feedback on acquisition and measurement quality and provides local PWV online. Future large population and animal studies are required to establish the device's clinical usability.

OCAL APPROACH TO IMPROVE THE AERODYNAMIC CHARACTERISTICS OF THE FINAL DRYING PROCESS

Energy-saving technologies are widely used in various technological processes, in particular for the final drying of plant waste. The purpose of the study is to ensure optimal flow distributions and making targeted changes in the design of the coolant supply system based on measurements of local velocities at characteristic points in space, using the methods of hot-wire anemometry.The measurements were carried out in stages and covered eight modifications of the installation. Based on the analysis of the data obtained, specific measures were developed to improve the design of the coolant supply system.

Evaluation of the multi-sensor probe methods for the measurement of local bubble velocity and diameter

The evaluation of the multi-sensor probe methodology is required to accurately measure local bubbles or droplet parameters in the two-phase flow conditions. This study evaluated two- and four-sensor probes through Monte Carlo simulation and air-water benchmark experiments. In the simulation, it was found that the lateral distance of sensing elements should be minimized, and their axial distance should be longer than 10% of bubble diameter for the optimal design of the probe. From the benchmark experiments, the Vb,axial uncertainties of two- and four-sensor probes were 6.5% and 4.5% in the velocity range of 0.4–3.7 m/s, respectively. The D32 uncertainty was significantly affected by the bubble shape and data reduction methods for each probe. For the two-sensor probe, the maximum error was 9% when the bubble shape was close to the sphere of which diameter was less than 2 mm, and it increased to 28% when the bubble diameter exceeded 2 mm due to the bubble shape distortion in the experiment. While, the four-sensor probe showed excellent performance with a 14% error regardless of the bubble shape under the distorted bubbly flow.

Development of a miniature electromagnet probe for the measurement of local velocity in heavy liquid metals

ABSTRACT Electromagnetic induction is an effective technique for local velocity measurements in heavy liquid metals, such as mercury and lead/lead–bismuth eutectic. In this regard, Ricou and Vives’ probe and von Weissenfluh’s probe are well-known instruments that use permanent magnets. However, the sensitivity and measurement volume of the probes unexpectedly vary because the permanent magnet is demagnetized as the temperature increases up to the Curie temperature. Furthermore, such probes do not work for local velocity measurements over the Curie temperature. In this study, a new electromagnetic probe using a miniature electromagnet was developed as a prototype sensor to overcome such disadvantages of the permanent magnet. The diameter and the length of the sensor were 6 and 155 mm, respectively. The electromagnet incorporated in the sensor was excited by a direct current of 50 mA. The fundamental performance of the sensor was confirmed in a room-temperature experiment by measuring the local velocity of flowing mercury in a square channel. Numerical velocity profiles were calculated and compared with those of the experiment to clarify the validity of the measured velocity profiles. In this paper, the sensitivity and the measurement volume of the probe were assessed. The validity of the measured velocity profiles was confirmed by the calculated results.

Counter-flow orbiting of the vortex centre in turbulent thermal convection

We present an experimental study of the large-scale vortex (or large-scale circulation, LSC) in turbulent Rayleigh–Bénard convection in a $\varGamma =\text {diameter}/\text {height}=2$ cylindrical cell. The working fluid is deionized water with Prandtl number ( $Pr$ ) around 5.7, and the Rayleigh number ( $Ra$ ) ranges from $7.64\times 10^7$ to $6.06\times 10^8$ . We measured the velocity field in various vertical cross-sectional planes by using the planar particle image velocimetry technique. The velocity measurement in the LSC central plane shows that the flow is in the single-roll form, and the centre of the single-roll (vortex) does not always stay at the centre of the cell; instead, it orbits periodically in the direction opposite to the flow direction of the LSC, with its trajectory in the shape of an ellipse. The velocity measurements in the three vertical planes in parallel to the LSC central plane indicate that the flow is in the vortex tube form horizontally filling almost the whole cell, and the centre line of the vortex tube is consistent with the so-called ‘jump rope’ form proposed by a previous study that combined numerical simulation and local velocity measurements in the low $Pr$ case (Vogt et al., Proc. Natl Acad. Sci. USA, vol. 115, 2018, pp. 12674–12679). In addition, we found that the oscillation of the local velocity in $\varGamma =2$ cells originates from the periodical orbiting of the vortex centre. Our velocity measurements further indicate that the vortex centre orbiting is absent in $\varGamma =1$ cells, at least in the $Ra$ range of our experiments.

Evaluation of the Multi-Sensor Probe Methods for the Measurement of Local Bubble Velocity and Diameter

Evaluation of the Multi-Sensor Probe Methods for the Measurement of Local Bubble Velocity and Diameter