Development Of Velocity Profile Research Articles

Developing a Computational Model of Lungs for Patients With Acute Respiratory Distress Syndrome

Abstract Acute respiratory distress syndrome (ARDS) is a condition secondary to direct or indirect insult to lungs, leading to acute respiratory failure, and is associated with high mortality. Majority of the ARDS patients require mechanical ventilation, which acts as double-edged sword. Ventilator induced lung injury (VILI) is considered secondary to high inspiratory pressure and cyclical opening during inspiration, and collapse during expiration as suggested by ARDS network clinical trials. Other mechanism for VILI exist secondary to heterogeneous ventilation. To enumerate these mechanisms leading to VILI, a computational fluids dynamics (CFD) study was performed in this study to explore the flow patterns and the pressure distribution in a human tracheobronchial airway model from third to sixth generation branches. The authors validated the computational methodology and analyzed the results to obtain velocity profiles in the primary and secondary flow directions. The study investigated the role of various flow velocities corresponding to Reynolds number (Re) from 100 to 2000 on the pressure drops along branches and bifurcation zones. The identification of secondary flow patterns was critical in understanding the development of asymmetric velocity profiles in the triple bifurcation geometry. The observed patterns in pressure drops and velocity profiles over the laminar flow regime pave the path toward further development of a numerical model to aid treatment for patients with ARDS.

New insights on the layer uniformity of multilayered films produced by coextrusion with interfacial surface generators

AbstractPolymer coextrusion is a manufacturing process whereby at least two polymer melts feed a die to form an extrudate made up of different layers, typically up to 12, to achieve a better product performance. Extruded films with hundreds or thousands of layers can be produced by using sequences of layer multipliers, also known as interfacial surface generators (ISG), at the die inlet. Each ISG splits, stacks, and merges the flow by means of various geometrical channel transformations (GT), in such a way that the number of layers at the outlet is doubled. However, in practice, the thicknesses of the individual layers generated after each transformation are often non‐uniform. This work deals with the numerical simulation of multilayer co‐extrusion of Newtonian polymer melts, aiming at providing new insights on the influence of the ISG geometry on the layer uniformity. It was found that depending on the combination of GT taking place, uneven layers may form due to the development of unsymmetrical velocity profiles along the direction perpendicular to the fluid interface. From this information, improved ISG dies, capable of producing coextruded films with uniform layer distribution, are proposed and assessed numerically.Highlights The polymer coextrusion process produces multilayer products. Extruded films can be produced using Interfacial surface generators (ISG). Polymers flow through ISG by several channel geometric transformations (GTs). Polymer melts flow through ISG undergoing various channel geometric transformations (GTs). Non‐uniform layers can be generated in the ISG. ISG performance can be improved when GTs are thoughtfully combined.

Development of shear-wave velocity profiles and kappa compatible with Ground Motion model for Taiwan

A new velocity model (GMM) compatible with a ground motion prediction model (GMM) for Taiwan is presented in this study. The model is developed using the data set extracted from the flatfile compiled for Taiwan Senior Seismic Hazard Analysis Committee (SSHAC) level 3 project (NCREE, 2015). The Phung et al. (2020) ergodic Sa GMM was used as a backbone model for estimating the site amplification in the frequency domain using inverse Random vibration theory (IRVT). The main motivation for developing a velocity model is that the estimation of the site scaling in terms of the time-averaged shear-wave velocity over the top 30 m (VS30), the method also provides the corresponding depth-dependent VS(z) profiles and the value for the selected VS30 value as a result of the inverse quarter-wave-length method (IQWL). Not all of the empirical amplification can be explained by the 1-D VS profiles andvalues. For soft sites (VS30 < 500 m/s), and intermediate periods (0.5-2.0 sec), there is additional amplification in the empirical data which is attributed to 3-D path and site effects. Using the proposed method, the resulting GMM provides a VS profile, k, and 3-D effect for each VS30 value, which provides a more informative handoff of ground-motion information for use in site-specific site response studies.

A coupled level-set and volume-of-fluid (CLSVOF) method for prediction of microgravity flow boiling with low inlet subcooling on the international space station

The present study is part of a series of NASA-supported investigations of flow boiling of n-perfluorohexane (n-PFH, C6F14) under microgravity on the International Space Station (ISS). The fluid physics and heat transfer characteristics of flow boiling with low inlet subcooling are explored using the Flow Boiling and Condensation Experiment (FBCE) (which is actual name of the test facility), the largest endeavor in microgravity two-phase research conducted to date. Experimental data are collected from the FBCE's Flow Boiling Module (FBM), which features a rectangular channel with 5.0-mm x 2.5-mm cross-section and 114.6-mm heated length. Results for three flow rates are used to explore the effects of mass velocity on flow structure and heat transfer characteristics in the absence of the body force. A Computational Fluid Dynamics (CFD) model is constructed to predict the measured FBM results. The CFD model employs the Coupled Level-Set and Volume-of-Fluid (CLSVOF) method, which is modified with improved interface capture and additional force terms in the momentum equation to determine the bubble dynamics more accurately. Validity of the CFD model is assessed in two ways, by comparing predictions against video-captured interfacial behavior and heat transfer data. The CFD model shows good ability to capture detailed evolution of the interfacial structure both across and along the flow channel, including bubble nucleation, growth, departure, and coalescence, as well as axial development of dominant flow patterns. Details of the flow structure are examined via axial development of both flow velocity and void fraction profiles. Similarly, heat transfer results are presented in terms of streamwise variations of both wall temperature and fluid temperature, which are also predicted accurately with the CFD model. Overall, this study proves the CFD model is an effective method for both design and performance assessment of flow boiling subsystems in space vehicles.

FreeFEM++ based heat transfer analysis of an electrically induced magnetic flow within the framework of micropolar continuum

In this article, we aim to analyze electrically induced magnetic incompressible flow and heat transfer through a channel within the framework of micropolar continuum. Finite element method is employed to compute the numerical solution of the governing dynamics formulated in the form of PDEs along with associated boundary conditions on the channel. The weak form is presented and variational problem is implemented in FreeFem++ language. To validate, the correct implementation of the problem and obtained numerical results, a reduced micropolar magnetohydrodynamic model is taken into consideration. The analytical solution is presented. Computed numerical results are compared with the exact solution in case of reduced micropolar model and a good agreement is achieved. An excellent convergence of the numerical solution to the exact solution is shown through Tables where L 2 -norm and H 1 -errors are computed at refined meshes. Effect of different physical parameters such as magnetic Reynolds number ( R m ), Hartmann number (Ha), micorpolar constants (m and l 1 2 ), micropolar coupling number (N), Prandtl number (Pr) and Brinkmann number (Br) are studied and discussed in detail. The development of thermal, translational and micro-rotational velocity profiles over the cross-sectional domain of the channel is shown for varying values of these material parameters. Some interesting and new findings in this investigation are presented and discussed. It is observed that the maximum temperature in the medium shifts from the center of the domain toward the boundaries if the micropolar coupling constant N is increased. Maximum micro-rotations are always found near the channel’s boundary where it is evidenced that the particle’s micro-rotations have a direct proportionality with the micropolar constant m. Moreover, the counter rotations of the continuum particles are evidenced at the channel’s boundary. Furthermore, the micorpolar coupling constant l 1 2 is found to resist the micro motions of the particles in the channel. The successful implementation of one and higher dimensional magnetohydrodynamic model in FreeFEM++ in general and within the context of micorpolar continuum in particular is delineated. This shows that it provides an efficient platform to simulate magnetohydrodynamic problems in higher order continuum which has applications in designing magneto-rheological airbags, aircraft take-off gear, mechanical heart valves and cooling systems.

Dimensional Characterization of Groundwater Oblique Flow Problems with Heat Transport.

A dimensional study of two problems in which the groundwater flow is oblique has been carried out in order to characterize the vertical profiles of temperature along the domain affected by the flow, determining an input region in which the profiles depend on the horizontal position follow by a region in which profiles only depend on the vertical component of the flow. In the first problem, the horizontal and vertical components of velocity are constant. In the second scenario, the oblique flow of groundwater is generated because in the boundary conditions, the hydraulic potentials present a constant value. From the discriminated dimensional analysis of the mathematical model (governing equations and boundary conditions), the dependencies of the unknowns of greatest interest, characteristic lengths for the development of temperature-depth profiles and velocity profiles and the temperature field, with the dimensionless groups deduced are established. Once these dependencies have been verified, they are graphically represented by means of curves and surfaces as universal solutions to these problems. Based on these universal solutions an inverse problem protocol for estimating water flows from temperature measurements is proposed. The use of universal graphs of the two proposed scenarios avoids the large number of numerical simulations that this type of problem required.

Development of a comprehensive laminar burning velocity and flame instability profile of refined producer gas (H2:CO:CH4) – Air mixtures at elevated pressures

Unstretched laminar burning velocity (LBV) and intrinsic instabilities of Refined producer gas (H2:CO:CH4)-Air mixtures were systematically investigated at 300 K, 1–4 bar and ϕ = 0.8–1.2 using freely expanding spherical flame method. In H2/CO/CH4 rich mixtures, LBV increased with increase in CO (and reduction in CH4)/H2 (and reduction in CH4)/H2 (and reduction in CO) at any given equivalence ratio, while peak LBV occurred at ϕ = (1.2 and remained at 1.2)/(1.2 and shifted to 1.1)/(1.1 and remained at 1.1). Computed unstretched LBV using GRI Mech 3.0 and FFCM mechanisms deviated from measurements with initial pressure. From the comprehensive susceptibility analysis (to instabilities), the composition H2:CO:CH4 = 0:1:1 had the highest resilience towards thermo-diffusive and hydrodynamic instabilities. Refined producer gas with higher mole fractions of H2 were vulnerable to intrinsic instabilities, while increment in CH4 suppressed the susceptibility to hydrodynamic instability and increment in CO suppressed the thermo-diffusive instability.

Shear wave velocities of prominent geologic formations in the Nelson-Tasman region

This paper presents the development of representative shear wave velocity profiles for the prominent geologic formations in the Nelson-Tasman region of New Zealand. Shear wave velocity (VS) profiles to depths of up to 100 m were developed at over 50 sites using a combination of active source and passive source surface wave testing. Using this data and regional geologic information, VS-depth functions were developed for six of the prominent geologic formations. Comparison with existing VS-depth functions from New Zealand and international studies highlighted the significantly higher shear wave velocities of the deposits in this region. VS exceeded 750 m/s for the Moutere Gravels and Port Hills Gravels at relatively shallow depths, representative of rock deposits. However, while the Port Hills Gravels transition to a conglomerate rock below depths of 30 m or less, the Moutere Gravel formation is an uncemented clay-bound gravel. The young gravel and sand deposits have VS higher than those from other regions. As the region is thought to have undergone cycles of geologic uplift, the resulting over-consolidation of these deposits could explain the high VS. Horizontal-to-vertical spectral ratio testing was not able to characterise the fundamental site period across the region, likely due to the weak impedance contrast that would exist at the gravel-rock interface at depth. These outcomes highlight the importance of regional geotechnical and geophysical characterisation to constrain the salient features that control potential seismic site amplification and site classification.

Hydrodynamic response time of magnetorheological fluid in valve mode: an initial study

The transient behaviour of magnetorheological (MR) damper is a very important parameter affecting the performance of this technology in modern semi-actively controlled suspension systems. Currently, the transient behaviour of the MR damper is limited by dynamics of the MR fluid (MRF) itself. The significant part of MRF response time is a hydrodynamic response time which is connected with transient rheology and development of velocity profile in the slit gap. In this paper, the method for measuring the hydrodynamic response time of MRF operating in valve mode is presented. The hydrodynamic response time of MRF-132DG achieved value of τ90 = 0.78 ms for H = 17.5 kA/m a value of τ90 = 0.65 ms for H = 34 kA/m for given geometry of gap. The difference between model and experiment is lower in higher yield stresses of MRF.

Approaches to Modeling Bed Drag in Pine Forest Litter for Wildland Fire Applications

Modeling flow in vegetative fuel beds is a key component in any detailed physics-based tool for simulating wildland fire dynamics. Current approaches for drag modeling, particularly those employed in multiphase computational fluid dynamics (CFD) models, tend to take a relatively simple form and have been applied to a wide range of fuel structures. The suitability of these approaches has not been rigorously tested for conditions which may be encountered in a wildland fire context. Here, we focus on beds of Pinus rigida needle litter and undertake a two-part study to quantify the drag and evaluate the capabilities of a multiphase large eddy simulation CFD model, the NIST Fire Dynamics Simulator. In the first part, bed drag was measured in a wind tunnel under a range of conditions. The results were fit to a Forchheimer model, and the bed permeability was quantified. A traditional approach employed in the multiphase formulation was compared to the parameterized Forchheimer equation and was found to over-predict the drag by a factor of 1.2–2.5. In the second part, the development of a velocity profile above and within a discrete fuel layer was measured. Using the Forchheimer equation obtained in the first part of the study, the CFD model was able to replicate a qualitatively consistent velocity profile development. Within the fuel bed, the model appeared to under-predict the velocity magnitudes, which may be the result of unresolved pore-scale flow dynamics.

Developing Turbulent Flow in Pipes and Analysis of Entrance Region

Turbulent flows have complex structures due to its nature and its’ analyses are hard either by numerical or experimental means. Hydrodynamic development of turbulent flow is also complex. In this study, velocity distribution in hydrodynamic entrance length of pipes is investigated depending on axial and radial locations. Literature was surveyed for a single empirical expression that provides velocity profile directly according to Reynolds number, radial and axial locations. Requisite for computational fluid dynamics in hydrodynamic entry length of pipes is stressed by assessing turbulence magnitudes in radial and axial directions. Evaluation of the region and its properties are conducted from heat transfer perspective. An axisymmetric pipe entrance region was analyzed by means of a commercial CFD code with nondimensional parameters. Four different Reynolds numbers that are 5x103, 1x104, 5x104, 1x105 were used in calculations. k-ϵ turbulence model and standard wall functions were used for turbulence modeling. Hydrodynamic entry length, velocity profiles and turbulence indicator parameters results are presented by means of axial and radial profiles. According to the obtained results, radial velocity component values exist that would lead to radial thermal convection in hydrodynamic entrance length. It is found that simultaneous development of velocity profiles and turbulence quantities leads to characteristic velocity profiles. Also, it is seen that a good resolution in hydrodynamic entrance length can be easily achieved by computational fluid dynamics.

MODIFICATION OF THE GEOMETRY OF THE FLOW CONDITIONER

MODIFICATION OF THE GEOMETRY OF THE FLOW CONDITIONER

Analysis of entrance region flow of Bingham nanofluid in concentric annuli with rotating inner cylinder

This work analyses the entrance region flow of Bingham nanofluids in cylindrical concentric annuli. In this discussion, water is used as the base fluid which is embedded with the silver(Ag) and copper(Cu) nanoparticles coalescing with Bingham fluid. The investigation has been carried out by rotating the inner cylinder, while the outer cylinder is assumed to be at rest. A finite-difference analysis is used to obtain the axial, radial, tangential velocity components and the pressure along the radial direction. With the Prandtl's boundary layer assumptions, the continuity and momentum equations are solved iteratively using a finite difference method. Computational results are obtained for various non-Newtonian flow parameters, different volume fraction parameters and geometrical considerations. This work’s main interest is to study the development of velocity profiles and pressure drop in the entrance region of the annuli. The present results are compared with the results available in the literature for various particular cases and it is found to be in good agreement.

CFD simulation of bubble in flow field: Investigation of dynamic interfacial behaviour in presence of surfactant molecules

This work presents the results of numerical simulation of liquid flow on a static bubble. Velocity and surfactant concentration profiles of the liquid around a bubble exposed in flow field were estimated via unsteady CFD solution. Governing equations are the Navier-Stokes and conservation of mass in the liquid bulk and at the interface. Resulted profiles of surfactant concentration and velocity in the liquid bulk are used to determine the dynamic surface tension data via two adsorption isotherms of Langmuir and Frumkin. Data of dynamic surface tension were validated via experimental data of “bubble in flow field” protocol. Surface concentrations of surfactants were also numerically estimated. At longer flow times, surface concentration increases due to adsorption and accumulation of surfactants at the interface. The rate of mass transfer is increased by development of velocity profile around the bubble surface. Steady state was reached about 36 s after flow starts.

Starting Poiseuille Flow in a Circular Tube With Two Immiscible Fluids

Starting flow due to a suddenly applied pressure gradient in a circular tube containing two immiscible fluids is solved using eigenfunction expansions. The orthogonality of the eigenfunctions is developed for the first time for circular composite regions. The problem, which is pertinent to flow lubricated by a less viscous near-wall fluid, depends on the ratio of the radius of the core region to that of the tube, and the ratios of dynamic and kinematic viscosities of the two fluids. In general, a higher lubricating effect will lead to a longer time for the starting transient to die out. The time development of velocity profile and slip length are examined for the starting flows of whole blood enveloped by plasma and water enveloped by air in a circular duct. Owing to a sharp contrast in viscosity, the starting transient duration for water/air flow can be ten times longer than that of blood/plasma flow. Also, the slip length exhibits a singularity in the course of the start-up. For blood with a thin plasma skimming layer, the singularity occurs very early, and hence for the most part of the start-up, the slip length is nearly a constant. For water lubricated by air of finite thickness, the singularity may occur at a time that is comparable to the transient duration of the start-up, and hence, an unsteady slip length has to be considered in this case.

Development of Deep Shear Wave Velocity Profiles in the Canterbury Plains, New Zealand

Deep (typically > 1,000 m) shear wave velocity ( V S) profiles were developed across the Canterbury region of New Zealand at nine strong-motion stations using a combination of active and passive surface wave methods. A multimode, multimethod joint inversion process, which included Rayleigh and Love wave dispersion and horizontal-to-vertical spectral ratio data, was used to develop the V S profiles at each site. A priori geologic information was used in defining preliminary constraints on the complex geologic layering of the deep basin underlying the region, including velocity reversals in locations where interbedded terrestrial gravels and marine sediments are present. Shear wave profiles developed as part of this study had characteristics comparable to the profiles from 14 Christchurch sites detailed in a separate study. The profiles developed in the two studies were combined to form region-specific V S profiles for typical deposits, which can be used to improve the accuracy of current three-dimensional (3-D) crustal velocity models of the region.

Development of Deep Shear Wave Velocity Profiles with Estimates of Uncertainty in the Complex Interbedded Geology of Christchurch, New Zealand

Deep (+500-m) shear wave velocity ( VS) profiles were developed at 14 sites throughout Christchurch, New Zealand, using a combination of active-and passive-source surface wave testing. The geology of Christchurch is complex and presents several challenges for surface wave testing. Specifically, the complex interlayering of relatively stiff gravels with soft sands, silts, and clays makes (1) the interpretation of experimental dispersion data ambiguous and (2) complicates the determination of appropriate inversion-layering parameterizations. In order to address the first issue, dispersion data uncertainty was quantified and several mode interpretations were considered during inversion. To address the second issue, 155 geotechnical boreholes and 199 geologic well logs in the vicinity of the test sites were used to guide the choice of layering parameterizations such that geologically realistic VSprofiles were obtained via surface wave inversion. At each site, a suite of 1,000 VSprofiles representing the combined effects of epistemic uncertainty and apparent aleatory variability in VSwas obtained. These VSprofiles are available on the DesignSafe-CI web site ( https://doi.org/10.17603/DS21D4D ) and are intended to aid in future seismic site response analyses.

Flow speed has little impact on propulsive characteristics of oscillating foils

Experiments are reported on the performance of a pitching and heaving two-dimensional foil in a water channel in either continuous or intermittent motion. We find that the thrust and power are independent of the mean freestream velocity for two-fold changes in the mean velocity (four-fold in the dynamic pressure), and for oscillations in the velocity up to 38\% of the mean, where the oscillations are intended to mimic those of freely swimming motions where the thrust varies during the flapping cycle. We demonstrate that the correct velocity scale is not the flow velocity but the mean velocity of the trailing edge. We also find little or no impact of streamwise velocity change on the wake characteristics such as vortex organization, vortex strength, and time-averaged velocity profile development---the wake is both qualitatively and quantitatively unchanged. Our results suggest that constant velocity studies can be used to make robust conclusions about swimming performance without a need to explore the free-swimming condition.

A Systematic Design Approach of a Float Type Sluice Gate for Flow Measurement Automation

With the rapid development of microelectronics, computer, sensor and communication technology, the measuring and controlling of hydraulic structures has gradually realized automation and intelligent information collection will be more and more perfect. As a commonly used hydraulic structure, sluice gate needs to be combined with modern technology to provide basic data and control flow in more scientific and efficient ways. Different discharge methods are available to determine discharge under sluice gates. The present paper designs a new float type float and proposes a way to measure the discharge through the gate. This paper compares the new equation of (Q) with (e/H) under free flow condition with proposed equations by other researchers. The results shows that other equations fail to accurately determine the flow rate for the cases of free flow, while employing the new proposed equations can result in more accurate discharge estimation within the given ranges of the experimental study. The development of velocity profile under sluice gate is examined, and the effects of shear stress are studied. The new method can be used to predict the performance of sluice gates with different sizes under free -flow situations. These results may attract and guide numerical modelers of flow. A free flow automation measuring and controlling system based on single chip microcomputer and sensor can be designed, which will be application of computer, sensors and other modern technology. Thus realizing scientific water management, optimal allocation and accurate measurement of water resources.

A simple hydrodynamic model of a laminar free-surface jet in horizontal or vertical flight

A useable model for laminar free-surface jet evolution during flight, for both horizontal and vertical jets, is developed through joint analytical, experimental, and simulation methods. The jet’s impingement centerline velocity, recently shown to dictate stagnation zone heat transfer, encompasses the entire flow history: from pipe-flow velocity profile development to profile relaxation and jet contraction during flight. While pipe-flow is well-known, an alternative analytic solution is presented for the centerline velocity’s viscous-driven decay. Jet-contraction is subject to influences of surface tension (We), pipe-flow profile development, in-flight viscous dissipation (Re), and gravity (Nj = Re/Fr). The effects of surface tension and emergence momentum flux (jet thrust) are incorporated analytically through a global momentum balance. Though emergence momentum is related to pipe flow development, and empirically linked to nominal pipe flow-length, it can be modified to incorporate low-Re downstream dissipation as well. Jet contraction’s gravity dependence is extended beyond existing uniform-velocity theory to cases of partially and fully developed profiles. The final jet-evolution model relies on three empirical parameters and compares well to present and previous experiments and simulations. Hence, micro-jet flight experiments were conducted to fill-in gaps in the literature: jet contraction under mild gravity-effects, and intermediate Reynolds and Weber numbers (Nj = 5–8, Re = 350–520, We = 2.8–6.2). Furthermore, two-phase direct numerical simulations provided insight beyond the experimental range: Re = 200–1800, short pipes (Z = L/d · Re ≥ 0.01), variable nozzle wettability, and cases of no surface tension and/or gravity.