Flow Pathlines Research Articles

Designing Manhole in Water Transmission Lines Using Flow3D Numerical Model

Using cascades and drops existing in flow path has a history of 3000 years. Particularly, Roman engineers employed stepped spillways with the same idea in several countries; however, there are few information about the hydraulic performance of aqueducts. Most of these channels have flat long cross sections with low torsions (variable slope) such that they can encompass cascade and steep spillways or dopshaft. Given that there are few studies conducted on dropshafts, the present paper attempted to discuss about such structures in flow path and water transmission lines as well as introducing the existing principles and relations and present, the obtained results of designing though Flow3D. The obtained error percentage was about 20% which is acceptable for numerical studies.

MORPHOLOGICAL EFFECT OF FLOOD WATER PATHWAY IN RESERVOIRS ON THE DISTRIBUTION OF SEDIMENTATION

In the North Africa countries, sediments deposition in the reservoir dams reduces the available surface water resources by 2 to 5% per year. In Tunisia, even many efforts are made to protect reservoir dams against soil erosion, the sedimentation still very important and constitute a limitation their time duration. In order to better understand these phenomena, bathymetry, turbidity, suspended soil particles and sediments were monitored for two reservoir dams in Tunisia: Joumine and Sejnane. These data will be interpreted in order to better characterize the sedimentation process and identify the determinant factors. Geostatistical Technics are applied to the bathymetric data in order to simulate the evolution, in time and in space, of the morphology of the reservoir dams and to estimate the distribution of the sediments deposits. The results for the two dams will permit to better understand the influence of the initial geometry of the reservoir dams on the sedimentation process and to deduce the main water flow path lines. Turbidity, suspended particles and sediments particles size profiles established for fixed stations in the reservoir dams will be interpreted in order to better understand the sedimentation process in the reservoirs dams and to characterize the influence of the initial reservoir geometry.

MORPHOLOGICAL EFFECT OF FLOOD WATER PATHWAY IN RESERVOIRS ON THE DISTRIBUTION OF SEDIMENTATION

In the North Africa countries, sediments deposition in the reservoir dams reduces the available surface water resources by 2 to 5% per year. In Tunisia, even many efforts are made to protect reservoir dams against soil erosion, the sedimentation still very important and constitute a limitation their time duration. In order to better understand these phenomena, bathymetry, turbidity, suspended soil particles and sediments were monitored for two reservoir dams in Tunisia: Joumine and Sejnane. These data will be interpreted in order to better characterize the sedimentation process and identify the determinant factors. Geostatistical Technics are applied to the bathymetric data in order to simulate the evolution, in time and in space, of the morphology of the reservoir dams and to estimate the distribution of the sediments deposits. The results for the two dams will permit to better understand the influence of the initial geometry of the reservoir dams on the sedimentation process and to deduce the main water flow path lines. Turbidity, suspended particles and sediments particles size profiles established for fixed stations in the reservoir dams will be interpreted in order to better understand the sedimentation process in the reservoirs dams and to characterize the influence of the initial reservoir geometry.

MORPHOLOGICAL EFFECT OF FLOOD WATER PATHWAY IN RESERVOIRS ON THE DISTRIBUTION OF SEDIMENTATION

In the North Africa countries, sediments deposition in the reservoir dams reduces the available surface water resources by 2 to 5% per year. In Tunisia, even many efforts are made to protect reservoir dams against soil erosion, the sedimentation still very important and constitute a limitation their time duration. In order to better understand these phenomena, bathymetry, turbidity, suspended soil particles and sediments were monitored for two reservoir dams in Tunisia: Joumine and Sejnane. These data will be interpreted in order to better characterize the sedimentation process and identify the determinant factors. Geostatistical Technics are applied to the bathymetric data in order to simulate the evolution, in time and in space, of the morphology of the reservoir dams and to estimate the distribution of the sediments deposits. The results for the two dams will permit to better understand the influence of the initial geometry of the reservoir dams on the sedimentation process and to deduce the main water flow path lines. Turbidity, suspended particles and sediments particles size profiles established for fixed stations in the reservoir dams will be interpreted in order to better understand the sedimentation process in the reservoirs dams and to characterize the influence of the initial reservoir geometry.

Retrospectively gated intracardiac 4D flow MRI using spiral trajectories

PurposeTo develop and evaluate retrospectively gated spiral readout four‐dimensional (4D) flow MRI for intracardiac flow analysis.MethodsRetrospectively gated spiral 4D flow MRI was implemented on a 1.5‐tesla scanner. The spiral sequence was compared against conventional Cartesian 4D flow (SENSE [sensitivity encoding] 2) in seven healthy volunteers and three patients (only spiral). In addition to comparing flow values, linear regression was used to assess internal consistency of aortic versus pulmonary net volume flows and left ventricular inflow versus outflow using quantitative pathlines analysis.ResultsTotal scan time with spiral 4D flow was 44% ± 6% of the Cartesian counterpart (13 ± 3 vs. 31 ± 7 min). Aortic versus pulmonary flow correlated strongly for the spiral sequence (P < 0.05, slope = 1.03, R2 = 0.88, N = 10), whereas the linear relationship for the Cartesian sequence was not significant (P = 0.06, N = 7). Pathlines analysis indicated good data quality for the spiral (P < 0.05, slope = 1.02, R2 = 0.90, N = 10) and Cartesian sequence (P < 0.05, slope = 1.10, R2 = 0.93, N = 7). Spiral and Cartesian peak flow rate (P < 0.05, slope = 0.96, R2 = 0.72, N = 14), peak velocity (P < 0.05, slope = 1.00, R2 = 0.81, N = 14), and pathlines flow components (P < 0.05, slope = 1.04, R2 = 0.87, N = 28) correlated well.ConclusionRetrospectively gated spiral 4D flow MRI permits more than two‐fold reduction in scan time compared to conventional Cartesian 4D flow MRI, while maintaining similar data quality. Magn Reson Med 75:196–206, 2016. © 2015 Wiley Periodicals, Inc.

Visualization of Aspirated Flow Pathlines in a Thrombectomy Catheter with Three Extra Holes: A CFD Study

The aspiration catheter design requires the good understanding of blood flow, based on a complex analysis of its hemodynamic characteristics. Computational fluid dynamics (CFD) is an important approach in studying the blood flow. In this paper the effect of extra upper holes - designed for the aspiration catheter - on the aspirated fluid pathlines are studied and discussed.

Analytical and computational solutions for three-dimensional flow-field and relative pathlines for the rotating flow in a Tesla disc turbine

The three-dimensional flow field and the flow pathlines within a Tesla disc turbine have been investigated analytically and computationally. The description of the flow field includes the three-dimensional variation of the radial velocity, tangential velocity and pressure of the fluid in the flow passages within the rotating discs. A detailed comparison between the results obtained from the analytical theory and computational fluid dynamic (CFD) solutions of Navier–Stokes equations is presented in order to establish the reliability of the simplified mathematical model. The present work reveals the dependence of the shape, size and orientation of the pathlines on various operating parameters (such as tangential speed ratio, radial pressure drop, inlet nozzle angle, and position of the exit) and local balance of various forces (viz. inertial, viscous, centrifugal and Coriolis). The relative merits of two possible ways of representing the pathlines in the absolute and relative frame of reference are discussed that provide physical understanding of subtle flow features.

Groundwater flow and mixing in a wetland–stream system: Field study and numerical modeling

Summary We combined electrical resistivity tomography (ERT) on land and in a stream with zone-based hydraulic conductivities (from multi-level slug testing) to investigate the local geological heterogeneity of the deposits in a wetland–stream system. The detailed geology was incorporated into a numerical steady-state groundwater model that was calibrated against average head observations. The model results were tested against groundwater fluxes determined from streambed temperature measurements. Discharge varied up to one order of magnitude across the stream and the model was successful in capturing this variability. Water quality analyses from multi-level sampling underneath the streambed and in the wetland showed a stratification in groundwater composition with an aerobic shallow zone with oxygen and nitrate (top ∼3 m) overlying a reduced, anoxic zone. While NO 3 - concentrations up to 58 mg L−1 were found in the top of the aquifer and immediately underneath the streambed no NO 3 - was detected deeper within the aquifer. An inverse relationship between NO 3 - and SO 4 2 - suggests that pyrite oxidation takes place in the deeper parts of the aquifer. Simulated flow path lines showed very different origins for deeper groundwater samples. No nitrate reduction is believed to occur in the shallow zone, where oxygen is present, and the residence time is on the order of 1 year. Nitrate reduction can, however, occur in the deeper parts, which are oxygen-free, and where the residence time is on the order of 7 years. A simulation with a homogeneous model did not match the observations nearly as well as a heterogeneous model based on ERT and a spatially distributed hydraulic conductivity. Furthermore, the origin of the sampled groundwater could not have been predicted from groundwater hydraulic head and the groundwater chemistry alone. The presented approach of integrating such methods in groundwater–surface water exchange studies, proved efficient to obtain information of the controlling factors.

Numerical Analysis of Erosion Caused by Biomimetic Axial Fan Blade

Damage caused by erosion has been reported in several industries for a wide range of situations. In the present work, a new method is presented to improve the erosion resistance of machine components by biomimetic method. A numerical investigation of solid particle erosion in the standard and biomimetic configuration blade of axial fan is presented. The analysis consists in the application of the discrete phase model, for modeling the solid particles flow, and the Eulerian conservation equations to the continuous phase. The numerical study employs computational fluid dynamics (CFD) software, based on a finite volume method. User-defined function was used to define wear equation. Gas/solid flow axial fan was simulated to calculate the erosion rate of the particles on the fan blades and comparatively analyzed the erosive wear of the smooth surface, the groove-shaped, and convex hull-shaped biomimetic surface axial flow fan blade. The results show that the groove-shaped biomimetic blade antierosion ability is better than that of the other two fan blades. Thoroughly analyze of antierosion mechanism of the biomimetic blade from many factors including the flow velocity contours and flow path lines, impact velocity, impact angle, particle trajectories, and the number of collisions.

Assessment of left ventricular 2D flow pathlines during early diastole using spatial modulation of magnetization with polarity alternating velocity encoding: A study in normal volunteers and canine animals with myocardial infarction

A high-temporal resolution 2D flow pathline analysis method to study early diastolic filling is presented. Filling patterns in normal volunteers (n = 8) and canine animals [baseline (n = 1) and infarcted (n = 6)] are studied. Data are acquired using spatial modulation of magnetization with polarity alternating velocity encoding, which permits simultaneous quantification of 1D blood velocities (using phase contrast encoding) and myocardial strain (using spatial modulation of magnetization tagging and harmonic phase analysis) at high-temporal resolution of 14 ms within a single breath hold. Virtual emitter particles, released from the mitral valve plane every time frame during rapid filling, are tracked to depict the 2D pathlines on the imaged plane. The pathline regional distribution is compared with myocardial longitudinal strains and to regional pressure gradients. Quantitative analysis of net kinetic energy of pathlines is finally performed. Our results demonstrate a linear correlation (r(2) = 0.85) between pathline spatial distribution and myocardial strain. Peak net kinetic energy of 0.06 ± 0.01 mJ in normal volunteers, 0.043 mJ in baseline dog, 0.143 ± 0.03 mJ in infarcted dogs with nominal flow dysfunction, and 0.016 ± 0.007 mJ in infarcted dogs with severe flow dysfunction is observed. In conclusion, 2D pathline analysis provides a direct regional assessment of early diastolic filling patterns and is sensitive to abnormalities in early diastolic filling.

Influence of segmentation on morphological parameters and computed hemodynamics in cerebral aneurysms

This article focuses on the effects of segmentation on cerebral aneurysm's morphological parameters and on blood flow patterns computed using computational fluid dynamics. Segmentation is a non-negligible source of uncertainty that may have a consequent impact on the morphological assessment and the resulting hemodynamical simulations, the latter potentially being a key element in the decision-making therapeutic armamentarium for neuroradiologists and neurosurgeons. From the three patient-specific cases investigated, medical imaging data sets were collected, and four different three-dimensional segmentations were generated by the same senior technician. Morphological parameters were measured, and the aspect ratio was derived. Numerical simulations were performed; flow pattern changes, their impact on wall shear stress (WSS) and their sensitivity within the four reconstructed geometries were analyzed. Aneurysm velocity, vorticity and shear magnitudes were computed and compared. The morphological parameters having the highest variability were the aneurysm lobe dimensions (20 %). The neck length was the second parameter presenting the highest variability (21 %). The neck width variability reached 13.8 %, and the aspect ratio variability reached 14.2 %. The artery height and the artery width presented a variability of 13.7 and 10.8 %, respectively. Finally, the aneurysm depth, aneurysm height and aneurysm width presented variabilities of 12.8, 9.4 and 7.3 %, respectively. Differences in the flow path lines, velocity magnitude, wall shear stress and vorticity are also reported and discussed. The average variability reached 15.6 % for velocity, 25.2 % for vorticity and 25.2 % for shear, these parameters being computed inside the aneurysm. The maximum variability reached 31.0 % for velocity, 54.8 % for vorticity and 58.1 % for shear. A segmentation process reconstructing anatomies that is less sensitive to human intervention would be a future goal worth pursuing.

Computational Modeling of Effects of Mechanical Shaking on Hemodynamics in Hollow Fibers

Blood-membrane interaction during hemodialysis develops a secondary protein layer on the dialysis membrane surface, resulting in reduction of hemodialyzer performance. Wall shear stress at the surface of the hollow-fiber membrane is one of the determinant factors able to influence dialysis efficiency. Shaking of hemodialyzer during treatment could increase the wall shear stress of the membrane, which could enhance hemodialyzer performance. In this study, hemodynamic changes in hollow fibers were analyzed using computational fluid dynamics software for various shaking conditions of hemodialyzer (longitudinal, transverse, rotational motions). Longitudinal motion induced reverse flow, while transverse motion induced symmetric swirling inside the hollow fiber. During rotational motions, nonuniform vortices were developed according to the rotational radius of the hollow fiber. These changes in flow pathlines induced by different shaking profiles increased the relative motion of blood, transmembrane pressure, and wall shear stress on dialysis membrane surfaces. Both longitudinal and transverse shaking profiles showed a linear relationship between shaking velocity (the product of amplitude and frequency) and wall shear stress. Performance of hemodialyzer can be enhanced with simple mechanical shaking motions, and optimal shaking profiles for clinical application can be investigated and predicted with the computational fluid dynamics model proposed in this study.

Early diastolic function observed in canine model of reperfused transmural myocardial infarction using high temporal resolution MR imaging

Summary We have applied a novel high temporal resolution MR imaging sequence to study diastolic function in canines with reperfused transmural infarction. Our results demonstrate abnormal diastolic strain-rates in infarct and viable risk region with corresponding abnormal filling patterns, as observed through the visualization of 2D flow pathlines 3 days post reperfusion. Background Coronary angioplasty limits infarct expansion post myocardial infarction (MI). However, under certain conditions such as prolonged ischemia, the procedure induces reperfusion injury (RI), linked to adverse left ventricular (LV) remodeling and heart failure (HF). The functional mechanisms involved in adverse remodeling post reperfusion are still unclear. We have developed a new high temporal resolution MR imaging technique, SPAMMPAV (SPAtially Modulated Magnetization with Polarity Alternated Velocity encoding) that provides regional assessment of early diastolic flow velocity and myocardial strain. This method was applied in a canine animal model with prolonged occlusion followed by reperfusion. We examine the diastolic strain-rates (index of stiffness) of infarct regions relative to remote regions and the 2D diastolic flow pathlines 3 days post reperfusion to provide insight into early diastolic function in these animals. Methods Studies were performed in six dogs following 5-6 hours of balloon occlusion of the left anterior descending

Magnetic resonance 4D flow characteristics of cerebrospinal fluid at the craniocervical junction and the cervical spinal canal

To evaluate the applicability of 4D phase contrast (4D PC) MR imaging in the assessment of cerebrospinal fluid dynamics in healthy volunteers and patients with lesions at the craniocervical junction or the cervical spinal canal. Ten healthy volunteers and four patients with lesions including Chiari I malformation and cervical canal stenoses were examined by a cardiac-gated 4D PC imaging sequence on 1.5T MRI. Phase contrast images were postprocessed allowing for flow quantification and flow pathline visualisation. Velocity data were compared with conventional axial 2D phase contrast images. The 4D PC sequence allowed for flow quantification and visualisation in all individuals. Bland-Altman analysis showed good agreement of 2D and 4D PC velocity data. In healthy volunteers, CSF flow was homogeneously distributed in the anterior and anterolateral subarachnoid space with the flow directed caudally during systole and cranially during diastole. Flow velocities were closely related to the width of the subarachnoid space. Patients showed grossly altered CSF flow patterns with formation of flow jets with increased flow velocities. 4D PC MR imaging allows for a detailed assessment of CSF flow dynamics helping to distinguish physiological from complex pathological flow patterns at the craniocervical junction and the cervical spine.

Computer Aided Design of Coat-Hanger Die in Polymer Film Processing

With the aid of computer simulations, coat-hanger die was designed for more uniform residence time distribution. Analysis of velocity distribution and flow path line indicate that stagnation areas exist in the coat-hanger die, which is caused by the geometry abrupt change between the circular section manifold and the rectangular section slot gap. The stagnation areas affect the melt residence time directly. After changing the circular section manifolds to tear-drop section manifolds, the stagnation areas decrease from 8.21 mm2 to 5.40 mm2. Compared with the melt residence time in circular section manifolds, both the maximum residence time and the residence time dispersion were decreased.

Computational fluid dynamics simulation of a transpiring wall reactor for supercritical water oxidation

A computational fluid dynamic (CFD) model of a transpiring wall reactor for supercritical water oxidation has been implemented and solved using the commercial software Fluent 6.3. Model results have been validated by comparison with experimental temperature profiles, and the influence of model simplifications on the accuracy of the results has been discussed. It has been found that the model presents some inaccuracies in the calculation of the maximum reaction temperature, which have been attributed to the simplifications in the calculation of thermal properties of the fluids imposed by limitations of the software. The effect of different process parameters has been studied, including transpiring water flow ratio, transpiring water temperature, flow rate and composition of the oxidant (pure oxygen or air) on different indicators of reactor performance such as temperature and composition contours, flow path lines and effluent compositions. The behaviour of three different transpiring wall designs comprising different sections of porous and non-porous materials has also been investigated. It has been found that making the upper cup of the reactor of a porous material has a very little influence on reactor performance, and therefore it is preferable to build this part of the reaction chamber using a non-porous, more durable material. On the other hand, the maximum reaction temperature in the reaction chamber can be increased if the upper part of the reaction chamber is made with a non-porous material, which is favourable for treating diluted feeds. Model results complement previous information obtained by experiments and by simplified models.

Air flow aerodynamic on a wall-mounted hemisphere for various turbulent boundary layers

Abstract Air flow field around a surface-mounted hemisphere of a fixed height for two different turbulent boundary layers (thin and thick) are investigated experimentally and numerically. Flow measurements are performed in a wind tunnel using hot-wire anemometer and streamwise component of velocity fluctuation are calculated using a special developed program of the hardware system. Mean surface pressure coefficients and velocity field for the same hemisphere are determined by the numerical simulation. Turbulent flow field and intensity are measured for two types of boundary layers and compared at various sections in both streamwise and spanwise directions. Numerical scheme based on finite volume and SIMPLE algorithm is used to treat pressure and velocity coupling. Studies are performed for Reynolds number, Re H = 32,000. Based on the numerical simulation using RNG k – e turbulence model, flow pathlines, separation region and recirculation area are determined for the two types of turbulent boundary layer flows and complex flow field and recirculation regions are identified and presented graphically.

Three-Dimensional Mapping of Air Flow at an Urban Canyon Intersection

In this experimental work both qualitative (flow visualisation) and quantitative (laser Doppler anemometry) methods were applied in a wind tunnel in order to describe the complex three-dimensional flow field in a real environment (a street canyon intersection). The main aim was an examination of the mean flow, turbulence and flow pathlines characterising a complex three-dimensional urban location. The experiments highlighted the complexity of the observed flows, particularly in the upwind region of the intersection. In this complex and realistic situation some details of the upwind flow, such as the presence of two tall towers, play an important role in defining the flow field within the intersection, particularly at roof level. This effect is likely to have a strong influence on the mass exchange mechanism between the canopy flow and the air aloft, and therefore the distribution of pollutants. This strong interaction between the flows inside and outside the urban canopy is currently neglected in most state-of-the-art local scale dispersion models.

Computational hemodynamics in the human aorta: A computational fluid dynamics study of three cases with patient-specific geometries and inflow rates

To demonstrate the potential role of computational fluid dynamics (CFD) in therapeutic decision making for treatment of vascular pathologies of the human aorta. CFD simulations with patient specific geometries and patient-specific inflow boundary conditions obtained with magnetic resonance imaging were performed in three cases: 1) mobile thrombus in the aortic arch in a patient with ischemic stroke 2) acute type II B aortic dissection 3) abdominal aortic aneurysm repaired with an endoluminal graft. Blood flow pathlines, wall shear stresses (WSS), dynamic pressures, blood velocities and flow particle resident times were calculated. Aortic thrombus was indicated as possible source of emboli by flowlines and elevated WSS (8% higher than average WSS at aortic wall) in case 1. This was not identified on conventional imaging. In case 2, the false lumen of the dissection showed elevated pressures and high blood velocities at systole but low pressures and stagnant flow at other times (blood velocity < 0.02 m/s and WSS < 0.1 Pa). Flow disturbances at the reentrance zone of blood from the false lumen were recognized. For case 3, elevated WSS at the landing zone of the endoluminal graft and at the right iliac section together with disturbed flow patterns and increased flow particle resident times were noted. Focal stenoses coincided with the flow disturbances. Measured velocity patterns were qualitatively in agreement with velocity patterns calculated with CFD. CFD simulations provide additional information of the hemodynamics in the diseased human aorta and may have potential in aiding the therapeutic decision making process.

Modeling the interaction between objects and cartoon water

AbstractIn this paper, we describe a method for modeling the interaction between objects and the cartoon water which does not involve physics simulations. Our method involves the definition of flow path lines in the presence of obstacles, modeling of different types of water forms, and combinations of them in space and time. There are several notable features with our method: easy setting with little user intervention, modeling of complex water forms that represent more energetic water behavior than has been encompassed by semi‐automatic means so far, and the adaptive change of animated water forms to the variation of obstacle object in number, size, and shape in the water path. A number of formulae for managing shape and time variance in these animations are given. We tested our method with both still and moving objects that have different shape and size in the water and relevant examples are given in the paper. Copyright © 2008 John Wiley &amp; Sons, Ltd.