scholarly journals Computational Study of Zigzag Spacer Design with Elliptical Cross-Section Filaments

2020 ◽  
Vol 307 ◽  
pp. 01047
Author(s):  
Gohar Shoukat ◽  
Farhan Ellahi ◽  
Muhammad Sajid ◽  
Emad Uddin
Keyword(s):  
Mass Transfer ◽  
Cross Section ◽  
Cross Sections ◽  
Computational Study ◽  
Flow Direction ◽  
Three Dimensional ◽  
Circular Cross Section ◽  
Two Dimensional ◽  
Permeate Flux ◽  
Elliptical Cross

The large energy consumption of membrane desalination process has encouraged researchers to explore different spacer designs using Computational Fluid Dynamics (CFD) for maximizing permeate per unit of energy consumed. In previous studies of zigzag spacer designs, the filaments are modeled as circular cross sections in a two-dimensional geometry under the assumption that the flow is oriented normal to the filaments. In this work, we consider the 45° orientation of the flow towards the three-dimensional zigzag spacer unit, which projects the circular cross section of the filament as elliptical in a simplified two-dimensional domain. OpenFOAM was used to simulate the mass transfer enhancement in a reverse-osmosis desalination unit employing spiral wound membranes lined with zigzag spacer filaments. Properties that impact the concentration polarization and hence permeate flux were analyzed in the domain with elliptical filaments as well as a domain with circular filaments to draw suitable comparisons. The range of variation in characteristic parameters across the domain between the two different configurations is determined. It was concluded that ignoring the elliptical projection of circular filaments to the flow direction, can introduce significant margin of error in the estimation of mass transfer coefficient.

scholarly journals Membrane analogy for multi-material bars under torsion

2019 ◽  
Vol 475 (2225) ◽  
pp. 20190124 ◽  
Author(s):  
Laura Galuppi ◽  
Gianni Royer-Carfagni
Keyword(s):  
Finite Element ◽  
Cross Section ◽  
Cross Sections ◽  
Three Dimensional ◽  
Element Model ◽  
Elastic Problem ◽  
Two Dimensional ◽  
Torsion Problem ◽  
Linear Elastic ◽  
Physical Apparatus

Prandtl's membrane analogy for the torsion problem of prismatic homogeneous bars is extended to multi-material cross sections. The linear elastic problem is governed by the same equations describing the deformation of an inflated membrane, differently tensioned in regions that correspond to the domains hosting different materials in the bar cross section, in a way proportional to the inverse of the material shear modulus. Multi-connected cross sections correspond to materials with vanishing stiffness inside the holes, implying infinite tension in the corresponding portions of the membrane. To define the interface constrains that allow to apply such a state of prestress to the membrane, a physical apparatus is proposed, which can be numerically modelled with a two-dimensional mesh implementable in commercial finite-element model codes. This approach presents noteworthy advantages with respect to the three-dimensional modelling of the twisted bar.

Numerical Study of Incomplete Stent Apposition Caused by Deploying Undersized Stent in Arteries With Elliptical Cross Sections

2019 ◽  
Vol 141 (5) ◽  
Author(s):  
Bo Jiang ◽  
Vikas Thondapu ◽  
Eric K. W. Poon ◽  
Peter Barlis ◽  
Andrew S. H. Ooi
Keyword(s):  
Shear Rate ◽  
Cross Section ◽  
Cross Sections ◽  
Numerical Study ◽  
Circular Cross Section ◽  
Blood Stream ◽  
Cfd Simulations ◽  
Elliptical Cross ◽  
Incomplete Stent Apposition ◽  
Computational Fluid Dynamics Cfd

Incomplete stent apposition (ISA) is one of the causes leading to poststent complications, which can be found when an undersized or an underexpanded stent is deployed at lesions. The previous research efforts have focused on ISA in idealized coronary arterial geometry with circular cross section. However, arterial cross section eccentricity plays an important role in both location and severity of ISA. Computational fluid dynamics (CFD) simulations are carried out to systematically study the effects of ISA in arteries with elliptical cross section, as such stents are partially embedded on the minor axis sides of the ellipse and malapposed elsewhere. Overall, ISA leads to high time-averaged wall shear stress (TAWSS) at the proximal end of the stent and low TAWSS at the ISA transition region and the distal end. Shear rate depends on both malapposition distance and blood stream locations, which is found to be significantly higher at the inner stent surface than the outer surface. The proximal high shear rate signifies increasing possibility in platelet activation, when coupled with low TAWSS at the transition and distal regions which may indicate a nidus for in-stent thrombosis.

On the Choice of Initial Geometric Imperfections in Externally Pressurized Shells

1999 ◽  
Vol 121 (1) ◽  
pp. 71-76 ◽  
Author(s):  
J. Błachut ◽  
O. R. Jaiswal
Keyword(s):  
Cross Section ◽  
Cross Sections ◽  
Carrying Capacity ◽  
Circular Cross Section ◽  
Load Carrying Capacity ◽  
Geometric Imperfections ◽  
Elliptical Cross ◽  
Buckling Strength ◽  
Load Carrying ◽  
Initial Geometric Imperfections

Localized and global, of eigenmode type, initial geometric imperfections were superimposed on perfect torispherical, ellipsoidal, and toroidal shells of circular and elliptical cross section. Reduction of the load-carrying capacity was then calculated numerically for various geometries and the yield point of material which was assumed to be mild steel. Results show that the buckling strength of torispheres and ellipsoids could be strongly affected by imperfections, but reduction of its magnitude was dependent on the choice of imperfection shape and, more importantly, on the imperfection’s location. Calculations carried out for closed toroids of circular cross section show that these shells are not sensitive to eigenmode-type imperfections, while toroids with elliptical cross sections are sensitive to eigen-imperfections.

A Numerical Study on Squat of a Wigley Hull

2011 ◽  
Author(s):  
Mahmoud Alidadi ◽  
Sander Calisal
Keyword(s):  
Boundary Element Method ◽  
Cross Section ◽  
Cross Sections ◽  
Numerical Study ◽  
Three Dimensional ◽  
Two Dimensional ◽  
Slender Body Theory ◽  
Flow Potential ◽  
Wigley Hull ◽  
Body Theory

A numerical study is conducted to calculate the squat for a wigley hull. An approach based on slender body theory is used to convert the three dimensional ship problem into a series of two dimensional problems in cross sections from bow to stern (solved sequentially in time). A boundary element method is used to compute the flow potential at every cross section. The ship squat is calculated from the pressure integration over the hull. Numerical results for the Wigley hull is presented and compared with the experimental results.

Flow of Microfluids in Converging Microchannels

2009 ◽  
Author(s):  
Nelson Macken ◽  
Jong Hsien Lim
Keyword(s):  
Reynolds Number ◽  
Fluorescence Microscopy ◽  
Cross Section ◽  
Cross Sections ◽  
Three Dimensional ◽  
Main Channel ◽  
Two Dimensional ◽  
Water Flows ◽  
The Third ◽  
Confocal Fluorescence

The interface between intersecting microfluidic multicomponent flow is investigated experimentally. Three microchannel configurations are studied. Each configuration has a main channel and an intersecting daughter channel. In two configurations, the channel cross sections are equal and square with the intersection either at 90 or 45 degrees. In the third configuration, the intersection is at 90 degrees, the cross sections are square and the daughter cross section is smaller than the main cross section. In the configurations with equal channel cross sections, microsphere solutions of 2, 4 and 7% spheres (by weight) are compared to each other as well as all water flows. Flow visualization is achieved using confocal fluorescence microscopy. A three-dimensional rendering of the location and shape of the interface is examined for a Reynolds number of approximately one. The presence of microspheres does not appear to strongly influence the location of the flow interface. For flows with equal cross section, the interface downstream of the junction is reasonably planer (two dimensional). Strong three-dimensional effects are shown for flows with unequal cross section.

scholarly journals Three-dimensional stability of an elliptical vortex in a straining field

1984 ◽  
Vol 142 ◽  
pp. 451-466 ◽  
Author(s):  
A. C. Robinson ◽  
P. G. Saffman
Keyword(s):  
Steady State ◽  
Linear Stability ◽  
Cross Section ◽  
Dimensional Stability ◽  
Growth Rates ◽  
Finite Strain ◽  
Three Dimensional ◽  
Two Dimensional ◽  
Elliptical Cross ◽  
Dimensional Instability

The three-dimensional linear stability of a rectilinear vortex of elliptical cross-section existing as a steady state in an irrotational straining field is studied numerically in the case of finite strain. It is shown that the instability predicted analytically for weak strain persists for finite strain and that the weak-strain results continue to be quantitatively valid for finite strain. The dependence of the growth rates of the unstable modes on the strain and the axial-disturbance wavelength is discussed. It is also shown that a three-dimensional instability is always more unstable than a two-dimensional instability in the range of parameters of most interest.

On the Critical Plunger Speed and Three-Dimensional Effects in High-Pressure Die Casting Injection Chambers

2003 ◽  
Vol 125 (3) ◽  
pp. 529-537 ◽  
Author(s):  
J. Lo´pez ◽  
F. Faura ◽  
J. Herna´ndez ◽  
P. Go´mez
Keyword(s):  
Molten Metal ◽  
Cross Section ◽  
Die Casting ◽  
Three Dimensional ◽  
Circular Cross Section ◽  
Water Model ◽  
Two Dimensional ◽  
Shallow Water Model ◽  
One Dimensional ◽  
Pressure Die Casting

During the initial slow stage of the injection process in high-pressure die casting machines with horizontal cold chamber, a plunger pushes the molten metal which partially fills the injection chamber, causing the formation of a gravity wave. The evolution of the wave surface profile, which depends on the plunger acceleration law, may trap air in the molten metal, causing porosity when the metal solidifies. In this work, a one-dimensional shallow-water model, which is solved numerically using the method of characteristics, and a three-dimensional numerical model, based on a finite element formulation and the volume of fluid (VOF) method for treating the free surface, are used to analyze the flow of molten metal in an injection chamber of circular cross section. The results for the evolution of the free surface obtained from both models for different plunger motion laws and initial filling fractions of the injection chamber were in good agreement for broad ranges of operating conditions. The existence of a critical plunger speed, above which the reflection of the wave of molten metal against the chamber ceiling might appreciably increase air entrapment effects, is investigated. The results for the wave profiles in chambers of circular cross section are compared with those obtained in an equivalent two-dimensional configuration of the injection chamber, for which the shallow-water model is solved analytically. It is shown how the results obtained by applying the one-dimensional model to a two-dimensional chamber configuration can be used to reproduce, with an acceptable degree of accuracy, the salient characteristics of the flow of molten metal in a real injection chamber of circular cross section.

scholarly journals Processing of two-dimensional velocity fields for reconstructing three-dimensional flow patterns

2021 ◽  
Vol 2127 (1) ◽  
pp. 012031
Author(s):  
S Yu Belov
Keyword(s):  
Cross Section ◽  
Cross Sections ◽  
Three Dimensional ◽  
Velocity Fields ◽  
Optical Methods ◽  
Two Dimensional ◽  
Three Dimensional Flow ◽  
Dimensional Flow ◽  
Optimal Type

Abstract The paper is concerned with the obtaining three-dimensional velocity fields of a gas or liquid flow based on the available cross-sections of this flow. The descriptions of the main optical methods for studying flows are designed to construct a cross-section of the observed process, but it would be much more informative to obtain information in the visualization not in the cross-section of a volume, but in this volume itself. The paper deals with obtaining three-dimensional flow velocity fields using various approximation methods. The method of estimating the most suitable approximating function is also given. The determination of the optimal type of approximation for the reconstruction of the three-dimensional velocity field was tested on an artificially created vortex.

FIV Energy Harvesting From Sharp-Edge Oscillators

2019 ◽  
Author(s):  
Vahid Tamimi ◽  
Milad Armin ◽  
Selda Shahvaghar-Asl ◽  
Seyed Taghi Omid Naeeni ◽  
Mostafa Zeinoddini
Keyword(s):  
Cross Section ◽  
Cross Sections ◽  
Flow Direction ◽  
Circular Cross Section ◽  
Energy Performance ◽  
Sharp Edge ◽  
Circular Cylinders ◽  
New Right ◽  
Ideal Solution ◽  
Third Places

Abstract The relative incompetency of rectangular galloping excavators against conventional circular VIV harvesters is already known. In this experimental study, the hydroelastic energy performances of new right-angle isosceles triangular cylinder against circular, square and diamond cross-sections are investigated. The triangular cylinder displays VIV or galloping type of response in four different symmetrical and unsymmetrical configurations tested. The results show the distinct higher overall galloping energy performance of the triangular cylinder in Config. 2 among other VIV and galloping harvesters. The Technique for Order of Preference by Similarity to Ideal Solution (TOPSIS) is employed to order the remaining tested cross-sections using the averaged and maximum values of the mechanical power and efficiency as criteria. The TOPSIS algorithm shows that the VIV diamond and circular harvesters stay at the second and third places of the energy performance, respectively. The preference value of the diamond and circular cross-sections are almost comparable but are less than half of that in Config. 2. In general, the sharp-edge cylinders display superior energy performance over circular cross-section. However, the axisymmetric circular cylinders, because of their omnidirectional performances, are more efficient in places with the varying flow direction.

scholarly journals Comparisons of Local Scouring for Submerged Square and Circular Cross-Section Piles in Steady Currents

Water ◽  
2019 ◽  
Vol 11 (9) ◽  
pp. 1820
Author(s):  
Shengtao Du ◽  
Bingchen Liang
Keyword(s):  
Cross Section ◽  
Boundary Point ◽  
Three Dimensional ◽  
Circular Cross Section ◽  
Scour Depth ◽  
Two Dimensional ◽  
Exponential Equation ◽  
Equilibrium Scour Depth ◽  
Over Time

The local scouring that occurs around submerged vertical piles in steady currents was studied experimentally in this paper. Three experiments were carried out for square cross-section (SC) piles and a circular cross-section (CC) pile with the same width. The key point scour depths, including the center of the upstream boundary point (KC) and the two upstream corners (KM), were observed over time. The two-dimensional profiles and the three-dimensional topography around each pile were measured using a Seatek. The different scouring characteristics of the SC and CC piles were investigated. The experiment results show that the scour depth at KC is much smaller than that of KM. The equilibrium scour depth of the CC pile is far less than that of the SC piles. The scour and deposition distributions were different between the CC and SC piles. The maximum scour depth was found at the lateral rear of the CC pile, and the maximum deposition was observed in sections of the SC piles. The evolutions of the scour depths at KM are predicted using a developed exponential equation.

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