scholarly journals Mechanically driven accumulation of microscale material at coupled solid–fluid interfaces in biological channels

2014 ◽  
Vol 11 (91) ◽  
pp. 20130922 ◽  
Author(s):  
T. I. Zohdi
Keyword(s):  
Shear Stress ◽  
Accumulation Rate ◽  
Critical Value ◽  
Rate Equations ◽  
Fluid Interfaces ◽  
Sectional Area ◽  
Fluid Interface ◽  
Cross Sectional ◽  
Initial Stage ◽  
Biological Channels

The accumulation of microscale materials at solid–fluid interfaces in biological channels is often the initial stage of certain growth processes, which are present in some forms of atherosclerosis. The objective of this work is to develop a relatively simple model for such accumulation, which researchers can use to qualitatively guide their analyses. Specifically, the approach is to construct rate equations for the accumulation at the solid–fluid interface as a function of the intensity of the shear stress. The accumulation of material subsequently reduces the cross-sectional area of the channel until the fluid-induced shear stress at the solid–fluid interface reaches a critical value, which terminates the accumulation rate. Characteristics of the model are explored analytically and numerically.

Effect of Weld Defects on Tensile Properties of Lightweight Materials and Correlations With Phased Array Ultrasonic Nondestructive Evaluation

2014 ◽  
Author(s):  
Mohammad W. Dewan ◽  
M. A. Wahab ◽  
Ayman M. Okeil
Keyword(s):  
Tensile Strength ◽  
Aluminum Alloy ◽  
Tensile Properties ◽  
Phased Array ◽  
Critical Value ◽  
Area Ratio ◽  
Cross Sectional Area ◽  
Sectional Area ◽  
Cross Sectional ◽  
Strength And Toughness

Fusion welding of Aluminum and its alloys is a great challenge for the structural integrity of lightweight material structures. One of the major shortcomings of Aluminum alloy welding is the inherent existence of defects in the welded area. In the current study, tests have been conducted on tungsten inert gas (TIG) welded AA6061-T651 aluminum alloy to determine the effects of defect sizes and its distribution on fracture strength. The information will be used to establish weld acceptance/rejection criteria. After welding, all specimens were non-destructively inspected with phased array ultrasonic and measured the projected area of the defects. Tensile testing was performed on inspected specimens containing different weld defects: such as, porosity, lack of fusion, and incomplete penetration. Tensile tested samples were cut along the cross section and inspected with Optical Microscope (OM) to measure actual defect sizes. Tensile properties were correlated with phased array ultrasonic testing (PAUT) results and through microscopic evaluations. Generally, good agreement was found between PAUT and microscopic defect sizing. The tensile strength and toughness decreased with the increase of defect sizes. Small voids (area ratio <0.04) does not have significant effect on the reduction of tensile strength and toughness values. Once defective “area ratio (cross sectional area of the defect) / (total specimen cross sectional area)” reached a certain critical value (say, 0.05), both strength and toughness values decline sharply. After that critical value both the tensile strength and toughness values decreases linearly with the increase of defect area ratio.

scholarly journals Bimodal optimization with constraints: Critical value of the constraint and post-critical configurations

2011 ◽  
Vol 38 (2) ◽  
pp. 107-124
Author(s):  
Teodor Atanackovic ◽  
Alexander Seyraniany
Keyword(s):  
Total Energy ◽  
Critical Value ◽  
Optimal Shape ◽  
Cross Sectional Area ◽  
Point Of View ◽  
Sectional Area ◽  
Cross Sectional ◽  
Critical Configurations ◽  
Bimodal Optimization ◽  
Elastic Column

By using a method based on Pontryagin?s principle, formulated in [13], and [14] we study optimal shape of an elastic column with constraints on the minimal value of the cross-sectional area. We determine the critical value of the minimal cross-sectional area separating bi from unimodal optimization. Also we study the post-critical shape of optimally shaped rod and find the preferred configuration of the bifurcating solutions from the point of view of minimal total energy.

Generalized Models for Laminar Developing Flows in Heat Sinks and Heat Exchangers

2011 ◽  
Author(s):  
Y. S. Muzychka
Keyword(s):  
Heat Transfer ◽  
Shear Stress ◽  
Nusselt Number ◽  
Heat Transfer Coefficient ◽  
Heat Exchangers ◽  
Heat Sinks ◽  
Length Scale ◽  
Square Root ◽  
Sectional Area ◽  
Cross Sectional

Recent models for laminar friction and heat transfer in non-circular ducts and channels are reviewed. Models for both hydrodynamically and thermally developing flows are presented. These models are based on the superposition of asymptotic characteristics for short and long ducts. The non-dimensional mean wall shear stress (or fRe) and non-dimensional heat transfer coefficient (or Nusselt number) are shown to be only functions the dimensionless hydrodynamic or thermal duct length, respectively, and the duct aspect ratio. This is achieved by means of using a new transversal length scale, the square root of cross-sectional area, rather than the hydraulic diameter. Additional definitions more appropriate to single fluid devices such as heat sinks are also discussed.

Geometric Design of Rectangular Cross-Sectional Springs

2018 ◽  
Vol 920 ◽  
pp. 126-131
Author(s):  
Yeong Maw Hwang ◽  
D.S. Lin ◽  
Sheng Liang Lin
Keyword(s):  
Shear Stress ◽  
Cross Section ◽  
Maximum Shear Stress ◽  
Cross Sectional Area ◽  
Sectional Area ◽  
Rectangular Section ◽  
Cross Sectional ◽  
Short Side ◽  
The Cross ◽  
Sectional Shape

In order to study the influence of the cross-sectional shape on the stiffness of a spring, a finite element analysis software DEFORM is used to simulate and analyze the torsion of rectangular cross-section bars. The material of the bar is TS1800 SAE9254 and the cross-section of aspect ratio (w / h) is 1.5. From literature it is known that when the rectangular section bar is twisted, the shear stress at the four corners is zero, so elliptical corners can decrease the volume and increase the stiffness with the same volume. Five levels for the long side of the elliptical corner are set as 1 to 5 mm, and 3 levels are set for the short side. Torsion of the rectangular section bars under 15 kinds of geometric designs are simulated to find the preferred cross-sectional shape design by evaluating the cross-sectional area, load, and the maximum shear stress. The objective of the design is obtaining a uniform stress distribution with a larger spring stiffness and lighter weight. The optimal cross section of the bars is established as the spring geometry, and the pre-loading processing of the spring is simulated. The required load and the maximum shear stress data are obtained. The effects of load, cross-sectional area and maximum shear stress on the springs performance are investigated.

scholarly journals Potential Applications of Computational Fluid Dynamics for Predicting Hemolysis in Mitral Paravalvular Leaks

2021 ◽  
Vol 10 (24) ◽  
pp. 5752
Author(s):  
Michał Kozłowski ◽  
Krzysztof Wojtas ◽  
Wojciech Orciuch ◽  
Marek Jędrzejek ◽  
Grzegorz Smolka ◽  
...  
Keyword(s):  
Blood Flow ◽  
Shear Stress ◽  
Cross Sectional Area ◽  
Sectional Area ◽  
Cross Sectional ◽  
Ansys Fluent ◽  
Potential Applications ◽  
Fluent Software ◽  
Flow Through

Paravalvular leaks (PVLs) may lead to hemolysis. In vitro shear stress forces above 300 Pa cause erythrocyte destruction. PVL channel dimensions may determine magnitude of shear stress forces that affect erythrocytes; however, this has not been tested. It remains unclear how different properties of PVL channels contribute to presence of hemolysis. A model of a left ventricle was created based on data from computer tomography with Slicer software PVLs of various shapes and sizes were introduced. Blood flow was simulated using ANSYS Fluent software. The following variables were examined: wall shear stress, shear stress in fluid, volume of PVL channel with shear stress exceeding 300 Pa, and duration of exposure of erythrocytes to shear stress values above 300 Pa. In all models, shear stress forces exceeded 300 Pa. Shear stress increased with blood flow rates and cross-sectional areas of any PVL. There was no linear relationship between cross-sectional area of a PVL and volume of a PVL channel with shear stress > 300 Pa. Blood flow through mitral PVLs is associated with shear stress above 300 Pa. Cross-sectional area of a PVL does not correlate with volume of a PVL channel with shear stress > 300 Pa and duration of exposure of erythrocytes to shear stress > 300 Pa.

Effect on the Reconstruction of Blood Vessel Geometry to the Thresholds Image Intensity Level for Patient Aneurysm

2015 ◽  
Vol 22 ◽  
pp. 89-95 ◽  
Author(s):  
Mohd Azrul Hisham Mohd Adib ◽  
Nur Hazreen Mohd Hasni
Keyword(s):  
Shear Stress ◽  
Blood Vessel ◽  
Cerebral Aneurysms ◽  
Intensity Level ◽  
Sectional Area ◽  
Computational Simulations ◽  
Cross Sectional ◽  
Image Intensity ◽  
Flow Feature ◽  
Vascular Geometry

Thresholding is the greenest and most generally used techniques in image segmentation. This threshold determination can be used to extract various features of the vascular geometry that is used for understanding and analyzing of the image. Our objective is to investigate the influence of the modernization of blood vessel geometry to the threshold image intensity level difference in vessel segmentation. This study included a patient with cerebral aneurysms. We employed three different threshold levels from 200, 400 and 600 in order to determine the influence of the threshold objectively. The flow solution variation on exemplified by wall shear stress (WSS) presents similarity due to the location and magnitude of geometry variation resulting from the different threshold image intensity level and relatively small changes can lead to important dissimilarity in geometry of vessel and flow feature, predominantly in location with an enormous variety of cross sectional area. This is the significance of the understanding of modeling computational simulations of blood flow and can be expressively effected by alterations in geometry different.

Observation of pseudoelastic behavior in large Cu-Ni composite multilayer nanowires

2014 ◽  
Vol 1659 ◽  
pp. 205-212
Author(s):  
N. Abdolrahim ◽  
I.N. Mastorakos ◽  
D. Bahr ◽  
H.M. Zbib
Keyword(s):  
Molecular Dynamics ◽  
Critical Value ◽  
Sectional Area ◽  
Individual Layer ◽  
Cross Sectional ◽  
Partial Dislocations ◽  
Multilayer Nanowires ◽  
Dynamics Simulations ◽  
The Individual ◽  
Pseudoelastic Behavior

ABSTRACTIn recent years, studies have shown that single crystal metallic nanowires (NWs) can exhibit unique pseudoelastic behavior when their cross-sectional area is smaller than a certain critical value, which is on the order of a few nms. The mechanism responsible for this behavior is the formation of partial dislocations (twinning). In this paper we demonstrate using molecular dynamics simulations that thicker composite nanowires can exhibit pseudoelastic behavior at large cross-sectional dimensions to 28 nm and higher, as long as the individual layer thickness do not exceed a critical value of 1.8-2 nm, thus making their manufacturing feasible and more attractive.

Pelvic Canal Narrowing Caused by Triple Pelvic Osteotomy in the Dog

1994 ◽  
Vol 07 (03) ◽  
pp. 110-113 ◽  
Author(s):  
D. L. Holmberg ◽  
M. B. Hurtig ◽  
H. R. Sukhiani
Keyword(s):  
Postoperative Complications ◽  
Pelvic Osteotomy ◽  
Cross Sectional Area ◽  
Sectional Area ◽  
Cross Sectional ◽  
Canal Width ◽  
Operative Complications ◽  
Post Operative Complications

SummaryDuring a triple pelvic osteotomy, rotation of the free acetabular segment causes the pubic remnant on the acetabulum to rotate into the pelvic canal. The resulting narrowing may cause complications by impingement on the organs within the pelvic canal. Triple pelvic osteotomies were performed on ten cadaver pelves with pubic remnants equal to 0, 25, and 50% of the hemi-pubic length and angles of acetabular rotation of 20, 30, and 40 degrees. All combinations of pubic remnant lengths and angles of acetabular rotation caused a significant reduction in pelvic canal-width and cross-sectional area, when compared to the inact pelvis. Zero, 25, and 50% pubic remnants result in 15, 35, and 50% reductions in pelvic canal width respectively. Overrotation of the acetabulum should be avoided and the pubic remnant on the acetabular segment should be minimized to reduce postoperative complications due to pelvic canal narrowing.When performing triple pelvic osteotomies, the length of the pubic remnant on the acetabular segment and the angle of acetabular rotation both significantly narrow the pelvic canal. To reduce post-operative complications, due to narrowing of the pelvic canal, overrotation of the acetabulum should be avoided and the length of the pubic remnant should be minimized.

DETERMINATION OF THE FUNCTION OF THE ROD’S CROSS-SECTIONAL AREA USING VIBRATION EIGENFREQUENCIES

2020 ◽  
Vol 0 (4) ◽  
pp. 19-24
Author(s):  
I.M. UTYASHEV ◽  
◽  
A.A. AITBAEVA ◽  
A.A. YULMUKHAMETOV ◽  
◽  
...  
Keyword(s):  
Cross Sectional Area ◽  
Variable Cross ◽  
Sectional Area ◽  
Longitudinal Vibrations ◽  
Cross Sectional ◽  
Method Error ◽  
Various Boundary Conditions ◽  
Elastic Fixation ◽  
Crosssectional Area

The paper presents solutions to the direct and inverse problems on longitudinal vibrations of a rod with a variable cross-sectional area. The law of variation of the cross-sectional area is modeled as an exponential function of a polynomial of degree n . The method for reconstructing this function is based on representing the fundamental system of solutions of the direct problem in the form of a Maclaurin series in the variables x and λ. Examples of solutions for various section functions and various boundary conditions are given. It is shown that to recover n unknown coefficients of a polynomial, n eigenvalues are required, and the solution is dual. An unambiguous solution was obtained only for the case of elastic fixation at one of the rod’s ends. The numerical estimation of the method error was made using input data noise. It is shown that the error in finding the variable crosssectional area is less than 1% with the error in the eigenvalues of longitudinal vibrations not exceeding 0.0001.

Sign in / Sign up

Export Citation Format

Share Document