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Computational fluid dynamics

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https://www.readbyqxmd.com/read/28324943/overcoming-spatio-temporal-limitations-using-dynamically-scaled-in-vitro-pc-mri-a-flow-field-comparison-to-true-scale-computer-simulations-of-idealized-stented-and-patient-specific-left-main-bifurcations
#1
Susann Beier, John Ormiston, Mark Webster, John Cater, Stuart Norris, Pau Medrano-Gracia, Alistair Young, Kathleen Gilbert, Brett Cowan
The majority of patients with angina or heart failure have coronary artery disease. Left main bifurcations are particularly susceptible to pathological narrowing. Flow is a major factor of atheroma development, but limitations in imaging technology such as spatio-temporal resolution, signal-to-noise ratio (SNRv), and imaging artefacts prevent in vivo investigations. Computational fluid dynamics (CFD) modelling is a common numerical approach to study flow, but it requires a cautious and rigorous application for meaningful results...
August 2016: Conference Proceedings: Annual International Conference of the IEEE Engineering in Medicine and Biology Society
https://www.readbyqxmd.com/read/28317393/structural-analysis-of-two-different-stent-configurations
#2
M Simão, J M Ferreira, J Mora-Rodriguez, H M Ramos
Two different stent configurations (i.e. the well known Palmaz-Schatz (PS) and a new stent configuration) are mechanically investigated. A finite element model was used to study the two geometries under combining loads and a computational fluid dynamic model based on fluid structure interaction was developed investigating the plaque and the artery wall reactions in a stented arterial segment. These models determine the stress and displacement fields of the two stents under internal pressure conditions. Results suggested that stent designs cause alterations in vascular anatomy that adversely affect arterial stress distributions within the wall, which have impact in the vessel responses such as the restenosis...
March 20, 2017: Computer Methods in Biomechanics and Biomedical Engineering
https://www.readbyqxmd.com/read/28314236/methods-to-model-particulate-matter-clarification-of-unit-operations-subject-to-unsteady-loadings
#3
David Spelman, John J Sansalone
Stormwater, and also wastewater unit operations (UOs) to a much lower extent, are subject to unsteady hydrodynamic and particulate matter (PM) fluxes. Simulating fully transient clarification of hetero-disperse PM requires much greater computational expense compared to steady simulations. An alternative to fully unsteady methods are stepwise steady (SS) methods which use stepwise steady flow transport and fate to approximate unsteady PM clarification of a UO during transient hydraulic loadings such as rainfall-runoff...
February 23, 2017: Water Research
https://www.readbyqxmd.com/read/28314103/computational-study-of-the-forces-driving-aggregation-of-ultrasmall-nanoparticles-in-biological-fluids
#4
Sergio A Hassan
Nanoparticle (NP) aggregation can lead to prolonged retention in tissues or embolism, among other adverse effects. Successful use in biomedicine thus requires the capability to make NPs with limited aggregative potential. Rational design is presently a challenge due to incomplete knowledge of their interactions in biofluids. Recently, ultrasmall gold NPs passivated with endogenous antioxidant glutathione have shown promise for use in vivo. Computer simulations are here conducted to identify the forces underlying aggregation (or lack thereof) of these NPs in a cell culture...
March 17, 2017: ACS Nano
https://www.readbyqxmd.com/read/28302669/propulsive-efficiency-of-frog-swimming-with-different-feet-and-swimming-patterns
#5
Fan Jizhuang, Zhang Wei, Yuan Bowen, Liu Gangfeng
Aquatic and terrestrial animals have different swimming performances and mechanical efficiencies based on their different swimming methods. To explore propulsion in swimming frogs, this paper calculated mechanical efficiencies based on data describing aquatic and terrestrial webbed foot shapes and swimming patterns. First, a simplified frog model and dynamic equation were established, and hydrodynamic forces on the foot were computed according to computational fluid dynamic calculations. Then, a two-link mechanism was used to stand in for the diverse and complicated hind legs found in different frog species, in order to simplify the input work calculation...
March 16, 2017: Biology Open
https://www.readbyqxmd.com/read/28298037/impact-of-bifurcation-angle-and-inflow-coefficient-on-the-rupture-risk-of-bifurcation-type-basilar-artery-tip-aneurysms
#6
Sherif Rashad, Shin-Ichiro Sugiyama, Kuniyasu Niizuma, Kenichi Sato, Hidenori Endo, Shunsuke Omodaka, Yasushi Matsumoto, Miki Fujimura, Teiji Tominaga
OBJECTIVE Risk factors for aneurysm rupture have been extensively studied, with several factors showing significant correlations with rupture status. Several studies have shown that aneurysm shape and hemodynamics change after rupture. In the present study the authors investigated a static factor, the bifurcation angle, which does not change after rupture, to understand its effect on aneurysm rupture risk and hemodynamics. METHODS A hospital database was retrospectively reviewed to identify patients with cerebral aneurysms treated surgically or endovascularly in the period between 2008 and 2015...
March 3, 2017: Journal of Neurosurgery
https://www.readbyqxmd.com/read/28297958/extensivity-and-additivity-of-the-kolmogorov-sinai-entropy-for-simple-fluids
#7
Moupriya Das, Anthony B Costa, Jason R Green
According to the van der Waals picture, attractive and repulsive forces play distinct roles in the structure of simple fluids. Here, we examine their roles in dynamics; specifically, in the degree of deterministic chaos using the Kolmogorov-Sinai (KS) entropy rate and the spectra of Lyapunov exponents. With computer simulations of three-dimensional Lennard-Jones and Weeks-Chandler-Andersen fluids, we find repulsive forces dictate these dynamical properties, with attractive forces reducing the KS entropy at a given thermodynamic state...
February 2017: Physical Review. E
https://www.readbyqxmd.com/read/28297868/start-up-inertia-as-an-origin-for-heterogeneous-flow
#8
Marko Korhonen, Mikael Mohtaschemi, Antti Puisto, Xavier Illa, Mikko J Alava
For quite some time nonmonotonic flow curve was thought to be a requirement for shear banded flows in complex fluids. Thus, in simple yield stress fluids shear banding was considered to be absent. Recent spatially resolved rheological experiments have found simple yield stress fluids to exhibit shear banded flow profiles. One proposed mechanism for the initiation of such transient shear banding process has been a small stress heterogeneity rising from the experimental device geometry. Here, using computational fluid dynamics methods, we show that transient shear banding can be initialized even under homogeneous stress conditions by the fluid start-up inertia, and that such mechanism indeed is present in realistic experimental conditions...
February 2017: Physical Review. E
https://www.readbyqxmd.com/read/28297853/semi-lagrangian-off-lattice-boltzmann-method-for-weakly-compressible-flows
#9
Andreas Krämer, Knut Küllmer, Dirk Reith, Wolfgang Joppich, Holger Foysi
The lattice Boltzmann method is a simulation technique in computational fluid dynamics. In its standard formulation, it is restricted to regular computation grids, second-order spatial accuracy, and a unity Courant-Friedrichs-Lewy (CFL) number. This paper advances the standard lattice Boltzmann method by introducing a semi-Lagrangian streaming step. The proposed method allows significantly larger time steps, unstructured grids, and higher-order accurate representations of the solution to be used. The appealing properties of the approach are demonstrated in simulations of a two-dimensional Taylor-Green vortex, doubly periodic shear layers, and a three-dimensional Taylor-Green vortex...
February 2017: Physical Review. E
https://www.readbyqxmd.com/read/28296907/generation-of-the-pitch-moment-during-the-controlled-flight-after-takeoff-of-fruitflies
#10
Mao Wei Chen, Jiang Hao Wu, Mao Sun
In the present paper, the controlled flight of fruitflies after voluntary takeoff is studied. Wing and body kinematics of the insects after takeoff are measured using high-speed video techniques, and the aerodynamic force and moment are calculated by the computational fluid dynamics method based on the measured data. How the control moments are generated is analyzed by correlating the computed moments with the wing kinematics. A fruit-fly has a large pitch-up angular velocity owing to the takeoff jump and the fly controls its body attitude by producing pitching moments...
2017: PloS One
https://www.readbyqxmd.com/read/28294580/effect-of-cerebrospinal-fluid-modelling-on-spherically-convergent-shear-waves-during-blunt-head-trauma
#11
Amit Madhukar, Ying Chen, Martin Ostoja-Starzewski
The MRI-based computational model, previously validated by tagged MRI and HARP imaging analysis technique on in vivo human brain deformation, is employed to study transient wave dynamics during blunt head trauma. Three different constitutive models are used for the cerebrospinal fluid (CSF): incompressible solid elastic, viscoelastic and fluid-like elastic using an equation of state model. Three impact cases are simulated which indicate that the blunt impacts give rise not only to a fast pressure wave but also to a slow, and potentially much more damaging, shear (distortional) wave that converges spherically towards the brain center...
March 14, 2017: International Journal for Numerical Methods in Biomedical Engineering
https://www.readbyqxmd.com/read/28293137/nonlinear-information-fusion-algorithms-for-data-efficient-multi-fidelity-modelling
#12
P Perdikaris, M Raissi, A Damianou, N D Lawrence, G E Karniadakis
Multi-fidelity modelling enables accurate inference of quantities of interest by synergistically combining realizations of low-cost/low-fidelity models with a small set of high-fidelity observations. This is particularly effective when the low- and high-fidelity models exhibit strong correlations, and can lead to significant computational gains over approaches that solely rely on high-fidelity models. However, in many cases of practical interest, low-fidelity models can only be well correlated to their high-fidelity counterparts for a specific range of input parameters, and potentially return wrong trends and erroneous predictions if probed outside of their validity regime...
February 2017: Proceedings. Mathematical, Physical, and Engineering Sciences
https://www.readbyqxmd.com/read/28291964/application-of-a-parallelizable-perfusion-bioreactor-for-physiologic-3d-cell-culture
#13
Dominik Egger, Sarah Spitz, Monica Fischer, Stephan Handschuh, Martin Glösmann, Benedikt Friemert, Monika Egerbacher, Cornelia Kasper
It is crucial but challenging to keep physiologic conditions during the cultivation of 3D cell scaffold constructs for the optimization of 3D cell culture processes. Therefore, we demonstrate the benefits of a recently developed miniaturized perfusion bioreactor together with a specialized incubator system that allows for the cultivation of multiple samples while screening different conditions. Hence, a decellularized bone matrix was tested towards its suitability for 3D osteogenic differentiation under flow perfusion conditions...
March 15, 2017: Cells, Tissues, Organs
https://www.readbyqxmd.com/read/28291699/in-silico-investigation-of-cornea-deformation-during-irrigation-aspiration-in-phacoemulsification-in-cataract-surgery
#14
Dariush Bayatpour, Omid Abouali, Alireza Ghaffarieh, Goodarz Ahmadi
To analyze the stress, strain and displacement of the human cornea under the action of negative intraocular pressure, which occurs during phacoemulsification in cataract surgery, a multidisciplinary approach including biomedical engineering, solid mechanics, numerical analysis, and fluid dynamics was used. Fluid-structure interaction method was implemented using 3-dimensional nonlinear finite element analysis of cornea tissue in conjunction with CFD analysis of anterior chamber fluid flow to study the deformation of the cornea under negative gage pressure during irrigation and aspiration (I/A)...
March 10, 2017: Medical Engineering & Physics
https://www.readbyqxmd.com/read/28290070/parieto-frontal-gyrification-and-working-memory-in-healthy-adults
#15
Sophie Green, Karen Blackmon, Thomas Thesen, Jonathan DuBois, Xiuyuan Wang, Eric Halgren, Orrin Devinsky
Gyrification of the cortical mantle is a dynamic process that increases with cortical surface area and decreases with age. Increased gyrification is associated with higher scores on cognitive tasks in adults; however, the degree to which this relationship is independent of cortical surface area remains undefined. This study investigates whether regional variation in gyrification is associated with domain-general and domain-specific cognition. Our hypothesis is that increased local gyrification confers a functional advantage that is independent of surface area...
March 13, 2017: Brain Imaging and Behavior
https://www.readbyqxmd.com/read/28285454/association-between-hemodynamics-morphology-and-rupture-risk-of-intracranial-aneurysms-a-computational-fluid-modeling-study
#16
Tianlun Qiu, Guoliang Jin, Haiyan Xing, Haitao Lu
The objective of the study was to examine the correlations between intracranial aneurysm morphology and wall shear stress (WSS) to identify reliable predictors of rupture risk. Seventy-two intracranial aneurysms (41 ruptured and 31 unruptured) from 63 patients were studied retrospectively. All aneurysms were divided into two categories: narrow (aspect ratio ≥1.4) and wide-necked (aspect ratio <1.4 or neck width ≥4 mm). Computational fluid dynamics was used to determine the distribution of WSS, which was analyzed between different morphological groups and between ruptured and unruptured aneurysms...
March 11, 2017: Neurological Sciences
https://www.readbyqxmd.com/read/28280481/the-optic-canal-a-bottleneck-for-cerebrospinal-fluid-dynamics-in-normal-tension-glaucoma
#17
Achmed Pircher, Margherita Montali, Jatta Berberat, Luca Remonda, Hanspeter E Killer
PURPOSE: To report on the optic canal cross-sectional area (OCA) in Caucasian patients with normal-tension glaucoma (NTG) compared with Caucasian control subjects without known optic nerve (ON) diseases. METHODS: Retrospective analysis of computed tomographic images of the cranium and orbits in 56 NTG patients (30 females and 26 males; 99 of 112 eyes; mean age 67.7 ± 11.1 years). Fifty-six age- and gender-matched subjects (mean age: 68.0 ± 11.2 years) without known ON diseases served as controls...
2017: Frontiers in Neurology
https://www.readbyqxmd.com/read/28278356/computational-fluid-dynamics-and-trigeminal-sensory-examinations-of-empty-nose-syndrome-patients
#18
Chengyu Li, Alexander A Farag, James Leach, Bhakthi Deshpande, Adam Jacobowitz, Kanghyun Kim, Bradley A Otto, Kai Zhao
OBJECTIVE: The precise pathogenesis of empty nose syndrome (ENS) remains unclear. Various factors such as nasal aerodynamics and sensorineural dysfunction have been suspected, although evidence is limited. This study reported the first examination of both nasal aerodynamics and trigeminal sensory factors in actual ENS patients. STUDY DESIGN: Prospective case control. METHODS: We enrolled six patients diagnosed with ENS. Three patients had pre- and post-inferior turbinate (IT) reduction computed tomography scans, which allowed comparison of their nasal aerodynamics changes through computational fluid dynamic (CFD) simulation...
March 9, 2017: Laryngoscope
https://www.readbyqxmd.com/read/28276494/image-deformation-as-a-cue-to-material-category-judgment
#19
Takahiro Kawabe, Rok Kogovšek
Human observers easily recognize complex natural phenomena, such as flowing water, which often generate highly chaotic dynamic arrays of light on the retina. It has not been clarified how the visual system discerns the source of a fluid flow. Here we show that the magnitude of image deformation caused by light refraction is a critical factor for the visual system to determine the perceptual category of fluid flows. Employing a physics engine, we created computer-rendered scenes of water and hot air flows. For each flow, we manipulated the rendering parameters (distortion factors and the index of refraction) that strongly influence the magnitude of image deformation...
March 9, 2017: Scientific Reports
https://www.readbyqxmd.com/read/28276071/cfd-and-bernoulli-based-pressure-drop-estimates-a-comparison-using-patient-anatomies-from-heart-and-aortic-valve-segmentation-of-ct-images
#20
Jürgen Weese, Angela Lungu, Jochen Peters, Frank M Weber, Irina Waechter-Stehle, D Rodney Hose
PURPOSE: An aortic valve stenosis is an abnormal narrowing of the aortic valve (AV). It impedes blood flow and is often quantified by the geometric orifice area of the AV (AVA) and the pressure drop (PD). Using the Bernoulli equation, a relation between the PD and the effective orifice area (EOA) represented by the area of the vena contracta (VC) downstream of the AV can be derived. We investigate the relation between the AVA and the EOA using patient anatomies derived from cardiac computed tomography (CT) angiography images and computational fluid dynamic (CFD) simulations...
March 9, 2017: Medical Physics
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