Computational Analyses of an In-Vitro Aneurysm Model Based on Three-Dimensional Angiography With Comparison to Phase Contrast Magnetic Resonance Imaging and Dye Injection Studies

2010 ◽  
Author(s):  
Stephanie M. George ◽  
Pierre Watson ◽  
John N. Oshinski ◽  
Charles W. Kerber ◽  
Daniel Karolyi ◽  
...  
Keyword(s):  
High Speed ◽  
Phase Contrast ◽  
Cfd Simulation ◽  
Fluid Dynamic ◽  
Three Dimensional ◽  
Cerebral Aneurysms ◽  
Computational Fluid Dynamic Simulation ◽  
Poor Correlation ◽  
Aneurysm Model

Computational fluid dynamic simulation (CFD) is a valuable tool that has been used to understand some of the fundamental conditions of cerebrovascular flow. Current methods include anatomic modeling of cerebral aneurysms derived from vascular imaging such as MRA, CTA, and three-dimensional angiography. The input blood flow waveforms can be represented from either mathematical models or physiologic sampling of flow with phase contrast MR techniques or particle image velocimetry (1). While there has been general acceptance of the validity of computational fluid dynamics, some research suggests that there can be poor correlation between CFD flow calculations and directly measured flow (2). Therefore, the purpose of this study is to qualitatively compare flow patterns in a cerebral aneurysm model using data derived from three sources: (i) direct phase contrast MRA measurement in the model; (ii) CFD simulation using computer models created from three dimensional angiography, and (iii) previously published high speed injection dye studies.

Quantitative Hemodynamic Comparison of Velocity Values From Computational Fluid Dynamics and Phase-Contrast MRI in an In-Vitro Aneurysm Model

2012 ◽  
Author(s):  
Stephanie M. George ◽  
Amos Cao ◽  
Don P. Giddens ◽  
John N. Oshinski ◽  
Frank C. Tong
Keyword(s):  
Fluid Dynamics ◽  
Computational Fluid Dynamics ◽  
Phase Contrast ◽  
Poor Correlation ◽  
Phase Contrast Mri ◽  
General Acceptance ◽  
Contrast Magnetic Resonance ◽  
Measured Flow ◽  
Aneurysm Model

Intracranial aneurysms affect thousands of people every year, therefore the ability to monitor their growth or predict their rupture would be invaluable for planning treatment. One proposed method to address this issue of predicting rupture is to use computational fluid dynamics (CFD) based on phase contrast magnetic resonance (PC-MR). CFD and PCMR have been used to understand some of the fundamental conditions of cerebrovascular flow. While there has been general acceptance of the validity of CFD, some research suggests that there can be poor correlation between CFD flow calculations and directly measured flow (1). Previous research has qualitatively compared CFD to PC-MR and demonstrated similar pathlines (2). To the authors’ knowledge a systematic quantitative comparison has not been preformed. Therefore the purpose of this work is to quantitatively compare velocity data from phase-contrast MRI measurements and from a CFD model derived from MRI geometry and flow boundary conditions in an in-vitro aneurysm model.

scholarly journals Validation of CFD Simulations of Cerebral Aneurysms With Implication of Geometric Variations

2006 ◽  
Vol 128 (6) ◽  
pp. 844-851 ◽  
Author(s):  
Yiemeng Hoi ◽  
Scott H. Woodward ◽  
Minsuok Kim ◽  
Dale B. Taulbee ◽  
Hui Meng
Keyword(s):  
Flow Field ◽  
Cfd Simulation ◽  
Three Dimensional ◽  
Cerebral Aneurysms ◽  
Patient Specific ◽  
Hemodynamic Parameters ◽  
Cfd Simulations ◽  
Piv Measurements ◽  
Cfd Method ◽  
Aneurysm Model

Background. Computational fluid dynamics (CFD) simulations using medical-image-based anatomical vascular geometry are now gaining clinical relevance. This study aimed at validating the CFD methodology for studying cerebral aneurysms by using particle image velocimetry (PIV) measurements, with a focus on the effects of small geometric variations in aneurysm models on the flow dynamics obtained with CFD. Method of Approach. An experimental phantom was fabricated out of silicone elastomer to best mimic a spherical aneurysm model. PIV measurements were obtained from the phantom and compared with the CFD results from an ideal spherical aneurysm model (S1). These measurements were also compared with CFD results, based on the geometry reconstructed from three-dimensional images of the experimental phantom. We further performed CFD analysis on two geometric variations, S2 and S3, of the phantom to investigate the effects of small geometric variations on the aneurysmal flow field. Results. We found poor agreement between the CFD results from the ideal spherical aneurysm model and the PIV measurements from the phantom, including inconsistent secondary flow patterns. The CFD results based on the actual phantom geometry, however, matched well with the PIV measurements. CFD of models S2 and S3 produced qualitatively similar flow fields to that of the phantom but quantitatively significant changes in key hemodynamic parameters such as vorticity, positive circulation, and wall shear stress. Conclusion. CFD simulation results can closely match experimental measurements as long as both are performed on the same model geometry. Small geometric variations on the aneurysm model can significantly alter the flow-field and key hemodynamic parameters. Since medical images are subjected to geometric uncertainties, image-based patient-specific CFD results must be carefully scrutinized before providing clinical feedback.

scholarly journals Simulation of Hydraulic Cylinder Cushioning

2021 ◽  
Vol 13 (2) ◽  
pp. 494
Author(s):  
Antonio Algar ◽  
Javier Freire ◽  
Robert Castilla ◽  
Esteban Codina
Keyword(s):  
Dynamic Model ◽  
Cfd Simulation ◽  
Fluid Dynamic ◽  
Computational Fluid Dynamic Simulation ◽  
Hydraulic Cylinder ◽  
Outlet Port ◽  
Optimal Behavior ◽  
Radial Movement ◽  
Mechanical Shocks ◽  
Radial Gap

The internal cushioning systems of hydraulic linear actuators avoid mechanical shocks at the end of their stroke. The design where the piston with perimeter grooves regulates the flow by standing in front of the outlet port has been investigated. First, a bond graph dynamic model has been developed, including the flow throughout the internal cushion design, characterized in detail by computational fluid-dynamic simulation. Following this, the radial movement of the piston and the fluid-dynamic coefficients, experimentally validated, are integrated into the dynamic model. The registered radial movement is in coherence with the significant drag force estimated in the CFD simulation, generated by the flow through the grooves, where the laminar flow regime predominates. Ultimately, the model aims to predict the behavior of the cushioning during the movement of the arm of an excavator. The analytical model developed predicts the performance of the cushioning system, in coherence with empirical results. There is an optimal behavior, highly influenced by the mechanical stress conditions of the system, subject to a compromise between an increasing section of the grooves and an optimization of the radial gap.

The inlet flow structure of a conceptual open-nose supersonic drone

2021 ◽  
pp. 095441002098304
Author(s):  
Eiman B Saheby ◽  
Xing Shen ◽  
Anthony P Hays ◽  
Zhang Jun
Keyword(s):  
Flow Structure ◽  
Stokes Equations ◽  
Fluid Dynamic ◽  
Three Dimensional ◽  
Computational Fluid Dynamic Simulation ◽  
Navier Stokes ◽  
Ansys Fluent ◽  
Navier Stokes Equations ◽  
Aerodynamic Efficiency ◽  
Performance Effects

This study describes the aerodynamic efficiency of a forebody–inlet configuration and computational investigation of a drone system, capable of sustainable supersonic cruising at Mach 1.60. Because the whole drone configuration is formed around the induction system and the design is highly interrelated to the flow structure of forebody and inlet efficiency, analysis of this section and understanding its flow pattern is necessary before any progress in design phases. The compression surface is designed analytically using oblique shock patterns, which results in a low drag forebody. To study the concept, two inlet–forebody geometries are considered for Computational Fluid Dynamic simulation using ANSYS Fluent code. The supersonic and subsonic performance, effects of angle of attack, sideslip, and duct geometries on the propulsive efficiency of the concept are studied by solving the three-dimensional Navier–Stokes equations in structured cell domains. Comparing the results with the available data from other sources indicates that the aerodynamic efficiency of the concept is acceptable at supersonic and transonic regimes.

A Hybrid Coil/Polymer Device for Occlusion of Cerebral Aneurysms

2009 ◽  
Vol 3 (4) ◽  
Author(s):  
Fangmin Xu ◽  
Kevin Hart ◽  
Claire E. Flanagan ◽  
John C. Nacker ◽  
Roham Moftakhar ◽  
...  
Keyword(s):  
Cerebral Aneurysms ◽  
In Vitro Models ◽  
In Vivo Studies ◽  
Polymer Shell ◽  
Device Implantation ◽  
Occlusion Device ◽  
Aneurysm Occlusion ◽  
Aneurysm Model

The treatment of cerebral aneurysms is frequently accomplished via endovascular delivery of metal coils in order to occlude the aneurysm and prevent rupture. This procedure involves imprecise packing of large lengths of wire into the aneurysm and often results in high rates of aneurysm recanalization. Over time, this incomplete aneurysm occlusion can lead to aneurysm enlargement, which may have fatal consequences. This report describes the fabrication and preliminary testing of a novel aneurysm occlusion device composed of a single metal coil surrounded by a biocompatible polymer shell. These coil-in-shell devices were tested under flow conditions in synthetic in vitro models of saccular aneurysms and deployed in vivo in a short-term porcine aneurysm model to study occlusion efficacy. A single nickel titanium shape memory wire was used to deploy a biocompatible, elastic polymeric shell, leading to aneurysmal sac filling in both in vitro and in vivo aneurysm models. The deployment of this coil-in-shell device in synthetic aneurysm models in vitro resulted in varying degrees of aneurysm occlusion, with less than 2% of trials resulting in significant leakage of fluid into the aneurysm. Meanwhile, in vivo coil-in-shell device implantation in a porcine aneurysm model provided proof-of-concept for successful occlusion, as both aneurysms were completely occluded by the devices. Both in vitro and in vivo studies demonstrated that this coil-in-shell device may be attractive as an alternative to traditional coil embolization methods in some cases, allowing for a more precise and controlled aneurysm occlusion.

CFD Simulation of Particle Transport and Dispersion in Indoor Environment by Human Walking

2012 ◽  
Author(s):  
Iman Goldasteh ◽  
Goodarz Ahmadi ◽  
Andrea Ferro
Keyword(s):  
Particulate Matter ◽  
High Speed ◽  
Cfd Simulation ◽  
Three Dimensional ◽  
Study Data ◽  
Turbulent Dispersion ◽  
Experimental Chamber ◽  
Indoor Environments ◽  
Three Dimensional Model ◽  
Particle Resuspension

Particle resuspension is an important source of particulate matter in indoor environments that significantly affects the indoor air quality and could potentially have adverse effect on human health. Earlier efforts to investigate indoor particle resuspension hypothesized that high speed airflow generated at the floor level during the gate cycle is the main cause of particle resuspension. The resuspended particles are then assumed to be dispersed by the airflow in the room, which is impacted by both the ventilation and the occupant movement, leading to increased PM concentration. In this study, a three dimensional model of a room was developed using FLUENT™ CFD package. A RANS approach with the RNG k-ε turbulence model was used for simulating the airflow field in the room for different ventilation conditions. The trajectories of resuspended particulate matter were computed with a Lagrangian method by solving the equations of particle motion. The effect of turbulent dispersion was included with the use of the eddy lifetime model. The resuspension of particles due to gait cycle was estimated and included in the computational model. The dispersion and transport of particles resuspended from flooring as well as particle re-deposition on flooring and walls were simulated. Particle concentrations in the room generated by the resuspension process were evaluated and the results were compared with experimental chamber study data as well as simplified model predictions, and good agreement was found.

Three-Dimensional CFD Analysis of Meshing Losses in a Spur Gear Pair

2018 ◽  
Author(s):  
T. Fondelli ◽  
D. Massini ◽  
A. Andreini ◽  
B. Facchini ◽  
F. Leonardi
Keyword(s):  
High Speed ◽  
Numerical Study ◽  
Fluid Dynamic ◽  
Three Dimensional ◽  
Spur Gear ◽  
Computational Domain ◽  
Gear Pair ◽  
Transient Pressure ◽  
Numerical Effort ◽  
Free Environment

The reduction of fluid-dynamic losses in high speed gearing systems is nowadays increasing importance in the design of innovative aircraft propulsion systems, which are particularly focused on improving the propulsive efficiency. Main sources of fluid-dynamic losses in high speed gearing systems are windage losses, inertial losses resulting by impinging oil jets used for jet lubrication and the losses related to the compression and the subsequent expansion of the fluid trapped between gears teeth. The numerical study of the latter is particularly challenging since it faces high speed multiphase flows interacting with moving surfaces, but it paramount for improving knowledge of the fluid behavior in such regions. The current work aims to analyze trapping losses in a gear pair by means of three-dimensional CFD simulations. In order to reduce the numerical effort, an approach for restricting computational domain was defined, thus only a portion of the gear pair geometry was discretized. Transient calculations of a gear pair rotating in an oil-free environment were performed, in the context of conventional eddy viscosity models. Results were compared with experimental data from the open literature in terms of transient pressure within a tooth space, achieving a good agreement. Finally, a strategy for meshing losses calculation was developed and results as a function of rotational speed were discussed.

A Novel Method for Optical High Spatiotemporal Strain Analysis for Transcatheter Aortic Valves In Vitro

2016 ◽  
Vol 138 (3) ◽  
Author(s):  
Simon Heide-Jørgensen ◽  
Sellaswasmy Kumaran Krishna ◽  
Jonas Taborsky ◽  
Tommy Bechsgaard ◽  
Rachid Zegdi ◽  
...  
Keyword(s):  
High Speed ◽  
Three Dimensional ◽  
Strain Analysis ◽  
Image Correlation ◽  
Deformation Analysis ◽  
Flow Loop ◽  
Transcatheter Aortic Valve ◽  
Wear And Tear ◽  
Valve Implantation

The transcatheter aortic valve implantation (TAVI) valve is a bioprosthetic valve within a metal stent frame. Like traditional surgical bioprosthetic valves, the TAVI valve leaflet tissue is expected to calcify and degrade over time. However, clinical studies of TAVI valve longevity are still limited. In order to indirectly assess the longevity of TAVI valves, an estimate of the mechanical wear and tear in terms of valvular deformation and strain of the leaflets under various conditions is warranted. The aim of this study was, therefore, to develop a platform for noncontact TAVI valve deformation analysis with both high temporal and spatial resolutions based on stereophotogrammetry and digital image correlation (DIC). A left-heart pulsatile in vitro flow loop system for mounting of TAVI valves was designed. The system enabled high-resolution imaging of all three TAVI valve leaflets simultaneously for up to 2000 frames per second through two high-speed cameras allowing three-dimensional analyses. A coating technique for applying a stochastic pattern on the leaflets of the TAVI valve was developed. The technique allowed a pattern recognition software to apply frame-by-frame cross correlation based deformation measurements from which the leaflet motions and the strain fields were derived. The spatiotemporal development of a very detailed strain field was obtained with a 0.5 ms time resolution and a spatial resolution of 72 μm/pixel. Hence, a platform offering a new and enhanced supplementary experimental evaluation of tissue valves during various conditions in vitro is presented.

The Pipeline Versus Telescoping Stents: In Vitro Flows in a Treated Cerebral Aneurysm Model

2012 ◽  
Author(s):  
Breigh N. Roszelle ◽  
M. Haithem Babiker ◽  
Justin Ryan ◽  
L. Fernando Gonzalez ◽  
Felipe Albuquerque ◽  
...  
Keyword(s):  
Cerebral Aneurysms ◽  
World Population ◽  
High Porosity ◽  
Recurrence Rates ◽  
Interventional Devices ◽  
Aneurysm Occlusion ◽  
Basilar Tip Aneurysm ◽  
Aneurysm Model ◽  
Low Porosity

Cerebral aneurysms are a significant concern; they are found in 2% of the world population [1]. While endovascular treatments have become a successful option for patients with cerebral aneurysms, recurrence rates remain as high as 50% [2]. Accordingly, many interventional devices are being developed with the hope of increasing the success rate of endovascular aneurysm occlusion. One of these devices is the low-porosity Pipeline emboilzation device (PED). Compared to more traditional intracranial stents, the PED contains a higher ratio of metal to surface area. Previously, similar reductions in porosity were obtained by sequentially deploying multiple high-porosity stents inside of one another, which is known as “telescoping.” The hemodynamic effects of using a single low-porosity device, versus telescoped high-porosity stents, have not been investigated thoroughly. In this study flow was quantified for idealized and anatomical basilar tip aneurysm models. The models were treated with sequentially placed high-porosity stents and a single low-porosity PED.

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