A seepage outlet boundary condition in hemodynamics modeling

2017 ◽  
Vol 62 (5) ◽  
Author(s):  
Fan He ◽  
Lu Hua ◽  
Li-jian Gao
Keyword(s):  
Boundary Condition ◽  
Boundary Conditions ◽  
Shear Stresses ◽  
Arterial Circulation ◽  
Cfd Models ◽  
Fluctuation Range ◽  
New Type ◽  
Computational Fluid Dynamics Cfd ◽  
Methodological Paper ◽  
Outlet Boundary Condition

AbstractBackground:In computational fluid dynamics (CFD) models for hemodynamics applications, boundary conditions remain one of the major issues in obtaining accurate fluid flow predictions.Objective:As an important part of the arterial circulation, microcirculation plays important roles in many aspects, such as substance exchange, interstitial fluid generation and inverse flow. It is necessary to consider microcirculation in hemodynamics modeling. This is a methodological paper to test and validate a new type of boundary condition never applied to microcirculation before.Methods:In order to address this issue, we introduce microcirculation as a seepage outlet boundary condition in computational hemodynamics. Microcirculation is treated as a porous medium in this paper. Numerical comparisons of the seepage and traditional boundary conditions are made.Results:The results show that the seepage boundary condition has significant impacts on numerical simulation. Under the seepage boundary condition, the fluctuation range of the pressures progressively rises in the artery zone. The results obtained from the traditional boundary condition show that the pressure fluctuation range gradually falls. In addition, the wall shear stresses under the traditional outlet boundary condition are much higher than those under the seepage outlet boundary condition.Conclusions:The proposed boundary condition is more suitable in hemodynamics modeling.

VALIDATION OF LOSS-COEFFICIENT-BASED OUTLET BOUNDARY CONDITIONS FOR SIMULATING AORTIC FLOW

2016 ◽  
Vol 16 (02) ◽  
pp. 1650011 ◽  
Author(s):  
ALI CEMAL BENIM ◽  
FETHI GÜL ◽  
ALEXANDER ASSMANN ◽  
PAYAM AKHYARI ◽  
ARTUR LICHTENBERG ◽  
...  
Keyword(s):  
Boundary Condition ◽  
Boundary Conditions ◽  
Constant Pressure ◽  
Loss Coefficient ◽  
Human Aorta ◽  
Retrograde Perfusion ◽  
Heart Lung Machine ◽  
Perfusion Mode ◽  
Good Agreement ◽  
Outlet Boundary Condition

Flow in a polyurethane model of a human aorta, driven by a heart-lung machine, is analyzed experimentally and computationally for antegrade and retrograde perfusion. The purpose of the analysis is the validation of the previously proposed loss-coefficient-based outlet boundary condition for aortic branches. This model is claimed to be commonly applicable to different perfusion modes of the aorta, unlike the alternative straightforward constant-pressure outlet boundary condition. First, the antegrade perfusion is analyzed computationally and experimentally. This step delivers the loss-coefficients that are to be used in any other perfusion mode of the aorta. Subsequently, a retrograde perfusion is applied to the same aorta, where the flow rates at the outlets of the aortic branches are measured and predicted by applying the loss-coefficient-based outlet boundary conditions. A very good agreement of the predictions with the measurements is observed. The predictions delivered by the standard constant-pressure outlet boundary condition are observed, on the contrary, to be highly in error. Thus, the advocated loss-coefficient-based outlet boundary condition is experimentally validated. It is shown that it is applicable to different perfusion modes with a quite good accuracy, which is much higher compared to the straightforward constant-pressure outlet boundary condition.

Full Sliding Adhesive-Like Contact of V-Belts

2002 ◽  
Vol 124 (4) ◽  
pp. 706-712 ◽  
Author(s):  
Go¨ran Gerbert ◽  
Francesco Sorge
Keyword(s):  
Boundary Condition ◽  
Boundary Conditions ◽  
Power Transmission ◽  
A Priori ◽  
Belt Drive ◽  
Natural Boundary ◽  
Condition Problem ◽  
New Type ◽  
Wrap Angle ◽  
Natural Boundary Conditions

Analysis of power transmission in a belt drive consisting of, e.g., two pulleys might be treated as a boundary value problem. Tight side tension FT, slack side tension FS and the wrap angle α are the three natural boundary conditions. In the literature, theories are developed where seating and unseating as well as the power transmitting part of the contact are considered. The solutions presented so far don’t fulfill the boundary conditions properly, since a certain tension ratio FT/FS is associated with a certain contact angle and not an a priori specified one. It appears that a new type of full sliding solution must be introduced to handle the boundary condition problem. During part of the contact there is almost no tension variation in spite of the full sliding conditions. The designation adhesive-like solution is here introduced for that part. Conditions and character of the adhesive-like solution are outlined in the paper.

Development of a “Solar Patch” Calculator to Evaluate Heliostat-Field Irradiance as a Boundary Condition in CFD Models

2010 ◽  
Author(s):  
Siri Sahib S. Khalsa ◽  
Clifford K. Ho
Keyword(s):  
Boundary Condition ◽  
Cfd Simulation ◽  
Time Of Day ◽  
Discrete Ordinates ◽  
Microsoft Excel ◽  
Radiation Model ◽  
Receiver Domain ◽  
Cfd Models ◽  
Multiple Beams ◽  
Computational Fluid Dynamics Cfd

A rigorous computational fluid dynamics (CFD) approach to calculating temperature distributions, radiative and convective losses, and flow fields in a cavity receiver irradiated by a heliostat field is typically limited to the receiver domain alone for computational reasons. A CFD simulation cannot realistically yield a precise solution that includes the details within the vast domain of an entire heliostat field in addition to the detailed processes and features within a cavity receiver. Instead, the incoming field irradiance can be represented as a boundary condition on the receiver domain. This paper describes a program, the Solar Patch Calculator, written in Microsoft Excel VBA to characterize multiple beams emanating from a “solar patch” located at the aperture of a cavity receiver, in order to represent the incoming irradiance from any field of heliostats as a boundary condition on the receiver domain. This program accounts for cosine losses; receiver location; heliostat reflectivity, areas and locations; field location; time of day and day of year. This paper also describes the implementation of the boundary conditions calculated by this program into a Discrete Ordinates radiation model using Ansys® FLUENT (www.fluent.com), and compares the results to experimental data and to results generated by the code DELSOL.

Use of Computational Fluid Dynamics for the Replication of Clinical Blood Flow and Pressure Measurements and Characterization of Hemodynamics in the Normal Ascending and Thoracic Aorta

2007 ◽  
Author(s):  
John F. LaDisa ◽  
C. Alberto Figueroa ◽  
Irene E. Vignon-Clementel ◽  
Frandics P. Chan ◽  
Jeffrey A. Feinstein ◽  
...  
Keyword(s):  
Fluid Dynamics ◽  
Computational Fluid Dynamics ◽  
Blood Flow ◽  
Boundary Conditions ◽  
Thoracic Aorta ◽  
Vascular Anatomy ◽  
Data Set ◽  
Cfd Models ◽  
Computational Fluid Dynamics Cfd

Complications associated with abnormalities of the ascending and thoracic aorta are directly influenced by mechanical forces. To understand hemodynamic alterations associated with diseases in this region, however, we must first characterize related indices during normal conditions. Computational fluid dynamics (CFD) models of the ascending and thoracic aorta to date have only provided descriptions of the velocity field using idealized representations of the vasculature, a single patient data set, and outlet boundary conditions that do not replicate physiologic blood flow and pressure. Importantly, the complexity of aortic flow patterns, limited availability of methods for implementing appropriate boundary conditions, and ability to replicate vascular anatomy all contribute to the difficulty of the problem and, likely, the scarcity of more detailed studies.

A Continuity Outlet Boundary Condition for the Lattice Boltzmann Method

2012 ◽  
Author(s):  
Yasemin Vural ◽  
Suryanarayana R. Pakalapati ◽  
Ismail B. Celik
Keyword(s):  
Boundary Condition ◽  
Lattice Boltzmann Method ◽  
Lattice Boltzmann ◽  
Mass Conservation ◽  
Reynolds Numbers ◽  
Ansys Fluent ◽  
Macroscopic Properties ◽  
Computational Fluid Dynamics Cfd ◽  
Boltzmann Method ◽  
Outlet Boundary Condition

A continuity outlet boundary condition for the Lattice Boltzmann Method (LBM) is proposed based on the assurance of the mass conservation of the system. The main advantage of the proposed boundary condition over the conventional Computational Fluid Dynamics (CFD) techniques is that the macroscopic properties, e.g. velocity, pressure etc. are not needed to be prescribed at the outlet, these properties are automatically calculated with the imposed boundary condition. This is especially useful in practice where the macroscopic properties at the outlet are difficult or impossible to be measured and described as in the biological flows. In order to test the feasibility of the proposed method, the LBM simulations are first verified for its capability to simulate flow in a symmetrically bifurcated channel. Then asymmetrically bifurcated geometries representing the blood vessels have been designed with different bifurcation angles. The new boundary condition is also tested for multi-component LBM simulations. For these cases, LBM predictions have been compared with the predictions for the commercial CFD software, namely ANSYS FLUENT at different Reynolds numbers. The results show that there is a good agreement between the LBM and FLUENT predictions, and this proves the capability of the proposed boundary condition as a viable method that can be used in practice.

Full Sliding “Adhesive-Like” Contact of V-Belts

2000 ◽  
Author(s):  
Göran Gerbert ◽  
Francesco Sorge
Keyword(s):  
Boundary Condition ◽  
Boundary Conditions ◽  
Power Transmission ◽  
A Priori ◽  
Belt Drive ◽  
Natural Boundary ◽  
Condition Problem ◽  
New Type ◽  
Wrap Angle ◽  
Natural Boundary Conditions

Abstract Analysis of power transmission in a belt drive consisting of e. g. two pulleys might be treated as a boundary value problem. Tight side tension FT, slack side tension FS and the wrap angle α are the three natural boundary conditions. In the literature, theories are developed where seating and unseating as well as the power transmitting part of the contact are considered. The solutions presented so far don’t fulfil the boundary conditions properly, since a certain tension ratio FT/FS is associated with a certain contact angle and not an a priori specified one. It appears that a new type of full sliding solution must be introduced to handle the boundary condition problem. During part of the contact there is almost no tension variation in spite of the full sliding conditions. The designation adhesive like solution is here introduced for that part. Conditions and character of the adhesive like solution are outlined in the paper.

scholarly journals Association between aneurysm hemodynamics and wall enhancement on 3D vessel wall MRI

2020 ◽  
pp. 1-11 ◽  
Author(s):  
Muhammad Owais Khan ◽  
Veronica Toro Arana ◽  
Christian Rubbert ◽  
Jan F. Cornelius ◽  
Igor Fischer ◽  
...  
Keyword(s):  
Signal Intensity ◽  
Vessel Wall ◽  
Imaging Biomarker ◽  
Shear Stresses ◽  
Hemodynamic Forces ◽  
Cfd Models ◽  
Aneurysm Wall ◽  
Risk Of Rupture ◽  
Computational Fluid Dynamics Cfd

OBJECTIVEAneurysm wall enhancement (AWE) on 3D vessel wall MRI (VWMRI) has been suggested as an imaging biomarker for intracranial aneurysms (IAs) at higher risk of rupture. While computational fluid dynamics (CFD) studies have been used to investigate the association between hemodynamic forces and rupture status of IAs, the role of hemodynamic forces in unruptured IAs with AWE is poorly understood. The authors investigated the role and implications of abnormal hemodynamics related to aneurysm pathophysiology in patients with AWE in unruptured IAs.METHODSTwenty-five patients who had undergone digital subtraction angiography (DSA) and VWMRI studies from September 2016 to September 2017 were included, resulting in 22 patients with 25 IAs, 9 with and 16 without AWE. High-resolution CFD models of hemodynamics were created from DSA images. Univariate and multivariate analyses were performed to investigate the association between AWE and conventional morphological and hemodynamic parameters. Normalized MRI signal intensity was quantified and quantitatively associated with wall shear stresses (WSSs) for the entire aneurysm sac, and in regions of low, intermediate, and high WSS.RESULTSThe AWE group had lower WSS (p < 0.01) and sac-averaged velocity (p < 0.01) and larger aneurysm size (p < 0.001) and size ratio (p = 0.0251) than the non-AWE group. From multivariate analysis of both hemodynamic and morphological factors, only low WSS was found to be independently associated with AWE. Sac-averaged normalized MRI signal intensity correlated with WSS and was significantly different in regions of low WSS compared to regions of intermediate (p = 0.018) and high (p < 0.001) WSS.CONCLUSIONSThe presence of AWE was associated with morphological and hemodynamic factors related to rupture risk. Low WSS was found to be an independent predictor of AWE. Our findings support the hypothesis that low WSS in IAs with AWE may indicate a growth and remodeling process that may predispose such aneurysms to rupture; however, a causality between the two cannot be established.

Boundary Conditions Analysis of Circular Capacitive Micromachined Ultrasonic Transducer (CMUT) Devices

2021 ◽  
Vol 15 ◽  
Author(s):  
Jiujiang Wang ◽  
Yuanyu Yu ◽  
Jiangming Kuang ◽  
Shuang Zhang ◽  
Jing Xu ◽  
...  
Keyword(s):  
Boundary Condition ◽  
Boundary Conditions ◽  
Integrated Circuit ◽  
Ultrasonic Transducer ◽  
Equilibrium Conditions ◽  
Elastic Boundary ◽  
Capacitive Micromachined Ultrasonic Transducer ◽  
New Type ◽  
Release Method ◽  
Fixed Boundary Condition

Background: Capacitive micromachined ultrasonic transducer (CMUT) is a new type ultrasound transducer which has gained more and more research interests in ultrasound imaging because of its wider bandwidth, higher receiving sensitivity and more likely to be integrated with integrated circuit (IC). Analytical solution is intuitive, fast and convergent among simulation methods. The membrane deflection is important to the CMUT performance. The deformation for a circular CMUT under an external force can be described by von Kármán equations. Objective: To find suitable boundary conditions that are crucial for the governing equations to be properly solved to get the analytical solutions for membrane deformation. Methods: Features of two commonly used CMUT fabrication methods, sacrificial release method (SR) and wafer bonding (WB) method, are introduced. The force and moment equilibrium conditions of the supporting post are analyzed to get the boundary condition equations. Results: The analytical results match well with finite element method (FEM) results for the fixed boundary condition while there are still some difference for the elastic boundary condition. Conclusion: The boundary conditions for SR fabricated devices are elastic support while the boundary conditions for WB fabricated devices are fixed.

Use of Surface Flow Visualization Methods in Centrifugal Pump Design

2002 ◽  
Vol 124 (2) ◽  
pp. 314-318 ◽  
Author(s):  
Christopher P. Hamkins ◽  
Stephan Bross
Keyword(s):  
Fluid Dynamics ◽  
Boundary Condition ◽  
Centrifugal Pump ◽  
Flow Patterns ◽  
Surface Flow ◽  
Pump Design ◽  
New Type ◽  
Measured Flow ◽  
Computational Fluid Dynamics Cfd ◽  
Modern Image

Surface flow patterns generated with oils or oil paint have been used in centrifugal pump design for many years. Here it is shown how modern image analysis methods allow quantitative predictions of the corresponding pressure distribution by analyzing surface flow patterns. Further, the surface flow patterns can be used to confirm computational fluid dynamics (CFD) results, improve their boundary conditions and determine their limits of validity. The authors see the need for a new type of boundary condition for CFD packages, in which a measured flow pattern could be used as “input.”

Sturm-Liouville Problem for Stationary Differential Operator with Nonlocal Two-Point Boundary Conditions

2006 ◽  
Vol 11 (1) ◽  
pp. 47-78 ◽  
Author(s):  
S. Pečiulytė ◽  
A. Štikonas
Keyword(s):  
Boundary Condition ◽  
Differential Operator ◽  
Boundary Conditions ◽  
Nonlocal Boundary Condition ◽  
Nonlocal Boundary ◽  
Liouville Problem ◽  
Complex Case ◽  
Qualitative Behavior ◽  
Point Boundary ◽  
Sturm Liouville

The Sturm-Liouville problem with various types of two-point boundary conditions is considered in this paper. In the first part of the paper, we investigate the Sturm-Liouville problem in three cases of nonlocal two-point boundary conditions. We prove general properties of the eigenfunctions and eigenvalues for such a problem in the complex case. In the second part, we investigate the case of real eigenvalues. It is analyzed how the spectrum of these problems depends on the boundary condition parameters. Qualitative behavior of all eigenvalues subject to the nonlocal boundary condition parameters is described.

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