• Proceedings of the KSME Conference
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• 2001.06e
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• pp.748-753
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• 2001

The objective of the present study is to visualize the pulsatile flow fields by using three-dimensional computer simulation and the PIV system. A closed flow loop system was built for the steady and unsteady experiments. The Harvard pulsatile pump was used to generate the pulsatile pressure and velocity waveforms. Conifer powder as the tracing particles was added to water to visualize the flow field. Two consecutive particle images were captured by a CCO camera for the image processing at several cross section. The range validation and the area interpolation methods were used to obtain the final velocity vectors with high accuracy. The finite volume predictions were used to analyze three-dimensional flow patterns in the bifurcation model. The results of the PIV experiment and the computer simulation are in good agreement and the results show the recirculation zones and formation of the paired secondary flow distal to the apex of the bifurcated model. The results also show that the branch flow is pushed strongly to the inner wall due to the inertial force effect and helical motions are generated as the flow proceeds toward the outer wall.

• Journal of Mechanical Science and Technology
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• v.17 no.7
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• pp.1073-1082
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• 2003

Many researchers have investigated the blood flow characteristics through bileaflet mechanical heart valves using computational fluid dynamics (CFD) models. Their numerical approach methods can be classified into three types; steady flow analysis, pulsatile flow analysis with fixed leaflets, and pulsatile flow analysis with moving leaflets. The first and second methods have been generally employed for two-dimensional and three-dimensional calculations. The pulsatile flow analysis interacted with moving leaflets has been recently introduced and tried only in two-dimensional analysis because this approach method has difficulty in considering simultaneously two physics of blood flow and leaflet behavior interacted with blood flow. In this publication, numerical calculation for pulsatile flow with moving leaflets using a fluid-structure interaction method has been performed in a three-dimensional geometry. Also, pulsatile flow with fixed leaflets has been analyzed for comparison with the case with moving leaflets. The calculated results using the fluid-structure interaction model have shown good agreements with results visualized by previous experiments. In peak systole. calculations with the two approach methods have predicted similar flow fields. However, the model with fixed leaflets has not been able to predict the flow fields during opening and closing phases. Therefore, the model with moving leaflets is rigorously required for advanced analysis of flow fields.

• Proceedings of the KSME Conference
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• 2000.04b
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• pp.535-540
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• 2000

The objective of the present study is to visualize the pulsatile flow fields by using three-dimensional computer simulation and the PIV system. A closed flow loop system was built for the steady and unsteady experiments. The Harvard pulsatile pump was used to generate the pulsatile pressure and velocity waveforms. Conifer powder as the tracing particles was added to water to visualize the flow field. Two consecutive particle images were captured by a CCD camera for the image processing. The cross-correlation method in combination with the moving searching area algorithm was applied for the image processing of the flow visualization. The pulsatile flow fields were visualized effectively by the PIV system in conjunction with the applied algorithm. The range validation and the area interpolation methods were used to obtain the final velocity vectors with high accuracy. The finite volume predictions were used to analyze three-dimensional flow patterns in the bifurcation model. The results of the PIV experiment and the computer simulation are in good agreement and the results show the recirculation zones and formation of the paired secondary flow distal to the apex of the bifurcated model. The results also show that the branch flow is pushed strongly to the inner wall due to the inertial force effect and helical motions are generated as the flow proceeds toward the outer wall.

• Proceedings of the KSME Conference
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• 2003.11a
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• pp.765-768
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• 2003

The objective of the present study was to visualize the pulsatile flow field in a branching model by using the high-resolution PIV system. A bifurcated flow system was built for the experiments in the pulsatile flow. Harvard pulsatile pump was used to generate the pulsatile velocity waveforms. Conifer powder as the tracing particles was added to water to visualize the flow fields. Two consecutive particle images at several cross sections of the flow filed were captured by the CCD cameras ($1K{\ast}1K$ and $640{\ast}480$). The results after the image processing clearly showed the recirculation zones and the formation of the paired secondary flows from the distal to the apex in the bifurcated model. The results also indicated that the flow velocities in the inner wall moved faster than those in the outer wall due to the inertial force effects and the helical motions generated in the branch flows as the flow proceeded toward the outer wall. While the PIV images from the $1K{\ast}1K$ camera were closer to the simulation results thantheimagesfromthe640${\ast}$480camera,bothresultsofthePIVexperimentsusingthetwocamerasgenerallyagreed quitewellwiththeresultsfromthenumericalsimulation.

• International Journal of Vascular Biomedical Engineering
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• v.2 no.2
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• pp.27-32
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• 2004

The objective of the present study is to visualize the steady and pulsatile flow fields in a branching model by using a high-resolution PIV system. A bifurcated flow system was built for the experiments in the steady and pulsatile flows. Harvard pulsatile pump was used to generate the pulsatile velocity waveforms. Conifer powder as the tracing particles was added to water to visualize the flow fields. CCD cameras($1K{\times}1K$(high resolution camera) and $640{\times}480$(low resolution camera)) captured two consecutive particle images at once for the image processing of several cross sections on the flow system. The range validation method and the area interpolation method were used to obtain the final velocity vectors with high accuracy. The results of the image processing clearly showed the recirculation zones and the formation of the paired secondary flows from the distal to the apex of the branch flow in the bifurcated model. The results also indicated that the particle velocities at the inner wall moved faster than the velocities at the outer wall due to the inertial force effects and the helical motions generated in the branch flows as the flow proceeded toward the outer wall. Even though the PIV images from the high resolution camera were closer to the simulation results than the images from the low resolution camera at some locations, both results of the PIV experiments from the two cameras generally agreed quite well with the results from the computer simulations. Therefore, instead of using the expensive stereoscopic PIV or 3D PIV system, the three-dimensional flow fields in a bifurcated model could be easily and exactly investigated by this study.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.20 no.11
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• pp.3607-3619
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• 1996

Experimental and numerical studies for three-dimensional pulsatile flows are conducted to investigate the flow characteristics in the bifurcated tubes. Velocity measurements in experimental study were made by both Pulsed Doppler Ultrasound(PDU) machine and Laser Doppler Anemometer(LDA) system. Glycerin is used for experimental study. Experimental results are used to verify the results of the numerical simulation. Flow characteristics of Newtonian fluid and blood in the bifurcated tubes under the steady and pulsatlie flows are numerically investigated. Finite volume method is employed for three-dimensional numerical simulations. Blood is considered as a non-Newtonian fluid and the constitutive equation of blood is used for the numerical analysis. Numerical analyses are focused on the flow patterns for various branch angles ranging from 30.deg. to 90.deg. and diameter ratios such as 1.0, 0.8, and 0.6. Pulsatile flow characteristics of blood are compared with those of Newtonian fluid. Parameter effects on axial velocity, pressure and wall shear stress distribution along the bifurcated tubes are discussed in terms of the branch angle, diameter ratio, and Reynolds number.

• Proceedings of the KOSOMBE Conference
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• v.1994 no.05
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• pp.115-118
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• 1994

Three-dimensional steady and pulsatile flows in an end-to-side anastomosis were investigated using a finite difference method in order to understand the flow dynamics in the preferential development of distal anastomotic intimal hyperplasia or thrombosis. Steady flow results revealed that a double helical vortex was formed in the host artery and flow recirculations near tow and heel regions were limited due to the secondary flow. Oscillating wall shear stress with significant secondary flow might be the flow dynamic reason of developing intimal hyperplasia or thrombosis.

• Coupled systems mechanics
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• v.1 no.4
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• pp.361-379
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• 2012

This paper presents a fully coupled three-dimensional solver for the analysis of interaction between pulsatile flow and large deformation structure. A partitioned time marching algorithm is employed for the solution of the time dependent coupled discretised problem, enabling the use of highly developed, robust and well-tested solvers for each field. Conservative transfer of information at the fluid-structure interface is combined with an effective multi-predict-correct iterative scheme to enable implicit coupling of the interacting fields at each time increment. The three-dimensional unsteady incompressible fluid is solved using a powerful implicit time stepping technique and an ALE formulation for moving boundaries with second-order time accurate is used. A full spectrum of total variational diminishing (TVD) schemes in unstructured grids is allowed implementation for the advection terms and finite element shape functions are used to evaluate the solution and its variation within mesh elements. A finite element dynamic analysis of the highly deformable structure is carried out with a numerical strategy combining the implicit Newmark time integration algorithm with a Newton-Raphson second-order optimisation method. The proposed model is used to predict the wave flow fields of a particular flow-induced vibrational phenomenon, and comparison of the numerical results with available experimental data validates the methodology and assesses its accuracy. Another test case about three-dimensional biomedical model with pulsatile inflow is presented to benchmark the algorithm and to demonstrate the potential applications of this method.

• Journal of Biomedical Engineering Research
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• v.15 no.3
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• pp.253-258
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• 1994

Three-dimensional steady and pulsatile flows in an end-to-side anastomosis were investigated using a finite difference method in order to understand the flow dynamics in the preferential development of distal anastomotic intimal hyperplasia or thrombosis. Steady flow results revealed that a double helical vortex was formed in the host artery and flow recirculations near toe find heel regions were restricted due to the secondary flow. Oscillating wall shear stress with significant secondary flow might be flow dynamic reason of developing intimal hyperplasia or thrombosis near the anastomotic region.

• Proceedings of the KOSOMBE Conference
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• v.1995 no.05
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• pp.15-18
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• 1995

Three-dimensional steady and pulsatile flow experiments and numerical simulations have conducted to investigate the flow characteristics in the aortic bifurcation model. In vitro velocity measurements were made using both laser Doppler anemometry and pulsed Doppler ultrasound velocimetry. In this study, flow phenomena in the aortic bifurcation model are discussed extensively and the numerical results are compared with experimental results.