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Biomedical subjects

I D Chang

Publications and source records attributed to I D Chang.

4 recordsLinked to original sources
PubMed1997

Computational approach for probing the flow through artificial heart devices.

Computational fluid dynamics (CFD) has become an indispensable part of aerospace research and design. The solution procedure for incompressible Navier-Stokes equations can be used for biofluid mechanics research. The computational approach provides detailed knowledge of the flowfield complementary to that obtained by experimental measurements. This paper illustrates the extension of CFD techniques to artificial heart flow simulation. Unsteady incompressible Navier-Stokes equations written in three-dimensional generalized curvilinear coordinates are solved iteratively at each physical time step until the incompressibility condition is satisfied. The solution method is based on the pseudocompressibility approach. It uses an implicit upwind-differencing scheme together with the Gauss-Seidel line-relaxation method. The efficiency and robustness of the time-accurate formulation of the numerical algorithm are tested by computing the flow through model geometries. A channel flow with a moving indentation is computed and validated by experimental measurements and other numerical solutions. In order to handle the geometric complexity and the moving boundary problems, a zonal method and an overlapped grid embedding scheme are employed, respectively. Steady-state solutions for the flow through a tilting-disk heart valve are compared with experimental measurements. Good agreement is obtained. Aided by experimental data, the flow through an entire Penn State artificial heart model is computed.

Algorithms↗
PubMed1971

Effects of viscosty and constraints on the dispersion and dissipation of waves in large blood vessels. I. Theoretical analysis.

The propagation of sounds and pulse waves within the cardiovascular system is subject to strong dissipative mechanisms. To investigate the effects of blood viscosity on dissipation as well as dispersion of small waves in arteries and veins, a parametric study has been carried out. A linearized analysis of axisymmetric waves in a cylindrical membrane that contains a viscous fluid indicates that there are two families of waves: a family of slow waves and one of fast waves. The faster waves are shown to be more sensitive to variations in the elastic properties of the medium surrounding the blood vessels and at high values of the frequency parameter alpha defined by alpha = radicalrhoomegaR(2) (0)/mu the blood viscosity attenuates them more strongly over a length than the slow waves. At low values of alpha, the effects of viscosity on attenuation are reversed; that is, the family of slow waves is much more attenuated than the family of fast waves. For the slow waves the radial displacement component generally exceeds the axial component except at very low frequencies. Conversely the axial displacements are much larger than the radial displacement for the faster waves. The presence of external constraints, however, can modify these results. In the case of the slow waves the phase angle between pressure and radial wall displacement is virtually negligible in the presence of mild external constraints, while the phase angles between pressure and fluid mass flow are at most 45 degrees . The corresponding phase angles for the fast waves exhibit much larger variations with changes in the elastic properties of the surrounding medium.

Blood Flow Velocity↗
PubMed1971

Effects of viscosity and constraints on the dispersion and dissipation of waves in large blood vessels. II. Comparison of analysis with experiments.

The theoretical predictions described in part I of this study are compared with in vivo data from anesthetized dogs. It is shown that the observed attenuation of the pressure and axial waves cannot be accounted for by fluid viscosity alone. For large values of the frequency parameter alpha = radicalrhoomegaR(2) (0)/mu, the analysis of part I is extended to include the effects of viscoelasticity of the vessel wall. The results indicate that the speeds of both types of waves are essentially not affected by a realistic viscoelasticity model while the attenuation per wavelength is significantly increased and becomes frequency independent. The application of this analysis to in vivo data from the carotid arteries of anesthetized dogs demonstrates partial agreement between theory and experiment and suggests that the carotid arteries are anisotropically viscoelastic.

Animals↗