The Experts below are selected from a list of 252 Experts worldwide ranked by ideXlab platform

Nathan J. Quinlan - One of the best experts on this subject based on the ideXlab platform.

  • Effect of Eddy Length Scale on Mechanical Loading of Blood Cells in Turbulent Flow
    Annals of Biomedical Engineering, 2009
    Co-Authors: Patrick N. Dooley, Nathan J. Quinlan
    Abstract:

    Non-physiological turbulent blood flow is known to occur in and near implanted cardiovascular devices, but its effects on blood are poorly understood. The objective of this work is to investigate the effect of turbulent eddy length scale on blood cell damage, and in particular to test the hypothesis that only eddies similar in size to blood cells can cause damage. The microscale flow near a red blood cell (RBC) in an idealized turbulent eddy is modeled computationally using an immersed boundary method. The model is validated for the special case of a tank-treading RBC. In comparisons between turbulent flow fields, based on Kolmogorov theory, the model predicts that damage due to the smallest eddies is almost independent of the Kolmogorov length scale. The model predicts that within a given flow field, however, eddies of sub-cellular scale are less damaging than larger eddies. Eddy decay time and the turbulent Energy Spectral Density are highlighted as important factors. The results suggest that Kolmogorov scale is not an adequate predictor of flow-induced blood trauma, and highlights the need for deeper understanding of the microscale structure of turbulent blood flow.

  • Models of Flow-Induced Loading on Blood Cells in Laminar and Turbulent Flow, with Application to Cardiovascular Device Flow
    Annals of Biomedical Engineering, 2007
    Co-Authors: Nathan J. Quinlan, Patrick N. Dooley
    Abstract:

    Viscous shear stress and Reynolds stress are often used to predict hemolysis and thrombosis due to flow-induced stress on blood elements in cardiovascular devices. These macroscopic stresses are distinct from the true stress on an individual cell, which is determined by the local microscale flow field. In this paper the flow-induced stress on blood cells is calculated for laminar and turbulent flow, using simplified models for cells and for turbulent eddies. The model is applied to estimate shear stress on red blood cells in flow through a prosthetic heart valve, using the Energy Spectral Density measured by Liu et al. [ J. Biomech. Eng . 122:118–124, 2000]. Results show that in laminar flow, the maximum stress on a cell is approximately equal to the macroscopic viscous shear stress. In turbulent flow through a prosthetic heart valve, the estimated root mean square of flow-induced stress on a cell is at least an order of magnitude less than the Reynolds stress. The results support the hypothesis that smaller turbulent eddies cause higher stress on cells. However, the stress due to an eddy depends on the velocity scale of the eddy as well as its length scale. For the heart valve flow investigated, turbulence contributes to flow-induced stress on cells almost equally across a broad range of the frequency spectrum. The model suggests that Reynolds stress alone is not an adequate predictor of cell damage in turbulent flow, and highlights the importance of the Energy Spectral Density.

Patrick N. Dooley - One of the best experts on this subject based on the ideXlab platform.

  • Effect of Eddy Length Scale on Mechanical Loading of Blood Cells in Turbulent Flow
    Annals of Biomedical Engineering, 2009
    Co-Authors: Patrick N. Dooley, Nathan J. Quinlan
    Abstract:

    Non-physiological turbulent blood flow is known to occur in and near implanted cardiovascular devices, but its effects on blood are poorly understood. The objective of this work is to investigate the effect of turbulent eddy length scale on blood cell damage, and in particular to test the hypothesis that only eddies similar in size to blood cells can cause damage. The microscale flow near a red blood cell (RBC) in an idealized turbulent eddy is modeled computationally using an immersed boundary method. The model is validated for the special case of a tank-treading RBC. In comparisons between turbulent flow fields, based on Kolmogorov theory, the model predicts that damage due to the smallest eddies is almost independent of the Kolmogorov length scale. The model predicts that within a given flow field, however, eddies of sub-cellular scale are less damaging than larger eddies. Eddy decay time and the turbulent Energy Spectral Density are highlighted as important factors. The results suggest that Kolmogorov scale is not an adequate predictor of flow-induced blood trauma, and highlights the need for deeper understanding of the microscale structure of turbulent blood flow.

  • Models of Flow-Induced Loading on Blood Cells in Laminar and Turbulent Flow, with Application to Cardiovascular Device Flow
    Annals of Biomedical Engineering, 2007
    Co-Authors: Nathan J. Quinlan, Patrick N. Dooley
    Abstract:

    Viscous shear stress and Reynolds stress are often used to predict hemolysis and thrombosis due to flow-induced stress on blood elements in cardiovascular devices. These macroscopic stresses are distinct from the true stress on an individual cell, which is determined by the local microscale flow field. In this paper the flow-induced stress on blood cells is calculated for laminar and turbulent flow, using simplified models for cells and for turbulent eddies. The model is applied to estimate shear stress on red blood cells in flow through a prosthetic heart valve, using the Energy Spectral Density measured by Liu et al. [ J. Biomech. Eng . 122:118–124, 2000]. Results show that in laminar flow, the maximum stress on a cell is approximately equal to the macroscopic viscous shear stress. In turbulent flow through a prosthetic heart valve, the estimated root mean square of flow-induced stress on a cell is at least an order of magnitude less than the Reynolds stress. The results support the hypothesis that smaller turbulent eddies cause higher stress on cells. However, the stress due to an eddy depends on the velocity scale of the eddy as well as its length scale. For the heart valve flow investigated, turbulence contributes to flow-induced stress on cells almost equally across a broad range of the frequency spectrum. The model suggests that Reynolds stress alone is not an adequate predictor of cell damage in turbulent flow, and highlights the importance of the Energy Spectral Density.

M T Manry - One of the best experts on this subject based on the ideXlab platform.

  • recursive approximation of the Energy Spectral Density
    IEEE Transactions on Signal Processing, 1992
    Co-Authors: L A Anderson, M T Manry
    Abstract:

    In a previous paper, R.Z. Kham et al. (ibid., vol.35, p.102-5, Jan. 1988) described a fast technique for estimating the Energy Spectral Density of a noisy waveform via Taylor series. A fast sliding-time window approach for recursively updating the series is introduced in this work. A method for automatically determining the required series degree using the estimated truncation error is given. The application of the method is demonstrated in an example. The technique is shown to be more efficient than interpolation of the DFT modulus. >

  • n i recursive approximation of the Energy Spectral Density
    1992
    Co-Authors: L A Anderson, M T Manry
    Abstract:

    In a previous paper, a fast technique was described for estimating the Energy Spectral Density (ESD) of a noisy waveform via Taylor series. Here, we introduce a fast sliding time window approach for recursively updating the series. We introduce a method for auto- matically determining the required series degree, using the estimated truncation error. The application of the new method is demonstrated in an example. The technique is shown to be more efficient than inter- polation of the DFT modulus.

Jun Sakakibara - One of the best experts on this subject based on the ideXlab platform.

  • measurement of Energy Spectral Density of a flow in a rotating couette system
    Physical Review Letters, 1993
    Co-Authors: Yasushi Takeda, W E Fischer, Jun Sakakibara
    Abstract:

    The Energy Spectral Density of axial velocity components in a rotating Couette-Taylor system was obtained using a Fourier transform of axial velocity distributions. As this configuration has well defined spatial periodicity, strong peaks appear on the spectrum corresponding to Taylor vortex flow and wavy vortex flow modes and their harmonics. A continuous background shows an exponential decay with wave number, which supports the results of the numerical simulations. A variation in the decay rate at reduced Reynolds number shows a maximum at R * ≃22. At this Reynolds number, an Energy exchange between the first and second harmonics was observed

L A Anderson - One of the best experts on this subject based on the ideXlab platform.

  • recursive approximation of the Energy Spectral Density
    IEEE Transactions on Signal Processing, 1992
    Co-Authors: L A Anderson, M T Manry
    Abstract:

    In a previous paper, R.Z. Kham et al. (ibid., vol.35, p.102-5, Jan. 1988) described a fast technique for estimating the Energy Spectral Density of a noisy waveform via Taylor series. A fast sliding-time window approach for recursively updating the series is introduced in this work. A method for automatically determining the required series degree using the estimated truncation error is given. The application of the method is demonstrated in an example. The technique is shown to be more efficient than interpolation of the DFT modulus. >

  • n i recursive approximation of the Energy Spectral Density
    1992
    Co-Authors: L A Anderson, M T Manry
    Abstract:

    In a previous paper, a fast technique was described for estimating the Energy Spectral Density (ESD) of a noisy waveform via Taylor series. Here, we introduce a fast sliding time window approach for recursively updating the series. We introduce a method for auto- matically determining the required series degree, using the estimated truncation error. The application of the new method is demonstrated in an example. The technique is shown to be more efficient than inter- polation of the DFT modulus.