Shinjiro Miyawaki | The University of Iowa (original) (raw)

Papers by Shinjiro Miyawaki

Research paper thumbnail of Numerical evaluation of the effects of planform geometry and inflow conditions on flow, turbulence structure, and bed shear velocity at a stream confluence with a concordant bed

Journal of Geophysical Research: Earth Surface, 2014

ABSTRACT

Research paper thumbnail of Early Airway Structural Changes in Cystic Fibrosis Pigs as a Determinant of Particle Distribution and Deposition

Annals of Biomedical Engineering, 2014

The pathogenesis of cystic fibrosis (CF) airway disease is not well understood. A porcine CF mode... more The pathogenesis of cystic fibrosis (CF) airway disease is not well understood. A porcine CF model was recently generated, and these animals develop lung disease similar to humans with CF. At birth, before infection and inflammation, CF pigs have airways that are irregularly shaped and have a reduced caliber compared to non-CF pigs. We hypothesized that these airway structural abnormalities affect airflow patterns and particle distribution. To test this hypothesis we used computational fluid dynamics (CFD) on airway geometries obtained by computed tomography of newborn non-CF and CF pigs. For the same flow rate, newborn CF pig airways exhibited higher air velocity and resistance compared to non-CF. Moreover we found that, at the carina bifurcation, particles greater than 5-μm preferably distributed to the right CF lung despite almost equal airflow ventilation in non-CF and CF. CFD modeling also predicted that deposition efficiency was greater in CF compared to non-CF for 5- and 10-μm particles. These differences were most significant in the airways included in the geometry supplying the right caudal, right accessory, left caudal, and left cranial lobes. The irregular particle distribution and increased deposition in newborn CF pig airways suggest that early airway structural abnormalities might contribute to CF disease pathogenesis.

Research paper thumbnail of Effect of Carrier Gas Properties on Aerosol Distribution in a CT-based Human Airway Numerical Model

Annals of Biomedical Engineering, 2012

Research paper thumbnail of Numerical analysis of the effect of momentum ratio on the dynamics and sediment-entrainment capacity of coherent flow structures at a stream confluence

Journal of Geophysical Research, 2012

ABSTRACT

Research paper thumbnail of Numerical Investigation of Three-Dimensional Flow Structure at a River Confluence

Detached Eddy Simulation (DES) is performed to investigate the 3-D flow dynamics and the role of ... more Detached Eddy Simulation (DES) is performed to investigate the 3-D flow dynamics and the role of the large-scale coherent structures at an asymmetrical river confluence with concordant bed. The mean flow predictions are validated using data from a field study. The geometry of the confluence induces strong flow convergence and large-scale secondary circulation. DES is conducted at field conditions (average channel Reynolds number is 160,000). DES accurately predicts most of the largescale features of the mean streamwise velocity distributions in cross-sections situated downstream of the junction. The present study demonstrates the important role played by the large-scale streamwise oriented vortices and associated helical motion in the momentum exchange processes between the two streams. It is shown the presence of these vortical cells on both sides of the shallow mixing layer developing downstream of the junction is responsible for some of the large-scale characteristics of the stre...

Research paper thumbnail of The structure of turbulent flow at a river confluence with a momentum ratio close to one: insight provided by an eddy-resolving simulation

Water Resources Research, 2010

Streamwise-oriented vortical (SOV) cells form on both sides of the mixing layerSOV cells enhance ... more Streamwise-oriented vortical (SOV) cells form on both sides of the mixing layerSOV cells enhance bed shear stresses more than quasi-2-D eddiesMixing layer structure resembles that of a wake behind a bluff body (wake mode)

Research paper thumbnail of Correlations of Flow Structure and Particle Deposition with Structural Alterations in Severe Asthmatic Lungs

Bulletin of the American Physical Society, 2014

Research paper thumbnail of The flow and turbulence structure at a rectangular bridge pier with a low angle of attack

Detached Eddy Simulation (DES) is used to study the vortical structure of the flow around a high-... more Detached Eddy Simulation (DES) is used to study the vortical structure of the flow around a high-aspect-ratio rectangular bridge pier with a small angle of attack. Though piers are generally de- signed to be closely aligned with the incoming flow at normal flow conditions, the angle of attack can in- crease significantly at flood conditions. This is particularly the case when a pier is situated near an abut- ment in a compound channel which is, in many cases, subject to varying flow orientations as the flow stage rises. Simulations are conducted with two angles of attack (0 0 and 15 0 ) at a channel Reynolds num- ber of 2.4× 10 5 . The paper focuses on the dynamics of the large-scale coherent structures forming around the bridge pier and their role in controlling the sediment entrainment and transport mechanisms at condi- tions corresponding to the start of the scour process (flat-bed channel). Simulation results show that for these conditions the horseshoe vortex system plays a rel...

Research paper thumbnail of An automatic generation of non-uniform mesh for CFD analyses of image-based multiscale human airway models

Bulletin of the American Physical Society, 2014

Research paper thumbnail of CFD simulations of a deforming human lung using dynamic and static CT images

Research paper thumbnail of An image-based automatic mesh generation and numerical simulation for a population-based analysis of aerosol delivery in the human lungs

Bulletin of the American Physical Society, 2013

Research paper thumbnail of Changes in Three-Dimensional Flow Structure at a River Confluence with Changes in Momentum Ratio

High-resolution eddy-resolving numerical simulations of the flow at an asymmetric river confluenc... more High-resolution eddy-resolving numerical simulations of the flow at an asymmetric river confluence with concordant bed are used to investigate the effect of the momentum ratio on the flow and turbulence structure. The focus is on a case with a value of the momentum ratio between the two streams close to five. To better understand the effect of the momentum ratio on the flow hydrodynamics, comparison is shown with results from a numerical simulation of the flow at the same confluence but with a momentum ratio close to one. The Detached Eddy Simulation (DES) solutions are used to investigate the changes in the dynamics of large-scale coherent structures, in particular, the mixing layer vortices and the streamwise oriented vortical cells forming on the sides of the mixing layer. The comparison between the two cases shows that: (1) the quasi two-dimensional vortices shed in the mixing layer change from wake type to vortex sheet type as the momentum ratio increases from one to five; the ...

Research paper thumbnail of A Feasible Computational Fluid Dynamics Study for Relationships of Structural and Functional Alterations with Particle Depositions in Severe Asthmatic Lungs

Computational and Mathematical Methods in Medicine

This study aims to investigate the effect of altered structures and functions in severe asthma on... more This study aims to investigate the effect of altered structures and functions in severe asthma on particle deposition by using computational fluid dynamics (CFD) models. Airway geometrical models of two healthy subjects and two severe asthmatics were reconstructed from computed tomography (CT) images. Subject-specific flow boundary conditions were obtained by image registration to account for regional functional alterations of severe asthmatics. A large eddy simulation (LES) model for transitional and turbulent flows was applied to simulate airflows, and particle transport simulations were then performed for 2.5, 5, and 10 μm particles using CFD-predicted flow fields. Compared to the healthy subjects, the severe asthmatics had a smaller air-volume change in the lower lobes and a larger air-volume change in the upper lobes. Both severe asthmatics had smaller airway circularity (Cr), but one of them had a significant reduction of hydraulic diameter (Dh). In severe asthmatics, the larg...

Research paper thumbnail of Automatic construction and meshing of multiscale image-based human airway models for simulations of aerosol delivery

Research paper thumbnail of Aerosol deposition predictions in computed tomography-derived skeletons from severe asthmatics: A feasibility study

Clinical biomechanics (Bristol, Avon), Jan 4, 2017

The authors numerically investigated the correlation between airway skeletons of severe asthmatic... more The authors numerically investigated the correlation between airway skeletons of severe asthmatic human subjects and predicted aerosol deposition to shed light on the effect of environmental factors on asthma risk. We hypothesized that there are asthmatic subjects whose airway skeletal structure can expose the subject to a risk of higher local aerosol deposition compared to subjects with a more common/normal branching pattern. From a population of severe asthmatics studied at total lung capacity via computed tomography we randomly selected 8 subjects whose Forced Expiratory Volume in 1s, percent predicted fell below 45% predicted. To simulate aerosol motion in the human lungs, we employed in-house three-dimensional eddy-resolving computational fluid dynamics and particle tracking models utilizing 3 of the 8 severe asthmatic subjects. One of the 3 subjects was found to have a distinct, localized airway narrowing chosen for further investigation. In the simulation, we controlled flow ...

Research paper thumbnail of Numerical simulations of aerosol delivery to the human lung with an idealized laryngeal model, image-based airway model, and automatic meshing algorithm

Computers & Fluids

The authors proposed a new method to automatically mesh computed tomography (CT)-based three-dime... more The authors proposed a new method to automatically mesh computed tomography (CT)-based three-dimensional human airway geometry for computational fluid dynamics (CFD)-based simulations of pulmonary gas-flow and aerosol delivery. Traditional methods to construct and mesh realistic geometry were time-consuming, because they were done manually using image-processing and mesh-generating programs. Furthermore, most of CT thoracic image data sets do not include the upper airway structures. To overcome these issues, the proposed method consists of CFD grid-size distribution, an automatic meshing algorithm, and the addition of a laryngeal model along with turbulent velocity inflow boundary condition attached to the proximal end of the trachea. The method is based on our previously developed geometric model with irregular centerlines and cross-sections fitted to CT segmented airway surfaces, dubbed the "fitted-surface model." The new method utilizes anatomical information obtained from the one-dimensional tree, e.g., skeleton connectivity and branch diameters, to efficiently generate optimal CFD mesh, automatically impose boundary conditions, and systematically reduce simulation results. The aerosol deposition predicted by the proposed method agreed well with the prediction by a traditional CT-based model, and the laryngeal model generated a realistic level of turbulence in the trachea. Furthermore, the computational time was reduced by factor of two without losing accuracy by using the proposed grid-size distribution. The new method is well suited for branch-by-branch analyses of gas-flow and aerosol distribution in multiple subjects due to embedded anatomical information.

Research paper thumbnail of Effect of static vs. dynamic imaging on particle transport in CT-based numerical models of human central airways

Journal of aerosol science, Oct 1, 2016

Advances in quantitative computed tomography (CT) has provided methods to assess the detailed str... more Advances in quantitative computed tomography (CT) has provided methods to assess the detailed structure of the pulmonary airways and parenchyma, providing the means of applying computational fluid dynamics-based modeling to better understand subject-specific differences in structure-to-function relationships. Most of the previous numerical studies, seeking to predict patterns of inhaled particle deposition, have considered airway geometry and regional ventilation derived from static images. Because geometric alterations of the airway and parenchyma associated with regional ventilation may greatly affect particle transport, we have sought to investigate the effect of rigid vs. deforming airways, linear vs. nonlinear airway deformations, and step-wise static vs. dynamic imaging on particle deposition with varying numbers of intermediate lung volume increments. Airway geometry and regional ventilation at different time points were defined by four-dimensional (space and time) dynamic or...

Research paper thumbnail of A 4DCT imaging-based breathing lung model with relative hysteresis

Journal of computational physics, 2016

To reproduce realistic airway motion and airflow, the authors developed a deforming lung computat... more To reproduce realistic airway motion and airflow, the authors developed a deforming lung computational fluid dynamics (CFD) model based on four-dimensional (4D, space and time) dynamic computed tomography (CT) images. A total of 13 time points within controlled tidal volume respiration were used to account for realistic and irregular lung motion in human volunteers. Because of the irregular motion of 4DCT-based airways, we identified an optimal interpolation method for airway surface deformation during respiration, and implemented a computational solid mechanics-based moving mesh algorithm to produce smooth deforming airway mesh. In addition, we developed physiologically realistic airflow boundary conditions for both models based on multiple images and a single image. Furthermore, we examined simplified models based on one or two dynamic or static images. By comparing these simplified models with the model based on 13 dynamic images, we investigated the effects of relative hysteresi...

Research paper thumbnail of Automatic construction of subject-specific human airway geometry including trifurcations based on a CT-segmented airway skeleton and surface

Biomechanics and modeling in mechanobiology, Apr 4, 2016

We propose a method to construct three-dimensional airway geometric models based on airway skelet... more We propose a method to construct three-dimensional airway geometric models based on airway skeletons, or centerlines (CLs). Given a CT-segmented airway skeleton and surface, the proposed CL-based method automatically constructs subject-specific models that contain anatomical information regarding branches, include bifurcations and trifurcations, and extend from the trachea to terminal bronchioles. The resulting model can be anatomically realistic with the assistance of an image-based surface; alternatively a model with an idealized skeleton and/or branch diameters is also possible. This method systematically identifies and classifies trifurcations to successfully construct the models, which also provides the number and type of trifurcations for the analysis of the airways from an anatomical point of view. We applied this method to 16 normal and 16 severe asthmatic subjects using their computed tomography images. The average distance between the surface of the model and the image-bas...

Research paper thumbnail of Influence of planform geometry and momentum ratio on thermal mixing at a stream confluence with a concordant bed

Environmental Fluid Mechanics, 2016

Research paper thumbnail of Numerical evaluation of the effects of planform geometry and inflow conditions on flow, turbulence structure, and bed shear velocity at a stream confluence with a concordant bed

Journal of Geophysical Research: Earth Surface, 2014

ABSTRACT

Research paper thumbnail of Early Airway Structural Changes in Cystic Fibrosis Pigs as a Determinant of Particle Distribution and Deposition

Annals of Biomedical Engineering, 2014

The pathogenesis of cystic fibrosis (CF) airway disease is not well understood. A porcine CF mode... more The pathogenesis of cystic fibrosis (CF) airway disease is not well understood. A porcine CF model was recently generated, and these animals develop lung disease similar to humans with CF. At birth, before infection and inflammation, CF pigs have airways that are irregularly shaped and have a reduced caliber compared to non-CF pigs. We hypothesized that these airway structural abnormalities affect airflow patterns and particle distribution. To test this hypothesis we used computational fluid dynamics (CFD) on airway geometries obtained by computed tomography of newborn non-CF and CF pigs. For the same flow rate, newborn CF pig airways exhibited higher air velocity and resistance compared to non-CF. Moreover we found that, at the carina bifurcation, particles greater than 5-μm preferably distributed to the right CF lung despite almost equal airflow ventilation in non-CF and CF. CFD modeling also predicted that deposition efficiency was greater in CF compared to non-CF for 5- and 10-μm particles. These differences were most significant in the airways included in the geometry supplying the right caudal, right accessory, left caudal, and left cranial lobes. The irregular particle distribution and increased deposition in newborn CF pig airways suggest that early airway structural abnormalities might contribute to CF disease pathogenesis.

Research paper thumbnail of Effect of Carrier Gas Properties on Aerosol Distribution in a CT-based Human Airway Numerical Model

Annals of Biomedical Engineering, 2012

Research paper thumbnail of Numerical analysis of the effect of momentum ratio on the dynamics and sediment-entrainment capacity of coherent flow structures at a stream confluence

Journal of Geophysical Research, 2012

ABSTRACT

Research paper thumbnail of Numerical Investigation of Three-Dimensional Flow Structure at a River Confluence

Detached Eddy Simulation (DES) is performed to investigate the 3-D flow dynamics and the role of ... more Detached Eddy Simulation (DES) is performed to investigate the 3-D flow dynamics and the role of the large-scale coherent structures at an asymmetrical river confluence with concordant bed. The mean flow predictions are validated using data from a field study. The geometry of the confluence induces strong flow convergence and large-scale secondary circulation. DES is conducted at field conditions (average channel Reynolds number is 160,000). DES accurately predicts most of the largescale features of the mean streamwise velocity distributions in cross-sections situated downstream of the junction. The present study demonstrates the important role played by the large-scale streamwise oriented vortices and associated helical motion in the momentum exchange processes between the two streams. It is shown the presence of these vortical cells on both sides of the shallow mixing layer developing downstream of the junction is responsible for some of the large-scale characteristics of the stre...

Research paper thumbnail of The structure of turbulent flow at a river confluence with a momentum ratio close to one: insight provided by an eddy-resolving simulation

Water Resources Research, 2010

Streamwise-oriented vortical (SOV) cells form on both sides of the mixing layerSOV cells enhance ... more Streamwise-oriented vortical (SOV) cells form on both sides of the mixing layerSOV cells enhance bed shear stresses more than quasi-2-D eddiesMixing layer structure resembles that of a wake behind a bluff body (wake mode)

Research paper thumbnail of Correlations of Flow Structure and Particle Deposition with Structural Alterations in Severe Asthmatic Lungs

Bulletin of the American Physical Society, 2014

Research paper thumbnail of The flow and turbulence structure at a rectangular bridge pier with a low angle of attack

Detached Eddy Simulation (DES) is used to study the vortical structure of the flow around a high-... more Detached Eddy Simulation (DES) is used to study the vortical structure of the flow around a high-aspect-ratio rectangular bridge pier with a small angle of attack. Though piers are generally de- signed to be closely aligned with the incoming flow at normal flow conditions, the angle of attack can in- crease significantly at flood conditions. This is particularly the case when a pier is situated near an abut- ment in a compound channel which is, in many cases, subject to varying flow orientations as the flow stage rises. Simulations are conducted with two angles of attack (0 0 and 15 0 ) at a channel Reynolds num- ber of 2.4× 10 5 . The paper focuses on the dynamics of the large-scale coherent structures forming around the bridge pier and their role in controlling the sediment entrainment and transport mechanisms at condi- tions corresponding to the start of the scour process (flat-bed channel). Simulation results show that for these conditions the horseshoe vortex system plays a rel...

Research paper thumbnail of An automatic generation of non-uniform mesh for CFD analyses of image-based multiscale human airway models

Bulletin of the American Physical Society, 2014

Research paper thumbnail of CFD simulations of a deforming human lung using dynamic and static CT images

Research paper thumbnail of An image-based automatic mesh generation and numerical simulation for a population-based analysis of aerosol delivery in the human lungs

Bulletin of the American Physical Society, 2013

Research paper thumbnail of Changes in Three-Dimensional Flow Structure at a River Confluence with Changes in Momentum Ratio

High-resolution eddy-resolving numerical simulations of the flow at an asymmetric river confluenc... more High-resolution eddy-resolving numerical simulations of the flow at an asymmetric river confluence with concordant bed are used to investigate the effect of the momentum ratio on the flow and turbulence structure. The focus is on a case with a value of the momentum ratio between the two streams close to five. To better understand the effect of the momentum ratio on the flow hydrodynamics, comparison is shown with results from a numerical simulation of the flow at the same confluence but with a momentum ratio close to one. The Detached Eddy Simulation (DES) solutions are used to investigate the changes in the dynamics of large-scale coherent structures, in particular, the mixing layer vortices and the streamwise oriented vortical cells forming on the sides of the mixing layer. The comparison between the two cases shows that: (1) the quasi two-dimensional vortices shed in the mixing layer change from wake type to vortex sheet type as the momentum ratio increases from one to five; the ...

Research paper thumbnail of A Feasible Computational Fluid Dynamics Study for Relationships of Structural and Functional Alterations with Particle Depositions in Severe Asthmatic Lungs

Computational and Mathematical Methods in Medicine

This study aims to investigate the effect of altered structures and functions in severe asthma on... more This study aims to investigate the effect of altered structures and functions in severe asthma on particle deposition by using computational fluid dynamics (CFD) models. Airway geometrical models of two healthy subjects and two severe asthmatics were reconstructed from computed tomography (CT) images. Subject-specific flow boundary conditions were obtained by image registration to account for regional functional alterations of severe asthmatics. A large eddy simulation (LES) model for transitional and turbulent flows was applied to simulate airflows, and particle transport simulations were then performed for 2.5, 5, and 10 μm particles using CFD-predicted flow fields. Compared to the healthy subjects, the severe asthmatics had a smaller air-volume change in the lower lobes and a larger air-volume change in the upper lobes. Both severe asthmatics had smaller airway circularity (Cr), but one of them had a significant reduction of hydraulic diameter (Dh). In severe asthmatics, the larg...

Research paper thumbnail of Automatic construction and meshing of multiscale image-based human airway models for simulations of aerosol delivery

Research paper thumbnail of Aerosol deposition predictions in computed tomography-derived skeletons from severe asthmatics: A feasibility study

Clinical biomechanics (Bristol, Avon), Jan 4, 2017

The authors numerically investigated the correlation between airway skeletons of severe asthmatic... more The authors numerically investigated the correlation between airway skeletons of severe asthmatic human subjects and predicted aerosol deposition to shed light on the effect of environmental factors on asthma risk. We hypothesized that there are asthmatic subjects whose airway skeletal structure can expose the subject to a risk of higher local aerosol deposition compared to subjects with a more common/normal branching pattern. From a population of severe asthmatics studied at total lung capacity via computed tomography we randomly selected 8 subjects whose Forced Expiratory Volume in 1s, percent predicted fell below 45% predicted. To simulate aerosol motion in the human lungs, we employed in-house three-dimensional eddy-resolving computational fluid dynamics and particle tracking models utilizing 3 of the 8 severe asthmatic subjects. One of the 3 subjects was found to have a distinct, localized airway narrowing chosen for further investigation. In the simulation, we controlled flow ...

Research paper thumbnail of Numerical simulations of aerosol delivery to the human lung with an idealized laryngeal model, image-based airway model, and automatic meshing algorithm

Computers & Fluids

The authors proposed a new method to automatically mesh computed tomography (CT)-based three-dime... more The authors proposed a new method to automatically mesh computed tomography (CT)-based three-dimensional human airway geometry for computational fluid dynamics (CFD)-based simulations of pulmonary gas-flow and aerosol delivery. Traditional methods to construct and mesh realistic geometry were time-consuming, because they were done manually using image-processing and mesh-generating programs. Furthermore, most of CT thoracic image data sets do not include the upper airway structures. To overcome these issues, the proposed method consists of CFD grid-size distribution, an automatic meshing algorithm, and the addition of a laryngeal model along with turbulent velocity inflow boundary condition attached to the proximal end of the trachea. The method is based on our previously developed geometric model with irregular centerlines and cross-sections fitted to CT segmented airway surfaces, dubbed the "fitted-surface model." The new method utilizes anatomical information obtained from the one-dimensional tree, e.g., skeleton connectivity and branch diameters, to efficiently generate optimal CFD mesh, automatically impose boundary conditions, and systematically reduce simulation results. The aerosol deposition predicted by the proposed method agreed well with the prediction by a traditional CT-based model, and the laryngeal model generated a realistic level of turbulence in the trachea. Furthermore, the computational time was reduced by factor of two without losing accuracy by using the proposed grid-size distribution. The new method is well suited for branch-by-branch analyses of gas-flow and aerosol distribution in multiple subjects due to embedded anatomical information.

Research paper thumbnail of Effect of static vs. dynamic imaging on particle transport in CT-based numerical models of human central airways

Journal of aerosol science, Oct 1, 2016

Advances in quantitative computed tomography (CT) has provided methods to assess the detailed str... more Advances in quantitative computed tomography (CT) has provided methods to assess the detailed structure of the pulmonary airways and parenchyma, providing the means of applying computational fluid dynamics-based modeling to better understand subject-specific differences in structure-to-function relationships. Most of the previous numerical studies, seeking to predict patterns of inhaled particle deposition, have considered airway geometry and regional ventilation derived from static images. Because geometric alterations of the airway and parenchyma associated with regional ventilation may greatly affect particle transport, we have sought to investigate the effect of rigid vs. deforming airways, linear vs. nonlinear airway deformations, and step-wise static vs. dynamic imaging on particle deposition with varying numbers of intermediate lung volume increments. Airway geometry and regional ventilation at different time points were defined by four-dimensional (space and time) dynamic or...

Research paper thumbnail of A 4DCT imaging-based breathing lung model with relative hysteresis

Journal of computational physics, 2016

To reproduce realistic airway motion and airflow, the authors developed a deforming lung computat... more To reproduce realistic airway motion and airflow, the authors developed a deforming lung computational fluid dynamics (CFD) model based on four-dimensional (4D, space and time) dynamic computed tomography (CT) images. A total of 13 time points within controlled tidal volume respiration were used to account for realistic and irregular lung motion in human volunteers. Because of the irregular motion of 4DCT-based airways, we identified an optimal interpolation method for airway surface deformation during respiration, and implemented a computational solid mechanics-based moving mesh algorithm to produce smooth deforming airway mesh. In addition, we developed physiologically realistic airflow boundary conditions for both models based on multiple images and a single image. Furthermore, we examined simplified models based on one or two dynamic or static images. By comparing these simplified models with the model based on 13 dynamic images, we investigated the effects of relative hysteresi...

Research paper thumbnail of Automatic construction of subject-specific human airway geometry including trifurcations based on a CT-segmented airway skeleton and surface

Biomechanics and modeling in mechanobiology, Apr 4, 2016

We propose a method to construct three-dimensional airway geometric models based on airway skelet... more We propose a method to construct three-dimensional airway geometric models based on airway skeletons, or centerlines (CLs). Given a CT-segmented airway skeleton and surface, the proposed CL-based method automatically constructs subject-specific models that contain anatomical information regarding branches, include bifurcations and trifurcations, and extend from the trachea to terminal bronchioles. The resulting model can be anatomically realistic with the assistance of an image-based surface; alternatively a model with an idealized skeleton and/or branch diameters is also possible. This method systematically identifies and classifies trifurcations to successfully construct the models, which also provides the number and type of trifurcations for the analysis of the airways from an anatomical point of view. We applied this method to 16 normal and 16 severe asthmatic subjects using their computed tomography images. The average distance between the surface of the model and the image-bas...

Research paper thumbnail of Influence of planform geometry and momentum ratio on thermal mixing at a stream confluence with a concordant bed

Environmental Fluid Mechanics, 2016