Previous investigations of morphology for human carotid artery bifurcation from infancy to young ... more Previous investigations of morphology for human carotid artery bifurcation from infancy to young adulthood found substantial growth of the internal carotid artery with advancing age, and the development of the carotid sinus at the root of the internal carotid artery during teen age years. Although the reasons for the appearance of the carotid sinus are not clearly understood yet, it has been hypothesized that the dilation of the carotid sinus serves to support pressure sensing, and slows the blood flow to reduce pulsatility to protect the brain. In order to understand this interesting evolvement at the carotid bifurcation in the aspects of fluid mechanics, we performed in vitro phasecontrast MR flow experiments using compliant silicone replicas of age-dependent carotid artery bifurcations. The silicone models in childhood, adolescence, and adulthood were fabricated using a rapid prototyping technique, and incorporated with a bench-top flow mock circulation loop using a computer-controlled piston pump. The results of the in vitro flow study showed highly complex flow characteristics at the bifurcation in all age-dependent models. However, the highest magnitude of kinetic energy was found at the internal carotid artery in the child model. The high kinetic energy in the internal carotid artery during childhood might be one of the local hemodynamic forces that initiate morphological long-term development of the carotid sinus in the human carotid bifurcation.
Steady streaming flow fields induced by a 500 mm bubble oscillating at 12 kHz were measured using... more Steady streaming flow fields induced by a 500 mm bubble oscillating at 12 kHz were measured using microscopic particle image velocimetry (PIV). The accuracy of velocity measurement using a micro PIV system was checked by comparing the measured velocity fields with the theoretical velocity profiles in fully developed laminar flow. The steady streaming flow velocities were measured in the sagittal plane of the bubble attached on the wall. Measured velocity fields showed upward jet flow with two symmetric counter-rotating vortices, and the maximum streaming velocity was about 12 mm/s, which was within the velocity ranges measured by other researchers. The measured streamlines were compared with the analytical solution, and they also showed a reasonable agreement.
To investigate the hemodynamic alterations of a deformed parent vessel after stenting, flow field... more To investigate the hemodynamic alterations of a deformed parent vessel after stenting, flow field change after parent vessel stenting was analyzed using computational fluid dynamics. Effects of branch angle change in the vessel bifurcation after stenting on hemodynamic parameters were considered. The results showed that inflow rate, mean velocity, and mean kinetic energy in an aneurysm decreased in the stented vessel comparing to those in the vessel without a stent, which showed flow diversion effects of a stent. Inflow rate, mean velocity, mean kinetic energy in an aneurysm, and maximum wall shear stresses in the parent vessel and in the aneurysm dome increased in the deformed vessel model due to branching angle increase. Parent vessel deformation after stenting should be considered because it could provide unfavorable hemodynamic environment for aneurysm embolization.
Journal of the Korean Society for Precision Engineering, 2007
Analysis of elders' behavioral characteristic during showering provides important fundamental... more Analysis of elders' behavioral characteristic during showering provides important fundamental data when developing an automatic showering system. We recorded showering behavior of 37 elders' at the front, back, left and right view using four CCTV cameras. The photographic data were analyzed by counting the frequencies of body scrub and identifying zones where hands could reach. And we measured their body sizes, and conducted questionnaire of showering for 302 peoples. Analysis was done according to the analysis criteria established. The human body was divided into 14 zones from a body, and the numbers of body scrub for each zone were counted. The average total numbers of body scrub were 170.8 excluding the head, the face and the neck. The average numbers of body scrub with right hand were 70.2, left hand were 88.2, and both hands were 81.8. The percentages of body scrub frequencies were 16.3% (breast), 12.2%(crotch), 8.8% (abdomen), 7.5% (waist), 8.8% (shoulder), 7% (hips), ...
International Journal of Precision Engineering and Manufacturing, 2004
Aneurysm embolization method using coils has been widely used. When partial blocking of an aneury... more Aneurysm embolization method using coils has been widely used. When partial blocking of an aneurysm is inevitable, the locations of coils are important since they change the flow patterns inside the aneurysm, which affect the embolization process. We calculated the flow fields inside the partially blocked lateral aneurysm models for different coil locations- proximal neck, distal neck, proximal dome and distal dome. Flow into the aneurysm sac was significantly reduced in the distally blocked models, and coils at the distal neck blocked inflow more effectively comparing to those at the distal dome. This study suggests that the distal neck should be the most effective location for aneurysm embolization.
Numerical analysis was performed on the enzyme transport and the flow fields in order to predict ... more Numerical analysis was performed on the enzyme transport and the flow fields in order to predict the effectiveness of urokinase injection regimens in clot dissolution. The species and momentum transport equations were numerically solved for the case of uniform perfusion of enzyme into a fibrin clot for an arterial thrombus and a deep vein thrombus models. In order to predict the thrombus lysis efficiency of continuous and forced intermittent injections, enzyme perfusion and clot lysis were simulated for the different injection velocities. Intermittent injection showed faster clot lysis compared to continuous perfusion, and lysis efficiency was increased as injection velocity increased.
ABSTRACT In order to dissolve a blood clot and restore the patency of a blood vessel, various tre... more ABSTRACT In order to dissolve a blood clot and restore the patency of a blood vessel, various treatments have been used. Direct or intravenous injection of thrombolytic agents, such as tissue plasminogen activator (tPA), urokinase(uPA), streptokinase (SK), has been used for the treatment of thrombosis. Direct injection of thrombolytic agents to the clot may increase the effectiveness of thrombolysis by enhancing the permeation of a thrombolytic agent into the blood clot. Injection velocity and methodology, such as continuous infuson and pulsed injection, would affect the thrombolytic efficiecy. In order to explore the effectivenesss of injection methods, we modeled clot dissolution numerically. Species transport equation was solved along with three dimensional momentum equations. The blood clots were modeled as prorous media. Pressure, velocity and species concentration fields were calculated by computational fluid mechanics methods. Two different thrombus models - arterial and venous thrombus - were simulated. The results showed that thrombolytic speed increased as the injection velocity increased, and intermittent injection was more efficient in dissolving clots comparing to comtinuous perfusion.
The hemodynamic changes induced by stent deployment and vascular remodeling in bifurcation aneury... more The hemodynamic changes induced by stent deployment and vascular remodeling in bifurcation aneurysms were investigated using computational fluid dynamics. The stent deployment reduced the intra-aneurysmal flow activity by decreasing the mean velocity, mean kinetic energy, mean wall shear stress, and mean vorticity. These hemodynamic parameters increased with an increase in the branching angle because of the vessel deformation caused by stent straightening. The maximum wall shear stress and its spatial gradient occurred near the neck of the aneurysm in the stented left daughter vessel, whereas a maximum oscillatory shear index was detected near the neck of the right aneurysm of the right daughter vessel. Theses parameters, which might be related to the recurrence of aneurysms, were also increased by stent-induced vessel deformation.
Journal of Biomechanical Science and Engineering, 2012
ABSTRACT Aneurysm recanalization can be attributed to coil compaction and migration, which are af... more ABSTRACT Aneurysm recanalization can be attributed to coil compaction and migration, which are affected by hemodynamic forces acting on the packed coil inside the aneurysm. The effects of coil bundle deformation on the hemodynamic changes in coil-inserted lateral aneurysm models were investigated using computational fluid dynamics methods incorporating fluid–structure interactions. Lateral aneurysms with normal and wide necks were modeled, and coil bundles were modeled as elastic spheres. The time-averaged mean velocity magnitude at the neck (MVN) and the time-averaged mean kinetic energy (MKE) were calculated to quantify the overall inflow strength and intra-aneurysmal flow activity, respectively. The MVNs and MKEs were higher in elastic coil models than in rigid models, and elastic coil models with lower Young’s moduli had higher MVNs. Therefore, coil deformation caused by hemodynamic forces is suspected to provide an unfavorable hemodynamic environment for aneurysm embolization.
2012 International Conference on Biomedical Engineering (ICoBE), 2012
ABSTRACT Recurrence of aneurysm rupture can be attributed to coil migration and compaction. In or... more ABSTRACT Recurrence of aneurysm rupture can be attributed to coil migration and compaction. In order to verify the effects of hemodynamics on coil compaction and migration, we analyze the forces and displacements on the coil bundle using a computational method. Lateral aneurysms partially filled coils are modeled, and blood flow fields and coil deformations are simulated considering fluid and solid interaction. Effects of coil locations and parent vessel geometry are also investigated. The results showed that mean coil displacements were larger at the distal neck coil location, which implied that coil at the neck might experience more migration. Parent vessel geometry affected the mean coil displacement negligibly, but it influenced mean pressure force profiles on the coil surface. Pressure forces were higher in the straight parent vessel model during diastole, which might promote coil compaction.
Journal of vascular and interventional radiology : JVIR, 2015
To investigate the feasibility of polyvinyl alcohol (PVA) polymer coil as a new endovascular embo... more To investigate the feasibility of polyvinyl alcohol (PVA) polymer coil as a new endovascular embolic agent and to gauge the related histologic response in a canine vascular model. PVA polymer coil was fabricated by cross-linking PVA and tantalum particles. Basic properties were then studied in vitro via swelling ratio and bending diameter. Normal renal segmental arteries and wide-necked aneurysms of carotid sidewalls served as canine vascular models. Endovascular PVA coil embolization of normal renal segmental arteries (N = 20) and carotid aneurysms (N = 8) was performed under fluoroscopic guidance in 10 dogs. Degree of occlusion was assessed immediately and at 4 weeks after embolization by conventional and computed tomographic angiography. Histologic features were also graded at acute (day 1, six segmental arteries and four aneurysms) and chronic phases (week 4, 14 segmental arteries and four aneurysms) after embolization to assess inflammation, organization of thrombus, and neoint...
Proceedings of the Institution of Mechanical Engineers, Part H: Journal of Engineering in Medicine, 2007
Dissolution of a blood clot in thrombolytic procedure is affected by permeation of a thrombolytic... more Dissolution of a blood clot in thrombolytic procedure is affected by permeation of a thrombolytic agent into a clot, and permeation of plasminogen activator into a clot is dependent on the permeation pressure. A controlled experimental study on the effects of permeation pressure on clot lysis was carried out. The effects of intra-thrombus perfusion on thrombolyis were also explored. In vitro clot lysis tests were performed for perfusion pressures of 0, 1, and 10 kPa. Two perfusion media were used: buffer and urokinase solution. Clot lysis by diffusion was enhanced in urokinase solution compared with buffer solution, but the effects of perfusion medium were not significant in pressurized perfusion. Clot lysis was accelerated with the perfusion pressure in the early stage of perfusion, but the pressure effect on thrombolysis was not significant in the later stage (after 2 h). Intra-thrombus perfusion was more efficient in clot lysis than surface perfusion was. It is suggested that fluid flow inside the thrombus should be the most important factor in thrombolytic therapy.
Medical & Biological Engineering & Computing, 2013
To study the effects of the geometrical characteristics of a framing coil on aneurysm thromboembo... more To study the effects of the geometrical characteristics of a framing coil on aneurysm thromboembolization efficacy, the hemodynamics in lateral aneurysms filled with coils having a different shape, orientation, and thickness were analyzed using computational fluid dynamics. The aneurysms packed with vortex and cage-shaped coils were modeled using three different coil orientations: transverse, parallel, and orthogonal. The orthogonal orientation of a vortex coil and parallel orientation of a cage-shaped coil showed higher inflow, vorticity, and wall shear stress in the dome region, which provide an unfavorable hemodynamic environment for thromboembolization. Thicker coils also produced unfavorable hemodynamic conditions compared to normal coils having the same shape, orientation, and total coil volume. Though the effects of coil shape and orientation on the hemodynamic parameters of interest were not consistent, the open area at the distal half of the mid-transverse plane of an aneurysm showed significant positive correlation with flow into the dome region and mean vorticity in the dome region. Therefore, blocking the distal mid-transverse plane of an aneurysm using coils would effectively reduce the intra-aneurysmal flow activity and provide a more efficient hemodynamic environment for thromboembolization.
Journal of Mechanical Science and Technology, 2009
Hemodynamics including flow pattern, shear stress, and blood viscosity characteristics has been b... more Hemodynamics including flow pattern, shear stress, and blood viscosity characteristics has been believed to affect the development and progression of arterial stenosis, but previous studies lack of realistic physiological considerations such as irregular surface geometry, non-Newtonian viscosity characteristics and flow pulsatility. The effects of surface irregularities and non-Newtonian viscosity on flow fields were explored in this study using the arterial stenosis models with 48% arterial occlusions under physiological flow condition. Computational flow dynamics based on the finite volume method was employed for Newtonian and non-Newtonian fluid. The wall shear stresses (WSS) in the irregular surface model were higher compared to those in the smooth surface models. Also, non-Newtonian viscosity characteristics increase the peak WSS significantly. The dimensionless pressure drop and the time averaged WSS in pulsatile flow were higher than those in steady flow. But pulsatility effects on pressure and WSS were less significant compared to non-Newtonian viscosity effects. Therefore, irregular surface geometry and non-Newtonian viscosity characteristics should be considered in predicting pressure drop and WSS in stenotic arteries.
ABSTRACT Steady streaming flow fields of a 5 μm bubble oscillating with uniform radial wall motio... more ABSTRACT Steady streaming flow fields of a 5 μm bubble oscillating with uniform radial wall motion and a 500 μm bubble oscillating with wavy wall motion were simulated using a computational fluid dynamics method that incorporated fluid–structure interactions. The steady streaming flow fields for both bubbles were calculated, and they exhibited upward jet flow with two symmetrical counter-rotating vortices. The maximum streaming velocity ranged from a few to tens of millimeters per second. The simulated flow fields were compared with the theory and experimental measurements using particle image velocimetry. The simulation results agreed well with the theoretical and experimental data. Therefore, the proposed computational method would provide a useful tool to predict steady streaming flow fields of oscillating bubbles.
International Journal of Mechanical Sciences, 2014
ABSTRACT Recently, many studies for flow characteristics have used commercial computational fluid... more ABSTRACT Recently, many studies for flow characteristics have used commercial computational fluid dynamics (CFD) software to simulate flow phenomena in various fields. The aim of this study is to contribute to the discussion on the efficiency of finite element (FE) and finite volume (FV) methods, which have mainly used as CFD solvers for situations with the same number of mesh elements and geometries. We compared the accuracy of the results and the flow patterns among three different commercial codes – Ansys CFX, Fluent and ADINA, which are used in many fields. We calculated three-dimensional incompressible laminar flow problems with simple pipe and bifurcation models. Our results showed that FEM CFD codes (ADINA) were more influenced by the mesh type and quality compared to FVM CFD codes (Ansys CFX, Fluent). The computation time was found to be significantly shorter for the FVM compared to the FEM codes.
Previous investigations of morphology for human carotid artery bifurcation from infancy to young ... more Previous investigations of morphology for human carotid artery bifurcation from infancy to young adulthood found substantial growth of the internal carotid artery with advancing age, and the development of the carotid sinus at the root of the internal carotid artery during teen age years. Although the reasons for the appearance of the carotid sinus are not clearly understood yet, it has been hypothesized that the dilation of the carotid sinus serves to support pressure sensing, and slows the blood flow to reduce pulsatility to protect the brain. In order to understand this interesting evolvement at the carotid bifurcation in the aspects of fluid mechanics, we performed in vitro phasecontrast MR flow experiments using compliant silicone replicas of age-dependent carotid artery bifurcations. The silicone models in childhood, adolescence, and adulthood were fabricated using a rapid prototyping technique, and incorporated with a bench-top flow mock circulation loop using a computer-controlled piston pump. The results of the in vitro flow study showed highly complex flow characteristics at the bifurcation in all age-dependent models. However, the highest magnitude of kinetic energy was found at the internal carotid artery in the child model. The high kinetic energy in the internal carotid artery during childhood might be one of the local hemodynamic forces that initiate morphological long-term development of the carotid sinus in the human carotid bifurcation.
Steady streaming flow fields induced by a 500 mm bubble oscillating at 12 kHz were measured using... more Steady streaming flow fields induced by a 500 mm bubble oscillating at 12 kHz were measured using microscopic particle image velocimetry (PIV). The accuracy of velocity measurement using a micro PIV system was checked by comparing the measured velocity fields with the theoretical velocity profiles in fully developed laminar flow. The steady streaming flow velocities were measured in the sagittal plane of the bubble attached on the wall. Measured velocity fields showed upward jet flow with two symmetric counter-rotating vortices, and the maximum streaming velocity was about 12 mm/s, which was within the velocity ranges measured by other researchers. The measured streamlines were compared with the analytical solution, and they also showed a reasonable agreement.
To investigate the hemodynamic alterations of a deformed parent vessel after stenting, flow field... more To investigate the hemodynamic alterations of a deformed parent vessel after stenting, flow field change after parent vessel stenting was analyzed using computational fluid dynamics. Effects of branch angle change in the vessel bifurcation after stenting on hemodynamic parameters were considered. The results showed that inflow rate, mean velocity, and mean kinetic energy in an aneurysm decreased in the stented vessel comparing to those in the vessel without a stent, which showed flow diversion effects of a stent. Inflow rate, mean velocity, mean kinetic energy in an aneurysm, and maximum wall shear stresses in the parent vessel and in the aneurysm dome increased in the deformed vessel model due to branching angle increase. Parent vessel deformation after stenting should be considered because it could provide unfavorable hemodynamic environment for aneurysm embolization.
Journal of the Korean Society for Precision Engineering, 2007
Analysis of elders' behavioral characteristic during showering provides important fundamental... more Analysis of elders' behavioral characteristic during showering provides important fundamental data when developing an automatic showering system. We recorded showering behavior of 37 elders' at the front, back, left and right view using four CCTV cameras. The photographic data were analyzed by counting the frequencies of body scrub and identifying zones where hands could reach. And we measured their body sizes, and conducted questionnaire of showering for 302 peoples. Analysis was done according to the analysis criteria established. The human body was divided into 14 zones from a body, and the numbers of body scrub for each zone were counted. The average total numbers of body scrub were 170.8 excluding the head, the face and the neck. The average numbers of body scrub with right hand were 70.2, left hand were 88.2, and both hands were 81.8. The percentages of body scrub frequencies were 16.3% (breast), 12.2%(crotch), 8.8% (abdomen), 7.5% (waist), 8.8% (shoulder), 7% (hips), ...
International Journal of Precision Engineering and Manufacturing, 2004
Aneurysm embolization method using coils has been widely used. When partial blocking of an aneury... more Aneurysm embolization method using coils has been widely used. When partial blocking of an aneurysm is inevitable, the locations of coils are important since they change the flow patterns inside the aneurysm, which affect the embolization process. We calculated the flow fields inside the partially blocked lateral aneurysm models for different coil locations- proximal neck, distal neck, proximal dome and distal dome. Flow into the aneurysm sac was significantly reduced in the distally blocked models, and coils at the distal neck blocked inflow more effectively comparing to those at the distal dome. This study suggests that the distal neck should be the most effective location for aneurysm embolization.
Numerical analysis was performed on the enzyme transport and the flow fields in order to predict ... more Numerical analysis was performed on the enzyme transport and the flow fields in order to predict the effectiveness of urokinase injection regimens in clot dissolution. The species and momentum transport equations were numerically solved for the case of uniform perfusion of enzyme into a fibrin clot for an arterial thrombus and a deep vein thrombus models. In order to predict the thrombus lysis efficiency of continuous and forced intermittent injections, enzyme perfusion and clot lysis were simulated for the different injection velocities. Intermittent injection showed faster clot lysis compared to continuous perfusion, and lysis efficiency was increased as injection velocity increased.
ABSTRACT In order to dissolve a blood clot and restore the patency of a blood vessel, various tre... more ABSTRACT In order to dissolve a blood clot and restore the patency of a blood vessel, various treatments have been used. Direct or intravenous injection of thrombolytic agents, such as tissue plasminogen activator (tPA), urokinase(uPA), streptokinase (SK), has been used for the treatment of thrombosis. Direct injection of thrombolytic agents to the clot may increase the effectiveness of thrombolysis by enhancing the permeation of a thrombolytic agent into the blood clot. Injection velocity and methodology, such as continuous infuson and pulsed injection, would affect the thrombolytic efficiecy. In order to explore the effectivenesss of injection methods, we modeled clot dissolution numerically. Species transport equation was solved along with three dimensional momentum equations. The blood clots were modeled as prorous media. Pressure, velocity and species concentration fields were calculated by computational fluid mechanics methods. Two different thrombus models - arterial and venous thrombus - were simulated. The results showed that thrombolytic speed increased as the injection velocity increased, and intermittent injection was more efficient in dissolving clots comparing to comtinuous perfusion.
The hemodynamic changes induced by stent deployment and vascular remodeling in bifurcation aneury... more The hemodynamic changes induced by stent deployment and vascular remodeling in bifurcation aneurysms were investigated using computational fluid dynamics. The stent deployment reduced the intra-aneurysmal flow activity by decreasing the mean velocity, mean kinetic energy, mean wall shear stress, and mean vorticity. These hemodynamic parameters increased with an increase in the branching angle because of the vessel deformation caused by stent straightening. The maximum wall shear stress and its spatial gradient occurred near the neck of the aneurysm in the stented left daughter vessel, whereas a maximum oscillatory shear index was detected near the neck of the right aneurysm of the right daughter vessel. Theses parameters, which might be related to the recurrence of aneurysms, were also increased by stent-induced vessel deformation.
Journal of Biomechanical Science and Engineering, 2012
ABSTRACT Aneurysm recanalization can be attributed to coil compaction and migration, which are af... more ABSTRACT Aneurysm recanalization can be attributed to coil compaction and migration, which are affected by hemodynamic forces acting on the packed coil inside the aneurysm. The effects of coil bundle deformation on the hemodynamic changes in coil-inserted lateral aneurysm models were investigated using computational fluid dynamics methods incorporating fluid–structure interactions. Lateral aneurysms with normal and wide necks were modeled, and coil bundles were modeled as elastic spheres. The time-averaged mean velocity magnitude at the neck (MVN) and the time-averaged mean kinetic energy (MKE) were calculated to quantify the overall inflow strength and intra-aneurysmal flow activity, respectively. The MVNs and MKEs were higher in elastic coil models than in rigid models, and elastic coil models with lower Young’s moduli had higher MVNs. Therefore, coil deformation caused by hemodynamic forces is suspected to provide an unfavorable hemodynamic environment for aneurysm embolization.
2012 International Conference on Biomedical Engineering (ICoBE), 2012
ABSTRACT Recurrence of aneurysm rupture can be attributed to coil migration and compaction. In or... more ABSTRACT Recurrence of aneurysm rupture can be attributed to coil migration and compaction. In order to verify the effects of hemodynamics on coil compaction and migration, we analyze the forces and displacements on the coil bundle using a computational method. Lateral aneurysms partially filled coils are modeled, and blood flow fields and coil deformations are simulated considering fluid and solid interaction. Effects of coil locations and parent vessel geometry are also investigated. The results showed that mean coil displacements were larger at the distal neck coil location, which implied that coil at the neck might experience more migration. Parent vessel geometry affected the mean coil displacement negligibly, but it influenced mean pressure force profiles on the coil surface. Pressure forces were higher in the straight parent vessel model during diastole, which might promote coil compaction.
Journal of vascular and interventional radiology : JVIR, 2015
To investigate the feasibility of polyvinyl alcohol (PVA) polymer coil as a new endovascular embo... more To investigate the feasibility of polyvinyl alcohol (PVA) polymer coil as a new endovascular embolic agent and to gauge the related histologic response in a canine vascular model. PVA polymer coil was fabricated by cross-linking PVA and tantalum particles. Basic properties were then studied in vitro via swelling ratio and bending diameter. Normal renal segmental arteries and wide-necked aneurysms of carotid sidewalls served as canine vascular models. Endovascular PVA coil embolization of normal renal segmental arteries (N = 20) and carotid aneurysms (N = 8) was performed under fluoroscopic guidance in 10 dogs. Degree of occlusion was assessed immediately and at 4 weeks after embolization by conventional and computed tomographic angiography. Histologic features were also graded at acute (day 1, six segmental arteries and four aneurysms) and chronic phases (week 4, 14 segmental arteries and four aneurysms) after embolization to assess inflammation, organization of thrombus, and neoint...
Proceedings of the Institution of Mechanical Engineers, Part H: Journal of Engineering in Medicine, 2007
Dissolution of a blood clot in thrombolytic procedure is affected by permeation of a thrombolytic... more Dissolution of a blood clot in thrombolytic procedure is affected by permeation of a thrombolytic agent into a clot, and permeation of plasminogen activator into a clot is dependent on the permeation pressure. A controlled experimental study on the effects of permeation pressure on clot lysis was carried out. The effects of intra-thrombus perfusion on thrombolyis were also explored. In vitro clot lysis tests were performed for perfusion pressures of 0, 1, and 10 kPa. Two perfusion media were used: buffer and urokinase solution. Clot lysis by diffusion was enhanced in urokinase solution compared with buffer solution, but the effects of perfusion medium were not significant in pressurized perfusion. Clot lysis was accelerated with the perfusion pressure in the early stage of perfusion, but the pressure effect on thrombolysis was not significant in the later stage (after 2 h). Intra-thrombus perfusion was more efficient in clot lysis than surface perfusion was. It is suggested that fluid flow inside the thrombus should be the most important factor in thrombolytic therapy.
Medical & Biological Engineering & Computing, 2013
To study the effects of the geometrical characteristics of a framing coil on aneurysm thromboembo... more To study the effects of the geometrical characteristics of a framing coil on aneurysm thromboembolization efficacy, the hemodynamics in lateral aneurysms filled with coils having a different shape, orientation, and thickness were analyzed using computational fluid dynamics. The aneurysms packed with vortex and cage-shaped coils were modeled using three different coil orientations: transverse, parallel, and orthogonal. The orthogonal orientation of a vortex coil and parallel orientation of a cage-shaped coil showed higher inflow, vorticity, and wall shear stress in the dome region, which provide an unfavorable hemodynamic environment for thromboembolization. Thicker coils also produced unfavorable hemodynamic conditions compared to normal coils having the same shape, orientation, and total coil volume. Though the effects of coil shape and orientation on the hemodynamic parameters of interest were not consistent, the open area at the distal half of the mid-transverse plane of an aneurysm showed significant positive correlation with flow into the dome region and mean vorticity in the dome region. Therefore, blocking the distal mid-transverse plane of an aneurysm using coils would effectively reduce the intra-aneurysmal flow activity and provide a more efficient hemodynamic environment for thromboembolization.
Journal of Mechanical Science and Technology, 2009
Hemodynamics including flow pattern, shear stress, and blood viscosity characteristics has been b... more Hemodynamics including flow pattern, shear stress, and blood viscosity characteristics has been believed to affect the development and progression of arterial stenosis, but previous studies lack of realistic physiological considerations such as irregular surface geometry, non-Newtonian viscosity characteristics and flow pulsatility. The effects of surface irregularities and non-Newtonian viscosity on flow fields were explored in this study using the arterial stenosis models with 48% arterial occlusions under physiological flow condition. Computational flow dynamics based on the finite volume method was employed for Newtonian and non-Newtonian fluid. The wall shear stresses (WSS) in the irregular surface model were higher compared to those in the smooth surface models. Also, non-Newtonian viscosity characteristics increase the peak WSS significantly. The dimensionless pressure drop and the time averaged WSS in pulsatile flow were higher than those in steady flow. But pulsatility effects on pressure and WSS were less significant compared to non-Newtonian viscosity effects. Therefore, irregular surface geometry and non-Newtonian viscosity characteristics should be considered in predicting pressure drop and WSS in stenotic arteries.
ABSTRACT Steady streaming flow fields of a 5 μm bubble oscillating with uniform radial wall motio... more ABSTRACT Steady streaming flow fields of a 5 μm bubble oscillating with uniform radial wall motion and a 500 μm bubble oscillating with wavy wall motion were simulated using a computational fluid dynamics method that incorporated fluid–structure interactions. The steady streaming flow fields for both bubbles were calculated, and they exhibited upward jet flow with two symmetrical counter-rotating vortices. The maximum streaming velocity ranged from a few to tens of millimeters per second. The simulated flow fields were compared with the theory and experimental measurements using particle image velocimetry. The simulation results agreed well with the theoretical and experimental data. Therefore, the proposed computational method would provide a useful tool to predict steady streaming flow fields of oscillating bubbles.
International Journal of Mechanical Sciences, 2014
ABSTRACT Recently, many studies for flow characteristics have used commercial computational fluid... more ABSTRACT Recently, many studies for flow characteristics have used commercial computational fluid dynamics (CFD) software to simulate flow phenomena in various fields. The aim of this study is to contribute to the discussion on the efficiency of finite element (FE) and finite volume (FV) methods, which have mainly used as CFD solvers for situations with the same number of mesh elements and geometries. We compared the accuracy of the results and the flow patterns among three different commercial codes – Ansys CFX, Fluent and ADINA, which are used in many fields. We calculated three-dimensional incompressible laminar flow problems with simple pipe and bifurcation models. Our results showed that FEM CFD codes (ADINA) were more influenced by the mesh type and quality compared to FVM CFD codes (Ansys CFX, Fluent). The computation time was found to be significantly shorter for the FVM compared to the FEM codes.
Uploads
Papers by Woowon Jeong