Dynamic state of low-Reynolds-number turbulent channel flow.

We numerically study the dynamic state of a low-Reynolds-number turbulent channel flow from the viewpoints of symbolic dynamics and nonlinear forecasting. A low-dimensionally (high-dimensionally) chaotic state of the streamwise velocity fluctuations emerges at a viscous sublayer (logarithmic layer). The possible presence of the chaotic states is clearly identified by orbital instability-based nonlinear forecasting and ordinal partition transition network entropy in combination with the surrogate data method.

Relationship between hemodynamic parameters and cerebral aneurysm initiation.

Research on the relationship between cerebralaneurysm initiation and hemodynamic parameters, but several open questions remain on initiation and growth mechanisms of cerebral aneurysms. If factors contributing to initiation were identified, it would be possible to predict the initiation of aneurysms. The purpose of this study is to investigate the relationship between cerebral aneurysm initiation and hemodynamic factors.

Hemodynamic Change In A Cerebral Aneurysm Treated By Double Stenting Technique.

Rupture of cerebral aneurysms often causes subarachnoid hemorrhage which is a life-threatening condition with high mortality rates. Larger aneurysms are believed to be more likely to rupture and should therefore be treated. Recently, flow diverters (FDs) are widely used to treat large or wide neck aneurysms.

Multivariate Analysis For Predicting Internal Carotid (IC) And Middle Cerebral (MC) Aneurysmal Rupture By Hemodynamic Parameters.

Currently, aneurysmal rupture can hardly be predicted and the search for an objective and precise indicator is ongoing. The objective of this study was to find a rupture prediction indicator (RPI) based on hemodynamic parameters of unruptured aneurysms focusing on the internal carotid (IC) and middle cerebral (MC) arteries. Computational fluid dynamics simulations were performed and hemodynamic parameters were calculated using three-dimensional C-arm computed tomography (3D C-arm CT) images of a total of 137 unruptured aneurysms (69 IC and 68 MC artery aneurysms) with known outcomes of rupture or unrupture.

Blood Flow Analysis in Coil Embolized Aneurysms: Difference between Porous Media and Real Coil Geometry Model.

To clarify the mechanism of aneurysmal recanalization, it is necessary to understand the characteristics of the blood flow inside the aneurysm in particular the flow resistance generated by the coil. In studies using computational fluid dynamics (CFD), mainly two approaches have been used to model the coil embolized aneurysm; modeling the coils as porous media or by real coil geometries. In this study, we calculated the pressure drop along a vessel through a coiled region modeled as porous media or by real coil geometry and compared the pressure drop generated by the two coil models.

Hemodynamics and coil distribution with changing coil stiffness and length in intracranial aneurysms.

Purpose: The purpose of this study was to investigate hemodynamics and coil distribution with changing coil stiffness and length using the finite element method (FEM) and computational fluid dynamics (CFD) analysis.

Methods: Basic side-wall and bifurcation type aneurysm models were used. Six types of coil models were generated by changing the coil stiffness and length, based on commercially available embolic coils.

A new combined parameter predicts re-treatment for coil-embolized aneurysms: a computational fluid dynamics multivariable analysis study.

Purpose: Coil embolization is a minimally invasive method used to treat cerebral aneurysms. Although this endovascular treatment has a high success rate, aneurysmal re-treatment due to recanalization remains a major problem of this method. The purpose of this study was to determine a combined parameter that can be useful for predicting aneurysmal re-treatment due to recanalization.

Effect of catheter positions on hemodynamics and coil formation after coil embolization.

Coil embolization using a micro catheter and coils is one of the most popular surgical methods used for treating intracranial aneurysms. Surgeons need to better understand the effects of changing catheter position because this is under their control during operations. In this study, we simulate coil embolization for a basic bifurcation-type aneurysm using finite element method and computational fluid dynamics.

Relationships between geometrical parameters and mechanical properties for a helical braided flow diverter stent.

Background: Although flow diversion is a promising procedure for aneurysm treatment, the safety and efficacy of this strategy have not been sufficiently characterized. Both mechanical properties and flow reduction effects are important factors in the design of an optimal stent.

Objective: We aimed to clarify the contributions of strut size and pitch to the mechanical properties (radial stiffness and longitudinal flexibility) and geometric characteristics (porosity and pore density) related to flow reduction effects.

Hemodynamic effects from coil distribution with realistic coil models in an aneurysm.

Because of its minimal invasiveness, coil embolization has become a popular way to treat aneurysms. The main problem with this method, however, is the poor understanding of the hemodynamics in the aneurysm after coil embolization. To improve this situation, we used a finite element method and computational fluid dynamics to investigate how hemodynamic parameters depend on the spatial distribution of coils.

Verification of a research prototype for hemodynamic analysis of cerebral aneurysms.

Owing to its clinical importance, there has been a growing body of research on understanding the hemodynamics of cerebral aneurysms. Traditionally, this work has been performed using general-purpose, state-of-the-art commercial solvers. This has meant requiring engineering expertise for making appropriate choices on the geometric discretization, time-step selection, choice of boundary conditions etc.

Selection of helical braided flow diverter stents based on hemodynamic performance and mechanical properties.

Background: Although flow diversion is a promising procedure for the treatment of aneurysms, complications have been reported and it remains poorly understood. The occurrence of adverse outcomes is known to depend on both the mechanical properties and flow reduction effects of the flow diverter stent.

Objective: To clarify the possibility of designing a flow diverter stent considering both hemodynamic performance and mechanical properties.

Variability of hemodynamic parameters using the common viscosity assumption in a computational fluid dynamics analysis of intracranial aneurysms.

Background: In most simulations of intracranial aneurysm hemodynamics, blood is assumed to be a Newtonian fluid. However, it is a non-Newtonian fluid, and its viscosity profile differs among individuals. Therefore, the common viscosity assumption may not be valid for all patients.

Phase relationship in laminar channel flow controlled by traveling-wave-like blowing or suction.

The phase relationship between the streamwise and the wall-normal velocity disturbances induced by a traveling-wave-like blowing or suction control [T. Min, J. Fluid Mech.