Juan C. Heinrich

The role of fluid dynamics in plaque excavation and rupture in the human carotid bifurcation: a computational study

A 3D computational fluid dynamics model of the human carotid bifurcation has been created to explore plaque excavation and plaque rupture. The model considers different degrees of atherosclerotic stenosis, the form of which is determined using computerised tomography scans of a patient with moderate plaque stenosis. The results suggest that 70% stenosis will diminish blood flow to the brain from 245 ml/min to 71 ml/min. Pressure in the 50% stenosis model is increased by only 3.3%, while pressure in the 70% and 80% stenosis models are increased by 8.8% and 15.4%, respectively. Starting at 30% stenosis, each increase of 10% stenosis increases the peak wall shear stress value by a factor of two. Severely elevated magnitudes in the product of the pressure and the wall shear stress gradient were found on the upstream face of the stenosis. In specific cases, these peaks can be correlated to excavation points observed clinically.

Three-dimensional ALE-FEM method for fluid flow in domains with moving boundaries part 1: algorithm description

A three-dimensional finite element method for simulating fluid flow in domains containing moving objects or boundaries is developed. This method is a type of arbitrary-Lagrangian-Eulerian, based on a fixed mesh that is locally fitted at the moving interfaces and recovers its original shape once the moving interfaces go past the elements. The moving interfaces are defined by marker points so that the global mesh is not affected by the interfaces motion, eliminating potential for mesh entanglement. The result is an efficient and robust formulation for multi-physics simulations. The mesh never becomes unsuitable by continuous deformation, thus eliminating the need for repeated re-meshing. The interface boundaries are exactly imposed Dirichlet type. The total domain volume is always calculated exactly thus automatically satisfying the geometric conservation law. This work supports the internal combustion engines simulator KIVA developed at Los Alamos National Laboratories; in this paper, only the interface moving aspect is addressed.

Three Dimensional Numerical Analysis of Flow Through the Human Carotid Bifurcation With Varying Degrees of Stenotic Plaque Formation

The human carotid artery bifurcation is often affected by plaque and atherosclerotic formations. A high degree of stenosis due to plaque deposit in the carotid artery can significantly diminish blood flow to the brain [1]. For three decades, local flow anomalies such as flow separation, recirculation, low wall shear stress, and high local particle residence time are factors that have been implicated in the development of arterial diseases [3, 1]. Numerical analysis of flow through a stenotic carotid bifurcation provides insight into local flow dynamics and an assessment of the risks of particular modes and degrees of stenosis.Copyright

EFFECT OF VARIABLE DENSITY IN DENDRITIC SOLIDIFICATION

Dendritic solidification with natural convection caused by solidification contraction and thermal and solutal buoyancy in two-dimensional space is numerically studied using a sharp-interface model. The model is formulated using the finite element method and works directly with primitive variables. Both pure substances and binary alloys are considered. The model solves the coupled energy and solutal concentration equations and the Navier-Stokes equations for incompressible flow while tracking the solid-liquid interface explicitly using marker points. The energy equation is solved on a fixed mesh that covers the whole domain of the solid and liquid phases. The solutal concentration and Navier-Stokes equations are solved on an adaptive mesh of triangular elements that covers only the liquid phase. The adaptive mesh conforms to the interface and the velocity boundary conditions are applied directly at the nodes on the interface. Three examples that consider solidification contraction, thermal buoyancy and all three of contraction and thermal and solutal buoyancy are presented. The simulations show that, for equiaxial dendritic growth into an undercooled pure melt, the contraction-induced convection enhances the solidification rate symmetrically while the thermal convection causes the dendrite to grow faster in the downward direction and slower in the upward direction. For directional solidification with the growth direction perpendicular to the gravity, thermo-solutal buoyancy causes circulatory convection while contraction induces unidirectional flow. The mixed convection alters the concentration distribution in the solutal-boundary layer ahead of the interface and changes the local solidification rate.