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Abdominal aortic aneurysm (AAA) is a dilation of the abdominal aorta (above 50 % of its original diameter), which can cause death upon rupturing. It usually grows asymptomatically leading to late clinical intervention. The medical criteria to indicate surgery are based on measuring the diameter and growth rate, but in many cases aneurysms fail at uncharacterized critical values. In search of a more efficient technique in predicting AAA failure, there is consensus on the importance of studying its geometric characteristics and estimation of the wall stress, but no fully successful correlation has been found between the two yet. This work examines the relationship between a parameterized geometry (18 input variables and 10 dependent indices) and 1 output variable: the maximum wall stress. Design of Experiments (DOE) techniques are used to generate 183 geometric configurations, for which Finite Element Analyses are performed using ANSYSTM state-of-the-artsolver with a hyperelastic, isotropic and homogeneous arterial model for the wall, considering systolic internal pressure (steady state) and the restriction of longitudinal movement at the blood vessel end-sections. Due to the large number of independent parameters to consider, a preliminary Parameters Correlation analysis was performed to determine if a correlation between all input parameters and the maximum stress existed. The correlations between input parameters and the output variable were determined using the Spearman Rank correlation. Correlations with the maximum wall stress for: maximum diameter (??= 0.46), wall thickness (??= - 0.35), dc parameter (? = 0.21) and tortuosity (? = 0.55) were found. The response surface function between geometry and maximum wall stress was estimated by three models: Universal Kriging geostatistical regression (18 parameters), multiple linear regression (4 parameters) and multiple exponential regression (4 parameters). The models accounted for the stress variance by 99 %, 61 % and 66 %, respectively, with average percentage errors of 0.12 %, 16 % and 17 %, respectively. The solution spaces obtained from this study might provide physicians with a better estimation of the AAA rupture potential and thus, facilitate safer and anticipated treatments of the condition.

In recent years, CFD has become an increasingly used tool in the design of blood-based devices. Particularly, the estimation of red blood cells damage (hemolysis) becomes a very important challenge to CFD scientists since the blood is a complex fluid present in turbulent regime in most pumping devices. Thus, previous CFD studies on blood hemolysis lack of appropriate turbulence modeling and consequently, reliable relationships between hydraulic results and hematological responses. Cannula geometries were studied to numerically assess a relatively simple flow with well documented laboratory hematological data. For benchmarking purposes, numerical data from a coaxial jet array direct numerical simulation (DNS) was used in the selection of the most appropriate and economical turbulence model to be used in the cannula numerical analysis. Velocity and stress time-averaged profiles were compared between DNS results and RANS simulations with different turbulence models. These results, pointed to the Shear Stress Transport with Gamma-Theta transition model as the appropriate turbulence model in that geometry. Accurate and reliable hydrodynamic CFD results were obtained for the cannula as an important previous step to the study and development of further hematological calculations with a minimum degree of uncertainty in the flow field. These hematological calculations led to interesting results about the important role played by turbulence modeling in hemolysis estimation. En años recientes, la dinámica de fluidos computacional (CFD por sus siglas en inglés) se ha venido utilizando en forma creciente en el diseño de dispositivos que manejen sangre. En particular, la estimación de la ruptura de glóbulos rojos (hemólisis) representa un importante reto para los científicos, ya que la sangre es un fluido complejo presente en régimen turbulento en la mayoría de los dispositivos. Asimismo, los estudios previos de hemólisis utilizando CFD carecen de un modelaje apropiado de turbulencia, y consecuentemente, de una relación confiable entre los resultados hidráulicos y la respuesta hematológica. Se estudió la geometría de cánulas para evaluar un flujo relativamente simple del cual se disponen datos experimentales de hemólisis. Para la validación del modelo de turbulencia, se utilizó una simulación numérica directa (DNS por sus siglas en inglés) de un arreglo de chorros coaxiales, para así seleccionar el modelo de turbulencia más apropiado para el análisis de las cánulas. Los perfiles de velocidad y de esfuerzo cortante promediados temporalmente fueron comparados entre el DNS y las simulaciones RANS con distintos modelos de turbulencia. Se obtuvo que el modelo de turbulencia más adecuado para la cánula es el de Transporte de Esfuerzos Cortantes con transición modelo Gamma- Theta. De esta manera se pudieron obtener resultados hidrodinámicos confiables, que serán utilizados en posteriores cálculos de hemólisis, con un mínimo de incertidumbre en el campo de flujo.