Jenn Stroud Rossmann

Effect of non-newtonian behavior on hemodynamics of cerebral aneurysms.

Blood flow dynamics near and within cerebral aneurysms have long been implicated in aneurysm growth and rupture. In this study, the governing equations for pulsatile flow are solved in their finite volume formulation to simulate blood flow in a range of three-dimensional aneurysm geometries. Four constitutive models are applied to investigate the influence of non-Newtonian behavior on flow patterns and fluid mechanical forces. The bloods non-Newtonian behavior is found to be more significant, in particular, vascular geometries, and to have pronounced effects on flow and fluid mechanical forces within the aneurysm. The choice of constitutive model has measurable influence on the numerical prediction of aneurysm rupture risk due to fluid stresses, though less influence than aneurysm morphology.

Influence of the renal artery ostium flow diverter on hemodynamics and atherogenesis

The structure and function of the renal artery ostium flow diverter on the caudal side of the renal branch point were previously reported; in this study, we further evaluate the diverter׳s possible functions. The protrusion of this structure into the abdominal aorta suggests that the diverter may preferentially direct blood flow to the renal arteries, and that it may also influence flow patterns and recirculation known to be involved in atherogenesis. Three-dimensional computational fluid dynamics (CFD) simulations of steady and pulsatile blood flow are performed to investigate the influence of diverter size and position, and vascular geometry, on the flow patterns and fluid mechanical forces in the neighborhood of the diverter. CFD results show that the flow diverter does affect the blood distribution; depending on the diverter׳s position, the flow to the renal arteries may be increased or reduced. Calculated results also demonstrate the diverter׳s effect on the wall shear stress (WSS) distribution, and suggest that the diverter contributes to an atherogenic environment in the abdominal aorta, while being atheroprotective in the renal arteries themselves. These results support previous clinical findings, and suggest directions for further clinical study. The results of this work have direct implications in understanding the physiological significance of the diverter, and its potential role in the pathophysiological development of atherosclerosis.

Influence of Shape on Saccular Aneurysm Hemodynamics and Risk of Rupture

Although the mechanisms of the formation, growth and rupture of aneurysms are not fully understood, hemodynamic forces play an important role. Computational fluid dynamics (CFD) software can be used to determine velocity and pressure fields within saccular aneurysms; such information is not possible to obtain in vivo. To analyze the influence of shape on aneurysm hemodynamics, nine aneurysm geometries are created and examined using CFD-ACE+. Characteristics of the aneurysm geometry are evaluated using quantitative indices previously developed by Ma et al [1]. Velocity fields calculated in all aneurysm geometries show multiple recirculation zones. The wall shear stresses acting at the fundi of the aneurysms are recorded over a complete cardiac cycle and compared. Some trends are suggested by this preliminary study.

Pressure Loss Coefficients for Asymmetric Bifurcations of Pulmonary Airways with Predetermined Flow Distributions

Computational Fluid Dynamics simulations of inspiratory airflow in asymmetric bifurcations have been performed in order to determine the influence of the asymmetry and Reynolds number on pressure losses over a physiological relevant range for pulmonary airways; thus the results of this work can contribute to the understanding of respiratory ventilation in health and in disease. A key a priori insight to the design of the study is that the flow distribution in respiratory bifurcations can be largely independent of the local losses; and therefore, is predetermined by the boundary conditions in these calculations. The results, presented in the form of pressure loss coefficients, indicate that asymmetry and downstream conditions are significant for severe restrictions and laminar flow; but are relatively insignificant for turbulent flow conditions and for flow through the healthy branch.

Sociotechnical engineering is one facet of prismatic liberal education

The ideas of mutual integration of the liberal arts and engineering resonate powerfully with our institutional values and with many ongoing practices at Lafayette College, an undergraduate-only liberal arts college whose 35+ major options include 4 ABET-accredited BS engineering disciplines and 1 non-accredited AB in Engineering Studies. In addition to many course-level integration efforts, the Colleges program in Engineering Studies offers a model and a history that may be of interest to those designing new programs.

Numerical Simulation of Blood Flow in the Renal Arteries: Influence of the Ostium Flow Diverter

The tendency of atherosclerotic plaques to develop at arterial branch points is likely due to both the hemodynamics and macromolecular environment associated with these branch points. Arterial branches experience flow separation, which results in regions of low shear stress[1–3], and contributes to longer residence times that may allow for deposition of pro-atherogenic material in the vessel wall [2]. In addition, low shear stress itself may provide cellular signals that alter the tissue microenvironment in favor of atherogenesis [3, e.g.].Copyright

Effect of Asymmetric Branching on Respiratory Flow and Pressure Losses: Implications for Asthma

The distribution of inhaled air throughout human lungs is determined by the pressure losses in lung airways. These losses are reflections of patient health; alterations in measured pressure drops can indicate the presence of respiratory disease [1]. Pressure losses also have implications for the effective treatment of such diseases, as they affect how effectively inhaled medication can be distributed throughout the lung.Copyright

Quantifying Confidence Envelopes for Efficiency Values in the SR-30 Turbojet Engine

Turbojet engines power most of the large military and commercial aircraft in production today. These types of engines are chosen over conventional piston-driven engines because of the turbojet’s superior fuel economy and thrust. To understand how turbojet engines can be compared and optimized, it is necessary to fully characterize their performance. This is generally achieved by calculating thermodynamic efficiency values for each component in the engine, and for the engine as a whole. For this research project, the Turbine Technologies SR-30 centrifugal flow turbojet engine was investigated. An adjustable coupling was designed to permit a single-point thermocouple to be moved and secured within the engine. From the data taken at multiple locations and throttle settings, temperature profiles of the compression and combustion chambers were created. A thermal/fluid dynamic equation routine was developed using Engineering Equation Solver (EES), in order to propagate these temperature profiles through efficiency and thrust calculations. The temperature profiles did not significantly affect theoretical thrust values. However, the dependence of component efficiency values on spatial temperature variation within the engine was significant. In the compression chamber, it was found that a 30°C variation in the temperature across the chamber resulted in a 15% variation in the calculated compressor efficiency. In the inner region of the combustion chamber, a variation in 20°C yielded a 20% variation in calculated turbine efficiency. In the outer region of the combustion chamber, where the temperature varied by almost 400 degrees Celsius, the turbine efficiency varied by about 600%. This work suggests optimal placement of the compression and combustion stage thermocouples when the SR-30 turbojet is to be used for undergraduate laboratories. It also highlights the risks posed by relying on single-point measurements to characterize complex flows.© 2011 ASME

Toward Improved Models for Hemodynamics in Stenotic Vessels: PIV and CFD Results Including Turbulence and Compliance

Due to the mortality and morbidity of cardiovascular disease, there is great interest in the flow dynamics and fluid mechanical forces in stenotic vessels. Critical stress conditions both on [1–2] and within [3] atherosclerotic plaque deposits have been implicated in plaque rupture. The presence of atherosclerotic lesions constricting and accelerating blood flow changes the wall behavior, and can also trigger intermittent, unstable, or transitional flows [4–5]. The current work evaluates the effect of incorporating flow turbulence and wall compliance in hemodynamic models.Copyright

A Continuum Approach to Introductory Biomechanics

An introduction to biomechanics based on a continuum mechanics approach is described. This approach introduces a spectrum of material behavior that has Hookean solids at one extreme, and Newtonian fluids at the other, with many interesting combinations such as biomaterials in between. By building progressively from one-dimensional to higher dimension formulations, this approach makes continuum concepts such as the Cartesian stress tensor accessible to early undergraduate students. From this gradual development of ideas, with many illustrative case studies interspersed, students develop both physical intuition for how bioengineering materials behave, and the mathematics used to describe this behavior.Copyright