Bulletin of the American Physical Society
64th Annual Meeting of the APS Division of Fluid Dynamics
Volume 56, Number 18
Sunday–Tuesday, November 20–22, 2011; Baltimore, Maryland
Session E13: Biofluids: Cardiovascular: FSI and CFD |
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Chair: Melissa Green, Naval Research Laboratory Room: 316 |
Sunday, November 20, 2011 4:40PM - 4:53PM |
E13.00001: Computational analysis of fluid-structure interaction in blood vessels Yulia Peet, Michael Miksis, Stephen Davis, David Chopp Vessels carrying blood flow in a human body are known to be flexible tissues. Interaction of the internal blood flow with the vessel wall compliance, in addition to significant alteration of the fluid mechanical properties (shear and normal stresses), can also result in a variety of interesting mechanical phenomena, such as flow limitation, self-exciting oscillations (flutter), wall collapse. We investigate computationally an unsteady behavior of flexible vessels carrying a blood flow assuming incompressible newtonian fluid approximation for blood. We first utilize a membrane model with constant tension for the vessel walls and apply it to simulate the coupled fluid-wall behavior in 2D collapsible channels and 3D collapsible tubes. We show that although the model works well for 2D cases, it always leads to a complete wall collapse for 3D cases for any negative transmural pressure difference, showing the necessity of including the bending rigidity. We revisit the same problems using full linear elasticity fluid-structure interaction model for finite thickness walls developed in a high-order spectral element fluid solver. We finally investigate the unsteady flow behavior in flexible channels and tubes with the newly-developed FSI solver. [Preview Abstract] |
Sunday, November 20, 2011 4:53PM - 5:06PM |
E13.00002: An Immersed Boundary Finite-Element Solver for Flow-Induced Deformation of Soft Structures with Application in Cardiac Flows Rajneesh Bhardwaj, Rajat Mittal The modeling of complex biological phenomena such as cardiac mechanics is challenging. It involves complex three dimensional geometries, moving structure boundaries inside the fluid domain and large flow-induced deformations of the structure. We present a fluid-structure interaction solver (FSI) which couples a sharp-interface immersed boundary method for flow simulation with a powerful finite-element based structure dynamics solver. An implicit partitioned (or segregated) approach is implemented to ensure the stability of the solver. We validate the FSI solver with published benchmark for a configuration which involves a thin elastic plate attached to a rigid cylinder. The frequency and amplitude of the oscillations of the plate are in good agreement with published results and non-linear dynamics of the plate and its coupling with the flow field are discussed. The FSI solver is used to understand left-ventricular hemodynamics and flow-induced dynamics of mitral leaflets during early diastolic filling and results from this study are presented. [Preview Abstract] |
Sunday, November 20, 2011 5:06PM - 5:19PM |
E13.00003: Fluid-structure Interaction Simulations of Deformable Soft Tissue Iman Borazjani Soft tissue interacts with the surrounding fluid environment in many biological and biomedical applications. Simulating such an interaction is quite challenging due to the large non-linear deformations of tissue, flow pulsatility, transition to turbulence, and non-linear fluid-structure interaction. We have extended our previous three-dimensional fluid-structure interaction (FSI) framework for rigid bodies (Borazjani, Ge, and Sotiropoulos, Journal of Computational Physics, 2008) to deformable soft tissue by coupling our incompressible Navier-Stokes solver for fluids with a non-linear large deformation finite element method for soft tissue. We use Fung-type constitutive law for the soft tissue that can capture the stress-strain behavior of the tissue. The FSI solver adopts a strongly-coupled partitioned approach that is stabilized with under-relaxation and Aitken acceleration technique. We validate our solvers against the experimental data for tissue valves and elastic tubes. We show the capabilities of our solver by simulating the fluid-structure interaction of tissue valves implanted in the aortic positions and elastic collapsible tubes. [Preview Abstract] |
Sunday, November 20, 2011 5:19PM - 5:32PM |
E13.00004: Towards a Fast Dynamic Model of the Human Circulatory System Carolyn Kaplan, Melissa Green, Jay Boris, Elaine Oran We describe a model for systems-level transport in the human circulatory system that is based on a set of equations for a one-dimensional unsteady elastic pipe flow circuit. The system is collapsed from three spatial dimensions and time to one spatial dimension and time by assuming axisymmetric vessel geometry and a parabolic velocity profile across the cylindrical vessels. To drive the fluid, the contractions of a beating heart are modeled as periodic area changes of the elastic vessels. Two different models are compared, both including and neglecting fluid acceleration. Time-resolved distributions of pressure, velocity and area compare reasonably well with reference data. Increasing the rigidity of the vasculature is found to increase peak arterial pressures on the order of ten percent, and including a distributed vascular contraction to model distributed skeletal muscle contractions monotonically increases time-averaged blood flow in the veins, consistent with human physiological response. The circulatory system model presented here simulates the circulatory system on the order of one hundred times faster than real-time; that is, we can compute thousands of heartbeats per minute of CPU time. [Preview Abstract] |
Sunday, November 20, 2011 5:32PM - 5:45PM |
E13.00005: A comparison between Dirichlet and Neumann boundary conditions for 0D/3D coupling in cardiovascular simulations Mahdi Esmaily Moghadam, Tain-Yen Hsia, Alison Marsden Implementation of boundary conditions (BCs) in cardiovascular simulations poses numerical challenges due to the complex dynamic behavior of the circulatory system. A closed-loop lumped parameter network (LPN) coupled to a 3D domain is a powerful tool that can be used to model the global dynamics of the circulatory system and its response to local changes in surgery design. In this study, the essential formulations for coupling a 0D model using both Dirichlet and Neumann BCs to a discretized 3D finite element domain are discussed. Using a closed loop LPN with a heart model and pure Dirichlet or Neumann BCs, the limitations of these two approaches are studied and stability, accuracy, and computational cost are compared. Results show that the Dirichlet BC is more accurate for the tested mesh sizes with better stability characteristic at larger time step sizes, although this method requires additional velocity profile information. Application to patient specific models is also presented and discussed. [Preview Abstract] |
Sunday, November 20, 2011 5:45PM - 5:58PM |
E13.00006: Resolving Low-Density Lipoprotein (LDL) on the Human Aortic Surface Using Large Eddy Simulation Jonas Lantz, Matts Karlsson The prediction and understanding of the genesis of vascular diseases is one of the grand challenges in biofluid engineering. The progression of atherosclerosis is correlated to the build- up of LDL on the arterial surface, which is affected by the blood flow. A multi-physics simulation of LDL mass transport in the blood and through the arterial wall of a subject specific human aorta was performed, employing a LES turbulence model to resolve the turbulent flow. Geometry and velocity measurements from magnetic resonance imaging (MRI) were incorporated to assure physiological relevance of the simulation. Due to the turbulent nature of the flow, consecutive cardiac cycles are not identical, neither in vivo nor in the simulations. A phase average based on a large number of cardiac cycles is therefore computed, which is the proper way to get reliable statistical results from a LES simulation. In total, 50 cardiac cycles were simulated, yielding over 2.5 Billion data points to be post-processed. An inverse relation between LDL and WSS was found; LDL accumulated on locations where WSS was low and vice-versa. Large temporal differences were present, with the concentration level decreasing during systolic acceleration and increasing during the deceleration phase. This method makes it possible to resolve the localization of LDL accumulation in the normal human aorta with its complex transitional flow. [Preview Abstract] |
Sunday, November 20, 2011 5:58PM - 6:11PM |
E13.00007: Computational Fluid Dynamics Analysis of Thoracic Aortic Dissection Yik Sau Tang, Yi Fan, Stephen Wing Keung Cheng, Kwok Wing Chow Thoracic Aortic Dissection (TAD) is a cardiovascular disease with high mortality. An aortic dissection is formed when blood infiltrates the layers of the vascular wall, and a new artificial channel, the false lumen, is created. The expansion of the blood vessel due to the weakened wall enhances the risk of rupture. Computational fluid dynamics analysis is performed to study the hemodynamics of this pathological condition. Both idealized geometry and realistic patient configurations from computed tomography (CT) images are investigated. Physiological boundary conditions from in vivo measurements are employed. Flow configuration and biomechanical forces are studied. Quantitative analysis allows clinicians to assess the risk of rupture in making decision regarding surgical intervention. [Preview Abstract] |
Sunday, November 20, 2011 6:11PM - 6:24PM |
E13.00008: Investigation of geometry effects on blood flow in flexible carotid artery bifurcation Sang Hoon Lee, Hyoung Gwon Choi, Jung Yul Yoo To investigate the effect of the flexible artery wall on the flow field, numerical simulations for the blood flow are carried out. For solving the equation of motion for the structure in fluid-structure interaction problems, it is necessary to calculate the fluid force on the surface of the structure explicitly. To avoid the complexity due to the necessity of additional mechanical constraints, we use the combined formulation which includes both the fluid and structural equations of motion into single coupled variational equation. The Navier-Stokes equations for fluid flow are solved using a P2P1 Galerkin finite element method and mesh movement is achieved using arbitrary Lagrangian-Eulerian formulation. The Newmark method is employed for solving the dynamic equilibrium equations for linear elastic solid mechanics. The pulsatile, three-dimensional, incompressible flows of Newtonian fluids constrained in the flexible wall are analyzed. The study shows that flexibility of carotid wall affects significantly the flow phenomena during the pulse cycle. It is found that the flow field is also strongly influenced by bifurcation angle. [Preview Abstract] |
Sunday, November 20, 2011 6:24PM - 6:37PM |
E13.00009: Optimum Heart Rate to Minimize Pulsatile External Cardiac Power Niema Pahlevan, Morteza Gharib The workload on the left ventricle is composed of steady and pulsatile components. Clinical investigations have confirmed that an abnormal pulsatile load plays an important role in the pathogenesis of left ventricular hypertrophy (LVH) and progression of LVH to congestive heart failure (CHF). The pulsatile load is the result of the complex dynamics of wave propagation and reflection in the compliant arterial vasculature. We hypothesize that aortic waves can be optimized to reduce the left ventricular (LV) pulsatile load. We used an in-vitro experimental approach to investigate our hypothesis. A unique hydraulic model was used for in-vitro experiments. This model has physical and dynamical properties similar to the heart-aorta system. Different compliant models of the artificial aorta were used to test the hypothesis under various aortic rigidities. Our results indicate that: i) there is an optimum heart rate that minimizes LV pulsatile power (this is in agreement with our previous computational study); ii) introducing an extra reflection site at the specific location along the aorta creates constructive wave conditions that reduce the LV pulsatile power. [Preview Abstract] |
Sunday, November 20, 2011 6:37PM - 6:50PM |
E13.00010: Intraventricular vorticity favors conservation of kinetic energy along the cardiac cycle: analysis in patients with dilated cardiomyopathy by post-processing color-doppler images Marta Alhama, Yolanda Benito, Javier Bermejo, Raquel Yotti, Esther Perez-David, Alicia Barrio, Candelas Perez del Villar, Ana Gonzalez Mansilla, Francisco Fernandez Aviles, Juan Carlos del Alamo Background: This study assesses if the left ventricle (LV) filling vortex developed during diastole may be a mechanism that improves systolic efficiency. 19 patients with dilated cardiomyopathy (DCM) and 37 healthy volunteers were studied. Recently, we have developed and validated a method that derives two-dimensional maps of the LV flow from standard color-Doppler sequences. Two-dimensional maps of instantaneous LV flow were obtained, and circulation, energy and position of the main and secondary vortices were calculated along the cardiac cycle. At aortic valve opening (AVO) the vortex circulation is higher in DCM subjects than healthy volunteers. However, the position of the vortex is farthest form LV outflow tract (LVOT), and this results in lower flow velocity in LVOT at AVO. This phenomenon is altered in patients with DCM. [Preview Abstract] |
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