Bulletin of the American Physical Society
68th Annual Meeting of the APS Division of Fluid Dynamics
Volume 60, Number 21
Sunday–Tuesday, November 22–24, 2015; Boston, Massachusetts
Session H24: Biofluids: Cardiovascular Fluid Dynamics I |
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Chair: Michael Plesniak, Washington University Room: 302 |
Monday, November 23, 2015 10:35AM - 10:48AM |
H24.00001: Secondary flow structure in a model curved artery: 3D morphology and circulation budget analysis Kartik V Bulusu, Michael W Plesniak In this study, we examined the rate of change of circulation within control regions encompassing the large-scale vortical structures associated with secondary flows, i.e. deformed Dean-, Lyne- and Wall-type (D-L-W) vortices at planar cross-sections in a 180$^{\circ}$ curved artery model (curvature ratio, 1/7). Magnetic resonance velocimetry (MRV) and particle image velocimetry (PIV) experiments were performed independently, under the same physiological inflow conditions (Womersley number, 4.2) and using Newtonian blood-analog fluids. The MRV-technique performed at Stanford University produced phase-averaged, three-dimensional velocity fields. Secondary flow field comparisons of MRV-data to PIV-data at various cross-sectional planes and inflow phases were made. A wavelet-decomposition-based approach was implemented to characterize various secondary flow morphologies. We hypothesize that the persistence and decay of arterial secondary flow vortices is intrinsically related to the influence of the out-of-plane flow, tilting, in-plane convection and diffusion-related factors within the control regions. Evaluation of these factors will elucidate secondary flow structures in arterial hemodynamics. [Preview Abstract] |
Monday, November 23, 2015 10:48AM - 11:01AM |
H24.00002: A Mixed Approach for Modeling Blood Flow in Brain Microcirculation Sylvie Lorthois, Myriam Peyrounette, Yohan Davit, Michel Quintard Consistent with its distribution and exchange functions, the vascular system of the human brain cortex is a superposition of two components. At small-scale, a homogeneous and space-filling mesh-like capillary network. At large scale, quasi-fractal branched veins and arteries. From a modeling perspective, this is the superposition of: (a) a continuum model resulting from the homogenization of slow transport in the small-scale capillary network; and (b) a discrete network approach describing fast transport in the arteries and veins, which cannot be homogenized because of their fractal nature. This problematic is analogous to fast conducting wells embedded in a reservoir rock in petroleum engineering. An efficient method to reduce the computational cost is to use relatively large grid blocks for the continuum model. This makes it difficult to accurately couple both components. We solve this issue by adapting the “well model” concept used in petroleum engineering to brain specific 3D situations. We obtain a unique linear system describing the discrete network, the continuum and the well model. Results are presented for realistic arterial and venous geometries. The mixed approach is compared with full network models including various idealized capillary networks of known permeability. [Preview Abstract] |
Monday, November 23, 2015 11:01AM - 11:14AM |
H24.00003: Automated Tuning for Parameter Identification in Multi-Scale Coronary Simulations Justin Tran, Daniele Schiavazzi, Abhay Ramachandra, Andrew Kahn, Alison Marsden Computational simulations of coronary flow can provide non-invasive information on hemodynamics that can aid in disease research. In this study, patient-specific geometries are constructed and combined with finite element flow simulations using the open source software SimVascular. Lumped parameter networks (LPN), consisting of circuit representations of hemodynamic behavior, can be used as coupled boundary conditions for the flow solver. The parameters of the LPN are tuned so the outputs match a patient's clinical data. However, the parameters are usually manually tuned, which is time consuming and does not account for uncertainty in the measurements. We thus propose a Bayesian approach to parameter tuning that provides optimal parameter statistics through sampling from their posterior distribution and is particularly well suited for models characterized by a large number of parameters and scarce data. We also show that analysis of the local and global identifiability play an important role for dimensionality reduction in the estimation. We present the results of applying the proposed approach to a cohort of patients, and demonstrate the ability to match high priority targets. After identifying the LPN parameters for each patient, we demonstrate their use in 3D simulations. [Preview Abstract] |
Monday, November 23, 2015 11:14AM - 11:27AM |
H24.00004: Validity of computational hemodynamics in human arteries based on 3D time-of-flight MR angiography and 2D electrocardiogram gated phase contrast images Huidan (Whitney) Yu, Xi Chen, Rou Chen, Zhiqiang Wang, Chen Lin, Stephen Kralik, Ye Zhao In this work, we demonstrate the validity of 4-D patient-specific computational hemodynamics (PSCH) based on 3-D time-of-flight (TOF) MR angiography (MRA) and 2-D electrocardiogram (ECG) gated phase contrast (PC) images. The mesoscale lattice Boltzmann method (LBM) is employed to segment morphological arterial geometry from TOF MRA, to extract velocity profiles from ECG PC images, and to simulate fluid dynamics on a unified GPU accelerated computational platform. Two healthy volunteers are recruited to participate in the study. For each volunteer, a 3-D high resolution TOF MRA image and 10 2-D ECG gated PC images are acquired to provide the morphological geometry and the time-varying flow velocity profiles for necessary inputs of the PSCH. Validation results will be presented through comparisons of LBM vs. 4D Flow Software for flow rates and LBM simulation vs. MRA measurement for blood flow velocity maps. [Preview Abstract] |
Monday, November 23, 2015 11:27AM - 11:40AM |
H24.00005: Sharp Interface Methods for Cardiac Fluid-Solid Interaction Ebrahim M. Kolahdouz, Benjamin L. Vadala-Roth, Amneet P. S Bhalla, Boyce E. Griffith Fluid-solid systems are common in scientific and engineering applications. The immersed boundary (IB) method is a general approach to simulating fluid-structure interaction (FSI) in such systems, but a difficulty of the IB formulation of these problems is that the pressure and viscous stress are generally discontinuous at fluid-solid interfaces. The immersed interface (II) method is an IB-like approach to FSI that exactly imposes stress jump conditions, but this method has largely been limited to FSI problems involving thin elastic boundaries. We present extensions of the IB method that sharply resolve stress discontinuities at fluid-solid interfaces that can be viewed as extensions of the immersed interface method to non-interfacial (codimension-0) solid bodies, and the application of these methods to cardiovascular FSI, including the dynamics of the cardiac valves. [Preview Abstract] |
Monday, November 23, 2015 11:40AM - 11:53AM |
H24.00006: ABSTRACT WITHDRAWN |
Monday, November 23, 2015 11:53AM - 12:06PM |
H24.00007: Accuracy and Robustness Improvements of Echocardiographic Particle Image Velocimetry for Routine Clinical Cardiac Evaluation Brett Meyers, Pavlos Vlachos, John Charonko, Matthew Giarra, Craig Goergen Echo Particle Image Velocimetry (echoPIV) is a recent development in flow visualization that provides improved spatial resolution with high temporal resolution in cardiac flow measurement. Despite increased interest a limited number of published echoPIV studies are clinical, demonstrating that the method is not broadly accepted within the medical community. This is due to the fact that use of contrast agents are typically reserved for subjects whose initial evaluation produced very low quality recordings. Thus high background noise and low contrast levels characterize most scans, which hinders echoPIV from producing accurate measurements. To achieve clinical acceptance it is necessary to develop processing strategies that improve accuracy and robustness. We hypothesize that using a short-time moving window ensemble (MWE) correlation can improve echoPIV flow measurements on low image quality clinical scans. To explore the potential of the short-time MWE correlation, evaluation of artificial ultrasound images was performed. Subsequently, a clinical cohort of patients with diastolic dysfunction was evaluated. Qualitative and quantitative comparisons between echoPIV measurements and Color M-mode scans were carried out to assess the improvements delivered by the proposed methodology. [Preview Abstract] |
Monday, November 23, 2015 12:06PM - 12:19PM |
H24.00008: Strategies for Pile-up and Over-refinement to improve performance of the Surrogate Management Framework in cardiovascular flow optimization Aekaansh Verma, Alison Marsden Engineering optimization problems are often limited by the cost of function evaluations. Furthermore, calculation of gradients in such problems can be expensive or even infeasible. Derivative free optimization methods such as variants of the Surrogate Management Framework (SMF) are suitable for such problems, and offer a well-established convergence theory. The SMF is comprised of a search step that is accelerated by a surrogate-based global search, typically using Kriging. Traditionally, Kriging-based SMF develop problems during the course of the optimization which affect both global and local search performance. We propose strategies to alleviate two such issues - pile-up of evaluations in a certain region in parameter space and improper refinement of the local search grid. We quantify the performance of these strategies on analytical test cases and discuss the mechanisms of improvement. Finally, we apply these strategies to some illustrative problems in cardiovascular blood flow simulations and growth and remodeling. [Preview Abstract] |
Monday, November 23, 2015 12:19PM - 12:32PM |
H24.00009: 4D-Flow validation, numerical and experimental framework Kurt Sansom, Haining Liu, Gador Canton, Alberto Aliseda, Chun Yuan This work presents a group of assessment metrics of new 4D MRI flow sequences, an imaging modality that allows for visualization of three-dimensional pulsatile flow in the cardiovascular anatomy through time-resolved three-dimensional blood velocity measurements from cardiac-cycle synchronized MRI acquisition. This is a promising tool for clinical assessment but lacks a robust validation framework. First, 4D-MRI flow in a subject's stenotic carotid bifurcation is compared with a patient-specific CFD model using two different boundary condition methods. Second, Particle Image Velocimetry in a patient-specific phantom is used as a benchmark to compare the 4D-MRI in vivo measurements and CFD simulations under the same conditions. Comparison of estimated and measureable flow parameters such as wall shear stress, fluctuating velocity rms, Lagrangian particle residence time, will be discussed, with justification for their biomechanics relevance and the insights they can provide on the pathophysiology of arterial disease: atherosclerosis and intimal hyperplasia. Lastly, the framework is applied to a new sequence to provide a quantitative assessment. A parametric analysis on the carotid bifurcation pulsatile flow conditions will be presented and an accuracy assessment provided. [Preview Abstract] |
Monday, November 23, 2015 12:32PM - 12:45PM |
H24.00010: Experimental and Computational In Vitro Models of Left Ventricular Fluid Dynamics Arvind Santhanakrishnan, Milad Samaee, Jae Ho Lee, Amneet P. S. Bhalla, Boyce E. Griffith Computational fluid dynamics (CFD) and fluid-structure interaction (FSI) models of the heart promise to accelerate the design, testing, and regulatory approval of cardiovascular devices, but rigorous validation is required before such models can be used to design, optimize, or test device designs, or to customize patient treatment strategies. Obstacles to validation include difficulties in obtaining high-resolution in vivo data from healthy volunteers and patients and knowledge of in vivo loads and material parameters. In vitro platforms can provide a more controllable approach to obtaining high-resolution experimental data to use in the testing, development, and validation of cardiac and cardiovascular FSI models. We describe an experimental in vitro model of left ventricular fluid dynamics and progress towards using these models to validate computational models of left ventricular fluid dynamics based on the immersed boundary method. [Preview Abstract] |
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