Bulletin of the American Physical Society, Nov 21, 2005
Submitted for the DFD05 Meeting of The American Physical Society The Hemodynamics of Total Cavo-P... more Submitted for the DFD05 Meeting of The American Physical Society The Hemodynamics of Total Cavo-Pulmonary Connection Anatomies 1 CHANG WANG, Georgia Institute of Technology, ANVAR GILMANOV, LIANG GE, FOTIS SOTIROPOULOS, AJIT YOGANATHAN-The single ventricle is a congenital heart defect in which the right side of the heart is hypoplastic or totally absent. This anomaly results in mixing of the oxygenated and deoxygenated blood in the single ventricle, reducing the amount of oxygen transferred to the body. In U.S. two in 1000 babies are born with a single ventricle heart defect. Palliative surgical treatments are performed in stages as the child grows. The last stage is the total cavo-pulmonary connection (TCPC), which bypasses the right side of the heart and the single ventricle drives blood throughout the pulmonary and systemic circulations. We simulate the flow in two TCPC anatomies using a sharp-interface, hybrid Cartesian/Immersed Boundary approach. The computed solutions are compared with PIV in-vitro experiments and analyzed in detail to elucidate the richness of the hemodynamics in the surgically create pouch region where the inferior and superior vena cava flows collide and bifurcate into the left and right pulmonary arteries. The effect of the connection anatomy on the flow dynamics will also be discussed.
Submitted for the DFD14 Meeting of The American Physical Society On the wake dynamics of flapping... more Submitted for the DFD14 Meeting of The American Physical Society On the wake dynamics of flapping inverted flags 1 ANVAR GILMANOV, FOTIS SOTIROPOULOS, Univ of Minn-Minneapolis, JULIA COSSE, MORY GHARIB, California Institute of Technology-As recently shown experimentally by Kim et al. (JFM, 2013), when a flexible flag with a fixed trailing edge (an inverted flag) is exposed to a uniform inflow it can exhibit complex structural response and rich fluid-structure interaction (FSI) dynamics. We employ a new FSI numerical method to carry out large-eddy simulation (LES) of inverted flags in the range where large-amplitude flapping instabilities have been found experimentally. The numerical method integrates the curvilinear immersed boundary (CURVIB) FSI method of Borazjani et al. (JCP, 2008) with the thin-shell, rotationfree, finite-element (FE) formulation of Stolarski et al. (Int. JNME, 2013) and is able to simulate FSI of flexible thin bodies undergoing oscillations of arbitrarily large amplitude. The dynamic Smagorinsky model is employed for subgrid scale closure and a wall model is employed for reconstructing velocity boundary conditions. Comparisons with the experimental data show that the simulations are able to capture the structural response of the flag with very good accuracy. The computed results are analyzed to elucidate the structure and dynamics of the massively separated, unsteady flow shed off the flag edges.
In the present note a general reconstruction algorithm for simulating incompressible flows with c... more In the present note a general reconstruction algorithm for simulating incompressible flows with complex immersed boundaries on Cartesian grids is presented. In the proposed method an arbitrary three-dimensional solid surface immersed in the fluid is discretized using an unstructured, triangular mesh, and all the Cartesian grid nodes near the interface are identified. Then, the solution at these nodes is reconstructed via linear interpolation along the local normal to the body, in a way that the desired boundary conditions for both pressure and velocity fields are enforced. The overall accuracy of the resulting solver is second-order, as it is demonstrated in two test cases involving laminar flow past a sphere.
We present a new numerical methodology for simulating fluid-structure interaction (FSI) problems ... more We present a new numerical methodology for simulating fluid-structure interaction (FSI) problems involving thin flexible bodies in an incompressible fluid. The FSI algorithm uses the Dirichlet-Neumann partitioning technique. The curvilinear immersed boundary method (CURVIB) is coupled with a rotation-free finite element (FE) model for thin shells enabling the efficient simulation of FSI problems with arbitrarily large deformation. Turbulent flow problems are handled using largeeddy simulation with the dynamic Smagorinsky model in conjunction with a wall model to reconstruct boundary conditions near immersed boundaries. The CURVIB and FE solvers are coupled together on the flexible solid-fluid interfaces where the structural nodal positions, displacements, velocities and loads are calculated and exchanged between the two solvers. Loose and strong coupling FSI schemes are employed enhanced by the Aitken acceleration technique to ensure robust coupling and fast convergence especially for low mass ratio problems. The coupled CURVIB-FE-FSI method is validated by applying it to simulate two FSI problems involving thin flexible structures: 1) vortex-induced vibrations of a cantilever mounted in the wake of a square cylinder at different mass ratios and at low Reynolds number; and 2) the more challenging high Reynolds number problem involving the oscillation of an inverted elastic flag. For both cases the computed results are in excellent agreement with previous numerical simulations and/or experiential measurements. Grid convergence tests/studies are carried out for both the cantilever and inverted flag problems, which show that the CURVIB-FE-FSI method provides their convergence. Finally, the capability of the new methodology in simulations of complex cardiovascular flows is demonstrated by applying it to simulate the FSI of a trileaflet, prosthetic heart valve in an anatomic aorta and under physiologic pulsatile conditions.
Virtual Flow Simulator (VFS) is a state-of-the-art computational fluid mechanics (CFD) package th... more Virtual Flow Simulator (VFS) is a state-of-the-art computational fluid mechanics (CFD) package that is capable of simulating multi-physics/multi-phase flows with the most advanced turbulence models (RANS, LES) over complex terrains. The flow solver is based on the Curvilinear Immersed Boundary (CURVIB) method to handle geometrically complex and moving domains. Different modules of the VFS package can provide different simulation capabilities for specific applications ranging from the fluid-structure interaction (FSI) of solid and deformable bodies, the two-phase free surface flow solver based on the level set method for ocean waves, sediment transport models in rivers and the large-scale models of wind farms based on actuator lines and surfaces. All numerical features of VFS package have been validated with known analytical and experimental data as reported in the related journal articles. VFS package is suitable for a broad range of engineering applications within different industries. VFS has been used in different projects with applications in wind and hydrokinetic energy, offshore and near-shore ocean studies, cardiovascular and biological flows, and natural streams and river morphodynamics. Over the last decade, the development of VFS has been supported and assisted with the help of various United States companies and federal agencies that are listed in the sponsor lists. In this version, VFS-Wind contains all the necessary modeling tools for wind energy applications, including land-based and offshore wind farms. VFS is highly scalable to run on either desktop computers or high performance clusters (up to 16,000 CPUs). This released version comes with a detailed user's manual and a set of case studies designed to facilitate the learning of the various aspects of the code in a comprehensive manner. The included documentation and support material has been elaborated in a collaboration effort with Sandia National Labs under the contract DE-EE0005482. The VFS-Wind source code is distributed under the GNU General [...]
Coupling the Curvilinear Immersed Boundary Method with Rotation-Free Finite Elements for Simulating Fluid–Structure Interaction: Concepts and Applications
The sharp interface curvilinear immersed boundary (CURVIB) method coupled with a rotation-free fi... more The sharp interface curvilinear immersed boundary (CURVIB) method coupled with a rotation-free finite element (FE) method for thin shells provides a powerful framework for simulating fluid–structure interaction (FSI) problems for geometrically complex, arbitrarily deformable structures. The CURVIB and FE solvers are coupled together on the flexible solid–fluid interfaces, which contain the structural nodal positions, displacements, velocities, and loads calculated at each time level and exchanged between the flow and structural solvers. Loose and strong coupling FSI schemes are employed, enhanced by the Aitken acceleration technique to ensure robust coupling and fast convergence, especially for low mass ratio problems. Large-eddy simulation (LES) of turbulent flow FSI problems employ the dynamic Smagorinsky subgrid scale model with a wall model for reconstructing velocity boundary conditions near the immersed boundaries. In this chapter, the CURVIB-FE FSI algorithm is reviewed and i...
Hydrodynamics of Planktonic Microcrustacean Locomotion: Turning Wake Vortices into Communication Signals
It has long been hypothesized that aquatic microcrustaceans, such as planktonic copepods, are abl... more It has long been hypothesized that aquatic microcrustaceans, such as planktonic copepods, are able to distinguish an attractive mate from a lunging predator by sensing their respective hydrodynamic signatures in the form of coherent vortical structures. We develop a hybrid Cartesian/Immersed-Boundary numerical method for simulating the flow around a swimming copepod. A realistic copepod-like body is constructed, which includes most important parts of the animals anatomy: the antenulles, legs, and tail. The kinematics of the individual body parts are prescribed using laboratory observations and measurements. We will report numerical simulations for a copepod advancing at steady velocity over a range of Reynolds numbers, 10<Re<300. The computed flowfields will be analyzed to elucidate the structure and dynamics of the coherent vortices shed by the copepod, quantify the persistence of these vortices in the wake, and explore hypotheses about the possible role of coherent hydrodynamic structures as communication signals.
Application of dynamically adaptive grids to the analysis of flows with a multiscale structure
Computational Mathematics and Mathematical Physics, 2001
Dynamically adaptive grids combined with a high-order TVD scheme are applied to time-independent ... more Dynamically adaptive grids combined with a high-order TVD scheme are applied to time-independent and time-dependent problems of supersonic inviscid and high-Reynolds-number viscous flows. The adaptive grids employed include moving and nested grids.
A non-boundary conforming method for unsteady incompressible flows with moving boundaries
ABSTRACT In the present study a methodology to perform simulations of three-dimensional unsteady ... more ABSTRACT In the present study a methodology to perform simulations of three-dimensional unsteady incompressible flows around complex moving boundaries on fixed Cartesian grids is presented. With this approach boundary conditions on a moving body which does not coincide with the grid are imposed through local reconstructions of the solution in the vicinity of the boundary. To facilitate this process a three-dimensional interface tracking methodology coupled with a novel local reconstruction scheme has been developed. The method allows for a precise imposition of the boundary conditions without affecting the stability of the solver. A detailed study on the accuracy and efficiency of the method is presented for laminar flow around a circular cylinder, a sphere, and fully developed turbulent flow in a plane channel with a wavy wall. It is demonstrated that the method is second-order accurate, and that the solid boundaries are mimicked exactly on the Cartesian grid within the accuracy of the scheme. For all cases under consideration the results obtained are in very good agreement with analytical and numerical data.
INTRODUCTION In spite of significant recent advances in imaging modalities for studying cardiac h... more INTRODUCTION In spite of significant recent advances in imaging modalities for studying cardiac hemodynamics, present day in vivo measurement techniques can only resolve large scale blood flow features. Understanding flow patterns in the heart at physiological conditions and scales sufficiently fine for establishing quantitatively links between disease and patientspecific hemodynamics continues to remain a major research challenge. For instance, in vitro experiments and FSI computational studies have clearly shown that at physiological conditions the presence of a prosthetic heart valve gives rise to complex flow patterns characterized by fine scale flow structures and transition to turbulence. This complex and dynamically rich flow environment is widely believed to be a major culprit for the clinical complications that arise following implantation of valve prosthesis. High-resolution numerical simulation appears to be the only viable option for advancing our understanding of cardia...
CFD-AB User Manual for simulation of fish swimming through navigation dams
The threat of invasive bigheaded carp swimming into the upper reaches of the Mississippi River (U... more The threat of invasive bigheaded carp swimming into the upper reaches of the Mississippi River (USA) demands new and effective approaches to blocking these species. To explore how navigational Lock and Dams (LDs) on the Mississippi River could be used to deter the upstream migration of invasive fish species, computer modelling that combined computational fluid dynamics (CFD) and agent-based (AB) fish passage model (CFD-AB model) could be used to hypothetically quantify the passage of bigheaded carp (Hypophthalmichthys spp.) through LDs (Zielinski, et al., 2018). Agent-based fish (AB-fish) in the original algorithm of (Zielinski, et al., 2018) are always located on a node of the CFD mesh and move by selecting the neighboring node that minimizes fatigue. A possible limitation of this approach is that the AB-fish movement exhibits a dependence upon the CFD mesh. The modified approach (Gilmanov, et al., 2019) allows the AB-fish to occupy any point in the computational domain and to cont...
The threat of invasive bigheaded carp swimming into the upper reaches of the Mississippi River (U... more The threat of invasive bigheaded carp swimming into the upper reaches of the Mississippi River (USA) demands new and effective approaches to block these species. To explore how navigational Lock and Dams (LDs) on the Mississippi River could be used to deter the upstream migration of invasive fish species, computer modelling that combined computational fluid dynamics (CFD) and agent-based (AB) fish passage model (CFD-AB model) could be used to hypothetically quantify the passage of bigheaded carp (Hypophthalmichthys spp.) through LDs. Agent-based fish (AB-fish) are always located on a node of the CFD mesh and move by selecting the neighboring node that minimizes fatigue. A possible limitation of this approach is that the AB-fish movement exhibits a dependence upon the CFD mesh. The proposed modified approach allows the AB-fish to occupy any point in the computational domain and to continually (within the size of the time step) update their minimum fatigue path. Computations in a simp...
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