Papers by H. S. Udaykumar
ASME 2012 Summer Bioengineering Conference, Parts A and B, 2012
ABSTRACT Analysis of blood as a two phase flow of densely packed finite size particles is a chall... more ABSTRACT Analysis of blood as a two phase flow of densely packed finite size particles is a challenging problem that requires a numerical approach that can efficiently and accurately handle large numbers of objects moving through a fluid. Numerical schemes such as the Arbitrary Lagrangian-Eulerian method (ALE), Distributed Lagrangian Multiplier (DLM) or the Immersed Boundary Method (IBM) are useful for simulating particulate flows. However, in the development of a multiscale framework where the dynamics of particles may be evolved at different scales, these methods may be too expensive for the desired resolution.
ASME 2012 Summer Bioengineering Conference, Parts A and B, 2012
Congenital Bicuspid Aortic Valve (BAV) is a valvular anomaly where a patient is born with a valve... more Congenital Bicuspid Aortic Valve (BAV) is a valvular anomaly where a patient is born with a valve with two leaflets instead of a normal tri-leaflet valve. It has also been reported that BAVs are prone to progressive calcification and also other complications such as ascending aortic dilatation, dissection and rupture [1]. The geometrical variations with the BAV may be a factor in altering the deformation and stresses on the leaflets resulting in calcification of the leaflets earlier than with normal tri-leaflet aortic valves. Altered flow patterns past BAV into the ascending aorta can also be anticipated. Analysis of flow dynamics during the opening phase, and the resultant fluid forces on the aortic root could improve our understanding of aortic aneurysms and dissections observed in patients with BAV [2]. In this study, the valvular deformation and the flow across a patient-specific BAV and root are simulated using the method of fluid structural interaction analysis. The patient-sp...
47th AIAA Aerospace Sciences Meeting including The New Horizons Forum and Aerospace Exposition, 2009
Shock waves interacting with multi-material interfaces in compressible flows result in complex sh... more Shock waves interacting with multi-material interfaces in compressible flows result in complex shock diffraction patterns involving total or partial reflection, refraction and transmission of the impinging shock wave. To simulate such complicated interfacial dynamics problems, a fixed Cartesian grid approach in conjunction with level set interface tracking is attractive. In this regard, a unified Riemann solver based Ghost Fluid Method (GFM) was developed to accurately resolve and represent the embedded solid and fluid object(s) in high speed compressible multiphase flows. While the GFM-based Cartesian grid approach significantly alleviates the complexity associated with mesh management, the method lacks flexibility in effective grid point placement in regions with rich structures in the flow field. Thus for higher-order and highly accurate sharp interface Cartesian grid based calculations with optimal computational effort, it is imperative to supplement the solution with adaptive mesh refinement technique. Hence in this work, a simple procedure is presented to complement the Riemann solver based GFM approach with quadtree (octree in three dimensions) based Local Mesh Refinement (LMR) technique for efficient and high fidelity computations involving strong shock interactions in multiphase compressible flows. The paper reports on a simple, conservative formulation for accurate calculation of ENO-based numerical fluxes at the fine-coarse mesh boundary. The numerical examples displayed in this paper clearly demonstrate that the methodology is consistent in generating satisfactory solutions, and effectively capturing fine structures in the flow.
Volume 1: Fora, Parts A, B, C, and D, 2003
Numerical simulations have been used to study the phenomenon of autorotation of a flat plate hing... more Numerical simulations have been used to study the phenomenon of autorotation of a flat plate hinged about its center in a freestream. The focus of the paper is on examining the effect of Reynolds number and plate thickness ratio on vortex induced rotation. The numerical solver employed is based on a sharp interface, Cartesian grid method that allows us to simulate flow with moving boundaries on stationary Cartesian grids. Simulations indicate that vortex shedding is the primary instigator of the plate motion and the transition from fluttering to autorotation depends on both these parameters.
ASME 2007 Summer Bioengineering Conference, 2007
ABSTRACT Hemodynamic forces have been proposed as a major factor in thrombosis (thrombus formatio... more ABSTRACT Hemodynamic forces have been proposed as a major factor in thrombosis (thrombus formation) in the human cardiovascular system [1]. It has been suggested that platelet activation, aggregation and adhesion to the surface of the implants result in the formation of the mural thrombi [2]. Red blood cells (RBCs) are thought to play a significant role in the dynamics and the activation of the platelets and hence thrombus formation in the human arterial system. Previous experimental works indicate that RBCs cause platelets to migrate and move toward the vessel walls [3]. Thrombus formation has also been shown to increase as the hematocrit (Hct) increases [4]. In order to simulate the platelet dynamics requires the computational analysis of the transport and collision of the formed elements under physiological flow. In the present study, a two-dimensional (2D) simulation of the RBC/platelet dynamics in the arterioles is described.
Advances in Bioengineering, 2002
Research has been conducted by the authors with the objective to produce a computational model th... more Research has been conducted by the authors with the objective to produce a computational model that will clearly display the coupled nature of the hemodynamics/fluid mechanics of blood flow and atherosclerotic plaque growth in the human carotid artery. The motivation for this investigation is the serious nature of atherosclerosis. Atherosclerosis is an inflammatory disease, which occurs in medium and large size arteries. Among the many effects stemming from the disease are heart attack, stroke, ischemia, and peripheral vascular disease. In healthy arteries, the collagen and elastin allow the artery to expand and contract with blood flow. This function enables the artery to maintain constant wall shear stress [1]. Plaque existence in the arterial wall results in decreased ductility of the wall, which inhibits the wall from maintaining constant shear stress. Plaque formations along the arterial wall then protrude into the artery, disturbing the blood flow. Characteristics of the fluid...
20th AIAA Computational Fluid Dynamics Conference, 2011
Shock waves interacting with heterogeneous materials are important in studies related to impact, ... more Shock waves interacting with heterogeneous materials are important in studies related to impact, penetration and detonation in condensed media, with applications in propulsive devices, munitions and explosive-target interactions. The study of release of energy is a crucial requirement in these systems. Traditional models for these applications are based on continuum theories where the microstructural heterogeneities of the material is ignored or homogenized. These simulations based on a continuum mechanics approach at the macro scale miss the key aspect of modeling energy release at a scale corresponding to particle size. Designing propulsion devices and munitions for precise operational performances demands comprehensive understanding and manipulation of the spatial and temporal distribution of energy release in activated energetic materials. Localized events, such as void collapse and inter-particle friction must be accounted for in detailed study of these materials. The proposed work seeks to develop a computational tool to conduct realistic modeling of the multi scale dynamics of shocked heterogeneous media. A key aspect of modeling energy deposition from activated energetic materials is that the fundamental mechanism of energy release manifests at the scale corresponding to particle size.
49th AIAA Aerospace Sciences Meeting including the New Horizons Forum and Aerospace Exposition, 2011
Shock Waves and Detonation waves have been topic of cutting edge research for decades. The intera... more Shock Waves and Detonation waves have been topic of cutting edge research for decades. The interaction of these waves with multi materials can result in complex wave structures in two and three dimensions. Large-scale computations are required to simulate physical phenomena involving detonation and shock waves like supernova formation, explosions and hypervelocity impact and penetration. In this paper we describe the parallel implementation of fixed Cartesian grid flow solver with moving boundaries. A higher order conservation scheme such as ENO is used for calculating the numerical fluxes and level sets are used to define the objects immersed in flow field. A Riemann solver based Ghost fluid method is used for interface treatment of embedded objects. This paper describes the methodology for parallelization with emphasis on strong shocks interacting with embedded interfaces (solid-fluid, solid-solid and fluidfluid) in three-dimensional compressible flow framework. It also explains the handling of moving boundaries in multi-processor environment and definition and treatment of ghost layer in three dimensions.
Physics of Fluids, 2004
Computational analysis of the deformability of leukocytes modeled with viscous and elastic struct... more Computational analysis of the deformability of leukocytes modeled with viscous and elastic structural components. [Physics of Fluids 16, 244 (2004)]. Saikrishna V. Marella, HS Udaykumar. Abstract. The objective of this work is ...
Physics of Fluids, 1998
We study the dynamics of a compound liquid drop which is comprised of an outer membrane surface, ... more We study the dynamics of a compound liquid drop which is comprised of an outer membrane surface, a shell layer, and a core. The deformation due to an imposed extensional flow and the subsequent recovery are investigated computationally employing a combined Eulerian-Lagrangian technique. The numerical method allows for large viscosity and capillarity differences between layers. The present study reports several findings which provide direct insight into developing a dynamic model for leukocytes. A compound drop behaves like a homogeneous, simple liquid drop if the core is sufficiently deformed and the time scale of the core, related to the combination of its viscosity and capillarity, is comparable to that of the shell layer. Disparate time scales between the core and shell layer result in a rapid initial recoil of the drop during which the shell fluid is the primary participant in the hydrodynamics, followed by a slower relaxation period during which the core and shell layer interact with each other. Consequently, the apparent viscosity of the drop depends not only on the rheological properties of the drop, but also on the flow dynamics surrounding it. The findings obtained with the three-layer compound drop model can explain several main characteristics of leukocytes reported in the literature. Furthermore, our study suggests that unless the presence and possible deformation of the nucleus are explicitly accounted for, neither Newtonian nor non-Newtonian models for leukocytes can adequately predict the hydrodynamics of leukocytes.
Numerical Heat Transfer, Part B: Fundamentals, 1998
We report on measures to improve the robustness and performance of a three-dimensional pressure-b... more We report on measures to improve the robustness and performance of a three-dimensional pressure-based multiblock algorithm. In particular, we demonstrate the implementation of the treatment at block interfaces for arbitrary orientations of the blocks and investigate the ...
Numerical Heat Transfer, Part B: Fundamentals, 1995
A mefhodo[ogy is presented lo simulate the growth and interaction of umtablefronts. Such fronts o... more A mefhodo[ogy is presented lo simulate the growth and interaction of umtablefronts. Such fronts ore found to be important in instabilities arising in several natural and indmtriul processes, such as solidificah'on, spray dywmics, and bubble growth. The numerical simulation of such phenome~ is challenging on account of the highly dirloried moving boundary at which, open, curvature-dependent boundary conditions need be applied in each phase. Herein is presented a numerical technique to capture highly distorted interfaces. llw interface is represented employing marker prtr'cles. Joining successiue markers with circular arcs yields values of curvatures and normals on the interjace. The markers are followed over an underlying Cartesian grid and new marker parh'cles are generated at each time step by an intersection procedure. The issue of mergers of inlerfaces is also anncked and the use of cells permits the simulation of merger-breakup processes. Thus, the method presented here, unlike previom marker particle-based schemes, eon handle pam'cle depletion /accumulation and merger / breakup issues with good accuracy. Resuhs are presented, employing oelocify jimdons modeled to mimic the actual imtabilily phmomem, to demomtraie the accuracy and capabiliry offhe scheme developed.
Numerical Heat Transfer, Part A: Applications, 1998
... This work has been partially supported by the US Air Force. We acknowledge continuous communi... more ... This work has been partially supported by the US Air Force. We acknowledge continuous communication and discussions with Dr. Dave Belk, Mr. Rudy Johnson, and Dr. Kirk Vanden of Eglin Air Force Base. Address correspondence to Prof. ...
Journal of Propulsion and Power, 2006
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Journal of Propulsion and Power, 1997
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Journal of Crystal Growth, 2006
Numerical simulations are performed to study the interaction of a solidification front with an em... more Numerical simulations are performed to study the interaction of a solidification front with an embedded particle. A sharp-interface method is used to track both the phase boundary and the particle. The solidification front dynamics is fully coupled with particle motion. The main objective of the paper is to distinguish the role played by the premelted layer between the solidification front and the particle in determining conditions for particle engulfment. Results are obtained by assuming a premelted layer exists in the gap between the particle and the solidification front and compared to those assuming no premelted layer. In the absence of a premelted layer, arbitrary cut-off values for particle-front gap thickness need to be invoked in order to define the critical velocity for which the pushing–engulfment transition occurs. When a premelted layer is assumed to exist, the prediction of the critical velocity is determined solely from the dynamics of the coupled front–particle interaction. In addition, model predictions for the critical velocity based on a steady-state heat transfer analysis are shown to differ from that when the full dynamics of the phase boundary are taken into account.
Journal of Computational Physics, 1992
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Journal of Computational Physics, 2003
A technique is presented for the numerical simulation of high-speed multimaterial impact. Of part... more A technique is presented for the numerical simulation of high-speed multimaterial impact. Of particular interest is the interaction of solid impactors with targets. The computations are performed on a fixed Cartesian mesh by casting the equations governing material deformation in Eulerian conservation law form. The advantage of the Eulerian setting is the disconnection of the mesh from the boundary deformation
Journal of Computational Physics, 2004
An Eulerian, sharp interface, Cartesian grid method is developed for the numerical simulation of ... more An Eulerian, sharp interface, Cartesian grid method is developed for the numerical simulation of the response of materials to impact, shocks and detonations. The mass, momentum, and energy equations are solved along with evolution equations for deviatoric stresses and equivalent plastic strain. These equations are cast in Eulerian conservation law form. The Mie-Gr€ u uneisen equation of state is used to obtain pressure and the material is modeled as a Johnson-Cook solid. The ENO scheme is employed to capture shocks in combination with a hybrid particle level set technique to evolve sharp immersed boundaries. The numerical technique is able to handle collisions between multiple materials and can accurately compute the dynamics of the immersed boundaries. Results of calculations for axisymmetric Taylor bar impact and penetration of a Tungsten rod into steel plate show good agreement with moving finite element solutions and experimental results. Qualitative agreement with theory is shown for the void collapse phenomenon in an impacted material containing a spherical void.
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Papers by H. S. Udaykumar