Browsing by Author "Basu, Saikat"
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- Development of a multiphase perfusion model for biomimetic reduced-order dense tumorsAkash, Mohammad Mehedi Hasan; Chakraborty, Nilotpal; Mohammad, Jiyan; Reindl, Katie; Basu, Saikat (Springer Nature, 2023-03)Dense fibrous extracellular constitution of solid tumors exerts high resistance to diffusive transport into it; additionally, the scarcity of blood and lymphatic flows hinders convection. The complexity of fluidic transport mechanisms in such tumor environments still presents open questions with translational end goals. For example, clinical diagnosis and targeted drug delivery platforms for such dense tumors can ideally benefit from a quantitative framework on plasma uptake into the tumor. In this study, we present a computational model for physical parameters that may influence blood percolation and penetration into simple biomimetic solid tumor geometry. The model implements three-phase viscous-laminar transient simulation to mimic the transport physics inside a tumor-adhering blood vessel and measures the constituent volume fractions of the three considered phases, viz. plasma, RBCs (red blood cells, also known as "erythrocytes "), and WBCs (white blood cells, also known as "leukocytes ") at three different flow times, while simultaneously recording the plasma pressure and velocity at the entry point to the tumor's extracellular space. Subsequently, to quantify plasma perfusion within the tumor zone, we proposed a reduced-order two-dimensional transport model for the tumor entry zone and its extracellular space for three different fenestra diameters: 0.1, 0.3, and 0.5 mu m; the simulations were two-phase viscous-laminar transient. The findings support the hypothesis that plasma percolation into the tumor is proportional to the leakiness modulated by the size of fenestra openings, and the rate of percolation decays with the diffusion distance.
- Dynamics of vortices in complex wakes: modeling, analysis, and experimentsBasu, Saikat (Virginia Tech, 2014-05-01)The thesis develops singly-periodic mathematical models for complex laminar wakes which are formed behind vortex-shedding bluff bodies. These wake structures exhibit a variety of patterns as the bodies oscillate or are in close proximity of one another. The most well-known formation comprises two counter-rotating vortices in each shedding cycle and is popularly known as the vk vortex street. Of the more complex configurations, as a specific example, this thesis investigates one of the most commonly occurring wake arrangements, which consists of two pairs of vortices in each shedding period. The paired vortices are, in general, counter-rotating and belong to a more general definition of the 2P mode, which involves periodic release of four vortices into the flow. The 2P arrangement can, primarily, be sub-classed into two types: one with a symmetric orientation of the two vortex pairs about the streamwise direction in a periodic domain and the other in which the two vortex pairs per period are placed in a staggered geometry about the wake centerline. The thesis explores the governing dynamics of such wakes and characterizes the corresponding relative vortex motion. In general, for both the symmetric as well as the staggered four vortex periodic arrangements, the thesis develops two-dimensional potential flow models (consisting of an integrable Hamiltonian system of point vortices) that consider spatially periodic arrays of four vortices with their strengths being +/-1 and +/-2. Vortex formations observed in the experiments inspire the assumed spatial symmetry. The models demonstrate a number of dynamic modes that are classified using a bifurcation analysis of the phase space topology, consisting of level curves of the Hamiltonian. Despite the vortex strengths in each pair being unequal in magnitude, some initial conditions lead to relative equilibrium when the vortex configuration moves with invariant size and shape. The scaled comparisons of the model results with experiments conducted in a flowing soap film with an airfoil, which was imparted with forced oscillations, are satisfactory and validate the reduced order modeling framework. The experiments have been performed by a collaborator group at the Department of Physics and Fluid Dynamics at the Technical University of Denmark (DTU), led by Dr. Anders Andersen. Similar experiments have also been run at Virginia Tech as part of this dissertation and the preliminary results are included in this treatise. The thesis also employs the same dynamical systems techniques, which have been applied to study the 2P regime dynamics, to develop a mathematical model for the P+S mode vortex wakes, with three vortices present in each shedding cycle. The model results have also been compared favorably with an experiment and the predictions regarding the vortex circulation data match well with the previous results from literature. Finally, the thesis introduces a novel concept of clean and renewable energy extraction from vortex-induced vibrations of bluff bodies. The slow-moving currents in the off-shore marine environments and riverine flows are beyond the operational capabilities of the more established hydrokinetic energy converters and the discussed technology promises to be a significant tool to generate useful power from these copiously available but previously untapped sources.