Between Dec 19, 2024 and Jan 2, 2025, datasets can be submitted to DRUM but will not be processed until after the break. Staff will not be available to answer email during this period, and will not be able to provide DOIs until after Jan 2. If you are in need of a DOI during this period, consider Dryad or OpenICPSR. Submission responses to the UDC may also be delayed during this time.

Browsing by Subject "Fluid-structure interactions"

Now showing 1 - 2 of 2
  • Thumbnail Image
    Item
    Biomechanical characterization and computational modeling of the anterior eye
    (2013-02) Jouzdani, Sara
    Glaucoma is the second leading cause of blindness worldwide. Certain types of glaucoma are directly related to the iris contour. For example, in primary angle closure glaucoma (ACG), the iris is positioned abnormally to the anterior. In my research project, I tried to reveal the mechanisms underlying iris contour abnormalities using a combination of computational and experimental studies. The iris contour is determined by the balance of three forces: muscular contractions, iris elastic responses, and hydrodynamic forces. The iris muscular forces arise from activation of the iris constituent muscles while the elastic forces are the result of passive mechanical behavior of the iris. Unlike the other two forces that are generated by the iris, the hydrodynamic forces are caused by the continuous flow of the aqueous humor (AH) in the anterior eye. An accurate and predictive computational model, which could provide insights into pathophysiology of glaucoma and possibly lead to novel therapeutic strategies, must accounts for all of the three elements contributing to the iris contour. As part of the continues investigations in Dr. Barocas’s lab at the University of Minnesota, the main purposes of this study were (1) to characterize the passive mechanical properties of the iris, (2) to characterize iris-related risk factors to ACG using anterior segment optical coherence tomography (AS-OCT) technique, and (3) to develop a computational model of the iris-aqueous-humor interaction in the anterior eye during dilation. The iris is composed of three constituent components: the stroma, the sphincter iridis, and the dilator pupillae. To quantify the relative stiffness of different sections of the iris, mechanical indentation tests and histological analysis in combination with a three- dimensional finite element (FE) simulation were performed. The iris was divided into three regions and the indentation tests were performed on both anterior and posterior sides of porcine irides. The effective moduli and viscoelastic parameters for all regions were calculated. Three-dimensional anatomically accurate models of iris indentation were generated in ABAQUS, based on histological data. An inverse method was developed to determine depth-dependent elastic properties of the iris by comparing experimental results and FE predictions. The study outcomes supported the hypothesis that the posterior layer was the stiffest and produced larger force with increasing depth. In addition to the differences in their passive stiffness, the iris constituent components also differ in their physiological function and/or pathophysiological roles. For example, there is clinical evidence that in high-risk patients, pupil dilation, caused by relaxation of sphincter iridis and contraction of dilator pupillae, can lead to acute ACG or exacerbate chronic ACG. To study such risk factors, experimental and computational studies were performed. In the experimental study, twenty normal subjects underwent complete ophthalmic examination and AS-OCT in a controlled-light study. Dynamic changes of the anterior chamber and the iris configuration were captured during light-to-dark (dilation) and dark-to-light (constriction) conditions in a series of AS-OCT images. The relationship between iris parameters (like iris volume) and anterior chamber parameters (like anterior chamber angle and anterior chamber volume) with changes of pupil diameter were evaluated. We observed a decrease (increase) in iris volume and anterior chamber angle during dilation (constriction), and no significant change in anterior chamber volume. The results of this experimental study emphasized the idea that relative compressibility of the iris and dynamic pupillary block play important roles in angle closure mechanism. Furthermore, a mathematical model of the anterior segment was developed to study ACG risk factors. In a fluid-solid interaction model of the anterior segment, the contribution of three anatomical and physiological factors (dilator thickness, AH blockage, and iris compressibility) to changes in anterior chamber angle during pupil dilation was investigated. The model predicted that iris bowing during dilation was driven primarily by posterior location of the dilator muscle and aqueous humor blockage. The model also predicted that the risk of ACG during dilation increased with iris incompressibility, a result consistent with several clinical observations.
  • Thumbnail Image
    Item
    Numerical Simulations of the Two-phase flow and Fluid-Structure Interaction Problems with Adaptive Mesh Refinement
    (2022-03) Zeng, Yadong
    Numerical simulations of two-phase flow and fluid structure interaction problems are of great interest in many environmental problems and engineering applications. To capture the complex physical processes involved in these problems, a high grid resolution is usually needed. However, one does not need or maybe cannot afford a fine grid of uniformly high resolution across the whole domain. The need to resolve local fine features can be addressed by the adaptive mesh refinement (AMR) method, which increases the grid resolution in regions of interest as needed during the simulation while leaving general estimates in other regions. In this work, we propose a block-structured adaptive mesh refinement (BSAMR) framework to simulate two-phase flows using the level set (LS) function with both the subcycling and non-subcycling methods on a collocated grid. To the best of our knowledge, this is the first framework that unifies the subcycling and non-subcycling methods to simulate two-phase flows. The use of the collocated grid is also the first among the two-phase BSAMR framework, which significantly simplifies the implementation of multi-level differential operators and interpolation schemes. We design the synchronization operations, including the averaging, refluxing, and synchronization projection, which ensures that the flow field is divergence-free on the multi-level grid. It is shown that the present multi-level scheme can accurately resolve the interfaces of the two-phase flows with gravitational and surface tension effects while having good momentum and energy conservation. We then develop another consistent scheme, in which the conservative momentum equations and the mass equation are solved in the aforementioned BSAMR framework. This consistent mass and momentum transport treatment greatly improves the accuracy and robustness for simulating two-phase flows with a high density ratio and high Reynolds number. We demonstrate that the consistent scheme results in a numerically stable solution in flows with high density ratios~(up to $10^6$) and high Reynolds numbers~(up to $10^6$), while the inconsistent scheme exhibits nonphysical fluid behaviors in these tests. For solving single- and multiphase fluid-structure interaction (FSI) problems, we present an adaptive implementation of the distributed Lagrange multiplier (DLM) immersed boundary (IB) method on multilevel collocated grids. We also developed a force-averaging algorithm to maintain the consistency of Eulerian immersed boundary (IB) forces across multiple levels. The efficacy of the force averaging algorithm is validated using the lid-driven cavity with a submerged cylinder problem. We demonstrate the versatility of the present multilevel framework by simulating problems with various types of kinematic constraints imposed by structures on fluids, such as imposing a prescribed motion, free motion, and time-evolving shape of a solid body. The accuracy and robustness of the codes are validated using several canonical test problems.