Surface-Only Simulation of Fluids

Surface-only simulation methods for fluid dynamics are those that perform computation only on a surface representation, without relying on any volumetric discretization. Such methods have superior asymptotic complexity in time and memory than the traditional volumetric discretization approaches, and thus are more tractable for simulation of complex fluid phenomena. Although for most computer graphics applications and many engineering applications, the interior flow inside the fluid phases is typically not of interest, the vast majority of existing numerical techniques still rely on discretization of the volumetric domain. My research first tackles the mesh-based surface tracking problem in the multimaterial setting, and then proposes surface-only simulation solutions for two scenarios: the soap-films and bubbles, and the general 3D liquids. Throughout these simulation approaches, all computation takes place on the surface, and volumetric discretization is entirely eliminated

Culinary fluid mechanics and other currents in food science

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Star-shaped bubbles and cubic feces: geometry through soft matter

In this thesis, we consider how mammals use soft tissue to generate geometric shapes out of non-living materials. The star-nosed mole sniffs for prey underwater by rapidly exhaling and inhaling bubbles without letting the bubbles pinch off. The bare-nosed wombat forms cubic feces, displaying 6 flat sides and 8 rounded corners. We develop mathematical models supported by simple table-top experiments to better understand how these mammals accomplish such amazing feats. These species control the fluids through interactions with solid tissue. Understanding these interactions could lead to innovations in chemical sensing and manufacturing.Ph.D

Multimaterial Mesh-Based Surface Tracking

© ACM, 2014. This is the author's version of the work. It is posted here by permission of ACM for your personal use. Not for redistribution. The definitive version was published in Da, F., Batty, C., & Grinspun, E. (2014). Multimaterial Mesh-Based Surface Tracking. Acm Transactions on Graphics, 33(4), 112. https://doi.org/10.1145/2601097.2601146We present a triangle mesh-based technique for tracking the evolution of three-dimensional multimaterial interfaces undergoing complex deformations. It is the first non-manifold triangle mesh tracking method to simultaneously maintain intersection-free meshes and support the proposed broad set of multimaterial remeshing and topological operations. We represent the interface as a non-manifold triangle mesh with material labels assigned to each half-face to distinguish volumetric regions. Starting from proposed application-dependent vertex velocities, we deform the mesh, seeking a non-intersecting, watertight solution. This goal necessitates development of various collision-safe, label-aware non-manifold mesh operations: multimaterial mesh improvement; T1 and T2 processes, topological transitions arising in foam dynamics and multiphase flows; and multimaterial merging, in which a new interface is created between colliding materials. We demonstrate the robustness and effectiveness of our approach on a range of scenarios including geometric flows and multiphase fluid animation.This work was supported in part by the NSF (Grants IIS-1319483, CMMI-1331499, IIS-1217904, IIS-1117257, CMMI-1129917, IIS-0916129), the Israel-US Binational Science Founda-tion, the Natural Sciences and Engineering Research Council of Canada (NSERC), Intel, The Walt Disney Company, Autodesk, Side Effects Software, NVIDIA, and the Banting Postdoctoral Fel-lowships program

Droplet levitation and underwater plastron restoration using aerophilic surface textures

Thesis: Ph. D., Massachusetts Institute of Technology, Department of Mechanical Engineering, 2018.Cataloged from PDF version of thesis.Includes bibliographical references (pages 155-167).This thesis explores the use of active components in liquids and responsive surfaces to resist the wetting of water on solid surface textures. When a superhydrophobic surface comes into contact with water, it traps a thin layer of air (plastron) within its surface texture. This entrapped air is advantageous for reducing the contact line pinning of water droplets on the surface and lowering the skin friction drag experienced by the surface underwater. However, these aerophilic textures are prone to impregnation by water due to turbulent pressure fluctuations from external flows and dissolution of the trapped gas into the water. It is therefore desirable to develop strategies to restore the plastron underwater. A common method used to reduce the contact line pinning of water droplets on surfaces is the Leidenfrost effect, wherein the droplets are levitated on a cushion of vapor over the surface. But this typically requires the substrate to withstand high temperatures and also results in the loss of the droplet volume due to thermal evaporation. In this work, we explore new methodologies for locally generating gas near superhydrophobic surfaces to achieve room temperature droplet levitation and recover submerged superhydrophobic surfaces from wetting failure. In the first part of this thesis, we explore a novel chemical method to replenish the plastron in situ on superhydrophobic textures which have undergone a Cassie-to-Wenzel transition underwater. We use the decomposition reaction of hydrogen peroxide on superhydrophobic surfaces prepared with a catalytic coating to generate oxygen gas for plastron recovery. We also provide a thermodynamic framework for designing superhydrophobic surfaces with optimal texture and chemistry for underwater plastron regeneration. We finally demonstrate the practical utility of this method by fabricating periodic microtextures on aluminum surfaces that incorporate a cheap catalyst, manganese dioxide. We perform drag reduction experiments under turbulent flow conditions in a Taylor-Couette cell which show that more than half of the drag increase ensuing from plastron collapse can be recovered spontaneously using this method. In the second part of this thesis, we demonstrate room-temperature Leidenfrost effect by using carbonated water droplets on superhydrophobic surfaces. We observe the levitation-to-wetting transition of these degassing droplets using light interferometry on transparent superhydrophobic substrates. We characterize the timescales of wetting transitions with respect to the concentration of dissolved carbon dioxide, and show that a critical dissolved CO₂ concentration of at least 10 mM is required for achieving droplet levitation. We also derive a model based on lubrication theory combined with a lumped capacitance approach to predict the levitation time of degassing droplets. We finally display the practical utility of this phenomena for reducing friction between droplets and surfaces, droplet sorting, droplet self-propulsion, and triggering on-demand droplet levitation using chemical reactions.by Divya Panchanathan.Ph. D

Microgravity Science and Application Program tasks, 1989 revision

The active research tasks, as of the fiscal year 1989, of the Microgravity Science and Applications Program, NASA Office of Space Science and Applications, involving several NASA Centers and other organizations are compiled. The purpose is to provide an overview of the program scope for managers and scientists in industry, university, and government communities. The scientists in industry, university, and government communities. An introductory description of the program, the strategy and overall goal, identification of the organizational structures and people involved, and a description of each task are included. Also provided is a list of recent publications. The tasks are grouped into several major categories: electronic materials, solidification of metals, alloys, and composites; fluids, interfaces, and transport; biotechnology; glasses and ceramics; combustion science; physical and chemistry experiments (PACE); and experimental technology, facilities, and instrumentation

Index to 1985 NASA Tech Briefs, volume 10, numbers 1-4

Short announcements of new technology derived from the R&D activities of NASA are presented. These briefs emphasize information considered likely to be transferrable across industrial, regional, or disciplinary lines and are issued to encourage commercial application. This index for 1985 Tech Briefs contains abstracts and four indexes: subject, personal author, originating center, and Tech Brief Number. The following areas are covered: electronic components and circuits, electronic systems, physical sciences, materials, life sciences, mechanics, machinery, fabrication technology, and mathematics and information sciences

Air-Water Gas Transfer

A more complete understanding of the mechanisms involved in the exchange of gases between the atmosphere and the sea is needed if we are to address various environmental issues, and is essential to improved modeling of global climate. This volume contains selected papers from the Third International Symposium on Air-Water Gas Transfer, held at the University of Heidelberg, in Heidelberg, Germany from July 24-27, 1995. The papers are arranged into seven parts: Physical and Chemical Mechanisms, Waves and Turbulence, Breaking Waves and Bubbles, Measuring Technology, Laboratory Measurements and Facilities, Field Measurements, Remote Sensing, and Global Modeling. Emphasis is given to the transfer of carbon dioxide and other radiatively important gases, reflecting current interest in potential global warming. Breaking waves and the bubbles thereby generated play a prominent role in that regard. Also featured are non-invasive measurement technologies, many of which lend themselves to remote sensing applications. Those interested in chemical engineering, fluid mechanics, hydrology, hydraulics, environmental engineering, water quality engineering, climatology, meteorology, and oceanography will find this work a valuable resource

From Perturbation to Ejecta: An Exploration of Mixing Regimes in the Blast-Driven Instability using High-speed Experiments and Hydrocode Simulations.

The fluid mixing caused by variable-density instabilities is important in a wide variety of scenarios from ocean mixing and astrophysical phenomena to nuclear fusion techniques and atomic weapons. This thesis explores the mixing resulting from a specific instability known as the Blast-Driven Instability (BDI). A novel experimental platform was designed and built with the intention of studying the BDI for this thesis. Using high speed experimental techniques, the first fully time-resolved observations of the BDI are made. An understanding of the general dynamics caused by the BDI are established. Analytical models used successfully in the literature are also shown to need modifications in order to capture the BDI behavior. These observations are then used to test two common mixing models (RANS and LES) in a digital-twin simulation designed to precisely match the novel facility used in the high-speed experiments. Simulation results are analyzed against the data and reasons for their agreement, or lack thereof, are explored in detail. The RANS and LES simulation are shown to capture the BDI development to the 0th order, at the least. The LES simulations are also shown to be crucially dependent upon the characterization of initial conditions. The experimental data is used in conjunction with the simulation results to explore the BDI's sensitivity to two key governing parameters. How changes in the governing parameters create qualitative and quantitative changes in the BDI's behavior is explored extensively. Incident blast-wave strength is shown to change the hydrodynamic time scale, while changes in density difference cause much more non-linear effects. Finally, various scaling attempts are investigated in an attempt to decipher how the mixing induced by the BDI can be explicitly linked to the governing parameters.Ph.D