Nematic Films and Radially Anisotropic Delaunay Surfaces

We develop a theory of axisymmetric surfaces minimizing a combination of surface tension and nematic elastic energies which may be suitable for describing simple film and bubble shapes. As a function of the elastic constant and the applied tension on the bubbles, we find the analogues of the unduloid, sphere, and nodoid in addition to other new surfaces.Comment: 15 pages, 18 figure

Vibrating soap films: An analog for quantum chaos on billiards

We present an experimental setup based on the normal modes of vibrating soap films which shows quantum features of integrable and chaotic billiards. In particular, we obtain the so-called scars -narrow linear regions with high probability along classical periodic orbits- for the classically chaotic billiards. We show that these scars are also visible at low frequencies. Finally, we suggest some applications of our experimental setup in other related two-dimensional wave phenomena.Comment: 5 pages, 7 figures. Better Postscript figures available on reques

Simulating incompressible thin-film fluid with a Moving Eulerian-Lagrangian Particle method

In this thesis, we introduce a Moving Eulerian-Lagrangian Particle (MELP) method, a mesh-free method to simulate incompressible thin-film fluid systems: soap bubbles, bubble clusters, and foams. The realistic simulation of such systems depends upon the successful treatment of three aspects: (1) the soap film\u27s deformation due to the tendency to minimize the surface energy, giving rise to the bouncy characteristics of soap bubbles, (2) the tangential fluid flow on the thin film, causing the thickness to vary spatially, which in conjunction with thin-film interference creates evolving and highly sophisticated iridescent color patterns, (3) the topological changes due to collision, separation, and fragmentation, which may create partition surfaces and non-manifold junctions that spontaneously settle into honeycomb structures due to force balance. The interleaving complexities from all three fronts render the task of accurately and affordably simulating thin-film fluid an open problem for the Computational Physics and Computer Graphics community. The proposed MELP method tackles these multifaceted challenges by employing a novel, bi-layer particle structure: a sparse set of Eulerian particles for dynamic interface tracking and PDE solving, and a fine set of Lagrangian particles for material and momentum transport. Such a design provides crucially advantageous numerical traits compared to existing frameworks. Compared to mesh-based methods, MELP\u27s particle-based nature makes it topologically agnostic, which allows it to conveniently simulate topological changes such as bubble-cluster formation and thin-film rupture. Furthermore, these Lagrangian structures carry out fluid advection naturally, conserve mass by design, and track sub-grid flow details. Compared to existing particle methods, our bi-layer design improves drastically on the computational performance in terms of both stability and efficiency. The advantage of this design will manifest in a wide range of experiments, including dynamic foam formation, Rayleigh-Taylor instability, Newton Black Films, and bubble bursting, showing an increased level of flow detail, increased number of regions in bubble clusters, and increased flexibility to recreate multi-junction formation on-the-fly. Furthermore, we validate its physical correctness against a variety of analytical baselines, by successfully recovering the equilibrium dihedral and tetrahedral angles, the exponential thickness profile of drainage under gravity, the curvature of partition surfaces, and the minimum surface area of double-bubbles

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

Flow visualization and flow field measurements of a 1/12 scale tilt rotor aircraft in hover

The results are given of flow visualization studies and inflow velocity field measurements performed on a 1/12 scale model of the XV-15 tilt rotor aircraft in the hover mode. The complex recirculating flow due to the rotor-wake-body interactions characteristic of tilt rotors was studied visually using neutrally buoyant soap bubbles and quantitatively using hot wire anemometry. Still and video photography were used to record the flow patterns. Analysis of the photos and video provided information on the physical dimensions of the recirculating fountain flow and on details of the flow including the relative unsteadiness and turbulence characteristics of the flow. Recirculating flows were also observed along the length of the fuselage. Hot wire anemometry results indicate that the wing under the rotor acts to obstruct the inflow causing a deficit in the inflow velocities over the inboard region of the model. Hot wire anemometry also shows that the turbulence intensities in the inflow are much higher in the recirculating fountain reingestion zone

Bubble formation during the collision of a sessile drop with a meniscus

The impact of a sessile droplet with a moving meniscus, as encountered in processes such as dip-coating, generically leads to the entrapment of small air bubbles. Here we experimentally study this process of bubble formation by looking through the liquid using high-speed imaging. Our central finding is that the size of the entrapped bubble crucially depends on the location where coalescence between the drop and the moving meniscus is initiated: (i) at a finite height above the substrate, or (ii) exactly at the contact line. In the first case, we typically find bubble sizes of the order of a few microns, independent of the size and speed of the impacting drop. By contrast, the bubbles that are formed when coalescence starts at the contact line become increasingly large, as the size or the velocity of the impacting drop is increased. We show how these observations can be explained from a balance between the lubrication pressure in the air layer and the capillary pressure of the drop

Abyss Aerosols

Bubble bursting on water surfaces is believed to be a main mechanism to produce submicron drops, including sea spray aerosols, which play a critical role in forming cloud and transferring various biological and chemical substances from water to the air. Over the past century, drops production mechanisms from bubble bursting have been extensively studied. They usually involve the centrifugal fragmentation of liquid ligaments from the bubble cap during film rupture, the flapping of the cap film, and the disintegration of Worthington jets after cavity collapse. Here, we show that a dominant fraction of previously identified as 'bubble bursting' submicron drops are in fact generated via a new mechanism underwater, inside the bubbles themselves before they have reached the surface. These drops are then carried within the rising bubbles towards the water surface and are released in air at bubble bursting. Evidence suggests that these drops originate from the flapping instability of the film squeezed between underwater colliding bubbles. This finding fundamentally reshapes our understanding of sea spray aerosol production and establishes a new role for underwater bubble collisions regarding the nature of transfers through water-air interfaces.Comment: 50 pages, 4 figures, and 10 extended data figure