Computational Fluid Dynamics seminars

Atmospheric gravity waves arise from processes including flow over mountains, moist convection and geostrophic imbalance. They connect atmospheric layers, influence tropospheric jet streams and play a major dynamical role in the stratosphere and mesosphere. Yet much of their spectrum is unresolved by typical climate models, and observations provide limited constraints. Aditi Sheshadri presents research combining observations, high-resolution simulations and data-informed methods to understand their effects on climate variability and improve their representation in global models. Attend online via Zoom. The colloquium runs from 11:30 to 13:00 India Standard Time.

NOAA's Mussel Watch records are examined as a unified framework for coastal contamination. The study combines sediment chemistry, toxicity, benthic condition and tissue measurements, using AMBI and M-AMBI scores at 732 national assessment sites and 33 Hudson–Raritan stations. Random-forest and Bayesian models associate urbanization with benthic condition in the New York region (ρ=0.62), but not nationally (ρ=0.05). A Delft3D estuary model reproduces observed tides and predicts increased deep-channel bed shear under sea-level rise. The work asks whether sediment contaminants mediate urbanization impacts and whether legacy cleanup remains effective as sea level changes. It was conducted through a NOAA NERTO graduate internship with Kimani Kimbrough and Erik Davenport at NCCOS.

Lurdes Ondaro Mallea examines whether current models of the kinematic Sunyaev–Zeldovich signal accurately recover diffuse baryons and the strength of astrophysical feedback. The analysis uses hydrodynamic simulations to generate mock stacked measurements for realistic DESI-like galaxy samples, separating contributions from gas density, velocities and nonlinear astrophysics. It tests baryonic changes to density and velocity fields, satellite galaxies, nonlinear velocities and velocity reconstruction. Neglecting satellites can underestimate halo gas fractions at today's measurement precision; further corrections become significant for future datasets. The talk explains how including these effects can improve gas-distribution measurements and assessments of feedback. Online via Zoom. Monday 28 September 2026, 11:00–12:00 PDT (America/Los_Angeles; UTC−7). Follow Join the zoom meeting on the organizer's event page. Lurdes Ondaro Mallea is affiliated with Cambridge. Organized by the Kavli Institute for Particle Astrophysics and Cosmology (KIPAC), Stanford University. This listing advertises the verified remote option.

Shane Davis presents simulations of stellar disruption and the subsequent return of debris to a black hole. Observed light curves and spectra offer tests of accretion physics and black-hole spacetime, but interpreting them requires accounting for strong radiation forces during rapid fallback. Using Athena++ and AthenaK, the research models radiation transfer, including recent calculations in Kerr spacetime. Although the debris circularizes slowly, shocks involving the returning stream and an eccentric disk dominate early energy release and angular-momentum transport. Radiation drives unbound outflows and builds a weakly bound envelope that reprocesses emission. These results offer an explanation for the strong optical and ultraviolet signals observed in many tidal disruption events.

Planets form from dust embedded in gaseous protoplanetary disks. Hydrodynamic instabilities can hinder growth by stirring turbulence, yet also help by creating structures that collect solids and promote planetesimal formation. Min-Kai Lin will discuss analytical and numerical studies of the vertical shear instability and convective overstability, their interactions with dust, and generalisations of the streaming instability to disks with accretion or magnetic fields. The seminar examines how these processes alter the conditions for concentrating solids and the challenges that remain in connecting disk dynamics to planet formation.

Brain microstructure plays a key role in driving the transport of drug molecules directly administered to the brain tissue as in Convection-Enhanced Delivery procedures. This study reports the first systematic attempt to characterize the cytoarchitecture of commissural, long association and projection fiber, namely: the corpus callosum, the fornix and the corona radiata. Ovine samples from three different subjects have been imaged using scanning electron microscope combined with focused ion beam milling. Particular focus has been given to the axons. For each tract, a 3D reconstruction of relatively large volumes (including a significant number of axons) has been performed. Namely, outer axonal ellipticity, outer axonal cross-sectional area and its relative perimeter have been measured. This study [1] provides useful insight into the fibrous organization of the tissue that can be described as composite material presenting elliptical tortuous tubular fibers, leading to a workflow to enable accurate simulations of drug delivery which include well-resolved microstructural features. As a demonstration of the use of these imaging and reconstruction techniques, our research analyses the hydraulic permeability of two white matter (WM) areas (corpus callosum and fornix) whose three-dimensional microstructure was reconstructed starting from the acquisition of the electron microscopy images. Considering that the white matter structure is mainly composed of elongated and parallel axons we computed the permeability along the parallel and perpendicular directions using computational fluid dynamics [2]. The results show a statistically significant difference between parallel and perpendicular permeability, with a ratio about 2 in both the white matter structures analysed, thus demonstrating their anisotropic behaviour. This is in line with the experimental results obtained using perfusion of brain matter [3]. Moreover, we find a significant difference between permeability in corpus callosum and fornix, which suggests that also the white matter heterogeneity should be considered when modelling drug transport in the brain. Our findings, that demonstrate and quantify the anisotropic and heterogeneous character of the white matter, represent a fundamental contribution not only for drug delivery modelling but also for shedding light on the interstitial transport mechanisms in the extracellular space. These and many other discoveries will be discussed during the talk." "1. https://www.researchsquare.com/article/rs-686577/v1, 2. https://www.pnas.org/content/118/36/e2105328118, 3. https://ieeexplore.ieee.org/abstract/document/9198110

Filaments (slender, microscopic elastic bodies) are prevalent in biological and industrial settings. In the biological case, the filaments are often active, in that they are driven internally by motor proteins, with the prime examples being cilia and flagella. For cilia in particular, which can appear in dense arrays, their resulting motions are coupled through the surrounding fluid, as well as through surfaces to which they are attached. In this talk, I present numerical simulations exploring the coordinated motion of active filaments and how it depends on the driving force, density of filaments, as well as the attached surface. In particular, we find that when the surface is spherical, its topology introduces local defects in coordinated motion which can then feedback and alter the global state. This is particularly true when the surface is not held fixed and is free to move in the surrounding fluid. These simulations take advantage of a computational framework we developed for fully 3D filament motion that combines unit quaternions, implicit geometric time integration, quasi-Newton methods, and fast, matrix-free methods for hydrodynamic interactions and it will also be presented.

Many microorganisms and cells function in complex (non-Newtonian) fluids, which are mixtures of different materials and exhibit both viscous and elastic stresses. For example, mammalian sperm swim through cervical mucus on their journey through the female reproductive tract, and they must penetrate the viscoelastic gel outside the ovum to fertilize. In micro-scale swimming the dynamics emerge from the coupled interactions between the complex rheology of the surrounding media and the passive and active body dynamics of the swimmer. We use computational models of swimmers in viscoelastic fluids to investigate and provide mechanistic explanations for emergent swimming behaviors. I will discuss how flexible filaments (such as flagella) can store energy from a viscoelastic fluid to gain stroke boosts due to fluid elasticity. I will also describe 3D simulations of model organisms such as C. Reinhardtii and mammalian sperm, where we use experimentally measured stroke data to separate naturally coupled stroke and fluid effects. We explore why strokes that are adapted to Newtonian fluid environments might not do well in viscoelastic environments.

Microorganisms can swim in a variety of environments, interacting with chemicals and other proteins in the fluid. In this talk, we will highlight recent computational methods and results for swimming efficiency and hydrodynamic interactions of swimmers in different fluid environments. Sperm are modeled via a centerline representation where forces are solved for using elastic rod theory. The method of regularized Stokeslets is used to solve the fluid-structure interaction where emergent swimming speeds can be compared to asymptotic analysis. In the case of fluids with extra proteins or cells that may act as friction, swimming speeds may be enhanced, and attraction may not occur. We will also highlight how parameter estimation techniques can be utilized to infer fluid and/or swimmer properties.

Bacteria exhibit a bewildering diversity of morphologies, but despite their impact on nearly all aspects of life, they are frequently classified into a few general categories, usually just “spheres” and “rods.” Curved-rod bacteria are one simple variation observed in many environments, particularly the ocean. However, why so many species have evolved this shape is unknown. We used a regularized Stokeslet Boundary Element Method to model the motility of flagellated, curved bacteria. We show that curvature can increase swimming efficiency, revealing a widely applicable selective advantage. Furthermore, we show that the distribution of cell lengths and curvatures observed across bacteria in nature is predicted by evolutionary trade-offs between three tasks influenced by shape: efficient swimming, the ability to detect chemical gradients, and reduced cost of cell construction. We therefore reveal shape as an important component of microbial fitness.