Scalable Simulation of High-Frequency Wave Propagation

Friday, April 19th, 2024, 4:00 p.m. Central Time

Jacob Badger
Oden Institute
The University of Texas at Austin
https://www.oden.utexas.edu/people/directory/Jacob-Badger/

Developing fast and scalable solvers for high-frequency wave propagation is a notoriously difficult problem in mathematics and scientific computing. One challenge is that classical numerical discretizations yield indefinite discrete systems that preclude use of classical scalable solvers. Simulation of high-frequency wave propagation has thus been limited to problems on the order of 1 billion degrees of freedom (DOFs). This talk outlines a novel scalable and efficient multigrid solver for high-frequency wave propagation problems. The solver is based on the discontinuous Petrov–Galerkin (DPG) finite element method and is demonstrated to solve wave propagation problems in acoustics, electromagnetics, and elasticity with complex geometries, high-contrast heterogeneous media, and other challenging features. Scaling is demonstrated to nearly 1 trillion DOFs, an unprecedented scale in high-frequency wave simulation.

Spatiotemporally-Resolved Kinematic and Stress Measurements of Interfacial Cavitation in Soft Matter

Friday, April 12th, 2024, 4:00 p.m. Central Time

Professor Jin Yang
Department of Aerospace Engineering and Engineering Mechanics
The University of Texas at Austin
https://www.ae.utexas.edu/people/faculty/faculty-directory/yang

Inertial cavitation is a common phenomenon found in nature and many engineering systems. When harnessed carefully, laser or ultrasound-focused, energy-driven cavitation can be a very beneficial tool in a wide range of medical and materials applications, including laser surgery, lithotripsy, drug delivery, and, more recently, soft material characterization. In this talk, we will begin by describing our recent developments in the material property characterization method, called Inertial Microcavitation Rheometry (IMR), to investigate laser-induced inertial cavitation (LIC) in soft matter, where the surrounding material is subjected to ballistic and ultra- high strain rates (103 ∼ 108s−1). Through IMR, we can precisely quantify the nonlinear viscoelastic, finite deformation constitutive behavior of soft materials at ultra-high strain rates. At such high rates, we will also show soft hydrogels and biological materials might exhibit significant strain-stiffening effects, dynamic surface instabilities, and fracture patterns. Following this, I will present our recent findings on the dynamics of laser-induced inertial cavitation (LIC) near the gel-water interface. Historically, studies of cavitation dynamics at liquid-solid interfaces were limited to observations of surface deformations and cavitation bubble morphology due to challenges in measuring subsurface behavior. However, understanding the intricate dynamics of cavitation at these interfaces holds significant implications for engineering and medical applications. For the first time, we provide high-fidelity and high-throughout full-field measurements on the spatiotemporal deformation behavior and wave propagation within soft materials near interfaces due to laser-induced inertial cavitation at extremely high rates. Our results provide critical insights into how soft biological tissues respond to the immense forces generated by the violent collapse of a cavitation event. These measurements will be particularly useful for minimizing collateral damage to non-target tissues in cavitation-based medical therapies.

The Acoustics and Psychoacoustics of the JFK Assassination

Friday, April 5th, 2024, 4:00 p.m. Central Time

Professor Dennis McFadden
Ashbel Smith Professor Emeritus in Experimental Psychology
The University of Texas at Austin
https://liberalarts.utexas.edu/psychology/faculty/dm8797

This talk is unusual for this audience because it covers US history as well as acoustics and psychoacoustics. In 1978, the US House Select Committee on Assassinations (HSCA) conducted a partial re-enactment of the 1963 assassination of President John F. Kennedy in Dealey Plaza, Dallas, Texas. One goal was to measure the acoustics existing at various locations around the plaza in response to rifle shots from the 6th floor window of the building housing the Texas School-Book Depository and from behind the fence on the grassy knoll. On the basis of those measurements, the physical acoustics team concluded that there were four gunshots and two assassins, not three gunshots from one assassin as was concluded by the Warren Commission in 1964. The HSCA’s four-shot conclusion soon was proved wrong, for reasons that will be discussed. I was a member of the team responsible for making psychoacoustical observations from various locations around Dealey Plaza during the re-enactment rifle shots in 1978. One goal was to determine why earwitnesses to the JFK assassination did not agree about the location of the gunman. To be discussed are the acoustical and psychoacoustical factors making it difficult for people to localize a rifle firing supersonic rounds in an echoic environment. No evidence supporting any of the common alternative theories of the assassination was obtained.

Acoustic Emissions-based Rodent Behavior Analysis

Friday, March 8th, 2024, 4:00 p.m. Central Time

Dr. Shivashankar Peruvazhuthi
Maseeh Department of Civil, Architectural and Environmental Engineering
Center for Learning and Memory, Department of Neuroscience, (collaboration)
The University of Texas at Austin
https://sites.google.com/view/ssrg/home?authuser=0

Over the past few decades, capturing and analyzing acoustic emissions (AE) from processes such as corrosion and crack propagation has been vital to characterize their effect on the integrity of structures. My research, too, is based on the AE technology, but instead of studying structural integrity, I take a deeper look at the behavior of rodents using AE generated by the animal. In the tests, mice were introduced, one at a time, in an open-field arena with an aluminum plate as the floor. As the rodent moved around this open field, its voluntary and involuntary movement applied subtle forces to the aluminum plate, leading to the generation of Lamb and Shear horizontal (SH) waves in the plate. The generated waves were detected with ultrasonic sensors (attached to the plate’s bottom), and acquired by treating the animal as an acoustic source and the generated waves as Acoustic Emissions. The generated waves, i.e., the acquired AE, contain information about the rodent’s physiology, behavior, and underlying mental states and offer a new modality to investigate the animal’s behavior. Two types of tests were undertaken in the open field, one in which the animal was allowed to move and behave freely without any external stimulus, and one in which a loud tone was played to evoke an acoustic startle response. Results from these studies demonstrated the potential of the AE technology to enhance rodent behavior analysis, with the possibility of identifying hidden behavioral modules and tracking behavioral differences due to genetic differences, prior experiences, and neural manipulations.

Nonclassical Nonlinear Acoustics of Structured Media

Friday, March 1st, 2024, 4:00 p.m. Central Time

Professor Lev A. Ostrovsky
University of Colorado, Boulder
https://www.colorado.edu/amath/lev-ostrovsky

In this presentation we outline the area of “nonclassical nonlinear acoustics” related to many solid materials with a complex structure, such as grainy media, concrete, and various kinds of rock. Such media are characterized by (i) strong elastic nonlinearity, (ii) stress-strain hysteresis, and (iii) a long-time recovery after an impact (“slow dynamics”). The latter can take hours in laboratory samples and years after earthquakes. Our theory is based on the physics of grain contacts. In particular, the slow recovery is described by an Arrhenius-type equation commonly used for chemical reactions. Earlier we proposed a physical model of granular materials with an inter-grain contact potential that includes adhesion and an elastic (Hertz) force. After an initial impact, the recovery occurs irreversibly, with hysteresis, whereas some contacts remain in the “excited,” metastable state, and then slowly (commonly logarithmically in time) return to the initial state due to thermal processes. The slow dynamics are described by an Arrhenius-type equation commonly used for chemical reactions. In this presentation, the state of the problem is outlined, and new developments are discussed. Particularly, the data of logarithmic soil recovery, which can take years after strong earthquakes, are discussed and described using the theory. In conclusion, some yet unsolved problems are indicated.

Wireless E-Tattoos for the Mobile Tracking of Cardiovascular Health

Friday, February 23rd, 2024, 4:00 p.m. Central Time

Professor Nanshu Lu
Department of Aerospace Engineering and Engineering Mechanics
The University of Texas at Austin
https://sites.utexas.edu/nanshulu/

The research objective of my research group is to bridge humans and robots through soft electronics. We have developed skin-soft, hair-thin, and skin-conformable electronic tattoos (e-tattoos) for human body digitization, as well as stretchable electronic skins (e-skins) that can mimic the softness and sensations of human skin. This talk will focus on two different types of wearable e-tattoos for continuous and ambulatory cardiovascular health monitoring. The first one is a chest-laminated trimodal e-tattoo that can synchronously and simultaneously perform electrocardiography (ECG), seismocardiography (SCG) and plethysmography (PPG). This trimodal chest e-tattoo can provide a comprehensive monitoring of the electrical and mechanical and activities of the heart, as well as the perfusion of blood to the skin, out of which various cardiac time intervals and cardiac output can be extracted, even during light movements. We are also exploring the possibility of using a PPG sensor array for differentiating arterial vs. venous oxygenation. The second one is a wearable low-power ultrasound e-tattoo, which is a work in progress. While ultrasound is a promising modality to capture absolute hemodynamic metrics, state-of-the-art wearable ultrasound sensors are still constrained by bulky and complex back-end control and data acquisition systems. Our innovative analog-edge-computing method of hemodynamic feature detection can dramatically reduce power consumption, computational costs, and sensor size, enabling wireless implementation. The ultimate goal of this line of research is to paint a full picture of one’s cardiovascular health in real-time through a multimodal, distributed, and noninvasive e-tattoo body sensor network.

Distilling the Acoustics from Multi-Rotor Platforms Using New Methods in Signal Processing.

Friday, February 16th, 2024, 4:00 p.m. Central Time

Dr. Charles E. Tinney
Applied Research Laboratories
The University of Texas at Austin
https://www.arlut.utexas.edu

In a recent article by Tinney, Zhao-Dubuc, and Valdez (International Journal of Aeroacoustics, 2023, DOI: 10.1177/1475472X231199186), proper orthogonal decomposition (POD) and the Vold-Kalman order tracking filter (VKF) were combined to evaluate the most energetic signals in the sound field of a coaxial, corotating rotor in hover. The method comprised a covariance matrix for the POD problem that was constructed using auto- and cross-spectral densities of a stationary sensor set. The POD technique isolates structures in space while VKF methods filter structures in time. The current study reconsiders the same unique combination of analysis techniques, but develops the framework using a different form of the covariance matrix for occasions when the stationary sensor set is large, or when a spectral domain representation of the signals is not necessary. As such, this defaults to the conventional form of Lumley’s POD. The combined use of these techniques (conventional POD with Vold-Kalman filters) is then exercised using the same database of the sound-field generated by a coaxial, corotating rotor in hover to study the effect that changes to the rotor index angle has on the sound directed at listeners located below the rotor disk plane. Filtered acoustic waveforms are extracted using the first four spatial POD modes and VKF phasors associated with the first four rotor blade-pass frequency harmonics; these filtered signals are responsible for the impulsive like signatures that drive community annoyance. An assessment of the trade-space between these filtered waveforms and the rotor’s aerodynamic performance demonstrates that an 8% shift in rotor figure of merit is obtainable without changing the sound pressure levels generated by the stacked rotor. Alternatively, 6.3 dB and 4.0 dB reductions in sound pressure levels propagating along the rotor disk plane and below, respectively, can be achieved without any changes to rotor performance.

In Situ Measurements of Sediment Compressional and Shear Wave Speed from the New England Mud Patch and Shelf Break Areas
Using the Acoustic Coring System

Friday, February 2, 2024, 4:00 p.m. Central Time

Dante D. Garcia
Applied Research Laboratories
The University of Texas at Austin
https://www.arlut.utexas.edu

In situ measurements of geoacoustic properties provide direct characterization of the seabed at near ambient conditions. The Acoustic Coring System (ACS) is a gravity corer equipped with acoustic probes that obtains in situ compressional wave (30–200 kHz) and shear wave (400–1200 Hz) measurements as the corer penetrates the seabed. During the April 2022 R/V Endeavor coring survey, the ACS was deployed at 36 locations within the New England Mud Patch (NEMP) and New England Shelf Break areas. Data from these experiments were analyzed to characterize the depth-dependent structure of the seabed geoacoustic properties as well as their spatial variability. The in situ measurements are interpreted in the context of stratigraphic layering measured by a seismic survey. Depth-dependent profiles of compressional wave speed from a subset of these deployments in the NEMP are compared to profiles previously collected at nearby locations in 2016. In situ compressional wave records from both areas are compared with ex situ sediment core measurements, including data collected from core loggers and laboratory analyses. Additionally, novel in situ shear wave speed measurements from the NEMP and surrounding areas are introduced.

Integrated Optomechanical Systems for Sensing and Communications

Friday, January 26, 2024, 4:00 p.m. Central Time

Dr. Jason J. Gorman
Physical Measurement Laboratory
National Institute of Standards and Technology
https://www.nist.gov/people/jason-j-gorman

Optomechanical resonators that combine low-loss micromechanical resonators and optical microcavities have been shown to provide exquisite sensitivity to changes in the effective cavity length and exhibit complex nonlinear behavior that can be controlled optically. To date, the focus for optomechanical resonators has been on fundamental physical measurements under well-controlled laboratory conditions. In this presentation, I will describe our efforts to use integrated optomechanical resonators for more applied measurements, with the prospect of significantly improving resolution and accuracy compared to traditional technologies, such as microelectromechanical sensors. Examples will include an optomechanical accelerometer that provides high precision, low-uncertainty measurements without calibration, a phononic-photonic crystal resonator developed for quantum-limited force detection, a pulsed laser interferometer that has been used to measure vibrations out to 12 GHz for applications in mobile communications filters and quantum acoustic devices, and a high-overtone bulk acoustic resonator designed for microwave-to-optical frequency conversion.