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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 361 records · Page 20
All sourcesNASA NTRSDOE OSTI
NASA NTRS1999

Vortex-Body Interactions: A Critical Assessment. Coupled Gap-Wake Instabilities/Turbulence: A Source of Noise

This program has involved, first of all, a critical state-of-the-art assessment of vortex-body interactions. Then, efforts were focused on experimental investigation on coupled-wake instabilities and turbulence occurring in a two-cylinder system. An extensive review was undertaken on the effect of incident vortices on various types of bodies. These incident vortices have a length scale of the same order of magnitude as the scale of the body. The body can take on various forms, including, for example, a circular cylinder, a blade or a wing. The classes of vortex-body interaction that were critically assessed include: (1) Periodic distortion of the incident (primary) vortex and shedding of secondary vorticity from the surface of the body. (2) Modulated vortex distortion and shedding at a leading-edge or surface due to incidence of a complex system of vortices. (3) Vortex distortion and shedding in presence of body oscillation. (4) Three-dimensional vortex interaction and shedding. For all of these classes of vortex-body interaction, quantitative topologies of the vorticity distributions and streamline patterns were found to be central to a unified description of mechanisms of vortex distortion and shedding. In most cases, it was possible to define relationships between vortex interactions and unsteady loading at the body surface. This phase of the program was an experimental investigation of a two-cylinder system, which simulated a central aspect of a four-wheel bogie on a large-scale commercial aircraft. The overall aim of this experimental research program was to determine the crucial elements of the unsteadiness in the gap and near-wake regions as a function of time using cinema-based techniques. During the research program, various image evaluation techniques were employed. They involved assessment of instantaneous velocity fields, streamline topology and patterns of vorticity. Experiments were performed in a large-scale water channel using a high-resolution version of digital particle image velocimetry. The program has focused on acquisition of images of velocity and vorticity for varying gap widths between the two-cylinder system. As a result of analysis of a relatively large number of images, it is demonstrated that low frequency instabilities can occur in the gap region between the cylinder. These low frequency instabilities are hypothesized to influence the near-wake structure of the entire two-cylinder system. The nature of the unstable shear layers in the gap region involves generation of small-scale Kelvin-Helmholtz instabilities. These unsteady shear layers then impinge upon the upper and lower surfaces of the cylinders, thereby influencing both the unsteady structure and the time-averaged patterns of the near-wake. Initial efforts have focused on characterization of the patterns of instantaneous and averaged streamlines using topological concepts. The end result of this investigation is a series of documented instantaneous images. They will serve as a basis for various types of post-processing, which will lead to a fuller understanding of the instantaneous and time-averaged unstable-turbulent fields in the gap region and downstream of the two-cylinder system. This further assessment is the focus of a subsequent program.

Rockwell, Donald↗
NASA NTRS1974

An experimental and theoretical study of the flow phenomena within a vortex sink rate sensor

A description of the flow field within a vortex sink rate sensor was obtained, and the influence of viscous effects on its performance was observed. The sensor basically consisted of a vortex chamber and a sink tube. The vortex chamber consisted of two circular coaxial disks held apart, at their periphery, by a porous coupling. One circular disk had an opening to permit the mounting of the sink tube, in such a manner that the vortex chamber as well as the sink tube had a common axis of rotation. Air was supplied radially to the sensor through its porous coupling as the sensor was rotated at various speeds. Particular emphasis was directed toward an understanding of the flow field in the sink tube region. Thus velocity measurements at various stations along the length of the sink tube as well as along a given radius at any designated station were taken.

Patel, D. K.↗
NASA NTRS2011

Uncertainty Analysis in Space Radiation Protection

Space radiation is comprised of high energy and charge (HZE) nuclei, protons, and secondary radiation including neutrons. The uncertainties in estimating the health risks from galactic cosmic rays (GCR) are a major limitation to the length of space missions, the evaluation of potential risk mitigation approaches, and application of the As Low As Reasonably Achievable (ALARA) principle. For long duration space missio ns, risks may approach radiation exposure limits, therefore the uncertainties in risk projections become a major safety concern and methodologies used for ground-based works are not deemed to be sufficient. NASA limits astronaut exposures to a 3% risk of exposure induced death (REID) and protects against uncertainties in risks projections using an assessment of 95% confidence intervals in the projection model. We discuss NASA s approach to space radiation uncertainty assessments and applications for the International Space Station (ISS) program and design studies of future missions to Mars and other destinations. Several features of NASA s approach will be discussed. Radiation quality descriptions are based on the properties of radiation tracks rather than LET with probability distribution functions (PDF) for uncertainties derived from radiobiology experiments at particle accelerators. The application of age and gender specific models for individual astronauts is described. Because more than 90% of astronauts are never-smokers, an alternative risk calculation for never-smokers is used and will be compared to estimates for an average U.S. population. Because of the high energies of the GCR limits the benefits of shielding and the limited role expected for pharmaceutical countermeasures, uncertainty reduction continues to be the optimal approach to improve radiation safety for space missions.

Cucinotta, Francis A.↗
DOE OSTI2021

Investigating 3,4-bis(3-nitrofurazan-4-yl)furoxan detonation with a rapidly tuned density functional tight binding model

In this work, we describe a machine learning approach to rapidly tune density functional tight binding models for the description of detonation chemistry in organic molecular materials. Resulting models enable simulations on the several 10s of ps scales characteristic to these processes, with “quantum-accuracy.” We use this approach to investigate early shock chemistry in 3,4-bis(3-nitrofurazan-4-yl)furoxan, a hydrogen-free energetic material known to form onion-like nanocarbon particulates following detonation. We find that the ensuing chemistry is significantly characterized by the formation of large C x N y O z species, which are likely precursors to the experimentally observed carbon condensates. Beyond utility as a means of investigating detonation chemistry, the present approach can be used to generate quantum-based reference data for the development of full machine-learned interatomic potentials capable of simulation on even greater time and length scales, i.e., for applications where characteristic time scales exceed the reach of methods including Kohn–Sham density functional theory, which are commonly used for reference data generation.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2021

Powering the Blue Economy: A Survey of Station-Keeping Methods for Mooringless Platforms

The term “ocean platform” is used to reference everything from stationary, typically moored, buoys to mobile water vehicles, whether they operate on the ocean’s surface or underwater. For certain applications for which relatively stationary station-keeping conditions are desired, the use of mooring systems is not always a viable alternative either for economic, environmental, regulatory, or otherwise practical reasons, or a combination thereof, (e.g., short deployments, sensitive ecosystems, very deep project sites). Maintaining a platform at a single waypoint or reference location without being moored would require additional control systems and a power source to counteract the drift forces that would naturally displace it. Mobile platforms, which are usually untethered except for remotely operated vehicles, typically require energy input to power their station-keeping capabilities so that they hold or control their location in the ocean. Currently, most of these platforms use combustion engines or batteries for this purpose, which, depending on the specific systems, may be costly, pollute the environment, or create limitations on the length of the deployment. However, powering this kind of platforms with surrounding renewable resources (waves, currents, winds, or sun) has been identified as a promising solution to expand their application. The intent of this report is to investigate station-keeping methods for various ocean platforms that are not moored or otherwise anchored to the ocean floor, or another platform or vessel, paying particular interest to technologies that use marine renewable resources to power their operation, because that is of particular interest to the U.S. Department of Energy’s Powering the Blue Economy (PBE) initiative. As a first step, 72 articles and technical reports related to mooringless station-keeping methods were collected for review. The preliminary literature review provided a broad overview of common themes across the literature from which a descriptive methodology for analyzing various platforms was developed. That is, station-keeping methods were categorized based on their predominant energy source and consumption (renewable, nonrenewable, or hybrid if the platform uses renewable and nonrenewable resources equally), and their localization strategy (drift reduction, “path-planning or “waypoint-holding”). In addition, platform types were segregated into the following groups: buoys, surface drifters, and unoccupied surface vehicles (USVs); offshore renewable energy systems; and unoccupied underwater vehicles (UUVs). The main types of station-keeping methods encountered in this report achieve their intended localization strategy by means of drift mitigation, steering, and/or propulsion. Drift mitigation is commonly accomplished via drogues and sea anchors. Stand-along steering subsystems use control surfaces (e.g., ship rudder, wing sail, etc.) that react to ocean currents, waves, or winds to provide varying-degrees of course adjustments. Combined steering and propulsion subsystems include differential thrusters, directional thrusters separate from a primary thruster that cause the platform to pitch up/down or yaw clockwise/counterclockwise, or vectored thrusters that direct the propulsion in a range of directions relative to the platform’s local coordinate system. Propulsion is often achieved by running a motor and applying active control strategies but can also involve buoyancy shifts and using sails to generate lifting forces that propel a platform in a desired direction. Future research is primarily expected to take place in the form of a technoeconomic analysis that would aim to determine the technological viability, cost, and added value of mooringless station-keeping use cases identified through this research, including docking for UUV recharging or for georeferencing drifter buoys, deep-sea floating wind farms, U.S. Navy sonar arrays, and a Pacific Ocean wave buoy network.

32 ENERGY CONSERVATION, CONSUMPTION, AND UTILIZATI↗
DOE OSTI2021

Scaling of magnetic dissipation and particle acceleration in ABC fields

Using particle-in-cell numerical simulations with electron–positron pair plasma, we study how the efficiencies of magnetic dissipation and particle acceleration scale with the initial coherence length λ 0 in relation to the system size L of the two-dimensional ‘Arnold–Beltrami–Childress’ (ABC) magnetic field configurations. Topological constraints on the distribution of magnetic helicity in two-dimensional systems, identified earlier in relativistic force-free simulations, that prevent the high-(L/λ 0 ) configurations from reaching the Taylor state, limit the magnetic dissipation efficiency to about ϵ diss ≃60% . Here we find that the peak growth time scale of the electric energy τ E,peak scales with the characteristic value of initial Alfvén velocity β A,ini like τ E,peak ∝(λ 0 /L)β$^{–3}_{A,ini}$ . The particle energy change is decomposed into non-thermal and thermal parts, with non-thermal energy gain dominant only for high initial magnetisation. The most robust description of the non-thermal high-energy part of the particle distribution is that the power-law index is a linear function of the initial magnetic energy fraction.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2022

Ultrafast visualization of incipient plasticity in dynamically compressed matter

Plasticity is ubiquitous and plays a critical role in material deformation and damage; it inherently involves the atomistic length scale and picosecond time scale. A fundamental understanding of the elastic-plastic deformation transition, in particular, incipient plasticity, has been a grand challenge in high-pressure and high-strain-rate environments, impeded largely by experimental limitations on spatial and temporal resolution. Here, we report femtosecond MeV electron diffraction measurements visualizing the three-dimensional (3D) response of single-crystal aluminum to the ultrafast laser-induced compression. We capture lattice transitioning from a purely elastic to a plastically relaxed state within 5 ps, after reaching an elastic limit of ~25 GPa. Our results allow the direct determination of dislocation nucleation and transport that constitute the underlying defect kinetics of incipient plasticity. Large-scale molecular dynamics simulations show good agreement with the experiment and provide an atomic-level description of the dislocation-mediated plasticity.

36 MATERIALS SCIENCE↗
NASA NTRS1999

Weakly Nonlinear Description of Parametric Instabilities in Vibrating Flows

This project focuses on the effects of weak dissipation on vibrational flows in microgravity and in particular on (a) the generation of mean flows through viscous effects and their reaction on the flows themselves, and (b) the effects of finite group velocity and dispersion on the resulting dynamics in large domains. The basic mechanism responsible for the generation of such flows is nonlinear and was identified by Schlichting [21] and Longuet-Higgins. However, only recently has it become possible to describe such flows self-consistently in terms of amplitude equations for the parametrically excited waves coupled to a mean flow equation. The derivation of these equations is nontrivial because the limit of zero viscosity is singular. This project focuses on various aspects of this singular problem (i.e., the limit C equivalent to (nu)((g)(h(exp 3)))exp -1/2 << 1,where nu is the kinematic viscosity and h is the liquid depth) in the weakly nonlinear regime. A number of distinct cases is identified depending on the values of the Bond number, the size of the nonlinear terms, distance above threshold and the length scales of interest. The theory provides a quantitative explanation of a number of experiments on the vibration modes of liquid bridges and related experiments on parametric excitation of capillary waves in containers of both small and large aspect ratio. The following is a summary of results obtained thus far.

Knobloch, E.↗
DOE OSTI2022

Simulations of x-ray absorption spectra for CO desorbing from Ru(0001) with transition-potential and time-dependent density functional theory approaches

The desorption of a carbon monoxide molecule from a Ru(0001) surface was studied by means of X-ray Absorption Spectra (XAS) computed with Transition Potential (TP-DFT) and Time Dependent (TD-DFT) DFT methods. By unraveling the evolution of the CO electronic structure upon desorption, we observed that at 2.3 Å from the surface, the CO molecule has already predominantly gas-phase character. While C 1s XAS is quite insensitive to changes in the C–O bond length, the O 1s excitation is very sensitive with the π* coming down in energy upon CO bond stretching, which competes with the increase in orbital energy due to the repulsive interaction with the metallic surface. We show in a systematic way that the TP-DFT method can describe the XAS rather well at the endpoints (chemisorbed and gas phase) but is affected by artificial charge transfer and/or incorrect spin treatment in the transition region in cases like CO, where there are low-lying π* orbitals and large exchange interactions between the core 1s and valence-acceptor π* orbitals. As an alternative, we demonstrate by comparing with experimental data that a linear response approach using TD-DFT employing common exchange-correlation functionals and finite-size clusters can yield a good description of the spectral evolution of the 1s → π* transition with correct spin and gas-to-chemisorbed chemical shifts in good agreement with experiment.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2021

Quantum Nature of Dielectric Laser Accelerators

Dielectric laser accelerators (DLAs) hold great promise for producing economic and compact on-chip radiation sources. On-chip DLAs benefit from fabrication capabilities of the silicon industry and from breakthroughs in silicon-photonic nanostructures to enhance the interaction between particles and laser fields. Seemingly unrelated recent advances in the quantum interactions of electrons and light have raised interest in the underlying classical-quantum correspondence principle at the foundations of electron acceleration. Here, we present the observation of the underlying quantum nature of DLAs: observing quantized peaks in the electron-energy spectra. Our findings demonstrate quasi-phase-matching between an electron wave function and a light wave, which also demonstrates the role of the quantum wave function in the inverse Smith-Purcell effect. We harness the capabilities of an ultrafast transmission electron microscope (UTEM) to maintain a long electron-light interaction length extending over hundreds of periods of the laser pulse, mediated by a silicon-photonic nanograting DLA. The UTEM is shown as a new platform for characterization of future DLA concepts. The results raise fundamental questions regarding the role of quantum mechanics in DLA design, and more generally about the prospects of manipulating particles’ quantum wave functions in accelerator physics.

43 PARTICLE ACCELERATORS↗
NASA NTRS1986

Propagation of sound waves in tubes of noncircular cross section

Plane-acoustic-wave propagation in small tubes with a cross section in the shape of a flattened oval is described. Theoretical descriptions of a plane wave propagating in a tube with circular cross section and between a pair of infinite parallel plates, including viscous and thermal damping, are expressed in similar form. For a wide range of useful duct sizes, the propagation constant (whose real and imaginary parts are the amplitude attenuation rate and the wave number, respectively) is very nearly the same function of frequency for both cases if the radius of the circular tube is the same as the distance between the parallel plates. This suggests that either a circular-cross-section model or a flat-plate model can be used to calculate wave propagation in flat-oval tubing, or any other shape tubing, if its size is expressed in terms of an equivalent radius, given by g = 2 x (cross-sectional area)/(length of perimeter). Measurements of the frequency response of two sections of flat-oval tubing agree with calculations based on this idea. Flat-plate formulas are derived, the use of transmission-line matrices for calculations of plane waves in compound systems of ducts is described, and examples of computer programs written to carry out the calculations are shown.

Richards, W. B.↗
NASA NTRS1991

Detection of reflector surface from near field phase measurements

The deviation of a reflector antenna surface from a perfect parabolic shape causes degradation of the performance of the antenna. The problem of determining the shape of the reflector surface in a reflector antenna using near field phase measurements is not a new one. A recent issue of the IEEE tansactions on Antennas and Propagation (June 1988) contained numerous descriptions of the use of these measurements: holographic reconstruction or inverse Fourier transform. Holographic reconstruction makes use of measurement of the far field of the reflector and then applies the Fourier transform relationship between the far field and the current distribution on the reflector surface. Inverse Fourier transformation uses the phase measurements to determine the far field pattern using the method of Kerns. After the far field pattern is established, an inverse Fourier transform is used to determine the phases in a plane between the reflector surface and the plane in which the near field measurements were taken. These calculations are time consuming since they involve a relatively large number of operations. A much faster method can be used to determine the position of the reflector. This method makes use of simple geometric optics to determine the path length of the ray from the feed to the reflector and from the reflector to the measurement point. For small physical objects and low frequencies, diffraction effects have a major effect on the error, and the algorithm provides incorrect results. It is believed that the effect is less noticeable for large distortions such as antenna warping, and more noticeable for small, localized distortions such as bumps and depressions such as might be caused by impact damage.

Ida, Nathan↗
NASA NTRS2016

Category B Plastic Pane Testing for JSC 66320 Rev A Requirements Verifiable Through Acceptance Testing

JSC 66320, Revision A, Optical Property Requirements for Glasses, Ceramics, and Plastics in Spacecraft Window Systems, lists several quantitative requirements that spacecraft windowpanes must meet. Recently, we were asked to establish a capability at the Kennedy Space Center to perform these measurements on category B plastic panes, i.e., plastic panes that could be used on a spacecraft for long-focal-length photography and piloting. Two of the criteria, normal wavefront and 30-degree wavefront attributes, can be measured with existing equipment and processes (see NASA TM NESC-RP-14-00951, April 2016) and are not discussed in this document. However, the other six criteria-haze, wedge angle, birefringence, reflectance, transmittance, and color balance-required substantial development and are the subject of this document. In this document, we do not discuss the rationale behind the requirements, but we did engage in discussions with the authors of JSC 66320 in order to better understand the requirements and the verifications being imposed on windows and their testing. Accordingly, this document presents our best understanding of the requested requirements and verifications. We also present our methodology for performing each of the six measurements, along with applicable mathematics and a description, with photos, of the hardware used. In addition, we supply the results of a test on a low-quality in-house plastic window as an example of the system operation. Only requirements that can be met by acceptance test and analysis, as opposed to optical inspection, are considered in this document.

spaceflight windows↗
DOE OSTI2026

Neural-network quantum states for the nuclear many-body problem

A long-standing goal of nuclear theory is to explain how the structure and dynamics of atomic nuclei and neutron-star matter emerge from the underlying interactions among protons and neutrons. Achieving this goal requires solving the nuclear quantum many-body problem with high accuracy across a wide range of length scales and density regimes. In this review, we discuss how artificial neural network representations of the nuclear many-body wave function have significantly extended the capabilities of continuum quantum Monte Carlo methods. In particular, neural network quantum states enable calculations of larger systems than were previously accessible and provide a flexible framework for capturing phenomena that challenge conventional approaches, including the emergence of nuclear clusters and superfluid phases in dense matter. We highlight recent applications to finite nuclei, infinite nuclear and neutron matter, and dynamical processes relevant to lepton-nucleus and nucleus-nucleus scattering. We also discuss conceptual and methodological connections with condensed matter physics, emphasizing developments in neural network quantum states that bridge strongly correlated systems across disciplines. Together, these developments demonstrate how neural-network methods open new avenues toward unified and accurate descriptions of nuclear structure, matter, and reactions.

Lovato, Alessandro [Argonne; TIFPA-INFN, Trento; V↗
NASA NTRS1998

Studies of Avalanche Photodiodes (APDS) as Readout Devices for Scintillating Fibers for High Energy Gamma-Ray Astronomy Telescopes

New gamma ray and charged particle telescope designs based on scintillating fiber arrays could provide low cost, high resolution, lightweight, very large area and multi radiation length instrumentation for planned NASA space exploration. The scintillating fibers low visible light output requires readout sensors with single photon detection sensitivity and low noise. The sensitivity of silicon Avalanche Photodiodes (APDS) matches well the spectral output of the scintillating fibers. Moreover, APDs have demonstrated single photon capability. The global aim of our work is to make available to NASA a novel optical detector concept to be used as scintillating fiber readouts and meeting the requirements of the new generations of space-borne gamma ray telescopes. We proposed to evaluate the feasibility of using RMD's small area APDs ((mu)APD) as scintillating fiber readouts and to study possible alternative (mu)APD array configurations for space borne readout scintillating fiber systems, requiring several hundred thousand to one million channels. The evaluation has been conducted in accordance with the task description and technical specifications detailed in the NASA solicitation "Studies of Avalanche Photodiodes (APD as readout devices for scintillating fibers for High Energy Gamma-Ray Astronomy Telescopes" (#8-W-7-ES-13672NAIS) posted on October 23, 1997. The feasibility study we propose builds on recent developments of silicon APD arrays and light concentrators advances at RMD, Inc. and on more than 5 years of expertise in scintillating fiber detectors. In a previous program we carried out the initial research to develop a high resolution, small pixel, solid-state, silicon APD array which exhibited very high sensitivity in the UV-VIS spectrum. This (mu)APD array is operated in Geiger mode and results in high gain (greater than 10(exp 8)), extremely low noise, single photon detection capability, low quiescent power (less than 10 (mu)W/pixel for 30 micrometers sensitive area diameter) and output in the 1-5 volt range. If successful, this feasibility study will make possible the development of a scintillating fiber detector with unsurpassed sensitivity, extremely low power usage, a crucial factor of merit for space based sensors and telescopes.

Vasile, Stefan↗
NASA NTRS1998

Test of a flexible spacecraft dynamics simulator

There are a number of approaches one can take to modeling the dynamics of a flexible body. While one can attempt to capture the full dynamical behavior subject to disturbances from actuators and environmental torques, such a detailed description often is unnecessary. Simplification is possible either by limiting the amplitude of motion to permit linearization of the dynamics equations or by restricting the types of allowed motion. In this work, we study the nonlinear dynamics of bending deformations of wire booms on spinning spacecraft. The theory allows for large amplitude excursions from equilibrium while enforcing constraints on the dynamics to prohibit those modes that are physically less relevant or are expected to damp out fast. These constraints explicitly remove the acoustic modes (i.e., longitudinal sound waves and shear waves) while allowing for arbitrary bending and twisting, motions which typically are of lower frequency. As a test case, a spin axis reorientation maneuver by the Polar Plasma Laboratory (POLAR) spacecraft has been simulated. POLAR was chosen as a representative spacecraft because it has flexible wire antennas that extend to a length of 65 meters. Bending deformations in these antennas could be quite large and have a significant effect on the attitude dynamics of the spacecraft body. Summary results from the simulation are presented along, with a comparison with POLAR flight data.

Dichmann, Donald↗
DOE OSTI2024

DAISY Benchmark Performance Data

This repository contains the underlying data from benchmark experiments for Drifting Acoustic Instrumentation SYstems (DAISYs) in waves and currents described in "Performance of a Drifting Acoustic Instrumentation SYstem (DAISY) for Characterizing Radiated Noise from Marine Energy Converters" (https://link.springer.com/article/10.1007/s40722-024-00358-6). DAISYs consist of a surface expression connected to a hydrophone recording package by a tether. Both elements are instrumented to provide metadata (e.g., position, orientation, and depth). Information about how to build DAISYs is available at https://www.pmec.us/research-projects/daisy. The repository's primary content is three compressed archives (.zip format), each containing multiple MATLAB binary data files (.mat format). A table relating individual data files to figures in the paper, as well as the structure of each file, is included in the repository as a Word document (Data Description MHK-DR.docx). Most of the files contain time series information for a single DAISY deployment (file naming convention: [site]_DAISY_[Drift #].mat) consisting of processed hydrophone data and associated metadata. For a limited number of DAISY deployments, the hydrophone package was replaced with an acoustic Doppler velocimeter (file naming convention: [site]_DAISY_[Drift #]_ADV.mat). Data were collected over several years at three locations: (1) Sequim Bay at Pacific Northwest National Laboratory's Marine & Coastal Research Laboratory (MCRL) in Sequim, WA, the energetic tidal channel in Admiralty Inlet, WA (Admiralty Inlet), and the U.S. Navy's Wave Energy Test Site (WETS) in Kaneohe, HI. Brief descriptions of data files at each location follow. - MCRL - (1) Drift #4 and #16 contrast the performance of a DAISY and a reference hydrophone (icListen HF Reson), respectively, in the quiescent interior of Sequim Bay (September 2020). (2) Drift #152 and #153 are velocity measurements for a drifting acoustic Doppler velocimeter in in the tidally-energetic entrance channel inside a flow shield and exposed to the flow, respectively (January 2018). (3) Two non-standard files are also included: DAISY_data.mat corresponds to a subset of a DAISY drift over an Adaptable Monitoring Package (AMP) and AMP_data.mat corresponds to approximately co-temporal data for a stationary hydrophone on the AMP (February 2019). - Admiralty Inlet - (1) Drift #1-12 correspond to tests with flow shielded DAISYs, unshielded DAISYs, a reference hydrophone, and drifting acoustic Doppler velocimeter with 5, 10, and 15 m tether lengths between surface expression and hydrophone recording package (July 2022). (2) Drift #13-20 correspond to tests of flow shielded DAISYs with three different tether materials (rubber cord, nylon line, and faired nylon line) in lengths of 5, 10, and 15 m (July 2022). - WETS - (1) Drift #30-32 correspond to tests with a heave plate incorporated into the tether (standard configuration for wave sites), rubber cord only, and rubber cord, but with a flow shielded hydrophone (November 2022). (2) Drift #49-58 and Drift #65-68 correspond to measurements around mooring infrastructure at the 60 m berth where time-delay-of-arrival localization was demonstrated for different DAISY arrangements and hydrophone depths (November 2022).

16 TIDAL AND WAVE POWER↗
NASA NTRS1995

Wave and ion evolution downstream of quasi-perpendicular bow shocks

Distribution functions of ions heated in quasi-perpendicular bow shocks have a large perpendicular temperature anisotropy that provides free energy for the growth of Alfven ion cyclotron (AIC) waves and mirror waves. Both types of waves have been observed in the Earth's magnetosheath downstream of quasi-perpendicular shocks. We use a two-dimensional hybrid simulations to give a self-consistent description of the evolution of the wave spectra downstream of quasi-perpendicular shocks. Both mirror and AIC waves are identified in the simulated magnetosheath. They are generated at or near the shock front and convected away from it by the sheath plasma. Near the shock, the waves have a broad spectrum, but downstream of the shock, shorter-wavelength modes are heavily damped and only longer-wavelength modes persist. The characteristics of these surviving modes can be predicted with reasonable accuracy by linear kinetic theory appropriate for downstream conditions. We also follow the evolution of the ion distribution function. The shocked ions that provide the free energy for wave growth have a two-component distribution function. The halo is initially gyrophase-bunched and extremely anisotropic. Within a relatively short distance downstream of the shock (of the order of 10 ion inertial lengths), wave-particle interactions remove these features from the halo and reduce the anisotropy of the distribution to near-threshold levels for the mirror and AIC instabilities. A similar evolution has been observed for ions at the Earth's bow shock.

Mckean, M. E.↗