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NASA NTRSDate not supplied

X-57 Mod III Wing Ground Vibration Test

The X-57 “Maxwell” all-electric experimental aircraft was an electric propulsion demonstrator developed by the National Aeronautics and Space Administration to inform airworthiness standards for electrified aircraft. The development of the X-57 aircraft was separated into configuration modifications culminating in a distributed electric propulsion flight demonstrator named Modification IV (a.k.a., Mod IV). One of these configurations, the X-57 Mod III aircraft, involved flight-testing of a long, slender, high-aspect-ratio wing with two electric motors located at the wingtips. The X-57 Mod III wing ground vibration test was performed in the Flight Loads Laboratory at the National Aeronautics and Space Administration Armstrong Flight Research Center to measure the structural dynamics properties of the newly developed wing, and to confirm airworthiness of the Mod III/IV aircraft. This paper describes the testing performed to acquire the modal data and the subsequent results from the test.

Samson Truong↗
NASA NTRS1990

Optimization of rotor blades for combined structural, dynamic, and aerodynamic properties

Optimal helicopter blade design with computer-based mathematical programming has received more and more attention in recent years. Most of the research has focused on optimum dynamic characteristics of rotor blades to reduce vehicle vibration. There is also work on optimization of aerodynamic performance and on composite structural design. This research has greatly increased our understanding of helicopter optimum design in each of these aspects. Helicopter design is an inherently multidisciplinary process involving strong interactions among various disciplines which can appropriately include aerodynamics; dynamics, both flight dynamics and structural dynamics; aeroelasticity: vibrations and stability; and even acoustics. Therefore, the helicopter design process must satisfy manifold requirements related to the aforementioned diverse disciplines. In our present work, we attempt to combine several of these important effects in a unified manner. First, we design a blade with optimum aerodynamic performance by proper layout of blade planform and spanwise twist. Second, the blade is designed to have natural frequencies that are placed away from integer multiples of the rotor speed for a good dynamic characteristics. Third, the structure is made as light as possible with sufficient rotational inertia to allow for autorotational landing, with safe stress margins and flight fatigue life at each cross-section, and with aeroelastical stability and low vibrations. Finally, a unified optimization refines the solution.

He, Cheng-Jian↗
DOE OSTI2025

Surface acoustic waves and lattice vibrations in two-dimensional Ti 3 ⁢C 2 ⁢𝑇 𝑥 (𝑇 =O, F) MXene films

We investigated surface acoustic wave (SAW) propagation and lattice vibrations in two-dimensional (2D) titanium carbide (Ti 3 ⁢C 2 ⁢𝑇 x ) MXene films as a function of surface termination and layer stacking, using atomistic simulations. We found that SAW propagation velocity is highly sensitive to both single-layer properties and interlayer bonding. Surface terminations significantly modulate wave behavior, with oxygen and fluorine terminations producing distinct effects on wave propagation, with oxygen-terminated monolayers exhibiting 20% higher wave speeds than fluorine counterparts due to strengthened intralayer bonds. Key observations include the transition from one to two layers causing wave speed variations, and the development of interlayer modes that generate more dispersed lattice vibrations. As the film layer thickness increases, SAW propagation becomes predominantly confined to the upper surface, with coherence of vibrational modes diminishing in multilayer structures. These findings suggest MXene terminations and layer stacking are crucial parameters for controlling SAW behavior, offering promising avenues for novel acoustic wave device applications.

2-dimensional systems↗
DOE OSTI2023

The structure of plastocyanin tunes the midpoint potential by restricting axial ligation of the reduced copper ion

Blue copper proteins are models for illustrating how proteins tune metal properties. Nevertheless, the mechanisms by which the protein controls the metal site remain to be fully elucidated. A hindrance is that the closed shell Cu(I) site is inaccessible to most spectroscopic analyses. Carbon deuterium (C-D) bonds used as vibrational probes afford nonperturbative, selective characterization of the key cysteine and methionine copper ligands in both redox states. The structural integrity of Nostoc plastocyanin was perturbed by disrupting potential hydrogen bonds between loops of the cupredoxin fold via mutagenesis (S9A, N33A, N34A), variably raising the midpoint potential. The C-D vibrations show little change to suggest substantial alteration to the Cu(II) coordination in the oxidized state or in the Cu(I) interaction with the cysteine ligand. They rather indicate, along with visible and NMR spectroscopy, that the methionine ligand distinctly interacts more strongly with the Cu(I) ion, in line with the increases in midpoint potential. Here we show that the protein structure determines the redox properties by restricting the interaction between the methionine ligand and Cu(I) in the reduced state.

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

Electronic structure of NdO via slow photoelectron velocity-map imaging spectroscopy of NdO –

Electronically excited NdO is a possible product of the chemistry associated with the release of Nd into the ionosphere, and emission from these states may contribute to the observations following such experiments. To better characterize the energetics and spectroscopy of NdO, we report a combined experimental and theoretical study using slow photoelectron velocity-map imaging spectroscopy of cryogenically cooled NdO – anions (cryo-SEVI) supplemented by wave function-based quantum-chemical calculations. Using cryo-SEVI, we measure the electron affinity of NdO to be 1.0091(7) eV and resolve numerous transitions to low-lying electronic and vibrational states of NdO that are assigned with the aid of the electronic structure calculations. Additionally, temperature-dependent data suggest contributions from the (2)4.5 state of NdO – residing 2350 cm –1 above the ground anion state. Finally, photodetachment to higher-lying excited states of NdO is also reported, which may help to clarify observations from prior release experiments.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2025

Spectroscopic Properties of Americium(III) in Mineral Acid Media

We report the preparation and optical characterization of three solutions of Am(III) in common aqueous (aq.) mineral acids (HCl, HNO 3 and HBr), including absorption, emission, and Raman vibrational analyses. To our knowledge, this study provides the first detailed absorption spectra of Am(III) spanning the entire UV/Vis/NIR region in these mineral acids reported since the 1960s. Here, using this high-resolution absorption data, provided in an open access format for the broader field, we build on prior work by Carnall and others to provide detailed optical analysis including all transition assignments. This work also includes the first reported absorption spectrum of Am(III) in aq. HBr. Characteristic Am(III) luminescence could be detected from all three samples. These are the first reports of emission from Am(III) in these acid systems, which build on prior emission reports collected from aq. HClO 4 solutions. The acquired emission spectra display anion-dependent shifting of the visible-region transitions by up to 21 nm from their predicted positions, akin to the nephelauxetic effect. The shift magnitude trends linearly according to the acid p K a and more generally according to the transition metal spectrochemical series. These ligand field effects, coupled with luminescence lifetime experiments, indicate that weak Am-X interactions persist in solution.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
NASA NTRS2013

Granular Media-Based Tunable Passive Vibration Suppressor

and vibration suppression device is composed of statically compressed chains of spherical particles. The device superimposes a combination of dissipative damping and dispersive effects. The dissipative damping resulting from the elastic wave attenuation properties of the bulk material selected for the granular media is independent of particle geometry and periodicity, and can be accordingly designed based on the dissipative (or viscoelastic) properties of the material. For instance, a viscoelastic polymer might be selected where broadband damping is desired. In contrast, the dispersive effects result from the periodic arrangement and geometry of particles composing a linear granular chain. A uniform (monatomic) chain of statically compressed spherical particles will have a low-pass filter effect, with a cutoff frequency tunable as a function of particle mass, elastic modulus, Poisson fs ratio, radius, and static compression. Elastic waves with frequency content above this cutoff frequency will exhibit an exponential decay in amplitude as a function of propagation distance. System design targeting a specific application is conducted using a combination of theoretical, computational, and experimental techniques to appropriately select the particle radii, material (and thus elastic modulus and Poisson fs ratio), and static compression to satisfy estimated requirements derived for shock and/or vibration protection needs under particular operational conditions. The selection of a chain of polymer spheres with an elastic modulus .3 provided the appropriate dispersive filtering effect for that exercise; however, different operational scenarios may require the use of other polymers, metals, ceramics, or a combination thereof, configured as an array of spherical particles. The device is a linear array of spherical particles compressed in a container with a mechanism for attachment to the shock and/or vibration source, and a mechanism for attachment to the article requiring isolation (Figure 1). This configuration is referred to as a single-axis vibration suppressor. This invention also includes further designs for the integration of the single-axis vibration suppressor into a six-degree-of-freedom hexapod "Stewart"mounting configuration (Figure 2). By integrating each singleaxis vibration suppressor into a hexapod formation, a payload will be protected in all six degrees of freedom from shock and/or vibration. Additionally, to further enable the application of this device to multiple operational scenarios, particularly in the case of high loads, the vibration suppressor devices can be used in parallel in any array configuration.

Dillon, Robert P.↗
DOE OSTI2024

Transferable Water Potentials Using Equivariant Neural Networks

Machine learning interatomic potentials (MLIPs) have emerged as a technique that promises quantum theory accuracy for reduced cost. It has been proposed [J. Chem. Phys. 2023, 158, 084111] that MLIPs trained on solely liquid water data cannot accurately transfer to the vapor–liquid equilibrium while recovering the many-body decomposition (MBD) analysis of gas-phase water clusters. This suggests that MLIPs do not directly learn the physically correct interactions of water molecules, limiting transferability. In this work, we show that MLIPs using equivariant architecture and trained on 3200 liquid water structures reproduces liquid-phase water properties (e.g., density within 0.003 g/cm 3 between 230 and 365 K), vapor–liquid equilibrium properties up to 550 K, the MBD analysis of gas-phase water cluster up to six-body interactions, and the relative energy and the vibrational density of states of ice phases. We show that potentials developed using equivariant MLIPs allow transferability for arbitrary phases of water that remain stable in nanosecond long simulations.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
NASA NTRS1978

Odd nitrogen production by meteoroids

The process by which odd nitrogen species (atomic nitrogen and nitric oxide) are formed during atmospheric entry of meteoroids is analyzed theoretically. An ablating meteoroid is assumed to be a point source of mass with a continuum regime evolving in its wake. The amounts of odd nitrogen species, produced by high-temperature reactions of air in the continuum wake, are calculated by numerical integration of chemical rate equations. Flow properties are assumed to be uniform across the wake, and 29 reactions involving five neutral species and five singly ionized species are considered, as well as vibrational and electron temperature nonequilibrium phenomena. The results, when they are summed over the observed mass, velocity, and entry-angle distribution of meteoroids, provide odd-nitrogen-species annual global production rates as functions of altitude. The peak production of nitric oxide is found to occur at an altitude of about 85 km; atomic nitrogen production peaks at about 95 km. The total annual rate for nitric oxide is 40 million kg; for atomic nitrogen it is 170 million kg.

Park, C.↗
NASA NTRS2009

Objectives and Progress on Integrated Vehicle Ground Vibration Testing for the Ares Launch Vehicles

As NASA begins design and development of the Ares launch vehicles to replace the Space Shuttle and explore beyond low Earth orbit, Integrated Vehicle Ground Vibration Testing (IVGVT) will be a vital component of ensuring that those vehicles can perform the missions assigned to them. A ground vibration test (GVT) is intended to measure by test the fundamental dynamic characteristics of launch vehicles during various phases of flight. During the series of tests, properties such as natural frequencies, mode shapes, and transfer functions are measured directly. This data is then used to calibrate loads and control systems analysis models for verifying analyses of the launch vehicle. The Ares Flight & Integrated Test Office (FITO) will be conducting IVGVT for the Ares I crew launch vehicle at Marshall Space Flight Center (MSFC) from 2011 to 2012 using the venerable Test Stand (TS) 4550, which supported similar tests for the Saturn V and Space Shuttle vehicle stacks.

Tuma, Margaret L.↗
DOE OSTI2021

Temperature Dependent Local Atomic Structure and Vibrational Dynamics of Barium Hydride and Calcium Hydride

Solid-state ionic conductors that exhibit pure ionic transport of hydride anions are rare. Here, we investigate two alkaline earth metal hydrides, barium hydride and calcium hydride, using neutron scattering techniques to understand how the local atomic environment plays a role in the diffusion of hydride ions. At high temperatures, barium hydride exhibits exceptional transport properties with ionic conductivities that are higher than those of many of the typical proton and oxide ion conductors in use today. Total neutron scattering and pair distribution function analysis reveal how a structural phase transition converts barium hydride from a modest ionic conductor into a fast ionic conductor through the introduction of disorder, deuterium site splitting, and dynamic structural fluctuations. Furthermore, neutron vibrational spectroscopy is employed to probe changes in the temperature evolution of the lattice dynamics and local energy landscape. These results improve our fundamental knowledge of the interplay between structure and dynamics governing a rare conduction process of hydride ions in solid-state materials.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2023

Accurate prediction of short-range order and its effect on thermodynamic, structural, and electronic properties of disordered alloys: exemplified in archetypical Cu 3 Au

Electronic-structure methods based on density-functional theory (DFT) were used to quantify the effect of chemical short-range order (SRO) on thermodynamic, structural, and electronic properties of archetypal face-centered-cubic (fcc) Cu3Au alloy. We showed that SRO can be tuned to alter bonding and lattice dynamics (i.e., phonons) and detail how these properties are changed with SRO. Thermodynamically favorable SRO significantly improved the phase stability of fcc Cu3Au from -0.0343 eV-atom -1 to –0.0682 eV-atom -1 . We used our DFT-based linear-response theory to predict SRO and its electronic origin, and accurately estimate the observed transition temperature, ordering instability (L1 2 ), and Warren-Cowley SRO parameters, in agreement with experiments. The accurate prediction of real-space SRO gives an edge over computationally and resource intensive approaches such as monte-carlo methods or experiments, which will enable large scale molecular dynamic simulations by providing supercells with optimized SRO. Here we also analyzed phonon dispersion and estimated the vibrational entropy change (from 9kB at 300 K to 6kB at 100 K) in fcc Cu3Au. We established from SRO analysis that exclusion of chemical interactions may lead to a skewed view of true properties in chemically complex alloys. The first-principles methods described in this work are generally applicable to any arbitrary solid-solution alloys, including multi-principal-element alloys, therefore, holds promise for designing technologically useful materials.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Programmable Catalyst Structures via Adsorbate-Induced Adatom Assembly

The electronic structure and geometric configuration of oxide-supported metal ions are important coordination properties that can be related to catalytic activity and stability. Herein, we interrogate the coordination environment of mononuclear Pd ions supported on ceria using CO adsorption, infrared vibrational spectroscopy, and DFT modeling. We observed the 15 h continuous co-evolution of a palladium- (2167 cm -1 ) and cerium-carbonyl (2177 cm -1 ) complex by monitoring the $\nu$(CO) infrared region. The slow CO adsorption kinetics were caused by the reactive ligand exchange between an oxygen atom of the support and the CO adsorbate to yield an oxygen vacancy and adsorbed CO 2 . We hypothesize that the co-evolved cerium-carbonyl complex was formed upon CO adsorption at or adjacent to this oxygen vacancy. Our hypothesis was experimentally supported by a dramatic attenuation of the cerium carbonyl signal upon pre-adsorption of water through an apparent competitive adsorption mechanism. The attenuation was also accompanied by a 6 cm -1 redshift of the palladium carbonyl band (2161 cm -1 ) attributed to hydrogen bonding between the carbonyl and a nearby hydroxyl. Characteristic n(CO) stretch frequencies catalogued through CO adsorption onto single crystal ceria by Wöll et al.1 led us to index the cerium carbonyl to the {100} nanofacet of the polycrystalline ceria support. It follows from the observed co-evolution of the two carbonyl complexes that Pd was also adsorbed at the {100} nanofacet. Redeployment of a previously developed DFT model by Ivanova-Shor et al.2 featuring square-planar coordination of Pd2+ at the {100} nanofacet (O 4 Pd) of a Ce 21 O 42 nanoparticle model qualitatively reproduced several experimental observations.

36 MATERIALS SCIENCE↗
NASA NTRS1972

Neutron stars.

Particular attention is given to the physical concepts underlying neutron stars. The characteristics of an equation of state which is suitable for a neutron star configuration are discussed. Cold neutron star models are examined, including the properties of a particular model in the intermediate range of stable models. Questions regarding the thermal energy of a neutron star are discussed together with aspects of vibrational energy, rotational energy, magnetic energy, and problems in connection with the Vela pulsar.

Cameron, A. G. W.↗
NASA NTRS1989

Dust coagulation in ISM

Coagulation is an important mechanism in the growth of interstellar and interplanetary dust particles. The microphysics of the coagulation process was theoretically analyzed as a function of the physical properties of the coagulating grains, i.e., their size, relative velocities, temperature, elastic properties, and the van der Waal interaction. Numerical calculations of collisions between linear chains provide the wave energy in individual particles and the spectrum of the mechanical vibrations set up in colliding particles. Sticking probabilities are then calculated using simple estimates for elastic deformation energies and for the attenuation of the wave energy due to absorption and scattering processes.

Chokshi, Arati↗
DOE OSTI2020

Ultrafast vibrational dynamics of a trigonal planar anionic probe in ionic liquids (ILs): A two-dimensional infrared (2DIR) spectroscopic investigation

A major impediment limiting the widespread application of ionic liquids (ILs) is their high shear viscosity. Incorporation of a tricyanomethanide (TCM - ) anion in ILs leads to low shear viscosity and improvement of several characteristics suitable for large scale applications. However, properties including interactions of TCM - with the local environment and dynamics of TCM - have not been thoroughly investigated. Herein, we have studied the ultrafast dynamics of TCM - in several imidazolium ILs using linear IR and two-dimensional infrared spectroscopy techniques. The spectral diffusion dynamics of the CN stretching modes of TCM - in all ILs exhibit a nonexponential behavior with a short time component of ~2 ps and a long time component spanning ~9 ps to 14 ps. The TCM - vibrational probe reports a significantly faster relaxation of ILs compared to those observed previously using linear vibrational probes, such as thiocyanate and selenocyanate. Our results indicate a rapid relaxation of the local ion-cage structure embedding the vibrational probe in the ILs. The faster relaxation suggests that the lifetime of the local ion-cage structure decreases in the presence of TCM - in the ILs. Linear IR spectroscopic results show that the hydrogen-bonding interaction between TCM - and imidazolium cations in ILs is much weaker. Shorter ion-cage lifetimes together with weaker hydrogen-bonding interactions account for the low shear viscosity of TCM - based ILs compared to commonly used ILs. In addition, this work demonstrates that TCM - can be used as a potential vibrational reporter to study the structure and dynamics of ILs and other molecular systems.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
NASA NTRS2008

Integrated Vehicle Ground Vibration Testing in Support of NASA Launch Vehicle Loads and Controls Analysis

The National Aeronautics and Space Administration (NASA) Ares Projects Office (APO) is continuing to make progress toward the final design of the Ares I crew launch vehicle and Ares V cargo launch vehicle. Ares I and V will form the space launch capabilities necessary to fulfill NASA's exploration strategy of sending human beings to the Moon, Mars, and beyond. As with all new space vehicles there will be a number of tests to ensure the design can be Human Rated. One of these is the Integrated Vehicle Ground Vibration Test (IVGVT) that will be measuring responses of the Ares I as a system. All structural systems possess a basic set of physical characteristics unique to that system. These unique characteristics include items such as mass distribution, frequency and damping. When specified, they allow engineers to understand and predict how a structural system like the Ares I launch vehicle behaves under given loading conditions. These physical properties of launch vehicles may be predicted by analysis or measured through certain types of tests. Generally, these properties are predicted by analysis during the design phase of a launch vehicle and then verified through testing before the vehicle is Human Rated. The IVGVT is intended to measure by test the fundamental dynamic characteristics of Ares I during various phases of operational/flight. This testing includes excitations of the vehicle in lateral, longitudinal, and torsional directions at vehicle configurations representing different trajectory points. During the series of tests, properties such as natural frequencies, mode shapes, and transfer functions are measured directly. These data will then be used to calibrate loads and Guidance, Navigation, and Controls (GN&C) analysis models for verifying analyses of Ares I. NASA launch vehicles from Saturn to Shuttle have undergone Ground Vibration Tests (GVTs) leading to successful launch vehicles. A GVT was not performed on the unmanned Delta III. This vehicle was lost during launch. Subsequent analyses indicated that had a GVT been conducted on the vehicle, problems with vehicle modes and control may have been discovered and corrected, avoiding loss of the vehicle/mission. This paper will address GVT planning, set-up, conduction and analyses, for the Saturn and Shuttle programs, and also focus on the current and on-going planning for the Ares I and V IVGVT.

Tuma, Margaret L.↗
DOE OSTI2020

Oxide-Free Three-Dimensional Germanium/Silicon Core–Shell Metalattice Made by High-Pressure Confined Chemical Vapor Deposition

Metalattices are crystalline arrays of uniform particles in which the period of the crystal is close to some characteristic physical length scale of the material. In this work, we explore the synthesis and properties of a germanium metalattice in which the similar to 70 nm periodicity of a silica colloidal crystal template is close to the similar to 24 nm Bohr exciton radius of the nanocrystalline Ge replica. The problem of Ge surface oxidation can be significant when exploring quantum confinement effects or designing electronically coupled nanostructures because of the high surface area to volume ratio at the nanoscale. To eliminate surface oxidation, we developed a coreshell synthesis in which the Ge metalattice is protected by an oxide-free Si interfacial layer, and we explore its properties by transmission electron microscopy (TEM), Raman spectroscopy, and electron energy loss spectroscopy (EELS). The interstices of a colloidal crystal film grown from 69 nm diameter spherical silica particles were filled with polycrystalline Ge by high-pressure confined chemical vapor deposition (HPcCVD) from GeH4. After the SiO2 template was etched away with aqueous HF, the Ge replica was uniformly coated with an amorphous Si shell by HPcCVD as confirmed by TEM-EDS (energy-dispersive X-ray spectroscopy) and Raman spectroscopy. Formation of the shell prevents oxidation of the Ge core within the detection limit of XPS. The electronic properties of the core-shell structure were studied by accessing the Ge 3d edge onset using STEM-EELS. A blue shift in the edge onset with decreasing size of Ge sites in the metalattices suggests quantum confinement of the Ge core. The degree of quantum confinement of the Ge core depends on the void sizes in the template, which is tunable by using silica particles of varying size. The edge onset also shows a shift to higher energy near the shell in comparison with the Ge core. This shift along with the observation of Ge-Si vibrational modes in the Raman spectrum indicate interdiffusion of Ge and Si. Both the size of the voids in the template and core-shell interdiffusion of Si and Ge can in principle be tuned to modify the electronic properties of the Ge metalattice.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗