Search NASA⌕ Search

SEARCH · Search NASA

Results for “EIGENFREQUENCY”

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.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 19 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2020

Eigenfrequency constrained topology optimization of finite strain hyperelastic structures

This paper incorporates hyperelastic materials, nonlinear kinematics, and preloads in eigenfrequency constrained density–based topology optimization. The formulation allows for initial finite deformations and subsequent small harmonic oscillations. The optimization problem is solved by the method of moving asymptotes, and the gradients are calculated using the adjoint method. Both simple and degenerate eigenfrequencies are considered in the sensitivity analysis. A well-posed topology optimization problem is formulated by filtering the volume fraction field. Numerical issues associated with excessive distortion and spurious eigenmodes in void regions are reduced by removing low volume fraction elements. The optimization objective is to maximize stiffness subject to a lower bound on the fundamental eigenfrequency. Numerical examples show that the eigenfrequencies drastically change with the load magnitude, and that the optimization is able to produce designs with the desired fundamental eigenfrequency.

42 ENGINEERING↗
DOE OSTI2019

Eigenfrequency-Based Prediction of the Cutting Properties of Superhard Inserts

The relation between the cutting properties of superhard tool inserts and their eigenfrequency is studied. The relation between the life of inserts and their acoustic properties is confirmed experimentally in the turning of high-temperature nickel alloys and quenched steels. A method is developed for determining the eigenfrequency of cutting inserts, along with the corresponding equipment.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Acoustic manipulation of fluids based on eigenfrequency

An acoustic resonator device includes a fluid chamber with a carrier surface and a reflector surface. The fluid chamber is filled with a volume of a fluid that includes a phase-separate material such as algae. The carrier surface is coupled to a transducer, which may be a lead zirconate titanate (PZT) transducer. The transducer, when supplied with electricity, emits an acoustic wave-based output of an output frequency (e.g., ultrasound). A sensor may be used to track one or more eigenfrequencies of the volume of fluid, the acoustic resonator device, or some combination thereof. A controller may receive tracking data from the sensor and control the voltage source, the transducer, or some combination thereof to ensure that the output frequency matches one of the tracked eigenfrequencies, thereby maximizing excitation of the fluid to improve efficiency of mixing, stimulation, and separation of materials from fluid (e.g., for algal biocrude production).

09 BIOMASS FUELS↗
DOE OSTI2018

Determining Eigenfrequencies and Homogeneous Widths of Lines of Intermolecular Vibrations in Water and in Aqueous Solutions of Hydrogen Peroxide Using Raman Spectroscopy

We have examined low-frequency Raman spectra of intermolecular vibrations of weak aqueous solutions of hydrogen peroxide and water. The differences between the observed Raman frequencies and the data from the literature on the IR-absorption frequencies of the same vibrations, as well as the interrelations between the frequencies and the widths of Lorentzian contours that approximate the vibrational spectra of the dynamic susceptibility, have been discussed. Based on a model of free damped vibrations of a classical oscillator with an inhomogeneous broadening, we have explained these effects for the first time. The homogeneous line widths and the damping times of the observed intermolecular vibrations have been determined. The eigenfrequencies of these vibrations have been calculated, and they have been shown to agree well with the data from the literature on the frequencies of IR absorption of water. We have shown that these parameters of intermolecular vibrations for water and for aqueous solutions of hydrogen peroxide differ from each other.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2018

Mill Eigenfrequency in Thermal Fitting

A method is proposed for the analytical calculation of the elastic displacement of a shaft relative to a bush in joints with interference under the action of radial force and a bending torque. Those displacements are associated with elastic deformation of the shaft, the bush, and the contact layer formed by their rough surfaces. On the basis of that approach, a method is proposed for estimating the lower eigenfrequency of the shaft–bush system. As an example, the thermal fitting of an axial tool in a mandrel is considered.

42 ENGINEERING↗
DOE OSTI2023

Gravitational Wave Eigenfrequencies from Neutrino-driven Core-collapse Supernovae

Abstract Core-collapse supernovae (CCSNe) are predicted to produce gravitational waves (GWs) that may be detectable by Advanced LIGO/Virgo. These GW signals carry information from the heart of these cataclysmic events, where matter reaches nuclear densities. Recent studies have shown that it may be possible to infer the properties of the proto-neutron star (PNS) via GWs generated by hydrodynamic perturbations of the PNS. However, we lack a comprehensive understanding of how these relationships may change with the properties of CCSNe. In this work, we build a self-consistent suite of over 1000 exploding CCSNe from a grid of progenitor masses and metallicities combined with six different nuclear equations of state (EOS). Performing a linear perturbation analysis on each model, we compute the resonant GW frequencies of the PNS, and we motivate a time-agnostic method for identifying characteristic frequencies of the dominant GW emission. From this, we identify two characteristic frequencies, of the early- and late-time signal, that measure the surface gravity of the cold remnant neutron star, and simultaneously constrain the hot nuclear EOS. However, we find that the details of the CCSN model, such as the treatment of gravity or the neutrino transport, and whether it explodes, noticeably change the magnitude and evolution of the PNS eigenfrequencies.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2018

Nonlocal Analysis of Natural Vibrations of Carbon Nanotubes

When the atomic level is considered, the dynamic properties have a major influence on nanostructures behavior because of their ultrahigh or very high natural frequencies. Vibrations are essential in the analysis of resonators, oscillators, and sensors for carbon nanotube-based devices. The present paper is dedicated to the eigenfrequencies analysis of single-walled carbon nanotubes. In the analysis, the small-scale coefficient is introduced, and the nonlocal elasticity theory is applied in the modal analysis of the carbon nanotubes. The correlation between nonlocal small-scale parameter and the vibrational behavior of the carbon nanotubes is studied. The determination of nonlocal parameter is based on the structural finite element model of the nanotube. A detailed parametric study is realized to investigate the effects of the length-to-diameter ratio L/D, nonlocal coefficient, the influence of boundary conditions on eigenfrequencies of carbon nanotubes. The main contribution of this work is the evaluation of the nonlocal parameter for single-walled carbon nanotubes based on the finite element approximation in modeling the dynamic behavior instead of commonly used MD simulations. It was clearly displayed that the application of the nonlocal beam models involves analysis of the small-scale parameter, whose value determines the final eigenfrequencies. The highest values of eigenfrequencies were observed for the local beam model. It was presented that the eigenfrequencies for carbon nanotubes decrease when the nanotube length increases for all analyzed modes. On the other hand, when the diameter of carbon nanotubes increases, the eigenfrequency values rise. The numerical validation of the nonlocal parameter revealed the high dependence on the boundary conditions and the mode number. However, the influence of the mode number and the boundary conditions is vanishing for long single-walled carbon nanotubes.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Coupled Electronic–Nuclear Magnetostatic Oscillations in Magnetic Materials

Magnetization dynamics in spheroidal ferromagnetic samples is studied theoretically. It is shown that, in a magnetostatic approximation, electronic-nuclear magnetostatic modes with a discrete spectrum of eigen oscillations exist in such samples. The structure and the field dependence of the frequencies of these oscillations are substantially dependent on the parameter of the spheroid shape that is the ratio of it’s axes and also on the external magnetic field value. In a certain region of values of these parameters, the dependence of the eigenfrequencies of the system on them becomes nontrivial. The external field strength and the sample shape determine not only the eigenfrequencies in the system, but also the number of the eigenmodes. In addition, for each of the eigenmodes, there exists a “forbidden” region of magnetic fields and shape parameters in which this mode cannot be observed.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2017

Optimisation of the prism coupling of optical whispering-gallery-mode microcavities

The methods for increasing the coupling efficiency of a prism with spheroidal microcavities, aimed at exciting whispering-gallery modes, have been analytically investigated. Optimal angles of incidence and incident beam parameters are obtained for a spheroidal cavity. The cavity eigenfrequency shift caused by the presence of a prism and the introduced loss by it is calculated. (resonators)

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2019

Measurements of water molecule isotopomer concentrations in a discharge of inert gas with addition of H{sub 2}O and D{sub 2} vapours by the method of external-cavity diode laser spectroscopy

Discharge plasma in inert gases with added water vapours and deuterium is studied by using the optimised diode laser spectroscopy with an external cavity. Formation of a spectrally dense grid of cavity transverse mode eigenfrequencies allows one to determine the parameters of Doppler broadening for absorption lines, a kinetic temperature of molecules, and their statistical sums. By using these parameters and the value of an absorption coefficient, correlations of concentrations are found for H{sub 2}O and HDO isotopomers at various ratios of plasma-forming gas components. An important contribution of initial gas molecules adsorbed on walls into the formation of plasma composition is stressed. It is found that the ratio of H{sub 2}O and HDO concentrations is the same at various ratios of H{sub 2}O and D{sub 2} concentrations in plasma-forming gases and is constant during the discharge burning process. (laser applications and other topics in quantum electronics)

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2019

Multifrequency Stimulated Raman Scattering on Rotational Transitions of Molecules

The theory of multifrequency stimulated Raman scattering (SRS) of light on rotational transitions of molecules, which are simulated by a three-level quantum system, is developed. It is shown that the application of bichromatic pumping increases the scattered radiation spectrum width. The exact algebraic solution for the wave amplitudes is obtained in the simplest version of synchronous SRS on transitions with a negligibly low eigenfrequency. It is found that an increase in the ratio of the Raman transition frequency to the pump radiation frequency leads to predominance of the anti-Stokes scattering branch. The effect of wave asynchronism emerging due to linear and nonlinear dispersion of the medium as well as the phase difference of the pump waves on SRS is considered. All types of asynchronism narrow generated frequency spectrum and suppress the anti-Stokes scattering branch. Nonlinear dispersion ensures positive values of wave amplitudes due to phase jumps by π during the propagation of waves in a medium.

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2019

Polariton-Type Dispersion Laws for Three-Level Atoms Interacting with Two Laser Radiation Pulses

Behavioral features of polariton dispersion laws are studied for three-level atoms interacting with two coherent laser radiation pulses with frequencies ω{sub 1} and ω{sub 2} that are in resonance with optically resolved one-photon transitions between levels 1⇆2 and 2⇆3, respectively, and with regard to the direct two-photon transition between levels 1 and 3. The approximation of given photon densities of both pulses compared with the densities of atoms is used. It is shown that the dispersion law consists of three branches whose position and shape are determined by the Rabi frequencies of the above three optical transitions and the photon densities in both pulses. The direct consideration of all three optical transitions leads to the dependence of the dispersion law of atomic polaritons on a new quantum parameter—the phase difference between the three Rabi frequencies. The values of the system parameters are found for which the branches of the dispersion law may intersect. The concept of the surface of the dispersion law is introduced in the dependence of the eigenfrequencies of atomic polaritons on the photon wave vectors in both pulses.

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2018

Dipole Mechanism Generation of Terahertz Waves under Laser-Cluster Interaction

The feasibility of dipole radiation of terahertz waves under the action of a femtosecond laser pulse on a cluster is demonstrated theoretically. It is shown that the dipole mechanism of terahertz radiation generation plays a decisive role in the interaction of a laser pulse with small-size clusters with a sufficiently high electron collision frequency. The dependences of the spectral, angular, energetic, and spatiotemporal characteristics of the terahertz signal on the density of free electrons in the cluster plasma under the conditions in which dipole radiation is dominant are investigated. It is shown that the energy of terahertz radiation is maximal under the resonance conditions, when the laser frequency coincides with the eigenfrequency of a spherical cluster.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2018

Dynamics of Magnetic Skyrmions in Nanodots

Bloch and Neel magnetic skyrmions have been studied in systems of confined geometry (nanodots, a linear array of nanodots). The spectra of low- and high-frequency excitation modes of a skyrmion state have been calculated. It has been shown that skyrmion spectrum asymmetry, namely, the characteristic difference between the frequencies of the azimuthal modes of the azimuthal skyrmion modes rotating clockwise and counterclockwise, is associated with asymmetry in the magnetization profiles of high-frequency spin waves propagating on the background of a skyrmion state in a nanodot. The low-frequency spectrum contains the only gyrotropic mode localized near the center of a nanodot. The gyrotropic frequency depends on the material parameters of a nanodot and the size of a skyrmion. The eigenfrequency of the gyrotropic mode of an isolated skyrmion in a nanodot in ultrathin films (L ~ 1 nm) does not depend on the internal structure of a skyrmion and is the same for Bloch and Neel skyrmions. The interaction of skyrmions, in particular, in a linear chain of nanodots with the ground skyrmion state, leads to distinctions in low-frequency spectra. The structure of a skyrmion (of Bloch or Neel type) is exhibited as a shift of dispersion curves and a difference between the frequencies of ferromagnetic resonance in a system of interacting skyrmions.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2018

Mechanism of Formation of Carbon–Vacancy Structures in Silicon Carbide during Its Growth by Atomic Substitution

The mechanism of formation of carbon-vacancy structures in silicon carbide SiC from silicon vacancies that inevitably form during synthesizing SiC from Si by atomic substitution has been studied. It is shown that it is useful for one of four nearest carbon C atoms to be displaced to the place of a silicon vacancy with the decrease in the total energy by 1.5 eV in the case of polytype 3C and by 0.9–1.4 eV in the case of polytype 4H. In this case, the C atom must overcome the activation barrier of 3.1 eV in the case of polytype 3C and by 2.9–3.2 eV in the case of polytype 4H. This transition is realized during synthesizing SiC due to thermal fluctuations, since the synthesis temperature is T ≈ 1200–1300°C. Thus, the carbon–vacancy structure is a nearly flat cluster of four C atoms and related carbon vacancy with a characteristic diameter of ∼4 Å at a distance of 2.4 Å from it. All the characteristics of this transformation, namely, the energy profile, the transformation pathway, the transient state, its frequency spectrum, the eigenvector corresponding to the only negative eigenfrequency are calculated by the elastic band method. The infrared spectrum (IR) and the permittivity of SiC containing carbon–vacancy structures are considered. The new line at 960 cm{sup –1} detected recently in the IR spectrum of grown by the atomic substitution is unambiguously identified with vibrations of C atoms in carbon–vacancy structures. It is concluded that carbon–vacancy structures stabilize cubic polytype SiC–3C.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Optimizing the Support of a Stellar Sensor

The mass of a support for a stellar sensor in a spacecraft is minimized in the light of requirements on the first eigenfrequency and the reactive force in the connectors. Topological and parametric optimization is employed. The finite-element method is adopted, within the capabilities of the Altair Optistruct system.

42 ENGINEERING↗
DOE OSTI2019

Dynamic Characteristics of a Lathe’s Torsional System

The dynamic characteristics of the torsional system in a lathe gearbox are analyzed. The forms of vibration of the torsional system are identified, and the amplitude–frequency characteristics of the gearbox’s dynamic pliability are determined. The resonant peaks at the eigenfrequencies are considered.

42 ENGINEERING↗