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Results for “dissipative media”

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 19 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS1973

Measurement techniques for antennas in dissipative media.

Methods used to simulate dissipative media environments for antennas are reported, and special techniques are developed to determine the electrical properties of antennas in such media. A new device for measuring antenna input admittance is presented which permits a simple measurement of admittance over a broad frequency range where conventional methods are cumbersome in field use. An apparatus for measuring antenna current and charge distributions is described, and the associated probing errors are discussed. Measured admittances and current and charge distributions are compared with current theories for thin wire linear and loop antennas in the dissipative media and are found to be in good agreement.

Scott, L. D.↗
DOE OSTI2021

Quasioptical modeling of wave beams with and without mode conversion. IV. Numerical simulations of waves in dissipative media

We report the first quasi-optical simulations of wave beams in a hot plasma using the quasi-optical code PARADE (PAraxial RAy DEscription) [K. Yanagihara, I. Y. Dodin, and S. Kubo, Phys. Plasmas 26, 072112 (2019)]. This code is unique in that it accounts for inhomogeneity of the dissipation-rate across the beam and mode conversion simultaneously. We show that the dissipation-rate inhomogeneity shifts beams relative to their trajectories in cold plasma and that the two electromagnetic modes are coupled via this process, an effect that was ignored in the past. Additionally, we propose a simplified approach to account for the dissipation-rate inhomogeneity. This approach is computationally inexpensive and simplifies the analysis of actual experiments.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
NASA NTRS1995

Small scales formation via Alfven wave propagation in compressible nonuniform media

In weakly dissipative media governed by the magnetohydrodynamics (MHD) equations, any efficient mechanism of energy dissipation requires the formation of small scales. The possibility to produce small scales has been studied by Malara et al. in the case of MHD disturbances propagating in an incompressible and inhomogeneous medium, for a strictly 2D geometry. We extend the work of Malara et al. to include both compressibility and the third component for vector quantities. Using numerical simulations we show that, when an Alfven wave propagates in a compressible nonuniform medium, the two dynamical effects responsible for the small scales formation in the incompressible case are still at work: energy pinching and phase-mixing. Moreover, the interaction between the initial Alfven wave and the inhomogeneity gives rise to the formation of compressible perturbations (fast and slow waves or a static entropy wave). Some of these compressive fluctuations are subject to the steepening of the wave front and become shock waves, which are extremely efficient in dissipating their energy, their dissipation being independent of the Reynolds number. A rough estimate of the typical times which the various dynamical processes take to produce small scales and then to dissipate the energy show that these times are consistent with those required to dissipate inside the solar corona the energy of Alfven waves of photospheric origin.

Malara, F.↗
NASA NTRS1974

Farfield viscous effects in nonlinear noise propagation

Discussion of the method of parametric differentiation in application to predictions of farfield noise propagation in both lossless and dissipative media. It is shown that, in the lossless medium, the governing equation, transformed to parameter space, reduces to a wave equation in the farfield. In the dissipative medium, the system of nonlinear partial differential equations, transformed to parameter space, reduces to a linear partial differential equation of the propagating type which contains a third-order derivative as well as the wave operator.

Harris, W. L., Sr.↗
DOE OSTI2024

Nonlinear propagation of chirped laser pulses through a dispersive and turbulent atmosphere

The evolution of ultrashort laser pulses in dispersive, turbulent, nonlinear, and dissipative media is discussed in connection with nonlinear self-focusing collapse and the onset of laser filamentation. In quiescent air, a laser pulse propagating with a peak power greater than a critical power for self-focusing will undergo a catastrophic, transverse collapse until the intensity is large enough for photoionization. At this point, self-focusing is arrested and balanced by plasma refraction, forming a laser filament. By applying an appropriate chirp, the dispersive properties of the medium can be used to enhance this process and control its onset, and to counter dissipative effects such as molecular absorption and atmospheric scattering. This paper presents an analysis of the effect of atmospheric turbulence on the propagation of nonlinear pulses with dispersion compensation (chirp). Furthermore, the analytical results are compared with wave optics simulations and found to be in reasonable agreement as long as the pulse maintains a near-Gaussian spatiotemporal profile.

47 OTHER INSTRUMENTATION↗
NASA NTRS1972

Finite elements of nonlinear continua.

The finite element method is extended to a broad class of practical nonlinear problems, treating both theory and applications from a general and unifying point of view. The thermomechanical principles of continuous media and the properties of the finite element method are outlined, and are brought together to produce discrete physical models of nonlinear continua. The mathematical properties of the models are analyzed, and the numerical solution of the equations governing the discrete models is examined. The application of the models to nonlinear problems in finite elasticity, viscoelasticity, heat conduction, and thermoviscoelasticity is discussed. Other specific topics include the topological properties of finite element models, applications to linear and nonlinear boundary value problems, convergence, continuum thermodynamics, finite elasticity, solutions to nonlinear partial differential equations, and discrete models of the nonlinear thermomechanical behavior of dissipative media.

Oden, J. T.↗
DOE OSTI2022

Tensor Network Path Integral Study of Dynamics in B850 LH2 Ring with Atomistically Derived Vibrations

The recently introduced multisite tensor network path integral (MS-TNPI) allows simulation of extended quantum systems coupled to dissipative media. We use MS-TNPI to simulate the exciton transport and the absorption spectrum of a B850 bacteriochlorophyll (BChl) ring. The MS-TNPI network is extended to account for the ring topology of the B850 system. Accurate molecular-dynamics-based description of the molecular vibrations and the protein scaffold is incorporated through the framework of Feynman–Vernon influence functional. To relate the present work with the excitonic picture, an exploration of the absorption spectrum is done by simulating it using approximate and topologically consistent transition dipole moment vectors. Comparison of these numerically exact MS-TNPI absorption spectra are shown with second-order cumulant approximations. Finally, the effect of temperature on both the exact and the approximate spectra is also explored.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
NASA NTRS1973

Slow growth of cracks in a rate sensitive Tresca solid.

Extension of the classical theory of fracture to viscoelastic and elastic-plastic materials in which the plasticity effects are confined to a narrow band encompassing the crack front. It is suggested that the Griffith-Irwin criterion of fracture, which requires that the energy release rate computed for a given boundary value problem equal the critical threshold, ought to be replaced by a differential equation governing the slow growth of a crack prior to the onset of rapid propagation. A new term which enters the equation of motion in the dissipative media is proportional to the energy lost within the end sections of the crack, and thus it reflects the extent of inelastic behavior of a solid. A concept of 'apparent' surface energy is introduced to account for the geometry-dependent and the rate-dependent phenomena which influence toughness of an inelastic solid. Three hypotheses regarding the condition for fracture in the subcritical range of load are compared.

Wnuk, M. P.↗
NASA NTRS1972

Slow and fast motion of cracks in inelastic solids. Part 1: Slow growth of cracks in a rate sensitive tresca solid. Part 2: Dynamic crack represented by the Dugdale model

An extension is proposed of the classical theory of fracture to viscoelastic and elastic-plastic materials in which the plasticity effects are confined to a narrow band encompassing the crack front. It is suggested that the Griffith-Irwin criterion of fracture, which requires that the energy release rate computed for a given boundary value problem equals the critical threshold, ought to be replaced by a differential equation governing the slow growth of a crack prior to the onset of rapid propagation. A new term which enters the equation of motion in the dissipative media is proportional to the energy lost within the end sections of the crack, and thus reflects the extent of inelastic behavior of a solid. A concept of apparent surface energy is introduced to account for the geometry dependent and the rate dependent phenomena which influence toughness of an inelastic solid. Three hypotheses regarding the condition for fracture in the subcritical range of load are compared. These are: (1) constant fracture energy (Cherepanov), (2) constant opening displacement at instability (Morozov) and (3) final stretch criterion (Wnuk).

Wnuk, M. P.↗
DOE OSTI2019

Real and complex valued geometrical optics inverse ray-tracing for inline field calculations

In this work, a 3-D ray based model for computing laser fields in dissipative and amplifying media is presented. The eikonal equation is solved using inverse ray-tracing on a dedicated nonstructured 3-D mesh. Inverse ray-tracing opens the possibility of using Complex Geometrical Optics (CGO), for which we propose a propagation formalism in a finite element mesh. Divergent fields at caustics are corrected using an etalon integral method for fold-type caustics. This method is successfully applied in dissipative media by modifying the ray-ordering and root selection rules, thereby allowing one to reconstruct the field in the entire caustic region. In addition, we demonstrate how caustics in the CGO framework can disappear entirely for sufficiently dissipative media, making the complex ray approach valid in the entire medium. CGO is shown to offer a more precise modeling of laser refraction and absorption in a dissipative medium when compared to Geometrical Optics (GO). In the framework of Inertial Confinement Fusion (ICF), this occurs mostly at intermediate temperatures or at high temperatures close to the critical density. Additionally, GO is invalid at low temperatures if an approximated expression of the permittivity is used. The inverse ray-tracing algorithm for GO and CGO is implemented in the IFRIIT code, in the framework of a dielectric permittivity described in 3-D using a piecewise linear approximation in tetrahedrons. Fields computed using GO and CGO are compared to results from the electromagnetic wave solver LPSE. Excellent agreement is obtained in 1-D linear and nonlinear permittivity profiles. Good agreement is also obtained for ICF-like Gaussian density profiles in 2-D. Finally, we demonstrate how the model reproduces Gaussian beam diffraction using CGO. The IFRIIT code will be interfaced inline to 3-D radiative hydrodynamic codes to describe the nonlinear laser plasma interaction in ICF and high-energy-density plasmas.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2019

New Directions in Strong-Field Control

The thrust of our AMOS-supported research was initially the problem of strong-field alignment in complex systems. Over the years, this research was generalized to strong field coherent control, including alignment, three-dimensional alignment, torsional control and molecular focusing in moderately intense laser fields. A second, related theme that was added to our AMOS-supported research was the physics, theory and potential applications of high harmonic generation from aligned molecules. This second thrust was motivated by the intense interest of the AMOS Program in attosecond science and rescattering electrons physics, and has been carried out in collaboration with AMOS experimentalists colleagues. This research led to 60 peer refereed publications.

74 ATOMIC AND MOLECULAR PHYSICS↗
NASA NTRS1993

Electromagnetic fluctuations for anisotropic media and the generalized Kirchhoff's law

In this paper the polarimetric emission parameters for anisotropic media are derived using the generalized Kirchhoff's law for media with a uniform temperature and the fluctuation-dissipation theory for media with a temperature profile. Both finite-size objects and half-space media are considered. When the object has a uniform temperature across its body, the Kirchhoff's law, based on the condition of energy conservation in thermal equilibrium is generalized to obtain the emission parameters of an anisotropic medium, which can be interpreted as the absorptivity or the absorption cross section of the complementary object with a permittivity that is the transpose of the original object. When the medium has a nonuniform temperature distribution, the fluctuation-dissipation theory is applied for deriving the covariances between vector components of the thermal currents and, consequently, the covariances of the polarizations of electric fields radiated by the thermal currents. To verify the formulas derived from the fluctuation-dissipation theory, we let the temperature of the object be a constant and show that the results reduce to those obtained from the generalized Kirchhoff's law.

Yueh, Simon H.↗
DOE OSTI2020

Viscous Dissipation and Apparent Permeability of Gas Flow in Nanoporous Media

The nanopore confinement effect can increase the mobility for gas flow in shale rocks, and the apparent permeability is usually adopted to account for this effect. However, most of the apparent permeability calculation models are derived based on straight channels (capillaries) and neglect the influence of end effect. The end effect is caused by the bending of streamlines which yields more viscous dissipation and additional flow resistance for gas flow in nanoporous media. Here, for the first time the viscous dissipation for gas flow in nanoporous media is analyzed. In addition, an improved apparent permeability calculation model is proposed based on the Beskok-Karniadakis (B-K) model by introducing the influence of end effect, which is characterized by the ratio of the length to the width of a short channel (L/H). The accuracy of this model is validated by lattice Boltzmann simulations of gas flow in three different geometries: an infinite-length straight channel, a finite-length straight channel, and nanoporous media. For the infinite-length straight channel, there is no end effect therefore both the B-K model and the improved model can well predict the apparent permeability. However, for the finite-length straight channel and nanoporous media, the original B-K model overestimates the gas apparent permeability as it neglects the influence of end effect, while the improved model can still well predict the gas apparent permeability. In summary, the improved apparent permeability calculation model is more reasonable in predicting gas mobility in nanoporous media.

58 GEOSCIENCES↗
NASA NTRS1987

Transverse deflection and dissipation of small plasma beams and clouds in magnetized media

Propagation of a quasi-neutral plasma beam or cloud across a magnetic field is considered for the case where the transverse dimension of the beam or cloud is sufficiently small compared to ion gyroradii. This situation commonly arises for active experiments in near-earth space. Two mechanisms are presented for transverse deflection of a beam or cloud in the -v0 x B0 direction where v0 is the velocity relative to the ambient medium. In the first, asymmetric escape of ions from an electrically polarized beam or cloud causes transverse deflection by means of a rocket effect. The transverse deflection distance is estimated to be a few times the initial transverse dimension of the beam or cloud. Dissipation occurs within a few times the thermal ion transverse crossing time. In the second mechanism, asymmetric charging results from localized accumulation of incident ions from the ambient medium. This excess positive charge distorts electric equipotentials and drives electron Hall currents that maintain an asymmetric compressed magnetic field region. The asymmetry of the magnetic stress contributes to transverse deflection with the same sign as the rocket effect. The asymmetric magnetic field also focuses incident ions to yield the localized charge accumulation. These ideas are qualitatively consistent with observations of the Active Magnetospheric Particle Tracer Explorers artificial comet releases.

Cheng, Andrew F.↗
DOE OSTI2023

Simulation of Linear Non-Hermitian Boundary-Value Problems with Quantum Singular-Value Transformation

Herein we propose a quantum algorithm for simulating dissipative waves in inhomogeneous linear media as a boundary-value problem. Using the so-called quantum singular value transformation (QSVT), we construct a quantum circuit that models the propagation of electromagnetic waves in a one-dimensional system with outgoing boundary conditions. The corresponding measurement procedure is also discussed. Limitations of the QSVT algorithm are identified in connection with the large condition numbers that the dispersion matrices exhibit at weak dissipation.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
NASA NTRS1970

Weak shock waves in turbulent media

Weak shock thicknesses with turbulent scattering as dissipative mechanism compared with magnitude in sonic boom flight tests and explosions

George, A. R.↗
NASA NTRS1985

Stimulated Raman scattering of light absorbing media excited by ultrashort laser pulses

The fluctuation-dissipation theory of spontaneous and stimulated vibration Raman scattering is worked out taking into account the dissipation losses at frequencies of laser pump and scattering radiation. General expressions are found, which describe the absolute intensities and shape, energy and duration of scattered pulses in terms of the parameters of the medium and the the input laser pulses. The general regularities are analyzed in detail. Conditions are found for the realization of spontaneous or stimulated Raman scattering and its dependence on absorption, pulse duration and other parameters of the problem.

Marchevskiy, F. N.↗