Engineering Papers⌕ Search

SEARCH · Engineering Papers

Results for “nonlinear oscillation”

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 559 records · Page 31
All sourcesNASA NTRSDOE OSTI
DOE OSTI2021

Light-wave control of correlated materials using quantum magnetism during time-periodic modulation of coherent transport

Light–wave quantum electronics utilizes the oscillating carrier wave to control electronic properties with intense laser pulses. Without direct light–spin interactions, however, magnetic properties can only be indirectly affected by the light electric field, mostly at later times. A grand challenge is how to establish a universal principle for quantum control of charge and spin fluctuations, which can allow for faster-than-THz clock rates. Using quantum kinetic equations for the density matrix describing non–equilibrium states of Hubbard quasiparticles, here we show that time–periodic modulation of electronic hopping during few cycles of carrier–wave oscillations can dynamically steer an antiferromagnetic insulating state into a metalic state with transient magnetization. While nonlinearities associated with quasi-stationary Floquet states have been achieved before, magneto–electronics based on quasiparticle acceleration by time–periodic multi–cycle fields and quantum femtosecond/attosecond magnetism via strongly–coupled charge–spin quantum excitations represents an alternative way of controlling magnetic moments in sync with quantum transport.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2023

Lagrangian displacement field estimators in cosmology

The late-time nonlinear Lagrangian displacement field is highly correlated with the initial field, so reconstructing it could enable us to extract primordial cosmological information. Our previous work carefully studied the displacement field reconstructed from the late-time density field using the iterative method proposed and found that it does not fully converge to the true, underlying displacement field (e.g., ~8 % offset at k ~ 0.2 h Mpc –1 at z = 0.6 ). We also constructed the Lagrangian perturbation theory model for the reconstructed field, but the model could not explain the discrepancy between the true and the reconstructed fields in the previous work. Here, the main sources of the discrepancy were speculated to be a numerical artifact in the displacement estimator due to the discreteness of the sample. In this paper, we develop two new estimators of the displacement fields to reduce such a numerical discreteness effect, the normalized momentum estimator and the rescaled resumed estimator. We show that the discrepancy reported is not due to the numerical artifacts. We conclude that the method cannot fully reconstruct the shape of the nonlinear displacement field at the redshift we studied, while it is still an efficient baryon acoustic oscillation reconstruction method. In parallel, by properly accounting for the UV-sensitive term in a reconstruction procedure with an effective field theory approach, we improve the theoretical model for the reconstructed displacement field, by almost 5 times, from ~15% to the level of a few percent at k ~ 0.2 h Mpc –1 at the redshift z = 0.6.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS1977

Implicit finite-difference computations of unsteady transonic flows about airfoils, including the treatment of irregular shock-wave motions

A computer code, LTRAN2, has been constructed that efficiently computes low-frequency unsteady transonic flows about airfoils in motion. The code solves the two-dimensional, nonlinear, low-frequency, small-disturbance equation by an alternating-direction implicit (ADI) algorithm. First, as a check on the code, LTRAN2 is used to solve the linear, low-frequency, small-disturbance equation. The results are compared with known answers from linear theory. Then nonlinear results are presented. Tijdeman's experimental observations of shock wave motions resulting from airfoil flap oscillations are qualitatively reproduced by LTRAN2. These computations compare favorably with those of Magnus and Yoshihara and are obtained in substantially less computer time. Also the underlying theory of the governing equation and the construction of the algorithm are discussed.

Ballhaus, W. F.↗
NASA NTRS1977

Unsteady transonic flow computations

The numerical procedures previously developed for computing nonlinear and time-linearized small-perturbation unsteady transonic flows are briefly reviewed, and the effects of unsteady modes of motion on two-dimensional transonic flows are evaluated. The numerical procedure used comprises an alternating-direction implicit scheme and treats shock waves as discontinuities in the flow. Comparison of the time-linearized results with fully nonlinear calculations delineates their range of applicability. The unsteady behavior due to harmonic pitching and flap oscillations of an NACA airfoil is also examined.

Seebass, A. R.↗
NASA NTRS1985

Dynamical behavior of a theoretical chromosphere model

Time dependent calculations of a solar chromosphere model perturbed by a spectrum of short period acoustic waves superimposed on the observed power spectrum of five minute oscillations are presented. The resulting data is analyzed by Fourier techniques and discussed in terms of nonlinear interaction of various modes.

Bohn, H. U.↗
NASA NTRS2009

All-Solid-State UV Transmitter Development for Ozone Sensing Applications

In this paper, recent progress made in the development of an all-solid-state UV transmitter suitable for ozone sensing applications from space based platforms is discussed. A nonlinear optics based UV setup based on Rotated Image Singly Resonant Twisted Rectangle (RISTRA) optical parametric oscillator (OPO) module was effectively coupled to a diode pumped, single longitudinal mode, conductively cooled, short-pulsed, high-energy Nd:YAG laser operating at 1064 nm with 50 Hz PRF. An estimated 10 mJ/pulse with ~10% conversion efficiency at 320 nm has been demonstrated limited only by the pump pulse spatial profile. The current arrangement has the potential for obtaining greater than 200 mJ/pulse. Previously, using a flash-lamp pumped Nd:YAG laser with round, top-hat profile, up to 24% IR-UV conversion efficiency was achieved with the same UV module. Efforts are underway to increase the IR-UV conversion efficiency of the all solid-state setup by modifying the pump laser spatial profile along with incorporating improved OPO crystals.

Prasad, Narasimha S.↗
DOE OSTI2021

Cooling and instabilities in colliding flows

ABSTRACT Collisional self-interactions occurring in protostellar jets give rise to strong shocks, the structure of which can be affected by radiative cooling within the flow. To study such colliding flows, we use the AstroBEAR AMR code to conduct hydrodynamic simulations in both one and three dimensions with a power-law cooling function. The characteristic length and time-scales for cooling are temperature dependent and thus may vary as shocked gas cools. When the cooling length decreases sufficiently and rapidly, the system becomes unstable to the radiative shock instability, which produces oscillations in the position of the shock front; these oscillations can be seen in both the one- and three-dimensional cases. Our simulations show no evidence of the density clumping characteristic of a thermal instability, even when the cooling function meets the expected criteria. In the three-dimensional case, the nonlinear thin shell instability (NTSI) is found to dominate when the cooling length is sufficiently small. When the flows are subjected to the radiative shock instability, oscillations in the size of the cooling region allow NTSI to occur at larger cooling lengths, though larger cooling lengths delay the onset of NTSI by increasing the oscillation period.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS1980

Nonlinear dynamic response of a uni-directional model for the tile/pad space shuttle thermal protection system

A unidirectional analysis of the nonlinear dynamic behavior of the space shuttle tile/pad thermal protection system is developed and examined for imposed sinusoidal and random motions of the shuttle skin and/or applied tile pressure. The analysis accounts for the highly nonlinear stiffening hysteresis and viscous behavior of the pad which joins the tile to the shuttle skin. Where available, experimental data are used to confirm the validity of the analysis. Both analytical and experimental studies reveal that the system resonant frequency is very high for low amplitude oscillations but decreases rapidly to a minimum value with increasing amplitude. Analytical studies indicate that with still higher amplitude the resonant frequency increases slowly. The nonlinear pad is also responsible for the analytically and experimentally observed distorted response wave shapes having high sharp peaks when the system is subject to sinusoidal loads. Furthermore, energy dissipation in the pad is studied analytically and it is found that the energy dissipated is sufficiently high to cause rapid decay of dynamic transients. Nevertheless, the sharp peaked nonlinear responses of the system lead to higher magnification factors than would be expected in such a highly damped linear system.

Housner, J. M.↗
NASA NTRS2014

Roll Damping Derivatives from Generalized Lifting-Surface Theory and Wind Tunnel Forced-Oscillation Tests

Improving aerodynamic models for adverse loss-of-control conditions in flight is an area being researched under the NASA Aviation Safety Program. Aerodynamic models appropriate for loss of control conditions require a more general mathematical representation to predict nonlinear unsteady behaviors. As more general aerodynamic models are studied that include nonlinear higher order effects, the possibility of measurements that confound aerodynamic and structural responses are probable. In this study an initial step is taken to look at including structural flexibility in analysis of rigid-body forced-oscillation testing that accounts for dynamic rig, sting and balance flexibility. Because of the significant testing required and associated costs in a general study, it makes sense to capitalize on low cost analytical methods where possible, especially where structural flexibility can be accounted for by a low cost method. This paper provides an initial look at using linear lifting surface theory applied to rigid-body aircraft roll forced-oscillation tests.

Pototzky, Anthony S↗
NASA NTRS1991

Solid-state lasers for coherent communication and remote sensing

Work in the stabilization of monolithic Nd:YAG lasers and the application of these lasers to nonlinear optical frequency conversion is discussed. The intrinsic stability of semiconductor diode laser pumped solid state lasers has facilitated a number of demonstration in external resonant cavity harmonic generation and stable optical parametric oscillation. Relative laser frequency stabilization of 0.3 Hz was achieved, and absolute stability of a few hundred hertz is anticipated. The challenge is now to reproduce this frequency stability in the output of tunable nonlinear optical devices. Theoretical and experimental work toward this goal are continuing.

Byer, Robert L.↗
DOE OSTI2021

Comprehensive anisotropic linear optical properties of the Weyl semimetals TaAs and NbAs

We report that TaAs and NbAs are two of the earliest identified Weyl semimetals that possess many intriguing optical properties, such as chirality-dependent optical excitations and giant second harmonic generation (SHG). Linear and nonlinear optics have been employed as tools to probe the Weyl physics in these crystals. Here, we extend these studies to address two important aspects: determining the complete anisotropic dielectric response and exploring if and how they can reveal essential Weyl physics. We determine the complete anisotropic dielectric functions of TaAs and NbAs by combining spectroscopic ellipsometry and density functional theory (DFT). Parameterized Lorentz oscillators are reported from 1.2 - 6 eV (experiment) and 0 - 6 eV (DFT), and good agreement is shown between them. Both linear and nonlinear optical properties have been previously reported to reveal Weyl physics. We suggest that strong optical resonances from trivial bands are the likely origin of the large optical SHG previously reported at these energies. Furthermore, by comparing the contribution of a small k -space centered around the Weyl cones with the total linear dielectric function, we find that these contributions are highly anisotropic and are < 25% of the total dielectric function below 0.5 eV; abov1 eV, these contributions are negligible. Thus, the study of Weyl physics using optical techniques requires very low energies, and even there, a careful assessment is required in distinguishing the much smaller contributions of the Weyl bands from the dominant contributions of the trivial bands and Drude response to the total dielectric function.

36 MATERIALS SCIENCE↗
DOE OSTI2026

Hierarchical Testing of a Hybrid Machine Learning‐Physics Global Atmosphere Model

Machine learning (ML)-based models have demonstrated high skill and computational efficiency, often outperforming conventional physics-based models in weather and subseasonal predictions. While prior studies have assessed their fidelity in capturing synoptic-scale atmospheric dynamics, their performance across timescales and under out-of-distribution forcing, such as +3K or +4K uniform-warming forcings, and the sources of biases remain elusive, to establish the model's reliability for Earth science. Here, we design three sets of experiments targeting synoptic-scale phenomena, interannual variability, and out-of-distribution uniform-warming forcings. We evaluate the Neural General Circulation Model (NeuralGCM), a hybrid model integrating a dynamical core with ML-based component, against observations and physics-based Earth system models (ESMs). At the synoptic scale, NeuralGCM captures the evolution and propagation of extratropical cyclones with performance comparable to ESMs. At the interannual scale, when forced by El Niño-Southern Oscillation sea surface temperature (SST) anomalies, NeuralGCM successfully reproduces associated teleconnection patterns but exhibits deficiencies in capturing nonlinear response. Under out-of-distribution uniform-warming forcings, NeuralGCM simulates similar responses in global-average temperature and precipitation and reproduces large-scale tropospheric circulation features similar to those in ESMs. Notable weaknesses include overestimating the tracks and spatial extent of extratropical cyclones, biases in the teleconnected wave train triggered by tropical SST anomalies, and differences in upper-level warming and stratospheric circulation responses to SST warming compared to physics-based ESMs. The causes of these weaknesses were explored. Despite the noted weaknesses, NeuralGCM reproduces responses across experiments reasonably and performs comparably to ESMs. By integrating a dynamical core with ML, NeuralGCM shows potential for developing ML-based ESMs.

global warming↗
NASA NTRS1971

Theory of the unmagnetized plasma.

The Vlasov mathematical model of a plasma, which has come to be thought more useful than any other in describing the dynamical behavior of the majority of plasmas of interest, is first examined. Macroscopic variables and moment equations; linear electrostatics solutions; plasma oscillations, ion acoustic waves, and linear instabilities are treated, as well as external fields, 'test' charges, and nonlinear Vlasov phenomena. Plasmas are statistically described, and attention is given to the kinetic theory of the stable, uniform plasma and the Balescu-Lenard equation; two-time ensemble averages and fluctuation spectra in stable plasmas; the kinetic theory of the unstable plasma; and ensembles of Vlasov plasmas. Some illustrative experiments are described. Four appendixes deal with the electrostatic approximation and transverse waves; solution of the linearized Vlasov equation in a magnetic field; estimates of correlation functions from thermal equilibrium; and equivalence of spatially uniform BBGKY and Klimontovich correlations.

Montgomery, D. C.↗
NASA NTRS1990

A software system for laser design and analysis

A laser-material database and laser-modeling software system for designing lasers for laser-based Light Detection And Ranging (LIDAR) systems are presented. The software system consists of three basic sections: the database, laser models, and interface software. The database contains the physical parameters of laser, optical, and nonlinear materials required by laser models. The models include efficiency calculations, electrooptical component models, resonator, amplifier, and oscillator models, and miscellaneous models. The interface software provides a user-friendly interface between the user and his personal data files, the database, and models. The structure of the software system is essentially in place, while future plans call for upgrading the computer hardware and software in order to support a multiuser multitask environment.

Cross, P. L.↗
NASA NTRS2003

Aeroelastic System Development Using Proper Orthogonal Decomposition and Volterra Theory

This research combines Volterra theory and proper orthogonal decomposition (POD) into a hybrid methodology for reduced-order modeling of aeroelastic systems. The out-come of the method is a set of linear ordinary differential equations (ODEs) describing the modal amplitudes associated with both the structural modes and the POD basis functions for the uid. For this research, the structural modes are sine waves of varying frequency, and the Volterra-POD approach is applied to the fluid dynamics equations. The structural modes are treated as forcing terms which are impulsed as part of the uid model realization. Using this approach, structural and uid operators are coupled into a single aeroelastic operator. This coupling converts a free boundary uid problem into an initial value problem, while preserving the parameter (or parameters) of interest for sensitivity analysis. The approach is applied to an elastic panel in supersonic cross ow. The hybrid Volterra-POD approach provides a low-order uid model in state-space form. The linear uid model is tightly coupled with a nonlinear panel model using an implicit integration scheme. The resulting aeroelastic model provides correct limit-cycle oscillation prediction over a wide range of panel dynamic pressure values. Time integration of the reduced-order aeroelastic model is four orders of magnitude faster than the high-order solution procedure developed for this research using traditional uid and structural solvers.

Lucia, David J.↗
NASA NTRS2011

Method for Implementing Optical Phase Adjustment

A method has been developed to mechanically implement the optical phase shift by adjusting the polarization of the pump and probe beams in an NMOR (nonlinear magneto-optical rotation) magnetometer as the proper phase shift is necessary to induce self-oscillation. This innovation consists of mounting the pump beam on a ring that surrounds the atomic vapor sample. The propagation of the probe beam is perpendicular to that of the pump beam. The probe beam can be considered as defining the axis of a cylinder, while the pump beam is directed radially. The magnetic field to be measured defines a third vector, but it is also taken to lie along the cylinder axis. Both the pump and probe beams are polarized such that their electric field vectors are substantially perpendicular to the magnet field. By rotation of the ring supporting the pump beam, its direction can be varied relative to the plane defined by the probe electric field and the magnetic field to be measured.

Hovde, David C.↗
NASA NTRS1989

Nonlinear interaction between the diurnal and semidiurnal tides: Terdiurnal and diurnal secondary waves

Many years of measurements obtained using French meteor radars at Garchy (latitude 47 N) and Montpazier (latitude 44 N) are used to show the existence of an 8 hour oscillation. Some examples of the structure of this wave are displayed and compared with measurements performed at Saskatoon (latitude 52 N) and Budrio (latitude 45 N). This wave can be interpreted as the solar driven terdiurnal tide, or as the result of the nonlinear interaction between the diurnal and semidiurnal tides. Both hypotheses are tested with numerical models. Incidentally, the possible existence of a 24 hour wave resulting from this interaction is also studied.

Teitelbaum, H.↗