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At least 379 records · Page 21

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NASA NTRS1996

Time-Dependent Parabolic Finite Difference Formulation for Harmonic Sound Propagation in a Two-Dimensional Duct with Flow

An explicit finite difference real time iteration scheme is developed to study harmonic sound propagation in aircraft engine nacelles. To reduce storage requirements for future large 3D problems, the time dependent potential form of the acoustic wave equation is used. To insure that the finite difference scheme is both explicit and stable for a harmonic monochromatic sound field, a parabolic (in time) approximation is introduced to reduce the order of the governing equation. The analysis begins with a harmonic sound source radiating into a quiescent duct. This fully explicit iteration method then calculates stepwise in time to obtain the 'steady state' harmonic solutions of the acoustic field. For stability, applications of conventional impedance boundary conditions requires coupling to explicit hyperbolic difference equations at the boundary. The introduction of the time parameter eliminates the large matrix storage requirements normally associated with frequency domain solutions, and time marching attains the steady-state quickly enough to make the method favorable when compared to frequency domain methods. For validation, this transient-frequency domain method is applied to sound propagation in a 2D hard wall duct with plug flow.

Kreider, Kevin L.↗

NASA NTRS2000

A Compact Ti:Sapphire Laser With its Third Harmonic Generation (THG) for an Airborne Ozone Differential Absorption Lidar (DIAL) Transmitter

A compact and high-pulse-energy Ti:Sapphire laser with its Third Harmonic Generation (THG) has been developed for an airborne ozone differential absorption lidar (DIAL) to study the distributions and concentrations of the ozone throughout the troposphere. The Ti:Sapphire laser, pumped by a frequency-doubled Nd:YAG laser and seeded by a single mode diode laser, is operated either at 867 nm or at 900 nm with a pulse repetition frequency of 20 Hz. High energy laser pulses (more than 110 mJ/pulse) at 867 nm or 900 nm with a desired beam quality have been achieved and utilized to generate its third harmonic at 289nm or 300nm, which are on-line and off-line wavelengths of an airborne ozone DIAL. After being experimentally compared with Beta-Barium Borate (beta - BaB2O4 or BBO) nonlinear crystals, two Lithium Triborate (LBO) crystals (5 x 5 x 20 cu mm) are selected for the Third Harmonic Generation (THG). In this paper, we report the Ti:Sapphire laser at 900 nm and its third harmonic at 300 nm. The desired high ultraviolet (UV) output pulse energy is more than 30 mJ at 300 nm and the energy conversion efficiency from 900 nm to 300 nm is 30%.

Chen, Songsheng↗

NASA NTRS2002

Tracking the harmonic response of magnetically-soft sensors for wireless temperature, stress, and corrosive monitoring

This paper describes the application of magnetically-soft ribbon-like sensors for measurement of temperature and stress, as well as corrosive monitoring, based upon changes in the amplitudes of the higher-order harmonics generated by the sensors in response to a magnetic interrogation signal. The sensors operate independently of mass loading, and so can be placed or rigidly embedded inside nonmetallic, opaque structures such as concrete or plastic. The passive harmonic-based sensor is remotely monitored through a single coplanar interrogation and detection coil. Effects due to the relative location of the sensor are eliminated by tracking harmonic amplitude ratios, thereby, enabling wide area monitoring. The wireless, passive, mass loading independent nature of the described sensor platform makes it ideally suited for long-term structural monitoring applications, such as measurement of temperature and stress inside concrete structures. A theoretical model is presented to explain the origin and behavior of the higher-order harmonics in response to temperature and stress. c2002 Elsevier Science B.V. All rights reserved.

Non-NASA Center↗

NASA NTRS2005

Evidence for Harmonic Content and Frequency Evolution of Oscillations During the Rising Phase of X-ray Bursts From 4U 1636-536

We report on a study of the evolution of burst oscillation properties during the rising phase of X-ray bursts from 4U 1636-536 observed with the proportional counter array (PCA) on board the Rossi X-Ray Timing Explorer (RXTE) . We present evidence for significant harmonic structure of burst oscillation pulses during the early rising phases of bursts. This is the first such detection in burst rise oscillations, and is very important for constraining neutron star structure parameters and the equation of state models of matter at the core of a neutron star. The detection of harmonic content only during the initial portions of the burst rise is consistent with the theoretical expectation that with time the thermonuclear burning region becomes larger, and hence the fundamental and harmonic amplitudes both diminish. We also find, for the first time from this source, strong evidence of oscillation frequency increase during the burst rise. The timing behavior of harmonic content, amplitude, and frequency of burst rise oscillations may be important in understanding the spreading of thermonuclear flames under the extreme physical conditions on neutron star surfaces.

Bgattacharyya, Sudip↗

NASA NTRS2008

Second Harmonic Imaging improves Echocardiograph Quality on board the International Space Station

Ultrasound (US) capabilities have been part of the Human Research Facility (HRF) on board the International Space Station (ISS) since 2001. The US equipment on board the ISS includes a first-generation Tissue Harmonic Imaging (THI) option. Harmonic imaging (HI) is the second harmonic response of the tissue to the ultrasound beam and produces robust tissue detail and signal. Since this is a first-generation THI, there are inherent limitations in tissue penetration. As a breakthrough technology, HI extensively advanced the field of ultrasound. In cardiac applications, it drastically improves endocardial border detection and has become a common imaging modality. U.S. images were captured and stored as JPEG stills from the ISS video downlink. US images with and without harmonic imaging option were randomized and provided to volunteers without medical education or US skills for identification of endocardial border. The results were processed and analyzed using applicable statistical calculations. The measurements in US images using HI improved measurement consistency and reproducibility among observers when compared to fundamental imaging. HI has been embraced by the imaging community at large as it improves the quality and data validity of US studies, especially in difficult-to-image cases. Even with the limitations of the first generation THI, HI improved the quality and measurability of many of the downlinked images from the ISS and should be an option utilized with cardiac imaging on board the ISS in all future space missions.

Garcia, Kathleen↗

NASA NTRS2012

Localized, Non-Harmonic Active Flap Motions for Low Frequency In-Plane Rotor Noise Reduction

A first-of-its-kind demonstration of the use of localized, non-harmonic active flap motions, for suppressing low frequency, in-plane rotor noise, is reported in this paper. Operational feasibility is verified via testing of the full-scale AATD/Sikorsky/UTRC active flap demonstration rotor in the NFAC's 40- by 80-Foot anechoic wind tunnel. Effectiveness of using localized, non-harmonic active flap motions are compared to conventional four-per-rev harmonic flap motions, and also active flap motions derived from closed-loop acoustics implementations. All three approaches resulted in approximately the same noise reductions over an in-plane three-by-three microphone array installed forward and near in-plane of the rotor in the nearfield. It is also reported that using an active flap in this localized, non-harmonic manner, resulted in no more that 2% rotor performance penalty, but had the tendency to incur higher hub vibration levels.

FLAPS(CONTROL SURFACES)↗

NASA NTRS2013

Region Spherical Harmonic Magnetic Modeling from Near-Surface and Satellite-Altitude Anomlaies

The compiled near-surface data and satellite crustal magnetic measured data are modeled with a regionally concentrated spherical harmonic presentation technique over Australia and Antarctica. Global crustal magnetic anomaly studies have used a spherical harmonic analysis to represent the Earth's magnetic crustal field. This global approach, however is best applied where the data are uniformly distributed over the entire Earth. Satellite observations generally meet this requirement, but unequally distributed data cannot be easily adapted in global modeling. Even for the satellite observations, due to the errors spread over the globe, data smoothing is inevitable in the global spherical harmonic presentations. In addition, global high-resolution modeling requires a great number of global spherical harmonic coefficients for the regional presentation of crustal magnetic anomalies, whereas a lesser number of localized spherical coefficients will satisfy. We compared methods in both global and regional approaches and for a case where the errors were propagated outside the region of interest. For observations from the upcoming Swarm constellation, the regional modeling will allow the production a lesser number of spherical coefficients that are relevant to the region of interest

Modeling↗

DOE OSTI2012

Quaternionic Harmonic Analysis of Texture

QHAT uses various functions and data structures native to MATLAB to analyze crystallographic texture information using harmonic functions on the space of rotations represented as normalized quaternions. These harmonic functions generalize the spherical harmonics in three dimensions, and form the basis for the irreducible representations of the four-dimensional rotation group. This allows the basis of harmonic functions to be reduced to linearly independent combinations that satisfy the crystal and sample symmetry point groups.

Mason, J.↗

DOE OSTI2021

Modeling and Simulation of Inrush Currents in Harmonic Domain

Modeling and simulation capabilities are critical to the stability analysis and evaluation of power distribution systems, with respect to the emphasis on resiliency, microgrids, and distributed energy resources. In this paper, a computational method in the harmonic domain is proposed for the periodic steady-state analysis of the nonlinear inrush current phenomenon. The efficient inrush calculation facilitates the predictions of current amplitudes for the power system operation and control. To demonstrate the accuracy and efficiency, simulation results in the harmonic domain are compared with results from PSCAD in an electromagnetic timescale, as well as the authors’ previous works in the frequency-domain. Impacts of the settings of both offset flux and interested harmonic order are discussed. In addition, within the proposed harmonic-domain method, a general approach that utilizes the discrete Fourier transform to obtain the response of a nonlinear device from a stimulus represented in the frequency-domain is utilized. This method can also be extended to perform the transient analysis in future, using trapezoidal rule for the integration.

Xie, Jing↗

DOE OSTI2022

Analysis of Inter Converter Interactions using Harmonic State Space Modeling

Power converters have become a key participant within the modern grid, facilitating the grid's interaction with renewable energy sources and various loads, among others. These converters can also interact with each other, creating harmonics that were previously absent in the grid. While some previous research studies have focused on inter-converter interactions, not much focus has been on the role of pulse width modulators in these inter-converter interactions. This paper focuses on the issue and builds upon harmonic state-space modeling (HSS) to observe inter-converter harmonic interactions. A new modulator model is developed, and its implementation within HSS modeling to observe harmonic coupling between multiple inverters is highlighted. A simulation testbench is developed, and to verify the advantages and limitations of the proposed modeling approach, it is compared with two other traditional modeling methods: namely, average and switching models. The proposed method is shown to be significantly more accurate and informative than conventional average modeling methods and has considerably lower computation costs and simulation time than detailed switching models. The results are verified using extensive simulations on MATLAB.

Xue, Yaosuo↗

DOE OSTI2011

Simultaneous generation of ions and high-order harmonics from thin conjugated polymer foil irradiated with ultrahigh contrast laser

We report the manufacturing of an (ultra-)thin foil target made of conjugated polymer, poly(9,9'-dioctylfluorene-co-benzothiadiazole) (F8BT), and the simultaneous observation of laser-accelerated ions and second harmonic radiation, when irradiated with ultrahigh-contrast laser pulse at a maximum intensity of 4 x 10{sup 19 }W/cm{sup 2}. Maximum proton energy of 8 MeV is achieved along the target normal direction. Strong second harmonic with over 6% energy ratio compared to fundamental is emitted along the specular direction. Two-dimensional particle-in-cell simulations confirm the simultaneous generation of protons and high-order harmonics, which demonstrates the feasibility of applications requiring particle and radiation sources at once, effectively using the same laser and target.

43 PARTICLE ACCELERATORS↗

DOE OSTI2011

Effects of the Spatial Extent of Multiple Harmonic Layers

An analytic model for single particle motion in the presence of a wave field and multiple cyclotron harmonics is developed and investigated. The model suggests that even in the absence of Doppler broadening, cyclotron harmonic layers have finite spatial extent. This allows for particles to interact with more than one harmonic layer simultaneously, provided the layers are tightly packed. The latter phenomenon is investigated in the context of the model using symplectic mapping techniques. Then the model behavior is compared with numerical simulations of neutral beam particle trajectories in NSTX using the full-orbit code SPIRAL.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗

DOE OSTI2013

Enhanced high harmonic generation and the phase effect in double-sided relativistic laser-foil interaction

High harmonic generation (HHG) from relativistic laser-foil interaction is investigated analytically and through particle-in-cell simulations. Previous work has shown that when two counter-propagating circularly polarized (CP) laser pulses interact with a thin foil, electrons can be well confined spatially to form a high density layer. The layer electrons oscillate in certain transversal direction and radiate intense high order harmonics. It is demonstrated here that there is a critical foil thickness, only below which can high harmonics be generated efficiently. Furthermore, to enhance the intensity in higher order region, the third linearly polarized (LP) short-wavelength laser pulse with much lower intensity is introduced. Analysis and simulations both show that the enhancement is determined by the relative phase {delta}{phi} between the driving CP laser pulses and LP pulse. The enhancement at high order is quite considerable and very sensitive to the relative phase {delta}{phi}, thus offering not only a way to efficiently produce HHG but also a new method to measure the phase of intense high-frequency laser pulses.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗

DOE OSTI2013

Efficiency enhancement of nonlinear odd harmonics in thermal free electron laser

The effect of axial energy spread on the radiation of third harmonic is studied in the free electron laser with planar wiggler and ion-channel guiding. Spread in the longitudinal momentum and so in the initial energy of electron beam, without any spread in the transverse velocity, is assumed in the form of Gaussian distribution function. The technique that is employed is a one-dimensional and steady-state simulation. A set of self consistent nonlinear differential equations that describes the system is solved numerically by Runge-Kutta method. Due to the sensitivity of harmonics to thermal effects, gain improvement of third harmonic radiation is achieved by using ion-channel guiding technique and efficiency enhancement is applied by tapering the magnetic field of wiggler to optimize radiation. The bunching parameter of the electron beam is also studied. It is found that the growth of the magnitude of the bunching parameter that is caused by the ponderomotive wave stops before the saturation point of the radiation. This means that ponderomotive wave saturates at a shorter distance compared to the radiation.

43 PARTICLE ACCELERATORS↗

DOE OSTI2013

High order harmonic generation in dual gas multi-jets

High order harmonic generation (HHG) in gas media suffers from a low conversion efficiency that has its origins in the interaction of the atom/molecule with the laser field. Phase matching is the main way to enhance the harmonic flux and several solutions have been designed to achieve it. Here we present numerical results modeling HHG in a system of multi-jets in which two gases alternate: the first gas jet (for example Ne) generates harmonics and the second one which ionizes easier, recover the phase matching condition. We obtain configurations which are experimentally feasible with respect to pressures and dimensions of the jets.

42 ENGINEERING↗

DOE OSTI2015

Second harmonic generation of q-Gaussian laser beam in preformed collisional plasma channel with nonlinear absorption

This paper presents a scheme for second harmonic generation of an intense q-Gaussian laser beam in a preformed parabolic plasma channel, where collisional nonlinearity is operative with nonlinear absorption. Due to nonuniform irradiance of intensity along the wavefront of the laser beam, nonuniform Ohmic heating of plasma electrons takes place. Due to this nonuniform heating of plasma, the laser beam gets self-focused and produces strong density gradients in the transverse direction. The generated density gradients excite an electron plasma wave at pump frequency that interacts with the pump beam to produce its second harmonics. The formulation is based on a numerical solution of the nonlinear Schrodinger wave equation in WKB approximation followed by moment theory approach. A second order nonlinear differential equation governing the propagation dynamics of the laser beam with distance of propagation has been obtained and is solved numerically by Runge Kutta fourth order technique. The effect of nonlinear absorption on self-focusing of the laser beam and conversion efficiency of its second harmonics has been investigated.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗

DOE OSTI2011

Tracing the structure of asymmetric molecules from high-order harmonic generation

We investigate high-order harmonic generation (HHG) from asymmetric molecules exposed to intense laser fields. We show that the emissions of odd and even harmonics depend differently on the orientation angle, the internuclear distance, as well as the effective charge. This difference mainly comes from different roles of intramolecular interference in the HHG of odd and even harmonics. These roles map the structure of the asymmetric molecule to the odd vs even HHG spectra.

74 ATOMIC AND MOLECULAR PHYSICS↗

DOE OSTI2011

Influence of gas pressure on high-order-harmonic generation of Ar and Ne

We study the effect of gas pressure on the generation of high-order harmonics where harmonics due to individual atoms are calculated using the recently developed quantitative rescattering theory, and the propagation of the laser and harmonics in the medium is calculated by solving the Maxwell's wave equation. We illustrate that the simulated spectra are very sensitive to the laser focusing conditions at high laser intensity and high pressure since the fundamental laser field is severely reshaped during the propagation. By comparing the simulated results with several experiments we show that the pressure dependence can be qualitatively explained. The lack of quantitative agreement is tentatively attributed to the failure of the complete knowledge of the experimental conditions.

74 ATOMIC AND MOLECULAR PHYSICS↗