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Results for “Frequency Domain Analysis”

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 55 records · Page 3
All sourcesNASA NTRSDOE OSTI
DOE OSTI2016

A harmonic balance method for PDEs

In this report, we describe some approaches to calculate the non-linear system of equations prescribed by the harmonic balance method (HB), a frequency domain analysis technique for modelling a non-linear system of partial differential equations (PDEs). The approach which we ultimately pursue can be seen as a time-collocation approach, except that the harmonic balance equations are obtained weakly (in the sense used in the calculus of variations). This weak formulation allows us to adapt existing transient or stationary PDEs models in the Panzer/Trilinos framework for frequency domain analysis via the harmonic balance method. We begin with a motivatation for the harmonic balance method and outline its mathematical formulation. We then describe some approaches to calculate the harmonic balance formulae, and their means of implementation through the modification of a Panzer tutorial problem - a stationary Helmholtz equation with a constant Dirichlet boundary condition and a non-linear source. For each of these approaches, we outline the necessary adaptations to solve the corresponding (periodically) transient Helmholtz equation with a (temporally) periodic Dirichlet boundary condition and non-linear source.

97 MATHEMATICS AND COMPUTING↗
DOE OSTI2015

Preliminary Analysis of an Oscillating Surge Wave Energy Converter with Controlled Geometry: Preprint

The aim of this paper is to present a novel wave energy converter device concept that is being developed at the National Renewable Energy Laboratory. The proposed concept combines an oscillating surge wave energy converter with active control surfaces. These active control surfaces allow for the device geometry to be altered, which leads to changes in the hydrodynamic properties. The device geometry will be controlled on a sea state time scale and combined with wave-to-wave power-take-off control to maximize power capture, increase capacity factor, and reduce design loads. The paper begins with a traditional linear frequency domain analysis of the device performance. Performance sensitivity to foil pitch angle, the number of activated foils, and foil cross section geometry is presented to illustrate the current design decisions; however, it is understood from previous studies that modeling of current oscillating wave energy converter designs requires the consideration of nonlinear hydrodynamics and viscous drag forces. In response, a nonlinear model is presented that highlights the shortcomings of the linear frequency domain analysis and increases the precision in predicted performance.

17 WIND ENERGY↗
DOE OSTI2025

IDENTIFICATION OF POTENTIAL SUPERCONDUCTOR QUENCH PRECURSORS USING FREQUENCY DOMAIN FEATURE ANALYSIS

Superconducting magnets are important pieces of technology in the world of particle accelerators, allowing researchers to study atomic and subatomic phenomena, among other things. In some instances, superconductors can lose this non-resistive property in a phenomenon known as quenching, which can cause damage to the magnets. This potential danger prompts the introduction of systems to predict when a quench is imminent; one such implementation is through the use of acoustic sensors that detect vibrations within the magnet. Within these acoustic sensor signals, significantly above-noise disturbances (referred to as ”events”) can be identified. Our research applies the statistical framework of a permutation test to features calculated from the power spectral density (PSD) to distinguish between events far from the quench at the end of the signal to events at the start of the signal. We found that dividing the PSD into frequency bands produced a feature capable of distinguishing between events early in the signal and late in the signal leading up the quench, providing a promising starting place for future quench prediction systems.

Roehrig, Benjamin [Northern Illinois U.]↗
NASA NTRS1994

Evaluating the dynamic response of in-flight thrust calculation techniques during throttle transients

New flight test maneuvers and analysis techniques for evaluating the dynamic response of in-flight thrust models during throttle transients have been developed and validated. The approach is based on the aircraft and engine performance relationship between thrust and drag. Two flight test maneuvers, a throttle step and a throttle frequency sweep, were developed and used in the study. Graphical analysis techniques, including a frequency domain analysis method, were also developed and evaluated. They provide quantitative and qualitative results. Four thrust calculation methods were used to demonstrate and validate the test technique. Flight test applications on two high-performance aircraft confirmed the test methods as valid and accurate. These maneuvers and analysis techniques were easy to implement and use. Flight test results indicate the analysis techniques can identify the combined effects of model error and instrumentation response limitations on the calculated thrust value. The methods developed in this report provide an accurate approach for evaluating, validating, or comparing thrust calculation methods for dynamic flight applications.

Ray, Ronald J.↗
NASA NTRS1999

Lockheed Martin Skunk Works Single Stage to Orbit/Reusable Launch Vehicle

Lockheed Martin Skunk Works has compiled an Annual Performance Report of the X-33/RLV Program. This report consists of individual reports from all industry team members, as well as NASA team centers. This portion of the report is comprised of a status report of Lockheed Martin's contribution to the program. The following is a summary of the Lockheed Martin Centers involved and work reviewed under their portion of the agreement: (1) Lockheed Martin Skunk Works - Vehicle Development, Operations Development, X-33 and RLV Systems Engineering, Manufacturing, Ground Operations, Reliability, Maintainability/Testability, Supportability, & Special Analysis Team, and X-33 Flight Assurance; (2) Lockheed Martin Technical Operations - Launch Support Systems, Ground Support Equipment, Flight Test Operations, and RLV Operations Development Support; (3) Lockheed Martin Space Operations - TAEM and A/L Guidance and Flight Control Design, Evaluation of Vehicle Configuration, TAEM and A/L Dispersion Analysis, Modeling and Simulations, Frequency Domain Analysis, Verification and Validation Activities, and Ancillary Support; (4) Lockheed Martin Astronautics-Denver - Systems Engineering, X-33 Development; (5) Sanders - A Lockheed Martin Company - Vehicle Health Management Subsystem Progress, GSS Progress; and (6) Lockheed Martin Michoud Space Systems - X-33 Liquid Oxygen (LOX) Tank, Key Challenges, Lessons Learned, X-33/RLV Composite Technology, Reusable Cyrogenic Insulation (RCI) and Vehicle Health Monitoring, Main Propulsion Systems (MPS), Structural Testing, X-33 System Integration and Analysis, and Cyrogenic Systems Operations.

Source record↗
DOE OSTI2022

RAFT (Response Amplitudes of Floating Turbines) [SWR-22-40]

RAFT is a Python code for frequency-domain analysis of floating wind turbines. RAFT works in the frequency domain to provide efficient computations of a floating wind system's response spectra accounting for platform hydrodynamics, quasi-static mooring reactions, rotor aerodynamics, and linearized control. It can be used to calculate response amplitude operators (RAO's), power spectral densities, mean/static properties, and response metrics based on mean and root-mean-square values of each output. RAFT serves as the Level 1 model in the WEIS (Wind Energy with Integrated Servo-control) toolkit, and features an OpenMDAO wrapper.

Hall, Matthew↗
NASA NTRS2012

Characterization of Deficiencies in the Frequency Domain Forced Response Analysis Technique for Turbine Bladed Disks

Turbine blades in rocket and jet engine turbomachinery experience enormous harmonic loading conditions. These loads result from the integer number of upstream and downstream stator vanes as well as the other turbine stages. The standard technique for forced response analysis to assess structural integrity is to decompose a CFD generated flow field into its harmonic components, and to then perform a frequency response analysis at the problematic natural frequencies. Recent CFD analysis and water-flow testing at NASA/MSFC, though, indicates that this technique may miss substantial harmonic and non-harmonic excitation sources that become present in complex flows. These complications suggest the question of whether frequency domain analysis is capable of capturing the excitation content sufficiently. Two studies comparing frequency response analysis with transient response analysis, therefore, have been performed. The first is of a bladed disk with each blade modeled by simple beam elements. It was hypothesized that the randomness and other variation from the standard harmonic excitation would reduce the blade structural response, but the results showed little reduction. The second study was of a realistic model of a bladed-disk excited by the same CFD used in the J2X engine program. The results showed that the transient analysis results were up to 10% higher for "clean" nodal diameter excitations and six times larger for "messy" excitations, where substantial Fourier content around the main harmonic exists.

Brown, Andrew M.↗
NASA NTRS1976

Pulse analysis of acoustic emission signals

A method for the signature analysis of pulses in the frequency domain and the time domain is presented. Fourier spectrum, Fourier transfer function, shock spectrum and shock spectrum ratio are examined in the frequency domain analysis, and pulse shape deconvolution is developed for use in the time domain analysis. To demonstrate the relative sensitivity of each of the methods to small changes in the pulse shape, signatures of computer modeled systems with analytical pulses are presented. Optimization techniques are developed and used to indicate the best design parameters values for deconvolution of the pulse shape. Several experiments are presented that test the pulse signature analysis methods on different acoustic emission sources. These include acoustic emissions associated with: (1) crack propagation, (2) ball dropping on a plate, (3) spark discharge and (4) defective and good ball bearings.

Houghton, J. R.↗
NASA NTRS1977

Pulse analysis of acoustic emission signals

A method for the signature analysis of pulses in the frequency domain and the time domain is presented. Fourier spectrum, Fourier transfer function, shock spectrum and shock spectrum ratio were examined in the frequency domain analysis, and pulse shape deconvolution was developed for use in the time domain analysis. Comparisons of the relative performance of each analysis technique are made for the characterization of acoustic emission pulses recorded by a measuring system. To demonstrate the relative sensitivity of each of the methods to small changes in the pulse shape, signatures of computer modeled systems with analytical pulses are presented. Optimization techniques are developed and used to indicate the best design parameters values for deconvolution of the pulse shape. Several experiments are presented that test the pulse signature analysis methods on different acoustic emission sources. These include acoustic emissions associated with: (1) crack propagation, (2) ball dropping on a plate, (3) spark discharge and (4) defective and good ball bearings. Deconvolution of the first few micro-seconds of the pulse train are shown to be the region in which the significant signatures of the acoustic emission event are to be found.

Houghton, J. R.↗
NASA NTRS1977

Pulse analysis of acoustic emission signals

A method for the signature analysis of pulses in the frequency domain and the time domain is presented. Fourier spectrum, Fourier transfer function, shock spectrum and shock spectrum ratio were examined in the frequency domain analysis and pulse shape deconvolution was developed for use in the time domain analysis. Comparisons of the relative performance of each analysis technique are made for the characterization of acoustic emission pulses recorded by a measuring system. To demonstrate the relative sensitivity of each of the methods to small changes in the pulse shape, signatures of computer modeled systems with analytical pulses are presented. Optimization techniques are developed and used to indicate the best design parameter values for deconvolution of the pulse shape. Several experiments are presented that test the pulse signature analysis methods on different acoustic emission sources. These include acoustic emission associated with (a) crack propagation, (b) ball dropping on a plate, (c) spark discharge, and (d) defective and good ball bearings. Deconvolution of the first few micro-seconds of the pulse train is shown to be the region in which the significant signatures of the acoustic emission event are to be found.

Houghton, J. R.↗
DOE OSTI2019

Numerical analysis and wave tank validation on the optimal design of a two-body wave energy converter

To improve the performance of a ‘point absorber’ type wave energy converter (WEC), an additional submerged body can be deployed. The submerged body can be used to increase the equivalent excitation force on the WEC, as well as provide resonance tuning. This paper presents numerical analysis and experimental validation of a two-body point absorber type WEC using a mechanical motion rectifier (MMR) based power takeoff. The two-body point absorber consists of a floating buoy connected to a neutrally buoyant submerged body via the power-takeoff. The mechanical motion rectifier and a ball screw translate the relative heave motion of the two bodies into unidirectional rotation, which in turn spins a generator. Frequency domain analysis suggests there is an optimal submerged body mass for maximum WEC power absorption. Regular wave simulations in the time domain are compared to the results obtained in the frequency domain. While the time domain and frequency domain results predict the same optimal mass ratio, time domain analysis provides a more complex and accurate power result. To validate the time domain model, experimental wave tank testing is conducted using a 1:30 scale model WEC. The experiment shows the two-body WEC can produce twice the amount of power as the single-body WEC with same floating buoy and can be further increased by PTO design and power electronics optimization. Furthermore, wave tank testing shows the two-body WEC has a capture width ratio up to 58% at 59 kW/m and 51% at 36 kW/m.

16 TIDAL AND WAVE POWER↗
NASA NTRS1974

SUSSA ACTS: A computer program for steady and unsteady, subsonic and supersonic aerodynamics for aerospace complex transportation systems

The computer program SUSSA ACTS (Steady and Unsteady, Subsonic and Supersonic Aerodynamics for Complex Transportation Systems) are presented in the final version. The numerical formulation and the description of the program and numerical results are included. In particular, generalized forces for fully unsteady (complex frequency) aerodynamics for a wing-body configuration, in both subsonic and supersonic flows, are discussed. The mathematical analysis includes completely arbitrary motion. The numerical implementation was limited to steady and oscillatory flows. A more general aerodynamic formulation in the form of a fully transient response for time-domain analysis and the aerodynamic transfer function (Laplace transform of the fully unsteady operator) for frequency-domain analysis is outlined.

Tseng, K.↗
DOE OSTI2026

Eliminating beam-induced depolarizing effects in the hydrogen jet target for high-precision proton beam polarimetry at the electron-ion collider

We analyze beam-induced depolarizing effects in the hydrogen jet target (HJET) at the relativistic heavy ion collider (RHIC), which has been used for absolute hadron beam polarimetry and shall be employed at the electron-ion collider (EIC). The EIC’s higher bunch repetition frequencies and shorter bunch durations shift beam harmonics to frequencies that can resonantly drive hyperfine transitions in hydrogen, threatening to depolarize the target atoms. Using frequency-domain analysis of beam harmonics and hyperfine transition frequencies, we establish a photon emission threshold above which beam-induced fields are too weak to cause significant depolarization. For EIC injection (23.5 GeV) and flattop (275 GeV), beam-induced depolarization through the bunch structure renders operation at the current RHIC magnetic guide field at the target (𝐵 0 =120⁢ mT) untenable. Increasing the magnetic guide field at the target to 𝐵 0 ≈ 400⁢ mT moves all hyperfine transition frequencies to at least 3 times the cutoff frequency, ensuring reliable absolute beam polarimetry with the required 1% precision at the EIC.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
NASA NTRS1979

Directional spectra of ocean waves from microwave backscatter: A physical optics solution with application to the short-pulse and two-frequency measurement techniques

Two simple microwave radar techniques that are potentially capable of providing routine satellite measurements of the directional spectrum of ocean waves were developed. One technique, the short pulse technique, makes use of very short pulses to resolve ocean surface wave contrast features in the range direction; the other technique, the two frequency correlation technique makes use of coherency in the transmitted waveform to detect the large ocean wave contrast modulation as a beat or mixing frequency in the power backscattered at two closely separated microwave frequencies. A frequency domain analysis of the short pulse and two frequency systems shows that the two measurement systems are essentially duals; they each operate on the generalized (three frequency) fourth-order statistical moment of the surface transfer function in different, but symmetrical ways, and they both measure the same directional contrast modulation spectrum. A three dimensional physical optics solution for the fourth-order moment was obtained for backscatter in the near vertical, specular regime, assuming Gaussian surface statistics.

Jackson, F. C.↗
NASA NTRSDate not supplied

Aeroelastic Analysis of Highly Flexible Wings with Linearized Frequency-Domain Aerodynamics

Flutter analysis of configurations with geometric structural nonlinearities typically is done with time-domain analysis. The results from this process are computationally expensive and can yield cumbersome results that may be difficult to manage/interpret. Compared to time-domain methods, frequency-domain flutter analysis can provide additional insight into the characteristics of a flutter stability problem. By linearizing the aeroelastic problem about the nonlinear equilibrium state, this work applies frequency-domain aeroelastic analysis to the Pazy wing, the subject of the Large Deformation Working Group in the Aeroelastic Prediction Workshop. Generalized aerodynamic forces (GAFs) are computed with both a doublet-lattice method and a computational fluid dynamics solver at a range of reduced frequencies as well as a range of dynamic pressures to account for the dependence of the mode shapes on the nonlinear equilibrium state. These GAFs are used in a p-k flutter solver, which is modified to handle the dependence of the stiffness matrix and GAFs on the dynamic pressure.

Bret K Stanford↗
NASA NTRS1979

Robustness of multiloop linear feedback systems

This paper presents a new approach to the frequency-domain analysis of multiloop linear feedback systems. The properties of the return difference equation are examined using the concepts of singular values, singular vectors and the spectral norm of a matrix. A number of new tools for multiloop systems are developed which are analogous to those for scalar Nyquist and Bode analysis. These provide a generalization of the scalar frequency-domain notions such as gain, bandwidth, stability margins and M-circles, and provide considerable insight into system robustness.

Doyle, J. C.↗