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Results for “SPHERICAL WAVE”

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 OSTI2020

Overdriven-detonation states produced by spherically diverging waves

A series of experiments are currently underway at the Detonation Science and Technology group, within Los Alamos National Laboratory, to study the overdriven-detonation states achievable in energetic materials as a result of detonation-wave interactions. A multi-component, energetic-material array was designed to study the amplification of velocity and pressure states produced by spherically diverging detonation waves in pentaerythritol tetranitrate (PETN) output charges. The unique geometry provides a low-jitter, highly controlled series of interactions between three independent-detonation inputs. Streak-camera imaging was performed on the output face of PETN pellets ranging in thickness from 2.5 – 10 mm to characterize the resulting breakout profile. Additionally, photonic Doppler velocimetry (PDV) measurements were collected at the output-pellet surface to determine simultaneity within the system. Detonation-wave velocities upwards of 16 mm/µs were measured, as compared to a steady-state detonation velocity of 7.9 mm/µs for the PETN pressing density investigated. Finally, additional experiments are being conducted to measure the pressure amplification generated at key areas of interaction.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
NASA NTRS2004

Backscattering enhancement with a finite beam width for millimeter - wavelength weather radars

Backscattering enhancement from random hydrometeors should increase as wavelengths of radars reach millimeter regions. For 95 GHz radars, the reflectivity of backscattering is expected to increase by 2 dB, due to multiple scattering including backscattering enhancement, for water droplets of diameter of 1 mm with a density of 5×103 m−3. Previous theoretical studies of backscattering enhancement considered infinitely extending plane waves. In this paper, we expand the theory to spherical waves with a Gaussian antenna pattern, including depolarizing effects. While the differences from the plane wave results are not great when the optical thickness is small, as the latter increases the differences become significant, and essentially depend on the ratio of radar footprint radius to the mean free path of hydrometeors. In this regime, for a radar footprint that is smaller than the mean free path, the backscattering-enhancement reflectivity corresponding to spherical waves is significantly less pronounced than in the case of the plane wave theory. Hence this reduction factor must be taken into account when analyzing radar reflectivity factors for use in remote sensing applications.

Im, Eastwood↗
DOE OSTI2020

Analytical expressions of the surface shape of ‘diaboloid’ mirrors

Modern deterministic polishing processes allow fabrication of x-ray optics with almost any arbitrary aspherical surface shape. Among these optics, the so called "diaboloid"mirror is of special interest. The diaboloid mirror that converts a cylindrical wave to a spherical wave would improve focusing in x-ray beamlines implementing a diffraction element between a parabolic cylinder and a toroidal mirror. The replacement of the toroidal mirror in existing beamlines by the diaboloid mirror would mitigate aberrations. The shape of the diaboloid mirror is usually calculated numerically based on a truncated polynomial solution of the optical path problem. Here, we present an exact analytical solution for the shape of a diaboloid mirror as a function of the conjugate parameters of the mirror placed in a beamline. The derived analytical expressions for the diaboloid mirror in both the canonical and mirror-based coordinate systems are implemented in ray-tracing simulations to verify the beamline performances.

Yashchuk, Valeriy V.↗
NASA NTRS2019

Co- and Counter-Propagating Wave Effects in an Absorbing Medium

In this semi-tutorial paper, we revisit the interference phenomena caused by pairs of copropagating or counter-propagating transverse electromagnetic waves by letting the host medium be absorbing. We first consider plane waves in an unbounded medium, summarize the standingwave solution of the Maxwell equations, and discuss specific effects caused by nonvanishing absorption. We then consider the superposition of plane and spherical waves in the context of fartfield electromagnetic scattering by a particle. To this end we modify the classical Jones lemma by allowing nonzero absorption in the host medium and consider its most obvious consequences such as forward- and backscattering interference. The physical similarity of the two scenarios (superpositions of plane waves and superpositions of plane and spherical waves) is discussed.

Interference↗
NASA NTRS1972

Gain calibration of a horn antenna using pattern integration

Gain measurement of a horn antenna using three different techniques is discussed. The methods include a two-antenna insertion loss measurement, a pattern integration method, and a near-field measurement method. The application of the pattern integration method is considered, as well as the evaluation of the near-field gain correction factors for the horn, which are determined by a method based directly on measured data. This method involves a spherical wave expansion of the experimental radiation pattern of the specific antenna being tested, rather than evaluation of an assumed analytical model. The spherical wave expansion is also compared to experimental near-field pattern data.

Ludwig, A. C.↗
NASA NTRS1971

Focusing of Finite-Amplitude Cylindrical and Spherical Sound Waves in a Viscous and Heat-Conducting Medium

The focusing of acoustic pulses is studied analytically by considering the region of study in three parts: the converging, interaction and diverging regions. First, the linear problem of a pulse of infinitesimal amplitude is studied. For the spherical case, the expected phase change as a result of focusing is verified. The nonlinear case of finite-amplitude pulses leads to the development of M-waves, as determined by applying the method of matched-asymptotic expansions to Burges equation.

Chu, T.↗
NASA NTRS1999

Laser Interferometer Space Antenna (LISA) Far Field Phase Patterns

The Laser Interferometer Space Antenna (LISA) for the detection of Gravitational Waves is a very long baseline interferometer, which will measure the changes in the distance of a five million kilometer arm to picometer accuracies. Knowledge of the phase deviations from a spherical wave and what causes these deviations are needed considerations in (as a minimum) the design of the telescope and in determining pointing requirements. Here we will present the far field phase deviations from a spherical wave for given Zernike aberrations of the exit pupil and discuss how these results affect the choice of a telescope design.

Waluschka, Eugene↗
NASA NTRS1999

Laser Interferometer Space Antenna (LISA) Far Field Phase Pattern

The Laser Interferometry Space Antenna (LISA) for the detection of Gravitational Waves is a very long baseline interferometer that will measure the changes in the distance of a five million kilometer arm to pico meter accuracies. Knowledge of the phase deviations from a spherical wave and what causes these deviations are needed considerations in (as a minimum) the design of the telescope and in determining pointing requirements. Here we present the far field phase deviations from a spherical wave for given Zernike aberrations and obscurations of the exit pupil.

Waluschka, Eugene↗
NASA NTRS1996

Waveform Perturbations os Spherical Transiet Waves Propagating in a Random Medium

Of those aspects of sonic-boom propagation that are not yet fully understood, one of the more important is that which relates to the perturbations of the waveform. This phenomenon, which arises also in connection with the propagation of other types of transient waves in real media, generally take the form, in the case of sonic-boom N-waves, of a random high-frequency structure (sometimes called fine structure) that is most prominent in the regions immediately behind each of the shocks. The perturbations in those regions can be large, occasionally attaining magnitudes comparable to that of th incident wave itself. Such magnitudes, in combination with the high-frequency character of the perturbations, can lead to a considerable increase in the perceived noisiness of the sonic boom. Waveform perturbations are consequently an important factor as regards the question of sonic-boom acceptability. On the basis of observations, and some early theoretical studies, it is now generally accepted that perturbations of sonic-boom waveforms are a manifestation of the effect on the propagating wave of relatively small-scale variations in the acoustic properties of the atmosphere- variations that are usually associated with turbulence. Although the mechanism underlying perturbations of sonic-boom waveforms seems thus to be well understood, no fully-satisfactory theory of such perturbations has emerged. Indeed, even for the relatively simple case of an incident step-function pulse, no theory of waveform perturbations, formulated in a realistic three-dimensional context, has been advanced that is valid in the region of strongest perturbations; viz., the region immediately behind, and including, the wave front. The work reported herein represents an attempt to develop such a theory.

Wenzel, Alan R.↗
NASA NTRS1959

Effect of Surface Roughness on Characteristics of Spherical Shock Waves

Measurements of peak overpressure and Mach stem height were made at four burst heights. Data were obtained with instrumentation capable of directly observing the variation of shock wave movement with time. Good similarity of free air shock peak overpressure with larger scale data was found to exist. The net effect of surface roughness on shock peak overpressures slightly. Surface roughness delayed the Mach stem formation at the greatest charge height and lowered the growth at all burst heights. A similarity parameter was found which approximately correlates the triple point path at different burst heights.

Huber, Paul W.↗
NASA NTRS1997

A Spherical to Plane Wave Transformation Using a Reflectarray

A reflectarray has generally been used as a replacement for a reflector antenna. Using in this capacity, different configurations (prime focus, offset etc.) and various applications (dual frequency, scanning etc.) have been demonstrated with great success. Another potential application that has not been explored previously is the use of reflectarrays to compensate for phase errors in space power combining applications such as space-fed lens and power combining amplifier. In these applications, it is required to convert a spherical wave to a plane wave with proper phase correction added to each element of the reflectarray. This paper reports an experiment to investigate the feasibility of using a reflectarray as an alternative to a lens in space power combining. The experiment involves transforming a spherical wave from a orthomode horn to a plane wave at the horn aperture. The reflcctarray consists of square patches terminated in open stubs to provide necessary phase compensation. In this paper, preliminary results will be presented and the feasibility of such compensation scheme will be discussed.

Zaman, Afroz J.↗
NASA NTRS1990

Reflection and trapping of Alfven waves in a spherically symmetric stellar atmosphere

Alfven wave propagation in a spherically symmetric isothermal and stratified stellar atmosphere are analzyed using a time-dependent MHD numerical model. Particular consideration is given to wave reflection and the resultant trapping of the wave due to a peak in the Alfven speed in the atmosphere. Resonance frequencies in the trapping region and the effect of trapping on Alfven wave pressure force and propagation are examined. The data reveal that Alfven wave trapping has a potentially important role in accelerating winds from cool stars.

An, C.-H.↗