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At least 127 records · Page 7
All sourcesNASA NTRSDOE OSTI
NASA NTRS1995

Dynamics and control of instrumented harmonic drives

Since torque in harmonic drives is transmitted by a pure couple, harmonic drives do not generate radial forces and therefore can be instrumented with torque sensors without interference from radial forces. The installation of torque sensors on the stationary component of harmonic drives (the Flexipline cup in this research work) produce backdrivability needed for robotic and telerobotic compliant maneuvers. Backdrivability of a harmonic drive, when used as torque increaser, means that the output shaft can be rotated via finite amount of torque. A high ratio harmonic drive is non-backdrivable because its output shaft cannot be turned by applying a torque on it. This article first develops the dynamic behavior of a harmonic drive, in particular the non-backdrivability, in terms of a sensitivity transfer function. The instrumentation of the harmonic drive with torque sensor is then described. This leads to a description of the control architecture which allows modulation of the sensitivity transfer function within the limits established by the closed-loop stability. A set of experiments on an active hand controller, powered by a DC motor coupled to an instrumented harmonic drive, is given to exhibit this method's limitations.

NASA Discipline Space Human Factors↗
NASA NTRS2014

Some Interesting Applications of Probabilistic Techiques in Structural Dynamic Analysis of Rocket Engines

Numerical and Analytical methods developed to determine damage accumulation in specific engine components when speed variation included. Dither Life Ratio shown to be well over factor of 2 for specific example. Steady‐State assumption shown to be accurate for most turbopump cases, allowing rapid calculation of DLR. If hot‐fire speed data unknown, Monte Carlo method developed that uses speed statistics for similar engines. Application of techniques allow analyst to reduce both uncertainty and excess conservatism. High values of DLR could allow previously unacceptable part to pass HCF criteria without redesign. Given benefit and ease of implementation, recommend that any finite life turbomachine component analysis adopt these techniques. Probability Values calculated, compared, and evaluated for several industry‐proposed methods for combining random and harmonic loads. Two new excel macros written to calculate combined load for any specific probability level. Closed form Curve fits generated for widely used 3(sigma) and 2(sigma) probability levels. For design of lightweight aerospace components, obtaining accurate, reproducible, statistically meaningful answer critical.

Brown, Andrew M.↗
NASA NTRS2001

Plasma Waves Observed in the Cusp Turbulent Boundary Layer: An Analysis of High Time Resolution Wave and Particle Measurements from the Polar Spacecraft

The boundary layer located in the cusp and adjacent to the magnetopause is a region that is quite turbulent and abundant with waves. The Polar spacecraft's orbit and sophisticated instrumentation are ideal for studying this region of space. Our analysis of the waveform data obtained in this turbulent boundary layer shows broadband magnetic noise extending up to a few kilohertz (but less than the electron cyclotron frequency); sinusoidal bursts (a few tenths of a second) of whistler mode waves at around a few tens of hertz, a few hundreds of hertz, and just below the electron cyclotron frequency; and bipolar pulses, interpreted as electron phase-space holes. In addition, bursts of electron cyclotron harmonic waves are occasionally observed with magnetic components. We show evidence of broadband electrostatic bursts covering a range of approx. 3 to approx. 25 kHz (near but less than the plasma frequency) occurring in packets modulated at the frequency of some of the whistler mode waves. On the basis of high time resolution particle data from the Polar HYDRA instrument, we show that these bursts are consistent with generation by the resistive medium instability. The most likely source of the whistler mode waves is the magnetic reconnection site closest to the spacecraft, since the waves are observed propagating both toward and away from the Earth, are bursty, which is often the case with reconnection, and do not fit on the theoretical cold plasma dispersion relation curve.

Pickett, J. S.↗
NASA NTRS2003

Light Microscopy Module Fan Disturbance Characterized Through Microgravity Emissions Laboratory Testing

A Light Microscopy Module (LMM) is being engineered, designed, and developed at the NASA Glenn Research Center. The LMM is planned as a remotely controllable on-orbit microscope subrack facility, allowing flexible scheduling and control of physical science and biological science experiments within Glenn s Fluids Integrated Rack on the International Space Station. The LMM concept is a modified commercial research imaging light microscope with powerful laser-diagnostic hardware and interfaces, creating a one-of-a-kind, state-of-the-art microscopic research facility. The microscope will house several different objectives, corresponding to magnifications of 10, 40, 50, 63, and 100. Features of the LMM include high-resolution color video microscopy, brightfield, darkfield, phase contrast, differential interference contrast, spectrophotometry, and confocal microscopy combined in a single configuration. Also, laser tweezers are integrated with the diagnostics as a sample manipulation technique. As part of the development phase of the LMM, it was necessary to quantify the microgravity disturbances generated by the control box fan. Isolating the fan was deemed necessary to reduce the fan speed harmonic amplitudes and to eliminate any broadband disturbances across the 60- to 70-Hz and 160- to 170-Hz frequency ranges. The accelerations generated by a control box fan component of the LMM were measured in the Microgravity Emissions Laboratory (MEL). The MEL is a low-frequency measurement system developed to simulate and verify the on-orbit International Space Station (ISS) microgravity environment. The accelerations generated by various operating components of the ISS, if too large, could hinder the science performed onboard by disturbing the microgravity environment. The MEL facility gives customers a test-verified way of measuring their compliance with ISS limitations on vibratory disturbance levels. The facility is unique in that inertial forces in 6 degrees of freedom can be characterized simultaneously for an operating test article. Vibratory disturbance levels are measured for engineering or flight-level hardware following development from component to subassembly through the rack-level configuration. The MEL can measure accelerations as small as 10-7g, the accuracy needed to confirm compliance with ISS requirements.

McNelis, Anne M.↗
NASA NTRS2004

Space Application Requirements for Organic Avionics

The NASA Marshall Space Flight Center is currently evaluating polymer based components for application in launch vehicle and propulsion system avionics systems. Organic polymers offer great advantages over inorganic corollaries. Unlike inorganics with crystalline structures defining their sensing characteristics, organic polymers can be engineered to provide varying degrees of sensitivity for various parameters including electro-optic response, second harmonic generation, and piezoelectric response. While great advantages in performance can be achieved with organic polymers, survivability in the operational environment is a key aspect for their practical application. The space environment in particular offers challenges that must be considered in the application of polymer based devices. These challenges include: long term thermal stability for long duration missions, extreme thermal cycling, space radiation tolerance, vacuum operation, low power operation, high operational reliability. Requirements for application of polymer based devices in space avionics systems will be presented and discussed in light of current polymer materials.

Watson, Michael D.↗
NASA NTRS1973

Mars - Crustal structure inferred from Bouguer gravity anomalies.

Bouguer gravity has been computed for the equatorial region of Mars by differencing free air gravity and the gravity predicted from topographic variations. The free air gravity was generated from an eighth-order set of spherical harmonic coefficients. The gravity from topographic variations was generated by integrating a two-dimensional Green's function over each contour level. The Bouguer gravity indicates crustal inhomogeneities on Mars that are postulated to be variations in crustal thickness. The Tharsis ridge is a region of thick continental type crust. The gravity data, structural patterns, topography, and surface geology of this region lead to the interpretation of the Tharsis topographic high as a broad crustal upwarp possibly associated with local formation of lower-density crustal material and subsequent rise of a thicker crust. The Amazonis region is one of several basins of relatively thin crust, analogous to terrestrial ocean basins. The Libya and Hellas basins, which are probable impact features, are also underlain by thin crust and are possible regions of mantle upwelling.

Phillips, R. J.↗
NASA NTRS1995

Boundary layer transition studies

A small-scale wind tunnel previously used for turbulent boundary layer experiments was modified for two sets of boundary layer transition studies. The first study concerns a laminar separation/turbulent reattachment. The pressure gradient and unit Reynolds number are the same as the fully turbulent flow of Spalart and Watmuff. Without the trip wire, a laminar layer asymptotes to a Falkner & Skan similarity solution in the FPG. Application of the APG causes the layer to separate and a highly turbulent and approximately 2D mean flow reattachment occurs downstream. In an effort to gain some physical insight into the flow processes a small impulsive disturbance was introduced at the C(sub p) minimum. The facility is totally automated and phase-averaged data are measured on a point-by-point basis using unprecedently large grids. The evolution of the disturbance has been tracked all the way into the reattachment region and beyond into the fully turbulent boundary layer. At first, the amplitude decays exponentially with streamwise distance in the APG region, where the layer remains attached, i.e. the layer is viscously stable. After separation, the rate of decay slows, and a point of minimum amplitude is reached where the contours of the wave packet exhibit dispersive characteristics. From this point, exponential growth of the amplitude of the disturbance is observed in the detached shear layer, i.e. the dominant instability mechanism is inviscid. A group of large-scale 3D vortex loops emerges in the vicinity of the reattachment. Remarkably, the second loop retains its identify far downstream in the turbulent boundary layer. The results provide a level of detail usually associated with CFD. Substantial modifications were made to the facility for the second study concerning disturbances generated by Suction Holes for laminar flow Control (LFC). The test section incorporates suction through interchangeable porous test surfaces. Detailed studies have been made using isolated holes in the impervious test plate that used to establish the Blasius base flow. The suction is perturbed harmonically and data are averaged on the basis of the phase of the disturbance, for conditions corresponding to strong suction and without suction. The technique was enhanced by using up to nine multiple probes to reduce the experimental run-time. In both cases, 3D contour surfaces in the vicinity of the hole show highly 3D TS waves which fan out in the spanwise direction forming bow-shaped waves downstream. The case without suction has proved useful for evaluating calculation methods. With suction, the perturbations on the centerline are much stronger and decay less rapidly, while the TS waves in the far field are similar to the case without suction. Downstream, the contour surfaces of the TS waves develop spanwise irregularities which eventually form into clumps. The spanwise clumping is evidence of a secondary instability that could be associated with suction vortices. Designers of porous surfaces use Goldsmith's Criterion to minimize cross-stream interactions. It is shown that partial TS wave cancellation is possible, depending on the hole spacing, disturbance frequency and free-stream velocity. New high-performance Constant Temperature Hot-Wire Anemometers were designed and built, based on a linear system theory analysis that can be extended to arbitrary order. The motivation was to achieve the highest possible frequency reponse while ensuring overall system stability. The performance is equal to or superior to commercially available instruments at about 10% of the cost. Details, such as fabrication drawings and a parts list, have been published to enable the instrument to be construced by others.

Watmuff, Jonathan H.↗
NASA NTRS1981

The Deep Space Network: An instrument for radio science research

Doppler and ranging data routinely generated at the Deep Space Stations of the California Institute of Technology-Jet Propulsion Laboratory Deep Space Network serve as an excellent source of radio science information. Important radio science experiments based on Deep Space Network generated radio metric data have included confirmation of Einstein's Theory of Relativity, measurement of the masses and gravitational harmonics of the planets out to Saturn, and measurement of electron density distribution and turbulence in the solar corona. In response to an increased level of radio science requirements, the Deep Space Network chose in 1976 to implement a new radio science system, which was completed in late 1978. Key features include (1) highly phase stable open loop receivers, (2) reduction of recorded data bandwidth through use of programmed local oscillators, and (3) real time digitization and recording on computer compatible tape.

Renzetti, N. A.↗
NASA NTRS1991

GaAs Schottky barrier varactor diodes for submillimeter wavelength power generation

The development of GaAs Schottky barrier diodes for frequencies well into the submillimeter wavelength range is discussed. These devices have the highest cutoff frequencies yet obtained for varactor diodes and have produced sufficient output power to drive Schottky mixers at frequencies as high as 640 GHz. The fundamental design tradeoff between cutoff frequency and capacitance modulation is explored. As the doping density is increased and the anode diameter is reduced, the dynamic cutoff frequency increases, reaching a maximum of roughly 5 THz. It is concluded that the maximum output frequency from harmonic multipliers based on standard GaAs varactor diodes will be about 1 THz.

Crowe, T. W.↗
NASA NTRS1989

High-frequency instability of the sheath-plasma resonance

Coherent high-frequency oscillations near the electron plasma frequency are generated by electrodes with positive dc bias immersed in a uniform Maxwellian afterglow plasma. The instability occurs at the sheath-plasma resonance and is driven by a negative RF sheath resistance associated with the electron inertia in the diodelike electron-rich sheath. With increasing dc bias, i.e., electron transit time, the instability exhibits a hard threshold, downward frequency pulling, line broadening, and copious harmonics. The fundamental instability is a bounded oscillation caused by wave evanescence, but the harmonics are radiated as electromagnetic waves from the electrodes acting like antennas. Wavelength and polarization measurements confirm the emission process. Electromagnetic waves are excited by electrodes of various geometries (planes, cylinders, spheres), which excludes other radiation mechanisms such as orbitrons or beam-plasma instabilities. The line-broadening mechanism has been identified as a frequency modulation via the electron transit time by dynamic ions. Ion oscillations at the sheath edge give rise to burstlike RF emissions. These laboratory observations of a new instability are important for antennas in space plasmas, generation of coherent beams with diodes, and plasma diagnostics.

Stenzel, R. L.↗
NASA NTRS2004

Far-Field Acoustic Characteristics of Multiple Blade-Vane Configurations for a High Tip Speed Fan

The acoustic characteristics of a model high-speed fan stage were measured in the NASA Glenn 9- by 15-Foot Low Speed Wind Tunnel at takeoff and approach flight conditions. The fan was designed for a corrected rotor tip speed of 442 m/s (1450 ft/s), and had a powered core, or booster stage, giving the model a nominal bypass ratio of 5. A simulated engine pylon and nozzle bifurcation was contained within the bypass duct. The fan stage consisted of all combinations of 3 possible rotors, and 3 stator vane sets. The 3 rotors were (1) wide chord, (2) forward swept, and (3) shrouded. The 3 stator sets were (1) baseline, moderately swept, (2) swept and leaned, and (3) swept integral vane/frame which incorporated some of the swept and leaned features as well as eliminated the downstream support structure. The baseline configuration is considered to be the wide chord rotor with the radial vane stator. A flyover Effective Perceived Noise Level (EPNL) code was used to generate relative EPNL values for the various configurations. The swept and leaned stator showed a 3 EPNdB reduction at lower fan speeds relative to the baseline stator; while the swept integral vane/frame stator showed lowest noise levels at high fan speeds. The baseline, wide chord rotor was typically the quietest of the three rotors. A tone removal study was performed to assess the acoustic benefits of removing the fundamental rotor interaction tone and its harmonics. Reprocessing the acoustic results with the bypass tone removed had the most impact on reducing fan noise at transonic rotor speeds. Removal of the bypass rotor interaction tones (BPF and nBPF) showed up to a 6 EPNdB noise reduction at transonic rotor speeds relative to noise levels for the baseline (wide chord rotor and radial stator; all tones present) configuration.

Woodward, Richard P.↗
NASA NTRS2013

Chaos and Beyond in a Water Filled Ultrasonic Resonance System

Finite amplitude ultrasonic wave resonances in a one-dimensional liquid-filled cavity, formed by a narrow band transducer and a plane reflector, are reported. The resonances are observed to include not only the expected harmonic and subharmonic signals (1,2) but chaotic signals as well. The generation mechanism requires attaining a threshold value of the driving amplitude that the liquid-filled cavity system becomes sufficiently nonlinear in response. The nonlinear features of the system were recently investigated via the construction of an ultrasonic interferometer having optical precision. The transducers were compressional, undamped quartz and lithium niobate crystals having the frequency range 1-10 MHz, driven by a high power amplifier. Both an optical diffraction system to characterize the diffraction pattern of laser light normally incident to the cavity and a receiving transducer attached to an aligned reflector with lapped flat and parallel surfaces were used to assess the generated resonance response in the cavity. At least 5 regions of excitation are identified.

Lazlo, Adler↗
NASA NTRS1984

Rotational frequency splitting of solar oscillations

Prograde and retrograde sectoral oscillations of the sun have been observed so as to determine frequency differences produced by rotation. Oscillations in the frequency range 2.1-3.7 mHz and with spherical harmonic degrees from 1 to 100 have been identified. Average frequency shifts due to rotation in a sidereal reference frame are found to range from a high of about 660 nHz at degree 1 to a low of about 423 nHz at degree 6, rising to about 471 nHz at degree 100. These results indicate that most of the sun's volume rotates at a rate close to that of the surface, but also that the energy-generating core may rotate more rapidly than the surface.

Duvall, T. L., Jr.↗
NASA NTRS2005

NASA Tech Briefs, July 2005

Thin-Film Resistance Heat-Flux Sensors Circuit Indicates that Voice-Recording Disks are Nearly Full Optical Sensing of Combustion Instabilities in Gas Turbines Topics include: Crane-Load Contact Sensor; Hexagonal and Pentagonal Fractal Multiband Antennas; Multifunctional Logic Gate Controlled by Temperature; Multifunctional Logic Gate Controlled by Supply Voltage; Power Divider for Waveforms Rich in Harmonics; SCB Quantum Computers Using iSWAP and 1-Qubit Rotations; CSAM Metrology Software Tool; Update on Rover Sequencing and Visualization Program; Selecting Data from a Star Catalog; Rotating Desk for Collaboration by Two Computer Programmers; Variable-Pressure Washer; Magnetically Attached Multifunction Maintenance Rover; Improvements in Fabrication of Sand/Binder Cores for Casting; Solid Freeform Fabrication of Composite-Material Objects; Efficient Computational Model of Hysteresis; Gauges for Highly Precise Metrology of a Compound Mirror; Improved Electrolytic Hydrogen Peroxide Generator; High-Power Fiber Lasers Using Photonic Band Gap Materials; Ontology-Driven Information Integration; Quantifying Traversability of Terrain for a Mobile Robot; More About Arc-Welding Process for Making Carbon Nanotubes; Controlling Laser Spot Size in Outer Space; or Software-Reconfigurable Processors for Spacecraft.

Source record↗
NASA NTRS1991

Nonlinear disturbances in a hypersonic laminar boundary layer

Three separate but similar experiments on the growth of naturally-occurring instability waves in the laminar boundary-layers on sharp cones at hypersonic Mach numbers have been conducted. Each provided clear evidence that the theoretically-predicted second mode of instability was responsible for high-amplitude wave trains observed to prevail upstream of boundary-layer transition to turbulence. However, each also seemed to reveal the presence of an additional instability not accounted for by the linear theory. Here, examination is made of the tape-recorded hot-wire anemometer signals of one experiment on a sharp cone at Mach 8 for evidence of nonlinearity, the finding of which would explain the presence of the additional mode as a consequence of harmonic generation. Several approaches for identification of the residual effects of nonlinearity are described and utilized. Also, a simplified model describing certain fluctuation characteristics has been developed. Altogether, the evidence of nonlinear wave development is found to be strong. Quantitative comparisons of linear theory to experiments must be made with caution when nonlinearity is present in the experiment.

Kimmel, Roger L.↗
NASA NTRS1991

System and component design and test of a 10 hp, 18,000 rpm AC dynamometer utilizing a high frequency AC voltage link, part 1

Hard and soft switching test results conducted with one of the samples of first generation MOS-controlled thyristor (MCTs) and similar test results with several different samples of second generation MCT's are reported. A simple chopper circuit is used to investigate the basic switching characteristics of MCT under hard switching and various types of resonant circuits are used to determine soft switching characteristics of MCT under both zero voltage and zero current switching. Next, operation principles of a pulse density modulated converter (PDMC) for three phase (3F) to 3F two-step power conversion via parallel resonant high frequency (HF) AC link are reviewed. The details for the selection of power switches and other power components required for the construction of the power circuit for the second generation 3F to 3F converter system are discussed. The problems encountered in the first generation system are considered. Design and performance of the first generation 3F to 3F power converter system and field oriented induction moter drive based upon a 3 kVA, 20 kHz parallel resonant HF AC link are described. Low harmonic current at the input and output, unity power factor operation of input, and bidirectional flow capability of the system are shown via both computer and experimental results. The work completed on the construction and testing of the second generation converter and field oriented induction motor drive based upon specifications for a 10 hp squirrel cage dynamometer and a 20 kHz parallel resonant HF AC link is discussed. The induction machine is designed to deliver 10 hp or 7.46 kW when operated as an AC-dynamo with power fed back to the source through the converter. Results presented reveal that the proposed power level requires additional energy storage elements to overcome difficulties with a peak link voltage variation problem that limits reaching to the desired power level. The power level test of the second generation converter after the addition of extra energy storage elements to the HF link are described. The importance of the source voltage level to achieve a better current regulation for the source side PDMC is also briefly discussed. The power levels achieved in the motoring mode of operation show that the proposed power levels achieved in the generating mode of operation can also be easily achieved provided that no mechanical speed limitation were present to drive the induction machine at the proposed power level.

Lipo, Thomas A.↗
NASA NTRS2009

Synthesis of Submillimeter Radiation for Spectroscopy

The frequency-multiplier submillimeter spectrometer (FMSS) is a laboratory apparatus for far-infrared molecular spectroscopy, embodying several advances over prior such apparatuses. The most innovative part of the FMSS is a source of monochromatic submillimeter- wavelength radiation that can be tuned over a wide frequency range, as needed for trace gas analyses and molecular- structure studies for which such apparatuses are typically used. The radiation source features a modular design and is built mostly from commercially available components. It includes a computer-controlled radio-frequency synthesizer, amplifiers, and frequency multipliers of a type heretofore used in local oscillators for heterodyne far-infrared receivers. In conjunction with the rest of the apparatus, this source makes it possible to perform measurements over large portions of the submillimeter-wavelength spectrum with resolution, accuracy, and sensitivity greater than those achievable in Fourier-transform infrared spectroscopy. In comparison with prior laboratory submillimeter- wavelength radiation sources, this source is much lighter in weight, less cumbersome, less power-hungry, and capable of sustained operation with less intervention by laboratory personnel. Also, unlike some prior submillimeter-wavelength sources, this source does not require a high-voltage power source. As shown in more detail in the figure, the radiation source includes a sweep frequency synthesizer connected to an external waveform generator, the output of which is used as a reference signal. The synthesizer is computer-controlled through a standard general-purpose interface bus (GPIB) and is operated in phase-locked continuous- wave mode for all measurements. The synthesizer output ranges in frequency from 11 to 18 GHz. For suppression of frequency spurs and harmonics, the output of the frequency synthesizer is fed through a tunable yttrium iron garnet (YIG) filter, which is swept in frequency simultaneously with the frequency synthesizer.

Maiwald, Frank↗
NASA NTRS2010

Miniature MMIC Low Mass/Power Radiometer Modules for the 180 GHz GeoSTAR Array

We have developed and demonstrated miniature 180 GHz Monolithic Microwave Integrated Circuit (MMIC) radiometer modules that have low noise temperature, low mass and low power consumption. These modules will enable the Geostationary Synthetic Thinned Aperture Radiometer (GeoSTAR) of the Precipitation and All-weather Temperature and Humidity (PATH) Mission for atmospheric temperature and humidity profiling. The GeoSTAR instrument has an array of hundreds of receivers. Technology that was developed included Indium Phosphide (InP) MMIC Low Noise Amplifiers (LNAs) and second harmonic MMIC mixers and I-Q mixers, surface mount Multi-Chip Module (MCM) packages at 180 GHz, and interferometric array at 180 GHz. A complete MMIC chip set for the 180 GHz receiver modules (LNAs and I-Q Second harmonic mixer) was developed. The MMIC LNAs had more than 50% lower noise temperature (NT=300K) than previous state-of-art and MMIC I-Q mixers demonstrated low LO power (3 dBm). Two lots of MMIC wafers were processed with very high DC transconductance of up to 2800 mS/mm for the 35 nm gate length devices. Based on these MMICs a 180 GHz Multichip Module was developed that had a factor of 100 lower mass/volume (16x18x4.5 mm3, 3g) than previous generation 180 GHz receivers.

Monolithic Microwave Integrated Circuit (MMIC)↗