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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 253 records · Page 14
All sourcesNASA NTRSDOE OSTI
NASA NTRS2015

Three-Dimensional Vibration Isolator for Suppressing High-Frequency Responses for Sage III Contamination Monitoring Package (CMP)

The Stratospheric Aerosol and Gas Experiment (SAGE) III - International Space Station (ISS) instrument will be used to study ozone, providing global, long-term measurements of key components of the Earth's atmosphere for the continued health of Earth and its inhabitants. SAGE III is launched into orbit in an inverted configuration on SpaceX;s Falcon 9 launch vehicle. As one of its four supporting elements, a Contamination Monitoring Package (CMP) mounted to the top panel of the Interface Adapter Module (IAM) box experiences high-frequency response due to structural coupling between the two structures during the SpaceX launch. These vibrations, which were initially observed in the IAM Engineering Development Unit (EDU) test and later verified through finite element analysis (FEA) for the SpaceX launch loads, may damage the internal electronic cards and the Thermoelectric Quartz Crystal Microbalance (TQCM) sensors mounted on the CMP. Three-dimensional (3D) vibration isolators were required to be inserted between the CMP and IAM interface in order to attenuate the high frequency vibrations without resulting in any major changes to the existing system. Wire rope isolators were proposed as the isolation system between the CMP and IAM due to the low impact to design. Most 3D isolation systems are designed for compression and roll, therefore little dynamic data was available for using wire rope isolators in an inverted or tension configuration. From the isolator FEA and test results, it is shown that by using the 3D wire rope isolators, the CMP high-frequency responses have been suppressed by several orders of magnitude over a wide excitation frequency range. Consequently, the TQCM sensor responses are well below their qualification environments. It is indicated that these high-frequency responses due to the typical instrument structural coupling can be significantly suppressed by a vibration passive control using the 3D vibration isolator. Thermal and contamination issues were also examined during the isolator selection period for meeting the SAGE III-ISS instrument requirements.

Li, Y.↗
NASA NTRS1993

A reevaluation of the vestibulo-ocular reflex: new ideas of its purpose, properties, neural substrate, and disorders

Conventional views of the vestibulo-ocular reflex (VOR) have emphasized testing with caloric stimuli and by passively rotating patients at low frequencies in a chair. The properties of the VOR tested under these conditions differ from the performance of this reflex during the natural function for which it evolved--locomotion. Only the VOR (and not visually mediated eye movements) can cope with the high-frequency angular and linear perturbations of the head that occur during locomotion; this is achieved by generating eye movements at short latency (< 16 msec). Interpretation of vestibular testing is enhanced by the realization that, although the di- and trisynaptic components of the VOR are essential for this short-latency response, the overall accuracy and plasticity of the VOR depend upon a distributed, parallel network of neurons involving the vestibular nuclei. Neurons in this network variously upon a distributed, parallel network of neurons involving the vestibular nuclei. Neurons in this network variously encode inputs from the labyrinthine semicircular canals and otoliths, as well as from the visual and somatosensory systems. The central vestibular pathways branch to contact vestibular cortex (for perception) and the spinal cord (for control of posture). Thus, the vestibular nuclei basically coordinate the stabilization of gaze and posture, and contribute to the perception of verticality and self-motion. Consequently, brainstem disorders that disrupt the VOR cause not just only nystagmus, but also instability of posture (eg, increased fore-aft sway in patients with downbeat nystagmus) and disturbance of spatial orientation (eg, tilt of the subjective visual vertical in Wallenberg's syndrome).

Review↗
NASA NTRS2016

Liftoff and Time Equivalent Duration Data Evaluation of Exploration Flight Test 1 Orion Multi-Purpose Crew Vehicle

The liftoff phase induces high acoustic loading over a broad frequency range for a launch vehicle. These external acoustic environments are used in the prediction of the internal vibration responses of the vehicle and components. There arises the question about time equivalent (Teq) duration of the liftoff phase and similarity to other launch vehicles. Vibroacoustic engineers require the fatigue-weighted time duration values for qualification testing inputs. In order to determine the Teq for the Space Launch System, NASA's newest launch vehicle, the external microphone data from the Exploration Flight Test 1 (EFT-1) flight of the Orion Multi-Purpose Crew Vehicle (MPCV) was evaluated. During that evaluation, a trend was observed in the data and the origin of that trend is discussed in this paper. Finally, the Teq values for the EFT-1 Orion MPCV are presented.

Houston, Janice↗
NASA NTRS1999

Liquid Methane/Oxygen Injector Study for Mars Ascent Engines

As a part of the advancing technology of the cryogenic propulsion system for the Mars exploration mission, this effort aims at evaluating propellant injection concepts for liquid methane/liquid oxygen (LOX) rocket engines. Split-triplet and unlike impinging injectors were selected for this study. A total of four injector configurations were tested under combustion conditions in a modular combustor test article (MCTA), equipped with optically accessible windows, at MSFC. A series of forty hot-fire tests, which covered a wide range of engine operating conditions with the chamber pressure ranging from 320 to 510 and the mixture ratio from 1.5 to 3.5, were conducted. The test matrix also included a variation in the combustion chamber length for the purpose of investigating its effects on the combustion performance and stability. Initial assessments of the test results showed that the injectors provided stable combustion and there were no injector face overheating problems under all operating conditions. The Raman scattering signal measurement method was successfully demonstrated for the hydrocarbon/oxygen reactive flow field. The near-injector face flow field was visually observed through the use of an infrared camera. Chamber wall temperature, high frequency chamber pressure, and average throat section heat flux were also recorded throughout the test series. Assessments of the injector performance are underway.

Trinh, Huu Phuoc↗
NASA NTRS2014

Hexavalent Chrome Free Coatings for Electronics; Electromagnetic Interference (EMI) Shielding Effectiveness (SE)

The purpose of this testing is to determine the suitability of trivalent chromium conversion coatings that meet the requirements of MIL-DTL-5541, Type II, for use in applications where high-frequency electrical performance is important. This project will evaluate the ability of coated aluminum to form adequate EMI seals. Testing will assess performance of the trivalent chromium coatings against the known control hexavalent chromium MIL-DTL-5541 Type I Class 3 before and after they have been exposed to a set of environmental conditions. Performance will be assessed by evaluating shielding effectiveness (SE) test data from a variety of test samples comprised of different aluminum types and/or conversion coatings.

hexavalent chrome↗
NASA NTRS1971

Response of aerospace structures to reentry aerodynamic excitation

A bibliography on aerodynamic excitation and associated structural response is presented. Very little applicable data under actual reentry conditions was found, but many wind tunnel tests and some in-flight data were. Aerodynamic excitation and proposed space shuttle configurations and reentry trajectories were studied. Attached turbulent boundary layer, separated turbulent boundary layer, and base pressure fluctuations are the region of aerodynamic excitation most applicable to exterior panels of space shuttle-type vehicles; prediction techniques are presented for these environments. Methods for predicting the response of panel structures to acoustic excitation were investigated. A normal mode approach was developed for the low frequency response and a statistical energy approach was utilized for the high frequency response. A finite element model was made of a thermal protective system test panel. Computer programs were used to determine the natural frequencies and mode shapes of the panel and to calculate the response of the panel to a reverberant acoustic field. Power spectral densities of response displacement and acceleration are presented.

Carlin, D., Jr.↗
NASA NTRS1978

Development of structural dynamic test environments for subsystems and components

Structural dynamic environmental test levels were developed for the thematic mapper instrument, components of the Tandberg-Hanssen instrument, and components of the International Ultraviolet Explorer spacecraft using NASTRAN structural models and test data. Both static and dynamic NASTRAN analyses were used. The model size required could be as small as 300 degrees of freedom for the static analysis and as large as 4000 degrees of freedom or more for the high frequency dynamic analysis. An important step in the development of the levels is model verification by test. The launch environments that generally dictate many important features of the design of an instrument or component are steady state acceleration, sinusoidal vibration, and random vibration.

Coladonato, R. J.↗
NASA NTRS1973

Acoustic emission studies of large advanced composite rocket motor cases.

Acoustic emission (AE) patterns were measured during pressure testing of advanced composite rocket motor cases made of boron/epoxy and graphite/epoxy. Both accelerometers and high frequency AE transducers were used, and both frequency spectrum and amplitude distribution were studied. The AE patterns suggest that precursor emission might be used in certain cases to anticipate failure. The technique of hold-cycle AE monitoring was also evaluated and could become a valuable decision gate for test continuation/termination. Data presented show similarity of accelerometers and AE transducer responses despite the different frequency response, and suggest that structural AE phenomena are broadband.

Robinson, E. Y.↗
NASA NTRS1991

Evaluation of components, subsystems, and networks for high rate, high frequency space communications

The development of new space communications technologies by NASA has included both commercial applications and space science requirements. At NASA's Lewis Research Center, methods and facilities have been developed for evaluating these new technologies in the laboratory. NASA's Systems Integration, Test and Evaluation (SITE) Space Communication System Simulator is a hardware-based laboratory simulator for evaluating space communications technologies at the component, subsystem, system, and network level, geared toward high frequency, high data rate systems. The SITE facility is well-suited for evaluation of the new technologies required for the Space Exploration Initiative (SEI) and advanced commercial systems. This paper describes the technology developments and evaluation requirements for current and planned commercial and space science programs. Also examined are the capabilities of SITE, the past, present, and planned future configurations of the SITE facility, and applications of SITE to evaluation of SEI technology.

Kerczewski, Robert J.↗
NASA NTRS1990

En route noise of turboprop aircraft and their acceptability: Report of tests

The development of propfan-powered aircraft has been observed with great interest. It is obvious that during cruising flight, the aircraft powerplant (propellers) cause a noise clearly perceivable on the ground. It is the audible frequency spectrum of the propfan powerplants relative to the high tip speeds that presents the problem. A flight test was conducted on 30 April, 1989 at the Frankfurt Airport. Results of the test flight are present.

Held, Wolf↗
NASA NTRS1992

A Reevaluation of the Vestibulo-Ocular Reflex: New Ideas of its Purpose, Properties, Neural Substrate, and Disorders

Conventional views of the Vestibulo-Ocular Reflex (VOR) have emphasized testing with caloric stimuli and by passively rotating patients at low frequencies in a chair. The properties of the VOR tested under these conditions differ from the performance of this reflex during the natural function for which it evolved-locomotion. Only the VOR (and not visually mediated eye movements) can cope with the high-frequency angular and linear perturbations of the head that occur during locomotion; this is achieved by generating eye movements at short latency (less than 16 msec). Interpretation of vestibular testing is enhanced by the realization that, although the di- and trisynaptic components of the VOR are essential for this short-latency response, the overall accuracy and plasticity of the VOR depend upon a distributed, parallel network of neurons involving the vestibular nuclei. Neurons in this network variously encode inputs from the labyrinthine semicircular canals and otoliths, as well as from the visual and somatosensory systems. The central vestibular pathways branch to contact vestibular cortex (for perception) and the spinal cord (for control of posture). Thus, the vestibular nuclei basically coordinate the stabilization of gaze and posture, and contribute to the perception of verticality and self-motion. Consequently, brainstem disorders that disrupt the VOR cause not just only nystagmus, but also instability of posture (eg, increased fore-aft sway in patients with downbeat nystagmus) and disturbance of spatial orientation (eg, tilt of the subjective visual vertical in Wallenberg's syndrome).

Leigh, R. John↗
NASA NTRS2013

High Bypass Ratio Jet Noise Reduction and Installation Effects Including Shielding Effectiveness

An experimental investigation was performed to study the propulsion airframe aeroacoustic installation effects of a separate flow jet nozzle with a Hybrid Wing Body aircraft configuration where the engine is installed above the wing. Prior understanding of the jet noise shielding effectiveness was extended to a bypass ratio ten application as a function of nozzle configuration, chevron type, axial spacing, and installation effects from additional airframe components. Chevron types included fan chevrons that are uniform circumferentially around the fan nozzle and T-fan type chevrons that are asymmetrical circumferentially. In isolated testing without a pylon, uniform chevrons compared to T-fan chevrons showed slightly more low frequency reduction offset by more high frequency increase. Phased array localization shows that at this bypass ratio chevrons still move peak jet noise source locations upstream but not to nearly the extent, as a function of frequency, as for lower bypass ratio jets. For baseline nozzles without chevrons, the basic pylon effect has been greatly reduced compared to that seen for lower bypass ratio jets. Compared to Tfan chevrons without a pylon, the combination with a standard pylon results in more high frequency noise increase and an overall higher noise level. Shielded by an airframe surface 2.17 fan diameters from nozzle to airframe trailing edge, the T-fan chevron nozzle can produce reductions in jet noise of as much as 8 dB at high frequencies and upstream angles. Noise reduction from shielding decreases with decreasing frequency and with increasing angle from the jet inlet. Beyond an angle of 130 degrees there is almost no noise reduction from shielding. Increasing chevron immersion more than what is already an aggressive design is not advantageous for noise reduction. The addition of airframe control surfaces, including vertical stabilizers and elevon deflection, showed only a small overall impact. Based on the test results, the best overall nozzle configuration design was selected for application to the N2A Hybrid Wing Body concept that will be the subject of the NASA Langley 14 by 22 Foot Subsonic Tunnel high fidelity aeroacoustic characterization experiment. The best overall nozzle selected includes T-fan type chevrons, uniform chevrons on the core nozzle, and no additional pylon of the type that created a strong acoustic effect at lower bypass ratios. The T-fan chevrons are oriented azimuthally away from the ground observer locations. This best overall nozzle compared to the baseline nozzle was assessed, at equal thrust, to produce sufficient installed noise reduction of the jet noise component to enable the N2A HWB to meet NASA s noise goal of 42 dB cumulative below Stage 4.

Thomas, Russell H.↗
NASA NTRSDate not supplied

Uncertainty Quantification of Inducer Natural Frequency using Conditional Assessment of Modeling and Modal Testing of Simpler Systems

The low pressure fuel pump inducer of the new Space Launch System RS25 core stage engine operates in a highly complex environment that substantially affects its modal characteristics. Some of the more important effects are fluid-added mass resulting from operation within a light liquid (Hydrogen), and the magnification of this effect due to tight tip clearance. Since higher order cavitation has been identified as a significant harmonic driver, knowledge of the natural frequency of potentially excitable modes is critical for safe operation, but this frequency cannot be measured during the severe operational environment. A comprehensive testing and analysis program has therefore been performed over the last four years to identify the nominal value and uncertainty of the frequency by modeling and testing four simpler structures which share some of the characteristics of the operational inducer. This testing was used to assess and adjust modeling techniques and excellent correlation was achieved. Identification of the uncertainty in the inducer frequency itself was still problematic, however. This difficulty led to an investigation of Bayesian uncertainty quantification techniques, and to the application of the relatively simple technique of Multi-Variate Normal conditional distributions to calculate the inducer natural frequency uncertainty. Assumptions on prior distributions of uncertainty of the fluid-added mass and tip clearance effect are initially applied to models of each of the simple structures and the inducer itself, and these uncertainties are propagated to generate natural frequencies using design of experiments. Simple response surfaces are then created from this data in order to calculate a Covariance Matrix relating all of these natural frequencies. Finally, the results from modal test of the simple structures are considered to be observations and used to calculate the conditional variance of the desired inducer frequencies. As this method is less rigorous than more complicated Bayesian methods reported in the literature, a conservative factor is applied to the result, but the resulting uncertainty is still significantly less than originally estimated and will greatly assist certification of the inducer for use in the engine.

Uncertainty Quantification↗
NASA NTRS1994

Measurement of the frequency stability of responders in aircraft

Measurement on an aircraft orbit, such as a satellite launching orbit, is made by the responder in the aircraft along with several remote track stations on the ground. During the launching, the system is required to have precise time synchronization and frequency accuracy. At the same time, accurate measurement of aircraft velocity requires high frequency stability of the system. However, atomic frequency standards in the ground stations supply time and frequency reference standard with excellent long term and short term frequency stability for the above-mentioned goals. The stability of responder is also an important factor affecting the performance of the system and there are more requirements for the corresponding time/frequency measurements. In the system, the responders do not use continuous wave (CW) but narrow pulse modulated wave; consequently, the characterization theory of their stability is more complicated and the measurement technique is more difficult for pulsed wave than that for CW. A systematic characterization theory of the frequency stability for pulsed wave is demonstrated and the measuring methods are discussed. The measurement systems, which have been set up in Beijing Institute of Radio Metrology and Measurement (BIRMM) and can be used to test the frequency stability of pulse coherent responders in time domain and frequency domain with high sensitivity and accuracy, are described. Using these measurement systems, successful measurements for the responders were made with which the satellite launching orbits were precisely obtained and tracked.

Liu, Xiaofan↗
NASA NTRS1987

Space power demonstrator engine, phase 1

The design, analysis, and preliminary test results for a 25 kWe Free-Piston Stirling engine with integral linear alternators are described. The project is conducted by Mechanical Technology under the direction of LeRC as part of the SP-100 Nuclear Space Power Systems Program. The engine/alternator system is designed to demonstrate the following performance: (1) 25 kWe output at a specific weight less than 8 kg/kW; (2) 25 percent efficiency at a temperature ratio of 2.0; (3) low vibration (amplitude less than .003 in); (4) internal gas bearings (no wear, no external pump); and (5) heater temperature/cooler temperature from 630 to 315 K. The design approach to minimize vibration is a two-module engine (12.5 kWe per module) in a linearly-opposed configuration with a common expansion space. The low specific weight is obtained at high helium pressure (150 bar) and high frequency (105 Hz) and by using high magnetic strength (samarium cobalt) alternator magnets. Engine tests began in June 1985; 16 months following initiation of engine and test cell design. Hydrotest and consequent engine testing to date has been intentionally limited to half pressure, and electrical power output is within 15 to 20 percent of design predictions.

Source record↗
NASA NTRSDate not supplied

Preliminary Findings of the Experimental Development Unit Cold Flow Test for a Generation Zero Nuclear Propulsion Engine

Nuclear thermal propulsion (NTP) technology will greatly benefit human travel to Mars by significantly shortening transit times, improving crew safety, and providing more mission flexibility than traditional chemical rockets. As part of DRACO follow-on work to develop, build, and fly a generation zero NTP engine, a full scale flight-like experimental design unit (EDU) reactor was constructed to collect sufficient on-ground performance data to characterize flow induced vibrations (FIV) of critical reactor structures/components, inform development of the engine and reactor control algorithm, and collect pressure drop and flow distribution data across the reactor. The fluid conditions for the test program were designed to achieve system responses equivalent to that of an operational engine through all phases of engine operation including reactor startup, mainstage operation, reactor shutdown, and reactor cooldown. Over 100 tests were executed, flowing either GN2 or GHe through the EDU at varying flow rates and pressures. This experiment provided early validation of flow behavior and vibration risks before nuclear testing, boosted critical subsystem TRLs, informed design iterations, and reduced future test costs. The steady-state flow parameters for the experiment were modeled in Ansys Thermal Desktop, allowing rapid tuning and experiment-informed updates to a flight-like test matrix. The EDU dynamic environment was characterized with accelerometers, strain gauges, and high-frequency pressure transducers all sampled at 20 kHz. While many narrow-band oscillations were identified, no significant FIV occurred; the reactor structural responses tend to be enveloped by typical launch vehicle ascent vibration environments (defined up to 2 kHz), although significant energy is also present at higher frequencies.

Flow Induced Vibration↗
NASA NTRS1984

Study of stator-vane fluctuating pressures in a turbofan engine for static and flight tests

As part of a program to study the fan noise generated from turbofan engines, fluctuating surface pressures induced by fan-rotor wakes were measured on core- and bypass-stator outlet guide vanes of a modified JT15D-1 engine. Tests were conducted with the engine operating on an outdoor test stand and in flight. The amplitudes of pressures measured at fan-rotor blade-passage fundamental frequencies were generally higher and appeared less stable for the static tests than for the flight tests. Fluctuating pressures measured at the blade-passage frequency of the high-speed core compressor were interpreted to be acoustic; however, disturbance trace velocities for either the convected rotor wakes or acoustic pressures were difficult to interpret because of the complex environment.

Mueller, A. W.↗
NASA NTRS1988

Recent advances in capacitance type of blade tip clearance measurements

Two recent electronic advances at NASA-Lewis that meet the blade tip clearance needs of a wide class of fans, compressors, and turbines are described. The first is a frequency modulated (FM) oscillator that requires only a single low cost ultrahigh frequency operational amplifier. Its carrier frequency is 42.8 MHz when used with a 61 cm long hermetically sealed coaxial cable. The oscillator can be calibrated in the static mode and has a negative peak frequency deviation of 400 kHz for a typical rotor blade. High temperature performance tests of the probe and 13 cm of the adjacent cable show good accuracy up to 600 C, the maximum which produces a clearance error of + or - 10 microns at a clearance of 500 microns. In the second advance, a guarded probe configuration allows a longer cable capacitance. The capacitance of the probe is part of a small time constant feedback in a high speed operational amplifier. The solution of the governing differential equation is applied to a ramp type of input. The results show an amplifier output that contains a term which is proportional to the derivative of the feedback capacitance. The capacitance is obtained by subtracting a balancing reference channel followed by an integration stage.

Barranger, John P.↗