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At least 757 records · Page 42

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NASA NTRS1993

Resource utilization model for the algorithm to architecture mapping model

The analytical model for resource utilization and the variable node time and conditional node model for the enhanced ATAMM model for a real-time data flow architecture are presented in this research. The Algorithm To Architecture Mapping Model, ATAMM, is a Petri net based graph theoretic model developed at Old Dominion University, and is capable of modeling the execution of large-grained algorithms on a real-time data flow architecture. Using the resource utilization model, the resource envelope may be obtained directly from a given graph and, consequently, the maximum number of required resources may be evaluated. The node timing diagram for one iteration period may be obtained using the analytical resource envelope. The variable node time model, which describes the change in resource requirement for the execution of an algorithm under node time variation, is useful to expand the applicability of the ATAMM model to heterogeneous architectures. The model also describes a method of detecting the presence of resource limited mode and its subsequent prevention. Graphs with conditional nodes are shown to be reduced to equivalent graphs with time varying nodes and, subsequently, may be analyzed using the variable node time model to determine resource requirements. Case studies are performed on three graphs for the illustration of applicability of the analytical theories.

Stoughton, John W.↗

NASA NTRS1993

Faint object camera observations of the shape and expansion of SN 1987A

A comparison is made between HST Faint-Object Camera visible and near-IR imagery of SN 1987A obtained 1754 days after outburst and those obtained after 1278 days. The SN has dimmed by a factor of 0.35 +/- 0.04 between the two observations; this corresponds to an exponential decay time 450 +/- 50 days. Detailed fits to image profiles show that this SN's envelope is heavily limb-darkened, and well-characterized by a surface brightness profile that decreases with angular radius. The apparent size of the envelope also varies significantly with wavelength.

Jakobsen, P.↗

NASA NTRS1993

Acoustic oscillations of Jupiter

We calculate low-degree l acoustic (p-mode) oscillations of the giant planet Jupiter. We use two Jupiter models, both of which contain a rocky core, an ice mantle, and a hydrogen-rich envelope. One of the models incorporates the 'plasma phase transition' of hydrogen, a first-order phase transition that yields a density discontinuity in the hydrogen-rich envelope. Our calculations of the acoustic oscillation spectrum of Jupiter have taken account of the effects of the rapid rotation of the planet: the Coriolis force, centrifugal force, and deformation of the equilibrium state. The p-mode frequency spectra of the Jupiter models are summarized in several echelle diagrams. We show that the frequency spectra of the low-degree p-modes are strongly affected by the existence of the rocky core and by avoided crossings among high radial-order p-modes with different l's.

Lee, Umin↗

NASA NTRS1992

Proportional proximity sensing for telerobots using Coherent Laser Radar

The ability of a telerobotic manipulator to operate in confined spaces while avoiding unwanted collisions is enhanced by the accurate sensing of its proximate environment. To achieve the fidelity required for precise manipulator control, a proportional proximity sensor system with a sufficiently large measurement envelope is required. Current proximity sensors provide a binary indication of the presence of obstacles within a small envelope with coarse or no proportional measurement of their location. A proportional proximity sensor system configured as a Frequency Modulated Continuous Wave (FMCW) Coherent Laser Radar (CLR) using a semiconductor laser as the energy source is described and analyzed. The source and reflected energies mix coherently to generate a radio frequency (RF) signal whose frequency is proportional to the range. The system is tested for accuracy, range, depth of range, speed, and sensitivity and the results are presented. Techniques to derive orientation information and an application to telerobotic control are also described.

Vazquez, Sixto L.↗

NASA NTRS1993

Infrared studies of circumstellar matter around Herbig Ae/Be and related stars

The study presents high spatial resolution data at 50 and 100 microns for seven young intermediate-mass stars with flat or rising spectral energy distributions. Five stars, namely, LkH-alpha 198, R Mon, CD -42 deg 11721, R CrA, and V645 Cyg, are resolved at 100 microns. The emission comes from spatially extended envelopes, with sizes varying between 0.025 and 0.4 pc. The wavelengths are optically thin at mid-IR and FIR wavelengths but become optically thick in the visual where the extinction amounts to 5-10 mag. In two cases, R CrA and V 645 Cyg, dust density distributions with steep density gradients are obtained, alpha is approximately equal to 2, while for LkH-alpha, R Mon, and CD -42 deg 11721, alpha is approximately equal to 0.5. Model fitting to the spectral energy distributions, combined with the constraints on the size of the emitting regions, indicates that inside the circumstellar envelopes a large fraction of the stellar radiation is already degraded to longer wavelengths.

Natta, Antonella↗

NASA NTRS1992

Advanced Technology Blade testing on the XV-15 Tilt Rotor Research Aircraft

The XV-15 Tilt Rotor Research Aircraft has just completed the first series of flight tests with the Advanced Technology Blade (ATB) rotor system. The ATB are designed specifically for flight research and provide the ability to alter blade sweep and tip shape. A number of problems were encountered from first installation through envelope expansion to airplane mode flight that required innovative solutions to establish a suitable flight envelope. Prior to operation, the blade retention hardware had to be requalified to a higher rated centrifugal load, because the blade weight was higher than expected. Early flights in the helicopter mode revealed unacceptably high vibratory control system loads which required a temporary modification of the rotor controls to achieve higher speed flight and conversion to airplane mode. The airspeed in airplane mode was limited, however, because of large static control loads. Furthermore, analyses based on refined ATB blade mass and inertia properties indicated a previously unknown high-speed blade mode instability, also requiring airplane-mode maximum airspeed to be restricted. Most recently, a structural failure of an ATB cuff (root fairing) assembly retention structure required a redesign of the assembly. All problems have been addressed and satisfactory solutions have been found to allow continued productive flight research of the emerging tilt rotor concept.

Wellman, Brent↗

NASA NTRS1992

Linear dynamic analysis of the Space Station Freedom thermal/environmental control system

A methodology for dynamic analysis of the Space Station Freedom thermal/environmental control system is described which uses linear system analysis techniques to determine the ability of the system to accommodate thermal load transients. A nonlinear integrated model of the system as it exists at Stage 6, Man Tended Capability (MTC), is described which encompasses the cabin air cooling system, avionics air cooling system, internal and external thermal control systems. The nonlinear model is linearized at an assumed design operating point, and the linear model is evaluated by comparison with the nonlinear model. Transfer functions are derived to determine the response of the heat rejection system to time-varying thermal loads applied at various points in the heat acquisition system. The frequency response calculated from the transfer functions is used to determine allowable operating envelopes of thermal load magnitude and frequency for each point of application of thermal load. The dynamic operating envelopes provide a quantitative indication of the degree and duration of peak loads which the thermal/environmental system is able to transport and reject.

Tandler, John↗

NASA NTRS1993

Detection of O I and Si II far-infrared fine-structure emission from Alpha Orionis

We have detected forbidden O I 63 micron and forbidden Si II 35 micron emission from the oxygen-rich, M2 lab supergiant, Alpha Orionis (Betelgeuse). The forbidden O I line flux is 2.4 +/- 0.2 x 10 exp -18 W/sq cm, and the forbidden Si II line flux is 0.9 +/- 0.4 x 10 exp -18 W/sq cm. These fluxes are consistent with the thermal model of Rodgers and Glassgold (1991), which indicates that the emission arises in dense, warm gas in Alpha Ori's inner envelope and implies that nearly all of the available O and Si is in atomic form. This is the first reported detection of FIR, fine-structure emission from the inner or transition region of a circumstellar envelope, where molecules and dust are expected to form.

Haas, Michael R.↗

NASA NTRS1993

Vortex flap flight test operations, a safe approach

A flight test experiment was conducted at the Langley Research Center to evaluate a wing leading-edge vortex flap concept designed for use on an aircraft with highly swept wings. The flap concept was designed as a modification to the wing leading edge of an F-106B airplane. The flight testing required operations at conditions that would exceed the structural load envelope of the basic airplane in order to acquire desired research data for the modified configuration. Accordingly, the operational envelope of the modified aircraft was incrementally expanded and real-time monitoring of airframe strains at critical wing locations was mandated to insure safety of flight. The flight tests were conducted in two phases: Phase I to establish baseline data with the unmodified wing, and Phase II to determine the effects of the vortex flap on performance, handling qualities, and flow field characteristics. This paper focuses on a description of the approach and procedures used to provide the strain-gage monitoring to insure structural integrity. Highlights of the wing modification and the overall operation are also included. Within a -year period, 110 research flights were successfully completed, providing researchers with sufficient data to assess the potential benefits ascribed to the vortex flap concept without encountering severe structural problems or mishaps.

Dicarlo, Daniel J.↗

NASA NTRS1993

Dynamic model testing of the X-31 configuration for high-angle-of-attack flight dynamics research

High-angle-of-attack flight dynamics of the X-31 configuration were studied using dynamic model test techniques. These tests identified phenomena including wing rock, spins, and departures that could dominate the high-alpha behavior of the configuration and restrict its usable flight envelope. Results of these tests have been used to design flight control concepts and configuration modifications to minimize adverse effects of these phenomena. The conclusion of the high-alpha envelope expansion flight tests of the X-31 aircraft will complete the database against which the dynamic model results can be correlated.

Croom, Mark A.↗

NASA NTRS1993

The progenitor of supernova 1993J - A stripped supergiant in a binary system?

Supernova 1993J in the spiral galaxy M81 is the brightest supernova since SN1987A and, like the latter, appears to be another 'peculiar' type II supernova. The available photometry of the supernova region before the explosion requires the presence of at least two supergiants (one of early spectral type and the other of late type), but the actual progenitor has yet to be identified. We show that the explosion of a late-type supergiant can explain the initial sharp peak in the supernova light curve, provided that the star had lost almost all of its hydrogen-rich envelope before the explosion. In our model, the secondary brightening of the supernova, about 10 days later, is then a consequence of the radioactive decay of Ni-56 (and subsequently Co-56) produced in the explosion. The progenitor could have lost its hydrogen-rich envelope either in a strong stellar wind or, as seems more likely, through mass transfer to a companion star. In the latter case, the companion should reappear after the supernova photosphere has receded, the system having become a binary composed of a neutron star with a massive stellar companion.

Podsiaklowski, PH.↗

NASA NTRS1922

Hydrostatic Tests of an Airship Model

An airship model made by the Goodyear Rubber Company was filled with water and suspended from a beam. The deformations of the envelope were studied under the following conditions: 1) both ballonets empty; 2) forward ballonets filled with air; 3) rear ballonets filled with air; and 4) both ballonets filled with air. Photographs were taken to record the deflections under each of these conditions, and a study was made to determine the minimum head of water necessary to maintain the longitudinal axis of the envelope under these conditions. It was concluded that any pressure sufficient to keep the airship full may be used. It appears that a pressure of one inch of water would provide a suitable factor of safety, and therefore it is the pressure that is recommended.

Source record↗

NASA NTRS1923

The effect of bow stiffeners in nonrigid airships

It is now well known that all nonrigid airships constructed at the present time have bow stiffeners consisting of battens curved to the form of the envelope and designed to hold the nose of the ship in its true form despite the very large pressure which exists at the extreme forward point. The effect of the stiffeners is to reduce considerably the apparent pressure which has to be maintained inside the envelope in order to prevent the nose from caving in.

AIRSHIP NOSES - STIFFENING↗

NASA NTRS1946

Analysis of V-G Records from the SNB-1 Airplane

Availability data obtained on SNB-1 trainer-class airplanes were analyzed and results presented as flight envelopes which predict occurrences of large values of air speed and acceleration. Comparison is made with SNJ-4 trainer-class airplane data analyzed by the same method. It is concluded that flight envelopes are satisfactory; that the two types show large differences in flight loads and speeds experience; and that SNB-1 will seldom, if ever, exceed design limit load factor and restricted speed, which SNJ-4 can be expected to exceed design-limit load factor and restricted speed in a very small number of flight hours.

Meadows, May T.↗

NASA NTRS1993

Extraction of stability and control derivatives from orbiter flight data

The Space Shuttle Orbiter has provided unique and important information on aircraft flight dynamics. This information has provided the opportunity to assess the flight-derived stability and control derivatives for maneuvering flight in the hypersonic regime. In the case of the Space Shuttle Orbiter, these derivatives are required to determine if certain configuration placards (limitations on the flight envelope) can be modified. These placards were determined on the basis of preflight predictions and the associated uncertainties. As flight-determined derivatives are obtained, the placards are reassessed, and some of them are removed or modified. Extraction of the stability and control derivatives was justified by operational considerations and not by research considerations. Using flight results to update the predicted database of the orbiter is one of the most completely documented processes for a flight vehicle. This process followed from the requirement for analysis of flight data for control system updates and for expansion of the operational flight envelope. These results show significant changes in many important stability and control derivatives from the preflight database. This paper presents some of the stability and control derivative results obtained from Space Shuttle flights. Some of the limitations of this information are also examined.

Iliff, Kenneth W.↗

NASA NTRS1992

A feasibility study regarding the addition of a fifth control to a rotorcraft in-flight simulator

The addition of a large movable horizontal tail surface to the control system of a rotorcraft in-flight simulator being developed from a Sikorsky UH-60A Black Hawk Helicopter is evaluated. The capabilities of the control surface as a trim control and as an active control are explored. The helicopter dynamics are modeled using the Generic Helicopter simulation program developed by Sikorsky Aircraft. The effect of the horizontal tail on the helicopter trim envelope is examined by plotting trim maps of the aircraft attitude and controls as a function of the flight speed and horizontal tail incidence. The control power of the tail surface relative to that of the other controls is examined by comparing control derivatives extracted from the simulation program over the flight speed envelope. The horizontal tail's contribution as an active control is evaluated using an explicit model following control synthesis involving a linear model of the helicopter in steady, level flight at a flight speed of eighty knots. The horizontal tail is found to provide additional control flexibility in the longitudinal axis. As a trim control, it provides effective control of the trim pitch attitude at mid to high forward speeds. As an active control, the horizontal tail provides useful pitching moment generating capabilities at mid to high forward speeds.

Turner, Simon↗

NASA NTRS1993

Strategies and methodologies to develop techniques for computer-assisted analysis of gas phase formation during altitude decompression

It would be of operational significance if one possessed a device that would indicate the presence of gas phase formation in the body during hypobaric decompression. Automated analysis of Doppler gas bubble signals has been attempted for 2 decades but with generally unfavorable results, except with surgically implanted transducers. Recently, efforts have intensified with the introduction of low-cost computer programs. Current NASA work is directed towards the development of a computer-assisted method specifically targeted to EVA, and we are most interested in Spencer Grade 4. We note that Spencer Doppler Grades 1 to 3 have increased in the FFT sonogram and spectrogram in the amplitude domain, and the frequency domain is sometimes increased over that created by the normal blood flow envelope. The amplitude perturbations are of very short duration, in both systole and diastole and at random temporal positions. Grade 4 is characteristic in the amplitude domain but with modest increases in the FFT sonogram and spectral frequency power from 2K to 4K over all of the cardiac cycle. Heart valve motion appears to characteristic display signals: (1) the demodulated Doppler signal amplitude is considerably above the Doppler-shifted blow flow signal (even Grade 4); and (2) demodulated Doppler frequency shifts are considerably greater (often several kHz) than the upper edge of the blood flow envelope. Knowledge of these facts will aid in the construction of a real-time, computer-assisted discriminator to eliminate cardiac motion artifacts. There could also exist perturbations in the following: (1) modifications of the pattern of blood flow in accordance with Poiseuille's Law, (2) flow changes with a change in the Reynolds number, (3) an increase in the pulsatility index, and/or (4) diminished diastolic flow or 'runoff.' Doppler ultrasound devices have been constructed with a three-transducer array and a pulsed frequency generator.

Powell, Michael R.↗

NASA NTRS1993

Analysis of gas turbine engines using water and oxygen injection to achieve high Mach numbers and high thrust

An analysis of gas turbine engines using water and oxygen injection to enhance performance by increasing Mach number capability and by increasing thrust is described. The liquids are injected, either separately or together, into the subsonic diffuser ahead of the engine compressor. A turbojet engine and a mixed-flow turbofan engine (MFTF) are examined, and in pursuit of maximum thrust, both engines are fitted with afterburners. The results indicate that water injection alone can extend the performance envelope of both engine types by one and one-half Mach numbers at which point water-air ratios reach 17 or 18 percent and liquid specific impulse is reduced to some 390 to 470 seconds, a level about equal to the impulse of a high energy rocket engine. The envelope can be further extended, but only with increasing sacrifices in liquid specific impulse. Oxygen-airflow ratios as high as 15 percent were investigated for increasing thrust. Using 15 percent oxygen in combination with water injection at high supersonic Mach numbers resulted in thrust augmentation as high as 76 percent without any significant decrease in liquid specific impulse. The stoichiometric afterburner exit temperature increased with increasing oxygen flow, reaching 4822 deg R in the turbojet engine at a Mach number of 3.5. At the transonic Mach number of 0.95 where no water injection is needed, an oxygen-air ratio of 15 percent increased thrust by some 55 percent in both engines, along with a decrease in liquid specific impulse of 62 percent. Afterburner temperature was approximately 4700 deg R at this high thrust condition. Water and/or oxygen injection are simple and straightforward strategies to improve engine performance and they will add little to engine weight. However, if large Mach number and thrust increases are required, liquid flows become significant, so that operation at these conditions will necessarily be of short duration.

Henneberry, Hugh M.↗