Engineering Papers⌕ Search

SEARCH · Engineering Papers

Results for “recovery”

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.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 739 records · Page 41
All sourcesNASA NTRSDOE OSTI
NASA NTRS1992

Branch recovery with compiler-assisted multiple instruction retry

In processing systems where rapid recovery from transient faults is important, schemes for multiple instruction rollback recovery may be appropriate. Multiple instruction retry has been implemented in hardware by researchers and also in mainframe computers. This paper extends compiler-assisted instruction retry to a broad class of code execution failures. Five benchmarks were used to measure the performance penalty of hazard resolution. Results indicate that the enhanced pure software approach can produce performance penalties consistent with existing hardware techniques. A combined compiler/hardware resolution strategy is also described and evaluated. Experimental results indicate a lower performance penalty than with either a totally hardware or totally software approach.

Alewine, N. J.↗
NASA NTRS1992

The analytical control program for the NASA Space Station Freedom Environmental Control and Life Support System (ECLSS) Water Recovery Test

NASA-Marshall has striven to maximize quality assurance and quality control measures in the course of Water Recovery Test (WRT) development for the Space Station Freedom ECLSS. The WRT was subjected to an independent analytical control program that is governed by the Analytical Control Test Plan and the Microbiological Methods for Water Recovery Testing Plan. Attention is given to analysis results for volatiles, sodium, and conductivity.

Tatara, James D.↗
NASA NTRS1992

A hybrid regenerative water recovery system for lunar/Mars life support applications

Long-duration manned space missions will require integrated biological and physicochemical processes for recovery of resources from wastes. This paper discusses a hybrid regenerative biological and physicochemical water recovery system designed and built at NASA's Crew and Thermal Systems Division at Johnson Space Center. The system is sized for a four-person crew and consists of a two-stage, aerobic, trickling filter bioreactor; a reverse osmosis system; and a photocatalytic oxidation system. The system was designed to accommodate high organic and inorganic loadings and a low hydraulic loading. The bioreactor was designed to oxidize organics to carbon dioxide and water; the reverse osmosis system reduces inorganic content to potable quality; and the photocatalytic oxidation unit removes residual organic impurities (part per million range) and provides in situ disinfection. The design and performance of the hybrid system for producing potable/hygiene water is described. Aspects of the system such as closure, automation and integration are discussed and preliminary results presented.

Verostko, Charles E.↗
NASA NTRS1993

Rapid transaction-undo recovery using twin-page storage management

This paper presents a twin-page storage method, which is an alternative to the TWIST (twin slot) approach by Reuter, for rapid transaction-undo recovery. In contrast to TWIST, our twin-page approach allows dirty pages in the buffer to be written at any instant onto disk without the requirement of undo logging, and, when a transaction is aborted, no explicit undo is required. As a result, all locks accumulated by the aborted transaction can be released earlier, allowing other transactions waiting for the locks to proceed. Through maintenance of aborted transaction identifiers, invalid pages written by the aborted transaction coexist with other valid pages and are guaranteed not be accessed by subsequent transactions. Instead of an explicit undo, most of the invalid pages are overwritten by subsequent normal updates. Performance in terms of disk I/O and CPU overhead for transaction-undo recovery is analyzed and compared with TWIST. It is shown that our scheme is particularly suited for applications where there are a large number of updates written onto disk when transactions are aborted, and there are frequent aborts. The approach, however, is not as applicable to environments where transactions are typically short or rarely aborted, or most updates are not written onto disk before a commitment.

Wu, Kun-Lung↗
NASA NTRS1991

Experimental evaluation of multiprocessor cache-based error recovery

Several variations of cache-based checkpointing for rollback error recovery in shared-memory multiprocessors have been recently developed. By modifying the cache replacement policy, these techniques use the inherent redundancy in the memory hierarchy to periodically checkpoint the computation state. Three schemes, different in the manner in which they avoid rollback propagation, are evaluated. By simulation with address traces from parallel applications running on an Encore Multimax shared-memory multiprocessor, the performance effect of integrating the recovery schemes in the cache coherence protocol are evaluated. The results indicate that the cache-based schemes can provide checkpointing capability with low performance overhead but uncontrollable high variability in the checkpoint interval.

Janssens, Bob↗
NASA NTRS1991

Implementing forward recovery using checkpointing in distributed systems

The paper describes the implementation of a forward recovery scheme using checkpoints and replicated tasks. The implementation is based on the concept of lookahead execution and rollback validation. In the experiment, two tasks are selected for the normal execution and one for rollback validation. It is shown that the recovery strategy has nearly error-free execution time and an average redundancy lower than TMR.

Long, Junsheng↗
NASA NTRS1948

Ram-recovery Characteristics of NACA Submerged Inlets at High Subsonic Speeds

Results are presented of an experimental investigation of the characteristics of NACA submerged inlets on a model of a fighter airplane for Mach numbers from 0.30 to 0.875. The effects on the ram-recovery ratio at the inlets of Mach number, angle of attack, boundary-layer thickness on the fuselage, inlet location, and boundary-layer deflectors are shown. The data indicate only a slight decrease in ram-recovery ratio for the inlets ahead of or just behind the wing leading edge as Mach number increased, but showed large decreases at high Mach numbers for the inlets aft of the point of maximum thickness of the wing.

INLETS, SIDE - DUCTED BODIES↗
NASA NTRS1993

Asynchronous timing and Doppler recovery in DSP based DPSK modems for fixed and mobile satellite applications

While conventional analog modems employ some kind of clock wave regenerator circuit for synchronous timing recovery, in sampled modem receivers the timing is recovered asynchronously to the incoming data stream, with no adjustment being made to the input sampling rate. All timing corrections are accomplished by digital operations on the sampled data stream, and timing recovery is asynchronous with the uncontrolled, input A/D system. A good timing error measurement algorithm is a zero crossing tracker proposed by Gardner. Digital, speech rate (2400 - 4800 bps) M-PSK modem receivers employing Gardner's zero crossing tracker were implemented and tested and found to achieve BER performance very close to theoretical values on the AWGN channel. Nyguist pulse shaped modem systems with excess bandwidth factors ranging from 100 to 60 percent were considered. We can show that for any symmetric M-PSK signal set Gardner's NDA algorithm is free of pattern jitter for any carrier phase offset for rectangular pulses and for Nyquist pulses having 100 percent excess bandwidth. Also, the Nyquist pulse shaped system is studied on the mobile satellite channel, where Doppler shifts and multipath fading degrade the pi/4-DQPSK signal. Two simple modifications to Gardner's zero crossing tracker enable it to remain useful in the presence of multipath fading.

Koblents, B.↗
NASA NTRS1993

Application of compiler-assisted multiple instruction rollback recovery to speculative execution

Speculative execution is a method to increase instruction level parallelism which can be exploited by both super-scalar and VLIW architectures. The key to a successful general speculation strategy is a repair mechanism to handle mispredicted branches and accurate reporting of exceptions for speculated instructions. Multiple instruction rollback is a technique developed for recovery from transient processor failure. Many of the difficulties encountered during recovery from branch misprediction or from instruction re-execution due to exception in a speculative execution architecture are similar to those encountered during multiple instruction rollback. The applicability of a recently developed compiler-assisted multiple instruction rollback scheme to aid in speculative execution repair is investigated. Extensions to the compiler-assisted scheme to support branch and exception repair are presented along with performance measurements across ten application programs.

Alewine, N. J.↗
NASA NTRS1992

Closed-loop transfer recovery with observer-based controllers. I - Analysis. II - Design

A detailed study is presented of three fundamental issues related to the problem of closed-loop transfer (CLT) recovery. The first issues concerns what can and cannot be achieved for a given system and for an arbitrary target CLT function (TCLTF). The second issue involves developing necessary and/or sufficient conditions for a TCLTF to be recoverable either exactly or approximately. The third issue involves the necessary and/or sufficient conditions on a given system such that it has at least one recoverable TCLTF. The results of the analysis identify some fundamental limitations of the given system as a consequence of its structural properties which enables designers to appreciate at the outset different design limitations incurred in the synthesis of output-feedback controllers. Then, the actual design of full-order or reduced-order observer-based controllers is addressed which will achieve as close as possibly the desired TCLTF. Three design methods are considered: (1) the ATEA method, (2) a method that minimizes the H2-norm of a recovery matrix, and (3) a method that minimizes the respective H(infinity) norm. The relative merits of the methods are discussed.

Chen, Ben M.↗
NASA NTRS1994

Shock recovery analogs and the origin of mesosiderites

The origin of mesosiderites, which consist of approximately equal-weight proportions of Fe-Ni metal and silicates (gabbros, basalts, orthopyroxenites, dunites), remains an interesting and complex problem in meteoritics. There is general agreement that multiple impact events were probably involved in the formation of these brecciated stony-iron meteorites, but given the heterogeneity of mesosiderites, additional processes have been invoked to explain the unique and intricate textural and compositional makeup of mesosiderites. We conducted a series of shock recovery experiments to test the impact event(s) scenario. The results indicated significant similarities between the shocked analogs and many mesosiderites. We have compared our analogs with a suite of thin sections of Barea mesosiderite. I have conducted a series of flash heating experiments in which equal-weight proportions of gabbro and stainless steel (SS304) powders were compressed into small charges and heated under reducing conditions for short times. These experiments were used to bracket localized, peak postshock temperatures in our analog shots and to compare the mixing relations between the silicate and metal. The shock recovery experiments used porous metal-silicate powder starting mixtures, therefore our experiments are most analogous to an impact scenario where the target is an asteroidal regolith surface composed of a loose mixture of Fe-Ni metal and heterogeneous silicates. Analog experiments may really describe a secondary impact process similar to the late-stage, localized impact melting event. This leaves one of the crucial questions about mesosiderite genesis unanswered, namely what is the source of the Fe-Ni metal that is so intimately distributed in these meteorites?

Rowan, L. R.↗
NASA NTRS1993

Recovery of interplanetary cosmic ray intensity following the great Forbush decrease of mid-1991

There was a succession of major solar flares in late-May to mid-June 1991. Their effects on cosmic ray intensity were observed by six spacecraft at various points in the heliosphere and by terrestrial neutron monitors. Study of these observations is summarized as followed: (1) An abrupt and extraordinarily large Forbush decrease in intensity occurred at the Earth on day of year (DOY) 164/1993 (13 June) and ones of similar magnitude (approximately equal 20 percent) occurred in an orderly sequence of timing thereafter over ranges of heliocentric ecliptic longitude of essentially 360 degrees; of heliographic latitude +32 degrees to -5 degrees; and of radial distance 1.0 to 53 AU. (2) The apparent radial speed of propagation of the presumably causative blast wave was 865 (+/- 75)km/s. (3) It appears likely that the distinctive solar flare of DOY 162/1991 (11 June) was the dominant cause of the blast wave. Two different representations of the subsequent recoveries of intensity yield substantially different numerical values of 'recovery time' but either set of values shows an increase by a factor of about three between 1.0 and 53 AU.

Van Allen, James A.↗
NASA NTRS1995

Compiler-assisted multiple instruction rollback recovery using a read buffer

Multiple instruction rollback (MIR) is a technique that has been implemented in mainframe computers to provide rapid recovery from transient processor failures. Hardware-based MIR designs eliminate rollback data hazards by providing data redundancy implemented in hardware. Compiler-based MIR designs have also been developed which remove rollback data hazards directly with data-flow transformations. This paper describes compiler-assisted techniques to achieve multiple instruction rollback recovery. We observe that some data hazards resulting from instruction rollback can be resolved efficiently by providing an operand read buffer while others are resolved more efficiently with compiler transformations. The compiler-assisted scheme presented consists of hardware that is less complex than shadow files, history files, history buffers, or delayed write buffers, while experimental evaluation indicates performance improvement over compiler-based schemes.

Alewine, Neal J.↗
NASA NTRS1996

A Fluorescence Recovery After Photobleaching (FRAP) Technique for the Measurement of Solute Transport Across Surfactant-Laden Interfaces

The technique of Fluorescence Recovery After Photobleaching (FRAP) has been applied to the measurement of interfacial transport in two-phase systems. FRAP exploits the loss of fluorescence exhibited by certain fluorophores when over-stimulated (photobleached), so that a two-phase system, originally at equilibrium, can be perturbed without disturbing the interface by strong light from an argon-ion laser and its recovery monitored by a microscope-mounted CCD camera as it relaxes to a new equilibrium. During this relaxation, the concentration profiles of the probe solute are measured on both sides of the interface as a function of time, yielding information about the transport characteristics of the system. To minimize the size of the meniscus between the two phases, a photolithography technique is used to selectively treat the glass walls of the cell in which the phases are contained. This allows concentration measurements to be made very close to the interface and increases the sensitivity of the FRAP technique.

Browne, Edward P.↗
NASA NTRS1996

Six Degree-of-Freedom Entry Dispersion Analysis for the METEOR Recovery Module

The present study performs a six degree-of-freedom entry dispersion analysis for the Multiple Experiment Transporter to Earth Orbit and Return (METEOR) mission. METEOR offered the capability of flying a recoverable science package in a microgravity environment. However, since the Recovery Module has no active control system, an accurate determination of the splashdown position is difficult because no opportunity exists to remove any errors. Hence, uncertainties in the initial conditions prior to deorbit burn initiation, during deorbit burn and exo-atmospheric coast phases, and during atmospheric flight impact the splashdown location. This investigation was undertaken to quantify the impact of the various exo-atmospheric and atmospheric uncertainties. Additionally, a Monte-Carlo analysis was performed to statistically assess the splashdown dispersion footprint caused by the multiple mission uncertainties. The Monte-Carlo analysis showed that a 3-sigma splashdown dispersion footprint with axes of 43.3 nm (long), -33.5 nm (short), and 10.0 nm (crossrange) can be constructed. A 58% probability exists that the Recovery Module will overshoot the nominal splashdown site.

Desai, Prasun N.↗
NASA NTRS1994

Survival and Recovery of Methanotrophic Bacteria Starved Under Oxic and Anoxic Conditions

The effects of carbon deprivation on survival of methanotrophic bacteria were compared in cultures incubated in the presence and absence of oxygen in the starvation medium. Survival and recovery of the examined methanotrophs were generally highest for cultures starved under anoxic conditions as indicated by poststarvation measurements of methane oxidation, tetrazolium salt reduction, plate counts, and protein synthesis. Methylosinus trichosporium OB3b survived up to 6 weeks of carbon deprivation under anoxic conditions while maintaining a physiological state that allowed relatively rapid (hours) methane oxidation after substrate addition. A small fraction of cells starved under oxic and anoxic conditions (4 and 10%, respectively) survived more than 10 weeks but required several days for recovery on plates and in liquid medium. A non-spore-forming methanotroph, strain WP 12, displayed 36 to 118% of its initial methane oxidation capacity after 5 days of carbon deprivation. Oxidation rates varied with growth history prior to the experiments as well as with starvation conditions. Strain WP 12 starved under anoxic conditions showed up to 90% higher methane oxidation activity and 46% higher protein production after starvation than did cultures starved under oxic conditions. Only minor changes in biomass and niorpholow were seen for methanotrophic bacteria starved tinder anoxic conditions. In contrast, starvation under oxic conditions resulted in morphology changes and an initial 28 to 35% loss of cell protein. These data suggest that methanotrophic bacteria can survin,e carbon deprivation under anoxic conditions by using maintenance energy derived Solelyr from an anaerobic endogenous metabolism. This capability could partly explain a significant potential for methane oxidation in environments not continuously, supporting aerobic methanotrophic growth.

Roslev, Peter↗
NASA NTRS1959

Wind-Tunnel Measurements of Effect of Dive-Recovery Flaps at Transonic Speeds on Models of a Seaplane and a Transport

The effects of wing-lower-surface dive-recovery flaps on the aero- dynamic characteristics of a transonic seaplane model and a transonic transport model having 40 deg swept wings have been investigated in the Langley 16-foot transonic tunnel. The seaplane model had a wing with an aspect ratio of 5.26, a taper ratio of 0.333, and NACA 63A series airfoil sections streamwise. The transport model had a wing with an aspect ratio of 8, a taper ratio of 0.3, and NACA 65A series airfoil sections perpendicular to the quarter-chord line. The effects of flap deflection, flap longitudinal location, and flap sweep were generally investigated for both horizontal-tail-on and horizontal-tail-off configurations. Model force and moment measurements were made for model angles of attack from -5 deg to 14 deg in the Mach number range from 0.70 to 1.075 at Reynolds numbers of 2.95 x 10(exp 6) to 4.35 x 10(exp 6). With proper longitudinal location, wing-lower-surface dive-recovery flaps produced lift and pitching-moment increments that increased with flap deflection. For the transport model a flap located aft on the wing proved to be more effective than one located more forward., both flaps having the same span and approximately the same deflection. For the seaplane model a high horizontal tail provided added effectiveness for the deflected-flap configuration.

Heath, Atwood R., Jr.↗
NASA NTRS1961

Recovery Temperature, Transition, and Heat Transfer Measurements at Mach 5

Schlieren, recovery temperature, and heat-transfer measurements were made on a hollow cylinder and a cone with axes alined parallel to the stream. Both the cone and cylinder were equipped with various bluntnesses, and the tests covered a Reynolds number range up to 20 x 10(exp 6) at a free-stream Mach number of 4.95 and wall to free-stream temperature ratios from 1.8 to 5.2 (adiabatic). A substantial transition delay due to bluntness was found for both the cylinder and the cone. For the present tests (Mach 4.95), transition was delayed by a factor of 3 on the cylinder and about 2 on the cone, these delays being somewhat larger than those observed in earlier tests at Mach 3.1. Heat-transfer tests on the cylinder showed only slight effects of wall temperature level on transition location; this is to be contrasted to the large transition delays observed on conical-type bodies at low surface temperatures at Mach 3.1. The schlieren and the peak-recovery-temperature methods of detecting transition were compared with the heat-transfer results. The comparison showed that the first two methods identified a transition point which occurred just beyond the end of the laminar run as seen in the heat-transfer data.

Brinich, Paul F.↗