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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 1,243 records · Page 69

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NASA NTRS1991

Testing interconnected VLSI circuits in the Big Viterbi Decoder

The Big Viterbi Decoder (BVD) is a powerful error-correcting hardware device for the Deep Space Network (DSN), in support of the Galileo and Comet Rendezvous Asteroid Flyby (CRAF)/Cassini Missions. Recently, a prototype was completed and run successfully at 400,000 or more decoded bits per second. This prototype is a complex digital system whose core arithmetic unit consists of 256 identical very large scale integration (VLSI) gate-array chips, 16 on each of 16 identical boards which are connected through a 28-layer, printed-circuit backplane using 4416 wires. Special techniques were developed for debugging, testing, and locating faults inside individual chips, on boards, and within the entire decoder. The methods are based upon hierarchical structure in the decoder, and require that chips or boards be wired themselves as Viterbi decoders. The basic procedure consists of sending a small set of known, very noisy channel symbols through a decoder, and matching observables against values computed by a software simulation. Also, tests were devised for finding open and short-circuited wires which connect VLSI chips on the boards and through the backplane.

Onyszchuk, I. M.↗

NASA NTRS1991

Numerical, experimental, and theoretical study of convective instability of flows over pointed bodies at incidence

A study is conducted to investigate whether the behavior of the asymmetric mean flow observed on pointed bodies of revolution at incidence remains consistent with the presence of a convective instability of an original symmetric flow, even in the incidence range where virtually bistable behavior of the asymmetric flow is observed. By means of a retractable wire located near the tip, it is determined experimentally that for all angles of attack tested (30 to 60 degs), changing the size or location of the controlled disturbance results in a finite change in the asymmetric flow field, even to the extent of reversing the sign of the side force or becoming almost symmetric. The process is reversible; returning the wire to an original position likewise restores the corresponding flow field and mean side force. The effect of wire location (roll angle and distance from the tip) as well as angle of attack and flow conditions are evaluated experimentally by means of flow visualization and side-force measurements for a generic ogive-cylinder model in a low-speed wind tunnel. Evaluation of the results in the light of computational observations and theoretical considerations yields an affirmative answer to the question posed.

Degani, David↗

NASA NTRS1991

Flow visualization and flow field measurements of a 1/12 scale tilt rotor aircraft in hover

The results are given of flow visualization studies and inflow velocity field measurements performed on a 1/12 scale model of the XV-15 tilt rotor aircraft in the hover mode. The complex recirculating flow due to the rotor-wake-body interactions characteristic of tilt rotors was studied visually using neutrally buoyant soap bubbles and quantitatively using hot wire anemometry. Still and video photography were used to record the flow patterns. Analysis of the photos and video provided information on the physical dimensions of the recirculating fountain flow and on details of the flow including the relative unsteadiness and turbulence characteristics of the flow. Recirculating flows were also observed along the length of the fuselage. Hot wire anemometry results indicate that the wing under the rotor acts to obstruct the inflow causing a deficit in the inflow velocities over the inboard region of the model. Hot wire anemometry also shows that the turbulence intensities in the inflow are much higher in the recirculating fountain reingestion zone.

Coffen, Charles D.↗

NASA NTRS1992

Method of producing a plug-type heat flux gauge

A method of making a plug-type heat flux gauge in a material specimen in which a thermoplug is integrally formed in the specimen is disclosed. The thermoplug and concentric annulus are formed in the material specimen by electrical discharge machining and trepanning procedures. The thermoplug is surrounded by a concentric annulus through which thermocouple wires are routed. The end of each thermocouple wire is welded to the thermoplug, with each thermocouple wire welded at a different location along the length of the thermoplug.

Liebert, Curt H.↗

NASA NTRS1991

Direct sequence spread spectrum CDMA in shared spectrum applications

Personal Communication Network (PCN) is an entirely wireless communication system with the capability of assessing the wired telephone system to reach anyone processing only a wired telephone. It is expected to compete with the existing mobile cellular system which connects directly to the wired telephone system. While many PCN systems employ TDMA technology, the PCN system described here uses Broadband CDMA (BCDMA(sup SM)) which is capable of sharing the spectrum with other users and which is extremely resistant to fading caused by multipath.

Schilling, Donald L.↗

NASA NTRS1992

A cable detection lidar system for helicopters

Helicopters in low-level flight are endangered by power lines or telephone wires, especially when flying at night and under poor visibility conditions. In order to prevent 'wire strike', Thomson has developed a lidar system consisting of a pulsed diode laser emitting in the near infrared region (lambda = 0.9 microns). The HOWARD (Helicopter Obstacle Warning and Detection) System utilizes a high repetition rate diode laser (PRE = 20 KHz) along with counter-rotating prisms for laser beam deflection with a total field of view of 30 degrees. This system was successfully field tested in 1991. HOWARD can detect one inch wires at ranges up to 200 meters. We are presently in the process of developing a flyable compact lidar system capable of detection ranges in the order of 400 meters.

Grossmann, Benoist↗

NASA NTRS1992

Device for removing foreign objects from anatomic organs

A device is disclosed for removing foreign objects from anatomic organs such as the ear canal or throat. It has a housing shaped like a flashlight, an electrical power source such as a battery or AC power from a wall socket, and a tip extending from the housing. The tip has at least one wire loop made from a shape-memory-effect alloy, such as Nitinol, switchably connected to the electrical power source such that when electric current flows through the wire loop the wire loop heats up and returns to a previously programmed shape such as a curet or tweezers so as to facilitate removal of the foreign object.

Angulo, Earl D.↗

NASA NTRS1992

Page turning system

A device for holding reading materials for use by readers without arm mobility is presented. The device is adapted to hold the reading materials in position for reading with the pages displayed to enable turning by use of a rubber tipped stick that is held in the mouth and has a pair of rectangular frames. The frames are for holding and positioning the reading materials opened in reading posture with the pages displayed at a substantially unobstructed sighting position for reading. The pair of rectangular frames are connected to one another by a hinge so the angle between the frames may be varied thereby varying the inclination of the reading material. A pair of bent spring mounted wires for holding opposing pages of the reading material open for reading without substantial visual interference of the pages is mounted to the base. The wires are also adjustable to the thickness of the reading material and have a variable friction adjustment. This enables the force of the wires against the pages to be varied and permits the reader to manipulate the pages with the stick.

Kerley, James J.↗

NASA NTRS1991

On the reflectivity of complex mesh surfaces

Poorer than expected surface reflectivity was observed in an early Tracking and Data Relay Satellite System antenna utilizing a tricot mesh weave. This poor reflectivity was determined to be caused by inadequate electrical contact at wire crossover points. A proper mathematical and numerical approach to assess the impact of wire junctions on reflectivity performance is developed. A mathematical method is presented for computing the surface reflectivity of complex mesh configurations like those on unfurlable-type spacecraft antennas. The method is based on the Floquet mode expansion to establish an integral equation for mesh wire currents. The equation is solved using the method of moments with triangular basis functions. It is observed that it is necessary to give special attention to the junction treatment among different branches of the mesh configurations. A vector junction current approach that resulted in satisfactory solutions for the current is described. The results of numerical simulations are compared against measured data and excellent agreement is observed.

Imbriale, William A.↗

NASA NTRS1991

Fundamental and practical limitations of FUV/EUV photon-counting image detectors

In EUV and FUV space-astronomy applications, the best contemporary detector designs are based on the use of microchannel plates due to their ability to deliver photon-counting performance with high efficiency. The major unresolved issue is the choice of position-readout system for the individual photoevents. Electrical event-readout systems are divided into two classes: the discrete wire anodes that perform coordinate digitization by wire-group selection, and the continuous centroid-position encoders for which coordinates are digitized in the associated electronics. The centroid-position encoder techniques are discussed in terms of how they overcome the four chief limitations of the discrete-wire readouts - their limited format size, their flat focal surface, their fundamental hex-channel vs squared-pixel moire pattern, and their image undersampling. With these limitations overcome, microchannel based image systems can deliver the performance demanded by the forthcoming generation of applications in space astronomy.

Lampton, M.↗

NASA NTRS1992

An assessment of particle velocimetry potential in hypersonic flow

Future progress in the computation of hypersonic flow fields is restricted by the need for a reliable turbulence modeling data base which could be used for the development of empirical models for use in numerical codes. Currently, there are few compressible flow measurements which could be used for this purpose. Procedures for hot wire measurements in hypersonic flows are presently outlined, and assessments are made of the potential for hot wire and laser velocimeter measurements of turbulent fluctuations in hypersonic flow fields. The results of recent experiments conducted in two hypersonic wind tunnels will be presented and comparisons made with previous hot wire turbulence measurements.

Owen, F. K.↗

NASA NTRS1993

Apparatus Splits Glass Tubes Longitudinally

Tubes split into half cylinders by hot-wire/thermal-shock method. Tube to be cut placed on notched jig in apparatus. Nichrome wire stretched between arms of pivoted carriage and oriented parallel to notch. Wire heated by electrical current while resting on tube. After heating for about 1 minute for each millimeter of thickness of glass, tube quenched in water and split by resulting thermal shock. Apparatus used to split tubes in sizes ranging from 3/8 in. in diameter by 1 in. long to 1 1/2 in. in diameter by 4 in. long.

Shaw, Ernest↗

NASA NTRS1993

Reducing Magnetic Fields Around Power Cables

Four power conductors arranged symmetrically about fifth grounded conductor. Four current-carrying wires arranged symmetrically around central grounded wire that nominally carries no current. In comparison with other cable configurations, this one results in smaller magnetic fields around cable. Technique for use when size of wires in cable makes twisting impractical.

Sargent, Noel B.↗

NASA NTRS1991

Flow visualization and flow field measurements of a 1/12 scale tilt rotor aircraft in hover

Coffen, Charles D.↗

NASA NTRS1993

Design of a constant tension thermocouple rake suitable for flame studies

An improved, spring-loaded thermocouple rake, suitable for studying flame structure, has been designed. This design keeps the thermocouple under tension thereby ensuring that the thermocouple does not droop due to the thermal expansion of the sensing wire when inserted in the flame. The present design allows the usage of thermocouple wire as small as 0.0508 mm and relative ease in changing thermocouple wire.

Ahuja, Sandeep↗

NASA NTRS1922

Aerial navigation : on the problem of guiding aircraft in a fog or by night when there is no visibility

The use of magnetic fields and wire to navigate aircraft in conditions of poor visibility is presented. This field may be considered to be derived from a double lemniscate, considered in the particular case where the origin is a double point formed from the magnetic field of the slack wire, from the field produced by the return currents and from the field due to the currents induced in the conducting mass. These fields are dephased in two ways, one in the direction of the wire, the other in a direction perpendicular to it.

Loth, William↗

NASA NTRS1944

Fatigue Strength and Related Characteristics of Aircraft Joints I : Comparison of Spot-Weld and Rivet Patterns in 24s-t Alclad and 75s-t Alclad

Report contains detailed results of a number of fatigue tests on spot-welded joints in aluminum alloys. The tests described include: (1) fatigue tests on spot-welded lap joints in sheets of unequal thickness of alclad 24s-t. These tests indicate that the fatigue strength of a spot-welded joint in sheets of two different gages is slightly higher than that of a similar joint in two sheets of the thinner gage but definitely lower than that of a similar joint in two sheets of the thicker gage. (2) Fatigue tests on spot-welded alclad 75s-t spot-welded lap-joint specimens of alclad 75s-t were not any stronger in fatigue than similar specimens of alclad 24s-t. (3) Fatigue tests on lap-joint specimens spot -welded after various surface preparations--these included ac welding wire-brushed surfaces, dc welding wire-brushed surfaces, and dc welding chemically cleaned surfaces. While the ac welds were strongest statically, the dc welds on wire-brushed surfaces were strongest in fatigue. Specimens prepared in this way were very nearly as strong as the best riveted specimens tested for comparison. (4) Fatigue tests on specimens spot-welded with varying voltage so as to include a wide range of static spot-weld strengths. The fatigue strengths were in the same order as the static strengths but showed less range. (author)

Russell, H W↗

NASA NTRS1920

The Airplane Tensiometer

Certain parts of an airplane are subjected not only to the stresses imposed by the aerodynamic or flying load, but also to the initial stresses, caused by the tension in the stay and drift wires. Report describes a tensiometer that measures such stresses which is simple in construction, accurate, and easily and quickly operated even by inexperienced persons. Two sizes of the instrument are available. One is suitable for wires up to one-fourth inch in diameter and the other for wires from one-fourth to three-eights inch in diameter.

Larson, L J↗