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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 55 records · Page 3
All sourcesNASA NTRSDOE OSTI
NASA NTRS2017

Metallic Junction Thermoelectric Device Simulations

Thermoelectric junctions made of semiconductors have existed in radioisotope thermoelectric generators (RTG) for deep space missions, but are currently being adapted for terrestrial energy harvesting. Unfortunately, these devices are inefficient, operating at only 7% efficiency. This low efficiency has driven efforts to make high-figure-of-merit thermoelectric devices, which require a high electrical conductivity but a low thermal conductivity, a combination that is difficult to achieve. Lowered thermal conductivity has increased efficiency, but at the cost of power output. An alternative setup is to use metallic junctions rather than semiconductors as thermoelectric devices. Metals have orders of magnitude more electrons and electronic conductivities higher than semiconductors, but thermal conductivity is higher as well. To evaluate the viability of metallic junction thermoelectrics, a two dimensional heat transfer MATLAB simulation was constructed to calculate efficiency and power output. High Seebeck coefficient alloys, Chromel (90%Ni-10%Cr) and Constantan (55%Cu-45%Ni), produced efficiencies of around 20-30%. Parameters such as the number of layers of junctions, lateral junction density, and junction sizes for both series- and parallel-connected junctions were explored.

Duzik, Adam J.↗
NASA NTRS1996

LTI Representations of Adaptive Systems with Tap Delay-Line Regressors under Sinusoidal Excitation

It is shown that and adaptive system whose regressor is formed by tap delay-line (TDL) filtering of a multitone sinusoidal signal is representable as a parallel connection of a linear time-invariant (LTI) block and a linear time-varying (LTV) block. Furthermore, a norm-bound (induced 2-norm) is computed explicity on the LTV block and is shown to decrease as N -1 where N is the number of taps.

adaptive↗
NASA NTRS2013

Stacked Transformer for Driver Gain and Receive Signal Splitting

In a high-speed signal transmission system that uses transformer coupling, there is a need to provide increased transmitted signal strength without adding active components. This invention uses additional transformers to achieve the needed gain. The prior art uses stronger drivers (which require an IC redesign and a higher power supply voltage), or the addition of another active component (which can decrease reliability, increase power consumption, reduce the beneficial effect of serializer/deserializer preemphasis or deemphasis, and/or interfere with fault containment mechanisms), or uses a different transformer winding ratio (which requires redesign of the transformer and may not be feasible with high-speed signals that require a 1:1 winding ratio). This invention achieves the required gain by connecting the secondaries of multiple transformers in series. The primaries of these transformers are currently either connected in parallel or are connected to multiple drivers. There is also a need to split a receive signal to multiple destinations with minimal signal loss. Additional transformers can achieve the split. The prior art uses impedance-matching series resistors that cause a loss of signal. Instead of causing a loss, most instantiations of this invention would actually provide gain. Multiple transformers are used instead of multiple windings on a single transformer because multiple windings on the same transformer would require a redesign of the transformer, and may not be feasible with high-speed transformers that usually require a bifilar winding with a 1:1 ratio. This invention creates the split by connecting the primaries of multiple transformers in series. The secondary of each transformer is connected to one of the intended destinations without the use of impedance-matching series resistors.

Driscoll, Kevin R.↗
NASA NTRS2005

Mechanically Biased, Hinged Pairs of Piezoelectric Benders

The upper part of the figure depicts an actuator that comprises two mechanically biased piezoelectric benders hinged together at their ends and equipped with tabs at their mid-length points for attachment to the relatively moving objects that are to be actuated. In the example of the figure, the attachment tabs are labeled to indicate that the actuator is used to drive a pump piston relative to a base plate. Actuators of this type could be used to drive low-power, small-volume pumps in consumer, medical, and aerospace applications, and to generate and measure linear displacements in such robotic applications as teleoperation and tactile feedback. Each bender is a bimorph a unitary plate that comprises an upper and a lower piezoelectric layer plus electrode layers. Benders may also be made of several layers arranged to produce the same effect at the lower operating voltages. As stated above, each bender is mechanically biased; it is fabricated to have a small permanent curvature (the bias curvature) in the absence of applied voltage. As on other bimorphs, the electrical connections on each bender are arranged so that an applied voltage of suitable polarity causes the upper layer to expand and the lower layer to contract. In this case, the net effect of applying the voltage is that the plate becomes more concave as viewed from below. Conversely, an applied voltage of the opposite polarity causes the plate to become less concave as viewed from below. The benders in a hinged pair are oriented with their bias curvatures concave inward, so that there is a bias distance between the attachment tabs. The two benders are connected electrically in parallel, with their connection polarities chosen so that an applied voltage of one polarity causes both benders to become more convex inward (more bent), while an applied voltage of the opposite polarity causes both benders to become less convex inward (less bent). An increase or decrease in bend is accompanied by an increase or decrease in distance between the attachment tabs; this increase or decrease is the linear displacement desired for actuation. Because the displacement can be either positive or negative relative to the bias distance, depending on the polarity of the applied voltage, the overall stroke achievable for a given magnitude of applied voltage is double the stroke achievable in the absence of mechanical bias. Each hinged pair can be regarded as a unit cell that can serve as a building block for a larger actuator: Multiple unit cells can be stacked (mechanically connected in series), as shown in the lower part of the figure, and electrically connected in parallel to multiply the overall stroke achievable at a given applied voltage.

Sager, Frank E.↗
NASA NTRS1987

Temperature responsive transmitter

A temperature responsive transmitter is provided in which frequency varies linearly with temperature. The transmitter includes two identically biased transistors connected in parallel. A capacitor, which reflects into the common bases to generate negative resistance effectively in parallel with the capacitor, is connected to the common emitters. A crystal is effectively in parallel with the capacitor and the negative resistance. Oscillations occur if the magnitude of the absolute value of the negative resistance is less than the positive resistive impedance of the capacitor and the inductance of the crystal. The crystal has a large linear temperature coefficient and a resonant frequency which is substantially less than the gain-bandwidth product of the transistors to ensure that the crystal primarily determines the frequency of oscillation. A high-Q tank circuit having an inductor and a capacitor is connected to the common collectors to increase the collector current flow which in turn enhances the radiation of the oscillator frequency by the inductor.

Kleinberg, Leonard L.↗
NASA NTRS1985

Sealed bipolar multi-cell battery

A low maintenance battery comprises a sealed casing (102) having a cavity (204) receiving a stack (108) of monopolar and bipolar plates (110, 112) interspersed with mats (122) of fiberglass felt immobilizing electrolyte and forming a gas path for diffusion of oxygen to the negative electrode (112). The casing contains a single, resealable vent (202). During charging, oxygen generated at the positive plate (110) diffuses through the mat (122) and decomposes at the negative plate (112). The negative plate (112) has a larger capacity than the positive plate (110) to prevent evolution of hydrogen. Voltage potential is increased or decreased by placing one or more bipolar plates (120) in series relation between alternating positive and negative monopolar plates that are connected in parallel to respective positive and negative battery terminals (104, 106). The monoplates (110, 112) are connected in parallel to respective positive and negative battery terminals (104, 106) by way of bus plates (114, 116, 130, 132). The resealable vent permits operation by way of the oxygen cycle which prevents loss of electrolyte. The vent prevents invasion of oxygen from the ambient to discharge negative plates.

Rowlette, John J.↗
NASA NTRS1976

Analysis of a solar collector field water flow network

A number of methods are presented for minimizing the water flow variation in the solar collector field for the Solar Building Test Facility at the Langley Research Center. The solar collector field investigated consisted of collector panels connected in parallel between inlet and exit collector manifolds to form 12 rows. The rows were in turn connected in parallel between the main inlet and exit field manifolds to complete the field. The various solutions considered included various size manifolds, manifold area change, different locations for the inlets and exits to the manifolds, and orifices or flow control valves. Calculations showed that flow variations of less than 5 percent were obtainable both inside a row between solar collector panels and between various rows.

Rohde, J. E.↗
NASA NTRS1989

Frequency domain model for analysis of paralleled, series-output-connected Mapham inverters

The Mapham resonant inverter is characterized as a two-port network driven by a selected periodic voltage. The two-port model is then used to model a pair of Mapham inverters connected in series and employing phasor voltage regulation. It is shown that the model is useful for predicting power output in paralleled inverter units, and for predicting harmonic current output of inverter pairs, using standard power flow techniques. Some examples are compared to data obtained from testing hardware inverters.

Brush, Andrew S.↗
NASA NTRS1989

Frequency domain model for analysis of paralleled, series-output-connected Mapham inverters

The Mapham resonant inverter is characterized as a two-port network driven by a selected periodic voltage. The two-port model is then used to model a pair of Mapham inverters connected in series and employing phasor voltage regulation. It is shown that the model is useful for predicting power output in paralleled inverter units, and for predicting harmonic current output of inverter pairs, using standard power flow techniques. Some sample results are compared to data obtained from testing hardware inverters.

Brush, Andrew S.↗
NASA NTRS1988

Parallel matrix multiplication on the Connection Machine

Matrix multiplication is a computation and communication intensive problem. Six parallel algorithms for matrix multiplication on the Connection Machine are presented and compared with respect to their performance and processor usage. For n by n matrices, the algorithms have theoretical running times of O(n to the 2nd power log n), O(n log n), O(n), and O(log n), and require n, n to the 2nd power, n to the 2nd power, and n to the 3rd power processors, respectively. With careful attention to communication patterns, the theoretically predicted runtimes can indeed be achieved in practice. The parallel algorithms illustrate the tradeoffs between performance, communication cost, and processor usage.

Tichy, Walter F.↗
NASA NTRS1992

Parallel algorithms for geometric connected component labeling on a hypercube multiprocessor

Different algorithms for the geometric connected component labeling (GCCL) problem are defined each of which involves d stages of message passing, for a d-dimensional hypercube. The major idea is that in each stage a hypercube multiprocessor increases its knowledge of domain. The algorithms under consideration include the QUAD algorithm for small number of processors and the Overlap Quad algorithm for large number of processors, subject to the locality of the connected sets. These algorithms differ in their run time, memory requirements, and message complexity. They were implemented on an Intel iPSC2/D4/MX hypercube.

Belkhale, K. P.↗
NASA NTRS2011

Cable Tester Box

Cables are very important electrical devices that carry power and signals across multiple instruments. Any fault in a cable can easily result in a catastrophic outcome. Therefore, verifying that all cables are built to spec is a very important part of Electrical Integration Procedures. Currently, there are two methods used in lab for verifying cable connectivity. (1) Using a Break-Out Box and an ohmmeter this method is time-consuming but effective for custom cables and (2) Commercial Automated Cable Tester Boxes this method is fast, but to test custom cables often requires pre-programmed configuration files, and cables used on spacecraft are often uniquely designed for specific purposes. The idea is to develop a semi-automatic continuity tester that reduces human effort in cable testing, speeds up the electrical integration process, and ensures system safety. The JPL-Cable Tester Box is developed to check every single possible electrical connection in a cable in parallel. This system indicates connectivity through LED (light emitting diode) circuits. Users can choose to test any pin/shell (test node) with a single push of a button, and any other nodes that are shorted to the test node, even if they are in the same connector, will light up with the test node. The JPL-Cable Tester Boxes offers the following advantages: 1. Easy to use: The architecture is simple enough that it only takes 5 minutes for anyone to learn how operate the Cable Tester Box. No pre-programming and calibration are required, since this box only checks continuity. 2. Fast: The cable tester box checks all the possible electrical connections in parallel at a push of a button. If a cable normally takes half an hour to test, using the Cable Tester Box will improve the speed to as little as 60 seconds to complete. 3. Versatile: Multiple cable tester boxes can be used together. As long as all the boxes share the same electrical potential, any number of connectors can be tested together.

Lee, Jason H.↗
NASA NTRS1989

Microwave field effect transistor

Electrodes of a high power, microwave field effect transistor are substantially matched to external input and output networks. The field effect transistor includes a metal ground plane layer, a dielectric layer on the ground plane layer, a gallium arsenide active region on the dielectric layer, and substantially coplanar spaced source, gate, and drain electrodes having active segments covering the active region. The active segment of the gate electrode is located between edges of the active segments of the source and drain electrodes. The gate and drain electrodes include inactive pads remote from the active segments. The pads are connected directly to the input and output networks. The source electrode is connected to the ground plane layer. The space between the electrodes and the geometry of the electrodes extablish parasitic shunt capacitances and series inductances that provide substantial matches between the input network and the gate electrode and between the output network and the drain electrode. Many of the devices are connected in parallel and share a common active region, so that each pair of adjacent devices shares the same source electrodes and each pair of adjacent devices shares the same drain electrodes. The gate electrodes for the parallel devices are formed by a continuous stripe that extends between adjacent devices and is connected at different points to the common gate pad.

Huang, Ho-Chung↗
NASA NTRS1998

Recent Progress on the Parallel Implementation of Moving-Body Overset Grid Schemes

Viscous calculations about geometrically complex bodies in which there is relative motion between component parts is one of the most computationally demanding problems facing CFD researchers today. This presentation documents results from the first two years of a CHSSI-funded effort within the U.S. Army AFDD to develop scalable dynamic overset grid methods for unsteady viscous calculations with moving-body problems. The first pan of the presentation will focus on results from OVERFLOW-D1, a parallelized moving-body overset grid scheme that employs traditional Chimera methodology. The two processes that dominate the cost of such problems are the flow solution on each component and the intergrid connectivity solution. Parallel implementations of the OVERFLOW flow solver and DCF3D connectivity software are coupled with a proposed two-part static-dynamic load balancing scheme and tested on the IBM SP and Cray T3E multi-processors. The second part of the presentation will cover some recent results from OVERFLOW-D2, a new flow solver that employs Cartesian grids with various levels of refinement, facilitating solution adaption. A study of the parallel performance of the scheme on large distributed- memory multiprocessor computer architectures will be reported.

Wissink, Andrew↗
NASA NTRS1994

Active antenna

An antenna, which may be a search coil, is connected to an operational amplifier circuit which provides negative impedances, each of which is in the order of magnitude of the positive impedances which characterize the antenna. The antenna is connected to the inverting input of the operational amplifier; a resistor is connected between the inverting input and the output of the operational amplifier; a capacitor-resistor network, in parallel, is connected between the output and the noninverting input of the operational amplifier; and a resistor is connected from the noninverting input and the circuit common. While this circuit provides a negative resistance and a negative inductance, in series, which appear, looking into the noninverting input of the operational amplifier, in parallel with the antenna, these negative impedances appear in a series loop with the antenna positive impedances, so as to algebraically add. This circuit is tuned by varying the various circuit components so that the negative impedances are very close, but somewhat less, in magnitude, to the antenna impedances. The result is to increase the sensitivity of the antenna by lowering its effective impedance. This, in turn, increases the effective area of the antenna, which may be broadband.

Sutton, John F.↗
NASA NTRS1977

Phase substitution of spare converter for a failed one of parallel phase staggered converters

Failure detection and substitution of a spare module is provided in a system having a plurality of phase staggered modules connected in parallel to deliver regulated voltage from an unregulated source. Phase control signals applied to the active converter modules are applied to the spare module through NOR gates associated with and disabled by the power output of respective modules such that failure of any one enables its phase control signal to be applied to the spare module, thus controlling the spare module to operate in the phase position of the failed module. A NAND gate detects when any one active module fails and enables a gate in the spare module, thus activating the spare module.

Mclyman, W. T.↗