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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 397 records · Page 22
All sourcesNASA NTRSDOE OSTI
NASA NTRS1994

Planar rotational magnetic micromotors with integrated shaft encoder and magnetic rotor levitation

Deep x-ray lithography and electroplating may be combined to form a fabrication tool for micromechanical devices with large structural heights, to 500 micron, and extreme edge acuities, less than 0.1 micron-run-out per 100 micron of height. This process concept which originated in Germany as LIGA may be further extended by adding surface micromachining. This extension permits the fabrication of precision metal and plastic parts which may be assembled into three-dimensional micromechanical components and systems. The processing tool may be used to fabricate devices from ferromagnetic material such as nickel and nickel-iron alloys. These materials when properly heat treated exhibit acceptable magnetic behavior for current to flux conversion and marginal behavior for permanent magnet applications. The tool and materials have been tested via planar, magnetic, rotational micromotor fabrication. Three phase reluctance machines of the 6:4 configuration with 280 micron diameter rotors have been tested and analyzed. Stable rotational speeds to 34,000 rpm with output torques above 10 x 10(exp -9) N-m have been obtained. The behavior is monitored with integrated shaft encoders which are photodiodes which measure the rotor response. Magnetic levitation of the rotor via reluctance forces has been achieved and has reduced frictional torque losses to less than 1 percent of the available torque. The results indicate that high speed limits of these actuators are related to torque ripple. Hysteresis motors with magnetic bearings are under consideration and will produce high speed rotational machines with excellent sensor application potential.

Guckel, Henry↗
NASA NTRS2002

Heat Shield Cavity Parametric Experimental Aeroheating for a Proposed Mars Smart Lander Aeroshell

The proposed Mars Smart Lander is to be attached through its aeroshell to the main spacecraft bus, thereby producing cavities in the heat shield. To study the effects these cavities will have on the heating levels experienced by the heat shield, an experimental aeroheating investigation was performed at the NASA Langley Research Center in the 20-Inch Mach 6 Air Tunnel. The effects of Reynolds number, angle-of-attack, and cavity size and location on aero-heating levels and distributions were determined and are presented. To aid the discussion on the effects of the cavities, laminar, thin-layer Navier-Stokes flow field solutions were post-processed to calculate relevant boundary layer properties such as boundary layer height and momentum thickness, edge Mach number, and streamwise pressure gradient. It was found that the effect of the cavities varies with angle-of-attack, freestream Reynolds number, and cavity size and location. The presence of a cavity raised the downstream heating rates by as much as 325% as a result of boundary layer transition.

Liechty, Derek S.↗
NASA NTRS2011

Nanoparticle Filtration in a RTM Processed Epoxy/Carbon Fiber Composite

Several epoxy matrix composite panels were fabricated by resin transfer molding (RTM) E862/W resin onto a triaxially braided carbon fiber pre-form. Nanoparticles including carbon nanofiber, synthetic clay, and functionalized graphite were dispersed in the E862 matrix, and the extent of particle filtration during processing was characterized. Nanoparticle dispersion in the resin flashing on both the inlet and outlet edges of the panel was compared by TEM. Variation in physical properties such as Tg and moisture absorption throughout the panel were also characterized. All nanoparticle filled panels showed a decrease in Tg along the resin flow path across the panel, indicating nanoparticle filtration, however there was little change in moisture absorption. This works illustrates the need to obtain good nano-particle dispersion in the matrix resin to prevent particle agglomeration and hence particle filtration in the resultant polymer matrix composites (PMC).

Miller, Sandi G.↗
NASA NTRS2013

Direct Numerical Simulation of Transition in a Swept-Wing Boundary Layer

Direct numerical simulation (DNS) is performed to examine laminar to turbulent transition due to high-frequency secondary instability of stationary crossflow vortices in a subsonic swept-wing boundary layer for a realistic natural-laminar-flow airfoil configuration. The secondary instability is introduced via inflow forcing derived from a two-dimensional, partial-differential-equation based eigenvalue computation; and the mode selected for forcing corresponds to the most amplified secondary instability mode which, in this case, derives a majority of its growth from energy production mechanisms associated with the wall-normal shear of the stationary basic state. Both the growth of the secondary instability wave and the resulting onset of laminar-turbulent transition are captured within the DNS computations. The growth of the secondary instability wave in the DNS solution compares well with linear secondary instability theory when the amplitude is small; the linear growth is followed by a region of reduced growth resulting from nonlinear effects before an explosive onset of laminar breakdown to turbulence. The peak fluctuations are concentrated near the boundary layer edge during the initial stage of transition, but rapidly propagates towards the surface during the process of laminar breakdown. Both time-averaged statistics and flow visualization based on the DNS reveal a sawtooth transition pattern that is analogous to previously documented surface flow visualizations of transition due to stationary crossflow instability. The memory of the stationary crossflow vortex is found to persist through the transition zone and well beyond the location of the maximum skin friction.

Duan, Lian↗
NASA NTRS2003

Fabrication And Evaluation Of Sic/Sic Tubes With Various Fiber Architectures

SiC/SiC composites are excellent material candidates for high temperature applications where the performance requirements are high strength, high creep-rupture resistance, high environmental durability, and high thermal conductivity. In the past, the NASA UEET program has demonstrated fabrication of high-performance SiC/SiC flat panels reinforced by Sylramic-iBN SiC fibers. Currently NASA UEET is scaling up this SiC/SiC system by fabrication of more complex shaped components using the same fiber type. This paper reports the effects of various fiber architectures on the processing, mechanical, and durability behavior of small-diameter 0.5" ID SiC/SiC tubes, which are potential sub-elements for leading edges and cooling channels in turbine vanes and blades. Nine different fiber architectures were utilized for construction of seamless tube preforms, from simple 2D jelly-rolling to complex braiding, pin-weaving, filament-winding and 3D orthogonal weaving with approximately 5% fibers in the thru-thickness direction. Using the BN interphase and Sic matrix processing steps established for the flat panels, SiC/SiC tubes were fabricated with wall thicknesses of approximately 60 mils and total fiber fractions of approximately 35%. The "D" split ring tests for hoop tensile properties, micro-structural examinations for relationship between fiber architecture formation and matrix infiltration, and the low-pressure burner rig tests for the high temperature durability under thru-thickness thermal gradient were conducted. The better matrix infiltration and higher hoop strength were achieved using the tri-axial braided and the three-float pin woven SiC/SiC tubes. In general, it needs not only higher hoop direction fibers but also axial direction fibers for the higher hoop strength and the better infiltration, respectively. These results are analyzed to offer general guidelines for selecting fiber pre-form architectures and SiC/SiC processes that maximize tube hoop strength, thru-thickness thermal conductivity, and burner-rig durability under a high thermal gradient.

Yun, H. M.↗
NASA NTRS2004

The Explorer of Diffuse Galactic Emission (EDGE): Determination of Large-Scale Structure Evolution from Measurement of the Anisotropy of the Cosmic Infrared Background

The formation of the first objects, stars and galaxies and their subsequent evolution remain a cosmological unknown. Few observational probes of these processes exist. The Cosmic Infrared Background (CIB) originates from this era, and can provide information to test models of both galaxy evolution and the growth of primordial structure. The Explorer of Diffuse Galactic Emission (EDGE) is a proposed balloon-borne mission designed to measure the spatial fluctuations in the CIB from 200 micrometers to 1 millimeter on 6' to 3 degree scales with 2 microKelvin sensitivity/resolution element. Such measurements would provide a sensitive probe of the large-scale variation in protogalaxy density at redshifts approximately 0.5-3. In this paper, we present the scientific justification for the mission and show a concept for the instrument and observations.

Silverberg, R. F.↗
NASA NTRS1990

A 4-node assumed-stress hybrid shell element with rotational degrees of freedom

An assumed-stress hybrid/mixed 4-node quadrilateral shell element is introduced that alleviates most of the deficiencies associated with such elements. The formulation of the element is based on the assumed-stress hybrid/mixed method using the Hellinger-Reissner variational principle. The membrane part of the element has 12 degrees of freedom including rotational or drilling degrees of freedom at the nodes. The bending part of the element also has 12 degrees of freedom. The bending part of the element uses the Reissner-Mindlin plate theory which takes into account the transverse shear contributions. The element formulation is derived from an 8-node isoparametric element. This process is accomplished by assuming quadratic variations for both in-plane and out-of-plane displacement fields and linear variations for both in-plane and out-of-plane rotation fields along the edges of the element. In addition, the degrees of freedom at midside nodes are approximated in terms of the degrees of freedom at corner nodes. During this process the rotational degrees of freedom at the corner nodes enter into the formulation of the element. The stress field are expressed in the element natural-coordinate system such that the element remains invariant with respect to node numbering.

Aminpour, Mohammad A.↗
NASA NTRS1990

Lunar occultations for gamma-ray source measurements

The unambiguous association of discrete gamma-ray sources with objects radiating at other wavelengths, the separation of discrete sources from the extended emission within the Galaxy, the mapping of gamma-ray emission from nearby galaxies and the measurement of structure within a discrete source cannot presently be accomplished at gamma-ray energies. In the past, the detection processes used in high-energy gamma-ray astronomy have not allowed for good angular resolution. This problem can be overcome by placing gamma-ray detectors on the moon and using the horizon as an occulting edge to achieve arcsec resolution. For purposes of discussion, this concept is examined for gamma rays above 100 MeV for which pair production dominates the detection process and locally-generated nuclear gamma rays do not contribute to the background.

Koch, David G.↗
NASA NTRS1993

The systems engineering overview and process (from the Systems Engineering Management Guide, 1990)

The past several decades have seen the rise of large, highly interactive systems that are on the forward edge of technology. As a result of this growth and the increased usage of digital systems (computers and software), the concept of systems engineering has gained increasing attention. Some of this attention is no doubt due to large program failures which possibly could have been avoided, or at least mitigated, through the use of systems engineering principles. The complexity of modern day weapon systems requires conscious application of systems engineering concepts to ensure producible, operable and supportable systems that satisfy mission requirements. Although many authors have traced the roots of systems engineering to earlier dates, the initial formalization of the systems engineering process for military development began to surface in the mid-1950s on the ballistic missile programs. These early ballistic missile development programs marked the emergence of engineering discipline 'specialists' which has since continued to grow. Each of these specialties not only has a need to take data from the overall development process, but also to supply data, in the form of requirements and analysis results, to the process. A number of technical instructions, military standards and specifications, and manuals were developed as a result of these development programs. In particular, MILSTD-499 was issued in 1969 to assist both government and contractor personnel in defining the systems engineering effort in support of defense acquisition programs. This standard was updated to MIL-STD499A in 1974, and formed the foundation for current application of systems engineering principles to military development programs.

Source record↗
NASA NTRS1993

Characteristics of products generated by selective sintering and stereolithography rapid prototyping processes

The trend in the modern global economy towards free market policies has motivated companies to use rapid prototyping technologies to not only reduce product development cycle time but also to maintain their competitive edge. A rapid prototyping technology is one which combines computer aided design with computer controlled tracking of focussed high energy source (eg. lasers, heat) on modern ceramic powders, metallic powders, plastics or photosensitive liquid resins in order to produce prototypes or models. At present, except for the process of shape melting, most rapid prototyping processes generate products that are only dimensionally similar to those of the desired end product. There is an urgent need, therefore, to enhance the understanding of the characteristics of these processes in order to realize their potential for production. Currently, the commercial market is dominated by four rapid prototyping processes, namely selective laser sintering, stereolithography, fused deposition modelling and laminated object manufacturing. This phase of the research has focussed on the selective laser sintering and stereolithography rapid prototyping processes. A theoretical model for these processes is under development. Different rapid prototyping sites supplied test specimens (based on ASTM 638-84, Type I) that have been measured and tested to provide a data base on surface finish, dimensional variation and ultimate tensile strength. Further plans call for developing and verifying the theoretical models by carefully designed experiments. This will be a joint effort between NASA and other prototyping centers to generate a larger database, thus encouraging more widespread usage by product designers.

Cariapa, Vikram↗
NASA NTRS1994

An introduction to the Astro Edge solar array

The Astro Edge solar array is a new and innovative low concentrator power generating system which has been developed for applications requiring high specific power, high stiffness, low risk, light modular construction which utilizes conventional materials and technology, and standard photovoltaic solar cells and laydown processes. Mechanisms, restraint/release devices, wiring harnesses, substrates, and support structures are designed to be simple, functional, lightweight, and modular. A brief overview of the Astro Edge solar array is discussed.

Spence, B. R.↗
NASA NTRS2016

Assembly and Integration Process of the First High Density Detector Array for the Atacama Cosmology Telescope

The Advanced ACTPol (AdvACT) upgrade on the Atacama Cosmology Telescope (ACT) consists of multichroicTransition Edge Sensor (TES) detector arrays to measure the Cosmic Microwave Background (CMB) polarization anisotropies in multiple frequency bands. The first AdvACT detector array, sensitive to both 150 and 230 GHz, is fabricated on a 150 mm diameter wafer and read out with a completely different scheme compared to ACTPol. Approximately 2000 TES bolometers are packed into the wafer leading to both a much denser detector density and readout circuitry. The demonstration of the assembly and integration of the AdvACT arrays is important for the next generation CMB experiments, which will continue to increase the pixel number and density. We present the detailed assembly process of the first AdvACT detector array.

Li, Yaqiong↗
NASA NTRS1979

Aerodynamic characteristics at Mach numbers of 1.5, 1.8, and 2.0 of a blended wing-body configuration with and without integral canards

An exploratory, experimental, and theoretical investigation was made of a cambered, twisted, and blended wing-body concept with and without integral canard surfaces. Theoretical calculations of the static longitudinal and lateral aerodynamic characteristics of the wing-body configurations were compared with the characteristics obtained from tests of a model in the Langley Unitary Plan wind tunnel. Mach numbers of 1.5, 1.8, and 2.0 and a Reynolds number per meter of 6.56 million were used in the calculations and tests. Overall results suggest that planform selection is extremely important and that the supplemental application of new calculation techniques should provide a process for the design of supersonic wings in which spanwise distribution of upwash and leading-edge thrust might be rationally controlled and exploited.

Robins, A. W.↗
NASA NTRS1981

An adaptive filter for smoothing noisy radar images

A spatial domain adaptive Wiener filter for smoothing radar images corrupted by multiplicative noise is presented. The filter is optimum in a minimum mean squared error sense, computationally efficient, and preserves edges in the image better than other filters. The proposed algorithm can also be used for processing optical images with illumination variations that have a multiplicative effect.

Frost, V. S.↗
NASA NTRS1983

Examination, evaluation and repair of laminated wood blades after service on the Mod-OA wind turbine

Laminated wood blades were designed, fabricated, and installed on a 200-KW wind turbine (Mod-OA). The machine uses a two-blade rotor with a diameter of 38.1 m (125 ft). Each blade weights less than 1361 kg (3000 lb). After operating in the field, two blade sets were returned for inspection. One set had been in Hawaii for 17 months (7844 hr of operation) and the other had been at Block Island, Rhode Island, for 26 months (22 months operating - 7564 hr). The Hawaii set was returned because of one of the studs that holds the blade to the hub had failed. This was found to be caused by a combination of improper installation and inadequate corrosion protection. No other problems were found. The broken stud (along with four others that were badly corroded) was replaced and the blades are now in storage. The Block Island set of blades was returned at the completion of the test program, but one blade was found to have developed a crack in the leading edge along the entire span. This crack was found to be the result of a manufacturing process problem but was not structurally critical. When a load-deflection test was conducted on the cracked blade, the response was identical to that measured before installation. In general, the laminate quality of both blade sets was excellent. No significant internal delamination or structural defects were found in any blade. The stud bonding process requires close tolerance control and adequate corrosion protection, but studs can be removed and replaced without major problems. Moisture content stabilization does not appear to be a problem, and laminated wood blades are satisfactory for long-term operation on Mod-OA wind turbines.

Faddoul, J. R.↗
NASA NTRS1984

Rapidly Solidified Alloys Made by Chill Block Melt-spinning Processes

Chill block melt-spinning (CBMS) processes are used to make rapidly solidified microcrystalline and amorphous alloy ribbon, flakes, etc. Fundamentals of CBMS processes are discussed in light of recent advances. Special regard is given to ribbon geometric defects (edge serrations, surface asperities, etc.). Photomicrographs of CBMS ribbon solidification microstructures are used to compare local solidification rates, especially in the vicinity of ribbon defects.

Liebermann, H. H.↗
NASA NTRS1989

Image processing by Intensity-Dependent Spread (IDS)

As retinal illuminance is lowered, the human visual system integrates the effects of photon absorptions over larger areas and longer times. A theory of the process that might underlie these changes is called Intensity-Dependent Spread (IDS). Each input point gives rise to a pattern of excitation that spreads to a region of the total excitation it sees. The unique aspect of the theory is the assumption that, although the amplitude of the excitation pattern at its center increases with input illuminance, its width decreases in such a way that its volume remains constant. Application of this theory to image processing reveals that it displays a number of unexpected and potentially useful properties. Among them are edge enhancement and independence from scene illumination.

Cornsweet, Tom N.↗
NASA NTRS1991

Edge technique for measurement of laser frequency shifts including the Doppler shift

A method is disclosed for determining the frequency shift in a laser system by transmitting an outgoing laser beam. An incoming laser beam having a frequency shift is received. A first signal is acquired by transmitting a portion of the incoming laser beam to an energy monitor detector. A second signal is acquired by transmitting a portion of the incoming laser beam through an edge filter to an edge detector, which derives a first normalized signal which is proportional to the transmission of the edge filter at the frequency of the incoming laser beam. A second normalized signal is acquired which is proportional to the transmission of the edge filter at the frequency of the outgoing laser beam. The frequency shift is determined by processing the first and second normalized signals.

Korb, Larry↗