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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 487 records · Page 27

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NASA NTRS2000

Nonlinear simulations of Jupiter's 5-micron hot spots

Large-scale nonlinear simulations of Jupiter's 5-micron hot spots produce long-lived coherent structures that cause subsidence in local regions, explaining the low cloudiness and the dryness measured by the Galileo probe inside a hot spot. Like observed hot spots, the simulated coherent structures are equatorially confined, have periodic spacing, propagate west relative to the flow, are generally confined to one hemisphere, and have an anticyclonic gyre on their equatorward side. The southern edge of the simulated hot spots develops vertical shear of up to 70 meters per second in the eastward wind, which can explain the results of the Galileo probe Doppler wind experiment.

Jupiter↗

NASA NTRS1991

Active sound attenuation across a double wall structure

The possibility of achieving significant local and global sound attenuation across a flat double wall is demonstrated. It is also shown that sound can be prevented from entering the interior of a cabinlike environment. The approach used is unlike established active noise control techniques.

Grosveld, Ferdinand W.↗

NASA NTRS1993

A tri-state optical switch for local area network communications

This novel structure is a heterojunction phototransistor which can be used as an emitter-detector, and when placed in a quiescent mode, the device becomes a passive transmitter. By varying the voltage bias, this novel device will switch between all three modes of operation. Such a device has broad application in network environments with operation speeds of less than 50 MHz and distances of less than 1 km, e.g. automobiles, airplanes, and intra-instrumentation. During this period, the emission mode for this device was studied and mathematically modeled.

Simms, Garfield↗

NASA NTRS1986

Flutter and Vibration Animation Program

Flutter and Vibration Animation (FLUVIAN) program produces animated picture of structure as it vibrates at constant amplitude. Permits visual observation of fluttering motion of components as they oscillate in combination of modes. Animated display provides insight into local deflection patterns induced in structure, overlooked if modal deflection patterns were separately examined and combined mentally. FLUVIAN program written in FORTRAN 77 for interactive execution.

Tischner, R. L.↗

NASA NTRS2011

Structural Efficiency and Behavior of Pristine and Notched Stitched Structure

Two driving factors in aircraft panel design are structural efficiency and response to in-service damage. Stitching through the thickness can improve both of these considerations. Combining stitching with a post-buckling design approach can provide additional improvements. The buckling behavior of stitched structure is considered since lighter structures can be achieved if local skin buckling is allowed to occur at less than design ultimate load. Through-the-thickness stitching can suppress delamination between skin and flange, thereby allowing the structure to reliably carry load into the postbuckling range. Hat-stiffened and rod-stiffened panels in which the skin and flanges were stitched together through-the-thickness prior to curing are considered through experiment and analysis. In both types of panels no mechanical fasteners were used for the assembly. Specimens were loaded to failure in axial compression. In this study all specimens buckled in the skin between the stiffeners and continued to carry load. In addition, the behavior of panels with a severed stringer or notch are considered. Failure loads and strain distributions in the notched panel are compared to those in the unnotched panel.

Jegley, Dawn C.↗

NASA NTRS1999

Nitric-oxide synthase is a mechanical signal transducer that modulates talin and vinculin expression

Mechanical stimuli can cause changes in muscle mass and structure which indicate that mechanisms exist for transducing mechanical stimuli into signals that influence gene expression. Myotendinous junctions show adaptations to modified muscle loading which suggest that these are transcriptionally distinct domains in muscle fibers that may experience local regulation of expression of structural proteins that are concentrated at these sites. Vinculin and talin are cytoskeletal proteins that are highly enriched at myotendinous junctions that we hypothesize to be subject to local transcriptional regulation. Our findings show that mechanical stimulation of muscle cells in vivo and in vitro causes an increase in the expression of vinculin and talin that is mediated by nitric oxide. Furthermore, nitric oxide-stimulated increases in vinculin and talin expression occur through a protein kinase G-dependent pathway and therefore differ from other mechanisms through which nitric oxide has been shown previously to modulate transcription. Analysis of vinculin mRNA distribution in mechanically stimulated muscle fibers shows that the mRNA is highly concentrated at myotendinous junctions, which supports the hypothesis that myotendinous junctions are distinct domains in which the expression of cytoskeletal proteins is modulated by mechanical stimuli through a nitric oxide and protein kinase G-dependent pathway.

NASA Discipline Musculoskeletal↗

NASA NTRS1988

The Clouds distributed operating system - Functional description, implementation details and related work

Clouds is an operating system in a novel class of distributed operating systems providing the integration, reliability, and structure that makes a distributed system usable. Clouds is designed to run on a set of general purpose computers that are connected via a medium-of-high speed local area network. The system structuring paradigm chosen for the Clouds operating system, after substantial research, is an object/thread model. All instances of services, programs and data in Clouds are encapsulated in objects. The concept of persistent objects does away with the need for file systems, and replaces it with a more powerful concept, namely the object system. The facilities in Clouds include integration of resources through location transparency; support for various types of atomic operations, including conventional transactions; advanced support for achieving fault tolerance; and provisions for dynamic reconfiguration.

Dasgupta, Partha↗

NASA NTRS1991

Damaged stiffened shell research at NASA. Langley Research Center

The structural behavior of stiffened fuselage shells with local cracks is influenced by the local deformations and stress gradients near the cracks, and this behavior must be understood to predict fuselage structural integrity and residual strength. As a crack grows, the stiffness and internal load distributions in a stiffened shell change, affecting the local deformations and stress gradients near the crack. Transport fuselage shells are designed to support internal pressure and mechanical loads which cause a geometrically nonlinear response. Research is being conducted at NASA LaRC to develop and demonstrate a verified nonlinear stiffened shell analysis methodology for accurately predicting the global and local behavior of nonlinear stiffened fuselage shells with local cracks and with combined internal pressure and mechanical loads. The nonlinear structural analysis methodology being developed and planned at NASA LaRC for damaged stiffened fuselage shells and the experiments being planned to verify this analysis methodology are summarized in the present paper.

Aging Aircraft↗

NASA NTRS1974

Ruemker Hills - A lunar volcanic dome complex

The Ruemker Hills, a volcanic dome-flow complex in the northern Oceanus Procellarum, is characterized by overlapping plains-forming units with lobate scarps, volcanic domes, a 60-km ring, and a scarp which separates the plateau from surrounding mare materials. Plains-forming units are interpreted as fluid volcanic flows, and domes as viscous extrusions. One dome may be a stratovolcano. The ring system is discordant with regional structural trends and probably has a local origin. The Ruemker Hills is the closest lunar analog to the large Martian shield structures revealed on the Mariner 9 photographs of Mars.

Smith, E. I.↗

NASA NTRS2012

Instrumentation for the Characterization of Inflatable Structures

Current entry, descent, and landing technologies are not practical for heavy payloads due to mass and volume constraints dictated by limitations imposed by launch vehicle fairings. Therefore, new technologies are now being explored to provide a mass- and volume-efficient solution for heavy payload capabilities, including Inflatable Aerodynamic Decelerators (IAD) [1]. Consideration of IADs for space applications has prompted the development of instrumentation systems for integration with flexible structures to characterize system response to flight-like environment testing. This development opportunity faces many challenges specific to inflatable structures in extreme environments, including but not limited to physical flexibility, packaging, temperature, structural integration and data acquisition [2]. In the spring of 2012, two large scale Hypersonic Inflatable Aerodynamic Decelerators (HIAD) will be tested in the National Full-Scale Aerodynamics Complex s 40 by 80 wind tunnel at NASA Ames Research Center. The test series will characterize the performance of a 3.0 m and 6.0 m HIAD at various angles of attack and levels of inflation during flight-like loading. To analyze the performance of these inflatable test articles as they undergo aerodynamic loading, many instrumentation systems have been researched and developed. These systems will utilize new experimental sensing systems developed by the HIAD ground test campaign instrumentation team, in addition to traditional wind tunnel sensing techniques in an effort to improve test article characterization and model validation. During the 2012 test series the instrumentation systems will target inflatable aeroshell static and dynamic deformation, structural strap loading, surface pressure distribution, localized skin deflection, and torus inflation pressure. This paper will offer an overview of inflatable structure instrumentation, and provide detail into the design and implementation of the sensors systems that will be utilized during the 2012 HIAD ground test campaign.

Swanson, Gregory T.↗

NASA NTRS1984

Saturn's rings - Properties and processes

In the present consideration of the structural and particle properties of Saturn's rings, emphasis is given to spacecraft observations and an attempt is made to relate observed properties to favored causative processes. While the ring particles are primarily icy, there is evidence for compositional variation on both local and regional scales. Ring structure is generally dominated by collisional and gravitational dynamics. On the basis of such features as orbital resonances with various satellites, which drive spiral density and bending waves, the ring mass density and local vertical thickness can be determined.

Cuzzi, J. N.↗

NASA NTRS1991

Static Footprint Local Forces, Areas, and Aspect Ratios for Three Type 7 Aircraft Tires

The National Tire Modeling Program (NTMP) is a joint NASA/industry effort to improve the understanding of tire mechanics and develop accurate analytical design tools. This effort includes fundamental analytical and experimental research on the structural mechanics of tires. Footprint local forces, areas, and aspect ratios were measured. Local footprint forces in the vertical, lateral, and drag directions were measured with a special footprint force transducer. Measurements of the local forces in the footprint were obtained by positioning the transducer at specified locations within the footprint and externally loading the tires. Three tires were tested: (1) one representative of those used on the main landing gear of B-737 and DC-9 commercial transport airplanes, (2) a nose landing gear tire for the Space Shuttle Orbiter, and (3) a main landing gear tire for the Space Shuttle Orbiter. Data obtained for various inflation pressures and vertical loads are presented for two aircraft tires. The results are presented in graphical and tabulated forms.

Howell, William E.↗

NASA NTRS2005

Computational Modeling of Liquid and Gaseous Control Valves

In this paper computational modeling efforts undertaken at NASA Stennis Space Center in support of rocket engine component testing are discussed. Such analyses include structurally complex cryogenic liquid valves and gas valves operating at high pressures and flow rates. Basic modeling and initial successes are documented, and other issues that make valve modeling at SSC somewhat unique are also addressed. These include transient behavior, valve stall, and the determination of flow patterns in LOX valves. Hexahedral structured grids are used for valves that can be simplifies through the use of axisymmetric approximation. Hybrid unstructured methodology is used for structurally complex valves that have disparate length scales and complex flow paths that include strong swirl, local recirculation zones/secondary flow effects. Hexahedral (structured), unstructured, and hybrid meshes are compared for accuracy and computational efficiency. Accuracy is determined using verification and validation techniques.

Daines, Russell↗

NASA NTRS2006

Overview of Boundary Layer Transition Research in Support of Orbiter Return To Flight

A predictive tool for estimating the onset of boundary layer transition resulting from damage to and/or repair of the thermal protection system was developed in support of Shuttle Return to Flight. The boundary layer transition tool is part of a suite of tools that analyze the aerothermodynamic environment to the local thermal protection system to allow informed disposition of damage for making recommendations to fly as is or to repair. Using mission specific trajectory information and details of each damage site or repair, the expected time (and thus Mach number) at transition onset is predicted to help define the aerothermodynamic environment to use in the subsequent thermal and stress analysis of the local thermal protection system and structure. The boundary layer transition criteria utilized for the tool was developed from ground-based measurements to account for the effect of both protuberances and cavities and has been calibrated against select flight data. Computed local boundary layer edge conditions were used to correlate the results, specifically the momentum thickness Reynolds number over the edge Mach number and the boundary layer thickness. For the initial Return to Flight mission, STS-114, empirical curve coefficients of 27, 100, and 900 were selected to predict transition onset for protuberances based on height, and cavities based on depth and length, respectively.

Berry, Scott A.↗

NASA NTRS1972

Binary index for assessing local bow shock obliquity.

The earth's collisionless plasma bow shock has, overall, a nonuniform structure whose magnetic profile is simultaneously that of a monotonic or laminar perpendicular shock and of a multigradient oblique shock, depending on the local orientation of the interplanetary field to the nominal shock surface. A 'pulsation index' Ip has been devised from empirical results to provide a simple convenient means of assessing the probable local character of the shock's structure; Ip = 0 or 1, according to whether local field geometry favors perpendicular or oblique structure, respectively, at a chosen point of observation on the nominal shock surface.

Greenstadt, E. W.↗

NASA NTRS1995

Optimization of composite box-beam structures including effects of subcomponent interactions

Minimum mass designs are obtained for a simple box beam structure subject to bending, torque and combined bending/torque load cases. These designs are obtained subject to point strain and linear buckling constraints. The present work differs from previous efforts in that special attention is payed to including the effects of subcomponent panel interaction in the optimal design process. Two different approaches are used to impose the buckling constraints. When the global approach is used, buckling constraints are imposed on the global structure via a linear eigenvalue analysis. This approach allows the subcomponent panels to interact in a realistic manner. The results obtained using this approach are compared to results obtained using a traditional, less expensive approach, called the local approach. When the local approach is used, in-plane loads are extracted from the global model and used to impose buckling constraints on each subcomponent panel individually. In the global cases, it is found that there can be significant interaction between skin, spar, and rib design variables. This coupling is weak or nonexistent in the local designs. It is determined that weight savings of up to 7% may be obtained by using the global approach instead of the local approach to design these structures. Several of the designs obtained using the linear buckling analysis are subjected to a geometrically nonlinear analysis. For the designs which were subjected to bending loads, the innermost rib panel begins to collapse at less than half the intended design load and in a mode different from that predicted by linear analysis. The discrepancy between the predicted linear and nonlinear responses is attributed to the effects of the nonlinear rib crushing load, and the parameter which controls this rib collapse failure mode is shown to be the rib thickness. The rib collapse failure mode may be avoided by increasing the rib thickness above the value obtained from the (linear analysis based) optimizer. It is concluded that it would be necessary to include geometric nonlinearities in the design optimization process if the true optimum in this case were to be found.

Ragon, Scott A.↗

NASA NTRS1966

Tooling concepts for assembly of large structures

Manufacture of the S-IC stage of the Saturn V space vehicle has resulted in new. concepts and innovations in the field of tooling. The structure size (35-ft diameter), the high reliability and accuracy requirements, and the low density or production quantity lead to a greater degree of simplicity, economy, and versatility in fabrication and assembly tooling. There are three specific concepts which should be applicable in industry, local jigging for welding, rotation of structures in vertical assemblies, and the assembly of two structures. The usual weld jigging serves a two-fold purpose: (a) to support the molten weld puddle and (b) to force and maintain alinement of the parts being welded. The extension of this method to large-diameter tanks is expensive and difficult. An alternate procedure used at MSFC is to perform free-state welding and use local jigging (stra1rclamps) and intermittent tack welding. Cylindrical structures can be accurately rotated for routing or welding on a simplified ring turntable. The tool consists of a ring of the structure diameter resting on rollers. Torque is nearly zero since the ring is rotated by friction rollers with the force being applied at the ring perimeter. Two such turntables are used at MSFC. The horizontal mating of two large components, where controlled motions of small magnitude are necessary, can be easily done by positioning units equipped with air-bearings. Such bearings are usable on concrete of minimum surface preparation and require no special air pressure source. This concept is used in assembly of the two S-IC containers.

Saturn S-IC stage↗

NASA NTRS2000

Significant Centers of Tectonic Activity as Identified by Wrinkle Ridges for the Western Hemisphere of Mars

The western hemisphere region of Mars has been the site of numerous scientific investigations regarding its tectonic evolution. For this region of Mars, the dominant tectonic region is the Tharsis province. Tharsis is characterized by an enormous system of radiating grabens and a circumferential system of wrinkle ridges. Past investigations of grabens associated with Tharsis have identified specific centers of tectonic activity. A recent structural analysis of the western hemisphere region of Mars which includes the Tharsis region, utilized 25,000 structures to determine the history of local and regional centers of tectonic activity based primarily on the spatial and temporal relationships of extensional features. This investigation revealed that Tharsis is more structurally complex (heterogeneous) than has been previously identified: it consists of numerous regional and local centers of tectonic activity (some are more dominant and/or more long lived than others). Here we use the same approach as Anderson et al. to determine whether the centers of tectonic activity that formed the extensional features also contributed to wrinkle ridge (compressional) formation.

Anderson, R.C.↗