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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 NTRS1959

Wind-Tunnel Investigation at Mach Numbers from 0.40 to 1.14 of the Static Aerodynamic Characteristics of a Nonlifting Vehicle Suitable for Reentry

An investigation was conducted in the Langley 8-foot transonic pressure tunnel to investigate the static pitching-moment, normal-force, and axial-force characteristics on a model of a nonlifting vehicle suit- able for reentry. The vehicle was designed to use a heat sink and blunt shape to alleviate the effects of the heating encountered during reentry of the earth's atmosphere. The effects of modifying the intersection of the face of the model with the afterbody from a sharp corner to a rounded edge were also investigated. Tests were conducted at Mach numbers from 0.40 to 1.14 and at angles of attack from approximately -3 deg to 20 deg. The Reynolds number varied from about 2.0 x 10(exp 6) to 3.6 x 10(exp 6). The results show that the model had a low positive static-stability level, low normal-force coefficients, and large axial-force coefficients. The model trimmed, for the angle-of-attack range investigated, at angles of attack near zero. The effects on the stability as a result of rounding the corner were negligible.

Pearson, Albin O.↗
NASA NTRS1959

Low-Speed Static Stability and Control Characteristics of a Model of a Right Triangular Pyramid Reentry Configuration

An investigation of the low-speed static stability and control characteristics of a model of a right triangular pyramid reentry configuration has been made in the Langley free-flight tunnel. The investigation showed that the model had generally satisfactory longitudinal and lateral static stability characteristics. The maximum lift-drag ratio was increased from about 3 to 5 by boattailing the base of the model.

Paulson, John W.↗
NASA NTRS1961

Static Longitudinal Characteristics at High Subsonic Speeds of a Complete Airplane Model with a Highly Tapered Wing having the 0.80 Chord Line Unswept and with Several Tail Configurations

An investigation was made at high subsonic speeds of a complete model having a highly tapered wing and several tail configurations. The basic aspect-ratio-4.00 wing had zero taper and an unswept 0.80 chord line. Several aspect-ratio modifications to the basic wing were made by clipping off portions of the wing tips. The complete model was tested with a chord-plane tail, a T-tail, and a biplane tail (combined T-tail and chord-plane tail). The model was tested in the Langley high-speed 7- by 10-foot tunnel at Mach numbers from 0.60 to 0.92. The data show that, when reduced to the same static margin, all the tail configurations tested on the model provided fairly good stability characteristics, the biplane tail giving the.best overall characteristics as regards pitching-moment linearity. Changes in static margin at zero lift coefficient with Mach number were small for the model with these tails over the Mach number range investigated.

Goodson, Kenneth W.↗
NASA NTRS1959

Low-Speed Measurements of Static and Oscillatory Lateral Stability Derivatives of a 1/5 Scale Model of a Jet-Powered Vertical-Attitude VTOL Research Airplane

Force tests of the static and dynamic lateral stability characteristics of a VTOL airplane having a triangular wing mounted high on the fuselage with a triangular vertical tail on top of the wing and no horizontal tail have been made in the Langley free-flight tunnel. The static lateral stability parameters and the rolling, yawing, and sideslipping dynamic stability derivatives are presented without analysis.

Shanks, Robert E.↗
NASA NTRS1997

Current Collection in Plasmas by a Static Bare Tether

Current collection in plasmas by a static bare tether is studied. Considering the geometry effect, we modify the static Parker-Murphy current collection model to accommodate a cylindrical probe. It is shown that a long cylindrical configuration (length is much greater than diameter) can collect more current than the spherical configuration whose effective surface area and surface potential are identical. However, when the cylinder is not long (length and diameter are same order), it collects less current than the effective sphere. This indicates that Myers et al. might over estimate the PM current when they neglected the geometry effect. Compared to the orbit limit model and the chamber experiment, our predictions are in the range of the adiabatic limits and the upper-bound currents obtained by Rubinstein and Laframboise. It shows that the present results are in agreement with the bare tether chamber test experimental data given by Sorenson, Stone, and Wright. In addition we have applied this model to study the IR drop and the orientation effects which are important in the space condition.

Zhang, T. X.↗
NASA NTRS1999

Reducing and Inducing Convection in Ge-Si Melts with Static Magnetic Field

Results of a study of the effectiveness of using static magnetic fields to reduce convection in Ge-Si melts will be presented. Lenz's law causes a retardation of convection when a static magnetic field is applied to an electrically conducting liquid. However, during the solidification of a solid-solution system such as Ge-Si, the interface is neither isothermal nor isoconcentrational. The variation of temperature and chemical composition along the interface causes thermoelectric currents to be generated within the solidifying material (and the container if it is electrically conductive). These currents, in the presence of a magnetic field, can cause movement (stirring, convection) in the melt which can exceed convection induced by normal thermosolutal mechanisms. Crystals have been grown by both the Bridgman and floating-zone methods. Clear evidence for the existence of this thermoelectromagnetic convection, especially in the case of Si floating-zone growth, will be presented.

Szofran, Frank R.↗
NASA NTRS1997

Molecular Static Third-Order Polarizabilities of Carbon-Cage Fullerenes and their Correlation with Three Geometric Parameters: Group Order, Aromaticity, and Size

Calculations were performed on the valence contribution to the static molecular third-order polarizabilities (gamma) of thirty carbon-cage fullerenes (C60, C70, five isomers of C78, and twenty-three isomers of C84). The molecular structures were obtained from B3LYP/STO-3G calculations. The values of the tensor elements and an associated numerical uncertainty were obtained using the finite-field approach and polynomial expansions of orders four to eighteen of polarization versus static electric field data. The latter information was obtained from semiempirical calculations using the AM1 hamiltonian.

Moore, Craig E.↗
NASA NTRS1998

Molecular Static Third-Order Polarizabilities of Carbon-Cage Fullerene and Their Correlation with Three Geometric Properties: Symmetry, Aromaticity, and Size

The static third-order polarizabilities (gamma) of C60, C70, five isomers of C78 and two isomers of C84 were analyzed in terms of three properties, from a geometric point of view: symmetry, aromaticity and size. The polarizability values were based on the finite field approximation using a semiempirical Hamiltonian (AM1) and applied to molecular structures obtained from density functional theory calculations. Symmetry was characterized by the molecular group order. The selection of 6-member rings as aromatic was determined from an analysis of bond lengths. Maximum interatomic distance and surface area were the parameters considered with respect to size. Based on triple linear regression analysis, it was found that the static linear polarizability (alpha) and gamma in these molecules respond differently to geometrical properties: alpha depends almost exclusively on surface area while gamma is affected by a combination of number of aromatic rings, length and group order, in decreasing importance. In the case of alpha, valence electron contributions provide the same information as all-electron estimates. For gamma, the best correlation coefficients are obtained when all-electron estimates are used and when the dependent parameter is ln(gamma) instead of gamma.

Moore, C. E.↗
NASA NTRS2000

MSC/NASTRAN Stress Analysis of Complete Models Subjected to Random and Quasi-Static Loads

Space payloads, such as those which fly on the Space Shuttle in Spacelab, are designed to withstand dynamic loads which consist of combined acoustic random loads and quasi-static acceleration loads. Methods for computing the payload stresses due to these loads are well known and appear in texts and NASA documents, but typically involve approximations such as the Miles' equation, as well as possible adjustments based on "modal participation factors." Alternatively, an existing capability in MSC/NASTRAN may be used to output exact root mean square [rms] stresses due to the random loads for any specified elements in the Finite Element Model. However, it is time consuming to use this methodology to obtain the rms stresses for the complete structural model and then combine them with the quasi-static loading induced stresses. Special processing was developed as described here to perform the stress analysis of all elements in the model using existing MSC/NASTRAN and MSC/PATRAN and UNIX utilities. Fail-safe and buckling analyses applications are also described.

Hampton, Roy W.↗
NASA NTRS2000

Dynamic Investigation of Static Divergence: Analysis and Testing

The phenomenon known as aeroelastic divergence is the focus of this work. The analyses and experiment presented here show that divergence can occur without a structural dynamic mode losing its oscillatory nature. Aeroelastic divergence occurs when the structural restorative capability or stiffness of a structure is overwhelmed by the static aerodynamic moment. This static aeroelastic coupling does not require the structural dynamic system behavior to cease, however. Aeroelastic changes in the dynamic mode behavior are governed not only by the stiffness, but by damping and inertial properties. The work presented here supports these fundamental assertions by examining a simple system: a typical section airfoil with only a rotational structural degree of freedom. Analytical results identified configurations that exhibit different types of dynamic mode behavior as the system encounters divergence. A wind tunnel model was designed and tested to examine divergence experimentally. The experimental results validate the analytical calculations and explicitly examine the divergence phenomenon where the dynamic mode persists. Three configurations of the wind tunnel model were tested. The experimental results agree very well with the analytical predictions of subcritical characteristics, divergence velocity, and behavior of the noncritical dynamic mode at divergence.

Heeg, Jennifer↗
NASA NTRS1994

Elevated Temperature Slow Crack Growth of Silicon Nitride Under Dynamic, Static and Cyclic Flexural Loading

The slow crack growth parameters of a hot-pressed silicon nitride were determined at 1200 and 1300 C in air by statically, dynamically and cyclicly loading bend specimens. The fatigue parameters were estimated using the recently developed CARES/Life computer code. Good agreement exists between the flexural results. However, fatigue susceptibility under static uniaxial tensile loading, reported elsewhere, was greater than in flexure. Cyclic flexural loading resulted in the lowest apparent flexural fatigue susceptibility.

Choi, Sung R.↗
NASA NTRS2003

AWS Figure of Merit (FOM) Developed Parameters from Static, Transonic Model Tests

This paper provides an approach to answer the question of whether one can rely solely on static data taken during a transonic model test to provide the certainty needed that a new aircraft will or will not have Abrupt Wing Stall (AWS) events during its flight operations. By comparing traditional- and alternate-static-Figures of Merit (FOMs) with the Free-To-Roll (FTR) response data, a rational basis for assessing the merits of using standard testing techniques for the prediction of AWS events has been established. Using the FTR response data as a standard, since these results compare well with flight, the conclusion from this study is that neither traditional nor alternate FOMs can be trusted to provide an indication as to whether a configuration will or will not have AWS tendencies. Even though these FOMs may flag features which have a high degree of correlation with the FTR response data, there are as many or more of these FOM flagged features which do not correlate. Thus, one needs to use the FTR rig to assess AWS tendencies on new configurations.

Lamar, J. E.↗
NASA NTRS2003

Sea-Level Static Testing of the Penn State Two-Dimensional Rocket-Based Combined Cycle (RBCC) Testbed

Twin thruster tests have been conducted with the Penn State RBCC test article operating at sea- level static conditions. Significant differences were observed in the performance characteristics for two different thruster centerline spacings. Changing the thruster spacing from 2.50 to 1.75 in. reduced the entrained air velocity (-17%) and the thrust (-7%) for tests at a thruster chamber pressure of 200 psia and MR = 8. In addition, significant differences were seen in the static pressure profiles, the Raman spectroscopy profiles, and the acoustic power spectrum for these two configurations.

Cramer, J. M.↗
NASA NTRS2004

Static Testing of an Inflatable/Rigidizable Hexapod Structure

Scientific application of large space antennas and telescopes is fostering the study of ultralightweight and inflatable structures. These so-called gossamer structures are tightly packaged for launch and subsequent deployment. Of particular interest is a hexapod configuration often found in vehicle ride simulators, ground-based telescopes, and antennas. One such configuration was modeled and tested at NASA Langley. Discrepancies between dynamic test data and predictions from a finite element model prompted additional static testing. This paper discusses static tests that were conducted to update stiffness parameters in the finite element model.

Berger, K. T.↗
NASA NTRS2004

Precise and Efficient Static Array Bound Checking for Large Embedded C Programs

In this paper we describe the design and implementation of a static array-bound checker for a family of embedded programs: the flight control software of recent Mars missions. These codes are large (up to 250 KLOC), pointer intensive, heavily multithreaded and written in an object-oriented style, which makes their analysis very challenging. We designed a tool called C Global Surveyor (CGS) that can analyze the largest code in a couple of hours with a precision of 80%. The scalability and precision of the analyzer are achieved by using an incremental framework in which a pointer analysis and a numerical analysis of array indices mutually refine each other. CGS has been designed so that it can distribute the analysis over several processors in a cluster of machines. To the best of our knowledge this is the first distributed implementation of static analysis algorithms. Throughout the paper we will discuss the scalability setbacks that we encountered during the construction of the tool and their impact on the initial design decisions.

Venet, Arnaud↗
NASA NTRS2003

Mode Jumping of an Isogrid Panel Under Quasi-Static Compression

A wide column test of a composite isogrid panel subjected to quasi-static, axial compression is modeled with a hybrid-static dynamic computational method. The data from the test panel exhibited discontinuous responses in the compressive load for slowly increased end-shortening. The computational model was developed to corroborate these discontinuities with the phenomenon of mode jumping. Mode jumping refers to the transient response of the panel from an unstable bifurcation point on a postbuckled equilibrium path to a second stable equilibrium state on a new equilibrium path. On the new equilibrium path, both the analysis and test show that the panel can resist increased endshortening beyond that of the unstable critical point. Fair agreement is achieved between the analysis and test.

Muheim, Danniella M.↗
NASA NTRS2004

Intricate Crystal Structure of Dihydrolipoamide Dehydrogenase (E3) with its Binding Protein: Multiple Copies, Dynamic and Static Disorders

Human E3 and binding protein E3BP are two components of the pyruvate dehydrogenase complex. Crystallization of E3 with 221-amino acid fragment of E3BP (E3BPdd) led to crystals that diffracted to a resolution of 2.6 Angstroms. Structure determination involved molecular replacement using a dimer of E3 homolog as a search model and de novo building of the E3BPdd peptide. Solution was achieved by inclusion of one E3 dimer at a time, followed by refinement until five E3 dimers were located. This complete content of E3 provided electron density maps suitable for tracing nine peptide chains of E3BPdd, eight of them being identified with partial occupancies. Final content of the asymmetric unit consists of five E3 dimers, each binding one E3BPdd molecule. In four of these molecular complexes, E3BPdd is in static disorder resulting in E3BPdd binding to either one or the other monomer of the E3 dimer. However, E3BPdd of the fifth E3 dimer forms specific contacts that lock it at one monomer. In addition to this static disorder, E3BPdd reveals high mobility in the limited space of the crystal lattice. Support from NIH and NASA.

Makal, A.↗
NASA NTRS1999

Subsonic Static and Dynamic Aerodynamics of Blunt Entry Vehicles

The incompressible subsonic aerodynamics of four entry-vehicle shapes with variable c.g. locations are examined in the Langley 20-Foot Vertical Spin Tunnel. The shapes examined are spherically-blunted cones with half-cone angles of 30, 45, and 60 deg. The nose bluntness varies between 0.25 and 0.5 times the base diameter. The Reynolds number based on model diameter for these tests is near 500,000. Quantitative data on attitude and location are collected using a video-based data acquisition system and reduced with a six deg-of-freedom inverse method. All of the shapes examined suffered from strong dynamic instabilities which could produced limit cycles with sufficient amplitudes to overcome static stability of the configuration. Increasing cone half-angle or nose bluntness increases drag but decreases static and dynamic stability.

Mitcheltree, Robert A.↗