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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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A combined docking and grasping device for use with a manipulator arm on a docking vehicle and the like for mechanically connecting a docking vehicle with an orbital payload having a receptacle for receiving the device is described. The device includes a pair of opposing jaw members having opposing serrated surfaces for grasping an object and a triangular cam portion on an outer surface for insertion and interlocking with an orbital payload.
An improved Kalman filter algorithm based on a modified Givens matrix triangularization technique is proposed for solving a nonstationary discrete-time linear filtering problem. The proposed U-D covariance factorization filter uses orthogonal transformation technique; measurement and time updating of the U-D factors involve separate application of Gentleman's fast square-root-free Givens rotations. Numerical stability and accuracy of the algorithm are compared with those of the conventional and stabilized Kalman filters and the Potter-Schmidt square-root filter, by applying these techniques to a realistic planetary navigation problem (orbit determination for the Saturn approach phase of the Mariner Jupiter-Saturn Mission, 1977). The new algorithm is shown to combine the numerical precision of square root filtering with the efficiency of the original Kalman algorithm.
A new mechanization of the Kalman updating algorithm based on a U-D factorization of the estimate error covariance is introduced. Efficient and stable updating recursions are developed for the unit upper triangular factor U and the diagonal factor D, treating only the parameter estimation problem. Properties of the factorization update performed here include efficient one point at a time processing that requires little more computation than the optimal but numerically unstable conventional Kalman measurement update algorithm, and stability that compares with the square root filter.
The nucleation of small monolayer ice-like clusters at the basal and prism ice-vapor interfaces is considered. It is found that the basal surfaces prefer triangular embryos with an orientation that reverses from layer to layer, whereas the most stable clusters on the prism surfaces are rectangular in configuration. At any given saturation ratio, the preferred prism clusters are found to have a critical energy of formation significantly lower than that of the basal clusters, basically because of differences in cluster corner free energies.
This paper describes an element streamlined for the analysis of doubly-curved, variable-thickness structural components and illustrates its effective application to vibration and static problems. The element is isoparametric, doubly-curved, thin-shell and triangular with variable thickness and accounts for anisotropic, inhomogeneous elastic material behavior. The element has six nodes (three corner and three mid-side) with five degrees-of-freedom (DOF) per node - three translations and two rotations. Quadratic isoparametric interpolation polynomials are used to express the element geometry and displacement variables in terms of corresponding nodal variables.
The Shuttle Infrared Telescope Facility (SIRTF) will combine high sensitivity with the flexibility offered by the Space Transportation System. A recently completed study has generated a preliminary design which demonstrates the feasibility of SIRTF. The 1.0 to 1.5 meter aperture, f/8 Gregorian telescope will be cooled to 20 K by a stored supercritical helium system. The telescope will be pointed and stabilized at two levels: the European-developed Instrument Pointing System provides primary pointing and stabilization; and an internal star tracker senses residual errors and drives a folding mirror inside the telescope to null the errors. The folding mirror can also be driven by square or triangular waves to provide space chopping or small-area scanning.
Time response effects of atmospheric-type disturbances on inlets and some implications regarding inlet controls are considered. A study involving the simulation of a mixed-compression inlet is described. The study employs a linear dynamic analysis, modified for a significant nonlinearity. Transient disturbances in ambient temperature and pressure and wind gusts are considered independently at the inlet cruise Mach number of 2.5. The presented results show the maximum amplitude of a triangular-wave disturbance, that does not cause inlet unstart, as a function of disturbance pulse width.
Mixed shear-flexible isoparametric elements are presented for the stress and free vibration analysis of laminated composite shallow shells. Both triangular and quadrilateral elements are considered. The 'generalized' element stiffness, consistent mass, and consistent load coefficients are obtained by using a modified form of the Hellinger-Reissner mixed variational principle. Group-theoretic techniques are used in conjunction with computerized symbolic integration to obtain analytic expressions for the stiffness, mass and load coefficients. A procedure is outlined for efficiently handling the resulting system of algebraic equations. The accuracy of the mixed isoparametric elements developed is demonstrated by means of numerical examples, and their advantages over commonly used displacement elements are discussed.
Triangular-cross-section Teflon ring seals against cryogenic fluid at temperature where standard wedge of U-rings fail. Ring can be mounted in groove in either piston or bore.
The elastic and plastic singularities near a crack tip are obtained from higher order isoparametric elements. This is simply accomplished by collapsing the quadrilateral element into the triangular element and by judicious choice of adjacent mid-side nodes. Specifically for the cubic element the elastic singularity is obtained by placing the mid-side nodes adjacent to the crack tip at 1/9th and 4/9th locations. The plastic singularity is constructed using the sliding node concept. These elements have been implemented in NASTRAN as user dummy elements.
The investigation of the effects of variations of mesh refinement and mesh pattern were conducted using a basic rectangular mesh pattern. When employing the constant strain TRMEM element, the basic rectangular pattern was subdivided into triangles. This subdivision employs two different triangular patterns and allows results to be obtained which demonstrate the effect of modelling bias. Errors in tip deflection, direct stress, and shearing stress as a function of mesh size and element aspect ratio were obtained as well as mid-span stress distributions. All problems were solved on an IBM 360/95 computer using MacNeal-Schwendler Version MSC-38 Rigid Format-1 of the NASTRAN computer program. While NASTRAN uses double precision arithmetic for the solution of the global equations for displacements, subsequent computations to obtain element stresses are carried out in single precision. This suggests that some improvement in stress recovery might be expected when using the higher precision DCD machines.
The objective of this program was to investigate analytically and experimentally the performance of heat pipes with composite wicks--specifically, those having pedestal arteries and screwthread circumferential grooves. An analytical model was developed to describe the effects of screwthreads and screen secondary wicks on the transport capability of the artery. The model describes the hydrodynamics of the circumferential flow in triangular grooves with azimuthally varying capillary menisci and liquid cross-sections. Normalized results were obtained which give the influence of evaporator heat flux on the axial heat transport capability of the arterial wick. In order to evaluate the priming behavior of composite wicks under actual load conditions, an 'inverted' glass heat pipe was designed and constructed. The results obtained from the analysis and from the tests with the glass heat pipe were applied to the OAO-C Level 5 heat pipe, and an improved correlation between predicted and measured evaporator and transport performance were obtained.
The conceptual equipment and techniques for fabricating and assembling a ladder-like structure of triangular cross section trusses suitable for mounting solar cell arrays are described. The detail information is presented in the context of a proposed experiment to be conducted from the shuttle in the 1980-84 time period as an early experiment in the development of techniques for the construction of large space structures that would be required for space solar power stations and other large systems.
A method is described for solving the linearized supersonic flow over planar wings using panels bounded by two families of Mach lines. Polynomial distributions of source and doublet strength lead to simple, closed form solutions for the aerodynamic influence coefficients, and a nearly triangular matrix yields rapid solutions for the singularity parameters. The source method was found to be accurate and stable both for analysis and design boundary conditions. Similar results were obtained with the doublet method for analysis boundary conditions on the portion of the wing downstream of the supersonic leading edge, but instabilities in the solution occurred for the region containing a portion of the subsonic leading edge. Research on the method was discontinued before this difficulty was resolved.
The preliminary design of a deployable Extravehicular Activity Translation Arm (EVATA) assembly which will allow an EVA crewman to perform tasks in the vicinity of the External TNK (ET) umbilical doors and to inspect most of the underside of the shuttle spacecraft is reported. The concept chosen for the boom structure was the Astro Extendable Support Structure (ESS) which formed the main structure for the Synthetic Aperture Radar (SAR) Antenna System on the SEASAT A spacecraft. This structure is a deployable triangular truss. A comparison of the EVATA and the SEASAT A ESS is shown. The development of status of the ESS is shown. The satellite configuration, the stowed truss load path, and the envelope deployment sequence for the ESS are also shown.
A solar energy collector system characterized by an improved concentrator for directing incident rays of solar energy on parallel vacuum-jacketed receivers or absorbers is described. Numerous individually mounted reflector modules of a common asymmetrical triangular cross-sectional configuration are supported for independent reorientation. Asymmetric vee-trough concentrators are defined.
Isoparametric quadrilateral and triangular elements were used to represent the vacuum vessel shell structure. For toroidally symmetric loadings, MPCs were employed across model boundaries and rigid format 24 was invoked. Nonsymmetric loadings required the use of the cyclic symmetry analysis available with rigid format 49. NASTRAN served as an important analysis tool in the Tokamak design effort by providing a reliable means for assessing structural integrity. Interactive graphics were employed in the finite element model generation and in the post-processing of results. It was felt that model generation and checkout with interactive graphics reduced the modelling effort and debugging man-hours significantly.
Supercooling of silicon-tin alloy melts was studied. Values as high as 78 C at 1100 C and 39 C at 1200 C were observed, corresponding to supersaturation parameter values 0.025 and 0.053 at 1050 C and 1150 C, respectively. The interaction of tin with silane gas streams was investigated over the temperature range 1000 to 1200 C. Single-pass conversion efficiencies exceeding 30% were obtained. The growth habit of spontaneously-nucleated surface growth was determined to be consistent with dendritic and web growth from singly-twinned triangular nucleii. Surface growth of interlocking silicon crystals, thin enough to follow the surface of the liquid and with growth velocity as high as 5 mm/min, was obtained. Large area single-crystal growth along the melt surface was not achieved. Small single-crystal surface growth was obtained which did not propagate beyond a few millimeters.