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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 271 records · Page 15
All sourcesNASA NTRSDOE OSTI
NASA NTRS1977

Structural analysis of ultra-high speed aircraft structural components

The buckling characteristics of a hypersonic beaded skin panel were investigated under pure compression with boundary conditions similar to those found in a wing mounted condition. The primary phases of analysis reported include: (1) experimental testing of the panel to failure; (2) finite element structural analysis of the beaded panel with the computer program NASTRAN; and (3) summary of the semiclassical buckling equations for the beaded panel under purely compressive loads. A comparison of each of the analysis methods is also included.

Lenzen, K. H.↗
NASA NTRS1981

Structural dynamics and control of large space structures

The focus of the workshop was the basic research program assembled by LaRC to address the fundamental technology deficiencies that were identified in several studies on large space systems (LSS) conducted by NASA in the last several years. The staffs of the respective participants were assembled at the workshop to review the current state of research in the control technology for large structural systems and to plan the efforts that would be pursued by their respective organizations.

Lightner, E. B.↗
NASA NTRS1983

Structural Dynamics and Control of Large Space Structures, 1982

Basic research in the control of large space structures is discussed. Active damping and control of flexible beams, active stabilization of flexible antenna feed towers, spacecraft docking, and robust pointing control of large space platform payloads are among the topics discussed.

Brumfield, M. L.↗
NASA NTRS1984

Environmental and structural assessment of four year in-commercial service composite helicopter structures

This paper presents the technical background for including environmental effects in the design of helicopter composite structures. This effort was supported by test results of components and panels having up to four years of field exposure. The preceeding was part of an eight year program to evaluate in-service environmental factors for comparison with laboratory test results. Full scale static and fatigue tests were conducted on composite components removed from S-76 helicopters used in commercial operations in the Gulf Coast region of Louisiana. Small scale tests were conducted using coupons removed from panels exposed to the outdoor environment in Stratford, Connecticut and West Palm Beach, Florida. Panel configurations were representative of S-76 components. Moisture analysis and strength tests on components and panels are reported after two, three and four years of exposure. Moisture levels were compared with predicted values. Mechanical test results were compared to initial certification tests for component strength, and to baseline laboratory coupon testing.

Ezzo, M. B.↗
NASA NTRS1986

Mast flight system beam structure and beam structural performance

An overall understanding of the beam assembly and data with which potential experimenters can begin to conduct analyses relevant to their experiments is given. Data is given on the beam structural concept, the tip remote station layout, the intermediate remote station layout with and without actuators, beam element materials, equivalent beam characteristics, beam element properties, remote station mass properties, and MAST Flight System modal characteristics.

Lenzi, David C.↗
NASA NTRS1987

Structural Dynamics and Control Interaction of Flexible Structures

A Workshop was held to promote technical exchange between the structural dynamic and control disciplines, foster joint technology, and provide a forum for discussing and focusing critical issues in the separate and combined areas. The workshop was closed by a panel meeting. Panel members' viewpoints and their responses to questions are included.

Ryan, Robert S.↗
NASA NTRS1987

Innovative design of composite structures: Use of curvilinear fiber format to improve structural efficiency

To increase the effectiveness and efficiency of fiber-reinforced materials, the use of fibers in a curvilinear rather than the traditional straightline format is explored. The capacity of a laminated square plate with a central circular hole loaded in tension is investigated. The orientation of the fibers is chosen so that the fibers in a particular layer are aligned with the principle stress directions in that layer. Finite elements and an iteration scheme are used to find the fiber orientation. A noninteracting maximum strain criterion is used to predict load capacity. The load capacities of several plates with different curvilinear fibers format are compared with the capacities of more conventional straightline format designs. It is found that the most practical curvilinear design sandwiches a group of fibers in a curvilinear format between a pair of +/-45 degree layers. This design has a 60% greater load capacity than a conventional quasi-isotropic design with the same number of layers. The +/-45 degree layers are necessary to prevent matrix cracking in the curvilinear layers due to stresses perpendicular to the fibers in those layers. Greater efficiencies are achievable with composite structures than now realized.

Hyer, M. W.↗
NASA NTRS1986

Microwave spectrum and structure of bicyclo /1.1.1/ pentanone and comparison with several theoretical structures

The microwave spectra of five isotopic species of bicyclo (1.1.1) pentanone have been investigated. The rotational constants along with various centrifugal distortion constants for each species have been determined. From the rotational constants, a complete r(s) structure has been determined for the heavy atoms. Analysis of Stark effect measurements has shown the dipole moment to be along the a principal inertial axis with a magnitude of 3.164 (5) D. These results are compared with those obtained by four current theoretical methods: molecular mechanics (MM2), MNDO, and Hartree-Fock ab initio theory with STO-3G and 3-21G basis sets.

Mcrae, Glenn A.↗
NASA NTRS1988

Structural efficiency study of graphite-epoxy aircraft rib structures

Attention is given to the structural efficiencies obtainable with optimally designed graphite/epoxy wing rib panel configurations that are potentially economically manufacturable. Some ribs are commonly used as fuel cell closeout panels, and are accordingly subjected to out-of-plane pressure loads in addition to the in-plane axial compressive and shear loads resulting from the wing loading. The present minimum-weight panel designs satisfy buckling and strength constraints for wing rib panels subjected to a wide range of combined load conditions.

Swanson, Gary D.↗
NASA NTRS1988

Structural efficiency study of composite wing rib structures

A series of short stiffened panel designs which may be applied to a preliminary design assessment of an aircraft wing rib is presented. The computer program PASCO is used as the primary design and analysis tool to assess the structural efficiency and geometry of a tailored corrugated panel, a corrugated panel with a continuous laminate, a hat stiffened panel, a blade stiffened panel, and an unstiffened flat plate. To correct some of the shortcomings in the PASCO analysis when shear is present, a two step iterative process using the computer program VICON is used. The loadings considered include combinations of axial compression, shear, and lateral pressure. The loading ranges considered are broad enough such that the designs presented may be applied to other stiffened panel applications. An assessment is made of laminate variations, increased spacing, and nonoptimum geometric variations, including a beaded panel, on the design of the panels.

Swanson, Gary D.↗
NASA NTRS1989

Research in structures, structural dynamics and materials, 1989

Topics addressed include: composite plates; buckling predictions; missile launch tube modeling; structural/control systems design; optimization of nonlinear R/C frames; error analysis for semi-analytic displacement; crack acoustic emission; and structural dynamics.

Hunter, William F.↗
NASA NTRS1989

Investigation of structural behavior of candidate Space Station structure

Quantitative evaluations of the structural loads, stiffness and deflections of an example Space Station truss due to a variety of influences, including manufacturing tolerances, assembly operations, and operational loading are reported. The example truss is a dual-keel design composed of 5-meter-cube modules. The truss is 21 modules high and 9 modules wide, with a transverse beam 15 modules long. One problem of concern is the amount of mismatch which will be expected when the truss is being erected on orbit. Worst-case thermal loading results in less than 0.5 inch of mismatch. The stiffness of the interface is shown to be less than 100 pounds per inch. Thus, only moderate loads will be required to overcome the mismatch. The problem of manufacturing imperfections is analyzed by the Monte Carlo approach. Deformations and internal loads are obtained for ensembles of 100 example trusses. All analyses are performed on a personal computer. The necessary routines required to supplement commercially available programs are described.

Hedgepeth, John M.↗
NASA NTRS1989

Structural optimization of framed structures using generalized optimality criteria

The application of a generalized optimality criteria to framed structures is presented. The optimality conditions, Lagrangian multipliers, resizing algorithm, and scaling procedures are all represented as a function of the objective and constraint functions along with their respective gradients. The optimization of two plane frames under multiple loading conditions subject to stress, displacement, generalized stiffness, and side constraints is presented. These results are compared to those found by optimizing the frames using a nonlinear mathematical programming technique.

Kolonay, R. M.↗
NASA NTRS1990

Innovative design of composite structures: The use of curvilinear fiber format in composite structure design

The gains in structural efficiency are investigated that can be achieved by aligning the fibers in some or all of the layers in a laminate with the principal stress directions in those layers. The name curvilinear fiber format is given to this idea. The problem studied is a plate with a central circular hole subjected to a uniaxial tensile load. An iteration scheme is used to find the fiber directions at each point in the laminate. Two failure criteria are used to evaluate the tensile load capacity of the plates with a curvilinear format, and for comparison, counterpart plates with a conventional straightline fiber format. The curvilinear designs for improved tensile capacity are then checked for buckling resistance. It is concluded that gains in efficiency can be realized with the curvilinear format.

Hyer, M. W.↗
NASA NTRS1990

Structure and evolution of irradiated accretion disks. I - Static thermal equilibrium structure. II - Dynamical evolution of a thermally unstable torus

The thermal equilibrum structure and dynamical behavior of externally irradiated accretion disks are investigated. For radiative disks only the surface layer is heated, while for convective disks the heat penetrates deeply into the disk. For sufficiently strong radiation and given irradiation flux F(irr), the disk is completely stabilized against thermal instabilities of the sort invoked to explain dwarf novae. For moderately strong irradiation there is still an unstable branch in the thermal equilibrium curve. In typical soft X-ray transients, the disk is unstable against the dwarf-nova type instability. Fixed F(irr) on accretion disk annuli reduces the amplitude and the quiescent times and increases the outburst duration of the resultant light curves. Varying F(irr) in proportion to the mass accretion rate at the disks's inner edge results in light curves with a plateau in the decay from outbursts. In the case when irradiation is suddenly switched on, a temperature inversion results which leads to the formation of an accretion corona.

Tuchman, Y.↗
NASA NTRS1990

Research in Structures, Structural Dynamics and Materials, 1990

The Structural Dynamics and Materials (SDM) Conference was held on April 2 to 4, 1990 in Long Beach, California. This publication is a compilation of presentations of the work-in-progress sessions and does not contain papers from the regular sessions since those papers are published by AIAA in the conference proceedings.

Barthelemy, Jean-Francois M.↗
NASA NTRS1992

Structural optimization of large structural systems by optimality criteria methods

The fundamental concepts of the optimality criteria method of structural optimization are presented. The effect of the separability properties of the objective and constraint functions on the optimality criteria expressions is emphasized. The single constraint case is treated first, followed by the multiple constraint case with a more complex evaluation of the Lagrange multipliers. Examples illustrate the efficiency of the method.

Berke, Laszlo↗
NASA NTRS1991

The electronic structure and second-order nonlinear optical properties of donor-acceptor acetylenes - A detailed investigation of structure-property relationships

A series of donor-acceptor acetylene compounds was synthesized in which systematic changes in both the conjugation length and the donor-acceptor strength were made. The effect of these structural changes on the spectroscopic and electronic properties of the molecules and, ultimately, on the measured second-order molecular hyperpolarizabilities (beta) was investigated. It was found that increases in the donor-acceptor strength resulted in increases in the magnitude of beta. For this class of molecules, the increase is dominated by the energy of the intramolecular charge-transfer transition, while factors such as the ground to excited-state dipole moment change and the transition-moment integral are much less important. Increasing the conjugation length from one to two acetylene linkers did not result in an increase in the value of beta; however, beta increased sharply in going from two acetylenes to three. This increase is attributed to the superposition of several nearly isoenergetic excited states.

Stiegman, A. E.↗