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At least 415 records · Page 23
All sourcesNASA NTRSDOE OSTI
NASA NTRS1986

Static deflection control of flexible beams by piezo-electric actuators

This study deals with the utilization of piezo-electric actuators in controlling the static deformation of flexible beams. An optimum design procedure is presented to enable the selection of the optimal location, thickness and excitation voltage of the piezo-electric actuators in a way that would minimize the deflection of the beam to which these actuators are bonded. Numerical examples are presented to illustrate the application of the developed optimization procedure in minimizing the structural deformation of beams of different materials when subjected to different loading and end conditions using ceramic or polymeric piezo-electric actuators. The results obtained emphasize the importance of the devised rational procedure in designing beam-actuator systems with minimal elastic distortions.

Baz, A. M.↗
NASA NTRS1987

Optimum shape control of flexible beams by piezo-electric actuators

The utilization of piezoelectric actuators in controlling the static deformation and shape of flexible beams is examined. An optimum design procedure is presented to enable the selection of the optimal location, thickness and excitation voltage of the piezoelectric actuators in a way that would minimize the deflection of the beam to which these actuators are bonded. Numerical examples are presented to illustrate the application of the developed optimization procedure in minimizing structural deformation of beams using ceramic and polymeric piezoelectric actuators bonded to the beams with a typical bonding agent. The obtained results emphasize the importance of the devised rational produce in designing beam-actuator systems with minimal elastic distortions.

Baz, A.↗
NASA NTRS1986

The zodiacal background in the IRAS data

The IRAS sky survey yielded a very extensive picture of bright diffuse thermal emission from interplanetary dust grains at wavelengths from 12 to 100 micrometers. These data provide insights into the character, spatial distribution, and perhaps origin of these particles which both confirm and expand upon those gained from previous zodiacal light studies. The zodiacal emission is a major component of the large scale infrared brightness of the sky at all IRAS wavelengths. It must therefore be carefully characterized both to facilitate study of large-angular-scale sources in the Galaxy and beyond using IRAS data, and to permit optimum design of future space infrared instrument.

Hauser, M. G.↗
NASA NTRS1987

Control augmented structural synthesis with transient response constraints

An integrated approach to the optimum design of control augmented structural systems is presented in which structural variables and control variables are changed simultaneously during the design process. Constraints are imposed on peak transient dynamic displacements and accelerations, static displacements, natural frequencies, and control system effort. Side constraints imposed on structural member sizes and control system thresholds and actuator output forces insure the generation of physically meaningful designs. Example problems are presented which bring out the benefits of simultaneous treatment of both the structural design variables and the control design variables.

Manning, R. A.↗
NASA NTRS1987

Structural tailoring of advanced turboprops

A computer program has been developed for the performance of numerical optimizations of highly swept propfan blades by minimizing an objective function that is defined either as direct operating cost or the aeroelastic difference between a blade and its scaled model. Three component analysis categories are employed: an optimization algorithm, approximate analysis procedures for objective function and constraint evaluation, and refined analysis procedures for optimum design validation. The analyses conducted by the program encompass aerodynamic efficiency evaluation, finite element stress and vibration analysis, acoustics, flutter, and forced response life prediction.

Brown, K. W.↗
NASA NTRS1986

A grazing incidence extreme ultraviolet spectrometer for use with a diverging beam

Attention is given to the 100-350 A performance of a grazing incidence spectrometer configuration that accepts a diverging beam for the conduct of moderate resolution spectroscopy. Assuming a focal ratio of 10 for the diverging beam, the first optic of the configuration is an off-axis ellipsoid that is used at grazing incidence to refocus the diverging beam and increase the focal ratio. A detailed study is made of the performance of a plane, straight-groove, variable-line-space grating; the aberrations are evaluated analytically and verified by geometrical ray tracing. System resolution is a function of telescope image quality. An optimum design is found by varying six parameters and maximizing the average resolution over the bandpass. The spectrometer can be located far from the optical axis, and fed by a small grazing incidence pick-off mirror.

Hurwitz, Mark↗
NASA NTRS1986

Thermal and flammability characterization of graphite composites

Thermal, mechanical, and flammability properties of graphite composites fabricated with XU71775/H795, a bismaleimide/vinyl-polystyrylpyridine formulation; H795, a bismaleimide; Cycom 6162, a phenolic; and PSP 6022M, a polystyrylpyridine and two types of graphite reinforcement were evaluated and compared with a composite made with an epoxy resin as a matrix. The measured properties included limiting-oxygen index, smoke evolution, thermal degradation products, total-heat release, heat-release rates, mass loss, flame spread, ignition resistance, thermogravimetric analysis, and selected mechanical properties. It was found that the combination of XU71775/H795 with the graphite tape was the optimum design giving the lowest heat release rate.

Kourtides, D. A.↗
NASA NTRS1988

The development of CFD methods for rotor applications

The optimum design of the advancing helicopter rotor for high-speed forward flight always involves a tradeoff between transonic and stall limitations. However, the preoccupation of the rotor industry was primarily concerned with stall until well into the 1970s. This emphasis on stall resulted from the prevalent use of low-solidity rotors with rather outdated airfoil sections. The use of cambered airfoil sections and higher-solidity rotors substantially reduced stall and revealed the advancing transonic flow to be a more persistent limitation to high-speed rotor performance. Work in this area was spurred not only by operational necessity but also by the development of a tool for the prediction of these flows (the method of computational fluid dynamics). The development of computational fluid dynamics for these rotor problems was a major Army and NASA achievement. This work is now being extended to other rotor flow problems. The developments are outlined.

Caradonna, F. X.↗
NASA NTRS1987

Review of thermal properties of graphite composite materials

Flammability, thermal, and selected mechanical properties of composites fabricated with epoxy and other thermally stable resin matrices are described. Properties which were measured included limiting-oxygen index, smoke evolution, thermal degradation products, total-heat release, heat-release rates, mass loss, flame spread, ignition resistance, thermogravimetric analysis, and selected mechanical properties. The properties of 8 different graphite composite panels fabricated using four different resin matrices and two types of graphite reinforcement are described. The resin matrices included: XU71775/H795, a blend of vinyl polystyryl pyridine and bismaleimide; H795, a bismaleimide; Cycom 6162, a phenolic; and PSP 6022M, a polystyryl pyridine. The graphite fiber used was AS-4 in the form of either tape or fabric. The properties of these composites were compared with epoxy composites. It was determined that the blend of vinyl polystyryl pyridine and bismaleimide (XU71775/H795) with the graphite tape was the optimum design giving the lowest heat release rate.

Kourtides, D. A.↗
NASA NTRS1988

Bismaleimide-vinylpolystyrylpyridine graphite composites

Flammability, thermal, and selected mechanical properties of composites fabricated with epoxy and other thermally stable resin matrices are described. Properties which were measured included limiting-oxygen index, smoke evolution, thermal degradation products, total-heat release, heat-release rates, mass loss, flame spread, ignition resistance, thermogravimetric analysis and selected mechanical properties. This paper describes the properties of eight different graphite composite panels fabricated using four different resin matrices and two types of graphite reinforcement. The resin matrices included: XU71775/H795, a blend of vinylpolystyrylpyridine and bismaleimide; H795, a bismaleimide; Cycom 6162, a phenolic; and PSP 6022M, a polystyrylpyridine. The graphite fiber used was AS-4 in the form of either tape or fabric. The properties of these composites were compared with epoxy composites. It was determined that the blend of vinylpolystyrylpyridine and bismaleimide (XU71775/H795) with the graphite tape was the optimum design giving the lowest heat release rate.

Kourtides, D. A.↗
NASA NTRS1988

Thermal properties of composites with bismaleimide-vinyl poly(styrylpyridine) blends

Thermal properties, flammability, and selected mechanical properties of eight different graphite composite panels fabricated using four different resin matrices and two types of graphite reinforcement were investigated and compared with the properties of an epoxy composite, MXB 7203. The resin matrices included XU71775/H795, a blend of vinyl poly(styrylpyridine) and bismaleimide; H795, a bismaleimide; Cycom 6162, a phenolic; and PSP 6022M, a poly(styrylpyridine). The graphite fiber was AS-4 used in the form of tape or fabric. It was found that the XU71775/H795 blend with the graphite tape was the optimum design giving the lowest heat release rate, while the control epoxy panel exhibited the highest total heat release and heat release rates, highest smoke and CO evolution, highest mass losses, and lowest oxygen index of all the composites tested.

Kourtides, D. A.↗
NASA NTRS1988

Infrared observations of planetary atmospheres

The goal of this research in to obtain infrared data on planetary atmospheres which provide information on several aspects of structure and composition. Observations include direct mission real-time support as well as baseline monitoring preceding mission encounters. Besides providing a broader information context for spacecraft experiment data analysis, observations will provide the quantitative data base required for designing optimum remote sensing sequences and evaluating competing science priorities. In the past year, thermal images of Jupiter and Saturn were made near their oppositions in order to monitor long-term changes in their atmospheres. Infrared images of the Jovian polar stratospheric hot spots were made with IUE observations of auroral emissions. An exploratory 5-micrometer spectrum of Uranus was reduced and accepted for publication. An analysis of time-variability of temperature and cloud properties of the Jovian atomsphere was made. Development of geometric reduction programs for imaging data was initiated for the sun workstation. Near-infrared imaging observations of Jupiter were reduced and a preliminary analysis of cloud properties made. The first images of the full disk of Jupiter with a near-infrared array camera were acquired. Narrow-band (10/cm) images of Jupiter and Saturn were obtained with acousto-optical filters.

Orton, Glenn S.↗
NASA NTRS1989

Structural optimization of rotor blades with straight and swept tips subject to aeroelastic constraints

The main conclusions obtained in the present study are summarized. Their application to the structural optimization of a helicopter blade should be limited by the assumptions used in obtaining the numerical results presented here. The optimum design procedure described here is very efficient, and can produce improved designs with a very limited number of precise analyses. The method of constructing the approximate problem is such that previously conducted aeroelastic analyses can be reused in a new optimization problem. For example, if an optimization study is preceded by a parametric study in which the effect of various combinations of blade design parameters is examined, all the aeroelastic analyses performed for the parametric study can be reutilized in the optimization study. This is not possible when the approximate problem is built from Taylor series expansions. The results of the optimization are quite sensitive to the aeroelastic stability margins required of the blade. In the optimization of case 2, changing the aeroelastic stability constraints from simply requiring that the blade be stable in hover, to requiring that the stability margins be maintained during the course of the optimization, reduced the gains in n/rev vibration levels by more than 50 percent. The introduction of tip sweep can reduce the n/rev vertical hub shears beyond the level that can be obtained by just modifying the mass and stiffness distributions of the blade.

Friedmann, Peretz P.↗
NASA NTRS1990

Screening actuator locations for static shape control

Correction of shape distortion due to zero-mean normally distributed errors in structural sizes which are random variables is examined. A bound on the maximum improvement in the expected value of the root-mean-square shape error is obtained. The shape correction associated with the optimal actuators is also characterized. An actuator effectiveness index is developed and shown to be helpful in screening actuator locations in the structure. The results are specialized to a simple form for truss structures composed of nominally identical members. The bound and effectiveness index are tested on a 55-m radiometer antenna truss structure. It is found that previously obtained results for optimum actuators had a performance close to the bound obtained here. Furthermore, the actuators associated with the optimum design are shown to have high effectiveness indices. Since only a small fraction of truss elements tend to have high effectiveness indices, the proposed screening procedure can greatly reduce the number of truss members that need to be considered as actuator sites.

Haftka, Raphael T.↗
NASA NTRS1991

Key factors limiting the open circuit voltage of n(+)pp(+) indium phosphide solar cells

Solar cells made from gallium arsenide (GaAs), with a room temperature bandgap of E(sub g) = 1.43 eV have exhibited the best measured open circuit voltage (V sub OC) of 1.05 V at 1 AMO, 25 C. The material InP is in many ways similar to GaAs. A simple calculation comparing InP to GaAs then shows that solar cells made from InP, with E(sub g) = 1.35 at 300 K, should exhibit the best measured (V sub OC) of approximately 950 mV at 1 AMO, 300 K. However, to date, the best measured V(sub OC) for InP solar cells made by any fabrication method is 899 mV at AM1.5, 25 C which would translate to 912 mV at 1 AMO, 25 C. The V(sub OC) of an n(+)pp(+) InP solar cell is governed by several factors. Of these, some factors, such as the thickness and doping of the emitter and base regions, are easily controlled and can be adjusted to desired values dictated by a good performance optimizing model. Such factors were not considered. There are other factors which also govern V(sub OC), and their values are not so easily controlled. The primary ones among these are (1) the indirect or Hall-Shockley-Read lifetimes in the various regions of the cell, (2) the low-doping intrinsic carrier concentration n(sub i) of the InP material, (3) the heavy doping factors in the emitter and BSF regions, and (4) the front surface recombination velocity S(sub F). The influence of these latter factors on the V(sub OC) of the n(+)pp(+) InP solar cell and the results were used to produce a near-optimum design of the n(+)pp(+) InP solar cell.

Goradia, Chandra↗
NASA NTRS1991

Flame-retardant composite materials

The properties of eight different graphite composite panels fabricated using four different resin matrices and two types of graphite reinforcement are described. The resin matrices included: VPSP/BMI, a blend of vinylpolystyryl pyridine and bismaleimide; BMI, a bismaleimide; and phenolic and PSP, a polystyryl pyridine. The graphite fiber used was AS-4 in the form of either tape or fabric. The properties of these composites were compared with epoxy composites. It was determined that VPSP/BMI with the graphite tape was the optimum design giving the lowest heat release rate.

Kourtides, Demetrius A.↗
NASA NTRS1990

Key factors limiting the open circuit voltage of n(+)pp(+) indium phosphide solar cells

Solar cells made from gallium arsenide (Gaas), with a room temperature bandgap of E(sub g) = 1.43 eV have exhibited the best measured open circuit voltage (V sub oc) of 1.05 V at 1 AM0, 25 C. The material InP is in many ways similar to GaAs. A simple calculation comparing InP to GaAs then shows that solar cells made from InP, with E(sub g) = 1.35 at 300 K, should exhibit the best measured V sub oc of approximately 950 mV at 1 AM0, 300 K. However, to date, the best measured V sub oc for InP solar cells made by any fabrication method is 899 mV at AM1.5, 25 C which would translate to 912 mV at 1 AM0, 25 C. The V sub oc of an n(+)pp(+) InP solar cell is governed by several factors. Of these, some factors, such as the thickness and doping of the emitter and base regions, are easily controlled and can be adjusted to desired values dictated by a good performance optimizing model. Such factors were not considered. There are other factors which also govern V sub oc, and their values are not so easily controlled. The primary ones among these are (1) the indirect or Hall-Shockley-Read lifetimes in the various regions of the cell, (2) the low-doping intrinsic carrier concentration n(sub i) of the InP material, (3) the heavy doping factors in the emitter and BSF regions, and (4) the front surface recombination velocity S(sub F). The influence of these latter factors on the V sub oc of the n(+)pp(+) InP solar cell and the results were used to produce a near-optimum design of the n(+)pp(+) InP solar cell.

Goradia, Chandra↗
NASA NTRS1992

Paraboloidal Reflector With Movable Subreflector

Subreflector of 34-m-diameter paraboloidal radio-antenna reflector tilted and translated to compensate for gravitational distortions of antenna structure. Position and orientation of subreflector adjusted to focus with respect to phase center of radio-frequency feed horn and primary focus of computed paraboloid best fitting gravitationally distorted main paraboloidal reflector. Restores gain lost when antenna aimed at angle other than design optimum elevation.

Katow, Masakazu S.↗