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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 1,567 records · Page 87
All sourcesNASA NTRSDOE OSTI
NASA NTRS1983

Analytical prediction of aerothermal environment in a wing-elevon cove

The fluid/thermal environment in the cove between the wing and elevon surfaces was a concern throughout the design and initial operational phases of the space shuttle. Experimenal and analytical investigations provided some understanding of the environmental in the wing-elevon cove. An incompressible finite element analysis of flow through straight parallel walls and curved parallel walls to determine the effects of cove geomtry on the fluid/thermal environment is described. Results from this analysis agree qualitatively with experimental data. The centerline gas temperatures and cold wall heating rates are virtually identical for the two cases indicating that the slight curvature has little effect on the overall thermal environment.

Bey, K. S.↗
NASA NTRS1983

Development of a simplified procedure for rocket engine thrust chamber life prediction with creep

An analytical method for predicting engine thrust chamber life is developed. The method accounts for high pressure differentials and time-dependent creep effects both of which are significant in limiting the useful life of the shuttle main engine thrust chamber. The hot-gas-wall ligaments connecting adjacent cooling channels ribs and separating the coolant flow from the combustion gas are subjected to a high pressure induced primary stress superimposed on an alternating cyclic thermal strain field. The pressure load combined with strain-controlled cycling produces creep ratcheting and consequent bulging and thinning of these ligaments. This mechanism of creep-enhanced ratcheting is analyzed for determining the hot-gas-wall deformation and accumulated strain. Results are confirmed by inelastic finite element analysis. Fatigue and creep rupture damage as well as plastic tensile instability are evaluated as potential failure modes. It is demonstrated for the NARloy Z cases analyzed that when pressure differentials across the ligament are high, creep rupture damage is often the primary failure mode for the cycle times considered.

Badlani, M. L.↗
NASA NTRS1983

Impact resistance of fiber composites: Energy absorbing mechanisms and environmental effects

Energy absorbing mechanisms were identified by several approaches. The energy absorbing mechanisms considered are those in unidirectional composite beams subjected to impact. The approaches used include: mechanic models, statistical models, transient finite element analysis, and simple beam theory. Predicted results are correlated with experimental data from Charpy impact tests. The environmental effects on impact resistance are evaluated. Working definitions for energy absorbing and energy releasing mechanisms are proposed and a dynamic fracture progression is outlined. Possible generalizations to angle-plied laminates are described.

Chamis, C. C.↗
NASA NTRS1983

Interply layer degradation effects on composite structural response

Recent research activities at NASA Lewis Research Center to computationally evaluate the effects of interply layer progressive weakening (degradation) on the structural response of a composite beam are summarized. The structural responses of interest include: (1) bending, (2) buckling, (3) free vibrations, (4) periodic excitation, and (5) impact. Finite element analysis was used for the computational evaluations. The interply layer degradation effects on the various structural responses were determined and assessed as a function of the interply layer modulus varying from 1 million psi down to 1000 psi and even lower for some limiting cases. The results obtained show that the interply layer degradation has generally negligible effects on composite structural response and, therefore, structural integrity, unless the interply layer modulus degrades to about 10,000 psi or less.

Chamis, C. C.↗
NASA NTRS1983

Impact of new computing systems on finite element computations

Recent advances in computer technology that are likely to impact finite element computations are reviewed. The characteristics of supersystems, highly parallel systems, and small systems (mini and microcomputers) are summarized. The interrelations of numerical algorithms and software with parallel architectures are discussed. A scenario is presented for future hardware/software environment and finite element systems. A number of research areas which have high potential for improving the effectiveness of finite element analysis in the new environment are identified.

Noor, A. K.↗
NASA NTRS1984

Development and characterization of orthotropic-birefringent materials

Materials were selected and fabrication procedures developed for orthotropic birefringent materials. An epoxy resin (Maraset 658/558 system) was selected as the matrix material. Fibers obtained from style 3733 glass cloth and type 1062 glass roving were used as reinforcement. Two different fabrication procedures were used. In the first one, layers of unidirectional fibers removed from the glass cloth were stacked, impregnated with resin, bagged and cured in the autoclave at an elevated temperature. In the second procedure, the glass roving was drywound over metal frames, impregnated with resin and cured at room temperature under pressure and vacuum in an autoclave. Unidirectional, angle-ply and quasi-isotropic laminates of two thicknesses and with embedded flaws were fabricated. The matrix and the unidirectional glass/epoxy material were fully characterized. The density, fiber volume ratio, mechanical, and optical properties were determined. The fiber volume ratio was over 0.50. Birefringent properties were in good agreement with predictions based on a stress proportioning concept and also, with one exception, with properties predicted by a finite element analysis. Previously announced in STAR as N81-26183

Daniel, I. M.↗
NASA NTRS1984

Initial experience with distributing structural calculations among computers operating in parallel

An existing program is currently being adapted to perform finite element analysis by distributing substructures over a network of four Apple IIe microcomputers connected to a shared disk. In this network, one microcomputer controls the entire process while the others perform the analysis on each substructure in parallel. This substructure analysis is used in an iterative, fully stressed, structural resizing procedure. This procedure allows experimentatation with resizing in which all analyses are not completed during a single iteration. This research gives some insight on how to configure multidiscriplinary analysis and optimization procedures for decomposable engineering systems using either high performance engineering workstations or a parallel processor supercomputer. In addition, the operational experience gained facilitates the implementation of analysis programs on these new computers when they become available in an engineering environment.

Rogers, J. L., Jr.↗
NASA NTRS1984

Single-drop impact damage prediction for low density, coated ceramic materials

A technique utilizing finite element analysis, liquid impact kinematics, and momentum theory is described and compared to single-drop impact test data performed on various configurations of coated ceramic material. The method correlates well with test data and is useful in predicting the single-drop impact damage velocity threshold for low-density, coated ceramic materials.

Mustelier, D.↗
NASA NTRS1984

Analytical and experimental investigation of rubbing interaction in labyrinth seals for a liquid hydrogen fuel pump

Cracking of the titanium knife edges on the labyrinth seals of the liquid hydrogen fuel pump in the Space Shuttle main engine is considered. Finite element analysis of the thermal response of the knife edge in sliding contact with the wear ring surface shows that interfacial temperatures can be quite high and they are significantly influenced by the thermal conductivity of the surfaces in rubbing contact. Thermal shock experiments on a test specimen similar to the knife edge geometry demonstrate that cracking of the titanium alloy is possible in a situation involving repeated thermal cycles over a wide temperature range, as might be realized during a rub in the liquid hydrogen fuel pump. High-speed rub interaction tests were conducted using a representative knife edge and seal geometry over a broad range of interaction rates and alternate materials were experimentally evaluated. Plasma-sprayed aluminum-graphite was found to be significantly better than presently used aluminum alloy seals from the standpoint of rub performance. Ion nitriding the titanium alloy knife-edges also improved rub performance compared to the untreated baseline.

Dolan, F. X.↗
NASA NTRS1985

An optimization study to minimize surface distortions of a hoop-column antenna

An automated procedure to lessen the tedium of manual approach currently used to minimize surface distortions in a hoop/column antenna is studied. Three fundamental elements are used for the study: (1) The finite element analysis program is used to calculate the antenna surface distortions due to externally applied loads; (2) a general purpose optimization program is used to determine the set of control cable tensions which minimize the antenna surface distortions; and (3) another program is used to calculate the best fit parabola passing through a distorted antenna shape and to calculate the RMS distortion error. The interim results of this feasibility study are given.

Wrenn, G. A.↗
NASA NTRS1985

On the Interconnection of Incompatible Solid Finite Element Meshes Using Multipoint Constraints

Incompatible meshes, i.e., meshes that physically must have a common boundary, but do not necessarily have coincident grid points, can arise in the course of a finite element analysis. For example, two substructures may have been developed at different times for different purposes and it becomes necessary to interconnect the two models. A technique that uses only multipoint constraints, i.e., MPC cards (or MPCS cards in substructuring), is presented. Since the method uses only MPC's, the procedure may apply at any stage in an analysis; no prior planning or special data is necessary.

Fox, G. L.↗
NASA NTRS1985

Antenna pointing of large flexible telecommunications spacecraft

Attitude control problems for large flexible telecommunications spacecraft were investigated. A typical S/C configuration is described and modeled by modal data derived from a finite element analysis. The effect of structural flexibility on radio-frequency sensor is analyzed. Model reduction using modal gain considerations is applied. Two control concepts are investigated: separate central body and antenna pointing control using direct feedback laws, centralized control using modal observer and optimal control. Performances of each concept and the algorithm implementation are assessed.

Govin, B.↗
NASA NTRS1984

Edge-defined film-fed growth of thin silicon sheets

Finite element analysis was used on two length scales to understand crystal growth of thin silicon sheets. Thermal-capillary models of entire ribbon growth systems were developed. Microscopic modeling of morphological structure of melt/solid interfaces beyond the point of linear instability was carried out. The application to silicon system is discussed.

Ettouney, H. M.↗
NASA NTRS1984

Interply layer degradation effects on composite structural response

Recent research activities at NASA Lewis Research Center to computationally evaluate the effects of interply layer progressive weakening (degradation) on the structural response of a composite beam are summarized. The structural responses of interest include: (1) bending, (2) buckling, (3) free vibrations, (4) periodic excitation, and (5) impact. Finite element analysis was used for the computational evaluations. The interply layer degradation effects on the various structural responses were determined and assessed as a function of the interply layer modulus varying from 1 million psi down to 1000 psi and even lower for some limiting cases. The results obtained show that the interply layer degradation has generally negligible effectss on composite structural response and, therefore, structural integrity, unless the interply layer modulus degrades to about 10,000 psi or less.

Chamis, C. C.↗
NASA NTRS1984

A mirror mount for cryogenic environments

The finite element method was used to study the effect of mount-induced aberrations on the optical surface of a lightweight double arch mirror subjected to cryogenic temperatures. The mount design was controlled by the requirements imposed on the optical surface quality and stress levels. The finite element analysis was used to define the feasible range of mount parameters and the selection of a design within the feasible region. The final design consisted of three spring-loaded Invar T-clamps that uniquely define the location of the mirror, three radially compliant parallel spring guides that remove the effect of radial contraction of structure in cryogenic temperatures, and a flexible baseplate that was used to reduce the effect of temperature-induced baseplate tilt errors. The experimental results from the application of this system to an existing 20-inch fused silica double arch mirror are shown, and possible improvements in system performance are discussed.

Iraninejad, B.↗
NASA NTRS1985

Postbuckling behavior of selected curved stiffened graphite-epoxy panels loaded in axial compression

Results of an experimental and analytical study of the postbuckling behavior of selected curved stiffened graphite-epoxy panels loaded in axial compression are presented. The postbuckling response and failure characteristics of the panels are described. Each panel had four equally-spaced I-shaped stiffeners and 16-ply quasi-isotropic skins. Panels with three different stiffener spacings were tested. Failure of all panels initiated in a skin-stiffener interface region. Analytical results from a nonlinear general shell finite element analysis computer code correlate well with typical postbuckling test results up to failure. The analytical modeling detail necessary to predict accurately the response of the panel is described. Measured initial geometric imperfections were included in the postbuckling analysis.

Knight, N. F., Jr.↗
NASA NTRS1985

A design technique for determining actuator gains in spacecraft vibration control

A design procedure is described which determines the gains of a diagonal damping matrix to control the vibrations of a flexible structure with application to orbiting spacecraft. The procedure is based on minimizing the energy dissipated by control actuators using nonlinear mathematical programming. Each damping gain is assumed to be an active viscous damper and the design process is formulated so that the force or torque output of the actuator does not exceed a specified value. The response of the structure at some specified time after the termination of the disturbance is constrained to be less than some prescribed value based upon spacecraft mission performance requirements. A grillage example is used to demonstrate the design process for determining gains for two representative cases. Resulting designs are verified by a finite element analysis of the structure augmented by the control actuators.

Horner, G. C.↗