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At least 127 records · Page 7

A continuum deformation theory for metal-matrix composites at high temperature

A continuum theory is presented for representing the high temperature, time dependent, hereditary deformation behavior of metallic composites that can be idealized as pseudohomogeneous continua with locally definable directional characteristics. Homogenization of textured materials (molecular, granular, fibrous) and applicability of continuum mechanics in structural applications depends on characteristic body dimensions, the severity of gradients (stress, temperature, etc.) in the structure and the relative size of the internal structure (cell size) of the material. The point of view taken here is that the composite is a material in its own right, with its own properties that can be measured and specified for the composite as a whole.

Robinson, D. N.↗

Use of optimization to predict the effect of selected parameters on commuter aircraft performance

The relationships between field length and cruise speed and aircraft direct operating cost were determined. A gradient optimizing computer program was developed to minimize direct operating cost (DOC) as a function of airplane geometry. In this way, the best airplane operating under one set of constraints can be compared with the best operating under another. A constant 30-passenger fuselage and rubberized engines based on the General Electric CT-7 were used as a baseline. All aircraft had to have a 600 nautical mile maximum range and were designed to FAR part 25 structural integrity and climb gradient regulations. Direct operating cost was minimized for a typical design mission of 150 nautical miles. For purposes of C sub L sub max calculation, all aircraft had double-slotted flaps but with no Fowler action.

Wells, V. L.↗

Formation of the lamellar structure in Group IA and IIID iron meteorites

Analytical EM, light microscopy, and electron microprobe analysis are used to study the lamellar plessite structure of Group IA and IIID iron meteorites. The alpha lamellae in IIID structures contained a compositional gradient from 6.1 + or - 0.7 wt pct Ni at the center of the alpha lamellae to 3.6 + or - 0.5 wt pct at the alpha/gamma interface. For the Group IA irons, compositions of 4 wt pct Ni in alpha and about 48 wt pct Ni in gamma are found. Convergent beam electron diffraction was used to characterize the orientation relations at the alpha/gamma interface in the lamellar regions of both Group IA and IIID. The phase transformations responsible for the observed lamellar structure in the IA and IIID chemical groups were also investigated.

Kowalik, J. A.↗

Development of an Additively Manufactured Subscale Secondary Sealed Container for the NASA FROSTE Project

This presentation details the development of an additively manufactured (AM) subscale test article for the secondary sealed container (SSC) as part of the NASA FROSTE project. FROSTE is focused on the collection of regolith samples from shadowed regions of the Moon and the preservation of those samples at cryogenic temperatures for return to Earth. Our team was integrated into the FROSTE program to leverage innovative design approaches and additive manufacturing capabilities in support of a scalable development strategy, where the subscale configuration serves as the development path toward a full-scale SSC. Scalmalloy was selected as the primary material for all AM components due to its favorable strength-to-weight ratio, thermal conductivity, and demonstrated performance in aerospace applications. Its aluminum-based composition supports robust mechanical behavior at cryogenic temperatures while enabling efficient heat transfer and control of thermal gradients within the containment system. The SSC architecture consists of an outer container assembly that houses a phase change material (PCM) tank, which in turn contains primary containers holding the regolith. Thermal management relies on controlled conductive and radiative heat transfer, including a thermal connection assembly that interfaces the PCM tank to an external cryocooler via a thermal strap, and IMLI surrounding the PCM tank to inhibit radiative heat transfer. The outer container assembly incorporates sealing interfaces, thermal connection ports, and I/O feedthroughs, with PTFE spring seals used at critical interfaces to maintain containment integrity. The PCM tank is manufactured as a single monolithic Scalmalloy component and incorporates an integral lattice structure to minimize thermal gradients, internal channels for thermocouple routing, and interface features for thermal connection assembly integration. The tank is centrally suspended within the outer container using support rings, with G10 insulating components employed to inhibit thermal leaks. This work describes the design methodology, AM approach, and key considerations used to inform the design.

regolith↗

Parallel Aeroelastic Analysis Using ENSAERO and NASTRAN

A high fidelity parallel static structural analysis capability is created and interfaced to the multidisciplinary analysis package ENSAERO-MPI of Ames Research Center. This new module replaced ENSAERO's lower fidelity simple finite element and modal modules. Full aircraft structures may be more accurately modeled using the new finite element capability. Parallel computation is performed by breaking the full structure into multiple substructures. This approach is conceptually similar to ENSAERO's multi-zonal fluid analysis capability. The new substructure code is used to solve the structural finite element equations for each substructure in parallel. NASTRAN/COSMIC is utilized as a front end for this code. Its full library of elements can be used to create an accurate and realistic aircraft mode. It is used to create the stiffness matrices for each sub-structure. The new parallel code then uses an iterative preconditioned conjugate gradient method to solve the global structural equations for the sub-structure boundary nodes. Results are presented for a wing-body configuration.

Eldred, Lloyd B.↗

Multifluids description of dynamics of upper atmosphere

A multifluids model to investigate ionospheric dynamics was established on kinetic theory. Its resultant equations are used to examine the following dynamic problems in the gamma region of 80-2000 Km of the ionosphere: (1) propagation of acoustic modes in the 500-2,000 Km of the ionosphere (two fluid model); (2) the relation between the cross field plasma drift instabilities and type I and type II ionospheric irregularities; and (3) time dependent neutral wind structure and horizontal pressure gradient.

Wu, S. T.↗

Cross correlation between cosmic-ray fluctuations and interplanetary magnetic-field fluctuations

Study of the cross-correlation between cosmic-ray intensity fluctuations and the interplanetary magnetic field, using the low-frequency limit of the theory of the interplanetary scintillations of cosmic rays. Cross-spectral analysis of the flux of the Alert neutron monitor and simultaneous values of the interplanetary magnetic field components are presented which support the theory. A model of cosmic-ray fluctuations is described, with effects of gradients and interplanetary sector structure dominating for very low frequencies (less than or about equal to .000005 Hz) and magnetic-field induced interplanetary scintillations of cosmic rays dominating for higher frequencies.

Jokipii, J. R.↗

Space qualification of optical instruments using the NASA Long-Duration Exposure Facility

The NASA Long-Duration Exposure Facility (LDEF), designed for the in situ testing of optical instrumentation in the space environment is described. The LDEF is basically a reusable structure which is three-axis gravity-gradient stabilized when flying free in space. The structure weighs about 8,000 lbs. and accommodates experiment trays weighing about 10,000 lbs. A vacuum exposure control canister is being designed for controlled exposure experiments. The LDEF will have an experiment power and data system and a shuttle bay environmental measurements system is being designed for measuring parameters such as acoustics, vibration, acceleration. The induced environment contamination monitor will evaluate the contamination levels of shuttle payloads. Experiments currently under development include the evaluation of active optical components and the study of fiber optic data transmission.

Clark, L. G.↗

Convection and segregation in directional solidification of dilute and non-dilute binary alloys - Effects of ampoule and furnace design

A Petrov-Galerkin/finite-element method is used to analyze the effect of furnace configuration and ampoule design on the temperature field, the convection in the melt, the shape of the melt-solid interface, and the segregation of solute in the crystal, in the directional solidification of several dilute and nondilute binary semiconductor alloys. The vertical Bridgman-Stockbarger system leads to a two-cell flow structure, and the constant gradient furnace has only a single cell near the interface. Radial temperature gradients interact with the solute field to cause the previously predicted sideways diffusive instability, and addition of a solute that is less dense than the bulk melt and that is incorporated upon solidification decreases the intensity of the flow near the interface by increasing the melt density there. The present results have application to understanding of the effects on solute segregation of microgavity solidification and of applied magnetic fields.

Adornato, Peter M.↗

Conserved variable analysis of the convective boundary layer thermodynamic structure over the tropical oceans

An analysis of FGGE dropwindsonde data using conserved thermodynamic variables shows mixing line structures for the convective boundary layer over the equatorial Pacific. Deeper boundary layers show a double structure. Reversals of the gradients of mixing ratio and equivalent potential temperature above the boundary-layer top are present in all the averages and suggest that the origin of the air sinking into the boundary layer needs further study.

Betts, Alan K.↗

A test-bed for space interferometry: Space Platform Interferometer (SPI)

The Space Platform Interferometer (SPI), a 20-m two-mirror Michelson interferometer, which can reach magnitude 14 at UV and visible wavelengths, is described. The SPI is attached to a platform serviced from the space station. In addition to its ability to produce unique science in the UV, SPI is intended to demonstrate the feasibility of larger projects in the field. Dynamical behavior of the structure in the gravity gradient environment and fringe stabilization at low photon rate are studied by picking up an adjacent bin (in the near IR) on the same object and using it to track the white light fringe in a separate differential interferometer. The same subsystem also corrects for tilt. Active control of critical parameters ensures optical rigidity. Performances are evaluated in low orbit.

Faucherre, M.↗

Recent experiences using finite-element-based structural optimization

Structural optimization has been available to the structural analysis community as a tool for many years. The popular use of displacement method finite-element techniques to analyze linearly elastic structures has resulted in an ability to calculate the weight and constraint gradients inexpensively for numerical optimization of structures. Here, recent experiences in the investigation and use of structural optimization are discussed. In particular, experience with the commercially available ADS/NASOPT code is addressed. An overview of the ADS/NASOPT procedure and how it was implemented is given. Two example problems are also discussed.

Paul, B. K.↗

Ozone budgets from the Dynamics and Chemistry of Marine Stratocumulus experiment

Measurements from the Dynamics and Chemistry of marine Stratocumulus experiment have been used to study components of the regional ozone budget. The surface destruction rate is determined by eddy correlation of ozone and vertical velocity measured by a low-flying aircraft. Significant variability is found in the measured surface resistance; it is partially correlated with friction velocity but appears to have other controlling influences as well. The mean resistance is 4190 s/m which is higher (slower destruction) than most previous estimates for seawater. Flux and mean measurements throughout the marine boundary layer are used to estimate the net rate of in situ photochemical production/destruction of ozone. Averaged over the flights, ozone concentration is found to be near steady state, and a net of photochemical destruction of 0.02-0.07 ng/cu m per sec is diagnosed. This is an important confirmation of photochemical model results for the remote marine boundary layer. Ozone vertical distributions above the boundary layer show a strongly layered structure with very sharp gradients. These distributions are possibly related to the stratospheric ozone source.

Kawa, S. R.↗

Three-dimensional aerodynamics of an annular airfoil cascade including loading effects

A series of experiments are described which investigate and quantify the effect of loading on the three-dimensional flow through a subsonic annular cascade of cambered airfoils. At two levels of loading, detailed data quantify the cascade inlet velocity, the intrapassage flow field, the airfoil surface pressure distributions, the exit flow field, and the total pressure loss distributions. Aerodynamic loading is shown to strengthen the radial pressure gradient, the passage vortex structure, the vortex-endwall boundary layer interactions, and the losses.

Fleeter, S.↗

Thermoelastic vibration test techniques

The structural integrity of proposed high speed aircraft can be seriously affected by the extremely high surface temperatures and large temperature gradients throughout the vehicle's structure. Variations in the structure's elastic characteristics as a result of thermal effects can be observed by changes in vibration frequency, damping, and mode shape. Analysis codes that predict these changes must be correlated and verified with experimental data. The experimental modal test techniques and procedures used to conduct uniform, nonuniform, and transient thermoelastic vibration tests are presented. Experimental setup and elevated temperature instrumentation considerations are also discussed. Modal data for a 12 by 50 inch aluminum plate heated to a temperature of 475 F are presented. These data show the effect of heat on the plate's modal characteristics. The results indicated that frequency decreased, damping increased, and mode shape remained unchanged as the temperature of the plate was increased.

Kehoe, Michael W.↗

Determination of the effects of heating on modal characteristics of an aluminum plate with application to hypersonic vehicles

The structural integrity of proposed high speed aircraft can be seriously affected by the extremely high surface temperatures and large temperature gradients throughout the vehicle's structure. Variations in the structure's elastic characteristics as a result of thermal effects can be seen by changes in vibration characteristics. Analysis codes that predict these changes must be correlated and verified with experimental data. Analytical and experimental modal test results are given from uniform, nonuniform, and transient thermoelastic vibration tests of a 12 x 50 x 0.19 aluminum plate. The data show the effect of heat on the modal characteristics of the plate. The results showed that frequencies decreased, damping increased, and mode shapes remained unchanged as the temperature of the plate increased. Analytical predictions provided good correlation with experimental results.

Snyder, H. Todd↗

Voyager radio occultation by the Uranian rings: Structure, dynamics, and particle sizes

Diffraction of Voyager 2's 3.6 and 13 cm wavelength microwaves by the Uranian rings is removed through an inverse Fresnel transform filtering procedure that accommodates the significant eccentricity of the rings. Resulting 50 m resolution profiles at two observation longitudes: (1) reveal remarkably detailed and longitudinally varying structure, (2) provide eccentricity gradient profiles of Rings alpha, beta, and epsilon which bring into question current theoretical models for observed rigid precession, and (3) suggest that two possible unseen satellites may confine some of the very sharp edges observed via resonant interactions.

Gresh, Donna Leigh↗

The structure of a passive scalar field with a uniform mean gradient in rapidly sheared homogeneous turbulent flow

The effect of an arbitrarily oriented mean passive scalar gradient on one-point passive scalar statistics is studied in homogeneous turbulent shear flow in the limit of rapid shearing. By neglecting the nonlinear inertial transfer to small scales an analytical solution for individual Fourier modes is obtained for the case of unity Prandtl number. This solution is used to compute the development of one-point statistics for the velocity and scalar fields in the inviscid limit. Comparisons to direct numerical simulations of the full nonlinear equations for the same flow show that, in addition to describing the early time response to the imposed shear, the linear solution gives reasonable estimates of several correlation coefficients for the developed shear flow.

Rogers, Michael M.↗