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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 469 records · Page 26
All sourcesNASA NTRSDOE OSTI
NASA NTRS1984

Natural large-scale structures in the axisymmetric mixing layer

The present study is concerned with the optimization of conditional sampling techniques for eduction of naturally occurring large-scale structures in an axisymmetric mixing layer, and a comparison of the natural structure with that induced by means of controlled excitation. Questions regarding the sensitivity of the educed structure to the excitation amplitude are also explored. Aspects regarding the eduction with the high-speed-side reference signal are considered, taking into account structure identification, the smearing effect and a comparison with the structure under excitation, the effects of the threshold level, and the effect of a trigger-level window. Attention is given to structure characteristics and their dependence on Reynolds number and initial condition.

Zaman, K. B. M. Q.↗
NASA NTRS1984

Interferometer applications of VHF radars, part 3.6A

Using a spaced antenna setup of a VHF radar, the spatial distribution of amplitudes and phases of the radar echoes from the troposphere, stratosphere and mesosphere can be measured. Combining in a suitable analysis procedure the complex digital samples from the different receiving antennas is consistent with the radar interferometer method. In addition to the well-known parameters measured with the commonly applied Doppler and drifts methods, i.e., reflectivity and mean fluctuation velocity, the interferometer technique allows to measure the regular spectrum of the returns. This technique, which was first applied with the spaced antenna system of the SOUSY-VHF-Radar in W. Germany, as well as some first examples of results are described here. These comprise the measurements of the horizontal and vertical velocities of the mean flow as well as of turbulence structures, the aspect sensitivity and the tilt of layers from which the baroclinicity can be estimated. Particularly, results of interferometer measurements of the vertical and horizontal phase velocities and wavelengths of gravity waves in the stratosphere are displayed. The latter results are also discussed in terms of the generation and propagation of these waves.

Rottger, J.↗
NASA NTRS1985

Chemistry of MOS-LSI radiation hardening

The objective of this task was to obtain chemical information on MOS test samples. Toward this end, high resolution X-ray photoemission spectroscopy (XPS) has been the primary techniques used to characterize the chemistry and structure of the SiO2/Si interface for a variety of MOS structures with differing degrees of susceptibility to damage by ionizing radiation. The major accomplishments of this program are: (1) the identification of a structurally distinct region of SiO2 in the near-interfacial region of thermal SiO2 on Si; (2) the identification in the near-interfacial region of SiO2 structural differences between radiation hard and soft gate oxides; (3) the direct observation of radiation-induced damage sites in thermal SiO2 with XPS using in situ electron stress; (4) the correlation of suboxide state distributions at the SiO2/Si interface with processing parameters and radiation susceptibility; (5) the development of a chemical mechanism for radiation-induced interface state generation in SiO2/Si structures; and (6) the development benign chemical profiling techniques which permit the investigation of oxide/semiconductor structures using surface sensitive electron spectroscopic techniques.

Grunthaner, P.↗
NASA NTRS1987

Sensitivity of overall vehicle stiffness to local joint stiffness

How overall vehicle stiffness is affected by local joint stiffness is discussed. By using the principle of virtual work and the minimum strain energy theorem, a closed form expression for the sensitivity coefficient was derived. The insensitivity of the vehicle stiffness to a particular joint, when its stiffness exceeds a certain value (or threshold value), was proven mathematically. In order to investigate the sensitivity of the structure to the joint stiffness, a so-called stick model was created, and the modeling technique is briefly described. Some data on joint stiffness of tested vehicles are also presented.

Chon, Choon T.↗
NASA NTRS1987

On computing eigensolution sensitivity data using free vibration solutions

A simplified method of computing eigensolution sensitivity derivatives in structural dynamics is developed. It is shown that if the elements of stiffness and mass matrices associated with a design variable are homogeneous functions of that design variable, then eigenvalue derivatives can be computed from element strain and kinetic energies. Furthermore, if cross-mode energies are known, eigensolution derivatives of modified systems can be computed approximately using assume mode reanalysis formulation. A ten bar truss example is used to illustrate the present formulations.

Wang, B. P.↗
NASA NTRS1987

Dual keel space station control/structures interaction study

A study was made to determine the influence of truss bay size on the performance of the space station control system. The objective was to determine if any control problems existed during reboost and to assess the level of potential control/structures interaction during operation of the control moment gyros used for vertical stabilization. The models analyzed were detailed finite-element representations of the 5 meter and 9 foot growth versions of the 300 kW dual keel station. Results are presented comparing the performance of the reboost control system for both versions of the space station. Standards for comparison include flexible effects at the attitude control sensor locations and flexible contributions to pointing error at the solar collectors. Bode analysis results are presented for the attitude control system and control, structural, and damping sensitivities are examined.

Young, John W.↗
NASA NTRS1986

Simulations of collisionless shocks

A problem of critical importance to space and astrophysics is the existence and properties of high-Mach-number shocks. In this letter the results of simulations of perpendicular shocks with Alfven Mach number 22 are presented. It is shown that the shock structure is a sensitive function of resistivity, becoming turbulent when the resistivity is too low. The problem of electron heating, and the extension of the results to higher Mach numbers are discussed.

Quest, K. B.↗
NASA NTRS1987

Physically based sensitivity derivatives for finite-element programs

Attention is given to a virtual-work approach to the definition of sensitivity in terms of physical quantities; sensitivity fields are treated as a solution to loadings that consist of body forces, initial strains, and initial stresses. The method can accordingly be implemented in a finite element package, with only minimal knowledge of its programming detail and without access to its source code. The application of the approach to one- and two-dimensional problems is demonstrated. The sensitivity of the structural response for truss structures was computed with respect to the cross-sectional areas of the members.

Barthelemy, Bruno↗
NASA NTRS1990

A superconducting tunnel junction receiver for 345 GHz

The design, fabrication, and testing of a quasi-particle tunnel junction receiver for use at 345 GHz are discussed. The design employs small area Nb/Nb-oxide/PbInAu edge junctions in order to keep the device capacitance small and maintain a modest value for omega R(N)C. For optimum noise performance and beam properties the mixer is contained in a waveguide mounting structure. The best sensitivity was obtained at 312 GHz where a double sideband (DSB) noise temperature of 275 K was measured. Noise temperatures of 400 K (DSB) or better were obtained out to 350 GHz.

Sutton, E. C.↗
NASA NTRS1991

Parametric study in weld mismatch of longitudinally welded SSME HPFTP inlet

Welded joints are an essential part of pressure vessels such as the Space Shuttle Main Engine (SSME) Turbopumps. Defects produced in the welding process can be detrimental to weld performance. Recently, review of the SSME high pressure fuel turbopump (HPFTP) titanium inlet x rays revealed several weld discrepancies such as penetrameter density issues, film processing discrepancies, weld width discrepancies, porosity, lack of fusion, and weld offsets. Currently, the sensitivity of welded structures to defects is of concern. From a fatigue standpoint, weld offset may have a serious effect since local yielding, in general, aggravates cyclic stress effects. Therefore, the weld offset issue is considered. Using the finite element method and mathematical formulations, parametric studies were conducted to determine the influence of weld offsets and a variation of weld widths in longitudinally welded cylindrical structures with equal wall thickness on both sides of the joint. From the study, the finite element results and theoretical solutions are presented.

Min, J. B.↗
NASA NTRS1989

Probabilistic structural analysis methods for select space propulsion system components

The Probabilistic Structural Analysis Methods (PSAM) project developed at the Southwest Research Institute integrates state-of-the-art structural analysis techniques with probability theory for the design and analysis of complex large-scale engineering structures. An advanced efficient software system (NESSUS) capable of performing complex probabilistic analysis has been developed. NESSUS contains a number of software components to perform probabilistic analysis of structures. These components include: an expert system, a probabilistic finite element code, a probabilistic boundary element code and a fast probability integrator. The NESSUS software system is shown. An expert system is included to capture and utilize PSAM knowledge and experience. NESSUS/EXPERT is an interactive menu-driven expert system that provides information to assist in the use of the probabilistic finite element code NESSUS/FEM and the fast probability integrator (FPI). The expert system menu structure is summarized. The NESSUS system contains a state-of-the-art nonlinear probabilistic finite element code, NESSUS/FEM, to determine the structural response and sensitivities. A broad range of analysis capabilities and an extensive element library is present.

Millwater, H. R.↗
NASA NTRS1992

Transient/structural analysis of a combustor under explosive loads

The 8-Foot High Temperature Tunnel (HTT) at NASA Langley Research Center is a combustion-driven blow-down wind tunnel. A major potential failure mode that was considered during the combustor redesign was the possibility of a deflagration and/or detonation in the combustor. If a main burner flame-out were to occur, then unburned fuel gases could accumulate and, if reignited, an explosion could occur. An analysis has been performed to determine the safe operating limits of the combustor under transient explosive loads. The failure criteria was defined and the failure mechanisms were determined for both peak pressures and differential pressure loadings. An overview of the gas dynamics analysis was given. A finite element model was constructed to evaluate 13 transient load cases. The sensitivity of the structure to the frequency content of the transient loading was assessed. In addition, two closed form dynamic analyses were conducted to verify the finite element analysis. It was determined that the differential pressure load or thrust load was the critical load mechanism and that the nozzle is the weak link in the combustor system.

Gregory, Peyton B.↗
NASA NTRS1994

Ultraluminous starbursts in major mergers

We use numerical simulation to investigate the triggering of starbursts in merging disk galaxies. The properties of the merger-driven starbursts are sensitive to the structure of the progenitor galaxies; specifically, to the amount of material in a dense central bulge. Galaxies without bulges develop bars shortly after their first close passage, driving significant gas inflow and subsequent starbursts in the centers of the galaxies. These starbursts significantly deplete the star-forming gas, so that only relatively weak starbursts arise during the final merger. By contrast, models of galaxies with central bulges show that a bulge acts to stabilize the galaxies against inflow and starbursts until the galaxies actually merge. At this time, strong dissipation leads to the formation of a massive central gas mass and an ensuing star-formation rate two orders of magnitude greater than that in our isolated disk models. These starbursts are very short in duration, typically approximately 50 Myr, suggesting that the rarity of ultraluminous infrared galaxies is a result of their being in a very short evolutionary phase, rather than special and rare formation conditions. The fact that these mergers display many of the properties of ultraluminous infrared galaxies--tidal features, double nuclei, massive compact gas concentrations, and extreme levels of starburst activity--suggets that merger-driven starbursts can explain the emission from many ultraluminous infrared galaxies without an active nucleus.

Mihos, J. Christopher↗
NASA NTRS1996

Using BEEM To Probe Strains In Semiconductors

Ballistic-electron-emission microscopy (BEEM) useful in determining strains in semiconductors under some conditions. More specifically, BEEM is variant of scanning tunneling microscopy and sensitive to electronic structure of probed material. In present approach, BEEM used to obtain data on those aspects of variations in electronic structures related to variations in strains. Then by use of mathematical modeling of relationships between electronic structures and strains, variations in strains deduced from BEEM data.

Bell, L. Douglas↗
NASA NTRS1992

Problem: Thirst, Drinking Behavior, and Involuntary Dehydration

The phenomenon of involuntary dehydration, the delay in full restoration of a body water deficit by drinking, has been described extensively but relatively little is known about its physiological mechanism. It occurs primarily in humans when they are exposed to various stresses including exercise, environmental heat and cold, altitude, water immersion, dehydration, and perhaps microgravity, singly and in various combinations. The level of involuntary dehydration is approximately proportional to the degree of total stress imposed on the body. Involuntary dehydration appears to be controlled by more than one factor including social customs that influence what is consumed, the capacity and rate of fluid absorption from the gastrointestinal system, the level of cellular hydration involving the osmotic-vasopressin interaction with sensitive cells or structures in the central nervous system, and, to a lesser extent, hypovolemic-angiotensin II stimuli. Since humans drink when there is no apparent physiological stimulus, the psychological component should always be considered when investigating the total mechanisms for drinking.

Greenleaf, John E.↗
NASA NTRS2001

Simultaneous Aerodynamic Analysis and Design Optimization (SAADO) for a 3-D Flexible Wing

The formulation and implementation of an optimization method called Simultaneous Aerodynamic Analysis and Design Optimization (SAADO) are extended from single discipline analysis (aerodynamics only) to multidisciplinary analysis - in this case, static aero-structural analysis - and applied to a simple 3-D wing problem. The method aims to reduce the computational expense incurred in performing shape optimization using state-of-the-art Computational Fluid Dynamics (CFD) flow analysis, Finite Element Method (FEM) structural analysis and sensitivity analysis tools. Results for this small problem show that the method reaches the same local optimum as conventional optimization. However, unlike its application to the win,, (single discipline analysis), the method. as I implemented here, may not show significant reduction in the computational cost. Similar reductions were seen in the two-design-variable (DV) problem results but not in the 8-DV results given here.

Gumbert, Clyde R.↗
NASA NTRS2001

Simultaneous Aerodynamic Analysis and Design Optimization (SAADO) for a 3-D Flexible Wing

The formulation and implementation of an optimization method called Simultaneous Aerodynamic Analysis and Design Optimization (SAADO) are extended from single discipline analysis (aerodynamics only) to multidisciplinary analysis - in this case, static aero-structural analysis and applied to a simple 3-D wing problem. The method aims to reduce the computational expense incurred in performing shape optimization using state-of-the-art Computational Fluid Dynamics (CFD) flow analysis, Finite Element Method (FEM) structural analysis and sensitivity analysis tools. Results for this small problem show that the method reaches the same local optimum as conventional optimization. However, unlike its application to the rigid wing (single discipline analysis), the method, as implemented here, may not show significant reduction in the computational cost. Similar reductions were seen in the two-design-variable (DV) problem results but not in the 8-DV results given here.

Gumbert, Clyde R.↗
NASA NTRS2001

Simultaneous Aerodynamic and Structural Design Optimization (SASDO) for a 3-D Wing

The formulation and implementation of an optimization method called Simultaneous Aerodynamic and Structural Design Optimization (SASDO) is shown as an extension of the Simultaneous Aerodynamic Analysis and Design Optimization (SAADO) method. It is extended by the inclusion of structure element sizing parameters as design variables and Finite Element Method (FEM) analysis responses as constraints. The method aims to reduce the computational expense. incurred in performing shape and sizing optimization using state-of-the-art Computational Fluid Dynamics (CFD) flow analysis, FEM structural analysis and sensitivity analysis tools. SASDO is applied to a simple. isolated, 3-D wing in inviscid flow. Results show that the method finds the saine local optimum as a conventional optimization method with some reduction in the computational cost and without significant modifications; to the analysis tools.

Gumbert, Clyde R.↗