1,229 research outputs found
Structural tailoring using the SSME/STAEBL code
Space Shuttle Main Engine/Structural Tailoring of Engine Blades (SSME/STAEBL) was developed by systematically modifying and enhancing the STAEBL code developed by Pratt and Whitney under contract to NASA Lewis Research Center. STAEBL was designed for application to gas turbine blade design. Typical design variables include blade thickness distribution and root chord. Typical constraints include resonance margins, root stress, and root to chord ratios. In this program, the blade is loaded by centrifugal forces only. Additions and modifications of STAEBL included in SSME/STAEBL include (1) thermal stress analysis; (2) gas dynamic (pressure) loads; (3) temperature dependent material and thermal properties; (4) forced vibrations; (5) tip displacement constraints; (6) single crystal material analysis; (7) blade cross section stacking offsets; and (8) direct time integration algorithm for transient dynamic response. Capabilities are also included which permit data transfer from finite element models and stand-alone analysis
Structural tailoring of high-speed turbine blades (SSME/STAEBL)
Space shuttle main engine (SSME) blades are subject to severe thermal, pressure, and forced vibration environments. Structural optimization provides an automated alternative to time consuming iterations. Any number of analyses, design variables, and constraints can be incorporated in a structural optimization computer code. This idea was applied to develop the code SSME/STAEBL, which is a stand alone code suitable for automated design of SSME turbopump blades. Additions and modifications of STAEBL included in SSME/STAEBL include the following: (1) thermal stress analysis, (2) gas dynamic (pressure) loads, (3) temperature-dependent material and thermal properties, (4) forced vibrations, (5) tip displacement constraints, (6) single crystal material analysis, (7) blade cross-section stacking offsets, and (8) direct time integration algorithm for transient dynamic response
On the strength of the nonlinearity in isotropic turbulence
Turbulence governed by the Navier-Stokes equations shows a tendency to evolve
towards a state in which the nonlinearity is diminished. In fully developed
turbulence this tendency can be measured by comparing the variance of the
nonlinear term to the variance of the same quantity measured in a Gaussian
field with the same energy distribution. In order to study this phenomenon at
high Reynolds numbers, a version of the Direct Interaction Approximation is
used to obtain a closed expression for the statistical average of the
mean-square nonlinearity. The wavenumber spectrum of the mean-square nonlinear
term is evaluated and its scaling in the inertial range is investigated as a
function of the Reynolds number. Its scaling is dominated by the sweeping by
the energetic scales, but this sweeping is weaker than predicted by a random
sweeping estimate. At inertial range scales, the depletion of nonlinearity as a
function of the wavenumber is observed to be constant. At large it is observed
that the mean-square nonlinearity is larger than its Gaussian estimate, which
is shown to be related to the non-Gaussianity of the Reynolds-stress
fluctuations at these scales.Comment: Accepted for publication in J. Fluid Mec
Microgravity acoustic mixing for particle cloud combustors
Experimental and theoretical investigations of acoustic mixing procedures designed to uniformly distribute fuel particles in a combustion tube for application in the proposed Particle Cloud Combustion Experiment (PCCE) are described. Two acoustic mixing methods are investigated: mixing in a cylindrical tube using high frequency spinning modes generated by suitably phased, or quadrature speakers, and acoustic premixing in a sphere. Quadrature mixing leads to rapid circumferential circulation of the powder around the tube. Good mixing is observed in the circulating regions. However, because axial inhomogeneities are necessarily present in the acoustic field, this circulation does not extend throughout the tube. Simultaneous operation of the quadrature-speaker set and the axial-speaker was observed to produce considerably enhanced mixing compared to operation of the quadrature-speaker set alone. Mixing experiments using both types of speakers were free of the longitudinal powder drift observed using axial-speakers alone. Vigorous powder mixing was obtained in the sphere for many normal modes: however, in no case was the powder observed to fill the sphere entirely. Theoretical analysis indicated that mixing under steady conditions cannot fill more than a hemisphere except under very unusual conditions. Premixing in a hemisphere may be satisfactory; otherwise, complete mixing in microgravity might be possible by operating the speaker in short bursts. A general conclusion is that acoustic transients are more likely to produce good mixing than steady state conditions. The reason is that in steady conditions, flow structures like nodal planes are possible and often even unavoidable. These tend to separate the mixing region into cells across which powder cannot be transferred. In contrast, transients not only are free of such structures, they also have the characteristics, desirable for mixing, of randomness and disorder. This conclusion is corroborated by mixing experiments using axial waves
Non-Equilibrium Turbulence and Two-Equation Modeling
Two-equation turbulence models are analyzed from the perspective of spectral closure theories. Kolmogorov theory provides useful information for models, but it is limited to equilibrium conditions in which the energy spectrum has relaxed to a steady state consistent with the forcing at large scales; it does not describe transient evolution between such states. Transient evolution is necessarily through nonequilibrium states, which can only be found from a theory of turbulence evolution, such as one provided by a spectral closure. When the departure from equilibrium is small, perturbation theory can be used to approximate the evolution by a two-equation model. The perturbation theory also gives explicit conditions under which this model can be valid, and when it will fail. Implications of the non-equilibrium corrections for the classic Tennekes-Lumley balance in the dissipation rate equation are drawn: it is possible to establish both the cancellation of the leading order Re1/2 divergent contributions to vortex stretching and enstrophy destruction, and the existence of a nonzero difference which is finite in the limit of infinite Reynolds number
Back to the Future?: Peacekeeping and the Return of Imperial Policing
Streaming video requires Flash Player, RealPlayer, or Windows Media Player to view.Rubinstein's discussion addressed his concern for the future of peacekeepi​ng missions.Ohio State University. Mershon Center for International Security StudiesEvent Web Page, streaming video, event photo
Structural tailoring of select fiber composite structures
A multidisciplinary design process for aerospace propulsion composite structures was formalized and embedded into computer codes. These computer codes are streamlined to obtain tailored designs for select composite structures. The codes available are briefly described with sample cases to illustrate their applications. The sample cases include aircraft engine blades, propfans (turboprops), flat, and cylindrical panels. Typical results illustrate that the use of these codes enable the designer to obtain designs which meet all the design requirements with maximum benefits in efficiency, noise, weight or thermal distortions
Probabilistic SSME blades structural response under random pulse loading
The purpose is to develop models of random impacts on a Space Shuttle Main Engine (SSME) turbopump blade and to predict the probabilistic structural response of the blade to these impacts. The random loading is caused by the impact of debris. The probabilistic structural response is characterized by distribution functions for stress and displacements as functions of the loading parameters which determine the random pulse model. These parameters include pulse arrival, amplitude, and location. The analysis can be extended to predict level crossing rates. This requires knowledge of the joint distribution of the response and its derivative. The model of random impacts chosen allows the pulse arrivals, pulse amplitudes, and pulse locations to be random. Specifically, the pulse arrivals are assumed to be governed by a Poisson process, which is characterized by a mean arrival rate. The pulse intensity is modelled as a normally distributed random variable with a zero mean chosen independently at each arrival. The standard deviation of the distribution is a measure of pulse intensity. Several different models were used for the pulse locations. For example, three points near the blade tip were chosen at which pulses were allowed to arrive with equal probability. Again, the locations were chosen independently at each arrival. The structural response was analyzed both by direct Monte Carlo simulation and by a semi-analytical method
Motivation et maintien de la paix : Élaboration d’un lien entre agir et structure
Le maintien de la paix multilatéral est, de plus en plus fréquemment, le moyen par lequel la communauté internationale répond aux conflits violents, qu’ils soient internes ou entre États. L’étude du maintien de la paix requiert des investigations transnationales et multi-sites dont l’importance est croissante en anthropologie. En dépit de ce fait, peu d’études anthropologiques du maintien de la paix ont été réalisées. Cet article prolonge un programme ininterrompu de recherche anthropologique sur le maintien de la paix. Il utilise la théorie de l’inversion psychologique pour interpréter des données ethnographiques recueillies par l’Organisme des Nations Unies chargé de la surveillance de la trêve (ONUST). Dans le maintien de la paix, les actions individuelles sont liées, dans un processus d’implications mutuelles, à des schémas à grande échelle de légitimité et d’efficacité du maintien de la paix. L’analyse présentée ici crée un échafaudage théorique permettant de connecter l’analyse des motivations au niveau individuel à un exposé de l’inversion culturelle dans le maintien de la paix à de plus hauts niveaux d’organisation sociale.Multilateral peacekeeping is an increasingly important way that the international community responds to violent conflicts within and between states. Studying peacekeeping requires transnational, multisided investigation, which is increasingly important for anthropology. Despite this, there have been few anthropological studies of peacekeeping. This paper extends an ongoing program of anthropological research on peacekeeping. This paper uses psychological reversal theory to interpret ethnographic data collected from the United Nations Truce Supervision Organization. Individual actions in peacekeeping are linked in a mutually implicative process to broad-scale patterns of peacekeeping legitimacy and effectiveness. The analysis presented here creates a theoretical scaffolding to connect the analysis of motivation at an individual level to a cultural inversion account of peacekeeping at higher levels of social organization.El mantenimiento multilateral de la paz es el medio que, con mayor frecuencia, utiliza la comunidad internacional en tanto que respuesta a los conflictos violentos, sean internos o entre naciones. El estudio del mantenimiento de la paz exige investigaciones trasnacionales y multi-situacionales, que son cada dÃa más importantes en antropologÃa. A pesar de ello, se han realizado pocos estudios antropológicos sobre el mantenimiento de la paz. Este artÃculo prolonga un continuo programa de investigación antropológica sobre el mantenimiento de la paz. Utiliza la teorÃa de la inversión sicológica en la interpretación de los datos etnográficos recogidos por la Organización de la Naciones Unidas encargada de la vigilancia de la tregua (ONUVT). En el mantenimiento de la paz, las acciones individuales están ligadas, al interior de un proceso de implicaciones mutuas, con esquemas a gran escala de legitimidad y eficacia del mantenimiento de la paz. El análisis que aquà se presenta, propone un andamiaje teórico que permite conectar el análisis de las motivaciones a escala individual con una explicación de la inversión cultural en el mantenimiento de la paz a niveles más altos de la organización socia
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