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  • Chemistry  (19,494)
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  • 1
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    M.D.-Ph.D. degrees (1993)
    American Association for the Advancement of Science (AAAS)
    Details
    Publication Date: 1993-12-17
    Description: 〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Gottheil, D L -- Waldrop, T G -- New York, N.Y. -- Science. 1993 Dec 17;262(5141):1801-2.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/8266063" target="_blank"〉PubMed〈/a〉
    Keywords: *Education, Graduate ; *Education, Medical ; Engineering ; Humanities ; Humans ; Research ; Science ; Social Sciences
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Computer Science , Medicine , Natural Sciences in General , Physics
    Published by American Association for the Advancement of Science (AAAS)
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  • 2
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    Flow and acoustic field due to an inclined plate with a downstream splitter (1993)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: In the present work, the high Reynolds number flow past an inclined plate with a splitter plate placed in its wake is considered numerically. A numerical conformal mapping technique is employed to transform the two-plate system into the same number of cylinders: the flow field is assumed to be two-dimensional. The vortex shedding from the inclined plate is modelled using the discrete vortex method. It is shown that the splitter plate has a profound effect on the development of the flow over a range of values of a suitably defined offset parameter and for a range of positions of the leading edge of the splitter plate. The acoustic field is also calculated and the spectrum reflects the flow results.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: Journal of Sound and Vibration (ISSN 0022-460X); 166; 2; p. 209-235
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  • 3
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    Equidistribution of energy and other quantities in oscillating systems (1993)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: Energy of a high harmonic standing wave tends to be distributed equally over the whole wave even in a stratified medium where the wave's peak amplitude can be much larger near the upper boundary than the lower one. This fact is generalized to the many diverse physical problems which solve second-order differential equations of Sturm-Liouville type. For any such solution y(z) whose sign fluctuates along the z-axis, quantities are found which have the same value between any two neighboring zeros of y. One of the equidistributed quantities for an oscillating fluid sphere is similar to kinetic energy but is identical only in limiting cases. The acoustic midpoint of a cavity can be a unique place where some nonlinear perturbations have extra strength. This may apply to the puzzling solar phenomenon called supergranulation.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 414; 2; p. 892-897.
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  • 4
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    Navier-Stokes calculations for vortex rings in an unbounded domain (1993)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: A computational code for the vorticity-potential method is developed for a three-dimensional bounded vorticity field. The evaluation of the boundary data for the vector potential in the code is improved so that the numerical solution simulates that in an unbounded domain to a high order. The time evolution of two vortex rings and that of an elliptic ring are investigated with this code. The cut-and-connect phenomena of vortex rings are successfully captured. The results are compared with those of asymptotic theory and the experiment. They also highlight the need for additional theoretical and numerical investigations.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: Computers & Fluids (ISSN 0045-7930); 22; 4-5; p. 589-605.
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  • 5
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    Flexible structure experiments at JPL and WPAFB - H(infinity) controller designs (1993)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: Control system experiments are described that were carried out on flexible structure facilities at the Jet Propulsion Laboratory (JPL) and the Wright-Patterson Air Force Base (WPAFB). The feedback controllers were designed using the technique of weighted gap optimization to increase structural damping and achieve robust control.
    Keywords: STRUCTURAL MECHANICS
    Type: International Journal of Control (ISSN 0020-7179); 58; 1; p. 1-19.
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  • 6
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    Delaminations in composite plates under transverse impact loads - Experimental results (1993)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: Tests were performed measuring the locations and geometries of delaminations in Fiberite T300/976 graphite/epoxy, Fiberite IM7/977-2 graphite-toughened epoxy, and ICI APC-2 graphite/PEEK plates subjected to transverse impact loads. The data provide specific information on the effects of impactor velocity, impactor mass, material, thickness of back ply group, difference in fiber orientation between adjacent ply groups, plate thickness, and impactor nose radius. The data were compared to the results of the Finn-Springer model. The model was found to describe the data with reasonable accuracy.
    Keywords: STRUCTURAL MECHANICS
    Type: Composite Structures (ISSN 0263-8223); 23; 3; p. 191-204.
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  • 7
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    A multidimensional flux function with applications to the Euler and Navier-Stokes equations (1993)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: In the present grid-independent approximate Riemann solver for 2D and 3D flows that are governed by the Euler or Navier-Stokes equations, fluxes on grid faces are obtained by wave decomposition; the assumption of information-propagation in the velocity-difference directions leads to a more accurate resolution of shear and shock waves, when these are are oblique to the grid. The model, which yields significantly greater accuracy in both supersonic and subsonic first-order spatially accurate computations, describes the difference in states at each grid interface by the action of five waves.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: Journal of Computational Physics (ISSN 0021-9991); 105; 2; p. 306-323.
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  • 8
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    Thermal buoyancy and Marangoni convection in a two fluid layered system (1993)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: Journal of Thermophysics and Heat Transfer (ISSN 0887-8722); 7; 2; p. 352-360.
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  • 9
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    Density measurements in an expanding flow using holographic interferometry (1993)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: Journal of Thermophysics and Heat Transfer (ISSN 0887-8722); 7; 2; p. 261-268.
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  • 10
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    The development of a mixing layer under the action of weak streamwise vortices (1993)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: The action of weak, streamwise vortices on a plane, incompressible, steady mixing layer is examined in the large Reynolds number limit. The outer, inviscid region is bounded by a vortex sheet to which the viscous region is confined. It is shown that the local linear analysis becomes invalid at streamwise distances O(epsilon sup -1), where (epsilon much less than 1) is the crossflow amplitude, and a new nonlinear analysis is constructed for this region. Numerical solutions of the nonlinear problem show that the vortex sheet undergoes an O(1) change in position and that the solution is ultimately terminated by a breakdown in the numerical procedure. The corresponding viscous layer shows downstream thickening, but appears to remain well behaved up to the terminal location.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: Physics of Fluids A (ISSN 0899-8213); 5; 3; p. 600-607.
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  • 11
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    Linear stability of the confined compressible reacting mixing layer (1993)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: This paper investigates the linear stability of confined mixing layers with special emphasis on the effects of heat release and compressibility. The results show that reflection of supersonic disturbances by the walls makes the confined supersonic mixing layer more unstable than the unconfined free shear layer. Decreasing the distance between the walls makes the flow more unstable. However, subsonic disturbances are relatively unaffected by the walls. Heat release and Mach number hardly change the growth rates of supersonic disturbances. The most unstable supersonic disturbances are two-dimensional in rectangular channel flows, but three-dimensional in partially confined flows. Finally, the reactants are not strongly mixed by supersonic instabilities, which mainly disturb one side of the layer.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: AIAA Journal (ISSN 0001-1452); 31; 3; p. 571-577.
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  • 12
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    Aerostructural safety factor criteria using deterministic reliability (1993)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Keywords: STRUCTURAL MECHANICS
    Type: Journal of Spacecraft and Rockets (ISSN 0022-4650); 30; 2; p. 244-247.
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  • 13
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    Isotropy of the small scales of turbulence at low Reynolds number (1993)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: Spectral local isotropy tests are applied to direct numerical simulation data, mainly at the centerline of a fully developed turbulent channel flow. Despite the small Reynolds number of the simulation, the high-wavenumber behavior of velocity and vorticity spectra is consistent with local isotropy. This consistency is verified by the relationship between streamwise wavenumber spectra and spanwise wavenumber spectra. The high-wavenumber behavior of the pressure spectrum is also consistent with local isotropy and compares favorably with the calculation of Batchelor (1951), which assumes isotropy and joint normality of the velocity field at two points in space. The latter assumption is validated by the shape but not the magnitude of the quadruple correlation of the streamwise velocity fluctuation at small separations. There is only partial support for local spectral isotropy away from the centerline as the magnitude of the mean strain rate increases.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: Journal of Fluid Mechanics (ISSN 0022-1120); p. 219-238.
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  • 14
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    A small-scale turbulence model (1993)
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    Publication Date: 2011-08-24
    Description: A previously derived analytical model for the small-scale structure of turbulence is reformulated in such a way that the energy spectrum may be computed. The model is an ensemble of two-dimensional (2D) vortices with internal spiral structure, each stretched by an axially symmetric strain flow. Stretching and differential rotation produce an energy cascade to smaller scales in which the stretching represents the effect of instabilities and the spiral structure is the source of dissipation at the end of the cascade. The energy spectrum of the resulting flow may be expressed as a time integration involving only the enstrophy spectrum of the time evolving 2D cross section flow, which may be obtained numerically. Examples are given in which a k exp -5/3 spectrum is obtained by this method. The k exp -5/3 inertial range spectrum is shown to be related to the existence of a self-similar enstrophy preserving range in the 2D enstrophy spectrum. The results are found to be insensitive to time dependence of the strain rate, including even intermittent on-or-off strains.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: Physics of Fluids A (ISSN 0899-8213); 5; 6; p. 1472-1483.
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  • 15
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    New time scale based k-epsilon model for near-wall turbulence (1993)
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    Publication Date: 2011-08-24
    Description: A k-epsilon model is proposed for wall bonded turbulent flows. In this model, the eddy viscosity is characterized by a turbulent velocity scale and a turbulent time scale. The time scale is bounded from below by the Kolmogorov time scale. The dissipation equation is reformulated using this time scale and no singularity exists at the wall. The damping function used in the eddy viscosity is chosen to be a function of R(sub y) = (k(sup 1/2)y)/v instead of y(+). Hence, the model could be used for flows with separation. The model constants used are the same as in the high Reynolds number standard k-epsilon model. Thus, the proposed model will be also suitable for flows far from the wall. Turbulent channel flows at different Reynolds numbers and turbulent boundary layer flows with and without pressure gradient are calculated. Results show that the model predictions are in good agreement with direct numerical simulation and experimental data.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: AIAA Journal (ISSN 0001-1452); 31; 7; p. 1191-1198.
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  • 16
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    Impact-damaged graphite-thermoplastic trapezoidal-corrugation sandwich and semi-sandwich panels (1993)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: The results of a study of the effects of impact damage on compression-loaded trapezoidal-corrugation sandwich and semi-sandwich graphite-thermoplastic panels are presented. Sandwich panels with two identical face sheets and a trapezoidal corrugated core between them, and semi-sandwich panels with a corrugation attached to a single skin are considered in this study. Panels were designed, fabricated and tested. The panels were made using the manufacturing process of thermoforming, a less-commonly used technique for fabricating composite parts. Experimental results for unimpacted control panels and panels subjected to impact damage prior to loading are presented. Little work can be found in the literature about these configurations of thermoformed panels.
    Keywords: STRUCTURAL MECHANICS
    Type: Journal of Composite Materials (ISSN 0021-9983); 27; 5; p. 526-538.
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  • 17
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    Experimental and numerical study of a turbulent boundary layer with pressure gradients (1993)
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    Publication Date: 2011-08-24
    Description: Results are presented of an experimental and numerical study of a turbulent boundary layer with pressure gradients conducted using the recent 'fringe method' with its numerical advantages and good inflow quality. After an inflow transient good agreement is observed; the differences, of up to 13 percent, are discussed. Moderate deviations from the law of the wall are found in the velocity profiles of the simulation. They are fully correlated with the pressure gradient, are in fair quantitative agreement with the experimental results of Nagano et al. (1992), and are roughly the opposite of uncorrected mixing-length-model predictions. Large deviations from the wall scaling are observed for other quantities, notably for the turbulence dissipation rate. The a(1) structure parameter drops mildly in the upper layer with adverse pressure gradient.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: Journal of Fluid Mechanics (ISSN 0022-1120); p. 337-371.
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  • 18
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    Large-amplitude finite element flutter analysis of composite panels in hypersonic flow (1993)
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    Publication Date: 2011-08-24
    Keywords: STRUCTURAL MECHANICS
    Type: AIAA Journal (ISSN 0001-1452); 31; 6; p. 1090-1099.
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  • 19
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    A Reynolds stress model for near-wall turbulence (1993)
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    Publication Date: 2011-08-24
    Description: The paper formulates a tensorially consistent near-wall second-order closure model. Redistributive terms in the Reynolds stress equations are modeled by an elliptic relaxation equation in order to represent strongly nonhomogeneous effects produced by the presence of walls; this replaces the quasi-homogeneous algebraic models that are usually employed, and avoids the need for ad hoc damping functions. The model is solved for channel flow and boundary layers with zero and adverse pressure gradients. Good predictions of Reynolds stress components, mean flow, skin friction, and displacement thickness are obtained in various comparisons to experimental and direct numerical simulation data. The model is also applied to a boundary layer flowing along a wall with a 90-deg, constant-radius, convex bend.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: Journal of Fluid Mechanics (ISSN 0022-1120); p. 465-498.
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  • 20
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    A Navier-Stokes solver for turbomachinery applications (1993)
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    Publication Date: 2011-08-24
    Description: A computer code for solving the Reynolds-averaged full Navier-Stokes equations has been developed and applied using H- and C-type grids. The Baldwin-Lomax eddy-viscosity model is used for turbulence closure. The integration in time is based on an explicit four-stage Runge-Kutta scheme. Local time stepping, variable coefficient implicit residual smoothing, and a full multigrid method have been implemented to accelerate steady-state calculations. A grid independence analysis is presented for a transonic rotor blade. Comparisons with experimental data show that the code is an accurate viscous solver and can give very good blade-to-blade predictions for engineering applications.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: ASME, Transactions, Journal of Turbomachinery (ISSN 0889-504X); 115; 2; p. 305-313.
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  • 21
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    Numerical study of shock-wave/boundary-layer interactions with bleed (1993)
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    Publication Date: 2011-08-24
    Description: A numerical study was conducted to investigate how bleed through a two-dimensional slot affects shock-wave induced, boundary-layer separation on a flat plate. This study is based on the ensemble-averaged, compressible, Navier-Stokes equations closed by the Baldwin-Lomax, algebraic turbulence model. The algorithm used to obtain solutions was the implicit, partially split, two-factored scheme of Steger. This study examined the effects of the following parameters in controlling shock-wave induced flow separation: location of slot in relation to where the incident shock wave impinged on the boundary layer, size of slot in relation to the boundary-layer thickness, number of slots, spacings between slots, and strength of the incident shock wave. This study also showed the nature of the very complex flowfield about the slot or slots and how the plenum affects the bleed process. The results of this study are relevant to problems where bleed is used to control shock-wave induced, boundary-layer separation (e.g., inside jet engine inlets and wind tunnels).
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: AIAA Journal (ISSN 0001-1452); 31; 5; p. 869-876.
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  • 22
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    Fluid flow of a row of jets in crossflow - A numerical study (1993)
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    Publication Date: 2011-08-24
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: AIAA Journal (ISSN 0001-1452); 31; 5; p. 806-811.
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  • 23
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    Singularity in structural optimization (1993)
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    Publication Date: 2011-08-24
    Description: The conditions under which global and local singularities may arise in structural optimization are examined. Examples of these singularities are presented, and a framework is given within which the singularities can be recognized. It is shown, in particular, that singularities can be identified through the analysis of stress-displacement relations together with compatibility conditions or the displacement-stress relations derived by the integrated force method of structural analysis. Methods of eliminating the effects of singularities are suggested and illustrated numerically.
    Keywords: STRUCTURAL MECHANICS
    Type: International Journal for Numerical Methods in Engineering (ISSN 0029-5981); 36; 6; p. 931-944.
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  • 24
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    Turbulent flow in a channel with transverse rib heat transfer augmentation (1993)
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    Publication Date: 2011-08-24
    Description: Turbulent flow in a 2D channel with repeated rectangular rib roughness was numerically simulated using a low Reynolds number form of the k-epsilon turbulence model. Friction factors and average Stanton numbers were calculated for various pitch to rib height ratios and bulk Reynolds numbers. Comparisons with experiment were generally adequate, with the predictions of friction superior to those for heat transfer. The effect of variable properties for channel flow was investigated, and the results showed a greater effect for friction than for heat transfer. Comparison with experiment yielded no clear conclusions. The turbulence model was also validated for a related problem, that of flow downstream of an abrupt pipe expansion.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: International Journal of Heat and Mass Transfer (ISSN 0017-9310); 36; 6; p. 1459-1469.
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  • 25
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    A note on the distortion of a flat-plate boundary layer by free-stream vorticity normal to the plate (1993)
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    Publication Date: 2011-08-24
    Description: The purpose of this note is to construct a local solution that eliminates a residual velocity discontinuity in the inviscid portion of a solution obtained in a recent paper by Goldstein, Leib and Cowley (1992). This result is of importance because it shows that the solution obtained in that paper is entirely non-singular outside the viscous wall boundary layer and that any singularity in the problem will have to arise in the usual way through a breakdown in the viscous boundary layer.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: Journal of Fluid Mechanics (ISSN 0022-1120); p. 531-541.
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  • 26
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    On the 'delta-equations' for vortex sheet evolution (1993)
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    Publication Date: 2011-08-24
    Description: We use a set of equations, sometimes referred to as the 'delta-equations', to approximate the two-dimensional inviscid motion of an initially circular vortex sheet released from rest in a cross-flow. We present numerical solutions of these equations for the case with delta-square = 0 (for which the equations are exact) and for delta-square greater than 0. For small values of the smoothing parameter delta, a spectral filter must be used to eliminate spurious instabilities due to round-off error. Two singularities appear simultaneously in the vortex sheet when delta-square = 0 at a critical time t(c). After t(c), the solutions do not converge as the computational mesh is refined. With delta-square greater than 0, converged solutions were found for all values of delta-square when t is less than t(c), and for all but the two smallest values of delta-square used when t is greater than t(c). Our results show that, when delta-square is greater than 0, the vortex sheet deforms into two doubly branched spirals some time after t(c). The limiting solution as delta approaching 0 clearly exists and equals the delta = 0 solution when t is less than t(c).
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: Journal of Fluid Mechanics (ISSN 0022-1120); p. 527-549.
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  • 27
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    The three-dimensional evolution of a plane mixing layer - Pairing and transition to turbulence (1993)
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    Publication Date: 2011-08-24
    Description: The evolution of three-dimensional temporally evolving plane mixing layers through as many as three pairings has been simulated numerically. All simulations were begun from a few low-wavenumber disturbances, usually derived from linear stability theory, in addition to the mean velocity. Three-dimensional perturbations were used with amplitudes ranging from infinitesimal to large enough to trigger a rapid transition to turbulence. Pairing is found to inhibit the growth of infinitesimal three-dimensional disturbances, and to trigger the transition to turbulence in highly three-dimensional flows. The mechanisms responsible for the growth of three-dimensionality and onset of transition to turbulence are described. The transition to turbulence is accompanied by the formation of thin sheets of spanwise vorticity, which undergo secondary rollups. The post-transitional simulated flow fields exhibit many properties characteristic of turbulent flows.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: Journal of Fluid Mechanics (ISSN 0022-1120); p. 275-320.
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  • 28
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    Relations for local radiative heat transfer between rectangular boundaries of an absorbing-emitting medium (1993)
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    Publication Date: 2011-08-24
    Description: An analytical solution was obtained by Siegel (1991, 1992) for local boundary heat fluxes by a radiating medium at uniform temperature in a 2D rectangular region. It is shown here that, after local fluxes from the medium to the walls have been evaluated, it is very easy to compute local fluxes arriving from the adjacent and opposite walls. This extends the previous analysis and provides convenient relations to include radiation from a black boundary, each side of the rectangle being at a different uniform temperature. The final expressions are helpful in performing spectral calculations that must be made for many spectral bands.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: ASME, Transactions, Journal of Heat Transfer (ISSN 0022-1481); 115; 1; p. 272-276.
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  • 29
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    The isolation limits of stochastic vibration (1993)
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    Publication Date: 2011-08-24
    Description: The vibration isolation problem is formulated as a 1D kinematic problem. The geometry of the stochastic wall trajectories arising from the stroke constraint is defined in terms of their significant extrema. An optimal control solution for the minimum acceleration return path determines a lower bound on platform mean square acceleration. This bound is expressed in terms of the probability density function on the significant maxima and the conditional fourth moment of the first passage time inverse. The first of these is found analytically while the second is found using a Monte Carlo simulation. The rms acceleration lower bound as a function of available space is then determined through numerical quadrature.
    Keywords: STRUCTURAL MECHANICS
    Type: Journal of Sound and Vibration (ISSN 0022-460X); 160; 2; p. 205-223.
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    Statistical analysis of the effects of helicity in inhomogeneous turbulence (1993)
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    Publication Date: 2011-08-24
    Description: Effects of helicity in three-dimensional incompressible inhomogeneous turbulence are examined with the aid of a two-scale direct-interaction approximation (DIA). The turbulent helicity gives a measure of the reflectional asymmetry in a turbulent flow and its inhomogeneity contributes to the sustainment of large-scale vorticity field in a three-dimensional mean flow. The importance of helicity effects is discussed in the context of flows in a rotating system and swirling flows in a pipe. A three-equation model with the turbulent helicity incorporated is proposed using the theoretical results. The validity of the model is confirmed quantitatively through the application to a decaying swirling flow in a pipe.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: Physics of Fluids A (ISSN 0899-8213); 5; 2; p. 464-477.
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    Central difference TVD schemes for time dependent and steady state problems (1993)
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    Publication Date: 2011-08-24
    Description: A Runge-Kutta formula in time is presently used to advance schemes in which central differences are used to solve the time-dependent Euler equations; a second difference is added near shocks as an artificial viscosity to reduce the given scheme to a first-order upwind one at shocks. A matrix-valued dissipation is introduced and compared with the scalar viscosity; a connection is shown between this artificial viscosity and flux limiters. The use of various flux limiters for this central difference scheme is compared.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: Journal of Computational Physics (ISSN 0021-9991); 107; 2; p. 297-308.
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    Composite sandwich construction with syntactic foam core - A practical assessment of post-impact damage and residual strength (1993)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: An account is given of an inspection method that has been successfully used to assess the postimpact damage and residual strength of syntactic (glass microspheres in epoxy matrix) foam-core sandwich panels with hybrid (carbon and glass fiber-reinforced) composite skins, which inherently possess high damage tolerance. SEM establishes that the crushing of the microspheres is responsible for the absorption of most of the impact energy. Damage tolerance is a function of the localization of damage by that high impact energy absorption.
    Keywords: STRUCTURAL MECHANICS
    Type: Composites (ISSN 0010-4361); 24; 5; p. 447-450.
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    A new constitutive equation for elastomers (1993)
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    Publication Date: 2011-08-24
    Description: A new mathematical approach for quantifying the mechanical properties of elastomeric materials under biaxial loads is presented. Specific equations relating principal strains and principal true stresses for a homogeneous, isotropic, and elastic material are proposed that resemble the conventional Hooke's law of linear elasticity. The predicted stresses are compared to those from three different sets of experimental data and to stresses from three different theories based on Rivlin's work-of-deformation approach. The proposed approach is considered to be of benefit to design engineers involved in a broad range of rubber products.
    Keywords: STRUCTURAL MECHANICS
    Type: Rubber & Plastics News (ISSN 0300-6123); p. 15-21.
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    Effect of stiffness characteristics on the response of composite grid-stiffened structures (1993)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Keywords: STRUCTURAL MECHANICS
    Type: Journal of Aircraft (ISSN 0021-8669); 30; 4; p. 541-546.
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    Time-accurate Navier-Stokes calculations with multigrid acceleration (1993)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: An efficient method for calculating unsteady flows is presented, with emphasis on a modified version of the thin-layer Navier-Stokes equations. Fourier stability analysis is used to illustrate the effect of treating the source term implicitly instead of explicity, as well as to illustrate other algorithmic choices. A 2D circular cylinder (with a Reynolds number of 1200 and a Mach number of 0.3) is calculated. The present scheme requires only about 10 percent of the computer time required by global minimum time stepping.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: In: AIAA Computational Fluid Dynamics Conference, 11th, Orlando, FL, July 6-9, 1993, Technical Papers. Pt. 2 (A93-44994 18-34); p. 1041, 1042.
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    Visualization of internal swirling flows (1993)
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    Publication Date: 2011-08-24
    Description: Flow solutions were analyzed using three visualization tools, FAST, UFAT, and Visual3. The simulation models axisymmetric unsteady flow inside a closed circular cylinder with a rotating lid. The capabilities and limitations of these visualization packages are presented. The versatility of these tools enhances scientific study and presentation of numerical results.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: In: AIAA Computational Fluid Dynamics Conference, 11th, Orlando, FL, July 6-9, 1993, Technical Papers. Pt. 2 (A93-44994 18-34); p. 1029, 1030.
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    A coupled implicit method for chemical non-equilibrium flows at all speeds (1993)
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    Publication Date: 2011-08-24
    Description: The present time-accurate coupled-solution procedure addresses the chemical nonequilibrium Navier-Stokes equations over a wide Mach-number range uses, in conjunction with the strong conservation form of the governing equations, five unknown primitive variables. The numerical tests undertaken address steady convergent-divergent nozzle flows with air dissociation/recombination, dump combustor flows with n-pentane/air chemistry, and unsteady nonreacting cavity flows.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: Journal of Computational Physics (ISSN 0021-9991); 106; 2; p. 306-318.
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    A study of the effects of macrosegregation and buoyancy-driven flow in binary mixture solidification (1993)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: A generalized anisotropic porous medium approach is developed for modelling the flow, heat and mass transport processes during binary mixture solidification. Transient predictions are obtained using FEM, coupled with an implicit time-marching scheme, for solidification inside a two-dimensional rectangular enclosure. A parametric study focusing attention on the effects of solutal buoyancy and thermal buoyancy is presented. It is observed that three parameters, namely the thermal Rayleigh number, the solutal Rayleigh number, and the relative density change parameter, significantly alter the flow fields in the liquid and the mushy regions. Depending upon the nature of these flow fields, the solute enrichment caused by macrosegregation may occur in the top or the bottom region of the enclosure.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: International Journal of Heat and Mass Transfer (ISSN 0017-9310); 36; 9; p. 2349-2358.
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    Low Reynolds number k-epsilon modelling with the aid of direct simulation data (1993)
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    Publication Date: 2011-08-24
    Description: The constant C sub mu and the near-wall damping function f sub mu in the eddy-viscosity relation of the k-epsilon model are evaluated from direct numerical simulation (DNS) data for developed channel and boundary layer flow at two Reynolds numbers each. Various existing f sub mu model functions are compared with the DNS data, and a new function is fitted to the high-Reynolds-number channel flow data. The epsilon-budget is computed for the fully developed channel flow. The relative magnitude of the terms in the epsilon-equation is analyzed with the aid of scaling arguments, and the parameter governing this magnitude is established. Models for the sum of all source and sink terms in the epsilon-equation are tested against the DNS data, and an improved model is proposed.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: Journal of Fluid Mechanics (ISSN 0022-1120); p. 509-529.
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    A technique for measuring the heat transfer coefficient inside a Bridgman furnace (1993)
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    Publication Date: 2011-08-24
    Description: Knowledge of the amount of heat that is conducted, advected and radiated between an ampoule and the furnace is important for understanding vertical Bridgman crystal growth. This heat transfer depends on the temperature, emissivities and geometries of both the furnace and ampoule, as well as the choice of ambient gas inside the furnace. This paper presents a method which directly measures this heat transfer without the need to know any physical properties of the furnace, the ampoule, or the gaseous environment. Data are given for one specific furnace in which this method was used.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: Journal of Crystal Growth (ISSN 0022-0248); p. 1187-1192.
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    Delaminations in composite plates under transverse static or impact loads - A model (1993)
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    Publication Date: 2011-08-24
    Description: A method is presented for calculating the locations, shapes, and sizes of delaminations which occur in a fiber reinforced composite plate subjected to transverse static or dynamic (impact) loads. The plate may be simply supported, clamped, or free along its edges. A model of the delamination formation was developed. This model was then coupled with a finite element analysis. The model and the finite element analysis were implemented by a computer code which can be used to estimate the load at which damage is initiated as well as the locations, shapes, and sizes of the delaminations.
    Keywords: STRUCTURAL MECHANICS
    Type: Composite Structures (ISSN 0263-8223); 23; 3; p. 177-190.
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    Non-oscillatory and non-diffusive solution of convection problems by the iteratively reweighted least-squares finite element method (1993)
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    Publication Date: 2011-08-24
    Description: A comparative description is presented for the least-squares FEM (LSFEM) for 2D steady-state pure convection problems. In addition to exhibiting better control of the streamline derivative than the streamline upwinding Petrov-Galerkin method, numerical convergence rates are obtained which show the LSFEM to be virtually optimal. The LSFEM is used as a framework for an iteratively reweighted LSFEM yielding nonoscillatory and nondiffusive solutions for problems with contact discontinuities; this method is shown to convect contact discontinuities without error when using triangular and bilinear elements.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: Journal of Computational Physics (ISSN 0021-9991); 105; 1; p. 108-121.
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    Vibrational relaxation of anharmonic oscillators in expanding flows (1993)
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    Publication Date: 2011-08-24
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: Journal of Spacecraft and Rockets (ISSN 0022-4650); 30; 1; p. 59-68.
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    Linear stability of the compressible reacting mixing layer (1993)
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    Publication Date: 2011-08-24
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: AIAA Journal (ISSN 0001-1452); 31; 4; p. 677-685.
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    Inertial transfers in the helical decomposition (1993)
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    Publication Date: 2011-08-24
    Description: The directions of the triadic energy transfers assumed in a previous paper agree with the spectral closures, in a similarity range, if the exponent of the power-law energy spectrum is less than unity. The helical interactions showing a strong local energy transfer when the triad is nonlocal, sum up to a reverse cascade unless the spectrum falls off faster than a -7/3 power of the wave number. The energy cascades from each type of helical interaction are calculated for a -5/3 inertial range using the eddy damped quasinormal Markovian model. One type of interaction is responsible for 86 percent of the cascade. The contributions of the two classes of helical interactions to the subgrid-scale eddy viscosity are presented, together with the contributions from the forward and reverse cascading interactions. An application of the assumption on the triadic energy transfers to turbulence under rapid rotation gives a simple argument for the tendency toward nonlinear two-dimensionalization of the flow.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: Physics of Fluids A (ISSN 0899-8213); 5; 3; p. 677-685.
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    Propagation velocity of perturbations in turbulent channel flow (1993)
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    Publication Date: 2011-08-24
    Description: A database obtained from direct numerical simulation of a turbulent channel flow is analyzed to extract the streamwise component of the propagation velocity V of velocity, vorticity, and pressure fluctuations from their space-time correlations. A surprising result is that V is approximately the same as the local mean velocity for most of the channel, except for the near-wall region. For y(+) less than 15, V is virtually constant, implying that perturbations of all flow variables propagate like waves near the wall. In this region V is 55 percent of the centerline velocity Uc for velocity and vorticity perturbations and 75 percent of U sub c for pressure perturbations. This is equal to U at y(+) = 15 for velocity and vorticity perturbations, and equal to U at y(+) = 20 for pressure perturbations, indicating that the dynamics of the nearwall turbulence is controlled by turbulence structures present near y(+) about 15-20. Scale dependence of V is also examined by analyzing the bandpass-filtered flow fields. This paper contains comprehensive documentation on the propagation velocities, which should prove useful in the evaluation of Taylor's hypothesis.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: Physics of Fluids A (ISSN 0899-8213); 5; 3; p. 695-706.
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    Design considerations for a Space Shuttle Main Engine turbine blade made of single crystal material (1993)
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    Publication Date: 2011-08-24
    Description: Nonlinear finite-element structural analyses were performed on the first stage high-pressure fuel turbopump blade of the Space Shuttle Main Engine. The analyses examined the structural response and the dynamic characteristics at typical operating conditions. Single crystal material PWA-1480 was considered for the analyses. Structural response and the blade natural frequencies with respect to the crystal orientation were investigated. The analyses were conducted based on typical test stand engine cycle. Influence of combined thermal, aerodynamic, and centrifugal loadings was considered. Results obtained showed that the single crystal secondary orientation effects on the maximum principal stresses are not highly significant.
    Keywords: STRUCTURAL MECHANICS
    Type: Computers & Structures (ISSN 0045-7949); 46; 2; p. 249-259.
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    Reliability analysis of laminated ceramic matrix composites using shell subelement techniques (1993)
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    Publication Date: 2011-08-24
    Keywords: STRUCTURAL MECHANICS
    Type: AIAA Journal (ISSN 0001-1452); 31; 11; p. 2181-2183.
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    Mass-additive modal test method for verification of constrained structural models (1993)
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    Publication Date: 2011-08-24
    Description: A method for deriving constrained or fixed-base modes and frequencies from free-free modes of a structure with mass-loaded boundaries is developed. Problems associated with design and development of test fixtures can be avoided with such an approach. The analytical methodology presented is used to assess applicability of the mass-additive method for three types of structures and to determine the accuracy of derived constrained modes and frequencies. Results show that mass loading of the boundaries enables local interface modes to be measured within a desired frequency bandwidth, thus allowing constrained modes to be derived with considerably fewer free-free modes than for unloaded boundaries. Good convergence was obtained for a simple beam and a truss-like Shuttle payload, both of which had well-spaced modes and stiff interface support structures. Slow convergence was obtained for a space station module prototype, a shell-like structure having high modal density.
    Keywords: STRUCTURAL MECHANICS
    Type: AIAA Journal (ISSN 0001-1452); 31; 11; p. 2148-2153.
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    Optimization by decomposition in structural and multidisciplinary applications (1993)
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    Publication Date: 2011-08-24
    Description: An algorithm for a general, multilevel structural optimization by substructuring is derived, based on the linear decomposition concept that is rooted in the Bellman's Optimality Criterion enhanced with the optimum sensitivity derivatives used as a means to account for coupling among the subproblems, each of which is limited to optimization of a substructure. The algorithm applies also to those multidisciplinary problems whose subproblems form a hierarchy similar to that of substructures. In systems where the subproblems communicate with each other at the same level, the decomposition becomes non-hierarchic and the system may be optimized as a whole based on the derivatives of the system behavior with respect to the design variables computed by a method that bypasses finite differencing on the system analysis. When a multidisciplinary system includes a structure as its part, a hybrid, hierarchic/non-hierarchic decomposition applies. Numerical examples and references to computational experience accumulated to date illustrate the discussion.
    Keywords: STRUCTURAL MECHANICS
    Type: In: Optimization of large structural systems; Proceedings of the NATO(DFG Advanced Study Institute, Berchtesgaden, Germany, Sept. 23-Oct. 4, 1991. Vol. 1 (A93-54501 24-39); p. 193-233.
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    Effect of radiation on convection in a top-heated enclosure (1993)
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    Publication Date: 2011-08-24
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: Journal of Thermophysics and Heat Transfer (ISSN 0887-8722); 7; 4; p. 561-568.
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    Frequency domain stress intensity calibration of damped cracked panels (1993)
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    Publication Date: 2011-08-24
    Description: This paper discusses two schemes for doing finite element K calibration in the frequency domain. The baseline scheme uses the definition of K as a limit toward the crack tip. The limiting process requires using a very fine mesh around the crack tip making the scheme computationally very expensive. It is shown that the behavior of K as a function of frequency is very similar to a modal response. Taking advantage of this, a more efficient scheme involves a modal analysis of the cracked sheet and scaling the response to that of the static stress intensity. In this way, only a static K calibration need be performed. All the examples shown are for a frequency range spanning multiple resonances and with two levels of damping.
    Keywords: STRUCTURAL MECHANICS
    Type: International Journal of Fracture (ISSN 0376-9429); 61; 2; p. 123-130.
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    On the measurement of lateral velocity derivatives in turbulent flows (1993)
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    Publication Date: 2011-08-24
    Description: Direct numerical simulation data for the lateral velocity derivative delta(u)/delta(y) at the centerline of a fully developed turbulent channel flow provide reasonable support for Wyngaard's analysis of the error involved in measuring this quantity using parallel hot wires. Numerical data in the wall region of the channel flow also provide a useful indication of how to select the separation between the wires. Justification for this choice is obtained by comparing several measured statistics of delta(u)/delta(y) with the corresponding numerical data.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: Experiments in Fluids (ISSN 0723-4864); 15; 1; p. 65-69.
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    Streamwise vortices in heated boundary layers (1993)
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    Publication Date: 2011-08-24
    Description: The nonlinear instability of the boundary layer on a heated flat plate placed in an oncoming flow is investigated. Such flows are unstable to stationary vortex instabilities and inviscid travelling wave disturbances governed by the Taylor-Goldstein equation. For small temperature differences the Taylor-Goldstein equation reduces to Rayleigh's equation. When the temperature difference between the wall and free stream is small the preferred mode of instability is a streamwise vortex. It is shown in this case that the vortex, assumed to be of small wavelength, restructures the underlying mean flow to produce a profile which can be massively unstable to inviscid travelling waves. The mean state is shown to be destabilized if the Prandtl number is less than unity.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: Journal of Fluid Mechanics (ISSN 0022-1120); p. 301-324.
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    Progress towards understanding and predicting heat transfer in the turbine gas path (1993)
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    Publication Date: 2011-08-24
    Description: A new era is dawning in the ability to predict convection heat transfer in the turbine gas path. We feel that the technical community now has the capability to mount a major assault on this problem, which has eluded significant progress for a long time. In this paper we hope to make a case for this bold statement by reviewing the state of the art in three major and related areas, which we believe are indispensable to the understanding and accurate prediction of turbine gas path heat transfer: configuration-specific experiments, fundamental physics and model development, and code development. We begin our review with the configuration-specific experiments, whose data have provided the big picture and guided both the fundamental modeling research and the code development. Following that, we examine key modeling efforts and comment on what will be needed to incorporate them into the codes. In this region we concentrate on bypass transition, 3D endwalls, and film cooling. We then review progress and directions in the development of computer codes to predict turbine gas path heat transfer. Finally, we cite examples and make observations on the more recent efforts to do all this work in a simultaneous, interactive, and more synergistic manner. We conclude with an assessment of progress, suggestions for how to use the current state of the art, and recommendations for the future.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: International Journal of Heat and Fluid Flow (ISSN 0142-727X); 14; 2; p. 106-128.
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    One-equation near-wall turbulence modeling with the aid of direct simulation data (1993)
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    Publication Date: 2011-08-24
    Description: The length scales appearing in the relations for the eddy viscosity and dissipation rate in one-equation models were evaluated from direct numerical (DNS) simulation data for developed channel and boundary-layer flow at two Reynolds numbers each. To prepare the ground for the evaluation, the distribution of the most relevant mean-flow and turbulence quantities is presented and discussed, also with respect to Reynolds-number influence and to differences between channel and boundary-layer flow. An alternative model is tested as near wall component of a two-layer model by application to developed-channel, boundary-layer and backward-facing-step flows.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: ASME, Transactions, Journal of Fluids Engineering (ISSN 0098-2202); 115; 2; p. 196-205.
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    Comparison of advanced reduced-basis methods for transient structural analysis (1993)
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    Publication Date: 2011-08-24
    Keywords: STRUCTURAL MECHANICS
    Type: AIAA Journal (ISSN 0001-1452); 31; 9; p. 1712-1719.
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    Analytical stress intensity solution for the Stable Poisson Loaded specimen (1993)
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    Publication Date: 2011-08-24
    Description: An analytical calibration of the Stable Poisson Loaded (SPL) specimen is presented. The specimen configuration is similar to the ASTM E-561 compact-tension specimen with displacement controlled wedge loading used for R-curve determination. The crack mouth opening displacements (CMODs) are produced by the diametral expansion of an axially compressed cylindrical pin located in the wake of a machined notch. Due to the unusual loading configuration, a three-dimensional finite element analysis was performed with gap elements simulating the contact between the pin and specimen. In this report, stress intensity factors, CMODs, and crack displacement profiles, are reported for different crack lengths and different contacting conditions. It was concluded that the computed stress intensity factor decreases sharply with increasing crack length thus making the SPL specimen configuration attractive for fracture testing of brittle, high modulus materials.
    Keywords: STRUCTURAL MECHANICS
    Type: International Journal of Fracture (ISSN 0376-9429); 60; 3; p. 209-220.
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    Optimal design of a composite structure (1993)
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    Publication Date: 2011-08-24
    Description: This paper presents a design methodology for a laminated composite stiffened panel, subjected to multiple in-plane loads and bending moments. Design variables include the skin and stiffener ply orientation angles and stiffener geometry variables. Optimum designs are sought which minimize structural weight and satisfy mechanical performance requirements. Two types of mechanical performance requirements are placed on the panel, maximum strain and minimum strength. Minimum weight designs are presented which document that the choice of mechanical performance requirements cause changes in the optimum design. The effects of lay-up constraints which limit the ply angles to user specified values, such as symmetric or quasi-isotropic laminates, are also investigated.
    Keywords: STRUCTURAL MECHANICS
    Type: Composite Structures (ISSN 0263-8223); 24; 4; p. 273-281.
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    Degrees of locality of energy transfer in the inertial range (1993)
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    Publication Date: 2011-08-24
    Description: Measured raw transfer interactions from which local energy transfer is argued to result are summed in a way that directly indicates the scale disparity (s) of contributions to the net energy flux across the spectrum. It is found that the dependence upon s closely follows the s exp -4/3 form predicted by classical arguments. As a result, it is concluded that direct numerical simulation measurements lend support to the classical Kolmogorov phenomenology of local interactions and local transfer in an inertial range.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: Physics of Fluids A (ISSN 0899-8213); 5; 5; p. 1092-1094.
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    Transition to chaos in an open unforced 2D flow (1993)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: The present numerical study of unsteady, low Reynolds number flow past a 2D airfoil attempts to ascertain the bifurcation sequence leading from simple periodic to complex aperiodic flow with rising Reynolds number, as well as to characterize the degree of chaos present in the aperiodic flow and assess the role of numerics in the modification and control of the observed bifurcation scenario. The ARC2D Navier-Stokes code is used in an unsteady time-accurate mode for most of these computations. The system undergoes a period-doubling bifurcation to chaos as the Reynolds number is increased from 800 to 1600; its chaotic attractors are characterized by estimates of the fractal dimension and partial Liapunov exponent spectra.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: Journal of Computational Physics (ISSN 0021-9991); 105; 1; p. 133-149.
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    Navier-Stokes solutions with surface catalysis for Martian atmospheric entry (1993)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: Journal of Spacecraft and Rockets (ISSN 0022-4650); 30; 1; p. 32-42.
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    Spanwise scale selection in plane mixing layers (1993)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: Direct numerical simulations of temporally evolving plane mixing layers undergoing as many as three pairings have been examined for evidence of spanwise scale change. All simulations were begun from a few low-wavenumber disturbances, usually derived from linear stability theory, in addition to the mean velocity. The amplitude of the initial three-dimensional disturbances varied from infinitesimal to large enough to trigger a rapid transition to turbulence. The time required for a change of characteristic spanwise scale with infinitesimal three-dimensional disturbances was found to be very long, requiring three or more pairings to complete a doubling of the spanwise scale. Stronger three-dimensionality can produce more rapid scale changes, but it is also likely to trigger transition to turbulence. No evidence was found for a change from an organized array of rib vortices at one spanwise scale to a similar array at a larger spanwise scale.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: Journal of Fluid Mechanics (ISSN 0022-1120); p. 321-337.
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    Implicit treatment of diffusion terms in lower-upper algorithms (1993)
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    Publication Date: 2011-08-24
    Description: A method is presented which allows diffusion terms to be treated implicitly in the lower-upper (LU) algorithm (which is a commonly used method for solving 'compressible' Euler and Navier-Stokes equations) so that the algorithm's good stability properties will not be impaired. The new method generalizes the concept of LU factorization from that associated with the sign of eigenvalues to that associated with backward- and forward-difference operators without regard to eigenvalues. The method is verified in a turbulent boundary layer study.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: AIAA Journal (ISSN 0001-1452); 31; 4; p. 788-791.
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    Three-dimensional boundary-layer instability and separation induced by small-amplitude streamwise vorticity in the upstream flow (1993)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: We consider the effects of a small-amplitude, steady, streamwise vorticity field on the flow over an infinitely thin flat plate in an otherwise uniform stream. We show how the initially linear perturbation, ultimately leads to a small-amplitude but nonlinear cross flow far downstream from the leading edge. This motion is imposed on the boundary-layer flow and eventually causes the boundary layer to separate. The streamwise velocity profiles within the boundary layer become inflexional in localized spanwise regions just upstream of the separation point. The flow in these regions is therefore susceptible to rapidly growing inviscid instabilities.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: Journal of Fluid Mechanics (ISSN 0022-1120); p. 21-41.
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    Structural design for control (1993)
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    Publication Date: 2011-08-24
    Description: Recent advances in structural design for control are reviewed. Attention is given to adaptive structures, passive damping, ground testing, and system identification. Directions for future research are suggested.
    Keywords: STRUCTURAL MECHANICS
    Type: In: Flight-vehicle materials, structures, and dynamics - Assessment and future directions. Vol. 5 - Structural dynamics and aeroelasticity (A94-12676 02-39); p. 85-94.
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    General modeling methods (1993)
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    Publication Date: 2011-08-24
    Description: The benefits of structural dynamics modeling methods in aerospace structures are reviewed. Four major issues in structural dynamics modeling are discussed which encompass most of its subdisciplines: reduced order modeling, constraints in problems with large motions, computational strategies, and fundamental methods. Directions for future research in these areas are addressed.
    Keywords: STRUCTURAL MECHANICS
    Type: In: Flight-vehicle materials, structures, and dynamics - Assessment and future directions. Vol. 5 - Structural dynamics and aeroelasticity (A94-12676 02-39); p. 5-17.
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    Component modes damping assignment methodology for articulated, multiflexible body structures (1993)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: To simulate the dynamical motion of articulated, multiflexible body structures, one can use multibody simulation packages such as DISCOS. To this end, one must supply appropriate reduced-order models for all of the flexible components involved. The component modes projection and assembly model reduction (COMPARE) methodology is one way to construct these reduced-order component models, which when reassembled capture important system input-to-output mapping of the full-order model at multiple system configurations of interest. In conjunction, we must also supply component damping matrices which when reassembled generate a system damping matrix that has certain desirable properties. The problem of determining the damping factors of components' modes to achieve a given system damping matrix is addressed here. To this end, we must establish from first principles a matrix-algebraic relation between the system's modal damping matrix and the components' modal damping matrices. An unconstrained/constrained optimization problem can then be formulated to determine the component modes' damping factors that best satisfy that matrix-algebraic relation. The effectiveness of the developed methodology, called ModeDamp, has been successfully demonstrated on a high-order, finite element model of the Galileo spacecraft.
    Keywords: STRUCTURAL MECHANICS
    Type: Journal of Guidance, Control, and Dynamics (ISSN 0731-5090); 16; 6; p. 1101-1108.
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    Direct correlation of test-analysis cross-orthogonality (1993)
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    Publication Date: 2011-08-24
    Description: This paper presents an alternative to the correlation of individual components of a mode shape vectors by directly examining the sensitivity of the cross-orthogonality between test and analytical mode shapes. If the test and analysis mode shapes are identical, the diagonal elements of the cross-orthogonality will be identical to the test orthogonality matrix, so the cross-orthogonality matrix provides a concise measure of the 'closeness' between test and analysis mode shapes. There are two major advantages to the cross-orthogonality correlation approach. The first is that a direct correlation of this matrix will more directly meet the goal of the correlation effort (measured by cross-orthogonality). Secondly, and more importantly, the correlation of cross-orthogonality greatly reduces the amount of data that needs to be handled when compared to the correlation of mode shapes.
    Keywords: STRUCTURAL MECHANICS
    Type: Modal Analysis: The International Journal of Analytical and Experimental Modal Analysis (ISSN 1066-0763); 8; 3; p. 247-255.
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    Discussion of 'Comparison of turbulence models for the natural convection boundary layer along a heated vertical plate' (1993)
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    Publication Date: 2011-08-24
    Description: The paper presents a critical comment on the work of Henkes and Hoogendoorn. In particular, it is argued that the model of To and Humphrey (TH) (1986) has been implemented incorrectly, rendering invalid the conclusion that the TH model considerably deviates from the other models evaluated. In their response to the criticism, the authors present arguments in support of the correctness of their implementation of the TH model and of the validity of the conclusions reached in their work.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: International Journal of Heat and Mass Transfer (ISSN 0017-9310); 36; 1; p. 245, 246; Authors
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    Lagrangian solution of supersonic real gas flows (1993)
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    Publication Date: 2011-08-24
    Description: The present extention of a Lagrangian approach of the Riemann solution procedure, which was originally proposed for perfect gases, to real gases, is nontrivial and requires the development of an exact real-gas Riemann solver for the Lagrangian form of the conservation laws. Calculations including complex wave interactions of various types were conducted to test the accuracy and robustness of the approach. Attention is given to the case of 2D oblique waves' capture, where a slip line is clearly in evidence; the real gas effect is demonstrated in the case of a generic engine nozzle.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: Journal of Computational Physics (ISSN 0021-9991); 104; 1; p. 150-161.
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    Acceleration of convergence and spectrum transformation of implicit finite difference operators associated with Navier-Stokes equations (1993)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: Implicit difference operator spectra are presently computed by applying eigensystem analysis techniques to finite-difference formulations of 2D Euler and Navier-Stokes equations, and attention is given to these iterative methods' convergence and stability characteristics by taking into account the effects of grid geometry, time-step, numerical viscosity, and boundary conditions. On the basis of the eigenvalue distributions for various flow configurations, the feasibility of applying such convergence-acceleration techniques as eigenvalue annihilation and relaxation is discussed. Spectrum-shifting is applied to NASA-Ames' ARC2D flow code, achieving a 20-33 percent efficiency.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: Journal of Computational Physics (ISSN 0021-9991); 104; 1; p. 1-13.
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    Direct solution of two-dimensional Navier-Stokes equations for static aeroelasticity problems (1993)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Keywords: STRUCTURAL MECHANICS
    Type: AIAA Journal (ISSN 0001-1452); 31; 1; p. 148-153.
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    Earth atmosphere entry thermal protection by radiation backscattering ablating materials (1993)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: Journal of Thermophysics and Heat Transfer (ISSN 0887-8722); 7; 1; p. 74-81.
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    Analytical comparison of convective heat transfer correlations in supercritical hydrogen (1993)
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    Publication Date: 2011-08-24
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: Journal of Thermophysics and Heat Transfer (ISSN 0887-8722); 7; 1; p. 68-73.
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    Finite element solution for the structural behavior of a scientific balloon (1993)
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    Publication Date: 2011-08-24
    Description: A finite element solution for the structural behavior of a scientific balloon has been obtained using a non-linear finite element code. The pneumatic skin is modelled by shell elements that are given a small artificial bending stiffness to overcome numerical problems yet the membrane solution remains unaffected. Validation of the analysis approach is provided through strain measurements on a small scale balloon that exhibits all essential features of a full scale balloon.
    Keywords: STRUCTURAL MECHANICS
    Type: Advances in Space Research (ISSN 0273-1177); 13; 2; p. 45-48.
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    Micrometeoroid/space debris effects on materials (1993)
    In:  CASI
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    Publication Date: 2013-08-31
    Description: The Long Duration Exposure Facility (LDEF) micrometeoroid/space debris impact data has been reduced in terms that are convenient for evaluating the overall quantitative effect on material properties. Impact crater flux has been evaluated as a function of angle from velocity vector and as a function of crater size. This data is combined with spall data from flight and ground testing to calculate effective solar absorption and emittance values versus time. Results indicate that the surface damage from micrometeoroid/space debris does not significantly affect the overall surface optical thermal physical properties. Of course the local damage around impact craters radically alter optical properties. Damage to composites and solar cells on an overall basis was minimal.
    Keywords: STRUCTURAL MECHANICS
    Type: LDEF Materials Results for Spacecraft Applications; p 259-279
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    Investigation of the asymptotic state of rotating turbulence using large-eddy simulation (1993)
    In:  CASI
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    Publication Date: 2013-08-31
    Description: Study of turbulent flows in rotating reference frames has long been an area of considerable scientific and engineering interest. Because of its importance, the subject of turbulence in rotating reference frames has motivated over the years a large number of theoretical, experimental, and computational studies. The bulk of these previous works has served to demonstrate that the effect of system rotation on turbulence is subtle and remains exceedingly difficult to predict. A rotating flow of particular interest in many studies, including the present work, is examination of the effect of solid-body rotation on an initially isotropic turbulent flow. One of the principal reasons for the interest in this flow is that it represents the most basic turbulent flow whose structure is altered by system rotation but without the complicating effects introduced by mean strains or flow inhomogeneities. The assumption of statistical homogeneity considerably simplifies analysis and computation. The principal objective of the present study has been to examine the asymptotic state of solid-body rotation applied to an initially isotropic, high Reynolds number turbulent flow. Of particular interest has been to determine the degree of two-dimensionalization and the existence of asymptotic self-similar states in homogeneous rotating turbulence.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: Stanford Univ., Annual Research Briefs, 1993; p 157-170
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    Dynamic localization and second-order subgrid-scale models in large eddy simulations of channel flow (1993)
    In:  CASI
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    Publication Date: 2013-08-31
    Description: The objective here is to test the Dynamic Localization (DL) model in a wall-bounded channel flow for numerical stability and accuracy of results. Algebraic stress models suggest that the model for the residual subgrid-scale (SGS) Reynolds stress and scalar flux should generally have terms comprising most of the unique products of the resolved strain (S) and rotation (R) tensors with S and the resolved scalar gradient. The standard dynamic SGS model uses a simple (Smagorinsky) base model for the residual Reynolds stress, which is made proportional to S, and down-gradient base models for residual scalar fluxes; these correspond to the lowest, 'first-order' terms in algebraic stress models. Temporal scaling terms in these base models are formed from the magnitude of the resolved strain rate. While this is appropriate for simple shear flows, it may not be appropriate for more complicated flows (relevant to geophysical and astrophysical problems) that include any combination of shear, rotation, buoyancy, etc. On the other hand, the coefficient in the dynamic SGS model readily adjusts itself to different flow conditions and may adequately take account of these effects without the need for more complicated base models. Cabot (1993) has begun to test the dynamic SGS model in buoyant flows (Rayleigh-Benard and internally heated convection) with and without buoyancy terms explicitly included in the scaling terms of the base model; no great differences were found in large eddy simulation (LES) results for the different base model scalings. The second objective in this work is to test base models with additional, 'second-order' terms (e.g., S(sup 2) and RS for the residual Reynolds stress). These terms have been found to improve large-scale flow predictions by kappa-epsilon models in the presence of rotation and shear. Second-order base models will be tested here in the LES of channel flow with and without solid-body rotation and compared with results from the standard first-order base models to determine if there are significant differences or improvements in results that would warrant the added complexity of the second-order base models.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: Stanford Univ., Annual Research Briefs, 1993; p 129-144
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    On streak spacing in wall-bounded turbulent flows (1993)
    In:  CASI
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    Publication Date: 2013-08-31
    Description: The present study is a continuation of the examination by Hamilton et al. of the regeneration mechanisms of near-wall turbulence and an attempt to investigate the conjecture of Waleffe et al. The basis of this study is an extension of the 'minimal channel' approach of Jimenez and Moin that emphasizes the near-wall region and reduces the complexity of the turbulent flow by considering a plane Couette flow of near minimum Reynolds number and stream-wise and span-wise extent. Reduction of the flow Reynolds number to the minimum value which will allow turbulence to be sustained has the effect of reducing the ratio of the largest scales to the smallest scales or, equivalently, of causing the near-wall region to fill more of the area between the channel walls. A plane Couette flow was chosen for study since this type of flow has a mean shear of a single sign, and at low Reynolds numbers, the two wall regions are found to share a single set of structures.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: Stanford Univ., Annual Research Briefs, 1993; p 249-257
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    Numerical simulation of non-Newtonian free shear flows (1993)
    In:  CASI
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    Publication Date: 2013-08-31
    Description: Free shear flows, like those of mixing layers, are encountered in aerodynamics, in the atmosphere, and in the ocean as well as in many industrial applications such as flow reactors or combustion chambers. It is, therefore, crucial to understand the mechanisms governing the process of transition to turbulence in order to predict and control the evolution of the flow. Delaying transition to turbulence as far downstream as possible allows a gain in energy expenditure while accelerating the transition can be of interest in processes where high mixing is desired. Various methods, including the use of polymer additives, can be effective in controlling fluid flows. The drag reduction obtained by the addition of small amounts of high polymers has been an active area of research for the last three decades. It is now widely believed that polymer additives can affect the stability of a large variety of flows and that dilute solutions of these polymers have been shown to produce drag reductions of over 80 percent in internal flows and over 60 percent in external flows under a wide range of conditions. The major thrust of this work is to study the effects of polymer additives on the stability of the incompressible mixing layer through large scale numerical simulations. In particular, we focus on the two dimensional flow and examine how the presence of viscoelasticity may affect the typical structures of the flow, namely roll-up and pairing of vortices.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: Annual Research Briefs, 1993; p 259-268
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    A transport equation for the scalar dissipation in reacting flows with variable density: First results (1993)
    In:  CASI
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    Publication Date: 2013-08-31
    Description: Although the different regimes of premixed combustion are not well defined, most of the recent developments in turbulent combustion modeling are led in the so-called flamelet regime. The goal of these models is to give a realistic expression to the mean reaction rate (w). Several methods can be used to estimate (w). Bray and coworkers (Libby & Bray 1980, Bray 1985, Bray & Libby 1986) express the instantaneous reaction rate by means of a flamelet library and a frequency which describes the local interaction between the laminar flamelets and the turbulent flowfield. In another way, the mean reaction rate can be directly connected to the flame surface density (Sigma). This quantity can be given by the transport equation of the coherent flame model initially proposed by Marble & Broadwell 1977 and developed elsewhere. The mean reaction rate, (w), can also be estimated thanks to the evolution of an arbitrary scalar field G(x, t) = G(sub O) which represents the flame sheet. G(x, t) is obtained from the G-equation proposed by Williams 1985, Kerstein et al. 1988 and Peters 1993. Another possibility proposed in a recent study by Mantel & Borghi 1991, where a transport equation for the mean dissipation rate (epsilon(sub c)) of the progress variable c is used to determine (w). In their model, Mantel & Borghi 1991 considered a medium with constant density and constant diffusivity in the determination of the transport equation for (epsilon(sub c)). A comparison of different flamelet models made by Duclos et al. 1993 shows the realistic behavior of this model even in the case of constant density. Our objective in this present report is to present preliminary results on the study of this equation in the case of variable density and variable diffusivity. Assumptions of constant pressure and a Lewis number equal to unity allow us to significantly simplify the equation. A systematic order of magnitude analysis based on adequate scale relations is performed on each term of the equation. As in the case of constant density and constant diffusivity, the effects of stretching of the scalar field by the turbulent strain field, of local curvature, and of chemical reactions are predominant. In this preliminary work, we suggest closure models for certain terms, which will be validated after comparisons with DNS data.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: Stanford Univ., Annual Research Briefs, 1993; p 219-228
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    A large eddy simulation scheme for turbulent reacting flows (1993)
    In:  CASI
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    Publication Date: 2013-08-31
    Description: The recent development of the dynamic subgrid-scale (SGS) model has provided a consistent method for generating localized turbulent mixing models and has opened up great possibilities for applying the large eddy simulation (LES) technique to real world problems. Given the fact that the direct numerical simulation (DNS) can not solve for engineering flow problems in the foreseeable future (Reynolds 1989), the LES is certainly an attractive alternative. It seems only natural to bring this new development in SGS modeling to bear on the reacting flows. The major stumbling block for introducing LES to reacting flow problems has been the proper modeling of the reaction source terms. Various models have been proposed, but none of them has a wide range of applicability. For example, some of the models in combustion have been based on the flamelet assumption which is only valid for relatively fast reactions. Some other models have neglected the effects of chemical reactions on the turbulent mixing time scale, which is certainly not valid for fast and non-isothermal reactions. The probability density function (PDF) method can be usefully employed to deal with the modeling of the reaction source terms. In order to fit into the framework of LES, a new PDF, the large eddy PDF (LEPDF), is introduced. This PDF provides an accurate representation for the filtered chemical source terms and can be readily calculated in the simulations. The details of this scheme are described.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: Stanford Univ., Annual Research Briefs, 1993; p 187-194
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    On the large eddy simulation of turbulent flows in complex geometry (1993)
    In:  CASI
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    Publication Date: 2013-08-31
    Description: Application of the method of Large Eddy Simulation (LES) to a turbulent flow consists of three separate steps. First, a filtering operation is performed on the Navier-Stokes equations to remove the small spatial scales. The resulting equations that describe the space time evolution of the 'large eddies' contain the subgrid-scale (sgs) stress tensor that describes the effect of the unresolved small scales on the resolved scales. The second step is the replacement of the sgs stress tensor by some expression involving the large scales - this is the problem of 'subgrid-scale modeling'. The final step is the numerical simulation of the resulting 'closed' equations for the large scale fields on a grid small enough to resolve the smallest of the large eddies, but still much larger than the fine scale structures at the Kolmogorov length. In dividing a turbulent flow field into 'large' and 'small' eddies, one presumes that a cut-off length delta can be sensibly chosen such that all fluctuations on a scale larger than delta are 'large eddies' and the remainder constitute the 'small scale' fluctuations. Typically, delta would be a length scale characterizing the smallest structures of interest in the flow. In an inhomogeneous flow, the 'sensible choice' for delta may vary significantly over the flow domain. For example, in a wall bounded turbulent flow, most statistical averages of interest vary much more rapidly with position near the wall than far away from it. Further, there are dynamically important organized structures near the wall on a scale much smaller than the boundary layer thickness. Therefore, the minimum size of eddies that need to be resolved is smaller near the wall. In general, for the LES of inhomogeneous flows, the width of the filtering kernel delta must be considered to be a function of position. If a filtering operation with a nonuniform filter width is performed on the Navier-Stokes equations, one does not in general get the standard large eddy equations. The complication is caused by the fact that a filtering operation with a nonuniform filter width in general does not commute with the operation of differentiation. This is one of the issues that we have looked at in detail as it is basic to any attempt at applying LES to complex geometry flows. Our principal findings are summarized.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: Stanford Univ., Annual Research Briefs, 1993; p 111-128
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    Unified approach for incompressible flows (1993)
    In:  CASI
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    Publication Date: 2013-08-31
    Description: An unified approach for solving both compressible and incompressible flows was investigated in this study. The difference in CFD code development between incompressible and compressible flows is due to the mathematical characteristics. However, if one can modify the continuity equation for incompressible flows by introducing pseudocompressibility, the governing equations for incompressible flows would have the same mathematical characters as compressible flows. The application of a compressible flow code to solve incompressible flows becomes feasible. Among numerical algorithms developed for compressible flows, the Centered Total Variation Diminishing (CTVD) schemes possess better mathematical properties to damp out the spurious oscillations while providing high-order accuracy for high speed flows. It leads us to believe that CTVD schemes can equally well solve incompressible flows. In this study, the governing equations for incompressible flows include the continuity equation and momentum equations. The continuity equation is modified by adding a time-derivative of the pressure term containing the artificial compressibility. The modified continuity equation together with the unsteady momentum equations forms a hyperbolic-parabolic type of time-dependent system of equations. The continuity equation is modified by adding a time-derivative of the pressure term containing the artificial compressibility. The modified continuity equation together with the unsteady momentum equations forms a hyperbolic-parabolic type of time-dependent system of equations. Thus, the CTVD schemes can be implemented. In addition, the boundary conditions including physical and numerical boundary conditions must be properly specified to obtain accurate solution. The CFD code for this research is currently in progress. Flow past a circular cylinder will be used for numerical experiments to determine the accuracy and efficiency of the code before applying this code to more specific applications.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: NASA. Johnson Space Center, National Aeronautics and Space Administration (NASA)(American Society for Engineering Education (ASEE) Summer Faculty Fellowship Program, 1993, Volume 1 6 p (SEE N94-25348; NASA. Johnson Space
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    Compressible turbulent flow simulation with a multigrid multiblock method (1993)
    In:  CASI
    Details
    Publication Date: 2013-08-31
    Description: We describe a multigrid multiblock method for compressible turbulent flow simulations and present results obtained from calculations on a two-element airfoil. A vertex-based spatial discretization method and explicit multistage Runge-Kutta time-stepping are used. The slow convergence of a single grid method makes the multigrid method, which yields a speed factor of about 20, indispensable. The numerical predictions are in good agreement with experimental results. It is shown that the convergence of the multigrid process depends considerably on the ordering of the various loops. If the block loop is put inside the stage loop, the process converges more rapidly than if the block loop is situated outside the stage loop when a three-stage Runge-Kutta method is used. If a five-stage scheme is used, the process does not converge in the latter block ordering. Finally, the process based on the five-stage method is about 60 percent more efficient than with the three-stage method, if the block loop is inside the stage loop.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: NASA. Langley Research Center, The Sixth Copper Mountain Conference on Multigrid Methods, Part 1; p 305-315
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  • 87
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    FAS multigrid calculations of three dimensional flow using non-staggered grids (1993)
    In:  CASI
    Details
    Publication Date: 2013-08-31
    Description: Grid staggering is a well known remedy for the problem of velocity/pressure coupling in incompressible flow calculations. Numerous inconveniences occur, however, when staggered grids are implemented, particularly when a general-purpose code, capable of handling irregular three-dimensional domains, is sought. In several non-staggered grid numerical procedures proposed in the literature, the velocity/pressure coupling is achieved by either pressure or velocity (momentum) averaging. This approach is not convenient for simultaneous (block) solvers that are preferred when using multigrid methods. A new method is introduced in this paper that is based upon non-staggered grid formulation with a set of virtual cell face velocities used for pressure/velocity coupling. Instead of pressure or velocity averaging, a momentum balance at the cell face is used as a link between the momentum and mass balance constraints. The numerical stencil is limited to 9 nodes (in 2D) or 27 nodes (in 3D), both during the smoothing and inter-grid transfer, which is a convenient feature when a block point solver is applied. The results for a lid-driven cavity and a cube in a lid-driven cavity are presented and compared to staggered grid calculations using the same multigrid algorithm. The method is shown to be stable and produce a smooth (wiggle-free) pressure field.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: NASA. Langley Research Center, The Sixth Copper Mountain Conference on Multigrid Methods, Part 1; p 17-29
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  • 88
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    An application of small-gap equations in sealing devices (1993)
    In:  CASI
    Details
    Publication Date: 2013-08-31
    Description: The study of a thin, incompressible Newtonian fluid layer trapped between two almost parallel, sliding surfaces has been actively pursued in the last decades. This subject includes lubrication applications such as slider bearings or the sealing of non-pressurized fluids with rubber rotary shaft seals. In the present work we analyze numerically the flow of lubricant fluid through a micro-gap of sealing devices. The first stage of this study is carried out assuming that a 'small-gap' parameter delta attains an extreme value in the Navier-Stokes equations. The precise meaning of small-gap is achieved by the particular limit delta = 0 which, within the bounds of the hypotheses, predicts transport of lubricant through the sealed area by centrifugal instabilities. Numerical results obtained with the penalty function approximation in the finite element method are presented. In particular, the influence of inflow and outflow boundary conditions, and their impact in the simulated flow, are discussed.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: NASA. Lewis Research Center, The Fifth Annual Thermal and Fluids Analysis Workshop; p 499-512
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  • 89
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    J-integral patch for finite element analysis of dynamic fracture due to impact of pressure vessels (1993)
    In:  CASI
    Details
    Publication Date: 2013-08-31
    Description: Prediction of whether a pressurized cylinder will fail catastrophically when impacted by a projectile has important applications ranging from perforation of an airplane's skin by a failed turbine blade to meteorite impact of a space station habitation module. This report summarizes the accomplishment of one task for a project whose aim is to simulate numerically the outcome of a high velocity impact of pressure vessels. A finite element patch covering the vicinity of a growing crack has been constructed to estimate the J-integral (crack driving force) during the impact. Explicit expressions for the J-integral through the nodal values of displacement, strain, and stress have been written. The patch is to be used repeatedly to estimate the amount of crack growth during the time of the impact. The resulting crack size is to be compared to an estimated critical crack size for the pressurized cylinder.
    Keywords: STRUCTURAL MECHANICS
    Type: The 1993 NASA(ASEE Summer Faculty Fellowship Program; 5 p
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  • 90
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    CFD simulation of coaxial injectors (1993)
    In:  CASI
    Details
    Publication Date: 2013-08-31
    Description: The development of improved performance models for the Space Shuttle Main Engine (SSME) is an important, ongoing program at NASA MSFC. These models allow prediction of overall system performance, as well as analysis of run-time anomalies which might adversely affect engine performance or safety. Due to the complexity of the flow fields associated with the SSME, NASA has increasingly turned to Computational Fluid Dynamics (CFD) techniques as modeling tools. An important component of the SSME system is the fuel preburner, which consists of a cylindrical chamber with a plate containing 264 coaxial injector elements at one end. A fuel rich mixture of gaseous hydrogen and liquid oxygen is injected and combusted in the chamber. This process preheats the hydrogen fuel before it enters the main combustion chamber, powers the hydrogen turbo-pump, and provides a heat dump for nozzle cooling. Issues of interest include the temperature and pressure fields at the turbine inlet and the thermal compatibility between the preburner chamber and injector plate. Performance anomalies can occur due to incomplete combustion, blocked injector ports, etc. The performance model should include the capability to simulate the effects of these anomalies. The current approach to the numerical simulation of the SSME fuel preburner flow field is to use a global model based on the MSFC sponsored FNDS code. This code does not have the capabilities of modeling several aspects of the problem such as detailed modeling of the coaxial injectors. Therefore, an effort has been initiated to develop a detailed simulation of the preburner coaxial injectors and provide gas phase boundary conditions just downstream of the injector face as input to the FDNS code. This simulation should include three-dimensional geometric effects such as proximity of injectors to baffles and chamber walls and interaction between injectors. This report describes an investigation into the numerical simulation of GH2/LOX coaxial injectors. The following sections will discuss the physical aspects of injectors, the CFD code employed, and preliminary results of a simulation of a single coaxial injector for which experimental data is available. It is hoped that this work will lay the foundation for the development of a unique and useful tool to support the SSME program.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: The 1993 NASA(ASEE Summer Faculty Fellowship Program; 6 p
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  • 91
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    A comparison of TSS and TRASYS in form factor calculation (1993)
    In:  CASI
    Details
    Publication Date: 2013-08-31
    Description: As the workstation and personal computer become more popular than a centralized mainframe to perform thermal analysis, the methods for space vehicle thermal analysis will change. Already, many thermal analysis codes are now available for workstations, which were not in existence just five years ago. As these changes occur, some organizations will adopt the new codes and analysis techniques, while others will not. This might lead to misunderstandings between thermal shops in different organizations. If thermal analysts make an effort to understand the major differences between the new and old methods, a smoother transition to a more efficient and more versatile thermal analysis environment will be realized.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: The Fifth Annual Thermal and Fluids Analysis Workshop; p 41-46
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  • 92
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    An engineering code to analyze hypersonic thermal management systems (1993)
    In:  CASI
    Details
    Publication Date: 2013-08-31
    Description: Thermal loads on current and future aircraft are increasing and as a result are stressing the energy collection, control, and dissipation capabilities of current thermal management systems and technology. The thermal loads for hypersonic vehicles will be no exception. In fact, with their projected high heat loads and fluxes, hypersonic vehicles are a prime example of systems that will require thermal management systems (TMS) that have been optimized and integrated with the entire vehicle to the maximum extent possible during the initial design stages. This will not only be to meet operational requirements, but also to fulfill weight and performance constraints in order for the vehicle to takeoff and complete its mission successfully. To meet this challenge, the TMS can no longer be two or more entirely independent systems, nor can thermal management be an after thought in the design process, the typical pervasive approach in the past. Instead, a TMS that was integrated throughout the entire vehicle and subsequently optimized will be required. To accomplish this, a method that iteratively optimizes the TMS throughout the vehicle will not only be highly desirable, but advantageous in order to reduce the manhours normally required to conduct the necessary tradeoff studies and comparisons. A thermal management engineering computer code that is under development and being managed at Wright Laboratory, Wright-Patterson AFB, is discussed. The primary goal of the code is to aid in the development of a hypersonic vehicle TMS that has been optimized and integrated on a total vehicle basis.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: NASA. Lewis Research Center, The Fifth Annual Thermal and Fluids Analysis Workshop; p 13-26
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  • 93
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    Multigrid properties of upwind-biased data reconstructions (1993)
    In:  CASI
    Details
    Publication Date: 2013-08-31
    Description: The multigrid properties of two data reconstruction methods used for achieving second-order spatial accuracy when solving the two-dimensional Euler equations are examined. The data reconstruction methods are used with an implicit upwind algorithm which uses linearized backward-Euler time-differencing. The solution of the resulting linear system is performed by an iterative procedure. In the present study only regular quadrilateral grids are considered, so a red-black Gauss-Seidel iteration is used. Although the Jacobian is approximated by first-order upwind extrapolation, two alternative data reconstruction techniques for the flux integral that yield higher-order spatial accuracy at steady state are examined. The first method, probably most popular for structured quadrilateral grids, is based on estimating the cell gradients using one-dimensional reconstruction along curvilinear coordinates. The second method is based on Green's theorem. Analysis and numerical results for the two dimensional Euler equations show that data reconstruction based on Green's theorem has superior multigrid properties as compared to the one-dimensional data reconstruction method.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: The Sixth Copper Mountain Conference on Multigrid Methods, Part 2; p 663-677
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  • 94
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    Transient dynamics capability at Sandia National Laboratories (1993)
    In:  CASI
    Details
    Publication Date: 2013-08-31
    Description: A brief overview of the transient dynamics capabilities at Sandia National Laboratories, with an emphasis on recent new developments and current research is presented. In addition, the Sandia National Laboratories (SNL) Engineering Analysis Code Access System (SEACAS), which is a collection of structural and thermal codes and utilities used by analysts at SNL, is described. The SEACAS system includes pre- and post-processing codes, analysis codes, database translation codes, support libraries, Unix shell scripts for execution, and an installation system. SEACAS is used at SNL on a daily basis as a production, research, and development system for the engineering analysts and code developers. Over the past year, approximately 190 days of CPU time were used by SEACAS codes on jobs running from a few seconds up to two and one-half days of CPU time. SEACAS is running on several different systems at SNL including Cray Unicos, Hewlett Packard PH-UX, Digital Equipment Ultrix, and Sun SunOS. An overview of SEACAS, including a short description of the codes in the system, are presented. Abstracts and references for the codes are listed at the end of the report.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA. Langley Research Center, Computational Methods for Crashworthiness; p 207-249
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  • 95
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    Numerical simulation of vehicle crashworthiness and occupant protection (1993)
    In:  CASI
    Details
    Publication Date: 2013-08-31
    Description: Numerical simulation of vehicle crashworthiness and occupant protection are addressed. The vehicle crashworthiness design objectives are to design the vehicle structure for optimum impact energy absorption, and to design the restraint system (seatbelts, airbags, bolsters, etc.) for optimum occupant protection. The following approaches are taken; a major part of the impact energy is to be absorbed by the vehicle structure; the restraint components will provide protection against the remaining crash energy; certain vehicle components are designed to deform under specific types and speeds of impact in a desired mode for sound energy management; structural components such as front side rails, rear rails, door structure and pillars undergo large amounts of deformation; and with properly designed geometry and material these components assist in mitigating the effects of impact.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA. Langley Research Center, Computational Methods for Crashworthiness; p 125-139
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  • 96
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    Impact analysis of composite aircraft structures (1993)
    In:  CASI
    Details
    Publication Date: 2013-08-31
    Description: The impact analysis of composite aircraft structures is discussed. Topics discussed include: background remarks on aircraft crashworthiness; comments on modeling strategies for crashworthiness simulation; initial study of simulation of progressive failure of an aircraft component constructed of composite material; and research direction in composite characterization for impact analysis.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA. Langley Research Center, Computational Methods for Crashworthiness; p 65-94
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  • 97
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    A coupled implicit solution method for turbulent spray combustion in propulsion systems (1993)
    In:  CASI
    Details
    Publication Date: 2013-08-31
    Description: Many reacting flows in propulsion devices cannot be efficiently calculated by modern compressible flow CFD algorithms. Most low-speed reacting flow codes based on TEACH-type technologies are inefficient and lack robustness for complex flows. Tremendous progress has been made in high-speed compressible flow CFD in the past two decades; extending its application range to low-speed regimes is highly desirable. The objectives of this document is to present an efficient and robust algorithm for multi-phase chemically reacting flows at all speeds, with emphasis on low Mach number flows, and to calculate turbulent spray combustion flow in a gas turbine combustor.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: NASA. Lewis Research Center, Workshop on Computational Turbulence Modeling; 16 p
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  • 98
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    Modelling chaotic vibrations using NASTRAN (1993)
    In:  CASI
    Details
    Publication Date: 2013-08-31
    Description: Due to the unavailability and, later, prohibitive cost of the computational power required, many phenomena in nonlinear dynamic systems have in the past been addressed in terms of linear systems. Linear systems respond to periodic inputs with periodic outputs, and may be characterized in the time domain or in the frequency domain as convenient. Reduction to the frequency domain is frequently desireable to reduce the amount of computation required for solution. Nonlinear systems are only soluble in the time domain, and may exhibit a time history which is extremely sensitive to initial conditions. Such systems are termed chaotic. Dynamic buckling, aeroelasticity, fatigue analysis, control systems and electromechanical actuators are among the areas where chaotic vibrations have been observed. Direct transient analysis over a long time period presents a ready means of simulating the behavior of self-excited or externally excited nonlinear systems for a range of experimental parameters, either to characterize chaotic behavior for development of load spectra, or to define its envelope and preclude its occurrence.
    Keywords: STRUCTURAL MECHANICS
    Type: COSMIC, The Twenty-First NASTRAN (R) Users' Colloquium; p 17-40
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  • 99
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    Long Duration Exposure Facility (LDEF) low temperature Heat Pipe Experiment Package (HEPP) flight results (1993)
    In:  CASI
    Details
    Publication Date: 2013-08-31
    Description: The Low Temperature Heat Pipe Flight Experiment (HEPP) is a fairly complicated thermal control experiment that was designed to evaluate the performance of two different low temperature ethane heat pipes and a low-temperature (182 K) phase change material. A total of 390 days of continuous operation with an axially grooved aluminum fixed conductance heat pipe and an axially grooved stainless steel heat pipe diode was demonstrated before the data acquisition system's batteries lost power. Each heat pipe had approximately 1 watt applied throughout this period. The HEPP was not able to cool below 188.6 K during the mission. As a result, the preprogrammed transport test sequence which initiates when the PCM temperature drops below 180 K was never exercised, and transport tests with both pipes and the diode reverse mode test could not be run in flight. Also, because the melt temperature of the n-heptane PCM is 182 K, its freeze/thaw behavior could not be tested. Post-flight thermal vacuum tests and thermal analyses have indicated that there was an apparent error in the original thermal analyses that led to this unfortunate result. Post-flight tests have demonstrated that the performance of both heat pipes and the PCM has not changed since being fabricated more than 14 years ago. A summary of HEPP's flight data and post-flight test results are presented.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: NASA. Langley Research Center, LDEF: 69 Months in Space. Part 4: Second Post-Retrieval Symposium; p 1455-1475
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  • 100
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    Evaluation of actuators for the SDOF and MDOF active microgravity isolation systems (1993)
    In:  CASI
    Details
    Publication Date: 2013-08-31
    Description: The University of Virginia examined the design of actuators for both single-degree-of-freedom (SDOF) and multiple-degree-of-freedom (MDOF) active microgravity isolation systems. For SDOF systems, two actuators were considered: a special large gap magnetic actuator and a large stroke Lorentz actuator. The magnetic actuator was viewed to be of greater difficulty than the Lorentz actuator with little compelling technical advantage and was dropped from consideration. A Lorentz actuator was designed and built for the SDOF test rig using magnetic circuit and finite element analysis. The design and some experimental results are discussed. The University also examined the design of actuators for MDOF isolation systems. This includes design of an integrated 1 cm gap 6-DOF noncontacting magnetic suspension system and of a 'coarse' follower which permits the practical extension of magnetic suspension to large strokes. The proposed 'coarse' actuator was a closed kinematic chain manipulator known as a Stewart Platform. The integration of the two isolation systems together, the isolation tasks assigned to each, and possible control architectures were also explored. The results of this research are examined.
    Keywords: STRUCTURAL MECHANICS
    Type: Magnetic Actuators and Suspension for Space Vibration Control; 45 p
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