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At least 919 records · Page 51
All sourcesNASA NTRSDOE OSTI
NASA NTRS1981

The compressive failure of graphite/epoxy plates with circular holes

The results of an experimental investigation of the compressive behavior of T300/5203 graphite/epoxy laminated plates measuring 127.0 by 254.0 mm and containing circular holes ranging to 38.1 mm are reported. Two thicknesses, 24-ply and 48-ply, were chosen to differentiate between stability failures resulting from buckling and strength failures caused by the hole. Both quasi-isotropic and orthotropic stacking arrangements were used. The critical buckling load of the 24-ply panels was independent of hole size. Bifurcation occurred in the two half-wave mode longitudinally and one half-wave mode laterally in the quasi-isotropic panels. For the orthotropic 24-ply panels, bifurcation began in the one half-wave mode shape in each direction, but changed to the two half-wave mode before failure. Consistent post-buckling strength was exhibited by both laminated configurations. Panels with hole diameters below 3.175 mm displayed buckling before failure; those with holes larger than 6.35 mm experienced material failure around the hole before panel collapse.

Knauss, J. F.↗
NASA NTRS1982

Mode propagation in nonuniform circular ducts with potential flow

A previously reported closed form solution is expanded to determine effects of isentropic mean flow on mode propagation in a slowly converging-diverging duct - a circular cosh duct. On the assumption of uniform steady fluid density, the mean flow increases the power transmission coefficient. The increase is directly related to the increase of the cutoff ratio at the duct throat. With the negligible transverse gradients of the steady fluid variables, the conversion from one mode to another is negligible, and the power transmission coefficient remains unchanged with the mean flow direction reversed. With a proper choice of frequency parameter, many different modes can be made subject to a single value of the power transmission loss. The paper also describes a systematic method to include the effects of the gradients of the steady fluid variables.

Cho, Y. C.↗
NASA NTRS1982

Recent developments in transonic Euler flow over a circular cylinder

Numerical solutions to the Euler equations for transonic flow over a circular cylinder suggest that the inviscid flow separates ahead of the rear stagnation point. The present understanding of this phenomenon and various solutions presented at a workshop on this subject are discussed. All the evidence suggests that inviscid separation is a feature of the Euler equations induced by vorticity and/or stagnation pressure loss in the flow. The possibility of multiple solutions suggested by Hafez (1981) and the oscillatory behavior for the full circle observed by Steger (1977) are seen as needing further investigation.

Salas, M. D.↗
NASA NTRS1982

An experiment on the flow past a finite circular cylinder at high subcritical and supercritical Reynolds numbers

The complicated flow in the tip region of a finite circular cylinder in uniform cross flow has been examined at the Reynolds numbers 85,000, 180,000, and 770,000. Simultaneous measurements of the surface-pressure and wake-velocity fluctuations have revealed the existence of a shedding regime in the tip region that is distinct from the one prevailing on the main body of the cylinder. In particular, this regime can be unstable and intermittent, can have a cellular structure in the wake, or can be subcritical when the main flow is supercritical.

Ayoub, A.↗
NASA NTRS1982

Nonlinear Marangoni convection in bounded layers. I - Circular cylindrical containers. II - Rectangular cylindrical containers

Liquid undergoing nonlinear Marangoni instability in a circular cylinder is examined, with attention given to roll-cell development and interaction. Surface deflections are neglected and the side walls are considered as adiabatic and impenetrable, allowing the liquid to freely slip. The nonlinear convective states are calculated and their stability is defined. The behavior and amplitude of cells forming in the liquid, heated from below, are modeled in order to derive all the transport properties. A new small parameter is formulated which is related to the critical Marangoni number of the infinite matrix expressing the eigenvalue expansion of the problem. The observed roll cell amplitudes and transport properties are shown to be available from simple eigenvalues, with double eigenvalues, indicating the existence of two roll-states as predicted by linear theory, nonlinear theory indicates transitions from one steady convective state to another.

Rosenblat, S.↗
NASA NTRS1982

Linearized transfer between coplanar circular orbits using blow down propulsion system

A closed form solution is presented for the coplanar transfer between nearby circular orbits for spacecraft using their own blow down propulsion system. The decaying thrust is applied along the local horizontal and the linearized equation of motion in the orbital elements formulation are used to describe the transfer which consists of a thrust-coast-relight program. Sensitivity partials are also presented analytically in order to study the effect of maneuver execution errors and various other parameters affecting the blow down propulsion system characteristics on the transfer. This strategy is applied to study the transfer of the TOPEX spacecraft from the Shuttle parking orbit to its final operational orbit.

Kechichian, J. A.↗
NASA NTRS1982

Turbulence effect on crossflow around a circular cylinder at subcritical Reynolds numbers

An investigation of the effect of freestream turbulence on the flow around a smooth circular cylinder at subcritical Reynolds numbers from 5.2 x 10 to the 4th power to 2.09 x 10 to the 5th power was conducted. Measurements show that the interaction of incident turbulence with the initial laminar boundary layer: (1) modifies the characteristics of the mean surface pressure distribution; (2) induces an aft shift in the separation point ranging from 5 to 50 beyond the laminar separation angle of 80 degrees; and, (3) reduces the mean drag coefficient to values between 97 and 46% of its nearly constant laminar counterpart. The extent of these changes depends on the particular Reynolds number background turbulence combination. These results demonstrate that a boundary-layer flow similar to that found in critical, supercritical and/or transcritical flow regimes is induced by turbulence at subcritical Reynolds numbers and, hence, the effect of turbulence is equivalent to an effective increase in the Reynolds number. The change in the nature and properties of the boundary layer in the subcritical regime, consequent upon the penetration of turbulence into it, is in agreement with the model proposed by the vorticity-amplification theory.

Sadeh, W. Z.↗
NASA NTRS1981

High-sensitivity circular polarimetry of the Sun, 0.5 - 1.7 microns

Using an isometric (symmetrical) photoelastic-modulator polarimeter and a Cassegrain telescope, broadband polarization measures of the Sun were obtained with unprecedented sensitivity. With an instrumental background of x 10 to the minus 6th power differential effects delta q = V/I of 1 x 10 to the minus 7th power were detectable. Some results: (1) the lambda dependence of broadband circular polarization in spots was observed out to 1.7 mu, extending the visible-light measurements of Illing, Landman, and Mickey. The q drops to of the order of 1 x 10 to the minus 5 power at 1.2 mu (in a strong spot), then rises at 1.6 mu. While molecules or other special mechanisms must play a role in the visible-light polarization, at lambda 1.5 mu the q values seem consistent with gray magneto-opacity. (2) By surveying inactive regions upper limits are set to broadband polarization due to global or deep-seated magnetic fields. For a double-toroidal pattern a differential measure is found, q sub b = (q sub ne + q sub sw - q sub nw - q sub - se) 14, at 1.7 mu, of (+1.2 + or = 0.7) x 10 to the minus 7th power a mean from three series in 1981. Based on a simple estimate by L. Biermann this would correspond to deep-down toroidal fields of or approx 2000 gauss. Extension of this work are discussed.

Kemp, J. C.↗
NASA NTRS1983

Vortex motion behind a circular cylinder

Vortex motion behind a circular cylinder moving through water is discussed. It is shown that a pair of vortices form behind a moving cylinder and that their centers will move along a predictable curve. This curve represents an equilibrium condition which, however, is subject to perturbation. The stability of the vortex pair is investigated. Movement of the vortex pair away from the cylinder is calculated as an explanation of the resistance of the cylinder. Finally, the principles elaborated are applied to the flow around a flat plate.

Foeppl, L.↗
NASA NTRS1983

Sound diffraction at wall impedance discontinuities in a circular cylinder, investigated using Wiener-Hopf technique

Rigorous solutions are presented for sound diffraction in a circular cylinder with axial discontinuities of the wall admittance (or impedance). Analytical expressions are derived for the reflection and the transmission coefficients for duct modes. The results are discussed quantitatively in the limits of small admittance shifts (delta) and of low frequencies (ka). One of the results is the low frequency behavior of the reflection coefficient R(o) sub 00 of the fundamental mode. For the mode of a hardwall duct reflected from the junction with a softwall duct, (R(o) sub oo yields - (1-square root of (ka) square root of (2/i delta)); this result is in contrast to the frequency dependence of the reflection from the open end of a hardwall duct, for which R(o) sub oo yields - 1-(ka) squared/2 .

Cho, Y. C.↗
NASA NTRS1983

Geometrical analysis of circular-cut spiral bevel gears

Geometrical studies of circular cut spiral bevel gears are reported. Tooth profile changes heel to toe are studied in the transverse plane. Pressure angle changes are determined. The radiuses of curvature of the tooth surfaces generated by various cutter profiles are also determined. The consequences of cutter profile changes are explored. Crown gears are emphasized and the implications for conical gears are discussed.

Huston, R. L.↗
NASA NTRS1982

The dominant coherent structure of the circular jet organized by controlled perturbation

The dominant large-scale coherent structure of a circular jet has been organized through controlled perturbation at the jet Strouhal number of 0.3, induced acoustically in two air jets through cavity resonance. Selected phases of the coherent structure were studied for three Reynolds numbers (25,000; 55,000; and 110,000), and two limiting initial conditions; laminar and fully turbulent initial boundary layers. Distributions of phase-average structure properties, i.e., longitudinal and lateral velocities, coherent vorticity and Reynolds stress, phase-random turbulence intensities and Reynolds stress, and streamline and pseudo-streamfunction patterns are obtained. The phase-random turbulence intensity is greatest at the structure center where the coherent vorticity is also the maximum. Some properties of the structure show mild but systematic dependence on Reynolds number.

Zaman, K. B. M. Q.↗
NASA NTRS1983

Linearized transfer between inclined circular orbits using low-thrust blow down propulsion system

Noncoplanar transfers between neighboring circular orbits are presented for spacecraft using their own low-thrust blow down propulsion system. It is assumed that the out-of-plane angle between the decaying thrust vector and the current orbit plane remains constant for each extended burn. Switching conditions are derived for the cutoff and relight of the propulsion system in order to carry out a given transfer with inclination change. Furthermore the location where the thrust acceleration is initially applied with respect to the line of nodes of the two orbits is uniquely determined. Finally an analytic derivation of the linearized coplanar motion for stationkeeping and terminal rendezvous studies is also presented and a scheme for deriving the second order correction shown.

Kechichian, J. A.↗
NASA NTRS1983

Analysis of progressive damage in thin circular laminates due to static-equivalent impact loads

Clamped circular graphite/epoxy plates (25.4, 38.1, and 50.8 mm radii) with an 8-ply quasi-isotropic layup were analyzed for static-equivalent impact loads using the minimum-total-potential-energy method and the von Karman strain-displacement equations. A step-by-step incremental transverse displacement procedure was used to calculate plate load and ply stresses. The ply failure region was calculated using the Tsai-Wu criterion. The corresponding failure modes (splitting and fiber failure) were determined using the maximum stress criteria. The first-failure mode was splitting and initiated first in the bottom ply. The splitting-failure thresholds were relatively low and tended to be lower for larger plates than for small plates. The splitting-damage region in each ply was elongated in its fiber direction; the bottom ply had the largest damage region. The calculated damage region for the 25.4-mm-radius plate agreed with limited static test results from the literature.

Shivakumar, K. N.↗
NASA NTRS1983

Turbulent heat transfer in the separated reattached and redevelopment regions of a circular tube

A numerical study is reported on a flow in a circular pipe with an abrupt expansion. In this paper the behavior of flow in the domain including recirculating and redeveloping regions has been reviewed carefully and a new grid system is employed which provides finer grids in the recirculating region and monotonically expanding grids in the redeveloping region. The predicted results were improved for the class of this flow by incorporating and adapting the low-Reynolds number model of turbulence throughout the solution domain. The computational results obtained by the present model generally are better than the former results of the authors, particularly in the prediction of the reattachment points.

Amano, R. S.↗
NASA NTRS1983

Vibrations of cantilevered circular cylindrical shells Shallow versus deep shell theory

Free vibrations of cantilevered circular cylindrical shells having rectangular planforms are studied in this paper by means of the Ritz method. The deep shell theory of Novozhilov and Goldenveizer is used and compared with the usual shallow shell theory for a wide range of shell parameters. A thorough convergence study is presented along with comparisons to previously published finite element solutions and experimental results. Accurately computed frequency parameters and mode shapes for various shell configurations are presented. The present paper appears to be the first comprehensive study presenting rigorous comparisons between the two shell theories in dealing with free vibrations of cantilevered cylindrical shells.

Lee, J. K.↗
NASA NTRS1983

Measurements of compressible secondary flow in a circular S-duct

This paper presents the results of an experimental study of secondary flow in a circular cross section 30 deg - 30 deg S-duct with entrance Mach number of 0.6. Local flow velocity vectors have been measured along the length of the duct at six stations. These measurements have been made using a five-port cone probe. Static and total pressure profiles in the transverse planes are obtained from the cone probe measurements. Wall static pressure measurements along three azimuth angles of 0 deg, 90 deg, and 180 deg along the duct are also made. Contour plots presenting the three dimensional velocity field as well as the total- and static-pressure fields are obtained. Surface oil flow visualization technique has been used to provide details of the flow on the S-duct boundaries. The experimental observations have been compared with typical computational results.

Vakili, A.↗
NASA NTRS1983

An experimental investigation of multiple shock wave/turbulent boundary layer interactions in a circular duct

Detailed pitot, static and wall pressure measurements have been obtained for multiple shock wave/turbulent boundary layer interactions in a circular duct at a free-stream Mach number of 1.49 and at a unit Reynolds number of 4.90 x 10 to the 6th per meter. The details of the flow field show the formation of a series of normal shock waves with successively decreasing strength and with decreasing distance between the successive shock waves. The overall pressure recovery is much lower than the single normal shock pressure recovery at the same free-stream Mach number. A one-dimensional flow model based on the boundary layer displacement buildup is postulated to explain the formation of a series of normal shock waves.

Om, D.↗