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At least 325 records · Page 18
All sourcesNASA NTRSDOE OSTI
NASA NTRS1992

Rapid oscillations in cataclysmic variables. VIII - YY Draconis (=3A 1148 + 719)

A 16th magnitude cataclysmic variable presumably a dwarf nova, was detected near one of the positions permitted for the hard (2-10 keV) X-ray source 3A 1148 + 719. The optical and UV spectra of YY Dra are fairly typical of cataclysmic variables, except that the TiO absorption bands of an M dwarf can be seen for greater than 5000 A. This shows that the accretion disk is intrinsically faint in quiescence, suggesting a very low accretion rate. Yet the fairly blue continuum slope in the vacuum UV indicates the presence of a small hot object, presumably the white dwarf. The radial velocities at H-alpha indicate a 4.0-hr orbital period, and the IR light curve appears to show the expected 'double-humped' waveform from the distorted secondary. High-speed photometry in the U band reveals a stable periodicity of about 1-percent semiamplitude at a period of 275 s, with some power also in the subharmonic at about 550 s.

Patterson, J.↗
NASA NTRS1992

Receptivity of a laminar boundary layer to the interaction of a three-dimensional roughness element with time-harmonic free-stream disturbances

Receptivity of a laminar boundary layer to the interaction of time-harmonic free-stream disturbances with a 3D roughness element is studied. The 3D nonlinear triple-deck equations are solved numerically to provide the basic steady-state motion. At high Reynolds numbers, the governing equations for the unsteady motion are the unsteady linearized 3D triple-deck equations. These equations can only be solved numerically. In the absence of any roughness element, the free-stream disturbances, to the first order, produce the classical Stokes flow, in the thin Stokes layer near the wall (on the order of our lower deck). However, with the introduction of a small 3D roughness element, the interaction between the hump and the Stokes flow introduces a spectrum of all spatial disturbances inside the boundary layer.

Tadjfar, M.↗
NASA NTRS1992

Ring current instabilities in the magnetohydrodynamic frequency range

This report summarizes recent theoretical developments in ring current plasma instabilities in the magnetohydrodynamic (MHD) frequency range but with the effect of finite Larmor radius, and discusses its relevance to satellite-based observations. Possible instabilities are the bounce resonant instabilities caused by a humped energy distribution, the drift mirror instability caused by an anisotropic pressure and the drift wave type instability caused by a combination of drift-bounce resonance and reduced Alfven frequency due to a high beta loading of the flux tube. Here, beta is proportional to plasma/magnetic pressures. Mechanisms leading to turbulence are also discussed.

Hasegawa, A.↗
NASA NTRS1992

Aeroservoelasticity in HiSAIR

The High Speed Airframe Integration Research project is a multidisciplinary effort to bridge disciplinary boundaries in the analysis and design of aircraft. Aeroservoelasticity provides calculations of various critical speeds (such as flutter, divergence, and control reversal), of hump mode dampings, and of the effects of flexibility on vehicle stability and control derivatives. For design iterations, sensitivity derivatives of these characteristics with respect to structural design variables are also calculated. For executing this function, a set of computer programs was developed or adapted to perform routine calculations of basic aeroelastic characteristics. This set of programs, named the Aeroelastic Vehicle Analysis system, has also become a useful tool within the Aeroservoelasticity Branch of NASA's Langley Research Center.

Zeiler, Thomas A.↗
NASA NTRS1993

Nonlinear waves and solitons in molecular clouds

We begin a study of nonlinear wave phenomena in molecular clouds. These clouds exhibit highly nonlinear structure that is often described in terms of 'clumps' and 'filaments' which are bouncing around, twisting, and colliding within the cloud. These clouds are important because they ultimately produce the initial conditions for the star formation process. Our motivation is to explore the possibility that solitons (i.e., spatially localized, single-hump wave entities which often exhibit remarkable stability) can live in these molecular clouds and produce their observed structure. In this paper we focus on the case of one spatial dimension, and we show that a rich variety of nonlinear waves can exist in molecular cloud fluid systems (where self-gravity is included). We show that in the absence of magnetic fields no true soliton solutions are allowed, although highly nonlinear waves (whose crests become widely spaced and thus soliton-like) do exist. For clouds with embedded magnetic fields, we derive a model equation which describes the behavior of wave phenomena; this model equation allows solutions which correspond to nonlinear waves, solitons, and topological solitons. We briefly consider the stability of these wave entities and discuss the possible role they play in molecular cloud dynamics.

Adams, Fred C.↗
NASA NTRS1991

Analysis of aeroelastic and resonance responses of a wind tunnel model support system

Vibrations of the National Transonic Facility model support system were analyzed using CAP-TSD (Computational Aeroelasticity Program-Transonic Small Disturbance), a three-dimensional transonic small disturbance potential code designed for aeroelastic analysis of complex configurations. The model support system was represented as a tunnel-spanning flexible wing whose structural properties were obtained from measured responses. Aeroelastic transients were calculated, assuming no structural damping, and analyzed to obtain modal stability characteristics. The results showed that there is a tendency toward a hump mode instability in one of the modes and that there are other weakly damped or unstable modes. The close proximity of the solid wind-tunnel diffuser side walls to the model support system was shown to have adverse effects on its aeroelastic stability characteristics. When the effects of the wind-tunnel walls were modeled, the analyses indicated the presence of wind-tunnel resonance modes which were not present when free-air boundary conditions were used.

Whitlow, Woodrow, Jr.↗
NASA NTRS1993

Plasma expansion and evolution of density perturbations in the polar wind - Comparison of semikinetic and transport models

Comparisons are made between transport and semikinetic models in a study of the time evolution of plasma density perturbations in the polar wind. The situations modeled include plasma expansion into a low-density region and time evolution of localized density enhancements and cavities. The results show that the semikinetic model generally yields smoother profiles in density, drift velocity, and ion temperature than the transport model, principally because of ion velocity dispersion. While shocks frequently develop in the results of the transport model, they do not occur in the semikinetic results. In addition, in the semikinetic results, two ion streams, or double-humped distributions, frequently develop. In the transport model results the bulk parameters, at a given time, often have a one-to-one correspondence in the locations of their local minima or maxima. This is a consequence of the coupling of the fluid equations. There is, however, no such relationship among the moments produced by the semikinetic model where the local moment maxima and minima are often shifted in altitude. In general, incorporation of enhanced heat fluxes in the transport model leads to somewhat improved agreement with the semikinetic results.

Ho, C. W.↗
NASA NTRS1936

Tank Tests of a Model of the NC Flying-boat Hull - N.A.C.A. Model 44

A 1/7.06 full-size model of the NC-type hull was tested in the N.A.C.A. tank by both the general method and the specific or free-to-trim method. The results of the tests are given in curves plotted as non dimensional coefficients and are compared with the test results of N.A.C.A. model 11-A. The NC model (N.A.C.A. model 44) shows higher resistance than model 11-A at hump speed but lower resistance at high speeds. Model 44 has a higher best trim angle at the jump and a lower maximum positive trimming moment than model 11-A. At high speeds the best trim angle and the trimming moments of the two models are approximately the same.

Bell, Joe W↗
NASA NTRS1935

The effect of depth of step on the water performance of a flying-boat hull model

NACA model 11-C was tested with four different depths of step to obtain information as to the effect of the depth of step on the water performance. The depths of step were selected to cover the practicable range of depths and in each case the included angle between the forebody and afterbody keels was kept the same 6-1/2 degrees. Small depths of step were found to give lower resistance at speeds below and at the hump speed of the model and greater depths of step lower resistance at high speeds. For low resistance throughout the speed range of the model investigated the most desirable depth of step is from 2.5 to 4.0 percent of the beam. The change of the best trim angle caused by variation of the depth of step was not appreciable. Increased depth of step caused increases in the maximum positive trimming moments at all trim angles investigated.

Bell, Joe W↗
NASA NTRS1935

The Effect of the Angle of Afterbody Keel on the Water Performance of a Flying-Boat Hull Model

NACA model 11-C was tested according to the general method with the angle of afterbody keel set at five different angles from 2-1/2 degrees to 9 degrees, but without changing other features of the hull. The results of the tests are expressed in curves of test data and of non-dimensional coefficients. At the depth of step used in the tests, 3.3 percent beam, the smaller angles of afterbody keel give greater load-resistance ratios at the hump speed and smaller at high speed than the larger angles of afterbody keel. Comparisons are made of the load-resistance ratios at several other points in the speed range. The effect of variation of the angle of afterbody keel upon the take-off performance of a hypothetical flying boat of 15,000 pounds gross weight having a hull of model 11-C lines is calculated, and the calculations show that the craft with the largest of the angles of afterbody keel tested, 9 degrees, takes off in the least time and distance.

Allison, John M.↗
NASA NTRS1936

Tank Tests of Models of Flying Boat Hulls Having Longitudinal Steps

Four models with longitudinal steps on the forebody were developed by modification of a model of a conventional hull and were tested in the National Advisory Committee for Aeronautics (NACA) tank. Models with longitudinal steps were found to have smaller resistance at high speed and greater resistance at low speed than the parent model that had the same afterbody but a conventional V-section forebody. The models with a single longitudinal step had better performance at hump speed and as low high-speed resistance except at very light loads. Spray strips at angles from 0 degrees to 45 degrees to the horizontal were fitted at the longitudinal steps and at the chine on one of the two step models having two longitudinal steps. The resistance and the height of the spray were less with each of the spray strips than without; the most favorable angle was found to lie between 15 degrees and 30 degrees.

Allison, John M↗
NASA NTRS1936

Tanks Test of a Model of the Hull of the Navy PB-1 Flying Boat - N.A.C.A. Model 52

A model of the hull of the Navy PB-1 flying boat was tested in the N.A.C.A. tank as part of a program intended to provide information regarding the water performance of hulls of flying boats of earlier design for which hydrodynamic data have heretofore been unavailable. Tests were made according to the general method over the range of practical loadings with the model both fixed in trim and free to trim. A free-to-trim test according to the specific method was also made for the design load and take-off speed corresponding to those of the full-scale flying boat. The resistance obtained from the fixed-trim test was found to be about the same as that of the model of the NC flying-boat hull, and greater at the hump but smaller at high speeds than that of a model of the Sikorsky S-40 flying-boat hull.

Allison, John M↗
NASA NTRS1935

Tank Tests of a Model of a Flying-boat Hull Having a Longitudinally Concave Planing Bottom

The NACA model 11-B, which has a longitudinally concave planing bottom forward of the step, was tested over a wide range of loading. The results of the tests are presented as curves of resistance and trimming moment plotted against speed for various trim angles and as curves of resistance coefficient at best trim angle, and trimming-moment coefficient. The characteristics of the form at the optimum trim are compared with those of NACA model 11-C which has the same form with the exception of a planing bottom longitudinally straight near the step. Photographs of the models being towed in the tank are included for a comparison of the spray patterns. At the best angles of trim in each case model 11-B has lower resistance at high speeds, a higher maximum positive trimming moment near the hump speed, and a more favorable spray pattern than of model 11-C.

Parkinson, J B↗
NASA NTRS1936

A General Tank Test of a Model of the Hull of the British Singapore IIC Flying Boat

A general test was made in the N.A.C.A. tank of a 1/12-size model of the hull of the British Singapore IIC flying boat loaned by the Director of Research, British Air Ministry. The results are given in charts and are compared with the results of tests of a model of an American flying-boat hull, the Sikorsky S-40. The Singapore hull has a greater hump resistance but a much lower high-speed resistance than the S-40.

Dawson, John R↗
NASA NTRS1936

Tank tests of three models of flying-boat hulls of the pointed-step type with different angles of dead rise - NACA model 35 series

The results of tank tests of three models of flying-boat hulls of the pointed-step type with different angles of dead rise are given in charts and are compared with results from tests of more conventional hulls. Increasing the angle of dead rise from 15 to 25 degrees: had little effect on the hump resistance; increased the resistance throughout the planning range; increased the best trim angle; reduced the maximum positive trimming moment required to obtain best trim angle; and had but a slight effect on the spray characteristics. For approximately the same angles of dead rise the resistance of the pointed-step hulls were considerably lower at high speeds than those of the more conventional hulls.

Dawson, John R↗
NASA NTRS1938

Tank Tests to Show the Effect Rivet Heads on the Water Performance of a Seaplane-Float

A 1/3.5 full-sized model of a seaplane float constructed from lines supplied by the Bureau of Aeronautics, Navy Department, was tested first with smooth painted bottom surfaces and then with round-head rivets, plate laps, and keel plates fitted to simulate the actual bottom of a metal float. A percentage increase in water resistance caused by the added roughness was found to be from 5 to 20 percent at the hump speed and from 15 to 40 percent at high speeds. The effect of the roughness of the afterbody was found to be negligible except at high trims. The model data were extrapolated to full size by the usual method that assumes the forces to vary according to Froude's law and, in the case of the smooth model, by a method of separation that takes into account the effect of scale on the frictional resistance. It was concluded that the effect of rivet heads on the take-off performance of a relatively high-powered float seaplane is of little consequence, but it may be of greater importance in the case of more moderately powered flying boats.

FLOATS - RESISTANCE EFFECT OF SURFACE ROUGHNESS↗
NASA NTRS1934

Tank Tests of Auxiliary Vanes as a Substitute for Planing Area

The results of towing tests made on two models at the request of the Bureau of Aeronautics, Navy Department, are presented. The first model represents the hull of the U.S. Navy PN-8 flying boat, in which the sponsors of the original hull are removed and auxiliary lifting vanes are fitted at the chines immediately forward of the main step. The tests showed that the altered form gave a large increase in hump resistance and a very undesirable spray formation through a large part of the speed range.

Parkinson, John B↗
NASA NTRS1938

Tank Tests of Model 36 Flying Boat Hull

N.A.C.A. Model 36, a hull form with parallel middle body for half the length of the forebody and designed particularly for use with stub wings, was tested according to the general fixed-trim method over the range of practical loads, trims, and speeds. It was also tested free to trim with the center of gravity at two different positions. The results are given in the form of nondimensional coefficients. The resistance at the hump was exceptionally low but, at high planing speeds, afterbody interference made the performance only mediocre.

Allison, John↗