Engineering Papers⌕ Search

Engineering topics

Brown, R. D.

Publications and source records attributed to Brown, R. D..

At least 19 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS1994

The effect of inlet swirl on the dynamics of long annular seals in centrifugal pumps

This paper describes additional results from a continuing research program which aims to identify the dynamics of long annular seals in centrifugal pumps. A seal test rig designed at Heriot-Watt University and commissioned at Weir Pumps Research Laboratory in Alloa permits the identification of mass, stiffness, and damping coefficients using a least-squares technique based on the singular value decomposition method. The analysis is carried out in the time domain using a multi-fiequency forcing function. The experimental method relies on the forced excitation of a flexibly supported stator by two hydraulic shakers. Running through the stator embodying two symmetrical balance drum seals is a rigid rotor supported in rolling element bearings. The only physical connection between shaft and stator is the pair of annular gaps filled with pressurized water discharged axially. The experimental coefficients obtained from the tests are compared with theoretical values.

Ismail, M.↗
NASA NTRS1992

Using single buffers and data reorganization to implement a multi-megasample fast Fourier transform

Data ordering in large fast Fourier transforms (FFT's) is both conceptually and implementationally difficult. Discribed here is a method of visualizing data orderings as vectors of address bits, which enables the engineer to use more efficient data orderings and reduce double-buffer memory designs. Also detailed are the difficulties and algorithmic solutions involved in FFT lengths up to 4 megasamples (Msamples) and sample rates up to 80 MHz.

Brown, R. D.↗
NASA NTRS1992

Recent observations of interstellar molecules - Detection of CCO and a limit on H2C3O

In order to test gas-phase reaction schemes for the production of small oxides of carbon in cold, dense interstellar clouds, we have searched for the radical CCO and for propadienone (H2C3O) in Taurus Molecular Cloud 1, a nearby cloud which exhibits a rich organic chemistry. The radical CCO has been detected with a fractional abundance some two orders of magnitude less than that of CCS, about one order of magnitude less than that of H2CCO, and slightly less than that of C3O. An upper limit has been obtained on the abundance of propadienone which is slightly less than that of its isomer propynal (HC2CHO).

Brown, R. D.↗
NASA NTRS1990

Analysis of altimetry over inland seas

Satellite-based altimetric data taken by GEOS-3 and SEASAT over the Black Sea and Caspian Sea are analyzed and a least squares collocation technique is used to predict the geoid undulation on a .25-degree by .25-degree grid and to transform these geoid undulations to free air gravity anomalies. This project entailed processing satellite altimeter data over inland seas for recovery of area mean gravity information. Gravity information in this area of the world is not readily available, so the possibility of obtaining it from the processing of altimeter observations is attractive. The principal objective was to complete and extend analyses done in a previous study, verify those results, and document the results and techniques. A secondary objective was to improve the algorithms and results, if possible. The approach used involved editing geoid height data to remove overland data; evaluating geoid height differences at crossover points; removing orbit errors from geoid heights using crossover differences; gridding geoid height data at .25-degree by .25-degree intervals; and estimating the gravity anomalies from gridded geoid heights using the collocation technique.

Au, A. Y.↗
NASA NTRS1989

User's guide: Programs for processing altimeter data over inland seas

The programs described were developed to process GEODYN-formatted satellite altimeter data, and to apply the processed results to predict geoid undulations and gravity anomalies of inland sea areas. These programs are written in standard FORTRAN 77 and are designed to run on the NSESCC IBM 3081(MVS) computer. Because of the experimental nature of these programs they are tailored to the geographical area analyzed. The attached program listings are customized for processing the altimeter data over the Black Sea. Users interested in the Caspian Sea data are expected to modify each program, although the required modifications are generally minor. Program control parameters are defined in the programs via PARAMETER statements and/or DATA statements. Other auxiliary parameters, such as labels, are hard-wired into the programs. Large data files are read in or written out through different input or output units. The program listings of these programs are accompanied by sample IBM job control language (JCL) images. Familiarity with IBM JCL and the TEMPLATE graphic package is assumed.

Au, A. Y.↗
NASA NTRS1987

A novel form of damper for turbo-machinery

Anti-swirl vanes are used by some manufacturers to delay the full development of half speed circulation in annular clearance spaces. The objective is to reduce the aerodynamic cross-coupling in the forward direction. The novel feature of a jet damper is a number of tangential nozzles discharging against the rotor surface speed. Some preliminary results on a 33.9 Kg rotor demonstrate that significant reductions in amplitude are obtained at the synchronous critical speeds.

Brown, R. D.↗
NASA NTRS1986

International Halley Watch: Discipline specialists for radio science

Some 34 radio observatories in 18 countries are participating in the Radio Science Net of the International Halley Watch. Approximately 100 radio astronomers are contributing to this effort, which has included observations of comets P/Crommelin and P/Giacobini-Zinner as well as P/Halley. It is clear that the record of data for the 18 cm OH ground state lambda doublet, which provides fundamental information on the gas production rate, kinematics, and potentially the magnetic field in the coma, will be vastly more complete and of higher accuracy than has even been obtained on any previous comet. The coverage by a number of radio observatories will enable short period variations to be studied and correlated with simultaneous data obtained at other wavelengths. Likewise, the first definitive detection of the important parent molecule hydrogen cyanide in a comet was obtained and is being studied by groups in the United States, Sweden, and France. The first detection of the comet with the Very Large Array telescope operated by NRAO was achieved and has produced exciting results for the distribution of emission at high angular resolution from the OH radical. At this writing data are still being obtained and being processed, and there are still strong indications that exciting information will be obtained from radar studies of P/Halley and from searches for additional parent molecules.

Irvine, W. M.↗
NASA NTRS1986

New interstellar masers in nonmetastable ammonia

The first astronomical detections of several ammonia inversion transitions involving nonmetastable levels with energies as high as 1090 K above the ground state are reported. The (J, K) = (9, 6) inversion transition shows maser-like emission in the directions of W51, NGC 7538, W49, and DR 21(OH). The NH3 (6, 3) line exhibits similar characteristics in W51 but is seen in absorption in NGC 7538. These are the first definite detections of ammonia masers in space. The intensities and narrow line widths (0.5-1.5 km/s) for the emission features are in contrast to the previously detected broad, weak, nonmetastable lines attributed to thermal emission in these sources. Temporal variability appears to be evident in the (9, 6) emission in W49 over a 4 month period. The highly excited (J, K) = (9, 6) and (6, 3) ammonia lines are found in regions containig compact H II regions and strongly infrared sources with associated H2O and OH masers; i.e., in regions of active star formation.

Madden, S. C.↗
NASA NTRS1985

Seeding materials: Health and safety considerations

The choice of a proper seeding material for laser velocimeters must include health and safety considerations. Failure to do so can lead to catastrophic results. All materials are toxic, and laser velocimeter seeding materials are no exception. Toxicity may be considered an inherent property of a given material. The manifestation of that property or the physiological response to the material is dependent on dose and exposure conditions. An approximate physiological classification of toxicity is given in tablular form. Toxicity in some situations is not necessarily the most restrictive factor in selection of materials. It is also very important to consider how the material is used so that actual exposure to the material in a damaging form can result. For example, nickel and cadmium are both extremely toxic as systemic poisons and in the case of nickel as a carcinogen. Seeding materials are dispersed in air under conditions that favor personnel exposure. Dispersal equipment is frequently if not normally manned, and personnel are often required to make frequent adjustments to assure proper operations.

Brown, R. D.↗
NASA NTRS1984

Experimental investigation of lateral forces induced by flow through model labyrinth glands

The lateral forces induced by flow through model labyrinth glands were investigated. Circumferential pressure distributions, lateral forces and stiffness coefficients data obtained are discussed. The force system is represented as a negative spring and a tangential force orthogonal to eccentricity. The magnitude of these forces are dependent on eccentricity, entry swirl, rotor peripheral velocity and seal size. A pressure equalization chamber at midgland tests should in significantly reduced forces and stiffness coefficients.

Leong, Y. M. M. S.↗
NASA NTRS1984

A new interstellar molecule - Tricarbon monoxide

The C3O molecule, whose pure rotational spectrum has only recently been studied in the laboratory, has been detected in the cold, dark interstellar Taurus Molecular Cloud 1. Since C3O is the first interstelar carbon chain molecule to contain oxygen, its existence places an important new constraint on chemical schemes for cold interstellar clouds. The abundance of C3O can be understood in terms of purely gas-phase ion-molecule chemistry.

Matthews, H. E.↗
NASA NTRS1984

Non-catalytic surfaces for metallic heat shields

The magnitude of the atom recombination coefficients needed for metal heat shield surfaces on Shuttle-type vehicles is analyzed and discussed. Prior work which identifies surfaces having low catalytic activity is reviewed. Arc tunnel tests to evaluate catalytic activity are described and the difficulties of such tests are discussed. Results are presented which show major differences between atom recombination and atom exchange from molecules. Results of surface analysis show that bulk and surface composition of a coating are different.

Swann, R. T.↗
NASA NTRS1984

Evaluation of a non-catalytic coating for metallic TPS

A commercially available ceramic coating was evaluated for application to metallic heat shields for Shuttle-type entry vehicles. Coated Inconel 617 specimens were subjected to thermal shock cycles, surface emittances were measured, and surface equilibrium temperatures were measured for coated and oxidized specimens exposed to an arc-tunnel environment. The coating adhered very well to the metal and appeared to be very non-catalytic.

Pittman, C. M.↗
NASA NTRS1983

Roughness of the marine geoid from Seasat altimetry

The geographical variability of short wavelength geoid power spectra (geoid roughness) has been mapped for the world's oceans between latitudes 72 deg N and 72 deg S. A spectral analysis of Seasat altimeter data, reduced to sea surface heights, has been performed at 2-min intervals for 15 consecutive days of the 3-day repeat orbit. The geoid roughness represented by these spectra for wavelengths shorter than about 220 km is separated from the total sea height variance and is displayed in the form of a global contour map. The global average geoid roughness is 32 cm RMS, varying from a high in excess of 2 m RMS near deep ocean trenches to a low of 2 cm RMS in the southeast Pacific near the east Pacific rise. This average value agrees well with previous estimates based on gravimetry and GEOS 3 altimetry. In general, the smoothest areas in the marine geoid overlie relatively young sea floor adjacent mid-ocean spreading centers, where even short wavelength topographic variations tend to be isostatically compensated.

Brown, R. D.↗
NASA NTRS1982

Circumferential pressure distributions in a model labyrinth seal

A research program to isolate and study leakage flow through labyrinth glands was initiated. Circumferential pressure distributions were measured in the labyrinth glands with geometry appropriate to the high pressure labyrinths in large steam turbines. Knowledge of this pressure distribution is essential as it is this unequal pressure field that results in the destabilizing force. Parameters that are likely to affect the pressure distributions are incorporated into the test rig. Some preliminary pressure profiles are presented.

Leong, Y. M. M. S.↗
NASA NTRS1982

Improved definition of crustal magnetic anomalies for MAGSAT data

The routine correction of MAGSAT vector magnetometer data for external field effects such as the ring current and the daily variation by filtering long wavelength harmonics from the data is described. Separation of fields due to low altitude sources from those caused by high altitude sources is affected by means of dual harmonic expansions in the solution of Dirichlet's problem. This regression/harmonic filter procedure is applied on an orbit by orbit basis, and initial tests on MAGSAT data from orbit 1176 show reduction in external field residuals by 24.33 nT RMS in the horizontal component, and 10.95 nT RMS in the radial component.

Brown, R. D.↗
NASA NTRS1980

Limit cycles of a flexible shaft with hydrodynamic journal bearings in unstable regimes

A symmetric 3 mass rotor supported on hydrodynamic bearings is described. An approximate method of representing finite bearings is used to calculate bearing forces. As the method sums forces from a number of independent circular lobes lemon 3 and 4 lobe bearings are taken into account. The calculations are based on an axial groove bearing. Linear analysis precedes nonlinear simulation of some unstable conditions. The demonstration of small limit cycles suggests that necessarily flexible rotors e.g., helicopter tail rotors, may be practical without either tilt pad bearings or external dampers.

Brown, R. D.↗