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At least 109 records · Page 6

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NASA NTRS1985

Application of High Order Acoustic Finite Elements to Transmission Losses and Enclosure Problems

A family of acoustic finite elements was developed based on C continuity (acoustic pressure being the nodal variable) and the no-flow condition. The family include triangular, quadrilateral and hexahedral isoparametric elements with linear quadratic and cubic variation in modelling and distortion. Of greatest use in problems with irregular boundaries are the cubic isoparametric elements: the 32 node hexahedral element for three-dimensional systems; and the twelve node quadrilateral and ten node triangular elements for two-dimensional/axisymmetric applications. These elements were applied to problems involving cavity resonances, transmission loss in silencers and the study of end effects, using a Floating Point Systems 164 attached array processor accessed through an Amdahl 5860 mainframe. The elements are presently being used to study the end effects associated with duct terminations within finite enclosures. The transmission losses with various silencers and sidebranches in ducts is also being studied using the same elements.

Craggs, A.↗

NASA NTRS1985

Effect of enclosure shape on natural convection velocities in microgravity

Natural convection velocities within two-dimensional enclosures of various shapes are estimated with reasonable accuracy, for Rayleigh numbers up to at least 5000, by considering the area to be equivalent to a circle of equal area. For the class of figures including the square, upright half-circle, and upright 2 x 1 aspect ratio rectangle, excellent agreement is obtained by considering the temperature difference across the maximum horizontal dimension to be equal to that across the equal area circle horizontal diameter. The agreement of two upright oblong shapes indicates probable agreement for any similar upright oblong shape of roughly the same aspect ratio. The horizontal oblong shapes have natural convection velocities approximately one-half that estimated based on the equal area circle, with the temperature difference across the maximum horizontal dimension taken to be equal to that across the equal area circle diameter.

Robertson, S. J.↗

NASA NTRS1986

Noise transmission into enclosures

This paper describes analytical and experimental studies of noise transmission into rectangular and cylindrical enclosures. The solutions of the governing acoustic-structural equations are developed by modal decomposition of structural vibrations and the interior acoustic field. Particular attention is directed toward the low frequencies, that is, frequencies up through the first few structural and cavity resonant modes. The structural vibrations are driven by the external acoustic and/or mechanical point loads which are taken to be Gaussian stationary random processes. The structural models include rectangular panels and cylindrical shells.

Vaicaitis, R.↗

NASA NTRS1988

Thermosolutal convection in high-aspect-ratio enclosures

Convection in high-aspect-ratio rectangular enclosures with combined horizontal temperature and concentration gradients is studied experimentally. An electrochemical system is employed to impose the concentration gradients. The solutal buoyancy force either opposes or augments the thermal buoyancy force. Due to a large difference between the thermal and solutal diffusion rates the flow possesses double-diffusive characteristics. Various complex flow patterns are observed with different experimental conditions.

Wang, L. W.↗

NASA NTRS1988

Fingering flow patterns of thermosolutal convection in rectangular enclosures

Convection in rectangular enclosures with combined horizontal temperature and concentration gradients is studied. An electrochemical system is employed to impose the concentration gradients. Due to a large difference between the thermal and solutal diffusion rates the flow possesses double-diffusive characteristics. Very complex fingering flow patterns are observed around the two-phase interfaces. The main objective of the present work is to obtain more information on the flows near the two vertical phase interfaces under various parametric conditions. The fingering flows near the crystal could be one of the most important factors to cause the crystal imperfections. The ranges of the parameters studied are Sc (Schmidt number)=2200 to 2400, Pr (Prandtl number)=4.0 to 7.0, Gr sub T (Grashof number)=2.50 x 10 to the 6th to 5.10 x 10 to the 7th power, Ar (aspect ratio)=0.61 to 3.0, and N (buoyancy ratio)=0.05 to 54.8.

Wang, L. W.↗

NASA NTRS1988

Fingering flow patterns of thermosolutal convection in rectangular enclosures

Convection in rectangular enclosures with combined horizontal temperature and concentration gradients is studied. An electrochemical system is employed to impose the concentration gradients. Due to a large difference between the thermal and solutal diffusion rates the flow possesses double-diffusive characteristics. Very complex fingering flow patterns are observed around the two-phase interfaces. The main objective of the present work is to obtain more information on the flows near the two vertical phase interfaces under various parametric conditions. The fingering flows near the crystal could be one of the most important factors to cause the crystal imperfections. The ranges of the parameters studied are Sc (Schmidt number) = 2200 to 2400, Pr (Prandtl number) = 4.0 to 7.0, Gr sub T (Grashof number) = 2.50 x 10 to the 6th to 5.10 x 10 to the 7th power, Ar (aspect ratio) = 0.61 to 3.0, and N (buoyancy ratio) = 0.05 to 54.8.

Wang, L. W.↗

NASA NTRS1988

Convective flows in enclosures with vertical temperature or concentration gradients

The transport process in the fluid phase during the growth of a crystal has a profound influence on the structure and quality of the solid phase. In vertical growth techniques the fluid phase is often subjected to vertical temperature and concentration gradients. The main objective is to obtain more experimental data on convective flows in enclosures with vertical temperature or concentration gradients. Among actual crystal systems the parameters vary widely. The parametric ranges studied for mass transfer are mainly dictated by the electrochemical system employed to impose concentration gradients. Temperature or concentration difference are maintained between two horizontal end walls. The other walls are kept insulated. Experimental measurements and observations were made of the heat transfer or mass transfer, flow patterns, and the mean and fluctuating temperature distribution. The method used to visualize the flow pattern in the thermal cases is an electrochemical pH-indicator method. Laser shadowgraphs are employed to visualize flow patterns in the solutal cases.

Wang, L. W.↗

NASA NTRS1989

Convective flows in enclosures with vertical temperature or concentration gradients

Wang, L. W.↗

NASA NTRS1988

Radiative transfer in rectangular enclosures - A discretized exchange factor solution

The discretized exchange factor method is used to analyze radiative exchange in a rectangular enclosure. The results compare excellently with those of other methods, especially the zonal method. Since the direct exchange factors are between nodal points no integration is necessary for evaluation of these factors. It is found that the present approach provides accurate results even when a small number of nodes is used.

Naraghi, M. H. N.↗

NASA NTRS1988

Thermosolutal convection in high-aspect-ratio enclosures

Wang, L. W.↗

NASA NTRS1989

Numerical modeling of enclosure convection

A numerical study on the steady and unsteady natural convection in two-dimensional rectangular enclosures has been performed by a time-accurate ADI finite difference scheme. The study covered a range of Rayleigh numbers between 1000 and 10 to the 7th, aspect ratios between 0.2 and 10.0, and tilt angles between -90 (heating from bottom) and +90 deg (heating from top). Various Prandtl numbers have been studied, but only the results of water (Pr = 7.0) are reported here due to space limitations. The physics revealed, however, includes the convection phenomena and the Rayleigh-Benard stability, as well as the combined mechanism of these two. The onset of secondary cells is determined by using a velocity map, which is simpler and cleaner, instead of a streamline plot. The critical Ra number for the occurrence of these secondary cells is shown to be lower than can be detected by experimental studies. On the Rayleigh-Benard stability part, a second transition from stable single-cell convection to periodic multicellular convection is disclosed.

Duh, J. C.↗

NASA NTRS1989

Steerable windowed enclosures

A gyro-stabilized mechanism that is to be carried on a vehicle, such as a helicopter, is provided with a protective enclosure consisting of a dome, usually of glass fibre reinforced plastic. The dome must be provided with a window transparent to the radiation involved, and this must be steered with the mechanism so that they remain in register with one another. Prior art structures employ elongated windows of sufficiently large size to accommodate the tilting and rolling of the mechanism, while pan movements are accommodated by rotating the entire dome. The invention provides a structure employing a small window that can be steered or slaved with the mechanism by rotation of the part of the dome including the window relative to the other part, which has the pan or yaw rotation motor connected to it. This rotation between the dome parts takes place in a skew plane disposed at as small a skew angle to the vertical as is possible, the compensation for the resulting transverse movement of the window being effected by a programmed rotation of the dome about the pan axis. Optically flat glass can then be used for the window, it can be coated to reduce reflections, etc, and it can also be wiped in operation to remove moisture. A broadcast antenna can be mounted on the part of the dome out of the line-of-sight of the apparatus.

John N Leavitt↗

NASA NTRS1991

Thermal and solutal convection with conduction effects inside a rectangular enclosure

We numerically investigate the effects of various boundary conditions on the flow field characteristics of the physical vapor transport process. We use a prescribed temperature profile as boundary condition on the enclosure walls, and we consider parametric variations applicable to ground-based and space microgravity conditions. For ground-based applications, density gradients in the fluid phase generate buoyancy-driven convection which in turn disrupts the uniformity of the mass flux at the interface depending on the orientation. Heat conduction in the crystal can affect the fluid flow near the interface of the crystal. When considering isothermal source and sink at the interfaces, we observe a diffusive mode and three modes (i.e., thermal, solutal, and thermo-solutal). The convective modes show opposing flow field trends between thermal and solutal convection; theoretically, these trends can be used to achieve a uniform mass flux near the crystal. However, under the physical conditions chosen, the mathematical condition necessary for uniform mass flux cannot be satisfied because of thermodynamic restrictions. When a longitudinal thermal gradient is prescribed on the boundary of the crystal, a non-uniform interface temperature results, which induces a symmetrical fluid flow near the interface for the vertical case. For space microgravity applications, we show that the flow field is dominated by the Stefan wind and a uniform mass flux results at the interface.

Mennetrier, Christophe↗

NASA NTRS1993

Contamination design of a Scientific Instrument Protective Enclosure for the Hubble Space Telescope Servicing Mission

A Scientific Instrument Protective Enclosure (SIPE) was designed to accommodate second generation science instruments (SIs) for the Hubble Space Telescope (HST) First Servicing Mission (FSM). One of the main design drivers for the SIPE is to provide a protective environment for the SIs against particulate and molecular contaminants that pose a viable threat to the SI performance. The focus of this paper will detail the methodology incorporated in the design of the SIPE to provide a controlled environment for SI protection at the launch site, during pre-launch/launch activities, and during on-orbit operations in the Shuttle bay.

Hedgeland, Randy J.↗

NASA NTRS1994

Thermal enclosure system functional simulation user's manual

A form and function simulation of the thermal enclosure system (TES) for a microgravity protein crystal growth experiment has been developed as part of an investigation of the benefits and limitations of intravehicular telerobotics to aid in microgravity science and production. A user can specify the time, temperature, and sample rate profile for a given experiment, and menu options and status are presented on an LCD display. This report describes the features and operational procedures for the functional simulation.

Morris, A. Terry↗

NASA NTRS1993

A Large Hemi-Anechoic Enclosure for Community-Compatible Aeroacoustic Testing of Aircraft Propulsion Systems

A large hemi-anechoic (absorptive walls and acoustically hard floor) noise control enclosure has been erected around a complex of test stands at the NASA Lewis Research Center in Cleveland, Ohio. This new state-of-the-art Aeroacoustic Propulsion Laboratory (APL) provides an all-weather, semisecure test environment while limiting noise to acceptable levels in surrounding residential neighborhoods. The 39.6 m (130 ft) diameter geodesic dome structure houses the new Nozzle Aeroacoustic Test Rig (NATR), an ejector-powered M = 0.3 free jet facility for acoustic testing of supersonic aircraft exhaust nozzles and turbomachinery. A multi-axis, force-measuring Powered Lift Facility (PLF) stand for testing of Short Takeoff Vertical Landing (STOVL) vehicles is also located within the dome. The design of the Aeroacoustic Propulsion Laboratory efficiently accomodates the research functions of two separate test rigs, one of which (NATR) requires a specialized environment for taking acoustic measurements. Absorptive fiberglass wedge treatment on the interior surface of the dome provides a hemi-anechoic interior environment for obtaining the accurate acoustic measurements required to meet research program goals. The APL is the first known geodesic dome structure to incorporate transmission-loss properties as well as interior absorption into a free-standing, community-compatible, hemi-anechoic test facility.

Cooper, Beth A.↗

NASA NTRS1994

Radiative Heat Transfer in Finite Cylindrical Enclosures with Nonhomogeneous Participating Media

Results of a numerical solution for radiative heat transfer in homogeneous and nonhomogeneous participating media are presented. The geometry of interest is a finite axisymmetric cylindrical enclosure. The integral formulation for radiative transport is solved by the YIX method. A three-dimensional solution scheme is applied to two-dimensional axisymmetric geometry to simplify kernel calculations and to avoid difficulties associated with treating boundary conditions. As part of the effort to improve modeling capabilities for turbulent jet diffusion flames, predicted distributions for flame temperature and soot volume fraction are used to calculate radiative heat transfer from soot particles in such flames. It is shown that the nonhomogeneity of radiative property has very significant effects. The peak value of the divergence of radiative heat flux could be underestimated by 2 factor of 7 if a mean homogeneous radiative property is used. Since recent studies have shown that scattering by soot agglomerates is significant in flames, the effect of magnitude of scattering is also investigated and found to be nonnegligible.

Hsu, Pei-Feng↗

NASA NTRS2000

NASA Animal Enclosure Module Mouse Odor Containment Study for STS-107 September 15, 1999;SJSU Odor Panel Data

Experiment #153 by Scott Brady is manifested for shuttle flight STS-107. This evaluation of space flight induced stress and its effects on neuronal plasticity will use 18 six month old C57Bl/6 male mice. A 21 day evaluation study was proposed to determine the length of time groups of 6, 9, or 12 mice could be housed in the Animal Enclosure Module (AEM) without odor breakthrough. This study was performed at NASA-Ames Research Center beginning on September 15, 1999. NASA personnel, were responsible for animal care, maintenance, facilities, hardware, etc. San Jose State personnel performed the odor panel evaluations and data reduction. We used similar procedures and methods for earlier tests evaluating female mice.

Holley, Daniel C.↗