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At least 271 records · Page 15

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NASA NTRS1981

Engine dynamic analysis with general nonlinear finite-element codes. I Overall approach and development of bearing damper element

NASA-sponsored research on engine dynamic simulation using general finite element nonlinear time transient computer codes available on the open market is reviewed. The approach taken was to develop software packages to model engine components which are not typically found on dynamical structures and are therefore not already computer codes. The software package developed for squeeze-film bearing dampers is outlined, and the results of a parametric study of damper pressure for a variety of specified circular orbits are presented for both long-bearing and short-bearing solutions. The data from a four-degree-of-freedom rotor-damper-stator model under conditions of small rotor unbalance through large rotor unbalance are also given.

Adams, M. L.↗

NASA NTRS1983

Tubing Cutter is Activated Hydraulically

Hydraulically-actuated tubing cutter severs tubing when operator squeezes handle grip. "Gooseneck" extension enables cutter to be used in areas where accessiblity is limited. Cutter has potential as flight-line tool and is useful in automobile and fire rescue work.

Mcsmith, D. G.↗

NASA NTRS1982

Bearings: Technology and needs

A brief status report on bearing technology and present and near-term future problems that warrant research support is presented. For rolling element bearings a material with improved fracture toughness, life data in the low Lambda region, a comprehensive failure theory verified by life data and incorporated into dynamic analyses, and an improved corrosion resistant alloy are perceived as important needs. For hydrodynamic bearings better definition of cavitation boundaries and pressure distributions for squeeze film dampers, and geometry optimization for minimum power loss in turbulent film bearings are needed. For gas film bearings, foil bearing geometries that form more nearly optimum film shapes for maximum load capacity, and more effective surface protective coatings for high temperature operation are needed.

Anderson, W. J.↗

NASA NTRS1982

Engine dynamic analysis with general nonlinear finite element codes. II - Bearing element implementation, overall numerical characteristics and benchmarking

Second-year efforts within a three-year study to develop and extend finite element (FE) methodology to efficiently handle the transient/steady state response of rotor-bearing-stator structure associated with gas turbine engines are outlined. The two main areas aim at (1) implanting the squeeze film damper element into a general purpose FE code for testing and evaluation; and (2) determining the numerical characteristics of the FE-generated rotor-bearing-stator simulation scheme. The governing FE field equations are set out and the solution methodology is presented. The choice of ADINA as the general-purpose FE code is explained, and the numerical operational characteristics of the direct integration approach of FE-generated rotor-bearing-stator simulations is determined, including benchmarking, comparison of explicit vs. implicit methodologies of direct integration, and demonstration problems.

Padovan, J.↗

NASA NTRS1982

Nonlinear analysis of rotor-bearing systems using component mode synthesis

The method of component mode synthesis is developed to determine the forced response of nonlinear, multishaft, rotor-bearing systems. The formulation allows for simulation of system response due to blade loss, distributed unbalance, base shock, maneuver loads, and specified fixed frame forces. The motion of each rotating component of the system is described by superposing constraint modes associated with boundary coordinates and constrained precessional modes associated with internal coordinates. The precessional modes are truncated for each component and the reduced component equations are assembled with the nonlinear supports and interconnections to form a set of nonlinear system equations of reduced order. These equations are then numerically integrated to obtain the system response. A computer program, which is presently restricted to single shaft systems, has been written and results are presented for transient system response associated with blade loss dynamics with squeeze film dampers, and with interference rubs.

Nelson, H. D.↗

NASA NTRS1983

Expander for Thin-Wall Tubing

Tool locally expands small-diameter tubes. Tube expander locally expands and deforms tube: Compressive lateral stress induced in elastomeric sleeve by squeezing axially between two metal tool parts. Adaptable to situations in which tube must have small bulge for mechanical support or flow control.

Pessin, R.↗

NASA NTRS1983

Vapor Cavitation in Dynamically Loaded Journal Bearings

High speed motion camera experiments were performed on dynamically loaded journal bearings. The length to diameter ratio of the bearing, the speed of the roller and the tube, the surface material of the roller, and the static and dynamic eccentricity of the bearing were varied. One hundred and thirty-four cases were filmed. The occurrence of vapor cavitation was clearly evident in the films and figures presented. Vapor cavitation was found to occur when the tensile stress applied to the oil exceeded the tensile strength of the oil or the binding of the oil to the surface. The physical situation in which vapor cavitation occurs is during the squeezing and sliding motion within a bearing. Besides being able to accurately capture the vapor cavitation on film, an analysis of the formation and collapse of the cavitation bubbles and characteristics of the bubble content are presented.

Jacobson, B. O.↗

NASA NTRS1983

Power turbine dynamics - An evaluation of a shear-mounted elastomeric damper

As an alternative to the more conventional squeeze-film bearing damper designs, a Viton-70 shear-mounted, elastomeric damper was built and tested in a T-55 power turbine high-speed balancing rig. This application demonstrated, for the first time, the feasibility of using elastomers as the primary rotor damping source in production turbine engine hardware. The shear-mounted damper design was selected because of its compatibility with actual gas turbine engine radial space constraints, its accommodation of both the radial and axial thrust loads present in gas turbine engines, and its capability of controlled axial preload. Test results showed that the Viton-70 elastomeric damper operated successfully and provided excellent control of both synchronous and nonsynchronous vibrations through all phases of testing to the maximum rotor speed of 1676 rad/s (16,000 rpm). Excellent correlation between the predicted and experienced critical speeds, mode shapes, and log decrements for the power turbine rotor and elastomer damper assembly was also achieved.

Zorzi, E. S.↗

NASA NTRS1984

Hydrodynamic lubrication of rigid nonconformal contacts in combined rolling and normal motion

A numerical solution to the problem of hydrodynamic lubrication of rigid point contacts with an isoviscous, incompressible lubricant was obtained. The hydrodynamic load-carrying capacity under unsteady (or dynamic) conditions arising from the combined effects of squeeze motion superposed upon the entraining motion was determined for both normal approach and separation. Superposed normal motion considerably increases net load-carrying capacity during normal approach and substantially reduces net load-carrying capacity during separation. Geometry was also found to have a significant influence on the dynamic load-carrying capacity. The ratio of dynamic to steady state load-carrying capacity increases with increasing geometry parameter for normal approach and decreases during separation. The cavitation (film rupture) boundary is also influenced significantly by the normal motion, moving downstream during approach and upstream during separation. For sufficiently high normal separation velocity the rupture boundary may even move upstream of the minimum-film-thickness position. Sixty-three cases were used to derive a functional relationship for the ratio of the dynamic to steady state load-carrying capacity in terms of the dimensionless normal velocity parameter (incorporating normal velocity, entraining velocity, and film thickness) and the geometry parameter.

Ghosh, M. K.↗

NASA NTRS1983

IPE 7

A description is given of the collection and treatment of samples of Prochloron cells. The cells of Prochloron were obtained and prepared in the following way. Colonies of the symbiotic host, the giant didemnid ascidian Lissoclinum patella, were collected at low-tide level on reef-flat sand between Kamori Island and Koror, Palau, Western Caroline Islands. The animal colonies were taken, immersed in sea water, to an 8,000-litre holding tank and kept with constantly running sea water at 30 deg. Individual colonies were picked clean of contaminants, rinsed in sea water buffered with 40 nM or 100 mM Tris buffer at pH 8.4, and squeezed by hand to express the algal cells from the cloacal atria. The algae were received in about an equal volume of the same buffered sea water; this neutralized the acids liberated by the bruised ascidians and thereby maintained the Ph high enough to keep the algal cells green. The Prochloron cells were washed twice with buffered sea water and concentrated by centrifugation at about 50 g for 90 seconds. Microscopic examination revealed that contamination by animal host cells or bacteria was negligible (much less than 1%).

Source record↗

NASA NTRS1984

Energetics of the magnetosphere, revised

The approximate magnitudes of power inputs and energies associated with the Earth's magnetosphere were derived. The nearest 40 R sub E of the plasma sheet current receive some 3.10 to the 11th power watt, and much of this goes to the Birkeland currents, which require 1-3 10 to the 11th power watt. Of that energy, about 30% appears as the energy of auroral particles and most of the rest as ionosphere joule heating. The ring current contains about 10 to the 15th power joule at quiet times, several times as much during magnetic storms, and the magnetic energy stored in the tail lobes is comparable. Substorm energy releases may range at 1.5 to 30 10 to the 11th power watt. Compared to these, the local energy release rate by magnetic merging in the magnetosphere is small. Merging is essential for the existence of open field lines, which make such inputs possible. Merging also seems to be implicated in substorms: most of the released energy only becomes evident far from the merging region, though some particles may gain appreciable energy in that region itself, if the plasma sheet is squeezed out completely and the high latitude lobes interact directly.

Stern, D. P.↗

NASA NTRS1984

Interactive Finite Elements for General Engine Dynamics Analysis

General nonlinear finite element codes were adapted for the purpose of analyzing the dynamics of gas turbine engines. In particular, this adaptation required the development of a squeeze-film damper element software package and its implantation into a representative current generation code. The ADINA code was selected because of prior use of it and familiarity with its internal structure and logic. This objective was met and the results indicate that such use of general purpose codes is viable alternative to specialized codes for general dynamics analysis of engines.

Adams, M. L.↗

NASA NTRS1984

Nonlinear transient finite element analysis of rotor-bearing-stator systems

This paper extends the finite element scheme to handle the highly nonlinear interfacial fields generated in the fluid filled annulli of squeeze film and journal bearings so as to model the transient response of rotor-bearing-stator systems. Since such simulations are highly nonlinear, direct numerical integration schemes are employed to generate the overall response. In this context, the paper gives consideration to such items as (1) numerical efficiency/stability, (2) comparison of implicit and explicit schemes, (3) determines extent of response nonlinearity as well as (4) extensively benchmarks the overall concept/methodologies.

Padovan, J.↗

NASA NTRS1984

Violation of Bell's inequalities in quantum optics

An optical field produced by intracavity four-wave mixing is shown to exhibit the following nonclassical features: photon antibunching, squeezing, and violation of Cauchy-Schwarz and Bell's inequalities. These intrinsic quantum mechanical effects are shown to be associated with the nonexistence of a positive normalizable Glauber-Sudarshan P function.

Reid, M. D.↗

NASA NTRS1985

Electrically Connecting to Pressure Vessels

Resilient conductive disk eliminates need for holes in vessel walls. Grounding disk made from wire and solder and sandwiched between electrical-component support and pressure-vessel wall. Emplaced in component support, disk squeezed to 66 percent of its thickness. Disk conforms to surfaces of support and vessel wall when support attached to wall with adhesive. Disk thus forms reliable electrical contact from support (and its electrical component) to wall.

Rossi, P. J.↗

NASA NTRS1985

Instabilities in decelerating supersonic flows with applications to cosmic ray shocks

The nature of instabilities in cosmic ray shocks is investigated by using two distinct models for the shock wave. For wavelengths which are short relative to the thickness of the shock wave, the shock is treated as a smoothly decelerating low, and an appropriate JWKB type expansion is used to describe the perturbations to the flow. In this, the short wavelength regime, the presence of squeezing and an effective g renders strong cosmic ray shocks unstable in a way which is similar to instabilities in other supersonic flows, such as in de Laval nozzle flow or a heat conduction dominated shock wave. In the long wavelength limit, where the shock is treated as a discontinuous transition, a stability function is derived which, if negative, corresponds to unstable disturbances growing exponentially in time. In this case, it was found that if the cosmic ray fluid is relativistic (gamma sub c = 4/3) and the background plasma ideal (gamma = 5/3), then strong shocks are unstable.

Zank, A. P.↗

NASA NTRS1985

Hydrodynamic lubrication of rigid nonconformal contacts in combined rolling and normal motion

Ghosh, M. K.↗

NASA NTRS1984

Energetics of the magnetosphere

The approximate magnitudes of power inputs and energies associated with the earth's magnetosphere were derived. The nearest 40 R sub E of the plasma sheet current receive some 3.10 to the 11th power watt, and much of this goes to the Birkeland currents, which require 1-3 10 to the 11th power watt. Of that energy, about 30 percent appears as the energy of auroral particles and most of the rest as ionosphere joule heating. The ring current contains about 10 to the 15th power joule at quiet times, several times as much during magnetic storms, and the magnetic energy stored in the tall lobes is comparable. Substorm energy releases may range at 1.5 to 30 10 to the 11th power watt. Compared to these, the local energy release rate by magnetic merging in the magnetosphere is small. Merging is essential for the existence of open field lines, which make such inputs possible. Merging also seems to be implicated in substorms: most of the released energy only becomes evident far from the merging region, though some particles may gain appreciable energy in that region itself, if the plasma sheet is squeezed out completely and the high latitude lobes interact directly.

Stern, D. P.↗