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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 73 records · Page 4
All sourcesNASA NTRSDOE OSTI
NASA NTRS1975

Design and application of squeeze film dampers for turbomachinery stabilization

The steady-state transient response of the squeeze film damper bearing was investigated. Both the steady-state and transient equations for the hydrodynamic bearing forces are derived; the steady-state equations were used to determine the damper equivalent stiffness and damping coefficients. These coefficients are used to find the damper configuration which will provide the optimum support characteristics based on a stability analysis of the rotor-bearing system. The effects of end seals and cavitated fluid film are included. The transient analysis of rotor-bearing systems was conducted by coupling the damping and rotor equations and integrating forward in time. The effects of unbalance, cavitation, and retainer springs are included. Methods of determining the stability of a rotor-bearing system under the influence of aerodynamic forces and internal shaft friction are discussed.

Gunter, E. J.↗
NASA NTRS1975

A damper for ground wind-induced launch vehicle oscillations

Prelaunch oscillatory bending deflections of the Atlas/Centaur launch vehicle are restrained by a damper mechanism mounted on the end of a horizontal boom supported from the umbilical tower. A single vertical pin on the vehicle engages the mechanism, and the damper is connected to the vehicle until liftoff. As the attach pin rises with the vehicle, a retractable arm mechanism provides initial clearance. An explosive release mechanism allows the boom to swing clear of the vehicle like a pendulum, while a snubber mechanism decelerates the free swinging boom and damper mechanism to a safe stop.

Bodle, J. G.↗
NASA NTRS1977

Correlation of part-span damper losses through transonic rotors operating near design point

The design-point losses caused by part-span dampers (PSD) were correlated for 21 transonic axial flow fan rotors that had tip speeds varying from 350 to 488 meters per second and design pressure ratios of 1.5 to 2.0. For these rotors a correlation using mean inlet Mach number at the damper location, along with relevant geometric and aerodynamic loading parameters, predicts the variation of total pressure loss coefficient in the region of the damper to a good approximation.

Roberts, W. B.↗
NASA NTRS1976

Shear dampers for deflections of micro-inch magnitudes

The rotation of the TV camera on the Mariner Jupiter/Saturn 1977 (MJS77) spacecraft will excite the long magnetometer and heavy RTG booms which are slightly damped perturbances that have long settling times. To ensure clear TV pictures additional damping was required over micro-inch displacements and at low frequencies. The solution incorporated elastomeric shear dampers at the base of these booms which possessed high loss tangent values in the expected frequency and temperature ranges. Presented are the shear damper design, results of full scale horizontal boom tests and relative effects of damper sizing and temperature. Boom instrumentation and excitation used for the full scale tests are also discussed.

Otth, D.↗
NASA NTRS1977

An active nutation damper for spacecraft

An active nutation damping device, consisting of an angular accelerometer, a dc motor driven flywheel, and associated electronics, was developed for spacecraft use. This damping system was used on the Lageos spacecraft, launched 4 May 1976, to control nutation buildup during the long coast period after the third stage separation. Of many electrical and mechanical design choices, an angular rather than linear accelerometer offered some advantages but problems developed in adapting the angular accelerometer to spacecraft use. The damper package was evaluated and proven on a three axis gas-bearing simulator that duplicated the Lageos spacecraft critical flight dynamics. A failure analysis of the damper assembly was performed. Performance of the damper during the Lageos flight has confirmed the preflight evaluation and analysis.

Abercrombie, R. A.↗
NASA NTRS1977

An active nutation damper for spacecraft

An active nutation damping device, consisting of an angular accelerometer, a dc-motor-driven flywheel, and associated electronics, developed for spacecraft use is described. This damping system was used on the LAGEOS spacecraft to control nutation buildup during the long coast period (approximately 75 minutes) after the third stage separation. The damper package was evaluated and proven on a three-axis gas-bearing simulator that duplicated the LAGEOS spacecraft critical flight dynamics. In addition, a failure analysis of the damper assembly was performed. Performance of the damper during the LAGEOS flight has confirmed the preflight evaluation and analysis.

Abercrombie, R. A.↗
NASA NTRS1979

Performance of two-stage fan with a first-stage rotor redesigned to account for the presence of a part-span damper

The NASA two-stage fan was tested with a redesigned first-stage rotor. The redesign included a new design approach to account for the presence of a part-span damper. At design speed the fan achieved a peak efficiency of 0.803, which is 1.9 percentage points higher than the original design. The peak efficiencies of the first stage and first rotor were 0.789 and 0.821, respectively. An improvement in efficiency of up to 5 percentage points in the damper region was achieved over the original large damper version. The stall margin, based on flow conditions at peak efficiency, was 10 percent at design speed.

Gorrell, W. T.↗
NASA NTRS1979

An off-design correlation of part span damper losses through transonic axial fan rotors

The experimental performance of 10 transonic fan rotors was used to correlate losses caused by midchord part-span dampers (PSD) during off-design operation between 50 and 100 percent of design speed. The design tip speed for the rotors used varied from 419 to 425 m/s and the design pressure ratios from 1.6 to 2.0. The loss attributable to the damper and the region influenced along the blade height was correlated with relevant aerodynamic and geometric parameters. The losses at the design point were estimated by a previously reported correlation (Roberts, 1978). Using this as a base, the off-design losses were correlated with variation in blade suction surface incidence. A check with independent data showed that the prediction of damper losses and region of influence was fair to good for most of the off-design data examined.

Roberts, W. B.↗
NASA NTRS1980

Off-design correlation for losses due to part-span dampers on transonic rotors

Experimental data from 10 transonic fan rotors were used to correlate losses created by part-span dampers located near the midchord position on the rotor blades. The design tip speed of these rotors varied from 419 to 425 m/sec, and the design pressure ratio varied from 1.6 to 2.0. Additional loss caused by the dampers for operating conditions between 50 and 100 percent of design speed were correlated with relevant aerodynamic and geometric parameters. The resulting correlation predicts the variation of total-pressure-loss coefficient in the damper region to a good approximation.

Roberts, W. B.↗
NASA NTRS1980

Elastomer damper performance - A comparison with a squeeze film for a supercritical power transmission shaft

This paper describes the design and testing of an elastomer damper on a super-critical power transmission shaft. The elastomers were designed to provide acceptable operation through the fourth bending mode and to control synchronous as well as nonsynchronous vibration throughout the operating range. The design of the elastomer was such that it could be incorporated into the system as a replacement for a squeeze-film damper without a reassembly, which could have altered the imbalance of the shaft. This provided a direct comparison of the elastomer and squeeze-film dampers without having to assess the effect of shaft imbalance changes.

Zorzi, E. S.↗
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

Coulomb Friction Damper

Standard hydraulic shock absorber modified to form coulomb (linear friction) damper. Device damps very small velocities and is well suited for use with large masses mounted on soft springs. Damping force is easily adjusted for different loads. Dampers are more reliable than fluid dampers and also more economical to build and to maintain.

Appleberry, W. T.↗
NASA NTRS1981

Analysis of high load dampers

High load damping requirements for modern jet engines are discussed. The design of damping systems which could satisfy these requirements is also discusseed. In order to evaluate high load damping requirements, engines in three major classes were studied; large transport engines, small general aviation engines, and military engines. Four damper concepts applicable to these engines were evaluated; multi-ring, cartridge, curved beam, and viscous/friction. The most promising damper concept was selected for each engine and performance was assessed relative to conventional dampers and in light of projected damping requirements for advanced jet engines.

Bhat, S. T.↗
NASA NTRS1983

The analysis and testing of blade platform friction dampers used in the high pressure fuel turbopump (HPFTP) of the Space Shuttle Main Engine (SSME)

Premature cracking of the first stage turbine blades in HPFTP of the SSME could be alleviated by redesign of the platform friction dampers that are used to reduce the vibration response of the blades. Analytical studies by the lumped mass method of friction damper effectiveness and spin pit tests of a straingaged bladed disk have been performed. Methodologies used in the program are described. Preliminary results show that the effectiveness of the blade platform dampers can be increased if the frequency and amplitude of the most damaging forcing functions can be defined.

Dominic, R. J.↗
NASA NTRS1981

Optimal damper location in the vibration control of large space structures

The problem of finding the optimal location of active dampers for the vibration control of space structures is investigated. The optimal location is where maximum damping can be introduced to a particular vibration mode. To this end, classical root locus techniques are used to study the effect on eigenvalues of placing a damper on an undamped structure. An efficient formulation is derived which avoids the solution of the damped eigenvalue problem. Based on the observation of the results for a free-free beam model, a Minimum Constrained Frequency Criterion (MCFC) for locating the optimal damper location is proposed.

Wang, B. P.↗
NASA NTRS1984

Digital control system for space structural dampers

A recently developed concept for a damper was improved by adding a small taper to the proof-mass, and using a proximeter to determine position. Also, an experimental damper was built using a three-inch stroke in place of the standard one-inch stroke. The analog controller initially used was replaced by an independent digital controller slaved to a TRS-80 Model I computer, which also serves as a highly effective, low-cost development system. An overall system concept for the use of proof-mass dampers is presented.

Haviland, J. K.↗
NASA NTRS1983

Forced response of a cantilever beam with a dry friction damper attached. I - Theory. II - Experiment

A theoretical and experimental study of the forced vibration response of a cantilevered beam with Coulomb damping nonlinearity is described. Viscous damping in the beam is neglected. Beam and dry friction damper configurations of interest for applications to turbine blade vibrations are considered. It is shown that the basic phenomena found by Dowell (1983) for a simply supported beam with an attached dry friction damper of specific geometry also apply to a cantilevered beam and a more general representation of the dry friction damper and its associated mass and stiffness.

Dowell, E. H.↗
NASA NTRS1987

Non-linear identification of a squeeze-film damper

Described is an experimental study to identify the damping laws associated with a squeeze-film vibration damper. This is achieved by using a non-linear filtering algorithm to process displacement responses of the damper ring to synchronous excitation and thus to estimate the parameters in an nth-power velocity model. The experimental facility is described in detail and a representative selection of results is included. The identified models are validated through the prediction of damper-ring orbits and comparison with observed responses.

Stanway, Roger↗