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  • 1
    Publication Date: 2011-08-16
    Description: Herringbone grooved gas lubricated journal bearing load capacity, attitude angle and power loss measurements
    Keywords: MACHINE ELEMENTS AND PROCESSES
    Type: ; TA FREQUENZA (
    Format: text
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  • 2
    Publication Date: 2016-06-07
    Description: Some preliminary results have been obtained for the dynamic response of a rotor operating over a speed range of 800 to 10,000 rpm. Amplitude frequency plots show the lateral vibratory response of an unbalanced rotor with and without external damping. The mode of damping is by means of eddy currents generated with 4 c shaped permanent magnets installed at the lower bearing of a vertically oriented rotor. The lower ball bearing and its damper assembly are totally immersed in liquid nitrogen at a temperature of -197 deg C (-320 deg F). These preliminary results for a referenced or base line passive eddy current damper assembly show that the amplitude of synchronous vibration is reduced at the resonant frequency. Measured damping coefficients were calculated to phi = .086; this compares with a theoretically calculated value of phi = .079.
    Keywords: MECHANICAL ENGINEERING
    Type: NASA. Marshall Space Flight Center Advan. High Pressure O2(H2 Technol.; p 366-380
    Format: application/pdf
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  • 3
    Publication Date: 2019-06-28
    Description: Lateral shaft vibrations produced by a rotating unbalance weight were damped by means of eddy currents generated in copper conductors that were precessing cyclicly in the gap formed by the pole faces of C-shaped, permanent magnets. The damper assembly, which was located at the lower bearing support of a vertically oriented rotor was completely immersed in liquid nitrogen during the test run. The test rotor was operated over a speed range from 800 to 10,000 rpm. Three magnet/conductor designs were evaluated. Experimental damping coefficients varied from 180 to 530 N sec/m. Reasonable agreement was noted for theoretical values of damping for these same assemblies. Values of damping coefficients varied from 150 to 780 N sec/m. The results demonstrate that passive eddy-current damping is a viable candidate for vibration control in cryogenic turbomachinery.
    Keywords: LAUNCH VEHICLES AND SPACE VEHICLES
    Type: NASA-TP-2562 , E-2762 , NAS 1.60:2562
    Format: application/pdf
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  • 4
    Publication Date: 2019-05-23
    Keywords: MACHINE ELEMENTS AND PROCESSES
    Type: NASA-TN-D-2223
    Format: application/pdf
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  • 5
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    In:  CASI
    Publication Date: 2019-06-28
    Description: An object of the invention is to provide variable damping for resonant vibrations which may occur at different rotational speeds in the range of rpms in which a rotating machine is operated. A variable force damper in accordance with the invention includes a rotating mass carried on a shaft which is supported by a bearing in a resilient cage. The cage is attached to a support plate whose rim extends into an annular groove in a housing. Variable damping is effected by tabs of electrically conducting nonmagnetic material which extend radially from the cage. The tabs at an index position lie between the pole face of respective C shaped magnets. The magnets are attached by cantilever spring members to the housing.
    Keywords: MECHANICAL ENGINEERING
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  • 6
    Publication Date: 2019-06-27
    Description: Experimental data were obtained for the unbalance response of a flexible rotor to speeds above the third lateral bending critical. Squeeze-film damping coefficients calculated from measured data showed good agreement with short-journal-bearing approximations over a frequency range from 5000 to 31,000 cmp. Response of a rotor to varying amounts of unbalance was investigated. A very lightly damped rotor was compared with one where oil-squeeze dampers were applied.
    Keywords: AIRCRAFT PROPULSION AND POWER
    Type: NASA-TP-1094 , E-9091
    Format: application/pdf
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  • 7
    Publication Date: 2019-06-27
    Description: Load capacity, attitude angle, and power loss were determined for 1-1/2-in.-diam herringbone grooved journal bearings operating in air to speeds of 60,000 rpm. Results showed that groove-to-ridge-clearance ratios of 2.0 to 2.4 give a greater load capacity than do ratios outside this optimum range. Agreement with a small-eccentricity pressure perturbation theory was good for groove-to-ridge-clearance ratios in the optimum range. Power loss, relative to that calculated for a plain bearing of the same dimensions, did not vary widely for the range of geometric variables used. Relative power loss generally increased with speed and was generally comparable to that for a plain bearing.
    Keywords: MACHINE ELEMENTS AND PROCESSES
    Type: ASME PAPER 71-LUB-B
    Format: text
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  • 8
    Publication Date: 2019-06-27
    Description: A rigid vertical shaft was operated with known amounts of unbalance at speeds to 30,000 rpm and gas supply pressure ratios to 4.8. From measured amplitude and phase angle data, dynamic stiffness and damping coefficients of the bearings were determined. The measured stiffness was proportional to the supply pressure, while damping was little affected by supply pressure. Damping dropped rapidly as the fractional frequency whirl threshold was approached. A small-eccentricity analysis overpredicted the stiffness by 20 to 70 percent. Predicted damping was lower than measured at low speeds but higher at high speeds.
    Keywords: MECHANICAL ENGINEERING
    Type: NASA-TN-D-8270 , E-8636
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  • 9
    Publication Date: 2019-07-27
    Description: This paper describes the methods used to design elastomerically damped supports for high-speed, flexible rotor-bearing systems. The procedure consists of using a damped natural frequency analysis to identify stiffness and damping requirements for the supports over the speed range. Optimum values for these coefficients are found and unbalance response analysis is used to calculate expected rotor behavior. Equations for calculating the shear and compressive stiffness and damping of button-type elastomer mounts are given, as is a procedure for their application to the design of the elastomeric mounts. These techniques were successfully applied to the design of damped elastomeric supports for a high-speed rotor, which traverses two bending critical speeds. Results of the testing showed that the rotor was well behaved and showed linear response to unbalance. Measured modal damping exceeded expectations and tests were conducted with both high- and low-loss elastomers, enabling the exploration of the practical range of elastomer damping capability.
    Keywords: MECHANICAL ENGINEERING
    Type: ASME PAPER 79-DET-88 , Design Engineering Technical Conference; Sept. 10-12, 1979; St. Louis, MO
    Format: text
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  • 10
    Publication Date: 2019-06-27
    Description: Values of damping and stiffness were determined experimentally for an externally pressurized, inherently compensated, compressible squeeze-film damper up to excitation frequencies of 36,000 cycles per minute. Experimental damping values were higher than theory predicted at low squeeze numbers and less than predicted at high squeeze numbers. Experimental values of air film stiffness were less than theory predicted at low squeeze numbers and much greater at higher squeeze numbers. Results also indicate sufficient damping to attenuate amplitudes and forces at the critical speed when using three dampers in the flexible support system of a small, lightweight turborotor.
    Keywords: MECHANICAL ENGINEERING
    Type: NASA-TN-D-7987 , E-8207
    Format: application/pdf
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