Engineering Papers⌕ Search

SEARCH · Engineering Papers

Results for “VISCOUS DAMPING”

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.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 37 records · Page 2
All sourcesNASA NTRSDOE OSTI
NASA NTRS1971

Stability of circulatory elastic systems in the presence of magnetic damping.

The effect of a type of magnetic damping on the stability of equilibrium of some circulatory elastic systems is examined. A simple system with two degrees of freedom is considered first, and a destabilization is found to be caused by the magnetic field. The nature of the destabilization, however, is not identical to that caused by internal viscous damping. The differences and similarities between the two effects are discussed, and the results are also compared with those of linear external viscous damping. A continuous cantilever bar subjected to a follower force at its free end is then examined. It is found that the critical load is independent of the strength of the magnetic field, and is considerably lower than the corresponding critical load in the absence of a magnetic field. Finally, the continuous cantilever is treated approximately by Galerkin's procedure and also by using a two-degree-of-freedom model of the cantilever; the results obtained are qualitatively the same.

Smith, T. E.↗
NASA NTRS2002

Constitutive properties of hypertrophied myocardium: cellular contribution to changes in myocardial stiffness

Recent studies have suggested that pressure overload hypertrophy (POH) alters the viscoelastic properties of individual cardiocytes when studied in isolation. However, whether these changes in cardiocyte properties contribute causally to changes in the material properties of the cardiac muscle as a whole is unknown. Accordingly, a selective, isolated, acute change in cardiocyte constitutive properties was imposed in an in vitro system capable of measuring the resultant effect on the material properties of the composite cardiac muscle. POH caused an increase in both myocardial elastic stiffness, from 20.5 +/- 1.3 to 28.4 +/- 1.8, and viscous damping, from 15.2 +/- 1.1 to 19.8 +/- 1.5 s (normal vs. POH, P < 0.05), respectively. Recent studies have shown that cardiocyte constitutive properties could be acutely altered by depolymerizing the microtubules with colchicine. Colchicine caused a significant decrease in the viscous damping in POH muscles (19.8 +/- 1.5 s at baseline vs. 14.7 +/- 1.3 s after colchicine, P < 0.05). Therefore, myocardial material properties can be altered by selectively changing the constitutive properties of one element within this muscle tissue, the cardiocyte. Changes in the constitutive properties of the cardiocytes themselves contribute to the abnormalities in myocardial stiffness and viscosity that develop during POH.

Non-NASA Center↗
NASA NTRS1996

Expendable Launch Vehicle Studies

Analytical support studies of expendable launch vehicles concentrates on the stability of the dynamics during launch especially during or near the region of maximum dynamic pressure. The in-plane linearized dynamic equations of a generic launch vehicle with multiple flexible bending and fuel sloshing modes are developed. The design of a robust LQR controller based on the reduced order system is accomplished using the parameter perturbation technique. The ELV modeling and analysis team has spent the past three years working on the theoretical development and application of sensitivity analysis to solve eigenvalue problems associated with structural dynamics. Specific application areas include stochastic vibrations, viscously damped vibrations and nonlinear dynamics. In stochastic linear vibrations, sensitivity analysis methods have been developed which determined the expectation and variance of the response for given probability density functions of various stochastic parameters. Examples worked include beam vibrations with up to six stochastic parameters; and the eigensensitivity results differ little from those obtained, with much effect, from Monte Carlo techniques. For viscously damped vibrations, eigensensitivity analysis has given excellent results for homogeneous beams, modeled by either quadratic or quartic eigenvalue equations. Specific applications include Kevin and Maxwell-type viscoelastic beams.

Bainum, P. M.↗
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 NTRS2016

Vibration Control via Stiffness Switching of Magnetostrictive Transducers

In this paper, a computational study is presented of structural vibration control that is realized by switching a magnetostrictive transducer between high and low stiffness states. Switching is accomplished by either changing the applied magnetic field with a voltage excitation or changing the shunt impedance on the transducer's coil (i.e., the magnetostrictive material's magnetic boundary condition). Switched-stiffness vibration control is simulated using a lumped mass supported by a damper and the magnetostrictive transducer (mount), which is represented by a nonlinear, electromechanical model. Free vibration of the mass is calculated while varying the mount's stiffness according to a reference switched-stiffness vibration control law. The results reveal that switching the magnetic field produces the desired change in stiffness, but also an undesired actuation force that can significantly degrade the vibration control. Hence, a modified switched-stiffness control law that accounts for the actuation force is proposed and implemented for voltage-controlled stiffness switching. The influence of the magneto-mechanical bias condition is also discussed. Voltage-controlled stiffness switching is found to introduce damping equivalent to a viscous damping factor up to about 0.13; this is shown to primarily result from active vibration reduction caused by the actuation force. The merit of magnetostrictive switched-stiffness vibration control is then quantified by comparing the results of voltage- and shunt-controlled stiffness switching to the performance of optimal magnetostrictive shunt damping. For the cases considered, optimal resistive shunt damping performed considerably better than both voltage- and shunt-controlled stiffness switching.

vibration control↗
NASA NTRS2016

Vibration Control via Stiffness Switching of Magnetostrictive Transducers

This paper presents a computational study of structural vibration control that is realized by switching a magnetostrictive transducer between high and low stiffness states. Switching is accomplished by either changing the applied magnetic field with a voltage excitation or changing the shunt impedance on the transducer's coil (i.e., the magnetostrictive material's magnetic boundary condition). Switched-stiffness vibration control is simulated using a lumped mass supported by a damper and the magnetostrictive transducer (mount), which is represented by a nonlinear, electromechanical model. Free vibration of the mass is calculated while varying the mount's stiffness according to a reference switched-stiffness vibration control law. The results reveal that switching the magnetic field produces the desired change in stiffness, but also an undesired actuation force that can significantly degrade the vibration control. Hence, a modified switched-stiffness control law that accounts for the actuation force is proposed and implemented for voltage-controlled stiffness switching. The influence of the magnetomechanical bias condition is also discussed. Voltage-controlled stiffness switching is found to introduce damping equivalent to a viscous damping factor up to about 0.25; this is shown to primarily result from active vibration reduction caused by the actuation force. The merit of magnetostrictive switched-stiffness vibration control is then quantified by comparing the results of voltage- and shunt-controlled stiffness switching to the performance of optimal magnetostrictive shunt damping.

stiffness tuning↗
NASA NTRS1983

Parameter estimation in truss beams using Timoshenko beam model with damping

Truss beams with members having viscous damping are modeled with a Timoshenko beam. Procedures for deriving the equivalent bending rigidity, transverse shear rigidity, and damping are presented. Explicit expressions for these equivalent beam properties are obtained for a specific truss beam. The beam model thus established is then used to investigate the effect of damping in free vibration. Finally, the beam is employed in the estimation of structural parameters in a simply-supported truss beam using a random search algorithm.

Sun, C. T.↗
DOE OSTI2025

Measurement of the structural damping ratio of some common materials at 293 K and 77 K in air

The structural damping ratio of various materials has been measured at 293 K and 77 K through a rod bending excitation setup. The aim was to extract the material-dependent structural damping ratio as a first approach to in-vacuum damping. However, for simplicity, testing has been conducted in air with measures to minimize the effect of viscous damping from viscous drag. The setup and methodology are described in this paper, as well as the setup limitations and proposed ways to overcome these limitations for an improved setup. The results are presented in a summary table and discussed.

43 PARTICLE ACCELERATORS↗
NASA NTRS1988

Design of ground test suspension systems for verification of flexible space structures

A simple model demonstrates the frequency-increasing effects of a simple cable suspension on flexible test article/suspension systems. Two passive suspension designs, namely a negative spring mechanism and a rolling cart mechanism, are presented to alleviate the undesirable frequency-increasing effects. Analysis methods are provided for systems in which the augmentations are applied to both discrete and continuous representations of test articles. The damping analyses are based on friction equivalent viscous damping. Numerical examples are given for comparing the two augmentations with respect to minimizing frequency and damping increases.

Cooley, V. M.↗