Jin Wei Liang

Identifying Coulomb and Viscous Friction from Free-Vibration Decrements

This study focuses on an algorithm for the simultaneous identification of Coulomb and viscous damping effects from free-vibration decrements in a damped linear single degree-of-freedom (DOF) mass-spring system. Analysis shows that both damping effects can indeed be separated. Numerical study of a combined-damping system demonstrates a perfect match between the simulation parameters and the estimated values. Experimental study includes two types of real systems. The method is applied to an experimental industrial bearing. Experimental results are compared with numerical simulations to illustrate the reliability of this method. An analysis provides conservative bounds on error estimates. An example of the effect of quantization error on the estimations is included.

Dynamical friction behavior in a forced oscillator with a compliant contact

Contact compliance, which may arise from elastic deformation near the contact point or in the surrounding structure, affects the dynamical friction behaviors in mechanical oscillators. An idealized model consisting ofa mass sliding harmonically on a massless compliant contact produces hysteresis in friction-velocity plots. Dynamical friction features, depending on the contact stillness, friction level, and the frequency and amplitude of oscillation, are predicted and quantified. Contact compliance can also lead to oscillations at the transition from slip to stick. Experiments and simulations verify the model and tie together phenomena of both continuous sliding and stick-slip.

Identifying Coulomb and Viscous Friction in Forced Dual-Damped Oscillators

This paper presents a method for estimating Coulomb and viscous friction coefficients from responses of a harmonically excited dual-damped oscillator with linear stiffness. The identification method is based on existing analytical solutions of non-sticking responses excited near resonance. The method is applicable if the damping ratio of viscous component can be considered small. The Coulomb and viscous friction parameters can be extracted from two or more input-output amplitude pairs at resonance. The method is tested numerically and experimentally. Experimental results are cross checked with estimations from free-vibration decrements and also from friction measurements.

Phase-Space Reconstructions and Stick-Slip

Nonsmooth processes such as stick-slip may introduce problems with phase-space reconstructions. We examine chaotic single-degree-of-freedom stick-slip friction models and use the method of delays to reconstruct the phase space. We illustrate that this reconstruction process can cause pseudo trajectories to collapse in a way that is unlike, yet related to, the dimensional collapse in the original phase-space. As a result, the reconstructed attractor is not topologically similar to the real attractor. Standard dimensioning tools are applied in effort to recognize this situation. The use of additional observables is examined as a possible remedy for the problem.

WAVELET ANALYSIS OF STICK-SLIP SIGNALS IN OSCILLATORS WITH DRY-FRICTION CONTACT

Wavelet transforms were compared between various simulated friction models and real stick-slip data. While simulations of several models produced stick-slip transition oscillations seen in the real data, the wavelet features of the compliant contact model with light damping best captured the characteristics of the experimental signal. The wavelet contours were also used to estimate the contact stiffness.

Identifying Coulomb and Viscous Friction in Forced Oscillators by Using a Harmonic Energy Balance

This study makes use of energy dissipation to identify damping from mechanical vibration systems. Both the viscous damping and dry friction are assumed to coexist in vibration systems. By balancing the energy loss as registered in the force-displacement relationship of the real system against that of a theoretical model, consisting of viscous damping and dry friction components, the identification algorithms are developed and the equivalent viscous-damping and dry-friction parameters are estimated. We apply the estimation equations to both numerical and experimental systems to show the effectiveness and reliability of the new identification method.Copyright