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An effective vibration control device, the pendulum tuned mass damper (P-TMD), can be easily realized as a mass supported on rolling or sliding pendulum bearings. While the bearings' concavity provides the desired gravitational restoring force, the necessary dissipative force can be obtained either from additional dampers installed in parallel with the bearings or from the same friction resistance developing within each bearing between the roller/slider and the rolling/sliding surface. The latter solution may prove cheaper and more compact but implies that the P-TMD effectiveness will be amplitude dependent if the friction coefficient is kept uniform along the rolling/sliding surface, as in conventional friction bearings. In this case, the friction P-TMD will be as efficient as a viscous P-TMD only at a given vibration level, with large performance reductions at other levels. To avoid this inconvenience, this paper proposes a new type of sliding variable friction pendulum (VFP) TMD, called the VFP-TMD, in which the sliding surface is divided into two concentric regions: a circular inner region, having the lowest possible friction coefficient and the same dimensions of the slider, and an annular outer region, having a friction coefficient set to an optimal value. A similar arrangement has been recently proposed to realize adaptive seismic isolation devices, but no specific application to TMDs is reported. To assess the VFP-TMD performance, first its analytical model is derived, rigorously accounting for geometric nonlinearities as well as for the variable (in time and space) pressure distribution along the contact area, and then, an optimal design methodology is presented. Finally, numerical simulations show the influence of the main design parameters on the device behavior and demonstrate that the VFP-TMD can achieve nearly the same effectiveness of viscous P-TMDs, while considerably outperforming conventional uniform-friction P-TMDs. The proposed analytical model can be used to enhance or validate existing models of VFP isolators that assume a constant and uniform contact pressure distribution. [ABSTRACT FROM AUTHOR]

This paper analyses the thermal and roughness effects on different characteristics of finite rough tilted pad slider bearings. The roughness is assumed to be stochastic, Gaussian randomly distributed. Density and viscosity are assumed to be temperature dependent. In this study, two models of one-dimensional roughness, longitudinal and transverse, are considered. The irregular domain due to roughness is mapped to a regular domain so that the numerical method can be easily applied. The modified Reynolds equation, momentum equation, continuity equation and energy equation are coupled and solved using the finite difference method to yield various bearing characteristics. It is observed that for nonparallel slider bearing the load carrying capacity due to the combined effect is less than the load capacity due to the roughness effect for both longitudinal and transverse roughness models. However, in case of a parallel pad slider bearing, the reverse is true, though the load capacity is not significant. It is also observed that the load carrying capacity due to the combined effect is larger than the load carrying capacity due to the thermal effect for both roughness models. [ABSTRACT FROM AUTHOR]

This paper analyzes the thermal and roughness effects on different characteristics of an infinite tilted pad slider bearing. The roughness is assumed to be stochastic, Gaussian randomly distributed. Density and viscosity are assumed to be temperature-dependent. In this study, two models of one-dimensional roughness, longitudinal and transverse, are considered. The irregular domain due to roughness is mapped to a regular domain so that the numerical method can be easily applied. The modified Reynolds equation, momentum equation, continuity equation and energy equation are coupled and solved using the finite difference method to yield various bearing characteristics. It is observed that for a non-parallel slider bearing, the load carrying capacity due to the combined effect is less than the load capacity due to the roughness effect for both models. However, in the case of a parallel pad slider bearing the reverse is true, though the load capacity is not significant. It is also observed that the load carrying capacity due to the combined effect is less than the load carrying capacity due to the thermal effect for the longitudinal roughness model, and it is the opposite for the transverse roughness model. [ABSTRACT FROM AUTHOR]

A numerical analysis of a rigid rotor supported by relatively short externally pressurized porous gas journal bearings is presented for nonlinear dynamic behavior and bifurcation. The compressible Reynolds' equation is solved by the finite differences method, and the successive over relaxation method and a time-dependent mathematical model for porous gas journal bearings are studied. A comparison of the results for the system state trajectory, Poincaré maps, power spectra, and bifurcation diagrams is made, and the dynamic behavior of the rotor center in the horizontal and vertical directions under different operating conditions is analyzed. The analysis shows the existence of a complex dynamic behavior comprising periodic and quasi-periodic response of the rotor center. This paper shows how the dynamic behavior of this type of system varies with changes in rotor mass and bearing number. [ABSTRACT FROM AUTHOR]

The present paper analyzes the porous constant gap externally pressurized conical bearings when the slider is rotating with uniform angular velocity. The lubricant is assumed to be incompressible, and its viscosity varies exponentially with temperature. The lubricant inertia due to rotation of the slider is considered but the convective inertia is neglected. The energy equation is used to determine the temperature generated in the lubricant film. The governing system of coupled momentum and energy equation is solved numerically, using finite difference method, to determine various bearing characteristics. It is observed that for the surfaces which are highly porous the inlet pressure decreases remarkably, resulting in reduced load capacity of the bearing, and thc torque remains unaffected with respect to variation in the permeability. [ABSTRACT FROM AUTHOR]