Stability analysis and control of a flywheel energy storage rotor with rotational damping and nonsynchronous damping

Based on the principle of Lagrange mechanics, especially considering the effects of rotation damping and nonsynchronous damping, a radial 4-dimensional dynamic model of the flywheel bearing rotor system is proposed. Applying the Laplace eigenvalue method, the stability effects of rotational damping, nonsynchronous damping, and their coupling effects are investigated by means of root locus method. Under the control of the linear quadratic regulator, dynamical characteristics of the flywheel bearing rotor system with varied rotational damping and nonsynchronous damping are also studied. The results show that the rotation damping, nonsynchronous damping, and their coupling effects have vast and complex instability effects on high-speed flywheel bearing rotor system. However, there are three exceptions. The tiny proportional rotational damping, remaining below 12%, and the minuscule proportional co-nonsynchronous damping; the product of the nonsynchronous damping and the speed ratio below 5% both can enhance the stability of the system. Furthermore, in the situation that the counter-nonsynchronous damping is coupled with the large proportion of rotational damping, the stability of the system can also be boosted distinctly. On the other hand, the numerical experimental results show that the rotational damping and nonsynchronous damping have a beneficial effect on the flywheel system controlled by linear quadratic regulator. In addition, under the control of linear quadratic regulator, the transient dynamical behavior of the flywheel rotor system with rotational damping or co-nonsynchronous damping performed better than the flywheel rotor system with the coupled damping. The numerical simulations of the transient response of the flywheel rotor system under active control are consistent with some of the derived stability analysis results. The results about the stability analysis and the performance in vibration control give the suggestions for the instability control and fault detection of the system.

Vibration Characteristics of Rotor System with Loose Disc Caused by the Insufficient Interference Force

The loose of mechanical parts is one of the common failures in rotating machinery. The current researches of loose fault mainly focus on non-rotating components. However, the loose of disc, which is the main work part in the rotor system, is less paid attention, and the mechanism and dynamics characteristics of the loose fault are also almost ignored. In this paper, a dynamic contact model of the rotor system with loose disc is established considering the microscopic surface topography. Through the numerical simulation, the vibration characteristics of the disc-shaft rotor system are analyzed and discussed. The simulation results are further verified by experiments. The results show that the rotation state of the disc is affected by the rotation speed of the shaft, contact stiffness, a gap between the disc and shaft, damping of the disc, and the rotational damping. When the speed difference between the disc and shaft is zero or large, the collision frequency is mainly composed of one frequency component. When the rotational speed of the disc approaches the shaft, the beating vibration phenomenon of the disc occurs in the horizontal direction. As the decreases of relative speed between the disc and shaft, the disc trajectory changes from ‘circular’ to ‘double ring’ and then ‘circular’. The research results on nonlinear dynamics characteristics of the loose disc has important theoretical value and practical application value, and makes up for its shortcomings in the rotor system with loose disc.

On the Frequency Dependency of Tilting-Pad Journal Bearings

Controversy regarding the dynamic modeling of tilting-pad journal bearings (TPJB) has existed for years, with the question of the effective stiffness and damping properties, and the requirement for consideration of frequency dependency, being of great concern. There is a partial disconnect between the results of theoretical and many experimental investigations. This paper attempts to examine this issue in more of a macro sense; broadening the scope of the geometric and operating domains, and in turn expanding an understanding of related frequency effects. The investigation hinges on a single-pad, single degree-of-freedom (DOF) model that represents various geometries and operating conditions for a full bearing. The results clearly show that the dynamic coefficients must be dependent upon the “exciting” frequency, and that the dependency is primarily associated with the pad rotational damping.

Decoherence of collective motion in warm nuclei

Collective states in cold nuclei are represented by a wave function that assigns coherent phases to the participating nucleons. The degree of coherence decreases with excitation energy above the yrast line because of coupling to the increasingly dense background of quasiparticle excitations. The consequences of decoherence are discussed, starting with the well studied case of rotational damping. In addition to superdeformed bands, a highly excited oblate band is presented as a new example of screening from rotational damping. Suppression of pair correlation leads to incoherent thermal M1 radiation, which appears as an exponential spike (LEMAR) at zero energy in the γ strength function of spherical nuclei. In deformed nuclei a Scissors Resonance appears and LEMAR changes to damped magnetic rotation, which is interpreted as partial restoration of coherence.