Presence Of Internal Friction Research Articles

Нечеткие фазовые траектории волновых твердотельных гироскопов

The paper considers elementary fuzzy oscillator models represented by hard and fuzzy second-order differential equations with hard and fuzzy initial conditions. Linear models describe wave processes in ring resonators of hemispherical resonator gyroscopes.We show that in the case 1 (a hard model with fuzzy initial conditions), when there is no internal friction (model 1), phase trajectories appear as a fuzzy centre shaped as an elliptical ring. When internal friction is present (model 2), phase trajectories appear as a fuzzy focus shaped as a circular logarithmic spiral. In the case 2, for a fuzzy hemispherical resonator gyroscope model with hard initial conditions, when there is no internal friction (model 1), a representative point of a fuzzy phase trajectory does not stop or increase its oscillations with time, meaning that the system is asymptotically unstable, while for the model 2 the origin singularity is a fuzzy stable focus. In the case 3, for a fuzzy hemispherical resonator gyroscope model with fuzzy initial conditions, when there is no internal friction (model 1), there is a fuzzy asymptotic instability in the model 1 of a hemispherical resonator gyroscope, while in the presence of internal friction (model 2), the phase trajectory is also a function of time and controls the asymptotic stability of the fuzzy model 2 of a hemispherical resonator gyroscope. Asymptotic stability is determined for all cases and models

Asymptotic Analysis of the Forced Oscillations of Double-Layered Plates with Viscous Resistance

The three-dimensional dynamic problem of forced oscillations of an orthotropic two-layered plate in the presence of internal friction in the layers is solved by the asymptotic method. It is assumed that the friction is proportional to the velocity of the points. The values of stress set on the front faces of the double-layered packet harmonically vary in time. The general asymptotic solution of the interior problem is found. It is shown that, due to friction (dissipation), the oscillation amplitudes always remain finite, while, in the absence of internal friction, there are frequencies at which the oscillation amplitude becomes infinite.

Irreversible work and internal friction in a quantum Otto cycle of a single arbitrary spin

We propose an arbitrary driven spin as the working fluid of a quantum Otto cycle in the presence of internal friction. The role of total allocated time to the adiabatic branches of the cycle, generated by different control field profiles, on the extractable work and the thermal efficiency are analyzed in detail. The internal friction is characterized by the excess entropy production and quantitatively determined by studying the closeness of an actual unitary process to an infinitely long one via quantum relative entropy. It is found that the non-ideal, finite-time adiabatic transformations negatively effect the work output and the thermal efficiency of the quantum heat engine. The non-monotone dependence of the work output, thermal efficiency, entropy production and the internal friction on the total adiabatic time are elucidated. It is also found that almost frictionless adiabatic transformations with small entropy production can be obtained in a short adiabatic time.

Reconfiguration dynamics in folded and intrinsically disordered protein with internal friction: Effect of solvent quality and denaturant

We consider a flexible chain with internal friction in a harmonic confinement and extend it to include the effects of solvent quality at the mean field level by introducing a Flory type exponent ν. The strength of the harmonic confinement (kc) accounts for the denaturant concentration and connects to the internal friction of the chain (ξint) through an ansatz. Our calculated reconfiguration times falling in the range of 5–50 ns are found out to be within 10%–15% of the experimentally measured reconfiguration times of the folded cold shock protein and the intrinsically disordered protein prothymosin α. In addition, our calculations show that the reconfiguration time scales with the chain length N as ∼Nα, where α depends weakly on the internal friction but has rather stronger dependence on the solvent quality. In the absence of any internal friction, α=2ν+1 and it goes down in the presence of internal friction, but chain reconfiguration slows down in general. On the contrary, in a poorer solvent chain reconfiguration and looping become faster even though the internal friction is higher in the collapsed state.

Active stabilisation of a piezoelectric fiber composite shaft subject to follower load

The paper is concerned with active stabilisation of self-excited vibration of slender rotating columns subject to tangential follower forces. Such systems exhibit flutter-type instability as a result of energy transfer from rotation and to transverse motion of the shaft. There are two reasons for the instability to occur in rotating slender shafts––rotation in the presence of internal friction in the shaft material, and the follower load. The study reveals an interesting coupled effect of these parameters on the system stability as they create a concave set in which the system remains stable, and this means that one parameter neutralises influence of the other. The paper also takes up the problem of near-critical behaviour of the system. Non-linear bifurcation analysis is carried out to predict type of the self-excitation (either soft or hard), near-critical vibration amplitude and jump phenomena. In the second part of the paper a method of active stabilisation based on making use of piezoelectric fibre composites (PFC) is presented. The composites containing active fibres made of piezoceramics constitute the state-of-the-art structural materials capable of adjusting their mechanical state according to dynamic loading conditions. Some fundamentals concerning the operation of PFCs as rotating columns are given in the paper.

Active stabilization of a rotating shaft transmitting static torque

The paper is concerned with the problem of stability of a power transmitting thin-walled shaft made of the active laminate PFC (piezoelectric fiber composite). The shaft rotates with a given operational angular velocity, and is loaded by a static torque. Such a system is known to exhibit divergence or oscillating type of instability. On the one hand presence of internal friction in the material of the shaft leads to loss of stability at a certain critical rotation speed. The static torque can be responsible for spatial deformation of the shaft axis on the other. A method preventing the system from such behavior is discussed in the paper. The method is based on application of a composite material, which contains active piezoelectric fibers. The fibers produce bending moments, and this way affect the dynamics of the entire system. Two control strategies are investigated. Results of numerical simulations are presented graphically.