On Stability of a Circulatory System With Bilinear Hysteresis Damping

1969 ◽  
Vol 36 (1) ◽  
pp. 76-82 ◽  
Author(s):  
I. C. Jong
Keyword(s):  
Steady State ◽  
Initial Perturbation ◽  
Viscoelastic Model ◽  
Circulatory System ◽  
Stability Limit ◽  
Viscous Damping ◽  
Hysteretic Model ◽  
Damping Effect ◽  
Circulatory Force ◽  
Stability Limits

Dynamic stability problems of a two-degree-of-freedom system with bilinear hysteresis damping and subjected to a circulatory force are considered. Steady-state oscillations and critical loads for flutter of the system are investigated using energy considerations and the method of slowly varying parameters. Problems concerning stability limits (limiting values of the critical load) for vanishing hysteresis damping are examined and compared with those found by earlier investigators for vanishing viscous damping. It is shown that, in a circulatory system, small hysteresis damping may have a destabilizing effect similar to linear viscous damping, but the hysteretic model generally yields a satisfactory stability limit as the hysteresis damping effect approaches zero. The viscoelastic model generally leads to unsatisfactory stability limits as the viscous damping effect varies from small values to zero. Thus, the hysteretic model is shown to be more adequate than the viscoelastic model. The study also shows that for some different sets of initial perturbation there may exist two disparate states of steady-state oscillations of the system under the same loading.

An Exercise for Teaching Transient Stability

1994 ◽  
Vol 31 (4) ◽  
pp. 357-361
Author(s):  
C. S. Indulkar
Keyword(s):  
Steady State ◽  
Transient Stability ◽  
Stability Limit ◽  
Synchronous Machine ◽  
Stability Limits ◽  
Steady State Stability

An exercise for teaching transient stability In this paper, the transient stability limits of a synchronous machine for various initial loadings have been determined in terms of its steady-state stability limit.

Steady-State Dynamic Response of a Limited Slip System

1968 ◽  
Vol 35 (2) ◽  
pp. 322-326 ◽  
Author(s):  
W. D. Iwan
Keyword(s):  
Steady State ◽  
Dynamic Response ◽  
Slip System ◽  
External Load ◽  
Initial Conditions ◽  
Viscous Damping ◽  
Steady State Response ◽  
Response Curves ◽  
State Response ◽  
System Nonlinearity

The steady-state response of a system constrained by a limited slip joint and excited by a trigonometrically varying external load is discussed. It is shown that the system may possess such features as disconnected response curves and jumps in response depending on the strength of the system nonlinearity, the level of excitation, the amount of viscous damping, and the initial conditions of the system.

scholarly journals Characteristics of Functional Stability in Young Adolescent Female Artistic Gymnasts

2021 ◽  
Vol 77 (1) ◽  
pp. 51-59
Author(s):  
Agnieszka Opala-Berdzik ◽  
Magdalena Głowacka ◽  
Kajetan J. Słomka
Keyword(s):  
Postural Control ◽  
Center Of Pressure ◽  
National Level ◽  
Stability Limit ◽  
Young Adolescent ◽  
Quiet Standing ◽  
Adolescent Female ◽  
Functional Stability ◽  
Postural Control System ◽  
Stability Limits

Abstract The aim of this study was to determine whether young adolescent female artistic gymnasts demonstrate better functional stability than age- and sex-matched non-athletes. Different characteristics of the gymnasts’ postural control were expected to be observed. Twenty-two 10- to 13-year-old healthy females (ten national-level artistic gymnasts and twelve non-athletes) participated in the study. To assess their forward functional stability, the 30-s limit of stability test was performed on a force plate. The test consisted of three phases: quiet standing, transition to maximal forward leaning, and standing in the maximal forward leaning position. Between-group comparisons of the directional subcomponents of the root mean squares and mean velocities of the center of pressure and rambling-trembling displacements in two phases (quiet standing and standing in maximal leaning) were conducted. Moreover, anterior stability limits were compared. During standing in maximal forward leaning, there were no differences in the center of pressure and rambling measures between gymnasts and non-athletes (p > 0.05). The values of trembling measures in both anterior-posterior and medial-lateral directions were significantly lower in gymnasts (p < 0.05). Both groups presented similar values for anterior stability limits (p > 0.05). The comparisons of rambling components may suggest a similar supraspinal control of standing in the maximal leaning position between gymnasts and healthy non-athletes. However, decreased trembling in gymnasts may indicate reduced noise in their postural control system possibly due to superior control processes at the spinal level. The anterior stability limit was not influenced by gymnastics training in female adolescents.

scholarly journals Studies on dielectric relaxation in relation to viscosity of some anilines, phenol, and their binary mixtures at microwave frequencies

2019 ◽  
Vol 97 (2) ◽  
pp. 210-215
Author(s):  
C.V. Maridevarmath ◽  
G.H. Malimath
Keyword(s):  
Relaxation Time ◽  
Steady State ◽  
Dynamic Viscosity ◽  
Room Temperature ◽  
Viscoelastic Model ◽  
Frictional Resistance ◽  
Nonlinear Behaviour ◽  
Viscoelastic Relaxation ◽  
Microwave Frequencies ◽  
Loss Formula

In the present work, the study of variation of relaxation time (τ) with viscosity of the medium (η) is carried out on four polar samples: 2-Nitroaniline, 4-Bromoaniline, 4-Chloroaniline, 4-Chlorophenol, and also on the binary mixture of 2-Nitroaniline + 4-Bromoaniline at room temperature by using microwave bench operating at a frequency of 9.59 GHz. In this regard, the different parameters like dielectric constant ([Formula: see text]), dielectric loss ([Formula: see text]), relaxation time (τs), macroscopic steady state viscosity (ηs), dynamic viscosity (ηd), and viscoelastic relaxation time (τve) were determined for all the systems. It is observed that the relaxation time (τs) increases with the increase in the viscosity of the medium for all the systems. Plots of log(τs) versus log(ηs) for all the systems show that variation of relaxation time is found to be nonlinear in the higher viscosity regions. This suggests the failure of Debye’s theory at these regions. Further, the nonlinear behaviour of relaxation time with the viscosity is explained by using the viscoelastic model suggested by Barlow et al. (Proc. R. Soc. A 309, 473 (1969). doi: 10.1098/rspa.1969.0053 ). It is also observed that macroscopic steady state viscosity (ηs) values are greater than the dynamic viscosity (ηd), and viscoelastic relaxation time (τve) values were found to be lower compared to the relaxation time (τs). These results suggest that the effective frictional resistance experienced by the molecules during reorientation is lower and the measured values of macroscopic steady state viscosity (ηs) are frequency dependent.

Rubbing Phenomena in Rotor-Stator Contact

2000 ◽  
Author(s):  
Z. C. Feng ◽  
Xiao-Zhang Zhang
Keyword(s):  
Steady State ◽  
Radial Velocity ◽  
Analytical Model ◽  
Contact Surface ◽  
Initial Perturbation ◽  
Instantaneous Change

Abstract This paper discusses the vibration phenomena of a rotor rubbing with a stator caused by an initial perturbation. The analytical model consists of a simple disc-shaft rotor and a fixed stator. The perturbation is an instantaneous change of the radial velocity when the rotor is rotating in its normal steady state. It is found that under certain conditions, the rotor will remain rubbing with the stator, even if the initial perturbation no longer exists. In the case of no friction on the contact surface between the rotor and the stator, the full rubbing behaves as forward whirling. When friction is present, the full rubbing behaves as backward whirling.

Dynamic Analysis of a Coupled Dual-Rotor With Squeeze Film Damper Considering Sudden Unbalance

2021 ◽  
Author(s):  
Ying Cui ◽  
Yuxi Huang ◽  
Guogang Yang ◽  
Yongliang Wang ◽  
Han Zhang
Keyword(s):  
Steady State ◽  
Transient Response ◽  
Rotor System ◽  
Lubricating Oil ◽  
Squeeze Film ◽  
Radial Clearance ◽  
Oil Viscosity ◽  
Squeeze Film Damper ◽  
Damping Effect ◽  
Bistable State

Abstract A nonlinear multi-degree-of-freedom dynamic model of a coupled dual-rotor system with an intershaft bearing and uncentralized squeeze film damper is established by using finite element method. Based on the model, the critical speed characteristic diagram and vibration modes of the system were calculated. The steady-state unbalance response is obtained by using Newmark-β algorithm. The numerical results show the effect of SFD position in the dual-rotor system on response amplitude. It is found that with the decrease of radial clearance and the increase of length-diameter ratio and lubricating oil viscosity, the damping effect of SFD is enhanced and the bistable state phenomenon can be suppressed. The transient response of the system in case of sudden unbalance occurring at the fan was simulated by applying a step function. It is demonstrated that the SFD can effectively reduce the duration and maximum amplitude of the transient process, but at certain speeds, the SFD will increase the amplitude after the system returns to steady state, the damping effect on the transient response is also enhanced with the increase of length-diameter and the decrease of radial clearance, and with the increase of the sudden unbalance value, the response is more likely to stabilized at the high amplitude state of the bistable state.

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