Parametric instability in the Watt governor with periodic loading

The paper deals with the example of application of the two continuum rheological model of materials with microdefects, nanodefects and solute hydrogen for calculation of stress and strain in cylindrical specimen under periodic loading. The model suggested allows one to relate the mechanical characteristics with the hydrogen concentration.The stability analysis of the system metal-hydrogen is carried out. The influence of parameters of the mechanical loading, hydrogen concentration and parameters of sorption and desorption of hydrogen from the surface of the internal defects (traps) of various nature on the system stability is performed.It is shown that influence of hydrogen can be considered as parametric instability of a continuous medium under mechanical deformation.This can be important during forming or plastic deformation of materials and nanomaterials containing hydrogen.

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Fatigue of Unidirectional Cord-Rubber Composites

Tire Science and Technology ◽

10.2346/1.2135975 ◽

1999 ◽

Vol 27 (1) ◽

pp. 48-57 ◽

Cited By ~ 5

Author(s):

Y. Liu ◽

Z. Wan ◽

Z. Tian ◽

X. Du ◽

J. Jiang ◽

...

Keyword(s):

Damage Accumulation ◽

Fatigue Testing ◽

Fatigue Behavior ◽

Constant Load ◽

Testing System ◽

Rubber Composites ◽

Cycle Frequency ◽

Periodic Loading ◽

Fatigue Damage Accumulation ◽

Rubber Composite

Abstract A fatigue testing system is established with which the real-time recording of stress, strain, temperature, and hysteresis loss of rubbers or cord-rubber composite specimens subjected to periodic loading or extension can be successfully carried out. Several problems are connected with the experimental study of the fatigue of rubber composites. In constant extension cycling, the specimen becomes relaxed because of the viscoelasticity of rubber composites, and the imposed tension-tension deformation becomes complex. In this method, the specimen is unlikely to fail unless the imposed extensions are very large. Constant load cycling can avoid the shortcomings of constant extension cycling. The specially designed clamps ensure that the specimen does not slip when the load retains a constant value. The Deformation and fatigue damage accumulation processes of rubber composites under periodic loading are also examined. Obviously, the effect of cycle frequency on the fatigue life of rubber composites can not be ignored because of the viscoelasticity of constituent materials. The increase of specimen surface temperature is relatively small in the case of 1 Hz, but the temperature can easily reach 100°C at the 8 Hz frequency. A method for evaluating the fatigue behavior of tires is proposed.

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Online Real-Time Monitoring System Through Using Adaptive Angular-Velocity VKF Order Tracking

Volume 1: 24th Conference on Mechanical Vibration and Noise, Parts A and B ◽

10.1115/detc2012-70506 ◽

2012 ◽

Cited By ~ 1

Author(s):

Ting-Chi Yeh ◽

Min-Chun Pan

Keyword(s):

Angular Velocity ◽

Real Time ◽

Monitoring System ◽

Condition Monitoring ◽

Theoretical Derivation ◽

Periodic Loading ◽

Order Tracking ◽

Computation Scheme ◽

Condition Monitoring System ◽

Operation Status

When rotary machines are running, acousto-mechanical signals acquired from the machines are able to reveal their operation status and machine conditions. Mechanical systems under periodic loading due to rotary operation usually respond in measurements with a superposition of sinusoids whose frequencies are integer (or fractional integer) multiples of the reference shaft speed. In this study we built an online real-time machine condition monitoring system based on the adaptive angular-velocity Vold-Kalman filtering order tracking (AV2KF_OT) algorithm, which was implemented through a DSP chip module and a user interface coded by the LabVIEW®. This paper briefly introduces the theoretical derivation and numerical implementation of computation scheme. Experimental works justify the effectiveness of applying the developed online real-time condition monitoring system. They are the detection of startup on the fluid-induced instability, whirl, performed by using a journal-bearing rotor test rig.

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Parametric instability in a free-evolving warped protoplanetary disc

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/staa3504 ◽

2020 ◽

Vol 500 (3) ◽

pp. 4248-4256

Author(s):

Hongping Deng ◽

Gordon I Ogilvie ◽

Lucio Mayer

Keyword(s):

Wave Equations ◽

Hydrodynamic Instability ◽

Parametric Instability ◽

Low Viscosity ◽

Crossing Time ◽

Particle Hydrodynamics ◽

Smoothed Particle ◽

First Time ◽

Bending Wave ◽

Grid Based

ABSTRACT Warped accretion discs of low viscosity are prone to hydrodynamic instability due to parametric resonance of inertial waves as confirmed by local simulations. Global simulations of warped discs, using either smoothed particle hydrodynamics or grid-based codes, are ubiquitous but no such instability has been seen. Here, we utilize a hybrid Godunov-type Lagrangian method to study parametric instability in global simulations of warped Keplerian discs at unprecedentedly high resolution (up to 120 million particles). In the global simulations, the propagation of the warp is well described by the linear bending-wave equations before the instability sets in. The ensuing turbulence, captured for the first time in a global simulation, damps relative orbital inclinations and leads to a decrease in the angular momentum deficit. As a result, the warp undergoes significant damping within one bending-wave crossing time. Observed protoplanetary disc warps are likely maintained by companions or aftermath of disc breaking.

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