scholarly journals A Study of the Stability of Externally Pressurized Gas Bearings

1960 ◽  
Vol 27 (2) ◽  
pp. 250-258 ◽  
Author(s):  
Lazar Licht ◽  
Harold Elrod
Keyword(s):  
Equations Of Motion ◽  
Stability Criteria ◽  
Small Deviations ◽  
Gas Bearings ◽  
Lumped Parameter ◽  
Nozzle Size ◽  
The Subject ◽  
The Stability ◽  
Annular Clearance ◽  
Limiting Values

The subject of this paper is the stability of externally pressurized gas bearings. The pertinent equations of motion are linearized and the stability criteria stated in terms of small deviations from the equilibrium operating point. The flow in the bearing clearance is treated on a distributed rather than on a lumped-parameter basis. Results obtained from present analysis when compared with those previously arrived at by means of simplified analyses [1, 3] show a marked divergence in the limiting values of parameters which influence the stability of the bearing. These results and divergences are discussed in terms of permissible compression volume, pressure ratios, supply-nozzle size, length of annular clearance, and bearing mass.

On the Dynamic Stability of Self-Aligning Journal Gas Bearings

1977 ◽  
Vol 99 (4) ◽  
pp. 434-440 ◽  
Author(s):  
M. J. Cohen
Keyword(s):  
Dynamic Stability ◽  
Journal Bearing ◽  
Equations Of Motion ◽  
Stability Boundary ◽  
Initial Condition ◽  
Small Motion ◽  
Gas Bearings ◽  
Loading Case ◽  
The Stability ◽  
Small Disturbances

The report presents an investigation of the dynamic stability behaviour of self-aligning journal gas bearings when subjected to arbitrary small disturbances from an initial condition of operational equilibrium. The method is based on an approach similar to the nonlinear-ph solution of the author for the quasi-static loading case but the equations of motion of the journal are the linearized forms for small motion in the two degrees (translational) of freedom of the journal center. The stability domains for the infinite journal bearing are presented for the whole of the eccentricity (ε) and rotational speed (Λ) ranges for any given bearing geometry, in the shape of stability boundaries in that domain. It is shown that a given bearing will be stable within a corridor in the (ε, Λ) parametral domain having as its lower bound the so called “half-speed” whirl stability boundary and as its upper bound another whirling instability at a higher characteristic (relative) frequency, the instability occurs generally at the higher eccentricities and lower rotational speeds.

PHASE STABILITY OF RANDOM BRASSES: PSEUDOPOTENTIAL THEORY REVISITED

1988 ◽  
Vol 02 (03n04) ◽  
pp. 301-354
Author(s):  
S. M. MUJIBUR RAHMAN
Keyword(s):  
Phase Stability ◽  
Theoretical Development ◽  
Band Model ◽  
Stability Criteria ◽  
Atom Ratio ◽  
Pseudopotential Theory ◽  
The Subject ◽  
The Stability ◽  
Introductory Discussion ◽  
Static Lattice

We review the theoretical development concerning the phase stability of random brasses. The introductory discussion of the subject embraces the rules of metallurgy in general, but we emphasize the roles of electron-per-atom ratio in the major bulk of our discussion. Starting from the so-called rigid-band model the discussion goes up to the recent higher-order pseudopotential theory. The theoretical refinements within the pseudopotential framework are discussed briefly. The stability criteria of the random phases are analysed both in the static lattice and dynamic lattice approximations.

Parametric Study of Stability Criteria for Rotor Bearing Model With Viscoelastic Support

2017 ◽  
Author(s):  
S. Chandraker ◽  
J. K. Dutt ◽  
H. Roy
Keyword(s):  
Classical Method ◽  
Equations Of Motion ◽  
Weight Ratio ◽  
High Strength ◽  
Point Of View ◽  
Stability Criteria ◽  
Engineering Structures ◽  
Rotor Bearing ◽  
The Stability ◽  
Bearing System

In the last few decades, intensive research has been carried out on viscoelastic materials. Among them, most importantly polymers and composites thereof find extensive applications in engineering structures and rotors primarily due to quite high strength to weight ratio in comparison with metals. In dynamic modeling of rotor bearing system, incorporation of damping is very important as stationary (external) damping always helps in stability, however rotary damping (internal) promotes instability of rotors above a certain speed. Therefore for modeling point of view, it is very important to consider both internal or external damping effect. For this reason, the dissipation mechanism has been handled in such a way that it provides proper forces irrespective of its presence in a stationary or a rotary frame. Also in present work, both classical method and operator multiplier method are suggested to derive the equations of motion. The analysis also shows the stability zones of the rotor bearing system for various parametric values of different viscoelastic supports. It is found that choosing a right viscoelastic support can increase the stability criteria of the system to some extent.

Gravity-Gradient Excitation of a Rotating Cable-Counterweight Space Station in Orbit

1963 ◽  
Vol 30 (4) ◽  
pp. 547-554 ◽  
Author(s):  
V. Chobotov
Keyword(s):  
Parametric Excitation ◽  
Equations Of Motion ◽  
Space Station ◽  
Type A ◽  
Gravity Gradient ◽  
Viscous Damping ◽  
Stability Criteria ◽  
Axial Vibrations ◽  
The Stability ◽  
Transverse Oscillations

The gravity-gradient excitation of a whirling cable-counterweight space station in orbit is investigated. The Lagrange’s equations of motion for transverse oscillations of the system are derived and shown to be of the Mathieu type. A few representative cases are investigated analytically and on an IBM 7090 computer. The stability criteria for the axial vibrations are also considered and shown to be of the same kind as those for the transver se vibrations of the cable. Viscous damping is included in the analyses and found to be effective and essential for prevention of parametric excitation instability of the system.

Simple First-Order Models for Surging in Pump and Compressor Systems

1995 ◽  
Vol 209 (3) ◽  
pp. 149-154
Author(s):  
A Anderson
Keyword(s):  
Distributed Systems ◽  
Stable Operation ◽  
Duct System ◽  
Stability Criteria ◽  
System Configuration ◽  
First Order ◽  
Lumped Parameter ◽  
Lumped Parameter Models ◽  
The Stability ◽  
Discharge Pressure

For turbomachine surging arising from interaction between the turbomachine and duct system discharge-pressure characteristics, simple lumped-parameter models for duct inertia, elasticity and losses are used to review existing stability criteria for and descriptions of the phenomenon. Conventional descriptions are shown to relate specifically to lumped-inertia models, whereas different conditions for stable operation are given by lumped-elasticity models. For systems with both inertia and physically discrete elasticity, the stability criteria depend on system configuration and hence such models are not suitable for application to distributed systems. An approach to distributed systems to overcome this limitation is suggested.

ROCKING AND SLIDING OF ANCIENT TEMPLE COLUMNS UNDER EARTHQUAKE EXCITATIONS

2014 ◽  
Vol 14 (02) ◽  
pp. 1350058 ◽  
Author(s):  
GEORGE T. MICHALTSOS ◽  
IOANNIS G. RAFTOYIANNIS
Keyword(s):  
Southern Italy ◽  
Equations Of Motion ◽  
Earthquake Excitation ◽  
Stone Block ◽  
The Subject ◽  
The Stability ◽  
The One ◽  
Nonlinear Equations Of Motion ◽  
Static Conditions ◽  
Earthquake Characteristics

This paper deals with the rocking and sliding behavior of a monolithic stone block or a system of stone blocks under earthquakes, a problem commonly observed for ancient temples in Greece and Southern Italy. The analysis for the above monolithic or multi-drum columns is conducted by a simple process based on generally accepted simplifications. The effects of column geometry, earthquake characteristics and restitution ratio due to impact are also studied herein. Furthermore, an analytical approach for the solution of the complete nonlinear equations of motion (including the one for the vertical earthquake excitation) for the subject considered is proposed. Finally, characteristic representative examples are presented with useful conclusions drawn. It was found that the stability criteria based on static conditions are reliable, while the corresponding dynamic criteria may lead to erroneous results.

scholarly journals The necessary and sufficient condition for the stability of a rigid body

2017 ◽  
Vol 13 (4) ◽  
pp. 4999-5003 ◽  
Author(s):  
W. S. Amer
Keyword(s):  
Rigid Body ◽  
Equations Of Motion ◽  
Center Of Mass ◽  
First Integrals ◽  
Body Motion ◽  
Sufficient Condition ◽  
Stability Criteria ◽  
Necessary And Sufficient Condition ◽  
The Stability ◽  
Necessary And Sufficient

In this paper, the stability of the unperturbed rigid body motion close to conditions, related with the center of mass, is investigated. The three first integrals for the equations of motion are obtained. These integrals are used to achieve a Lyapunov function and to obtain the necessary and sufficient condition satisfies the stability criteria.

Bankenwettbewerb und die Stabilität von Finanzsektoren

2021 ◽  
Vol 70 (1) ◽  
pp. 1-36
Author(s):  
Toni Richter
Keyword(s):  
Economic Policy ◽  
Precise Measurement ◽  
Policy Discourse ◽  
Competitive Effect ◽  
Too Big To Fail ◽  
Financial Systems ◽  
The Subject ◽  
State Of Research ◽  
The Stability ◽  
Elementary Basis

Abstract Since the financial crisis of 2008 and intensified during the corona crisis, the interdependence between the stability of the financial systems and the prevailing degree of competition (DC) has been the subject of scientific and economic policy discourse on fragmented markets and „too-big-to-fail“ banks. In theory and empiricism, two fundamentally contrary causal concepts are opposed, the elementary basis of which is the precise measurement of the DC: Competition-stability- versus Fragility-Hypothesis. Based on the recent state of research, it can be shown that alternative DC-Measurements consistently show significantly different competitive conditions and in consequence the evidence for or against a stability-enhancing competitive effect seems to be predetermined by the chosen DC-Measurement.

Dissipative instability of the MHD tangential discontinuity in magnetized plasmas with anisotropic viscosity and thermal conductivity

1996 ◽  
Vol 56 (2) ◽  
pp. 285-306 ◽  
Author(s):  
M. S. Ruderman ◽  
E. Verwichte ◽  
R. Erdélyi ◽  
M. Goossens
Keyword(s):  
Thermal Conductivity ◽  
Dispersion Equation ◽  
Viscosity Coefficient ◽  
Tangential Discontinuity ◽  
Stability Criteria ◽  
Threshold Velocity ◽  
Cold Plasmas ◽  
The Difference ◽  
The Stability ◽  
Anisotropic Viscosity

The stability of the MHD tangential discontinuity is studied in compressible plasmas in the presence of anisotropic viscosity and thermal conductivity. The general dispersion equation is derived, and solutions to this dispersion equation and stability criteria are obtained for the limiting cases of incompressible and cold plasmas. In these two limiting cases the effect of thermal conductivity vanishes, and the solutions are only influenced by viscosity. The stability criteria for viscous plasmas are compared with those for ideal plasmas, where stability is determined by the Kelvin—Helmholtz velocity VKH as a threshold for the difference in the equilibrium velocities. Viscosity turns out to have a destabilizing influence when the viscosity coefficient takes different values at the two sides of the discontinuity. Viscosity lowers the threshold velocity V below the ideal Kelvin—Helmholtz velocity VKH, so that there is a range of velocities between V and VKH where the overstability is of a dissipative nature.

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