scholarly journals The Structure and Dynamic Instability of Isothermal Relativistic Star Clusters

1976 ◽  
Vol 29 (4) ◽  
pp. 311 ◽  
Author(s):  
Edward D Fackerell ◽  
Kevin G Suffern
Keyword(s):  
Dynamic Stability ◽  
Dynamic Instability ◽  
Rest Mass ◽  
Star Clusters ◽  
Relativistic Star ◽  
The Stability

The structure and dynamic stability of isothermal relativistic star clusters are discussed both for the case of clusters without dispersion in stellar rest mass and for two families of clusters with dispersion in stellar rest mass. We show that the former are dynamically unstable if the central redshift is greater than about 0'5, and that the latter are dynamically unstable if the central redshift is greater than about O' 6, so that the inclusion of dispersion in mass does not greatly affect the stability of isothermal relativistic star clusters.

The dynamic instability of isothermal relativistic star clusters

1976 ◽  
Vol 203 ◽  
pp. 477 ◽  
Author(s):  
K. G. Suffern ◽  
E. D. Fackerell
Keyword(s):  
Dynamic Instability ◽  
Star Clusters ◽  
Relativistic Star

scholarly journals Research on Dynamic Stability Optimization of Rock Spreader considering Prevention of Geological Subsidence and Local Collapse in Reclamation Area

2021 ◽  
Vol 2021 ◽  
pp. 1-20
Author(s):  
Baofu Kou ◽  
Pengliang Huo ◽  
Xin Shi
Keyword(s):  
Dynamic Stability ◽  
Maximum Stress ◽  
Dynamic Instability ◽  
Optimization Method ◽  
Static And Dynamic Analysis ◽  
Actual Application ◽  
Reclamation Area ◽  
The Stability ◽  
Fifth Order ◽  
Load Conditions

The uneven stacking of waste rock materials caused by the dynamic instability of rock spreaders cannot be ignored for geological subsidence and local collapse in reclamation areas. Based on the dynamic stability of the existing rock spreader, combined with the actual application conditions, the load conditions of the rock spreader are analyzed. The static and dynamic analysis and optimization of the key structures such as the receiving arm, the discharging arm, and the main tower are carried out by using the topology optimization method. The optimized virtual prototype of the whole machine is established to verify its rationality. The research results show that the total weight of key parts such as receiving boom, discharging boom, and the main tower is reduced by about 4.5% (4650 kg), the lower-order vibration frequencies below the fifth order of those parts are not within the resonance range, and the stability of the whole machine is greatly improved, which fundamentally solves the problem of uneven rock stacking caused by impact stability. And, the maximum stress and deflection of the whole machine under the worst working conditions meet the actual requirements. The research ideas and conclusions can provide solutions to prevent the subsidence or local collapse of reclamation areas caused by uneven stacking materials.

scholarly journals ABOUT THE STABILITY OF NONCONSERVATIVE UNDAMPED ELASTIC SYSTEMS: SOME NEW ELEMENTS

2009 ◽  
Vol 09 (02) ◽  
pp. 357-367 ◽  
Author(s):  
JEAN LERBET ◽  
ELIE ABSI ◽  
ALAIN RIGOLOT
Keyword(s):  
Dynamic Stability ◽  
Dynamic Instability ◽  
Static Stability ◽  
Stability Domain ◽  
Dynamic Approach ◽  
Linear Approach ◽  
Elastic Systems ◽  
The Common ◽  
The Stability ◽  
New Criterion

It is well-known that the domains of static stability and dynamic stability (even for a linear approach) do not match each other when the system is no more conservative and the dynamic approach is usually privileged, meaning that the dynamic stability domain is included in the static one. Following previous works proposing a new criterion of static stability of nonconservative systems and prolonging a paper of Gallina devoted to linear dynamic instability (flutter), we show in this paper some remarkable relations between the two approaches: contrary to the common thought, the new static stability criterion implies partially the dynamic one.

To What Extent Does Not Wearing Shoes Affect the Local Dynamic Stability of Walking?: Effect Size and Intrasession Repeatability

2014 ◽  
Vol 30 (2) ◽  
pp. 305-309 ◽  
Author(s):  
Philippe Terrier ◽  
Fabienne Reynard
Keyword(s):  
Dynamic Stability ◽  
Effect Size ◽  
Intraclass Correlation ◽  
Clinical Findings ◽  
Local Dynamic ◽  
Gait Stability ◽  
Local Dynamic Stability ◽  
Gait Parameters ◽  
Absolute Agreement ◽  
The Stability

Local dynamic stability (stability) quantifies how a system responds to small perturbations. Several experimental and clinical findings have highlighted the association between gait stability and fall risk. Walking without shoes is known to slightly modify gait parameters. Barefoot walking may cause unusual sensory feedback to individuals accustomed to shod walking, and this may affect stability. The objective was therefore to compare the stability of shod and barefoot walking in healthy individuals and to analyze the intrasession repeatability. Forty participants traversed a 70 m indoor corridor wearing normal shoes in one trial and walking barefoot in a second trial. Trunk accelerations were recorded with a 3D-accelerometer attached to the lower back. The stability was computed using the finite-time maximal Lyapunov exponent method. Absolute agreement between the forward and backward paths was estimated with the intraclass correlation coefficient (ICC). Barefoot walking did not significantly modify the stability as compared with shod walking (average standardized effect size: +0.11). The intrasession repeatability was high (ICC: 0.73–0.81) and slightly higher in barefoot walking condition (ICC: 0.81–0.87). Therefore, it seems that barefoot walking can be used to evaluate stability without introducing a bias as compared with shod walking, and with a sufficient reliability.

Study on Wear-Preventing of Needle Valve in Fuel Injection System Mounted on DME Engine

2011 ◽  
Vol 228-229 ◽  
pp. 1057-1062
Author(s):  
Xin Rong Wen ◽  
Guang De Zhang ◽  
Wei Hua Wang ◽  
Xie Lu ◽  
Sun Jing
Keyword(s):  
Dynamic Stability ◽  
Structural Design ◽  
Fuel Injection ◽  
Dynamic Instability ◽  
Calculation Model ◽  
The Other ◽  
Injection System ◽  
Needle Valve ◽  
Fuel Injection System ◽  
Theoretical Support

The purpose of this paper is to provide theoretical support for the structural design to prevent the wear of needle. The actual wear of the orientation part of the needle in scrapped needles was researched. The presented results showed that the main reason to the wear of the orientation part of needle was the dynamic instability and the abrasives enter into the surface of orientation part which increases the wear, and that the calculation model of dynamic stability was proposed to prevent the wear of needle. This model was a pressure rod, one end of which was fixed, the other was free, and the two ends were pressed on axial force which changes with time. Besides, the classic formula of dynamic stability of pressure rod was changed rationally, so as to correspond with the calculation model. It will play a part in preventing the wear of needle.

Effect of Load Carrying on Local Dynamic Stability

2007 ◽  
Vol 51 (15) ◽  
pp. 909-913 ◽  
Author(s):  
Jian Liu ◽  
Thurmon E. Lockhart ◽  
Kevin Granata
Keyword(s):  
Dynamic Stability ◽  
Load Condition ◽  
Local Dynamic ◽  
Fall Injuries ◽  
Local Dynamic Stability ◽  
Load Carrying ◽  
Trunk Acceleration ◽  
The Stability ◽  
Major Factors

Occupational load carrying tasks are considered one of the major factors contributing to slip and fall injuries. The objective of the current study was to explore the feasibility to assess the stability changes associated with load carrying by local dynamic stability measures. Twenty-five young participants were involved in a treadmill walking study, with their trunk acceleration profiles measured wirelessly by a tri-axial accelerometer. Finite time local dynamic stability was quantified by maximum Lyapunov exponents (maxLE). The results showed a significant increase in long term maxLE in load condition, indicating the declined local dynamic stability due to the load carrying. Thus, current study confirmed the discriminative validity and sensitivity of local dynamic stability measure and its utility in the load carrying scenario.

Dynamic Instability in Quartering Seas—Part III: Nonlinear Effects on Periodic Motions

1997 ◽  
Vol 41 (03) ◽  
pp. 210-223 ◽  
Author(s):  
K. J. Spyrou
Keyword(s):  
Periodic Motion ◽  
Horizontal Plane ◽  
Dynamic Instability ◽  
Parametric Instability ◽  
Nonlinear Effects ◽  
Ship Motions ◽  
Nonlinear Phenomena ◽  
Specific Sequence ◽  
The Stability ◽  
Two Stages

The loss of stability of the horizontal-plane periodic motion of a steered ship in waves is investigated. In earlier reports we referred to the possibility of a broaching mechanism that will be intrinsic to the periodic mode, whereby there will exist no need for the ship to go through the surf-riding stage. However, about this point the discussion was essentially conjectural. In order to provide substance we present here a theoretical approach that is organized in two stages: Initially, we demonstrate the existence of a mechanism of parametric instability of yaw on the basis of a rudimentary, single-degree model of maneuvering motion in waves. Then, with a more elaborate model, we identify the underlying nonlinear phenomena that govern the large-amplitude horizontal ship motions, considering the ship as a multi-degree, nonlinear oscillator. Our analysis brings to light a very specific sequence of phenomena leading to cumulative broaching that involves a change in the stability of the ordinary periodic motion on the horizontal plane, a transition towards subharmonic response and, ultimately, a sudden jump to resonance. Possible means for controlling the onset of such undesirable behavior are also investigated.

scholarly journals Analytical and Experimental Investigation of the Stability of the Rotor-Bearing System of a New Small Turbocharger

1987 ◽  
Author(s):  
H. R. Born
Keyword(s):  
Experimental Investigation ◽  
Dynamic Stability ◽  
Squeeze Film ◽  
Test Results ◽  
Flow Capacity ◽  
Squeeze Film Dampers ◽  
Rotor Bearing ◽  
The Stability ◽  
Turbine Design ◽  
Bearing System

This paper presents an overview of the development of a reliable bearing system for a new line of small turbochargers where the bearing system has to be compatible with a new compressor and turbine design. The first part demonstrates how the increased weight of the turbine, due to a 40 % increase in flow capacity, influences the dynamic stability of the rotor-bearing system. The second part shows how stability can be improved by optimizing important floating ring parameters and by applying different bearing designs, such as profiled bore bearings supported on squeeze film dampers. Test results and stability analyses are included as well as the criteria which led to the decision to choose a squeeze film backed symmetrical 3-lobe bearing for this new turbocharger design.

scholarly journals COMPARISON OF DYNAMIC STABILITY DURING WALKING AND RUNNING ON NONMOTORIZED CURVED TREADMILL ACCORDING TO CURVATURE RADIUS

2017 ◽  
Vol 17 (08) ◽  
pp. 1750105
Author(s):  
SAYUP KIM ◽  
JONGRYUN ROH ◽  
JOONHO HYEONG ◽  
YOUNGHO KIM
Keyword(s):  
Dynamic Stability ◽  
Repeated Measures ◽  
The Elderly ◽  
Curvature Radius ◽  
Adult Men ◽  
High Speeds ◽  
Slow Walking ◽  
Study Results ◽  
The Stability ◽  
Post Hoc

It is generally believed that running on a curved surface is more unstable than running on a flat surface. In this study, the dynamic stability of locomotion on a nonmotorized curved treadmill (NMCT) with three curvature radii was compared with that on a motorized flat treadmill. Sixteen healthy adult men maintained four different self-paced speeds: slow walking, fast walking, jogging, and running. Significant differences were statistically verified using two-way repeated-measures analysis of variance (ANOVA) according to the curvature radii and speeds, and the interaction effects were confirmed. Furthermore, to understand the significant differences between the speed and curvature radius, post hoc analyses were performed using one-way ANOVA. Except for the step width, the other parameters showed differences and correlation effects between the curvature radius and speed. As the curvature radius decreased, the stability decreased at slow speeds (slow walking) but increased at fast speeds (running). However, as the curvature radius increased, the stability increased at slow speeds (slow walking) but decreased at high speeds (running). The study results will help in suggesting the appropriate curvature radius for different user types such as athletes, the elderly, and people who require rehabilitation and will serve as preliminary data for designing the curvature radii of NMCTs.

Dynamic Instability of a High-Speed Planing Boat Model

2000 ◽  
Vol 37 (03) ◽  
pp. 146-152
Author(s):  
Eric Thornhill ◽  
Brian Veitch ◽  
Neil Bose
Keyword(s):  
Dynamic Stability ◽  
High Speed ◽  
Research Council ◽  
Dynamic Instability ◽  
National Research Council ◽  
Scale Model ◽  
Clear Water ◽  
Towing Tank ◽  
Stability Limits ◽  
Resistance Tests

A series of bare-hull resistance and self-propulsion tests were carried out on a 1/8 scale model of a 11.8 m long, waterjet-propelled planing hull in the clear water towing tank at the National Research Council of Canada's Institute for Marine Dynamics. The bare-hull resistance tests, performed with the waterjet inlets closed, spanned a range of eight model velocities and nine ballast conditions consisting of three displacements each with three positions of the longitudinal center of gravity. The hull was then fitted with two model waterjet thrusters and tested over the same speeds and ballast conditions. Dynamic instability, or porpoising, was seen during certain high-speed tests. A discussion of this behavior and its relation to published dynamic stability limits is given.

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