The nonlinear dynamics of journal bearings

1990 ◽  
Vol 332 (1624) ◽  
pp. 107-119 ◽  
Keyword(s):  
Dynamic Behaviour ◽  
Journal Bearing ◽  
Hopf Bifurcations ◽  
Qualitative Behaviour ◽  
Conceptual Approach ◽  
Theoretical Understanding ◽  
Geometrical Features ◽  
Wide Range ◽  
Dimensional Parameters ◽  
Analytical Approaches

The journal bearing is ubiquitous in moving mechanical systems, and is a major potential target for study in the field of lubrication theory. Despite this, theoretical understanding of its dynamic behaviour is far from complete ; in particular the essentially nonlinear interplay of rotor dynamics and fluid dynamics of the lubricant has been studied only very recently. Our own investigations have been mainly numerical, and have revealed a wide range of qualitative behaviour. They have confirmed the great importance of cavitation of the lubricant, and the sensitivity to geometrical features of the bearing. Additionally they have enabled us to identify the crucial non-dimensional parameters and their critical values. Finally they have stimulated analytical approaches (e.g. searches for Hopf bifurcations). In this paper we exploit the conceptual approach of dynamical systems theory to present many of our results in a succinct form. Our aim is to make clear not only the extent of understanding of the problem, but also the present shortcomings of theory that require further study.

Nonlinear dynamic behaviour of guy cables in turbulent winds

2001 ◽  
Vol 28 (1) ◽  
pp. 98-110 ◽  
Author(s):  
Bruce F Sparling ◽  
Alan G Davenport
Keyword(s):  
Finite Element ◽  
Dynamic Behaviour ◽  
Aerodynamic Drag ◽  
Numerical Study ◽  
Horizontal Displacement ◽  
Wind Loading ◽  
Second Phase ◽  
Nonlinear Coupling ◽  
Wide Range ◽  
Cable Vibrations

Large amplitude cable vibrations are difficult to predict using linear theory due to the presence of sag in the suspended profile. A numerical study was therefore undertaken to investigate the dynamic behaviour of inclined cables excited by imposed displacements. To model the nonlinear nature of cable response, a time domain finite element approach was adopted using nonlinear catenary cable elements. Two types of horizontal displacement patterns were enforced at the upper end of the guy. In the first phase of the study, harmonic displacement histories with a wide range of forcing frequencies were considered. In the second phase, random enforced displacements were used to simulate the motion of a guyed mast in gusty winds. The influence of aerodynamic drag and damping forces was investigated by performing analyses under still air, steady wind, and turbulent wind conditions. It was found that nonlinear coupling of related harmonic response components was significant at certain critical frequencies, particular when the excitation was harmonic and acted in the plane of the guy. Positive aerodynamic damping was shown to effectively suppress resonant and nonlinear coupling response.Key words: cables, structural dynamics, wind loading, finite element method, nonlinear analysis, guyed towers.

scholarly journals Flux rope axis geometry of magnetic clouds deduced from in situ data

2013 ◽  
Vol 8 (S300) ◽  
pp. 265-268
Author(s):  
Miho Janvier ◽  
Pascal Démoulin ◽  
Sergio Dasso
Keyword(s):  
Interplanetary Medium ◽  
Magnetic Cloud ◽  
Flux Rope ◽  
Magnetic Clouds ◽  
Direct Integration ◽  
Axis Orientation ◽  
In Situ Data ◽  
Geometrical Features ◽  
Wide Range

AbstractMagnetic clouds (MCs) consist of flux ropes that are ejected from the low solar corona during eruptive flares. Following their ejection, they propagate in the interplanetary medium where they can be detected by in situ instruments and heliospheric imagers onboard spacecraft. Although in situ measurements give a wide range of data, these only depict the nature of the MC along the unidirectional trajectory crossing of a spacecraft. As such, direct 3D measurements of MC characteristics are impossible. From a statistical analysis of a wide range of MCs detected at 1 AU by the Wind spacecraft, we propose different methods to deduce the most probable magnetic cloud axis shape. These methods include the comparison of synthetic distributions with observed distributions of the axis orientation, as well as the direct integration of observed probability distribution to deduce the global MC axis shape. The overall shape given by those two methods is then compared with 2D heliospheric images of a propagating MC and we find similar geometrical features.

Measurements of Rotordynamic Forces on an Artificial Heart Pump Impeller

2007 ◽  
Vol 129 (11) ◽  
pp. 1422-1427 ◽  
Author(s):  
Takayuki Suzuki ◽  
Romain Prunières ◽  
Hironori Horiguchi ◽  
Tomonori Tsukiya ◽  
Yoshiyuki Taenaka ◽  
...  
Keyword(s):  
Artificial Heart ◽  
Journal Bearing ◽  
Centrifugal Pumps ◽  
Pump Impeller ◽  
Fluid Forces ◽  
Heart Pump ◽  
Wide Range ◽  
Artificial Hearts ◽  
Rotordynamic Forces ◽  
Magnetic Drive

In centrifugal pumps for artificial hearts, a magnetic drive with lightly loaded journal bearing system is often used. In such a system, the rigidity of the bearing is small and the impeller usually rotates over the critical speed. In such cases, the rotordynamic fluid forces play an important role for shaft vibration. In the present study, the characteristics of the rotordynamic fluid forces on the impeller were examined. The rotordynamic fluid forces were measured in the cases with/without the whirling motion. It was found that the rotordynamic forces become destabilizing in a wide range of positive whirl. The effect of leakage flow was also examined.

scholarly journals A Model for Analysing the Collective Dynamic Behaviour and Characterising the Exploitation of Population-Based Algorithms

2014 ◽  
Vol 22 (1) ◽  
pp. 159-188 ◽  
Author(s):  
Mikdam Turkey ◽  
Riccardo Poli
Keyword(s):  
Population Dynamics ◽  
Dynamic Behaviour ◽  
Fitness Landscape ◽  
Population Based ◽  
Levels Of Abstraction ◽  
Collective Dynamic ◽  
Model Studies ◽  
Proposed Model ◽  
Wide Range ◽  
Multiple Levels

Several previous studies have focused on modelling and analysing the collective dynamic behaviour of population-based algorithms. However, an empirical approach for identifying and characterising such a behaviour is surprisingly lacking. In this paper, we present a new model to capture this collective behaviour, and to extract and quantify features associated with it. The proposed model studies the topological distribution of an algorithm's activity from both a genotypic and a phenotypic perspective, and represents population dynamics using multiple levels of abstraction. The model can have different instantiations. Here it has been implemented using a modified version of self-organising maps. These are used to represent and track the population motion in the fitness landscape as the algorithm operates on solving a problem. Based on this model, we developed a set of features that characterise the population's collective dynamic behaviour. By analysing them and revealing their dependency on fitness distributions, we were then able to define an indicator of the exploitation behaviour of an algorithm. This is an entropy-based measure that assesses the dependency on fitness distributions of different features of population dynamics. To test the proposed measures, evolutionary algorithms with different crossover operators, selection pressure levels and population handling techniques have been examined, which lead populations to exhibit a wide range of exploitation-exploration behaviours.

Theoretical analysis of SWCNT- MWCNT/H2O hybrid flow over an upward/downward moving rotating disk

2021 ◽  
pp. 239779142098028
Author(s):  
R.J. Punith Gowda ◽  
R. Naveenkumar ◽  
J.K. Madhukesh ◽  
B.C. Prasannakumara ◽  
Rama Subba Reddy Gorla
Keyword(s):  
Heterogeneous Reaction ◽  
Three Dimensional ◽  
Rotating Disk ◽  
Heterogeneous Reactions ◽  
Hybrid Nanofluid ◽  
Boundary Constraints ◽  
Wide Range ◽  
Contraction Parameter ◽  
Dimensional Parameters ◽  
Source Sink

The flow-through various disk movement has wide range of applications in manufacturing processes like, computer storage equipment’s, rotating machines, electronic and various types of medical equipment’s. Inspired from these applications, here we scrutinised the consequences of homogeneous-heterogeneous reactions and uniform heat source/sink on the three-dimensional (3D) hybrid SWCNT-MWCNT’s flow on time dependent moving upward/downward rotating disk. The renowned innovation of this paper is the application of the hybrid nanofluid made up of SWCNT and MWCNT’s. Heat generation/absorption effect for the disk that does not move up or down creates a dual flow on the disk. Alternatively, the rotation and upright motion of the disk creates a 3D flow on the surface which has not been considered in the open literature. The modelled PDE’s are reduced in to ODE’s by opting suitable similarity variables and boundary constraints. Here, we used RKF-45 method to obtain the numerical approximations by adopting shooting technique. The analysis of rate of heat transfer is done through graphs. Further, change in velocity, thermal and concentration profiles for various non-dimensional parameters are deliberated briefly and illustrated with the help of suitable plots. The results reveal that, the, rise in values of homogeneous and heterogeneous reaction parameters improve the rate of reaction which results in reduction of the distribution rate and diminishes the concentration gradient. An increase in expansion/contraction parameter enhances the velocity and thermal gradients.

Actual Challenges, Risks and Security Safety

2020 ◽  
Vol 1 (1) ◽  
pp. 65-83
Author(s):  
Božidar Forca ◽  
Dragoljub Sekulović ◽  
Igor Vukonjanski
Keyword(s):  
National Security ◽  
Modern World ◽  
Security Strategy ◽  
Theoretical Understanding ◽  
National Security Strategy ◽  
Security Challenges ◽  
Wide Range ◽  
The Subject ◽  
Almost All ◽  
The Relationship

Security is one of the most common terms in the modern world. This statement is supported by the fact that the term security is used in a wide range of areas. The subject of this paper is national security and the challenges, risks and threats to that security in contemporary international relations. The purpose of the work is twofold. First, to show the diversity of theoretical understanding of the term challenge, risk and threat by various authors. On the other hand, the overriding goal is to analyze the relationship to the challenges, risks and threats in different countries. When it comes to national security, challenges, risks and threats, most often, are identified in a document called the national security strategy. This document, as one of the highest in the hierarchy of political acts of every state, when it comes to security, is passed by almost all modern states of the world. The analysis of numerous national security strategies has revealed that it is possible to identify: 1) the challenges, risks and threats that appear in all strategies, 2) the challenges, risks and threats of security that appear in most strategies, and 3) the challenges, risks and threats of security which are country specific.

Analysis of financial and economic activities

2021 ◽  
Author(s):  
Elena Gerasimova
Keyword(s):  
Economic Analysis ◽  
Vocational Education ◽  
Undergraduate Students ◽  
Independent Solution ◽  
Federal State ◽  
Economic Activities ◽  
Secondary Vocational Education ◽  
Wide Range ◽  
State Educational ◽  
Analytical Approaches

The textbook comprehensively describes the basics of the theory of economic analysis and the practice of applying analytical approaches to economic entities of various types. It consists of three interrelated sections that reveal a comprehensive and systematic approach to conducting economic analysis. The practical part of the textbook includes exercises, examples of solving situational problems and tasks for independent solution. Meets the requirements of the federal state educational standards of secondary vocational education of the latest generation. For students of secondary vocational education institutions studying in the specialty 38.02.07 "Banking". It can be useful for undergraduate students studying in the areas of 38.03.01 " Economics "and 38.03.02" Management", specialists in the field of analysis of the activities of organizations, a wide range of readers interested in the problems of analysis of the activities of economic entities.

CONCEPTUAL DIRECTIONS OF THE TAXATION THEORIES DEVELOPMENT THROUGH THE REALIZING PRISM INTERESTS OF THE STATE AND TAXPAYERS

2021 ◽  
Vol 7 (1) ◽  
pp. 188-204
Author(s):  
Yulia G. TYURINA ◽  
Kristina A. BANNOVA
Keyword(s):  
Income Tax ◽  
The State ◽  
Personal Income ◽  
Point Of View ◽  
Theoretical Point ◽  
Personal Income Tax ◽  
State Budget ◽  
Theoretical Understanding ◽  
Direct Taxation ◽  
Wide Range

Nowadays, direct taxation of personal income is used in almost all countries of the world, and to this day there are various changes that shift the share of revenue from these taxes towards increasing the state budget. The significance of the personal income tax in economic policy is also due to the fact that it affects the interests of almost the entire population of the country. A variety of disputes constantly arise around the personal income tax, which can be explained by a wide range of taxpayers in various social strata. The ongoing transformations in the tax area predetermine the construction of the individuals taxation fair system as the fulfillment of one of the conditions for improving the living standards of the population. The relevance of the study lies in the need to reform the tax system in Russia, namely, the taxation of personal income, in order to implement the principle of social justice, as well as to satisfy the fiscal component of this tax, respectively, to fulfill the interests of participants in tax relations. The purpose of the article is a theoretical understanding of the conceptual directions of the taxation theories development through the prism of realizing the interests of the state and taxpayers in the taxation system of personal income. The subject of this research is the set of economic relations between the state and individuals, formed in the process of taxation of personal income in Russia. The methodological basis was the conceptual provisions of the theories of taxation, scientific methods and methods of analysis. The scientific novelty of the work lies in the fact that the results of the methodological analysis of the taxation theories development through the prism of realizing the state interests and taxpayers will make it possible to solve from a theoretical point of view the issue of interests balance achieving of all parties, which will contribute to the development of practical measures to achieve a decent standard of living for the population.

Reimagining transnational validity under the CISG

2018 ◽  
Vol 17 (3) ◽  
pp. 156-168
Author(s):  
Ndubuisi Nwafor ◽  
Collins Ajibo ◽  
Chidi Lloyd
Keyword(s):  
United Nations ◽  
Design Methodology ◽  
Conceptual Approach ◽  
Content Type ◽  
United Nations Convention ◽  
The United Nations ◽  
International Sale Of Goods ◽  
Analytical Approaches

Purpose The aims and objectives of the United Nations Convention on Contracts for the International Sale of Goods (CISG) have been defeated by the intrusion of domestic laws of different contracting states in the interpretation of the provisions of this Convention. One of the most abused channels of this un-uniform interpretation is through art 4 of the CISG, which excludes the matters of validity and property from the Convention’s jurisdiction. This paper, therefore, aims to critically analyze the dangers of unsystematic reliance on the domestic laws in the interpretation of art 4 of the CISG on matters involving transnational validity and property. Design/methodology/approach The paper will use doctrinal methodology with critical and analytical approaches. The paper will incisively study the doctrines, theories and principles of law associated with validity of commercial contracts and the implications of exclusion of the doctrine of “validity” under the CISG. Findings The findings and contribution to knowledge will be by way of canvassing for a uniform transnational validity doctrine that will streamline and position the CISG to serve as a uniform international commercial convention. Originality/value This paper adopted a conceptual approach. Even though the paper ventilated the views of many writers on the issue of application of the doctrine of validity under the CISG, the paper, however, carved its own niche by making original recommendations on how to create a uniform validity jurisprudence under the CISG.

Performance Analysis of a Nonrecessed Hybrid Conical Journal Bearing Compensated With Capillary Restrictors

2015 ◽  
Vol 138 (1) ◽  
Author(s):  
Prashant G. Khakse ◽  
Vikas M. Phalle ◽  
S. S. Mantha
Keyword(s):  
Performance Analysis ◽  
Film Thickness ◽  
Journal Bearing ◽  
Fluid Film ◽  
Load Parameter ◽  
Radial Load ◽  
Wide Range ◽  
Bearing Stiffness ◽  
Fluid Film Thickness ◽  
Film Stiffness

The present paper deals with the performance analysis of a nonrecessed hole-entry hydrostatic/hybrid conical journal bearing with capillary restrictors. Finite element method has been used for solving the modified Reynolds equation governing the flow of lubricant in the clearance space of journal and bearing. The hole-entry hybrid conical journal bearing performance characteristics have been depicted for a wide range of radial load parameter (W¯r  = 0.25–1.5) with uniform distribution of holes at an angle of 30 deg in the circumferential direction. The numerically simulated results have been presented in terms of maximum fluid film pressure, minimum fluid film thickness, lubricant flow rate, direct fluid film stiffness coefficients, direct fluid film damping coefficients, and stability threshold speed. However, the proposed investigation of nonrecess hole-entry hybrid conical journal bearing shows important performance for bearing stiffness and minimum fluid film thickness at variable radial load and at given operating speed.

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