scholarly journals Stability Analysis of Rotor-Bearing Systems under the Influence of Misalignment and Parameter Uncertainty

2021 ◽  
Vol 11 (17) ◽  
pp. 7918
Author(s):  
Xiaodong Sun ◽  
Kian K. Sepahvand ◽  
Steffen Marburg
Keyword(s):  
Computation Time ◽  
Parametric Uncertainty ◽  
Parameter Uncertainties ◽  
Misalignment Effect ◽  
Stability Threshold ◽  
Rotating Systems ◽  
Rotor Bearing ◽  
Run Up ◽  
The Stability ◽  
The Impact

Stability is a well-known challenge for rotating systems supported by hydrodynamic bearings (HDBs), particularly for the condition where the misalignment effect and the parametric uncertainty are considered. This study investigates the impact of misalignment and inherent uncertainties in bearings on the stability of a rotor-bearing system. The misalignment effect is approximately described by introducing two misaligned angles. The characteristics of an HDB, such as pressure distribution and dynamic coefficients, are calculated by the finite difference method (FDM). The stability threshold is evaluated as the intersection of run-up curve and borderline. Viscosity and clearance are considered as uncertain parameters. The generalized polynomial chaos (gPC) expansion is adopted to quantify the uncertainty in parameters by evaluating unknown coefficients. The unknown gPC coefficients are obtained by using the collocation method. The results obtained by the gPC expansion are compared with those of the Monte Carlo (MC) simulation. The results show that the characteristics of the HDB and the stability threshold are affected by misalignment and parameter uncertainties. As the uncertainty analysis using the gPC expansion is performed on a relatively small number of predefined collocation points compared with the large number of MC samples, the method is very efficient in terms of computation time.

Evaluation of Available Transfer Capability Using Transient Stability Constrained Line Flows

2014 ◽  
Vol 15 (1) ◽  
pp. 59-68
Author(s):  
Lazarus Okechukwu Uzoechi ◽  
Satish M. Mahajan
Keyword(s):  
Transient Stability ◽  
Direct Determination ◽  
Computation Time ◽  
Critical Energy ◽  
Energy Performance ◽  
Electric Power System ◽  
Available Transfer Capability ◽  
Transfer Capability ◽  
The Stability ◽  
The Impact

Abstract This paper presents a methodology to evaluate transient stability constrained available transfer capability (ATC). A linear and fast line flow–based (LFB) method was adopted to optimize the ATC values. This enabled the direct determination of the system source–sink locations. This paper formulated different market transactions considering bilateral and multilateral impacts in the stability constrained ATC. The proposed method was demonstrated on the WECC 9-bus and IEEE 39-bus systems. The critical energy performance index (CEPI) enabled the direct identification of candidates for contingency screening based on ranking. This index helped to reduce the list of credible contingencies for ATC evaluation and, therefore, the computation time. The results of the proposed ATC method are consistent with the literature and can be deployed for fast assessment of the impact of transactions in an electric power system.

Estimation of the Damping Matrix in Rotating Machinery for the Calculation of the Stability Threshold Speed

2014 ◽  
Vol 14 (06) ◽  
pp. 1450012 ◽  
Author(s):  
Bram Vervisch ◽  
Kurt Stockman ◽  
Mia Loccufier
Keyword(s):  
Internal Damping ◽  
Gyroscopic Effect ◽  
Rotating System ◽  
Linear Speed ◽  
System Parameters ◽  
Stability Threshold ◽  
Damping Matrix ◽  
Rotating Systems ◽  
Dependent Model ◽  
The Stability

Rotor internal damping is recognized as one of the main causes for instabilities in rotating systems. In a linear speed dependent model, the stability threshold speed can be calculated numerically. However, this threshold depends highly on the modeling choice and mainly on the relation between rotating and nonrotating damping. In this paper, the importance of a well-founded knowledge of the system parameters is highlighted and a method is proposed to estimate the damping of a rotating system not only influenced by the gyroscopic effect but also by rotating damping. With this method, it is possible to reconstruct the physical damping matrix and distinguish between rotating and nonrotating damping. Moreover, the gyroscopic effect can be identified. After a description of the method, a numerical validation is performed.

Research on Periodic Motion Stability of Multi-DOF Rotor-Bearing System with Crack Fault

2011 ◽  
Vol 148-149 ◽  
pp. 3-6 ◽  
Author(s):  
Chao Feng Li ◽  
Qin Liang Li ◽  
Jie Liu ◽  
Bang Chun Wen
Keyword(s):  
Stability Analysis ◽  
Vibration Control ◽  
Shooting Method ◽  
Crack Depth ◽  
Continuous System ◽  
Oil Film ◽  
Rotor Bearing ◽  
The Stability ◽  
The Impact ◽  
Bearing System

Multi-DOF model of double-disc rotor-bearing system taking crack and oil film support into account is established, and the continuation shooting method combined with Newmark is also applied to stability analysis of continuous system. This paper mainly studied the variation law of five parameters domain in crack depth and location, then a number of conclusions are found: first, it’s feasible to study the stability of nonlinear rotor-bearing system with crack faults using FEM; secondly, the crack depth and location has a certain impact on instability speed, but the impact is not great and owns its certain law. As the crack depth and location is getting close to the middle position of rotor, due to its impact on the oil film support, the instability speed of system increases. This method and results in this paper provides a theoretical reference for stability analysis and vibration control in more complex relevant rotor-bearing system with crack fault.

Stability Analysis of Rotating Systems Supported by Textured Journal Bearings

2019 ◽  
Vol 142 (3) ◽  
Author(s):  
Douglas Jhon Ramos ◽  
Leandro Ito Ramos ◽  
Gregory Bregion Daniel
Keyword(s):  
Vibration Mode ◽  
Surface Texturing ◽  
Industrial Applications ◽  
Journal Bearings ◽  
Rotating System ◽  
Stability Threshold ◽  
Rotating Systems ◽  
Unstable Vibration ◽  
The Stability ◽  
Volume Method

Abstract Fluid-induced instability in rotating systems due to the presence of hydrodynamic journal bearings consists of an undesirable phenomenon with a considerable destructive potential. Surface texturing of journal bearings is currently investigated as a possible approach to improve the stability characteristics of rotating systems. Thereby, this work aims to evaluate the influence of textured journal bearings in the stability threshold and unstable vibration mode of rotating systems. The classical Reynolds equation is used to model the pressure distribution inside the bearing, being solved by the finite volume method (FVM). The rotating system evaluated in this work is a steam turbine that is modeled using the finite element method (FEM). Numerical results show that textured geometric parameters, i.e., shape, area density, and maximum depth, are capable of changing the stability threshold (for worse or better) as well as the corresponding unstable vibration mode. Moreover, the present study also indicates that a full texturing of journal bearings is desirable to achieve a better improvement in the stability threshold when compared with partial texturing. Based on the results obtained in this work, the textured journal bearings represent a promising and feasible tool to improve the stability conditions of rotating systems in industrial applications.

The Excitability of Flexible Rotors in Short Sleeve Bearings

1975 ◽  
Vol 97 (1) ◽  
pp. 105-115 ◽  
Author(s):  
E. J. Hahn
Keyword(s):  
Flexible Rotor ◽  
External Disturbances ◽  
Stability Threshold ◽  
Flexible Rotors ◽  
Rotor Bearing ◽  
Operating Regions ◽  
The Stability ◽  
Linearized Model ◽  
Lubricant Viscosity ◽  
Bearing System

Assuming the short bearing approximation and constant lubricant properties, the root loci of the pertinent characteristic function were obtained for the linearized model of a simple symmetric flexible rotor bearing system. Using these loci, design maps consisting of lines of constant damping and vibration frequency pertaining to the dominant roots are presented as a function of the equilibrium eccentricity ratio and a frequency parameter for relevant degrees of flexibility. These maps display undesirable operating regions where external disturbances such as shock or unbalance loading are likely to excite undesirable vibrations, as well as regions of instability. The maps may conveniently be used to determine the effect of changing journal speed, lubricant viscosity and/or bearing clearance. Increased flexibility is seen to reduce the stability threshold in a predictable manner and to reduce damping at the pin-pin critical speed. The approach is applicable to more complex rotor bearing systems. It is felt that the use of such maps will enhance the understanding of rotor bearing system behavior, particularly at operating regions close to the stability threshold.

Mechanism and Impact of Damper Seal Clearance Divergence on the Rotordynamics of Centrifugal Compressors

2005 ◽  
Author(s):  
Thom M. Eldridge ◽  
Thomas A. Soulas
Keyword(s):  
Practical Experience ◽  
Logarithmic Decrement ◽  
Stable Operation ◽  
Recent Experience ◽  
Centrifugal Compressors ◽  
Rotor Bearing ◽  
The Subject ◽  
The Stability ◽  
Definition Of ◽  
The Impact

Damper seals (such as honeycomb and hole pattern seals) have been widely used in the turbomachinery industry to counterbalance destabilizing aerodynamic forces acting on the rotor system and to provide the necessary amount of damping for stable operation of the machine. Recent experience and research developments have focused the interest of the turbomachinery community on the dynamic characteristics of the divergent-taper damper seal. In addition to offering a review of the current literature on the subject of interest (in order to provide a comprehensive vision of the overall phenomenon), this paper extends the discussion for a better understanding of the mechanism and impact of damper seal clearance divergence on the rotordynamics of a rotor-bearing-seal system (as applied to centrifugal compressors). The analysis of a damper seal alone is insufficient to assess the influence of this component on the rotordynamic stability of a turbocompressor. This paper will show the variation of a complete rotor-bearing-seal system’s logarithmic decrement as a function of the hole pattern seal clearance divergence for a sample centrifugal compressor application, as analyzed with the proprietary, state-of-the-art rotordynamic software suite from the author’s company. This divergence-based transition of system logarithmic decrement from positive to zero (thereby implying the onset of instability) leads to the definition of a “damper seal divergence stability threshold.” Divergence in a damper seal can originate from numerous sources, including taper produced during manufacture, and pressure or thermal-driven distortion of the seal under operation. While small damper seal divergence may first produce an increase of the system logarithmic decrement, additional seal divergence has a dramatic effect on the first forward whirling mode natural frequency, as well as on the logarithmic decrement of that mode. This paper describes the analytical methods used to derive the stability of the rotor-bearing-seal system. It also presents a practical experience that stresses the necessity for a sound approach to properly evaluate the impact of a divergent damper seal on the stability of centrifugal compressors.

Methods for Restricting Maximum Exposure Rate in Computerized Adaptative Testing

Methodology ◽  
2007 ◽  
Vol 3 (1) ◽  
pp. 14-23 ◽  
Author(s):  
Juan Ramon Barrada ◽  
Julio Olea ◽  
Vicente Ponsoda
Keyword(s):  
Measurement Accuracy ◽  
Computerized Adaptive Testing ◽  
Computation Time ◽  
Adaptive Testing ◽  
Exposure Rate ◽  
Control Parameters ◽  
The Impact ◽  
Two Alternatives ◽  
Selection Of ◽  
Maximum Exposure

Abstract. The Sympson-Hetter (1985) method provides a means of controlling maximum exposure rate of items in Computerized Adaptive Testing. Through a series of simulations, control parameters are set that mark the probability of administration of an item on being selected. This method presents two main problems: it requires a long computation time for calculating the parameters and the maximum exposure rate is slightly above the fixed limit. Van der Linden (2003) presented two alternatives which appear to solve both of the problems. The impact of these methods in the measurement accuracy has not been tested yet. We show how these methods over-restrict the exposure of some highly discriminating items and, thus, the accuracy is decreased. It also shown that, when the desired maximum exposure rate is near the minimum possible value, these methods offer an empirical maximum exposure rate clearly above the goal. A new method, based on the initial estimation of the probability of administration and the probability of selection of the items with the restricted method ( Revuelta & Ponsoda, 1998 ), is presented in this paper. It can be used with the Sympson-Hetter method and with the two van der Linden's methods. This option, when used with Sympson-Hetter, speeds the convergence of the control parameters without decreasing the accuracy.

Dietary Vitamin and Stability of Oral Anticoagulation: Proposal of a Diet with Constant Vitamin K1 Content

1997 ◽  
Vol 77 (03) ◽  
pp. 504-509 ◽  
Author(s):  
Sarah L Booth ◽  
Jacqueline M Charnley ◽  
James A Sadowski ◽  
Edward Saltzman ◽  
Edwin G Bovill ◽  
...  
Keyword(s):  
Dietary Intake ◽  
Vitamin K ◽  
High Performance ◽  
Case Reports ◽  
Food Composition ◽  
Dietary Guidelines ◽  
Dietary Vitamin ◽  
Vitamin K1 ◽  
The Stability ◽  
The Impact

SummaryCase reports cited in Medline or Biological Abstracts (1966-1996) were reviewed to evaluate the impact of vitamin K1 dietary intake on the stability of anticoagulant control in patients using coumarin derivatives. Reported nutrient-drug interactions cannot always be explained by the vitamin K1 content of the food items. However, metabolic data indicate that a consistent dietary intake of vitamin K is important to attain a daily equilibrium in vitamin K status. We report a diet that provides a stable intake of vitamin K1, equivalent to the current U.S. Recommended Dietary Allowance, using food composition data derived from high-performance liquid chromatography. Inconsistencies in the published literature indicate that prospective clinical studies should be undertaken to clarify the putative dietary vitamin K1-coumarin interaction. The dietary guidelines reported here may be used in such studies.

IMPACT OF GOVERNMENT DEBT ON FINANCIAL SECURITY OF UKRAINE

2017 ◽  
Author(s):  
Olena Pikaliuk ◽  
◽  
Dmitry Kovalenko ◽  
Keyword(s):  
Economic Development ◽  
Public Debt ◽  
Positive Impact ◽  
The State ◽  
Financial Security ◽  
State Budget ◽  
The Public ◽  
Debt Security ◽  
The Stability ◽  
The Impact

One of the main criteria for economic development is the size of the public debt and its dynamics. The article considers the impact of public debt on the financial security of Ukraine. The views of scientists on the essence of public debt and financial security of the state are substantiated. An analysis of the dynamics and structure of public debt of Ukraine for 2014-2019. It is proved that one of the main criteria for economic development is the size of public debt and its dynamics. State budget deficit, attracting and using loans to cover it have led to the formation and significant growth of public debt in Ukraine. The volume of public debt indicates an increase in the debt security of the state, which is a component of financial security. Therefore, the issue of the impact of public debt on the financial security of Ukraine is becoming increasingly relevant. The constant growth and large amounts of debt make it necessary to study it, which will have a positive impact on economic processes that will ensure the stability of the financial system and enhance its security.

Influence of internal and external risks on sustainability of financial system of Аltai krai

2018 ◽  
Vol 35 (4) ◽  
pp. 133-136
Author(s):  
R. N. Ibragimov
Keyword(s):  
Sustainable Development ◽  
Financial Stability ◽  
Management Strategy ◽  
Financial System ◽  
Risk Management Strategy ◽  
The Sustainable Development ◽  
The Stability ◽  
The Impact

The article examines the impact of internal and external risks on the stability of the financial system of the Altai Territory. Classification of internal and external risks of decline, affecting the sustainable development of the financial system, is presented. A risk management strategy is proposed that will allow monitoring of risks, thereby these measures will help reduce the loss of financial stability and ensure the long-term development of the economy of the region.

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