Improve the Stability of Rotor Subjected to Fluid Leakage by Optimum Diameters Design

1990 ◽  
Vol 112 (1) ◽  
pp. 59-64 ◽  
Author(s):  
J. H. Wang ◽  
F. M. Shih
Keyword(s):  
Total Mass ◽  
High Performance ◽  
Optimization Technique ◽  
Slight Modification ◽  
Labyrinth Seal ◽  
Rotor System ◽  
Fluid Leakage ◽  
Rotor Bearing ◽  
The Stability

For high performance turbomachinery, the fluid leakage in the shroud of the blades and the labyrinth seal may cause instability and limit the output rating. In this work, an optimization technique has been used to find the optimum diameters of shaft elements so that the optimized rotor can sustain maximum fluid leakage excitation. The results show that, even without the increase of total mass of the rotor system, the threshold performance of rotor-bearing systems can be significantly improved by slight modification of the shaft diameters.

Threshold Performance Optimization of a Rotor-Bearing System Subjected to Leakage Excitation

1989 ◽  
Author(s):  
J. H. Wang ◽  
F. M. Shih
Keyword(s):  
Performance Optimization ◽  
Optimization Technique ◽  
Slight Modification ◽  
Labyrinth Seal ◽  
Fluid Leakage ◽  
Rotor Bearing ◽  
Bearing System

The fluid leakage in shroud of the blades and the labyrinth seal of turbomachinery may induce instability and limit the output rating. In this work, the optimization technique has been used to find the diameters of shaft elements and the bearing supports so that the optimized rotor-bearing system can sustain larger fluid leakage force. The results show that the threshold performance of rotor-bearing systems can be significantly improved by slight modification of the shaft diameters. The results also indicate that, the threshold performance can be improved more significantly by the combination of optimum bearing supports and optimum shaft diameters.

Threshold Performance Optimization of a Rotor-Bearing System Subjected to Leakage Excitation

1990 ◽  
Vol 112 (4) ◽  
pp. 439-444 ◽  
Author(s):  
J. H. Wang ◽  
F. M. Shih
Keyword(s):  
Performance Optimization ◽  
Optimization Technique ◽  
Fluid Leakage ◽  
Rotor Bearing ◽  
Bearing System ◽  
Blade Tips

Fluid leakage in blade tips in turbomachinery may induce instability and limit and output rating. In this work, the optimization technique has been used to find diameters of shaft elements and bearing supports so that the optimized rotor-bearing system can sustain a larger fluid leakage force. The results show that the threshold performance of rotor-bearing systems can be significantly improved by slight modifications of the shaft diameters. The results also indicate that the threshold performance can be improved more significantly by the combination of optimum bearing supports and optimum shaft diameters.

Numerical and experimental study on dynamic characteristics of tilting-pad journal bearings considering pivot stiffness in a vertical rotor system

2021 ◽  
Vol ahead-of-print (ahead-of-print) ◽  
Author(s):  
Fan Zhang ◽  
Peng Yin ◽  
Yuyang Liu ◽  
Jianmei Wang
Keyword(s):  
Dynamic Characteristics ◽  
Journal Bearings ◽  
Rotor System ◽  
Obvious Effect ◽  
Content Type ◽  
Vertical Rotor ◽  
Tilting Pad ◽  
Rotor Bearing ◽  
The Stability ◽  
Tilting Pad Journal Bearings

Purpose The purpose of this paper is to study the influence of pivot stiffness on the dynamic characteristics of tilting-pad journal bearings (TPJBs) and the stability of the bearing-rotor system. Design/methodology/approach A theoretical numerical model is established, and the influences of pivot stiffness on TPJBs and a bearing-rotor system are analyzed. Then, two kinds of pivot structures with different stiffness are designed and the vibration characteristics are tested on the vertical rotor bearing test bench. Findings The pivot stiffness has an obvious effect on the dynamic characteristics of the TPJBs and the stability of the bearing-rotor system. As a result of appropriate pivot stiffness, the critical speed and the vibration amplification factor can be reduced, the logarithmic decay rate and the stability of the rotor system can be effectively increased. While the journal whirl orbit is smoother and the rubbing is obviously reduced when the bearings have flexible pivots. Originality/value The influence of pivot stiffness on TPJBs and a vertical rotor-bearing system is studied by theoretical and experimental methods.

Numerical and experimental analysis of the rotor—bearing—seal system

2008 ◽  
Vol 222 (8) ◽  
pp. 1435-1441 ◽  
Author(s):  
X Y Shen ◽  
J H Jia ◽  
M Zhao ◽  
J P Jing
Keyword(s):  
Finite Element ◽  
Labyrinth Seal ◽  
Rotor System ◽  
Equivalent Model ◽  
Stable Region ◽  
The Finite Element Method ◽  
Oil Whip ◽  
Oil Whirl ◽  
Rotor Bearing ◽  
Set Up

The rotor—bearing—seal system is simulated by a model consisting of the rotor, the bearing, the foundation, and the labyrinth seal. Governing equations are set up theoretically using the finite-element method. The equivalent model of the bearing—foundation support system is analysed. Forces from the bearing—foundation support and gas-excited forces in the labyrinth seal are imposed in the finite-element equations. Then an experimental rotor—bearing—seal device is designed and many tests are carried out. The Bode, orbit, and waterfall plots are all constructed from the experimental data. An experimental rotor system is studied using the developed equations. Theoretical results from the developed model are in agreement with the ones from the experiment. Analysis proves that although the gas-excited force in the labyrinth seal can improve the stable region of the rotor—bearing—seal system, it makes the rotor vibrate more violently and initiates destructive impacts within the rotor system when the rotor running speed reaches a certain level. Oil whirl and oil whip of journal bearings are found in both the theoretical calculation and the experiment.

Instability Due to Fluid Leakage of a Rotor System With Anisotropic Support

1989 ◽  
Vol 111 (1) ◽  
pp. 27-34
Author(s):  
J. H. Wang ◽  
M. T. Tsai
Keyword(s):  
Element Model ◽  
Point Of View ◽  
Simplified Model ◽  
Optimum Range ◽  
Fluid Leakage ◽  
Rotor Bearing ◽  
The Stability ◽  
Anisotropic Stiffness ◽  
The Finite Element Model ◽  
Bearing System

The instability caused by the fluid leakage leads to a limited performance of turbomachines. This instability may be improved by using flexible bearing supports with anisotropic stiffness. With a simplified model this effect is investigated including the influence of many parameters. The results show that the optimum range of anisotropy is strongly dependent on the parameters of rotor-bearing systems. In this paper an explanation from an energy point of view is presented to clarify the different stability behaviors with anisotropic bearing supports. Beside the simplified model, the stability of the complex rotor-bearing system with anisotropic bearing supports is investigated by the finite element model. An example of a typical 900 MW turbogenerator system is presented.

Effect of Axial Force on Rotordynamics of a Rigid Rotor Supported by Foil Bearings

2018 ◽  
Author(s):  
Wanhui Liu ◽  
Daejong Kim ◽  
Kai Feng
Keyword(s):  
Natural Frequency ◽  
Axial Force ◽  
Time Domain ◽  
Rotor System ◽  
Rigid Rotor ◽  
Rotor Bearing ◽  
Asymmetric Rotor ◽  
The Asymmetry ◽  
The Stability ◽  
Bearing System

This paper investigates the effect of gas foil thrust bearing (GFTB) on the rotordynamic performance of the rotor-gas foil bearing (GFB) system. A rigid rotor supported on two gas foil journal bearings (GFJB) and a pair of GFTBs is studied using a five degree of freedom (5-DOF) model. The studies were performed in both frequency domain using excitation frequency-dependent bearing coefficients (modal analyses) and non-linear analyses (time domain orbit simulations). Modal analyses were performed for both symmetrically and asymmetrically supported rotor systems. For the symmetric rotor, the modal stiffness for the conical mode increases with the axial force, while cylindrical mode is not affected. The axial force has little effects on the modal damping for both the cylindrical mode and conical mode. Thus, the natural frequency and threshold speed (stability limit) for the conical mode increases as the axial force increases, while these values for the cylindrical mode remain almost constant. For the asymmetric rotor, the modal stiffness for both the cylindrical mode and conical mode increases with the axial force, and thus both natural frequency and threshold speed increase with the axial force. Rotor lateral vibrations were also predicted using synchronous bearing coefficients (of both GFJB and GFTB) for both conical and cylindrical modes. The predicted rotor lateral responses show the critical speed increases with axial force for both cylindrical mode and conical mode. The nonlinear analysis using time-domain orbit simulation was also performed including the effect of axial force on the GFTB. The effect of axial force on the stability of the rotor system were discussed. The predicted results showed that the stability of rotor system improved as the axial force increases for Case 1 when the out of phase imbalances were added on the rotor. However, the stability of the rotor system for Case 2 not only influenced by the axial force but also influenced by how asymmetry the rotor is. For the in phase imbalances, the onset speed of subsynchronous motion decreases as axial force increases for the large asymmetric rotor bearing system and the decrement of the onset speed of subsynchronous decreases as the asymmetry of the rotor bearing system decreases. For the out of phase imbalances, the onset speed of subsynchronous motion also decreases as axial force increases for the large asymmetric rotor, but an opposite trend was shown as the asymmetry of the rotor decreases.

Stability of Two-Span Rotor-Bearing System with Coupling Faults of Crack and Rub-Impact

2007 ◽  
Vol 353-358 ◽  
pp. 2501-2504
Author(s):  
Yue Gang Luo ◽  
Song He Zhang ◽  
Xiao Dong Liu ◽  
Bang Chun Wen
Keyword(s):  
Floquet Theory ◽  
Period Doubling ◽  
Rotor System ◽  
Failure Diagnosis ◽  
Coupling Faults ◽  
Rotor Bearing ◽  
Set Up ◽  
The Stability ◽  
Shooting Algorithm ◽  
Bearing System

A dynamic model was set up for the two-span rotor–bearing system with coupling faults of crack and rub-impact. Using the continuation-shooting algorithm for periodic solution of nonlinear non-autonomous system, the stability of the system periodic motion was studied by the Floquet theory. The unstable form of the rotor system with coupling faults is Hopf bifurcation when the depth of crack is smaller. The influence to the response of the system increased along with the depth of crack, the unstable form of the rotor system with coupling faults is period-doubling bifurcation. The conclusions provide theoretic basis reference for the failure diagnosis of the rotorbearing system.

Parametric Influences on the Nonlinear Dynamic Responses of a Rotor-Bearing-Foundation-Labyrinth Seal System

2017 ◽  
Author(s):  
Enjie Zhang ◽  
Yinghou Jiao ◽  
Zhaobo Chen ◽  
Wenchao Mo ◽  
Shuai Wang
Keyword(s):  
Nonlinear Dynamic ◽  
Labyrinth Seal ◽  
Rotor System ◽  
Operating Conditions ◽  
Dynamic Responses ◽  
Lubricating Oil ◽  
Geometrical Parameters ◽  
Dynamic Behaviors ◽  
Highly Nonlinear ◽  
Rotor Bearing

The modern engineering industries rely heavily on the reliable operation of rotating machinery, e.g., steam turbine and gas turbine. These rotating machineries are inevitable to be excited by the unbalance mass forces, the oil film forces and seal forces. Moreover, the turbines installed in an aircraft as well as vessel are also excited by the base vibration. In order to retain the healthy operation and prolong the interval between overhauls, an enormous amount of experimental and theoretical investigations have been focused on the dynamic behaviors of the rotor system. The dynamic characteristics of the rotor system influenced by the single source of vibration, such as unbalance, flowing lubricating oil, sealing medium etc., and combined sources of vibration have also been thoroughly researched. However, the dynamic responses of the rotor-bearing-foundation system subjected to labyrinth seal forces have seldom been studied. Furthermore, the previous analyses of the rotor dynamics mostly were linear. In fact, the fluid film forces are strongly nonlinear functions of the displacement and velocity of the rotor. As a result, the rotordynamics of the turbine is highly nonlinear. It is not accurate enough to be considered from a linear point of view. Applying the energy method, this paper established a dynamic model of the rotor-bearing-foundation-labyrinth seal system. The influences of the geometrical parameters and operating conditions, such as mass eccentricities, inlet pressure and rotational speed etc., on the nonlinear dynamic behaviors of the rotor system are numerically studied. The responses of the same system excited by one side of and both sides of base movement are also comparatively analyzed by means of spectrum cascades, bifurcation diagrams and whirl orbits as well as Poincaré maps.

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.

Photochemical stability of warfarin potassium in powdered pharmaceutical tablets

2021 ◽  
Vol 32 (2) ◽  
pp. 115-129
Author(s):  
Emi Horiguchi-Babamoto ◽  
Makoto Otsuka
Keyword(s):  
High Performance ◽  
Partial Least Squares Regression ◽  
Pediatric Patients ◽  
Reversed Phase ◽  
Least Squares Regression ◽  
Brand Name ◽  
Pharmaceutical Tablets ◽  
Light Stability ◽  
Warfarin Potassium ◽  
The Stability

BACKGROUND: Warfarin potassium (Wf) commercial tablets originally formulated for adults are ground before administration to pediatric patients and elderly patients with dysphagia. OBJECTIVE: The present study investigated the effect of tablet grinding on the photostability of four types of commercial Wf tablets and predicted the photostability of the tablet powders by chemometric analysis. METHODS: The photodegradation of Wf content was evaluated by reversed-phase column high-performance liquid chromatography with ultraviolet (HPLC-UV). RESULTS: The bulk Wf powder was relatively photostable, whereas ground Wf tablets underwent substantial photodegradation. The photostability of the ground powders of a brand-name Wf commercial tablet and three generic Wf commercial tablets was quantitatively assessed and compared. In certain cases, the Wf in all the three ground generic tablets was less photostable than in the ground brand-name tablets. After 28 days of light irradiation, the Wf content decreased to 69.79% in the brand-name tablets, while it was 31.90% in some generic tablets. To clarify the factors influencing the relative photostability in various Wf formulations, we analyzed the intermolecular interactions between the active ingredient and the excipients by partial least-squares regression analysis based on photostability screening for each additive. CONCLUSION: The results suggested that the additives light anhydrous silicic acid and povidone adversely affect the stability of Wf tablets. In addition, the light stability of ground tablets was affected considerably by their formulation.

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