Nonlinear Numerical Investigation Around Instability Point of the Flexible Rotor Supported by the Journal Bearing

2017 ◽  
Author(s):  
Mugen Ito ◽  
Tsuyoshi Inoue
Keyword(s):  
Numerical Simulation ◽  
Hopf Bifurcation ◽  
Numerical Investigation ◽  
Finite Length ◽  
Journal Bearing ◽  
Rotating Machinery ◽  
Flexible Rotor ◽  
Rotor Systems ◽  
Instability Point ◽  
Nonlinear Numerical Simulation

Rotating machinery supported by the journal bearing may be subject to instability. This instability is classified as the Hopf bifurcation. Either a sub-critical bifurcation or super-critical bifurcation appears depending on the parameters of rotor systems. Conventionally, an infinitely short journal bearing model was used for the investigation of this bifurcation. In this paper, the force transmitted by the oil film of the journal bearing is represented by the finite length model. Nonlinear numerical simulation is performed at around instability point of the flexible rotor supported by the journal bearing. The bifurcation characteristic and the change of bifurcation type are investigated when the ratio L / D, which is the ratio of bearing length L to the bearing diameter D, increases.

Nonlinear Vibration Analysis of a Flexible Rotor Supported by a Flexure Pivot Tilting Pad Journal Bearing in Comparison to a Fixed Profile Journal Bearing with Experimental Verification

2021 ◽  
Author(s):  
Nuntaphong Koondilogpiboon ◽  
Tsuyoshi Inoue
Keyword(s):  
Hopf Bifurcation ◽  
Journal Bearing ◽  
Flexible Rotor ◽  
Maximum Test ◽  
Operating Region ◽  
Stable Operating ◽  
Subcritical Hopf Bifurcation ◽  
Tilting Pad ◽  
Calculation Results ◽  
Tilting Pad Journal Bearing

Abstract In this paper, an efficient numerical method consisting of the real mode component mode synthesis (CMS) model reduction, shooting method with parallel computing, and Floquet analysis was developed for nonlinear rotordynamics analysis of a flexible rotor supported by a 4-lobe flexure pivot tilting pad journal bearing (FPTPJB) in load-on-pad (LOP) and load-between-pad (LBP) orientations in comparison to a fixed profile journal bearing (JB) of the same pad geometry. The method used the rotor's finite elements and bearing forces obtained from directly solving the Reynolds equation to determine the limit cycles and Hopf bifurcation types. For the investigated rotor and bearing parameters, the numerical results indicated that the onset speed of instability (OSI) of FPTPJB is considerably higher than that of JB of the same orientation. Also, FPTPJB in LOP orientation yielded higher OSI than the LBP one, whereas the OSI of JB in LOP orientation was substantially higher than the LBP counterpart. Nonlinear calculation results indicated that all bearing types and orientations gave subcritical Hopf bifurcation. The FPTPJB in LOP orientation produced the largest stable operating region, whereas the JB in LBP configuration yield the smallest one. The experiment showed subcritical Hopf bifurcation occurred at speed close to the calculated OSI in all cases except FPTPJB in LOP orientation that the OSI is higher than the maximum test rig speed. The whirling orbit had the same frequency as the first critical speed and precessed in the direction of shaft rotation.

scholarly journals Kriging Metamodeling in Rotordynamics: Application for Predicting Critical Speeds and Vibrations of a Flexible Rotor

Complexity ◽  
2018 ◽  
Vol 2018 ◽  
pp. 1-26 ◽  
Author(s):  
J.-J. Sinou ◽  
L. Nechak ◽  
S. Besset
Keyword(s):  
Predictive Models ◽  
Correlation Functions ◽  
Weighted Average ◽  
Rotating Machinery ◽  
Flexible Rotor ◽  
Critical Speeds ◽  
Rotor Systems ◽  
Kriging Estimation ◽  
Kriging Predictor ◽  
Kriging Metamodeling

Rotating machinery produces vibrations depending upon the design of the rotor systems as well as any faults or uncertainties in the machine that can increase the vibrations of such systems. This study illustrates the effectiveness of using surrogate modeling based on kriging in order to predict the vibrational behavior (i.e., the critical speeds and the vibration amplitudes) of a complex flexible rotor in the presence of uncertainties. The basic idea of kriging is to predict unknown values of a function by using a small size set of known data. The kriging estimation is based on a weighted average of the known values of the function in the neighborhood of the point for which the value of the function has to be calculated. The crucial dependence of a kriging predictor versus the correlation functions and different orders will be illustrated. This paper also shows that reducing the number of samples required to have predictive models can be achieved by performing an initial understanding of the mechanical system of interest and by considering certain characteristics directly deriving from the physics of the problem studied.

NUMERICAL INVESTIGATION OF FILM DISTRIBUTION IN HORIZONTAL-TUBE FALLING FILM EVAPORATOR

2011 ◽  
Vol 19 (03) ◽  
pp. 177-183 ◽  
Author(s):  
JIN-BO CHEN ◽  
QING-GANG QIU
Keyword(s):  
Numerical Simulation ◽  
Fluid Flow ◽  
Film Thickness ◽  
Liquid Film ◽  
Numerical Investigation ◽  
Horizontal Tube ◽  
Flow Density ◽  
Falling Film ◽  
Film Distribution ◽  
Simulation Results

The technique of horizontal-tube falling film has been used in the cooling and heating industries such as refrigeration systems, heating systems and ocean thermal energy conversion systems. The comprehensive performance of evaporator is directly affected by the film distribution characteristics outside tubes. In this paper, numerical investigation was performed to predict the film characteristics outside the tubes in horizontal-tube falling film evaporator. The effects of liquid flow rate, tube diameter and the circular degree of tube on the film thickness were presented. The numerical simulation results were compared with that of the empirical equations for calculating the falling film thickness, and agreements between them were reasonable. Numerical simulation results show that, at the fixed fluid flow density, the liquid film is thicker on the upper and lower tube and the thinnest liquid film appears at angle of about 120°. The results also indicate that, when the fluid flow density decreases to a certain value, the local dryout spot on the surface of the tube would occur. In addition, the film thickness decreases with the increases of the tube diameter at the fixed fluid flow density.

A Numerical Investigation on the Volute/Diffuser Interaction due to the Axial Distortion at Impeller Exit

2000 ◽  
Author(s):  
Fahua Gu ◽  
Abraham Engeda ◽  
Mike Cave ◽  
Jean-Luc Di Liberti
Keyword(s):  
Experimental Data ◽  
Numerical Simulation ◽  
Numerical Investigation ◽  
Steady Flow ◽  
Centrifugal Compressor ◽  
Vortex Structure ◽  
Flow Model ◽  
Single Stage ◽  
Mass Flows

Abstract A numerical simulation is performed on a single stage centrifugal compressor using the commercially available CFD software, CFX-TASCflow. The steady flow is obtained by circumferentially averaging the exit fluxes of the impeller. Three runs are made at design condition and off-design conditions. The predicted performance is in agreement with experimental data. The flow details inside the stationary components are investigated, resulting in a flow model describing the volute/diffuser interaction at design and off-design conditions. The recirculation and twin vortex structure are found to explain the volute loss increase at lower and higher mass flows, respectively.

Nonlinear Dynamics of Flexible Rotors Supported on Journal Bearings—Part I: Analytical Bearing Model

2017 ◽  
Vol 140 (2) ◽  
Author(s):  
Mohammad Miraskari ◽  
Farzad Hemmati ◽  
Mohamed S. Gadala
Keyword(s):  
Journal Bearing ◽  
Nonlinear Coefficient ◽  
Journal Bearings ◽  
Flexible Rotor ◽  
Dynamic Coefficients ◽  
Flexible Rotors ◽  
Rotor Bearing ◽  
Bearing Force ◽  
Derivatives Of ◽  
Bearing System

To determine the bifurcation types in a rotor-bearing system, it is required to find higher order derivatives of the bearing forces with respect to journal velocity and position. As closed-form expressions for journal bearing force are not generally available, Hopf bifurcation studies of rotor-bearing systems have been limited to simple geometries and cavitation models. To solve this problem, an alternative nonlinear coefficient-based method for representing the bearing force is presented in this study. A flexible rotor-bearing system is presented for which bearing force is modeled with linear and nonlinear dynamic coefficients. The proposed nonlinear coefficient-based model was found to be successful in predicting the bifurcation types of the system as well as predicting the system dynamics and trajectories at spin speeds below and above the threshold speed of instability.

Optimization of Bearing Locations for Rotor Systems With Magnetic Bearings

1995 ◽  
Author(s):  
Sriram Srinivasan ◽  
Eric H. Maslen ◽  
Lloyd E. Barrett
Keyword(s):  
Design Process ◽  
Magnetic Bearing ◽  
Rotating Machinery ◽  
Rotor Systems ◽  
Infinity Norm ◽  
Multi Stage ◽  
Scalar Measure ◽  
Bearing Design ◽  
The Stability ◽  
Practical Measure

This paper presents a method for quickly evaluating the effect of changes in bearing location on bearing design for stability of rotating machinery. This method is intended for use by rotating machinery designers to select the “best” bearing locations prior to the bearing design process. The purpose of the method is to improve the design process by separating the problem of determining the “best” bearing locations from that of determining the actual bearing design. The method is independent of the type of bearing employed. For each candidate bearing configuration, the method provides a scalar measure of the relative ability of bearings to meet stability specifications. Within certain limits, the stability specifications are defined by the designer. The scalar measure is used to rank the candidate bearing locations and thereby select the best one. The scalar measure is compared to a practical measure of magnetic bearing design such as the infinity norm of the controller for an example design of a multi-stage centrifugal compressor.

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