Construction of Shock Response Map for a Flexible Rotor-Bearing System With Mount System to Base Excitations Using the FE Transient Analysis Method

Author(s):  
An Sung Lee ◽  
Byung Ok Kim

Turbomachinery such as turbines, pumps and compressors, which are installed in transportation systems such as warships, submarines and space vehicles, etc., often perform crucial missions and are exposed to potential dangerous impact environments such as base-transferred shock forces. To protect the machines from such excessive shock forces, one may need to accurately analyze transient responses of rotors earlier on in their design stages, considering the dynamics of mount designs to be applied with. In this study, utilizing the generalized FE transient response analysis method of a flexible rotor-bearing system with a mount system to base-transferred shock forces, constructions of the shock response and static deflection maps of turbine rotor-bearing and mount system are devised, introducing the mount mass, resilient support stiffness and damping ratios to the counterpart rotor mass, bearing stiffness and damping and the mount system natural frequency. For the given turbine rotor system design a best available mount system design, composed of a mount plate and resilient support, can be readily selected from the constructed maps to meet the rotor’s shock response and mount’s static design limits. The shock response maps also show that for the same shock the FE flexible rotor model used herein yield a more compact light-weighed mount system design than the conventional simple rigid rotor model. Therefore, the shock response map approach in conjunction with the more complicated FE flexible rotor transient response analysis method is justified.

Author(s):  
An Sung Lee ◽  
Byung Ok Kim

Turbomachinery such as turbines, pumps and compressors, which are installed in transportation systems such as warships, submarines and space vehicles, etc., often perform crucial missions and are exposed to potential dangerous impact environments such as base-transferred shock forces. To protect turbomachinery from excessive shock forces, it may be needed to accurately analyze transient responses of rotors, considering the dynamics of mount designs to be applied with. In this study a generalized FE transient response analysis model, introducing relative displacements, is firstly proposed to accurately predict transient responses of a flexible rotor-bearing system with mount systems to base-transferred shock forces. In the transient analyses the state-space Newmark method of a direct time integration scheme is utilized, which is based on the average velocity concept. Results show that for the identical mount systems considered, the proposed FE-based detailed flexible rotor model yields more reduced transient vibration responses to the same shocks than a conventional simple model or a Jeffcott rotor. Hence, in order to design a rotor-bearing system with a more compact light-weighted mount system, preparing against any potential excessive shock, the proposed FE transient response analysis model herein is recommended.


Author(s):  
Cristinel Mares ◽  
Cecilia Surace

Abstract In this paper, the possibility of updating the finite element model of a rotor-bearing system by estimating the bearing stiffness and damping coefficients from a few measured Frequency Response Functions using a Genetic Algorithm is investigated. The issues of identifiability and parameters estimation errors, computational costs and algorithm tuning are addressed. A simulated example of a flexible rotor supported by orthotropic bearings is used for illustrating the method.


2005 ◽  
Vol 38 (8) ◽  
pp. 749-756 ◽  
Author(s):  
Sanxing Zhao ◽  
Hua Xu ◽  
Guang Meng ◽  
Jun Zhu

Author(s):  
Zachary S. Zutavern ◽  
Dara W. Childs

A method is presented for parameter identification of an annular gas seal on a flexible-rotor test rig. Dynamic loads are applied by magnetic bearings (MBs) that support the rotor. MB forces are measured using fiber-optic strain gauges (FOSGs) that are bonded to the poles of the MBs. In addition to force and position measurements, a finite element rotor model is required for the identification algorithm. The FE rotor model matches free-free characteristics of the test rotor. The addition of smooth air seals to the system introduces stiffness and damping terms for identification that are representative of reaction forces in turbomachines. Tests are performed to experimentally determine seal stiffness and damping coefficients for different running speeds and preswirl conditions. Stiffness and damping coefficients are determined using a frequency domain identification method. This method uses an iterative approach to minimize error between theoretical and experimental transfer functions. Test results produce seal coefficients with low uncertainties.


Wear ◽  
1986 ◽  
Vol 107 (4) ◽  
pp. 343-354 ◽  
Author(s):  
C. Rajalingham ◽  
N. Ganesan ◽  
B.S. Prabhu

1974 ◽  
Vol 96 (2) ◽  
pp. 509-517 ◽  
Author(s):  
J. W. Lund

A method is described for calculating the threshold speed of instability and the damped critical speeds of a general flexible rotor in fluid-film journal bearings. It is analogous to the Myklestad-Prohl method for calculating critical speeds and is readily programmed for numerical computation. The rotor model can simulate any practical shaft geometry and support configuration. The bearings are represented by their linearized dynamic properties, also known as the stiffness and damping coefficients of the bearing, and the calculation includes hysteretic internal damping in the shaft and destabilizing aerodynamic forces. To demonstrate the application of the method, results are shown for an industrial, multistage compressor.


Author(s):  
Zachary S. Zutavern ◽  
Dara W. Childs

A method is presented for parameter identification of an annular gas seal on a flexible-rotor test rig. Dynamic loads are applied by magnetic bearings (MBs) that support the rotor. MB forces are measured using fiber-optic strain gauges that are bonded to the poles of the MBs. In addition to force and position measurements, a finite element rotor model is required for the identification algorithm. The FE rotor model matches free-free characteristics of the test rotor. The addition of smooth air sealed to the system introduces stiffness and damping terms for identification that are representative of reaction forces in turbomachines. Tests are performed to experimentally determine seal stiffness and damping coefficients for different running speeds and preswirl conditions. Stiffness and damping coefficients are determined using a frequency domain identification method. This method uses an iterative approach to minimize error between theoretical and experimental transfer functions. Test results produce seal coefficients with low uncertainties.


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