scholarly journals An Approximate Modal Method for Rotordynamic Stability Prediction of Flexible Rotors

1995 ◽  
Author(s):  
Dennis S. H. Chan
Keyword(s):  
Mode Shape ◽  
High Performance ◽  
System Stability ◽  
Parameter Method ◽  
Flexible Rotors ◽  
Lumped Parameter ◽  
Rotor Bearing ◽  
Lumped Parameter Method ◽  
Bearing System ◽  
Modal Method

The prediction of rotordynamic stability is important in the design and diagnosis of high-performance turbomachinery. An approximate method using the mode shape and natural frequency of the first undamped vibration mode of the rotor-bearing system is developed and verified to be accurate for practical cases. The assumption that the damping does not significantly affect the first mode modal parameters can be relaxed if the damped mode shape is available. It confirms previous findings that the mode deflection at the bearing position is most critical to rotor-bearing system stability. The modal method, despite its simplicity, is superior to the lumped parameter method since it can easily account for the distributed shaft parameters and the effective modal contribution of other component properties including the aerodynamic excitation. When provided with the results of the undamped vibration analysis (i.e. only one eigensolution for a specified system configuration), the method predicts a linear relationship between stability measured in terms of logarithmic decrement and system (bearing) damping. The method allows very efficient parameter studies for the effect of bearing damping and aerodynamic cross-coupling on system stability.

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.

An improved lumped parameter method for calculating static characteristics of multi-recess hydrostatic journal bearings

2019 ◽  
Vol 234 (2) ◽  
pp. 301-310
Author(s):  
Yongtao Zhang ◽  
Shijie Yu ◽  
Changhou Lu ◽  
Haixia Zhao ◽  
Peng Liang
Keyword(s):  
Total Pressure ◽  
Control Volume ◽  
Journal Bearings ◽  
Parameter Method ◽  
Static Characteristics ◽  
Application Range ◽  
Continuity Equations ◽  
Pressure Distributions ◽  
Lumped Parameter ◽  
Lumped Parameter Method

This paper proposes an improved lumped parameter method for calculating the static characteristics of multi-recess hydrostatic journal bearings. The improved lumped parameter method can estimate the total pressure distribution in the circumferential direction by introducing control volume in the middle of each inter-recess land, and utilizing the flow continuity equations for each recess and each control volume with the assumption that the pressure distributions are parabolic on the inter-recess land. Then the recess pressure and the fluid film force can be calculated. The calculation accuracy of the improved lumped parameter method and the traditional lumped parameter method is comparatively discussed under different eccentricity ratios and wrap angles of the recess. The results show that the improved lumped parameter method has higher calculation accuracy and wider application range.

scholarly journals Analysis and Application of Screens for Acoustic Impedance in a Speaker Box with a Passive Radiator to Decrease Standing-Wave Influence

2020 ◽  
Vol 10 (3) ◽  
pp. 866
Author(s):  
Yuan-Wu Jiang ◽  
Dan-Ping Xu ◽  
Zhi-Xiong Jiang ◽  
Jun-Hyung Kim ◽  
Ki-Hong Park ◽  
...  
Keyword(s):  
Standing Wave ◽  
Acoustic Resonance ◽  
Experimental Result ◽  
Parameter Method ◽  
Analysis Tool ◽  
Analysis Method ◽  
The Finite Element Method ◽  
Lumped Parameter ◽  
Acoustic Domain ◽  
Lumped Parameter Method

Micro speakers are playing an increasingly important role with the development of multimedia devices. This study applies the lumped-parameter method, which uses an equivalent circuit to model the electromagnetic and mechanical domains. The acoustic domain is modeled using the finite element method. Based on the analysis tool, the use of a screen is analyzed, and the screen is designed to depress the acoustic resonance in the sound-pressure-level curve and improve the performance. The samples are fabricated, and the experiment verifies the analysis method. The experimental result shows that the peak and dip due to the standing wave are cancelled, and the frequency response is smooth when the screen is used.

A Simple Shear and Torsion-Free Beam Model for Multibody Dynamics

2017 ◽  
Vol 12 (5) ◽  
Author(s):  
Juan Carlos García Orden ◽  
Javier Cuenca Queipo
Keyword(s):  
Computer Animation ◽  
Axial Stiffness ◽  
Parameter Method ◽  
Beam Model ◽  
Nonlinear Dynamical ◽  
Lumped Parameter ◽  
Proposed Model ◽  
Space Mechanisms ◽  
Lumped Parameter Method ◽  
Free Beam

This paper describes a very simple beam model, amenable to be used in multibody applications, for cases where the effects of torsion and shear are negligible. This is the case of slender rods connecting different parts of many space mechanisms, models useful in polymer physics, computer animation, etc. The proposed new model follows a lumped parameter method that leads to a rotation-free formulation. Axial stiffness is represented by a standard nonlinear truss model, while bending is modeled with a force potential. Several numerical experiments are carried out in order to assess accuracy, which is usually the main drawback of this type of approach. Results reveal a remarkable accuracy in nonlinear dynamical problems, suggesting that the proposed model is a valid alternative to more sophisticated approaches.

scholarly journals Analysis and Design of Helmholtz Protector to Improve High-Frequency Response of Insert Earphone

2019 ◽  
Vol 9 (12) ◽  
pp. 2541 ◽  
Author(s):  
Yuan-Wu Jiang ◽  
Dan-Ping Xu ◽  
Zhi-Xiong Jiang ◽  
Jun-Hyung Kim ◽  
Sang-Moon Hwang
Keyword(s):  
Frequency Response ◽  
High Frequency ◽  
Experimental Result ◽  
Parameter Method ◽  
Analysis Tool ◽  
Analysis Method ◽  
Analysis And Design ◽  
High Frequency Response ◽  
Lumped Parameter ◽  
Lumped Parameter Method

With the development of multimedia devices, earphones are playing an increasingly important role. This article applies the lumped parameter method using an equivalent circuit to model the electromagnetic, mechanical, and acoustic domains of earphones. Then, parameters are determined according to the dimensions and material properties of earphone parts. On the basis of the analysis tool and determined parameters, a Helmholtz protector is analyzed and designed to improve the high-frequency response. Samples are fabricated, and the experiment verifies the analysis method. The experimental result shows that the peaks at 7 k and 10 k are decreased at 8.05 dB and 7.89 dB. The root means square value of SPL deviation compared with target curve decreased from 9.77 to 4.39. High-frequency response is improved by using the Helmholtz protector.

The Bending Vibration Analysis on the Main Drive Axis of CNC Spiral Bevel Gear Milling Machine

2013 ◽  
Vol 655-657 ◽  
pp. 1296-1299
Author(s):  
Li Juan Yu ◽  
Zhao Jun Yang ◽  
Fu You Liu
Keyword(s):  
Drive Shaft ◽  
Resonance Problem ◽  
Parameter Method ◽  
Force Model ◽  
Lumped Mass ◽  
Mass Model ◽  
Bending Vibration ◽  
Lumped Parameter ◽  
Lumped Mass Model ◽  
Lumped Parameter Method

Gear machine tool main drive shaft to avoid resonance problem is studied.The force of the drive shaft is analyzed, and the vibration form of the drive shaft is confirmed. Using the lumped parameter method to simplify the main drive shaft, the lumped mass model and the force model were been obtained. When bending vibrating, the natural frequency of the main drive shaft is calculated using the transfer matrix method. The calculated critical speed is 43755r/min, which far outweighs the motor rated speed .It means that the drive shaft under normal work won't be resonance, which accords with the request of production.

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