The Estimation of Rotor Unbalance

1997 ◽  
Author(s):  
A. W. Lees ◽  
M. I. Friswell
Keyword(s):  
Numerical Model ◽  
Mode Shape ◽  
Approximate Model ◽  
Operational Mode ◽  
Single Plane ◽  
Supporting Structure ◽  
Rotating Machine ◽  
Consistent Manner ◽  
Bearing System ◽  
Rotor Axis

Abstract A method is presented to determine the state of unbalance of a rotating machine. The only requirement of the procedure is a good numerical model for the rotor and an approximate model for the bearing behaviour. No assumptions are made concerning the operational mode shape of the rotor and the influence of the supporting structure is included in a consistent manner. For simplicity the analysis is presented in a single plane orthogonal to the rotor axis, but no difficulty is foreseen in extending the method to two planes. Examples are given for a two bearing system with both constant and varying bearing coefficients.

Simulation Investigations of the Effect of a Supporting Structure Defect on the Dynamic State of the Rotor Supported on Slide Bearings

2007 ◽  
Author(s):  
Grzegorz Z˙ywica
Keyword(s):  
Numerical Model ◽  
Present Article ◽  
Dynamic State ◽  
Structure Defect ◽  
Supporting Structure ◽  
Second Stage ◽  
Applied Method ◽  
Rotating Machine ◽  
Wide Range ◽  
Real Matrices

The present article reports an attempt to assess the effect of the defect having the form of supporting structure fracture on the dynamic state of the rotor supported on slide bearings. The investigations were conducted on an experimentally verified numerical model of a selected large-dimension rotating machine. Within the framework of the investigations, selected cases of a defect localised in the region of one of bearing supports were analysed. The applied method of calculations comprised two basic stages. The first stage consisted in determining complex flexibility characteristics of the supporting structure at the rotor foundation place. In the second stage the obtained flexibility characteristics, after transformation to real matrices of stiffness, damping, and apparent masses, were used for determining parameters of rotor motion. As a result of the calculations, characteristics were obtained that provide opportunities for assessing the effects of the examined defects on rotor vibrations within a wide range of rotational speeds.

Analysis of Instabilities in Railway Vehicles Employing Operational Modal Analysis

2015 ◽  
Author(s):  
Lara Erviti Calvo ◽  
Gorka Agirre Castellanos ◽  
Germán Gimenez
Keyword(s):  
Numerical Model ◽  
Modal Analysis ◽  
Mode Shape ◽  
Operational Modal Analysis ◽  
Mode Shapes ◽  
Correct Identification ◽  
Unstable Condition ◽  
Static Tests ◽  
Railway Vehicles ◽  
Damping Rate

The application of Operational Modal Analysis (OMA) in the railway sector opens a broad field of opportunities. The validation of the numerical model employed in the design phase is usually performed employing data obtained in static tests. The drawback is that some suspension parameters, such as dampers, only have an influence in the dynamic behavior and not in the static behavior. Because of that, the use of the mode shapes identified from track measurements in combination with the static tests leads to a more accurate validation of the numerical model. Apart from that, most passenger comfort and dynamic problems are associated to slightly damped modes. A correct identification of the modal parameters can be used as a continuous design improvement tool to improve the comfort and dynamic characteristics of future designs. Another valuable application of OMA techniques is the identification of the mode shapes corresponding to instabilities, due to the safety impact that they have. In railway vehicles, instabilities are associated to mode shapes that present a damping rate which decreases with the increase of the running speed. Above a certain speed value, the excitation coming from track cannot be damped by the vehicle and it reaches an unstable condition. This unstable condition leads to high acceleration levels experienced by the passengers and high interaction forces between the wheel and the rail that may lead to safety hazards. The speed above which the vehicle is unstable is known as critical speed, and has to be greater than the maximum speed of the vehicle with a reasonable safety margin. The use of OMA techniques allows identifying the mode shape that causes the instability. This paper presents the application of OMA techniques to measurements performed on a passenger vehicle, in which the speed was increased until the vehicle was unstable. The mode shape that caused the instability was identified as well as its corresponding natural frequency and damping rate.

Gyroscopic Effects of a Vibrationally Isolated Rotating Disk and Shaft

1997 ◽  
Author(s):  
Donald L. Margolis
Keyword(s):  
Vibrational Energy ◽  
Rotating Disk ◽  
Aircraft Engine ◽  
Energy Transmission ◽  
Sound Energy ◽  
Supporting Structure ◽  
Rotating Machine ◽  
Established Fact ◽  
Radiated Sound ◽  
Gyroscopic Effects

Abstract An aircraft engine is an example of a rotating machine whose rotating imbalance will be transmitted as vibrational energy into the structure to which it is attached. There is considerable interest in understanding this energy transmission in order to design mounting systems, both passive and active, which can control this transmission the best possible way in order to reduce structurally borne noise in the cabin. It is a well established fact in acoustics[1] that in order to reduce perceived sound at the listener, the noise transmission path must be severed by 1) eliminating the source of the disturbance (usually difficult if not impossible), 2) preventing propagation of energy into the structure and ultimately to structural surfaces, 3) preventing radiation of sound energy from vibrating surfaces, and 4) preventing radiated sound from reaching the listener. In this paper we address only the prevention of energy transmission from the source into the supporting structure through use of some type of mounting system.

scholarly journals Dynamic Characteristics and Experimental Research of a Two-Span Rotor-Bearing System with Rub-Impact Fault

2019 ◽  
Vol 2019 ◽  
pp. 1-15 ◽  
Author(s):  
Rui Zhu ◽  
Guang-chao Wang ◽  
Qing-peng Han ◽  
An-lei Zhao ◽  
Jian-xing Ren ◽  
...  
Keyword(s):  
Dynamic Characteristics ◽  
Critical Speed ◽  
Great Influence ◽  
Experimental Platform ◽  
Rotating Machine ◽  
Rotor Bearing ◽  
Before And After ◽  
Analysis System ◽  
The Stability ◽  
Bearing System

Rotor rub-impact has a great influence on the stability and safety of a rotating machine. This study develops a dynamic model of a two-span rotor-bearing system with rubbing faults, and numerical simulation is carried out. Moreover, frictional screws are used to simulate a rubbing state by establishing a set of experimental devices that can simulate rotor-stator friction in the rotor system. Through the experimental platform and its analysis system, the rubbing experiment was conducted, and the vibration of the rotor-bearing system before and after the critical speed is observed. Rotors running under normal condition, local slight rubbing, and severe rubbing throughout the entire cycle are simulated. Dynamic trajectories, frequency spectrum diagrams, chart of axis track, and Poincare maps are used to analyze the features of the rotor-bearing system with rub-impact faults under various parameters. The vibration characteristics of rub impact are obtained. Results show that the dynamic characteristics of the rotor-bearing system are affected by the change in velocity and degree of impact friction. The findings are helpful in further understanding the dynamic characteristics of the rub-impact fault of the two-span rotor-bearing system and provide reference for fault diagnosis.

Sensor Fusion for Operational Mode Shape Analysis of Multi DoF Systems

2018 ◽  
Vol 5 (11) ◽  
pp. 24871-24879
Author(s):  
R. Rahul ◽  
Rohit Rajpal ◽  
Sai Aditya Raman Kuchibhatla ◽  
K.V. Gangadharan
Keyword(s):  
Sensor Fusion ◽  
Shape Analysis ◽  
Mode Shape ◽  
Operational Mode

scholarly journals Dynamic Response of a Rotating Assembly under the Coupled Effects of Misalignment and Imbalance

2020 ◽  
Vol 2020 ◽  
pp. 1-26
Author(s):  
Mohamed Desouki ◽  
Sadok Sassi ◽  
Jamil Renno ◽  
Samer Abdelazim Gowid
Keyword(s):  
Numerical Model ◽  
Rotational Speed ◽  
Rotating Machinery ◽  
Angular Misalignment ◽  
Simultaneous Effect ◽  
Frequency Responses ◽  
Parallel Misalignment ◽  
Misalignment Fault ◽  
Coupling Type ◽  
Bearing System

In rotating machinery, the second most common fault after imbalance is misalignment. Misalignment can have a severe impact on equipment and may reduce the machine’s lifetime considerably. In this paper, the simultaneous effect of imbalance and misalignment (parallel or angular) on the vibration spectra of rotating machinery will be discussed. A numerical model is developed and used to obtain the time and frequency responses of the rotor-coupling-bearing system to the simultaneous effect of these faults. The numerical model shows that the imbalance was mainly related to the peak located around 1X, whereas misalignment was linked to the peak around 2X. In addition, the parallel misalignment fault magnifies the 2X amplitude of the displacement response, whereas the response of angular misalignment is captured at the 2X and 4X amplitudes. This study also examines the effects of changing the model’s rotational speed, misalignment level, and coupling type for angular and parallel misalignments.

SENSITIVITY-BASED OPERATIONAL MODE SHAPE NORMALISATION

2002 ◽  
Vol 16 (5) ◽  
pp. 757-767 ◽  
Author(s):  
E. PARLOO ◽  
P. VERBOVEN> ◽  
P. GUILLAUME ◽  
M. VAN OVERMEIRE
Keyword(s):  
Mode Shape ◽  
Operational Mode

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.

Sign in / Sign up

Export Citation Format

Share Document