Effect of Higher-Than-Rated-Speed Rotordynamic Modes on Rotor Balancing

2015 ◽  
Author(s):  
John J. Yu ◽  
Siddharth Ashar
Keyword(s):  
Critical Speed ◽  
Measured Data ◽  
Vibration Response ◽  
Vibration Level ◽  
Generator Rotor ◽  
Vibration Data ◽  
Unbalance Response ◽  
Nodal Points ◽  
Rotor Balancing

It was surprisingly reported that a generator rotor could not be balanced to an acceptable vibration level by weights at two balance planes at the drive end (DE) and the non-drive end (NDE) fan rings. Both real measured vibration data and rotordynamic calculations indicate that the rotor at rated speed of 3600 rpm appears to run just above the 2nd critical speed (couple or conical mode). However, couple weights (same weights placed at both DE and NDE with 180-degree-out-of-phase) have little effect on 1X vibration response. A third balance plane had to be utilized to effectively reduce vibration. This paper uses measured data and rotordynamic modelling to explain these findings. It is found that the 4th mode could affect synchronous vibration response at rated speed significantly besides the 3rd mode. The two fan ring balance planes appear to be near the nodal points of the 4th mode, which explains ineffectiveness of the couple weights to vibration response at rated speed in the field. Measured data from real machines including influence vectors are presented from third balance planes such as the coupling and the exciter ends, besides the fan ring wheels. The 3rd and 4th rotordynamic modes are also given along with unbalance response studies.

Prediction and Comparison of Critical Speeds and Potential Excitation Using In-House Developed Software for an Integrally Geared Centrifugal Air Compressor

2014 ◽  
Author(s):  
Mathew P. James ◽  
Pavan Kumar Reddy Pandillapalli ◽  
Swaminathan Gopalakrishnan
Keyword(s):  
Steady State ◽  
Computer Program ◽  
Critical Speed ◽  
Maximum Amplitude ◽  
Sound Intensity ◽  
Industrial Applications ◽  
Lateral Direction ◽  
Critical Speeds ◽  
Vibration Data ◽  
Unbalance Response

Integrally Geared Centrifugal Air Compressors (IGCAC) are becoming popular in many industrial applications. Development of such compressors requires in depth Rotordynamic Design and Analysis. To facilitate this, an in-house computer program based on transfer matrix method was developed using MATLAB® software. This computer program is capable of computing rotordynamic parameters such as static deflection, critical speed and interference diagram, and can output critical speed map, mode shape, unbalance response, orbit, for lateral direction. This software was used to analyze a two stage IGCAC with two impellers on a simply supported rotor running above second critical speed, driven by a two pole induction motor through a step-up gearbox. Undamped critical speed map, an output from the program was used to predict intended bearing stiffness for design. Using the above data and commercially available software DyRoBeS© a suitable bearing was designed. The speed dependent bearing characteristics, an output from DyRoBeS©, were used to determine damped unbalance response plot for a given residual unbalance. Corresponding to a maximum peak in unbalance response the damped critical speed and amplification factors (AF) were found out. The results from the newly developed software were compared with prediction from DyRoBeS©. It was found that critical speed was within 5% and AF was of the same order. Results from in-house software were comparable to that from DyRoBeS©. Based on the guidelines from API 684, the AF and separation margins were determined. A prototype IGCAC compressor as described above was built and tested. The testing included the collection of steady state, coast-up and coast-down data. Using the coast-up, coast-down data, a Bode plot was created. From this the critical speeds and AF’s were determined and compared with results from in-house software. It was found there was an error of less than 5% for the critical speed and around 5% for AF from the predicted results. For the same compressor a study on the potential excitation frequencies due to unbalance, impeller-diffuser and impeller-scroll tongue interactions were calculated. FFT of the steady state vibration data was deduced. It was found that the calculated frequency and measured frequency at maximum amplitude were aligning. Further noise measurements were recorded based on sound intensity as per guidelines in ISO 9614. The impeller-tongue interaction frequencies for stages were seen in the processed noise data. It was found that the predictions were in good agreement with the test results.

The Necessity of a Third Balance Plane for Generator Rotor Field Balancing

2014 ◽  
Author(s):  
John J. Yu
Keyword(s):  
Relative Phase ◽  
Vibration Response ◽  
Couple Mode ◽  
Vibration Level ◽  
Generator Rotor ◽  
Alarm Limit ◽  
Mode Response

When balancing a generator rotor in the field, one often assumes that two balance planes at the drive end (DE) and non-driven end (NDE) fan rings would be sufficient to bring 1X vibration down. This paper, however, presents a case where a third balance plane must be utilized in order to reduce 1X vibration level below the alarm limit. Though this type of generator with rated speed of 3600 rpm appears to run just above the second couple mode from Bode and polar plots, couple weights (same weights placed at both DE and NDE with 180-degree out-of phase) have little effect on 1X vibration response. For vibration vectors at DE and NDE bearings presenting certain relative phase, it became impossible to further reduce vibration level at both ends from weights at DE and NDE fan ring planes only as indicated in obtained influence data. A third balance plane at the exciter end was attempted to change their relative phase, which proved to be successful. From the exciter end weights combined with the NDE fan ring weights, the generator rotor was balanced successfully. The purpose of this paper is to show in some cases ineffectiveness of couple weights to couple (pivotal mode) response and success of field balancing with a third balance plane on a generator rotor.

Multi Objective Optimisation of an Aero Engine Rotor System Using Nondominated Sorting Genetic Algorithm (NSGA)

2017 ◽  
Author(s):  
Joseph Shibu Kalloor ◽  
Ch. Kanna Babu ◽  
Girish K. Degaonkar ◽  
K. Shankar
Keyword(s):  
Genetic Algorithm ◽  
Critical Speed ◽  
Rotor System ◽  
Pareto Optimal ◽  
Multi Objective ◽  
Rayleigh Beam ◽  
Unbalance Response ◽  
Aero Engine ◽  
Nondominated Sorting ◽  
Engine Rotor

A comprehensive multi-objective optimisation methodology is presented and applied to a practical aero engine rotor system. A variant of Nondominated Sorting Genetic Algorithm (NSGA) is employed to simultaneously minimise the weight and unbalance response of the rotor system with restriction imposed on critical speed. Rayleigh beam is used in Finite Element Method (FEM) implemented in-house developed MATLAB code for analysis. The results of practical interest are achieved through bearing-pedestal model and eigenvalue based Rayleigh damping model. Pareto optimal solutions generated and best solution selected with the help of response surface approximation of the Pareto optimal front. The outcome of the paper is a minimum weight and minimum unbalance response rotor system which satisfied the critical speed constraints.

Effects of High-Speed Railway in Tunnel on Vibration Response of Upper Building

2013 ◽  
Vol 482 ◽  
pp. 155-162
Author(s):  
Si Hui Xu ◽  
Xiao Hui Zhang ◽  
Han Chen
Keyword(s):  
Dynamic Model ◽  
High Speed ◽  
Reaction Force ◽  
Element Model ◽  
Vibration Response ◽  
Vibration Level ◽  
High Speed Railway ◽  
Proper Distance ◽  
Coupling Dynamic ◽  
Coupling Dynamic Model

In order to study the effects of high-speed railway in tunnel on vibration response of upper building, the Vehicle-Track-Tunnel-Soil-Building coupling dynamic model was established, and the reaction force of fasteners was used to transmit between Vehicle-Track coupling dynamic model and Tunnel-Soil-Building finite element model. According to modal analysis for typical section of building, sensitive frequency range and sensitive structure locations were obtained. In terms of two conditions, Tunnel-Building Integrated Structure and building are evaded from tunnel for some distance, 1/3 octave vibration level and VLZ vibration acceleration level for all measuring points were calculated to analyze the vibration response of building. The results are shown as follows: for Tunnel-Building Integrated Structure, the overall vibration level is high,which is above 65dB. 2-3dB will be reduced by decreasing speed and improving standard of track. when building is evaded from tunnel for some distance, with larger evaded distance, the vibration response is slighter. However, when evaded distance is above 30m, vibration may be amplified ,so its necessary to select proper distance. Vibration response of structure is most strong when 4 lines meet under building, so strict limitation on meeting condition of trains can effectively reduce vibration level.

Influence of People Walking on Floor Performance due to Low Level Vibration

2015 ◽  
Vol 802 ◽  
pp. 208-213
Author(s):  
Tuan Norhayati Tuan Chik ◽  
Shurl Yabi ◽  
Mohd Haziman Wan Ibrahim ◽  
Nor Azizi Yusoff ◽  
Taksiah A. Majid ◽  
...  
Keyword(s):  
Software Package ◽  
Laser Doppler Vibrometer ◽  
Vibration Response ◽  
Dynamic Loads ◽  
Mode Shapes ◽  
Low Level ◽  
Vibration Data ◽  
Finite Element Software ◽  
Floor Structure ◽  
Floor Vibrations

Abstract. Vibration in building is one of the important problems which need to consider, especially in designing the floor. Floor vibrations are generally caused by dynamic loads applied particularly by human activity especially walking. Although it is specified as low level amplitude, walking induced vibrations can cause discomfort to human occupants and alarming for a certain items of precision sensitive equipment. This paper investigates the vibration response on floor performance due to one, three and five of people walking. Laser Doppler Vibrometer was used to obtain vibration data when people are walking. Further analysis was carried out by using finite element software package ANSYS to simulate the floor under vibration inputs to obtain natural frequency and mode shapes of the floor structure. The vibration data was then analysed in ModalV analysis to generate the vibration response. Then, the results were checked against the vibration criteria level guideline as a crude tool comparison. As a result, the numbers of people walking were influenced the floor performance, which indicated five peoples walking show the highest response up to ISO level due to vibration compared with one people walking.

Unbalance Response of Rotors Supported on Hydrodynamic Bearings Placed Close to Nodal Points of Excited Vibration Modes

2002 ◽  
Author(s):  
Demetrio C. Zachariadis
Keyword(s):  
Tilt Angle ◽  
Rotor Dynamics ◽  
Journal Bearings ◽  
Vibration Modes ◽  
Time Varying ◽  
Rotor Systems ◽  
Unbalance Response ◽  
Nodal Points ◽  
Excited Vibration ◽  
Modes Of Vibration

The traditional 8-coefficient bearing model, used in linear rotor dynamics, is shown here to be inadequate for the unbalance response calculation of rotor systems supported on hydrodynamic journal bearings placed close to nodal points of excited modes of vibration. In such situations, one cannot neglect the time varying tilt angle between journals and bearings, whose consideration leads to the adoption of a 32-coefficient bearing model. Numerical results indicate that the differences between vibration amplitudes calculated using both bearing models can be greater than 100%, while discrepancies in the predicted stability thresholds are small. The conclusions of the study are coherent with previously published theoretical and experimental results.

Inductive Estimation Arithmetic for Random Vibration Data

2011 ◽  
Vol 219-220 ◽  
pp. 1113-1116
Author(s):  
Yong Jie Zhang ◽  
Xiao Hu Zhang ◽  
Bin Tuan Wang
Keyword(s):  
Data Processing ◽  
Numerical Experiments ◽  
Random Vibration ◽  
Measured Data ◽  
Reliability Test ◽  
Vibration Data ◽  
Inductive Methods

The vibration data processing of environmental spectrum is an important part of environmental reliability test for the aircraft. Based on the inductive methods for environmental measured data of vibration, an inductive arithmetic is employed to estimate the random vibration data of aircraft surface in Matlab system. Numerical experiments show that the inductive estimation arithmetic is effective, reliable and applicable for the environmental measured data of random vibration.

The Effect of Soft Sub Grade on Train Ride Quality

2015 ◽  
Author(s):  
Yin Gao ◽  
Shelby Stigers ◽  
Hai Huang
Keyword(s):  
Critical Condition ◽  
Critical Speed ◽  
Commercial Vehicle ◽  
Critical Conditions ◽  
Ride Quality ◽  
Vibration Level ◽  
Vehicle Dynamic ◽  
Vehicle Model ◽  
Train Operation ◽  
Speed Effect

Train ride quality plays an important role in train operation. In this paper, the aim is to explore the train ride quality when trains run on soft sub grade at different speeds especially critical conditions and operation safety on the sub grades with different properties. The responses of track and vehicle such as lateral wheel-rail force (L/V ratio), acceleration of vehicle are studied in this research. It is important to note that a critical condition is when train runs on soft sub grade. In this case, the critical speed effect will occur and resonance between vehicle and track could rise up the vibration level which could cause derailment and bad riding experience. In order to measure the track and vehicle responses, it should combine a detailed vehicle model and a track dynamic model. However, most commercial modeling programs do not have the ability to combine both detailed vehicle and track models. In this research, by integrating a computer program with a 2-D track model to a commercial vehicle dynamic program, the responses of vehicle and track can be calculated at the same time. Conclusions and findings will be illustrated in this paper.

Stabilizing a 46 MW Multistage Utility Steam Turbine Using Integral Squeeze Film Bearing Support Dampers

2015 ◽  
Vol 137 (5) ◽  
Author(s):  
Bugra Ertas ◽  
Vaclav Cerny ◽  
Jongsoo Kim ◽  
Vaclav Polreich
Keyword(s):  
Steam Turbine ◽  
Critical Speed ◽  
Stability Margin ◽  
Experimental Tests ◽  
Turbine Rotor ◽  
Squeeze Film ◽  
Full Load ◽  
Vibration Data ◽  
Full Speed ◽  
Full Load Operation

A 46 MW 5500 rpm multistage single casing utility steam turbine experienced strong subsynchronous rotordynamic vibration of the first rotor mode; preventing full load operation of the unit. The root cause of the vibration stemmed from steam whirl forces generated at secondary sealing locations in combination with a flexible rotor-bearing system. Several attempts were made to eliminate the subsynchronous vibration by modifying bearing geometry and clearances, which came short of enabling full load operation. The following paper presents experimental tests and analytical results focused on stabilizing a 46 MW 6230 kg utility steam turbine experiencing subsynchronous rotordynamic instability. The paper advances an integral squeeze film damper (ISFD) solution, which was implemented to resolve the subsynchronous vibration and allow full load and full speed operation of the machine. The present work addresses the bearing-damper analysis, rotordynamic analysis, and experimental validation through waterfall plots, and synchronous vibration data of the steam turbine rotor. Analytical and experimental results show that using ISFD improved the stability margin by a factor of 12 eliminating the subsynchronous instability and significantly reducing critical speed amplification factors. Additionally, by using ISFD the analysis showed significant reduction in interstage clearance closures during critical speed transitions in comparison to the hard mounted tilting pad bearing configuration.

Field Measurement and Numerical Simulation of Vibration Effect on Metro Depot Superstructure Caused by Passing Trains

2013 ◽  
Vol 303-306 ◽  
pp. 2893-2897
Author(s):  
Yu Bin Wu ◽  
Bin Zhang ◽  
Ying Hua Liu ◽  
Xian Hui Li
Keyword(s):  
Field Measurement ◽  
Element Model ◽  
Vibration Response ◽  
Vibration Level ◽  
Running Speed ◽  
3D Finite Element ◽  
Vibration Effect ◽  
Pull Out ◽  
Calculation Results ◽  
Environmental Vibration

In recent years, more attention had paid to the vibration and noise influence on nearby building caused by passing trains. The metro depot superstructure is directly built above the train garage, the vibration of superstructure is very serious when the trains get into or go out of the garage. In order to investigate the law of vibration influence on metro depot and superstructure, a field measurement has been carried out and a 3D finite element model of building-platform-column is established. The attenuation law and degree of environmental vibration influence is obtained by analyzing the measurement date and calculation results. The results show that the vibration response of superstructure is obvious, the vibration level is related with the running state of train. The vibration response is more serious when trains pull out of the garage than go into garage, because the running speed is faster when trains pull out of garage. The vibration intensity does not monotonically increase or monotonically reduce with the increasing of floor and it tends to change wave upon wave with the increasing of floor.

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