The Effect of an Electromagnetic Damper on Vibrations in Rotating Machinery

1991 ◽  
Author(s):  
M. E. F. Kasarda ◽  
P. E. Allaire ◽  
R. R. Humphris ◽  
E. J. Gunter
Keyword(s):  
Critical Speed ◽  
Rotating Machinery ◽  
Response Mode ◽  
Unbalanced Rotor ◽  
Stiffness Properties ◽  
Vibration Problems ◽  
Bending Modes ◽  
Stiffness And Damping ◽  
Mass Test ◽  
Electromagnetic Damper

Abstract Compressors, turbines and other rotating machines often have long thin shafts which may cause vibration problems. An electromagnetic damper placed on the rotor of a machine represents one method of controlling high levels of vibrations. This paper discusses experimental results of an electromagnetic damper placed on a small three mass test rotor. Experimental data was taken for cases with the damper at three different locations on the highly unbalanced rotor to study the effectiveness of the damper in controlling vibrations at the first and second rotor bending modes and at a pedestal response mode. Reductions of vibrations up to 88%, 40%, and 19% were achieved for the first critical speed, second critical speed, and pedestal response mode, respectively. Values of magnetic damper stiffness and damping used to obtain these reductions were only a small fraction of the fluid film bearing damping and stiffness properties.

scholarly journals Effect of Rotor Geometry on Bending Stiffness Variation

Machines ◽  
2021 ◽  
Vol 9 (2) ◽  
pp. 23
Author(s):  
Risto Viitala ◽  
Tuomas Tiainen ◽  
Raine Viitala
Keyword(s):  
Cross Sections ◽  
Critical Speed ◽  
Rotating Machinery ◽  
Bending Stiffness ◽  
Lateral Bending ◽  
Rotational Angle ◽  
Stiffness Variation ◽  
Vibration Problems

Bending stiffness variation (BSV) is a common problem causing vibration in large rotating machinery. BSV describes lateral bending stiffness and its variation as a function of the rotational angle. It has been observed that BSV causes excitation exactly twice per revolution, which leads to vibration problems, especially at half critical speed. BSV is caused by rotor geometry errors if the material is assumed to be homogeneous and linearly elastic. Therefore, the study investigated BSV with harmonic roundness components, which are commonly used in industry to describe the geometry of a rotor. Hence, the results are easily applicable in the industry. The research was conducted primarily by analytical means, but also static simulations and numeric calculations were used. The results clearly showed that when the effect of single harmonic roundness components in rotor cross-sections were observed, only the second component could produce BSV. However, when component pairs were studied, they produced BSV also without the second component. If the second component was included, the profile produced BSV the most aggressively. A generated arbitrary roundness profile, including components 3–50 with random phases and amplitudes, indicated that BSV occurs always twice per revolution despite different components in the profile. The results improve the possibilities of eliminating excessive BSV in the industry, when certain components and component pairs can be avoided.

Rotordynamic Performance of a Rotor Supported on Bump Type Foil Gas Bearings: Experiments and Predictions

2006 ◽  
Vol 129 (3) ◽  
pp. 850-857 ◽  
Author(s):  
Luis San Andrés ◽  
Dario Rubio ◽  
Tae Ho Kim
Keyword(s):  
High Speed ◽  
Critical Speed ◽  
Load Capacity ◽  
Test System ◽  
Foil Bearings ◽  
Rotor Imbalance ◽  
Synchronous Motion ◽  
Damping Characteristics ◽  
Rotor Surface ◽  
Stiffness And Damping

Gas foil bearings (GFBs) satisfy the requirements for oil-free turbomachinery, i.e., simple construction and ensuring low drag friction and reliable high speed operation. However, GFBs have a limited load capacity and minimal damping, as well as frequency and amplitude dependent stiffness and damping characteristics. This paper provides experimental results of the rotordynamic performance of a small rotor supported on two bump-type GFBs of length and diameter equal to 38.10mm. Coast down rotor responses from 25krpm to rest are recorded for various imbalance conditions and increasing air feed pressures. The peak amplitudes of rotor synchronous motion at the system critical speed are not proportional to the imbalance introduced. Furthermore, for the largest imbalance, the test system shows subsynchronous motions from 20.5krpm to 15krpm with a whirl frequency at ∼50% of shaft speed. Rotor imbalance exacerbates the severity of subsynchronous motions, thus denoting a forced nonlinearity in the GFBs. The rotor dynamic analysis with calculated GFB force coefficients predicts a critical speed at 8.5krpm, as in the experiments; and importantly enough, unstable operation in the same speed range as the test results for the largest imbalance. Predicted imbalance responses do not agree with the rotor measurements while crossing the critical speed, except for the lowest imbalance case. Gas pressurization through the bearings’ side ameliorates rotor subsynchronous motions and reduces the peak amplitudes at the critical speed. Posttest inspection reveal wear spots on the top foils and rotor surface.

Internal Rotor Friction Induced Instability in High-Speed Rotating Machinery

1993 ◽  
Author(s):  
James F. Walton ◽  
Michael R. Martin
Keyword(s):  
Internal Friction ◽  
Natural Frequency ◽  
High Speed ◽  
Critical Speed ◽  
Rotating Machinery ◽  
Rotor System ◽  
Analytical Models ◽  
Interference Fit ◽  
Internal Rotor

Abstract Results of a program to investigate internal rotor friction destabilizing effects are presented. Internal-friction-producing joints were shown to excite the rotor system first natural frequency, when operating either below or above the first critical speed. The analytical models used to predict the subsynchronous instability were also confirmed. The axial spline joint demonstrated the most severe subsynchronous instability. The interference fit joint also caused subsynchronous vibrations at the first natural frequency but these were bounded and generally smaller than the synchronous vibrations. Comparison of data from the two test joints showed that supersynchronous vibration amplitudes at the first natural frequency were generally larger for the interference fit joint than for the axial spline joint. The effects of changes in imbalance levels and side loads were not distinguishable during testing because amplitude-limiting bumpers were required to restrict orbits.

Rotordynamics Analysis: Experimental and Numerical Investigations

2003 ◽  
Author(s):  
Jean-Jacques Sinou ◽  
David Demailly ◽  
Cristiano Villa ◽  
Fabrice Thouverez ◽  
Michel Massenzio ◽  
...  
Keyword(s):  
Finite Element ◽  
Finite Element Model ◽  
Critical Speed ◽  
Experimental Tests ◽  
Element Model ◽  
Test Rig ◽  
Turbofan Engine ◽  
Rotating Structure ◽  
Vibration Problems ◽  
The Finite Element Model

This paper presents a research devoted to the study of vibration problems in turbofan application. Several numerical and experimental tools have been developed. An experimental test rig that simulates the vibrational behavior of a turbofan engine is presented. Moreover, a finite element model is used in order to predict the non-linear dynamic behavior of rotating machines and to predict the first critical speed of engineering machine. A comparison between the experimental tests and the numerical model is conducted in order to evaluate the critical speed of the rotating structure and to update the finite element model.

More Comprehensive Vibration Limits for Rotating Machinery

1986 ◽  
Vol 108 (4) ◽  
pp. 583-590 ◽  
Author(s):  
A. Lifshits ◽  
H. R. Simmons ◽  
A. J. Smalley
Keyword(s):  
Failure Mechanisms ◽  
Field Studies ◽  
Rotating Machinery ◽  
Machine Design ◽  
Correction Factors ◽  
Vibration Measurements ◽  
Bearing Clearance ◽  
Actual Operating ◽  
Vibration Problems ◽  
Rotating Equipment

Vibrations are often found to be the cause of rotating machinery failures. To minimize these outages a large number of vibration criteria have been introduced by technical societies, equipment manufacturers, and experienced individuals. While useful, these vibration criteria have often been found to be contradictory and restricted to particular transducer types, machine design, or failure mechanisms. Based on this work and adding the experience accumulated by SwRI with various types of rotating equipment, more comprehensive combined vibration severity limits are established. These limits are divided into several severity regions, and cover filtered and unfiltered vibration. The appropriate correction factors are also introduced to equitably accommodate different machine designs, installations, and vibration problems. Vibration severity limits are provided for relative shaft displacement, for shaft displacement with respect to bearing clearance, and for vibration measurements taken on machine casing or bearing housing. The use of these limits is clarified by reviewing the results obtained from five field studies of actual operating equipment. Advantages, disadvantages, and use of various transducer types (proximity probes, velocity pickups, accelerometers, dual probes), as well as sources of machinery vibration (subsynchronous instabilities, resonance, imbalance, misalignment, etc.) are analyzed to assure proper application of the vibration limits.

Deceleration of an Unbalanced Rotor Through a Critical Speed

1967 ◽  
Vol 89 (4) ◽  
pp. 582-585
Author(s):  
W. K. Bodger
Keyword(s):  
Critical Speed ◽  
Degree Of Freedom ◽  
Bending Stress ◽  
Rotor Speed ◽  
Single Degree Of Freedom ◽  
Closed Solution ◽  
Rotor Shaft ◽  
Single Degree ◽  
Unbalanced Rotor ◽  
Maximum Increment

The problem of a single-degree-of-freedom rotor decelerating slowly through its critica speed is solved by an energy approach; a closed solution is obtained. A small discontinuous downward jump of rotor speed across the critical speed is shown to be required, either with or without damping in the system. The maximum increment of deflection, hence bending stress, in the rotor shaft is shown to be small, provided the rotor is carefully balanced and/or the system is sufficiently damped.

Successful Vibration Trouble-Shooting of Large Power Plant Rotating Machinery

2005 ◽  
Author(s):  
Maurice L. Adams ◽  
Michael L. Adams
Keyword(s):  
Power Plant ◽  
Computer Modeling ◽  
Case Studies ◽  
Specific Problem ◽  
Rotating Machinery ◽  
Feed Water ◽  
Large Power ◽  
Trouble Shooting ◽  
Vibration Problems ◽  
Water Pumps

This paper presents several recent case studies where the application of cutting-edge measurement and computer modeling have been successfully combined to correctly diagnose and fix power plant rotating machinery excessive vibration problems. These case studies include large turbogenerators and feed water pumps. Each case presented here shows an overall trouble-shooting strategy appropriate to the specific problem symptoms, and describes the measurement and computer modeling phases that successfully resolved the specific problem in each case.

scholarly journals A Magnetic Damper for First Mode Vibration Reduction in Multimass Flexible Rotors

1989 ◽  
Author(s):  
M. E. F. Kasarda ◽  
P. E. Allaire ◽  
R. R. Humphris ◽  
L. E. Barrett
Keyword(s):  
Vibration Reduction ◽  
Working Fluid ◽  
Test Rig ◽  
Flexible Rotors ◽  
Fluid Environment ◽  
Bearing Stiffness ◽  
Mode Vibration ◽  
Vibration Problems ◽  
Set Up ◽  
Stiffness And Damping

Many rotating machines such as compressors, turbines and pumps have long thin shafts with resulting vibration problems. They would benefit from additional damping near the center of the shaft. Magnetic dampers have the potential to be employed in these machines because they can operate in the working fluid environment unlike conventional bearings. This paper describes an experimental test rig which was set up with a long thin shaft and several masses to represent a flexible shaft machine. An active magnetic damper was placed in three locations: near the midspan, near one end disk, and close to the bearing. With typical control parameter settings, the midspan location reduced the first mode vibration 82%, the disk location reduced it 75% and the bearing location attained a 74% reduction. Magnetic damper stiffness and damping values used to obtain these reductions were only a few percent of the bearing stiffness and damping values. A theoretical model of both the rotor and the damper was developed and compared to the measured results. The agreement was good.

scholarly journals Suppression of Self-Excited Vibrations in Rotating Machinery Utilizing Leaf Springs

2019 ◽  
pp. 599-608
Author(s):  
Chang Wang ◽  
Jun Liu ◽  
Zhiwei Luo
Keyword(s):  
Dry Friction ◽  
Critical Speed ◽  
Rotating Machinery ◽  
The Self ◽  
Internal Damping ◽  
Structural Damping ◽  
Leaf Springs ◽  
Excited Vibration ◽  
Hysteretic Damping ◽  
Theoretical Analyses

When rotating machinery is operated above the major critical speed, self-excited vibrations appear due to internal friction of the shaft. Internal frictions are classified into hysteretic damping due to the friction in the shaft material and structural damping due to the dry friction between the shaft and the mounted elements. In this paper, a method to suppress the self-excited vibration using leaf springs are proposed. The structural damping is considered as the internal damping. The characteristics of a rotor with leaf springs are investigated systematically by using simulative and theoretical analyses. The validity of the proposed method is also proved by experiments.

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