Damping Ratio Estimation Techniques for Rotordynamic Stability Measurements

2008 ◽  
Vol 131 (1) ◽  
Author(s):  
C. Hunter Cloud ◽  
Eric H. Maslen ◽  
Lloyd E. Barrett
Keyword(s):  
Complex Systems ◽  
Damping Ratio ◽  
Ratio Estimation ◽  
Single Degree Of Freedom ◽  
Estimation Techniques ◽  
Single Degree ◽  
Modal Damping ◽  
Alternative Approach ◽  
Measurement Setting ◽  
Stability Measurements

Rotor stability is most commonly estimated using methods derived from a simple single degree of freedom system. When the modes of more complex systems, such as rotors, are closely spaced, we demonstrate that such methods can yield very poor estimates of the modal stability (damping ratio). Multiple output backward autoregression (MOBAR) is proposed as an alternative approach and is demonstrated to yield reasonably accurate estimates of modal damping even when modes are closely spaced. The performance of the MOBAR approach is then examined on an experimental rotor in tilt-pad bearings, demonstrating good performance in a realistic measurement setting.

Damping Ratio Estimation Techniques for Rotordynamic Stability Measurements

2008 ◽  
Author(s):  
C. Hunter Cloud ◽  
Eric H. Maslen ◽  
Lloyd E. Barrett
Keyword(s):  
Complex Systems ◽  
Damping Ratio ◽  
Ratio Estimation ◽  
Single Degree Of Freedom ◽  
Estimation Techniques ◽  
Single Degree ◽  
Modal Damping ◽  
Alternative Approach ◽  
Measurement Setting ◽  
Stability Measurements

Rotor stability is most commonly estimated using methods derived from a simple, single degree of freedom (SDOF) system. When the modes of more complex systems, such as rotors, are closely spaced, we demonstrate that such methods can yield very poor estimates of the modal stability (damping ratio). Multiple output backward autoregression (MOBAR) is proposed as an alternative approach and is demonstrated to yield reasonably accurate estimates of modal damping even when modes are closely spaced. The performance of the MOBAR approach is then examined on an experimental rotor in tilt-pad bearings, demonstrating good performance in a realistic measurement setting.

Forced Vibration of a Base-Excited Single-Degree-of-Freedom System With Coulomb Friction

1984 ◽  
Vol 106 (4) ◽  
pp. 280-285 ◽  
Author(s):  
Etsuo Marui ◽  
Shinobu Kato
Keyword(s):  
Friction Force ◽  
Coulomb Friction ◽  
Damping Ratio ◽  
Force Frequency ◽  
Vibratory System ◽  
Single Degree Of Freedom ◽  
Analytical Technique ◽  
Single Degree ◽  
Dimensional Parameters ◽  
Coulomb Friction Force

Using the “stopping region of motion” concept, a brief analytical technique is worked out for the behavior of the linear forced vibratory system under the influence of a Coulomb friction force. The following points are clarified by the above technique: 1. The behavior of the system is completely determined by the three non-dimensional parameters of nondimensional friction force, frequency ratio and damping ratio. 2. The vibratory system undergoes a periodic vibration with stopping periods when the mass cannot move. These stopping periods increase at lower exciting frequencies, owing to Coulomb friction. 3. The relation between the kind of motion occurring in the system and the above three parameters can be obtained theoretically and verified experimentally.

Analysis of Frequency and Damping Ratio on the Shock Isolation Efficiency

2013 ◽  
Vol 791-793 ◽  
pp. 835-838
Author(s):  
Shi Jie Wu ◽  
Lin He ◽  
Xi Zhi Zhao
Keyword(s):  
Damping Ratio ◽  
Relative Displacement ◽  
Displacement Amplitude ◽  
Vibration Isolator ◽  
Isolation System ◽  
Single Degree Of Freedom ◽  
Absolute Acceleration ◽  
Single Degree ◽  
Acceleration Amplitude ◽  
Shock Isolation

The traditional shock isolation system is only designed in stiffness regardless of damping, which causes acute contradiction between absolute acceleration amplitude and relative displacement amplitude. Based on the single degree of freedom negative shock isolation system, numerical analysis demonstrates that relative little amplitude of absolute acceleration and relative displacement could be attained within a certain range of damping and frequency ratio. Selecting appropriate damping and stiffness of vibration isolator can resolve contradiction between absolute acceleration amplitude and relative displacement amplitude and consequently improve shock isolation efficiency.

scholarly journals Development of equivalent linear systems for single-degree-of-freedom structures with magneto-rheological dampers for seismic design application

2017 ◽  
Vol 28 (19) ◽  
pp. 2675-2687 ◽  
Author(s):  
Yunbyeong Chae ◽  
James M Ricles ◽  
Richard Sause
Keyword(s):  
Response Spectrum ◽  
Damping Ratio ◽  
Time History ◽  
Analysis Procedure ◽  
Degree Of Freedom ◽  
Single Degree Of Freedom ◽  
Single Degree ◽  
Design Response Spectrum ◽  
Simplified Analysis ◽  
Magneto Rheological

Numerous studies have been conducted for magneto-rheological dampers, but the application of magneto-rheological dampers in seismic design is limited due to the lack of a systematical design procedure. In this article, a simplified analysis procedure is proposed to estimate the response of a single-degree-of-freedom structure with diagonal bracing and a magneto-rheological damper without performing the time history analysis. The proposed simplified analysis procedure is based on the equivalent linear system of a magneto-rheological damper. The equivalent damping ratio and the effective period of the single-degree-of-freedom system are determined from the loss factor and the effective stiffness of the magneto-rheological damper based on the quasi-static model. Design response spectrum is utilized to calculate the displacement of the single-degree-of-freedom system. The equivalent damping ratio and the effective stiffness of the single-degree-of-freedom system are dependent on the displacement of the system; thus, the proposed procedure is iterated until the displacement from the design response spectrum converges. The accuracy of the simplified analysis procedure is evaluated by comparing the estimated response from this procedure with the response from the time history analysis. The results show a good agreement between two methods, demonstrating the robustness of the proposed simplified analysis procedure.

Application of Viscous and Iwan Modal Damping Models to Experimental Measurements From Bolted Structures

2013 ◽  
Author(s):  
Brandon J. Deaner ◽  
Matthew S. Allen ◽  
Michael J. Starr ◽  
Daniel J. Segalman
Keyword(s):  
Nonlinear Damping ◽  
Beam Structure ◽  
Single Degree Of Freedom ◽  
Free Boundary Conditions ◽  
Mechanical Joints ◽  
Single Degree ◽  
Mechanical Joint ◽  
Damped System ◽  
Modal Damping ◽  
Nonlinear Mechanical

Measurements are presented from a two-beam structure with several bolted interfaces in order to characterize the nonlinear damping introduced by the joints. The measurements (at force levels below macro-slip) reveal that each underlying mode of the structure is well approximated by a single degree-of-freedom system with a nonlinear mechanical joint. At low enough force levels the measurements show dissipation that scales as the second power of the applied force, agreeing with theory for a linear viscously damped system. This is attributed to linear viscous behavior of the material and/or damping provided by the support structure, which simulates free-free boundary conditions. At larger force levels the damping is observed to behave nonlinearly, suggesting that damping from the mechanical joints is dominant. A model is presented that captures these effects, consisting of a spring and viscous damping element in parallel with a 4-Parameter Iwan model. The parameters of this model are identified for each mode of the structure and comparisons suggest that the model captures the linear and nonlinear damping accurately over a range of forcing levels.

Application of Viscous and Iwan Modal Damping Models to Experimental Measurements From Bolted Structures

2015 ◽  
Vol 137 (2) ◽  
Author(s):  
Brandon J. Deaner ◽  
Matthew S. Allen ◽  
Michael J. Starr ◽  
Daniel J. Segalman ◽  
Hartono Sumali
Keyword(s):  
Nonlinear Damping ◽  
Beam Structure ◽  
Single Degree Of Freedom ◽  
Mechanical Joints ◽  
Single Degree ◽  
Mechanical Joint ◽  
Damped System ◽  
Modal Damping ◽  
Nonlinear Mechanical ◽  
Stiffness And Damping

Measurements are presented from a two-beam structure with several bolted interfaces in order to characterize the nonlinear damping introduced by the joints. The measurements (all at force levels below macroslip) reveal that each underlying mode of the structure is well approximated by a single degree-of-freedom (SDOF) system with a nonlinear mechanical joint. At low enough force levels, the measurements show dissipation that scales as the second power of the applied force, agreeing with theory for a linear viscously damped system. This is attributed to linear viscous behavior of the material and/or damping provided by the support structure. At larger force levels, the damping is observed to behave nonlinearly, suggesting that damping from the mechanical joints is dominant. A model is presented that captures these effects, consisting of a spring and viscous damping element in parallel with a four-parameter Iwan model. The parameters of this model are identified for each mode of the structure and comparisons suggest that the model captures the stiffness and damping accurately over a range of forcing levels.

scholarly journals Design of Anti-Parallelogram Loop Assemblies

2019 ◽  
Vol 60 (3) ◽  
pp. 232-240
Author(s):  
Şebnem Gür ◽  
Koray Korkmaz ◽  
Gökhan Kiper
Keyword(s):  
Degree Of Freedom ◽  
Single Degree Of Freedom ◽  
Single Degree ◽  
Assembly Method ◽  
Design Alternatives ◽  
Alternative Approach ◽  
The Subject ◽  
Planar Linkages ◽  
Symmetry Operations ◽  
Selection Of

Scissor mechanisms are frequently used for deployable structures and many studies have been conducted on the subject. Most of the studies consider scissor units as modules in the design process. An alternative approach is to utilize loops as the modules for design. In this paper, the design alternatives of single degree-of-freedom planar linkages comprising anti-parallelogram loops using the loop assembly method is presented. First, scissor mechanisms are reviewed. Next, the types of four-bar loops and the resulting linkages in the literature are introduced and those which are yet to be explored, anti-parallelogram being one of them, are identified. Then the loop assembly method and the examples in the literature are reviewed. As a method to form as many alternatives as possible, symmetry operations are proposed. Suitable frieze symmetry groups utilized for obtaining the assemblies are explained and the anti-parallelogram loop patterns are derived. Next, the single degree-of-freedom linkages are obtained from the loop assemblies. Finally, a selection of the resulting linkages with novel properties are presented. This study shows that loop assemblies are efficient in systematic type synthesis of scissor linkages, some types of which could not be foreseen by using units as modules.

Exact Evaluation of Natural Frequency and Damping Ratio from a Frequency Response Curve

2000 ◽  
Vol 123 (3) ◽  
pp. 403-405 ◽  
Author(s):  
M. V. Drexel ◽  
J. H. Ginsberg
Keyword(s):  
Frequency Response ◽  
Natural Frequency ◽  
Damping Ratio ◽  
Fundamental Property ◽  
Response Curves ◽  
Single Degree Of Freedom ◽  
Analysis Techniques ◽  
Modal Damping ◽  
Exact Evaluation ◽  
Simple Characteristic

Several experimental modal analysis techniques fit resonance peaks to the response curves of a single degree of freedom system in order to identify the natural frequencies and modal damping ratios. The present study identifies a fundamental property of frequency response curves that allows the natural frequency to be identified from a simple characteristic of the curve, independently of the damping ratio. After the natural frequency has been determined, the damping ratio can be computed directly. The fundamental property holds for all values of damping, which eliminates the need to approximate either the natural frequency or damping ratio.

Optimum Design of a New Tuned Inerter Mass Damper (TIMD) Passive Vibration Control for Stochastically Motion-Excited Structures

2019 ◽  
Author(s):  
Wei-Che Tai
Keyword(s):  
Vibration Control ◽  
Damping Ratio ◽  
Degree Of Freedom ◽  
Rotational Inertia ◽  
Single Degree Of Freedom ◽  
Single Degree ◽  
Tuning Ratio ◽  
Mass Damper ◽  
Two Degree Of Freedom ◽  
H2 Optimization

Abstract The inerter that is referred to as a two-terminal device that provides resisting forces proportional to the relative accelerations between its two terminals has been widely applied in vibration control due to its mass amplification effect. In this paper, a new inerter-based damper is proposed to take advantage of the inerter, which consists of a rack-pinion inerter in conjunction with a tuned rotational inertia damper. Unlike any other inerter-based dampers, the rotational inertia damper is connected to the pinion of the inerter via a rotational spring and damper. As a result, the weight of the damper can be significantly reduced. The proposed damper is applied to single-degree-of-freedom primary structures and a two-degree-of-freedom structure and the H2 optimization is conducted to obtain the optimum tuning ratio and damping ratio analytically. When comparing the proposed damper with its counterpart reported in the literature, the proposed damper achieves 20% to 70% improvement when their weights are identical.

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