Identification of natural frequencies and modal damping ratios from response data

1976 ◽  
Vol 60 (S1) ◽  
pp. S74-S74
Author(s):  
C. D. Michalopoulos
Keyword(s):  
Natural Frequencies ◽  
Response Data ◽  
Modal Damping

Vibrational characteristics of an earth dam

1966 ◽  
Vol 56 (6) ◽  
pp. 1207-1226
Author(s):  
W. O. Keightley
Keyword(s):  
Theoretical Analysis ◽  
Natural Frequencies ◽  
Forced Vibrations ◽  
Earth Dam ◽  
Mode Shapes ◽  
Modal Damping ◽  
Vibrational Characteristics ◽  
Good Agreement ◽  
Lower Frequencies

Abstract An earth dam was excited into vibrations, in the upstream-downstream direction, by four rotating eccentric-mass vibration generators which were operated on the crest. Natural frequencies, mode shapes, and equivalent viscous modal damping constants of the dam were revealed by the forced vibrations. A theoretical analysis of the dam, based on consideration of shearing deformations only, shows moderately good agreement with the behavior which was observed at the lower frequencies.

Torsional damping of a back-to-back gearbox rig: Experimental measurements and frequency domain modelling

2002 ◽  
Vol 216 (2) ◽  
pp. 157-168 ◽  
Author(s):  
S J Drew ◽  
B J Stone
Keyword(s):  
Frequency Domain ◽  
Natural Frequencies ◽  
Model Parameters ◽  
Modal Damping ◽  
Torsional Damping ◽  
Analysis Of Results ◽  
Torsional Frequency ◽  
Signal Processing Methods ◽  
Parameter Values ◽  
Future Work

This paper is concerned with the experimental measurement and modelling of the torsional damping levels of a back-to-back gearbox rig. The aims of the investigation were to experimentally measure and analyse modal damping levels for the first nine torsional natural frequencies; to optimize damping parameters for modelling and to assess any limitations of the models for future work. Standard signal processing methods were used to determine modal damping levels from measured torsional frequency responses, with good confidence in the results. A damping sensitivity analysis for the two frequency domain receptance (FDR) models was used to determine optimum damping parameter values. Damping levels for six of nine natural frequencies were well matched with the experimental data. Discrepancies at other frequencies were attributed mainly to torsional-transverse coupling, present in the rig but not the model. Analysis of results for the ninth natural frequency determined a very low level of damping for the gearbox. It was also concluded that the model parameters may be used with confidence in a time domain receptance model for future investigations related to the test gearbox damping.

Dynamic Testing and Analysis of Inflatable Beams

2012 ◽  
Vol 226-228 ◽  
pp. 546-552 ◽  
Author(s):  
Jian Zheng Wei ◽  
Hui Feng Tan ◽  
Jian Xin Yu ◽  
Xing Wen Du
Keyword(s):  
Thin Film ◽  
Internal Pressure ◽  
Dynamic Characteristics ◽  
Natural Frequencies ◽  
Dynamic Testing ◽  
Composite Fiber ◽  
Film Structure ◽  
The Self ◽  
Modal Damping ◽  
Local Stiffness

Dynamic testing of an inflatable beam has been performed to evaluate structural natural frequencies and modal damping ratios. The inflatable beam has a pattern of six composite fiber strips inside thin-film structure that increases its local stiffness that the structure can be self-supporting in the gravity environment when the internal pressure is released. A measurement setup was installed, and the dynamic testing was performed in this self-supporting state. Dynamic characters of the beams were tested with internal pressure or not when the beam had a 2.0kg mass on the top. Moreover, the dynamic characters before rolled up were contrasted to one after. The experimental results indicate that the self-supporting inflatable beams had better bending stiffness, and the curl folding process had an impact on the dynamic characteristics of the inflatable beam. The pressure affection is not obvious on dynamics of the beam.

Extending Blind Modal Identification to the Underdetermined Case for Ambient Vibration

2012 ◽  
Author(s):  
Scot McNeill
Keyword(s):  
Natural Frequencies ◽  
Second Order ◽  
Modal Identification ◽  
Ambient Vibration ◽  
Mode Shapes ◽  
Frequency Domain Method ◽  
Blind Identification ◽  
Vibration Data ◽  
Modal Damping ◽  
Six Dof

The modal identification framework known as Blind Modal Identification (BMID) has recently been developed, drawing on techniques from Blind Source Separation (BSS). Therein, a BSS algorithm known as Second Order Blind Identification (SOBI) was adapted to solve the Modal IDentification (MID) problem. One of the drawbacks of the technique is that the number of modes identified must be less than the number of sensors used to measure the vibration of the equipment or structure. In this paper, an extension of the BMID method is presented for the underdetermined case, where the number of sensors is less than the number of modes to be identified. The analytic signal formed from measured vibration data is formed and the Second Order Blind Identification of Underdetermined Mixtures (SOBIUM) algorithm is applied to estimate the complex-valued modes and modal response autocorrelation functions. The natural frequencies and modal damping ratios are then estimated from the corresponding modal auto spectral density functions using a simple Single Degree Of Freedom (SDOF), frequency-domain method. Theoretical limitations on the number of modes identified given the number of sensors are provided. The method is demonstrated using a simulated six DOF mass-spring-dashpot system excited by white noise, where displacement at four of the six DOF is measured. All six modes are successfully identified using data from only four sensors. The method is also applied to a more realistic simulation of ambient building vibration. Seven modes in the bandwidth of interest are successfully identified using acceleration data from only five DOF. In both examples, the identified modal parameters (natural frequencies, mode shapes, modal damping ratios) are compared to the analytical parameters and are demonstrated to be of good quality.

scholarly journals VARIATIONALLY-BASED EFFECTIVE DYNAMIC THICKNESS FOR LAMINATED GLASS BEAMS

2017 ◽  
Vol 13 ◽  
pp. 109
Author(s):  
Jaroslav Schmidt ◽  
Alena Zemanová ◽  
Tomáš Janda ◽  
Jan Zeman ◽  
Michal Šejnoha
Keyword(s):  
Mechanical Response ◽  
Natural Frequencies ◽  
Free Vibrations ◽  
Effective Thickness ◽  
Laminated Glass ◽  
New Approach ◽  
Acceptable Accuracy ◽  
Modal Damping ◽  
Effective Dynamic ◽  
Marine Engineering

Laminated glass, consisting of glass layers connected with transparent foils, has found its applications in civil, automotive, or marine engineering. Due to a high contrast in layer properties, mechanical response of laminated glass structures cannot be predicted using classical laminate theories. On the other hand, engineering applications demand easy-to-use formulas of acceptable accuracy. This contribution addresses such simplified models for free vibrations of laminated glass beams, with the goal to determine their natural frequencies and modal damping properties. Our strategy is to approximate the complex behavior of a laminated structure with that of an equivalent monolithic beam. Its effective thickness is determined by the variational method proposed by Galuppi and Royer-Carfagni for static problems, which we extended for modal analysis. We show that this new approach overcomes inaccuracies of the currently used dynamic effective thickness model by López-Aenlle and Pelayo.

Estimation of the dynamic properties of floors using Heel Drop Tests

2021 ◽  
Author(s):  
Mehdi Setareh ◽  
Jiang Li
Keyword(s):  
Dynamic Response ◽  
Natural Frequency ◽  
Natural Frequencies ◽  
Dynamic Properties ◽  
Accurate Estimate ◽  
Inexpensive Method ◽  
Structure Interaction ◽  
Modal Damping ◽  
Drop Tests ◽  
Interaction Phenomenon

<p>To evaluate the dynamic response of floors, it is important to estimate their dynamic properties, in particular natural frequencies and modal damping ratios. Heel drop test is a simple and inexpensive method of floor excitation to measure its dynamic properties. Even though this test can result in a relatively accurate estimate of the floor natural frequency, this may not be the case for the modal damping ratios. With the help of a number of volunteers, heel drop tests were conducted on a force platform placed on a test floor. The tests were also repeated using an instrumented hammer. The results showed that the measured natural frequency using heel drops was close to that found using the instrumented hammer. However, the modal damping ratios found using the heel drop tests were higher, which can be attributed to the human-structure interaction phenomenon.</p>

ARX Model Identification of Shui-Kou Concrete Gravity Dam Based on Seismic Response Data

2013 ◽  
Vol 353-356 ◽  
pp. 1959-1964
Author(s):  
Wen Qiao ◽  
Guo Ming Liu ◽  
Jin Wen He
Keyword(s):  
Seismic Response ◽  
Dynamic Characteristics ◽  
Natural Frequencies ◽  
Model Identification ◽  
Modal Identification ◽  
Gravity Dam ◽  
Concrete Gravity Dam ◽  
Arx Model ◽  
Response Data ◽  
Peak Point

Research on the dynamic characteristics of gravity dam was carried out by adopting ARX model using the seismic response data of concrete gravity dam at Shui-Kou hydropower station. The applicability and effectiveness of single-output-multiple-input ARX model were deduced and verified. A corresponding computer program was developed, and performed to identify the modal parameters of the system. The identified natural frequencies and damping ratios were basically same with the results by traditional peak point pick-up method, and also close to the finite element method (FEM) results. It is indicated that the structure natural frequencies and damping ratios are determined by the characteristics of the structure, the dynamic characteristics identified by ARX model are correct, and ARX model can avoid frequency leakiness when smoothing processing and Fourier transform are conducted in solving process of the peak point pick-up method. The modal identification can be applied to other structures.

On the Nature of Natural Control

1989 ◽  
Vol 111 (4) ◽  
pp. 412-422 ◽  
Author(s):  
L. Silverberg ◽  
M. Morton
Keyword(s):  
Control Systems ◽  
Structural Control ◽  
Natural Frequencies ◽  
Dynamic Performance ◽  
Natural Control ◽  
Space Truss ◽  
Natural Modes ◽  
Modal Damping ◽  
Modes Of Vibration ◽  
Control Forces

This paper examines families of structural control systems and reveals inherent properties that provide the essential motivation behind the theory of Natural Control. It is determined that the associated fuel consumed by the controls is near minimal when the natural frequencies are identical to the controlled modal frequencies, and when the natural modes of vibration are identical to the controlled modes of vibration. Also, by casting the objective to suppress vibration in the form of an exponential stability condition, it is found that vibration is most efficiently suppressed when the modal damping rates are identical to a designer chosen decay rate. The use of a limited number of control forces over distributed control is characterized by a change in fuel consumed by the controls and by a deterioration in the dynamic performance reflected by changes in the modal damping rates. The Natural Control of a space truss demonstrates the results.

Use of viscoelastic links for seismic pounding mitigation under random input

2019 ◽  
Vol 11 (3) ◽  
pp. 471-496
Author(s):  
Hamed Ahmadi Taleshian ◽  
Alireza Mirzagoltabar Roshan ◽  
Javad Vaseghi Amiri
Keyword(s):  
White Noise ◽  
Natural Frequencies ◽  
Dominant Frequency ◽  
Inelastic Behavior ◽  
Random Input ◽  
Content Type ◽  
Adjacent Buildings ◽  
Modal Damping ◽  
The Difference ◽  
Seismic Pounding

Purpose The purpose of this paper is to study the effects of viscoelastic links between two adjacent buildings for pounding mitigation under white-noise seismic input. Design/methodology/approach A formulation is first extracted for the effective modal damping ratios of the system. Then, two single DOF linear buildings connected by viscoelastic links are considered with both classical and non-classical damping schemes. The inelastic behavior is also taken into account by using equivalent natural frequencies and damping ratios of the buildings. The effect of ground dominant frequency and damping on the displacement response is also investigated by using Kanai‒Tajimi filtered white noise as the random input. Findings The difference between classical and non-classical damping is shown to be less than 20 percent, implying the permission in using the simpler classical damping scheme. Finally, the problem is extended to two-storey buildings, where using viscoelastic links only at the top story level of the buildings is shown to be sufficient for controlling individual, as well as relative, motions of the structures. Originality/value Results demonstrate that the use of link with a moderate stiffness may reduce the stiffer building displacement up to approximately 20 percent in comparison to the free displacement, while the seismic pounding of the adjacent buildings is effectively controlled. Further, an upper limit of link stiffness is obtained for preventing the increase in the stiffer building displacement, which may be exceeded by the minimum link stiffness necessary for pounding prevention if small gap size exists.

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