An Experiment to Identify the Structural Dynamics of a Portal Frame

1990 ◽  
Vol 112 (1) ◽  
pp. 78-83 ◽  
Author(s):  
J. E. Mottershead ◽  
T. K. Tee ◽  
C. D. Foster ◽  
R. Stanway
Keyword(s):  
Physical Parameters ◽  
Response Functions ◽  
Engineering Structures ◽  
Transmission Towers ◽  
Portal Frame ◽  
Engineering Problems ◽  
Measured Frequency Response ◽  
Frequency Domain Techniques ◽  
Stiffness And Damping ◽  
Sequential Frequency

This paper describes the application of sequential frequency domain techniques to the estimation of mass, stiffness, and damping parameters using measured frequency response functions from a portal frame rig. The theory of the method has been described in the authors’ previous publications. A portal frame is representative of many engineering structures. It is lightly damped and may be thought of as an element of several larger structures such as bridges, transmission towers, and the steel foundations of modern power generating plant. The results offered in this paper are thus of interest to a broad range of engineering problems where it is required to obtain mathematical models in terms of physical parameters.

Elimination of Multi-Points Support Effects in Modal Testing

2013 ◽  
Vol 290 ◽  
pp. 79-84
Author(s):  
Jun Ren ◽  
Shu Sheng Bi ◽  
Wei Wang ◽  
Guang Hua Zong
Keyword(s):  
Single Point ◽  
Noisy Data ◽  
Modal Testing ◽  
Response Functions ◽  
Support Effects ◽  
Modal Test ◽  
Measured Frequency Response ◽  
Support Conditions ◽  
Stiffness And Damping ◽  
Free Beam

The measured Frequency Response Functions (FRFs) often have errors due to the support effects in free-free modal testing. In [1], elimination of support effects from the measured FRFs has been investigated and both stiffness and damping have been considered in support conditions. However, the method is only applicable for single point support occasion while the test structure is usually supported from more than one location in a practical testing. Therefore, this paper further investigates this method to extend its application to multi-points support conditions. Firstly, general formulas of removing the multipoint support effects from the measured FRFs are derived based on the dynamic substructure method. Then a simulated modal test of free-free beam with two points suspension is proposed to verify this method. Finally, the performance of the method is investigated with simulated noisy data. It is shown that the proposed method is effective in removing support stiffness as well as support damping from the measured FRFs as long as the measured data are not heavily contaminated by the noise.

A method for vibration absorber tuning based on baseline frequency response functions

2007 ◽  
Vol 221 (9) ◽  
pp. 1071-1078 ◽  
Author(s):  
C Q Liu ◽  
C C Chang
Keyword(s):  
Frequency Response ◽  
Experimental Methods ◽  
Vibration Absorber ◽  
Physical Parameters ◽  
Primary System ◽  
Vibration Absorbers ◽  
Response Functions ◽  
Frequency Response Functions ◽  
Baseline Frequency ◽  
Stiffness And Damping

This paper presents explicit expressions for new frequency response functions (FRFs) of a primary system when a vibration absorber is attached to it. The new FRF is expressed in terms of the baseline (‘old’) FRFs of the primary system and the physical parameters (the mass, stiffness, and damping) of the vibration absorber. The baseline FRF of the primary system can be obtained by either analytical or experimental methods. This approach allows engineers and designers to evaluate a number of alternative vibration absorbers before these absorbers are physically implemented on the structure. Therefore a considerable amount of time and effort for engineers and designers can be saved. Several examples are provided to illustrate the use of the method.

Calculation of Component Mode Synthesis Matrices From Measured Frequency Response Functions, Part 2: Application

1998 ◽  
Vol 120 (2) ◽  
pp. 509-516 ◽  
Author(s):  
J. A. Morgan ◽  
C. Pierre ◽  
G. M. Hulbert
Keyword(s):  
Frequency Response ◽  
Coupled System ◽  
Companion Paper ◽  
Component Mode Synthesis ◽  
Response Functions ◽  
Frequency Response Functions ◽  
Measured Frequency ◽  
Measured Frequency Response ◽  
Coupled Beams ◽  
The Individual

This paper demonstrates how to calculate Craig-Bampton component mode synthesis matrices from measured frequency response functions. The procedure is based on a modified residual flexibility method, from which the Craig-Bampton CMS matrices are recovered, as presented in the companion paper, Part I (Morgan et al., 1998). A system of two coupled beams is analyzed using the experimentally-based method. The individual beams’ CMS matrices are calculated from measured frequency response functions. Then, the two beams are analytically coupled together using the test-derived matrices. Good agreement is obtained between the coupled system and the measured results.

Elimination of Support Effects in Modal Testing

2012 ◽  
Vol 226-228 ◽  
pp. 48-51
Author(s):  
Jun Ren ◽  
Shu Sheng Bi ◽  
Wei Wang ◽  
Guang Hua Zong
Keyword(s):  
Correction Method ◽  
Modal Testing ◽  
Mass Loading ◽  
Data Simulation ◽  
Support Effects ◽  
Loading Effects ◽  
Measured Frequency Response ◽  
Support Conditions ◽  
Stiffness And Damping ◽  
The Given

In modal testing, the measured Frequency Response Functions (FRFs) are often inaccurate due to the adverse mechanical effects, such as mass-loading effects of transducers, shaker-structure interaction and the support effects. This paper deals with the elimination of the support effects from measured FRFs using dynamic substructure method. Both stiffness and damping are considered in the support effects. The validity of the method is proved in a simulated modal test. It is shown that with the given support conditions the affected FRFs can be corrected provided that some additional FRFs concerned with the support point are also measured. Finally, performance of this method is assessed with noisy measured data. Simulation shows that 1% white noise is acceptable in the proposed correction method.

scholarly journals Diagnostics for spectropolarimetry and magnetography

2010 ◽  
Vol 6 (S273) ◽  
pp. 37-43
Author(s):  
Jose Carlos del Toro Iniesta ◽  
Valentín Martínez Pillet
Keyword(s):  
Analytical Approach ◽  
Spectral Lines ◽  
Physical Parameters ◽  
Instrumental Effects ◽  
Response Functions

AbstractAn assessment on the capabilities of modern spectropolarimeters and magnetographs is in order since most of our astrophysical results rely upon the accuracy of the instrumentation and on the sensitivity of the observables to variations of the sought physical parameters. A contribution to such an assessment will be presented in this talk where emphasis will be made on the use of the so-called response functions to gauge the probing capabilities of spectral lines and on an analytical approach to estimate the uncertainties in the results in terms of instrumental effects. The Imaging Magnetograph eXperiment (IMaX) and the Polarimetric and Helioseismic Imager (PHI) will be used as study cases.

Updating Rotor-Bearing Finite Element Models

1997 ◽  
Author(s):  
Cristinel Mares ◽  
Cecilia Surace
Keyword(s):  
Finite Element ◽  
Element Model ◽  
Parameters Estimation ◽  
Flexible Rotor ◽  
Estimation Errors ◽  
Rotor Bearing ◽  
Bearing Stiffness ◽  
Measured Frequency Response ◽  
Stiffness And Damping ◽  
The Finite Element Model

Abstract In this paper, the possibility of updating the finite element model of a rotor-bearing system by estimating the bearing stiffness and damping coefficients from a few measured Frequency Response Functions using a Genetic Algorithm is investigated. The issues of identifiability and parameters estimation errors, computational costs and algorithm tuning are addressed. A simulated example of a flexible rotor supported by orthotropic bearings is used for illustrating the method.

GEOPHYSICAL METHODS ADAPTED TO HIGHWAY ENGINEERING PROBLEMS

Geophysics ◽  
1952 ◽  
Vol 17 (3) ◽  
pp. 505-530 ◽  
Author(s):  
R. Woodward Moore
Keyword(s):  
Seismic Refraction ◽  
Geophysical Methods ◽  
Engineering Structures ◽  
Highway Engineering ◽  
Earth Resistivity ◽  
The Earth ◽  
Ore Bodies ◽  
Geophysical Surveys ◽  
Engineering Problems ◽  
Test Use

Of the several geophysical methods used in exploration for oil and useful ore bodies, the earth‐resistivity and seismic‐refraction tests have been found to be the most adaptable to the shallow tests generally required in highway construction work. Of these, the earth‐resistivity test is the faster and has a wider range of application to highway problems than does the seismic test. Use of both methods of tests in subsurface explorations for engineering structures is expanding. The paper cites a growing need for a more thorough subsurface investigation of all engineering structure sites and gives examples of field data obtained by the Bureau of Public Roads when making preliminary geophysical surveys of proposed highway locations or structure sites. The economic aspects and the advantages and limitations of the two methods of test are discussed with particular reference to their application to highway engineering problems.

Joint Parameters Identification of a Structure With Large Number of Discrete Joints

2003 ◽  
Author(s):  
J. H. Wang ◽  
S. C. Chuang
Keyword(s):  
Frequency Response ◽  
Dynamic Behavior ◽  
Error Function ◽  
Parameters Identification ◽  
New Method ◽  
Response Functions ◽  
Traditional Methods ◽  
Measured Frequency Response ◽  
Joint Parameters ◽  
Better Than

The joint parameters of a structure with a large number of discrete joints generally are very difficult to identify accurately. The difficulty is due to the fact that the dynamic behavior of a structure becomes more complex with more number of joints. A new identification method which uses the measured frequency response functions (FRFs) to identify the joint parameters is proposed in this work to overcome this difficulty. The new method uses an error function to select different best data to identify different joints so that the accuracy of the identification can be improved. The accuracy of the new method and other two traditional methods is compared in this work. The results show that the accuracy of the proposed new method is far better than other two previous methods. The proposed new method has special advantage when (1) the number of joints is large, (2) the orders of magnitude of the joint parameters are different significantly.

On Blade Damping Technology Using Passive Piezoelectric Dampers

2012 ◽  
Author(s):  
Sebastian M. Schwarzendahl ◽  
Jaroslaw Szwedowicz ◽  
Marcus Neubauer ◽  
Lars Panning ◽  
Jörg Wallaschek
Keyword(s):  
Mode Shape ◽  
Mechanical Strain ◽  
Piezoelectric Element ◽  
Measured Data ◽  
Experimental Investigations ◽  
Response Functions ◽  
Ambient Conditions ◽  
Optimal Position ◽  
Measured Frequency Response ◽  
Good Agreement

This paper deals with a new damping concept for turbine blade vibrations utilizing piezoelectric material. A passive piezo damper consists of a piezoelectric element and a passive electric network connected to its electrodes. The damping performance depends on the size and location of the piezoelectric element with respect to the mode shape of the mechanical strain. Numerical and experimental investigations are carried out on a rigidly clamped simplified compressor blade at stand still and ambient conditions. An optimization process incorporating electromechanical finite element calculations determines the optimal position of the piezo damper in regard to the mode shape of interest. By applying the computed and measured Frequency Response Functions, the damping performance with and without piezo-damper are compared and referred to the measured material damping. The obtained numerical results are in very good agreement with the measured data, leading to a promising damping performance in real application.

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