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Effects of Shaker Impedance and Transducer Cross-Axis Sensitivity in Frequency Response Function Estimation

Hassan Pour Dargah, Mahmoud
http://rave.ohiolink.edu/etdc/view?acc_num=ucin1342729500

Abstract Details

2012, MS, University of Cincinnati, Engineering and Applied Science: Mechanical Engineering.
This study investigates the interaction of the shakers and structures in structural measurements and the how the transducers and stingers can affect the measurements and estimations. The instrumental variable frequency response function (FRF) algorithm is first used to see if this estimation algorithm is capable of removing the shaker effects from the measurements, which was not successful. The force transmissibility function in different setups was analytically formulated and it is shown that the force drop-out is due to two reasons: The use of voltage-controlled shaker amplifiers and the resonating frequency of the structure itself. Equations that were derived to explain the force transmissibility function show that the major parameters affecting the force level transmitted to the structure is the shaker impedance, frequency of interest and the structure’s response in that frequency. It was observed that for a single degree of freedom system, the drop out occurs exactly at the resonating frequency of structure. For multiple degree of freedom systems, the same governing equations are at play but when excited by more than one shaker, other parameters such as response at each DOF and the level of the force transmitted at each shaker connection are also at play. Experimental results on a circular plate (C-Plate) reinforces the findings in the theory and it is shown that the low cost, prototype, pancake shakers are not able to transfer force to the structure at higher frequencies due to their higher impedance. The stinger effects were also studied and it is shown experimentally that the stinger material and dimension can also affect the force transmissibility. The nylon stingers undergo resonance when tested on a stiff, H shaped test structure (H-Frame) and are not able to transfer enough force at higher frequencies. The metallic stingers on the other hand do not experience any resonances in the same frequency band and they are able to transfer force up to higher frequencies. Finally the effect of the transducers on the measurements was studied on the H-Frame and it is observed that the type of transducer will also introduce some abnormalities in the measurements. It is shown, that the impedance heads are not the best choice for structural measurements, based upon the structures evaluated, and better results can be obtained by using separate force and acceleration transducers.
Randall Allemang, PhD (Committee Chair)
David Brown, PhD (Committee Member)
Allyn Phillips, PhD (Committee Member)
116 p.
Engineering
Force transmissibility; Shaker/structure interaction; cross-axis sensitivity; Stinger; ; ;

Recommended Citations

Citations

  • Hassan Pour Dargah, M. (2012). Effects of Shaker Impedance and Transducer Cross-Axis Sensitivity in Frequency Response Function Estimation [Master's thesis, University of Cincinnati]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1342729500

    APA Style (7th edition)

  • Hassan Pour Dargah, Mahmoud. Effects of Shaker Impedance and Transducer Cross-Axis Sensitivity in Frequency Response Function Estimation. 2012. University of Cincinnati, Master's thesis. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=ucin1342729500.

    MLA Style (8th edition)

  • Hassan Pour Dargah, Mahmoud. "Effects of Shaker Impedance and Transducer Cross-Axis Sensitivity in Frequency Response Function Estimation." Master's thesis, University of Cincinnati, 2012. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1342729500

    Chicago Manual of Style (17th edition)

ucin1342729500
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© 2012, all rights reserved.
This open access ETD is published by University of Cincinnati and OhioLINK.
Release 3.2.12