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Damping Estimation from Free Decay Responses of Cables with MR Dampers.

Weber F, Distl H - ScientificWorldJournal (2015)

Bottom Line: This paper discusses the damping measurements on cables with real-time controlled MR dampers that were performed on a laboratory scale single strand cable and on cables of the Sutong Bridge, China.The control approach aims at producing amplitude and frequency independent cable damping which is confirmed by the tests.The experimentally obtained cable damping in comparison to the theoretical value due to optimal linear viscous damping reveals that support conditions of the cable anchors, force tracking errors in the actual MR damper force, energy spillover to higher modes, and excitation and sensor cables hanging on the stay cable must be taken into consideration for the interpretation of the identified cable damping values.

View Article: PubMed Central - PubMed

Affiliation: Structural Engineering Research Laboratory, Swiss Federal Laboratories for Materials Science and Technology (Empa), Überlandstrasse 129, 8600 Dübendorf, Switzerland.

ABSTRACT
This paper discusses the damping measurements on cables with real-time controlled MR dampers that were performed on a laboratory scale single strand cable and on cables of the Sutong Bridge, China. The control approach aims at producing amplitude and frequency independent cable damping which is confirmed by the tests. The experimentally obtained cable damping in comparison to the theoretical value due to optimal linear viscous damping reveals that support conditions of the cable anchors, force tracking errors in the actual MR damper force, energy spillover to higher modes, and excitation and sensor cables hanging on the stay cable must be taken into consideration for the interpretation of the identified cable damping values.

No MeSH data available.


Related in: MedlinePlus

Free decay test of mode 3 with CEC controlled MR damper (a); PSDs of unfiltered and bandpass filtered cable accelerations (b).
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fig15: Free decay test of mode 3 with CEC controlled MR damper (a); PSDs of unfiltered and bandpass filtered cable accelerations (b).

Mentions: The excitation of mode 1 turned out to be impossible because the excitation of mode 1 requires elongating the cord length of the cable for which the two men powered excitation force was too small [51]. Modes 2 and 3 could be excited to sufficient large amplitudes which evoked imract > 0 A in the MR damper due to the CEC approach as seen from Figures 14(a) and 15(a). As seen from Figures 14(b) and 15(b), when the cable was excited by the steel wire at the pace of mode 2 (0.497 Hz), also modes 4, 6, 8, and so forth were excited because the time period of mode 2 is a multiple of the time periods of these modes. Similarly, the excitation of the cable at the pace of mode 3 (0.749 Hz) also triggered modes 6, 9, 12, and so forth since the time period of mode 3 is a multiple of the time periods of these modes. The undesired excitation of these higher harmonics evokes additional local peaks in the free decay responses of the targeted modes, that is, modes 2 and 3. In order to be able to estimate the damping of the targeted modes from the free decay curve by the logarithmic decrement method, the raw data must therefore be filtered for the targeted modal component. The applied filter is a Butterworth filter of order 6 where the lower and upper cut-off frequencies are selected as the frequency of the targeted mode ±0.12 Hz to generate a sharp filter. The PSDs of the bandpass filtered accelerations shown in Figures 14(b) and 15(b) prove that this sharp filter design leads to a stable filter, the filtered signal only includes the modal component of interest, and its magnitude is hardly attenuated. Thus, the time records in Figures 14 and 15 show the true acceleration amplitudes of modes 2 and 3, respectively. The mean logarithmic decrement of the cable is then determined from the exponential fit of the peaks of the bandpass filtered cable acceleration during the free decay phase.


Damping Estimation from Free Decay Responses of Cables with MR Dampers.

Weber F, Distl H - ScientificWorldJournal (2015)

Free decay test of mode 3 with CEC controlled MR damper (a); PSDs of unfiltered and bandpass filtered cable accelerations (b).
© Copyright Policy - open-access
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC4488159&req=5

fig15: Free decay test of mode 3 with CEC controlled MR damper (a); PSDs of unfiltered and bandpass filtered cable accelerations (b).
Mentions: The excitation of mode 1 turned out to be impossible because the excitation of mode 1 requires elongating the cord length of the cable for which the two men powered excitation force was too small [51]. Modes 2 and 3 could be excited to sufficient large amplitudes which evoked imract > 0 A in the MR damper due to the CEC approach as seen from Figures 14(a) and 15(a). As seen from Figures 14(b) and 15(b), when the cable was excited by the steel wire at the pace of mode 2 (0.497 Hz), also modes 4, 6, 8, and so forth were excited because the time period of mode 2 is a multiple of the time periods of these modes. Similarly, the excitation of the cable at the pace of mode 3 (0.749 Hz) also triggered modes 6, 9, 12, and so forth since the time period of mode 3 is a multiple of the time periods of these modes. The undesired excitation of these higher harmonics evokes additional local peaks in the free decay responses of the targeted modes, that is, modes 2 and 3. In order to be able to estimate the damping of the targeted modes from the free decay curve by the logarithmic decrement method, the raw data must therefore be filtered for the targeted modal component. The applied filter is a Butterworth filter of order 6 where the lower and upper cut-off frequencies are selected as the frequency of the targeted mode ±0.12 Hz to generate a sharp filter. The PSDs of the bandpass filtered accelerations shown in Figures 14(b) and 15(b) prove that this sharp filter design leads to a stable filter, the filtered signal only includes the modal component of interest, and its magnitude is hardly attenuated. Thus, the time records in Figures 14 and 15 show the true acceleration amplitudes of modes 2 and 3, respectively. The mean logarithmic decrement of the cable is then determined from the exponential fit of the peaks of the bandpass filtered cable acceleration during the free decay phase.

Bottom Line: This paper discusses the damping measurements on cables with real-time controlled MR dampers that were performed on a laboratory scale single strand cable and on cables of the Sutong Bridge, China.The control approach aims at producing amplitude and frequency independent cable damping which is confirmed by the tests.The experimentally obtained cable damping in comparison to the theoretical value due to optimal linear viscous damping reveals that support conditions of the cable anchors, force tracking errors in the actual MR damper force, energy spillover to higher modes, and excitation and sensor cables hanging on the stay cable must be taken into consideration for the interpretation of the identified cable damping values.

View Article: PubMed Central - PubMed

Affiliation: Structural Engineering Research Laboratory, Swiss Federal Laboratories for Materials Science and Technology (Empa), Überlandstrasse 129, 8600 Dübendorf, Switzerland.

ABSTRACT
This paper discusses the damping measurements on cables with real-time controlled MR dampers that were performed on a laboratory scale single strand cable and on cables of the Sutong Bridge, China. The control approach aims at producing amplitude and frequency independent cable damping which is confirmed by the tests. The experimentally obtained cable damping in comparison to the theoretical value due to optimal linear viscous damping reveals that support conditions of the cable anchors, force tracking errors in the actual MR damper force, energy spillover to higher modes, and excitation and sensor cables hanging on the stay cable must be taken into consideration for the interpretation of the identified cable damping values.

No MeSH data available.


Related in: MedlinePlus