Optimum parameters of tuned liquid column–gas damper for mitigation of seismic-induced vibrations of offshore jacket platforms

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Optimum parameters of tuned liquid column–gas damper for
mitigation of seismic-induced vibrations of offshore jacket platforms
Seyed Amin Mousavi*,†, Khosrow Bargi and Seyed Mehdi Zahrai
University of Tehran, School of Civil Engineering, Tehran, Iran, Islamic Republic of Iran
SUMMARY
The effectiveness of tuned liquid column–gas damper, TLCGD, on the suppression of seismic-induced vibrations
of steel jacket platforms is evaluated in this study. TLCGD is an interesting choice in the case of jacket platforms
because it is possible to use the structural elements as the horizontal column of the TLCGD. In this study, optimum
parameters of the TLCGD are obtained, considering nonlinear damping of the TLCGD and water–structure interaction
between jacket platform and sea water. Equation of motions and other related formulas are derived, and using a
SIMULINK model, the frequency and the head loss coefficient of the TLCGD are optimized. Results are in general
agreement with those obtained in earlier studies for typical building structures. However, effects of period of the
structure and ground motion characteristics on the optimum parameters are also evaluated in this study. Results show
that until a particular threshold for the mass ratio, the higher the mass ratio, the higher the efficiency of the damper.
After that, by increasing the mass ratio, there is no improvement on the damper efficiency. It is also found that PGA
and frequency content of a ground motion have no important effect on the optimum frequency ratio, but they have a
noticeable effect on the optimum head loss coefficient. Besides, frequency content has some effect on the TLCGD
efficiency. It is shown that the optimum frequency of a TLCGD is uncoupled with the area ratio and the head loss
coefficient, and they have no effect on the optimum frequency ratio. Copyright © 2011 John Wiley & Sons, Ltd.
Received 23 November 2010; Revised 6 July 2011; Accepted 14 October 2011
KEY WORDS: passive control; tuned liquid column–gas damper; TLCD; offshore platform; seismic excitation;
optimization

 

STRUCTURAL CONTROL AND HEALTH MONITORING
Struct. Control Health Monit. 2013; 20:422–444
Published online 19 December 2011 in Wiley Online Library (wileyonlinelibrary.com). DOI: 10.1002/stc.505

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