Optimum parameters of tuned liquid columngas damper for mitigation of seismic-induced vibrations of offshore jacket platforms

Abstract

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. © 2011 John Wiley & Sons, Ltd.