Passive Vibration Control Of Offshore Platform Based On Rocking Wall System

Offshore platforms are often subjected to dynamic loads such as waves, winds,tides, ice vibration and earthquakes, and in order to ensure normal production and theworker’s comfortable living, platform vibration control is necessary. This paperproposes a new high performance offshore platform-rocking wall structural system,which attaches a rocking wall with large stiffness to the platform, and combined withseveral vibration control approaches to do research on passive control of offshoreplatforms. The main contents are as follows:Firstly, the mechanism of stress on ocean platform rocking wall system is analyzed.Based on the basic principle of structural dynamics, the stresses of the structure areanalyzed. Analytical expression of equations is calculated. See natural frequency as thefocal point, which is calculated using analytical expression and ANSYS, and the resultsare analyzed and comparedSecondly, the stiffness and mass distribution of the offshore platform rocking wallsystem are studied in this paper. With the rocking wall’s stiffness measured by elasticmodulus, the influence of the rocking wall stiffness on natural frequency is analyzed,and the optimal solution of stiffness is presented; In an ideal state, how the stiffnessbetween the story influence the material utilization is calculated. The results show thatlarger second story column stiffness can better use the materials, which can betterconsume energy. How the inclination angle of the wall influences the offshore platformis studied and the results show that rocking wall is set inclining to the building side canbe more conducive to improve the seismic performance of the structure.Thirdly, a viscoelastic rotary damper is set at the hinge point between ground andthe wall for passive energy dissipation, and use finite element software ANSYS to maketime history analysis subjected to seismic loading for the offshore platform-rockingwall system. Then optimal stiffness and optimum damping of a viscoelastic rotarydamper is studied. The results show that the damper can effectively decrease seismicresponse.Finally, combining the characteristics of rocking wall systems and tuned massdamper (TMD), both methods are applied to the offshore platforms for vibration control.The wall is use to eliminate offshore platform’s higher mode, while the TMD is used to control lower modes. ANSYS calculation results show that the combination of rockingwall and TMD can significantly reduce the seismic response of offshore platforms.