Mitigating ice-induced jacket platform vibrations utilizing a TMD system

Field observations conducted on oil platforms in the Bohai Sea revealed that the offshore jacket structures, which can withstand the maximum static ice force, might suffer from severe vibrations when ice sheets pass through the legs of the structure. It has been proved that, when the natural frequency of narrow or flexible structures is close to or coincides with the predominant frequency of cyclical ice forces, severe ice-induced vibrations will be evoked. Excessive and consistent vibration will cause the discomfort of working crew, failure of deck facilities even structural fatigue failure. Therefore, it is imperative to seek economical ways to reduce the vibrations to an acceptable level. Based on full-scale tests and technical feasibility, the strategies of vibration mitigation are investigated and compared in this paper. The primary studies demonstrate that adding a Tuned Mass Damper (TMD, also called a Dynamic Vibration Absorber, DVA) is a feasible and practical approach to reduce vibrations. The efficiency of optimally designed TMD and one-directional conceptual TMD device has been presented in this study. Field ice load time history was used as loading scenario to assess the performance of TMD system. The results show that the supplemental device can favorably reduce the dynamic response of platform. (C) 2008 Elsevier B.V. All rights reserved.