Hybrid damping systems in offshore jacket platforms with float-over deck

• Using hybrid damping systems in offshore jacket platforms is quite effective.
• The best combination for HDS is using FDD for seismic load and TMD for fatigue.
• HDS is more effective in fatigue mitigation of platforms that are in deeper water.
• Effectiveness of HDS is mainly dependent upon FDD rather than TMD.

Employing dampers to control wave-induced and seismic vibrations of offshore jacket platforms is an attractive method in order to mitigate fatigue and seismic damage. However, adjustable parameters of a damper are designed by considering only one type of environmental loads; either normal-condition load or extreme-condition load. So, it is important to investigate effectiveness of damping system, for both of two main categories of environmental loads. Also it is ideal for the system to have an acceptable performance in both normal and extreme conditions. The idea investigated in the current study is to use a friction damper device (FDD) and a tuned mass damper (TMD) simultaneously in offshore jacket platforms with float-over deck to control both fatigue damage as well as seismic vibration. To develop the idea, adjustable parameters of FDD and TMD have been adjusted for wave loading. Afterward, they are combined with those designed for earthquake, so the hybrid damping system (HDS) is introduced. By introducing HDS, it is intended to make damping system have a high seismic performance while being effective in fatigue damage mitigation. Moreover, HDS can have different combinations. So, certain variants of HDS are determined which have much higher performance than the other variants.