A Study on Passive Control of Wave induced Vibration of Offshore Fixed Jacket Platforms and Floating Production Storage and Offloading Systems

Abstract

The continuous wave-induced vibrations of offshore structures lead to various detrimental newlineeffects, ranging from discomfort of crews and consequent reduction in work efficiency and newlineproductive capacity, to the loosening of fasteners and wearing down of bearings that may cause newlinedeck breakdown and even platform collapse due to fatigue. Since stiffening the structure newlineimplies the use of greater construction material, and hence a substantial increase in the overall newlinecost of the structure, structural vibration control techniques offer a more economic as well as newlineeffective solution to the problem of vibrations in offshore structures. Amongst the various newlinestructural control strategies, those that employ electronic devices as in active, semi-active and newlinehybrid control, are not particularly suited to the harsh marine environment. Passive control newlinesystems are thus more appealing. While the incorporation of damping braces can entail the newlineproblems of the functioning and maintenance of the damper in water, and cause an increase in newlinethe force on the offshore structure, deck isolation and the use of tuned dampers on the deck are newlinefree from the aforementioned issues. The current research has therefore focussed on these two newlinecontrol methodologies for two types of offshore structures, one from the fixed platform newlinecategory, namely, the fixed offshore jacket platform, and, one from the floating platform newlinecategory, the Floating Production, Storage and Offloading System or FPSO. While the former newlineis one of the most frequently encountered marine structures, the latter is rapidly gaining newlineimportance in recent years. newlineThe effectiveness of passive deck isolation under wave-induced vibrations of offshore jacket newlineplatforms have been examined through frequency domain and time domain investigations. newlineBoth regular and random wave models, the latter characterized by the Pierson-Moskowitz (PM) newlineand Joint North Sea Wave Observation Project (JONSWAP) spectra, have been considered. In newlinethe frequency domain analysis, the frequency response functions