SEISMIC CONTROL OF OFFSHORE STEEL JACKET PLATFORMS USING TUNED LIQUID COLUMN DAMPER

Offshore platforms are widely used to explore, drill, produce, store, and transport ocean resources and are usually subject to environmental loading, such as waves, winds, ice, earthquake and currents, which may lead to failure of deck facilities, fatigue failure of platforms, inefficiency of operation, and even discomfort of crews. In order to ensure reliability and safety of offshore platforms, it is of great significance to explore a proper way of suppressing vibration of offshore platforms. Earthquake loading has to be considered when the offshore platform is constructed in active fault zone. There are mainly three types of control schemes, i.e. passive control schemes, semi-active control schemes, and active control schemes, to deal with vibration of offshore platforms. While general seismic control strategies have been investigated and demonstrated to be effective for structural seismic mitigation, there currently is limited research highlighting the specific methods available for design engineers and researchers concerned with vibrations of marine offshore structures. This paper provides a seismic passive control technique and its application for marine offshore structures. Tuned Liquid Column Dampers (TLCDs) have been recently considered as a viable passive control mechanism in this regard but limited information is available in relation to their experimental performance. Although there has been an increasing use of these devices for structural seismic control, it is shown that the existing model does not always lead to accurate prediction of the liquid motion. Tuned systems (such as Tuned Mass Dampers (TMDs)), Tuned Liquid Dampers (TLDs) and tuned liquid column dampers are used for the vibration control of tall and slender structures (such as offshore platforms). TLCD which was first proposed by TLCD relies on the motion of a column of liquid in a U-tube container to counteract the forces acting on the structure. This device has drawn significant attention of the researchers as one type of secondary systems. The frequency of a TLCD is tuned with the fundamental frequency of the structure by changing the length of the liquid column in the U-tube. Damping is introduced in the oscillating liquid column through an orifice in the liquid passage. Unlike TMDs, the damping in TLCD is amplitude dependent and hence the damping is non-linear. The advantages of TLCD systems include low cost and maintenance. Let us consider a U-shaped TLCD installed on a SDOF system. The schematic diagram showing the combined structure-TLCD is provided in Figure 1.

کلیدواژه ها:

Steel jacket platform ، Passive control ، Earthquake ، Tuned liquid column damper