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Semi Active Vibration Control of A Marine Offshore Structure Using Magnetorheological Dampers
| 2010
805
Viewed
- Type of Document: M.Sc. Thesis
- Language: English
- Document No: 40590 (58)
- University: Sharif University of Technology
- Department: Science and Engineering
- Advisor(s): Abolghasem, Zabihollah
- Abstract:
- Marine offshore structures are huge structures constructed in very harsh environments, like oceans and seas. These structures are highly exposed vibration due to ocean’s waves, wind, helicopter landing, etc. Preventing the damage to these structures due unpredicted vibration using a semi active vibration control is being considered. Magnetrorehological (MR) dampers have been used as active element to control the vibration and to provide the structural integrity of the structure. Providing high dynamic range, lower power requirements, large force capacity, robustness, and safe manner operation in case of fail made the MR dampers attractive devices to passive, semi-active and active control in civil infrastructures.In the present study, a marine off shore structure, having 12 links, and 21 nodes located in Persian Gulf exposed to different excitations has been considered. In which some members have been substituted by the MR dampers has been considered. To control the vibration of the structure, several MR dampers have been installed at pre-designed locations. Linear Quadratic Regulator (LQR) as well as linear Quadratic Gaussian (LQG) is utilized as the control algorithms. It has been observed that adding the active members of MR dampers may highly improve the vibration response of the structure, and thus, significantly increase the safety and life time of the structure
- Keywords:
- Semiactive Control ; Linear Quadratic Requlator (LQR) ; Linear Quadratic Gaussian (LQG)Controller ; Offshore Structures ; Offshore Platforms ; Vibration Control ; Magnetorheological Damper
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Bookmark- Introduction and Literature Review
- Marine Offshore Structures
- The earliest offshore structure for oil drilling was built about 1887 off the coast of southern California near Santa Barbara. This was simply a wooden wharf outfitted with a rig for drilling vertical wells into the sea floor. More elaborate platforms...
- Offshore mooring systems have a variety of configurations. All have anchors or groups of piles in the seabed with flexible lines (cables, ropes, chains) leading from them to buoys, ships, or platform structures. The function of the mooring system is t...
- Six general types of offshore platforms are depicted in Figure (2.3). The first three are designed for depths up to about 500m, and the last three are for depths to 2000 m. Not shown are subsea production platforms, which are presently rated for 3000 ...
- A mobile structure often used for exploratory oil-drilling operations is the self-elevating platform commonly called a jack up or mat-supported rig. A constructed version of this platform depicted schematically in Figure (2.3)-a, is shown in Figure (...
- A platform designed to be used in a fixed location as a production unit is shown in Figure (2.3)-b. such a unit, called a gravity platform, consists of a cluster of concrete oil-storage tanks surrounding hollow, tapered concrete legs that extend above...
- Found more frequently among the permanent, fixeed-bottom structures, however, is the steel truss or jacket template structure shown schematically in Figure (2.3)-c, where an installed structure is depicted in Figure (2.4). As for the gravity platform,...
- An alternative class of offshore structures meant for dephts from 300 to 800 m is the compliant tower such as that shown in Figure (2.3)-d. Such a tower may or may not have mooring lines. It is a pile-supported steel truss structure designed to comply...
- The first compliant tower was the Lena, which was installed in the early 1980s in the Gulf of Mexico. Including its three-level drilling and production deck and its drilling rigs, this tower reaches a total hight of 400 m. Each of the 20 stabilizing c...
- The tention leg platform (TLP) can be economically competitve with compliant towers for water dephts between 300 m and 1200 m. The schematic design of the TLP is depicted in Figure (2.3)-e. In such designs, the total buoyant force of the submerged pon...
- For water depths of about 1500 m, a subsea production system provides an exellent alternative to a fixed surface facility. Much of a subsea system rests on the ocean floor, and its production of oil and gas is controlled by computer from a ship or oth...
- A popular buoyant structure is the floating production system. Such a structure is practica for water depths up to 3000 m, and also at lesser dephts where the field life of the structure is the semi-submersible with fully submerged hulls, shown schem...
- Spars are floating vertical cylinders that support production decks above storm waves. These structures are controlled to remain essentially still in stormy seas. Some need to be towed from place to place. Others are self propelled. During drilling an...
- Finite Element Modeling of Marine offshore Structures
- Semi-Active Vibration Control of Offshore Structure
- After that there are two kinds of forces as input to this structure. Based on Equation (4.30) in equation of motion it is 5 terms in the case study. Matrix T is reaction forces from dampers which are applied to this structure. T matrix is written in a...
- Conclusions