The present invention relates to an apparatus for reducing a rolling motion of a floating structure.
A technique for mooring a floating structure on water and using the floating structure for various use applications is put to practical use or researched. For example, in a plant referred to as FLNG (Floating LNG) or FPSO (Floating Production Storage & Offloading unit), a floating structure is floated offshore, and natural gas collected from an undersea gas field is liquidized to produce and accumulate LNG (Liquified Natural Gas). The accumulated LNG is transferred to a seaport by an LNG ship.
For example, the floating structure is swung by waves generated on the water surface on the ocean. The swing motion of the floating structure is not desirable for the work on the floating structure. For example, in a case of the FLNG, a technique for suppressing the swing operation of the floating structure is required in order to improve an operation rate.
A technique is known in which a perpendicular plate is provided on the side above the wave in the main body of the floating structure to penetrate through the water surface, so that the swing motion of the floating structure is reduced. Patent Literature 1 (JP 2004-16105A) is its one example.
A technique which can reduce a swing motion of a floating structure is demanded. A technique is demanded which reduces a swing motion effectively according to the situation of the swing motion of the floating structure.
In a view of the present invention, a rolling suppression apparatus is provided with a pair of plate members attached to both of ends in a width direction on a bottom of a floating structure. Each of the plate members includes a plurality of through-holes arranged in a longitudinal direction of the plate member.
Preferably, an upper end of each of the plate members in the motion suppression apparatus is attached to the bottom of the floating structure.
Preferably, the plate members of the motion suppression system are attached to the floating structure by a support member to have a gap from the floating structure.
Preferably, the rolling reduction apparatus is further provided with a control unit which controls the opening area of each of a plurality of through-holes.
Preferably, each of the plate members is provided with a first plate and a second plate which is fixed on the floating structure. The first plate and the second plate are overlapped such that a first hole formed in the first plate and a second hole formed in the second plate to overlap with each other. The control unit slides the first plate along the second plate.
In another view of the present invention, a floating structure is provided with the above rolling reduction apparatus.
According to the present invention, the technique is provided which can reduce a rolling motion of the floating structure. Moreover, the technique is provided which can effectively reduce the rolling motion according to the situation of the rolling motion of the floating structure.
The above-mentioned objects, other objects, effects and features of the present invention would be clarified from the descriptions of the embodiments in conjunction with the following drawings:
Hereinafter, embodiments of the present invention will be described in detail with reference to the attached drawings.
A rolling reduction apparatus is attached to both ends of the floating structure main body 1 in a width direction, namely, an X-axis direction orthogonal to the longitudinal direction within a horizontal plane. The rolling reduction apparatus contains a pair of slender plate-shaped members. The longitudinal direction of each of plates 4 is parallel to a front—rear direction (in many cases, the longitudinal direction) of the floating structure main body 1. The long side of the plate 4 is attached to a bottom of the floating structure main body 1. The plate 4 is attached to protrude from the bottom of the floating structure main body 1 into a vertically downward direction. Many holes (through-holes) 5 are formed to be arranged in the longitudinal direction of the plate 4. A Z-axis is orthogonal to the X-axis and the Y-axis.
Such a floating structure is floated and used on water. The floating structure swings by the influence of waves inputted to the floating structure main body 1. As one of main swing motions, there is a case of generation of rolling. In such a case, the plate 4 is cyclically moved in a rolling direction against the water. In association with the motion, the water passes through the holes 5 of the plate 4 attached to the bottom of the floating structure. Eddy is generated on the downstream side of the water flow passing through the holes 5, and the energy of wave is attenuated. As a result, the rolling motion of the floating structure is suppressed. The rolling motion of the floating structure can be suppressed more effectively when the size of the hole 5 is determined on the basis of the situation of the rolling motion such as a period of the rolling motion of the floating structure.
In even those modification examples, the rolling motion of the floating structure main body 1 can be suppressed.
Even in the second embodiment, the modification examples similar to
The sizes of the hole and gap when the energy of wave is efficiently attenuated are different on the basis of the wavelength of an input wave. The sizes of the hole and gap are selected appropriately to the first or second embodiment. The second embodiment is advantageous because not only the holes 5 but also the gap 6 can be used to reduce the rolling motion. In the first embodiment, it is easy to accomplish high strength only by using few members because the plate 4 can be directly attached to the bottom surface of the floating structure main body 1. In particular, since the force of the wave is greatly applied to the plate 4, the high strength is required.
The first plate member 8-1 and the second plate member 8-2 are attached such that their planar shapes overlap with each other. Each of the first plate member 8-1 and the second plate member 8-2 can be slid in the longitudinal direction. A relative displacement L1 in the longitudinal direction between the first plate material 8-1 and the second plate material 8-2 can be controlled by a controller section (that is not shown). For example, in the controller section, a driving mechanism such as an actuator can be used to control the displacement L1 to be a setting value and fix it to the value. In the situation in which the first plate member 8-1 and the second plate member 8-2 overlap, a hole 10 is formed at a portion at which the hole 9-1 and the hole 9-2 overlap. This hole 10 corresponds to the hole 4 in the first and second embodiments. By controlling the displacement L1, it is possible to change the size of the hole 10.
The rolling reduction apparatus is attached to both of the ends in the width direction on the bottom in the floating structure main body 1, for example, as the plate 4 shown in
As mentioned above, the present invention has been described with reference to the embodiments. However, the present invention is not limited to the above-mentioned embodiments. Various modifications can be performed on the above-mentioned embodiments. The above-mentioned embodiments can be combined with each other.
This application claims a priority based on Japanese Patent Application No. JP 2010-244092 filed on Oct. 29, 2010, and the disclosure thereof is incorporated herein by reference.
Number | Date | Country | Kind |
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2010-244092 | Oct 2010 | JP | national |
Filing Document | Filing Date | Country | Kind | 371c Date |
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PCT/JP2011/074508 | 10/25/2011 | WO | 00 | 12/27/2012 |