JP7786982B2 - Sway suppression structure for freestanding storage tank - Google Patents

Description

This disclosure relates to a rocking suppression structure for a freestanding storage tank installed on a ship.

Ships that transport liquefied gases such as LPG (liquefied petroleum gas), ammonia, and liquefied carbon dioxide, as well as ships that use liquefied gases as fuel, store the liquefied gases in storage tanks installed in the hold. One type of conventional storage tank, the freestanding tank, is installed away from the inner surface of the hold and stands on its own within the hold.

All of the tanks mentioned above sway together with the ship's hull. Excessive tank swaying can exacerbate phenomena such as sloshing. Patent Document 1 discloses a chock and stopper as a structure for suppressing the swaying of a freestanding tank. The chock is installed at the top of the tank, and stoppers are installed on both sides of the chock in the direction of swaying. When the tank sways, the chock comes into contact with the stopper, suppressing excessive swaying of the tank.

Japanese Patent Application Laid-Open No. 2019-151191

The self-supporting tank is installed in a storage compartment such as a ship's hold. The chocks and stoppers described above are used to prevent the tank from swinging excessively within the storage compartment. The tank is installed in the storage compartment with the chocks already installed on top of the tank. The stoppers are installed on the roof of the storage compartment (e.g., the deck of a ship). The stoppers have a plate-shaped member that comes into contact with the swinging chocks, and this plate-shaped member is attached after the tank is installed.

While the dimensions of a tank are on the order of several tens of meters, the distance between the chock and the stopper is generally set to several millimeters. Furthermore, to maximize the use of the interior space of the containment chamber, the distance between the tank and the roof of the containment chamber is also set to several tens of centimeters. As mentioned above, the installation of the stopper's plate-shaped components is carried out after the tank has been installed, so it is difficult to ensure sufficient work space, making the work difficult. In other words, the burden of the installation work can become significant as it takes longer.

This disclosure was made in consideration of the above-mentioned circumstances, and aims to provide a sway suppression structure for a freestanding storage tank that can reduce the burden of installation work on floating structures.

A first aspect of the present disclosure is a rocking suppression structure for a free-standing storage tank installed on an offshore structure, comprising a pair of collision buffers located on either side of a protrusion provided on the top of the storage tank. Each collision buffer includes a buffer member installed on the protrusion, a plate-shaped member facing the buffer member, and a stopper including a support member having a mounting surface for the plate-shaped member, and only both sides of the plate-shaped member in a direction horizontally perpendicular to the arrangement direction of the pair of collision buffers are attached to the mounting surface by fastening members.

Each of the collision buffers may include a fabric portion attached to the surface of the buffer member facing the plate-like member or to the surface of the plate-like member facing the buffer member, and made of thread containing a friction-reducing material. The fabric portion may have a static friction coefficient of 0.3 or less measured in accordance with JIS K7218. The friction-reducing material may include a fluororesin. The fabric portion may have a two-layer structure aligned in the thickness direction of the fabric portion and having different filling rates. The stopper may include a protruding portion located below the plate-like member in the vertical direction. The protruding portion may have a surface facing the lower edge of the plate-like member.

A second aspect of the present disclosure is a vessel equipped with the rocking suppression structure according to the first aspect.

This disclosure provides a sway suppression structure for a freestanding storage tank that can reduce the burden of installation work on floating structures.

1 is a side view of a vessel to which a rocking suppression structure according to an embodiment of the present disclosure is applied. FIG. 2 is a cross-sectional view taken along line II-II in FIG. FIG. 1 is a front view of a rocking suppression structure according to an embodiment of the present disclosure. FIG. 4 is a partial enlarged view of FIG. 3 . FIG. 2 is a front view of a buffer member and its holder according to an embodiment of the present disclosure. FIG. 1 is a front view of a stopper according to an embodiment of the present disclosure.

A sway suppression structure according to an embodiment of the present disclosure will be described with reference to the drawings. Note that common parts in each drawing are given the same reference numerals, and redundant explanations will be omitted. The sway suppression structure according to this embodiment is applied to an offshore structure on which a self-supporting storage tank is installed. Examples of offshore structures include transport ships such as LNG ships (LNG tankers), LPG ships (LPG tankers), oil tankers, and chemical tankers, gravity-based structures (GBSs) such as concrete bottom-mounted storage and gasification facilities, and floating bodies such as liquefied natural gas production units, liquefied petroleum gas production units, oil drilling rigs, oil storage facilities, and megafloats. However, offshore structures are not limited to the above ships and facilities, and may also be other floating structures or bottom-mounted structures.

For ease of explanation, this embodiment will be described below using a ship 1 as an example of an above-water structure. Furthermore, the X, Y, and Z directions, which are perpendicular to each other, are defined. The X direction is the length direction of the ship 1, in other words, the direction of travel of the ship 1. The Y direction is the width direction of the ship 1, and the Z direction is the height direction of the ship 1. The X and Y directions lie within a horizontal plane. Therefore, the Z direction is the vertical direction.

Figure 1 is a side view of a ship 1 to which a rolling suppression structure 10 according to this embodiment is applied. Figure 2 is a cross-sectional view taken along line II-II in Figure 1. The ship 1 comprises a hull 2 and a storage tank 3 mounted on the hull 2. The storage tank 3 is a self-supporting storage tank. The storage tank 3 is housed in a hold 4 and stores liquefied gas 5. Therefore, the ship 1 is a so-called liquefied gas fueled ship.

The storage tank 3 is formed, for example, by welding metal plate members. The material of the plate members is selected to provide sufficient mechanical strength for the tank and sufficient toughness at low temperatures, such as aluminum alloy, stainless steel, 9% nickel steel, low-temperature steel, and high-manganese steel. The storage tank 3 is housed in the hold 4, spaced from the inner surface of the hold 4 by a distance of approximately 1 to several meters. An inlet (not shown) for the liquefied gas 5 is provided at the top 3a of the storage tank 3 (see Figure 2).

As shown in Figure 2, the storage tank 3 is not connected to the hull 2, but is placed on multiple legs 6 and stands free-standing in the hold 4. The legs 6 are approximately rectangular wooden members made of laminated timber or the like, and are arranged at predetermined intervals in the X and Y directions. Each leg 6 is placed on a corresponding base 7. The base 7 is fixed to the bottom of the hold 4 by welding or the like. Therefore, the storage tank 3 is placed slidably in the horizontal direction, which allows the storage tank 3 to expand and contract due to heat.

Figure 3 is a front view of the rocking suppression structure 10 according to this embodiment. Figure 4 is a partially enlarged view of Figure 3. Figure 5 is a front view of the buffer member 13 and its retaining portion 15, and Figure 6 is a front view of the stopper 14.

The sway suppression structure 10 according to this embodiment suppresses excessive swaying of the storage tank 3 in the X direction. As shown in FIG. 3, the sway suppression structure 10 includes a pair of collision buffers 11, 11. The pair of collision buffers 11, 11 are located on either side of a protrusion 12 acting as a chock provided on the top 3a of the storage tank 3, and are aligned in the X direction with this protrusion 12 sandwiched between them. Each collision buffer 11 includes a buffer member 13 installed on the protrusion 12 and a stopper 14 attached to a structure 8 (e.g., a deck) (see FIG. 2) that covers the storage tank 3 from above.

The buffer member 13 is a roughly rectangular wooden member made of laminated wood such as resin-impregnated plywood. As shown in Figures 4 and 5, the buffer member 13 is attached to the protrusion 12 via a retaining portion 15. The buffer member 13 has a surface 13a that faces the plate-shaped member 20 of the stopper 14. This surface 13a has a roughly rectangular shape with a long side along the X direction and a short side along the Z direction. Insertion holes 17 for bolts 30 are formed on both side surfaces 13b, 13b of the buffer member 13 in the X direction.

The retaining portion 15 is made of a metal such as stainless steel and has a recess 16 capable of accommodating part of the buffer member 13. The retaining portion 15 is attached to the protrusion 12 and holds the buffer member 13 so that the surface 13a of the buffer member 13 faces the plate-shaped member 20 of the stopper 14. Threaded holes 18 for bolts 30 are formed on both side surfaces 15a, 15a of the retaining portion 15 in the X direction. When part of the buffer member 13 is inserted into the recess 16, the threaded holes 18 and the corresponding insertion holes 17 are aligned when viewed from the Y direction.

When attaching the buffer member 13 to the holding portion 15, insert the buffer member 13 into the recess 16 until the screw hole 18 and the insertion hole 17 are aligned when viewed from the Y direction. While maintaining this position, insert the bolt 30 into the insertion hole 17 via the screw hole 18, thereby holding the buffer member 13 in place in the holding portion 15.

As shown in Figures 3 and 4, the stopper 14 includes a plate-shaped member 20 facing the buffer member 13 and a support member 23 having a mounting surface 23a for the plate-shaped member 20. The plate-shaped member 20 has a rectangular shape extending in the X and Z directions. The dimensions of this rectangle are sufficiently larger than the dimensions of the surface of the buffer member 13. Specifically, the dimensions are set so that the buffer member 13, as viewed from the Y direction, is positioned within the area of the plate-shaped member 20 even when the storage tank 3 oscillates.

The plate-shaped member 20 includes a first plate portion 21 and a second plate portion 22 that overlap each other. The second plate portion 22 is farther from the buffer member 13 than the first plate portion 21 and contacts the mounting surface 23a of the support member 23. The first plate portion 21 is made of a metal such as stainless steel to be corrosion-resistant and able to withstand the impact of the buffer member 13.

The second plate portion 22 is formed from laminated wood such as plywood, which allows the thickness of the plate member 20 to be adjusted by cutting or other means when attaching the plate member 20 to the support member 23, and is less susceptible to damage such as cracks. Furthermore, by making the second plate portion 22 out of wood, impact noise caused by the buffer member 13 can be reduced. The second plate portion 22 is divided into, for example, an upper plate 22a and a lower plate 22b.

Only the portions 20s, 20s (see Figure 6) on both sides of the plate-shaped member 20 in the direction horizontally perpendicular to the arrangement direction of the pair of collision buffers 11, 11, i.e., in the X direction, are attached to the mounting surface 23a by bolts 30 as fastening members. Therefore, a plurality of through holes 24 for inserting the bolts 30 are formed in these portions 20s. The through holes 24 are aligned at intervals in the Z direction.

The support member 23 is a bracket that is fixed to a structure 8, such as a deck, by welding or the like. The support member 23 has a mounting surface 23a for the plate-shaped member 20. The mounting surface 23a faces the buffer member 13 and is approximately parallel to the retaining portion 15 of the buffer member 13. A plurality of through holes 25 (see Figure 4) are formed in the mounting surface 23a. The through holes 25 are formed at positions corresponding to the through holes 24 in the plate-shaped member 20. A plurality of ribs 26 (see Figure 6) that reinforce the mounting surface 23a are provided on the back side of the mounting surface 23a.

When attaching the plate-shaped member 20 to the mounting surface 23a, the thickness of the second plate portion 22 is measured and adjusted by cutting or other means so that the gap between the plate-shaped member 20 and the buffer member 13 is a predetermined value (e.g., 5 mm). Next, the first plate portion 21 is temporarily fastened to the support member 23 with bolts 30. This temporary fastening prevents the first plate portion 21 from falling and sets a gap between the first plate portion 21 and the mounting surface 23a that allows the second plate portion 22 to be inserted.

Next, the lower plate 22b of the second plate portion 22 is inserted in the X direction between the first plate portion 21 and the mounting surface 23a. At this time, the bolts 30 that interfere with the insertion of the lower plate 22b are temporarily removed and then reinstalled after the lower plate 22b has been inserted.

Next, the upper plate 22a of the second plate portion 22 is inserted between the first plate portion 21 and the mounting surface 23a along the X direction. At this time, any bolts 30 that interfere with the upper plate 22a are temporarily removed and then reinstalled after the upper plate 22a has been inserted. This temporarily fastens all plates to the mounting surface 23a with the bolts 30. After that, each bolt 30 is fully tightened, completing the installation of the plate-shaped member 20.

As described above, according to this embodiment, the fastening members in the installation of the plate-shaped member 20 are fastened only on both sides of the plate-shaped member 20 in the X direction. For example, the work of installing conventional retainers that are provided along the upper and lower edges of the plate-shaped member 20 to support (hold) them is eliminated. When installing a retainer on a support member, a tool must be inserted while avoiding the rib 26 on the back side of the installation surface 23a, and it takes time to install the retainer until the appropriate torque is achieved. In contrast, this embodiment ensures sufficient working space when tightening bolts, and the number of bolts can be reduced, thereby shortening the installation work of the plate-shaped member. In other words, the burden of the installation work can be reduced.

Next, a modification of this embodiment will be described.
As shown in Figures 4 and 6, the stopper 14 may include an overhang 27 located below the plate-shaped member 20 in the Z direction (vertical direction). The overhang 27 is fixed to the support member 23 by welding or the like. The overhang 27 has a surface 27a facing the lower edge of the plate-shaped member 20. The plate-shaped member 20 is placed on the surface 27a when temporarily fastened. This reduces the burden of the installation work of the plate-shaped member 20. Note that the overhang 27 may be divided into multiple segments (small pieces) spaced apart in the X direction (see Figure 6), or may extend in the X direction as a single member.

Each collision buffer 11 may include a fabric portion 28 made of thread containing a friction-reducing substance. In this case, the fabric portion 28 is attached, for example, using an adhesive 29 to the surface 13a of the buffer member 13 facing the plate-shaped member 20 or the surface 20a of the plate-shaped member 20 facing the buffer member 13. Figure 4 shows an example in which the fabric portion 28 is attached to the surface 20a of the plate-shaped member 20. The adhesive 29 may be applied to the fabric portion 28 during the attachment process, or may be formed in advance as an adhesive layer on the back surface 28b of the fabric portion 28.

When the buffer member 13 collides with the plate-like member 20 due to the vibration of the storage tank 3, the frictional force between the two generates shear stress and bending stress inside the bolt 30. Because the bolt 30 must withstand these stresses, the greater the frictional force, the larger the bolt 30 and the greater the number of bolts 30.

This modified example therefore employs a fabric portion 28 made of yarn containing a friction-reducing substance. The fabric portion 28 according to this embodiment has a static friction coefficient of 0.3 or less. This static friction coefficient is a value measured in accordance with the provisions of JIS K7218. The friction-reducing substance includes, for example, fluororesin. One example of a yarn containing fluororesin is Toyoflon (registered trademark). However, the friction-reducing substance is not limited to fluororesin, and other substances with friction-reducing effects may be used as long as they can be formed into yarn with the desired tensile strength. Furthermore, the fabric portion 28 may be a woven fabric, a knitted fabric, or a laminate of these.

The threads that make up the fabric portion 28 move flexibly in accordance with the approaching direction and speed of the buffer member 13 while maintaining the overall shape of the fabric through crossings or loops caused by weaving or knitting the threads. This movement of the threads effectively disperses the energy of the impact from the buffer member 13. For example, this provides greater durability than a sheet material made of the same material as the fabric portion 28 (i.e., a solid, flat plate with no fibers).

Furthermore, by having the fabric portion 28 interposed between the buffer member 13 and the plate-like member 20, it is possible to reduce the frictional force during a collision. This not only avoids increasing the size and number of bolts 30, but also makes it possible to reduce the size and number of bolts 30. The latter contributes to reducing the burden of installation work.

In order to minimize interference with the movement of the threads described above, when attaching the fabric portion 28, the adhesive 29 may be applied only to the surface of the fabric portion 28 that is attached to the cushioning member 13 or the plate-like member 20 (i.e., the back surface 28b). In this case, the adhesive 29 is prevented from seeping into the surface of the fabric portion 28 that faces the space between the plate-like member 20 and the cushioning member 13 (i.e., the front surface 28a), and the threads on the front surface 28a are exposed from the adhesive 29. This prevents a decrease in the friction reduction performance of the fabric portion 28 on the front surface 28a. Furthermore, because the movement of the threads on the front surface 28a can be maintained, a decrease in the energy dispersion performance described above can also be suppressed.

The fabric portion 28 may have a single-layer structure, or a multi-layer structure (e.g., a two-layer structure) in which layers are arranged in the thickness direction of the fabric portion 28 and have different filling rates (thread filling rates). Each layer is formed by a two-dimensional or three-dimensional arrangement of one or more thread patterns. The filling rate is an index of the coarseness of the fabric, and is the percentage of threads per unit area. For example, as shown in FIG. 4, the fabric portion 28 may have a first fiber layer 28c forming the front surface 28a and a second fiber layer 28d forming the back surface 28b. The second fiber layer 28d has a higher thread filling rate (i.e., a tighter weave), lower air permeability (water permeability), and higher tensile strength than the first fiber layer 28c. This improves the durability of the fabric portion 28. It also prevents the adhesive 29 from seeping from the back surface 28b to the front surface 28a.

The present disclosure is not limited to the above-described embodiments, but is defined by the claims, and includes all modifications within the meaning and scope equivalent to the claims.
For example, in the above embodiment, the storage tank 3 is a fuel tank, but the storage tank 3 may also be a cargo tank that transports LNG (liquefied natural gas). In other words, the ship 1 may be an LNG ship equipped with one or more storage tanks 3 that transport LNG, and the rocking suppression structure 10 may be applied to such an LNG ship. In this case as well, the rocking suppression structure 10 can suppress excessive rocking of the storage tank 3 as a cargo tank and reduce the burden of installation work.

1...ship, 2...hull, 3...storage tank, 3a...top, 4...hold, 5...liquefied gas, 6...leg, 7...base, 8...structure, 10...swing suppression structure, 11...collision buffer, 12...convex portion, 13...buffer member, 13a...surface, 13b...both side surfaces, 14...stopper, 15...retaining portion, 15a...both side surfaces, 16...recess, 17...insertion hole, 18...screw hole, 20...plate-shaped member, 20a...surface, 20s...portion, 21...first plate portion, 22...second plate portion, 22a...upper plate, 22b...lower plate, 23...support member, 23a...mounting surface, 24...through hole, 25...through hole, 26...rib, 27...projection portion, 27a...surface, 28...fabric portion, 30...bolt

Claims (7)

A rocking suppression structure for a self-supporting storage tank installed on an offshore structure,
a pair of impact buffers located on both sides of a protrusion provided on the top of the storage tank;
Each of the collision buffers is
a buffer member disposed on the protruding portion;
a stopper including a plate-like member facing the buffer member and a support member having an attachment surface for the plate-like member;
the plate-like member is attached to the mounting surface only at both sides in a direction horizontally orthogonal to the arrangement direction of the pair of collision buffers by fastening members that penetrate the plate-like member in a thickness direction of the plate-like member ,
the plate-like member includes a first plate portion and a second plate portion that overlap each other,
The second plate portion is located farther from the buffer member than the first plate portion and is divided in the vertical direction . The sway suppression structure described in claim 1, wherein each of the collision buffer portions includes a fabric portion attached to the surface of the buffer member facing the plate-shaped member or the surface of the plate-shaped member facing the buffer member, and made of thread containing a friction-reducing substance. 3. The oscillation suppression structure according to claim 2, wherein the fabric portion has a static friction coefficient of 0.3 or less as measured in accordance with Japanese Industrial Standard JIS K7218. The vibration suppressing structure according to claim 3, wherein the friction reducing material includes a fluororesin. The fabric portion has a two-layer structure that is aligned in a thickness direction of the fabric portion and has different filling rates from each other,
the two-layer structure includes a first fiber layer that forms a surface of the fabric portion that faces the space between the plate-like member and the cushioning member, and a second fiber layer that forms a back surface of the fabric portion that is attached to the plate-like member or the cushioning member,
The second fiber layer has a higher filling rate than the first fiber layer.
The oscillation suppression structure according to any one of claims 2 to 4. the stopper includes a protruding portion located below the plate-like member in the vertical direction,
The rocking suppression structure according to claim 1 , wherein the protruding portion has a surface facing the lower edge of the plate-like member. A vessel equipped with a rocking suppression structure according to any one of claims 1 to 6.