JP2008215481A - Pressure vessel, floating structure with pressure vessel, and pressure vessel design method - Google Patents

Abstract

A pressure vessel having excellent accommodation efficiency and easy handling, a floating structure provided with the pressure vessel, and a method for designing the pressure vessel are provided.
A pressure vessel according to the present invention has a shape in which three cylinder-type pressure vessels each having a barrel portion having a circular cross section and a substantially hemispherical end plate portion at both ends are arranged so as to intersect each other. The outer shell has an outer shape, and the outer shell includes a trunk portion 2, an upper head portion 3a, and a lower head portion 3b. Further, inside the pressure vessel 1, a partition wall 4 is connected that is disposed on a line segment connecting the intersections of the trunk portions of adjacent cylinder type pressure vessels.
[Selection] Figure 1

Description

  The present invention relates to a pressure vessel used for storing and transporting low-temperature liquefied gas, a floating structure provided with the pressure vessel, and a pressure vessel design method.

  When storing a large amount of low-temperature liquefied gas such as liquefied petroleum gas (LPG), it is common to store it in a large pressure vessel (gas tank) installed on land or on a ship. Such a pressure vessel is made of steel in order to satisfy the conditions of low temperature and high pressure, and has a spherical or cylinder shape in consideration of pressure. The cylinder type pressure vessel includes a cylindrical barrel portion and hemispherical end plate portions connected to both ends of the barrel portion. As the cylinder type pressure vessel, there are already known a double-drum type and a multi-drum type in which a plurality of body parts are connected (see, for example, Patent Document 1 and Patent Document 2). These twin-cylinder type and multi-cylinder type pressure vessels, in the case of a single-cylinder type pressure vessel, increase the diameter and the thickness of the steel plate as the scale becomes larger. It was invented in view of the fact that the accommodation efficiency is lowered.

  In the pressure vessel described in Patent Document 1, a plurality of cylindrical tank cylinders arranged in parallel are joined to the upper ends of the partition walls in a liquefied gas tank formed by integrally joining the adjacent tank cylinders via the partition walls. It is characterized by having a structure in which the radius of the shell portion of each tank body of the portion to be joined is made larger than the radius of the shell portion of the other portion, and the crossing angle between the partition wall and the shell portion is increased. . Therefore, the pressure vessel described in Patent Document 1 improves the volume efficiency by paying attention to the shape of the joint portion of the adjacent tank cylinders, and how to arrange the tank cylinders improves the volume efficiency. It does not mention whether it is optimal.

In the pressure vessel described in Patent Document 2, each surface of the tank is constituted by a corrugated or vine-like outer shell in which a plurality of cylindrical surfaces or spherical surfaces having arbitrary radii of curvature are connected, and a connecting portion of each cylindrical surface or spherical surface. And a strength member that is combined and arranged in the vertical and horizontal directions. Such a pressure vessel has an outer shell in which a large number of small-diameter cylindrical tanks are arranged, and although it is stated that the arrangement of the cylindrical tanks is arbitrary, a large number are arranged by overlapping two adjacent cylindrical tanks In addition, only an outline of the entire outer shell is disclosed. That is, the pressure vessel described in Patent Document 2 is merely a configuration in which a plurality of pressure vessels arranged in parallel (for example, a twin-barrel type) are arranged in parallel. Further, it is intended to form a large and single pressure vessel having an outer shell in which a large number of small-diameter cylindrical tanks are arranged in the accommodation space of the pressure vessel.
Japanese Patent Laid-Open No. 9-4795 Japanese Patent Publication No.37-4393

  When installing a pressure vessel on land, a ship such as an LNG ship or an LPG ship, a rectangular outer shell as described above can be adopted. For example, a pressure vessel is used for a floating structure. In the case of installation, it may be difficult to secure a wide accommodation space like on land or a ship. In such a case, the method of disposing a plurality of single pressure vessels creates a useless space between the pressure vessels, and the method of disposing a plurality of pressure vessels in parallel as in Patent Document 2 increases the size of the entire pressure vessel. As a result, problems such as difficulty in production and transportation arise.

  The present invention was devised in view of the above-described problems, and aims to provide a pressure vessel that is excellent in accommodation efficiency and easy to handle, a floating structure including the pressure vessel, and a method for designing the pressure vessel. To do.

  According to the present invention, assuming three or more virtual pressure vessels provided with a substantially circular cross-sectional body, at least three of the virtual pressure vessels, the outer shape of the shape arranged so as to intersect each other There is provided a pressure vessel characterized by having an outer shell. In addition, a partition wall disposed on a line segment connecting the intersections of the adjacent body portions may be connected to the inside of the outer shell, and a communication hole may be formed in the partition wall. Furthermore, the virtual pressure vessel has a substantially hemispherical end plate portion at both ends, and the outer shell has a pair of heads made of the outer shape of the end plate portion determined with the arrangement of the body portion. Is preferred.

  In addition, according to the present invention, assuming three or more virtual pressure vessels provided with a substantially circular cross-sectional body, at least three of the virtual pressure vessels of the shape arranged so as to intersect each other A floating structure including a pressure vessel having an outer shell having an outer shape, a housing surface on which the pressure vessel is placed, an outer wall surrounding an outer periphery of the housing surface, and the housing surface having a plurality of polygonal shapes The pressure vessel placed for each of the polygonal regions divided into, an inner wall disposed between an outer shell of the pressure vessel and the outer wall, and a lid member covering the accommodation surface, and the outer wall A floating structure having a pressure vessel is provided in which a space surrounded by the inner wall and the lid member forms a ballast tank. Here, a partition wall disposed on a line connecting the intersections of the adjacent body portions may be connected to the inside of the outer shell of the pressure vessel, and a communication hole may be formed in the partition wall. The virtual pressure vessel may have a substantially hemispherical end plate at both ends, and the outer shell may have a pair of heads formed of the outer shape of the end plate determined by the arrangement of the body. .

  Moreover, it is preferable that the said polygonal area | region is divided | segmented into the triangle shape. The storage surface may be a substantially horizontal plane, and the pressure vessel may be placed so that the longitudinal direction is substantially perpendicular to the storage surface. Further, when the floating structure has a deck disposed on the draft and a plurality of legs connected to the lower part of the deck and having a submerged part, the lid member is attached to the leg. You may make it connect.

  Furthermore, according to the present invention, there is provided a pressure vessel design method for setting the outer shape of a pressure vessel suitable for a receiving surface on which the pressure vessel is placed. Assuming the above virtual pressure vessel, the pressure vessel is arranged on the receiving surface so that at least three of the virtual pressure vessels intersect each other, and the outer shape is set as an outer shell. A design method is provided. In addition, after the accommodation surface is divided into a plurality of polygonal regions, the virtual pressure vessel may be arranged in the polygonal regions. The polygonal region is preferably divided into triangles.

  According to the above-described pressure vessel of the present invention, the use of the outer shell, which can be called a three-cylinder type, makes the liquefied gas particularly for the triangular accommodation surface, as compared with a mere twin-cylinder type or multi-cylinder type pressure vessel. The housing efficiency can be improved. Moreover, since the outline of the outer shell is triangular, the arrangement of the pressure vessel is versatile, and it can easily accommodate complex and polygonal containing surfaces. Therefore, even when it is desired to store a large amount of liquefied gas, it can be handled by arranging a plurality of pressure vessels according to the present invention, and a single large-bottle type or multi-cylinder type pressure vessel is manufactured. Easier to manufacture and transport. Moreover, since it can stand by three heads, a pressure vessel can be easily installed vertically and a pressure vessel can be mounted and installed easily. Therefore, the pressure vessel of the present invention can improve the accommodation efficiency and can easily handle the pressure vessel in various situations.

  According to the floating structure provided with the pressure vessel of the present invention described above, the pressure vessel of the present invention is placed by dividing the accommodating surface of the pressure vessel formed in the floating structure into a polygonal shape. The accommodation efficiency of liquefied gas can be improved. In addition, the pressure vessel of the present invention can be easily arranged even for a floating structure having a limited accommodation space for the pressure vessel. In addition, when a plurality of pressure vessels of the present invention are installed vertically, the cross-sectional area of the pressure vessel can be made smaller than when a single large pressure vessel is arranged, and sloshing caused by waves (the fluid in the pressure vessel is reduced). And the load applied to the outer shell of the pressure vessel and the like can be reduced.

  According to the pressure vessel design method of the present invention described above, since the outer shell can be designed by bringing at least three virtual pressure vessels close to each other, the housing surface is more than a double-body type or a multi-body type in which a plurality of double-body types are connected. The gap between the outer shell and the outer shell can be narrowed, and the housing efficiency can be improved. In particular, it is effective for triangular accommodation surfaces, and by dividing the accommodation surface into polygonal shapes and arranging the virtual pressure vessel, a pressure vessel that is excellent in accommodation efficiency, easy to manufacture and easy to transport is designed. be able to.

  Hereinafter, embodiments of the present invention will be described with reference to FIGS. Here, FIG. 1 is a figure which shows 1st embodiment of the pressure vessel of this invention, (A) is a side view, (B) is BB sectional drawing in FIG. 1 (A).

  As shown in FIG. 1, the pressure vessel 1 of the present invention is arranged so that the body portions of three cylinder type pressure vessels having a body portion having a circular cross section and a substantially hemispherical end plate portion at both ends intersect each other. The outer shell is composed of a body portion 2, an upper head portion 3a, and a lower head portion 3b. That is, the outer shell formed by the body portion of the cylinder type pressure vessel is the body portion 2, and the outer shell formed by the end plate portion of the cylinder type pressure vessel is the upper head portion 3a and the lower head portion 3b. Here, since it is assumed that the pressure vessel 1 is placed vertically (the longitudinal direction of the pressure vessel 1 is placed perpendicular to the accommodation surface), for convenience, the heads at both end portions are They are referred to as an upper head 3a and a lower head 3b.

  Further, as shown in FIG. 1B, a partition wall 4 is connected to the inside of the pressure vessel 1 arranged on a line segment connecting the intersections of the trunk portions of adjacent cylinder type pressure vessels. In the present embodiment, the partition walls 4 are arranged in a Y shape. In addition, each partition wall 4 is formed with communication holes 4a at predetermined intervals in the longitudinal direction of the pressure vessel 1 so that the liquefied gases stored in the pressure vessel 1 can pass back and forth. Although not shown, a reinforcing material may be appropriately disposed on the body portion 2, the upper head portion 3a, the lower head portion 3b, and the partition wall 4, or the three top portions of the upper head portion 3a may be liquefied. A required number of valves for sealing the gas in the pressure vessel 1 may be provided.

  Next, a method for designing the pressure vessel 1 will be described with reference to FIG. Here, FIG. 2 is an explanatory diagram of the design method of the pressure vessel shown in FIG. 1, (A) is a preparation process, (B) is an outer shell design process, (C) is a partition wall design process, (D) FIG.

  As shown in FIG. 2A, here, a case where the accommodation surface 5 of the pressure vessel 1 has an equilateral triangle shape will be described. The accommodation surface 5 refers to a cross section obtained by cutting the accommodation space in which the pressure vessel 1 is placed along a plane perpendicular to the longitudinal direction of the pressure vessel 1. Then, three virtual pressure vessels having a circular cross-section body 2a having a predetermined radius are prepared.

  As shown in FIG. 2 (B), the body 2a of the virtual pressure vessel is arranged on the accommodation surface 5 so as to be in contact with two adjacent sides. At this time, the radius of the body portion 2a of the virtual pressure vessel is appropriately adjusted, and the position of the body portion 2a is determined so that at least three body portions 2a intersect each other. Preferably, the radius of the body part 2a is set so that the total sum of the areas of the shapes of the three body parts 2a is maximized. As a result, the shape of the body portion 2 of the pressure vessel 1 is determined. Further, when the arrangement of the body portion 2a of the virtual pressure vessel is determined, the arrangement of the end plate portion (not shown) of the virtual pressure vessel is automatically determined, and the upper head 3a and lower head 3b (not shown) of the pressure vessel 1 are determined. ) Is determined. If the shape of the trunk | drum 2, the upper head 3a, and the lower head 3b is decided, the shape of the outer shell of the pressure vessel 1 will be decided.

  As shown in FIG. 2C, line segments L1, L2, and L3 connecting the intersections of the body portions 2a of the adjacent virtual pressure vessels are drawn, and the intersection points of the three line segments L1, L2, and L3 and the body portion 2a. Are connected to the intersections existing on the outer shape, and the arrangement of the partition walls 4 is determined.

  As shown in FIG. 2D, if the outer shell of the pressure vessel 1 determined in the outer shell design process and the partition wall 4 determined in the partition design process are combined, the final pressure vessel 1 (completed body) The shape is determined. The thickness of the outer shell, the reinforcing material, the valve, the communication hole of the partition wall 4 and the like are separately designed.

  Next, a design method for different shapes of the pressure vessel 1 will be described with reference to FIG. Here, FIG. 3 is explanatory drawing which shows the pressure vessel and its design method of this invention, (A) is 2nd embodiment, (B) is 3rd embodiment, (C) is 4th embodiment. Show.

  The second embodiment shown in FIG. 3 (A) shows a case where the base of the accommodation surface 31 is an isosceles triangle shape shorter than the other two sides. In this case, it is preferable to arrange a virtual pressure vessel having body portions 32a and 32a having a circular cross section on the bottom side with a large angle. And since the remaining space is elongate, the virtual pressure vessel which has the trunk | drum 32b of an elliptical cross section is arrange | positioned here. By arranging the virtual pressure vessel in this way, the shape of the outer shell 32 of the pressure vessel 1 can be designed as in the case of the first embodiment. Similarly to the case of the first embodiment, the Y-shaped partition wall 33 can be designed on the line segments L1, L2, and L3. In the present application, the “substantially circular cross section” means not only a circular cross section but also an elliptical cross section as in this embodiment and other cross sections similar to a circle.

  The third embodiment shown in FIG. 3B shows a case where the base of the accommodation surface 34 has an isosceles triangle shape that is longer than the other two sides. Here, the virtual pressure vessel having the body 35a having a circular cross section with the same radius is disposed so as to contact two adjacent sides. And since there is still a sufficient gap in the space near the base angle, a virtual pressure vessel having a small-diameter circular cross-section body portion 35b is arranged. Therefore, in the third embodiment, five virtual pressure vessels are used, and the design method of the present invention is applied to the main part. By arranging the virtual pressure vessel in this way, the shape of the outer shell 35 of the pressure vessel 1 can be designed as in the case of the first embodiment. Further, in the same manner as in the first embodiment, a Y-shaped partition wall 36 can be designed on the line segments L1, L2, and L3, and a flat partition wall 37 is designed on the line segments L4 and L5. can do. In addition, you may use the thing of an elliptical cross section for the trunk | drum 35a and / or trunk | drum 35b of the virtual pressure vessel arrange | positioned in a bottom corner | angular part.

  The fourth embodiment shown in FIG. 3C shows a case where the accommodation surface 38 has a rhombic square shape. Here, the virtual pressure vessel having the body 39a having a circular cross section with the same radius is disposed so as to contact two adjacent sides. The three virtual pressure vessel trunks 39a arranged on the upper side of the figure intersect with each other, and the three virtual pressure vessel trunks 39a arranged on the lower side of the figure are also arranged with each other. . That is, in this embodiment, four virtual pressure vessels are used, and the design method of the present invention is applied at two locations. By arranging the virtual pressure vessel in this way, the shape of the outer shell 39 of the pressure vessel 1 can be designed as in the case of the first embodiment. Similarly to the case of the first embodiment, the partition wall 40 having a shape in which two Y-shaped members are vertically inverted and connected to each other on the line segments L1, L2, L3, L4, and L5 can be designed. it can.

  Next, a design method of the pressure vessel 1 when the accommodation surface of the pressure vessel 1 is large will be described with reference to FIG. Here, FIG. 4 is explanatory drawing which shows the pressure vessel of this invention, and its design method, (A) is 5th embodiment, (B) is 6th embodiment, (C) is 7th embodiment. Show.

  The fifth embodiment shown in FIG. 4A shows a case where the accommodation surface 41 is hexagonal. In the case of such a polygonal shape, if the pressure vessel is designed considering the whole as one accommodation surface, a wasteful space is created and the accommodation efficiency is reduced, or the pressure vessel is increased in size and manufactured, transported, etc. If the labor is increased, or if it is arranged on a ship or a floating structure, the effect of sloshing due to waves will increase. Therefore, in the present invention, the accommodation surface 41 is first divided into a plurality of triangular regions 41a to 41f. Thereafter, the shape of the pressure vessel 1 is designed for each of the triangular regions 41a to 41f by applying the design method shown in FIG. In this case, a gap is formed in the central portion, but a pressure vessel having a circular cross section may be further disposed in this portion, and a reinforcing member for the accommodation surface 41 or a space for arranging piping or the like may be used. You may do it.

  The sixth embodiment shown in FIG. 4B shows a case where the accommodation surface 42 has a trapezoidal shape. Also in this case, as in the case of the fifth embodiment, the accommodation surface 42 is divided into a plurality of triangular regions 42a to 41c. Thereafter, the shape of the pressure vessel 1 is designed for each of the triangular regions 42a to 41c by applying the design method shown in FIG. This accommodation surface 42 is assumed, for example, when the pressure vessel 1 is placed horizontally on a ship or the like.

  The seventh embodiment shown in FIG. 4C shows a case where the accommodation surface 43 is square. In this case as well, as in the case of the fifth embodiment, the accommodation surface 43 is divided into a plurality of triangular regions 43a to 43d. Thereafter, the shape of the pressure vessel 1 is designed for each of the triangular regions 43a to 43d by applying the design method shown in FIG. Here, the pressure vessel 1 according to the third embodiment shown in FIG. 3B is used.

  As described above, when the accommodation surface is divided into a plurality of triangular regions, from the viewpoint of manufacturing the pressure vessel 1, it is preferable to equally divide the accommodation surface so as to have a triangular shape with the same shape as possible. When the surface has a complicated shape, triangular or quadrangular regions having partially different shapes may be mixed. Further, depending on the shape of the divided polygonal region, the pressure vessel 1 of the second embodiment shown in FIG. 3 (A) or the pressure vessel 1 of the fourth embodiment shown in FIG. 3 (C) is used. It may be.

  Next, the floating structure provided with the pressure vessel 1 of the present invention will be described with reference to FIG. Here, FIG. 5 is a figure which shows the floating body structure provided with the pressure vessel of this invention, (A) is a horizontal sectional view in 1st embodiment of a floating body structure, (B) is the 1st embodiment. Side surface sectional drawing in (C) is a side surface schematic sectional drawing in 2nd embodiment of a floating structure.

  As shown in FIGS. 5A and 5B, the floating structure 51 including the pressure vessel 1 of the present invention surrounds the accommodation surface 52 on which the pressure vessel 1 is placed and the outer periphery of the accommodation surface 52. An outer wall 53; a pressure vessel 1 placed in each of the triangular regions obtained by dividing the accommodation surface 52 into six triangles; an inner wall 54 disposed between the outer shell of the pressure vessel 1 and the outer wall 53; The space surrounded by the outer wall 53, the inner wall 54, and the lid member 55 forms a ballast tank 56. Reinforcing materials 1a and 53a are disposed on the inner circumferences of the pressure vessel 1 and the outer wall 53, respectively.

  In the floating structure 51, since the outer shape of the accommodation surface 52 is a hexagonal shape, the actual accommodation surface 52a on which the pressure vessel 1 is actually placed is set to a hexagonal shape similar to the accommodation surface 52, and FIG. The six pressure vessels 1 are arranged on the accommodation surface 52 by applying the design method of the pressure vessel 1 of the fifth embodiment shown in FIG. By designing and arranging the pressure vessel 1 in this way, a space can be formed between the outer shell of the pressure vessel 1 and the outer wall 53, and the above-described ballast tank 56 can be arranged. Accordingly, the floating structure 51 can be floated and lowered. Further, a cylindrical tube wall 57 is connected to the central space where the pressure vessel 1 is disposed, and the inside of the tube wall 57 may be used as a closed space for the ballast tank or opened up and down. The space may be a working space for pumping natural gas from the seabed. Further, as shown in FIG. 5B, a mooring line 58 is connected to the outer wall 53, and the floating structure 51 is fixed to the seabed. Although not shown, the pressure vessel 1 is fixed to the receiving surface 52 via a pedestal, and a valve for supplying and discharging seawater to the ballast tank 55 is provided on the outer wall 53, and is provided above the lid member 55. Necessary equipment and piping are arranged as appropriate.

A floating structure 59 shown in FIG. 5C includes a deck 60 disposed on the draft, and a plurality of leg portions 61 connected to the lower portion of the deck 60 and having a submerged portion. The lid member 55 of the floating structure 51 shown in FIGS. 5 (A) and 5 (B) is connected. In the floating structure 59 according to the second embodiment, in order to minimize the influence of the waves, the legs 61 having a substantially circular cross section are provided at the draft portion to reduce the resistance. Further, in the vicinity of the draft portion of the leg portion 61, a belt portion 61a swelled in the radial direction may be formed. By providing the belt portion 61a, it is possible to reduce the vertical shaking in the waves in the region where the wave cycle is short, and it is possible to increase the tuning cycle of the vertical shaking in the region where the wave cycle is long. In addition, a cylindrical wall 62 connected to the cylindrical wall 57 is provided at the center of the deck 60 so as to protect pipes and the like inserted from the deck 60 into the sea from waves. Note that fins 63 may be provided on the outer peripheral portion of the outer wall 53 to reduce the swing of the floating structure 59.

  In the floating structures 51 and 59 described above, the pressure vessel 1 is vertically arranged. That is, the accommodation surface 52 of the pressure vessel 1 is a substantially horizontal surface, and the pressure vessel 1 is placed so that the longitudinal direction is substantially perpendicular to the accommodation surface 52. Since the pressure vessel 1 of the present invention has at least three tops, the pressure vessel 1 can be independent only by the pressure vessel 1 and is suitable for vertical installation. Further, in the case of the floating structures 51 and 59 as shown in FIG. 5, it is easier to secure the accommodation space for the pressure vessel 1 in the vertical direction than in the horizontal direction. In the pressure vessel 1 of the present invention, the accommodation surface 52 is divided into a plurality of polygonal regions, and the shape of the pressure vessel 1 is designed for each polygonal region, so that the cross-sectional area of the pressure vessel is improved while improving the accommodation efficiency. Can be reduced. Therefore, even if the floating structures 51 and 59 are arranged at a place where the rocking occurs like on the sea, the influence of sloshing of the liquefied gas stored in the pressure vessel 1 can be reduced.

  The present invention is not limited to the above-described embodiment. For example, the pressure vessel of the present invention may be applied to land or a ship, may be placed horizontally according to the installation space of the pressure vessel, or a virtual pressure vessel. Of course, various modifications can be made without departing from the spirit of the present invention, such as designing a pressure vessel by applying a spherical pressure vessel.

It is a figure which shows 1st embodiment of the pressure vessel of this invention, (A) is a side view, (B) is BB sectional drawing in FIG. 1 (A). It is explanatory drawing of the design method of the pressure vessel shown in FIG. 1, (A) is a preparatory process, (B) is an outer shell design process, (C) is a partition design process, (D) is a figure which shows a completed body. is there. It is explanatory drawing which shows the pressure vessel of this invention, and its design method, (A) is 2nd embodiment, (B) is 3rd embodiment, (C) has shown 4th embodiment. It is explanatory drawing which shows the pressure vessel of this invention, and its design method, (A) is 5th embodiment, (B) is 6th embodiment, (C) has shown 7th embodiment. It is a figure which shows the floating body structure provided with the pressure vessel of this invention, (A) is a horizontal sectional view in 1st embodiment of a floating body structure, (B) is a side schematic sectional drawing in the same 1st embodiment, C) is a schematic side cross-sectional view of a floating structure in a second embodiment.

Explanation of symbols

1 Pressure Vessel 2, 32, 35, 39 Body 2a, 32a, 32b, 35a, 35b, 39a Virtual Pressure Vessel 3a Upper Head 3b Lower Head 4, 33, 36, 37, 40 Bulkhead 4a Communication Hole 5, 31, 34, 38, 41, 42, 43, 52 Accommodating surface 41a-f, 42a-c, 43a-d Triangular region 51, 59 Floating structure 52a Actual accommodating surface 53 Outer wall 53a, 1a Reinforcement material 54 Inner wall 55 Lid member 56 Ballast tank 57, 62 Cylindrical wall 58 Mooring line 60 Deck 61 Leg part 61a Belt part 63 Fin

Claims (10)

  Assuming three or more virtual pressure vessels with a substantially circular cross-sectional body, and having an outer shell having an outer shape of the shape arranged so that at least three of the virtual pressure vessels intersect each other, A pressure vessel characterized by that.   2. A partition wall disposed on a line segment connecting the intersections of the adjacent body portions is connected to the inside of the outer shell, and a communication hole is formed in the partition wall. A pressure vessel according to 1.   The virtual pressure vessel has a substantially hemispherical end plate at both ends, and the outer shell has a pair of heads formed of the outer shape of the end plate determined by the arrangement of the body. The pressure vessel according to claim 1 or 2.   It is a floating body structure provided with the pressure vessel in any one of Claims 1-3, Comprising: The accommodation surface for mounting the said pressure vessel, The outer wall surrounding the outer periphery of this accommodation surface, The said accommodation The pressure vessel placed for each polygonal region obtained by dividing the surface into a plurality of polygonal shapes, an inner wall disposed between the outer shell and the outer wall of the pressure vessel, and a lid member covering the accommodation surface , And a space surrounded by the outer wall, the inner wall, and the lid member forms a ballast tank.   The floating structure having a pressure vessel according to claim 4, wherein the polygonal region is divided into a triangular shape.   The said accommodating surface is a substantially horizontal surface, The said pressure vessel is mounted so that a longitudinal direction may become substantially perpendicular | vertical with respect to the said accommodating surface, The Claim 4 or Claim 5 characterized by the above-mentioned. Floating structure.   The floating structure has a deck disposed on the draft and a plurality of legs connected to the lower part of the deck and having a submerged part, and the lid member is connected to the legs. The floating structure provided with the pressure vessel in any one of Claims 4-6 characterized by the above-mentioned.   A pressure vessel design method for setting an outer shell shape of a pressure vessel suitable for a receiving surface for placing the pressure vessel, assuming three or more virtual pressure vessels having a substantially circular cross-section body. A design method of a pressure vessel, wherein at least three body portions of the virtual pressure vessel are arranged on the receiving surface so as to intersect each other, and an outer shape thereof is set as an outer shell.   The pressure vessel design method according to claim 8, wherein the virtual pressure vessel is arranged in the polygonal region after the accommodating surface is divided into a plurality of polygonal regions. The method for designing a pressure vessel according to claim 9, wherein the polygonal region is divided into triangular shapes.