Patent Description:
In general, natural gas is supplied in the form of pipe-line natural gas (PNG) that is fed to a consumption place from a production place through a pipe line or in the form of liquefied natural gas (LNG) that is liquefied through a vessel when a production place and a consumption place are far from each other and, in this case, LNG is used directly as fuel of transportation such as a vessel, a bus, and an automobile as well as general uses of liquefied natural gas and, to this end, LNG is generally stored in a cylindrical pressure tank and is stored and used in a pressure tank installed in transportation.

A general cylindrical pressure tank is conveniently used in an automobile or the like due to high pressure-resistant performance and a small volume but, when a large amount of liquefied natural gas is required like in a vessel, a plurality of cylindrical pressure tanks needs to be installed and, in particular, when liquefied natural gas is also used as fuel of a vessel, more cylindrical pressure tanks need to be installed in the vessel and, thus, there is a problem in that a space occupied in the vessel is excessively increased due to an interval between the cylindrical pressure tanks when the plurality of cylindrical pressure tanks are arranged.

When a cylindrical pressure tank is installed in a bus and an automobile, an installation space is limited due to its shape, thereby degrading space utilization. To overcome the problem, a membrane or circular tank system, but not a cylindrical tank system, has been developed and <CIT> discloses a square pressure tank configured by improving defects of the membrane or circular tank system, like in <FIG> of the present application. There have been proposed a cryogenic tank as disclosed in <CIT>, but it was made by joining elongated lobes and had limitation to make various shape tanks. Also, <CIT> proposed a container for storing compressed gas with the connected cladding layer, but it also had limitation to make various shape tanks. <CIT> proposed cryogenic storage tank with a substantially rectangular parallelepiped shaped double wall container wherein the inner wall is somewhat flexible, and therefore there is no concern about discontinuity of stress. <CIT> and <CIT> show further pressure tanks. Particularly relevant are the pressure tanks disclosed in <CIT>, <CIT> and <CIT>.

The polygonal pressure tank advantageously and largely improves space efficiency, which is disadvantage of the conventional membrane or circular tank system, but it is required to overcome a problem in terms of its high weight.

An object of the present invention is to provide a curve-combined polygonal pressure tank for reducing a weight while enhancing space efficiency as well as maintaining high pressure inside the pressure tank.

Another object of the present invention is to provide a method of overcoming a structural problem when a polygonal pressure tank and a curved surface are combined.

In particular, a structural alternative is provided to enhance pressure-resistant performance and to prevent buckling.

In addition, various embodiments of a curve-combined polygonal pressure are proposed to provide an ideal model of a curve-combined polygonal pressure tank applicable to an actual vessel.

A pressure tank according to the present invention includes the curve-combined polygonal pressure tank in accordance with independent claim <NUM>. Preferred embodiments can be found in the dependent claims.

A curve-combined polygonal pressure tank according to the present invention may advantageously reduce space utilization and a weight as well as maintaining high internal pressure.

When the curve-combined polygonal pressure tank is manufactured, imbalance of internal stress applied to a connection portion between a curved surface and a flat surface may be advantageously overcome to enhance pressure-resistant performance.

When the curve-combined polygonal pressure tank is manufactured, the connection portion between the curved surface and the flat surface may be advantageously prevented from buckling due to external load applied to the connection portion.

A pressure tank according to the present invention may include flat members disposed at upper and lower portions of the pressure tank, a first curved member that connects the flat member disposed at the upper portion and an edge of the flat member disposed at the lower portion and is formed with predetermined curvature, and a second curved member connecting neighboring curved edges of the first curved member and, in this case, a stress-buffer portion for preventing stress discontinuity may be formed at a connection portion between the flat member and the first curved member.

The curve-combined polygonal pressure tank according to the present invention includes, in a first variant, a plurality of tension members disposed between the flat member disposed at the upper portion and the flat member disposed at the lower portion, and the outermost tension member among the plurality of tension members may be spaced apart from an edge at which the first curved member and the flat member contact each other by a constant distance toward the flat member to form a stress-buffer portion.

The curve-combined polygonal pressure tank according to the present invention includes, in a second variant, a plurality of tension members disposed between the flat member disposed at the upper portion and the flat member disposed at the lower portion, and the outermost tension member among the plurality of tension members may be coupled to an edge at which the first curved member and the flat member contact each other and is formed to be thinner than a tension member disposed inward to form a stress-buffer portion.

The curve-combined polygonal pressure tank according to the present invention includes, in a third variant, a plurality of tension members disposed between the flat member disposed at the upper portion and the flat member disposed at the lower portion, and the outermost tension member among the plurality of tension members may be coupled to an edge at which the first curved member and the flat member contact each other and is curved with predetermined curvature in an opposite direction to the first curved member or is formed with a bent portion that is bent in an opposite direction to the first curved member, to form a stress-buffer portion.

In this case, the outermost tension member among the plurality of tension members may include a connection reinforcing member that extends to the first curved member.

The connection reinforcing member may have one end that contacts the outermost tension member and the other end that extends to a flat portion of the first curved member.

A shape of the flat member viewed from an upper portion thereof may be a square shape, a rectangular shape, an asymmetrical shape with different facing surfaces, a trapezoidal shape, or a polygonal shape with one narrow side.

The flat member may have a polygonal shape and may be formed in such a way that one of facing sides is shorter than the other side.

An internal grid structure including a grid reinforcing member that is formed in grid patterns by arranging a plurality of H-type beams perpendicularly to each other and a plurality of ring-type reinforcing members that extend from a portion of the H-type beams and are coupled to an internal side of the adjacent first curved member with predetermined curvature, may be disposed between the flat members.

A grid-type reinforcing structure including flat plate-type reinforcing members having hollow portions and linear-type reinforcing members for connecting the flat plate-type reinforcing members may be disposed between the flat members.

A plurality of horizontal grid plates and a plurality of vertical grid plates, each of which includes a reinforcing ring formed therein, may cross each other between the flat members and, as necessary an internal grid structure including a plurality of linear-type reinforcing members disposed therein may be disposed between the horizontal grid plates or the vertical grid plates.

The curve-combined polygonal pressure tank may include one or more pairs of flat members.

In this case, cross frames for connection between lateral end portions may each be disposed in up and down directions at the lateral end portions of the pair of flat members.

A plurality of parallel plates may be stacked in up and down directions and opposite ends of the parallel plate may extend up to the curved member.

The parallel plate may be formed with a uniform thickness perpendicularly to a lateral flat member and may be formed to surround an internal portion of the curved member.

The parallel plate may be formed with a uniform thickness perpendicularly to a lateral flat member and may be formed only up to an edge of a flat member.

Hereinafter, a curve-combined polygonal pressure tank <NUM> having the above features is described in detail with reference to the accompanying drawings. The following descriptions are merely examples shown for explanation of some embodiments of the present invention, but not for being limited to a specific embodiment.

<FIG> is a perspective view showing an outer appearance of the curve-combined polygonal pressure tank <NUM> according to the present invention. As shown in the drawing, the curve-combined polygonal pressure tank <NUM> according to the present invention may include a pair of flat members <NUM>, a plurality of first curved members <NUM> that connect facing edges of the pair of flat members <NUM>, and a plurality of second curved members <NUM> that connect neighboring edges of the plurality of first curved members <NUM>.

In general, a cylindrical pressure tank with an external curved surface may be maintained at predetermined internal pressure only by a thickness of the pressure tank without a special reinforcing structure therein, but the polygonal pressure tank has a limit in maintaining internal pressure only by the flat member <NUM> and, thus, the flat members <NUM> need to be connected by a tension member <NUM> such as a tension beam or a tension plate to satisfy pressure-resistant performance.

However, when the tension member <NUM> is installed in a pressure tank obtained by combining a curved surface and a flat surface, bending stress is applied to the flat member <NUM> and membrane stress is applied to the curved member <NUM> as shown in <FIG>, and stress discontinuity occurs at a connection portion between the flat member <NUM> and the curved member <NUM> as shown in <FIG> and, thus, there is a problem in that pressure-resistant performance of the pressure tank is remarkably degraded.

<FIG> illustrates a cross sectional shape of the curve-combined polygonal pressure tank <NUM> according to the present invention along the Y axis to overcome the above problem. A position of the outermost tension member <NUM> that is installed to be closest to the curved member <NUM> among the plurality of tension members <NUM> may be determined as a position spaced apart from the curved member by a constant distance toward the flat member <NUM>, but not a boundary between the flat member <NUM> and the curved member and, thus, a stress-buffer portion for preventing stress discontinuity may be formed.

<FIG> is a schematic diagram showing a principle for overcoming stress discontinuity, which corresponds to the first object of the present invention. A position of the outermost tension member <NUM> that is installed to be closest to the curved member <NUM> among the plurality of tension members <NUM> may be determined as a position spaced apart from the curved member by a constant distance toward the flat member, but not a boundary between the flat member <NUM> and the curved member and, thus, stress discontinuity generated at the boundary between the flat member <NUM> and the curved member <NUM> may be reduced.

<FIG> is a schematic diagram showing Embodiment <NUM>-<NUM> and modified embodiments thereof for the first object of the present invention in the curve-combined polygonal pressure tank <NUM> according to the present invention. In <FIG>, the outermost tension member <NUM> may be disposed at a connection portion between the flat member <NUM> and the curved member and the outermost tension member <NUM> may have a smaller thickness than that of the other tension members <NUM> disposed inside the polygonal pressure tank <NUM>, thereby achieving a stress balancing effect that is similar to the case in which a stress-buffer portion with a predetermined region is formed at an end portion of the flat member <NUM>. As other modified embodiments, as shown in <FIG>, the outermost tension member <NUM> may be curved in an opposite direction to the curved member <NUM> and, as shown in <FIG>, the outermost tension member <NUM> may be formed like a 'U' shape or an angular 'U' shape with a curved portion.

<FIG> is a schematic diagram showing Embodiment <NUM>-<NUM> and modified embodiments thereof for the first object of the present invention in the curve-combined polygonal pressure tank <NUM> and, here, a connection reinforcing member <NUM> for connection between the outermost tension member <NUM> and the curved member <NUM> is added. The connection reinforcing member <NUM> may be shaped like an arced connection reinforcing member <NUM> that is formed at only a portion of the curved member <NUM> as shown in <FIG>, or a circular connection reinforcing member <NUM> that is formed at an entire portion of the curved member <NUM> as shown in <FIG> and, in this case, the connection reinforcing member <NUM> may be shaped like the circular connection reinforcing member <NUM> that is thinned toward a central portion of a curved portion as shown in <FIG>.

<FIG> is a schematic diagram showing Embodiment <NUM>-<NUM> and modified embodiments thereof for the first object of the present invention in the curve-combined polygonal pressure tank <NUM>. As shown in <FIG>, when curvature of a curved portion (<NUM>) is increased to enhance space efficiency, much higher stress may be applied to a central portion of the curved portion than a cylindrical tank with small curvature. In Embodiment <NUM>-<NUM> as a method of overcoming this, the circular connection reinforcing member <NUM> may be thickened toward a central portion of the curved portion as shown in <FIG> and, as another modified embodiment, the separate circular connection reinforcing member <NUM> may be formed only at the central portion of the curved portion as shown in <FIG>.

Differently from a cylindrical pressure tank, an entire external surface of which is formed with a curved surface, a problem in terms of buckling needs to be overcome in the case of a pressure tank including the flat member <NUM> as shown in <FIG>. In particular, an end of the curved member <NUM>, adjacent to the outermost tension member <NUM>, and the outermost tension member <NUM> may be a portion BW that is vulnerable with respect to buckling.

<FIG> and <FIG> are schematic diagrams showing an embodiment and a modified embodiment for the second object of the present invention in the curve-combined polygonal pressure tank <NUM> according to the present invention and, here, as a method of overcoming the second object, according to the present invention, a reinforcing member may be added to a lateral surface of a tension beam that is an example of the tension member <NUM>.

<FIG> is a diagram showing an embodiment and a modified embodiment of a cross sectional shape of a tension beam for preventing buckling. <NUM>-shape reinforcing members <NUM> shown in <FIG>, T-shape reinforcing members <NUM> shown in <FIG>, or L-shape reinforcing members <NUM> shown in <FIG> may be added to facing lateral surfaces of the tension beam, or the tension beam may be formed with a H-shape sectional view as shown in <FIG>. The shape of the tension beam reinforcing member <NUM> is not limited to the above embodiments and may be modified in various ways.

<FIG> is a diagram showing an embodiment and a modified embodiment of a cross sectional shape of the connection reinforcing member <NUM> for preventing buckling. As shown in <FIG>, the connection reinforcing member <NUM> may be formed with a T-shape sectional view or, as shown in <FIG>, may be formed with an L-shape sectional view. The cross sectional shape of the connection reinforcing member <NUM> for preventing buckling is not limited to the above embodiment and may be modified in various ways.

As described above, the curve-combined polygonal pressure tank according to the present invention may be configured in such a way that discontinuity of internal pressure is overcome by thinning the tension member <NUM> to overcome a problem in terms of tension stress and, simultaneously, section modulus is increased by forming a reinforcing member in the tension beam to simultaneously overcome a problem in terms of compression stress.

<FIG> shows a curve-combined polygonal pressure tank including a tension plate formed therein instead of a tension beam, as an example of the tension member <NUM> and, here, similarly to a curve-combined polygonal pressure tank including a tension beam formed therein, the outermost pressure plate may be spaced apart from a connection point between the flat member <NUM> and the curved member <NUM> by a constant distance d toward the flat member <NUM>.

Hollow portions <NUM> may be formed in the tension plate, liquefied natural gas (LNG) may be moved in the tank through the hollow portions <NUM> and, during manufacture of the tank, the hollow portions <NUM> may function as a path through which a worker moves.

The aforementioned additional method for enhancing the effect of preventing discontinuity of internal pressure may also be applied to the outermost tension plate and, as shown in <FIG>, the outermost tension plate may be thinned or may be formed with a curved shape or a U-shape.

In addition, the connection reinforcing member <NUM> for connection between the outermost tension plate and a portion of the curved member may be added and, as shown in <FIG>, the connection reinforcing member <NUM> may be shaped like an arced connection reinforcing member that is formed at only a portion of the curved member or a circular connection reinforcing member that is formed at an entire portion of the curved member, or the connection reinforcing member <NUM> may be thinned toward a central portion of the curved portion.

The aforementioned additional method for preventing buckling may also be applied to the outermost tension plate and, as shown in <FIG> and <FIG>, a reinforcing member with various cross sectional shapes may be added to the outermost tension plate and the connection reinforcing member <NUM> to enhance the effect of preventing buckling.

As shown in <FIG>, the curve-combined polygonal pressure tank <NUM> according to the present invention may be formed with various shapes and, referring to <FIG>, a shape of the curve-combined polygonal pressure tank <NUM> according to the present invention viewed in the Z-axis direction, that is, a shape of the flat member <NUM> viewed from an upper portion thereof may be a flat rectangular shape as shown in <FIG> but may be an asymmetrical shape with different facing surfaces depending on a shape of a space for cumulating pressure tanks and, for example, may be a trapezoidal shape as shown in <FIG>, or may be a polygonal shape with one narrow side as shown in <FIG>, or may have another polygonal shape.

<FIG> shows the embodiment shown in <FIG> in a 3D shape to aid in understanding and, here, one side with a narrow width is disposed toward a stem or a stern or is disposed downward depending on a shape of a vessel, thereby enhancing space efficiency. That is, the flat member <NUM> may have a polygonal shape and may be formed in such a way that one of the facing sides is shorter than the other side.

<FIG> are shown for explanation of a structure of an internal grid structure <NUM> of the embodiment of <FIG> and, here, the internal grid structure <NUM> may include a grid reinforcing member <NUM> that is formed in grid patterns by arranging a plurality of H-type beams perpendicularly to each other between the flat members <NUM>, and a plurality of ring-type reinforcing members <NUM> that extend from a portion of the H-type beams and are coupled to an internal side of the adjacent first curved member <NUM>, with predetermined curvature. In this case, the outermost H-type beam among the plurality of H-type beams may be disposed in the tank to be spaced apart from an edge connected between the flat member <NUM> and the first curved member <NUM> by a constant distance and some of the plurality of ring-type reinforcing members <NUM> may have a T-shape sectional view.

<FIG> and <FIG> show a curve-combined polygonal pressure tank with a tension plate formed therein according to a third embodiment and, according to the third embodiment, a grid-type reinforcing structure <NUM> may be formed between the flat members <NUM> and may include flat plate-type reinforcing members <NUM> having the hollow portions <NUM> and linear-type reinforcing members <NUM> for connecting the flat plate-type reinforcing members <NUM>. In this case, a reinforcing flange <NUM> may be formed on an outer periphery of the hollow portion <NUM>.

In this case, a distance by which the outermost member is spaced apart from a boundary between the flat member <NUM> and the curved member <NUM> may be configured with different distances d1 and d2 in width and length directions, respectively.

In addition, when curvature of the curved member <NUM> of the curve-combined polygonal pressure tank <NUM> is large, a reinforcing ring may be additionally included inside the curved member <NUM> to prevent influence of buckling. <FIG> show a modified embodiment of the third embodiment of the curve-combined polygonal pressure tank that additionally includes the reinforcing ring.

The reinforcing ring additionally included inside the curved member may also be applied to the aforementioned curve-combined polygonal pressure tank with the tension beam therein as shown in <FIG>.

This is now described in more detail with reference to <FIG> and <FIG>. In the case of the internal grid structure <NUM> with the reinforcing ring formed therein, a plurality of horizontal grid plates <NUM> and a plurality of vertical grid plates <NUM>, each of which includes a reinforcing ring formed therein, may cross each other and, as necessary, a plurality of linear-type reinforcing members <NUM> may be disposed between the horizontal grid plates <NUM> or the vertical grid plates <NUM> to reinforce strength.

<FIG> shows the curve-combined polygonal pressure tank <NUM> according to another embodiment and shows an embodiment of two pairs of flat members <NUM>, but not a pair of flat members. The curve-combined polygonal pressure tank <NUM> according to a fourth embodiment shown in <FIG> may be different from the aforementioned embodiment in that the fourth embodiment has the feature in which the number of curved surfaces except for edge portions is two.

Due to the above feature, there is a problem in terms of stress imbalance at the connection portion between the flat member <NUM> and the curved member according to the aforementioned embodiment and, also, there are a problem in terms of stress imbalance or degradation in pressure-resistant performance at a connection portion between a lateral end portion of another flat member <NUM> disposed on a lateral surface and a lateral surface of the curved member and a problem in terms of pressure-resistant performance of the flat member <NUM> at an lateral end portion that is a region connected to the curved member, as shown in <FIG>.

<FIG> shows an embodiment for overcoming the above problem and, here, cross frames <NUM> for connection between lateral end portions may each be disposed in up and down directions to achieve an effect of overcoming stress imbalance at the lateral end portion and enhancing pressure-resistant performance. <FIG> shows an arrangement viewed from the above and <FIG> shows an arrangement viewed from the lateral aspect.

Claim 1:
A curve-combined polygonal pressure tank (<NUM>) for accommodating a fluid at high pressure therein, the pressure tank (<NUM>) comprising:
flat members (<NUM>) disposed at upper and lower portions of the pressure tank (<NUM>);
a first curved member (<NUM>) that connects edges of the flat member disposed at the upper portion and the flat member disposed at the lower portion and is formed with predetermined curvature; and
a second curved member (<NUM>) connecting neighboring curved edges of the first curved member,
wherein the curve-combined polygonal pressure tank (<NUM>) comprises a stress-buffer portion formed therein to prevent stress discontinuity at a connection portion between the flat member (<NUM>) and the first curved member (<NUM>) wherein the curve-combined polygonal pressure tank (<NUM>) includes a plurality of tension members (<NUM>) disposed between the flat member (<NUM>) disposed at the upper portion and the flat member (<NUM>) disposed at the lower portion; and
wherein the outermost tension member (<NUM>) among the plurality of tension members (<NUM>) is spaced apart from a boundary P at which the first curved member (<NUM>) and the flat member (<NUM>) contact each other by a constant distance d toward the flat member (<NUM>) to form the stress-buffer portion, or
wherein the outermost tension member (<NUM>) among the plurality of tension members (<NUM>) is coupled to a boundary P at which the first curved member (<NUM>) and the flat member (<NUM>) contact each other and is formed to be thinner than a tension member disposed inward to form the stress-buffer portion, or
wherein the outermost tension member (<NUM>) among the plurality of tension members (<NUM>) is coupled to a boundary P at which the first curved member (<NUM>) and the flat member (<NUM>) contact each other and is curved with predetermined curvature in an opposite direction to the first curved member (<NUM>) or is formed with a bent portion that is bent in an opposite direction to the first curved member (<NUM>), to form a stress-buffer portion.