LNG ship bilge rib plate system

Abstract

The invention discloses an LNG ship bilge rib plate system. The LNG ship bilge rib plate system comprises a bulkhead reverse jacking rib plate fixed to the lower portion of an inner watertight bulkhead, a watertight rib plate fixed to the lower portion of an outer watertight bulkhead and a plurality of ballast tank rib plates evenly distributed below a liquid cargo tank. The main bearing ribs and the longitudinal supporting ribs are arranged on the bulkhead reverse top rib plates, the watertight rib plates and the ballast tank rib plates, lattices are formed on the surfaces of the rib plates, and the loading capacity of the rib plates is guaranteed. The rib plate is provided with the multiple plate joints, the manufacturing difficulty of the rib plate, especially the ballast tank rib plate with a large opening is reduced, the rib plate is divided into different areas according to the plate joints, the plate thicknesses of the different areas are set according to different pressures borne by the areas, and the cost is saved as much as possible on the premise that the bearing load of the rib plate is guaranteed.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of shipbuilding, in particular to a LNG ship's bilge rib system. BACKGROUND

[0002] Due to the need of loading liquid cargo, the transverse bulkhead of the liquid cargo tank of the LNG ship is a double bulkhead. In the structural design, the bilge is designed as a ballast tank, and the ballast tank is a single bulkhead. Therefore, in the bilge, the bilge rib is usually designed as a watertight bulkhead, a bulkhead isolation bulkhead and a liquid cargo tank corresponding to the watertight rib, the bulkhead counter rib and the ballast tank rib respectively, to adapt to the needs of different strength and structure forms. The bulkhead counter rib in the prior art is usually provided with a large opening to reduce the weight of the rib, thereby increasing the manufacturing cost of the LNG ship's bilge rib system. However, in order to ensure the bearing capacity of the bulkhead counter rib, a plurality of reinforcing structures are arranged on the side of the bulkhead counter rib close to the liquid cargo tank. The bulkhead counter rib with a large opening increases the manufacturing difficulty of the LNG ship's bilge rib system. SUMMARY

[0003] In view of the defects in the prior art, the present application provides a LNG ship's bilge rib system to solve the technical problems of high manufacturing cost and great manufacturing difficulty of the LNG ship's bilge rib system in the prior art.

[0004] In order to achieve the above-mentioned purpose of the application, the technical scheme provided by the present application is as follows:

[0005] A LNG ship's bilge rib system, the bilge of the LNG ship is arranged below the liquid cargo tank, and the front and rear ends of the liquid cargo tank are both provided with an isolation empty tank, the isolation empty tank comprises an inner watertight bulkhead and an outer watertight bulkhead, the inner watertight bulkhead is used to isolate the liquid cargo tank and the isolation empty tank, and the outer watertight bulkhead is used to isolate the isolation empty tank and another liquid cargo tank, the bilge rib system comprises a bulkhead counter rib fixed below the inner watertight bulkhead, a watertight rib fixed below the outer watertight bulkhead and a plurality of ballast tank ribs uniformly distributed below the liquid cargo tank, the bulkhead counter rib is used to support the inner watertight bulkhead, and the watertight rib is used to support the outer watertight bulkhead.

[0006] The bulkhead top rib is provided with several manholes. Multiple longitudinal ribs are provided at the outer end of the bulkhead top rib. The bulkhead top rib is divided into a first upper part and a first lower part along the straight line where the ballast tank end platform is located. A first main bearing rib is fixedly provided on the first upper part. The first main bearing rib is perpendicular to the first upper part. The upper end of the first main bearing rib is fixed to the upper end of the first upper part, and the lower end of the first main bearing rib is fixed to the lower end of the first upper part. The distance between the upper end of the first main bearing rib and the center line of the hull in the beam direction is greater than the distance between the lower end of the first main bearing rib and the center line of the hull in the beam direction. The top of the longitudinal rib of the bulkhead top rib is provided with a longitudinal rib stiffener. The longitudinal rib stiffener is perpendicular to the bulkhead top rib. One end of the longitudinal rib stiffener on the first upper part is fixedly connected to the longitudinal rib, and the other end of the longitudinal rib stiffener on the first upper part is fixedly connected to the first main bearing rib. One end of the longitudinal rib stiffener on the first lower part is fixedly connected to the longitudinal rib, and the other end of the longitudinal rib stiffener on the first lower part is fixed to the upper end of the first lower part.

[0007] In one embodiment, the first upper part is provided with two slab joints. One slab joint is parallel to the first main reinforcing bar, and the other slab joint is located between the slab joint parallel to the first main reinforcing bar and the inclined inner bottom plate. The other slab joint intersects the slab joint parallel to the first main reinforcing bar at an angle in a "Y" shape. The two slab joints divide the first upper part into region h, region f and region g. Region h is the area between the upper boundary of the first lower part and the slab joint parallel to the first main reinforcing bar. Region f is the upper area where the two slab joints intersect. Region g is the area enclosed by the two slab joints and the upper boundary of the first lower part. The thickness of region g is greater than the thickness of region f, and the thickness of region f is greater than the thickness of region h.

[0008] In one embodiment, the watertight rib has multiple longitudinal ribs at its outer end. The watertight rib is divided into a second upper part and a second lower part along the straight line where the ballast tank end platform is located. A second main bearing rib is fixedly installed on the second upper part. The second main bearing rib is perpendicular to the second upper part. The upper end of the second main bearing rib is fixed to the upper end of the second upper part, and the lower end of the second main bearing rib is fixed to the lower end of the second upper part. The distance between the upper end of the second main bearing rib and the center line of the hull in the beam direction is greater than the distance between the lower end of the second main bearing rib and the center line of the hull in the beam direction. The top of the longitudinal rib of the watertight rib has a longitudinal rib stiffener. The longitudinal rib stiffener is perpendicular to the watertight rib. One end of the longitudinal rib stiffener on the second upper part is fixedly connected to the longitudinal rib, and the other end of the longitudinal rib stiffener on the second upper part is fixedly connected to the second main bearing rib. One end of the longitudinal rib stiffener on the second lower part is fixedly connected to the longitudinal rib, and the other end of the longitudinal rib stiffener on the second lower part is fixed to the upper end of the second lower part. No holes are opened in the watertight rib.

[0009] In one embodiment, the second main support bar is welded to the second upper part, the strength of the second main support bar is greater than the strength of the first main support bar, and an elbow plate is welded between the end of the second main support bar and the second upper part.

[0010] In one embodiment, two slab joints are provided on the second upper part. One slab joint is parallel to the second main reinforcing bar, and the other slab joint is located between the slab joint parallel to the second main reinforcing bar and the inclined inner bottom plate. The other slab joint intersects the slab joint parallel to the second main reinforcing bar at an angle in a "Y" shape. The two slab joints divide the second upper part into region k, region i, and region j. Region k is the region between the upper boundary of the second lower part and the slab joint parallel to the second main reinforcing bar. Region i is the upper region where the two slab joints intersect. Region j is the region enclosed by the two slab joints and the upper boundary of the second lower part. The slab thickness of region j is greater than that of region i, and the slab thickness of region i is greater than that of region k.

[0011] In one embodiment, the outer end of the ballast tank rib is provided with multiple longitudinal ribs. The ballast tank rib is divided into a third upper part and a third lower part along the straight line where the ballast tank end platform is located. The ballast tank rib is provided with a large opening, which is an equiangular triangle with rounded corners. The larger corner of the large opening is close to the outer side of the bilge, and the other two corners of the large opening are close to the upper boundary of the ballast tank rib and the ballast tank end platform, respectively. A third main bearing rib is fixedly provided on the third upper part, and the third main bearing rib is perpendicular to the second upper part. The upper end of the third main support is fixed to the upper end of the third upper part, and the lower end of the third main support is fixed at the large opening. The top of the longitudinal rib of the ballast tank rib is provided with a longitudinal rib stiffener, which is perpendicular to the watertight rib. One end of the longitudinal rib stiffener is fixed to the top of the longitudinal rib, and the other end of the longitudinal rib stiffener is fixed at the opening of the large opening, the upper boundary of the third main support or the third lower part. A bent rib is provided between the bottom edge of the large opening and the inclined inner bottom plate. The bent rib passes vertically through the longitudinal rib stiffener and is parallel to the inclined inner bottom plate.

[0012] In one embodiment, the distance between the flexor tendon and the bottom edge of the large opening is [(a / 2)+b] / 2, where a is the distance between the top of the longitudinal bone on the inclined inner bottom plate and the inclined inner bottom plate, and b is the distance between the top of the longitudinal bone on the inclined inner bottom plate and the bottom edge of the large opening.

[0013] In one embodiment, the radius of the rounded corner at the larger corner of the large opening is twice the radius of the rounded corner at the smaller corner. The radius of the rounded corner at the smaller corner of the large opening is defined as c, then 800mm≤c≤1000mm. The distance between the boundary of the large opening and the outer boundary of the ballast tank rib is 1.4a, the distance between the boundary of the large opening and the bottom boundary of the ballast tank rib is 1.6c, and the distance between the boundary of the large opening and the inclined inner bottom is 1.6c.

[0014] In one embodiment, a reverse small elbow plate and a triangular large elbow plate are respectively provided on the left and right sides of the longitudinal rib stabilizing tendon with flexor tendons. The bottom edges of the reverse small elbow plate and the triangular large elbow plate are fixed to the top of the longitudinal rib, the sides of the reverse small elbow plate and the triangular large elbow plate are fixed to the longitudinal rib stabilizing tendon, and the top of the triangular large elbow plate is fixed to the end panel of the longitudinal rib stabilizing tendon.

[0015] In one embodiment, at least one slab joint is provided on the third upper part, one of which is parallel to the third main support bar. The slab joint parallel to the third main support bar divides the third upper part into a region d close to the inclined inner bottom plate and a region e away from the inclined inner bottom plate, wherein the thickness of region d is greater than the thickness of region e.

[0016] Compared with the prior art, this application has at least the following beneficial effects:

[0017] The LNG ship bilge rib system of this invention eliminates the large openings in the bulkhead top ribs of the prior art, only providing manholes on the bulkhead top ribs. Main load-bearing ribs and longitudinal stiffeners are provided on the bulkhead top ribs, watertight ribs, and ballast tank ribs, forming a grid pattern on the rib surface to ensure the load-bearing capacity of the ribs. Multiple rib seams are provided, reducing the manufacturing difficulty of the ribs, especially the ballast tank ribs with large openings. The ribs are divided into different areas according to the seams, and different plate thicknesses are set for different areas based on the pressure they bear, achieving cost savings while ensuring the ribs can bear the load. This application also provides buckling ribs on the ballast tank ribs with large openings. Reverse small elbow plates and triangular large elbow plates are respectively provided on the left and right sides of the longitudinal stiffeners with buckling ribs 305, increasing the load-bearing capacity of the ballast tank ribs. Attached Figure Description

[0018] Figure 1 This is a schematic diagram of the structure of the LNG ship's bilge section in an embodiment of this application;

[0019] Figure 2 This is a structural schematic diagram of the anti-top rib plate of the bulkhead in the embodiment of this application;

[0020] Figure 3 This is a schematic diagram of the structure of the watertight rib in the embodiment of this application;

[0021] Figure 4 This is a schematic diagram of the structure of the ballast tank rib in the embodiment of this application;

[0022] Figure 5 yes Figure 4 View from AA direction;

[0023] Reference numerals: 01, LNG bilge; 02, cargo tank; 021, inner watertight bulkhead; 022, outer watertight bulkhead; 1, bulkhead top rib; 101, first upper part; 102, first lower part; 103, first main bearing reinforcement; 104, manhole; 2, watertight rib; 201, second upper part; 202, second lower part; 203, second main bearing reinforcement; 3, ballast tank rib; 301, third upper part; 302, third lower part; 303, large opening; 304, elbow plate panel; 305, buckling reinforcement; 306, third main bearing reinforcement; 4, ballast tank end platform; 5, plate joint; 6, longitudinal rib; 7, longitudinal rib stiffener; 8, reverse small elbow plate; 9, triangular large elbow plate; 10, inclined inner bottom plate. Detailed Implementation

[0024] To make the objectives, technical solutions, and advantages of this invention clearer, the invention is described below with reference to specific embodiments shown in the accompanying drawings. However, it should be understood that these descriptions are merely exemplary and not intended to limit the scope of the invention. Furthermore, descriptions of well-known structures and technologies are omitted in the following description to avoid unnecessarily obscuring the concept of the invention.

[0025] The terminology used in this disclosure is for the purpose of describing particular embodiments only and is not intended to be limiting of the disclosure. The singular forms “a,” “the,” and “the” as used in this disclosure and the appended claims are also intended to include the plural forms unless the context clearly indicates otherwise. It should also be understood that the term “and / or” as used herein refers to and includes any and all possible combinations of one or more of the associated listed items.

[0026] It should be understood that although the terms first, second, third, etc., may be used in this disclosure to describe various information, such information should not be limited to these terms and should not be construed as indicating or implying relative importance. These terms are used only to distinguish information of the same type from one another. For example, without departing from the scope of this disclosure, first information may also be referred to as second information, and similarly, second information may also be referred to as first information. Depending on the context, the word "if" as used herein may be interpreted as "when," "when," or "in response to determination."

[0027] In the description of this invention, unless otherwise specified and limited, it should be noted that the terms "installation", "connection" and "linking" should be interpreted broadly. For example, they can refer to mechanical connection or internal connection between two components. They can be direct connection or indirect connection through an intermediate medium. Those skilled in the art can understand the specific meaning of the above terms according to the specific circumstances.

[0028] To better understand the technical solution of the present invention, the present invention will be described in detail below with reference to the accompanying drawings.

[0029] This embodiment provides an LNG ship bilge rib system, as shown in the attached figure. Figure 1 As shown, the bilge 01 of the LNG vessel is located below the cargo tank 02. Both ends of the cargo tank 02 are equipped with isolation compartments. The isolation compartments include an inner watertight bulkhead 021 and an outer watertight bulkhead 022. The inner watertight bulkhead 021 is used to isolate the cargo tank 02 and the isolation compartment, and the outer watertight bulkhead 022 is used to isolate the isolation compartment and another cargo tank 02. The bilge rib system includes a bulkhead top rib 1 fixed below the inner watertight bulkhead 021, a watertight rib 2 fixed below the outer watertight bulkhead 022, and several ballast tank ribs 3 evenly distributed below the cargo tank 02. The bulkhead top rib 1 is used to support the inner watertight bulkhead 021, and the watertight rib 2 is used to support the outer watertight bulkhead 022.

[0030] As attached Figure 2 As shown, several manholes 104 are provided on the bulkhead top rib 1, and multiple longitudinal ribs 6 are provided on the outer end of the bulkhead top rib 1. The bulkhead top rib 1 is divided into a first upper part 101 and a first lower part 102 along the straight line where the ballast tank end platform 4 is located. A first main bearing rib 103 is fixedly provided on the first upper part 101. The first main bearing rib 103 is perpendicular to the first upper part 101. The upper end of the first main bearing rib 103 is fixed to the upper end of the first upper part 101, and the lower end of the first main bearing rib 103 is fixed to the lower end of the first upper part 101. The upper end of the first main bearing rib 103 is perpendicular to the width of the hull. The distance between the centerline and the first main supporting rib 103 is greater than the distance between the lower end of the first main supporting rib 103 and the centerline of the ship's beam direction. A longitudinal stiffener 7 is provided at the top of the longitudinal rib 6 of the bulkhead top rib 1. The longitudinal stiffener 7 is perpendicular to the bulkhead top rib 1. One end of the longitudinal stiffener 7 on the first upper part 101 is fixedly connected to the longitudinal rib 6, and the other end is fixedly connected to the first main supporting rib 103. One end of the longitudinal stiffener 7 on the first lower part 102 is fixedly connected to the longitudinal rib 6, and the other end is fixed to the upper end of the first lower part 102. This application reduces the span of the longitudinal rib 6 by providing the longitudinal stiffener 7. Through the cooperation of the longitudinal stiffener 7 and the first main supporting rib 103, a grid pattern is formed on the surface of the bulkhead top rib 1, ensuring the load-bearing capacity of the bulkhead top rib 1. In this embodiment, the longitudinal stiffener 7 in the bulkhead top rib 1 is made of bulb flat steel.

[0031] Two plate joints 5 are provided on the first upper part 101. One plate joint is parallel to the first main bearing rib 103, and the other plate joint is located between the plate joint parallel to the first main bearing rib 103 and the inclined inner bottom plate 10. The other plate joint 5 intersects the plate joint parallel to the first main bearing rib 103 at an angle in a "Y" shape. The two plate joints 5 divide the first upper part 101 into region h, region f and region g. Region h is the area between the upper boundary of the first lower part 102 and the plate joint parallel to the first main bearing rib 103. Region f is the upper area where the two plate joints intersect. Region g is the area enclosed by the two plate joints and the upper boundary of the first lower part 102. Since the pressure is greater closer to the liquid cargo tank area, in order to save costs as much as possible while ensuring the load-bearing capacity of the rib plate, the plate thickness of region g is greater than that of region f, and the plate thickness of region f is greater than that of region h.

[0032] like Figure 3 As shown, multiple longitudinal ribs 6 are provided at the outer end of the watertight rib 2. The watertight rib 2 is divided into a second upper part 201 and a second lower part 202 along the straight line where the ballast tank end platform 4 is located. A second main bearing rib 203 is fixedly provided on the second upper part 201. The second main bearing rib 203 is perpendicular to the second upper part 201. The upper end of the second main bearing rib 203 is fixed to the upper end of the second upper part 201, and the lower end of the second main bearing rib 203 is fixed to the lower end of the second upper part 201. The distance between the upper end of the second main bearing rib 203 and the centerline of the hull in the beam direction is greater than that of the second main bearing rib 202. The distance between the lower end of the second main bearing reinforcement 203 and the centerline of the hull in the beam direction; the top of the longitudinal stiffener 6 of the watertight rib 2 is provided with a longitudinal stiffener 7, which is perpendicular to the watertight rib 2; one end of the longitudinal stiffener 7 on the second upper part 201 is fixedly connected to the longitudinal stiffener 6, and the other end of the longitudinal stiffener 7 on the second upper part 201 is fixedly connected to the second main bearing reinforcement 203; one end of the longitudinal stiffener 7 on the second lower part 202 is fixedly connected to the longitudinal stiffener 6, and the other end of the longitudinal stiffener 7 on the second lower part 202 is fixed to the upper end of the second lower part 202. Unlike the bulkhead top rib 1, the watertight rib 2 does not have holes. Similar to the bulkhead top rib 1, a grid pattern is formed on the surface of the rib through the cooperation of the longitudinal stiffener 7 and the main bearing reinforcement, ensuring the load-bearing capacity of the rib. Because the load borne by the watertight rib plate 2 is greater than the load borne by the bulkhead top rib plate 1, the second main bearing rib 203 is welded to the second upper part 201. The strength of the second main bearing rib 203 is greater than the strength of the first main bearing rib 103. An elbow plate is welded between the end of the second main bearing rib 203 and the second upper part to enhance the bearing capacity of the second main bearing rib 103.

[0033] Two plate joints 5 are provided on the second upper part 201. One plate joint is parallel to the second main bearing rib 103, and the other plate joint is located between the plate joint parallel to the second main bearing rib 103 and the inclined inner bottom plate 10. The other plate joint 5 intersects the plate joint parallel to the second main bearing rib 103 at an angle in a "Y" shape. The two plate joints 5 divide the second upper part 201 into region k, region i and region j. Region k is the area between the upper boundary of the second lower part 202 and the plate joint parallel to the second main bearing rib 203. Region i is the upper area where the two plate joints intersect. Region j is the area enclosed by the two plate joints and the upper boundary of the second lower part 202. Since the pressure is greater closer to the liquid cargo tank area, in order to save costs as much as possible while ensuring the load-bearing capacity of the rib plate, the plate thickness of region j is greater than that of region i, and the plate thickness of region i is greater than that of region k.

[0034] like Figure 4 As shown, multiple longitudinal ribs 6 are provided at the outer end of the ballast tank rib 3. The ballast tank rib 3 is divided into a third upper part 301 and a third lower part 302 along the straight line where the ballast tank end platform 4 is located. A large opening 303 is provided on the ballast tank rib 3. The large opening 303 is an equiangular triangle with rounded corners. The larger corner of the large opening 303 is close to the outer side of the bilge. The other two corners of the large opening 303 are close to the upper boundary of the ballast tank rib 3 and close to the ballast tank end platform 4, respectively. A third main bearing rib 30 is fixedly provided on the third upper part 301. 6. The third main support rib 306 is perpendicular to the second upper part 201. The upper end of the third main support rib 306 is fixed to the upper end of the third upper part 301, and the lower end of the third main support rib 306 is fixed at the opening of the large opening 303. The top of the longitudinal rib 6 of the ballast tank rib plate 3 is provided with a longitudinal rib stiffener 7. The longitudinal rib stiffener 7 is perpendicular to the watertight rib plate 2. One end of the longitudinal rib stiffener 7 is fixed to the top of the longitudinal rib 6, and the other end of the longitudinal rib stiffener 7 is fixed at the opening of the large opening 303, or at the upper boundary of the third main support rib 306 or the third lower part 302. A buckling rib 305 is provided between the bottom edge of the large opening 303 and the inclined inner bottom plate 10. The buckling rib 305 passes vertically through the longitudinal stiffener 7 and is parallel to the inclined inner bottom plate 10. In this embodiment, the distance between the buckling rib 305 and the bottom edge of the large opening 303 is [(a / 2)+b] / 2, where a is the distance between the top of the longitudinal stiffener 6 on the inclined inner bottom plate 10 and the inclined inner bottom plate 10, and b is the distance between the top of the longitudinal stiffener 6 on the inclined inner bottom plate 10 and the bottom edge of the large opening 303. Because the pressure borne by the ballast tank rib 3 near the inclined inner bottom plate 10 is relatively large, the longitudinal stiffener 7 alone cannot meet the design requirements. Therefore, the buckling rib 305 is provided to increase the plate size of the ballast tank rib 3, thereby increasing the load-bearing capacity of the ballast tank rib 3.

[0035] Because the bilge rib system includes several ballast tank ribs 3, and the ballast tank ribs 3 bear relatively little load, this embodiment provides a large opening 303 on the ballast tank ribs 3 to reduce their weight. Setting the large opening as a rounded triangle reduces stress concentration. The radius of the rounded corner at the larger corner of the large opening 303 is twice the radius of the rounded corner at the smaller corner. Let c be the radius of the rounded corner at the smaller corner of the large opening 303, then 800mm ≤ c ≤ 1000mm. In this embodiment, the distance between the boundary of the large opening 303 and the outer boundary of the ballast tank rib 3 is 1.4a, the distance between the boundary of the large opening 303 and the bottom boundary of the ballast tank rib 3 is 1.6c, and the distance between the boundary of the large opening 303 and the inclined inner bottom plate 10 is 1.6c.

[0036] As attached Figure 5 As shown, the longitudinal rib stabilizing tendon 7, which is equipped with flexor tendons 305, has reverse small elbow plates 8 and triangular large elbow plates 9 on its left and right sides, respectively. The bottom edges of the reverse small elbow plates 8 and triangular large elbow plates 9 are fixed to the top of the longitudinal rib 6, and the sides of the reverse small elbow plates 8 and triangular large elbow plates 9 are fixed to the longitudinal rib stabilizing tendon 7. The top of the triangular large elbow plate 9 is fixed to the elbow plate panel 304 at the end of the longitudinal rib stabilizing tendon 7. The strength of the longitudinal rib stabilizing tendon 7 is enhanced by the reverse small elbow plates 8 and triangular large elbow plates 9.

[0037] To facilitate the fabrication of the ballast tank ribs 3 with large openings, reduce waste during layout, and maximize the use of steel plates, at least one plate joint 5 is provided on the third upper part 301. In this embodiment, the third upper part 301 has two plate joints 5, one of which is parallel to the third main bearing rib 306. The plate joint 5 parallel to the third main bearing rib 306 divides the third upper part 301 into a region d close to the inclined inner bottom plate 10 and a region e far away from the inclined inner bottom plate 10. The plate thickness of region d is greater than that of region e.

[0038] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit them; although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications can still be made to the specific implementation of the invention or equivalent substitutions can be made to some technical features without departing from the spirit of the technical solutions of the present invention, and all such modifications and substitutions should be covered within the scope of the technical solutions claimed in the present invention.

Claims

1. A bilge rib system for an LNG carrier, wherein the LNG bilge is disposed below the cargo tank, and isolation compartments are provided at both the fore and aft ends of the cargo tank, each isolation compartment comprising an inner watertight bulkhead and an outer watertight bulkhead, the inner watertight bulkhead separating the cargo tank from the isolation compartment, and the outer watertight bulkhead separating the isolation compartment from another cargo tank, characterized in that, The bilge rib system includes a bulkhead top rib fixed below the inner watertight bulkhead, a watertight rib fixed below the outer watertight bulkhead, and several ballast tank ribs evenly distributed below the cargo tank. The bulkhead top rib is used to support the inner watertight bulkhead, and the watertight rib is used to support the outer watertight bulkhead. The bulkhead top rib is provided with several manholes. Multiple longitudinal ribs are provided at the outer end of the bulkhead top rib. The bulkhead top rib is divided into a first upper part and a first lower part along the straight line where the ballast tank end platform is located. A first main bearing rib is fixedly provided on the first upper part. The first main bearing rib is perpendicular to the first upper part. The upper end of the first main bearing rib is fixed to the upper end of the first upper part, and the lower end of the first main bearing rib is fixed to the lower end of the first upper part. The distance between the upper end of the first main bearing rib and the center line of the hull in the beam direction is greater than the distance between the lower end of the first main bearing rib and the center line of the hull in the beam direction. The top of the longitudinal rib of the bulkhead top rib is provided with a longitudinal rib stiffener. The longitudinal rib stiffener is perpendicular to the bulkhead top rib. One end of the longitudinal rib stiffener on the first upper part is fixedly connected to the longitudinal rib, and the other end of the longitudinal rib stiffener on the first upper part is fixedly connected to the first main bearing rib. One end of the longitudinal rib stiffener on the first lower part is fixedly connected to the longitudinal rib, and the other end of the longitudinal rib stiffener on the first lower part is fixed to the upper end of the first lower part.

2. The LNG ship bilge rib system according to claim 1, characterized in that, The first upper part has two slab joints. One slab joint is parallel to the first main support bar, and the other slab joint is located between the slab joint parallel to the first main support bar and the inclined inner bottom plate. The other slab joint intersects the slab joint parallel to the first main support bar at an angle in a "Y" shape. The two slab joints divide the first upper part into region h, region f and region g. Region h is the area between the upper boundary of the first lower part and the slab joint parallel to the first main support bar. Region f is the upper area where the two slab joints intersect. Region g is the area enclosed by the two slab joints and the upper boundary of the first lower part. The slab thickness of region g is greater than the slab thickness of region f, and the slab thickness of region f is greater than the slab thickness of region h.

3. The LNG ship bilge rib system according to claim 1, characterized in that, The watertight rib has multiple longitudinal ribs at its outer end. The watertight rib is divided into a second upper part and a second lower part along the straight line of the ballast tank end platform. A second main bearing rib is fixedly installed on the second upper part. The second main bearing rib is perpendicular to the second upper part. The upper end of the second main bearing rib is fixed to the upper end of the second upper part, and the lower end of the second main bearing rib is fixed to the lower end of the second upper part. The distance between the upper end of the second main bearing rib and the center line of the hull in the beam direction is greater than the distance between the lower end of the second main bearing rib and the center line of the hull in the beam direction. The top of the longitudinal rib of the watertight rib has a longitudinal rib stiffener. The longitudinal rib stiffener is perpendicular to the watertight rib. One end of the longitudinal rib stiffener on the second upper part is fixedly connected to the longitudinal rib, and the other end of the longitudinal rib stiffener on the second upper part is fixedly connected to the second main bearing rib. One end of the longitudinal rib stiffener on the second lower part is fixedly connected to the longitudinal rib, and the other end of the longitudinal rib stiffener on the second lower part is fixed to the upper end of the second lower part. No holes are opened in the watertight rib.

4. The LNG ship bilge rib system according to claim 3, characterized in that, The second main support bar is welded to the second upper part. The strength of the second main support bar is greater than that of the first main support bar. An elbow plate is welded between the end of the second main support bar and the second upper part.

5. The LNG ship bilge rib system according to claim 3, characterized in that, The second upper part has two slab joints. One slab joint is parallel to the second main support bar, and the other slab joint is located between the slab joint parallel to the second main support bar and the inclined inner bottom plate. The other slab joint intersects the slab joint parallel to the second main support bar at an angle in a "Y" shape. The two slab joints divide the second upper part into region k, region i and region j. Region k is the area between the upper boundary of the second lower part and the slab joint parallel to the second main support bar. Region i is the upper area where the two slab joints intersect. Region j is the area enclosed by the two slab joints and the upper boundary of the second lower part. The slab thickness of region j is greater than that of region i. The slab thickness of region i is greater than that of region k.

6. The LNG ship bilge rib system according to claim 1, characterized in that, The outer end of the ballast tank rib is provided with multiple longitudinal ribs. The ballast tank rib is divided into a third upper part and a third lower part along the straight line of the ballast tank end platform. The ballast tank rib is provided with a large opening, which is an equiangular triangle with rounded corners. The larger corner of the large opening is close to the outer side of the bilge, and the other two corners are close to the upper boundary of the ballast tank rib and the ballast tank end platform, respectively. A third main bearing rib is fixedly provided on the third upper part, and the third main bearing rib is perpendicular to the second upper part. The upper end of the rib is fixed to the upper end of the third upper part, and the lower end of the third main bearing rib is fixed at the large opening. The top of the longitudinal rib of the ballast tank rib is provided with a longitudinal rib stiffener, which is perpendicular to the watertight rib. One end of the longitudinal rib stiffener is fixed to the top of the longitudinal rib, and the other end of the longitudinal rib stiffener is fixed at the opening of the large opening, the upper boundary of the third main bearing rib, or the third lower part. A bent rib is provided between the bottom edge of the large opening and the inclined inner bottom plate. The bent rib passes vertically through the longitudinal rib stiffener and is parallel to the inclined inner bottom plate.

7. The LNG ship bilge rib system according to claim 6, characterized in that, The distance between the flexor tendon and the bottom edge of the large opening is [(a / 2)+b] / 2, where a is the distance between the top of the longitudinal bone on the inclined inner bottom plate and the inclined inner bottom plate, and b is the distance between the top of the longitudinal bone on the inclined inner bottom plate and the bottom edge of the large opening.

8. The LNG ship bilge rib system according to claim 7, characterized in that, The radius of the rounded corner at the larger corner of the large opening is twice the radius of the rounded corner at the smaller corner. The radius of the rounded corner at the smaller corner of the large opening is defined as c. Then, 800mm≤c≤1000mm. The distance between the boundary of the large opening and the outer boundary of the ballast tank rib is 1.4a. The distance between the boundary of the large opening and the bottom boundary of the ballast tank rib is 1.6c. The distance between the boundary of the large opening and the inclined inner bottom plate 1 is 1.6c.

9. The LNG ship bilge rib system according to claim 6, characterized in that, On the left and right sides of the longitudinal rib stabilizing tendon with flexor tendons, there are reverse small elbow plates and triangular large elbow plates respectively. The bottom edges of the reverse small elbow plates and triangular large elbow plates are fixed to the top of the longitudinal rib, the sides of the reverse small elbow plates and triangular large elbow plates are fixed to the longitudinal rib stabilizing tendon, and the top of the triangular large elbow plate is fixed to the end panel of the longitudinal rib stabilizing tendon.

10. The LNG ship bilge rib system according to claim 6, characterized in that, At least one slab joint is provided on the third upper part, one of which is parallel to the third main support bar. The slab joint parallel to the third main support bar divides the third upper part into a region d close to the inclined inner bottom plate and a region e far away from the inclined inner bottom plate. The thickness of region d is greater than the thickness of region e.

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