LNG liquid cargo tank with reduced sloshing impact and design method

Abstract

The application discloses an LNG liquid cargo tank capable of reducing sloshing impact and a design method, and relates to the field of LNG liquid cargo tanks.The LNG liquid cargo tank comprises a tank body, the cross section of the tank body is a polygon, the two sides of the polygon correspond to vertical tank walls of the tank body, the top of the polygon corresponds to a horizontal tank wall of the tank body, the horizontal tank wall extends to the vertical tank walls and is provided with an impact surface, the included angle between the impact surface and the horizontal tank wall is greater than 135° and smaller than 180°, the impact surface is arranged corresponding to a gas-liquid interface of the liquid cargo tank, at least one transition surface is arranged between the impact surface and the vertical tank walls, and the transition surface is located below the gas-liquid interface under full-load working conditions.The application effectively weakens the peak value of the impact force in the vertical direction generated by the liquid sloshing inside the liquid cargo tank on the inclined surface of the tank body by arranging a differential-angle buffer structure, the impact of the sloshing impact is weakened, the inclined surface subjected to the impact can use a low-strength high-thermal-insulation-performance thermal insulation layer, the disadvantage that the thermal insulation effect of high-strength thermal insulation materials is limited is avoided, and the low-temperature thermal insulation performance of the liquid cargo tank is effectively improved.

Description

Technical Field

[0001] This invention relates to the field of LNG ship cargo tanks, and more specifically to an LNG cargo tank and design method for reducing sloshing impact. Background Technology

[0002] LNG carriers use their cargo tanks to store cryogenic liquefied natural gas. During navigation, the ship will roll due to waves and wind, and the liquid in the tank will slosh around. The liquid impacts the tank wall structure, which will generate a large sloshing impact load. Especially near the gas-liquid interface, the peak value of the fluid impact load is high, which is the high-risk area for failure of the cargo tank containment system.

[0003] In existing membrane-type LNG containment systems, the area near the gas-liquid interface is subjected to severe liquid impact. To resist the enormous impact load, high-strength insulation materials must be used in this location. However, increasing the strength of the insulation material often sacrifices its insulation performance. High-strength insulation materials have a high thermal conductivity, leading to increased heat leakage in the cargo tank. If materials with excellent insulation performance are selected, their own strength may be insufficient, making it difficult to withstand the impact of swaying, which can easily lead to failures such as cracking and detachment of the insulation blocks, and deformation and damage of the shielding layer.

[0004] Currently available octagonal cargo tanks, under normal loading conditions, have the gas-liquid interface located precisely at the two upper sloping surfaces. These two surfaces form a fixed 135° angle with the top horizontal bulkhead, failing to dissipate the impact energy of the sloshing fluid in stages. This results in concentrated impact loads and places high strength requirements on the containment system materials. Therefore, there is an urgent need to improve cargo tank designs to reduce sloshing impact loads while maintaining cryogenic insulation performance. Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings of the prior art and provide an LNG cargo tank with reduced swaying impact. This invention solves the technical problem that existing LNG cargo tanks have large swaying impact loads at the gas-liquid interface, and the enclosure system needs to make trade-offs between material strength and thermal insulation performance. It reduces the peak value of swaying impact, allows the use of a high-insulation, relatively low-strength enclosure insulation structure, and reduces heat leakage of the tank.

[0006] To achieve the above objectives, the present invention adopts the following technical solution: An LNG cargo tank for reducing swaying impact includes a tank body with a polygonal cross-section. The two sides of the polygon correspond to vertical walls of the tank body, and the top of the polygon corresponds to a horizontal wall. The horizontal walls extend towards the vertical walls with impact surfaces. The angle between the impact surfaces and the horizontal walls is greater than 135° and less than 180°. At least one transition surface is provided between the impact surfaces and the vertical walls. The impact surfaces and the transition surfaces together form an arched shape towards the outside of the tank body. Under full-load conditions, the impact surfaces correspond to the gas-liquid interface of the LNG within the tank body, such that the gas-liquid interface is located within the impact surfaces, and the transition surfaces are located below the gas-liquid interface.

[0007] Furthermore, multiple transition surfaces are provided, and the angles between the multiple transition surfaces and the horizontal bulkhead increase sequentially from bottom to top.

[0008] Furthermore, the transition surface is provided with one.

[0009] Furthermore, the angle between the impact surface and the horizontal bulkhead is greater than the angle between the transition surface and the horizontal bulkhead.

[0010] Furthermore, the impact surface and the transition surface are symmetrically arranged on both sides of the horizontal bulkhead.

[0011] Furthermore, the angle between the impact surface and the horizontal bulkhead is 145°-160°.

[0012] Furthermore, the angle between the transition surface and the horizontal bulkhead is 110°-125°.

[0013] Furthermore, a dihedral membrane enclosure system is provided at the dihedral angle between the impact surface and the transition surface. The dihedral membrane enclosure system includes an insulation layer and a shielding layer. The insulation layer is formed by splicing together a plurality of first insulation blocks provided corresponding to the impact surface and a plurality of second insulation blocks provided corresponding to the transition surface. The shielding layer includes a metal plate that fixes the first insulation blocks and the second insulation blocks at a preset angle and a corrugated plate that connects the metal plate.

[0014] Furthermore, the side length of the impact surface along the cross-section of the cabin is smaller than the side length of the transition surface along the cross-section of the cabin.

[0015] This invention also discloses a design method for reducing LNG cargo tank sloshing impact as described above, comprising the following steps: S1, determining the position of the gas-liquid interface of the cargo tank under full load conditions; S2, designing an impact surface connected to the horizontal bulkhead at the top of the cargo tank, such that the angle between the impact surface and the horizontal bulkhead is greater than 135° and less than 180°, and the lower edge of the impact surface extends below the gas-liquid interface; S3, connecting the impact surface to the vertical bulkhead on the side of the cargo tank through a transition surface, such that the transition surface is located below the gas-liquid interface; S4: adjusting the height and / or width of the cargo tank according to the proportion constraints of the cargo tank to other functional areas on the LNG ship, so that the loading capacity of the cargo tank remains at a preset value.

[0016] Compared with the prior art, the present invention has the following beneficial effects: 1. This invention incorporates an impact surface and a transition surface located below the gas-liquid interface between the horizontal and vertical bulkheads at the top of the hull. The impact surface and transition surface arch outwards from the hull, forming a multi-level buffer structure with differentiated inclination angles. The sloshing fluid generated by the ship's rolling motion first acts on the impact surface at the gas-liquid interface. The inclined surface changes the direction of fluid movement, dissipating the fluid's impact kinetic energy and effectively weakening the peak value of the vertical impact force of the liquid on the bulkhead, thus reducing the impact load borne by the containment system.

[0017] 2. After the swaying impact load is reduced, the enclosure system at the impact surface and transition surface can use insulation layer materials with better thermal insulation performance and relatively lower strength to avoid the defects of poor thermal insulation effect of high-strength insulation materials, reduce overall heat leakage of the liquid cargo tank, and improve the low-temperature cold preservation capacity of the liquid cargo tank.

[0018] 3. Multiple transition surfaces can be set, and the angle between each transition surface and the horizontal bulkhead gradually increases from bottom to top, so as to achieve graded flow guidance and dissipate kinetic energy of the swaying fluid step by step, further reducing the peak impact. The impact surface and the transition surface are symmetrically arranged on both sides of the horizontal bulkhead, which is suitable for the ship's rolling conditions, and can achieve sway buffering on both sides. Attached Figure Description

[0019] Figure 1 This is a schematic diagram of the cross-sectional structure of the liquid cargo tank of the present invention; Figure 2 This is a schematic diagram of the cross-sectional structure of a liquid cargo tank in the prior art; Figure 3 This is a comparison diagram of the stress conditions of the liquid cargo tank of the present invention and the existing liquid cargo tank; Figure 4 This is a three-dimensional diagram of a dihedral membrane enclosure system.

[0020] The labels in the diagram are as follows: 1. Hull; 2. Horizontal bulkhead; 3. Vertical bulkhead; 4. Impact surface; 5. Transition surface; 6. Gas-liquid interface; 7. First insulation block; 8. Second insulation block; 9. Metal plate. Detailed Implementation

[0021] The present invention will be further described below with reference to the accompanying drawings and specific embodiments, so that those skilled in the art can better understand and implement the present invention. However, the embodiments described are not intended to limit the present invention.

[0022] like Figures 1-4As shown, this invention specifically relates to an LNG cargo tank designed to reduce sloshing impact. The tank body 1 has a polygonal cross-section, specifically a decagon in this invention. A horizontal bulkhead 2 is provided at the top of the tank body 1, and vertical bulkheads 3 are provided on the left and right sides of the tank body 1. Impact surfaces 4 extend from the left and right ends of the horizontal bulkhead 2 towards the vertical bulkhead 3, with an angle greater than 135° and less than 180° between the impact surfaces 4 and the horizontal bulkhead 2. At least one transition surface 5 connects to the bottom of the impact surfaces 4, and the transition surface 5 continues downward to the vertical bulkhead 3. The impact surfaces 4 and the transition surfaces 5 together form an arched profile that extends outward from the tank body. Under full load conditions, the LNG gas-liquid interface 6 falls within the height range of the impact surfaces 4, and the transition surfaces 5 are positioned below the gas-liquid interface 6. The impact surfaces 4 and the transition surfaces 5 are arranged symmetrically on the left and right sides of the horizontal bulkhead 2 to accommodate the sloshing of liquid inside the tank caused by the ship's rolling to the left and right during navigation. A dihedral membrane enclosure system is installed at the dihedral angle corresponding to the impact surface and the transition surface. The dihedral membrane enclosure system includes an insulation layer and a shielding layer. The insulation layer is formed by splicing multiple first insulation blocks 7 corresponding to the impact surface and multiple second insulation blocks 8 corresponding to the transition surface. The shielding layer includes a metal plate 9 fixing the first and second insulation blocks at a preset angle and a corrugated plate connecting the metal plate 9. Based on the difference in the swaying impact load borne by the impact surface and the transition surface, the first and second insulation blocks can be made of different materials. The first insulation block at the impact surface uses an insulation material with relatively better impact resistance, while the second insulation block at the transition surface uses an insulation material with lower strength but better insulation performance, thereby reducing heat leakage of the enclosure system while meeting impact resistance safety requirements. The shielding layer is arranged inside the insulation layer, and the metal plate is set at the junction of the dihedral corners. The first and second insulation blocks are fixed and constrained at the pre-designed angle to prevent the insulation blocks from deflecting or misaligning under the alternating impact of fluid and low-temperature contraction. This ensures the stability of the geometric configuration of the impact surface and the transition surface arching to the outside of the cabin, making the effect of the inclined surface guiding and dissipating the swaying impact kinetic energy and weakening the impact peak of the vertical bulkhead effective. Corrugated plates are connected between adjacent metal plates. The corrugated plates can absorb the thermal contraction deformation of the enclosure system under low-temperature conditions, release the structural thermal stress, and at the same time, together with the metal plates, form a continuous and complete metal shielding barrier to prevent the low-temperature medium from corroding the inner insulation layer. This effectively improves the sealing performance and fatigue resistance under alternating loads in the high-impact dihedral corner area near the gas-liquid interface.

[0023] Example 1, see Figures 1-4The angle between the impact surface and the horizontal bulkhead is preferably 145°-160°, and the angle between the transition surface and the horizontal bulkhead is preferably 110°-125°. In this embodiment, the angle between the impact surface 4 and the horizontal bulkhead 2 is specifically selected as 150°, and there is one transition surface 5. The angle between the transition surface 5 and the horizontal bulkhead 2 is specifically selected as 118°, which satisfies the relationship that the angle between the impact surface and the horizontal bulkhead is greater than the angle between the transition surface and the horizontal bulkhead. Since when the ship rolls, the sloshing fluid in the compartment first impacts the impact surface at the gas-liquid interface, the larger angle makes the impact surface closer to the horizontal, which can reduce the impact component of the sloshing fluid acting on the impact surface, preferentially dissipate the main impact kinetic energy of the fluid, and reduce the peak impact value borne by the containment system.

[0024] When a ship rolls due to wave excitation during navigation at sea, the LNG liquid inside the tank sloshes with the hull, splashing upwards and impacting the upper part of the tank. The sloshing fluid first strikes the impact surface 4 at the gas-liquid interface 6. Existing conventional octagonal LNG tank designs have a steeply sloping top, resulting in a large impact component perpendicular to the slope after the sloshing fluid impacts, placing a high impact load on the containment system. (Refer to...) Figure 3 As shown, the difference between this invention and the existing octagonal cabin type is that this invention splits the upper inclined surface of the original cabin into multiple inclined surfaces, making the angle of the impact surface corresponding to the gas-liquid interface gentler. Therefore, for swaying fluid with the same incident angle, when the fluid hits the impact surface of this invention, the impact component perpendicular to the impact surface is smaller, and more kinetic energy is converted into kinetic energy flowing tangentially downward along the impact surface.

[0025] This embodiment utilizes a multi-stage buffer structure of impact surface and transition surface to significantly reduce the overall impact load. Therefore, insulation materials can be differentiated according to the actual impact load at different locations. Impact surface 4, located at the gas-liquid interface, remains the location with the greatest relative impact from swaying throughout the cabin. The first insulation block 7, corresponding to this, is made of insulation material with medium impact resistance and medium-to-high insulation performance, capable of withstanding the remaining swaying impact. Transition surface 5, located below the gas-liquid interface, further reduces the impact load transmitted to transition surface 5 after the fluid is dissipated by the impact surface. The impact load is much smaller than that of impact surface 4. Therefore, the second insulation block 8 corresponding to transition surface 5 can be made of insulation material with lower impact resistance and better thermal insulation performance.

[0026] Example 2, see Figures 1-4This embodiment is basically the same as the main structure of Embodiment 1, except that: two transition surfaces 5 are provided between the impact surface 4 and the vertical bulkhead 3, namely the upper transition surface and the lower transition surface; the included angles between the multiple transition surfaces 5 and the horizontal bulkhead 2 increase from bottom to top. In this embodiment, the included angle between the impact surface 4 and the horizontal bulkhead is 155°, the included angle between the lower transition surface and the horizontal bulkhead is 112°, and the included angle between the upper transition surface and the horizontal bulkhead is 123°, satisfying the arrangement relationship that the closer to the impact surface, the larger the included angle between the transition surface and the horizontal bulkhead; the impact surface 4 and the two layers of transition surfaces 5 still arch outwards from the bulkhead as a whole, and are symmetrically arranged on both sides of the horizontal bulkhead.

[0027] This embodiment can also incorporate the unused corner space under the original single-sloping configuration into the liquid storage space inside the cabin, thereby increasing the effective loading volume of the cabin without changing the outer envelope size of the hull. When the loading capacity is determined, the outer dimensions of the cabin can be compressed, the layout of other functional areas on the ship can be optimized, and the overall utilization rate of cabin capacity and hull space can be improved.

[0028] When the ship rolls, the LNG inside the tank sloshes. The high-speed fluid first impacts the impact surface 4 located at the gas-liquid interface 6. The impact surface changes the fluid flow direction, dissipating the first part of the impact kinetic energy and reducing the peak impact value in the direction perpendicular to the bulkhead. The fluid then moves downwards, flowing sequentially through the upper and lower transition surfaces. Due to the gradual change in the inclination angle of the two transition surfaces, the sloshing fluid is guided in stages. Each time it passes through a transition surface, a portion of the residual kinetic energy is dissipated, gradually weakening the fluid impact energy. Compared to the single transition surface scheme, this can further reduce the peak fluid impact pressure.

[0029] The load decreases gradually from top to bottom, so the insulation material can be selected in a gradient manner: 1. The impact surface bears the highest residual impact, so the first insulation block uses a medium impact strength insulation material; 2. The upper transition surface adjacent to the impact surface has a smaller impact load than the impact surface, so the second insulation block uses an insulation material with slightly lower strength and better thermal insulation performance; 3. The lower transition surface, which is further down, has had its fluid impact fully dissipated by the previous two inclined surfaces, and therefore experiences the smallest impact load. Here, the second insulation block can use an insulation material with the lowest strength and best thermal insulation performance.

[0030] Example 3, see Figures 1-4 This embodiment focuses on explaining the technical means that "the side length of the impact surface along the cross-section of the cabin is less than the side length of the transition surface along the cross-section of the cabin". The rest of the basic structure is consistent with that of Embodiment 1.

[0031] The gas-liquid interface is the core area of ​​sloshing fluid impact. Impact surface 4 is specifically designed to correspond to the height range of the gas-liquid interface; it only needs to cover the main impact height range, therefore it does not need to be too long. Setting impact surface 4 as a short slope and the lower transition surface 5 as a long slope serves multiple purposes: First, the short impact surface 4 precisely covers the gas-liquid interface under full load conditions. The sloshing fluid generated by the ship's rolling is concentrated in this height range and impacts the surface. The short slope can concentrate the first fluid turning and kinetic energy dissipation, converting the impact kinetic energy of the vertical bulkhead into the downward flow kinetic energy along the slope. If the side length of the impact surface is too large, some slope areas will be far away from the actual gas-liquid interface. These slope areas will be less affected by fluid impact, resulting in a waste of the enclosure structure material.

[0032] Secondly, the lower transition surface 5 uses a longer slope to receive all the fluid flowing down from the impact surface 4. The longer flow distance allows the fluid sufficient travel along the surface, further dissipating residual impact kinetic energy and effectively weakening the downward-transmitted fluid energy, thus reducing the impact pressure transmitted by the fluid to the vertical bulkhead. If the design is reversed, with the side length of the impact surface being greater than that of the transition surface, the impact surface extends too far downwards while the transition surface becomes shorter. In this case, after the fluid passes through the impact surface, there is not enough transition surface travel to dissipate residual kinetic energy, and the fluid will quickly and directly impact the vertical bulkhead, significantly reducing the effect of weakening the swaying impact.

[0033] Example 4, see Figures 1-4 This embodiment describes the design method for reducing the sloshing impact of LNG cargo tanks, used to implement the engineering design of the above structure, and includes the following steps: S1. Based on the full-load loading technical indicators of the liquid cargo tank, conduct a cargo tank loading condition analysis to determine the height position of the LNG gas-liquid interface 6 under the full-load condition of the liquid cargo tank. S2. Design the impact surface 4 of the horizontal bulkhead 2 at the top of the liquid cargo tank, control the angle between the impact surface 4 and the horizontal bulkhead 2 to be greater than 135° and less than 180°, and make the lower edge of the impact surface 4 extend to the bottom of the gas-liquid interface 6, so that the gas-liquid interface falls within the height range of the impact surface 4 when fully loaded, and ensure that the main impact surface of the sloshing fluid is the impact surface. S3. A transition surface 5 is arranged between the lower edge of the impact surface 4 and the vertical bulkhead 3 on the side of the cabin. One or more transition surfaces can be set, and all transition surfaces 5 are arranged below the gas-liquid interface 6. When multiple transition surfaces are set, the angle between each transition surface and the horizontal bulkhead 2 is controlled to gradually increase from bottom to top. The impact surface and the transition surface are arched outward from the cabin and are symmetrically arranged on both sides of the horizontal bulkhead. S4. After completing the configuration design of the impact surface and transition surface, compared with the existing single-sloping transition hull configuration, this configuration has already achieved an increase in hull volume. Considering the constraints on hull height and width in the overall layout of the LNG ship, the height and / or width of the hull are finely adjusted to maintain the final loading capacity of the hull at the preset design value, that is, to keep the volume of the adjusted hull the same as the volume of the original octagonal hull. In this step, it is possible to either keep the hull shape unchanged to obtain a larger hull volume, or keep the hull volume unchanged and appropriately reduce the hull size to make room for other functional areas on board.

[0034] After the configuration dimensions are determined, the insulation materials are selected for different inclined plane zones based on the impact load results of the impact surface and each transition surface obtained from the swaying simulation: the area with higher impact load uses a relatively higher strength insulation material, and the area with lower impact load uses a lower strength insulation material with better thermal insulation performance; then, a matching dihedral membrane enclosure system is arranged at each dihedral corner intersection of the impact surface and the transition surface to complete the engineering design of the entire liquid cargo tank.

[0035] The liquid cargo tank produced by this method can achieve all the technical effects of multi-stage inclined plane dissipation swaying impact, allow the use of high-insulation and low-strength insulation materials, and improve the utilization rate of tank capacity and hull space, making it easy to implement in marine engineering.

[0036] The above-described embodiments are merely preferred embodiments provided to fully illustrate the present invention, and the scope of protection of the present invention is not limited thereto. Equivalent substitutions or modifications made by those skilled in the art based on the present invention are all within the scope of protection of the present invention. The scope of protection of the present invention is defined by the claims.

Claims

1. An LNG cargo tank for reducing sloshing impact, characterized in that, The container includes a hull with a polygonal cross-section. The two sides of the polygon correspond to the vertical walls of the hull, and the top of the polygon corresponds to the horizontal wall of the hull. The horizontal wall extends to the vertical wall with an impact surface. The angle between the impact surface and the horizontal wall is greater than 135° and less than 180°. At least one transition surface is provided between the impact surface and the vertical wall. The impact surface and the transition surface together form an arched shape towards the outside of the hull. Under full-load conditions, the impact surface is positioned corresponding to the gas-liquid interface of LNG inside the hull, such that the gas-liquid interface is located within the impact surface, and the transition surface is located below the gas-liquid interface.

2. The LNG cargo tank for reducing sloshing impact as described in claim 1, characterized in that, The transition surface is provided in multiple ways, and the angle between the multiple transition surfaces and the horizontal bulkhead increases sequentially from bottom to top.

3. An LNG cargo tank for reducing sloshing impact as described in claim 1, characterized in that, One transition surface is provided.

4. An LNG cargo tank for reducing sloshing impact as described in claim 1, characterized in that, The angle between the impact surface and the horizontal bulkhead is greater than the angle between the transition surface and the horizontal bulkhead.

5. An LNG cargo tank for reducing sloshing impact as described in claim 1, characterized in that, The impact surface and the transition surface are symmetrically arranged on both sides of the horizontal bulkhead.

6. An LNG cargo tank for reducing sloshing impact as described in claim 1, characterized in that, The angle between the impact surface and the horizontal bulkhead is 145°-160°.

7. An LNG cargo tank for reducing sloshing impact as described in claim 6, characterized in that, The angle between the transition surface and the horizontal bulkhead is 110°-125°.

8. An LNG cargo tank for reducing sloshing impact as described in claim 1, characterized in that, A dihedral membrane enclosure system is provided at the dihedral angle between the impact surface and the transition surface. The dihedral membrane enclosure system includes an insulation layer and a shielding layer. The insulation layer is formed by splicing together a plurality of first insulation blocks provided corresponding to the impact surface and a plurality of second insulation blocks provided corresponding to the transition surface. The shielding layer includes a metal plate that fixes the first insulation blocks and the second insulation blocks at a preset angle and a corrugated plate that connects the metal plate.

9. An LNG cargo tank for reducing sloshing impact as described in claim 1, characterized in that, The side length of the impact surface along the cross-section of the cabin is less than the side length of the transition surface along the cross-section of the cabin.

10. A design method for reducing sloshing impact in an LNG cargo tank as described in any one of claims 1-9, characterized in that, Includes the following steps: S1. Determine the position of the gas-liquid interface of the liquid cargo tank under full-load conditions; S2. Design an impact surface connected to the horizontal bulkhead at the top of the liquid cargo tank, such that the angle between the impact surface and the horizontal bulkhead is greater than 135° and less than 180°, and the lower edge of the impact surface extends below the gas-liquid interface. S3. Connect the impact surface to the vertical bulkhead on the side of the liquid cargo tank through a transition surface, so that the transition surface is located below the gas-liquid interface; S4. Based on the proportion constraints of the cabin to other functional areas on the LNG ship, adjust the height and / or width of the cabin to keep the loading capacity of the cabin at a preset value.

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