A method for determining the overall scheme of C-type independent storage tank

Abstract

A method for determining the overall design of a C-type independent tank is proposed. The method first determines the load distribution characteristics of the tank along its length based on the density of the tank bulkhead material and the density of the liquid cargo inside. Based on the load distribution characteristics, a saddle placement calculation scheme is determined. Then, based on the ship's size characteristics and the stress characteristics of the tank structure, the optimal range for the tank radius, tank length, and saddle placement is preliminarily determined. The saddle placement, tank length, and tank radius are then optimized. The evaporation rate of the liquid cargo tank under different schemes is calculated to determine the final design scheme. Based on the target tank capacity requirements and the basic constraints of the target ship, the method can quickly determine the radius, tank length, and saddle placement of the C-type tank, resulting in an overall tank design that balances structural safety and economy.

Description

Technical Field

[0001] The present invention belongs to the field of ship LNG storage tank construction and design, and particularly relates to a method for determining an overall scheme of a C-type independent storage tank. Background Art

[0002] Affected by international carbon emission restrictions, gas carriers and dual-fuel ships have become popular ship types at present. As a key equipment of liquefied gas carriers and dual-fuel ships, the overall design scheme of C-type tanks must take into account two key factors: safety and economy. When designing C-type tanks, it is necessary to consider the characteristics of the hull structure layout, taking into account issues such as structural optimization, reducing heat transmission and reducing the LNG evaporation rate. At present, gas carriers with multiple sizes and multiple tank capacities are in a critical period of ship development worldwide, and there may be multiple different overall design schemes for liquid cargo tanks for the same cargo hold volume requirement. How to achieve fast and efficient design scheme determination among many feasible technical solutions under the background of different ship type requirements is an issue that needs to be urgently addressed in response to the current boom in the research and development of liquefied gas ships.

[0003] The present invention provides a standardized method for determining the overall design scheme of a C-type tank. Based on the target tank capacity requirements and the basic constraints of the target ship, the radius, length, and saddle location of the C-type tank can be quickly determined, thereby obtaining an overall tank scheme that takes into account both structural safety and economy. Summary of the Invention

[0004] To solve the above problems, the present invention provides a method for determining the overall scheme of a C-type independent storage tank, which aims to achieve the purpose of quickly determining the structural dimensions of each C-type storage tank based on the target tank capacity requirements and the basic constraints of the target ship. The technical solution adopted is:

[0005] A method for determining the overall scheme of a C-type independent storage tank is characterized in that the C-type storage tank is composed of a straight tube section in the middle and head sections at both ends. The straight tube section is a cylindrical structure with a circular cross-section, and the head section is spherical. The ends of the straight tube section and the head section are butt-jointed and welded together. Two saddles are symmetrically provided at the bottom of the straight tube section. The overall determination method of the C-type storage tank is as follows:

[0006] S1: Determine the load distribution characteristics along the length of the tank based on the density of the tank bulkhead material and the density of the internal liquid cargo. Calculate the load distribution of the straight section and the head section separately.

[0007] The length of the straight section is L, and the load q is evenly distributed on the straight section. L The calculation formula is as follows:

[0008] q L =πR i 2 ρc +2πRtρ m

[0009] Where,

[0010] t is the average wall thickness of the cylinder. The initial value is calculated using the following formula. For LNG tanks, t is not less than 0.02m. For CO2 tanks, t is not less than 0.05m.

[0011]

[0012] R i is the inner radius of the C-type tank, which can be obtained from the initial design drawing. i_0 .

[0013] ρ c It is the density of liquid cargo in type C tank, which is determined according to the type of liquid cargo to be loaded in the tank.

[0014] ρ m The density of the material of type C tank container is determined according to the type of material selected for the tank bulkhead.

[0015] R is the average value of the inner and outer radius of the straight tube section, R = R i +t / 2.

[0016] P0 is the tank design pressure.

[0017] σ m is the allowable stress corresponding to the tank material.

[0018] The length of the head section is H, and the total load of the head section is Q H It can be calculated by the following formula:

[0019]

[0020] The head section is equivalent to a straight section with the same diameter as the straight section, and the uniformly distributed load is q L , then the equivalent length L0 of the head section length H is calculated as follows:

[0021]

[0022] S2: Determine the saddle setting position based on the load distribution characteristics.

[0023] S2.1: First, select two saddles at arbitrary positions and set them symmetrically. Calculate the support reaction force of the saddles at this time. The distance between the saddle and the end of the straight section is A. Based on the load distribution of the head section and the straight section, calculate the support reaction force Q at the saddle as:

[0024]

[0025] S2.2: Next, calculate the bending moment at the saddle and mid-span of the tank. Combining the load distribution along the tank length in S1 and the support reaction at the saddle in step S2.1, calculate the bending moment at the saddle as:

[0026]

[0027] The bending moment at the mid-span of the tank is:

[0028]

[0029] S2.3: The final calculation of the saddle position for the tank size shows that the bending moment at the tank mid-span is equal to the bending moment at the saddle according to static equilibrium:

[0030] |M a |=|M b |

[0031] That is:

[0032]

[0033] The distance A between the saddle and the end of the straight section can be calculated as follows:

[0034]

[0035] Further calculation is performed to obtain the distance X between the two saddles:

[0036]

[0037] S3: Based on the ship size characteristics and the stress characteristics of the tank structure, preliminarily determine the optimal range of the tank radius, tank length and saddle location.

[0038] S3.1 Determine the constraints for optimizing tank size.

[0039] The constraints for tank size optimization include those provided by the ship layout, such as ship width, tank length, cabin height, blind area, deck equipment layout, and the constraints provided by the force angle of the tank structure.

[0040] 1) The constraints provided by the ship layout need to be determined in the early stage of determining the overall layout plan of the storage tanks based on the actual ship design characteristics.

[0041] If the above-mentioned storage tanks are arranged in the cargo area below the hull deck, they must meet the following requirements:

[0042] - Tank diameter range determined by the ship's tank length: the tank's outer diameter in the longitudinal direction shall be no less than 700mm from the structural member at the transverse bulkhead.

[0043] - Tank diameter range determined by the ship width: the outer diameter of the tank is not less than 700mm from the nearby hull structure in the ship width direction.

[0044] - The range of tank diameter determined by the height of the ship's cabin: the minimum distance between the tank's outer diameter and the bottom hull continuous longitudinal member in the height direction is not less than 920mm, and the minimum distance between the tank's outer diameter and the top hull strong transverse beam panel in the height direction is not less than half the width of the strong transverse beam panel.

[0045] If the storage tank is arranged above the hull deck, the storage tank layout position must be considered based on the existing ship deck equipment and must not affect the ship's blind area.

[0046] 2) Considering the structural stress characteristics of the tank, the tank aspect ratio γ of the C-type tank arranged above the deck is usually limited. The preferred range of γ is 3 to 6. γ is calculated by the following formula:

[0047]

[0048] That is, the length of the straight section L and R i The functional relationship between them.

[0049] L = 2γR i

[0050] S3.2: Based on the tank size constraints, obtain the tank inner radius R i and the optimal interval of the length L of the tank straight section, and further determine the saddle setting position,

[0051] 1) Calculate the tank inner radius R i Optimal interval and straight section length L:

[0052] According to the target capacity requirement V, the relationship between the storage tank capacity and the storage tank size can be expressed as:

[0053]

[0054] According to the expression of aspect ratio γ, the relationship between aspect ratio γ and target tank capacity V is calculated:

[0055]

[0056] Then get

[0057]

[0058] According to S3.1, the preferred range of the aspect ratio γ is 3 to 6, and the tank inner diameter R is obtained. i The optimal interval: R imin ~R imax ,in

[0059]

[0060] 2) Calculate the length L of the straight section of the tank:

[0061] According to the expression of target tank capacity V, the length L of the tank straight section can be expressed as:

[0062]

[0063] That is, according to R i , V calculates the corresponding L value and its optimal interval L min ~L max .

[0064] 3) Calculate the wall thickness t of the tank straight section according to the formula in S1, and obtain the optimal interval L of the equivalent length L0 of the head section 0min ~L 0max .

[0065] 4) The distance A from the end of the saddle to the straight section and the optimal interval A can be calculated according to formula S2.3. min ~A max , the distance between the two saddles X and the optimal interval X min ~X max .

[0066] S4: Based on the hull strong support structure layout plan, determine the feasible arrangement plan of the tank saddle. Based on the feasible arrangement plan of the saddle and the tank load distribution characteristics obtained in S2, carry out the optimization design of the tank length and tank radius, and obtain multiple solutions.

[0067] The hull strong support structure arrangement scheme is obtained from the hull design drawings and refers to the arrangement position of the hull transverse strong frame structure.

[0068] The location of the tank saddle should be consistent with the location of the hull's strong support structure to fully utilize the hull's structural features and reduce the additional structural reinforcement design brought by the tank.

[0069] 1) Based on the optimal interval X between the two saddles of the tank min ~X max And the span of the hull frame support structure X S , and the feasible tank saddle distance and feasible setting scheme are calculated.

[0070] In the feasible saddle arrangement scheme, the tank saddle distance is calculated by the following formula:

[0071] X=n×X S

[0072] n is the number of hull frame spans.

[0073] 2) According to the determined tank saddle distance X, combined with the tank distribution characteristics in step S2, the corresponding A, L0, and L are calculated in sequence.

[0074] 3) According to the relevant formula in step S3.2, calculate the corresponding tank inner diameter R i .

[0075] S5: Calculate the evaporation rate of the cargo tank under each scheme in S4 and determine the final design scheme.

[0076] S5.1: Calculate the heat flux density q at different insulation materials in the tank bulkhead.

[0077]

[0078] Where,

[0079] T1 and T2 are the inner and outer surface temperatures of the cylinder wall, in K.

[0080] λ is the thermal conductivity of the material, which is determined by the specific material parameters.

[0081] R o is the outer radius of the tank, R o =R i +t.

[0082] S5.2 Calculation of cargo tank evaporation rate

[0083] A simplified method is used to calculate the cargo tank evaporation rate (BOR). The cargo tank evaporation rate (BOR) can be calculated using the following formula:

[0084]

[0085] Where,

[0086] Q is the total heat entering the cargo tank, Q = ∑q = S, which is the sum of the product of the heat flux density q of different materials in different areas of the tank outer surface and the corresponding area S.

[0087] r is the latent heat of vaporization of the liquid cargo in the storage tank, which is a parameter that matches the liquid cargo.

[0088] The calculated evaporation rates of the cargo tanks of various schemes are compared and the final optimal scheme is selected, that is, the scheme with the smallest evaporation rate of the cargo tanks.

[0089] Furthermore, in the aforementioned method for determining the overall design of a C-type independent tank, the saddle position A should ensure uniform stress in the C-type tank, with all stresses not exceeding the allowable material stress, thereby improving the structural safety of the C-type tank design. Furthermore, the saddle position should be aligned with the hull structural frame to fully utilize the hull structural characteristics and minimize the impact of the additional tank installation.

[0090] The beneficial effects of the invention are:

[0091] The key parameters of the 1C tank length and tank radius are determined in a coordinated manner with the saddle layout position, so that the saddle layout position fully meets the stress characteristics of the tank structure, avoids additional bending moment loads in the length direction of the tank, makes the tank stress uniform, and lays the foundation for the optimized design of the tank.

[0092] 2. For large marine pressure vessel tanks, the tank aspect ratio is used as a limiting factor for the optimized design of tank length and tank radius. This reduces storage and transportation costs while meeting large volume requirements. It also avoids tank strength risks caused by unconventional designs and improves the safety of tank structural design.

[0093] 3. During the tank design process, the main hull parameters, such as ship width, tank length, and tank depth, are used as key tank parameter constraints, making the tank-ship design interface more user-friendly and avoiding major adjustments to the entire ship design scheme due to the optimization of a single tank element.

[0094] 4. The layout of the storage tank saddle fully considers the layout characteristics of the hull support structure. The saddle position is kept consistent with the position of the hull structure strong frame, which can fully utilize the hull structure characteristics and reduce the impact of adding storage tanks.

[0095] 5. For early design, the hull's strong frame layout can be adjusted based on the optimized tank design parameters to avoid adding strong structures at the tank saddles, which would introduce structural design redundancy. If the installation of a tank significantly impacts the overall hull performance, adjustment targets can be proposed based on the actual ship's needs to adjust the tank design parameter range, thereby optimizing the tank design and avoiding significant impacts on the actual ship.

[0096] The design process of the present invention can be applied to both fuel tanks installed on the deck and liquid cargo tanks located below the deck, and can quickly determine storage tank solutions for different tank capacity solutions and different ship types, thereby improving efficiency and ensuring the feasibility of the solutions. BRIEF DESCRIPTION OF THE DRAWINGS

[0097] Figure 1 It is a schematic diagram of the C-type storage tank structure;

[0098] Figure 2 This is a schematic diagram of the C-type tank head section being equivalent to a straight cylinder section;

[0099] Figure 3 It is a schematic diagram of load distribution in C-type storage tank;

[0100] Figure 4 This is a schematic diagram of the limitation of the inner diameter of the tank by the blind area of ​​the ship;

[0101] Figure 5 It is a schematic diagram of the radius and length ratio of the C-type tank;

[0102] Figure 6 This is a schematic diagram of the maximum spacing between storage tank saddles.

[0103] Figure 7 It is a tank saddle arrangement scheme that takes into account the strong frame arrangement characteristics of the hull. DETAILED DESCRIPTION

[0104] The present invention will be further described with reference to the accompanying drawings.

[0105] A method for determining the overall scheme of a C-type independent storage tank, such as Figure 1 As shown, the C-type tank consists of a straight section in the middle and head sections at both ends. The straight section is a cylindrical structure with a circular cross section, and the head section is spherical. The two ends of the straight section and the head section are butt-jointed and welded together. Two saddles are symmetrically arranged at the bottom of the straight section. The overall determination method of the C-type tank is as follows:

[0106] S1: Determine the load distribution characteristics along the length of the tank based on the density of the tank bulkhead material and the density of the internal liquid cargo. Calculate the load distribution of the straight section and the head section separately.

[0107] The length of the straight section is L, and the load q is evenly distributed on the straight section. L The calculation formula is as follows:

[0108] q L ×πR i 2 ρ c +2πRtρ m

[0109] Where,

[0110] t is the average wall thickness of the cylinder. The initial value is calculated using the following formula. For LNG tanks, t is not less than 0.02m. For CO2 tanks, t is not less than 0.05m.

[0111]

[0112] R i is the inner radius of the C-type tank, which can be obtained from the initial design drawing. i_0 .

[0113] ρ c It is the density of liquid cargo in type C tank, which is determined according to the type of liquid cargo to be loaded in the tank.

[0114] ρ m The density of the material of type C tank container is determined according to the type of material selected for the tank bulkhead.

[0115] R is the average value of the inner and outer radius of the straight tube section, R = R i +t / 2.

[0116] P0 is the tank design pressure.

[0117] σ m is the allowable stress corresponding to the tank material.

[0118] The length of the head section is H, and the total load of the head section is Q H It can be calculated by the following formula:

[0119]

[0120] The head section is equivalent to a straight section with the same diameter as the straight section, and the uniformly distributed load is q L , then the equivalent length L0 of the head section length H is calculated as follows:

[0121]

[0122] S2: Determine the saddle setting position based on the load distribution characteristics.

[0123] S2.1: First, select two saddles at arbitrary positions and set them symmetrically. Calculate the support reaction force of the saddles at this time. The distance between the saddle and the end of the straight section is A. Based on the load distribution of the head section and the straight section, calculate the support reaction force Q at the saddle as:

[0124]

[0125] S2.2: Next, calculate the bending moment at the saddle and mid-span of the tank. Combining the load distribution along the tank length in S1 and the support reaction at the saddle in step S2.1, calculate the bending moment at the saddle as:

[0126]

[0127] The bending moment at the mid-span of the tank is:

[0128]

[0129] S2.3: The final calculation of the saddle position for the tank size shows that the bending moment at the tank mid-span is equal to the bending moment at the saddle according to static equilibrium:

[0130] |M a |=|M b |

[0131] That is:

[0132]

[0133] The distance A between the saddle and the end of the straight section can be calculated as follows:

[0134]

[0135] Further calculation is performed to obtain the distance X between the two saddles:

[0136]

[0137] S3: Based on the ship size characteristics and the stress characteristics of the tank structure, preliminarily determine the optimal range of the tank radius, tank length and saddle location.

[0138] In this embodiment, the C-type storage tank is the LNG fuel tank of a very large crude oil carrier (VLCC), and the target tank capacity requirement V is 3500m 2 , filled with LNG liquid cargo at -160℃, liquid cargo density ρ c 0.5t / m 3 , storage tank bulkhead density ρ m 7.85t / m 3 , the storage tank design pressure P0 is 0.45MPa.

[0139] S3.1 Determine the constraints for optimizing tank size.

[0140] The constraints for tank size optimization include those provided by the ship layout, such as ship width, tank length, cabin height, blind area, deck equipment layout, and the constraints provided by the force angle of the tank structure.

[0141] 1) Constraints provided by ship layout

[0142] In this embodiment, the storage tank is arranged above the hull deck. The storage tank layout position needs to be considered based on the existing ship deck equipment conditions and must not affect the ship's blind area.

[0143] 2) Constraints determined by tank forces

[0144] In this embodiment, the storage tank is arranged above the hull deck, and the preferred range of the aspect ratio γ of the C-type storage tank is 3 to 6, which is calculated by the following formula:

[0145]

[0146] S3.2: Based on the tank size constraints, obtain the optimal range of tank radius and tank length to further determine the saddle setting position.

[0147] like Figure 4 As shown, combined with the requirements of S3.1-1), this embodiment is arranged above the deck. First, according to the layout of the deck equipment, a feasible storage tank layout space is selected. At the same time, the storage tank layout must meet the blind area requirements of the ship. Therefore, the corresponding storage tank diameter range is R i ≤7.25m;

[0148] Combined with the optimal range of the tank aspect ratio γ determined in S3.1-2), the optimal range of the tank radius and the tank length can be obtained, and further the range of the distance X between the two tank saddles can be obtained.

[0149] The optimal range of tank radius is calculated by the following formula:

[0150]

[0151] The optimal range of the length of the straight section of the tank is calculated by the following formula:

[0152]

[0153] like Figure 5 As shown in the figure, according to the optimal range of the aspect ratio, the relationship between the length L of the straight section and the inner diameter is a curve distribution feature. It is necessary to further combine the characteristics of the hull strong frame layout and the evaporation rate of the tank to determine the optimal size.

[0154] Calculate the wall thickness t of the tank straight section according to the formula in S1 and obtain the optimal interval L of the equivalent length L0 of the head section 0min ~L 0max , L 0min =3.10m, L 0max =3.63m;

[0155] Then, the distance A between the saddle and the end of the straight section and the optimal interval A are calculated according to formula S2.3. min ~A max , the distance between the two saddles X and the optimal interval X min ~X max .

[0156] A min =4.50m, A max =9.05m

[0157] X min =22.93m, X max =34.18m

[0158] S4: Optimal interval X based on the distance between the two saddles in the tank min ~X max And the span of the hull frame support structure X S , calculate the feasible tank saddle distance and feasible setting scheme, such as Figure 6 As shown;

[0159] In this embodiment, the span of the hull strong frame support structure is X S is 5.64m. Based on the range of the distance X between tank saddles determined in S3.2, a feasible arrangement scheme for tank saddles is obtained, that is, the number n of strong frame spans between two saddles can be 4, 5, or 6;

[0160] Under different schemes, the distance between the two storage tank saddles is X = n × X S , respectively 22.56m, 28.2m, 33.84m, such as Figure 7 shown.

[0161] According to the determined tank saddle setting scheme, combined with the tank distribution characteristics in step S2, the corresponding A, L0, and L are calculated in sequence;

[0162] According to the relevant formula in step S3.2, the corresponding tank inner diameter R is calculated. i A total of three plans were formed, see Table 1 for details.

[0163] plan Ri / m L / m X / m Option 1 5.3 32.59 22.56 Option 2 4.7 44.17 28.2 Option 3 4.4 51.68 33.84

[0164] Table 1

[0165] S5: For cryogenic pressure tanks, the evaporation rate of cryogenic liquid cargo is not only related to the material and thickness of the insulation layer, but also closely related to the size of the tank. Based on the three schemes determined in S4, the evaporation rate of each scheme is calculated, see Table 2 for details.

[0166]

[0167]

[0168] Table 2 Solution 1 is the optimal solution.

[0169] plan Ri / m L / m X / m Option 1 5.3 32.59 22.56

[0170] Table 3.

Claims

1. A method for determining the overall scheme of a C-type independent storage tank, characterized in that: The C-type tank consists of a straight section in the middle and head sections at both ends. The straight section is a cylindrical structure with a circular cross section, and the head section is spherical. The ends of the straight section and the head section are butt-jointed and welded together. Two saddles are symmetrically arranged at the bottom of the straight section. The overall determination method of the C-type tank is as follows: S1: Determine the load distribution characteristics along the length of the tank based on the density of the tank wall material and the density of the internal liquid cargo, and calculate the load distribution of the straight section and the load distribution of the head section respectively; The length of the straight section is L, and the load q is evenly distributed on the straight section. L The calculation formula is as follows: Where, t is the average wall thickness of the cylinder, and the initial value is calculated by the following formula; for LNG storage tanks, t is not less than 0.02m; for CO2 storage tanks, t is not less than 0.05m; R i is the inner radius of the C-type tank; R can be obtained from the initial design drawings i_0 ; ρ c The density of liquid cargo in a Type C tank is determined based on the type of liquid cargo to be loaded in the tank; ρ m The density of the material of type C tank container shall be determined according to the material type selected for the tank bulkhead; R is the average value of the inner and outer radius of the straight tube section, R = R i +t / 2; P0 is the tank design pressure; σ m is the allowable stress corresponding to the tank material; The length of the head section is H, and the total load of the head section is Q H It can be calculated by the following formula: The head section is equivalent to a straight section with the same diameter as the straight section, and the uniformly distributed load is q L , then the equivalent length L0 of the head section length H is calculated as follows: S2: Determine the saddle setting position based on the load distribution characteristics; S2.1: First, select two saddles at arbitrary positions and set them symmetrically. Calculate the support reaction force of the saddles at this time. The distance between the saddle and the end of the straight section is A. Based on the load distribution of the head section and the straight section, calculate the support reaction force Q at the saddle as: S2.2: Next, calculate the bending moment at the saddle and mid-span of the tank. Combining the load distribution along the tank length in S1 and the support reaction at the saddle in step S2.1, calculate the bending moment at the saddle as: The bending moment at the mid-span of the tank is: S2.3: The final calculation of the saddle position for the tank size shows that the bending moment at the tank mid-span is equal to the bending moment at the saddle according to static equilibrium: |M a |=|M b | That is: The distance A between the saddle and the end of the straight section can be calculated as follows: Further calculation is performed to obtain the distance X between the two saddles: S3: Based on the ship's size characteristics and the load characteristics of the tank structure, preliminarily determine the optimal range of the tank radius, tank length and saddle location; S3.1 Determine the constraints for optimizing tank size. The constraints for tank size optimization include those provided by the ship layout, ship width, tank length, cabin height, blind area, deck equipment layout, and the constraints provided by the load angle of the tank structure; 1) The constraints provided by the ship type layout must be determined in the early stage of determining the overall tank layout plan based on the actual ship design characteristics; When the storage tank is arranged in the cargo area under the hull deck, it must meet the following requirements: - The outer diameter range of the tank is determined by the ship's tank length: the outer diameter of the tank in the longitudinal direction is not less than 700mm from the structural member at the transverse bulkhead; - The outer diameter of the tank is determined by the width of the ship: the outer diameter of the tank is not less than 700mm from the adjacent hull structure in the direction of the ship's width; - The outer diameter range of the tank is determined by the height of the ship's cabin: the minimum distance from the tank's outer diameter to the bottom hull continuous longitudinal member in the height direction is not less than 920mm, and the minimum distance from the top hull strong transverse beam panel in the height direction is not less than half the width of the strong transverse beam panel; When the storage tank is arranged above the hull deck, the storage tank layout position must be considered based on the existing ship deck equipment and must not affect the ship's blind area; 2) Considering the structural stress characteristics of the tank, the tank aspect ratio γ of the C-type tank arranged above the deck is usually limited. The preferred range of γ is 3 to 6. γ is calculated by the following formula: That is, the length of the straight section L and R i The functional relationship between L=2γR i S3.2: Based on the tank size constraints, obtain the tank inner radius R i and the optimal interval of the length L of the tank straight section, and further determine the saddle setting position, 1) Calculate the tank inner radius R i Optimal interval and straight section length L: According to the target capacity requirement V, the relationship between the storage tank capacity and the storage tank size can be expressed as: According to the expression of aspect ratio γ, the relationship between aspect ratio γ and target tank capacity V is calculated: Then get According to S3.1, the preferred range of the aspect ratio γ is 3 to 6, and the tank inner diameter R is obtained. i The preferred interval: R imin ~R imax ,in 2) Calculate the length L of the straight section of the tank: According to the expression of target tank capacity V, the length L of the tank straight section can be expressed as: That is, according to R i , V calculates the corresponding L value and its optimal interval L min ~L max ; 3) Calculate the wall thickness t of the tank straight section according to the formula in S1, and obtain the optimal interval L of the equivalent length L0 of the head section 0min ~L 0max ; 4) The distance A from the end of the saddle to the straight section and the optimal interval A can be calculated according to formula S2.

3. min ~A max , the distance between the two saddles X and the optimal interval X min ~X max ; S4: Determine a feasible arrangement scheme for the tank saddles based on the hull strong support structure layout scheme; Based on the determined feasible arrangement scheme for the saddles and the tank load distribution characteristics obtained in S2, optimize the tank length and tank radius to obtain multiple schemes; The layout of the hull's strong support structure is obtained from the hull design drawings, which refers to the layout position of the hull's transverse strong frame structure; The location of the tank saddle should be consistent with the location of the hull's strong support structure to fully utilize the hull's structural features and reduce the additional structural reinforcement design required by the tank; 1) Based on the optimal interval X between the two saddles of the tank min ~X max And the span of the hull frame support structure X S , calculate the feasible storage tank saddle distance and feasible setting scheme; In the feasible saddle arrangement scheme, the tank saddle distance is calculated by the following formula: X=n×X S n is the number of hull frame spans; 2) Based on the determined tank saddle distance X and the tank distribution characteristics in step S2, the corresponding A, L0, and L are calculated in sequence; 3) According to the relevant formula in step S3.2, calculate the corresponding tank inner diameter R i ; S5: Calculate the evaporation rate of the cargo tank under each scheme in S4 and determine the final design scheme; S5.1: Calculate the heat flux density q at different insulation materials in the tank bulkhead. Where, T1, T2 are the inner and outer surface temperatures of the cylinder wall, in K; λ is the thermal conductivity of the material, which is determined by the specific material parameters; R o is the outer radius of the tank, R o =R i +t; S5.2 Calculation of cargo tank evaporation rate A simplified method is used to calculate the cargo tank evaporation rate (BOR). The cargo tank evaporation rate (BOR) can be calculated using the following formula: Where, Q is the total heat entering the cargo tank, Q = ∑q × S, which is the sum of the product of the heat flux density q of different materials in different areas of the tank outer surface and the corresponding area S; r is the latent heat of vaporization of the liquid cargo in the tank, which is a parameter that matches the liquid cargo; The calculated evaporation rates of the cargo tanks of various schemes are compared and the final optimal scheme is selected, that is, the scheme with the smallest evaporation rate of the cargo tanks.

2. A method for determining an overall plan of a C-type independent storage tank according to claim 1, characterized in that: The saddle setting position A should make the stress of the C-type tank uniform and the various stresses do not exceed the allowable stress of the material, so as to improve the safety of the C-type tank structure design; at the same time, the saddle position should be consistent with the position of the hull structure strong frame to fully utilize the hull structure characteristics and reduce the impact of the installation of the tank.

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