A strength assessment method for methanol tank on deck of green ship based on FEM

Abstract

The present invention discloses a strength assessment method for a methanol tank on a green ship deck based on FEM, comprising the following steps: determining relevant loads, designing typical working conditions of a methanol tank, calculating complex loads in a table, establishing a methanol tank model, deducting corrosion allowance, applying loads and boundary conditions, evaluating yield buckling results, screening concentrated stress points, and fine grid yield analysis. The present invention realizes the strength assessment of the structural safety of the methanol tank on the ship deck, ensures the structural safety of the methanol tank and its surrounding structures, and ensures the safety of personnel, equipment, operations and property on board during the operation of a methanol dual-fuel ship.

Description

Technical Field

[0001] The invention relates to a methanol tank strength assessment method, in particular to a FEM-based methanol tank strength assessment method for a green ship deck, belonging to the technical field of ships. Background Art

[0002] Under the pressure of global carbon emission restrictions and environmental protection, the shipping industry faces the challenges of environmental protection and green transformation. The application of green fuels and energy-saving technologies is of great significance to promoting the development of the shipping industry. Therefore, both at the national level and shipping companies will focus on the application of green fuels to achieve the future decarbonization path of the fleet. Among them, the application of green methanol as a fuel on bulk carriers is one of the most promising alternative fuels for the future decarbonization of the shipping industry. Methanol is a dangerous chemical that is flammable and toxic. Its vapor density is higher than that of air. It is easy to accumulate in a confined space, increasing the risk of inhalation by crew members. Steam mixed with a certain proportion of air is prone to explosion. Water-containing methanol is corrosive to steel, and contact with the skin, inhalation or ingestion will cause harm to the human body. In addition, the combustion flame of methanol is invisible, smokeless, and not easy to detect. It has a certain fire risk. If the methanol tank is damaged due to structural strength problems and methanol leaks, it will cause serious harm to the life safety of the crew and the safety of ship operation. In order not to reduce the cargo loading capacity of the ship, it has become the best choice to arrange the methanol tank on the rear deck and behind the superstructure. The methanol tank arranged on the stern deck of the ship is different from the superstructures such as the living area. In addition to participating in the deformation of the hull structure and bearing external wave loads, it also needs to consider the load of liquid methanol on the cabin after loading methanol fuel. Therefore, the conventional method of designing superstructures can no longer guarantee the structural safety of the methanol tank.

[0003] Based on the above, in order to ensure the safety of personnel, equipment, operations and property on board during operation, a reliable and feasible structural safety assessment of the methanol tank is an extremely important part of ship safety design. At present, there is no clear assessment method for the strength assessment of the methanol tank structure on the ship deck. Therefore, it is urgent to seek a reasonable strength assessment method for the methanol tank on the ship deck to ensure the structural safety of the methanol tank and its surrounding structures. Summary of the invention

[0004] The technical problem to be solved by the present invention is to provide a green strength assessment method for a methanol tank on a ship deck based on FEM, so as to achieve strength assessment of the structural safety of the methanol tank on a ship deck.

[0005] In order to solve the above technical problems, the technical solution adopted by the present invention is:

[0006] A strength assessment method for methanol tank on deck of green ship based on FEM, characterized by comprising the following steps:

[0007] S1. Determine the relevant loads;

[0008] S2. Typical working condition design of methanol tank;

[0009] S3, list calculation of complex loads;

[0010] S4. Establish a methanol tank model;

[0011] S5, deduct corrosion allowance;

[0012] S6, apply loads and boundary conditions;

[0013] S7, yield buckling result evaluation;

[0014] S8, concentrated stress point screening;

[0015] S9. Fine mesh yield analysis.

[0016] Furthermore, the relevant loads in step S1 include structural gravity, static pressure of methanol fuel, draft pressure of ship outer plate, dynamic pressure of methanol fuel and wave load.

[0017] Furthermore, the typical operating conditions in step S2 include a methanol two-tank full loading mode, a methanol left-tank full loading mode, a methanol right-tank full loading mode, and a methanol tank full empty loading mode;

[0018] Methanol two-tank full loading mode includes:

[0019] Condition 1: minimum ballast draft with maximum longitudinal forward acceleration and maximum vertical downward acceleration;

[0020] Condition 2: Structural draft with maximum longitudinal forward acceleration and maximum vertical downward acceleration;

[0021] Condition 3: minimum ballast draft with maximum longitudinal aft acceleration and maximum vertical downward acceleration;

[0022] Condition 4: Structural draft with maximum longitudinal rearward acceleration and maximum vertical downward acceleration;

[0023] Condition 5: Structural draft with maximum lateral left acceleration;

[0024] Condition 6: Structural draft with maximum lateral rightward acceleration;

[0025] Condition 7: minimum ballast draft with maximum lateral left acceleration;

[0026] Condition 8: minimum ballast draft with maximum lateral acceleration to the right;

[0027] Methanol left tank full loading mode includes:

[0028] Condition 9: minimum ballast draft with maximum longitudinal forward acceleration and maximum vertical downward acceleration;

[0029] Condition 10: Structural draft with maximum longitudinal forward acceleration and maximum vertical downward acceleration;

[0030] Condition 11: minimum ballast draft with maximum longitudinal aft acceleration and maximum vertical downward acceleration;

[0031] Condition 12: Structural draft with maximum longitudinal rearward acceleration and maximum vertical downward acceleration;

[0032] Condition 13: Structural draft with maximum lateral left acceleration;

[0033] Condition 14: Structural draft with maximum lateral rightward acceleration;

[0034] Condition 15: minimum ballast draft with maximum lateral left acceleration;

[0035] Condition 16: minimum ballast draft with maximum lateral acceleration to the right;

[0036] The methanol right tank full loading mode includes:

[0037] Condition 17: minimum ballast draught with maximum longitudinal forward acceleration and maximum vertical downward acceleration;

[0038] Condition 18: Structural draft with maximum longitudinal forward acceleration and maximum vertical downward acceleration;

[0039] Condition 19: minimum ballast draft with maximum longitudinal aft acceleration and maximum vertical downward acceleration;

[0040] Condition 20: Structural draft with maximum longitudinal aft acceleration and maximum vertical downward acceleration;

[0041] Condition 21: Structural draft with maximum lateral left acceleration;

[0042] Condition 22: Structural draft with maximum lateral rightward acceleration;

[0043] Condition 23: minimum ballast draft with maximum lateral left acceleration;

[0044] Condition 24: minimum ballast draft with maximum lateral acceleration to the right;

[0045] Methanol tank empty loading mode includes:

[0046] Condition 25: Structural draft with maximum wave pressure at the port waterline;

[0047] Condition 26: Structural draft with maximum wave pressure at the starboard waterline;

[0048] Condition 27: minimum ballast draft with maximum wave pressure at the port waterline;

[0049] Condition 28: Minimum ballast draught with maximum wave pressure at the starboard waterline.

[0050] Furthermore, the step S3 is specifically as follows:

[0051] Load 1: Structural deadweight; applies downward gravity acceleration to all structural members in all conditions;

[0052] Load 2: Methanol fuel tank static pressure; liquid tank static pressure P ms Take

[0053] P ms = ρ m g (z mtop – z m ) + P PV

[0054] In the formula, ρ m is the density of methanol; g is the acceleration due to gravity; z mtop is the height of the methanol tank top; z m is the height of any point on the methanol tank bulkhead; P PV is the air valve pressure of the methanol tank; when the methanol tank is fully loaded, the static pressure acts on the wall panels around the cabin and points to the outside of the cabin;

[0055] Load 3: Ship's outer plate draft pressure; outer plate pressure P Take

[0056] P = ρ L g (T–z)

[0057] In the formula, ρ L is the density of seawater; g is the acceleration due to gravity; T The ship's draft is divided into structural draft and minimum ballast draft; z is the height of any point on the ship's outer plate below the corresponding waterline; the outer plate pressure acts on the ship's outer plate below the corresponding waterline, and the direction is toward the inside of the outer plate;

[0058] Load 4: Methanol fuel dynamic pressure;

[0059] According to the loading conditions of the ship's aft cargo hold and the definition of the ship's motion acceleration under various loading conditions of the aft cargo hold in relevant specifications, the acceleration values ​​of the center of gravity of the two compartments of the methanol tank in three directions under various conditions are calculated;

[0060] The envelope values ​​of the absolute values ​​of acceleration in the corresponding directions of all working conditions are selected in three directions as the acceleration values ​​for calculating the dynamic load of methanol;

[0061] The above-mentioned acceleration of the center of gravity of the methanol tank in all directions during the ship's motion is obtained. The dynamic load on the methanol tank wall caused by this acceleration needs to determine its reference point coordinates according to various working conditions. The reference point is taken as all nodes on the top boundary of the methanol tank, so that the following formula V j The node corresponding to the maximum value of

[0062] V j = a x (x mj – x G ) + a y (y mj – y G ) + (a z + g) (z mj – z G )

[0063] In the formula, a X 、ay、az is the acceleration at the center of gravity of the methanol tank; x G 、y G 、z G is the coordinate of the center of gravity of the methanol tank compartment; x mj 、 y mj 、z mj Methanol tank roof j Point coordinates;

[0064] Then, according to the liquid dynamic pressure formula, the dynamic pressure generated by methanol under various working conditions is obtained: P md :

[0065] P md = 1.05ρ m [a x (x mj – x m ) + a y (y mj – y m ) + a z (z mj – z m )]

[0066] P md When it is positive, the direction of the dynamic load acting on the cabin wall points to the outside of the cabin;

[0067] Load 5: wave load; the wave load is mainly aimed at the working condition of the two methanol tanks being completely empty. When the methanol tanks are completely empty, the equivalent design wave of the transverse wave with the largest hydrodynamic force at the midship waterline is applied to the port and starboard sides of the model respectively, in order to verify the strength of the methanol tanks under the outer wave pressure.

[0068] Furthermore, the step S4 specifically includes establishing a coarse mesh model of the methanol tank, taking into account the need for applying loads such as the draft of the outer plate and the factor that the model results at the boundary constraints are not reliable, based on the FEM analysis software, combined with the position and structural characteristics of the methanol tank, all structures from the front wall of the cabin to the rear are selected for coarse mesh modeling, and the unit size is about 800 mm x 800 mm ; Among them, the board uses Plate Unit simulation, tendons, Carling And small bracket using line unit bar / beam simulation.

[0069] Furthermore, the step S5 specifically includes, referring to the corrosion allowance requirements of conventional bulk carriers, deducting 0.5 from the methanol tank model. t c The method of deducting the corrosion allowance is as follows: flexibly use the classification society software to splice the partial model of the methanol tank into a three-tank model that can be recognized by the classification society software. According to the corrosion requirements of the methanol tank and its surrounding structures, manually adjust or add the corrosion allowance parameters of the software to complete the three-tank model from structural size to Net After the size conversion, the original methanol tank model is finally cut out from the three-tank model.

[0070] Furthermore, the step S6 is specifically as follows:

[0071] The model boundary conditions and loads are implemented in the FEM analysis software;

[0072] Boundary conditions affect the effect of load application. According to the range characteristics of the model, the hull cross section in the rigid constraint model is adopted to optimize and adjust the cross section of the constraint according to the deformation effect and stress size.

[0073] The applied loads include:

[0074] Load 1: Structural self-weight; in FEM software, a vertical downward gravity acceleration is applied to the entire model;

[0075] Load 2: Methanol fuel static pressure; Substitute the known data that affect the methanol fuel static pressure into the formula to obtain the model node height z m Formula for variables

[0076] P ms = 0.8 x 9810 x (z mtop – z m ) x 10 -9 + P PV

[0077] The above formula is input into the load function of the FEM analysis software, and then applied to the wall panels around the left and right cabins of the methanol tank, with the direction pointing to the outside of the cabin;

[0078] Load 3: Draft pressure of ship outer plate; Substitute the known data affecting the draft pressure of outer plate into the formula to obtain the model node height z The formula is a variable, taking the structural draft as an example,

[0079] P = 1.025 x 9810 x (T SC – z) x 10 -9

[0080] The above formula is input into the load function of the FEM analysis software and then applied to the outer plate below the waterline of the structure, with the direction pointing to the inside of the hull;

[0081] Load 4: Methanol fuel dynamic pressure; Substitute the known data that affect the dynamic pressure of methanol into the formula to obtain a formula with the coordinates of the methanol bulkhead node as variables; Take the port methanol tank fully loaded as an example, there are 8 working conditions in total, which can be divided into 4 groups according to the acceleration and reference point values;

[0082] Each group of loads is applied to the left methanol tank bulkhead, and the direction is toward the outside of the tank when the dynamic pressure is positive;

[0083] Load 5: Wave load; wave load is mainly applied to the ship's outer plate, upper deck, superstructure and the outer wall of the methanol tank. The load on the ship's outer plate should also be applied according to the waterline height and the front / back wave surface, and the corresponding formula should be selected for application.

[0084] Furthermore, step S7 specifically includes yield buckling result evaluation. In view of some assumptions and simplifications in the modeling, loading and constraint steps, when evaluating the results, in order to ensure the structural safety as much as possible, the yield allowable factor in the relevant specifications is adjusted to 0.85 times and the buckling allowable factor is adjusted to 0.9 times to evaluate the results, wherein the allowable stress is: the allowable stress of mild steel MS is 200 MPa, the allowable stress of high-strength steel HT32 is 256 MPa, and the allowable stress of high-strength steel HT36 is 277 MPa.

[0085] Furthermore, the step S8 is specifically to screen the concentrated stress points; in order to prevent the stress concentration points from not being displayed in the coarse mesh model, it is necessary to screen the results that meet the yield requirements. In order to select as many stress concentration points as possible, the screening coefficient is selected as 0.75, that is, the units with a yield utilization factor greater than 0.75 in the coarse mesh model are selected, and 50 mm x 50 mm Fine mesh yield analysis.

[0086] Compared with the prior art, the present invention has the following advantages and effects: The present invention provides a FEM-based green ship deck methanol tank strength assessment method, which realizes the strength assessment of the structural safety of the methanol tank on the ship deck, ensures the structural safety of the methanol tank and its surrounding structures, and ensures the safety of personnel, equipment, operations and property on board during the operation of methanol dual-fuel ships. BRIEF DESCRIPTION OF THE DRAWINGS

[0087] Figure 1 The present invention is a flow chart of a strength assessment method of a methanol tank on a green ship deck based on FEM.

[0088] Figure 2 The embodiment of the present invention BSP-1P Load diagram.

[0089] Figure 3 The embodiment of the present invention BSP-1SLoad diagram.

[0090] Figure 4 Schematic diagram of an FEM model of an embodiment of the present invention.

[0091] Figure 5 It is a schematic diagram of setting constraint conditions of an embodiment of the present invention.

[0092] Figure 6 It is a schematic diagram of the static pressure of the left methanol tank of an embodiment of the present invention.

[0093] Figure 7 It is a schematic diagram of the outer plate pressure under water structure of an embodiment of the present invention.

[0094] Figure 8 It is a schematic diagram of the grouping of dynamic pressure conditions of the left methanol tank fully loaded in an embodiment of the present invention.

[0095] Fig. 9 It is a schematic diagram of the dynamic pressure in the methanol compartment on the left side of working condition 9 of an embodiment of the present invention. DETAILED DESCRIPTION

[0096] In order to elaborate on the technical scheme adopted by the present invention to achieve the predetermined technical purpose, the technical scheme in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only partial embodiments of the present invention, rather than all embodiments, and the technical means or technical features in the embodiments of the present invention can be replaced without paying creative work. The present invention will be described in detail below with reference to the drawings and in conjunction with the embodiments.

[0097] like Figure 1 As shown, a strength assessment method for a methanol tank on a green ship deck based on FEM of the present invention comprises the following steps:

[0098] S1. Determine the relevant loads.

[0099] The methanol tank is used as a fuel tank and is divided into two compartments by the middle groove bulkhead. The front wall of the methanol tank is connected to the A, B and C decks of the living area, the left part of the structure is connected to the chimney, and the right part of the structure is connected to the carbon dioxide room and the emergency generator room.

[0100] In order to check the strength of the methanol tank and surrounding structures, the loads of the internal fuel and external waves of the methanol tank should be considered first, and the influence of the whole ship motion load on the methanol tank should also be considered. Since the methanol tank of this ship is arranged at the very end, it is not included in the calculation of the cross-sectional area of ​​the hull beam. After comprehensive consideration, the loads that affect the structural strength of the methanol tank are mainly the following five: structural gravity, static pressure of methanol fuel, draft pressure of the ship's outer plate, dynamic pressure of methanol fuel and wave load.

[0101] S2. Typical operating condition design of methanol tank.

[0102] According to the states of the five loads in step 1 under different working conditions, 28 typical working conditions are combined. For example, for the outer plate draft, the present invention selects two extreme cases, the structural draft and the minimum ballast draft; the dynamic pressure of methanol fuel is calculated using the envelope acceleration under various working conditions of the aftmost cabin; the wave load selects the transverse wave design wave. The above loads are selected according to conservative or extreme conditions and are considered to be the loads that must be selected. If other loads need to be verified, other working conditions can also be combined for analysis.

[0103] The 28 typical operating conditions include methanol two-tank full loading mode, methanol left tank full loading mode, methanol right tank full loading mode and methanol tank empty loading mode.

[0104] Methanol two-tank full loading mode includes:

[0105] Condition 1: minimum ballast draft with maximum longitudinal forward acceleration and maximum vertical downward acceleration;

[0106] Condition 2: Structural draft with maximum longitudinal forward acceleration and maximum vertical downward acceleration;

[0107] Condition 3: minimum ballast draft with maximum longitudinal aft acceleration and maximum vertical downward acceleration;

[0108] Condition 4: Structural draft with maximum longitudinal rearward acceleration and maximum vertical downward acceleration;

[0109] Condition 5: Structural draft with maximum lateral left acceleration;

[0110] Condition 6: Structural draft with maximum lateral rightward acceleration;

[0111] Condition 7: minimum ballast draft with maximum lateral left acceleration;

[0112] Condition 8: Minimum ballast draft with maximum lateral acceleration to the right.

[0113] Methanol left tank full loading mode includes:

[0114] Condition 9: minimum ballast draft with maximum longitudinal forward acceleration and maximum vertical downward acceleration;

[0115] Condition 10: Structural draft with maximum longitudinal forward acceleration and maximum vertical downward acceleration;

[0116] Condition 11: minimum ballast draft with maximum longitudinal aft acceleration and maximum vertical downward acceleration;

[0117] Condition 12: Structural draft with maximum longitudinal rearward acceleration and maximum vertical downward acceleration;

[0118] Condition 13: Structural draft with maximum lateral left acceleration;

[0119] Condition 14: Structural draft with maximum lateral rightward acceleration;

[0120] Condition 15: minimum ballast draft with maximum lateral left acceleration;

[0121] Condition 16: Minimum ballast draft with maximum lateral acceleration to the right.

[0122] The methanol right tank full loading mode includes:

[0123] Condition 17: minimum ballast draught with maximum longitudinal forward acceleration and maximum vertical downward acceleration;

[0124] Condition 18: Structural draft with maximum longitudinal forward acceleration and maximum vertical downward acceleration;

[0125] Condition 19: minimum ballast draft with maximum longitudinal aft acceleration and maximum vertical downward acceleration;

[0126] Condition 20: Structural draft with maximum longitudinal aft acceleration and maximum vertical downward acceleration;

[0127] Condition 21: Structural draft with maximum lateral left acceleration;

[0128] Condition 22: Structural draft with maximum lateral rightward acceleration;

[0129] Condition 23: minimum ballast draft with maximum lateral left acceleration;

[0130] Condition 24: minimum ballast draft with maximum lateral acceleration to the right.

[0131] Methanol tank empty loading mode includes:

[0132] Condition 25: Structural draft with maximum wave pressure at the port waterline;

[0133] Condition 26: Structural draft with maximum wave pressure at the starboard waterline;

[0134] Condition 27: minimum ballast draft with maximum wave pressure at the port waterline;

[0135] Condition 28: Minimum ballast draught with maximum wave pressure at the starboard waterline.

[0136] S3. List and calculate complex loads. The above five loads are different in the 28 working conditions, which requires determining the specific load values ​​or formulas for each working condition.

[0137] Load 1: Structural self-weight; according to the needs of the subsequent FEM modeling unit, use mm-T / mm 3 -N Unit system, downward gravity acceleration is applied to all components in 28 working conditions.

[0138] Load 2: Methanol fuel tank static pressure; refer to relevant specifications and tank static pressure P ms Take

[0139] P ms = ρ m g (z mtop – z m ) + P PV

[0140] In the formula, ρ m is the density of methanol, take 0.8x10 -9 T / mm 3 ; g is the acceleration due to gravity, take 9810 mm / s 2 ; z mtop is the height of the methanol tank top; z m is the height of any point on the methanol tank bulkhead, which is a variable; P PV is the air valve pressure of the methanol tank. When the methanol tank is fully loaded, the static pressure acts on the wall panels around the cabin and points to the outside of the cabin.

[0141] Load 3: Ship's outer plate draft pressure; outer plate pressure P Take

[0142] P = ρ L g (T–z)

[0143] In the formula, ρ L is the density of seawater, take 1.025x10 9 T / mm 3 ; g is the acceleration due to gravity, take 9810 mm / s 2 ; T The ship's draft is divided into structural draft and minimum ballast draft; zis the height of any point on the ship's outer plate below the corresponding waterline, and is a variable. The outer plate pressure acts on the ship's outer plate below the corresponding waterline, and the direction points to the inside of the outer plate.

[0144] Load 4: Dynamic pressure of methanol fuel. The existing ship specifications and corresponding calculation software have not yet considered the dynamic pressure of the liquid in the tank on the deck. For the methanol tank designed this time, it is located above the ship deck and occupies half of the width of the stern. The cabin capacity is large and the structure is complex. The dynamic pressure of methanol inside it cannot be ignored. How to determine its impact on the methanol tank and its surrounding structures is crucial.

[0145] The methanol tank is integrated with the hull structure. As the whole ship moves, the methanol in the methanol tank will also generate corresponding dynamic loads with the movement of the hull. According to the loading condition of the aft cargo hold of the ship and the definition of the ship motion acceleration of each loading condition of the aft cargo hold in the relevant specifications, the acceleration values ​​of the center of gravity of the two compartments of the methanol tank in three directions under each condition are calculated, see Table 1.

[0146] Table 1: Motion acceleration of methanol tank ship under various working conditions

[0147]

[0148]

[0149] For the rigor of the calculation, the envelope values ​​of the absolute values ​​of acceleration in the corresponding directions of all working conditions are selected in three directions as the acceleration values ​​for calculating the dynamic load of methanol.

[0150] Table 2: Acceleration at the center of gravity of methanol tank

[0151]

[0152] Table 2 above shows the acceleration of the center of gravity of the methanol tank in all directions during the ship's motion. The dynamic load on the methanol tank wall caused by this acceleration needs to determine its reference point coordinates according to various working conditions. The reference point is taken as the node of the top boundary of the methanol tank, so that the following formula V j The node corresponding to the maximum value of .

[0153] V j = a x (x mj – x G ) + a y (y mj – y G ) + (az + g) (z mj – z G )

[0154] In the formula, a X 、ay、az is the acceleration at the center of gravity of the methanol tank; x G 、y G 、z G is the coordinates of the center of gravity of the methanol tank compartment, as shown in Table 3; x mj 、y mj 、z mj Methanol tank roof j Point coordinates.

[0155] Table 3: Coordinates of the center of gravity of the methanol tank

[0156]

[0157] Take the left methanol tank filled with methanol as an example, that is, in step S2, condition 9 ~ 16. According to the formula requirements, it is known that g is 9810, x G 、y G 、z G is the center of gravity of the left methanol tank. V j The maximum value, then the composition V j The monomial must be the largest. a x For positive time, x mj It should be as large as possible, so the front wall of the cabin is taken x coordinate, a x When it is negative, x mj Should be as small as possible, so take the back wall x coordinate; a y For positive time, y mj It should be as large as possible, so the left longitudinal wall of the cabin is taken y coordinate, a y When it is negative, y mjIt should be as small as possible, so the smallest value on the groove wall is taken. y Coordinates; From Table 2, we can see that the vertical acceleration of the methanol tank a z Always less than 9810 mm / s 2 ,Right now a z +g is always positive, so z j Take the methanol tank top plate z For the direction where the acceleration is zero, the reference point coordinates can be any point on the cabin top plate. The selected reference point coordinate information is shown in Table 4.

[0158] Table 4: Coordinates of reference points of the left methanol tank

[0159]

[0160] The coordinates of the reference point of the right methanol tank are obtained using the same method, as shown in Table 5.

[0161] Table 5: Coordinates of reference points of the right methanol tank

[0162]

[0163] Then, according to the liquid dynamic pressure formula, the dynamic pressure generated by methanol under various working conditions is obtained: P md :

[0164] P md = 1.05ρ m [a x (x mj – x m ) + a y (y mj – y m ) + a z (z mj – z m )]

[0165] P md When it is positive, the direction of the dynamic load acting on the cabin wall points to the outside of the cabin; P ms + P md≥ 0 , otherwise the dynamic load exceeding the static load needs to be optimized.

[0166] Load 5: Wave load; The wave load is mainly aimed at the working condition of two methanol tanks being completely empty. When the methanol tanks are completely empty, the equivalent design wave with the largest hydrodynamic force at the midship waterline is applied to the port and starboard sides of the model respectively. BSP-1P& BSP-1S ), is intended to verify the strength of the methanol tank under the pressure of the outer waves. Taking the structural draft as an example, Figure 2 and Figure 3 Demonstrated the bearing capacity of methanol tanks and ship outer plates BSP-1P&BSP-1S Load diagram.

[0167] Calculate the height of the wave action point from the baseline. BSP Hydrodynamic pressure for load cases P w There are also different methods, which can be calculated by referring to the hydrodynamic pressure formula in the relevant specifications, and the present invention will not go into details.

[0168] S4. Establish a methanol tank model.

[0169] A coarse mesh model of the methanol tank was established. Considering the need to apply loads such as the draft of the outer plate and the low credibility of the model results at the boundary constraints, based on the FEM analysis software, combined with the position and structural characteristics of the methanol tank, all structures from the front wall of the cabin to the rear were selected for coarse mesh modeling (only the three lowest floors connected to the methanol tank were modeled in the residential area), and the unit size was about 800 mm x 800 mm ; Among them, the board uses Plate Unit simulation, tendons, Carling And small bracket using line unit bar / beam Simulation, such as Figure 4 shown.

[0170] S5. Deduct corrosion allowance.

[0171] In step S4, the modeling process completely refers to the structural dimensions of the drawings, and the number of model units built is nearly 60,000, and the material properties are nearly 400. Because there are many drawings involved, if the modeling is based on the dimensions after deducting the corrosion allowance, it is necessary to calculate the corrosion allowance while modeling, which is inefficient and prone to errors.

[0172] With reference to the corrosion allowance requirements for conventional bulk carriers, 0.5 is deducted from the methanol tank model. t cThe method of deducting the corrosion allowance is as follows: flexibly use the classification society software to splice the partial model of the methanol tank into a three-tank model that can be recognized by the classification society software. According to the corrosion requirements of the methanol tank and its surrounding structures, manually adjust or add the corrosion allowance parameters of the software to complete the three-tank model from structural size to Net After the size conversion, the original methanol tank model is finally cut out from the three-tank model.

[0173] S6. Apply loads and boundary conditions.

[0174] Model boundary conditions and loads are implemented in FEM analysis software.

[0175] Boundary conditions affect the effect of load application. According to the range characteristics of the model, the hull cross section in the rigid constraint model is adopted. According to the deformation effect and stress magnitude, the cross section of the constraint can be optimized and adjusted. In this embodiment, the front wall of the cabin is rigidly fixed, so that the entire model is in a cantilever beam state, which better simulates the actual deformation effect of the ship's tail structure. Figure 5 As shown, the nodes on the bold dashed line will be implemented Fixed constraint.

[0176] The applied loads include:

[0177] Load 1: Structural self-weight; in the FEM software, the load is applied vertically downward to the entire model, with a value of 9810 mm / s 2 The acceleration due to gravity.

[0178] Load 2: Methanol fuel static pressure; Substitute the known data that affect the methanol fuel static pressure into the formula to obtain the model node height z m Formula for variables

[0179] P ms = 0.8 x 9810 x (z mtop – z m ) x 10 -9 + P PV

[0180] The above formula is input into the load function of the FEM analysis software, and then applied to the wall panels around the left and right cabins of the methanol tank, with the direction pointing to the outside of the cabin; Figure 6 Taking the left tank of the methanol tank as an example, it shows the situation after the static pressure of methanol is applied. The darker the color, the greater the load.

[0181] Load 3: Draft pressure of ship outer plate; Substitute the known data affecting the draft pressure of outer plate into the formula to obtain the model node height z The formula is a variable, taking the structural draft as an example,

[0182] P = 1.025 x 9810 x (T SC – z) x 10 -9

[0183] The above formula is input into the load function of the FEM analysis software and then applied to the outer plate below the waterline of the structure, with the direction pointing to the inside of the hull; Figure 7 As shown, it shows the pressure distribution of the outer plate when the structure is watertight. The darker the color, the greater the load.

[0184] Load 4: Methanol fuel dynamic pressure; Substitute the known data that affect the dynamic pressure of methanol into the formula to obtain a formula with the coordinates of the methanol bulkhead node as variables; Take the port methanol tank fully loaded as an example, there are a total of 8 working conditions, which can be divided into 4 groups according to the acceleration and reference point values, such as Figure 8 shown.

[0185] The above load is applied to the left methanol tank bulkhead. When the dynamic pressure is positive, the direction points to the outside of the tank. Fig. 9 As shown, the dynamic pressure distribution of the left methanol tank under the first group of working conditions 9 and 10 is displayed. The darker the color, the greater the load. In the same way, each group of loads is applied.

[0186] Load 5: Wave load; wave load is mainly applied to the ship's outer plate, upper deck, superstructure and the outer wall of the methanol tank. The load on the ship's outer plate should also be applied according to the waterline height and the front / back wave surface, and the corresponding formula should be selected for application.

[0187] S7. Evaluation of yield buckling results.

[0188] In view of some assumptions and simplifications in the modeling, loading and constraint steps, in order to ensure the structural safety as much as possible, the yield allowable factor in the relevant specifications was adjusted to 0.85 times and the buckling allowable factor was adjusted to 0.9 times for result evaluation. The allowable stress is: the allowable stress of mild steel MS is 200 MPa, the allowable stress of high-strength steel HT32 is 256 MPa, and the allowable stress of high-strength steel HT36 is 277 MPa.

[0189] S8. Screening of concentrated stress points.

[0190] In order to prevent stress concentration points from not being displayed in the coarse mesh model, it is necessary to screen the results that meet the yield requirements. In order to select as many stress concentration points as possible, the screening coefficient is selected as 0.75, that is, the units with a yield utilization factor greater than 0.75 in the coarse mesh model are selected for 50 mm x 50 mm Fine mesh yield analysis.

[0191] S9. Fine mesh yield analysis.

[0192] The present invention provides a strength assessment method for a methanol tank on a green ship deck based on FEM, which realizes the strength assessment of the structural safety of the methanol tank on the ship deck, ensures the structural safety of the methanol tank and its surrounding structures, and ensures the safety of personnel, equipment, operations and property on board during the operation of a methanol dual-fuel ship.

[0193] The above is only a preferred embodiment of the present invention and does not limit the present invention in any form. Although the present invention has been disclosed as a preferred embodiment as above, it is not used to limit the present invention. Any technician familiar with this profession can make some changes or modify the technical contents disclosed above into equivalent embodiments without departing from the scope of the technical solution of the present invention. However, any simple modification, equivalent replacement and improvement made to the above embodiments without departing from the content of the technical solution of the present invention, based on the technical essence of the present invention, within the spirit and principles of the present invention, still fall within the protection scope of the technical solution of the present invention.

Claims

1. A strength assessment method for methanol tank on green ship deck based on FEM, characterized in that The following steps are involved: S1. Determine the relevant load; The relevant loads in step S1 include structural gravity, static pressure of methanol fuel, draft pressure of ship outer plate, dynamic pressure of methanol fuel and wave load; S2. Typical working condition design of methanol tank; The typical working conditions in step S2 include a methanol two-tank full loading mode, a methanol left-tank full loading mode, a methanol right-tank full loading mode, and a methanol tank full empty loading mode; Methanol two-tank full loading mode includes: Condition 1: minimum ballast draft with maximum longitudinal forward acceleration and maximum vertical downward acceleration; Condition 2: Structural draft with maximum longitudinal forward acceleration and maximum vertical downward acceleration; Condition 3: minimum ballast draft with maximum longitudinal aft acceleration and maximum vertical downward acceleration; Condition 4: Structural draft with maximum longitudinal rearward acceleration and maximum vertical downward acceleration; Condition 5: Structural draft with maximum lateral left acceleration; Condition 6: Structural draft with maximum lateral rightward acceleration; Condition 7: minimum ballast draft with maximum lateral left acceleration; Condition 8: minimum ballast draft with maximum lateral acceleration to the right; Methanol left tank full loading mode includes: Condition 9: minimum ballast draft with maximum longitudinal forward acceleration and maximum vertical downward acceleration; Condition 10: Structural draft with maximum longitudinal forward acceleration and maximum vertical downward acceleration; Condition 11: minimum ballast draft with maximum longitudinal aft acceleration and maximum vertical downward acceleration; Condition 12: Structural draft with maximum longitudinal rearward acceleration and maximum vertical downward acceleration; Condition 13: Structural draft with maximum lateral left acceleration; Condition 14: Structural draft with maximum lateral rightward acceleration; Condition 15: minimum ballast draft with maximum lateral left acceleration; Condition 16: minimum ballast draft with maximum lateral acceleration to the right; The methanol right tank full loading mode includes: Condition 17: minimum ballast draft with maximum longitudinal forward acceleration and maximum vertical downward acceleration; Condition 18: Structural draft with maximum longitudinal forward acceleration and maximum vertical downward acceleration; Condition 19: minimum ballast draft with maximum longitudinal aft acceleration and maximum vertical downward acceleration; Condition 20: Structural draft with maximum longitudinal rearward acceleration and maximum vertical downward acceleration; Condition 21: Structural draft with maximum lateral left acceleration; Condition 22: Structural draft with maximum lateral rightward acceleration; Condition 23: minimum ballast draft with maximum lateral left acceleration; Condition 24: minimum ballast draft with maximum lateral acceleration to the right; Methanol tank empty loading mode includes: Condition 25: Structural draft with maximum wave pressure at the port waterline; Condition 26: Structural draft with maximum wave pressure at the starboard waterline; Condition 27: minimum ballast draft with maximum wave pressure at the port waterline; Condition 28: minimum ballast draft with maximum wave pressure at the starboard waterline; S3, list calculation of complex loads; The step S3 is specifically as follows: Load 1: Structural deadweight; applies downward gravity acceleration to all structural members in all conditions; Load 2: Methanol fuel tank static pressure; liquid tank static pressure P ms Take P ms = ρ m g (z mtop – z m ) + P PV In the formula, ρ m is the density of methanol; g is the acceleration due to gravity; z mtop is the height of the methanol tank top; z m is the height of any point on the methanol tank bulkhead; P PV is the air valve pressure of the methanol tank; when the methanol tank is fully loaded, the static pressure acts on the wall panels around the cabin and points to the outside of the cabin; Load 3: Ship's outer plate draft pressure; outer plate pressure P Take P = ρ L g (T–z) In the formula, ρ L is the density of seawater; g is the acceleration due to gravity; T The ship's draft is divided into structural draft and minimum ballast draft; z is the height of any point on the ship's outer plate below the corresponding waterline; the outer plate pressure acts on the ship's outer plate below the corresponding waterline, and the direction is toward the inside of the outer plate; Load 4: Methanol fuel dynamic pressure; According to the loading conditions of the ship's aft cargo hold and the definition of the ship's motion acceleration under various loading conditions of the aft cargo hold in relevant specifications, the acceleration values ​​of the center of gravity of the two compartments of the methanol tank in three directions under various conditions are calculated; The envelope values ​​of the absolute values ​​of acceleration in the corresponding directions of all working conditions are selected in three directions as the acceleration values ​​for calculating the dynamic load of methanol; The above results in the acceleration of the center of gravity of the methanol tank in all directions during the ship's motion. The dynamic load on the methanol tank wall caused by this acceleration needs to determine its reference point coordinates according to various working conditions. The reference point is taken as all nodes on the top boundary of the methanol tank, so that the following formula V j The node corresponding to the maximum value of V j = a x (x mj – x G ) + a y (y mj – y G ) + (a z + g) (z mj – z G ) In the formula, a x 、a y 、a z is the acceleration at the center of gravity of the methanol tank; x G 、y G 、z G is the coordinate of the center of gravity of the methanol tank compartment; x mj 、y mj 、 z mj Methanol tank roof j Point coordinates; Then, according to the liquid dynamic pressure formula, the dynamic pressure generated by methanol under various working conditions is obtained: P md : P md = 1.05ρ m [a x (x mj – x m ) + a y (y mj – y m ) + a z (z mj – z m )] P md When it is positive, the direction of the dynamic load acting on the cabin wall points to the outside of the cabin; Load 5: Wave load; the wave load is mainly aimed at the working condition of the two methanol tanks being completely empty. When the methanol tanks are completely empty, the equivalent design wave of the transverse wave with the largest hydrodynamic force at the midship waterline is applied to the port and starboard sides of the model respectively, in order to verify the strength of the methanol tanks under the outer wave pressure; S4. Establish a methanol tank model; S5, deduct corrosion allowance; Specifically, step S5 is to deduct 0.5 from the methanol tank model by referring to the corrosion allowance requirements of conventional bulk carriers. t c The method of deducting the corrosion allowance is as follows: flexibly use the classification society software to splice the partial model of the methanol tank into a three-tank model that can be recognized by the classification society software. According to the corrosion requirements of the methanol tank and its surrounding structures, manually adjust or add the corrosion allowance parameters of the software to complete the three-tank model from structural size to Net The size conversion, and finally the original methanol tank model is cut out from the three-tank model; S6, apply loads and boundary conditions; S7, yield buckling result evaluation; S8, concentrated stress point screening; S9. Fine mesh yield analysis.

2. A strength assessment method for methanol tank on deck of green ship based on FEM according to claim 1, characterized in that: Specifically, step S4 is to establish a coarse mesh model of the methanol tank, taking into account the need to apply loads such as the draft of the outer plate and the low credibility of the model results at the boundary constraints. Based on the FEM analysis software and in combination with the position and structural characteristics of the methanol tank, all structures from the front wall of the cabin to the rear are selected for coarse mesh modeling, and the unit size is about 800. mm x 800 mm ; Among them, the board uses Plate Unit simulation, tendons, Carling And small bracket using line unit bar / beam simulation.

3. The strength assessment method of methanol tank on deck of green ship based on FEM according to claim 1 is characterized by: The step S6 specifically comprises: The model boundary conditions and loads are implemented in the FEM analysis software; Boundary conditions affect the effect of load application. According to the range characteristics of the model, the hull cross section in the rigid constraint model is adopted to optimize and adjust the cross section of the constraint according to the deformation effect and stress size. The applied loads include: Load 1: Structural self-weight; in FEM software, a vertical downward gravity acceleration is applied to the entire model; Load 2: Methanol fuel static pressure; Substitute the known data that affect the methanol fuel static pressure into the formula to obtain the model node height z m Formula for variables P ms = 0.8 x 9810 x (z mtop – z m ) x 10 -9 + P PV The above formula is input into the load function of the FEM analysis software, and then applied to the wall panels around the left and right cabins of the methanol tank, with the direction pointing to the outside of the cabin; Load 3: Draft pressure of ship outer plate; Substitute the known data affecting the draft pressure of outer plate into the formula to obtain the model node height z The formula is a variable, taking the structural draft as an example, P = 1.025 x 9810 x (T SC – z) x 10 -9 The above formula is input into the load function of the FEM analysis software and then applied to the outer plate below the waterline of the structure, with the direction pointing to the inside of the hull; Load 4: Methanol fuel dynamic pressure; Substitute the known data that affect the dynamic pressure of methanol into the formula to obtain a formula with the coordinates of the methanol bulkhead node as variables; Take the port methanol tank fully loaded as an example, there are 8 working conditions in total, which can be divided into 4 groups according to the acceleration and reference point values; Each group of loads is applied to the left methanol tank bulkhead, and the direction is toward the outside of the tank when the dynamic pressure is positive; Load 5: Wave load; wave load is mainly applied to the ship's outer plate, upper deck, superstructure and the outer wall of the methanol tank. The load on the ship's outer plate should also be applied according to the waterline height and the front / back wave surface, and the corresponding formula should be selected for application.

4. The strength assessment method of methanol tank on deck of green ship based on FEM according to claim 1 is characterized by: The step S7 is specifically, yield buckling result evaluation; in view of some assumptions and simplifications in the modeling, loading and constraint steps, when evaluating the results, in order to ensure the structural safety as much as possible, the yield allowable factor in the relevant specifications is adjusted to 0.85 times and the buckling allowable factor is adjusted to 0.9 times to evaluate the results, wherein the allowable stress is: the allowable stress of mild steel MS is 200 MPa, the allowable stress of high-strength steel HT32 is 256 MPa, and the allowable stress of high-strength steel HT36 is 277 MPa.

5. The FEM-based strength assessment method for methanol tanks on green ship decks according to claim 1 is characterized by: The step S8 specifically includes screening the concentrated stress points. In order to prevent the stress concentration points from not being displayed in the coarse mesh model, the results that meet the yield requirement need to be screened. In order to select as many stress concentration points as possible, the screening coefficient is selected as 0.75, that is, the units with a yield utilization factor greater than 0.75 in the coarse mesh model are selected, and 50 mm x 50 mm Fine mesh yield analysis.

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