Method for evaluating strength of a keel-to-heel joint

Abstract

A kind of quick evaluation method of ship bottom deadwood joint strength, deadwood is fixed below the stern plate of ship body, propeller, deadwood is welded and fixed with ship body plate by backing plate, deadwood and backing plate adopt deep fusion welding connection, backing plate and plate adopt fillet welding connection, the strength of plate joint is quickly evaluated. By simplifying analysis method, the yield stress R1 and R2 of deadwood are obtained by simplifying finite element analysis method, R1 and R2 are compared, the maximum value R is obtained, the maximum value R is compared with allowable result, the transverse evaluation is carried out, the yield stress value R meeting the requirements is finally obtained, and the thickness of deadwood is finally determined to ensure the strength of deadwood. It is judged whether the weld between deadwood and backing plate meets the connection strength requirement. The two methods of the present application can improve work efficiency by about 80%, and confirm the strength of weld after welding, which is closer to the actual situation and can replace complex contact analysis.

Description

Technical Field

[0001] This invention belongs to the field of shipbuilding and design, and specifically relates to a method for evaluating the strength of the connection of the bottom timber of a ship. Background Technology

[0002] To achieve energy conservation, emission reduction, and improved navigation safety, some ships have a symmetrical directional stabilizing fin, commonly known as a "stabilizing fin," installed at the stern, below the propeller, and at the center of the hull (see patent CN201120441275.0). By installing the stabilizing fin, the ship's side projection area is increased, and the center of the side projection area is shifted towards the stern, thereby improving the ship's navigation stability.

[0003] The problems include: (1) Because it is welded to the outer plating of the ship's bottom, it will be subjected to the pressure and lateral forces of the ship's bottom for a long time. Therefore, its strength must be assessed in the early stages of the design. Moreover, since it is welded to the outer plating, if it is damaged and replaced, the welding will damage the paint and curvature of the outer plating. (To prevent damage to the outer plating) (2) The wooden structure is welded to the outside of the hull, and there are currently no standards for evaluating this type of structure.

[0004] (3) In the past, the finite element method was used for evaluation. It usually required to calculate hydrodynamic data under different geometric parameters, perform loading analysis on the log structure, and if the requirements were not met, the finite element model had to be modified and the hydrodynamic analysis had to be performed again, followed by model loading analysis. The method was complicated and time-consuming.

[0005] (4) Previous calculation methods only calculated the log structure itself, and the connecting structure was considered to be integrated with the hull structure, and the problem of insufficient welds could not be considered. Summary of the Invention

[0006] To solve the above problems, the present invention provides a solution that aims to achieve the desired objective, and the technical solution adopted is as follows: A method for evaluating the strength of a hull hull tie rod connection is characterized in that a tie rod is fixed to the outer stern plate of the hull and below the propeller. The tie rod is welded to the outer hull plate via a pad, the tie rod and the pad are connected by a deep penetration weld, and the pad and the outer hull plate are connected by a fillet weld. The strength of the tie rod connection is evaluated, and the specific operation method is as follows: S1: The yield stress R1 of the tail log is obtained using a simplified analysis method. 1.1 An equivalent analysis model of the log structure is established, and the log is equivalent to a beam FB according to its area S. One end of the beam is rigidly fixed, and the other end is free. The length of the beam FB is L·t. net。

[0007] Where S is the projected area of ​​the front view of the log structure, and L is the distance between the tangent line M1 of the welding area between the log and the outer plate and the tangent line M2 of the log arc parallel to M1.

[0008] tnet is the thickness t of the log, minus 1 times the corrosion allowance.

[0009] 1.2 Based on the resistance calculation theory, the compressive load P1 on the log is calculated as P1 = 0.5·c·ρ·v 2 .

[0010] in: c is a constant not greater than 1.

[0011] ρ is the density of seawater, 1.025 t / m³. 3。

[0012] v represents the maximum lateral velocity at the tail section of the log structure.

[0013] 1.3 According to the theory of mechanics of materials, the load P1 is uniformly distributed on the beam FB=L·t net The maximum axial stress R1 at the fixed end of beam FB is obtained.

[0014] S2: The yield stress R2 of the tail section log is obtained by using a simplified finite element analysis method.

[0015] 2.1 Establish a finite element model of the log and stern structure based on the structural drawings, with the boundary set at the far end of the hull and rigidly fixed.

[0016] 2.2 The water pressure at the centroid of the log structure is taken as the simplified equivalent pressure load P2 of the log structure, P2=c1·ρ·g·t s .

[0017] in: ρ is the density of seawater, 1.025 t / m³. 3。

[0018] g is the acceleration due to gravity.

[0019] t s The distance from the centroid of the log structure to the waterline of the log structure.

[0020] c1 is a statistical coefficient, 0.2≤c1≤0.25.

[0021] When the ratio of the ship's depth D to its breadth B, D / B, is less than 0.5, c1 = 0.25.

[0022] When the ratio of the ship's depth D to its breadth B, D / B > 0.5, c1 = 0.2.

[0023] 2.3 Apply the pressure load P2 uniformly and vertically to the finite element model of the log structure to obtain the yield stress R2 of the log structure and the connection between the log and the hull.

[0024] S3: Compare the yield stresses R1 and R2 obtained in S1 and S2, and find the maximum value R of the two yield results, R=max{R1,R2}, and compare it with the allowable result.

[0025] S4: Cross-sectional assessment: R≤R eH / γ Where: R eH R is the yield strength of the log structure; γ is the safety factor, γ≥1.5; when R≤R eH When / γ, proceed to the next step S5.

[0026] When R>R eH When / γ, the thickness t of the rigid board is strengthened, and steps S1, S2, and S3 are repeated until the required R value is obtained, and then the next step S5 is performed.

[0027] S5: The maximum load on the log is obtained according to the following formula, and the minimum weld area A formed by the pad plate and the hull plate is obtained according to the maximum load. weld。

[0028] A weld =f·(235 / R eH_weld ) 0.75 ·F weld。

[0029] F weld =M / (0.5·L3) / 2.

[0030] M = P·S·L4.

[0031] in: P = max{P1, P2}, representing the maximum load calculated in steps S1 and S2, where S is the area of ​​the log, L4 is the vertical distance from the log's centroid to the outer plate, M is the bending moment from the log's force to the outer plate, L3 is the width of the pad, and R... eH_weld The yield strength of the welding material used for the log.

[0032] f is a coefficient; when the support is under pressure, f = 0.05, and when the log is under tension, f = 0.14.

[0033] S6: Verify the effective area A of the weld formed by the backing plate and the outer plate of the ship, A=H1·X.

[0034] Where H1 is the weld throat, H1 = H2 / H2 is the weld leg length.

[0035] X represents the length of the weld along the ship's length. When A>A weld When the strength of the log joint is considered to meet the requirements, When A≤A weld At this point, increase the weld area until the weld area A is greater than A. weld until.

[0036] Furthermore, in step S5 of the above-mentioned method for evaluating the strength of the hull bottom joint, only the effective weld area required for the weld on one side of the hull to be under tension needs to be calculated.

[0037] The beneficial effects of this invention are as follows: (1) This patent provides a rapid assessment method for the strength of the connection between the log structure welded to the outer hull of a ship, which can quickly and accurately calculate the strength of attachment structures such as logs welded to the outside of the hull. This can prevent the log structure from falling off or bending due to water pressure during ship navigation, thereby improving the safety of navigation.

[0038] (2) This patent presents two algorithms to address the design requirements at different stages. Method 1 uses a simple formula method instead of the complex finite element method, saving time in establishing the finite element model and improving work efficiency. Method 2 uses an empirical formula statistical method instead of the traditional hydrodynamic method to calculate the additional load, achieving the expected rapid evaluation. The two methods can improve work efficiency by nearly 80%.

[0039] (3) This patent provides a method for calculating the weld strength after the external appendages are welded to the hull. This method is closer to the actual situation and can replace complex contact analysis. Attached Figure Description

[0040] Figure 1 Flowchart for invention; Figure 2 This is a schematic diagram of the log structure of the present invention; Figure 3 This is a simplified static analysis diagram of the algorithm of this invention; Figure 4 This is a schematic diagram of the welded joint structure of the wooden part in this patent. Among them: 1-log, 2-hull plate, 3-fillet weld, 4-deep penetration weld, 5-backing plate. Detailed Implementation

[0041] The invention will be further described with reference to the accompanying drawings.

[0042] A method for evaluating the strength of the joints of the hull timbers of a ship is provided, involving a joint strength test on the timbers of a real ship. For example... Figure 2As shown, a log is fixed to the outer stern plate of the hull below the propeller. The log is fixed to the outer hull plate by welding with a pad. The log and the pad are connected by deep penetration welding, and the pad and the outer plate are connected by fillet welding. The strength of the connection of the outer plate is evaluated.

[0043] like Figure 1 As shown, the yield stresses R1 and R2 of the log are obtained through simplified analysis and simplified finite element analysis, respectively. R1 and R2 are compared to obtain the maximum value R. This maximum value R is then compared with the allowable result for lateral alignment evaluation, ultimately obtaining the required yield stress value R. This allows for the final determination of the log thickness to ensure its strength. Finally, it is determined whether the weld between the log and the backing plate meets the connection strength requirements. The specific operation is as follows: S1: The yield stress R1 of the log is obtained using a simplified analysis method. 1.1 Establish an equivalent analysis model for the log structure, such as... Figure 3 As shown, the log is equivalent to a beam FB with an area S. One end of the beam is rigidly fixed, and the other end is free. The length of the beam FB is L·t. net .

[0044] Where S is the projected area of ​​the front view of the log structure.

[0045] L is the distance between the tangent line M1 of the welding area between the log and the outer plate and the tangent line M2 of the log's circular arc parallel to M1.

[0046] t net Subtract one times the corrosion allowance from the thickness t of the log.

[0047] According to the theory of resistance calculation, the lateral pressure on the log is calculated to be P1, which is the pressure load P1, P1 = 0.5·c·ρ·v 2 .

[0048] in: c is a constant not greater than 1, and can be conservatively taken as 1.

[0049] ρ is the density of seawater, 1.025 t / m³. 3 .

[0050] v is 7.75 m / s.

[0051] P1 = 0.5 × 1 × 10.25 × 7.75 2 = 30.79 kN / m 2 .

[0052] A mathematical model is established with a slab thickness of 50EH36mm and a corrosion allowance of 2.5mm. The equivalent beam dimensions are FB100 x 47.5mm. Based on the theory of mechanics of materials, a load P1 is uniformly applied to the beam FB = L·t. netThe maximum axial stress at the fixed end of beam FB is obtained as R1 = 153 N / mm. 2 .

[0053] S2: The yield stress R2 of the tail section log was obtained using a simplified finite element analysis method. Based on the structural drawings, a finite element model of the log and tail structure is established. The mesh size is 50.50 mm, the thickness is the net dimension, and the boundary conditions are taken at the farthest end of the model.

[0054] The mold depth D = 44m, mold width B = 21m, c1 = 0.25, and t s =13m, P2=0.25·1.025·9.81·13=32.68KN / m 2 Analysis revealed that the maximum stress R2 = 146 N / mm. 2 .

[0055] S3: Compare the yield stresses R1 and R2 obtained in S1 and S2. The maximum value is R = 153 N / mm. 2 .

[0056] S4: Cross-sectional assessment: R≤R eH / γ.

[0057] R eH R is the yield strength of the material in the log structure. eH =355N / mm 2。

[0058] R eH / 1.5 = 355 / 1.5 = 237 N / mm 2 At this time, R≤R eH / γ, meets the requirements.

[0059] S5: The maximum value of the deadwood load is obtained according to the formula for end connection of struts and bracing materials in Chapter 12, Section 3, 5.3 of the Common Structural Code for Bulk Carriers and Oil Tankers published by the International Association of Classification Societies in January 2022, and the minimum value of the weld area Aweld formed by the pad plate and the hull plate is obtained based on the maximum value of the load.

[0060] M=P·S·L4, M=32.68·0.195·0.95=6.05 KNm.

[0061] F weld =M / (0.5·L3) / 2=6.05 / 0.04 / 2=75.7 KN.

[0062] A weld =f·(235 / R eH_weld ) 0.75 ·F weld =0.14·(235 / 375)0.75 75.7 = 7.46 cm 2 .

[0063] S6: Verify the effective area A of the weld formed by the backing plate and the outer plate of the ship.

[0064] A = H1·X.

[0065] Where H1 is the weld throat, H1 = H2 / H2 is the weld leg length = 12mm, X is the weld length along the ship's length = 100mm, therefore, A = 8.48 cm. 2， A>A weld The requirements are met.

Claims

1. A method for evaluating the strength of a hull hull tie rod connection, characterized in that a tie rod (1) is fixed to the outer stern plate of the hull and below the propeller, the tie rod is fixed to the outer hull plate (2) by welding through a pad (5), the tie rod and the pad are connected by a deep penetration weld (4), and the pad and the outer plate are connected by a fillet weld (3). The strength of the tie rod connection is evaluated, and the specific operation method is as follows: S1: The yield stress R1 of the tail section log is obtained using a simplified analysis method. 1.1 Establish an equivalent analysis model for the log structure. The log is equivalent to a beam FB based on its area S. One end of the beam is rigidly fixed, while the other end is free. The length of beam FB is L·t. net Where S is the projected area of ​​the front view of the log structure, and L is the distance between the tangent M1 of the welding area between the log and the outer plate and the tangent M2 of the log arc parallel to M1. t net Subtract one times the corrosion allowance from the thickness t of the log; 1.2 Based on the resistance calculation theory, the pressure load P1 on the log is calculated. P1=0.5·c·ρ·v 2 ; in: c is a constant not greater than 1; ρ is the density of seawater, 1.025 t / m³. 3 ; v is the maximum lateral velocity at the tail section of the log structure; 1.3 According to the theory of mechanics of materials, the pressure load P1 is uniformly applied to the beam FB, and the maximum axial stress R1 at the fixed end of the beam FB is obtained; S2: The yield stress R2 of the tail section log was obtained using a simplified finite element analysis method. 2.1 Establish a finite element model of the log and stern structure based on the structural drawings, with the boundary set at the far end of the hull and rigidly fixed; 2.2 The water pressure at the centroid of the log structure is taken as the simplified equivalent pressure load P2 of the log structure. P2=c1·ρ·g·t s ; in: ρ is the density of seawater, 1.025 t / m³. 3 ; g is the acceleration due to gravity; t s The height from the centroid of the log structure to the waterline of the log structure; c1 is a statistical coefficient, 0.2 ≤ c1 ≤ 0.25; When the ratio of the ship's depth D to its breadth B, D / B, is less than 0.5, c1 = 0.25; When the ratio of the ship's depth D to its breadth B, D / B > 0.5, c1 = 0.2; 2.3 Apply the pressure load P2 uniformly and vertically to the finite element model of the log structure to obtain the yield stress R2 of the log structure and the connection between the log and the hull. S3: Compare the yield stresses R1 and R2 obtained in steps S1 and S2, and calculate the maximum value R of the two yield results, R=max{R1,R2}, and compare it with the allowable result. S4: Cross-sectional assessment: R≤R eH / γ in: R eH The yield strength of the material in the log structure; γ is the safety factor, γ≥1.5; When R≤R eH When / γ is reached, proceed to the next step S5. When R>R eH When / γ, the thickness t of the rigid board is strengthened, and steps S1, S2, and S3 are repeated until the required R value is obtained, and then the next step S5 is performed. S5: The maximum load on the log is obtained according to the following formula, and the minimum weld area A formed by the pad plate and the hull plate is obtained according to the maximum load. weld A weld =f·(235 / R eH_weld 0.75·F weld ; F weld =M / (0.5·L3) / 2; M = P·S·L4; Where P = max{P1, P2} is the maximum load calculated in steps S1 and S2; S is the area of ​​the log; L4 is the vertical distance from the core of the log to the outer panel; M is the bending moment of the outer plate caused by the force exerted by the log. L3 is the width of the pad; R eH_weld The yield strength of the welding material used for the log. f is a coefficient; when the log is under pressure, f = 0.05, and when the support is under tension, f = 0.

14. S6: Verify the effective weld area A formed by the backing plate and the hull plating; A = H1·X; Where H1 is the weld throat, H1 = H2 / H2 is the weld leg length. X represents the length of the weld along the ship's length. When A>A weld When the strength of the log joint is considered to meet the requirements; When A≤A weld At this point, increase the weld area until the weld area A is greater than A. weld until.

Images