Ship sitting pier head structure strength evaluation method

Abstract

The invention provides a ship pier head structure strength evaluation method, which aims at the problem that a ship bow structure is easy to damage or deform under a ship pier falling working condition, obtains an accurate rigidity coefficient of a docking block through actual measurement and conversion, and establishes a complete real ship finite element model in an evaluation range to reflect accurate mass distribution and rigidity. Coarse grid and fine grid grading evaluation is adopted, the efficiency is improved while the calculation precision is guaranteed, coarse grid analysis is used for obtaining docking block counter-force, fine grid analysis can consider actual counter-force distribution in contact with a docking block, and the yield strength and buckling strength evaluation safety coefficient of the ship bow structure is provided; the damage or deformation risk of the ship docking pier falling structure can be systematically and accurately evaluated, the ship pier falling optimization design is guided, and the ship construction period can be shortened.

Description

Technical Field

[0001] The present invention relates to the field of ship engineering, and particularly to a method for evaluating the structural strength of a ship. Background Art

[0002] For a ship with an outflaring bow, the bottom line of the bow is slender. When the ship is in the dock, the mid-longitudinal area at the bottom of the bow can often only be supported by a row of dock blocks arranged along the ship length direction. In some severe cases, such as in a dock with a partially fixed dock block layout; or a dock with movable dock blocks, in order to reduce the waste of manpower, material resources and cycle caused by dock block adjustment, a method of arranging dock blocks shared by multiple ships is adopted. Inevitably, some dock blocks will be located at the weak positions of the ship bottom, and it is easy to cause insufficient structural strength or stiffness due to excessive reaction force and superposition with the ship construction stress, which will further lead to hull structure deformation problems, resulting in additional repair costs and construction cycle, and is not conducive to efficient ship construction.

[0003] Therefore, reasonable evaluation of the strength of the bow structure when the ship is sitting on the dock is the key to avoiding the risk of structural deformation.

[0004] In the existing finite element evaluation method for structural strength, the method of establishing a finite element model of the bottom local structure is often used, which is difficult to simulate the weight distribution and overall structural stiffness of the relevant area of the actual ship, and is not conducive to the calculation accuracy; and the use of fine grid division for the entire calculation area to build the calculation workload is large and inefficient. In addition, the existing technology only obtains the stress value of the structure in the sitting-on-dock state through calculation, and does not clarify the evaluation method and evaluation criteria for structural yield failure and buckling deformation, which is not conducive to providing engineering design decisions. Summary of the Invention

[0005] Aiming at the deficiencies of the existing technology, the purpose of the present invention is to provide a method for evaluating the strength of the bow structure of a ship sitting on the dock. Aiming at the problem that the bow structure of the ship is prone to damage or deformation under the condition of the ship sitting on the dock, the accurate stiffness coefficient of the dock block is obtained through actual measurement and conversion, and a complete actual ship finite element model within the evaluation range is established to reflect the accurate mass distribution and stiffness, and a hierarchical evaluation using coarse grids and fine grids is adopted to improve the efficiency while ensuring the calculation accuracy. The coarse grid analysis is used to obtain the dock block reaction force, the fine grid analysis can consider the actual reaction force distribution in contact with the dock block, and the safety factors for evaluating the yield strength and buckling strength of the bow structure are proposed, which can systematically and accurately evaluate the risk of structural damage or deformation of the ship when entering the dock and sitting on the dock, guide the optimization design of the ship sitting on the dock, and is conducive to shortening the ship construction cycle.

[0006] To achieve the above purpose, the present invention adopts the following technical solutions:

[0007] A method for evaluating the strength of the bow structure of a ship sitting on the dock includes the following steps:

[0008] S1. Use finite element modeling and analysis software to establish a finite element calculation model for the structural analysis area of the ship's bow. The mesh size is the longitudinal girder spacing × frame spacing, and establish a finite element analysis model for the docking blocks. The docking block finite element model is selected as a one-dimensional vertical spring element at the proposed docking points. The stiffness K of the docking block is K = EA / L, where E is the elastic modulus of the packing material, A is the contact area between the packing and the ship bottom structure, and L is the height of the packing.

[0009] S2. Adjust the weight distribution and center of gravity of the finite element calculation model of the ship's bow structural analysis area to be basically the same as that of the actual ship within the same range, and the deviation rate does not exceed the preset value. The preset value is preferably 1%.

[0010] S3. Set boundary conditions and loads in the finite element analysis model, and execute the static analysis module of the finite element analysis software to obtain the reaction forces of each docking block.

[0011] S4. Select one or more positions with larger reaction forces of the docking blocks or weaker ship bottom structures for local finite element mesh refinement.

[0012] S5. Set the first calculation condition and the second calculation condition to respectively check the structural yield strength and buckling strength of the one or more local ship bottom structures under the reaction forces of the docking blocks. The first calculation condition is checked according to the fourth strength criterion.

[0013] The second calculation condition is checked according to the eigenvalue buckling check under the linear elastic assumption.

[0014] Further, the range of the ship's bow structural analysis area described in S1 is selected as follows: in the ship length direction, from 0.25 times the ship length from the ship's bow end to the ship's bow, and includes the entire ship width and the ship depth direction structure.

[0015] Further, the stiffness K of the docking block described in S1 is obtained by actual measurement, and the formula is:

[0016] K = mg / (x1 + x2 + x3 + x4)

[0017] Where m is the weight of the structural segment arranged on 4 docking blocks, and x1, x2, x3, x4 are the measured vertical deformations of the 4 docking blocks.

[0018] Further, the method of adjusting the calculation model described in S2 is to adjust the deck material density and / or add mass units of large equipment and ballast water weight in the analysis area.

[0019] Further, the boundary condition described in S3 is to constrain the translational and rotational degrees of freedom of the lower end points of the docking block finite element model; the load is to apply the vertical free fall acceleration g.

[0020] Further, the mesh size refinement described in S4 is a fine mesh of 50×50 mm.

[0021] Further, the dock pier finite element analysis model described in S4 is replaced with the application of distributed loads of equal magnitude.

[0022] Further, the checking formula for the first calculation condition described in S5 is:

[0023]

[0024] where σ1, σ2, σ3 represent the principal stresses of the ship bottom structure above the dock pier, and τ xy , τ yz , τ zx represent the shear stresses of the ship bottom structure above the dock pier;

[0025] The checking formula for the second calculation condition is:

[0026] [K a +λ[K c {Δu} = {ΔF}

[0027] where [K a is the bending stiffness matrix of the local ship bottom structure, [K c is the geometric stiffness matrix of the local ship bottom structure, {ΔF} is the increment of the external load, {Δu} is the structural deformation, and λ is the critical buckling eigenvalue;

[0028] In the unstable state of the structure, when {ΔF} is approximately equal to 0, that is, when the external force no longer changes and the structure has a deformation {Δu}, in this state, the above formula is transformed into solving for λ:

[0029] [K a +λ[K c = 0.

[0030] Further, the safety margin of the yield strength of the local ship bottom structure described in S5 is u, and the formula is:

[0031]

[0032] σ c is the stress obtained according to the fourth strength criterion in the finite element calculation, and σ s is the material yield strength; under the given reaction force F of the dock pier on the local ship bottom structure, the safety margin of the yield strength of the local ship bottom structure is u ≥ 1.

[0033] Further, under the given reaction force F of the dock pier on the local ship bottom structure, the first-order buckling eigenvalue λ of the local ship bottom structure is λ ≥ 1.1.

[0034] The beneficial technical effects of the present invention are as follows: It can evaluate the yield strength and buckling strength of the bow structure for the ship landing condition, assess the risk of structural damage or deformation during ship docking and landing, guide the optimization design of ship landing, and is beneficial to shortening the ship construction cycle. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 It is a flow chart of a method for evaluating the strength of the bow structure of a ship when sitting on a dock.

[0036] Figure 2 It is a top view of the dock pier layout plan of the bow of a certain ship.

[0037] Figure 3 It is Figure 2 a typical transverse cross-sectional view in

[0038] Figure 4 It is a strength calculation model for the ship's bow landing.

[0039] Figure 5 The yield strength check result of the first calculation condition of the local structure at the bottom of the ship.

[0040] Figure 6 The buckling strength check result of the first calculation condition of the local structure at the bottom of the ship. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0041] The present invention will be further described in detail below in conjunction with the drawings and specific embodiments. These embodiments are only used to illustrate the present invention and are not intended to limit the present invention.

[0042] In the description of the present invention, it should be noted that the terms "center", "longitudinal", "transverse", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", etc. indicate the orientation or positional relationship based on the orientation or positional relationship shown in the drawings. They are only for describing the present invention and simplifying the description, rather than indicating or implying that the indicated position or element must have a specific orientation, be constructed and operated in a specific orientation, and thus cannot be understood as a limitation to the present invention. In addition, the terms "first" and "second" are only used for descriptive purposes and cannot be understood as indicating or implying relative importance.

[0043] S1. Use Patran, Ansys or other finite element modeling software to establish a finite element calculation model 100 for the structure of the bow analysis area of the ship, and the mesh size is the longitudinal frame spacing × the rib spacing.

[0044] In an implementable manner, the range of the bow analysis area of the ship is selected as follows: In the ship length direction, from 0.25 times the ship length from the bow end to the bow, and including the entire structure in the ship width and ship depth directions.

[0045] In an implementable manner, in step S1, it further includes establishing a finite element analysis model 101 of the dock pier.

[0046] Specifically, a common dock pier is composed of a cement square body and a wooden block installed on the square body. In the finite element analysis model, a one-dimensional vertical spring element is established at the point where the pier is to be dropped to simulate the dock pier.

[0047] It should be noted that the stiffness k of the one-dimensional vertical spring element can be calculated by the formula EA / L, where E is the elastic modulus of the material of the wooden block, A is the contact area between the wooden block and the ship bottom structure, and l is the height of the wooden block.

[0048] Preferably, due to factors such as secondary processing, aging or other factors of the wooden block, there is an error in the theoretical elastic modulus of the wooden block. The present invention provides a preferred method for obtaining the stiffness of the dock pier by actual measurement.

[0049] Specifically, the actual measurement method is as follows: During the shipbuilding process, a square structural section 100 with an appropriate weight m can always be conveniently found. Four dock piers are arranged within the size range of the structural section 100, and the structural section 101 is hoisted and placed on the four dock piers. The vertical deformation amounts of the four dock piers are measured as x1, x2, x3, and x4 respectively. The stiffness k of the dock pier is calculated by the formula mg / (x1 + x2 + x3 + x4).

[0050] S2. Adjust the weight distribution and the center of gravity of the finite element calculation model to be basically consistent with that of the actual ship within the same range, and the deviation rate does not exceed 1%.

[0051] In an implementable manner, the method of adjusting the material density of the finite element calculation model or adding mass units is adopted to obtain the weight and the center of gravity that are basically consistent with those of the actual ship.

[0052] Specifically, large equipment and the weight of ballast water within the analysis area of the ship's bow are simulated by mass units, and other weights are simulated by adjusting the material density of each deck structure.

[0053] Exemplarily, the following table is Figure 4 Comparison of the weight and the center of gravity between the calculation model and the actual ship,

[0054]

[0055] In the above table, L represents the coordinate of the center of gravity in the ship length direction, T represents the coordinate of the center of gravity in the ship width direction, and V represents the coordinate of the center of gravity in the ship depth direction.

[0056] S3. Set boundary conditions and loads in the Figure 4 finite element analysis model, execute the static analysis module of the finite element analysis software, and obtain the reaction forces of each dock pier.

[0057] Further, the boundary conditions in the finite element analysis model are as follows: the translational and rotational degrees of freedom of the lower endpoints of all 1D vertical spring elements 101 used to simulate dock piers in the constrained finite element model are constrained to simulate the support state of the dock piers.

[0058] Further, the load in the finite element model is as follows: the inertial load generated by the self-weight of the hull is simulated by applying a vertical free-fall acceleration g.

[0059] S4. Select one or more positions where the reaction force of the dock pier is large or the bottom structure of the ship is weak for local finite element mesh refinement;

[0060] Specifically, as Figure 5 , Figure 6 shown, the local finite element mesh refinement is based on the structural finite element calculation model of the ship's bow analysis area, and the local position is refined from a mesh with a longitudinal frame spacing × rib spacing dimension to a fine mesh of about 50×50 mm.

[0061] Further, the 1D vertical spring elements used to simulate the dock piers within the local position range are deleted and replaced by applying a distributed load of equal magnitude.

[0062] S5. Set the first calculation condition and the second calculation condition to check the structural yield strength and buckling strength of the local structure of the bottom of the ship at the one or more positions under the reaction force of the dock pier respectively;

[0063] Specifically, the first calculation condition is to check the yield strength of the local structure of the bottom of the ship;

[0064] Further, the yield strength of the local structure of the bottom of the ship is checked according to the fourth strength criterion, and the formula is:

[0065]

[0066] In the formula, σ1, σ2, σ3 represent the principal stresses of the bottom structure of the ship above the dock pier; τ xy , τ yz , τ zx represent the shear stresses of the bottom structure of the ship above the dock pier;

[0067] Further, the safety margin of the yield strength of the local structure of the bottom of the ship is u, and the formula is:

[0068]

[0069] σ c is the stress obtained by finite element calculation according to the fourth strength criterion, and σ s is the material yield strength,

[0070] Preferably, the present invention proposes that under the given reaction force F of the dock pier on the local structure of the ship bottom, the safety margin of the yield strength of the local structure of the ship bottom is u≥1

[0071] Specifically, the second calculation condition is to check the buckling strength of the local structure of the ship bottom;

[0072] Furthermore, the buckling strength of the local structure of the ship bottom is checked according to the eigenvalue buckling under the linear elastic assumption, and the formula is:

[0073] [[K a +λ[K c {Δu}={ΔF}

[0074] In the formula, [K a is the bending stiffness matrix of the local structure of the ship bottom;

[0075] [K c is the geometric stiffness matrix of the local structure of the ship bottom;

[0076] {ΔF} is the external load increment;

[0077] {Δu} is the structural deformation;

[0078] λ is the critical buckling eigenvalue;

[0079] It should be noted that in the unstable state of the structure, when {ΔF} is approximately equal to 0, that is, the external force is not changing, the structure has a deformation {Δu}. In this state, the above formula is transformed into solving λ:

[0080] [K a +λ[K c =0

[0081] Preferably, the present invention proposes that under the given reaction force F of the dock pier on the local structure of the ship bottom, the first-order buckling eigenvalue λ of the local structure of the ship bottom is λ≥1.1

[0082] Exemplarily, Figure 5 the yield strength check result of the first calculation condition of the local structure of the ship bottom, Figure 6 the buckling strength check result of the first calculation condition of the local structure of the ship bottom. The following table extracts the calculation results and compares them with the criteria

[0083] The first calculation condition The second calculation condition The maximum stress / Mpa The critical buckling eigenvalue Criterion <355 >1.1 Calculation result 340 1.3 Judgment Meet the requirements Meet the requirements

[0084] In summary, according to the method provided by the present application, it is possible to evaluate the yield strength and buckling strength of the bow structure for the ship landing condition before the ship lands on the dock, evaluate the risk of structural deformation during ship docking and landing, guide the optimization design of ship docking and landing, and is beneficial to shortening the ship construction cycle.

Claims

1. A method for evaluating the strength of the bow structure of a ship sitting on a dock, characterized in that, It includes the following steps: S1. Use finite element modeling and analysis software to establish a finite element calculation model of the structure in the bow analysis area of the ship. The mesh size is selected as the longitudinal frame spacing × rib spacing, and establish a finite element analysis model of the dock block. The dock block finite element model is selected as a 1D vertical spring element at the intended landing point. The stiffness K of the dock block is K = EA / L, where E is the elastic modulus of the fender material, A is the contact area between the fender and the ship bottom structure, and L is the height of the fender; S2. Adjust the weight distribution and center of gravity of the finite element calculation model of the structure in the bow analysis area of the ship so that the deviation rate between the model and the actual ship in the same range does not exceed the preset value; S3. Set boundary conditions and loads in the finite element analysis model, and execute the static analysis module of the finite element analysis software to obtain the reaction forces of each dock block; S4. Select the model of the position of the ship bottom structure corresponding to at least one dock block for local finite element mesh refinement; S5. Set the first calculation condition and the second calculation condition, and respectively check the structural yield strength and buckling strength of the local ship bottom structure under the reaction forces of the dock blocks. The first calculation condition is checked according to the fourth strength criterion, The second calculation condition is checked according to the eigenvalue buckling check under the linear elastic assumption.

2. The strength evaluation method for the bow structure of a ship sitting on a pier according to claim 1, characterized in that, The range of the bow analysis area of the ship described in S1 is selected as: in the longitudinal direction of the ship length, from 0.25 times the ship length from the ship bow end to the ship bow, and includes the entire ship width and the structure in the ship depth direction.

3. A method for evaluating the structural strength of the bow of a ship sitting on a pier, characterized in that, The stiffness K of the dock block described in S1 is obtained by actual measurement, and the formula is: K = mg / (x1 + x2 + x3 + x4) where m is the weight of the structural segment arranged on 4 dock blocks, and x1, x2, x3, x4 are the measured vertical deformation amounts of the 4 dock blocks.

4. The method for evaluating the structural strength of the bow of a ship sitting on a pier according to claim 1, characterized in that, The method of adjusting the calculation model described in S2 is to adjust the material density of the deck and / or add mass units of large equipment and the weight of ballast water in the analysis area.

5. A method for evaluating the structural strength of the bow of a ship sitting on a pier, characterized in that, The boundary condition described in S3 is to constrain the translational and rotational degrees of freedom of the lower end point of the dock block finite element model, and the load is to apply the vertical free-fall acceleration g.

6. A method for evaluating the structural strength of the bow of a ship sitting on a pier, characterized in that, The mesh size refinement described in S4 is a fine mesh of 50×50mm.

7. A method for evaluating the structural strength of the bow of a ship sitting on a pier, characterized in that, The dock block finite element analysis model described in S4 is replaced by applying distributed loads of equal magnitude.

8. A method for evaluating the strength of the bow structure of a ship sitting on a pier, characterized in that, The check formula for the first calculation condition described in S5 is: Among them, σ1, σ2, σ3 represent the principal stresses of the ship bottom structure above the dock block, and τ xy , τ yz , τ zx represent the shear stresses of the ship bottom structure above the dock block; The check formula for the second calculation condition described in S5 is: [[K a + λ[K c {Δu} = {ΔF} Among them, [K a is the bending stiffness matrix of the local structure of the ship bottom, [K c is the geometric stiffness matrix of the local structure of the ship bottom, {ΔF} is the increment of the external load, {Δu} is the structural deformation, and λ is the critical buckling eigenvalue; In the state of structural instability, when {ΔF} is approximately equal to 0, that is, the external force no longer changes, and the structure has a deformation {Δu}. In this state, the above formula is transformed into solving λ: [K a +λ[K c = 0。 9. The method for evaluating the strength of the bow structure of a ship sitting on a pier according to claim 1, characterized in that, The safety margin of the yield strength of the local ship bottom structure described in S5 is u, and the formula is: σ c is the stress obtained by the finite element calculation according to the fourth strength criterion, and σ s is the material yield strength; under the given reaction force F of the dock pier on the local structure of the ship bottom, the safety margin of the yield strength of the local structure of the ship bottom is u ≥ 1.

10. The strength evaluation method for the bow structure of a ship sitting on a pier according to claim 1, characterized in that, Under the reaction force F of the dock block on the given local ship bottom structure, the first-order buckling eigenvalue λ of the local ship bottom structure ≥ 1.1.

Images