A structural strength analysis method for polar ship cranes

Abstract

The present invention discloses a method for analyzing the structural strength of a polar ship crane, comprising: establishing a geometric model of the crane structure and performing grid division on the geometric model; determining a temperature range for polar operations, wherein the lowest operating temperature is taken as the polar service temperature; setting operating temperature conditions for the crane, solving the temperature field of the crane structure using a steady-state thermal analysis method, and calculating the temperature field of the crane structure; determining polar calculated wind speed; simulating the dynamic wind load on the polar ship crane structure; performing modal analysis on the crane structure using a modal analysis method to obtain its natural frequency and vibration mode, thereby determining the weak direction of the dynamic stiffness of the crane structure; solving the stress on the crane structure to obtain the equivalent stress distribution, maximum equivalent stress change curve, and maximum stress position of the polar ship crane structure under the combined action of temperature load and dynamic wind load, and determining the load safety of the structure based on the structural strength analysis result and the material strength.

Description

Technical Field

[0001] The present invention relates to the field of strength analysis of polar equipment structures, and in particular to a strength analysis process and method for polar ship crane structures under the combined effects of polar temperature loads and wind loads. Background Art

[0002] Polar ships operate in a harsh environment, including sea ice, low visibility, extremely low temperatures, ice accumulation, snow, sea fog, high latitudes, and remoteness, which pose difficulties to the reliability and safety of polar ships and equipment. Among them, the polar low temperature environment and wind loads have a significant impact on the strength of polar ship crane structures, and are important issues that must be considered in structural safety design. At present, the design and evaluation of polar ship crane structures often consider the impact of polar environmental temperatures from the perspective of material selection, that is, selecting materials with a ductile-brittle transition temperature lower than the operating environment temperature, but does not consider the impact of temperature stress on the strength of the structure caused by changes in the operating environment temperature. For the wind loads on the crane structure, the design usually considers the wind loads as static loads in accordance with the specifications, ignoring the dynamic force of the wind loads, making the strength analysis results of the structure inaccurate. Summary of the Invention

[0003] In response to the problems existing in the prior art, the present invention discloses a strength analysis process and method for polar ship crane structures under the combined effects of polar temperature loads and wind loads, which specifically includes the following steps:

[0004] Establish a geometric model of the crane structure and perform mesh division on the geometric model;

[0005] Determine the temperature range for polar operations, with the lowest operating temperature being the polar service temperature;

[0006] Set the operating temperature conditions of the crane, use the steady-state thermal analysis method to solve the temperature field of the crane structure, and calculate the temperature field of the crane structure;

[0007] Determine polar calculated wind speed;

[0008] Simulate dynamic wind loads on polar ship crane structures;

[0009] Use modal analysis methods to conduct modal analysis on the crane structure to obtain its natural frequency and vibration mode, thereby determining the weak direction of the crane structure's dynamic stiffness;

[0010] The transient dynamic analysis method is used to set the boundary conditions, import the temperature load, and apply the simulated dynamic wind load, deadweight load, and lifting load to the crane structure. The stress on the crane structure is solved within a defined solution time. The equivalent stress distribution, maximum equivalent stress change curve, and maximum stress position of the polar ship crane structure under the combined action of temperature load and dynamic wind load are obtained. The load safety of the structure is determined based on the structural strength analysis results and material strength.

[0011] Furthermore, the simulation of the dynamic wind loads on the polar ship crane structure includes:

[0012] Determine the center of gravity height of the crane structure model under each working condition and use this location as the target simulation point for wind load;

[0013] The exponential law model is used to calculate the average wind speed at the simulation point height. The calculation formula is as follows:

[0014]

[0015] Where z is any height of the structure; is the average wind speed at height z; r is the reference height; is the average wind speed at the reference height; a is the ground roughness index.

[0016] Calculate the average wind speed at the height of the crane structure's center of gravity based on the average wind speed data at the measuring point height;

[0017] Simulate fluctuating wind speeds and calculate total wind speed and total wind pressure.

[0018] Furthermore, the simulated pulsating wind speed includes:

[0019] Determine the target fluctuating wind speed power spectrum:

[0020] The Davenport wind speed spectrum is selected as the target spectrum, and its expression is as follows:

[0021]

[0022] Where S v (n) is the wind speed spectrum; K is the ground roughness coefficient; is the average wind speed at a height of 10m above the ground; n is the pulsating wind frequency;

[0023] The autoregressive linear filter AR method is used to generate the fluctuating wind speed time history:

[0024] Establish the AR model expression of the fluctuating wind speed time history:

[0025] The AR model of the column vector of the fluctuating wind speed time history at m spatial points is:

[0026]

[0027] Where X, Y, and Z are the column vector matrices of the spatial point coordinates; p is the order of the AR model; Δt is the time step for simulating the fluctuating wind; ψ K is the autoregressive coefficient matrix of the AR model; N(t) is the independent random process vector;

[0028] Solve the autoregressive coefficient ψ based on the relationship between the covariance matrix R and the regression coefficient matrix ψ k :

[0029]

[0030] Where, I is the m-order unit matrix; O p is a zero matrix; the covariance matrix R can be obtained from the power spectrum S v (n) and the covariance are solved in accordance with the Weiner-Schinchin formula, that is:

[0031]

[0032] The autoregressive coefficient ψ can be obtained by formula (4): k and matrix R N .

[0033] Solve the independent random process vector N(t): by the matrix R N Perform Cholesky decomposition and solve N(t):

[0034]

[0035] Where n(t)=[n1(t),L,n m (t)] T , n i (t) is a normal random distribution process with mean 0 and variance 1;

[0036] The autoregressive coefficient matrix ψ K Substituting the independent random process vector N(t) into formula (3) yields the fluctuating wind speed time history.

[0037] Due to the adoption of the above technical solution, the present invention provides a method for analyzing the structural strength of a polar ship crane under the action of temperature load and wind load. Through this method, the equivalent stress distribution, maximum equivalent stress change curve and maximum stress position of the polar ship crane structure under the combined action of temperature load and dynamic wind load can be obtained, thereby determining the load safety of the structure based on the structural strength analysis results and material strength. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments recorded in this application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0039] Figure 1 This is a schematic diagram of the structural strength assessment process of a polar ship crane according to the present invention;

[0040] Figure 2 This is a schematic diagram of format conversion based on ANSYS Mechanical APDL in the present invention;

[0041] Figure 3 This is the time history process of simulating dynamic wind load in polar environment by AR method in the present invention;

[0042] Figure 4 This is a schematic diagram of the time history of wind speed and pressure calculated at 20m / s in an embodiment of the present invention;

[0043] Figure 5 This is the equivalent stress cloud diagram of the crane structure considering temperature load and dynamic wind load in the present invention;

[0044] Figure 6 Schematic diagram of the maximum equivalent stress variation curve of the crane structure in the present invention;

[0045] Figure 7 This is the equivalent stress cloud diagram of the crane structure without considering the polar environmental load in the present invention. DETAILED DESCRIPTION

[0046] To make the technical solutions and advantages of the present invention more clear, the technical solutions in the embodiments of the present invention are clearly and completely described below in conjunction with the accompanying drawings in the embodiments of the present invention:

[0047] like Figure 1 As shown, the present invention proposes a polar crane structural strength analysis method considering the combined effects of temperature load and wind load based on the characteristics of the polar service environment on the polar ship crane structural strength. The method specifically includes the following steps:

[0048] S1: Establishment of crane structure model

[0049] Use 3D modeling software such as Solidworks to build the geometric model of the crane structure. After the model is built, export the crane geometric model in .x_t format.

[0050] S2: Finite element model establishment

[0051] The exported .x_t model was imported into the professional pre-processing software HyperMesh for meshing. For thin-walled structures like ribbed plates, mid-surface processing was performed, resulting in a quadrilateral mesh, which was then assigned thickness. For non-thin-walled structures, hexahedral meshing was performed. After meshing, material properties and element types were defined, assigned to the mesh model, and then exported as a .cdb file.

[0052] HyperMesh and ANSYS Mechanical APDL (classic) can achieve good data transfer, and ANSYS Workbench has a high degree of automation and is easy to operate, so it can be used Figure 2 Steps: Convert the .cdb format file exported from HyperMesh to ANSYS Classic, and then import the converted .cdb file into Workbench for subsequent analysis settings.

[0053] S3: Determine the polar operating temperature range

[0054] During the analysis, the minimum operating temperature was taken as the polar service temperature (PST), which is 10°C below the lowest mean daily low temperature (LMDLT) in the intended operating area for calculation.

[0055] S4: Calculate the temperature field of the structure

[0056] Import the exported .cdb format file into the ANSYS Workbench finite element analysis software, use the steady-state thermal analysis module, set the operating temperature conditions of the crane, perform the solution, and calculate the temperature field of the structure.

[0057] S5: Determine polar calculated wind speed

[0058] According to the "Specifications for Lifting Equipment on Ships and Offshore Installations" (hereinafter referred to as the "Specifications"), the calculated wind speed for a crane in operation should be 20m / s, and the calculated wind speed for a crane in a stationary state should be 55m / s. If higher wind speeds are expected, the higher wind speed should be used. Therefore, the calculated wind speed for a crane in a stationary state is based on the polar meteorological data recorded over the past ten years, with the average annual maximum wind speed as a comparison value to determine the calculated wind speed for subsequent wind load simulation.

[0059] S6: Numerical simulation of wind loads

[0060] Wind load, also known as wind dynamic pressure, can be considered as the superposition of average wind with static effects and pulsating wind with dynamic effects. The steps to simulate the dynamic wind load on polar ship crane structures are as follows:

[0061] S61: Determine wind speed simulation point

[0062] Determine the center of gravity height position of the crane structure model under each working condition as the target simulation point of the wind load.

[0063] S62: Average wind speed calculation

[0064] The exponential law model is used to calculate the average wind speed at the simulation point height. The calculation formula is as follows:

[0065]

[0066] Where z is any height of the structure; is the average wind speed at height z; r is the reference height; is the average wind speed at the reference height; a is the ground roughness index.

[0067] Based on the average wind speed data at the measuring point height, the average wind speed at the height of the crane structure's center of gravity can be calculated.

[0068] S63: Fluctuating wind speed simulation

[0069] Determine the target fluctuating wind speed power spectrum

[0070] The Davenport wind speed spectrum is selected as the target spectrum, and its expression is as follows:

[0071]

[0072] Where S v (n) is the wind speed spectrum; K is the ground roughness coefficient; is the average wind speed at a height of 10m above the ground; n is the pulsating wind frequency.

[0073] The autoregressive linear filter AR method is used to generate the fluctuating wind speed time history. The calculation process is as follows: Figure 3 The specific calculation process is as follows:

[0074] Establish the AR model expression of the fluctuating wind speed time history:

[0075] The AR model of the column vector of the fluctuating wind speed time history at m spatial points is:

[0076]

[0077] Where X, Y, and Z are the column vector matrices of the spatial point coordinates; p is the order of the AR model; Δt is the time step for simulating the fluctuating wind; ψ K is the autoregressive coefficient matrix of the AR model; N(t) is the independent random process vector.

[0078] Solve for the autoregressive coefficient ψ k :

[0079] According to the relationship between the covariance matrix R and the regression coefficient matrix ψ:

[0080]

[0081] Where, I is the m-order unit matrix; O p is a zero matrix; the covariance matrix R can be obtained from the power spectrum S v (n) and the covariance are solved in accordance with the Weiner-Schinchin formula, that is:

[0082]

[0083] The autoregressive coefficient ψ can be obtained by formula (4): k and matrix R N .

[0084] Solve for the independent random process vector N(t):

[0085] By the matrix R N Perform Cholesky decomposition and solve N(t):

[0086]

[0087] Where n(t)=[n1(t),L,n m (t)] T , n i (t) is a normal random distribution process with mean 0 and variance 1.

[0088] The autoregressive coefficient matrix ψ K Substituting the independent random process vector N(t) into formula (3) yields the fluctuating wind speed time history.

[0089] Calculate total wind speed

[0090] The average wind speed and the fluctuating wind speed are superimposed to obtain the total wind speed time history:

[0091]

[0092] Calculate total wind pressure

[0093] Substituting the total wind speed time series into the wind pressure calculation formula in the Code, we can obtain the total wind pressure time series:

[0094] q=0.613v t 2 (8)

[0095] S7: Crane structure modal analysis

[0096] The modal analysis module in ANSYS Workbench was used to perform modal analysis on the crane structure to obtain its natural frequency and vibration mode, thereby determining the weak direction of the crane structure's dynamic stiffness, which served as the loading direction of the wind load in subsequent analysis.

[0097] S8: Structural strength analysis considering the combined effects of polar temperature loads and wind loads

[0098] Using the transient dynamics analysis module in ANSYS Workbench, we set boundary conditions, imported temperature loads, applied simulated dynamic wind loads, deadweight loads, and lifting loads, defined a solution time, and performed the solution. This yielded the equivalent stress distribution, maximum equivalent stress curve, and maximum stress location for the polar ship crane structure under the combined effects of temperature and dynamic wind loads. Based on the structural strength analysis results and material strength, the load safety of the structure was determined.

[0099] Example:

[0100] The above analysis method is used to evaluate the structural strength of a polar ship crane under the combined action of temperature load and dynamic wind load, and the results are compared with the analysis results without considering the polar environmental load.

[0101] The main performance parameters of the polar ship crane are shown in Table 1. Four operating conditions of the crane were analyzed. Conditions 2 and 4 represent the crane's two extreme operating conditions. The operating condition parameters are shown in Table 2.

[0102] Table 1 Main performance parameters of crane

[0103]

[0104] Table 2 Crane operating parameters

[0105]

[0106] A three-dimensional model of the crane structure was established, and HyperMesh was used for meshing. Thin-walled structures such as the base, tower body, main boom, and auxiliary boom were divided into quadrilateral shell meshes, while the slewing mechanism, shaft, and luffing cylinder were divided into hexahedral meshes. The model was divided into a total of 493,318 nodes and 390,828 units, with an average mesh size of approximately 50 mm.

[0107] Define materials and elements, assign a mesh model, and export a .cdb file. Import the converted .cdb file into ANSYS Workbench for steady-state thermal analysis. Given an initial temperature of 0°C for the crane structure and an ambient temperature of -30°C, perform the solution.

[0108] The crane is in working condition, given a calculated wind speed of 20m / s, the wind pressure time history (simulation time is 200s) when the calculated wind speed is 20m / s is obtained by simulating the Matlab program written based on the AR method. Figure 4 shown.

[0109] A modal analysis was performed on the crane structure. The modal analysis results for Condition 2 are shown in Table 3. It can be seen that the crane structure has the worst dynamic stiffness in the Z direction. Therefore, in the next step of the analysis, the wind load was applied to the windward surface of the crane structure in the Z direction.

[0110] Table 3 Modal analysis results of working condition 2

[0111]

[0112] Using the transient dynamics analysis module, we defined the boundary conditions as a fixed base, introduced temperature loads, and applied the simulated wind loads to the windward Z-direction surface of the crane structure. We also applied deadweight and hoisting loads, and set the analysis time to 20 seconds. Table 4 compares the crane structure's strength before and after considering polar environmental loads for each operating condition. The stresses in the crane structure after considering environmental loads are the stress analysis results after the wind loads stabilized.

[0113] Table 4 Comparison of crane structure strength before and after polar environmental loads

[0114]

[0115] Take crane working condition 2 as an example to explain in detail. The stress analysis results are as follows: Figure 5 As shown in the figure, the maximum equivalent stress variation curve of the structure is as follows: Figure 6 As shown in the figure, the pulsating stress is the maximum equivalent stress change curve under the action of dynamic wind load, and the static load stress is the stress result calculated by using the wind pressure calculation formula in the "Code" to calculate the wind pressure and then considering the wind load with static load. Figure 7 This is the equivalent stress cloud diagram of the crane structure when the polar environmental load is not considered. From the comparative analysis of the results, it can be seen that after considering the combined effect of polar temperature load and wind load, the structure will be subjected to the strong impact of wind load in the first few seconds, and then tend to stabilize. The instantaneous impact of wind load causes a large stress in the crane structure, and the maximum equivalent stress increases by 60.7% compared with the case when the polar environmental load is not considered. From the analysis results, the wind-induced vibration effect and vibration time of the crane structure can also be seen. At the same time, the equivalent stress distribution of the structure, the change pattern of the maximum equivalent stress with time, and the location of the maximum equivalent stress can be obtained. By considering the effect of polar environmental load through this method, the strength assessment results of polar ship crane structures are more in line with the actual situation of the polar operating environment, providing a basis for the safety design and assessment of polar ship crane structures.

[0116] The above description is only a preferred specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any technician familiar with the technical field, within the technical scope disclosed by the present invention, who makes equivalent replacements or changes based on the technical solution and inventive concept of the present invention, should be covered by the scope of protection of the present invention.

Claims

1. A method for analyzing the structural strength of a polar ship crane, characterized in that include: Establish a geometric model of the crane structure and perform mesh division on the geometric model; Determine the temperature range for polar operations, with the lowest operating temperature being the polar service temperature; Set the operating temperature conditions of the crane, use the steady-state thermal analysis method to solve the temperature field of the crane structure, and calculate the temperature field of the crane structure; Determine polar calculated wind speed; Simulate dynamic wind loads on polar ship crane structures; Use modal analysis methods to conduct modal analysis on the crane structure to obtain its natural frequency and vibration mode, thereby determining the weak direction of the crane structure's dynamic stiffness; The transient dynamics analysis method was used to set boundary conditions, import temperature loads, and apply simulated dynamic wind loads, deadweight loads, and lifting loads to the crane structure. The stresses acting on the crane structure were solved over a defined solution time. The equivalent stress distribution, maximum equivalent stress variation curve, and maximum stress location of the polar ship crane structure were obtained under the combined effects of temperature and dynamic wind loads. The load safety of the structure was determined based on the structural strength analysis results and material strength. Determine the center of gravity height of the crane structure model under each working condition and use this location as the target simulation point for wind load; The exponential law model is used to calculate the average wind speed at the simulation point height. The calculation formula is as follows: Where, Any height of the structure; For height Average wind speed at the location; is the reference height; is the average wind speed at the reference height; is the surface roughness index; Calculate the average wind speed at the height of the crane structure's center of gravity based on the average wind speed data at the measuring point height; Simulate fluctuating wind speeds and calculate total wind speed and total wind pressure.

2. The method according to claim 1, wherein: Simulated fluctuating wind speed includes: Determine the target fluctuating wind speed power spectrum: The Davenport wind speed spectrum is selected as the target spectrum, and its expression is as follows: Where, is the wind speed spectrum; is the surface roughness coefficient; is the average wind speed at a height of 10m above the ground; is the pulsating wind frequency; The autoregressive linear filter AR method is used to generate the fluctuating wind speed time history: Establish the AR model expression of the fluctuating wind speed time history: The AR model of the column vector of the fluctuating wind speed time history at m spatial points is: （3） Where X, Y, and Z are column vector matrices of spatial point coordinates; p is the order of the AR model; is the time step for simulating fluctuating wind; is the autoregressive coefficient matrix of the AR model; is an independent random process vector; According to the covariance matrix R and the regression coefficient matrix Solving the relationship between autoregressive coefficients : （4） Where I is the m-order unit matrix; is a zero matrix; the covariance matrix R can be obtained from the power spectrum The covariance is solved according to the Weiner-Schinchin formula, that is: The autoregressive coefficient can be obtained by formula (4): and matrix ; Solving for independent random process vectors :By the matrix Perform Cholesky decomposition and solve : Where, , is a normal random distribution process with mean 0 and variance 1; The autoregressive coefficient matrix obtained by solving With independent random process vector Substituting into formula (3) we can obtain the pulsating wind speed time history.

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