A Welding Method for a Floating Photovoltaic Structure

Abstract

The present invention discloses a welding method for a floating photovoltaic structure, comprising the following steps: S1. Based on the physical properties of the structure to be welded, a complete thermo-mechanical coupling model of the welding process is established to simulate the stress field generated during the welding process of the structure to be welded; boundary conditions are set, and the bending stress and strain generated during the welding process of the structure to be welded are calculated; S2. Position the structure to be welded; S3. Apply prestress to the structure to be welded to resist welding deformation; S4. Weld each longitudinal girder to the structure to be welded one by one. The present invention can be used to control the minimum welding residual stress, can effectively prevent the deformation generated during the welding process of the floating photovoltaic structure, and reduces the workload of straightening during the sectional construction process. And the present invention achieves the purpose of reducing the construction cost and improving the construction efficiency by reducing the forced / water-fire straightening operation during the welding process.

Description

Technical Field

[0001] The present invention relates to the technical field of welding methods, and particularly to a welding method for a floating photovoltaic structure. Background Art

[0002] A floating photovoltaic structure refers to a sheet steel structure that forms a segment of a floating photovoltaic platform. This structure is an integral part of the hull and will float on the sea surface as part of the floating photovoltaic platform. In the manufacturing of offshore engineering platforms and floating photovoltaic structures, controlling the minimum welding residual deformation is one of the main technical problems to be solved in this process. As is well known, the more the number of welded joints in a metal structure, the greater the welding residual deformation, and the more difficult the problem is to solve.

[0003] In order to eliminate the welding deformation of the structure, the methods of using strong force or fire and water straightening have been used in the past to control the structural deformation. However, these methods are all post-treatment methods. Repeated external forces and heat input not only increase the investment in additional manpower, material resources, and construction costs, but also cannot guarantee that the subsequent processes will release the residual stress inside the structure, and cause unpredictable cumulative deformation during or after the hull erection process.

[0004] For example, there are the following two ways of assembling and welding the longitudinal stiffeners on one side of the surface of a large-area steel plate:

[0005] 1) In the free state, the steel plate is placed on a flat jig, and the longitudinal stiffeners are successively tack-welded on the surface of the steel plate, and then double-sided fillet welding is carried out along the direction of the longitudinal stiffeners, as Figure 1 shown;

[0006] 2) In the free state, the steel plate is placed on a curved jig, and the longitudinal stiffeners are successively tack-welded on the surface of the steel plate, and then double-sided fillet welding is carried out along the direction of the longitudinal stiffeners, as Figure 3 shown.

[0007] In the above two ways, as Figure 2 and Figure 4 shown, when welding in the free state, the welding will be affected by the heat input and produce angular deformation and shrinkage deformation. Summary of the Invention

[0008] Therefore, the technical problem to be solved by the present invention is to overcome the problem of controlling the minimum welding residual deformation during the installation and welding of the longitudinal stiffeners in the segmented construction process of the floating photovoltaic structure, so as to provide a welding method for the floating photovoltaic structure to prevent the deformation generated during the welding process.

[0009] To achieve the above object, the technical solution adopted by the present invention is:

[0010] A welding method for a floating photovoltaic structure, comprising the following steps:

[0011] S1. Based on the physical properties of the structure to be welded, establish a fully thermo-mechanical coupling model for the welding process, simulate the stress field generated during the welding process of the structure to be welded; set boundary conditions, and calculate the bending stress and strain generated during the welding process of the structure to be welded;

[0012] S2. Position the structure to be welded;

[0013] S3. Apply prestress to the structure to be welded to resist welding deformation;

[0014] S4. Weld each longitudinal girder to the structure to be welded one by one.

[0015] Further optimize the technical solution. The specific steps of step S1 include the following steps:

[0016] S11. Establish a geometric model of the welded joint;

[0017] S12. Conduct finite element mesh division;

[0018] S13. Establish a heat source model and define the properties of welding materials;

[0019] S14. Set boundary conditions and complete the finite element calculation of the welded joint;

[0020] S15. Extract the average eigenstrain value of all nodes at the weld, and then use the elastic analytical method to predict the welding deformation of the entire structure to be welded;

[0021] Set the weld width according to the welding process parameters, and perform a primary elastic calculation on the welds in sequence according to the preset welding sequence; solve the overall deformation result according to the weld shrinkage amount generated by the eigenstrain.

[0022] Further optimize the technical solution. In step S12, according to the heat conduction analysis results, densify the mesh in the weld and the heat affected zone; coarsen the mesh for the remaining part;

[0023] Select tetrahedron or hexahedron elements for the mesh type.

[0024] Further optimize the technical solution. In step S13, defining the properties of welding materials means defining the temperature-dependent welding material properties of each part of the structure to be welded, and defining the high-temperature properties of the weld;

[0025] Through the analysis of the welding material and the heat source model, customize the welding material properties according to the mechanical properties and phase composition of the corresponding welding material.

[0026] Further optimize the technical solution. The boundary conditions set in step S14 are:

[0027] The angular deformation and the eigenstrain amount of transverse shrinkage generated at the welding part are considered to be evenly distributed along the welding line.

[0028] Further optimize the technical solution, and in step S2, a jig under the structure to be welded is used to restrict the six degrees of freedom of the structure to be welded.

[0029] Further optimize the technical solution, and in step S3, a jacking device with an adjustable shape is used to adjust the amount of reverse deformation of the pre-deformation of the welding position of the structure to be welded, so that the deformation generated by welding is offset by the applied reverse deformation.

[0030] Further optimize the technical solution, and in step S3, a longitudinal girder positioning and clamping device is used to adjust the shape and position accuracy of each longitudinal girder relative to the structure to be welded, and a prestress against welding deformation is applied at the welding position.

[0031] Further optimize the technical solution, and step S3 includes the following steps:

[0032] S31. The stress-strain state of the elastic bending of the structure to be welded is theoretically calculated by using finite element analysis software, and various load schemes are used for simulation;

[0033] S32. The correctness of the theoretical data in step S31 and the stress-strain state of the structure to be welded are tested through experiments; the temperature rise curve, stress-strain curve and deformation amount of key points are extracted and compared with the test results or empirical formulas to verify the accuracy of the finite element model.

[0034] Further optimize the technical solution, and step S31 specifically includes the following steps:

[0035] Determine the load and calculate the magnitude of the binding force required for the elastic bending of the structure to be welded;

[0036] Determine the necessary stiffness and strength values of the main components of the jig;

[0037] Determine the optimal boundary conditions;

[0038] Use finite element analysis software to calculate the stress-strain state of the elastic bending of the structure to be welded;

[0039] Combined with the size of the structure to be welded, each load scheme and environmental factors, set the boundary conditions as follows: the structure to be welded under elastic bending is in a horizontal position; the external bending force is evenly distributed along the two longitudinal edges of the structure to be welded, or is distributed along parallel lines at a given distance along the main support; the gravity or the total weight of the structure to be welded is evenly distributed as a load over the entire area; use the theoretical value of the welding heat input as the basis for finite element calculation, and use the simulated temperature result as the thermal load for loading;

[0040] Specify the maximum bending transverse stress value of each load scheme;

[0041] Using the above boundary conditions, the calculation data of the vertical force required for the elastic bending of the structure to be welded, as well as the obtained transverse bending stress and the maximum deflection of the plate, are obtained.

[0042] Further optimizing the technical solution, step S3 further includes the following steps:

[0043] Optimization analysis: On the basis of passing the verification, optimize the welding process parameters to find a welding plan with relatively small stress value and relatively good uniformity.

[0044] Further optimizing the technical solution, step S3 further includes the following steps:

[0045] Provide an analysis report: Summarize the stress and strain analysis results and predict the welding quality and service performance.

[0046] Further optimizing the technical solution, step S4 is to use a double-sided automatic welding device to weld each longitudinal girder to the structure to be welded one by one.

[0047] The technical solution of the present invention has the following advantages:

[0048] 1. A welding method for a floating photovoltaic structure provided by the present invention is mainly used for the assembly and welding process of longitudinal girders on one side of the surface of a large-area steel plate during the manufacture of offshore oil platforms and ship hull sections. After predicting the bending stress and strain generated during the welding process of the structure to be welded, a reverse acting force is applied to the structure to be welded to offset the residual stress generated by welding, effectively controlling the welding residual stress, being able to control the minimum welding residual stress, and thus being able to effectively prevent the deformation generated during the welding process of the floating photovoltaic structure, reducing the workload of straightening during the sectional construction process.

[0049] And the present invention reduces the strong force / fire and water straightening operations during the welding process to achieve the purpose of reducing the construction cost and improving the construction efficiency.

[0050] 2. A welding method for a floating photovoltaic structure provided by the present invention, compared with traditional welding technologies, has high welding efficiency, and the welding deformation is well controlled, improving the welding quality of the hull structure, saving costs, and improving efficiency during the production practice process. BRIEF DESCRIPTION OF THE DRAWINGS

[0051] In order to more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the following will briefly introduce the drawings required for the description of the specific embodiments or the prior art. Obviously, the drawings in the following description are some embodiments of the present invention. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative efforts.

[0052] Figure 1Schematic diagram of a traditional flat jig

[0053] Figure 2 Schematic diagram of longitudinal girder installation and post-welding deformation of a traditional flat jig

[0054] Figure 3 Schematic diagram of a traditional curved jig

[0055] Figure 4 Schematic diagram of longitudinal girder installation and post-welding deformation of a traditional curved jig

[0056] Figure 5 Schematic diagram of the adjustable jig of the present invention

[0057] Figure 6 Schematic diagram of longitudinal girder installation and post-welding deformation of the adjustable jig of the present invention

[0058] Figure 7 Schematic diagram of the strong jacking and longitudinal girder positioning and clamping device of the adjustable jig of the present invention

[0059] Figure 8 Schematic diagram of the double-sided automatic welding device of the present invention

[0060] Figure 9 Simplified T-joint model of the present invention

[0061] Figure 10 Schematic diagram of the double-ellipsoid distribution area of the present invention

[0062] Figure 11 Table of the forces, maximum deflections (w max ) and maximum transverse bending stresses (s max ) of Scheme A of the present invention

[0063] Figure 12 Table of the forces, maximum deflections (w max ) and maximum transverse bending stresses (s max ) of Scheme B of the present invention

[0064] Figure 13 Table of the forces, maximum deflections (w max ) and maximum transverse bending stresses (s max ) of Scheme C of the present invention

[0065] Figure 14 Schematic diagram of the vertical displacement distribution during the bending of a thin plate under the maximum transverse bending stress s max = 300 MPa in Scheme A of the present invention

[0066] Figure 15 Schematic diagram of the vertical displacement distribution during the bending of a thin plate under the maximum transverse bending stress s maxSchematic diagram of the deflection of the central section during the bending of a thin plate under 300 MPa

[0067] Figure 16 This is the maximum transverse bending stress s in Solution A of the present invention max Schematic diagram of the transverse stress distribution of the plate during the bending of a thin plate under 300 MPa;

[0068] Figure 17 This is the maximum transverse bending stress s in Solution B of the present invention max Schematic diagram of the vertical displacement distribution during the bending of a thin plate under 300 MPa;

[0069] Figure 18 This is the maximum transverse bending stress s in Solution B of the present invention max Schematic diagram of the deflection of the central section during the bending of a thin plate under 300 MPa;

[0070] Figure 19 This is the maximum transverse bending stress s in Solution B of the present invention max Schematic diagram of the transverse stress distribution of the plate during the bending of a thin plate under 300 MPa;

[0071] Figure 20 This is the maximum transverse bending stress s in Solution C of the present invention max Schematic diagram of the vertical displacement distribution during the bending of a thin plate under 300 MPa;

[0072] Figure 21 This is the maximum transverse bending stress s in Solution C of the present invention max Schematic diagram of the deflection of the central section during the bending of a thin plate under 300 MPa;

[0073] Figure 22 This is the maximum transverse bending stress s in Solution C of the present invention max Schematic diagram of the transverse stress distribution of the plate during the bending of a thin plate under 300 MPa;

[0074] Figure 23 Distribution diagram (top view) of the welding residual deformation of the present invention under different conditions;

[0075] Figure 24 Schematic diagram of the structure of the present invention when three bulb flats are evenly arranged and welded on an A36 steel plate;

[0076] Figure 25 This is the present invention Figure 24 Partial enlarged view;

[0077] Figure 26 Force analysis diagram of the plate of the present invention under the action of Load Scheme A;

[0078] Figure 27Force analysis diagram of the plate of the present invention under the action of load scheme B;

[0079] Figure 28 Force analysis diagram of the plate of the present invention under the action of load scheme C;

[0080] Figure 29 Flow chart of the present invention.

[0081] Reference numerals:

[0082] 1. Pre-bent steel plate; 2. Longitudinal girder; 3. Adjustable jig; 4. Positioning device; 5. Clamping device; 6. Working reference plane; 7. Double-sided welding trolley. Detailed implementation manners

[0083] Next, the technical solution of the present invention will be clearly and completely described in conjunction with the accompanying drawings. Obviously, the described embodiments are part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0084] In addition, the technical features involved in different implementation manners of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0085] In order to obtain the optimal overall efficiency of hull structure construction and reduce product costs. It is necessary to consider methods for reducing external forces and heat input throughout the process of structure construction. Therefore, the present invention discloses a welding method for a floating photovoltaic structure, as Figure 29 shown, including the following steps:

[0086] S1. Based on the physical characteristics of the structure to be welded, establish a complete thermo-mechanical coupling model for the welding process, and simulate the stress field generated during the welding process of the structure to be welded. Predict the stress and strain generated in the structure to be welded, and make preparations in advance for eliminating and reducing stress and strain in the later stage.

[0087] Set boundary conditions and calculate the bending stress and strain generated during the welding process of the structure to be welded.

[0088] Step S1 specifically includes the following steps:

[0089] S11. Establish a geometric model of the welded joint. In step S11, the geometric model of the welded joint is an accurate three-dimensional model established according to the dimensions of the welded parts and the characteristics of the weld, including the base metal, weld, and heat affected zone.

[0090] The floating photovoltaic structure is composed of a bottom plate and longitudinal girders. The welds are divided into three major types according to different groove forms: TY type, TK type, and T type without groove opening. In this embodiment, the weld is simplified to the T type without groove opening form (T joint model) according to common practices, asFigure 9 as shown

[0091] S12. Perform finite element mesh generation. According to the results of heat conduction analysis, densify the mesh in the weld and heat affected zone; coarsen the mesh for the remaining part. Select tetrahedron or hexahedron elements as the mesh type.

[0092] In this embodiment, two-dimensional shell element meshes are used, and three-dimensional solid meshes are used for local T-joints, and their thickness is the same as that of the longitudinal web thickness, as Figure 9 shown

[0093] S13. Define the properties of welding materials: Define the temperature-dependent welding material properties (such as density, thermal conductivity, elastic modulus, and thermal expansion coefficient, etc.) of each part of the structure to be welded, and define the high-temperature properties of the weld.

[0094] The welding thermal process depends on the distribution form of the external heat source, the thermophysical properties of the material, and the heat dissipation of the material to the surroundings. Among them, the distribution of the heat source model has a great influence on the distribution of the stress and strain fields during the welding process. The MAG welding method uses a 3D double-ellipsoid heat source physical model, and the heat source model is as Figure 10 shown. The volumetric heat source acting on the welding is divided into two parts, the front and the back. The front and back arc heat fluxes are asymmetrically distributed. Therefore, the heat flux distribution in the front and back semi-ellipsoids is as follows:

[0095] (1) The front semi-ellipsoid is:

[0096]

[0097] (2) The back semi-ellipsoid is:

[0098]

[0099] In the formula: η is the welding thermal efficiency; U is the welding voltage; I is the welding current; f f 、f r are the heat input shares of the front and back semi-ellipsoids; a f 、a r 、b, and c are the heat source distribution parameters of the double-ellipsoid body respectively.

[0100] Through the analysis of welding materials and heat source models, customize the welding material properties according to the mechanical properties and phase composition of the corresponding materials.

[0101] Preset the melting length, melting depth, and melting width of the molten pool according to the physical model of the double-ellipsoid heat source, clamp the T-joint according to the actual situation, and then perform a thermo-elastoplastic finite element extreme on the local T-joint to extract the inherent strain.

[0102] S14. Set boundary conditions and complete the finite element calculation of the welded joint. The inherent deformations such as angular deformation and transverse shrinkage generated at the welding part are mainly determined by the material, plate thickness, welding heat input, etc. of the welded joint, and such inherent deformation amounts are considered to be evenly distributed along the welding line. Complete the finite element calculation of the T-joint according to the above boundary conditions.

[0103] Indirectly apply the inherent strain value through the coefficient of linear expansion in the material database. According to the following formula ε t =α*ΔT, given the temperature change difference, changing the coefficient of linear expansion changes the strain value. In the formula, ε t is the strain value; α is the coefficient of linear expansion; ΔT is the welding temperature difference.

[0104] S15. Extract the average inherent strain value of all nodes at the weld, and then use the elastic analytical method to predict the welding deformation of the entire structure to be welded.

[0105] Set the weld width according to the welding process parameters, and perform a single elastic calculation on the weld in sequence according to the preset welding sequence. Solve the overall deformation result according to the weld shrinkage amount generated by the inherent strain.

[0106] S2. Position the structure to be welded. Step S2 is to restrict the six degrees of freedom of the structure to be welded by the jig under the structure to be welded.

[0107] S3. Apply prestress to resist welding deformation to the structure to be welded, that is, after obtaining the deformation shrinkage amount, perform anti-deformation treatment. Step S3 includes the following steps:

[0108] Step S3 is to use the powerful jacking device with adjustable shape (adjustable jig 3) to adjust the anti-deformation amount of pre-deformation of the longitudinal ribs of the structure to be welded, and use the adjustable jig to apply reverse deformation under the same deformation amount to the steel plate in advance. After welding is completed, the deformation generated by welding is offset by the reverse deformation, and the deformation of the steel plate caused by welding can be eliminated or reduced.

[0109] Step S3 is to use the longitudinal rib positioning and clamping device to adjust the shape and position accuracy of each longitudinal rib relative to the structure to be welded, and apply prestress to resist welding deformation at the position to be welded.

[0110] Step S31 specifically includes the following steps:

[0111] Determine the load and calculate the magnitude of the binding force required for the elastic bending of the structure to be welded;

[0112] Determine the necessary stiffness and strength values of the main components of the tooling jig;

[0113] Determine the optimal boundary conditions;

[0114] Use finite element analysis software to calculate the stress-strain state of the elastic bending of the structure to be welded;

[0115] Combined with the dimensions of the structure to be welded, each load scheme and environmental factors, the boundary conditions are set as follows: The structure to be welded under elastic bending is in a horizontal position; The external bending force is evenly distributed along the two longitudinal edges of the structure to be welded, or distributed along parallel lines at a given distance along the main support; Gravity or the total weight of the structure to be welded is evenly distributed as a load over the entire area; The theoretical value of the welding heat input is used as the basis for finite element calculation, and the simulated temperature results are loaded as thermal loads.

[0116] When loading: Apply the temperature field and heat conduction analysis results as the initial temperature conditions, and consider the arc or gas protection during the welding process. Perform transient thermal analysis to obtain the temperature rise curve and temperature field. Use the temperature results of the above steps as thermal loads, and combine the mechanical properties of the weld and base metal at high temperatures to perform transient structural analysis to obtain the stress and deformation results during the welding process.

[0117] Specify the maximum bending transverse stress value for each load scheme.

[0118] Using the above boundary conditions, obtain the calculation data of the vertical force required for the elastic bending of the structure to be welded, as well as the obtained transverse bending stress and the maximum deflection of the plate.

[0119] S4. Weld each longitudinal girder to the structure to be welded one by one. As Figure 8 shown, in step S4, a double-sided automatic welding device (i.e., the double-sided welding trolley 7) is used to precisely control the heat input to complete the double-sided fillet welding of each longitudinal girder and the steel plate to be welded.

[0120] The double-sided welding trolley 7 is a common product on the market and is used to automatically weld the fillet welds of two metal materials. The driving method is motor drive, and the internal motor drives the movement of the sprocket, chain, helical gear and rubber wheel. The rubber wheel is horizontally placed on the steel plate, and the rotation of the rubber wheel is converted into the translational movement of the welding trolley, thereby generating a linear movement of the welding torch relative to the weld. When the welding power supply is turned on, the welding torch starts to work, thus completing the relevant welding operations.

[0121] As Figure 7 shown, the adjustable support frame 3 is supported and arranged below the pre-bent steel plate 1 and above the working reference plane 6. The height of the adjustable support frame 3 is adjustable, and the longitudinal girder 2 is welded and positioned above the pre-bent steel plate 1. Both sides of the pre-bent steel plate 1 are respectively arranged on the positioning device 4 and clamped and positioned by the clamping device 5. As Figure 6 shown, after being processed by the present invention, the pre-bent steel plate 1 is in a flat state after welding.

[0122] The structural schematic diagram of the adjustable support frame 3 is as Figure 5 shown, and the reverse deformation is applied to the steel plate by using the adjustable support frame 3. The structural schematic diagram of the steel plate after welding the longitudinal girder is as Figure 6As shown, the state of the steel plate after welding is flat, and the welding deformation is thus controlled.

[0123] In the above-mentioned welding method for a floating photovoltaic structure, after predicting the bending stress and strain generated during the welding process of the structure to be welded, a reverse acting force is applied to the structure to be welded to offset the residual stress generated by welding, effectively controlling the welding residual stress, capable of controlling the minimum welding residual stress, and thus effectively preventing the deformation generated during the welding process of the floating photovoltaic structure, eliminating problems such as welding residual deformation of large sheet structures, and reducing the workload of straightening during the sectional construction process.

[0124] Compared with traditional welding techniques, the welding method of the present invention has high welding efficiency, and the welding deformation is well controlled, improving the welding quality of the hull structure, saving costs, and increasing efficiency during the production practice process.

[0125] Example 1

[0126] In this example, the technical solution is described by taking an A36 steel plate with dimensions of 2000mm×1800mm×6mm as an example.

[0127] As Figure 24 and Figure 25 shown, when welding three bulb flats with a height of 120mm and a web thickness of 7mm uniformly arranged (spacing 600mm) on an A36 steel plate with dimensions of 2000mm×1800mm×6mm, a device for manual pressing by workers is designed, and at the same time, the method of the present invention is used to achieve the effect of controlling welding deformation.

[0128] The theoretical calculation has the following steps:

[0129] 1. Determine the load and calculate the magnitude of the binding force required for the elastic bending of the welded plate.

[0130] 2. Determine the necessary stiffness and strength values of the main components (beams) of the tooling jig.

[0131] 3. Determine the optimal boundary conditions (the position of the support for fixing the edge of the steel plate before and during the welding process).

[0132] 4. Use ANSYS to calculate the stress-strain state of the elastic bending of the large sheet, and compare using the following three load schemes:

[0133] 4.1 Load scheme A

[0134] As Figure 26As shown, three longitudinal supports with different heights are used. Support No. 1 corresponds to P1, Support No. 2 corresponds to P2, and Support No. 3 corresponds to P3 (hereinafter referred to as Support 1, Support 2, and Support 3 respectively). The plates on these supports are bent and deformed by two external forces or bending forces (Q1 and Q2), which are evenly distributed along their longitudinal edges. The plates are subjected to transverse bending. In the area of each of the three welded bulb flats (i.e., the three support areas), the condition that the maximum bending transverse stress (σ max ) of the steel plate surface is equal must be provided. The height of each support can also be adjusted.

[0135] 4.2 Load Scheme B

[0136] As Figure 27 shown, the plate is only located on the middle support 2, below the bulb flat area. The external vertical loads or bending forces (Q1 and Q2) of the plate act on the longitudinal edges of the plate, similar to the case of Load Scheme A.

[0137] Therefore, the value of the total transverse bending of the plate is determined by changing the height of the central support.

[0138] In this load scheme, the maximum bending transverse stress (σ max ) in the plate is only in the area of Support 2. The required bending load has the maximum M w value (1000 mm), and obviously the required vertical pressing load is the smallest.

[0139] 4.3 Load Scheme С

[0140] As Figure 28 shown, in Scheme C, there is local transverse bending of the plate. Only one middle support 2 (in the middle of the plate) is used. The bending forces (Q1 and Q2) of the plate are located at a distance of 400 mm from the center on both sides of the No. 2 bulb flat. Local pre-elastic deformation of the plate is formed in the area of the welded bulb flat here. The selection of this distance is related to the size of the spacing or the distance between the welded bulb flats (known condition: the spacing between bulb flats is 600 mm). In order to make the welding process controllable, the free passage of the welding trolley must be considered. A compact welding trolley is selected in this embodiment. Since its maximum width is 165 mm, the spacing from the adjacent unwelded bulb flats on both sides can reach 100 - 125 mm, so its welding passability is better.

[0141] To sum up, considering the sample size (2000x1800x6 mm), each load scheme and environmental factors, the boundary conditions are set as follows:

[0142] - The plate subjected to elastic bending is in a horizontal position;

[0143] - The external bending forces (Q1 and Q2) are uniformly distributed along the two longitudinal edges of the plate, or are distributed along parallel lines at a given distance along the main support 2;

[0144] - For loading scenario A, the plate is located below three welded bulb flats, and supports 1, 2, and 3 exert forces on these three welded bulb flat plates. The weights of the plate are designated as P1, P2, and P3;

[0145] - For loading scenarios B or C, only one central support No. 2 is used, and its action on the bending force on the plate and the weight of the plate are designated as P2;

[0146] - The values of the external bending forces (Q1 and Q2) on the plate are determined by the condition that the maximum bending transverse stress (σ max ) reaches the specified level on the surface of the plate within the area of any welded bulb flat (loading scenarios B and C) or all three longitudinal bulb flats (loading scenario A);

[0147] - Gravity or the total weight of the steel plate (169 kg in this embodiment) is evenly distributed as a load over the entire area.

[0148] - The theoretical value of the welding heat input is used as the basis for finite element calculation to simulate the temperature results as thermal load loading. (The parameter range of the general welding heat input Q N : welding current, 140 - 160 A; arc voltage, 24.1 - 24.3 V; welding speed 8.3 mm / s; welding wire GFL - 71, φ1 mm; weld leg 4.0 - 4.5 mm).

[0149] Finally, when any one of the above three loading scenarios is used, the maximum bending moment and the corresponding maximum transverse stress (σ max ) on the plate surface are achieved in the support area (the position of the welded bulb flat). In this case, pre - elastic bending of the plate with the minimum external force (Q1 and Q2) will have the greatest effect to reduce the residual angular deformation of the plate caused by welding with the bulb flat.

[0150] Specify the values of the maximum bending transverse stress (σ max ) for the three scenarios, namely:

[0151] 1) 300 MPa (close to the yield strength or σ0.2 of low - carbon steel A36);

[0152] 2) 180 MPa (or 60% of σ0.2); 3) 105 MPa (35% of σ0.2).

[0153] Using the above - mentioned boundary conditions, the calculation data of the vertical force required for elastic bending of the large steel plate (2000x1800x6 mm) can be obtained, as well as the resulting transverse bending stress and the maximum deflection of the plate. The data are asFigure 11 , Figure 12 and Figure 13 as shown.

[0154] The stress-strain results simulated by the three schemes are as shown in Figures 14 to 22 as shown. Among them, Figures 14 to 16 are successively the schematic diagram of the vertical displacement distribution in the thin plate bending case, the schematic diagram of the deflection of the central section, and the schematic diagram of the transverse stress distribution of the plate under the maximum transverse bending stress s max = 300 MPa in Scheme A. Figures 17 to 19 are successively the schematic diagram of the vertical displacement distribution in the thin plate bending case, the schematic diagram of the deflection of the central section, and the schematic diagram of the transverse stress distribution of the plate under the maximum transverse bending stress s max = 300 MPa in Scheme B. Figures 20 to 22 are successively the schematic diagram of the vertical displacement distribution in the thin plate bending case, the schematic diagram of the deflection of the central section, and the schematic diagram of the transverse stress distribution of the plate under the maximum transverse bending stress s max = 300 MPa in Scheme C.

[0155] Finally, the correctness of the above theoretical data and the stress-strain state of the plate are tested through experiments. The operations are as follows:

[0156] 1. Spot weld the bulb flat bars on the plate to form a pre-welded assembly. Position along the weld length direction using double-sided fillet welding, with a weld length of 10 mm, a weld leg height of 3 mm, and a spacing of 150 - 200 mm;

[0157] 2. Fix the pre-welded assembly before welding, and apply a pre-tightening force of P2 = 10 kN at the position of L Q = ±400 mm. Specifically, use a manual wrench to complete this work through the pressure beam and the pressure head (the pressure gauge on this device can display the pressure magnitude. In this embodiment, the height of the fixed support - support 2 is 40 mm, and adjustable supports can be used for larger samples);

[0158] 3. Measure the deflection and vertical displacement on the surface of the steel plate, record the measured values, which can be used for comparison with the actual values simulated by ANSYS;

[0159] 4. Use a compact welding machine (welding carriage) with a welding power supply to automatically weld the T-joints with double-sided fillet joints;

[0160] 5. After welding, reverse-rotate and loosen the compression wrench, and place the welded assembly on a horizontal platform for re-measuring the deformation dimensions.

[0161] Welding tests are carried out under different parameter conditions in the above manner, and the results are as shown in Figure 23The optimized control scheme 4 shown. It can be seen that this scheme can better control the welding deformation caused by heat input.

[0162] Obviously, the above embodiments are only examples for clear illustration and not limitations on the implementation manners. For those of ordinary skill in the art, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to list all implementation manners here. And the obvious changes or modifications derived therefrom are still within the protection scope of the present invention.

Claims

1. A welding method for a floating photovoltaic structure, characterized in that, The method includes the following steps: S1. Based on the physical properties of the structure to be welded, establish a fully thermo-mechanical coupling model for the welding process to simulate the stress field generated during the welding of the structure to be welded; set boundary conditions and calculate the bending stress and strain generated during the welding of the structure to be welded. The specific steps of step S1 include the following: S11. Establish a geometric model of the welded joint; S12. Perform finite element mesh division; S13. Establish a heat source model and define the properties of the welding material; S14. Set boundary conditions to complete the finite element calculation of the welded joint. The set boundary conditions are: angular deformation is generated at the welding part, and the inherent deformation amount of transverse shrinkage is considered to be evenly distributed along the welding line; S15. Extract the average inherent strain value of all nodes at the weld, and then use the elastic analytical method to predict the welding deformation of the entire structure to be welded; set the weld width according to the welding process parameters, and perform an elastic calculation on the weld in sequence according to the preset welding sequence; solve the overall deformation result according to the weld shrinkage amount generated by the inherent strain. S2. Position the structure to be welded. S3. Apply prestress to the structure to be welded to resist welding deformation. The steps of step S3 include the following: S31. The stress-strain state of the elastic bending of the structure to be welded is theoretically calculated by finite element analysis software, and multiple load schemes are used for simulation. The specific steps of step S31 include the following: Determine the load and calculate the magnitude of the binding force required for the elastic bending of the structure to be welded. Determine the necessary stiffness and strength values of the main components of the tooling fixture. Determine the optimal boundary conditions. Use finite element analysis software to calculate the stress-strain state of the elastic bending of the structure to be welded. Combined with the size of the structure to be welded, each load scheme and environmental factors, set the boundary conditions as follows: the structure to be welded under elastic bending is in a horizontal position; the external bending force is evenly distributed along the two longitudinal edges of the structure to be welded, or distributed along parallel lines at a given distance along the main support; gravity or the total weight of the structure to be welded is evenly distributed over the entire area; use the theoretical value of the welding heat input as the basis for finite element calculation, and use the simulated temperature result as the thermal load for loading. When loading: Apply the temperature field and heat conduction analysis results as the initial temperature conditions, and consider the arc or gas protection during the welding process; perform transient thermal analysis to obtain the temperature rise curve and temperature field; use the temperature result as the thermal load, and combine the mechanical properties of the weld and the base metal at high temperature to perform transient structural analysis to obtain the stress and deformation results during the welding process. Specify the maximum bending transverse stress value of each load scheme. Using the above boundary conditions, obtain the calculation data of the vertical force required for the elastic bending of the structure to be welded, as well as the obtained transverse bending stress and the maximum deflection of the plate. S32. Through experimental testing, verify the correctness of the theoretical data in step S31 and the stress-strain state of the structure to be welded; extract the temperature rise curve, stress-strain curve and deformation amount of key points, and compare them with the test results or empirical formulas to verify the accuracy of the finite element model. S33. Optimization analysis: On the basis of passing the verification, optimize the welding process parameters to find a welding scheme with relatively small stress value and relatively good uniformity. S4. Use a double-sided automatic welding device to weld each longitudinal girder to the structure to be welded one by one.

2. A welding method for a floating photovoltaic structure according to claim 1, characterized in that, In the step S12, according to the thermal conduction analysis results, densify the mesh in the weld and heat affected zone; coarsen the mesh for the remaining part; Select tetrahedron or hexahedron elements for the mesh type.

3. A welding method for a floating photovoltaic structure according to claim 1, characterized in that, In the step S13, define the welding material properties as defining the temperature-dependent welding material properties of each part of the structure to be welded, and defining the high-temperature properties of the weld; Through the analysis of the welding material and heat source model, customize the welding material properties according to the mechanical properties and phase composition of the corresponding welding material.

4. A welding method for a floating photovoltaic structure according to claim 1, characterized in that, The step S3 is to use a jacking device with an adjustable shape to adjust the amount of reverse deformation of the pre-deformation of the welding position of the structure to be welded, so that the deformation generated by welding is offset by the applied reverse deformation.

5. A welding method for a floating photovoltaic structure according to claim 4, characterized in that The step S3 is to use a longitudinal girder positioning and clamping device to adjust the shape and position accuracy of each longitudinal girder relative to the structure to be welded, and apply prestress to resist welding deformation at the welding position.

6. A welding method for a floating photovoltaic structure according to claim 1, characterized in that, The step S3 further includes the following steps: Provide an analysis report: summarize the stress and strain analysis results, and predict the welding quality and service performance.

Images