A floating photovoltaic structure based on fluid-structure coupling dynamic response analysis method

Abstract

The floating photovoltaic structure of the present application is based on the dynamic response analysis method of fluid-structure coupling, the anchoring system of the floating photovoltaic structure is equivalent to a concentrated force, a simplified numerical model of the floating photovoltaic structure is established, and then the numerical analysis method of safety evaluation of the floating photovoltaic structure under given wind, wave and current conditions is established based on fluid-structure coupling. The method of the present application can obtain the instantaneous stress and strain field of each component of the floating photovoltaic structure with high precision, which can provide a basis for the design of each component of the floating photovoltaic structure and provide a reference for the safety evaluation of the floating photovoltaic structure.

Description

Technical Field

[0001] This invention relates to the field of marine engineering and hydraulic engineering technology, and more specifically, to a dynamic response analysis method for floating photovoltaic structures based on fluid-structure interaction. Background Technology

[0002] Solar energy, as a renewable, green, and pollution-free clean energy source, has attracted much attention. The rapid development of the solar photovoltaic industry has promoted the rise of the floating photovoltaic sub-market. Unlike land-based photovoltaic systems, floating photovoltaic systems do not have the stable foundation of ground-based solar power plants, and their lighter weight and smaller moment of inertia make them easily damaged in the complex and harsh marine environment.

[0003] While experimental research methods can most realistically reflect the performance of floating photovoltaic systems under specific water conditions, they are expensive, have long research cycles, and can only obtain data under specific water surface conditions over a period of time. They cannot obtain data on floating photovoltaic systems under various wind, wave, and current conditions. Therefore, experimental research methods have many limitations and a narrow range of applications.

[0004] Numerical simulation methods are low-cost and can analyze the dynamic response characteristics of different types of floating structures under varying water surface conditions. However, commercial software such as AQWA and OrcaFlex primarily provide fluid dynamics assessment and analysis for marine structural engineering applications, focusing on the dynamic characteristics of rigid bodies and failing to capture the deformation, stress, and strain of photovoltaic structures. While there is considerable research in numerical simulation of ship dynamics, typically employing a combination of CFD solvers and finite element numerical simulations to obtain ship motion and forces, directly applying these findings to the strength assessment of floating photovoltaic structures is unsuitable. This is because, to ensure the normal operation of floating photovoltaic structures, their position needs to be determined by an anchoring system; therefore, floating photovoltaic structures consist of photovoltaic panels and an anchoring system. Strength analysis of floating photovoltaic structures requires establishing a finite element model of the entire structure. However, the anchoring system has a large slenderness ratio and high flexibility, necessitating a large number of elements and requiring the simulation to reflect geometric nonlinearity. Furthermore, when performing stress analysis on floating photovoltaic structures, the real-time changes in added mass and damping caused by waves are difficult to represent in the finite element model of the anchoring system. Therefore, it is very difficult to establish a finite element model of a floating photovoltaic structure that conforms to the actual engineering situation, which makes it impossible to conduct dynamic response analysis of floating photovoltaic structures based on numerical simulation methods.

[0005] In order to enable floating photovoltaic systems to adapt to complex aquatic environments and ensure their safe, stable, and reliable operation, it is necessary to conduct strength analysis studies on offshore floating photovoltaic systems to ensure their safety.

[0006] The limitations of existing research lead to the following problems: ① The test method is expensive and can only obtain the stress and deformation results under specific water surface conditions, and cannot obtain the stress distribution and failure results of floating photovoltaic structure modules under arbitrary wind, wave and current conditions.

[0007] ② Numerical methods for floating photovoltaic structures based on fluid-structure interaction require the establishment of a mechanical model of the mooring cable in the FEM solver. However, this model is not only difficult to implement, but also difficult to accurately account for the real-time changes in the additional mass and additional damping caused by wave motion on the mooring cable.

[0008] Therefore, it is necessary to establish a suitable numerical model for floating photovoltaic structures to simulate their mechanical properties. The model also needs to be highly accurate so as to provide a basis for the mechanical performance design of floating photovoltaics and to improve the safety assessment methods for floating photovoltaics. Summary of the Invention

[0009] This invention provides a dynamic response analysis method for floating photovoltaic structures based on fluid-structure interaction, which can provide a reference for the design and safety assessment of various components of floating photovoltaic structures, thereby solving the technical problem that the low accuracy of existing numerical models of floating photovoltaic structures leads to low reliability of safety assessment.

[0010] According to one aspect of the present invention, a method for dynamic response analysis of a floating photovoltaic structure based on fluid-structure interaction is provided, comprising the following steps: Step 1: Solve for the tension of the mooring cable of the floating photovoltaic structure in the CFD solver; Step 2: Establish a floating photovoltaic structure model of the unmoored system in the FEM solver, import the mooring cable tension obtained from the CFD solver, and apply it as a load to the floating photovoltaic structure model of the unmoored system. Step 3: Determine the coupling region of the CFD solver and FEM solver in the co-simulation analysis, and establish a co-simulation coupling platform for the CFD solver and FEM solver. In the calculation, the co-simulation coupling platform will transfer the pressure and wall shear force calculated in the coupling region by the CFD solver to the FEM solver, and transfer the deformation calculated in the coupling region by the FEM solver to the CFD solver. Step 4: Perform fluid-structure interaction calculations using the CFD-FEM co-simulation analysis method to obtain the stress field distribution of the floating photovoltaic structure module over the entire time history, and determine the stress peak value of each floating photovoltaic structure module over the entire time history; compare the stress peak value with the material strength design value to obtain the safety of each floating photovoltaic structure module.

[0011] Based on the above scheme, step 1 specifically includes: Step 1.1: Establish a finite element model of the floating photovoltaic structure including the mooring system in the CFD solver; Step 1.2: Calculate the tension of the mooring cable at different times under given wind, wave and current conditions, including the magnitude and direction of the tension.

[0012] Based on the above scheme, the preferred conditions in step 1.2 include: without considering scaling, the upper air portion of the entire solution domain is about 25-35 times the thickness of the floating body, and the depth of the liquid fluid portion is selected according to the actual water depth of the actual floating photovoltaic working area; the two ends of the mooring cable are directly fixed to the floating photovoltaic and the bottom of the water according to the actual position.

[0013] Based on the above scheme, step 2 specifically includes: Step 2.1: Establish a finite element model of the floating photovoltaic structure without the mooring system in the FEM solver; Step 2.2 Apply the mooring cable tension at different times as a load to the connection node between the mooring cable and the floating photovoltaic structure to obtain the tension of the mooring cable of the floating photovoltaic structure in the FEM solver.

[0014] The present invention provides a dynamic response analysis method for floating photovoltaic structures based on fluid-structure interaction. The method equates the mooring system of the floating photovoltaic structure to a concentrated force, establishes a simplified numerical model of the floating photovoltaic structure, and then establishes a numerical analysis method for safety assessment of the floating photovoltaic structure under given wind, wave and current conditions based on fluid-structure interaction.

[0015] The method of this invention can obtain the instantaneous stress-strain field of each component of a floating photovoltaic structure with high accuracy, which can provide a basis for the design of each component of the floating photovoltaic structure and a reference for the safety assessment of floating photovoltaics. Attached Figure Description

[0016] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort. In the drawings: Figure 1 This is a flowchart of the dynamic response analysis method for the floating photovoltaic structure based on fluid-structure interaction of the present invention. Figure 2 This is a model diagram of the floating photovoltaic structure of the present invention; Figure 3 This is a diagram showing the mooring cable arrangement of the floating photovoltaic structure of the present invention; Figure 4 This is a tension diagram of a single mooring cable for the floating photovoltaic structure of the present invention; Figure 5 The displacement response time history curve of this invention; Figure 6 This is a displacement response contour plot of the present invention; Figure 7 This is a stress-time history curve diagram of the present invention; Figure 8 This is a stress cloud diagram of the present invention. Detailed Implementation

[0017] The specific embodiments of the present invention will be described in further detail below with reference to the accompanying drawings and examples. The following examples are for illustrative purposes only and are not intended to limit the scope of the invention.

[0018] It should be understood that, when used in this specification and the appended claims, the term "comprising" indicates the presence of a descriptive feature, integral, step, operation, element, and / or component, but does not exclude the presence or addition of one or more other features, integrals, steps, operations, elements, components, and / or sets.

[0019] To keep the drawings concise, only the parts relevant to the invention are shown schematically in each figure, and they do not represent the actual structure of the product. Furthermore, for ease of understanding, in some figures, only one of components with the same structure or function is shown schematically, or only one is labeled. In this document, "one" can mean not only "only one" but also "more than one".

[0020] It should also be further understood that the term “and / or” as used in this application specification and the appended claims means any combination of one or more of the associated listed items and all possible combinations, and includes such combinations.

[0021] In the embodiments shown in the accompanying drawings, the directional indications (such as up, down, left, right, front, and back) used to explain the structure and movement of the various components of the invention are relative rather than absolute. These descriptions are appropriate when these components are in the positions shown in the drawings. If the descriptions of the positions of these components change, these directional indications also change accordingly.

[0022] Furthermore, in the description of this application, the terms "first," "second," etc., are used only to distinguish descriptions and should not be construed as indicating or implying relative importance.

[0023] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the specific implementation methods of the present invention will be described below with reference to the accompanying drawings. Obviously, the drawings described below are merely some embodiments of the present invention. For those skilled in the art, other drawings and other implementation methods can be obtained based on these drawings without any creative effort.

[0024] Please see Figure 1 As shown, the present invention provides a dynamic response analysis method for a floating photovoltaic structure based on fluid-structure interaction, comprising the following steps: Step 1: Input various parameters of the mooring cable into the CFD solver, and solve the tension of the mooring cable of the floating photovoltaic structure through the CFD solver. Step 1.1: Establish a finite element model of the floating photovoltaic structure including the mooring system in the CFD solver; that is, simplify the entire photovoltaic float according to the specific shape and size of the actual floating photovoltaic, and omit small designs such as grooves and stripes, as well as the detailed structure of connecting components and other components that have little impact on the floating photovoltaic.

[0025] Step 1.2: Calculate the tension of the mooring cable at different times under given wind, wave and current conditions, including the magnitude and direction of the tension.

[0026] Regarding the solution domain, without considering scaling, the upper air portion of the entire solution domain is approximately 25-35 times the thickness of the floating body. The depth (water depth) of the liquid fluid portion should be selected according to the actual water depth of the floating photovoltaic working area. The two ends of the mooring cable can be directly fixed to the floating photovoltaic and the bottom of the water according to their actual positions.

[0027] Step 2, Tension of the mooring cable of the floating photovoltaic structure without anchoring system in the FEM solver; Step 2.1: Establish a floating photovoltaic structure finite element model without the mooring system in the FEM solver. It should be noted that the floating photovoltaic finite element model in the FEM solver should be the same as that in the CFD solver, but there is no need to establish finite element models of the mooring cable and fluid.

[0028] Step 2.2: Apply the mooring cable tension at different times as a load to the connection node between the mooring cable and the floating photovoltaic structure to obtain the tension of the mooring cable of the floating photovoltaic structure in the FEM solver.

[0029] Specifically, the actual mooring cable is not directly connected to the floating photovoltaic hull. Instead, the mooring cable is typically connected to a steel truss, which is then bolted to the floating photovoltaic hull. For details, please refer to [link to structural description]. Figure 2 As shown. Therefore, firstly, the mooring cable tension needs to be distributed to each fixing point according to the static equivalence principle based on the number of fixing points of the steel truss; then, in order to avoid stress concentration, a reference point coupled to the surface of the bolt hole is set, and the distributed mooring cable tension is applied to the reference point.

[0030] Step 3: Determine the coupling region for CFD and FEM co-simulation analysis, establish a CFD and FEM co-simulation coupling platform, transfer the pressure and wall shear force calculated in the coupling region from CFD to FEM, and transfer the deformation calculated in the coupling region from FEM to CFD. Step 4: Perform fluid-structure interaction calculations in CFD to obtain the stress field distribution of the floating photovoltaic structure module over the entire time history, and determine the stress peak value of each floating photovoltaic structure module over the entire time history; compare the stress peak value with the material strength design value. If the stress peak value exceeds the material strength design value, the module is unsafe and will fail due to strength failure; otherwise, it is safe.

[0031] To facilitate a better understanding of the technical solution of the present invention, specific embodiments will be described in detail below.

[0032] Taking a floating photovoltaic project as an example, the material of a single 3×4 float array is high-density polyethylene (HDPE). The mooring cables are connected to the outer bottom corners of the platform's floats at a horizontal angle of 45°. The platform model and mooring cable arrangement are as follows. Figure 1 As shown, the wind and wave conditions are a 50-year return period. The water flow is mainly affected by wind-driven currents with a flow velocity of 0.5 m / s, a wave height of 0.5 m, and a period of 3.5 s. The average wind speed at 10 m above the water surface is 25 m / s, and the water depth is 7 m.

[0033] The mooring cable uses a Ф12×48 galvanized chain, which is made of 20Mn2 alloy steel.

[0034] Based on the above parameters, establish the following in CFD: Figure 2 and Figure 3The floating body array model and fluid domain model are shown, and mesh generation and mesh refinement are performed for key areas. Input data such as wind speed, water flow velocity, wave height, period, water depth, and the mass of the floating body array for the entire flow field are used. A body coupling model of the mooring cables and the floating body array is established. After importing the mooring cable parameters into this body coupling model, time-domain hydrodynamic analysis is performed in CFD using the multiphase flow dynamic fluid-structure interaction (DFBI) method. The tension magnitude and direction data for each of the four mooring cables are extracted. The extracted tension magnitude and direction of a single mooring cable are shown below. Figure 4 As shown. Finally, on the floating array model, the coupling surface that needs to transmit pressure and wall shear force to the FEM and receive the stress and strain field is selected, and a data transmission link with the FEM is established.

[0035] In FEM, a similar floating array model was established using shell elements. After meshing, the material parameters of the floating array, such as wall thickness, density of the floating material (HDPE), tensile modulus of elasticity, and Poisson's ratio, were input. A dynamic implicit analysis step was then used for calculation. In setting the boundary conditions, the same displacement boundary conditions as in CFD were first set. Then, when setting the load boundary conditions, static loads other than the self-weight of the floating array (such as the mass of photovoltaic modules and cables) were applied to the surface of the floating array as uniformly distributed loads. The tension of the extracted mooring cable was then applied as a concentrated force to the connection between the mooring cable and the floating array. The boundary conditions were then set. Finally, a coupling surface for co-analysis with CFD was selected, and a data transmission link was established to transmit the stress-strain field to CFD and receive pressure and wall shear forces.

[0036] Once the data transmission link between CFD and FEM is established, the co-simulation platform is also set up. During CFD-FEM co-simulation analysis, CFD initialization is performed first to generate the initial flow field and loads on the coupled surfaces to complete the initial data transmission. Subsequently, at each time step, CFD and FEM transmit data to each other: CFD transmits the calculated loads on the coupled surfaces to FEM, and FEM transmits the calculated stress-strain fields on the coupled surfaces to CFD. CFD and FEM then use their received data as additional boundary conditions to perform their respective multiphase flow dynamic fluid-structure interaction and implicit dynamic analysis calculations, and then transmit their calculation results to each other, thus achieving CFD-FEM co-simulation analysis in a cyclical manner. Finally, the time history curves of the displacement and stress response of the floating body array, as well as the contour plot at the maximum moment, are obtained, as shown below. Figure 5-8 As shown in the diagram, the shade of color in the cloud map represents the magnitude of the value; the closer to red, the larger the value, and the closer to blue, the smaller the value.

[0037] The present invention provides a dynamic response analysis method for floating photovoltaic structures based on fluid-structure interaction. The method equates the mooring system of the floating photovoltaic structure to a concentrated force, establishes a simplified numerical model of the floating photovoltaic structure, and then establishes a numerical analysis method for safety assessment of the floating photovoltaic structure under given wind, wave and current conditions based on fluid-structure interaction.

[0038] The method of this invention can obtain the instantaneous stress-strain field of each component of a floating photovoltaic structure with high accuracy, which can provide a basis for the design of each component of the floating photovoltaic structure and a reference for the safety assessment of floating photovoltaics.

[0039] Finally, the method described in this application is merely a preferred embodiment and is not intended to limit the scope of protection of this invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this invention should be included within the scope of protection of this invention.

Claims

1. A method for analyzing the dynamic response of a floating photovoltaic structure based on fluid-structure interaction, characterized in that, Includes the following steps: Step 1: Solve for the tension of the mooring cable of the floating photovoltaic structure using the CFD solver. Establish a finite element model of the floating photovoltaic structure, including the mooring system, in the CFD solver. Based on the actual shape and dimensions of the floating photovoltaic structure, simplify the entire photovoltaic float, omitting the design of grooves and stripes, as well as the details of connecting components that have little impact on the floating photovoltaic structure. Calculate the tension of the mooring cable under different wind, wave, and current conditions, including the magnitude and direction of the tension. Without considering scaling, the upper air portion of the solution domain is 25-35 times the thickness of the float, and the depth of the liquid fluid portion is selected according to the actual water depth of the floating photovoltaic working area. The two ends of the mooring cable are directly fixed to the floating photovoltaic structure and the seabed according to their actual positions. Step 2: Establish a floating photovoltaic structure model of the unmoored system in the FEM solver, import the mooring cable tension obtained from the CFD solver, and apply it as a load to the floating photovoltaic structure model of the unmoored system. Step 3: Determine the coupling region of the CFD solver and FEM solver in the co-simulation analysis, and establish a co-simulation coupling platform for the CFD solver and FEM solver. In the calculation, the co-simulation coupling platform will transfer the pressure and wall shear force calculated in the coupling region by the CFD solver to the FEM solver, and transfer the deformation calculated in the coupling region by the FEM solver to the CFD solver. Step 4: Perform fluid-structure interaction calculations using the CFD-FEM co-simulation analysis method to obtain the stress field distribution of the floating photovoltaic structure module over the entire time history, and determine the stress peak value of each floating photovoltaic structure module over the entire time history; compare the stress peak value with the material strength design value to obtain the safety of each floating photovoltaic structure module.

2. The method of claim 1, wherein the floating photovoltaic structure is based on fluid-structure interaction dynamic response analysis. Step 2 specifically includes: Step 2.1: Establish a finite element model of the floating photovoltaic structure without the mooring system in the FEM solver; Step 2.2 Apply the mooring cable tension at different times as a load to the connection node between the mooring cable and the floating photovoltaic structure to obtain the tension of the mooring cable of the floating photovoltaic structure in the FEM solver.

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