Method for evaluating hail impact resistance of composite interlayer heliostat and method for designing heliostat

Abstract

The invention discloses a method for evaluating the hail impact resistance of a composite interlayer heliostat and designing the heliostat, and the method comprises the steps: investigating the hail reduction diameter distribution of a use environment of the heliostat, and determining a researched hail diameter range; establishing a hail impact heliostat finite element model through finite element software; and carrying out numerical simulation on the impact behavior of hail on the heliostat with the composite interlayer, and carrying out quantitative analysis on the hail impact resistance of the heliostat at different positions, different interlayers and different thickness ratios to obtain a speed threshold value of the heliostat with the composite interlayer under the optimal thickness ratio. According to the method, the hail impact resistance of the composite interlayer heliostat is evaluated, a heliostat structure design optimization database can be established through the method, and the structural design of the heliostat is guided in combination with the hail disaster risk evaluation result of the heliostat use environment. And the heliostat is more reasonable in structural design.

Description

Technical Field

[0001] The present invention relates to the technical field of solar thermal power generation, and in particular to a method for evaluating the hail impact resistance of a composite sandwich heliostat and designing a heliostat. Background Art

[0002] With the development of emerging energy technologies, tower solar thermal power generation technology has become the mainstream development target of concentrated solar power generation due to its strong technical advantages and high competitiveness. Among them, tower solar thermal power generation technology, which can fully utilize solar energy and achieve large-scale power generation due to its high concentration ratio, high heat flux density and high stability, is currently the most promising development direction of solar thermal power generation technology. The open mirror field environment makes heliostats vulnerable to hail disasters during service, thereby reducing the operating efficiency and effectiveness of heliostats.

[0003] There are technologies for the anti-hail design of single-layer heliostats, but there are also composite sandwich heliostats, and the structure of the composite sandwich heliostat is composed of three parts: the first glass plate, the interlayer and the back plate. This also shows that on the one hand, it is not enough to only study the anti-hail impact performance of single-layer heliostats. On the other hand, the "Design Standard for Tower Solar Thermal Power Stations" (GB / T51307-2018), which is currently used in the design of heliostat structures in my country, requires that the mirror strength meet the requirements of "Solar Glass Part 3: Glass Reflectors" (GB / T30984.3-2016) and "Test Method for Anti-hail Impact of Photothermal Power Generation Glass Reflectors" (GB / T33235-2016), but there is no design basis for hail loads. In particular, the climate distribution characteristics of hail in my country are obviously regional. For areas where hail occurs frequently and the hail size is large, the existing design basis of the heliostat structure cannot fully meet the hail resistance needs of the heliostat. For areas where hail occurs less frequently and the hail size is small, the existing design basis of the heliostat structure may cause the heliostat structure to be overly conservative, resulting in additional economic costs. Summary of the invention

[0004] The purpose of the present invention is to provide a method for evaluating the hail impact resistance of a composite sandwich heliostat and designing a heliostat, so as to solve one or more technical problems existing in the prior art and at least provide a beneficial choice or create conditions.

[0005] The technical solutions adopted to solve the above technical problems are:

[0006] The present invention provides a method for evaluating the hail impact resistance performance of a composite sandwich heliostat, comprising:

[0007] Investigate the hail diameter distribution in the heliostat operating environment and determine the hail diameter range to be studied;

[0008] Finite element model of hail impact heliostat is established by finite element software;

[0009] The behavior of the composite sandwich heliostat impacted by hail is numerically simulated, and the anti-hail impact performance of the heliostat with different impact positions, different interlayers and different thickness ratios is quantitatively analyzed to obtain the velocity threshold of the composite sandwich heliostat under the optimal thickness ratio.

[0010] The beneficial effects of the present invention are:

[0011] The present invention evaluates the anti-hail impact performance of the composite sandwich heliostat, and then through the present invention, a heliostat structural design optimization database can be established, and the structural design of the heliostat can be guided in combination with the hail disaster risk assessment results of the heliostat use environment. The heliostat structural design is made more reasonable. For example, for areas with a high frequency of hail and large hail sizes, the existing heliostat structural design basis can meet the anti-hail requirements of the heliostat, and for areas with a low frequency of hail and small hail sizes, the existing heliostat structural design based on the stress analysis design of the method is more reasonable, and the designed heliostat structural strength will not be much higher than the actual structural strength of the heliostat structure, thereby reducing the generation of additional economic costs.

[0012] As a further improvement of the above technical solution, the step of establishing a finite element model of a hail impact heliostat includes separately establishing a hail model and a finite element model of a heliostat unit sub-mirror. When establishing the hail model, the method used to simulate the hail crushing process is selected as a smooth particle fluid dynamics method, which can avoid the grid distortion encountered by traditional grids, improve calculation efficiency and stability, and is often used to simulate large deformation, disintegration, and rupture of structures such as hail impact.

[0013] As a further improvement of the above technical solution, when establishing the finite element model of the heliostat unit sub-mirror, a material database is constructed according to the different types of materials of the sandwich components of the heliostat unit sub-mirror.

[0014] As a further improvement of the above technical solution, when the hail impacts the heliostat finite element model, the mesh division of the hail and the heliostat unit sub-mirrors includes the selection of unit type, mesh type and mesh size, and the optimization solution is sought based on the consideration of calculation time and calculation accuracy, so that the result is more accurate.

[0015] As a further improvement of the above technical solution, in the numerical model of hail impact composite sandwich heliostat, S4 thin shell units are used for the first glass plate and the glass back plate of the composite sandwich heliostat reflector. The plane size of the interlayer of the composite sandwich heliostat reflector is consistent with the reflector. C3D8R entity units are used for simulation. The grid side length and the number of grids are consistent with those of the first glass plate. In addition, the interlayer and the upper and lower glass plates are bound to form a whole. The supporting structure adopts a square cross-section hollow steel pipe. C3D8R entity units are used for hail units. The mesh is divided based on the SPH method. The Conversion to particles option is selected in ElementType so that the meshed hail is converted into particles in the calculation. MPC multi-point constraints are performed on the reflector and the supporting structure, and the end nodes of the supporting structure are completely fixed.

[0016] As a further improvement of the above technical solution, the first strength theory is adopted, and the tensile strength of the material is used as the failure criterion. When the maximum tensile stress of the first layer of glass of the heliostat glass reflector exceeds its tensile strength, the reflector is determined to be damaged.

[0017] As a further improvement of the above technical solution, the steps of setting the working conditions of the hail impact composite sandwich heliostat include: selecting the hail diameter, the hail impact position, the thickness of the composite sandwich heliostat, and selecting the impact speed of the hail.

[0018] As a further improvement of the above technical solution, the impact velocity of hail is selected based on the relatively fixed relationship between the falling velocity of hail and the size of hail. It is assumed that the hail is only affected by gravity and air resistance during its falling process. When the falling gravity of hail is equal to the air resistance, the terminal velocity of the hail at this time is taken as the impact velocity of the hail.

[0019] As a further improvement of the above technical solution, the step of setting the working condition of the hail impact composite sandwich heliostat also includes: determining the position of the hail impact composite sandwich heliostat according to the national standard "Test method for anti-hail impact of glass reflectors for solar thermal power generation".

[0020] The present invention also provides a method for designing a heliostat, including any one of the above-mentioned methods for evaluating the anti-hail impact performance of a composite sandwich heliostat and designing a heliostat, and establishing a heliostat structure design optimization database, and guiding the structural design of the heliostat in combination with the hail disaster risk assessment results of the heliostat use environment. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] The present invention will be further described below in conjunction with the accompanying drawings and embodiments;

[0022] Figure 1 Schematic diagram of the composite sandwich heliostat structure;

[0023] Figure 2 Schematic diagram of the finite element model of the hail impact composite sandwich heliostat;

[0024] Figure 3 Schematic diagram of hail impact point;

[0025] Figure 4 Comparison of the maximum principal stress in the plane at different positions;

[0026] Figure 5 Time history diagrams of the impact point of the first glass plate of three different interlayer types, including (a) the maximum principal stress time history comparison diagram at the impact point of the first glass plate, and (b) the displacement time history comparison diagram at the impact point of the first glass plate;

[0027] Figure 6 Time history diagrams at the impact point of the first layer of glass under different thickness ratios, where (a) is the time history comparison diagram of the maximum principal stress at the impact point of the first layer of glass, and (b) is the time history comparison diagram of the displacement at the impact point of the first layer of glass;

[0028] Figure 7 Time history diagrams of the impact point of the first layer of glass under different thickness ratios, including (a) the maximum principal stress time history comparison diagram at the impact point of the first layer of glass, (b) the displacement time history comparison diagram at the impact point of the first layer of glass;

[0029] Figure 8 Time history diagram of the maximum principal stress in the first layer of glass at different thicknesses, including (a) 2mm, (b) 3mm, and (c) 4mm. DETAILED DESCRIPTION

[0030] This section will describe in detail the specific embodiments of the present invention. The preferred embodiments of the present invention are shown in the accompanying drawings. The purpose of the accompanying drawings is to supplement the description of the text part of the specification with graphics, so that people can intuitively and vividly understand each technical feature and the overall technical solution of the present invention, but it cannot be understood as a limitation on the scope of protection of the present invention.

[0031] In the description of the present invention, it should be understood that descriptions involving orientations, such as up, down, front, back, left, right, etc., and orientations or positional relationships indicated are based on the orientations or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be understood as a limitation on the present invention.

[0032] In the description of the present invention, if there are words such as "several", it means one or more, "more" means more than two, greater than, less than, exceed, etc. are understood as not including the number, and above, below, within, etc. are understood as including the number.

[0033] In the description of the present invention, unless otherwise clearly defined, terms such as setting, installing, connecting, etc. should be understood in a broad sense, and technicians in the relevant technical field can reasonably determine the specific meanings of the above terms in the present invention based on the specific content of the technical solution.

[0034] In the research on hail resistance of heliostats, the current research mainly focuses on the hail resistance performance of single-layer heliostats, as well as the impact of hail impact diameter, hail impact position, heliostat plate thickness, heliostat pitch angle and other factors on the hail resistance performance of single-layer heliostats. However, according to the specification "Part 3 of Solar Glass: Glass Reflectors" (GB / T 30984.3-2016), heliostats can be divided into single-layer glass reflectors and composite glass reflectors according to their structure, in which the composite glass reflector is composed of three parts: the first layer of glass plate, the interlayer and the back plate. Different heliostat structures have a significant impact on their hail resistance performance, so it is insufficient and in-depth to only evaluate the hail resistance performance of single-layer heliostats.

[0035] On the other hand, the "Design Standard for Tower Solar Thermal Power Stations" (GB / T51307-2018) based on which the heliostat structure design in my country is based requires that the mirror strength meet the requirements of "Glass for Solar Energy Part 3: Glass Reflectors" (GB / T30984.3-2016) and "Test Method for Hail Impact Resistance of Glass Reflectors for Photothermal Power Generation" (GB / T33235-2016), but there is no design basis for hail loads. In particular, the climate distribution characteristics of hail in my country are obviously regional. For areas with a high frequency of hail and large hail sizes, the existing design basis for heliostat structures cannot fully meet the anti-hail needs of heliostats. For areas with a low frequency of hail and small hail sizes, the existing design basis for heliostat structures may cause the heliostat structure design to be overly conservative, resulting in additional economic costs.

[0036] Therefore, the present invention aims to solve the problem that the tower solar heliostat is damaged by hail impact, thereby affecting the operating efficiency and effectiveness of the heliostat, and proposes a method for evaluating the hail impact resistance of the composite sandwich heliostat. Figures 1 to 8 The method for evaluating the anti-hail impact performance of the composite sandwich heliostat and designing the heliostat of the present invention is as follows:

[0037] Firstly, according to the hail diameter distribution in the Qinghai-Tibet Plateau region that has been investigated, the hail diameter range of the study is determined to be 30mm to 50mm. Assuming that the hail is only affected by gravity and air resistance during the falling process, when the gravity of the hail is equal to the air resistance, the final speed of the hail at this time is taken as the impact speed of the hail. Secondly, according to the content of the national standard "Part 3 of Solar Glass: Glass Reflector", it can be known that the intermediate layer material of the composite laminated glass for solar energy can be composed of three materials: PVB, EVA and SGP. Finally, the finite element model of the hail impact heliostat is established by finite element software, and the behavior of hail impacting the composite laminated heliostat is numerically simulated. The quantitative analysis of the anti-hail impact performance of the heliostat with different positions, different interlayers, and different thickness ratios is carried out, and the velocity threshold of the composite laminated heliostat under the optimal thickness ratio is obtained, thereby establishing a heliostat structural design optimization database, combined with the hail disaster risk assessment results in the Qinghai-Tibet Plateau region, to guide the structural design of the heliostat.

[0038] (1) Finite element model of hail impact heliostat

[0039] Taking a tower solar heliostat in China as an example, a unit sub-mirror of the heliostat is selected to establish a finite element model of the hail impact heliostat. The first step is to establish the hail model. Ice is a strain rate sensitive material, and its compression strength is much higher than its tensile strength. Therefore, when the pressure is high, it will change from solid to liquid. Therefore, the hail shows strain rate-related elastic-plastic characteristics before breaking, and the mechanical properties after breaking are similar to fluid properties. Scholars have proved that when simulating large deformations of objects, the smooth particle hydrodynamics method (Smooth Particle Hydrodynamic, referred to as SPH) can avoid the grid distortion encountered by traditional grids, improve computational efficiency and stability, and is often used to simulate large deformation, disintegration, and rupture of structures such as hail impact. Therefore, the method used to simulate the hail crushing process is the SPH method. The hail material parameters are as follows: density 846kg·m -3 , elastic modulus 9.31GPa, Poisson's ratio 0.33, yield stress 5.2GPa, tensile failure stress 0.517GPa. Hail load is reflected by the falling speed of hail.

[0040] The SPH equation needs to be constructed in two steps. The first step is the integral representation and the second step is the particle approximation. In the SPH method, for any function f(x) and its spatial derivative function The approximate integral expressions are:

[0041] <f(x)> =∫ Ω f(x′)W(xx′,h)dx′ (1)

[0042]

[0043] in,<f(x)> is the approximation of the function f(x), x is the position vector, Ω is the integration domain containing x, and W(xx′, h) is a smooth function that depends on the distance |xx′| between the two points and the smooth length h.

[0044] The SPH method ultimately transforms the function integral approximation expression into a discretized form that supports the superposition and summation of all particles in the domain. The discretized function f(x) and The integral expression can be written as the following particle approximation

[0045]

[0046]

[0047] Among them, m i and ρ i are the mass and density of particle i respectively, and N is the total number of particles in the support domain.

[0048] SPH uses a smooth function to represent the integral. The choice of the smooth function determines the approximation of the integral representation and will also affect the cost of subsequent SPH calculations. The smooth function used in this study is the cubic β-spline function.

[0049]

[0050] Where R = xx′, α d =1 / h, 15 / 7πh 2 , 3 / 2πh 3 , corresponding to one-dimensional, two-dimensional, and three-dimensional problems respectively.

[0051] The second step is to establish a finite element model of the heliostat unit sub-mirror and build a material database based on the different materials of the heliostat unit sub-mirror (single-layer glass mirror, composite glass mirror, etc.). In the heliostat structure, the reflector is the most basic focusing unit. A large reflector is made up of multiple unit sub-mirrors, which are then connected to the foundation through a back bracket, rigid beams and columns. This example studies the hail impact on the unit sub-mirrors in a rectangular independent column bracket heliostat in China. The schematic diagram of the composite sandwich structure of the composite sandwich heliostat is shown in the figure below. Figure 1 shown.

[0052] from Figure 1It can be seen that the heliostat mirror is mainly composed of a reflector 1 and a steel support structure 2, which are connected by a suction cup 3, a connecting bolt 4 and a steel plate 5, and the suction cup 3 and the reflector 1 are connected by an adjusting bolt 6. The reflector 1 is composed of a first-layer ultra-white glass mirror, a sandwich structure and a glass back panel. The main way to judge whether the reflector 1 is damaged is to observe the damage of the first layer of glass. The damage of the first layer of glass is controlled by strength, and the damage feature is that the surface cracks are generated due to tensile stress and it breaks. Therefore, this paper adopts the first strength theory and takes the tensile strength of the material as the failure criterion. When the maximum tensile stress (Max Principal Stress) of the first layer of glass of the heliostat glass reflector 1 exceeds its tensile strength, the reflector 1 is considered to be damaged. The relevant material parameters of the support structure 2, the first layer of glass reflector 1 and the glass back panel in the reflector 1 are as follows: The density of steel is 7850kg / m 3 , elastic modulus 206GPa, Poisson's ratio 0.3, yield strength 235MPa; glass density 2500kg / m3, elastic modulus 70GPa, Poisson's ratio 0.2, tensile strength 58.8MPa, compressive strength 500MPa.

[0053] In the numerical model of hail impact composite sandwich heliostat, the plane size of composite sandwich heliostat reflector 1 is 1250mm×1250mm, and the total thickness is 4mm. The first glass plate and the glass back plate are both S4 thin shell elements, the grid side length is 5mm, and 5 Gaussian integration points are selected along the shell thickness direction. The number of grids for both is the same, 62500 units. The plane size of the sandwich is consistent with that of reflector 1, and C3D8R entity elements are used for simulation. The grid side length and number of grids are consistent with those of the first glass plate. In addition, the sandwich and the upper and lower glass plates are bound to form a whole. Support structure 2 uses a square cross-section hollow steel pipe with a cross-sectional size of 60mm×60mm×3mm (length×width×wall thickness), a unit type of B31 unit, a unit size of 5mm, and a total of 620 units. The hail unit uses C3D8R entity elements, and the mesh is divided based on the SPH method. The option of Conversion to particles is selected in Element Type so that the hail after meshing is converted into particles in the calculation. Taking into account the role of the five suction cups 3, MPC multi-point constraints are performed on the reflector 1 and the supporting structure 2, and the end nodes of the supporting structure 2 are completely fixed. Figure 2 The grid schematic diagram of the finite element model of hail impact composite sandwich heliostat is given.

[0054] Since the microscopic process of hailstones colliding with heliostats occurs within a very small millisecond time period, the impact characteristics are more likely to reflect nonlinear complex impact dynamics problems. In finite element software, explicit dynamic finite element solution mode is usually used. For example, the ABAQUS / Explicit module is highly applicable to certain dynamic instantaneous events with a short duration and very high change rate, such as impact, explosion and other obvious nonlinear problems. The meshing of hailstones and heliostat unit sub-mirrors, including the selection of unit type, mesh type and mesh size, can seek an optimal solution based on the calculation time and calculation accuracy. (2) Working condition setting of hailstone impact composite sandwich heliostat

[0055] The proposed hail diameter is 30-50mm, the support point position is 7, the impact position is P1-P5, and the thickness of the composite sandwich heliostat is 2-4mm. There is a relatively fixed relationship between the falling speed of hail and the size of hail, as shown in Section (3) for details. The position of the composite sandwich heliostat where hail impact is determined according to the national standard "Test Method for Anti-Hail Impact of Glass Reflector for Solar Thermal Power Generation" is shown in the schematic diagram. Figure 3 , where P1 is the center of the two support points 7 (horizontally), P2 is 12 mm from the boundary, P3 is the center of the two support points 7 (longitudinally), P4 is 12 mm from the boundary, and P5 is 25 mm from the corner. There are three types of interlayers studied in this paper, namely PVB, EVA and SGP. All three interlayer materials are selected as viscoelastic materials. The specific material coefficients are shown in Table 1.

[0056] Table 1 Sandwich material coefficient table

[0057]

[0058] (3) Final speed of hail falling

[0059] The formula for the air resistance encountered by hail when falling is shown in Formula 6.

[0060]

[0061] Among them C d is the air resistance coefficient, ρ is the air density, the unit is g / cm 3 , v is the terminal velocity of the hail falling, the unit is m / sS; and v is the maximum cross-sectional area of ​​the hail perpendicular to the falling direction.

[0062] When the air resistance is equal to gravity, the formula for the terminal velocity of hail is shown in Formula 7.

[0063]

[0064] Enter the appropriate air resistance coefficient C d The resulting formula is 8.

[0065] C a =0.41D 0.185 (8)

[0066] Substituting formula 8 into formula 7, we can obtain formula 9 for the final velocity of falling hail.

[0067]

[0068] The ρ in formula 9 is 1.1 kg / m 3 , g is 9.80m / s 2 Substituting the above two parameters into Formula 9, the hail end velocity results required in this paper are obtained as shown in Table 2 below.

[0069] Table 2 Hail size and falling speed

[0070]

[0071] (4) Calculation results

[0072] According to the national standard "Test Method for Anti-Hail Impact of Glass Reflectors for Solar Thermal Power Generation" (GB / T33235-2016), the location diagram of the hail impact composite laminated heliostat is determined, such as Figure 3 As shown. P1-P5 are the impact points of hail. Taking 30mm hail impacting a PVB composite laminated heliostat with a total thickness of 4mm at a speed of 25.2m / s as an example, the influence of different positions of P1-P5 on the maximum principal stress of the composite laminated heliostat is studied. The PVB composite laminated heliostat consists of a 1.5mm first layer glass plate, a 1mm PVB interlayer and a 1.5mm back plate. The cloud map of the maximum principal stress value at the P1-P5 position after impact is extracted, as shown Figure 4 shown.

[0073] from Figure 4 It is found that from the specific values ​​of the maximum principal stress, the maximum in-plane principal stress values ​​at positions P1-P5 are 29.68MPa, 29.14MPa, 29.67MPa, 12.60MPa and 18.18MPa respectively. By comparison, it is found that the maximum principal stress value at position P1 in the plane is the largest, which is the most unfavorable impact position.

[0074] According to the national standard "Part 3 of Solar Glass: Glass Reflectors", the intermediate layer materials of solar laminated glass can be composed of three materials: PVB, EVA and SGP. The numerical simulation of hail with a diameter of 30 mm independently impacting three different types of 4 mm thick composite laminated heliostat unit sub-mirror panels (the thickness of the first glass panel and the back glass are both 1.5 mm, and the thickness of the laminated glass is 1 mm) was carried out in sequence, and the dynamic response results of the first glass panel at the impact point of the composite laminated heliostat under the corresponding working conditions were extracted and analyzed. Figure 5 a shows the maximum principal stress time history comparison of the first glass plate of the composite laminated heliostat under three interlayer types and the single-layer glass with the same thickness. Figure 5 b shows the displacement time history comparison of the first glass plate of the composite laminated heliostat under three interlayer types at the impact point and that of the single-layer glass of equal thickness.

[0075] The displacement amplitude and maximum principal stress amplitude of different types of heliostats under hail impact are extracted, as shown in Table 3.

[0076] Table 3 Displacement amplitude and maximum principal stress amplitude of different types of heliostats

[0077]

[0078]

[0079] from Figure 5 It is observed in a that when the interlayer is SGP and PVB, the maximum principal stress at the impact point of the first glass plate of the composite laminated heliostat is similar to that of the single-layer heliostat. Therefore, taking the PVB interlayer as an example, the influence of different thickness ratios on the dynamic response and damage mechanism of the PVB laminated heliostat with a total thickness of 4 mm under hail impact is mainly studied. The thickness ratio calculation conditions are shown in Table 4.

[0080] Table 4 Thickness ratio calculation conditions

[0081]

[0082] The above six working conditions are numerically simulated in sequence, and the dynamic response results of the first layer of glass plate at the impact point of the composite laminated heliostat under the corresponding working conditions are extracted for analysis. Figure 6 a shows the maximum principal stress time history comparison diagram of the first layer glass plate of the composite laminated heliostat at different thickness ratios and the single layer glass with the same thickness. Figure 6 b shows the displacement time history comparison of the first layer glass plate of the composite laminated heliostat at different thickness ratios and the single layer glass of equal thickness at the impact point.

[0083] In order to study the law of the optimal thickness ratio of composite sandwich heliostats with different thicknesses, this section also studies the influence of different thickness ratios on the dynamic response and damage mechanism of hail impact on PVB sandwich heliostats with a total thickness of 3 mm. The thickness ratio calculation conditions used are shown in Table 5.

[0084] Table 5 Thickness ratio calculation conditions

[0085]

[0086] The above five working conditions are numerically simulated in sequence, and the dynamic response results of the first layer of glass plate at the impact point of the composite laminated heliostat under the corresponding working conditions are extracted for analysis. Figure 7 a shows the maximum principal stress time history comparison diagram of the first layer glass plate of the composite laminated heliostat at different thickness ratios and the single layer glass with the same thickness. Figure 7 b shows the displacement time history comparison of the first layer glass plate of the composite laminated heliostat at different thickness ratios and the single layer glass of equal thickness at the impact point.

[0087] The displacement amplitude and maximum principal stress amplitude of the heliostat under hail impact of the single-layer heliostat and the heliostats with different PVB interlayer thicknesses are extracted, as shown in Table 6.

[0088] Table 6 Displacement amplitude and maximum principal stress amplitude of single-layer heliostat and heliostat with different PVB interlayer thickness

[0089]

[0090] from Figure 6 as well as Figure 7 It can be found that no matter the total thickness is 3mm or 4mm, the optimal thickness ratio occurs when the thickness of the PVB sandwich panel is the thickest and the back panel is the thinnest. Therefore, this section studies the velocity threshold of the composite sandwich heliostat with a total thickness of 2 to 4mm under hail impact. When the total thickness is 2mm, the thickness of the first glass panel is 0.5mm, the thickness of the PVB sandwich is 1mm, and the thickness of the back panel is 0.5mm; when the total thickness is 3mm, the thickness of the first glass panel is 0.5mm, the thickness of the PVB sandwich is 2mm, and the thickness of the back panel is 0.5mm; when the total thickness is 4mm, the thickness of the first glass panel is 0.5mm, the thickness of the PVB sandwich is 2mm, and the thickness of the back panel is 0.5mm. Figure 8 a shows the time history curve of the maximum principal stress in the first glass plate when the total thickness is 2 mm; Figure 8 b shows the time history curve of the maximum principal stress in the first glass plate when the total thickness is 3 mm; Figure 8 c shows the time history curve of the maximum principal stress in the first glass panel when the total thickness is 4 mm.

[0091] The displacement amplitude and maximum principal stress amplitude of the heliostat under hail impact with different total PVB interlayer thicknesses under the optimal thickness ratio are extracted, as shown in Table 7.

[0092] Table 7 Displacement amplitude and maximum principal stress amplitude of heliostat with different total thickness of PVB interlayer

[0093]

[0094] As can be seen from Table 3, when the interlayer material is SGP or PVB, the maximum principal stress value at the impact point of the first glass plate is 1.44 and 1.45 times the maximum principal stress value at the impact point of the single-layer heliostat, respectively. When the interlayer material is EVA, the maximum principal stress value at the impact point of the first glass plate is 1.84 times the maximum principal stress value at the impact point of the single-layer heliostat. This shows that when the interlayer material is PVB and SGP, the maximum principal stress at the impact point of the first glass plate of the composite interlayer heliostat when it is impacted by hail is closer to that of the single-layer heliostat. When the interlayer material is EVA, the maximum principal stress at the impact point of the first glass plate of the composite interlayer heliostat when it is impacted by hail is much greater than that of the single-layer heliostat. When the interlayer material is SGP or PVB, the anti-hail performance of the composite interlayer heliostat is better, while when the interlayer material is EVA, the anti-hail performance of the composite interlayer heliostat is weaker. This example shows that when selecting the type of interlayer material, PVB or SGP materials can be given priority.

[0095] From the maximum principal stress values ​​of the PVB laminated heliostat under hail impact at different total thicknesses in Table 6, it can be obtained that the optimal thickness ratio of the composite laminated heliostat with a total thickness of 4mm is 1mm thickness of the first glass plate, 2.5mm thickness of the PVB laminated layer, and 0.5mm thickness of the back plate. At the optimal thickness ratio, the composite laminated heliostat has better hail impact resistance than the single-layer heliostat. The optimal thickness ratio of the composite laminated heliostat with a total thickness of 3mm is 0.5mm thickness of the first glass plate, 2mm thickness of the PVB laminated layer, and 0.5mm thickness of the back plate. At the optimal thickness ratio, the composite laminated heliostat has better hail impact resistance than the single-layer heliostat. And it can be inferred that the optimal thickness ratio occurs when the PVB laminated layer thickness is the largest while ensuring the thinnest back plate.

[0096] It can be observed from Table 7 that when the total thickness is 2mm, the composite laminated glass plate can withstand the impact of hail in the range of 30mm to 40mm in diameter. When the total thickness is 3mm, the composite laminated heliostat can withstand the impact of hail in the range of less than 45mm. When the total thickness is 4mm, the composite laminated heliostat can withstand the impact of hail in the range of less than 50mm. With the increase of the thickness of the composite laminated heliostat, the anti-hail impact velocity threshold of the heliostat is also increasing. Domestic scholars Ji Baifeng and others have concluded that under the impact of 30mm hail, the thickness of the single-layer heliostat should be higher than 3mm, under the impact of 40mm hail, the thickness of the single-layer heliostat should be higher than 4mm, and under the impact of 50mm hail, the thickness of the single-layer heliostat should be higher than 6mm. By comparison, it is found that under the same thickness, the anti-hail impact performance of the composite laminated heliostat under the optimal thickness ratio is due to the single-layer heliostat. This has important reference value for the anti-hail design of the heliostat in terms of saving materials.

[0097] The preferred embodiments of the present invention are specifically described above, but the invention is not limited to the embodiments. Those skilled in the art may make various equivalent modifications or substitutions without violating the spirit of the invention. These equivalent modifications or substitutions are all included in the scope defined by the claims of this application.

Claims

1. A method for evaluating the hail impact resistance of a composite sandwich heliostat, characterized in that: include: Investigate the hail diameter distribution in the heliostat operating environment and determine the hail diameter range to be studied; Finite element model of hail impact heliostat is established by finite element software; The behavior of the composite sandwich heliostat impacted by hail is numerically simulated, and the anti-hail impact performance of the heliostat with different impact positions, different interlayers and different thickness ratios is quantitatively analyzed to obtain the velocity threshold of the composite sandwich heliostat under the optimal thickness ratio.

2. The method for evaluating the hail impact resistance of a composite sandwich heliostat according to claim 1, characterized in that: The steps of establishing a finite element model of hail impacting a heliostat include establishing a hail model and a finite element model of a heliostat unit sub-mirror respectively. When establishing the hail model, the method used to simulate the hail breaking process is selected as a smooth particle fluid dynamics method.

3. The method for evaluating the anti-hail impact performance of a composite sandwich heliostat according to claim 2, characterized in that: When establishing the finite element model of the heliostat unit sub-mirror, a material database is constructed according to the different types of sandwich materials that make up the heliostat unit sub-mirror.

4. The method for evaluating the hail impact resistance of a composite sandwich heliostat according to claim 1, characterized in that: When the hail impact heliostat finite element model is used, the meshing of hail and heliostat unit sub-mirrors is performed, including the selection of unit type, mesh type and mesh size, and the optimization solution is sought based on the consideration of calculation time and calculation accuracy.

5. The method for evaluating the hail impact resistance of a composite sandwich heliostat according to claim 2, characterized in that: In the numerical model of hail impact composite sandwich heliostat, S4 thin shell units are used for the first glass plate and the glass back plate of the composite sandwich heliostat reflector. The plane size of the sandwich of the composite sandwich heliostat reflector is consistent with that of the reflector. C3D8R entity units are used for simulation. The grid side length and number of grids are consistent with those of the first glass plate. In addition, the sandwich and the upper and lower glass plates are bound to form a whole. The supporting structure adopts a square cross-section hollow steel tube. C3D8R entity units are used for hail units. The meshing is performed based on the SPH method. The Conversion toparticles option is selected in the Elemem Type to convert the meshed hail into particles in the calculation. MPC multi-point constraints are performed on the reflector and the supporting structure, and the end nodes of the supporting structure are completely fixed.

6. The method for evaluating the anti-hail impact performance of a composite sandwich heliostat according to claim 1, characterized in that: The first strength theory is adopted, and the tensile strength of the material is used as the failure criterion. When the maximum tensile stress of the first layer of glass of the heliostat glass reflector exceeds its tensile strength, the reflector is judged to be damaged.

7. The method for evaluating the hail impact resistance of a composite sandwich heliostat according to claim 1, characterized in that: The steps of setting the working condition of the hail impact composite sandwich heliostat include: selecting the hail diameter, the hail impact position, the thickness of the composite sandwich heliostat, and selecting the impact speed of the hail.

8. The method for evaluating the hail impact resistance of a composite sandwich heliostat according to claim 7, characterized in that: The impact velocity of hail is selected based on the relatively fixed relationship between the falling speed of hail and the size of hail. It is assumed that the hail is only affected by gravity and air resistance during its fall. When the gravity of the hail is equal to the air resistance, the terminal velocity of the hail at this time is taken as the impact velocity of the hail.

9. The method for evaluating the anti-hail impact performance of a composite sandwich heliostat according to claim 8, characterized in that: The steps of setting the working conditions of the hail impact composite sandwich heliostat also include: determining the position of the hail impact composite sandwich heliostat according to the national standard "Test Method for Hail Impact Resistance of Solar Thermal Power Generation Glass Reflector".

10. A method for designing a heliostat, characterized in that: The method comprises the method for evaluating the anti-hail impact performance of a composite sandwich heliostat and designing a heliostat as described in any one of claims 1 to 9, and establishing a heliostat structure design optimization database, and guiding the structural design of the heliostat in combination with the hail disaster risk assessment results of the heliostat use environment.

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