Lightning stroke attachment point calculation method for flat plate structure with complex surface

Abstract

The invention discloses a lightning stroke attachment point calculation method of a complex surface flat plate structure, and aims to overcome the defects of an existing lightning stroke attachment point numerical calculation method, and on the basis that finite element software is utilized to construct a typical needle plate model based on an electric field model method, an electrode is moved downwards to simulate the thunder and lightning development process under first guidance. A pilot / corona onset criterion is established based on short-gap discharge and material corona discharge theories, a numerical simulation algorithm is provided for evaluating the lightning protection design of a complex surface flat plate structure, the determination accuracy of the attachment points of the flat plate structure with similar surface material conductivity, complex surface microstructure and no salient points is improved, the attachment point simulation algorithm is optimized, and the method is suitable for application and popularization. And tedious and high-cost test links are effectively avoided.

Description

Technical Field

[0001] The invention belongs to the technical field of lightning attachment point calculation, and in particular relates to a method for calculating lightning attachment points of a complex surface flat plate structure. Background Art

[0002] With the frequent occurrence of lightning strikes, it has become a necessary step to ensure flight safety to determine the lightning attachment points on the surface of the aircraft and to zone them for lightning in order to take necessary protective measures. Accurately evaluating the lightning attachment points on complex surfaces, especially those that can be partially equivalent to flat plates, is the key basis for aircraft lightning zoning and surface lightning protection design and evaluation. Since lightning tests are time-consuming and costly, determining lightning attachment points through numerical calculation models has the advantages of being fast, efficient, and cost-saving. At present, the calculation of lightning attachment points in China mostly uses the static electric field method and the probabilistic evaluation method based on fractal theory. The static electric field method is suitable for test models with large differences in conductivity or obvious three-dimensional geometric features. The probabilistic evaluation method based on fractal theory is suitable for the evaluation of the protective effectiveness of lightning rods. For flat plate structures with similar surface material conductivity, complex surface microstructure, and no significant protruding points, the calculation results of the above two methods are quite different from the test results. Summary of the invention

[0003] The purpose of the present invention is to provide a method for calculating the lightning attachment point of a flat plate structure with a complex surface, which solves the problem of large errors in the calculation of the lightning attachment point of a flat plate structure with similar surface materials, complex surface microstructures and no significant protruding points in the prior art.

[0004] The technical solution adopted by the present invention is a method for calculating the lightning attachment point of a complex surface flat plate structure, which is specifically implemented according to the following steps: Step 1, establish a geometric model of a complex surface flat plate structure; Step 2, define the material properties of each part of the structure; Step 3, setting the model electrical boundary conditions; Step 4: Apply to the electrode The voltage value is , at this time, except for the voltage source, the field strength on the surface of the structure and the field strength in the air are both zero; Step 5, calculating the induced electric field distribution of the structure and the surrounding air under this voltage source according to Maxwell's equations; Step 6: Based on the calculated spatial field strength distribution, determine whether a material on the surface of the flat structure has reached its own corona threshold and whether the air field strength near it has reached the air breakdown threshold. If the above two criteria are met, it is determined that the lightning strike attachment point is located in this part of the material. If not, proceed to the next step of calculation. Step 7, the electrode moves downward and continues to apply However, at this time, the initial values ​​of the surface field strength and the space field strength of the structure are no longer zero. It is necessary to inherit the results of the previous step and repeat step 5 to calculate the induced electric field. After the calculation, follow step 6 again to determine whether there is a part of the surface of the flat structure that meets the above two criteria. If not, repeat step 7 until the lightning attachment point is found.

[0005] The present invention is also characterized in that: Specifically, step 1 is to establish a three-dimensional geometric needle plate model of a complex surface flat plate structure based on the electric field model method.

[0006] Step 2 is as follows: Different materials of the flat plate structure are defined at corresponding positions of the three-dimensional geometric model of the flat plate structure established in step 1, and material parameters are attached. The material parameters include electrical conductivity and dielectric constant.

[0007] Step 3 is as follows: Determine the grounding terminal of the three-dimensional geometric model of the flat plate structure established in step 1, that is, set the grounding terminal potential to 0. At the same time, the surface potential of the air domain is also set to 0 to simulate the ground in the laboratory.

[0008] Step 4 Voltage value applied to the electrodes The calculation process is as follows: The amount of charge in the natural lightning downward leader channel Q and lightning current amplitude I The relationship is as follows: (2) In formula (2), the charge Q The unit is C, the lightning current amplitude I The unit is kA; Set the charge inside the downward pilot channel to be uniformly distributed, and add a point charge to the pilot head to simulate the large amount of charge gathered at the actual pilot head. Select the charge amount of the point charge on the pilot head for: (3) In formula (3), Unit: C; is the dielectric constant of air; is the average field strength of the streamer in front of the leader head, unit: V / m; is the radius of the pilot channel, unit: m; and lightning current amplitude I The relationship is as follows: (4) In formula (4), the lightning current amplitude is I The unit is kA; It is known that when the laboratory simulates short gap discharge, the current output by the device is I 0 According to formula (2) and formula (4), we can calculate I = I 0 The charge amount and channel radius of the downward leader of the lightning are calculated, and then the charge amount and channel radius of the downward leader of the lightning are substituted into formula (3), and the lightning current amplitude is obtained as I 0 When , the average field strength of the downlink leader head is E S0 In this calculation model, rod electrodes are used to simulate the downward leader head. Therefore, the rod electrodes have different diameters and the average field strength is E s0 , calculate the voltage required for simulation V 0 .

[0009] Step 5 is as follows: The induced electric field generated by the high voltage source in space follows the Maxwell equation, namely: (1) In formula (1), V is the unit volume; J is the unit current density; S is the unit cross-sectional area; r c is the unit charge density; n For face S The external normal direction of Unit current density J Described by Ohm's law: (5) In formula (5), is the conductivity, E is the electric field strength, represents the electric potential, Represents the gradient operator.

[0010] In step 7, the result of the previous step is inherited, and the induced electric field distribution of the structure and the air under this voltage source is calculated according to Maxwell's equations. Specifically, the initial values ​​of all variables are set to the results calculated in step 5, and then step 5 is repeated to calculate the induced electric field distribution at this time according to Maxwell's equations.

[0011] Step 7: The electrode downward distance is 100 mm.

[0012] The beneficial effects of the present invention are: The method for calculating the lightning attachment point of a flat plate structure with a complex surface of the present invention aims at the defects of the existing numerical calculation method of the lightning attachment point. On the basis of constructing a typical pin-plate model based on the electric field model method (EFM) using finite element software, the electrode is moved downward to simulate the process of the lightning leader developing downward, and the leader / corona criterion is established based on the short gap discharge and material corona discharge theory. A numerical simulation algorithm is provided for evaluating the lightning protection design of a flat plate structure with a complex surface, the accuracy of determining the attachment point of a flat plate structure with similar surface material conductivity, complex surface microstructure and no significant protruding points is improved, the attachment point simulation algorithm is optimized, the cumbersome and costly test links are effectively avoided, the test cost is greatly saved, and a solid theoretical support is provided for practical operations in the field of lightning protection engineering. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Figure 1 It is a schematic diagram of calculation of lightning attachment point of composite material flat plate; Figure 2 It is a flow chart of the method for calculating the lightning attachment point of a complex surface flat plate structure of the present invention. DETAILED DESCRIPTION

[0014] The present invention is described in detail below in conjunction with the accompanying drawings and specific implementation methods. The described embodiments are only 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 ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0015] In the following description of the present invention, the terms "first\second\third" involved are merely used to distinguish similar objects and do not represent a specific ordering of the objects. It can be understood that "first\second\third" can be interchanged with a specific order or sequence where permitted, so that the embodiments of the present application described herein can be implemented in an order other than that illustrated or described herein.

[0016] Unless otherwise defined, all technical and scientific terms used in the present invention have the same meaning as those commonly understood by those skilled in the art of the present invention. The terms used in the present invention are only for the purpose of describing the embodiments of the present application and are not intended to limit the present invention.

[0017] Example 1 This embodiment provides a method for calculating the lightning attachment point of a complex surface flat plate structure. Figure 1 As shown, short-gap discharge simulates the long-gap discharge process of natural lightning, which is also the essence of the lightning attachment point experiment; The process of short-gap discharge: under the action of high-voltage power supply, the spherical electrode (needle) generates an arc toward the complex surface flat structure, i.e., the downward leader; during the downward development of the downward leader, the surface field strength of the structure gradually increases, and when it exceeds its corona field strength, initial corona discharge occurs. The components of the corona area are multiple filamentary streamers starting from the root of the material. The charged particles in the corona area collide and transfer heat frequently, so that the corona streamers are heated to transform into upward leaders; The upward leader needs to continuously obtain energy from the head corona area in order to develop stably and continuously. After forming a stable leader, it continues to grow upward until it connects with the downward leader developing downward, forming a lightning discharge channel and completing the discharge process. like Figure 2 As shown, the method is specifically implemented according to the following steps: Step 1, establish a geometric model of a complex surface flat plate structure; Use finite element software to establish a three-dimensional geometric model of a complex surface plate structure based on the electric field model method; Step 2, define the material properties of each part of the structure; Define the material of the flat plate structure itself at the corresponding position of the three-dimensional geometric model of the flat plate structure established in step 1, and attach material parameters, which include conductivity and dielectric constant; Step 3, setting the model electrical boundary conditions; Step 4: Apply to the electrode The voltage value is , at this time, except for the voltage source, the field strength on the surface of the structure and the field strength in the air are both zero; Step 5, calculating the induced electric field distribution of the structure and the surrounding air under this voltage source according to Maxwell's equations; Step 6: Based on the calculated spatial field strength distribution, determine whether a material on the surface of the flat structure has reached its own corona threshold and whether the air field strength near it has reached the air breakdown threshold. If the above two criteria are met, it is determined that the lightning strike attachment point is located in this part of the material. If not, proceed to the next step of calculation. Step 7, the electrode moves downward and continues to apply However, at this time, the initial values ​​of the surface field strength and the space field strength of the structure are no longer zero. It is necessary to inherit the results of the previous step and repeat step 5 to calculate the induced electric field. After the calculation, follow step 6 again to determine whether there is a part of the surface of the flat structure that meets the above two criteria. If not, repeat step 7 until the lightning attachment point is found.

[0018] This embodiment only represents a preferred implementation of the method for calculating the lightning attachment point of a complex surface flat plate structure of the present invention. Any method for calculating the lightning attachment point designed using technical features similar to the present invention will fall within the protection scope of the method for calculating the lightning attachment point of a complex surface flat plate structure of the present invention.

[0019] Example 2 This embodiment provides a method for calculating the lightning attachment point of a complex surface flat plate structure. Based on Embodiment 1, step 3 is specifically as follows: Determine the grounding terminal of the three-dimensional geometric model of the flat plate structure established in step 1, that is, set the grounding terminal potential to 0. At the same time, the surface potential of the air domain is also set to 0 to simulate the ground in the laboratory.

[0020] This embodiment only represents a preferred implementation of the method for calculating the lightning attachment point of a complex surface flat plate structure of the present invention. Any method for calculating the lightning attachment point designed using technical features similar to the present invention will fall within the protection scope of the method for calculating the lightning attachment point of a complex surface flat plate structure of the present invention.

[0021] Example 3 This embodiment provides a method for calculating the lightning attachment point of a complex surface flat plate structure. Based on Embodiment 1-2, the voltage value applied to the electrode in step 4 is The calculation process is as follows: The amount of charge in the natural lightning downward leader channel Q and lightning current amplitude I The relationship is as follows: (2) In formula (2), the charge Q The unit is C, the lightning current amplitude I The unit is kA; Set the charge inside the downward pilot channel to be uniformly distributed, and add a point charge to the pilot head to simulate the large amount of charge gathered at the actual pilot head. Select the charge amount of the point charge on the pilot head for: (3) In formula (3), The unit is C; is the dielectric constant of air; is the average field strength of the streamer in front of the leader head, unit: V / m; is the radius of the pilot channel, unit: m; and lightning current amplitude I (Unit: kA) is as follows: (4) In formula (4), the lightning current amplitude is I The unit is kA; It is known that when the laboratory simulates short gap discharge, the current output by the device is I 0 According to formula (2) and formula (4), we can calculate I =I 0 The charge amount and channel radius of the downward leader of the lightning are calculated, and then the charge amount and channel radius of the downward leader of the lightning are substituted into formula (3), and the lightning current amplitude is obtained as I 0 When , the average field strength of the downlink leader head is E S0 In this calculation model, rod electrodes are used to simulate the downward leader head. Therefore, the rod electrodes have different diameters and the average field strength is E s0 , calculate the voltage that needs to be applied to it for simulation V 0 .

[0022] This embodiment only represents a preferred implementation of the method for calculating the lightning attachment point of a complex surface flat plate structure of the present invention. Any method for calculating the lightning attachment point designed using technical features similar to the present invention will fall within the protection scope of the method for calculating the lightning attachment point of a complex surface flat plate structure of the present invention.

[0023] Example 4 This embodiment provides a method for calculating the lightning attachment point of a complex surface flat plate structure. Based on Embodiments 1-3, step 5 is specifically as follows: The induced electric field generated by the high voltage source in space follows the Maxwell equation, namely: (1) In formula (1), V is the unit volume; J is the unit current density; S is the unit cross-sectional area; r c is the unit charge density; n For face S The external normal direction of Unit current density J Described by Ohm's law: (5) In formula (5), is the conductivity, E is the electric field strength, represents the electric potential, Represents the gradient operator.

[0024] This embodiment only represents a preferred implementation of the method for calculating the lightning attachment point of a complex surface flat plate structure of the present invention. Any method for calculating the lightning attachment point designed using technical features similar to the present invention will fall within the protection scope of the method for calculating the lightning attachment point of a complex surface flat plate structure of the present invention.

[0025] Example 5 This embodiment provides a method for calculating the lightning attachment point of a complex surface flat plate structure. Based on the embodiments 1-4, step 6, based on the calculated spatial field strength distribution, determines whether a certain material on the surface of the flat plate structure reaches its own corona threshold and whether the air field strength near it reaches the air breakdown threshold. If the above two criteria are met, it is determined that the lightning attachment point is located in the part of the material. If not, continue to the next step of calculation; For the criterion of the attachment point, it is first determined whether the material has reached its own corona threshold under the action of the downward leader generated by the high-voltage power supply. Corona discharge occurs on the surface of the material before it can develop into a stable upward leader. For the formation of a stable upward leader, the concept of critical streamer length is defined. It is believed that once the streamer length reaches a certain value, the upward leader can develop stably. For the long gap discharge test, the critical length for the transformation of an unstable leader into a stable leader is 2m.

[0026] This model is based on the short-gap discharge process, and the critical length of a stable upward leader is only a few millimeters or a few tenths of a millimeter. Therefore, this criterion is converted into the air field strength near the material to reach the breakdown field strength.

[0027] In summary, the criteria for simulating lightning attachment points are divided into two categories: 1) The field strength on the surface of the material reaches its own corona threshold; 2) The air field strength near the material reaches the breakdown strength threshold of the air.

[0028] This embodiment only represents a preferred implementation of the method for calculating the lightning attachment point of a complex surface flat plate structure of the present invention. Any method for calculating the lightning attachment point designed using technical features similar to the present invention will fall within the protection scope of the method for calculating the lightning attachment point of a complex surface flat plate structure of the present invention.

[0029] Example 6 This embodiment provides a method for calculating the lightning attachment point of a complex surface flat plate structure. Based on Embodiments 1-5, step 7 is as follows: the electrode is moved down 100 mm and the lightning is continuously applied. However, at this time, the initial values ​​of the surface field strength and the spatial field strength of the structure are no longer zero. It is necessary to inherit the results of the previous step and repeat step 5 to calculate the induced electric field. After the calculation, follow step 6 to determine whether there is a part of the surface of the flat structure that meets the above two criteria. If not, repeat step 7 until the lightning attachment point is found.

[0030] Among them, inheriting the result of the previous step, repeating step 5 to calculate the induced electric field distribution of the structure and the air under this voltage source according to Maxwell's equations is specifically as follows: the initial values ​​of all variables are set to the results calculated in step 5, and then repeating step 5 to calculate the induced electric field distribution at this time according to Maxwell's equations. All variables refer to the potential, electric field strength, and current density of the material and air that have been calculated in the previous step.

[0031] The electrode moves downward for 100 mm, which is a process in which the downward movement of the electrode in the present invention simulates the downward movement of the fixed electrode during the actual test.

[0032] This embodiment only represents a preferred implementation of the method for calculating the lightning attachment point of a complex surface flat plate structure of the present invention. Any method for calculating the lightning attachment point designed using technical features similar to the present invention will fall within the protection scope of the method for calculating the lightning attachment point of a complex surface flat plate structure of the present invention.

[0033] Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present invention, and that the scope of the present invention is defined by the appended claims and their equivalents.

[0034] The above is a detailed introduction to the method for calculating the lightning attachment point of a complex surface flat plate structure provided by the present invention. This article uses specific examples to illustrate the implementation of the present invention. The description of the above embodiments is only used to help understand the structure of the present invention and its core idea; at the same time, for technical personnel in this field, according to the idea of ​​the present invention, there will be changes in the specific implementation method and application scope. In summary, the content of this specification should not be understood as a limitation on this application.

Claims

1. A method for calculating the lightning attachment point of a complex surface flat plate structure, characterized in that: The specific steps are as follows: Step 1, establish a geometric model of a complex surface flat plate structure; Step 2, define the material properties of each part of the structure; Step 3, setting the model boundary conditions; Step 4: Apply to the electrode The voltage value is , at this time, except for the voltage source, the field strength on the surface of the structure and the field strength in the air are both zero; Step 5, calculating the induced electric field distribution of the structure and the surrounding air under this voltage source according to Maxwell's equations; Step 6: Based on the calculated spatial field strength distribution, determine whether a material on the surface of the flat structure has reached its own corona threshold and whether the air field strength near it has reached the air breakdown threshold. If the above two criteria are met, it is determined that the lightning strike attachment point is located in this part of the material. If not, proceed to the next step of calculation. Step 7, the electrode moves downward and continues to apply However, at this time, the initial values ​​of the surface field strength and the space field strength of the structure are no longer zero. It is necessary to inherit the results of the previous step and repeat step 5 to calculate the induced electric field. After the calculation, follow step 6 again to determine whether there is a part of the surface of the flat structure that meets the above two criteria. If not, repeat step 7 until the lightning attachment point is found.

2. The method for calculating the lightning attachment point of a complex surface flat plate structure according to claim 1 is characterized in that: Specifically, the step 1 is to establish a three-dimensional geometric model of a complex surface flat plate structure based on an electric field model method.

3. The method for calculating the lightning strike attachment point of a complex surface flat plate structure according to claim 2 is characterized in that: The step 2 is specifically as follows: Different materials of the flat plate structure are defined at corresponding positions of the three-dimensional geometric model of the flat plate structure established in step 1, and material parameters are attached. The material parameters include electrical conductivity and dielectric constant.

4. The method for calculating the lightning attachment point of a complex surface flat plate structure according to claim 3 is characterized in that: The step 3 is specifically as follows: Determine the grounding terminal of the three-dimensional geometric model of the flat plate structure established in step 1, that is, set the grounding terminal potential to 0. At the same time, the surface potential of the air domain is also set to 0 to simulate the ground in the laboratory.

5. The method for calculating the lightning attachment point of a complex surface flat plate structure according to claim 4 is characterized in that: The voltage value applied to the electrode in step 4 The calculation process is as follows: The amount of charge in the downward leader channel of natural lightning Q and lightning current amplitude I The relationship is as follows: （2） In formula (2), the charge Q The unit is C, the lightning current amplitude I The unit is kA; Set the charge inside the downward pilot channel to be uniformly distributed, and add a point charge to the pilot head to simulate the large amount of charge gathered at the actual pilot head. Select the charge amount of the point charge at the pilot head for: （3） In formula (3), The unit is C; is the dielectric constant of air; is the average field strength of the streamer in front of the leader head, unit: V / m; is the radius of the pilot channel, unit: m; and lightning current amplitude I The relationship is as follows: （4） In formula (4), the lightning current amplitude is I The unit is kA; It is known that when the laboratory simulates short gap discharge, the current output by the device is I 0, according to formula (2) and formula (4), calculate the current I = I The charge amount and channel radius of the downward leader of the lightning at time 0, and then substitute the calculated charge amount and channel radius of the downward leader of the lightning into formula (3), and the lightning current amplitude is obtained I At 0, the average field strength of the downlink leader head is E S0 In this calculation model, rod electrodes are used to simulate the downward leader head. Therefore, the rod electrodes have different diameters and the average field strength is E s0 , calculate the voltage that needs to be applied to it for simulation V 0.

6. The method for calculating the lightning attachment point of a complex surface flat plate structure according to claim 5 is characterized in that: The step 5 is specifically as follows: The induced electric field generated by the high voltage source in space follows the Maxwell equation, namely: （1） In formula (1), V is the unit volume; J is the unit current density; S is the unit cross-sectional area; r c is the unit charge density; n For face S The external normal direction of Unit current density J Described by Ohm's law: （5） In formula (5), is the conductivity, E is the electric field strength, represents the electric potential, Represents the gradient operator.

7. The method for calculating the lightning attachment point of a complex surface flat plate structure according to claim 1 is characterized in that: In step 7, the result of the previous calculation is inherited, and the induced electric field distribution of the structure and the air under this voltage source is calculated according to Maxwell's equations. Specifically, the initial values ​​of all variables are set to the results calculated in step 5, and then step 5 is repeated to calculate the induced electric field distribution at this time according to Maxwell's equations.

8. The method for calculating the lightning attachment point of a complex surface flat plate structure according to claim 1 is characterized in that: In step 7, the electrode downward distance is 100 mm.

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