Calculation Method for Lightning Strike Attachment Points on Complex Surface Flat Plate Structures

Abstract

The present invention discloses a method for calculating the lightning strike attachment points of a flat structure with a complex surface. Aiming at the defects of the existing numerical calculation methods for lightning strike attachment points, based on the finite element software and on the basis of constructing a typical needle-plate model using the electric field model method, the process of downward development of the lightning leader is simulated by moving the electrode downward, and a leader / corona inception criterion is established based on the short-gap discharge and material corona discharge theories, providing a numerical simulation algorithm for evaluating the lightning protection design of a flat structure with a complex surface, improving the determination accuracy of the attachment points of a flat structure with similar surface material conductivity, complex surface microstructure, and no significant protruding points, optimizing the attachment point simulation algorithm, and effectively avoiding the cumbersome and costly test links.

Description

Technical Field

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

[0002] With the frequent occurrence of lightning strikes, determining the lightning strike attachment points on the surface of an aircraft and performing lightning zone division on it to take necessary protection measures have become essential steps to ensure flight safety. Accurately evaluating the lightning strike attachment points on a complex surface, especially a structure whose local part can be equivalent to a flat plate, is the key basis for aircraft lightning zone division and surface lightning protection design and evaluation. Since lightning strike tests are time-consuming and costly, determining lightning strike attachment points through a numerical calculation model has the advantages of being fast, efficient, and cost-saving. Currently, static electric field method and probability evaluation method based on fractal theory are mostly used for lightning strike attachment point calculation in China. The static electric field method is applicable to test models with large differences in conductivity or obvious three-dimensional geometric features, and the probability evaluation method based on fractal theory is applicable to the protection efficiency evaluation of lightning rods. For flat plate structures with similar surface material conductivity, complex surface microstructures, and no significant protruding points, the calculation results of the above two methods differ greatly from the test results. Summary of the Invention

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

[0004] The technical solution adopted by the present invention is that the method for calculating lightning strike attachment points on a flat plate structure with a complex surface is specifically implemented according to the following steps:

[0005] Step 1, establish a geometric model of the flat plate structure with a complex surface;

[0006] Step 2, define the material properties of each part of the structure;

[0007] Step 3, set the electrical boundary conditions of the model;

[0008] Step 4, apply a voltage value to the electrode. At this time, except for the voltage source, the surface field strength of the structure and the air field strength are both zero;

[0009] Step 5, calculate the induced electric field distribution of the structure and the surrounding air under this voltage source according to Maxwell's equations;

[0010] Step 6: Based on the calculated spatial field strength distribution, determine whether a certain material on the surface of the flat structure reaches its own corona threshold and whether the air field strength near it reaches the air breakdown threshold. If both of the above criteria are met, it is determined that the lightning attachment point in this case is located on this part of the material; if not, continue with the next calculation.

[0011] Step 7: The electrode moves downward and continues to apply , but at this time, the initial values of the field strength on the surface of the structure and the spatial field strength are no longer zero. It is necessary to inherit the results after the previous calculation and repeat Step 5 on this basis to calculate the induced electric field. After the calculation, again judge according to Step 6 whether there is a certain part on the surface of the flat structure that meets the above two criteria. If not, repeat Step 7 until the lightning attachment point is found.

[0012] The features of the present invention also lie in:

[0013] Specifically, Step 1 is to establish a three-dimensional geometric needle-plate model of a flat structure with a complex surface based on the electric field model method.

[0014] Specifically, Step 2 is:

[0015] Define different materials of the flat structure at the corresponding positions of the three-dimensional geometric model of the flat structure established in Step 1, and attach material parameters, including conductivity and permittivity.

[0016] Specifically, Step 3 is:

[0017] Determine the grounding end of the three-dimensional geometric model of the flat structure established in Step 1, that is, set the potential of the grounding end to 0. At the same time, set the potential of the lower surface of the air domain to 0 to simulate the ground in the laboratory.

[0018] The calculation process of the voltage value applied to the electrode in Step 4 is specifically as follows:

[0019] The electric charge Q in the downward leader channel in nature I has the following relationship with the lightning current amplitude

[0020] (2)

[0021] In formula (2), the unit of the electric charge Q is C, and the unit of the lightning current amplitude I is kA;

[0022] It is assumed that the charges inside the downward leader channel are evenly distributed, and at the same time, a point charge is added to the leader head to simulate the large amount of charges concentrated at the actual leader head. The selected electric charge of the point charge at the leader head is:

[0023] (3)

[0024] In formula (3), The unit of is C; is the dielectric constant of air; is the average field strength of the streamer in front of the leader head, and the unit is V / m; is the radius of the leader channel, and the unit is m; and the lightning current amplitude I The relationship is as follows:

[0025] (4)

[0026] In formula (4), the lightning current amplitude I The unit of is kA;

[0027] It is known that when simulating short-gap discharge in the laboratory, the current output by the device is I 0 , according to formula (2) and formula (4), calculate the charge and channel radius of the lightning downward leader at this time, that is I = I 0 When, then substitute the calculated charge and channel radius of the lightning downward leader into formula (3) to obtain the lightning current amplitude as I 0 When, the average field strength generated by the downward leader head is E S0 , this calculation model uses a rod electrode to simulate the downward leader head. Therefore, due to different diameters of the rod electrode, and then according to the average field strength E s0 , calculate the voltage V 0 that needs to be applied for the simulation.

[0028] Step 5 is specifically:

[0029] The induced electric field generated by the high-voltage source in space follows Maxwell's equations, that is:

[0030] (1)

[0031] 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 volume charge density; n is the outer normal of the surface S ;

[0032] The unit current density J is described by Ohm's law:

[0033] (5)

[0034] In formula (5), is the conductivity,[[]] E is the electric field strength,[[]] represents the electric potential,[[]] represents the gradient operator.[[]]

[0035] In step 7, inherit the result calculated in the previous step, and calculate the induced electric field distribution of the structure and air under this voltage source according to Maxwell's equations. Specifically: set the initial values of all variables to the result calculated in step 5, and then repeat step 5 to calculate the induced electric field distribution at this time according to Maxwell's equations.[[]]

[0036] In step 7, the downward distance of the electrode is 100 mm.[[]]

[0037] The beneficial effects of the present invention are as follows:[[]]

[0038] The calculation method of lightning attachment points for the complex surface flat plate structure of the present invention aims at the defects of the existing numerical calculation methods for lightning attachment points. Based on the electric field model method (EFM) using finite element software to construct a typical needle-plate model, the process of downward development of the lightning leader is simulated by moving the electrode downward, and the leader / corona initiation criterion is established based on the short-gap discharge and material corona discharge theories, providing a numerical simulation algorithm for evaluating the lightning protection design of complex surface flat plate structures, improving the determination accuracy of attachment points for flat plate structures with similar surface material conductivities, complex surface microstructures, and no significant protrusions, optimizing the attachment point simulation algorithm, effectively avoiding the cumbersome and costly test links, greatly saving the test cost, and providing a solid theoretical support for the practical operation in the field of lightning protection engineering.[[]] Description of the Drawings[[]]

[0039] Figure 1 is a schematic diagram for calculating the lightning attachment point of a composite material flat plate;[[]]

[0040] Figure 2 is a flowchart of the calculation method of lightning attachment points for the complex surface flat plate structure of the present invention.[[]] Detailed Embodiments[[]]

[0041] The present invention will be described in detail below in conjunction with the drawings and specific embodiments. The described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts fall within the scope of protection of the present invention.[[]]

[0042] In the following description of the present invention, the terms "first", "second", and "third" are only used to distinguish similar objects and do not represent a specific order for the objects. It can be understood that, where permitted, "first", "second", and "third" can be interchanged in a specific order or sequence so that the embodiments of the present application described herein can be implemented in an order other than that illustrated or described herein.

[0043] Unless otherwise defined, all technical and scientific terms used in the present invention have the same meaning as commonly understood by those skilled in the technical field to which the present invention belongs. 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.

[0044] Embodiment 1

[0045] This embodiment provides a method for calculating the lightning strike attachment points of a complex surface flat structure. As Figure 1 shown, the long-gap discharge process of natural lightning is simulated by short-gap discharge, which is also the essence of the lightning strike attachment point experiment;

[0046] Process of short-gap discharge: Under the action of a high-voltage power supply, a spherical electrode (needle) generates an arc towards the complex surface flat structure, i.e., a downward leader; during the downward development of the downward leader, the field strength on the structure surface gradually increases. When it exceeds its corona field strength, initial corona discharge occurs. The corona region consists of multiple filamentary streamers starting from the root of the material. The charged particles in the corona region collide and transfer heat frequently, causing the corona streamers to be heated and converted into upward leaders;

[0047] The upward leader needs to continuously obtain energy from the head corona region to develop stably and continuously. After forming a stable leader, it continues to grow upward until it connects with the downward-developing downward leader to form a lightning discharge channel and complete the discharge process;

[0048] As Figure 2 shown, this method is specifically implemented according to the following steps:

[0049] Step 1: Establish a geometric model of the complex surface flat structure;

[0050] Use finite element software to establish a three-dimensional geometric model of the complex surface flat structure based on the electric field model method;

[0051] Step 2: Define the material properties of each part of the structure;

[0052] Define the material of the flat structure itself at the corresponding positions of the three-dimensional geometric model of the flat structure established in Step 1 and attach material parameters, including conductivity and permittivity;

[0053] Step 3: Set the electrical boundary conditions of the model;

[0054] Step 4: Apply a voltage value to the electrode. At this time, except for the voltage source, the surface field strength of the structure and the air field strength are both zero;

[0055] Step 5: Calculate the induced electric field distribution of the structure and the surrounding air under this voltage source according to Maxwell's equations;

[0056] Step 6: Based on the calculated spatial field strength distribution, determine 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 in this case is located in this part of the material. If not, continue with the next calculation;

[0057] Step 7: Move the electrode downward and continue to apply , but at this time, the initial values of the surface field strength of the structure and the spatial field strength are no longer zero. It is necessary to inherit the results of the previous calculation. On this basis, repeat Step 5 to calculate the induced electric field, and then judge again according to Step 6 whether there is a certain part on the surface of the flat plate structure that meets the above two criteria. If not, repeat Step 7 until the lightning attachment point is found.

[0058] This embodiment only represents the preferred implementation manner of the calculation method for the lightning attachment point of the complex surface flat plate structure of the present invention. Any calculation method for the lightning attachment point designed by using similar technical features to the present invention will fall within the protection scope of the calculation method for the lightning attachment point of the complex surface flat plate structure of the present invention.

[0059] Embodiment 2

[0060] This embodiment provides a calculation method for the lightning attachment point of a complex surface flat plate structure. On the basis of Embodiment 1, Step 3 is specifically as follows:

[0061] Determine the grounding end of the three-dimensional geometric model of the flat plate structure established in Step 1, that is, set the potential of the grounding end to 0, and at the same time, set the potential of the lower surface of the air domain to 0 to simulate the earth in the laboratory.

[0062] This embodiment only represents the preferred implementation manner of the calculation method for the lightning attachment point of the complex surface flat plate structure of the present invention. Any calculation method for the lightning attachment point designed by using similar technical features to the present invention will fall within the protection scope of the calculation method for the lightning attachment point of the complex surface flat plate structure of the present invention.

[0063] Embodiment 3

[0064] This embodiment provides a calculation method for the lightning attachment point of a complex surface flat plate structure. On the basis of Embodiments 1-2, the calculation process of the voltage value applied to the electrode in Step 4 is specifically as follows:

[0065] The electric charge quantity of the downward leader channel in nature Q and the lightning current amplitude I are related as follows:

[0066] (2)

[0067] In formula (2), the unit of the electric charge quantity Q is C, and the unit of the lightning current amplitude I is kA;

[0068] It is assumed that the charges are evenly distributed inside the downward leader channel. At the same time, a point charge is added to the leader head to simulate the large amount of charges accumulated at the actual leader head. The electric charge quantity of the point charge at the leader head is:

[0069] (3)

[0070] In formula (3), the unit is C; is the permittivity of air; is the average field strength of the streamer in front of the leader head, unit: V / m; is the radius of the leader channel, unit: m; and the lightning current amplitude I (unit: kA)are related as follows:

[0071] (4)

[0072] In formula (4), the unit of the lightning current amplitude I is kA;

[0073] It is known that when simulating short-gap discharge in the laboratory, the current output by the equipment is I 0 . According to formula (2) and formula (4), the electric charge quantity and channel radius of the lightning downward leader at this time, that is I = I 0 are calculated. Then, the calculated electric charge quantity and channel radius of the lightning downward leader are substituted into formula (3) to obtain the average field strength of the generated downward leader head when the lightning current amplitude is I 0 is E S0 . In this calculation model, a rod electrode is used to simulate the downward leader head. Therefore, due to different diameters of the rod electrode, and then according to the average field strength E s0 , the voltage V 0 that needs to be applied to it for simulation is calculated.

[0074] This embodiment only represents the preferred implementation of the lightning strike attachment point calculation method for the complex surface flat structure of the present invention. Any lightning strike attachment point calculation method designed with technical features similar to those of the present invention will fall within the protection scope of the lightning strike attachment point calculation method for the complex surface flat structure of the present invention.

[0075] Embodiment 4

[0076] This embodiment provides a lightning strike attachment point calculation method for a complex surface flat structure. On the basis of Embodiments 1-3, step 5 is specifically as follows:

[0077] The induced electric field generated by the high-voltage source in space follows Maxwell's equations, that is:

[0078] (1)

[0079] 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 volume charge density; n is the S outer normal of the surface;

[0080] The unit current density J is described by Ohm's law:

[0081] (5)

[0082] In formula (5), is the conductivity, E is the electric field strength, represents the electric potential, represents the gradient operator.

[0083] This embodiment only represents the preferred implementation of the lightning strike attachment point calculation method for the complex surface flat structure of the present invention. Any lightning strike attachment point calculation method designed with technical features similar to those of the present invention will fall within the protection scope of the lightning strike attachment point calculation method for the complex surface flat structure of the present invention.

[0084] Embodiment 5

[0085] This embodiment provides a lightning strike attachment point calculation method for a complex surface flat structure. On the basis of Embodiments 1-4, in step 6, based on the calculated spatial field strength distribution, it is judged whether a certain material on the surface of the flat 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 strike attachment point of this time is located in this part of the material. If not, the next step of calculation is continued;

[0086] For the criterion of the attachment point, it is first determined whether the material reaches its own corona threshold under the action of the downward leader generated by the high-voltage power supply. Only when corona discharge occurs on the material surface can a stable upward leader develop. For the formation of a stable upward leader, the concept of the critical streamer length is defined. It is considered 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 conversion from an unstable leader to a stable leader is 2m.

[0087] However, this model is based on the short-gap discharge process. The critical length of the stable upward leader only needs to reach a few millimeters or a fraction of a millimeter. Therefore, this criterion is converted into the air field strength near the material reaching the breakdown field strength.

[0088] In summary, the criteria for simulating the lightning strike attachment point are divided into two:

[0089] 1) The field strength on the material surface reaches its own corona threshold;

[0090] 2) The air field strength near the material reaches the breakdown strength threshold of the air.

[0091] This embodiment only represents the preferred implementation manner of the calculation method for the lightning strike attachment point of the complex surface flat structure of the present invention. Any calculation method for the lightning strike attachment point designed by using similar technical features to the present invention will fall within the protection scope of the calculation method for the lightning strike attachment point of the complex surface flat structure of the present invention.

[0092] Embodiment 6

[0093] This embodiment provides a calculation method for the lightning strike attachment point of a complex surface flat structure. On the basis of Embodiments 1-5, step 7 is specifically as follows: The electrode moves downward by 100 mm, and continue to apply , but at this time, the initial values of the field strength on the structure surface and the space field strength are no longer zero, and the results calculated in the previous step need to be inherited. On this basis, repeat step 5 to calculate the induced electric field, and after the calculation, judge again according to step 6 whether a certain part of the flat structure surface satisfies the above two criteria. If not, repeat step 7 until the lightning strike attachment point is found.

[0094] Among them, inheriting the results calculated in the previous step and repeating step 5 to calculate the induced electric field distribution of the structure and air under this voltage source according to Maxwell's equations is specifically as follows: Set the initial values of all variables to the results calculated in step 5, and then repeat step 5 to calculate the induced electric field distribution at this time. All variables refer to the electric potential, electric field strength, and current density of the material and air that have been calculated in the previous step.

[0095] The electrode moving downward by 100 mm is a process in which the present invention uses the downward movement of the electrode to simulate the downward development of the downward leader generated by the fixed electrode in the actual test process.

[0096] This embodiment only represents the preferred implementation of the lightning strike attachment point calculation method for the complex surface flat plate structure of the present invention. Any lightning strike attachment point calculation method designed with technical features similar to those of the present invention will fall within the protection scope of the lightning strike attachment point calculation method for the complex surface flat plate structure of the present invention.

[0097] Although the embodiments of the present invention have been shown and described, for those of ordinary skill in the art, it can be understood that various changes, modifications, substitutions, and variations can be made to these embodiments without departing from the principles and spirit of the present invention. The scope of the present invention is defined by the appended claims and their equivalents.

[0098] The above has introduced in detail a lightning strike attachment point calculation method for a complex surface flat plate structure provided by the present invention. Specific examples are used herein to elaborate on the implementation manners of the present invention. The description of the above embodiments is only for helping to understand the structure and its core idea of the present invention; at the same time, for those skilled in the art, according to the idea of the present invention, there will be changes in the specific implementation manners and application scopes. In summary, the content of this specification should not be construed as a limitation to 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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