A design method of variable recoil length of artillery based on hybrid excitation control under different charges

Abstract

The application discloses a design method of variable recoil length of a cannon under different charges based on hybrid excitation control, and establishes a structure model of a hybrid excitation eddy current recoil brake; a finite element model of the recoil brake is established in COMSOL, and steady-state and transient-state solutions are carried out under different charges, so that the recoil displacement and the eddy current damping force under different charges and different currents are obtained; the optimal Latin hypercube method is adopted to carry out simulation analysis in COMSOL, so that a plurality of groups of data of the eddy current damping force and the speed under different charges and different currents are obtained, the charge and the current are taken as inputs, the eddy current damping force and the speed are taken as outputs, and a BP neural network is trained; a control system based on the Comsol operation module and the neural network is established in Simulink, the minimum difference between the peak value and the valley value of the resistance is taken as an optimization target, current optimization is carried out, the optimized current is brought into the Comsol, and finally, the eddy current damping force curve with the optimized'saddle' effect is obtained. The application can provide a new reference direction for engineering application of the variable recoil length of the cannon.

Description

TECHNICAL FIELD

[0001] The application relates to a recoil displacement control technology of a gun, in particular to a variable recoil length design method of a gun under different charges based on hybrid excitation control. BACKGROUND

[0002] The gun has a large difference in bore force under different charges, so that the recoil distance may be too long or too short, resulting in problems such as damage to the barrel and failure to eject the shell. The stability of the overall structure of the gun is affected. The variable recoil length gun can limit the recoil of the gun under different charge numbers within a certain length, has the advantages of optimizing the recoil structure, improving the large charge angle, and reducing the weight of the recoil device. The variable charge number design of the hydraulic recoil device is usually to adjust the relationship between the flow hole area and the recoil displacement, and there are problems such as complex structure and great difficulty in design and processing. The eddy current recoil machine is a new type of recoil machine based on electromagnetic induction principle, and the hybrid excitation eddy current recoil machine can realize resistance control by adjusting the external input current, and has great advantages in the design of variable recoil length.

[0003] For the problem of variable recoil length of the gun, Li Hui-bin designed a hydraulic variable recoil length recoil device overall scheme, the flow hole area formed by the angle change control cylinder and the rod was changed to change the size of the recoil resistance; and for the control problem of damping force, Arunesh Kumar Singh et al. developed a fuzzy logic controller, which can automatically change the size of the excitation current according to the required braking force of the electromagnetic damper. At the same time, an artificial neural network controller is designed, which can give more reliable and accurate results in the same time compared with the fuzzy controller; He et al. designed a fuzzy controller based on matlab for the eddy current electro-hydraulic hybrid braking system, and verified and analyzed the performance of the eddy current electro-hydraulic hybrid braking system. At present, the method for controlling the variable recoil length of the gun is mainly hydraulic, but its structure is complex and prone to liquid leakage, sealing and other problems, while the variable recoil length structure under hybrid excitation control is simpler and more reliable, and the research in this aspect is still relatively short. SUMMARY

[0004] The purpose of the present application is to provide a variable recoil length design method of a gun under different charges based on hybrid excitation control, which provides a certain design direction for controlling the variable recoil length of the gun.

[0005] The technical scheme of the present application is as follows: a variable recoil length method of a gun under different charges based on hybrid excitation control, comprising the following steps:

[0006] Step 1, establish a hybrid excitation eddy current recoil machine structure model, analyze the magnetic induction lines and magnetic circuit, and perform constant current simulation analysis and verification to select the optimal scheme structure;

[0007] Step 2, establish the recoil brake finite element model in COMSOL, solve the steady state and transient state under different charges, and obtain the recoil displacement and eddy current damping force under different charges and currents;

[0008] Step 3, use the optimal Latin hypercube method to perform simulation analysis in COMSOL, obtain multiple sets of data of eddy current damping force and speed under different charges and currents, take charge and current as input, take eddy current damping force and speed as output, train the BP neural network, establish a control system based on the Comsol running module and neural network in Simulink, take the minimum difference between the peak and valley values of the resistance as the optimization objective, optimize the current, and finally obtain the eddy current damping force curve optimized for the "saddle" effect.

[0009] Further, step 1, establish a hybrid excitation eddy current recoil brake structure model, perform magnetic induction line and magnetic circuit analysis, and perform constant current simulation analysis and verification to select the optimal scheme structure, wherein:

[0010] Three hybrid excitation eddy current recoil brake structure models are constructed, and the hybrid excitation eddy current recoil brake structure model is divided into two parts, primary and secondary, wherein the barrel, permanent magnet, magnetic shoe and coil constitute the primary, and the secondary is composed of the inner and outer cylinders; but the arrangement and distribution of the permanent magnet and the coil are different, which are arranged according to the cross arrangement of the permanent magnet and the coil, the coil outside the permanent magnet inside, and the coil inside the permanent magnet outside; when the gun is fired, the primary part moves backward under the recoil force, and relative motion occurs with the secondary part, the magnetic flux in the inner cylinder changes to generate induced electromotive force to form eddy current, and the electromagnetic damping force generated by the eddy current under the action of the magnetic field achieves the recoil effect.

[0011] Under the condition that the number of turns and the size of the current are consistent, the barrel is simulated at a speed of 5m / s. The electromagnetic damping force generated under the three schemes is compared, and the structure that can generate the maximum eddy current damping force under the same conditions is selected as the optimal structure.

[0012] Further, step 1, establish a hybrid excitation eddy current recoil brake structure model, perform magnetic induction line and magnetic circuit analysis, and perform constant current simulation analysis and verification to select the optimal scheme structure, wherein:

[0013] Under the condition that the number of turns and the size of the current are consistent, the barrel is simulated at a speed of 5m / s. The electromagnetic damping force generated under the three schemes is compared, and the structure that can generate the maximum eddy current damping force under the same conditions is selected as the optimal structure.

[0014] Further, step 2, a recoil brake finite element model is established in COMSOL, and steady-state and transient solutions are carried out under different charges to obtain the recoil displacement and eddy current damping force under different charges and currents, and the specific method is as follows:

[0015] A recoil brake finite element model is established in COMSOL, and the recoil brake finite element model adopts a two-dimensional axisymmetric model of a hybrid excitation eddy current recoil brake, including a barrel, a permanent magnet, a coil winding, an inner cylinder, an outer cylinder and an air domain;

[0016] Material parameters are set, including barrel material, permanent magnet material, coil winding material, inner cylinder material, outer cylinder material and air domain;

[0017] Initial conditions and boundary conditions are set, including bore force, recoil mechanism force, coil turns and current;

[0018] The constitutive relationship of the moving rod, the permanent magnet, the coil winding, the inner cylinder, the outer cylinder and the air domain is determined;

[0019] The recoil total differential equation is set, and the unknown quantity is constrained;

[0020] Overall meshing is carried out, and each part is discretized, and different grid elements are used for each different part, wherein the moving rod, the permanent magnet and the coil winding are set as dynamic grids, and the remaining parts are set as fixed grids, and the movement of the dynamic grid is realized by the recoil total differential equation.

[0021] Further, in step 3, step 3, the optimal Latin hypercube method is adopted to carry out simulation analysis in COMSOL to obtain a plurality of groups of data of eddy current damping force and speed under different charges and currents, to take charge and current as input, to take eddy current damping force and speed as output, to train a BP neural network, to establish a control system based on a Comsol running module and a neural network in Simulink, to take the minimum difference between the peak value and the valley value of the resistance as the optimization target, to optimize the current, to bring the optimized current into Comsol, and to finally obtain an eddy current damping force curve with optimized "saddle" effect, wherein:

[0022] The control system based on the Comsol operation module and the neural network is established in Simulink, the expected damping force is input to start with the speed of 0, the expected current is obtained by BP neural network calculation, due to environmental problems, the expected current is not more than 300A at most, the expected current is compared with 300A by using the Simulink comparison module, the smaller value before 12mm is input into the COMSOL module through the Simulink timing module, the stable 280A current after 12mm is input into the COMSOL module, the electromagnetic damping force, the setback displacement, the acceleration and the speed are calculated, and the calculated speed is returned to the BP neural network to calculate the next time, finally, the expected damping force is adjusted according to the calculation result, and the cycle is repeated until the current reaches the expected effect, the calculation is completed, and the calculation result is saved, the current calculation result is brought into the Comsol, and the electromagnetic damping force curve of the eddy current damper with the optimized'saddle' effect is finally obtained.

[0023] A variable recoil length system of a cannon under different charges based on hybrid excitation control, implementing the design method of the variable recoil length system of the cannon under different charges based on hybrid excitation control, and realizing the COMSOL-Simulink combined simulation of the hybrid excitation eddy current recoil brake electromagnetic resistance control based on BP neural network.

[0024] Compared with the prior art, the present application has the following advantages: (1) the hybrid excitation recoil brake is used to control the variable recoil length of the cannon, the structure is simple and reliable, and problems such as liquid leakage and sealing do not need to be considered; (2) through further optimization of the control model parameters, the stability of the resistance is effectively improved, and the engineering value is stronger. BRIEF DESCRIPTION OF DRAWINGS

[0025] Figure 1 It is the structure and magnetic circuit distribution of three hybrid excitation type eddy current recoil brakes.

[0026] Figure 2 It is the damping force comparison of three hybrid excitation type eddy current recoil brakes under constant current and constant speed.

[0027] Figure 3 It is the structure and mesh division of the hybrid excitation type eddy current recoil brake.

[0028] Figure 4 It is the setback displacement comparison of the hybrid excitation type eddy current recoil brake under different charges and different currents.

[0029] Figure 5 It is the electromagnetic damping force curve under the first charge before optimization.

[0030] Figure 6 It is the COMSOL-Simulink combined simulation flowchart of the hybrid excitation type eddy current recoil brake.

[0031] Figure 7 This is a Simulink flowchart.

[0032] Figure 8 The damping force curve of the hybrid excitation electromagnetic damper under charge 0, obtained by COMSOL-Simulink co-simulation optimization in this invention, is shown.

[0033] Figure 9 The damping force curve of the hybrid excitation electromagnetic damper under charge 1, obtained by COMSOL-Simulink co-simulation optimization in this invention, is shown. Detailed Implementation

[0034] To make the intent, technical implementation, and advantages of this application clearer, the following sections will elaborate on them with accompanying drawings and specific examples. It should be clarified that the specific implementation examples shown here are merely for illustrating the core ideas of this application and are not intended to limit it in any way.

[0035] A method for designing variable recoil length of artillery under different propellant charges based on hybrid excitation control includes the following steps:

[0036] Step 1: Three different hybrid excitation eddy current deceleration mechanism structures are proposed. Magnetic field lines and magnetic circuits are analyzed for each of the three structures, and constant current simulation analysis is performed for verification.

[0037] Figure 1 This paper presents three structural schemes and corresponding magnetic circuit distributions for a hybrid-excitation eddy current recoil brake. All three schemes consist of a primary and a secondary stage. The primary stage comprises the barrel, permanent magnet, magnetic shoe, and coil, while the secondary stage consists of inner and outer cylinders. The main difference between the three schemes lies in the arrangement of the permanent magnet and coil: a staggered arrangement, a coil-on-outside permanent magnet arrangement, and a coil-on-outside permanent magnet arrangement. When the cannon fires, the primary stage experiences recoil and moves backward, creating relative motion with the secondary stage. This changes the magnetic flux in the inner cylinder, generating an induced electromotive force that forms eddy currents. These eddy currents, under the influence of the magnetic field, produce electromagnetic damping force, achieving the recoil braking effect.

[0038] Depend on Figure 1 The comparison shows that among the three schemes, Scheme 1 has the weakest magnetic field strength. The main difference between Scheme 2 and Scheme 3 lies in the different positions of the coil and the permanent magnet. The magnetic flux flow directions of Scheme 2 and Scheme 3 are basically the same, but during the movement, the magnetic field strength generated inside the coil is much smaller than the magnetic field generated inside the permanent magnet. Compared with Scheme 2, Scheme 3 has the permanent magnet on the outside, and the permanent magnet has a greater impact on the magnetic field strength at the air gap than the coil. Therefore, Scheme 3 has the strongest magnetic field strength.

[0039] In the case of consistent winding number and current size, the simulation is carried out when the barrel moves at a speed of 5 m / s. The electromagnetic damping forces generated in the three schemes are compared, the structure capable of generating the maximum electromagnetic eddy current damping force under the same conditions is obtained, and the optimal structure is selected.

[0040] Step 2, a brake finite element model is established in COMSOL, each structure size, material, grid and differential relationship between each parameter are given, and then steady-state and transient solutions are carried out under different charges to obtain the electromagnetic eddy current damping force and speed under different charges and currents, wherein the grid division is as shown in Figure 3

[0041] Step 3, the initial value range of the current parameter is determined through multiple attempts, sample points are generated by using optimal Latin hypercube, a large number of simulation analysis is carried out to obtain a plurality of groups of data of electromagnetic eddy current damping force and speed under different charges and currents, a BP neural network is trained and generated, and then the BP neural network is substituted into COMSOL-Simulink joint simulation for current optimization, and the minimum difference between the peak value and the valley value of the resistance is selected as the optimization target.

[0042] The application proposes to use a hybrid excitation brake to achieve the purpose of variable recoil length, the size of the damping force is changed by adjusting the input current, and the damping force fluctuation is optimized through joint simulation, which can provide a new reference direction for engineering application of variable recoil length of artillery.

[0043] Embodiment

[0044] In order to verify the effectiveness of the scheme, the recoil displacement of different charges of the hybrid excitation type electromagnetic eddy current brake is controlled by using commercial software COMSOL and MATLAB Simulink module, and the specific method is as follows:

[0045] Step 1, three different hybrid excitation type electromagnetic eddy current brake structures are proposed, the magnetic induction lines and the magnetic circuit of the three structures are analyzed, and the constant current simulation analysis is verified, and the optimal scheme structure is selected.

[0046] Figure 1 The three structure schemes of the hybrid excitation type electromagnetic eddy current brake and the corresponding magnetic circuit distribution. The hybrid excitation type electromagnetic eddy current brake in the three schemes can be divided into two parts, the primary and the secondary, the barrel, the permanent magnet, the magnetic shoe and the coil constitute the primary, and the secondary is composed of the inner and outer cylinders. The three schemes mainly differ in the arrangement and distribution of the permanent magnet and the coil, which are respectively arranged according to the cross arrangement of the permanent magnet and the coil, the coil outside the permanent magnet inside and the coil inside the permanent magnet outside. When the artillery is fired, the primary part moves backward under the action of the recoil force, and the secondary part moves relatively, the magnetic flux in the inner cylinder changes to generate an induced electromotive force to form eddy current, and the electromagnetic damping force generated by the eddy current under the action of the magnetic field achieves the effect of brake.​

[0047] In the case of the number of turns of the winding consistent with the current size, the simulation is carried out when the barrel moves at a speed of 5 m / s. The comparison of the electromagnetic damping forces generated in the three schemes can be obtained as shown in Figure 2 The second scheme is the optimal structure.

[0048] Step 2, on the basis of selecting the optimal structure of the hybrid excitation type eddy current recoil mechanism in step 1, a finite element model of the recoil mechanism is established, after the structure size, material, grid and the differential relationship between the parameters are given, the steady state and transient state are solved under different charges to obtain the recoil displacement and eddy current damping force under different charges and currents.

[0049] The COMSOL finite element model of the recoil mechanism is as follows:

[0050] (1) According to the structure in the scheme, a two-dimensional axisymmetric model of the hybrid excitation eddy current recoil mechanism is established in the finite element simulation software, mainly including barrel, permanent magnet, coil winding, inner cylinder, outer cylinder and air domain.

[0051] (2) The specific parameters of the material are set, the barrel material is iron, the permanent magnet material is sintered neodymium iron boron, the coil winding material is copper, the inner cylinder material is aluminum, the outer cylinder material is magnetic steel, and the air domain is air.

[0052] (3) The initial conditions and boundary conditions are set, such as bore force, recoil mechanism force, coil turns and current.

[0053] (4) The constitutive relationship of the moving rod, permanent magnet, coil winding, inner cylinder, outer cylinder and air domain is determined.

[0054] (5) Set the recoil full differential equation, link each parameter together, and constrain the unknown quantity.

[0055] (6) The whole grid is divided, and each part is discretized, each different part uses different grid units, and corresponds to different grid types, among which the moving rod, permanent magnet and coil winding are set as dynamic grid, the rest are set as fixed grid, and the movement of dynamic grid is realized by the recoil full differential equation buffer motion differential equation in (5).

[0056] (7) After adding the size, material, grid and the differential relationship between the parameters of each part, the whole model forms a close whole, and the steady state and transient state are solved under different charges and currents.

[0057] (8) After the solution is completed, the calculation results are extracted and processed to obtain the required speed and eddy current damping force information.

[0058] The setback displacement is 538 mm under the condition of No. 2 charge without current. Based on this, the simulation of mixed excitation eddy current brake under different currents and different charges is carried out, and the setback displacement under different conditions is obtained as shown in Figure 4 As shown in the figure, under the condition of No. 0 charge, the corresponding setback displacements under the conditions of 150 A, 200 A and 250 A current are 851 mm, 725 mm and 611 mm respectively. Under the condition of No. 1 charge, the corresponding setback displacements under the conditions of 150 A, 180 A and 250 A current are 632 mm, 582 mm and 464 mm respectively. Based on the setback displacement of No. 2 charge, combined with the difficulty of current input in actual application, the scheme of inputting 250 A current under No. 0 charge and inputting 180 A current under No. 1 charge is adopted, and No. 2 charge is not inputted. The corresponding setback displacements of No. 0, No. 1 and No. 2 charges after inputting current are 611 mm, 582 mm and 538 mm respectively. The setback displacement under different charges is greatly reduced, and the difference between the setback displacements of No. 0 charge and No. 2 charge is only 64 mm.

[0059] Step 3, the initial value range of current parameter is determined by multiple attempts, sample points are generated by using optimal Latin hypercube, a large number of simulation analysis is carried out, a plurality of data of eddy current damping force and speed under different charges and different currents are obtained, BP neural network is trained and generated, and then the BP neural network is substituted into COMSOL-Simulink combined simulation for current optimization, and the minimum difference between peak value and valley value of resistance is selected as the optimization target.

[0060] Under the initial parameter design condition of mixed excitation eddy current brake, the eddy current damping force under No. 0 and No. 1 charges reaches the peak value, and then rapidly decreases due to the influence of demagnetization effect, thus a common "saddle" curve is produced, as shown in Figure 5 The damping force fluctuates greatly, which affects the stability of the whole setback process. The joint simulation design block diagram of Simlink and Comsol is as shown in Figure 6The calculation of different charges and different currents is first carried out in Comsol, the running module of Comsol is generated, and the eddy current damping force, speed and the like generated by calculation are summarized, the Neural Net Fitting module of Matlab is used to train a large amount of calculation data, and the BP neural network corresponding to the current under different charges is formed. The control system based on the Comsol running module and the neural network is established in Simulink, the speed is 0, the expected damping force is input to carry out BP neural network calculation, the expected current is obtained, due to environmental problems, the expected current is not more than 300A, the expected current is compared with 300A by using the Simulink comparison module, the smaller value before 12mm is input into the COMSOL module through the Simulink timing module, the stable 280A current is input into the COMSOL module after 12mm, the electromagnetic damping force, the setback displacement, the acceleration and the speed are calculated, and the calculated speed is returned to the BP neural network for calculation at the next time, finally the calculation is completed, the expected damping force is adjusted according to the calculation result, and the cycle is repeated until the current reaches the expected effect, and the calculation result is saved. The calculation result current is brought into Comsol, and the eddy current damping force curve with the optimized'saddle' effect is finally obtained. The flowchart in Simulink is as shown in Figure 7 .

[0061] The designed control model is applied to the hybrid excitation type eddy current recoil brake model for control simulation. By continuously adjusting the expected electromagnetic damping force, the control results of the recoil brake under different expectations are obtained as shown in Figures 8-9 . Under the No. 0 charge, after the optimization of the eddy current damping force, the wave peak is reduced from 629kN to 623kN, and the wave trough is increased from 574kN to 595kN, the fluctuation range is reduced from 55kN to 28kN, and the damping force fluctuation is reduced by 49%. Under the No. 1 charge, the wave peak is reduced from 466kN to 439kN, and the wave trough is increased from 414kN to 420kN, the fluctuation range is reduced from 52kN to 19kN, and the damping force fluctuation is reduced by 63.4%.

[0062] In summary, the method for controlling the variable setback length of the gun under different charges by using the hybrid excitation control is adopted, the control current of the hybrid excitation type eddy current recoil brake under different charges is realized to control the displacement effect, the variable setback length can be effectively controlled from the root, and the control parameters can be further optimized to improve the stability of the resistance, which can provide a reference and direction for controlling the variable setback length of the gun.

[0063] Any technical features in the above embodiments can be combined, and for the sake of brevity, not all possible combinations are described above, however, as long as the combinations of technical features do not contradict each other, they shall be considered within the scope of the present disclosure.

[0064] The above embodiments only express several implementation manners of the present application, and the description is relatively specific and detailed, but it shall not be understood as a limitation on the scope of the present application. It should be noted that, for those skilled in the art, several modifications and improvements can be made without departing from the concept of the present application, and these shall be within the protection scope of the present application. Therefore, the protection scope of the present application shall be subject to the appended claims.

Claims

1. A method for designing variable recoil length of a gun with different propellant charges based on hybrid excitation control, characterized in that, Includes the following steps: Step 1: Establish a structural model of the hybrid excitation eddy current deceleration machine, perform magnetic field line and magnetic circuit analysis, and verify the constant current simulation analysis to select the optimal structural scheme. Step 2: Establish a finite element model of the recoil mechanism in COMSOL, and solve the steady-state and transient conditions under different propellant charges to obtain the recoil displacement and eddy current damping force under different propellant charges and different currents. Step 3: Using the optimal Latin hyperisotropic method, simulation analysis is performed in COMSOL to obtain multiple sets of data on eddy current damping force and velocity under different charges and currents. Using the charge and current as inputs and the eddy current damping force and velocity as outputs, a BP neural network is trained. A control system based on the COMSOL runtime module and neural network is established in Simulink. Current optimization is performed with the goal of minimizing the difference between the peak and valley values ​​of the damping force. The optimized current is then fed into COMSOL to finally obtain the eddy current damping force curve optimized for the "saddle" effect. The specific method is as follows: A control system based on the Comsol runtime module and neural network was built in Simulink. Starting with a velocity of 0, the desired damping force was input and calculated using a BP neural network to obtain the desired current. Due to environmental factors, the desired current was limited to a maximum of 300A. The Simulink comparison module was used to compare the desired current with 300A. The smaller value was input into the Comsol module before 12mm using the Simulink timing module. After 12mm, a stable 280A current was input into the Comsol module to calculate the electromagnetic damping force, recoil displacement, acceleration, and velocity. The calculated velocity was then fed back into the BP neural network for the next time step. After the calculation was completed, the desired damping force was adjusted based on the calculation results. This process was repeated until the current reached the expected effect, and the calculation results were saved. The calculated current was then input into Comsol to obtain the final eddy current damping force curve optimized for the "saddle" effect.

2. The method for designing variable recoil length of a gun with different propellant charges based on hybrid excitation control according to claim 1, characterized in that, Step 1: Establish a structural model of the hybrid excitation eddy current deceleration mechanism, perform magnetic field line and magnetic circuit analysis, and simultaneously conduct constant current simulation analysis and verification to select the optimal structural scheme, wherein: Three hybrid excitation eddy current recoil control mechanism structural models were constructed. Each model consists of a primary and a secondary part. The primary part comprises the barrel, permanent magnet, magnetic shoe, and coil, while the secondary part consists of an inner and an outer cylinder. However, the arrangement of the permanent magnet and the coil differs, with the permanent magnet and coil arranged alternately, the coil on the outside and the permanent magnet on the inside, and the coil on the inside and the permanent magnet on the outside, respectively. When the cannon fires, the primary part moves backward due to recoil, creating relative motion with the secondary part. The magnetic flux in the inner cylinder changes, generating an induced electromotive force that forms eddy currents. These eddy currents, under the influence of the magnetic field, produce an electromagnetic damping force, achieving the recoil control effect. When the number of winding turns and the current are the same, simulation is performed on the tube moving at a speed of 5 m / s. The electromagnetic damping force generated under the three schemes can be compared. The structure that can generate the maximum eddy current damping force under the same conditions is selected as the optimal structure.

3. The method for designing variable recoil length of a gun with different propellant charges based on hybrid excitation control according to claim 2, characterized in that, Step 1: Establish a structural model of the hybrid excitation eddy current deceleration mechanism, perform magnetic field line and magnetic circuit analysis, and simultaneously conduct constant current simulation analysis and verification to select the optimal structural scheme, wherein: Simulations were performed on the tube moving at a speed of 5 m / s with the same number of winding turns and current magnitude. The electromagnetic damping forces generated under the three schemes were compared, and the structure that can generate the maximum eddy current damping force under the same conditions was selected as the optimal structure.

4. The method for designing variable recoil length of a gun with different propellant charges based on hybrid excitation control according to claim 1, characterized in that, Step 2: Establish a finite element model of the recoil mechanism in COMSOL, and perform steady-state and transient solutions under different propellant charges to obtain the recoil displacement and eddy current damping force under different propellant charges and currents. The specific method is as follows: A finite element model of the braking machine was established in COMSOL. The finite element model of the braking machine adopts a two-dimensional axisymmetric model of the hybrid excitation eddy current braking machine, which includes the body tube, permanent magnet, coil winding, inner cylinder, outer cylinder and air domain. Set material parameters, including tube material, permanent magnet material, coil winding material, inner cylinder material, outer cylinder material, and air domain; Set initial and boundary conditions, including barrel force, recoil mechanism force, number of coil turns, and current; Determine the constitutive relations of the moving rod, permanent magnet, coil winding, inner cylinder, outer cylinder, and air domain; Set up a total differential equation with a rearrangement, while constraining the unknowns; The overall mesh is divided, and each part is discretized. Different mesh elements are used for different parts. The moving rod, permanent magnet and coil winding are set as moving meshes, and the rest are set as fixed meshes. The motion of the moving mesh is realized by the back-coupling total differential equation.

5. A design system for variable recoil length of a gun under different propellant charges based on hybrid excitation control, characterized in that, Implement the gun recoil length design method based on hybrid excitation control under different charges as described in any one of claims 1-4, and realize the electromagnetic resistance control of the hybrid excitation eddy current recoil mechanism based on COMSOL-Simulink co-simulation under BP neural network.

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