Grain loading method influences solid rocket engine combustion oscillation characteristic evaluation method and system

Abstract

The application provides a method and system for evaluating the influence of charge mode on the combustion oscillation characteristics of a solid rocket engine, comprising the following steps: S1: dividing the continuous process of the burning surface retreat of the solid rocket engine into multiple simulation structure models; S2: performing finite element calculation of the acoustic mode of the combustion chamber for each simulation structure model to obtain acoustic mode parameters; S3: calculating the burning surface pressure oscillation amount of the combustion chamber gas under unit pressure disturbance based on the acoustic mode parameters; S4: calculating the mass burning rate oscillation amount under the pressure coupling response based on the burning surface pressure oscillation amount, and further evaluating the influence effect of different charge modes on the combustion oscillation characteristics of the solid rocket engine, and outputting the evaluation result. The application calculates the mass burning rate oscillation amount by using the pressure coupling response function, and realizes the evaluation of the influence effect of different charge modes on the combustion oscillation characteristics of the solid rocket engine.

Description

Technical Field

[0001] This invention belongs to the field of rocket engine technology, specifically, it relates to a method and system for evaluating the impact of propellant loading method on the combustion oscillation characteristics of solid rocket engines. Background Technology

[0002] To improve the thrust and range of spacecraft, solid rocket motors are being developed towards larger aspect ratios, higher fill ratios, and higher-energy propellants. While these engines often perform normally during ground tests, combustion instability occurs during flight tests, exhibiting significant inconsistencies between ground and air travel. This has a substantial negative impact on rocket flight. Combustion instability in solid rocket motors is a long-standing problem that has plagued industry and academia. It results from the coupled effects of propellant combustion, unsteady flow within the combustion chamber, and structural acoustic characteristics.

[0003] To suppress combustion oscillations caused by combustion instability in solid rocket motors during rocket flight tests, researchers have employed various methods. Among these, methods involving adjusting propellant formulations or altering engine structure are costly and difficult. Therefore, methods to suppress combustion instability often focus on changing the propellant charge configuration to alter the combustion chamber's shape, thereby suppressing combustion chamber acoustic vibrations by adjusting the combustion chamber's acoustic modes.

[0004] Currently, there are two main types of propellant loading in solid rocket engines used in actual engineering models: free-filling propellant loading with end-face combustion and wall-mounted casting propellant loading with internal combustion.

[0005] There is a lack of research on the effects of two specific propellant loading methods, free loading and wall-mounted casting, on the suppression of combustion oscillations. Therefore, there is an urgent need to develop an evaluation method for the impact of propellant loading methods on the combustion oscillation characteristics of solid rocket engines, so as to provide a reference for rocket and engine engineering design.

[0006] Patent document CN113094830A discloses a system and method for predicting the linear combustion stability of solid rocket engines, including: an acoustic mode calculation module, where the user needs to input the axial grid number for discretizing the acoustic cavity, the combustion chamber sound velocity, the average gas density, the geometric operation tolerance, the modal order to be extracted, and the initial calculation frequency; a combustion surface range definition module, where the user needs to provide the combustion surface number, the starting axial coordinates of the combustion surface, and the ending axial coordinates of the combustion surface, with no limit on the number of combustion surfaces; and a linear growth constant solution module, where the user can calculate the linear growth constant components, including combustion surface gain, nozzle damping, particle damping, and wall damping, to evaluate the linear combustion stability of solid rocket engines. This prediction system significantly improves the efficiency and accuracy of linear combustion stability prediction. However, this method cannot analyze the changes in combustion chamber acoustic mode characteristics, pressure oscillation frequency response characteristics, and solid propellant mass burning rate oscillation response during combustion due to different propellant types, nor can it compare the suppression effects of different propellant types on combustion oscillations.

[0007] Therefore, in order to evaluate the impact and suppression effect of the propellant loading method on the combustion oscillation characteristics of solid rocket engines and provide a reference for rocket and engine design, it is necessary to study and develop a new method to calculate and analyze the changes in the combustion chamber acoustic modal characteristics, pressure oscillation frequency response characteristics, and solid propellant mass burning rate oscillation response of the propellant loading method during combustion, and to make a horizontal comparison of the suppression effect of different propellant loading methods on combustion oscillation, so as to provide a reference for actual engineering design.

[0008] This problem urgently needs to be solved. Summary of the Invention

[0009] To address the shortcomings of existing technologies, the purpose of this invention is to provide a method and system for evaluating the impact of propellant loading methods on the combustion oscillation characteristics of solid rocket engines.

[0010] According to the present invention, a method for evaluating the impact of propellant loading method on the combustion oscillation characteristics of a solid rocket motor includes: step S1: dividing the continuous process of the solid rocket motor combustion surface retraction into multiple simulation structural models; Step S2: Perform finite element analysis of the combustion chamber acoustic modes for each of the simulated structural models to obtain the acoustic mode parameters.

[0011] Step S3: Calculate the oscillation of the combustion chamber gas surface pressure under unit pressure disturbance based on the acoustic modal parameters; Step S4: Based on the combustion surface pressure oscillation, calculate the mass burning rate oscillation considering the pressure coupling response, and then evaluate the impact of different propellant loading methods on the combustion oscillation characteristics of solid rocket motors, and output the evaluation results.

[0012] Preferably, in step S1, the simulation structural model is obtained by dividing the continuous process of the solid rocket engine's burner surface retreat into multiple structural models at equal time intervals; the specific propellant form includes free-filling propellant or wall-mounted casting propellant.

[0013] Preferably, in step S2, finite element calculations of the combustion chamber acoustic modes are performed on each of the simulated structural models using finite element software; the finite element software includes Abaqus; the acoustic modal parameters include acoustic modal frequencies and acoustic mode shapes; After step S2 and before step S3, the method further includes: for free-filling charges and wall-mounted casting charges, by establishing the acoustic wave equation in the combustion chamber and combining it with boundary conditions, constructing a function to solve the analytical solution of the acoustic modal frequency of the combustion chamber, comparing the analytical solution with the finite element simulation results to verify the accuracy, and then reporting the result.

[0014] Preferably, the functions of the analytical solution of the combustion chamber acoustic modal frequencies, in the cases of free-loading and wall-mounted casting charges, are expressed as follows from top to bottom:

[0015]

[0016] in, The function for solving the acoustic frequency of the combustion chamber. Indicates frequency, L 1. A 1, L 2. A 2 represents the axial length and cross-sectional area of ​​the burned cavity, and the axial length and cross-sectional area of ​​the gap between the propellant and the free-loading chamber, respectively. L c This is the total length of the engine combustion chamber. L c = L 1 +L 2, The speed of sound.

[0017] Preferably, in step S4, the mass burn rate oscillation is calculated using a pressure coupling response function, which is defined as the ratio of the relative mass burn rate oscillation to the relative pressure oscillation.

[0018] A system for evaluating the impact of propellant loading method on the combustion oscillation characteristics of a solid rocket motor, according to the present invention, includes: Module M1: Divides the continuous process of solid rocket motor burner surface retraction into multiple simulation structural models; Module M2: Perform finite element analysis of the combustion chamber acoustic modes for each of the simulated structural models to obtain the acoustic mode parameters.

[0019] Module M3: Calculates the oscillation of the combustion chamber gas surface pressure under unit pressure disturbance based on the aforementioned acoustic modal parameters; Module M4: Based on the aforementioned combustion surface pressure oscillation, calculate the mass burning rate oscillation considering the pressure coupling response, and then evaluate the impact of different propellant loading methods on the combustion oscillation characteristics of solid rocket motors, and output the evaluation results.

[0020] Preferably, in module M1, the simulation structural model is obtained by dividing the continuous process of the solid rocket engine's burner surface retreat into multiple structural models at equal time intervals; the specific propellant form includes free-filling propellant or wall-mounted casting propellant.

[0021] Preferably, in module M2, finite element calculations of the combustion chamber acoustic modes are performed on each of the simulated structural models using finite element software; the finite element software includes Abaqus; the acoustic modal parameters include acoustic modal frequencies and acoustic mode shapes; After module M2 operates and before module M3 operates, the following steps are also included: for free-filling and wall-mounted casting charges, by establishing the acoustic wave equations in the combustion chamber and combining them with boundary conditions, constructing a function to solve the analytical solution of the acoustic modal frequencies of the combustion chamber, comparing the analytical solution with the finite element simulation results to verify the accuracy, and then reporting the results.

[0022] Preferably, the functions of the analytical solution of the combustion chamber acoustic modal frequencies, in the cases of free-loading and wall-mounted casting charges, are expressed as follows from top to bottom:

[0023]

[0024] in, The function for solving the acoustic frequency of the combustion chamber. Indicates frequency, L 1. A 1, L 2. A 2 represents the axial length and cross-sectional area of ​​the burned cavity, and the axial length and cross-sectional area of ​​the gap between the propellant and the free-loading chamber, respectively. L c This is the total length of the engine combustion chamber. L c = L 1 +L 2, The speed of sound.

[0025] Preferably, in module M4, the mass burn rate oscillation is calculated using a pressure coupling response function, which is defined as the ratio of the relative mass burn rate oscillation to the relative pressure oscillation.

[0026] Compared with the prior art, the present invention has the following beneficial effects: 1. This invention utilizes the solidification of state method to transform the time-varying combustion chamber state into a short-time invariant system, providing conditions for numerical simulation and theoretical calculation of acoustic modes; furthermore, it considers the influence of the shell-propellant gap of the freely loaded propellant charge, and realizes high-precision finite element calculation of the acoustic modes of the combustion chamber with specific charge configuration.

[0027] 2. This invention uses theoretical formulas to calculate the acoustic modal frequencies of the combustion chamber in each state during the burner surface retreat process, which can verify the accuracy of the numerical simulation. Furthermore, based on the acoustic modal frequencies and mode shapes, the structural dynamics frequency response function formula is used to calculate the combustion chamber pressure frequency response, thus realizing the calculation of the burner surface pressure oscillation under unit pressure disturbance.

[0028] 3. This invention uses the pressure coupling response function to calculate the mass burn rate oscillation, and realizes the evaluation of the influence of different propellant loading methods on the combustion oscillation characteristics of solid rocket engines. Attached Figure Description

[0029] Other features, objects, and advantages of the present invention will become more apparent from the following detailed description of non-limiting embodiments with reference to the accompanying drawings: Figure 1 This is a schematic diagram illustrating the principle of the evaluation method provided by the present invention; Figure 2 A schematic diagram of a specific propellant configuration provided by the present invention, namely a freely loaded solid rocket motor combustion chamber; Figure 3 A schematic diagram illustrating the variation of the first-order mode shape of the axial acoustic mode of the free-loading propellant with the retraction of the combustion surface, provided by the present invention. Figure 4 The diagram shows a comparison of the acoustic modal frequencies obtained from finite element simulation and theoretical formulas for free-loading propellant provided by this invention, with Figure (a) representing the finite element simulation results and Figure (b) representing the theoretical formula calculation results. Figure 5 The spectrum of the maximum normalized burn surface pressure oscillation of the free-filled charge under different combustion times is provided by the present invention. Figure 6 The spectrum of the oscillation of the burn surface mass and burning rate under different combustion times for the free-filled charge provided by the present invention is shown in the figure. Detailed Implementation

[0030] The present invention will now be described in detail with reference to specific embodiments. These embodiments will help those skilled in the art to further understand the present invention, but do not limit the invention in any way. It should be noted that those skilled in the art can make several changes and improvements without departing from the concept of the present invention. These all fall within the protection scope of the present invention.

[0031] This invention provides an evaluation method for the combustion oscillation characteristics of solid rocket motors under the influence of propellant loading methods, providing a reference for the design of solid rocket motors to suppress combustion oscillations.

[0032] An evaluation method for assessing the impact of propellant loading on the combustion oscillation characteristics of a solid rocket motor, provided by the present invention, includes: S1. Based on the concept of solidification, the continuous process of solid rocket engine burn-out is divided into multiple short-time time-invariant acoustic modal simulation structural models, referred to as multiple simulation structural models; S2. Use finite element software to perform finite element calculations of the combustion chamber acoustic modes for each simulation structural model; S3. Apply theoretical formulas to calculate and verify the accuracy of the acoustic modal finite element calculation results; S4. Based on the acoustic modal frequencies and mode shapes, calculate the surface pressure oscillation of the combustion chamber gas under unit pressure disturbance; S5. Calculate the mass burn rate oscillation considering pressure coupling response to evaluate the impact of different propellant loading methods on the combustion oscillation characteristics of solid rocket motors.

[0033] Specifically, the short-time time-invariant acoustic modal simulation structure model refers to the time-slicing of the continuous combustion process of the engine. Each slice is very short, and it is assumed that the acoustic modal simulation structure model of the combustion chamber is fixed and does not change with time within this slice.

[0034] Specifically, the multiple short-time time-invariant acoustic modal simulation structural models are obtained by dividing the continuous process of the burner surface regression of a solid rocket engine with a specific propellant type into multiple structural models at equal time intervals.

[0035] Specifically, the combustion chamber acoustic modal parameters are calculated using the finite element software Abaqus to perform acoustic modal calculations on each short-time time-invariant simulation structural model used as the simulation structural model. The calculation results include acoustic modal frequencies and acoustic mode shapes. It should be noted that for commonly used end-face combustion free-loading propellant systems, the simulation calculation model needs to consider the influence of the propellant-shell gap.

[0036] Specifically, the aforementioned combustion chamber acoustic mode theory formula method, by establishing the acoustic wave equations within a specific combustion chamber and combining them with various boundary conditions of the combustion chamber acoustic field, can derive and construct functions for solving the analytical solutions of the combustion chamber acoustic mode frequencies.

[0037] By establishing the acoustic wave equations within the combustion chamber and combining them with boundary conditions, a function is constructed to solve for the analytical solutions of the combustion chamber acoustic modal frequencies. In other words, for commonly used free-loading and wall-casting charges, the combustion chamber acoustic modal frequencies during the burner retreat process are obtained by finding the zeros of the following function: In the free-loading charge configuration, the expression is:

[0038] For the wall-mounted casting method of explosive charge, the expression is:

[0039] in, The function for solving the acoustic frequency of the combustion chamber. Indicates frequency, L 1. A 1, L 2. A 2 represents the axial length and cross-sectional area of ​​the burned cavity, and the axial length and cross-sectional area of ​​the gap between the propellant and the free-loading chamber, respectively. L c This is the total length of the engine combustion chamber. L c = L 1 +L 2, The speed of sound.

[0040] By comparing the analytical solutions of acoustic modal frequencies calculated by theoretical formulas with the finite element simulation results, the accuracy of the finite element acoustic modal results can be verified, and the verification results can then be reported.

[0041] Specifically, the pressure oscillation of the combustion chamber gas under unit pressure disturbance is calculated using the pressure frequency response function under forced vibration.

[0042] Pressure frequency response function elements Representing the system's number j When the nth degree of freedom is excited by a unit, the th i The steady-state vibration sound pressure oscillation amplitude of each degree of freedom is expressed as:

[0043] In the formula, For generalized stiffness matrix, For the generalized mass matrix, For the generalized damping matrix, Represents angular frequency. Representing the imaginary unit, all of the above matrices can be obtained from the natural mode shapes of acoustic modes in finite element simulation, and further...

[0044] In the formula, The natural mode matrix, r The modal order is... For the first r First-order natural mode vector, , and The first r Modal stiffness, modal mass, and modal damping. Represents a diagonal matrix; superscript T Represents the transpose of a matrix; n Indicates the total order.

[0045] Located in the combustion chamber j Apply a unit amplitude disturbance at the location Then on the burning surface i Pressure oscillation at the point The expression is:

[0046] Specifically, the mass burning rate oscillation under the pressure coupling response is obtained by further calculating the surface pressure oscillation using the pressure coupling response function formula. The pressure coupling response function is defined as the ratio of the relative mass burning rate oscillation to the relative pressure oscillation. ; Where, in the formula, R p This is the pressure coupling response function. The mass combustion rate oscillation quantity. For average burning rate, This is the average pressure. The division sign, combined with the pressure oscillation formula, allows for further calculation of the mass combustion rate oscillation:

[0047] in, It represents the product.

[0048] The above formula can be used to obtain the mass burning rate oscillation at the combustion surface under the influence of acoustic vibration in the combustion chamber, and can be used to evaluate the effect of a specific charging method on combustion oscillation characteristics.

[0049] like Figure 1 As shown in the figure, this invention provides a method for evaluating the impact of propellant loading on the combustion oscillation characteristics of a solid rocket motor, comprising the following steps: Step 1: A schematic diagram of a combustion chamber for a specific propellant configuration, i.e., a freely loaded solid rocket motor, as shown below. Figure 2 As shown, by dividing the continuous process of its burning surface retreat into several structural models with equal time intervals, multiple short-time time-invariant acoustic modal simulation structural models are obtained.

[0050] The total length of the combustion chamber is L c ,diameter d Shell-drug gap The length of the main combustion chamber on the right side, excluding gaps, is... L 1. The length of the space between the propellant and the shell on the left side is... L 2. Define the ratio of propellant column length. L 2 / L c The length of the left-side propellant column L 2% of the total length of the combustion chamber L c The ratio of the propellant grain length to the combustion chamber length was gradually changed from 0.98 to 0. The combustion chamber retraction process was divided into 11 combustion chamber structural models.

[0051] Step 2: Perform acoustic modal calculations of the combustion chamber gas on each short-time time-invariant simulation structural model using the finite element software Abaqus to obtain the calculation results of the combustion chamber acoustic modal parameters, including acoustic modal frequencies and acoustic mode shapes.

[0052] It is important to note that for commonly used end-face combustion free-loading propellant systems, the simulation model needs to consider the influence of the shell-propellant gap. In the finite element simulation, the combustion chamber gas mesh uses hexahedral acoustic elements throughout. Combustion chamber gas parameters include: density... speed of sound bulk modulus The calculated acoustic mode shapes during the burner retreat process, such as Figure 3 As shown.

[0053] Step 3: Solve for the acoustic modal frequencies of the free-loading propellant structure using the combustion chamber acoustic modal theory formula method. By establishing the acoustic wave equations within a specific combustion chamber and combining the various boundary conditions of the combustion chamber acoustic field, the function for solving the analytical solution of the combustion chamber acoustic modal frequencies can be derived and constructed. The combustion chamber acoustic modal frequencies during the free-loading propellant burning surface retreat process are obtained by finding the zero points of the following function: Free-loading charge:

[0054] in, The function for solving the acoustic frequency of the combustion chamber. L 1. A 1, L 2. A2 represents the axial length and cross-sectional area of ​​the burned cavity and the free-loading propellant gap, respectively. L c This is the total length of the engine combustion chamber. L c = L 1 +L 2, The speed of sound.

[0055] The analytical solutions of the acoustic modal frequencies calculated by the theoretical formulas are compared with the finite element simulation results. The acoustic modal frequency variation graph is shown below. Figure 4 As shown, the two calculation results are highly consistent, with a maximum error of only 0.09%, which verifies the accuracy of the finite element acoustic modal results.

[0056] Step 4: Calculate the pressure oscillation of the combustion chamber gas under unit pressure disturbance using the pressure frequency response function under forced vibration. Specifically, Pressure frequency response function elements Representing the system's number j When the nth degree of freedom is excited by a unit, the th i The steady-state vibration sound pressure oscillation amplitude of each degree of freedom is given by the following formula:

[0057] In the formula, For generalized stiffness matrix, For the generalized mass matrix, The generalized damping matrix is ​​given above. All of these matrices can be obtained from the acoustic modal natural modes in finite element simulation. Furthermore,

[0058] In the formula, The natural mode matrix, r The modal order is... For the first r First-order natural mode vector, , and The first r Modal stiffness, modal mass, and modal damping. Assuming this is in the combustion chamber... j Apply a unit amplitude disturbance at the location Then on the burning surface i Pressure oscillation at the point That is

[0059] The spectrum of the maximum normalized burner surface pressure oscillation of free-loaded propellant at different combustion times is shown in the figure below. Figure 5 As shown, it includes the trajectory line of the pressure oscillation frequency.

[0060] Step 5: Using the calculation results of the surface pressure oscillation, further calculate the mass burning rate oscillation under pressure coupling response using the pressure coupling response function formula. The pressure coupling response function is defined as the ratio of the relative mass burning rate oscillation to the relative pressure oscillation. ; Where, in the formula, R p This is the pressure coupling response function. The mass combustion rate oscillation quantity. For average burning rate, To calculate the average pressure, we can further calculate the mass burning rate oscillation using the pressure oscillation formula:

[0061] The above formula yields the mass burning rate oscillation at the burning surface under the influence of acoustic vibration in the combustion chamber for a freely loaded propellant. The spectrum of the normalized mass burning rate oscillation at the burning surface for different combustion times is shown in the figure. Figure 6 As shown. In the first 60% of the combustion time ( The normalized mass burning rate oscillation amplitude of the free-loading propellant is less than 0.1, indicating that the surface free-loading method can significantly suppress combustion oscillation in the first 9.6 seconds of combustion time.

[0062] The present invention also provides an evaluation system for assessing the impact of propellant loading method on the combustion oscillation characteristics of a solid rocket engine. This evaluation system can be implemented by executing the process steps of the evaluation method for assessing the impact of propellant loading method on the combustion oscillation characteristics of a solid rocket engine. That is, those skilled in the art can understand the evaluation method for assessing the impact of propellant loading method on the combustion oscillation characteristics of a solid rocket engine as a preferred embodiment of the evaluation system for assessing the impact of propellant loading method on the combustion oscillation characteristics of a solid rocket engine.

[0063] A system for evaluating the impact of propellant loading method on the combustion oscillation characteristics of a solid rocket motor, according to the present invention, includes: Module M1: Divides the continuous process of solid rocket motor burner surface retraction into multiple simulation structural models; Module M2: Perform finite element analysis of the combustion chamber acoustic modes for each of the simulated structural models to obtain the acoustic mode parameters.

[0064] Module M3: Calculates the oscillation of the combustion chamber gas surface pressure under unit pressure disturbance based on the aforementioned acoustic modal parameters; Module M4: Based on the aforementioned combustion surface pressure oscillation, calculate the mass burning rate oscillation considering the pressure coupling response, and then evaluate the impact of different propellant loading methods on the combustion oscillation characteristics of solid rocket motors, and output the evaluation results.

[0065] Those skilled in the art will understand that, besides implementing the system and its various devices, modules, and units provided by this invention in the form of purely computer-readable program code, the same functions can be achieved entirely through logical programming of the method steps, making the system and its various devices, modules, and units of this invention function in the form of logic gates, switches, application-specific integrated circuits, programmable logic controllers, and embedded microcontrollers. Therefore, the system and its various devices, modules, and units provided by this invention can be considered as a hardware component, and the devices, modules, and units included therein for implementing various functions can also be considered as structures within the hardware component; alternatively, the devices, modules, and units for implementing various functions can be considered as both software modules implementing the method and structures within the hardware component.

[0066] Specific embodiments of the present invention have been described above. It should be understood that the present invention is not limited to the specific embodiments described above, and those skilled in the art can make various changes or modifications within the scope of the claims, which do not affect the essence of the present invention. Unless otherwise specified, the embodiments and features described in this application can be arbitrarily combined with each other.

Claims

1. A method for evaluating the impact of propellant loading method on the combustion oscillation characteristics of a solid rocket motor, characterized in that, include: Step S1: Divide the continuous process of regressing the solid rocket motor combustion surface into multiple simulation structural models; Step S2: Perform finite element analysis of the combustion chamber acoustic modes for each of the simulated structural models to obtain the acoustic mode parameters; Step S3: Calculate the oscillation of the combustion chamber gas surface pressure under unit pressure disturbance based on the acoustic modal parameters; Step S4: Based on the combustion surface pressure oscillation, calculate the mass burning rate oscillation considering the pressure coupling response, and then evaluate the impact of different propellant loading methods on the combustion oscillation characteristics of solid rocket motors, and output the evaluation results.

2. The method for evaluating the impact of propellant loading method on the combustion oscillation characteristics of solid rocket motors according to claim 1, characterized in that, In step S1, the simulation structural model is obtained by dividing the continuous process of the burner surface retreat of a solid rocket engine with a specific charge form into multiple structural models at equal time intervals; the specific charge form includes free-filling charge or wall-mounted casting charge.

3. The method for evaluating the impact of propellant loading method on the combustion oscillation characteristics of solid rocket motors according to claim 1, characterized in that, In step S2, finite element analysis of the combustion chamber acoustic modes is performed on each of the simulated structural models using finite element software, including Abaqus; the acoustic modal parameters include acoustic modal frequencies and acoustic mode shapes. After step S2 and before step S3, the method further includes: for free-filling charges and wall-mounted casting charges, by establishing the acoustic wave equation in the combustion chamber and combining it with boundary conditions, constructing a function to solve the analytical solution of the acoustic modal frequency of the combustion chamber, comparing the analytical solution with the finite element simulation results to verify the accuracy, and then reporting the result.

4. The method for evaluating the impact of propellant loading method on the combustion oscillation characteristics of solid rocket motors according to claim 3, characterized in that, The functions of the analytical solution for the acoustic modal frequencies of the combustion chamber, in the cases of free-loading and wall-mounted casting, are expressed as follows, from top to bottom: in, The function for solving the acoustic frequency of the combustion chamber. Indicates frequency, L 1. A 1, L 2. A 2 represents the axial length and cross-sectional area of ​​the burned cavity, and the axial length and cross-sectional area of ​​the gap between the propellant and the free-loading chamber, respectively. L c This is the total length of the engine combustion chamber. L c = L 1 +L 2, The speed of sound.

5. The method for evaluating the impact of propellant loading method on the combustion oscillation characteristics of solid rocket motors according to claim 1, characterized in that, In step S4, the mass burning rate oscillation is calculated using a pressure coupling response function, which is defined as the ratio of the relative mass burning rate oscillation to the relative pressure oscillation.

6. A system for evaluating the impact of propellant loading method on the combustion oscillation characteristics of a solid rocket motor, characterized in that, include: Module M1: Divides the continuous process of solid rocket motor burner surface retraction into multiple simulation structural models; Module M2: Perform finite element analysis of the combustion chamber acoustic modes for each of the simulated structural models to obtain the acoustic mode parameters; Module M3: Calculates the oscillation of the combustion chamber gas surface pressure under unit pressure disturbance based on the aforementioned acoustic modal parameters; Module M4: Based on the aforementioned combustion surface pressure oscillation, calculate the mass burning rate oscillation considering the pressure coupling response, and then evaluate the impact of different propellant loading methods on the combustion oscillation characteristics of solid rocket motors, and output the evaluation results.

7. The system for evaluating the impact of propellant loading method on the combustion oscillation characteristics of solid rocket motors according to claim 6, characterized in that, In module M1, the simulation structural model is obtained by dividing the continuous process of the burner surface retreat of a solid rocket engine with a specific charge form into multiple structural models at equal time intervals; the specific charge form includes free-filling charge or wall-mounted casting charge.

8. The evaluation system for the impact of propellant loading method on the combustion oscillation characteristics of solid rocket motors according to claim 6, characterized in that, In module M2, finite element analysis of the combustion chamber acoustic modes is performed on each of the simulated structural models using finite element software, including Abaqus; the acoustic modal parameters include acoustic modal frequencies and acoustic mode shapes. After module M2 operates and before module M3 operates, the following steps are also included: for free-filling and wall-mounted casting charges, by establishing the acoustic wave equations in the combustion chamber and combining them with boundary conditions, constructing a function to solve the analytical solution of the acoustic modal frequencies of the combustion chamber, comparing the analytical solution with the finite element simulation results to verify the accuracy, and then reporting the results.

9. The system for evaluating the impact of propellant loading method on the combustion oscillation characteristics of solid rocket motors according to claim 8, characterized in that, The functions of the analytical solution for the acoustic modal frequencies of the combustion chamber, in the cases of free-loading and wall-mounted casting, are expressed as follows, from top to bottom: in, The function for solving the acoustic frequency of the combustion chamber. Indicates frequency, L 1. A 1, L 2. A 2 represents the axial length and cross-sectional area of ​​the burned cavity, and the axial length and cross-sectional area of ​​the gap between the propellant and the free-loading chamber, respectively. L c This is the total length of the engine combustion chamber. L c = L 1 +L 2, The speed of sound.

10. The evaluation system for the impact of propellant loading method on the combustion oscillation characteristics of solid rocket motors according to claim 6, characterized in that, In module M4, the mass burn rate oscillation is calculated using a pressure coupling response function, which is defined as the ratio of the relative mass burn rate oscillation to the relative pressure oscillation.

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