A rocket system level structure vibration simulation and verification method

Abstract

A rocket system level structure vibration simulation and verification method, comprising: constructing a rocket system level structure finite element model based on modal superposition method, carrying out harmonic response analysis, constructing excitation-response transfer function in frequency domain, and determining dynamic load transfer path and amplification effect; combining the power spectral density of the rocket vibration environment, implementing random vibration analysis, quantifying the system level structure strength safety margin by calculating the fatigue life; selecting weak components or typical components to carry out targeted vibration test, and verifying the reliability of the system level vibration simulation method in the above steps through test data. The method can effectively improve the vibration environment prediction accuracy and structure design reliability.

Description

Technical Field

[0001] This invention relates to the field of rocket structure design and simulation verification technology, specifically to a method for simulation and verification of vibration of rocket system-level structures. Background Technology

[0002] During flight, rockets are subjected to a variety of complex dynamic loads, including engine operation, aerodynamic noise, and transonic flutter. The vibration environment generated by these loads poses a severe challenge to the structural strength and reliability of onboard instruments, equipment, and piping systems. To ensure rocket flight safety, it is essential to accurately predict and verify the vibration response of the system-level structures during the design phase.

[0003] Traditional vibration adaptability testing methods primarily focus on system-level whole-machine testing and verification, which has inherent limitations such as lengthy development cycles, complex assembly and testing procedures, and high overall costs. In addition, with the increasing demand for rocket payload capacity, the size of the rocket body continues to increase, and the onboard systems are located in rocket body structures with larger diameters. The technical specifications of existing vibration table equipment in China are no longer sufficient to meet the requirements for full-scale ground testing of system structures.

[0004] Therefore, a comprehensive approach is needed that combines system-level vibration simulation, fatigue life assessment, and targeted experimental verification to improve the accuracy of predicting the vibration environment of rocket structures and to achieve the scientific quantification of structural strength safety margins. Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings of existing technologies and provide a method for simulating and verifying the vibration of rocket system-level structures. To achieve the above objective, the technical solution adopted by this invention is as follows:

[0006] A method for simulating and verifying vibration of rocket system-level structures, comprising:

[0007] A finite element model of the rocket system-level structure was constructed based on the modal superposition method. Harmonic response analysis was carried out, the excitation-response transfer function in the frequency domain was constructed, and the transmission path and amplification effect of dynamic loads were clarified.

[0008] By combining the power spectral density of the vibration environment on the rocket, random vibration analysis is performed, and the strength safety margin of the system-level structure is quantified by calculating fatigue life;

[0009] Select weak or typical components to conduct targeted vibration tests, and verify the reliability of the system-level vibration simulation method in the above steps through test data.

[0010] Furthermore, the construction of the rocket system-level structural finite element model based on the modal superposition method includes:

[0011] For thin-walled components such as single-unit housings, tank walls, and pipelines, shell elements are used for discretization to accurately simulate their in-plane and bending mechanical properties.

[0012] For critical load-bearing components, such as the main load-bearing frame, engine frame, compartment docking frame, and key weld locations, solid elements are used for detailed modeling. Boundary conditions strictly follow the actual constraints under flight conditions to ensure that the model's dynamic characteristics are realistic and reliable.

[0013] Furthermore, the construction of the excitation-response transfer function in the frequency domain includes:

[0014] Modal analysis identifies the system's characteristic frequencies and principal modes of motion, which follow the following motion control equations:

[0015]

[0016] Where [M] is the structural mass matrix, [C] is the structural damping matrix, [K] is the structural stiffness matrix, and {F} is the input load vector. Based on the obtained modal parameters, the transfer function of the system in the frequency domain is calculated through harmonic response analysis.

[0017] Furthermore, the power spectral density of the combined onboard vibration environment includes:

[0018] Using the power spectral density of the vibration environment measured in flight or specified in regulations as the input load, the stress response power spectral density of key components (such as single-unit mounting points, pipeline support points, etc.) is obtained through the following formula:

[0019]

[0020] Where G(f) is the response power spectral density, H(f) is the structural transfer function, and W(f) is the input load power spectral density.

[0021] Furthermore, the quantification of system-level structural strength safety margin by calculating fatigue life includes:

[0022] Based on the three-interval method and fatigue damage accumulation theory, fatigue life prediction of structures under vibration environment is completed. First, the random vibration response time history is equivalent to cycles with different stress levels (e.g., 1σ, 2σ, and 3σ). Then, fatigue damage is calculated using the material's SN curve. The calculation formula is as follows:

[0023]

[0024] In the above formula , and These represent the number of cycles corresponding to the 1σ, 2σ, and 3σ stress levels obtained from the SN curves. , , The actual number of cycles for stress levels 1σ, 2σ, and 3σ is given. When the cumulative damage degree D < 1, the structure is considered not to have experienced fatigue failure. When D = 1, the structure theoretically experiences fatigue failure, and the vibration fatigue life is obtained. The safety margin can be quantified based on the ratio of allowable life to predicted life.

[0025] Furthermore, after quantifying the system-level structural strength safety margin by calculating fatigue life, the process also includes an optimization iteration step:

[0026] For components whose safety margins do not meet design requirements as shown by the calculation results, optimization iterations are carried out until all components meet the vibration strength design requirements.

[0027] Furthermore, the optimization iteration includes:

[0028] Multiple rounds of optimization design were carried out using methods such as modal frequency avoidance (adjusting the natural frequency of the structure to avoid coinciding with the main excitation frequency), adjusting connection stiffness (such as fastening torque and connector specifications), optimizing mass distribution (such as adjusting equipment layout), and setting local reinforcement structures (such as reinforcing ribs and reinforcing rings).

[0029] Furthermore, the targeted testing of weak or typical components includes:

[0030] For components (typical components) whose safety margin is critical or which have a significant impact on the vibration characteristics of the system, design the test range, test fixtures and loading conditions to ensure that the dynamic characteristics of the components under test conditions are consistent with those under flight conditions.

[0031] Furthermore, ensuring that the dynamic characteristics of the component in the test state are consistent with those in the flight state includes:

[0032] By comparing and analyzing system-level vibration simulation with component-level (considering test fixture) vibration simulation, we can ensure that the boundary conditions (such as weight distribution and stiffness characteristics) and main vibration response characteristics of the tested components remain consistent in the test state and the system-level assembly state.

[0033] Furthermore, verifying the reliability of the system-level vibration simulation method in the above steps using experimental data includes:

[0034] Acceleration test data (such as characteristic frequency, peak response, and total acceleration magnitude) obtained from acceleration measurement points of components are compared and analyzed with simulation results. If the agreement is good, the reliability of the simulation model is verified; if there are significant differences, the key parameters in the finite element model, such as the connection stiffness between components and the structural damping coefficient, are corrected using the experimental data until the simulation and experimental results are consistent within an acceptable error range.

[0035] The rocket system-level structural vibration simulation and verification method in this invention constructs a high-fidelity system-level finite element model, combines it with vibration environment spectrum for response analysis and fatigue life assessment, and selects key components for experimental verification and model correction, forming a complete closed-loop process from simulation analysis to experimental verification, which can effectively improve the accuracy of vibration environment prediction and the reliability of structural design.

[0036] It should be understood that the above general description and the following specific embodiments are merely exemplary and illustrative, and do not limit the scope of the invention. Attached Figure Description

[0037] The accompanying drawings, which are part of the specification of this invention, illustrate exemplary embodiments of the invention. The drawings, together with the description in the specification, serve to illustrate the principles of the invention.

[0038] Figure 1 This is a flowchart illustrating the method for simulating and verifying the vibration of a rocket system-level structure provided in an embodiment of the present invention. Detailed Implementation

[0039] The features and exemplary embodiments of various aspects of the present invention will now be described in detail. To make the objectives, technical solutions, and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. It should be understood that the specific embodiments described herein are only configured to explain the present invention and to exemplify the principles of the present invention, and are not configured to limit the present invention. In addition, the structural components in the drawings are not necessarily drawn to scale. For example, the dimensions of some structural components or regions in the drawings may be enlarged for other structural components or regions to aid in the understanding of the embodiments of the present invention.

[0040] The directional terms used in the following description refer to the directions shown in the figures and are not intended to limit the specific structure of the embodiments of the present invention. In the description of the present invention, it should be noted that, unless otherwise stated, the terms "installation," "connection," and "joining" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a direct connection or an indirect connection through an intermediate medium. Those skilled in the art can understand the specific meaning of the above terms in the present invention according to the specific circumstances.

[0041] Furthermore, the terms "comprising," "including," "having," or any other variations thereof are intended to cover non-exclusive inclusion, such that a structure or component that includes a list of elements includes not only those elements but also other structural elements that are not expressly listed or inherent to the structure or component. Without further limitations, an element defined by the phrase "comprising..." does not exclude the presence of other identical elements in the article or apparatus that includes the element.

[0042] Spatial relation terms such as "below," "under," "under," "low," "above," "on," and "high" are used for descriptive convenience to explain the positioning of one element relative to a second element, indicating that these terms are intended to cover different orientations of the device, in addition to those different from those shown in the figure. Furthermore, phrases such as "one element on / below another element" can indicate that two elements are in direct contact, or that there are other elements between the two elements. In addition, terms such as "first" and "second" are also used to describe individual elements, areas, parts, etc., and should not be considered limiting. Similar terms are used throughout the description to refer to similar elements.

[0043] It will be apparent to those skilled in the art that the present invention can be practiced without requiring some of these specific details. The following description of embodiments is merely intended to provide a better understanding of the invention by illustrating examples of the invention.

[0044] This invention provides a method for simulating and verifying the vibration of rocket system-level structures, such as... Figure 1 As shown, the specific implementation steps are as follows:

[0045] Step S1: Construct a system-level finite element model.

[0046] For the instrument compartment of a certain type of launch vehicle, a system-level model was established using finite element software to predict and quantitatively evaluate the mechanical performance of the product, guiding rapid design iteration.

[0047] Shell elements are used for discretization and meshing of individual components such as the fuselage, piping, bulkheads, and equipment plates. Solid elements are used for fine-grained modeling of critical load-bearing components and weld locations, such as the main load-bearing frame and key bolted connection areas. Boundary conditions follow the constraints under flight conditions.

[0048] Based on the actual installation conditions, equipment mass points, spring connection units, etc. are defined in the model to simulate the mass effect and connection stiffness of equipment and cables.

[0049] Modal analysis is performed based on the model to obtain the first few natural frequencies and mode shapes of the compartment under constrained conditions.

[0050] Step S2: Harmonic response analysis and transfer function construction.

[0051] Based on the modal analysis, harmonic response analysis is performed. A unit acceleration excitation is applied to the bottom of the model, with a frequency range covering the main vibration environment frequency band of the rocket (e.g., 5-2000 Hz).

[0052] The acceleration transfer function (frequency response function) of the key equipment installation points and pipeline support locations relative to the foundation excitation was calculated, the frequency corresponding to the peak response was identified, and the load transfer path and resonance risk points were clarified. Modal analysis was used to identify the system's characteristic frequencies and principal modes of motion, following the following motion control equations:

[0053]

[0054] Where M is the structural mass, C is the structural damping, K is the structural stiffness, and F is the input load.

[0055] Step S3, random vibration analysis.

[0056] Based on the rocket flight mission profile, the vibration environment conditions of the instrument compartment location are determined, and its power spectral density (PSD) curve is obtained as input.

[0057] The input load power spectral density is combined with the transfer function obtained in step 2, according to the formula:

[0058]

[0059] Where G(f) is the response power spectral density, H(f) is the structural transfer function, and W(f) is the input load power spectral density, the response power spectral density of the critical parts is calculated.

[0060] The root mean square (Grms) and 3σ peak value of the acceleration response at each measuring point are calculated using the response power spectral density and used as input for subsequent intensity assessment.

[0061] Step S4: Fatigue life assessment and safety margin quantification.

[0062] Based on the stress response power spectral density obtained from random vibration analysis, the random stress time history is converted into stress cycles of different amplitudes using the three-interval method. The allowable number of cycles corresponding to each stress level is obtained by consulting the SN curve of the structural material (e.g., aluminum alloy). The calculation formula is as follows:

[0063]

[0064] In the above formula , and These represent the number of cycles corresponding to the 1σ, 2σ, and 3σ stress levels obtained from the SN curves. , , The actual number of cycles for stress levels 1σ, 2σ, and 3σ.

[0065] The cumulative damage D of critical components over a given vibration duration is calculated using the fatigue damage accumulation theory. If D < 1, the service life is considered to meet the requirements. The safety margin (MS) can be defined as:

[0066]

[0067] In one embodiment, the calculated value at the connection of a certain equipment bracket is D=0.25, with a safety margin of MS=3, which meets the requirements; while the calculated value at the weld of a certain thin-walled pipeline is D=1.2, indicating insufficient lifespan, requiring optimization iteration until the weld of the thin-walled pipeline meets the vibration strength design requirements.

[0068] Step S5: Optimize the iterative design.

[0069] For the thin-walled pipe welds with insufficient lifespan, an optimized design was implemented. Firstly, the pipe support position was adjusted to change its natural frequency, avoiding the peak response frequency. Simulation results showed that the damage degree D decreased to 0.9, still close to the critical value.

[0070] Further reinforcement was added near the weld (local reinforcement). After remodeling and analysis, the stress level at this location decreased significantly, and the calculated damage degree D dropped to 0.3, providing sufficient safety margin and meeting the design requirements.

[0071] Step S6: Targeted vibration test verification.

[0072] Optimized thin-walled piping components were selected as typical components for vibration testing. The test scope was clearly defined, and through comparative analysis of system-level and component-level vibration simulations, it was ensured that the weight distribution, stiffness characteristics, and vibration response of the thin-walled piping components within the test scope remained consistent between the test state and the system-level assembly state. If necessary, strategies such as adding tooling supports or counterweights were adopted.

[0073] Based on the acceleration response characteristics at both ends of the pipeline in the system-level simulation, an experimental fixture was designed to ensure that the boundary stiffness and vibration response of the pipeline in the experiment are consistent with those in the system model. When verifying the dynamic characteristics of the fixture, its natural frequency is required to be higher than the first three characteristic frequencies of the component to avoid interference from the fixture's own response to the test results. Based on the analysis results of the system-level vibration energy transfer path, the vibration environment conditions are tailored and decomposed to obtain the vibration magnitude input at the component, thereby determining a reasonable excitation spectrum for the component-level vibration test.

[0074] The pipeline was mounted on a vibration table, and random vibration tests were conducted according to the aforementioned vibration environment power spectral density. Based on the vibration response distribution characteristics predicted by simulation, acceleration measurement points were arranged along the vibration transmission path to obtain the dynamic response. Acceleration sensors were placed at key locations in the pipeline, such as cantilever sections and points of abrupt changes in structural stiffness, to measure their vibration response. The structural strength and sealing reliability were verified through visual inspection and airtightness checks.

[0075] Step 7: Simulation and experimental comparison and model correction.

[0076] By comparing and analyzing acceleration test data with simulation results, the focus is on comparing the characteristic frequencies, peak response values, and total acceleration levels of each key measurement point. This is done to verify or correct the parameter settings in the calculation model, such as connection stiffness (simulation parameters of bolt, joint, and contact surface connection stiffness) and structural damping coefficient, thereby verifying the effectiveness and reliability of the system-level vibration simulation method.

[0077] Extract the response power spectral density and total acceleration magnitude of key pipeline measurement points obtained from the experiment. For example, after a verification experiment, a comparison with the component-level (with fixture) simulation results revealed that a certain frequency measured in the experiment was about 6% lower than the simulation value, and the resonance peak was wider.

[0078] Analysis revealed that the connection stiffness of the weld region in the simulation model was set too high, and the damping coefficient was too small. Therefore, the finite element model was revised, the contact stiffness of the weld region was fine-tuned, and the material damping ratio was adjusted from 0.03 to 0.035.

[0079] Recalculation using the corrected model yielded simulation results that showed good agreement with experimental data in terms of frequency, peak value, and total magnitude, with errors controlled within 5%. The corrected model parameters can be fed back into the system-level model, improving the confidence level of the overall system-level vibration simulation predictions.

[0080] In the simulation and experimental verification method of this application, multiple sets of modular experimental verifications conducted through the above steps complete the entire process from system-level simulation analysis, strength assessment, and optimized design to component experimental verification and system-level model correction, forming a complete and reliable method for rocket structural vibration simulation and verification. Through iterative optimization, the simulation and experimental verification method of this application ultimately replaces whole-engine vibration testing with simulation, and the simulation structure and experimental verification results show high consistency, solving problems such as tight development cycles, insufficient ground test coverage, and cost control for large-scale tests.

[0081] The rocket system-level structural vibration simulation and verification method in this application can shorten the development cycle, enable rapid iteration during the product design stage, shorten the test cycle, greatly simplify the scale of test products and test systems, make test implementation more convenient and efficient, and significantly reduce development costs.

[0082] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for simulating and verifying vibration of rocket system-level structures, characterized in that, include: A finite element model of the rocket system-level structure was constructed based on the modal superposition method. Harmonic response analysis was carried out, the excitation-response transfer function in the frequency domain was constructed, and the transmission path and amplification effect of dynamic loads were clarified. By combining the power spectral density of the vibration environment on the rocket, random vibration analysis is performed, and the strength safety margin of the system-level structure is quantified by calculating fatigue life; After optimizing the iterative design, targeted vibration tests are conducted on weak or typical components to verify the reliability of the system-level vibration simulation method in the above steps using test data.

2. The method for simulation and verification of rocket system-level structural vibration according to claim 1, characterized in that, The finite element model of the rocket system-level structure constructed based on the modal superposition method includes: For thin-walled components such as single-unit housings and pipelines, shell elements are used for discretization. For key load-bearing components and weld locations, solid elements are used for detailed modeling, and the boundary conditions follow the constraint states under flight conditions.

3. The method for simulation and verification of rocket system-level structural vibration according to claim 2, characterized in that, The constructed frequency domain excitation-response transfer function includes: The characteristic frequencies and principal modes of the system are identified through modal analysis, and the following motion control equations are followed: Where M is the structural mass, C is the structural damping, K is the structural stiffness, and F is the input load.

4. The method for simulation and verification of rocket system-level structural vibration according to claim 1, characterized in that, The power spectral density of the combined onboard vibration environment includes: The stress response power spectral density of the critical parts is obtained using the following formula: Where G(f) is the response power spectral density, H(f) is the structural transfer function, and W(f) is the input load power spectral density.

5. The method for simulation and verification of rocket system-level structural vibration according to claim 1, characterized in that, The method of quantifying the structural strength safety margin by calculating fatigue life includes: Based on the three-interval method and the fatigue damage accumulation theory, the fatigue life of the structure under vibration environment is predicted. The calculation formula is as follows: In the above formula , and These represent the number of cycles corresponding to the 1σ, 2σ, and 3σ stress levels obtained from the SN curves. , , denoted as 1σ, 2σ, and 3σ, respectively, and D represents the cumulative damage degree.

6. The method for simulation and verification of rocket system-level structural vibration according to claim 1, characterized in that, The optimization iterative design includes: For components whose safety margin does not meet the design requirements as shown by the calculation results, optimization iterations are carried out until the components meet the vibration strength design requirements.

7. The method for simulation and verification of rocket system-level structural vibration according to claim 6, characterized in that, The optimization iteration also includes: Multiple rounds of optimization were carried out using methods such as modal frequency avoidance, adjustment of connection stiffness, optimization of mass distribution, and setting of local reinforcement structures.

8. The method for simulation and verification of rocket system-level structural vibration according to claim 1, characterized in that, The targeted testing of weak or typical components includes: For components with safety margins at a critical level, design the test range, tooling, and conditions to ensure that the dynamic characteristics of the components under test and in flight are consistent.

9. The method for simulation and verification of rocket system-level structural vibration according to claim 8, characterized in that, Ensuring that the dynamic characteristics of components are consistent with those in flight conditions includes: By comparing and analyzing the vibration simulations at the system level and the component level, it is ensured that the weight distribution, stiffness characteristics and vibration response of the components within the test range remain consistent in the test state and the system-level assembly state.

10. The method for simulation and verification of rocket system-level structural vibration according to claim 1, characterized in that, The verification of the reliability of the system-level vibration simulation method in the above steps through experimental data includes: Acceleration test data obtained from acceleration measurement points of components are compared and analyzed with simulation results to verify or correct the connection stiffness and structural damping coefficient in the finite element model. The parameters for comparison and analysis include the characteristic frequency, peak response, and total acceleration level of each measurement point.

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