A method for calculating point connection stiffness of a launch vehicle

Abstract

The application relates to the technical field of carrier rockets, in particular to a carrier rocket point connection rigidity calculation method, which comprises the following steps: establishing an upper and lower cabin section full binding reference model and an upper and lower cabin section point connection model; the same fixed constraint is adopted for the lower end frame in the two models, the same bending angle is applied to the upper end frame, the mechanical responses of the two models are solved; the overall bending rigidity of the upper and lower cabin section full binding reference model and the overall bending rigidity of the upper and lower cabin section point connection model are calculated according to the solving of the mechanical responses of the two models; and the point connection rigidity of the carrier rocket is calculated according to the overall bending rigidity of the upper and lower cabin section full binding reference model and the overall bending rigidity of the upper and lower cabin section point connection model. The point connection rigidity of the carrier rocket is calculated early and accurately by using finite element simulation, which can improve the accuracy of a rocket dynamic characteristic calculation model and the precision of a rocket dynamic characteristic calculation result.

Description

Technical Field

[0001] This application relates to the field of launch vehicle technology, and in particular to a method for calculating the stiffness of point connections in launch vehicles. Background Technology

[0002] During flight, the mass of a launch vehicle changes continuously as propellant is consumed, causing drastic changes in its dynamic characteristics. These dynamic characteristics are a crucial basis for the design of the rocket's attitude control system. The calculation of rocket dynamic characteristics typically uses a point beam model as the analysis tool, with the connections between rocket sections simulated using springs of equivalent stiffness. For connections with a large number of bolts, their high connection stiffness means they have little impact on the calculation of rocket dynamic characteristics; therefore, they are generally modeled as rigid connections. However, for point connections with a small number of bolts (point connections are generally separation surfaces), experimental results clearly show that point connections have low bending stiffness, and this bending stiffness significantly affects the rocket's dynamic characteristics, thus impacting the subsequent stability design of the rocket's attitude control system.

[0003] For newly developed rockets, in the early stages of development, the stiffness of the point connection surfaces is generally assumed based on the point connection type and experience from previous models. Later, this stiffness needs to be corrected based on full-rocket modal tests. However, the modal testing of a large launch vehicle often takes six months or even a year from product launch to test implementation. The long cycle of full-rocket modal testing, coupled with the potential for significant changes in the rocket's dynamic characteristics after stiffness correction, is detrimental to the design of the rocket's attitude control system.

[0004] In addition, existing technologies rarely involve the calculation of point connection stiffness. For example, the patent with authorization publication number CN109583057B, "A Finite Element Modeling Method and Device for Launch Vehicles Based on Stiffness Analysis", introduces a finite element modeling method for launch vehicles based on stiffness analysis. This method mainly focuses on the equivalent stiffness of each section of the structure and does not involve the calculation of point connection stiffness.

[0005] Therefore, how to calculate the stiffness of point connections in launch vehicles earlier and more accurately in order to improve the accuracy of rocket dynamic characteristic calculation results is a technical problem that urgently needs to be solved by those skilled in the art. Summary of the Invention

[0006] This application provides a method for calculating the point connection stiffness of a launch vehicle. By using finite element simulation, the point connection stiffness of the launch vehicle can be calculated accurately and early, which helps to improve the accuracy of the rocket dynamic characteristic calculation model and the precision of the rocket dynamic characteristic calculation results.

[0007] To solve the above-mentioned technical problems, this application provides the following technical solution: A method for calculating the point connection stiffness of a launch vehicle includes the following steps: Step S10, establishing a fully bonded reference model for the upper and lower modules and a point connection model for the upper and lower modules; Step S20, applying the same fixed constraint to the lower frame and the same bending angle to the upper frame in both models, and solving for the mechanical response of both models; Step S30, calculating the overall bending stiffness of the fully bonded reference model for the upper and lower modules and the overall bending stiffness of the point connection model for the upper and lower modules based on the solution of the mechanical response of the two models; Step S40, calculating the point connection stiffness of the launch vehicle based on the overall bending stiffness of the fully bonded reference model for the upper and lower modules and the overall bending stiffness of the point connection model for the upper and lower modules.

[0008] The method for calculating the stiffness of point connections in a launch vehicle as described above preferably involves establishing a fully bonded reference model for the upper and lower modules based on the structural parameters of the launch vehicle using finite element simulation; and establishing a point connection model for the upper and lower modules based on the structural parameters of the point connection surfaces of the launch vehicle using finite element simulation.

[0009] In the above-described method for calculating the stiffness of point connections in a launch vehicle, a preferred approach is to connect the mating surfaces of the upper and lower end frames using a fully bonded constraint method to establish a fully bonded reference model for the upper and lower modules.

[0010] The method for calculating the stiffness of point connections in a launch vehicle as described above preferably involves establishing solid models of bolts and nuts, binding the bolt heads to the mating surfaces of the upper frame, binding the nuts to the mating surfaces of the lower frame, binding the contact surfaces of the screw and the nut, and setting the mating surfaces of the upper and lower frames to a frictionless contact form, thereby establishing a point connection model for the upper and lower compartments.

[0011] In the above-described method for calculating the stiffness of point connections in launch vehicles, it is preferable to set full constraints on the bottom end face of the lower frame in both models to apply fixed constraints to the lower frame; and to apply a bending angle to the top end face of the upper frame in both models.

[0012] In the above-described method for calculating the stiffness of point connections in a launch vehicle, it is preferable that the bending angle is between 0.0005 rad and 0.001 rad.

[0013] In the method for calculating the stiffness of point connections in a launch vehicle as described above, preferably, the axial bolt preload applied during actual assembly is applied to each bolt in the point connection model of the upper and lower compartments before applying the bending angle.

[0014] The method for calculating the stiffness of point connections in a launch vehicle as described above preferably employs a linear static solution method to solve for the mechanical response of both models.

[0015] The method for calculating the point connection stiffness of a launch vehicle as described above preferably involves extracting the reaction moment at the fixed constraint of the lower frame in the fully bonded reference model and the reaction moment at the fixed constraint of the lower frame in the point connection model of the upper and lower sections, respectively, based on the solution of the mechanical response of the two models. The overall bending stiffness of the fully bonded reference model of the upper and lower sections is calculated based on the reaction moment at the fixed constraint of the lower frame in the fully bonded reference model and the bending angle applied at the top end face of the upper frame in the fully bonded reference model of the upper and lower sections. Finally, the overall bending stiffness of the point connection model of the upper and lower sections is calculated based on the reaction moment at the fixed constraint of the lower frame in the point connection model of the upper and lower sections and the bending angle applied at the top end face of the upper frame in the point connection model of the upper and lower sections.

[0016] The method for calculating the point connection stiffness of a launch vehicle as described above, preferably, involves calculating the point connection stiffness of the launch vehicle. ; in, The overall bending stiffness of the fully bonded reference model for the upper and lower compartments. The overall bending stiffness of the point-connected model of the upper and lower compartments.

[0017] Compared with the aforementioned background technology, the method for calculating the point connection stiffness of the launch vehicle in this application can obtain a more accurate point connection stiffness by establishing two different models through finite element simulation. Compared with determining the point connection stiffness using previous experience, the point connection stiffness obtained by the method for calculating the point connection stiffness of the launch vehicle in this application is more accurate, and it has a significant advantage in terms of cycle time compared with obtaining the point connection stiffness by modal testing. Attached Figure Description

[0018] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments recorded in the present invention. For those skilled in the art, other drawings can be obtained based on these drawings.

[0019] Figure 1 This is a flowchart of a method for calculating the point connection stiffness of a launch vehicle according to an embodiment of this application; Figure 2 This is a schematic diagram of the upper and lower compartment model of the point-connected surface provided in the embodiments of this application. Detailed Implementation

[0020] Embodiments of the present invention are described in detail below. Examples of these embodiments are shown in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain the present invention, and should not be construed as limiting the present invention.

[0021] like Figure 1 As shown, this application provides a method for calculating the stiffness of point connections in a launch vehicle, including the following steps: Step S10: Establish a fully bonded baseline model for the upper and lower compartments and a point-connection model for the upper and lower compartments; First, obtain the structural parameters of the point connection surfaces of the launch vehicle. These parameters include: the geometric dimensions of the upper and lower compartment end frames (outer diameter, inner diameter, thickness, and flatness of the mating surface), material properties (elastic modulus E, Poisson's ratio μ, density ρ, with priority given to measured parameters of the actual materials used in the rocket body), specifications of bolts and nuts (nominal diameter, length, thread profile, and material strength grade), assembly quantity, and distribution pattern (circumferential distribution / matrix distribution, bolt center distance, and edge distance).

[0022] Then, based on the structural parameters of the launch vehicle, a fully bonded benchmark model of the upper and lower modules was established through finite element simulation. Similarly, based on the structural parameters of the point connection surfaces of the launch vehicle, a point connection model of the upper and lower modules was established through finite element simulation. The point connection models of the upper and lower modules are as follows: Figure 2 As shown, this is to ensure that the established benchmark model for the full binding of the upper and lower modules and the point connection model for the upper and lower modules are fully matched with the actual assembly conditions of the launch vehicle.

[0023] Fully Bound Baseline Model for Upper and Lower Cabin Sections: The docking surfaces of the upper and lower cabin sections are directly connected using a fully bound method. Specifically, the upper and lower end frames of the upper and lower cabin sections are selected as the core modeling objects, and the docking surfaces of the upper and lower end frames are connected using a fully bound constraint method. This forces the nodal displacements (linear displacements and angular displacements) at the docking surfaces of the upper and lower end frames to be completely consistent, in order to simulate the ideal state of the upper and lower cabin sections as a rigid whole and eliminate the influence of the stiffness of the connection surface itself on the overall stiffness.

[0024] Point-connection model of upper and lower compartments: Solid models of bolts and nuts are created, including the bolt head, bolt, threaded section, and all geometric features of the nut. The threaded section can be modeled using a real thread or equivalent stiffness. The bolt head is bound to the mating surface of the upper frame to simulate a tight fit without relative slippage. The nut is bound to the mating surface of the lower frame to simulate the fixed state of the nut after tightening. The contact surfaces of the bolt and nut are bound to simulate the force transmission characteristics of the threaded pair after bolt preload. The mating surfaces of the upper and lower frames are set to a frictionless contact type, surface-to-surface contact, allowing slight separation or contact under stress, replicating the contact state of the mating surfaces of the upper and lower frames in a real connection, and avoiding stiffness distortion caused by forced binding. This model is used to simulate the real point-connection conditions between the upper and lower compartments of a launch vehicle, accurately reproducing the influence of bolt preload and contact state on connection stiffness.

[0025] Step S20: Apply the same fixed constraint to the lower frame of both models and apply the same bending angle to the upper frame, and solve for the mechanical response of both models; The same fixed constraints are applied to the lower frame in both the fully bonded baseline model and the point-connected model of the upper and lower modules. Specifically, the bottom end face (the end furthest from the docking surface) of the lower frame in both models is set to full constraint, that is, the linear displacement of the lower frame in the X, Y, and Z directions and the angular displacement around the X, Y, and Z axes are restricted to simulate the boundary condition of the lower end of the launch vehicle being fixed, thus eliminating the influence of the difference in boundary conditions on the calculation results.

[0026] Apply a bending angle to the top end face (the end furthest from the docking surface) of the upper frame in both the fully bonded datum model and the point-connected model of the upper and lower sections. The recommended value is 0.0005rad-0.001rad (this range falls within the material's elastic deformation range, avoiding nonlinear errors caused by large deformations while ensuring a clear and measurable reaction torque signal), with 0.001rad being the preferred value. The application method can employ a "forced rotation" constraint, applying a bending angle around a specified axis (usually a horizontal axis perpendicular to the center of the docking surface, i.e., the launch vehicle's radial axis). Ensure that the load direction is consistent with the direction of the bending stiffness assessment of the connection surface.

[0027] According to the actual assembly process requirements of the launch vehicle, axial bolt preload is applied to each bolt in the point connection model of the upper and lower compartments, based on the actual assembly requirements. The preload value can be 60%-80% of the bolt yield strength (compliant with aerospace bolt assembly standards). The application method uses the "bolt preload" load type, acting axially on the bolt thread to ensure that the preload is evenly transmitted to the threaded pair and the end frame mating surface, simulating the actual stress state after bolt tightening. The application of the preload must be completed before the bending angle is applied to avoid calculation deviations caused by load superposition.

[0028] Due to the bending angle applied to the top end face of the upper frame in both models The angle (0.0005rad-0.001rad) is a small rotation angle, so the structural deformation is strictly within the elastic range, without plastic deformation, large deflection or other nonlinear behaviors. Therefore, this application can use the linear static solution method to solve the mechanical response of these two models under the preset "constraint + load". The specific solution accuracy can be set to high-order accuracy. The convergence criterion can be controlled by both displacement convergence and force convergence. The displacement convergence accuracy is not less than 1e-8m and the force convergence accuracy is not less than 1e-3N to ensure that the calculation results are stable and reliable.

[0029] Step S30: Based on the solution of the mechanical response of the two models, calculate the overall bending stiffness of the fully bonded reference model of the upper and lower compartments and the overall bending stiffness of the point connection model of the upper and lower compartments. Based on the solution of the mechanical response of the two models, the reaction moment at the fixed constraint of the lower frame in the fully bonded benchmark model of the upper and lower sections is extracted respectively. The reaction moment at the fixed constraint of the lower frame in the point connection model of the upper and lower compartments Then, based on the reaction moment at the fixed constraint of the lower frame in the fully bonded benchmark model of the upper and lower compartments... The bending angle applied at the top end face of the upper frame in the fully bonded baseline model of the upper and lower sections. The overall bending stiffness of the fully bonded reference model of the upper and lower compartments was calculated. Based on the reaction moment at the fixed constraint of the lower frame in the point connection model of the upper and lower compartments The bending angle applied at the top end face of the upper frame in the point connection model of the upper and lower compartments The overall bending stiffness of the point-connected model of the upper and lower compartments was calculated. .

[0030] Among them, the overall bending stiffness of the fully bonded reference model of the upper and lower compartments Overall bending stiffness of the point-connected model of upper and lower compartments ; It is the combined bending stiffness of the upper and lower end frames (without stiffness loss at the connecting surfaces). It is the total stiffness after the stiffness of the upper and lower end frames and the stiffness of the point connection surface are connected in series (there is stiffness loss of the connection surface).

[0031] Step S40: Calculate the point connection stiffness of the launch vehicle based on the overall bending stiffness of the fully bonded reference model of the upper and lower sections and the overall bending stiffness of the point connection model of the upper and lower sections. Since the stiffness of the upper and lower end frames is in series with the stiffness of the point connection surface, based on the principle of stiffness series, the overall bending stiffness of the fully bonded reference model of the upper and lower sections is used to determine the stiffness. Overall bending stiffness of the point-connected model of upper and lower compartments The point connection stiffness of the launch vehicle can be calculated. The rigidity of the launch vehicle is achieved through point-connected joints. It can directly reflect the actual bending stiffness of the point connection surface (bolt group) of the launch vehicle, thus eliminating the influence of the stiffness of the upper and lower end frames.

[0032] This application establishes two different models through finite element simulation to obtain more accurate point connection stiffness. Compared with determining point connection stiffness using previous experience, the point connection stiffness obtained by the calculation method of launch vehicle point connection stiffness in this application is more accurate, and has a significant advantage in cycle time compared with obtaining point connection stiffness by modal test.

[0033] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other specific forms without departing from its spirit or essential characteristics. Therefore, the embodiments should be considered in all respects as exemplary and non-limiting, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, all variations falling within the meaning and scope of equivalents of the claims are intended to be included within the present invention. No reference numerals in the claims should be construed as limiting the scope of the claims.

[0034] Furthermore, it should be understood that although this specification describes embodiments, not every embodiment contains only one independent technical solution. This narrative style is merely for clarity. Those skilled in the art should consider the specification as a whole, and the technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.

Claims

1. A method for calculating the stiffness of point connections in a launch vehicle, characterized in that, Includes the following steps: Step S10: Establish a fully bonded baseline model for the upper and lower compartments and a point-connection model for the upper and lower compartments; Step S20: Apply the same fixed constraint to the lower frame of both models and apply the same bending angle to the upper frame, and solve for the mechanical response of both models; Step S30: Based on the solution of the mechanical response of the two models, calculate the overall bending stiffness of the fully bonded reference model of the upper and lower compartments and the overall bending stiffness of the point connection model of the upper and lower compartments. Step S40: Calculate the point connection stiffness of the launch vehicle based on the overall bending stiffness of the fully bonded reference model of the upper and lower sections and the overall bending stiffness of the point connection model of the upper and lower sections.

2. The method for calculating the point connection stiffness of a launch vehicle according to claim 1, characterized in that, Based on the structural parameters of the launch vehicle, a fully bonded benchmark model of the upper and lower compartments was established through finite element simulation. Based on the structural parameters of the point-type connection surface of the launch vehicle, a point-type connection model of the upper and lower compartments was established through finite element simulation.

3. The method for calculating the stiffness of point connections in a launch vehicle according to claim 2, characterized in that, The mating surfaces of the upper and lower end frames are connected using a fully bonded constraint method to establish a fully bonded benchmark model for the upper and lower compartments.

4. The method for calculating the stiffness of point connections in a launch vehicle according to claim 2, characterized in that, Create solid models of bolts and nuts, bind the bolt heads to the mating surfaces of the upper frame, bind the nuts to the mating surfaces of the lower frame, bind the contact surfaces of the screw and the nut, and set the mating surfaces of the upper and lower frames to a frictionless contact form to establish a point connection model for the upper and lower compartments.

5. The method for calculating the point connection stiffness of a launch vehicle according to any one of claims 1 to 4, characterized in that, In both models, a full constraint is set on the bottom end face of the lower frame to apply a fixed constraint to the lower frame; a bending angle is applied to the top end face of the upper frame in both models.

6. The method for calculating the stiffness of point connections in a launch vehicle according to claim 5, characterized in that, The bending angle is between 0.0005 rad and 0.001 rad.

7. The method for calculating the stiffness of point connections in a launch vehicle according to any one of claims 1 to 4, characterized in that, Before applying the bending angle, apply the axial bolt preload to each bolt in the point connection model of the upper and lower compartments, the same as that applied during actual assembly.

8. The method for calculating the point connection stiffness of a launch vehicle according to any one of claims 1 to 4, characterized in that, The mechanical response of these two models is solved using the linear static method.

9. The method for calculating the point connection stiffness of a launch vehicle according to any one of claims 1 to 4, characterized in that, Based on the solution of the mechanical response of the two models, the reaction moment at the fixed constraint of the lower frame in the fully bonded benchmark model of the upper and lower compartments and the reaction moment at the fixed constraint of the lower frame in the point connection model of the upper and lower compartments are extracted respectively. The overall bending stiffness of the fully bonded reference model of the upper and lower compartments is calculated based on the reaction moment at the fixed constraint of the lower frame in the fully bonded reference model of the upper and lower compartments and the bending angle applied at the top end face of the upper frame in the fully bonded reference model of the upper and lower compartments. The overall bending stiffness of the upper and lower compartment point connection model is calculated based on the reaction moment at the fixed constraint of the lower frame and the bending angle applied at the top end face of the upper frame in the upper and lower compartment point connection model.

10. The method for calculating the point connection stiffness of a launch vehicle according to any one of claims 1 to 4, characterized in that, Point connection stiffness of launch vehicle ; in, The overall bending stiffness of the fully bonded reference model for the upper and lower compartments. The overall bending stiffness of the point-connected model of the upper and lower compartments.

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