A design method for frequency adjustment of a rocket body wind load model

Abstract

This invention provides a design method for frequency adjustment of a rocket body wind load model. First, the target value of the first-order frequency of the wind load model is determined based on the first-order frequency of the actual rocket body erected on the launch pad and the similarity principle of the Strouhal number (Sr). The wind load model is then designed based on the target first-order frequency value. A frequency adjustment device is designed to ensure that the adjusted frequency value is between 0.9 and 1.2 times the target value. Modal tests of the wind load model are conducted outside a wind tunnel to verify whether the first-order mode of the model meets the requirements after adjustment. The model is then installed inside the wind tunnel and modal tests are performed. Through frequency adjustment, the first-order frequency of the model is ultimately guaranteed to meet the requirements. This invention solves the problems of frequency deviation between theoretical models and actual products, as well as the deviation of the first-order frequency of products with different fixed support boundaries. It ensures that the first-order bending frequency of the wind load model installed in the wind tunnel for wind testing meets the design requirements. Furthermore, this frequency adjustment device can be used for rocket wind load models of similar diameters and can be repeatedly applied to multiple models.

Description

Technical Field

[0001] This invention belongs to the field of arrow tower combined wind load model design, specifically involving a frequency adjustment design method for arrow body wind load model. Background Technology

[0002] Wind load is a major design load for rocket structure, especially tail structure. However, the influence of wind load on the dynamic response of rocket is difficult to grasp, making ground wind load testing a necessary project for all types of rockets. Wind tunnel testing of the rocket tower combined with wind load model is used as a quantitative assessment method for wind load effects.

[0003] Since the wind-induced oscillations of a rocket standing on the launch pad are mainly first-order responses, and are responses of a small-damped structure, especially for the dynamic bending moment at the root and the dynamic displacement at the nose, the first-order response is much larger than the higher-order response. Therefore, the complete dynamic similarity of the scaled-down model can be reduced to the similarity of the Strauhaus number (Sr). That is, as long as the first-order bending vibration frequency needs to be designed according to the Sr number similarity requirement, the structural damping ratio, whether for a physical rocket or a scaled-down model, is generally in the range of 0.5% to 1%. The first-order bending mode shape is not much different for any cantilever beam structure with any mass and stiffness distribution. From this discussion, it can be seen that the key to the design of the wind load model is to satisfy the Sr number similarity, that is, the similarity of the first-order bending vibration frequency.

[0004] The rocket erected on the launch pad is designed based on a wind load model with a fixed bottom boundary. Its first-order bending frequency is highly dependent on the boundary stiffness and mass distribution. Even if the frequency of the theoretical model meets the requirements, deviations will still occur during actual testing of the manufactured product based on the theoretical model. Furthermore, the first-order bending frequency will vary depending on the stiffness of the fixed boundary. Therefore, the frequency of the rocket body's wind load model must be easily adjustable to ensure that its first-order bending frequency meets the design requirements, i.e., satisfies the Strouhal number (Sr) similarity, when installed in a wind tunnel for wind tunnel testing. Summary of the Invention

[0005] To address the aforementioned issues, this invention provides a frequency adjustment design method for a wind-loaded rocket body model. This method resolves the frequency deviation between the theoretical model and the actual product, as well as the deviation of the first-order frequency of products with different fixed support boundaries. It ensures that the first-order bending frequency of the wind-loaded model installed in a wind tunnel for wind testing meets the design requirements, i.e., satisfies the Strouhal number (Sr) similarity.

[0006] A method for frequency adjustment design of a rocket body wind load model includes the following steps: 1) Determine the target value of the first-order frequency of the wind load model based on the similarity principle of the first-order frequency and the Strauha number Sr of the actual rocket body erected on the launch pad; 2) Design a wind load model based on the first-order frequency target value; 3) Design a frequency adjustment device to ensure that the adjusted frequency value is between 0.9 and 1.2 times the target value; 4) Conduct modal tests on the model under external wind load in the wind tunnel to verify whether the first-order mode of the model meets the requirements through adjustment; 5) Install the model in the wind tunnel and conduct modal tests. Adjust the frequency to ensure that the first-order frequency of the model meets the requirements.

[0007] In step 2), the design value of the first-order frequency of the wind load model is between 1.1 and 1.2 times the target value.

[0008] In step 3), the frequency adjustment device is installed at the top of the arrow body and includes a counterweight plate and a counterweight block. The counterweight block is radially connected and positioned to the upper end of the column section at the top of the arrow body. The counterweight block is bolted to the counterweight plate. By adjusting the mass of the counterweight block, the adjusted frequency value is between 0.9 and 1.2 times the target value.

[0009] Furthermore, the counterweight plate is shaped like a flat-bottomed pan, made of A3 steel with a thickness of 15mm; and weight reduction holes are provided on the counterweight plate.

[0010] Furthermore, the counterweight includes 1kg counterweight, 2kg counterweight, 5kg counterweight, and 10kg counterweight.

[0011] Furthermore, both the counterweight block and the counterweight plate have a Φ50 hole in the middle.

[0012] The beneficial effects of this invention are as follows: This solution addresses the frequency discrepancies between theoretical models and actual products, as well as the first-order frequency deviations of products with different fixed support boundaries. It ensures that the first-order bending frequency of the wind-load model installed in the wind tunnel for wind testing meets design requirements. Furthermore, this frequency adjustment device can be used on rocket wind-load models of similar diameters and can be repeatedly applied to multiple models. Attached Figure Description

[0013] Figure 1 It is a model diagram of a cantilever beam; Figure 2 This is a schematic diagram of the frequency adjustment device and the rocket body assembly; Figure 3 This is a schematic diagram of a frequency adjustment device; Figure 4 This is a diagram illustrating a 1kg counterweight. Figure 5 This is a diagram illustrating a 2kg counterweight. Figure 6 This is a diagram illustrating the 5kg counterweight; Figure 7 This is a diagram showing a 10kg counterweight; Figure 8 This is a schematic diagram of the counterweight plate. Detailed Implementation

[0014] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection claimed by the present invention.

[0015] A method for frequency adjustment design of a rocket body wind load model includes the following steps: 1) First, determine the target value of the first-order frequency of the wind load model based on the similarity principle between the first-order frequency of the actual rocket body erected on the launch pad and the Strouhal number (Sr); 2) Design the wind load model based on the first-order frequency target value. Because the calculation uses an ideal fixed support state, the actual product frequency is about 10% lower than the calculated frequency. In order to ensure that the first-order frequency of the product is not lower than the target value, the design value of the first-order frequency of the wind load model is between 1.1 and 1.2 times the target value. 3) Design frequency adjustment devices such as counterweight discs and counterweight blocks. Installing the counterweight discs and counterweight blocks at the top of the rocket body achieves the highest frequency adjustment efficiency. The theoretical model and formulas are as follows: Figure 1 As shown in Formula 1, by adjusting the counterweight, i.e. the mass m, the adjusted frequency value is between 0.9 and 1.2 times the target value; (1) in, n The angular natural frequency is represented by rad / s; E represents the elastic modulus of the material by Pa; and I represents the area moment of inertia of the beam's cross-section by m. 4 L represents the beam length, in meters (m). m This indicates the concentrated mass at the end, in kg. m b This indicates the mass of the beam, expressed in kg.

[0016] 4) Conduct modal tests on the model under external wind load in the wind tunnel to verify whether the first-order mode of the model meets the requirements through adjustment; 5) Install the model in the wind tunnel and conduct modal tests. Adjust the frequency to ensure that the first-order frequency of the model meets the requirements.

[0017] To achieve frequency adjustment, a counterweight plate and counterweight blocks are installed, such as... Figure 2 , Figure 3 , Figure 8As shown, the counterweight plate is shaped like a frying pan, made of A3 steel with a thickness of 15mm. For precise adjustment, weight-reducing holes are provided on the counterweight plate. Both the head cone and the column section are made of aluminum. Without the counterweight plate, they are radially connected by 12 M8 screws, with a support plate securing the nut on the inside. With the counterweight plate added, the counterweight plate and the upper end of the column section are radially connected and positioned using 4 countersunk screws, and then connected to the steel counterweight plate by 8 M8 cylindrical head screws passing through the head cone and column section. The support plate and nut are no longer used on the inside. The counterweight base blocks are provided with one 1kg block, two 2kg blocks, one 5kg block, and one 10kg block, as shown... Figures 4-7 As shown, the counterweights can be added or removed according to the actual situation. The first layer of counterweight is connected to the counterweight plate by eight M16 bolts, and the upper and lower layers of counterweight are also connected by eight M16 bolts. A Φ50 hole is provided in the middle of both the counterweight and the counterweight plate for threading.

[0018] The above description of the disclosed embodiments enables those skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the scope of the invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for frequency adjustment design of a wind loading model of a missile body, characterized by, The method comprises the following steps: 1) determining the target value of the first frequency of the wind load model according to the first frequency of the actual missile erected on the launching platform and the principle of similar Strouhal number Sr; 2) designing the wind load model according to the target value of the first frequency; 3) designing the frequency adjusting device, so that the adjusted frequency value is between 0.9-1.2 times of the target value; 4) performing the modal test of the wind load model outside the wind tunnel, and verifying whether the first mode of the model meets the requirements through the adjustment; 5) installing the model in the wind tunnel and performing the modal test, and finally ensuring that the first frequency of the model meets the requirements through the frequency adjustment.

2. The method of claim 1, wherein, In the step 2), the designed value of the first frequency of the wind load model is between 1.1-1.2 times of the target value.

3. The method of claim 1, wherein, In the step 3), the frequency adjusting device is installed at the top end of the missile body, and comprises a counterweight disc, counterweight blocks, the counterweight blocks are radially connected and positioned with the upper end of the column segment at the top end of the missile body, the counterweight blocks are bolted with the counterweight disc, the mass of the counterweight blocks is adjusted, so that the adjusted frequency value is between 0.9-1.2 times of the target value.

4. The method of claim 3, wherein, The counterweight disc is in the shape of a flat-bottomed pot, the material is A3 steel, and the thickness is 15mm; the counterweight disc is provided with weight-reducing holes.

5. The method of claim 3, wherein, The counterweight blocks comprise 1Kg counterweight blocks, 2Kg counterweight blocks, 5kg counterweight blocks and 10kg counterweight blocks.

6. The method of claim 3, wherein, The counterweight blocks and the counterweight disc are both provided with a Φ50 hole in the middle.

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