CN109902439B - Aeronautical power generation pipeline modeling and vibration characteristic analysis method considering bolt connection - Google Patents

Abstract

The invention belongs to the technical field of mechanical dynamics, and in particular relates to a modeling and vibration characteristic analysis method of an aircraft pipeline considering bolt connections. The method includes the following steps: establishing a physical contact finite element model constrained by a pipe clamp, and correcting the elastic modulus of the pipe through a free modal test to obtain a corrected pipe model; The natural frequency is simulated and calculated, and the simulation calculation is verified by modal test and basic excitation response test; the influence of bolt tightening torque, clamp span and pipe length on the natural frequency of the double clamp pipeline system is analyzed. The method adopts the finite element contact model and combines it with the test for comparative study. The calculation result of this modeling method is accurate and consistent with the actual structure.

Description

A Method for Modeling and Vibration Characteristic Analysis of Aircraft Pipelines Considering Bolted Connections

technical field

The invention belongs to the technical field of mechanical dynamics, and in particular relates to a method for modeling and analyzing vibration characteristics of an aircraft pipeline considering bolt connections.

Background technique

The external pipeline of aero-engine is an important part of the aero-engine, known as the "cardiovascular" of the aero-engine. For a long time, the failure of the external pipeline of the aero-engine caused by vibration has been one of the important problems affecting the reliability of the engine. Therefore, it is particularly important to study the vibration characteristics of the clamp piping system.

In view of the connection characteristics of the external pipelines of the aircraft engine using clamp constraints, Yin Zeyong et al. performed finite element calculations on the clamp stiffness, and verified the stiffness of typical clamps through experiments, and obtained a calculation method for the clamp stiffness. Can be used in engineering practice. Ulanov and Bezborodov determined the clamp stiffness and equivalent viscous damping through hysteresis loops, and proposed a vibration characteristic analysis method based on ANSYS, and the simulation calculations were in good agreement with the test results. Nassar et al. analyzed the influence of factors such as tightening speed on the performance of bolted connections through experiments, which improved the reliability of estimating the clamping force. Li Zhanying et al. analyzed the actual structure of the flexible clamp, and concluded that the lateral stiffness of the clamp has a piecewise linear characteristic, and further analyzed its influence on the vibration response. Based on the finite element method, Qiu et al. analyzed various parameters that affect the performance of bolted connections, and the research results showed that pretightening force is the most important parameter. Gao et al. used beam elements to simulate pipelines and springs to simulate clamps to establish a clamp pipeline system model, and verified the effectiveness of the model through experiments. Rao and Wei put forward the algorithm of reverse bolt pretightening force based on finite element, and obtained the pretightening force range of bolt not loosening. Kim et al. used finite element software to establish a structure with bolt connections through different modeling methods, and the results showed that the calculation results of the solid bolt model were the most accurate.

From the analysis of the above literature, it can be seen that the boundary conditions of the clamp constraint are mostly considered in the constraint model of the external pipeline clamp of the aviation engine, but the influence of the clamp bolt pre-tightening is not considered, and there is a certain gap with the actual structure.

Contents of the invention

(1) Technical problems to be solved

Aiming at the technical problem that the existing model is different from the actual structure, the present invention provides a modeling and vibration characteristic analysis method of the aviation development pipeline considering the bolt connection.

(2) Technical solution

In order to achieve the above object, the main technical solutions adopted in the present invention include:

A method for modeling and analyzing vibration characteristics of aero-engine pipelines considering bolted connections, comprising the following steps:

Establish the physical contact finite element model of the pipe clamp constraint, and correct the elastic modulus of the pipe through the free modal test to obtain the corrected pipe model;

Under the set tightening torque, the natural frequency is simulated and calculated, and the simulation calculation is verified by the modal test and the basic excitation response test;

The influence of bolt tightening torque, clamp span and pipe body length on the natural frequency of the double-clamp pipeline system is analyzed.

Preferably, based on ANSYS finite element software, an entity contact finite element model constrained by pipe clamps is established;

The pipe body, metal rubber and hoop band are all meshed with Solid45 solid elements, with a total of 46,690 nodes and 43,156 elements;

The common node operation is adopted between the metal rubber and the hoop, simulating the real welding structure;

The metal rubber and the pipeline are in standard contact, the metal rubber surface is the contact surface, the pipeline surface is the target surface, and the contact unit and the target unit are respectively selected as Conta174 and Targe170 units;

The clamp bolt part is modeled with Beam188 beam element, each bolt is divided into 4 units and 5 nodes, and the Prets179 pretightening force unit is added to the central node of the bolt to simulate the pretightening effect of the clamp bolt;

The bolt head and the bolt platform are simulated in a rigid area, that is, all nodes in the area where the bolt head is in contact with the band are bound together by a rigid area;

The displacement constraints of the three nodes on the edge of the upper hoop are 0 to achieve the purpose of fixed constraints.

Preferably, the modal test is to obtain the natural frequency and mode shape of the pipeline system by hammering.

Preferably, the simulation model is a modified finite element model, and different tightening torques are applied to the bolts to analyze the natural frequencies of the pipeline clamp bolts under different tightening torques.

Preferably, by fixing the clamp at one end of the pipeline and adjusting the position of the clamp at the other end, analyze the natural frequency of the pipeline system within 2000 Hz under different clamp spans, and verify the accuracy of the simulation calculation through experiments.

Preferably, the law of fundamental frequency variation of pipelines of different lengths under different tightening torques is analyzed.

(3) Beneficial effects

The beneficial effects of the present invention are: the method for modeling and analyzing the vibration characteristics of the aviation development pipeline considering the bolt connection provided by the invention takes the clamp constraint model of the aviation development pipeline as the research object, adopts the finite element contact model and combines it with the test The method of this modeling method is used for comparative research, and the calculation results of this modeling method are accurate and consistent with the actual structure.

Description of drawings

Fig. 1 is a schematic flow chart of the modeling and vibration characteristic analysis method of the aviation development pipeline considering the bolt connection provided by the specific embodiment of the present invention;

Fig. 2 is a schematic structural view of the hammer test equipment provided by the specific embodiment of the present invention, and the hammer is not shown in the figure;

Fig. 3 is the comparative schematic diagram of the test mode shape and the simulated mode shape provided by the specific embodiment of the present invention, wherein Fig. 3a is the test mode shape, and Fig. 3b is the simulated mode shape;

Fig. 4 is the simulation and test vibration response comparison provided by the specific embodiment of the present invention, wherein Fig. 4a is a time domain comparison, and Fig. 4b is a frequency domain comparison;

Fig. 5 is a comparison of simulation and test vibration responses provided by a specific embodiment of the present invention, wherein Fig. 5a is the first 2 orders in the x direction, and Fig. 5b is the first 2 orders in the y direction;

Fig. 6 is a vibration test system of the clamp pipeline system provided by the specific embodiment of the present invention under basic excitation;

FIG. 7 is a frequency response function under different spans provided by a specific embodiment of the present invention;

Fig. 8 shows the influence of the tightening torque provided by the specific embodiment of the present invention on the inherent characteristics of pipelines of different lengths, where the pipe lengths in Fig. 8a, Fig. 8b, and Fig. 8c are 0.2m, 0.4m, and 0.6m, respectively.

[Description of Reference Signs]

1: clamp; 2: pipeline; 3: acquisition acceleration sensor; 4: vibration table feedback acceleration sensor; 5: fixture.

detailed description

In order to better explain the present invention and facilitate understanding, the present invention will be described in detail below through specific embodiments in conjunction with the accompanying drawings.

As shown in Figure 1, the present invention discloses a method for modeling and analyzing vibration characteristics of aero-engine pipelines considering bolt connections, including the following steps:

The entity contact finite element model constrained by the pipeline clamp is established, and the elastic modulus of the pipeline is corrected through the free modal test to obtain the corrected pipeline model.

Under the set tightening torque, the natural frequency is simulated and calculated, and the simulation calculation is verified by the modal test and the basic excitation response test.

The influence of bolt tightening torque, clamp span and pipe body length on the natural frequency of the double-clamp pipeline system is analyzed.

The method is specifically as follows:

1 Establishment of finite element model

1.1 Establishment of solid model

Considering the actual structure of the clamp pipeline system, based on the ANSYS finite element software, the entity contact finite element model of the pipeline clamp constraint is established

The selected model is the pipeline model clamped by double clamps, in which the structural size parameters of the pipe body are as follows: outer diameter 8mm, inner diameter 6.4mm, length 500mm, clamp span 450mm and symmetrical distribution. The metal rubber clamp of the pipeline is the standard clamp of the external pipeline of Hangfa, and the material parameters of the corresponding pipeline and clamp are shown in Table 1.

Table 1 Pipeline and clamp material parameters

The pipe body, metal rubber and hoop band are all meshed with Solid45 solid elements, with a total of 46,690 nodes and 43,156 elements. The common node operation is adopted between the metal rubber and the band to simulate the real welding structure; the standard contact between the metal rubber and the pipeline, in which the metal rubber surface is the contact surface, the pipeline surface is the target surface, and the contact unit and the target unit are respectively selected Conta174 and the Targe170 unit; the clamp bolt part is modeled by the Beam188 beam unit, and each bolt is divided into 4 units and 5 nodes, and the Prets179 pretightening force unit is added to the central node of the bolt to simulate the pretightening effect of the clamp bolt; the bolt head The head part and the bolt platform are simulated in a rigid area, that is, all nodes in the contact area between the bolt head and the band are bound together by a rigid area; considering the actual contact length of the upper and lower bands after tightening, the upper band edge 3 The displacement constraints of each node are 0 to achieve the purpose of fixed constraints.

1.2 Optimization of elastic modulus of pipe body

Since it is difficult to accurately guarantee the manufacturing accuracy of self-purchased pipelines, the elastic modulus of pipelines is corrected through free modal tests. The optimal elastic modulus is optimized by using the first-order optimization algorithm, the optimization range is 1.8×1011～2.4×1011Pa, the number of iterations is 50, and the initial value is 2.04×1011Pa. The elastic modulus after optimization is 1.99×1011Pa, and the comparison results of the first 8 natural frequencies are shown in Table 2.

Table 2 Comparison of experiment and optimization results

2 Model Validation

2.1 Modal test verification

Using the pipeline model revised in the previous section, considering the influence of the pre-tightening force effect of clamp bolts on the inherent characteristics of the pipeline, the natural frequency is simulated and calculated under the tightening torque of 7N·m, and the empirical formula F=(T+1 )/(0.22×d) to calculate the pretightening force, where T is the tightening torque, d is the bolt diameter, and the bolt diameter in this paper is 6mm. Due to the existence of pretightening force, static analysis should be carried out before ANSYS software modal solution to consider the effect of prestressing.

In order to prove the validity of the simulation model, the natural frequency and mode shape of the pipeline system are obtained by the hammering method. The test site is shown in Figure 2, and the DH5956 test system is used for data collection and analysis.

The comparison results of simulation calculation and test test are shown in Table 3. It can be seen that under the tightening torque of 7N m, the first two natural frequencies of the simulation calculation in all directions of the pipeline are basically consistent with the test results, and the errors are all within 4%, which can meet the actual engineering needs. . The natural frequency in the x direction of the pipeline is lower than that in the y direction of the pipeline. This is because the y direction of the metal rubber clamp is the direction of the bolt pre-tightening, and in the x direction the pipeline is clamped by the shape of the clamp structure, so the inherent frequency of the pipeline in the x direction The frequency is lower than the natural frequency in the y direction of the pipeline, which also reflects the inconsistency of the stiffness of the clamp in different directions.

Table 3 Comparison of simulation and test results

The comparison of the y-direction test and the first two order vibration shapes of the pipeline is shown in Figure 3, and the x-direction vibration shape is similar to it, so it will not be described again.

2.2 Basic incentive test verification

Aeroengine pipelines are often excited by periodic imbalances generated by rotating machinery such as engines. When the excitation frequency is close to the natural frequency of the pipeline, it will often cause a large resonance in the pipeline. This section studies the vibration response characteristics of the double-clamp pipeline system under the basic harmonic excitation of 159Hz. The vibration test system of the clamp pipeline system under the basic excitation is shown in Figure 6. The electromagnetic vibration table is used to simulate the basic excitation of the casing, and the excitation acceleration is 0.5g.

In the response calculation, the proportional damping is selected for solution, and the modal damping ratio is 0.04. The comparison results of the simulation calculation and the test test are shown in Fig. 4. The two are in good agreement, which fully verifies the validity of the model in this paper.

3 Analysis of intrinsic characteristic parameters

3.1 Influence of tightening torque

From domestic actual production, it is known that the external pipelines of aero-engines are tightened manually based on operating experience during the assembly process outside the casing, so the tightening torques are different. This section discusses the effects of different tightening torques on the natural frequency of the pipelines. effect and compare it with the experimental results. The simulation model uses the revised finite element model above, and different tightening torques are applied to the bolts to analyze the natural frequency of the pipeline clamp bolts under the tightening torque of 2-13N·m.

The comparison results of simulation calculation and experimental test are shown in Fig. 5.

It can be seen from Figure 5 that as the tightening torque increases, the natural frequency of the pipeline increases gradually. This is because the metal rubber is gradually squeezed and the support stiffness gradually increases with the tightening of the bolts, so the natural frequency of the pipeline continues to increase. Increase. Under different tightening torques, the maximum error of the first-order and second-order natural frequencies in different directions of the pipeline is within 8%, which meets the actual engineering needs. In addition, when the tightening torque reaches above 8N·m, the natural frequency of the pipeline increases slowly and tends to be stable, because the metal rubber has been compacted, and the support stiffness increases very little.

3.2 Influence of clamp span

Clamps play the role of fixed constraints in the layout of aviation pipelines. However, due to the assembly space of aero-engines, the fixed clamp spans of many pipelines are different. This section analyzes the inherent influence of different clamp spans on pipelines. The effect of frequency. The pipeline model is the same as the previous one. By fixing the clamp at one end of the pipeline and adjusting the position of the clamp at the other end, analyze the natural frequency of the pipeline system within 2000Hz under different clamp spans, and verify the accuracy of the simulation calculation through experiments. sex. The frequency response function of the test under different spans is shown in Figure 7.

The comparison results of simulation calculation and experimental test are shown in Table 4. It can be seen that under different clamp spans, the natural frequencies are in good agreement, and the maximum error does not exceed 6.06%. On the one hand, it can illustrate the accuracy of the clamp model, and the corresponding clamp model can be applied to engineering practice; on the other hand, according to the calculation results, when one end of the clamp is fixed and the pipe length is kept This will cause the fundamental frequency of the pipeline to increase first and then decrease. This is because the pipeline cantilever at one end when the span is small. As the span increases, the cantilever end of the pipeline gradually decreases, so this trend appears.

Table 4 Natural frequency of pipelines under different spans (frequency unit Hz, error unit %)

3.3 The effect of tightening torque on the inherent characteristics of different pipe lengths

In the actual pipeline layout and installation, usually the length, span and tightening torque of the pipeline will be different. This section analyzes the influence of different tightening torques on the natural frequencies of pipelines of different lengths. Analyze and study the change law of the fundamental frequency of the pipeline with the length of 0.2, 0.4, 0.6m under the tightening torque of 2-13N·m. In the modeling process, the distance between the clamp center and both ends of the pipeline is a certain value, both 0.025m, and the remaining parameters refer to the finite element model mentioned above.

The simulation calculation results are shown in Figure 8. It can be seen that for different pipe lengths, the natural frequency in the y direction of the pipe is greater than that in the x direction, which is the same as the reason above. In addition, it can be seen from the figure that when the pipeline is 0.2m, as the tightening torque increases, the first-order natural frequency in the y direction of the pipeline increases by 205Hz; when the pipeline is 0.6m, as the tightening torque increases, , the first-order natural frequency in the y direction of the pipeline only increases by 20Hz, that is, as the length of the pipeline increases, the natural frequency is gradually reduced by the influence of the tightening torque, that is, the influence of the support stiffness of the clamp on the natural frequency of the pipeline is gradually reduced , this is because as the length of the pipeline increases, the influence of the structural stiffness of the pipeline on the natural frequency gradually increases, while the influence of the support stiffness gradually weakens.

5 Conclusion

1) For the double clamp clamping pipeline system, a finite element model of the pipeline system considering bolt connection was established based on ANSYS software, and was verified by hammer test and foundation stimulus response test. The results fully showed the effectiveness of the model in this paper.

2) Due to the asymmetry of the clamp's own structure, the stiffness of the clamp also has the characteristics of asymmetry, and the stiffness of the bolt pre-tightening direction is greater than that of the other direction. Both the test results and simulation calculations verify this conclusion.

3) Through the test and simulation comparison, it can be seen that with the increase of the tightening torque, the natural frequency of the pipeline increases. For the research object of this paper, the natural frequency of the pipeline tends to be stable after the tightening torque reaches 8N·m.

4) The tightening torque has different effects on the natural characteristics of pipelines with different lengths. The longer the pipeline, the weaker the effect of the tightening torque, that is, the weaker the influence of the support stiffness of the clamp on the natural frequency of the pipeline.

The technical principle of the present invention has been described above in conjunction with specific embodiments. These descriptions are only for explaining the principle of the present invention, and cannot be interpreted as limiting the protection scope of the present invention in any way. Based on the explanations herein, those skilled in the art can think of other specific implementation modes of the present invention without creative work, and these modes will all fall within the protection scope of the present invention.

Claims (5)

1. A method for modeling and analyzing vibration characteristics of aero-engine pipelines considering bolted connections, characterized in that: comprising the following steps: Based on the ANSYS finite element software, a physical contact finite element model constrained by the pipeline clamp is established, and the elastic modulus of the pipeline is corrected through the free modal test to obtain the corrected pipeline model; In the solid contact finite element model, the pipe body, the metal rubber and the hoop band all use Solid45 solid elements for grid division, with a total of 46,690 nodes and 43,156 elements; The common node operation is adopted between the metal rubber and the hoop, simulating the real welding structure; The metal rubber and the pipeline are in standard contact, the metal rubber surface is the contact surface, the pipeline surface is the target surface, and the contact unit and the target unit are respectively selected as Conta174 and Targe170 units; The clamp bolt part is modeled with Beam188 beam element, each bolt is divided into 4 units and 5 nodes, and the Prets179 pretightening force unit is added to the central node of the bolt to simulate the pretightening effect of the clamp bolt; The bolt head and the bolt platform are simulated in a rigid area, that is, all nodes in the area where the bolt head is in contact with the band are bound together by a rigid area; The displacement constraint of the three nodes on the edge of the upper band is 0, so as to achieve the purpose of fixed constraint; Under the set tightening torque, the natural frequency is simulated and calculated, and the simulation calculation is verified by the modal test and the basic excitation response test; The influence of bolt tightening torque, clamp span and pipe body length on the natural frequency of the double-clamp pipeline system is analyzed. 2. The method for modeling and analyzing vibration characteristics of aero-engine pipelines considering bolted connections according to claim 1, wherein the modal test is to obtain the natural frequency and mode shape of the pipeline system by hammering. 3. The aviation development pipeline modeling and vibration characteristic analysis method considering bolt connection according to claim 1, is characterized in that, The modified finite element model is selected as the simulation model, and different tightening torques are applied to the bolts to analyze the natural frequency of the pipeline clamp bolts under different tightening torques. 4. The aviation development pipeline modeling and vibration characteristic analysis method considering bolt connection according to claim 1, characterized in that by fixing the clamp at one end of the pipeline and adjusting the position of the clamp at the other end, the analysis pipeline is in different clamps. Under the hoop span, the natural frequency of the pipeline system is within 2000Hz, and the accuracy of the simulation calculation is verified through experiments. 5. The method for modeling and analyzing the vibration characteristics of aero-engine pipelines considering bolt connections according to claim 1, characterized in that the law of fundamental frequency variation of pipelines of different lengths under different tightening torques is analyzed.

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