Vibration fatigue life calculation method of variable frequency air conditioner pipeline system

Abstract

The invention provides a method for calculating the vibration fatigue life of a variable frequency air conditioner pipeline system, and relates to the technical field of air conditioners, and the method comprises the steps: building a mathematical model of the maximum stress value and the vibration fatigue life through obtaining the maximum stress value of the pipeline system of a variable frequency air conditioner under various set working conditions and the working frequency corresponding to the maximum stress value; calculating the vibration fatigue life under the set working mode and the environment temperature, calculating the vibration damage of each working condition according to the vibration fatigue life, taking starting and stopping as working conditions, calculating the starting damage and stopping damage, calculating the sum of the vibration damage, the starting damage and the stopping damage of each working condition, and obtaining accumulated damage; the problem that the vibration fatigue life of an existing variable frequency air conditioner pipeline system is not accurate is solved, and the method is suitable for vibration fatigue life calculation of the variable frequency air conditioner pipeline system.

Description

Technical Field

[0001] The present invention relates to the technical field of air conditioning, and in particular to a method for calculating the vibration fatigue life of a variable frequency air conditioning piping system. Background Art

[0002] Currently, the air conditioning industry generally uses pipeline stress-strain testing to evaluate pipeline vibration reliability and assess pipeline vibration life. Evaluation and fatigue life calculations are typically based on the measured maximum stress value of pipeline vibration. If the maximum stress value exceeds the company's internal standard, the product is considered unqualified. However, unlike fixed-speed compressors, variable-frequency air conditioners operate at multiple frequencies. Each frequency contributes differently to pipeline vibration during compressor startup, operation, and shutdown. Furthermore, the probability of each frequency operating during normal operation also varies. Therefore, the calculation method for pipeline vibration fatigue life of variable-frequency air conditioners differs from that of fixed-speed air conditioners. However, a method for calculating the vibration fatigue life of pipeline systems specifically for variable-frequency air conditioners has not yet been proposed. Companies still use the same calculation method for fixed-speed air conditioners, using a constant allowable stress to estimate the vibration fatigue life of variable-frequency air conditioner pipeline systems. Summary of the Invention

[0003] Technical problem solved by the present invention: The present invention provides a method for calculating the vibration fatigue life of a variable frequency air-conditioning piping system, which solves the problem of inaccurate vibration fatigue life of the existing variable frequency air-conditioning piping system.

[0004] The present invention solves the above technical problems by adopting a technical solution: a method for calculating the vibration fatigue life of a variable frequency air conditioning piping system, comprising the following steps: S1. Obtaining a maximum stress value of a piping system of a variable frequency air conditioner under multiple predetermined operating conditions and an operating frequency corresponding to the maximum stress value; the operating conditions include an operating mode and an ambient temperature, and the operating mode includes cooling and heating; S2. Construct a mathematical model of maximum stress value and vibration fatigue life, and calculate the vibration fatigue life under the set working mode and ambient temperature; S3. Calculate the vibration damage of each working condition based on the vibration fatigue life; S4. Consider both startup and shutdown as working conditions and calculate startup damage and shutdown damage; S5. Calculate the sum of vibration damage, startup damage, and shutdown damage under each operating condition to obtain cumulative damage, and calculate vibration fatigue life based on the cumulative damage.

[0005] Furthermore, by pasting strain gauges on the pipeline to test the stress value of the pipeline during vibration, and through compressor pipeline vibration simulation, the position of the pipeline system corresponding to the maximum stress is analyzed, and the maximum stress value of the pipeline system is calculated using the stress value measured by the strain gauge closest to the position path of the pipeline system corresponding to the maximum stress.

[0006] Furthermore, the locations of the strain gauges include the connection between the compressor intake port and the intake pipeline, the first bend of the intake pipeline, the second bend of the intake pipeline, the connection between the compressor exhaust port and the exhaust pipeline, the first bend of the exhaust pipeline and the second bend of the exhaust pipeline.

[0007] Furthermore, the formula for calculating the maximum stress value of the pipeline system is Sa0= Sa1×Sb0÷Sb1, where Sa0 represents the maximum stress value of the management system, Sa1 represents the stress value measured by the strain gauge closest to the position path of the pipeline system corresponding to the maximum stress value, Sb0 represents the simulated stress at the position of the pipeline system corresponding to the maximum stress value, and Sb1 represents the simulated stress at the position of the strain gauge closest to the position path of the pipeline system corresponding to the maximum stress value.

[0008] Furthermore, under the same working mode, a fitting relationship between temperature and stress is fitted, and the maximum stress corresponding to each ambient temperature under the working mode is calculated by the fitting relationship. The fitting relationship is: ,in, The table shows the ambient temperature corresponding to the jth working mode of the i-th ambient temperature. Indicates that the ambient temperature of the jth working mode is known, represents the maximum stress corresponding to the jth working mode at the i-th ambient temperature, It represents the maximum stress corresponding to the jth working mode at a certain ambient temperature, represents the fitting coefficient.

[0009] Furthermore, in S2, the mathematical model is ,in, It represents the maximum stress value corresponding to the jth working mode at the i-th ambient temperature, It represents the vibration fatigue life corresponding to the jth working mode at the i-th ambient temperature, represents the first coefficient, represents the second coefficient, Represents the impact factor.

[0010] Furthermore, if the material of the piping system is copper, then A is -0.0822 and B is 2.5795. is 3.

[0011] Furthermore, in S3, the calculation formula for vibration damage is: ,in, represents the vibration damage corresponding to the jth working mode at the i-th ambient temperature, It represents the vibration fatigue life corresponding to the jth working mode at the i-th ambient temperature, , Indicates the operating time corresponding to the jth working mode at the i-th ambient temperature, It represents the frequency corresponding to the maximum stress of the jth working mode at the i-th ambient temperature.

[0012] Furthermore, in S4, when calculating the startup damage, the maximum stress is the peak of the startup stress waveform, the corresponding frequency is 30 Hz, and the startup time is 3 seconds.

[0013] Furthermore, in S4, when calculating the shutdown damage, the maximum stress is the peak of the shutdown stress waveform, the corresponding frequency is 10 Hz, and the shutdown time is 1 second.

[0014] Beneficial effects of the present invention: The present invention provides a method for calculating the vibration fatigue life of a variable frequency air-conditioning piping system. By obtaining the maximum stress value of the piping system of the variable frequency air-conditioning under a plurality of set working conditions and the working frequency corresponding to the maximum stress value, a mathematical model of the maximum stress value and the vibration fatigue life is constructed, and the vibration fatigue life under the set working mode and ambient temperature is calculated. The vibration damage of each working condition is calculated based on the vibration fatigue life, and both startup and shutdown are regarded as working conditions. The startup damage and shutdown damage are calculated, and the sum of the vibration damage, startup damage and shutdown damage of each working condition is calculated to obtain the cumulative damage. The vibration fatigue life is calculated based on the cumulative damage, thereby solving the problem of inaccurate vibration fatigue life of the existing variable frequency air-conditioning piping system. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 The present invention provides a flow chart of a method for calculating the vibration fatigue life of a variable frequency air conditioning piping system. DETAILED DESCRIPTION

[0016] The present invention aims to solve the problem that the vibration fatigue life of the existing variable frequency air conditioning piping system is inaccurate, and provides a method for calculating the vibration fatigue life of the variable frequency air conditioning piping system. Figure 1 As shown, the following steps are included: S1. Obtaining a maximum stress value of a piping system of a variable frequency air conditioner under a plurality of set working conditions and an operating frequency corresponding to the maximum stress value; the working conditions include a working mode and an ambient temperature, and the working mode includes cooling and heating.

[0017] Specifically, the operating conditions include the ambient temperature in the cooling mode and the ambient temperature in the heating mode in accordance with the national standard GB7725. The ambient temperatures in the cooling mode include: 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, and 38, for a total of 15 operating conditions. The ambient temperatures in the heating mode include: -6, -5, -4, -3, -2, -1, 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, and 16, for a total of 23 operating conditions. That is, there are 15 cooling conditions and 23 heating conditions.

[0018] For each working condition, the maximum stress value of the pipeline system under each working condition and the operating frequency corresponding to the maximum stress value can be obtained through frequency sweep testing. For the maximum stress value, the stress value of the pipeline during vibration is tested by pasting a strain gauge on the pipeline. However, the position where the strain gauge is pasted is not necessarily the position with the maximum stress on the pipeline. Therefore, during the test, the stress at each bend of the pipeline and the stress at the connection between the pipeline and the compressor can be tested, such as the connection between the compressor suction port and the suction pipeline, the first bend of the suction pipeline, and the second bend of the suction pipeline; the connection between the compressor exhaust port and the exhaust pipeline, the first bend of the exhaust pipeline, and the second bend of the exhaust pipeline. Through the vibration simulation of the compressor pipeline, the position of the pipeline system corresponding to the maximum stress is analyzed, and the maximum stress value of the pipeline system is calculated using the stress value measured by the strain gauge closest to the position path of the pipeline system corresponding to the maximum stress. For example, the maximum stress value position of the pipeline system is P0, the simulated stress is Sb0, the strain gauge closest to the path of P0 is the strain gauge at P1, the measured stress is Sa1, and the simulated stress at P1 is Sb1. Through Sa0= The measured stress Sa0 at P0 is calculated by Sa1×Sb0÷Sb1.

[0019] As for the maximum stress, through the analysis of test data, it is found that as the outdoor temperature increases, the maximum stress value of the piping system gradually increases. For every 2°C increase in temperature, the maximum stress increases by about 10%. Therefore, under the same working mode, the fitting relationship between temperature and stress is fitted. The maximum stress corresponding to each ambient temperature under the working mode is calculated based on the fitting relationship. The fitting relationship is: ,in, The table shows the ambient temperature corresponding to the jth working mode of the i-th ambient temperature. Indicates that the ambient temperature of the jth working mode is known, represents the maximum stress corresponding to the jth working mode at the i-th ambient temperature, It represents the maximum stress corresponding to the jth working mode at a certain ambient temperature, represents the fitting coefficient.

[0020] S2. Construct a mathematical model of maximum stress value and vibration fatigue life, and calculate the vibration fatigue life under the set working mode and ambient temperature.

[0021] Specifically, the mathematical model is ,in, It represents the maximum stress value corresponding to the jth working mode at the i-th ambient temperature, It represents the vibration fatigue life corresponding to the jth working mode at the i-th ambient temperature, represents the first coefficient, represents the second coefficient, Indicates the impact factor. If the material of the piping system is copper, then A is -0.0822, B is 2.5795, is 3.

[0022] S3. Calculate the vibration damage of each working condition based on the vibration fatigue life.

[0023] Specifically, the calculation formula for vibration damage is: ,in, represents the vibration damage corresponding to the jth working mode at the i-th ambient temperature, It represents the vibration fatigue life corresponding to the jth working mode at the i-th ambient temperature, , Indicates the operating time corresponding to the jth working mode at the i-th ambient temperature, It represents the frequency corresponding to the maximum stress of the jth working mode at the i-th ambient temperature. Substituting the calculation formula of vibration damage into the mathematical model, the formula obtained is: , that is, when the pipe material is known, the first coefficient can be determined , the second coefficient , impact factor , that is, you only need to know the running time of each working condition , maximum stress The frequency corresponding to the maximum stress can be used to solve the vibration damage of each working condition , the average operating time per year for each operating condition It can be obtained by looking up the table in the national standard GB7725, with the unit being seconds. Therefore, the vibration damage of the variable frequency compressor in each working condition for one year can be calculated.

[0024] S4. Consider both startup and shutdown as operating conditions and calculate startup damage and shutdown damage.

[0025] Specifically, when calculating the startup damage, the maximum stress is the peak of the startup stress waveform, the corresponding frequency is 30Hz, and the startup time is 3 seconds. When calculating the shutdown damage, the shutdown is regarded as a working condition, the maximum stress is the peak of the shutdown stress waveform, the corresponding frequency is 10Hz, and the shutdown time is 1 second. The average operating time of the variable frequency compressor in the GB7725 national standard is 1569 hours a year. According to statistics, it is started and stopped once every 2 hours. Therefore, for startup, it starts an average of 784.5 times a year, and the startup time is 3 seconds, that is, the corresponding startup time is 2353.5 seconds; for shutdown, it stops an average of 784.5 times a year, and the shutdown time is 1 second, that is, the corresponding shutdown time is 784.5 seconds; using , by substituting the corresponding parameters, the one-year startup damage and one-year shutdown damage can be calculated.

[0026] S5. Calculate the sum of vibration damage, startup damage, and shutdown damage under each operating condition to obtain cumulative damage, and calculate vibration fatigue life based on the cumulative damage.

[0027] Specifically, the vibration damage calculated for each working condition in one year is added together to obtain the vibration damage for all working conditions in one year. Then, the one-year startup damage and the one-year shutdown damage are added together to obtain the one-year cumulative damage. The inverse of the one-year cumulative damage is the vibration fatigue life.

[0028] In particular, for variable-frequency air conditioners whose vibration fatigue life does not meet the requirements, the vibration fatigue life can be extended by adjusting the pipeline direction or avoiding the corresponding frequency under maximum stress.

Claims

1. A method for calculating the vibration fatigue life of a variable frequency air conditioning piping system, characterized in that: The following steps are involved: S1. Obtaining a maximum stress value of a piping system of a variable frequency air conditioner under multiple predetermined operating conditions and an operating frequency corresponding to the maximum stress value; the operating conditions include an operating mode and an ambient temperature, and the operating mode includes cooling and heating; S2. Construct a mathematical model of maximum stress value and vibration fatigue life, and calculate the vibration fatigue life under the set working mode and ambient temperature; S3. Calculate the vibration damage of each working condition based on the vibration fatigue life; S4. Consider both startup and shutdown as working conditions and calculate startup damage and shutdown damage; S5. Calculate the sum of vibration damage, startup damage, and shutdown damage under each operating condition to obtain cumulative damage, and calculate vibration fatigue life based on the cumulative damage.

2. The vibration fatigue life calculation method of the variable frequency air conditioning piping system according to claim 1 is characterized in that: By sticking strain gauges on the pipeline to test the stress value of the pipeline during vibration, and through compressor pipeline vibration simulation, the position of the pipeline system corresponding to the maximum stress is analyzed, and the maximum stress value of the pipeline system is calculated using the stress value measured by the strain gauge closest to the position path of the pipeline system corresponding to the maximum stress.

3. The vibration fatigue life calculation method of the variable frequency air conditioning piping system according to claim 2 is characterized in that: The locations of the strain gauges include the connection between the compressor intake port and the intake pipeline, the first bend of the intake pipeline, the second bend of the intake pipeline, the connection between the compressor exhaust port and the exhaust pipeline, the first bend of the exhaust pipeline and the second bend of the exhaust pipeline.

4. The vibration fatigue life calculation method of the variable frequency air conditioning piping system according to claim 2 is characterized in that: The formula for calculating the maximum stress value of the piping system is Sa0 = Sa1 × Sb0 ÷ Sb1, where Sa0 represents the maximum stress value of the management system, Sa1 represents the stress value measured by the strain gauge closest to the position path of the piping system corresponding to the maximum stress value, Sb0 represents the simulated stress at the position of the piping system corresponding to the maximum stress value, and Sb1 represents the simulated stress at the position of the strain gauge closest to the position path of the piping system corresponding to the maximum stress value.

5. The vibration fatigue life calculation method of the variable frequency air conditioning piping system according to claim 1 is characterized in that: Under the same working mode, the fitting relationship between temperature and stress is fitted, and the maximum stress corresponding to each ambient temperature under the working mode is calculated based on the fitting relationship. The fitting relationship is: ,in, The table shows the ambient temperature corresponding to the jth working mode of the i-th ambient temperature. Indicates that the ambient temperature of the jth working mode is known, represents the maximum stress corresponding to the jth working mode at the i-th ambient temperature, It represents the maximum stress corresponding to the jth working mode at a certain ambient temperature, represents the fitting coefficient.

6. The vibration fatigue life calculation method of the variable frequency air conditioning piping system according to claim 1 is characterized in that: In S2, the mathematical model is ,in, It represents the maximum stress value corresponding to the jth working mode at the i-th ambient temperature, It represents the vibration fatigue life corresponding to the jth working mode at the i-th ambient temperature, represents the first coefficient, represents the second coefficient, Represents the impact factor.

7. The vibration fatigue life calculation method of the variable frequency air conditioning piping system according to claim 6, characterized in that: If the material of the piping system is copper, then A is -0.0822 and B is 2.5795. is 3.

8. The vibration fatigue life calculation method of the variable frequency air conditioning piping system according to claim 1 is characterized in that: In S3, the calculation formula for vibration damage is: ,in, represents the vibration damage corresponding to the jth working mode at the i-th ambient temperature, It represents the vibration fatigue life corresponding to the jth working mode at the i-th ambient temperature, , Indicates the operating time corresponding to the jth working mode at the i-th ambient temperature, It represents the frequency corresponding to the maximum stress of the jth working mode at the i-th ambient temperature.

9. The vibration fatigue life calculation method of the variable frequency air conditioning piping system according to claim 1, characterized in that: In S4, when calculating the startup damage, the maximum stress is the peak of the startup stress waveform, the corresponding frequency is 30 Hz, and the startup time is 3 seconds.

10. The vibration fatigue life calculation method of the variable frequency air conditioning piping system according to claim 1, characterized in that: In S4, when calculating the shutdown damage, the maximum stress is the peak of the shutdown stress waveform, the corresponding frequency is 10 Hz, and the shutdown time is 1 second.

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