A general theory of dynamic design of a gear-coupled rotor sliding bearing system
1.1 coupling model
1.2 Natural vibration equation of gear-coupled rotor sliding bearing system
1.3 Forced vibration of gear-coupled rotor sliding bearing system
If there are a total of n rotors in the gear shaft system, and there is external excitation in each rotor, then the system will have n different frequency excitations at the same time.
Dynamic Design of Gear-Coupled Rotor Sliding Bearing System of 2DH Turbine Compressor
2.1 Tuning of the dynamic parameters of the rotor system
After the structural design, the structural parameters of the three rotors are initially determined after the strength check. The bearing used in the same type of compressor group determines that the support bearing of the G-axis adopts a circular bearing, and the H-axis and the L-axis adopt a tilting-wafer bearing. Then the dynamic design and modification of the structural parameters of the compressor rotor sliding bearing system are carried out according to the gear coupled rotor dynamics theory introduced in this paper. The parameters and detailed dynamics analysis of the rotor bearing system of the unit after setting.
2.2 System stability
The calculation results show that the instability speed of the compressor rotor bearing system is nG3450r/min, which exceeds the maximum working speed by 14%.
2.3 critical speed of the system
In the rotor system #20% operating speed range, there are 14791 r / min, 17998r / min two critical speed. The critical speed of 14791r/min is 5.7% lower than the operating speed of the L-axis, corresponding to a bending-torsional coupling mode with a torsion dominated by the L-axis. The critical speed of 17998r/min is 4.1% higher than the operating speed of the H-axis, corresponding to A bending and torsion coupling mode of the H axis.
2.4 Unbalanced response of the system
Although there are 14791 r/min and 17998r/min two critical speeds near the operating speed of the H-axis and the L-axis, the calculations show that the gear coupling has an excellent suppression effect on the unbalanced response of the L-axis, and because of the 17998r/ At the critical speed of min, the logarithmic decay rate of the rotor system is large (=2.7), and the resonance amplification factor AH is small (AH= 1.38), so the unbalanced response of the L-axis and H-axis is very small <4>251 -252<5>58-75. According to the unbalanced amount given above, the maximum unbalanced vibration at the H, G, and L3 rotor bearings is only 4.2%, 1.4%, 2% at the working speed point, which is much less than the 26.6% allowed by the API standard. 63.8%, 27.8%. In summary, the compressor rotor bearing system has good dynamic performance.
3 machine test
In order to test the correctness of the theory of this paper, the stability and vibration of a DH-type compressor rotor bearing system designed and calibrated according to the above theory were tested in the field. The test was carried out at the Turbine branch of the Hangzhou Oxygen Generator Group.
3.1 Introduction to the test system
A total of 10 Bently 7200 eddy current displacement sensors were installed at the six bearings of the rotor system. No.1 and No.2 sensors are installed at the H-axis left bearing, No.3 and No.4 sensors are installed at the H-axis right bearing; No.5 and No.6 sensors are installed at the L-axis left bearing, and No.7 and No.8 sensors are installed. L-axis right bearing; No. 9 and No. 10 sensors are installed at the G-axis right bearing. The mounting orientation of each sensor is 45 in the horizontal direction.
The eddy current signal picked up from the displacement sensor is input to the computer for data acquisition through the preamplifier and A/D conversion, and then the FFT analysis is performed on the acquired time domain signal to obtain a spectrogram of the rotor system.
3.2 Test results and analysis
The test is carried out at the rated operating speed of the unit.
3.2.1 Vibration signal and spectrum analysis.
The spectrum of the 3 rotors is mainly based on power frequency, and has 2 times frequency and 3 times frequency. There is no half frequency component, which indicates that the system vibration is mainly caused by the initial imbalance of the rotor, and there is no instability caused by bearing oil film whirl. . The entire rotor bearing system is stable, which is identical to the theoretical analysis.
3.2.2 Measurement and analysis of rotor imbalance vibration
The vibration values ​​of the L-axis and the G-axis are in full compliance with the API standard, and the H-axis is also very close to the API standard, and the vibration amplitude of the entire rotor system fluctuates little and the operation is stable. The factory believes that the design indicators are fully met.
Since the exact amount of unbalance of the actual rotor cannot be known, especially since the sensor installation direction is inconsistent with the coordinate direction used in the theoretical calculation, the actual measured rotor amplitude is significantly different from the theoretical calculation value. Relatively speaking, the H-axis vibration is large, and the L-axis and G-axis vibrations are small. This vibration characteristic of the unit is consistent with the theoretical result.
4 Summarize the test test of a DH turbine compressor designed according to the theory and procedure of this paper:
(1) The compressor rotor sliding bearing system has excellent dynamic performance and fully meets the design specifications;
(2) The dynamic design theory of the gear-coupled rotor sliding bearing system is correct. The dynamic design software of the gear-coupled rotor sliding bearing system developed fully meets the engineering practical requirements.
(3) The theory and practice described in this paper show that in the dynamic design of the gear-coupled rotor bearing system system of the DH-type turbine compressor rotor bearing system, the coupling effect of the gear must be considered, and the gear-coupled shaft system is used to bend and twist. Coupling vibration theory can ensure the reasonable and reliable dynamic design of the rotor system.
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