# Improved FULMS Algorithm for Multi-Modal Active Control of Compressor Vibration and Noise Reduction
## 3 Test and Analysis of Compressor Excitation Signal
### Simulation Analysis of Excitation Signal  
According to the stress analysis of the compressor, the main vibration forces of the compressor are electromagnetic force and aerodynamic force generated by compressed gas, and there are mainly two aerodynamic forces: one is pulsating pressure, and the other is cylinder pressure. The action mode of electromagnetic noise is generally as follows: electromagnetic force acts on the slot gap between stator and rotor, causing slot air pulsation and stator yoke vibration through tangential and radial electromagnetic force. The coupling relationship between stator and main shell is generally formed through rib connection or interference fit, so as to make the main shell vibrate and radiate noise outward. The main action positions of pulsating pressure include the upper surface of the bearing, the inner and outer surfaces of the outer muffler, the inner and outer surfaces of the inner muffler, the shaft diameter wall in the rotor area, and the shaft diameter wall in the lower cavity. However, its action energy is limited and has little effect on the sound radiation of the shell. For the cylinder pressure, due to the fast speed of the compressor rotor and the short compression cycle, a large pressure will be generated in the compression chamber and the suction chamber inside the cylinder. Finally, the vibration energy will be transmitted to the main shell through the \"cylinder bearing main shell\" path, resulting in radiated noise. According to the action relationship of each force on the compressor, the relevant finite element model is established in ABAQUS, and the force at each position is measured by the real machine. According to the measured electromagnetic force data, the magnitude of electromagnetic force is not equal on different pins, and its magnitude is also different at different positions of the same pin. Therefore, each pin is divided into several parts, and each part has a corresponding electromagnetic force data. After converting its time domain data into the frequency domain, it is directly loaded at the corresponding position, as showed in Figure 3a. The figure only shows the loading of the pin and force. For the pulsating pressure, its active position has not changed, so its loading method is also relatively simple. Refer to the extraction of pulsating pressure and apply pulsating pressure at the corresponding position, as showed in Figure 3b. However, the cylinder pressure always changes with the rotation of the crankshaft, which increases the difficulty of loading. Here, firstly, COMSOL software is used to analyze the cylinder separately; the stress amplitude and direction of the whole cylinder at different time are calculated, and then the data is input into ABAQUS to load the cylinder volume force. The loading condition is shown in Figure 3c. According to the action relationship of the main force, the finite element model of the compressor is loaded, and the acceleration of the compressor shell is simulated and calculated. The arrangement of measuring points is shown in Figure 1. Measuring points 1, 4, 7, and 10 are 50 mm away from the upper surface. Measuring points 3, 6, 9, and 12 are 50 mm away from the lower surface, and measuring points 2, 5, 8, and 11 are 140 mm away from the lower surface. Extract data and draw graphics. It is found that for measuring points 1-6, the acceleration comparison between simulation and test is similar to that of measuring point 2. For test points 7-12, the comparison between simulation and test data is similar to that of test point 7. Therefore, it is only necessary to draw the relationship curve between acceleration level and frequency at measuring point 2 and measuring point 7 to reflect the noise distribution of the compressor. The comparison between simulation and test data is shown in Figure 4.  
It can be seen from the above figure that the change trend of simulation and test data is consistent, and there is only a certain gap in amplitude.