# Characteristic Analysis of Bump Foil Gas Bearing Under Multi-Physical Field Coupling
## 3 Case Study
### Static Characteristics Analysis  
Figure 5 shows the comparison between the experimental data and the model calculation data at an air bearing speed of 30,000 r/min. The relationship between the load and the minimum gas film thickness data solved by the model in this paper was compared with the reference experimental data [24], as shown in Figure 5. It can be seen from Figure 5 that the model data are highly consistent with some of the experimental data, and the overall trend is the same, indicating the correctness of the model. The steady-state characteristics analysis of the air bearing needed to combine the foil elastic mechanics model and the compressible gas equation, considering the comprehensive influence on its bearing capacity, stability, and stiffness exercised by eccentricity, rotational speed, and some structural size changes in the foil. By optimizing the geometric parameters of the air bearing (such as the thickness of the foil, the shape of the foil, etc.) and optimizing the operating parameters (speed, eccentricity, etc. ), the performance of the air bearing can be improved. An in-depth study of the steady-state characteristics analysis can provide help in combination with the research of the physical field coupling model. Figure 4: Flow chart of calculation procedure. Figure 6 shows that when other parameters are constant, the numerical value of gas film bearing capacity changes under different eccentricities and different journal radius clearances. The bearing capacity of the gas film decreases with the increase in the journal radius gap and increases with the increase in eccentricity. When the eccentricity increases to a certain extent, the influence of changes in journal radius gap on the bearing capacity of the gas film becomes smaller. Figure 7 shows the change in gas film bearing capacity under different foil thicknesses and different eccentricities. In a certain range, the gas film bearing capacity increases with the increase in foil thickness. The increase in thickness leads to an increase in foil stiffness and bearing capacity. Under the condition of high eccentricity, the influence of foil thickness on bearing capacity increases. Figure 5: Comparison diagram of model data and experimental data. Figure 6: Influence of journal radius clearance on gas film bearing capacity under different eccentricities. Figure 8 shows that, within a certain range, the length of the half-wave foil has an effect on the bearing capacity of the gas film. As the length of the half-wave foil increases, the bearing capacity of the gas film decreases. This is because, within a certain range, as the length of the half-wave foil increases, the stiffness of the wave foil decreases, the atmospheric film pressure cannot be supported, and the total gas film bearing capacity decreases. The air itself is viscous, although its viscosity is not as high as the viscosity of the liquid; as long as there is shear relative motion, it produces viscous resistance, that is, friction  
Figure 8: The influence of half-wave foil length on gas film load-carrying capacity under different eccentricities. Figure 7: The influence of the thickness of the wave foil on the gas film load-carrying capacity under different eccentricities. resistance. The magnitude of the viscous force is related to the contact area and relative velocity. In the case of high-speed operation, the shear rate of the contact between the gas film and the shaft increases, and the friction torque generated by the viscous resistance may increase linearly. At the same time, in the case of high-speed operation, the thickness of the gas film changes so that the air bearing maintains a stable gas film. When the speed is low, although the take-off speed is reached, the thickness of the gas film becomes thinner, and local contact may occur. Especially in the take-off and stop state, the friction torque generated by the contact will increase significantly.