| Porous gas journal bearings(PGJBs)show considerable potential in the highspeed and high precision rotating machinery field due to several excellent characteristics such as high accuracy,low friction,high carrying capacity and high speed.However,the damping of porous gas bearings is not sufficient as the rotational speed of the rotor continues to increase.There are some problems with the stability of the bearing-rotor system.In the field of aerodynamic gas bearings,researchers have installed a damping structure between the bearing and the housing hole to increase the damping value of the system and limit the vibration of the rotor relative to the bearing.However,the researchers have not used this way at present in the field of aerostatic gas bearing.Thus,this paper from the theoretical simulation and experimental research two aspects to study the damper effects on porous gas bearing-rotor system.On the theory and simulation hand,this article establishes a nonlinear model to study the nonlinear dynamic characteristics of the PGJBs system with O-rings.The calculation of stiffness and damping for O-rings uses the Voigt model.In the porous layer and film,Darcy’s law and Reynolds’ equation are used to establish a gas lubrication model.By combining the above two models and the motions of the rotor and bearings,a numerical nonlinear model is established.Among them,Newton’s iterative method and finite difference method are used to solve the Reynolds equation,and Euler’s method is used to solve the equation of motions.In order to study the nonlinear dynamic characteristics of the PGJBs system with O-rings,the presence or absence of O-rings,rotational speed,gas supply pressure,nominal clearance,and permeability are selected as research parameters.Rotor orbit,FFT,Poincare maps and bifurcation diagrams are adopted.The results show that PGJBs with O-rings can significantly reduce rotor vibration relative to the bearing,compared with rigidly supported bearings.The advantage of O-rings can greatly reduce the risk of friction between the rotor and the bearing,especially in the high-speed section.In addition,high gas supply pressure,low nominal clearance and high permeability can significantly improve the stability of the PGJBs system with O-rings.On the experiment research hand,excitation test and rotor dynamic experiment are carried out in this paper.The excitation test is used to test the change of stiffness damping value of different material O-rings with frequency.On the one hand,it can be used in the simulation program as the stiffness and damping value of O-ring set during simulation.on the other hand,it can be used for experimental research data to study the actual effect of O-ring stiffness and damping value on bearing-rotor system.For rotor dynamic experiment,it is used to verify the accuracy of the established nonlinear model and compare the difference between theoretical calculation and experimental value.In addition,it can study the influence of rotational speed,gas supply pressure,unbalance mass and phase on the stability of bearing-rotor system.The experimental results can be shown in the way of waterfall map and Bode map.The experimental results show that the gas supply pressure has little effect on the 1X frequency amplitude of the rotor center.However,increasing the gas supply pressure can inhibit subsynchronization.The change of unbalanced mass will obviously affect the 1X frequency amplitude.Moreover,the stability effect of the O-ring made of silicone is relatively better,while the O-ring made of silicone is the most likely to occur secondary synchronous vibration and 1X frequency amplitude value is also too large leading to the worst stability.In this paper,the nonlinear characteristics of porous gas journal bearing-rotor system with O-ring are studied.It can provide a reference for the design of porous bearings and their application in the field of higher speed. |
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