## 1 Introduction
Oil pressure distribution for the sliding bearing system with double-oil groove circular bush was calculated by [PERSON] [12], and the influence of oil inlet pressure and journal disturbance speed on the internal flow field of sliding bearing and the bearing capacity were elaborated, which provides a theoretical basis for nonlinear characteristics analysis of rotor system and bearing design. The numerical investigation given by [PERSON] [13] indicated that the maximum pressure in the bearing would be increased by slotting the lower tile. In contrast, the influence of slotting from the upper tile on the oil film pressure is insignificant, but the amount of oil intake will increase. [PERSON] [14] derived an approximate analytical expression of nonlinear oil film force and defined the correlation coefficient in the expression by analyzing and studying the structural parameters of bearings, journal, and lubricating oil. [PERSON] [15] solved the Reynolds equation based on the finite difference method and obtained the distribution of oil film pressure and stress at the bearing bush. In addition, the relationship between the oil film pressure, the stress of bearing bush alloy layer, eccentricity, and the damping parameters are built. [PERSON] [16] established calculation models of sliding bearings with three different oil inlet holes, and the oil film bearing capacity, pressure distribution, and oil temperature distribution are analyzed and studied under different oil inlet holes. [PERSON] [17] studied the influence of oil inlet pressure and its position on the dynamic characteristics of axial inlet groove sliding bearings by solving the motion differential equation of the journal center track and determining the critical speed of instability by using the trial-and-error method. The influence of Reynolds numbers at the inlet on the flow structure, internal pressure, and shear force in the oil chamber was investigated by [PERSON] [18] with the PIV velocimetry system and numerical simulation. The numerical results were validated against experimental data. [PERSON] [19] provided experimental data of sliding bearings under different inlet pipe arrangements, relative values of inlet pipe pressure, and rotating shaft speed, and analyzed the influence of the inclination of the throttle element shaft on fuel consumption. The published research on the influence of oil pressure on system stability is mainly based on finite element analysis and theoretical analysis by means of solving the differential equation. However, experimental investigation of the issue is considerably infrequent. In addition, there is limited research available on the dynamic response of rotating systems to the critical conditions of the oil pressure. The vibration characteristics of the rotor-sliding bearing system are closely related to the inlet oil pressure of the sliding bearing. The innovative points and main research of this paper are: (1) experimental rigs of a single-rotor system and a dual-rotor system are established innovatively; (2) Through the application of an oil supply system. The vibration characteristics of the single-rotor system and dual-rotor system under different bearing inlet oil pressure were investigated. (3) The dynamic characteristics of the dual-rotor system near the critical speed were analyzed. Its nonlinear characteristics under different inlet oil pressure conditions and the steady operating state were also investigated.