## 1 Introduction  
Support provided by bearings for rotating parts has always been a major problem in the rotating machinery system, such as pumps, hydraulic turbines and compressors. According to the support mode, the bearing can be classified into two types, the rolling bearing, and the sliding bearing. Compared with the rolling bearing, sliding bearings are more widely used in the industrial field due to its significant advantages of low vibration noise, low energy loss, high bearing capacity with low accident rate. The supporting force of the sliding bearing is mainly provided by the lubricating oil in the clearance between the bearing and the shaft. In fact, the lubricating oil continuously features squeezing movement in the sliding bearing. It forms a thin oil film to bear the movement of the rotating shaft, which is responsible for the narrow clearance between the bearing and the shaft journal, as well as the rotation effect of the shaft. The pressure generated by the oil film between the bearing bush and shaft journal can be decomposed into radial force and circumferential force, and the shaft journal is supported by the radial force. For the circumferential force, it is susceptible to cause can the rotor to produce violent lateral vibration and puts at risk the stability of the rotating machinery system because of its consistent direction with the rotating direction. Therefore, the influence of pressure produced by the oil film on the stability of the rotating system has gained more interest among researchers and designers. The dynamic response of the sliding bearing system is generally solved by the methodology named nonlinear kinetics due to its features of being strongly nonlinear and influenced by some factors such as time and rotating speed. In addition, the dynamic parametersare bound to affect the vibration response of the sliding bearing system and degrade the performance of the whole system. The boundary conditions perform a critical function in analyzing the pressure field distribution of the oil film towards the sliding bearing system, which can be classified into four types: the semi-Sommerfeld boundary condition, the Sommerfeld boundary condition, the Reynolds boundary condition, and the mass conservation boundary condition. The oil pressure distribution, the size of the cavity region, and its location are directly affected by the above boundary conditions [1; 2; 3; 4]. The establishment of a nonlinear oil film force database provides a new solution for efficiently and accurately calculating oil film force and analyzing the dynamic characteristics of the rotor system. The accuracy of the numerical calculation method can be guaranteed by the database retrieval interpolation, as well as improved calculation efficiency [5; 6; 7; 8]. [PERSON] [9] obtained the analytical expression of oil film pressure by using the vibrational principle and variable separation method and compared the calculation results with finite element simulation to study the influence of oil inlet pressure and position on oil film pressure distribution and its filled area including the initial edge and rupture edge. [PERSON] [10] calculated the oil film force sliding bearings limited in a finite length by solving the N-S equations and obtained the influence regulation of the degree of eccentricity, journal speed, bearing width-diameter ratio, and action-angle on the rotation subsystem. A database calculation method analyzing the nonlinear oil film force with inlet oil pressure taken into account was proposed by [PERSON] [11] to finitely process the axis velocity and boundary condition of inlet oil pressure. The results show that the method is convenient for solving the rotor's transient operation with more calculation efficiency.