Comparative study of nonlinear dynamic behavior of perfectly balanced horizontal rotor and vertical rotor supported by tilting pad journal bearings by computing frequency response.

The nonlinear dynamic analysis has been carried out to investigate the dynamic behavior of a perfectly balanced horizontal rotor (HR)-tilting pad journal bearing (TPJB) system and perfectly balanced vertical rotor (VR)-tilting pad journal bearing (TPJB) system by computing frequency response of both the systems. To do so, governing differential equations (GDEs) of motion for HR-TPJB system and VR-TPJB system has been derived and they were solved by finite element method (FEM). The GDE of motion of both systems have been combined to form a unit set. This unit set represents the HR/VR-TPJB system. Implementation of computational numerical integration technique has been employed to solve equations of motion of both the systems which has been solved using the MATLAB® ODE-15s solver. Indigenous MATLAB® program has been created to compute the above-mentioned frequency response of the system efficiently. Time-Amplitude Response and Frequency-Amplitude Response with Phase at both the TPJB's and rigid disc locations have been computed by Fast Fourier Transform (FFT). The dynamic behavior of the perfectly balanced HR-TPJB and VR-TPJB systems have been analyzed for different rotor speeds. The results and discussions on the nonlinear dynamic behavior of perfectly balanced HR-TPJB and VR-TPJB systems operating at low and high rotor speed have been explained which indicates HR-disc is more unstable than HR-journal inside identical 4-pad TPJBs at low rotational speed (1500 rpm). The frequency response of both HR-TPJB system and VR-TPJB system at low speed (1500 rpm) shows that peak amplitude appeared much before in VR than HR, which indicates even in low rotational speed, VR-TPJB system is more unstable than HR-TPJB system. Results demonstrated that the balanced VR operated at high speed (6000 rpm) is more prone to instabilities than its horizontal counterpart (HR-TPJB system) at the same speed (6000 rpm). [ABSTRACT FROM AUTHOR]