Solving the static equilibrium position is one of the most important parts of dynamic coefficients calculation and further coupled calculation of rotor system. The main contribution of this study is testing the superlinear iteration convergence method—twofold secant method, for the determination of the static equilibrium position of journal bearing with finite length. Essentially, the Reynolds equation for stable motion is solved by the finite difference method and the inner pressure is obtained by the successive over-relaxation iterative method reinforced by the compound Simpson quadrature formula. The accuracy and efficiency of the twofold secant method are higher in comparison with the secant method and dichotomy. The total number of iterative steps required for the twofold secant method are about one-third of the secant method and less than one-eighth of dichotomy for the same equilibrium position. The calculations for equilibrium position and pressure distribution for different bearing length, clearance and rotating speed were done. In the results, the eccentricity presents linear inverse proportional relationship to the attitude angle. The influence of the bearing length, clearance and bearing radius on the load-carrying capacity was also investigated. The results illustrate that larger bearing length, larger radius and smaller clearance are good for the load-carrying capacity of journal bearing. The application of the twofold secant method can greatly reduce the computational time for calculation of the dynamic coefficients and dynamic characteristics of rotor-bearing system with a journal bearing of finite length.

In this paper, a theoretical analysis method for leakage rate and dynamic characteristics of herringbone-grooved liquid seals is proposed. Steady-state velocities and leakage rate are figured out first with the inertia term of the fluid combined with mass conservation within the seals. Subsequently, the rotordynamic coefficients are solved based on the investigation of Iwatsubo and Childs. Laboratory tests were performed on a specially designed test rig. Detailed comparisons between the experimental results and theoretical predictions show a good agreement on the leakage rate and hydraulic forces for five model seals, which provide an evidence of validation of the analysis method developed in this paper. Moreover, the influence of rotational speed and pressure difference on the leakage rate and rotordynamic coefficients of herringbone-grooved seals is discussed. The results show that the operating conditions and seal structures greatly influence the sealing and rotordynamic performances, which is helpful for designing herringbone-grooved seals.

Francis turbine is a core energy conversion part and low frequency vibrations caused by unsteady vortex rope in the draft tube may damage the unit through resonance. Therefore, a more comprehensive assessment and monitoring of the status of Francis turbine is of great significance for unit stability. In this hydraulic machinery, mechanical impulses and hydraulic excitation are co-existing. The former manifests as a narrow low frequency band with high kurtosis, while the latter represents a wide high frequency band with energy associated with the vortex rope. Based on that, a novel method coined Convkurgram is proposed to suppress the extreme high kurtosis mechanical components and extract the hydraulic carrier wave efficiently. Besides, it takes multiple information frequency bands into consideration in case of contamination waves exist. Finally, the method is evaluated by means of actual vibration signals collected from the hydroelectric generating unit under normal and cavitation conditions. The results show the proposed method recognizes the characteristic frequency bands of mechanical components and hydraulic carriers as well as extracts the shaft frequency and blade passing frequency successfully.