Numerical and Experimental Stability Investigation of a Flexible Rotor on Two Different Tilting Pad Bearing Configurations

Abstract

Rotordynamic stability is crucial for high performance centrifugal compressors. In this paper, the weighted instrumental variable (WIV) based system identification method for rotating machinery stability is investigated based on a sine sweep forward excitation with an electromagnetic actuator. The traditional multiple input multiple output (MIMO) frequency response function (FRF) is transformed into a directional frequency response function (dFRF). The rational polynomial method (RPM) combined with WIV is developed to identify the rotor’s first forward mode parameters. This new approach is called the COMDYN method. Experimental work using the COMDYN method is carried out under different rotating speeds, oil inlet temperatures, and pressure conditions. Two sets of bearings with preloads 0.1 and 0.3 are investigated. A numerical rotor-bearing model is also built. The numerical results correlate reasonably well with the experimental results. The investigation results indicate that the new method satisfies the desired features of rotating machine stability identification. Furthermore, the system log decrement was improved somewhat with the increase of oil inlet temperature. The increase of oil supply pressure affects the rotor-bearing system stability very slightly. The results of this paper provide new and useful insights for potentially avoiding instability faults in centrifugal compressors.

Rotor-System Log-Decrement Identification Using Short-Time Fourier-Transform Filter

“…Figure 3 has shown that the theoretical first forward natural frequency and damped log decrement are 76.88 Hz and 0.2643, respectively. The identification method with IV [6] was used to estimate the modal parameters, and we did some improvements described in the appendix.…”

“…A stability identification method combining the PEM and IV method to estimate the frequency response function (FRF) in frequency domain was developed by Wang et al [5], and numerical simulation results show that the method can identify the damping ratio of the first forward and backward modes with high accuracy, even in a severe noise environment; furthermore, two example centrifugal compressors (nine-stage straight-through and six-stage backto-back) were employed to verify the feasibility of identification method in industrial configurations as well. With this method, Wang et al [6,7] carried out experiments to investigate two sets of bearings with preloads 0.1 and 0.3 under different rotating speeds, oil inlet temperatures, and pressure conditions; Wang et al [8] studied the effect of specific load on rotor stability as well. Recently, a new method, Operational Modal Analysis (OMA) method, which was used in structure modal analysis successfully, is very 2 International Journal of Rotating Machinery popular for its reputation of being convenient to use and having no need of any artificial excitation to the rotor system.…”

A Hybrid Strategy of Differential Evolution and Modified Particle Swarm Optimization for Numerical Solution of a Parallel Manipulator

“…Analysis of kinematics can be divided into two approaches: analytical methods and numerical methods [17,18]. In numerical methods, the forward kinematic solution is found by solving a nonlinear global optimization problem to find the numerical solution [19]. Many numerical calculation methods for solving nonlinear equations have been utilized in kinematic problems.…”

Active tilting-pad journal bearings supporting flexible rotors: Part I – The hybrid lubrication

“…Works related to control design for active TPJBs can be found in [20,21,22,23,24,25,26]. In the industry, the majority of the critical machines feature flexible rotors which make them worth analysing when supported by active TPJBs, in the same way as when they are supported by conventional TPJBs [27,28,29,30,31,32]. In rotating systems, the bearing dynamic properties heavily influence the whole system dynamics because they provide the main source of energy dissipation through the lubricating fluid film.…”