Haipeng Geng

Research on the Static and Dynamic Characteristics of Misaligned Journal Bearing Considering the Turbulent and Thermohydrodynamic Effects

Journal misalignment usually exists in journal bearings that affect nearly all the bearings static and dynamic characteristics including minimum oil film thickness, maximum oil film pressure, maximum oil film temperature, oil film stiffness, and damping. The main point in this study is to provide a comprehensive analysis on the oil film pressure, oil film temperature, oil film thickness, load-carrying capacity, oil film stiffness, and damping of journal bearing with different misalignment ratios and appropriately considering the turbulent and thermo effects based on solving the generalized Reynolds equation and energy equation. The results indicate that the oil thermo effects have a significant effect on the lubrication of misaligned journal bearings under large eccentricity ratio. The turbulent will obviously affect the lubrication of misaligned journal bearings when the eccentricity or misalignment ratio is large. In the present design of the journal bearing, the load and speed become higher and higher, and the eccentricity and misalignment ratio are usually large in the operating conditions. Therefore, it is necessary to take the effects of journal misalignment, turbulent, and thermal effect into account in the design and analysis of journal bearings.

Rotordynamics analysis of a quill-shaft coupling-rotor-bearing system

A quill-shaft coupling-rotor-bearing system is modeled and reported in this paper. The system consists of two rotors connected by a quill-shaft coupling in which each rotor is supported by two bearings. The stiffness matrix of the quill-shaft coupling is deduced and the equation of motion of the system is obtained by using the finite element method. Finally, the rotordynamics analysis of the system is conducted. The numerical results show that more frequency veering points occur for the quill-shaft coupling-rotor-bearing system compared with those of single rotor. In addition, the stiffness of the flexural element has significant effects on the first bending natural frequency of the quill shaft when the length of the quill shaft becomes shorter.

Axial stiffness of a rotating trunnion joint

A trunnion joint is modeled as a circular plate with two types of outer boundary conditions. One is clamped supported and the other is simply supported. Symmetrical bending deflection is produced when an external force acts on the inner side of the circular plate. The governing equations of the circular plate with these two kinds of boundary conditions are solved by using finite difference method, and the axial stiffness of the circular plate is obtained according to the relationship between the external force and the bending deflection of the circular plate. In order to verify the accuracy of the finite difference method, a finite element method was also given. The effects of rotational speed and the ratio of inner radius to outer radius of the circular plate on the axial stiffness are studied. It is shown that the rotational speed can significantly affect the axial stiffness of the trunnion joint for these two cases, especially for a lower ratio of inner radius to outer radius of the circular plate. The axial stiffness increases monotonically with the increase in rotational speed. More specifically, for a lower ratio of inner radius to outer radius of the circular plate, the axial stiffness with the simply supported boundary condition at high rotational speed is more than twice as much as the case without considering the rotational speed. Correspondingly, it is more than one and a half times for the clamped supported boundary condition.

Thermoanalysis of the permanent magnet rotor of the microturbine generator

To evaluate the rotor temperature field of a high speed permanent magnet synchronous generator (PMSG), an electromagnetic-eddy current-thermal coupled field model is constructed using 2D Time-stepping Finite-Element-Method (FEM). In the model, the electromagnetic field and the temperature field have the same meshed grids to make a node-to- node data transmission and are solved independently. The data transmission ensures the coupling of the fields and the solve order of these fields is controlled by an external program. Temperature-dependent parameters, for example conductivity, can be set in the model. Windage loss of the rotor calculated by empirical formulas is loaded to the temperature field. Distribution of the rotor temperature is obtained by a calculation example of a 100 kW, 45000 r/min microturbine generator. Experimental data are used to show the validity of the proposed model which is helpful to the thermal design of the high speed PM generator.

Analytical and Experimental Study of Dynamic Characteristics of Rod Fastened Rotor-Bearing System Under Preload Saturation

This paper investigates the dynamic characteristics of a composite rotor fastened by rods. Contact stiffness and equivalent bending stiffness between discs with different rod preloads of the rotor are obtained respectively by using the elastic and elastic-plastic contact theory. The finite element model of rotor-bearing system is built with Timoshenko beam elements. Critical speeds are respectively calculated with and without the consideration of contact effect, including the changing bearing dynamic coefficients. A test rig of rod fastening rotor-bearing system has been constructed to verify the numerical model results. The results show that the critical speed increases with rod preload and it keeps almost constant when the rod preload reaches a certain value, called preload saturation. The experiments demonstrate that the rod fastening rotor under preload saturation has the similar dynamic characteristics as integral rotor, such as the critical speed and backward whirl with asymmetric support stiffnesses. This kind of rotors which are under preload saturation can be analyzed and designed as an integral one without considering the contact effect. The study gives referential recommendations for analysis and design of a class of composite rotors which contain discs and rods.© 2013 ASME

An investigation on the static performance of hydrodynamic wave journal bearings

The wave journal bearing was first reported by Dimofte In the early 1990s. The static behavior of a hydrodynamic wave journal bearing is present in this paper. It is found that the static performance is related to the design parameters including eccentricity ratio, wave number, wave amplitude ratio and wave position angle. It is shown by the numerical results that the influence of the wave number to the load capacity and attitude angle is significant. The load capacity of the wave bearing decreases with the rise of wave number when the wave amplitude ratio is lower than 0.1 under the assumption that the load is applying on the sleeve between the two groove. The wave bearing has a larger load capacity than the plain one in general, except that the wave amplitude ratio is less than 0.15 and the wave position angle is smaller than 20 degree. There is a minimum value of the load capacity as the increasing of wave position angle with wave amplitude ratio smaller than 0.15, while in the larger wave amplitude ratio situation, the load capacity rises as first and then decreases in the end as an increasing wave position angle.

High cycle fatigue analysis of third stage blade based on shroud gap effect

Due to the very small gap of the contact relaxation, which is attributed to the abrasion of blade shrouds in the gas turbine, the fatigue failure of the blade occurs severely. So the gap effect and the high cycle fatigue properties of the turbine blade need to be studyed. Based on the theoretical calculation, the equation of the maximum value of shroud gap is given. Then through the finite element method, A modal analysis is used to determine the vibration characteristics. Meanwhile, based on a new test apparatus, the dynamic stress experiment is carried out. According to the simulation and experiment, the relationship between the gap effect and the high cycle fatigue of the third stage blade are analysed in detail. Finally, some results of the vibration characteristics and dynamic stress value are got and the relationship between the shroud gap and the high cycle fatigue damage is quantificationally given. From the above results, there is a good agreement between experiment and simulation, which shows that the gap effect on the high cycle fatigue can increase the damage and reduce the fatigue life of blades. Due to the influence of the shroud gap, the resonant frequency almost change into two times of the original one. And the experimental stress value suggests that there is a nolinear exponential relationship between the gap value and the fatigue damage ratio value.

Unbalance response analysis of the circumferential tie-rod combined rotor considering different support

The combined circumferential tie rod rotor with the advantages of light weight, good cooling effect and easy assembly is widely used in gas turbines, especially in heavy-duty gas turbines. In this paper, a circumferential tie-rod combined rotor was investigated using two-dimensional finite element model and three-dimensional finite element model with ANSYS. The critical speed of the rotor were calculated by finite element method and compared with experiments. The dynamic characteristics and stability of rotor are closely related to the supporting performance of bearing. The unbalance response analysis of the tie-rod rotor supported by elliptical pad bearing and tilting pad bearings which are loads acting on the tile pad and loads acting between the tiling pads are investigated respectively. The results show that the critical speed calculates with two-dimensional finite element model is closer to the experimental value. Selecting different support bearing has a great influence on the critical speed and vibration amplitude of the rotor. In addition, the tie-rod rotor supporting by tilting-pad bearing have a better stability when the load is between the pads.

Optimum design of ultra high speed hybrid rotor of PM machines

For the ultra high speed PM rotor, a metallic sleeve is usually interference fitted onto a cylinder or ring shaped PM to against the huge centrifugal force. The initial interference hinges not only on the loose of the rotor, but also strongly on the strength of the PM and the sleeve. In order to determinate the initial interference, this paper proposes an analytical model of stress/displacement field of the rotor which is verified by the Finite Element (FE) Method. Then, the initial interference which facilitates the optimal design of this type of rotor is deduced.

Study on Load Capacity and Dynamic Characteristics of the Wave Bearing at Infinite Compressibility Number

The wave bearing developed by Dimofte in the 1990’s features a continuous wave profile and presents numerous advantages compared to plain journal bearings. One of the main advantages of the wave bearing is that it has a higher degree of stability than the plain journal bearing and this load capacity is close to the load capacity of the plain journal bearing. Predicting these coefficients for the wave bearing with high bearing numbers is difficult, although there are many studies on the aerodynamic bearing. This paper presents an analytical method for calculating the limiting values of load capacity, dynamic stiffness and damping coefficients of the wave bearing for compressible fluids by simplifying the compressible Reynolds equation at high journal operation speed. A computational method is submitted which is derived from simple algebraic equations combined with infinitesimal perturbation method. The limiting characters of the wave bearing are compared with the plain journal bearing for all eccentricity ratios. Special emphasis is placed on investigating the effects of wave number, wave eccentricity ratio and wave starting angle on the limiting characteristics. Numerical results obtained indicate that the load capacity and stiffness of the wave bearing is better than the plain journal bearing at the same eccentricity ratio.Copyright