Stability Analysis on Rotor Systems Supported by Self-acting Tilting-pad Gas Bearings with Frequency Effects

The recent research on stability of gas bearing-rotor systems still mostly adopts the same method as in oil-lubricated bearing-rotor systems.The dynamic coefficients of gas bearings in the case that the perturbation frequencies are same as the rotating speed are used to carry out the stability analysis of rotor systems.This method does not contact the frequency characteristics of dynamic stiffness and damping coefficients of gas bearings with the dynamical behaviors of rotor systems.Furthermore,the effects of perturbation frequencies on the stability of systems are not taken into account.In this paper,the dynamic stiffness and damping coefficients of tilting-pad gas bearings are calculated by the partial derivative method.On the base of solution of dynamic coefficients,two computational models are produced for stability analysis on rotor systems supported by tilting-pad gas bearings according to whether the degrees of the freedom of pads tilting motions are included in the equations of motion or not.In the condition of considering the frequency effects of dynamic coefficients of tilting-pad gas bearings,the corresponding eigenvalues of the rigid and first five vibration modes of the system with the working speeds of 8-30 kr/min are computed through iteratively solving the equations of motion of rotor-system by using two computational models,respectively.According to the obtained eigenvalues,the stability of rotor system is analyzed.The results indicate that the eigenvalues and the stability of rotor system obtained by these two computational models are well agreement each other.They all can more accurately analyze the stability of rotor systems supported by tilting-pad gas bearings.This research has important meaning for perfecting the stability analysis method of rotor systems supported by gas bearings.

A simple theoretical model for evaluating the ability to form a single crystal

A simple theoretical model proposed recently to evaluate the ability of bulk materials to form single crystals is further tested via vast molecular dynamics simulations of growth for fcc （Ni, Cu, A1, Ar） and hcp （Mg） crystals, especially applied to the growth of bcc （Fe） crystal, showing that the validity of the model is independent of crystal types and the interaction potentials of the constitute atoms.

Study on Multi-objective Cutting Parameters Optimization of Titanium Alloy

In order to explore the cutting rules, optimize the cutting parameters and improve cutting efficiency of tita- nium alloy, multiple sets of test parameters were schemed out by using the uniform design method. Test cutting research of cutting forces and surface roughness with these parameters were conducted under the condition of 12 ℃ dry cutting and -50 ℃ cold blast machining, respectively. Through the regression analysis about the results of the test, a multiple linear regression model which was applicable for titanium alloy clean cutting on its surface roughhess and cutting force has been established. On this basis, a multi-objective optimization model aimed at suogace roughness, cutting force and cutting efficieney had been set up. And by means of the multi-objective data weighted method, successfully converted the multi-objective optimization model into a single-objective one. Verification tests were done under these cutting parameters, and the results are in good agreement with those calculated.

Flutter analysis of compressor blades under travelling wave modes using an efficient fluid–structure interaction method

Flutter is a self-sustained vibration which could create serious damage to compressor blades.Improving the efficiency and accuracy of Fluid-Structure Interaction(FSI)method is crucial to flutter analysis.An efficient FSI method which combines a fast mesh deformation technology and Double-Passage Shape Correction(DPSC)method is proposed to predict blades flutter under traveling wave modes.Firstly,regarding the fluid domain as a pseudo elastic solid,the flow mesh deformation and blade vibration response can be quickly obtained by solving the governing equations of the holistic system composed of blade and pseudo elastic solid.Then,by storing and updating the Fourier coefficients on the circumferential boundary,the phase-lagged boundary condition is introduced into the computational domain.Finally,the aerodynamic stability for the blades of an axial compressor under various Inter-Blade Phase Angle(IBPA)is analyzed.The results show that the proposed method can effectively predict the characteristics of aerodynamic damping,aerodynamic force and blade displacement.And a conceptual model is proposed to describe the motion behavior of the shock wave.Compared with the multi-passage method,the proposed method obtains almost the same unstable IBPA interval and the blade displacement error is less than 3.4%.But the calculation time is significantly shortened especially in small IBPA cases.