Qing Kai Han

EXPERIMENT OF OIL-FILM WHIRL IN ROTOR SYSTEM AND WAVELET FRACTAL ANALYSES

An oil-film whirl experiment is carried out in a rotor test rig and some nonlinear analyses are achieved in the paper. Firstly, the experiment schemes for measuring oil-whirl of a rotor system are introduced. The shaft vibrations are measured both in stable rotating process and running up and coast down. And then, the detailed signals of level 3, reconstructed by wavelet transform, representing the oil-film whirl motions are analyzed. At last, a wavelet fractal method is proposed, based on wavelet package transform and fractal geometry theory, and the correlative dimensions of signals in every frequency bands are calculated. This method describes the chaotic properties of the oil-film whirl vibration well, and wavelet fractals prove to be more effective than any other nonlinear parameters of the corresponding original shaft vibration signals.© 2005 ASME

Similitude Analysis on Mechanical Parameters of Thin Walled Shells

The relationship of the kinetic fundamental parameters for both the prototype and model are derived by employing the finite method. Based on the relations, the scaling laws of the thin walled cylinder for the free vibration are found by applying the similitude transformation to the governing equation. In the absence of the experimental data, the validity of the scaling laws is testified by numerical data. This is done by calculating theoretically the natural frequencies for free vibration of the cylinders. By substituting the model frequencies in the scaling laws, the frequencies of the prototype are obtained. Consequently, the frequencies of the model and prototype are compared. Examples that one end of the thin walled shell is clamped and the other is simply supported show exact agreement.

FE Analysis on Contact Properties between Root- Blade and Slot-Disc

The contact problem between root-blade and slot-disk structure of compressor is of much importance, because there is serious stress concentration in the structure, which is one of the parts with multi faults in aero-engine. First, finite element model for dovetail attachment is established to analyze stress concentration effects. Then, the stress distribution and other parameters such as contact pressure is obtained through contact analysis. In this paper, the finite element method based on contact analysis is used. Calculating results show that equivalent stress, contact pressure of blade-disk structure increase steadily as the rotating speed increases.

Damage Process Simulation of Damping Coating of Thin Plate

In this paper, the element birth and death technique is used to simulate the damping stripping process of damping coating, and the interface of substrate and damping coating is simulated by contact elements or interface elements. The stress intensity factors and crack length are also calculated based on finite element method under different thicknesses and elastic modulus The simulation could provide reference for the design and optimize of damping coating.

Free Vibration of a CLD Combination Cylindrical Shells

Based on elasticity plate theory and the theory of viscoelasticity, the solution of the natural frequency and dissipation factor are given under different boundary conditions. In this paper, the differential equation of the cylindrical shells is set up based on Love shell theory. Then the transfer matrix method is introduced to calculate the entirety transfer matrix and the expression of different frequency and dissipation factor. At last the natural character of CLD cylindrical shell under two different boundary conditions is researched.

Design Method of Dynamic Similarity of the Rotor-Bearing System

To predict the vibration characteristics of the rotor-bearing system by using the scale model and the associated scaling laws may significantly reduce the time and money required by the experiments. To this end, the dynamic similarity criteria are investigated inferring from the model behavior of rotor-bearing system to the vibration response of the prototype. The similar relationship was established by combining method of dimensional analysis and equation analysis based on similarity theory, and the effectiveness was verified through the finite element method. The result provide the theoretical rational for further study of the similarity design of the rotor-bearing system.

Kinematic Analysis on Materials on Counter Flow Screen and Selection of Dynamic Parameters of Machine

The paper presents the structural characteristics of counter flow screen. Pieces of plastic film and sandstones with different friction factors and elasticity coefficients are chosen as the research objects. The motion state and the sorting mechanism of materials in the sorting process are studied. According to the motion analysis on pieces of plastic film and sandstones on counter flow screen, it can be concluded that the materials with different friction factors and elasticity coefficients can all be sorted by counter flow screen. The more difference they have in friction factors and elasticity coefficients, the better sorting performance can be achieved. The selection and computation on the dynamical parameters of counter flow screen is carried out, which provides the theory evidence for the design of new friction sorting equipment and opens up new prospects for the application of counter flow screen.

Model-Based Fault Diagnosis Approach for Rotor System with Unidentified Supporting Parameters

The model based diagnosis method can detect both the fault location and the fault extent of the rotating machinery at the same time as it can combine the dynamics and fault diagnosis method together. However, the modal test of the supporting part is necessary when using the existing model based method, and the precision of the modal test results make a strong impact on the diagnosis results. In order to improve this case, an improved model based diagnosis method is presented herein by combining the fixed-interface modal synthesis method with the traditional model based diagnosis method. The DOF of the unidentified parameter due to the supporting parts are partitioned to interface DOF, and the displacement information of the supporting parts can be measured by the mounted sensors. Therefore, the model based diagnosis method can be carried out by only using the parameters of the rotor without considering the effects from the supporting, which can greatly improve the diagnosis precision and efficiency. This method is fit for the rotor systems with unidentified supporting parameter, and the rotor systems with unknown nonlinear supporting parameter. Both the numerical simulation results and the experiment results in the example proved the efficiency of this method.

Sealing Teeth Effects on Natural Frequencies of a Short Cylindrical Shell

Natural frequencies are calculated for a short cylindrical shell based on semi-analytical method of transfer matrix, especially considering the structural effects of sealing teeth. The thin wall shell with some sealing teeth can be divided into finite segments where the diameters are different. According to the theory of the state vector expression of a structure cross-section, a first-order ordinary differential equation referring to state vectors of continuous segment sections of a short cylindrical shell is established based on governing equations of thin cylindrical shell. Then a total transfer matrix of the shell with sealing teeth is obtained after producing all the transfer matrices of all the segments. The boundary conditions investigated in the study are free-free, free-clamped and clamped-clamped of the two ends of the shell. The natural frequencies can be solved by precise integration of the differential equation of the whole shell with divided segments. The obtained numerical examples show that the sealing teeth have influence on the frequency values of higher circumferential modes, and they also have influence on the natural frequencies in different boundary conditions. The results by the proposed method are also compared with those of finite element method.

Kinematic Analysis of Three-Wire-Driven Parallel (TWDP) Robot

In the paper, a novel new gravity-constrained (GC) three-wire-driven (TWD) parallel robot is proposed. With its mechanism model, three typical kinematics analytical models, including horizontal up-down motion, pitching motion and heeling motion and their corresponding simulations are given in detail. In static analysis, the change of tensions in the wires is calculated based on previous kinematics analysis. The simulation results show the robot has good movement stability. The paper can provide useful materials to study of dynamics and control on wire-driven robot.