1988 Vol. 3, No. 4

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THEORETICAL BASIS OF VIBRATION DIAGNOSIS
Gu Jialiu
1988, 3(4): 295-298,380.
Abstract PDF(473KB) icon1323 icon428
Abstract:
Three vibration diagnosis methods are discussed, which are normal spectrum analysis method, modal parameter recognition method and time series analysis method. It is demonstrated that the modal parameter recognition method is far from a practical one due to its threoretical shortcomings. The time series analysis method is promising to diagnose the machine defaults while ased as a tool to recognize the "input form filter". Therefore, this method is comparable with the maximum entropy spectrum analysis but performed in the time domain. A perfect diagnosis software should contain both the normal spectrum and time series analysis methods.
A THEORETICAL STUDY ON DYNAMIC CHARACTERISTICS OF A HIDH-SPEED ROTOR-SUPPORT-SQUEEZE FILM DAMPER SYSTEM
Feng Xinhai, Fu Caigao, Xu Shian, Li Xifan
1988, 3(4): 299-303,381.
Abstract PDF(540KB) icon1695 icon434
Abstract:
Some major achievements in the theoretical study on dynamic characteristics of a high-speed rotor-support-SFD system are reviewed. A practical program to calculate unbalance response of a complex rotor system has been worked out by means of "standard component",and "body information" concepts in the unbalance response prediction research, while the steady, transient and sudden unbalance behaviours of SFD have been comprehensively considered in the dynamic characteristics research. The centralized and uncentralized SFD models are compared, and therefrom a conclusion is drawn that the uncentralized SFD may gain much better damping effect. The design procedure and recommended SFD design parameters from theoretical analysis and practical experience has been verified to be a success.
AN EXPERIMENTAL INVESTIGATION ON DAMPING OF HIGH-SPEED ROTOR-SUPPORT-SQUEEZE-FILM DAMPER SYSTEM
Fu Caigao, Feng Xinhai, Xu Shian, Li Xifan, Zhu Changsheng
1988, 3(4): 304-308,381.
Abstract PDF(671KB) icon1621 icon411
Abstract:
The main experimental outcomes of this damper system(SFD) are introduced, which has laid a foundation for design application. Bistable jump depicts deep nonlinearity of SFD. Experimental results demonstraue the bi-stable jumpings of both centralized and uncentralized SFD systems and illustrate that the jump can be distinguished from an abrupt amplitude change of critical speed according to whether the mass center of the disc rotates to the opposite direction. In order to examine the structural integrity of SFD, a 256 hours life-test has been carried out. It is shown that the SFD not only exhibits quite good damping effect, but also stands the long-time test under severe working conditions.
ON DAMPING MECHANISM OF SQUEEZE FILM
Xue Zhongqing and, Meng Guang
1988, 3(4): 309-314,382.
Abstract PDF(685KB) icon1639 icon376
Abstract:
This paper surveys our researches on non-Newtonian viscosity effects, jump bifucation phenomena, and sudden unbalance response in squeeze-film dampers (SFD).The effects of a polymer thickened VI improved oil as pseudo-ptastastic fluid (PPF) on a SFD are investigated theoretically and experimentally. A modified Reynolds equation for pressure distribution of PPF in SFD has been derived and dynamic characteristics of SFD are evaluated. It is found that the film pressure distribution of PPF in SFD is smaller than that of a Newtonian fluid(NF), the centralized SFD is expected to have better film rigidity, while the uncen-tralized SFD is better in damping, the damping capacity of PPF film is inferior to that of NF film, and the effects of non-Newtonian viscosity on the dynamic characteristics of a SFD can be neglected in practice.The jump bifucation phenomena of a flexible rotor-SFD bearing system are examined with the aid of a Duffing equation. The phenomena that the frequency response curve of flexible rotor-SFD bearing system bends to right and becomes multivalued in a certain frequency range are due to the stiffening spring non-linearity of the squeeze-film force. The nonlinear cllaracteristics of the jump bifucation can, be estimated by the nature of the, backbone curves and boundary curves of the frequency response curve.A new mathematical model of sudden unbalance is introduced in calculating unbalance response. The analysis completed with this model shows that SFD is good at depressing the sudden unbalance vibration, and the uncentralized SFD is better than the centralized one in this aspect.
A TRANSFER MATRIX IMPEDANCE COUPLING METHOD IN ROTORDYNAMICS
Huang Taiping
1988, 3(4): 315-318,382-383.
Abstract PDF(635KB) icon1710 icon372
Abstract:
A transfer matrix impedance coupling method for eigensolutions in rotor-dynamics is developed. The concepts of substructure synthesis and coupling of mechanical impedance data are applied to this method,so that the application of the traditional transfer matrix method can be extended to the dynamic analysisof complex rotor-support sysems. For the systems with only one interconnection, such as single rotor with one flexible support, the eigenvalues can be readily obtained without any iteration form intersections of the critical speed map of rotor subsystem and the mechanical impedance curve of flexible support one. The present method can be used for eigensolution of the complex multi-spool rotor system with intershaft bearings and special shape of rotor structure, no matter whether it has isotropic or orthotopic properties, as well as it is undamped or damped,The analysis can be completed by calculation only or in combination with test data. Numerical examples show that this method is suitable for engi-neering application with high accuracy, convenience and low cost.
SIMPLE BALANCE METHODS OF HIGH-SPEED ROTORS IN FIELD
Yan Litang, Zhu Zigen, Li Qihan
1988, 3(4): 319-322,383.
Abstract PDF(481KB) icon1466 icon504
Abstract:
Some simple dynamic balance methods of rotor systems are investigated These methods featuring simplicity and ease without recourse to any complicated instrumentation and calculation system are particularly suitable for rotor balance in field. The simple rotor balance method with influence coefficients and that with least quadratic are presented. The balance problems of rotors with non-axisymmetrical support stiffness and for rigid rotor systems in field are also discussed. Some practical examples prove the methods presented are applicable.
A METHOD FOR DETERMINING MAJOR UNBALANCE ROTOR
Yang Litang and, Li Qihan
1988, 3(4): 323-326,383.
Abstract PDF(471KB) icon1449 icon406
Abstract:
This paper provides a method to determine whether a compressor or a turbine rotor is the major unbalance rotor according to the vibration signals measured from transducers mounted on the engine ease. The method only needs to choose two or three thansducers sensitive to unbalance responses in different places. The major unbalance rotor can thus be recognized by comparison of the vibration data measured at some sensitive speeds with the standard vibration data which have been previously measured and analyzed. The method can be readily applied to rotor balance of aeroengine in field and save time and cost.
RESEARCH ON CONTROL TECHNIQUE OF BLADE FLUTTER
Song Zhaohong
1988, 3(4): 327-332,384.
Abstract PDF(606KB) icon1545 icon394
Abstract:
This paper summarizes our work on the control techniques of blade flutter in recent years. It involves a numerical method for predicting blade flutter boundary in all frequence range, the flutter characteristics of the blades with different disposition of the three centers, the flutter depression characteristics of the mistuning blades, the technique of aeroelastic tailoring for controlling the blade flutter, and the experimentation on a series of blade fluttering rotor designed by us to reproduce flutter.
COUPLING VIBRATION CHARACTERISTICS OF MISTUNED BLADED-DISK ASSEMBLY
Shen Dakuan, Chen Qun, Liao Mingfu, Yan Yunju
1988, 3(4): 333-336,384.
Abstract PDF(416KB) icon1580 icon372
Abstract:
A 16-blades-disk of flat plate is made as a test and mathematical model to study the effects of blade mistuning on the dynamic characteristics of bladed-disk assembly, as well as the effects of mistuning amplitude,mistiming order and six distribution types of mistuning on the response to forced vibration. The results show that the natural mode of a tuning system can be categorized into single-mode and double-mode. Mistuning separates the double-mode into two modes of similar frequency. The response to forced vibration of a mistuned system is greater than that of the tuning system and the former will rise with increase of mistuning amplitude. At the same exciting frequency the influences of the various distribution types on the response to the forced vibration are different, that is to say, there exists an optimal distribution type. The blade bearing the greatest response is generally the extremely mistuned one, and there certainly exists one or more blades bearing the greatest response at any exciting frequency. This might be one of the causes leading to damage of one or more blade.
STUDY ON DIRECT IDENTIFICATION OF DISPLACEMENT MODE AND STRAIN MODE BY IMPULSE EXCITATION
Yi Liyan
1988, 3(4): 337-340,385.
Abstract PDF(419KB) icon1611 icon396
Abstract:
The theory and method of direct identification of displacement and strain modes for vibration modal test with strain guages are described. The concept of strain mobility, strain displacement relationships and derivation of formulae of transfer functions in terms of strains are considered. The system modalparameters, including the strain mode and stress mode etc., can be identified by the present method. This is a new development for modal tests of impules excitation.
ANALYSIS OF DAMAGE TOLERANCE FOR TURBINE DISKS
Nie Jingxu
1988, 3(4): 341-346,385.
Abstract PDF(621KB) icon1554 icon483
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This paper deals with the analysis and design of the damage tolerance for turbine disks. A practical design method is worked out and verified through analysing the damage tolerance of an existing engine. A "twice evaluation algorithm" for evaluating J-integral is provided, in which J is estimated in the light of the linear elastic fracture mechanics, and then a plastic correction with iterative procedure is made to obtain J. On the basis of breakdown tests and elaborate theoretical calculations, a criterion and a solution algorithm for determining the critical crack length are suggested. A method calculating residual life or turbine disk initiating cracks is provided, which is proved practical. The numerical results obtained by this method are in good agreement with the statistics of crack propagation collected from the actual turbine disks.
THERMOELASTOPLASTIC CREEP ANALYSIS FOR TURBINE DISK
Mu Xiaying and, Liu Xirui
1988, 3(4): 347-350,385-386.
Abstract PDF(515KB) icon1241 icon401
Abstract:
This paper deals with the strength analysis for turbine disk of aeroengine. A finite element analysis program of thermoelastoplastic creep is formulated,which imitates a cyclic loading in flight. Considering the influence of factors of creep, change of material's properties, and process of temperature elevation,the stress analysis of the disk-body is accomplished under various working conditions. Moreover, the residual stress resulting from a cyclic loading is calculated. Some useful conclusions have been drawn for engineering design.
EXPERIMENTAL AND APPLIED RESEARCH ON CREEP-RECOVERY
Mu Xiaying and, Liu Xirui
1988, 3(4): 351-354,386.
Abstract PDF(471KB) icon1690 icon463
Abstract:
Creep recovery testing of nickel-alloy at three temperatures is reported, from which some useful rules are found. A simple and efficient analytical method of creep recovery stress is provided. The effect of creep recovery is demonstrated by a numerical example.
TEST RESEARCH ON MAIN SHAFT SERVICE LIFE OF AEROENGINE
Fang Zuying and, Liu Dunhui
1988, 3(4): 355-360,386.
Abstract PDF(592KB) icon1729 icon351
Abstract:
The method for determining damage. conversion of main shaft of aeroengine is introduced. In accordance with the linear accumulating fatigue damage theory and S-N curve,the standard damage cycles per flight hours,or damage conversion ratio Ap for flight can he obtained from the comparative residual life tests of the shafts with different service life. The main shaft fatigue life tests indicate that even the worst main shaft can resist the standard load cycle, or predicted safe standard cycle life. If it is divided by Ap,the service life (hours) of a main shaft can be determined. Further, the determination method of target service life is provided for general maneuver flight load conbined with spin flight load.
STRENGTH ANALYSIS AND FATIGUE LIFE PREDICTION FOR LOAD-BEARING CASE OF AEROENGINE UNDER COMPLEX LOADING
Shang Weijun and, Li Mingda
1988, 3(4): 361-364,387.
Abstract PDF(480KB) icon1744 icon475
Abstract:
The calculations and tests of stress distributions for load-bearing case of aeroengine are presented. It is noted that the stress finite element analysis of the case may be divided into three steps, namely model evaluation, stress distribution calculation of the actual case and detailed calculation of partial structures. The basic approach and major achievements of the theoretical and experimental researches on thermal stresses in cylindrical case are described. Finally, the progress in the low-cycle fatigue life, prediction of notched members at room and elevated temperatures, and the essential feactures of the finite element analysis program for elastoplastic creep are briefed.
LIFE PREDICTION 0F COOLED TURBINE BLADE
Liang Guowei
1988, 3(4): 365-370,387.
Abstract PDF(660KB) icon1576 icon381
Abstract:
The major factors affecting life prediction of turbine blade are discussed, i.e. fatigue life data of materials employed and stress and strain analysis of the blade, which in turn is governed by constitutive relation of the materials, temperature distribution within the blade and its boundary conditions, and also dependent on finite element analysis technique. The emphasis is placed on the influence of material's constitutive relation under cyclic loading on the life prediction and the problems encountered in determining the transient temperature field of the turbine blade under thermal cycling. It is shown that the life prediction components by "Local Stress-Strain Approach" can narrow its scattered band down to + 50%.
SELECTlON OF R&D STRENGTH PROJECTS OF AEROENGINE
Feng Xinhai and, Hu Jiusheng, Liu Wenge
1988, 3(4): 371-374,388.
Abstract PDF(482KB) icon1757 icon464
Abstract:
Fuzzy ISODATA (Iterative Self-Organizing Data Analysis Technique A) and interdependence matrix method are applied to selecting interdependent projects of aeroengine strength and vibration research program,which comprises 23 project candidates. By using fuzzy ISODATA algorithms,the projects are fuzzily classified into 5 priority grades according to the evaluations made by experts in terms of the benefit contributions and the interrelationships of the projects. R&D project managers can obtain a number of feasible project sets by choosing and combining the priority grades of the benefit contribution and the project interrelations, and then select a set of projects on the basis of their experiences, preferences and resource restraints.
EVALUATION OF TECHNOLOGICAL BENEFITS OF HPPSARP
Shao Zhongpu, Si Yonghua, Feng Baosheng, Liu Wenge
1988, 3(4): 375-378,388.
Abstract PDF(458KB) icon1378 icon391
Abstract:
An approach to measuring technological change is presented and applied to evaluating technological benefits of the HPPSARP, (High Performance Propulsion System Advanced Research Program)which comprises 72 projects relating to 228 technical feature aspects. The technological changes in theoretical and experimental aspects are illustrated. Technological gaps between Chinese and international advanced levels and relative technological change rates are analyzed. The analysis shows that the technological benefits of the program raise the state-of-the-art of China's aeroengine in the 228 technical aspects and reduce the technological gaps by 1.6 year. Moreover, the relative technological change rate is estimated to be up to 1.225.

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