Showing papers in "Journal of Tsinghua University in 1998"

Extraction of partial discharge signals using wavelet transform

Abstract: Using Mallat's algorithm of dyadic wavelet transform and Daubechies wavelet, low pass and band pass filters were designed to suppress narrow band disturbance for extracting partial discharge signals. In numerical simulation experiments the exponential damping or oscillating damping functions were used to simulate discharge signals and the effect of extracting signal as well as some other influential factors was investigated. The processing results of numerical simulation and on site monitoring data show that based on the feature of multi scales the wavelet transform could extract discharge signals quickly and efficiently from up to 10 narrow band disturbances and under adequate circumstances complete wave form could be obtained. Because of the faster processing speed this method is more suitable for real time application during on-line monitoring.

Damage detection of suspension bridges

Abstract: Damage detection of suspension bridges was discussed. The detection is based on comparison of initial signature (FRF, mode shapes and so on) of intact bridges with that of damaged bridges. Three waveform recognition indices based on FRF: the waveform chain code (WCC), the adaptive template methods ( I ATM ) and the signature assurance criterion ( I SAC ), and three mode shape based methods: the coordinate modal assurance criterion ( I COMAC ), the flexibility and the curvature mode shapes are used for damage detection of suspension bridges. Their sensibilities to damage in deck of Tsing Ma suspension bridge are compared. The application of the strain mode shape method to damage detection was discussed. The results show that among the three waveform recognition indexes, I ATM and WCC are more sensitive to damage than I SAC . All of them, however, can not predict damage locations. The results also show that among the three mode shape based methods, the flexibility and the curvature mode shape are more sensitive to damage than I COMAC , and can localize damage. It is demonstrated by experiment and analysis on clamped uniform beams that strain modal shapes are better for damage detection in some aspects.

On Pan’s principles of soil and rock stability analysis

Abstract: This paper gives a formal demonstration on Pan Jiazheng’s principles of soil and rock stability analysis, which states that: (1) among all possible slip surfaces of a soil or rock structure, the real one renders the minimum resistance against the external load; (2) the real internal force or stress distribution along the slip surface is the one that provides the maximum resistance against the external load. The demonstration was based on Drucker's Postulates and Sarma's stability analysis method of nonvertical slices. The virtual work principle and the upper and lower bound theorems in plasticity played an important role in the theoretical work. The paper also presents an example which shows that by proper implementations of Pan's principle, it is possible to find the accurate results given by the closedform solutions.

Neural networks compensate control for unknown systems with time delay

Abstract: A neural network discrimination method for time delay system and the parameter of delay time is discussed. Using the abrupt mutation resulted from the training error sumsquare of the real output and the expected output of the network, this control method changes the input sample period of the neural network so that it can discriminate the delay time of the non linear model. Combining the discrimination of neural network system with long time delay and the control method based on model compensation, it can be applied to the control of the long time delay system with variable parameters or with unknown delay time. The results of the simulation show that the control of system with time delay based on neural network model compensation method has a very good control effect.

Protocol integrated test system based on formal technology——PITS

Abstract: The usage of the formal technology in protocol testing will make protocol testing more accurate and efficient This paper proposes a protocol conformance testing strategy with formal technology, and based on the strategy introduces the design and implementation of a protocol integrated test system, call as PITS The system not only used for protocol conformance testing, but also for both interoperability and performance testing The paper also given its architecture design, testing procedure, and description of every components Finally, this paper illustrates several real applications of the PITS in OSI, TCP/IP and ATM protocol testing

Review of stress frequency effect of quartz crystal resonators and its applications

Abstract: The stress frequency effect of quartz crystal resonators has been investigated both experimentally and theoretically for almost half a century since it was discovered. As a result, a corpus of empirical and analytical results are available for quantifying the effect and many benefits such as the development of sensors based on the effect have resulted from the large body of investigations. However, interest in the effect and especially in practical applications of the effect have not waned up until now. This paper reviews the effect and its applications given in last 50 years. This work is very significant for researcher who investigates its practical applications.

Study on the “spot energy effect” of ultrasound ——Influence of ultrasound on desorption equilibrium for hydrogen association system

Abstract: NKA Ⅱ resin/TBP/50% alcohol and CL TBP resin phenol water were used as experimental systems. The dynamics of desorption process for adsorbate was measured at the condition of ultrasound. The influences of power density of ultrasound and temperature on the concentration of desorbed solute were studied. Results show that the concentration of desorbed solute increases with the increasing temperature and the increasing power density of ultrasound. The equilibrium concentrations of desorbed solute under ultrasound are much larger than that under the same temperature for normal desorption process. It means there exists the intensifying effect of “spot energy effect” under ultrasonic condition.

Carbon emission permit allocation and trading

Abstract: Our earth is faced with a grim challenge of global climate change and it is important for all countries in the world to go into action jointly to mitigate climate change. Carbon emission permit allocation and trading are two important issues to realize global cooperation. Two kinds of comprehensive carbon emission permit allocation mechanisms considering equity and efficiency were studied. After the carbon permit price was determined, the trading situations in various regions or countries in the world and the global benefits gained from the trading were expounded. The impact of carbon emission permit trading on China's economy was analyzed.

Calculating air age in a ventilated room with CFD method

Abstract: To evaluate indoor air quality and ventilation effectiveness instead of tracer gas technique, a new method to obtain air age is presented The transport equation of air age is derived based on tracer gas technique The form of this equation is the same as the general transport equation and can be solved numerically with the computational fluid dynamics (CFD) method The numerical results in a ventilated chamber are compared with the test data by Sandberg and Sjoberg It is shown that the predicted results agree well with the test data, which means that the CFD method is another way to get air age instead of tracer gas

Current status and developing trend of job shop scheduling research

Abstract: For the job shop planning and scheduling problems in the environment of CIMS, the status of the current research efforts is discussed. The classification and properties of job shop scheduling problem, and the varied research methods on solving it are discussed. Based on analyzing the various research methods, some useful solution strategies and methodology are proposed, such as paralleled/distributed strategy, resolution/group strategy, manmachine interaction strategy, dynamic rescheduling strategy and multi objective strategy, etc. several prospective research direction and its developing trends are proposed.

Adaptive and parallel genetic algorithm based on solving premature convergence

Abstract: Premature convergence is still the preeminent problem in genetic algorithms (GAs). Some excellent individuals or genes are lost due to premature convergence, which causes local optimum. This paper presents an improved genetic algorithm based on multiple populations evolution and adaptive parameter adjusting. Experimental results show that this method alleviates the problem of premature convergence and improves the efficiency of searching.

Advanced nodal Green's function method on Neumann boundary condition

Abstract: The presently broadly used code of nodal Green's function method for multidimensional neutron diffusion calculations is based on the third kind boundary condition. the form of this kind Green's function is relatively complex, and it must be converted so that the discontinuity factors can be used and the core power can be reconstructed. An advanced nodal Green's function method for three dimensional geometry which is based on the Neumenn (second kind) boundary condition was developed. Advantages of the method are: a) the Green's fuction is simplfed; b) it is easy to use discontinuity factors in the continuity condition of interface partial flux, and the fine flux distribution in the assembly is obtained by pin power reconstruction. the code NNGFM which is based on present method shows higher speed and accuracy through actual computation. It becomes the kernel code in the light water reactor (LWR) physics design and nuclear fuel management calculations.

A kind of method to improve controlling precision of fuzzy controller

Abstract: To counter the problem of lower controlling precision of fuzzy controller, this paper puts forward a method to improve controlling precision of fuzzy controller. First, the paper analyses the reason of lower controlling precision of conventional fuzzy controller, then puts forward a method to solve this problem and gives its design method, finally gives the simulating results of the improved fuzzy controller and compares with conventional fuzzy controller. The simulating results prove that the improved fuzzy controller can really eliminate stable state error and improve the controlling precision of fuzzy controller. The improved fuzzy controller retains the nonlinear controlling property of conventional fuzzy controller, its design is simple and its realization is easy, it has certain practical application value.

Seismic behaviour of composite steel concrete beams

Abstract: In order to study the performance of composite steel concrete beams with combined precast slabs and concrete sast in situ under the low cyclic loading, Experiments are conducted of six specimens of composite steel concrete beams. The types of loading include repeat loading and cyclic loading. The loading capacity and deformation performance of composite steel concrete beams under repeat and cyclic loading are analyzed and discussed in detail. Test results show that composite beams with combined precast slabs and concrete cast in situ behave as composite beams with all concrete cast in situ and possess excellent seismic performance. Deformation ductility ratio and reduction coefficient of rigidity are proposed. The research results are valulable in seismic designs of composite steel concrete beams.

Confidence analysis in character recognition

Abstract: In order to estimate the accuracy of character recognition, the defination of classifier's confidence value and the concept of generalized confidence are given. Based on the confidence value the optimal rejection theorem is proven. The relationship between confidence value and recognition rate is disclosed. The formula for evaluating the generalized confidence values for several commonly used pattern classifiers is presented and an algorithm to convert generalized confidence to confidence value is introduced. Three possible applications of confidence analysis: the selection of rejection area, the estimation of recognition rate and the combination of multiple classifier are proposed. Practice in handwritten numeral recognition and off line handwritten Chinese character recognition strongly supports the ideas and the methods.

Prosody learning and simulation for Chinese text to speech system

Abstract: In the research of speech synthesis, prosody expression and study are the kernels of improving performance of speech synthesis. The authors established a Chinese text to speech (TTS) system, Sonic. The researchers have designed prosody symbols and algorithm, basing on studying prosody descriptions and models, then marked up the text with prosody symbols, and implemented simulation of stress and intonation. To get the better naturalness and expressivity of the output speech, the system have been improved and a prosody learning TTS system, Sonic L, have been developed. In sonic L, learning with neural network is splitted two levels: based on words and based on sentences. The article introduces the actuality of technology of text to speech, describe the author's research and result on prosody studying, description and stimulation.

Dynamic analysis of hydraulic turbine runner and blade system(I) —Mechanics model and formulation

Abstract: A method for the dynamic analysis of hydraulic turbine runner is presented The method is based on the dynamics of rotationally periodic structure and the theory of added mass In accordance to the rotationally periodic characteristic of the runner, the concept of complex constraint is intoduced to simplify the structure It reduces significantly the dimension of structural dynamic analysis In order to consider the influence of the water on the dynamic response of the runner, the water has been assumed to be incompressible, irrotational and inviscid, and is induced into the governing equation for the vibration of the runner as the hydrodynamic added mass In the coefficient matrix of dynamic equation, the main part corresponding to the inner degrees of freedom of the substructure is real matrix Using this characteristic in calculation, the computer time can be saved to a great extent

Study on short and long term rigidity of composite steel concrete beams

Abstract: The slip effect on the interface of steel beam and concrete flange has an evident contribution to the deformation and reduction of the rigidity of the composite steel concrete beams. However, it is not taken into account by the current “transformed section method”. So the deformation is under evaluated at present. Formulae with consideration of slip effect are derived for predicting the short term and long term regidity of composite steel concrete beams. The simplified expression for determining the reduction coefficient of regidity is founded. The concrete creep and shrinkage are also taken into account simutaneously in the derived formula of long term regidity. The predicting deflection according to the suggested formula of short term regidity is in good agreement with the measured results from different available literatures. The suggested formulae are applicable to composite steel concrete beams with complete and incomplete shear connection.

Relationship between porosity and permeability of the particles packed bed

Abstract: Porosity and permeability of the particle packed bed are both important properties for soil science, petroleum physical principle, civil and environment engineering, chemical industry and materials engineering. The relationship between permeability k and porosity φ of the particle packed bed was measured by passing little flow with little pressure drop. The repeated experimental results show that, for a given unconsolidated porous medium, the permeability porosity relationship is unique. The relationship between the flow rate and pressure drop in the capillary porous media following linearity recovered by Darcy's law is consistent with that of the layer flow in ordinary pipes and channels. However, the conventional hydrodynamic theory and dimensional analysis are not sufficiently applied to the penetrate flow in the porous media. The permeability can not be expressed by a linear function of the square of the particle size. For the screened sand whose particle size rangesd from 100μm to 450μm and size ratio is 1∶1.25, the permeability can be estimated from the formula: k/ μm 2=1.72×10 4 ( d /mm) 1.465 φ 4.69 .

Swing phase control of intelligent lower limb prosthesis using electrorheological fluid

Abstract: The dynamic model of stump prosthesis for above knee amputee was established The solutions of inverse dynamic problem were adopted to obtain the function of knee moments for optimum gait patterns A damper using electrorheological fluid and its corresponding micro NC power supply have been developed to conduct the control of knee moment Based on speed measurement during walking, the corresponding moment pattern which has been stored in a micro computer, will start Therefore, the knee moments can be changed automatically The knee moment patterns are obtained by using a learning system, which let the gait of prosthetic side similar to the sound side The effectiveness of the swing phase control has been shown by experiments

Design of self adaptive micro tribology multiple measuring test rig and experimental studies on nano lubrication

Abstract: The basic principle and design of the self adaptive micro tribology multiple measuring test rig have been described. In the rig, by adopting widely used self adaptive floating contact system, precise loading by lever and precise friction force measuring system, the friction force in milli Newton scale can be obtained and the tribology characteristics of nano films in the different contact statues are studied. Using relative optical intensity technology, the film thickness in nanometer scale is measured simultaneously. The lubrication characteristics of 10 # standard liquid of viscosity have been investigated with the test rig. The variant trends of friction coefficient and film thickness with load, sliding velocity and lubrication ways (pure sliding in surface contact, pure rolling and pure sliding in point contact) have been studied. The experiments show that the test rig meets the design requirements.

Adaptive control scheme of induction motors with unknown rotor resistance

Abstract: An adaptive nonlinear tracking control scheme for current fed induction motors is proposed in order to reach high performance speed regulation as rotor resistance is unknown and rotor fluxes need observing. The controller bases on two phase fixed reference frame and adopts Lyapunov adaptive control structure. After introducing certain approximate algorithm, the estimate of rotor resistance reduces to a first order dynamic equation. In rotor flux adaptive observers, the influence of flux amplitude tracking error estimate and rotor resistance estimate error in addition to speed tracking error is considered. The stability and tracking ability of the control scheme are proved. Moreover, the simulation results are provided.

HTR 10 primary cavity cooling system and its features

Abstract: The primary cavity cooling system of the 10MW high temperature gas cooled test reactor (HTR 10) is one of the important safety related systems of the reactor It is composed of the residual heat removal system (RHRS) and the shielding cooling system The passive RHRS removes the residual heat from the reactor core by natural circulation, so it gets rid of the dependence on external power Finally, the residual heat can be discharged to the atmosphere via aircoolers by natural convection of air Presented in this paper are the design concept and features of the HTR 10 primary cavity cooling system, namely the passive RHRS with a heatshading board for controlling the radiation heat transfer, cooperating with the active shielding cooling system The detailed design, which is based on the above mentioned design idea, is completed This design has not only simplified the system, reduced the cost, curtailed the duration of construction, but also increased the reliability of the system

Sensitivities of natural modes of suspension bridges to structural parameters

Abstract: On the basis of perturbation stochastic finite element method, the fundamental equations of eigenproblems of suspension bridges with random structural parameters were derived The random parameters were discretized with the local averaging theory of random fields The statistics of the natural frequencies of Tsing Ma bridge were calculated under the assumptions that the elasticity moduli and the mass densities of the main cables, stiffening deck and the towers were considered as random variables The sensitivities of the natural modes were analyzed to these random variables The numerical results show that the sensitivities to the basic variables at different locations are significantly different

Prototype of a cooperative design support system CoDesign

Abstract: With the large installations and wide usage of computer aided design (CAD) systems and the rapid advances in the researches on computer supported cooperative work (CSCW), researchers are integrating CAD and CSCW technologies together to develop computer supported cooperative design (CSCD) systems In this paper, we will present some issues we encountered in the design and implementation of a real time CSCD prototype system We will place emphasis on the cooperation aspect, describing its architecture and the strategies and algorithms used in the user management, access control, group interface design, concurrency control Finally we give our concluding remarks and future plan

Dynamic analysis of hydraulic turbine runner and blade system(II) —Analysis of examples

Abstract: The method based on the dynamics of rotationally periodic structure and the theory of added mass developed in Part Ⅰ is used for the dynamic analysis of hydraulic turbine runner in this paper. The 16 noded relative degree of freedom shell element is discussed and used to mesh the blades of the runner. The coordinates of the nodes are acquired by spline interpolation. A hydraulic turbine runner and blade system is calculated. Its natural frequencies and mode shapes are acquired and the influence of the added mass on the frequency is discussed.

Study on stability and kinematic function of above knee prostheses

Abstract: The stability is one of the main problems of study of the lower limb prostheses. Based on analyzing the knee joints of the four bar linkage, this paper presents the concepts of the stable well off angle, absolute and relative instantaneous distance. Those concepts are used to evaluate the characters of above knee (A/K) prosthesis. Through discussion of stable area of knee, the concept of the relative stability is explained. The multi axis A/K prostheses increase the clearance between the foot and the ground. Therefore the possibility of strike between foot and ground is reduced. On the basis of quantitative analysis, a concept of the rising amount of ankle during the swing phase is presented to describe the evaluation of the kinematic performance of the multi axis A/K prostheses. The evaluation method presented in this paper will have significance to design and assemble of A/K prosthese.

Generalized fault tree knowledge representation method for power plant boiler fault diagnostic systems

Abstract: Fault diagnosis knowledge representation is a most basic issue in knowledge process. It is aimed at representing the knowledge of field experts with knowledge expression paradigms. A knowledge representation method of generalized fault tree is proposed and approached by applying objectoriented methodology in accordance with the issues of power plant boiler system fault diagnosis and its specific property. This method centers around diagnosis object. It is based upon a fault tree and is based on integrating of frame, rule, model and procedure. The application examples of power plant boiler system fault diagnosis are given. The method of knowledge representation has characteristics of terseness, agility, transparency and is easy to diagnose and infer.

Solidliquid twophase turbulent flowcalculation and measurement through centrifugal slurry pump impellers

Abstract: In order to further understand the flow structure of the liquidparticle twophase flows through slurry pump impellers, the twodimensional turbulent liquidparticle twophase flow through the impellers has been simulated by using the keAp turbulence model and the SIMPLEC algorithm. Calculated results indicate the main flow characteristics of the liquidparticle twophase flows through the impellers. The calculation reliability was proved by the comparison between calculated results and experimental data by using pressure gages for the pressure distribution at the solidliquid flow conditions and the comparison between calculated results and test results by using the PIV technique for the pure liquid flow velocity distribution through the impellers. Research results indicate that under the dilute concentration condition of particle phase, the existence of particle has a little influence to liquid phase flow, and makes the pressure developed by the impeller decrease. The more dense the particle concentration is, the more the pressure decreases.

One of case based reasoning product conceptual design systems

Abstract: Product conceptual design is an innovative activity that is to form and optimize the projects of products. It is a bottle neck problem in the process of product concurrent design. This paper introduces a case based reasoning product conceptual design system. Case model has been established according to the design requirements and the features of products. The case is described based on object oriented and the case library is built. Product conceptual design can be carried out by means of case based reasoning based on case model according to user requirements. Product similar case can be evaluated based on the knowledge of design and manufacturing, so the optimum solution of product conceptual design can be acquired. This system has been used successfully in design of six types of feedboxes of Beijing No.1 Machine Tool Plant. The efficience of case based reasoning can be improved dramatically based on the case model.