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Dynamics analysis and experiment on the fishtailing type of valveless piezoelectric pump with rectangular vibrator

Science china(Technological Sciences) 2010年第12期53卷 3241-3247页

作者： HUANG Yi1, ZHANG JianHui1, HU XiaoQi1, XIA QiXiao2, HUANG WeiQing1 & ZHAO ChunSheng1 1 department of Aerospace engineering, Nanjing university of Aeronautics and Astronautics, Nanjing 210016, china 2 department of mechanical and electrical engineering, beijing union university, beijing 100020, china department of Aerospace engineering Nanjing University of Aeronautics and Astronautics Nanjing China department of mechanical and electrical engineering Beijing Union University Beijing China

In recent years, the research and development of piezoelectric pumps have become an increasingly popular topic. Minimization, structure simplification and stronger output become the focus of piezoelectric pumps’ research due to its possible application in MEMS technology. The valveless fishtailing piezoelectric pump, neither a volumetric nor a rotating pump, was invented according to the bionics of fish swimming. With assumption that the head of the fish is fixed while its tail is swinging, fluid would flow toward the end of the tail, achieving the function of a valveless pump. This type of pumps creates a new branch for the piezoelectric pump research, which is proposed for the first time in this paper. The relationship between the flow rates and vibrating frequencies was derived from the interaction between the vibrator and fluid. Numerical simulations with FEM software were conducted to study the first and second vibration modes of the piezoelectric vibrator. The results showed that the maximum amplitude of the vibrator was 0.9 mm at the frequency of 76 Hz for the first vibration mode, while the maximum amplitude of the vibrator was 0.22 mm at the frequency of 781 Hz for the second vibration mode. Experiments were conducted with the Doppler laser vibration measurement system, and the results were compared to those of the FEM simulation. It was shown that in the first vibration mode the piezoelectric vibrator reached its maximum amplitude of about 0.9 mm at the driving frequency of 49 Hz, which gives the flow rate of 2.0 mL/min, in the second vibration mode, the maximum amplitude was about 0.25 mm at the frequency of 460 Hz with the flow rate being 6.4 mL/min.

关键词： piezoelectric pump valveless fishtailing rectangular vibrator dynamics analysis experiment

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Analysis on ignition and extinction of n-heptane in homogeneous systems

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Science china(Technological Sciences) 2005年第5期48卷 556-569页

作者： LIU Yongfeng1 & PEI Pucheng2 1. mechanical and electrical engineering department, beijing Institute of Civil engineering and Architec-ture, beijing 100044, china 2. State Key Laboratory of Automotive Safety and Energy, Tsinghua university, beijing 100084, china mechanical and electrical engineering department Beijing Institute of Civil Engineering and Architecture Beijing China State Key Laboratory of Automotive Safety and Energy Tsinghua University Beijing China

To calculate ignition delay times, the governing equations about species and temperature, which are in a closed volume based on the theory of thermal explosion and in a continuously stirred flow reactor, are deducted. The method referred to steady state assumptions is based on the observation that due to very fast chemical processes in combustion problems many chemical species and reactions are in a quasi-steady state or partial equilibrium. When a species is assumed to be in the steady state, the corresponding differential equation can be replaced by an algebraic relation, which reduces the computational costs. The steady state solution of the reactor equations describes the three ignition temperature regimes and get “S-shaped curve”. The reduced simplified 4-step mechanism for n-heptane from 1011 elementary reactions leads with the steady state assumptions to linear differential equations, which is solved. The simulation results of the 4-step reduced mechanism for n-heptane are fitted well with the experiment data. At last, two important parameters are discussed thoroughly and the temperature perturbation is given. It reduces the computational efforts considerably without losing too much accuracy and further supplies numerical methods for turbulent combustion in the diesel engine.

关键词： ignition delay times, thermal runaway, steady state assumptions, continuously stirred flow reactor.

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Parameter identification theory of a complex model based on global optimization method

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Science china(Physics,Mechanics & Astronomy) 2008年第11期51卷 1722-1732页

作者： QU Jie1, JIN QuanLin2 & XU BingYe3 1 College of Automotive engineering, South china university of Technology, Guangzhou 510640, china 2 beijing Research Institute of mechanical and electrical Technology, beijing 100083, china 3 department of engineering Mechanics, Tsinghua university, beijing 100084, china College of Automotive engineering South China University of Technology Guangzhou China beijing Research Institute of mechanical and electrical Technology Beijing China department of engineering Mechanics Tsinghua University Beijing China

With the development of computer technology and numerical simulation technology, computer aided engineering (CAE) technology has been widely applied to many fields. One of the main obstacles, which hinder the further application of CAE technology, is how to successfully identify the parameters of the selected model. An elementary framework for parameter identification of a complex model is provided in this paper. The framework includes the construction of objective function, the design of the optimization method and the evaluation of the identified results, etc. The parameter identification process is described in this framework, taking the parameter identification of the superplastic constitutive model considering grain growth for Ti-6Al-4V at 927°C as an example. The objective function is the weighted quadratic sums of the difference between the experimental and computational data for the stress-strain relationship and the grain growth relationship; the designed optimization method is a hybrid global optimization method, which is based on the feature of the objective function and incorporates the strengths of genetic algorithm (GA), the Levenberg-Marquardt algorithm and the augmented Gauss-Newton algorithm. The reliability evaluation of parameter identification result is made through the comparison between the calculated and experimental results and between the theoretical values of the parameters and the identified ones.

关键词： constitutive model parameter identification theory inverse analysis global optimization

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Preparation of MWNTs/Al_2O_3 composites and their mechanical and electrical properties

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Science china(Technological Sciences) 2005年第6期48卷 622-631页

作者： FAN Jinpeng1,2, ZHAO Daqing1,2, XU Zening1,2 & WU Minsheng1,2 1. department of mechanical engineering, Tsinghua university, beijing 100084, china 2. Key Laboratory for Advanced Manufacturing by Materials Processing Technology, Tsinghua university, beijing 100084, china department of mechanical engineering Tsinghua University Beijing China Key Laboratory for Advanced Manufacturing by Materials Processing Technology Tsinghua University Beijing China

The mechanical and electrical properties of MWNTs/Al2O3 composite prepared fabricated by hot pressing are investigated. The relation between properties and microstructure of composites is also discussed. With 4wt% MWNTs as reinforcement, the fracture toughness of composite obtained reaches 5.55 MPa·m1/2, which is 80% higher than that of pure Al2O3 obtained in the same conditions. The main toughening mechanism is CNTs’ pinning alumina grain boundaries, and the pullout of CNTs takes effect also. Through adding 2wt% MWNTs and altering the mix method, the fracture toughness of the composite obtained is 3.97 MPa·m1/2. Furthermore, the electrical resistivity is as low as 8.4×10?3 ?·m, decreasing by 14 orders of magnitude compared with pure alumina ceramics. The function of CNTs in composite is related to the distribution state of CNTs in composite, and the distribution state of CNTs in matrix is dependent on preparation procedures.

关键词： MWNTs, alumina, composite, fracture toughness, electrical properties.

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New method for computing unstable equilibrium points of power systems with induction motors

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Science china(Technological Sciences) 2010年第4期53卷 881-885页

作者： CHEN Lei,XU Fei & MIN Yong State Key Lab of Power Systems,department of electrical engineering,Tsinghua university,beijing 100084,china State Key Lab of Power Systems Department of Electrical Engineering Tsinghua University Beijing China

The computation of the unstable equilibrium point(UEP) is a key step involved in stability region estimation of nonlinear dynamic systems.A new continuation-based method to compute the UEPs of a power system with induction motors is *** mechanical torques of motors are changed to form a parameterized equation *** the solution curve of the equation set is traced by the continuation method from the stable equilibrium point to a *** direction of mechanical torque change is varied to get multiple *** obtained UEPs are mostly *** fast assessment of induction motor stability is studied by approximating the stable manifolds of the *** method is tested in several systems and satisfactory results are obtained.

关键词： power system stability transient voltage stability unstable equilibrium point(UEP) stability boundary induction motor

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Experimental measurement of growth patterns on fossil corals:Secular variation in ancient Earth-Sun distances

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Chinese Science Bulletin 2010年第35期55卷 4010-4017页

作者： ZHANG WeiJia1,3,4,LI ZhengBin2,3 & LEI Yang1 1 department of Physics,Peking university,beijing 100871,china 2 department of electrical engineering and Computer Science,Peking university,beijing 100871,china 3 State Key Laboratory of Advanced Optical Communication Systems & Networks,Peking university,beijing 100871,china 4 Committee of Yuanpei Honors Program,Peking university,beijing 100871,china department of Physics Peking University Beijing China State Key Laboratory of Advanced Optical Communication Systems & Networks Peking University Beijing China Committee of Yuanpei Honors Program Peking University Beijing China department of electrical engineering and Computer Science Peking University Beijing China

In recent years,much attention has been given to the increase in the Earth-Sun distance,with the modern rate reported as 5-15 m/cy on the basis of astronomical ***,traditional methods cannot measure the ancient leaving rates,so a myriad of research attempting to provide explanations were met with unmatched *** this paper we consider that the growth patterns on fossils could reflect the ancient Earth-Sun *** mechanical analysis of both the Earth-Sun and Earth-Moon systems,these patterns confirmed an increase in the Earth-Sun *** a large number of well-preserved specimens and new technology available,both the modern and ancient leaving rates could be measured with high precision,and it was found that the Earth has been leaving the Sun over the past 0.53 billion *** Earth's semi-major axis was 146 million kilometers at the beginning of the Phanerozoic Eon,equating to 97.6% of its current *** modern leaving rates are 5-14 m/cy,whereas the ancient rates were much *** results indicate a special expansion with an average expansion coefficient of 0.57H0 and deceleration in the form of Hubble *** the basis of experimental results,the Earth's semi-major axis could be represented by a simple formula that matches fossil measurements.

关键词：地球太阳古代距离生长模式实验石珊瑚量化

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APPLICATION OF GLEEBLE 1500 ON SUPERPLASTICITY

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Acta Metallurgica Sinica(English Letters) 2000年第2期13卷 514-520页

作者： B. Z. Bai X.J.Sun and L.Y.Yang 1) department of Materials Science and engineering, Tsinghua university, beijing 100084, china 2) beijing Research Institute of mechanical and electrical Technology, beijing 100083, china

Gleeble1500 thermo-mechanical simulation machine is considered to be the first grade equipment in materials' research. However, it is seldom used in superplastic research. Perhaps this is because its specimen's heating method is not suitable to get large elongation. Elongation is an important parameter to evaluate superplasticity, but some other parameters such as the relationship between stress and strain rate are more important than elongation-it is an essential property to superplasticity. The stress-strain rate relationship can be very easily and very accu- rately got with Gleeble machine than with some other simlar equipment, and the relationship between microstructure and superplastic deformation is more easily examined with Gleeble. Present authors have got some new achievement in anisotropy, heterogeneity of superplastic deformation, and first put forward the regulation of dynamic equilibrium in microstructural evolution during superplastic deformation. All of these have been concluded from the experimental results mainly through Gleeble as well as the microstructural *** research work has got the support of National Natural Science Foundation and some international cooperation. Some theoretic and experimental results have been used in the practice of superplastic forming. Obvious effect of reducing cost and improving quality of formed parts has been achieved.

关键词： thermo-mechanical simulation superplasticity

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The Boiler Tube Wall Thickness Quantitative Evaluation Fusing the Magnetic and Ultrasonic Technique

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武汉理工大学学报 2006年第S3期28卷 800-804页

作者： SONG Xiaochun~(1,2) HUANG Songling~2 ZHAO Daxing~1 (1.School of mechanical engineering,Hubei university of Technology,Wuhan 430068,china, 2.State Key Lab ef Power Systems,department of electrical engineering,Tsinghua university,beijing 100084,china) School of mechanical engineering Hubei University of TechnologyWuhan 430068China State Key Lab of Power Systems Department of Electrical EngineeringTsinghua UniversityBeijing 100084China State Key Lab of Power Systems Department of Electrical EngineeringTsinghua UniversityBeijing 100084China School of mechanical engineering Hubei University of TechnologyWuhan 430068China

Wall thickness is always a key index for boiler tube inspection in power plant,in order to improve the inspection efficiency and accuracy,a new method fusing the magnetic and ultrasonic technique was *** magnetic technique was used to do full inspection and locate the flaws,and the ultrasonic was employed to implement further quantitative inspection accu- *** comparing the precision of the polynomial,exponential and logarithmic function,the polynomial model was selected to fit the relations between the wall thickness and the peak value of magnetic signals,and the data measured by ultrasonic thickness meter was used to calibrate the model parameters online,the defect depth can be sized *** experimental results demon- grate that the model used in this system has better accuracy than the statistics relation model clearly,and it is also suitable for defect evaluation ***,it is unnecessary to have much more experimental data for the curve fitting technology,so it has better practicability than the other methods.

关键词： boiler tube main magnetic flux ultrasonic non-destructive testing

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Model of Current Threshold for Perception in Testing electrical Safety Performance

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Transactions of Tianjin university 2010年第1期16卷 11-16页

作者：王晓飞张朝晖李东刘国忠赵旭 School of Information engineering University of Science and Technology Beijing School of Electro-Optical engineering Beijing Information Science and Technology University department of Neurology The 306th Hospital of PLA

A generalized mathematical model of human body current threshold for perception was established and the current flowing through human body could be arbitrary cyclical *** relationship between human body current threshold for perception and current frequency, true root mean square(RMS) value and influence factor was described.A test system was established based on electroencephalogram(EEG) to study the relationship between human body current threshold for perception and current waveform, frequency ...

关键词： electrical safety performance leakage current current threshold for perception current waveform electroencephalogram(EEG)

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Study on hemodynamics in patient-specific thoracic aortic aneurysm

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Theoretical & Applied Mechanics Letters 2011年第1期1卷 69-72页

作者： Ai-Ke Qiao,~(1,a)) Wen-Yu Fu,~(2,3) and You-Jun Liu~(1,b)) 1)College of Life Science and Bioengineering,beijing university of Technology,beijing 100124,china 2)College of mechanical and electrical engineering,beijing union university,beijing 100124,china 3)College of mechanical engineering and Applied Electronics Technology,beijing university of Technology, beijing 100101,china beijing Univ Technol Coll Life Sci & Bioengn Beijing 100124 Peoples R China beijing union Univ Coll Mech & Elect Engn Beijing 100124 Peoples R China beijing Univ Technol Coll Mech Engn & Appl Elect Technol Beijing 100101 Peoples R China

The objective of this study is to investigate the hemodynamics in patient-specific thoracic aortic aneurysm and discuss the reason for formation of aortic plaque.A 3-Dimensional pulsatile blood flow in thoracic aorta with a fusiform aneurysm and 3 main branched vessels was studied numerically with the average Reynolds number of 1399 and the Womersley number of *** on the clinical 2-Dimensional CT slice data,the patient-specific geometry model was constructed using medical image process ***,incompressible,3-Dimensional Navier-Stokes equations were employed to solve the flow *** temporal distributions of hemodynamic variables during the cardiac cycle such as streamlines,wall shear stresses in the arteries and aneurysm were analyzed. Growth and rupture mechanisms of thoracic aortic aneurysm in the patient can be analyzed based on patient-specific model and hemodynamics simulation.

关键词： thoracic aneurysm CT image CFD model wall shear stress hemodynamics

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