Table of Content

    28 April 2016, Volume 50 Issue 04 Previous Issue    Next Issue
    Performance Simulation of Natural Gas Supply System of a Heavy Duty Gas Turbine
    MENG Cheng,SU Ming
    2016, 50 (04):  483-489. 
    Abstract ( 813 )   Save
    Abstract: The performance of the natural gas supply system has a great influence on the performance of the heavy duty gas turbine. Therefore, the modeling and simulation approach was used to study the performance of the natural gas supply system. First, the main components of the system were modeled based on the modular modeling concept. Next, according to the practical operation data provided by power plants, the setting criterion of pressure and pilot gas/premix gas flow were analyzed by BP neural network. Finally, the pressure, temperature and flow controller based on PID principle were added to the whole simulation model. The steady simulation and dynamic simulation were both implemented in this simulation model. The simulation results approximately conform to the practical operating data, indicating that the model can accurately describe the whole performance of the natural gas supply system.
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    Effects of HighFrequency Alternating Electric Fields of Different Frequencies on Spherical Propagation Flame
    CUI Yuchen1,GAO Zhongquan1,DUAN Hao1,ZHANG Cong1,WU Xiaomin1,2
    2016, 50 (04):  490-495. 
    Abstract ( 627 )   Save
    Abstract: An experiment was conducted under a lean combustion condition to investigate the influences of highfrequency alternating electric fields of different frequencies on the flame propagation and combustion characteristics of premixed CH4/air mixtures at an excess air ratio of 1.6, room temperature and atmospheric pressure. The results show that the flame is stretched horizontally when a highfrequency alternating electric field is applied to the electrodes. When the voltage virtual value is invariable, the flame stretches more severely with the frequency increasing. Compared with those without the applied voltage, when the voltage virtual value is 5 kV and the frequencies are 5, 7.5, 10, 12.5 and 15 kHz, the average flame propagation speed increases by 43.10%, 53.45%, 63.79%, 74.14% and 84.48%. The maxima of the increase rate of relative combustion pressure are 0.15, 0.21, 0.27, 0.36 and 0.50, respectively. These results indicate that highfrequency alternating electric fields are beneficial to the flame combustion and as the frequency increases, the promoting effect also increase.
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    Numerical Simulation and Analysis of Leakage Process in Twin Screw Expander
    QI Yuanqu,YU Yuefeng
    2016, 50 (04):  496-501. 
    Abstract ( 742 )   Save
    Abstract: A 3D geometry model of a twin screw expander was developed using PROE to measure and analyze geometric parameters such as groove volume, suction port area and leakage area as a function of rotation angle of the male rotor. Then, based on the geometry model, a thermodynamic model was developed using the continuity and energy conservation equation and taking the suction loss, leakage loss and real gas effect into consideration. Based on the model, the mass flow rate through inlet port and leakage path as a function of rotation angle of male rotor as well as the effects of expander inlet parameter and operating parameter on the performance of the expander was analyzed. It is found that leakage in the suction process and the early stage of expansion process is one of the main factors affecting the internal efficiency, leakage through contact line and rotor tiphousing clearance is the main leakage path, and that the increase in inlet pressure and decrease in rotor speed would lead to the increase of leakage mass.
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    Thermal Contraction Measurement of GFRP at Low Temperature
    JIA Hong,ZHANG Peng
    2016, 50 (04):  502-505. 
    Abstract ( 953 )   Save
    Abstract: An experimental system based on a twostage GM cryocooler was built to measure the thermal contraction from 15K to 293 K. The thermal contraction of the material at low temperature was measured by using the strain gauge method. The effects of variation of the resistance and gage factor (Ks) of karma foil strain gauge at low temperature on the measurement were analyzed and eliminated. The experimental thermal contraction of 304 stainless steel was first measured and compared with standard data to verify the reliability of the measurement and to obtain the correction coefficient (η′) of Ks at different temperatures. Then, the thermal contraction of Al6061T6 was measured and compared with standard data, and the maximum deviation is -4.8%, which proved that η′ was reasonable. Finally, the transversal and longitudinal thermal contraction of GFRP (glass fiber weight content of 70%) was measured at different temperatures. The experimental results show that the transversal thermal contraction of GFRP is approximately 1.12 times of the longitudinal thermal contraction in the same temperature range.
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    Performance Analysis of Three Different Refrigerants in a Directexpansion Solar-Assisted Heat Pump Water Heater
    KONG Xiangqiang,LI Junxiao,LI Ying
    2016, 50 (04):  506-513. 
    Abstract ( 825 )   Save
    Abstract: In order to study the performance of R22, R410A and R290 in a directexpansion solarassisted heat pump water heater (DXSAHPWH) system, the distributed parameter and homogeneous flow models of solar collector/evaporator and condenser were established, and the lumped parameter models of compressor and expansion valve and the working fluid charge model were built. Besides, a simulation program of a DXSAHPWH system was coded. The comparison indicates that the simulation results are in good agreement with the reported experimental results. The coefficient of performance(COP), collector efficiency and heat power of the DXSAHPWH using R22, R410A and R290 were compared and analyzed at different environmental parameters and operating parameters. The results show that the COP of the R290 system is apparently higher than that of the R22 and R410A system in the DXSAHPWH. The collector efficiency and heat power of the R410A system are slightly higher than those of the R22 and R290 system. In comparison with the R22 and R401A system, the environmental parameter has a greater influence on the R290 system. The variation of compressor speed remarkably affects the R410A system, and the variation of water temperature has a great impact on the R290 system. In addition, the optimum refrigerant charge of the R290 system is 46% of that of the R22 system, and the optimum refrigerant charge of the R410A system is 95% of that of the R22 system.
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    Electrochemical Corrosion Behaviors of Alloy 690 in High-Temperature and Highpressure Water
    WANG Jiamei1,DUAN Zhengang1,ZHANG Lefu1,MENG Fanjiang2,SHI Xiuqiang2
    2016, 50 (04):  514-520. 
    Abstract ( 679 )   Save
    Abstract: The effects of temperature (25 to 285°C) and dissolved oxygen(20 μg/L, 2.1 mg/L, 8.4 mg/L) on hightemperature electrochemical corrosion behaviors of Alloy 690, and the uniform corrosion behaviors of Alloy 690 were investigated in stimulated pressurized water reactor (PWR) primary water. The results of potentionamic polarization measurements and Xray photoelectron spectroscopy (XPS) reveal that the corrosion potential(Ecorr) decreases, the corrosion current density(Icorr) increases, and the passive potential region shrinks with the increase of temperature while the corrosion potential increases, the corrosion current density decreases, and the passive potential region shrinks with the increase of DO. The uniform corrosion rate of Alloy 690 exposed in investigated conditions is 0.244 mg/(dm2·h1/2),and the oxide, of which the outer layer is rich in FeCrNi hydroxide and the inner layer is rich in FeCrNi oxide, is formed on Alloy 690.
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    Speed Control Modeling of Modular Screw Expander Generation System
    BAO Wenlong,YU Yuefeng
    2016, 50 (04):  521-527. 
    Abstract ( 741 )   Save
    Abstract: A dynamic response model of screw expander was established to study the speed control method of the modular screw expander generation system based on the organic Rankine cycle(ORC). A new method of fixed boundary multisection model was adopted in building the expander model. Because the modular ORC screw expander generation system does not have the steam regulating valve, the engine speed cannot be controlled directly by regulating the steam flow rate. Therefore, an indirectly method for regulating heat fluid flow rate was adopted. When the heat fluid flow rate was regulated, the steam rate and enthalpy changed at the same time. So, two types of physical model was established based on it. A simulation model was established in Matlab and the control model was tested and optimized. The simulation result show that this indirect method to control the speed of the engine is feasible and the steam rate plays a major role in the speed control system.
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    Formation Mechanism and Properties of Oxide Film on 310-ODS Steel in Supercritical Water
    LU Hui,SHEN Zhao,ZHANG Lefu
    2016, 50 (04):  528-533. 
    Abstract ( 694 )   Save
    Abstract: The general corrosion susceptibility of 310ODS steel was evaluated in 600℃ supercritical deaerated water by weight gain. The sample periods were 100, 300, 600, 1 000, and 1 500 h. The surface oxide film of 310ODS steel was analyzed by using scanning electron microscope (SEM), energy disperse spectroscopy (EDS) and Xray diffractometer (XRD). The results show that a dense oxide film is formed on the surface of 310ODS steel during the early days (300 h) and the corrosion rate decreases rapidly. The oxide film is a doublelayer structure with a dense Crenriched inner layer and a porous Feenriched outer layer. The inner layer becomes uniform and the outer layer does not change with the immersing time. The oxidation process of 310-ODS steel in 600℃ supercritical deaerated water meets the solidstate growth mechanism and Y2O3 in the grain boundaries improves the corrosion resistance.
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    Gas Path Diagnosis Based on Sigma Point Kalman Filter of Gas Turbine
    HUANG Yikun,CHEN Meishan,ZHANG Huisheng,WENG Shilie
    2016, 50 (04):  534-539. 
    Abstract ( 913 )   Save
    Abstract: In this paper, the Sigma Point Kalman Filter for gas turbine was proposed to estimate health parameters and diagnose gas turbine fault. First, a discrete nonlinear mechanism model of gas turbine was established. Then, an improved Sigma Point Kalman Filter based on simplex sampling was designed and a gas path fault diagnosis system was developed on Simulink platform. The results of verification, including the single fault, compound faults, gradual faults as well as abrupt fault, show that the diagnosis system has accurate detection, stable tracking performance and good adaptability of fault mode and gas turbine operational conditions. This paper is meaningful for achieving online gas path fault diagnosis and advanced model based control.
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    Optimization of IGV Temperature Control Strategy for Gas Turbine Considering Ambient Temperature and Load
    CHEN Jinwei,CHEN Meishan,MEI Jiaojiao,ZHANG Huisheng
    2016, 50 (04):  540-544. 
    Abstract ( 1036 )   Save
    Abstract: In view of the importance of exhaust temperature of gas turbine to the operation of a power unit under offdesign condition, the function and principles of temperature control of inlet guide vane (IGV) were introduced by taking the gas turbine of a combine cycle as a study object. With the conditions of load and ambient temperature changed, the dynamic response process of thermodynamic parameters of gas turbine was compared and analyzed under three different control strategies, ie., pure feedback control, feedforwardfeedback control and double feedforwardfeedback control. The results show that the control characteristic of double feedforwardfeedback control strategy is better than that of other control strategies.
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    Experimental Study of Performance of LowSwirl MultiNozzle Burner
    LIU Weijie,GE Bing,JIANG Zhijian,ZANG Shusheng,WENG Shilie
    2016, 50 (04):  545-550. 
    Abstract ( 712 )   Save
    Abstract: Experimental investigations were conducted on the performance of the lowswirl multinozzle burner in a gas turbine model combustor. The effect of equivalence ratio and nozzle exit velocity on the dynamic characteristic, exhaust temperature and emission was analyzed. The experimental results show that there are three types of operation mode, ie., stable combustion region, unstable combustion region, and flashback region for the lowswirl multinozzle burner. The multinozzle flames tend to be unstable with the amplitude of pressure oscillation increasing and frequency decreasing when the equivalence ratio is decreased. The flames become stable and the frequency of pressure fluctuation increases when the inlet velocity is increased. NOx emissions for the multinozzle burner show a loglinear dependency on the adiabatic flame temperature and are less sensitive to the flame temperature than those for single nozzle.
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    Influencing Factors of Acoustic Agglomeration of Ultrafine Particles
    KANG Yubo,ZHU Yijia,LIN Feng,ZHANG Wugao
    2016, 50 (04):  551-556. 
    Abstract ( 1227 )   Save
    Abstract: A smallscaled acoustic agglomeration test bench was built. Chosing the high intensity ultrasound as the sound source, selecting the aerosol with large amount of ultrafine particles which were produced by combustion as research objects, and using SMPS to measure the number of particles, the influence of initial particles parameters and the acoustic agglomeration periods on the agglomeration efficiency was studied. The results show that the acoustic wave of 20 kHz has some effect on the particles whose diameter range from 10 nm to 487 nm. Within the measuring range, a higher acoustic agglomeration efficiency can be obtained if the acoustic agglomeration acting period is longer. Besides, 18 seconds is an ideal duration under the test condition. If the initial particle diameter in peak concentrations is bigger, the acoustic agglomeration efficiency will be improved with a maximum of 82.4%.The acoustic agglomeration efficiency also has a positive correlation with initial particle concentration. The particles with a diameter in peak concentration often have a better agglomeration efficiency.
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    Laminar Heat Transfer Enhancement of Graphite Tube with Internal FanShaped Fins
    LI Pengchenga,SUN Zhijiana,TANG Zhoua,YU Zitaoa,b,HU Yacaia
    2016, 50 (04):  557-562. 
    Abstract ( 807 )   Save
    Abstract: Numerical investigation of different fin angles (0°, 30°, 45°, 60°, 75°, 90°) was conducted to analyze the flow mechanism and heat transfer characteristics of highviscosity oil medium in graphite tube with internal fanshaped fins. The simulation results show that heat transfer enhancement is significant. Over the range of the Reynolds number studied, the Nusselt number at different arrangement angles (0°, 30°, 45°, 60°, 75°, 90°) is 22.69%,42.49%,62.28%,63.44%,65.47% and 66.47% higher than that for graphite tubes without internal fanshaped fins, respectively. The flow resistance for the tube with fins are found increasing by 191.88%,252.01%,333.10%,364.33%,385.51% and 400.43%, respectively. The evaluation index PEC has been introduced for the comparison of six different arrangement angle fins. The results show that the integral average PEC at 45° achieves a maximum value of 1.265 and that when the arrangement angle of fins is 45°, the graphite tubes with internal fanshaped fins has the best thermal and flow performance.
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    Hydrodynamic Performance of Vertical Axis Tidal Turbine Under Yawing Motion
    WANG Kai,SUN Ke,ZHANG Liang,SHENG Qihu,ZHANG Xuewei
    2016, 50 (04):  563-568. 
    Abstract ( 982 )   Save
    Abstract: In order to study the effect of hydrodynamic performance on vertical axis tidal turbines, the ANSYSCFX software was used to simulate the yawing motion of two blade vertical axis turbines. Besides, the influence of yawing on energy utilization of the turbine was studied, the thrust coefficient and lateral force coefficient time history curves also were analyzed under different frequency and different speed ratios, and the method of least squares was used to analyze the load of turbines. The results show that compared with turbine only rotating in uniform stream, yawing motions have little influence on energy utilization of the turbine, but it has a great impact on the instantaneous fluctuation amplitude of thrust and lateral force. As the speed ratio and yawing frequency increase, the instantaneous fluctuation amplitude increases, too. The damping coefficient of thrust and lateral force is related to speed ratio but has nothing to do with yawing frequency. Besides, the speed ratio increases, the damping coefficient increases. The results can provide reference for the design of floating tidal power stations.
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    Performance Analysis of Dual Source Heat Pump in Electric Vehicles
    QIAN Chenga,GU Boa,TIAN Zhena,MA Leia,YANG Linb
    2016, 50 (04):  569-574. 
    Abstract ( 871 )   Save
    Abstract: For the dual source heat pump in electric vehicles, experiments were conducted in air source heat pump(ASHP) and dual source heat pump(DSHP) mode. The heating performance characteristics were obtained and exergy loss ratio was deduced. It turns out that the heating capacity is 46.58% higher than that without waste heat and the coefficient of performance(COP) is 28.07% higher at most. The compressor accounts for most exergy losses of up to 46.64% to 50.07% while the condenser reaches 30.09% to 33.40%.
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    Noise Reduction by Actively Leaning Blades in Centrifugal Pump as Turbine
    DAI Cuia,DONG Liangb,KONG Fanyub,BAI Yuxingb,XIA Binb
    2016, 50 (04):  575-582. 
    Abstract ( 719 )   Save
    Abstract: To reduce the fluidinduced interior/exterior noise in centrifugal pump as turbine (PAT), from the relation between inphase hydrodynamic action and radiated noise, the leaned angle formula of blade in ideal condition was derived, and the noisereduction activecontrol approach was proposed, without affecting the hydraulic performance. The hydraulic performance and interior noise of two types of PATs were compared based on the experiments. After verifying the finite element model of the casing structure, the finite element method/automatically matched layer (FEM/AML) method was used to reduce the exterior noise. The results show that the leaned blade can keep the original hydraulic performance of PAT and reduce the peak value at fundamental frequency and the total sound energy. The efficiency at larger flow rates can be mostly improved by 1.09 percentage point, the Aweighted sound pressure level (OASPL) of interior noise is basically reduced by 0.07% to 3.02%, and the overall sound power of exterior noise is approximately reduced by 11.97% at 110 m3/h.
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    Adsorption/Desorption NonEquilibrium Characteristics of Composite MnCl2NH3 Working Pair
    ZHOU Zhisong,JIANG Long,WANG Liwei,WANG Ruzhu,GAO Peng
    2016, 50 (04):  583-587. 
    Abstract ( 766 )   Save
    Abstract: This paper investigated the adsorption/desorption nonequilibrium characteristics of composite MnCl2NH3 working pair by comparing with the Clapeyron reaction equilibrium curve. The experimental results showed that under the same condensation/evaporation conditions, for the sorption/desorption process of MnCl2NH3 the Clapeyron curves for different sorption molar quantities were different, i.e., the process of nonequilibrium sorption/desorption was controlled by dual variables, rather than a single variable. The results were much different from theoretical Clapeyron curves. To verify the results, the isobaric sorption process of sorbent was tested. The results showed that the adsorption process was in accord with the experimental Clapeyron curves, whereas the serious desorption hysteresis existed especially for the sorption quantity of 4 mol mol-1. By considering the results of desorption hysteresis, the coefficient of performance (COP) and specific cooling power (SCP) of the working pair were analyzed. A comparison of the equilibrium theoretical and the experimental nonequilibrium analysis results showed that the error of conventional theoretical results of COP and SCP reached 25% and 40%, respectively, indicating that the performance analysis of chemical sorption refrigeration processes should be based on the nonequilibrium sorption performance test.
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    Experimental Study of Surface Energy on Growth of Icing in Supercooled Water
    WANG Jing,KONG Weiliang,WANG Fuxin,LIU Hong
    2016, 50 (04):  588-584. 
    Abstract ( 695 )   Save
    Abstract: Icing on the airplane is an important factor for the safety of aviation, but the impact of surfaces on icing growth is not fully understood. In this paper, the icing process of the supercooling water on the substrate was studied. The vertical and horizontal growth of ice were recorded respectively by using 2view high speed cameras.The influence of contact angle and thermal conductivity on the ice growth was studied respectively. The influence of contact angle and surface energy on horizontal ice growth was analyzed in detail. The results show that the thermal conductivity can significantly influence the horizontal velocity and shape ofice.The contact angle has little influence on thehorizontal velocity when the thermal conductivity is large,but it has a great influence at a lower thermal conductivity.
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    Residual Stresses of AlLi Alloy Sheets in Automatic Drilling Riveting Process
    ZHENG Bin1,YU Haidong1,LIN Zhongqin1,ZOU Cheng2
    2016, 50 (04):  595-600. 
    Abstract ( 744 )   Save
    Abstract: Residual stress induced by riveting process is critical to the fatigue life of riveted structures. In this paper, the principal stress method was employed to calculate the pressure on the surface of rivet hole and the stress between upset head and sheet. The radial and circumferential residual stresses were solved by using the spatial axisymmetric elastoplasticity theory, where the sheets were equivalent to a thickwalled cylinder. The change of residual stresses caused by various process parameters was explained by the analytical results reasonably. The results show that the circumferential residual stress decreases with the increase of the upset head height and the rivet hole diameter. However, the radial residual stress is approximately independent of the two parameters. The distribution of residual stress on the surface of rivet hole along the thickness direction was investigated by using the finite element method. The results indicate that the residual stress on the faying surface is discontinuous. A Cshaped distribution of residual stress was introduced into the surface of rivet hole in the lower sheet. Reasonable process parameters were given for the Al-Li alloy sheets in the automatic drilling riveting process.
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    Numerical Simulation and Flattening Tests of Compression and Pulling of Lenticular ThinWalled Tubular Space Booms
    CAI Qiyao1,CHEN Wujun1,ZHANG Daxu1,PENG Fujun2,FANG Guangqiang2
    2016, 50 (04):  601-607. 
    Abstract ( 740 )   Save
    Abstract: Space mast is one of the basic deployable space structures which is widely used and studied. First, the work mechanism of compression and pulling flattening of thinwalled tube was analyzed. Then, a numerical simulation method was proposed, and a comparative analysis was performed thoroughly of the structural behavior, including the stress, strain, and loaddisplacement variation. After that, the test of thinwalled tube flattening by compression and pulling were conducted, and the test results were verified with numerical simulation. Finally, the detailed test results were presented, such as strain, tip displacement, and a numerical simulation was performed for the test. The results indicate that the numerical simulation is effective and correct. Large displacement with small strain appears in flattening. Meanwhile, the stress, strain and loaddisplacement vary similarly in flattening by compression and pulling. This paper is valuable for the optimization design of lenticular thinwalled tube.
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    Analysis of Trajectory and Thermal Performance during Descent Stage of High Altitude Scientific Balloons
    YANG Xixiang
    2016, 50 (04):  608-612. 
    Abstract ( 768 )   Save
    Abstract: Considering the coupled relation between dynamics and thermodynamics, the trajectory and thermal performance of helium gas during the descent stage of high altitude scientific balloons were studied. The thermal model and vertical dynamic model of high altitude balloons were established, including the solar radiation model, the infrared radiation model, and the heat convection model. The trajectory and thermal performance of a balloon during the descent stage were simulated, including height, velocity, and volume and temperature of helium gas, while the variation regularity of parameters were analyzed. The research results show that the superheated phenomenon exits during the descent stage of balloons, state changing of superheated results in the changing of descent velocity, and changing of descent velocity results in the state changing of superheated. The discharge mass of helium gas in the initial stage has an important influence on descent velocity, descent time and superheated state. This paper can provide theoretical reference for design, flight test and application of high altitude balloons.
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    Subspace Model Identification Method for Flight Dynamics of FixedWing Airplane
    QI Xiaohui1,WANG Jianchen2
    2016, 50 (04):  613-618. 
    Abstract ( 903 )   Save
    Abstract: Due to notable advantages of simplicity and high efficiency, the subspace model identification (SMI) method becomes an attractive modeling approach for flight dynamics of the airplane system. However, because of the nonlinearity in the airplane system, SMI based model identification approaches which are designed for linear systems always generate some modeling errors. To deal with this problem, a novel twostage system identification approach for flight dynamics of the fixedwing airplane system was proposed. An instrumental variable aided closedloop SMI was first adopted to obtain the approximate linear model of the airplane dynamics. Then, an extended state observer (ESO) able to estimate the nonlinear dynamics of the airplane system was constructed using the obtained linear model. Based on the estimates by the ESO, a group of neural networks were trained to identify the decentralized model of the system nonlinearity. Finally, the nonlinear, six degreeoffreedom (6DOF) model of a B747 airplane was applied to system identification test, and the results obtained verify the effectiveness of the proposed approach.
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    New Calculation Methods for Dynamic Derivatives of Advanced Flight Vehicles
    MI Baigang,ZHAN Hao
    2016, 50 (04):  619-624. 
    Abstract ( 1105 )   Save
    bstract: Combining with rigid dynamic mesh technique, a new systematic method to calculate combined and single dynamic derivatives was developed taking longitudinal direction as an example. First, the combined derivative was extracted using the differential method by forcing the aircraft pitching to the same angle of attack (AOA) with two identical pitching rates. Then, acceleration derivative were obtained by forcing the aircraft plunging to the same AOA with two constant accelerations. Finally, the angular velocity derivative was identified by the combination of constant pitching and plunging motion. To discuss the evaluation of dynamic derivatives computed using the three CFD methods, two configurations, that is, the stability and control configuration (SACCON) and Finner missile model, were considered. The results presented are in good agreement with the available experimental data which shows that each single derivative has a different proportion of the combined derivative of different geometries. Compared to general CFD methods, the unsteady motions used in the new methods are much simpler and more effective, and the methods can also be used for combined and single lateral and directional dynamic derivatives identification.
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    Mixed Finite Element Methods for Elliptic Partial Differential Equations with Random Data
    GAO Leia,XIE Fujib
    2016, 50 (04):  625-630. 
    Abstract ( 627 )   Save
    Abstract: A class of mixed finite element methods for a linear elliptic problem with stochastic input data and homogeneous Dirichlet boundary conditions were considered to approximate statistical moments of the scalar function and its flux. Theoretical analysis shows that these methods have the first order optimal error estimates for the mean values of the stochastic solutions. Numerical experiments were developed to support the theoretical findings.
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    Convergence Exponent of Small Function Points for Solutions of Higher Order Differential Equations
    JIN Jin1,ZHAO Haolan2
    2016, 50 (04):  631-635. 
    Abstract ( 846 )   Save
    Abstract: In this paper, the problems of convergence between the zeros of the solution of higher order linear differential equations with meromorphic coefficients and small order of growth function were studied, and some precise estimates between the meromorphic solution of linear differential equations and small order of growth function were obtained.
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    Analysis of Transient Thermal Resistance of LED Based on Bayesian Probability and Statistics
    CHEN Weia,b,QUE Xiufua,FENQ Weia,b,ZHANG Jianhuaa,YANG Lianqiaoa
    2016, 50 (04):  636-640. 
    Abstract ( 1061 )   Save
    Abstract: Based on the theoretical basis of transient thermal test, backstepping algorithm from the result of transient thermal measurement to structure function generally include data fitting, smoothing, derivation, deconvolution and network structure conversion. The Bayesian probability and statistics method was presented for the network identification by deconvolution (NID) in analyzing transient thermal resistance of light emitting diode (LED), which effectively avoided the ill posed problems in the frequency domain method of the computer and the choice of the iteration number in the Bayesian iterative method. The relationship between the optimization parameter ε and halfwave width, and its relationship with ripple of time constant spectrum were discussed. The proposed method successfully extracted the transient thermal resistance in the transformation from Foster network model to Cauer network model with an optimized ε. Meanwhile, the reliability of this method in deconvolution of noisy signal and the accuracy in obtaining the thermal resistance of LED package devices were discussed.
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    Simplified Method to Predict ExcavationInduced Settlements of Adjacent Buildings Considering Space Effect
    ZHANG Hongbing,FAN Fan,HU Hao
    2016, 50 (04):  641-646. 
    Abstract ( 906 )   Save
    Abstract: The soil deformation induced by excavation behind the retaining wall was analyzed by statistical analysis of the engineering monitoring data and calculation result analysis of the basic model using the finite element method. The spatial distribution of soil deformation was studied in detail, which indicated that Gauss function could be used to describe the spatial distribution of the soil deformation behind the retaining wall quantitatively. A simplified approach for settlement prediction of buildings caused by adjacent excavation was presented combining this study and the study on building deformation response to soil deformation induced by excavation. The study shows that the spatial distribution of soil deformation is not notable in the short side of the excavation and the deformation in the corner of the excavation is much less than that in the middle of the excavation. The stiffness of the buildingshortside has a small impact on the spatial distribution of soil deformation. Based on the statistical analysis of the engineering monitoring data, the simplified approach can be used to predict the building settlement and soil properties taking the construction factor into consideration using empirical coefficient γ. The case analysis shows that the monitoring result and the calculated result obtained by the simplified approach are in good agreement and the simplified approach can be used to predict the building settlement adjacent to the excavation.
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