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DYNAMIC STABILITY AND ACTIVE CONTROL OF ELASTIC VEHICLES WITH UNSTEADY AERODYNAMIC FORCES MODELING

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Chinese Journal of Aeronautics 1994年第1期7卷 8-16页

作者： Chen Shilu Tang Shuo Zhu xiaoping(northwestern polytechnical university,xi’an, China, 710072)

In this paper,longitudinal equations of disturbance motions under the action ofunsteady aerodynamic forces are derived.A method of analysis of the effect ofaeroelasticity on the dynamic stability of elastic vehicles by using a simplifiedmathematical model of unsteady aerodynamic forces is proliosed. Synthesis of optimal de-sign of the active control system is studied from the view-point of coordinating the designof active feedback control with the choice of positions of control surfaces and sensors(gyros) Iocations from the stand point for the efficient suppression of elastic vibration ofthe vehicle.

关键词： DYNAMIC

Finite element simulation on the deep drawing of titanium thin-walled surface part

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Rare Metals 2010年第1期29卷 108-113页

作者： GAO Enzhi, LI Hongwei, KOU Hongchao, CHANG Hui, LI Jinshan, and ZHOU Lian State Key Laboratory of Solidification Processing, northwestern polytechnical university, xi’an 710072, China State Key Laboratory of Solidification Processing Northwestern Polytechnical University

The deep drawing of titanium thin-walled surface part was simulated based on a self-developed three-dimensional finite element model. After an investigation on forming rules, a virtual orthogonal experimental design was adopted to determine the significance of processing parameters, such as die radius, blank holder force, and friction coefficient, on the forming process. The distributions of thickness and equivalent plastic strain of the drawn part were evaluated. The results show that die radius has a relative major influence on the deep drawing process, followed by friction coefficient and blank holder force.

关键词： deep drawing titanium alloy finite element simulation orthogonal experiment processing parameters

TIME ACCURATE 2D NAVIER-STOKES CALCULATIONS WITH A DUAL-TIME STEPPING METHOD

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Chinese Journal of Aeronautics 1997年第3期10卷 9-14页

作者： Yang Yong, Qiao Zhide (Faculty 503, northwestern polytechnical university, xi′an, 710072, China)

With the cell vertex finite volume discretization in space and second order backward implicit discretization in time, 2D unsteady Navier Stokes equations are solved by a dual time stepping method to simulate compressible viscous flow around rigid airfoils in arbitrary unsteady motion. The selection of physical time step is not restricted by stability condition any more, and most of the successful acceleration techniques used in steady calculations can be implemented to increase the computation efficiency.

关键词： two dimensional flow unsteady flow Navier Stokes equation viscous flow implicit discretization dual time stepping

AN　INVESTIGATION　OF　CHEMICAL　SHORT　CRACK　CHARACTERISTICS　IN　GC－4　HIGH－STRENGTH　STEEL

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Chinese Journal of Aeronautics 1994年第4期7卷 295-300页

作者： Wang Rong Lou Minxiu Zheng xiulin(northwestern polytechnical university, xi’an, China, 710072)

A method of constant △K value is applied experimentally to investigatechemical short crack characteristics of GC-4 high-strength steel in 3.5%NaClsolution. Experimental results show that there is a critical point of crack geometry aon da / dN-a curve of the crack propagation at constant △K value. When the cracklength a < a , chemical short crack effect appears. The value of a is almost not af-fected by the loading frequency, stress ratio and △K level. The ratio of characteristiccrack propagation rate of chemical short cracks to that of long cracks is a weak func-tion of the loading frequency, stress ratio and △K level. Based on the analysis, the rela-tion between the short crack propagation rate and crack size is suggested.

关键词： high strength steel chemical properties short cracks crack propagation

Cell size effects for vibration analysis and design of sandwich beams

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Acta Mechanica Sinica 2009年第3期25卷 353-365页

作者： Gaoming Dai Weihong Zhang Engineering Simulation and Aerospace Computing (ESAC), The Key Laboratory of Contemporary Design and Integrated Manufacturing Technology, northwestern polytechnical university, 710072 xi’an, Shaanxi, China Engineering Simulation and Aerospace Computing (ESAC) The Key Laboratory of Contemporary Design and Integrated Manufacturing Technology Northwestern Polytechnical University 710072 Xi’an Shaanxi China

In this work, sandwich beams are studied to reveal the underlying size effects of the periodic core cells for the first time within the framework of free vibration analysis of such an advanced lightweight structure. The energy equivalence method is formulated as a theoretical approach that takes into account the cell size effect. It is compared with the asymptotic homogenization method and direct finite element method systematically to show their consistence and applicability. The accuracy of free vibration responses predicted by the detailed finite element model is used as the standard of comparison. It is shown that the cell size is an important parameter characterizing the cellular core rigidities that influence vibration responses. The homogenization model agrees exactly with the asymptotic solution of the analytical expression of the beam model only whenever the cell size tends to be infinitely small.

关键词： Sandwich beamanalysis Energy equivalencemethodSize effect Vibrationmethod Homogenization

DESIGN PROBLEMS OF THREEDIMENSIONAL CONTRACTIONS

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Chinese Journal of Aeronautics 1993年第1期 25-31页

作者： Su Yao-xi,Lin Chao-qiang,Hong Liu (northwestern polytechnical university,xi’an,China,710072)

The numerical analysis of incompressible flow in rectangular contractions is performedby using a finite-difference method and body-fitted coordinates. Three types ofcommonly used wall contours are chosen and compared, i.e., contours with Witozinskycurve, the 5-th power curve and matched cubic curves respectively. Two desigh criteriahave been generally used for axisymmetric contractions, i.e., (1) no separation on nozzledwalls, (2) nonuniformity at exit cross section lower than 2%. These criteria are revised andapplied to three-dimensional contractions to compare the performance of the above-mentionedthree types of contours. It is found that the contour with matched cubic curves, whenoptimized, gives the most satisfactory results, while the contour with Witozinsky curve performsbadly because of serious adverse pressure gradient near the entrance. Some problemsof three-dimensional contraction design are discussed. The cross section similaritywhich is usually considered as a requirement in three-dimensional contraction design practiceis found to be of no real value.

关键词： Design In DESIGN PROBLEMS OF THREEDIMENSIONAL CONTRACTIONS Wind length

RELATIONSHIP BETWEEN PRIMARY MORPHOLOGY AND CRYSTAL STRUCTURE OF CARBIDES GROWING IN SUPERALLOYS

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Acta Metallurgica Sinica(English Letters) 1990年第1期3卷 46-51页

作者： LIU Lin FU Hengzhi SHI Zhengxing northwestern polytechnical university,xi’an,China Dr.LIU Lin Lecturer,Department of Applied Physics,northwestern polytechnical university,xi’an 710072,China

The SEM analysis of decply etched specimens of Ni-base superalloys K38 and K19H+Ta in- dicates that both the primary morphologies under normal growth conditions and the final morphologies near equilibrium of MC carbides are octahedral *** classification of MC crystal faces by means of PBC(Periodic Bond Chains)theory confirms that{100}, {110}and{111}are F faces,and that{212}are S *** calculations of the attachment energy for each F face show that{111}are most easily *** has also been inferred that one of the MC growth units is a coordination octahedron composed of one metal atom sur- rounded by six carbon *** octahedral growth units can be attached to the growth sur- faces of MC carbides through laver stacking mechanism on the{111}faces.

关键词： carbide crystal growth

Experimental Investigation and Numerical Simulation of the Grain Size Evolution during Isothermal Forging of a TC6 Alloy

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Journal of Materials Science & Technology 2005年第2期21卷 155-160页

作者： Miaoquan LI, Shankun XUE, Aiming xiONG and Shenghui CHEN State Key Laboratory of Solidification Processing, School of Materials Science and Engineering, northwestern polytechnical university, xi’an 710072, China State Key Laboratory of Solidification Processing School of Materials Science and Engineering Northwestern PolytechnicalUniversity Xi'an 710072 China

Hot compression was conducted at a Thermecmaster-Z simulator, at deformation temperatures of 800-1040℃, with strain rates of 0.001-50 s-1 and height reduction of 50%. Grain size of the prior α phase was measured with a Leica LABOR-LUX12MFS/ST microscope to which QUANTIMET 500 software for image analysis for quantitative metallography was linked. According to the present experimental data, a constitutive relationship for a TC6 alloy and a model for grain size of the prior a phase were established based on the Arrhenius' equation and the Yada's equation, respectively. By finite element (FE) simulation, deformation distribution was determined for isothermal forging of a TC6 aerofoil blade at temperatures of 860-940℃ and hammer velocities of 9-3000.0 mm/min. Meanwhile, the grain size of the prior α phase is simulated during isothermal forging of the TC6 aerofoil blade, by combining FE outputs with the present grain size model. The present results illustrate the grain size and its distribution in the prior α phase during the isothermal forging of the TC6 aerofoil blade. The simulated results show that the height reduction, deformation temperature, and hammer velocity have significant effects on distribution of the equivalent strain and the grain size of the prior α phase.

关键词： Titanium alloy Isothermal forging Grain size Model Finite element (FE) simulation

Kinetic limit for incubation period of primary phase produced by the combination reaction between two solid heterogeneous pure metals

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Science China(Technological Sciences) 2008年第12期51卷 2232-2243页

作者： xiONG JiangTao1,2,LI JingLong1,ZHANG FuSheng1,LIN xin2 & HUANG WeiDong2 1 Shaanxi Key Laboratory of Friction Welding Technologies,northwestern polytechnical university,xi’an 710072,China 2 State Key Laboratory of Solidification Processing,northwestern polytechnical university,xi’an 710072,China Shaanxi Key Laboratory of Friction Welding Technologies Northwestern Polytechnical University Xi’an 710072 China State Key Laboratory of Solidification Processing Northwestern Polytechnical University Xi’an 710072 China

An irreversible thermodynamics model was constructed to study the combination reaction of two heterogeneous pure metals in diffusion bonding based on the theorem of minimum entropy production and the Curie *** correlation between the irreversible reaction and diffusion was discussed,which provided the kinetic inevitability of an incubation period of a primary *** analytical descriptions of the incubation period and the kinetically critical grain size of the primary phase were *** of the experimental results of Al/Mo interfacial reaction with the calculations indicated that the performed theoretical analysis was reliable.

关键词： incubation period primary phase interfacial reaction irreversible thermodynamics