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Fold-Hopf bifurcation in a simplified four-neuron BAM (bidirectional associative memory) neural network with two delays

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Science China(Technological Sciences) 2010年第3期53卷 633-644页

作者： GE JuHong & XU Jian school of aerospace engineering and Applied Mechanics,Tongji University,Shanghai 200092,China school of aerospace engineering and Applied Mechanics Tongji University Shanghai China

The bidirectional associative memory (BAM) neural network with four neurons and two delays is considered in the present paper.A linear stability analysis for the trivial equilibrium is firstly employed to provide a possible critical point at which a zero and a pair of pure imaginary eigenvalues occur in the corresponding characteristic equation.A fold-Hopf bifurcation is proved to happen at this critical point by the nonlinear *** coupling strength and the delay are considered as bifurcation parameters to investigate the dynamical behaviors derived from the fold-Hopf *** dynamical behaviours are qualitatively classified in the neighbourhood of the fold-Hopf bifurcation point by using the center manifold reduction (CMR) together with the normal *** bifurcating periodic solutions are expressed analytically in an approximate *** validity of the results is shown by their consistency with the numerical simulation.

关键词： codimension-two bifurcation time delay solution classification unfolding centre manifold

Reliability analysis of ship structure system with multi-defects

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Science China(Physics,Mechanics & Astronomy) 2010年第11期53卷 2113-2124页

作者： AN Hai 1,AN WeiGang 1 & ZHAO WeiTao 2 1 school of aerospace and Civil engineering,Harbin engineering University,Harbin 150001,China 2 school of Aeronautics and Astronautics,Shenyang Institute of Aeronautical engineering,Shenyang 110034,China school of aerospace and Civil engineering Harbin Engineering University Harbin China school of Aeronautics and Astronautics Shenyang Institute of Aeronautical Engineering Shenyang China

This paper analyzes the influence of multi-defects including the initial distortions,welding residual stresses,cracks and local dents on the ultimate strength of the plate element,and has worked out expressions of reliability calculation and sensitivity analysis of the plate *** analysis is made for the system with multi-defects plate *** mechanism,failure paths and the calculating approach to global reliability index are also worked *** plate elements with multi-defects fail,the formula of reverse node forces which affect the residual structure is deduced,so are the sensitivity expressions of the system reliability *** ensures calculating accuracy and rationality for reliability analysis,and makes it convenient to find weakness plate elements which affect the reliability of the structure ***,for the validity of the approach proposed,we take the numerical example of a ship cabin to compare and contrast the reliability and the sensitivity analysis of the structure system with multi-defects with those of the structure system with no *** approach has implications for the structure design,rational maintenance and renewing strategy.

关键词： initial distortions welding residual stresses cracks and local defects ultimate strength reverse node forces sensitivity expression reliability analysis

NUMERICAL ANALYSIS OF THE 3-D FLOW FIELD OF PRESSURE ATOMIZERS WITH V-SHAPED CUT AT ORIFICE

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Journal of Hydrodynamics 2011年第2期23卷 187-192页

作者： ZHOU Hua school of aerospace engineering and Applied Mechanics Tongji University Shanghai 200092 China

Axisymmetric liquid jets have been studied extensively for more than one century, while non-axisymmetric jets are also very common in engineering applications but attract less concern. Based on Eulerian fluid-fluid model in Fluent software, this article analysizes the 3-D flow fields of pressure atomizers with V-shaped cut at orifice, which will result in a non-axisymmetric liquid jet. Flow rate analysis and jet structure analysis are carried out, the results show that the flow rate can be formulated by adding a correction coefficient to the formula of inviscid axisymmetric jets in atomization regime, when the Weber number is low enough to make the flow fall out of atomization regime, and the jet structure together with the flow rate formula will change. Analysis shows that the evolution of the spray and therefore the structure of the liquid jet are affected much by relative velocity and the local volume fraction of liquid phase.

关键词： flow rate fraction distribution gas-liquid interference non-axisymmetric liquid jet pressure atomizer

Prediction of separation flows around a 6:1 prolate spheroid using RANS/LES hybrid approaches

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Acta Mechanica Sinica 2007年第4期23卷 369-382页

作者： Zhixiang Xiao Yufei Zhang Jingbo Huang Haixin Chen Song Fu school of aerospace engineering,Tsinghua University,Beijing 100084,China school of aerospace engineering Tsinghua University Beijing China

This paper presents hybrid Reynolds-averaged Navier-Stokes （RANS） and large-eddy-simulation （LES） methods for the separated flows at high angles of attack around a 6：1 prolate spheroid. The RANS/LES hybrid meth- ods studied in this work include the detached eddy simulation （DES） based on Spalart-Allmaras （S-A）, Menter＇s k-ω shear-stress-transport （SST） and k-o9 with weakly nonlinear eddy viscosity formulation （Wilcox-Durbin＋, WD＋） models and the zonalANS/LES methods based on the SST and WD＋ models. The switch from RANS near the wall to LES in the core flow region is smooth through the implementation of a flow-dependent blending function for the zonal hybrid method. All the hybrid methods are designed to have a RANS mode for the attached flows and have a LES behavior for the separated flows. The main objective of this paper is to apply the hybrid methods for the high Reynolds number separated flows around prolate spheroid at high-incidences. A fourth-order central scheme with fourth-order artificial viscosity is applied for spatial differencing. The fully implicit lower-upper symmetric-Gauss-Seidel with pseudo time sub-iteration is taken as the temporal differentiation. Comparisons with available measurements are carried out for pressure distribution, skin friction, and profiles of velocity, etc. Reasonable agreement with the experiments, accounting for the effect on grids and fundamental turbulence models, is obtained for the separation flows.

关键词： RANS/LES hybrid methods DES Zonal-RANS/LES Weakly nonlinear correction

The influence of synthetic jet excitation on secondary flow in compressor cascade

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Journal of Thermal Science 2010年第6期19卷 500-504页

作者： Yanming LIU, Tuo SUN, Chaobin GUAN and Baoguo WANG school of aerospace engineering, Beijing Institute of Technology, Beijing, 100081, China Assistant Professor school of aerospace engineering Beijing Institute of Technology Beijing China

The detailed numerical simulation has been carried out to investigate the effect of synthetic jet excitation on the secondary flow at 5° incidence in a compressor cascade, in which the synthetic jet actuation is equipped on the suction surface. The influence of excitation position, one fixed near the trailing edge and the other fixed a little far from the trailing edge, has also been studied. The results show that unsteady disturbance of desirable synthetic jet effectively enhances the mixing of the fluid inside the separation region, which reduces the vortex intensity and the energy loss, improves the flow status in the cascade, and also suppresses velocity fluctuation near the trailing edge. Additionally, the actuation fixed near the separation region proves to be more effective and exit load distribution is more uniform due to the employment of the synthetic jet.

关键词： synthetic jet actuator compressor cascade loss velocity fluctuation

STUDY ON VARIATION OF SETTING AND STOPPING PRESSURES OF SAFETY VALVE WITH STRUCTURAL MODIFICATION

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Chinese Journal of Mechanical engineering 2001年第2期14卷 127-138页

作者： Lee Jinho Kwangzin Valve Industrial Co ,Ltd,Korea Kim Harkbong Kim Moonsang school of aerospace and Mechanical engineering,Hankook Aviation University,Korea 韩国光进阀门工业公司韩国韩国航空大学航空宇宙及机械工学部韩国

The possibility of pressure control with the structural change of a safety valve is investigated Safety valve is commonly used as safety devices for numerous applications which include boilers,ships,industrial plants,and piping Setting and stopping pressures of a safety valve, p set and p sto ,are traditionally adjusted with a fine tuning of seat ring and valve ring heights, h sr and h vr However, it is not easy to achieve the proper setting and stopping pressures of a safety valve in practice The depth of inside and outside grooves in a valve, d i and d o are modified and their effects on setting and stopping pressures of a safety vlave are tested The most appropriate values appear 1 0 mm in d i and 0 5～1 0 mm in d o,respectively The valve ring height, h vr ,shows that the best results can be achieved at 2 3 mm for setting pressures of 0 1～0 4 MPa and 1 0 mm for setting pressures of 0 5～1 0 MPa The stopping pressures increases with the increase of seat ring height, h sr , upto certain h sr value and then becomes independent to the seat ring height This implies that there exists the optimum h sr ,which provides the largest flow rate and the proper stopping pressure Stopping pressures of a safety valve are adjusted with the seat ring and valve ring heights This study,however,demonstrated that the modification of value grooves also changes setting and stopping pressures of a safety valve Therefore,the proper selection in dimensions of the inside and outside grooves should be considered for the safety valve design

关键词： Safety valve Compressive flow Isentropic flow theory Isentropic comressibility theory Setting pressure Stopping pressure Continuity equation Momentum equation

Two kinds of generalized gradient representations for holonomic mechanical systems

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Chinese Physics B 2016年第1期25卷 653-656页

作者：梅凤翔吴惠彬 school of aerospace engineering Beijing Institute of Technology school of Mathematics Beijing Institute of Technology

Two kinds of generalized gradient systems are proposed and the characteristics of the two systems are studied. The conditions under which a holonomic mechanical system can be considered as one of the two generalized gradient systems are obtained. The characteristics of the generalized gradient systems can be used to study the stability of the holonomic system. Some examples are given to illustrate the application of the results.

关键词： holonomic mechanical system generalized gradient system Lyapunov function stability

Fracture analysis of a functionally graded interfacial zone between two dissimilar homogeneous materials

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Science China(Physics,Mechanics & Astronomy) 2006年第5期49卷 540-552页

作者： CHENG Zhanqi1,2 & ZHONG Zheng1 1. school of aerospace engineering and Applied mechanics, Tongji University, Shanghai 200092, China 2. College of Civil engineering, Zhengzhou University, Zhengzhou 450002, China school of aerospace engineering and Applied mechanics Tongji University Shanghai China College of Civil engineering Zhengzhou University Zhengzhou China

In this paper the plane elasticity problem for a functionally graded interfacial zone containing a crack between two dissimilar homogeneous materials has been considered. It is assumed that in the interfacial zone the reciprocal of the shear modulus is a linear function of the coordinate, while Possion’s ratio keeps constant. By utilizing the Fourier transformation technique and the transfer matrix method, the mixed boundary problem is reduced to a system of singular integral equations that are solved numerically. The influences of the geometric parameters and the graded parameter on the stress intensity factors are investigated. The numerical results show that the graded parameters, the thickness of interfacial zone, the crack size and location have significant effects on the stress intensity factors.

关键词： functionally graded material interfacial zone fracture stress intensity factor

Two-dimensional thermoelasticity solution for functionally graded thick beams

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Science China(Physics,Mechanics & Astronomy) 2006年第4期49卷 451-460页

作者： Lü Chaofeng1, CHEN Weiqiu1 & ZHONG Zheng2 1. Department of Civil engineering, Zhejiang University, Hangzhou 310027, China 2. Key Laboratory of Solid Mechanics of Ministry of Education, school of aerospace engineering and Ap- plied Mechanics, Tongji University, Shanghai 200092, China Department of Civil engineering Zhejiang University Hangzhou China Key Laboratory of Solid Mechanics of Ministry of Education School of Aerospace Engineering and Applied Mechanics Tongji University Shanghai China

Two-dimensional thermoelasticity analysis of functionally graded thick beams is presented using the state space method coupled with the technique of differential quadrature. Material properties vary continuously and smoothly through the beam thickness, leading to variable coefficients in the state equation derived from the elasticity equations. Approximate laminate model is employed to translate the state equation into the one with constant coefficients in each layer. To avoid numerical instability, joint coupling matrices are introduced according to the continuity conditions at interfaces in the approximate model. The differential quadrature procedure is applied to discretizing the beam in the axial direction to make easy the treatment of arbitrary end conditions. A simply-supported beam with exponentially varying material properties is considered to validate the present method. Numerical examples are performed to investigate the influences of relative parameters.

关键词： state equation differential quadrature approximate laminate model joint coupling matrices thermal stresses.