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Experimental and numerical investigation on opposing plasma synthetic jet for drag reduction

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Chinese Journal of Aeronautics 2022年第8期35卷 75-91页

作者： Wei XIE Zhenbing LUO Yan ZHOU Wenqiang PENG Qiang LIU Dengpan WANG College of Aerospace Engineering National University of Defense TechnologyChangsha 410073China Beijing Special Engineering Design and Research Institute Beijing 100000China

Experimental and numerical studies are carried out to validate the potential of opposing Plasma Synthetic Jet(PSJ)for drag reduction for a hemisphere.Firstly,flow field changes of opposing PSJ are analyzed by comparing the experimental schlieren images and simulation results in a supersonic free stream of Mach number 3.As PSJ is a kind of unsteady pulsed jet,the shock standoff distance increases initially and then decreases under the control of PSJ,which corresponds to the change of the strength of PSJ.Accordingly,the amount of drag reduction of the hemisphere increases initially and then decreases.It is found that there is a short period of“drag rise”during the formation of PSJ before the drag reduction,which is induced by the generation of normal shock waves and the area difference of the cavity wall of PSJ Actuator(PSJA).Secondly,the effects of five parameters,including exit diameter,discharge energy of PSJA,Mach number,static pressure of incoming flow and angle of attack,on drag reduction of opposing PSJ were studied in detail by using numerical method.It is found that the Maximum Pressure Ratio(MPR)has a significant impact on the average drag reduction for a configuration-determined PSJA.For the configuration selected in this study,the flow field of opposing PSJ shows typical Short Penetration Mode(SPM)in a control cycle of PSJ when the MPR is less than 0.89.However,the flow field shows typical Long Penetration Mode(LPM)at some time when the MPR is bigger than 0.89.Relatively better drag reduction is achieved in this case.

关键词： Drag reduction Opposing jet Parameter study Plasma synthetic jet(PSJ) Supersonic flow

parameter studies and evaluation principles of delamination damage in laminated composites

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Chinese Journal of Aeronautics 2021年第7期34卷 62-72页

作者： Kangkang WANG Libin ZHAO Haiming HONG Jianyu ZHANG Yu GONG School of Astronautics Beihang UniversityBeijing 100083China Shenyang Aircraft Design and Research Institute Shenyang 110035China College of Aerospace Engineering Chongqing UniversityChongqing 400044China

Delamination represents one of the most severe failure modes in composite laminates,especially when they are subjected to uniaxial compression loads.The evaluation of the delamination damage has always been an essential issue of composite laminates for durability and damage tolerance in engineering practice.Focusing on the most typical and representative elliptical delamination issue,an analytical model simultaneously considering the conservative buckling process and non-conservative delamination propagation process is implemented.Various computational cases considering different delamination depths,directions,aspect ratios,and areas are established,and the predicted results based on the analytical model are carefully compared.Effects of these geometrical delamination parameters on the buckling,delamination propagation,and failure behaviors of composite laminates are thoroughly analyzed,and innovative evaluation principles of the delamination damage have been concluded.It is found that the delamination area is the key factor that truly affecting the failure behaviors of delaminated composites,and the local/global buckling and failure loads show clear linearity with the delamination area,whilst the delamination depth and direction only have slight effects.

关键词： Analytical model Composite Delamination Evaluation principles Parameter study

Bending of Timoshenko beam with effect of crack gap based on equivalent spring model

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Applied Mathematics and Mechanics(English Edition) 2016年第4期37卷 513-528页

作者： Xiao YANG Jin HUANG Yu OUYANG Department of Civil Engineering Shanghai University

Considering the effect of crack gap, the bending deformation of the Timoshenko beam with switching cracks is studied. To represent a crack with gap as a nonlinear unidirectional rotational spring, the equivalent flexural rigidity of the cracked beam is derived with the generalized Dirac delta function. A closed-form general solution is obtained for bending of a Timoshenko beam with an arbitrary number of switching cracks. Three examples of bending of the Timoshenko beam are presented. The influence of the beam＇s slenderness ratio, the crack＇s depth, and the external load on the crack state and bending performances of the cracked beam is analyzed. It is revealed that a cusp exists on the deflection curve, and a jump on the rotation angle curve occurs at a crack location. The relation between the beam＇s deflection and load is bilinear, each part corresponding to an open or closed state of crack, respectively. When the crack is open, flexibility of the cracked beam decreases with the increase of the beam＇s slenderness ratio and the decrease of the crack depth. The results are useful in identifying non-destructive cracks on a beam.

关键词： Timoshenko beam switching crack crack gap generalized function Parameter study

Axisymmetrical analytical solution for vertical vibration of end-bearing pile in saturated viscoelastic soil layer

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Applied Mathematics and Mechanics(English Edition) 2010年第2期31卷 193-204页

作者：杨骁潘元 Department of Civil Engineering Shanghai University

Based on elasticity and the theory of saturated porous media, and regarding the pile and the soil as a single phase elastic and a saturated viscoelastic media, respectively, the dynamical behavior of vertical vibration of an end-bearing pile in a saturated viscoelastic soil layer is investigated in the frequency domain using the Helmholtz decomposition and variable separation method. The axisymmetrical analytical solutions for vertical vibrations of the pile in a saturated viscoelastic soil layer are obtained, and the analytical expression of the dynamical complex stiffness of the pile top is presented. Responses of dynamic stiffness factor and equivalent damping of pile top with respect to the frequency are shown in figures using a numerical method. Effects of the saturated soil parameters, modulus ratio of the pile to soil, slenderness ratio of pile and pile＇s Poisson ratio, etc. on the stiffness factor and damping are examined. It is shown that, due to the effect of the transversal deformation of the pile and the radial force of the saturated viscoelastic soil acting on the pile, the dynamic stiffness factor and the damping derived from the axisymmetrical solution are greatly different from those derived from the classical Euler-Bernoulli rod model, especially at some specific excitation frequencies. Therefore, there are limitations on applicability of the Euler-Bernoulli rod model in analyzing verticai vibration of the pile. More accurate analysis should be based on a three-dimensional model.

关键词： saturated porous medium pile-soil dynamical interaction axisymmetricalanalytical solution vertical vibration Parameter study

Parametric study on damage control design of SMA dampers in frame-typed steel piers

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Frontiers of Structural and Civil Engineering 2009年第4期3卷 384-394页

作者： Xiaoqun LUO Hanbin GE Tsutomu USAMI Advanced Research Center for Seismic Experiments and Computations Meijo UniversityNagoya 468-8502Japan Department of Building Engineering Tongji UniversityShanghai 200092China Department of Civil Engineering Meijo UniversityNagoya 468-8502Japan

This paper focuses on damage control design of SMA dampers in steel frame piers.A parametric study based on time history analyses is carried out on frametyped bridge piers with axial-type SMA damping device.The parameters examined are design parameters of strength ratioαF and stiffness ratioαK.Seismic performance indexes on displacement and strain are investigated under three JRA recommended Level 2 Ground TypeПstrong earthquake motions.Design recommendations are suggested following the results of the parametric study.

关键词： damage control design shape memory alloy Parameter study displacement-based verification strainbased verification time history analysis

NONLINEAR DYNAMICAL CHARACTERISTICS OF PILES UNDER HORIZONTAL VIBRATION

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Applied Mathematics and Mechanics(English Edition) 2005年第6期26卷 700-708页

作者：胡育佳程昌钧杨骁 Shanghai Institute of Applied Mathematics and Mechanics Department of Mechanics Shanghai University

The pile-soil system is regarded as a visco-elastic half-space embedded pile. Based on the method of continuum mechanics, a nonlinear mathematical model of pile-soil interaction was established-a coupling nonlinear boundary value problem. Under the case of horizontal vibration, the nonlinearly dynamical characteristics of pile applying the axis force were studied in horizontal direction in frequency domain. The effects of parameters, especially the axis force on the stiffness were studied in detail. The numerical results suggest that it is possible that the pile applying an axis force will lose its stability. So,the effect of the axis force on the pile is considered.

关键词： system of pile-soil interaction nonlinear visco-elasticity half-space continuum mechanics Parameter study dynamical stiffness