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Analysis of a permeable interface crack in elastic dielectric/piezoelectric bimaterials

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Acta Mechanica Sinica 2007年第6期23卷 681-687页

作者： Qun Li Yiheng Chen school of aerospace,Xi’an Jiaotong University,Xi’an 710049,China school of aerospace Xi’an Jiaotong University Xi’an 710049 China

A permeable interface crack between elasticdielectric material and piezoelectric material is studied basedon the extended Stroh’s *** by strong engi-neering demands to design new composite materials,theauthors perform numerical analysis of interface crack tip sin-gularities and the crack tip energy release rates for 35 typesof dissimilar bimaterials,respectively,which are constructedby five kinds of elastic dielectric materials:Epoxy,Poly-mer,Al;O;.SiC,and Si;N;and seven kinds of practicalpiezoelectric ceramics:PZT-4,BaTiO;,PZT-5H,PZT-6B,PZT-7A,P-7,and PZT-PIC 151,*** elasticdielectric material with much smaller permittivity than com-mercial piezoelectric ceramics is treated as a special trans-versely isotropic piezoelectric material with extremely *** present investigation shows that thestructure of the singular field near the permeable interfacecrack tip consists of three singularities:r;and r;,which is quite different from that in the impermeable inter-face *** can be concluded that different far field load-ing cases have significant influence on the near-tip fracturebehaviors of the permeable interface *** on thepresent theoretical treatment and numerical analysis,the elec-tric field induced crack growth is well explained,which pro-vides a better understanding of the failure mechanism inducedfrom interface crack growth in elastic dielectric/piezoelectricbimaterials.

关键词： Elastic dielectric Piezoelectric Permeable Interface crack Singularity Energy release rate

Multi-swingby optimization of mission to Saturn using global optimization algorithms

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Acta Mechanica Sinica 2009年第6期25卷 839-845页

作者： Kaijian Zhu Junfeng Li Hexi Baoyin school of aerospace, Tsinghua University,100084 Beijing, China school of aerospace Tsinghua University 100084 Beijing China

Based on the trajectory design of a mission to Saturn, this paper discusses four different trajectories in various swingby cases. We assume a single impulse to be applied in each case when the spacecraft approaches a celestial body. Some optimal trajectories ofEJS, EMS, EVEJS and EVVEJS flying sequences are obtained using five global optimization algorithms： DE, PSO, DP, the hybrid algorithm PSODE and another hybrid algorithm, DPDE. DE is proved to be supe- rior to other non-hybrid algorithms in the trajectory optimi- zation problem. The hybrid algorithm of PSO and DE can improve the optimization performance of DE, which is vali- dated by the mission to Saturn with given swingby sequences. Finally, the optimization results of four different swingby sequences are compared with those of the ACT of ESA.

关键词： Swingby trajectory . Global optimization .Hybrid algorithm . Mission design

Investigation of the crack problem in non-local piezoelectric materials under combined electromechanical loadings

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Acta Mechanica Sinica 2009年第2期25卷 219-225页

作者： Q. Li Y. Chen school of aerospace, Xi’an Jiao-Tong University,710049 Xi’an, China school of aerospace Xi’an Jiao-Tong University 710049 Xi’an China

The present investigation of the crack problem in piezoelectric materials is performed based on the non-local theory. After some manipulations, the impermeable crack, the permeable crack （the crack gap is full of NaCI solution）, and the semi-permeable crack （the crack gap is full of air or silicon oil） are reduced to a uniform formulation by assuming the normal electric displacement on the crack surfaces to be an unknown variable. Thus, a triple integral equation with the unknown normal electric displacement is established. By using the Newton iterative method and solving the triple integral equation, it is found that the normal electric displacement on the crack surfaces is no longer a constant as determined by previous studies, rather, it depends upon the remote combined electromechanical loadings. Numerical results of the stresses and electric displacement fields show that there are no singularities at the crack tips so that the stresses remain finite. It is of great significance that the concrete electric boundary condition on the crack surfaces exerts significant influence on the near-tip fields and in this way plays an important role in evaluating the crack stability in the non-local piezoelectric materials. More specifically, the impermeable crack model always overestimates the finite stresses at the crack tips, whereas the permeable crack model always underestimates them.

关键词： Crack Non-local piezoelectric materialsImpermeable Permeable Semi-permeable

ANALYSIS OF CRACK-TIP SINGULARITIES FOR AN INTERFACIAL PERMEABLE CRACK IN METAL/PIEZOELECTRIC BIMATERIALS

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Acta Mechanica Solida Sinica 2007年第3期20卷 247-257页

作者： Li Qun Chen Yiheng~* (school of aerospace,Xi’an Jiao-Tong University,Xi’an 710049,China) school of aerospace Xi''an Jiao-Tong University Xi''an 710049 China

By modeling metal as a special piezoelectric material with extremely small piezoelec- tricity and extremely large permittivity,we have obtained the analytical solutions for an interfacial permeable crack in metal/piezoelectric bimaterials by means of the generalized Stroh formalism. The analysis shows that the stress fields near a permeable interfacial crack tip are usually with three types of singularities:r;and r;.Further numerical calculation on the oscillatory indexεare given for 28 types of metal/piezoelectric bimaterials combined by seven commercial piezoelectric materials: PZT-4,BaTiO;,PZT-5H,PZT-6B,PZT-7A,P-7 and PZT-PIC 151 and four metals:copper,silver,lead and aluminum,*** explicit expressions of the crack tip energy release rate（ERR）and the crack tip generalized stress intensity factors（GSIF）are *** is found that both the ERR and GSIF are independent of the electric displacement loading,although they seriously depends on the mechanical loadings.

关键词： interfacial permeable crack metal/piezoelectric bimaterials energy release rate intensity factor

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 1. school of aerospace Engineering and Applied Mechanics Tongji University Shanghai 200092 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

The apparent contact angle of water droplet on the micro-structured hydrophobic surface

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Science China Chemistry 2010年第4期53卷 912-916页

作者： YANG ChangWei, HE Feng & HAO PengFei school of aerospace, Tsinghua University, Beijing 100084, China 1. school of aerospace Tsinghua University Beijing 100084 China

The apparent contact angle of Cassie-Baxter state water droplets can be calculated by the existing theoretical formula, but due to the defects of the micro-structured hydrophobic surface and some inevitable tiny disturbances in the experiment, Cassie-Baxter state water droplets will appear partly in Wenzel state, that is, the mixed state water droplets. In this paper, apparent contact angles of Cassie-Baxter state and mixed state water droplets on micro-structured hydrophobic surfaces are compared. The research shows that if the projected area fraction of water-solid F in the Cassie-Baxter formula is replaced by the local projected area fraction of water-solid F′, the apparent contact angles of water droplets in both Cassie-Baxter state and the mixed state can be calculated. Further experimental results indicate that the contact state of water droplets nearby the outermost three-phase contact line plays a more important role in determining the apparent contact angle. This conclusion is significant to the understanding of the apparent contact angle and wetting property.

关键词： apparent contact angle three-phase contact line mixed model Cassie-Baxter model Wenzel model

An analysis of the Circumferential Grooves Casing Treatment for transonic compressor flow

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Science China(Physics,Mechanics & Astronomy) 2010年第2期53卷 353-359页

作者： HUANG XuDong,CHEN HaiXin,SHI Ke & FU Song school of aerospace,Tsinghua University,Beijing 100084,China 1. school of aerospace Tsinghua University Beijing 100084 China

The stall mechanism of the NASA Rotor 37 is investigated through the analysis of the critical flow structures near the stall under the transonic condition. The performance of the rotor with Circumferential Grooves Casing Treatment (CGCT) is also studied based on the Reynolds-Averaging Navier-Stokes approach. The study finds that stall margin improvement can be achieved without significant penalty on the efficiency for the two CGCT configurations applied. The effects of circumferential grooves on the critical flow structures are studied through the analysis of the tip leakage mass and momentum transport that further re-veal the CGCT mechanism.

关键词： transonic compressor Circumferential Grooves Casing Treatment stall margin leakage mass and momentum trans-portation analysis

Particle modulations to turbulence in two-phase round jets

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Acta Mechanica Sinica 2009年第5期25卷 611-617页

作者： Bing Wang Huiqiang Zhang Yi Liu Xiaofen Yan Xilin Wang school of aerospace, Tsinghua University, 100084 Beijing, China school of aerospace Tsinghua University 100084 Beijing China

The particle modulations to turbulence in round jets were experimentally studied by means of two-phase velocity measurements with Phase Doppler Anemometer （PDA）. Laden with very large particles, no significant attenuations of turbulence intensities were measured in the farfields, due to small two-phase slip velocities and particle Reynolds number. The gas-phase turbulence is enhanced by particles in the near-fields, but it is significantly attenuated by the small particles in the far-fields. The smaller particles have a more profound effect on the attenuation of turbulence intensities. The enhancements or attenuations of turbulence intensities in the far-fields depends on the energy production, transport and dissipation mechanisms between the two phases, which are determined by the particle prop- erties and two-phase velocity slips. The non-dimensional parameter CTI is introduced to represent the change of turbulence intensity.

关键词： Particle modulations Turbulence intensity Particle sizes Two-phase slip velocity Particle-laden round turbulent jet

Dynamics and control of a solar collector system for near Earth object deflection

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Research in Astronomy and Astrophysics 2011年第2期11卷 205-224页

作者： Shen-Ping Gong,Jun-Feng Li and Yun-Feng Gao school of aerospace,Tsinghua University,Beijing 100084,China school of aerospace Tsinghua University Beijing 100084 China

A solar collector system is a possible method using solar energy to deflect Earth-threatening near-Earth *** investigate the dynamics and control of a solar collector system including a main collector （MC） and secondary collector （SC）.The MC is used to collect the sunlight to its focal point,where the SC is placed and directs the collected light to an *** the relative position and attitude of the two collectors should be accurately controlled to achieve the desired optical ***,the dynamical equation of the relative motion of the two collectors in the vicinity of the asteroid is ***,the nonlinear sliding-mode method is employed to design a control law to achieve the desired configuration of the two ***,the deflection capability of this solar collector system is compared with those of the gravitational tractor and solar sail gravitational *** results show that the solar collector is much more efficient with respect to deflection capability.

关键词： minor planets asteroids -- techniques: miscellaneous -- solar collector