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August 15,2013
Volume 6,Issue 15
Pages -
Subject Area:Fluid-solid Coupling Vibration,Flexible Multi-body Mechanics,Fracture Mechanics,Fluid Mechanics,Gas Dynamics,Elementary Particle Physics,Condensed Matter Physics

Title: Nonlinearity static aeroelastic trim analysis of flexible aircraft based on 3D lifting-line theory

Authors: XIE Changchuan, LIU Yi, YANG Chao
PP: 1464-1472
Abstract: Since the geometric nonlinearity of the flexible aircraft is significant, the traditional aeroelastic analysis method for linearity aeroelastic trim based on small deformation hypothesis is no longer available. In this paper, a new method based on the 3D lifting-line theory was applied to compute the nonplanar steady aerodynamics. Surface spine interpolation method was responsible for the structure/aerodynamics coupling. Moreover, the nonlinear finite element method gave the final nonlinear deformation. By combing these creative methods and using the iterative computation based on rigid aircraft trim, the results considering the nonlinear effects were obtained and compared with the linear results. The results indicated that the new method was much more effective and reliable for the facts and therefore it was very suitable for the rapid and efficient analysis in the preliminary stage of very flexible aircraft design.
Keywords: fluid-soild coupled vibration; static aeroelasticity trim; geometric nonlinearity; nonplanar aerodynamics; flight loads

Title: Rigid-flexible-thermal coupling dynamics investigation of flexible plate

Authors: PAN Keqi, LIU Jinyang
PP: 1457-1463
Abstract: Rigid-flexible-thermal coupling dynamic modeling method for flexible plate is proposed. For the cases of nonconstant thermal loading, based on the heat conductive variational equations of isotropic material, considering the coupling among the attitude motion, structural deformations and temperature change, the relationship among the heat flux density and the attitude motion coordinates as well as the elastic coordinates is firstly established. Finite element method is used for discretizing the temperature and deformation, the attitude motion coordinates, node elastic deformation and node temperature are adopted as generalized coordinates. Considering the geometric nonlinearity, combining variational equations and introducing the constraint function, rigid-flexible-thermal coupling dynamic equation is established. Dynamic performance is analyzed by mumerical simulation, which can be used for explanation of the thermally induced fluttering phenomena.
Keywords: flexible multibody mechanics; rigid-flexible-thermal coupling; heat flux density; geometric nonlinearity

Title: Testing research of crack tip opening angle for high toughness pipeline steels

Authors: WANG Junqiang, SHUAI Jian
PP: 1450-1456
Abstract: In order to accurately measure the fracture toughness of high-grade pipeline steels, new modified compact tension (MCT) specimen were designed by the tearing failure analysis for the modified double cantilever beam (MDCB) specimen. Furthermore, the crack tip opening angle (CTOA) of X80 pipeline steel was measured using digital image correction technology, and the rule of three-dimensional crack propagation for X80 steel was simulated on the basis of the Gurson damage model. By comparing the CTOA results with two specimens, it was showed that the MCT specimen had a larger measuring range in the thickness direction, and the obtained CTOA values had higher accuracy. The measured CTOA values of X80 steel was consistent with those from experimental and FE simulation method, which verified the validity of the Gurson damage model for evaluating the fracture toughness of pipeline steels. In addition, the same CTOA values were obtained with the different thickness layer in the steady-state crack growth stage.
Keywords: fracture mechanics; crack tip opening angle; testing method; pipeline steel; ductile tearing; damage and fracture simulation

Title: Study on force transmission in 2D disk granular arrays

Authors: LIU Yuan, MU Qingsong, MIAO Fuxing
PP: 1443-1449
Abstract: The force transmission in some 2D granular arrays consisting of aluminium disks is investigated experimentally, under varying boundary conditions and external forces. The following phenomena are found: 1) Under gravitational force, the stable “arching structure” can be observed and the“arching effect” exists. 2) Under external forces, for every packing geometry, there are some no-displacement stable regions taking the different shapes of some equilateral triangles. In addition, some dimensional analyses on these results are presented and the basic static theory is employed to explain them.
Keywords: physical mechanics; force transmission; experiment; arching effect

Title: Experimental research on rheological forming of the titanium alloy vane disk with complex shape

Authors: LUO Yingshe, LUO Shuling, LIU Bangping, YU Min, YIN Shuiping
PP: 1438-1442
Abstract: In order to save machine working time, save valuable metal material and improve the mechanical properties of part, on the basis of numerical simulation, the experimental research of rheological forming was carried out for the titanium alloy vane disk with complex shape. The testing results show that the above forming method is in keeping with the modern producing requirements of excellent quality, high efficiency and less consumption compared with those of the traditional machine-milling method. It is the application of rheological theory to the field of material plastic forming.
Keywords: rheology; vane disk with complex shape; rheological forming; experimental research; titanium alloy

Title: Characteristics of association of local side force with surface pressure distribution over a slender circular cone

Authors: MENG Xuanshi, GAO Chao, LUO Shijun, LIU Feng
PP: 1428-1437
Abstract: A pressure distribution measurement was performed on a circular cone cylinder model in the low-turbulence 3.0 m .6 m low-speed wind tunnel at angles of attack of 0-35 The semi-apex angle of the cone is 10 The Reynolds number range based on the base diameter of the circular cone is from 0.1 to 0.9 million, and the tests encompassed a complete coverage of roll orientations in 9 intervals. The test data at 0.3 million Reynolds number is analyzed in this paper, and the local side forces over the cone are calculated from the measured pressure over nine stations. The local side force coefficient versus roll angle is a continuous-wave curve at angles of attack from 25 to 30 and nearly a square-wave curve at 35 angle of attack. It is found for the first time that local side force is associated with a characteristic pressure distribution for all asymmetries, which is independent of roll angle and thus generally applicable to cone of the same geometry specifications.
Keywords: fluid mechanics; high angle of attack; slender circular cone; surface pressure distribution; local side force

Title: Theoretical study on condensation effects on combustion heated wind tunnel flows

Authors: LIN Longyuan, LUO Xisheng, QIN Fenghua
PP: 1419-1427
Abstract: An analytic method to estimate the condensation effects in combustion heated wind tunnel flows is proposed. The complex process of hypersonic flows with condensation is decoupled into an isentropic expansion process and a condensation process, and the concept of isentropic expansion interface and condensation interface is proposed. Based on the effects of mass reduction and heat addition in the condensation process, a theoretical model is established. The comparison of calculation results verifies the reliability of the proposed theoretical analytic methool. The theoretical analysis is then applied to the combustion-heated hypersonic tunnel flows. Results show that under the condition of the same total temperature, with the increase of mass fraction of the condensed water, the heat addition effect plays a dominant role in the variation law of Mach number, static pressure and static temperature parameters in the flow field of the tunnel exit, while the mass reduction effect plays a leading role in the variation law of density.
Keywords: gas dynamics; condensation effect; theoretical model; combustion heated wind tunnel; water vapor

Title: Study on the equilibrium properties in spin chain by Lindblad and Redfield equation

Authors: HUANG Jie, LIU Huiping, XU Zhen, ZHONG Ming
PP: 1411-1418
Abstract: In this paper, we derived the concrete forms of Lindblad equation and Redfield equation in the spin chain. Then the average magnetic moment and nearest neighbor correlation functions of one-dimensional homogeneous quantum Ising chain whose two ends are connected with baths with the same temperature were numerically simulated. By contrast of analytical results, we found that when the system internal was in weak coupling which the external field h was greater than the exchange interaction between the spin J, the calculated results of two equations above were both very closed to the analytical result. However, when the system internal was in tight coupling which h was closed to J, both of results calculated by two equations above had a gap. It was proved that the two equations were derived through different approximation conditions of kinetic equation. Moreover, when the temperature was higher, compared with the Lindblad equation, the Redfield equation was more close to the analytical results.
Keywords: statistic physics; spin model; Lindblad equation; Redfield equation; weak coupling; tight coupling

Title: Constraints on anomalous tcZ coupling from Bs→μ+μ- decay

Authors: LI Xinqiang, YANG Yadong, YUAN Xingbo
PP: 1404-1410
Abstract: In this paper, the anomalous tcZ coupling effects in the pure leptonic Bs→μ+μ- decay are analyzed. After exploiting the available experimental data, constraints on the anomalous coupling XLct are derived, which are then used to set the upper limit for the branching ratio of rare t→cZ decay. For a general complex coupling XLct, the predicted upper bounds on B(t→cZ) are compatible with that from the recent compact muon solenoid (CMS) direct search. In particular, for the case of real coupling XLct, the upper bound is Br(t→cZ)<1.0×10-4, which is much lower than the current CMS bound but is still accessible at the large hadron collider (LHC). With improved precision of measurements made at the LHC, the closer correlations between the decays t→cZ and Bs→μ+μ- are expected in the near future.
Keywords: elementary particle physics; anomalous tcZ coupling; numerical analysis; Bs meson; pure leptonic decays; t→cZ

Title: Investigations on the charge ordering and spin ordering of NaxCoO2(x=0.5) with triangular lattice

Authors: WANG Weihua, WEI Anbang, LUO Xiaoguang
PP: 1399-1403
Abstract: The dependence of the order parameters λc and λs of charge ordering and spin ordering on the interactions between electrons regarding the correlated electron system NaxCoO2, especially at x=0.5, by using the slave-boson approach which excludes the double occupation is investigated in this paper. It is found that λc is mainly affected by the inter-site Coulomb interaction (V) and λs is mainly decided by the spin exchange interaction (J). The charge ordering and spin ordering interact with each other. On the one hand, the spin frustration effect is enhanced by the large J, which leads to the spin ordering of system. On the other hand, the inhomogeneity results from the large V, which corresponds to charge ordering. Based on the experimental results, this work will provide the order parameters and the reasonable electron interaction parameters, which can be used for further study on the electronic structure of NaxCoO2.
Keywords: condensed matter physics; triangular lattice; slave-boson approach; charge ordering; spin ordering

Title: Research of blue light excitation phosphor of YAG on enhancing the warm tone

Authors: WANG Changlai, YU Hai, XU Gang, YANG Yang, YANG Bo, LI Guang
PP: 1393-1398
Abstract: Ce3+∶yttrium aluminum garnet （YAG） and Eu3+∶Gd2(WO4)3 nanophosphors were prepared by co-precipitation method, respectively. X-ray diffraction (XRD), scanning electron microscopy (SEM) and photoluminescence (PL) were used to characterize the structure, morphology and properties of the nanocrystal samples. After gaining the best ratio of doping concentration (Ce3+ 4%, Eu3+ 40%), the Ce3+∶YAG and Eu3+∶Gd2(WO4)3 were mixed in different ratio (2∶1, 1∶1, 1∶3, 1∶5) in order to find the most suitable ratio. The fine mixed nanophosphors gave a white light while excited by 465 nm blue light. The mixed nanophosphors will compensate for the cold tone of Ce3+∶YAG given by the traditional phosphors by adding the red light thus might have a potential application for white light emitting diode (LED).
Keywords: optics; white light emitting diode; Ce3+∶YAG; Eu3+∶Gd2(WO4)3; warm color

Title: Investigation on the surface structure of highly oriented pyrolytic graphite ablated by femtosecond laser pulses with different laser fluence

Authors: ZHANG Nan, FENG Peipei
PP: 1388-1392
Abstract: In this paper, 50 fs laser pulses with different laser fluences ranging from 1.1 to 178.0 J/cm2 are used to ablate highly oriented pyrolytic graphite (HOPG). Multiple kinds of carbon micro-/nano-structures are obtained at the ablated target surface, including branch-like graphite structure and carbon nano-particles with sizes down to 100 nm. These carbon nano-materials can form rainbow-like or parallel colorful pattern when irradiated by a white light source. In addition, it is found that the generated micro-structures on the ablated graphite surface still retain the sp2 bond by using the micro-Raman spectroscopy, but except for the branch-like structures do not have the graphite’s layer structures. Therefore it can be deduced that the brach-like structure is formed mainly by the optomechanical mechanism and other structures all undergo the thermal transition process during the ablation.
Keywords: optics; carbon micro-/nano-structure; femtosecond laser ablation; highly oriented pyrolytic graphite

Title: Diode pumped low threshold Yb:LuAG ceramic laser

Authors: DING Jingxin, ZHOU Hui, YANG Kangwen, PAN Haifeng, LI Wenxue, JIANG Benxue, PAN Yubai
PP: 1385-1387
Abstract: The diode pumped ceramic laser was demonstrated in this paper with Yb:LuAG sample which was doped with atom fraction of 3%. A stable three-folded resonator was adopted in this experiment and the obtained laser wavelength was centered at 1 031 nm. The laser performance was checked with different high brightness fiber-coupled diode lasers. The highest output power of 2.2 W with TEM00 model was obtained at a non-lasing absorbed pump power of 11.3 W when the diode laser with a core diameter of 100 μm was applied, with the corresponding slope efficiency of 27%.
Keywords: optics; laser technology; Yb:LuAG ceramic; low threshold; diode pumped

Title: Study on the mode expansion method of the wlrashort pulse Laguerre-Gaussian beam

Authors: YANG Fuping, HUANG Li, LIU Yidong
PP: 1379-1384
Abstract: A model of ultrashort pulse beam was generated by chopping the single mode continuous Laguerre-Gaussian beam (LGB) into thin slices in this work. The pulse LGB was expanded into a series of LGBs with the same angular number and different radial numbers. The expansion coefficients might show the time-varying and propagating characteristics of the pulse helical beam. Our analysis showed that mode dispersion was more serious with bigger radial number of incident LGB. In this work, we focused on the case of zero radial number of incident beams. In short propagation distance, e.g. less than 2zR, the beam with the same angular number with the incident beam, i.e. original mode, had similar propagating characteristics. The amplitude attenuation, spatial spreading and time delay would occur when original mode propagated. This phenomenon was even evident for the case of bigger angular number of the incident beam. The abovementioned conclusions are significant for optical communication using the orbital angular momentum division multiplexing (OAM-DM) technology.
Keywords: optics; ultrashort pulse; Laguerre-Gaussian beam; orbital angular momentum division multiplexing

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