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The solidification of two-phase heterogeneous materials:Theory versus experiment

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science China(Technological sciences) 2009年第6期52卷 1688-1697页

作者： KIM Tongbeum moe key laboratory for Strength and Vibration School AerospaceXi'an Jiaotong University

The solidification behavior of two-phase heterogeneous materials such as close-celled aluminum foams was analytically studied. The proposed analytical model can precisely predict the location of solidification front as well as the full solidification time for a two-phase heterogeneous material composed of aluminum melt and non-conducting air pores. Experiments using distilled water simulating the aluminum melt to be solidified (frozen) were subsequently conducted to validate the analytical model for two selected porosities (ɛ), ɛ=0 and 0.5. Full numerical simulations with the method of finite difference were also performed to examine the influence of pore shape on solidification. The remarkable agreement between theory and experiment suggests that the delay of solidification in the two-phase heterogeneous material is mainly caused by the reduction of bulk thermal conductivity due to the presence of pores, as this is the sole mechanism accounted for by the analytical model for solidification in a porous medium.

关键词： effective thermal conductivity porous materials solidification shape factor

Acoustic band gaps in two-dimensional square arrays of semi-hollow circular cylinders

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science China(Technological sciences) 2009年第2期52卷 303-312页

作者： T. Kim moe key laboratory for Strength and Vibration School of Aerospace Xi'an Jiaotong University

Concave surfaces focus sound while convex surfaces disperse sound. It is therefore interesting to know if it is possible to make use of these two opposite characteristics to enhance the band gap performance of periodic arrays of solid cylinders in air. In this paper, the band gap characteristics of a 2-D square array of semi-hollow circular cylinders embedded in air are investigated, both experimentally and theoretically. In comparison with the types of inclusion studied by previous researchers, a semi-hollow circular cylinder is unique in the sense that it has concave inner surfaces and convex outer surfaces. The finite difference time domain (FDTD) method is employed to study the propagation behavior of sound across the new phononic crystal of finite extent, and the influences of sample size and inclusion orientation on band gap characteristics are quantified in order to obtain the maximum band gap. For reference, the band gap behaviors of solid circular cylinder/air and hollow circular cylinder/air systems are considered and compared with those of semi-hollow circular cylinder/air systems. In addition to semi-hollow circular cylinders, other inclusion topologies such as semi-hollow triangular and square cylinders are also investigated. To validate the theoretical predictions, experimental measurements on square arrays of hollow Al cylinders in air and semi-hollow Al cylinders in air are carried out. The results demonstrate that the semi-hollow circular cylinder/air system has the best overall band gap performance.

关键词： phononic crystals PDTD semi-hollow circular cylinders band gaps experimental verification

AI based on frequency slicing deep neural network for underwater visible light communication

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science China(Information sciences) 2020年第6期63卷 47-54页

作者： Nan CHI Fangchen HU Guoqiang LI Chaofan WANG Wenqing NIU key laboratory for Information science of Electromagnetic Waves (moe) Fudan University

In this paper, we propose a low-complexity frequency slicing deep neural network(FSDNN) for wide-band signal post-equalization in a 1.2 m underwater visible light communication system. FSDNN and deep neural network(DNN) outperform the least mean square equalizer. Then, by splitting the received signal into two parallel signals using a digital low-pass filter and a high-pass filter, we demonstrate that the FSDNN significantly reduces the complexity of the traditional DNN post-equalizer. Moreover, the complexity of the FSDNN decreases considerably to 11.15% compared with the conventional DNN for a 2.7 Gbit/s wide-band transmitted signal with a similar bit error ratio performance.

关键词： deep neural network frequency slicing underwater visible light communication visible light communication

First-principles investigation of structural and electronic properties of oxygen adsorbing phosphorene

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Progress in Natural science:Materials International 2019年第3期29卷 316-321页

作者： Zhiqiang Wang Dianlong Zhao Shidong Yu Zikai Nie Yuwei Li Lijun Zhang key laboratory of Automobile Materials of moe and School of Materials science and Engineering Jilin University North China Institute of aerospace Engineering

Two-dimensional （2D） phosphorene has been extensively studied for potential electronic and optoelectronic *** is easily oxidized by adsorbing oxygen in the air,exhibiting changed materials stability and *** the impact of oxygen concentrations on stability and electronic properties of oxygen adsorbing phosphorene has never been systematically *** this article,the oxygen adsorbing phosphorene at different oxygen concentrations are studied via first-principles crystal structure *** considered stoichiometries of P;O,P;O;) P;O and P;O;with both single-side and dual-side adsorption for selected case P;*** energetically stable structure of each stoichiometry is *** has been found that the band gaps show rather wide range change,strongly depending on the oxygen ***,at the higher oxygen concentration the relatively low band gaps and small carrier effective masses emerge,comparable with the pristine black *** may be associated with the appearance of bridged P-O-P bonds as oxygen concentration *** electronic properties are discussed in relation to structural features and chemical bonding.

关键词： Phosphorene Oxygen adsorption Electronic structures First-principles calculations

Active Control Law Design for Flutter/LCO Suppression Based on Reduced Order Model Method

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Chinese Journal of Aeronautics 2010年第6期23卷 639-646页

作者： Chen Gang Li Yueming Yan Guirong moe key laboratory for Strength&Vibration School of AerospaceXi’an Jiaotong UniversityXi’an710049China

Active stability augmentation system is an attractive and promising technology to suppress flutter and limit cycle oscillation (LCO). In order to design a good active control law, the control plant model with low order and high accuracy must be provided, which is one of the most important key points. The traditional model is based on low fidelity aerodynamics model such as panel method, which is unsuitable for transonic flight regime. The physics-based high fidelity tools, reduced order model (ROM) and CFD/CSD coupled aeroservoelastic solver are used to design the active control law. The Volterra/ROM is applied to constructing the low order state space model for the nonlinear unsteady aerodynamics and static output feedback method is used to active control law design. The detail of the new method is demonstrated by the Goland+ wing/store system. The simulation results show that the effectiveness of the designed active augmentation system, which can suppress the flutter and LCO successfully.

关键词： limit cycle oscillation aeroelasticity reduced order model active control law static output feedback

Variational principles and governing equations in nano-dielectrics with the flexoelectric effect

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science China(Physics,Mechanics & Astronomy) 2010年第8期53卷 1497-1504页

作者： HU ShuLing SHEN ShengPing moe key laboratory for Strength and Vibration School of AerospaceXi’an Jiaotong UniversityXi’an 710049China

The flexoelectric effect is very strong and coupled with large strain gradients for nanoscale dielectrics. At the nanoscale, the electrostatic force cannot be ignored. In this paper, we have established the electric enthalpy variational principle for nanosized dielectrics with the strain gradient and the polarization gradient effect, as well as the effect of the electrostatic force. The complete governing equations, which include the effect of the electrostatic force, are derived from this variational principle, and based on the principle the generalized electrostatic stress is obtained, the generalized electrostatic stress contains the Maxwell stress corresponding to the polarization and strain, and stress related to the polarization gradient and strain gradient. This work provides the basis for the analysis and computations for the electromechanical problems in nanosized dielectric materials.

关键词： flexoelectric effect variational principle governing equations dielectrics electrostatic stress nanoscale

Bleustein-Gulyaev waves in a functionally graded piezoelectric material layered structure

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science China(Physics,Mechanics & Astronomy) 2009年第4期52卷 613-625页

作者： CAO Xiaoshan JIN Feng WANG ZiKun LU TianJian moe key laboratory for Strength and Vibration School of AerospaceXi’an Jiaotong UniversityXi’an 710049China

This work presents a theoretical study of the propagation behavior of Bleustein-Gulyaev waves in a layered structure consisting of a functionally graded piezoelectric material(FGPM) layer and a transversely isotropic piezoelectric substrate. The influence of the graded variation of FGPM coefficients on the dispersion relations of Bleustein-Gulyaev waves in the layered structure is investigated. It is demonstrated that,for a certain frequency range of Bleustein-Gulyaev waves,the mechanical perturbations of the particles are restricted in the FPGM layer and the phase velocity is independent of the electrical boundary conditions at the free surface. Results presented in this study can not only provide further insight on the electromechanical coupling behavior of surface waves in FGPM layered structures,but also lend a theoretical basis for the design of high-performance surface acoustic wave(SAW) devices.

关键词： Bleustein-Gulyaev waves functionally graded piezoelectric material electro-mechanical coupling factor surface acoustic wave device

Probabilistic description of extreme oscillations and reliability analysis in rolling motion under stochastic excitation

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science China(Technological sciences) 2023年第9期66卷 2586-2596页

作者： ZHAO Dan LI YongGe XU Yong LIU Qi KURTHS Jürgen School of Mathematics and Statistics Northwestern Polytechnical UniversityXi’an 710072China moe key laboratory for complexity science in aerospace Northwestern Polytechnical UniversityXi’an 710072China Potsdam Institute for Climate Impact Research Potsdam 14412Germany Department of Physics Humboldt University BerlinBerlin 12489Germany

Large-amplitude rolling motions, also regarded as extreme oscillations, are a great threat to marine navigation, which may lead to capsizing in ship motion. Therefore, it is important to quantify extreme oscillations, assess reliability of ship systems, and establish a suitable indicator to characterize extreme oscillations in ship systems. In this work, extreme events are investigated in a ship model considering a complex ocean environment, described by a single-degree-of-freedom nonlinear system with stochastic harmonic excitation and colored Gaussian noise. The stationary probability density function(PDF) of the system is derived through a probabilistic decomposition-synthesis method. Based on this, we infer the classical damage rate of the system. Furthermore, a new indicator, independent of the PDF, is proposed to quantify the damage related only to the fourth-order moment of the system and the threshold for extreme events. It is more universal and easier to determine as compared with the classical damage rate. A large damping ratio, a large noise intensity, or a short correlation time can reduce the damage rate and the value of the *** findings provide new insights and theoretical guidance to avoid extreme oscillations and assess the reliability of practical ship movements.

关键词： rolling motion colored noise extreme oscillations reliability probabilistic decomposition-synthesis method

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Photonic band structures of quadrangular multiconnected networks

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Chinese Physics B 2010年第7期19卷 313-321页

作者：宋欢欢杨湘波 moe key laboratory of Laser Life science & Institute of Laser Life science South China Normal University

By means of the network equation and generalized dimensionless Floquet-Bloch theorem, this paper investigates the properties of the band number and width for quadrangular multiconnected networks （QMNs） with a different number of connected waveguide segments （NCWSs） and various matching ratio of waveguide length （MRWL）. It is found that all photonic bands are wide bands when the MRWL is integer. If the integer attribute of MRWL is broken, narrow bands will be created from the wide band near the centre of band structure. For two-segment-connected networks and three-segment-connected networks, it obtains a series of formulae of the band number and width. On the other hand, it proposes a so-called concept of two-segment-connected quantum subsystem and uses it to discuss the complexity of the band structures of QMNs. Based on these formulae, one can dominate the number, width and position of photonic bands within designed frequencies by adjusting the NCWS and MRWL. There would be potential applications for designing optical switches, optical narrow-band filters, dense wavelength-division-multiplexing devices and other correlative waveguide network devices.

关键词： multiconnected network waveguide photonic band structure