Global attractors for plate equations with critical exponent in locally uniform spaces

A plate equation with critical exponent in locally uniform spaces with a coefficient β(x) belonging to the locally uniform spaces is studied. This equation is shown to generate a dissipative semigroup in locally uniform spaces , which possesses global attractors in weighted spaces .     

两种湍流模型时域颤振计算方法研究

采用时域计算分析方法进行了机翼跨音速颤振特性研究。在结构运动网格的基础上,采用格点格式有限体积方法进行空间离散和双时间全隐式方法进行时间推进求解雷诺平均N-S方程。针对流动粘性分别应用了SST湍流模型和SSG雷诺应力模型,通过对跨音速标模算例AGARD445.6机翼的计算结果与实验值的对比分析,其中应用SST湍流模型得到的颤振速度与实验值最为接近,特别是在跨音速段平均相对误差在3%以内;并且计算结果整体上反映了跨音速颤振"凹坑"物理特性,验证了方法的有效性。     

蝴蝶翅膀表面水滴各向异性黏附性质

采用扫描电子显微镜(SEM)观察了双带闪蝶(Morpho Achilles)翅膀表面的微观形貌, 通过样品的表观接触角表征了其浸润性, 采用高敏感性微电力学天平比较了水滴在蝴蝶翅膀表面不同方向运动时受到的黏附力. 实验结果表明, 水滴沿着干燥的蝴蝶翅膀鳞片堆叠方向运动时受到的黏附力要明显小于其它方向运动时受到的力, 且受力较稳定; 当蝴蝶翅膀被水滴浸润后, 水滴沿着湿润的蝴蝶翅膀鳞片堆叠方向运动时受到的黏附力接近甚至大于逆着鳞片堆叠方向运动时受到的力.     

Plate/shell topological optimization subjected to linear buckling constraints by adopting composite exponential filtering function

In this paper, a model of topology optimization with linear buckling constraints is established based on an independent and continuous mapping method to minimize the plate/shell structure weight. A composite exponential function (CEF) is selected as filtering functions for element weight, the element stiffness matrix and the element geomet-ric stiffness matrix, which recognize the design variables, and to implement the changing process of design variables from“discrete”to“continuous”and back to“discrete”. The buck-ling constraints are approximated as explicit formulations based on the Taylor expansion and the filtering function. The optimization model is transformed to dual programming and solved by the dual sequence quadratic programming algo-rithm. Finally, three numerical examples with power function and CEF as filter function are analyzed and discussed to demonstrate the feasibility and efficiency of the proposed method.     

Influence of stiffeners on plate vibration and radiated noise excited by turbulent boundary layers

The influence of stiffeners on plate vibration and noise radiation induced by turbulent boundary layers is investigated by wind tunnel measurements. Plates with and without stiffeners are tested under the flow speed of 60 m/s, 71 m/s and 86 m/s, respectively. The stiffeners are set either perpendicular or parallel to the direction of the free stream. Measured vibration and noise levels are compared with theoretical calculations, where wall pressure cross-spectra are described by the Corcos model. For the plates tested, it is evident that stiffeners perpendicular to the direction of the free stream could increase noise radiation, but have almost no influence on vibration level of plates.     

Investigation of quasi lateral-field-excitation on (yxl)-17° LiNbO3 single crystal

Quasi lateral-field-excitation (LFE) on LiNbO₃ crystal is investigated both theoretically and experimentally. It is found that when the driving electric field direction is parallel to the crystallographic X-axis of the piezoelectric substrate, (yxl)-17° LiNbO₃ LFE bulk acoustic wave devices work on quasi-LFE mode. The experimental results agreed with the theoretical prediction well. The results provide the cut of LiNbO₃ crystal for quasi-LFE bulk acoustic wave devices, which is important for designing high performance LFE sensors on LiNbO₃ substrates.     

Hybrid phononic crystal plates for lowering and widening acoustic band gaps

We propose hybrid phononic-crystal plates which are composed of periodic stepped pillars and periodic holes to lower and widen acoustic band gaps. The acoustic waves scattered simultaneously by the pillars and holes in a relevant frequency range can generate low and wide acoustic forbidden bands. We introduce an alternative double-sided arrangement of the periodic stepped pillars for an enlarged pillars’ head diameter in the hybrid structure and optimize the hole diameter to further lower and widen the acoustic band gaps. The lowering and widening effects are simultaneously achieved by reducing the frequencies of locally resonant pillar modes and prohibiting suitable frequency bands of propagating plate modes.     

基于串联哑铃型微环谐振腔的二维相干光码分多址编解码器

利用微环谐振腔阵列进行光码分多址编解码过程中,微环谐振腔反射谱的自由频谱宽度(FSR)范围制约该系统用户容量的提升.本文提出了一种新型的基于游标效应的串联哑铃型微环谐振腔光编解码器.利用Matlab建立了半径分别为40μm-30μm-40μm的哑铃型微环谐振腔光编解码器模型.详细分析了光反射谱伪模抑制与耦合系数的关系,研究了耦合系数、码片速率对串联哑铃型微环谐振腔光编解码器性能的影响.结果表明,与半径分别为40μm-40μm-40μm的传统串联微环谐振腔编解码器相比,哑铃型微腔编解码器FSR值扩大了4倍.理想情况下,用户容量可呈指数增长.同时,互相关峰值比(P/W)与自相关峰值旁瓣比(P/C)分别提高了约33%和8%.     

Aeroelastic instability of composite wings by the consideration of different structural constitutive assumptions

The aeroelastic instability of composite wings modeled as Circumferentially Asymmetric Stiffness (CAS) thin-walled composite beams with closed cross-section is carried out. The objective has been to investigate the effects of different assumptions of constitutive equations on the aeroelastic instability behavior. Non-classical effects such as restrained warping and transverse shear are included in the beam model. The unsteady incompressible airloads are presented using Wagner׳s function. A comparison of the results based on different constitutive equations for a number of configurations including three types of stacking sequence for a box cross-section and two types of stacking sequence for a biconvex cross-section, is performed. The effects of the values of twist as well as twist-bending stiffness coefficients have been studied carefully on the results. As an outcome of this investigation it is revealed that the different choices of structural constitutive equations which result in different values of stiffness quantities; namely, twist and twist-bending stiffness, significantly affect the predicted results. For example, a difference of up to 45% in the aeroelastic critical speed has been observed between different sets of constitutive equations in some cases.