超静定型钢桁架优化设计的面积比法

满应力准则是对超静定型钢桁架进行优化设计的有效方法．但这种方法的主要缺点在于收敛速度很慢甚至不收敛,这给设计工作带来很大的不便．对问题进行了研究,在“型钢压杆稳定设计直接法”的基础上,提出了满应力优化设计的一种新方法——面积比法,有效地提高了设计过程的收敛速度,降低了设计成本,供有关结构设计人员参考．     

Large amplitude free flexural vibrations of laminated composite skew plates

Here, the large amplitude free flexural vibration behaviors of thin laminated composite skew plates are investigated using finite element approach. The formulation includes the effects of shear deformation, in-plane and rotary inertia. The geometric non-linearity based on von Karman's assumptions is introduced. The non-linear governing equations obtained employing Lagrange's equations of motion are solved using the direct iteration technique. The variation of non-linear frequency ratios with amplitudes is brought out considering different parameters such as skew angle, number of layers, fiber orientation, boundary condition and aspect ratio. The influence of higher vibration modes on the non-linear dynamic behavior of laminated skew plates is also highlighted. The present study reveals the redistribution of vibrating mode shape at certain amplitude of vibration depending on geometric and lamination parameters of the plate. Also, the degree of hardening behavior increases with the skew angle and its rate of change depends on the level of amplitude of vibration.     

松质骨弹性模量计算的均匀化方法

对松质骨建立了六种单胞微观结构模型，采用均匀化方法和有限元方法计算松质骨的宏观等效弹性模量。给出了六种单胞模型的松质骨弹性模量与材料密度(体分比）的关系，与实验数据进行了对比，分析了不同微观结构模型在不同骨骼中的应用。结果表明，本文方法及六种单胞模型可以对松质骨微观结构和材料性能进行有效的模拟计算。同时本文又着重对松质骨的宏观等效弹性模量与体分比的指数关系进行了探讨。     

滑带土动力学性质试验研究

为了研究地震高烈度区老滑坡的复活变形原因,本文对滑坡滑带土的动力学特性进行了系列研究。本次试验采用扰动土样,制样基本物理指标按滑带土的现场测试指标确定,在不固结不排水条件下,运用MTS810Teststar程控液压伺服土动三轴仪对单个样品逐级放大动应力的分级试验方法进行。侧向压力 (围压 )分别采用 100kPa、20 0kPa、300kPa三级,通过施加轴向振动荷载 (力 )模拟地震作用,振动波形为正弦波,频率为 1Hz,振幅随试样性质确定。研究结果表明,滑带土在动荷载作用下的动力学性质与其静荷载作用下的力学性质有着较大的差异,主要表现在滑带土的动应力与动应变关系的非线性、滞后性及变形积累特点,动弹性模量与动强度的显著降低以及动阻尼比的显著增大特性。这揭示了动力作用下的滑坡复活原因之一,同时为滑坡稳定性评价和动力作用下的变形机制模拟分析提供了基础资料,也为分析滑带土动力本构模型提供了基本内容。     

Aspect ratio effect on natural convection in water near its density maximum temperature

The effect of the aspect ratio on natural convection in water subjected to density inversion has been investigated in this study. Numerical simulations of the two-dimensional, steady state, incompressible flow in a rectangular enclosure with a variety of aspect ratios, ranging from 0.125 to 100, have been accomplished using a finite element model. Computations cover Rayleigh numbers from 10³ to 10⁶. Results reveal that the aspect ratio, A, the Rayleigh number, Ra, and the density distribution parameter, R, are the key parameters to determine the heat transfer and fluid flow characteristics for density inversion fluids in an enclosure. A new correlation for predicting the maximum mean Nusselt number is proposed in the form of , with the constants a and b depending on density distribution number R. It is demonstrated that the aspect ratio has a strong impact on flow patterns and temperature distributions in rectangular enclosures. The stream function ratio Ψ_inv/|Ψ_reg| is introduced to describe quantitatively the interaction between inversional and regular convection. For R=0.33, the density inversion enhancement is observed in the regime near A=3.     

Wide-band circular polarization-keeping reflection mediated by metasurface

In this paper,we show that circular polarization-keeping reflection can be achieved using reflective metasurfaces.The underlying physical mechanism of the polarization-keeping reflection is analyzed using a reflection matrix.A wideband circular polarization-keeping reflector is demonstrated using N-shaped resonators.Both the simulation and experiment results show that the polarization-keeping reflection can be achieved with a high efficiency larger than 98%over the frequency range from 9.2 GHz to 17.7 GHz for both incident left-and right-handed circularly polarized waves.Under oblique incidence,the bandwidth increases as the incident angle varies from 0°to 80°. Moreover,the co-polarization reflection is independent of the incident azimuth angles.     

光阑对偏振高斯-谢尔模型光束偏振特性的影响（英文）

根据广义惠更斯-菲涅尔原理和Collins公式,基于复高斯函数展开法,推导出椭圆偏振的高斯-谢尔模型光束经过矩形光阑衍射后的交叉谱密度公式,结合斯托克斯矢量理论推导了椭圆偏振高斯-谢尔模型光束在接收平面的光强、偏振度、方位角和椭圆度的表达式,数值分析了光阑的孔径遮拦比对光强、偏振度及方位角和椭圆度的影响.结果表明,光阑的孔径遮拦比在近场区对经过光阑后椭圆偏振高斯-谢尔模型光束的光强和偏振特性有显著影响;随着传输距离的增大,光强和偏振特性受孔径遮拦比的影响减小,光强和偏振特性变化平稳.     

基于荧光强度比值法可用于现场测量的低成本聚合物光纤温度传感器

基于荧光强度比值法,设计了一种使用两种荧光染料的光纤温度传感器.实验中,罗丹明B和罗丹明110分别为对温度敏感和对温度不敏感的荧光传感物质,利用聚合物光纤来传导激发光及接收荧光.由于两种染料的荧光谱峰相距60 nm,因此容易将二者对应的荧光谱分开.通过确定能代表两种染料的最优荧光光谱范围,获得具有良好线性度的温度-荧光强度标定曲线.实验研究了不同浓度的荧光染料对标定曲线的影响,当染料浓度为0.3 g/L时,可获得0.28℃的最小均方误差及0.0128/℃的灵敏度.此外,该传感器还具备一定的抗光源扰动和抗荧光染料漂白的能力.     

Toward automatic evaluation of defect detectability in infrared images of composites and honeycomb structures

Non-destructive testing (NDT) refers to inspection methods employed to assess a material specimen without impairing its future usefulness. An important type of these methods is infrared (IR) for NDT (IRNDT), which employs the heat emitted by bodies/objects to rapidly and noninvasively inspect wide surfaces and to find specific defects such as delaminations, cracks, voids, and discontinuities in materials. Current advancements in sensor technology for IRNDT generate great amounts of image sequences. These data require further processing to determine the integrity of objects. Processing techniques for IRNDT data implicitly looks for defect visibility enhancement. Commonly, IRNDT community employs signal to noise ratio (SNR) to measure defect visibility. Nonetheless, current applications of SNR are local, thereby overseeing spatial information, and depend on a-priori knowledge of defect’s location. In this paper, we present a general framework to assess defect detectability based on SNR maps derived from processed IR images. The joint use of image segmentation procedures along with algorithms for filling regions of interest (ROI) estimates a reference background to compute SNR maps. Our main contributions are: (i) a method to compute SNR maps that takes into account spatial variation and are independent of a-priori knowledge of defect location in the sample, (ii) spatial background analysis in processed images, and (iii) semi-automatic calculation of segmentation algorithm parameters. We test our approach in carbon fiber and honeycomb samples with complex geometries and defects with different sizes and depths.     

300 W侧面分布式抽运掺Yb全光纤放大器

采用角度磨抛的方式, 在纤芯/包层为20/400 μm双包层掺Yb光纤上制作了侧面抽运耦合器. 该耦合器对975 nm的半导体二极管抽运光的耦合效率最高可达97%, 对1080 nm信号光的泄漏比小于2%. 分析了侧面抽运耦合器的性能以及多个侧面抽运耦合器的级联分布对抽运耦合效率的影响; 同时, 在前向抽运和双向抽运方式下, 分析了级联耦合器的分布及信号光泄漏比对激光器整体效率的影响, 并进行了数值模拟. 采用自行研制的侧面抽运耦合器, 搭建了侧面耦合分布式抽运、掺Yb双包层全光纤主振荡功率放大器, 获得了波长为1080 nm、功率为303 W 的基模激光输出. 进一步增加抽运点个数, 提高抽运功率, 可获得更高的输出功率.