精密挤压(拔制)圆角方型材等相似成形模具映射建模优化

本文针对亟待实现的挤压 (拔制 )异型材模具精密快速加工设计理论课题 ,借助于近代共形映射理论研究成果 ,求解了异型材挤压 (拔制 )模具相似成形塑性流动的数学模型 ,建立了圆角方型材精密挤压 (拔制 )模具模腔数学模型及其优化函数方程 ,建立了为实现模腔精密快速的CAD/CAM一体化的理论模型     

异形件双动拉深时局部变形条件的改善

分析了异形件在双动拉深时坯料的变形过程与规律,找出了产生缺陷的原因并提出了改进措施。改进了双动拉深压边装置的结构,实现了拉深过程中不同部位压边力的改变,能根据工艺需要调整压边力的大小,并利用凹模上的浅盲孔润滑措施改善制件局部变形条件。     

A study of 3D cover glass design that improves handheld device drop reliability

Cover glass in commercial handheld devices is now evolving from flat (2D) to curved (3D) shapes. For example, some commercial devices have utilized sled‐shape cover glass, 1 which partially covers long edges of the device. According to the patents published by key handheld manufacturers, 2 , 3 we can expect more variety of 3D shaped cover glass for handheld devices in the market. In this study, we have focused on the reliability of 3D cover glass when it is dropped to a rigid surface. The key parameters under study are the corner/edge bend radius and angle of the cover glass, which determines the 3D shape of the cover glass. To achieve this goal, we developed a finite element model to simulate the drop 4 - 13 of a handheld device with 3D‐shaped glass. The model uses explicit algorithm to simulate the high speed impact on the device during the drop test. The glass performance was evaluated based on contact force between the glass and the ground and maximum principal stress in the glass. We showed that to avoid severe damage because of first impact between the glass and the ground, the bend angle of 3D glass has to be in the range between 0 and 45°. For drop angles of 45° and higher, with the proposed glass bend angle, the impact can be taken over by the edge of the back cover of the device. In addition, we showed that optimum glass bend radius is in the range of 3.8 mm and larger. This is required to reduce stress in glass because of impact. The approach and conclusions from the current study can serve as a general guideline to improve the 3D cover glass reliability of a handheld device.     

Broadband planar dipole array Antenna with double C‐shaped slit elements for digital TV broadcasting transmission

This research has proposed a planar rectangular dipole antenna enclosed in double C‐shaped parasitically slit elements (i.e., radiator element) on a double‐cornered reflector for bandwidth enhancement. In the study, simulations were first carried out to determine the optimal parameters of the radiator element and then a radiator element prototype was fabricated and mounted onto a double‐cornered aluminum reflector. The simulated and measured |S₁₁|<–10 dB of the antenna element covered the frequency ranges of 451–901 MHz (66.6%) and 455–886 MHz (64.3%), respectively. The gain was enhanced by the subsequent deployment of multiple radiator elements to fabricate a four‐element vertically array antenna on an elongated double‐cornered reflector. The simulated and measured |S₁₁|20 and 相似文献   

A novel compact planar ultra‐wideband antenna with dual band‐notched characteristics

A novel planar ultrawideband monopole antenna with dual notched bands is presented. The antenna mainly consists of a radiation patch and a modified ground plane. To realize dual band‐notched characteristics, a U‐shaped stub embedded in the rectangular slot of the radiation patch and a novel coupled open‐/shorted‐circuit stub resonator are used on the backside of the substrate. The bandwidth of the dual notched bands can be controllable by adjusting some key parameters. The simulated and measured results indicate that the proposed antenna offers a very wide bandwidth from 2.6 to 18 GHz with Voltage Standing Wave Ratio (VSWR) < 2, except the dual notched bands of 3.3–3.7 GHz (World Interoperability for Microwave Access [WiMAX]) and 5.15–5.825 GHz (Wireless Local Area Network [WLAN]). Furthermore, good group delay and stable gains can be achieved over the operating frequencies. © 2014 Wiley Periodicals, Inc. Int J RF and Microwave CAE 25:48–55, 2015.     

T形柱正反向受剪承载力和变形能力特性研究

由于T形柱特殊的截面形式,正反向受剪时将分别处于腹板受压、翼缘受拉和腹板受拉、翼缘受压两种状态,故其正反向受剪承载力和变形能力与十字形柱相比差异较大。通过对国内T形柱受剪承载力试验进行分析,探讨了T形截面柱正反向受剪承载力特性,并对某一T形柱进行低周反复荷载试验,分析了低剪跨比状态下T形柱正反向加载破坏特征、承载能力和变形能力特性。研究表明,T形柱截面不规则,当狭义剪跨比小于3.0时,正反两个方向受剪承载能力和变形能力存在显著差异,两个方向的抗震性能亦存在差异,腹板受压时,柱脚腹板混凝土破坏严重,降低了异形柱的截面刚度和承载力,成为异形柱结构的薄弱部位。     

一种圆形感兴趣区域图像压缩算法

研究了圆形感兴趣区域, 推导了相应的掩码计算公式, 将多级树集合分裂算法 (Set partitioning in hierarchical trees, SPIHT) 加以改进, 得到适用于圆形感兴趣区域的图像压缩算法. 实验结果表明, 本文提出的圆形感兴趣区域掩码计算公式简单实用, 改进后的压缩算法效果明显.     

Multistable electro‐optical modes in ferroelectric liquid crystals

Abstract— Multistable electro‐optical modes exist under certain conditions in ferroelectric liquid‐crystal (FLC) cells, which means that any light‐transmission level can be memorized after the driving voltage is switched off. The multistability is responsible for three new electro‐optical modes with different shapes of the gray‐scale curve that can be either S‐shaped (double or single dependent upon the applied‐voltage pulse sequence and boundary conditions) or V‐shaped dependent upon boundary conditions and FLC cell parameters. The origin of these modes will be described.     

T形异形柱的非线性有限元分析

分析了T形异形柱的受力问题,利用ABAQUS有限元软件对T形异形柱进行了弹塑性非线性有限元分析.着重从混凝土的非线性本构关系和破坏准则,受拉开裂后的行为,钢筋的本构关系几方面进行分析,通过计算绘制出了梁柱混凝土的应力云图、裂缝图及钢筋的应力云图.用ABAQUS计算所得的裂缝图与拟静力试验结果裂缝进行比较,两者结果吻合.结果表明:应用ABAQUS对异形柱进行非线性分析是可靠的,从而论证了软件的实际应用能力,也为进一步进行更复杂的非线性分析打下了基础.     

基于Zadoff-Chu序列的频控阵稳健波束成形方法

不同于传统相控阵,频控阵（Frequency Diverse Array,FDA）在所有阵元间引入频率偏差,可以生成具有精准指向特性的点状辐射方向图,有效克服传统相控阵方位角相关性导致的接收方向射频信号安全性下降的问题。作为与传统相控阵的本质区别,FDA阵元频偏设置直接影响FDA辐射方向图的形状。为了生成理想的点状方向图,提出了一种Zadoff-Chu FDA（ZC-FDA）稳健波束成形方案,利用Zadoff-Chu序列调整阵元频偏,消除FDA辐射方向图周期性,抑制距离-方位角耦合性。与现有FDA系统相比,ZC-FDA方案在理想点状辐射方向图生成和波束旁瓣水平抑制方面具有明显优势。