对于具有大范围运动和非线性变形的柔性梁的有限元动力学建模

研究具有大范围运动和非线性变形的柔性梁的有限元动力学建模.采用有限元方法对梁结构进行离散,利用Lagrange方程建立系统的精确动力学方程.该方程不仅增加了新的表征纵向、横向、侧向弯曲变形,以及扭转变形的耦合项,同时包含了变形运动与大范围运动之间的相互耦合项.     

On the elliptic equation on complete Riemannian manifolds and their geometric applications

We study the elliptic equation on complete noncompact Riemannian manifolds with nonnegative. Three fundamental theorems for this equation are proved in this paper. Complete analyses of this equation on the Euclidean space and the hyperbolic space are carried out when is a constant. Its application to the problem of conformal deformation of nonpositive scalar curvature will be done in the second part of this paper.

     

焊接变形光学测量技术研究

针对薄板焊接变形测量难的问题,提出了一种非接触式三维光学实时测量薄板焊接变形的新方法。首先通过2个高分辨率高速数字相机从不同观察点同时拍摄物体运动的视频图像;然后运用三维重建技术,包括共线方程、基于共面方程的像片定向、直接线性变换解法、外极线几何约束和光束平差解法等重建待测标志点的三维坐标;最后依据同名点将不同时刻薄板的变形状态关联起来,计算出待观测点的焊接变形量,并实时绘制显示出变形曲线。与传统方法相比,该方法具有不受焊接温度及强烈干扰影响和实时、高效、高精度等优点。     

温度对潜望式激光通信终端SiC反射镜性能影响

分析了温度梯度和均匀温度对潜望式激光通信终端反射镜形变的影响,利用椭圆域上的Zernike多项式对椭圆反射镜的波前进行拟合,计算由于热形变导致的波前畸变误差,给出了星间激光通信终端反射镜均方根值、发射光束瞄准误差、接收端光强随温度梯度和均匀温度的变化关系。结果表明:温度梯度对反射镜的影响只是引起峰值光强的漂移和少许下降,当温度梯度为14 ℃/m时瞄准误差达2.1 μrad。均匀温度会引起接收端的光强分布变化,从而导致很大的瞄准误差和光强衰减,当均匀温度与参考温度的差值小于0.6 ℃时,由波前畸变误差引起的瞄准误差小于1 μrad,当差值大于0.6 ℃时,瞄准误差突然增大到几μrad,接收端光强分布发生变化,此时反射镜热形变引起的像散项对光强分布起重要作用。     

Boundary of Anosov dynamics and evolution equations for surfaces

We show that a compact surface of genus greater than one, without focal points and a finite number of bubbles (“good” shaped regions of positive curvature) is in the closure of Anosov metrics. Compact surfaces of nonpositive curvature and genus greater than one are in the closure of Anosov metrics, by Hamilton's work about the Ricci flow. We generalize this fact to the above surfaces without focal points admitting regions of positive curvature using a “magnetic” version of the Ricci flow, the so‐called Ricci Yang‐Mills flow.     

Effect of ZnAl2O4 coating on the compressive behaviors of aluminum borate whiskers-reinforced aluminum composites at elevated temperatures

Aluminum borate whiskers (ABOw) with or without ZnAl₂O₄ coating reinforced pure aluminum composites (ABOw/Al, ABOw/ZnAl₂O₄/Al) were fabricated by squeeze casting. The effects of ZnAl₂O₄ coating on the compressive behaviors, microstructures, and matrix textures of the composites were investigated at different temperatures and strain rates. The results indicate that the maximum compressive flow stress of the composites almost linearly decreases with the increase in temperature. The maximum compressive flow stress of ABOw/ZnAl₂O₄/Al composite is higher than that of ABOw/Al composite at the same temperature when the strain rate is larger, however, it is reversed when the strain rate is smaller. It is more serious for the fracture of whiskers in ABOw/ZnAl₂O₄/Al composite than that in ABOw/Al composite at the high compressive strain rate. However, the average length of whiskers in ABOw/ZnAl₂O₄/Al composite is larger than that in ABOw/Al composite at the low compressive strain rate. The strong matrix texture in ABOw/ZnAl₂O₄/Al composite appears at the high compressive strain rate, however, it is observed in ABOw/Al composite at the low compressive strain rate.     

Biomechanical behaviors of dragonfly wing: relationship between configuration and deformation

In this paper, the natural structures of a dragonfly wing, including the corrugation of the chordwise cross-section, the sandwich microstructure veins, and the junctions between the vein and the membrane, have been investigated with experimental observations, and the morphological parameters of these structural features are measured. The experimental result indicates that the corrugated angle among the longitudinal veins ranges from 80° to 150°, and the sandwiched microstructure vein mainly consists of chitin and protein layers. Meanwhile, different finite element models, which include models I and I^* for the planar forewings, models II and II^* for the corrugated forewings, and a submodel with solid veins and membranes, are created to investigate the effects of these structural features on the natural frequency/modal, the dynamical behaviors of the flapping flight, and the deformation mechanism of the forewings. The numerical results indicate that the corrugated forewing has a more reasonable natural frequency/modal, and the first order up-down flapping frequency of the corrugated wing is closer to the experimental result (about 27.00 Hz), which is significantly larger than that of the planar forewing (10.94 Hz). For the dynamical responses, the corrugated forewing has a larger torsional angle than the planar forewing, but a lower flapping angle. In addition, the sandwich microstructure veins can induce larger amplitudes of torsion deformation, because of the decreasing stiffness of the whole forewing. For the submodel of the forewing, the average stress of the chitin layer is much larger than that of the protein layer in the longitudinal veins. These simulative methods assist us to explain the flapping flight mechanism of the dragonfly and to design a micro aerial vehicle by automatically adjusting the corrugated behavior of the wing.     

径向基函数插值方法在动网格技术中的应用

分析用于非结构网格的弹簧比拟和用于结构网格的无限插值动态网格方法在实际应用中的优缺点,提出无需网格连接关系的基于径向基函数(radial basis functions,RBF)插值的动网格技术并编制相应的网格运动计算程序.以二维菱形翼的旋转运动及三维菱形翼的柔性变形为例,分析不同基函数和紧支半径的选取对网格质量及计算效率的影响,并通过与弹簧比拟方法的对比验证了RBF方法的有效性.结果表明:RBF方法数据结构简单,计算效率高,适应大变形能力强,可以有效地实现计算流体力学中的网格运动问题.     

大直径W1/O/W2乳粒的稳定性

在准静态条件和旋转流体场中采用乳液微封装技术制备约2 mm的大直径W1/O/W2乳粒,研究了有机相浓度和水溶性聚合物浓度对W1/O/W2乳粒稳定性的影响。从乳粒受力和变形的角度,探索了旋转流体场对W1/O/W2乳粒动力学稳定性的增强作用机制。研究表明:无论是在准静态条件下还是旋转流场中,乳粒稳定性都随聚苯乙烯浓度单一上升,随聚乙烯醇浓度呈现先上升后下降的趋势;相对于准静态条件,旋转流体场在一定条件下对大直径W1/O/W2乳粒的动力学稳定具有明显增强作用。     

形变量对MAE及BN的影响

研究了无取向硅钢Ｗ２３Ｇ，Ｗ１０，Ｗ１４和取向硅钢Ｑ８Ｇ４种材料在不同形变量下的磁声发射（ＭＡＥ）和巴克豪森噪音（ＢＮ），结果表明ＭＡＥ随形变量增大而减少，ＢＮ随形变量的增大而增大．测量了形变量为１０．４％的Ｗ１８和Ｗ２３Ｇ在１００，２００，３００，…，７００°Ｃ各退火１ｈ的ＭＡＥ与ＢＮ值．其中ＭＡＥ值随退火温度的升高逐渐增大，ＢＮ值在高于５００°Ｃ退火时明显下降．并对上述实验结果进行了详细讨论．