大型陀螺特征值问题的广义Arnoldi减缩算法

基于Ａｒｎｏｌｄｉ法，建立陀螺特征值问题的广义Ａｒｎｏｌｄｉ格式，并利用系统矩阵的反对称特性，得到极其简洁的甚至比对称矩阵Ｌａｎｃｚｏｓ法更为简单的递推格式，可称为陀螺Ａｒｎｏｌｄｉ减缩算法．这种方法从根本上避免了复数运算．此外，将重起动技术引入后，使算法具有迭代特点，不仅对计算重根非常有效，而且提供了判断是否漏根的机制，从而使该方法成为大型陀螺特征值问题完善的实用计算方法．算例表明了方法的有效性．

压电周期板中耦合禁带影响规律分析

近年来,利用周期结构中弹性波禁带特性减振的研究思路受到了广泛关注。针对以往周期结构难以实现宽频且可调禁带的问题,设计了一种含电路网络的压电周期结构。该结构中的弯曲波和电路网络中的电波通过压电效应可以产生一个较宽的耦合禁带,且通过调整电路参数就可以达到调节禁带位置的目的。首先,为了高效计算该结构的波动特性,开发了适用于压电周期结构的减缩波有限元算法,该算法可以在保证结果准确性的基础上节约90%以上的计算时间。利用该算法研究了压电材料尺寸和形状对耦合禁带性能的影响。结果表明:相同电学参数下,随着压电片尺寸的增大,耦合禁带向低频移动,且禁带带宽增加;相同面积下含圆形和方形压电片的机电系统内耦合禁带差异较小,即形状对耦合禁带的分布影响不大。其次,针对不同尺寸和形状的机电系统,设计了电学参数使得在同一频率附近产生耦合禁带,并分析了其性能差异。最后,为了证明耦合禁带的减振效果,设计了一种有限压电周期板模型,其强迫响应的结果证明了耦合禁带对结构内弹性波可以进行有效调控。

Evolution of downsized crescent-shaped dune in wind tunnel experiment

The migration of a downsized crescent-shaped dune was investigated in a wind tunnel experiment.Quantified upwind influx and vertical oscillation of the sand bed were introduced to modulate the saturation level of the sand flux above the dune surface to affect dune evolution.The evolution was recorded by top-view photography and then abstracted as the evolution of self-defined characteristic quantities using a digital image processing algorithm.The results showed that,in contrast to the case for spanwise quantities,the evolution of streamwise quantities corresponds to a linear increase in the modulation magnitude more positively and in a monotonic and convergent manner.In contrast with quantities on the windward face,the changes in quantities with respect to the horns were nonmonotonic with time and almost uncorrelated with the variation in modulation strength,which reveals the distinctiveness of leeside evolution.