梯温充液拉深成形数值模拟分析

提出梯温充液拉深工艺,即在板料温充液拉深实验装置中的凹模和压料板表面分别打上有规律的孔,通过接触加热在板料上形成梯度分布温度场。通过有限元模拟0Cr18Ni9不锈钢板料筒形件拉深过程,对比分析均匀加热与梯温加热2种不同加热方式对板料成形性能的影响。研究表明,与均匀加热相比,梯温加热拉深工艺能进一步提高板料的极限拉深比。     

砂砾石层渗透灌浆模拟试验

在砂砾石地层介质中进行灌浆时,地下水的渗流作用对浆液不同方向的扩散半径产生影响,对此进行室内渗透灌浆模拟试验.采用均匀设计的理念,构造了整体试验方案,通过分析各影响因素与浆液扩散半径和灌浆量的线性关系,得出灌浆压力、浆液水灰比、地层渗透系数、渗流流速等因素对浆液扩散半径、灌浆量的影响规律.试验结果表明:影响浆液扩散半径、灌浆量的显著因素是地下水渗流作用,其次是灌浆介质本身的渗透系数和浆液水灰比;渗流速度与浆液下侧扩散半径呈正相关关系,与浆液上侧扩散半径呈负相关关系,对浆液侧向扩散半径影响较小且呈正相关关系.     

A new method to obtain ultimate bounds and convergence rates for perturbed time‐delay systems

A new method is proposed to determine the ultimate bounds and the convergence rates for perturbed time‐delay systems when the Lyapunov–Krasovskii functionals and their derivatives are available. Compared with existing methods, the proposed method is more concise, more widely applicable, and the obtained results are less conservative. To show the three features, the proposed method is applied to improve three existing results, respectively. Copyright © 2011 John Wiley & Sons, Ltd.     

Practical Output Regulation of Uncertain Strict‐Feedback Form Systems

In this paper, an output feedback control is proposed to solve the practical output regulation problem of a class of nonlinear systems. In the first step of the design procedure, two sets of coordinate transformations are used to convert the output regulation problem of the system in the strict‐feedback form into the regulation problem of the transformed system in the uncertain normal form. Then, for the resulting system, a state feedback in the cast of nested sliding mode control is designed. Finally, by using the nonlinear separation principle, the output feedback controller is achieved by substituting the estimated states, resulting from the high‐gain observer, instead of real states. It can be shown that the states of the closed‐loop system are ultimately bounded. Copyright © 2011 John Wiley and Sons Asia Pte Ltd and Chinese Automatic Control Society     

基于均匀设计与Powell算法的全局最优化算法及并行实现*

复杂函数的全局最优化问题是在求解各种复杂工程与科学计算问题中提炼出来的亟待解决的计算问题,均匀设计具有让试验点在高维空间内均匀分散的特点,而Powell算法具有很好的求解局部最优解的能力,将两种方法进行有效改进后使之相结合,设计出并行全局最优化算法.通过经典的全局最优化函数对算法进行了比较测试,发现该算法具有比以前的算法更好的寻优能力,并对算法时间、空间复杂度以及并行性进行分析和测试.基于均匀设计与Powell算法的全局最优化并行算法具有寻优能力强,时间开销与问题因素个数的平方和布点数成线性复杂度,空间开销与因素个数和布点数成线性复杂度,并行效率好的特点.     

基于改进MUSIC的声源定位方法

为设计更有效的声源定位方法,深入研究了传统 MUSIC 算法,并针对其分辨率低且在麦克风数目较少时波达方向 (direction of arrival,DOA)估计精度较差等问题,对传统 MUSIC 算法进行了优化,利用广义互相关算法估计出声源信号到达各 麦克风之间的时间差,并据此构建出对应的矢量信号,最后通过计算谱函数确定 DOA 估计值。 仿真和实验结果表明,优化后的 MUSIC 算法可以得到更加尖锐的指向性波束,更低的旁瓣,并且能使方位角的定位精度达到±4°,俯仰角的定位精度达到±5°。     

Enhanced mechanical and thermal properties of AlN ceramics via a chemical precipitation process

A uniform dispersion of sintering additives is crucial to improve the thermal and mechanical properties of AlN ceramics. In this study, the Y₂O₃-coated AlN composite powder was successfully prepared by the chemical precipitation (CP) process, thereby improving the homogenization of Y₂O₃ in AlN green compacts. The precipitation coating behavior of Y₂O₃ precursor was investigated by FTIR and TG-DSC, and the corresponding reaction equation was proposed. The results of TEM, XRD, and XPS for the CP processed AlN powder indicated that a uniform amorphous Y₂O₃ layer was fully wrapped on the surface of AlN powder. The microstructures and phases of the sintered AlN samples prepared via the CP and conventional ball-milling (BM) processes, respectively, were compared. The CP process can result in decreasing oxygen content in AlN grains, facilitating the formation of the desirable isolated second phases, and strengthening the grain and grain boundary of AlN ceramic. As a result, the thermal conductivity, bending strength and fracture toughness of the CP processed AlN ceramic are 9.43%, 10.56%, and 18.50% higher than those of the BM processed sample, respectively, illustrating the CP process is a pretty effective way to simultaneously improve the thermal and mechanical properties of AlN ceramics.     

不同精度冗余数据的融合

针对融合误差的最大值和数学期望,提出了一个评判数据融合方法优劣的标准.随后,提出了一种新的数据融合方法,扩展加权平均法.当待融合数据为两个时,通过理论分析得到了计算融合参数的公式.当有更多的数据参与融合时,通过数值仿真得到了该方法的各个融合参数.该方法能解决最大似然估计法所难以解决的均匀分布数据的融合问题,且具有比包括最大似然估计法在内的其它三种有代表性的数据融合方法更高的精度.     

Non-conservative ultimate bound estimation in LTI perturbed systems

A closed formula for ultimate bound estimation in LTI systems with non-vanishing perturbations is presented. The formula, based on geometrical properties of the system, provides an alternative to Lyapunov's second method based study. Although it is not proven that the bound obtained is always less conservative than the Lyapunov's bound, some examples are introduced where the estimations are significantly improved. An extension of the idea for nonlinear systems is also sketched.     

气吸式排种器排种性能影响因素的试验研究

采用均匀设计的方法进行了气吸式排种器排种大豆质量影响因素的试验研究,考察了排种器排种盘转速和真空室压力与性能参数之间的关系,建立了粒距合格率、漏播率与重播率与影响因素之间的数学模型,获得了回归方程和最优结构参数。对于该气吸式排种器排种盘转速和真空室压力的最优化值分别为0.58r.s-1和0.003MPa,对气吸式排种器的设计具有指导意义。