Irreducible decompositions of physical tensors of high orders

In this paper we use the term 'physical tensor' to stand for a tensor that belongs to a tensor subspace. Based on the relationship among the characters of rotation representation, some techniques are developed in order to give the numbers of independent deviatoric tensors contained in the irreducible decompositions of physical tensors, even prior to the constructions of the irreducible decompositions. A number of examples are shown and many of them are new results.     

基于GLM的多模光纤放大器模式控制研究

为了提高多模光纤放大器输出光束质量,基于多模纤芯中各个模式的传输和放大机理,提出了一种新的模式控制方法——增益-损耗控制,通过变化纤芯中掺杂的浓度、形状和材料,实现对高阶模式的抑制。根据多模纤芯双包层掺镱光纤放大器模型,对基于增益-损耗控制的选模特性进行了数值模拟和实例分析,得到了优化设计方法。结果表明,该方法可以有效抑制放大器中的高阶模,输出基模功率百分比可达90%以上。     

基于高阶循环累积量的载波频率估计

首先系统总结了高阶循环累积量估计载波频率的研究成果,从理论上推导出MASK、MPSK和MFSK信号的测频原理,并对平方降价法的性能进行了测试,指出了平方降阶法的局限性。然后以16QAM信号为例,从理论上证明此方法同样可以应用于MQAM的载波频率估计,并进行了仿真验证,从而扩展了此方法的适用范围。最后,进行了小结,指出测频方法存在的问题及解决方法。     

Iterative design of variable fractional-order IIR differintegrators

In this paper, the variable fractional-order (VFO) differintegrator is designed based on IIR-typed Farrow structure. The stability of the designed VFO IIR differintegrator is achieved by incorporating a constrained function into the objective error function. But the minimization of the original objective error function is a highly nonlinear problem, so an iterative quadratic method is proposed to overcome it. Comparing with the design based on FIR-typed Farrow structure, several designed examples, including a VFO differintegrator, a pure VFO differentiator and a pure VFO integrator, are presented to demonstrate the effectiveness of the proposed method.     

Further results on global state feedback stabilization of nonlinear high-order feedforward systems

In this paper, by introducing a combined method of sign function, homogeneous domination and adding a power integrator, and overcoming several troublesome obstacles in the design and analysis, the problem of state feedback control for a class of nonlinear high-order feedforward systems with the nonlinearity's order being relaxed to an interval rather than a fixed point is solved.     

基于虚拟样机技术倾转四旋翼飞行器联合仿真

为了解决倾转四旋翼飞行器的机械系统及控制系统的设计问题,首先在ADAMS软件中建立倾转四旋翼飞行器的虚拟样机机械模型,同时在MATLAB/Simulink环境中引入了跟踪微分器并建立了非线性串级PID控制系统模型,然后通过搭建共享的虚拟样机模型实现联合仿真,最终得到机械系统和控制系统优化后的设计方案.仿真结果表明:倾转四旋翼飞行器的姿态调整过程稳定,具有很好的动态响应特性,为今后旋翼倾转过程的理论分析打下了良好的基础.     

热分层湍流直接模拟的高精度算法和数值分析

该文发展了高阶精度有限差分格式的直接数值模拟方法,并将其成功地应用于带有自由面的热分层槽道湍流问题的计算,与低阶精度格式相比,高精度格式有着更宽的低耗散波段,对中高波数分量有较好的模拟能力。该文直接在非均匀网格上采用Lagrange多项式插值构造迎风偏置格式,克服了传统二阶格式在网格变化剧烈时精度损失的缺点,提高了在近壁区的计算精度。对三维槽道湍流以及带有自由面的热分层湍流的流场和温度场的统计特征、脉动特征以及能谱进行了分析,进一步验证了高精度差分方法对热分层剪切湍流问题直接模拟的有效性。总体上讲,该格式精度高,对高频非物理振荡有抑制作用,可以适应变化的空间网格,有效地模拟复杂湍流流动结构,并正确地揭示其流动机理.     

Eight-node conforming straight-side quadrilateral element with high-order completeness (QH8-C1)

A new eight-node conforming quadrilateral element with high-order completeness, denoted as QH8-C1, is proposed in this article. First, expressions for the interpolation displacement function satisfying the requirements for high-order completeness in the global coordinate system are constructed. Second, the displacement function expression in global coordinates is transformed into isoparametric coordinates, and the relationships between the two series of coefficients for the two kinds of displacement function expressions are found. Third, the displacement function expression is modified to satisfy the requirements of nodal freedom and interelement boundary continuity. The key to the new element construction is the derivation of the linear relationship expressions among 12 coefficients of element displacement interpolation polynomials in the global and isoparametric coordinate systems. As a result, the relationship between quadratic completeness and interelement continuity is explicitly given, and a proof of the completeness and the continuity was conducted to theoretically guarantee the validity of the derivation results. Furthermore, in order to verify the correctness of the theoretical work, nine numerical examples were performed. The computation results from these examples demonstrate that QH8-C1 exhibited excellent performance, including high simulation accuracy, fast convergence, insensitivity to mesh distortion, and monotonic convergence.     

用高阶累积量投影法检测红外弱小目标

为检测弱小红外运动目标,提出了一种基于高阶累积量投影的检测算法.红外图像序列经背景抑制后,首先计算时域数据的归一化三阶累积量,并将其投影到二维空间,然后在二维空间内对目标轨迹进行统计判决,以实现目标检测.推导出了目标和噪声在二维投影空间中的分布公式.通过与相关算法对比分析,该算法计算量小,检测率随目标信噪比增长较快.利用实际录制的图像序列进行了仿真实验,成功检测到了信噪比不小于2、像面运动速度为2帧/像素的目标,验证了算法的有效性.     

一种多自由度阻尼体系动力问题的高阶分析方法

传统动力时程直接积分法多采用低阶数值格式,需要选择非常小的时间步距才能获得满足精度要求的动力分析结果.该文将结构动力时程分析的积分求微法推广至多自由度情形,发展了一种具有较高计算效率的多自由度阻尼体系的动力时程高阶分析方法.将相邻的ρ个时步组成一个待求解时段,基于多自由度体系动力响应积分解,以精细积分法结合秦九韶算法计...