Comments on "Inversion of multivariable linear systems"

The purpose is to give a simple algebraic proof to the necessary part of the criterion of functional reproducibility of multivariable linear systems given by Silverman and to incorporate a slight correction to his criterion. Furthermore, the criteria of the functional reproducibility of Silverman and Sain and Massey [1] are shown to be equivalent.     

The role of zeros in the performance of multiinput, multioutputfeedback systems

A review of the early history attached to the idea of zeros for systems with multiple inputs and outputs is provided. A discussion of the consensus definitions for such zeros is given together with the ways in which they are involved in control thinking and control applications. A control zero principle and a control pole principle explain the intuitive way in which zeros and poles influence the performance of feedback systems. These are presented in the multivariable case by means of a pair of new results, this provides a framework to unify the overall presentation. Zeros at infinity are introduced; the causality of controllers is fitted onto place; and developments in time-varying zeros, nonlinear zeros, and generic zeroes are described     

Control of linear systems according to the minimal variance criterion--A new approach to the disturbance problem

The problem of minimizing the ensemble average of a performance index in the presence of control noise has received substantial attention in the literature. This work considers a generalization of viewpoint, in which the index variance is minimized while its expectation is constrained. Necessary and sufficient relations are derived for linear, time-invariant systems and disturbances having rational spectra. The open-loop, optimal-feedback solution is specified by its characteristic equation and boundary conditions for Gaussian noises and plants with distinct eigenvalues. The canonic structure of a noise-free plant incorporating covariance data from the disturbance process is shown to have fundamental significance in the optimal solution. Several examples are presented.     

Damage indices for failure of concrete beams under fatigue

In this study, an analytical method is proposed to correlate local damage variables such as relative crack depth and crack tip opening displacement with a newly defined global damage index for a concrete beam under fatigue loading. This global damage index may be used to assess the response of a degraded concrete beam under service loading. The damage is assumed to appear in the form of a major crack that propagates under constant amplitude fatigue loading. The progressive cracking phenomenon is modeled within a finite element framework using a crack beam element, which takes into account the compliance variation due to discrete cracking within the member. The flexural stiffness degradation of the member is computed based on an Eigen analysis of the global stiffness matrix. It is seen that the degree of flexural stiffness degradation due to discrete cracking is the same for geometrically similar specimens when the relative crack depth is used as a local damage parameter. Further, in order to improve the accuracy of the response prediction using the above global damage index, another global damage parameter is defined based on the nature of applied loading.     

考虑结构因素的蜂窝纸板等效模型适用性研究

为提高蜂窝纸板的数值计算精度、适用不同规格蜂窝纸板等效模型选择,分析了不同等效模型对不同结构蜂窝纸板固有频率的对应等效精度。首先,对Reissner等效模型、Ekavall等效模型和三明治夹芯板模型分别进行有限元建模;其次,将等效板的模态分析与实验结果进行对比,分析不同胞元边长、厚度与芯纸克重对等效模型的精度影响;最后,总结这3个变量对不同模型计算精度的影响规律,在此基础上得到蜂窝纸板固有频率解析方程。结果表明：Reissner理论模型适用于厚度小于等于20 mm的蜂窝纸板;Ekavall等效模型整体精度最高,误差基本低于10%;三明治夹芯板模型在蜂窝纸板胞元边长为10 mm时精度最高;在胞元边长与厚度相同的情况下,芯纸克重对计算精度影响较小;所得解析方程的解析结果与实验结果对比误差在12.43%以内。该结论为蜂窝纸板的模型选取提供依据。     

场协同拉伸螺杆强化混合与传热机理的研究

基于聚合物场协同塑化输运混炼原理,设计开发强化混合与换热的场协同拉伸螺杆新结构——场协同拉伸元件,利用ANSYS Polyflow 对普通双头螺纹螺杆和不同拉伸元件排布的场协同拉伸螺杆进行了数值模拟,对比分析了不同螺杆构型对聚合物胶料的混合性能、传热性能以及塑化均匀性的影响。结果表明,场协同拉伸螺杆综合性能均优于普通螺纹螺杆,其中,场协同拉伸元件集中排布的螺杆B传热性能最优,场协同拉伸元件分散排布的螺杆F混合性能最优;场协同拉伸螺杆中拉伸元件的径向收敛流道改变了速度场的方向,使速度矢量产生了径向分量,促进了速度场与温度梯度场、速度梯度场的协同相互作用,增加流场中的拉伸流动和拉伸形变,强化了热质传递输运过程。