EFG approximation with discontinuous derivatives

A technique for incorporating discontinuities in derivatives into meshless methods is presented. The technique enriches the approximation by adding special shape functions that contain discontinuities in derivatives. The special shape functions have compact support which results in banded matrix equations. The technique is described in element-free Galerkin context, but is easily applicable to other meshless methods and projections. Numerical results for problems in one and two dimensions are reported. © 1998 John Wiley & Sons, Ltd.     

黄河下游河道冲淤分布模式及冲淤特征

为揭示黄河下游河道的沿程冲淤分布模式及分布特征,对黄河下游1952—2021年间共70年的河段实测冲淤量数据进行了系列统计分析。研究表明：(1)黄河下游河道存在7种沿程冲淤分布模式,其中全线冲刷、全线淤积、上冲下淤、上淤下冲等4种为基本模式。上淤下冲模式的冲淤临界位置在孙口附近,上冲下淤模式的冲淤临界位置在游荡性河段。各模式对河道整体冲淤的贡献率存在较大差异,两边冲中间淤模式对冲刷量的贡献率最大,全线淤积模式对淤积量的贡献率最大;(2)1952年以来,黄河下游河道沿程冲淤分布模式的变化过程可分为1952—1959年、1960—1985年、1986—1999年、2000年后共4个阶段;(3)各河段冲淤量大小以0点为中心近似呈偏态分布,冲淤量在多年尺度下具有沿程减小的趋势性特征以及“冲久必淤、淤久必冲”的周期性特征;(4)各河段整体冲淤发生年数差别不大,反映了河道冲淤的平衡趋向性;70年内淤积于黄河下游河床底部的泥沙有一半左右被冲走,花园口到孙口河段的累计冲淤量接近下游总冲淤量的8成,孙口以下河段很小;(5)全线冲刷模式为小浪底水库运用后下游河道的主要冲淤模式,小花段前期淤积的泥沙基本被冲完,夹高段、高孙段及孙艾段仅冲走了前期淤积泥沙的二到三成。研究结果总结了黄河下游河道的沿程冲淤分布模式,分析了冲淤分布特征,有助于深化对下游河道冲淤现象的整体认识。     

基于相位补偿的过热汽温自抗扰控制

随着可再生能源接入电网比例的逐步增大,热力发电厂需要应对更频繁、更大范围的负荷变化,这给电厂高阶、大惯性过热汽温过程的控制,带来了严峻的挑战。为此,本文针对一类高阶大惯性过程,提出了一种基于相位补偿的低阶自抗扰控制方法（Phase Compensation based Active Disturbance Rejection Control, PC-ADRC）。首先,阐述了过热汽温系统的工作原理和控制难点。然后,采用低频近似法详细推导了相位补偿网络模型。提出了采用相位补偿网络对模型动态特性进行补偿,得到等效降阶模型的模型简化思路。为便于工程应用,给出了PC-ADRC控制系统的简单实现方法和等效模型分析。最后,对PC-ADRC控制系统的稳定性和鲁棒性进行了研究。理论分析和仿真结果表明,所提出的控制器能有效提升高阶过程控制系统的鲁棒性和快速响应能力。     

High‐quality rendering of smooth isosurfaces

Animation and visualization of rectilinear data require interpolation schemes for smooth image generation. Piecewise trilinear interpolation, the de facto standard for interpolating rectilinear data, usually leads to significant visual artifacts in the resulting imagery. These artifacts reduce the confidence in the resulting visualization and may even lead to false interpretations of the data. This paper is concerned with the generation of smooth isosurface image sequences, obtained by casting rays through the image plane and computing their intersections with an isosurface. We describe a novel solution to this problem: we replace trilinear interpolation by tricubic interpolation, smoothing out the artifacts in the images; and we simplify the ray–isosurface intersection calculations by rotating and resampling the original rectilinear data in a second rectilinear grid—a grid with one family of grid planes parallel to the image plane. Our solution significantly reduces artifacts in individual images and leads to smooth animations. Copyright © 1999 John Wiley & Sons, Ltd.     

Adaptive fuzzy neuro-observer applied to low cost INS/GPS

A combined MEMS Inertial Navigation System (INS) with GPS is used to provide position and velocity data of land vehicles. Data fusion of INS and GPS measurements are commonly achieved through a conventional Extended Kalman filter (EKF). Considering the required accurate model of system together with perfect knowledge of predefined error models, the performance of the EKF is decreased due to unmodeled nonlinearities and unknown bias uncertainties of MEMS inertial sensors. Universal knowledge based approximators comprising of neural networks and fuzzy logic methods are capable of approximating the nonlinearities and the uncertainties of practical systems. First, in this paper, a new fuzzy neural network (FNN) function approximator is used to model unknown nonlinear systems. Second, the process of design and real-time implementation of an adaptive fuzzy neuro-observer (AFNO) in integrated low-cost INS/GPS positioning systems is proposed. To assess the long time performance of the proposed AFNO method, wide range tests of a real INS/GPS with a car vehicle have been performed. The unbiased estimation results of the AFNO show the superiority of the proposed method compared with the classic EKF and the adaptive neuro-observer (ANO) including a pure artificial neural network (ANN) function approximator.     

A generalized control framework of assistive controllers and its application to lower limb exoskeletons

Various control methods have been studied for the natural assistance of human motions by exoskeletal robots, i.e., wearable robots for assisting the human motions. For example, impedance control and compliance control are widely used for controlling interaction forces between a human and a robot. When an accurate measurement of the human muscular force is available (e.g., electromyography), a direct use of the estimated human joint torque is possible in the control of an assistive robot. The human motions in a daily living, however, are so complex that they are constituted by multiple phases, such as walking, sitting, and standing, where the walking can be further categorized into multiple sub-phases. Therefore, a single control method cannot be the best option for all the motion phases; a switch in the control algorithms may be necessary for assisting human movements in multiple motion phases. In this paper, a generalized control framework is proposed to incorporate the various assistive control methods in one general controller structure, which consists of Feedforward Disturbance Compensation Control, Reference Tracking Feedback Control, Reference Tracking Feedforward Control, Model-based Torque Control. The proposed control framework is designed taking into consideration of the linearity of each control algorithm, and thus it enables the continuous and smooth switching of assistive control algorithms, and makes it possible to analyze the stability of the overall control loop. The proposed method is implemented into a lower-limb exoskeleton robot and is verified by experimental results.     

Preparation and characterization of directional conducting and lower methanol permeable ultrathin membrane based on poly (vinyl alcohol) and imidazolium compounds

To produce directional conducting and lower methanol permeable ultrathin membrane for fuel cell, the imidazolium salt as both cross-linking agent and proton donor has been designed to build a directional proton conducting channel in a poly (vinyl alcohol)-based membrane. The methanol permeability of directional conducting membrane is very low, which is about twice smaller than that of Nafion₁₁₇. In addition, the membranes show a relatively high oxidative durability in H₂O₂ solutions, with only about 10% weight loss after the membrane being immersed in 3% H₂O₂ solution for 120 h. All the properties of prepared directional conducting membrane indicate their promising prospects in proton conducting membrane applications.     

不同通信模型下的全光树环网波长分配算法

研究了波分复用全光树环网在不同通信模型下的波长分配算法及其最坏性能分析.对于静态模型,证明了5L/2是树环网所需波长数的紧界.对于动态模型,提出了一种近似比为∑_i=1^hmax_r∈Ri[log|V(r)|]+h的波长分配算法,其中h为树环网的基树的层数,R_i为树环网中处于第i层的环的集合,|V(r)|为环r上的节点数.对于增量模型,提出了一种近似度为O[log₂(t+1)]的波长分配算法,其中t为树环网中的环数.     

Percus-Yevick近似下硬球多元系统的动态光散射

在粒子狭多分散性的近似下,分析了同时具有粒径和光学多分散性溶液中散射光的归一化一阶振幅自相关函数g~((1))(τ),得到了K≠0情况下散射光的动态结构因子的近似解析关系式。     

Fractional frequency domain identification of NaCl–glucose solutions at physiological levels

Electrical impedance spectroscopy (EIS) has been used to characterize different biological materials. This article exposes a methodology oriented to estimate glucose levels of a solution based on a rational fractional parametric model of the impedance data. The methodology is applied over saline–glucose solutions at five physiological glucose levels, using three sensors and five repetitions for each glucose concentration and employed sensor. The results suggest that changes in the glucose concentration produce significant changes in the impedance that should be reflected in the parametric model. The modeling procedure shows that the poles and zeros of an integer model presents a degree of correlation. However, the correlation is clearly explicit employing fractional models where the mean location of the complex zeros is highly related to the glucose content in the sample.