电压型PWM逆变器输出误差分析及其补偿

由于死区时间和电力电子器件IGBT非理想特性的影响 ,PWM逆变器存在输出误差 ,使得众多的调速方案在低速运行时性能不佳或无法实现调速。本文详细分析死区时间和IGBT非理想特性对输出电压的影响 ,提出测量IGBT非理想特性方法和输出误差补偿法 ,并通过实验验证了误差补偿法的有效性。     

面向狭小环境检测的柔性机器人运动建模与控制研究

针对传统刚性检测手段因其体积大、自由度低、灵活性差等缺陷,难以适应复杂狭小非结构化环境中的检测需求,且传统组装式连续体机器人存在结构复杂、运动变形差、控制精度低等问题,提出一种面向狭小环境检测应用的柔性一体化连续体机器人,并对其进行运动建模和控制方法研究。在常曲率假设下基于几何分析方法建立机器人的正逆运动学模型,构建其驱动空间、关节空间及操作空间的映射关系,并对其运动特性进行仿真分析。基于蛇形运动机制提出一种柔性连续体机器人运动控制方法,以蛇行运动模型和逆运动学为基础来控制连续体机器人的推送运动。搭建相应的物理样机平台对所建运动模型和所提控制方法进行实验验证,结果表明：所建运动模型能够较为准确地描述柔性检测机器人的弯曲运动特性,所提控制方法实现了机器人的运动控制,且控制效果和控制精度在合理范围内。     

2P3R型机器人运动学及工作空间分析

针对目前企业中存在的人工打磨大型船用螺旋桨叶面效率低、质量不均匀以及工人劳动强度大等问题,提出了一种用于加工大型船用螺旋桨叶面的2P3R型5自由度工业机器人,建立了其完整模型。将末端执行器考虑在内,采用改进D-H法建立了机器人正运动学数学模型并求得其正运动学方程。基于蒙特卡罗法,在Matlab环境下,利用机器人工具箱对机器人工作空间进行求解,描绘出该机器人末端刀具可达工作空间点云图。通过曲面拟合与空间包容对比,结果表明,所设计的2P3R型5自由度工业机器人能够实现对直径4~10 m的大型船用螺旋桨单个桨叶上表面的全部覆盖,为后续对大型螺旋桨加工机器人的运动控制与路径规划等研究奠定了基础。     

Molecular design of the cellulose ester-based forward osmosis membranes for desalination

This work has investigated the fundamental science of phase inversion and formation mechanism of cellulose ester membranes at the interface between polymer and casting substrate. It also explores the desired membrane preparation conditions for forward osmosis (FO) applications. With the aid of positron annihilation lifetime spectroscopy (PALS), the similarity in physicochemical properties between the polymer and the substrate was found to play a significant role in determining the porosity of the bottom interfacial layer. The structure of the dense interfacial layer was also strongly dependent on membrane thickness and solvent composition. Experimental results surprisingly reveal that the original pore size of the as-cast membrane plays a critical role determining the final performance of the subsequent annealed membrane independently of annealing temperature and time. In addition, since a threshold pore size exists during annealing above which pores become difficult to downsize, we have found that a thin dense selective layer integrated in an asymmetric membrane may not always be the best option for FO. A balanced membrane structure consisting of a thin porous support and a thin dense selective layer has been developed for FO, which shows a low internal concentration polarization (ICP) and a relatively high water flux when seawater was employed as the feed.     

全波场正演模拟技术在ZBTD区块的应用与分析

在复杂地表条件下的地震资料处理中,正确识别和应用各种波非常重要。应用全波场正演模拟技术,可以在地震资料处理中数值模拟实际资料的理论模型,从而分析各种波在地层中的传播规律,利用波场快照识别有效波和干扰波。全波场正演模拟可将看不到,摸不着的波场,形象地展现出来,有助于观察地质结构与地震反射同相轴之间的因果联系。全波场正演模拟成为地质和地球物理学家之间实现相互理解和达成共识的最有效的工具。     

八面河地区地层剥蚀线研究

地层剥蚀线在地震剖面上由于处在地层超覆或剥蚀削蚀点附近,受地震资料分辨率的限制,地震反射往往提前变弱或消失,依据地震资料追踪的地层超覆和剥蚀削蚀线与实际地层超覆和剥蚀削蚀线存在较大的差异,因而不能根据砂组顶面反射同相轴的特征来准确判断砂组超覆和剥蚀削蚀线的位置。如何准确确定地层剥蚀削蚀线的位置,对于正确认识地层油藏分布和规模,指导油气勘探开发具有重要意义。瞬时相位及地层剥蚀线综合外推法能有效地解决剥蚀削蚀线外推问题。     

Rejection of micropollutants by clean and fouled forward osmosis membrane

As forward osmosis (FO) gains attention as an efficient technology to improve wastewater reclamation processes, it is fundamental to determine the influence of fouling in the rejection of emerging contaminants (micropollutants). This study focuses on the rejection of 13 selected micropollutants, spiked in a secondary wastewater effluent, by a FO membrane, using Red Sea water as draw solution (DS), differentiating the effects on the rejection caused by a clean and fouled membrane. The resulting effluent was then desalinated at low pressure with a reverse osmosis (RO) membrane, to produce a high quality permeate and determine the rejection with a coupled forward osmosis - low pressure reverse osmosis (FO-LPRO) system. When considering only FO with a clean membrane, the rejection of the hydrophilic neutral compounds was between 48.6% and 84.7%, for the hydrophobic neutrals the rejection ranged from 40.0% to 87.5%, and for the ionic compounds the rejections were between 92.9% and 96.5%. With a fouled membrane, the rejections were between 44.6% and 95.2%, 48.7%-91.5% and 96.9%-98.6%, respectively. These results suggest that, except for the hydrophilic neutral compounds, the rejection of the micropollutants is increased by the presence of a fouling layer, possibly due to the higher hydrophilicity of the FO fouled membrane compared to the clean one, the increased adsorption capacity of hydrophilic compounds and reduced mass transport capacity, membrane swelling, and the higher negative charge of the membrane surface, related to the foulants composition, mainly NOM acids (carboxylic radicals) and polysaccharides or polysaccharide-like substances. However, when coupled with RO, the rejections in both cases increased above 96%. The coupled FO-LPRO system was an effective double barrier against the selected micropollutants.     

"正在施工"--2004中国国际建筑艺术双年展·国际青年与学生作品展

本文介绍了2004年9月20日至10月10日在北京UHN国际村举行的国际青年与学生建筑作品展,该展览包括四部分．快进〉〉;热点．智囊组;建筑/非建筑。     

一种8自由度空间机械臂运动学及工作空间分析

针对太空环境,提出一种带有移动副的8自由度机械臂,可完成太空环境中的设备维修、物品抓取等工作。通过标准D-H参数法,推导了8自由度机械臂的位姿变换矩阵和正运动学方程;利用MatlabRobotics工具箱,建立机械臂的仿真模型,将仿真模型与机械臂运动学方程进行对比验证;采用蒙特卡罗法对机械臂工作空间进行求解,绘制了机械臂末端执行器的工作空间点云图;通过Matlab对机械臂进行轨迹规划仿真研究,绘制运动过程中各关节的位移、速度、加速度变化曲线,验证了机械臂结构设计的合理性,为后续的研究工作提供参考依据。     

BP神经网络求6PTRT型并联机器人正运动学精确解

采用BP神经网络,利用位置逆解结果,通过训练学习,实现操作从关节变量空间到工作变量空间的非线性映射,从而求出6PTRT型并联机器人的正运动学解.计算实例表明单用BP神经网络得到的精度并不高,所以为提高正解结果精度,引入误差补偿算法,并设计相应软件,所得数据表明,该算法计算精度高.