An optimal location of static VAr compensator based on Gramian critical energy for damping oscillations in power systems

The increase in the scale and complexity of interconnected power systems leads to multiple electromechanical oscillations. Therefore, the electric network needs to be made more stable. One type of Flexible alternating current transmission systems (FACTS) devices, namely the static VAr compensator (SVC), can be installed at buses to increase the stability margins and dampen the power system oscillations by exchanging capacitive and/or inductive load to maintain and/or control specific parameters of electrical power systems. The efficiency and performance of the SVC depend on its optimal location. Consequently, seeking the optimal placement for SVC has become a key issue. In this paper, we propose a novel method to find the optimal location for the SVC based on a two‐step approach. First, an energetic approach based on the combination of the controllability Gramian critical energy analysis with the balanced realization reduction technique is used to search for several feasible locations; then the transient stability is analyzed to compare and determine an optimal location through various test cases. The effectiveness of the proposed method has been demonstrated on the IEEE 39‐bus England power system and compared with the modal controllability index. © 2016 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.     

河谷气候影响下的生态城市形态浅析 ——以重庆市奉节县整体城市设计为例

古往今来,气候特征对人类历史上 各种文明的产生和发展发挥着不同程度的作 用。虽然现代文明已经发展到可以抵御部分 气候带来的灾害,但是在目前所倡导的城市双 修、节能减排、绿色宜居,建设低碳生态城市 大背景下,通过城市的空间形态充分利用自然 气候带来的益处,减少不良气候带来的危害, 从而达到生态宜居,成为了城市建设的最终目 的。山地城市地形地貌复杂、生态环境敏感、 气候多变,在山地气候研究中又以河谷气候变 化最为复杂,河谷城市形态受气候及其它因素 影响与平原城市相比也有很大的不同。因此 本文选取具有典型河谷特征地形的奉节县为 例,研究通过城市形态利用较为复杂的局地 气候,最终达到建设生态城镇的目的。     

Assessment of different machine learning techniques in predicting the compressive strength of self-compacting concrete

The compressive strength of self-compacting concrete (SCC) needs to be determined during the construction design process. This paper shows that the compressive strength of SCC (CS of SCC) can be successfully predicted from mix design and curing age by a machine learning (ML) technique named the Extreme Gradient Boosting (XGB) algorithm, including non-hybrid and hybrid models. Nine ML techniques, such as Linear regression (LR), K-Nearest Neighbors (KNN), Support Vector Machine (SVM), Decision Trees (DTR), Random Forest (RF), Gradient Boosting (GB), and Artificial Neural Network using two training algorithms LBFGS and SGD (denoted as ANN_LBFGS and ANN_SGD), are also compared with the XGB model. Moreover, the hybrid models of eight ML techniques and Particle Swarm Optimization (PSO) are constructed to highlight the reliability and accuracy of SCC compressive strength prediction by the XGB_PSO hybrid model. The highest number of SCC samples available in the literature is collected for building the ML techniques. Compared with previously published works’ performance, the proposed XGB method, both hybrid and non-hybrid models, is the most reliable and robust of the examined techniques, and is more accurate than existing ML methods (R² = 0.9644, RMSE = 4.7801, and MAE = 3.4832). Therefore, the XGB model can be used as a practical tool for engineers in predicting the CS of SCC.     

基于分子动力学的胶粉改性沥青中胶粉与沥青相容性研究

为了研究胶粉改性沥青中胶粉与沥青之间的相容性,采用Materials Studio分子模拟软件,构建了沥青四组分代表分子模型与橡胶代表分子模型;同时以四组分分析试验为基础,构建了沥青分子组,在不同温度下对沥青分子组模型和橡胶代表分子模型进行了分子动力学计算,得到了两者的溶解度参数和分子势能.结果表明:沥青体系溶解度参数随着温度的升高逐渐减小;在160℃下沥青溶解度参数与橡胶代表分子——丁苯橡胶(SBR)溶解度参数差值达到最小,沥青与橡胶分子之间的势能达到最大,表明在160℃下沥青与胶粉达到最佳相状态;胶粉改性沥青整体相容稳定.     

武汉市汉正街区历史形态演变与水环境的耦合关系研究

研究城市历史形态与自然环境在演进中的作用关系是认知城市、保护历史风貌和地域性建设的重要基础。以武汉汉正街区为例,基于文献与场地研究,选取边界、街巷、商业中心、水利基础设施作为历史形态的四要素,按时间发展视角分析其与水环境的演变过程和耦合关系。研究发现:汉正街区历史形态和水环境经历了高度耦合—较高耦合—较高耦合—中度耦合—较低耦合的过程,在历史演进过程中要素之间存在着复杂的作用机制,对城市历史形态的形成有重要影响,城市景观特征的保护要重视发现形态要素之间的耦合关系和内在秩序。     

固定化微生物技术在废水处理中的应用

目前废水处理是环境治理的难题之一,采用固定化微生物进行治理具有一定的优势。本文主要介绍固定化微生物技术在印染废水、含氰废水、高浓度氨氮废水、石油化工废水处理中的应用。     

陕西汉阴县黄龙金矿成矿物质来源及成矿模式探讨

陕西省汉阴县黄龙金矿位于陕西石泉-旬阳金矿带整装勘查区中部,是区内重点调查的典型矿床之一,本次工作通过对黄龙金矿不同地质体的氢氧同位素、硫同位素、石英包裹体均一温度及稀土元素等方面的研究,以及成矿物理化学条件的分析,结合矿体地质特征,认为黄龙金矿床成矿物质是多源的,主要来源有3个方面:(1)中-下志留统梅子垭岩组;(2)煌斑岩脉;(3)早期剥离断层。通过对该矿床成矿物质来源及区内构造变形特征分析,建立了黄龙金矿岩浆热液叠加改造型金成矿模式图。为区内寻找同类型金矿床提供新的思路。     

AgInCd合金压缩蠕变性能研究

用RDL-50型拉伸蠕变试验机进行改装后的实验装置研究了铸态AgInCd合金在温度300~400℃及应力范围12~24 MPa内的压缩蠕变行为,分析了稳态速率与温度和应力的关系,计算了应力指数(n)和蠕变激活能(Q_a),并结合蠕变后样品在透射电子显微镜下的微观形貌及位错组态,探讨了合金的压缩蠕变机制。结果表明:随温度和应力水平的升高,合金的稳态蠕变速率增加。相比较指数关系,蠕变速率与应力之间更符合幂函数关系。300、350和400℃条件下,合金的蠕变应力指数n分别为3.31、4.09和5.77;12、18和24 MPa条件下,合金的蠕变激活能Q_a分别为68.1、103.7和131.6 kJ/mol。微观形貌以层错为主,孪生为300℃的主要蠕变机制,位错攀移生成位错墙为400℃的主要蠕变机制。     

直接喷墨打印成形铁磁软磁材料的工艺研究

本文以羰基铁粉为原料,用DISPER-Y220为分散剂,制备出粘度为0.55Pa.s,流动性良好的料浆,以此料浆作为打印“墨水”,利用直接喷墨打印成形技术制备纯铁软磁材料制件。喷头直径分别以0.5mm、0.8mm和1.0mm打印零件,打印成形后通过脱脂和烧结制备出制件。结果表明：分散添加量为1wt%时,料浆粘度最低,随着固含量的增大,料浆粘度变大,随着剪切速率的增大,料浆表现为剪切变稀特征;喷头直径为0.8mm所打印的烧结体,表面粗糙度最低,其Ra为0.8μm;在1300℃保温2h烧结后,喷头直径为0.5mm的烧结体致密度最高,为96.3%,其磁饱和感应强度B_s达到1.53T,最大磁导率μ_max达到2630。     

Effect of Boron Content on Hot Ductility and Hot Cracking Susceptibility in 316L Austenitic Stainless Steel for Welding Components

Liquation cracking may occur in the heat-affected zone during welding. Two factors influence this phenomenon: the tensile stresses generated during welding and the potential loss of ductility due to the presence of a liquid film at grain boundaries depending on their chemical composition. Gleeble hot ductility tests have been used to study the combined effect of boron content and holding time on ductility drop in the liquation temperature range of a 316L type austenitic stainless steel. It is shown that high boron contents and short holding times promote the loss of ductility in this temperature range. Secondary ion mass spectrometry has been used to correlate mechanical results to boron distribution either at grain boundaries or in the bulk. Other welding tests have been performed to confirm the influence of boron content on hot cracking sensitivity of AISI 316L stainless steels. Results indicate that cracks appear on all specimens but at different strain levels. The higher the boron content is, the more the specimen exhibits tendency to hot cracking.