中压型大功率电子束焊机电控系统的研制

本文介绍了７０ｋＶ、３０ｋＷ电子束焊机电子枪电源──加速电源、灯丝电源、轰击电源和偏压电源的特点及其控制原理。     

提升海上风电经柔直联网系统频率稳定性的协调控制策略

针对大规模海上风电经柔直联网引起的受端电网惯量降低、频率调节能力下降等问题,提出了海上风电与柔直主动支撑系统频率的协调控制策略。在惯量支撑方面,利用直流电容能量主动支撑系统惯量,并通过直流电压建立风机转速与频率的耦合关系,提出了基于差异化转子动能调节的风电场惯量支撑协调控制策略,以提升受端电网惯量水平。在频率偏差调节方面,根据本地直流电压偏差量,提出了基于风机变速控制与桨距角控制的风电场一次调频策略,并设计了基于附加桨距角控制的风电场二次调频策略,以提高系统的频率稳定性。最后,设计了多时间尺度频率支撑控制策略的协调配合流程,并基于RT-LAB OP5600实时数字仿真平台验证了所提策略可有效提升系统的频率支撑能力。     

多馈入直流受端电网换相失败风险区域快速识别方法

针对多馈入直流受端电网换相失败风险区域准确识别难题,计及直流控制系统影响,提出基于广义节点电压交互作用因子的风险区域快速识别方法。将交流母线和故障点视为广义节点,构建考虑直流控制影响的广义节点电压交互作用因子指标,并给出其计算方法;建立换流母线电压跌落期间的换流站暂态电路模型,计算临界换相失败风险电压,进而获取指标临界值,依据指标值与临界值的大小进行换相失败风险的判断;结合指标值的故障位置分布特性,提出换相失败风险区域的快速识别方法;在CIGRE HVDC测试系统和含三馈入直流的39节点测试系统中,验证所提计算方法和识别方法的有效性,与传统方法相比,临界换相失败风险电压的计算误差由7.7%降低到2.4%,提高了换相失败风险区域识别的准确性。     

大型泵站进水流道技术改造优选设计

进水流道的出口流态决定了水泵的进水条件,直接影响到水泵的能量性能、汽蚀性能和安全运行性能,在进水流道水力设计和模型试验中应给予特别重视。本文采用数值计算的方法,模拟了南水北调东线工程某大型泵站不同进水流道设计方案时的内部三维流动,计算结果与模型试验和泵站运行中观察到的实际情况相当吻合。把水泵进水条件和流道水头损失作为流道水力设计的目标函数,通过计算机数值模拟和优选,获得了优秀的进水流道设计方案。流道出口水流轴向流速的分布均匀度提高了3.26%,出口水流的偏流角减小了1°,水头损失减少了24.1%,水泵的进水条件得到了大幅度的改善。     

VENUS：一个通用的并行性能可视化环境

本文介绍了一个通用的并行程序性能可视化环境ＶＥＮＵＳ。在分析当前并行性能可视化工具不足的基础上，ＶＥＮＵＳ系统采用了基于可扩展的多层性能视图模型的可视化方法，并改进了ＰＶＭ的跟踪机制以支持性能可视化分析与程序源代码的直接对应。实验表明，ＶＥＮＵＳ系统能够有效地帮助发现并行程序中的性能瓶颈。     

Cavitation optimization for a centrifugal pump impeller by using orthogonal design of experiment

Cavitation is one of the most important performance of centrifugal pumps. However, the current optimization works of centrifugal pump are mostly focusing on hydraulic efficiency only, which may result in poor cavitation performance. Therefore, it is necessary to find an appropriate solution to improve cavitation performance with acceptable efficiency. In this paper, to improve the cavitation performance of a centrifugal pump with a vaned diffuser, the influence of impeller geometric parameters on the cavitation of the pump is investigated using the orthogonal design of experiment(DOE) based on computational fluid dynamics. The impeller inlet diameter D_1, inlet incidence angle Δβ, and blade wrap angle φ are selected as the main impeller geometric parameters and the orthogonal experiment of L_9(3*3) is performed. Three-dimensional steady simulations for cavitation are conducted by using constant gas mass fraction model with second-order upwind, and the predicated cavitation performance is validated by laboratory experiment. The optimization results are obtained by the range analysis method to improve cavitation performance without obvious decreasing the efficiency of the centrifugal pump. The internal flow of the pump is analyzed in order to identify the flow behavior that can affect cavitation performance. The results show that D_1 has the greatest influence on the pump cavitation and the final optimized impeller provides better flow distribution at blade leading edge. The final optimized impeller accomplishes better cavitation and hydraulic performance and the NPSHR decreases by 0.63 m compared with the original one. The presented work supplies a feasible route in engineering practice to optimize a centrifugal pump impeller for better cavitation performance.     

Statistical characteristics of suction pressure signals for a centrifugal pump under cavitating conditions

Centrifugal pumps are often used in operating conditions where they can be susceptible to premature failure. The cavitation phenomenon is a common fault in centrifugal pumps and is associated with undesired effects. Among the numerous cavitation detection methods, the measurement of suction pressure fluctuation is one of the most used methods to detect or diagnose the degree of cavitation in a centrifugal pump. In this paper, a closed loop was established to investigate the pump cavitation phenomenon, the statistical parameters for PDF (Probability Density Function), Variance and RMS (Root Mean Square) were used to analyze the relationship between the cavitation performance and the suction pressure signals during the development of cavitation. It is found that the statistical parameters used in this research are able to capture critical cavitation condition and cavitation breakdown condition, whereas difficult for the detection of incipient cavitation in the pump. At part-load conditions, the pressure fluctuations at the impeller inlet show more complexity than the best efficiency point (BEP). Amplitude of PDF values of suction pressure increased steeply when the flow rate dropped to 40 m³/h (the design flow rate was 60 m³/h). One possible reason is that the flow structure in the impeller channel promotes an increase of the cavitation intensity when the flow rate is reduced to a certain degree. This shows that it is necessary to find the relationship between the cavitation instabilities and flow instabilities when centrifugal pumps operate under part-load flow rates.     

关于马钢1985年实物型投入产出表的编制与分析

文章概括地叙述了企业实物型投入产出模型的结构原理、编制方法以及模型所提供的系数的应用价值。文章认为模型所提供的直接消耗系数和完全消耗系数可以确切地描述联合企业内部各产品部门之间的技术性和经济性的联系,并能为制订计划,进行预测,综合平衡、决策提供科学依据。     

水产养殖动物营养与饲料工程发展战略研究

本文综述了我国水产养殖动物营养学研究和饲料工程方面近期的研究,分析了产业发展的问题,探讨了下一步的政策措施。可以发现,过去10多年里,水产动物营养与饲料的发展在营养素需求、动物的摄食与投喂、仔稚鱼饲料、亲本营养、添加剂等方面取得了重要的进展,但仍然存在饵料系数高、环境排放大、饲料成本高、效益不稳定等问题。下一步的研究应该以"安全高效,节约环保"为目标,引入生态学和现代组学理念,开展水产动物营养代谢的分子机理、动物的营养需要与精准饲料配方技术、饲料质量控制与加工工艺、精准投喂技术、品质调控技术等方面的研究,同时在政策上应该扩大学科交流、实行长期稳定支持等。     

某汽车排气系统安装过程中人机工程仿真及改善

首先分析了排气系统安装工位的现状,利用DELMIA仿真软件对现场的操作工序进行模拟,结合人机工程学理论对现场的人机工程学问题进行评估和改善;然后用DELMIA仿真软件对改善后的方案进行仿真,给出结论。对比改善前、后的结果可以看出,改善效果明显。