Surface performance of workpieces processed by electrical discharge machining in gas

The surface performance of workpieces processed by electrical discharge machining in gas(dry EDM)was studied in this paper.Firstly,the composition,micro hardness and recast layer of electrical discharge machined(EDMed)surface of 45 carbon steels in air were investigated through different test analysis methods.The results show that the workpiece surface EDMed in air contains a certain quantity of oxide,and oxidation occurs on the workpiece surface.Compared with the surface of workpieces processed in kerosene,fewer cracks exist on the dry EDMed workpiece surface,and the surface recast layer is thinner than that obtained by conventional EDM.The micro hardness of workpieces machined by dry EDM method is lower than that machined in kerosene,and higher than that of the matrix.In addition,experiments were conducted on the surface wear resistance of workpieces processed in air and kerosene using copper electrode and titanium alloy electrode.The results indicate that the surface wear resistance of workpieces processed in air can be improved,and it is related with tool material and dielectric.     

泄洪雨雾输运的数学模型研究

针对泄洪雨雾在河谷中的对流与沉降问题,提出一种3维有限元计算模型,该模型通过对浓度梯度矢的求解,可保证浓度计算的非负性与单调性.同时,根据气象学中雨滴谱函数与水滴沉降速度等概念,导出雨雾浓度与降雨强度间的定量转换关系,使其与其他雾化近区数学模型实现边界耦合.运用本文模型对瀑布沟电站泄洪洞雾化分布进行模拟,计算结果与真实的物理规律相一致,为今后类似工程问题的研究提供了适用手段.     

Investigation on film cooling characteristics from a row of converging slot-holes on flat plate

Experimental and numerical researches were conducted to investigate the cooling performance of a single row of consoles (converging slot-hole) on a large-scale flat-plate model. The results show that the coolant flow from a row of consoles shows good lateral uniformity of adiabatic effectiveness, with regions of slightly enhanced cooling occurring between the consoles. For the console cooling geometry, the interaction between coolant jet from inclined console and the mainstream flow results in reasonable vo...     

江水源热泵尾水排放方式优选试验研究

为研究江水源热泵尾水在不同排放方式下对江河水域温升的影响,利用数字式温度传感器构建实时温度传感器网络,针对江水源热泵尾水淹没式、表面式和射流式3种排水方式及其在12种出流方式下江河水域的温升情况进行了模拟试验研究。对各种排放方式下的温升均值、温升方差、最高温升值、超温升均值点数等指标项采用加权平均法计算优选值,并结合三维温升图对试验结果进行了分析。结果表明,从整体上看射流式排放方式优于表面式和淹没式排放方式,双口出流方式优于单口出流方式,其中对河道水域温升影响最小的排放方式为表面式排水顺流双口出流方式。     

三相流管道输送技术研究

通过模型试验的方法研究了管道输送加气减阻的机理,分析了影响减阻效果的因素,进行了延长排距的计算,利用模型试验研究的结果进行了实船试验。研究表明,在绞吸式挖泥船的排泥管中加入适当压力和一定体积分数的气体,可以降低管道输送阻力和延长排距。     

浅谈解的存在唯一性定理在《偏微分方程数值解》中的应用

从一个新的角度讨论常微分方程中解的存在唯一性定理在偏微分方程数值解法中的重要应用。给出一类伪双曲型偏微分方程的新的分裂混合有限元数值格式,将该格式转化成常微分方程系统,利用解的存在唯一性定理证明该系统是存在唯一解的。通过简短的讨论、概述明确解的存在唯一定理在偏微分方程数值解中的应用方法．并希望能够在教学科研未来的发展中有新的观念。     

Endohedral metallofullerenes M@C82 (M=La, Y): synthesis and transport properties

Endohedral metallofullerenes M@C_2n (M=La, Y) were synthesized by the arc-discharge method using optimum electric arc parameters. It was also shown that an organic solvent (N,N-dimethylformamide) is successfully used in selective extraction of M@C_2n. We identified the resulting products by mass spectrometry, electron spectrophotometry, EPR and X-ray fluorescence spectroscopy. The resulting N,N-dimethylformamide extracts of La@C_2n and Y@C_2n are shown to be free of empty fullerenes and appear as a mixture of endometallofullerenes M@C_2n whose main ingredient is M@C₈₂ (∼80 wt%). Transport properties of the extracts of La@C₈₂ and Y@C₈₂ were studied using pressed pellets. It was found that oxygen and heat treatment affect conductivity of endometallofullerenes. Heat treatment results in a three-order increase of conductivity from 10⁻⁵ upto 10⁻² Ohm⁻¹ cm⁻¹     

高频脉冲电流法在在线检测电力变压器局部放电中的应用

介绍高频脉冲电流检测技术的原理,及其在在线检测电力变压器的局部放电中的应用。     

利用EXCEL工具率定典型流量数学模型方法探讨

介绍EXCEL【规划求解】功能拟合流量数学模型的操作方法和步骤,并与EXCEL内置图形函数拟合的流量数学模型进行对比分析,说明该功能拟合流量数学模型的优越性。分别以天然河道、水库堰闸、水电站实测流量系列资料为实例,应用该功能拟合不同类型的流量数学模型,结果表明【规划求解】功能拟合流量数学模型均能满足水文资料整编规范要求。     

荆江门弯道近期滩槽演变特点及影响因素分析

三峡水库运用改变了下泄水沙条件,坝下游弯曲河型均呈现“凸冲凹淤”演变规律,以致碍航问题日益突出。为研究弯曲河型滩槽演变特点及其成因,以下荆江河段荆江门弯道为例,利用三峡蓄水后近15 a实测地形资料,采用逻辑推理及统计分析方法分析其影响因素并预测了航道变化趋势。结果表明:三峡工程运用后,凸岸边滩年际间呈持续冲刷趋势,冲刷位置不断下移导致河段展宽引起航道条件恶化;在平滩流量(20 000~25 000 m³/s)持续时间＞15 d的年份,凸岸边滩冲刷后退,反之淤长;冲淤幅度与年均来沙量,尤其细沙(d≤0.125 mm)含量密切相关,基本呈同步变化趋势;荆江一期工程实施后,在当前水沙条件下凸岸边滩会继续受冲,形成枯水双槽,航道条件将恶化。水沙过程的改变是弯曲河型滩槽演变的主要原因,遇大水且来沙量较少的年份,荆江门河段很可能出浅碍航,这可为下荆江弯曲河段航道治理提供一定的参考价值。