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随着我国高坝建设的发展,西部高海拔地区低气压环境下的高速水流特性对高原建坝提出了新的挑战。本文采用实验的方法来研究环境气压变化对水舌挑距和水垫塘内动水压力特性的影响,为高海拔地区建坝提供技术指导。研究发现减压使水垫塘中的动水压强增大,气压降低10 kPa,时均压强最大可达3.9%,脉动压强最大可达5.5%;同时在低气压环境中水舌的挑距受到水舌在空中掺气扩散的影响,由于模型和原型相似律的原因,空气阻力对水舌挑距的影响在模型和原型中有所不同,但环境气压降低,空气密度和空气阻力减小,水舌在空中的掺气也会减少,即水舌扩散程度降低,低气压下水舌更加集中。 相似文献
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This paper presents the results of a continuing investigation into effect of water on water absorption and density of crosslinked polyethylene (XLPE). The experimental set up was made for the following XLPE cable insulations: steam and dry cured with water tree retardant crosslinked polyethylene (TR-XLPE) and without water tree retardant crosslinked polyethylene (natural XLPE). During tests, the tap water was injected (1) into the cable conductor with cable ends closed, (2) into the cable conductor with cable ends opened, and (3) into the metallic screen with cable ends opened. The XLPE cable insulation together with the water present in the cable was subjected to electrical stress and heating. The results were analyzed theoretically and experimentally. The aim of this paper is to present the results of the influence of the water on water absorption and density of various kinds of XLPE cable insulation in different service conditions 相似文献
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为研究老化电缆绝缘层弹性模量变化对界面压力的影响,本文实测三根不同运行年限电缆绝缘的击穿场强与介质损耗角正切表征其电性能,以及在不同温度下的弹性模量表征力学性能。基于超弹性材料本构理论,计算电缆接头与本体装配后的界面压力,并建立电缆接头的二维轴向仿真模型,计算轴向上的界面压力。仿真与理论计算结果的对比表明,运用二维轴向仿真模型计算电缆接头与本体之间的界面压力的误差不超过3.2%,仿真模型计算的准确度可为研究接头轴向上的界面压力分布提供可靠的数据,虽然不同运行年限电缆绝缘层电性能不同,且弹性模量最大差异为29%,但界面压力仅变化0.275%。因此,全新接头与已运行一定年限的电缆装配后,仍能保证足够的界面压力。 相似文献
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水电开发对天然河流的水文情势、水环境等势必会产生一定影响,尤其对于开发影响区内存在饮用水水源地此类敏感环境保护目标的情况,影响更是不容忽视.本文以汉江上游拟建旬阳水电站对其库区内安康马坡岭、许家台饮用水水源地水质的影响为研究实例,采用三维水动力学水质数学模型为研究手段,对电站水库兴建前后上述两水源地的COD、NH_3-N污染物浓度分布状况进行了计算,并对比分析了建库前后水源地水质的变化趋势,得出了电站开发对其影响区内饮用水水源地水质的影响结论,为水电开发影响区内饮用水水源地保护措施的提出提供了理论依据. 相似文献
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石化设备为保温会包裹一层由隔热层与金属保护层组成的包覆层,应用脉冲涡流检测技术可实现不拆包覆层条件下设备的壁厚检测。但在实际检测中由于金属保护层材质与厚度不一致,会对检测结果与检测误差产生影响。本文搭建了脉冲涡流实验平台,分析不同类型、厚度金属保护层在不同隔热层厚度下对脉冲涡流检测信号影响,结果表明:当金属保护层为铝板与不锈钢板时,其厚度或隔热层厚度增加会增大特征值离散程度,但不影响特征曲线趋势,可通过特征曲线计算被测试件厚度;当金属保护层为镀锌钢板时,其高磁导率特性产生的屏蔽效应与感生涡流会对检测信号衰减及特征曲线产生影响。随着镀锌钢板厚度增加,不同厚度试件检测信号后期衰减差异越小。当隔热层厚度增大到50 mm时,检测信号基本重合,无法通过特征曲线计算被测试件厚度。 相似文献
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This paper describes the electrical conductivity of ceria nanoparticles under high pressure ranging from 2 to 6 GPa. The samples used were pure and acceptor-doped ceria nanoparticles with a grain size of approximately 2 nm prepared by mixing hexamethylenetramine and metal nitrate solutions. The size of ceria nanoparticles was controlled to be 2 to 15 nm by varying heat-treatment conditions. The in-situ electrical conductivity measurements under high pressure were conducted by using an ac-impedance spectroscopy. By applying a pressure of 6 GPa at 300 °C, the green compact of 6 mol % Sm-doped ceria nanoparticles was densified; a relative density of 93% was achieved. The sample showed an electrical conductivity of 3?×?10???3 S/cm at 300 °C under 6 GPa. The enhancement of electrical conductivity under high pressure seems to be related to ionic conduction in the vicinity of grain boundaries. 相似文献
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Analysis of the radial flow of heat in a multilayer stranded conductor carrying current indicates that most of the heat is conducted through the very thin air gaps at the contracts between strands in adjacent layers and through the triangular or rectangular voids between layers. The theory predicts that, with constant current, the radial temperature difference increases as the axial tension decreases, and as the air pressure decreases. To confirm these predictions, a length of 91/4.04-mm AAC conductor was tensioned within a vacuum chamber, and the temperature of each layer of wires was measured for various total currents. It was found that the radial temperature difference increased with increasing resistive power loss per unit length, with decreasing axial tension, and with decreasing air pressure. The effective radial thermal conductivity is independent of the power loss, and increases with increasing axial tension and increasing air pressure. The calculated effective gap at the contacts is 0.5 to 0.9 μm 相似文献
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利用1961—2015年青海湖的实测水位及气象观测资料建立了青海湖年水量平衡方程,估算了青海湖逐年的湖面降水、湖面蒸发及入湖流量,分析了水量平衡各要素的变化趋势。在此基础上,通过回归分析等方法研究了不同因子对青海湖水位变化的贡献率。结果表明,青海湖水位在2005年之前呈下降趋势,2005年之后水位上升。青海湖多年平均降水量为14.6×108 m3,多年平均入湖径流量为24.4×108 m3,多年平均蒸发量为40.1×108 m3。1961—2015年间湖面降水呈增加趋势,入湖径流在2003年后增加显著,而湖面蒸发在2000年后呈减少趋势。入湖径流和湖面降水的增加及湖面蒸发的减少共同导致了青海湖水位在2005年之后回升,其中入湖径流对水位变化的贡献率最大,为38.2%。 相似文献
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水涝灾害的发生会严重影响河道周边人民生命安全和财产安全,及时准确掌握河道的水位变化十分重要。针对目前传统水位测量与监测方式的时效性、安全性等不足,设计了一种基于脉冲激光和云平台的水位远程监测系统。该测量装置以STM32单片机为核心,发射脉冲激光到测量桶内漂浮板,探测装置到水面漂浮板的距离,最终计算得出待监测的河道水位深度。实验室模拟实验结果表明:将测量装置固定在1m高度处,当水位深度在200mm~800mm时,相对误差小于1.7% ,变异系数小于1.2% 。经过无线传输模块可以实现对水位数据的实时上传,云平台能够准确显示水位及测量时间,表明该远程水位监测系统可行,能够实现对河道水位的远程实时监测,有一定的应用价值。 相似文献
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E. V. Somova V. I. Kisina A. L. Shvarts A. V. Kolbasnikov V. P. Kanishchev 《Thermal Engineering》2009,56(1):69-77
A physical model for condensation of steam in water flow at high pressure is developed, and analytical dependences for calculating heat transfer are obtained, in particular as applied to the operation of a direct-contact feedwater heater for a new-generation reactor plant with lead coolant. 相似文献
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The primary mechanism for sterilization of microorganisms by high-voltage pulses has been considered to be an electrical breakdown of the cell membrane. However, it is expected that many kinds of chemically active species would be generated by an electrical discharge in a needle-plate or rod-rod electrode system. Therefore it is necessary to identify the chemical species produced by the discharge and to investigate lethal effects of the active species on microorganisms. In the present study, the formation of active species in water (without O 2 flow) and their effects on yeast cells were investigated using needle-plate electrodes. In the presence of the streamer discharge, H and OH radicals were detected by means of emission spectroscopic analysis of the discharge light. Hydrogen peroxide (H2O2) was also detected by absorption spectrophotometry using a reaction of peroxidase and catalase. The effect of the electrical conductivity of the water on the formation of the active species was investigated. Maximum ·OH and H2O2 concentrations were obtained at a water conductivity of about 10-5 S/cm. The H2O2 formation mechanism was considered to be a recombination reaction of ·OH. The lethal effects on beer yeast of ·OH and H2O2 generated by the pulsed electrical discharge in water were also investigated. It was found that ·OH had almost no effect in reducing the survivors. However, the H2H2 did kill the yeast cells: the logarithm of the survival ratio decreased linearly with increasing H2O2 concentration 相似文献
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The impossibility of unambiguously estimating phosphate concentration by measuring boiler-water conductivity in a high-pressure drum boiler (p b = 13.8 MPa) is shown. Mathematical models of ion equilibria in boiler water, which allow one to determine the concentration of phosphates and other ion admixtures from the measurement data obtained with the use of standard (conductormeters and pH-meters) in cooled samples of feedwater and boiler water, are described. 相似文献