相对压强对白炭黑氮吸附表面积测试稳定性的影响

研究相对压强对白炭黑氮吸附表面积测试稳定性的影响。结果表明:在相同液氮纯度、脱气温度、脱气时间、氮吸附点数量条件下,与相对压强范围为0.05~0.1时相比,相对压强范围为0.05~0.2时白炭黑的氮吸附表面积测量值偏低,且差值随氮吸附表面积的增大呈增大趋势;相对压强范围较小时,氮吸附表面积测试结果的线性相关因数较大,再现性较好,测试结果较稳定。     

CO2体积分数对燃煤细颗粒物在水汽环境中凝结长大的影响

为研究燃煤烟气中CO₂体积分数对细颗粒物在水汽环境中凝结长大效果的影响,建立了计算模型并搭建了实验平台,分别从理论计算和实验研究两方面探讨了CO₂体积分数对细颗粒物凝结长大效果的影响。结果表明:随着CO₂体积分数升高,混合烟气的热、质扩散系数均降低,生长管内平均过饱和度增加,细颗粒物长大效果明显;管壁温度越高,随着CO₂体积分数的提高,细颗粒物粒径越大。     

基于PCC-RBF网络的风电功率短期预测方法

风电功率预测对风电场安全平稳运行、电网调度具有重要意义。针对风电功率短期预测指标选择不合理、预测精确度偏低的问题,提出一种基于皮尔逊相关系数(PCC)和径向基函数(RBF)神经网络的风电功率短期预测方法。该方法利用PCC筛选出与风电功率密切相关的3个指标,即电流、温度、风速,然后以这3个指标作为预测模型的输入对风电功率进行RBF样本训练与短期预测。试验结果表明,所提的预测模型预测误差更小,预测精度更高,能够满足风电功率短期预测的要求,具有广泛的应用前景。     

改进的永磁同步电机双矢量模型预测转矩控制

针对永磁同步电机（PMSM）传统模型预测转矩控制（MPTC）权重系数设置复杂、转矩和磁通脉动大的问题,提出了一种改进的PMSM双矢量MPTC方法。该方法扩展虚拟矢量以增加候选电压矢量,结合电压矢量作用于转矩和磁链的原则,减少选择候选矢量的计算量。同时,针对转矩无差拍和磁通无差拍,运用候选矢量的转矩占空比和磁通占空比构造了优化规则代替传统预测转矩控制中的代价函数,避免权重系数的整定问题。仿真结果表明,所提改进方法不仅提高稳态性能,而且能保持MPTC动态响应迅速的特点。     

Experimental determination of gas holdup and volumetric mass transfer coefficient in a jet bubbling reactor

The hydrodynamics and mass transfer characteristics of a lab-scale jet bubbling reactor(JBR) including the gas holdup, volumetric mass transfer coefficient and specific interfacial area were assessed experimentally investigating the influence of temperature, p H and superficial gas velocity. The reactor diameter and height were 11 and 30 cm,respectively. It was equipped with a single sparger, operating at atmospheric pressure, 20 and 40℃, and two p H values of 3 and 6. The height of the liquid was 23 cm, while the superficial gas velocity changed within 0.010–0.040 m·s~(-1) range. Experiments were conducted with pure oxygen as the gas phase and saturated lime solution as the liquid phase. The liquid-side volumetric mass transfer coefficient was determined under unsteady-state oxygen absorption in a saturated lime solution. The gas holdup was calculated based on the liquid height change, while the specific interfacial area was obtained by a physical method based on the bubble size distribution(BSD) in different superficial gas velocities. The results indicated that at the same temperature but different p H, the gas holdup variation was negligible, while the liquid-side volumetric mass transfer coefficient at the p H value of 6 was higher than that at the p H = 3. At a constant p H but different temperatures, the gas holdup and the liquid-side volumetric mass transfer coefficients at 40℃ were higher than that of the same at 20℃. A reasonable and appropriate estimation of the liquid-side volumetric mass transfer coefficient(kla) in a pilot-scale JBR was provided which can be applied to the design and scale-up of JBRs.     

采用VSG策略的MMC阻抗建模及并网稳定性分析

随着分布式能源并网的增多,局部电网逐渐呈现出弱电网特性,虚拟同步发电机（VSG）控制由于可以模拟同步发电机的特性,能够为弱电网提供惯性和阻尼支撑。本文采用谐波线性化方法对采用VSG控制策略的模块化多电平换流器(MMC)进行阻抗建模。所得到的阻抗模型在低频段主要呈容性,在高频段主要呈感性,在复杂电力系统中,可能会与电网阻抗存在谐振点。分析了VSG主要控制参数对MMC阻抗的影响,发现有功-频率下垂系数、阻尼系数和虚拟转动惯量主要影响50Hz附近的阻抗。根据阻抗稳定性判据对MMC并网系统进行稳定性分析,发现并网系统在高频段有振荡的风险。     

Effect of SiC nanowhisker addition on microstructure and mechanical properties of regenerated cemented carbides by low-pressure sintering

The hardness and toughness of regenerated cemented carbides, in general, are contradictory. Therefore, it is critical to explore regenerated cemented carbides with both high hardness and high toughness. In this study, regenerated WC-8-wt% Co cemented carbide with SiC nanowhisker were prepared by low-pressure sintering. The influence of SiCw contents on the microstructure and mechanical properties of regenerated WC-8-wt% Co cemented carbide was investigated. The results indicated that the hardness, density, flexural strength, and fracture toughness of regenerated cemented carbide first increased and then decreased with the addition of SiCw. The Vickers hardness, density, flexural strength, and fracture toughness could reach 1575 HV, 14.6 g/cm³, 2204 MPa, 16.85 MPa·m^1/2, respectively, with SiCw content 0.5 wt%, which were increased by 14.4%, 0.7%, 12.2%, and 17.3%, respectively, when compared with the regenerated cemented carbide without SiCw. The lowest friction coefficient and the best wear resistance could be also reached when 0.5-wt% SiCw was added. The fracture mechanism of the regenerated cemented carbide contained both transgranular and intergranular fracture through the microscopic observation of fracture surface via scanning electron microscope.     

粗轧过程中轧制力和宽展的预测与分析

 板带轧制数学模型是实现自动控制的基础,高精度的数学模型是提升产品质量和市场竞争力的重要保障。在热连轧粗轧过程控制中,轧制力和宽展是关键参数,其模型精度不仅会影响粗轧轧制规程的设定,而且会影响最终热连轧带钢产品凸度。以矩形板坯热连轧粗轧过程为研究对象,针对轧制变形区建立了三维运动许可加权速度场,在此基础上充分考虑自然宽展效应,基于刚塑性材料的第一变分原理,采用可变上限积分法对塑性变形、剪切功率和摩擦功率进行积分获得变形区总功率泛函。利用Matlab优化工具箱对总功率泛函进行最小化,得到了轧制力、宽度分布的理论解。最后利用理论模型计算数据回归得到了板坯宽展及速度场中的加权系数模型。将基于所提出模型的轧制力和宽展预测值与现场实测值及部分有关学者所建立模型的预测值进行了对比,结果验证了所建立模型的准确性。研究得到的宽展模型和速度场加权系数表达式可以方便、灵活、快速地应用到粗轧现场中,为更高质量热连轧带钢产品的生产奠定了坚实基础。     

马氏体不锈钢不同剩余磁场条件下短时干摩擦的摩擦损伤行为研究

本文研究了马氏体不锈钢磨削加工产生的剩余磁场对其短时干摩擦过程中摩擦系数的影响.结果表明:剩余磁场对摩擦行为的影响与外加载荷有关,当外加载荷较低时,摩擦系数随剩余磁场强度的升高无明显变化;随外加载荷的升高,剩余磁场强度对摩擦系数的影响作用增大;当外加载荷较高时,摩擦系数随剩余磁场强度的升高而增大;在短时摩擦过程中,随着剩余磁场强度的升高,摩擦界面吸附磨损颗粒的能力增强,加速了摩擦界面的磨粒磨损,使摩擦系数升高.     

Roll force,torque, lever arm coefficient,and strain distribution in edge rolling

Due to the growing importance of width control in strip and plate mills, edge rolling is currently an im-portant process in hot rolling mills. Research in edge rolling has been carried out, and in the present ar-ticle, models for roll force, torque, and lever arm coefficient are derived using the upper bound method. A simple, kinematically admissible deformation zone and velocity field, independent of friction in the roll gap, is proposed, and the energy dissipation rate is derived. The formula for energy dissipation rate has, in practice, no limitation because all edge rolling geometries are safely in the area where the formula is valid. Roll force and torque are derived by means of two independent integrals. Thus, the lever arm coef-ficient is evaluated from the expressions for roll force and torque using conventional rolling theory. Roll-ing trials report good agreement with theory. Measured roll forces are similar to calculated forces. Furthermore, the shape of the dogbone that arises during edge rolling is in fairly good agreement with the calculated dogbone shape. Deviations are due to the deviation from ideally plastic material in the ex-periments. Also, the strain distribution over the dogbone is similar to the proposed deformation zone. Thus, a new formula has been developed to a stage that it can be implemented in width control systems for edge rolling stands in hot strip and plate mills.