Effect of thermomechanical processing on microstructure and mechanical properties of CoCrFeNiMn high entropy alloy

The CoCrFeNiMn high entropy alloy was produced by homogenization, cold rolling and recrystallization. The effects of thermomechanical processing on microstructures and tensile properties at different temperatures were investigated using X-ray diffractometry (XRD), optical microscopy (OM), scanning electron microscopy (SEM) and multi-functional testing machine. The results show that dendritic structures in cast alloy evolve into equiaxed grains after being recrystallized, with single face-centered cubic (FCC) phase detected. The most refined alloys, stemming from the highest rolling ratio (40%), exhibit the highest strength due to the grain boundary strengthening, while the variation of elongation with temperature shows a concave feature. For the coarse-grained alloys, both the ductility and work hardening ability decrease monotonically with increasing temperature. Serrated flow observed at intermediate temperatures is attributed to the effective pinning of dislocations, which manifests the occurrence of dynamic strain hardening and results in the deterioration in ductility. Besides, dimples on the fracture surfaces indicate the typical ductile rupture mode.     

阶梯溢流坝面坡度对一体化消能工水力特性的影响

为探求高水头、大单宽流量下坝面坡度对一体化消能工水力特性的影响,以阿海水电站为原型,采用三维k-ε双方程紊流模型,引入水气两相流VOF计算方法,利用几何重建格式来迭代生成自由水面,对1∶0.80、1∶0.75、1∶0.65三种阶梯面坡比进行数值模拟研究。结果表明:①最大负压值均位于首级阶梯立面凸角下1/4附近,并随坡度增加而增大。坡度为56.98°时,最大负压值为61.02 kPa,超过了6×9.81 kPa。②水流空化数在宽尾墩水舌出口位置出现最小值,空化数随坡度变陡而减小。坡度为56.98°时,空化数最小为0.358。坡度为51.34°时,空化数最大,为0.381。③随着阶梯溢流坝坝面坡度变缓,消力池最大临底流速增大。当坡度为51.34°时,消力池最大临底流速最大,达到26.84 m/s,超过了25 m/s,易发生冲磨破坏。当坡度为56.98°时,消力池最大临底流速最小,为24.00 m/s。消力池尾坎前最大临底流速随坡度增加而减小,坡度为56.98°时最小,为9.63 m/s;坡度为51.34°时,消力池尾坎前最大临底流速最大,为9.96 m/s。④坡度的变化对一体化消能工消能率的影响不大,坡度从51.34°增加到56.98°,消能率只提升0.15%。     

Correlation of the leakage flow rate with pressure changes in a clearance-sealed piston prover

Leakage flow rate is one of the most important contributions to the measurement uncertainty when measuring small gas flow rates with a clearance-sealed piston prover. Our previous study has shown that the systematic effects related to the change of the gas viscosity can be successfully corrected, whereas the effects related to the reproducibility of the leakage flow rate are poorly understood. This paper focuses on the interpretation and correction of the reproducibility related effects by analysing experimentally identified variations of the leakage flow rate and the gas pressure in the inclined piston prover. Small changes of the leakage flow in the inclined piston prover indicate that the position of the piston relative to the cylinder remains approximately the same. The obtained relationship between the leakage flow rate and the gas pressure below the piston led to the pressure-based correction of the leakage flow rate.     

基于多层感知器的气液两相流流型识别方法

通过对电阻层析成像数据采集原理和深度学习网络的研究,提出了一种基于阵列电阻值和多层感知器深度学习网络相结合的流型识别方法。利用电阻层析成像系统中的16个电极传感器来获取流型样本数据,并构建出流型识别数据库,然后对多层感知器深度学习网络进行训练,获得可以识别不同流型的网络。实验结果表明,采用阵列电阻值结合多层感知器网络对流型进行学习和识别的方法,流型识别准确率可以达到95%,解决了流型图像生成过程与数据特征预选过程中流型特征损失的问题,流型识别性能得到了提高。     

Features of Cattaneo‐Christov heat flux model for Stagnation point flow of a Jeffrey fluid impinging over a stretching sheet: A numerical study

The present work focuses on a two‐dimensional steady incompressible stagnation point flow of a Jeffery fluid over a stretching sheet. The Cattaneo‐Christov heat flux model is incorporated into this study. Simulation is conducted via the Runge‐Kutta fourth‐order cum shooting method for the transformed system of nonlinear equations. The influence of the governing parameters on the dimensionless velocity, temperature, skin friction, streamlines, and isotherms is incorporated. A significant outcome of the current investigation is that an increase in the relaxation time parameter uplifts temperature; however, a gradual decrease is observed in the velocity field. Another important outcome of the present analysis is that the momentum boundary layer augments due to an increase in the Deborah number; however, a decrease is observed in the temperature. Furthermore, it is also observed that the skin friction coefficient escalates with an increase in the relaxation time parameter for the assisting flow, but a reverse trend is observed for the opposing flow.     

空化对液膜密封流场特性及密封性能的影响

为进一步探索液膜空化对密封性能的影响，以螺旋槽液膜密封为研究对象，基于JFO空化模型及坐标变换建立其数学模型并采用有限体积法离散求解。探讨Reynolds和JFO两空化边界下的密封速度场和流量场分布规律以及空穴压力对密封性能如承载能力和摩擦扭矩等影响。结果表明：空穴区的形成具有动态性，速度矢量在空穴区内部为0，在液膜始破边界和靠近内径处的液膜重生边界上速度矢量朝向空穴区，而在靠近外径处的液膜重生边界上速度矢量远离空穴区；液膜流量场主要集中于槽区内且JFO空化边界下的流量场分布比Reynolds空化边界下值更为密集；空穴压力的增加可提升液膜承载能力但增幅较小，而对摩擦扭矩的影响可忽略不计。     

基于关键拓扑变动项辨识的调度操作潮流校核方法

为解决传统调度操作潮流校核中的有效性问题，定义了一种面向调度操作的关键拓扑变动概念，提出并实现了基于关键拓扑变动辨识的调度操作潮流校核方法。首先，剖析了调度操作安全校核的实施目的，围绕其运行断面潮流校验的校核目的，定义了面向调度操作的关键拓扑变动概念，并基于网络拓扑连接关系设计了其辨识方法。在此基础上，提出了基于关键拓扑变动项辨识的调度操作潮流校核方法，明确了其实施流程和要点。最后基于当前电网调度自动化系统实际，构建了其实施框架，并介绍了其在某电网的实施效益。     

大方坯结晶器电磁搅拌器结构优化

为改善连铸结晶器内钢液的流动状况，采用有限元法和有限容积法研究了大方坯结晶器电磁搅拌器结构对连铸结晶器内电磁场、流场和温度场分布的影响。结果表明，新型结晶器电磁搅拌器在400 A、3 Hz时产生的电磁力比传统结晶器电磁搅拌器在500 A、3 Hz时产生的电磁力更加均匀，对结晶器内钢液的扰动更强，可提高结晶器内的传热效率，有助于初始凝固坯壳和等轴晶的形成，改善方坯质量。     

The primary dynamic gravimetric system for gas mass flow measurement

High accuracy mass flow measurement is an enabling technology at the base of many industries. HORIBA STEC Co., Ltd. developed its own primary gas mass flow measurement system. We employed the dynamic gravimetric method in a vacuum chamber, and we use only mass and time information for mass flow rate calculation, with no correction for temperature, pressure and humidity. The system achieved 0.036% uncertainty as lowest of results with satisfactory performance of proficiency testing with NIST (National Institute of Standards and Technology). Then the laboratory has been granted ISO/IEC 17025 accreditation since 2017. This paper describes the system details and uncertainty analysis.     

城市排水管网混合流数值模拟研究进展

全球气候变化背景下,城市洪涝灾害事件频发,城市雨洪模型将扮演愈发重要的角色。精细化的城市雨洪模型离不开对排水管网水流的准确模拟。混合流在排水管网系统中普遍存在,研究其机理和精确模拟技术对城市排水模型和雨洪模拟精度的提升意义重大。因此,从混合流数值模拟方法、混合流物理模型及城市排水管网模型等三个方面综合分析了国内外在混合流模拟和计算方面的研究进展,并分析了当前研究存在的不足,在此基础上对未来排水管网混合流方面的研究工作进行了展望。