Characterization and analysis about the heterogeneity of inclusions in a 500kg steel ball

The distribution and transfer mechanism of MnS inclusions are distinguished from the solute segregation in a 500 kg steel ball. The increase of MnS inclusions is obvious from the surface to the center of the steel ball, while the increase of solute content is slight. The massive MnS inclusions converge in the channel zone and in heterogeneous zones. During solidification, the interface tension drives MnS inclusions to the frontier of the dendritic zone. Some inclusions trapped may float to induce the channel zone. Solidification contraction tears such channel zone to attract more melt enriched with inclusions. Some inclusions converge in the extra-dendritic melt. At later solidification stage, solidification contraction dominates the macro-distribution of extra-dendritic melt to produce the heterogeneous zones.     

Discrete-time contraction constrained nonlinear model predictive control using graph-based geodesic computation

Modern chemical processes need to operate around time-varying operating conditions to optimize plant economy, in response to dynamic supply chains (e.g., time-varying specifications of product and energy costs). As such, the process control system needs to handle a wide range of operating conditions whilst optimizing system performance and ensuring stability during transitions. This article presents a reference-flexible nonlinear model predictive control approach using contraction based constraints. Firstly, a contraction condition that ensures convergence to any feasible state trajectories or setpoints is constructed. This condition is then imposed as a constraint on the optimization problem for model predictive control with a general (typically economic) cost function, utilizing Riemannian weighted graphs and shortest path techniques. The result is a reference flexible and fast optimal controller that can trade-off between the rate of target trajectory convergence and economic benefit (away from the desired process objective). The proposed approach is illustrated by a simulation study on a CSTR control problem.     

Tunable Ni/Fe-Mo carbide catalyst with high activity toward hydrogen evolution reaction

Cost-effective catalysts for hydrogen evolution reaction (HER) are attractive for sustainable production of H₂ fuel. Herein, a series of tunable Ni/Fe-Mo carbide catalysts have been synthesized via a sol-gel method coupling with a subsequent high temperature carbonization process. The amount of nickel and iron was tuned in the Mo₇/C precursors, accomplishing a favourable performance of noble-metal-free electrocatalysts for HER. As expected, the designed Ni₁₀Fe₄Mo₇/C catalyst displays an enhanced catalytic activity toward hydrogen production with an ultralow overpotential (η₁₀ = 110 mV) and striking kinetics (η_onset = 58 mV, k = 54 mV · dec⁻¹) in the alkaline electrolyte (1 M KOH), which are comparable to those of the commercial 20% Pt/C catalyst. Such excellent performance of Ni₁₀Fe₄Mo₇/C could be attributed to the high intrinsic activities of Ni-based alloys (NiMo₄) and Mo₂C, as well as to the lattice contraction in the Mo₂C unit cell, in accordance with its high electrochemical surface area (~133 m² · g⁻¹) and low charge-transfer resistance (~31.5 Ω) for the associated electrode.     

X65Q钢级管线管焊接缺陷的成因分析

在X65Q钢级管线管的焊接过程中,焊缝出现显微裂纹和缩孔缺陷,为此,对管体的化学成分和显微组织进行了检测,并对焊缝的凝固过程进行了分析。分析表明,焊接线能量强度偏高和焊后冷却强度偏低是产生上述焊接缺陷的主要原因,在此基础上,提出相应的改进措施。     

水泥混凝土在耐久性路面中的应用

研究通过自行配制的防裂高效减水剂改善路面水泥混凝土的力学性能、细观结构、收缩性能以及耐磨性能,以提高水泥混凝土路面的使用质量和寿命,并以铺筑试验路检测数据检验实际效果,为在特殊路段使用水泥混凝土路面提供广阔的应用前景.     

球阀流量系数的研究

针对球阀中液流流动情况提出了计算球阀收缩系数μ的简化模型及流量系数计算方法,并进行了实验分析。     

两相流射流的最小半径数值研究

针对大气中水射流的动态特性,使射流形状、特性难以精确预测,提出了判定射流缩流截面的准则,进行了多工况下自由射流非定常两相流数值解析,对射流特别是两相流分界面区域的能量分布及涡度进行了分析,根据VOF法对射流自由表面进行数值预测的结果,获得了射流缩流半径、射流膨胀率等重要参数,并对自由射流尺度效应进行了探讨。     

Inertia Effects on the Flow of Bingham Plastics Through Sudden Contractions in a Pipe

The present numerical study concentrates on the effects of moderate and high Reynolds numbers on the laminar flow of a non-Newtonian rigid viscoplastic (Bingham) fluid through a sudden contraction in a pipe. The flow is assumed to be steady, incompressible, and isothermal. Results are presented for a wide range of the governing Reynolds and yield numbers and the significant effects of these two parameters both on the integral and local kinematic properties of the flow field are established. Low yield numbers result in the disappearance of the recirculating flow region at the corner replacing it with a region of very low rates of deformation. The evolution of the centerline velocity in the vicinity of the contraction plane is shown to be independent of the yield number and dependent on the Reynolds number, while the concavities in the streamwise velocity profiles appearing at high Reynolds numbers are independent of the yield number. The pressure losses through the contraction increase with yield number with the effect being more pronounced at lower Reynolds numbers.     

降低腰线砖硅橡胶模具线收缩率的研究

本文主要研究了固化剂、纳米二氧化硅粉和碳酸钙粉等外加剂对硅橡胶模具线收缩率的影响。实验结果表明:当固化剂的用量为2.3%时,模具的线收缩率为3.342%。外加纳米二氧化硅粉和碳酸钙粉可以明显地降低硅橡胶模具的线收缩率,外加CaCO3粉(球磨20min)的质量为硅橡胶质量的8%时,模具线收缩率为2.256%,较未加入时的3.342%减少了1.086%。     

黏弹性复杂流动的微观-宏观确定性模拟

Deterministic simulation approach was applied to simulating viscoelastic complex flows,in which,the SIMPLE algorithm based on collocated grid was used to solve the conservation equations on the macroscopic level and the spectral method was used to solve the Fokker-Planck equation on the mesoscopic level.Here,the transient 4∶1 planar contraction flow for dilute polymer solution was computed by using the coupled technique and the calculated polymeric stress distributions at steady state were identical with the results of continuum approach as well as the corresponding references.Therefore,the presented results indicated that the SIMPLE algorithm based on collocated grid coupled with the spectral method can be used to simulate viscoelastic complex flows effectively.Moreover,the influence of Deborah number and viscosity ratio on polymeric stress was also investigated.