Analysis of operating limits and combustion state regulation for low-calorific value gases in industrial burners

The effective and efficient utilization of low-calorific value (LCV) gases has gained increasing attention in scientific research and industrial fields. In this study, the combustion characteristics of three LCV gases in practical devices are analyzed by using a nonadiabatic perfectly stirred reactor model. The complete steady-state solution in the temperature-residence time parameter space is obtained with arc-length continuation. The stable operation region is quantified by the eigenvalue analysis. The transition of solution curves is quantified with heat loss coefficient. Five key system parameters are systematically investigated on their effects on stability limits. With the combustion performance being quantified by a combustion state index, a combustion state regulation method is proposed to find the optimal regulation path of system parameters. Active subspace method is further applied to shorten the regulation step by identifying the active direction. The proposed method and findings are useful for optimal regulation of burning LCV gases in industrial burners.     

Symmetry properties and bifurcation analysis of a class of periodically forced chemical reactors

In this work, we discuss how periodic forcing may induce symmetry properties into mathematical models of chemical reactors. We define a class of reactors subjected to discontinuous periodic forcing, and show that all the reactors belonging to this class have spatio-temporal symmetry. This symmetry and its influence on the possible bifurcation scenarios are discussed. The bifurcation analysis is carried out with suitable discrete systems that exploit a property of the Poincaré map. In fact, it is shown that the spatio-temporal symmetry induced by the forcing makes the Poincaré map of the continuous system an iterate of another map. On this basis, a technique to implement parameter continuation methods is proposed. With such a technique, it is also possible to characterize symmetric and nonsymmetric regimes and unstable limit sets otherwise undetected with “bruteforce” approaches. Examples for reverseflow reactors and networks of n-reactors with periodically switched feed and discharge positions are presented.     

城市设计中的记忆追寻——2014郑州滨水新区国际联合设计工作营后的思考

《城市意象》开启了认知城市的新方式,它打破了《雅典宪章》中传统的"功能规划"思想.城市除了功能外对人有更多的意义,城市景观在城市的众多角色中,依然是人们可见、可忆、可喜的源泉.景观都市主义的兴起,改变了整个城市系统的设计理念.它把建筑与基础设施看成是景观的延续,景观系统成为整个城市的载体.进一步延续这条线索,在郑州滨水新区国际设计工作营的三个追寻城市特色的概念方案的探索中,追寻城市记忆成为又一个最重要问题.回溯记忆的源头,从江户一路发展到今天的东京能给我们带来启发.中国传统城市格局中蕴含着先人们认知、建造城市的方式,回到最初才能找到城市设计中要追寻和保留的城市记忆.     

现代化小型型钢轧机建设的若干问题

本文阐述了实现小型型钢轧机连续化的重要性和迫切性，并指出了在建设小型连轧机中应重视的若干技术问题。     

含混合多端直流的电力系统静态电压稳定域构建

针对含混合多端直流输电(Hybrid-MTDC)的交直流系统静态电压稳定域(SVSR)构建难题,提出一种含Hybrid-MTDC的交直流系统静态电压稳定域边界(SVSRB)快速搜索的预测-校正方法。计及多类型换流站的控制策略切换特性和站间控制策略协同,构建含Hybrid-MTDC的交直流系统连续潮流模型,搜索SVSRB上的首个临界点。借助获取的首个临界点信息,根据SVSRB拓扑特性,通过所提预测-校正模型实现含Hybrid-MTDC的交直流系统SVSRB上相邻临界点的快速、准确获取,进而构建出含Hybrid-MTDC的交直流系统SVSR。通过含Hybrid-MTDC的IEEE 5节点和IEEE 118节点测试系统对所提方法进行分析验证,结果表明所提方法可实现含Hybrid-MTDC的交直流系统SVSR高效、准确构建。     

Extension of the decidability of the marked PCP to instances with unique blocks

In the Post Correspondence Problem (PCP) an instance (h,g)$(h,g)$ consists of two morphisms h$h$ and g$g$, and the problem is to determine whether or not there exists a nonempty word w$w$ such that h(w)=g(w)$h\left(w\right)=g\left(w\right)$. Here we prove that the PCP is decidable for instances with unique blocks using the decidability of the marked PCP. Also, we show that it is decidable whether an instance satisfying the uniqueness condition for continuations has an infinite solution. These results establish a new and larger class of decidable instances of the PCP, including the class of marked instances.     

Pseudo-transient continuation-based variable relaxation solver in nonlinear magnetohydrodynamic simulations

Efficient and robust Variable Relaxation Solver, based on pseudo-transient continuation, is developed to solve nonlinear anisotropic thermal conduction arising from fusion plasma simulations. By adding first- and/or second-order artificial time derivatives to the system, this type of method advances the resulting time-dependent nonlinear PDEs to steady state, which is the solution to be sought. In this process, only the stiffness matrix itself is involved so that the numerical complexity and errors can be greatly reduced. In fact, this work is an extension of integrating efficient linear elliptic solvers for fusion simulation on Cray X1E. Two schemes are derived in this work, first- and second-order variable relaxations. Four factors are observed to be critical for efficiency and preservation of solution's symmetric structure arising from periodic boundary condition: refining meshes in different coordinate directions, initializing nonlinear process, varying time steps in both temporal and spatial directions, and accurately generating nonlinear stiffness matrix. First finer mesh scale should be taken in strong transport direction; next the system is carefully initialized by the solution with linear conductivity; third, time step and relaxation factor are vertex-based varied and optimized at each time step; finally, the nonlinear stiffness matrix is updated by just scaling corresponding linear one with the vector generated from nonlinear thermal conductivity.     

一类二阶时滞微分方程非局部共振问题解的存在性与唯一性

利用Mawhin连续性定理研究了一类具有时滞的二阶微分方程三点共振边值问题,获得了该边值问题解的存在性和唯一性的一些新的结果。     

基于禁忌算法的多目标无功优化

提出一种基于禁忌算法的多目标无功优化方法。在多目标优化中,包括了距离裕度和网损两项性能指标。首先在给定负荷增长方式的前提下,利用改进连续潮流法快速地找到电压崩溃点,进而求得当前运行点离崩溃点间的距离,并以此距离作为裕度指标,然后采用模糊集理论将裕度指标和网损指标两个目标优化问题转化为单目标优化问题,最后利用改进的禁忌算法对该单目标进行优化,使系统在满足约束的情形下既经济又安全地运行。文章在IEEE14节点系统上验证了该算法的优越性。     

边际函数的绝对连续性

本文给出边际函数的绝对连续性性质．