CFD application for coal/air balancing in power plants

Unbalanced coal/air flow in the pipe systems of coal-fired power plants will lead to non-uniform combustion in the furnace, and hence a overall lower efficiency of the boiler. A common solution to this problem is to put orifices in the pipe systems to balance the flow. It is well known that if the orifices are sized to balance clean air flow to individual burners connected to a pulverizer, the coal/air flow would still be unbalanced and vice versa. However, the current power industry practice throughout the world is to size orifices for balancing the clean air flow and accept the resulting imbalance in coal/air flow. Field tests are mostly conducted to verify a balanced clean air flow.     

基于成本效用分析的电能替代实证研究

近年来的雾霾让人们逐渐意识到环境保护的重要性,国网公司基于我国“多煤、少气、贫油”的国情,提出了以电代煤的电能替代方案。本文以在电力和煤炭的使用过程中可获得的热值作为效用,以使用过程中所需要的年费用作为成本,建立了电能替代的成本效用模型,计算出实现电力和煤炭相互替代的排污费临界值,并通过一个算例进行了实证分析。分析结果表明:电价、单位电力排污量、燃煤设备寿命对排污费临界值有正向影响;煤价、单位燃煤排污量、电力设备寿命对其有负向影响。最后,在分析的基础上给出了电能替代的政策建议。     

基于峰谷分时电价机制的节能发电调度优化模型

为减少能源消耗,电力工业在发电侧推行节能发电调度,而在用电侧则施行需求侧管理。事实上,发电侧与用电侧可以通过联合优化实现更好的节能效果。峰谷分时电价将改变原有系统负荷的分布,发电侧机组发电调度的安排将随之改变,发电煤耗水平也将相应地变动。有鉴于此,首先分别构建了需求侧峰谷分时电价响应分析模型以及发电侧节能发电调度的机组组合模型;其次,为了实现分时电价响应向机组煤耗效益的传递,以机组发电煤耗与启停煤耗最少为目标构建了需求侧与发电侧的联合优化模型;最后,通过算例分析发掘模型的节能效益,借助GAMS求解上述模型,优化结果表明分时电价的优化将有助于改进发电侧的节能调度效果,同时将实现一定的环境效益。     

基于计量经济模型的煤炭消费与经济增长关系实证研究——以世界主要煤炭消费国为例

经济的发展和能源(包括煤炭)的利用有着密不可分的关系.运用国际上研究能源消费与经济增长之间关系的重要工具-协整分析、格兰杰因果关系检验对世界主要煤炭消费国家(中国、美国、印度、俄罗斯、日本和南非)1981-2005的煤炭消费与GDP之间因果关系及其内在规律进行了分析和研究.实证研究结果表明,这些国家能源消费结构、经济政策不同,煤炭消费同经济增长之间的因果关系也不完全一致,中国、日本和南非存在经济增长对煤炭消费的因果关系,俄罗斯存在煤炭消费对经济增长的因果关系,而印度煤炭消费和经济增长之间则不存在因果关系.据此各国根据自身能源国情及国际比较形势,制定科学的能源战略与政策.     

电力市场环境下计及V2G和多类型需求响应的综合能源系统多目标优化模型

园区综合能源系统(Park integrated energy system,PIES)是满足用户多种用能需求的一种重要途径,但由于内部分布式能源机组出力具有不确定性,且与负荷在时间维度上存在一定的不匹配性,限制了能源利用效率和经济效益的提升.因此,本文首先在构建耦合热电的PIES的基础上,构建了多类型需求响应模型;其次,构建了考虑风光机组出力不确定性的以系统净收益、清洁能源弃能率为多目标函数的优化模型;然后,构建了"不确定性处理-多目标处理-单目标处理"的三阶段求解模型,最后,以V2G和需求响应为考虑条件,设计多情景.算例结果表明:V2G可以为清洁能源不稳定发电提供有效备用,在一定程度上提供清洁能源利用效率;引入电热需求响应,能够改变用户负荷,增加经济效益.     

可再生能源发电商最优减排补贴政策的激励效应研究

针对传统减排补贴激励政策的突出矛盾, 本文借助委托代理理论并从激励相容约束和参与约束条件的角度出发解析政府如何有效地设计优化减排补贴政策, 以此为基础分析了政府最优减排补贴政策的激励效应:首先, 基于最优发电量的最大减排量确定政府对增加环境经济效益和节约电煤消耗量的社会福利的平衡系数在减排水平对电能生产强弱敏感条件下的最大临界值和最小临界值; 其次, 以临界最值为基准, 基于发电商最优收益分析在强弱敏感条件下减排补贴政策存在负向激励效应的合理性和可靠性; 最后, 基于政府最优减排补贴成本分析在强弱敏感条件下减排补贴政策对发电商所产生的正向激励效应。研究结论为燃煤发电区域政府科学引导可再生能源发电商积极参与减排合作而制定有效的减排补贴激励政策提供了决策依据和管理启示。     

Global optimization of mathematical programs with complementarity constraints and application to clean energy deployment

We study the problem of clean energy introduction under emission regulations using the generation expansion models developed by He et al. (Comput Ind Eng 63:708–716, 2012). A game theoretic approach was used to model capacity investments and new technology introduction in response to carbon emission regulations. We report algorithmic advancements that were made to enhance the performance of BARON (Tawarmalani and Sahinidis, Math Progr 103:225–249, 2005) on this and other mathematical programs with complementarity constraints.     

On weakly clean rings

A ring is called clean if every element is a sum of a unit and an idempotent, while a ring is said to be weakly clean if every element is either a sum or a difference of a unit and an idempotent. Commutative weakly clean rings were first discussed by Anderson and Camillo [2 Anderson, D. D., Camillo, V. P. (2002). Commutative rings whose elements are a sum of a unit and idempotent. Commun. Algebra 30(7):3327–3336.[Taylor & Francis Online], [Web of Science ®] , [Google Scholar]] and were extensively investigated by Ahn and Anderson [1 Ahn, M.-S., Anderson, D. D. (2006). Weakly clean rings and almost clean rings. Rocky Mountain J. Math. 36:783–798.[Crossref], [Web of Science ®] , [Google Scholar]], motivated by the work on clean rings. In this paper, weakly clean rings are further discussed with an emphasis on their relations with clean rings. This work shows new interesting connections between weakly clean rings and clean rings.     

On Strongly Clean Matrix and Triangular Matrix Rings

A ring R with identity is called “clean” if every element of R is the sum of an idempotent and a unit, and R is called “strongly clean” if every element of R is the sum of an idempotent and a unit that commute. Strongly clean rings are “additive analogs” of strongly regular rings, where a ring R is strongly regular if every element of R is the product of an idempotent and a unit that commute. Strongly clean rings were introduced in Nicholson (1999 Nicholson , W. K. (1999). Strongly clean rings and Fitting's lemma. Comm. Algebra 27:3583–3592. [CSA] [Taylor &; Francis Online], [Web of Science ®] , [Google Scholar]) where their connection with strongly π-regular rings and hence to Fitting's Lemma were discussed. Local rings and strongly π-regular rings are all strongly clean. In this article, we identify new families of strongly clean rings through matrix rings and triangular matrix rings. For instance, it is proven that the 2 × 2 matrix ring over the ring of p-adic integers and the triangular matrix ring over a commutative semiperfect ring are all strongly clean.     

A Note on Strongly Clean Matrix Rings

Let R be an associative ring with identity. An element a ∈ R is called strongly clean if a = e + u with e ² = e ∈ R, u a unit of R, and eu = ue. A ring R is called strongly clean if every element of R is strongly clean. Strongly clean rings were introduced by Nicholson [7 Nicholson , W. K. ( 1999 ). Strongly clean rings and Fitting's lemma . Comm. Algebra 27 : 3583 – 3592 .[Taylor &; Francis Online], [Web of Science ®] , [Google Scholar]]. It is unknown yet when a matrix ring over a strongly clean ring is strongly clean. Several articles discussed this topic when R is local or strongly π-regular. In this note, necessary conditions for the matrix ring 𝕄 _n (R) (n > 1) over an arbitrary ring R to be strongly clean are given, and the strongly clean property of 𝕄₂(RC ₂) over the group ring RC ₂ with R local is obtained.     

Unifying strongly clean power series rings

It is unknown whether a power series ring over a strongly clean ring is, itself, always strongly clean. Although a number of authors have shown that the above statement is true in certain special cases, the problem remains open, in general. In this article, we look at a class of strongly clean rings, which we call the optimally clean rings, over which power series are strongly clean. This condition is motivated by work in [10 Diesl, A. J., Dorsey, T. J., Garg, S., Khurana, D. (2012). A note on completeness and strongly clean rings, preprint. [Google Scholar]] and [11 Diesl, A. J., Dorsey, T. J., Iberkleid, W., LaFuente-Rodriguez, R., McGovern, W (2013). Strongly clean triangular matrices over abelian rings, preprint. [Google Scholar]]. We explore the properties of optimally clean rings and provide many examples, highlighting the role that this new class of rings plays in investigating the question of strongly clean power series.     

A Question on Strongly Clean Rings

A new characterization of a strongly clean ring is given. And it is proven that if R is a strongly clean ring, then eRe is a strongly clean ring for e ² = e ∈ R, which answers a question of Nicholson (1999 Nicholson , W. K. ( 1999 ). Strongly clean rings and Fitting's lemma . Comm. Algebra 27 ( 8 ): 3583 – 3592 . [CSA] [Taylor &; Francis Online], [Web of Science ®] , [Google Scholar]) in the affirmative.     

The Graphical Horseshoe Estimator for Inverse Covariance Matrices

We develop a new estimator of the inverse covariance matrix for high-dimensional multivariate normal data using the horseshoe prior. The proposed graphical horseshoe estimator has attractive properties compared to other popular estimators, such as the graphical lasso and the graphical smoothly clipped absolute deviation. The most prominent benefit is that when the true inverse covariance matrix is sparse, the graphical horseshoe provides estimates with small information divergence from the sampling model. The posterior mean under the graphical horseshoe prior can also be almost unbiased under certain conditions. In addition to these theoretical results, we also provide a full Gibbs sampler for implementing our estimator. MATLAB code is available for download from github at http://github.com/liyf1988/GHS. The graphical horseshoe estimator compares favorably to existing techniques in simulations and in a human gene network data analysis. Supplementary materials for this article are available online.     

Consistency of Probability Measure Quantization by Means of Power Repulsion–Attraction Potentials

This paper is concerned with the study of the consistency of a variational method for probability measure quantization, deterministically realized by means of a minimizing principle, balancing power repulsion and attraction potentials. The proof of consistency is based on the construction of a target energy functional whose unique minimizer is actually the given probability measure \(\omega \) to be quantized. Then we show that the discrete functionals, defining the discrete quantizers as their minimizers, actually \(\Gamma \)-converge to the target energy with respect to the narrow topology on the space of probability measures. A key ingredient is the reformulation of the target functional by means of a Fourier representation, which extends the characterization of conditionally positive semi-definite functions from points in generic position to probability measures. As a byproduct of the Fourier representation, we also obtain compactness of sublevels of the target energy in terms of uniform moment bounds, which already found applications in the asymptotic analysis of corresponding gradient flows. To model situations where the given probability is affected by noise, we further consider a modified energy, with the addition of a regularizing total variation term and we investigate again its point mass approximations in terms of \(\Gamma \)-convergence. We show that such a discrete measure representation of the total variation can be interpreted as an additional nonlinear potential, repulsive at a short range, attractive at a medium range, and at a long range not having effect, promoting a uniform distribution of the point masses.     

The nonlinear future stability of the FLRW family of solutions to the Euler–Einstein system with a positive cosmological constant

In this article, we study small perturbations of the family of Friedmann–Lemaître–Robertson–Walker cosmological background solutions to the 1 + 3 dimensional Euler–Einstein system with a positive cosmological constant. These background solutions describe an initially uniform quiet fluid of positive energy density evolving in a spacetime undergoing accelerated expansion. Our nonlinear analysis shows that under the equation of state ${p = c^2_s \rho}$ , ${0 < c^2_s < 1/3}$ , the background solutions are globally future-stable. In particular, we prove that the perturbed spacetime solutions, which have the topological structure ${[0,\infty) \times \mathbb{T}^3}$ , are future-causally geodesically complete. These results are extensions of previous results derived by the author in a collaboration with I. Rodnianski, in which the fluid was assumed to be irrotational. Our novel analysis of a fluid with non-zero vorticity is based on the use of suitably defined energy currents.     

Equivalent solutions to additive two-stage network data envelopment analysis

In the additive approach of two-stage network data envelopment analysis (DEA), the non-linear DEA model is transformed into a parametric linear model and then solved by computing a series of linear programs. Lim and Zhu (2013; Integrated data envelopment analysis: Global vs. local optimum.European Journal of Operational Research, 229(1), 276–278) and Ang and Chen (2016; Pitfalls of decomposition weights in the additive multi-stage DEA model. Omega, 58, 139–153) propose two parametric linear approaches to solve additive two-stage network DEA model. The current study shows that the two approaches are equivalent and use the same parameter in searching for the global optimal solution.     

Clean matrices and unit-regular matrices

An element in a ring R is said to be clean (respectively unit-regular) if it is the sum (respectively product) of an idempotent element and an invertible element. If all elements in R are unit-regular, it is known that all elements in R are clean. In this note, we show that a single unit-regular element in a ring need not be clean. More generally, a criterion is given for a matrix to be clean in a matrix ring M₂(K) over any commutative ring K. For K=Z, this criterion shows, for instance, that the unit-regular matrix is not clean. Also, this turns out to be the “smallest” such example.     

Spatial competition and collaboration networks

We model the formation of collaboration networks among firms that are located in a circular city as a two-stage game. In the first stage, the firms form collaboration links, and in the second stage, they engage in price competition. If two firms form a link, their production costs in the second stage are reduced. The second stage is a generalization of Salop??s (Bell J Econ 10(1):141?C156, 1979) circular city model. We provide a complete characterization of equilibrium prices of the model. We show that a firm prefers forming a link with a more distant firm if the cost-reducing effects are the same. We discuss the stability and social efficiency of the collaboration networks. When link costs are small, there is no conflict between efficiency and stability of networks. When link costs are significant, there is a conflict between efficiency and stability of networks. We also examine the average distances between linked firms.     

基于SPA-TOPSIS方法的能源结构优化程度评价

以能源低碳化发展为基础,从社会经济发展程度、能源规划合理程度、环境和谐程度三个准则层入手,构建能源结构优化程度评价指标体系。运用改进惯性权重的PSO算法确定评价体系权重,并基于SPA-TOPSIS法构建能源结构优化程度评价模型,对30个省、自治区、直辖市的区域能源结构优化程度进行实证研究。实证结果表明:区域社会经济发展水平对能源结构优化程度有直接影响,且各区域能源结构优化程度差异较大,总体呈现“东高西低”的格局;清洁能源消费占比、原煤消费占比、烟尘排放等因素对能源结构优化程度影响显著。     

A generalization of the HSS-based sequential two-stage method for solving non-Hermitian saddle point problems

For non-Hermitian saddle point problems with non-Hermitian positive definite (1,1)-block, Zhu et al. studied the HSS-based sequential two-stage method (see Zhu et al. Appl. Math. Comput. 242, 907–916 19). However, this approach may not work when the (1,1)-block of the saddle point problems is weakly Hermitian or skew-Hermitian dominant. By introducing a new preconditioning matrix, a generalization of the HSS-based sequential two-stage method is proposed for solving non-Hermitian saddle-point problems with non-Hermitian positive definite and Hermitian or skew-Hermitian dominant (1,1)-block. Theoretical analysis shows that the proposed iterative method is convergent. Numerical experiments are provided to confirm the theoretical results, which demonstrate that the generalized method is effective and feasible for solving saddle point problems with non-Hermitian positive definite and Hermitian or skew-Hermitian dominant (1,1)-block.