Parabolic Heat Conduction Specialized Applications Involving Imperfect Contact Surfaces: Local Discontinuous Galerkin Finite Element Method—Part 2

Parabolic heat conduction specialized applications involving imperfect thermal contact surfaces are analyzed via the Local Discontinuous Galerkin (LDG) finite element method. In this paper, we describe the advantages of the LDG finite element formulation over the traditional continuous Galerkin (CG) finite element method for modeling imperfect thermal contact between surfaces. To-date, mostly interface/gap elements have been primarily used to model the imperfect contact between two surfaces to solve thermal contact resistance problems. The LDG method eliminates the use of such interface/gap elements and provides a higher degree of accuracy. Several illustrative 2-D applications highlight the effectiveness of the present LDG finite element formulations for this class of problems.     

Correlation between Chinese and international energy prices based on a HP filter and time difference analysis

To establish a reasonable system and mechanism for Chinese energy prices, we use the Granger causality test, Hodrick–Prescott (HP) filter and time difference analysis to research the pricing relationship between Chinese and international energy prices. We find that Chinese and international crude oil prices changed synchronously while Chinese refined oil prices follow the changes of international oil prices with the time difference being about 1 month to 2 months. Further, Australian coal prices Granger causes Chinese coal prices, and there is a high correlation between them. The U.S. electricity price is influenced by the WTI crude oil price, the U.S. gasoline price and the HenryHub gas price. Due to the unreasonable price-setting mechanism and regulation from the central government, China′s terminal market prices for both electricity and natural gas do not reflect the real supply–demand situation. This paper provides quantitative results on the correlation between Chinese and international energy prices to better predict the impact of international energy price fluctuations on China′s domestic energy supply and guide the design of more efficient energy pricing policies. Moreover, it provides references for developing countries to improve their energy market systems and trading, and to coordinate domestic and international energy markets.     

断续节理扩展机制的离散元分析

采用离散元数值法研究断续节理扩展贯通机制对工程岩体的稳定性具有重要意义,为此引入应力强度因子,基于裂纹Ⅱ型断裂判据,提出了考虑岩桥渐进破坏特征的粘聚力弱化函数,将粘聚力弱化函数用FISH编程语言内嵌至UDEC中,并在变形块体内预设潜在节理面表征岩桥的破坏路径,按Mohr-Coulomb屈服准则进行节理扩展分析,实现了断续节理在不同压应力状态下的直剪试验模拟,且真实反映了断续节理中节理面开裂、贯通、扩展的全动态过程,数值仿真结果与已有的试验结果吻合较好,从而验证了该方法的正确有效性。     

Identification of congestion and valuation of transport infrastructures in the European natural gas market

Rising import dependency, increasing market liberalization and cross-border trade and security of supply fears facilitate investments in natural gas supply infrastructures in Europe. In order to ensure an efficient allocation of capital resources, it is important to identify congestion in the existing system and investment requirements based on economic principles. This paper first outlines an analytical framework for the identification of bottlenecks and the evaluation of transport capacities and the cost of congestion based on nodal prices. Secondly, an infrastructure model of the European gas market with high temporal and spatial granularity which exhibits the characteristics of the theoretical model is introduced. Parameterizing the model with the existing infrastructure and applying a demand and supply scenario for the year 2015, congestion mark-ups between countries in Europe are estimated. This approach indicates potential bottlenecks which might arise within the next five years and quantifies their economic costs. With only some temporary congestion, physical market integration is found to be high in Western Europe. In Eastern Europe, severe bottlenecks are identified and discussed. Implications for efficient investment decisions arising from the findings are examined in the context of the theoretical considerations.     

阶梯电价是我国电价改革的阶梯

我国自改革开发以来,电价存在三大问题:一是电价水平偏低,二是电价结构严重扭曲,三是电能与其他能源的比价不合理。电价结构扭曲中最大的问题是居民生活用电价格严重偏低。实行阶梯电价的根本目的是为了建立一种居民生活电价走向合理化的机制,是对我国居民用电长期采取低电价政策的纠正和调整,也是让居民电价做到反映用电成本的合理回归。国家发改委在征求意见稿中所提出的阶梯电价第一档电量是相当高的,第一档电量占每月每户平均用电量的比重两个方案分别为22.7%和28.9%,第一档电量占每月每户平均居民生活用电量的比重分别为193.3%和246.0%,均高于对比的其他国家和地区,因此第一档电量不宜再提高。我国以现行的居民生活用电价格作为第一档电价是比较合理的,不应再降价;第二、第三档电价应提高电价水平,拉大各档之间的电价差距。通过实行居民阶梯电价政策,可以充分发挥价格杠杆的作用,促进合理、节约用电,从而有利于建设资源节约型和环境友好型社会。推行阶梯电价,使电价逐渐回归合理水平还能促进能源的合理替代,起到节能减排的作用。     

The crucial relationship among energy commodity prices: Evidence from the Spanish electricity market

The main purpose of this article is twofold to analyze: (a) the long-term relation among the commodities prices and between spot electricity market price and commodity prices, and (b) the short-term dynamics among commodity prices and between electricity prices and commodity prices. Data between 2002 and 2005 from the Spanish electricity market was used. Econometric methods were used in the analysis of the commodity spot price, namely the vector autoregression model, the vector error correction model and the granger causality test. The co-integration approach was used to analyze the long-term relationship between the common stochastic trends of four fossil fuel prices. One of the findings in the long-term relation is that the prices of fuel and the prices of Brent are intertwined, though the prices of Brent ten to “move” to reestablish the price equilibrium. Another finding is that the price of electricity is explained by the evolution of the natural gas series.     

三角网格间断有限元法弹性波模拟精度分析

精度分析是地震波数值模拟的基础.针对基于三角形网格的间断Galerkin有限元方法(DGFEM)的稳定性、数值频散及耗散问题,构建了周期性三角形单元网格,可以更灵活地分析不同形态的三角形单元对模拟精度的影响.理论和数值实验的分析结果表明:三角形网格中基于Runge-Kutta时间格式的DGFEM的稳定性条件与三角形的形...     

Energy consumption,economic growth and prices: A reassessment using panel VECM for developed and developing countries

This paper reinvestigates the energy consumption–GDP growth nexus in a panel error correction model using data on 20 net energy importers and exporters from 1971 to 2002. Among the energy exporters, there was bidirectional causality between economic growth and energy consumption in the developed countries in both the short and long run, while in the developing countries energy consumption stimulates growth only in the short run. The former result is also found for energy importers and the latter result exists only for the developed countries within this category. In addition, compared to the developing countries, the developed countries’ elasticity response in terms of economic growth from an increase in energy consumption is larger although its income elasticity is lower and less than unitary. Lastly, the implications for energy policy calling for a more holistic approach are discussed.     

Trends in prices to commercial energy consumers in the competitive Texas electricity market

To date, the price of electricity to commercial or business energy consumers has generally increased at greater rates in the areas of Texas where retail competition has been introduced than in areas that do not enjoy competition. Trends in commercial competitive prices have largely mirrored trends in residential prices. Market restructuring has tended to increase the sensitivity of retail electricity prices to changes in the price of natural gas, the marginal fuel used for generation in Texas. Consequently, the rapid increases in the commodity price of natural gas following restructuring led to increases in competitive electric rates which exceeded the increases in areas not exposed to restructuring, where the fuel component of electric rates tend to reflect a weighted average of the utilities’ fuel costs. There is some evidence that pricing behavior by competitive retailers changed when the retailers affiliated with the incumbent utilities were permitted some pricing flexibility, resulting in a reduction in prices.     

Effects of stochastic energy prices on long-term energy-economic scenarios

In view of the currently observed energy prices, recent price scenarios, which have been very moderate until 2004, also tend to favor high future energy prices. Having a large impact on energy-economic scenarios, we incorporate uncertain energy prices into an energy systems model by including a stochastic risk function. Energy systems models are frequently used to aid scenario analysis in energy-related studies. The impact of uncertain energy prices on the supply structures and the interaction with measures in the demand sectors is the focus of the present paper.

For the illustration of the methodological approach, scenarios for four EU countries are presented. Including the stochastic risk function, elements of high energy price scenarios can be found in scenarios with a moderate future development of energy prices. In contrast to scenarios with stochastic investment costs for a limited number of technologies, the inclusion of stochastic energy prices directly affects all parts of the energy system. Robust elements of hedging strategies include increasing utilization of domestic energy carriers, the use of CHP and district heat and the application of additional energy-saving measures in the end-use sectors. Region-specific technology portfolios, i.e., different hedging options, can cause growing energy exchange between the regions in comparison with the deterministic case.