Potential method in the theory of thermoviscoelastic mixtures

In this article, the linear theory of binary thermoviscoelastic mixtures is considered and the basic boundary value problems (BVPs) of steady vibrations are investigated. Namely, the fundamental solution of the system of equations of steady vibrations is constructed explicitly and its basic properties are established. Green’s second and third identities are obtained and the uniqueness theorems for classical solutions of the internal and external basic BVPs of steady vibrations are proved. The surface and volume potentials are constructed and their basic properties are given. The determinants of symbolic matrices are calculated explicitly. The BVPs are reduced to the always solvable singular integral equations for which Fredholm’s theorems are valid. Finally, the existence theorems for classical solutions of the internal and external BVPs of steady vibrations are proved by the potential method and the theory of singular integral equations.     

自然通风技术研究方法及工具

目前自然通风主要有三种研究方法:简单的理论分析法、实验法和数值模拟法。本文概括介绍了后两种方法的研究现状,并对它们进行了分析比较,提出各种方法的适用场合。在数值模拟法中还介绍了几种可用于分析自然通风系统的通风特性和热特性的常用工具软件,对各自工作原理和应用特点进行了比较,并对使用方法和应用场合提出了建议。     

微电网能量管理和控制简述

首先介绍了微电网的概念和微电网的基本结构以及运行方式。其次,给出了微电网能量管理系统的定义,分析了其与传统大电网的不同,并提出了其3种控制结构。在分析比较3种控制结构的优缺点之后,介绍了微电网能量优化调度的模型和算法以及能量管理的频率和电压控制策略。最后,提出了今后微电网能量管理系统可能采用的方法和频率电压控制的研究方向。     

纤维喷涂工艺在退火炉中的应用及前景

综述了纤维喷涂工艺的原理和特点以及对辅助工艺的要求，并与其它工艺进行经济技术指标的实例对比。重点介绍了纤维喷涂工艺在退火炉中的应用及前景。     

Exergy analysis of compression and expansion processes

The thermodynamics of compression and expansion processes in turbomachinery are examined. Rational efficiencies are defined and their relation to isentropic and polytropic efficiencies are discussed. Multistage turbines with extractions are optimized. This approach yields expressions that are independent of the concept of thermodynamic irreversibility.     

Study of contact melting inside isothermally heated vertical cylindrical capsules

Close-contact melting processes of phase change material (PCM) inside vertical cylindrical capsule are studied. PCM are heated by the capsule isothermally at the bottom and side. The theoretical formulas of the melting rate and thickness of liquid layer during the heat transfer process are obtained by analysis, which are convenient for engineering predictions. Finally, the factors that affect melting are discussed, and conclusions are drawn.     

US nuclear energy policy Provision of funds for decommissioning

The five recognized methods of decommissioning nuclear power plants are reviewed, and are linked with US nuclear regulatory policy. Although over 60 US nuclear reactors have been decommissioned since 1960, none have been large-scale commercial facilities. Costs of the decommissioning alternatives are estimated, but are acknowledged to be highly tentative and uncertain. Five methods of providing funds for decommissioning and the actual practices of US electric utilities are analysed in terms of the policy issues they present. Revenue bonding and sinking fund approaches are argued to be the soundest means to recover decomissioning uncertainties surrounding decommissioning are considered.     

A review of cells based on lithium negative electrodes (anodes)

This review traces the development of lithium cells from their inception to the present day: about 500 references are included. Primary and secondary cells are dealt with and the most useful anode/cathode combinations, in both fields, are noted. Electrolytes and separators are also discussed, as are the effects of film formation and the charge/discharge mechanisms.Shortcomings are emphasised where they are known to exist and attention is drawn to some areas where the present authors consider advances may be made.     

The prospects of cost reductions in willow production in Sweden

The current and future costs of willow short rotation coppice production in Sweden are analysed, considering all relevant cost factors explicitly. The future production costs are estimated considering effects of coppice area expansion and learning. The current and future costs of land and of risk premiums are subsequently estimated. Subsidies for farmers are not considered. If the area of willow cultivation were to expand enough to generate economies of scale, the production cost could be cut by about 10% compared to the current level. When learning effects are also considered, the total cost reduction potential is about 35%. Two major cost components (fertilization and road transport) are roughly stable while two other major cost components (establishment and harvest) have larger prospects for cost reduction, primarily due to potential for learning. Land costs and risk premiums vary and are uncertain, but both are estimated to be potentially significant compared to other cost components. Requirements of risk premiums may become lower as a consequence of area expansion and learning. Land costs are subject to many factors that are inherently uncertain, not the least future food prices. Efficient policies promoting an expansion of willow cultivation are discussed.     

Hydroelectric power potential and its use in Turkey

Hydroelectric development in Turkey is briefly reviewed. The results of estimates of gross and economically exploitable hydroelectric power potentials are compared. Dam sites and their order for construction are identified. Present and future developments in the power sector are analyzed and projections are given for electricity consumption and production to the year 2010. Hydraulic, thermal and nuclear contributions to total electricity generation are discussed. Finally, problems associated with hydroelectric power are identified.     

Features of The Netherlands' electricity supply system

Regulations concerning the supply of electricity in The Netherlands are discussed, and important issues are identified. Large-scale conventional generation, cogeneration, and wind energy are examined. The grid structures and characteristic materials used in the Dutch networks are described. Specific developments in The Netherlands are reviewed     

Thermoelectrics: a review of present and potential applications

Thermoelectric devices are solid state devices. They are reliable energy converters and have no noise or vibration as there are no mechanical moving parts. They have small size and are light in weight. As refrigerators, they are friendly to the environment as CFC gas or any other refrigerant gas is not used. Due to these advantages, the thermoelectric devices have found a large range of applications. In this paper, basic knowledge of the thermoelectric devices and an overview of these applications are given. The prospects of the applications of the thermoelectric devices are also discussed.     

Engineering aspects of geothermal development with emphasis on the Imperial Valley of California

This review was prepared in support of a geothermal planning activity of the County of Imperial. Engineering features of potential geothermal development are outlined. Acreage requirements for drilling and powerplants are estimated, as are the costs for wells, fluid transmission pipes, and generating stations. Rough scaling relationships are developed for cost factors as a function of reservoir temperature. Estimates are made for cooling water requirements, and possible sources of cooling water are discussed. Availability and suitability of agricultural wastewater for cooling are emphasized. The utility of geothermal resources for fresh water production in the Imperial Valley is considered.     

An adaptive degrees-of-freedom finite element method for 3-D nonlinear magneto-thermal field analysis

An adaptive degrees-of-freedom finite element method (FEM) for 3-dimensional nonlinear magneto-thermal fields is proposed in this article. Both magnetic field and thermal field are discretized using a single FEM mesh, and their degrees of freedom (DoFs) are individually controlled based on the field characteristics. Before solving the algebraic equations, the constrained DoFs are removed using the slave-master technique. The computing time and the storage resources of the second set of FEM mesh are saved while meeting the different requirements on discretization. Data transfer between the thermal and magnetic fields are easily implemented, and mapping errors between different meshes are avoided. To showcase the feasibility and the effectiveness of this method, several numerical examples are tested.     

Techniques for tuning excitation system parameters

The basic small signal-characteristics that are typical for most modern excitation systems are examined. A common-sense approach to model tuning is suggested. The procedure is based on emulation of the open-circuit step response test, a standard control-tuning practice for several decades. Where simulations with excitation system and generator model data result in unacceptable responses, guidelines are provided for tuning models until well-behaved, realistic responses are achieved. Frequency-response techniques are used. Two basic types of models are analyzed, and the means of reducing most models to these are shown. An application example is given     

质子交换膜燃料电池系统控制与应用现状

描述了质子交换膜燃料电池(PEMFC)系统的控制及其在中低功率领域中的应用现状。首先概述了过程模型和电压预测模型，对影响电堆性能的各参数进行分析。其次，从目前运用的简单控制方法、混合动力驱动、效率优化、故障容许等方面对PEMFC系统的分析与控制结构作了说明。然后介绍了PEMFC的几种具体应用。最后结合国内外的相关研究进展，提出了一些有待进一步研究的方向。     

用面向对象方法开发现代制造企业的管理信息系统

现代制造企业经营管理环境及思想正发生着深刻的变化,现代软件工程思想和方法也正朝着面向对象方向发展,通过将二者融入制造企业的管理信息系统,探讨了现代制造企业管理信息系统的结构及功能,并给出了用面向对象技术分析和设计管理信息系统的方法。     

Dynamic modelling and control of fully rated converter wind turbines

Today, many countries are integrating large amount of wind energy into the grid and many more are expected to follow. The expected increase of wind energy integration is therefore a concern particularly to transmission grid operators. Based on the past experience, some of the relevant concerns when connecting significant amount of wind energy into the existing grid are: fault ride through requirement to keep wind turbines on the grid during faults and wind turbines have to provide ancillary services like voltage and frequency control with particular regard to island operation.While there are still a number of wind turbines based on fixed speed induction generators (FSIG) currently running, majority of wind turbines that are planned to be erected are of variable speed configurations. The reason for this is that FSIG are not capable of addressing the concern mentioned above. Thus, existing researches in wind turbines are now widely directed into variable speed configurations. This is because apart from optimum energy capture and reduction of mechanical stress, preference of these types is also due to the fact that it can support the network such as its reactive power and frequency regulation. Variable wind turbines are doubly fed induction generator wind turbines and full converters wind turbines which are based on synchronous or induction generators.This paper describes the steady state and dynamic models and control strategies of wind turbine generators. The dynamic models are presented in the dq frame of reference. Different control strategies in the generator side converter and in the grid side converter for fault ride through requirement and active power/frequency and reactive/voltage control are presented for variable speed wind turbines.     

Bioclimatic rehabilitation of existing building stock

Bioclimatic rehabilitation of existing building stock can result in significant energy savings. Different rehabilitation measures are available, but low-cost measures are mostly in use. In Belgrade those are closing of balconies and loggias and annex of attics built in purpose of dwelling. Those are measures that tenants were able to realize in personal arrangement and measures that created benefits for the community. The review of rehabilitation measures is given and measures that are mostly in use in Belgrade are analyzed in the paper.     

STABILIZED FLUX-BASED FLOW / THERMAL FINITE ELEMENT REPRESENTATIONS WITH APPLICATIONS TO CONVECTIVELY COOLED STRUCTURES

Stabilized flux-based finite element representations for steady two-dimensional incompressible flow / thermal problems with emphasis on subsequently applying such techniques to convectively cooled structures are described in this article. First, the discretized equations are derived from a mixed formulation using both primary and flux variables in conjunction with the Streamline-Upwind-Petrov-Galerkin and Pressure-Stabilizing-Petrov-Galerkin features that are used to stabilize the solutions. The constitutive equations are then introduced into the discretized representations and the equations are finally solved for the primary variables. Equal-order linear quadrilateral interpolation functions are used for the velocities, pressure, and temperature. Numerical results are presented for a variety of situations, and finally emphasis is placed on applications to convectively cooled structures that are subjected to intense localized heating.