Integrity assessment of a 3D tubeplate using the linear matching method. Part 2: Creep relaxation and reverse plasticity

In an accompanying paper [Int J Pres Ves Pip, 2004], a 3D tubeplate in a typical AGR superheater header was analysed for the shakedown limit, reverse plasticity and ratchet limit based on the application of the linear matching method (LMM). Both the perfectly plastic model and the cyclic hardening model were adopted for the evaluation of the plastic strain range. In the present paper, based on the creep-reverse plasticity model, the accumulated creep strain during a creep dwell at the steady cyclic state is assessed by the LMM. The accumulated creep strains, the creep flow stresses as well as the elastic follow-up factors with differing dwell times are evaluated in detail. The total inelastic strain over the cycle at the steady cyclic state is calculated. By comparing these results with ABAQUS step-by-step inelastic analyses, the applicability of the methods is demonstrated.     

Integrity assessment of a 3D tubeplate using the linear matching method. Part 1. Shakedown,reverse plasticity and ratchetting

The Linear Matching Method (LMM) has been developed recently for the integrity assessment for the high temperature response of structures. In this article, a complex 3D tubeplate in a typical AGR superheater header is analysed for the shakedown limit, reverse plasticity and ratchet limit based upon the LMM. At this stage, both the perfectly plastic model and the cyclic hardening model are adopted for the evaluation of the plastic strain range. Comparisons of LMM results with other results by ABAQUS step-by-step inelastic analyses for several material models are given. Further cyclic creep-reverse plasticity analyses are presented in an accompanying paper [Int. J. Pressure Vessels Piping (2004)].     

Shakedown and limit analyses for 3-D structures using the linear matching method

A recently developed method for 3-D shakedown and limit analyses is evaluated in the present paper. The shakedown and limit loads of a holed plate subjected to biaxial loading are calculated by implementing the upper bound linear matching method into the commercial FE code ABAQUS. A defective pipeline under the combined action of internal pressure and axial tension is also analysed for both shakedown and limit capacities and the results compared with a standard programming method. All the numerical examples confirm the applicability of this procedure to complex 3-D structures.     

Linear matching method for creep rupture assessment

The recently developed linear matching method (LMM), which is easily implemented within commercial FE codes, has been successfully used to evaluate elastic and plastic shakedown loads. In this paper, the method is extended to the prediction of the creep rupture life of a structure, based upon a bounding method currently used in the life assessment method R5. The method corresponds to the requirement that, for the operating load history, the structure should shakedown where the yield stress is given by the lesser of the plastic yield stress and a high temperature rupture stress corresponding to a rupture time. A holed plate subjected to cyclic thermal load and constant mechanical load is assessed in detail as a typical example to confirm the applicability of the above procedures. The examples show that the method remains numerically stable, even when the method is inverted.     

某型号牵引车冷却模块匹配计算方法

为缩短牵引车用冷却模块匹配选型时间,提出一种牵引车用冷却模块匹配计算方法.以某型号牵引车为计算原型,对由中冷器、散热器和风扇组成的牵引车用冷却模块进行匹配计算,并通过整车转毂热平衡试验检验计算方法的准确性.整车转毂热平衡试验结果表明:本文中提出的冷却模块匹配计算方法能成功预测冷却模块的冷却能力,整车实车试验与理论计算结...     

Nodal integral method for convection-diffusion transport using linear and higher order quadrilateral elements

Abstract

Generic nodal integral method (NIM) based scheme, utilizing nine noded 2D quadratic elements along with four noded 2D linear elements, is developed to solve the fluid flow and heat transfer equations in complex geometries. Non-linear (quadratic) quadrilateral elements are used for discretization of boundary region and linear quadrilateral elements are used for interior region. Lagrange interpolation functions are used to map both type of elements to corresponding square computational elements. The scheme for Neumann and mixed type of boundary conditions are also developed for quadratic elements. C¹ type continuity condition is imposed at the interfaces of adjacent elements. Numerical results are compared with analytical solutions for diffusion and advection-diffusion equations. Results for Navier–Stokes equations in curved domain are compared with previously reported experimental as well as numerical results. The comparative study has also been done between presently developed scheme using quadratic and linear elements (referred as scheme-1) and scheme based on complete discretization with linear elements (referred as scheme-2). The comparison shows that both the schemes are of nearly second order accurate while the scheme-1 is more accurate than scheme-2. The results show that the efficient mapping of curved surface with quadratic elements improves the accuracy of NIM schemes.     

Short term wind speed forecasting for wind turbine applications using linear prediction method

In this paper a new method, based on linear prediction, is proposed for wind speed forecasting. The method utilizes the ‘linear prediction’ method in conjunction with ‘filtering’ of the wind speed waveform. The filtering eliminates the undesired parts of the frequency spectrum (i.e. smoothing) of the measured wind speed which is less effective in an application, for example, in a wind energy conversion system. The linear prediction method is intuitively explained with some easy to follow case studies to clarify the complex underlying mathematics. For verification purposes, the proposed method is compared with real wind speed data based on experimental results. The results show the effectiveness of the linear prediction method.     

Comparison between the bivariate Weibull probability approach and linear regression for assessment of the long-term wind energy resource using MCP

A detailed investigation of a measure–correlate–predict (MCP) approach based on the bivariate Weibull (BW) probability distribution of wind speeds at pairs of correlated sites has been conducted. Since wind speeds are typically assumed to follow Weibull distributions, this approach has a stronger theoretical basis than widely used regression MCP techniques. Building on previous work that applied the technique to artificially generated wind data, we have used long-term (11 year) wind observations at 22 pairs of correlated UK sites. Additionally, 22 artificial wind data sets were generated from ideal BW distributions modelled on the observed data at the 22 site pairs. Comparison of the fitting efficiency revealed that significantly longer data periods were required to accurately extract the BW distribution parameters from the observed data, compared to artificial wind data, due to seasonal variations. The overall performance of the BW approach was compared to standard regression MCP techniques for the prediction of the 10 year wind resource using both observed and artificially generated wind data at the 22 site pairs for multiple short-term measurement periods of 1–12 months. Prediction errors were quantified by comparing the predicted and observed values of mean wind speed, mean wind power density, Weibull shape factor and standard deviation of wind speeds at each site. Using the artificial wind data, the BW approach outperformed the regression approaches for all measurement periods. When applied to the real wind speed observations however, the performance of the BW approach was comparable to the regression approaches when using a full 12 month measurement period and generally worse than the regression approaches for shorter data periods. This suggests that real wind observations at correlated sites may differ from ideal BW distributions and hence regression approaches, which require less fitting parameters, may be more appropriate, particularly when using short measurement periods.     

A creep life assessment method for boiler pipes using small punch creep test

The small punch creep (SPC) test is considered as a highly useful method for creep life assessment for high temperature plant components. SPC uses miniature-sized specimens and does not cause any serious sampling damages, and its assessment accuracy is at a high level. However, in applying the SPC test to the residual creep life assessment of the boiler in service, there are some issues to be studied. In order to apply SPC test to the residual creep life assessment of the 2.25Cr–1Mo steel boiler pipe, the relationship between uniaxial creep stress and the SPC test load has been studied.     

Isothermal kinetic predictions from nonisothermal data by using the iterative linear integral isoconversional method

A key issue in kinetic analysis is the prediction of the evolution of a thermally stimulated solid-state reaction for a given isothermal temperature from nonisothermal kinetic parameters. However, the conventional methods neglect the dependence of the activation energy on the conversion degree during the isothermal process; therefore, they may lead to some important errors in the isothermal kinetic predictions when the kinetic parameters vary significantly with the conversion degree. A new method for the determination of the isothermal conversion-time data from the nonisothermal kinetic parameters determined by the iterative linear integral isoconversional method has been developed. Two theoretically simulated data sets have been analyzed. And the analysis results have shown that the new method can give accurate isothermal kinetic predictions.     

Transportation of powders using a linear motor device

The theory of linear motors has been formulated for both magnetic and non-magnetic reaction plates and criteria established to assess their performance. The predominant mechanism involved in the transportation of ferromagnetic powders cannot be the same as that in a motor device, because basic calculations show that the induced currents in the particles at 50 Hz are small. Instead, the ferromagnetic particles seem to follow the movement of the travelling magnetic field itself.A study of the phenomena associated with the transportation of powders using linear motor devices has been commenced in a SERC project at Loughborough University of Technology. This paper illustrates the motion of the particles along a linear motor device and also reviews the experimental work done previously, especially that associated with powder cleaning devices. Areas of future research work to be followed are discussed and possible new industrial applications mentioned.     

A comparative assessment of thin-film photovoltaic production processes using the ELECTRE III method

The use of renewable energy sources for the production of electric power brings huge benefits both in terms of environmental protection as well as savings in non-renewable resources. Photovoltaic stands out from other renewable energy sources for its simplicity and the modularity of its energy conversion system. To date, the most highly developed technology for the construction of solar cells is one based on mono and polycrystalline silicon. An alternative production line is currently under development to produce, thin-film modules. There are currently a variety of processes and materials available to make thin-film cells but their relative costs and performance differ. Therefore, it would be useful to make a comparative evaluation of the different processes using a multiple criteria method.     

基于自适应线性逻辑网络的风电功率预测方法性能评估与分析

介绍了一种基于自适应线性逻辑网络(ALLN)的风电功率预测方法,描述了ALLN算法的特点、基本结构、建模方法以及预测与学习方法;采用该方法进行了风速预测试验,对试验结果进行了对比分析,详细分析了影响试验结果的因素。首次提出了模型适应性的概念,并给出了计算公式。从模型训练输入数据和预测输入数据的角度,分析了影响ALLN算法模型适应性与预测结果的主要因素。     

Temperature matching method of selecting working fluids for geothermal heat pumps

The fact, that some areas need district heating through heat pumps and at the same time recover residual heat from geothermal water, presents a new working condition: feed water temperature of heat network 80 °C, return water temperature 65 °C; discarded geothermal water temperature 40 °C and its emission standard temperature below 30 °C. But none of known pure refrigerants and mixtures can meet this requirement. The paper introduces a novel approach named temperature-matching method, which provides a direction in selecting high-performance working fluids for further research. It is shown from the results that the mean COPs of binary and ternary mixtures are 4.85 and 4.74 respectively, but that of pure refrigerants is 4.12 under the same ambient condition. This point indicates that temperature matching contributes to energy saving. The novel approach to high-performance working fluids can be conveniently introduced into other working conditions.     

A new method for an economic assessment of heat and power plants using dimensionless numbers

A comparison of economic data for different technologies and fuels is difficult due to the number of parameters that can alter the profitability of heat and power production. In addition, the variation of currency exchange rates considerably reduces the possibility of comparing plants in different countries. In the present study, a new method based on dimensionless costs is proposed to overcome these difficulties. Dimensionless capital costs C (including maintenance) and dimensionless fuel costs F are introduced by dividing the costs by the price for heat or electricity. In a diagram of C versus F the economy of different technologies can be compared. The diagram is divided into a profitable and an unprofitable area. The orientation of the data from one specific plant shows immediately whether the plant can be operated economically or not. Furthermore it can be seen by which factor either the fuel costs have to be reduced, or the price for electricity or heat has to be increased, or the capital and maintenance costs have to be reduced to reach the profitable area. The dimensionless diagram is independent from currency exchange rates. To demonstrate the application of the method, data from an economic assessment study of power production plants from biomass using pyrolysis, gasification and combustion technologies are presented.     

The linear matching method applied to the high temperature life integrity of structures. Part 1. Assessments involving constant residual stress fields

Design and life assessment procedures for high temperatures are based on ‘expert knowledge’ in structural mechanics and materials science, combined with simplified methods of structural analysis. Of these, R5 is one of the most widely used life assessment methods internationally with procedures based on reference stress techniques and shakedown calculations using linear elastic solutions. These have been augmented by full finite element analysis and, recently, the development of a new programming method, the linear matching method (LMM), that allows a range of direct solutions that include shakedown methods and simplified analysis in excess of shakedown. In this paper, LMM procedures are compared with calculations typical of those employed in R5 for cyclic loading problems when the assumption of a constant residual stress field is appropriate including shakedown and limit analyses, creep rupture analysis and the evaluation of accumulated creep deformation. A typical example of a 3D holed plate subjected to a cyclic thermal load and a constant mechanical load is assessed in detail. These comparisons demonstrate the significant advantages of linear matching methods for a typical case. For a range of cyclic problems when the residual stress field varies during the cycle, which include the evaluation of plastic strain amplitude, ratchet limit and accumulated creep strains during a high temperature dwell periods, the corresponding LMM and R5 procedures are discussed in an accompanying paper.     

Thermal matching performance of a geothermal ORC system using zeotropic working fluids

The thermal matching performance analysis is conducted for a geothermal organic Rankine cycle system using zeotropic mixtures as working fluids. The constant isentropic efficiency is replaced by internal efficiency of an axial flow turbine with given size for each condition, and the zeotropic mixtures of isobutane and isopentane is used as working fluids of the organic Rankine cycle, in order to improve thermal match in evaporator and condenser. The results showed the use of zeotropic mixtures leads to the prominent thermodynamic first law and second law efficiencies, especially at high minimum temperature difference in evaporator (Δt₁), and there exists an optimal thermal performance at some certain mole fraction of isopentane in zeotropic mixtures (x) and Δt₁. The geothermal organic Rankine cycle with x of 0.2 and Δt₁ of 16 K shows the maximal thermodynamic first law and second law efficiency in this research. The geothermal organic Rankine cycle system using zeotropic mixtures shows the optimal overall thermal performance at some certain x, which is not necessary to be the point with the maximal temperature glide. The use of zeotropic mixtures is not always lead to a high thermal to electricity efficiency compared to the pure working fluid, and its overall net power output of P_ORC is even lower than the pure working fluids compositions at some certain x.     

Evaluation of a building using the emergy method

Emergy (spelled with an m) is the energy of one kind, usually solar energy, which is required to make a service or product. The yearly emergy consumption/production of a building is evaluated considering the Solar Energy Laboratory (LESO) building on the campus of the Swiss Federal Institute of Technology of Lausanne (Switzerland). This experimental building was constructed according to special environmental considerations, such as important the use of passive gains (heat emitted from solar radiations, electric appliances and building users). It is therefore characterized by a very low energy consumption, equal to 232 MJ/m² year. The LESO building is occupied by faculty and students. Undergraduate and graduate students as well as faculty represent information inputs to the system with their emergy accounting for 94.6% of the emergy inputs to the building, equal to 3.3E18 sej/year (solar emjoules per year).“Educated students” (students who have completed a semester project, master’s or PhD research in the laboratory), publications, courses and services are the main outputs of the system. The four outputs are considered as co-outputs, as such the total emergy associated to the operation of the building as a structure is entirely assigned to each of them. The evaluation established that a student leaving the LESO building has a transformity (emergy per unit energy) equal to 2.4E8 sej/J, which is about three times higher than the one which he/she had upon arrival, representing the knowledge gained through conferences and interactions with other students and professors.Considering only energy and materials inputs, electricity was established to be the largest input to the system (2.7E16 sej/year). The total emergy of the material inflows was determined to equal 1.7E16 sej/year, paper being the largest material input (5.7E15 sej/year). The specific emergy (per mass) of some common building materials was also evaluated and compared to NRE (non-renewable energy).Finally, the question of uncertainties related to the determination and use of average transformities and emergy per mass values is addressed, and advantages and drawbacks of the emergy method are discussed in relation to other common evaluation methodology (exergy, embodied energy, life-cycle analysis).     

倾向性评分匹配法评价非ST段抬高型急性冠状动脉综合征介入治疗与保守治疗效果

【摘要】 目的 采用倾向性评分匹配（PSM）法评价经皮冠状动脉介入治疗（PCI）与保守治疗对非ST段抬高型急性冠状动脉综合征（NSTE- ACS）终点事件的影响。方法 回顾性分析2006年10月至2010年1月收治的408例NSTE- ACS患者临床资料,其中接受早期PCI治疗131例（PCI组）,保守治疗277例（保守治疗组）。采用1︰1最邻近匹配法对两组患者行PSM,获得组间协变量均衡样本。采用Cox比例风险模型评估PSM匹配前后影响急性冠状动脉终点事件发生的危险因素。所有患者随访1年,终点事件定义为心源性死亡、发生ST段抬高型心肌梗死（STEMI）、心绞痛再发作、严重心力衰竭。结果 与保守治疗组相比,PCI组有更多高血压史、高血脂史、糖尿病史、心绞痛发作史、内生肌酐清除率（CCr）降低、心肌肌钙蛋白（cTnI）升高、心电图ST段改变患者（P＜0.05）。PSM法评价后成功匹配两组108对患者,匹配后两组患者临床资料差异均无统计学意义（P＞0.05）。PCI组、保守治疗组术后1年内发生急性冠状动脉终点事件风险概率分别为17.6%（19/108）、37.0%（40/108）,差异有显著统计学意义（Log- rank检验,P＜0.001）。Cox比例风险模型多因素分析发现,糖尿病史（HR:2.13,95%CI:1.08～4.20,P=0.029）、心房颤动史（HR:2.65,95%CI:1.25～5.62,P=0.011）、CCr下降（HR:2.24,95%CI:1.11～4.50,P=0.024）、cTnI升高（HR:2.68,95%CI:1.18～6.09,P=0.019）、冠状动脉多支病变（HR:2.14,95%CI:1.13～4.05,P=0.020）、PCI（HR:0.43,95%CI:0.26～0.65,P=0.001）是影响NSTE- ACS患者急性冠状动脉终点事件发生的独立因素。结论PSM法可有效均衡非随机研究组间协变量。早期PCI术可降低有高危因素的NSTE- ACS患者1年内急性冠状动脉终点事件发生率。