基于多位置NWP的超短期风速预测研究

数值天气预报(NWP)是影响风电场超短期预测精度的主要因素。采用数据挖掘技术中的主成分分析方法,对位于一个风电场多个位置的NWP各指标数据进行主成分提取,获取几个综合指标,使得新的输入变量维数降低,分量间相关性减小。在此基础上,利用BP神经网络和泛化回归神经网络(GRNN)建立超短期风速预测模型,实验结果显示,基于主成分分析提取的GRNN预测模型预测精度更高。     

基于PCA-GABP神经网络的发动机负荷特性预测

针对BP算法存在的不足,本文提出了一种PCA-GABP神经网络方法预测发动机负荷特性,该方法由主成分分析(PCA)和遗传神经网络(GABP)两部分构成,采用PCA技术减少网络输入变量、精简网络结构、提高学习效率;GABP算法采用局部改进遗传算法优化神经网络权值,并采用自适应学习速率动量梯度下降算法对神经网络进行训练。预测结果表明该方法在准确性和收敛性方面都优于BP算法。     

基于PCA-GABP神经网络的发动机负荷特性预测

针对BP算法存在的不足，本文提出了一种PCA—GABP神经网络方法预测发动机负荷特性，该方法由主成分分析（PCA）和遗传神经网络（GABP）两部分构成，采用PCA技术减少网络输入变量、精简网络结构、提高学习效率；GABP算法采用局部改进遗传算法优化神经网络权值，并采用自适应学习速率动量梯度下降算法对神经网络进行训练。预测结果表明该方法在准确性和收敛性方面都优于BP算法。     

基于相似日和主成分分析的光伏发电系统短期出力预测

针对光伏发电功率的间歇性和波动性,提出了一种基于主成分分析(PCA)和粒子群优化(PSO)算法的BP神经网络短期发电功率预测方法。该方法先对原始输入数据进行主成分分析,再将分析结果作为BP神经网络的输入数据。由于粒子群算法搜索速度较慢,但全局搜索能力较强,而传统的BP神经网络搜索速度较快,但易陷入局部极值点,因此将两者结合起来,既弥补了各自的劣势,又避免了预测模型的失效,从而提高了预测模型的预测精度。分析结果表明,当天气类型改变时,该预测模型的有效性不变,预测误差均小于20%。     

城市燃气小时负荷预测模型研究

城市燃气小时负荷预测的研究对燃气调度系统的安全与稳定具有重要意义。为了提高城市燃气小时负荷预测精度,在分析讨论主成分分析特性和BP神经网络优缺点的基础上,建立了利用主成分分析法对BP神经网络进行优化的小时负荷预测模型。该模型综合了主成分分析的降维特性和BP神经网络具有强大的自学习和自适应能力等特点,首先通过主成分分析法对所有相关影响因子进行降维处理,再将处理后累计贡献率占比85%以上的几种主成分作为输入层神经元输入BP神经网络进行训练,最后运用该组合模型对某县的小时负荷进行预测。实例分析表明:与单一模型相比,提出的PCA-BPNN组合预测模型精度更高,是一种更为有效的城市燃气小时负荷预测方法。     

基于KG-BP神经网络在秦淮河洪水水位预测中的应用

为了提高BP神经网络模型的预测精度,提出了一种基于KNN算法及GA算法优化的BP神经网络的水位预测方法(KG-BP),即通过KNN邻近算法从全样本数据中剔除与待测点相关度较低的样本集,并允许保留K个"优质"训练数据集;将筛选出的"优质"训练数据集代入GA算法中实现初始权阈值的优化;再将"优质"的样本和初始权阈值代入BP模型中进行训练。将该预测方法应用于东山站水位实际预测中,并与BP模型、GA-BP模型的预测结果进行对比分析,验证了KG-BP模型具有较高的预测精度。     

基于KPCA与IHHO-LSSVM的电力变压器故障诊断方法研究

为提高电力变压器故障识别精确度,提出基于核主成分分析(Kernel principal component analysis,KPCA)与改进哈里斯鹰算法(Improved Harris hawk algorithm,IHHO)优化最小二乘支持向量机(Least square support vector machine,LSSVM)的电力变压器故障诊断方法。首先,利用核主成分分析对变压器原始故障数据进行预处理,去除冗余数据;其次,结合Sigmoid变形函数以及点对称策略改进传统哈里斯鹰算法(HHO),并与HHO和遗传算法(Genetic algorithm,GA)进行性能对比,证明求解精度和网络收敛速度有所提升;最后,采用IHHO对LSSVM的相关超参数进行优化求解,获取KPCA与IHHO-LSSVM相结合的变压器故障诊断模型。结果表明所提模型的诊断精度为95.6%,同其他故障诊断模型相比分别提高了8.9%、16.7%,证明了所提方法能够有效地提升变压器故障诊断性能。     

基于随机森林的火电机组SCR脱硝反应器建模

火电机组选择性催化还原技术(SCR)脱硝反应器过程复杂多变,采用机理建模的SCR脱硝反应器出口NO_x质量浓度预测难以取得良好的效果。基于火电厂的历史运行数据,将主成分分析(PCA)和随机森林(RF)相结合建立了SCR脱硝反应器出口NO_x质量浓度预测模型。在建模过程中,采用主成分分析方法计算各个变量的贡献率来筛选变量,进而对随机森林模型进行试验验证,并与支持向量机(SVM)模型和BP神经网络模型的预测性能进行对比。结果表明:采用PCA变量选择方法确定SCR系统模型的输入变量是可行和有效的;与SVM和BP神经网络模型相比,RF算法得到的SCR系统模型具有更好的预测效果。     

基于KPCA-RF的风电场功率预测方法研究

为了提高风电场输出功率的预测精度,文章提出了一种核主成分分析与随机森林相结合的预测方法。利用核主成分分析从多种气象数据中提取出最主要的影响因素,将这些因素作为预测模型的输入,采用随机森林算法进行功率预测。实测运行数据的实验结果表明,文章算法具有较高的预测准确性。     

基于KPCA-ISHO-LSSVM的接地网腐蚀速率预测

为了提高接地网腐蚀速率预测精度,利用核主成分分析法对接地网腐蚀速率的主元进行提取,依据KPCA分析结果进行了指标重构,减少了接地网腐蚀预测模型建模工作量。通过收敛因子非线性调整及莱维飞行策略对斑点鬣狗算法进行改进,基于改进后的斑点鬣狗算法对最小二乘支持向量机的惩罚参数和核函数参数进行优化,建立了基于KPCA-ISHO-LSSVM的接地网腐蚀速率预测模型。仿真结果表明,经ISHO优化LSSVM接地网腐蚀速率预测模型的平均相对误差、均方根误差、全局最大相对误差均定系数分别为2.79%、0.139、3.53%和0.995,均优于其他接地网腐蚀预测模型,验证了模型的正确性和优越性。     

Ash-forming elements in four Scandinavian wood species. Part 1: Summer harvest

Woody biomass in Finland and Sweden comprises mainly four wood species: spruce, pine, birch and aspen. To study the ash, which may cause problems for the combustion device, one tree of each species were cut down and prepared for comparisons with fuel samples. Well-defined samples of wood, bark and foliage were analyzed on 11 ash-forming elements: Si, Al, Fe, Ca, Mg, Mn, Na, K, P, S and Cl. The ash content in the wood tissues (0.2–0.7%) was low compared to the ash content in the bark tissues (1.9–6.4%) and the foliage (2.4–7.7%). The woods’ content of ash-forming elements was consequently low; the highest contents were of Ca (410–1340 ppm) and K (200–1310), followed by Mg (70–290), Mn (15–240) and P (0–350). Present in the wood was also Si (50–190), S (50–200) and Cl (30–110). The bark tissues showed much higher element contents; Ca (4800–19,100 ppm) and K (1600–6400) were the dominating elements, followed by Mg (210–2400), P (210–1200), Mn (110–1100) and S (310–750), but the Cl contents (40–330) were only moderately higher in the bark than in the wood. The young foliage (shoots and deciduous leaves) had the highest K (7100–25,000 ppm), P (1600–5300) and S (1100–2600) contents of all tissues, while the shoots of spruce had the highest Cl contents (820–1360) and its needles the highest Si content (5000–11,300). This paper presented a new approach in fuel characterization: the method excludes the presence of impurities, and focus on different categories of plant tissues. This made it possible to discuss the contents of ash element in a wide spectrum of fuel-types, which are of large importance for the energy production in Finland and Sweden.     

NEXT GENERATION ENGINEERED MATERIALS FOR ULTRA SUPERCRITICAL STEAM TURBINES

正1 ABSTRACT To reduce the effect of global warming on our climate,the levels of CO2emissions should be reduced.One way to do this is to increase the efficiency of electricity production from fossil fuels.This will in turn reduce the amount of CO2emissions for a given power output.Using US practice for efficiency calculations,then a move from a typical US plant running at 37%efficiency to a 760℃/38.5 MPa(1 400/5 580 psi)plant running at 48%efficiency would reduce CO2emissions by 170kg/MW.hr or 25%.     

Aerodynamic performance effects of leading-edge geometry in gas-turbine blades

The purpose of this paper is to illustrate the advantages of the direct surface-curvature distribution blade-design method, originally proposed by Korakianitis, for the leading-edge design of turbine blades, and by extension for other types of airfoil shapes. The leading edge shape is critical in the blade design process, and it is quite difficult to completely control with inverse, semi-inverse or other direct-design methods. The blade-design method is briefly reviewed, and then the effort is concentrated on smoothly blending the leading edge shape (circle or ellipse, etc.) with the main part of the blade surface, in a manner that avoids leading-edge flow-disturbance and flow-separation regions. Specifically in the leading edge region we return to the second-order (parabolic) construction line coupled with a revised smoothing equation between the leading-edge shape and the main part of the blade. The Hodson–Dominy blade has been used as an example to show the ability of this blade-design method to remove leading-edge separation bubbles in gas turbine blades and other airfoil shapes that have very sharp changes in curvature near the leading edge. An additional gas turbine blade example has been used to illustrate the ability of this method to design leading edge shapes that avoid leading-edge separation bubbles at off-design conditions. This gas turbine blade example has inlet flow angle 0°, outlet flow angle −64.3°, and tangential lift coefficient 1.045, in a region of parameters where the leading edge shape is critical for the overall blade performance. Computed results at incidences of −10°,   −5°,   +5°,   +10° are used to illustrate the complete removal of leading edge flow-disturbance regions, thus minimizing the possibility of leading-edge separation bubbles, while concurrently minimizing the stagnation pressure drop from inlet to outlet. These results using two difficult example cases of leading edge geometries illustrate the superiority and utility of this blade-design method when compared with other direct or inverse blade-design methods.     

Hydrogen production by steam-gasification of carbonaceous materials using concentrated solar energy – V. Reactor modeling,optimization, and scale-up

A chemical reactor for the steam-gasification of carbonaceous particles (e.g. coal, coke) is considered for using concentrated solar radiation as the energy source of high-temperature process heat. A two-phase reactor model that couples radiative, convective, and conductive heat transfer to the chemical kinetics is applied to optimize the reactor geometrical configuration and operational parameters (feedstock's initial particle size, feeding rates, and solar power input) for maximum reaction extent and solar-to-chemical energy conversion efficiency of a 5 kW prototype reactor and its scale-up to 300 kW. For the 300 kW reactor, complete reaction extent is predicted for an initial feedstock particle size up to 35 μm at residence times of less than 10 s and peak temperatures of 1818 K, yielding high-quality syngas with a calorific content that has been solar-upgraded by 19% over that of the petcoke gasified.     

Contents in Volume 23,2014

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汽轮机数字电液调节系统挂闸异常的技术完善

分析了200MW汽轮机数字电液调节系统在运行中存在的挂闸异常问题,采取了相应的技术处理措施,且运行实践效果良好。     

新型高压共轨ECU升压模块的数字化开发与优化

为了提高喷油器电磁阀的响应速率,提出了一种基于CPLD(复杂可编程逻辑器件)应用于高压共轨ECU的数字升压模块。鉴于该升压电路结构参数多,其升压电压的恢复响应要求高等特征,基于Pspice建立了升压电路的仿真模型,研究了不同电路参数下升压模块的输出特性,全面优化了该升压模块的性能。结果显示,该升压模块的最大转换效率可以达90%以上。在柴油发动机上对ECU的试验表明,升压电压最大波动不超过10%,其恢复时间仅为1.3ms,功率管最大温升仅为41℃,满足整机运行范围内ECU的需求。     

Trace metal chemistry and silicification of microorganisms in geothermal sinter, Taupo Volcanic Zone, New Zealand

As part of a pilot study investigating the role of microorganisms in the immobilisation of As, Sb, B, Tl and Hg, the inorganic geochemistry of seven different active sinter deposits and their contact fluids were characterised. A comprehensive series of sequential extractions for a suite of trace elements was carried out on siliceous sinter and a mixed silica-carbonate sinter. The extractions showed whether metals were loosely exchangeable or bound to carbonate, oxide, organic or crystalline fractions. Hyperthermophilic microbial communities associated with sinters deposited from high temperature (92–94°C) fluids at a variety of geothermal sources were investigated using SEM. The rapidity and style of silicification of the hyperthermophiles can be correlated with the dissolved silica content of the fluid. Although high concentrations of Hg and Tl were found associated with the organic fraction of the sinters, there was no evidence to suggest that any of the heavy metals were associated preferentially with the hyperthermophiles at the high temperature (92–94°C) ends of the terrestrial thermal spring ecosystems studied.     

Assessment methods of material ageing using Sdobyrev''s creep rupture model

The physical aspects of the activation energy, in higher and high temperatures, of the metal creep process were examined. The research results of creep-rupture in a uniaxial stress state and the criterion of creep-rupture in biaxial stress states, at two temperatures, are then presented. For these studies creep-rupture, taking case iron as an example the energy and pseudoenergy activation was determined. For complex stress states the criterion of creep-rupture was taken to be Sdobyrev's, i.e. σ_red = σ₁ β + (1 − β)σ_i, where: σ₁-maximal principal stress, σ_i-stress intensity, β-material constant (at variable temperature β = β(T)). The methods of assessment of the material ageing grade are given in percentages of ageing of new material in the following mechanical properties: 1) creep strength in uniaxial stress state, 2) activation energy in uniaxial stress state, 3) criterion creep strength in complex stress states, 4) activation pseudoenergy in complex stress states. The methods 1) and 3) are the relatively simplest because they result from experimental investigations only at nominal temperature of the structure work, however, for methods 2) and 4) it is necessary to perform the experimental investigations at least at two temperatures.     

Production of hydrogen from sewage biosolids in a continuously fed bioreactor: Effect of hydraulic retention time and sparging

Hydrogen was produced from primary sewage biosolids via mesophilic anaerobic fermentation in a continuously fed bioreactor. Prior to fermentation the sewage biosolids were heated to 70 °C for 1 h to inactivate methanogens and during fermentation a cellulose degrading enzyme was added to improve substrate availability. Hydraulic retention times (HRT) of 18, 24, 36 and 48 h were evaluated for the duration of hydrogen production. Without sparging a hydraulic retention time of 24 h resulted in the longest period of hydrogen production (3 days), during which a hydrogen yield of 21.9 L H₂ kg⁻¹ VS added to the bioreactor was achieved. Methods of preventing the decline of hydrogen production during continuous fermentation were evaluated. Of the techniques evaluated using nitrogen gas to sparge the bioreactor contents proved to be more effective than flushing just the headspace of the bioreactor. Sparging at 0.06 L L min⁻¹ successfully prevented a decline in hydrogen production and resulted in a yield of 27.0  L H₂ kg⁻¹ VS added, over a period of greater than 12 days or 12 HRT. The use of sparging also delayed the build up of acetic acid in the bioreactor, suggesting that it serves to inhibit homoacetogenesis and thus maintain hydrogen production.