基于Matlab的混凝土平面温度自应力差分解法

针对传统的混凝土温度应力计算方法存在的不足,采用基于Matlab的混凝土平面温度自应力的差分解法,对大体积混凝土平面温度自应力进行仿真计算,即依据混凝土热传导方程及其边界控制条件,在构建混凝土平面温度场求解模型的基础上,考虑温度自应力的计算模型,建立温度自应力的差分计算格式,利用Matlab的编程与可视化功能,对工程实例中的大体积混凝土温度自应力进行仿真计算,并与有限元计算结果进行比较。结果表明,该算法计算结果与有限元计算结果一致,精度可满足工程需要,且可对温度场及温度自应力进行可视化的实时输出,为大体积混凝土施工与仿真计算提供了参考。     

基于Matlab软件的混凝土湿度场差分算法

基于混凝土湿度扩散方程,建立混凝土内部与边界的差分格式,并利用Matlab软件的编程和可视化功能,对闸墩典型截面的湿度场进行仿真计算。结果表明,该算法可有效求解混凝土的湿度场,且可将其湿度场分布适时进行可视化输出,为同类问题提供了参考。     

差分算法在自由板温度应力场中的应用

针对有限元方法求解自由板温度应力存在计算模型复杂、工作量大等问题,以混凝土热传导方程为基础,推导出自由板温度场有限差分格式,并在温度场求解基础上,利用广义虎克定律和自由板特性,推导出自由板温度应力差分公式,并通过实例对自由板温度和应力进行求解。结果表明,差分算法求解自由板温度和应力场与有限元求解结果一致,且效率较高。     

基于人工蜂群算法的大体积混凝土温度场参数反演

针对传统混凝土热学参数反分析计算量大、计算效率不高等特点,将人工蜂群算法引入到混凝土温度场计算中,提出基于该算法的反分析法,通过室内二期通水冷却试验,对通水冷却过程中大体积混凝土试件的导温系数及表面散热系数进行反演分析,并利用反演参数结果进行温度场反馈分析。结果表明,人工蜂群算法在温度场参数反演中具有很好的适用性,有效地提高了温度场参数反演的效率。     

基于改进蚁群算法的混凝土坝热学参数反演

鉴于混凝土坝温度场仿真演算中通过试验得到的温度参数与实际参数相差较大,且传统温度场反分析算法计算量很大,计算效率低下,引进人工蚁群算法(ACA)并将其优化,利用优化后的算法对混凝土坝热学参数进行反分析,基于反演参数,用有限元方法对其温度场进行正演算,对比所得结果与监测数据真实值的差异,发现两者拟合程度较高,说明改进的ACA算法在大坝混凝土热力学参数反分析中具有较好的适应性。     

嵌固板温度应力场差分算法探讨

针对有限元方法求解嵌固板温度应力存在计算模型复杂、工作量大等问题,在一维差分算法的基础上,建立了温度场差分模型,利用广义虎克定律和嵌固板特性,推导出嵌固板温度应力差分模型,并通过实例对嵌固板温度和应力进行求解。结果表明,差分算法求解嵌固板温度应力场与有限元求解结果一致,且效率较高,可为类似工程提供参考。     

基于ANSYS的大体积混凝土温度应力 计算程序开发研究

通过对ANSYS有限元计算软件进行二次开发,实现了对大体积混凝土结构施工期与运行期温度场、应力场的仿真模拟。该计算程序可考虑实际工程中的各种荷载和边界条件,具有计算效率高、通用性好的特点。利用本程序对某碾压混凝土重力坝28号非溢流坝段的施工与运行过程进行了完整的数值仿真计算,计算结果表明本程序能很好地模拟大体积混凝土结构施工期和运行期的温度场和应力场     

基于ANSYS的冷却水与混凝土之间对流换热模拟方法

热流耦合算法计算含有冷却水管的大体积混凝土温度场时,无需在水管处细化网格,网格划分方便,且可精细模拟水温的沿程温升及水管附近混凝土温度场,但需逐对耦合流体单元的附加节点与同一位置的混凝土节点来模拟冷却水与混凝土之间的对流换热,比较麻烦。对此,特描述了热流耦合算法模拟冷却水与混凝土之间对流换热的本质,并提出了一种新的方法来模拟冷却水与混凝土之间的对流换热,即用nummrg,all命令代替耦合来模拟冷却水与混凝土之间的对流换热。实例应用结果表明,新方法与传统耦合方法的计算结果相差不超过2%,由此验证了新方法可行、正确,为热流耦合算法在实际工程中的应用提供了参考。     

基于热流耦合算法的含有冷却水管的大体积混凝土温度场仿真技术

针对采用等效算法求解含有冷却水管的大体积混凝土温度场时无法考虑水管中水温沿程变化、不能精细计算靠近水管处的混凝土温度场问题,特提出改进的热流耦合算法,并基于ANSYS软件中的solid70单元、fluid116单元、mass flow等子程序,构建了含有冷却水管的大体积混凝土热流耦合算法的单元选择、网格划分、自由度耦合、载荷施加等关键技术,并将其应用于锦屏一级拱坝#14坝段1~4仓含有冷却水管的大体积混凝土温度场仿真计算中。仿真结果表明,采用改进的热流耦合算法的计算值与实测值十分接近,从而验证了改进算法的可行性。     

考虑水管冷却及表面保温的闸墩施工期温度应力场仿真分析

鉴于施工期的混凝土内外温差及变形约束是闸墩产生温度裂缝的主要原因,基于温度应力场和水管冷却算法等基本理论,通过与施工现场的温度监测数据的对比分析,反演混凝土热学计算参数,利用三维有限元计算软件进行闸墩施工期考虑水管冷却的温度场及应力场仿真计算。结果表明,水管冷却温控效果良好,但混凝土表面因降温幅度较大而产生早期较大的拉应力,应进一步做好表面保温措施,降低混凝土内外温差。     

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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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.     

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.