考虑临界状态的堆石料广义塑性本构模型

基于大型静力三轴剪切试验结果,构造了考虑颗粒破碎的塑性模量表达式和考虑临界状态的剪胀方程,建立了适用于堆石料的广义塑性本构模型,并利用本构模型对堆石料三轴试验进行预测。结果表明,考虑和不考虑临界状态的本构模型均能较好地模拟堆石料在高围压下的剪缩性、在低围压下的剪胀性以及由于颗粒破碎引起峰值和剪胀应力比的非线性特性;考虑临界状态的本构模型能模拟应力——应变曲线逐渐逼近临界状态的规律,但其对三轴试验的预测精度略低于不考虑临界状态本构模型。     

广义塑性模型在海洋砂土中的适用性研究

为研究广义塑性模型在海洋砂土中的适应性,采用静、动三轴仪对海洋砂土进行了固结排水剪切及固结不排水循环剪切试验,根据试验结果拟合出砂土的广义塑性模型参数,并利用此参数对动模量和阻尼比试验进行了数值模拟,比较了试验结果与模型拟合结果的差异。结果表明,计算结果与试验测定的动模量、阻尼比与动应变的变化规律一致,该模型能很好地反映砂土单调加载的应力－应变特性及小应变阶段的循环加载条件下的变形特性。     

土的超固结和结构性本构模型评述

针对以剑桥模型为代表的常规弹塑性本构模型不能反映土的超固结和结构性的缺陷,对前人研究的本构模型进行了分类,总结和评价了土的超固结和结构性弹塑性本构模型,指出了模型的不足和深入研究的重点,并探讨了建立能同时反映土的超固结和结构性本构模型的重要性,提出了进一步研究的建议。     

那兰水电站面板堆石坝变形反馈分析

合理确定覆盖层和坝体的本构模型参数对正确预测覆盖层上面板坝应力应变特性十分重要.结合那兰水电站面板堆石坝变形观测资料及覆盖层大型载荷试验结果,采用“南水”双屈服面弹塑性模型反馈分析了坝体和覆盖层的本构模型参数,并采用反馈所得参数进一步分析了坝体的应力变形分布情况.结果表明,采用反馈分析参数计算所得的坝体变形与相应的实测值吻合较好.     

广义塑性模型在面板堆石坝静力计算中的应用

为了探讨广义塑性模型在土石坝仿真分析中的适用性,分别采用广义塑性模型和邓肯E-B模型对卡基娃堆石坝进行三维有限元静力计算,并结合现场监测资料,对比分析了不同本构模型下堆石和面板应力变形的差异。结果表明,两种模型计算的堆石应力变形规律相似,广义塑性模型计算的水平位移和沉降远小于邓肯E-B模型,更符合实际观测资料;第一主应力比较接近,第三主应力相差较大;竣工时面板变形规律基本一致,蓄水期时面板坝轴线方向位移分布差别较大,邓肯E-B模型计算的面板挠度大于广义塑性模型。与广义塑性模型相比,邓肯E-B模型计算的面板压应力偏大、拉应力区域较大。     

超固结对防渗墙与高塑性粘土接触结构渗透性的影响

试验中概化了高塑性粘土保护层与混凝土防渗墙之间的接触冲刷过程,模拟了心墙与混凝土防渗墙连接部位过渡区粘土的应力状态和渗流状态,对比了超固结土体与普通土体的渗透性。结果表明,超固结土体在短时间内渗透性明显下降,下降的程度与土体所处的工作应力状态有关,且随时间增长,超固结土渗透性有逐渐恢复的趋势,为高塑性粘土经不同应力历史后的工作状态预测提供了依据。     

地基液化条件下沉箱码头变形非线性数值分析

针对液化土体大变形易引起沉箱码头破坏问题,基于有效应力分析法,采用Flac3D内嵌的Byrne本构关系为砂土液化模型,对1995年日本阪神地震中沉箱码头进行完全非线性有限差分数值模拟,分别从码头残余变形、超孔压比、应力应变等方面探讨沉箱码头地基液化特性和破坏机理。结果表明,该模型能较好地模拟可液化土体的动力特性,数值计算与震害调查结果较吻合,与置换砂土液化相比,回填砂土液化对沉箱破坏影响更大。     

超高心墙堆石坝长期运行应力变形研究

鉴于超高心墙堆石坝的长期变形规律对其正常运行维护具有重要意义,基于广义塑性模型,综合考虑坝料流变和湿化特性,采用三维固结有限元法对300m级超高心墙堆石坝进行变形和应力分析,分别讨论了循环水荷载、坝料流变及湿化特性对大坝长期变形的影响。结果表明,三维固结有限元计算得到的坝体变形满足安全要求,符合土石坝变形基本规律;统一广义塑性模型可反映坝体心墙在循环加、卸载作用下的塑性变形累积现象,流变对超高心墙堆石坝的长期变形有重要影响;大坝长期运行过程中,上游坝壳的湿化特性所引起的大幅湿陷变形是后期沉降的主要原因,同时会导致坝体向上游倾斜;竣工期大坝心墙内存在一定的孔隙水压力,水库蓄水运行后,随着大坝变形趋于稳定,坝体应力分布亦趋于稳定状态。     

考虑饱和度影响的红壤土抗剪强度模型及应用

鉴于降雨入渗过程中土体饱和度变化对库区边坡稳定性的影响,基于Bishop非饱和土抗剪强度理论和van Genuchten土水特征曲线模型,建立了直接考虑饱和度影响的多参数土体抗剪强度理论模型,并采用三峡库区红壤土设计了土水特征曲线试验和三轴剪切试验,获得了基质吸力和抗剪强度随饱和度变化的试验结果,进而验证了模型的合理性。结果表明,模型预测值与试验实测值的吻合度较好,建立的模型能较好地预测三峡库区红壤土的抗剪强度。进一步分析可知,红壤土抗剪强度指标——粘聚力和内摩擦角均随饱和度的增加呈非线性递减;在净总应力一定的情况下,红壤土抗剪强度随饱和度的增加呈对数关系递减。     

土体静止侧压力系数定义及其确定方法综述

在比较总应力法、有效应力法、有效应力增量法的静止土侧压力（K0）系数定义差异基础上,简述了影响K0系数的主要影响因素（如物理力学性质、应力历史、土体结构、土样受扰动程度、孔隙水压力、土体固结程度）的研究现状,综述了室内试验、原位测试试验、经验公式、本构模型、数值仿真试验确定K0系数的方法的研究进展,可为未来K0系数的深入研究提供借鉴。     

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.