基于剪应变增量的岩质边坡开挖卸荷深度判别

鉴于确定卸荷破坏程度和深度是岩质边坡稳定性分析首先要解决的问题,基于卸荷岩体力学基本理论,提出以岩体剪应变增量确定卸荷分区的方法,将开挖后的岩体划分为剪切变形区、开挖扰动区和应力不变区,并以锦屏水电站缆机平台边坡为例,对开挖过程进行数值模拟计算,通过与卸荷量百分比法的对比分析,验证以剪应变增量为标准判别卸荷深度的合理性,同时表明卸荷破坏程度和深度与岩体结构密切相关,存在结构面的岩体比完整岩体卸荷破坏深度更大。     

卸荷岩体尺寸效应数值模拟研究

针对边坡及地下工程中确定卸荷岩体变形和强度参数是掌握卸荷岩体的尺寸效应的关键,采用大型有限元软件ADINA构建了不同卸荷岩体尺度的数值仿真模型进行计算分析,并研究了卸荷岩体的变形和强度参数,与试验结果比较,获得了卸荷岩体尺寸效应的相关规律.     

卸荷损伤节理岩体加载条件下力学试验研究

岩体在卸荷作用下力学参数会发生劣化,导致承载力大幅减小。基于卸荷岩体力学理论,预制不同节理的砂岩岩样,在不同围压和卸荷量的条件下,对岩体的波速、应力应变特征、弹性模量、泊松比等参数进行试验测定。结果表明,节理岩体的波速与卸荷量关系呈阶段性变化。随着卸荷量的增加,波速衰减率明显增大;卸荷量越大,节理岩体的压密过程就越长;在卸荷量为0%和60%时,一定节理倾角的岩体,围压为5 MPa和10 MPa的弹性模量变化规律极为相似,并且弹性模量差值在10%以内,而围压为0 MPa和5 MPa的弹性模量相差在30%以上;在卸荷量和围压(都不为0)一定时,岩体的弹性模量与节理倾角呈类似正弦函数的变化规律;节理岩体的泊松比与卸荷量之间满足y=a+b(xc-1)关系。     

卸荷损伤节理岩体加载条件下力学试验研究

岩体在卸荷作用下力学参数会发生劣化，导致承载力大幅减小。基于卸荷岩体力学理论，预制不同节理的砂岩岩样，在不同围压和卸荷量的条件下，对岩体的波速、应力应变特征、弹性模量、泊松比等参数进行试验测定。结果表明，节理岩体的波速与卸荷量关系呈阶段性变化。随着卸荷量的增加，波速衰减率明显增大；卸荷量越大，节理岩体的压密过程就越长；在卸荷量为0%和60%时，一定节理倾角的岩体，围压为5 MPa和10 MPa的弹性模量变化规律极为相似，并且弹性模量差值在10%以内，而围压为0 MPa和5 MPa的弹性模量相差在30%以上；在卸荷量和围压（都不为0）一定时，岩体的弹性模量与节理倾角呈类似正弦函数的变化规律；节理岩体的泊松比与卸荷量之间满足y=a+b(xc-1)关系。     

地下厂房洞室群开挖卸荷力学特性及岩体质量评价

针对地下厂房洞室群开挖导致围岩卸荷回弹、岩体质量发生劣化问题,以金沙江某地下厂房洞室群为工程背景,基于卸荷岩体力学理论,采用有限差分法研究了洞室群各期开挖对洞周围岩卸荷力学特性的影响,并根据岩体开挖卸荷后的力学参数,采用岩体分类指数法对洞室群开挖后的岩体质量进行评价。结果表明,随洞室群的施工开挖,洞周围岩卸荷区不断发生演化,其卸荷区深度、范围逐渐增大;洞室群开挖完成后,三大洞室间均有程度不同的卸荷贯通区出现;洞周围岩部分卸荷区岩体质量由开挖前的Ⅱ类变为Ⅲ类。     

初始地应力对岩体边坡开挖松动的影响

为分析计算岩体边坡开挖卸荷时地应力的释放对边坡松动的影响,基于卸荷岩体力学理论,考虑了节理加载和卸荷时不同的本构关系,采用离散元法进行计算。结果表明,节理面的松动和岩块的松动共同构成了边坡岩体的松动,随着侧压力系数的增大,岩体向开挖临空面的松动位移将迅速增加,二者之间大致呈线性关系,且随着水平地应力的增大,最大松动位移出现的位置将向坡顶方向转移,整个坡面的卸荷回弹特征趋于明显,建议开挖边坡的走向尽可能与较大的水平应力方向平行。     

大型地下厂房围岩参数反演及位移监测分析

基于卸荷岩体力学分析方法建立了考虑岩体强、弱卸荷区地下洞室二维ADINA有限元模型,建立了BP神经网络模型,采用搜索算法确定了训练误差最小网络训练参数,将训练好的网络保存并用于仿真,利用工程监测的位移资料反演了岩体主要参数,参考卸荷岩体力学参数折减方法确定了卸荷区岩体参数,并将反演的参数代入有限元模型计算,计算位移值与监测位移值的对比结果表明,二者吻合较好,反演的参数可靠性较大.     

基于卸围压试验的砂岩卸荷本构模型及其应用

鉴于岩体本构模型受岩样应力路径、加卸载状态等因素的影响,为研究卸荷条件下砂岩的本构模型,采用RMT-150C岩石力学试验系统对宜昌砂岩岩样进行了升轴压峰前卸围压、轴压和围压等量减小两种应力路径下的卸围压试验。结果表明,卸荷应力路径不同时,卸荷变形阶段的应力—应变曲线形态有很大差异,但岩样变形模量随围压降低而劣化的规律一致;岩样卸荷破坏强度特征可用Hoek-Brown准则拟合。由此推导出增量形式的卸荷弹脆塑型本构模型,并以算例分析验证了该模型的正确性。     

基于Hoek Brown准则的砂岩卸荷强度损伤试验研究

为研究卸荷效应对岩体强度变化的影响,以三峡地区砂岩为样本,通过三轴加载和卸荷试验,运用Hoek Brown岩体破坏准则,探讨砂岩在不同卸荷速率条件下的强度损伤规律,并提出采用卸荷强度损伤因子来表征卸荷造成的强度变化。结果表明,卸荷条件下砂岩强度损伤明显,且与围压密切相关;随着围压的增大,卸荷效应造成的强度损伤量增大,最终趋于稳定。最后,基于工程设计最不利原则,修正了Hoek Brown卸荷强度准则公式,为工程应用提供了建议和参考。     

Hoek-Brown准则在卸荷岩体中的应用探析

针对采用传统加载条件下计算边坡开挖卸载过程的结果与实际相差较大,以清江隔河岩水电站厂房开挖高边坡为例,分别采用Hoek-Brown和Mohr-Coulumb准则模拟卸荷岩体的力学性质.结果表明,Hoek-Brown准则描述开挖卸荷岩体的破坏模式更准确.     

6110直喷式柴油机排放特性分析

测量了 6 110直喷式柴油机排气污染物 THC、CO、NOx 以及 PT的排放量 ,并分析了各种污染物的排放规律 ,对 THC排放与有效燃油消耗率 be、PT与 NOx 排放、SOF与 THC排放之间的关系做了研究。结果表明 6 110直喷式柴油机 THC和 CO的高排放区出现在小负荷工况 ;PT的高排放区出现在低负荷和高负荷工况 ;降低 NOx 排放的重点应放在小负荷工况和高速工况。柴油机的 be 与 THC排放随工况的变化表现出相似的变化规律。在较大的工况范围之内 ,PT和 NOx 排放之间存在折中关系 ;而在少数工况区域 ,PT和 NOx 排放之间存在一致性。 PT中的 DS与 NOx 排放之间始终存在着折中关系 ,而 SOF与 NOx 排放之间却存在着一定程度的一致性。在 THC的高排放工况 ,SOF也具有比较高的排放量     

整体煤气化联合循环_IGCC_系统变工况特性

作者分析了影响IGCC系统变工况的因素,基于通用性模块化建模思想,建立了IGCC系统变工况特性模型和开发出相应程序软件,通过大量的计算,得出三种调节方式下系统随负荷与大气温度变化时的变工况特性曲线簇,揭示了系统特性随主要变量变化关系。     

Off‐design performance and operation strategy of expansion process in compressed air energy systems

Compressed air energy storage (CAES) systems usually operate under off‐design conditions due to load fluctuations, environmental factors, and performance characteristics of the system. In order to optimize design and operation of CAES systems, it is significant to study off‐design performance. The expansion process plays an important role in the whole system. The main objective of this study is to explore the off‐design characteristics and optimization strategy of the multistage expansion process of CAES systems with thermal storage. Two kinds of off‐design operating modes, which are equal‐power‐ratio (EPR) operation and optimizing variable stator vane rotation angle (OVRA) operation, are proposed and compared for the first time. Correlation between key parameters such as total output power ratio, exergy efficiency, outlet air/water temperature versus mass flow rate ratio, and inlet pressure are revealed. Furthermore, optimal operation principles are obtained. The primary optimizing operation principle is to optimize the isentropic efficiencies of low‐pressure stages to improve the whole efficiency of expansion process. Lastly, the optimized regulating law for variable stator vane is expressed in a polynomial form.     

Combustion characteristics of mixture of anode off gas and LNG in reformer

Fuel processing system which converts hydrocarbon fuel into hydrogen rich gas (by stream reforming, partial oxidation, auto-thermal reforming) needs high temperature environment (600-1000 °C). Generally, anode off gas or mixture of anode off gas and LNG are used as input gas for a fuel reformer. In order to constitute efficient and low emission burner system for fuel reformer, it is necessary to elucidate the combustion and emission characteristics of fuel reformer burner. In this study, lean flat flame using the ceramic porous burner was analyzed numerically and experimentally. Burning velocity of anode off gas calculated by CHEMKIN simulation was 51.8 cm, which was faster than that of LNG having 40.63 cm/s at the stoichiometric ratio because of high composition of hydrogen in anode off gas. As composition of LNG in mixture of anode off gas + LNG is increased, the burning velocity decreases and in the other hand the adiabatic temperature increases. CO, NO_x were measured below 50 ppm in operating load range of the reformer. Blue flame pattern was found as stable flame region for design of fuel reformer and anode off gas flame was maintained in blue flame pattern at equivalence ratio 0.55-0.62 under 1-5 kW power range.     

某型舰用汽轮机末级_次末级叶片弯扭改型设计

应用S2流面正问题计算程序、S1流面计算程序和全三元Euler方程计算程序对某型舰用汽轮机低压末级、次末级静叶进行了弯扭改型设计,分析了舰用汽轮机变工况时叶栅流场的特点和采用弯扭叶片后机组性能的变化。结果表明：在低工况运行时,弯扭叶片抑帛了根部反动度随负荷降低而加速下降的趋势和顶部反动度随负荷降低而增大的趋势,提高了叶栅低工况运行时的抗分离能力,同时顶部漏泄损失也有所减小。     

A fast classification method of retired electric vehicle battery modules and their energy storage application in photovoltaic generation

The fading characteristics of 60 Ah decommissioned electric vehicle battery modules were assessed employing capacity calibration, electrochemical impedance spectroscopy, and voltage measurement of parallel bricks inside modules. The correlation between capacity and internal resistance or voltage was analyzed. Then, 10 consistent retired modules were packed and configured in a photovoltaic (PV) power station to verify the practicability of their photovoltaic energy storage application. The results show that the capacity attenuation of most retired modules is not severe in a pack while minor modules with state of health (SOH) less than 80% bring about the retirement of the whole pack as a result of the buckets effect. There is no obvious correlation between capacities of retired battery modules and their lithium-ion diffusion coefficients or charge transfer resistance or ohmic resistance, whose reliability is low as the consistency indexes of decommissioning battery modules. The maximum off load voltage difference ΔU_max at low state of charge (SOC) values has a good negative linear correlation with the capacity of retired modules, suggesting that the ΔU_max value at low SOC values can be considered as a characteristic index for fast classification of retired battery modules for large-scale second-life application. A PV power station equipped with retired battery energy storage system (RBESS) can maximize the photovoltaic self-utilization rate. It is an important way to reutilization of retired battery that RBESSs are configured with distributed PV power stations.     

A comparison of direct methanol fuel cell degradation under different modes of operation

The degradation test of direct methanol fuel cells (DMFCs) under on–off operation with variable load profile, known as a variable load on-off operation (VLOO) mode, was compared to continuous operation with a constant load, known as a constant load continuous operation (CLCO) mode. It was found that the performance loss in the VLOO mode was higher than that under the CLCO mode in terms of open circuit voltage drop (3.6 times higher) and the maximum power density reduction rate (1.23 times greater). Under both operation modes, the anode catalyst was deteriorated by Ru dissolution. However, the faster decay of cell performance under VLOO mode was mainly caused by the increase of cathode polarization due to higher methanol crossover and the decrease of Pt activity to the oxygen reduction reaction induced by Ru deposition.     

地震波倾斜入射对土石坝动力反应的影响

为研究土石坝在地震波倾斜入射时的动力反应,采用粘性人工边界及其对应的等效荷载地震动输入方法,对某典型土石坝有限元模型,分别计算了SV波和P波以不同角度、不同方向入射时的坝体动力反应,探讨了坝顶加速度放大系数随入射角度的变化规律。结果表明,随地震波入射角度的变化,坝顶加速度反应存在明显的差异,且在入射角度较大时表现得更加显著,说明行波效应的影响增强;此外,地震波自上、下游两侧入射时的结果截然不同。因此,在土石坝抗震设计及安全评价中,考虑地震波倾斜入射以及行波效应的影响是十分必要的。     

船用燃气轮机低压压气机气动布局规律研究

为缩短燃气轮机低压压气机的设计周期,获取一维设计中各关键设计参数分布规律,同时得到最优的一维设计参数选取方案,采用基于HARIKA算法的压气机一维设计与分析程序对某型船用低压压气机流量系数、载荷系数和反动度的轴向布局方法进行了研究并提炼了各参数分布的数学模型。其中,流量系数和载荷系数沿级分布为近似单峰值的三次多项式曲线,反动度分布为"二段式",通过改变流量系数和载荷系数的峰值点坐标和改变特定级反动度和反动度变化步长的方法,研究了不同布局方式对效率、喘振裕度以及压比的影响,最后结合优化算法得到了最优参数分布方案。结果发现:流量系数峰值位置在第6级,载荷系数在第5级或第6级时效率和喘振裕度性能较好;第四级反动度取值0.5～0.52时效率较高;相比载荷系数和反动度,流量系数对非设计工况性能影响更为显著,优化后的参数分布方案在各转速下喘振裕度均有所提高。     

Site‐specific variability of load extremes of offshore wind turbines exposed to hurricane risk and breaking waves

Much of the US offshore wind energy resource is located in shallow water off the Atlantic coast, which is exposed to both hurricanes and breaking waves. Current practice in offshore wind turbine (OWT) design is to realize a target structural reliability by amplifying loads using fixed load factors that do not vary with structural or site characteristics. Given that variability in both hurricane conditions and breaking waves is structure‐ and site‐specific, the structural reliability of OWTs may vary significantly from site to site if fixed load factors are used. To understand the implications of this situation, there is a need to compare the numerical values of fixed load factors with those calculated using methods that prescribe structure‐specific and site‐specific load amplification that reflects variability in long‐term conditions. In this paper, site‐specific load amplification is considered for four Atlantic coast locations and four water depths per location and then compared with fixed load factors commonly used in the design of OWTs. The study shows that decreasing water depth and increasing hurricane exposure tend to increase the required load amplification for consistent structural reliability. Another influential factor is the mean return period at which impact loads due to breaking waves begin to dominate the loading. Copyright © 2016 John Wiley & Sons, Ltd.