Effect of heat treatment and zircon addition on the properties of low-cement castables based on recycled alumina grog

In this investigation, low-cement castables were prepared using 70% alumina grog aggregates obtained from crushed alumina brick waste. The aggregates were thermally treated at 1550 °C for 3 h. Four types of low-cement castables were prepared with various types of aggregates (alumina grog with or without thermal treatment) and fillers (with or without zircon addition), and they were evaluated in terms of their physical, thermal, and chemical properties. Microstructural analysis via scanning electron microscopy (SEM) was performed on the castables before and after slag attack. Compared to the other fabricated castables, the thermally treated alumina grog castables with zircon showed better physical properties, such as a higher bulk density, cold crushing strength, and modulus of rupture and a lower apparent porosity and water absorption. In addition, they had a higher positive linear thermal expansion, refractoriness under load, permanent linear change, and hot modulus of rupture. The results of the SEM with energy dispersive X-ray analysis of the prepared castables confirmed that the mullite and anorthite phases were predominant when zircon was not added and the zircon–mullite phase additionally appeared upon the incorporation of zircon. A quantitative elemental analysis via X-ray fluorescence spectroscopy was employed to determine the composition of the castables. X-ray diffraction analysis showed that the alumina grog castables had a high mullite and low anorthite content, and the thermally treated alumina grog had a high anorthite, low mullite, and high zircon content. The improvement in the mechanical and thermo-mechanical properties of the castables with thermally treated alumina grog and added zircon can be attributed to the formation of the zircon–mullite phase with a low mullite phase content.     

Effects of external light load on posture and foot pressure distribution in young adults: A pilot study

Holding an asymmetrical load, like a rucksack, grocery bag, or travel backpack, is a part of daily and occupational activities. This pilot study was aimed to determine the effects of light, asymmetrical, handheld load on the body posture and foot pressure distribution in young adults. Thirteen young volunteers, free of any injury or pain, took part in the study (aged 21.53 ± 1.10 years). All the study participants were right-handed. An additional load (4 kg, placed in the rucksack) was asymmetrically held in each hand while standing still. For evaluation of the posture and foot pressure distribution, the investigation focused on three positions, i.e., no-load, a rucksack in the right hand, a rucksack in the left hand. We used a surface topography system and force platform for evaluation of the body posture and foot pressure examination, respectively. The results showed that the main changes in the body posture caused by an external load application manifested in trunk imbalance. The trunk was shifted in the direction opposite to the load. Trunk imbalance changes were statistically significant in all three comparisons (p = 0.001). Interestingly, changes in the rotations and lateral deviation seem to be dependent on the hand dominance. Greater foot pressure was observed on the loaded limb (p < 0.01), and highly significant differences were noted between the left and right foot in both loaded postures (p < 0.001). Further research needs to be done to check if lateralization is connected with body posture while holding an external load.     

基于跨临界CO2热泵的茶叶生产能源系统负荷削减潜力

乡村产业中的化石能源设备逐渐被电能技术替代，引起了乡村负荷波动增大、部分时段产生集中高负荷的问题。为了解决以上问题，将低品位清洁能源应用至乡村的茶叶生产中，针对烘茶全过程的工艺要求提出了跨临界CO₂热泵烘茶技术；并以某茶叶生产乡村为对象，对其代表台区的全年日用电量及产茶日负荷进行了分析，得出采用CO₂热泵烘茶后其负荷得到大幅度削减，整体可降低至原负荷的39.6%~46.8%，峰值负荷与平时负荷的比值由原本的13.6降至5.4~6.2。跨临界CO₂热泵应用至农产品生产中可有效缓解乡村供电压力。     

Large eddy simulation of a 660 MW utility boiler under variable load conditions

Large eddy simulation (LES) has become a promising tool for pulverized coal combustion with the development of computational fluid dynamics (CFD) technologies in recent years. LES can better capture the unsteady features and turbulent structures of coal jet flame than Reynolds averaged Navier Stokes (RANS). The coal-fired power plants in China are now required to be operated in a wide load range and quickly respond to the electric grid. The boiler performance of variable loads should be evaluated in terms of flow, heat transfer, and combustion processes. In this paper, LES was applied to simulate a 660 MW ultra-supercritical boiler under BMCR (boiler maximum continue rate), 75%THA-100, and 50%THA-100 conditions. The predicted gas velocities agree well with the thermal calculation and the temperature error is less than 130 K. The simulation results show that the operation load has significant effects on the boiler performance. It is also proved that LES can provide guidance for the design and operation of advanced coal-fired boilers.     

Dynamic load-altering attack detection based on adaptive fading Kalman filter in power systems

This paper presents an effective and feasible method for detecting dynamic load-altering attacks (D-LAAs) in a smart grid. First, a smart grid discrete system model is established in view of D-LAAs. Second, an adaptive fading Kalman filter (AFKF) is designed for estimating the state of the smart grid. The AFKF can completely filter out the Gaussian noise of the power system, and obtain a more accurate state change curve (including consideration of the attack). A Euclidean distance ratio detection algorithm based on the AFKF is proposed for detecting D-LAAs. Amplifying imperceptible D-LAAs through the new Euclidean distance ratio improves the D-LAA detection sensitivity, especially for very weak D-LAA attacks. Finally, the feasibility and effectiveness of the Euclidean distance ratio detection algorithm are verified based on simulations.     

Three-dimensional finite element analysis of geosynthetic-reinforced soil walls with turning corners

The paper presents in-depth three-dimensional finite element analyses investigating geosynthetic-reinforced soil walls with turning corners. Validation of the 3D numerical procedure was first performed via comparisons between the simulated and reported results of a benchmark physical modeling built at the Royal Military College of Canada. GRS walls with corners of 90°, 105°, 120°, 135°, 150°, and 180° were simulated adopting the National Concrete Masonry Association guidelines. The behaviors of the GRS walls with corners, including the lateral facing displacement, maximum reinforcement load, factor of safety, potential failure surface, vertical separation of facing blocks, and types of corners were carefully evaluated. Our comprehensive results show (i) minimum lateral displacement occurs at the corner; (ii) lower strength of reinforcements are required at the corner; (iii) higher corner angles lead to lower stability; (iv) potential failure surface forms earlier at the end walls; (v) deeper potential failure surfaces are found at the corners; (vi) larger numbers of vertical separations are found at walls with smaller corner angles. The paper highlighted the salient influence of the corners on the behaviors of GRS walls and indicated that a 3D analysis could reflect the required reinforcement length and the irregular formation of the potential failure surfaces.     

1 GWt PB-FHR负荷跟踪运行特性分析

为研究熔盐堆系统在商业应用中的价值，分析其是否满足电网负荷的变化需求和安全运行的能力，本文以1 GWt球床式氟盐冷却高温堆（PB-FHR）为研究对象，仿真计算其在负荷跟踪模式下的瞬态行为和运行特性。以RELAP5/MOD4.0程序为研究工具，并植入相关的熔盐物性与计算关系式，建立氟盐冷却高温堆的热工水力系统与功率控制系统的仿真模型，对典型负荷工况参数变化情况下控制系统的响应特性进行仿真分析。结果表明：该氟盐冷却高温堆系统在设计的控制逻辑的调控下，展示出良好的负荷跟踪运行能力，堆芯功率能迅速响应负荷变化，功率超调和温度超调小，反应堆的运行参数始终处于合理的运行范围内。     

Effect of element Ru on microstructure and creep behaviour of single crystal nickel-based superalloy

By means of creep property measurement and microstructure observation, the influence of element Ru on the microstructure and creep behaviour of single crystal nickel-based superalloy is investigated. The results show that the plate-like μ phase is precipitated along {111} plane of the Ru-free alloy during thermal exposure at 1080°C and creep at 980°C. And the precipitation of μ phase in the alloy with 6(wt)%Mo and 6(wt)%W may be restrained by adding 2% Ru element. Compared to Ru-free alloy, the creep life of the 2% Ru single crystal alloy at 980°C200 MPa increases form 123 h to 333h. Compared to the 2% Ru alloy, the precipitated plate-like μ phase in the Ru-free alloy may promote the initiation and propagation of cracks along the γ matrix up to fracture, which is thought to be the main reason of the alloy having a lower creep resistances and shorter lifetime.