混凝土重力坝纵缝研究现状和发展趋势

本文在分析混凝土重力坝纵缝应用和研究现状的基础上,比较了纵缝各种处理措施的优缺点,探讨了其在实践中的应用,指出了混凝土重力坝纵缝研究方面的不足之处,指出了混凝土重力坝纵缝研究的方向,及其发展趋势。     

重力储能技术研究进展

储能技术主要是指电能的储存,是智能电网的重要环节。当前应用最广泛的储能系统为抽水储能,但其选址困难、对环境影响较大、对水资源依赖严重。重力储能作为一种新型的储能技术,以重物为储能媒介,原理简单且形式多样,能够充分发挥不同的地理优势进行储能。相对于传统储能技术,重力储能技术具有非常明显的优势。根据山地重力储能、悬重式重力储能、塔吊式重力储能、铁轨重力储能和重力储能式飞机等5种形式的重力储能技术,对现阶段重力储能技术的研究进展进行了综述。结合重力储能技术的原理、特点以及我国储能领域的发展方向和需求,对重力储能技术的应用前景进行了分析并提出建议。研究内容和提出的建议可以为我国重力储能技术的理论研究和发展应用提供参考。     

太平湾大坝过渡区及左岸挡水坝段水平变形差分析

针对低温季节太平湾大坝过渡区及左岸挡水坝段出现的变形差问题,以实测位移量为基础,结合坝体结构布置和运行环境等展开研究,初步认为随着挡水坝高度向左岸降低,静水压力逐渐减弱和坝体温度梯度分布发生改变是坝体产生相异变形的两个主要影响因素,但目前坝体尚处于弹性变形范围。该研究成果不仅对指导大坝安全运行具有积极意义,还可为今后进一步深入研究提供思路和技术借鉴。     

基于小波变换的某重力拱坝背水坡转异裂缝序列的分析

裂缝转异诊断对分析大坝安全稳定运行有重要意义。将小波变换应用于大坝裂缝转异分析中,并结合某重力拱坝背水坡裂缝X18-1的实测数据,分别从小波系数图的过零点和极值点、多尺度下模极大值线及奇异性变化角度讨论其与裂缝转异时刻的关系,最终综合判断出裂缝的转异时刻。分析结果表明,小波系数图、模极大值线和奇异性均可反映裂缝的转异,但各自独立的诊断结果不完全相同,综合分析可准确判定裂缝的转异时刻,为裂缝转异诊断提供了新思路。     

g‐Jitter–Induced Electrothermoconvection in a Dielectric Fluid Saturated Porous Layer

This paper presents linear and nonlinear stability analyses of thermal convection in a dielectric fluid saturated sparsely packed porous layer subject to the combined effect of time‐periodic gravity modulation (GM) and an AC electric field. In the domain of linear theory, the critical stability parameters are computed by the regular perturbation method in the form of a perturbation series in powers of frequency of modulation. The local nonlinear theory based on the truncated Fourier series method gives information on convection amplitudes and heat transfer. The principle of the exchange of stabilities is found to be valid and subcritical instability is ruled out. Based on the governing linear autonomous system, several qualitative results on stability are discussed. The sensitive dependence of the solution of a Lorenz system of electrothermal convection subject to the choice of initial conditions points to the possibility of chaos. Low‐frequency g‐jitter is found to have a significant stabilizing influence, which is in turn diminished by an imposed AC electric field. The role of sparseness of the porous layer, viscosity ratio, and normalized porosity on the stability criterion and on heat transport is determined.     

Growth of microalgae using CO2 enriched air for biodiesel production in supercritical CO2

The optimum conditions for lipids productivity and CO₂ fixation of two freshwater strains, namely Chlorella sp. and Pseudochlorococcum sp. and a marine strain; namely Nannochlorpsis sp. have been determined in this work. The species were grown autotrophically under aeration with different CO₂ concentrations, ranging from 0.04 to 2% (v/v). The growth was tested in nitrogen sufficient and deficient media at different salinities (0.49–680 mM) and temperatures of 27 and 31 °C. The optimum CO₂ enrichment was found to be 1% (v/v) in both media. Nitrogen starvation resulted in an increase in lipid contents, but at lower growth rate, which resulted in a lower overall lipid productivity. The experimental data were used to determine the kinetic parameters of Haldane model. The Chlorella sp. grew well at salinity levels of up to 460 mM. The highest CO₂ biofixation rate was observed when Chlorella sp. was grown at 27 °C in seawater (230 mM NaCl).Lipids were extracted from harvested marine strain, Nannochlorpsis sp., and enzymatically transesterified to produce biodiesel in supercritical CO₂ (SC–CO₂) medium. It was found that the conversion of biodiesel produced from microalgae lipids was 35% higher than that achieved using lamb fat in a similar system.     

Co-evaporative multi-component fuel design for in-cylinder PLIF measurement and application in gasoline direct injection research

For in-cylinder fuel mixture distribution measurement, a method for designing a multi-component fuel for planar laser-induced fluorescence (PLIF) experiments is developed based on thermal gravity analysis and vapor–liquid equilibrium calculation. The goal is to create fuel that has a volatility similar to real gasoline and good co-evaporation ratios (near 1.0) with tracers. Acetone, toluene, and trimethylbenzene are chosen as tracers for light, medium, and heavy fractions, respectively, and a five-component test fuel is developed. The test fuel is used to study the influence of components and temperature on co-evaporation ratios. Any variation in tracer or fuel component proportions affects all co-evaporation ratios, but a variation within 5% is considered acceptable. Results show that acetone presents the most significant influence on co-evaporation ratios. Temperature is also a key factor. Saturated vapor pressure and activity coefficient of the tracer and components in a fraction group affect co-evaporation optimization substantially, indicating that these values are a primary consideration in tracer selection. Finally, the test fuel is applied to an in-cylinder gasoline direct injection fuel mixture distribution measurement using PLIF. Differences between light, medium, and heavy fraction groups are studied under different strategies. Cycle-to-cycle variation analysis shows that the influence of absorption attenuation of the aromatic is distinct in a typical stratified strategy. In the area near the spark plug, cycle-to-cycle variation decreases as injection is delayed.     

振荡翼型气动及其噪声特性的数值研究

针对低雷诺数下翼型的非定常气动噪声特性,采用计算流体力学(CFD)与Lighthill声类比相结合的方法,分别对俯仰、平振以及俯仰与平振耦合运动的翼型进行了分析,通过自定义程序控制翼型的运动规律,并对其流场及诱导的声场特性进行了数值仿真.结果表明:随着折合频率、振幅的增加,翼型表面升力系数的峰值增大,非定常迟滞效应增强;耦合运动的相位差改变了气动力的响应特性;对于振荡翼型激发的噪声,低频下单极子声源占主要地位;随着声源频率的增大,远场声压指向性逐渐体现出偶极子声源的特性.     

Highly dispersed MnO nanoparticles supported on N-doped rGO as an efficient oxygen reduction electrocatalyst via high-temperature pyrolysis

Transition metal-based compounds, due to their excellent ORR catalytic performance under alkaline condition, have recently emerged as one of the most promising alternatives to noble metal-based ORR catalysts. It is worth noting that manganese oxide can take an unique advantage for decomposition of intermediate adsorption products H₂O₂ and can effectively reduce O₂ to OH⁻. However, most research has focused on MnO₂, while attention has rarely been paid to MnO catalysts. In addition, under high-temperature pyrolysis condition, MnO is the most stable manganese oxide but MnO nanoparticles easily agglomerate. Hence, it is very difficult to obtain well-dispersed and small-sized MnO nanoparticles. Herein, on the basis of pre-synthesizing uniformly distributed manganese complexes on the reduced graphene oxide (rGO), we innovatively prepare highly dispersed and small-sized MnO nanoparticles (~3.94 nm) via high-temperature pyrolysis, which are uniformly anchored on N-doped reduced graphene oxide (NrGO) as an efficient oxygen reduction electrocatalyst. The as-obtained MnO/NrGO (1050 °C) electrocatalyst achieves satisfactory onset potential (0.942 V) and half-wave potential (0.820 V) under alkaline condition. And the limiting current density is 4.17 mA cm⁻², which is very close to that of Pt/C (20 wt%, JM). Meanwhile, MnO/NrGO (1050 °C) catalyst presents superior longstanding durability and methanol resistance than Pt/C (JM). This work indicates that high-temperature pyrolysis can improve the purity of manganese oxide, simultaneously the defects of NrGO can reduce particle size of MnO nanoparticles, which are greatly beneficial to improve ORR performance. This work provides a new idea for research of MnO catalysts for ORR in the future.     

H2 production from the hydrolytic dehydrogenation of methylamine-borane catalyzed by sulfonated reduced graphene oxide-aided synthesis of ruthenium nanoparticles

A new catalyst was prepared using sulfonated reduced graphene oxide support with a large surface area containing ruthenium nanoparticles (Ru@rGO-SO₃H). The developed Ru@rGO-SO₃H catalyst was used in the hydrogen production process from the hydrolytic dehydrogenation of methylamine-borane (MeAB). Sulfonated reduced graphene oxide and the developed catalyst were characterized by Raman and FT-IR spectroscopies, ICP-OES, XRD, XPS, TEM, TEM-EDX, SEM and SEM-EDX techniques. The average particle size of Ru nanoparticles, which were homogeneously distributed on the sulfonated reduced graphene oxide surface, was found as 2.2 ± 0.2 nm. After analyzing the effect of nanocatalyst and substrate concentrations on the catalytic reaction, reactions were realized at different temperatures, the efficiency of the Ru@rGO-SO₃H nanocatalyst in initial turnover frequency (TOF_initial) and the activation parameters (E_a, ΔH^# and ΔS^#) were calculated. According to the data obtained, the TOF_initial value was calculated as 5300.86 h^{− 1} (88.35 min^{− 1}). E_a, ΔH^# and ΔS^# values were also calculated as 53.83 kJ/mol, 50.73 kJ/mol and −51.55 J/mol.K, respectively. Finally, when the reusability performance results of the catalyst are evaluated, it is found that the catalyst is very stable and retains its initial effectiveness to a great extent (>95%) after the 5th reuse.