考虑LVRT能力的风电场联络线距离保护研究

具备低电压穿越(LVRT)能力的风电场能够在系统故障及电网电压跌落期间连续运行,因此,对具备LVRT能力的风电场联络线距离保护配置时,要综合考虑风电场LVRT时间。本文采用卸荷保护电路措施来提高永磁直驱风机(PMSG)的LVRT的能力,通过分析风电场LVRT与风机低电压保护动作时间配合关系,提出风电场联络线的距离保护时间配合的改进方案,最后仿真验证了提出方案的有效性和可行性。     

Electrochemical performance study of proton exchange membrane electrolyzer considering the effect of bubble coverage

Bubble dynamics are closely related to the electrochemical performance of a proton exchange membrane electrolyzer (PEMEC). However, tiny bubbles need to be clustered together to affect the electrochemical performance of PEMEC significantly. In this paper, the effect of microscopic bubbles on macroscopic electrochemical properties were assessed by bubble coverage. The bubble dynamics, two-phase flow, and electrochemical performance were captured under different conditions using a high-speed, microscopic visualization experimental system. The results show that various factors influence the two-phase flow pattern. At 60 °C, 1.5 A/cm² and 5 mL/min, the annular flow occupied 76.8% of the gas phase area, and when the water flow increased to 80 mL/min, the annular flow ratio decreased substantially to 2.7%. The two-phase flow of bubbles in the flow channel showed different flow patterns over time. Under the experimental conditions (60 °C, 20 mL/min, 0.8 A/cm²), the bubble flow pattern experienced the emergence of bubbles, bubble flow, segmental plug flow, annular flow, and final steady state with the occurrence times of 0.15 s, 1.5 s, 5.0 s, 10.5 s, and 21.2 s, respectively. The bubble coverage increased with current density and temperature, while it decreased with the increase of water velocity. In addition, the effects of temperature and water velocity on bubble coverage and PEMEC performance vary in principle. Specifically, higher temperature mainly improves the bubble coverage by increasing the electrochemical performance of PEMEC. In contrast, higher water velocity mainly improves the electrochemical performance of PEMEC by decreasing the bubble coverage. This study elucidates the relationship between microscopic bubbles and macroscopic electrochemical performance, contributing to a better understanding of the processes and principles of bubble effects on the electrochemical performance of PEMEC. The results may provide a theoretical basis and experimental data for operating condition optimization, operating efficiency improvement, multiphase flow study, gas diffusion layer structure, and flow field design of PEMEC.     

煤矸石还原酸性废水中Cr(Ⅵ)的机理分析

通过试验探讨了煤矸石与Cr(Ⅵ)反应的动力学行为以及作用机制。研究表明,煤矸石还原Cr(Ⅵ)的过程分为两个阶段:第一阶段为煤矸石中的菱铁矿和黄铁矿与氢离子作用生成Fe(Ⅱ)、S、H₂S,由于该阶段为固—液反应,反应速率与传质速率密切相关,在搅拌条件下反应速率常数为0.169 mg/(L·min),远大于静态条件下的反应速率常数0.048 mg/(L·min);第二阶段为Cr(Ⅵ)的还原,通过元素分析,结合红外和XRD表征,说明菱铁矿和黄铁矿中的铁和硫元素最终被Cr(Ⅵ)氧化成Fe（Ⅲ）和硫酸根,而Cr(Ⅵ)被还原成低毒性的Cr(Ⅲ)。菱铁矿和黄铁矿均是煤矸石常见成分,根据上述研究和分析,将煤矸石用于含Cr(Ⅵ)废水的处理,不仅提高了煤矸石的综合利用效率,同时为处理含Cr(Ⅵ)废水提供了低廉高效的方法。      

考虑多变量因素影响的光伏PEM制氢系统建模与分析

针对复杂工况对光伏制氢系统性能产生不确定性的影响,提出考虑多变量因素影响的光伏制氢系统模型,探索辐照度、温度、膜厚、压力等因素对光伏质子交换膜（PEM）制氢系统的影响。系统首先建立考虑辐照度、温度、膜厚、压力等因素影响的光伏-质子交换膜电解槽-氢储罐的光伏制氢模型,之后对系统进行定量计算和定性分析,并依据实际光伏数据进行实验验证。结果表明,在额定功率范围内,太阳电池输出电流和功率随辐照度的增加而增大,随温度的升高而降低。质子交换膜电解槽电压随辐照度、膜厚、压力的增加而增大,随温度的升高而减小。太阳电池输出功率、质子交换膜电解槽电压的变化趋势与辐照度变化趋势具有一致性。最终计算得到太阳电池系统、质子交换膜电解槽系统和总系统效率分别为16.8%、72.2%和12.1%。     

Energy-based insight into characterization of shakedown behavior of fully weathered red mudstone

Weathered Red mudstone is widely distributed in Sichuan basin. The compacted weathered red mudstone has been used as subgrade fill materials of high-speed railway in southwestern of China. Dynamic responses of such materials under cyclic loading are critical to long-term stability of subgrade. Shakedown concept is widely employed in characterizing the permanent deformation behavior of soils. According to the evolution of axial strain (Werkmeister’s theory) or unit dissipated energy (Tao’s theory) with loading cycles, the behavior of unbound granular materials can be classified into three categories: plastic shakedown, plastic creep and incremental collapse. However, both theories are more suitable for the unbound granular materials with some limitations when used to separate the plastic creep and incremental collapse behavior. To overcome the limitations of the current theories, 26 cyclic triaxial tests were conducted on a saturated fully weathered red mudstone (SFWRM) to study the evolution of axial strain and unit dissipated energy during cyclic loading. A clear dependency of axial strain, axial strain rate on the unit dissipated energy level under various cyclic stress states were observed. A new criterion which is based on the responses of unit dissipated energy with cyclic stress ratio, was proposed to determine the limit between plastic creep and incremental collapse. Comparing with Werkmeister’s criterion and Tao’s criterion, the proposed criterion showed a better performance in identifying the incremental collapse behavior of the SFWRM.     

电液伺服泵控系统柔性传动比理论研究

电液伺服泵控系统具有高效节能、高功重比和环境友好等技术优点,但受诸多非线性因素的影响,系统传动特性表现出极强的非线性。通过深入研究电液伺服泵控系统的传动特性,提出柔性传动比理论,建立电液伺服泵控系统的数学模型,得到伺服电机-定量泵-液压缸之间的柔性传动比规律。对柔性传动比应用进行研究,提出基于广义排量的压力控制策略。搭建系统柔性传动比仿真与试验平台,对柔性传动比理论应用进行仿真和试验研究。研究结果表明,柔性传动比理论的应用对压力控制具有良好的控制效果,将为电液伺服泵控系统的工程推广与应用奠定良好的基础。     

一种基于局部变换处理的干扰抵消后置处理方法

针对基于阻塞矩阵方式抵消干扰产生的探测影区问题,提出了一种基于局部变换处理的干扰抵消后置处理方法。首先根据干扰抵消方位对接收阵拾取数据进行线性变换处理,合成一组新数据;其次采用空间谱合成方法对新数据进行变换处理,得到空间各方位对应空间谱;然后采用局部变换处理方法,提取空间谱基底变化量;最后采用空间谱基底变化量对空间谱进行均衡处理,降低探测影区。数值仿真和数据处理均表明,该方法通过对干扰抵消后空间谱进行局部非线性均衡处理,减小了空间谱基底变化量,将探测影区缩小到了3°以内,改善了基于阻塞矩阵方式干扰抵消方法。     

《纺织机械概论》课程思政的探讨

《纺织机械概论》课程作为纺织工程专业机械方向的专业基础课程,专业性较强,课程思政引入结合效果并不理想.通过对《纺织机械概论》课程资源的梳理,摸排课程思政切入点和可行的方式,希望对纺织专业的课程思政建设建设提供参考.     

K层层间单向耦合星形网络的同步能力分析

复杂网络是网络科学的一个研究热点.复杂网络同步能力的研究重点正从单层网络同步能力转向更加接近实际网络的多层有向网络同步能力.文章基于主稳定函数方法,深入研究4层层间单向耦合星形网络的特征值谱及其同步能力,给出了4层层间单向耦合星形网络的超拉普拉斯矩阵的特征值谱;在同步域有界和无界2种情况下,分析了K层层间单向耦合星形网...     

Experimental study on the mechanical properties and consolidation mechanism of microbial grouted backfill

Backfill mining technology is the practice of returning waste materials underground for both disposal and geotechnical stability, however, a challenge with current technologies is that they commonly require cement-based binders which have a relatively high environmental impact. Finding alternatives to cement-based binders can improve environmental performance and this paper proposes microbial grouted backfill (MGB) as a potential solution. In this paper, the effects of the cementation solution concentration (CSC), volume ratio of bacterial solution to cementation solution (VRBC), particle sizes of the aggregates, and the number of grouting batches on the mechanical properties of MGB are studied. The experimental results show that MGB strength increased, up to a peak value, as CSC was increased, before decreasing as CSC was increased further. The results also show that MGB strength increased, up to a peak value, as VRBC decreased, before decreasing as the VRBC was decreased further. The peak strength was achieved at a CSC of 2 mol/L and a VRBC of 1:9. The strength of the MGB also increased as the number of grouting batches increased. Graded MGB samples showed the highest UCS, 25.12 MPa, at particle sizes of 0.2 to 0.8 mm, while full (non-graded) MGB samples displayed mean UCS values ranging from 1.56 MPa when the maximum particle size was 0.2 mm, up to 13 MPa when the maximum particle size was 1.2 mm. MGB samples are consolidated by the calcium carbonate that is precipitated during microbial metabolism, and the strength of MGB increases linearly as calcium carbonate content increases. The calcium carbonate minerals produced in MGB materials are primarily calcite, with secondary amounts of vaterite.