工况变化对贯流式水轮机叶顶间隙流态的影响

贯流式水轮机是低水头水能资源开发的主力机型之一,而转轮叶片叶顶间隙流动特性是影响其空化、稳定性能的关键因素.基于数值模拟的方法,本文研究了工况变化引发转轮叶片叶顶间隙泄漏涡初生位置、形态变化的机理,分析了间隙泄漏涡形态改变对水轮机空化、稳定性的影响规律.主要结果表明:工况变化必然伴随导叶开度变化,导叶开度的改变使得转轮...     

基于多模型随机组合的水文集合预报方法研究

准确、可靠的水文预报是水资源开发利用的基础.集合预报以概率或区间的形式表征预报的不确定性,是未来水文预报研究的重点发展方向.本文提出了一种基于多模型随机组合的水文集合预报方法.首先通过加权形式将多种预报模型进行组合;再采用多目标优化算法率定各成员模型权重的上、下限;最后在优化的上、下限内随机生成权重以构建集合预报.以汉...     

基于二维波束聚焦算法的低速冲击监测研究

冲击损伤监测是结构健康监测的主要研究内容之一,为提高冲击定位的精度以及传感器的利用效率,提出了一种基于十字阵列型传感器布置方法的二维波束聚焦冲击定位算法,在高精度的前提下有效减少了传统定位方法所需布置的传感器数量.通过十字阵列型的压电传感器布置方法,可以将远场的定位精度大大提高,对于内场的盲区采用四点圆弧定位算法进行冲...     

混合双轴控制的太阳自动跟踪系统研究

文中主要针对斯特林碟架,设计了以ARM处理器和可编程逻辑控制器(PLC)为控制核心,视日运行轨迹跟踪与图像处理相结合的混合跟踪方式实现太阳自动跟踪.首先,利用太阳位置算法(SPA)定位太阳位置,确保太阳光斑在摄像头视场范围内;其次,使用CMOS图像传感器采集太阳图像,通过ARM处理器处理图像获取太阳跟踪角度误差;最后利...     

Co-reinforcing of ZrB2–SiC ceramics with optimized ZrC to Cf ratio

Characteristics of ZrB₂–SiC ultrahigh temperature ceramic matrix composites (UHTCMCs) reinforced with ZrC and carbon fiber (C_f) were investigated in this article. Spark plasma sintering (SPS) process was utilized to fabricate the samples at 1800 °C for 5 min under 30 MPa punch pressure and vacuumed atmosphere. In all samples, the volume ratio of ZrB₂: SiC was equal to 4:1, and the summation of ZrC and C_f reinforcements was 7.5 vol% with different ZrC: C_f ratios. Field emission scanning electron microscopy (FE-SEM), energy dispersive spectroscopy (EDS), densitometry, flexural strength, and hardness measurements were employed for characterization of the prepared samples. Microstructural inspection revealed the formation of SiC sheath around the carbon fibers due to several reactions in the surface SiO₂ layers existed on the SiC particles. Optimal flexural strength (628.4 MPa) and hardness (20.8 GPa) values were achieved for the sample co-reinforced with 6.5 vol% ZrC and 1 vol% C_f, with a relative density of 97.7%.     

Structural and dielectric properties of B2O3/Li2O-added Ba0.6Sr0.4TiO3 multilayer ceramics for tunable devices

B₂O₃ and Li₂O (B/L)-added Ba_0.6Sr_0.4TiO₃ (BST) ceramics sintered at 940 °C exhibited a dense microstructure with large grains. The amount of B/L additive was 4.5 wt% with a B/L ratio of 1.5:1. The B/L-related liquid phase assisted the densification of the BST ceramics. This BST ceramic displayed a large dielectric constant (ε_r) of 2834 with a low dielectric loss (tan δ) of 0.21% at 1.0 MHz. It also displayed a large tunability (28.2% at 10 kV/cm) and a high figure of merit (FOM) of 134. BST thick-films were synthesized using the tape casting method. The thick-film densified at 940 °C exhibited a large tunability of 18.7% at 10.0 kV/cm and an FOM of 208; these are higher than the values reported in the literature. Multilayer ceramics (MLCs) consisting of five layers of 40-μm-thick BST thick-films and Ag electrodes were also fabricated at 940 °C. No diffusion occurred between the Ag electrode and BST thick-film. A large tunability of 67.6% at 52 kV/cm with a high FOM of 294 was obtained from this MLC. This verified that the B/L-added BST ceramic is effective for application in tunable multilayer devices.     

Ecology dynamics model on Chinese apparel industry cluster

To explore the crucial driving forces and dynamics of the Chinese apparel industry cluster, the authors analysed current situations, characteristics and the dilemma in the Chinese apparel industry based on surveys conducted in the Yangtze River Delta. This study classified the factors impacting apparel industry cluster development into necessary conditions and evolutionary factors according to logistic differential equation, and proposed a dynamics model framework of apparel industry cluster with positive and negative feedback mechanism. The authors believe that the Chinese apparel industry cluster is an ecology system involving outsourcing, specialisation agglomerating, competition, resource complementary, etc. and has a quick response ability of adapting to environment.     

服装流行色的季节差异及关联性研究

为揭示服装流行色的季节差异及其变化规律,以2012-2019年中国服装流行色定案为研究对象,依据中国色彩标准体系(CNCS)对色彩进行量化,采用统计分析与灰色关联分析,探究季节服装流行色的波动规律与色彩特征。结果表明:服装流行色呈现一定的季节差异,不同色彩存在不同的季节模式,即春夏以高明度、高纯度和暖色系为主,秋冬则会增大低/中明度、低/中纯度和冷色系色彩的使用比例;秋冬服装流行色会受到春夏流行色的影响,但不同色彩的关联度存在差异;秋冬服装流行色的波动较大,春夏服装流行色的波动则比较平缓。     

助染剂处理芳纶纤维的阳离子染色性能探究

通过对芳纶1414纤维助染剂预处理,进行阳离子染料染色实验,探讨染色工艺参数对芳纶1414纤维染色性能的影响。实验表明,染色最佳工艺为染料用量5%(omf),助染剂用量2%,氯化钠用量15g/L,染浴pH为4.5,染色温度110℃,染色保温时间60min;染色后耐皂洗色牢度可达到4～5级。     

In situ hydrothermal synthesis of Y-TiO2/graphene heterojunctions with improved visible-light-driven photocatalytic properties

The Y-TiO₂/graphene heterojunctions were prepared using a facile one-pot hydrothermal method. The SEM and TEM images showed that titanium dioxide and flaky graphene were tightly bound together, and XPS indicated that yttrium was doped uniformly into the complex. The crystal phase of titanium dioxide in Y-TiO₂/graphene composite was anatase, and the yttrium doping caused distortion of the titanium dioxide lattice, resulting in a new valence type and more defects. An appropriate amount of yttrium doping and graphene modification significantly improved the separation of photogenerated electron-hole pairs. In the degradation of rhodamine B, the co-modification of yttrium and graphene effectively improved the photocatalytic activity under visible and UV–vis light irradiation. With the amount of yttrium increasing, the photocatalytic activity of the Y-TiO₂/graphene complex first increased and reached the highest level of 40% and 63% for visible and ultraviolet-visible light, respectively, when the ratio of yttrium was increased to 1.0%. The enhancement of photocatalytic activity can be explained by the presence of yttrium ions increased the visible light absorption of titanium dioxide. Besides, the synergistic effect between yttrium ions and graphene effectively improved the separation rate of photoinduced electron-hole pairs.