Microsphere tensiometry to measure advancing and receding contact angles on individual particles

In this paper, a method to measure the advancing and receding contact angles on individual colloidal spheres is described. For this purpose, the microspheres were attached to atomic force microscope cantilevers. Then the distance to which the microsphere jumps into its equilibrium position at the air-liquid interface of a drop or an air bubble was measured. From these distances the contact angles were calculated. To test the method, experiments were done with silanized silica spheres (4.1 μm in diameter). From the experiments with drops, an advancing contact angle of 101 ± 4° was determined. A receding contact angle of 101 ± 2° was calculated from the jump-in distance into a bubble. Both experimental techniques gave the same contact angle. In contrast, on similarly prepared planar silica surfaces, a clear hysteresis was measured with the sessile drop method; contact angles of 104.5 ± 1° and 93.8 ± 1° were determined for the advancing and receding contact angles, respectively.     

Improvement in D-E Hysteresis Curve Squareness of PZT Thin Films—Effect of Oxygen Partial Pressure in High-Pressure Post-Annealing

A high-pressure annealing was applied to a post-annealing process for sol-gel derived PZT thin films. The squareness of D-E hysteresis curves changes depending on both total pressure and oxygen concentration. Moreover, the change follows the product of the total pressure and the oxygen concentration, which correspond to oxygen partial pressure P_O2. Where the P_O2 is higher than 0.03 MPa, few of the squareness of the hysteresis curve are excellent. The squareness of the hysteresis curves dramatically improve as the P_O2 decreases. Where the P_O2 is lower than 0.01 MPa, the squareness deteriorates slightly. These changes in the D-E hysteresis curves are thought to be explained by the generation of lead and oxygen vacancies as a function of the P_O2.     

光伏电源友好并网系统及其仿真研究

为提高主电网电能质量,对光伏电源并网逆变器及其控制方法进行研究和仿真。该逆变器采用DC/DC+DC/AC的双级结构,以三相瞬时无功理论为基础,将光伏并网逆变器与有源滤波器相结合,使得光伏电源不仅可以输出有功功率,还能进行无功和谐波补偿,实现友好并网。其DC/DC部分采用Boost升压电路,通过电导增量法进行最大功率跟踪(MPPT); DC/AC部分采用电压型三相桥式逆变电路和滞环控制方法。最后给出了较详细的仿真结果,验证了所采用方法的可行性。     

Representation of fatigue for wind turbine control

Fatigue is a critical factor in structures such as wind turbines exposed to harsh operating conditions, both in the design stage and in the control during their operation. In the present paper, the most recognized approaches to estimate the damage caused by fatigue in the component level are discussed and compared. The aim of this paper is to address the applicability of those fatigue damage estimation methods to control of wind turbines. Accordingly, for our discussion and comparison, we categorize fatigue estimation methods in a macroscopic scale as counting, spectral, stochastic and hysteresis operator methods. Copyright © 2016 John Wiley & Sons, Ltd.     

膨胀石墨表面化学镀Ag及Ni-Co-Fe合金的研究

采用化学镀技术在膨胀石墨表面包覆Ag及Ni-Co-Fe合金,用扫描电子显微镜（SEM）、X射线能谱仪（EDS）、X射线衍射仪（XRD）及振动磁强计等方法对镀层形貌、组分、结构及磁性能进行表征,结果表明,膨胀石墨表面镀层较平整光滑,厚度均匀,包覆银后的膨胀石墨没有磁性能,而包覆镍铁钴、镍铁钴/银、银/镍铁钴后的膨胀石墨磁性能明显增强,饱和磁化强度σs-Ni-Fe-Co=10.2emu/g、σs-Ni-Fe-Co/Ag=6.3emu/g、σs-Ag/Ni-Fe-Co=2.4emu/g。     

基于滞回环的含蜡原油触变模型评价

触变性是含蜡原油的一个重要流变特性,对输油管道停输再启动过程的水力特性及安全性至关重要。通过实验,研究了4种含蜡原油在剪切速率先呈线性增大后呈线性减小这一循环加载条件下的滞回环特性。利用最小二乘原理,分别对剪切速率循环一次得到的单一滞回环和剪切速率变化率不同的多个循环得到的多个滞回环进行了拟合。用平均偏差作为统计指标,对8个触变模型进行了评价。结果表明,基于Cheng的含蜡油品中存在完全可逆和完全不可逆两类结构,在Houska模型的基础上建立的模型最适合于描述含蜡原油的滞回环特性。     

配电网中分布式并网发电装置的复合控制策略

针对分布式并网发电中特别是光伏发电设备在夜晚情况下和风力发电设备在无风情况下利用率低,以及有源电力滤波器（APF）成本高、功能单一这一问题,提出了一种分布式并网发电装置的新型复合控制策略,它能在分布式电源最佳功率并网输出的情况下,同时实现电网谐波和无功电流补偿。详细分析了控制系统的结构,并采用改进的谐波及无功检测和并网...     

RSD应用中磁开关饱和时间测量

采用串联RLC振荡电路脉冲测量磁开关的电压电流,拟合它的磁滞回线,并提取相关参数对它的饱和时间进行了设计。通过Saber仿真证明了该方法的可行性。通过计算和实验,获得其在300V～3000V下的饱和时间,计算结果在51.4μs到5.1μs之间,实验结果在51.0μs到5.0μs之间。     

Experimental study on rate dependence of macroscopic domain and stress hysteresis in NiTi shape memory alloy strips

NiTi polycrystalline shape memory alloys, when stretched, can deform through the formation and growth of localized macroscopic martensite domains. In this paper, we study the effects of stretching rate on the stress-induced domains and stress hysteresis in NiTi strips. Synchronized measurements of the nominal stress–strain curve, macroscopic domain pattern and the associated temperature field were conducted in the strain rate range of 10⁻⁴–10⁻¹/s. It was found that the nominal stress–strain curve changed from the near-isothermal plateau-type with distinct stress drops at the very low strain rate to the near-adiabatic smooth hardening-type in the high strain-rate region. The corresponding deformation mode changed from the nucleation propagation mode with a few parallelepiped martensite domains to the near-homogeneous multiple-nucleation mode with many fine alternating austenite–martensite stripes. The number of the domains (domain spacing) increased (decreased) monotonically with the strain rate and followed a power law scaling, while the stress hysteresis (or material damping capacity) changed non-monotonically with the strain rate, reaching a peak at strain rate of 2.0×10⁻³/s. We show that, though the rate dependence of both pattern and hysteresis originates from the transfer of the released/absorbed heat and the thermo-mechanical coupling, the domain spacing in the test of static air is mainly controlled by heat conduction and the hysteresis change is mainly controlled by the heat convection with the ambient.     

基于模糊控制的微操作平台位置精度补偿方法

由于压电式微操作平台的迟滞非线性会导致其位置精度和动态性能下降,且难以建立精确的迟滞非线性模型,采用一种基于模糊控制策略的位置精度补偿方法,以摆脱对迟滞模型的依赖。以一种一维压电式微操作平台为对象,以平台的位置偏差与偏差变化率为模糊输入,压电驱动器输入电压变化量为模糊输出,提出采用基于PID控制的实验数据获取经验来制定模糊规则的方法。通过模糊推理和解模糊过程,建立平台输入量与输出量之间的模糊关系,实现了可消除迟滞现象的自适应补偿。为了说明所提出的位置精度补偿方法的可行性,通过实验与PID控制进行比较,分析平台跟踪不同频率正弦信号的位置误差。实验结果表明,所提出的模糊控制方法能使平台具有更高的位置跟踪精度和更快的跟踪速度,并具有较好的自适应性。