Experimental Study on Local Scour Around Bridge Piers in Tidal Current

Local scour around a bridge pier is an important parameter for the design of a bridge. Compared with the local scour in a mono-directional current, the local scour in a tidal current has its unique characteristics. In this paper, several aspects of local scour around bridge piers in tidal current, including the scour development process, the plane form of a scour hole and the maximum scour depth, are studied through movable bed flume experiments.

Local leakage current behaviours of BiFeO_3 films

The leakage current behaviours of polycrystalline BiFeO3 thin films are investigated by using both conductive atomic force microscopy and current-voltage characteristic measurements. The local charge transport pathways are found to be located mainly at the grain boundaries of the films. The leakage current density can be tuned by changing the post-annealing temperature, the annealing time, the bias voltage and the light illumination, which can be used to improve the performances of the ferroelectric devices based on the BiFeOa films. A possible leakage mechanism is proposed to interpret the charge transports in the polycrystalline BiFeO3 films.

Experimental and Numerical Investigation of Local Scour Around Submarine Piggyback Pipeline Under Steady Current

As a new type of submarine pipeline, the piggyback pipeline has been gradually adopted in engineering practice to enhance the performance and safety of submarine pipelines. However, limited simulation work and few experimental studies have been published on the scour around the piggyback pipeline under steady current. This study numerically and experimentally investigates the local scour of the piggyback pipe under steady current. The influence of prominent factors such as pipe diameter, inflow Reynolds number, and gap between the main and small pipes, on the maximum scour depth have been examined and discussed in detail. Furthermore, one formula to predict the maximum scour depth under the piggyback pipeline has been derived based on the theoretical analysis of scour equilibrium. The feasibility of the proposed formula has been effectively calibrated by both experimental data and numerical results. The findings drawn from this study are instructive in the future design and application of the piggyback pipeline.

Experimental Investigation of Local Scour Around A New Pile-Group Foundation for Offshore Wind Turbines in Bi-Directional Current

The local scour around a new pile-group foundation of offshore wind turbine subjected to a bi-directional current was physically modeled with a bi-directional flow flume. In a series of experiments, the flow velocity and topography of the seabed were measured based on a system composed of plane positioning equipment and an ADV.Experimental results indicate that the development of the scour hole was fast at the beginning, but then the scour rate decreased until reaching equilibrium. Erosion would occur around each pile of the foundation. In most cases, the scour pits were connected in pairs and the outside widths of the scour holes were larger than the inner widths. The maximum scour depth occurred at the side pile of the foundation for each test. In addition, a preliminary investigation shows that the larger the flow velocity, the larger the scour hole dimensions but the shorter equilibrium time. The field maximum scour depth around the foundation was obtained based on the physical experiments with the geometric length scales of 1:27.0, 1:42.5 and 1:68.0, and it agrees with the scour depth estimated by the HEC-18 equation.

Effect of Distortion Ratio on Local Scour Under Tidal Currents and Waves

Five generalized physical models of different distortion ratios were built according to DOU Guo-ren's similarity theory of total sediment transport modeling for estuarine and coastal regions. Experiments on local scour in front of groins were made under the actions of tidal currents and waves with clear and sediment entraining water. The scour depths under different dynamic actions are compared. The effect of the distortion ratio on the depth of scour hole is discussed. A relationship between scour depths for distorted and undistorted models is given.

Local Perception on the Exploitation, the Current State and Taboos Related to Pangolins (Pholidota, Mammalia) by the Communities Living in the Tayna Nature Reserve and Its Surroundings (RNT) North Kivu DRC

Pangolins are currently considered the most endangered mammal species due to their high rank in local and international traffic. This species is protected in DRC and worldwide, unfortunately it is threatened by numerous human actions. The objective of this study is to identify the different reasons for which these animals are exploited, to provide information to determine from the opinions of the respondents the current state of the population from 2015 to today and to identify their hunting techniques by the local populations. We carried out surveys in the households of hunters, farmers and people practicing other professions in 12 villages, located within the RNT and surroundings areas. Two interview techniques were used: the individual interview and the participatory diagnostic technique. 175 people were interviewed individually. Nearly 97% of our respondents are motivated to consume pangolin as bush meat obtaining by hunting. The main reason for eating pangolin meat is 44% preference and 33% habit. The zone does not know the foreign solicitation of the exploitation of pangolins and its derivatives. The opinions of the population regarding the current state of pangolin in the Tayna Nature Reserve indicate that from 2015 to the present day the common pangolin “Manis tricuspis” has been abundant. Hunters use different hunting techniques, dominated by pickup for the Manis tricuspis, digging burrow, fire at the entrance of the burrow for Manis gigantea and the shotgun for the Manis tetradactyla.

Vertical plane depth-resolved surface potential and carrier separation characteristics in flexible CZTSSe solar cells with over 12% efficiency

Cu2ZnSn(S,Se)4(CZTSSe)solar cells have resource distribution and economic advantages.The main cause of their low efficiency is carrier loss resulting from recombination of photo-generated electron and hole.To overcome this,it is important to understand their electron-hole behavior characteristics.To determine the carrier separation characteristics,we measured the surface potential and the local current in terms of the absorber depth.The elemental variation in the intragrains(IGs)and at the grain boundaries(GBs)caused a band edge shift and bandgap(Eg)change.At the absorber surface and subsurface,an upward Ec and Ev band bending structure was observed at the GBs,and the carrier separation was improved.At the absorber center,both upward Ec and Ev and downward Ec-upward Ev band bending structures were observed at the GBs,and the carrier separation was degraded.To improve the carrier separation and suppress carrier recombination,an upward Ec and Ev band bending structure at the GBs is desirable.

引入ESO的永磁超环面电机无模型预测电流控制

为改善无差拍预测电流控制(DPCC)对永磁超环面电机系统参数的依赖性,研究了引入扩张状态观测器(ESO)的永磁超环面电机无模型预测电流控制(MFPCC-ESO)策略。根据永磁超环面电机的复合转子结构,引入自转运动影响系数与磁势系数,在旋转坐标系下建立该电机的时变数学模型;利用永磁超环面电机系统的输入与输出,建立该电机具有时变比例因子的超局部模型,同时引入ESO对超局部模型的干扰部分进行实时估计,并利用朱利稳定判据证明了ESO的稳定性;结合延时补偿的DPCC预测得到参考电压矢量,从而实现永磁超环面电机的MFPCC-ESO策略。对参数匹配和失配下永磁超环面电机MFPCC-ESO策略与DPCC策略进行对比分析,仿真结果表明:MFPCC-ESO策略下的永磁超环面电机具有优越的动态和稳态性能及强鲁棒性,同时该控制策略还能有效降低永磁超环面电机的输出波动。

多谐振控制的同步磁阻电机鲁棒预测电流控制系统转矩脉动抑制方法

为抑制同步磁阻电机的转矩脉动并提高系统的鲁棒性,文中提出了一种基于多谐振速度环控制与自抗扰电流环的复合控制策略。由于同步磁阻电机的磁阻变化不均匀,从而导致电机电感随着磁饱和与交叉耦合效应变化,一方面,电感参数的变化会给电流环控制带来影响;另一方面,电感参数的变化还会引起转矩的脉动。因此提出基于多比例谐振的速度环控制策略,以抑制同步磁阻电机的转矩谐波。基于超局部模型的无差拍电流预测控制,利用改进的锁相环观测器对下一拍的电流和扰动进行预测,在电机参数变化时可以很好地实现电流的跟踪,从而提高系统的抗干扰能力。

预测控制与滑模控制结合的永磁同步电机控制

提出一种改进型无差拍预测电流控制方法与改进型滑模控制方法结合的控制策略。基于永磁同步电机的数学模型,构建电流内环控制算法,设计扩张状态观测器,解决无差拍预测电流控制因参数扰动及模型失配导致的电流误差问题。速度外环设计一种超局部模型滑模控制器,设计滑模扰动观测器削弱滑模抖振。仿真结果证明,结合后的控制方法有效提高了电机暂、稳态性能,提升了系统抗干扰能力、鲁棒性及响应速度。

分段式双三相永磁直线同步电机的无模型电流预测控制

分段式结构的双三相永磁直线同步电机(PMLSM),动子穿入和穿出定子分段时,传统的无差拍预测电流控制(DPCC)易受反电动势动态扰动的影响,无法实现精确的电流跟踪和推力控制。同时,该电机模型的参数失配会增大DPCC电流和推力控制的难度。针对以上问题,该文提出了一种基于无模型电流预测控制(MFPCC)的电流控制策略。首先,构建了分段式双三相PMLSM的超局部模型。其次,基于该超局部模型设计了预测电流控制器,并设计扰动观测器以补偿反电动势动态扰动和参数失配的影响。最后,实验验证了所提MFPCC能够抑制分段式双三相PMLSM的反电动势和参数失配的扰动,有效提升参数鲁棒性、电流跟踪性能并降低推力波动。

基于扩张状态观测器的PMSM三电平无模型预测控制

针对传统永磁同步电机三电平控制策略由于参数变化导致系统性能下降的问题,提出一种基于扩张状态观测器的无模型预测电流控制方法来增强系统的鲁棒性。首先,建立系统超局部模型实现未来电流状态的预测,其中不涉及任何电机参数,解决了参数变化影响系统性能的问题;接着,针对系统总扰动,设计d、q轴扩张状态观测器估计超局部模型中的非线性部分;然后,通过价值函数筛选出最优电压矢量,并利用小矢量的冗余特性实现中点电位平衡控制;最后,在DSP实验平台上进行传统三电平模型预测电流控制、无模型预测电流控制及所提出方法的对比实验,实验结果表明所提出方法具有较好的动稳态性能并且有效提高了三电平驱动系统的抗扰动能力。

基于波形分析的电流互感器局部暂态饱和检测方法

为避免由于电流互感器局部暂态饱和故障引起的差动保护误动行为,提高暂态饱和状态的检测精度,引进波形分析技术,设计一种针对电流互感器局部暂态饱和的全新检测方法。根据电流互感器在运行过程中二次电流波形图的数学形态,掌握互感器的运行工况,获取基于波形分析的电流互感器二次电流暂态信息;通过电流互感器局部暂态相位偏移饱和识别,完成暂态饱和状态的检测。以某电力系统为例,使用EMTDC/PSCAD软件,在终端建立电流互感器局部暂态饱和仿真模型,设计对比实验。实验结果表明:设计的检测方法应用效果良好,该方法的检测结果更加可靠,可以通过此种方式,降低由于互感器故障造成的电力系统供电服务异常。

基于非线性扰动补偿的超局部无模型永磁同步电机电流预测控制

在电机运转过程中,电机参数会发生变化,产生参数漂移,同时电机会受到内外部未知扰动,导致控制性能下降,抗干扰性和鲁棒性较差。为解决这些问题,提出非线性扰动补偿的超局部无模型电流预测控制方法。只利用电流环的输入和输出,建立超局部无模型电流预测控制模型,不涉及任何电机参数,解决了因参数变化导致的模型失配问题。针对系统总扰动,建立非线性扰动补偿模型,能够较为准确和稳定地估计系统总扰动,并进行前馈补偿,实时更新控制信息,仅需调节两个控制参数。为防止产生较大的电流,建立电流限幅控制,提高电机控制性能。仿真和实验结果表明,提出的控制方法对于参数变化和外部扰动,具有较强的鲁棒性、抗干扰能力,能够实现较快的动态响应,减小电流纹波,降低电流静差,获得较优的电流环动静态性能;抑制转速脉动和超调量,稳定跟踪额定转速,有利于电机的平稳运行。

结合全局特征与局部互通的河流断流接续优化

高分辨率遥感影像的水体提取常因地物类型复杂、部分河流狭窄等因素导致水体提取结果不完整、不连续。因此,结合水体自身光谱和纹理特征,提出了一种结合全局特征与局部互通的遥感影像水体提取优化方法。首先,在水体提取初始结果的基础上,通过多尺度Frangi滤波和大津法(OTSU)分割算法提取线性支流,对河流进行补充得到初步优化结果。然后,结合局部互通的断流接续算法,对初步优化结果中的断流部分进行连接。最后,通过K-means聚类提取水体部分,并与精确优化结果进行拓扑检查及光谱检查,实现块状水体的验证筛选。实验结果表明,本文方法能够提取到细小支流,提高优化的准确度;断流接续算法的加入,有助于提高河流提取的完整性。与其他方法相比,本文方法的总体精度分别提高1.04%、1.50%,F1分别提高5.84%、8.28%,可以作为有效提升水体优化后处理的手段,提高了水体提取的完整度和精度。

Swin-Transformer故障信息挖掘的海底观测网故障定位方法

海底观测网长期受海洋环境与人为因素影响,易使光电复合缆绝缘破损与海水接触形成电学故障点。如何准确地定位电学故障点,对提高海底观测网输电与信息传输的可靠性至关重要。首先根据海底观测网输电结构建立海底观测网输电模型,推导与模拟电学故障点传播至观测点的暂态电流,然后由连续小波变换提取暂态电流与故障点对应的内在关联特征量,最后通过Swin-Transformer神经网络挖掘内在关联特征量与故障距离的匹配关系来定位电学故障点。研究结果表明,在内在关联特征量样本测试集条件下,光电复合缆≤160 km的电学故障点定位误差小于400 m,可为长距离光电复合缆的海底观测网电学故障点定位提供参考。

山东省地方本科高校国际化办学现状及其发展对策——以7所院校为例

国际化办学是地方本科高校实现高质量发展的重要途径。山东省地方本科高校制定了国际化发展战略,树立了国际化办学理念并进行了实践。山东省地方本科高校国际化办学具有“一带一路”定位取向和阶段特征。山东省地方本科高校在国际化办学理念、国际化办学效能、国际化实践等方面存在不足。因此,山东省地方本科高校应该提高国际化办学理念水平,定位于“在地国际化”,重点面向本校学生,提升国际化办学水平,从教学、科研及教师等内部要素出发,具象化国际化办学。

地方高校内部教学质量保障体系建设现状与优化路径

伴随着教育技术的更新迭代、教育改革的持续推进、教学样态的多元并存、学习方式的灵活多样,新形势下地方高校亟待建设精准完善的高校内部教学质量保障体系。虽然地方高校普遍建立了内部教学质量保障体系,但是建设历程不长,仍面临教学质量评估体系不健全、教学质量管理机构欠专业、教学质量监控环节未闭合、教学质量文化建设不重视等诸多问题和挑战。强化质量标准的引领作用、完善质量保障体系的顶层设计、健全质量保障体系的运行机制、提升多元质量主体追求卓越质量的内生动力,成为当前高校优化内部教学质量保障体系的重要路径。

HCN通道在听觉传导通路中的作用研究进展

超极化激活环核苷酸门控阳离子通(hyperpolarization-activated cyclic nucleotide-gated channel,HCN channel)广泛表达于中枢和周围神经系统,通过其介导的超极化激活阳离子电流(hyperpolarization-activated cation current,Ih)调节神经元的静息膜电位和兴奋性来影响听觉的精确加工和传导,对时间信息的精确分析起着至关重要的作用。因此,本文通过对HCN通道结构和分布以及电生理作用进行综述,进一步探讨HCN通道在正常及单侧聋或双侧聋情况下听觉传导通路中的作用及机制。

光储直柔在整县光伏开发中的应用分析

整县屋顶分布式光伏开发试点过程中面临着光伏项目并网困难、就地消纳能力不足等技术难题。介绍光储直柔新型电力系统技术,分析在整县光伏推进工作中采用光、储、直、柔等技术解决以上两个难题面临的机遇与挑战,并给出相应的建议。分析山西芮城县东夭村国内首个农村“光储直柔”低压直流系统在新能源消纳、安全性和可靠性等方面的优势和经济效益。分析国家能源集团BIPV中心采用“光储直柔”技术,利用建筑的立面和屋顶实现较大规模的光伏装机量,实现光伏发电就地消纳和柔性供用能。推广光储直柔技术是解决整县分布式光伏大规模开发中并网难和就地消纳不足等技术难点的有效途径之一。