System Strength Assessment Based on Multi-task Learning

Increase in permeability of renewable energy sources(RESs)leads to the prominent problem of voltage stability in power system,so it is urgent to have a system strength evaluation method with both accuracy and practicability to control its access scale within a reasonable range.Therefore,a hybrid intelligence enhancement method is proposed by combining the advantages of mechanism method and data driven method.First,calculation of critical short circuit ratio(CSCR)is set as the direction of intelligent enhancement by taking the multiple renewable energy station short circuit ratio as the quantitative indicator.Then,the construction process of CSCR dataset is proposed,and a batch simulation program of samples is developed accordingly,which provides a data basis for subsequent research.Finally,a multi-task learning model based on progressive layered extraction is used to simultaneously predict CSCR of each RESs connection point,which significantly reduces evaluation error caused by weak links.Predictive performance and anti-noise performance of the proposed method are verified on the CEPRI-FS-102 bus system,which provides strong technical support for real-time monitoring of system strength.

Review of System Strength and Inertia Requirements for the National Electricity Market of Australia

Synchronous generators(SGs)are still making major contributions to the re-stabilization of a power system following voltage/frequency disturbances,attributed to their inherent capability of providing system strength and inertia.However,SGs powered by fossil fuels are operating to a lesser extent and scheduled for decommissioning in the National Electricity Market(NEM)of Australia due to the accelerating increase of low bidding priced asynchronous generation of wind and solar,which leads to the reduction and even in some cases,a shortage of system strength and inertia.This paper comprehensively reviews the requirements of system strength and inertia in the NEM from an operational security perspective.Australia is the first country that established the regulation rules of system strength and inertia to accommodate issues of an emerging high penetration level of non-synchronous renewable generation.

A Study of Tensile Strength Tests of Arborous Species Root System in Forest Engineering Technique of Shallow Landslide

One experiment was conducted, through tensile tests of Albazzia and Eucalypt roots culled from the fields. The other experiment was conducted, by testing anti-drawing strength of these root systems in the Albazzia and Eucalypt lands. These two experiments had an aim to give insights into the maximum tensile strength and anti-drawing strength of the root systems. Results indicated that the maximum tensile strength of root system is in an exponential relation with the diameter of root system while the maximum tensile strength is positively correlative with the diameter of root system. Anti-drawing force of root system together with root diameter, length, and soil bulk density are folded into a regression equation in an attempt to figure out the static friction coefficient between root system and its ambient soil.

Coronary artery calcium data and reporting system: Strengths and limitations

Coronary artery calcium data and reporting system(CAC-DRS)is a recently introduced standardized reporting system for calcium scoring on computed tomography.CAC-DRS provides four risk categories(0,1,2 and 3)along with treatment recommendations for each category.As with any other new reporting platform,CAC-DRS has both advantages and disadvantages.Improved communication,better clarity of details,organized management recommendations and utility in future research and education are the major strengths of CAC-DRS.It has many limitations such as questionable need for a new system,few missing components,use of a less accurate visual method and treatment suggestions based on expert opinion instead of clinical trials.In this contemporary review,we discuss the new reporting system CAC-DRS,its application,strengths and limitations and conclude with some remarks for the future.

Multi-Variable Flocking Control for Multi-Agent Systems via a Received Signal Strength Indicator

A novel flocking control approach is proposed for multi-agent systems by integrating the variables of velocities, motion directions, and positions of agents. A received signal strength indicator （RSSI） is applied as a variable to estimate the inter-distance between agents. A key parameter that contains the local information of agents is defined, and a multi-variable controller is proposed based on the parameter. For the position control of agents, the RSSI is introduced to substitute the distance as a control variable in the systems. The advantages of RSSI include that the relative distance between every two agents can be adjusted through the communication quality under different environments, and it can shun the shortage of the limit of sensors. Simulation studies demonstrate the effectiveness of the proposed control approach.

铁尾矿基掺合料混凝土的抗压性能

为实现铁尾矿、钢渣和磷渣等固废资源化,减少水泥用量,并减轻铁尾矿单独做掺合料时对混凝土产生的不良影响,基于高硅型铁尾矿,引入磷渣、脱硫灰和钢渣3种掺合料,研究了铁尾矿-磷渣-脱硫灰(IPD)体系、铁尾矿-磷渣-钢渣(IPS)体系和铁尾矿-钢渣-脱硫灰(ISD)体系混凝土的抗压性能,利用压汞法和背散射电子成像技术分别对混凝土内部的孔隙、界面过渡区进行测试分析.结果表明:IPD体系、IPS体系和ISD体系28 d抗压强度分别达到纯水泥混凝土的80.1%、92.4%和82.5%;加入掺合料后,骨料与水泥的界面过渡区更加密实,孔隙率得到了不同程度的降低,掺合料的填充效应得到了较好发挥,减轻了内部孔隙对混凝土的不良影响.

提高新能源场站稳定性的构网型与跟网型变流器容量配比估算

大规模新能源接入使得电网短路比降低,系统电压支撑强度下降,导致静态电压稳定和次/超同步振荡等稳定问题凸显。构网型变流器具有较强的电压支撑能力,在新能源场站配置一定比例的构网型变流器可以提升系统稳定性,但由于构网型变流器容量与稳定裕度的解析关系不明,导致构网型变流器容量合理占比的理论值估算十分困难。该文针对新能源基地接入低短路比弱电网场景,从小干扰稳定视角探讨构网型与跟网型变流器容量配比的估算方法及其典型值。首先,对构网型变流器进行电压源等值,并通过广义短路比指标分析了构网型变流器配置比例对系统强度以及稳定裕度的影响规律;其次,针对改造构网型风电机组和额外加装构网型变流器两种技术方案,以行业相关标准为边界条件并结合典型升压变压器参数,估算了实际工程中容量配比的典型值;最后,利用多风电场系统案例验证了结论的有效性。

Effect of structural characteristics distribution on strength demand and ductility reduction factor of MDOF systems considering soil-structure interaction

It is known that structural stiffness and strength distributions have an important role in the seismic response of buildings. The effect of using different code-specified lateral load patterns on the seismic performance of fixed-base buildings has been investigated by researchers during the past two decades. However, no investigation has yet been carried out for the case of soil-structure systems. In the present study, through intensive parametric analyses of 21,600 linear and nonlinear MDOF systems and considering five different shear strength and stiffness distribution patterns, including three code-specified patterns as well as uniform and concentric patterns subjected to a group of earthquakes recorded on alluvium and soft soils, the effect of structural characteristics distribution on the strength demand and ductility reduction factor of MDOF fixed-base and soil-structure systems are parametrically investigated. The results of this study show that depending on the level of inelasticity, soil flexibility and number of degrees-of-freedoms (DOFs), structural characteristics distribution can significantly affect the strength demand and ductility reduction factor of MDOF systems. It is also found that at high levels of inelasticity, the ductility reduction factor of low-rise MDOF soil-structure systems could be significantly less than that of fixed-base structures and the reduction is less pronounced as the number of stories increases.

中国南北方植物对土壤加固机制的差异性

为深入分析植物对土壤加固的影响效益和机制,该研究选取重庆缙云山地区和陕西延安黄土丘陵区种植一年的乔木(火炬树、榆树)和灌木(荆条、酸枣),测定其根系形态、力学参数和土壤的抗剪强度,通过RBMw模型计算根系固土效益,综合评估不同植物的固土效能和贡献度。结果表明:2地种植的物种平均根直径的差异不显著(P>0.05),重庆种植的乔木(火炬树、榆树)的根长、分叉数和根尖数显著高于延安,灌木未出现显著差异(P<0.05)。根系的抗拉强度与直径都符合负幂函数关系,其中平均抗拉强度最大的为荆条。除荆条外,同种植物根系的抗拉强度并未因不同地区的种植产生显著差异。4个植物种根系的固土效率为0.65~4.12 kPa,各物种间存在显著差异(P<0.05)。重庆2种乔木种植下的根土复合体有效黏聚力高于裸地(约10%),灌木种植下则普遍略低于裸地。除酸枣外,种植于重庆的4种植物的根系固土作用和效率都显著的高于延安(P<0.05)。研究结果可为不同地区固土护坡的树种选择提供理论依据。

外墙保温一体化系统黏结性能影响因素及机理研究

外墙保温系统是建筑节能的主要路径之一,建筑外墙保温一体化系统是目前上海市主流应用的外墙保温系统。基于外墙保温一体化系统应用现状,分析了不同类型界面处理剂,不同施工环境条件和拉拔尺寸等因素对外墙保温一体化系统黏结性能的影响规律。研究成果对促进外墙保温一体化系统性能提升、保障建筑外立面安全具有指导意义。

含多电解槽的新能源制氢能量管理优化

新能源制氢系统是提升风能、太阳能等新能源消纳的有效途径。目前国内外关于电解槽能量管理的研究以单电解槽为主。单电解槽能量管理未考虑电解槽非线性的工作特性,难以兼顾多个电解槽制氢效率,影响系统经济性。文中针对含有多电解槽的新能源制氢系统的能量管理问题进行了研究,以新能源消纳率、经济收益、制氢率为目标,考虑单个电解槽运行特性以及生产约束条件,建立包含风电、光伏、蓄电池、多电解槽的能量管理优化模型,并采用强度Pareto进化算法2(strength Pareto evolutionary algorithm 2,SPEA2)求解多目标优化问题。仿真研究表明,文中所提能量管理策略能够实现新能源发电的100%消纳,单位制氢收益可提升5.15%。因此,对多电解槽制氢系统进行有效的能量管理有助于提高制氢效率,可有效克服单电解槽运行及能量管理的不足。

掺硅粉对普通硅酸盐水泥-硫铝酸盐水泥复合胶凝体系混凝土耐久性的影响研究

通过在m(普通硅酸盐水泥)∶m(硫铝酸盐水泥)=3∶7的复合胶凝体系(P·O-SAC)中掺入不同比例的硅粉,对复合胶凝体系的水化过程和混凝土的抗压强度、抗劈裂强度以及抗氯离子侵蚀进行试验,改善多元复合胶凝体系混凝土的耐久性能。研究表明:硅粉的掺入量越多,复合水泥的初凝和终凝时间越长;掺入适量的硅粉能有效提高P·O-SAC混凝土的抗压强度,改善P·O-SAC混凝土后期强度的发展;硅粉能提升P·O-SAC混凝土抗氯盐侵蚀的能力。

科技自立自强背景下的新型举国体制:基本内涵、适用范围与构建思路

进入新发展阶段,实现高水平科技自立自强成为中国统筹发展与安全的战略支撑和必然要求。其中,构建和完善关键核心技术攻关新型举国体制是实现科技自立自强的关键举措。本文认为,科技自立自强背景下进一步健全新型举国体制需要把握以下重点:在基本内涵上,理解新型举国体制的关键是同时抓住“举国”这个原内核和“新型”这个新内核,正确认识两个内核的关系;在适用范围上,运用新型举国体制的前提是提出需求明确、仅靠市场竞争难以突破的战略科技任务,并注意适用范围的动态演化性;在构建思路上,要围绕充分发挥国家作为重大科技创新组织者的作用,以系统化思维推进相关改革,强化中央层面的决策指挥体系,完善技术攻关组织管理体系,建立适配新型举国体制的政策体系;在推进实施上,应根据事项轻重缓急和难易程度等因素,确定当前重点。

开敞系统中冻土-混凝土界面抗拉强度试验研究

在寒区桩基工程中,冻土-混凝土界面强度对于桩基础的受力状态有着重要的影响。在开敞系统条件下进行了冻土-混凝土界面区的抗拉强度正交试验,利用极差方差分析法,厘清了界面粗糙度、土样含水率、试验温度及干密度4种试验因素对界面冻结抗拉强度影响的主次顺序。分析试验结果表明,土样含水率的增大、试验温度的降低及接触面粗糙度的提升均可使界面冻结抗拉强度不断提高;存在临界土样含水率,当含水率位于临界含水率两侧时,接触面粗糙度因水分迁移所形成冰膜改变的程度不同,导致接触面粗糙度的增加对界面冻结抗拉强度增幅的影响程度具有不同的规律。

基于等效电流源的级联混合直流馈入系统强度影响分析

级联型混合直流系统受端的模块化多电平换流器高压直流系统(modular multilevel converter high voltage direct current,MMC-HVDC)和电网换相换流器高压直流系统(line commutated converter high voltage direct current,LCC-HVDC)会因馈入点电气距离较近而存在强相互作用关系。为明确级联型混合直流馈入系统中MMC-HVDC对LCC-HVDC系统强度的影响,提出考虑幅值和相位的MMC等效电流源的简化等效方法,基于所提MMC等效原理将级联型混合直流馈入系统等效成单馈入LCC-HVDC系统,分析等效单馈入系统的参数计算方法,并提出等效单馈入短路比评估指标。最后通过该指标分析归纳了不同控制方式、不同电气距离下等效单馈入系统的系统强度变化情况,即为MMC-HVDC对LCC-HVDC系统强度的影响规律。机理分析和基于PSCDAD/EMTDC、MATLAB的仿真结果表明,所提等效方法具有有效性且所提指标能很好地反应MMC-HVDC对LCC-HVDC系统强度的影响。

煤矿巷道断层滑移型冲击地压试验系统研制与试验验证

断层滑移型冲击地压是煤矿冲击地压的主要类型,目前对其发生全过程缺乏系统研究,其机理与防控仍是根本难题。为实现断层滑移型冲击地压的试验模拟,研制了煤矿巷道断层滑移型冲击地压试验系统,开发了低强高脆相似模拟材料,制备了包含断层与巷道的大尺寸相似模型,开展了一系列验证试验,实现了巷道冲击破坏模拟与断层剪切滑移模拟。煤矿巷道断层滑移型冲击地压试验系统具备三向六面加载功能,竖向加载能力为20 MPa,模型尺寸为1.50 m×0.75 m×0.75 m;主体框架创新采用键板连接,确保了主体框架的高刚度;发明了蜂窝加载壳结构,实现了密集油缸群加载,能够满足断层滑移型冲击地压试验模拟的要求。开发了适用于断层滑移型冲击地压模拟的相似材料,材料以水玻璃为胶结物、以氟硅酸钠为固化剂、以滑石粉为骨料,单轴抗压强度介于3.44~7.81 MPa,冲击能指数为9.2,弹性能指数为8.83,兼具低强高脆特性。基于试验系统和低强高脆材料实现了静载巷道冲击破坏模拟,验证了低强高脆相似材料模拟巷道冲击破坏的可行性,获得了巷道极限平衡状态的加载条件,巷道帮部连续片落为巷道冲击破坏的显著前兆特征。实现了粗糙锯齿断层的剪切滑移模拟,证实粗糙断层剪切滑移会对巷道形成动载扰动,获得了断层剪切滑移的合理加载方式,采用动区顶部先加载、底部后卸载的方式能够实现断层的瞬间滑移,并能消除对静区应力状态的影响。

无线应变采集技术在飞机强度试验的应用研究

为解决应变测量过程中线缆过长、体量过大、工序复杂造成的测量准备周期长、工作量大、故障定位困难、试验空间紧张等问题,研制了基于超薄芯片封装技术的无线采集系统。该系统体积小、线缆少、就近采集、机体共形、安装方便,在MA600全机疲劳试验中进行了应用验证,取得了良好的效果,表明该系统能够满足试验的要求。

含跟网型储能的新能源多馈入系统小扰动电压支撑强度分析

储能正常工作时包含充电和放电两种运行模式,导致多储能变流器和多新能源变流器构成的多馈入系统工作点多变,加剧了系统小扰动同步稳定性分析的困难程度。为此,该文聚焦锁相环主导的小扰动同步稳定问题,首先,推导了兼顾储能充/放电运行模式的电网强度评估指标广义短路比,并提出了基于广义短路比及设备临界短路比的系统电压支撑强度分析方法,进而实现了系统小扰动同步稳定裕度的快速评估;然后,探究了跟网型储能变流器的充/放电运行模式对系统小扰动同步稳定裕度的影响规律,并根据矩阵联锁特征值定理论证了跟网型储能变流器工作在充电模式时,系统的小扰动同步稳定裕度高于放电模式;最后,基于仿真算例验证了所提系统小扰动同步稳定性分析方法的有效性。

低惯量交流系统并网变流器次/超同步振荡分析

低惯量电力系统中跟网型变流器可能会与同步机转子动态产生交互,给系统稳定性分析引入新的问题,仅靠跟网型设备动态和短路比衡量交流系统强度不再准确。为此,该文综合分析系统惯量和短路比对跟网型变流器小干扰同步稳定的影响,提出适用于分析低惯量系统中并网变流器稳定性的方法,所提方法计算量低、物理意义明确。首先,推导变流器和同步机混联系统的闭环模型,并提取出能表征低惯量动态的相互作用系数矩阵,定性分析两类设备间的交互关系。其次,基于模态摄动理论,将原多机系统解耦为稳定性等效的子系统。然后,选取适用于分析小干扰同步稳定问题的相位主导回路,根据该回路提出综合考虑惯量和短路比的稳定性分析方法。最后,基于仿真算例验证了所提低惯量系统中并网变流器小干扰同步稳定性分析方法的有效性。

抗疏力固化剂改性黄土物理力学性质试验研究

研究目的:使用改性材料(固化剂)是黄土地基加固处理的常见方法,但传统改性材料存在一定问题,如石灰改性土的强度相对较低,且耐水性较差;水泥改性黄土的收缩性大,容易开裂,且会对环境造成一定的影响。因此,寻求环境友好、性能优良的土壤固化剂来解决传统改性材料存在的不足,对改性黄土具有重要意义。本文对抗疏力固化剂改性黄土进行试验研究,同时与水泥和石灰改性黄土进行对比分析,通过无侧限抗压强度、崩解及SEM等试验研究固化剂掺量和养护龄期对黄土强度、水稳性及微观结构的影响。研究结论:(1)抗疏力固化剂改性黄土的强度随着固化剂掺量和养护龄期的增加而增大,当养护龄期为28 d时,随着固化剂掺量的增加(1%~5%),抗疏力改性黄土的强度由55 kPa增长至95 kPa,其中5%抗疏力改性黄土的强度介于水泥改性黄土(370 kPa)和石灰改性黄土之间(71 kPa);(2)改性黄土的水稳系数和抗崩解性随着固化剂掺量的增加而不断提升,随着固化剂掺量的增加(1%~5%),抗疏力改性黄土的水稳系数由0.13提升至0.36,5%抗疏力改性黄土的水稳性介于石灰改性黄土(0)和水泥改性黄土(0.75)之间;(3)抗疏力固化剂显著提升了土体的斥水性;(4)随着固化剂掺量的增加(1%~5%),抗疏力改性黄土的渗透系数由0.63×10^(-6)cm/s降低至0.36×10^(-6)cm/s, 5%抗疏力改性黄土的渗透性介于石灰改性黄土(0.88×10^(-6)cm/s)和水泥改性黄土(0.32×10^(-6)cm/s)之间;(5)SEM图像显示,随着抗疏力固化剂掺量的提高,土体内部的大孔隙明显减少,土颗粒之间的连接更加紧密,分布更为均匀;(6)本研究成果可为黄土地区地基加固处理提供参考。