A spatiotemporal evolution model of a short-circuit arc to a secondary arc based on the improved charge simulation method

The initial shape of the secondary arc considerably influences its subsequent shape.To establish the model for the arcing time of the secondary arc and modify the single-phase reclosing sequence,theoretical and experimental analysis of the evolution process of the short-circuit arc to the secondary arc is critical.In this study,an improved charge simulation method was used to develop the internal-space electric-field model of the short-circuit arc.The intensity of the electric field was used as an independent variable to describe the initial shape of the secondary arc.A secondary arc evolution model was developed based on this model.Moreover,the accuracy of the model was evaluated by comparison with physical experimental results.When the secondary arc current increased,the arcing time and dispersion increased.There is an overall trend of increasing arc length with increasing arcing time.Nevertheless,there is a reduction in arc length during arc ignition due to short circuits between the arc columns.Furthermore,the arcing time decreased in the range of 0°-90°as the angle between the wind direction and the x-axis increased.This work investigated the method by which short-circuit arcs evolve into secondary arcs.The results can be used to develop the secondary arc evolution model and to provide both a technical and theoretical basis for secondary arc suppression.

Hydrogen storage properties of Mg-TiO_2 composite powder prepared by arc plasma method

Mg-based Mg-TiO2 composite powder was prepared by arc plasma evaporation of the Mg＋5%TiO2 mixture followed by passivation in air. ICP, XRD and SEM techniques were used to characterize the composition, phase components and microstructure of the composite powder. The hydrogen sorption properties of the composite powder were investigated by DSC and PCT techniques. According to the data from PCT measurements, the hydrogenation enthalpy and entropy changes of the composite powder are calculated to be-71.5 kJ/mol and-130.1 J/（K·mol）, respectively. Besides, the hydrogenation activation energy is determined to be 77.2 kJ/ mol. The results indicate that TiO2 added into Mg by arc plasma method can act as a catalyst to improve the hydrogen sorption kinetic properties of Mg.

Optimization of back bead geometry in the PMAG-TIG twin arc hybrid root welding process using grey based Taguchi method

This study investigated multi-response optimization of the pulse metal active gas-tungsten inert gas( PMAG-TIG) twin arc hybrid root welding process for an optimal parametric combination to yield favorable back bead geometry of welded joints using grey relational analysis and Taguchi method.Eighteen experimental runs based on an orthogonal array following the Taguchi method were performed to derive objective functions to be optimized within the experimental domain.The objective functions were selected in relation to parameters of PMAG-TIG twin arc root welding back bead geometry: back bead width to root reinforcement ratio and deposited metal height.The Taguchi approach was followed by grey relational analysis to solve the multi-response optimization problem.The significance of factors on overall quality characteristics of the weld joint was also evaluated quantitatively using analysis of variance.Optimal results were verified through additional experiments,and showed to feasibility of applying grey relation analysis in combination with Taguchi technique for continuous improvement of product quality in the manufacturing industry.

An optimization method for passive muzzle arc control devices in augmented railguns

In this paper,a passive muzzle arc control device(PMACD)of the augmented railguns is studied.By discussing its performance at different numbers of extra rails,a parameter optimization model is proposed.Through the calculation model,it is found that the PMACD works well in the simple railgun,which refers to the gun that there is only one pair of rails in the inner bore.The PMACD may decrease the simple railgun’s armature peak current and muzzle arc,but affect its muzzle velocity not much.However,in the augmented railguns it has different characteristics.If the parameters of the PMACD are not selected suitable.It may increase the armature peak current and muzzle arc,but greatly decrease the velocity.The reason for this problem is that the extra rails generate a strong magnetic field in front of the armature,which induces a large current to change the armature current.It is also found that when the resistance and inductance parameters of the PMACD satisfy with the optimization formula,the PMACD can also play a good role in arc suppression in the augmented railguns.Experiments of an augmented railgun with a stainless steel PMACD are carried out to verify this optimization method.Results show that the muzzle arc is obviously controlled.This work may provide a reference for the design of the muzzle arc control device.

Numerical Simulation of Molten Metal Droplet Behavior in Gas Metal Arc Welding by Three-Dimensional Incompressible Smoothed Particle Hydrodynamics Method

The numerical model was developed using a SPH (Smoothed Particle Hydrodynamics) method and the projected transfer phenomena during a GMA (Gas Metal Arc) welding were simulated by the model to clarify mechanisms of the phenomena. As a result, the droplet transfer mode obtained from this calculation was regarded as a projected transfer mode in which the liquid column grew about 1 mm and a droplet grew up until its diameter became large the same as a wire diameter,?after that it was detached from the tip of the column. In addition, 10 droplets were formed for 0.1 s through these growth and detachment processes at the tip of a wire. To compare with the numerical results, actual GMA welding was carried out and molten metal droplet transfers were taken by high speed camera. The diameter of a wire, the length of a liquid column, the velocity of a droplet right before it reached a weld pool obtained by simulation showed good agreement with experiment.

A local pseudo arc-length method for hyperbolic conservation laws

A local pseudo arc-length method（LPALM）for solving hyperbolic conservation laws is presented in this paper.The key idea of this method comes from the original arc-length method,through which the critical points are bypassed by transforming the computational space.The method is based on local changes of physical variables to choose the discontinuous stencil and introduce the pseudo arc-length parameter,and then transform the governing equations from physical space to arc-length space.In order to solve these equations in arc-length coordinate,it is necessary to combine the velocity of mesh points in the moving mesh method,and then convert the physical variable in arclength space back to physical space.Numerical examples have proved the effectiveness and generality of the new approach for linear equation,nonlinear equation and system of equations with discontinuous initial values.Non-oscillation solution can be obtained by adjusting the parameter and the mesh refinement number for problems containing both shock and rarefaction waves.

IMPROVEMENTS ON THE ARC-LENGTH-TYPE METHOD

Arc-length-type and energy-type methods are two main strategies used in structural nonlinear tracing analysis, but the former is widely used due to the explicitness and clarity in conception, as well as the convenience and reliability in calculation. It is very important to trace the complete load-deflection path in order to know comprehensively the characteristics of structures subjected to loads. Unfortunately, the nonlinear analysis techniques are only workable for tracing the limit-point-type equilibrium path. For the bifurcation-point-type path, most of them cannot secure a satisfactory result. In this paper, main arc-length-type methods are reviewed and compared, and the possible reasons of failures in tracing analysis are briefly discussed. Some improvements are proposed, a displacement perturbation method and a force perturbation method are presented for tracing the bifurcation-point-type paths. Finally, two examples are analyzed to verify the ideas, and some conclusions are drawn with respect to the arc-length-type methods.

Synthesis and characterization of Fe_3Al intermetallic nanopowder by hydrogen arc plasma method (HP)

Nanostructured Fe3Al intermetallic compounds were produced by using hydrogen arc plasma method（HP）. The microstructures of the nano Fe3Al were characterized by means of XRD, DSC-TG and TEM. The results shows that the intermetallic compounds have ordered B2 structure and the average particle of the as synthesized is about 45nm. The B2 structure changes to highly ordered DO3 structure after annealing in vaccum at 480℃. The temperature of phase transformation is 545.3℃.

A novel wavelet method for electric signals analysis in underwater arc welding

Electric signals are acquired and analyzed in order to monitor the underwater arc welding process. Voltage break point and magnitude are extracted by detecting arc voltage singularity through the modulus maximum wavelet （MMW） method. A novel threshold algorithm, which compromises the hard-threshold wavelet （HTW） and soft-threshold wavelet （STW） methods, is investigated to eliminate welding current noise. Finally, advantages over traditional wavelet methods are verified by both simulation and experimental results.

AN IMPROVED ARC-LENGTH METHOD AND APPLICATION IN THE POST-BUCKLING ANALYSIS FOR COMPOSITE STRUCTURES

Based on the conventional arc-length method, an improved arc-length method with high-efficiency is proposed. The weighted modifications with respect to the variation of structural stiffness and extra-interpolation modification by using the information of known equilibrium points are introduced to improve the incremental arc-length. An approximate expansion method for the accumulated and expected arc-length is used to ensure the convergence at given load levels in large range of applications. Numerical results show that the improved arc-length method has well adaptability and higher efficiency in the post-buckling analysis of plates and shells structures for tracing whole load-deflection path and obtaining the convergence values at any specified load levels.

Arc Extraction Analysis for Circularity Measurement of Small Cylindrical Parts by the Segmenting-stitching Method

To reduce the stitching error of circularity measurement of small cylindrical workpieces(Diameter less than 3 mm)by the segmenting-stitching method,arc contour extraction is analyzed in this paper.The coordinates of cross-sectional circle of a small cylindrical part are segmented into several equal arcs to be obtained by a two-dimensional coordinate measuring machine.The circularity contour of the small cylindrical part can be formed by stitching a series of arc contours which are calculated by the obtained arc coordinate data.Due to the different measuring pressure angles of different measuring positions,the accuracy of obtained arc coordinate points is different.The bigger the pressure angle is,the accurate the obtained arc coordinate data are.The experiments show that the accuracy of two ends of the arc data is not as good as the central part.Therefore,the two ends of the obtained arc data are appropriately to be cut off,namely,only the central part of the arc data are extracted to be used for the stitching.As a result,the mean value of the matching coefficient is enhanced by 12%,the deviation between the overlap part of the neighbouring arc contour is reduced by 26%,and the average curvature of the arc contours is improved with the extraction method.Thus,the accuracy of the stitched circularity contour can be improved by this extraction procedure in the segmenting-stitching method for the circularity measurement of the small cylindrical parts.

基于ARCS的ASD儿童绘本角色设计研究

目的为提升ASD儿童情绪学习动机,探究不同角色形象在基本情绪学习中的激发作用,以绘本角色造型为切入点,为绘本角色设计和干预训练提供参考。提出一种基于ARCS动机模型的角色设计研究方法。方法首先,结合ARCS动机维度,建立了一套适用于绘本角色研究的指标体系。在文献研究的基础上,筛选出7项代表性眼动指标和1项情绪匹配数据,并利用眼动仪收集这些指标的实验数据;其次,采用熵权法计算眼动实验客观指标的权重,并使用逼近理想解法(TOPSIS)确定三大角色样本类型的综合排序。结果研究发现,与其他类型的角色相比,在ASD儿童中,器物角色的动机反馈效果更佳,并且这几类角色对ASD儿童的眼动指标都有不同程度的影响,因此每个角色的干预效果也不尽相同。结论将ARCS动机理论模型引入绘本角色设计中,结合眼动实验解析动机策略与角色特征元素之间的关联性,能更有效地改善干预训练中缺乏学习动机的情况;建立评价体系有助于为后续相关设计提供研究思路。

ArcCheck系统在鼻咽癌容积旋转调强剂量验证中的应用

目的:研究ArcCheck验证系统在鼻咽癌容积旋转调强剂量验证中的应用。在病人接受放射治疗之前,进行容积调强计划的验证,使其满足计划设计要求。保证患者实际照射中接受到准确的剂量,确保治疗的安全。方法:选择34例鼻咽癌病例用热塑型体部网罩固定,CT扫描定位,将计划CT传到Pinnacle计划系统(9.2版本)中进行容积旋转调强治疗计划设计,然后将设计好的计划传输至MOSAIQ网络系统上。同时把治疗计划导入ArcCheck模体中重新新型剂量计算。在验证之前,对Arccheck系统进行本底校准,矩阵校准,绝对剂量校准。分析方法采用的是Gamma方法在ArcCHECK自带软件中对治疗计划系统中计算的结果和实际测量的结果二者的差异,阈值标准选择3%,3mm,10%。采用微软Excel2003数据统计软件。结果:Gamma分析方法相对量通过率97.9%,绝对量通过率为95.9%;实测剂量分布图与理论计算剂量分布图在高低剂量点分布上重合很好;另外X方向和Y方向的平坦度,实测结果与计算结果很接近。结论:ArcCheck验证系统在鼻咽癌容积旋转剂量验证中是可行的。它是一种方便快捷准确的旋转调强剂量验证方法。

基于ArcGIS的液化小区划方法初步研究

本文对以GIS为基础的液化小区划技术进行了初步研究,收集唐山市区范围内的65个钻孔资料,将获得的有关砂土液化因素的属性信息和空间信息通过先进的Arc GIS技术组织成一个既能展现属性特征又能反映图形分布特征的地理信息数据库。根据钻孔勘测资料采用规范判别液化指数法和多因子线性回归液化判别法,运用Arc GIS中的VBA编程计算各测点的液化指数和液化势,采用克里格插值法由已知钻孔数据推测出未知钻孔数据区域的液化情况,最终得出基于Arc GIS的地震液化小区划图,为专家进行决策和工程应用提供直观系统的依据。借助专家对唐山大地震发生后三天拍摄的航拍片的解译,将其标定的液化范围与本文运用Arc GIS得出的液化小区划图进行对比,不同判别方法的液化等级分布与实际相符,验证了区划技术的适用性。此外虽然不同方法的液化判别成功率不同,但液化程度的分布都大致相同,与航拍片相一致,说明研究某一区域的液化程度和对某一种液化判别方法进行验证,不仅取决于测点的判别成功率,还可以从区划技术出发进行研究和验证。不同的判别方法得出的液化等级面积百分比有所不同,这取决于各个方法中参数的选取和方法的计算精度。

基于Arc/info的电压等高线的实现及应用

为了得到电力系统运行数据的全局宏观信息,需要将电力系统的节点运行数据转换为等高线来显示。以Arc/info为开发平台,提出电力系统节点电压等高线可视化的实现方法,将地理信息与电力系统节点运行数据相结合,先将地理上随机分布的节点转换为规则格网,再利用规则格网法生成电压等高线。最后也利用不规则格网法(TIN)生成等高线,以做效果和精确度的比较,并且已在河南省调度中心的GIS系统中应用该等高线系统。

GIS软件Mapinfo到Arc/Info的数据格式转换方法

以GIS软件MapInfo7.0和ArcGIS9.2为平台,研究MapInfo的唯一数据存储格式Tab向Arc/Info的数据存储格式Coverage转换的方法。结果是在实施转换时,需要根据矢量数据大小选择不同的方式;当文件数据量较小时,选择Tab-ShapeFile-Coverage方式转换,当数据量较大文件时,选择Tab-E00-Coverage方式转换,从而可以保证数据的准确性,提高工作效率。

94例容积旋转调强治疗宫颈癌ArcCHECK验证研究

目的:研究ArcCHECK在宫颈癌容积旋转调强治疗验证中两种不同评价方法通过率比较。方法:选择94例宫颈癌在Pinnacle计划系统中进行容积旋转调强治疗计划设计,然后将计划传输至MOSAIQ网络系统上。同时把治疗计划导入ArcCHECK模体中计算。对比模体计算的结果和ArcCHECK测量得到的剂量,采用DTA方法和Gamma方法对其进行分析。阈值选用3%,3mm,10%,使用Excel统计方法选用配对t检验。结果:Gamma方法相对量通过率97.67±2.94%,DTA方法相对量的通过率为95.86±3.31%,Gamma和DTA计划通过率有明显差异(t=1.99,P<0.001)。结论:容积旋转调强治疗的宫颈癌验证中,采用不同的评价方法其验证结果有差异。需要进一步研究评价方法的本质才能客观评价验证结果。

基于Arc Hydro Tools的祁连山国家公园小流域划分

以祁连山国家公园为研究区,基于30 m分辨率数字高程模型数据,利用Arc Hydro Tools水文数据模型与河网密度法,在确定最佳集水面积阈值的基础上提取河网并划分小流域,统计小流域的部分特征参数.结果表明,集水面积阈值与河网密度呈幂函数关系,祁连山国家公园最佳集水面积阈值为6000栅格数;河网提取结果与全国1∶250000三级水系流域数据集的河网套合差为2.62%,叠加至遥感图像对比,发现提取结果相较于全国1∶250000三级水系流域数据集更接近真实水系;共划分祁连山国家公园小流域5717个,约80%的小流域面积在3~50 km2.从提取效率和结果精度来看,Arc Hydro Tools模型与河网密度法相结合可较准确提取山地区域河网及小流域.

HTML5 Canvas API中arc方法的应用研究

目的针对HTML5Canvas API的方法、属性之多,方法的使用参数之多,各方法之间的联合使用之多,造成了初学者对HTML5Canvas API方法、属性掌握的困难。通过对HTML5Canvas API中方法、属性的文献阅读、案例研究的形式,探讨HTML5Canvas API的使用。方法选用HTML5Canvas API中arc方法,运用分析法、典型案例法来具体阐述arc方法的应用,最后用arc方法和各种功能实现了一个比较复杂的随系统时间变化的动态时钟,进而使读者了解HTML5Canvas API其它方法的运用。结果 HTML5Canvas API中arc方法需要在一定的环境下使用,通过各方法、属性的联合应用以及arc方法参数的调整,可以用arc方法绘制圆形边框或圆弧边框,绘制圆形填充或扇形填充,绘制直线。通过圆形边框、直线的绘制,就可以绘制一个比较复杂的时钟。结论 HTML5Canvas API中,面对大量的属性和方法,arc方法的剖析对全面掌握HTML5Canvas API的其它方法有更加深刻的认识,另外通过案例来研究掌握各种方法的使用,对于学习者是非常有效的,进而通过HTML5Canvas API的方法、属性来制作出丰富多彩的Web页面。

基于ARCS模型的游戏教学法在实验课程中的实践

以注意力(attention)、切身性(relevance)、自信心(confidence)、满意感(satisfaction)四要素为驱动的ARCS学习动机模型是一种激发学生学习动机的教学设计模型。本文介绍在课程“结构模型概念与实验”中基于ARCS模型,在课堂中引入游戏教学法的改革实践。以实践类游戏为例展示了如何基于ARCS学习动机模型进行教学游戏设计,并介绍了课程中所采用的“米粉-棉花糖结构游戏”、“结构仿真平台严肃游戏”、“结构知识、一站到底”游戏、“静动载模型实验竞赛”等案例的实施情况。调查问卷等反馈结果表明:根据课程的特点,精心设计教学游戏并有机融入到课程中去,可提高课堂活力,激励学生主动学习,达到良好的教学效果。文章对其他相似的实验课程具有借鉴意义。