Measurement of Swarm Parameters of c-C4F8/CO2 and Its Insulation Characteristics Analysis

In c-C4F8 and c-C4F8/CO2 mixtures, the swarm parameters including ionization coefficient, attachment coefficient and effective ionization coefficient were obtained at the ratio of the electric field strength to the gas density between 150-550 Td by the steady-state Townsend (SST) method. Static breakdown voltages at each ratio were also measured at the SST condition. The limiting field strengths were obtained by two methods:computing the density-normalized effective ionization coefficient as a function of the overall density-reduced electric field strength; and measuring static breakdown voltages as a function of the product of gas density and electrode separation. Good agreement was obtained by these two methods, which ensures the correctness of the former method. The limiting field strengths of c-C4F8 and c-C4F8/CO2 mixtures were compared with those ofpure SF6, SF6/CO2 mixtures and pure c-C4Fs. It is found that buffer gas CO2 does not reduce the limiting field strengths of c-C4F8 greatly, the limiting field strengths of c-C4F8/CO2 mixtures are higher than those of SF6/CO2 mixtures or even pure SF6, and so c-C4F8/CO2 mixtures are suggested to be possible substitutes for SF6.     

Predicting the Dielectric Strength of c-C4F8 and SF6 Gas Mixtures by Monte Carlo Method

An improved Monte Carlo method was used to simulate the motion of electrons in c-C_4F_8 and SF_6 gas mixtures for pulsed townsend discharge. The electron swarm parameters such as effective ionization coefficient, [AKα-] and drift velocity over the E/N range from 280～700 Td(1Td=10-21 V·m2) were calculated by employing a set of cross sections available in literature. From the variation cure of [AKα-] with SF_6 partial pressure p, the limiting field (E/N)_lim of gas mixture at different gas content was determined. It is found that the limiting field of c-C_4F_8 and SF_6 gas mixture is higher than that of pure SF_6 at any SF_6 mixture ratio. Simulation results show excellent agreement with experiment data available in previous literature.     

Monte Carlo simulation of electron swarms parameters in c-C4F8/CF4 gas mixtures

The swarm parametes for c-C₄F₈/CF₄ mixtures, including the density-normalized effective ionization coefficient, drift velocity and mean energy were calculated using Monte-Carlo method with the null collision technique. The overall density-reduced electric field strength could be varied between 150 and 500 Td, while the c-C₄F₈ content in gas mixtures is varied in the range of 0–100%. The value of the density-normalized effective ionization coefficient shows a strong dependence on the c-C₄F₈ content, becoming more electronegative as the content of c-C₄F₈ is increased. The drift velocity of c-C₄F₈/CF₄ mixtures is more affected by CF₄. The calculated limiting field strength for c-C₄F₈/CF₄ mixtures is higher than that of SF₆/CF₄. Foundation item: the National Natural Science Foundation of China (No. 50777041)     

Measurement of swarm parameters of c-C4F8/CO2 and its insulation characteristics analysis

In c-C₄F₈ and c-C₄F₈/CO₂ mixtures, the swarm parameters including ionization coefficient, attachment coefficient and effective ionization coefficient were obtained at the ratio of the electric field strength to the gas density between 150–550 Td by the steady-state Townsend (SST) method. Static breakdown voltages at each ratio were also measured at the SST condition. The limiting field strengths were obtained by two methods: computing the density-normalized effective ionization coefficient as a function of the overall density-reduced electric field strength; and measuring static breakdown voltages as a function of the product of gas density and electrode separation. Good agreement was obtained by these two methods, which ensures the correctness of the former method. The limiting field strengths of c-C₄F₈ and c-C₄F₈/CO₂ mixtures were compared with those of pure SF₆, SF₆/CO₂ mixtures and pure c-C₄F₈. It is found that buffer gas CO₂ does not reduce the limiting field strengths of c-C₄F₈ greatly, the limiting field strengths of c-C₄F₈/CO₂ mixtures are higher than those of SF₆/CO₂ mixtures or even pure SF₆, and so c-C₄F₈/CO₂ mixtures are suggested to be possible substitutes for SF₆. Foundation item: the National Natural Science Foundation of China (No. 50777041)     

甲烷气体放电特性的研究

在E/N为100～900Td（1Td=1017Vcm2）的场强范围内,对甲烷气体中的电子崩发展进行了仿真研究.采用蒙特卡罗模拟法对其电子崩参数诸如有效电离系数、电子漂移速度、纵向扩散系数等进行了求解计算,计算结果与实验数据相一致.仿真结果表明：随着E/N值的增大,即电离作用的增强,电子的各漂移速度也呈现出差异.     

外物损伤对25CrMo4合金车轴钢疲劳性能的影响

为研究外物损伤（FOD）与25CrMo4钢疲劳性能的关联，采用空气炮装置开展高铁车轴钢试样的FOD模拟试验. 首先于试样表面预制FOD缺陷；其次，通过旋转弯曲疲劳试验获得光滑试样和含FOD试样的应力-疲劳寿命（S-N）曲线；同时，基于有限元方法估算不同缺陷试样的应力集中系数，结合Peterson公式预测疲劳缺口系数（FNC）和疲劳极限. 研究结果表明:FOD车轴钢试样的疲劳性能明显低于光滑试样，冲击速度越高，疲劳性能越低；其中边缺陷的疲劳缺口系数最大为1.52，面缺陷最小，约为1.14，但疲劳寿命分散性较大；与试验结果相比，仿真模拟和理论计算可获得更低（偏于保守）的疲劳强度估算值.      

船舶疲劳强度校核中Weibull形状参数的影响

Weibull形状参数是研究船舶疲劳强度的一项重要参数，它由船长和浪高两个因素决定。利用Weibull形状参数对一艘实船的疲劳寿命进行了计算，结果表明：仍然具有很大的误差，必须根据船舶的实际情况，建立累积损伤模型，确立统一的Weibull形状参数表达式，消除误差，准确地计算船舶结构的疲劳累积损伤度，提高船舶疲劳寿命预报的可靠性。     

集中荷载作用下部分预应力混凝土箱形截面约束梁抗剪强度试验研究

本文应用变角桁架模型和软化斜压力场理论,对所做的12片部分预应力混凝土箱形截面约束梁在弯矩-剪力作用下的抗剪强度进行了分析。着重研究了抗剪强度随剪跨比、预应力值和配箍率变化的规律。并引入了随剪跨比变化的系数K以反映集中荷载作用下的竖向压应力Δσ,对抗剪强度的影响。理论分析和试验结果进行了比较,符合程度较好。     

纤维掺量对沥青混凝土强度的影响

为了研究纤维掺量对沥青混凝土强度的影响,选用5种纤维掺量沥青混凝土的马歇尔试件和圆柱体试件,在MTS810材料试验机上进行劈裂试验和单轴压缩试验,分析了劈裂试验结果和抗压强度随纤维掺量变化的规律。研究结果发现,劈裂强度和抗压强度随着纤维掺量的增加均出现先增大后缩小的变化,在纤维掺量为0.20%时取得最大值,反映出适量的纤维加入可以提高沥青混凝土的强度值。根据破裂试验和单轴压缩试验结果分析,给出此种纤维改善沥青混凝土强度的合理掺量约为0.20%。     

钢筋电极导电发热混凝土的研究

提出利用钢筋良好的导电性来制作导电发热混凝土的电极,并进行了相关的实验研究.通过实验发现此种发热混凝土电阻达到稳定的时间要比一般混凝土的固化期长,用细不锈钢钢筋为电极得到的电阻率最低,此种发热混凝土的电阻随电压的升高而降低明显,而升温实验表明所制造出的发热混凝土是成功的.文中所做的研究不仅可以将碳纤维导电发热混凝土所需的碳纤维体积含量降低到0.29%左右,大幅降低制造导电发热混凝土的成本,而且还可以有效地提高导电发热混凝土铺层的强度.     

黄土路基强度规律

通过黄土压实后土体(压实土体)的湿陷性、压缩性和抗剪强度等室内试验，分析了压实土体的湿陷性、水分入渗对其饱和度、渗透系数等的影响和其抗剪强度随压实度和含水量的变化规律。试验表明，黄土压实后土体仍具湿陷性；含水量对压实土体的饱和度、渗透系数和压缩性等基本性质影响较大，一般随含水量的增大其饱和度和压缩性显著减小，而渗透系数在最佳含水量附近达到一个峰值；对于压实土体抗剪强度，其与含水量呈非线性变化关系，而与土体压实度呈线性增长关系。结果表明，严格控制土体含水量，提高路基压实度标准是提高黄土路基整体稳定性的关键。     

纤维增强沥青混合料马歇尔稳定度及劈裂试验研究

为了研究玻璃纤维和木质素纤维对沥青混合料的增强作用及机理,对不同纤维用量的沥青混合料进行马歇尔稳定度和劈裂试验。结果表明,纤维的加入可以有效增加沥青混合料的马歇尔稳定度和劈裂抗拉强度。玻璃纤维对沥青混合料劈裂抗拉的增强作用优于木质素纤维。     

Calculation of Transient Stress Field During Laser Transformation Hardening Process

IntroductionHighpowerCOzlaserssdsetransformationhardeningtechniquehasbeensuccessfullyusedinindusnyforWYears.BecausethetemPeratUrefleldislocalizedinmaterialdurllglasertransfonnationhMngProcess,highthermstrCsswillgenerateinmatgrialduringlasertfansformationhardeningProcess.Therisalsohighresidualstressinmaterial,bothintCnsionandcomPression['-'].ComPressresidualstressishelptoincreasethefatigueldrimeofthelasertreatedmaterial,butthetensilestresswillshortenthefatiguelifetmeofthelasertreatedmator…     

沉入式大圆筒防波堤稳定性分析的有限元强度折减法

沉入式大圆筒结构的抗滑、抗倾稳定性是靠地基土的嵌固作用来维持的,可通过弱化土体强度来实现对结构极限破坏状态的模拟.在该假设的基础上,建立了沉入式大圆筒防波堤稳定性分析的有限元强度折减法.结合某工程实例,利用有限元强度折减法,分析了沉入式大圆筒防波堤结构的稳定性,并与加载系数法计算结果进行了比较.分析结果表明:用强度折减...     

Friction characteristics in green drilling titanium alloy Ti6Al4V

Titanium alloy Ti6Al4V, as difficult-to-cut material, has poor machinability. Conventional cutting fluid serves as a coolant and lubricant. In green drilling, water vapor is recognized as an effective coolant; however, its lubrication properties are not well known in drilling. This paper investigates the friction characteristics between chip and tool in green drilling Ti6Al4V, compared with that in sliding and turning process. A friction evaluation model is developed based on the equivalent model of drilling, then is used to calculate the effective friction coefficient. Results indicate that the friction coefficient on the tool-chip interface is considerably reduced in drilling by water vapor, so the drilling forces decrease, too. The friction coefficient decreases as velocity increases in drilling, which is different from the law of sliding tests; the friction coefficient increases when the distance to chisel edge increases.     

Design and Analysis of an Adaptive Handover Protocol for 4G Networks

The future generation networks or 4G networks constitute of varied technologies converged over the Internet protocol version 6(IPv6) core. The 4G networks offer varied services over different interfaces to the user nodes. Mobility management in 4G networks is an issue that exists. The handover protocols for mobility management in 4G networks that currently exist, do not consider wireless signal degradation during handover operations. This paper introduces the Noise Resilient Reduced Registration Time Care of Mobile IP(NR RRTC:MIP) protocol for handover management. A handover decision algorithm based on the signal strength measured by the user nodes is considered in the NR RRTC: MIP protocol. A simulation study is discussed in the paper to evaluate the performance of the NR RRTC: MIP protocol. The results obtained from the simulation study prove that the NR RRTC: MIP protocol effectively reduces handover latencies and improves network performance.     

基于非饱和非稳定渗流场的滑坡稳定性分析

以鹰厦铁路K290滑坡为原型,基于降雨入渗情况下滑坡体呈饱和-非饱和渗流状态下,通过计算得到坡体孔隙水压力和体积含水量随降雨及地下水位变化的基本规律,进一步导入SIGMA/W程序并依据坡体孔隙水压力和体积含水量及地下水位变化特征分析了滑坡应力场,探讨了降雨强度、降雨持时和水位变化对滑坡体稳定性的影响.     

强震边坡动力响应及安全系数计算

运用ANSYS大型通用软件,对一均质边坡进行地震荷载模拟分析;根据Wilson-θ时程分析方法,将天津地震波输入到边坡模型上,对该边坡进行了应力、位移、速度和加速度动力响应分析.并由摩尔-库伦强度理论对ANSYS通用后处理器进行编程,得出边坡的安全系数分布云图.当安全系数为0.521时,全图的部分穿越临空边界,有滑移的...     

Photothermal effect for Fe3O4 nanoparticles contained in micelles induced by near-infrared light

Near infrared (NIR) light induced photothermal effect for Fe₃O₄ nanoparticles, contained in Pluronic F127 micelles, has been studied and it exhibits high photothermal converting efficiency. Heat is found to be rapidly generated in micelles containing Fe₃O₄ nanoparticles by NIR laser irradiation. Upon irradiation at 808 nm light and with mass concentration of Fe₃O₄ nanoparticles in 4 g/L, the micelle temperature increase is higher than 34°C for 10min irradiation. The maximum temperature of micelles containing Fe₃O₄ nanoparticles in 4 g/L reaches 62°C.     

侧风环境下考虑行车安全的路堤风速场研究

为研究侧风环境下路堤风速场,建立了有限元模型,对不同高度路基风速场进行了仿真分析;现场实测了侧风环境下的路基风速变化规律,验证了仿真结果的正确性。提出了影响行车安全的计算风速区域。结果表明:路基越高局部风速的增强就越大,上风侧路肩和行车道风速增强最明显,对行车安全影响越大。研究结果提供了侧风环境下高大路堤行车安全的理论基础。