YAG laser welding with surface activating flux

YAG laser welding with surface activating flux has been investigated, and the influencing factors and mechanism are discussed. The results show that both surface activating flux and surface active element S have fantastic effects on the YAG laser weld shape, that is to obviously increase the weld penetration and D/W ratio in various welding conditions. The mechanism is thought to be the change of weld pool surface tension temperature coefficient, thus, the change of fluid flow pattern in weld pool due to the flux.

Activating Flux Design for Laser Weldingof Ferritic Stainless Steel

The behaviors of YAG laser welding process of ferritic stainless steel with activating fluxes were investigatedin this study. Some conventional oxides, halides and carbonates were applied in laser welding. The resultsshowed that the effect of oxides on the penetration depth was more remarkable. Most activating fluxes improved thepenetration more effectively at low power than that at high power. The uniform design was adopted to arrange theformula of multicomponent activating fluxes, showing that the optimal formula can make the penetration depth up to2.23 times as large as that without flux, including 50% ZrO2, 12.09% CaCO3, 10.43% CaO and 27.48% MgO. Throughthe high-speed photographs of welding process, CaF2 can minimize the plasma volume but slightly improve the penetrationcapability.

Stationarity Preservation Properties of the Active Flux Scheme on Cartesian Grids

Hyperbolic systems of conservation laws in multiple spatial dimensions display features absent in the one-dimensional case,such as involutions and non-trivial stationary states.These features need to be captured by numerical methods without excessive grid refine-ment.The active flux method is an extension of the finite volume scheme with additional point values distributed along the cell boundary.For the equations of linear acoustics,an exact evolution operator can be used for the update of these point values.It incorporates all multi-dimensional information.The active flux method is stationarity preserving,i.e.,it discretizes all the stationary states of the PDE.This paper demonstrates the experimental evidence for the discrete stationary states of the active flux method and shows the evolution of setups towards a discrete stationary state.

A Combination of Residual Distribution and the Active Flux Formulations or a New Class of Schemes That Can Combine Several Writings of the Same Hyperbolic Problem:Application to the 1D Euler Equations

We show how to combine in a natural way(i.e.,without any test nor switch)the conservative and non-conservative formulations of an hyperbolic system that has a conservative form.This is inspired from two different classes of schemes:the residual distribution one(Abgrall in Commun Appl Math Comput 2(3):341–368,2020),and the active flux formulations(Eyman and Roe in 49th AIAA Aerospace Science Meeting,2011;Eyman in active flux.PhD thesis,University of Michigan,2013;Helzel et al.in J Sci Comput 80(3):35–61,2019;Barsukow in J Sci Comput 86(1):paper No.3,34,2021;Roe in J Sci Comput 73:1094–1114,2017).The solution is globally continuous,and as in the active flux method,described by a combination of point values and average values.Unlike the“classical”active flux methods,the meaning of the point-wise and cell average degrees of freedom is different,and hence follow different forms of PDEs;it is a conservative version of the cell average,and a possibly non-conservative one for the points.This new class of scheme is proved to satisfy a Lax-Wendroff-like theorem.We also develop a method to perform nonlinear stability.We illustrate the behaviour on several benchmarks,some quite challenging.

Effect of activating flux on arc shape and arc voltage in tungsten inert gas welding

The effects of activating fluxes on welding arc were investigated. A special set of water-cooling system and stainless steel were used as parent material. During welding process, high-speed camera system and oscillograph were used for capturing instantaneous arc shape and arc voltage respectively. The experimental results indicate that the SiO2 flux can increase the arc voltage, while TiO2 has no this effect on arc voltage. Compared with conventional tungsten inert gas welding (C-TIG), it is found that the arc shape of A-TIG welding used with the SiO2 flux has changed obviously.

Effect of activating fluxes on weld mechanical properties in TIG welding

Activating TIG (A-TIG) welding has received many attentions worldwide since the end of 1990s. Compared with conventional TIG welding A-TIG welding can greatly improve the welding productivity and reduce the welding cost without altering the equipments under the same welding procedures and is considered as a innovative variant of conventional TIG welding. The materials applied by A-TIG welding have ranged from original titanium alloy to stainless steel, carbon steel, high temperature alloy steel and so forth. The effects of activating fluxes with single component on weld mechanical properties such as tensile strength, hardness and elastics during A-TIG welding of stainless steel are discussed in this paper. The experimental results show that different fluxes have different effects on the weld mechanical properties. Among these fluxes the flux SiO_2 is the best in the performance of tensile strength and ductility, while flux Cr_2O_3 is the best in the performance of weld hardness compared with conventional TIG welding. These experiments provide the foundation for selecting the most suitable fluxes for stainless steel in practical welding production.

Development of the active flux in superalloy laser welding and the effect on the weld formation

In this study,adopting uniform design method established a mathematical model to prepare multi-element active flux. GH4169 superalloy plates were welded by the Nd: YAG laser equipment with the prepared active flux. The results show all kinds of fluxes increase the depth to width ratio and the multi-component systems are more significant. The largest increment of the weld depth to width ratio is 159%,obtained by using of the F12 series flux. It is proved that by using of the active flux to increase the depth to width ratio of micro laser welding is feasible.

Experimental study on activating welding for aluminum alloys

TIG welding and EB welding Jbr aluminum alloy 3003 were carried out to study the effects of activating flux on weld penetration of activating welding for aluminum alloys. SiO2 was used as the activating flux. It is found that, SiO2 can increase the weld penetration and decrease the weld width of FBTIG when the flux gap is small. For A-TIG welding and EB welding with focused mode, the weld penetrations and the weld widths increase simultaneoudy. SiO2 has little effect on the weld penetration and weld width of EB welding with defocused mode. It is believed that, change of surface tension temperature gradient is not the main mechanism of SiO2 improving weld penetration of activating welding for aluminum alloys.

INTERFACIAL ACTIVITY BEHEAVIOR OF FLUX DURING ALUMINIUM BRAZING

A study on the interfacial activity behavior of flux during aluminium brazing has been made by using metallography,SEM and electron prob techniques.The results show that the activity, of a flux is caused by the wetting of base metal with the liquid heavy metal reduced from the flux,thus,some regions of liquid alloy created,at which no aluminium oxide film covers on the surfaces.The reduced metal drops are finally trapped in the fillet.The size of the metal drops increases with the decrease of brazing temperature.

Activated flux tungsten inert gas welding of 8 mm-thick AISI 304 austenitic stainless steel

AISI 304 stainless steel plates were welded with activated flux tungsten inert gas(A-TIG) method by utilizing self-developed activated flux. It is indicated from the experimental results that for 8 mm-thick AISI 304 stainless steel plate, weld joint of full penetration and one-side welding with good weld appearance can be obtained in a single pass without groove preparation by utilizing A-TIG welding. Moreover, activated flux powders do not cause significant effect on the microstructure of TIG weld and the mechanical properties of A-TIG weld joints are also superior to those of C-TIG(conventional TIG) welding.

Heat and mass flux estimation of modem seafloor hydrothermal activity

Research on heat and mass flux yielded by modern seafloor hydrothermal activity is very important, because it is involved not only in the base of ocean environment research, but also in the historical evolution of seawater properties. Currently, estimating heat flux is based on the observation data of hydrothermal smokers, low-temperature diffusive flow and mid-ocean ridge mainly. But there are some faults, for example, there is lack of a concurrent conductive item in estimating the heat flux by smokers and the error between the half-space cooling model and the observation data is too large. So, three kinds of methods are applied to re-estimating the heat flux of hydrothermal activity resepectively, corresponding estimation is 97. 359 GW by hydrothermal smoker and diffusive flow, 84.895 GW by hydrothermal plume, and 4. 11 TW by exponential attenuation method put forward by this paper. Research on mass flux estimation is relatively rare, the main reason for this is insufficient field observation data. Mass fluxes of different elements are calculated using hydrothermal vent fluid data from the TAG hydrothermal area on the Mid-Atlantic Ridge for the first time. Difference of estimations by different methods reflects the researching extent of hydrothermal activity, and systematically in - situ observation will help to estimate the contribution of hydrothermal activity to ocean chemical environment, ocean circulation and global climate precisely.

Flux measurements for a DD neutron generator using neutron activation analysis

The fast and maximum thermal neutron fluxes from the DD-109 neutron generator at the University of Sharjah were experimentally measured by the activation technique using different neutron reactions. The thermal and fast neutron fluxes were found to be 2.960 × 10~6 and6.186 × 10~7 n/cm^2 s, respectively. This was done to verify the modeling results for the optimum moderator thickness needed to maximize the thermal neutron flux. The optimum moderator thickness was found to be between 3.5 and4 cm. The present data were compared with the detailed MCNP model-based calculation performed in earlier work to simulate the generator.

THE CALCULATION OF BaO ACTIVITIES IN BaO-BaF_2-Cr_2O_3 SYSTEM FLUXES USING SCHUHMANN METHOD

The principle and steps for the calculation of component activities in fluxes using Schuhmann method are described. On the foris of Gibbs-Duhem equation and using Cr2O3 activities in BaO-BaF2-Cr2O3 system fiuxes, BaO activities at 1523 and 1673K are calculated, respectivelg,and the isoactivity diagrums of BaO are also obtained. The calculation results indicate that BaO activity increases with increasing its content in fiuxes, and decreaaes with the increase of Cr2O3 content at a given XBaO/XBaF2 ratio.

PPARαactivation inhibits astrocyte over acti⁃vation by restoring autophagy flux after tran⁃sient brain ischemia

OBJECTIVE Astrocytes activa⁃tion and glial scar formation are the important causes that hinder the recovery of motor function after cerebral ischemia.However,its precise mechanism has not been clarified.Peroxisome proliferator-activated receptorα(PPARα)is a ligand-activated nuclear transcriptional factor.This study aims to further clarify the role of PPARαin astrocyte activation after cerebral isch⁃emia and explore the underlying mechanism.METHODS Astrocyte activation in vivo model was induced by transient middle cerebral artery occlusion(tMCAO)in mice and in vitro model was induced by oxygen-glucose deprivation/reox⁃ygenation(OGD/R)in primary culture of mouse astrocyte.The effects of PPARαon astrocyte ac⁃tivation and autophagy flux were observed in the condition of PPARαdysfunction(PPARαnull mice)or PPARαactivation by oleoylethanol⁃amide(OEA).RESULTS PPARαmainly ex⁃pressed in activated astrocytes during the chron⁃ic phase of brain ischemia and PPARαdysfunc⁃tion promoted astrocytes activation after brain ischemia in vivo and in vitro.After cerebral isch⁃emia,the expressions of LC3-Ⅱ/Ⅰand P62 both increased in the brain tissue near the infarct core.Autophagic vesicles accumulation was ob⁃served by electron microscopy in astrocytes,and mRFP-GFP-LC3 adenovirus infection assay indi⁃cated the block of autophagy flux.PPARαdys⁃function aggravated autophagy flux block,while PPARαactivation preserved the lysosome func⁃tion and restored autophagy flux in astrocytes after OGD/R.Autophagy flux blocker bafilomycin A1 and chloroquine antagonized the effect of OEA on inhibiting astrocyte activation.CONCLU⁃SION PPARαactivation inhibites the over-activa⁃tion of astrocytes by restoring the autophagy flux after cerebral ischemia.

Determination of Neutron Fluxes and Spectrum Shaping Factors in Irradiation Sites of Ghana’S Miniature Neutron Source Reactor (mnsr) by Activation Method After Compensation of Loss of Excess Reactivty

Accurate neutron flux values in irradiation channels of research reactors are very essential to their usage. The total neutron flux of the Ghana Research Reactor-1(GHARR-1) was measured after a beryllium reflector was added to its shim to compensate for excess reactivity loss. The thermal, epithermal and fast neutron fluxes were determined by the method of foil activation. The experimental samples with and without a cadmium cover of 1-mm thickness were irradiated in the isotropic neutron field of the irradiation sites of Ghana Research Reactor-1 facility. The induced activities in the sample were measured by gamma ray spectrometry with a high purity germanium detector. The necessary correction for gamma attenuation, thermal neutrons and resonance neutron self-shielding effects were taken into account during the experimental analysis. By defining cadmium cutoff energy of 0.55eV, Al-0.1% Au wires of negligible thickness were irradiated at 3kW to determine the neutron fluxes of two irradiation channels, outer channel 7 and inner channel 2 whose Neutron Shaping Factor (α) were found to be (0.037 ± 0.001) and (–0.961 ± 0.034). The neutron flux ratios at the inner irradiation site 2 were found to be, (25.308 ± 3.201) for thermal to epithermal neutrons flux, (0.179 ± 0.021) for epithermal to fast neutrons flux and (4.528 ± 0.524) for thermal to fast neutrons flux, in the outer irradiation site 7, the neutron flux ratios were found to be, (40.865 ± 3.622) for thermal to epithermal neutrons flux, (0.286 ± 0.025) for epithermal to fast neutrons flux and (11.680 ± 1.030) for thermal to fast neutrons flux.

用RCPT研究功能梯度混凝土抗氯离子渗透性能

用非稳态迁移法(NSSM)和自然浸泡法评定功能梯度混凝土(FGC)的抗氯离子渗透性能都存在局限性,但快速氯离子渗透试验法(RCPT)没有局限性。该研究用RCPT法对基于各种胶凝材料的FGC的电通量进行了大量测试并得到如下结论:提出了FGC的电通量计算公式;FGC的电通量反映了FGC的抗氯离子渗透性能,FGC的电通量越低则其抗氯离子渗透性能越高;碱激发矿渣(AAS)砂浆具有极好的抗氯离子渗透性能,其氯离子渗透系数可低至2.1×10^(–13)m^(2)/s。

船舶永磁同步推进电机的优化I/f起动控制方法

为解决高转矩与高转动惯量的船舶推进电机在开环I/f控制中转速和转矩波动大、电机易失步、效率低的问题,提出一种I/f控制改进方法。通过建立转矩角观测器,调节给定电流矢量的幅值,使其跟随负载转矩变化,提高系统鲁棒性。同时,将电机运行状态推进至接近最大转矩电流比状态,提高电机的运行效率;通过瞬时有功功率调节电流矢量的角速度,降低电磁转矩波动,加快电机的转速收敛过程。最后,在Matlab/Simulink中进行仿真实验,实验结果表明该方法可以显著提高推进电机运行效率和稳定性。

1961-2020年华北地区7-8月份极端降水频次趋势转折及可能原因分析

区域性极端降水(Regional extreme precipitation,REP)破坏性强,会造成地质灾害和经济损失。本文利用逐日降水资料,研究了1961-2020年华北地区7-8月份REP频次趋势转折,并探讨其变化的可能原因。结果表明,华北地区7-8月REP天数存在1986、1995和2003年三个趋势突变点,在1961-1985年(P1)和1995-2002年(P3)时段有减少趋势,1986-1994年(P2)和2003-2020年(P4)时段呈现增多趋势。华北地区REP事件发生时有水汽通量辐合,并且中国东北部至朝鲜半岛对流层高层有异常高压(东北高压)存在。P2、P4时期较P1、P3时期东北高压位置偏南,38°N以南的华北地区水汽通量辐合增强,REP天数增多。P1、P2时期异常水汽通量来自印度洋和西北太平洋,而后两个时期只来自西北太平洋,这是东亚夏季风减弱、西太平洋副热带高压(西太副高)增强的结果。东北高压的发展在P1、P3时期与沿中纬度西风急流(急流)传输的波活动通量有关,在P2、P4时期高纬度活动中心发挥作用并且在季节背景上该高压较强,P2时期促使东北高压发展的波活动通量来自急流和高纬度活动中心两支路径,而P4时期波活动通量主要沿高纬度传播。REP天数减少在P1时期主要是东亚夏季风显著减弱不利于水汽向华北地区输送的结果,而P3时期是东亚夏季风减小和急流减弱共同作用所导致的;REP天数增多在P2时期是因为急流的显著增强,有利于东北高压的发展,而在P4时期西太副高的增强保证了东亚夏季风减弱之后向华北地区的水汽输送,并且北极海冰范围减少可能通过影响高纬度活动中心,在急流减弱之后建立了由高纬度向华北地区传输的波活动通量新路径,两者共同作用使得REP天数增多。

开关磁阻电机自抗扰无磁链直接转矩控制

针对传统直接转矩控制策略转矩脉动抑制性能弱、调速平稳性差和调速范围窄问题,提出一种基于自抗扰的开关磁阻电机无磁链直接转矩控制。分析传统直接控制转矩策略转矩脉动较大的原因,在此基础上设计了一种无磁链闭环控制方法并且重构了更适应电机运行特性的电压矢量;针对传统自抗扰参数过多难以整定问题,采用线性自抗扰控制器将其代替,提高了控制器的速度、抗扰动能力和鲁棒性。仿真验证结果表明,在不同转速、负载工况下,不仅动态响应性能提升,而且电机转矩脉动得到进一步抑制,电流峰值降低,进而提高了转矩电流比。

2021年北极典型平流层爆发性增温事件研究与预报

本文选取了对我国2021年冬季寒潮事件可能有重要影响的2021年1月北半球平流层爆发性增温(SSW)事件为例,利用观测资料、再分析资料和预报模式,探讨了2021年1月的SSW事件的特征和机制并对其进行了预报研究。此次SSW事件(简称为“事件”)发生期间,北极平流层温度几天内上升近30°C,绕极西风环流减弱甚至在此次事件中出现了三次逆转为东风环流的现象。事件发生前期,太平洋海温和巴伦支—喀拉海(BK)海冰的出现异常的降低和减少现象;使用Eliassen-Palm通量(E-P通量)研究发现,这导致更多的对流层异常行星波活动上传到平流层;海温和海冰所导致的行星波活动的异常增多可能是导致此次SSW事件的主要因素。除此之外还发现,事件期间平流层位势高度正异常下传到对流层,与2021年1月中旬亚欧大陆出现的极端低温事件,存在显著的联系。最后,本文使用基于WACCM6模式和DART同化工具建立的平流层预报模型对此次事件进行了回报研究。该模型成功的预报了2021年1月发生的这次SSW事件,预报的温度大小和纬向风强度基本和观测结果一致。对回报试验的进一步研究发现,同化平流层温度、臭氧和水汽,减少预报初始场中平流层环流和温度误差,对准确预报这次SSW事件有重要的作用。初始场中没有同化平流层温度、臭氧和水汽的预报试验结果,与观测结果之间存在很大差异,甚至结果完全相反。