Dynamic Response of Foundations during Startup of High-Frequency Tunnel Equipment

The specialized equipment utilized in long-line tunnel engineering is evolving towards large-scale,multifunctional,and complex orientations.The vibration caused by the high-frequency units during regular operation is supported by the foundation of the units,and the magnitude of vibration and the operating frequency fluctuate in different engineering contexts,leading to variations in the dynamic response of the foundation.The high-frequency units yield significantly diverse outcomes under different startup conditions and times,resulting in failure to meet operational requirements,influencing the normal function of the tunnel,and causing harm to the foundation structure,personnel,and property in severe cases.This article formulates a finite element numerical computation model for solid elements using three-dimensional elastic body theory and integrates field measurements to substantiate and ascertain the crucial parameter configurations of the finite element model.By proposing a comprehensive startup timing function for high-frequency dynamic machines under different startup conditions,simulating the frequency andmagnitude variations during the startup process,and suggesting functions for changes in frequency and magnitude,a simulated startup schedule function for high-frequency machines is created through coupling.Taking into account the selection of the transient dynamic analysis step length,the dynamic response results for the lower dynamic foundation during its fundamental frequency crossing process are obtained.The validation checks if the structural magnitude surpasses the safety threshold during the critical phase of unit startup traversing the structural resonance region.The design recommendations for high-frequency units’dynamic foundations are provided,taking into account the startup process of the machine and ensuring the safe operation of the tunnel.

A novel variable polarity welding power based on high-frequency pulse modulation

A new type of variable polarity welding power modulated with high-frequency pulse current is developed. Series of high-frequency pulse current is superimposed on direct-current-electrode-negative （DCEN）, which can improve the crystallization process in the weld bead as a result of the electromagnetic force generated by pulse current. Digital signal processor （DSP） is used to realize the closed-loop control of the first inverter, variable polarity output of the second inverter and high-frequency pulse current superposition.

A note for the mechanism of high-frequency oscillation instability resulted from absorbing boundary conditions

In this paper the explanation of the mechanism of high-frequency oscillation instability resulted from absorbing boundary conditions is further improved. And we analytically prove the proposition that for one dimensional discrete model of elastic wave motion, the module of reflection factor will be greater than 1 in high frequency band when artificial wave velocity is greater than 1.5 times the ratio of discrete space step to discrete time step. Based on the proof, the frequency band in which instability occurs is discussed in detail, showing such high-frequency waves are meaningless for the numerical simulation of wave motion.

Effects of controlled pulse current waveform on key-holing condition in plasma arc welding

To overcome the shortcomings of conventional plasma arc welding （ PAW）, the ＇ controlled pulse key-holing＇ strategy is proposed and the keyhole PAW experiment system is developed. ＇The efflux plasma voltage signal is detected in realtime to characterize the keyhole size and dimension. The welding current waveform for controlled pulse key-holing strategy is implemented, and two slow-decreasing slopes are added at the dropping point from peak current to base current to further reduce both heat input and arc force so that the controllability of keyhole dynamics is improved. Two kinds of PAW tests are conducted, anti the different parameters of the controlled pulse current and the relevant efflux plasma voltage are measured in real-time to investigate ihe effects of welding current waveform parameters on the key-holing condition.

Evaluation of automatic girth weldability of pipeline in special conditions

To meet the requirements of pipeline consumers abroad,in this study,an automatic gas metal arc welding type of girth welding was performed with a heat input of no more than 0.25 kJ/mm and high-strength solid-wire matching for an X70M large-diameter UOE pipeline.An integral evaluation of the X70M pipeline girth weldability was performed with respect to the girth-weld cold-cracking sensitivity during the welding process and the strengthening,hardening,and embrittlement of the girth weld joint after girth welding in especially rigorous welding conditions with accelerated failure characteristics.The performance of the above girth weld joint with joints welded using the main construction-field girth welding procedure was compared to ensure the good girth weldability of the X70M pipeline.The results of this study have important supervisory significance for field-construction girth welding.Finally,the girth weldability of the X70M pipeline was found to satisfy the field construction requirements even when the welding conditions are especially rigorous.

Investigation on the communication network of long wire transmitting in remote welding

According to the characteristics of remote welding, including multiple parameters, real-time, and reliability of long wire transmitting, a distributing computer control scheme is adopted. A serial communication network between the master and the slavery computers is constructed. A synchro-control network among slavery computers is designed. Uniform message format and communication protocols are made. Considering intensive high-frequency noises at the welding zone, a quadruple check mode, including data sum check, parameter type check, welding parameters check and Exclusive OR （ XOR ） check, is adopted to assure the reliability of communication among multiple computers. Based on disturbing circuit, common circuit and sensitive circuit, the measures are brought forward to ensure the stabilization of communication network of remote arc welding by analyzing the wiring principle of anti-high-frequency interference of system bus, signal wires and shielding twisted-pair（STP） wires. The results provide the theoretical and practical references for the manufacture of remote welding robot and the quality of remote welding.

Characterization of Dissimilar Welding between 304 Stainless Steel and Gray Iron Using Nickel Coated Electrode

This paper presents the study carried out to study the microstructure and mechanical properties of AISI 304 stainless steel and gray iron, in order to recognize the effect of welding parameters on the joint. The shielded metal arc welding technique was applied with a 3.2 mm diameter nickel coated electrode under preheating and post heat conditions at 350°C. Vickers hardness test and metallographic analysis were carried out at the heat affected zone and at the interface to determine the effect on mechanical and metallurgical characteristics. Vickers hardness differences among joint areas were directly related to microstructural changes. There are no significant differences in AISI 304 hardness, but the hardness increased at the heat affected zone and decreased at the filler metal. Grey iron hardness at the heat affected zone was even lower and more slightly superior than grey iron hardness.

Numerical simulation for the comparison of thermal and plastic material flow behavior between symmetrical and asymmetrical boundary conditions during friction stir welding

An accurate description of the contact condition between the tool and the workpiece material is one of the most important issues for expounding the underlying multi-physics coupled mechanism during friction stir welding(FSW)process.In the present study,a novel asymmetrical boundary condition around the tool-workpiece contact interface is proposed for the FSW of AA2024-T4 alloy.A three-dimensional computational fluid dynamics model is employed for the comparison of the coupled thermal and plastic material flow behavior between asymmetrical and symmetrical boundary conditions.Numerical results of heat generation,temperature distribution,tunnel defect formation and material flow streamline during the welding process are quantitatively analyzed.Besides,various experimental measuring methods are utilized to obtain information about temperature,thermal cycle,tool torque and horizontal cross-section around the exiting keyhole.It is revealed that the modeling results of heat flux density and temperature distribution around the pin,as well as material flow characteristics all change significantly for the two models with different boundary conditions.Particularly,the asymmetrical boundary condition is more capable of predicting temperature fluctuation,plastic material flow along the vertical direction,as well as tunnel defect formation during FSW.Therefore,the superiority of the model with asymmetrical boundary condition over the symmetrical one during the numerical simulation of FSW is elucidated.

基于SYSWELD的预热温度对焊接热输入影响的有限元模拟

采用数值模拟方法在有限元软件SYSWELD中建立了焊接三维有限元模型,利用非线性材料热物性参数和双椭球移动热源作为热传递方程的边界条件,得到了在不同预热温度条件下能熔透母材的最低焊接线能量。采用材料为API X65钢进行实验验证,表明模拟结果和实验结果基本吻合,为预热条件下采用合适的焊接工艺提供了科学的指导依据。

激光-MAG和MAG焊接Weldox960钢接头的组织与性能对比

分别采用激光-活性气体保护电弧焊(Laser-MAG焊)和MAG焊对Weldox960钢板进行焊接,对比分析了两种工艺焊接接头的显微组织及性能。结果表明:Laser-MAG焊接接头热影响区粗晶区的平均晶粒尺寸较小,为48μm,而MAG焊接接头的为95μm,两种焊接接头的显微组织基本相同,焊缝区组织为细小粒状贝氏体,细晶区组织为细小板条马氏体和粒状贝氏体,部分相变区组织为铁素体+粒状贝氏体;Laser-MAG焊接接头的热影响区宽度小于MAG焊接接头的,软化带也较窄,其拉伸性能和冲击性能均优于MAG焊接接头的,条件疲劳极限为320 MPa,高于MAG焊接接头的。

基于置信水平的钢轨焊接接头设备状态评定方法

[目的]为解决我国无缝线路钢轨设备状态评定体系不完善的问题,需要建立基于置信水平的钢轨焊接接头设备状态评定方法。[方法]阐述了目前我国规定的高速铁路钢轨平直度允许偏差、焊接接头平直度允许偏差。以我国某条已开通运营13年的高速铁路为案例,对该线钢轨焊接接头平直度数据进行分析,认为钢轨接头平直度检测数据总体服从正态分布。根据正态分布及置信区间原理,对均值和标准差评定法、置信水平评定法进行对比,提出了基于置信水平的钢轨焊接接头设备状态评定方法,得到高速铁路钢轨设备状态的评定标准。[结果及结论]该方法能够客观、直观地反映出钢轨焊接接头的设备状态,可以准确地掌握钢轨设备状态。该方法可为分析钢轨设备变化规律,以及制定大中修的标准、计划及方案等提供很好的理论依据。

镀锌钢表面状态对镁/镀锌钢MIG焊焊接性的影响

镁/镀锌钢复合结构件设计和使用可有效降低结构和车身质量,是汽车轻量化发展的热门研究方向之一。为了揭示镁/镀锌钢MIG焊中镀锌层的作用,通过对比未处理、硝酸腐蚀、机械打磨3种镀锌钢表面状态所得MIG焊接头的焊缝成形、界面组织、显微硬度和耐蚀性,开展了镀锌钢表面状态对镁/镀锌钢MIG焊焊接性的影响的研究。研究结果表明:镀锌层的存在有利于改善液态镁合金在钢表面的润湿铺展性,有利于界面区的氧化物夹杂的溢出,促进界面反应进行和界面过渡层的形成,且部分Zn元素可进入焊缝区参与焊缝合金化,因此镀锌钢未处理时所得接头焊缝成形美观,界面过渡层均匀连续,无焊接缺陷产生,焊缝区硬度升高,界面区耐蚀性最佳。在此基础上建立了镁/镀锌钢MIG焊中镀锌层的作用模型,可为揭示镁/镀锌钢焊接机理、改善镁/镀锌钢焊接性,以及提高镁/镀锌钢焊接质量提供一定的理论支持,具有重要的研究意义和应用价值。

汽车空调压缩机焊接设备自动化技术在生产中的应用与效益分析

随着汽车工业的迅猛发展,汽车空调压缩机的生产质量和效率对整个行业至关重要。本文旨在探讨汽车空调压缩机焊接设备自动化技术在生产中的应用与效益,并强调其在提高生产效率、降低成本、保证产品质量方面的重要性。通过分析该技术的原理、特点和优势,深入剖析其在汽车制造过程中的实际应用情况与效果。研究结果表明,该技术能够提高生产效率、降低劳动强度、减少人为失误,并且具有潜在的经济效益。

Computational fluid dynamics simulation of friction stir welding:A comparative study on different frictional boundary conditions

Numerical simulation based on computational fluid dynamics （CFD） is a useful approach for quantitatively investigating the underlying thermal-mechanical conditions during FSW, such as temperature field and material deformation field. One of the critical issues in CFD simulation of FSW is the use of the frictional boundary condition, which represents the friction between the welding tool and the workpiece in the numerical models. In this study, three-dimensional numerical simulation is conducted to analyze the heat transfer and plastic deformation behaviors during the FSW of AA2024. For comparison purposes, both the boundary velocity （BV） models and the boundary shear stress （BSS） models are employed in order to assess their performances in predicting the temperature and material deformation in FSW. It is interesting to note that different boundary conditions yield similar predictions on temperature, but quite different predictions on material deformation. The numerical predictions are compared with the experimental results. The predicted deformation zone geometry by the BSS model is consistent with the experimental results while there is large difference between the predictions by the BV models and the experimental measurements. The fact that the BSS model yields more reasonable predictions on the deformation zone geometry is attributed to its capacity to automatically adjust the contact state at the tool/workpiece interface. Based on the favorable predictions on both the temperature field and the material deformation field, the BSS model is suggested to have a better performance in numerical simulation of FSW than the BV model.

基于条件生成对抗网络识别噪声中相贯线焊缝

针对焊接中产生的电弧光和飞溅等噪声的干扰造成相贯线焊缝特征点识别困难这一问题,提出了一种基于条件生成对抗网络的激光图像修复网络与全卷积神经网络(FCN)相结合的相贯线焊缝识别方法。该方法将FCN的识别误差作为损失函数嵌入到生成网络中,并使用信噪比作为阈值控制焊缝图像的识别方法,生成无噪声的激光条纹图像,达到去除噪声干扰、识别焊缝特征点的目的。实验结果表明,该方法针对在不同程度的噪声干扰下,对相贯线型焊缝具有良好的识别效果,识别平均误差0.2 mm,满足自动焊接要求。

复杂工况条件下钢结构厚板焊接质量控制技术

结合深圳湾超级总部基地某地标性工程案例,通过六合一集束柱在有限焊接空间的复杂工况条件下超厚板的焊接研究,分析了超厚板焊接技术质量保障的主要问题,并总结其原因及制定相关解决措施。从超厚板焊接前准备以及焊接过程控制两个方面,合理地选用焊接工艺,提高了超厚板在有限焊接空间的复杂工况条件下的焊接效率以及焊缝质量,达到高标准焊接技术的要求。

双侧复合搅拌摩擦焊压电测力仪研究

针对平台式测力仪被放置在工作台上而不能测量双侧复合搅拌摩擦焊过程中焊接力的问题,设计了一款置于主轴前端的旋转式压电测力仪,并利用有限元仿真对其进行了静力学与模态分析。考虑到整套设备庞大、连线繁杂,不适用于长程焊接,设计了一块信号调理电路板内嵌于测力仪中,将传感器产生的微弱电荷信号转换放大为模拟电压信号。通过标定及实测,得到了电路板线性度误差、准确度误差等指标,结果表明其性能良好,满足压电测试需求。

极端条件下焊接技术的研究进展

随着科学技术的不断进步,工程应用标准的不断提高,越来越多的极端条件对焊接技术提出了更苛刻的要求。首先将服役情况分为环境温度、腐蚀环境、磨损情况、真空环境四个方面,综述了焊接结构在这些极端环境下的综合性能变化情况,同时对比了为克服这些极端环境的负面影响而研究的各类应对方法及其作用机制;其次以焊接的材料结构为出发点,介绍了大型结构与薄壁结构这两大极端尺寸结构件在焊接时的技术难题与疲劳寿命评估的现状。对当前极端条件下焊接技术存在的问题与难点进行总结与梳理,并对其未来发展方向进行展望。

电力电缆铝芯线与铜连接管的电磁焊接条件研究

目前,电磁焊接技术在电缆接头制作中的可行性和优越性已经得到国内外诸多学者的证实,然而关于电缆接头电磁焊接的焊接条件却鲜有研究。鉴于此,该文通过对70 mm^(2)铝绞线铜中间连接管电磁焊接进行了仿真模拟和实验研究。研究结果表明,集磁器中轴线上磁场大致呈“钟型”分布,工作区位置磁场最大,远离工作区的位置,磁场迅速减小,集磁器工作区径向不同位置,磁场分布较为均匀。对外管的形变过程进行了仿真、测量及理论推导,理论推导所得外管加速阶段速度曲线与仿真以及实测速度波形相近,理论计算碰撞速度与实测值偏差在10%以内,并且外管的碰撞速度与充电电压近似呈线性关系。电缆接头电阻随着充电电压的提升而减小,当充电电压为12 kV时,接头电阻为25.2μΩ,仅为要求值的60.8%;电缆接头强度随着充电电压的提升而提高,当充电电压大于12 kV时,铝绞线本体发生断裂,说明电磁焊接接头强度大于母材的强度。当充电电压为12 kV时,焊接接头切面观察到连续的波状界面,波峰约20μm,波长约70μm,已经达到焊接效果,此时实测碰撞速度为128.9 m/s,理论推导计算出的碰撞速度为134.7 m/s,与下限碰撞速度之间的偏差分别为5.6%和10.3%,因此可以较好地预测两种材料达到焊接条件所需的能量值,为今后的电磁焊接装置设计提供有效的参考。