Analysis of droplet transfer of pulsed MIG welding based on electrical signal and high-speed photography

In order to study how welding parameters affect welding quality and droplet transfer, a synchronous acquisition and analysis system is established to acquire and analyze electrical signal and instantaneous images of droplet transfer simultaneously, which is based on a self-developed soft-switching inverter. On the one hand, welding current and voltage signals are acquired and analyzed by a self-developed dynamic wavelet analyzer. On the other hand, images are filtered and optimized after they are captured by high-speed camera. The results show that instantaneous waveforms and statistical data of electrical signal contribute to make an overall assessment of welding quality, and that optimized high-speed images allow a visual and clear observation of droplet transfer process. The analysis of both waveforms and images leads to a further research on droplet transfer mechanism and provides a basis for precise control of droplet transfer.

Sound Source Localisation for a High-Speed Train and Its Transfer Path to Interior Noise

Noise is one of the key issues in the operation of high-speed railways, with sound source localisation and its transfer path as the two major aspects. This study investigates both the exterior and interior sound source distribution of a high-speed train and presents a method for performing the contribution analysis of airborne sound with regard to the interior noise. First, both exterior and interior sound source locations of the high-speed train are identified through in-situ measurements. Second, the sound source contribution for di erent regions of the train and the relationships between the exterior and interior noises are analysed. Third, a method for conducting the contribution analysis of airborne sound with regard to the interior noise of the high-speed train is described. Lastly, a case study on the sidewall area is carried out, and the contribution of airborne sound to the interior noise of this area is obtained. The results show that, when the high-speed train runs at 310 km/h, dominant exterior sound sources are located in the bogie and pantograph regions, while main interior sound sources are located at the sidewall and roof. The interior noise, the bogie area noise and the sound source at the middle of the coach exhibit very similar rates of increase with increasing train speed. For the selected sidewall area, structure-borne sound dominates in most of the 1/3 octave bands.

Mass transfer area in a multi-stage high-speed disperser with split packing

In this study, the mean droplet diameter in the cavity zone and the total mass transfer area of a multi-stage highspeed disperser(HSD) reactor with different packing combinations were measured and evaluated. The effects of rotational speed and packing radius, as well as the packing ring radius and numbers, on the mean droplet diameter and the total mass transfer area were evaluated. A model was established to calculate the mass transfer area in the cavity zone in the HSD reactor, and it was found that the packings contribute 61%–82% of the total mass transfer area. A correlation for predicting the mass transfer area in the packing zone was regressed by the dimensionless analysis method. An enhancement factor based on the mass transfer area in the packing zone was proposed to evaluate the effect of packing combination on mass transfer area. Two optimum packing combinations were proposed in consideration of the mean droplet diameter and the enhancement factor.

Turbulence flow and heat transfer of aluminum melt in tip cavity in process of thin-gauge high-speed casting

The uniformity of flow distribution of aluminum melt in tip cavity is a precondition to decide whether or not thin-gauge high-speed casting can be accomplished smoothly. The laws of aluminum melt flow and heat transfer in tip cavity can be found out through numerical simulation, which gives theoretical basis for solving the problem of the flow distribution of melt in tip cavity. A mathematical model with a low Reynolds number k—ε model for turbulence flow and heat transfer of aluminum melt in tip cavity was developed. The finite difference method was used to calculate the flow field and temperature field of aluminum melt in tip cavity. The phenomena and characteristics of turbulence flow and heat transfer were analyzed, including the characteristics of temperature distribution of turbulence similar to that of laminar flow. The simulation results are in good agreement with the experimental results for flow velocities and temperature at the exit of tip, which verifies the validity of the simulation results.

我国跨项速度滑冰运动员身体形态、机能和运动素质特征及训练策略

跨项运动员具有早期进行多项化训练、晚定项和晚进入选材与培养体系等特点,晚期定项与早期定项运动员存在较大差异性。以我国19名跨项速度滑冰运动员为研究对象,采用文献资料法、实验测试法和数理统计法,对其身体形态、机能、运动素质等进行统计分析。发现,我国跨项速度滑冰运动员体脂率和BMI等指标表现良好,但需关注下肢双侧差异、有氧能力不足以及专项技术的强化等问题。为提高跨项运动员的成才率和运动表现,未来训练应注重下肢双侧均衡发展,提升有氧与无氧能力,增加陆冰结合和技术模拟练习。

浅海内波环境下声速剖面的深度迁移时序预测

海水声速随时空起伏变化,水文资料稀缺海域声速剖面时序预测困难,为此构建了基于迁移学习的长短时记忆神经网络模型,并利用中国南海海域实测的两条温度链长时序观测数据对其进行验证。针对有无孤立子内波存在的两种场景,基于迁移学习对预训练网络模型进行微调,分析不同训练样本量下迁移网络的有效性。实验结果表明,迁移网络在有无孤立子内波存在的两种场景下均可实现高精度高效声速剖面预测,且预测性能明显优于未迁移的处理方法。

Research on Constant-Speed Rapeseed Drying Mechanism

This paper presents research on constantspeed rapeseed drying mechanism and the mathematical model established for constant speed drying period.

Influence of longitudinal magnetic field on metal transfer in MIG arc welding

Metal transfer is an important phenomenon in metal inert gas （MIG） arc welding with longitudinal alternating magnetic field. It is of great significance to observe the metal transfer modes under different excitatory currents and frequencies. However, it is very difficult to view the metal transfer process directly during welding, due to the strong interference from the arc light. To obtain the relationship between the metal transfer modes and the different magnetic fields, a high-speed video camera was used to acquire the images of globules. Different metal transfer modes under the conditions of different magnetic fields and welding parameters were studied. The experiment shows clear images of droplet transfer as well as influence of longitudinal magnetic field on both metal transfer and globule shape.

Interfacial heat transfer behavior at metal/die in finger-plated casting during high pressure die casting process

Heat transfer at the metal-die interface has a great influence on the solidification process and casting structure. As thin-wall components are extensively produced by high pressure die casting process(HPDC), the B390 alloy finger-plate casting was cast against an H13 steel die on a cold-chamber HPDC machine. The interfacial heat transfer behavior at different positions of the die was carefully studied using an inverse approach based on the temperature measurements inside the die. Furthermore, the filling process and the solidification rate in different finger-plates were also given to explain the distribution of interfacial heat flux(q) and interfacial heat transfer coefficient(h). Measurement results at the side of sprue indicates that qmax and hmax could reach 9.2 MW·m^(-2) and 64.3 kW ·m^(-2)·K^(-1), respectively. The simulation of melt flow in the die reveals that the thinnest(T_1) finger plate could accelerate the melt flow from 50 m·s^(-1) to 110 m·s^(-1). Due to this high velocity, the interfacial heat flux at the end of T_1 could firstly reach a highest value 7.92 MW·m^(-2) among the ends of T_n(n=2,3,4,5). In addition, the q_(max) and h_(max) values of T_2, T_4 and T_5 finger-plates increase with the increasing thickness of the finger plate. Finally, at the rapid decreasing stage of interfacial heat transfer coefficient(h), the decreasing rate of h has an exponential relationship with the increasing rate of solid fraction(f).

基于Buck-Boost的锂电池双层均衡方法研究

由于锂电池组的不一致性导致电池组使用寿命缩短和可用容量减少,为提高均衡速度,设计了一种基于Buck-Boost的分层均衡拓扑。以单体电池荷电状态(SOC)作为均衡变量,采用平均值比较法的均衡策略,将电池组分为两层来进行均衡。根据提出的均衡拓扑和相应的均衡策略,采用4节锂电池单体在MATLAB/Simulink实验平台做了双层均衡仿真实验,同时将其与传统均衡拓扑进行对比分析,经实验证明,所设计的均衡拓扑可以提高均衡速度和能量转移效率。

高速铁路无砟轨道车辆荷载传递特性研究

为进一步探讨无砟轨道荷载设计参数取值,为我国时速400 km及以上高速铁路建设提供重要理论支撑,通过开展无砟轨道静力分析以及钢轨焊缝、车轮扁疤激励下车辆-轨道动力相互作用,揭示列车静、动力载荷特征及传递规律;同时根据轨道承载特点和无砟轨道设计原理,提出车辆竖向设计荷载取值建议。研究结果表明:(1)高速列车车轮扁疤和钢轨焊缝不平顺将造成显著的轮轨冲击,其轮载动载系数最大可达5.79,远高于现行规范取值;扣件系统对扁疤和焊缝不平顺引起的轮轨力高频成分衰减作用明显,扣件支反力的动载系数最大为2.64;(2)钢轨焊缝不平顺引起的轮轨冲击力随着车速提高以及焊缝不平顺幅值的增大而迅速增大,建议500 km/h及以下高速铁路的钢轨焊缝平直度标准取0.2 mm/m;(3)列车轮载通过扣件支反力作用于轨道板,从传递特性的角度来说,以扣件支反力作为轨道板竖向设计荷载更为合理,其动载系数可取3.0,且能满足400 km/h及以上高速铁路的行车需求。

基于Buck-Boost电路与相对极差策略的锂电池组分层均衡技术研究

针对串联锂电池组均衡过程中出现的均衡速度慢、能量转移效率低等问题,提出一种基于Buck-Boost电路的分层均衡拓扑结构,以各单体电池的荷电状态(SOC)作为均衡变量,采用相对极差法的均衡控制策略以实现各层均衡单元的同步均衡。首先阐述了改进后均衡拓扑的整体结构以及分层分组的方法、最小均衡单元的均衡原理以及均衡过程中相关参数的计算过程;之后根据所设计的分层拓扑结构设计了与其相适应的均衡控制策略;最后在Matlab/Simulink中分别搭建了不同拓扑下的仿真模型并进行了均衡仿真验证。仿真结果表明,在8节电池与9节电池的不同情况下与传统单层均衡拓扑相比,文中所提出的采用相对极差控制策略的分层均衡拓扑结构在均衡速度上分别提高了86.06%和84.21%,在能量转移效率上分别提高了3.3%和4.22%,验证了所提均衡拓扑以及均衡策略的有效性。

前继列车晚点条件下换乘客流的接续方案优化

针对列车运行受到干扰下运行图调整问题,对前继列车晚点条件下换乘客流的接续方案进行研究,将换乘客流和在车客流影响最小化作为优化目标对列车运行图进行相应调整.在前继列车晚点条件下,假定换乘客流既可以换乘到原接续列车,也可以选择其他符合换乘条件的列车,建立所有列车上的旅客延误时间最小和换乘失败旅客数量最少的多目标模型,以期在保证换乘成功的前提下最小化列车运行计划调整.以京沪高铁和郑徐高铁上行部分区段为例验证模型的有效性.研究结果表明:当考虑列车总调整时间和换乘客流失败成本相互制约关系时,可以通过增加列车运行调整时间来提高换乘成功客流量;当考虑所有列车上的旅客延误时间和换乘旅客失败成本相互制约关系时,可以通过牺牲部分换乘旅客来减少在车旅客的总延误时间;当其他接续列车空余席位大幅减少时,接续方案倾向于调整原接续列车的到发时刻,避免换乘失败的旅客量大幅增加.

CFD Study of Forced Air Cooling and Windage Losses in a High Speed Electric Motor

High speed and high efficiency synchronized electric motors are favored in the automotive industry and turbo machinery industry worldwide because of the demands placed on efficiency. Herein an electric motor thermal control system using cooling air which enters from the drive end of the motor and exits from the non-drive end of the motor as the rotor experiences dissipates heat is addressed using CFD. Analyses using CFD can help to find the appropriate mass flow rate and windage losses while satisfying temperature requirements on the motor. Here, the air flow through a small annular gap is fed at 620 L/min (0.011 kg/sec) as the rotor spins at 100,000 rpm (10,472 rad/sec) and the rotor dissipates 200 W. The CFD results are compared with experimental results. Based upon the CFD findings, a novel heat transfer correlation suitable for large axial Reynolds number, large Taylor number, small annular gap Taylor-Couette flows subject to axial cross-flow is proposed herein.

基于转鼓转速传感的中低速新能源汽车联合制动系统控制方法

中低速新能源汽车是常见的交通工具,但是其制动控制存在响应时间长、控制效果差的问题,设计一种基于转鼓转速传感的中低速新能源汽车联合制动系统控制方法。首先,构建基于转鼓转速传感的中低速新能源汽车动力学方程,采集传感信息,然后,考虑开环控制容易导致控制系统的稳定性和鲁棒性差的问题,基于转鼓转速传感的联合制动系统传递函数推导出开环、闭环双传递函数,最后,根据系统传递函数,设计PID控制器的参数,通过PID控制器输出电-液联合制动控制信号,实现汽车联合制动系统控制。实验结果表明:所提方法的速度-位移曲线与现实速度-位移曲线基本一致,加速误差在-0.5 m/s2~0.5 m/s2范围内,平均制动控制响应时间为0.075 s,具有良好的制动控制能力。

基于深度残差收缩迁移网络的复杂工况下滚动轴承故障诊断

针对噪声和不同转速的复杂工况下滚动轴承故障诊断问题,提出一种基于深度残差收缩迁移网络的复杂工况下滚动轴承故障诊断方法。在深度残差收缩网络中加入领域适配层构建出具备降噪与适配能力的深度残差收缩迁移网络,从而减小噪声带来的干扰及转速变化导致的分布差异。首先,利用注意力机制学习经卷积层后各特征通道的重要性自动设定一组阈值,借助软阈值化将阈值范围内的特征置为零,减少噪声带来的干扰;然后,通过边缘分布适配对齐两域特征分布,减小转速变化带来的分布差异;最后,在Softmax分类层下实现端到端的复杂工况下滚动轴承故障诊断。复杂工况下滚动轴承故障诊断试验验证了所提方法的可行性和有效性。

面向车次取消的票额分配与停站方案组合优化研究

当列车因严重干扰而取消时,大量旅客将在车站滞留,同时铁路公司收益也会受到一定影响,合理的票额分配是解决此类问题的有效方法。在差异化设置换乘旅客优先权基础上,构建了以铁路公司收益最大化和偏离原时刻表最小化为目标的票额分配和停站方案组合优化模型,并通过增加不等式组约束条件将其线性化;利用求解器GUROBI对上述模型进行求解并分析算例。研究结果表明:当列车因干扰而取消时,与不采用任何措施相比,灵活停站策略能有效地减少滞留旅客数量19.7%以上;铁路公司收益增加21.8%以上。

K7-GTX与VU9P-GTY高速数据远距离通信应用

在现代高速数据通信领域,数据量快速增长,对通信速率需求越来越高,高速串行收发器GTX/GTH/GTY成为高速通信领域中非常重要的解决方案。文中对不同系列高速串行接口进行远距离高速数据通信与验证,采用Kintex-7 GTX与Virtex UltraScale+系列的VU9P GTY接口进行非板间接口测试,高速接口间通过1 m长的定制高速线缆连接,通过配置Aurora64B/66B协议IP核设计收发双向数据通信程序,实现了单通道10 Gbit/s的通信速率,并确保数据收发正确。通过IBERT的远端回环实验进行眼图测试和误码率测试,通过ILA测试接收到的有效数据传输无误码,并且系统稳定可靠,满足实际使用需求。

高铁网络对城市群空间结构的影响机理——基于要素转移与共享的视角

高铁网络对城市群空间结构造成了复杂的影响。一方面,高铁的开通带来的时空压缩效应降低了区域要素流动的成本,带来区域整体经济效率的提高;另一方面,高铁的网络效应会强化中心城镇的区位优势,形成对周边中小城市的“虹吸效应”,扩大城镇发展的不均衡。传统基于地点可达性测度的“土地利用-交通交互作用”理论难以解释高铁网络对城市群空间结构的复杂网络效应。本文从要素流动的视角,基于“转移型”(具备时空排他性,例如资本与劳动力)与“共享型”(无时空排他性,例如信息与技术)两类要素流,解析“高铁网络–要素转移与共享–城市群空间结构”级联作用路径;以武汉城市群为研究案例区,利用互联网位置服务平台提供的人口迁徙等大数据资源识别并测度城镇间要素转移与共享空间特征,综合应用空间交互模型、空间面板回归等方法实证高铁网络对要素转移与共享,以及对城市群空间结构的影响。研究结果表明,高速铁路的发展对武汉城市群经济发展具有异质性影响,高铁的发展促进了劳动力从周边中小城镇向中心城市转移,从而对武汉市经济具有明显的极化作用,对武汉周边城市的经济发展造成了挑战;同时,高铁也促进了信息与技术从中心城市向周边扩散,给地区经济转型带来了机遇。本研究克服了长期以来相关研究多基于单一类型“流数据”造成过度简化城镇间交互作用的缺点,尝试用统一的分析框架来解释高铁网络对城市群空间结构产生的影响。研究结果将为优化城市群空间结构提供政策参考。

基于预训练GoogleNet模型和迁移学习的齿轮箱故障检测方法

针对以往齿轮箱故障诊断中特征处理算法繁琐、人为因素影响较大等问题,提出了一种基于预训练GoogleNet模型和迁移学习(TL)的故障诊断方法。首先,利用连续小波变换(CWT)将离散时间序列转变为二维小波尺度图,构建了样本集;然后,对预训练模型进行了结构微调及参数微调使其符合任务需求,利用处理得到的训练样本对微调后的模型进行了微训练,使其达到理想精度,然后保存模型,再将其应用于故障分类任务;最后,为了对上述模型的可行性进行验证,利用昆明理工大学控制与优化重点实验室的平行齿轮箱数据以及东南大学的行星齿轮箱数据对微调模型进行了验证。研究结果表明:相比于传统卷积神经网络(CNN)以及未经预训练的GoogleNet模型,基于预训练GoogleNet模型和迁移学习的故障诊断方法在训练样本较少的情况下,其分类准确率均值仍然高达97.40%,且模型的收敛速度更快,对计算机算力的依赖程度更低。微调模型高层的方法能根据任务分类情况个性化设置模型输出,因此该模型能够适用于不同的场景。