Development of a Miniature Permanent Magnetic Circuit for Nuclear Magnetic Resonance Chip

The existing researches of miniature magnetic circuits focus on the single-sided permanent magnetic circuits and the Halbach permanent magnetic circuits. In the single-sided permanent magnetic circuits, the magnetic flux density is always very low in the work region. In the Halbach permanent magnetic circuits, there are always great difficulties in the manufacturing and assembly process. The static magnetic flux density required for nuclear magnetic resonance(NMR) chip is analyzed based on the signal noise ratio(SNR) calculation model, and then a miniature C-shaped permanent magnetic circuit is designed as the required magnetic flux density. Based on Kirchhoff’s law and magnetic flux refraction principle, the concept of a single shimming ring is proposed to improve the performance of the designed magnetic circuit. Using the finite element method, a comparative calculation is conducted. The calculation results demonstrate that the magnetic circuit improved with a single shimming has higher magnetic flux density and better magnetic field homogeneity than the one improved with no shimming ring or double shimming rings. The proposed magnetic circuit is manufactured and its experimental test platform is also built. The magnetic flux density measured in the work region is 0.7 T, which is well coincided with the theoretical design. The spatial variation of the magnetic field is within the range of the instrument error. At last, the temperature dependence of the magnetic flux density produced by the proposed magnetic circuit is investigated through both theoretical analysis and experimental study, and a linear functional model is obtained. The proposed research is crucial for solving the problem in the application of NMR-chip under different environmental temperatures.

水轮机修复堆焊技术研究现状分析

传统能源逐渐枯竭,且对环境影响较大.国家大力推动绿色清洁能源的发展.水力发电占比也逐年提高,对水轮机相关技术的研究有了更高要求.我国河流泥沙含量大,泥沙含量越高,水轮机关键零部件磨损就越大.水轮机零部件修复技术存在成本高、效率低且质量难以保证等问题,因此亟需研究低成本高效率的智能堆焊修复技术.应用于轮机的先进堆焊技术可以促进绿色环保、提高能源利用率,同时也可促进国民经济发展和振兴机械工业.

医疗机构水污染物标准定额研究探讨

医疗机构污水工程设计处理水量和进水水质是确定处理设施建设规模和处理工艺的重要基础参数,结合国家标准《医疗机构污水处理工程建设标准》制订,重点就医疗机构水污染物中关于水量和水质指标的确定进行介绍,为后续更好的理解和执行标准提供参考。

基于三维模型的机加工艺设计关键技术

基于三维模型的机加工艺设计方法可以有效地继承三维设计模型的信息,实现以三维工艺模型为核心的工艺信息表达方式,对实现工艺的智能设计与车间制造执行系统的深度集成具有支撑作用。分析与阐述了目前三维机加工艺设计关键技术的研究现状。分别对三维工艺信息的合理表达与组织管理、三维工艺模型的快速创建和工艺更改后的工艺模型动态重构等关键技术进行了论述,最后对三维机加工艺设计技术存在的问题及未来研究方向进行了展望。

基于工件与外部可消耗工具摩擦的焊接技术研究进展

摩擦焊是一类依靠摩擦产热来实现材料连接的固相焊接技术,具有接头质量高、焊接变形小、节能环保等优点,广泛应用于航空航天、交通运输、矿山机械、海洋装备等领域.近年来,摩擦焊技术发展迅速,一些改型的工艺相继产生.根据相互摩擦对象的属性对摩擦焊技术进行了分类,归纳了各自的主要工艺特点.对基于工件与外部可消耗工具相互摩擦的焊接技术进行了系统综述,重点介绍了径向摩擦焊、摩擦-铆接、摩擦塞补焊、摩擦堆焊和涡流搅拌摩擦焊的基本工艺原理和最新研究进展,同时对以上工艺技术的未来发展展开了讨论,以期为相关领域的科研工作者提供参考.

面向车载深冷高压供氢系统的控制策略研究

提出一种深冷高压储供氢系统的实时控制策略,用于管理控制燃料电池卡车的氢能储供过程。首先,基于流体热力学模型建立深冷高压储氢瓶泄放模型,预测氢的状态参数变化。其次,结合车辆热管理系统,设计一种新型深冷高压氢供给系统,综合利用燃料电池"废热"和深冷高压"冷能"。最后,通过数值建模对换热器运行参数进行定量研究,优化了控制策略。整体动态响应机制既满足了燃料电池正常运行的要求,又提升了整车能量利用率。

多次激光冲击导致的Ti17合金层裂

为研究激光冲击Ti17合金中厚样品的层裂特性和层裂阈值,对样品(厚5 mm)表面进行单点连续1~8次激光冲击,激光工艺参数为:频率1 Hz,脉宽15 ns,激光能量30 J,方形光斑4 mm×4 mm。采用白光干涉仪、超声波无损检测技术和扫描电镜,分析和检测中厚样品冲击区域的表面形貌、内部损伤以及层裂形貌。实验结果表明,连续从4次到5次激光冲击中厚样品的表面凹坑深度增加值最大为64.5%。连续5次激光冲击为中厚样品层裂阈值,层裂面积随冲击次数增加而增加。连续5~8次激光冲击中厚样品层裂厚度的实验值为280~310μm。层裂机理为韧性微孔洞的形核、增长和汇合,形成晶界失效和晶内失效。研究结果可为激光冲击强化整体叶盘改性提供工艺参考。

面向现场装配的产品装配工艺模型表达与管理方法

针对面向现场装配的工艺信息完整准确表达与高效管理的应用需求,提出以三维装配过程模型为载体实现面向现场装配的产品装配工艺模型表达与管理方法。分析了面向现场装配的产品装配工艺信息变迁特点,明确了从产品预规划装配工艺信息向现场实际装配工艺信息的实例化映射规则;定义了三维装配过程模型与装配工艺信息数据集,并确定了工艺信息在该模型上的装配工艺基于模型定义(MBD)表达方案;利用装配工艺信息层级嵌套管理模式实现了对面向现场装配的产品装配工艺信息的有效管理,并构建了装配工艺管理器进行工艺信息的组织与存储。将上述方法集成于三维装配工艺设计系统中,并以创建某型减速器产品的三维装配工艺模型为例,验证了所提方法的有效性。

《消防给水稳压设备选用与安装》(17S205)修编介绍

自《消防给水及消火栓系统技术规范》(GB 50974-2014)颁布实施以来,设计、审图和监管部门对稳压泵如何选型与应用有较大争议,为此《消防给水稳压设备选用与安装》(17S205)也依据规范要求进行了修编并完成报批。就该图集主要修编内容进行分析,以期为消防给水稳压设备在工程应用中选型提供依据和支撑。

大长径比管道汽油-空气混合气爆炸与抑制实验研究

为探究狭长受限空间中油气爆炸失控时的发展状态,探索高效环保的油气爆炸抑制方法,利用长径比155的管道开展92号汽油-空气混合气爆炸发展规律和七氟丙烷主动抑爆技术研究。通过测量不同端部开口条件下油气爆炸超压、火焰传播速度、火焰强度等参数,对比研究空爆和抑爆工况下的油气爆炸变化规律,探讨长直管道中的油气爆炸特性,分析七氟丙烷抑爆效果。结果表明:大长径比管道中,端部开口泄爆对降低油气爆炸破坏能力的作用较小,开口与否对最大超压峰值的出现位置有影响;长直管道空爆时,油气爆炸由爆燃发展成爆轰,管道尾部的爆轰波速可达近2000 m/s;密闭管道中,爆轰发生前火焰传播呈“已燃区-火焰锋面-待燃区-前驱激波-未燃区”的2波3区结构;主动抑爆方式下七氟丙烷抑爆效果良好,最大超压峰值降低幅度可达90%,火焰传播被及时阻断。

车载深冷高压氢节流过程冷能研究

对重型卡车储氢和供氢系统进行数值模拟,利用热力学模型描述卡车耗氢过程,对卡车行驶过程中的热力学工况进行监测,开展节流过程及冷能转移过程的研究。首先,针对深冷高压氢特点和重型卡车动力学参数建立面向低温流体的热力学模型,包括整车物理模型、储罐热扩散模型、供氢导热模型、供氢流动换热模型的构建,并对热力学预测模型的准确性进行验证;其次通过ANSYS Fluent流体仿真模型验证换热系数准确性。研究显示,供氢节流过程会使氢气发生液化导致供氢压力不足。为了改变这种现象,提高深冷高压氢的利用效率,对加热策略及其影响进行了研究,从能量角度对其进行了解释。

Numerical investigation of liquid sloshing in FLNG membrane tanks with various bottom slopes

To analyze the bottom slope's effect on the sloshing liquid in floating liquefied natural gas(FLNG)membrane tanks,a simulation model is built and applied to describe the liquid behavior in a sloshing container.The free surface motion is simulated by the volume-of-fluid method and the standard k-εturbulence model.Experimental data and numerical results from references are used to validate the accuracy of the proposed simulation model.To study the influence of the sloped bottom on the liquid sloshing,different slope sizes and filling ratios are numerically simulated at the lowest natural frequency.The results reveal that the natural frequency can be determined by the average peak values of hydrodynamic parameters.The natural frequency and pressure loading on the tank walls decrease with the increase in the slope size.The peak pressure on the wall decreases by 5.45 kPa with the increase in the slope ratio from 5%to 20%.However,the relationship between the peak pressure and slope ratio is more significant with lower filling rates.Liquid behavior is more stable and independent with the change of the slope structure at a high filling rate(60%).The results of numerical simulation and modeling are expected to provide reference data for the design and operation of the FLNG system.

Study on ultrasonic spray technology for the coating of vascular stent

The ultrasonic spray technology is studied by the method of theoretical derivation, CFD simulation, spray particle diameter detection and analysis, and experimental analysis. And the ultrasonic spray process for the coating of vascular stent is also optimized. Firstly, the ultrasonic atomization physical model is established and the equation of atomization particle diameter is derived. Secondly, the ultrasonic atomization process is simulated by the CFD method, and shows three atomization patterns： incomplete atomization pattern, critical atomization pattern and jet atomization pattem. The critical amplitude and power equation for ultrasonic atomization is derived. Thirdly, experiment is conducted to study the influence of parameters including power, gas pressure, and surface tension. The results show that the spray is stable though few particles are likely to collide each other during spray moving, and the droplet diameter is about 10μm. The Rosin-Rammler distribution equation for ultrasonic spray is created, and the uniform index number is between 7.11 and 11.48. The uniformity of spray particle diameter, the efficiency of adjustment and the energy consumption are better than traditional spray technology. Lastly, the ultrasonic spray process parameters for stent coating are optimized to eliminate the common defects and obtain fine coating.

Measurement of thermal boundary conductance between metal and dielectric materials using femtosecond laser transient thermoreflectance technique

The thermal boundary conductance of Al/SiO2, Al/Si, Au/SiO2, and Au/Si are measured by a femtosecond laser transient thermoreflectance technique. The distinct differences of the interfacial thermal conductance between these samples are observed. For the same metal film, the thermal boundary conductance between metal and substrate decreases with the thermal conductivity of the substrate. The measured results are explained with the phonon diffusion mismatch model by introducing a phonon transmission coefficient across the interface.

Research on critical technology of micro/nano bioparticles manipulation platform based on light-induced dielectrophoresis

On the basis of the research on the status and problems of micro/nano bio-particles manipulation using dielectrophoresis, the theoretical basis and the model simulation of micro/nano bio-particles manipu-lation using light-induced dielectrophoresis were discussed. The space distribution of electric field and dielectrophoresis forces in different heights were also obtained. On this basis, the core component of the micro manipulation system, that is, photoconductive layer of the chip, was completed in the mate-rial selection, fabricating process and performance analysis testing. Then the voltage drop of the sus-pension and the effective voltage frequency spectrum were obtained. Finally, by combining the machine vision detection with real-time tracking system, the micro/nano bio-particles manipulation platform based on the light-induced dielectrophoreisis was established, and then the manipulations for micro/nano bio-particles, such as quick collection, transport, separation, were implemented. This provided a basis for rapid, accurate, and low-cost detection of serious diseases based on the micro-fluidic biochip and early diagnosis.

Light-induced electro-rotation:Microspheres spin in micro-manipulation using light-induced dielectrophoresis

According to the equivalent circuit model(ECM),finite element model(FEM) and physical experiment,the LIDEP force induced by the spatial variations of the phase of AC electric fields produced by the bright and dark regions on the photoconductive layer was demonstrated.Besides,the phenomenon of the light-induced electro-rotation(LIER) caused by the light-induced rotating electric field was confirmed numerically and experimentally for the first time.It may be helpful to go out of the dilemma that only the dipole moment model,based on the effect of light-induced partial potentials,can be used for LIDEP theoretical calculation currently.Through the FEM simulation and the electro-rotating experiment of yeast cells,it was found that the direction of yeast's LIER is relevant to the distance between its location and the edge of optical electrode,and the spin velocity of LIER is inversely proportional to that distance.Nevertheless,the LIER torques in the three-electrode mode show a non-uniform distribution where the LIDEP forces are harmful for a particle spinning stably around a fixed axis.Moreover,a four-electrode double-layer mode was proposed for the first time and the finite element simulation results agreed with the expected design,suggesting a new way for the dielectric spectrum measurement based on LIER.

激光冲击强化TC17叶片前缘模拟件的抗FOD性能

为研究激光冲击强化(LSP)叶片前缘抗外物损伤(FOD)性能,设计截面尺寸近似叶片前缘的缺口模拟件。采用YAG激光器(30 J和15 ns)和方形光斑(4 mm×4 mm)对TC17模拟件的缺口尖端进行双面LSP。采用X射线衍射仪、透射电镜、高频疲劳试验机和扫描电镜分别对LSP前后的残余应力、微观组织、疲劳性能和疲劳断口进行测试分析。结果表明,与未强化缺口模拟件相比,LSP-TC17合金的表面残余压应力最大值为-403MPa。LSP-TC17合金表面形成高密度位错、孪晶和纳米晶。LSP-TC17缺口模拟件的疲劳强度提高55.6%。TC17缺口模拟件的疲劳强化机理为高幅残余压应力和表面纳米晶。研究结果为LSP-FOD叶片奠定理论基础并提供工艺参考。

水下定向能量沉积修复钛合金电化学腐蚀特性研究

水下定向能量沉积技术能够对水下结构件的表面损伤进行原位修复,在海洋工程领域具有广阔的应用前景。受损钛合金结构件水下修复后表面的耐蚀性对于其服役安全至关重要。本研究团队采用水下定向能量沉积技术对Ti-6Al-4V预制梯形槽进行水下修复,通过对比水下和陆上定向能量沉积结果,阐明了水下修复工艺对组织、硬度和电化学腐蚀特性的影响。结果表明:水冷淬火提高了水下熔池的冷却速率,并降低了沉积过程的热积累,生成了具有较高位错密度和较高硬度的针状马氏体组织;与陆上定向能量沉积试样、基体材料相比,水下定向能量沉积试样具有更好的耐蚀性,水下沉积Ti-6Al-4V的耐蚀性主要受组织晶粒度、合金元素分布以及表面组织状态的影响。本文研究结果能够为钛合金装备水下激光增材修复提供参考和理论基础。

车载深冷高压储供氢过程预测和影响因素研究

针对应用深冷高压储氢技术的车载系统,为补充现有研究中缺乏的描述系统实时运行状态的方法,提出利用储氢密度确定工况的预测模型。基于丰田Mirai氢燃料电池车型建立动力学部分的模型。电堆功率和氢气流量的相对误差分别不超过7%和1.3%。基于Refprop物性软件建立热力学部分的模型。储氢密度的相对误差不超过1%,从而验证储供氢过程预测模型的精度。此外,还研究储氢容器的初始温度和压力工况对汽车续驶里程和容器休眠期的影响。结果表明,35 MPa下,容器初温由40 K变为70 K,车辆的续航里程减少约18%。同时,增加容器初压可以延长续航里程,但在35 MPa左右的高压时,增压的效果很不明显。而初温70 K、初压5~35 MPa的常见工况范围内,行驶过程中容器压力变化很大,易发生疲劳破坏。为达到固定的休眠期,对漏热量更大的储罐,加注后需实现更低的初温来满足使用需求。

Separation of nanocolloids driven by dielectrophoresis:A molecular dynamics simulation

The nonequilibrium molecular dynamics (MD) method was used to model the nanocolloids and the solvent particles. By introducing a non-uniform electric field, colloids were polarized to have opposite polarities. Separation of colloids driven by dielectrophoresis (DEP) could be seen clearly under a strong electric field at low temperatures. Analyzing the ratio of DEP velocities of colloids to thermal velocities of neutral solvent particles showed that when the ratio was correspondingly big, collision between colloids and solvent particles would be intense, making the DEP velocity of colloids fluctuate frequently. By changing the electric field strength, it was found that the enhancement of electric field strength would quicken the separation of colloids. But when the electric field strength increased to a certain degree, the separation motion would be slow because of the strong friction resistance of the solvent particles to the colloids. Moreover, studying the separation reason of colloids based on the potential energy showed that after colloids were polarized, the attractive potential energy among the colloids would be weaker than before, while the increase of temperature would reduce the attractive potential energy and increase the repulsive potential energy, which accorded with the DLVO theory.