Experimental Study on the Electrochemical Performance of PEMFC under Different Assembly Forces

Proton exchange membrane fuel cell(PEMFC)is of paramount significance to the development of clean energy.The components of PEMFC are assembled using many pairs of nuts and bolts.The assembly champing bolt torque is critical to the electrochemical performance and mechanical stability of PEMFC.In this paper,a PEMFC with the threechannel serpentine flow field was used and studied.The different assembly clamping bolt torques were applied to the PEMFC in three uniform assembly bolt torque and six non-uniform assembly bolt torque conditions,respectively.And then,the electrochemical performance experiments were performed to study the effect of the assembly bolt torque on the electrochemical performance.The test results show that the assembly bolt torque significantly affected the electrochemical performance of the PEMFC.In uniform assembly bolt torque conditions,the maximal power density increased initially as the assembly bolt torque increased,and then decreased on further increasing the assembly torque.It existed the optimum assembly torque which was found to be 3.0 N·m in this work.In non-uniform assembly clamping bolt torque conditions,the optimum electrochemical performance appeared in the condition where the assembly torque of each bolt was closer to be 3.0 N·m.This could be due to the change of the contact resistance between the gas diffusion layer and bipolar plate and mass transport resistance for the hydrogen and oxygen towards the catalyst layers.This work could optimize the assembly force conditions and provide useful information for the practical PEMFC stack assembly.

Numerical simulation analysis for deformation deviation and experimental verification for an antenna thin-wall parts considering riveting assembly with finite element method

In the process of thin-wall parts assembly for an antenna,the parts assembly deformation deviation is occurring due to the riveting assembly.In view of the riveting assembly deformation problems,it can be analyzed through transient and static simulation.In this work,the theoretical deformation model for riveting assembly is established with round head rivet.The simulation analysis for riveting deformation is carried out with the riveting assembly piece including four rivets,which comparing with the measuring points experiment results of riveting test piece through dealing with the experimental data using the point coordinate transform method and the space line fitting method.Simultaneously,the deformation deviation of the overall thin-wall parts assembly structure is analyzed through finite element simulation;and its results are verified by the measuring experiment for riveting assembly with the deformation deviation of some key points on the thin-wall parts.Through the comparison analysis,it is shown that the simulation results agree well with the experimental results,which proves the correctness and effectiveness of the theoretical analysis,simulation results and the given experiment data processing method.Through the study on the riveting assembly for thin-wall parts,it will provide a theoretical foundation for improving thin-wall parts assembly quality of large antenna in future.

QUICK ASSESSMENT METHODOLOGY FOR RELIABILITY OF SOLDER JOINTS IN BALL GRID ARRAY(BGA)ASSEMBLY——PART Ⅱ:RELIABILITY EXPERIMENT AND NUMERICAL SIMULATION

In the present study,a facility,i.e.,a mechanical deflection system (MDS),was established and applied to assess the long-term reliability of the solder joints in plastic ball grid array (BGA) assembly.It was found that the MDS not only quickly assesses the long-term reliability of solder joints within days,but can also mimic similar failure mechanisms in accelerated thermal cycling (ATC) tests. Based on the MDS and ATC reliability experiments,the acceleration factors (AF) were obtained for different reliability testing conditions.Furthermore,by using the creep constitutive relation and fatigue life model developed in part I,a numerical approach was established for the purpose of virtual life prediction of solder joints. The simulation results were found to be in good agreement with the test results from the MDS.As a result,a new reliability assessment methodology was established as an alternative to ATC for the evaluation of long-term reliability of plastic BGA assembly.

Assembly and disassembly of mammalian chromosome pellicle

By means of indirect double immunofluorescent staining, the coordination of PI antigen and perichromonucleolin (PCN), the constituent of nuclear periphery and nucleolus respectively, in the assembly and disassembly of chromosome pellicle during mitosis was studied. It was found that in 3T3 cells, during mitosis PI antigen began to coat the condensing chromosome .surface earlier.than PCN did. However, both of them completed their coating on chromosome at approximately the same stage of mitosis, prometaphase metaphase. The dissociation of PI antigen from chromosome pellicle to participate the formation of nuclear periphery took, place also ahead of that of PCN. At early telophase PI antigen had been extensively involved in the formation of nuclear periphery, while PCN remained in association with the surface of decondensing chromosomes. At late telophase, when PI antigen was localized in an fairly well formed nuclear periphery, PCN was in a stage of forming prenucleolar bodies.

Research of the Assembly Model Based on Petri Net

Assembly model plans an important role in assembly sequence planning.Flexible assembly system (FAS) is a dis- crete event system (DES),so Petri net,as an important analytical tool for the DES,is used for modeling of an FAS.All of the feasible assembly sequences can be obtained by firing the Petri net model.In order to enhancing the efficiency of the assembly sequence planning,knowledge-based Petri net,combining an usual Petri net with expert’s knowledge and experiences,is proposed to con- struct the assembly model.So the feasible assembly sequences can be reduced greatly,and the optimum assembly sequence could be generated without the combinatorial explosion of solutions.

Application of Assembly Modeling and Simulation Technology to a Large Size Wind-drive Generator

Challenges still remain in carrying out assembly modeling efficiently in virtual assembly （VA） fields. One of the root causes is the apparent weakness in effective description of assembly knowledge and information. The assembly modeling, disassembly modeling, assembly interference inspection, assembly sequence planning and optimization, and assembly simulation display for key techniques is studied theoretically in this paper. An example of product assembly modeling is provided to illustrate the effectiveness of the proposed approach. On the basis of re- search, using assembly simulation techniques and multimedia techniques to finish structure design in linkage design of a large size wind-drive generator. The application of the modeling method has shortened the lead time dramatically.

On-demand assembly of polymeric nanoparticles for longer-blood-circulation and disassembly in tumor for boosting sonodynamic therapy

Sonodynamic therapy (SDT) is one of the promising strategies for tumor therapy, but its application is usually hindered by fast clearance in blood-circulation, abnormal tumor microenvironment, and inefficient generation of reactive oxygen species. To solve these problems, we proposed an on-demand assembly-disassembly strategy, where the assembly is favorable for longer-blood-circulation and then the disassembly in tumor is favorable for boosting SDT. Hematoporphyrin monomethyl ether (HMME) as the model of organic sonosensitizers were conjugated with hyaluronic acid (HA). Then HA-HMME was mixed with catalase (CAT) and assembled into polymeric nanoparticles (CAT@HA-HMME NPs) with size of ~80 nm. CAT@HA-HMME NPs exhibit good biocompatibility and a longer blood half-time (t1/2 = 4.17 h) which is obviously longer than that (~0.82 h) of HMME molecules. After HA receptor-mediated endocytosis of cancer cells, CAT@HA-HMME NPs can be cleaved by endogenous hyaluronidase, resulting in the on-demand disassembly in tumor to release HA-HMME molecules and CAT. The CAT catalyzes the endogenous H_(2)O_(2) into O_(2) to relieve the hypoxic microenvironment, and the released HA-HMME exhibits a higher ROS generation ability, greatly boosting SDT for the inhibition of tumor growth. Therefore, the on-demand assembly-disassembly strategy may provide some insight in the design and development of nanoagents for tumor therapy.

pH-Sensitive assembly/disassembly gold nanoparticles with the potential of tumor diagnosis and treatment

Due to the ability to combine the separately unique characteristics of assembled and disassembled nanoparticles(NPs), the stimuli-responsive self-assembly of NPs has attracted considerable interest in functional material applications especially biomaterials. Here we demonstrate a facile and versatile approach to regulate the self-assembly process and transition pH of Au NPs by fine-tuning the co-modified pH-responsive compounds and poly(ethylene glycol)(PEG). Importantly the transition pH(ΔpH=0.4) of the system can be predetermined in the range of 8.2–5.8(assembled to disassembled) and 8.2–4.2(disassembled to assembled), which ideally covers the pH of normal tissue, tumor tissue milieu and organelles. The results of fluorescence imaging, Raman spectroscopy and photothermal conversion of the stimuli-responsive Au NPs shows the potential application for tumor specificity theranostics. In a nutshell this study provides a useful toolkit to design tumor-activatable self-assembled NPs with high specificity and universality.

Reaction rates in blanket assemblies of a fusion-fission hybrid reactor

To validate neutronics calculation for the blanket design of fusion-fission hybrid reactor,experiments for measuring reaction rates inside two simulating assemblies are performed.Two benchmark assemblies were developed for the neutronics experiments.A D-T fusion neutron source is placed at the center of the setup.One of them consists of three layers of depleted uranium shells and two layers of polyethylene shells,and these shells are arranged alternatively.The ^(238)U capture reaction rates are measured using depleted uranium foils and an HPGe gamma spectrometer.The fission reaction rates are measured using a fission chamber coated with depleted uranium.The other assembly consists of depleted uranium and LiH shells.The tritium production rates are measured using the lithium glass scintillation detector which is placed in the LiH region of the assembly.The measured reaction rates are compared with the calculated ones predicted using MCNP code,and C/E values are obtained.

虚拟仿真技术引导汽车构造拆装实验系统开发

针对传统的汽车拆装训练在时间和空间上的学习限制,设计并开发了汽车构造拆装训练及展示系统,该系统包括基于虚拟现实的汽车构造拆装实验和基于增强现实的汽车构造拆装展示,通过丰富多样的学习方式,加强学生对汽车内部结构的认识和了解。汽车构造拆装训练及展示采用3Ds MAX制作了零部件拆装动画,以汽车的发动机、车轮、悬挂系统、制动系统、转向系统五大零部件为学习对象,基于Unity 3D软件、Holo Lens1代设计开发,实现了汽车部件拆装的理论学习、拆装逻辑实操、考核一体化的虚拟拆装训练与展示系统。该系统的全新体验方式激发了学生的学习兴趣、规范学生拆装过程中的操作步骤,进一步强化和巩固理论教学知识学习,并有效降低了教学成本和时间成本。

框定主线和边界模式下的汽车拆装实习改革与实践

汽车拆装实习是车辆工程等专业的重要实践课程,受限于实验室场地大小、设备台套数等客观因素,原有的教学模式难以调动全员学生的主动性和积极性,在汽车拆装实习的教学实践中引入拆装示范视频、拆装过程记录表、拍照记录、现场考题清单、测绘建模和3D打印等多种新内容,将传统的实习内容仅为“学生拆装-教师讲解-学生提交拆装心得”的被动接受式教学模式改革成教师定主线与边界、学生为全程主导的综合性探索型教学模式。实践表明,该改革能充分调动了全员学生的主动性和积极性,不但有助于培养学生一丝不苟的工程职业素养,而且学生的接受程度更高,实习的趣味性更足,对学生综合能力培养的效果明显。

基于专业教学资源库的模具拆装虚拟仿真实训构建

传统模具拆装实训受到设备条件、空间场地、安全隐患等因素影响,限制教学效果的提升。专业教学资源库、虚拟仿真系统等数字化平台的建设为该类实训的开展提供了新的载体和模式。模具专业教学资源库为该实训提供离散化、模块化的全过程数字资源支撑。虚拟仿真系统作为专业教学资源库的特色资源,为该实训提供可交互的立体操作平台。依托以上数字资源,构建了“三段式”模具拆装实训翻转课堂。

一种快速装调切割锯的设计与制造

为解决家庭中木料切割时受专用切割锯的质量、外形尺寸、动力输出、木屑清理等问题的制约,而设计与制造一种快速装调小型家用切割锯。切割锯采用手电钻做动力输出,设计易于夹紧锯片的连接定心夹紧机构、满足切割锯片的高度调整机构、木屑处理装置。通过设计制造与实际应用,设计切割锯的整体尺寸小,重量轻,易于快速组装、拆卸,解决了居家使用的需求,同时能很好地保证木材的切割尺寸。

液压调平举升平台虚拟拆装系统研究

在维修和培训过程中,机电产品的虚拟拆装系统可以降低对硬件设备的依赖,能够减少设备的损耗。通过研究液压调平举升平台的VR(Virtual Reality)拆装系统,分析其结构组成和工作原理,基于Unity3D开发环境,编写交互脚本,以HTC Vive Pro2.0作为交互设备,完成了三维模型的构建与处理、虚拟场景的设计、碰撞检测、拆装序列规划、交互功能的设计、用户界面的设计以及拆装功能的设计,开发出沉浸式人机交互的虚拟拆装系统,实现场景漫游、结构认知、拆装引导和虚拟拆装训练等功能。实验结果表明:所开发的虚拟拆装系统沉浸性良好,交互方便,虚拟拆装训练效率高。

不同连接节点的重型管道支吊架承载性能研究

随着装配式建筑的快速发展,装配式管道支吊架的应用范围越来越广,与传统焊接支吊架相比,装配式支吊架具有施工效率高、环境污染小等优势。目前针对装配式重型支吊架的设计规范及相关研究较为缺乏,因此针对不同连接方式的装配式重型支吊架展开足尺试验研究,结合数值仿真与理论分析,探究不同连接节点支吊架的破坏形态与承载能力。研究结果表明:不同节点的支吊架破坏形式均表现为横梁弯扭破坏,且符合极值点失稳特征;使用槽钢横梁及半槽型连接件的支吊架承载力明显低于采用端板连接的H型钢横梁支吊架,外伸竖向端板连接结构的承载力优于平齐竖向端板连接,也优于水平端板连接节点;在进行理论计算时,半槽型连接节点和外伸端板连接节点可采用半刚接模型计算,平齐端板连接节点可采用铰接模型计算,4种节点形式的支吊架整体稳定系数均高于规范计算数值,能够满足整体稳定性的要求。

轻轨车辆CW10型转向架拆装工艺设计

转向架是轨道车辆的走行部分,是轨道车辆结构组成中最为重要的部件之一,轨道车辆在运营过程中需要定期对转向架进行检修,而合理制定转向架拆装工艺,直接影响其组装质量,决定了车辆的稳定性和车辆的乘坐舒适性。在简介轻轨车辆CW10型转向架作用、组成和基本参数的基础上,重点阐述了转向架安装的基本技术要求,进行了机械拆卸和装配工艺设计。

隧道掘进机快速拆装举撑液压系统仿真

针对隧道掘进机(TBM)在施工现场因空间限制无法满足调试所需较大空地的问题,设计一种用于TBM洞内快速拆装变位的举撑液压系统。该液压系统由4组顶升单元构成,通过4组顶升单元同步运动实现TBM的起吊和举撑;液压顶升单元由4根四级液压缸、液压控制系统、激光位移传感器和机架构成。基于AMESim建立四级液压缸、变量泵和比例节流阀以及整个顶升单元的液压仿真模型,通过仿真分析负载下液压缸运动的速度、位移和压力曲线。结果表明:改变比例节流阀的输入信号可以实现四级液压缸速度的变化;泵出口压力可由比例溢流阀调整;在2.5×105 N的额定负载下,四级缸的换级工作腔压力逐级上升;随着换级,活塞杆伸出速度逐渐上升。与理论计算对比显示,建立的TBM洞内快速拆装液压系统顶升单元的AMESim仿真结果和理论值基本吻合。

空间机器人在轨组装多模块单元的对接力控制与地面实验

将空间结构模块化单元呈堆叠式发射后通过空间机器人实施在轨组装,是构建大型空间结构颇具前景的一种方式.空间机器人在轨组装空间结构模块单元过程中存在动力学模型复杂、对接力控制难和对接过程干扰强等问题.针对上述难点,分析了多模块单元在轨组装接触情景,建立了空间机器人在轨组装的动力学模型和三维空间接触动力学模型,在此基础上采用了一种基于模型参考自适应阻抗控制的对接过程接触力控制方法.该方法根据力跟踪误差值实时调整顺应轨迹以适应复杂工况和抵抗外界干扰,从而使接触力准确跟踪期望值,以保证模块单元成功对接的同时避免物理接触对机械结构造成损坏.搭建了空间机器人组装模块单元的仿真平台和地面实验平台,对空间机器人动力学模型和控制方法进行了验证.实验结果表明自适应阻抗控制方法在多模块单元同步对接的复杂接触情景下,仍具有良好的力控制性能和环境适应能力.该方法可应用于(超)大口径太空光学组合镜组等空间大型结构在轨组装过程的力控制.

地面爆炸作用下地下综合管廊动力响应的实验研究

为研究地下综合管廊结构的抗外部爆炸性能,针对整体现浇管廊和预制节段拼装管廊结构在地面爆炸作用下的动力响应特性和破坏模式开展了野外爆炸实验研究。通过11个工况的野外爆炸实验,观测了现浇管廊和预制节段拼装管廊在不同比例距离爆炸工况下的破坏特征和动力响应,对比分析了现浇管廊和预制节段拼装管廊的抗爆性能。结果表明:在地面爆炸作用下,现浇管廊和预制节段拼装管廊的顶板最终均出现弯剪破坏,整体现浇管廊的抗爆性能总体上优于预制节段拼装管廊。起爆位置对预制节段拼装管廊爆炸响应的影响较大,在节段中心上方起爆时结构损伤最严重。在小比例距离地面爆炸作用下,现浇管廊的损伤区域大于预制节段拼装管廊,预制节段拼装管廊的损伤集中在近爆心下方所在的节段或连接接缝处,节段间可产生较大残余滑移。

PS小球阵列制备及二维激光衍射综合实验设计

为促进本科生科研创新思维和工程实践能力的培养,践行“研教协同”育人理念,以Langmuir-Blodgett技术组装高度有序的聚苯乙烯(PS)小球阵列实验为例,要求学生分析制备样品的形貌特征、有序度和激光衍射现象。该综合实验设计涵盖了自组装原理、结构制备、形貌表征及二维激光衍射等多个知识点,有利于培养学生的科研意识和能力,为培养具有创新科研思维的新型复合人才进行了有益的探索。