Stress analysis of clamped-free grid composite cylindrical shell under various end loadings

Stress analysis of cylindrical grid-stiffened composite shells was conducted under transverse loading,pure bending,torsion and axial compression under clamped-free boundary condition.Electrical strain gauges were employed to measure the strains in transverse loading case to validate the finite element analysis which was conducted using ANSYS software.Good agreement was obtained between the two methods.It was observed that stiffening the composite shell with helical ribs decreased the average equivalent Von Mises stress on the shell.The reduction of the stress seemed to be higher in the intersection of two ribs.It was also seen that the stress reduction ratio was higher when the structure was under bending compared to torsion and axial compression.The reduction ratio was approximately 75% in pure bending in the intersection point of the ribs,while it was approximately 25% in torsion.Therefore,it is concluded that the presence of the ribs is more effective under bending.Failure analysis was done using Tsai-Wu criterion.The ribs were observed to result in maximum and minimum increase in the failure load of the structure under transverse bending and torsional loading,respectively.

Characteristics of Dynamic Load Response of a Fuel Cell with a Dead-ended Anode

The dynamic load characteristics of a proton exchange membrane fuel cell（PEMFC） with a dead-ended anode were studied. In a 70 h experiment, the effects of anode pressure, operating temperature, and relative humidity of the cathode on the performances of the fuel cell were investigated. The obtained results show that, with different relative humidity of the cathode at 65 ℃, dynamic loading has little effect on the performances of fuel cell and the electrochemically active surface area（ECSA）. However, the fuel cell operating under dynamic load is unstable when the relative humidity is 50%, and at 50 ℃ with 100% relative humidity, applying a dynamic load has a significant influence on the fuel cell performances. Scanning electron microscopy（SEM） showed that both the upstream and middle catalyst layers of the cell were unchanged, whereas the downstream cathode catalyst layer thinned as a response to dynamic load.

INFLUENCE OF THREAD PITCH ON LOAD DISTRIBUTION ON THREADED END OF PRESSURE CYLINDER

One of the design methods for closing the end of a pressure cylinder is to screw down a screw plug on the threaded end of the cylinder. In this case, there is the problem of stress concentration in the threaded end of the pressure cylinder. To solve the problem, it is necessary to know accurately the load distribution on the threaded end of the cylinder. To find the load distribution on the threaded end of the pressure cylinder engaged with the screw plug, the following experiments are carried out. Applying the tensile load between the screw plug and the pressure cylinder and regarding the situation above as equivalent to the situation in which the internal pressure is applied, the load distribution is measured with the strain gauge. The influence of thread pitch on the load distribution on the threaded end of the cylinder is presented and an optimum pitch for design is discussed.

Combined effects of axial load and temperature on finite deformation of incompressible thermo-hyperelastic cylinder

A finite deformation problem is examined for a cylinder composed of a class of incompressible thermo-hyperelastic Mooney-Rivlin materials under an equal axial load at its two fixed ends and a temperature field at its lateral boundary. Firstly, a thermomechanical coupling term is taken into account in the strain energy density function, and a governing equation of the problem is obtained. Secondly, an implicit analytical solution is derived by using the incompressibility and the boundary conditions. Significantly, numerical examples show that the middle portion of the cylinder undergoes almost a uniform radial deformation. However, the deformation near the two ends varies remarkably along the axial direction for relatively large axial loads. In addition, the rising temperature can increase the deformation of structures, and its influence is linear approximately. Specially,in the case of tensile load, the jump increase of the axial deformation may occur.

Study on the Girder-End Displacement of a Suspension Bridge Based on Field Measurements

The load-response correlation is a great concern for the management and maintenance agency of bridges. Based on both the load test data and the long-term structural health monitoring data, this study aims to characterize the variation in the girder-end longitudinal displacement of a long-span suspension bridge, i.e., the Zhaoyun Bridge in Guangdong Province of China. The load test provides a valuable chance to investigate the structural deformation in high loading levels, while the structural health monitoring system records the real-time, in-site, and long-term measurements in the normal operational stage of bridges. During the load test, the movement direction of the main girder is found to depend on the relative position of the center of gravity of the girder and the loading vehicles. However, over the period of normal operation, the quasi-static displacement at the ends of the main girder along the bridge axis is dominated by the temperature variations, rather than the traffic loading. The temperature-induced deformation is considerable so it should be filtered out from the structural total responses to highlight the live load effects or the anomalies of the bridge. As a case study, the temperature-displacement baseline model of the Zhaoyun Bridge is established and then utilized to identify the erroneous measurements in the structural health monitoring system. This paper serves as a reference for the structural behavior interpretation and performance evaluation of similar bridges.

Coefficient of consolidation by end of arc method

One of the most important issues in geotechnical engineering is excess pore pressure caused by clay soil loading and consolidation. Regarding uncertainties and complexities, this issue has long been the subject of attention of many researchers. In this work, a one-dimensional consolidation apparatus was equipped in a way that pore water pressure and settlement could be continuously read and recorded during consolidation process under static loading. The end of primary consolidation was obtained using water pressure changes helping to present a new method for determining the end of primary consolidation and consolidation coefficient. This method was then compared with two classical theory methods of lg t and t. Using Terzaghi's theory, the way of pore pressure dissipation for lg t, t and the new method was found and compared with experimental results. It is concluded that the new method has better results.

大跨度铁路桥梁端位移精细化计算研究

为针对大跨度铁路桥选择合适的梁端伸缩装置,保障列车行车的安全性,提高桥梁的使用性能,依据多座大跨度桥梁端位移实测值演化规律以及结构计算,开展温度荷载、列车荷载、风荷载及风与温度荷载组合引起的梁端位移精细化计算研究。提出温度荷载的取值类型和取值范围;明确列车荷载引起梁端位移的计算工况和计算方法;确定桁式主梁风荷载摩擦系数取值和所引起梁端位移的计算工况;结合风荷载、风与温度荷载联合分布模型,提出风与温度荷载组合时风荷载的折减系数。以某斜拉桥为背景,对比本文方法和常规方法计算梁端位移的结果。结果表明:温度荷载引起梁端位移可仅考虑体系温度,体系降温工况各结构的温度按大气温度取值;体系升温工况索结构和一半主梁结构考虑热辐射效应,桥塔结构和另一半主梁结构按大气温度取值;应考虑阻尼器、支座等边界阻力效应,采用动力时程法计算列车荷载引起的梁端位移,计算值与实测值吻合良好;对于采用桁式主梁的桥梁,分别按风偏角45°、90°计算风荷载引起的梁端位移,取两者最不利值;计算风与温度荷载组合下梁端位移时,风荷载引起的梁端位移可相应折减;常规方法所得的梁端位移较为保守,梁端位移的精细化计算更有利于选择合适的梁端伸缩装置。

有源前端组网的直流船舶电网高能效运行控制

直流船舶电网为航运业绿色转型提供了有效可行的解决方案。考虑到实际船舶的运行工况,本文提出一种分层协调控制策略,主要用于有源前端组网的直流船舶电网中功率单元协调运行的设备层控制系统和功率层控制系统。其中,设备层控制系统负责实现发电机组转速的无静差跟随与不同容量柴油发电机组间的动态/稳态功率共享;功率层控制系统负责提升母线电压质量,提高系统能效。最后,利用仿真与半实物仿真系统对控制策略进行验证,结果表明该控制策略可有效提高系统运行能效,最高节省约10%的燃油。

高校大科学设施推动高端装备制造业创新研究——以环境与载荷耦合全尺寸试验为例

大科学设施是推动前沿基础科学发展和技术创新的重要条件支撑,越来越多的高校承担了大科学设施的建设运行任务。重大工程材料服役安全研究评价设施通过研制开发能够实现真实服役工况的、复杂环境与载荷耦合的全尺寸试验装置,积极面向高端装备制造开展复杂工况下服役性能试验,对相关学科融合发展,以及国产高端装备制造的材料选型、新材料应用、设计优化和可靠性评价等方面发挥了不可替代的推动作用,在核心技术研发与产品验证等环节中加速国产化进程,是直接面向国民经济主战场的大科学设施。该文在总结环境与载荷耦合全尺寸试验技术创新的基础上,分析了大科学设施服务高端装备制造产业的实际案例。

随机车载激励下大跨度悬索桥中央扣振动控制研究

大跨度悬索桥车流荷载作用下振动响应明显,关键构件疲劳损坏直接影响结构服役状态及运营安全。为改善大跨度悬索桥结构振动响应,基于有限元模拟对柔性中央扣及刚性中央扣振动控制效应开展研究,分析了中央扣对结构模态特性的影响,并基于考虑参数相关性及车流参数聚类特征的随机车流模拟方法,分析了车流荷载下的中央扣振动控制效应及其对吊索钢丝寿命影响。研究结果表明:中央扣主要对悬索桥的反对称竖弯频率及一阶扭转频率存在影响,随着柔性中央扣数量的增加结构振动频率有所提升,刚性扣的提升效果与三柔性中央扣接近。车流作用下中央扣可显著减小梁端位移、梁端累计位移及缆梁相对位移,随柔性中央扣数目的增加,控制效率有所提升但提升效果逐渐减小。刚性中央扣对梁端位移及梁端累计位移的控制效果与三柔性扣索接近,其对缆梁相对位移的控制效果好于柔性中央扣。吊索钢丝的疲劳寿命与弯曲应力响应的变化趋势一致,长吊索整体弯曲应力水平相对较小,中央扣对其钢丝寿命影响不明显。短吊索钢丝疲劳寿命则大幅提升,但柔性中央扣数量的增加提升效果有限,刚性中央扣提升效果与三柔性扣索接近。

竖向循环荷载作用下粉土地基开口管桩承载力特性模型试验研究

竖向循环荷载作用下管桩承载力特性的演化规律对交通基础设施的正常使用具有重要意义。研制了新型双壁开口管桩,该新型桩基的特点是可以单独监测管桩内外侧的受力。利用双壁管桩开展了循环荷载作用下粉土地基中开口管桩承载力特性的模型试验,探究了竖向循环荷载的幅值和频率对开口管桩位移、沉降和管桩内外壁轴力的变化规律。得到如下结论:循环荷载加载初期,管桩产生明显的累积沉降,随着循环次数的增加沉降逐渐趋于稳定;当桩顶荷载幅值由10%极限承载力增大一倍时,开口管桩的累积沉降增大约65%;随着加载频率增加,开口管桩的累积沉降呈线性增长;土塞的约束会导致管桩内壁产生轴力,且随着循环次数增加管桩内壁轴力逐渐增大,但内壁轴力的大小仅为外壁轴力的23%。

端部无预应力的内嵌碳纤维加固梁试验研究

针对表层嵌贴(near-surface mounted,NSM)预应力碳纤维增强复合材料(carbon fiber reinforced polymer,CFRP)加固梁易发生端部剥离破坏的问题,提出了增设无预应力段的端部锚固改进措施,并设计了5个采用表层嵌贴预应力CFRP加固的钢筋混凝土梁进行静载试验,以分析增设端部无预应力段、延长端部无预应力段长度对加固梁承载性能及变形性能的影响。结果表明:端部增设无预应力段能显著地提升加固梁黏结端部的开裂荷载与极限荷载,有效地延缓并抑制加固梁端部的剥离破坏;与单纯采用预应力加固的方式相比,增设的端部无预应力段能弥补构件由施加预应力而导致的构件剩余变形能力降低;加固构件的承载能力和变形性能与端部增设的无预应力段长度之间均为正相关关系。

副簧下置式二级刚度板簧的相关计算

为解决副簧下置式二级刚度抛物线变截面少片簧,在副簧接触后的板簧总成挠度和刚度计算的问题,以2+1下置副簧为例,根据材料力学简支梁变形原理,分析板簧各片相应的挠度情况,建立变形一致方程。根据虚功原理,建立并求解端部载荷和挠度的积分方程,总结挠度、刚度和端部载荷的计算方法。通过试验验证可知,计算值与试验值最大偏差在5%以内,计算理论正确,可以为此类板簧正向设计提供参考。

发电机励磁在线监测系统的研制及应用

以分布式新能源为主的主动支撑技术还处于发展阶段,常规发电机的惯量支撑能力仍在发挥重要作用,励磁系统作为其控制核心,直接影响着供电可靠性。本文针对电厂端缺乏监测发电机励磁特性有效措施的现状,研制了发电机励磁在线监测系统。首先,介绍励磁在线监测系统的硬件和软件架构,根据四种主流的通信规约设计励磁监测模型。其次,提出适应多种通信规约的分布式前置采集架构,构建采集通道负载均衡数学模型,实现了励磁信号的分布式采集和集中监视。最后,研发励磁量测动态监视、发电机运行状态预警等功能。所研制的监测系统已在某660MW机组得到成功应用。

兼顾排屑与降载作用的叶轮拐角单笔清根刀具

清根加工作为叶轮拐角区域残余材料的补加工工艺,在整体叶轮数控加工中占据十分重要的地位。盖盘叶轮清根加工具有推刀进给、拐角曲面曲率大、切削余量大、空间几何受限等特点。而传统球头铣刀刀尖点切削性能不足,应用于盖盘叶轮清根加工会导致切削载荷大和切屑挤压,造成刀具过早失效、加工表面质量差等问题。本文针对盖盘叶轮清根加工的特点和难点,提出一种面向不同拐角尺寸的具有削顶结构以及大容屑槽结构的刀具,并推导了切削刃的表达式。对传统球头铣刀和新式削顶铣刀进行仿真与实验,结果表明,新式削顶铣刀较传统球头铣刀切削力降载高达77.6%,切削过程更平稳可靠,加工质量更高。

钻孔灌注桩竖向承载性能试验研究

为优化提升钻孔灌注桩的设计方案,文中对竖向受压载荷下钻孔灌注桩的荷载传递及受力特性进行了研究。结果表明,最大的桩身轴力均位于深度为3 m处,当加载荷载为1440 kN时,桩身的轴力最大值为1205 kN;随着桩顶荷载值的增加,桩身的最大桩侧阻力值也不断增大,最大的桩侧阻力值为140 kPa,最大负摩阻力达到-82 kPa。当桩顶荷载从160 kN增加至1600 kN时,桩端阻力增幅达到860.2%。桩端阻力占比与施加的桩顶荷载呈先负相关后正相关关系;当荷载达到1600 kN时,桩顶位移最大达到14.6 mm;卸载为0时,桩顶位移为8.8 mm。

对《砌体结构设计规范》中高厚比修正系数等问题的探讨

文章指出了《砌体结构设计规范》(GB 50003—2011)中关于带门窗洞口砌体墙允许高厚比的修正系数μ2的计算精度不足,并根据弹性稳定理论,提出了两端铰接变截面柱临界荷载Pcr的正确表达式,通过理论计算和有限元模拟对其给予了证明,此外,还推导了门窗洞口最不利布置时的μ2表达式。在此基础上,提出了比《砌体结构设计规范》(GB 50003—2011)更合理的有洞口墙体的允许高厚比修正系数μ2计算公式,同时对μ2的相关应用细则提出了修正建议。以修正后的两端铰接柱临界荷载Pcr为基础,提出了规范中变截面柱下段计算长度H0的更合理形式,为便于工程应用,最后对规范中有吊车房屋变截面柱计算长度的应用条款提出了修改建议。

大跨度反向芬克式桁架人行桥总体设计

某跨京杭大运河人行桥采用反向芬克式桁架桥,桥梁全长198 m,跨径布置为(15.9+150+15.9)m。桥体造型以运河帆影为设计灵感,梁、塔、索造型以运河上的漕运船为蓝本。主梁采用封闭式单箱三室钢箱梁,桥塔塔柱及撑杆均采用钢制梭形结构,布置在主梁中央,并与主梁固结。拉索采用双叉耳热挤压高密度聚乙烯高应力幅钢绞线拉索与冷铸镦头的组合体系,塔顶处为固定端,梁端为张拉端。反向芬克式桁架桥的整体刚度由拉索的张拉力提供,合理初索力的确定是反向芬克式桁架桥设计的关键。边跨成桥索力大,且锚固位置受选址红线限制,为保证传力路径可靠,在边索与主梁交接处设整体式传力板。经人致振动分析,采取在距主跨跨中两侧28 m处各安装1对TMD的减振措施,以满足人行舒适度要求。

面向温控负荷聚合调控的云边端网络资源分配

温控负荷是以空调和电热水器等为一类控制温度调节的柔性负荷,作为一类重要的需求侧资源,对负荷集群进行灵活的聚合调控可以充分调动清洁能源消纳能力,保障电网供需平衡。由于温控负荷常见于商业写字楼及居民区内,可对其采用较为稳定的控制与传输方式,故引入高效的分层分级传输网络,实现负荷与电网之间的数据传输与信息交互,灵活、实时、精准地利用负荷集群的调节潜力。首先提出了一种“中心云-边缘云-区域控制器-温控负荷”的云边端协同通信组网架构。接着,针对端-边部分,考虑不同聚合控制任务的需求,利用改进的聚类算法对任务进行分类,以减小传输开销。针对边-云协同部分,构建了考虑时延、能耗和误码率的传输开销效用函数,设计了基于稳定匹配和注水算法的子信道资源分配算法,并利用二进制粒子群算法解决了任务上传决策问题。最后,通过仿真验证了本文所提模型的有效性,并进行了对比实验。

基于静载试验的花岗岩持力层上覆厚层软土基桩弹性压缩分析

为使厚层软土地区花岗岩等“硬岩”为持力层的超长灌注桩的桩身弹性压缩量计算更加合理,通过对该类场地灌注桩抗压静载试验“荷载-沉降”数据进行分析,并采用有限元仿真计算和概率统计分析方法,得到了端阻比与长径比等参数的函数关系以及桩侧摩阻力分布系数的样本统计值,建立了通过长径比等参数估算桩身弹性压缩系数ξe的方法以及相应的简化计算公式。最后通过某案例计算与规范推荐的方法进行对比,验证该公式计算桩身弹性压缩量的准确性及便捷性。