Three-dimensional numerical simulation of crown spike due to coupling effect between bubbles and free surface

The motion of gas bubbles beneath a free surface will lead to a spike of fluid on the free surface. The distance of the bubbles to the free surface is the key factor to different phenomena. When the inception distance varies in some range, crown phenomenon would happen after the impact of weak buoyancy bubbles, so this kind of spike is defined as crown spike in the present paper. Based on potential flow theory, a three-dimensional numerical model is established to simulate the motion of the free-surface spike generated by one bubble or a horizontal line of two in-phase bubbles. After the downward jet formed near the end of the collapse phase, the simulation of the free surface is performed to study the crown spike without regard to the toroidal bubble＇s effect. Calculations about the interaction between one bubble and free surface agree well with the experimental results conducted with a high-speed camera, and relative error is within 15%. Crown spike in both single- and two-bubble cases are simulated numerically. Different features and laws of the motion of crown spike, depending on the bubble-boundary distances and the inter-bubble distances, have been investigated.

Three-Dimensional Exact Solution for Dynamic Damped Response of Plates with Two Free Edges

A three-dimensional state space method has been developed for the calculation of dynamic response of plates with two free edges and two simply supported edges.A complex damping model was introduced, then the exact solutions which satisfy all the governing equations and boundary conditions were obtained.In order to overcome the difficulty of satisfying all the stress conditions at free edges, the displacement functions of free edges were assumed.The boundary conditions were strictly satisfied when the convergence rate was good.The computing time was evidently less than that of finite element method.The comparison of the solution with those of finite element method show that there is an excellent agreement for displacements.When the imaginary parts of normal stress deviated, the finite element results showed existence of shear stresses at top and bottom surfaces, and the boundary conditions of FEM model were not strictly satisfied.

Detection and interpretation of the Earth's free oscillations excited by the great Sumatra-Andaman earthquake with GGP station data

The mode serials of the Earth’s free oscillation provide some important information on the Earth’s deep structure and superconducting gravimeters （SG） can investigate the phenomena of the Earth’s free oscillations with high accuracy. The great Sumatra-Andaman earthquake fully excited the Earth’s free oscillations and these signals were perfectly recorded by five superconducting gravimeters in the globe. After the pre-treatment and spectral analysis on the SG observation data, we obtained the experimented mode serials of the Earth’s free oscillations consisting of 147 modes with GGP station data. These observed modes were themselves some new important data for the study of the Earth’s deep structure. On the basis of the discussions on some checked inner-core-sensitive modes, we distinguished three layers from the inner core, and the boundary of the upper layer was compatible with the formerly known transition zone in the inner core based on seismic body waves and supported that there were the hemispherical variation and very lower shear velocity zone in the lower inner core.

Effects of Fiber Volume Fraction on Damping Properties of Three-Dimensional and Five-Directional Braided Composites

The effects of fiber volume fraction on damping properties of carbon fiber three-dimensional and five-directional( 3D-5Dir)braided carbon fiber / epoxyres in composite cantilever beams were studied by experimental modal analysis method. Meanwhile,carbon fiber plain woven laminated / epoxy resin composites with different fiber volume fraction were concerned for comparison. The experimental result of braided specimens shows that the first three orders of natural frequency increase and the first three orders of the damping ratios of specimens decrease, when the fiber volume fraction increases. Furthermore,larger fiber volume fraction will be valuable for the better anti-exiting property of braided composites,and get an opposite effect on dissipation of vibration energy. The fiber volume fraction is an important factor for vibration performance design of braided composites. The comparison between the braided specimens and laminated specimens reveals that 3D braided composites have a wider range of damping properties than laminated composites with the same fiber volume fractions.

Boundary effect of toppling failure based on three-dimensional mechanical model

Previous researches on the mechanical model of toppling failure mainly concentrated on twodimensional mechanical model(TwDM) analysis. The TwDM analysis assumes the width of the slab beam is unit width without considering the lateral constraint force. The assumed conditions are obviously different from the site conditions, thus there is a certain difference between the calculated results and the field work. A three-dimensional mechanical model(ThDM)of toppling failure was established, considering that the slab beam was mainly subject to self-weight, the frictional resistance of interlayer and lateral constraint force. Due to the progressive characteristics of toppling failure, the concept and the formula of the first fracture depth(FFD) of toppling was raised and constructed. The case study indicates that the ThDM is more effective and can be accurately used to calculate the toppling fracture depth of the slab beam. The FFD decreases proportionally with the increase of slab beam width. FFD grows fast when the slab beam width is less than 2.0 m and it tends to be stable when the slab beam width is above 2.0 m. The FFD decreases with the increase of the lateral constraint coefficient, indicating that the boundary condition of the free space is positively correlated with the stability and depth of toppling. This is a good explanation of the free space effect. This study provides a reference for the stability evaluation and prevention-control design of toppling slope in the future.

月球站所的法律地位浅析

目前,月球活动正进入新的阶段——月球站所的筹备与建设。然而,现有相关国际法规范尚需完善,其中月球站所的法律地位是需首要考虑的问题。对月球站所法律地位问题的思考始于月球站所活动的特殊性:以人类社会的可持续发展为长远目标,开展于天体之上,将对天体表面固定区域进行使用且产生事实上的活动范围。合乎《外空条约》的月球站所建设是为全人类谋福利的自由探索和利用月球的活动,不存在既排他又永久地使用月球表面区域的情形,且在互惠基础上对他国开放。为此,建议在国际月球科研站活动中考虑“非排他”和“有时限”二者择一的规范路径以履行相应的国际法义务,并且明确国际月球科研站对他国开放的“互惠”前提与“参观”范畴。同时,需将月球站所的四个方面作为判断其法律地位的具体考量因素,即月球站所的使用目的与活动范围大小,月球站所的可移动性,月球站所的使用期限以及月球站所信息的通知、更新与公开。

基于POI数据的公共免租站点数字化检测策略探索与应用

在5G网络大规模部署和刚性成本快速增长的局势下,为了节省基站建设场地租赁费用以及制定有效的选址策略,文章提出了一种公共免租站点智能检测的方法。该方法利用中文切词算法挖掘公共免租站点关键词并建立公共免租关键词库,引入广泛的POI数据、基站数据以及合同数据进行匹配和交叉运算,实现系统化、智能化地检测现有站点是否满足公共免租条件。通过建设公共免租关键词库,辅助锁定存量租用的现网物业站点,并以公共免租谈判的手段进行推动,有效地摆脱了传统人工判断的主观性与不确定性,为基站选址决策者提供可靠的参考,从而降低基站租金成本,提高5G网络的经济效益。

测量机器人在地铁变形监测中的应用研究

为了更好地监测基坑水平位移,研发了一种基于自由设站的测量机器人,它能够在极端环境下准确监测桩顶水平位移,具有良好的准确性和灵活性。这种技术不仅可以在深基坑桩顶水平位移监测上得以体现,还可以在新建隧道的施工过程中,有效监测隧道道床的沉降、收敛和水平位移,为施工带来更加可靠的数据支撑。经过多次实验,发现测量机器人使用实时自动化监控技术能够给出准确信息,并且在很大程度上改善了建筑物/构造物的三维变形检查。这种技术不仅为建设项目的安全提供了参考,而且也为其他领域的研究提供了新的思路。

錾高水电站首部枢纽水工模型试验

为了验证錾高水电站泄洪冲沙闸全开和局开、无闸溢流坝溢流等不同工况的过流能力、流态、下游冲刷及防冰凌等设计的合理性,通过对錾高水电站首部枢纽进行几何比尺为1∶50的水工模型试验,并对试验结果进行分析。结果表明:泄流能力满足设计要求;泄洪冲沙闸左侧边孔进口附近易出现强吸气旋涡,消力池出口冲刷较严重;将库水位抬升至1611.42 m可有效防冰凌。该模型试验可为下阶段的工程优化设计提供依据。

空间斯特林热电转换技术在轨试验

为提高空间同位素电源的效率和功率,满足深空探测、载人登月和火星登陆等航天任务对航天器能源的需求,梳理了空间自由活塞斯特林热电转换涉及的关键技术,设计了天宫空间站空间自由活塞斯特林热电转换装置的在轨试验方案,在轨开展了斯特林热电转换试验,验证了空间微重力环境下双活塞自由运动的间隙密封、双活塞相位保持等关键技术,获取了空间环境下双自由活塞精确的运动相位保持及漂移特性、动力学与热力学强耦合特性等关键参数。在轨试验结果表明,试验装置在轨运行性能良好,热电转换效率达到24.72%,为未来空间高效同位素电源等不依赖太阳能的能源技术应用奠定了基础。

基于全龄友好目标的铁路客站无障碍设计研究

国内以往的铁路客站一般按规范基本要求进行无障碍设计,从建成后的实际效果来看,人群覆盖范围和友好度尚显不足,为提高铁路客站无障碍设施的可用性、便利性,需对铁路客站无障碍设计的诸多关键点进行创新。通过对铁路旅客群体的分类研究,建立了以六大系统为核心的铁路旅客无障碍功能需求矩阵,提出了全龄覆盖的铁路客站通用无障碍设计理念;结合雄安站的工程实践,在对旅客使用需求、精神需求分析的基础上,从友好目标导控的无障碍细节设计、智能引领的无障碍卫生间设计、艺术集成的无障碍空间设计3个方面,提出了具有普遍适用性的全龄友好铁路客站无障碍设计新方法,为现代铁路客站无障碍设计进行开拓性的探索,可有效提升铁路客站的无障碍环境品质。上述成果方法可为新时代铁路客站无障碍环境建设提供指引。

基于部分参数约束的粒子加速器隧道控制网平差

为控制隧道控制网平差时的误差累积问题,提高隧道控制网平差精度,设计了3种约束方案。首先,考虑到测站铅垂线之间的不平行性,依据控制网规模计算测站铅垂线与储存环中心铅垂线之间的夹角,在平差时顾及该约束,使平差模型更加严密。然后,为提高隧道控制网的平面精度,使用全站仪对距离较远的控制点进行长边夹角测量,在平差过程中附加长边夹角约束。其次,按照一等水准规范,对隧道地面点进行水准测量,基于水准测量结果,采用最小二乘转换方法,将控制网转换至水平面,进一步提高控制网竖向精度。最后,对周长为1360 m的隧道控制网进行仿真试验。结果表明,顾及测站垂差及水准点高程或高差平差值可提高控制网竖向精度;附加长边夹角约束可提高控制网平面精度;同时顾及测站垂差、长边夹角观测值及水准高程或高差平差值可提高控制点的点位精度,验证了约束条件的有效性。研究成果可为相关工程布设控制网提供参考。

无柱大跨地铁车站结构选型优化及敏感性分析

针对无柱大跨地铁车站结构受力情况,以影响地下车站结构受力的不同顶底板结构模型及跨度、覆土、侧压力系数等影响因素为研究对象,采用Midas GTS数值模拟计算软件建立模型,计算分析出无柱大跨地铁车站较优的结构类型。研究结果表明,无柱结构设置拱形顶底板对改善结构受力有显著效果,跨度、覆土、侧压力系数等影响因素对无柱结构受力的敏感性影响不同。

苏州轨道交通无柱车站结构选型与受力分析

[目的]城市轨道交通车站所处场地狭小或净高富余时,为了创造大空间视觉效果,通常采用无柱结构形式。为了达到安全可靠、经济合理的目标,需对该无柱车站进行结构选型和受力分析。[方法]以苏州轨道交通8号线时家桥站工程为依托,采用有限元计算方法,详细分析了车站顶、中、底板采用不同结构形式时的受力特性,并提出该车站的整体结构方案。[结果及结论]无柱车站采用全拱形顶板时的受力和经济性最好;通过在车站站台层设一排柱,既改善中板受力,又利于楼扶梯孔洞的开设;底板从受力和经济性考虑采用全拱形最好,考虑施工的便利性和变形控制要求,也可采用平底拱形式。本站采用无柱拱形顶板+梁柱形式中板+平底拱形底板的结构形式,充分发挥拱形结构的受力特性,在工程造价变化不大的前提下,利用车站的富余净空,提升了站内公共区的大空间视觉效果。

顾及基准点误差的自由设站平差及精度分析

观测误差和基准点误差是影响全站仪自由设站精度的2个重要因素。目前通常采用经典约束平差法进行自由设站数据处理,测站平差后,基准点误差会以原始数据误差的形式影响设站点坐标和碎部点坐标。在分析全站仪自由设站基本原理基础上,基于坐标转换思想建立同时考虑基准点误差和全站仪观测误差的自由设站平差模型,并给出具体的求解方法。实验结果表明:较大的基准点误差会对自由设站平差结果的精确度带来不利影响,基准点精度较高时,新平差模型结果与约束平差结果相当;基准点精度较低时,新平差模型结果较约束平差结果更优。

全站仪自由设站法在基坑三维形变监测中的应用

针对传统基坑水平位移和竖向位移监测方法存在的作业烦琐、效率较低等弊端,采用徕卡TS15智能型全站仪自由设站法对其进行改善,实现基坑围护结构顶部水平和竖向位移的快速同步获取。通对自由设站法的原理及平差过程进行详细阐述,利用某建筑基坑项目进行实例应用,分析研究设站精度,并与传统监测方法获取的变形数据进行对比分析,结果表明:自由设站法设站点点位中误差在2mm左右,满足规范中点位中误差小于3mm的要求,与传统监测方法的差值相对较小,满足二等基坑监测规范精度要求;但当基坑监测等级为一级时,应采用测角精度为0.5"的高精度全站仪进行监测作业,确保监测数据满足规范精度要求。

数据驱动的风光场站次同步振荡多机协同阻尼控制方法

随着光伏、风电在电网中接入规模的快速增长,电力系统次同步振荡问题逐渐凸显。该文针对包含光伏、双馈风电机组的等效多机新能源场站,提出一种数据驱动的抑制次同步振荡的多机协同阻尼控制方法。首先,结合新能源并网系统的结构与次同步振荡阻尼方法,确定了阻尼控制器信号的输入、输出位置。其次,将次同步振荡场景下的新能源场站等效多机并网系统简化为多输入单输出系统,基于紧格式动态线性化理论,提出了适合光伏、风电多机协同的无模型自适应次同步振荡阻尼控制方法,并对控制参数进行了优化。最后,在IEEE 39节点系统增加新能源接入场景中进行测试,阻抗频率分析与仿真结果均体现出该控制方法能有效提升系统的阻尼。在考虑阻尼控制器投入时间、新能源场站规模、风光出力占比等不同的情况下,验证了该控制方法的有效性和适应性。该控制方法对振荡频率的偏移不敏感,并对系统的大小扰动具有较强的适应能力,体现出良好的次同步振荡阻尼性能。

隧道变形监测基准网稳定性分析研究

针对地铁隧道施工场地范围有限的特点,采用测量机器人自由设站法对地铁隧道的变形状态进行跟踪监测,由于自由设站法对基准网稳定性要求较高,因此每次监测作业前需要对基准网稳定性进行检验。本文采用后验单位权方差χ^(2)检验方法对地铁隧道基准网稳定性进行检验,通过对该方法的理论可行性及检验流程进行分析研究,利用基准网的后验单位权方差和先验单位权方差构建统计量,然后进行χ^(2)假设检验,验证了后验单位权方差χ^(2)检验在自由设站法基准网稳定性检验中的适用性及可靠性,有效识别基准网中的不稳定点,为地铁隧道安全分析提供准确可靠的监测数据。

充换储一体化电站布局及电缆供电的路径优化

随着电动汽车在城市电力系统中的渗透率逐渐增加,系统对电动汽车的支撑能力需要进一步提升。结合城市配电系统配置新型集中性充换电设施是解决该问题的有效途径,合理有效的优化规划是一大难点。针对该问题,提出了一种综合电动汽车充换储一体化电站(charging-swapping-storage integrated station,CSSIS)定容布局以及电缆供电路径优化的综合规划模型。基于充、换电设施的功能特点分析,分别构建充电站、换电站和储能电站运行和定容模型,并以此为基础建立一体站综合运行和定容布局模型,同时结合电动汽车在规划区的概率分布特点,分析一体站的电动汽车负荷。计及不同类型的负荷对供电可靠性的要求以及电缆供电走廊的类型,提出了结合一体站布局的电缆供电路径优化方法。基于公司自由现金流理论分析,优化电动汽车充换储一体化电站定容布局配置规划的累计净现值,并对电缆供电路径及其配套电缆走廊进行优化,采用YALMIP/CPLEX优化工具箱对模型进行求解。以某地区作为规划区,验证了所提方法的可行性和有效性,为电动汽车一体站及其配套的城市电缆配电系统的优化规划提供了新的思路和参考。

全站仪在公路高边坡监测中的技术要点及运用

在公路工程高边坡工程建设中,根据边坡的不稳定性,利用全站仪测量自由设站的原理,对公路工程高边坡位移变化进行非接触量计方法实施监控,以国道227线公路工程变更麦日(甘凉界)至巴亨垭口段边坡变形监控工作为案例,系统介绍了全站仪自由设站原理非接触量计方法在公路工程高边坡监控中的主要技术要求和运用情况,在施工过程中对边坡监控发挥的主要功能。