Application of bi-directional static loading test to deep foundations

Bi-directional static loading test adopting load cells is widely used around the world at present, with increase in diameter and length of deep foundations. In this paper, a new simple conversion method to predict the equivalent pile head load-settlement curve considering elastic shortening of deep foundation was put forward according to the load transfer mechanism. The proposed conversion method was applied to root caisson foundation in a bridge and to large diameter pipe piles in a sea wind power plant. Some new load cells, test procedure, and construction technology were adopted based on the applications to different deep foundations, which could enlarge the application scopes of bi-directional loading test. A new type of bi-directional loading test for pipe pile was conducted, in which the load cell was installed and loaded after the pipe pile with special connector has been set up. Unlike the conventional bi-directional loading test, the load cell can be reused and shows an evident economic benefit.

Dynamic strength of rock with single planar joint under various loading rates at various angles of loads applied

Intact rock-like specimens and specimens that include a single, smooth planar joint at various angles are prepared for split Hopkinson pressure bar（SHPB） testing. A buffer pad between the striker bar and the incident bar of an SHPB apparatus is used to absorb some of the shock energy. This can generate loading rates of 20.2-4627.3 GPa/s, enabling dynamic peak stresses/strengths and associated failure patterns of the specimens to be investigated. The effects of the loading rate and angle of load applied on the dynamic peak stresses/strengths of the specimens are examined. Relevant experimental results demonstrate that the failure pattern of each specimen can be classified as four types： Type A, integrated with or without tiny flake-off; Type B, slide failure; Type C, fracture failure; and Type D, crushing failure. The dynamic peak stresses/strengths of the specimens that have similar failure patterns increase linearly with the loading rate, yielding high correlations that are evident on semi-logarithmic plots. The slope of the failure envelope is the smallest for slide failure, followed by crushing failure, and that of fracture failure is the largest. The magnitude of the plot slope of the dynamic peak stress against the loading rate for the specimens that are still integrated after testing is between that of slide failure and crushing failure. The angle of application has a limited effect on the dynamic peak stresses/strengths of the specimens regardless of the failure pattern, but it affects the bounds of the loading rates that yield each failure pattern, and thus influences the dynamic responses of the single jointed specimen. Slide failure occurs at the lowest loading rate of any failure, but can only occur in single jointed specimen that allows sliding.Crushing failure is typically associated with the largest loading rate, and fracture failure may occur when the loading rate is between the boundaries for slide failure and crushing failure.

Modeling of Cross-Spring Pivots Subjected to Generalized Planar Loads

Cross-spring pivots, formed by crossing two identical flexural beams at their midpoint, have been broadly used in precision engineering and aerospace fields. Many researches have been conducted on modeling and analysis of cross-spring pivots. However the influence of application position and magnitude of the external loads on the load-rotation and parasitic motion characteristics has not yet been discussed. In order to reveal the effect of the external loads, this paper develops the accurate load-rotation and center shift models of cross-spring pivots, with generalized planar loads applied including bending moment, horizontal and vertical forces. Firstly, by using the energy method, the load-displacement models of the pivot are derived with the assumption of small rotational angles. Based on the models, the influence of generalized planar loads on the load-rotation relationship is discussed, which shows that both application position and magnitude of the vertical and horizontal forces influence the load-rotation behaviors. Then the accurate center shift expressions of the pivot with generalized planar loads are developed, which shows that the rotational angle is the dominant term for both components of the center shift while the vertical and horizontal forces are small. Finally, the accuracy of the proposed model is validated by finite element analysis（FEA）. Comparing the model data with the results obtained from FEA, the relative error of the load-rotation is less than 6% even if the rotational angle reaches 20°; the relative errors of the two components of center shift are less than 5% and 10% respectively when the rotational angle reaches 10°. The proposed model and analytical conclusions can be used to analyze and preliminarily design the compliant mechanisms containing cross-spring pivots.

Magnetic flux leakage analysis and compensation of high-frequency planar insulated core transformer

A novel high-frequency and high power density planar insulated core transformer(PICT) applied to high voltage DC generator is introduced. PICT's operating principle and fundamental configuration are described,and preliminary experimental results in self-designed PICT apparatus are presented. Emphatically, magnetic leakage flux(MFL) giving rise to the output voltage drop is analyzed in detail both theoretically and by finite element method(FEM). Showing good consistency with experimental result, FEM simulation is considered to be practicable in physical design of PICT. To cancel out leakage inductance and improve the voltage uniformity,compensation capacitor is adopted and experimental verification is also presented. All shows satisfactory results.

基于加载线型的平面太赫兹移相器设计

移相器是相控阵系统中的重要组成器件,随着频率的增加,金属的趋肤深度及波导表面粗糙度对器件的影响不可忽略,会使移相器的损耗增加。对此,提出一种基于加载线型的平面太赫兹移相器。将2个枝节并联在微带线上,在并联枝节上加载开关二极管,调节两段枝节的电长度得到所需的移相量;控制开关的导通和断开,实现不同的移相角度。仿真结果表明,在192~210 GHz频带范围内,导通和断开的反射系数都小于-10 dB,插入损耗小于0.5 dB,移相误差小于5°,其中在5 GHz带宽范围内,移相误差小于1°。提出的平面型移相器,加工容易,成本低,便于系统集成化,在太赫兹相控阵系统中具有广泛的应用前景。

A Three-state Dual-inductance Bi-directional Converter and Its Control in Pulse-loaded Three-port Converters

The current-pulse load is generally characterized by wide frequency band and pulse variation,when it is directly connected to the power supply bus.The load power is presented as the instantaneous power.In order to balance the instantaneous power difference between the pulse load and the DC bus,a bi-directional DC/DC converter is usually connected in parallel to compensate for the current fluctuation caused by the characteristics of the pulse load.However,there is a large current spike in the bus current in the pre-stage when the pulse load is changed between light and heavy load.In this paper,a three-state dual-inductance bi-directional converter is proposed.In addition,the load current waveform is directly used to control the inductive branch switches,and an adaptive current feedback control strategy based on the valley voltage loop is proposed to control the power switches.The control method is applicable to the arbitrary change of the frequency and power of the pulse load.Finally,the experimental results show that the threestate dual-inductance bi-directional converter not only eliminates excessive bus current spikes,but also improves the transient response of the three-port power supply system.

GIS局部放电检测用小型化平面螺旋天线研究

随着变电站中气体绝缘金属封闭开关设备(GIS)的广泛应用,局部放电检测逐渐成为发现故障隐患的重要手段。基于超高频(UHF)局部放电的检测原理,设计了一种工作于UHF频段的小型化天线。该天线基于传统阿基米德平面螺旋天线,利用一种振幅随着幅角线性增加的新型正弦波加载方式对天线进行进一步的小型化处理。通过HFSS软件进行仿真和试验验证,结果表明该天线在端口性能、方向性能以及增益等方面均满足局部放电检测的要求;同时天线尺寸较小,使用时易于安装,后续在GIS设备局部放电现场检测中有较大应用前景。

四足仿生机器人混联腿构型设计及比较

四足仿生机器人一直是机器人领域研究的热点之一。对国内外的研究现状和代表样机进行综述,总结现有四足机器人的腿构型的优缺点。混联腿构型结合了并联机构和串联机构的优点,可在提高机器人载重/自重比的同时,满足快速稳定响应的需求,从而实现高速、低能耗、高承载的运动。提出三种不同的3自由度混联腿机构,由1自由度的四杆机构和2自由度的平面并联机构串联组成。建立3种混联腿的运动学模型。根据四足机器人的行走设计需求,总结三种混联腿机构的特点,并建立其各自的工作空间模型。基于对角小跑的轨迹,分析三种混联结构在空间上的承载能力和各向同性度。通过对比分析选择第三种混联腿作为最优选项,并进一步与经典串联腿进行驱动力矩比较,证实混联腿的优越性。通过样机负重行走试验验证结果的可靠性,为四足混联腿机构机器人的后续研究奠定理论基础。

晶体的超精密平面抛光

修正环型抛光机用于超精密平面抛光 ,并对沥青抛光进行了运动学分析。基于得到的方程式 ,发现在相同条件下 ,计算出的抛光量和平面度与 60mm直径的玻璃圆板工件的实验值非常一致。提出了用于改善抛光平行度的偏心分布载荷技术。获得了 1 A～ 2 A表面粗糙度及小于 2

平面一维应变电炮加载技术研究

在分析电炮加载装置放电回路的基础上,探讨了电炮装置的设计原则。根据所提出的设计原则,设计和建立了一门储能14.4 kJ的电炮装置。实验测试结果表明,其性能参数诸如回路电感小于40 nH、放电周期7μs、飞片平面度小于40 ns、初始电流上升陡度达750 GA/s。与国内外的同类型装置的参数相比较,该电炮装置达到了较高水平,具有较好的性能。在此基础上,提出了获得平面一维应变加载对电炮装置的一般要求。

矩形平面天线风荷载的实验研究

车辆和舰船等上使用的移动雷达天线必须满足结构重量轻、风荷载小、对其不同方位易于操纵和控制等特点,以便达到准确、快捷、高效的应用目的。文中在西北工业大学NF-3风洞采用测力法对具有不同镂空度的车载矩形平面天线风荷载进行了实验研究。介绍了实验设备、模型构造和实验技术,给出了典型的实验结果,并进行了分析。实验结果表明,实体平面天线的最大阻力系数和方位力矩系数分别为1.877 5和0.135 0,而镂空度为50%的栅状平面天线的最大阻力系数和方位力矩系数分别为0.850 0和0.062 4,后者的阻力系数和方位力矩系数仅分别为前者的45%和46%。

全自动挂弹车相对位置测量方法

为了实现挂弹车全自动快速装填,需要精确测量挂弹车托盘与飞机挂架之间的相对位置关系,简要介绍了挂弹车的工作原理,提出了一种相对位置测量系统,详细介绍了该系统测量原理,推导出了参数测量公式,并分析了影响测量精度的因素。该系统主要由两组光学镜头、面阵CCD、激光器、合作目标及数据处理电路等组成。通过理论分析,能够实现挂弹车托盘与飞机挂架之间X、Y、Z和方位角α四维坐标的测量,X、Y方向测量精度能够达到0.73mm,Z方向测量精度能够达到7.91 mm,α方向测量精度能够达到87″。

平面相控阵系统自适应数字波束形成技术

面阵是雷达系统的主要形式之一,文中主要研究平面相控阵系统的自适应数字波束形成算法。面阵系统所用阵元数多,数据量大,要实现DBF有很大难度,目前针对面阵DBF技术的研究也较少。文中介绍了基于面阵的SM I自适应DBF算法,该算法有较好的性能,适于大型阵列的处理实现。为了提高实时性,改善SM I算法的副瓣性能,常常采用对角加载(DL)技术。DL加载值的选择非常关键,对此也进行了详细的讨论,并提出对角加载不仅可以改善SM I算法的副瓣性能,还可以在一定程度上抑制阵列通道幅相起伏误差对算法性能的影响。

爆炸荷载作用下平板网架结构破坏倒塌分析

主要研究4种不同柱布置形式的平板网架结构在受到室外爆炸荷载作用时的动态响应行为和破坏倒塌模式,并分别计算不同边柱作为爆炸荷载受力柱时的极限爆炸压强。采用Johnson-Cock修正模型模拟在爆炸荷载作用下低碳钢材料的本构关系,综合考虑钢材塑性强度强化、应变率效应、物理损伤等力学特性。利用有限元显式求解器和相应辅助子程序实现对平板网架结构在爆炸荷载作用下结构响应、破坏和倒塌过程的数值模拟。研究表明,柱布置方案对平板网架结构的抗爆能力影响明显,且不同边柱受爆条件下平板网架结构的抗爆性能存在差异。

超宽带脉冲天线研究综述

对脉冲天线技术进行了讨论并回顾总结了它们的研究和技术发展状况,主要包括脉冲天线的时域特征、脉冲天线的加载技术、高功率脉冲天线技术和超宽带平面天线技术几个方面。

无接触手机充电平台的设计

为了方便手机等小型电子设备的充电,讨论了无接触电能传输原理,采用了提高系统工作频率、电容补偿以及电路拓扑3种手段,实现了对小型电子设备的稳定、高效充电。通过采用平面电感代替传统的带铁芯的松耦合变压器进行了电磁能量的传输,实现了多负载工作。不仅完成了单部手机充电系统的制作,而且将该理论运用到充电平台的设计上。研究结果表明,通过对手机的简单改造,可以省去手机充电器实现无接触充电,简单便捷。

一种星载平面螺旋天线的小型化设计方法

探讨了某星载背腔式平面螺旋天线的小型化设计方法。通过螺旋线传输段进行蝶形加载;辐射段和截止段进行曲线锯齿加载;改善了螺旋天线的低频和高频特性,克服了传统阿基米德螺旋天线臂长、传输损耗大、效率低的缺点,增加了螺旋曲线的有效长度;通过合理设计天线的反射腔高度,提高了天线的增益。对背腔式平面螺旋天线各参数进行了综合优化设计,研制出了具有小型化、宽频带、高增益等特点的复合加载平面螺旋天线实物样机,并进行了测量,结果表明,所设计的天线在带宽为5∶1工作频带内具有良好的阻抗和圆极化辐射特性,与传统螺旋天线相比,天线的几何尺寸要远小于同频带的平面螺旋天线。

椭圆平片裂纹前沿应力强度因子解析解的超奇异积分方程方法

对无限大三维均质弹性体中任意平片裂纹的超奇异积分方程,巧妙地引入椭球坐标系和利用裂纹表面位移间断具有平方根的特性,获得了受任意方向均布内压力作用下椭圆平片裂纹问题的超奇异积分方程的解析解.运用这些解析解和应力强度因子的定义,得到了裂纹前沿Ⅰ型、Ⅱ型和Ⅲ型应力强度因子的精确表达式。

平面钢管桁架平面外稳定混合有限元分析

平面外失稳通常是无支撑平面钢管桁架在极限荷载作用下的破坏形式之一。在平面钢管桁架平面外稳定问题的求解方法中,采用梁-板壳混合有限元模型在完成整体稳定分析的同时,还可以得到节点区域实际的受力状况,且具有求解精度较高、单元数量较少的特点。根据混合有限元的基本原理,给出了混合单元交界上的结点约束方程。针对混合有限元求解方程的特点,为避免在求解上遇到数值困难,给出了混合单元模型在单元划分、求解方法上的原则和建议。数值算例与试验结果表明,混合有限元模型计算耗时较少,能较为准确的分析平面钢管桁架平面外失稳过程,提出的求解方法及建议较好的避免了数值困难的产生。

一种双U形槽加载的新型三频平面倒F天线

提出一种新型的三频平面倒F天线结构。通过在矩形贴片上开双U形槽,非常容易获得三频特性,而且可以很方便地实现对三个谐振频率的单独调节。文中设计了一个工作在GSM/DCS/ISM三个频段的平面倒F天线,采用基于矩量法的IE3D软件进行建模、仿真和分析,实测结果与仿真结果相当吻合。此外,由于这种天线只用一个同轴探针馈电,尺寸小并且结构简单,因而容易设计、制作和调节。