Sample size effect on the dynamic torsional behaviour of the 2A12 aluminium alloy

In order to investigate the effect of sample size on the dynamic torsional behaviour of the 2A12 aluminium alloy. In this paper, torsional split Hopkinson bar tests are conducted on this alloy with different sample dimensions. It is found that with the decreasing gauge length and thickness, the tested yield strength increases. However, the sample innerlouter diameter has little effect on the dynamic torsional behaviour. Based on the finite element method, the stress states in the alloy with different sample sizes are analysed. Due to the effect of stress concentration zone （SCZ）, the shorter sample has a higher yield stress. Furthermore, the stress distributes more uniformly in the thinner sample, which leads to the higher tested yield stress. According to the experimental and simulation analysis, some suggestions on choosing the sample size are given as well.

Experimental Study of the Flow in Helical Circular Pipes:Torsion Effect on the Flow Velocity and Turbulence

现在的纸的一个目的是试验性地在螺旋状的圆形的管子中在流动上澄清扭转效果。我们使六成为了有不同程度和大约 0.1 的普通非维的弯曲 δ 的螺旋状的圆形的管子。被 β0=τ/(2 δ) 定义的扭转参数 β0, 有非维的扭转 τ 的 1/2 ，被拿是 0.02， 0.45， 0.69， 1.01， 1.38 和 1.89 盖住从对很大的沥青小。速度分布和流动的骚乱从 200 ～ 20000 在雷纳兹数字的范围用一张 X 类型热电线的风速表被测量。获得的结果如下被总结：在管子的生气的节的吝啬的第二等的流动模式从没有扭转(toroidal 管子) ，在之一以后在一根弄弯的管子中被看见到一种单个旋涡类型的一种平常的成双旋涡的类型变化成双旋涡当 β0 增加，逐渐地消失。单个旋涡的循环方向与管子的扭转的方向一样。轴流的吝啬的速度分发类似于在小 β0, 的 toroidal 管子的，但是当 β0 在一根笔直地圆形的管子中增加，并且到达类似于那的形状，改变它的形状什么时候 β0= 1.89。这也被发现批评雷纳兹数字，流动在显示出边缘的行为到骚乱，为小 β0, 作为 β0 增加减少然后在拿在 β0≈ 的最小以后增加1.4 作为 β0 增加。试验性地获得的批评雷纳兹数字的最小在 β0≈ 是大约 4001.4。

Experimental Study of the Viscous Pump with a Helical Channel Rotor:Torsion Effect of the Channel

The viscous pump,which has a rotor with a helical square channel,is studied experimentally.The non-dimen-sional channel curvature is taken to be about 0.1.Three types of torsion of the channel are made to investigate the torsion effect on the flow characteristics.We measure the flux through the channel at a constant rotor speed by changing the pressures at the entrance and exit of the pump.We also observe the secondary flow at a cross-section of the channel.Some of the results obtained are shown as follows:The friction factor along the channel to get the same flux is large for large channel torsion at a constant rotation,and becomes small when the favorable rotation of the rotor to the flow is applied.As for the secondary flow in a cross-section,there appear several types of vortex.When there is no rotation,the secondary flow is almost a symmetric two-vortex type for small flux as is the ordinary Dean vortex,but it changes to a four-vortex type when the flux is large.The secondary flow becomes asymmetric as the rotation is applied.We have unsteady flow patterns at large flux and rotation.

Torsional effect of space structure in frequent earthquakes

Taking a concrete frame supporting space structure as the research object,we systematically studied its lateral-torsion coupling effect of reverse problems in consistent earthquake excitation.Firstly,based on its reverse forms and features,we put forward a mechanical analysis model(flexibility layer model) and a calculation method using the response spectrum method and the weighted average method,and verified their validity and feasibility using case analysis.The result shows that the translation displacement change trend of the space structure is basically the same whether reverse exists in the supporting structure or not,but the supporting structure torsion has an effect on the displacement with a relative increase of 10%.

Effect of Torsion on Cisplatin-Induced DNA Condensation

We investigate the effect of torsion on DNA condensation with the covalently closed circular DNA as the torsionconstrained system, using an atomic force microscope. It is found that there are two stages in the DNA condensation process under torsional constraint. At the early stage, the low torsion will accelerate DNA condensation by promoting the formation of micro-loops or intersection structures; while at the later stage, the increasing torsion will slow it down by preventing the crosslinking of cisplatin and DNA since the DNA molecule becomes more rigid. Our results show the important role of torsion in DNA condensation and sheds new light on the mechanism for DNA condensation.

考虑约束扭转二次剪力流影响的箱梁畸变效应分析

为了揭示箱梁约束扭转和畸变之间的耦联关系,研究约束扭转对箱梁畸变效应的影响,根据约束扭转二次剪力流形成的畸变荷载,建立了考虑约束扭转的箱梁畸变控制微分方程.基于乌曼斯基第二理论,提出约束扭转剪力流是基于约束扭转引起的畸变效应修正后的总扭矩布雷特剪力流,并通过Ansys有限元模型和能量法计算结果对理论公式进行了验证.数值算例结果表明:2种不同约束扭转剪力流分解方法计算所得结果完全一致;不同计算点处的约束扭转剪应力与Ansys有限元法计算结果吻合良好;扭转畸变翘曲总正应力、畸变翘曲正应力均与按能量法计算所得结果吻合良好,误差不超过10%.计入约束扭转二次剪应力的影响能够更准确地计算箱梁畸变效应.

考虑尺寸效应影响的FRP筋混凝土构件纯扭承载力计算方法

纤维增强聚合物(FRP)筋作为非腐蚀材料替代钢筋已成为解决锈蚀问题的创新方案,被应用于预应力结构、海洋平台、沿海码头和长期处于浸蚀性化学环境的构件中。关于FRP筋混凝土构件的纯扭承载力设计方法只有加拿大规范CSA S806-12提出,且以借鉴现有的钢筋混凝土构件纯扭承载力计算公式的形式给出,考虑了FRP筋与钢筋间材料力学参数的区别。该文通过已验证了的三维细观数值模拟方法,研究了最大横截面宽度为1000 mm的FRP筋混凝土柱纯扭破坏行为,揭示了其名义抗扭强度尺寸效应规律。基于模拟数据,对比了现有的FRP筋混凝土构件纯扭承载力计算公式,并在中国规范GB 50010-2010关于钢筋混凝土构件纯扭承载力计算方法的基础上,提出了考虑尺寸效应影响的FRP筋混凝土构件纯扭承载力的计算方法。通过对比现有的试验数据,验证了所提公式的正确性和合理性。

偏载作用下薄壁箱梁空间整体效应的综合分析

为了研究斜腹板箱梁在竖向偏心荷载作用下的受力性能,在合理构造各翘曲位移函数的基础上,用能量变分法建立全面反映竖向弯曲变形以及剪力滞、约束扭转、畸变等翘曲变形的控制微分方程,通过对既有文献中的模型梁进行计算分析,明确剪力滞、约束扭转及畸变翘曲应力在竖向弯曲应力中的占比情况,并揭示各翘曲广义内力的分布规律。结果表明:按文章解析法求得的模型梁应力理论值与实测值吻合良好,从而验证文章方法的合理性;在偏载作用下箱梁的约束扭转微分方程与畸变微分方程是相互耦联的,这在已有文献中往往被忽略;在剪力滞、约束扭转及畸变翘曲应力中,畸变翘曲应力占据主导地位,剪力滞和约束扭转翘曲应力相对较小,但仍不可忽略,在控制截面上因各种翘曲变形引起的应力放大系数达到1.362;偏心集中荷载引起的各翘曲广义内力均具有快速衰减的分布规律,剪力滞和约束扭转广义内力分布范围很小,而畸变广义内力分布范围广阔。建议在桥梁设计规范相关条文及实际箱梁桥设计中,对畸变效应给予充分重视。

基于流固耦合的单轴跟踪式光伏结构风致扭转研究

以某跟踪式光伏发电系统为研究对象,通过编写自定义程序代码UDF对Fluent进行二次开发,建立单轴跟踪式光伏结构的二维模型,研究其在风荷载作用下的扭转振动问题。研究结果表明:风速达到某一特值后,结构出现等幅周期性振动,发生软颤振现象,而其阻尼比对抑制扭转振动有一定的作用,这同实际情况较吻合;光伏组件倾角在0°~20°范围内时,倾角越大,扭转振动的临界风速越低。

双向水平地震作用下高桩码头地震效应组合方法研究

高桩码头在双向水平地震作用下会出现扭转效应,我国码头设计规范对此并无具体规定,但国内建筑结构设计规范和国外码头设计规范一般是将结构在两个主轴方向的单向水平地震作用效应进行组合来处理类似问题。为验证规范中的组合方法对码头的适用性和准确性,选取30组双向水平地震动记录,对码头案例进行时程分析和振型分解反应谱分析。按规范的组合方法计算反应谱分析得到的桩基内力,再计算组合值与时程分析所得内力之比,并进行统计分析。对内力比均值进行回归分析,以提出桩基内力修正系数计算公式。研究结果表明:1)双向地震作用下桩基内力比单向地震作用下大得多,抗震分析时应考虑双向地震的影响。2)相较于国外码头设计规范所用的组合方法,采用国内建筑规范中的平方和方根法组合得到的内力与时程分析结果的相关性更好,所得内力比服从对数正态分布且均值接近1,离散程度较小,建议将此法用于码头抗震分析。3)对于长周期码头结构,组合方法会低估地震反应,应使用所提出的公式对桩基内力予以修正。

上海市某超高层偏筒结构分析与设计

由于建筑功能、效果的需要,偏筒结构在高层及超高层项目中数量逐渐增多。位于上海市某280m超高层偏筒结构采用了钢管混凝土柱-钢框架-钢筋混凝土筒体的结构体系。结构设计的主要难点在于筒体偏置导致结构在地震与风荷载作用下产生较大的扭转效应;筒体部分因电梯井道开洞使得最外侧墙体易处于受拉状态,且因质量、刚度不均匀结构在竖向力作用下将产生较大的水平位移。分别对结构的抗扭性能、筒体墙构件承载力、考虑收缩徐变的结构整体水平变形进行了详细的分析,并通过大震弹塑性验证了结构整体及各构件均满足设定的性能目标,保证了结构整体及构件的安全可靠。

车辆基地全框支剪力墙结构大底盘效应分析

以某车辆基地全框支剪力墙结构为例,以底盘结构质量、刚度、频率、平面尺寸、裙房柱截面、塔楼高度等为参数,分析大底盘结构对塔楼地震响应的影响及多塔楼之间的影响、塔楼偏置对底盘的影响等。结果表明,底盘效应放大了塔楼受到的地震作用。楼高150m时,塔楼层剪力曲线形状变得弯曲,反映高阶振型带拐点的曲线形状;楼高50m时随裙房范围扩大,底盘效应明显增强,裙房范围每侧60m,裙房上一层的剪力比楼高150m时该层的剪力还要大50%左右,是楼高50m无裙房时该层剪力的2.5倍左右。在车辆基地全框支剪力墙结构设计中需考虑大底盘效应,按实际的底盘范围进行整体计算以真实反映底盘效应。

拼合式带翼缘冷弯薄壁型钢十字形构件抗扭刚度试验研究

拼合式带翼缘冷弯薄壁型钢十字形构件在轴心压力作用下的主要破坏形式为扭转失稳,其扭转失稳极限承载力取决于抗扭刚度,而拼合效应对构件抗扭刚度的影响没有明确的计算方法。为研究拼合式带翼缘十字形构件的抗扭性能及拼合效应对抗扭刚度的影响,对10个不同截面尺寸和拼合螺栓分布的带翼缘十字形冷弯薄壁构件进行了扭转试验,得到扭转全过程的扭矩-转角曲线和扭矩-应变曲线。设计了专用加载装置使构件在加载初期发生自由扭转,据此得到该拼合构件的自由扭转刚度。试验结果表明:减小螺栓间距能增强拼合效应,对于单列螺栓构件,螺栓间距的变化对拼合效应的影响更明显;拼合效应主要作用于构件的腹板,腹板尺寸增大,单位面积的螺栓数量减少,拼合效应对抗扭刚度的贡献相对减少;相较于非拼合构件,拼合构件抗扭刚度的提升可能是因为螺栓在一定程度上约束了相邻腹板的相对翘曲,提升程度可能与拼合节点间腹板的翘曲刚度有关。

高墩格构式支架风致响应和扭转效应分析

针对格构式高支架杆件长、直径小、整体结构轻极易受到风荷载影响的问题,采用有限元模拟的方法建立四腿和六腿格构式高支架精细有限元模型,并通过时域法对模型进行修正,得出格构式高支架在10级风荷载作用下的位移,获取风振系数并对扭转响应和扭转风荷载进行分析。结果表明,四腿单柱格构式高支架在10级风下纵桥向的最大位移为85.9 mm,六腿格构式高支架在10级风下纵桥向的最大位移为42.8 mm,精细有限元模型可以很好地模拟两种不同工况下风荷载对杆件的影响。

深部地层扭力冲击器破岩提速效果评价及应用

中深层是渤海油田进一步勘探开发的重点,但在钻探过程中面临各种各样的挑战,其地层抗压强度高,破岩难度大,机械钻速低,钻井周期长等特点导致渤海中深层勘探经济性差。为了解决中深层钻具憋跳严重及机械钻速慢的问题,渤海油田引入了扭力冲击器提速工具,为定量认识提速机理,建立了扭力冲击器的扭转力学特性模型,通过Abaqus有限元软件模拟了在扭冲条件下,PDC钻头的破岩过程,分析静载与扭冲条件下的破岩比功。结果表明,安装扭力冲击器后的破岩效率可提高约36%。在渤海某探井实现了现场实施,机械钻速提升了73%。研究成果对渤海油田中深层钻进提速及参数优化有一定的参考意义。

小半径曲线节段拼装箱梁设计和施工关键技术研究

为推动小半径曲线节段拼装箱梁在立交匝道桥梁中的应用,对该类桥梁受力特性、合理构造以及梁段制造、架桥机施工、拼装线形控制等关键技术进行研究。分析曲线半径对该类箱梁弯扭耦合和湿接缝受力的影响;研究梁高、腹板厚度和顶、底板厚度对梁剪扭承载力的影响;为适应平面曲线行走和吊装的需求,总结架桥机拼装施工过程中主要采用的转弯过孔、偏位和斜置起吊调整以及尾部喂梁关键技术;分析拼装过程中产生的轴线偏差和横向位移及线形控制措施。结果表明:曲线半径小于250 m的节段拼装箱梁需考虑弯扭耦合作用,曲线半径小于100 m时湿接缝截面的抗扭承载力和剪扭允许应力已不能满足要求;提高截面抗剪扭承载力最有效的构造措施是增加腹板厚度,其次是增加顶、底板厚度;曲线半径越小,小半径节段梁拼装轴线偏差越大、轴线横向位移越大,应根据曲线半径来规定安装精度验收标准、根据成桥轴线横向变形设置横向预拱度。

火电机组交互影响对次同步振荡的作用机理研究

有研究表明,多机系统发生SSO(次同步振荡)时,机组间具有相近扭振频率。为此,分析了相近频率机组轴系间的交互影响,及系统串补度、机组间电气距离和相近扭振频率对次同步振荡的作用机理。首先,基于特征矩阵,推导两台火电机组并列送出系统的复转矩系数表达式。然后,将单机的简化复转矩系数法扩展到多机系统,推导了双火电机组电气阻尼的简化表达式,分析了其他机组对待研机组阻尼的作用,结果表明,串补度、机组电气距离以及相近扭振频率都会影响到系统阻尼和稳定性。最后,通过算例验证了各影响因素对系统次同步稳定性的作用机理。

Finite elastic torsional instability of incompressible thermo-hyperelastic cylinder

Torsional instability of an incompressible thermo-hyperelastic cylindrical rod, subjected to axial stretching and large torsions, is examined within the framework of finite elasticity. When the cylinder is stretched and twisted by a sufficiently large degree, a knot may form suddenly at one point. This inherent elastic instability is analyzed with the minimum potential energy principle and the critical values of torsion are obtained. The distribution of stresses as well as the tensile force and the torque are studied. Effect of tem- perature change is specifically discussed.

Effects of shoulder on interfacial bonding during friction stir lap welding of aluminum thin sheets using tool without pin

To separately investigate the potential effects of shoulder on increasing interfacial bonded area and its mechanism,friction stir lap welding(FSLW)of 1.8 mm thick Al sheets without and with insert(copper foil or Al-12Si powders)was conducted using a special tool without pin,respectively.All the FSLW joints(without insert)fractured within top sheet but not along faying surface,suggesting that the shoulder plays an important role comparable or superior to pin in FSLW of thin sheets.Using several specially designed experimental techniques,the presence of forging and torsion actions of shoulder was demonstrated.The fracture surface of the joints with inserts indicates that interfacial wear occurs,which results in the oxide film disruption and vertically interfacial mixing over the area forged by shoulder with a larger diameter than a general pin,especially at the boundary region of weld.The boundary effect can be induced and enhanced by forging effect and torsion effect.

Precise Underground Observations of the Partial Solar Eclipse of 1 June 2011 Using a Foucault Pendulum and a Very Light Torsion Balance

Simultaneous observations of the solar eclipse on 06/01/2011 were carried out using a Foucault pendulum and a torsion balance. The instruments were installed in a salt mine, where the interference was minimal. Both instruments clearly reacted to the eclipse. We conclude that these reactions should not be considered as being gravitational effects.