Investigations on serviceability control of long-span structures under human-induced excitation

The increasing strength of new structural materials and the span of new structures, accompanied by aesthetic requirements for greater slenderness, are resulting in more applications of long-span structures. In this paper, serviceability control technology and its design theory are studied. First, a novel tuned mass damper （TMD） with controllable stiffness is developed. Second, methods for modeling human-induced loads are proposed, including standing up, walking, jumping and running, and an analysis method for long-span floor response is proposed based on a finite element model. Third, a design method for long-span floors installed with a multiple TMD （MTMD） system considering human comfort is introduced, largely based on a study of existing literature. Finally, a design, analysis and field test is conducted using several large scale buildings in China including the Beijing Olympic Park National Conference Center, Changsha New Railway Station and the Xi＇an Northern Railway Station. The analytical and field test results show that the MTMD system designed using the proposed method is capable of effectively mitigating the vertical vibration of long-span floor structures. The study presented in this paper provides an important reference for the analysis of vibration serviceability of similar long-span floors and design of control system for these structures.

Stability and local bifurcation of parameter-excited vibration of pipes conveying pulsating fluid under thermal loading

The parametric excited vibration of a pipe under thermal loading may occur because the fluid is often transported heatedly. The effects of thermal loading on the pipe stability and local bifurcations have rarely been studied. The stability and the local bifurcations of the lateral parametric resonance of the pipe induced by the pulsating fluid velocity and the thermal loading are studied. A mathematical model for a simply supported pipe is developed according to the Hamilton principle. Two partial differential equations describing the lateral and longitudinal vibration are obtained. The singularity theory is utilized to anMyze the stability and the bifurcation of the system solutions. The transition sets and the bifurcation diagrams are obtained both in the unfolding parameter space and the physical parameter space, which can reveal the relationship between the thermal field parameter and the dynamic behaviors of the pipe. The frequency response and the relationship between the critical thermal rate and the pulsating fluid velocity are obtained. The numerical results demonstrate the accuracy of the single-mode expansion of the solution and the stability and local bifurcation analyses. It also confirms the existence of the chaos. The presented work can provide valuable information for the design of the pipeline and the controllers to prevent the structural instability.

The Behavior of Rectangular and Circular Reinforced Concrete Columns Under Biaxial Multiple Excitation

The aim of this study is to investigate the dynamic performance of rectangular and circular reinforced concrete(RC)columns considering biaxial multiple excitations.For this purpose,an advanced nonlinear finite element model which can simulate various features of cyclic degradation in material and structural components is used.The implemented nonlinear fiber beam-column model accounts for inelastic buckling and low-cycle fatigue degradation of longitudinal reinforcement and can simulate multiple failure modes of RC columns under dynamic loading.Hypothetical rectangular and circular columns are used to investigate the failure modes of RC columns.A detailed ground motion selection is implemented to generate real mainshock and aftershocks.It was found that multiple excitations due to aftershock has the potential of increasing the damage of the RC columns and longitudinal reinforcements are significantly affected low-cycle fatigue.Also,it was found that rectangular column is more sensitive to accumulative damage due to cyclic fatigue.This study increases the accuracy of structural analysis of RC columns and consequently improves understanding the failure modes of RC columns with different cross-sectional shapes.

Local Bifurcation Analysis of Parameter-Excited Resonance of Pipes under Thermal Load

The stability and local bifurcation of the lateral parameter-excited resonance of pipes induced by the pulsating fluid velocity and thermal load are studied. A mathematical model for a simply supported pipe is developed according to Hamilton principle. The Galerkin method is adopted to discretize the partial differential equations to the ordinary differential equations. The method of multiple scales and the singularity theory are utilized to analyze the stability and bifurcation of the trivial and non-trivial solutions. The transition sets and bifurcation diagrams are obtained both in the unfolding parameter space and physical parameter space, which can reveal the relationship between the thermal field parameter and the dynamic behaviors of the pipe. The numerical results demonstrate the accuracy of the single-mode expansion of the solution and verify the stability and local bifurcation analyses. The critical thermal rates are obtained both by the numerical simulation and the local bifurcation analysis. The natural frequency of lateral vibration decreases as the mean fluid velocity or the thermal rate increases according to the numerical results. The present work can provide valuable information for the design of the pipeline and controllers to prevent structural instability.

Modal Parameters Identification of A Real Offshore Platform From the Response Excited by Natural Ice Loading

This paper investigates the possibility of utilizing response from natural ice loading for modal parameter identification of real offshore platforms.The test platform is the JZ20-2 MUQ jacket platform located in the Liaodong Bay,China.A field experiment is carried out in winter season,as the platform is excited by floating ices.The feasibility is demonstrated by the acceleration response of two different segments.By the SSI-data method,the modal frequencies and damping ratios of four structural modes can be successfully identified from both segments.The estimated information from both segments is almost identical,which demonstrates that the modal identification is trustworthy.Furthermore,by taking the Jacket platform as a benchmark,the numerical performance of five popular time-domain EMA methods is systematically compared from different viewpoints.The comparisons are categorized as:(1)stochastic methods versus deterministic methods;(2)high-order methods versus low-order methods;(3)data-driven versus covariance-driven stochastic subspace identification methods.

人行桥在行人荷载激励下的非平稳随机响应

采用虚拟激励法和微分求积法相结合的DQ-PEM法研究在行人荷载激励下人行桥的非平稳随机响应.与以往的虚拟激励法不同的是该方法以简单谱模型为基础,建立行人强迫函数的谱密度,求得多自由度体系人行荷载下的多模态.通过工程算例验证该方法的准确性与有效性,并进一步讨论不同速度和不同约束条件下梁式结构受行人荷载作用的随机振动问题.

水轮机调节系统与轴系耦合模型对系统参数的敏感性分析

抽水蓄能电站频繁地暂态过程对轴系振动有重要影响,建立一个能够反映水电机组暂态响应的调节系统与轴系的耦合模型对于研究抽水蓄能电站的安全运行至关重要。以拉日朗日公式推导的扭矩方程为纽带,构建了水轮发电机组调节系统与考虑多振动诱发因素的轴系系统的瞬态耦合模型。计算了甩不同负荷下轴系的动态响应过程,分析了发电机偏心质量以及发电机励磁电流对轴系暂态过程的影响。研究发现,甩去的负荷越多,轴系在动态响应的过程中振动越剧烈,甩30%负荷,甩60%负荷,以及甩100%负荷后,发电机转子在x方向上的振幅较甩负荷前分别增加了68.7%,109.3%,以及126.3%。发电机的偏心质量越大,水轮发电机组轴系在动态响应过程中的幅值越高,系统越不稳定,而励磁电流越大,轴系在响应过程中的幅值越小,越有利于系统稳定运行。本文的目的是为水轮发电机组调速系统-轴系系统瞬态耦合模型的建立提供一种方法,探讨和评价甩负荷下瞬态耦合模型的参数敏感性,保障机组暂态下的安全稳定运行。

周期规律增强的多视角短期电力负荷预测

短期电力负荷预测对电力系统的可靠运行具有重要意义。现有方法存在如下问题:缺乏对特征之间依赖关系的挖掘;忽略了电力负荷变化的周期性规律。为此,提出一种周期规律增强的多视角短期电力负荷预测网络(EPISODE)方法。EPISODE方法主要包括2个核心组件:多视角特征学习组件和周期规律增强的电力负荷预测组件。前者旨在有效提取电力负荷数据中的静态特征与时序特征,以得到增强的特征表示;后者则是对电力负荷数据进行一般性时序挖掘和周期性时序挖掘,从而得到全面的电力负荷历史数据表征。基于后期融合的方式,实现短期电力负荷预测。在真实公开的电力负荷预测数据集上进行了大量实验。实验结果证明了所提方法相比现有基准方法的先进性。

三种典型主梁断面的悬索桥颤振性能差异

为了揭示主梁基本气动外形对悬索桥颤振性能的影响,以一座大跨悬索桥为例,分别选取流线型箱型、边箱型与分离式双箱型3种典型断面作为大桥主梁的基本气动外形。采用强迫振动法并基于CFD数值模拟获取各断面的气动参数,并采用阶跃函数法建立主梁的气动自激力时域模型;然后利用ANSYS平台进行全桥时域颤振有限元分析,得到各断面对应的颤振临界风速与颤振频率。结果表明:分离式双箱断面的颤振性能最佳,其颤振临界风速达到109.6 m/s,远高于其他2种断面;流线型断面与边箱型断面的颤振临界风速分别为89.4 m/s与86.9 m/s,两者的颤振性能相差不大;由频谱及相位分析可知,3种断面的颤振频率介于竖弯与扭转基频之间,颤振形式表现为不同程度的扭弯耦合振动。

薄壁壳体构件复合加载试验及参数监测平台设计及应用

围绕复杂服役环境下某装备薄壁壳体构件失效模式不清和寿命评估困难等问题,研发复合加载试验及参数监测平台。通过静力加载装置和振动夹具组合设计的内平衡加载方式对薄壁壳体施加静力载荷,有效解决温湿振环境下力加载的解耦难题;通过多综合应力环境参数控制和监测系统集成设计,实现多应力监测和控制一体化功能。该平台能够赋予薄壁壳体构件相应的温度、湿度、力和振动环境,也能实时对温度、湿度、力、振动和应变等信号进行监测和记录,有效模拟装备更为真实的工作状态,为装备研制和考核提供有力支撑。

小波包分解重构的励磁变压器整流谐波附加损耗计算

谐波损耗是造成励磁变压器安全事故的主要原因之一,损耗值过大易影响正常变电和输电,为此提出基于小波包分解重构的励磁变压器整流谐波附加损耗计算方法。通过获取小波包分解和重构系数,分析励磁变压器两种谐波附加损耗;利用开路和短路实验得到励磁变压器等效电路参数,采用小波包分解重构算法,计算不同谐波次数下的电阻和电抗并与基准值对比,得到励磁变压器整流谐波附加损耗值。最后,选取某种型号的励磁变压器,利用所提方法计算其在不同谐波次数下的附加损耗值,结果表明,得到的损耗值计算结果与实际结果非常接近,验证了所提方法具有较高的实用价值。

考虑负载及误差激励下高速齿轮传动的动力学仿真分析

高速工况下,高速齿轮传动装置的动态特性对设备的可靠运行有重要影响。建立了高速斜齿轮副模型,在考虑齿轮动态激励的条件下,分析了高速齿轮传动的动态特性,进行了动力学仿真。结果表明,主动齿轮沿轴向移动0.2 mm、绕竖直方向旋转0.15°后,角速度波动幅值分别提高了6.12%、3.46%;接触力波动幅值分别提高了0.58%、4.56%;轴向位移误差对角速度的影响较大,角度误差对接触力的影响较大。加速时间从5 s增加到10 s后,角速度波动幅值降低了10.7%,角速度标准差从6.9748减少到6.406;接触力波动幅值增大了0.58%。负载从1000 N·m增大到1626.75 N·m和2000 N·m后,角速度标准差从6.9748分别减小到4.77475、4.74945,接触力波动幅值分别增大了4.3%、4.25%。额定载荷在轻载情况下,齿轮传动更加平稳;在重载情况下,角速度和接触力波动差异不明显。

驱动及负载激励下高速人字齿轮的动态特性分析

高速齿轮传动装置中通常采用人字齿轮传动,其高速工况下的动态特性对设备的可靠运行有重要影响。建立了人字齿轮传动的模型,在考虑驱动和负载激励的条件下,分析了人字齿轮增速传动的动态特性,进行了动力学仿真,并对产品进行了实验。结果表明,在负载恒定时,齿轮角速度越大,齿轮所受接触力越大,碰撞频率越高。随着输入转速逐步提高至500、1000、1488 r/min时,其速度波动幅值之差分别为2.27、4.76、9.37 rad/s,后两种工况下最大接触力分别是500 r/min工况下的1.87倍和2.44倍,角速度波动的次数分别增大到500 r/min工况下的1.94倍和2.94倍。负载增大,从动齿轮角速度波动幅度减小,接触力增大。研究为高速齿轮传动装置设计提供了参考。

采用PD控制的变质量座椅悬架主动控制研究

针对座椅悬架负载质量的变化而产生的系统非线性,以及对座椅振动的有效控制等问题,提出了一种基于比例-微分(Proportional-Derivative,PD)控制的变质量座椅悬架主动控制系统。该控制系统建立在几个不同的控制器基础上,主控制器用于评估应在悬架系统中产生所需主动力的实际值,次级控制器用于计算信号的瞬时值,该信号通过其反向模型控制有源元件。建立主动座椅悬架系统模型,对主动座椅悬架控制系统进行设计。对不同负载质量的座椅悬架系统的鲁棒性进行仿真验证,对控制器参数进行优化设计,实现了主动座椅悬架自适应质量识别的精细控制。对优化设计结果进行对比验证,结果表明,质量变化对主动座椅悬架系统的动态性能影响显著降低。在100 kg质量负载时,EM3、EM5和EM6激励信号下,主动系统的座椅有效幅值传递率(Seat Effective Amplitude Transmissibility,SEAT)因子分别降低了49.81%、20.96%和29.85%,同时悬架行程分别降低了4.76%、33.87%和18.18%。所建立的主动控制系统显著提高了座椅悬架的性能,对变化负载质量具有更好的鲁棒性,为主动座椅悬架隔振性能研究提供了参考。

等截面高耸烟囱涡激共振时风荷载的风力作用研究

关于锁定区域范围的描述,不同参考文献存在显著的差异。同一类型地形结构发生涡激共振时,横向风向的等效风荷载在基本一致的情况下可能仍存在显著差异。依托实际工程案例,在分析锁定区及横风向等效风荷载的基础上对组合等效风荷载进行确定,结果发现,实例计算检查测试结果与规范之间存在较大差异。

舰载设备在基础运动激励下的动力响应分析方法

为了解决舰载设备在基础运动激励下的动力响应问题,本文通过对比惯性载荷法、大质量法、大刚度法、直接激励法的动力学方程,探讨不同方法的特点和应用条件,并给出相应的算例与结果分析,为开展舰载设备的动力响应计算提供理论依据及方法。

中频变压器绕组非正弦周期载荷振动特性分析

针对非正弦周期载荷作用下的中频变压器绕组振动问题,建立柱坐标下的圆筒形绕组和笛卡尔坐标下的矩形绕组动力响应数值计算模型,模型考虑了电磁-结构扰动的耦合关系。根据屈服条件和流动理论,建立变压器绕组弹塑性变形的动力平衡方程。引入夹层模型简化计算,计算得到夹层模型薄层间距,可用于绕组拉伸、压缩变形等效建模。通过一台中频变压器算例进行非正弦周期载荷作用下绕组动力响应的实验测量和数值计算。研究表明,三角波载荷与正弦波载荷作用下绕组振动特性相同,而矩形波载荷作用下绕组振动在激励周期内几乎不衰减。发生故障工况时,由于高频振动,绕组残余形变迅速积累。2 kHz的矩形波载荷作用下绕组在1 ms内极限载荷强度可下降至1/4。

高速铁路声屏障气动荷载及结构振动响应特性

高速铁路声屏障是铁路噪声控制的常用措施,但声屏障距离线路中心较近,在列车动力作用下会产生振动响应。列车风作用在声屏障表面形成的气动荷载和轮轨接触力产生的钢轨振动会传递到声屏障基础,是导致声屏障结构产生风致振动与轮轨激励振动的主要振源。通过开展声屏障列车气动荷载及振动响应的测试及仿真计算,获得不同工况下声屏障气动荷载及振动响应特性。结果表明:动车组以350 km/h运行时,比300 km/h运行时声屏障气动荷载和振动响应大40%;同一速度级下,路基声屏障立柱的顶端位移比桥梁声屏障顶端大40%~50%,而桥梁声屏障单元板动位移比路基声屏障大20%~30%;轮轨激励振动直接影响了声屏障振动响应,在传递过程中呈有规律衰减的趋势;列车风压与自然横风组合作用时,声屏障立柱的动变形及动应力呈现明显增大的趋势。

动力荷载对后加结构竖向振动的影响及加固分析

近年来,动力设备不断进入民用建筑,比如排风设施的风机等。当两者之间的自振频率接近某一范围时将产生共振现象,引起人员的不适,甚至影响到结构的安全性。尤其是在房屋改建过程中的后加结构因与原结构连接整体性相对较弱,一旦两者产生共振现象将严重危害后加结构的安全。本文针对某办公楼悬挂在新加夹层楼板下方的厨房排风设施在运转时,处于新加夹层楼板上方人员感受到明显的振动,新加夹层楼板振动响应过大这一问题,在完成对结构进行现场振动测试的基础上,分析新加夹层楼板的动力特性,找到引起楼板振动原因,提出几种减振加固的方案,对比分析,找到最优的减振加固方案。结果表明:当后加楼板结构振动响应过大时,采用夹芯楼板加固方案可以有效地降低结构的振动响应,提高楼板的舒适度。