Infl uence of structural parameters on dynamic characteristics and wind-induced buffeting responses of a super-long-span cable-stayed bridge

A 3D finite element （FE） model for the Sutong cable-stayed bridge （SCB） is established based on ANSYS. The dynamic characteristics of the bridge are analyzed using a subspace iteration method. Based on recorded wind data, the measured spectra expression is presented using the nonlinear least-squares regression method. Turbulent winds at the bridge site are simulated based on the spectral representation method and the FFT technique. The influence of some key structural parameters and measures on the dynamic characteristics of the bridge are investigated. These parameters include dead load intensity, as well as vertical, lateral and torsional stiffness of the steel box girder. In addition, the influence of elastic stiffness of the connection device employed between the towers and the girder on the vibration mode of the steel box girder is investigated. The analysis shows that all of the vertical, lateral and torsional buffeting displacement responses reduce gradually as the dead load intensity increases. The dynamic characteristics and the structural buffeting displacement response of the SCB are only slightly affected by the vertical and torsional stiffness of the steel box girder, and the lateral and torsional buffeting displacement responses reduce gradually as the lateral stiffness increases. These results provide a reference for dynamic analysis and design of super-long-span cable-stayed bridges.

Research on electromagnetic relay's dynamic characteristics disturbed by uniform static magnetic field

Electromagnetic relay is a widely used apparatus which usually works in a magnetic disturbance environment. To evaluate its electromagnetic compatibility (EMC) in a static magnetic field, dynamic characteristics of a clapper relay in a uniform static magnetic field situation based on the finite element method (FEM) is studied. Influences of the magnetic field on dynamic parameters (delay time, pick-up time, end pressure, and final velocity) as well as a situation in which the relay cannot function normally are analyzed. Simulation reveals that the external magnetic field which weakens the relay’s air-gap field has a greater influence on the relay’s dynamic parameters than the one strengthening the field. The validity of the simulation is verified by measured results of coil current and armature displacement.

Analysis of structural dynamic characteristics of a high speed light special catamaran

In this paper,structural dynamic characteristics of a high-speed light special catamaran-wave piercing catamaran are analyzed using the FEA software MSC-NASTRAN. The dynamic reduction method is introduced to eliminate the local vibration modes in order to obtain the whole ship＇s mode shapes. In the post-processor, a lot of accessorial methods are adopted to eliminate the local vibrations, so that the whole ship＇s mode shapes can be identified. The modal analysis indicates that the dynamic reduction method fits for mode shapes identifying. In the end,the test results of a catamaran named Frederick G. Greed are used for reference to validate the obtained results. The comparison process shows that the results are credible. A special mode shape, which is quite different with that of conventional monohull ship, is also pointed out. The obtained results provide a valuable reference for the coming computation of catamaran＇s vihration characteristics.

Application of semi-analytical finite element method to analyze the bearing capacity of asphalt pavements under moving loads

To facilitate long term infrastructure asset management systems, it is necessary to determine the bearing capacity of pavements. Currently it is common to conduct such measurements in a stationary manner, however the evaluation with stationary loading does not correspond to reality a tendency towards continuous and high speed measurements in recent years can be observed. The computational program SAFEM was developed with the objective of evaluating the dynamic response of asphalt under moving loads and is based on a semi-analytic element method. In this research project SAFEM is compared to commercial finite element software ABAQUS and field measurements to verify the computational accuracy. The computational accuracy of SAFEM was found to be high enough to be viable whilst boasting a computational time far shorter than ABAQUS. Thus, SAFEM appears to be a feasible approach to determine the dynamic response of pavements under dynamic loads and is a useful tool for infrastructure administrations to analyze the pavement bearing capacity.

Shape Optimal Design of Hydrodynamic Bearing Based on Dynamic Characteristics

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Computational fluid dynamics simulations of respiratory airflow in human nasal cavity and its characteristic dimension study

To study the airflow distribution in human nasal cavity during respiration and the characteristic parameters of nasal structure, three-dimensional, anatomically accurate representations of 30 adult nasal cavity models were recons- tructed based on processed tomography images collected from normal people. The airflow fields in nasal cavities were simulated by fluid dynamics with finite element software ANSYS. The results showed that the difference of human nasal cavity structure led to different airflow distribution in the nasal cavities and variation of the main airstream passing through the common nasal meatus. The nasal resistance in the regions of nasal valve and nasal vestibule accounted for more than half of the overall resistance. The characteristic model of nasal cavity was extracted on the basis of characteristic points and dimensions deduced from the original models. It showed that either the geometric structure or the airflow field of the two kinds of models was similar. The characteristic dimensions were the characteristic parameters of nasal cavity that could properly represent the original model in model studies on nasal cavity.

Complex nonlinear behaviors of a rotor dynamical system with non-analytical journal bearing supports

Nonlinear dynamic behaviors of a rotor dynamical system with finite hydrodynamic bearing supports were investigated. In order to increase the numerical accuracy and decrease computing costs, the isoparametric finite element method based on variational constraint approach is introduced because analytical bearing forces are not available. This method calculates the oil film forces and their Jacobians simultaneously while it can ensure that they have compatible accuracy. Nonlinear motion of the bearing-rotor system is caused by strong nonlinearity of oil film forces with respect to the displacements and velocities of the center of the rotor. A method consisting of a predictor-corrector mechanism and Newton-Raphson method is presented to calculate equilibrium position and critical speed corresponding to Hopf bifurcation point of the bearing-rotor system. Meanwhile the dynamic coefficients of bearing are obtained. The nonlinear unbalance periodic responses of the system are obtained by using Poincaré-Newton-Floquet method and a combination of predic- tor-corrector mechanism and Poincaré-Newton-Floquet method. The local stability and bifuration behaviors of periodic motions are analyzed by the Floquet theory. Chaotic motion of long term dynamic behaviors of the system is analyzed with power spectrum. The numerical results reveal such complex nonlinear behaviors as periodic, quasi-periodic, chaotic, jumped and coexistent solutions.

Characteristic size research of human nasal cavity and the respiratory airflow CFD analysis

To study the airflow distribution in human nasal cavity during respiration and the characteristic parameters for nasal structure, thirty three-dimensional, anatomically accurate representations of adult nasal cavity models were reconstructed based on processed tomography images collected from normal people. The airflow fields in nasal cavities were simulated using the fluid dynamics with the finite element software ANSYS. The results showed that the difference of human nasal cavity structure led to varying airflow distribution in the nasal cavities and the main airflow passed through the common nasal meatus. The nasal resistance in the regions of nasal valve and nasal vestibule accounted for more than a half of overall resistance. The characteristic model of nasal cavity was extracted based on the characteristic points and dimensions deducted from the original models. It showed that either the geometric structure or the air-flow field of the two kinds of model was similar. The characteristic dimensions were the characteristic parameters of nasal cavity that properly represented the original model in research for nasal cavity.

脉冲风洞天平基础动力特征的简化计算方法

为了研究脉冲风洞天平基础在脉冲气动荷载作用下的动力响应特征,以某脉冲风洞为例,选择某典型气动荷载作用形式,建立了脉冲风洞天平基础在气动荷载作用下竖直方向、水平方向位移以及回转角度等动力特征的简化计算方法,并采用数值模拟的方法验证其可靠性.研究结果表明:天平基础在典型气动荷载作用下,竖直向最大振幅0.00175 mm,频率7.94 Hz,水平向最大振幅0.00283 mm,频率7.94 Hz,回转角度最大振幅0.00034°,频率7.94 Hz,典型气动荷载对天平基础振动影响较小,也未产生共振现象;基础振动最大振幅随气动荷载增大而增大,基础振动频率随气动荷载频率增大而增大;在气动荷载不变的条件下,基础振动的最大振幅与频率随尺寸的变大而变小,基础振动的最大振幅也随地基土性质的增强而减小,但地基土性质的变化对基础振动频率无影响.

考虑激励幅值慢变的卷绕头转子系统动力学建模

卷绕头转子系统结构之间的耦合振动和时频变激励使振动问题十分复杂,为了更准确地研究其动力学特性,根据转子动力学理论,使用有限元方法建立了考虑多盘质量慢变的卷绕头非线性转子系统整机动力学模型,运用Newmark-β数值积分方法对其动力学特性求解,得到仅存在初始不平衡量以及卷装不良带来的激励频率、幅值慢变下的非线性动力学行为。通过分析轴心轨迹、时域波形和幅频特性曲线等结果,发现卷绕头转子系统对因卷装不良引起的激励幅值慢变较为敏感,出现新的频率成分。进一步对比分析了不同节点处的振动频谱,其结果可为卷绕头转子系统动力学设计和故障识别提供一定理论支持。

平钢板-UHPC组合桥面板纵向抗负弯性能试验研究

某大桥次边跨及中跨主梁为钢-UHPC组合梁,钢-UHPC组合梁的桥面板首次采用一种通过PBL剪力键将8 mm平钢板与15 cm的UHPC层连接起来的新型组合桥面体系。为了探究该桥新型钢-UHPC组合桥面板抗负弯矩性能与安全性,完成了2块足尺模型的静力性能试验,进行了桥梁整体受力和桥面板局部受力计算,以及桥面板抗负弯矩极限承载力构成分析。结果表明:UHPC名义开裂强度达8.90 MPa以上,其值远大于实桥荷载作用下UHPC层上缘的纵桥向最大拉应力,组合桥面板负弯矩抗裂性能良好,能满足工程需求;组合桥面板抗负弯承载力的计算,UHPC受拉本构宜采用三折线模型,抗负弯承载力简化计算的UHPC受拉区等效均布应力折减系数可取0.76,抗负弯承载力状态的受压钢板受力仍处于线弹性阶段,抗负弯破坏模式与抗正弯明显不同,为受拉钢筋拉断;PBL剪力键能保证了钢板与UHPC板整体共同受力;组合桥面板在负弯矩作用下的延性良好,裂宽增长缓慢,UHPC的名义极限强度达名义开裂强度的4.1倍以上,到达极限荷载后,组合板承载力没有明显下降。

高温磁悬浮轴承-转子系统建模与动力学分析

在多电航空发动机中,主动磁悬浮轴承因其耐高温、非接触等特性可以突破温度对支承部位的限制,使支承部位能够更靠近燃烧室.为探究温度对磁悬浮轴承转子系统动态特性的影响规律,提出一种高温磁悬浮轴承转子系统动力学建模方法.通过仿真得到转子在不同温度下的温度分布,并使用多项式拟合转子轴向温度分布;基于有限元方法推导柔性转子单元的动力学模型,引入温度影响,建立考虑温度影响的磁悬浮轴承转子系统整体动力学模型,并通过模态试验验证模型的准确性;基于理论动力学模型分析系统的动态特性.结果表明:温度升高会导致转子的前三阶支承模态频率下降,增大各阶幅频响应幅值;当温度从常温升至450℃时,转子的前三阶弯曲支承模态频率分别降低了3.818%、5.670%、3.183%,前三阶弯曲模态幅频响应幅值分别升高了83.4%、34.4%、24.1%.

基于分层法的石墨烯增强功能梯度Timoshenko梁动力特性有限元分析

基于分层法对石墨烯增强功能梯度Timoshenko梁的动力特性问题进行有限元分析。在有限元建模过程中,首先将Timoshenko梁沿厚度方向分成若干层,然后利用改进的Halpin-Tsai细观力学模型计算各层的弹性模量,相应的泊松比和密度则根据混合率法则进行计算,最后对各层均采用4节点四边形板单元离散。通过数值算例分析分层数和单元尺寸比例的合理性,探究石墨烯片的分布形式、质量含量、几何形状和尺寸等因素对Timoshenko梁动力特性的影响。结果表明,添加少量的石墨烯能显著提高Timoshenko梁自由振动的频率,尤其在梁的上下部位分布较多正方形石墨烯片时效果最佳。随着石墨烯片长厚比的增加,Timoshenko梁的自由振动基频不断增大。当石墨烯片长厚比超过1 000之后,梁的基频变化不明显。

翁结水库碾压混凝土重力坝动力特性及其抗滑稳定分析

重力坝是水利工程中最常用的主要水工建筑物之一,混凝土重力坝在地震作用下的动力稳定是坝工设计中的重要问题.本文以翁结碾压混凝土重力坝为对象,取位于河谷中的7、8号溢流坝段和9号非溢流坝段,建立三维有限元模型,通过计算分析了碾压混凝土重力坝在不同工况下的应力变形规律及抗滑稳定性.结果表明:静力荷载作用下,坝体位移符合重力坝一般规律,坝踵主拉应力范围较小;动力荷载作用下,位移等响应在坝顶达到最大,符合鞭鞘效应特征,同时坝体残余位移较小,坝体在一些部位出现瞬时拉应力超标现象,坝基塑性区未发生贯通;对7、8号坝段和9号坝段在建基面及碾压层面进行抗滑稳定验算,坝体坝基均满足稳定要求.

海洋养殖柔性网衣结构水动力特性研究进展

发展深水网箱养殖是保障我国粮食及食品安全的长远战略,也是缓解近海网箱养殖环境胁迫力、拓展食物生产空间的必然选择。发展深水网箱养殖首先需要面对的突出挑战是养殖设施在外海恶劣海况下的安全性问题。网衣是深水网箱的主体结构,由于其自身具有高柔性、小尺度的特点,在波浪和水流作用下易出现大位移和大变形的极端响应。当前,网衣结构分析技术已成为我国深水网箱养殖工程技术的薄弱环节,一定程度上制约当前海上养殖网箱向大型化和深水化发展。因此,网衣水动力特性研究对于深远海网箱养殖的发展具有重要意义。本研究系统介绍了计算网衣水动力荷载的主要方法及其适用范围。同时,对网衣动态响应数值计算中的主流建模技术进行了总结和分析。最后,根据目前网衣水动力特性研究中存在的热点问题,提出了网衣流固耦合分析、生物污损分析、数字孪生技术等前沿发展方向,为网衣水动力学分析向数字化、精准化发展提供参考。

不同主横梁建模方式对弧门静动力学模拟结果影响

针对弧形闸门有限元分析中采用不同建模方式易造成数值模拟结果差异性的问题,以贵州乌江沙沱水电站大型露顶式弧形闸门为例,从计算原理角度探究了主梁翼缘采用节点耦合法、厚度叠加法两种建模方式对闸门静动力学计算结果(三维非线性静力学、模态分析和瞬态动力学)的影响。通过对比分析发现:采用厚度叠加的简化方式增加了构件的刚度,对闸门静力复核不利;两种建模方式对闸门干湿模态下的振型和自振频率影响较小;采用节点耦合法获取的支臂垂向振动程度较厚度叠加法结果略大,支臂与主横梁连接处敏感区域的动应力较厚度叠加法结果明显增大。两种建模方式对闸门整体结构属性影响有限,对支臂与主横梁连接处等敏感区域进行计算复核时应尽量采用节点耦合法,使计算结果更偏于安全。

龙羊峡重力拱坝模态识别与材料参数反演

基于龙羊峡重力拱坝实测振动数据,利用随机子空间法进行了大坝模态参数识别,建立了坝体-地基-库水系统的三维流固耦合有限元模型。根据识别出的一阶频率,分别考虑均质地基及分层地基,反演了坝体与基岩材料参数,并通过有限元软件ABAQUS进行了大坝的动力特征分析。结果表明:龙羊峡重力拱坝的一阶频率为2.778~3.196 Hz,反演得到坝体的弹性模量约为50 GPa~52 GPa;对于均值地基,其弹性模量的反演值为30 GPa;对于分层地基,2 490 m高程以下区域的弹性模量为34 GPa;实测振动数据反演得到的坝体弹性模量和地基弹性模量高于其设计值;龙羊峡重力拱坝的前3阶振型分别为正对称、反对称与正对称,其1阶频率和2阶频率相差较大,与重力坝自振频率分布特征相似。

悬臂同轴双转子系统不平衡耦合振动抑制试验研究

针对悬臂同轴双转子系统不平衡耦合振动突出问题,以某开式转子发动机输出端双转子系统为研究对象,对悬臂双转子系统振动耦合机理进行了理论推导、仿真分析和试验研究。首先,采用有限元法(FEM)建立了双转子系统等效动力学模型和耦合动力学方程,分析了悬臂同轴双转子系统耦合振动机理;然后,利用有限元软件对双转子系统进行了模态分析、临界转速分析以及不平衡响应分析,建立了自敏感系数概念以定量评价系统对不平衡振动的敏感度和耦合状态;最后,根据实际结构设计了悬臂同轴双转子实验台,进行了不同转速比下的不平衡振动抑制实验,并结合实验结果对仿真结果进行了验证。研究结果表明:模拟仿真提出的自敏感系数可作为双转子系统实际振动测点布置和不平衡振动抑制策略的理论依据;通过应用先平衡内转子后平衡外转子的不平衡振动分步抑振策略,可使双转子系统不平衡振动降幅达80%以上。该研究对双转子系统传感器测点布局和系统耦合振动抑制具有一定的指导意义。

滚动轴承打滑研究进展综述

随着航空航天、军工领域发展,对滚动轴承寿命和可靠性、精准度提出了更高要求。打滑作为一种滚动轴承工作中不可忽视的现象,影响着滚动轴承工作时的准确度和寿命。论文基于国内外学者对滚动轴承打滑问题研究,从滚动轴承打滑动力学建模、有限元仿真、轴承保持架转速测量方法三个方面对滚动轴承打滑研究进行总结。最后对滚动轴承打滑问题研究方向进行展望。

初始裂纹倾角对圆柱滚子轴承次表面裂纹扩展的影响

为探究次表面裂纹倾斜角度对圆柱滚子轴承应力分布及裂纹扩展的影响,文章基于断裂力学、损伤力学等理论基础,应用扩展有限元法建立圆柱滚子轴承的有限元模型,模拟滚道次表面不同倾角的初始裂纹在外力载荷下的动态扩展过程,分析讨论次表面裂纹尖端的应力随裂纹倾角的变化情况以及裂纹尖端的应力对裂纹扩展的影响。模拟结果表明:在圆柱滚子压力载荷作用下,初始倾角在0°~30.0°范围内的次表面裂纹扩展主要受水平方向应力S 11的影响,次表面水平裂纹两端处的扩展同步对称进行;随着初始次表面裂纹逆时针旋转后倾角的增加,裂纹扩展速率增大,裂纹左端扩展长度增长,且增幅均由快到慢并趋于稳定状态,裂纹左端扩展角度增大,裂纹右端的扩展受到抑制。次表面裂纹的扩展速率、扩展长度、扩展角度比较结果表明,水平或较小角度的次表面裂纹扩展对损伤轴承寿命的影响较小。