Determination of Natural Frequencies of Multilayered Plates by Mixed Finite Elements

Natural frequencies for multilayer plates are calculated by mixed finite element method. The main object of this paper is to use the mixed model for multilayer plates, analyzing each layer as an isolated plate, where the continuity of displacements is achieved by Lagrange multipliers （representing static variables）. This procedure allows us to work with any model for single plate （so as to ensure the proper behavior of each layer）, and the complexity of the multilayer system is avoided by ensuring the condition of displacements by the Lagrange multipliers （static variables）. The plate is discretized by finite element modeling based on a primary hybrid model, where the domain is divided by quadrilateral, both for the displacement field and static variables. This mixed element for plates was implemented and several examples of vibrations have been verified successfully by the results obtained by other methods in the literature.

Structural finite element model updating using incomplete ambient vibration modal data

This paper presents an effective approach for updating finite element dynamic model from incomplete modal data identified from ambient vibration measurements.The proposed method is based on the relationship between the perturbation of structural parameters such as stiffness and mass changes and the modal data measurements of the tested structure such as measured mode shape readings.Structural updating parameters including both stiffness and mass parameters are employed to represent the differences in structural parameters between the finite element model and the associated tested structure.These updating parameters are then evaluated by an iterative solution procedure,giving optimised solutions in the least squares sense without requiring an optimisation technique.In order to reduce the influence of modal measurement uncertainty,the truncated singular value decomposition regularization method incorporating the quasi-optimality criterion is employed to produce reliable solutions for the structural updating parameters.Finally,the numerical investigations of a space frame structure and the practical applications to the Canton Tower benchmark problem demonstrate that the proposed method can correctly update the given finite element model using the incomplete modal data identified from the recorded ambient vibration measurements.

Investigation of Microstructure, Natural Frequencies and Vibration Modes of Dragonfly Wing

In the present work, a thorough investigation on the microstructural and morphological aspects of dragonfly wings was carried out using scanning electron microscope. Then, based on this study and the previous reports, a precise three-dimensional numerical model was developed and natural frequencies and vibration modes of dragonfly forewing were determined by finite element method. The results shown that dragonfly wings are made of a series of adaptive materials, which form a very complex composite structure. This bio-composite fabrication has some unique features and potential benefits. Furthermore, the numerical results show that the first natural frequency of dragonfly wings is about 168 Hz and bending is the predominant deformation mode in this stage. The accuracy of the present analysis is verified by comparison of calculated results with experimental data. This paper may be helpful for micro aerial vehicle design concerning dynamic response.

Algorithm for solving problems related to the natural vibrations of electro-viscoelastic structures with shunt circuits using ANSYS data

An algorithm for numerical realisation of a mathematical statement of the natural vibrations problem for electro-viscoelastic bodies with passive external electric circuits(i.e.shunting circuits)with an arbitrary configuration using the finite element method is proposed in the present paper.The proposed algorithm allows considering the viscoelastic properties of materials using the model of linear hereditary viscoelasticity with complex dynamic moduli and is used to solve 3D solid structure problems that are compatible for ANSYS package element types.This technique implies the usage of the global assembled matrices of stiffness and mass,formed in the ANSYS package.The basis of the algorithm is a novel approach that allows performing decomposition of the global assembled stiffness matrix formed in the ANSYS software package into constituents that are needed for calculation of the natural vibration frequencies of the objects under study.These matrix components are used in the program that was written in FORTRAN(Formula Translation)language.This problem could be efficiently applied for analysis of the dynamic processes in smart systems based on piezoelectric materials and could also form a basis for the development of numerical finite element algorithms for optimization of the dissipative characteristics of electromechanical systems with shunted piezoelectric elements.

管路结构参数对液压管路振动特性的影响研究

为探究液压管路的结构参数对其振动特性的影响,建立了不同几何结构参数液压管路有限元模型,基于流固耦合研究了不同结构材料、不同弯曲半径以及不同弯曲内角对液压管路振动特性的影响。研究发现,在液压管路结构一定情况下,钛合金Ti-3Al-2.5V的固有频率最小,不锈钢1Cr18Ni9Ti的变形量最小;在固定液压管路总长的情况下,弯曲半径的增加会提升固有频率并会降低变形量,弯曲内角的增加会减小固有频率但会降低变形量;在固定直管段长度的情况下,弯曲半径的增加会导致固有频率减小并导致变形量增加,弯曲内角的增加会导致固有频率减小但会降低变形量。

基于施工全过程健康监测的装配式部分包覆钢-混凝土组合结构体系动力特性研究

为研究装配式部分包覆钢-混凝土组合结构的动力特性,基于世博文化公园双子山项目,采用全过程健康监测手段对装配式PEC结构体系施工全过程的应力、加速度进行监测,研究其阻尼比和自振频率在施工过程中的变化情况,将实测结果与有限元计算结果进行对比。结果表明:结构应力计算值、自振频率计算值等均与实测值吻合较好,验证了结构施工全过程仿真模拟计算的合理性。施工过程中PEC框架梁柱及节点后浇区的型钢及混凝土应力实际监测结果均满足强度要求。节点后浇区混凝土浇筑前后,结构自振周期和阻尼比差别较小;结构顶部覆土恒载施加完成后,结构的自振周期和阻尼比均较之前有所增大。结构设计时阻尼比取0.04,小于施工完成后的阻尼比实测值最小值0.046,阻尼比取值偏于安全,设计阻尼比取值合理。

地震下拉索损伤对矮塔斜拉桥索力的影响

为研究拉索损伤和地震双重作用下矮塔斜拉桥索力变化规律,以某矮塔斜拉桥为工程背景,采用Midas Civil软件建立有限元梁格模型,研究不同数量、不同位置拉索损伤对桥梁动力特性的影响,并深入分析地震和拉索损伤双重作用时拉索索力的变化规律。结果表明:边跨外侧及中跨索塔中部的拉索损伤对结构的自振频率影响较大,随着拉索损伤程度的增大,结构的自振频率变化率也在不断增大,且二者之间基本呈线性变化;地震下单索断裂会对矮塔斜拉桥剩余拉索索力产生规律性的影响,索力变化率的最大值一般出现在与断索相邻的拉索中,且距离断索越远,索力变化率越小,但索力变化率基本保持在10%以内;在拉索损伤程度不断增大的过程中,存在一个极值,使得剩余拉索的索力变化率在该极值两侧随拉索损伤程度的变化而基本呈线性变化。

一种航空发动机转子叶片振动特性及疲劳试验方法

对一种航空发动机转子叶片开展振动特性和疲劳试验方法研究,通过理论计算和试验验证获得叶片前3阶弯曲振动频率,并在1阶弯曲振动模态下获取叶片所受应力与叶片自振频率、振幅之间的关系。结果表明:该结构的理论、实测振动特性一致,试验件振动应力与振幅之间服从线性变化规律,表明提出的试验方法有效,可为该转子叶片的研制提供疲劳性能数据支撑。

独塔斜拉-自锚式协作体系悬索桥合理约束体系研究

为研究独塔斜拉-自锚式协作体系悬索桥合理约束体系,以主跨2×350 m的济南绕城高速二环线北环段工程黄河特大桥主桥为背景,采用BNLAS软件建立主桥空间有限元模型,对比不同纵向、竖向约束体系方案下结构的荷载响应、自振特性,分析不同塔梁约束体系对独塔斜拉-自锚式协作体系悬索桥静、动力性能的影响。结果表明:塔梁处竖向双排支座有效约束了塔梁之间的相对转动自由度,使塔梁协调受力,相较于传统的全飘浮体系和竖向单排支座体系,竖向双排支座体系提供了更大的整体结构刚度;设置纵向约束能显著增强独塔斜拉-自锚式协作体系悬索桥结构纵向刚度,建议在纵向上设置固定约束;相较于传统塔梁墩固结体系,竖向双排支座体系对主梁提供了更强的转动约束,且塔梁间约束在构造上处理简单。该桥桥塔处设置竖向双排支座并设置纵向固定限位装置。

基于ANSYS的甜玉米果穗圆锯片静力学和模态分析

目的:为确保圆锯片切割甜玉米果穗头时不发生共振,保证切割精度和安全性,对圆锯片进行设计和分析。方法:使用SolidWorks软件建立圆锯片的简化三维模型,利用ANSYS有限元分析软件对圆锯片进行静力学和模态分析。结果:通过静力学分析可知,圆锯片的最大等效应变为200 T/3000 r/min的6.3831×10^(-5)mm/mm,最大等效应力为200 T/3000 r/min的1.2665×10^(7)MPa,等效应变和等效应力均集中于圆锯片中心部连接处;通过模态分析可知,200 T/3000 r/min的前六阶固有频率变化范围为435.26~1345.70 Hz,该圆锯片的最大工作频率远低于其一阶模态,圆锯片不会发生共振,满足工作需求。结论:齿数和转速为200 T/3000 r/min的圆锯片高速旋转切割甜玉米果穗头时具备安全性与可靠性,为后续圆锯片结构优化设计提供了理论依据。

高墩大跨度连续刚构桥的动力力学特性分析思考

连续刚构桥是预应力混凝土连续梁桥中一种特殊结构型式,即是一种桥墩主墩与上部结构主梁固结的预应力混凝土连续梁桥。连续刚构桥多用于山区环境中,充分利用其跨径大、桥墩高的优点,完成对河谷、峡沟的跨越。其中,连续刚构桥的桥墩高度较大、桥墩柔性较强,且河谷、峡沟处风力往往较大,对连续刚构桥梁的动力影响较为突出。因此,连续刚构桥的动力研究分析,是连续刚构桥研究中的一个重难点。本论文为了研究高墩大跨连续刚构桥动力特性的影响,以国内某大桥为工程背景,利用有限元软件Midas Civil 2023建立主桥三维模型,从桥梁自震频率、地震反应谱、车桥耦合动力、桥墩高度、动力特性优化等方面分析该桥梁的动力特性。结果表明:○1主桥的自振频率与墩梁刚度比的变化呈正相关关系,变化速率呈先大后小的趋势;○2主桥的1阶纵向频率受主墩高度变化影响也很大,变化幅度大于50%。本论文研究结论可为高墩大跨连续刚构桥的动力分析设计提供参考和指导。

Experimental and Numerical Investigations on Vibration Characteristics of a Loaded Ship Model

In this paper, the vibration characteristics of the structure in the finite fluid domain are analyzed using a coupled finite element method. The added mass matrix is calculated with finite element method （FEM） by 8-node acoustic fluid elements. The vibration characteristics of the structure in the finite fluid domain are calculated combining structure FEM mass matrix. By writing relevant programs, the numerical analysis on vibration characteristics of a submerged cantilever rectangular plate in finite fluid domain and loaded ship model is performed. A modal identification experiment for the loaded ship model in air and in water is conducted and the experiment results verify the reliability of the numerical analysis. The numerical method can be used for further research on vibration characteristics and acoustic radiation problems of the structure in the finite fluid domain.

Analysis of the Behavior of a Square Plate in Free Vibration by FEM in Ansys

In the realization of mechanical structures, achieving stability and balance is a problem commonly encountered by engineers in the field of civil engineering, mechanics, aeronautics, biomechanics and many others. The study of plate behavior is a very sensitive subject because it is part of the structural elements. The study of the dynamic behavior of free vibration structures is done by modal analysis in order to calculate natural frequencies and modal deformations. In this paper, we present the modal analysis of a thin rectangular plate simply supported. The analytical solution of the differential equation is obtained by applying the method of separating the variables. We are talking about the exact solution of the problem to the limit values. However, numerical methods such as the finite element method allow us to approximate these functions with greater accuracy. It is one of the most powerful computational methods for predicting dynamic response in a complex structure subject to arbitrary boundary conditions. The results obtained by MEF through Ansys 15.0 are then compared with those obtained by the analytical method.

激光追踪测量系统机械结构模态参数影响

为了避免激光追踪测量系统机械结构在工作状态与电机产生共振现象,保证激光追踪测量系统的测量精度,本文提出了一种分析激光追踪测量系统机械结构模态参数影响的方法。基于两自由度的激光追踪测量系统机械结构,根据有限元法的模态分析理论,分析了结构材料密度、弹性模量和不同材料对系统固有频率的影响。研究结果表明:系统的固有频率随着结构密度的增大而增大,随着结构刚度的增大而减小,不同材料的影响差异较大;采用粘贴的固定方式可以增加系统的稳定性,有效保障系统的测量精度。本文的研究为激光追踪测量机械结构系统的振动特性分析、振动故障诊断和预报,以及结构动力特性的优化设计提供了依据。

特高压输电线路塔线体系风振响应特性及对登塔人员影响分析

登塔是输电线路施工、巡视和检修的重要技术手段,而特高压输电线路截面大且为高耸的塔线耦合的弱阻尼系统,其风致振动特性及其对登塔作业人员的影响对确保作业和人员安全具有重要意义。针对±800 kV直流输电线路建立了输电线路塔线耦合体系有限元模型,基于风速随高度变化的Kaimal谱和谐波叠加法生成了2 m高风速分别为6、8、10 m/s的风速时程,应用模拟的风荷载对三塔两线体系在A、B两种地形下的风振响应进行了时域分析,并讨论了铁塔振动对登塔作业人员的影响。结果表明:在2 m高风速为6 m/s时,A、B塔线体系整体风速都没有超过10 m/s,铁塔各部位风致振动的位移较小,典型作业位置处作业人员基本没有不舒适感;在2 m高风速为10 m/s时,铁塔横担以及地线支架处位移较大,作业人员的登塔作业人员感到极不舒适,存在高空坠落风险。建议登塔作业人员测量风速时将地面测量的风速修正到作业位置高度处,修正值小于10 m/s再进行登塔作业。

增材制造BCCZ点阵夹芯梁结构的自由振动分析

通过理论、有限元和试验方法研究了悬臂边界条件下BCCZ(体心立方点阵边界添加Z向杆件增强构型)点阵夹芯梁结构的振动行为。基于哈密顿原理和“改进折线”法,获得其振动频率理论模型。并使用SLM(选择性激光熔融)技术和钛合金TC4材料制备了BCCZ点阵夹芯梁试件,进行了模态试验,有限元和试验验证了理论模型的准确性。然后研究了胞元直径、面板厚度和芯子高度等结构几何参数和材料性能对BCCZ点阵结构振动性能的影响规律。结果表明:减小胞元直径,减小面板厚度,提高芯子高度均可以提高BCCZ点阵夹芯梁结构的一阶固有频率参数(一阶固有频率与同质量同面板面积的实体结构之比),胞元直径的影响最明显。面板-芯子-面板材料组合为钛-铝-钛时一阶固有频率最高。研究结果对BCCZ点阵夹芯结构的设计及工程应用具有一定的指导意义。

基于ANSYS的弧形钢闸门自振特性分析

以某工程弧形钢闸门为例,通过ANSYS软件构建弧形钢闸门有限元模型,并进行闸门闭门和刚刚提升两种状态时前10阶的自振特性分析。结果表明:闸门结构各阶振动频率的振型表现有明显不同,闭门状态时闸门结构和水流脉动频率发生共振的可能性较小,刚刚提升状态时发生共振的可能性增大;随着阶数的增加,闸门自振频率也逐渐增大,应采取必要的工程措施,减少闸门结构和水流脉动频率发生共振的可能性。

基于Ansys的高压输电塔风振特性分析

在电力大范围应用的背景下,研究输电线路的振动特性对电网整体的安全性有着极其重要的意义。文中推导了三线两塔耦合系统的力学简化模型,利用Ansys软件建立了典型的500 kV交流双回路耐张塔模型,在此基础上利用Davenport风速谱对电力塔模型节点的风载荷进行了模拟,阐明了分析的有效性。利用理论方法和有限元方法分别计算了塔-线耦合体系的动力特性,结果表明理论计算与有限元结果保持一致,证明了理论的有效性。此外通过有限元的分析还能看出耦合系统出现了一部分由塔或线诱发的新振型,且同阶下耦合的振动频率要小于单塔的振动频率。

星载光电跟瞄转台动态特性分析

针对目前利用有限元方法分析星载光电跟瞄转台动态特性时存在的建模失真问题,提出使用广义弹簧单元对轴承和锁紧机构等效建模,并通过定义模态阻尼比,精确模拟转台的固有频率及响应特性。通过理论计算和基于模态试验数据的参数辨识,确定各等效单元刚度;通过基于扫频试验数据的参数辨识,确定结构模态阻尼。基于建立的等效有限元模型进行仿真分析,模态分析中前6阶固有频率与试验结果的最大偏差为5.1%,谐响应分析中X、Y、Z三个主方向的最大响应与试验结果的最大偏差为3.2%,固有频率与响应一致性良好,均在允许的误差范围内。说明使用广义弹簧单元对轴承和锁紧机构进行等效建模,通过模态和扫频试验数据确定转台刚度和阻尼特性是可行的,对同类型转台的建模仿真有一定借鉴作用。

孔跨布置对大跨度铁路悬索桥刚度的影响研究

为探究孔跨布置对大跨度铁路悬索桥刚度的影响规律,以某主跨1092 m的公铁两用悬索桥主桥为背景,采用MIDAS Civil软件建立不同数量边跨(0~4边跨)的悬索桥有限元模型,对5种模型的主跨竖向刚度、跨中横向位移及梁端变位等指标进行对比分析。结果表明:孔跨布置对大跨度铁路悬索桥的主跨竖向刚度、跨中横向位移、梁端竖向转角、梁端横向折角、梁端横向位移、梁端纵向位移和桥梁自振特性有较显著的影响,但随着边跨数量的增加,影响逐渐趋于收敛;孔跨布置对主缆重力刚度影响较小。大跨度铁路悬索桥无边跨时,桥梁的梁端竖向转角、横向折角和纵向位移均明显增大,设计时应慎重选用;单边跨时,桥梁的梁端横向位移较大(横向限位支座约束时,对应的横向反力较大),需采取相应措施;地形条件允许时,建议增加边跨数量,同时加强梁端位移荷载组合方法、长效控制措施和高性能梁端伸缩装置的研究。