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.

Analytical and Experimental Study of Free Vibration of Beams Carrying Multiple Masses and Springs

The structures in engineering can be simplified into elastic beams with concentrated masses and elastic spring supports. Studying the law of vibration of the beams can be a help in guiding its design and avoiding resonance. Based on the Laplace transform method, the mode shape functions and the frequency equations of the beams in the typical boundary conditions are derived. A cantilever beam with a lumped mass and a spring is selected to obtain its natural frequencies and mode shape functions. An experiment was conducted in order to get the modal parameters of the beam based on the NExT-ERA method. By comparing the analytical and experimental results, the effects of the locations of the mass and spring on the modal parameter are discussed. The variation of the natural frequencies was obtained with the changing stiffness coefficient and mass coefficient, respectively. The findings provide a reference for the vibration analysis methods and the lumped parameters layout design of elastic beams used in engineering.

Ambient Vibration Testings and Field Investigations of Two Historical Buildings in Europe

In this study,the methodology and results of ambient vibration-based investigations of the historical Tash Mosque in Kosovo and a 3-story historical building in Bulgaria are presented.The investi gations include full-scale in situ testing of both structures due to ambient vibrations induced by micro-seismic,wind,traffic,and other human activities.To this aim,Ranger seismometers and Kinemetric products were used.Measurements were performed in both horizontal directions in several points along the structures'height utilizing a high-speed data acquisition device.All recorded data have been analyzed and processed by the software developed at IZIIS,and then the processed data were used as input for modal analysis.The basic assumption is that the excitation can be considered as a stationary random process to have a relatively flat spectrum.The paper clearly describes the procedure used for investigations and presents the dynamic properties of the whole structures.The inv estigated structures are both historical buildings and defined as architectural heritage and the outcome of this study including the natural vibration frequencies and mode shapes)can be very benefi-cial for the verification stage of the analytical/numerical models for future retro-fiting/rehabilitation schemes.

Aerodynamic Performance and Vibration Analyses of Small Scale Horizontal Axis Wind Turbine with Various Number of Blades

The need to generate power from renewable sources to reduce demand for fossil fuels and the damage of their resulting carbon dioxide emissions is now well understood. Wind is among the most popular and fastest growing sources of alternative energy in the world. It is an inexhaustible, indigenous resource, pollution-free, and available almost any time of the day, especially in coastal regions. As a sustainable energy resource, electrical power generation from the wind is increasingly important in national and international energy policy in response to climate change. Experts predict that, with proper development, wind energy can meet up to 20% of US needs. Horizontal Axis Wind Turbines (HAWTs) are the most popular because of their higher efficiency. The aerodynamic characteristics and vibration of small scale HAWT with various numbers of blade designs have been investigated in this numerical study in order to improve its performance. SolidWorks was used for designing Computer Aided Design (CAD) models, and ANSYS software was used to study the dynamic flow around the turbine. Two, three, and five bladed HAWTs of 87 cm rotor diameter were designed. A HAWT tower of 100 cm long and 6 cm diameter was considered during this study while a shaft of 10.02 cm diameter was chosen. A good choice of airfoils and angle of attack is a key in the designing of a blade of rough surface and maintaining the maximum lift to drag ratio. The S818, S825 and S826 airfoils were used from the root to the tip and 4° critical angle of attack was considered. In this paper, a more appropriate numerical models and an improved method have been adopted in comparable with other models and methods in the literature. The wind flow around the whole wind turbine and static behavior of the HAWT rotor was solved using Moving Reference Frame (MRF) solver. The HAWT rotor results were used to initialize the Sliding Mesh Models (SMM) solver and study the dynamic behavior of HAWT rotor. The pressure and velocity contours on different blades surfaces were analyzed and presented in this work. The pressure and velocity contours around the entire turbine models were also analyzed. The power coefficient was calculated using the Tip Speed Ratio (TSR) and the moment coefficient and the results were compared to the theoretical and other research. The results show that the increase of number of blades from two to three increases the efficiency;however, the power coefficient remains relatively the same or sometimes decreases for five bladed turbine models. HAWT rotors and shaft vibrations were analyzed for two different materials using an applied pressure load imported from ANSYS fluent environment. It has proven that a good choice of material is crucial during the design process.

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。

储液-桩基LNG储罐地震离心模型试验设计方法

LNG储罐作为国家重要的战略能源储备工程,正快速向超高容量、超大直径、半地下化趋势发展,并对抗震安全性要求极高。针对离心模型试验规格尺寸限制,提出一种以储罐自振周期、晃动周期和抗弯刚度为主要控制参数的LNG储罐试验设计方法,并以原型为27万m3的大型储罐开展了相应动力离心试验,验证了设计方法的合理性并分析了其地震响应。结果表明:试验得到的自振周期与规范计算值较为接近,误差为5.6%,验证了该试验设计方法的可靠性;储液晃动频率与荷载幅值变化关系不大,主要与储罐形状、液面高度有关,储液晃动波高与荷载幅值呈现明显正相关;桩基础可以提升LNG储罐的安全性,相同荷载激励下,有桩储罐比无桩储罐晃动波高减小约8.2%。

基于高阶剪切变形理论的功能梯度板自由振动分析简化模型

基于高阶剪切变形理论提出了一种功能梯度板自由振动分析的简化模型,该简化模型最显著的特点是适用于功能梯度板的振动分析,且不需要剪切修正。相比于其他具有更多未知变量的剪切变形理论,本文提出的简化模型只包含一个控制方程,极大地减少了计算量。基于该简化模型研究了功能梯度矩形板在简支边界条件下的自由振动,并与其他已有文献进行了比较。结果表明,本文提出的简化模型在分析功能梯度板的自由振动行为时简单且精确。此外,文中还通过多个数值算例分析讨论了不同的梯度指数、长宽比和边厚比对功能梯度板自由振动行为的影响。

基于锚杆系统横向振动频率响应特征的轴力检测方法

基于锚杆系统自由段横向振动特性的检测方法可实现对锚杆的大范围快速有效检测。为提升锚杆轴力检测精度,建立锚杆系统横向振动力学模型,测试了全尺寸锚杆系统轴向加载过程中的频率响应。结果表明:锚杆系统横向振动固有频率对转动刚度及锚杆自由段长度比较敏感;通过试验校准理论模型的转动刚度,所得理论预计轴力与试验结果的吻合度较好,频率阶次越低,轴力检测误差越小;轴力较低时,基频轴力检测的平均相对误差为5.8%,轴力较高时,平均相对误差仅为0.6%;当锚杆杆体进入塑性或界面脱粘滑移后,锚杆自由段长度变化较大,通过实时修正锚杆自由段长度,可实现锚杆系统损伤阶段的轴力检测,基频轴力检测的平均相对误差在4.1%以内。锚杆轴力的快速、无损检测方法对于支护系统及围岩稳定性评估具有重要意义。

新型无井道双立柱电梯纵向振动特性分析

针对传统的曳引式电梯占用空间大、土建要求高、对一楼用户遮挡光线多、费用高等缺点,提出一种新型无井道双立柱电梯结构。为确保该新型电梯运行的安全性及舒适性,考虑双立柱的刚度及曳引绳刚度具有时变特性,建立该电梯的纵向振动模型。根据牛顿第二定律,建立多自由度运动微分方程。求解微分方程组得出系统的固有频率和谐波响应,探讨了该电梯在不同承载质量、轿厢处于不同位置时各阶固有频率的变化规律及振动响应幅值随激振频率的变化规律。研究结果表明,该模型能很好地预测电梯在谐波激励下的动力学特性,为电梯的动态特性优化、减振降噪、故障诊断等提供了依据。

某型航空导叶作动筒振动性能仿真分析

针对航空导叶作动筒在复杂工况下的损坏问题,为在设计阶段预测产品可能出现的损坏,获取导叶作动筒标准载荷下的易损位置,利用有限元仿真建模方法建立了该型作动筒的模态分析、谐响应分析、随机振动分析与疲劳分析仿真模型。通过对数正弦扫频试验验证了模态分析仿真模型的准确性,获得了振型、固有频率与功率谱载荷下的应力响应等信息。考虑作动筒活塞的轴向伺服工作影响,在标准功率谱上叠加伺服工作正弦载荷模拟了该工况。建立随机振动情况下的疲劳寿命分析仿真模型,活塞与活塞密封圈的疲劳寿命结果在可接受范围内,为该航空作动筒结构优化设计提供了依据。

某振动夹具参数优化设计方法研究

为了提升航空发动机燃油控制系统附件产品振动夹具正向设计与优化能力,以某液压机械装置产品振动夹具为研究对象,通过对该振动夹具进行参数化建模,以振动夹具结构尺寸参数为设计变量,振动台尺寸约束和夹具重量指标要求为约束条件,利用多目标遗传算法等多目标优化设计,在兼顾振动夹具重量指标及一阶固有频率最大化目标前提下,使得优化后振动夹具一阶固有频率提高了22.5%,夹具重量减小了11.2%,提升了振动夹具的性能。优化验证与对比证明了设计方法的可行性及有效性。该方法可以推广应用到后续产品振动夹具优化设计中,从而提升振动夹具的振动传递特性品质,为保证振动试验考核结果的准确性奠定基础。

Vibration of composite beams with two overlapping delaminations

Delaminations in composite laminates may de-velop from small cracks due to fabrication and impact load-ing,or from places of high stress concentration.The locationsof the delaminations are not determinate.In this research,ananalytical solution for the free vibration of a composite beamwith two overlapping delaminations is presented.The dela-minated beam is analyzed as seven interconnected beamsusing the delaminations as their boundaries.The continuityand equilibrium conditions are satisfied between the adjoin-ing regions of the beams.Classical beam theory is applied toeach of the beams.Complex vibration behaviors emerge fordifferent sizes and locations of the delaminations.Compar-ison with analytical results reported in the literature verifiesthe validity of the present solution.

Natural Characteristic of Thin-Wall Pipe under Uniformly Distributed Pressure

Natural characteristics of thin?wall pipe of the compressor under uniformly distributed pressure were presented in this paper based on a cylindrical shell model. In the traditional method, the beam model was usually used to analyze the pipe system. In actual fact, the pipe segment of the compressor was always broken in the form of a long crack or a partial hole and the phenomenon was hardly explained by beam model. According to the structure characteristic of compressor pipe segment, whose radius is large and thickness is little, shell model shows the advantage in this kind of pipe problem. Based on Sanders’ shell theory, the vibration di erential equation of pipe was established by apply?ing the energy method. The influences of length to radius ratio(L/R), thickness to radius ratio(h/R), circumferential wave number(n) and pressure(q) on the natural frequencies of pipe were analyzed. The study shows: Pressure and structural parameters have a great e ect on the natural characteristics of the pipe. Natural frequency increases as the pressure increases, especially for the higher mode. The sensitivity of natural frequency on pressure becomes stronger with h/R ratio increases; when L/R ratio is greater than a certain critical value, the influence of the pressure on natural frequency will no longer be obvious. The value of n corresponding to the minimum natural frequency also depends on the value of pressure. In the end, analysis of the forced vibration of a specific pipeline model was given and the modal shapes were illustrated to understand the break of the pipe. The research here will provide the theory support for the dynamic design of related pressure pipe and further experiment study should be employed.

Finite Element Model Updating for Structural Health Monitoring

This paper provides a model updating approach to detect,locate,and char-acterize damage in structural and mechanical systems by examining changes in mea-sured vibration responses.Research in vibration-based damage identification has been rapidly expanding over the last few decades.The basic idea behind this technology is that modal parameters(notably frequencies,mode shapes,and modal damping)are functions of the physical properties of the structure(mass,damping,and sifies).Therefore,changes in the physical properties will cause changes in the modal proper-ties which could be obtained by structural health monitoring(SHM).Updating is a process fraught with numerical difficulties.These arise from inaccuracy in the model and imprecision and lack of information in the measurements,mainly taken place in joints and critical points.The motivation for the development of this technology is.presented,methods are categorized according to various criteria such as the level of damage detection provided from vibration testing,natural frequency and mode shape readings are then obtained by using modal analysis techniques,which are used for updating structural parameters of the associated finite element model The experi-mental studies for the laboratory tested bridge model show that the proposed model.updating using ME scope technique can provide reasonable model updating results.

Free Vibration Analysis of Functionally Graded Beams with General Elastically End Constraints by DTM

The differential transformation method (DTM) is applied to investigate free vibration of functionally graded beams supported by arbitrary boundary conditions, including various types of elastically end constraints. The material properties of functionally graded beams are assumed to obey the power law distribution. The main advantages of this method are known for its excellence in high accuracy with small computational expensiveness. The DTM also provides all natural frequencies and mode shapes without any frequency missing. Fundamental frequencies as well as their higher frequencies and mode shapes are presented. The significant aspects such as boundary conditions, values of translational and rotational spring constants and the material volume fraction index on the natural frequencies and mode shapes are discussed. For elastically end constraints, some available results of special cases for isotropic beams are used to validate the present results. The new frequency results and mode shapes of functionally graded beams resting on elastically end constraints are presented.

COUPLED VIBRATION OF STRUCTURAL THIN-WALLED CORES

This paper presents an analysis of the coupled vibration of asymmetric core structures in tall buildings. The governing equation of free vibration and its corresponding eigenvalue problem, which is a set of equations for laterally flexural vibrations in two different directions coupled by a warping-St. Venant torsional vibration, are derived. Based on the Calerkin method, a generalized approximate method is developed for the analysis of coupled vibration and thus proposed for determining the natural frequencies and mode shapes of the structure in triply-coupled vibration. The results of the proposed method for the example structure show good agreement with those of the FEM analysis. The proposed method has been shown to provide a simple and rapid, yet accurate, means for coupled vibration analysis of core structures.

Damage Detection in Reinforced Concrete Berthing Jetty Using a Plasticity Model Approach

A conventional method of damage modeling by a reduction in stiffness is insufficient to model the complex non-linear damage characteristics of concrete material accurately.In this research,the concrete damage plasticity constitutive model is used to develop the numerical model of a deck beam on a berthing jetty in the Abaqus finite element package.The model constitutes a solid section of 3D hexahedral brick elements for concrete material embedded with 2D quadrilateral surface elements as reinforcements.The model was validated against experimental results of a beam of comparable dimensions in a cited literature.The validated beam model is then used in a three-point load test configuration to demonstrate its applicability for preliminary numerical evaluation of damage detection strategy in marine concrete structural health monitoring.The natural frequency was identified to detect the presence of damage and mode shape curvature was found sensitive to the location of damage.

Detecting Damage in Reinforced Concrete Beams Using Vibrational Characteristics

This paper evaluates two methods of diagnosing damage, Natural frequency and Stiffness-Frequency change-Based damage detection method in reinforced concrete beams under load using vibration characteristics such as natural frequency and mode shape. The research uses finite element method with crack damage instead of deleting or reducing the bearing capacity of the element like in previous studies. First, a theory of the damage diagnosis method based on the change of natural frequency and mode shape is presented. Next, the simulation results of reinforced concrete beams using ANSYS will be compared with the experiment. Particularly, the investigated damage cases are cracks in reinforced concrete beams under loads. Finally, we will evaluate the accuracy of the damage diagnosis methods and suggest the location of the vibration data and specify the failure threshold of the methods.

基于损伤模态识别法的复杂采空区群中薄弱单元甄别

为甄别复杂采空区群中的薄弱单元,以某地下石灰石矿山采空区群为工程实例,通过构建离散振动力学模型,和应变改变量相关影响因素分析,创新地提出薄弱单元损伤模态识别法,给出甄别流程,并从算例计算和工程实际应用两方面验证其可靠性。研究结果表明:自振频率和应变模态的甄别指标能准确识别采空区群中的薄弱单元;单体和双体单元损伤都会使采空区群的自振频率甄别指标I_(M)(k)值大于0,损伤区域的应变模态甄别指标I_(N)(x)值会明显出现凸起,随着损伤程度增大,I_(M)(k)值和I_(N)(x)峰值越来越大;仅顶板B1损伤时,高阶I_(M)(k)比低阶更灵敏反映损伤变化程度,第四阶指标识别效果更优;仅矿柱Z6损伤时,第二、四阶I_(M)(k)识别效果更优;B1和Z6共同损伤时,I_(M)(k)对B1损伤程度变化较于Z6更为敏感,第二阶I_(M)(k)识别效果更佳。研究成果为地下采空区群安全定量评估开辟了一条新方向。

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。