利用结构动态特性修改及灵敏度分析减小机体振动

利用机体试验模态分析结果建立了用于机体结构动态特性分析的有限元模型，分析了机体振动模态及结构刚度的分布变化规律，将矩阵摄动理论及灵敏度分析方法应用于机体动态特性的修改之中，确定影响机体各阶动态特性的结构参数及其位置，优化结构动态特性，使得针对某一频率的减振降噪成为可能，文中对机体结构动态设计的几个主要步骤进行了探讨。     

内燃机机体模态分析及辐射噪声的预测

利用有限元技术，建立了内燃机机体模态分析及辐射噪声计算模型，并经过理论计算得到了机体的模态参数及表面噪声分布图。而且对机体进行了试验模态分析及表面声强测试。对比理论分析值与实测值表明，两较一致，说明核计算方法符合实际，可用作低噪声机体设计。     

由机体结构设计减小表面振动响应

本文利用所建立的机体动态分析有限元模型，分析计算了机体的动态特性，并得到了试验的验证。通过改变机体表面局部刚度，对减小机体表面振动响应的几种方法进行了探讨。阐述了曲面机体结构对振动响应的影响，为设计低噪声机体提供了设计方法和参考依据。     

基于实测数据的电缆桥架有限元模型修正

对电缆桥架有限元模型中螺栓连接的复杂结构进行了简化处理,基于实测数据对电缆桥架有限元模型进行了修正。应用ANSYS有限元分析软件对电缆桥架结构进行模态分析,提取了X、Y向整体振型的第1阶模态频率。为验证模型,设计了白噪声激励试验,利用随机子空间法进行模态识别,得到结构的实测频率。采用虚拟材料弹性模量对螺栓参数进行修正。修正前有限元模型模态频率与实测频率的相对误差X向为1.3%、Y向为26.7%,修正后有限元模型模态频率与实测频率的相对误差X向为0.04%、Y向为2.2%。采用修正后的电缆桥架模型进时程分析,并对模拟结果与实测结果进行了比较,结果表明修正后的有限元模型模拟结果与实测结果吻合较好,能更真实地反映结构动力特征。     

柴油机机体模态分析与试验验证

建立某直列四缸柴油机机体三维模型,对其进行自由模态有限元分析,并提取前5阶机体的固有频率及对应的振型,分析机体各频率范围内的振动规律和抗振薄弱区。为了验证有限元分析模型的准确性,对机体进行自由悬挂试验模态分析。对比结果表明,计算和试验的低阶振型基本一致,固有频率最大相对误差为6.3%,说明有限元模型具有较高的精度,可以作为后续优化和动力学分析之用。     

A Finite Element based State Model of Solid Rotor Synchronous Machines

In this work, a state model which portrays the dynamic electromagnetic characteristics of a synchronous machine is derived based upon the first order finite element method. The method of finite elements is used to determine the axial component of magnetic vector potential throughout the cross section of the machine. Algebraic relationships between the winding voltages and the magnetic vector potentials are derived. These are used to establish a state model which admits winding voltages as inputs. The resulting model consists of a set of first order, ordinary differential equations which predict vector potentials at grid nodes along with the winding currents as time proceeds following arbitrary disturbances in stator or rotor voltages. As an initial verification step, this method has been applied in two linear examples. The first involves a simplified geometric representation of the synchronous machine for which an analytical solution of the defining field equations can be obtained. The second involves a more detailed geometry which includes stator and rotor slots. Numerical solutions are shown to be in excellent agreement with analytical solutions for the simplified structure. In the detailed geometry, numerical solutions are shown to compare favorably with the classical equivalent circuit representation.     

大功率柴油机机体三维模态分析

本文采用三维有限元法对柴油机机体进行了模态分析和研究。其中，采用８节点６面体单元构造了较详细的计算模型。并采用频移法来处理总体刚度矩阵的奇异性。文中以一台高速大功率柴油机为例，计算了机体的固有频率和相应的振型。其计算结果与试验值很相吻合。     

低温环境中水工沥青混凝土动态抗压性能研究

为研究低温环境中水工沥青混凝土在地震作用下的动力特性及破坏模式,在不同温度和应变率下对水工沥青混凝土现场芯样进行了动态抗压试验,深入分析了温度和应变率对水工沥青混凝土的破坏形式、应力应变特性、峰值应力及弹性模量等力学性能的影响。结果表明,随着应变率的增加,水工沥青混凝土的破坏模式由微裂纹破坏、拉剪破坏过渡至劈裂破坏,应力应变曲线由应变硬化型向应变软化型转变,抗压强度和弹性模量也随之增大;随着温度的降低,水工沥青混凝土强度和刚度明显增大,具有明显的低温硬化效应。此外,基于试验结果建立了沥青混凝土的动态本构模型,该模型参数较少且与试验结果吻合度较高,具有一定的实用性。     

Evaluation of effective material properties of spiral wound gasket through homogenization

In this paper, a homogenization methodology is proposed to determine the material properties of spiral wound gaskets (SWGs) using finite element analysis through representative volume elements (RVE) of the gaskets. The constituents of this RVE are described by elasto-plastic material properties. The RVE are subjected to six load cases and the volume averaged responses are analyzed simultaneously to predict the anisotropic properties. The mechanical behaviour is simplified to an orthotropic material model with Hill’s plasticity model and the properties are verified with micro-mechanical simulation and experimental results available in the literature. Reasonable agreement is obtained between the results. Formulae for elastic properties are also derived by a simplified analytical method based on lamination theory and compared with those obtained from homogenization.     

柴油机组合结构的参数化建模及应用

应用特征技术和动态子结构法建立了某柴油机机体＋曲轴组合结构的参数化实体模型，并用有限元模态分析法进行模态参数的计算。计算出前五阶固有频率和主振型，与试验结果吻合，说明所建机体＋曲轴组合结构的参数化模型正确，为其下一步的动力学仿真研究奠定了基础。     

A model for the structural dynamic response of the CX‐100 wind turbine blade

A geometrically exact beam model for simulating the structural dynamic response of the CX‐100 wind turbine blade is presented. The underlying geometrically nonlinear theory is detailed, and its implementation into a finite‐element code, NLBeam, developed as part of this research is outlined. The parameters used to represent the varying cross‐sectional distributions of stiffness and mass are calculated consistent with the geometrically exact beam theory by using the variational asymptotic method, as developed by Hodges and Yu et al. through the commercially available code, (VABS) variational asymptotic beam sectional analysis. Code and calculation verification are documented through a systematic grid convergence study applied independently to both the cross‐sectional, and static and dynamic beam simulations. An initial assessment of the model is made by comparing simulation results with experimental test data for three cases: quasistatic loading, linearized modal dynamic behavior and steady‐state oscillating dynamic loads. Simulation results are shown to be in reasonable agreement with experimental data. Future improvements to the model, as well as additional experimental characterization that can benefit such modeling efforts, are outlined. Copyright © 2013 John Wiley & Sons, Ltd.     

Analytical solution of transverse shear strain vibration of gas detonation loaded tube near second critical speed (shear group velocity)

Analytical solution of transverse shear strain vibration of a tube caused by internal gaseous detonation near the second critical speed (shear group velocity) is not reported in the literature. It is performed based on a steady state model and first order shear deformation theories (model I and II) in this paper, and the results are verified through comparison with the finite element results reported in the literature. There are no known experimental ways of directly measuring dynamic transverse shear strain and only theoretical results and numerical data are available. The finite element method is very time consuming compared with the analytical solution. It is shown in this paper that the resonance phenomenon of the transverse shear strain vibration near the second critical speed can be predicted by steady state model and first order shear deformation theories. The first order shear deformation theory (model II) has a good agreement with finite element results in prediction of dynamic amplification factors and critical speeds.     

变刚度气门弹簧三维有限元计算分析

本文以变刚度气门弹簧为研究对象，建立了气门弹簧、弹簧座的三维有限元组合模型。使用有限元分析软件，在考虑各组件接触关系的基础上，对该气门弹簧在不同载荷下进行了三维有限元计算。通过有限元仿真计算，快速地得到了变刚度气门弹簧弹性特性曲线。并依据气门弹簧应力计算结果对该弹簧进行了静强度和疲劳强度校核。     

变刚度气门弹簧三维有限元计算分析

本文以变刚度气门弹簧为研究对象,建立了气门弹簧、弹簧座的三维有限元组合模型。使用有限元分析软件,在考虑各组件接触关系的基础上,对该气门弹簧在不同载荷下进行了三维有限元计算。通过有限元仿真计算,快速地得到了变刚度气门弹簧弹性特性曲线。并依据气门弹簧应力计算结果对该弹簧进行了静强度和疲劳强度校核。     

An analytical method for three-dimensional non-linear responses of prestressed concrete nuclear reactor vessels

This paper describes the results of an investigation to develop an analytical method for assessing the non-linear behaviour and strength of three-dimensional concrete structures such as prestressed concrete nuclear reactor vessels (PCRVs) under monotonically increasing internal pressure. This three-dimensional finite element method uses a proposed material model for the non-linear response of concrete under a multiaxial stress state. Three numerical examples were analysed to investigate the feasibility of the analysis. The first was the calculation of the two-dimensional response of Kupfer's plain concrete. The second involved the analysis of a small-scale axisymmetric PCRV test model with a solid end slab. The third was the analysis of a three-dimensional PCRV test model with penetrations in the end slab. Good agreeement between experimental and analytical results was obtained.     

Characterising the d-axis machine model of a turbogenerator usingfinite elements

An analysis of a long established fundamental assumption is presented. The assumption that superposition is valid in frequency response derived models is shown to be wrong, because eddy current losses in the solid rotor cannot be superimposed in the machine direct-axis. This implies that network theory is not valid in characterising the d-axis machine model. A machine model structure with one damper winding in the d-axis is derived from finite element analysis. Unequal mutual inductances in the machine d-axis are determined and hence the so-called differential leakage inductances are found and they are frequency dependent. The study is made on a 150 MVA turbine generator by simulating the standstill frequency response test with finite elements     

Analytical studies of four-inch pipe whip tests under BWR LOCA conditions

The purpose of pipe rupture studies in JAERI is to perform model tests on pipe whip, restraint behavior, jet impingement and jet thrust force, and to establish a computational method for analyzing these phenomena. This report presents the analytical results of 4-inch pipe whip tests under BWR LOCA conditions.Dynamic response analyses were performed using the general-purpose finite element program ADINA. The test pipe was modelled by straight beam elements and the four restraints were modelled by a single truss element. The analytical results were compared with the experimental results. Impact time and maximum total restraint force showed good agreement with experimental results. On the other hand, pipe strain and pipe deflection could not be predicted so well. The reason for this is that the sliding of the restraint during the pipe whip movement cannot be considered in the analyses.     

Identification of synchronous machine linear parameters fromstandstill step voltage input data

This paper presents the results of a time-domain identification procedure to estimate the linear parameters of a 15 kVA salient-pole synchronous machine at standstill. A step voltage input test is performed, and the parameters of the time constant models and equivalent circuit models are estimated. The maximum likelihood algorithm is used for the estimation, and the best-fit model is selected from a set of increasing order models. The initialization values for the parameters to be estimated are determined from the operational inductances derived directly from the measured time domain data. The simulated equivalent circuit model response is validated against the measured standstill time domain and frequency domain data. In addition, simulation of the model response to an on-line small disturbance test is compared to the measured dynamic response     

TEMPERATURE-DEPENDENT THERMOELASTIC PROPERTIES FOR MACRO FIBER COMPOSITE ACTUATORS

This research effort models the thermoelastic properties of the macro fiber composite actuator as a function of temperature. The required temperature-dependent properties of each constituent material are obtained, and the orthotropic layer properties are calculated using a variety of micromechanics models, with the most accurate being selected based on a comparison with ANSYS finite element models. Equations for the four independent stiffness parameters and two coefficients of thermal expansion of the entire actuator are derived using a classical lamination approach. These results agree closely with an ANSYS finite element model of the unit cell of the macro fiber composite actuator.     

A finite element model for pre‐stressed or post‐tensioned concrete wind turbine towers

Wind turbine support towers have been traditionally formed of structural steel tubular sections, being fabricated in large sections under factory conditions before being transported to site for erection. Given the trend towards developing turbines with hub heights in excess of 90 m, it is now necessary to develop towers of concrete and other materials that can provide improved dynamic properties and ease transportation difficulties over the structural steel solutions. Concrete towers of this height require pre‐stressing to overcome high vertical stresses induced in bending, which would otherwise lead to cracking in the concrete, with a resulting reduction in the tower's natural frequency. In order to properly understand the behaviour of concrete towers, it is necessary to take account of both material and geometric non‐linearity. Material non‐linearity of concrete is well understood, and geometric non‐linearity arises because of the imposition of an initial stress into the concrete by way of the application of pre‐stress. In this paper, a finite element model is proposed, which will describe the concrete as a continuum of four‐noded, two‐dimensional Reisser–Mindlin shell elements. The pre‐stressing tendons are to be represented by one‐dimensional bar elements, with an imposed pre‐stress. For the numerical examples considered in the paper, tendons are modelled to be post‐tensioned and debonded. The effect of varying the design parameter of magnitude of pre‐stress and the time dependence of pre‐stress force has been investigated using the model described. The impact that concrete compressive strength had on overall tower stiffness was also investigated. Copyright © 2014 John Wiley & Sons, Ltd.