圆柱壳结构的转角自由度频响函数估计方法研究

频响函数子结构综合方法是工程设计的重要途径.对于子结构综合方法中界面转角自由度不匹配问题,本文采用界面刚性等效方法解决该问题.对于工程中常见的圆柱壳结构,本文通过数值仿真和试验研究验证了该方法在此类结构中获取转角自由度信息的可行性.将估计得到的与转角自由度相关的频响函数结果与有限元仿真结果进行对比,结果表明界面刚性等效...     

实验／分析模态双协调综合的实现

本文讨论了实验/分析模态双协调综合实现中实验子结构转角自由度和集中力矩柔度的测量问题。首次提出基于有限元理论的双无加载概念,并通过仿真计算说明其在转角自由度测量的应用价值.最后以一汽车底架模型为实例,经过分析综合和实验(/分析)综合,实践了本文的主题.     

复杂结构系统非线性振动分析的自由度压缩技术

本文系统地总结了对复杂结构系统进行非线性振动分析时基于混合坐标法和模态综合法的自由度压缩技术,提出了局部非线性系统振动分析的具体接子结构的模态综合法,并给出了处例。最的指了利用非线性动力系统进行二次降低来研究超高自由度非线性系统复杂动力学行之一思路。     

基于SiPESC平台的模态综合法研究及实现

模态综合法作为主流的动力子结构方法,可在有效的精度下缩减整体结构的自由度,特别是对大型复杂结构的动力计算具有较高的效率,已被集成到许多商业CAE软件中,因此把它集成到SiPESC平台上是一项很有意义的工作.本文实现了两种模态综合法的集成,分别是Craig-Bampton方法、多层Craig-Bampton方法.研究工作同时提出了一种高效的子结构界面点搜寻算法,所实现的Craig-Bampton方法考虑了子结构的旋转及平移,多层Craig-Bampton方法可以考虑各种多层子结构的划分方式.SiPESC平台是由大连理工大学开发的新一代的有限元数值计算软件平台,它利用了新型的软件架构和程序设计思想,因此在SiPESC平台上进行程序设计开发是十分方便的.通过构建数值算例同Nastran的计算结果进行对比,数值算例验证了本文实现方法的正确性和有效性.     

组合神经网络在结构损伤检测中的应用

子结构的动态响应变化与整体结构相比,对结构内部损伤反应更为敏感。组合神经网络可以克服单个神经网络功能的单一局限性,实现更加全面综合的仿真识别功能。本文首先运用双协调自由界面模态综合法对结构进行模态分析,获取各子结构及整体结构的模态信息。然后,通过组合BP神经网络将损伤子结构与整体结构的模态频率变化率组合起来进行结构损伤检测。该方法在改善网络训练性能的同时,提高了检测结果的准确性和可靠性。文章最后通过数值算例验证了该方法的可行性和有效性。     

高层空间框架结构动力分析的超级元子结构模型

本文将超级元和子结构的思想相结合,根据框架结构的变形特点,建立了高层空间框架结构动力分析的超级元子结构模型。模型中将楼面划分为子结构,在总结构层次将各子结构假想为二维连续体后用超级元来描述,而在子结构内部仍用经典有限元三维梁单元模拟。据此,框架梁位于同一超级元内,而框架柱连接不同的超级元。通过假设子结构内部结点自由度与总结构结点自由度的位移关系,得到超级元的质量矩阵以及框架梁和框架柱的单元刚度方程。该模型中空间框架结构的动力和非动力自由度均有大幅度的缩减,而刚性楼面假定可以进一步减少计算量。最后通过一幢30层钢筋混凝土空间框架结构的动力特性分析验证本文理论的正确性和适用性。     

基于键合图法的多个子结构自由界面模态综合法研究和应用

将键合图方法用于动态子结构研究,提出了一种求解多个子结构自由界面模态综合法的新方法。通过一系列物理和数学上的分析,详细推导出多个子结构自由界面模态综合法的计算过程。在本文给出的算例中,基于键合图方法的自由界面模态综合法,通过建立各个子结构的状态空间方程,计算子结构相应的特征值矩阵和振型矩阵;这些子结构在进行模态综合后,获得整体结构的特征值矩阵和振型矩阵,该结果和原来整体结构完全相同,这进一步说明了本文提出的新方法的正确性。运用本文提出的方法建立状态空间方程,在子结构的模态综合过程中,不会产生系统特征值的增失根问题,确保了子结构在综合后其整体结构模态信息的完整性。     

裂纹扩展独立于网格的一种有限元单元子划分方法

提出了一种有限元模拟裂纹扩展的单元子划分结合子结构的方法。本方法中,裂纹可以进入或穿过一个单元,或沿单元的边界扩展,因此裂纹可以沿任意路径扩展而不受初始网格的限制。对上述几类包含裂纹的单元按照裂纹的路径进行子划分,覆盖一条裂纹的所有子划分单元就组成了一个子结构,子结构规模随裂纹的扩展而增大。子结构中因单元子划分而新增的结点自由度,通过自由度的凝聚用初始网格结点的自由度表示,因此结构整体分析的总自由度不变。以上述方法为基础建立了裂纹萌生和扩展的准则。用本文的方法分析了单（双）材料无限大平面中心（界面）裂纹的裂尖场,验证了本文方法的精度,并模拟了颗粒复合材料中微裂纹在颗粒、基体和界面中逐步扩展的过程,考核了本文方法对复杂裂纹扩展问题模拟的适用性。     

基于多重多级动力子结构的瞬态分析方法

提出利用多重多级子结构技术与Newmark算法求解结构动力学方程的高精度算法.该算法利用静凝聚技术列式简单,在凝聚过程中并不引入任何近似的优点,采用子结构周游树技术,分别对每个子结构求解Newmark等效平衡方程,最后通过回代求解得到整体结构的响应.由于该算法考虑了子结构内部自由度对整体求解的贡献,算法实施不受子结构划分方式的限制,因此可以得到系统高阶模态对响应分析的影响.该算法计算精度与传统的全结构求解相当,计算效率高,消耗计算机资源少,且可构造为统一的多重多级子结构综合分析算法框架.数值算例验证了该算法的正确性和有效性.     

固定界面模态综合法的两个简化措施

本文对固定界面模态综合法作出两点简化。其一是用所谓迭代Ritz矢代替子结构的固有振动模态,以节约计算机时。其二是由平衡条件消去全部或部分界面自由度,以减缩最后综合规模。这样做就要求采用集聚质量矩阵,而且对应于被消去自由度的质量应等于零或极小。附有算例。     

Six degrees of freedom coupled dynamic response of rotor with a transverse breathing crack

More coupling mechanisms between the six degrees of freedom (DOFs) are introduced by considering the contribution of the general transverse forces to stress intensity factor of mode I crack in predicting the crack additional flexibility matrix of the cracked rotor. And the obtained flexibility elements show a good agreement with the experiment result for a wide range of the crack depth ratio. Six DOFs coupled dynamic equations for cracked rotor are formulated by introducing three rotational DOFs. A response-dependent non-linear breathing crack model is applied to simulate the breathing behavior during operation in this paper. Numerical investigations are carried out to simulate the various parametric conditions on the dynamic characteristics of cracked rotor, including the crack depth, shaft slenderness ratio, and rotating speed ratio. A perturbation frequency component and its combinations with harmonic components are observed in the dynamic response obtained by six DOFs coupled models (SDCM). Some differences in evolution of whirling orbit obtained by SDCM and three DOFs coupled models are found, when the cracked rotor passes through the sub-critical speeds.     

结构静态拓扑重分析的迭代组合近似方法

提出一种拓扑修改的静态重分析的迭代组合近似方法. 这种方法基本上是两步法. 首先，将新增加的自由度通过Guyan缩减方法凝聚到原始自由度上，形成凝聚方程. 其次， 用迭代组合近似方法求出原始自由度的近似位移，从而求出原结构自由度的位移. 新增加自 由度的位移可以通过恢复得到. 通过板结构的加筋布局优化设计的数值例子表明， 该方法对拓扑修改较大时仍可得到满意的结果.     

Nonlinear dynamic response of an edge-cracked functionally graded Timoshenko beam under parametric excitation

This paper investigates the nonlinear flexural dynamic behavior of a clamped Timoshenko beam made of functionally graded materials (FGMs) with an open edge crack under an axial parametric excitation which is a combination of a static compressive force and a harmonic excitation force. Theoretical formulations are based on Timoshenko shear deformable beam theory, von Karman type geometric nonlinearity, and rotational spring model. Hamilton’s principle is used to derive the nonlinear partial differential equations which are transformed into nonlinear ordinary differential equation by using the Least Squares method and Galerkin technique. The nonlinear natural frequencies, steady state response, and excitation frequency-amplitude response curves are obtained by employing the Runge–Kutta method and multiple scale method, respectively. A parametric study is conducted to study the effects of material property distribution, crack depth, crack location, excitation frequency, and slenderness ratio on the nonlinear dynamic characteristics of parametrically excited, cracked FGM Timoshenko beams.     

车辆-轨道系统垂向随机振动的辛方法分析

将轨道视为无限长的周期结构,建立车辆轨道垂向耦合模型. 使用虚拟激励法将随机的轨道不平顺激励转化为确定性的简谐激励,再用辛数学方法求解轨道结构的频率响应特性和耦合系统的响应功率谱. 整个计算模型只有26个自由度,求解过程快速而精确.数值算例中,将该方法与常规有限元方法进行了比较,验证了方法的高效性和正确性,讨论了车辆速度对系统随机响应的影响.      

Finite memory quadratic Volterra model for the response prediction of a slender marine structure under a Morison load

A quadratic Volterra model with a finite nonlinear memory effect was introduced and applied to the time series prediction of a slender marine structure exposed to the Morison load. First, the unknown nonlinear single-input–single-output dynamic system was identified using the nonlinear autoregressive with exogenous input (NARX) technique based on the prepared datasets of the wave elevation and system response, which was obtained by running nonlinear time domain analysis for a certain short term sea state. The structure of NARX was designed in such a way that the linear part had infinite memory, whereas the nonlinear part had finite memory of a certain length. Second, the frequency domain Volterra kernels, both linear and quadratic, were derived analytically by applying the harmonic probing method to the identified system. To derive the frequency response functions, the sigmoidal function used in NARX to realize the nonlinear relationship between the input and output was expanded to polynomials based on the Taylor series expansion, so that the harmonics of same frequencies were easily matched between the input and output. Finally, the time series of the system response under arbitrarily given short term sea states were predicted using the quadratic Volterra series. The proposed methodology was used to predict the nonlinear dynamic response of a 2-dimentional free standing catenary riser exposed to a random ocean wave load, and the comparison between the prediction and simulation results was made on the probability distribution of the maximum excursion of riser top. The results show that the proposed methodology can successfully capture the nonlinear effects of the dynamic response of a slender marine structure induced by the quadratic term of the Morison formula.     

基于子结构解耦的连接特性识别新方法

连接部件动态特性的准确辨识对预测装配式机械结构的动力学行为有重要意义. 针对传统基于子结构解耦的连接结构动力学特性识别方法难以直接利用可测量数据进行辨识及辨识结果受噪声影响显著等问题, 本文提出了一种新方法. 首先, 提取子结构解耦基本方程在测试自由度上的分量, 并经矩阵变换得到显含连接动刚度矩阵的形式, 而后由真实连接动刚度矩阵分解为已知的初始矩阵与待求的增量矩阵, 推导了具有收敛性质的增量型方程以增强界面自由度较多时辨识的数值稳定性, 并采用多项式拟合动刚度将其转化为了拟合系数的频域估计方程, 按给定准则选取合适的频率点联立方程后, 得到了只需装配体测试自由度上的频响函数来辨识连接特性的迭代公式. 最后, 以若干算例说明了算法的具体流程. 对10自由度弹簧?质量块系统进行了数值仿真, 验证了所提方法的正确性及抗噪性; 对包含一处胶接连接的T形梁结构和包含两处螺栓连接的L形梁结构进行了试验, 所辨识连接结构与残余结构重组的装配体有限元模型计算的频响函数与测量值在较宽频带内吻合较好, 表明了该方法能有效识别实际装配体结构中的连接特性.      

Nanoscale Broadband Viscoelastic Spectroscopy of Soft Materials Using Iterative Control

A novel approach to nanoscale broadband viscoelastic spectroscopy is presented. The proposed approach utilizes the recently developed modeling-free inversion-based iterative control (MIIC) technique to achieve accurate measurement of the material response to the applied excitation force over a broad frequency band. Scanning probe microscope (SPM) and nanoindenter have become enabling tools to quantitatively measure the mechanical properties of a wide variety of materials at nanoscale. Current nanomechanical measurement, however, is limited by the slow measurement speed: the nanomechanical measurement is slow and narrow-banded and thus not capable of measuring rate-dependent phenomena of materials. As a result, large measurement (temporal) errors are generated when material is undergoing dynamic evolution during the measurement. The low-speed operation of SPM is due to the inability of current approaches to (1) rapidly excite the broadband nanomechanical behavior of materials, and (2) compensate for the convolution of the hardware adverse effects with the material response during high-speed measurements. These adverse effects include the hysteresis of the piezo actuator (used to position the probe relative to the sample); the vibrational dynamics of the piezo actuator and the cantilever along with the related mechanical mounting; and the dynamics uncertainties caused by the probe variation and the operation condition. In the proposed approach, an input force signal with frequency characteristics of band-limited white-noise is utilized to rapidly excite the nanomechanical response of materials over a broad frequency range. The MIIC technique is used to compensate for the hardware adverse effects, thereby allowing the precise application of such an excitation force and measurement of the material response (to the applied force). The proposed approach is illustrated by implementing it to measure the frequency-dependent plane-strain modulus of poly(dimethylsiloxane) (PDMS) over a broad frequency range extending over 3 orders of magnitude (~1 Hz to 4.5 kHz).     

Imposing nodes for linear structures during harmonic excitations using SMURF method

Vibration absorbers are usually designed using the finite element (FE) model of structures. It is generally believed that the modal models are more accurate than FE models, because in modal testing the model is built by direct measurement of the test structure. In this paper, a method is proposed to design a translational vibration absorber using the measured frequency response functions of a primary structure. The designed vibration absorber imposes a node on the structure when it is excited by a harmonic force. The method is based on the structural modification using experimental frequency response functions technique and determines the required receptance of the absorber at the excitation frequency. Moreover, a procedure is developed to suppress the vibration amplitude of two arbitrary points on a linear structure subjected to harmonic excitations by attaching two sprung mass absorbers. A cantilever beam is considered for the numerical case study, and the sprung masses are designed to suppress the vibration amplitude of the beam at the selected arbitrary points. A U-shape plate was considered for the experimental validation of the method for imposing a node using one absorber. Also, a beam was tested to demonstrate the effectiveness of method for imposing two nodes on the structures. The experimental results show that the designed absorbers can considerably suppress the vibration amplitude at the selected points on the structure.     

一种滞弹簧耗能的新型离散元滚动阻力模型研究

颗粒间滚动阻力对颗粒体系的稳定性起着重要作用. 在传统的离散元法中, 滚动阻力模型通常由转动弹簧、转动黏壶和摩擦元件表达, 颗粒滚动动能由黏滞力(矩)和摩擦力做功耗散. 由于黏滞力(矩)与滚动速度相关, 临近静止状态的颗粒滚动速度变小, 动能耗散减弱, 传统的离散元模拟得到颗粒由滚动到静止耗费的时间比试验观测的结果要长. 为解决这一问题, 基于摩擦学理论分析了滚动阻力产生的材料滞弹性机理, 将其引入离散元滚动阻力模型, 提出了一种速度无关型动能耗散的滞弹簧, 给出了滞弹簧的弹性恢复力计算公式, 建立了一种新型的离散元滞弹性滚动阻力模型(HDEM). 为验证新型滚动阻力模型的正确性, 通过一个光学物理试验对单个圆形颗粒试件的自由滚动过程进行了测量, 将测量数据与新型的滞弹型离散元模型和传统离散元模型计算结果进行了对比. 结果显示, 基于滞弹性滚动阻力模型HDEM计算结果与试验数据吻合程度更高, 而且模拟得到的颗粒摆动频率更符合试验现象.      

含剪力销(锥)螺栓法兰连接结构非线性特性

连接结构广泛应用于航空航天、化工装备和核电站等大型工业装备中。对于轴弯剪组合作用下的连接结构,需要螺栓、法兰和剪力销的联合工作以抵抗外力。本文针对含剪力销(锥)的螺栓法兰连接结构的动力学问题开展研究,将该类结构抽象为三自由度的质量-双线性弹簧系统,建立非线性动力学模型的数学列式,并进行数值求解。重点研究该系统在横向冲击(剪力)下的动力学特性。通过理论分析与数值计算,指出该非线性系统存在3个方向自由度全耦合的振动现象,并阐述该系统自由度的解耦条件;对纵向振动与横向错动的耦合振动频率关系进行讨论并分析其相互联系;研究剪力销倾角对螺栓最大轴向拉力的影响规律并给出关系曲线,指出其最佳设计角度区间。