深水无隔水管钻井全井钻柱纵-横-扭耦合非线性振动模型研究EI北大核心CSCD

无隔水管钻井是一项极具发展前景的深水钻井技术。针对深水无隔水管钻井缺乏有效的动力学分析模型的实际,通过能量法、微元法结合哈密顿原理,建立了考虑钻井船位移、风海流、潮流、波浪载荷、井壁接触、钻头-岩石互作用、海水段-地层段互作用的深水无隔水管钻井全井钻柱纵-横-扭耦合非线性振动模型;通过拉格朗日和三次埃尔米特函数离散控制方程,采用Newmark-β对模型进行数值求解;采用现有海洋立管模拟试验数据、Moharrami扭转振动模型结果及Kyllingstad现场测试数据,对模型进行了详细对比验证。结果表明,该模型精度较好,可用于深水无隔水管钻柱的耦合振动分析。     

某结构件的随机振动疲劳分析

为了对某机载产品进行结构疲劳分析,采用有限元分析软件ANSYS对产品结构进行了模态分析和随机振动分析。结合模态试验修正了有限元模型,由随机振动分析得到应力响应功率谱,最后利用频域方法计算结构的疲劳损伤。仿真结果基本吻合强化试验结果,并给出了产品结构设计改进方案。     

基于频域分析垂直轴风力发电机组旋转主轴的风致动力疲劳

使用ANSYS有限元软件研究在风荷载作用下垂直轴风力发电机组(Vertical-axis wind turbine,VAWT)主轴在旋转状态下的风致动力疲劳问题.首先,在频域内,研究在脉动风作用下机组旋转主轴(转速为15.5 m/s)三个关键位置处的风动力响应特性.然后,基于机组旋转主轴风动力响应的计算与分析,对机组旋转主轴进行风致动力疲劳分析,计算其疲劳寿命耗用系数,以评价该机组旋转主轴的工作状况.     

光滑有限元的声学研究：时域和频域分析

摘　要：在使用有限元进行声场的数值模拟中,存在着两个主要误差,一个是数值方法中常规的插值误差,另外一个是计算声学中所特有的耗散误差(dispersion error),后者则是影响声学模拟仿真置信度的最重要因素。产生耗散误差的本质原因是由于有限元的数值模型刚度“偏硬”造成的。为了控制耗散误差,最重要的是使数值模型更好的反映真实模型。本文采用了一种基于边光滑的有限元方法(ES-FEM)来对声场的时域和频域进行数值模拟研究。该方法只采用对复杂问题域适应性很强的三角形网格,通过引进基于边的广义梯度光滑技术,能够使得有限元系统得到适当的“软化”。关于时域和频域的算例表明了在使用同样网格的情况下,本方法在声学模拟中的精度都要比有限元模型的高。     

钻井泵阀寿命分析

通过对钻井泵阀疲劳寿命的研究,进一步阐明泵阀失效的主要机理。利用ANSYS/LS-DYNA软件构建泵阀三维实体模型,模拟阀盘冲击阀座的过程,得到阀盘受力分布图,据此分析脉动循环应力对泵阀疲劳破坏的影响。该分析着重考虑了在交变载荷作用下应力集中对加速泵阀失效所带来的危害性,完善了泵阀的无冲击理论。依据泵阀疲劳寿命曲线,对泵阀使用寿命进行估算,并提出一种泵阀结构改进的新方案,在一定程度上有效减缓了应力集中,对延长泵阀使用寿命具有重要的实用价值。     

不同频率比时立管两向涡激振动及疲劳分析

考虑四种不同频率比(流向荷载频率/横向荷载频率)情况下,立管两向涡激振动的幅值和疲劳的变化。结果表明：较低频率比且低约化速度条件下,流向自由度对横向振动具有一定的抑制作用;当6.3<约化速度<8.0时,考虑顺流向振动时横向振动幅值明显增加。随着频率比的增加,顺流向振动对横向振动的影响逐渐减弱。横向振动对顺流向振动的影响在四种情况下均较为显著,考虑横向振动时顺流向振动幅值急剧增大。两向自由度涡激振动的疲劳在低频率比时明显高于单自由度时的疲劳;顺流向振动疲劳随着频率比的增大受横向振动的影响越来越明显。     

频域颤振μ分析的连续性及复摄动方法研究

摘 要：经典的线性颤振分析方法需要求解颤振特征值问题,并需要对特征值进行跟踪排序,以消除在确定颤振临界点时可能出现的颤振模态分支的“窜支”问题,从而影响了颤振分析的效率及自动化程度。为避免此问题,根据现代鲁棒控制理论,提出了一种直接利用频域气动力的μ-ω方法;在气动弹性方程中,引入速压摄动,建立μ分析框架,从而可采用频域μ分析进行颤振临界点预测,无需求解颤振特征值问题。注意到速压摄动量必须为实参数的要求,使得结构奇异值μ可能存在不连续性;针对此问题,对一个二元机翼气动弹性系统,采用定常气动力模型,进行解析分析的结果表明,仅允许实数摄动时,μ不连续性的确存在;但若允许复数摄动,则可以解决该问题;且计算结果表明,本文提出的复摄动μ-ω方法是一种具有很好精度的频域颤振分析方法。     

基于ESLs结构优化法的搅拌车副车架疲劳设计

疲劳问题是搅拌车副车架设计中的重要研究内容之一。将ESLs结构优化方法、拓扑优化方法与疲劳预测相结合,提出一种在部件设计初期,通过动态拓扑优化得到合理的部件拓扑结构,从而使部件同时满足疲劳寿命和轻量化设计要求的疲劳设计方法。该方法首先建立了搅拌车瞬态响应分析的优化模型,并且通过实验验证了模型的准确性。然后生成路面谱,并对关键点疲劳寿命进行评估;最后在简化后的路面谱与重力的作用下进行疲劳设计。对某型搅拌车副车架的疲劳设计结果表明,采用该方法对结构进行疲劳设计能得到更加合理的部件结构,达到了疲劳设计的目标。     

直升机结构响应自适应控制的频域双LMS法

传统的频域结构响应自适应控制都是根据确定性最优准则求得控制量,这种方法计算量大,且对外扰敏感常常导致求得的电压有较大波动,尤其在控制开始时刻。本文提出对控制通道频响矩阵与外扰响应幅进行在线识别与最优控制量求取的双LMS法。对某型直升机空测数据与其控制通道频响函数实测数据进行仿真,结果表明改进方法在保证控制效果和识别结果与原方法基本不变的同时,不仅能大大降低计算量,减少调整参数,而且能有效地缓和控制量的波动,具有更好的鲁棒性。     

随机振动疲劳寿命评估频域法模型适用性研究

为了研究频域法中的应力幅值概率密度函数(Probability Density Function,PDF)模型在随机振动疲劳寿命评估过程中的适用性,首先介绍常用的5种频域法模型,接着设置由不同谱宽系数、中心频率和功率谱密度(Power Spectral Density,PSD)谱值组合的限带白噪声应力功率谱。在此基础上利用傅里叶逆变换得到对应的时域信号,并将频域法模型计算得到的应力幅值概率密度函数与模拟的时域信号经过雨流循环计数得到的结果进行对比,评估各种频域模型的适用性和精度。结果表明,在整个带宽范围内,ZhaoBaker模型和Dirlik模型都有较高的准确性和适用性,Weibull模型在模拟小谱宽系数(ε<0.15)的单峰谱和谱宽系数大于0.6的宽带PSD时拥有不错的精度;频域模型的精度误差都随中心频率和谱值的增加有不同程度的下降。     

深海钢悬链立管时域疲劳寿命预估研究

研究了钢悬链立管(SCR)时域非线性动力分析用于疲劳寿命预估。随着海洋工业不断往深海进发,过去十年内钢悬链立管成为众多油田开发的优选方案。然而,对于钢悬链立管设计而言疲劳是个关键难题。钢悬链立管的非线性动力特性显著,与频域方法相比,时域分析能够模拟非线性水动力载荷以及结构的非线性特性。本文数值模拟了海洋环境载荷作用下SCR的非线性结构动力响应,利用S-N曲线对立管进行整体疲劳寿命预估。对影响SCR疲劳寿命的各参数进行敏感度分析,输入的敏感度分析参数包括拖曳力系数、浮力因子、海床土体硬度等,研究表明疲劳寿命的预估结果与这些参数相关,所给出的结论便于设计人员更好理解钢悬链立管动力特性,选择合适的参数用于立管疲劳设计。     

深水钻井隔水导管挠曲方程和固有频率的计算及其研究

从深水钻井应用的隔水导管的使用实际情况出发,应用弹塑性力学中的位移复分原理的Ritz法,考虑了隔水导管所受到的轴向张力T和隔水导管受力产生的倾角α以及由于自重q所产生的自重横向分力qsinα和轴向分力qcosα,建立了较为合理的挠曲方程,并且由此得到隔水导管的固有振动频率的简易计算求解方法。由于该挠曲方程结合了钻具的实际情况,其挠曲方程的约束条件采用的是一端铰支、一端自由的形式,因此其研究更接近实际情况,研究旨在为深水钻井隔水导管的合理使用设计和选择,提供一种更快捷实用的方法,对深水钻井作业有一定的指导意义。     

Random multiaxial fatigue: A comparative analysis among selected frequency and time domain fatigue evaluation methods

Fatigue analysis of mechanical components subjected to random loads has been recently upgraded through several developments of calculation procedures, with the scope to support the designer within the loading condition numerical simulation. Under such scenario, the frequency domain approach is characterized by interesting features, which support its adoption in alternative or in conjunction with the classic time-domain approach, especially when the frequency domain is applied for the individuation of the component critical locations. The major goal of this paper consists of an overview about the strength and weaknesses of frequency approach with respect to the time domain one by comparing the reference time domain methods with their frequency domain translation. A significant test case development will be shown, representing a classic automotive one (chassis validation). Promising results of the frequency method application will be presented, encouraging its adoption on large scale.     

Recent developments in frequency domain multi-axial fatigue analysis

The purpose of this paper is to discuss the recent developments in multi-axial spectral methods, used for estimating fatigue damage of multi-axial random loadings from Power Spectral Density (PSD) data. The difference between time domain and frequency domain approaches in multi-axial fatigue is first addressed, the main advantages of frequency domain approach being pointed out. The paper then critically reviews some categories of multi-axial spectral methods: approaches based on uniaxial equivalent stress (strength criteria, “equivalent von Mises stress”, multi-axial rainflow counting), critical plane criteria (Matake, Carpinteri-Spagnoli, criterion based on resolved shear stress on critical plane), stress-invariants based criteria (Crossland, Sines, “Projection-by-Projection”). The “maximum variance” method and the Minimum Circumscribed Circle/Ellipse formulations defined in the frequency domain are also discussed. The paper critically analyses also non-proportional multi-axial loadings and the role of material fatigue parameters (e.g. S/N curves for bending/torsion) in relation to specific methods. The paper concludes with general comments on advantages and possible limitations in the use of multi-axial spectral methods, with special focus on the assumption of stationarity and Gaussianity in modelling multi-axial random loadings.     

A frequency domain approach for estimating multiaxial random fatigue life

This paper presents a probabilistic method for fatigue life estimation within the frequency domain for structural elements subjected to multiaxial random loadings. Multivariate Monte Carlo Simulation is used to account for the correlation between the stress components and their different probability of occurrence and, moreover, enables stochastics during damage analysis to be allowed for and, at the same time, uses any suitable, material dependent multiaxial fatigue criterion known from the time domain. Comparison of the evaluated fatigue damage with experimental results from vibration tests on a demonstrator, chosen from common application fields in the automobile industry, shows good correlation.     

Dynamic analysis of cracks using the SGBEM for elastodynamics in the Laplace-space frequency domain

Dynamic analysis of a system can be carried out either in the time or frequency domains. Time responses/histories of this system may be directly obtained using time-domain formulations. In the frequency domain, analysis can be performed in either the Fourier or Laplace spaces. The symmetric-Galerkin boundary element method (SGBEM) for 2-D elastodynamics in the Fourier-space frequency domain has been previously reported in the literature. In this paper, the SGBEM for elastodynamics in the Laplace-space frequency domain using the standard continuous quadratic element and its application to dynamic analysis of cracks is presented for the first time. The technique developed is employed together with the fast Laplace inverse transform by Durbin to obtain time-dependent results for several typical examples including both crack and non-crack problems. These results are highly accurate when compared to those obtained from other numerical techniques. It is shown in this work that the very same boundary element code can be utilized to perform frequency domain analysis in either the Fourier or Laplace spaces. However, if time responses are required, the accuracy and computational effectiveness of the analysis may depend on the type of space selected as it determines the type of transforms (inverse Fourier/Laplace transforms) needed for converting frequency solutions to the desired time responses.     

植物微弱电波信号的时、频域分析

在时域和频域上对植物电波信号进行了分析.植物电波信号的幅值处于μV级量级,是一种微弱信号;随时间变化剧烈,在不同时刻的取值关系松散;植物电波信号属于低频信号,其功率谱主要分布在小于5 Hz这一频段.     

A new frequency domain method for random fatigue life estimation in a wide‐band stationary Gaussian random process

A new frequency domain method for random fatigue life estimation in a wide‐band stationary Gaussian random process was proposed for application in fatigue analysis. Simulations of the power spectral densities of different types were firstly performed; the simulated results showed that the accuracy and applicability for the current frequency domain methods are not only related to the spectral type but also associated with the types of the analysed materials. Compared with the current methods, the proposed method, in which the rain‐flow amplitude obeys Nakagami distribution, has better universality and could significantly reduce the error for the random fatigue life estimation with simulated and actual spectra. Verified application in cast‐steel fatigue life analysis were performed between random fatigue life and constant amplitude fatigue life. It is shown that the fatigue life analysis under random load cannot be ignored and the proposed new method can serve as a recommended method.