基于应变分布响应的模态分析理论与应用

 模态分析技术经过近70年的发展已形成较为完整的独特理论和方法,这与模态测试手段的进步息息相关。由于传感技术的限制,既有的模态分析方法主要是基于加速度或速度测量开展的,重点关注位移、速度及加速度频响函数。过去5年间,本课题组研究和开发了用于重大工程结构的分布式应变传感技术,并以分布式动态应变测量为核心开展了包括模态分析理论、模态测试及工程应用在内的研究工作。本文简要介绍分布式动态应变传感技术的基本特点和系统构成,重点阐述基于应变分布响应的模态分析理论、应变频响函数的测试技术及相应的模态参数识别方法。应变模态分析表明,从时频域上看,应变频响是更类似于位移频响而不同于速度或加速度频响的物理量,因此对低频响应更为敏感;基于位移频响函数和基于应变频响函数提取结构固有频率和阻尼比等价有效;基于位移频响函数和基于应变频响函数提取的特征向量之间的相互关系与位移和应变测量之间的映射关系完全相同,即基于应变频响获得的特征向量是直接的应变模态测量。探讨了应变模态在大柔度结构低频测试、动力模型重构、结构损伤识别3方面工程应用中的优势。     

基于多响应频响函数的加筋壁板结构模型修正

针对有限元模型中结构特征的简化以及连接界面的处理给分析结果引入的误差,提出一种基于多响应频响函数的模型修正方法。简要介绍基于频响函数模型修正的基本原理,并以复杂加筋壁板结构为对象进行实例研究。首先,建立加筋壁板的各子结构模型,并采用连接单元将子结构模型组装成整体结构模型。其次,对加筋壁板结构进行动态测试与分析,根据对应的试验结果对模型中的材料参数、连接参数以及模态阻尼比进行修正。最后,分别对比修正前后结构的模态频率、频响函数,检验修正后模型的精度。研究结果表明:经过修正后的加筋壁板结构能复现用于修正的多响应频响函数,得到1个能同时反映结构加速度和应变特性的模型,从而验证了所提方法的有效性。     

基于多模态传递比的旋转叶片动应变场重构方法

针对旋转叶片非接触式应力/应变测试的需求,本文提出一种基于多模态传递比的叶片动应变场重构方法。首先,基于多自由度(MDOF)系统的振动微分方程,在模态坐标系下建立位移频响函数(FRF)和应变频响函数,进而得到位移-应变响应传递比表达式;以某12扇区的叶盘为分析对象,建立叶片有限元模型并进行模态分析,通过提取多模态叶尖位移和叶身应变,得到总位移-应变传递比矩阵和定向位移-应变传递比矩阵;最后,基于Simulink平台进行旋转叶片叶尖定时采样(BTT)仿真模拟,通过周向傅里叶拟合算法(CFF)对欠采样信号进行振动位移重构,将得到的叶尖位移代入传递比表达式,得到叶身应变。研究结果表明：在非共振态下,由叶尖位移重构得到的叶身总应变与有限元分析得到的总应变相对误差为0.12%～14.56%,定向应变相对误差为1.92%～14.70%,验证了本文提出的基于多模态传递比的叶片动应变场重构方法的有效性。     

神经网络法在定量损伤识别研究中的应用

为了探索一种可能的结构损伤在线监测方法,使结构损伤动力识别的研究更具工程实际意义,以工程上常用的截面开口槽形梁为试件,用试验模态分析与神经网络法相结合的方法,研究了位移频响函数指标、应变频响函数指标和模态频率指标在结构损伤定量辨识中的灵敏性。结果证明了神经网络法与试验模态分析技术相结合检测结构损伤的可行性,并指出应变指标对损伤更敏感。此外,指出了对于具有复杂模态的结构无法获取模态的完善信息时,用有限个点、有限个方向的测量数据进行损伤识别是可行的。     

一种光纤光栅加速度传感系统

研制了一种高精度、低成本适合于地震勘探和矿山安全等工程领域的光纤光栅加速度传感系统。该系统利用加速度改变光纤光栅中心波长的原理工作,可以有效消除温度漂移对动态应变测量的影响。实验结果表明,传感器频响在2-100Hz,灵敏度1．2pm／με,动态范围达80dB,是一种较为理想的光纤加速度传感系统。     

基于应变响应功率谱传递比的海上风机工作模态识别

利用传递比函数与应变响应的优势,提出了基于应变响应功率谱传递比(SPSDT)的海上风机工作模态识别方法.该方法无需通过复杂的信号预处理,仅基于传递比函数识别响应信号的统计特性差异,便可有效区分结构工作模态与谐波干扰.选择某海上风机结构为应用及验证对象,首先利用风机停机状态下的加速度和应变响应识别结构模态参数,验证了应变模态分析方法的可行性.随后利用风机在工作状态下多个工况的应变数据,进一步验证了通过结合SPSDT函数可使新方法有效克服转频谐波干扰,准确稳定地识别不同工况下风机工作模态.将该方法应用于风机结构的模态识别,具有良好的发展潜力和应用前景.     

环境激励下鹤洞大桥模态参数识别分析与比较

在已建立的鹤洞大桥结构健康监测系统的基础上,同时采用GPS变形监测和加速度振动测试系统,在环境激励下对桥塔和桥主跨段进行位移和加速度响应的同步测试.采用基于总体平均经验模态分解法(EEMD)的改进HHT方法,对GPS系统监测位移进行时频域联合分析,同时对于桥面加速度振动测试数据则采用常规的功率谱峰值法进行频域模态识别.通过2种不同信号采取2种不同模态参数识别方法,进行系统辨识结果对比分析,发现GPS监测位移可以较好地反映主整体结构的低阶振型响应,基于EEMD的改进HHT方法能较好地处理低频非平稳随机信号的干扰及模态混叠现象的发生;相对于常规的功率谱峰值法,本文所采用的改进HHT方法对模态参数辨识结果具有更强的优越性.同时通过2种不同测试信号对于部分阶次模态的系统参数识别结果,与有限元数值分析结果较为相近,验证了上述2种测试结果的正确和可靠性.GPS变形监测系统与加速度动力测试子系统相结合,能较好地识别鹤洞大桥主要模态参数,为大桥的安全有效运作提供坚实依据.     

工程振动信号微积分敏感性及其应用研究

工程施工监测中常常需要监测振动速度信号或振动加速度信号,振动速度信号和振动加速度信号的频谱特性差别很大,进而影响后续分析.本文采用傅立叶变换的时域微积分性来分析工程振动信号频谱的微积分敏感性,并通过拉普拉斯变换求取结构振动傅立叶谱,自功率谱,频响函数,并分析它们微积分敏感性.通过频响函数分析了其微分敏感性的物理意义.通过对背景工程中高层建筑实测自然激励的振动信号,验证了频谱微积分敏感性,并分析了频谱微积分敏感性对于振动信号分析的影响.研究结果表明：工程振动信号在数学上由于傅立叶变换的时域微积分性质,使得傅立叶谱峰值的频率分布具有微积分敏感性,随着振动信号微分阶次的升高,高频成分逐渐升高,低频成分逐渐降低;由不同信号的频响函数表达式,对结构动刚度、阻抗、动质量的频率分布规律进行了阐述;不同监测信号对于高、低频成分的识别精度不同,对于结构物高、阶模态的识别精度亦不同,对于高阶的频率成分的识别建议进行振动加速度信号监测,对于低阶频率的识别建议采用振动速度信号监测.     

光纤光栅传感技术在重大工程结构诊断与监测中的应用

光纤光栅传感技术具有传统传感器无可比拟的优势,重大工程结构的健康诊断与监测是跨学科的前沿研究领域。介绍了光纤光栅传感技术用于重大工程结构的原理、国内外研究以及在重大工程中应用的概况,阐述了基于光纤光栅传感技术和应变模态理论的损伤自诊断智能结构系统的基本构成、原理,并指出近期应当加强光纤光栅传感技术的结构诊断、动态解调、工业化批量生产及其埋设等方面研究工作。     

环境激励下湘潭莲城大桥模态参数识别研究

对环境激励下结构模态参数识别进行了理论分析和试验研究.基于随机振动理论阐述了峰值拾取法的基本原理和方法,并提出了虚拟响应的概念.从湘潭莲城大桥在环境激励下的加速度测试信号中提取高信噪比的虚拟响应信号,根据峰值拾取法对虚拟响应信号进行频域分析,识别了该桥主跨结构的固有频率、阻尼比和振型等模态参数.试验模态参数与理论模态参数基本吻合,验证了识别结果的可靠性.模态置信矩阵表明,结构的线性响应特性明显,竖向振动具有良好的正交特性.     

Markedness and its Interpretation in Language Use

Language markedness is a common phenomenon in languages, and is reflected from hearing, vision and sense, i.e. the variation in the three aspects such as phonology, morphology and semantics. This paper focuses on the interpretation of markedness in language use following the three perspectives, i.e. pragmatic interpretation, psychological interpretation and cognitive interpretation, with an aim to define the function of markedness.     

Features of Women's language

Language is a means of verbal communication. People use language to communicate with each other. In the society, no two speakers are exactly alike in the way of speaking. Some differences are due to age, gender, statue and personality. Above all, gender is one of the obvious reasons. The writer of this paper tries to describe the features of women＇s language from these perspectives： pronunciation, intonation, diction, subjects, grammar and discourse. From the discussion of the features of women＇s language, more attention should be paid to language use in social context. What＇s more, the linguistic phenomena in a speaking community can be understood more thoroughly.     

An Analysis of Catherine＇s Character——Wuthering Heights

Wuthering Heights, Emily Bronte＇s only novel, was published in December of 1847 under the pseudonym Ellis Bell. The book did not gain immediate success, but it is now thought one of the finest novels in the English language. Catherine is the key character of this masterpiece, because everybody and everything center on her though she had a short life. We can understand this masterpiece better if we know Catherine well.     

Lower Paleozoic oil relationships within Williston Basin, Canada

The Williston Basin is a significant petroleum province, containing oil production zones that include the Middle Cambrian to Lower Ordovician, Upper Ordovician, Middle Devonian, Upper Devonian and Mississippian and within the Jurassic and Cretaceous. The oils of the Williston Basin exhibit a wide range of geochemical characteristics defined as "oil families", although the geochemical signature of the Cambrian Deadwood Formation and Lower Ordovician Winnipeg reservoired oils does not match any "oil family". Despite their close stratigraphic proximity, it is evident that the oils of the Lower Palaeozoic within the Williston Basin are distinct. This suggests the presence of a new "oil family" within the Williston Basin. Diagnostic geochemical signatures occur in the gasoline range chromatograms, within saturate fraction gas chromatograms and biomarker fingerprints. However, some of the established criteria and cross-plots that are currently used to segregate oils into distinct genetic families within the basin do not always meet with success, particularly when applied to the Lower Palaeozoic oils of the Deadwood and Winnipeg Formation.     

低渗透非均质砂岩油藏启动压力梯度研究

理论推导与室内实验相结合,建立了低渗透非均质砂岩油藏启动压力梯度确定方法。首先借助油藏流场与电场相似的原理,推导了非均质砂岩油藏启动压力梯度计算公式。其次基于稳定流实验方法,建立了非均质砂岩油藏启动压力梯度测试方法。结果表明:低渗透非均质砂岩油藏的启动压力梯度确定遵循两个等效原则。平面非均质油藏的启动压力梯度等于各级渗透率段的启动压力梯度关于长度的加权平均;纵向非均质油藏的启动压力梯度等于各渗透率层的启动压力梯度关于渗透率与渗流面积乘积的加权平均。研究成果可用于有效指导低渗透非均质砂岩油藏的合理井距确定,促进该类油藏的高效开发。     

On Tragic Consciousness In The Works By Ernest Hemingway

As an American modern novelist who were famous in the literary world, Hemingway was not a person who always followed the trend but a sharp observer. At the same time, he was a tragedy maestro, he paid great attention on existence, fate and end-result. The dramatis personae's tragedy of his works was an extreme limit by all means tragedy on the meaning of fearless challenge that failed. The beauty of tragedy was not produced on the destruction of life, but now this kind of value was in the impact activity. They performed for the reader about the tragedy on challenging for the limit and the death.     

Design and analysis of generic LBS application developing platform

Location based services is promising due to its novel working style and contents.A software platform is proposed to provide application programs of typical location based services and support new applications developing efficiently. The analysis shows that this scheme is easy implemented, low cost and adapt to all kinds of mobile nework system.     

Achieving Unusual States of Matter Under High Pressure

正The periodicity of the elements and the non-reactivity of the inner-shell electrons are two related principles of chemistry,rooted in the atomic shell structure.Within compounds,Group I elements,for example,invariably assume the+1 oxidation state,and their chemical properties differ completely from those of the p-block elements.These general rules govern our understanding of chemical structures and reactions.Using first principles calcula-     

Exchange-Correlation and Electronic Excitation Energies from Pairing Matrix Fluctuations

We have developed an adiabatic connection to formulate the ground-state exchange-correlation energy in terms of pairing matrix linear fluctuations.This formulation of the exchange-correlation energy opens a new channel for density functional approximations based on the many-body perturbation theory.We illustrate the potential of such approaches with an approximation based on the particle-particle Random Phase Approximation(pp-RPA).This re-     

Density Functional Theory for the Response of Periodic Systems to Electric Fields Based on the Vector Potential Approach

正The electronic and nuclear(structural/vibrational)response of 1D-3D nanoscale systems to electric fields gives rise to a host of optical,mechanical,spectral,etc.properties that are of high theoretical and applied interest.Due to the computational difficulty of treating such large systems it is convenient to model them as infinite and periodic(at least,in first approximation).The fundamental theoretical/computational problem in doing so is that