风机法兰螺栓断裂对塔筒结构振动特性的影响分析

为研究螺栓断裂对风机塔筒结构振动特性的影响,应用数值模态分析方法,通过ABAQUS软件,建立含有法兰螺栓的风机有限元计算模型,获取了各工况前6阶频率和振型,研究了不同螺栓断裂比例塔筒的频率及振型变化规律。结果表明,各层法兰螺栓断裂时,塔筒1阶频率变化最为敏感,2阶次之,3、4阶最不敏感,高阶基本无变化,因此可根据塔筒的低阶频率来判断螺栓是否断裂;法兰高阶振型对螺栓断裂十分敏感,可根据法兰3、4阶振型来监测螺栓是否发生断裂。该结果对丰富风电塔螺栓断裂快速检测理论方法及风电厂的安全运行具有现实工程意义。

水电站厂房振动传递路径的仿真模拟及结构振动特性研究

基于泸定水电站厂房,研究提出了水电站厂房非定常湍流、机组及混凝土结构相互作用的流固耦合振动分析方法,对流体压力脉动的振动能量传递路径进行了仿真模拟,建立了厂房全流道湍流-整体结构流固耦合振动分析的全耦合仿真模型。通过流体和固体交错迭代考虑流体和固体间的耦合作用,进行时程振动计算分析。结果表明,水轮机叶片与导叶间静动干扰所引起的流体脉动压力对厂房整体结构振动影响较为显著,座环安放处混凝土的振动相对最为剧烈,研究成果揭示了水电站厂房的整体振动规律。

垂直轴风力机结构振动特性研究

垂直轴风力机有着优良的气动性能,近年来受到人们越来越多的关注。介绍了风力机结构动力特性在国内外研究现状。对风力机的结构振动特性进行了研究,分析了工作状态下风机的动力刚化问题。对某垂直轴风力机进行不同转速下的固有频率分析,绘制Campbell图,并计算了风机的临界转速,以判断其工作状态是否安全。

热环境下的金属热防护系统的动力学特性研究

研究了金属热防护系统(metallic thermal protection system,简称MTPS)在典型RLV再入热载荷作用下的动力学特性。首先,针对MTPS在热载荷作用下的动态响应问题,结合数值算例验证了有限元分析方法的可行性和正确性;其次,基于MTPS的有限元传热分析模型,计算了热环境下结构的瞬态温度响应;最后,使用有限元的分析方法对笔者建立的MTPS简化模型在热应力场和结构场耦合下的结构动力学特性进行了研究分析,给出了典型再入热环境下结构的固有振动频率随加热时间的变化曲线。计算结果发现,材料弹性模量等参数的变化比热应力场对MTPS结构固有频率的影响更大,热应力场对结构固有频率的影响最高达到10.3%的比例。

桥隧相连段隧道衬砌动力特性探讨

以宜万铁路160km／h单线隧道为例，研究了桥隧相连地段隧道结构在静载以及列车振动荷载下的响应，探讨了列车振动荷载下衬砌结构的薄弱部位及其相应的位移和应力。

损伤定位向量法原理及应用

该文中证明了损伤定位向量存在的条件,推导了梁、柱和支撑单元的特征应力计算公式,改进了损伤后振型质量归一化系数的简化求解。完成了一个空间钢支撑框架模型损伤定位的数值模拟分析,模拟了包括支撑损伤和连接损伤的7种损伤模式。分别采用力锤激励和环境激励两种激励方式;使用自然激励技术和特征系统实现算法进行模态参数识别,得到了模态频率和振型;使用损伤定位向量法判定损伤单元,并对两种损伤模式进行了误差分析。结果表明:当损伤达到一定程度时,损伤定位向量法能有效判定损伤单元。

基于损伤部位向量法的钢框架损伤识别研究

对损伤部位向量(DLV)法作了简单介绍,并用该方法对钢框架进行了损伤识别和损伤定位。该方法假定结构损伤前后为线性,对结构损伤前后柔度矩阵差进行奇异值分解,将奇异值为零所对应的向量,作为静荷载施加在无损结构的测点位置,则应力为零的单元为可能损伤的单元。对3种不同工况的钢框架进行了振动模态试验,用前3阶模态参数构造框架的柔度矩阵,按照DLV法对其进行了损伤识别,识别结果与已知损伤情况相一致。从测试自由度不完备、噪声和振型质量归一化系数这3个方面对识别效果进行了分析,结果表明:当损伤使结构动力特性有微小改变时,使用该方法不易定位损伤,应结合局部损伤识别方法进行判定;当损伤使结构动力特性有较大改变时,该方法能有效识别损伤的单元。DLV方法概念简单,理论明确,不受结构类型的限制,不需要结构的数学模型和模型缩聚或扩展技术,只需获得结构损伤前后的前几个低阶模态参数,即可识别结构一处或多处损伤,实际应用时可操作性强。

基于Imote2无线传感器的拱桥模型动力试验

介绍了Imote2高性能无线传感器的性能和特点,并利用Imote2建立了无线信号采集系统,解决了在数据采集和处理过程中传感器的时间不能同步等问题;通过在钢管混凝土拱桥模型上的试验测试,得到了拱桥模型的动力特性,并和有线传感器的测试结果进行了比较,利用频谱分析技术和频率稳定图方法验证了试验结果的准确性。结果表明:Imote2无线传感系统能够成功应用在土木工程结构监测中。

Microscopic damage and dynamic mechanical properties of rock under freeze-thaw environment

For understanding the rock microscopic damage and dynamic mechanical properties subjected to recurrent freeze-thaw cycles, experiments for five groups of homogeneous sandstone under different freeze-thaw cycles were conducted. After freezethaw, nuclear magnetic resonance(NMR) tests and impact loading tests were carried out, from which microscopic damage characteristics of sandstone and dynamic mechanical parameters were obtained. The results indicate that the porosity increases with the increase of cycle number, the rate of porosity growth descends at the beginning of freeze-thaw, yet accelerates after a certain number of cycles. The proportion of pores with different sizes changes dynamically and the multi-scale distribution of pores tends to develop on pore structure with the continuing impact of freeze-thaw and thawing. Dynamic compressive stress-strain curve of sandstone undergoing freeze-thaw can be divided into four phases, and the phase of compaction is inconspicuous compared with the static curve. Elastic modulus and dynamic peak intensity of sandstone gradually decrease with freeze-thaw cycles, while peak strain increases. The higher the porosity is, the more serious the degradation of dynamic intensity is. The porosity is of a polynomial relationship with the dynamic peak intensity.

Shaking table tests and numerical simulation of dynamic properties of underground structures

It is considered thai the damage of the underground structures caused by earthquakes is minor for a long time. However, the catastrophic damages induced by several recent earthquakes （e. g. Kobe earthquake in 1995 ） revealed that the study on the dynamic properties of the underground structures is indispensable. The dynamic behavior and damage mechanism of underground structure are analyzed by using shaking table tests （ both shallow-and deep-buried） and numerical simulation （3D FEM） including horizontal and vertical input motions, individually and simultaneously. From the results, the underground structure collapsed due to strong horizontal forces although vertical deformation is not negligible. The vertical excitation increases the response of structure, especially the stress and shear stress at the upper section; the soil influenced the property of soilstructure system. In the same excitation, the response in shallow-buried test is larger than deep case. Both overburden and vertical earthquake play important roles in the response of structure and those are two critical aspects in the design of the large-span underground structures, such as subway stations.

Human Comfort Evaluation of a Steel-Concrete Composite Building Subjected to Aerobics

The current steel-concrete composite floors design might be susceptible to the resonance phenomenon, causing undesirable vibrations in the frequency range that is the most noticeable to humans, i.e., 4 Hz to 8 Hz. This way, the main objective of this work is to investigate the dynamic structural behaviour of a steel-concrete composite multi-storey building when subjected to human rhythmic activities （aerobics）. The studied structural model represents a typical interior floor bay of a commercial building used for gym and is composed by three floor levels spanning 20 m by 20 m, with a total area of 3×400 m2. An extensive parametric study was developed aiming to obtain the peak accelerations, RMS （root mean square） accelerations and VDV （vibration dose value） values, based on two different mathematical formulations. The human comfort of the building was analysed and the vibration transmissibility related to the steel columns was verified. Based on the found results, the investigated structural model presented high vibration levels that compromise the human comfort.

Oscillating Guided Modes in Graphene-Based Asymmetric Waveguides

We investigate the guided modes in monolayer graphene-based waveguides with asymmetric quantum well structure induced by unequal dc voltages. The dispersion relation for the guided modes is obtained analytically, the structures of the guided modes are discussed under three distinct cases. For the cases of the classical motion and the Klein tunneling, the asymmetric structure does not influence the mode structures dramatically compared with that in the symmetric waveguide. But for the mixing case of the former two, the mode structures and the motion characteristics for the electron and the hole exhibit different behaviors at same condition. The results may be helpful for the practical application of graphene-based quantum devices.

Effects of a flexible joint on instability of a free-free jointed bipartite beam under the follower and transversal forces

This paper deals with the problem of the instability regions of a free-free flexible jointed bipartite beam under the follower and transversal forces as a realistic simulation of a two-stage aerospace structure. The aim of this study is to analyze the effects of the characteristics of a flexible joint on the beam instability to use maximum bearable propulsion force. A parametric study is conducted to investigate the effects of the stiffness and the location of the joint on the critical follower force by the Ritz method and the Newmark method, then to research the vibrational properties of the structure. It has been shown that the nature of instability is quite unpredictable and dependent on the stiffness and the location of the joint. The increase of the follower force or the transversal force will increase the vibration of the model and consequently cause a destructive phenomenon in the control system of the aerospace structure. Furthermore, this paper introduces a new concept of the parametric approach to analyze the characteristics effects of a flexible two-stage aerospace structure joint design.

Structural, Spectroscopic and Vibrational Properties for Low-Lying Electronic States of LiCl

A multireference configuration interaction （MRCI） study has been carried out on the LiCl molecule. The potential energy has been calculated over a wide range of internuclear separation for the 21 low-lying electronic states of the LiCl molecule dissociating into Li （^2S, ^2p, ^3S）＋Cl （^2p）. The （4）^1∑^＋, （3）∏, 1-3^3∑^＋, 1-3^3∏, 1,3Δ, ^1,3∑^-, （5）^1∑^＋,（4）^3∑^＋, （4）^3∏, （4）^3∏ excited states are studied for the first time in theory. Molecular spectroscopic constants .（Re, De,ωe, ωeΧe,Be and αe） have been derived for the 9 bound states （X^1∑^＋, （3）^1∑^＋, （2）^3∑^＋, ^1,3Δ, ^1,3∑^-, （4）^∏, （4）^3∏） with a regular shape, and the spectroscopic constants of ground states X^1 ∑^＋ are in good agreement with available experimental and theoretical values. The relative differences between experimental values and our values for Re, De, ωe, ωeΧe, Be and α3 are 1.02%, 0.60%, 1.72%, 9.46%, 2.0%, and 0.75%, respectively. Moreover, vibrational levels of 9 bound states, which have not been investigated experimentally, are computed.