磁悬浮系统结构静刚度与结构动刚度测量实验

在提出结构静刚度与结构动刚度定义的基础上,用加载砝码法和用B&K振动仪加载正弦信号的实验方法测量磁悬浮盘片系统结构静刚度与结构动刚度,得到激振频率—位移曲线图、激振频率—动刚度曲线图、外力—位移曲线、外力—动刚度曲线图,从中找出磁悬浮系统结构静刚度与动刚度的规律、特点,并比较不同实验方案的结果,验证了实验的合理性与数据的正确性,为进一步理论研究磁悬浮系统的支承特性提供实验依据。

立式循环泵结构动刚度对转子振动特性的影响

采用有限元法对AP1000核电厂立式循环泵转子部件的支承结构动刚度进行分析,结果显示其支承结构的动刚度值随着频率的增加而逐渐降低,其动刚度曲线在结构共振频率点发生急剧的下降。结合该分析结果,分别针对刚性支承、水润滑轴承支承以及考虑支承结构动刚度3种情况下的转子振动特性进行对比分析。分析结果显示,在上述3种情况下,转子1阶横向弯曲振动频率变化较小,其频率值分别为28.1、18.7、15.3 Hz,转子高阶振动频率及振型受支承动刚度影响较大。在考虑支承动刚度的影响情况时,转子高阶振动频率下降明显。

结构动刚度数据处理系统的开发和应用

本文针对结构动刚度试验-数据分析和处理中碰到的实际问题,配备了一套数据分析处理系统,并为此研究出了一套具有自动采样分析、计算、处理、存贮、打印及绘图等功能的软件。这使结构动刚度试验既方便又准确,而且试验范围得以扩充,能在获得结构动刚度的同时,又能得到相位、阻尼等参数,从而打破了以往试验数据单调、数据处理繁琐的局面。这为进一步研究结构动态特性提供了一套既有形象化曲线又有实用价值的数据文件的完整资料。

国产600MW汽轮发电机组振动问题分析及治理

国产600MW汽轮发电机组在运行过程中普遍存在某些振动问题,如低压转子轴承座振动大、高负荷工况高中压转子轴承突发性振动、发电机转子不稳定振动和集电小轴稳定轴承振动大等,严重影响机组的安全、可靠运行。对国产600MW机组的振动特征和振动原因进行分析,并总结了振动处理过程的有效措施。

国产600MW汽轮发电机组振动问题分析及治理

国内三大动力集团公司生产的600MW机组在运行过程中存在一些振动问题,如低压转子轴承座振动大、大负荷工况高中压转子轴承突发性振动、发电机转子不稳定振动和集电小轴稳定轴承振动大等,严重影响机组的安全可靠运行。本文阐述了国产600MW机组的振动特征,分析了振动原因,并总结了处理过程,给出现场振动治理的措施。

The Influence of Edge Restraining Stiffness on the Transverse Vibrations of Rectangular Plate Structures

This paper presents an analytical study on the influence of edge restraining stiffness on the transverse vibrations of rectangular plate structure. An improved Fourier series method was employed to analyze the transverse vibration of plate structure with general elastically restrained boundary conditions. A linear combination of a double Fourier series and eight auxiliary terms was sought as the admissible function of the flexural displacement of the plate, each term being a combination of a polynomial function and a single cosine series expansion. The auxiliary terms were introduced to ensure and improve the smoothness of the original displacement function and its derivatives at the boundaries. Several numerical examples were given to demonstrate the validity and accuracy of the current solution. The influences of translational and rotational stiffness on the natural frequencies and mode shapes of plate were analyzed by numerical results. The results show that the translational stiffness has bigger influence on the natural frequencies than the rotational stiffness. It is generally well known that little change of the rotational stiffness has little influence on the mode shapes of plate. However, the current work shows that a very little change of rotational stiffness value may lead to a large change of the mode shapes of a square plate structure.

Dynamic stiffness for thin-walled structures by power series

The dynamic stiffness method is introduced to analyze thin-walled structures including thin-walled straight beams and spatial twisted helix beam. A dynamic stiffness matrix is formed by using frequency dependent shape functions which are exact solutions of the governing differential equations. With the obtained thin-walled beam dynamic stiffness matrices, the thin-walled frame dynamic stiffness matrix can also be formulated by satisfying the required displacements compatibility and forces equilib-rium, a method which is similar to the finite element method (FEM). Then the thin-walled structure natural frequencies can be found by equating the determinant of the system dynamic stiffness matrix to zero. By this way, just one element and several elements can exactly predict many modes of a thin-walled beam and a spatial thin-walled frame, respectively. Several cases are studied and the results are compared with the existing solutions of other methods. The natural frequencies and buckling loads of these thin-walled structures are computed.

Changes in Coupled Vibration Frequencies and Modes of Wall-Cavity Systems Induced by Stiffness Variation in the Structure

Problems of fluid structure interactions are governed by a set of fundamental parameters. This work aims at showing through simple examples the changes in natural vibration frequencies and mode shapes for wall-cavity systems when the structural rigidity is modified. Numerical results are constructed using ANSYS software with triangular finite elements for both the fluid （2D acoustic elements） and the solid （plane stress） domains. These former results are compared to proposed analytical expressions, showing an alternative benchmark tool for the analyst. Very rigid wall structures imply in frequencies and mode shapes almost identical to those achieved for an acoustic cavity with Neumann boundary condition at the interface. In this case, the wall behaves as rigid and fluid-structure system mode shapes are similar to those achieved for the uncoupled reservoir case.

Influence of System Uncertainties on Structural Damage Identification through Ambient Vibrations of Steel Structures

The practical difficulties presented by forced vibration testing of large steel structures, such as tall buildings, transmission lines or bridges, led to an increased interest in structural monitoring through ambient vibrations, which usually allows the proper identification of modal properties, natural frequencies, damping and modes of vibration. Changes in these modal properties constitute an indication of structural damage, which may then be assessed on the basis of experimental evidence. The authors proposed an approach to determine the so-called damage damping and stiffness matrices, which are essential to identify the location and intensity of damage. No restrictions were introduced on the damping matrix of the system. The approach requires ambient vibration data of all relevant coordinates used in the structural model, which are processed employing the SSI method. In practice, the identification method is seriously hampered by ambient factors such as temperature or humidity. In general those effects must be filtered out in other to obtain a reliable diagnosis of damage, approach that demands long term monitoring. In this paper, an alternative approach is explored, based on the introduction of error damping and stiffness matrices. Data on both matrices is generated on the basis of observed variations of structural member stiffness and damping caused by ambient factors. The influence of this uncertainty on the identified spectral properties is assessed by simulation.

Modal Approach to the Condensed Dynamic Stiffness Evaluation

The author proposes to obtain the dynamic stiffness for the multiply-supported structures condensed to the supports in the frequency domain using the modal approach. Thus, previously proposed approach, requiring the dynamic inertia matrix for the single-base system, is extended for the multiply-supported systems. Modal analysis is performed twice： once for the structural model with one base fixed, then for the same model with all bases fixed. The applicability of the proposed approach is checked for a sample two-base system enabling analytical solutions both in precise and modal approaches. The format of the condensed dynamic stiffness in the frequency domain enables to combine finite-element-method （FEM） codes like ABAQUS and Soil-Structure Interaction （SSI） codes like SASSI or CLASSI in a complex to perform effective soil-structure interaction analysis.

Dynamic Behaviors of a Moored Floating Structure with Flexible Skirts

A numerical model was developed by using the dual boundary element method to investigate the dynamic behavior of a moored floating structure with a pair of vertical and flexible skirts attached at its bottom in the linear wave field. Theoretical conception is based on potential theory with linear external forces. The motions of the structure were assumed to be small and linear. The flexible skirts mounted beneath the structure were assumed uniform flexural rigidity and the thickness of the skirts was negligible. Comparison between the present model and Gesraha＇s solution was made to verify the results for a moored floating structure with or without rigid skirts. The influence of the skirt rigidity on the moored floating structure, moored lines and waves is investigated in this study. The results show that, the natural frequencies of structure＇s oscillation, moored force, wave reflection and transmission tend to the region of short-period waves when the flexible rigidity gradually decreases. Positive correlation exists between the aft mooring force and the pitch motion of the floating structure.