Non-linear vibration of bimaterial magneto-elastic cantilever beam with thermal loading

Formulas and numerical results are studied for the transient vibration and dynamic instability of a bimaterial magneto-elastic cantilever beam which is subjected to alternating magnetic field and thermal loading. Materials are assumed isotropic, and the physical properties are assumed to have unique values in each layer. The governing equation of motion is derived by the extended Hamilton's principle, in which the damping factor, the electromagnetic force, the electromagnetic torque, and the thermal load are considered. The solution of thermal effect is obtained by superposing certain fundamental linear elastic stress states which are compatible with the Euler–Bernoulli beam theory. The axial stresses results are found to be in good agreement with some known numerical solutions. Using Galerkin's method, the equation of motion is reduced to a time-dependent Mathieu equation. The numerical results of the regions of dynamic instability are determined by the incremental harmonic balance (IHB) method, and the transient vibratory behaviors are presented by the fourth-order Runge–Kutta method. The results show that the responses of the transient vibration and dynamic instability of the system are influenced by the magnetic field, the thickness ratio, the excitation frequency, but not by the temperature increase in this study.     

滑块在平面上是如何运动的

滑块在平面上的运动在完全刚性地基假设下其运动方程存在内在的矛盾. 在将地基看作 弹性的前提下求解了这个问题,并根据所得解的物理意义,解释了摩擦激振的基本原理.     

PI force feedback control for large flexible structure vibration with active tendons

Active tendon, consisting of a displacement actuator and a collocated force sensor, was first presented by Preumont and his co-workers to attenuate the vibration of large flexible space structures, and the control algorithm adopted by them was integral force feedback. This paper presents a new proportional-integral （PI） force feedback algorithm to achieve larger damping ratios for the structure without the requirement of structure model. Stability of the control system is shown, and simulations of a structure similar to JPL-MPI demonstrate the effectiveness of the proposed algorithm for vibration control of space structures.     

Analysis for the optimal location of cable damping systems on stayed bridges

Computational models are increasingly being used for the dynamic analysis of structures with nonlinear or uncertain behavior, such as cables in stayed bridges, which nowadays are progressively more used as an alternative for long span and slim structures. In this work, a 3D nonlinear model is described to evaluate the wind dynamic effects on cables for this type of bridges under different scenarios, but also for health monitoring and structural simulation to guarantee performance, evaluate load capacity and estimate life prediction. Fatigue is one of the most relevant and complex failure causes in highway bridges, particularly on the anchorage elements of the cables in stayed bridges; where dampers may be used to minimize the dynamic behavior of the structure and reduce fatigue damage. With this nonlinear simulation model, different damper locations and configurations are evaluated to find the optimal position. A feasibility function is used as a weighting function to take into account the damper’s size and design. Analysis is particularly focused for a real cable stayed bridge in the state of Veracruz in México. Although the geometry, the forces and the stresses on cable structures are a challenge, even for structural specialists, the results from this work using the proposed 3D nonlinear model showed to be accurate for the simulation of many different wind scenarios, and damper’s location and orientations. Finally, the feasibility weighting function enabled the geometrical limitations to estimate the best location of a damper system to minimize the risk for fatigue failure.     

Effects of shear deformation on vibration of doublewalled carbon nanotubes embedded in an elastic medium

In this study, free vibration of simply supported multi-walled carbon nanotubes (CNTs) embedded in an elastic medium was investigated by using the generalized shear deformation-beam theory (GSDBT). The effects of surrounding elastic medium, which is considered as a spring, defined by the Winkler model, and van der Waals forces from adjacent nanotubes are taken into account. Third-order shear deformation (TOSD) theory is used to study free vibration of a multi-walled carbon nanotube embedded in an elastic medium. Unlike Timoshenko beam theory, TOSD theory satisfies zero traction boundary conditions on the upper and lower surface of the structures, so there is no need to use a shear correction factor. Free vibration frequencies and amplitude ratios were obtained for various sides to thickness ratios and elastic medium effects and results are compared with previous studies. The results showed that significant difference exist between TOSD and Euler beam theory. It is also interesting to note that, although frequency parameter is increasing by increasing stiffness of embedded medium, amplitude ratios are insensitive to stiffness of embedded elastic medium. Dedicated to the honorable memory of my beloved mother Fatma Aydogdu (Romania,1933-Tekirdag, August 7, 2007)     

BSO晶体的高温拉曼光谱与高温结构特征

阐述了BSO晶体在常温下的结构特征,通过测量晶体在常温下的拉曼光谱,对晶格主要振动模式进行了指认,测量晶体升温至熔化过程中不同温度下的拉曼光谱,分析研究了其微观结构在升温过程中的变化以及在高温状态下的结构特征。     

换流站电力电容器塔的噪声预测

电力电容器塔是换流站的主要噪声源之一,因单元数量多、声波相干性作用复杂、单元间相互遮挡等,难以对其进行准确的噪声预测。该文通过实验方法获得电容器单元的表面振动加速度,采用边界元模型计算电容器塔辐射的噪声,并运用噪声预测评估软件对电容器塔进行建模,包括完整建模和简化为点声源、线声源及工业建筑物的建模。研究表明：边界元模型和完整建模方法能够考虑到电容器单元的声辐射指向性和单元间的遮挡作用,前者还能考虑到单元内不同壁面处相位差、单元间声波相干性的影响,比后者能较好地反映声场分布特点;简化点声源和线声源的方法预测结果相近,均无指向性且预测的总声功率偏高;简化工业建筑物的方法考虑了电容器塔的声辐射指向性和遮挡作用,方法简单且能较准确地预测总声功率。     

超导磁体螺栓结合面低温振动特性研究

振动特性对于超导磁体的各类工程应用具有重要意义, 螺栓法兰盘连接是超导磁体系统的一种常见的支撑结构类型, 然而螺栓结合面在低温条件下振动特性的相关研究目前尚少见报道. 本研究中设计加工了简化的连接结构, 在室温和液氮温度对其螺栓结合面进行振动特性的测试分析. 接下来, 采用集中质量法进行建模, 并利用振型、 频率与质量矩阵、 刚度矩阵的关系求解了不同螺栓预紧力情况下的刚度矩阵, 得到了系统总刚度和结合面刚度. 使用上述方法对振动测量数据计算发现, 该结构的系统总刚度与结合面刚度都随着预紧力增大而增大, 同时液氮低温条件可使系统总刚度和结合面刚度进一步增大.     

Understanding MOF Flexibility: An Analysis Focused on Pillared Layer MOFs as a Model System

Flexible porous frameworks are at the forefront of materials research. A unique feature is their ability to open and close their pores in an adaptive manner induced by chemical and physical stimuli. Such enzyme-like selective recognition offers a wide range of functions ranging from gas storage and separation to sensing, actuation, mechanical energy storage and catalysis. However, the factors affecting switchability are poorly understood. In particular, the role of building blocks, as well as secondary factors (crystal size, defects, cooperativity) and the role of host–guest interactions, profit from systematic investigations of an idealized model by advanced analytical techniques and simulations. The review describes an integrated approach targeting the deliberate design of pillared layer metal–organic frameworks as idealized model materials for the analysis of critical factors affecting framework dynamics and summarizes the resulting progress in their understanding and application.     

Piezoelectric atomization of liquids with dynamic viscosities up to 175 cP at room temperature

Piezoelectric atomization has been applied in the field of respiratory medicine delivery and chemistry. However, the wider application of this technique is limited by the viscosity of the liquid. High-viscosity liquid atomization has great potential for applications in aerospace, medicine, solid-state batteries and engines, but the actual development of atomization is behind expectations. In this study, instead of the traditional model of single-dimensional vibration as a power supply, we propose a novel atomization mechanism that uses two coupled vibrations to induce micro-amplitude elliptical motion of the particles on the surface of the liquid carrier, which produces a similar effect as localized traveling waves to push the liquid forward and induce cavitation to achieve atomization. To achieve this, a flow tube internal cavitation atomizer (FTICA) consisting of a vibration source, a connecting block and a liquid carrier is designed. The prototype can atomize liquids with dynamic viscosities up to 175 cP at room temperature with a driving frequency of 507 kHz and a voltage of 85 V. The maximum atomization rate in the experiment is 56.35 mg/min, and the average atomized particle diameter is 10 µm. Vibration models for the three parts of the proposed FTICA are established, and the vibration characteristics and atomization mechanism of the prototype were verified using the vibration displacement measurement experiment and the spectroscopic experiment. This study offers new possibilities for transpulmonary inhalation therapy, engine fuel supply, solid-state battery processing and other areas where high-viscosity microparticle atomization is needed.