抑制电力系统低频振荡综述

从低频振荡的起因开始,指出目前研究低频振荡的几种方法,综述了抑制低频振荡的措施.针对目前PSS仍然是抑制低频振荡的最好方法,重点比较了传统PSS和其他各种PSS抑制低频振荡的效果.文章还从大处着眼分别对低频振荡研究方法和抑制低频振荡策略进行了分析和比较,阐明了各自的优缺点.最后阐述了目前电力系统运行方式的复杂性,并分析了抑制低频振荡的策略,对未来的发展动向做了进一步的探讨.     

On the problem of dynamic damping of torsional oscillations of a machine drive

The efficiency of a Pringle dynamic damper used for suppressing forced and parametric torsional oscillations of a main drive taking into account the variable reduced moment of inertia of the machine and dynamic performance of the electric motor is investigated.     

Development of FAMD code to calculate the fluid added mass and damping of arbitrary structures submerged in confined

In this paper, the numerical finite element formulations were derived for the linearized Navier-Stokes’ equations with assumptions of two-dimensional incompressible, homogeneous viscous fluid field, and small oscillation and the FAMD (Fluid Added Mass and Damping) code was developed for practical applications calculating the fluid added mass and damping. In formulations, a fluid domain is discretized with C°-type quadratic quadrilateral elements containing eight nodes using a mixed interpolation method, i.e., the interpolation function for the velocity variable is approximated by a quadratic function based on all eight nodal points and the interpolation function for the pressure variable is approximated by a linear function based on the four nodal points at vertices. Using the developed code, the various characteristics of the fluid added mass and damping are investigated for the concentric cylindrical shell and the actual hexagon arrays of the liquid metal reactor cores.     

Dynamic damping of oscillations of the transmission output shaft of a car with an internal combustion engine

For the transmission gear box containing the mechanisms with immovable wheel axes and a planetary differential, the problem of synthesis of dynamic parameters of the model of the transmission output shaft providing dynamic damping of oscillations is solved. The problem is solved for the two highest stages of the transmission box on the fixed engine revolutions at two frequencies with the maximum amplitudes found during decomposition of the perturbing action of the engine into Fourier series. The method developed permits solving the problem of dynamic damping of oscillations for the transmission boxes with two-shaft composition. The unengaged gear wheels are used as the dynamic damper of oscillations transmitted from the engine crankshaft to the transmission. It permits reducing the wear of gear transmissions, decreasing the noise and vibration of transmission.     

粘性阻尼与可调阻尼的探讨

探对了粘性阻尼的实现原理,分析了在单自由度隔振和多维隔振中阻尼对于减小振动幅度和物体加速度的重要作用,介绍了基于电流变、磁流变的阻尼调节方法,又从粘性阻尼器原理出发,论述了电磁以外的调节阻尼的技术手段.最后提出将液压缸和气缸用作阻尼器的新思想,并说明气缸阻尼器在多维隔振中的应用.     

阻尼层对自由阻尼处理结构的影响

在表面阻尼处理结构中,介绍了描述普通的阻尼层材料的贮能模量以及损耗因子随温度变化的规律,建立了自由阻尼处理梁的结构损耗因子的计算公式.通过数值计算揭示了自由阻尼处理梁的耗散特性.通过改变温度、阻尼层厚度、敷设纤维材料等不同的方法达到改变损耗因子的目的,给出了在不同条件下通过数值计算得出的结论,并比较这几种不同的方法对损耗因子的改变有何不同.     

Decomposition of process damping ratios and verification of process damping model for chatter vibration

In the previous study, by the same authors, titled “A new process damping model (PDM) for chatter vibration (Measurement, 44 (8) (2011) 1342–1348)”, a new approach has been presented for obtaining process damping ratios (PDRs). This PDM has been constituted on the basis of the shear angle (φ)$(\phi )$ oscillations of the cutting tool and the alteration of the penetration forces when they penetrate into the wavy surface. Variation and quantity of PDR are predicted by reverse running analytical calculation procedure of traditional Stability Lobe Diagrams (SLDs). In this study, firstly, how the PDM in previous study results with different materials such as AISI-1050 and Al-7075 are examined. Then, two problems are solved: how much of the total PDR of cutting system is caused by the tool penetration and how much is caused by (φ)$(\phi )$ oscillation? Finally, verification of PDR values and PDM are performed by energy equations.     

Anomalous high-frequency oscillations in a field emission tube and their significance in pulsed field emission

Relaxation oscillations occur when a capacitor is inserted in series with a field emission tube, a DC high-voltage power supply, and a ballast resistor. The waveform of these oscillations is highly reproducible with a dominant frequency of 200 MHz and a decay time of 20 ns. The peak current as high as 320 mA has been observed although the tungsten emitter is only rated for 10 microA. We have shown that these oscillations are due to a displacement current, charging of the anode-tip capacitance, and are not of a field emission origin. We conclude that the effects of displacement current should be considered in measurements of field emission with microsecond pulses, where high-current densities can be observed.     

Stiffness and damping characteristics of finite width journal bearings with a non-newtonian film and their application to instability prediction

Starting from the most general fluid flow equation of the power law type expressing rate of shear in terms of powers of shear stress for non-Newtonian lubricants a modified form of Reynolds'equation is derived for dynamically loaded finite width journal bearings. The finite difference technique with successive over relaxation is used incorporating Reynolds' boundary conditions for pressure to obtain the pressure distribution. From the equations of fluid film forces, the values of stiffness and damping coefficients are obtained for a linearised case. The shear thinning effect of non-Newtonian lubricants at higher shear rates is shown to decrease the stiffness and damping values. Finally, the stability limit for such a bearing is obtained for different values of the nonlinear factor.     

Vertical oscillations of the working unit of a bucket-wheel excavator in a pit face and their suppression

The formation of a vertical component of the cutting force in the case of elastic flexibility of a working unit is investigated. The increased tendency of bucket-wheel excavators to oscillations is found to be associated with scoop periodicity and low dissipative ability of the oscillatory system, the latter additionally decreased during the cutting process due to “pumping” of energy to the oscillatory system from the drive of the working unit. Requirements on both the design and the parameters of the cutting equipment eliminating this pumping and ensuring effective suppression of different oscillations by dissipation of the energy of the oscillatory system directly in the cutting process have been determined.     

新型环槽锁固铆接元件及其应用

论述国内、外几种先进的环槽锁固铆接元件的典型结构、压塑成形机理和性能特点 ,并介绍它们在生产、施工中的实际应用     

Hydroelastic vibration of the bottom plate of the cylindrical tank coupled with sloshing

Journal of Mechanical Science and Technology - This study is concerned with the hydroelastic vibration of the flexible bottom plate of a cylindrical tank coupled with sloshing. The cylindrical tank...     

Passive vibration damping enhancement of piezoelectric shunt damping system using optimization approach

Piezoelectric materials can be used for structural damping because of their ability to efficiently transform mechanical energy to electrical energy and vice versa. The electrical energy may be dissipated through a connected load resistance. In this paper, a new optimization technique for the optimal piezoelectric shunt damping system is investigated in order to search for the optimal shunt electrical components of the shunt damping circuit connected to the piezoelectric patch on a vibrating structure for the structural vibration suppression of several modes. The vibration suppression optimization technique is based on the idea of using the piezoelectric shunt damping system, the integrated p-version finite element method (p-version FEM), and the particle swarm optimization algorithm (PSOA). The optimal shunt electrical components for the piezoelectric shunt damping system are then determined by wholly minimizing the objective function, which is defined as the sum of the average vibration velocity over a frequency range of interest. Moreover, the optimization technique is performed by also taking into account the inherent mechanical damping of the controlled structure with the piezoelectric patch. To numerically evaluate the multiple-mode damping capability by the optimal shunting damper, an integrated p-version FEM for the beam with the shunt damping system is modeled and developed by MATLAB. Finally, the structural damping performance of the optimal shunt damping system is demonstrated numerically and experimentally with respect to the beam. The simulated result shows a good agreement with that of the experimental result. This paper was recommended for publication in revised form by Associate Editor Eung-Soo Shin Jin-Young Jeon received his Ph.D. degree in Mechanical and Aerospace Engineering from Tokyo Institute of Technology in 2005. Dr. Jeon is currently a senior engineer at Digital Printing Division, Digital Media & Communications Business at Samsung Electronics Co., Ltd., Korea. His research interests are the areas of structural-acoustic optimization, sound quality, motion quality, and vibration control.     

Experimental and theoretical modal analysis of constructions with fatigue cracks

On the basis of experimental and theoretical modal analysis, the appearance of fatigue cracks with various depths within rotor systems is studied. For cracks with various depths, stress values in the place of occurrence of a defect are obtained. By means of obtained stresses, it is possible to reveal fatigue cracks with a depth of 15% of the cross-sectional area of a shaft.     

Variable stiffness and damping magnetorheological isolator

This paper presents the development and characterization of a magnetorheological (MR) fluid-based variable stiffness and damping isolator. The prototype of the MR fluid isolator is fabricated, and its dynamic behavior is measured under various applied magnetic fields. The parameters of the model under various magnetic fields are identified, and the dynamic performance of the isolator is evaluated in simulation. Experimental results indicate that both the stiffness and damping capability of the developed MR isolator can be controlled by an external magnetic field.     

Co-localization of the cellulose framework and cell-wall matrix in helicoidal constructions

Affinity methods (enzymes, lectins and antibodies used as specific probes) were applied in order to target cellulose and the major matrix components in cell walls of dicotyledons built up as helicoids. The probes were the enzyme cellobiohydrolase, CBH1, for cellulose, polyclonal antibodies and the lectin RCA (Ricinus communis agglutinin) for xyloglucans, and monoclonal antibodies JIM5 or JIM7 for homogalac-turonan sequences (according to their degree of esterification). Observations were performed: (i) in muro and/or on heteromolecular fractions following controlled cell-wall dissociation experiments; and (ii) at the light microscope level and/or at the electron miscroscope level by means of various visualization markers. Affinity labelling was complemented by subtractive cytochemistry and by the labelling of available anionic groups by means of cationic gold particles. Data confirm the importance of using a variety of probes, the combination of which allows the acquisition of convergent and complementary results. Concerning the particular case of helicoidal walls of elongating cells, it was shown that cellulose was always co-localized with xyloglucans and homogalacturonan polymers in zones where the cholesteric order was well defined. Cellulose was always associated with compatible hemicellulose polymers capable of binding tightly. Moreover, residual charges were always present along the microfibrils, forming an anionic coat able to repel the adjacent cellulose microfibrils. A possible role of the heteromolecular association of xyloglucan and pectate as a surfactant allowing the cholesteric assembly is hypothesized.     

Design evaluation of durability of extended constructions of mains

Basic concepts for evaluating durability of mains are formulated as problems of the strength and safety of extended constructions under the action of random operational loads and effects. A system of sequential operations resulting in determination of the critical time of exploitation of the pipeline section is constructed. Acceptable values of probability components of potential damage for pipeline sections belonging to three durability classes are given. The choice of the durability criterion of a construction element and conditions of safe operation of a pipeline section from the point of view of durability are considered as one of the fundamental blocks of the algorithm.     

浅谈不锈钢潜水泵的设计

根据生产试验过程中积累的一些经验．总结出潜水泵结构特点材料选用．从而引出不锈钢潜水泵在设计上的特点。