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Study of Magnetic Vibration Absorber with Permanent Magnets along Vibrating Beam Structure  [PDF]
F. B. Sayyad,N. D. Gadhave
Journal of Structures , 2013, DOI: 10.1155/2013/658053
Abstract: The vibration absorbers are frequently used to control and minimize excess vibration in structural system. Dynamic vibration absorbers are used to reduce the undesirable vibration in many applications such as pumps, gas turbines, engine, bridge, and electrical generator. To reduce the vibration of the system, the frequency of absorber should be equal to the excitation frequency. The aim of this study is to investigate the effect of magnetic vibration absorber along vibrating cantilever beam. This study will aim to develop a position of magnetic vibration absorber along the cantilever beam to adopt the change in vibratory system. The absorber system is mounted on a cantilever beam acting as the primary system. The objective is to suppress the vibration of the primary system subjected to a harmonic excitation whose frequencies are varying. It can be achieved by varying the position of magnetic vibration absorber along the length of beam. The advantage of magnetic vibration absorber is that it can be easily tuned to the excitation frequency, so it can be used to reduce the vibration of system subjected to variable excitation frequency. 1. Introduction Dynamic vibration absorbers are used to reduce undesirable vibrations in many applications such as electrical transmission lines, helicopters gas turbines, engines, and bridges. Traditional treatment methods of vibration control that involve structural modifications are often time consuming and expensive. Some of them can be used as tunable vibration absorbers to control vibrations. Tunable dynamic vibration absorber which is simple to construct can be easily tuned to excitation frequency to minimize the vibrations and can be effectively used to minimize vibrations of structure. Absorber with variable frequencies can be used to minimize vibrations of structures having variable frequency drive. Dynamic vibration absorbers (DVAs) were first invented in 1909 by Hermann Frahm, and since then it has been successfully used to suppress wind-induced vibration and seismic response in buildings. In recent studies, interest has also been focused on the use of feedback and feedforward control systems and the synthesis of DVAs for multiple-degree-of-freedom systems. Igarasi et al. [1] have developed a magnetic dynamic vibration absorber with adjustable natural frequency, in these three permanent magnets arranged with opposite pole to each other. Repelling force between two magnets was used as spring constant. In 1993 they developed a dynamic vibration absorber using permanent magnets to suppress the vibrations of beam
The Nonlinear Tuned Vibration Absorber  [cached]
Viguié R.,Kerschen G.
MATEC Web of Conferences , 2012, DOI: 10.1051/matecconf/20120105007
Abstract: The objective of this paper is to introduce a new nonlinear dynamical absorber, the nonlinear tuned vibration absorber, through a rigorous nonlinear extension of the tuning rule for the linear tuned vibration absorber. This nonlinear tuning methodology combined with the increased suppression bandwidth brought by the intentional use of nonlinearity leads to the development of an absorber that is effective in wide ranges of frequencies and motion amplitudes. The results are illustrated using a one-degree-of-freedom primary system.
Design of Hybrid Dynamic Balancer and Vibration Absorber  [PDF]
Y. R. Wang,C. Y. Lo
Shock and Vibration , 2014, DOI: 10.1155/2014/397584
Abstract: This study proposed a novel hybrid dynamic balancer and vibration absorber that is cheaper than active dampers and more effective than passive dampers. The proposed damping system does not need to be altered structurally to deal with different damping targets. Rather, the proposed vibration absorber is capable of self-adjustment to the optimal damping location in order to achieve balance and, thereby, optimize damping effects. The proposed device includes a groove under the damping target with inertial mass hung from a coil spring beneath. This allows the device to bounce vertically or rotate in order to reduce vibrations in the main body. The coil spring vibration absorber can also slide along the groove in order to adjust its location continuously until the vibrations in the system are minimized and the main body is balanced. Experiments verify the efficacy of the proposed device in improving damping performance beyond what has been achieved using conventional devices. We also provide an explanation of the theoretical underpinnings of the design as well as the implications of these findings with regard to future developments. 1. Introduction Vibration can affect the stability of a structure, and constant vibration can lead to fatigue and structural damage. Babitsky and Veprik [1] studied vibration suppression from the perspective of balance using an elastic beam with a sliding washer damping system. Their results proved that this type of self-damping system is capable of eliminating resonance and decreasing beam vibration. Another approach to maintaining balance is the ball-type automatic balancer system (ABS), comprising several balls moving along a fixed circular orbit. Under proper conditions, the balls move to specific positions of equilibrium, thereby suppressing unbalanced vibrations. The application of this approach in optical disk drives was outlined by Chao et al. [2, 3]. Lu and Hung [4] proposed the balancing of components using two or three balls. Their approach proved to be three times more effective than using a single-ball balancer system. Based on these achievements, this study sought to extend the application of free-moving components in vibrating rigid bodies for the elimination of vibration. Vibration damping methods can roughly be divided into two types: active and passive. Generally speaking, active damping is the most effective approach to vibration damping; however, most conventional machine tools vibrate in the vertical direction, which is best dealt with using a tuned-mass damper (TMD) comprising a mass and one or more springs.
Fatigue Reliability and Calibration of Fatigue Design Factors for Offshore Wind Turbines  [PDF]
Sergio Márquez-Domínguez,John D. S？rensen
Energies , 2012, DOI: 10.3390/en5061816
Abstract: Consequences of failure of offshore wind turbines (OWTs) is in general lower than consequences of failure of, e.g., oil & gas platforms. It is reasonable that lower fatigue design factors can be applied for fatigue design of OWTs when compared to other fixed offshore structures. Calibration of appropriate partial safety factors/Fatigue Design Factors ( FDF) for steel substructures for OWTs is the scope of this paper. A reliability-based approach is used and a probabilistic model has been developed, where design and limit state equations are established for fatigue failure. The strength and load uncertainties are described by stochastic variables. SN and fracture mechanics approaches are considered for to model the fatigue life. Further, both linear and bi-linear SN-curves are formulated and various approximations are investigated. The acceptable reliability level for fatigue failure of OWTs is discussed and results are presented for calibrated optimal fatigue design factors. Further, the influence of inspections is considered in order to extend and maintain a given target safety level.
Vibration Signals and Condition Monitoring for Wind Turbines  [PDF]
Dimitrios Koulocheris, Georgios Gyparakis, Andonios Stathis, Theodore Costopoulos
Engineering (ENG) , 2013, DOI: 10.4236/eng.2013.512116
Abstract:

Rolling element bearings are critical parts of modern wind turbines as they carry the loads of the turning structure and the wind force. The stochastic nature of the wind loads makes it difficult to estimate the useful operational life of the bearings. Condition monitoring of these bearings in a real time environment could be very helpful in estimating their performance and in scheduling maintenance actions when a condition-based maintenance strategy is followed. This procedure can be successfully implemented by using vibration analysis in the time domain or in the frequency domain, giving useful results about the current condition of bearings and the location of potential faults. Permanently located transducers on proper positions on the bearings’ housings can be used in order to collect, process and evaluate real time measurements and provide information about the bearing’s performance. In this work, a test rig is utilized in order to evaluate the performance of rolling bearings. The results of the experimentation are satisfactory and the progress of fatigue failures can be predicted through vibration analysis techniques showing that implementation in real scale may be useful.

Vehicle wheels vibration suppression by dynamic vibration absorber
Zinovij STOTSKO
Transport Problems : an International Scientific Journal , 2007,
Abstract: The article deals with the methods of calculation and optimization ofdynamic processes in vibroexcitated constructions with dynamic absorbers. The improved constructions of such absorbers for vehicle wheels vibration suppression are discussed.
Theoretical Analysis of Mechanical Vibration for Offshore Platform Structures  [PDF]
Saeed A. Asiri, Yousuf Z. AL-Zahrani
World Journal of Mechanics (WJM) , 2014, DOI: 10.4236/wjm.2014.41001
Abstract:

A new class of support structures, called Periodic Structures, is introduced in this paper as a viable means for isolating the vibration transmitted from the sea waves to offshore platform structures through its legs. A passive approach to reduce transmitted vibration generated by waves is presented. The approach utilizes the property of periodic structural components that create stop and pass bands. The stop band regions can be tailored to correspond to regions of the frequency spectra that contain harmonics of the wave frequency, attenuating the response in those regions. A periodic structural component is comprised of a repeating array of cells, which are themselves an assembly of elements. The elements may have differing material properties as well as geometric variations. For the purpose of this research, only geometric and material variations are considered and each cell is assumed to be identical. A periodic leg is designed in order to reduce transmitted vibration of sea waves. The effectiveness of the periodicity on the vibration levels of platform will be demonstrated theoretically. The theory governing the operation of this class of periodic structures is introduced using the transfer matrix method. The unique filtering characteristics of periodic structures are demonstrated as functions of their design parameters for structures with geometrical and material discontinuities, and determine the propagation factor by using the spectral finite element analysis and the effectiveness of design on the leg structure by changing the ratio of step length and area interface between the materials is demonstrated in order to find the propagation factor and frequency response.

An Effective Approach for Optimal PZT Vibration Absorber Placement on Composite Structures  [PDF]
Suresh Venna, Yueh-Jaw Lin
Modern Mechanical Engineering (MME) , 2013, DOI: 10.4236/mme.2013.31002
Abstract:

In this paper, an attempt is made to determine the electric potential that would be generated in the piezoelectric vibration absorber using finite element piezoelectric analysis to determine optimal locations for damping of the first mode. Optimal placement of piezoelectric vibration absorber for passive vibration control application of a cantilever composite plate is investigated. Finite element piezoelectric modal analysis is performed. Models based on placing piezoelectric vibration absorbers at five different locations on the surface of the plate and incorporating piezoelectric properties are built. Modal analysis is used to find the electric potential developed in the piezoelectric vibration absorber. The location that yields the highest amount of electric potential would naturally be the best location for the vibration absorber. First bending mode of the cantilever composite plate is aimed for damping. Results of the analysis are verified with an experimental testing of the composite plate with piezoelectric vibration absorber firmly attached to the plate on the most effective location. A good agreement is found between the analytical and experimental results. Further, a resistive shunt circuit is designed for the passive damping of the first mode and attached to the vibration absorber in which the electric potential developed would be dissipated as heat to obtain passive vibration compensation. The experiment also demonstrates that a damping of 6 percent is obtained in the first mode of vibration and a great amount of damping is achieved in the second and third modes as well.

 

Investigation of Factors Influencing the Structural Vibration in Ball Bearings  [PDF]
Kapil Mehra,Kambiz Farhang,Jayanta Datta
International Journal of Rotating Machinery , 2000, DOI: 10.1155/s1023621x00000300
Abstract: Hertzian equation for elastic contact is utilized along with lumped parameter approach to obtain the equations that govern the structural vibration of ball bearings. The lumped parameter formulation is obtained by treating various elements with mass lumped at their centers of gravity and the contact as nonlinear springs with nonlinear spring rates.
Fundaciones para turbinas eólicas costa afuera Foundations for offshore wind turbines  [cached]
Felipe Alberto Villalobos Jara
Revista ingeniería de construcción , 2009,
Abstract: Este artículo describe el comienzo y la evolución de la hoy en día creciente mundialmente industria de la energía eólica costa afuera. Como un caso particular, se describe la actual política de energías renovables en el Reino Unido. Se explican las características de las cargas ambientales existentes costa afuera, tipos de suelos del fondo marino y las fundaciones que se utilizan comúnmente. El tipo de estructura y régimen de carga establecen nuevas condiciones desde el punto de vista de la Ingeniería Civil. Se presentan las cámaras a succión como una fundación alternativa para turbinas de viento costa afuera. Las cámaras a succión son actualmente una alternativa aceptada en vez de usar pilotes en aplicaciones para la industria del petróleo y el gas. Sin embargo, este no es el caso todavía en aplicaciones para aerogeneradores costa afuera. This paper describes the beginning and evolution of the now worldwide growing offshore wind energy industry. In particular, the current renewable energy policy in the UK is described. The characteristics of the environmental loads offshore, type of seabed soils and foundations commonly adopted are explained. The type of structure and loading regime establish new conditions from a Civil Engineering point of view. Suction caissons are introduced as an alternative foundation for offshore wind turbines. Suction caissons are currently an accepted alternative to pile foundations in applications for the oil and gas industry. However, this is not yet the case in applications for offshore wind turbines.
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