• Journal of the Korean Society for Precision Engineering
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• v.13 no.12
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• pp.129-135
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• 1996

This paper presents the effectiveness of the dynamic vibration absorber consisting of a single mass, coil springs and oil damper on the resonance freauency ratio and amplitude ratio for damped linear systems, that is, primary vibration system with damping. The effects of the dynamic vibration absorber are investigated numerically and experimentally for values of mass ratio, natural frequency ratio, and damping ratio. The experimental results show good agreement with calculated ones. As a result, the characteristics shown by the present work are useful in optimal tuning the dynamic vibration absorber in practice.

• Journal of Ocean Engineering and Technology
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• v.25 no.1
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• pp.8-13
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• 2011

A compact array system of small buoys is used for wave energy extraction. To evaluate the performance of this system, hydrodynamic analysis is carried out in regular waves using the higher order boundary element method. The motion response of each buoy is calculated considering hydrodynamic interactions caused by other buoys. The effect of energy extraction device is modeled as a linear damping load. The efficiencies of energy conversion are compared using the various sizes and arrangements of the array system and the damping coefficients for energy extraction. The increase in size or the packing ratio of the system gives better efficiency. However, the wave condition and the cost for the system should be considered to optimize performance from the perspective of engineering and economics. The proposed nondimensionalized damping coefficient for energy extraction is 0.1~0.5.

• Earthquakes and Structures
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• v.9 no.1
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• pp.221-232
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• 2015

In this study, Homotopy Perturbation Method (HPM) is used to solve the nonlinear oscillators with damping. We have considered two strong nonlinear equations to show the application of the method. The Runge-Kutta's algorithm is used to obtain the numerical solution for the problems. The method works very well for the whole range of initial amplitudes and does not demand small perturbation and also sufficiently accurate to both linear and nonlinear physics and engineering problems. Finally to show the accuracy of the HPM, the results have been shown graphically and compared with the numerical solution.

• Transactions of the Korean Society of Automotive Engineers
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• v.11 no.5
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• pp.156-162
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• 2003

The shock absorber is a part having a direct influence on the ride comfort, stability and dynamic load prediction of a vehicle. Thus, a rationally modeled shock absorber should be required in the dynamic analysis of vehicles. This thesis presents a modified model, based on Worden's hyperbolic tangent function, in order to fit experimental data on the velocity-damping force of a shock absorber. The hyperbolic tangent function correctly indicates the characteristics of a shock absorber, and has the advantage of containing physical causality. To evaluate the method, comparative evaluations of the linear model, the 5th polynomial model and Worden's model were carried out. The function presented in this paper is not only simple but also makes it possible to estimate the function coefficients easily and visually. In addition, it has the advantage of containing physical causality. Lastly, it effectively models the damping force of a shock absorber.

• Proceedings of the Computational Structural Engineering Institute Conference
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• 2006.04a
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• pp.264-271
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• 2006

Stay cables, such as used in cable-stayed bridges, are prone to vibration due to their low inherent damping characteristics. It has been reported that a semiactive control system using MR dampers could potentially achieve both the better performance compared to a passive control system and the adaptability with few of the detractions. However, a control system including a power supply, a controller and sensors is required to improve the control performance of MR dampers. This complicated control system is not effective to most of large civil structures such as long-span bridges and high-rise buildings. This paper proposes a smart damping system which consists of an MR damper and the electromagnetic induction (EMI) part that is considered as an external power source to the MR damper. The control performance of the proposed damping system has been compared with that of the passive-type control systems employing an MR damper and a linear viscous damper.

• Transactions of the Korean Society of Mechanical Engineers
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• v.17 no.11
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• pp.2742-2751
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• 1993

Nonclassically damping domes from drastic variations of energy absorption rates of the materials in different parts of structures, or from the external damping sources inserted into the structures. In this study, an approximate method to calculate the frequency response of a method is superior to other approaches in respect of computational effort and accuracy. In addition, when frequency response is calculated by neglecting the off-diagonal elements of modal damping matrix, a criterion to ensure small errors is derived. In is shown that the criterion can be described as the vector sum of each modal coupling to the corresponding mode.

• Journal of the Society of Naval Architects of Korea
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• v.49 no.5
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• pp.425-432
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• 2012

Viscous flow fields of side-by-side arranged two-dimensional floating bodies are numerically simulated by a Navier-Stokes equation solver. Two identical bodies with a narrow gap are forced to heave and sway motions. Square and rounded bilge hull forms are compared to find out the effects of vortex shedding on damping force. Wave height, force RAOs, added mass and damping coefficients including non-diagonal cross coefficients are calculated and a similarity between the wave height and force RAOs is discussed. CFD which can take into account of viscous damping and vortex shedding shows better results than linear potential theory.

• Journal of KSNVE
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• v.10 no.1
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• pp.64-73
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• 2000

We present finite element equations in the Laplace-domain for linear viscoelastic and viscoelstically damped structures governed by a constitutive equation involving factional order derivative opeartors. These equations yield a nonstandard eigenproblem consisted of frequency dependent stiffness matrix. To solve this nonstandard eigenproblem we suggest an eigenvalue iteration procedure in the Laplace-domain. Improved Zenor and GHM material function type constitutive equations in the Laplace-domain are also available for this procedure. From above equations, complex eigenvalues and complex eigenvectors are obtained. Using obtained eigenvalues and eigenvectors, time domain analysis is performed by means of mode superposition. Finally, finite element solutions of viscoelastic and viscoeleastically damped sandwich beam are presented as an example.

• Journal of Ocean Engineering and Technology
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• v.22 no.1
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• pp.70-74
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• 2008

It is important to reduce the vibration and noise of submarines and ships. For the purpose of noise reduction, various researches are actively being conducted on the employment of complex structures. However, in the case of numerical analysis for complex structures with damping materials, substantial errors can be generated by the absence of an exact damping model. Thus experimental model analysis is necessary for the verification of a numerical analysis for complex structures. In this research, vibration experiments are conducted in order to ascertain the vibration properties of cantilever beam attached damping materials. First, an initial value is obtained by using a direct linear method. Next, based on this initial value, the exact modal parameters of the cantilever beam are obtained by using the Newton-Raphson method.

• Structural Engineering and Mechanics
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• v.34 no.1
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• pp.109-133
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• 2010

This paper addresses the modified Dynamic Relaxation algorithm, called mdDR by minimizing displacement error between two successive iterations. In the mdDR method, new relationships for fictitious mass and damping are presented. The results obtained from linear and nonlinear structural analysis, either by finite element or finite difference techniques; demonstrate the potential ability of the proposed scheme compared to the conventional DR algorithm. It is shown that the mdDR improves the convergence rate of Dynamic Relaxation method without any additional calculations, so that, the cost and computational time are decreased. Simplicity, high efficiency and automatic operations are the main merits of the proposed technique.