• Journal of Ocean Engineering and Technology
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• v.11 no.1
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• pp.65-73
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• 1997

The floating body discussed in this study is a 2-D rectangular floating unit supported by four vertical piles at its corners. Structures of this type are frequently seen as floating piers for the crafts in a small harbour. The movement in some modes of motion of such a flating body is fully or partially restrincted by the piles. The authors(Kim et al. 1994) carried out a series of model tests on its wave control function, its motion and the loads on piles. The experimental results showed that a certain degree of intial constriction force which clamps the floating unit in the horizontal direction can effectively reduce the body motion and wave energy without increasing mooring forces. This may be due to the friction forces occuring between the piles and the rollers installed in the mooring equipments on the floating unit. In this paper, we develop a numerical model for the prediction of wave transformation and floating body motions, where the friction force is idealized as the Coulomb friction and linearized into a damping force using the equivalent damping cofficient. This linearization is verified by comparing the results of motions between the linear and nonlinear analysis of the ezuations of motion. We further compare the caculation results by the linear model with the experimental results and discuss the effect of the friction force or the constriction force on body motions and wave energy dissipation.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.31 no.2A
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• pp.89-96
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• 2011

The damping ratio as an index of bridge vibration could be considered as one of the important dynamic characteristics of a suspension bridge. But estimating of damping ratio on an existing suspension bridge under ambient vibration condition could be a laborious task. Moreover, it is not simple to directly distinguish aerodynamic damping and friction damping from apparent damping. According to previous studies, the aerodynamic damping properties can be linearly affected by wind speed level, and apparent damping ratio can be affected by amplitude of vibration. Therefore, in this article, the relationships among damping ratio, wind speed level and amplitude of acceleration were studied for separating extract aerodynamic damping and friction damping from apparent damping. Damping ratios on Sorok Bridge, a suspension bridge which is a located in Go-Heung, Korea, were estimated by two different methods as using Hilbert transform and extended Kalman filter which were well known as effective estimation methods for non-linear state. It was possible to distinguish aerodynamic damping and friction damping from apparent damping using averaged normal components of wind speed, RMQ values of acceleration, and estimated damping ratios from wind-induced vibration responses and vehicle loading responses.

• Journal of the Earthquake Engineering Society of Korea
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• v.20 no.7_spc
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• pp.503-508
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• 2016

In this study, effectiveness of seismic retrofitting methods using passive damping devices was investigated through numerical analyses of short-period structures under earthquakes which have short-duration and high-frequency impulse characteristics similar to Geyongju earthquakes. Displacement spectra of elastic systems and ductility demand of inelastic systems were evaluated by increasing viscous or friction damping. The damping devices could reduce responses of the structures with shorter structural period than 0.2s. The earthquakes similar to impulse load did not induce the responses of the structures with longer period than 0.4s, and the effects of the damping devices which generates damping forces proportional to structural responses became insignificant.

• Journal of KSNVE
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• v.6 no.2
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• pp.197-203
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• 1996

This study is to analyze the rotordynamic effect of surface-friction- factor characteristics on an annular seal. The honeycomb geometry which shows friction-factor-jump phenomena is used in this study. A rotordynamic analysis for a contered annular seal has been developed by incorporating empirical friction-factor model for honeycomb stator surfaces. The results of the analysis for the honeycomb seal showing the friction-factor jump is compared to the non- friction-factor-jump case. The results yield that the friction-factor-jump decreasesdirect stiffness and cross coupled stiffness coefficients, and increases damping coefficient to stabilize rotating machinery in a rotordynamic point of view. The analysis of the honeyeomb seal for the friction-factor-jump case shows reasonably good compared to experimental results, especially, for cross coupled and damping coeffcients.

• Tribology and Lubricants
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• v.23 no.4
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• pp.162-169
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• 2007

This paper deals with friction effects on the performance of double-bumped AFBs. The stiffness and damping coefficients of the double bump vary depending on the external load and its friction coefficient. The double bump can be either in the single or double active region depending on vertical deflection. The equivalent stiffness and damping coefficients of the bump system are derived from the vertical and horizontal deflection of the bump, including the friction effect. A static and dynamic performance analysis is carried out by using the finite difference method and the perturbation technique. The results of the performance analysis for a double-bumped AFB are compared with those obtained for a single-bumped AFB. This paper successfully proves that a double bumped AFB has higher load capacity, stiffness, and damping than a single-bumped AFB in a heavily loaded condition.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2007.05a
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• pp.582-587
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• 2007

In this study, based on the results from the sinusoidal base excitation analyses of a single degree of freedom system with a tuned mass damper (TMD), it is verified that optimal friction force can improve the performance of a TMD like a linear viscous damper which has been usually used in general TMD. The magnitude of the optimal friction increases with increasing mass ratio of the TMD and decreases with increasing structural damping. Particularly, it is observed that the optimized friction force gives better control performance than the optimized viscous damping of the TMD. However, because the performance of the TMD considerably deteriorates when the friction force increases over the optimal value, it is required to keep the friction force from exceeding the optimal value.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.22 no.12
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• pp.1206-1212
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• 2012

The brake squeal propensity due to the friction-velocity curve is numerically investigated. The finite element models for the disc and pad are correlated with the modal test. In the friction-engaged system modeling, the friction function is linearized at the equilibrium. The damping term induced by friction-velocity slope is incorporated into the equations of motion. In the complex eigenvalue analysis, it is found that the pad shear mode is very sensitive to the friction curve. The results shows that the squeal propensity of the pad shear mode can be controlled by the design parameters such as pressure and stiffness.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.17 no.6 s.123
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• pp.553-559
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• 2007

In this study, based on the results from the sinusoidal base excitation analyses of a single degree of freedom system with a tuned mass damper (TMD), it is verified that optimal friction force can improve the performance of a TMD like a linear viscous damper which has been usually used in general TMD. The magnitude of the optimal friction increases with increasing mass ratio of the TMD and decreases with increasing structural damping. Particularly, it is observed that the optimized friction force gives better control performance than the optimized viscous damping of the TMD. However, because the performance of the TMD considerably deteriorates when the friction force increases over the optimal value, it is required to keep the friction force from exceeding the optimal value.

• Structural Engineering and Mechanics
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• v.8 no.3
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• pp.299-310
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• 1999

One problem with base isolators of the sliding type is that their dynamic responses are nonlinear, which cannot be solved in an easy manner, as distinction must be made between the sliding and non-sliding phases. The lack of a simple method for analyzing structures installed with base isolators is one of the obstacles encountered in application of these devices. As an initial effort toward simplification of the analysis procedure for base-isolated structures, an approach will be proposed in this paper for computing the equivalent damping for the resilient-friction base isolators (R-FBI), based on the condition that the sum of the least squares of errors of the linearized response with reference to the original nonlinear one is a minimum. With the aid of equivalent damping, the original nonlinear system can be replaced by a linear one, which can then be solved by methods readily available. In this paper, equivalent damping curves are established for all ranges of the parameters that characterize the R-FBI for some design spectra.

• Journal of the Korean Wood Science and Technology
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• v.26 no.4
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• pp.26-33
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• 1998

Acoustical properties of chestnut and paulownia woods have been determined in four film thicknesses of oriental lacquering and cashew varnishing on double surfaces of soundboard to elucidate effects of finishing. Accelerometer was attached to the specimen at one third position from one end, and specimen was hit by the impact hammer at one third position from opposite end. Data were processed by vibration analyzer. The ratio of axial-to-transverse sound velocity of untreated specimens of chestnut and paulownia were 3.25 and 5.34, respectively. Natural frequency, specific Young's modulus, acoustical coefficient, sound velocity, damping of sound radiation(DSR) and acoustical converting efficiency(ACE) decreased by oriental lacquering and cashew varnishing for both species. Damping of internal friction of chestnut decreased by oriental lacquering and cashew varnishing, but that of paulownia increased. Natural frequency. specific Young's modulus, acoustical coefficient, sound velocity, and DSR decreased with increased film thickness of both finishing materials. However, damping of internal friction and ACE showed irregular tendency with increased film thickness. Acoustical properties of cashew varnished chestnut specimen were better than those of oriental lacquered specimen. Acoustical properties of oriental lacquered paulownia specimen were better than those of cashew varnished specimen.