• Wind and Structures
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• 제4권3호
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• pp.261-276
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• 2001

This paper presents an experimental study on the effectiveness of viscous-damping walls in controlling the wind-induced vibrations of a building model. A simple four-story building model, square in plan, was constructed for wind tunnel study. In this paper the description of the model, its instrumentation, and the experimental set-up and methodology are reported. The effectiveness of viscous-damping walls in reducing vibrations was investigated for different fluid levels in the walls, and at varying wind speeds and attack angles. The results show that viscous-damping walls are highly effective in most cases.

• Structural Engineering and Mechanics
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• 제5권2호
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• pp.177-191
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• 1997

In the paper, a fractional derivative Kelvin-Voigt model describing the dynamic behavior of a special class of fluid viscous dampers, is presented. First of all, in order to verify their mechanical properties, two devices were tested the former behaving as a pure damper (PD device), whereas the latter as an elastic-damping device (ED device). For both, quasi-static and dynamic tests were carried out under imposed displacement control. Secondarily, in order to describe their cyclical behavior, a model composed by an elastic and a damping element connected in parallel was defined. The elastic force was assumed as a linear function of the displacement whereas the damping one was expressed by a fractional derivative of the displacement. By setting an appropriate numerical algorithm, the model parameters (fractional derivative order, damping coefficient and elastic stiffness) were identified by experimental results. The estimated values allowed to outline the main parameter properties on which depend both the elastic as well as the damping behavior of the considered devices.

• 한국정밀공학회지
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• 제25권3호
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• pp.73-82
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• 2008

Recently MR CDC damper has been applied to semi-active suspension control system gradually. Compared to former hydraulic CDC damper, it has rapid time response performance as well as simple internal structure and wide range of damping force. In order to develop control logic algorithm which enables to take maximum advantage of unique characteristics of MR CDC damper, it is inevitable to perform a thorough investigation into its nonlinear performance. In many previous researches, MR fluid model was either simply assumed as Bingham Plastic, or a phenomenological model based on experiment was established instead to predict damping performance of MR CDC damper. These experimental flow model which is not based on flow analysis but intentionally built to fit damping characteristics, may lead to totally different results in case of different configuration or structure of MR CDC damper. In this study, a generalized flow formula from mathematical flow model of MR fluid for annular orifice is derived to analyze and predict damping characteristics when current is excited at piston valve.

• 한국해양공학회지
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• 제32권1호
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• pp.1-8
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• 2018

In order to analyze the response of the offshore structure numerically, the linear potential theory is generally applied for simplicity, and only the radiation damping is considered among various damping forces. Therefore, the results of a numerical simulation can be different from the motion of the structure in a real environment. To reduce the differences between the simulation results and experimental results, the viscous damping, which affects the motion of the structure, is also taken into account. The appropriate damping model is essential for the numerical simulation in order to obtain precise responses of the offshore structure. In this study, various damping models such as linear or quadratic damping and the nonlinear drag force from numerous slender bodies were used to simulate the free decay motion of the platform, and its characteristics were confirmed. The optimized damping model was found by comparing the simulation results to the experimental results. The hydrodynamic forces and wave exciting forces of the structure were obtained using WAMIT, and the free decay test was simulated using OrcaFlex. A free decay test of the scale model was performed by KRISO.

• Journal of Advanced Marine Engineering and Technology
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• 제35권2호
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• pp.271-277
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• 2011

이 연구에서는 유전알고리즘을 이용하여 강봉의 감쇠행렬을 산출하는 방법을 제안하다. 감쇠행렬이 강성행렬과 비례한다는 가정을 전제로 각 요소강성행렬에 임의의 정수를 곱하여 감쇠행렬을 구성하여 주파수응답함수를 구성하고, 이를 실험 주파수응답함수와 비교한 값을 목적함수로 하여 목적함수가 가장 작은 정수의 감쇠행렬을 구한다. 비감쇠 해석의 경우보다 목적함수의 값이 약 1/60로 작아지는 것을 알 수 있었다. 이를 이용하면 큰 구조물의 감쇠가 큰 일부 부분구조물을 떼어내어 감쇠행렬을 구할 수 있어 구조물의 감쇠진동해석을 하는데 도움이 될 것으로 사료된다.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2005년도 춘계학술대회논문집
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• pp.656-661
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• 2005

An optimization formulation of unconstrained damping treatment on beams is proposed to minimize vibration responses using a numerical search method. The fractional derivative model is combined with RUK's equivalent stiffness approach in order to represent nonlinearity of complex modulus of damping materials with frequency and temperature. The loss factors of partially covered unconstrained beam are calculated by the modal strain energy method. Vibration responses are calculated by using the modal superposition method, and of which design sensitivity formula with respect to damping layout is derived analytically. Plugging the sensitivity formula into optimization software, we can determine optimally damping treatment region that gives minimum forced response under a given boundary condition. A numerical example shows that the proposed method is very effective in minimizing vibration responses with unconstrained damping layer treatment.

• 한국소음진동공학회논문집
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• 제15권7호
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• pp.829-835
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• 2005

An optimization formulation of unconstrained damping treatment on beam is proposed to minimize vibration responses using a numerical search method. The fractional derivative model is combined with RUK's equivalent stiffness approach in order to represent nonlinearity of complex modulus of damping materials with frequency and temperature. Vibration responses are calculated by using the modal superposition principle, and of which design sensitivity formula with respect to damping layout is derived analytically. Plugging the sensitivity formula into optimization software, we can determine optimally damping treatment region that gives minimum forced response under a given boundary condition. A numerical example shows that the proposed method is very effective in suppressing nitration responses by means of unconstrained damping layer treatment.

• 한국소음진동공학회논문집
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• 제13권12호
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• pp.938-946
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• 2003

Length of an unconstrained viscoelastic damping layer on beams is determined to maximizeloss factor using a numerical search method. The fractional derivative model can describe damping characteristics of viscoelastic damping materials accurately, and is used to represent nonlinearity of complex modulus with frequencies and temperatures. Equivalent flexural rigidity of the unconstrained beam is obtained using Ross, Ungar, Kelvin[RUK] equation. The loss factors of partially covered unconstrained beam are calculated by a modal strain energy method. Optimal lengths of the unconstrained viscoelastic damping layer of beams are identified with ambient temperatures and thickness ratios of beam and damping layer by using a finite-difference-based steepest descent method.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2003년도 추계학술대회논문집
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• pp.665-671
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• 2003

Length of an unconstrained viscoelastic damping layer on beams is determined to maximize loss factor using a numerical search method. The fractional derivative model can describe damping characteristics of the viscoelastic damping material, and is used to represent nonlinearity of complex modulus with frequencies and temperatures. Equivalent flexural rigidity of the unconstrained beam is obtained using Ross, Ungar, Kerwin(RUK) equation. The loss factors of partially covered unconstrained beam are calculated by a modal strain energy method. Optimal lengths of the unconstrained viscoelastic damping layer of beams are obtained with respect to ambient temperatures and thickness ratios of beam and damping layer.

• Wind and Structures
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• 제8권5호
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• pp.309-324
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• 2005

Aerodynamic damping often plays an important role in estimations of wind induced dynamic responses of super high-rise buildings. Across- and along-wind aerodynamic damping ratios of a square super high-rise building with a height of 300 m are identified with the Random Decrement technique (RDT) from random vibration responses of the SDOF aeroelastic model in simulated wind fields. Parametric studies on effects of reduced wind velocity, terrain type and structural damping ratio on the aerodynamic damping ratios are further performed. Finally formulas of across- and along-wind aerodynamic damping ratios of the square super high-rise building are derived with curve fitting technique and accuracy of the formulas is verified.