• 한국소음진동공학회논문집
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• 제14권5호
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• pp.377-384
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• 2004

An Amplitude Proportional Friction Damper (APFD), in which the friction force is proportional to the system displacement, has been introduced and mathematically modeled. To understand the damping characteristics of APFD, analytical solutions for the impulse response has been derivedand compared to the viscous damper. It is found that APFD system has very similar damping characteristics to viscous damper even though it is a friction damper. APFD may be used as a cost-effective substitution for the viscous damper and could also be used to improve the simple friction or Coulomb dampersince APFD works with no stick-slip and always returns to original position when external disturbance is disappeared.

• Earthquakes and Structures
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• 제18권5호
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• pp.609-623
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• 2020

This paper presents a displacement-based seismic design procedure for new structures with fluid viscous dampers and/or for existing structures, where these devices are required as a retrofit measure and damage control. To consider the non-proportional damping produced by these devices in a conventional modal spectral analysis, the effect of the fluid viscous dampers is approximated as the sum of a proportional damping matrix and a complementary matrix which is representative of non-proportional damping matrix. To illustrate the application of this procedure and evaluate the performance of structures designed with the procedure proposed, five regular plane frames: 8, 12, 17, 20 and 25-storey, and an 8-storey building are designed. The seismic demands used for design and validation were the records obtained at the SCT site during the 1985 Michoacan earthquake, and that of the 2017 Morelos - Puebla earthquake obtained at the Culhuacan site, both stations located on soft soil sites. To validate the procedure proposed, the performances and damage distributions used as design targets were compared with the corresponding results from the nonlinear step-by-step analyses of the designed structures subjected to the same seismic demands.

• Structural Engineering and Mechanics
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• 제33권6호
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• pp.709-724
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• 2009

In this paper a free-free uniform beam with damping effects subjected to follower and transversal forces at its end is considered as a model for a space structure. The effect of damping on the stability of the system is first investigated and the effects of the follower and transversal forces on the vibration of the beam are shown next. Proportional damping model is used in this work, hence, the effects of both internal (material) and external (viscous fluid) damping on the system are noted. In order to derive the frequency of the system, the Ritz method has been used. The mode shapes of the system must therefore be extracted. The Newmark method is utilized in the study of the system vibration. The results show that an increase in the follower and transversal forces leads to an increase of the vibrational motion of the beam which is not desirable.

• Structural Engineering and Mechanics
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• 제55권6호
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• pp.1241-1260
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• 2015

Any rational approach to define the configuration and size of viscous fluid dampers in a structure should be based on the dynamic properties of the system with the dampers. In this paper we propose an alternative representation of the complex eigenvalues of multi degree of freedom systems with dampers to calculate new equivalent natural frequencies. Analytical expressions for the dynamic properties of a two-story building model with a linear viscous damper in the first floor (i.e. with a non-proportional damping matrix) are derived. The formulas permit to obtain the equivalent damping ratios and equivalent natural frequencies for all the modes as a function of the mass, stiffness and damping coefficient for underdamped and overdamped systems. It is shown that the commonly used formula to define the equivalent natural frequency is not applicable for this type of system and for others where the damping matrix is not proportional to the mass matrix, stiffness matrix or both. Moreover, the new expressions for the equivalent natural frequencies expose a novel phenomenon; the use of viscous fluid dampers can modify the vibration frequencies of the structure. The significance of the new equivalent natural frequencies is expounded by means of a simulated free vibration test. The proposed approach may offer a new perspective to study the effect of viscous dampers on the dynamic properties of a structure.

• 한국자동차공학회논문집
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• 제10권2호
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• pp.150-158
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• 2002

Through experimental works, the damping force vibration problem was investigated, which results from valve and surge pressure in the oil return line of the hydraulic circuit of an active suspension system in a passenger cu. Experiments were carried out under passive system, where an orifice valve was closed and non-active system, where an orifice valve was opened, using a pressure control valve controlled by solenoid. The effects of parameters of the valve overlap and accumulator on smoothing surge pressure was elucidated. It was proved that the apparent variation of damping force due to the overlap amount of pressure control valve is the most important factor to control the damping force variation. The procedure of the experimental works shows the development process of a proportional pressure control valve in the hydraulics system of an active suspension system of passenger car.

• 대한기계학회논문집A
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• 제30권7호
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• pp.750-756
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• 2006

This study predicts the modified eigenvectors and eigenvalues of the non-proportional damped structure due to the change in the mass, damping and stiffness of structure by iterative method of the sensitivity coefficient using the original dynamic characteristic. The method is applied to the non-proportional damped 3 degree of freedom system by modifying the mass, damping and stiffness. The predicted dynamic characteristics are showed a good agreement with these from the structural reanalysis using the modified mass, damping and stiffness.

• 한국생산제조학회지
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• 제22권3호
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• pp.447-451
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• 2013

In this study, a shock absorber whose orifice area changes according to the oil pressure inside the absorber is developed. The orifice widens and narrows when the oil pressure is high and low, respectively; thus, the orifice area changes according to the oil pressure, in other words, according to the extension/compression velocity. It is well known that the damping force can be expressed as $C{\cdot}v^{\alpha}$. For fluid film damping, the force is proportional to velocity, i.e., ${\alpha}=1$, and for orifice damping, it is proportional to the square of velocity, i.e., ${\alpha}=2$. The shock absorber proposed in this paper can exhibit different relationships between the damping force and velocity because the orifice area changes according to the induced oil pressure. The motivation of this study is to develop a method for designing a shock absorber with desired values of C and ${\alpha}$ which is not just 1 or 2. Theoretical and experimental studies have been conducted to verify the damping characteristics of the shock absorber. The effect of some major design parameters on damping characteristics has been also examined to relate the design parameters to the damping characteristics.

• Journal of Power Electronics
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• 제18권5호
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• pp.1555-1566
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• 2018

Proportional capacitor-current-feedback active damping (AD) is a common damping method for the resonance of LCL-type grid-connected inverters. Proportional capacitor-current-feedback AD behaves as a virtual resistor in parallel with the capacitor. However, the existence of delay in the actual control system causes impedance in the virtual resistor. Impedance is manifested as negative resistance when the resonance frequency exceeds one-sixth of the sampling frequency ($f_s/6$). As a result, the damping effect disappears. To extend the system damping region, this study proposes a virtual resistor-inductor-capacitor (RLC) AD method. The method is implemented by feeding the filter capacitor current passing through a band-pass filter, which functions as a virtual RLC in parallel with the filter capacitor to achieve positive resistance in a wide resonance frequency range. A combination of Nyquist theory and system close-loop pole-zero diagrams is used for damping parameter design to obtain optimal damping parameters. An experiment is performed with a 10 kW grid-connected inverter. The effectiveness of the proposed AD method and the system's robustness against grid impedance variation are demonstrated.

• 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.

• 한국철도학회:학술대회논문집
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• 한국철도학회 2004년도 추계학술대회 논문집
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• pp.411-416
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• 2004

This paper introduces a fast Fourier transform (FFT)-based spectral analysis method for the transient responses as well as the steady-state responses of linear dynamic systems with non-proportional damping. The force vibration of a non-proportionally damped three-DOF system is considered as the illustrative numerical example. The proposed spectral analysis method is evaluated by comparing with the numerical solution obtained by the Runge-Kutta method