• 한국전산구조공학회:학술대회논문집
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• 한국전산구조공학회 2005년도 춘계 학술발표회 논문집
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• pp.497-504
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• 2005

Stay cables, such as are used in cable-stayed bridges, are prone to vibration due to their low inherent damping characteristics. Several methods have been proposed and implemented to mitigate this problem, though each has its limitations. Recently some studies have shown that active and semiactive control system using MR (Magnetorheological) damper can potentially achieve both higher performance levels than passive control system and adaptability with few of the detractions. However, a control system including a power supply, controller, and sensors is required to maximize the performance of the MR damper and this complicated control system is not effective to most of large civil structures. This paper proposes a smart passive damping system using MR dampers by introducing electromagnetic induction (EMI) system as an external power source to MR damper and verified the performance of smart passive damping system for mitigating the vibration of stay cables. The performances of smart passive damping system are compared with those of linear viscous damper and passive-mode MR damper.

• 한국소음진동공학회논문집
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• 제20권1호
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• pp.22-28
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• 2010

Approximate analysis for a building installed with a friction damper is performed to get insight of its dynamic behavior. Energy balance equation is used to have a closed analytical form solution of dynamic magnification factor(DMF). It is found out that DMF is dependent on friction force ratio and resonance frequency. Approximation of DMF and equivalent damping ratio of a friction damper is proposed with such assumption that the building with a friction damper shows harmonic steady-state response and narrow banded response behavior near resonance frequency. Linear transfer function from input external force to output building displacement is suggested from the simplified DMF equation. Root mean square of a building displacement is derived under earthquake-like random excitation. Finally, design procedure of a friction damper is proposed by finding friction force corresponding to target control ratio. Numerical analysis is carried out to verify the proposed design procedure.

• 한국정밀공학회지
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• 제17권10호
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• pp.69-76
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• 2000

Lots of semi-active control devices have been developed in recent years because they have the best features of passive and active system. Especially, controllable magneto-rheological(MR) fluid devices have received significant attention in these area of research. The MR fluid is the material that reversibly changes from a free-flowing, linear viscous fluid to a semisolid with a controllable yield strength in milliseconds when exposed to a magnetic field. If the magnetic field is induced by moving a permanent magnet instead of applying current to a solenoid, it is possible to design a MR damper consuming low power because the power consumption is reduced at steady state. This paper proposes valve mode MR damper using permanent magnetic circuit that has wide range of operation with low power consumption, a design parameter is adopted. The magnetic circuit, material of choke and choke type are selected experimentally with the design parameter. The behaviors of the damper are examined and torque tracking control using PID feedback controller is performed for step, ramp and sinusoidal trajectiories.

• 한국지진공학회논문집
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• 제10권3호
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• pp.85-100
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• 2006

이 논문에서는 서로 다른층 높이를 갖는 인접한 두 빌딩의 내진성능을 효율적으로 향상시킬 수 있는 선형 점성 감쇠기의 최적 설계방법을 제시하고자 한다. 이를 위하여 층간 대각 브레이싱 형태의 에너지 소산장치 연결방법과 인접 구조물간 에너지 소산장치 연결방법을 고려하였으며, 두 가지 연결방법을 적용한 시스템에 대한 감쇠용량별 주파수응답함수 비교를 통하여 구조물간 연결방법의 효율성을 확인하였다. 아울러 구조물간 연결방법에서 주파수응답함수를 최소화하는 최적 감쇠용량이 존재하는 것을 보이고, 최적 설계된 시스템에 대하여 감쇠용량별 구조물의 고유주파수 및 등가감쇠비의 민감도를 분석하였다. 민감도 분석 결과로부터 고층부에 설치되는 에너지 소산장치가 구조물의 등가 감쇠비를 효율적으로 증가시키는 것을 확인하였다. 따라서 민감도에 비례하는 새로운 감쇠기 설계방법을 제시하고, 대각 브레이싱 연결방법과 구조물간 연결로서 균등분포 및 제시하는 민감도 기반 분포에 따른 연결방법을 적용한 시스템들의 내진성능을 비교 분석하였다. 지진응답의 비교결과, 제시하는 방법이 인접 구조물의 효과적인 내진설계방법이 될 수 있음을 입증하였다.

• Earthquakes and Structures
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• 제7권6호
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• pp.1171-1186
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• 2014

Damping is one of the parameters that control the performance of structures when they are subjected to seismic, wind, blast or other transient shock and vibration disturbances. By adding supplemental viscous dampers, the energy input from a transient deformation is absorbed, not only by the structure itself, but also by the supplemental dampers. The aim of this study is to evaluate the values of both damping and ductility reduction factors for steel moment resisting frames with supplemental linear viscous dampers. Two-dimensional finite element models have been established for a range of low to mid rise buildings with different parameters: number of floors; number of bays; and number of dampers with different supplemental damping ratios (from 5% to 30%). A parametric study has been performed using time history analyses and a well-documented research method (N2-method). In addition, an equation has been proposed for each reduction factor based on regression analysis for the obtained results. The results of the Time history analyses are compared with those of a modified N2-method. Moreover, a comparison with values specified in the European code EC8 and the Egyptian code ECP-201 has been performed.

• 한국정밀공학회지
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• 제21권3호
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• pp.66-73
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• 2004

This paper presents wafer motion modeling of transfer unit in clean tube system, which was developed as a means for transferring the air-floated wafers inside the closed tube filled with the super clean airs. When the wafer is transferred in x direction with an initial velocity the motion along x direction can be modeled as a simple decaying motion due to viscous friction of the fluid. But, the motion in y direction is modeled as a mass-spring-damper system where the recovering force by air jets issued from the perforated is modeled as a linear spring. Experiments with a clean tube system built fur 12 wafer show the validity of the presented force and motion models.

• Structural Engineering and Mechanics
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• 제65권6호
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• pp.761-769
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• 2018

In this work, an optimization method of Friction Tuned Mass Damper (FTMD) parameters is presented. Friction tuned mass dampers (FTMD) are attached to mechanical structures to reduce their vibrations with dissipating the vibratory energy through friction between both bodies. In order to exploit the performances of FTMD, the determination of the optimum parameters is recommended. However, the presence of Coulomb's friction force requires the resolution of a non-linear stick-slip problem. First, this work aims at determining the responses of the vibratory system. The responses of the main mass and of the FTMD are determined analytically in the sticking and sliding phase using the equivalent damping method. Second, this work aims to optimize the FTMD parameters; the friction coefficient and the tuned frequency. The optimization formulation based on the Ricciardelli and Vickery method at the resonance frequencies, this method is reformulated for a system with a viscous damping. The inverse problem of finding the FTMD parameters given the magnitude of the force and the maximum acceptable displacement of the primary system is also considered; the optimization of parameters leads to conclude on the favorable FTMD giving significant vibration decrease, and to advance design recommendations.

• Ocean Systems Engineering
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• 제7권3호
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• pp.225-246
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• 2017

Excessive dynamic-tension variations on the top-tensioned risers (TTRs) deteriorate the structural integrity and cause potential safety hazards. This phenomenon has become more remarkable in the development of deep-water fields with harsher environmental loads. The conventional prediction method of tension variations in hydro-pneumatic tensioner (HPT) has the disadvantage to underestimate the magnitude of cyclic loads. The actual excessive dynamic tension variations are larger when considering the viscous frictional fluid effects. In this paper, a suppression method of tension variations in HPT is modeled by incorporating the magneto-rheological (MR) damper and linear-force actuator. The mathematical models of the combined HPT and MR damper are developed and a force-control scheme is introduced to compensate the excessive tension variations on the riser tensioner ring. Numerical simulations and analyses are conducted to evaluate the suppression of tension variations in HPT under both regular- and irregular-wave conditions for a drilling riser of a tensioned-leg platform (TLP). The results show that significant reduction of tension variations can be achieved by introducing the proposed system. This research has provided a theoretical foundation for the HPT tension control and related structural protection.

• 드라이브 ㆍ 컨트롤
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• 제16권1호
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• pp.7-13
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• 2019

The objective of this study was to present a damped pneumatic suspension, a bike fork suspension, which can adapt itself to incoming road excitations is presented in this paper. It consists of a hydraulic damper and a pneumatic spring in parallel with a linear spring. The study also proposed a variable and switchable orifice, in the hydraulic damper, to select appropriate damping property. Hydraulic-pneumatic circuit model for the bike fork suspension was established based on AMESim, in order to predict its performance. In addition, elastic-damping characteristics of the fork such as spring constant and viscous damping coefficient were computed and compared, for validation, with those evaluated by experiment using the universal test machine. Through simulation analysis and test, it was established that the hydraulic-pneumatic circuit model is effective and practical for development of future MTB suspensions.

• 한국지진공학회논문집
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• 제11권1호
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• pp.11-19
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• 2007

이 연구에서는 인접한 두 빌딩의 진동제어를 위한 방법으로 선형 점성 감쇠기의 위치별 용량의 최적설계방법을 제시하고자 한다. 기존 연구들에서는 감쇠기의 균등분포 또는 층별 감쇠비의 민감도에 비례하는 분포의 가정 하에서의 준최적(suboptimal) 설계문제를 다룬 반면, 이 연구에서는 감쇠기의 위치별 용량을 독립적인 설계인자로 고려함으로써 전역 최적해를 결정하는 최적화기법을 다루었다. 이를 위하여 넓은 영역에서 다수의 설계변수를 효율적으로 검색할 수 있는 유전자 알고리즘(genetic algorithm)을 도입하였으며, 제어 성능 및 감쇠용량에 대한 목적함수의 정의를 달리함으로써 얻어지는 여러 최적설계 결과를 상호 비교하여 보다 최적의 해를 구할 수 있는 목적함수를 정립하였다. 기존 연구결과와의 제어성능 및 감쇠용량의 비교를 통하여 제시하는 방법의 효율성을 검증하였다. 아울러 서로 상이한 주파수 성분을 띄는 실제 역사지진에 대한 시간이력해석을 통하여 제시하는 방법이 인접 구조물의 효과적인 제진설계방법이 될 수 있음을 입증하였다.