• 한국소음진동공학회논문집
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• 제25권12호
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• pp.866-873
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• 2015

The transverse vibration of the deploying beam from rigid hub was analyzed by simulation and experiment. The linear governing equation of the deploying beam was obtained using the Euler-Bernoulli beam theory. To discretize the governing equation, the Galerkin method was used. After transforming the governing equation into the weak form, the weak form was discretized. The discretized equation was expressed by the matrix-vector form, and then the Newmark method was applied to simulate. To consider the damping effect of the beam, we conducted the modal test with various beam length. The mass proportional damping was selected by the relation of the first and second damping ratio. The proportional damping coefficient was calculated using the acquired natural frequency and damping ratio through the modal test. The experiment was set up to measure the transverse vibration of the deploying beam. The fixed beam at the carriage of the linear actuator was moved by moving the carriage. The transverse vibration of the deploying beam was observed by the Eulerian description near the hub. The deploying or retraction motion of the beam had the constant velocity and the velocity profile with acceleration and deceleration. We compared the transverse vibration results by the simulation and experiment. The observed response by the Eulerian description were analyzed.

• Earthquakes and Structures
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• 제3권6호
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• pp.821-838
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• 2012

This paper proposes a new three-layer pillar-type hysteretic damper system for residential houses. The proposed vibration control system has braces, upper and lower frames and a damper unit including hysteretic dampers. The proposed vibration control system supplements the weaknesses of the previously proposed post-tensioning vibration control system in the damping efficiency and cumbersomeness of introducing a post-tension. The structural variables employed in the damper design are the stiffness ratio ${\kappa}$, the ductility ratio ${\mu}_a$, and the ratio ${\beta}$ of the damper's shear force to the maximum resistance. The hysteretic dampers are designed so that they exhibit the targeted damping capacity at a specified response amplitude. Element tests of hysteretic dampers are carried out to examine the mechanical property and to compare its restoring-force characteristic with that of the analytical model. Analytical studies using an equivalent linearization method and time-history response analysis are performed to investigate the damping performance of the proposed vibration control system. Free vibration tests using a full-scale model are conducted in order to verify the damping capacity and reliability of the proposed vibration control system. In this paper, the damping capacity of the proposed system is estimated by the logarithmic decrement method for the response amplitudes. The accuracy of the analytical models is evaluated through the comparison of the test results with those of analytical studies.

• 한국지반공학회지:지반
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• 제13권5호
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• pp.145-154
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• 1997

말뚝재하시험방법 중 정적재하시험은 시험에 소요되는 시간과 비용측면에서 불리하여 이를 개선하기 위한 여러 가지의 시험방법이 개발되어 소개되고 있다. 국내에 소개된 시험방법으로는 동재하시험으로 불리는 항타분석기 (PDA : Pile Driving Analyzer)를 이용한 방법을 비롯하여 STATNAMIC. Osterberg cell등이 있다. 이들 중 동재하시험의 사용은 상당히 활성화되어 있는 실정이나 지반조건과 말뚝시공방법에 따라서는 지지력산정시 추가적인 해석모델을 사용하여야 보다 정확한 지지력을 평가 할 수 있는 것으로 알려져 있다. 본 논문에서는 현장에서 수행한 정적 및 동적 재하시험결과의 비교1분석으로 부터 주로 SIP말뚝에 대한 동재하시험시 발생할수 있는 기하감쇠(geometrical damping)의 영향을 고찰하였다. 해석결과로 부터 기하감쇠가 발생한 지반의 경우 CAPWAP에 의해 산정된 지지력이 정재하시험에 의한 지지력에 비해 30~60% 정도 과소평가 되었으며 이때 말뚝주면에 대한 Smith의 감쇠계수 (SSkn)가 1.0 sec/m를 초과 하였다. CAPWAP해석시 기하감쇠를 고려한 해석모델을 사용함으로써 정재하 시험결과와 근사한 지지력을 얻을 수 있었으며 SSkn값도 0.7sec/m이하의 일반적인 범위로 해석되었다.

• Wind and Structures
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• 제29권6호
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• pp.431-440
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• 2019

The aim of this study was to explore the influence of structure coupling effect on structural damping of blade based on the blade vibration characteristic. For this purpose, the scaled blade model of NREL 5 MW offshore wind turbine was processed and employed in the wind tunnel test to validate the reliability of theoretical and numerical models. The attenuation curves of maximum displacement and the varying curves of equivalent damping coefficient of the blade under the rated condition were respectively compared and analyzed by constructing single blade model and whole machine model. The attenuation law of blade dynamic response was obtained and the structure coupling effect was proved to exert a significant influence on the equivalent damping coefficient. The results indicate that the attenuation trend of the maximum displacement response curve of the single blade varies more obviously with the increase of elastic modulus as compared to that under the structure coupling effect. In contrast to the single blade model, the varying curve of equivalent damping coefficient with the period is relatively steep for the whole machine model. The findings are of great significance to guide the structure design and material selection for wind turbine blades.

• 한국지반공학회논문집
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• 제37권12호
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• pp.33-45
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• 2021

본 연구에서는 비닐스트립-시멘트로 보강된 느슨한 중간 모래의 정규화 전단탄성계수 및 감쇠비 산정식을 제안하였다. 상대밀도 40%의 모래시편을 다양한 비닐스트립 혼합비(0.0, 0.1, 0.3, 0.4%)와 시멘트 혼합비(0, 1, 2%)로 보강한 후 15, 30, 60kPa의 구속압조건에서 수행한 공진주시험 자료(Yu, et al., 2018)를 분석하여 정규화 전단탄성계수와 감쇠비 산정식을 보강조건과 구속압조건의 함수로 제안하였다. 제안된 산정식을 적용한 결과와 시험결과를 비교한 결과 결정계수 0.9 이상의 높은 신뢰도를 보여주었다. 본 연구에서 제안된 산정식을 이용하면 비닐스트립-시멘트로 보강된 느슨한 중간모래의 전단탄성계수와 감쇠비를 공진주시험 수행없이 간단히 산정할 수 있어 시간과 비용이 절감될 것으로 기대한다.

• Earthquakes and Structures
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• 제5권1호
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• pp.83-109
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• 2013

A simple damper optimization method is proposed to find optimal damper allocation for shear buildings under both target added damping ratio and interstorey drift ratio (IDR). The damping coefficients of added dampers are considered as design variables. The cost, which is defined as the sum of damping coefficient of added dampers, is minimized under a target added damping ratio and the upper and the lower constraint of the design variables. In the first stage of proposed algorithm, Simulated Annealing, Nelder Mead and Differential Evolution numerical algorithms are used to solve the proposed optimization problem. The candidate optimal design obtained in the first stage is tested in terms of the IDRs using linear time history analyses for a design earthquake in the second stage. If all IDRs are below the allowable level, iteration of the algorithm is stopped; otherwise, the iteration continues increasing the target damping ratio. By this way, a structural response IDR is also taken into consideration using a snap-back test. In this study, the effects of the selection of upper limit for added dampers, the storey mass distribution and the storey stiffness distribution are all investigated in terms of damper distributions, cost function, added damping ratio and IDRs for 6-storey shear building models. The results of the proposed method are compared with two existing methods in the literature. Optimal designs are also compared with uniform designs according to both IDRs and added damping ratios. The numerical results show that the proposed damper optimization method is easy to apply and is efficient to find optimal damper distribution for a target damping ratio and allowable IDR value.

• 한국항공우주학회지
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• 제39권10호
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• pp.912-918
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• 2011

본 연구의 목적은 풍동실험을 통해 회전발사체에서 발생하는 동적 롤댐핑 특성을 실험적으로 측정하는데 있었으며, 이를 위해 약 12,000 rpm으로 회전하는 회전발사체 실험모형에 작용하는 롤댐핑 특성의 측정을 위한 고속풍동실험을 국방과학연구소 삼중음속풍동에서 수행하였다. 실험시의 마하수는 0.7~1.05까지의 천음속 영역이었으며 이때의 받음각 구간은 -4~+10 deg이었다. 풍동실험 측정기법의 유효성 평가를 위해 동일형상 모형에 대해 기 수행하였던 롤댐핑 측정결과와의 비교검토를 수행하였다.

• KCI Concrete Journal
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• 제14권1호
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• pp.23-29
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• 2002

Recent construction activities have given rise to civil petitions associated with vibration-induced damages or nuisances. To mitigate unfavorable effects of construction activities, the measures to reduce or isolate from vibration need to be adopted. In this research, a vibration-mitigated concrete, which is one of the active measures for reducing vibration in concrete structures, was investigated. Concrete was mixed with vibration-reducing materials (i.e. latex, rubber power, plastic resin, and polystyrofoam) to reduce vibration and tested to evaluate dynamic material properties and structural characteristics. Normal and high strength concrete specimens with a certain level of damage were also tested for comparisons. In addition, recycling tires and plastic materials were added to produce a vibration-reducing concrete. A total of 32 concrete bars and eight concrete beams were tested to investigate the dynamic material properties and structural characteristics. Wave measurements on concrete bars showed that vibration-mitigated concrete has larger material damping ratio than normal or high strength concrete. Styrofoam turned out to be the most effective vibration-reducing mixture. Flexural vibration tests on eight flexural concrete beams also revealed that material damping ratio of the concrete beams is much smaller than structural damping ratio for all the cases.

• 한국지진공학회논문집
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• 제8권2호
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• pp.45-53
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• 2004

본 연구에서는 자유진동, 조화하중, 그리고 백색잡음실험을 통해 얻어지는 진동수, 감쇠비, 모드 벡타와 같은 구조물의 모드정보를 이용하여 강성행렬과 감쇠행렬을 구성하였다. 입력신호로는 지진하중을 모사 하는 바닥판 가속도를 이용하였고, 출력신호는 각층 절대가속도를 사용하였다. 각각의 실험에서 얻어지는 구조물 모드정보의 제한조건과 그에 따른 시스템 식별 모델들의 특성을 비교하였다. 본 연구의 결과는 진동대 실험을 위한 기초적인 동적 실험 및 분석에 이용될 수 있을 것으로 판단된다.

• 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.