• Journal of Korean Association for Spatial Structures
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• v.12 no.3
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• pp.89-95
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• 2012

Post-tensioned void slab is frequently used for improving the deflection and sound proofing. Two one story 8m spanned structures were built. One structure applied post-tensioned solid slab, but the other did post-tensioned void slab. Dynamic characteristics, which is natural frequency and damping ratio, was compared between that of solid slab and void slab before and after post tension. The natural frequency of void slab was greater than that of solid slab before and after post tension. It was shown that damping ratio of solid slab and void slab was almost same at two stages.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2009.11a
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• pp.359-362
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• 2009

Damping characteristics of pressure oscillation induced by an orifice in fluid feeding line for are investigated numerically and experimentally. Assuming small pressure oscillation, acoustic damping effect of orifice is confirmed experimentally, and with the mean flow, damping characteristics of an orifice are investigated numerically. When an orifice is installed at the node of pressure oscillation corresponding to the anti-node of velocity oscillation, suppression of pressure oscillation is maximized and with the mean flow, the resonant frequency is decreased. And, it is found that the optimal position of an orifice for damping shouled be changed.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.29 no.1
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• pp.95-103
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• 2016

In this paper, aeroelastic instability and aerodynamic damping ratio of a helical $180^{\circ}$ model which shows better aerodynamic behavior in both along-wind and crosswind responses on a super tall building was investigated by an aeroelastic model test, and the aerodynamic damping ratio was evaluated from the wind-induced responses of the model by using Random Decrement Technique. Aerodynamic damping ratios evaluated in this study were verified through comparison with previous results obtained by quasi-steady theory. As a result, the aeroelastic instability of the helical $180^{\circ}$ model in crosswind direction were not occurred for any conditions with increasing the reduced wind velocity while the square model generally encounters aeroinstability due to the vortex shedding. The aerodynamic damping in along-wind direction for the helical $180^{\circ}$ and the square model increased monotonically both with reduced wind velocity, i.e., there is no relation with modifications of building shapes. On the other hand, in crosswind direction, the characteristics of aerodynamic damping ratio with reduced wind velocity for helical $180^{\circ}$ model were quit different from those of the square model.

• The Journal of the Convergence on Culture Technology
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• v.9 no.6
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• pp.927-933
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• 2023

In modern times, with advances in semiconductor technology such as electronic devices, the need to improve the quality of onboard equipment with advanced electronic parts in automobiles, drones, airplanes, projectiles, and various fields, and reduce the impact of various disturbances on onboard equipment is becoming more important. Vibration control through hardware must be determined to prevent damage and improve quality to equipment operating in various environments such as automobiles, drones, airplanes, and projectiles. This study focuses on the study of vibration damping systems to protect mounted equipment from various disturbances and improve stability. Dynamic characteristics analysis, including compressive stiffness, damping rate, and frequency response, and vibration characteristics in the frequency domain of rubber dampers were identified through FEM analysis to identify the characteristics of rubber dampers. Through these findings, we would like to present the criteria for selecting a suitable rubber damper under various disturbance conditions.

• 한국방재학회:학술대회논문집
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• 2010.02a
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• pp.35.1-35.1
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• 2010

최근 고층형 주거 시설이 많이 보편화됨에 따라 층고절감과 시공의 효율성 제고 등에 대한 요구가 크게 증가하고 있다. 이에 층고를 절감하면서 동시에 장스팬을 구현할 수 있는 GFRP를 이용한 경량 중공 합성 바닥을 개발하였다. 이 바닥 시스템은 웨브에 개구부를 가지는 비대칭 철골보와 중공 경량체, 콘크리트 그리고 내력 보강 및 내화 성능 증진을 위해 비대칭 철골보 하부에 부착한 GFRP(Glass Fiber Reinforced Plastics)로 구성된다. 본 연구에서는 이 GFRP를 이용한 경량중공 합성 바닥의 진동 특성을 부재 단위 실험체를 제작하여 실험적으로 검토하였으며, 이를 통해 본 개발 합성 바닥의 고유 진동수 및 감쇠율을 측정하였다, 그 결과 기존의 이론에 근접한 진동 특성을 나타내었다.

• 한국방재학회:학술대회논문집
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• 2011.02a
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• pp.74-74
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• 2011

본 연구에서는 중앙경간 54m, 교폭 4m의 사장교형식의 보도교로 측경간은 계단으로 이루어진 1경간 케이블교량을 대상으로 보행하중에 의한 수직진동을 제어하기 위해 제진장치(TMD)를 적용하기로 하고 실물 TMD의 설계 및 제작 그리고 설치 및 제어성능실험을 수행하였다. 우선 사장교형식의 교량. 그리고 1경간 교량이라는 점에서 상대적으로 감쇠율이 낮을 것으로 예측되었고 또한 54m의 경간장이 보행자가 가진 주파수에 근접한 고유진동수를 나타낼 것으로 사료되어 Eurocode 2 part 2(EC5-2)의 규준에 따라 1인 및 다수 보행하중에 의한 보도교의 발생가속도를 산출하였다. 이 경우 최대가속도는 다수의 보행자가 연속적으로 진행할 때 발생하였으며, 수직방향의 가속도가 사용성기준을 초과하는 것으로 나타났다. 또한 구조해석프로그램에 의한 고유치 해석결과, 보행하중의 주파수대역내에 진동모드가 존재하는 것으로 나타났다. 따라서 본 교량의 설계단계에 있어서 보행진동을 제어하기 위하여 유지관리가 용이한 수동형의 동조질량감쇠장치(Tuned Mass Damper)를 적용하기로 하였으며 TMD의 설계에서는 TMD의 제어목표를 만족시킬 수 있는 TMD의 가동질량(moving mass)을 우선적으로 결정하였고, 이로부터 Den Hartog의 제안식에 따라 TMD의 고유진동수비, 유효감쇠비를 산정하였다. 산정된 변수들을 이용하여 설계된 TMD는 현장설치 및 튜닝의 편의성을 고려하여 수평 외팔보형식으로 설계, 제작되었으며 제작된 TMD의 경우 회전축에 대해 질량, 스프링, 댐퍼의 중심거리를 조정함으로써 TMD의 진동수, 강성, 감쇠력을 상대적으로 매우 용이하게 조절할 수 있으며, 조정범위 또한 광범위하여 일반 TMD에 비해 현장설치시 대상구조물에 동조시키기가 용이하며, 작동시 마찰감쇠가 거의 없다는 장점이 있다. 현장설치전에 제작된 TMD를 대상으로 자유진동 시험을 통하여 질량의 중심거리, 스프링 크기 그리고 댐퍼의 설치유무를 각각 변화시키며 TMD의 자유진동 데이터를 취득하였다. 각각의 시험에서 얻어진 데이터로부터 스펙트럼해석을 통하여 고유진동수를 구하였고, 자유진동 파형으로 부터 감쇠비를 구하였다. TMD는 일반적으로 제어모드의 변형형상이 가장 큰 곳에 설치되었을 때 최대의 제진효과를 발휘할 수 있다. 그러나 현장여건상 설치가 불가능하거나 미관을 해치는 경우에는 가능한 범위 내에서 TMD 제어효율이 가장 크게 발휘할 수 있는 곳을 선택하여야 한다. 본 보도교의 경우, 중앙경간 중심부에서 가장 큰 모드변형형상을 나타내지만, 보도교의 상판 연결부 등에 따른 TMD 시공문제로 인하여 TMD 설치위치는 교량 중앙에서 양 방향으로 1.25m 떨어진 곳에 대칭으로 총 2기를 설치하기로 하였다. 일반적으로 TMD의 모든 설계변수는 구조물의 설계단계에서 수행된 구조해석결과에 근거하여 설정하므로 완공된 구조물, 즉 실제보도교의 동적특성을 계측하여 정확하게 진동수를 튜닝하여야 한다. 구조해석에 의한 보도교의 수직방향(TMD 작동방향) 고유진동수는 1.5225 Hz이며, 감쇠비는 규준에 의하여 0.6 %로 가정하였다. 그러나 이 값들은 구조해석모델 및 재료적 특성과 시공상의 오차에 의하여 실제와 다를 수 있으므로 현장계측에 의한 확인이 요구된다. 또한 TMD의 제진효율이 설계시의 목표대로 확보되었는지도 확인해야 하므로 현장튜닝 및 성능시험을 실시하였다. 보도교의 가진은 사전에 실시한 상시 미진동계측결과를 토대로 2Hz를 목표로 하여 인력가진실험을 수행하였고, 탁월진동 주파수는 1.9896Hz로 나타나 구조해석결과와 오차가 있음을 알 수 있다. 가진실험결과를 토대로 TMD의 진동수를 최적진동수비로 튜닝하고 인력가진 실험을 다시 실시하여 TMD의 진동제어성능을 검토하였다. TMD 튜닝 전, 후의 보도교 감쇠비를 비교한 결과, TMD를 설치함으로써 약 4.218%의 감쇠비 증가가 있음을 알 수 있다.

• Explosives and Blasting
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• v.34 no.2
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• pp.1-9
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• 2016

In this study, the field tests were performed on V-cut, PLHBM 1 hole, PLHBM 2 hole in gneiss area in order to compare the effects of the vibration decay of a tunnel cut-hole according to the number of PLHBM holes with scaled distance. Based on the prediction equation of blasting vibration from the result of the tests, the decay rate of vibration were confirmed 21.8~61.1% using PLHBM 1 hole, 35.7~79.3% using PLHBM 2 hole for scaled distance within $10{\sim}100m/kg^{1/2}$ on the basis of V-cut PPV. As the scaled distance was increased, the effect of vibration decay was decreased. The effect of vibration decay of cut-hole for intial PLHBM 1~2 hole was significantly high.

• Journal of the Earthquake Engineering Society of Korea
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• v.7 no.6
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• pp.9-15
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• 2003

This paper describes a vibration control by using tuned mass damper(i.e., TMD) for an existing footbridge. The footbridge is the simple steel box girder bridge with main span length of 47.7m. This bridge has light weight, low damping and the 1st bending frequency of 1.84㎐. Its frequency is close to a walking cycle, which is 2㎐. Therefore the uncomfortable resonant vibrations due to a pedestrian walking have occurred frequently. The vibration control by means of TMD for suppressing the pedestrian induced vibration was conducted. Taking into account economical benefits and the easiness of installation, a compact TMD installed within a handrail was designed. From field tests of the TMD, it was confirmed that the structural damping of the bridge via. the compact TMD was enhanced by 13 times and the resonant vibration due to pedestrian walking was suppressed.

• Transactions of the Korean Society of Mechanical Engineers
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• v.14 no.3
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• pp.554-570
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• 1990

he rolling contact behaviors between a smooth ball and a flat rough surface under dynamic load are intricately affected by many factors, such as the diameter of a ball, normal load and the roughness of a flat surface etc. Accordingly, the experimental study is done to find them on the base of elastic hysteresis loss as theoretical approach is very difficult. The experimental apparatus composed of damped-free vibration system is used. This paper investigates the damping characteristics on the rolling contact area through rolling friction force and logarithmic decrement versus displacement obtained in accordance with the variations of those factors, and presents a new experimental method to find out contact width using the relations of logarithmic decrement and rolling friction force with displacement.

• Journal of Korean Association for Spatial Structures
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• v.7 no.5
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• pp.57-65
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• 2007

After measuring wind induced response for a high-rise steel building, the damping ratio and natural frequency were analyzed in this paper. In order to examine amplitude dependence, random decrement method was used. Two methods were analyzed by comparing dynamic properties from random decrement method and half powered-band width method. In addition, through serviceability evaluation during strong wind, compatibility of two methods to Japanese guidelines for the evaluation of habitability to building vibration and national building code of Canada was considered. The amplitude dependence of the damping ratio by RD method was shown and the amplitude dependence of the natural frequency was relatively very small in an aspect of engineering sense. Moreover, the measured building was satisfied with serviceability and Japanese guideline is stricter than NBCC code.