• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2003년도 봄 학술발표회 논문집
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• pp.799-804
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• 2003

The purpose of this study was to investigate the effects of re-vibration and curing temperature onto the physical properties of latex-modified concrete with ordinary cement and rapid-setting cement, and thus to provide a guide line of re-vibration and curing conditions for good quality controls. The main experimental variables included two cement types(ordinary portland cement, rapid-setting cement), curing Temperature($10^{\circ}C$, $20^{\circ}C$, $30^{\circ}C$), re-vibration methods(continued, intermittent), and re-vibration times(initial setting, one day after mixing). The experimental results showed that the re-vibration affected little to the mechanical properties of LMC and RSLMC, while, the curing temperature a quite some. The early strength development was the highest at $20^{\circ}C$ curing temperature, and decreased at higher temperature. The permeability of concrete generally decreased with curing time. The rapid chloride permeability was a function of time and temperature. The chloride permeability of RSLMC was so small and negligible.

• International Journal of Naval Architecture and Ocean Engineering
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• 제11권2호
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• pp.835-850
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• 2019

The numerical simulations for the Vortex-induced Vibration (VIV) of the cylinders with different combinations of mass ratio and frequency ratio were performed under the Reynolds (Re) number ranges of 1450-10200, 5800-40800 and 13050-91800 by using the embedded programs in OpenFoam. By combining with the modified SST k-ω turbulence model, the coupled Unsteady Reynolds-Average Navier-Stokes equations and double-degree-of-freedom vibration equations were solved. After analyzing the results, it is found that the some characteristics of the VIV have changed with the increase of the range of Re number, and the effects of Re number on vibration characteristics are also different under different combinations of mass ratio and frequency ratio. On this basis, the influence law of Re number on the characteristics of VIV of the cylinders is summarized, which can provide a reference for the research of VIV under higher Re number.

• Smart Structures and Systems
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• 제21권5호
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• pp.653-668
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• 2018

This work proposes and investigates re-centering negative stiffness dampers (NSDs) for vibration suppression in high-speed trains. The merit of the negative stiffness feature is demonstrated by active controllers on a high-speed train. This merit inspires the replacement of active controllers with re-centering NSDs, which are more reliable and robust than active controllers. The proposed damper design consists of a passive magnetic negative stiffness spring and a semi-active positioning shaft for re-centering function. The former produces negative stiffness control forces, and the latter prevents the amplification of quasi-static spring deflection. Numerical investigations verify that the proposed re-centering NSD can improve ride comfort significantly without amplifying spring deflection.

• 한국유체기계학회 논문집
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• 제5권4호
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• pp.26-31
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• 2002

The heat produced by the fission in the fuel of HANARO, 30 MW of research reactor, was transferred from the primary cooling water to the secondary cooling water through heat exchangers. The secondary cooling water absorbing the heat was circulated by secondary cooling pumps and cooled through 33 MW of cooling tower. Each capacity of the three secondary cooling pumps was fifty percent ($50\%$) of full load. The two pumps were normally operated and the other pump was standby. One of the secondary cooling pumps has often made troubles by high vibration. To release these troubles the pump shaft has been re-aligned, the pump bearing has been replaced with new one, the shaft sleeve has been replaced with new one, the shaft and the impeller have been re-balanced representatively and/or the vibration of motor has been tested by disconnecting the shaft of pump. But the high vibration of pump cannot be cleared. We find out the weight balance trouble of the assembly in which the impeller is installed in the shaft. After clearing the trouble, the high vibration is relieved and the pump is operated smoothly. In this paper, the trouble solution shooting method of secondary cooling pump is described including the reason of high vibration

• 유체기계공업학회:학술대회논문집
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• 유체기계공업학회 2001년도 유체기계 연구개발 발표회 논문집
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• pp.197-202
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• 2001

The heat produced by the fission in the fuel of HANARO, 30 MW of research reactor, was transferred from the primary cooling water to the secondary cooling water through heat exchangers. The secondary cooling water absorbed the heat was circulated by secondary cooling pumps and cooled through 33 MW of cooling tower. Each capacity of the three secondary cooling pumps was fifty percent ($50\%$) of full load. The two pumps were normally operated and the other pump was standby. One of the secondary cooling pumps has often get troubles by high vibration. To release these troubles the pump shaft has been re-aligned, the pump bearing has been replaced with new one, the shaft sleeve has been replaced with new one, the shaft and the impeller have been re-weight balanced representatively or the vibration of motor has been tested by disconnecting the shaft of pump. But the high vibration of pump cannot be cleared. We find out the weight balance trouble of the assembly that the impeller is installed in the shaft. After clearing the trouble, the high vibration is released and the pump is operated with smooth. In this paper the trouble solution of secondary cooling pump is described including the reason of high vibration.

• 한국기계가공학회지
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• 제14권6호
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• pp.27-34
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• 2015

Dynamic vibration absorbers are widely used in machinery, buildings, and structures, including bridges. Two cases of their usage are considered in this paper. One is a simply supported beam subjected to either a moving force or a sequence of moving forces, which simulates a train-bridge interaction problem. The other is a case where a primary system is mounted on a base that is not grounded and is excited by an external force. The conditions that the dynamic vibration absorbers must meet in these cases are found and compared to those for usual cases where bases of primary systems are grounded.

• 화약ㆍ발파
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• 제35권1호
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• pp.34-42
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• 2017

발파에 의한 소음 진동의 물리적 크기 이외에 영향을 미치는 대상의 응답조건, 주변 환경에 적응상태 및 주관적 감정, 정신적 상태 등에 따라 크게 좌우되는 특성을 가지고 있어 명확히 피해영향을 판단하는 것은 매우 어려운 일이다. 특히 어류의 피해영향에 대해서는 실험을 통한 연구자체도 어렵고, 적용할 수 있는 제시기준이 모호하여 정확한 평가방법은 물론 실제 소음 진동 노출정도의 예측에 많은 어려움이 있다. 국내의 경우 수중소음 피해인정 기준을 140 dB re $1{\mu}Pa$, 수중 배경음과의 차가 어류에 미치는 피해기준은 20 dB re $1{\mu}Pa$ 이상으로 규정하고 있으나, 이는 연속음에 대한 것으로서 충격음인 발파음에 대한 평가로서는 적합하지 않다. 이 연구에서는 시험발파를 통해 바위갯지렁이 양식장 주변에서 발파 시 진동속도와 수중소음의 관계를 예측해보았다. 그리고 수중소음 피해인정기준에서 배경소음과의 차에 대한 의견을 제시해 보고자 한다.

• 공업화학
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• 제9권5호
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• pp.674-679
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• 1998

액체금속로 증기발생기 전열관 재질로 사용이 예상되는 ferrite steel 시편을 사용해서 소듐분위기에서 미량의 물 누출 실험을 수행하였다. 누출경로는 소듐-물 반응생성물 및 부식생성물에 의한 self-plugging 현상과 열적인 transient 및 전열관의 vibration에 의한 re-opening 메카니즘으로 설명이 가능하였다. 실험결과, 600 Psig의 injection 압력으로 5 g $H_2O$를 소듐분위기 속의 시편으로 누출시킨 경우, 누출초기와 약 70분 경과 후에 약간의 누출 흔적이 보였으나, self-plugging되었던 누출경로는 129분이 경과되자 완전 re-opening된 것으로 확인되었다. 누출시편의 re-opening shape은 2중으로 되어 있었으며, 소듐부위에서 시편 표면에 나타난 re-opening size 약 2 mm의 직경을 나타내었다.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2006년도 춘계학술대회논문집
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• pp.392-395
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• 2006

The configuration of coaxial co-rotating contained in shroud provides a useful model for investigating the characteristics of flow in the HDD. Reynolds number is defined as $Re_R={\Omega}{R_o}^2/{\upsilon},\;Re_H={\Omega}R_oH/{\upsilon}$ in present study. An experimental investigation was performed for turbulence profiles and PSD distribution and vortices frequency behavior for various range of $Re_R=2.43{\times}10^4{\sim}3.61{\times}10^5$. A laser Doppler anemometry (LDA) is used to obtain the velocity field of unobstructed co-rotating disks flow. Airflow pattern visualization between inner and outer region was compared with turbulence profiles measured from LDA. Outer detached shear layer and dead-zone without oscillating velocity fluctuation to circumferential mean were quantitively traced.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2003년도 춘계학술대회논문집
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• pp.770-774
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• 2003

We propose the re-design method of modal parameters to depress the 2nd resonance peak of the ultra-slim-height optical pick-up actuator. With the addition of tile counter mode near the 2nd resonance frequency, we can achieve the gain margin which is sufficient to meet the system requirement. It would alleviate the burden of the additional filter for a high-speed drive.