• Composites Research
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• 제28권6호
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• pp.395-401
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• 2015

본 연구에서는 자가손상보수에 적용되는 Grubbs' catalyst의 열안정성과 자가치료제와의 반응성을 조사하였다. 이를 위해 제조사에서 공급된 4종류를 고려하였으며 제조사에서 공급받은 상태와 기계적으로 분쇄시킨 상태로 시험하였다. 자가치료제는 Dicyclopentadiene (DCPD)과 5-ethylidene-2-norbonene (ENB)을 적절한 비율로 혼합한 4종류를 고려하였다. 촉매의 열안정성을 조사하기 위해 시차주사 열량측정장치를 통해 온도에 따른 열흐름 변화를 측정하였다. 자가치료제와의 반응성을 평가하기 위해 촉매와 혼합된 자가치료제의 반응열을 측정하였다. 이때 촉매는 자가치료제와 반응할 때의 최대온도와 최대온도 도달시간을 고려하여 Fluka Chemika Grubbs' catalyst를 적용하였다. 연구결과에 따르면 촉매는 제조사에 따라 다른 형상을 나타내며 입자의 크기가 작은 촉매가 자가치료제와 높은 반응성을 나타내었다. ENB의 혼합비가 높은 자가치료제가 촉매와 혼합되면 최대온도는 증가하고 최대온도 도달시간은 빨라졌다. 또한 촉매의 양이 많을수록 최대온도는 높아지고 최대온도 도달시간은 빨라졌다. 촉매의 열안정성과 자가치료제와의 반응성을 고려할 때 0.5 wt% 촉매와 D3E1 자가치료제가 자가손상보수를 위한 최적 조건임을 알 수 있었다. 마지막으로 노출된 분위기 온도에 따라 촉매에 열분해가 발생할 수 있기 때문에 촉매가 열안정성을 갖는 온도보다 높은 온도에 노출되지 않도록 하여야 한다.

• 터널과지하공간
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• 제33권6호
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• pp.445-471
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• 2023

수만년 이상의 기간동안의 장기 안전성을 확보하는 것이 처분장 건설에서의 최우선 조건이나, 건설 및 운영중 대심도 지하 사용후핵연료 처분장의 역학적 안정성 확보 역시 안전한 터널 공사 및 운영을 위해 필수적인 요소이다. 처분장의 장기 안전성에 중요한 요소인 벤트나이트 충전재 및 완충재의 차폐 성능을 저감시킬 가능성이 있는 숏크리트, 콘크리트, 그라우팅 등의 터널 지보공 및 차수공을 금지 내지는 제한하는 조건은 암반공학자 및 터널 기술자에게 매우 도전적인 과제로 판단된다. 본 연구에서는 처분장 부지 선정과정에서 올바른 처분장의 선정에 도움이 될 수 있는 대심도에 건설할 것으로 예상되는 처분장의 터널 네트워크, 처분 터널 및 처분공의 역학적 안정성을 확보하기 위한 제반 조건의 광범위한 탐색의 일환으로 지하 500 m 심도의 처분장을 무지보 상태로 건설할 경우 2차원 및 3차원 수치해석 검토를 통해 안정성의 확보 가능한 물성 범위를 탐색하고자 하였다. 예비 연구결과 처분장의 중앙터널과 처분터널 안정성 확보 가능 암반물성의 범위를 파악하였으며, 3차원 해석을 통해 수직구 주변 터널 네트워크의 안정성을 확인하여 처분장 건설을 위한 기초적인 암반 조건이 파악된 것으로 판단된다.

• Nuclear Engineering and Technology
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• 제41권3호
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• pp.347-354
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• 2009

Welding is required for a connection between two different components in the nuclear fuel of a pressurized water reactor. This work relies on a mechanical experiment and analytic results to investigate the structural integrity of nuclear fuel in a situation where some components are not welded to each other. A series of lateral vibration tests are performed in a test facility, and the test structures are examined in terms of dynamic behavior. In the tests, the displacement signal at every grid structure that sustains fuel rods is measured and processed to identify the dynamic properties. The fluid-elastic stability of the structure is also analyzed to evaluate susceptibility to a cross flow with an assumed conservative cross flow distribution. The test and analysis results confirm that the structural integrity can be maintained even in the absence of some welding connections.

• Coupled systems mechanics
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• 제12권1호
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• pp.21-40
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• 2023

In thisstudy, the vibration problem ofthermo elastic carbon nanotubes conveying pulsating viscous nano fluid subjected to a longitudinal magnetic field is investigated via Euler-Bernoulli beam model. The controlling partial differential equation of motion is arrived by adopting Eringen's non local theory. The instability domain and pulsation frequency of the CNT is obtained through the Galerkin's method. The numerical evaluation of thisstudy is devised by Haar wavelet method (HWM). Then, the proposed model is validated by analyzing the critical buckling load computed in presentstudy with the literature. Finally, the numerical calculation ofsystem parameters are shown as dispersion graphs and tables over non local parameter, magnetic flux, temperature difference, Knudsen number and viscous parameter.

• 한국해양공학회지
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• 제23권1호
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• pp.140-145
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• 2009

This paper deals with a stability evaluation of a butterfly valve using the body and disc of a valve seat. The experimental results of a strength evaluation are shown using STS316 stainless steel and spheroidal graphite cast iron (GCD450). The disc material was made from GCD450. The results of the strength analysis are as follows: Ultimate tensile strength 485MPa, Yield strength 370 MPa, Young's modulus $1.1{\times}10^5$, and Poisson's ratio v = 0.28. For the results of the disc analysis, the safety factor was about 4. This shows that a design was derived that satisfied the requirements of structural safety. However, some problems, such as the deflection and deformation of the disc, may occur when the sea water has back flow with a high pressure.

• 대한기계학회논문집
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• 제14권3호
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• pp.646-655
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• 1990

본 연구에서는 EPIES 프로그램의 상세한 내용과 이를 이용한 5가지 파괴역학 시편에 대한 사례 연구에 대하여 보고하고자 한다.

• 한국공작기계학회논문집
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• 제12권2호
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• pp.23-30
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• 2003

It is very important to detect and evaluate the surface or subsurface flaws because of their influences on mechanical properties of materials. Rayleigh wave and creeping wave are commonly used for the detection of surface and subsurface flaws. These techniques, however, have following problems. Each amplitudes are remarkably affected by the surface condition and evaluation of echo pattern is usually difficult because shear wave mode propagate in the material at the same time. On the other hand, surface SH-wave which is horizontally polarized shear wave traveling along near surface layer is an attractive technique for the surface or subsurface material characterization and this technique is useful to solve the problems mentioned above. In this paper, The stability and transmission coefficient of SH waves through a viscous fluid layer is theoretically studied and simulated. Its results agreed well with the theoretical expectation for the experimental verification. These experimental results show that viscosity of couplants, thickness of couplant and surface roughness are closely related to transfer efficiency in surface SH angle beam method.

• Geomechanics and Engineering
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• 제15권3호
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• pp.841-849
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• 2018

The purpose of a rock bolt is to improve the mechanical performance of a jointed-rock mass. The performance of a rock bolt is generally evaluated by conducting a field pullout test, as the analytical or numerical evaluation of the rock bolt behavior still remains difficult. In this study, wide range of field test was performed to investigate the pullout resistance of rock bolts considering influencing factors such as the rock type, water bearing conditions, rock bolt type and length. The test results showed that the fully grouted rock bolt (FGR) in water-bearing rocks can be inadequate to provide the required pullout resistance, meanwhile the inflated steel tube rock bolt (ISR) satisfied required pullout resistance, even immediately after installation in water-bearing conditions. The ISR was particularly effective when the water inflow into a drill hole is greater than 1.0 l/min. The effect of the rock bolt failure on the tunnel stability was investigated through numerical analysis. The results show that the contribution of the rock bolt to the overall stability of the tunnel was not significant. However, it is found that the rock bolt can effectively reinforce the jointed-rock mass and reduce the possibility of local collapses of rocks, thus the importance of the rock bolt should not be overlooked, regardless of the overall stability.

• 대한기계학회논문집A
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• 제24권2호
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• pp.347-354
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• 2000

This paper presents performance characteristics of a semi-active suspension featuring continuously variable ER (electro-rheological) dampers. These are evaluated through the field test of a passeng er car. Four ER dampers (two for front and two for rear part) are manufactured and their field-dependent damping properties are experimentally investigated. The damping force responses to step input fields are also identified by employing small size of high voltage amplifiers which are made adaptable to the field test. A skyhook controller considering the vertical, pitch and roll motions is formulated and incorporated with a car to be tested. The field test is then undertaken in order to evaluate both comfortability and steering stability showing bump, dive and squat responses.

• 설비공학논문집
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• 제24권4호
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• pp.289-296
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• 2012

The aim of this study is to investigate the performance of a heating and cooling system with aquifer thermal energy storage(ATES heat pump system) known as one of the underground thermal energy storage application systems. The ATES system was composed of heat pump unit and ATES, which was installed in a factory building located in Anseoung. The system represented very high heating and cooling performance, and showed nearly constant COP at each heating and cooling season due to the stability of EWT. The economic analysis about an ATES system and a conventional system was also executed. The conventional system adopted an air-conditioner in the summer season and a LNG boiler in the winter season. The payback period of the ATES system was estimated by 6.62 years.