• 한국융합학회논문지
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• 제10권4호
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• pp.147-151
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• 2019

현대인들은 가정, 학교 혹은 직장, 병원, 쇼핑몰, 지하철역과 객실, 주차장 등 일상생활의 대부분을 실내에서 보내게 된다. 이렇듯 실내에 갇힌 현대인들은 갇힌 공기 속에서 살아갈 수밖에 없다. 이에 실내 공기질 향상을 위한 공기정화장치는 많이 개발되었으나 대다수의 공기정화장치는 필터에 의한 필터링과 유해세균 살균방식에 있어 자외선이라는 제한된 영역에서의 살균방식에 국한 할 수밖에 없었다. 여기서는 실내 공기질 향상은 물론 원천적으로 실내공기중의 부유 세균을 제거하고, 자외선뿐만 아니라 가시광선에서도 활동하는 광촉매를 적용한 미디어광촉매필터를 활용한 광대역대 활성광촉매를 활용한 융 복합 구조 공기살균정화장치 개발하고자 한다.

• 대한조선학회논문집
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• 제60권3호
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• pp.193-201
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• 2023

A developed code based on the unified conservation laws of incompressible/compressible fluids is applied to analyze similarity in pressure oscillations caused by pulsating air pockets in sloshing tanks. It is shown that the nondimensional time histories of pressure show good agreements under Froude and geometric similarities, provided that there are no pulsating entrapped air pockets. However, the nondimesional period of pressure oscillation due to the pulsating air pocket becomes longer as the size of the sloshing tank increases. The discrepancy in the nondimensional period is attributed to the compressibility bias of the entrapped air. To get rid of the compressibility bias, the ullage pressure in a sloshing tank is adjusted based on the Bagnold's impact number. The variation in the period of pressure oscillation according to the ullage pressure is explained based on the spring-mass system. It is shown that the nondimensional period of pressure oscillation is virtually constant when the ullage pressure is adjusted based on the Bagnold's impact number, regardless of tank size. It is found that the Bagold's impact number should be the same, if the time history of pressure is important while an entrapped air pocket pulsates.

• 대한조선학회논문집
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• 제58권5호
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• pp.271-280
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• 2021

The code developed using a pressure-based method for unified conservation laws of incompressible/compressible fluids is expanded to handle moving or deforming body boundaries using the hybrid Cartesian/immersed boundary method. An instantaneous pressure field is calculated from a pressure Poisson equation for the whole fluid domain, including the compressible gas region. The polytropic gas is assumed for the compressible fluid so that the energy equation is decoupled. Immersed boundary nodes are identified based on edges crossing body boundaries. The velocity vector is reconstructed at the immersed boundary node using an interpolation along the assigned local normal line. The developed code is validated by comparing the time histories of pressure and wave elevation for sloshing in a rectangular and a membrane-type tank. The validated code is applied to simulate air cushion effects in a rectangular tank under sway motion. Time variations of pressure fields are analyzed in detail as the air pocket pulsates. It is shown that the contraction and expansion of the air pocket dominate the pressure loads on the wall of the tank. The present results are in good agreement with other experimental and computational results for the amplitude and the decay of the pressure oscillations measured at the pressure gauges.

• 대한조선학회논문집
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• 제55권1호
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• pp.56-65
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• 2018

Pressure oscillation caused by the compressibility of entrapped air in dam break flow is analyzed using an open source code, which is a two-phase compressible code for non-isothermal immiscible fluids. Since compressible flows are computed based on a pressure-based method, the code can handle the equation of state of barotropic fluid, which is virtually incompressible. The computed time variation of pressure is compared with other experimental and computational results. The present result shows good agreements with other results until the air is entrapped. As the entrapped air bubbles pulsate, pressure oscillations are predicted and the pressure oscillations damp out quickly. Although the compressibility parameter of water has been varied for a wide range, it has no effects on the computed results, because the present equation of state for water is so close to that of incompressible fluid. Grid independency test for computed time variation of pressure shows that all results predict similar period of pressure oscillation and quick damping out of the oscillation, even though the amplitude of pressure oscillation is sensitive to the velocity field at the moment of the entrapping. It is observed that as pressure inside the entrapped air changes quickly, the pressure field in the neighboring water adjusts instantly, because the sound of speed is much higher in water. It is confirmed that the period of pressure oscillation is dominated by the added mass of neighboring water. It is found that the temperature oscillation of the entrapped air is critical to the quick damping out of the oscillations, due to the fact that the time averaged temperature inside the entrapped air is higher than that of surrounding water, which is almost constant.

• 상하수도학회지
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• 제22권6호
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• pp.681-687
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• 2008

It is well known that the water infiltration rate depends on soil properties such as soil water content, water head, capillary suction, density, hydraulic conductivity, and porosity. However, most of proposed infiltration models assume that the air phase is continuous and in equilibrium with the atmosphere or air compression and air entrapment on infiltration was not considered. This study presents experimental results on unsaturated water infiltration to relate air entrapment and hydraulic conductivity function based on soil air properties. The objectives of this study were to measure change of soil air pressure ahead of wetting front under air drain and air confined condition to find the confined air effect on infiltration rate, to reduce the entrapped air volume related with soil air pressure to increase the soil permeability, and to make a basis of infiltration process model for the purpose of improvement of infiltration rate in the homogeneous soil column. The results of the work show that soil air pressure increases according to increasement of the saturated soil depth rather than the wetting front depth during infiltration process.

• 콘크리트학회논문집
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• 제23권6호
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• pp.701-709
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• 2011

콘크리트의 공극구조를 평가하기 위한 대표적인 모델 중 하나가 Power가 제안한 간격계수(SF : spacing factor)인데, 이 PSF(power spacing factor)는 평균단일공극 개념을 사용하여 갇힌 공극의 존재 여부에 따라 그 결과값이 실제와 상이하게 나올 수 있는 단점이 있다. 이에 이 연구에서는 실측된 공극 간격 데이터를 이용하여 지수화한 AMSF(실측간격계수 : actual measurement spacing factor)를 개발하였으며, 콘크리트 혼합물의 화상 분석 결과를 이용하여 PSF와 AMSF를 비교 평가하였다. 이 연구 결과, PSF와 AMSF는 전반적으로 유사한 경향을 나타내고 있으나, PSF가 $400{\mu}m$ 이상일 때 전반적으로 AMSF가 좀 더 큰 값을 나타내고 있어, 공기량이 작은 콘크리트 혼합물의 경우 PSF는 실제보다 좀 더 작은 값으로 예측할 가능성이 있는 것으로 나타났다. 또한 갇힌 공극의 유무에 따른 PSF와 AMSF 각각을 분석한 결과, AMSF는 갇힌 공극을 포함하지 않고 분석한 값이 더 크게 나타났고, PSF는 실제와 다르게 갇힌 공극을 포함하지 않고 분석한 값이 더 작게 나타났다. 이와 같이 PSF가 이와 같은 경향을 나타내는 이유는 평균단일공극 개념을 사용하기 때문이며, 이 분석 결과를 통해 AMSF가 좀 더 실제에 가까운 분석기법임을 확인할 수 있었다.

• 한국주조공학회지
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• 제24권4호
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• pp.238-248
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• 2004

고압 다이캐스팅에서 요구되고 있는 고품질의 주조를 위해, 비교적 간단한 개선 방안으로 용탕 주입 방법의 개선이 실험적으로 시도 되었으며, 그로 인해 많은 경우에 긍정적인 결과가 관찰 되었다. 특히, 냉가압 다이캐스트에서, 금형내 용탕의 예충전을 유도하는 용탕 주입의 속도 및 플렌저의 위치제어를 통해 기공율의 저하 및 그로 인한 기계적 강도의 개선 효과를 확인 할 수 있었다. 본 논문은, 그 원인과 결과 대한 연구를 위해, 상용 해석 도구인 Flow3D를 이용, 금형내 용탕의 흐름을 모델링을 통해 가시화하여 용탕의 주입속도 및 위치의 변화가 주물의 품질에 미치는 영향을 조사하였다. 용탕 주입을 위한 플런저의 속도 및 위치 제어의 변수로, 1) 금형내에 용탕의 예충전 유도를 위한 용탕 고속 주입 지연 정도, 2) 플런저의 저속운행에서 고속으로의 가속도, 3) 용탕의 예충전 동안의 플런저 속도를 선택, 그로 인한 영향을 연구 분석 하였고, 그 결과로 플런저의 속도 및 위치 조절을 통하여 금형내 갇힌 공기의 양이 줄어 들 수 있음을 알 수 있었다.

• 한국방재학회 논문집
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• 제10권2호
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• pp.47-53
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• 2010

초속경 LMC(Very-Early Strength Latex-Modified Concrete ; VES-LMC)는 작업성, 강도발현 및 장기 내구성 측면에서 콘크리트 타설 후 3시간 이내에 교통개방을 가능하게 할 목적으로 개발되었고, 교량바닥판 긴급보수 공사에 유용하게 사용되고 있다. 그러나 초속경 LMC에서 라텍스의 사용이 콘크리트의 내구성은 향상시키지만 다량의 갇힌 공기를 양산한다는 단점이 있다. 따라서 취약한 공극구조를 개선하기 위해서는 특별한 방법이 필요하며, 본 논문에서는 울트라파인 플라이 애시가 사용되었다. UFFA VES-LMC의 공기량은 재령 1일에 포졸란 반응의 대부분이 발생하여 재령 1일 공기량이 경화전 공기량보다 저하되었다. 또한 재령 28일 공기량은 재령 1일 공기량의 공극구조와 동일하게 나타나, 포졸란 반응에 의해 콘크리트의 전체 공기량이 감소함을 확인하였다. 수산화칼슘의 첨가는 200 ${\mu}m$이하 크기의 연행공기를 현저하게 증가시키고, UFFA를 15%이상 사용하면 간격계수를 200 ${\mu}m$ 이하까지 확보할 수 있어 VES-LMC의 공극구조 개선에 매우 효과적인 것으로 나타났다.

• 한국건축시공학회지
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• 제9권1호
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• pp.49-55
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• 2009

In this study, reduction methods of surface air void were examined for high performance concrete having high viscosity. The effects of assumed influencing factors such as form types, form-coating materials, tamping equipments and methods were examined based on the tests on mock-up specimens made of high performance concrete. The test results can be summarized as follows: As for form types, the most favorable results were obtained when coated plywood form was used with panel-shape tamping equipments at the contact region with concrete, the second and the third being the water/air-permeable sheets and steel with coated plywood, respectively. As for tamping equipments, a vibrator with 6.5cm diameter was most effective. Finally, the shorter the tamping intervals, the better the reduction effect of surface air void. As a conclusion, an improved method was proposed to reduce surface air void and it was verified with the test result that only four air voids as large as $5{\sim}10mm$ are found in the are of $1m^2$.

• 한국농공학회논문집
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• 제54권5호
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• pp.129-139
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• 2012

Accurate modeling rainfall induced landslide and slope stability requires a detailed knowledge of the distribution of material strength characteristics and suction distribution. However, material properties obtained from the drying cycle are still used for infiltration analysis in many cases, even though material properties of wetting cycle are quite different from those of drying cycle due to hydraulic hysteresis and air occlusion. Therefore, the selection of proper material properties such as soil-water retention curve (SWRC) and the hydraulic conductivity function (HCF) reflecting characteristics of wetting cycle and air occlusion is an essential prerequisite in order to simulate the infiltration phenomena and to predict the suction and water content distribution in unsaturated soils. It is concluded that the simulation of infiltration with material properties from the drying cycle did not reasonably match with experimental outputs. Further discussion is made on how to describe the material properties considering air occlusion during wetting cycle over the entire suction range in order to simulate infiltration phenomena.