• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2006.11a
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• pp.407-412
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• 2006

Most of the monopropellant thrusters use catalyst for decomposing hydrazine. The thruster lifetime is determined mainly by catalyst lifetime, which can be investigated by firing tests. For the development of hydrazine decomposition catalyst, Hot-fire test to verify long-life performance of catalyst is required. This study describes the development of test equipment for long duration hot-firing and test/evaluation plan.

• The Korean Journal of Applied Statistics
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• v.32 no.1
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• pp.69-81
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• 2019

We consider bivariate long range dependent (LRD) time series forecasting using a deep learning method. A long short-term memory (LSTM) network well-suited to time series data is applied to forecast bivariate time series; in addition, we compare the forecasting performance with bivariate fractional autoregressive integrated moving average (FARIMA) models. Out-of-sample forecasting errors are compared with various performance measures for functional MRI (fMRI) data and daily realized volatility data. The results show a subtle difference in the predicted values of the FIVARMA model and VARFIMA model. LSTM is computationally demanding due to hyper-parameter selection, but is more stable and the forecasting performance is competitively good to that of parametric long range dependent time series models.

• Korean Journal of Construction Engineering and Management
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• v.13 no.6
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• pp.13-23
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• 2012

While Category 1 and Category 2 bridges are intensively inspected and carefully managed, many small bridges that are not in the Category 1 and 2 are often forgotten until they decay in serious condition. Since many of these small bridges located in the populated city, failure of them would cause huge negative impact on the community. This paper focuses on the small size concrete bridges for timely repair and rehabilitation work for the effective operation and management. Test bed is developed to define the key parameters to forecast the long term performance of the bridges, mostly concrete box bridges. Key parameters suggested in this paper are cumulative fatigue due to repetitive heavy traffic loads and the acid attacks for concrete material deterioration. The cumulative fatigue is measured by the use of the mileage concept. For the long term data collection and inspection, stable and easy to use data collection system is installed as a test bed. The contribution of this research work is on the development of the test bed to define the key parameters of bridge deterioration.

• Magazine of the Korea Concrete Institute
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• v.11 no.3
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• pp.70-84
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• 1999

HPC를 사용한 장기수명 바닥판 콘크리트의 시공에 관한 4가지 접근방법을 제시하였다. Nebraska, New Hampshire, Texas 그리고 Virginia 등 4개주의 프로젝트에서 보면 아래와 같이 여러 가지 유사성을 알 수 있었다. $\cdot$ HPC의 사용은 장기 수명의 교량 바닥판을 건설하기 때문에 life cycle cost와 유지관리비의 감소가 예상된다. $\cdot$ 교량 바닥판에 대한 HPC의 중요성은 더 큰 강도보다는 내구성과 시공성을 일관성있게 양호하게 개선한다는 것이다. $\cdot$ 그 지역의 재료와 기존의 방법을 가능한 최대한 범위로 사용한다. $\cdot$ 많은 실험실 및 현장 시험 배합표가 개발되었고 배합되었다. 성능 특성은 혼합 재료의 형태, 상품 및 배합에 따라 다르게 나타났다. $\cdot$ 향상된 성질을 갖는 균일하고 일관성 있는 제품의 사용에 덧붙여 적절한 시공 기술은 장기 수명의 콘크리트 구조물을 위해서는 필수적이다. $\cdot$ 알카리-골재 반응을 갖고 있는 지역이나 높은 황산염을 갖고 있는 지역과 같이 특별한 문제점이 예상되는 지역에서는 화학적 내구성을 검토하기 위해 별도의 실험이 필요하다. $\cdot$ 현장에서 소요의 성능특성을 얻기 위해서는 시작부터 모든 분야 사이의 원활한 의견 교환과 협력이 요구된다.

• Journal of the Korean Geosynthetics Society
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• v.18 no.4
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• pp.15-23
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• 2019

The sprayable waterproofing membrane is a recently introduced material in the civil engineering field, and is a material that sprays and attaches a single phase or two phase powder or liquid material to a surface to be covered using a pump and nozzle. Although the material properties are gradually reported through researches, there is a lack of studies on long-term performance compared to concrete materials used with the membranes. In this study, the long-term performance of materials was estimated using the Arrhenius equation. The temperature conditions used in this study were 65℃, 80℃ and 95℃, and the temperature was maintained with the membrane attached to the concrete block for long-term behavior. Then the membranes were tested for tensile strength and adhesion strength in the order of 30, 90, 150, 200, and 300 days. The long-term performance of the material was determined from a long-term perspective by estimating the activation energy by the Arrhenius equation. Consequently, the time to reach 50% of the performance standard could be estimated by long-term test.

• The Journal of Engineering Geology
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• v.33 no.4
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• pp.725-736
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• 2023

The compliance of deep geological disposal facilities for high-level radioactive waste with safety objectives requires consideration of uncertainties owing to temporal changes in the disposal system. A comprehensive review and analysis of the characteristics of this evolution should be undertaken to identify the effects on multiple barriers and the biosphere. We analyzed the evolution of the buffer, backfill, plug, and closure regions during the early phase of the post-closure period as part of a long-term performance assessment for an operating license application for a deep geological repository in Finland. Degradation mechanisms generally expected in engineered barriers were considered, and long-term evolution features were examined for use in performance assessments. The importance of evolution features was classified into six categories based on the design of the Finnish case. Results are expected to be useful as a technical basis for performance and safety assessment in developing the Korean deep geological disposal system for high-level radioactive waste. However, for a more detailed review and evaluation of each feature, it is necessary to obtain data for the final disposal site and facility-specific design, and to assess its impact in advance.

• Proceedings of the Korea Water Resources Association Conference
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• 2009.05a
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• pp.991-995
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• 2009

최근 기후변화 등으로 우리나라의 경우 강수일수는 감소한 반면 집중호우의 발생빈도는 증가하고 있다. 실제 가뭄과홍수와 같은 극치사상의 피해가 증가될 가능성과 이러한 재해로부터 인명 및 재산을 보호하고 효율적인 수자원 활용을 위해서는 장기간 강우-유출과정의 정확한 해석이 필수적이다. 본 연구는 미호천 유역을 대상으로 장기유출을 모의하기 위해 개념적 강우유출모형을 적용하였다. 본 연구의 개념적 강우유출모형은 PDM(Probability Distributed Model)으로 유역을 한 개의 단위구역으로 사용한 집중형(lumped) 모형이고, 분포형 모형에 비하여 간단 (parsimonious)하며 영국의 수자원 및 홍수 관리 목적으로 널리 사용되고 있다. 모형의 검정은 MC(Monte Carlo) 방법과 SCE-UA(Shuffled Complex Evolution-University of Arizona) 방법을 적용하였으며, NSE(Nash Sutcliffe Efficiency) 목적함수를 사용하여 모형의 성능을 검토하였다. 그 결과, MC 방법과 SCE-UA 방법 모두 NSE의 값 0.9 이상으로 만족할 만한 모의성능을 나타내었다. 분포형 모형에 비하여 적은 수문자료 및 검정변수를 갖는 PDM 모형을 수문자료의 취득이 용이하지 않은 중 소규모 유역에 적용하여 모형의 검정 및 유량산정에 있어 우수함을 확인하였다. 이에 우리나라 전역에 걸쳐 다양한 유역을 대상으로 PDM 모형의 검토가 요구되고, 향후 우리나라의 홍수량 산정 및 수자원 관리에 적용될 수 있다고 판단된다.

• Proceedings of the Korea Institute of Fire Science and Engineering Conference
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• 2013.11a
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• pp.141-142
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• 2013

철골건축물은 화재에 취약한 구조로써 내화성능 확보를 위하여 내화피복이 필수적이다. 국내에서 가장 많이 사용되고 있는 철골내화피복재는 내화뿜칠재로 폭 넓게 사용되고 있으나, 기존 제도에서 인정 당시의 내화성능은 확인이 가능하나 시간경과에 따른 내구성저하와 이에 따른 내화성능 저하가 예상된다. 이에 본 연구에서는 실내조건에서 장시간 자연폭로실험을 실시함으로써 내화뿜칠피복재의 시간경과에 따른 내화성능 저하현상을 확인하였다.

• Journal of the Society of Disaster Information
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• v.14 no.1
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• pp.79-88
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• 2018

In this study, the changes of the expansion and strength according to the temperature of the emergency repairing expansion material were examined by cup foaming test and uniaxial compressive strength test, and the accelerated compression creep test was carried out to confirm the long term stability. Ramp & Hold test and accelerated compressive creep test were performed to evaluate the creep performance. The short - term creep test was used to determine the initial creep strain of the expanding material. The isothermal method using time - To evaluate the long - term compressive creep performance.

• Journal of the Korean Society of Propulsion Engineers
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• v.18 no.6
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• pp.68-74
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• 2014

During the life firing test of 1 N-class thruster development model, pulse mode performance and performance changes were examined. The deviation of pulse mode response time according to thruster feed pressure was relatively small and the resultant ignition delay, response time, tail-off time were 32-35 ms, 86-91 ms, 89-98 ms, respectively. For the stabilized pulse region the impulse bit revealed the outstanding reproducibility of 1.41, 1.32, 2.10% at $3{\sigma}$. During the life firing test, the impulse bit was decreased with limited amounts, therefore the pulse mode performance could be considered to be maintained. The thrust centroid was also maintained during the life firing test.