• Nuclear Engineering and Technology
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• v.53 no.8
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• pp.2488-2498
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• 2021

The wall film-wise condensation plays an important role in the heat transfer processes of heat exchangers, refrigerators, and air conditioner. In the field of nuclear engineering, steam condensation is often utilized in safety systems to remove the core decay heat under both transient and accident conditions. In particular, passive containment cooling system (PCCS), are designed to ensure containment safety under severe accident conditions. A computational fluid dynamics (CFD) scale analysis has been conducted to calculate the heat transfer rate of the PCCS. However, despite the increase in computing power, there are challenges in the long-term transient simulation of containment using CFD scale codes. In this study, a heat structure coupling between the CFD and system analysis codes was performed to efficiently analyze PCCS. In addition, the component unstructured program for interfacial dynamics (CUPID) was improved to analyze the condensation behavior of ternary gas mixtures. Thereafter, the condensation heat transfer on the primary side was calculated using the improved CUPID and CFD code, whereas that on the secondary side was simulated using MARS. Both the coupled codes were validated against the CONAN facility database. Finally, conjugate heat transfer simulations with wall condensation in the presence of non-condensable gases were appropriately performed.

• Journal of Ocean Engineering and Technology
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• v.36 no.1
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• pp.41-49
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• 2022

With the advancement of intelligent vehicles and unmanned systems, there is a growing interest in underwater surveys using autonomous marine vehicles (AMVs). This study presents an automated planning strategy for a long-term survey mission using a fleet of AMVs consisting of autonomous surface vehicles and autonomous underwater vehicles. Due to the complex nature of the mission, the actions of the vehicle must be of high-level abstraction, which means that the actions indicate not only motion of the vehicle but also symbols and semantics, such as those corresponding to deploy, charge, and survey. For automated planning, the planning domain definition language (PDDL) was employed to construct a mission planner for realizing a powerful and flexible planning system. Despite being able to handle abstract actions, such high-level planners have difficulty in efficiently optimizing numerical objectives such as obtaining the shortest route given multiple destinations. To alleviate this issue, a widely known technique in operations research was additionally employed, which limited the solution space so that the high-level planner could devise efficient plans. For a comprehensive evaluation of the proposed method, various PDDL-based planners with different parameter settings were implemented, and their performances were compared through simulation. The simulation result shows that the proposed method outperformed the baseline solutions by yielding plans that completed the missions more quickly, thereby demonstrating the efficacy of the proposed methodology.

• Structural Engineering and Mechanics
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• v.84 no.3
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• pp.323-335
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• 2022

The main idea of the framework is to seamlessly combine a reasonably accurate and fast surrogate model with the importance sampling strategy. Developing a surrogate model for predicting structures' dynamic responses is challenging because it involves high-dimensional inputs and outputs. For this purpose, a novel surrogate model based on cutting-edge deep learning architectures specialized for capturing temporal relationships within time-series data, namely Long-Short term memory layer and Transformer layer, is designed. After being properly trained, the surrogate model could be utilized in place of the finite element method to evaluate structures' responses without requiring any specialized software. On the other hand, the importance sampling is adopted to reduce the number of calculations required when computing the failure probability by drawing more relevant samples near critical areas. Thanks to the portability of the trained surrogate model, one can integrate the latter with the Importance sampling in a straightforward fashion, forming an efficient framework called TTIS, which represents double advantages: less number of calculations is needed, and the computational time of each calculation is significantly reduced. The proposed approach's applicability and efficiency are demonstrated through three examples with increasing complexity, involving a 1D beam, a 2D frame, and a 3D building structure. The results show that compared to the conventional Monte Carlo simulation, the proposed method can provide highly similar reliability results with a reduction of up to four orders of magnitudes in time complexity.

• New & Renewable Energy
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• v.5 no.3
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• pp.13-21
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• 2009

National wind atlas of Korea requires effective database management because it has been constructed by 5-year long-term time-series numerical wind simulation. Therefore, database of the national wind map has been developed to increase data structure efficiency using IDL scientific programming language which has outstanding feature in mega-capacity numerical dataset. Visualization module also has been developed under IDL environment and it is anticipated to maximize post processing efficiency and applicability of the national wind map especially in the standing points of researchers and developers.

• ETRI Journal
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• v.35 no.5
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• pp.739-747
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• 2013

This paper investigates the multifarious nature of the long-term evolution (LTE) scheme and that of the modified LTE scheme for symbol timing synchronization (STS). This investigation allows us to propose a new replica correlation-based STS scheme to overcome the inherent weaknesses of the other two schemes. The proposed STS signal combines a gold sequence and a half sine wave in the time domain, whereas conventional STS signals specify either binary sequences or complex sequences in the time domain or in the frequency domain. In the proposed scheme, a sufficient correlation property is realized by the gold sequence, and robustness against the frequency offset (FO) is achieved through the sine wave. Compared to the existing LTE-related schemes, the proposed scheme can better achieve immunity to FO and reduction in detector complexity, as well as a low peak-to-average power ratio and a low detection error rate. Performance evaluations through analysis and simulation are provided in the paper to demonstrate these attributes.

• Journal of IKEEE
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• v.16 no.3
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• pp.159-166
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• 2012

In this paper, we designed and implemented the MIMO (Multiple-Input Multiple-Output) antenna for the mobile handset that could be used for multiple services. Simulation results were obtained using SEMCAD X by SPEAG based on the FDTD (Finite Difference Time Domain) Method which showed that S11 values were less than -6 dB (VSWR < 3) for LTE (Long Term Evolution) 700/2300/2500, K-PCS (Korea-Personal Communication Service : 1,750 ~ 1,870 MHz), US-PCS (US-Personal Communication Service : 1,850 ~ 1,990 MHz), Wibro (2,300 ~ 2,390 MHz), Bluetooth (2,400 ~ 2,483 MHz), and US-WiMAX (US-World interoperability for Microwave Access: 2,400 ~ 2,590 MHz) frequency bands. Measured results of the fabricated antenna also showed that it could be used for LTE 700/2300/2500, K-PCS, US-PCS, Wibro, Bluetooth, and US-WiMAX. services.

• Journal of Korean Society on Water Environment
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• v.24 no.2
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• pp.221-229
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• 2008

This study revised a model for hydrologically analyzing rainwater harvesting facilities considering their rainfall-runoff properties and the data available. This model has only a few parameters, which can be estimated with rather poor measurements available. The model has a non-linear module for rainfall loss, and the remaining rainfall excess (effective rainfall) is assumed to be inflow to the storage tank. This model has been applied for the rainwater harvesting facilities in Seoul National University, Korea Institute of Construction Technology, and the Daejon World Cup Stadium. As a result, the runoff coefficients estimated were about 0.9 for the building roof as a rainwater collecting surface and about 0.18 for the playground. This result is coincident with that for designing the rainwater harvesting facilities to show the accuracy of model and the simulation results.

• Water Engineering Research
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• v.4 no.3
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• pp.111-126
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• 2003

Meteorological data are often needed to evaluate the long-term effects of proposed hydrologic changes. The evaluation is frequently undertaken using deterministic mathematical models that require daily weather data as input including precipitation amount, maximum and minimum temperature, relative humidity, solar radiation and wind speed. Stochastic generation of the required weather data offers alternative to the use of observed weather records. The precipitation is modeled by a Markov Chain-exponential model. The other variables are generated by multivariate model with means and standard deviations of the variables conditioned on the wet or dry status of the day as determined by the precipitation model. Ultimately, the objective of this paper is to compare Richardson's model and the improved weather generation model in their ability to provide daily weather data for the crop model to study potential impacts of climate change on the irrigation needs and crop yield. However this paper does not refer to the improved weather generation model and the crop model. The new weather generation model improved will be introduced in the Journal of KWRA.

• Proceedings of the Korea Water Resources Association Conference
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• 2009.05a
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• pp.1012-1016
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• 2009

수자원 시스템 거동예측은 수문학적 지속성여부에 대한 판단이 선행 되어야 하며 가용한 시계열자료에 대한 추계학적 분석을 통하여 실시하여야 한다. 본 연구에서는 계절형 ARIMA모형을 통한 안동댐 유역의 강우량, 증발산량 및 유출량 시계열자료를 예측함에 있어 전형적인 Box-jenkins의 방법을 따랐고 모형의 식별, 추정, 검진의 3단계를 거쳐 모형화 하였다. 최적 수문시계열 예측 모형을 통하여 안동댐 유역의 강우량, 증발산량 및 유출량 시계열자료로 월별 수문시스템 거동을 예측하였으며, 예측된 결과를 토대로 TANK모형과 ARIMA+TANK결합모형에 의한 장기유출모의를 실시하였다. 분석결과 관측자료의 특성을 비교적 잘 반영 하였으며, 댐 유입량 예측을 위한 추계학적 결합모형의 적용가능성을 검토하였다. 이는 유출량자료의 보유년한이 짧은 대상유역에 월강우량과 증발산량자료 등의 수문시계열 인자 예측을 통한 유출을 모의함으로서 수자원의 중 장기 전략수립에 도움을 줄 것으로 사료된다.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.58 no.4
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• pp.718-724
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• 2009

Recently, Increase of energy consumption is continued accordingly because economy is constant growth. so we need long term of energy supply stability and develop new energy source. The effort of environmental improvement is necessary and our country has to educe conservatory gas in these situation, our energy policy is summarized that minimizes energy consumption and uses kinds of energy source. This paper studied some effort of stability that distributed generation put in electric system through line fault, sudden load change. And then this paper calculated penetrated level of distributed generation in system transient stability.