• Journal of Internet Computing and Services
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• v.23 no.4
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• pp.45-55
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• 2022

The size of the cryptocurrency market is growing. For example, market capitalization of bitcoin exceeded 500 trillion won. Accordingly, many studies have been conducted to predict the price of cryptocurrency, and most of them have similar methodology of predicting stock prices. However, unlike stock price predictions, machine learning become best model in cryptocurrency price predictions, conceptually cryptocurrency has no passive income from ownership, and statistically, cryptocurrency has at least three times higher liquidity than stocks. Thats why we argue that a methodology different from stock price prediction should be applied to cryptocurrency price prediction studies. We propose Reverse Walk-forward Validation (RWFV), which modifies Walk-forward Validation (WFV). Unlike WFV, RWFV measures accuracy for Validation by pinning the Validation dataset directly in front of the Test dataset in time series, and gradually increasing the size of the Training dataset in front of it in time series. Train data were cut according to the size of the Train dataset with the highest accuracy among all measured Validation accuracy, and then combined with Validation data to measure the accuracy of the Test data. Logistic regression analysis and Support Vector Machine (SVM) were used as the analysis model, and various algorithms and parameters such as L1, L2, rbf, and poly were applied for the reliability of our proposed RWFV. As a result, it was confirmed that all analysis models showed improved accuracy compared to existing studies, and on average, the accuracy increased by 1.23%p. This is a significant improvement in accuracy, given that most of the accuracy of cryptocurrency price prediction remains between 50% and 60% through previous studies.

• Proceedings of the Korea Water Resources Association Conference
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• 2006.05a
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• pp.441-446
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• 2006

유역에서 발생한 고탁수가 저수지내에서 장기화하는 현상에 관한 대책은 장기간이 소요되는 유역관리 대책과 탁수저감일수를 최소화하는 선택취수 개념의 우선 방류기법 등이 있다. 하류하천으로의 탁수 우선배제를 실시하기 위해서는 댐 방류탁수가 하류에 미치는 영향을 정확히 예측할 수 있는 하천탁도 예측 및 관리시스템 구축이 필요하다. 최근 고탁수현상을 경험한 낙동강 수계에서는 본류의 탁도 관리를 위해 임하댐 및 안동댐의 연직 탁도 분포 변화에 따라 댐 방류탁수에 의한 영향을 최소 또는 기준치 이하로 할 수 있는 댐 연계운영에 관한 조건 도출이 필요하다. 선택취수에 관한 수치모의 결과를 이용하여 저수지내 온도 및 탁도 분포 변화와 취수탑의 수문운영에 따른 방류수의 온도 및 탁도를 예측할 수 있다. 본 연구에서는 이와 같은 결과를 이용하여 안동댐과 임하댐의 방류조건에 대한 하류하천 합류부에서의 2차원 이송 확산 수치모의를 수행하고자 하였다. 이와 같은 연구를 성공적으로 수행하기 위해서는 지속적인 현장조사를 통한 지점별 탁도-SS 상관관계 도출, 비정상 흐름 및 수질모의 검 보정, 탁도예측 결과 검증이 필요하다. 평면 2차원 흐름 및 수질 모의 결과에 의하면, 임하댐 방류 탁도로 인한 반변천의 고탁수는 안동댐 방류 수에 지배를 받는 낙동강 본류와 합류되는 지점에서부터 약 5 km 떨어진 지점에서 횡방향 완전혼합이 이루어지는 것으로 나타났다. 이와 같은 모의결과는 완전혼합을 가정하는 1차원 수질모델링의 초기 입력자료에 사용됨으로써 1차원 탁도 모의결과의 정확성을 높이는 데 사용될 수 있다. 이를 이용하여 낙동강 수계 댐 연계운영에 따른 낙동강 탁도 예측모의를 수행하고, 이 결과를 이용하여 낙동강 탁도 예경보 시스템을 구축해야 할 것이다. 또한 선택취수 등을 통해 저수지 관리를 효과적으로 수행하기 위해서는 저수지 내부의 탁도 거동을 정확히 예측할 수 있어야 한다. 따라서 추후 동수역학 및 열역학에 기초한 3차원 수치모형 연구와 성층흐름에 정밀한 밀도류 실험연구 및 이에 대한 적용이 필요할 것으로 판단된다.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.37 no.12
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• pp.1069-1078
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• 2013

Recently, condensation heat exchangers have been studied for applications to the passive cooling systems of nuclear plants. To design vertical-type condensation heat exchangers in secondary passive cooling systems, TSCON (Thermal Sizing of CONdenser), a thermal sizing program for a condensation heat exchanger, was developed at KAERI (Korea Atomic Energy Research Institute). In this study, the existing condensation heat transfer correlation of TSCON was evaluated using 1,157 collected experimental data points from the heat exchanger of a secondary passive cooling system for the case of pure steam condensation. The investigation showed that the Shah correlation, published in 2009, provided the most satisfactory results for the heat transfer coefficient with a mean absolute error of 34.8%. It is suggested that the Shah correlation is appropriate for designing a condensation heat exchanger in TSCON.

• The Journal of the Korea Contents Association
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• v.15 no.3
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• pp.32-39
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• 2015

In this paper, We propose the futuristic map using variety technology of advanced ICT-based. The futuristic maps are expected to developed into a new format of user participation to express the results in various formats through the understanding and interpretation of the facts and phenomena of tangible and intangible that exist in the real world. In the future, the map is expected to be developed into form of a new paradigm map made in real time that economy, industry, the collection of information necessary for everyday life, processing, usage, analysis, distribution and sharing. In this paper, we provide a real-time personalized contents to digitize the information of the real space based on the concept of map, databases, spatial analysis and describes the key technologies that characterized by the representation of time-series data by analyzing and prediction every field macro phenomena of society, economy, culture and etc. And we establish the concepts of the 'New Paradigm Map' for future creative economy.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2007.11a
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• pp.275-281
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• 2007

For a cooling performance research of the combustor operated in a extreme environment of a high temperature and high pressure, we accomplished a cooling performance analysis. Generally a heat transfer characteristic in cooling passage is known well experimentally and theoretically, however heat flux in the combustion chamber isn't. In this study, fluid flow combined with heat transfer analysis is accomplished about a combustor nozzle. We tried to analyze the cooling performance with a heat transfer characteristic of a gas and coolant side in the view point of quantity on the mass flow rate to be supplied to the cooling channel. And finally, evaluation on the thermal safety of nozzle wall material was accomplished.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.35 no.9
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• pp.955-960
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• 2011

This study was aimed at investigating the applicability of energy harvesting technologies, which are regarded as new and renewable energy sources for real-time/wireless monitoring of intelligent railroad vehicles. The surrounding energy generated in a normal operating environment was monitored using a high-speed railroad vehicle in operation. This monitoring was performed in an attempt to evaluate the effectives of energy harvesting and the applicability of energy-harvesting-monitoring technologies under the conditions in which thermal energy and vibration energy are generated.

• Proceedings of the Korea Institute of Fire Science and Engineering Conference
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• 2010.10a
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• pp.241-245
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• 2010

화재방호에 성능기반 개념을 도입함에 따라 화재모델링의 활용도는 점점 높아지고 있다. 본 연구의 목적은 FDS를 이용하여 원자력발전소 펌프실의 윤활유 화재 시 케이블의 손상여부를 평가하고, 확인분석을 통해 화재모델링의 적합성을 파악하는 데 있다. 화재는 펌프 주변의 누출된 윤활유에서 발생하며 화원의 면적은 $2.75m^2$이고 단위면적당 열방출율은 $1,794kW/m^2$로 가정하였다. 계산결과, 고온기체층의 온도는 $400^{\circ}C$를 상회하고 있으나 케이블 트레이의 온도는 $50^{\circ}C$ 아래로 예측되고 있어 본 화재시나리오에서 케이블의 건전성은 유지되고 있으며 밀폐된 격실에서의 대형화재는 환기지배형 화재가 된다는 것을 보여주고 있다. 또한 확인분석 결과, 화재 시나리오의 주요 변수인 열방출율, 격실크기 그리고 강제 환기 변수가 확인계산 범위 내에 있어 본 계산결과는 NUREG-1824의 확인요건을 만족하고 있다. 따라서 펌프실 윤활유 화재에 대한 모델링의 적합성을 확인하였다.

• Nuclear Engineering and Technology
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• v.27 no.3
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• pp.393-402
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• 1995

The structural analysis of the reactor coolant system mainly consist of too fields. The one is the static analysis considering the impact of pressure and temperature built up during normal operation. The other is the dynamic analysis to estimate the impact of postulated events such as the seismic loads or postulated branch line pipe breaks event. Since the most important goal of the RCS structural analysis is to prove the safety of the RCS during normal operation or postulated events, a widely proven theory having enough conservatism is adopted. The load occurring on the RCS during normal operation is considered as the basic design loading condition throughout whole plant life time. The most typical characteristic of the RCS during normal operation is the thermal expansion of the RCS caused by reactor coolant with high temperature and pressure. Therefore, the exact estimation on the thermal movement of the RCS is needed to get more clear understanding on the thermal movement behavior of the RCS. In this study, the general structural analysis concept and modeling method to evaluate the thermal movement of the RCS under the normal plant operation condition are presented. To discuss the validation of the suggested analysis, analysis results are compared with the measured data which ore referred from the standardized 1000 MWe PWR plant under construction.

• Composites Research
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• v.15 no.5
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• pp.27-34
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• 2002

The purpose of this study is to measure and predict the thermal conductivity of CF3327 plain-weave fabric composite made by Hankuk Fiber, Co. An experiment apparatus based on the comparative method has been made to measure the thermal conductivities of the composite material. Its accuracy was proved by measuring the thermal conductivity of graphite which is well-known. Micro-mechanical approaches are useful to assess the effect of parameters such as fiber and matrix material properties, fiber volume fraction and fabric geometric parameters on the effective material properties of composites. In this study, prediction was based on the concept of three dimensional series-parallel thermal resistance network. Thermal resistance network was applied to unit ceil model that characterized the periodically repeated pattern of a plain weave. The numerical results were compared with experimental one and good agreement was observed. Also, the effects of fiber volume fraction on the thermal conductivity of several composites has been investigated.

• Proceedings of the Korea Institute of Fire Science and Engineering Conference
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• 2011.11a
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• pp.378-381
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• 2011

대표적 가스계 소화약제인 $CO_2$의 소화기구(Extinguishing mechanism)를 재조명하기 위하여, $CH_4$/air 저 신장율 대향류 확산화염을 대상으로 $CO_2$가 소화에 미치는 영향에 대한 수치해석이 수행되었다. 부력이 지배적인 화염의 소화현상은 복사 열손실에 의해 큰 영향을 받기 때문에, 소화농도 예측에 대한 복사모델의 성능평가가 우선적으로 이루어졌다. 주요 결과로서, 공기류에 첨가된 $CO_2$의 소화농도는 복사모델이 고려되지 않은 경우 과다 예측되는 반면에, 간략화된 광학적으로 얇은 근사(Optically thin approximation) 모델과 비교적 높은 정확도를 갖는 좁은 밴드(Statistical narrow band) 모델은 실험의 오차범위 내에서 큰 차이를 보이지 않았다. $CO_2$가 소화에 미치는 순수 희석효과, 희석에 의한 복사효과, 화학적 효과 및 열적효과를 정량적으로 분석하기 위하여 가상의 소화약제의 개념을 도입하였다. 이를 통해 화염의 총괄신장율에 따른 $CO_2$ 소화효과에 대한 구체적인 이해가 시도되었다.