• Journal of Korea Water Resources Association
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• v.49 no.4
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• pp.275-282
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• 2016

The objective of this study is to propose a new method to determine the drought event and the design drought severity. In order to define a drought event from precipitation data, theory of run was applied with the cumulative rainfall deficit. When we have a large amount of rainfall over the threshold level, in this study, we compare with the previous cumulative rainfall deficit to determine whether the drought is relieved or not. The recurrence characteristics of the drought severity on the specific duration was analyzed by the conditional bivariate copula function and confidence intervals were estimated to quantify uncertainties. The methodology was applied to Seoul station with the historical dataset (1909~2015). It was observed that the past droughts considered as extreme hydrological events had from 10 to 50 years of return period. On the other hand, the current on-going drought event started from 2013 showed the significantly higher return period. It is expected that the result of this study may be utilized as the reliable criteria based on the concept of return period for the drought contingency plan.

• Proceedings of the Korea Water Resources Association Conference
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• 2016.05a
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• pp.98-98
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• 2016

본 연구에서는 유입량의 불확실성을 고려하여 미래 저수량을 확률론적으로 예측하였다. 월별 유입량을 표본으로 한 확률밀도함수를 핵밀도함수(kernel function)를 이용하여 추정하고, 추정된 확률분포로 월별 유입량을 모의 발생하였다. 모의 발생된 유입량을 통해 연속적인 조건부 확률을 산정하였고, 이의 누적확률분포(F(x))는 해당 저수량에 도달하지 못할 확률, 즉 실패확률을 의미하므로 1-F(x)로 해당 저수량 이상을 확보할 수 있는 확률을 산정하였다. 보령댐을 대상으로 분석한 결과 2016년 2월 말 저수량 27.8 백만$m^3$ 기준으로 3월부터 6월까지 정상용수공급환원 기준 저수량을 만족할 확률이 각각 2.3%, 12.5%, 24.2%, 33.5%로 나타났다. 지역적 가뭄에 대응하기 위해 하천유지용수 감량, 용수 대체공급, 자율 급수조정 및 금강-보령댐 도수로를 이용한 용수공급으로 20.6만$m^3/day$의 용수가 비축될 경우, 정상용수공급환원 기준 저수량을 만족할 확률이 10.2%, 40.3%, 73.8%, 78.7%로 용수비축의 효과가 크게 나타나는 것을 확인하였다. 저수량의 확률론적 예측을 통해 미래 저수량의 확률적 발생가능성을 추정할 수 있으며, 가뭄이 발생할 경우, 가뭄 대응효과를 정량적으로 나타낼 수 있어 가뭄 위험 상황 전달 및 용수공급조정 의사결정 시 활용할 수 있을 것으로 판단된다.

• Proceedings of the Korea Water Resources Association Conference
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• 2021.06a
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• pp.178-178
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• 2021

최근 들어 기후변화로 인한 극심한 가뭄 피해가 한반도에 발생하고 있다. 가뭄 상황에 대비하여 댐을 안정적으로 운영하기 위해서는 갈수빈도 유입량에 대한 분석이 필수적이다. 갈수빈도해석의 경우, 홍수빈도해석과 유사하게 확률밀도함수의 극값에 대한 확률값을 산정하며, 확률 분포형의 역함수에 비초과확률을 대입하여 산정한다. 그러나 홍수와 달리 가뭄은 지속기간이 긴 특성 탓에 자기상관을 고려해야하며, 댐 및 저수지 등 대규모 시설물의 경우 일반적인 하천과 달리 저류효과로 인해 누적 유량에 대한 고려가 필요하다. 이에 K-water는 자체 제작한 누가차분법 및 Disaggregation 두 가지 방법을 채택하여 실무에서 사용해왔다. 그러나 누가차분법을 사용할 경우, 빈도유입량이 지나치게 크게 산정되는 문제가 있으며, Disaggregation 방법을 사용하는 경우, 특정 빈도 이상의 극한가뭄에서 유입량의 차이가 유의미하지 않아 산정된 빈도유입량과 최근 발생한 극심한 가뭄의 실측유입량간 큰 차이가 발생하고 있다. 따라서 본 연구에서는 자기상관을 고려한 선형회귀모형에 근거하여 빈도유입량을 배분하는 방법을 제안한다. 또한, 앞서 서술한 네 가지 빈도유입량 방법(월빈도분석, 누가차분법, K-water Disaggregation, 자기상관 선형회귀모형)에 대한 수식적 비교를 수행하며, 국내 댐 유역에 적용 및 평가를 통해 자료 특성에 따른 적절한 빈도유입량 산정방식에 대한 기준을 제안한다. 본 연구를 통해 가뭄특성을 고려한 합리적인 댐 유입량을 산정함으로써 보다 유연한 수자원시설물의 가뭄대응이 이루어질 것으로 기대된다.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.27 no.4
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• pp.274-279
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• 2015

Wave data acquired over eleven years near Sokcho Harbor located in the central area of the east coast were analyzed using spectral method and wave-by-wave analysis method and its major wave characteristics were examined. Significant wave heights were found to be high in winter and low in summer, and peak periods were also found to be long in winter and short in summer. The maximum significant wave height observed was 8.95 m caused by the East Sea twister. The distributional pattern of the significant wave heights and peak periods were both fitted better by Kernel distribution function than by Generalized Gamma distribution function and Generalized Extreme Value distribution function. The wave data were compiled to subdivide the wave height into intervals for each month, and the cumulative occurrence rates of wave heights were calculated to be utilized for the design and construction works in nearby construction works.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.27 no.2
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• pp.142-147
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• 2015

Wave data acquired over seven years near Daejin Harbor located in the north central area of the east coast was analyzed using spectral method and wave-by-wave analysis method and its major wave characteristics were examined. Significant wave heights were found to be high in winter and low in summer, and peak periods were also found to be long in winter and short in summer. The maximum significant wave height observed was 6.59 m and was caused by Typhoon No. 1216, SANBA. The distributional pattern of the significant wave heights and peak periods were both reproduced better by Kernel distribution function than by Generalized Gamma distribution function and Generalized Extreme Value distribution function. Meanwhile, the wave data was subdivided by month and wave height level and the cumulative appearance rate was proposed to aid designing and constructing works in nearby coastal areas.

• Journal of the Korean Geotechnical Society
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• v.19 no.5
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• pp.7-14
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• 2003

In the back analysis of braced excavation based on displacement measurements, the accumulated errors of abnormal displacement caused by unexpected loads are usually observed. To minimize such errors, in this study, displacement increment was used fur back analysis rather than displacement for the conventional method. That is, the increment of sequential displacement is used as the objective function and the back analysis program is developed by taking advantage of sequential linear programming method by modified method of feasible directions. Based on small scale model test, the analysis of proposed method is verified.

• Journal of Korean Tunnelling and Underground Space Association
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• v.24 no.1
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• pp.1-13
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• 2022

A weighted linear combination of seismic fragility models previously developed for cut-and-cover railway tunnels was presented and the appropriateness of the combined model was evaluated. The seismic fragility function is expressed in the form of a cumulative probability function of the lognormal distribution based on the peak ground acceleration. The model uncertainty can be reduced by combining models independently developed. Equal weight is applied to four models. The new seismic fragility function was developed for each damage level by determining the median and standard deviation, which are model metrics. Comparing fragility curves developed for other bored tunnels, cut-and-cover tunnels for high-speed railway system have a similar level of fragility. We postulated that this is due to the high seismic design standard for high-speed railway tunnel.

• Proceedings of the Korean Information Science Society Conference
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• 2003.10a
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• pp.394-396
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• 2003

본 논문에서는 메시지 패싱 시스템에서의 태스크 스케줄링에 대해 다룬다. 병렬/분산 시스템의 어플리케이션의 태스크에 대한 적절한 스케줄링이 이루어지지 않는 경우, 정렬/분산 처리를 이용한 이득을 기대하기는 어렵기 때문에 이 주제에 대한 연구는 컴퓨터 아키텍처의 발달과 함께 지속되고 있으며, 많은 연구들이 태스크 스케줄링에 대한 다양한 기법들을 제안하고 있다. 하지만 통신비용을 데이터를 소모하는 한쪽의 테스크에만 부과하는 기존 기법들을 메시지 패싱 시스템에 적용하기는 부족한 면이 있다. 본 논문에서는 기존 연구의 모델과 메시지 패싱 시스템에서 통신비용이 통신과 관계된 모든 노드에서 발생함을 고려하여 리스트 스케줄링 기법에 기초한 개선된 우선순위 함수와 새로운 프로세서 선택 기준을 제안한다. 이들 두 가지 제안을 적용한 태스크 스케줄링 기법은 메시징 패싱 시스템에서 통신비용이 누적되는 특징으로 발생하는 비효율적인 스케줄링을 개선한다.

• Journal of Korea Water Resources Association
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• v.45 no.4
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• pp.409-418
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• 2012

A modified standardized precipitation index was developed by considering the length of dry period and surface run-off effect. The official reports and newspapers on drought from 1973 to 2009 were quantified to evaluate drought indices. The developed index was evaluated using the receiver operating characteristic analysis. In order to suggest improved drought index, we cut the precipitation amount that may do not contribute the mitigation of drought and weight dry period by considering cumulative distribution, decile distribution of dry periods. Drought detection capability of the suggested index has improved by weighting of dry period effects and considering precipitation amounts contributing drought mitigation.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.25 no.12
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• pp.1756-1761
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• 2021

Although the COVID-19 outbreak that occurred in Wuhan, Hubei around December 2019, seemed to be gradually decreasing, it was gradually increasing as of November 2020 and June 2021, and estimated confirmed cases were 192 million worldwide and approximately 184 thousand in South Korea. The Central Disaster and Safety Countermeasures Headquarters have been taking strong countermeasures by implementing level 4 social distancing. However, as the highly infectious COVID-19 variants, such as Delta mutation, have been on the rise, the number of daily confirmed cases in Korea has increased to 1,800. Therefore, the number of cumulative confirmed COVID-19 cases is predicted using ARIMA algorithms to emphasize the severity of COVID-19. In the process, differences are used to remove trends and seasonality, and p, d, and q values are determined and forecasted in ARIMA using MA, AR, autocorrelation functions, and partial autocorrelation functions. Finally, forecast and actual values are compared to evaluate how well it was forecasted.