• Communications for Statistical Applications and Methods
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• 제29권5호
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• pp.499-512
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• 2022

Intervention measures have been implemented worldwide to reduce the spread of the COVID-19 outbreak. The COVID-19 outbreak has occured in several waves of infection, so this paper is divided into three groups, namely those countries who have passed the pandemic period, those countries who are still experiencing a single-wave pandemic, and those countries who are experiencing a multi-wave pandemic. The purpose of this study is to develop a multi-wave Richards model with several changepoint detection methods so as to obtain more accurate prediction results, especially for the multi-wave case. We investigated epidemiological trends in different countries from January 2020 to October 2021 to determine the temporal changes during the epidemic with respect to the intervention strategy used. In this article, we adjust the daily cumulative epidemiological data for COVID-19 using the logistic growth model and the multi-wave Richards curve development model. The changepoint detection methods used include the interpolation method, the Pruned Exact Linear Time (PELT) method, and the Binary Segmentation (BS) method. The results of the analysis using 9 countries show that the Richards model development can be used to analyze multi-wave data using changepoint detection so that the initial data used for prediction on the last wave can be determined precisely. The changepoint used is the coincident changepoint generated by the PELT and BS methods. The interpolation method is only used to find out how many pandemic waves have occurred in given a country. Several waves have been identified and can better describe the data. Our results can find the peak of the pandemic and when it will end in each country, both for a single-wave pandemic and a multi-wave pandemic.

• 한국습지학회지
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• 제23권2호
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• pp.107-115
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• 2021

서해 개야수로 인근의 파랑전파, 해수유동, 퇴적물이동을 분석하기 위해서 각종 인공구조물 설치 전(CASE1W)과 후(CASE2W)로 분류하고, CASE1W와 CASE2W에 대한 계산결과를 비교하였다. 파랑전파에 대해서는 SWAN 수치모형을 이용하여 입사파와 반사파의 결과를 도출하였고, 해수유동에 대해서는 FLOW2DH 수치모형을 이용하여 해수유동에 따른 유속 결과를 도출하였다. SWAN 수치모형과 FLOW2DH 수치모형의 결과는 퇴적물이동을 예측하는 SEDTRAN 수치모형의 입력조건이 되어 개야수로 인근의 최대 저면전단응력과 부유사 농도분포를 계산하였다. SWAN 수치모형 계산결과, CASE2W의 경우 약 7 km 길이의 북측 도류제에 의해서 입사파가 회절 및 중첩되고, 반사파가 생성되어 개야수로 인근의 파고를 CASE1W에 비해 40~50 % 증가시켰다. FLOW2DH 수치모형 계산결과, 북방파제, 북측 도류제 및 금란도에 의해서 개야수로의 유속이 CASE1W과 대비하여 CASE2W가 10~30 % 빠르게 계산되었다. SEDTRAN 수침모형의 계산결과, 복합 파랑장(입사파, 반사파, 조석)에 따른 해양환경과 각종 인공구조물의 설치에 의해서 개야수로의 최대 저면전단응력이 1.0 N/m² 이상인 구간과 부유사농도가 80 mg/L 이상인 구간이 넓게 분포되었다는 것은 개야수로에 퇴적현상이 발생한 것이라고 판단된다.

• 한국멀티미디어학회논문지
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• 제19권8호
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• pp.1377-1385
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• 2016

Conventional X-band marine radar has been used as one of the effective tools for collecting and retrieving ocean surface information parameters for three decades. Several wave information extracting algorithms have been designed in such a way that they can be utilized for efficiently estimating sea surface wave parameters such as current velocities, wave direction, significant wave heights in VTS (Vessel Traffic Service). However, their performances are still restricted. For the purpose of overcoming the performance limits, in this paper, first the conventional algorithms are analyzed and their performances are compared, and then a new control algorithm is proposed. Furthermore, we try to improve the estimation performances of typical wave parameters including wave directions and significant wave heights by introducing linear regression model in the process of computing wave information extraction. Through several simulations with the X-band radar images, it is shown that the proposed method is very effective in estimating the wave information compared to the real measured buoy data.

• Geomechanics and Engineering
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• 제10권4호
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• pp.387-403
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• 2016

In this paper, an integrated model for the wave (current)-induced seabed response is presented. The present model consists of two parts: hydrodynamic model for wave-current interactions and poro-elastic seabed model for pore accumulations. In the wave-current model, based on the fifth-order wave theory, ocean waves were generated by adding a source function into the mass conservation equation. Then, currents were simulated through imposing a steady inlet velocity on one domain and pressure outlet on the other side. In addition, both of the Reynolds-Averaged Navier-Stokers (RANS) Equations and $k-{\varepsilon}$ turbulence model would be applied in the fluid field. Once the wave pressures on the seabed calculated through the wave-current interaction model, it would be applied to be boundary conditions on the seabed model. In the seabed model, the poro-elastic theory would be imposed to simulate the seabed soil response. After comparing with the experimental data, the effect of currents on the seabed response would be examined by emphasize on the residual mechanisms of the pore pressure inside the soil. The build-up of the pore water pressure and the resulted liquefaction phenomenon will be fully investigated. A parametric study will also be conducted to examine the effects of waves and currents as well as soil properties on the pore pressure accumulation.

• 한국분무공학회지
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• 제1권2호
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• pp.57-65
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• 1996

Breakup models are evaluated using the experimental drop trajectory ill this study. The experimental conditions corespond to Weber # 56, 260, 463. Computations are carried out using a modified KIVA-II program with 2 different breakup submodel(TAB and Wave breakup model) and dynamic drag model which the drag coefficient changes dynamically with distortion parameter. Results show that computation with wave breakup model represents the experimental drop trajectory better than that with TAB submodel. And result with wave breakup model shows similar breakup pattern to experimental breakup process. It is thought that in wave breakup model the small drops are shed from the parent drop throughout parcel lifetime such thai this modelling represents the real breakup process well.

• ETRI Journal
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• 제38권6호
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• pp.1031-1041
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• 2016

This paper presents millimeter-wave (mmWave) propagation characteristics and channel model parameters including path loss, delay, and angular properties based on 28 GHz and 38 GHz field measurement data. We conducted measurement campaigns in both outdoor and indoor at the best potential hotspots. In particular, the model parameters are compared to sub-6 GHz parameters, and system design issues are considered for mmWave 5G Giga communications. For path loss modeling, we derived parameters for both the close-in free space model and the alpha-beta-gamma model. For multipath models, we extracted delay and angular dispersion characteristics including clustering results.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2004년도 춘계학술대회
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• pp.1023-1028
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• 2004

A micro-pressure wave is generated by the high-speed train which enters a tunnel, and it causes explosive noise and vibration at the exit. It is known that train speed, train-tunnel area ratio, nose slenderness and nose shape mainly influence on generating micro-pressure wave. So it is required to minimize it by searching optimal values of such train shape factors and tunnel condition. In this study, response surface model, one of approximation models, is used to perform optimization effectively and analyze sensitivity of design variables. Owen's randomized orthogonal array and D-optimal Design are used to construct response surface model. In order to increase accuracy of model, stepwise regression is selected. Finally SQP(Sequential Quadratic Programming) optimization algorithm is used to minimize the maximum micro-pressure wave by using built approximation model.

• 한국해양공학회지
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• 제18권4호
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• pp.40-45
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• 2004

An efficient numerical model of the modified mild slope equation, based on the robust iterative method is presented. The model developed is verified against other numerical experimental results, related to wave reflection from an arc-shaped bar and wave transformation over a circular shoal. The results show that the modified mild slope equation model is capable of producing accurate results for wave propagation in a region where water depth varies substantially, while the conventional mild slope equation model yeilds large errors, as the mild slope assumption is violated.

• 한국해안해양공학회지
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• 제19권6호
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• pp.565-573
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• 2007

타원형 수중천퇴가 있는 지형을 통과하며 변형하는 파랑을 실험한 Vincent and Briggs(1989)의 불규칙파 실험조건을 수치모의하여 파랑과 흐름의 상호작용 효과를 연구하였다. 수치모의를 위해 SHORECIRC(흐름모형)와 REF/DIF S(파랑모형)를 결합한 모형과 파랑과 흐름을 동시에 계산하는 FUNWAVE를 이용하였다. 이 수치모의로부터 수중 천퇴상에서 발생된 쇄파류는 수중천퇴후면의 파 집중현상을 방해하고, 파랑을 천퇴중심축의 바깥쪽으로 굴절시켜, 파고를 상대적으로 감소시키는 역할을 하는 것을 확인할 수 있었다. 결합모형의 수치모의 결과는 쇄파류의 영향을 고려하지 않는 파랑모형만의 결과보다 실험치와 더 일치하였으며, FUNWAVE를 이용한 수치모의도 실험결과와 잘 일치하였다. 이는 파랑쇄파류의 파랑변형에 미치는 역할의 중요성을 확인시켜주는 것이다.

• 한국해안해양공학회지
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• 제19권6호
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• pp.557-564
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• 2007

타원형 수중천퇴가 있는 지형을 통과하며 변형하는 파랑을 실험한 Vincent and Briggs(1989)의 실험조건을 수치모의하여 규칙파 변형에 대한 파랑과 흐름의 상호작용 효과를 연구하였다. 수치모의를 위해 흐름모형 SHORECIRC와 파랑모형 REF/DIF 1 그리고 SHORECIRC와 파랑모형 SWAN을 결합한 모형과 파랑과 흐름을 동시에 계산하는 FUNWAVE를 이용하였다. 이 수치모의로 부터 수중천퇴상에서 발생된 쇄파류는 수중천퇴후면의 파집중현상을 방해하고, 파랑을 천퇴중심축의 바깥쪽으로 굴절시켜, 파고를 상대적으로 감소시키는 역할을 하는 것을 확인할 수 있었다. 두 결합모형의 수치모의 결과는 쇄파류의 영향을 고려하지 않는 파랑모형만의 결과보다 실험치와 일치하였으나, 중복파가 발생되는 경우 SWAN모형과 REF/DIF모형으로부터 계산되어지는 잉여응력(radiation stress)에 문제가 있다는 것을 알 수 있었다. 또한, FUNWAVE를 이용한 수치모의는 실험결과와 완벽히 일치하였다. 이는 파랑쇄파류의 파랑변형에 미치는 역할의 중요성을 확인시켜주는 것이다.