Analysis of Empirical Constant of Eddy Viscosity by Zero- and One- Equation Turbulence Model in Wake Simulation

박일흠,조영준,김태윤,이문옥,황성수 해양환경안전학회 2014 해양환경안전학회지 Vol.20 No.3

In this paper, the wakes behind a square cylinder were simulated using two kinds of different turbulence models for the eddy viscosity concept such as the zero- and the one-equation model in which the former is the mixing length model and the latter is the k-equation model. For comparison between numerical and analytical solutions, we employed three skill assessments: the correlation coefficient(r) for the similarity of the wake shape, the error of maximum velocity difference(EMVD) for the accuracy of wake velocity and the ratio of drag coefficient(RDC) for the pressure distribution around the structure. On the basis of the numerical results, the feasibility of each model for wake simulation was discussed and a suitable value for the empirical constant was suggested in these turbulence models. The zero-equation model, known as the simplest turbulence model, overestimated the EMVD and its absolute mean error(AME) for r, EMVD and RDC was ranging from 20.3% to 56.3% for all test. But the AME by the one-equation model was ranging from 3.4% to 19.9%. The predicted values of the one-equation model substantially agreed with the analytical solutions at the empirical mixing length scale L=0.6b½ with the AME of 3.4%. Therefore it was concluded that the one-equation model was suitable for the wake simulation behind a square cylinder when the empirical constant for eddy viscosity would be properly chosen.

해운대 해빈의 해안선변형 예측 모형

박일흠,이종섭 한국해안해양공학회 1989 한국해안해양공학회 논문집 Vol.1 No.1

지형이 복잡하고 해빈 배후에 안벽이 존재하는 해운대 해빈의 해안선변형을 계산하였다. 외력이되는 쇄파시 에너지플럭스 및 파향을 굴절 및 파고의 공간적 분포에 의한 회절을 고려하는 수치모형으로 계산하였다. 그리고 연안방향의 파고분포와 안벽의 간섭을 고려하는 연안표사량과 경험적 상수 및 sink항을 청정 매개변수로 취급하여 해안선변형을 계산하였다. 검정기간 중의 관측치와 계산치는 비교적 잘 일치하였다. 그리고 검증으로 구한 매개변수를 사용하여 해운대 해변의 장기변화 예측치를 제시하였다. Shoreline change of Haeundae beach was predicted by one-line model considering interaction of seawalls and longshore variation of wave height . Wave deformation was calculated by combined wave refraction-diffraction model . In this shoreline change model, empirical constants and offshore sediment transport rate are treated as calibration parameters, and the calculated results are in good agreement with the observed data.

파랑이 우세한 조립질 해안에서 해빈변화

박일흠,강성욱,정승명 해양환경안전학회 2016 해양환경안전학회 학술발표대회 논문집 Vol.2016 No.04

한국 서남해에서 자켓형 해상구조물에 의한 해수유동 변화

박일흠,정승명 해양환경안전학회 2018 해양환경안전학회 학술발표대회 논문집 Vol.2018 No.06

Analysis of Empirical Constant of Eddy Viscosity by k-ε and RNG k-ε Turbulence Model in Wake Simulation

박일흠,조영준,이종섭 해양환경안전학회 2019 海洋環境安全學會誌 Vol.25 No.3

The wakes behind a square cylinder were simulated using two-equation turbulence models, k-ε and RNG k-ε models. For comparisons between the model predictions and analytical solutions, we employed three skill assessments:, the correlation coefficient for the similarity of the wake shape, the error of maximum velocity difference (EMVD) of the accuracy of wake velocity, and the ratio of drag coefficient (RDC) for the flow patterns as in the authors’ previous study. On the basis of the calculated results, we discussed the feasibility of each model for wake simulation and suggested a suitable value for an eddy viscosity related constant in each turbulence model. The k-ε model underestimated the drag coefficient by over 40%, and its performance was worse than that in the previous study with one-equation and mixing length models, resulting from the empirical constants in the ε-equation. In the RNG k-ε model experiments, when an eddy viscosity related constant was six times higher than the suggested value, the model results were yielded good predictions compared with the analytical solutions. Then, the values of EMVD and RDC were 3.8% and 3.2%, respectively. The results of the turbulence model simulations indicated that the RNG k-ε model results successfully represented wakes behind the square cylinder, and the mean error for all skill assessments was less than 4%.

새만금 방조제 건설에 따른 조석·조류의 변화

박일흠 여수대학교 2002 論文集 Vol.17 No.-

Change of tide and tidal current due to the closing of Saemangeum dike is predicted by the numerical model, DIVAST, that is coded by an ADI scheme. And the influence area and level of this work is discussed. The numerical solutions are verified by the observed values in 6 tide stations. After construction of the dike, the speed of tidal flow and the amplitude of tide are generally decreased around the dike. the maximum outer atra of the dike where tide and tidal flow are affected by the work is 6.39 times compared with the inner area of dike.

저항물체 배후의 이차원 후류에 관한 대격자 수치모형

박일흠,이종섭,이문옥 한국해안해양공학회 1998 한국해안해양공학회 논문집 Vol.10 No.2

대격자망 수치모형에서 저항물체에 의한 유수저항을 평가하기 위하여, 항력으로부터 유도된 drag stress를 수심적분된 Reynolds 방정식에 도입하였다. 그리고, 해석해가 존재하는 조건에 대한 다양한 수치실험을 통하여 본 모형의 적용성 및 문제점을 검토하였다. 단일물체의 경우, 수치해는 해석해에 대하여 유속의 크기에 있어서±10% 정도의 오차범위를 나타내는 좋은 일치를 보였으며 후류폭의 크기도 전 경우에 있어서 해석해와 잘 일치 하였다. 또한, 열을 이룬 물체에 대한 항력계수와 와동점성계수가 정확하게 결정된다면, 본 모형은 열을 이룬 물체 배후에서 평균류의 흐름분포를 평가하는 데 효율적으로 이용될 수 있을 것이다. To evaluate the hydraulic resistance behind bodies in a large scale grid numerical model, a drag stress term which is formulated by the drag force is introduced in the depth-integrated Reynolds equations. And also, the applicability and problems of this model are discussed through various numerical experiments where the analytical solutions exist. In the case of a single body, the error range of velocity difference between analytical and numerical solutions is within ±10% and the wake width behind the body shows a good agreement with the analytical solution. When the drag coefficient and the eddy viscosity are precisely decided, the numerical solutions behind a row of bodies will be efficiently used in real situations.

파 * 흐름 공존장에서 해빈단면변형모형

박일흠 부산수산대학교 산업기술연구소 1995 産業技術硏究所 硏究報告 Vol.6 No.1

잠제설치에 따른 만성리해빈에서 해안선의 장기변화 예측

박일흠,강성욱,강태순,Park, Il Heum,Kang, Seong Wuk,Kang, Tae-Soon 해양환경안전학회 2016 海洋環境安全學會誌 Vol.22 No.5

만성리 해안은 중조차 해빈으로 조립한 해저질으로 구성되어 있으며, 외해에 대해 남동쪽으로 열려있어 조석 조류보다 파랑에 의한 해빈변형이 우세하게 나타났다. 파랑은 춘계와 하계에 강하여 유의파고가 2~3m에 달하는 폭풍파가 자주 출현하였으나 추계와 동계는 고파랑이 출현하지 않는 정온한 해상상태를 보였다. 관측된 해안선변화의 계절적 특징은 입사파와 깊은 관계를 나타내었다. 춘계와 하계의 고파랑시에 해안선이 침식하였고 추계과 동계의 정온시에 침식을 회복하였다. 이런 현장자료를 바탕으로 실측해안선자료를 사용하여 해안선변화의 검증수치실험을 수행하였는데, 검증매개변수 $C_1=0.2$와 $C_2=1C_1$일 때 사후예측된 해안선은 실측해안선과의 RMS 오차가 1.26 m 정도로 만족스러웠다. 이 값을 사용하여 잠제와 도류제 등이 완공된 10년 후 만성리 해빈의 해안선을 예측한 결과, 잠제배후역에서 5~15 m 정도 해안선이 전진하며, 잠제배후역 북측에서 5~15 m 정도 해안선이 후퇴하는 결과를 나타내었다. The Manseongri Coast meets the sea on the southeast and is composed of coarse sediment as a mesotidal beach. The waves that strike the beach are stronger than the tides or tidal currents as external forces of beach deformation. Storm waves frequently reach significant wave heights of 2-3m and hit in spring and summer, leaving the sea calm during fall and winter. Incident waves reach remarkable heights that correspond with observed shoreline changes. The shoreline erodes in spring and summer due to these strong waves but recovers in fall and winter as a result of the more moderate waves. On the basis of these observed results, a numerical calibration for experiments on shoreline change was established. Results revealed that according to hindcast data, calculated shoreline changes agreed with the observed shoreline, with a minimum RMS error of 1.26m with calibration parameters $C_1=0.2$ and $C_2=1C_1$. Using these calibration parameters, long-term shoreline change was predicted after the construction of submerged breakwaters and jetties, etc. The numerical model showed that the shoreline would move forward by 5-15m behind the submerged breakwaters and recede by 5-15m north of the structure.

조석, 조류 및 파랑을 고려한 완경사 모래해안에서 해빈변화 예측

박일흠,정승명 해양환경안전학회 2023 해양환경안전학회 학술발표대회 논문집 Vol.2023 No.04