• Proceedings of the KIEE Conference
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• 1999.11b
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• pp.460-465
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• 1999

액체 로켓용 충돌분사형 인젝터는 구조가 매우 간단하면서 고유량의 연료를 분사시킬 수 있기 때문에 여러 엔진에 응용된 바 있다. 본 연구에서는 이러한 인젝터의 특성을 산업용 보일러에 적용하기 위한 기초 실험 및 수치 계산을 수행하였다. 충돌분사 노즐로부터 형성되는 분무의 분포 특성을 실험적으로 측정하였고 이를 실제 조건에 모사하기 위해 수치 계산을 하여, 두 결과를 비교하여보았다. 이로부터 보일러의 효율과 공해물질 저감에 영향을 가져오는 액적의 미립화 특성을 향상시킬수 있는 연료 분사 조건을 제시하였다.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2001.05a
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• pp.232-235
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• 2001

본 논문은 주파수 범위가 0∼30MHz에서 전력선 통신 채널상에 나타나는 잡음에 대한 실험적인 특성 및 수치계산에 의한 이론적인 근거를 전력선 채널 파라미터의 스펙트럼상의 잡음밀도 측정으로부터 유도하였으며, 거리에 따른 채널 모의실험을 통해서 나타난 잡음 특성을 이론적인 정보전달 범위에서 비교ㆍ분석하였다.

• Journal of the Korean Society of Hazard Mitigation
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• v.10 no.1
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• pp.111-117
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• 2010

A three-dimensional numerical model is employed to investigate wave deformation due to a submerged structure. The three-dimensional numerical model solves the spatially averaged Navier-Stokes equations for two-phase flows. The LES(large-eddy-simulation) approach is adopted to model the turbulence effect by using the Smagorinsky SGS(sub-grid scale) closure model. The two-step projection method is employed in the numerical solutions, aided by the Bi-CGSTAB technique to solve the pressure Poisson equation for the filtered pressure field. The second-order accurate VOF(volume-of-fluid) method is used to track the distorted and broken free surface. A simple linear wave is generated on a constant depth and compared with analytical solutions. The model is then applied to study wave deformation due to a submerged structure and the predicted results are compared with available laboratory measurements.

• Proceedings of the Korea Water Resources Association Conference
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• 2016.05a
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• pp.400-400
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• 2016

자연하천에서 다양한 목적으로 설치된 수공구조물을 볼 수 있으며 대표적으로 교량의 교각을 들 수 있다. 교각 주위에서 발생하는 국부세굴은 교량붕괴의 가장 큰 원인이므로 이에 대한 연구는 필수적이다. 수리실험 또는 수치모형을 이용하여 교각주변의 국부세굴에 관한 많은 연구들이 수행되었지만 세굴인자의 특성 및 메커니즘에 대한 연구는 여전히 부족하다. 본 연구에서는 LES(large-eddy simulation)에 유사이송 및 하상변동 모형과 결합하여 2개의 원형교각 주변의 흐름 및 세굴을 수치모의 하였다. LES와 유사이송 및 하상변동 모형의 결합은 난류의 영향을 직접 모형에 고려할 수 있기 때문에 교각 주변에서 발생하는 말굽형 와 구조와 같은 복잡한 흐름에 의한 영향이 반영된다. 계산영역은 흐름방향으로 10 m, 횡 방향으로 2.4 m로 하였고, 지름(D) 0.16 m를 가지는 원형교각을 유입부로부터 2.4 m 떨어진 위치에 배치하였다. 이때 두 개 교각사이의 각은 $0^{\circ}{\sim90^{\circ}$이고 원형교각 사이의 거리는 5D로 하였다. 수치모의에 사용된 조건은 이전의 수리실험(Khosronejad et al., 2012)을 참고하여 접근평균유속은 0.25 m/s, 수심은 0.15m를 사용하였다. 수치모의는 원형교각 주변의 최대세굴심이 평형상태에 이를 때 까지 수행하였다. 접근각도 변화에 따른 원형교각 주변의 세굴과정 및 특성을 분석하였으며 최대 세굴심 결과를 Hannah(1978)의 수리실험결과와 비교하였다.

• Journal of the Korean Society of Marine Environment & Safety
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• v.18 no.6
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• pp.597-603
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• 2012

It is necessary to accurately evaluate the resistance performance and estimate the towing power of a tugboat for safety towing operation at actual seas. In this study, we have carried out the model tests firstly to investigate the resistance performance and flow characteristics around the tugboat in still water. The experiments are performed in infinite depth in circulation tank using 1/33.75 scaled model from 5kts to 10kts(designed speed 7kts) considering the effect of adverse and favorable current. Then the numerical calculations are executed to analyze the response amplitude operator and added resistance on tugboat due to the waves. The results obtained by the present computation are compared with the those acquired from the experiments in still water. As a result, it is noted that the added resistance become larger at head sea and higher speed conditions. We can also observe that the EHP increase 70 percent in comparison with those in still water.

• Journal of the Society of Naval Architects of Korea
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• v.37 no.1
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• pp.67-81
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• 2000

An accurate and efficient numerical method for two-dimensional nonlinear radiation problem has been developed. The wave motion due to a moving body is described by the assumption of ideal fluid flow, and the governing Laplace equation can be effectively solved by the higher-order boundary element method with the help of the GMRES (Generalized Minimal RESidual) algorithm. The intersection or corner problem is resolved by utilizing the so-called discontinuous elements. The implicit trapezoidal rule is used in updating solutions at new time steps by considering stability and accuracy. Traveling waves caused by the oscillating body are absorbed downstream by the damping zone technique. It is demonstrated that the present method for time marching and radiation condition works efficiently for nonlinear radiation problem. To avoid the numerical instability enhanced by the local gathering of grid points, the regriding technique is employed so that all the grids on the free surface may be distributed with an equal distance. This makes it possible to reduce time interval and improve numerical stability. Special attention is paid to the local flow around the body during time integration. The nonlinear radiation force is calculated by the "acceleration potential technique". Present results show good agreement with other numerical computations and experiments.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.33 no.6
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• pp.257-264
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• 2021

This study established a numerical model capable of calculating the wave overtopping rate of coastal structures by nonlinear irregular waves using the FUNWAVE-TVD model, a fully nonlinear Boussinesq equation model. Here, a numerical model was established by coding the mean value approach equations of EurOtop (2018) and empirical formula by Goda (2009), and adding them as subroutines of the FUNWAVE-TVD model. The verification of the model was performed by numerically calculating the wave overtopping rate of nonlinear irregular waves on vertical wall structures and comparing them with the experimental results presented in EurOtop (2018). As a result of the verification, the numerical calculation result according to the EurOtop equation of this model was very well matched with the experimental result in all relative freeboard (R_c/H_mo) range under non-impulsive wave conditions, and the numerical calculation result of empirical formula was evaluated slightly smaller than the experimental result in R_c/H_mo < 0.8 and slightly larger than the experimental result in R_c/H_mo > 0.8. The results of this model were well represented in both the exponential curve and the power curve under impulsive wave conditions. Therefore, it was confirmed that this numerical model can simulate the wave overtopping rate caused by nonlinear irregular waves in an vertical wall structure.

• Journal of Ocean Engineering and Technology
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• v.17 no.1
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• pp.16-20
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• 2003

본 연구에서는 입사파에 의한 항내 정온도 계산 시 사용되는 수치해석 기법에 대한 검증 및 실제 항만에 대한 적용을 하였다. 해석기법은 유한요소기법 (finite element technique) 을 사용하였고 기본방정식은 경계조건과 마찰을 고려한 완경사방정식 (mild-slope equation) 을 사용하였다. 해석의 검증을 위하여 임의형상 항만에 대해 본 해석법을 적용하여 수치해석을 실시한 결과와 다른 수치해석결과 및 실험결과를 비교했을 때 좋은 일치를 나타내었다. 제주항에 대해서 2가지의 각기 다른 입사파 조건을 적용하여 계산한 결과 제주항이 방파제 설계파인 NNW방향 (Case 2)인 경우가 NE 방향 (Case 1)인 경우보다 약간 양호한 정온을 확보하는 것을 알 수 있었다.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.14 no.9
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• pp.766-773
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• 2002

Flow distributions in a rectangular duct with two branch ducts are measured by 5 W laser doppler velocity meter. The fluid flows are also computed by commercial soft-ware of STAR-CD for comparison between them. The Reynolds numbers in the main duct are from 4,226 to 17,491. The ratios distributed into two branches from the main duct are in-variant to Reynolds numbers according to both of numerical and experimental results. However computed velocity profiles at exit of each branch are somewhat different from measured profiles at the same location.

• Water for future
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• v.20 no.1
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• pp.49-54
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• 1987

A numerical analysis of the characteristics of wave reflection over rippled beds (sand bars) was carried out By Boundary Element Method(B.E.M) using linear elements. It is assumed that the incident wave is normal and oblique to the rippled beds and the wave may be and the escribed by two-dimensional linear theory. The accuracy of the computational scheme is investigated by comparing the laboratory data, the analytic measured results of the other researchers. The B.E.M results for the normal incident wave is held for the mechanism of the resonant Bragg reflection at the point where the wave length of the bottom undulation is one half the wave length of the surface wave.