• Journal of Korean Society of Coastal and Ocean Engineers
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• v.4 no.4
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• pp.231-242
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• 1992

This study uses a numerical model to investigate the circulation patterns of the tidal and wind driven current components. The model is vertically averaged 2-D transient using explicit nume-rical scheme, based on equation of motion and continuity. forced by water elevation at open boundaries and wind stress. The model domain extends from 35$^{\circ}$N to 36$^{\circ}$40'N lat., and 125$^{\circ}$E to 126$^{\circ}$40'E long. with x, y grid spacing of 5 km. The model reproduces the tide and tidal currents by 4 major constituents successfully with more than 90% accuracy when compared to two offshore tidal records and currents at one offshore measurements for 22 days. Responses of coastal waters to six schematic wind events are analyzed in terms of current distribution patterns and local features. Regardless of wind directions. strong coastal currents were produced. Bottom topography plays a critical role in producing a local eddy Held whose center is located offshore Pu An with its major radius of 40 km.

• Journal of Mechanical Science and Technology
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• v.15 no.4
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• pp.500-509
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• 2001

Offshore subsea pipelines must be stable against external loadings, which are mostly due to waves and currents. To determine the stability of a subsea pipeline on the seabed, the Morrison equation has been applied with prediction of inertia and drag forces. When the pipeline is placed in a trench, the force acting on it is reduced considerably. Therefore, to consider the stability of a pipeline in a trench, one must employ reduction factors. To investigate the stability of various trenches, we numerically simulated flows over various trenches and compared them with experimental data from PIV (Particle Image Velocimetry) measurements. The present results were produced ar Reynolds numbers ranging from 6$\times$10$^3$to 3$\times$10(sub)5 based on the diameter of the cylinder. Quasi-periodic flow patterns computed by large-eddy simulation were compared with experimental data in terms of mean flow characteristics fro typical trench configurations (W/H=1 and H/D=3, 4). The stability for various trench conditions was addressed in terms of mean amplitudes of oscillating lift and drag, and the reduction factor for each case was suggested for pipeline design.

• Progress in Superconductivity and Cryogenics
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• v.4 no.2
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• pp.31-37
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• 2002

A 100 〔HP〕 rated synchronous motor with superconducting rotating field winding has been designed based on the formulated equations established from 2 dimensional magnetic field distributions in a cylindrical coordinate The cross-section was drawn based on calculated design results via Fortran program and then modeled with FEM (Finite Element Method) to investigate the machine performances. First of all, the magnetic field distributions are analysed in many ways according to the field directions and the armature currents. Especially after the rotating Held winding is arranged with BSCCO-2223 high-temperature superconducting(HTS) pancake coils, the exerted magnetic field normally on the HTS tape is calculated through FEM. And the machine output power is calculated according to the torque ang1es which lie between the field and the armature main flux lines. Moreover, this Paper includes the eddy-current loss variations of a copper damper located between the field and the armature coils and design considerations of the 100 HP HTS motor utilizing ferro-magnetic material.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.17 no.1
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• pp.80-85
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• 2003

Recently, induction heating cooker(IH-Cooker) is very interested for high efficiency, the quickness of heating time and the convenient regulation of heating spot. In this paper, we proposed the magneto-thermal analysis of an induction heating cooker(IH-Cooker) as an efficient design, and analyzed the magnetic fold intensity inside the axisymmetric shaped cooker using three-dimensional axisymmetric finite element method(Flux2D) and the effectual heat source was obtained by ohmic losses from eddy currents induced in the cooker. Also, we presented the temperature characteristics of the IH-Cooker according to input frequency and relative permeability in stainless parts and in aluminum parts.

• The Transactions of the Korean Institute of Power Electronics
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• v.2 no.1
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• pp.26-32
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• 1997

In this paper, numerical analysis of dynamic characteristics for the plunger-type solenoid was used for a high speed solenoid valve with fast switching is discussed. The theoretic analysis of the electromagnetic field including eddy currents in the solenoid is studied by using permeance. The optimum value of design parameters which are a mass and an area of the plunger, a source voltage, a elastic modulus of the spring, a stroke, a number of turns, are obtained by the results of the investigation on effect of a parameter on others. And dynamic characteristics of acting solenoid that is the variation of magnetic force, displacement, solenoid current are investigated.

• Proceedings of the Korea Water Resources Association Conference
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• 2019.05a
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• pp.98-98
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• 2019

중력류 또는 밀도류는 주변 유체에 비해 상대적으로 밀도가 큰 유체가 밀도차에 의한 추진력으로 흐르는 것이다. 중력류의 수치모델링에는 두 가지 어려움이 있다. 즉, 적합한 지배방정식을 구성하여 적용하는 것 그리고 난류의 영향을 합리적으로 반영하는 것이다. 기존 중력류 해석을 위한 지배방정식들은 유체의 연속방정식과 운동량 방정식 그리고 밀도 또는 농도의 이송방정식을 조합하여 구성된다. 이들 지배방정식을 이용한 연구들은 대부분 두 유체 사이의 밀도차가 충분히 작아서 밀도 변동(variations)의 영향은 오로지 부력항에서만 유지된다는 Boussinesq 근사에 근거를 둔다. 그리고 이송방정식에서 밀도 또는 농도의 확산계수을 점성계수의 함수로 표현하기 위해서 Schmidt 수를 이용한다. 수치모델링에서 Schimdt 수는 상수값을 적용하지만, 이 값은 밀도의 연직방향 경사에 근거한 부력빈도(buoyancy frequency)와 난류량의 따라 큰 차이를 보이는 것으로 알려져있다. 한편, 표준 통계학적 난류모델과 벽함수를 적용한 수치모델링은 초기 중력에 의해서 무너지는(slumping) 단계를 넘어 관성력으로 추진되는 단계와 점성 효과가 지배적인 단계에서는 정확도에 현저히 낮아지기 때문에 대부분 큰와모의(large-eddy simulation, LES) 또는 DNS(direct numerical simulation)수준의 고해상도(high-resolution) 해석기법을 적용하여 공학적인 문제에 적용하는 데는 한계가 있다. 이 연구에서는 Boussinesq 근사와 Schmidt 수를 사용하지 않으며, LES 보다 적용이 용이한 DES (detached-eddy simulation)기법을 조합한 다상흐름 수치모델을 적용하여 중력류를 해석을 시도하였다. 수치해석결과를 실험값과 함께 기존 수치모델링 기법으로 구한 수치해와 비교분석하여 이 연구에서 개발 및 적용된 수치모델링 기법의 적용성을 평가한다.

• Ocean Systems Engineering
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• v.9 no.1
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• pp.21-42
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• 2019

In this paper, the Finite-Analytic Navier-Stokes (FANS) code is coupled with an in-house finite-element code to study the dynamic interaction between a floating buoy and its mooring system. Hydrodynamic loads on the buoy are predicted with the FANS module, in which Large Eddy Simulation (LES) is used as the turbulence model. The mooring lines are modeled based on a slender body theory. Their dynamic responses are simulated with a nonlinear finite element module, MOORING3D. The two modules are coupled by transferring the forces and displacements of the buoy and its mooring system at their connections through an interface module. A free-decay model test was used to calibrate the coupled method. In addition, to investigate the capability of the present coupled method, numerical simulations of two degree-of-freedom vortex-induced motion of a CALM buoy in uniform currents were performed. With the study it can be verified that accurate predictions of the motion responses and tension responses of the CALM buoy system can be made with the coupling CFD-FEM method.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.16 no.2
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• pp.92-102
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• 2004

In this paper, an analytical solution of calculating the excess temperature field due to a point heat source is presented in the presence of spring-neap modulation of convective alongshore flow. The basic form of the solution is identical to that given by Jung et al. (2003) but the convective term in the exponential kernel function is extended and a spring-neap variation in the horizontal eddy diffusivity is newly introduced. A set of calculations have been performed to examine the sensitivity of the heat build-up to the change in current fields and turbulent dispersion. Results indicate that the excess temperature field is confined within the tidal excursion distance, while the excess temperature field beyond the distance is mainly controlled by the horizontal diffusion. The heat build-up within the distance is considerably affected by the spring-neap variation in the horizontal eddy diffusivity; the relatively high excess temperature more than 1$^{\circ}C$ is extended further when the eddy diffusivity has spring-neap modulation.

• Ecology and Resilient Infrastructure
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• v.5 no.4
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• pp.199-209
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• 2018

In river design, consideration of bed shear stresses is necessary to secure stability of levee and floodplain. In this study distributions of bed shear stresses in compound open channels are analyzed through numerical simulation for various width and depth. LES solver in OpenFOAM is applied to 12 cases of compound channel shapes considering secondary flow which effects distributions of bed shear stresses. By the results time averaged velocity distributions, secondary currents, and distributions of bed shear stresses are analyzed. Overall distributions of bed shears in floodplain show that higher shear stresses are seen in left of floodplain and the shears decrease toward right of floodplain. However, high local variations in shear stresses are shown due to the secondary flow effects. In shallow floodplain, bed shear stresses show low value below 0.8 times of averaged bed shear. In deep floodplain, bed shear stresses show high value over 1.2 - 1.4 times of averaged bed shear.

• Environmental Sciences Bulletin of The Korean Environmental Sciences Society
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• v.3 no.1
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• pp.57-73
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• 1999

Baroclinic hydraulic model experiments on the time-varying states of the flow pattern and water exchange in Sagami Bay were carried out based on quasi-steady state experiments on the flow pattern. For the model experiments, density changes as well as time changes in the volume transport of the upper layer were executed to investigate the flow response of the bay in the case of a sudden inflow of low density water and variable volume transport into the Sagami Bay. The results of the model experiments showed that when the volume transport was increased frontal eddies or frontal wave streamers from the Kuroshio Through Flow were transferred to the inner part of the bay along with cyclonic circulation in the bay. In addition, density boundary currents appeared and flowed along the eastern boundary of the bay. As the upper layer density decreased, frontal eddies, frontal streamers and coastal boundary density currents occurred and proceeded along the eastern boundary of the bay at a high speed.