• International Journal of Naval Architecture and Ocean Engineering
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• v.8 no.5
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• pp.442-455
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• 2016

The resistance and seakeeping performance of a high-speed monohull vessel were investigated through a series of model tests in a towing tank. The hull had a slender wave-piercing bow, round bilge, and small deadrise angle on stern. Tests on the bare hull in calm water were first conducted and tests on spray rails followed. The spray rails were designed to control the flow direction and induce a hydrodynamic lift force on the hull bottom to reduce trim angle and increase rise of the hull. The maximum trim of the bare hull was $4.65^{\circ}$ at the designed speed, but the spray rails at optimum location reduced trim by $0.97^{\circ}$. The ship motion in head seas was examined after the calm water tests. Attaching the rails on the optimum location effectively reduced the pitch and heave motion responses. The vertical acceleration at the fore perpendicular reduced by 11.3%. The effective power in full scale was extrapolated from the model test results and it was revealed that the spray rails did not have any negative effects on the resistance performance of the hull, while they effectively stabilized the vessel in calm water and waves.

• Journal of Power Electronics
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• v.11 no.4
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• pp.591-598
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• 2011

This paper investigates a power supply of medium voltage with enhanced ignition characteristics for plasma torches. A series resonant half-bridge topology is presented as a suitable ignition circuitry. The ignition circuitry is integrated into the main power conversion system of a multi-phase staggered three-level dc-dc converter with a diode front-end rectifier. A plasma torch rated at 3MW, 2kA and having a physical size of 1m is selected to be the high enthalpy source for a waste disposal system. The steady-state and transient operations of a plasma torch are simulated. The parameters of a Cassie-Mary arc model are calculated based on 3D magneto-hydrodynamic simulations. The circuit simulation waveform shows that the ripple of the arc current can be maintained within ${\pm}10%$ of its rated value under the presence of a load disturbance. This power conversion configuration provides a high enough ignition voltage, around 5KA, during the ignition phase and high arc stability under the existence of arc disturbance noise resulting in a high-performance plasma torch system.

• Korean Journal of Fisheries and Aquatic Sciences
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• v.35 no.4
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• pp.395-407
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• 2002

A 3D hydrodynamic-ecological coupled model was applied to estimate a food supply to oysters in Geoje-Hansan Bay where is one of the oyster culturing sites in Korea, In this study, the primary productivity (PP) was adopted as an index of food supply, and the spatial patterns of average chlorophyll a concentration during a culturing seasons from September to May of the following year were simulated by the model, The numerical result showed that PP was high in the inner part of the bay and the adjacent areas of Hwado island, but low in the outer. This result indicates that PP is essentially influenced by anthropogenic nutrient loadings in the system. The model was calibrated using the field data in May which is non culturing season of oysters and a simulated phytoplankton biomass agreed fairly well with the observed data ($R^{2}=0.70$, $RE=10.3\%$). The computed food supply varied from 0.19 to $1.27\;gC/m^{2}/day$ with a mean value of $0.62 gC/m^{2}/day$ from September to May. The highest value was showed in May ($1.27 gC/m^{2}/day$) and the lowest was in February ($0.19 gC/m^{2}/day$).

• Korean Journal of Ecology and Environment
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• v.46 no.4
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• pp.488-498
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• 2013

A three-dimensional hydrodynamic model was applied to the Lake Euiam. The lake has three inflows, of which Gongji Stream has the smallest flow rate and poorest water. The dam-storage volume, watershed area, lake shape and discharge type of the Chuncheon Dam and the Soyang Dam are different. Therefore, it is difficult to analyze the water plume and mixing pattern due to the difference of the two dams regarding the amount of outflow and water temperature. In this study, we analyzed the effects of different characteristics on temperature and conductivity using the model appropriate for the Lake Euiam. We selected an integrated system supporting 3-D time varying modeling (GEMSS) to represent large temporal and spatial variations in hydrodynamics and transport of the Lake Euiam. The model represents the water temperature and hydrodynamics in the lake reasonably well. We examined residence time and spreading patterns of the incoming flows in the lake based on the results of the validated model. The results of the water temperature and conductivity distribution indicated that characteristics of upstream dams greatly influence Lake Euiam. In this study, the three-dimensional time variable water quality model successfully simulated the temporal and spatial variations of the hydrodynamics in the Lake Euiam. The model may be used for efficient water quality management.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.31 no.2B
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• pp.175-185
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• 2011

This study investigates tsunami force acting on a group of onshore structures numerically by using three-dimensional one-field model for immiscible multi-phase flows, which is based on Navier-Stokes solver. In particular, we studied on the characteristics of tsunami with respect to the arrangement of onshore structures and the distance from seawall trough numerical experiments. For validation of the numerical method used in this study to calculate tsunami force, numerical results for tsunami force on the structures in coastal area are compared with available experimental data. Furthermore, a detail study on the efficiency of the numerical method is performed for the estimation of tsunami force based on the hydrostatic and hydrodynamic methods in which the numerical results are used. The obtained results are compared to the previous experimental one and design criteria. Considering both experimental results and numerical analysis results, semi-empirical formula by regression analysis is proposed. As a result, it was confirmed that the numerical analysis is effective to estimate on tsunami force acting on onshore structures.

• Journal of the Korean Association of Geographic Information Studies
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• v.12 no.3
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• pp.21-34
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• 2009

Usually in flood flow problems, one-dimensional approach does not provide the required details of complex flow phenomena such as the flow in braided rivers and river junction. In this study, two-dimensional finite element mesh is constructed using DEM and GIS tool, and applied to RMA-2model. The purpose of this study is to investigate the applicability of the two dimensional model in natural rivers and to analyze characteristics of river flow due to the change of cross section. For model calibration, the result of unsteady flow analysis was compared with the observed data. Accordingly, the SMS model in this study prove to be very effective and reliable tool for the simulation of hydrodynamic characteristics under the various flow conditions.

• Journal of Ocean Engineering and Technology
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• v.33 no.5
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• pp.400-410
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• 2019

In this study, the numerical code for the 3D nonlinear dynamic analysis of an SLWR (Steel Lazy Wave Riser) was developed using the lumped mass line model in a FORTRAN environment. Because the lumped mass line model is an explicit method, there is no matrix operation. Thus, the numerical algorithm is simple and fast. In the lumped mass line model, the equations of motion for the riser were derived by applying the various forces acting on each node of the line. The applied forces at the node of the riser consisted of the tension, shear force due to the bending moment, gravitational force, buoyancy force, riser/ground contact force, and hydrodynamic force based on the Morison equation. Time integration was carried out using a Runge-Kutta fourth-order method, which is known to be stable and accurate. To validate the accuracy of the developed numerical code, simulations using the commercial software OrcaFlex were carried out simultaneously and compared with the results of the developed numerical code. To understand the nonlinear dynamic characteristics of an SLWR, dynamic simulations of SLWRs excited at the hang-off point and of SLWRs in regular waves were carried out. From the results of these dynamic simulations, the displacements at the maximum bending moments at important points of the design, like the hang-off point, sagging point, hogging points, and touch-down point, were observed and analyzed.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.15 no.1
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• pp.39-50
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• 2003

This study aims to figure out water quality impacts due to sudden disturbances of sediments during dike construction in land reclamation for the northern part of the Siwhaho Lake where heavily deteriorated settlements from upstream loadings are outstanding. We exploit a 3-D water quality model CE-QUAL-ICM combined with a hydrodynamic model TIDE3D. Simulations are done accounting water-sediment interaction in a 4-$\sigma$ layers. Long-term simulation for 1-year shows that bottom layers around the disturbance location are only affected and marks very high concentration. Complete vertical mixing appears at least 5km apart to downward due to complex effects of geometry, bathymetry and river inflows. It should be addressed that existing condition of the Siwhaho Lake stands for high concentration of COD and TP in winter and spring due to relatively high incoming loadings, however the effect of sediment disturbances yields reverse phenomena, i.e., impacts of dike construction arise greatly in summer and fall. Refined grid system consisting of 150m${\times}$150m rectangular grid, which is doubled system compared to previous study (Suh et al.,2002), gives affordable results by reducing flux differences through a cell especially in front of gate.

• Korean Journal of Ecology and Environment
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• v.33 no.4 s.92
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• pp.342-349
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• 2000

This paper demonstrates the influence of intensity of the monsoon on morpho-hydrological fluctuations in Taechung Reservoir during 1993${\sim}$1994. During the study, hydrological variables including rainfall, inflow, and discharge volume showed distinct contrast between 1993 and 1994. Interannaul differences in rainfall occurred during the monsoon in July${\sim}$August monsoon and influenced inflow, discharge, and water residence time (WRT). Total inflow in 1993 was four times greater than that of 1994, and summer inflow in 1993 was 8 times greater than summer 1994. Annual Mean WRT was 93.2 d in 1993 vs. 158.6 d in 1994 and the largest differences occurred between monsoons of 1993 and 1994. Morphometric variables reflected the interannual contrasts of hydrology, so that in 1993 surface area, total volume, shoreline development, and mean depth increased consistently from premonsoon to postmonsoon and over this same period in 1994 they decreased. This outcome indicates that the area of shallow littoral zones in 1993 was greater than in 1994. Also, the drainage area to surface area (D/L) at 80 m MSL was 60.7 which was much greater than values in Soyang and Andong reservoirs and natural lakes world-wide. The morpho-hydrodynamic conditions seemed to influence in-reservoir nutrient concentration which is one of the most important factors regulating the eutrophication processes. I believe, under the maximum hydrodynamic fluctuations in Korean waterbodies during the monsoon, applications of mass balance models to man-made lakes for assessments of external loading should be considered because the models can be used under the seasonally stable inflow and water residence time.

• Journal of Environmental Impact Assessment
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• v.21 no.1
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• pp.25-39
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• 2012

This study was aimed to assess the effects of additional installation of two different types of weirs, one is a curtain-type weir and another is a submerged-type weir, on the control of algal growth in Daechung Reservoir. A two-dimensional(2D) coupled hydrodynamic and eutrophication model that can accommodate vertical movement of the curtain weir following the water surface variations was verified using field data obtained in two distinctive hydrological years; dry(2008) and wet(2010). The model adequately simulated the temporal and spatial variations of water temperature, nutrients and algal(Chl-a) concentrations during the periods. The effectiveness of curtain weir on the control of algal bloom was evaluated by applying the model to 2001(dry year) and 2010 assuming 6 different scenarios according to installation locations. The curtain weirs that already installed at 3, 5, 7 sites(scenario C-2) showed significant effect on the control of algal growth in the reservoir; the reduction rates of algal concentration were placed in the range of 7.5~31.5% and 9.1~44.9% for 2001 and 2010, respectively. However the simulation results revealed that additional installation of curtain weirs(scenario C-3~C-6) in the bay area (choosori) have marginal effect. The effectiveness of submerged weir was evaluated against 2010 assuming 7 different scenarios according to installation locations, but all scenarios(S-1~S-7) showed neglectable or negative effect on the control of algal growth.