• Journal of Ocean Engineering and Technology
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• v.28 no.3
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• pp.199-208
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• 2014

In this study, propeller open water characteristics ($K_P$, $K_T$ and ${\eta}_o$) were compared for three different ducted propellers using a Computational Fluid Dynamics (CFD) analysis, as well as an experimental test at a basin. The best shape of the duct was selected from the three types of specially designed ducts based on the CFD analysis results. The same propeller model (Kaplan type propeller) was used inside all three duct models, and the propeller open water characteristics were compared, predominantly at the design speed for an underwater vehicle. Finally, the results of the CFD test simulations for the selected duct case were verified by experimental open water tests in a towing tank.

• Journal of Environmental Science International
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• v.27 no.11
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• pp.1007-1021
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• 2018

Community dynamics of benthic macroinvertebrates and biological evaluation of water quality were investigated at Gigyecheon of Pohang and Gyeongju, Korea. The survey was carried out at 8 sites from May to October, 2017. As a result, total of 104 species under 54 families, 15 orders, 8 classes in 4 phyla with 5,052 individuals were revealed. The number of species was the most abundantly identified in aquatic insects, 76 species under 34 families, 6 orders. Among them, the order Odonata was the most abundant taxon as 21 species(20.2%). The most abundant individuals were collected in the phylum Mollusca as 1,453 individuals(28.8%). Various species appeared dominantly at each site by season, and the most dominant species was Caridina denticulata denticulata belonging to the class Malacostraca with 0.08 of dominance index. According to the results of community structure analyses, the diversity and richness indices were the highest at site II, the evenness index was the highest at site I, and the dominance index was the highest at site IV. The number of species and individuals of gathering collectors were the highest among functional feeding groups. Those of sprawlers were the highest among habitat orientation groups. The ESB showed a tendency to change according to season and site, and it was the highest in May at most surveyed sites. The KSI was also somewhat fluctuated according to season and site. From these indices, average biological water quality was evaluated as class II.

• Journal of Advanced Marine Engineering and Technology
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• v.39 no.6
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• pp.614-619
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• 2015

In this study, a dynamics model was developed to predict the motion performance of an Autonomous Underwater Vehicle (AUV). The dynamics model includes basic dynamic state variables of the hull and force terms to determine the motion of the AUV. The affecting terms for the forces are hydrostatic force, added mass, hydrodynamic damping, lift and drag forces. The force terms can be calculated using analytical and Computational Fluid Dynamics methods. For the underwater motion simulation, a simple PD controller was used. Also, the AUV was tested in a water tank and near sea for the partial verification of the fluid drag force coefficients and way-point tracking motions.

• Journal of Korea Multimedia Society
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• v.13 no.9
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• pp.1382-1390
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• 2010

We can see interactions between rigid body and fluid every day, anywhere. This kind of rigid body-fluid simulation is one of the most difficult problems in physically-based modeling, mainly due to heavy computations. In this paper, we present a real-time dynamics model for simulating stone skipping, which is a popular rigid body-fluid interaction in the real world. In comparison to the previous works, our improved dynamics model supports the rotation of the stones and also computes frictional forces with respect to the air. We can simulate a realistic result for various user input by using proposed model. Additionally, we present a water surface model to show more realistic ripples interactively. Our methods can be easily adapted to other interactive dynamics systems including 3D game engines.

• Korean System Dynamics Review
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• v.15 no.3
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• pp.5-36
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• 2014

The purpose of this paper is to develop a System Dynamics model for estimating the volume of forest resources in the future and simulating the volume of function of public benefit linked to forest resources in dynamic manner. Also it is to analyze the impact when the volume of forest land conversion is controlled by policy using the SD model. The analysis was done at nation-wide for the simulation period 2000 to 2040. Estimated forest area was 6.2 million ha and estimated growing stock was $4.7\;billion\;m^3$ in 2040 from the future forecast without policies. Changing of forest resources, 13.9 billion tons of forest-ground-water storage was estimated, $1.8\;million\;m^3$ of erosion control of forest was estimated and 377 million tons of $CO_2$ absorption was estimated. As a result of simulation with two alternatives, forest area was less reduced and growing stock was bigger than do nothing policy. Also, function of public benefit reflected by changes of forest resources was enhanced. This study contributes to estimate the quantitatively measured volume of forest resources and function of public benefit over the 30 years in Korean forest land in scientific way. Using this SD model, decision maker would develop forest land policies more delicately for deserving forest resources and increasing the volume of function of public.

• Journal of Ship and Ocean Technology
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• v.11 no.4
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• pp.55-71
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• 2007

The primary objective of this work is to develop methodologies for virtual model basin and to demonstrate the capabilities for generic multi-hull ship geometry. A computational fluid dynamics approach is used to simulate various model basin tests for steady resistance, maneuvering and seakeeping. For a catamaran hull configuration, the methodologies are used for solving these problems and the results are discussed. Computational results are compared with the results of a benchmarked potential flow theory method for calm water resistance.

• Proceedings of the PSK Conference
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• 2002.10a
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• pp.312.2-312.2
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• 2002

The metal-ligand complex, ［Ru(phen)$_2$(dppz)]^{2＋}$ (phen = 1.10-phenanthroline, dppz = dipyrido［3.2-a:2', 3'-c］phenazine) (RuPD), was used as a spectroscopic probe for studying nucleic acid dynamics. The RuPD complex displays a long lifetime and a molecular light switch property upon DNA binding due to shielding of its dppz ligand from water. (omitted)

• Magazine of the Korean Society of Agricultural Engineers
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• v.45 no.7
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• pp.57-69
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• 2003

To evaluate nutrient dynamics with different fertilization in paddy field and develop water quality model, mass balance analysis was performed during growing season of 2001-2002 in field experimental plots irrigated with groundwater. As a result of water balance analysis, most of outflow was surface drainage as about half of total outflow and about 500mm was lost by evapotranspiration. The water budget was well balanced. The runoff from paddy field was influenced by rainfall and forced drain. Especially runoff during early cultural periods more depends on the forced drain. As a result of mass balance analysis, most of nutrient was input by fertilization and lost by plant uptake. Significant amount of nitrogen were supplied by precipitation and input from upper paddy field, comprising 12%∼28% of total inflow. Nutrient loading by surface drainage was occurred showing about 15%∼29% for T-N and 6%∼13% for T-P. The response of rice yield with different fertilization was not significant in this study. Water quality model for paddy field developed using Dirac delta function and continuous source was calibrated and validated to surface water quality monitoring data. It demonstrates good agreement between observed and simulated. The nutrient concentration of surface water at paddy field was significantly influenced by fertilization. During early cultural periods when significant amount of fertilizer was applied, surface drainage from paddy field can cause serious water quality problem. Therefore, reducing surface drainage during fertilization period can reduce nutrient loading from paddy fields. Shallow irrigation, raising the weir height in diked rice fields, and minimizing forced surface drainage are suggested to reduce surface drainage outflow.

• Journal of Wetlands Research
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• v.7 no.4
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• pp.33-42
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• 2005

Wetlands often function as a nutrient sink. It is well known that increased input of nutrient increases the primary productivity but it is not well understood what is the fate of produced biomass in wetland ecosystem. Water and sediment quality, decomposition rate of cellulose, and sediment accumulation rate in 11 montane marshes in northern Sierra Nevada, California were analyzed to trace the effect of nitrogen and phosphorus content in water on nutrient dynamics. Concentrations of ammonium, nitrate, soluble reactive phosphorus (SRP) in water were in the range of 27 to 607, 8 to 73, and 6 to 109 ppb, respectively. Concentrations of ammonium, calcium, magnesium, sodium, and potassium in water were the highest in Markleeville, which has been impacted by animal farming. Nitrate and SRP concentrations in water were the highest in Snow Creek, which has been impacted by human residence and a golf course. Cellulose decomposition rates ranged from 4 to 75 % per 90 days and the highest values were measured in Snow Creek. Concentrations of total carbon, nitrogen, and phosphorus in sediment ranged from 8.0 to 42.8, 0.5 to 3.0, and 0.076 to 0.162 %, respectively. Accumulation rates of carbon, nitrogen, and phosphorus fluctuated between 32.7 to 97.1, 2.4 to 9.0, and 0.08 to $1.14gm^{-2}yr{-1}$, respectively. Accumulation rates of carbon and nitrogen were highest in Markleeville and that of phosphorus was highest in Lake Van Norden. Correlation analysis showed that decay rate is correlated with ammonium, nitrate, and SRP in water. There was no correlation between element content in sediment and water quality. Nitrogen accumulation rate was correlated with ammonium in water. These results showed that element accumulation rates in montane wetland ecosystems are determined by decomposition rate rather than nutrient input. This study stresses a need for eco-physiological researches on the response of microbial community to increased nutrient input and environmental change because the microbial community is responsible for the decomposition process.

• Journal of Korea Water Resources Association
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• v.56 no.spc1
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• pp.1015-1026
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• 2023

The confluence of rivers, where rivers meet, is a place known for complex water mixing dynamics. Sometimes, these rivers flow downstream without mixing. While this non-mixing can pose challenges for water quality management, it also offers the potential for improved water extraction in nearby water intakes (Chilseo). In this study, we analyzed the mixing dynamics at the confluence of the Nakdong River and the Nam River using drone imagery, water quality indicators like Electrical Conductivity, and hydraulic factor Secondary Flow. We found that meandering effects hindered mixing, as shown by the comparison of Secondary Flow and Electrical Conductivity distributions. Additionally, the Chilseo Water Purification Plant downstream of the Nakdong River-Nam River confluence extracted unmixed Nam River water during certain periods.