• Journal of Korean Society on Water Environment
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• v.28 no.4
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• pp.538-550
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• 2012

This study suggests a general methodology which is designed for assessing RDOC behavior at the catchment scale by coupling properly a series of steam flow and water quality simulation models and actual monitoring data set. The modified TANK model in which a river routing function is incorporated to the conventional one is applied to simulate the long-term daily stream flow data, and the simulated stream flow data is combined with the 7-parameter log-linear model coupled to the minimum variance unbiased estimator to simulate the long-term daily water quality (BOD, COD and TOC) loads. Finally, the regression analysis between the usually monitored water quality data (BOD, COD and TOC) and RDOC is combined with the simulated water quality data to manifest the spatio-temporal variability of RDOC flux behavior at the Korean TMDL catchment scale.

• Journal of Advanced Research in Ocean Engineering
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• v.4 no.1
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• pp.16-24
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• 2018

This paper addresses the heading control of an offshore floating storage and regasification unit (FSRU) using a resolved motion and acceleration control (RMAC) algorithm. A turret moored vessel tends to have the slewing motion. This slewing motion may cause a considerable decrease in working time in loading and unloading operation because the sloshing in the LNG containment tank might happen and/or the collision between FSRU and LNGC may take place. In order to deal with the downtime problem due to this slewing motion, a heading control system for the turret moored FSRU is developed, and a series of model tests with azimuth thrusters on the FSRU is conducted. A Kalman filter is applied to estimate the low-frequency motion of the vessel. The RMAC algorithm is employed as a primary heading control method and modified I-controller is introduced to reduce the steady-state errors of the heading of the FSRU.

• Journal of Ocean Engineering and Technology
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• v.24 no.4
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• pp.59-65
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• 2010

This study presents the design procedure for optimizing the semi-planing hull form, including appendages, using numerical and experimental methods. Four different referenced semi-planing hull forms were compared to determine their hydrodynamic performances, and one of the hull forms was modified for optimum operation at high-speed conditions (0.4 < $F_{NL}$ < 0.9). The optimized, semi-planing hull form was tested in the towing tank to investigate its resistance characteristics. Also, the results of the model tests with differing design parameters were used to choose the stern wedge and the spray strip to improve the hydrodynamic performance at high speeds.

• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.47 no.4
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• pp.435-442
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• 2011

In an attempt to respond to the increase in international oil prices and reduce operating expenses, ship remodeling was carried out on a 740ton class tuna purse seiner. To strengthen the competitiveness of the fisheries industry by improving vessel performance, a bulbous bow was newly equipped. The slipway and rudder area were also lengthened and enlarged with the propeller and main engine remained unchanged. To reduce the hull resistance, a circle type bulbous bow was attached on the hull behind bow thruster and thus the cost for exchanging electrical equipment for bow thruster was reduced. The new rudder area was expanded 15% more than the old one within the extent that the existing mechanical control part and rudder stock were not changed. To prevent fishing net damage and stabilize wake field, slipway was lengthened to the optimal position. All of the new design of remodeling parts went through the model tests in towing tank and CWC. Besides resistance test, all of necessary model test results were delivered for hydrodynamic character for the modified ship. The maneuvering simulation to verify that the remodeled ship satisfies the IMO rules was performed in both zigzag and turning tests. The estimated resistance with new bulbous bow and lengthened stern was reduced by 4.8% in the 2-dimensional analysis and 17.4% in the 3-dimensional analysis in comparison of conventional ship. The average reduction of resistance was estimated about 10%. Maneuvering character of modified hull form was found to satisfy all regulations under IMO. The remodeling of tuna purse seiner can not only improve fishing performance but also contribute to reduction of operating cost by saving energy for the fisheries industry.

• Journal of the Society of Naval Architects of Korea
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• v.60 no.1
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• pp.1-9
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• 2023

In order to improve the propeller cavitation performance composed of Cavitation Inception Speed (CIS), cavitation extent and pressure fluctuation, it needs to improve the wake distribution that flows into the propeller. The warship propeller cavitation is strongly influenced by the wake created at the V-strut of various appendages. The inflow characteristics of the V-strut were investigated using Computational Fluid Dynamics (CFD) and the twisted angles of the V-strut were aligned with upstream flow. The resistance and self-propulsion tests for the model ship with the existing and modified V-struts were conducted in Towing Tank (TT), and wake distribution, CIS, cavitation observation and pressure fluctuation tests were conducted in Large Cavitation Tunnel (LCT). The propeller behind the modified V-strut showed better cavitation characteristics than that behind the existing V-strut. Another model test was conducted to investigate rudder cavitation performance by the change of the V-strut. The rudder cavitation characteristics were not improved by the change of the operating conditions. On the basis of the present study, it is thought that the stern appendages for better propeller cavitation performance would be developed.

• The Journal of the Acoustical Society of Korea
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• v.23 no.5
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• pp.362-369
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• 2004

The High-frequency (30 ∼ 120 ㎑) bottom reflection loss at rough water-sediment interface is affected by the gram size distribution of the sediments. The roughness of the bottom surface is represented by "acoustical roughness. g/sub R/" The grain size of sandy sediments is g/sub R/∼O(1) and the dependence as a function of frequency. We suggest the modified bottom reflection loss model (HYBRL model , HanYang university Bottom Reflection Loss model) that include in the deviation of the reflection loss as a function of the grain size distribution and frequency dependence. And bottom reflection loss model of frequency dependence and deviation of bottom properties is verified by water tank and field experiments.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.36 no.6
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• pp.1037-1048
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• 2016

In this study, nonlinear wave interaction in the presence of a uniform current is studied using numerical model, named CADMAS-SURF which is based on the Navier-Stokes equations coupled with Volume of Fluid for tracking free surface deformation. The original CADMAS-SURF developed for interaction of wave with structure is modified/extended to simulate nonlinear fluid dynamic motions within wave-current coexisting field. The capability of Numerical Wave-Current Tank (NWCT) in this study is validated by comparing with available existing laboratory experiments for both wave-following and wave-opposing current. The numerical results for interaction between wave and current are shown to be in good agreement with experimental data. Then, this study focused on the dynamic motions of the water velocity, surface elevation and vorticity within combined wave-current field in demonstrating complex nonlinear physical phenomena due to interaction between wave and current. In addition, NWCT is applied to simulate a more complex wave-current-structure field for wave propagating over a submerged breakwater associated with current. Detailed discussion including characteristics of velocity and vorticity fields and the relation between free surface and vorticity are given.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.31 no.1
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• pp.73-84
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• 2003

A transient analysis on fuel temperatures in an aircraft was studied using the finite difference method. Numerical calculation was performed by an explicit method of modified Dufort-Frankel scheme. Among various missions, close air support mission was considered with 20% hot day ambient condition in subsonic region. The aircraft was assumed to be in turbulent flow. The fuel system model with additional fuel supplies and return concept was considered. As a result of this analysis, the fuel tank temperatures have increased with the increase of the additional fuel supplies. In contrast to tank temperatures, the fuel temperature at the engine inlet has decreased with the increase of additional fuel supplies except in some in-flight phases having high engine fuel flow. From this analysis, the fuel system with the additional fuel supplies and return concept has been shown to be an effective method to decrease the engine inlet fuel temperature. Also, it has been shown that fuel flow rate through fuel/oil heat exchanger is a key factor influencing fuel temperature.

• International Journal of Naval Architecture and Ocean Engineering
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• v.10 no.4
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• pp.491-498
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• 2018

The cost evaluation for voyage route planning in an ice-covered sea is one of the major topics among ship owners. Information of the ice properties, such as ice type, concentration of ice, ice thickness, strength of ice, and speed-power relation under ice conditions are important for determining the optimal route in ice and low operational cost perspective. To determine achievable speed at any designated pack ice condition, a model test of resistance, self-propulsion, and overload test in ice and ice-free water were carried out in a KRISO ice tank and towing tank. The available net thrust for ice and an estimation of the ice resistance under any pack ice condition were also performed by I-RES. The in-house code called 'I-RES', which is an ice resistance estimation tool that applies an empirical formula, was modified for the pack ice module in this study. Careful observations of underwater videos of the ice model test made it possible to understand the physical phenomena of underneath of the hull bottom surface and determine the coverage of buoyancy. The clearing resistance of ice can be calculated by subtracting the buoyance and open water resistance form the pre-sawn ice resistance. The model test results in pack ice were compared with the calculation results to obtain a correlation factor among the pack ice resistance, ice concentration, and ship speed. The resulting correlation factors were applied to the calculation results to determine the pack ice resistance under any pack ice condition. The pack ice resistance under the arbitrary pack ice condition could be estimated because software I-RES could control all the ice properties. The available net thrust in ice, which is the over thrust that overcomes the pack ice resistance, will change the speed of a ship according to the bollard pull test results and thruster characteristics (engine & propulsion combination). The attainable speed at a certain ice concentration of pack ice was determined using the interpolation method. This paper reports a procedure to determine the attainable speed in pack ice and the sample calculation using the Araon vessel was performed to confirm the entire process. A more detailed description of the determination of the attainable speed is described. The attainable speed in 1.0 m, 90% pack ice and 540 kPa strength was 13.3 knots.

• Journal of Korean Society on Water Environment
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• v.25 no.5
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• pp.792-802
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• 2009

The objective of this study is to construct the watershed management system with link of the non-point sources model and to estimate delivery ratio duration curves for various pollutants. For the total water pollution load management system, non-point source model should be performed with the study of the characteristic about non-point sources and loadings of non-point source and the allotment of pollutant in each area. In this study, daily flow rates and delivered pollutant loads of Nakdong river basin are simulated with modified TANK model and minimum variance unbiased estimator and SWAT model. Based on the simulation results, flow duration curves, load duration curves, and delivery ratio duration curves have been established. Then GIS analysis is performed to obtain several hydrological geomorphic characteristics such as watershed area, stream length, watershed slope and runoff curve number. As a result, the SWAT simulation results show good agreements in terms of discharge, BOD, TN, TP but for more exact simulation should be kept studying about variables and parameters which are needed for simulation. And as a result of the characteristic discharges, pollutants loading with the runoff and delivery ratios, non-point sources effects were higher than point sources effects in the small-scale test bed of Nakdong river basin.