• 한국물환경학회지
• /
• 제28권4호
• /
• pp.538-550
• /
• 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
• /
• 제4권1호
• /
• pp.16-24
• /
• 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.

• 한국해양공학회지
• /
• 제24권4호
• /
• pp.59-65
• /
• 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.

• 수산해양기술연구
• /
• 제47권4호
• /
• pp.435-442
• /
• 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.

• 대한조선학회논문집
• /
• 제60권1호
• /
• pp.1-9
• /
• 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.

• 한국음향학회지
• /
• 제23권5호
• /
• pp.362-369
• /
• 2004

수층과 사질 퇴적층이 이루는 경계면이 평탄할지라도 고주파수 (30∼120 ㎑) 음파의 반사손실은 퇴적물의 입도와 입사파의 파장에 따라 거친 경계면에서의 반사 효과를 갖게 된다. 경계면 거칠기 영향은 음향학적 거칠기 (acoustical roughness, g/sub R/)로 표현하며 사질 퇴적물의 경우 g/sub R/∼ O(1)이고 주파수에 따른 종속성을 가진다. 따라서 입도분포에 따른 반사손실의 편차 (deviation)와 주파수에 따른 종속성을 포함하는 개선된 해저면 반사손실 모델 (HYBRL 모델, Hanyang University Bottom Reflection Loss model)을 제안한다. 그리고 주파수 종속성과 해저면 물성이 갖는 편차를 포함하는 반사손실 모델을 검증하기 위해 수조실험과 해상실험을 실시하였다. 수조실험 및 해상실험에서 측정된 해저면 반사손실 결과 사질 퇴적물에서 모델의 특성을 잘 반영한다.

• 대한토목학회논문집
• /
• 제36권6호
• /
• pp.1037-1048
• /
• 2016

본 연구에서는 Navier-Stokes 방정식과 자유수면 추적에 VOF법을 채용하는 CADMAS-SURF를 이용하여 파랑과 흐름의 비선형 상호간섭현상을 연구하였다. 파-흐름 공존장에서의 유체거동 해석을 위해 CADMAS-SURF를 수정 및 확장하였고, 계산치를 실험치와 비교하여 본 연구의 타당성을 확인할 수 있었다. 본 연구의 수치수로를 파랑-흐름 공존장에서 주어지는 복잡한 물리 현상 규명과 파-흐름-잠제의 상호간섭해석에 적용하여, 유속장, 와도장, 자유수면과 와도와의 관계 등을 논의하였다.

• 한국항공우주학회지
• /
• 제31권1호
• /
• pp.73-84
• /
• 2003

항공기내 연료온도의 변화가 유한차분식에 의하여 해석되었다. 항공기의 여러 임무 가운데 근접항공지원 임무가 20% hot day 외부대기 조건과 함께 이음속 영역에서 고려되었다. 수정 Dufort-Frankel기법의 explicit방법에 의해 수치계산이 수행되었다. 항공기는 난류유동장내에 있는 것으로 가정되었다. 추가 연료공급-회송 개념을 갖는 항공기 연료시스템 모델이 고려되었다. 본 해석의 결과로써, 추가연료 공급이 증가함에 따라 연료탱크의 온도는 상승함을 보인 반면, 엔진 입구에서의 연료온도는 몇몇 비행단계 및 엔진 연료요구량이 많은 구간을 제외하고는 감소함을 보였다. 본 해석으로부터, 추가 연료공급-회송개념을 사용한 연료시스템이 엔진입구 연료온도를 낮추기 위한 효과적인 방법임을 나타났다. 또한, 연료/오일 열교환기로 흐르는 연료유동량이 연료온도 변화에 중요한 인자임이 밝혀졌다.

• International Journal of Naval Architecture and Ocean Engineering
• /
• 제10권4호
• /
• pp.491-498
• /
• 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.

• 한국물환경학회지
• /
• 제25권5호
• /
• pp.792-802
• /
• 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.