Yoon-Jin Ha

Resistance Performance of Korean Small Coastal Fishing Boat in Low-Speed Range

AbstractKorean small coastal fishing boats have the different kind of fisheries and customs against Japanese fishing boats. Those bring some influences on the principal parameters of hull form. In same displacement, Korean small coastal fishing boat has generally shorter length, draft and wider breadth than Japanese fishing boat. Fur thermore, even though the parameters of each hull form are similar, it is known that the resistance performance of Korean small coastal fishing boat is worse than that of Japanese fishing boat. In this study, the representative hull forms of Korean and Japanese small coastal fishing boats are selected and compared to evaluate the resistance performance of Korean fishing boat in low-speed range. The hull form of the Korean fishing boat is modified as comparison with that of the Japanese fishing boat to confirm the partial characteristic differences between the hull forms and the resistance performances. The representat ive partial characteristics of hull form are the gradient of chine line, keel shape and stern length. The resistance performances of the modified hull forms are evaluated by INHAWA VE which is one of CFD program and model tests in towing tank. The results of the present study will be used to

Reduction of Added Resistance by Internal Flow Control in the Moonpool of a Drillship

The internal flows of moonpool usually causes huge added resistance on drillships, and those are very complex to analyze. Therefore, not only experimental approaches but also numerical simulations are required for better investigations when dealing with the hydrodynamic problems of moonpool. In the present research, numerical simulations are used to find out why the resistance increases by moonpool on a running drillship. That is, the three-dimensional numerical simulations and model tests are carried out to examine the characteristics of internal flow and added resistance by changing the section of the moonpool in both longitudinal and transverse directions. Finally, based on the present studies, an optimized shape of the moonpool is suggested, which effectively reduces added resistance, and that is confirmed with three-dimensional numerical simulations and model tests.

A Study on the Resistance Performance of Korean High-Speed Small Coastal Fishing Boat

2,† ·Ae-Seon Park 1 ·Yoon-Jin Ha 1 ·Cheong-Kyu Park Abstract The study on the improvement of resistance performance is very important for coastal fishing boats in Korea, because the prices of fuel oil are gradually risen and the demand of high-speed fishing boats is increased lately. This study is concerned with the improvement of the resistance performance for Korean high-speed small coastal fishing boats. A semi-planing hull form of Korean small coastal fishing boat is selected in the role of initial hull. From the modification of the hull form parameters and the local characteristics of the hull form, the improvement of the resistance performance is achieved. The resistance performances of the initial and the modified hull forms are estimated by using a numerical simulation method. Also, ship model tests are carried out in ship model basin.

A Study on the Improvement of Resistance Performance for G/T 4.99ton Class Korean Coastal Fishing Boats

Korean fishing boats have had appropriate hull forms for the safety, stability and convenience of fishing ability. However, Korean fishermen are recently concerned about the resistance performance and speed of Korean fishing boats, because the prices of fuel oil are gradually risen, also the exhausting of fish resources and the demand of high speed fishing boats are increased. Therefore, the necessity of the study on the improvement of resistance performance for Korean small coastal fishing boats is gradually increased. This study compares the hull form characteristics of Korean fishing boats with those of Japanese fishing boats, and the hull form of a representative Korean fishing boat is modified. From the modification of the hull form parameters for the Korean fishing boat, the improvement of resistance performances is evaluated. Moreover, the increase of resistance performances is also achieved from the modification of local characteristics for the hull form of the Korean fishing boat. A computational method and ship model tests in towing tank are used for the conformations of the improvement of resistance performance.

Experimental and Numerical Study on the Effects of Bow Deck Shape on the Green Water

In this paper, the effects of bow deck shape on the green water are studied by numerical and experimental method. Varying the deck shapes to triangular, elliptic and circular, the thickness and advancing velocity of green water leading edge are compared using numerical method. Also the motion, the pressure on the vertical wall and the height on the deck of green water are compared among the three bow deck shapes in the heave and pitch motion free condition by experimental method. To remove the effects of the difference of motions among the deck shapes, numerical simulations are performed varying the deck shape with the same motion. In the same motion condition, smallest impulsive pressure occurred in the condition of elliptic deck shape.

A Study on the Estimation of the Form Factor of Full-Scale Ship by the Experimental Data of Geosim Models

Generally, form factor is determined through ITTC method. Determining the form factor from ITTC method includes the assumption that the form factor of a full-scale ship is the same value as its model ship. In other words, the form factor is independent on Reynolds number. However, for the more appropriate prediction of the resistance performance of a full-scale ship, the form factor must be determined with the consideration of the variation attendant on Reynolds number. In this research, several Geosim ship models are adopted to investigate the scale effect, and correlation lines of form factor are improved to suggest the better extrapolation method for the prediction of the form factor of full-scale ship. The corrected form factors using the correlation lines are compared with those determined from the results of low-speed resistance tests. To consider the influence of hull form, the correlation lines are determined for the group of high-speed ships and the group of low-speed ships, respectively. The corrected form factors have shown good agreement among the prediction results from each Geosim ship model to the full-scale ship.

A Study on the Bow Hull Form Design of Full Ship Considering the Nonlinear Waves

2 Abstract This paper introduces a new hull form design method for the bow of a full ship, by actively applying the relation between the fore-body hull form and its wave resistance characteristics. For the hull form design, the Series 60(CB=0.8) hull is chosen as the parent ship, and Krachts charts are used to determine the parameters of the bulbous bow in the early stages of hull form design. Several hull forms have been tested in order to obtain enough hull form variations with various bow shapes and design parameters in the search of the best design. In order to investigate the resistance characteristics of the designed hull forms, numerical simulations with corresponding model tests have been rigorously performed. For the numerical simulations, the Marker-density method is employed to track the nonlinear phenomena of the free surface(program IUBW). Model tests have also been performed to achieve an improved research performance using the designed hulls. Both numerical and experimental results show that the wave resistance of the hull forms can be effectively diminished if the bows are designed using the method introduced in this research. It is also expected that this research can facilitate better productivity in hull form design, especially at the preliminary design stage of a full ship type vessel.

Numerical Simulation of Flow around a Fixed Semi-submersible Offshore Structure Using the Modified Marker-density Method

Structure Using the Modified Marker-density Method Yoon-Jin Ha . Young-Gill Lee .Kwang-Leol Jeong . In-Jun Yang Korea Research Institute of Ships and Ocean Engineering, KRISO, Daejeon, Korea Dept. of Naval Architecture and Ocean Engineering, Inha University, Incheon, Korea Research Center, NEXTfoam Co., Ltd., Seoul, Korea Dept. of Naval Architecture and Ocean Engineering, Graduate School, Inha University, Incheon, Korea

A Study on the Resistance Test Method for Planning Hull Model using the High Speed Towing Carriage

활주선형 등 고속으로 항주하는 선박에 대한 모형 시험은 기존 예인전차의 속도와 수조 길이의 한계 등으로 인하여 많은 어려움 이 있다. 고속선의 모형 시험 시 예인전차를 이용할 경우 예인가 능 속도의 제한으로 모형선이 작아져야 하나 모형선이 작아지게 되면 모형 시험 결과의 신뢰성에 한계가 있을 것이다. 따라서 무 인 상태에서 고속으로 예인할 수 있는 경량화된 고속전차가 필요 하다. 인하대학교에서는 고속모형선의 저항시험을 위하여 최대 20m/s까지 예인할 수 있는 무인고속전차를 제작하였다. 하지만 무인고속전차가 고속으로 주행 할 때, 정속구간에서 모형선의 항 주자세가 정상상태에 이르러야 하지만 충분한 수조 길이가 확보 되지 않으면, 모형선의 항주자세가 정상상태에 이르기 전에 모형 시험이 끝나게 될 수도 있다. 따라서 무인고속전차를 이용한 고 속선 모형 시험 시 기존의 모형 시험기법과는 다른 모형 시험기 법이 요구된다. Kawahara, et al. (1993)의 연구에서는 모형선의 침하를 자유롭게 하여 트림만을 고정시키는 모형 시험기법(이하 : 자유 침하 시험기법)에 대하여 제안하였다. 하지만 이 시험기법 의 경우 분력계를 이용하여 추진축 방향의 힘을 측정하여 항주 시 모형선에 작용하는 부양력과 트림모멘트가 0에 근접 할 때까 지 반복시험을 수행하는 것이다. 그리고 추진축 방향의 힘을 측 정하여 별도의 수식에 의하여 저항이나 부양력, 트림모멘트를 추 정해야한다. Ikeda (1990)는 Kawahara, et al. (1993)의 연구와 는 다르게 모형선의 침하와 트림을 모두 구속하고 저항과 부양력, 트림모멘트를 3분력계를 이용하여 직접 계측하는 모형 시험기법 (이하 : 완전 구속 시험기법, fixed)을 제안하였다. 이 연구에서는 직접 각 방향의 힘들을 계측함으로써 수식에 의한 힘들의 추정을 수행하지 않은 장점이 있지만, 모형선의 침하와 트림을 모두 구 속하여 실험하기 때문에 예인 횟수가 증가하게 된다. 따라서 Lee, et al. (2008)은 이러한 단점들을 극복하고자 모형선의 트림을 자 유롭게 하여 침하만을 구속하는 모형 시험기법(이하 : 자유 트림 시험기법, trim free)을 제안하였다. 이 연구에서는 완전 구속 시 험기법에 비하여 예인 횟수가 줄었으며, 저항과 침하, 트림이 정 성적, 정량적으로 완전 구속 시험기법과 근접한 결과를 보였다. 본 연구에서는 Lee, et al. (2008) 연구에서의 고속선 모형 속 pISSN:1225-1143, Vol. 51, No. 5, pp. 349-355, October 2014The resistance test of a high speed craft such as planing ship is performed with a high speed towing carriage instead of ordinary towing carriage because of the speed limitation. In the resistance test using high speed towing carriage, the model ship is fixed to the carriage to restrain the running attitude for enough measuring time. Such method is called fixed model test method. In the fixed model test method, to get the appropriate running attitude, the model test is iteratively repeated until the trim moment and lift force are close to zero. In this research, trim free model test method is investigated to reduce the number of iteration. And, the limitation of towing speed range in the trim free model test method is investigated.

A Fundamental Study on the Power Prediction Method of Ship by using the Experiment of Small Model

선형시험수조에서 자유수면이 있는 모형시험은 두 가지 무차원 수 중 실선과 모형선의 프루드 수(Froude number, Fn)를 동일하게 만족시켜준다. 하지만 프루드 상사법칙을 적용하게 되면 레이놀즈 수(Reynolds number, Rn)를 동일하게 만족시키기 어렵다. 실선과 모형선 주위 유동은 레이놀즈 수의 큰 차이 즉, 축척효과로 일컬 어지는 영향으로 인하여 서로 다르다. 따라서 프루드 상사법칙 을 적용한 모형시험결과로부터 실선성능을 추정하기에는 어려 움이 따른다. 레이놀즈 수가 증가함에 따라 선미부에 빠른 압력 회복이 나타나고 선미부경계층의 두께가 감소하여 형상계수가 증가한며, 프로펠러 면으로 유입되는 축방향 속도가 증가하게 되어 유효반류비가 감소하게 된다 (Choi, et al., 2011). 이러한 모형선 저항추진성능에 미치는 축척효과의 영향들을 조사하는 유용한 방법 중 하나는 기하학적으로 상사하고 축척비가 다른 모형선의 실험 결과를 이용하는 방법이 있다 (García-Gómez, 2000; Min & Kang, 2010). 하지만 대부분의 모형시험은 레이 놀즈 수 범위가 106~107에서 이루어지나 실선의 레이놀즈 수의 경우 109~1010이기 때문에 실선과의 그 차이가 매우 커 여전히 축척효과를 무시할 수 없다 (Choi, et al., 2011). 더욱이 크기 가 작은 소형 선형시험수조에서의 모형시험 시 레이놀즈 수 가 105~106인 상태에서도 이루어지는 경우가 있기 때문에 소형 선형시험수조에서의 모형시험결과로 실선의 성능을 추정함에 있어서 매우 어렵다. ITTC 1978년 실선 성능해석법에서는 실선 의 성능을 추정하기 위하여 형상계수(form factor, k)를 사용하 게 된다. ITTC 1978년 실선 성능해석법에서 형상계수는 선체의 기하학적 형상에 의한 저항성분을 고려하기 위하여 도입되었다 (Min & Kang, 2010). 형상계수는 레이놀즈 수의 함수로 알려져 있기 때문에 이는 실선과 모형선이 서로 다를 수 있다. García-Gómez (2000)과 Min and Kang (2010)에서는 레이 놀즈 수가 증가함에 따라 형상계수가 증가하는 것을 모형시험으 로 확인한 바 있다. 형상계수는 실선의 저항성능을 추정하는 것 뿐 아니라 실선의 유효반류비를 추정할 때에도 고려된다. 하지 만 ITTC 1978년 실선 성능해석법의 경우 형상계수 뿐 아니라, 선체효율(ηH), 프로펠러 단독효율(η0) 등의 축척효과를 고려하지 않는다. 따라서 축척효과로 인하여 모형 크기마다 실선의 마력 추정결과는 다를 수 있다. 본 연구에서는 소형 저속비대모형선 과 상대적으로 고속으로 항주하는 소형 고속모형선에 대한 자항 시험을 수행하고 자항시험 시 모형선의 유효반류비 특성을 비교 하여 보았다. 또한 실선마력추정방법에 대한 기초자료를 제시하 pISSN:1225-1143, Vol. 51, No. 3, pp. 231-238, June 2014