• 대한조선학회논문집
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• 제56권6호
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• pp.541-549
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• 2019

In the present study, we investigated planing forces of supercavitated bodies by using the supercavitation shape produced by the disk type cavitator. The cavity shapes are observed to find the immersion draft and planing angle when the stern of the supercavitated body is partially immersed in the water. To make the planing the angle-of-attack (AOA) of the supercavitated body is varied statically against the main flow and the planing tests are carried out for different body shapes that are changed systematically. The drag, lift and pitch moment acting on the body are measured to understand the relation between the planing force and the immersion draft of the supercavitated body. It is found that the planing force increased in general linearly with the immersion draft ratio and the planing angle is certainly not proportional to the immersion draft ratio.

• International Journal of Naval Architecture and Ocean Engineering
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• 제6권1호
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• pp.151-161
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• 2014

In this study, an experimental investigation has been made of the applicability of outer-layer vertical blades to real ship model. After first devised by Hutchins and Choi (2003), the outer-layer vertical blades demonstrated its effectiveness in reducing total drag of flat plate (Park et al., 2011) with maximum drag reduction of 9.6%. With a view to assessing the effect in the flow around a ship, the arrays of outer-layer vertical blades have been installed onto the side bottom and flat bottom of a 300k KVLCC model. A series of towing tank test has been carried out to investigate resistance (CTM) reduction efficiency and improvement of stern wake distribution with varying geometric parameters of the blades array. The installation of vertical blades led to the CTM reduction of 2.15~2.76% near the service speed. The nominal wake fraction was affected marginally by the blades array and the axial velocity distribution tended to be more uniform by the blades array.

• 한국군사과학기술학회지
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• 제24권1호
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• pp.84-98
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• 2021

The hydrodynamic characteristics of amphibious assault vehicles are investigated using commercial CFD code, STAR-CCM+. Resistance performances of a displacement-type vehicle and a semi-planing type vehicle are analyzed in calm water. The self-propelled model is also computed for the semi-planing type vehicle. All computations are performed using an overset mesh system and a RANS based flow-solver coupled with a two-degree of freedom equations of motion. A moving reference frame is applied to simulate revolutions of impeller blades for a waterjet propulsion system. Grid dependency tests are performed to evaluate discretization errors for the mesh systems. The numerical analysis results are compared with the experimental results obtained from model tests. It is shown that RANS is capable of investigating the resistance and self-propulsion characteristics of high-speed amphibious assault vehicles. It is also found that a fully covered side skirt, which is covering tracks, reduces resistance and stern trim, besides increasing propulsive efficiency.

• 한국해양공학회지
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• 제35권4호
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• pp.247-256
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• 2021

In order to minimize carbon emissions and greenhouse gas, the Energy Efficiency Design Index (EEDI) has become a major factor to be considered in recent years in a ship's design and operation phases. Energy-Saving Devices (ESDs) improve the EEDI of a vessel and make them environmentally friendly. In this research, the performance of an equalizing duct-type ESD installed upstream of a Korea Research Institute of Ships & Ocean Engineering (KRISO) Container Ship (KCS) model's propeller was investigated by computational fluid dynamics (CFD). Open-source CFD libraries, OpenFOAM, were used for computational analysis of the KCS with and without the ESD to verify the performance improvement. The flow field near the stern region and propulsive coefficients were considered for comparison. The results showed a considerable improvement when an ESD was used on the model. Using different sizes of the duct, the performance of the ESD was also compared. It was observed that with an increased duct size, the propulsive performance was improved.

• International Journal of Naval Architecture and Ocean Engineering
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• 제13권1호
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• pp.585-598
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• 2021

The course-keeping stability of a high speed planing boat should be considered at the design stage for its safe operations. The shape of waterjet intake plane is one of important design parameters of a waterjet propelled planing boat. That has significant influences on the stern flow patterns and pressure distributions. In this study, the effects of the waterjet intake shapes of planing boats on the course-keeping stabilities are investigated. Two kinds of designed planing boats have the same dimensions, but there are differences in waterjet intake plane shapes. Captive and free-running model tests, Computational Fluid Dynamics (CFD) analyses are carried out in order to estimate their hydrodynamic performances including course-keeping stabilities. The results show that the flat and wide waterjet intake plane of the initially designed boat makes the course-keeping stability worse. The waterjet intake shape is redesigned to improve the course-keeping stability. The improved performances are confirmed by free-running model tests and full-scale trials.

• 한국지능시스템학회논문지
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• 제17권2호
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• pp.154-159
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• 2007

프로펠러 회전면에서의 반류분포는 주로 모형시험에 의해서 규명되어 왔다. 이렇게 축적된 데이터베이스를 통해 선박의 기하학적 형상정보와 반류분포 사이의 입출력관계를 모델링할 수 있다면 선박 초기설계시 유사선종의 설계에 도움이 된다. 뉴로퍼지시스템은 예측, 분류, 진단 등의 매우 복잡한 문제를 해결하는 기법으로 다양한 공학분야에서 응용되고 있다. 본 연구에서는 이들 입출력 사이의 관계를 뉴로퍼지시스템으로 모델링하고 학습한 후 새로운 입력에 대한 출력값의 검토를 통해 그 유용성을 확인한다. 3차원 선미형상을 입력으로 하고 선체 모형시험으로 얻어진 프로펠러 회전면에서의 반류분포 값을 출력으로 사용하여 학습 및 추론을 해 보았다. 이를 통해 뉴로퍼지시스템을 초기 선박설계 단계에서 특히 선미형상을 결정할 때 유용한 것을 확인하였다.

• 한국해양환경ㆍ에너지학회지
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• 제9권2호
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• pp.92-97
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• 2006

수치계산을 통해 소형 고속선의 선형설계를 수행하였다. 선형변환 프로그램인 HCAD를 사용하고 차인형 선형을 기준선으로 하여 둥근바닥 선형을 설계하였다. WAVIS를 시용하여 두 가지 선형에 대한 선체주위의 유동장과 조파저항 계산 결과를 보였다. 차인형 선형의 저항특성이 둥근 바닥선형에 비해 다소 크게 나타났으나 소형 조선소의 건조비를 감안하여 차인형 선형의 선수부 개량과 선미 웨지의 설계를 통해 조파저항의 감소를 시도하였다. 수치계산 결과 선미 웨지의 적용에 의해 차인형 선형의 조파저항성능이 고속영역에서 개선되었음을 확인하였다.

• 한국해양공학회지
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• 제24권4호
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• pp.23-31
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• 2010

The flow around a remotely-operated vehicle (ROV) has been investigated numerically to improve the resistant performance by modifying the hull form of the ROV. In the case of the base hull form considered in this study, form drag rather than friction drag was the dominant component of total drag. Subsequently, the surfaces that were most susceptible to local pressure effects were modified to give them a more streamlined shape. Eleven different hull forms were chosen to undergo surface modification for drag reduction. In addition, four different boat-tail appendages with different slant angles were installed at the stern to reduce the wake vortices that are induced by the local regions of very low pressure. Consequently, a total of 11 different hull forms for drag reduction were considered. The final hull form, which combined the hull for which surface modification resulted in the lowest drag with a boat-tail appendage with a 15-degree slant angle, resulted in a drag reduction of 20%.

• International Journal of Naval Architecture and Ocean Engineering
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• 제8권5호
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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.

• 한국항해항만학회지
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• 제38권6호
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• pp.585-591
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• 2014

본 논문의 주 목적은 프루드 수가 0.5 이상인 중형 경비정의 속도성능을 모형시험 이전에 CFD 결과를 바탕으로 기존의 모형시험자료를 활용하였다. 모형시험 이전에 CFD를 이용하여 선속 별로 추정된 제동마력이 주어진 엔진마력을 만족하는지를 평가 하였다. 대상선박은 선미가 서로 다른 두 가지 선형을 선정하였다. 점성 유동장 계산은 상용 CFD 코드인 STAR-CCM+를 사용하였으며, 자유수면과 자세 변화(동적 트림)를 모두 고려하였다. 알몸 선체의 저항 값은 CFD를 이용하여 추정되었다. 점성 유동 해석을 통해 두 가지 선형의 자유수면 파형, 압력분포, 한계유선 그리고 프로펠러 면에서의 속도분포를 비교하였다. 점성 유동 해석 결과를 바탕으로 두 가지 선형에 대한 유효마력 즉, 저항성능을 평가하였다. 부가물 부착에 따른 저항 증가량과 준추진효율 계수(ETAD, ${\eta}_D$)는 모형시험 자료를 활용하였다. 중형 경비정과 같은 고속선박에 관한 속도성능 추정법이 CFD와 기존 시험자료를 이용하여 개발되었다.