• Journal of the Korea Institute of Information and Communication Engineering
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• v.13 no.2
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• pp.330-340
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• 2009

A naval shipboard inevitably movies in a pitch and roll direction under the influence of wave and wind in the sea. As a result, the shipboard gets in a continuous turning motion back/front and right/left. And the shipboard is also constantly exposed to many different kinds of disturbance signals including the vibrations of various frequencies from the internal equipments and their vibrations, strong waves, and impact from explosion. This paper formulates multi-body dynamic models similar to an actual system and simulates the pitch/roll positions of a 2-axes gimbals with PI controller for consecutive behavior of a naval shipboard including disturbance.

• Journal of the Society of Naval Architects of Korea
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• v.47 no.4
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• pp.496-507
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• 2010

It is well known that when a high-speed planing craft travels in following seas it experiences long-periodic motions due to low encounter frequency, and it often loses its course keeping stability. Therefore, it is necessary to study the sea-keeping performance and stability of it in the following seas. In this paper, the vertical motions of a planing craft were measured in following regular waves, and the test results were compared with the theoretical results. In the case of the same encounter frequency, non-dimensionalized motion amplitudes become larger as Froude number is higher, and non-dimensionalized motion amplitudes in head waves are larger than those in following waves. The mean values of the motions in following waves are similar to the running attitudes of a craft in calm water at the same Froude number.

• Journal of Advanced Navigation Technology
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• v.15 no.4
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• pp.502-509
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• 2011

It is necessary to resolve integer ambiguity in GPS carrier based precise positioning. If there is no signal blockage or cycle slip, the integer ambiguity does not changed. however, signal blockage and cycle slip occur frequently under real operational environment. under this situation, integer ambiguity maintenance is indispensable for continuity of navigation information. In this paper, a cycle slip free technique is proposed for simplifying integer ambiguity maintenance procedure. this technique tested with simulated carrier phase signal with cycle slip aided intentionally. As a result, the proposed technique can give navigation information continuously even if cycle slip is occured.

• Journal of the Korean Society for Marine Environment & Energy
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• v.5 no.3
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• pp.35-44
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• 2002

In this paper, the analytic studies on the wave control performance of moored pontoon-type floating breakwater are presented. A two-dimensional eigenfunction expansion method is adopted to study the motion responses and the transmission coefficients of pontoon-type floating breakwater in beam waves. The stiffness coefficients of mooring line are idealized as linear elastic spring. Comparison of the analytical results with a numerical results (FEM) shows good agreement over a wide range of frequencies. The performance of mooed pontoon-type floating breakwater is tested with various design parameters such as sectional geometry, mooring line characteristics and wave frequencies. It is found that the properly designed floating breakwater can be an effective wave control structure.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.5 no.3
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• pp.182-190
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• 1993

A numerical technique is presented to calculate the motions of 6 d.o.f and mooring tensions for a catenary moored floating breakwater. The breakwater may be subjected to the 3-D combination of regular or irregular waves and stationary forces. The added mass coefficients at the infinitive frequency of input wave and the variations of damping and exciting force coefficients are calculated using the source distribution method. The coefficients are used to constitute motion equations in time domain which are solved by WiIson-$\theta$ method. The solutions agree quite well with either static displacement determined from Newton method under the stationary force only or 6 d.o.f determined from the frequency domain analysis under regular wave only. An example analysis is also done for a floating breakwater to demonstrate its applicability.

• Journal of the Korean Society of Propulsion Engineers
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• v.10 no.1
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• pp.54-63
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• 2006

Ejector system are used to transport a low momentum flow to the higher pressure flow by the momentum change between high and low momentum flows. This system is used to simulate the high altitude and Mach number condition over altitude 20 km and Mach 4 of the supersonic test facility. We applied the design and the performance analysis technique(EISIMP code) of the Ramjet Test Facility(RJTF) air system in JAXA to the ejector system of the ramjet test facility in KARI. After preliminary design of the ejector system, we performed a computational study using FLUENT and investigated shock structures and flow characteristics of the ejector system.

• Journal of the Society of Naval Architects of Korea
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• v.54 no.2
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• pp.132-142
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• 2017

As the International Maritime Organization (IMO) recently introduced the Energy Efficiency Design Index (EEDI) for new ships building and the Energy Efficiency Operational Indicator (EEOI) for ship operation, thus an accurate estimation of added resistance of ships advancing in waves has become necessary. In the present study, OpenFOAM, computational fluid dynamics libraries of which source codes are opened to the public, was used to calculate the added resistance and motions of the KCS. Unstructured grid using a hanging-node and cut-cell method was used to generate dense grid around a wave and KCS. A dynamic deformation mesh method was used to consider the motions of the KCS. Five wavelengths from a short wavelength (${\lambda}/LPP=0.65$) to a long wavelength (${\lambda}/LPP=1.95$) were considered. The added resistance and the heave & pitch motions calculated for various waves were compared with the results of model experiments.

• Journal of the Society of Naval Architects of Korea
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• v.46 no.4
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• pp.373-381
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• 2009

The running attitude of a high-speed planing craft may change significantly depending on its speed in seaway. Other variables that may influence its running attitude are its weight, center of gravity, sea conditions, and so on. In this paper, planing craft model tests were carried out with respect to above variables in SNU towing tank, and vertical motion responses of a planing craft in regular head waves were analyzed. The experimental results in regular waves were compared with those in calm water, and compared with the theoretical estimations. Finally, the effects of running speeds of a planing craft on its motion amplitudes are confirmed.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.30 no.2
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• pp.39-50
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• 2018

In this study, the nonlinear interaction of irregular waves with wave breaking and currents around permeable submerged breakwater was investigated with the aid of olaFlow model which is open source CFD software published under the GPL license. The irregular wave performance of olaFlow applied in this study was verified by comparing and evaluating the target frequency spectrum and the generated frequency spectrum for applicability to irregular waves. Based on the applicability of this numerical model to irregular wave fields, in the coexistence fields of irregular waves and currents, the characteristics of wave height, frequency spectrum, breaking waves, averaged velocity and turbulent kinetic energy around porous submerged breakwater with the respect to the beach type and current direction versus wave propagation were carefully investigated. The numerical results revealed that the shape of wave breaking on the crown of the submerged breakwater and the formation of the mean flow velocity around the structure depend greatly on the current directions and the type of the beach. In addition, it was found that the wave height fluctuation due to the current direction with respect to the wave propagation is closely related to the turbulent kinetic energy.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 1996.10a
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• pp.65-70
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• 1996

엔진소음을 소음특성에 따라 분류하면 공력소음(Aerodynamic Noise), 연소소음(Combustion Noise), 기계적인 소음(Mechanical Noise)으로 나눌 수 있으며 소음원의 종류에 따라 분류하면 배기계소음(Exhaust System Noise)으로 나눌 수 있으며 소음원의 종류에 따라 분류하면 배기계소음(Exhaust System Noise), 흡기계소음(Intake System Noise), 냉각계소음(Cooling System Noise), 엔진표면소음(Engine System Noise)등으로 분류할 수 있다. 이러한 여러소음중 엔진 내부의 유동에 의한 흡배기계통으로의 소음방출은 자동차 실 내외 소음의 중요한 문제로 대두되는데, 이를 줄이기 위해 그 동안 소음기 등의 서브시스템의 형태와 그 위치조정에 관한 연구가 수행되어 왔다. 그러나 이것이 비용 또는 성능에 영향을 미치므로 본질적인 소음원을 규명해 내는 것이 필요하게 되었다. 흡배기계의 소음은 엔진의 흡입, 배기행 정시 피스톤의 운동에 의해 팽창 및 압축파 형태의 압력파(pressure wave)로 발생하게 되고, 밸브근방에서는 유동의 박리(separation)에 의해 발생하게 된다. 소음기 등의 서브시스템에서도 유동의 박리에 의해 발생하게 되며 특히 배기행정시 발생하는 압력파는 비선형영역에 있게된다. 흡기소음은 배기에 비해 그 크기가 작아서 그동안 등한시 되어왔으나 이것이 소비자의 불평요인으로 작용하므로써 이에 대한 연구도 활발히 수행되어야 한다. Bender, Bramer[1]는 흡배기계 소음의 외부 방사에 관하여 전반적으로 기술하였고 Sierens등[2]은 흡기계에서 1차원 MOC(Method of Characteristics)방법으로 비정상 유동해석을 하고 실험결과와 비교하였다. J.S.Lamancusa 등[3]은 흡기 소음원을 실험을 통해 예측하였고, 흡기소음도 비선형 거동을 보인다고 밝혔다. Yositaka Nishio 등[4]은 새로운 흡기실험장치를 고안하여 공명기(resonator)의 위치 변화에 의한 저소음 흡기계를 설계 초기단계에서부터 적용하려 하였다. 일반적으로 흡배기계의 복잡한 형상 때문에 대부분 실험을 통해 문제를 해결하려 하였고, 수치해석은 피스톤의 운동을 배제한 단순화한 흡배기계의 정상상태 유동해석이 주를 이루어왔다. Taghaui and Dupont 등[5]은 KIVA코드를 사용하여 흡기포트와 연소실 그리고 밸브의 움직임을 동시에 고려한 수치해석을 도입하였다. 하지만 이들이 밸브의 운동을 고려하기 위해 사용한 이동격자는 격자점은 시간에 따라 변화하지만 그 격자의 수가 일정하게 유지되어 있어서 밸브의 완전개폐를 해석할 수가 없다. 강희정[6]은 단일 실린더와 단일 배기밸브를 갖는 문제로 단순화하여 피스톤과 밸브의 움직임을 고려하므로써 배기행정 후 소음이 어떻게 전파해 나가는가를 연구하였다. 본 연구에서도 최소밸브간격과 최대밸브간격 사이에서만 계산이 가능하나 흡기의 경우는 밸브가 닫힐 때 생기는 압력파가 중요하므로 실린더와 밸브사이에 벽면조건을 주어 밸브의 개폐를 모사하였다.