• Journal of the Society of Naval Architects of Korea
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• v.49 no.2
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• pp.158-163
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• 2012

Recently, reducing underwater radiated noise (URN) of ships has become an environmental issue to protect marine wildlife. URN of ships can be predicted by various methods considering its generating mechanism and frequency ranges. For URN prediction due to ship structural vibration in low frequency range, the fluid-structure interaction analysis technique based on finite element and boundary element methods (FE/BEM) is regarded as an useful technique. In this paper, URN due to a double bottom-shaped structure vibration has been numerically investigated based on a coupled method of FE/BEM to enhance the prediction accuracy of URN due to the vibration of real ship engine room structure. Acoustic radiation efficiency and URN transfer function in case of vertical harmonic excitation on the top plate of double bottom structure have been evaluated. Using the results, the validity of an existing empirical formula for acoustic radiation efficiency estimation and a simple URN transfer function, which are usually adopted for URN assessment in initial design stage, is discussed.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.21 no.5
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• pp.1049-1059
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• 2017

After patrol corvett Cheonan was hit and sank on duty, the Republic of Korea Navy has tried to install hybrid propulsion system on naval ship to reduce vibration and noise problems during navigation. The hybrid propulsion system has advantage that propulsion motor can be propelled in low speed operation of the vessel. This can be a better quietness than a mechanical propulsion system which consists of a conventional internal combustion engines. And more economical operation is possible by using a propulsion motor in a low speed operation where a fuel efficiency of the internal combustion engine is poor. In this paper, we set up virtual ship on the basis of a combat support ship in the Republic of Korea Navy, economically compared and analyzed fuel consumption between conventional and hybrid propulsion system. As a result, it was confirmed that the fuel efficiency of hybrid propulsion system which use electric motor had been relatively improved.

• Proceedings of the Korean Institute of Navigation and Port Research Conference
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• 2022.06a
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• pp.277-279
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• 2022

Rapid Development and adoption of AIS as a survailance tool has resulted in widespread application of data analysis technology, in addition to AIS ship trajectory clustering. AIS data-based clustering has become an increasingly popular method for marine traffic pattern recognition, ship route prediction and anomaly detection in recent year. In this paper we propose a route waypoint extraction by clustering ships CoG variance trajectory using Density-Based Spatial Clustering of Application with Noise (DBSCAN) algorithm in both port approach channel and coastal waters. The algorithm discovers route waypoint effectively. The result of the study could be used in traffic route extraction, and more-so develop a maritime anomaly detection tool.

• The Journal of the Acoustical Society of Korea
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• v.33 no.6
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• pp.358-365
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• 2014

When a ship propeller having wing type sections rotates at high speed underwater, local pressure on the blade decreases and various types of the cavitation inevitably occur where the local pressure falls below the vapor pressure. Fundamentally characteristics of the cavitation are determined by the shapes of the blade section and their operating conditions. Underwater noise radiated from a ship propeller is directly connected to the occurrence of the cavitation. In order to design low noise propeller, it is preferentially demanded to figure out key features: how the cavity is generated, developed and collapsed and how the effect of viscosity works in the process. In this study, we first perform inviscid analysis of the partial cavity generated on two dimensional hydrofoil. Secondly, viscous analysis using FLUENT with different turbulence and cavitation models are presented. Results from both approaches are also compared and estimated.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 1996.04a
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• pp.188-193
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• 1996

The purpose of resilient mounting for marine engine is to prevent noise and ship damages caused by engine vibration. Although many researches for the resilient mounting system have been carried out, these results have limit to apply on the marine engine systems. Because marine engine generally have low speed operating range and have to consider misfiring condition. In this paper, we studied the effect of engine's misfiring on the resilient mounting systems. And the influences of design parameters, such as dynamic characteristics and location angles of resilient rubber mountings, were also examined on the single and double resilient mounting systems.

• The Journal of the Acoustical Society of Korea
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• v.17 no.2
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• pp.18-24
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• 1998

선박내의 작업 환경에서 발생하는 소음은 엔진, 발전기, 펌프와 같은 다양한 소음원 에 기인하다. 이들은 대체적으로 저주파 대역에서 주기성을 가지며, 이로 인해 능동 소음 제 어 기법이 적용될 수 있다. 이 논문에서는 선박내 소음 환경을 개선하기 위해 소음 흡음 재·차단재를 이용한 헤드폰 착용과 같은 수동적인 방법이 아니라, 작업 상황에 따라 소음 을 줄이기 위한 능동소음제어(ANC: Active Noise Control) 시스템을 구현한다. 특히 선박내 의 침실 공간으로 적용 가능성을 컴퓨터 시뮬레이션을 통해 고찰하고, TMS320C50 DSP를 포함한 하드웨어 구성을 통해 그 성능을 실험하고 평가한다.

• Journal of Ship and Ocean Technology
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• v.7 no.3
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• pp.13-33
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• 2003

This paper presents a numerical study on tip vortex cavitation inception predictions based on non-spherical bubble dynamics including splitting and jet noise emission. A brief summary of the numerical method and its validation against a laboratory experiment are presented. The behavior of bubble nuclei is studied in a tip vortex flow field at two Reynolds numbers, provided by a viscous flow solver. The bubble behavior is simulated by an axisymmetric potential flow solver with the effect of surrounding viscous flow taken into account using one way coupling. The effects of bubble nucleus size and Reynolds number are studied. An effort to model the bubble splitting at lower cavitation numbers is also described.

• Korean Journal of Computational Design and Engineering
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• v.9 no.3
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• pp.183-191
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• 2004

This paper deals with smooth curve fitting of data corrupt by noise. Most research efforts have been concentrated on employing the smoothness penalty function with the estimation of its optimal parameter in order to avoid the 'overfilling and underfitting' dilemma in noisy data fitting problems. Our approach, called DBSF(Differentiation-Based Smooth Fitting), is different from the above-mentioned method. The main idea is that optimal functions approximately estimating the derivative of noisy curve data are generated first using genetic programming, and then their integral values are evaluated and used to recover the original curve form. To show the effectiveness of this approach, DBSP is demonstrated by presenting two illustrative examples and the application of estimating the principal dimensions of bulk cargo ships in the conceptual design stage.

• Bulletin of the Society of Naval Architects of Korea
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• v.21 no.4
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• pp.10-20
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• 1984

When the hydrodynamic coefficients of the ship maneuvering equation are estimated by captive model test, it is difficult to take account of the scale effect between model and full scale ship. This scale effect problem can be overcome by processing the sea trial data with system identification. Extended Kalman filter is used as a system identification technique for the modification of the simulation equation as well as the estimation of hydrodynamic coefficients The phenomena of simultaneous drifting of linear coefficients occur. It is confirmed that two coefficients in each pair-$(Y_v',\;Y_r'-m'u'),\;(N_v',\;N_r')$-are simultaneously drifting and all 4 coefficients are drifting together. Particularly simultaneous drifting and 2 coefficients in each pair is more significant. It is also shown that the simultaneous drifting of 4 coefficients can be reduced by choosing the input data which have the random v'/r' curve and 4 coefficients are estimated within $2{\sim}4%$ error, which may be noise level. So, it is recommended to operate the rudder randomly in sea trial or model test for the application of system identification technique.

• Journal of the Society of Naval Architects of Korea
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• v.57 no.6
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• pp.345-352
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• 2020

This study aims to investigate the crabbing motion of the research vessel "NARA" by full-scale maneuvering trials. The crabbing test method refers to ITTC recommended procedures and guidelines. In order to minimize the fluctuation of the heading angle due to the external force acting on the hull during the pure lateral motion, the tests are conducted using the dynamic positioning system applied to the ship. The test results are analyzed by applying a low-pass filter to remove the noise included in the measurement data. Three conditions are set to define the steady state of crabbing motion. The index to be derived from the crabbing test is quantitatively presented. The ship is confirmed to be capable of the lateral motion of up to 0.844m/s in Beaufort 3.