• Tribology and Lubricants
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• 제28권2호
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• pp.81-92
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• 2012

To product multi-grade oil like engine oil, a sort of mineral base oil is mixed with a fundamental additive liquid package and a polymer liquid as viscosity index improver in order to improve the lubricating property of oil. That is, engine oil is the mixture of more than two fluids. In this paper, it will be systematically organized the governing equation describing non-Newtonian thermo-hydrodynamic lubrication related with the mixture of incompressible fluids based on the principle of continuum mechanics. Then, in order to find how the thermal analysis effect on the bearing performance lubricated with the mixture of multi-fluids, it will be compared to the performances between the mixture of each liquid to be blended and multi-grade engine oil as a single fluid in a high speed journal bearing. It is found that, in the case of lower viscosity oil, the difference of pressure distribution between the above two cases turns out to be existed, even if the load capacity is same level.

• Journal of Advanced Marine Engineering and Technology
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• 제37권6호
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• pp.623-630
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• 2013

본 연구는 기 개발된 인플래터블 카약(RPO-2)과 새롭게 개발된 인플래터블 카약(RD-FK-11, RD-FK-12)의 유체역학적인 성능평가를 위하여 경사시험과 선회시험은 해양공학수조에서 저항시험은 축소된 모형선을 제작하여 회류수조에서 수행되었다. 결론적으로 각각의 카약에 대한 다양한 성능시험결과 복원성 측면에서는 KONA가 유리하고, 선회력과 무게중심 측면에서는 RD-FK-12가 우수하고, 저항성능 측면에서는 RD-FK-11이 KONA와 RPO-2에 비해 우수하였다.

• Journal of Ship and Ocean Technology
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• 제10권2호
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• pp.1-10
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• 2006

Numerical analysis of viscous flow around twin-skeg hull forms was conducted according to the variations of distance between skegs and vertical skeg inclinations by using a hydrodynamic analysis system, WAVIS. Six twin-skeg hull forms were derived by combining three distances between skegs (16m, 20m, 24m) and four vertical skeg angles ($0^{\circ},\;10^{\circ},\;15^{\circ},\;20^{\circ}$). It is found that the better resistance performance can be obtained with larger vertical skeg angle and smaller skeg distance for the present test cases. It also can be seen that the same trend is true for the nominal wake distributions in the propeller plane. Those tendencies were confirmed by the experimental results of MOERI. It is shown that numerical analysis can be a useful and practical tool for the evaluation and improvement of hydrodynamic performances for the complex stern hull forms with twin skegs.

• International Journal of Naval Architecture and Ocean Engineering
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• 제9권1호
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• pp.77-99
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• 2017

Offshore oscillating water columns (OWC) represent one of the most promising forms of wave energy converters. The hydrodynamic performance of such converters heavily depends on their interactions with ocean waves; therefore, understanding these interactions is essential. In this paper, a fully nonlinear 2D computational fluid dynamics (CFD) model based on RANS equations and VOF surface capturing scheme is implemented to carry out wave energy balance analyses for an offshore OWC. The numerical model is well validated against published physical measurements including; chamber differential air pressure, chamber water level oscillation and vertical velocity, overall wave energy extraction efficiency, reflected and transmitted waves, velocity and vorticity fields (PIV measurements). Following the successful validation work, an extensive campaign of numerical tests is performed to quantify the relevance of three design parameters, namely incoming wavelength, wave height and turbine damping to the device hydrodynamic performance and wave energy conversion process. All of the three investigated parameters show important effects on the wave-pneumatic energy conversion chain. In addition, the flow field around the chamber's front wall indicates areas of energy losses by stronger vortices generation than the rear wall.

• 한국해양공학회지
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• 제36권6호
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• pp.364-379
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• 2022

Coastal communities have been vulnerable to extreme coastal flooding induced by hurricanes and tsunamis. Many studies solely focused on the overland flow hydrodynamic and loading mechanisms on individual inland structures or buildings. Only a few studies have investigated the effects of flooding mitigation measures to protect the coastal communities represented through a complex series of building arrays. This study numerically examined the performance of flood-mitigation measures from tsunami-like wave-induced overland flows. A computational fluid dynamic model was utilized to investigate the performance of mitigation structures such as submerged breakwaters and seawalls in reducing resultant forces on a series of building arrays. This study considered the effects of incident wave heights and four geometrically structural factors: the freeboard, crest width of submerged breakwaters, and the height and location of seawalls. The results showed that prevention structures reduced inundation flow depths, velocities, and maximum forces in the inland environment. The results also indicated that increasing the seawall height or reducing the freeboard of a submerged breakwater significantly reduces the maximum horizontal forces, especially in the first row of buildings. However, installing a low-lying seawall closer to the building rows amplifies the maximum forces compared to the original seawall at the shoreline.

• 한국윤활학회:학술대회논문집
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• 한국윤활학회 2002년도 proceedings of the second asia international conference on tribology
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• pp.115-116
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• 2002

This study was carried out as one of efforts to overcome difficulties in air bearing design due to low stiffness and low damping. Hydrodynamic effects on hydrodynamic stiffness of a fluid film in a high speed air bearing with tow-row air sources are investigated. The hydrodynamic effects by the high speed over DN 1,000,000 and eccentricity of a proceeding which are not considered in conventional design of an air bearing need to be reconsidered. The hydrodynamic effects, which dominantly influence on the load capacity of air bearing, are caused mainly by proceeding speed, eccentricity, and the source positions. The two-row source arrangement in the air bearing produces quite unique hydrodynamic effects with respect to pressure distribution of the air film. Optimal arrangement of the two-row sources improves performance of an air bearing in film reaction force and loading capacity of high speed spindles. This study compares the pressure distribution by numerical simulation as a function of eccentricity of proceeding and the source positions. The air source position 1/7L form one end of an air bearing was found to be superior to source position of 1/4L. The dynamic stiffness were obtained using a two-dimensional cutting method which can directly measure the cutting reaction forces and the displacements of the spindle in two directions using a tool dynamometer and transducer sensors. Heat generation in the air film can not be negligible over the speed of DN 2,000,000. In order to analysis effects of heat generation on the characteristics of air bearing, high cooling bearing spindle and low cooling bearing spindle were tested and compared. Characteristics of the frequency response of shaft and motion of run out errors were different for the spindle. The test results show that, in the case of low cooling bearing spindle, the stiffness became smaller due to heat generation. The results, which were obtained for high speed region, may be used as a design information for spindle which can be applied to precision devices such as ultra precision grinding and ultra high speed milling.

• 대한기계학회논문집A
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• 제24권1호
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• pp.269-274
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• 2000

Frictions and electrical contact voltages of the herringbone-grooved hydrodynamic bearing(HHB) were 9, measured to use in a laser scanner motor. This bearing with varying loads, speeds, oil viscosity, and radial clearances successfully operated up to 28,000rpm and 0.5N. Experimental results under various environments confirmed that this bearing had excellent performance with low friction force, and operated without contact between shaft and sleeve.

• 한국유체기계학회 논문집
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• 제3권1호
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• pp.5-9
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• 2000

A study to minimize the error in water-meter is considered in this work. It is presumed that the large amount of error at large flowrate is occurred due to the vibration of the impeller shalt. After a newly designed bushing applying hydrodynamic journal bearing theory is adopted, the error at large flow rate is decreased remarkably comparing with the classical water-meter. It is concluded that the effect of a bushing in water-meter stabilizes the rotator of the impeller shaft.

• 한국해양환경ㆍ에너지학회지
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• 제1권1호
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• pp.66-82
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• 1998

해양오염 사고시 유출유의 수거를 위하여 사용되는 유회수기에 대하여 고찰하였다. 논문의 주요 내용은 (1) 유회수기의 종류, 장단점, 성능지표 및 시장현황에 대한 개괄적인 설명과 (2) 유회수 성능에 영향을 미치는 인자들에 대한 고찰, 그리고 (3) 유회수기 분야에 대하여 현재까지 발표된 논문들에 대한 핵심 아이디어들을 소개하였다. 끝으로 (4) 유체역학적 관점에서 본 유회수기의 특성과 해양, 토목, 기계등 유사관련분야의 연구결과가 유회수기 해석에 어떻게 이용될 수 있는지에 대하여 고찰하였다.

• International Journal of Naval Architecture and Ocean Engineering
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• 제8권1호
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• pp.22-37
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• 2016

This article investigates numerical modeling of surface piercing propeller (SPP) in unsteady open water condition using boundary element method. The home code based on BEM has been developed for the prediction of propeller performance, unsteady ventilation pattern and cross flow effect on partially submerged propellers. To achieve accurate results and correct behavior extraction of the ventilation zone, finely mesh has generated around the propeller and especially in the situation intersection of propeller with the free surface. Hydrodynamic coefficients and ventilation pattern on key blade of SPP are calculated in the different advance coefficients. The values obtained from this numerical simulation are plotted and the results are compared with experiments data and ventilation observations. The predicted ventilated open water performances of the SPP as well as ventilation pattern are in good agreement with experimental data. Finally, the results of the BEM code/experiment comparisons are discussed.