• Journal of Power System Engineering
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• v.11 no.4
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• pp.18-25
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• 2007

제 2세대 직접분사식 가솔린 기관에서 6공 연료분사기의 연료분무특성을 관찰하였다. 실험에 사용한 직접분사식 가솔린 기관은 2개의 흡입밸브와 2개의 배기밸브를 갖는 텀블형 Spray Guided 연소실과 Quartz로 제작된 실린더 라이너와 실린더 헤드 창으로 구성되어 있다. 선회유동을 유도하기 위하여 흡입매니폴드에 선회유동 제어밸브를 부착하였다. 2차원 Mie 스캐터링 기법을 이용하여 연료분사시기, 연료분사압력과 실린더 내 유동 및 냉각수 온도가 연료분무에 미치는 영향을 관찰하였다. 실험결과로는 흡기과정동안 흡기 선회유동은 분사된 연료의 공간적 분포에 크게 작용하였고, 압축과정동안에는 텀블 및 선회유동의 영향이 흡기과정에 비해 크지 않음을 확인하였다. 또한 성층연소를 위해서 압축과정에서 연료를 분사하는 경우 고압의 연료분사압은 분무도달거리의 성장을 촉진시키나 상승하는 피스톤과 이로 인한 실린더 압력의 상승으로 분무도달거리의 성장이 억제됨을 확인할 수 있었다.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.24 no.2
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• pp.77-83
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• 2012

Numerical analyses through Computational Fluid Dynamics have been performed to investigate the seawater flow field characteristics for various shrouds used in horizontal axis tidal current turbine systems. Seawater flow characteristics are largely influenced under constant tidal current velocity by the shroud geometry and there is considerable difference in fluid velocity distributions around the shrouds. Especially the location and magnitude of maximum seawater flow velocity directly affect turbine performance for power generation. For the cylinder-diffuser type shroud system whose cylinder and diffuser parts have the same length accelerated flow region is formed in the overall cylinder part while maximum velocity in the nozzle-diffuser type whose nozzle and diffuser parts have the same length with symmetry, locally appears near the minimum sectional area. In case of cylinder-diffuser type shroud fluid velocity increases rather high compared with current velocity. And fluid velocity at the centerline gradually increases from the entrance, and then decreases rapidly after reaching a peak close to the middle of the cylinder part unlike the nozzle-diffuser while there is not much variation near the rear of the shroud. These results of the seawater flow characteristics with various shroud geometries can be applied to optimal design for the development of efficient tidal current power generation systems.

• Journal of Energy Engineering
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• v.22 no.4
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• pp.399-405
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• 2013

The gas motion inside the engine cylinder plays a very important role in determining the thermal efficiency of an internal combustion engine. A precise information of in-cylinder three dimensional complex gas motion is crucial in optimizing engine design. Homogeneous charge compression ignition (HCCI) engine is a combustion concept, which is a hybrid between Otto and Diesel engine. The turbulent diffusion leads to increased rates of momentum, heat and mass transfer. The in-cylinder turbulence flow was found to affect the present HCCI combustion mainly through its influence on the wall heat transfer. This study investigates the effect of piston geometry shape on the turbulent flow characteristics of in-cylinder from the numerical analysis using the LES model and the results obtained can offer guidelines of the combustion geometries for better combustion process and engine performance.

• Journal of the Korean Society of Propulsion Engineers
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• v.21 no.1
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• pp.44-50
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• 2017

Vehicle Holding Device(VHD) has a role that holding the launch vehicle on its launch pad until the engine therust reaches a steady condition. The analytical study of shape parameters and dynamic characteristics of hydraulic cylinders is carried out. The contraction of cylinder is considered as the major factor of releasing mechanism. Through the analysis, the decreasing of cylinder slit size and increasing initial charging pressure increase the contraction force. Through the transient analysis, cylinder load, displacement and inner pressure distribution are confirmed. The cylinder contraction force is converged to the cylinder external force when the cylinder starts to move. Also, the pressure distribution in the hydraulic cylinder is constant.

• Journal of Advanced Marine Engineering and Technology
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• v.36 no.8
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• pp.1091-1096
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• 2012

The aerodynamic characteristics of circular cylinder in a channel are studied to make clear the flow feature by solving the Navier-Stokes equation based on the finite volume method with unstructured grids. Reviews are made on with the vorticity, velocity, dynamic pressure, residual and drag, where the Reynolds numbers are 50 and 100. The flows for $Re{\succeq}50$ shows the vortex shedding in the wake, and the result is the same as the case of moving cylinder. The ground effect of flat bottom results in the growth of vortex, being generated in the upper side of the cylinder and elongated in the rear. As the cylinder approaches to wall, for example 0.6, the cylinder plays as a role of blockage to obstruct the flow between the cylinder and wall. The drag coefficients are compared with others' results to confirm the validity of the present numerical simulation.

• Proceedings of the Acoustical Society of Korea Conference
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• 1992.06a
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• pp.96-99
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• 1992

섬유강화 복합재료의 동탄성계수와 감쇠특성을 규명하기 위하여 랜덤하게 분포된 무한 실린더 형상의 산란체를 가진 매질내에서, 조화운동을 하는 압축 및 SV탄성파의 전파에 관하여 연구하였다. 단일 실린더에 대한 산란계수로부터 La의 준결정근사법을 이용하여 다중산란에 관한 이론을 유도하였고, 매질내에서의 파동전파 특성을 내포하는 분산관계식을 얻었다. 수치적으로 분산관계식의 해를 구함으로써 2 차원 유효체적강성, 횡방향 유효전단강성 및 각 파동의 전파에 따른 감쇠계수를 주파수와 체적비의 함수로서 제시하였다.

• Proceedings of the Korean Society of Tribologists and Lubrication Engineers Conference
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• 1994.06a
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• pp.42-48
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• 1994

고압하에서 고속으로 작동하는 유압 피스톤 펌프(hydraulic piston pump) 또는 모터(motor) 등의 유압기계(hydrostatic machine)에서 피스톤과 실린더 사이의 간극(clearance)을 흐르는 유압유(hydraulic oil)의 유동에 관한 연구는 이러한 유압기계의 피스톤부 설계에서 특히 중요하다. 본 연구에서는 원통형 피스톤이 원통부와 테이퍼가 진 부분으로 나누어져 있는 복합(composite)형상의 피스톤에 대한 이론해석을 수행하여 피스톤의 형상이 유압 피스톤 펌프의 윤활성능에 미치는 영향을 조사하고자 한다.

• Proceedings of the Acoustical Society of Korea Conference
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• 1998.06e
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• pp.255-258
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• 1998

본 연구에서는 해석적인 방법을 사용하여 고감도 멘드릴형 광섬유 음향센서를 설계하고자 하였다. 음향감지부의 형상으로 실린더형 멘드릴 및 중공원통형 층상복합체 멘드릴을 선정하고, 음향감도에 대한 이론식을 유도하여 재질변수 및 형상변수 등에 따른 음향감도를 해석하였다. 또한 해석적 방법 및 유한요소법을 이용한 분석결과를 비교하여 해석적인 방법의 타당성을 검증하였다. 그 결과, 멘드릴의 외경변화에 의한 감도변화 경향만이 다소 차이를 보이고 있으나 그 이외의 재질변수 및 형상변수에 의한 음향감도 변화 경향은 서로 잘 일치하는 것으로 분석되었다.

• Journal of Power System Engineering
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• v.10 no.4
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• pp.127-132
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• 2006

Pneumatic cylinders that are usually applied in the factory automation line have complicated failure cause because they are composed of various elements. In this study, we performed life test and performance test of double acting pneumatic cylinders according to the international standards and then analyzed the life and the main failure mode of the cylinders in the same load condition. On the basis of these processes, we can estimate shape parameter for the reliability estimation of pneumatic cylinders and their data analysis of life distribution.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.39 no.4
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• pp.325-333
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• 2015

This study was devoted to elucidating the change in the flow characteristics of a laminar flow past a circular cylinder by modifying the cylinder shape with O-grooves. A numerical analysis was performed in a two-dimensional framework. The cylinder was represented using an immersed boundary method and marker particles on a Cartesian grid system. The number and locations of the O-grooves were the key parameters. An analysis of the flow pattern and flow-induced forces was performed at Re = 40 and 50. In addition, we calculated the critical Reynolds number depending on the number of O-grooves and their locations.