• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.17 no.3 s.120
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• pp.235-240
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• 2007

In this work, the operational deflection shape(ODS) of an automobile exhaust system is measured by using a recently-developed magnetic sensor. The magnetic sensor is composed of a solenoid and two pairs of permanent magnets generating an antisymmetric magnetic field in the lateral direction inside the solenoid. Lateral movement of a ferromagnetic pipe inside the magnetic field of the suggested sensor induces an electromotive force in the solenoid corresponding to the lateral velocity of the pipe. Due to the simplicity and non-contact characteristics of the magnetic sensor, dynamic behaviors of the structures operating under high temperature such as an exhaust pipe can be efficiently observed. It is shown that the lateral ODS of an exhaust system can be successfully measured by the suggested sensors.

• Journal of Power System Engineering
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• v.22 no.6
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• pp.58-66
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• 2018

The use of external gear pumps is an effective way to achieve adequate performance at low cost when composing hydraulic systems. The biggest drawback, on the other hand, is the accompanying noise. Gears of continuous contact shape are actively used for the pump recently. The continuous contact shape must be the helical type due to the nature of the gear pump that is driven only by the drive gear. In this paper the theoretical shape of continuous contact gear is analyzed using simple rack shape of straight lines and two circular arcs. Using such geometry, the theoretical equation will be developed by envelope curves according to the conjugate gear shape rules. After checking the validity of the theory by the shape of gear rules, the grinding shape was also developed. The 3D shapes using equation can be also drawn. It was also shown that contact ratio and radius of curvature are easily developed by the theoretical equations.

• Proceedings of the Korea Water Resources Association Conference
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• 2017.05a
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• pp.308-308
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• 2017

국내 하천에 설치된 횡단구조물은 2009년을 기준으로 약 20,753개로 알려져 있으며 수위 유지, 하상고 유지 등의 목적을 가지고 설치된다. 그러나 낙차를 가진 빠른 유속의 흐름을 형성시켜, 하류 하상에서 국소 세굴을 발생시킨다. 이를 방지하기 위해 횡단구조물 하류에 굴요성 구조(flexible structure)인 돌망태, 블록공, 사석 등으로 이루어진 바닥보호공(bed protection)이 설치되나 유실, 침하 등의 문제가 빈번히 발생되고 있어, 문제를 해결하기 위한 연구가 필요하다. 본 연구는 이러한 피복 대책에서 일어날 수 있는 파괴 기구인 전단파괴, 흡출 파괴, 경계 파괴, 하상 형태 변화에 따른 하부 침식 중 흡출 파괴(winnowing failure)를 유발하는 흐름을 검토하기 위한 수치모의를 수행하였다. 이때 흡출 파괴는 바닥보호공의 공극으로 미세한 하상 재료가 난류와 침투류의 작용에 의해 침식되어 바닥보호공이 침하되는 것을 말한다. 수치모의는 전산유체동역학(Computational Fluid Dynamics, CFD) 모형인 FLOW-3D 모형을 이용하였으며, 난류 모형으로 LES 모형을 적용하고 조밀한 격자를 부여하여 바닥보호공의 공극에서 발생되는 비교적 작은 척도의 와(vortex)를 해상할 수 있도록 하였다. 수치모의에 적용된 횡단구조물은 보, 물받이공, 바닥보호공으로 구성하였으며 특히, 바닥보호공의 형상은 구체(sphere)로 가정하여 다층으로 배치하였다. 바닥보호공의 공극 또는 구체 사이에서 발생되는 유속, 압력 등의 흐름특성을 분석한 결과, 바닥보호공 두께가 두꺼울수록 흡출 파괴에 대해 안정적인 것으로 나타났다. 이는 바닥보호공 설계를 위한 기초자료로 활용될 수 있으며, 향후 입자영상유속계(Particle Image Velocimeter, PIV)와 같이 공극에서 흐름을 측정할 수 있는 방법과 병행한 연구를 수행할 수 있을 것이다.

• Proceedings of the Korea Water Resources Association Conference
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• 2019.05a
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• pp.135-135
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• 2019

수제는 만곡부의 유로 조정이나 하상보호와 같은 하천공학적인 목적을 가진 수공구조물이다. 본 연구에서는 개수로 만곡부에 수제 설치 시 외측벽과 수제 사이의 거리에 따라 하상변동이 어떤 차이가 있는지를 파악하기 위해 이동상 수리실험을 했다. 본 연구에서는 폭 1.45 m, 길이 24 m인 $90^{\circ}$ 만곡수로에 $4.2{\times}8.4cm$의 직사각형 단면 수제를 외측으로부터 이격하여 2열로 설치하였다. 하상재료는 $d_{50}$이 3.3 mm인 잔자갈을 사용했고 하상경사는 1/300로 하였다. 실험은 평균 유량 163 l/s를 3시간 동안 공급했고, 종료 후 만곡부의 주요횡단면별 하상고를 측정했다. 여기서 실험별 이격거리는 8.4 cm, 14 cm, 19.6 cm로 하였다. 실험 결과 외측벽과 수제 사이의 거리가 멀어질수록 만곡부의 최대세굴심은 커지고 그 발생 위치는 하류로 이동하는 경향을 보였다. 만곡부 최대세굴이 발생한 횡단면 형상은 만곡 내측에서 외측방향으로 무차원 위치 $y_1$(=내측에서의거리/폭)가 0.27보다 작으면 퇴적에 의해 하상이 상승하고, 0.35보다 클 때는 세굴에 따른 하상저하가 나타났다. 만곡 외측벽 부근 하상은 이격거리가 짧을수록 수제 설치에 의한 하상고 변화가 작았다.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2004.10a
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• pp.210-214
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• 2004

This study proposes a design method for blade pitch control mechanism in order to regulate the power and to improve the starting characteristic. This power control unit which is assembled by spring and mass is planing to equip with 1kW class wind turbine system which is developed for low wind speed area like Korea. For the design of this control unit, the proper geometry of the hub was designed and the calculation of the mechanics was carried out. Especially, It is expected that the operational efficiency will be improved because of additional high pitch starting function by using 2 step spring structure.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2008.11a
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• pp.45-48
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• 2008

Micro power generators have been studying to provide high power that micro systems require. Micro power generators need micro combustor. Swiss-roll combustor has been studied about scale, geometry, material. From previous study experiments have shown that swiss-roll combustors require thin walls with low thermal conductivity for maximum performance at small scales. In this work, polyimide combustors with low thermal conductivity and thin thickness are built and tested.

• Solar Energy
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• v.14 no.2
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• pp.3-16
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• 1994

The major objectives of the study are to suggest the optimal basic design conditions for the horizontal storage tank system. For this purspose computer simulation has been carried out to find the characteristics of flow patterns in horizontal storage tank, and experiments have been carried out for the duration of one turnover, Experimental parameters are volume flow rate(1 LPM to 4 LPM), amount of heat generated from heat sources(0 W to 100 W), and inlet and outlet port types of the storage tank(DD type, DO type, ID type, IO type).

• Korean Journal of Optics and Photonics
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• v.16 no.5
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• pp.450-455
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• 2005

We have studied on operational characteristics of the nitrogen laser with sliding discharge and longitudinal excitation. We could observe radiation of nitrogen laser excited by a sliding discharge along the surface of a dielectric. The shape of the beam was a ring type which had 2 mm or 4mm in diameter depending on the sliding discharge tube shape. In this experiment, We show the possibilities to make other shapes of laser beam, for example, rectangle, ellipse, and to excite another gas laser system like an excimer laser.

• Tribology and Lubricants
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• v.35 no.1
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• pp.37-43
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• 2019

This paper presents an optimization method to determine the shoulder height of an angular contact ball bearing by 3D contact analysis using nondimensional-shaped variables. The load analysis of the ball bearing is performed to calculate the internal load distributions and contact angles of each rolling element. From the results of bearing load analysis and the contact geometry between the ball and inner/outer raceway, 3D contact analyses using influence function are conducted. The nondimensional shoulder height and nondimensional load are defined to give the generalized results. The relationship between the shoulder height and radius of curvature of the shoulder under various loading conditions is investigated in order to propose a design method for the two design parameters. Using nondimensional parameters, the critical shoulder heights are optimized with loads, contact angles, and conformity ratios. We also develop contour maps of the critical shoulder height as functions of internal loads and contact angles for the different contact angles using nondimensional parameters. The results show that the dimensionless shoulder height increased as the contact angle and dimensionless load increased. Conversely, when the conformity ratio increased, the critical shoulder height decreased. Therefore, if the contact angle is reduced and the conformity ratio is increased within the allowable range, it will be an efficient design to reduce the shoulder height of ball bearings.

• Journal of the Society of Naval Architects of Korea
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• v.56 no.2
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• pp.109-116
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• 2019

This paper carried out numerical analysis for estimating the propulsion performance of the model scale ONRT benchmark model of'Tokyo 2015 a workshop on CFD'. The method reflecting the scale effect of ITTC'78 method and form factor were used to compare the estimates of the effective wake ratio of full-scale. The numerical calculation was performed with Siemens's Star-CCM+, compared with IIHR model tests and the numerical analysis results of other research institutes, showing good agreement. In the case of an open stern and twin skeg ship, the validity of the ITTC'78 method can be confirmed by assuming that the effective wake ratio estimated from the numerical analysis results of model scale is similar to the effective wake ratio of full-scale.