• 소성∙가공
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• 제28권3호
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• pp.135-144
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• 2019

Electromagnetic impulse welding (EMIW) is a type of solid state welding using the Lorentz force generated by interaction between the magnetic field of the coil and the current induced in the workpiece. Although many experimental studies have been investigated on the expansion and compression welding of tube using the EMIW process, studies on the EMIW process of lap joint between flat sheets are uncommon. Since the magnetic field enveloped inside the tube can be controlled with ease, the electromagnetic technique has been widely used for tube welding. Conversely, it is difficult to control the magnetic field in the flat sheet welding so as to obtain the required welding velocity. The current study analyzed the effects of coil shape on the impulse velocity for suitable flat one-turn coil for the EMIW of the flat sheets. The finite element (FE) multi-physics simulation involving magnetic and structural field of EMIW were conducted with the commercial software LS-DYNA to evaluate the several shape variables, viz., influence of various widths, thicknesses, gaps and standoff distances of the flat one-turn coil on the impulse velocity. To obtain maximum impulse velocity, the flat one-turn coil was designed based on the FE simulation results. The experiments were performed using an aluminum alloy 1050 sheets of 1.0mm thickness using the designed flat one-turn coil. Through the microscopic interfacial analysis of the welded specimens, the interfacial connectivity was observed to have no defects. In addition, the single lap joint tests were performed to evaluate the welding strength, and a fracture occurred in the base material. As a result, a flat one-turn coil was successfully designed to guarantee welding with bond strength equal to or greater than the base material strength.

• 한국재난정보학회 논문집
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• 제17권1호
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• pp.1-9
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• 2021

연구목적: 본 연구는 계단식 공동주택의 화재 시 차압 및 방연풍속 특성을 분석하고, 화재안전기준에서 제시하고 있는 방연풍속 기준의 실효성을 검증하는 것을 목적으로 한다. 연구방법: 실제 모델의 계단식 공동주택의 제연설계 및 거실의 창문 개방조건에 따른 방연풍속의 성능을 CONTAM 프로그램을 이용하여 분석하였다. 연구결과: 공동주택 제연설비의 차압성능은 만족하더라도, 방연풍속 성능은 거실창문의 개방조건에 따라 방연풍속의 성능이 나오지 않음을 알 수 있었다. 결론: 계단식 공동주택의 경우 화재안전기준에서 요구하는 '방연풍속' 기준에 대해 예외를 두는 방안의 검토가 필요하다.

• 한국운동역학회지
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• 제20권1호
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• pp.49-55
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• 2010

The purpose of the study was to analyze kinetic factors required to the three-point jump shot of the basketball games through 3-D analysis and ground reaction force(GRF) analysis. Six university male players participated in this study. The results of the study were showed that (1) resultant velocity in the center of mass(COM) was $0.84{\pm}0.27\;m/s$ since a player didn't shot a ball in the highest peak and shot ball at the moment of going up forward and vertical movement. Therefore, it is necessary to find a proper timing to shot a ball; (2) the angular velocity was largely increased in upper arm and fore arm out of the upper-limb segments and the hands had the largest angular velocity since the body is in a fixed situation and angular speed is rapidly increased by the wrist' snap with the rapid movement of upper arm and forearm at the time of release a ball; (3) it is judged that a player can shot a ball at the accurate and high release point when the player collects power vertically to the maximum by keeping GRF to the right and the rear in a proper way and by keeping the body's balance so that a large power may not be dispersed.

• 대한기계학회논문집B
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• 제27권11호
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• pp.1637-1644
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• 2003

Stereoscopic particle image velocimetry is a measurement technique to acquire three dimensional velocity field by two cameras. With a laser sheet illumination, the third velocity component can be deduced from out-of$.$plane velocity components using a stereoscopic matching method. Most industrial fluid flows are three dimensional turbulent flows, so it is necessary to use the stereoscopic PIV measurement method. However the existing stereoscopic PIV system seems hard to use since it is very expensive and complex. In this study we have developed a Miniature Stereo-PIV(MSPIV) system based on the concept of the Miniature PIV system which we have already developed. In this paper, we address the design and some primitive experimental results of the Miniature Stereo-PIV system. The Miniature Stereo-PIV system features relatively modest performances, but is considerably smaller, cheaper and easy to handle. The proposed Miniature Stereo-PIV system uses two one-chip-only CMOS cameras with digital output. Only two other chips are needed, one for a buffer memory and one for an interfacing logic that controls the system. Images are transferred to a personal computer (PC) via its standard parallel port. No extra hardware is required (in particular, no frame grabber board is needed).

• 한국연소학회:학술대회논문집
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• 한국연소학회 2001년도 제23회 KOSCO SYMPOSIUM 논문집
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• pp.111-118
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• 2001

Many previous researches on the premixed flame in a tube have treated the unsteady flame behaviors but more detailed and fundamental research has been necessary. The study on the flame stabilization condition in a tube and the unsteady behaviors were carried out in recent years. In this paper, a mean velocity variation larger than the burning velocity was introduced to the stabilized flame for a period longer than the reaction time scale in order to examine the unsteady behavior of flame propagation. Through our previous work it was found that the effects of non-unity Lewis number on the flame extinction was negligible in the extinction by the boundary layer even though they were important in the extinction by the acoustic instability. In this paper we carried out an analytic approach to explain the previous experimental results. It showed that the heat loss, from a flame to the wall, is not a sufficient condition but a required one for the growth of the extinction boundary layer. In addition, the quenching and the flame stretch, under a strong unsteady flow field, are the main causes of the eventual extinction.

• Environmental Sciences Bulletin of The Korean Environmental Sciences Society
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• 제3권2호
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• pp.81-89
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• 1999

This study estimates the correlation dimensions of the land-sea breeze phenomenon, that has a clear diurnal cycle, in order to gain a more detailed understanding of this phenomenon. The data adopted include north-south wind velocity component(v) and temperature(T) time series that were observed at Kimhae Airport and Inje University over a period of 5 days, from the 4th to the 8th of August, 1994. The embedding phase space of the time series were reconstructed from 2 to 14 dimensions, and the correlation dimensions of the attractors were then estimated. The results show that the land-sea breeze phenomenon exhibits a deterministic chaos with non-integer correlation dimension values between 2 and 3. Accordingly, 3 is the minimum number of independent variables required to model the dynamics of the landsea breeze phenomenon in the Kimhae area. Since the saturated embedding dimension, when the correlation dimension remains unchanged, is larger for the wind velocity v-component than for temperature, this indicates that wind velocity is susceptible to topology.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2002년도 학술대회지
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• pp.517-520
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• 2002

Stereoscopic particle image velocimetry is a measurement technique to acquire of three dimensional velocity field by two cameras. With a laser sheet illumination, the third velocity component can be deduced by out-of-plane velocity components using a stereoscopic matching method. Industrial fluid flows are almost three dimensional turbulent flows, so it is necessary to use the stereoscopic PIV measurement method. However the existing stereoscopic PIV system seems hard to use since it is very expensive and complex. In this study we have developed a Stereoscopic Miniature PIV(MPIV) system based on the concept of the Miniature PIV system which we have already developed. In this paper, we address the design and some first experimental results of the stereoscopic PIV system. The Stereoscopic MPIV system features relatively modest performances, but is considerably smaller, cheaper and easy to handle. The proposed Stereoscopic MPIV system uses two one-chip-only CMOS cameras with digital output. Only two other chips are needed, one for a buffer memory and one for an interfacing logic that controls the system. Images are transferred to a personal computer (PC) via its standard parallel port. No extra hardware is required (in particular, no frame grabber board is needed).

• 한국추진공학회:학술대회논문집
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• 한국추진공학회 2007년도 제29회 추계학술대회논문집
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• pp.49-54
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• 2007

오일러나 Navier-Stokes방정식을 통한 터빈 캐스케이드 유동 해석은 비교적 정확한 해를 구할 수 있으나 많은 계산 시간을 필요로 한다. 비점성, 비압축성 유동에 적용이 가능한 패널법은 빠르고 합리적인 유동 정보를 얻을수 있지만 고속 유동의 경우 압축성 보정이 반드시 이뤄져야한다. 본 논문에서는 압축성이 보정된 패널법을 이용하여 터빈 블레이드 표면의 속도 분포를 계산하였다. 그 결과, 압축성이 보정된 패널법의 결과는 실험이나 유한 체적법에 의해 계산된 결과와 잘 일치하였다.

• 대한설비공학회:학술대회논문집
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• 대한설비공학회 2009년도 하계학술발표대회 논문집
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• pp.154-158
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• 2009

The vortex ventilation system (VV) which uses a rotating finned swirler installed coaxially with the exhaust duct is a very effective local ventilator. VV can enhance the capture depth by a factor of 3-5 compared to the conventional exhaust hood, in the absence of any solid walls nearby. In real situations there may exist ceiling, side wall and floor, all of which can affect the flow field and suction performance by way of the no-slip condition on the walls. 3D CFD simulation was performed in order to see the effect of the floor on the capture performance of the VV. The presence of floor reduced suction flow velocity, and increased the critical rotational speed which is the rotational speed required for stable vortex formation. Flow velocity profile along the axis could be well approximated by a universal functional form when the distance from the exhaust inlet is non-dimensionalized by the distance to the floor. Capture depth, define by the distance from the exhaust inlet to a point of velocity decreased to 10% of that at the inlet, is reduced by about 10% when the floor distance is 6 times the exhaust hood diameter.

• 한국가시화정보학회지
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• 제14권2호
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• pp.40-45
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• 2016

Magnetic resonance velocimeter (MRV) is a powerful tool to non-invasively measure the velocity of a fluid flow in various fields ranging from medicine to engineering. However, since the demands for accurate measurement in the solid/liquid interface for cardiovascular diseases and porous media increase, the improvement of spatial resolution is required. In this study, a solenoid RF coil is developed for high spatial resolution measurement. The signal-to-noise ratio in solenoid RF coil is increased seventeen times better than that in commercial coil. Moreover, the velocity distribution of Hagen-Poiseuille flow is measured with in-plane resolution of $36{\mu}m$ by $36{\mu}m$ and the accuracy of the measured velocity is compared with theoretical distribution of the laminar flow. Flow rate calculated by MRV is estimated with the flow rate injected by syringe pump.