• Journal of Welding and Joining
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• 제14권6호
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• pp.37-47
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• 1996

An ultrasonic testing uses the directivity of the ultrasonic wave which propagates in one direction. The directivity is expressed as the relationship between the propagate direction and its sound pressure. The directivity of ultrasonic wave is related to determination of testing sensitivity, scanning pitch and defect location. This paper investigated the directivity of ultrasonic wave, which scattered from slit defect located in heat-affected zone (HAZ) in butt joint using visualization method. The directivity of shear waves scattered from slit defect were different according to probe direction (far defect, near defect) and probe position (forward movement, maximum echo position, backward movement). The difference of directivity of reflection wave was existed between 2 MHz and 4 MHz angle probes. In the case of 2 MHz angle probe, the directivity of reflection wave was appeared sharp form because of the relation wave length and defect size.

• 한국공작기계학회:학술대회논문집
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• 한국공작기계학회 2001년도 추계학술대회(한국공작기계학회)
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• pp.91-96
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• 2001

When it is considered that many vehicle rides on the road and ride quality is an important method to evaluate vehicle performance with handling, running-over-bump manoeuvre may be suitable for testing ride quality. In this paper, a computed model has roughly steering system and lumped mass, connected by joint each rigid body, and suspension that has beam elements and has shock absorber as force element to represent nonlinear characteristics. A computer simulations for passing over a bump were made with two velocities. One side of vehicle passed over bump in due consideration of driver's habit that driver is subject to avoid a bad ride quality. On simulation, vertical acceleration, pitch angle and roll angle were measured at the mass center of chassis each case.

• 한국광학회:학술대회논문집
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• 한국광학회 2009년도 창립 20주년기념 특별학술발표회
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• pp.331-332
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• 2009

We present an analysis on the quality factors of the Fourier hologram generated from multiple orthographic view images of three-dimensional object. In the analysis, we analyze both the maximum size of the reconstructed object and its spatial resolution. For the maximum size of the reconstruction, we found that the main factor is the orthographic projection angle interval. Too large projection angle interval causes overlapping in the reconstruction space domain. For the spatial resolution, there are three factors, i.e. the capturing lens array pitch which determines the spatial sampling rate of the original three-dimensional objects, the maximum orthographic projection angle, and the spatial frequency bandwidth of the object. The dominant factor is determined by the relationship between those three factors.

• 한국윤활학회:학술대회논문집
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• 한국윤활학회 2003년도 학술대회지
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• pp.348-354
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• 2003

An analysis of the dynamic behavior between disk and roller has been performed when the torque is transmitted to toroidal IVT (Infinitely Variable Transmission). The contact area, shape and pressure with elliptical shapes between disk and roller are computed as the transmission ratios are changed. This study will give the information of contact shapes between roller-input dist and roller-output disk which are working under the most severe condition. The computed results are expected to guide the design criteria for the enhanced endurance li(e. Furthermore, the investigation of contact behaviors is very crucial to develop the traction oil that the efficiency of IVT system is most dependent on.

• 한국정보디스플레이학회:학술대회논문집
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• 한국정보디스플레이학회 2000년도 제1회 학술대회 논문집
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• pp.161-162
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• 2000

We propose multi-layer aspheric lenticular lens for rear projection screen to provide wide viewing angle. Each pitch of lenticular lens sheet is divided by three region and image light from projection optical system is propagated widely on each region due to different focal point. Besides, to improve vertical viewing angle of screen, we propose glass bead embedded screen on observer side of lenticular lens.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2008년도 추계학술대회B
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• pp.2574-2577
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• 2008

The screw-feeders are used at gathering the minerals at the seafloor, transportation of the sewage, and at the beverage industry. This study was carried out to study solid-liquid mixture hydraulic transport of solid particles in a horizontal and inclined screw-feeders with rotating. This study is about the amount of the alteration amount of the material transportation for regular transportation. In this study a clear acrylic pipe was used in order to observe the movement of solid particles. Relates to the angle, rpm and ratio of pitch ; finding the optimum condition and knowing about designing the screw feeders shape. As a result, we found the suitable rpm and a suitable angle. According to the experiment, the best rpm and angle are 100-200rpm and $10^{\circ}$, respectively.

• 한국신재생에너지학회:학술대회논문집
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• 한국신재생에너지학회 2006년도 춘계학술대회
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• pp.495-498
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• 2006

The Kaplan turbine model has been tested and analyzed. The blade angle and the guide vane opening of the turbine model were designed to be varied according to the best combination of guide vane and runner blade opening. When the changes in head and output were comparatively large, the efficiency drop were small, so the efficiency characteristics and stability of the entire operating condition were maintained in good condition. These results showed that the developed model in this study will be suitable for small hydropower stations with large changes In head and load such as agricultural reservoir.

• 설비공학논문집
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• 제17권11호
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• pp.1014-1021
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• 2005

Flow channels with non-circular cross-sections are encountered in a wide variety of heat exchangers. Accurate friction factor and Colburn j factor data are essential for the design and viable applications of such heat exchangers. In this study, an analysis is con ducted on heat transfer and pressure drop characteristics for tube-bundle heat exchanger with various arrangements of tubes, of which their geometry could easily be modified from a circular one in a harsh environment. The parameters investigated are aspect ratio, pitch, and inclined angle of tubes. The results obtained are: (1) Aspect ratio has larger influence on the j and f factor than pitch; (2) As aspect ratio increases, both j and f factors decrease; (3) The high performance is achieved when the pitch and aspect ratio are in the range of 1.5${\~}$2.5 and 1.25${\~}$2.0, respectively; and (4) the inclined arrangements of tubes show unfavorable results for both heat transfer and pressure drop characteristics in spite of the positive possibility of condensate removals in a latent heat recovery system.

• Bulletin of the Korean Chemical Society
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• 제30권9호
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• pp.1967-1972
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• 2009

The electrospinnability of pitch was improved by blending in a solution of polyacrylonitrile (PAN) resulting in the reduction of the average fiber diameter from 2000 to 750 nm. Activated carbon fibers (ACFs) derived by stabilization, carbonization and steam activation at 700, 800, and 900 ${^{\circ}C}$ of the PAN/pitch electrospun fibers for 60 min were investigated as electrodes for supercapacitors. The Brunauer, Emmett, Teller (BET) specific surface area ranged from 732 to 1877 $m^2g^{-1}$ and the specific capacitance from 75.5 to 143.5 $Fg^{-1}$, depending on the activation conditions. Electrodes from the electrospun web activated at 900 ${^{\circ}C}$ exhibited a particularly quick response showing a high frequency of 5.5 Hz at a phase angle of ‒$45^o$ of the impedance spectroscopy.

• 한국전자통신학회논문지
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• 제10권8호
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• pp.935-944
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• 2015

본 논문에서는 가변속 풍력발전시스템의 동적 모델링과 운전제어 시뮬레이션을 수행하였다. 풍속모델, 풍력터빈과 PMSG 모델, MPPT 및 피치 운전제어 모델 등을 구현하였다. 그리고 상용화된 5MW급 풍력터빈 데이터들을 참고하여 실제적인 시스템과 유사한 출력계수 및 가상 운전 조건으로 시뮬레이션 하였다. 시뮬레이션 결과 정격속도 12[m/s]까지 최대출력계수를 유지하면서 최대전력추종을 확인하였다. 또한 12[m/s]이상의 고속 풍속에서는 동적으로 피치 각도를 제어하면서, 정격상태의 안정적인 출력을 유지하였다.