• 한국정밀공학회지
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• 제27권4호
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• pp.79-86
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• 2010

Mechanical structures with power sources experience repeated force produced by motors. In result, the life of the pipes reduces and ultimately, the pipes collapse. Such pipes are formed into several shapes and particularly, the U-shape pipe is damaged frequently. In most cases, the U-shape pipe is made with a straight pipe by complicated bending work. During this work process, plastic deformation of the pipe produces residual stress in the pipe. This residual stress significantly affects the fracture behavior of the pipe and induces the change of the stress ratio (min. stress/Max. stress = R). For this reason, residual stress has to be evaluated. In this paper, the residual stress of a U-shaped pipe was evaluated by FEM analysis. In addition, fatigue tests of the U-shaped pipe were performed by using a uniaxial fatigue testing machine. The results of the fatigue test were modified with the results of FEM (Finite Element Method) analysis for residual stress. The modified fatigue test results of the U-shaped pipe were compared with those of a straight pipe.

• 한국원자력학회:학술대회논문집
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• 한국원자력학회 1995년도 추계학술발표회논문집(2)
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• pp.623-629
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• 1995

To investigate the effects of powder shape on U loading density of fuel meat, two kinds of fuel meats were prepared with atomized and comminuted U$_3$Si$_2$ powders by extrusion or rolling process. Extruded fuel meats with atomized spherical U$_3$Si$_2$ powder appeared to have much less porosity than those with comminuted irregular U$_3$Si$_2$ powder at higher U$_3$Si$_2$ fraction- The U$_3$Si$_2$ particles with spherical shape are less fractured in extrusion than in rolling. Most of atomized particles on the whole maintained to have spherical shapes in the extrusion. It has been shown that atomized spherical particles are expected to approach similar upper loading limits comparing with comminuted particles in rolled plates, but exceed comminuted powder loading limits in extruded rods.

• 조명전기설비학회논문지
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• 제29권5호
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• pp.41-49
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• 2015

In this paper, we studied an optimal design and efficiency improvement of the BLCD motor used in home electronic appliance. The number of stator slots is chosen depending on the rotor poles, phase number, and the winding configuration. In general, a fractional slots/pole design is preferred to minimize cogging torque. To reduce the winding resistance, we reduced the coil length and we improved the coil space factor. We proposed three types of stator slot shape design for the optimal BLDC motor design. One of them, U-type slot shape is a best optimal design, it proved by the simulated and tested. Optimal design of essential parameters aiming at high winding factor are presented to create for a high-quality system implementation. Design analysis is verified by testing and building a prototype motor.

• Nuclear Engineering and Technology
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• 제35권5호
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• pp.442-453
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• 2003

This study investigates the safety assessment of the potential for fretting-wear damages on steam generator (SG) U-tubes caused by foreign object in operating nuclear power plants. The operating SG shell-side flow field conditions are obtained from three-dimensional SG flow calculation using the ATHOS3 code. Modal analyses are performed for the finite element modelings of U-tubes to get the natural frequency, corresponding mode shape and participation factor. The wear rate of U-tube caused by foreign object is calculated using the Archard formula and the remaining life of the tube is predicted. Also, discussed in this study is the effect of the flow velocity and vibration of the tube on the remaining life of the tube.

• 연구논문집
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• 통권25호
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• pp.207-213
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• 1995

Board bridges are one of the most important structural components of the airport ground equipment. Passenger boarding bridges will be installed to provide enclosed passengers for persons moving between aircraft loading doors and second story terminal gates. In order to the understand of boarding bridge, type and structural components are investigated and analyzed by using the commercial finite element code for model of various loading conditions. As results, the deformed shape and stress distribution of WS-750T and Jetway system type are obtained. It is expected to establish basic technology to design and change the shape of boarding bridge to improve the function.

• 재무관리연구
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• 제26권4호
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• pp.141-163
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• 2009

Using the extensive datasets, I analyze the effect of tick size changes on the intraday patterns of spread and depth. I show that intraday variations in spread (depth) are greater (smaller) with smaller tick size during the early hour of trading and become smaller (larger) during the last hour of trading. And the standardized spreads (depths) are quoted at the lower (higher) levels as the tick size becomes smaller. I also find that U-shaped intraday spread pattern changes to the reverse flat S-shape while inverted U-shaped depth pattern does to the flat S-shape.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2010년도 추계학술대회 논문집
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• pp.819-820
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• 2010

• Current Optics and Photonics
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• 제3권2호
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• pp.143-149
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• 2019

Shape ellipticity dependence of the exciton fine energy levels in CdTe and CdSe nanocrystal quantum dots were compared theoretically by considering the crystal structure and the Coulomb interaction of an electron and a hole. While quantum dot ellipticity changes from an oblate to prolate quantum dot via spherical shape, both the fine energy levels and the dipole moment in wurtzite structure of a CdSe quantum dot change linearly for ellipticity. In contrast, CdTe quantum dots were found to show a level crossing between the bright and dark exciton states with a significant change of the dipole moment due to the cubic structure. Shape ellipticity dependence of the optical nonlinearities in CdTe and CdSe nanocrystal quantum dots was also calculated by using semiconductor Bloch equations. For a spherical shape quantum dot, only $1^L$ dominates the optical nonlinearities in a CdSe quantum dot, but both $1^U$ and $0^U$ contribute in a CdTe quantum dot. As excitation pulse area becomes strong (${\sim}{\pi}$), the optical nonlinearities of both CdSe and CdTe quantum dots are mainly governed by absorption saturation. However, in the case of a prolate CdTe quantum dot, the real part of the nonlinear refractive index becomes relatively significant.

• 대한기계학회논문집A
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• 제28권12호
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• pp.1937-1941
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• 2004

We present lateral actuated piezoelectric actuator using U-shaped PZT strip and lever structure for the RF switch application. In the previous study of RF switch, they used horizontal contact switch fabricated by thin film metals. However, thin film metals could not generate large contact force due to low stiffness. In this work, we suggest lateral contact switch which makes large contact force by increasing stiffness. In addition, we use PZT actuator for the high force actuation. Generally actuator using thin film PZT moves to the vertical direction due to the neutral axis shift. Therefore we need lateral motion generation mechanism based on the thin film PZT actuator. In order to increase lateral motion of thin film PZT actuator, we use U-shaped PZT actuator using residual stress control. Also, thin film PZT actuator can generate very small lateral motion of 120${\times}$10$^{-6}$ ${\mu}{\textrm}{m}$/V for d$_{31}$ mode, thus we suggest lever structure to increase stroke amplification. From the experimental study, fabricated PZT actuator shows maximum lateral displacement of 1 ${\mu}{\textrm}{m}$, and break down voltage of the thin film PZT actuator is above 16V.

• 콘크리트학회논문집
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• 제19권6호
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• pp.677-684
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• 2007

본 연구에서는 유리섬유시트로 휨보강된 RC 보의 파괴 양상을 분석하고, 부착파괴를 방지하기 위한 실험 연구를 수행하였다. 부착파괴를 방지하기 위한 방법으로 부착길이를 증가시키는 방법과 U형 보강 방법 및 에폭시 전단키 보강 상세에 대하여 검증하였다. 유리섬유시트의 부착길이는 콘크리트 계면과 보강재 사이의 부착강도를 가정하여 계산하였다. U형 보강 방법은 콘크리트 밑면에 부착된 유리섬유시트의 단부 혹은 중앙부를 U형으로 감싸서 보강하였다. 콘크리트 하부에 매립된 전단키는 유리섬유시트의 인장력에 대하여 충분한 부착력을 제공하도록 하였다. 단부 U 보강과 중앙부 U 보강은 부착파괴를 방지하기 위해 기존에 제안된 방법이며, 에폭시 전단키는 본 연구에서 제시된 새로운 방지 상세이다. 유리섬유시트의 부착파괴 방지 상세에 대한 효과를 검증하기 위하여 총 6개의 실험체를 제작 실험하였다. 본 실험 결과에 의하면 부착길이 및 단부 U 보강 상세를 적용하는 방법은 조기 부착파괴를 억제하지 못하는 것으로 나타났다. 반면 중앙부 U 보강 상세는 보강재를 따라 발생하는 박리균열의 진행을 억제시키기 때문에 부착파괴를 지연하는 효과가 있으며, 전단키의 경우는 부착파괴를 충분히 방지하며 유리섬유시트의 파단을 유도하는 것으로 나타났다.