• 한국세라믹학회지
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• 제20권4호
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• pp.315-323
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• 1983

Effect of NiO and $MnO_2$ addtivies on the dielectric piezoelectrics and polarization-reversal properties of $(Pb_{0.936} La_{0.064})$$(Zr_{0.60}Ti_{0.40})O_3$ ceramics have been investigated. The specimens were prepared by the mixed oxide techni-que and atmosphere sintering method. The room temperature X-ray diffraction studies show that perfect perovskite solution with tetragonal structure was obtained from PLZT and its additives. The dielectric constant and dissipation factor decreased with the addition of both NiO and $MnO_2$ The Curie of Curie temperature was not observed but they displayed broadened maxima. The planar coupling factor was improved by addition of NiO and also increased with increasing sintering time carried out at 105$0^{\circ}C$ Addition of $MnO_2$ yielded a markedly high mechanical quality factor. The space-charge field decreased with the addition of NiO but increased with the addition of $MnO_2$ The planar coupling factor and space-charge field showed same dependence on the additivies. The tetragonality Curie temperature and planar coupling factor of $(Pb_{0.936} La_{0.064})$$(Zr_{0.60}Ti_{0.40})O_3$ were higher than those of $(Pb_{0.936} La_{0.064})$$(Zr_{0.568}NU_{0.032}Ti_{0.40})_{0.984}O_3$ but the grain size lattic parameter dielectric constant dissipation factor mechanical quality factor and space-charge field of the former were lower than those of the latter.

• 한국항행학회논문지
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• 제24권4호
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• pp.261-266
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• 2020

항공기 장착물에 KW급 전력변환장치가 탑재되는 경우, 전력 변환 시 발생하는 대량의 발열에 대한 방열설계가 고려되어야 한다. 적절한 방열을 하지 못하는 경우, 장비 오작동 및 화재의 우려가 발생하며 이는 항공기 운항에 있어 치명적인 요인이 될 수 있다. 본 논문은 항공기 장착물에 탑재되는 KW급 전력변환장치의 방열설계에 관하여 기술하였다. 전산해석을 통한 설계 및 제작 후 시험을 수행하였으며, 고전력 변환에 따른 발열부품의 급격한 발열 현상을 확인하여 해석 모델을 보정하였다. 모델 보정 후 방열구조가 개선된 형상으로 설계를 개선하였으며, 미 군사규격인 MIL-STD-810G 의 고온동작 시험을 수행하여 개선된 형상의 타당성을 검증하였다.

• 한국추진공학회지
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• 제11권3호
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• pp.35-42
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• 2007

로켓 엔진의 음향 불안정을 제어하기 위해 모형 연소실에 배플형 분사기가 장착된 경우의 음향 감쇠 특성을 수치해석적으로 조사하였다. 기존에 보고된 배플형 분사기의 효용성을 확인하였고 분사기간 간극이 존재할 때 음향 감쇠 효과가 증대되는 메커니즘을 규명하였다. 여러 가지 크기의 간극에 따라 음향학적 감쇠능력을 조사하였고, 본 연소실에서는 0.1 mm 정도의 간극에서 최적의 감쇠능력을 가짐을 알 수 있었다. 음향 감쇠 효과가 증대되는 메커니즘을 규명하기 위해, 분사기 사이의 간극에 따른 에너지 소산율과 와도를 계산하였고, 소산율 변화 추이와 감쇠인자 변화 추이가 유사함을 알았다. 이를 통해, 간극에 의한 에너지 소산의 종대로 음향 감쇠 효과가 증가함을 알았다.

• Structural Engineering and Mechanics
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• 제13권4호
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• pp.369-385
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• 2002

Ductility capacity is comprehensively studied for steel moment-resisting frames. Local, story and global ductility are being considered. An appropriate measure of global ductility is suggested. A time domain nonlinear seismic response algorithm is used to evaluate several definitions of ductility. It is observed that for one-story structures, resembling a single degree of freedom (SDOF) system, all definitions of global ductility seem to give reasonable values. However, for complex structures it may give unreasonable values. It indicates that using SDOF systems to estimate the ductility capacity may be a very crude approximation. For multi degree of freedom (MDOF) systems some definitions may not be appropriate, even though they are used in the profession. Results also indicate that the structural global ductility of 4, commonly used for moment-resisting steel frames, cannot be justified based on this study. The ductility of MDOF structural systems and the corresponding equivalent SDOF systems is studied. The global ductility values are very different for the two representations. The ductility reduction factor $F_{\mu}$ is also estimated. For a given frame, the values of the $F_{\mu}$ parameter significantly vary from one earthquake to another, even though the maximum deformation in terms of the interstory displacement is roughly the same for all earthquakes. This is because the $F_{\mu}$ values depend on the amount of dissipated energy, which in turn depends on the plastic mechanism, formed in the frames as well as on the loading, unloading and reloading process at plastic hinges. Based on the results of this study, the Newmark and Hall procedure to relate the ductility reduction factor and the ductility parameter cannot be justified. The reason for this is that SDOF systems were used to model real frames in these studies. Higher mode effects were neglected and energy dissipation was not explicitly considered. In addition, it is not possible to observe the formation of a collapse mechanism in the equivalent SDOF systems. Therefore, the ductility parameter and the force reduction factor should be estimated by using the MDOF representation.

• 한국지진공학회논문집
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• 제18권3호
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• pp.133-140
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• 2014

The friction damper can be used for improving the seismic resistance of existing buildings. The damper is often installed in bracing members. The energy dissipation capacity of the damping systems depends on the type of the structure, the configuration of the bracing members, and the property of dampers. In Korea, there are numerous low- to mid-rise reinforced concrete moment frames that were constructed considering only gravity loads. Those frames may be vulnerable for future earthquakes. To resolve the problem, this study developed a toggle bracing system with a high density friction damper. To investigate the improvement of reinforced concrete frames after retrofit using the developed damped system, experimental tests were conducted on frame specimens with and without the damped system. The results showed that the maximum strength, initial stiffness and energy dissipation capacity of the framed with the damped system were much larger than those of the frame without the damped system.

• Earthquakes and Structures
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• 제18권2호
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• pp.185-199
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• 2020

A computationally-efficient method for multi-criteria optimisation is developed for performance-based seismic design of friction energy dissipation dampers in RC structures. The proposed method is based on the concept of Uniform Distribution of Deformation (UDD), where the slip-load distribution along the height of the structure is gradually modified to satisfy multiple performance targets while minimising the additional loads imposed on existing structural elements and foundation. The efficiency of the method is demonstrated through optimisation of 3, 5, 10, 15 and 20-storey RC frames with friction wall dampers subjected to design representative earthquakes using single and multi-criteria optimisation scenarios. The optimum design solutions are obtained in only a few steps, while they are shown to be independent of the selected initial slip loads and convergence factor. Optimum frames satisfy all predefined design targets and exhibit up to 48% lower imposed loads compared to designs using a previously proposed slip-load distribution. It is also shown that dampers designed with optimum slip load patterns based on a set of spectrum-compatible synthetic earthquakes, on average, provide acceptable design solutions under multiple natural seismic excitations representing the design spectrum.

• 한국정보통신학회논문지
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• 제12권8호
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• pp.1511-1518
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• 2008

무선 센서 네트워크는 소형의 무선 센서노드들로 구성된 네트워크이다. 무선으로 구성된 센서 네트워크는 사물과 환경의 변화를 감지하여 싱크로 전송한다. 무선 센서 네트워크에서 센서 노드는 무선으로 데이터를 전송할 때 가장 많은 에너지를 소모한다. 한정된 에너지 자원을 효율적으로 사용하기 위해서는 데이터 전송에 이용하는 라디오모듈의 사용을 최소화하여 네트워크 전체의 데이터 전송량을 감소시켜야 한다. 본 논문에서 제안하는 NRMC는 에너지 소모를 줄이기 위해 DPCM, 웨이블릿, 양자화, 가변 길이 부호화를 사용하여 전송되는 데이터의 양을 줄여 라디오모듈을 통한 데이터 전송 횟수를 줄였고, 결과적으로 센서네트워크의 트래픽을 감소시켜 에너지 소모를 줄였다.

• 한국세라믹학회지
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• 제41권8호
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• pp.605-609
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• 2004

다양한 금속산화물(NiO, MgO, Cr$_2$O$_3$) 첨가에 따른 ZnO 바리스터의 미세구조, 전기적, 유전적 특성을 조사하였다. 평균 결정립 크기는 NiO 첨가로 증가한 반면 Cr$_2$O$_3$ 첨가로 감소하였다 이로 인해 바리스터 전압은Cr$_2$O$_3$ 첨가시 더 높게 나타났다. 바리스터 가운데서 Cr$_2$O$_3$가 첨가된 바리스터가 비직선 지수가 40.5, 누설전류가 2.7 $\mu$A로 가장 우수한 비직선성을 나타내었으며, 유전손실도 0.0589로 비교적 낮게 나타났다.

• 전기학회논문지
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• 제58권4호
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• pp.788-794
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• 2009

To assess the condition of stator insulation, nondestructive tests were performed on twenty five coil groups and twenty six motors. The stator windings has nominal ratings of 6.6kV and are classified into five coil groups ;one group with healthy insulation and four groups with four different types of artificial defects. After completing nondestructive tests, the AC voltage applied to the stator windings was gradually increasing until insulation failure in order to obtain the breakdown voltage. No.1, No.2 and No.6 of 6.6kV motors failed near rated voltage of 14kV, 8.7kV and 14kV, respectively. The breakdown voltage of three motors was lower that expected for good quality coils(14.2kV) in 6.6kV motors. No.3 and No.6 of 4.16kV motors failed near rated voltage of 5.6kV and 4.2kV, respectively. Almost all of failures were located in a line-end coil at the exit from the core slot. The breakdown voltages and the types of defects showed strong relation to the stator insulation tests such as in the case of AC current, dissipation factor(tan${\delta}$) and partial discharge magnitude.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 1993년도 추계학술대회 논문집
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• pp.80-84
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• 1993

In this research, we studied the variation of the dielectric loss absorption of the dielectric loss absorption of the sample according with the change to $\^$60/Co-${\gamma}$-ray irradiation dose of the influence of temperature and applied voltage. In order to investigate the effect of irradiation oriented polypropylene film, we have observed dissipation factor within the temperature range of 30∼130 [$^{\circ}C$] and voltage range of 100∼250$^{\circ}C$ [V]. As for the dependency of temperature by dissipation factor, the ${\alpha}$-peak which appears at high temperature increases accordingly to the increasement of irradiation dose which is contributed by the crystal region and moves towards the high temperature. The ${\beta}$-peak which appears at low temperature is origined from dipoles and molecular motions in the amorphous region. As for the dependency of voltage by tan$\delta$, at low temperature the peak of the tan$\delta$, at low temperature the peak of the tan$\delta$ shifts accordingly to the increasement of irradiation dose towards the high temperature region.