• 제목, 요약, 키워드: Super stability

검색결과 130건 처리시간 0.111초

연속 전해드레싱을 적용한 세라믹재의 초정밀 래핑에 관한 연구 (A Study on Ultra-precision Lapping of Ceramics with In-Process Electrolytic Dressing)

  • 이은상
    • 한국생산제조학회지
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    • v.9 no.5
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    • pp.34-39
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    • 2000
  • Application of ceramics has grown considerably due to significant improvement in their mechanical properties such as light weight, chemical stability and superior wear resistance. Despite these character, the use of ceramics has not increased because of poor machinability. The method of using of super-abrasives metal bond wheel was proposed. But it is difficult that super-abrasives metal bond wheel can be dressed. Recently, the technology of in-process electrolytic dressing is developed to solve this problem. If this method is applied, loading and glazing are disappeared apparently. The aim of this study is to determine the machining characteristics in terms of lapping wheel speed, machining time, pressurized weight to the workpiece and peak current using in-process electrolytic dressing applied to the CIB-diamond lapping wheel to achieve ultra-precision lapping machining technique.

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Improved DC Model and Transfer Functions for the Negative Output Elementary Super Lift Luo Converter

  • Wang, Faqiang
    • Journal of Electrical Engineering and Technology
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    • v.12 no.3
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    • pp.1082-1089
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    • 2017
  • Negative output elementary super lift Luo converter (NOESLLC), which has the significant advantages including high-voltage transfer gain, high efficiency, high power density, and reduced output voltage/inductor current ripples when compared to the traditional DC-DC converters, is an attractive DC-DC converter for the field of negative DC voltage applications. In this study, in consideration of the voltage across the energy transferring capacitor changing abruptly at the beginning of each switching cycle, the improved averaged model of the NOESLLC operating in continuous conduction mode (CCM) is established. The improved DC model and transfer functions of the system are derived and analyzed. The current mode control is applied for this NOESLLC. The results from the theoretical calculations, the PSIM simulations and the circuit experiments show that the improved DC model and transfer functions here are more effective than the existed ones of the NOESLLC to describe its real dynamical behaviors.

Cooperative Guidance Law for Multiple Near Space Interceptors with Impact Time Control

  • Guo, Chao;Liang, Xiao-Geng
    • International Journal of Aeronautical and Space Sciences
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    • v.15 no.3
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    • pp.281-292
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    • 2014
  • We propose a novel cooperative guidance law design method based on the finite time disturbance observer (FTDO) for multiple near space interceptors (NSIs) with impact time control. Initially, we construct a cooperative guidance model with head pursuit, and employ the FTDO to estimate the system disturbance caused by target maneuvering. We subsequently separate the cooperative guidance process into two stages, and develop the normal acceleration command based on the super-twisting algorithm (STA) and disturbance estimated value, to ensure the convergence of the relative distance. Then, we also design the acceleration command along the line-of-sight (LOS), based on the nonsingular fast terminal sliding mode (NFTSM) control, to ensure that all the NSIs simultaneously hit the target. Furthermore, we prove the stability of the closed-loop guidance system, based on the Lyapunov theory. Finally, our simulation results of a three-to-one interception scenario show that the proposed cooperative guidance scheme makes all the NSIs hit the target at the same time.

Effect of taper on fundamental aeroelastic behaviors of super-tall buildings

  • Kim, Yong Chul;Tamura, Yukio;Yoon, Sung-Won
    • Wind and Structures
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    • v.20 no.4
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    • pp.527-548
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    • 2015
  • Aeroelastic wind tunnel experiments were conducted for conventional and tapered super-tall building models to investigate the effect of taper on fundamental aeroelastic behaviors in various incident flows. Three incident flows were simulated: a turbulent boundary-layer flow representing urban area; a low-turbulent flow; and a grid-generated flow. Results were summarized focusing on the effect of taper and the effect of incident flows. The suppression of responses by introducing taper was profound in the low-turbulence flow and boundary-layer flow, but in the grid-generated flow, the response becomes larger than that of the square model when the wind is applied normal to the surface. The effects of taper and incident flows were clearly shown on the normalized responses, power spectra, stability diagrams and probability functions.

발산 순압 로스비-하우어비츠 파동의 안정성 (Stability of the Divergent Barotropic Rossby-Haurwitz Wave)

  • 정한별;정형빈
    • 한국지구과학회지
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    • v.37 no.2
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    • pp.107-116
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    • 2016
  • 전구영역 수치모델을 이용하여 순압 로스비-하우어비츠 파동의 안정성을 조사하였다. 본 연구에서 조사한 로스비-하우어비츠 파동은 강체 회전하는 동서 기본류와 유한한 진폭을 가지는 구면조화 파동으로 구성된다. 로스비-하우어비츠 파동은 강체 회전하는 동서 평균류의 강도에 따라 정상 또는 비정상의 구조로 나타난다. 수치 실험을 통해 임의의 다른 두 시간에서 섭동장의 진폭을 비교하여 파동의 안정성뿐만 아니라 성장률을 결정하였다. 로스비-하우어비츠 파동의 불안정 모드는 다양한 동서 파수 성분이 결합된 형태로 나타났다. 파동의 속도가 느린 지역에서 와도 섭동장은 불연속적인 형태를 보이는데, 이는 모델의 수평 해상도와 관계가 없는 것으로 밝혀졌다. 푸리에-유한 요소 모델에서 더 이른 적분 시간에 불안정 모드가 나타났는데, 이는 구면조화 스펙트럴 모델 대비 더 낮은 수치 정확도를 가지기 때문인 것으로 보인다. 모델의 전체적인 정확도를 고려하여, 불안정 모드가 구면 조화 파동을 전체적으로 지배하기 시작하는 시간을 추정하였다.

Research on aerodynamic force and structural response of SLCT under wind-rain two-way coupling environment

  • Ke, Shitang;Yu, Wenlin;Ge, Yaojun
    • Wind and Structures
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    • v.29 no.4
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    • pp.247-270
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    • 2019
  • Wind-resistant design of existing cooling tower structures overlooks the impacts of rainfall. However, rainstorm will influence aerodynamic force on the tower surface directly. Under this circumstance, the structural response of the super-large cooling tower (SLCT) will become more complicated, and then the stability and safety of SLCT will receive significant impact. In this paper, surrounding wind fields of the world highest (210 m) cooling tower in Northwest China underthree typical wind velocities were simulated based on the wind-rain two-way coupling algorithm. Next, wind-rain coupling synchronous iteration calculations were conducted under 9 different wind speed-rainfall intensity combinations by adding the discrete phase model (DPM). On this basis, the influencing laws of different wind speed-rainfall intensity combinations on wind-driving rain, adhesive force of rain drops and rain pressure coefficients were discussed. The acting mechanisms of speed line, turbulence energy strength as well as running speed and trajectory of rain drops on structural surface in the wind-rain coupling field were disclosed. Moreover, the fitting formula of wind-rain coupling equivalent pressure coefficient of the cooling tower was proposed. A systematic contrast analysis on its 3D distribution pattern was carried out. Finally, coupling model of SLCT under different working conditions was constructed by combining the finite element method. Structural response, buckling stability and local stability of SLCT under different wind velocities and wind speed-rainfall intensity combinations were compared and analyzed. Major research conclusions can provide references to determine loads of similar SLCT accurately under extremely complicated working conditions.

안전율이 일정한 초전도 전류도입선의 안정성해석 (Stability Analysis ofn HTS Current Lead with Constant Safety Factor)

  • 설승윤
    • 한국초전도ㆍ저온공학회논문지
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    • v.2 no.2
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    • pp.15-19
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    • 2000
  • The stability of variable cross-sectional area HTS current lead is considered. The cross-sectional area is varied to have a constant safety factor which is defined as the ratio of operating current and critical current of superconductor. As the constant area HTS lead, the variable cross-sectional area HTS lead also has three steady states above the bifurcation point and only one steady state below the bifurcation point. The temperature profiles and current sharing ratios for each steady state are calculated. The heat dissipation into cryogenic system for super-conducting, intermediate, and upper states are compared. For Bi-2333 sheathed with silver-gold alloy 2m length of current lead, and the maximum temperature of upper state seems to be burn-out free below 5m length.

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어성초 추출물이 에멀젼에 미치는 영향에 관한 연구 (Study on the Effects of Houttuynia Cordata Extracts on Emulsions)

  • 박찬익
    • 대한본초학회지
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    • v.25 no.4
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    • pp.145-149
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    • 2010
  • Objectives : Since cosmetics have been one of the help of life, unlike medicine, natural products have been used for cosmetics, generally giving the image of safety and relief compared to synthetic products. Among them, Houttuynia cordata has been known as a useful herbal medicine with antibiotic, anti-inflammatory and anti-oxidative activities. In this study, we were to use Houttuynia cordata extract on formulation of cosmetic emulsions. Methods : The effects of Houttuynia cordata extract on emulsion stability and viscoelastic properties of emulsion were measured using turbiscan and rheometer. And we assessed the anti-oxidative and antibiotic activities of Houttuynia cordata extract. Results : 1. The results of this investigation for emulsion stability showed that the stability emulsion containing Houttuynia cordata extract was decreased depending on concentration of Houttuynia cordata extract. 2. Super oxide dismutase activity was strongly dependents on concentration of Houttuynia cordata extract. 3. Houttuynia cordata extract showed good anti-microbial activity against Staphylococcus aureus. Conclusions : Houttuynia cordata extract can be effectively used in cosmetic emulsions when the relation between natural product extracts and formulation of cosmetics is elucidated.

가스분사 분말로부터 고온 압출된 Al-Ni-Mm-(Cu, Fe)합금들의 미세구조 및 기계적 성질 (Microstructure and Mechanical Properties of Al-Ni-Mm-(Cu, Fe) Alloys Hot-Extruded from Gas-Atomized Powders)

  • 김혜성
    • 한국재료학회지
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    • v.16 no.2
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    • pp.137-143
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    • 2006
  • The effects of Cu and Fe additions on the thermal stability, microstructure and mechanical properties of $Al_{85}-Ni_{8.5}-Mm_{6.5},\;Al_{84}-Ni_{8.5}-Mm_{6.5}Cu_1,\;Al_{84}-Ni_{8.5}-M_{m6.5}Fe_1$ alloys, manufactured by gas atomization, degassing and hot-extrusion were investigated. Gas atomization, with a wide super-cooled liquid region, allowed the alloy powders to exhibit varying microstructure depending primarily on the powder size and composition. Al hotextruded alloys consisted of homogeneously-distributed fine-grained fcc-Al matrix and intermetallic compounds. A substitution of 1 at.% Al by Cu increased the thermal stability of the amorphous phase and produced alloy microstructure with smaller fcc-Al grains. On the other hand, the same substitution of 1 at.% Al by Fe decreased the stability of the amorphous phase and produced larger fcc-Al grains. The formation of intermetallic compounds such as $Al_3Ni,\;Al_{11}Ce_3\;and\;Al_{11}La_3$ was suppressed by the addition of Cu or Fe. Among the three alloys examined, the highest Vickers hardness and compressive strength were obtained for $Al_{84}-Ni_{8.5}-M_{m6.5}Cu_1$ alloy, and related to the finest fcc-Al grain size attained from increased thermal stability with Cu addition.

고밀도 스킵 연결을 통한 재귀 잔차 구조를 이용한 단일 이미지 초해상도 기법 (Single Image Super-resolution using Recursive Residual Architecture Via Dense Skip Connections)

  • 진건;정제창
    • 방송공학회논문지
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    • v.24 no.4
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    • pp.633-642
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    • 2019
  • 최근, 단일 이미지 초해상도 복원 기법(super-resolution)에서 컨볼루션 신경망 모델은 매우 성공적이다. 잔여 학습 기법은 컨볼루션 신경망 훈련의 안전성과 성능을 향상시킬 수 있다. 본 논문은 저해상도 입력 이미지에서 고해상도 목표 이미지로 비선형 매핑 학습을 위해 고밀도 스킵 연결(dense skip-connection)을 통한 재귀 잔차 구조를 이용한 단일 이미지 초해상도 복원 기법을 제안한다. 제안하는 단일 이미지 초해상도 복원 기법은 고밀도 스킵 연결 방식을 통해 재귀 잔차 학습 방법을 채택해서 깊은 신경망에서 학습이 어려운 문제를 완화하고 더 쉽게 최적화하기 위해 신경망 안에 불필요한 레이어를 제거한다. 제안하는 방법은 매우 깊은 신경망의 사라지는 변화도(vanishing gradient) 문제를 완화할 뿐만 아니고 낮은 복잡성으로 뛰어난 성능을 얻음으로써 단일 이미지 초해상도 복원 기법의 성능을 향상시킨다. 실험 결과를 통해 제안하는 알고리듬이 기존의 알고리듬 보다 결과가 더 우수함을 보인다.