• Journal of Power Electronics
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• 제16권3호
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• pp.1110-1121
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• 2016

The mathematical model of a three phase PWM converter under the stationary αβ reference frame is deduced and constructed based on a Proportional-Resonant (PR) regulator, which can replace trigonometric function calculation, Park transformation, real-time detection of a Phase Locked Loop and feed-forward decoupling with the proposed accurate calculation of the inductance voltage vector. To avoid the parallel resonance of the LCL topology, the active damping method of the proportional capacitor-current feedback is employed. As to current vector error elimination, an optimized PR controller of the inner current loop is proposed with the zero-pole matching (ZPM) and cancellation method to configure the regulator. The impacts on system's characteristics and stability margin caused by the PR controller and control parameter variations in the inner-current loop are analyzed, and the correlations among active damping feedback coefficient, sampling and transport delay, and system robustness have been established. An equivalent model of the inner current loop is studied via the pole-zero locus along with the pole placement method and frequency response characteristics. Then, the parameter values of the control system are chosen according to their decisive roles and performance indicators. Finally, simulation and experimental results obtained while adopting the proposed method illustrated its feasibility and effectiveness, and the inner current loop achieved zero static error tracking with a good dynamic response and steady-state performance.

• 한국마이크로전자및패키징학회:학술대회논문집
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• 한국마이크로전자및패키징학회 2002년도 춘계 기술심포지움 논문집
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• pp.193-197
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• 2002

The tribological properties and van der Waals attractive forces and the thermal stability of films are very important characteristics of highly hydrophobic fluorocarbon (FC) films for the long-term reliability of nano system. The effect of thermal annealing on films and van der Waals attractive forces and friction coefficient of films have been investigate d in this study. It was coated Al wafer which was treated O2 and Ar that ocatfluorocyclobutane ($C_4_{8}$) and Ar were supplied to the CVD chamber in the ratio of 2:3 for deposition of FC Films. Static contact angle and dynamic contact angle were used to characterize FC films. Thickness of films was measured by variable angle spectroscopy ellipsometer (VASE). Nanotribological data was got by atomic force microscopy (AFM) to measure roughness, lateral force microscopy (LFM) to measure friction force, and force vs. distance (FD) curve to evaluate adhesion force. FC films were cured in N2 and vacuum. The film showed the slight changes in its properties after 3 hr annealing. FTIR ATR studies showed the decrease of C-F peak intensity in the spectra as the annealing time increased. A significant decrease of film thickness has been observed. The friction force of Al surface was at least thirty times higher than ones with FC films. The adhesive force of bare Al was greater than 100 nN. After deposit FC films adhesive force was decreased to 40 nN. The adhesive force of films was decreased down to 10 nN after 24 hr annealing. During 24 hr annealing in $N_2$and vacuum at $100^{\circ}C$ film properties were not changed so much.

• 한국추진공학회지
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• 제24권1호
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• pp.34-46
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• 2020

직사각형 초음속 노즐의 3차원 역유동 추력벡터 제어 시스템에 대한 공기역학적 특성을 조사하기 위하여 수치해석을 수행하였다. 이 초음속 노즐은 특성곡선법에 의하여 설계되었으며, 그 설계 마하수는 2.5이다. 2차 유동 덕트의 갭 높이를 변수로 하여 역유동 추력벡터 제어 시스템의 성능을 조사하였다. 상부 흡입 칼라의 중심선을 따르는 정압 분포, 편향각, 2차 질량유량비 및 합성 추력계수와 같은 주요 매개변수가 정량적으로 분석되었다. 또한 전체 유동장의 특성을 알아보기 위하여 대칭 평면에서의 유선, 3차원 등마하수분포 및 3차원 난류에너지분포를 조사하였다.

• Wind and Structures
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• 제22권2호
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• pp.211-234
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• 2016

Super long-span bridges provide people with great convenience, but they also bring traffic safety problems caused by strong wind owing to their high decks. In this paper, the large eddy simulation together with dynamic mesh technology in computational fluid dynamics (CFD) is used to explore the mechanism of a moving vehicle's transient aerodynamic force in crosswind, the regularity and mechanism of the vehicle's aerodynamic forces when it passes through a bridge tower's wake zone in crosswind. By comparing the calculated results and those from wind tunnel tests, the reliability of the methods used in the paper is verified on a moving vehicle's aerodynamic forces in a bridge tower's wake region. A vehicle's aerodynamic force coefficient decreases sharply when it enters into the wake region, and reaches its minimum on the leeward of the bridge tower where exists a backflow region. When a vehicle moves on the outermost lane on the windward direction and just passes through the backflow region, it will suffer from negative lateral aerodynamic force and yaw moment in the bridge tower's wake zone. And the vehicle's passing ruins the original vortex structure there, resulting in that the lateral wind on the right side of the bridge tower does not change its direction but directly impact on the vehicle's windward. So when the vehicle leaves from the backflow region, it will suffer stronger aerodynamic than that borne by the vehicle when it just enters into the region. Other cases of vehicle moving on different lane and different directions were also discussed thoroughly. The results show that the vehicle's pneumatic safety performance is evidently better than that of a vehicle on the outermost lane on the windward.

• 폴리머
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• 제33권6호
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• pp.530-536
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• 2009

고리지방족 에폭시와 산무수물 경화제계에 탄소단섬유(SCF)와 유리단섬유(SGF)를 첨가하여 복합재를 제조한 다음 이들의 열적/기계적 특성을 조사하였다. 열기계분석법으로 측정된 열팽창계수(CTE)의 감소 효과를 보면 낮은 단섬유 함량에서는 두 섬유가 거의 비슷하나, 함량이 증가하면 SCF가 SGF에 비해 훨씬 효과적이었다. SCF 강화 복합재에 대한 CTE 실험값을 이론식에 적용해 본 결과 함량이 낮을 때는 혼합법칙(mixture rule)에 잘 맞으며, 함량이 높아지면 Craft-Christensen 식에 근접하였다. 또한, 유리상($30^{\circ}C$과 고무상($180^{\circ}C$)에서의 저장탄성률은 단섬유를 첨가하였을 때 크게 증가하였다. 전자주사현미경(SEM)으로 파단면을 관찰하여본 결과 이와 같은 결과는 단섬유와 에폭시 매트릭스간의 계면접착력과 밀접한 관계가 있음을 알 수 있었다.

• 한국안전학회지
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• 제27권6호
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• pp.78-83
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• 2012

In this study, some experimental results of the peroxide-degradation process of polypropylene(PP) in a co-rotating twin-screw extruder to produce controlled rheology polypropylene(CRPP) are presented. The peroxide was dicumyl peroxide(DCP) and the concentration of DCP was in the range 0-0.3 wt%. It was found that the rheological properties of PP change significantly during reactive extrusion. Melt flow index(MFI) increased with DCP concentration. Intrinsic viscosity decreases with increasing DCP concentration. From dynamic rheological data, number average molecular weight(Mn), weight average molecular weight(Mn) and molecular weight distribution(MWD) were calculated. Results indicated that Mw decreases and MWD becomes narrower with increasing peroxide concentration. Especially, particle size distribution of CRPP decreases with increasing DCP concentration by chemical powdering process, and anti-slip floor paint, CRPP(DCP 0.2 wt%) powder by 10phr was friction coefficient 2.15 ${\mu}$, abrasion resistance 511.18%.

• 한국항해항만학회:학술대회논문집
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• 한국항해항만학회 2006년도 Asia Navigation Conference
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• pp.134-143
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• 2006

Out of all types of motions the critical motions leading to capsize is roll. The dynamic amplification in case of roll motion may be large for ships as roll natural frequency generally falls within the frequency range of wave energy spectrum typical used for estimation of motion spectrum. Roll motion is highly non-linear in nature. Den are various representations of non-linear damping and restoring available in literature. In this paper an uncoupled non-linear roll equations with three representation of damping and cubic restoring term is solved using a perturbation technique. Damping moment representations are linear plus quadratic velocity damping, angle dependant damping and linear plus cubic velocity dependant damping. Numerical value of linear damping coefficient is almost same for all types but non-linear damping is different. Linear and non-linear damping coefficients are obtained form free roll decay tests. External rolling moment is assumed as deterministic with sinusoidal form. Maximum roll amplitude of non-linear roll equation with various representations of damping is calculated using analytical procedure and compared with experimental results, which are obtained form forced tests in regular waves by varying frequency with three wave heights. Experiments indicate influence of non-linearity at resonance frequency. Both experiment and analytical results indicates increase in maximum roll amplitude with wave slope at resonance. Analytical results are compared with experiment results which indicate maximum roll amplitude analytically obtained with angle dependent and cubic velocity damping are equal and difference from experiments with these damping are less compared to non-linear equation with quadratic velocity damping.

• 한국통신학회논문지
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• 제28권7B호
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• pp.628-637
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• 2003

본 논문에서는 VBR로 부호화된 복수 개의 지면 민감 서비스를 고속 망으로 제공하기 위한 새로운 다중화 방식을 제안한다. 본 논문의 주된 목표는 다중화 되는 각 비트 스트림에 부여되는 지연 제한 조건을 유지하고 또한 다중화되어 전송될 때 망 자원의 이용률을 개선하는데 있다. 이와 같은 목표를 위해, 각 비트 스트림에 부여된 지연 조건을 만족시키는 동적인 알고리즘을 제안한다. 제안된 알고리즘은 각 비트 스트림의 상관 관계가 매우 높다고 가정을 하고, 이 가정을 바탕으로 스트림 단위의 시간적 평균화와 동시에 다중화되는 복수 개의 스트림 간에 공간적인 다중화 효과를 이용한다. 본 논문에서 제안된 방식은 모의 실험을 통하여 첨두율과 시변화 계수에 있어서 뛰어난 성능을 보임을 확인할 수 있다.

• 한국항해항만학회지
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• 제26권3호
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• pp.311-316
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• 2002

본 연구에서는 항만하역장비인 스프레더용 충격흡수기의 개발을 위해 스프링과 오일댐퍼로 구성된 세 가지 형태의 모델에 대한 동적응답을 유한요소해석에 의해 수행하였다. 또한, 세 가지 모델의 충격흡수기에서 피스톤의 제한된 행정을 정적변수로 하고 목적함수인 충격에 대한 반력이 최소가 되도록 최적설계를 수행하였다. 본 연구의 결과로는 직렬식 2자유도계 모델의 반력이 가장 작게 나타났으며 그 다음으로는 1자유도계 모델, 병렬식 2자유도계 모델의 순으로 나타났다. 스프링상수와 감쇠계수의 변화가 반력에 미치는 영향을 확인하였으며, 최적설계 결과 각 모델에 대한 반력이 최소가 되는 스프링상수와 감쇠계수를 구하였다.

• 한국수자원학회논문집
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• 제30권5호
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• pp.449-457
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• 1997

본 연구의 목적은 현재 국내 홍수예경보 시스템의 유출량 계산모형으로 이용되고 있는 단일 홍수사상을 모의할 수 있는 유역저류함수모형을 추계통력학적 상태.공간형태의 모형으로 개선.발전시키고 실시간 홍수예보에 대한 모형의 적용성을 검토하는데 있다. 모형의 적용대상 유역은 개진을 유역출구로 하는 낙동강 회천유역(747.5$\textrm{km}^2$)이며, 매개변수의 적절성 및 모형의 적용성을 평가하기 위해서 1983년부터 1986년 사이에 발생한 8개의 단일 홍수사상을 선정하였다. 본 연구에 사용된 모형의 매개변수는 실무에서 사용하고 있는 값을 사용하였다. 그 결과 기존 모형의 적용성은 선택된 사상에 따라 많은 차이를 나타내는데 비해 본 연구에서 개발한 모형에 의한 결과는 모형의 효율성 계수가 0.90이상으로 정확한 값을 제시하였다. 따라서 홍수시 모형과 관측시스템의 오차를 고려할 수 있는 본 연구의 모형은 회천유역의 실시간 홍수예보 모형으로서 유용한 것으로 판단된다.