• 한국전자파학회논문지
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• 제14권10호
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• pp.1004-1010
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• 2003

본 논문에서는 유한한 도체 두께를 갖는 결합선로를 이용하여 1/4파장 역방향 방향성 결합기를 설계하였다. 방향성 결합기를 구성하는 유한 도체 두께를 갖는 결합선로를 해석하기 위한 방법으로 간단하고 빠른 수치해석 방법인 모드정합법을 사용하였다. 본 논문의 해석 결과는 도체 두께를 고려한 역방향 방향성 결합기의 설계가, 도체 두께를 고려하지 않고 설계한 경우 기존에 알려졌던 단점들인 약한 결합특성, 낮은 지향성, 그리고 비현실적인 결합선로의 폭을 극복할 수 있음을 보여준다. 또한, 수치해석 결과로부터 l/4파장 역방향 방향성 결합기에서는 도체 두께의 고려로 강한 결합특성을 만드는 것이 가능하지만, 결합길이가 약간 길어진다는 사실을 확인하였다. 본 논문에서 해석한 유한한 도체 두께는 역방향 방향성 결합기의 새로운 설계 변수로서 사용이 가능하며, 아울러 다양한 마이크로파 집적회로의 설계에도 응용이 가능함을 보여준다.

• Bulletin of the Korean Chemical Society
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• 제30권11호
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• pp.2595-2602
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• 2009

Hexamer cluster of N,N-dimethylformamide(DMF) based on the crystal structure was investigated for the equilibrium structure, the stabilization energies, and the vibrational properties in the density functional force field. The geometry (point group $C_i$) of fully optimized hexamer clustered DMF shows quite close similarity to the crystal structure weakly intermolecular hydrogen bonded each other. Stretching force constants for intermolecular hydrogen bonded methyl and formyl hydrogen atoms with nearby oxygen atom, methyl C–H${\cdots}$O and formyl C–H${\cdots}$O, were obtained in 0.055 $\sim$ 0.11 and $\sim$ 0.081 mdyn/$\AA$, respectively. In-plane bending force constants for hydrogen bonded methyl hydrogen atoms were in 0.25 $\sim$ 0.33, and for formyl hydrogen $\sim$ 0.55 mdynÅ. Torsion force constants through hydrogen bonding for methyl hydrogen atoms were in 0.038 $\sim$ 0.089, and for formyl hydrogen atom $\sim$ 0.095 mdynÅ. Calculated Raman and infrared spectral features of single and hexamer cluster represent well the experimental spectra of DMF obtained in the liquid state. Noncoincidence between IR and Raman frequency positions of stretching C=O, formyl C–H and other several modes was interpreted in terms of the intermolecular vibrational coupling in the condensed phase.

• International Journal of Naval Architecture and Ocean Engineering
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• 제10권3호
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• pp.329-347
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• 2018

The Smoothed Particle Hydrodynamics (SPH) method has proved to have great potentials in dealing with the wave-structure interactions. Compared with the Weakly Compressible SPH (WCSPH) method, the ISPH approach solves the pressure by using the pressure Poisson equation rather than the equation of state. This could provide a more stable and accurate pressure field that is important in the study of wave-structure interactions. This paper improves the solid boundary treatment of ISPH by using a high accuracy Simplified Finite Difference Interpolation (SFDI) scheme for the 2D wave-structure coupling problems, especially for free-moving structure. The proposed method is referred as the ISPH_BS. The model improvement is demonstrated by the documented benchmark tests and laboratory experiment covering various wave-structure interaction applications.

• International Journal of Naval Architecture and Ocean Engineering
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• 제3권1호
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• pp.37-52
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• 2011

The present paper introduced a computer program, called WISH, which is based on a time-domain Rankine panel method. The WISH has been developed for practical use to predict the linear and nonlinear ship motion and structural loads in waves. The WISH adopts three different levels of seakeeping analysis: linear, weakly-nonlinear and weak-scatterer approaches. Later, WISH-FLEX has been developed to consider hydroelasticity effects on hull-girder structure. This program can solve the springing and whipping problems by coupling between the hydrodynamic and structural problems. More recently this development has been continued to more diverse problems, including the motion responses of multiple adjacent bodies, the effects of seakeeping in ship maneuvering, and the floating-body motion in finite-depth domain with varying bathymetry. This paper introduces a brief theoretical and numerical background of the WISH package, and some validation results. Also several applications to real ships and offshore structures are shown.

• Journal of Magnetics
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• 제6권4호
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• pp.132-141
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• 2001

The switching characteristics and the magnetization-flop behavior in magnetic tunnel junctions exchange biased by synthetic antiferromagnets (SyAFs) are investigated by using a computer simulations based on a single-domain multilayer model. The bias field acting on the free layer is found to be sensitive to the thickness of neighboring layers, and the thickness dependence of the bias field is greater at smaller cell dimensions due to larger magnetostatic interactions. The resistance to magnetization flop increases with decreasing cell size due to increased shape anisotropy. When the cell dimensions are small and the synthetic antiferromagnet is weakly, or not pinned, the magnetization directions of the two layers sandwiching the insulating layer are aligned antiparallel due to a strong magnetostatic interaction, resulting in an abnormal magneto resistance (MR) change from the high-MR state to zero, irrespective of the direction of the free-layer switching. The threshold field for magnetization-flop is found to increase linearly with increasing antiferromagnetic exchange coupling in the synthetic antiferromagnet. Irrespective of the magnetic parameters and cell sizes, magnetization flop does not exist near zero applied field, indicating that magnetization flop is driven by the Zeeman energy.

• 대한조선학회논문집
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• 제48권6호
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• pp.560-568
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• 2011

In SPH(Smoothed Particle Hydrodynamics) method, the fluid has been assumed that it is weakly compressible to solve the basic equations composed of Navier-Stokes equations and continuity equation. That leads to some drawbacks such as non-physical pressure fluctuations and a restriction as like small time steps in computation. In this study, to improve these problems we assume that the fluid is incompressible and the velocity-pressure coupling problem is solved by a projection method(that is, by ISPH method). The two-dimensional computation results of dam breaking and gravitational wave generation are respectively compared with the results of finite volume method and analytical method to confirm the accuracy of the present numerical computation technique. And, the agreements are comparatively acceptable. Subsequently, the green water simulations of a two-dimensional fixed barge are carried out to inspect the possibility of practical application to ship hydrodynamics, those correspond to one of the violent free surface motions with impact loads. The agreement between the experimental data and the present computational results is also comparatively good.

• 전자공학회논문지
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• 제52권7호
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• pp.135-142
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• 2015

인체 구동 방식의 자가 발전기는 외부 환경에 덜 의존한다는 장점 덕분에 비상용 혹은 야외 활동 중의 소규모 전력 공급원으로 주목 받고 있다. 하지만 대부분의 자가 발전기는 전자기 유도 결합의 효율이 높지 않아 출력이 미미하며, 특정 부위의 근육만을 지속적으로 사용하는 단조로운 구동 방식을 택하고 있어, 사용 중에 쉽게 지루해질 뿐만 아니라 근피로가 쉽게 누적되어 실제 원하는 출력을 얻을 만큼 충분한 시간 동안 구동하는 것이 거의 불가능하다. 이러한 낮은 효율과 사용성의 문제로 인해 인체 구동 방식의 자가발전기가 실생활에서 사용되는 빈도는 높지 않다. 본 연구에서는 전자기 유도 효율이 높은 종축 결합 방식의 발전 장치를 간단한 구조로 구현하여 출력을 높이는 동시에, 자성체의 운동 관성에 의한 가속이 가능한 인체 구동 방식의 발전기를 설계 제작하였다. 개발된 발전기와 기존 상용 자가 발전기와의 비교 실험을 통해 높은 출력 뿐 아니라 장시간 구동이 가능함을 검증하였다. 아울러 인체 구동 발전기에서 실질적으로 중요한 요소임에도 불구하고 기존 연구에서 제시된 바 없는 인체의 투입 에너지를 실증적으로 파악하기 위해 호흡 가스 기반의 실제 운동 대사량 측정법에 근거한 실험을 시행하여 자가 발전기의 운동 부하를 추정하였다. 향후 성능 개선과 휴대성 증진을 통해 모바일 기기의 전력 지속 문제를 해결하는 데 기여할 수 있을 것으로 기대한다.

• 대한기계학회논문집B
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• 제25권10호
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• pp.1327-1336
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• 2001

The structural modes driven by the low wave-number components of smooth elastic wall pressure provide a relatively weak coupling between the flow and the wall motion. If the elastic thin plate has any resonant mode whose wave-number of resonance coincides with $\omega$/U$\sub$c/, the power will be transmitted to those modes of vibration by the flows. We examine the problem in which the elastic thin plate is subject to pressure fluctuations under turbulent boundary layer. Measurements are presented of the frequency spectra of the near- and far-field pressures and radiated sound contributed by the various wave modes of the thin elastic plate. Dispersion equation for wave motions of elastic plate is used to investigate the effect of bending waves of relatively low wave number on radiated sound. The low wave-number motion of elastic plate is observed to have much less influence on the low-frequency energy of wall pressure fluctuations than that of the rediated sound. High amplitude events of the wall pressure are observed to weakly couple with high-frequency energy of radiated sound for case of low tension applied to the plate. The sound source localization is applied to the measurement of radiated sound by using acoustic mirror system.

• Steel and Composite Structures
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• 제52권2호
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• pp.237-248
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• 2024

In order to make the dynamic analysis and design of improved composite beam with corrugated steel web (CBGSCC) bridge more efficient and economical, the parametric self-cyclic analysis model (SCAM) was written in Python on Anaconda platform. The SCAM can call ABAQUS finite element software to realize automatic modeling and dynamic analysis. For the CBGSCC bridge, parameters were set according to the general value range of CBGSCC bridge parameters in actual engineering, the SCAM was used to calculate the large sample model generated by parameter coupling, the optimal value range of each parameter was determined, and the sensitivity of the parameters was analyzed. The number of diaphragms effects weakly on the dynamic characteristics. The deck thickness has the greatest influence on frequency, which decreases as the deck thickness increases, and the deck thickness should be 20-25 cm. The vibration frequency increases with the increase of the bottom plate thickness, the web thickness, and the web height, the bottom plate thickness should be 17-23mm, the web thickness should be 13-17 mm, and the web height should be 1.65-1.7 5 m. Web inclination and Skew Angle should not exceed 30°, and the number of diaphragms should be 3-5 pieces. This method can be used as a new method for structural dynamic analysis, and the importance degree and optimal value range of each parameter of CBGSCC bridge can be used as a reference in the design process.

• 대한전자공학회논문지TC
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• 제44권7호통권361호
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• pp.105-111
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• 2007

본 논문에서는 W-band($75{\sim}110\;GHz$) 주파수 영역에서 동작하는 CPW(Coplanar Waveguide) 구조의 3-dB 방향성 커플러를 MIMIC(Millimeter-wane Monolithic Integrated Circuit) 공정기술로 설계 및 제작하였다. 강한 결합계수 특성을 갖는 edge-coupled CPW 라인은 서로 다른 우 기 모드 위상속도에 의해 좋지 않은 방향성을 갖는다. 이를 극복하기 위하여 같은 우 기 위상속도를 갖는 edge-coupled CPW 라인을 2단으로 평행하게 연결하여 3-dB의 강한 커플링을 유도할 수 있는 Tandem 구조를 W-band에서 제안하였다. 제안된 Tandem 커플러는 기존의 다층기판 구조나 와이어 본딩 구조가 아닌 에어브리지 MIMIC 공정기술을 통해서 단일평면상에 제작되었다. 제작된 커플러는 $75{\sim}100\;GHz$의 넓은 주파수 영역에서 $2.9{\sim}3.6\;dB$의 결합계수와 $91.2{\pm}2.9^{\circ}$의 우수한 위상차 특성을 나타내었다.