• 한국전자파학회논문지
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• 제10권1호
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• pp.32-43
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• 1999

본 논문에서는 QMSA에 전기력선의 제한이 없도록 용량을 장하한 변형된 QMSA를 설계했다. 설계.제작 된 안테나는 2.0 GHz의 중심 주파수에서 5.7 %의 대역폭을 갖고 임의의 급전점 변화에 따라 대역폭과 공진 주파수의 변화를 보였다. 용량을 장하하기 위한 좌. 우측 평행 평판사이 넓은 스롯폭의 크기는 매우 넓은 대역폭을 갖기 때문에 광대역 통신 시스템에 응용휠 수 있다. 설계된 안테나의 방사 패턴 특성은 다이폴 구조와 개구연 구조 해석법을 기초로 하였다. 계산 결과, 상대적인 후방 방사는 -5dB 정도였다.

• 천문학회보
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• 제42권2호
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• pp.42.2-42.2
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• 2017

The Large Magellanic Cloud (LMC) is a unique target to study the detail structures of molecular clouds and star-forming regions, due to its proximity and face-on orientation from us. Most part of the astrophysical subjects for the LMC have been investigated, but the magnetic field is still veiling despite its role in the evolution of the interstellar medium (ISM) and in the main force to influence the star formation process. Measuring polarization of the background stars behind interstellar medium allows us to describe the existence of magnetic fields through the polarization vector map. In this presentation, I introduce the near-infrared polarimetric results for the $39^{\prime}{\times}69^{\prime}$ field of the northeastern region of the LMC and the N159/N160 star-forming complex therein. The polarimetric observations were conducted at IRSF/SIRPOL 1.4 m telescope. These results allow us to examine both the global geometry of the large-scale magnetic field in the northeastern region and the close structure of the magnetic field in the complex. Prominent patterns of polarization vectors mainly follow dust emission features in the mid-infrared bands, which imply that the large-scale magnetic fields are highly involved in the structure of the dust cloud in the LMC. In addition, local magnetic field structures in the N159/N160 star-forming complex are investigated with the comparison between polarization vectors and molecular cloud emissions, suggesting that the magnetic fields are resulted from the sequential formation history of this complex. I propose that ionizing radiation from massive stellar clusters and the expanding bubble of the ionized gas and dust in this complex probably affect the nascent magnetic field structure.

• Journal of Advanced Marine Engineering and Technology
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• 제16권5호
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• pp.85-96
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• 1992

Engine enclosures are widely adopted to reduce the noise emission in various fields of application. The radiated noise, which is due to the vibration of enclosure's outer surface, is composed of two kinds of sound power with different path of propagation. One is the 'structure-borne sound power' which stems from the engine's vibratory force applied to the structure of enclosure through the mounting parts of engine etc., while the other is the 'air-borne sound power' which is originated by the sound power radiated from the engine surface to the inner space of enclosure that should excite the vibration of enclosure from inside. In order to get a most efficient engine enclosure is required a profound consideration upon the above structure-borne and air-borne noise, since the guiding principle of countermeasure for each noise is quite different. The controlling of input vibration and its isolation are major subject for the structure-borne sound power and the specifications of absorbing member and damping panels are the major interests for the air-borne sound power. Hence it seems very efficient to separate the total sound power into two categories with a great accuracy when one think of further reduction of engine noise from the exciting enclosure, however, its separating methods have not been made clear for many years. Then author proposes a new practical separation method of two propagation path's contribution to the total radiation sound power for the enclosure under the engine operating condition.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2002년도 학술대회지
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• pp.365-368
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• 2002

The design of industrial arc plasma systems is still largely based on trial and error although the situation is rapidly improving because of the available computational power at a cost which is still fast coming down. The desire to predict the behavior of arc plasma system, thus reducing the development cost, has been the motivation of arc research. To interrupt fault current, the most enormous duty of a circuit breaker, is achieved by separating two contacts in a interruption medium, $SF_{6}$ gas or air etc., and arc plasma is inevitably established between the contacts. The arc must be controlled and interrupted at an appropriate current zero. In order to analyze arc behavior in $SF_{6}$ gas circuit breakers, a numerical calculation method combined with flow field and electromagnetic field has been developed. The method has been applied to model arc generated in the Aachen nozzle and compared the results with the experimental results. Next, we have simulated the unsteady flow characteristics to be induced by arcing of AC cycle, and conformed that the method can predict arc behavior in account of thermal transport to $SF_{6}$ gas around the arc, such as increase of arc voltage near current zero and dependency of arc radius on arc current to maintain constant arc current density.

• 한국소음진동공학회논문집
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• 제12권1호
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• pp.42-47
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• 2002

Sirocco fans are widely used in HVAC and air conditioning systems, and the noise generated by these machines causes one of the most serious problems. In general, the sirocco fan noise is often dominated by tones at BPF(blade passage frequency) and broadband noise. However, only a few researches have been carried out on predicting the aeroacoustic noise because of the difficulty in obtaining detailed information about the flow field and casing effects on noise radiation. The objective of this study is to develop a prediction method for the unsteady flow field and the acoustic pressure field of a sirocco fan. We assume that the impeller rotates with a constant angular velocity and the flow field around the impeller is incompressible and inviscid. So, a discrete vortex method (DVM) is used to model the centrifugal fan and to calculate the flow field. The force of each element on the blade is calculated by the unsteady Bernoulli equation. Lowson\`s method is used to predict the acoustic source. Reasonable results are obtained not only fur the tonal noise but also far the amplitudes of the broadband noise. Acoustic pressure is proportional to (Ω)2.3, which is the similar value with the measured data.

• 한국소음진동공학회논문집
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• 제22권7호
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• pp.676-684
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• 2012

Numerical analysis was performed to investigate the heavy-weight impact noise of apartment houses. The FEM is practical method for prediction of low-frequency indoor noise. The results of numerical analysis, the shape of the acoustic modes in room-2 are similar to that of acoustic pressure field at the fundamental frequency of acoustic modes. And the acoustic pressure was amplified at the natural frequency of the acoustic modes and structural modes. The numerical analysis result of sound pressure level at 63 Hz and 125 Hz octave-band center frequency are similar to the test results, but at 250 Hz and 500 Hz have some errors. Considering most of bang-machine force spectrum exists below 100 Hz, the noise at 250 Hz and 500 Hz are not important for heavy-weight impact noise. Thus, the FEM numerical analysis method for heavy-weight impact noise can apply to estimate heavy-weight impact noise for various building systems.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2008년도 춘계학술대회논문집
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• pp.479-482
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• 2008

In order to more closely examine the vacuum arc phenomena, it is necessary to predict the magnetohydrodynamic (MHD) characteristics by the multidisciplinary numerical modeling, which is coupled with the electromagnetic and hydrodynamic fields, simultaneously. In this study, the thermal-fluid characteristics of high current vacuum arcs were calculated by a commercial multiphysics package, ANSYS, in order to obtain Joule heat, Lorentz force and the interactions with flow variables. We assumed the diffused-mode arc within an AMF vacuum interrupter. It was found with four different currents that the temperature distributions on the anode surface are diffused uniformly without concentration in 7kA for both types (cup and coil-type). But the arc plasma transition and an increase of thermal flux density for increasing the applied current have caused the change of temperature distributions on the anode surface. We should need further studies on the two-way coupling method and radiation model for arc plasmas in order to accomplish the advanced analysis method for multiphysics.

• 대기
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• 제18권4호
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• pp.417-427
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• 2008

In this paper, we analyzed the physical and thermodynamic characteristics of fog by using the integrated water vapor (IWV) from Global Positioning System (GPS) networks and the regular observation data of meteorological stations in GPS sites. The cases of a radiation and an advection fog were selected as samples, the conversions of water substance from the water vapor to cloud water in fog were detected by the Bulk Water-Continuity Model, and the pattern analysis is adapted on GPS IWV, temperature, wind and relative humidity. Under the specific hypothesis (saturation and stable), GPS IWV could detect quantitatively the phase changing between the water vapor and cloud water content with condensation/evaporation during the formation and dissipation of fog. After it reaches to the saturation, the relative humidity can be a limited indicator for fog. However, GPS IWV can detect the status change of fog even after the saturation. It has indicated that GPS IWV could be a new observing technique for the processes of the fog formation and the dissipation.

• Journal of Astronomy and Space Sciences
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• 제14권2호
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• pp.381-385
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• 1997

해석적 방법을 이용한 정지위성의 장기 궤도예측 알고리즘을 개발하였다. 적용된 섭동모델에는 5 $\times$5 지구중력포텐셜, 달과 태양의 중력, 태양복사압에 의한 섭동들이 포함되었으며, 모든 섭동들은 장반경, 이심률 백터, 궤도경사각 백터, 평균경도의 구성요소로 이루어진 춘분점 궤도요소의 영년변화, 단주기 변화, 장주기변화 섭동항들로 급수전개되었다. 해석적 방법에 의한 무궁화 위성의 궤도예측의 결과를 코웰방법을 이용한 궤도예측의 결과와 비교하였다. 이 비교를 통해서 새로 개발된 해석적 방법을 이용한 궤도예측 알고리즘은 3개월동안 약$pm35m$ 이내로 장반경을 정밀하게 예측할 수 있다는 것을 알 수 있다.

• Journal of Theoretical and Applied Mechanics
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• 제2권1호
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• pp.1-14
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• 1996

In this paper, breaking waves are generated in a 2-D wave tank and simulated by using a higher-order boundary element method. A piston-type wavemaker is operated by signals composed of elementary waves. The phase of elementary waves is determined by the linear theory such that they are focused to a prescribed position. Calculated plunging waves coincide well with experiment. A steel box with different plate thicknesses is installed at a predetermined position in the tank. Measured impulsive pressures due to breaking waves are found to be 0.8-1.2$\rho$C2, where $\rho$ corresponds to water density and C to wave celerity. The transverse displacement of the plate is described in terms of modal eigenfunctions. The natural frequencies measured by impact tests in air for thin plate coincide with the computational and theoretical values. The radiationpotential due to plate vibration is derived and the radiation force is expressed in terms of hydroelastic added mass and damping forces. Comparison of natural frequencies of plate in water proves that hydroelastic added mass and damping are properly considered. The measured strain due to regular waves supports the calculated one, but there are apparent discrepancies between theory and experiment in the impulsive case.