• 한국진공학회:학술대회논문집
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• 한국진공학회 2014년도 제46회 동계 정기학술대회 초록집
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• pp.151.1-151.1
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• 2014

Wake field effect on the electron beam from the undulator chamber in PAL-XFEL is analyzed. The wake field takeover some energy from the electron beam which will increase the energy spread of the electron beam. This will cause the degradation of the radiation power in PAL-XFEL. To decrease the effect, the surface of the undulator vacuum chamber should be fabricated with 200 nm surface roughness and 5 nm oxidation layer. In this presentation, the numerical calculation of the wake will be shown. Simulation results of the radiation generation in PAL-XFEL also will be presented.

• ETRI Journal
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• 제26권5호
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• pp.481-485
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• 2004

We consider electromagnetic field radiation properties of a current filament placed at the origin of a cylindrical frequency selective surface (CFSS). The CFSS consists of free standing metal strips with two-dimensional periodicity. The analysis is based on a cylindrical Floquet mode wave expansion technique. We observed that near the half wavelength resonance frequencies, there exist some specific frequencies at which the surface becomes totally transparent.

• 한국위성정보통신학회논문지
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• 제9권3호
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• pp.104-108
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• 2014

한국형발사체의 표면에 장착되는 UHF-대역 안테나의 표면에 발생하는 결빙을 모델링하고, 이러한 결빙이 안테나의 공진주파수, 반사손실 및 방사패턴 등의 주요 특성에 미치는 영향을 분석하였다. 안테나 표면결빙을 모델링하기 위해 $-180^{\circ}C$의 얼음층에 대한 비유전율을 추출하였고 추출된 비유전율을 이용하여 안테나 표면결빙 모델을 제안하였다. 중심주파수가 UHF-대역인 안테나 표면에 1mm의 결빙이 되었을 경우의 표면결빙 모델을 적용하여 시뮬레이션 한 결과, 표면결빙에 의해 안테나의 공진주파수가 21MHz 하향 되었고, 방사패턴도 전 방향에 대해 전체적으로 10dB 이상의 성능저하가 발생되었다. 따라서 실제 안테나 표면에 결빙이 발생할 경우 안테나 성능에 심각한 영향을 미칠 것으로 판단된다.

• 대한조선학회지
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• 제19권2호
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• pp.13-18
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• 1982

The method of Rankine source distribution is emerging as a powerful yet simple alternative for the solution of complicated free surface problems. But it has been uncertain whether the radiation condition could be satisfied exactly by distributing the simple sources on the free surface only. In this paper, it is proved rigorously that the Rankine sources, whose intensities are varying sinusoidally along the axis satisfying the free surface boundary condition, generate the radiation waves both in the infinite and finite-depth flows. A formula is derived to give the upper and lower bounds of the errors in the induced velocity computation that will be introduced by truncating the extent of source distribution on the free surface. Since the truncation is inevitable in the numerical analysis, this formula may be used as a criterion to limit the position of the field points, where velocity computation is made, away from the truncation boundary. A typical analysis shows that the maximum error will be 3.4 percent of the exact induced velocity when the field point is on the free surface two wave lengths away from the truncation boundary.

• Journal of Ship and Ocean Technology
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• 제10권1호
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• pp.10-26
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• 2006

The radiation problem for oscillating bodies on the free surface has been formulated by the over-determined Green integral equation, where the boundary condition on the free surface is satisfied by adopting the Kelvin-type Green function and the irregular frequencies are removed by placing additional control points on the free surface surrounded by the body. The B-Spline based higher order panel method is then applied to solve the problem numerically. Because both the body geometry and the potential on the body surface are represented by the B-Splines, that is in polynomials of space parameters, the unknown potential can be determined accurately to the order desired above the constant value. In addition, the potential expressed in B-Spline can be differentiated analytically to get the velocity on the surface without introducing any numerical error. Sample computations are performed for a semispherical body and a rectangular box floating on the free surface for six-degrees of freedom motions. The added mass and damping coefficients are compared with those by the already-validated constant panel method of the same formulation showing strikingly good agreements.

• 대한디지털의료영상학회논문지
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• 제11권2호
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• pp.101-107
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• 2009

With the recent development of diagnosis using radiation and increasing demand of the medical treatment, we need to minimize radiation exposure dose. So, This is the method which reduce patient dose by measuring surface dose of radiographic change factor and by comparing theoretical and actual dose, when we take an X-ray which is generally used. By changing the factor of kV, mAs, FSD, whose range is 60 to 120 kV, 20 to 100 mAs, 80 to 180 cm, we compared theoretical surface dose with actual surface dose calculated by the simple calculation program, Bit system, and NDD-M method As a result, when kV and mAs were higher, theoretical surface dose and actual surface dose were more increased. but the higher FSD was, the more decreased surface dose was. According to this, the error were measured about 0.1 to 0.2 mGy in low dose part and about 0.7 to 1.5 mGy in high dose part. Therefore, this shows that theoretical surface dose calculation method is more correct in low dose part than in high dose part. In conclusion, we will have to make constant efforts which can reduce patient and radiographer's exposure dose, studying methods which can predict patient's radiation exposure dose more exactly.

• 한국지리정보학회지
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• 제23권4호
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• pp.156-172
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• 2020

본 연구는 대상도로인 내부순환로에 대해 태양복사모델(SOlar and LongWave Environmental Irradiance Geometry-model, SOLWEIG)을 통해 산출한 도로의 그림자 패턴을 사용하여 항상 그늘이 지는 음영지역을 살펴보고, 열수지법을 기반으로 한 노면온도예측모델(road surface temperature prediction model, 이하 RSTPM)과 SOLWEIG 모델을 연계하여 고해상도의 태양복사정보를 활용한 도로의 노면온도를 예측하고자 하였다. 우선, 그림자 패턴 및 복사플럭스 산출의 정확도를 높이기 위하여 안개, 구름, 강수 등의 영향을 최소화할 수 있는 사례일을 선정하여, 고도 및 지형의 효과에 따른 그림자의 영향을 살펴보았다. 그 결과, 터널 입출구와 고도가 높은 지역에서 그림자 영역이 오래 지속되었고, 그림자의 영향을 많이 받는 구간의 복사량 감소가 뚜렷하게 나타났다. 이는 노면온도 예측결과에 반영되어 지형적으로 개방된 지점에서는 노면온도가 높게 예측되고, 고도가 높은 지점들은 그렇지 않은 지점에 비해 상대적으로 낮게 예측되었다. 본 연구의 결과는 겨울철 기상상황에 따른 도로 결빙구간을 예측하여 도로 관리자 및 운전자의 의사결정 자료로서의 활용이 기대된다.

• 한국항해항만학회지
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• 제28권3호
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• pp.199-205
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• 2004

라디에이션(radiation) 문제를 해결하기 위해서 중합격자법을 개발하였다. 중합격자계는 이동격자계와 고정격자계로 이루어져 있으며, 이동격자계는 운동하는 물체에 적용되어 운동하는 물체와 동시에 이동된다. 이러한 수치계산법은 자유표면 부근에서 운동하는 몰수평판에 작용하는 라디에이션 유체력을 계산하는데 응용되었다. 현재의 수치계산법에 의한 결과는 실험값 및 선형포텐셜 이론에 의한 결과와 상호 비교하였으며, 수치계산의 신뢰성을 확인하였다. 그리고, 몰수평판에 작용하는 비선형 점성감쇄효과에 대하여 평가하였다.

• 공학논문집
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• 제3권1호
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• pp.159-169
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• 1998

이 논문에서는 수정곡면 카세그레인 안테나의 복사특성을 해석하였다. 부반사판의 복사특성은 GTD를 이용하여 계산되었고, 완전한 복사패턴은 반사파와 회절파의 합으로 표현되었다. 부반사판의 해석을 위해서 부반사판의 1,2차 미분값을 국지보간법을 이용하여 구했다. 주반사판의 복사특성 해석은 PO를 사용하여 유도된 표면전류밀도를 적분하므로써 수행되었다. Jacobi-Bessel 급수를 이용하여 적분식을 변형시켜서 계산 시간을 단축시켰다.

• 한국생산제조학회지
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• 제7권2호
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• pp.81-90
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• 1998

Noise produced by surface transportation vehicles affects our daily lives, penetrating wherver man lives or works. In this paper, a theoretical model has been studied to describe the sound radiation by the surface vibration of in-service tires and studied about an experiment on sound radiation characteristic due to tire vibration. When a tire is analyzed, it has been modeled as a curved beams with distributed sprongs and dash-pots which represent the radial, tangential stiffnes and damping of tire, respectively. The experimental investigation for the sound radiation of a radial tire has been made. Based on the sound intensity and STSF(Spatial Transformation of Sound Field) techniques. the sound pressure and the sound radiation are measured. The comparison of numerically analyzed results with experimental results was made seperately for the tire in rotation. As a result of this study, a program for the prediction of the tire vibration sound radiation was intended to by developed which enables a designer of a tire to foresee the influence of the various design factors on the tire vibration sound radiation.