• ETRI Journal
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• 제40권5호
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• pp.592-603
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• 2018

In order to obtain better target identification performance, an efficient waveform design method with high range resolution and low sidelobe level for orthogonal frequency division multiplexing (OFDM) multiple-input multiple-output (MIMO) radar is proposed in this paper. First, the wideband CP-based OFDM signal is transmitted on each antenna to guarantee large bandwidth and high range resolution. Next, a complex orthogonal design (COD) is utilized to achieve code domain orthogonality among antennas, so that the spatial diversity can be obtained in MIMO radar, and only the range sidelobe on the first antenna needs suppressing. Furthermore, sidelobe suppression is expressed as an optimization problem. The integrated sidelobe level (ISL) is adopted to construct the objective function, which is solved using the Broyden-Fletcher-Goldfarb-Shanno (BFGS) algorithm. The numerical results demonstrate the superiority in performance (high resolution, strict orthogonality, and low sidelobe level) of the proposed method compared to existing algorithms.

• 한국염색가공학회지
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• 제17권4호
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• pp.7-14
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• 2005

The purpose of this study was to develop the color matching program with the excellent camouflage capacity in the near infrared range($\~$1100nm) including the visible light range for cotton fabrics. It was measured IR spectral reflectance in the range of $380\~1,100nm$ after dyed with vat dyes, and we made database for reflectance with various concentration on vat dyes which have a low reflectance value in the infrared range. The color matching algorithm that could be simulated in both the human visible light and the near infrared range was constructed by numerical analysis method using the database. In this study we also developed the dyeing conditions and dyeing process through the continuous-dyeing experiment with the vat dyes for cotton fabrics.

• 한국음향학회지
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• 제43권4호
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• pp.455-465
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• 2024

천해역에서 효과적인 거리추정 방법으로 알려진 배열 불변성은 도파관 불변성으로 요약될 수 있는 이상적인 도파관 내에서의 광대역 확산 특징을 기반으로 개발되었으며, 배열 기울기가 존재하는 상황에서도 배열 기울기와 거리를 동시에 추정할 정도로 강인하다. 최근에는 도파관 불변성의 각도 종속성을 완전히 고려할 수 있도록 확장되었다. 하지만, 거리-종속 환경에 대해 거리-독립 환경의 배열 불변성 기법을 적용한다면, 해저 지형 오정합에 의해 거리추정오차가 발생하게 된다. 본 논문에서는 이러한 거리추정 오차를 상응 거리 개념을 도입하여 해석하고자 한다. 거리-종속 환경에서의 수치 시뮬레이션 수행과 해상 실험 데이터를 통해 거리추정의 오차와 상응 거리 사이의 관계를 입증하였다.

• 한국광학회지
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• 제31권6호
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• pp.274-280
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• 2020

본 논문에서는 결맞음 빔결합 방식을 이용한 원거리 광학 에너지 전달 방법에 있어서 대기 외란의 영향을 위상판 모델을 사용하여 수치해석하고 분석한다. 결맞음 빔결합 방식은 3채널로 구성하고, 전송 거리는 1~2 km, 각 채널별 위상 및 조사 방향은 적절한 방식으로 보정된 것으로 가정하며, 각 채널 빔들이 자유공간을 진행할 때 발생하는 대기 외란 영향은 위상판 모델로 정량화한다. 위상판은 구조상수 Cn2 값의 변동 범위 10-15에서 10-13 [m-2/3] 내에서 통계적으로 생성하여 구성한다. 특별히, 본 논의에서는 대기 요동의 강도가 최종 빔결합 효율에 미치는 영향을 분석하기 위해 위상판 모델의 구조 상수를 변화시켜가며 해당 목표 지점에서 3채널 결맞음 빔결합 방식을 통해 전송된 빔의 결합 형태, 왜곡 정도 및 빔결합 효율을 계산한다. 본 수치 모델을 통해 분석한 결과, 상기 주어진 대기 요동 조건하에서도 원거리 광학 에너지 전송에 결맞음 빔결합 방식을 사용할 경우, 수신부 유효 도달 전력을 비결맞음 빔결합 방식 대비 최소 3배 이상 확보할 수 있음을 확인할 수 있다. 본 수치 모델은, 원거리 광학 에너지 전송을 전산모사함에 있어서 다양한 형태의 대기 외란의 영향 및 빔결합 방식을 분석하는데 효과적으로 활용될 수 있을 것으로 기대한다.

• 조명전기설비학회논문지
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• 제20권4호
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• pp.107-116
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• 2006

접지도체의 굵기를 결정하는 국외 규격은 재료의 특성값인 물리적 정수까지 적용하여 광범위하게 적용할 수 있는 반면 수식이 복잡한 문제점이 있고 JIS와 국내규격은 수식은 간단하나 제약조건이 많은 문제점이 있다. 또한 접지도체의 접속방법에 따라 최대허용온도가 다르게 적용되므로 접지도체 굵기 산정 방식이 복잡하고 적용 방법이 상이하여 시공현장에서 엔지니어들이 적용하는데 많은 어려움이 있다. 따라서 본 논문에서는 수식제어 모델링을 이용한 새로운 접지도체 굵기 산정방식과 접속방법에 따른 접지도체 굵기 산정 간이식을 제시하고 타당성을 입증, 분석하였으며 사례연구를 통해 논문의 신뢰성을 검증하였다.

• 한국통신학회논문지
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• 제37A권11호
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• pp.961-971
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• 2012

This article is concerned with effective numerical techniques for partial differential equation (PDE)-based image restoration. Numerical realizations of most PDE-based denoising models show a common drawback: loss of fine structures. In order to overcome the drawback, the article introduces a new time-stepping procedure, called the method of nonflat time evolution (MONTE), in which the timestep size is determined based on local image characteristics such as the curvature or the diffusion magnitude. The MONTE provides PDE-based restoration models with an effective mechanism for the equalization of the net diffusion over a wide range of image frequency components. It can be easily applied to diverse evolutionary PDE-based restoration models and their spatial and temporal discretizations. It has been numerically verified that the MONTE results in a significant reduction in numerical dissipation and preserves fine structures such as edges and textures satisfactorily, while it removes the noise with an improved efficiency. Various numerical results are shown to confirm the claim.

• 한국대기환경학회지
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• 제13권5호
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• pp.383-396
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• 1997

Numerical prediction of the pollutant dispersion over a two-dimensional hilly terrain is presented. The dispersion model used in the present work is based on the gradient diffusion theory and the finite-volume method on a non-orthogonal boundary-fitted grid system. The numerical model is validated by comparing the results with the available experimental data for the flat-floor dispersion within a turbulent boundary-layer. The numerical error analysis is performed based on the guideline of Kasibhatla et al.(1988) for the elevated-source dispersion in the flat-floor boundary layer having a power-law velocity and linear eddy-diffusivity profile. The influences of the two-dimensional hilly terrain on the dispersion from a continuously released source are numerically investigated by changing the emission locations and heights. It is found that the distributions of ground-level concentration are strongly influenced by the source location and the emission height. Hence, the terrain amplification factor is greatly enhanced when the pollutant source is located within a flow separation region. Dispersion from a source of short duration is also simulated and the duration time of the pollutant is compared at several downstream locations on a hilly terrain. The results of the numerical prediction are applied to the evaluation of environmental impacts due to the automobile exhausts at the seashore highway with a parallel mountain range.

• Korea-Australia Rheology Journal
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• 제13권3호
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• pp.131-139
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• 2001

A coupled approach is proposed for the prediction of sheet profile in sheet casting process, which combines one-dimensional analytical method on planar elongational flow region and three-dimensional numerical method on the other region. The strategy is constructed from the observations that the flow domain of sheet casting process can be separated into two parts based old the flow kinematics. The flow field in the central region of sheet, over which the planar elongational flow dominates, is possibly replaced by one-dimensional analytical solution. Then only a partial flow domain near the edge region of sheet, where the flow kinematics cannot be described by the planar elongational flow itself, requires three-dimensional numerical simulation. Good agreement is observed between the coupled approach developed in this study and the full three-dimensional numerical simulation previously developed and reported by the authors. This coupled approach may have provided flexibility with low costs to accommodate a wide range of die sizes in sheet casting process.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2006년도 춘계학술대회 논문집
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• pp.657-658
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• 2006

Although there are many numerical models to simulate fs laser ablation of metals, no model can analyze the ablation phenomena over a wide range of fluence. In this work, a numerical code for simulating the fs laser ablation phenomena of metals has been developed. The two temperature model is employed to predict the ablation rate and the crater shape of metals using phase explosion mechanism in the relatively high fluence regime. Also, the ultrashort thermoelastic model is used for the low fluence regime to account for spallation of the sample by high strain rate. It has been demonstrated that the thermoelastic stress generated within the sample can exceed the yield stress of the material even near the threshold fluence. Numerical computation results are compared with the experiment for Cu and Ni and show good agreement. Discussions are made on the hydrodynamic model considering phase change and hydrodynamic flow.

• 상하수도학회지
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• 제27권2호
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• pp.177-184
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• 2013

This study analyzed the hydraulic characteristics of a venturi flume with a circular cone using a 3-D numerical model which uses RANS(Reynolds-Averaged Navier-Stokes Equation) as the governing equation. The venturi flume with the circular cone efficiently measures the discharge in the low-flow to high-flow range and offers the advantage of accurate discharge measurements in the case of a low flow. With no influence of the tail-water depth, the stage-discharge relationship and the flow behaviors were analyzed to verify the numerical simulation results. Additionally, this study reviewed the effect of the tail-water depth on the flow. The stage-discharge relationship resulting from a numerical simulation in the absence of an effect by the tail-water depth showed a maximum margin of error of 4 % in comparison to the result of a hydraulic experiment. The simulation results reproduced the overall flow behaviors observed in the hydraulic experiment well. The flow starts to become influenced by the tail-water depth when the ratio of the tail-water depth to the total head exceeds approximately 0.7. As the ratio increases, the effect on the flow tends to grow dramatically. As shown in this study, a numerical simulation is effective for identifying the stage-discharge relationship of a venturi flume with various types of venturi bodies, including a venturi flume with a circular cone.