• 한국자동차공학회논문집
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• 제21권4호
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• pp.8-15
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• 2013

Recently many kinds of electric vehicles have been developed as many governments demand the environmental friendly vehicles. In this paper, study of load optimization for the electric vehicle which has multiple axle power system was conducted. For the analysis of the vehicle which has three or four driving axles, a method based on the geometry and assumptions that considering axles as a spring model and normal forces of the axles are proportional to the displacement of the axles was applied with basic vehicle dynamics. With the developed vehicle analysis technique, algorithm to find the optimal motor operating points was developed. Using this algorithm, it was possible to find the optimization of vehicle load distribution for multiple axles according to the driving cycles. Also, control logic for the vehicle can be developed based on the optimization simulation results.

• International Journal of Naval Architecture and Ocean Engineering
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• 제8권3호
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• pp.235-242
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• 2016

Among underwater noise sources around submerged bodies, turbulence-induced noise has not been well investigated because of the difficulty of predicting it. In computational aeroacoustics, a number of studies has been conducted using the Ffowcs Williamse-Hawkings (FW-H) acoustic analogy without consideration of quadrupole source term due to the unacceptable calculation cost. In this paper, turbulence-induced noise is predicted, including that due to quadrupole sources, using a large eddy simulation (LES) turbulence model and a developed formulation of permeable FW-H method with an open source computational fluid dynamics (CFD) tool-kit. Noise around a circular cylinder is examined and the results of using the acoustic analogy method with and without quadrupole noise are compared, i.e. the FW-H method without quadrupole noise versus the permeable FW-H method that includes quadrupole sources. The usability of the permeable FW-H method for the prediction of turbulence-noise around submerged bodies is shown.

• Journal of the Korean Society for Industrial and Applied Mathematics
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• 제24권1호
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• pp.1-22
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• 2020

An accurate and efficient gradient estimation method on unstructured grid is presented by proposing a switching process between two Least-Square methods. Diverse test cases show that the gradient estimation by Least-Square methods exhibit better characteristics compared to Green-Gauss approach. Based on the investigation, switching between the two Least-Square methods, whose merit complements each other, is pursued. The condition number of the Least-Square matrix is adopted as the switching criterion, because it shows clear correlation with the gradient error, and it can be easily calculated from the geometric information of the grid. To illustrate switching process on general grid, condition number is analyzed using stencil vectors and trigonometric relations. Then, the threshold of switching criterion is established. Finally, the capability of Switching Weighted Least-Square method is demonstrated through various two- and three-dimensional applications.

• International Journal of Naval Architecture and Ocean Engineering
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• 제13권1호
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• pp.75-85
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• 2021

The broadband noise can be dominant or important for total characteristics for marine propeller noise representing the minimum base of self-noise. Accurate prediction of such noise is crucial for survivability of underwater military vessels. While the FW-H Formulation 1B can be used to predict broadband trailing edge noise, the method required experiment measurements of surface pressure correlations, showing its limitations in generality. Therefore, in this study, the methods are developed to utilize wall pressure spectrum models to overcome those limitations. Chase model is adopted to represent surface pressure along with the developed formulations to reproduce pressure statistics. Newly developed method is validated with the experiments of airfoils at different velocities. Thereafter, with its feasibility and generality, the procedure incorporating computational fluid dynamics is established and performed for a propeller behind submarine hull. The results are compared with the experiments conducted at Large Cavitation Tunnel, thus showing its usability and robustness.

• 전자공학회논문지
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• 제53권12호
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• pp.3-12
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• 2016

본 논문은 지뢰탐지용 48채널 배열 UWB 임펄스 레이다 방식의 지면투과레이다 구현과 시험에 대해 기술한다. 지면투과레이더는 기존 금속탐지기의 한계인 비금속 지뢰 탐지의 어려움과 매질 내 금속 성분에 의해 발생하는 높은 오경보 문제점을 극복한다. 본 논문에서는 펄스폭이 600ps 급인 미세한 모노싸이클(Monocycle) 펄스 파형을 사용해, 높은 해상도의 지뢰 전자파 영상을 제공토록 시스템을 구현한다. 특히 신호처리를 통해 지뢰가 매설된 지점을 자동으로 추정하고, 해당 지점에서의 분할된 상세 지뢰 전자파 영상을 사용자에게 제공한다. 기준 성능 분석을 위해 한국 대표 토양인 거친 사양토를 사용한 실내 시험장을 구축하고, 시험장 내의 자동화된 측정 플랫폼에 구현한 레이다를 장착하여 영상 획득 및 탐지심도 분석 등의 시험을 수행한다. 지뢰는 비무장 지대에 매설된 지뢰와 동일한 형태의 모형 지뢰를 사용한다.

• 한국멀티미디어학회논문지
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• 제18권11호
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• pp.1332-1341
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• 2015

This paper proposes a novel reversible secret sharing scheme using AES algorithm in encrypted images. In the proposed scheme, a role of the dealer is divided into an image provider and a data hider. The image provider encrypts the cover image with a shared secret key and sends it to the dealer. The dealer embeds the secret data into the encrypted image and transmits encrypted shadow images to the corresponding participants. We utilize Galois polynomial arithmetic operation over 2⁸ and the coefficient of the higher-order term is fixed to one in order to prevent the overflow. In experimental results, we demonstrate that the PSNR is sustained close to 44dB and the embedding capacity is 524,288 bits.

• 해양환경안전학회지
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• 제21권6호
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• pp.737-743
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• 2015

본 논문에서는 표적의 레이다 반사면적 기여도 분석을 통한 전파흡수체 적용에 대한 레이다 반사면적 감소 효과와 최신 전파흡수체 기술인 메타물질을 적용한 레이다 반사면적 감소 효과를 고찰하였다. 레이다 반사면적 해석은 모형선 모델로 진행하였고, 레이다 반사면적 기여도 분석을 통하여 전파흡수체와 메타물질의 레이다 반사면적 평균값 감소 효과를 확인하였다.

• Journal of Power Electronics
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• 제16권3호
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• pp.1190-1199
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• 2016

This study proposes a classification and compensation algorithm of two non-ideal output signals of a resolver to reduce position errors. Practically, a resolver generates position errors because of amplitude imbalance and quadrature imperfection between the two output signals of the resolver. In this study, a digital signal processor system based on a resolver-to-digital converter is used to reconstruct the two output signals of the resolver. The two output signals, "sin" and "cos," can be represented by a unit circle on the xy-plot. The classification and compensation of the errors can be obtained by using the radius and area of the circle made by the resolver signals. The method computes the integration of the areas made by the two resolver output signals to classify and compensate the error. This system cannot be applied during transient response given that the area integration during the transient state causes an error in the proposed method. The proposed method does not need any additional hardware. The experimental results verify the effectiveness of the proposed algorithm.

• 한국군사과학기술학회지
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• 제17권4호
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• pp.422-429
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• 2014

Proximity sensor networks are aimed at estimation kinematic state of target using estimated position of the target by each sensor node or target parameter. To analyze the kinematic state of target, traditional approaches require detections on multiple sensors, very large number of sensors to achieve acceptable performance. In this paper, we propose a novel method which can estimate predicted position of the underwater target using minimum proximity sensor with bearing information to this problem. The proposed algorithm was verified performance through simulation.

• 전기전자학회논문지
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• 제24권4호
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• pp.1093-1097
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• 2020

본 논문에서는 위성 통신 시스템 응용을 위하여 Ku-대역에서 동작하는 3 W PHEMT MMIC 전력 증폭기의 특성을 기술한다. 3 W PHEMT MMIC 전력 증폭기는 WIN(wireless information networking) semiconductor Corp.에서 제공하는 게이트 길이가 0.25 ㎛인 GaAs 기반 PHEMT (pseudomorphic high electron mobility transistor) 공정을 사용하여 개발되었다. 개발된 Ku-대역 PHEMT MMIC 전력 증폭기는 13.75 GHz에서부터 14.5 GHz까지의 동작주파수 범위에서 22.2~23.1 dB의 소신호 이득과 34.8~35.4 dBm의 포화 출력 전력을 가진다. 최대 포화 출력 전력은 13.75 GHz에서 35.4 dBm (3.47 W)이었다. 전력 부가 효율은 30.8~37.83%의 특성을 얻었으며 칩의 크기는 4.4 mm×1.9 mm이다. 개발된 PHEMT MMIC 전력 증폭기는 다양한 Ku-대역 위성 통신 시스템 응용에 적용 가능할 것으로 예상된다.