• 한국유체기계학회 논문집
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• 제10권4호
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• pp.29-38
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• 2007

In this study, flow structure in a two-stage centrifugal compressor for a turbo-chiller with the refrigerant, R134a, was numerically investigated at the design point of the compressor using a commercial code. Flow characteristics in the passages of impeller, diffuser and return channel were analyzed in detail including velocity vector, secondary flow, Mach number and pressure contours in blade spanwise and meridional plane for each stage. The estimation on the one-dimensional output from the preliminary design and three-dimensional shape of the impeller blade and the meridional shape of the return channel were performed through the flow analysis, while some numerical schemes and techniques including Multiple Frames of Reference technique, real gas property data and inlet boundary condition changes, which were used in CFD, were compared with their features. The results will be used as reference data for a new design of 3-D impeller shape to improve R134a compressor performance.

• Journal of Advanced Marine Engineering and Technology
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• 제39권3호
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• pp.280-285
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• 2015

대용량 다중 송신 다중 수신 안테나 환경에서 정합 필터 송신기는 다중 사용자 하향 링크 전송 용량(capacity)을 달성하는 방법으로 알려져 있다. 그러나 기지국이 유한 개수의 대용량 안테나를 장착한 경우 정합 필터는 다중 사용자 하향링크 전송 용량을 제공할 수 없다. 본 논문에서는 유한 대용량 안테나를 갖춘 기지국이 낮은 신호 대 잡음비의 다수의 셀 경계 영역 사용자를 지원할 경우, 효율적 연산 복잡도로 전송 용량을 최대화하는 두 단계 선형 송수신기 설계 방법을 제안한다. 정합 필터로 구성된 첫째 단계 프리코더는 유효 채널 dimension 을 줄이면서 동시에 빔포밍 이득을 통해 수신 신호 대 잡음 비를 개선한다. 그리고 평균 자승 오류율 최소화 기법을 통해 전송 용량을 최대화하는 둘째 단계 선형 송수신기를 구한다. 시뮬레이션과 분석을 통해 전송 용량과 연산 복잡도 면에서 제안하는 방법이 우수함을 보인다.

• Journal of Communications and Networks
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• 제9권2호
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• pp.167-176
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• 2007

In multimedia communication systems, efficient transmission system design should incorporate the use of matching unequal error protection (UEP), since source coders exhibit unequal bit error sensitivity. In this paper, we present UEP schemes which exploit differences in bit error protection levels in orthogonal frequency division multiplexing (OFDM) systems over frequency selective fading channels. We introduce an UEP scheme which improves the link performance with multiple transmit and receive antennas. Especially, we propose a new receiver structure based on two stage Maximum Likelihood detection (MLD) schemes which can approach the performance of a full search MLD receiver with much reduced computational complexity. In the performance analysis, we derive a generalized pairwise error probability expression for the proposed UEP schemes. Simulation results show that the proposed schemes achieve a significant performance gain over the conventional equal error protection (EEP) scheme.

• International Journal of Naval Architecture and Ocean Engineering
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• 제12권1호
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• pp.387-398
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• 2020

In the design stage of the very large container ships, some methodologies for the whipping effects have been developed, but most of them are based on single sea state. We developed a methodology that considers multiple sea states. Fluid-structure Interaction (FSI) analyses with one dimensional structural model were carried out to capture slamming-induced transient whipping behaviors. Because of the nature of random phases of the applied wave spectra, the required period for entire FSI analyses was determined from the convergence study where the whipping effect became stable. Low pass filtering was applied to the transient whipping responses to obtain the hull girder bending moment processes. Peak counting method for the filtered whipping responses was used to obtain collection of the vertical bending moment peaks. The whipping effect from this new method is compared with that from based on single sea state approach. The efficiency and advantage of the new methodology are presented.

• 전력전자학회:학술대회논문집
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• 전력전자학회 2000년도 전력전자학술대회 논문집
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• pp.501-504
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• 2000

In this paper the PC power supply is studied from the point of system stability. The power stage model of a multiple output forward converter with weighted voltage mode control is derived including all the major parasitic components and the small signal model is also derived. Determination of the weighting factors and a design procedure for the loop compensation are presented. Finally the model is verified through the simulation of three output forward converter with SABER.

• Journal of Electrical Engineering and Technology
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• 제13권1호
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• pp.493-500
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• 2018

This paper addresses a decentralized observer-based output-feedback formation control problem for multiple unmanned underwater vehicles (UUVs). The complex nonlinear model for a UUV is feedback-linearized. It is assumed that each UUV in the formation exploits only the information regarding itself and the immediate predecessor, which imposes structural constraints on the formation controller gain matrices. The design condition is presented as a two-stage linear matrix inequalities problem. The synthesized controller demonstrates its own advantages through a numerical example.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2005년도 춘계학술대회 논문집
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• pp.75-80
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• 2005

A design for the front section of an excavator requires kinematic and kinetic mechanism consideration for several configurations. Key parameters for an appropriate configuration can be obtained through a mechanical verification and numerical formulation with a design expert's know-how. In this paper, we propose a knowledge-based system with an expert-shell(CATIA) and Visual Basic to assist for the design of the front section of an excavator. The designers can achieve more efficient design through a CAD model, implemented design knowledge, and a user friendly interface. The implemented design knowledge is retrieved through the whole design process from an early design stage to a detailed design stage based on the multiple levels of abstraction scheme.

• Structural Engineering and Mechanics
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• 제28권6호
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• pp.677-694
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• 2008

A vibration power minimization model is developed, based on the mobility matrix method, for a vibration isolation system consisting of a vibrating source placed on an elastic support structure through multiple resilient mounts. This model is applied to investigate the design optimization of an X-Y motion stage-based vibration isolation system used in semiconductor wire-bonding equipment. By varying the stiffness coefficients of the resilient mounts while constraining the dynamic displacement amplitudes of the X-Y motion stage, the total power flow from the X-Y motion stage (the vibrating source) to the equipment table (the elastic support structure) is minimized at each frequency interval in the concerned frequency range for different stiffnesses of the equipment table. The results show that when the equipment table is relatively flexible, the optimal design based on the proposed vibration power inimization model gives significantly little power flow than that obtained using a conventional vibration force minimization model at some critical frequencies. When the equipment table is rigid enough, both models provide almost the same predictions on the total power flow.

• 한국정보통신학회논문지
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• 제3권4호
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• pp.787-794
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• 1999

본 논문에서는 기존의 동적 CMOS 논리회로보다 동작속도가 타르고 면적이 작은 새로운 EMMODL (enhanced NORA MODL)의 설계방법을 제시하고, 이를 이용하여 32 비트 CLA(carry lookahead adder)를 구현하였다. 제안된 회로는 MODL(multiple output domino logic)의 출력 인버터를 제거하여 면적을 줄이고 동작속도를 증가시킬 수 있다. 0.8um 이중금속 CMOS 공정으로 구현된 CLA는 시차문제가 발생하지 않았고, 3.9nS 이내에 32 비트 연산이 가능하였다.

• 한국건설관리학회논문집
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• 제19권3호
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• pp.70-78
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• 2018

기후변화에 대한 우려가 커지면서 건설산업에서도 환경부하를 줄이기 위해 지속적으로 노력하고 있으며, 환경부하를 산정하기 위한 효과적인 방법론으로써 LCA (life cycle assessment)가 제시되고 있다. 그러나, LCA는 환경부하량 산정을 위해 작업에 투입되는 자원량에 대한 정보가 필요하기 때문에 이러한 정보의 확보가 어려운 초기 설계단계의 환경적 검토에는 활용되지 못하고 있다. 이 연구에서는 도로의 배수시설물을 대상으로 표준단면에 기반한 작업물량산출체계를 개발하고 환경부하량을 산출할 수 있는 모델에 활용하였다. 이 모델은 초기 설계단계의 가용정보만으로 LCA에 필요한 자원량을 산정함으로써 환경부하량을 산출할 수 있다. 모델의 유효성을 검증하기 위해 5개의 검증사례를 적용하였으며 원단위추정모델 및 회귀모델과 비교하였다. 그 결과 평균 9.94%의 절대오차율평균을 나타내 다른 모델보다 상대적으로 정확하며 초기 설계단계에서 사용할 수 있는 유효한 모델이라는 점이 확인되었다.