• Transactions of the Korean Society of Automotive Engineers
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• v.7 no.7
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• pp.54-65
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• 1999

In this study, the flow field, spray structure, and combustion process were investigated in a direct injection diesel engine having an offset bowl in a combustion chamber. The KIVA-3V code was used in this study. In order to obtain accurate results, a droplet atomization model, wall impingement model, and ignition delay concept were added to KIVA-3V code. The results showed that the offset bowl engine had a large vortex flow. The direction of this flow counteracted to the direction of fuel injection in one side of combustion chamber. It decreased local turbulent kinetic energy and eventually nonuniform combustion was resulted in an offset bowl engine. In comparison with a center bowl engine case, the peak cylinder pressure was decreased about 6%. Finally , the effect of swirl on combustion was investigated in an offset bowl engine . As the became stronger, the nouniform characteristics in combustion were increased.

• Nuclear Engineering and Technology
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• v.30 no.1
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• pp.26-39
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• 1998

The containment pressure and temperature transient analysis computer code CONTEMPT4/MOD5 is modified to incorporate the passive containment cooling models. The correlations are selected from the existing experimental heat transfer correlations to model the natural and mixed convection in annular space between the containment shell and the shield building. The evaporative heat transfer of the water film on the outer shell of the containment is modeled using the correlations derived from the analogy between the heat and mass transfer. The modified code is applied to the Ap600 containment transient analysis for the model verification and the results are compared to the results of GOTHIC calculation done by Westinghouse. Also, d series of parametric sensitivity studies of heat transfer correlations, water film ratio and delay time of the wet cooling on the containment peak pressure and temperature following LOCA are performed for the containment of 1000MWe passive plant, KP1000.

• Proceedings of the IEEK Conference
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• 1999.06a
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• pp.61-64
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• 1999

The turbo code appropriate to IMT-2000 is known to have a good performance whenever the size of frame increases. But it is not appropriate to a sort of video service to need real time because of decoding complexity and long delay time by the size of frame. Therefore this paper proposes decoding decision algorithm of short frame in which soft output is weighted according to iteration number in turbo decoder. Performance of the proposed algorithm is analysed in the AWGN channel when short length of frame is 100, 256, 640. As the result. it is appeared that the proposed decoding decision algorithm has improved in BER other than in the existing MAP decoding algorithm.

• Proceedings of the IEEK Conference
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• 2003.07a
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• pp.11-14
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• 2003

본 논문에서는 다중안테나 시스템(Multiple-Input Multiple-Output : MIMO)과 다중코드(Multicode)를 사용하는 코드분할 다중접속(Code Division Multiple Access : CDMA) 시스템의 하향링크(from the base station to the mobile) 환경하에서 채널응답의 중요한 요소인 전송지연시간(Propagation Delay Time)이 기존의 단일안테나(Single-Input Single-Output : SISO) 채널 환경에서 다중안테나 채널 환경으로 바뀌어 적용되었을 때 발생할 수 있는 환경 변화를 찾아보고 그러한 환경이 코드 동기 성능에 미치는 영향과 그러한 문제점을 해결할 수 있는 효율적인 파일롯(Pilot) 전송 기법을 제안 하였다. 또한 모의 실험을 통하여 도착 시간 지연 차이의 분산(variance)값이 검파 성능에 미치는 영향을 확인 하였다.

• Journal of the Korea Society of Computer and Information
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• v.11 no.5 s.43
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• pp.203-209
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• 2006

In this paper, proposed diversity algorithm that decrease fading. In the wireless channel, if fading occurs due to the multipaths the performance of the system is apparently reduced. This study applied tap-delay receiver. It applied QPSK and OQPSK modulation methods and applied the convolutional codes, where the code rate is 1/2 and 1/3 and the constraint length is 11 and the turbo code where the constraint length is 6. The diversity algorithm proposed in this paper could be compared and analyzed the average error probability of modulation method variable of fading factor to uplink and downlink channels.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.37 no.2B
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• pp.110-119
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• 2012

In this paper, we propose an efficient video streaming system over heterogeneous wireless networks. The proposed system modifies fountain code for the video streaming service and maximizes the target video encoding rate using multiple paths while satisfying delay and block recovery failure rate constraints of fountain code. Finally, the proposed system provides the seamless video streaming service of high quality to subscribers by dynamic adaptation of control parameters based on the states of each path over heterogeneous wireless networks.

• Journal of Broadcast Engineering
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• v.16 no.2
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• pp.226-236
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• 2011

In this paper, we propose the channel estimation for the space time coded-orthogonal frequency division multiplexing (ST-OFDM) muti-input multi-output (MIMO) system with comb type pilot arrangements. In the conventional method, specially constructed pilots are inserted in the OFDM symbols at all transmit antennas separately. The proposed algorithm multiplies the orthogonal code to be transmitted OFDM symbols to estimate channels at the receiver. This algorithm can estimate a long channel delay with high accuracy. It is proved by computer simulations.

• Transactions of the Korean Society of Pressure Vessels and Piping
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• v.11 no.2
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• pp.68-74
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• 2015

Time domain response analysis for vibro-impact nonlinear behavior of multi-span tube with loose supports was performed using commercial FEA code and user subroutine. Support geometry of multi-span tube with a finite gap is realistically modeled by analytical rigid surface. Model of hydrodynamic force is based on the Qusai-steady model which accounts for the inclined angle of relative flow velocity and time delay between flow force and resulting tube motion. During tube vibration from flow loading, impact and friction at the support location is simulated using commercial FEA code with master slave contact algorithm. Analysis results has reasonable agreement with those of references and test experience. Plan of further refinement of analysis model and future test verification is briefly introduced.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.27 no.7A
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• pp.659-667
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• 2002

In this dissertation, in the Turbo Code used for error correction coding of the recent digital communication systems, we propose a new S-R interleaver that has the better performance than the existing block interleaver, and the Turbo Decoder that has the parallel concatenated New structure using the MAP algorithm. For real-time voice and video services over the third generation mobile communications, the performance of two proposed methods is analyzed by the reduced decoding delay using the variable decoding method by computer simulation over multipath channels of DS-CDMA system. Also, a Modified NCMA based on conventional NCMA is proposed to improve the channel efficiency in the mobile communication system, and is investigated over the multi-user environment of DS-CDMA system through computer simulation.

• Proceedings of the Acoustical Society of Korea Conference
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• 1994.06c
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• pp.210-213
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• 1994

In this paper, we present a combination of trellis coded vector quantization and code-excited linear prediction coding, termed trellis excitation coding, for an efficient 4.8 kbps speech coding system. A training sequence-based algorithm is developed for designing an otimized codebook subject to the TEC structure. Also, we discuss the trellis symbol release rules that avoid excessive encoding delay. Finally, simulation results for the TEC coder are given at bit rate of 4.8 kbps.