• Journal of Energy Engineering
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• v.12 no.3
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• pp.197-206
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• 2003

A numerical analysis of the pulse-jet cleaning characteristics in a porous ceramic candle filter system was performed. To obtain the detailed velocity and pressure distribution during the cleaning process in a porous filter system, the axi-symmetric compressible Navier-Stokes equations including energy conservation equation were solved by using the FLUENT code which adopts FVM (Finite Volume Method). The effects of pulse cleaning nozzle diameter, nozzle tip position, permeability of a porous ceramic candle filter, diffuser throat diameter, and cleaning pressure on the cleaning flow characteristics were investigated extensively.

• Proceedings of the Acoustical Society of Korea Conference
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• spring
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• pp.183-186
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• 2004

본 논문에서는 수중 초음파 통신용 QPSK 버스트 수신기를 DSP시스템을 이용하여 구현하기위한 시스템 설계에 대하여 논한다. 본 논문에서 고려하는 시스템은 25kHz의 반송주파수를 사용하고, 심벌율은 5kHz이며, 데이터 전송율은 10,000bps이다. 송신기에서 심벌정보를 전송하기 위해 펄스성형필터를 거친 신호를 디지털 믹서기를 이용하여 디지털 영역에서 반송주파수 대역으로 신호를 변조한 후 200kHz로 샘플링하는 D/A변환기를 이용하여 전송 아날로그 신호를 생성한다. 수신기에서는 수신 신호를 디지털로 처리하기 위하여 100kHz로 free running하는 A/D 변환기를 이용하여 수신 데이터를 얻는다. 수신기에서는 32심벌 길이의 프리앰블을 이용하여 프레임 동기를 찾음과 동시에 개략적인 심벌시간 동기와 위상편이를 추정한다. 추정한 위상편이값은 2차 PLL (phase-looked loop)의 초기값으로 사용하여 위상 추적을 수행하는 전송 시스템이다. 또한, 된 논문에서는 실해역 전송 시험 테이터를 통하여 조류의 변화에 의해 발생하는 Doppler 편이를 보상하기 위하여 PLL이 필수적으로 필요함을 보인다.

• KOMUNHWA
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• no.58
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• pp.85-117
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• 2001

This paper is focused on Buddhistic and ancient fortress excavated recently in Cheonnam Province. The outcome of Buddhism is researching the building place of the period of the Unified Shilla Period in Geumdunsaji(金芚寺址). This is the first research for Bud

• Journal of Ocean Engineering and Technology
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• v.17 no.4
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• pp.73-80
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• 2003

This paper presents considerations on the results of the rotating arm test, which was carried out for assessment of an hybrid navigation system for a semi-autonomous underwater vehicle. The navigation system consists of an inertial measurement unit(IMU), an ultra-short baseline(USBL) acoustic navigation sensor and a doppler velocity log(DVL) accompanying a magnetic compass. A navigational systemmodel is derived to include the scale effect and bias errors of the DVL, of which the state equation composed of the navigation states and sensor parameters are 25 in the order. The extended Kalman filter was used to propagate the error covariance, The rotating arm tests were carried out in the Ocean Engineering Basin of KRISO, to generate circular motion. The hybrid underwater navigation system shows good tracking performance against the circular planar motion. Additionally this paper checked the effects of the sampling ratio of the navigation system and the possibility of the dead reckoning with the DVL and the magnetic compass to estimate the position of the vehicle.

• 한국신재생에너지학회:학술대회논문집
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• 2011.05a
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• pp.77.2-77.2
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• 2011

고온고압에서 운전되는 분류층 석탄가스화기에서 석탄의 회성분을 용융슬래그로 원활하게 배출하는 것은 석탄가스화기의 안정적인 운전을 위하여 매우 중요하다. 본 연구에서는 분류층 석탄가스화기에서 원활한 슬래그의 배출조건을 파악하기 위해서 여러 슬래그 점도예측 모델들을 사용하여 가스화기의 운전온도 변화에 따른 슬래그의 점도변화를 해석하여 점도해석모델들의 적용성을 비교분석하였다. 본 연구에서 선정한 가스화기 설계탄의 회 성분을 토대로 슬래그의 점도를 계산한 결과 점도해석 모델별로 온도에 대한 점도 값이 매우 상이하게 예측되었다. 또한 설계탄에 대한 점도예측 모델들을 적용한 계산결과로부터 슬래그의 점도가 80 poise가 되는 온도인 $T_{80}$이 매우 높은 값으로 예측되었다. 따라서 가스화기의 운전온도에서 용융 슬래그를 원활하게 배출하기 위해서 설계탄에 Flux를 첨가하여 슬래그의 점도를 낮추어 줄 필요가 있음을 알았다. 기존의 점도예측 모델들 중에 점도 예측 값이 중간치 정도의 경향을 보이는 Hoy가 개발한 모델을 기준으로 가스화기의 적정 운전온도에서 Flux로 첨가할 석회석 양을 산출하였다. 본 슬래그 점도모델들의 적용 결과로부터 실제 가스화기의 운전이나 설계에 슬래그의 특성을 파악하여 운전조건 도출이나 해석에 활용하기 위해서는 운전예정인 탄종에 대한 점도측정 실험을 병행하여 적정한 점도 예측모델을 선정하는 것이 중요함을 알 수 있었다.

• The KSFM Journal of Fluid Machinery
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• v.12 no.5
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• pp.39-46
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• 2009

This paper outlines how the on-line performance monitoring system can be used to improve the efficiency and maintenance of the equipments. And a method of the heat rate allocation to each equipment was suggested to monitor the performance of combined cycle power plants. This calculates the expected heat rate of current conditions and compares it with actual values. Loss allocation in heat rate is reconciled by calculating the magnitude of the deficiency contributed by major components, such as the gas turbine, heat recovery steam generator, steam turbine and condenser. Expected power output is determined by a detailed model and correction curves of the plant. This simulation models are found to reproduce high accuracy in behavior of the cycle for various operating conditions, both in design and in off-design condition. Errors are lower than 2% in most cases.

• Proceedings of the IEEK Conference
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• 2008.06a
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• pp.89-90
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• 2008

We present an implementation and it's real-sea test of an underwater acoustic communication system, which allows the system to reduce complexity and increase robustness in time variant underwater environments. For easy adaptation to complicated and time-varying environments of the ocean, all-digital transmitter and receiver systems were implemented. For frame synchronization the CAZAC sequence was used, and QPSK modulation/demodulation method with carrier frequency of 25kHz and a bandwidth of 5kHz were applied to generate 10kbps transmission rate including overhead. To improve transmission quality, we used several techniques and algorithms such as adaptive beamforming, adaptive equalizer, and convolution coding/Viterbi decoding. For the verification of the system performance, measurement of BER has been done in a very shallow water with depth of 20m at JangMok, Geoje. During the experiment, image data were successfully transmitted up to about 9.6km.

• The Journal of the Acoustical Society of Korea
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• v.16 no.5
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• pp.60-67
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• 1997

the famous King Song-dok Bell which was cast in A.D. 771, during Silla dynasty has significant xize of concave cavity which acts as Helmholtz resonator on the ground. To see the effect of this cavity and the bell's internal acoustic cavity on radiating sound of bell, three dimensional measurement of internal sound field was performed. In this paper, the dtail measurement procedure and results are carefully addressed. The effect of the cavity on the radiating sound of bell is investigated using simple and physically representative model. A new size of cavity is proposed.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2003.10a
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• pp.172-175
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• 2003

This paper deals with the network interface of research and observation instruments in the oceanographic research vessel with an establishment of related database for measured information. The system is implemented to integrated communication network system which allows to effective survey by using real time observation and GUI(Graphic User Interface). The system also consists of the LAN systems and serial interface to link chemical, physical, biological and environmental relations. And, other network service and vessel data service for data communication between vessel and earth station such as INMARSAT-B, WWW service, BBS, E-Mail etc. are needed for integrated communication network system.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2003.10a
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• pp.283-286
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• 2003

In this paper, we represent an implementation of burst QPSK receiver for underwater acoustic communication. Transmitter sends 5,000 symbols at 25kHz frequency with 200 kHz D/A sampling rate. The received signal is sampled at 100 kHz. Implemented receiver acquires the frame synchronization, coarse symbol timing estimate, and coarse phase offset estimate using 32 symbol length preamble. The estimated phase offset is used to initiate of 2nd order PLL. The transmission experiment results show that PLL is a mandatory to compensate Doppler shift due to the variation of tidal current.