• 한국소음진동공학회논문집
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• 제24권6호
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• pp.462-469
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• 2014

After drilling operations at the offshore plant, crude oil is producted under high pressure. After that time, oil recovery is reduced, because the pressure of the pipe inside is low during the secondary produce. At that time injection sea water at the pipe inside through water injection pump that the device increase to recovery. A variety of mathematical analysis during the detailed design analysis was not made through the dynamics characteristic at the domestic company. 2D model has reliability of analysis results for the uncomplicated model. Also element and the node the number of significantly less than in the 3D model. So, the temporal part is very effective. In addition, depending on the quality of mesh 3D is a real model and FEM model occurs error. So, user needs a lot of skill. In this paper, a 2D finite element analysis was performed through the dynamics analysis and the study model was validated.

• Journal of Communications and Networks
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• 제5권2호
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• pp.157-166
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• 2003

This paper deals with the problem of channel identification for Single Input Multiple Output (SIMO) slow fading channels using clustering algorithms. Due to the intrinsic memory of the discrete-time model of the channel, over short observation periods, the received data vectors of the SIMO model are spread in clusters because of the AWGN noise. Each cluster is practically centered around the ideal channel output labels without noise and the noisy received vectors are distributed according to a multivariate Gaussian distribution. Starting from the Markov SIMO channel model, simultaneous maximum ikelihood estimation of the input vector and the channel coefficients reduce to one of obtaining the values of this pair that minimizes the sum of the Euclidean norms between the received and the estimated output vectors. Viterbi algorithm can be used for this purpose provided the trellis diagram of the Markov model can be labeled with the noiseless channel outputs. The problem of identification of the ideal channel outputs, which is the focus of this paper, is then equivalent to designing a Vector Quantizer (VQ) from a training set corresponding to the observed noisy channel outputs. The Linde-Buzo-Gray (LBG)-type clustering algorithms [1] could be used to obtain the noiseless channel output labels from the noisy received vectors. One problem with the use of such algorithms for blind time-varying channel identification is the codebook initialization. This paper looks at two critical issues with regards to the use of VQ for channel identification. The first has to deal with the applicability of this technique in general; we present theoretical results for the conditions under which the technique may be applicable. The second aims at overcoming the codebook initialization problem by proposing a novel approach which attempts to make the first phase of the channel estimation faster than the classical codebook initialization methods. Sample simulation results are provided confirming the effectiveness of the proposed initialization technique.

• 한국소음진동공학회논문집
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• 제18권8호
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• pp.879-885
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• 2008

A rotordynamic analysis was performed with a decant-type centrifuge, which is a kind of industrial centrifuge. The system is composed of screw rotor, bowl rotor, driving motors, gear box, and support rolling element bearings. These rotors have a rated speed of 4300 rpm, and were modeled utilizing a rotordynamic FE method for analysis, which was verified through 3-D FE analysis. Design goals are to achieve wide separation margins of lateral critical speeds, and favorable unbalance responses of the rotor in the operating range. Then, a complex analysis rotordynamic analysis of the system was carried out to evaluate its forward synchronous critical speeds and mode shapes, whirl natural frequencies, and unbalance responses under various balance grade. As a result of analysis, the rotordynamic analysis performed by separating a screw rotor and bowl rotor may cause an error in predicting critical speed of entire system. Therefore, the rotordynamic analysis of a coupled rotor combining a screw and bowl rotor must be performed in order to more accurately estimate dynamic characteristics of the decanter-type centrifuge as presented in this paper. Also, rolling element bearings with suitable stiffness should be selected to keep enough separation margin. In addition, in establishing balance grade of a screw and bowl rotor, ISO G2.5 balance grade is more recommended than ISO G6.3, in particular balancing correction of a screw rotor based on ISO G2.5 grade is strongly recommended.

• 한국전자파학회논문지
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• 제29권9호
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• pp.668-676
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• 2018

위성통신에서는 낮은 PAPR(Peak-to-Average Power Ratio), 높은 전송효율, 낮은 BER(Bit Error Rate)을 갖는 변조 기술이 요구되며, DAPSK(Differential Amplitude and Phase Shift Keying) 변조는 이러한 요구조건을 만족시킬 수 있는 기술로 평가되고 있다. 그러나 기존 DAPSK 변조는 정규적인 성좌도를 사용하기 때문에 성좌도의 안쪽 동심원에 존재하는 심볼들의 유클리디안(Euclidean) 거리가 매우 가까워서 높은 성능을 내기에 적합하지 않다. 본 논문에서는 기존 DAPSK 시스템의 성능을 개선하기 위하여 대조표 기반의 효율적인 성좌도 배치법을 사용하는 DAPSK 시스템을 제안하고 성능을 평가한다. 시뮬레이션 결과, 기존 16-DAPSK 시스템과 비교하여 효율적인 성좌도 배치법을 사용하는 16-DAPSK 시스템은 수신 심볼 검출기에 사용되는 심볼의 수 K가 2일 때, $10^{-4}$의 BER 성능을 만족시키기 위한 SNR(Signal-to-Noise Ratio)을 약 0.8 dB 개선할 수 있음을 확인하였다.

• 대한전자공학회논문지
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• 제8권2호
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• pp.24-33
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• 1971

부성특성회로로서 쌍트랜지스터 회가의 양에미터단자사이에 용량 C와 저항 R의 병렬회로를 삽입하고, 표준화주파수의 단형파전류원를 에미터·바이어스전류원으로 하여 쌍회로를 구동하면, RC병렬회로는 정부변조회로의 적분회로로서 동작시킬 수 있다. 이 적분회로와 직렬로 신호파전압원을 접속시키면 쌍회로가 구동전원의 표준화펄스에 의하여 구동될 때 마다, RC 적분회로의 적분전압과 신호파전압이 서로 비교되기 때문에 그들의 차전압에 의하여 쌍회로의 트랜지스터들 중의 어느 한 쪽이 ON되기 때문에 그 베이스결합저항단자에는 one bit의 펄스가 송출된다. 본실험에서는 극히 간소한 회로구성을 갖는 쌍트랜지스터회로에 의한 정착변조회로를 제시하고 그들의 특성을 부기하였다. 정착변조파의 품질 혹은 S/N비의 향상을 위하여 고려하여야 할 문제로서, 적분회로의 회로정수 및 양자화전압의 구동펄스의 파고와 파폭의 관계를 검토한다.

• 전기전자학회논문지
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• 제18권2호
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• pp.263-271
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• 2014

본 논문에서는 모바일 기기의 배터리 전력관리 IC(Battery Management IC)에서 전압 및 온도를 측정하여 디지털 신호로 바꾸어 주는데 필요한 시그마-델타 모듈레이터를 설계하였다. 제안하는 이산-시간 시그마-델타 모듈레이터는 2차의 단일 비트 구조이고 0.13um CMOS 공정으로 제작되었다. 모듈레이터의 소모전류를 줄이기 위하여 switched-opamp 방식을 적용하여 설계하였다. 제안하는 모듈레이터는 오버 샘플링 비율이 256 일 때 256kHz의 클락 주파수에서 83-dB의 dynamic range와 81.7dB의 peak signal-to-(noise + distortion) ratio(SNDR)를 가진다. 3.3 V의 전원전압에서 0.66 mW의 전력을 소모하며 모듈레이터 코어의 면적은 $0.425mm^2$ 이다.

• 한국항해항만학회:학술대회논문집
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• 한국항해항만학회 2006년도 International Symposium on GPS/GNSS Vol.2
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• pp.15-22
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• 2006

This paper presents a novel signal tracking algorithm for GNSS receivers using a MLE technique. In order to perform a robust signal tracking in severe signal environments, e.g., high dynamics for navigation vehicles or weak signals for indoor positioning, the MLE based signal tracking approach is adopted in the paper. With assuming white Gaussian additive noise, the cost function of MLE is expanded to the cost function of NLSE. Efficient and practical approach for Doppler frequency tracking by the MLE is derived based on the assumption of code-free signals, i.e., the cost function of the MLE for carrier Doppler tracking is used to derive a discriminator function to create error signals from incoming and reference signals. The use of the MLE method for carrier tracking makes it possible to generalize the MLE equation for arbitrary codes and modulation schemes. This is ideally suited for various GNSS signals with same structure of tracking module. This paper proposes two different types of MLE based tracking method, i.e., an iterative batch processing method and a non-iterative feed-forward processing method. The first method is derived without any limitation on time consumption, while the second method is proposed for a time limited case by using a 1st derivative of cost function, which is proportional to error signal from discriminators of conventional tracking methods. The second method can be implemented by a block diagram approach for tracking carrier phase, Doppler frequency and code phase with assuming no correlation of signal parameters. Finally, a state space form of FLL/PLL/DLL is adopted to the designed MLE based tracking algorithm for reducing noise on the estimated signal parameters.

• Safety and Health at Work
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• 제9권1호
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• pp.25-29
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• 2018

Background: The understanding of the relationship between risk perception, knowledge, and protective behaviors could play a major role in occupational risk control and management. Research exploring how workers perceive, recognize, and react to risks in different occupational settings is scarce in Thailand. The aim of this study was to assess the relationship of noise-related risk perceptions and knowledge to the use of hearing protective devices (HPDs) among sawmill workers in Thailand. Methods: Sawmill workers (n = 540) from four factories in Trang, Southern Thailand, participated in a questionnaire interview from December 2015 to January 2016. Descriptive statistics and linear regression models were used to explore the risk factors related to HPD use. Path diagram analysis was demonstrated and used to evaluate associations. Results: Risk perception was significantly correlated with HPD use (p < 0.01), HPD training (p = 0.01), and the number of years of work experience (p = 0.03). Sawmill workers were likely to use HPDs based on their risk perception and HPD training. However, HPD training was inversely correlated with age and the number of years of work experience. Conclusion: The study highlights the importance of risk perceptions and knowledge, and these factors should be emphasized in the design and implementation of any personal safety intervention program for sawmill workers.

• 한국음향학회지
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• 제31권3호
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• pp.142-150
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• 2012

도파관유한요소법 (waveguide finite element method, WFEM)은 단면의 형상이 길이방향으로 일정한 도파관 구조물의 진동을 해석하기 위한 수치해석 기법이다. 도파관유한요소법은 2차원 단면만을 FE 모델링하여 길이방향 파동 전파를 해석하므로 기존의 유한요소법에 비해 해석 모델의 크기가 작고 연산 시간이 짧다는 장점을 가진다. 본 연구에서는 기존의 도파관유한요소법을 확장하여 내부 및 외부에 유체가 채워진 도파관 구조물에 대한 진동 해석을 수행하였다. 이를 위해 내부 유체와 도파관 구조물은 WFE로, 외부 유체는 파수경계요소 (waveguide boudnary element, WBE)로 모델링하고 이들을 연성시킨 운동방정식을 제시하였다. 이 방법의 적용 예로써 내부에 물이 채워진 몰수된 파이프의 진동 및 방사 음향 파워를 해석하였다. 내부 및 외부 유체의 유/무에 따른 분산 선도와 가진점 모빌리티 (point mobility)를 구하고 유체 연성의 효과를 살펴보았다.

• 한국정보과학회논문지:시스템및이론
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• 제29권1호
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• pp.1-9
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• 2002

비사실적 렌더링 기법(NPR, Non Photorealistic Rendering)에 대한 관심이 증가하면서 여러 컴퓨터 그래픽스 연구자들에 의해서 펜화, 수채화 , 인상파 기법 등 예술적 기법들을 표현하기 위한 연구가 진행되어 오고 있다. 비사실적 렌더링 기법에서 가장 초점을 두고있는 것은 사람이 직접 그리거나 조작 한 듯한 표현을 만들어 낼 수 있으냐 하는 것이다. 본 논문은 교육이나 예술적인 표현을 위해 사용되고 있는 종이를 찢어 붙여 표현하는 모자이크 작품을 자도으로 생성해 주는 기법을 제시하였다. 이를 위해 종 이를 칼이나 가위같은 도구에 의해 잘려진 것이 아닌 자연스럽게 찢어진 종이 표현 기술, 종이의 질감 표 현 기술, 붙여지는 종이의 형태를 결정하기 위한 다각형 생성기법등을 제시한다.