• 한국가스학회지
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• 제17권1호
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• pp.19-25
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• 2013

용접에 의한 가스설비, 교량, 선박 등 강 구조물의 접합 방법은 대부분 십자형이나 T형의 필릿 용접으로 이루어지며 구조물의 형상과 용도에 따라 완전 용입 또는 불완전 용입 상태로 이루어진다. 본 연구에서는 십자형 필릿용접 구조물에 대하여 재료 두께별 용입 깊이에 따른 피로 균열 특성을 파악하였고, 그 결과로부터 무한수명 영역내에서의 안전 설계응력에 대하여 고찰하였다. 미 용입 길이가 길면 루트 부 파괴가 되어 무한 수명 영역은 작고 미 용입 길이가 짧으면 토우부 파괴가 되어 무한 수명 영역은 크게 나타났다. 3층 용접한 재료 두께 20mm의 경우가 2층 용접한 재료 두께 10mm, 15mm의 경우보다 미세한 페라이트 침상 조직을 더 많게 형성시켜 노치 인성을 증가시키므로 서 피로강도와 무한 수명을 더 향상시킨 것으로 나타났다.

• 한국음향학회지
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• 제16권4호
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• pp.57-63
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• 1997

본 논문에서는 다양한 전화선 채널에서 수집된 한국통신(KT)의 데이터베이스를 이용하여 인식 시스템의 성능을 향상시키기 위한 효율적인 특징벡터 및 전처리방법을 연구하였다. 먼저 잡음 및 주변 환경 변화에 강인한 갓으로 알려져 있는 특징벡터들을 이용한 인식 성능을 비교하고, 가중 켑스트랄 거리측정 방법을 이용하여 인식시스템의 성능 향상을 검증하였다. 실험 결과, KT의 인식 시스템에서 이용하는 LPC 켑스트럼의 경우에 비하여 PLP(Perceptual Linear Prediction)과 MFCC)Mel Frequency Cepstral Coefficient)등에 대하여 인식률이 향상되었다. 켑스트럼간의 거리측정에 있어서는 RPS(Root Power Sums)와 BPL(Band Pass Lifter)과 같은 가중 켑스트랄 거리측정 함수들이 인식성능 향상에 도움을 주었다. 스펙트럼 차감법(Spectral Subtraction)의 적용은 왜곡에 의한 효과가 커서 인식률이 저하되었지만, RASTA(RelAtive SpecTrAl) 처리방법, CMS(Cepstral Mean Subtraction), SBR(Signal Bias Removal)의 적용시에는 인식 성능 향상을 보였다. 특히, CMS 방법은 간편하면서도 높은 인식 성능 향상을 보였다. 마지막으로, CMS의 실시간 구현을 위한 방법들의 인식 성능을 비교하고, 인식 성능 저하를 막기 위한 개선책을 제시하였다.

• 한국항행학회논문지
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• 제11권1호
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• pp.9-16
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• 2007

본 논문에서는 VDL(VHF Digital Link) 모드-2에 적용되는 D8PSK 변조 방식의 비트 오율(BER)을 송 수신기간 채널 필터의 정합여부 그리고 반송파 주파수 및 위상 오프셋에 따른 영향을 분석하였다. 일반적으로 디지털 전송 방식에서는 채널 필터로 Root Raised Cosine 필터를 송신기와 수신기에 모두 적용하여 ISI 경감 효과를 얻는다. 그러나 VDL 모드-2에서는 송신기에만 Raised Cosine 필터를 사용하고 수신기에서는 저역통과필터(LPF)를 사용하기 때문에 ISI 경감 효과는 없으나 스펙트럼 특성은 더 좋아진다. 모의실험 결과 비정합 채널 필터의 사용으로 오류 확률이 약간 증가(1~2dB)함을 확인 하였고, 반송파 위상 오프셋은 비트 오율에 대해 영향이 거의 없으나, 주파수 오프셋의 영향은 심각하다는 결론을 얻었다. 그리고 협대역(Narrow Band) D8PSK 변조 신호를 디지털 방식으로 생성하고 아날로그 방식과 비교하였다.

• 한국수산과학회지
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• 제20권2호
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• pp.89-94
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• 1987

쓰시마난류역 연안 8개 지점과 30년간 $(1941\~1970)$ 표면수온과 이상수온에 대한 경험적 직교함수(EOF) 분석을 통하여 수온의 시공간적 변동을 구명하였다. 본 해역 표면수온 계절변동의 전반적 양상은 전체 변동량의 $97.2\%$를 설명하는 제 1 EOF 모드로 기술된다. 표면수온 계절변동의 연교차는 상류에서 작고 하류에서 크다. EOF 분석에 의하면, 쓰시마난류역 표면이상수온은 전해역이 동시적으로 승강하는 변동 (전체 변동량의 $40.9\%$)과 상류역과 하류역의 이상수온승강이 반대인 "교차적 변동"(전체 변동량의 $19.3\%$)의 합으로 나타낼 수 있다. 주파수 영역별로 이상수온 변동의 특성을 구명하기 위해 각 관측점의 이상 수온을 중합필터 방법으로 장주기(주기 24개월 이상), 중간주기(주기 $6\~24$개월) 및 단주기(주기 6개월 미만) 영역의 시계열로 분리한 후, 각 주기 영역 이상수온에 대한 별도의 EOF 분석 결과에 의하면, 제 1 및 제 2 EOF 모드의 공간적 분포는 모든 주기 영역에서 비슷하다.

• 한국도로학회논문집
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• 제17권6호
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• pp.11-18
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• 2015

PURPOSES : The purpose of this thesis is to evaluate the effectiveness of an active noise cancellation (ANC) system in reducing the traffic noise level against frequencies from the predictive model developed by previous research. The predictive model is based on ISO 9613-2 standards using the Noble close proximity (NCPX) method and the pass-by method. This means that the use of these standards is a powerful tool for analyzing the traffic noise level because of the strengths of these methods. Traffic noise analysis was performed based on digital signal processing (DSP) for detecting traffic noise with the pass-by method at the test site. METHODS : There are several analysis methods, which are generally divided into three different types, available to evaluate traffic noise predictive models. The first method uses the classification standard of 12 vehicle types. The second method is based on a standard of four vehicle types. The third method is founded on 5 types of vehicles, which are different from the types used by the second method. This means that the second method not only consolidates 12 vehicle types into only four types, but also that the results of the noise analysis of the total traffic volume are reflected in a comparison analysis of the three types of methods. The constant percent bandwidth (CPB) analysis was used to identify the properties of different frequencies in the frequency analysis. A-weighting was applied to the DSP and to the transformation process from analog to digital signal. The root mean squared error (RMSE) was applied to compare and evaluate the predictive model results of the three analysis methods. RESULTS : The result derived from the third method, based on the classification standard of 5 vehicle types, shows the smallest values of RMSE and max and min error. However, it does not have the reduction properties of a predictive model. To evaluate the predictive model of an ANC system, a reduction analysis of the total sound pressure level (TSPL), dB(A), was conducted. As a result, the analysis based on the third method has the smallest value of RMSE and max error. The effect of traffic noise reduction was the greatest value of the types of analysis in this research. CONCLUSIONS : From the results of the error analysis, the application method for categorizing vehicle types related to the 12-vehicle classification based on previous research is appropriate to the ANC system. However, the performance of a predictive model on an ANC system is up to a value of traffic noise reduction. By the same token, the most appropriate method that influences the maximum reduction effect is found in the third method of traffic analysis. This method has a value of traffic noise reduction of 31.28 dB(A). In conclusion, research for detecting the friction noise between a tire and the road surface for the 12 vehicle types needs to be conducted to authentically demonstrate an ANC system in the Republic of Korea.

• 대한전기학회논문지:전기기기및에너지변환시스템부문B
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• 제52권5호
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• pp.211-220
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• 2003

The control method of programmable dynamometer for overall test of machine is to load the reference torque which is computed from torque transducer into motor under test. But the torque information detected from torque transducer have a lot of noise when the load torque of meter is a small quantity or changing. Thus, torque transducer must have a low pass filter to detect a definite torque information. But The torque delay generated by filter with torque transducer occur a torque trouble for meter torque of programmable dynamometer. Therefore, this kind of system could not perform dynamic and nonlinear load. In this paper, the control method using the load torque observer without a measure for torque transducer is Proposed. The proposed system improved the problem of the torque measuring delay with torque transducer, and the load torque is estimated by the minimal order state observer based on the torque component of the vector control induction meter. Therefore, the torque controller is not affected by a load torque disturbance. To verify a superiority of the proposed control algorithm, the analysis for a root locus of a conventional control method and the proposed one, and simulation and experiment is performed. Therefore we hope to be extended in industrial application.

• Nuclear Engineering and Technology
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• 제31권2호
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• pp.192-201
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• 1999

This paper proposes an improved signal processing strategy for accurate feedwater flowrate estimation in nuclear power plants. It is generally known that ∼2% thermal power errors occur due to fouling Phenomena in feedwater flowmeters. In the strategy Proposed, the noises included in feedwater flowrate signal are classified into rapidly varying noises and gradually varying noises according to the characteristics in a frequency domain. The estimation precision is enhanced by introducing a low pass filter with the wavelet analysis against rapidly varying noises, and an autoassociative neural network which takes charge of the correction of only gradually varying noises. The modified multivariate stratification sampling using the concept of time stratification and MAXIMIN criteria is developed to overcome the shortcoming of a general random sampling. In addition the multi-stage robust training method is developed to increase the quality and reliability of training signals. Some validations using the simulated data from a micro-simulator were carried out. In the validation tests, the proposed methodology removed both rapidly varying noises and gradually varying noises respectively in each de-noising step, and 5.54% root mean square errors of initial noisy signals were decreased to 0.674% after de-noising. These results indicate that it is possible to estimate the reactor thermal power more elaborately by adopting this strategy.

• 전기학회논문지
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• 제56권3호
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• pp.632-640
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• 2007

The low force estimation method of skeletal muscle was proposed by using ICA(independent component analysis) and neuro-transmission model. An EMG decomposition is the procedure by which the signal is classified into its constituent MUAP(motor unit action potential). The force index of electromyography was due to the generation of MUAP. To estimate low force, current analysis technique, such as RMS(root mean square) and MAV(mean absolute value), have not been shown to provide direct measures of the number and timing of motoneurons firing or their firing frequencies, but are used due to lack of other options. In this paper, the method based on ICA and chemical signal transmission mechanism from neuron to muscle was proposed. The force generation model consists of two linear, first-order low pass filters separated by a static non-linearity. The model takes a modulated IPI(inter pulse interval) as input and produces isometric force as output. Both the step and random train were applied to the neuro-transmission model. As a results, the ICA has shown remarkable enhancement by finding a hidden MAUP from the original superimposed EMG signal and estimating accurate IPI. And the proposed estimation technique shows good agreements with the low force measured comparing with RMS and MAV method to the input patterns.

• Journal of Welding and Joining
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• 제21권3호
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• pp.85-91
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• 2003

Narrow gap welding has many advantages over conventional V-grooved butt welding such as high productivity, small deformation and improved mechanical property of joints. With narrower groove gap, less arc heat input is expected will all the other advantages of narrow gap welding. The main defects of narrow gap welding include the lack of root fusion, convex bead surface and irregular surface, all of which have negative effects on the next welding pass. This paper suggests an up-and-down torch oscillation for ultra narrow gap welding with gap size of 5mm and investigates the proper welding conditions to fulfill the reliable and high welding quality. First, GMA welding model was suggested for ultra narrow gap welding system with Halmoy's model referenced for wire melting modeling. And the arc length in ultra narrow gap was defined. Secondly, based on the experimental results of up-and-down torch oscillation welding, phase shift of current and wire extension length were simulated for varying oscillation frequency to show that weld the bead shape in ultra narrow gap welding can be predicted. As the result, it was confirmed that reliable weld quality in ultra narrow gap welding can be achieved with up-and-down torch oscillation above 15Hz due to its ability to provide uniform heat input along the sidewall of gap.

• Journal of Welding and Joining
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• 제32권5호
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• pp.7-12
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• 2014

In this study, API-X100 steel pipes were welded with various kinds of welding wires in the laser-arc hybrid welding process. 10kW fiber laser source was combined to MIG arc welding process. API X-100 steel of base metal was of 16.9mm thickness, and butt welding applied. After welding, full penetration weld was acquired by 1-pass welding. A root porosity and the lack of fusion was observed in some welding conditions. By the mixing the melted wire, acicular ferrite, polygonal ferrite, pro-eutectoid, aligned side plate, and bainite structures were observed at the weld metal. From the observation of hybrid weld, unmixed zone had more Ni and Cr. The unmixed zone was a 1/3 area of the weld metal. As the mechanical test of the hybrid welding, tensile test and impact test applied. From the tensile test, all of the welding except SM70S was fractured at the base metal. The result of the impact test at -30 degree C led 60J~320J of the absorbed energy. The result of the low-absorbed energy might be from the coarse equiaxed structures of the weld metal.