• 한국소음진동공학회논문집
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• 제23권4호
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• pp.347-355
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• 2013

A damage estimation method for monopile support structure of offshore wind turbine using modal properties and committee of neural networks is presented for effective structural health monitoring. An analytical model for a monopile support structure is established, and the natural frequencies, mode shapes, and mode shape slopes for the support structure are calculated considering soil condition and added mass. The input to the neural networks consists of the modal properties and the output is composed of the stiffness indices of the support structure. Multiple neural networks are constructed and each individual network is trained independently with different initial synaptic weights. Then, the estimated stiffness indices from different neural networks are averaged. Ten damage cases are estimated using the proposed method, and the identified damage locations and severities agree reasonably well with the exact values. The accuracy of the estimation can be improved by applying the committee of neural networks which is a statistical approach averaging the damage indices in the functional space.

• 한국지반공학회논문집
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• 제19권2호
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• pp.123-133
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• 2003

사면안정 신뢰성 해석을 통해 다양한 불확실성을 체계적으로 모델링할 수 있는 실용적 인 확률통계 기법을 제시한다. 새로운 제안식은, 지반성질의 확률적 특성화를 위해 공간적 변화와 공간평균으로 인한 분산감소뿐만 아니라 통계 및 측정오차까지도 고려하였다. 지진하중의 불확실성은 인공지진파를 대량으로 생성하고 이를 응답해석에 이용함으로써 반영하였다. 예제 해석결과, 한반도와 같이 지진이 활발하지 않은 지역(중약진 지진대)에서는 일반적 수준의지반성질 변화특성화가 지진위험도 특성화만큼이나 사면 파괴 위험도와 과도한 사면변형 계산값에 영향을 준다는 결론에 도달하였다.

• 전기학회논문지
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• 제59권6호
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• pp.1120-1125
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• 2010

In the speech system, for example hearing aid as well as speech communication, speech quality is degraded by environmental noise. In this study, to enhance the speech quality which is degraded by environmental speech, we proposed an algorithm to reduce the noise and reinforce the speech. The minima controlled recursive averaging (MCRA) algorithm is used to estimate the noise spectrum and spectral weighting factor is used to reduce the noise. And partial masking effect which is one of the human hearing properties is introduced to reinforce the speech. Then we compared the waveform, spectrogram, Perceptual Evaluation of Speech Quality (PESQ) and segmental Signal to Noise Ratio (segSNR) between original speech, noisy speech, noise reduced speech and enhanced speech by proposed method. As a result, enhanced speech by proposed method is reinforced in high frequency which is degraded by noise, and PESQ, segSNR is enhanced. It means that the speech quality is enhanced.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 1993년도 춘계학술대회 논문집
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• pp.198-203
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• 1993

In this study, byusing EMAT(Electro Magnetic Acoustic Transducer) the artificial slit is installed on 12B-SUS pipe test piece. By mading 4 cycle SH-bust wave (EMA) incidence to 45 .deg. angle, the signaldata of pulse, which is recevied from EMAT translated intodigital-signal-processing-method SSP and Deconvolution method by using FACOM. Results of these indicated that (1) this method of this study shows exellent result more than Ultrasonic testing method; (2) noise is well removed by SSP using signal dataa and resolving power and S/N ratio are advanced; (3) regradless of Ultrasonic wave, whichhas properties of generalstainless steel is generated into multiscattering and reflection phenomena, the resolving power of more than two times is progressed by being translated into Decon-volution method; and (4) as addition-averaging-processing number is increaing, the resolving power and S/N ratio are improved and the satisfactory signal is obtained.

• 대한기계학회논문집A
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• 제21권11호
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• pp.1757-1764
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• 1997

The geometric and elastic models based on the unit cell have been proposed to predict the geometric characteristics and the engineering constants of plain and satin woven composites. In the geometric model, length and inclined angle of the yarn crimp and the fiber volume fraction of woven composites have been predicted. In the elastic model, the coordinate transformation has been utilized to transform the elastic constants of the yarn crimp to those of woven composites, and the effective elastic constants have been determined from the volume averaging of the constituent materials. Good correlations between the model predictions and the experimental results of carbon/epoxy and glass/epoxy woven composites have been observed. Based on the model, the effect of various geometric parameters and materials on the three-dimensional elastic properties of woven composites can be identified.

• Computers and Concrete
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• 제8권3호
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• pp.243-278
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• 2011

The paper presents simulations of the Brazilian test using two numerical models. Both models are regularized in order to obtain results independent of discretization. The first one, called gradient damage, is refined by additional averaging equation which contains gradient terms and an internal length scale as localization limiter. In the second one, called viscoplastic consistency model, the yield function depends on the viscoplastic strain rate. In this model regularization properties are governed by the assumed strain rate. The two models are implemented in the FEAP finite element package and compared in this paper. Parameter studies of the split test are performed in order to point out the features of each model.

• 한국주거학회논문집
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• 제13권4호
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• pp.27-33
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• 2002

In Gumi area, the heating and cooling loads for underground building could have not been correctly evaluated since there were no systems accurate underground temperature. For solving this problem two ways of predicting the underground temperature were propose. Firstly, it is to estimate the underground temperature of Gumi area by averaging out the underground temperature of the areas around Gumi city. However, the underground temperature data of the areas around Gumi city was only limited to 0.5m and 1.0m under the ground. Secondly, it is to calculate the underground temperature of Gumi area by using a periodic equation with variable about underground properties. Among these methods, the method of the average date was more correct, but the method of the variable date was more available.

• 한국가시화정보학회지
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• 제10권3호
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• pp.42-47
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• 2012

Experimental data for the flows in a mixing tank with a bottom agitator are useful for the validation of CFD commercial code. A hybrid volume PIV measurement technique was constructed to measure the flows inside of the mixing tank. The measurement system consists of three cameras. An agitator was installed at the bottom of the tank and it rotates clockwise and counterclockwise. Using the constructed measurement system, instantaneous vector fields were obtained. A phase averaging technique was adopted for the measured instantaneous three-dimensional velocity vector fields. Turbulent properties were evaluated from the instantaneous vector fields.

• 대한전자공학회논문지
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• 제20권4호
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• pp.41-46
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• 1983

The current-fed DC-DC converter has only one energy storage reactor in series with the input for any number of outputs and is insensitive to transformer volt-second unbalance. It is considered that these properties of the converter are considerable advantages over other maltiple-output circuits. The steady-state and dynamic characteristic and stability for the current-fed DC-DC con-verter are analyzed in detail. The analysis is carried out by the state-space averaging method for the operation with the duty ratio less than 50% and is confirmed by the experiment. From the evaluation of stability it is identified that the stability of this converter is excellent as compared with that of the conventional buck type converter.

• 한국방재학회 논문집
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• 제10권6호
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• pp.35-43
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• 2010

본 연구는 콘크리트 포장설계법에 사용되는 재료입력변수의 DB화를 염두에 두고 신뢰성 있는 콘크리트 물성 정량화 수립을 목적으로 수행되었다. 실험에 사용된 포장용 콘크리트는 화강암, 석회암, 사암의 조골재를 사용하였으며 화강암 배합의 경우 세 골재로서 자연사, 세척사, 부순모래 배합을 포함하였다. 먼저 콘크리트 강도시험을 통해 얻은 데이터를 이용하여 강도간의 상관관계 모델식을 정리하였다. 그리고 각 조골재별로 재령에 따른 압축강도, 휨강도, 쪼갬인장강도 및 탄성계수의 모델식을 제시하였다. 화강암 배합의 경우 세골재로서 사용된 자연사, 세척사, 부순모래 배합을 모두 포함한 산술평균을 적용하여 모델식을 제시하였다. 한편 쪼갬인장강도와 탄성계수는 실험방법 및 계측상 결과가 분산되는 경향이 있어서 상관관계식에서 예측된 값과 직접 구한 실험결과에 대해 산술평균을 적용후 보정하여 각 조골재별로 재령에 따른 탄성계수 및 쪼갬인장강도의 예측식을 제시하였다. 마지막으로 각 조골재 배합별 콘크리트의 포와송비 및 건조수축에 대한 기준 값을 제시하였다.