• 한국신뢰성학회지:신뢰성응용연구
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• 제17권4호
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• pp.280-288
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• 2017

Purpose: PBA buried in underwater requires high reliability because of its mission critical characteristic and harsh operational environment during its life cycle. Therefore, various reliability improvement activities are necessary. The defect on PBA manufacturing process have been studied, as a result, many activities and standards have been presented. However, there are less studies regarding failure pattern on physical features based on design. In this paper, we studied a possible failure patten based on physical features that is related with manufacturing process of PBA. And reliability improvement design based on PoF (Physical of Failure) were intruduced in this paper. Methods: A reliability prediction simulation were performed on the components A and B of the H system using Sherlock Software which is a PoF commercial tool from DFR solution. Solder fatigue and PTH fatigue analysis based on thermal cycling profiles and random vibration was analyzed on three earthquake response spectrum. Result: It was validated that life time and reliability improvement design through solder fatigue and PTH fatigue analysis in case of component. For compoenet B, random vibration fatigue was additionally analyzed and validated reliability for earthquakes profile. Conclusion: In design stage prior to manufacturing, PoF can be analyzed, and it is possible to make a reliability improvement/validated design using design data. This study can be applied in every design step and contribute to make more stable development product.

• 한국포장학회지
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• 제29권3호
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• pp.223-228
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• 2023

Sustainable energy supplies without the recharging and replacement of the charge storage device have become increasingly important. Among various energy harvesters, the triboelectric nanogenerator (TENG) has attracted considerable attention due to its high instantaneous output power, broad selection of available materials, eco-friendly and inexpensive fabrication process, and various working modes customized for target applications. In this study, the amount of voltage and current generated was measured by applying the PSD profile random vibration test of the electronic vibration tester and ISTA 3A according to the time of Anodized Aluminum Oxide (AAO) pore widening of the manufactured TENG device Teflon and AAO. The discharge and charging tests of the integrated module during the random simulated transport environment and the recognition distance of RFID were measured while agricultural products (onion) were loaded into the returnable folding plastic box. As a result, it was found that AAO alumina etching processing time to maximize TENG performance was optimal at 31 min in terms of voltage and current generation, and the integrated module applied with the TENG module showed a charging effect even during the continuous use of RFID, so the voltage was kept constant without discharge. In addition, the RFID recognition distance of the integrated module was measured as a maximum of 1.4 m. Therefore, it was found that the surface condition of AAO, a TENG element, has a great influence on the power generation of the integrated module, and due to the characteristics of TENG, the power generation increases as the surface dries, so it is judged that the power generation can be increased if the surface drying treatment (ozone treatment, etc.) of AAO is applied in the future.

• Earthquakes and Structures
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• 제13권1호
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• pp.79-87
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• 2017

Seismic analysis of local site conditions is fundamental for a reliable site seismic hazard assessment. It plays a major role in mitigation of seismic damage potential through the prediction of surface ground motion in terms of amplitude, frequency content and duration. Such analysis requires the determination of the transfer function, which is a simple tool for characterizing a soil profile by estimating its vibration frequencies and its amplification potential. In this study, numerical simulations are carried out and are then combined with a statistical study to allow the characterization of design sites classified by the Algerian Building Seismic Code (RPA99, ver 2003), by average transfer functions. The mean transfer functions are thereafter used to compute RPA99 average site factors. In this regard, coming up seismic fields are simulated based on Power Spectral Density Functions (PSDF) defined at the rock basement. Results are also used to compute average site factor where, actual and synthetic time histories are introduced. In absence of measurement data, it is found that the proposed approach can be used for a better soil characterization.

• 한국소음진동공학회논문집
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• 제23권4호
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• pp.365-371
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• 2013

The purpose of this study is to develop a sound absorbing material for indoor which manufactured by a clay and binding material. The seven kind of sound absorbing specimens which sintered through a mold process at high temperature were manufactured for the purpose of testing sound absorption performance. The random and normal sound absorption coefficients were measured for the sintered clay sound absorbing specimens with different particle size, density and mixture ratio. From the experimental results, it was found that its particle size was closely related to the sound absorption performance. It was shown that the sintered clay sound absorbing specimen had the sound absorption properties of a fiber-type or a resonance-type sound absorbing material depending on the particle size.

• Wind and Structures
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• 제27권6호
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• pp.399-416
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• 2018

In order to reveal the independent relationship between track irregularity and wind loads, the stochastic characteristics of train-bridge coupling systems subjected to wind loads were investigated by the multi-sample calculation. The vehicle was selected as 23 degrees of freedom dynamical model, and the bridge was described by three-dimensional finite element model. It was assumed that the wind loads were random processes with strong spatial correlation, while the track irregularities were stationary random ones. As a case study, a high-speed train running on a cable-stayed bridge subjected to wind loads was studied. The effect of rail irregularities was deemed to be independent of the effect of wind excitations on the coupling system in the same wind circumstance for the same project, leading to the conclusion that the effect of wind loads and moving vehicle could be calculated separately. The variance results of the stochastic responses of vehicle-bridge coupling system under the action of wind loads and rail irregularities together were equivalent to the sum of the variance of the responses induced by each excitation. Therefore, when one of the input excitations is different, only the effect of changed loads needs to be assessed. Moreover, the new calculated results were combined with the effect of unchanged loads to present the stochastic response of coupling system subjected to the different excitations, reducing the cost of computations. The stochastic characteristics, the CFD (cumulative distribution function) of the coupling system with different wind velocities, vehicle speed, and vehicle marshalling were studied likewise.

• 소음진동
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• 제8권4호
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• pp.706-714
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• 1998

The purpose of this study is to analyse the main factors and attributes of psychological evaluation to noise. For this purpose, a psycho-acustic experiment was conducted by using the method of rating scale. 52 subjects were participated in the experiment, 20 stimuli were presented to subjects in random order with 23 adjectives. As a result of factor analysis, it was found that the primary factors for evaluating the quality of noise subjectively are four factors of unpleasantness, intensity, irregularity, and sharpness. And, as a result of MDPREF(multi-dimensional analysis of preference data), it was found that the noise sources including the factors of unpleasantness, intensity, and irregularity are related to the sounds of hammering in construction field, car horn, road traffic, idling of car, and printing by computer printer, and the factor of sharpness are the sounds of car siren, claps of thunder, car horn, and snowstorm etc.

• Journal of electromagnetic engineering and science
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• 제8권1호
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• pp.6-11
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• 2008

Advances in low power design open the possibility to harvest energy from the environment to power electronic circuits. Electrical energy can be harvested from piezoelectric transducer. Piezoelectric materials can be used as mechanisms to transfer mechanical energy usually vibrating system into electrical energy that can be stored and used to power other devices. Micro- to milli-watts power can be generated from vibrating system. We developed definitive and analytical models to predict the power generated from a cantilever beam attached with piezoelectric transducer. Analytical models are pin-force method, enhanced pin-force method and Euler-Bernoulli method. Harmonic oscillations and random noise will be the two different forcing functions used to drive each system. It has been selected the best model for generating electric power based upon the analytical results obtained.

• 한국ITS학회 논문지
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• 제9권5호
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• pp.87-95
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• 2010

도시의 많은 교량 구조물은 내구연한 및 노후 상태에 따라 외형적 변형이 발생하고, 지진과 태풍 등은 노후 시설물의 변형을 더욱 악화시키고 있다. 불규칙하고 미세한 점진적 외형 변형은 육안으로 확인하기 어렵고, 시설물의 성능을 저하시키게 된다. 따라서 최근에 교량 구조물의 이상 거동을 실시간의 무선 방식으로 검지하는 기술이 연구되고 있다. 본 연구는 자이로스코프를 이용하여 구조물의 미소한 물리적 변화량을 실시간으로 측정하는 변위측정모듈을 개발하였다. 개발된 계측 모듈의 성능은 시뮬레이션 실험을 통해 검증하였다.

• 대한통합의학회지
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• 제1권3호
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• pp.63-78
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• 2013

PURPOSE : This study aims to investigate the positive correlation in pre-post test design between squat exercise on different baseform and the static/dynamic balance ability enhancement in adults. METHOD : This clinical study was designed into three different random-sampling adult groups (flat, balanced, vibration exercise device) and performed squat exercise. The static/dynamic balance ability was measured prior to the intervention and vice-versa. Balance was examined using the balance master 7.0 version systems. RESULT : 1) After the intervention, the controlled mat group in mCTSIB has showned the minimal mean value and the variation regards as acceptable by statistic value. 2) After the intervention, The mean value of LOS shows the minimal average variation in Randomised Trials, but the other two trials shows the maximal fluctuation. The difference variation regards as acceptable statistic value. 3)After the intervention, the mean value of mat group measrued as the maximal results, the difference variation regards as acceptable statistic value. 4)The striking correlation difference at mCTSIB has found in the vibration device exercise group, but LOS and Rhythmic W-S showed the correaltion in Mat group. CONCLUSION : The study found the positive correlation that enhanced balance ability on the different dynamic baseform squat exercise than static baseform environment. The significant difference found the balance pad squat effects on developing balance ability and the correlationship regards as statistically significant value.

• 한국항행학회논문지
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• 제27권1호
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• pp.111-118
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• 2023

스마트팩토리의 구축을 위해서는 제조환경에서 여러 센서 및 기기 등을 연결하여 데이터를 수집하고, 데이터 분석을 통해 생산설비 등의 장애를 진단하거나 예측하여야 한다. 본 논문에서는 공작기계에서 제품을 가공하기 위해 사용되는 절삭용 인서트의 잔여 유효 수명을 예측하기 위해 진동 신호를 기반으로 한 가중화 k-최근접이웃(Weighted k-NN) 알고리즘, 의사결정나무(Decision Tree), 서포트벡터회귀(SVM), XGBoost, 랜덤포레스트(Random forest), 1차원 합성곱신경망(1D-CNN), 그리고 진동 신호를 FFT한 주파수 스펙트럼에 대해 알아보았다. 연구결과, 주파수 스펙트럼으로는 잔여 유효수명의 정확한 예측에 대해서는 신빙성있는 기준을 제공하지 못한다는 것을 알수 있었고, 예측 모델 중 가중화 k-최근접이웃 알고리즘이 MAE가 0.0013, MSE가 0.004, RMSE가 0.0192로 가장 우수한 성능을 나타내었다. 이는 가중화 k-최근접이웃 알고리즘에 의해 예측되는 인서트의 잔여 유효 수명의 오차가 0.001초 수준으로 평가되어, 실제 산업현장에 적용이 가능한 수준으로 사료된다.