• Smart Structures and Systems
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• 제1권2호
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• pp.121-140
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• 2005

This paper presents a systematic investigation of the effect of sensor location on the data quality and subsequently, on the effectiveness of machine health monitoring. Based on an analysis of the signal propagation process from the defect location to the sensor, numerical simulations using finite element modeling were conducted on a bearing test bed to determine the signal strength at several representative sensor locations. The results showed that placing sensors closely to the machine component being monitored is critical to achieving high signal-to-noise ratio, thus improving the data quality. Using millimeter-sized piezoceramic plates, the obtained results were evaluated experimentally. A comparison with a set of commercial vibration sensors verified the developed structural dynamics-based sensor placement strategy. It further demonstrated that the proposed shock wave-based sensing technique provided an effective alternative to vibration measurement, while requiring less space for sensor installation.

• 품질경영학회지
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• 제33권2호
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• pp.87-99
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• 2005

Quality cost system is a key element of an organization's quality program. In this paper we suggest a quality cost evaluation system for aerospace industries considering the aircraft development and manufacturing processes. To reduce the cost of poor quality, we present an extended quality cost concept and detailed quality cost categories. The extended quality cost includes prevention cost, appraisal cost, failure cost, and the cost hidden in the processes. The evaluation of this extended quality cost will be helpful in identifying critical quality issues in aerospace industries.

• 대한기계학회논문집
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• 제19권3호
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• pp.647-660
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• 1995

Given the tetrahedron-based octree approximation of a solid as described in part(I) of this thesis, in this part(II) a systematic procedure of 'boundary moving' is developed for the fully automatic generation of 3D finite element meshes. The algorithm moves some vertices of the octants near the boundary onto the exact surface of a solid without transforming the topology of octree leaf elements. As a result, the inner octree leaf elements can be used as exact tetrahedral finite element meshes. In addition, as a quality measure of a tetrahedral element, 'shape value' is propopsed and used for the generation of better finite elements during the boundary moving process.

• 소성∙가공
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• 제13권2호
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• pp.115-121
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• 2004

Hemming is the last farming process in stamping and determines external quality of automotive outer panels. Few numerical approaches using 3-dimensional finite element model have been applied to a hemming process due to small element size which is needed to express the bending behavior of the sheet around small die comer and comparatively big model size of automotive opening parts, such as side door, back door and trunk lid etc In this study, part model assembling method is suggested and applied to the 3-dimensional finite element simulation of flanging and hemming process far an automotive front hood.

• 오토저널
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• 제10권6호
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• pp.54-60
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• 1988

During recent years, a great deal of interest has emerged on the use of adaptive approaches and a posteriori estimates in finite element method. The results are intended to be used to improve the quality of finite element solution by changing the location of the nodes within a fixed number of degrees of freedom-so called r method-, and by increasing the order of polynomial approximation with the new degrees of freedom-p method. This paper deals with error analysis that contains the basic theory and method of deriving error estimates and adaptive processes applied to finite element solutions underlying the rpm method that is the combination of r and p method of finite element. It is shown that we can obtain more accurate solution by applying the method to the 2-dimensional heat transfer problem.

• 품질경영학회지
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• 제46권3호
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• pp.641-650
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• 2018

Purpose: This article provides a cause of breakage and a method for improving reliability of the headlight system installed in the main battle tank K2. Method: The natural frequency of the headlight system is estimated by using the finite element method. In addition, the allowable stress level under the severe conditions is provided through vibration test of a single item and a system level. Results: Based on the finite element analysis and the vibration test in the frequency domain, the lamp of the left headlight system fails by the resonance effect. Conclusion: For improving the reliability of the headlight system, the thickness of protector frame is increased to avoid the resonance effect.

• Advances in environmental research
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• 제4권2호
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• pp.83-104
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• 2015

Air Quality Index (AQI) is a pointer to broadcast short term air quality. This paper presents one day ahead AQI forecasting on seasonal basis for three major cities in Maharashtra State, India by using Artificial Neural Networks (ANN) and Genetic Programming (GP). The meteorological observations & previous AQI from 2005-2008 are used to predict next day's AQI. It was observed that GP captures the phenomenon better than ANN and could also follow the peak values better than ANN. The overall performance of GP seems better as compared to ANN. Stochastic nature of the input parameters and the possibility of auto-correlation might have introduced time lag and subsequent errors in predictions. Spectral Analysis (SA) was used for characterization of the error introduced. Correlational dependency (serial dependency) was calculated for all 24 models prepared on seasonal basis. Particular lags (k) in all the models were removed by differencing the series, that is converting each i'th element of the series into its difference from the (i-k)"th element. New time series is generated for all seasonal models in synchronization with the original time line & evaluated using ANN and GP. The statistical analysis and comparison of GP and ANN models has been done. We have proposed a promising approach of use of GP coupled with SA for real time prediction of seasonal multicity AQI.

• 한국건설관리학회논문집
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• 제1권2호
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• pp.53-62
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• 2000

콘크리트는 콘크리트 구조 건물의 주요 구조 재료로서, 그 재료적 설계 물성은 생산ㆍ준비$\cdot$타설$\cdot$보양$\cdot$마감 및 보수/보강 등 여러 단계에 걸친 복합적 프로세스에 의해서 결정된다. 또한 콘크리트는 주요 설계 물성이 상당한 시일이 경과한 후 달성되는 재료적 특성으로 인해서 결함을 발견하기에 상당한 어려움이 있으며 결함을 수정하기 위해서 많은 비용과시간이 필요하다. 따라서 콘크리트의 재료적 설계 물성을 확보하기 위해서는 위에서 설명한 각 단계별로 소요 성능을 측정하고 선행 단계에서의 결함이 후속 단계로 전파되지 않도록 함으로써 최종 단계 프로세스가 완료되면 전체 설계 물성을 확보할 수 있도록 하기 위한 효율적인 관리 절차가 필수적이다. 따라서, 본 연구에서는 첫째 기존 품질관리 절차서를 분석하고, 둘째 분석 결과에 따라 새로운 다중 코드를 이용한 맞춤식 체크 리스트를 제시하며, 셋째 맞춤식 체크리스트를 활용함으로써 콘크리트 부재 유지관리시 유용하게 사용될 콘크리트 이력데이터 구축방법을 제시하고, 마지막으로 맞춤식 체크리스트를 현업에 적용하고 적용성을 보완한 개선된 체크리스트를 제시하였다.

• 대한공간정보학회지
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• 제4권2호
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• pp.123-136
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• 1996

최근 날로 정보기술이 발전하고 사회가 다양화되면서 다양한 데이터를 공유하기 위한 데이터 표준화에 대한 요구가 증대되고 있어 이와 같은 표준화를 위해 우선적으로 지형공간데 이터의 정확성과 신뢰도를 나타내는 데이터품질의 정의 및 평가과정에 관한 연구가 요망되고 있다. 본 연구에서는 세계 각 국에서 채택하고 있는 대표적인 데이터 품질요소의 정의 및 평가방법을 비교 고찰하여 다음과 같은 결과를 얻었다. 첫째, 우리나라의 국가지형공간데이터 교환포멧의 표준내에 데이터의 품질을 평가하기 위한 요소의 정의는 평가기준이 명확한 ISO/TC211의 안을 수용하는 것이 바람직하다고 판단된다. 둘째, 본 연구를 통하여 품질평가요소에 따른 보다 합리적인 지형공간정보 데이터의 품질평가과정을 제시하였으며, 이를 KSDTS에도 적용할 것과 데이터 품질평가결과의 보고형식 등을 더욱 더 명확히 하여 국립지리원의 수치지도작성 규칙 등에도 포함시키는 것을 제안하고자 한다. 셋째, 다양한 sampling방법에 관한 연구 및 우리나라에 적합한 품질허용기준(AQL)의 정립과 대량의 데이터품질을 신속하게 자동 평가할 수 있는 컴퓨터 프로그램 작성 등이 요망된다.

• 한국자동차공학회논문집
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• 제23권1호
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• pp.65-73
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• 2015

The ride quality has become a key component of not only design but car selling as the technology developed and the requirement of passengers grew up. Thus car industry invests lots of time and cost for the higher ride quality. The evaluation of the ride quality mainly is expressed by subjective element that drivers felt. In this paper, instead of the original transfer path analysis method, relatively new methods such as OPAX(Operational path analysis with eXogeneous inputs) and OTPA(operational transfer path analysis) are used for analyzing the main hindrance element of ride quality. With those new method, contribution rate of all paths that the vibration propagate along analyzed after driving test on the roads having different characteristic. The comprehensive hindrance elements of ride quality are deduced from the contribution rate and the improve experiment by changing one of hindrance elements for higher ride quality.