• 대한기계학회:학술대회논문집
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• 대한기계학회 2003년도 추계학술대회
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• pp.1115-1120
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• 2003

The recent tendency in the automobile industries is toward light weighting vehicle body to improve the problems by environmental pollution as well as improving fuel cost. The effective way to reduce the weight of vehicle body seems to be application of new materials for body structure and such trend is remarkable. Among the various materials for vehicle body, stainless steel sheet (for example, 301L and 304L), TRIP steel and cold rolled steel sheets are under the interests. However, in order to guarantee reliability of new material and to establish the long life design criteria of body structure, it is important and require condition to assess spot weldability of them and fatigue strength of spot welded lap joints which were fabricated under optimized spot welding condition. And, recently, a new issue in the design of the spot welded structure is to predict economically fatigue design criterion without additional fatigue tests. In general, for fatigue design of the spot-welded thin sheet structure, additional fatigue tests according to the welding condition, material, joint type, and fatigue loading condition are generally required. This indicates that much cost and time for it should be consumed. Therefore, in this paper, the maximum stresses at nugget edge of spot weld were calculated through nonlinear finite element analysis first. And next, obtained the ${\Delta}P-N_{f}$ relation through the actual fatigue tests on spot welded lap joints of similar and dissimilar high strength steel sheets. And then, the ${\Delta}P-N_{f}$ relation was rearranged in the ${\Delta}{\sigma}-N_{f}$ relation. From this ${\Delta}{\sigma}-N_{f}$ relation, developed the fatigue design technology for spot welded lap joints of them welded using the optimized welding conditions.

• 품질경영학회지
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• 제47권4호
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• pp.895-910
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• 2019

Purpose: The purpose of this study is to lighten the APU (Auxiliary Power Unit) structure of the KAAV (Korea Assault Amphibious Vehicle) through structural analysis. Methods: Commercially-available program (MIDAS.NFX) was used for finite element analysis. Frequency response analysis was performed through linear static and mode analyses to verify the structural stability according to the change of the structural materials. Results: Numerical simulation (linear static, mode and frequency response analyses) results showed that the safety factor of the APU was over 1.5 even under the worst case conditions. The APU made by aluminum structures was expected to be available in the military field, since every requirements in the KDS (Korean Defense Specifications) was fulfilled during the various tests and evaluations. Conclusion: The structural analysis was verified that the structural stability of the APU structure of the KAAV after change of the structural material.

• Journal of Astronomy and Space Sciences
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• 제31권4호
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• pp.341-346
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• 2014

A prototype of the GMT FSM has been developed to acquire and to enhance the key technology - mirror fabrication and tip-tilt actuation. The ellipsoidal off-axis mirror has been designed, analyzed, and fabricated from light-weighting to grinding, polishing, and figuring of the mirror surface. The mirror was tested by using an interferometer together with CGHs, which revealed the surface error of 13.7 nm rms in the diameter of 1030 mm. The SCOTS test was employed to independently validate the test results. It measured the surface error to be 17.4 nm rms in the diameter of 1010 mm. Both tests show the optical surface of the FSMP mirror within the required value of 20 nm rms surface error.

• 한국정보통신학회논문지
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• 제9권7호
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• pp.1479-1484
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• 2005

본 논문은 이동로봇을 위한 위치 및 물체인식용 지능형 센서 제어 시스템에 대해 기술한다. 개발된 센서시스템은 저가의 광 PSD(Position sensitive detector)를 사용하였다. PSD센서는 저가이고, 가볍다는 장점이 있지만 많은 noise를 갖고 있다. 본 논문에서는 이러한 noise를 효과적으로 제거하기 위해 hardware filter와 software filter를 제안한다. 또한 선분기반 map building을 위해 개선된 Hough transform 알고리즘과 이동로봇의 실내 환경에서의 navigation 알고리즘을 제안한다. 개발된 시스템은 실험을 통해 증명하였다.

• Communications for Statistical Applications and Methods
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• 제17권1호
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• pp.9-16
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• 2010

일반적으로 공간모집단에서의 표본설계에 대한 연구는 가정된 종속관계에 대해 설정된 모형 하에서 이루어지며, 이때 추정하고자 하는 모수들은 평균, 비율 그리고 면적 등이 될 수 있다. 본 연구에서는 연구대상이 지리적 조건이나, 모양에 의해 층화된 모집단에 대해 영역을 추정하고자 할 때, 공간적으로 관련이 있는 보조변수를 활용하여 가중치 조정방법을 제시하고, 이에 대한 효율성을 검증하고자 한다. 즉, 공간 추정량에 대한 보정추정과정을 적용하여 가중치 조정을 통한 추정량을 개선하고, 수치적 예제를 통해 제안된 추정량이 효율적임을 제시하였다.

• Journal of Welding and Joining
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• 제33권6호
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• pp.21-26
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• 2015

Recently, application of UHSS(Ultra High Strength Steels) whose tensile strength is over 1000MPa to car body structure are growing due to great needs for light weighting and improved crash worthiness. However, their poor weldability is one of obstacles to expand selecting to car body. In this study, effect of Phosphorus contents on resistance spot weldability of high elongation DP980 steel whose Si content is over 1% was investigated. The cross tension strength (CTS) was decreased showing partial interface fracture as Phosphorus content increase because of solidification segregation of Phosphorus. In order to improve resistance spot weldability by modification of welding condition, in-situ post-weld heating pulse was introduced after main pulse. The optimum cooling time between main and post pulse and post-pulse current condtion were determined through FEM welding simulation and DOE tests. The CTS was increased about 1.5 time showing plug fracture. The decrease of Phosphorus segregation was found to be a major reason for weld ductility and CTS improvement.

• 한국콘텐츠학회논문지
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• 제11권9호
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• pp.129-136
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• 2011

본 논문에서는 생활가전기기와 정보통신가전기기의 다양한 외형디자인에 응용할 수 있는 옻과 숯을 이용한 친환경 소재의 전자파 차폐 물질을 제시하였다. 제시된 전자파 차폐 물질은 전자레인지에서 사용되는 2.45 GHz에서는 약 96.3%, 이동전화의 사용 주파수 900 MHz, 1.8 GHz에서 각각 97.2%, 98.7%의 전자파를 차폐하였다. 기존에는 전자레인지와 이동전화에서는 방출되는 강한 전자파를 차단하기 위해 금속 재질이나 플라스틱 표면에 도전성 재료를 피복하는 방법이 이용되고 있으나, 친환경 소재인 옻과 숯을 활용함으로써 금속 재질을 탈피하여 제품의 경량화, 내열성, 내마모성, 내식성을 이룰 수 있는 한편, 부드럽고 친근한 이미지의 제품디자인이 가능하다.

• 제어로봇시스템학회논문지
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• 제6권3호
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• pp.273-283
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• 2000

In this paper we suggest an optimal design method of Fuzzy-Neural Networks(FNN) model for complex and nonlinear systems. The FNNs use the simplified inference as fuzzy inference method and Error Back Propagation Algorithm as learning rule. And we use a HCM(Hard C-Means) Clustering Algorithm to find initial parameters of the membership function. The parameters such as parameters of membership functions learning rates and momentum weighted value is proposed to achieve a sound balance between approximation and generalization abilities of the model. According to selection and adjustment of a weighting factor of an aggregate objective function which depends on the number of data and a certain degree of nonlinearity (distribution of I/O data we show that it is available and effective to design and optimal FNN model structure with a mutual balance and dependency between approximation and generalization abilities. This methodology sheds light on the role and impact of different parameters of the model on its performance (especially the mapping and predicting capabilities of the rule based computing). To evaluate the performance of the proposed model we use the time series data for gas furnace the data of sewage treatment process and traffic route choice process.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제9권9호
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• pp.3594-3610
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• 2015

Recent advancements in broadband wireless communication technologies enable mobile users to receive video streaming services with various smart devices. The long term evolution (LTE) network provides high bandwidth and low latency for several emerging mobile applications. This paper proposes the buffer aware scheduling (BAS) approach to schedule the downlink video traffic in LTE network. The proposed BAS scheme applies the weighting function to heuristically adjust the scheduling priority by considering the buffer status and channel condition of UE so as to reduce the time that UE stays in the connected state without receiving data. Both of 1080P and 2160P resolution video streaming sources were applied for exhaustive simulations to examine the performance of the proposed scheme by comparing to that of the fair bandwidth (FB) and the best channel quality indicator (CQI) schemes. The simulation results indicate that the proposed BAS scheme not only achieves better performance in power saving, streaming delivery time, and throughput than the FB scheme while maintaining the similar performance as the best CQI scheme in light traffic load. Specifically, the proposed scheme reduces streaming delivery time and generates less signaling overhead than the best CQI scheme when the traffic load is heavy.

• 자동차안전학회지
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• 제11권4호
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• pp.57-62
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• 2019

The seat back frame of the vehicle is subjected to load on the passenger behavior. Because of steel material, it is necessary to optimize the frame considering lightweight and safety. In this paper, finite element analysis is used for the optimal design of the seat back frame. First, a lightweight material is applied to reduce the weight of the seat back frame. Secondly, the design position of the pipe part fastened in the seat back frame was selected by considering the strength against the load generated by the occupant. Third, the shape of the side frame was derived by performing the phase optimization analysis for the AFT load condition. And we have compared the initial model with the optimal model to verify the light weighting and safety. As a result, the optimal design model of the seat back frame satisfying the weight reduction and safety has been proposed.