• 대한기계학회:학술대회논문집
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• 대한기계학회 2007년도 춘계학술대회A
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• pp.1383-1388
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• 2007

Accuracy and processing time are very important factors when the desired shape is fabricated with Selective Laser Sintering (SLS), one of Solid Freeform Fabrication (SFF) systems. In a conventional SLS process, laser spot size is fixed during laser exposing on the sliced figure. Therefore, it is difficult to accurately and rapidly fabricate the desired shape. In this paper, to deal with those problems an SFF system having ability of changing spot size is developed. The system provides high accuracy and optimal processing time. Specifically, a variable beam expander is employed to adjust spot size for different figures on a sliced shape. Finally, Design and performance estimation of the SFF system employing a variable beam expander are achieved and the mechanism will be addressed to measure the real spot size generated from the variable beam expander.

• 한국자동차공학회논문집
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• 제14권2호
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• pp.174-183
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• 2006

The resistance spot-welded region in most current finite element crash models is characterized as a rigid beam at the location of the welded spot. The region is modeled to fail with a failure criterion which is a function of the axial and shear load at the rigid beam. The role of this rigid beam is simply to transfer the load across the welded components. The calculation of the load acting on the rigid beam is important to evaluate the failure of the spot-weld. In this paper, numerical simulation is carried out to evaluate the calculation of the load at the rigid beam. The load calculated from the precise finite element model of the spot-welded region considering the residual stress due to the thermal history during the spot welding procedure is regarded as the reference value and the value of the load is compared with the one obtained from the spot-welded model using the rigid beam with respect to the element size, the element shape and the number of imposed constraints. Analysis results demonstrate that the load acting on the spot-welded element is correctly calculated by the change of the element shape around the welded region and the location of welded constrains. The results provide a guideline for an accurate finite element modeling of the spot-welded region in the crash analysis of vehicles.

• International Journal of Automotive Technology
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• 제7권3호
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• pp.329-336
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• 2006

The resistance spot-welded region in most current finite element crash models is characterized as a rigid beam at the location of the welded spot. The region is modeled to fail with a failure criterion which is a function of the axial and shear load at the rigid beam. The calculation of the load acting on the rigid beam is important to evaluate the failure of the spot-weld. In this paper, numerical simulation is carried out to evaluate the calculation of the load at the rigid beam. At first, the load on the spot-welded region is calculated with the precise finite element model considering the residual stress due to the thermal history during the spot welding procedure. And then, the load is compared with the one obtained from the model used in the crash analysis with respect to the element size, the element shape and the number of imposed constraints. Analysis results demonstrate that the load acting on the spot-welded element is correctly calculated by the change of the element shape around the welded region and the location of welded constrains. The results provide a guideline for an accurate finite element modeling of the spot-welded region in the crash analysis of vehicles.

• Journal of Welding and Joining
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• 제15권4호
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• pp.143-153
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• 1997

In this study, bending test was performed on the real-scale, built-up beam test model fabricated by the $CO_2$ arc spot welding to evaluate the applicability of the welding method to the production of the stiffened plate in car-carrying ship. The built-up beam models which were fixed at both ends in longitudinal direction or simply supported to the rigid foundation, depending on the restraint condition of the corresponding car decks considered, were subjected to simulated design vehicle loads or concentrated point loads. During the test, the central deflection and the longitudinal bending stresses were measured from several points on the longitudinal flange face to predict the section properties of the built-up beams. The longitudinal bending stress on each spot weld were also measured to calculate the average horizontal shear force subjected to spot welds. Test results revealed that the shear strength of spot welds with their current weld nugget size and welding pitch was adequate enough to withstand the horizontal shear forces under the design vehicle loads. Although the built-up beam fabricated by the arc spot welding was a discontinuous beam, its mechanical behavior was well explained by the continuous beam theory using the effective breadth of plate. Based on test results, the criterion for the size of spot weld of which the average shear stress might meet the allowable stress requirement of AWS Code could be established.

• 한국자기학회지
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• 제18권2호
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• pp.71-74
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• 2008

본 논문에서는 4분할 광 검출기 상에 입사된 광점의 크기에 따른 optical beam deflection방식에서의 변위 측정감도의 변화에 대해 살펴보았다. 3mW의 헬륨-네온 레이저를 사용하여 optical beam deflection방식의 광학적 변위 측정 장치를 제작하였으며 광 검출기에 도달하는 광점의 크기를 변화시켜가며 제작된 변위 측정 장비가 나타내는 변위 측정감도를 관찰하였다. 또한 광 검출기에 도달하는 optical beam power를 원형의 균일한 분포를 지닌 광점으로 설정하여 광점 크기의 변화에 따른 변위 측정감도를 계산하였다. 측정된 결과와 계산을 통하여 검출기 상에 입사하는 광점의 크기가 작을수록 변위 측정감도가 증가함을 알 수 있었으며 이는 나노미터 급의 변위측정 장비 개발에 있어 광 검출기에 도달하는 광점의 크기를 최소화함으로써 변위 측정감도를 최적화 할 수 있음을 나타낸다.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2007년도 춘계학술대회 논문집
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• pp.221-222
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• 2007

• ETRI Journal
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• 제34권4호
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• pp.613-616
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• 2012

A multi-spot-beam satellite is an attractive technique for future satellite communications since it can support high data rates by projecting high power density to each spot beam and can reuse a frequency in different cells to increase the total system capacity. In this letter, we propose a resource management technique adjusting the bandwidth of each beam to minimize the difference between the traffic demand and allocated capacity. This represents a reasonable solution for dynamic bandwidth allocation, considering a trade-off between the maximum total capacity and fairness among the spot beams with different traffic demands.

• 한국초전도ㆍ저온공학회논문지
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• 제18권4호
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• pp.40-43
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• 2016

Beam trajectory is needed to be controlled in heavy ion accelerator system. Quadruple magnets are widely used in heavy ion accelerator for focusing the transporting particles. A quadruple triplet system which consists of three consecutive quadrupoles, Q1, Q2 and Q3, is used to control beam trajectory at a focused position. Q1 and Q3 have symmetry with respect to Q2. The beam trajectory in magnet system is affected by higher order fields existed in real fields. For quadrupoles, the representation simulation of beam trajectory was carried out to study the beam trajectory and to estimate an effect of higher order field in triplet system. SCALA program was used to simulate the beam trajectory in $Opera^{TM}$. SCALA can analyze a large number of beam trajectories at the same time by adjusting the size of finite element of the emitter. With $Opera^{TM}$ and $Matlab^{TM}$ programs, the position of focused beam spot in quadruple triplet system can be increased or decreased using evolution strategy (ES) method, therefore the length of triplet system can be controlled. Finally, the quadruple triplet system with the appropriate length and expected beam spot range was suggested in this paper.

• 대한용접접합학회:학술대회논문집
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• 대한용접접합학회 2000년도 특별강연 및 추계학술발표대회 개요집
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• pp.277-278
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• 2000

• 한국전자통신학회논문지
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• 제7권3호
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• pp.573-578
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• 2012

광통신네트워크를 효율적으로 연결 시키기 위해 단순화 된 Spot-Size Converter 구조를 제안하였다. Spot-Size Converter를 설계하기 위해 수치해석으로 모드필드를 확인하고, 빔 전송법을 통해 최적화 설계를 도출하였다. 최적화 된 구조는 직선도파로와 Taper된 도파로를 조합하여 설계하였으며, 이를 시뮬레이션 한 결과 효율이 약 99%이상이 됨을 확인하였다.