• Journal of Mechanical Science and Technology
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• 제16권9호
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• pp.1054-1064
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• 2002

Numerical prediction of welding-induced residual stresses using the finite element method has been a common practice in the development or refinement of welded product designs. Various researchers have studied several thermal models associated with the welding process. Among these thermal models, ramp heat input and double-ellipsoid moving source have been investigated. These heat-source models predict the temperature fields and history with or without accuracy. However, these models can predict the thermal characteristics of the welding process that influence the formation of the inherent plastic strains, which ultimately determines the final state of residual stresses in the weldment. The magnitude and distribution of residual stresses are compared. Although the two models predict similar magnitude of the longitudinal stress, the double-ellipsoid moving source model predicts wider tensile stress zones than the other one. And, both the ramp heating and moving source models predict the stress results in reasonable agreement with the experimental data.

• 한국압력기기공학회 논문집
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• 제18권2호
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• pp.61-68
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• 2022

Accurate evaluation of residual stress is important for stress corrosion cracking assessment. In this paper, electron beam welding experiment is simulated via finite element analysis and the sensitivity of the parameters related to the combined heat source model is investigated. Predicted residual stresses arecompared with measured residual stresses. It is found that the welding efficiency affects the size of the tensile residual stress area and the magnitude of maximum longitudinal residual stress. It is also found that the parameter related to the ratio of energy distributed to the two-dimensional heat source has little effect on the size of tthe tensile residual stress area, but affects the size of the longitudinal residual stress in the center of the weld.

• ETRI Journal
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• 제37권4호
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• pp.780-786
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• 2015

This paper describes an audio source separation that is based on nonnegative matrix factorization (NMF) and expectation maximization (EM). For stable and highperformance separation, an effective auxiliary source separation that extracts source residuals and reprojects them onto proper sources is proposed by taking into account an ambiguous region among sources and a source's refinement. Specifically, an additional NMF (model) is designed for the ambiguous region - whose elements are not easily represented by any existing or predefined NMFs of the sources. The residual signal can be extracted by inserting the aforementioned model into the NMF-EM-based audio separation. Then, it is refined by the weighted parameters of the separation and reprojected onto the separated sources. Experimental results demonstrate that the proposed scheme (outlined above) is more stable and outperforms existing algorithms by, on average, 4.4 dB in terms of the source distortion ratio.

• Environmental Engineering Research
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• 제9권5호
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• pp.214-222
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• 2004

• Journal of Welding and Joining
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• 제35권1호
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• pp.49-54
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• 2017

In this study, the volumetric heat source in electron beam welding (EBW) is modeled through finite element method taking advantage of ABAQUS software package. Since this welding method is being applied in plates with different thicknesses and also considering that residual stresses reduce the strength of these weldments, the effect of thickness in the distribution and magnitude of residual stresses after welding is studied. Regarding the vast application of Inconel 706 super-alloy in aerospace industries, this material was selected in the current research. In order to validate the finite element model, the obtained results were compared to those of other researchers in this area, and good agreement was observed. The simulation results revealed that increase in the plate thickness leads to increase in the residual stresses. In addition heat treatment in the base metal (before welding) increases the residual stresses significantly.

• 한국대기환경학회지
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• 제16권5호
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• pp.477-485
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• 2000

The data set was collected on fifty-eight different days with a 24-h sampling period from October 27, 1995 through August 25, 1996. From the chemical mass balance (CMB) analysis of $PM_{2.5}$ in the Chongju area, the contributions from soil, gasoline, diesel, light and heavy oil combustion were 2.6%, 15.4%, 9.0%, 28.8% and 1.5%, respectively. Residual $NO_{3}^{-}$), residual $SO_{4}^{2-}$ and residual OC, possibly formed in the atmosphere. represented additional 8.0, 10.2, and 1.6% of the $PM_{2.5}$, respectively. Other unidentified sources constituted the remaining 22.9%. From the CMB analysis, the $PM_{2.5}$ source contribution for fall, winter, spring and summer were 92, 76.8, 77.5 and 59.2%, respectively.

• 지구물리와물리탐사
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• 제15권3호
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• pp.129-135
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• 2012

동시 송신원 전파형 역산 기법은 계산량을 획기적으로 줄여 전파형 역산의 적용성을 높여준다. 그러나 다수의 송신원 모음 자료를 동시에 모델링하여 사용하기 때문에 관측 자료의 수진기 위치가 송신원에 따라 다른 경우, 나머지(residual) 파동장에 불필요한 값을 생성하게 되고 이는 파형역산의 수렴성을 저해하게 된다. 특히, 제한된 벌림 거리(offset)를 갖는 스트리머 방식의 탐사자료는 동시 송신원 기법을 적용하기에 가장 어려운 자료 형태이다. 이러한 문제점을 극복하기 위해 최근에 global correlation에 기반한 목적함수가 제안되었고, 시간영역 전파형 역산에 성공적으로 적용되었다. 그러나 이 기법은 변형된 목적함수를 사용하기 때문에 나머지 파동장이 왜곡되고 경우에 따라 역산 결과에 부정적인 영향을 주기도 한다. 또한, 여러 가지 장점을 갖고 있는 주파수 영역 파형역산에 적용된 사례는 아직 보고된 적이 없다. 본 논문에서는 이러한 나머지 파동장의 왜곡을 최소화하기 위해 global correlation 계산 시 사용하는 자료에 진폭감쇠 기법을 적용한다. 진폭감쇠를 적용한 자료는 global correlation의 특성을 최적화하여 나머지 파동장의 왜곡을 줄이고 파형역산 결과를 향상시킨다. 시간 영역에서 구한 나머지 파동장을 주파수 영역에서 역전파시킴으로써 global correlation기법을 주파수 영역에서 구현한다. 스트리머 방식의 합성 탐사자료를 이용한 예제를 통해 본 논문에서 제안한 기법이 기존의 global correlation 목적함수에 기반한 동시 송신원 전파형 역산보다 향상된 결과를 얻을 수 있음을 보여준다.

• 대한기계학회논문집A
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• 제36권6호
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• pp.609-615
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• 2012

레이저 충격 피닝 처리 시 레이저 광원으로부터 금속표면에 조사되는 레이저 빔 형상은 다양하다. 레이저 형상은 표면에서 발생하는 압력파의 특성을 결정하기 때문에 금속 표면과 깊이 방향에 대한 잔류응력 분포에 영향을 미칠 수 있다. 본 논문에서는 레이저 충격 피닝 처리시 레이저 광원 형상이 인코넬 alloy 600 합금의 잔류응력에 미치는 영향을 분석하였다. 레이저 광원 형상은 원형, 사각형, 타원형 형상이 고려되었으며, 표면과 깊이 방향에 대한 압축잔류응력 특성을 비교하였다. 표면에서 생성되는 압축잔류응력은 원형 레이저 형상이 최대이지만 중심부에서 인장응력이 발생하고, 깊이 방향에서는 타원형 레이저 형상이 최대 압축잔류응력을 생성한다. 소성변형 발생 깊이는 사각형에 비해 원형과 타원형이 양호하다.

• 대한조선학회논문집
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• 제44권6호
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• pp.598-604
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• 2007

The purpose of this study is to establish the predictive method of welding distortion and residual stress for the channel I butt SA (submerged arc) weldment using FEA. In order to do it, the heat input model for the weldment was defined as the combined heat source with the surface heat flux of gaussian distribution and volumetric heat source uniformly distributed within weld groove by comparing the shapes of molten pool and temperature distribution obtained by FEA with those of experiments. The arc efficiency of SA welding for two-dimensional FE analysis was evaluated as 0.85. The welding distortion and residual stress of the weldment obtained by FEA and heat input model proposed have a good agreement with those obtained by experiment. Based on the results, it was suggested that the proper heat input model should be required to evaluate the welding distortion for weldment.

• 한국해양공학회지
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• 제21권1호
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• pp.64-68
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• 2007

Recently, there has been considerable research in the field of application of Laser-Arc hybrid welding for superstructures, such as ship-structures, transport vehicles etc. However, the study on heat distribution and welding residual stress of hybrid weld by numerical simulation leaves much to be desired. Therefore, in this study, an optimized welding condition and numerical simulation for hybrid welding, using previous numerical analysis to calculate the heat source for hybrid welding, has been analyzed. For this purpose, fundamental welding phenomena of the hybrid process, using Laser and, is investigated. In order to calculate temperature and residual stress distribution in hybrid welds, a finite element heat source model is developed on the basis of experimental results and characteristics of temperature. Residual stress distribution in hybrid welds are understood from the result of simulation, and compared with the experimental values.