• 전산구조공학
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• 제4권2호
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• pp.111-117
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• 1991

구조 공학에서의 고유치 문제는 좌굴해석, 진동해석 등 여러분야에 응용되고 있다. 일반적으로 구조물의 좌굴강도 해석에 사용되는 대부분의 변수들은 불확실성을 내포하고 있으므로 확률론적 해석을 수행해야 하지만, 구조물의 좌굴 신뢰성 해석을 위한 극한상태 방정식은 확률변수의 함수로 명확히 표현되지 않으므로 확률 유한 요소법의 사용이 필요하다. 따라서 본 논문에서는 직접미분법에 의해 정식화된 확률 유한요소법을 사용하여 고유치 문제의 신뢰성 해석방법을 정식화 하고, 이를 바탕으로 좌굴 신뢰성 해석을 수행하였으며, 결과의 타당성을 검증하기 위하여 Crude Monte Carlo Method 및 이 방법의 단점을 대폭 보완한 Importance Sampling Method를 사용하였다. 본 논문에 의해 좌굴 신뢰성 해석 방법이 정립됨으로서 신뢰성에 기초한 최적 설계를 수행하는 경우, 시스템 파괴확률로서 소성 파괴확률과 더불어 좌굴 파괴확률의 고려가 가능해졌다.

• 한국생산제조학회지
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• 제22권2호
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• pp.216-222
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• 2013

A solar power generator is usually installed outdoors and it is exposed to extreme environments such as heavy fall of snow and high speed wind. Therefore, the solar tracker structure should be designed to have sufficient static and dynamic stiffness against such environmental conditions. In this paper, eigenvalue analysis of the solar tracker is carried out by varying the pose of the solar panel and unsteady flow analysis around a single tracker or multi-trackers arranged in a line is performed by varying the parameters such as wind directions, wind speeds and the pose of the solar panel to evaluate whether there exists an instability of resonance due to vortex shedding. Finite element eigenvalue analysis shows that natural frequencies and modes are almost not influenced by the pose of the solar panel and the finite element flow analysis shows that there does not exist periodic vortex shedding due to the flow around single tracker or multiple solar trackers in a line.

• 대한기계학회논문집A
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• 제37권3호
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• pp.325-331
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• 2013

본 논문에서는 상용 프로그램 ABAQUS를 이용하여 브레이크 시스템의 불안정 모드를 알아보기 위한 복소고유치해석을 수행하였다. 또한 전체 시스템의 불안정 복소 고유모드에서 가장 진동에너지가 큰 부품을 알아보기 위한 기여도해석과 전체 복소 고유모드와 해당 부품의 부품모드간의 기여도해석을 통해 모드 연성의 가능성이 높은 모드를 알아보았다. 본 연구에서는 디스크 로터의 2차 굽힘모드와 토크멤버의 3차 축방향 횡모드의 연성에 의해 1.4kHz의 불안정 모드가 발생하는 것을 알 수 있었다. 이러한 모드 연성을 차단하기 위해 불안정성을 유발하는 토크멤버에서 해당모드의 주파수 변화에 대한 감도 해석을 실시하였다. 감도 해석 결과를 토대로 질량 가중에 의한 구조물 동특성 변경을 수행한 결과 저주파 영역에서 불안정 모드가 발생하지 않아 본 연구에서 제시된 저감방법의 유효성을 확인할 수 있었다.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2011년도 추계학술대회 논문집
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• pp.124-129
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• 2011

An improved NDIF method is introduced to efficiently extract eigenvalues of two-dimensional, arbitrarily shaped acoustic cavities. The NDIF method, which was developed by the authors for the eigen-mode analysis of arbitrarily shaped acoustic cavities, membranes, and plates, has the feature that it yields highly accurate eigenvalues compared with other analytical methods or numerical methods (FEM and BEM). However, the NDIF method has the weak point that the system matrix of the NDIF method depends on the frequency parameter and, as a result, a final system equation doesn't take the form of an algebra eigenvalue problem. The system matrix of the improved NDIF method developed in the paper is independent of the frequency parameter and eigenvalues can be efficiently obtained by solving a typical algebraic eigenvalue problem. Finally, the validity and accuracy of the proposed method is verified in two case studies, which indicate that eigenvalues and mode shapes obtained by the proposed method are very accurate compared to the exact method, the NDIF method or FEM(ANSYS).

• 한국소음진동공학회논문집
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• 제21권10호
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• pp.960-966
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• 2011

An improved NDIF method is introduced to efficiently extract eigenvalues and eigenmodes of two-dimensional, arbitrarily shaped acoustic cavities. The NDIF method, which was developed by the authors for the eigen-mode analysis of arbitrarily shaped acoustic cavities, membranes, and plates, has the feature that it yields highly accurate eigenvalues compared with other analytical methods or numerical methods(FEM and BEM). However, the NDIF method has the weak point that the system matrix of the NDIF method depends on the frequency parameter and, as a result, a final system equation doesn's take the form of an algebra eigenvalue problem. The system matrix of the improved NDIF method developed in the paper is independent of the frequency parameter and eigenvalues and mode shapes can be efficiently obtained by solving a typical algebraic eigenvalue problem. Finally, the validity and accuracy of the proposed method is verified in two case studies, which indicate that eigenvalues and mode shapes obtained by the proposed method are very accurate compared to the exact method, the NDIF method or FEM(ANSYS).

• 대한용접접합학회:학술대회논문집
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• 대한용접접합학회 2002년도 Proceedings of the International Welding/Joining Conference-Korea
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• pp.661-667
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• 2002

Welding-induced buckling distortion is one of the most problematic concerns in both design and fabrication of welded thin-plate structures. This paper deals with experimental and numerical results of the welding-induced longitudinal and/or buckling distortion occurring in welding of 6mm-thick AH36 high strength steel plates. Effects of the heat input and the plate size on the distortion were experimentally evaluated for square plates. Bead-on-plate welding was performed with the submerged arc welding process along the middle line of plate specimens. Experimental results showed that the longitudinal distortion made a single curvature in the plate, and the distortion magnitude along the weld centerline was proportional to the heat input and the plate size. The experimental results were used to examine the validity of the numerical simulation procedure for welding-induced distortion where the longitudinal distortion mode and magnitude were numerically quantified. Three-dimensional, large deformation, welding simulations were performed for selected weld models. Numerical results of the distortion mode and magnitude were in a good agreement with experimental ones. Depending on the presence of halting the distortion growth during the cooling cycle of welding, the condition discriminating buckling distortion from longitudinal distortion was established. Eigenvalue analyses were performed to check the buckling instability of tested plates with different sizes subjected to different heat inputs. The perturbation load pattern for the analysis was extracted from longitudinal inherent strain distributions. Critical buckling curve from the eigenvalue analyses revealed that the buckling instability is manifested when plate size or heat input increases.

• 한국치위생학회지
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• 제12권4호
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• pp.675-684
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• 2012

Objectives : The purpose of this study was to develop an instrument for Korean Scaling Fear (KSF)-1.1 in scaling patients. Methods : 402 sample size for scaling patients was studied in Daegu city in July and August of 2011. Mean and standard deviation was calculated in 3 dimensions(FWS: fear while scaling, DDH: distrust on dental hygienist, FAS: fear after scaling). Results : Age of 402 subjects was 36.5 years. In analyzing reliability for item-level, a range of correlation coefficient(${\alpha}$) on item-internal consistency(FWS, DDH, and FAS) was 0.58~0.88(${\alpha}$=0.90), 0.40~0.71(${\alpha}$=0.82), and 0.54~0.63(${\alpha}$=0.82), respectively. Floor(%) and ceiling(%) value on 3 dimensions were also 9.2% and 4.0%, 12.4% and 0.5%, and 17.7% and 1.2%, respectively, therefore, we found statistically high reliability for those(p<0.001). With explanatory factor analysis, this study could generate 3 dimensions(factor 1, eigenvalue 5.41, proportion 0.49; factor 2, eigenvalue 1.50, proportion 0.14; factor 3, eigenvalue 1.04, proportion 0.09) and 11 sub-scales. Also confirmatory factor analysis results showed that the KSF1.1 model was fitted very well in analysis of model fit($x^2$=112.94, df=41, p=0.000; goodness of fit index=0.95; adjusted goodness of fit index=0.92; root mean square residual=0.057). Conclusions : In conclusion, The findings of this study showed that developed reliable and valid instrument for measuring the KSF1.1 in the scaling patients.

• 대한토목학회논문집
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• 제39권1호
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• pp.147-154
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• 2019

유한요소모델 업데이팅은 계측에 의한 구조물의 실제 응답과 가장 가까운 응답을 내는 유한요소모델의 매개변수를 찾는 문제로 정의할 수 있다. 기존 연구에서는 실 구조물과 해석 모델의 응답의 오차를 최소화하는 최적화에 기반 한 방법이 개발되었다. 이 연구에서는 목표 모드 정보로부터 유한요소 모델의 매개변수를 직접 얻을 수 있는 역 고유치 문제를 구성하고 역 고유치 문제를 빠르고 정확하게 풀기 위한 깊은 신경망(Deep Neural Network)을 구성하는 방법을 제안한다. 개발한 방법의 적용 예로서 현수교의 역 고유치 함수를 모사하는 신경망을 이용한 동적 유한요소모델 업데이트를 보인다. 해석 결과 제시한 방법은 매우 높은 정확도로 목표 모드에 대응하는 매개변수를 찾아낼 수 있음을 보였다.

• Nuclear Engineering and Technology
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• 제55권1호
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• pp.310-323
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• 2023

The k-eigenvalue neutronics/thermal-hydraulics coupling calculation is a key issue for reactor design and analysis. Jacobian-free Newton-Krylov (JFNK) method, featured with super-linear convergence rate and high efficiency, has been attracting more and more attention to solve the multi-physics coupling problem. However, it may converge to the high-order eigenmode because of the multiple solutions nature of the k-eigenvalue form of multi-physics coupling issue. Based on our previous work, a modified JFNK with a line search method is proposed in this work, which can find the fundamental eigenmode together with thermal-hydraulics feedback in a wide range of initial values. In detail, the existing modified JFNK method is combined with the line search strategy, so that the intermediate iterative solution can avoid a sudden divergence and be adjusted into a convergence basin smoothly. Two simplified 2-D homogeneous reactor models, a PWR model, and an HTR model, are utilized to evaluate the performance of the newly proposed JFNK method. The results show that the performance of this proposed JFNK is more robust than the existing JFNK-based methods.

• 한국소음진동공학회논문집
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• 제16권8호
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• pp.830-839
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• 2006

The phenomenon of squeal noise in the disk brake system has been, and still is, a. problem for the automotive industry. Extensive research has been carried out in an attempt to understand the mechanism that causes squeal noise and In developing design procedures to reduce squeal noise to make vehicles more comfortable. In this paper, the study on the analysis of squeal noise is performed by using computer aided engineering to design the anti-squeal noise disk brake system. The first part describes the chassis dynamometer and the testing procedure, and second part explains the finite element model and the complex eigenvalue analysis. Finally, it is shown that the proposed squeal noise analysis could be useful to investigate the design parameters that affect the squeal noise characteristics.