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PGD-shooting method for steady-state response analysis of nonlinear dynamical system
Dae Guen Lim(임대근),Gil Yong Lee(이길용),Yong-Hwa Park(박용화) 대한기계학회 2021 대한기계학회 춘추학술대회 Vol.2021 No.11
The shooting method has been widely used to determine the steady-state responses of nonlinear dynamical systems. It formulates the steady-state solution of the governing equation as a two-point boundary value problem and finds an initial condition that satisfies the periodicity condition. Although the shooting method can avoid numerical simulation of the long transient process, iterative time integration over one period is still required, which leads to computational inefficiency when the underlying model is already intensive. In this work, we propose an efficient numerical approach combining proper generalized decomposition with the shooting method (PGD-Shooting). The response in the time integration is approximated as a tensor-product of a space and time domain, which yields decoupled equations as a spatial and temporal problem. Due to this representation, the shooting method in the temporal problem is reduced to a scalar form, and the computational efficiency can be greatly improved. A numerical example of the nonlinear system with dry friction illustrates the performance and validation of the proposed method.
Effect of Plane Strain on the Microstructure and Texture of AZ31 Sheet with Various Reduction Ratios
Kim, Dae Guen,Kim, Hak Young,Yoon, Young Ok,Kim, Shae K.,Lim, Hyun Kyu Trans Tech Publications, Ltd. 2014 Materials science forum Vol.783 No.-
<P>In this study, the effect of plane strain on the microstructure and texture of AZ31 sheet was investigated with various reduction ratios. To achieve plane strain, that is, to prevent shear deformation during warm-rolling, AZ31 sheet was capsuled by pure Cu tube. The large strain induced by simple one-pass warm-rolling led to the significant grain refinement and texture randomization. The two-dimensional finite-element method showed that the warm-rolling of AZ31 sheet capsuled by Cu tube imposed a uniform plane strain in the whole sheet thickness. The high reduction ratio caused the dynamic recrystallization during annealing of the rolled sheet.</P>
Effect of Rare Earth Element on Microstructure and Mechanical Properties of Mg-Sn-Ca Alloys
Kim, Dae Guen,Lee, Jae Seol,Park, Seul Ki,Kim, Young Mo,Son, Hyeon Taek,Huh, Moo Young Trans Tech Publications, Ltd. 2010 Materials science forum Vol.638 No.-
<P>In the present work, the effect of Nd addition on microstructure change, precipitation behaviours and mechanical properties, of Mg-5Sn-3Ca based alloys were investigated. With increasing of Nd addition, size of the Mg-Sn-Ca ternary phases with fine needle shape (A-type) was decreased and volume fraction of these phase were increased. As Nd was increase from 0.5, 1.0 and 3.0 wt.%, size and volume fraction of Mg2Sn with coarse needle shape phase (B-type) was decreased. However, in 3.0 wt.% Nd containing alloy, size of these Mg2Sn phase was smaller than that of 0.5 and 1.0 wt% Nd addition alloy and volume fraction of these phase was decreased.</P>
복대건(Dae-Guen Bok),김강민(Kang-Min Kim),이중우(Joong-Woo Lee),강석진(Seok-Jin Kan) 한국항해항만학회 2018 한국항해항만학회 학술대회논문집 Vol.2018 No.추계
낙동강 하구의 지형변화를 포함한 제 해양환경은 낙동강 하굿둑이 건설된 1987년 7월 이후로 분기된다. 즉, 낙동강 하굿둑이 건설되기 전에는 낙동강의 작은 하상구배로 담수와 해수가 혼합되는 구역이 현재의 하굿둑 보다 상류에 위치하였으나 하굿둑 건설 이후에는 하굿둑 수문 조작에 따라 방류되는 유출수에 의해 유동 양상이 변화되기에, 낙동강 하굿둑의 방류량을 파악하는 것은 매우 중요하다 하겠다. 이에 본연구에서는 낙동강 하굿둑 제원, 방류패턴, 하굿둑 주변 강수량, 하굿둑 방류량을 분석하였다. 또한, 낙동강 하굿둑 방류량에 의한 유사량 분석을 수행하여, 낙동강 하류역의 지형변동의 기초자료를 제공하였다. 연구결과, 낙동강 하굿둑 방류량은 최근 13년 동안의 연평균방류량은 19,274.56×106㎥이고 일평균 방류량은 52.81×106㎥이고 초당평균 방류량은 611.19㎥으로 산정되었다. 낙동강 하굿둑 건설 이후 퇴사량과 준설량을 근거하여 계산된 연간 평균 총유사량은 3,184,405㎥/yr이고, 낙동강 하굿둑의 경우 연평균 부유사량이 3,153,995㎥/yr, 소류사량 이 30,410㎥/yr이며 소유사량이 부유사량의 약 1.0%로 나타났다.
Kim, Dae-Guen,Son, Hyeon-Taek,Kim, Dae-Won,Kim, Yong-Ho,Lee, Kye-Man The Japan Institute of Metals 2011 Materials transactions Vol.52 No.12
<P>The objective of this study was to investigate the cross-roll rolling process effects on microstructures and mechanical properties of AZ31 Mg sheet about rolling angle, in which the roll axes were tilted 0°, 2.5°, 5° and 7.5° away from the transverse direction. Three-dimensional FEM simulation proved that increasing the cross-roll angle, the through-thickness variation of effective strains decreases extremely. The cross-roll rolled and subsequently annealed samples have the uniform and fine grain size at whole thickness layers with increasing the cross-roll angle from 0° to 7.5°. The result of tensile test discloses that while the increase in cross-roll angle can scarcely affect on the strength of samples, it can improve the formability of samples remarkably.</P>
BEM 이론을 적용한 풍력발전기 해석용 RecurDyn 모듈 개발
임대근(Dae Guen Lim),유완석(Wan Suk Yoo) 대한기계학회 2014 大韓機械學會論文集A Vol.38 No.2
본 연구에서는 다물체 동역학 해석 소프트웨어인 RecurDyn 을 이용하여 풍력 발전기를 쉽게 모델링하고 동적 거동 해석을 수행할 수 있는 기법을 개발하였다. 풍력 발전기는 타워, 너셀, 허브, 그리고 블레이드로 구성되어 있다. 타워와 블레이드는 탄성체로 가정하였고 탄성효과를 고려하기 위하여 탄성체 이론을 이용하여 모델링 하였다. 바람의 속도는 일정하다고 가정하였고 날개 요소 운동량 이론을 이용하여 공력하중을 모델링 하였다. 이를 통해 계산된 공력을 풍력 발전기에 적용시키고 동적 거동 해석을 수행하였다. 해석의 타당성을 검증하기 위하여 풍력 발전 시스템 상용 소프트웨어인 GH-Bladed 를 이용한 해석결과와 비교하였다. In this study, a module is developed for modeling and analyzing dynamic behavior of a wind turbine using RecurDyn, which is a commercial multi-body dynamics software developed by FunctionBay,Inc. The wind turbine consists of tower, nacelle, hub and blades. Tower and blades are regarded as flexible bodies for considering elastic effect using beam theory and spring force. In this paper, a constant speed wind was assumed and aerodynamic force is modeled using BEM theory. Dynamic analysis applying this aerodynamic force is carried out. To verify the validity of analysis results, these results are compared to those of GH-Bladed which is a commercial software for analyzing wind turbine system distributed by Garrad Hassan.
Effect of Calcium on Solidification Behavior of Mg-Sn Based Alloys
Kim, Dae Guen,Son, Hyeon Taek,Lee, Jae Seol Trans Tech Publications, Ltd. 2009 Materials science forum Vol.620 No.-
<P>The effect of Ca addition on microstructure change, precipitation behaviours and mechanical properties, in the present work, of Mg-Sn based alloys were investigated. With increasing of Ca additions, size of the Mg-Sn-Ca ternary phases (A-type) with fine needle shape was decreased and volume fraction of these phase were increased. As Ca was increase from 1 wt.%, 2 wt.%, size and volume fraction of Mg2Sn with coarse needle shape phase (B-type) was increased. However, in 3 wt.% Ca containing alloy, size of these Mg2Sn phase was smaller than that of 2 wt% Ca addition alloy and volume fraction of these phase was decreased.</P>
Kim, Dae-Guen,Son, Hyeon-Taek,Kim, Dae-Won,Kim, Yong-Ho,Lee, Kye-Man,Park, Joon-Sik The Japan Institute of Metals 2011 Materials transactions Vol.52 No.12
<P>The texture development and microstructural evolution have been investigated for the AZ31 alloys rolled by cross-roll rolling at 823 K. After the AZ31 magnesium sheets were rolled by cross-roll rolling at 823 K, the total reduction in thickness of 65% were achieved after two pass rolling. The resultant microstructures are homogeneous and refined for the surface and center layers. The (0002) basal texture is significantly weakened after annealing at 623 K for 1 h for the cross-roll rolled sheets.</P>