• 소성∙가공
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• 제15권6호
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• pp.445-452
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• 2006

In most of automobile body panel manufacturing, trimming process is generally performed before flanging. To find feasible trimming line is crucial in obtaining accurate edge profile after flanging. Section-based method develops blank along manually chosen section planes and find trimming line by generating loop of end points. This method suffers from inaccurate results of edge profile. On the other hand, simulation-based method can produce more accurate trimming line by iterative strategy. In this study, new fast simulation-based method to find feasible trimming line is proposed. Finite element inverse method is used to analyze the flanging process because final shape after flanging can be explicitly defined and most of strain paths are simple in flanging. In utilizing finite element inverse method, the main obstacle is the initial guess generation for general mesh. Robust initial guess generation method is developed to handle genera] mesh with very different size and undercut. The new method develops final triangular mesh incrementally onto the drawing tool surface. Also in order to remedy mesh distortion during development, energy minimization technique is utilized. Trimming line is extracted from the outer boundary after finite element inverse method simulation. This method has many advantages since trimming line can be obtained in the early design stage. The developed method is verified by shrink/stretch flange forming and successfully applied to the complex industrial applications such as door outer flanging process.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2001년도 봄 학술발표회 논문집
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• pp.201-206
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• 2001

This paper presents truss model that can be used to determine the deformation as well as strength of RC members. This model is constituted to address plastic hinge rotation at tile deformation concentrated regions under severe lateral load. The behavior of each element of truss model is evaluated on the basis of stress field analysis. The deformation is obtained by combining element deformations with joint rotation. Initial strength is calculated at the first failure of any element, and strength deterioration after failure depends on the strength reduction of this element. The proposed model will provide useful tools in seismic design of ductility-required members.

• Journal of the Korean Society for Industrial and Applied Mathematics
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• 제4권1호
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• pp.67-77
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• 2000

In this paper we consider finite element mathods for nonlinear parabolic problems defined in ${\Omega}{\subset}R^d$ ($d{\leq}4$). A new initial approximation is taken. Optimal order error estimates in $L_p$ for $2{\leq}p{\leq}{\infty}$ are established for arbitrary order finite element. One order superconvergence in $W^{1,p}$ for $2{\leq}q{\leq}{\infty}$ are demonstrated as well.

• Journal of Welding and Joining
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• 제14권5호
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• pp.69-77
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• 1996

This study aims to analyze the S. I. F. K value upon Mode I cracks in a finite-width plate of varying thickness, which is expressed in terms of width ratio ($\omega$), thickness ratio ($\beta$) and non-dimensional crack length (λ) by using the 2-dimensional finite element method. Then, by comparing the effectiveness of the results obtained by the two finite element methods, it is seen that the 2-dimensional finite element method can be used in order to analyse the S. I. F. K values upon a various thickness model. A model is developed in order to analyze the effects of initial residual stress upon the fatigue crack growth behavior in various thickness welded specimens. In this model, crack growth rate da/dN appears to be come small as the thickness ratio with the same ΔK is increased. Also, in the initial step, as ΔK is increased with crack growth rate is decreased and then increased because the repeated compressive residual stress retards crack growth rate.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2002년도 추계학술대회논문집
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• pp.810-815
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• 2002

Vibration analysis of rotating blade is the main purpose of this study. In the present work, general formulation is proposed to analyze the rotating shell-type structures including the effect of centrifugal force, Coriolis acceleration and initial twist. Furthermore, simplified equations are derived for the case of an open circular cylindrical shell. Based on the concept of degenerated shell element with the Reissner-Mindlin's assumptions, the finite element method is adopted for solving the governing equations. In addition, it is investigated the effect of thermal load on the vibration characteristics of pretwisted blade. Numerical results are summarized for the various parameters such as rotating speed, angle of pretwist and stacking sequence of a composite blade. Also, present results are compared with the previous works and experimental data.

• 한국해안해양공학회지
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• 제11권4호
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• pp.231-237
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• 1999

다절점 케이블요소를 이용하여 조류하중을 받는 해양 케이블의 자유진동해석을 수행한다. 등매개 곡선 케이블요소(isoparametric cable element)의 접선강성행렬과 질량행렬을 유도하고, 하중증분법을 이용하여 지점 변위를 일으키고 자중, 부력, 그리고 조류력을 받는 케이블의 초기평형 상태를 결정한다. 초기의 정적평형상태를 기준으로 부가질량을 고려한 해양케이블의 자유진동해석을 수행한다. 수중케이블의 자유진동해석을 통하여 얻은 해석결과와 기존의 문헌의 결과를 비교, 검토함으로써 본 논문에서 제시한 이론 및 해석방법의 타당성을 입증한다.

• 소성∙가공
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• 제7권4호
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• pp.364-374
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• 1998

It is the objective of this study to analyze the effect of various process variables on the quality of extruded product and extrusion force for semi-solid extrusion of Al2024 with solid phase structure of globular type by the finite element method. Process variables are initial solid fraction, ram speed, semi-angle of die, and reduction in area. The results of experiment are compared with those of simulation in order to verify the usefulness of the developed finite element program. The flow and deformation of semi-solid alloy are analyzed by coupling by coupling the deformation of porous skeleton and the flow of liquid phase. It is also assumed that initial solid fraction is homogeneous.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2002년도 추계학술대회논문초록집
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• pp.380.1-380
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• 2002

Vibration analysis of rotating blade is the main purpose of present study. In this work, general formulation is proposed to analyze rotating shell type structures including the centrifugal force, Coriolis acceleration and initial twist. Futhermore, simplified equations are derived for the case of an open circular cylindrical shell. Based on the concept of degenerated shell element with the Reissner-Mindlin's assumptions, the finite element method is adopted for solving the governing equations. (onitted)

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 1999년도 춘계학술대회논문집
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• pp.253-256
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• 1999

The Streamline Upwind Petrov-Galerkin(SUPG) finite element method is used to solve the two-dimensional laminar and turbulent flow. The flow is simulated by averaged Navier-Stokes equations with a penalty function approach and the lograithmic(k-$\varepsilon$) turbulent model is employed to take into account its turbulent behavior. The near-wall viscous sub-layer model is employed to approach the dominant viscous effects in the near wall zones. To find a good-enough initial guess of the Newton-Raphson iteration solving Nonlinear Matrix the Incremental method is considered for momentum and the Incomplete logarithmic turbu-lent equations for Turbulence. The validation of our method is investigated in comparision with published experimental data.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 1997년도 추계학술대회논문집
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• pp.89-92
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• 1997

Design of a weld line in a tailor welded blank is indispensable for good manufacturing of stamped parts as assigned, since the intial weld line is distorted severely with forming. The initial weld line has to be determined such that desired weld line in a formed part can be obtained. The initial weld line was predicted by inverse finite element analysis from the desired weld line in a formed part. The inverse approach is applied to the cylindrical and square cup drawing with tailor welded blanks. The applications demonstrates that the approach is useful for design of weld line of tailor welded blank.