샌드위치 사출성형공정에 관한 수치해석

문종신,신효철,Mun, Jong-Sin,Sin, Hyo-Cheol 대한기계학회 2000 大韓機械學會論文集A Vol.24 No.6

Recently, the sandwich injection molding has drawn attention because it offers the flexibility of using the optimal properties of two different but compatible polymers and is also one of the most p romising methods in connection with recycling of thermoplastics. In this paper, a new particle tracing algorithm is presented in order to describe the advancement of core polymer melt during filling stage. The main advantage of this algorithm is the use of identity field information rather than tracking a set of fluid particles. In addition, to model the process accurately, especially to detect the possible

다변수 변분해법에 의한 비적합 8절점 육면체 요소

주상백,신효철,Ju, Sang-Baek,Sin, Hyo-Chol 대한기계학회 1996 大韓機械學會論文集A Vol.20 No.7

This paper introduces two three-dimensional eight-node hexagonal elements obtained by using multivariable variational mehtod. Both of them are based on the modified hellinger-reissner principle to employ incompatible displacements and assumed stresses of assumed strains. The internal functions of element are introduced to as element formulation through two different methods : the first one uses the functions determined directly from the element boundary condition of the incompatible displacements ; while the second, being a kind of B-bar mehtod, employs the modification technique of strain-displacement matrix to pass the patch test. The elements are evaluated on the selective problems of bending and material incompressibility with regular and distorted meshes. The results show that the new elements perform with good accuracy in both of deformation and stress calculation and they are insensitive to distorted geometry of element.

변형률에 근거한 2-절점 곡선보 요소

유하상,신효철,Ryu, Ha-Sang,Sin, Hyo-Chol 대한기계학회 1996 大韓機械學會論文集A Vol.20 No.8

It is well known that in typical displacement-based curved beam elements, the stiffness matrix is overestimated and as a result displacement predictions show gross error for the thin beam case. In this paper, a stain based curved beam element with 2 nodes is formulated based on shallow beam geometry. At the element level, the curvature and membrane strain fields are approximated independently and the displacement fields are obtained by integrating the strain fields. Three test problems are given to demonstrate the numerical performance of the element. Analysis results obtained reveal that the element is free for locking and very effectively applicable to deeply as well as shallowly curved beams.

임의 형상의 단면을 갖는 박판보의 유한요소 해석

양웅필,신효철,Yang, Woong-Pill,Sin, Hyo-Chol 대한기계학회 1996 大韓機械學會論文集A Vol.20 No.1

In this paper, a new thin-walled beam finite elcment is developed to overmome the difficulties in the analysis of real structures by existing beam elements. The element is formulated by extending Benscoter's assumption and also by adopting the concept of the curvature-based element. It is applicable to the analysis of the beams with arbitrary cross-sectional shapes. The results obtained show that the element is locking-free and the accuracy of the finite element solutions is remarkably improved.

유전알고리듬을 이용한 사출성형 공정조건 최적화

최원준,신효철,곽신웅,Choe, Won-Jun,Sin, Hyo-Cheol,Gwak, Sin-Ung 대한기계학회 2000 大韓機械學會論文集A Vol.24 No.10

Precision injection molding is an important technology for improving productivity and lowering costs in the fields of medical components, lenses and electrical connectors. The quality of injection molded parts is affected by various processing conditions such as filling time and packing pressure profile. It is difficult to consider all the variables at the same time for prediction of the quality. In this study, the genetic algorithm was used to obtain the optimal processing conditions for minimizing the volumetric shrinkage of molded parts. For a higher convergence rate, the method of design of experiments was used to analyze the relationship between processing conditions and volumetric shrinkage of molded parts, which served as analysis tool for the capability of searching optimal processing conditions but also greatly reduces the calculation time by utilizing the information of searching area. As a practical example, compact disks that require micron-level precision were chosen for the study.

민감도가 고려된 알고리듬을 이용한 최적화 방법에 관한 연구

이재관,신효철,Lee, Jae-Gwan,Sin, Hyo-Cheol 대한기계학회 2000 大韓機械學會論文集A Vol.24 No.6

A newly developed optimization method which uses the genetic algorithm combined with the sensitivity analysis is presented in this paper. The genetic algorithm is a probabilistic method, searching the optimum at several points simultaneously, requiring only the values of the object and constraint functions. It has therefore more chances to find global solution and can be applied various problems. Nevertheless, it has such shortcomings that even it approaches the optimum rapidly in the early stage, it slows down afterward and it can't consider the constraints explicitly. It is only because it can't search the local area near the current points. The traditional method, on the other hand, using sensitivity analysis is of great advantage in searching the near optimum. Thus the combination of the two techniques makes use of the individual advantages, that is, the superiority both in global searching by the genetic algorithm and in local searching by the sensitivity analysis. Application of the method to the several test functions verifies that the method suggested is very efficient and powerful to find the global solutions, and that the constraints can be considered properly.

비압축성 문제에 대한 비적합 복합유한요소 정식화

주상백,신효철,Ju, Sang-Baek,Sin, Hyo-Chol 대한기계학회 1998 大韓機械學會論文集A Vol.22 No.2

In the present study, we attempted to add the incompatible functions as additional variable terms to the conventional u-p formulation. It is derived from the four-field generalized variational principle that encompasses velocity, pressure, velocity strains and stress fields as independent interpolated variables. As a severe test of the present formulation, we have investigated the driven cavity with the corner velocity singularity like leaky lid. Through the test, the present element performs very well without unstable oscillation of pressure distribution.

자오 변형률에 근거한 2절검 축대칭 셸요소

유하상,신효철,Ryu, Ha-Sang,Sin, Hyo-Chol 대한기계학회 1997 大韓機械學會論文集A Vol.21 No.6

Two shear-flexible curved axisymmetric shell elements with two nodes, LCCS(linear curvature and constant strain) and CCCS(constant curvature and constant strain) are designed based on the assumed meridional strain fields and shallow shell geometry. At the element level, meridional curvature, membrane strain and shear strain fields are assumed by using polynomials and the displacement fields are obtained by integrating the assumed strain fields along the shallowly curved meridian. The formulated elements have high order displacement fields consistent with the strain field. Several test problems are given to demonstrate the performance of the two elements. Analysis results obtained reveal that the elements are very accurate in the displacement and the stress predictions.

불확실한 물성치를 갖는 복합재료 적층 평판의 파괴 예측

김태욱,신효철,Kim, Tae-Uk,Sin, Hyo-Cheol 대한기계학회 2000 大韓機械學會論文集A Vol.24 No.1

Because of their superior mechanical properties to isotropic materials, composite laminated plates are used for many structural applications that require high stiffness-to-weight and strength-to-weight ratios. Composite materials are always subject to a certain amount of scatter in their elastic moduli, but most analyses and designs with the materials are usually conducted by assuming that the material properties are fixed and have no uncertainties. In this paper, a convex modeling approach is introduced to take account of such uncertainties in elastic moduli. It is used with the finite element method to predict the onset of failures in composite laminated plates subject to in-plane loading. Numerical results show that failures begin at the smaller load when the uncertainties of elastic moduli considered and therefore, such uncertainties should be considered at the design stage for the safety and reliability of the structures.

섬유 배열각의 이산성과 물성치의 불확실성을 고려한 복합재료 적층 평판의 최적 설계

김태욱,신효철,Kim, Tae-Uk,Sin, Hyo-Cheol 대한기계학회 2001 大韓機械學會論文集A Vol.25 No.3

Although extensive efforts have been devoted to the optimal design of composite laminated plates in recent years, some practical issues still need further research. Two of them are: the handling of the ply angle as either continuous or discrete; and that of the uncertainties in material properties, which were treated as continuous and ignored respectively in most researches in the past. In this paper, an algorithm for stacking sequence optimization which deals with discrete ply angles and that for thickness optimization which considers uncertainties in material properties are used for a two step optimization of composite laminated plates. In the stacking sequence optimization, the branch and bound method is modified to handle discrete variables; and in the thickness optimization, the convex modeling is used in calculating the failure criterion, given as constraint, to consider the uncertain material properties. Numerical results show that the optimal stacking sequence is found with fewer evaluations of objective function than expected with the size of feasible region taken into consideration; and the optimal thickness increases when the uncertainties of elastic moduli considered, which shows such uncertainties should not be ignored for safe and reliable designs.