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링압축시험에서 역해석을 이용한 유동응력과 마찰상수 결정법
최영,김호관,조해용,김병민,최재찬,Choi, Y.,Kim, H.K.,Cho, H.Y.,Kim, B.M.,Choi, J.C. 대한기계학회 1998 大韓機械學會論文集A Vol.22 No.3
An inverse analysis been applied to obtain the flow stress of the material. In this method, a ring-shaped specimen is compressed between two flat tools. This procedure employs, as the object function of inverse analysis, the balance of measured loads and reaction forces calculated by using rigid-plastic finite element method. The balance is explicit scalar function of flow stress which is a function of some unknown constants. For minimizing the balance, Newton-Raphon scheme is used. The friction factor, m, between flat tools and the specimen is determined by using friction area-divided method. The proposed method allows an accurate identification by avoiding the usual assumptions made in order to convert experimental measures into stress-strain relation. In this paper, the proposed method is numerically tested. A commercial pure aluminum was selected, as an example, to apply the method and the results are compared with stress-strain relation obtained by experiments.
Generalized Modeling Method for Compliant Mechanisms considering Rigid-body Deformations
Y. M. Choi(최영만),H. H. Lim(임현호) Korean Society for Precision Engineering 2021 한국정밀공학회 학술발표대회 논문집 Vol.2021 No.11월
The multi-rigid-body matrix method (MRBMM) is a generalized modeling method for obtaining the displacement, stress, and modal information of a compliant mechanism without performing inner-force analysis. MRBMM discretizes a compliant mechanism into flexible hinges and rigid bodies to implement a mass-spring model. The method designs the multi-body spring mechanism using coordinate transformations in a matrix form. In MRBMM, the deformations of the element assumed to be a rigid body are ignored. In some cases, such as displacement amplification mechanisms, non-negligible deformation occurs even in elements other than the flexible hinge. In this paper, we present a multi-compliant-body matrix-method that considers a rigid body as a compliant element, while retaining the generalized framework of the MRBMM. In the MCBMM, a rigid body in the MRBMM is segmented into a certain number of body nodes and flexure hinges. For bridge type displacement amplification mechanism, MCBMM yields the most accurate amplification ratio among several previous modeling methods. Finally, we confirmed that the MCBMM shows improved accuracy in estimating static and dynamic performances of compliant mechanism through an example of XY positioning mechanism with a double-lever mechanism.
CFD에 의한 2차원 후향계단에서의 재부착 유동특성에 관한 연구
최영도(Y. D. Choi),이영호(Y. H. Lee) 한국전산유체공학회 1998 한국전산유체공학회 학술대회논문집 Vol.1998 No.-
The present study is aimed to investigate flow characteristics of Two dimensional backward-facing step by numerical approach. A convection conservative difference scheme based upon SOLA algorithm is used for the solution of the two-dimensional incompressible Navier-Stokes equations to simulate the laminar, transitional and turbulent flow conditions at which the experimental data can be available for the backward-facing step. The twenty kinds of Reynolds number are used for the calculations. In an effort to demonstrate that the reported solutions are dependent on the mesh refinement, computations are performed on seven different meshes of uniformly increasing refinement. Also to investigate the result of inflow dependence, two kinds of the inflow profile are chosen for the laminar flow. As criterion of benchmarking the result of numerical simulation, reattachment length is used for the selected Reynolds numbers.