The Experts below are selected from a list of 240 Experts worldwide ranked by ideXlab platform
S. M. Hwang - One of the best experts on this subject based on the ideXlab platform.
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An analytical model for the prediction of strip temperatures in hot strip rolling
International Journal of Heat and Mass Transfer, 2008Co-Authors: Jaeboo Kim, Junghyeung Lee, S. M. HwangAbstract:Abstract In hot strip rolling, sound prediction of the temperature of the strip is vital for achieving the desired finishing mill draft temperature (FDT). In this paper, a precision on-line model for the prediction of temperature distributions along the thickness of the strip in the finishing mill is presented. The model consists of an analytic model for the prediction of temperature distributions in the inter-stand zone, and a semi-analytic model for the prediction of temperature distributions in the bite zone in which thermal boundary conditions as well as heat generation due to deformation are predicted by Finite Element-based, approximate models. The prediction accuracy of the proposed model is examined through comparison with predictions from a Finite Element Process model.
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Dimensional Analysis of Hot Strip Rolling for On-line Prediction of Thermo-mechanical Behavior of Roll—Strip System
ISIJ International, 2005Co-Authors: Seung-gon Kim, W. J. Kwak, Joungphil Lee, S. M. HwangAbstract:General, dimensionless expressions are derived for the parameters describing the thermo-mechanical behavior of the roll-strip system, on the basis of the boundary value problem associated with hot strip rolling. Then, it is shown that, by conducting Process simulation with an integrated Finite Element Process model, the dimensionless expressions may be transformed into various on-line models which may be applied to precision Process set-up and control. The validity of the proposed approach is examined through comparison with predictions from Finite Element Process simulation.
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Process optimal design in non-isothermal backward extrusion of a titanium alloy by the Finite Element method
Computer Methods in Applied Mechanics and Engineering, 2004Co-Authors: T.j. Shin, S.h. Chung, Y.h. Lee, J.t. Yeom, S.s. Hong, I.o. Shim, N.k. Park, C.s. Lee, S. M. HwangAbstract:A new approach to Process optimal design in non-isothermal, non-steady metal forming is presented. In this approach, an optimal design problem is formulated on the basis of an integrated thermo-mechanical Finite Element Process model so as to treat diverse Process parameters, either thermal or mechanical, as the design variables to be optimized, and a derivative based approach is adopted for conducting optimization. Described in detail are the integrated Process model, a formulation for Process optimal design, and the schemes for the evaluation of design sensitivity, in particular, a scheme for reflecting the effect of remeshing on design sensitivity. The validity of the schemes for the evaluation of design sensitivity is examined by performing a numerical test. Also examined is the integrated Process model regarding its capability of predicting defect formation, through comparison with experimental observations. Then, the proposed optimal design technique is applied to Process optimization in non-isothermal backward extrusion of a titanium alloy, with emphasis on preventing defect formation.
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Die shape optimal design in cold and hot extrusion
Journal of Materials Processing Technology, 2003Co-Authors: S.m. Byon, S. M. HwangAbstract:Abstract A Process optimal design methodology applicable to cold and hot forming is presented, on the basis of an integrated thermo-mechanical Finite Element Process model and a derivative-based optimization scheme. The Process model, the formulation for Process optimal design, and the schemes for the evaluation of the design sensitivity considering the effect of strain-hardening and heat transfer are described in detail. The capability of the proposed approach is demonstrated through applications to die shape optimal design in cold and hot extrusion.
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Process Optimal Design in Forging by Genetic Algorithm
Journal of Manufacturing Science and Engineering, 2002Co-Authors: J S Chung, S. M. HwangAbstract:A genetic algorithm based approach is presented for Process optimal design in forging. In this approach, the optimal design problem is formulated on the basis of the integrated thermo-mechanical Finite Element Process model so as to cover diverse design variables and objective functions, and a genetic algorithm is adopted for conducting design iteration for optimization. The Process model, the formulation for Process optimal design, and the genetic algorithm are described in detail. The approach is applied to several selected Process design problems in cold and hot forging.
S.h. Chung - One of the best experts on this subject based on the ideXlab platform.
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Process optimal design in non-isothermal backward extrusion of a titanium alloy by the Finite Element method
Computer Methods in Applied Mechanics and Engineering, 2004Co-Authors: T.j. Shin, S.h. Chung, Y.h. Lee, J.t. Yeom, S.s. Hong, I.o. Shim, N.k. Park, C.s. Lee, S. M. HwangAbstract:A new approach to Process optimal design in non-isothermal, non-steady metal forming is presented. In this approach, an optimal design problem is formulated on the basis of an integrated thermo-mechanical Finite Element Process model so as to treat diverse Process parameters, either thermal or mechanical, as the design variables to be optimized, and a derivative based approach is adopted for conducting optimization. Described in detail are the integrated Process model, a formulation for Process optimal design, and the schemes for the evaluation of design sensitivity, in particular, a scheme for reflecting the effect of remeshing on design sensitivity. The validity of the schemes for the evaluation of design sensitivity is examined by performing a numerical test. Also examined is the integrated Process model regarding its capability of predicting defect formation, through comparison with experimental observations. Then, the proposed optimal design technique is applied to Process optimization in non-isothermal backward extrusion of a titanium alloy, with emphasis on preventing defect formation.
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Process optimal design in non-steady forming of porous metals by the Finite Element method
International Journal of Mechanical Sciences, 2000Co-Authors: S.h. Chung, J.h. Lee, Hyungsik Chung, S. M. HwangAbstract:A new approach to Process optimal design in non-steady forming of porous metals is presented. In this approach, the optimal design problem involving diverse objective functions and design variables is formulated on the basis of the Finite Element Process model, and a derivative-based approach is adopted as the solution technique. The Process model, the formulation for Process optimal design, the schemes for the evaluation of the design sensitivity, and an iterative procedure for optimization are described in detail. The validity of the schemes for the evaluation of the design sensitivity is examined by performing a series of numerical tests. The capability of the proposed approach is demonstrated through application to a selected design problem.
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optimal Process design in non isothermal non steady metal forming by the Finite Element method
International Journal for Numerical Methods in Engineering, 1998Co-Authors: S.h. Chung, S. M. HwangAbstract:A new approach to Process optimal design in non-isothermal, non-steady-state metal forming is presented. In this approach, the optimal design problem is formulated on the basis of the integrated thermo-mechanical Finite Element Process model so as to cover diverse objective functions and design variables, and a derivative-based approach is adopted for conducting optimization. The Process model, the formulation for Process optimal design, and the schemes for the evaluation of the design sensitivity, and an iterative procedure for optimization are described in detail. The validity of the schemes for the evaluation of the design sensitivity is examined by performing a series of numerical tests. The capability of the proposed approach to deal with diverse Process parameters and objective functions is demonstrated through applications to some selected Process design problems. © 1998 John Wiley & Sons, Ltd.
S.m. Byon - One of the best experts on this subject based on the ideXlab platform.
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Die shape optimal design in cold and hot extrusion
Journal of Materials Processing Technology, 2003Co-Authors: S.m. Byon, S. M. HwangAbstract:Abstract A Process optimal design methodology applicable to cold and hot forming is presented, on the basis of an integrated thermo-mechanical Finite Element Process model and a derivative-based optimization scheme. The Process model, the formulation for Process optimal design, and the schemes for the evaluation of the design sensitivity considering the effect of strain-hardening and heat transfer are described in detail. The capability of the proposed approach is demonstrated through applications to die shape optimal design in cold and hot extrusion.
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FEM-based Process optimal design in steady-state metal forming considering strain-hardening
Computers & Structures, 2001Co-Authors: S.m. Byon, S. M. HwangAbstract:Abstract A Process optimal design methodology applicable to steady-state forming with a strain-hardening material is presented. In this approach, the optimal design problem is formulated on the basis of a rigid-viscoplastic Finite Element Process model, and a derivative based approach is adopted as an optimization technique. The Process model, the formulation for Process optimal design, and the schemes for the evaluation of the design sensitivity considering the effect of strain-hardening are described in detail. The validity of the proposed approach is demonstrated through numerical tests and application to die shape optimal design in extrusion.
Mehmet Firat - One of the best experts on this subject based on the ideXlab platform.
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Computer aided analysis and design of sheet metal forming Processes: Part II – Deformation response modeling
Materials & Design, 2007Co-Authors: Mehmet FiratAbstract:The continually decreasing lead-times for the design approval and the production of stamping dies enforce the stamping methods engineer to apply the Finite Element method more effectively in the industrial settings. The selection of a proper Finite Element plasticity model and the efficient utilization of the material formability data are main factors controlling the accuracy of the sheet metal deformation response prediction using a computer simulation code. Especially with the introduction of high strength sheet metals in to the stamping Processes the capabilities and limitations of a plasticity model used in Finite Element Process simulations should be reevaluated in order to have an accurate assessment of the part formability and springback deformations. In this part of the study, following a review of the sheet metal deformation properties in conjunction with the initial yield loci and plastic anisotropy concepts, two rate-independent anisotropic plasticity models are employed in the deformation modeling of a stamping part. Their performances in the formability and springback analyses are demonstrated and comparisons are presented.
J. N. Reddy - One of the best experts on this subject based on the ideXlab platform.
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Finite Element Processes Based on GM/WF in Non-Classical Solid Mechanics
American Journal of Computational Mathematics, 2017Co-Authors: K. S. Surana, R. Shanbhag, J. N. ReddyAbstract:In non-classical thermoelastic solids incorporating internal rotation and conjugate Cauchy moment tensor the mechanical deformation is reversible. This suggests that within the realm of linear mathematical models that only consider small strains and small deformation the mechanical deformation is reversible. Hence, it is possible to recast the conservation and balance laws along with constitutive theories in a form that adjoint A* of the differential operator A in mathematical model is same as the differential operator A. This holds regardless of whether we consider an initial value problem (IVP) (when the integrals over open boundary are neglected) or boundary value problem (BVP). Thus, in such cases Galerkin method with weak form (GM/WF) for BVPs and space-time Galerkin method with weak form (STGM/WF) for IVPs are highly meritorious due to the fact that: 1) the integral form for BVPs is variationally consistent (VC) and 2) the space-time integral forms for IVP are space time variationally consistent (STVC). The consequence of VC and STVC integral forms is that the resulting coefficient matrices are symmetric and positive deFinite ensuring unconditionally stable computational Processes for both BVPs and IVPs. Other benefits of GM/WF and space-time GM/WF are simplicity of specifying boundary conditions and initial conditions, especially traction boundary conditions and initial conditions on curved boundaries due to self-equilibrating nature of the sum of secondary variables that only exist in GM/WF due to concomitant. In fact, zero traction conditions are automatically satisfied in GM/WF, hence need not be specified at all. While VC and STVC feature also exists in least squares Process (LSP) and space-time least squares Finite Element Processes (STLSP) for BVPs and IVPs, the ease of specifying traction boundary conditions feature in GM/WF and STGM/WF is highly meritorious compared to LSP and STLSP in which zero traction conditions need to be explicitly specified. A disadvantage of GM/WF and STGM/ WF is that the mathematical models (momentum equations) needed in the desired form contain higher order derivatives of displacements (upto fourth order), hence necessitate use of higher order spaces in their solution. As well known, this problem can be easily overcome in LSP and STLSP by introduction of auxiliary equations and auxiliary variables, thus keeping the highest orders of the derivatives of the dependent variables to one or any other desired order. A serious disadvantage of this approach in LSP is the significant increase in the number of dependent variables, hence poor computational efficiency. In this paper we consider non-classical continuum models for internally polar linear elastic solids in which internal rotations due to displacement gradient tensor (hence internal polar physics) are considered in the conservation and the balance laws and the constitutive theories. For simplicity, we only consider isothermal case; hence energy equation is not part of mathematical model. When using mathematical models derived in displacements in GM/WF and LSP in constructing integral forms, we note that in GM/WF the number of dependent variables is reduced drastically (only three in R3), whereas in case of first order systems used in LSP and STLSP we may have as many as 22 dependent variables for isothermal case. Thus, GM/WF results in dramatic improvement in computational efficiency as well as accuracy when minimally conforming spaces are used for approximations. In this paper we only consider mathematical model in R2 for BVPs (for simplicity). Mathematical models for IVP and BVP in R3 will be considered in subsequent paper. The integral form is derived in R2 using GM/WF. Numerical examples are presented using GM/WF and LSP to demonstrate advantages of Finite Element Process derived using integral form based on GM/WF for non-classical linear theories for solids incorporating internal rotations due to displacement gradient tensor.
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Strong and Weak Form of the Governing Differential Equations in Least Squares Finite Element Processes in h,p,k Framework
International Journal for Computational Methods in Engineering Science and Mechanics, 2008Co-Authors: Karan S. Surana, L. R. Anthoni, Srikanth Allu, J. N. ReddyAbstract:This paper presents an investigation of performance of the least squares Finite Element Process in hpk mathematical framework utilizing: (i) governing differential equations (GDEs) containing highest order derivatives of the dependent variables (strong form of GDEs); (ii) GDEs containing only first order derivatives of the dependent variables and hence constituting a system of first order equations (weak form of GDEs) derived either directly from conservation laws or derived using auxiliary variables or auxiliary equations. It is shown that while the weak form of the GDEs may appear perfectly legitimate, the auxiliary equations in such forms cause irrecoverable inconsistencies in the resulting computational Processes due to the fact that local approximations for the dependent variables and the auxiliary variables always remain inconsistent regardless of the choices p-level and the orders of the approximation spaces. The inconsistency of local approximations in the auxiliary equations may introduce spuriou...
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Galerkin/Least-Squares Finite Element Processes for BVP in h, p, k Mathematical Framework
International Journal for Computational Methods in Engineering Science and Mechanics, 2007Co-Authors: Karan S. Surana, R. Kanti Mahanthi, J. N. ReddyAbstract:This paper presents an investigation of the details of mathematical and computational aspects of the Galerkin/least-squares and the Galerkin/weak form least-squares Finite Element Process within the mathematical and computational framework [1, 2, 3] based on h, p, k as independent computational parameters and requiring that the integral forms be variationally consistent (VC). Higher-order global differentiability of order (k−1) defined by the order k of the approximation space is essential for incorporating correct physics of the Processes in the computations and that k is an independent parameter in addition to h and p in all Finite Element computations. In this paper the attributes of the Galerkin method, the Galerkin method with weak form, and least-squares Processes in h, p, k framework with variationally consistent (VC) or variationally inconsistent (VIC) integral forms are utilized to investigate the mathematical features of the Galerkin/least-squares Processes (GAL/LSP) and Galerkin/weak form least...
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THE k-VERSION OF Finite Element METHOD FOR NON-SELF-ADJOINT OPERATORS IN BVP
International Journal of Computational Engineering Science, 2002Co-Authors: Karan S. Surana, A. R. Ahmadi, J. N. ReddyAbstract:In this paper a new mathematical and computational framework for boundary value problems described by self-adjoint differential operators is presented. In this framework, numerically computed solutions, when converged, possess the same degree of global smoothness in terms of differentiability up to any desired order as the theoretical solutions. This is accomplished using spaces Ĥk,p that contain basis functions of degree p and order k - 1 (or the order of the space k). It is shown that the order of space k is an intrinsically important independent parameter in all Finite Element computational Processes in addition to the discretization characteristic length h and the degree of basis functions p when the theoretical solutions are analytic. Thus, in all Finite Element computations, all quantities of interest (e.g., quadratic functional, error or residual functional, norms and seminorms, error norms, etc.) are dependent on h, p as well as k. Therefore, for fixed h and p, convergence of the Finite Element Process can also be investigated by changing k, hence k-convergence and thus the k-version of Finite Element method. With h, p, and k as three independent parameters influencing all Finite Element Processes, we now have k, hk, pk, and hpk versions of Finite Element methods. The issue of minimally conforming Finite Element spaces is reexamined and it is demonstrated that the definition of currently believed minimally conforming space which permit weak convergence of the highest-order derivatives of the dependent variables appearing in the bilinear form is not justifiable mathematically or from physics view point. A new criterion is proposed for establishing the minimally conforming spaces which is more in agreement with the physics and mathematics of the BVP. Significant features and merits of the proposed mathematical and computational framework are presented, discussed, illustrated, and substantiated mathematically as well as numerically with the Galerkin and least-squares Finite Element formulations for self-adjoint boundary-value problems.