• Transactions of the Korean Society of Mechanical Engineers
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• v.18 no.8
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• pp.2113-2122
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• 1994

The 3-D FEM analysis for simulating the stamping operation of planar anisotropic sheet metals with arbitrarily-shaped tools is introduced. An implicit, incremental, updated Lagrangian formulation with a rigid-viscoplastic constitutive equation is employed. Contact and friction are considered through the mesh-normal, which compatibly describes arbitrary tool surfaces and FEM meshes without depending on the explicit spatial derivatives of tool surfaces. The consistent full set of governing relations, comprising equilibrium equation and mesh-normal geometric constraints, is appropriately linearized. The linear triangular elements are used for depicting the formed sheet, based on membrane approximation. Barlat's non-quadratic anisotropic yield criterion(strain-rate potential) is employed, whose in-plane anisotropic properties are taken into account with anisotropic coefficients and non-quadratic function parameter. The planar anisotropic finite element formulation is tested with the numerical simulations of the stamping of an automotive hood inner panel and the drawing of a hemispherical punch. The in-plane anisotropic effects on the formability of both mild steel and aluminum alloy sheet metals are examined.

• Ocean Systems Engineering
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• v.5 no.3
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• pp.221-243
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• 2015

This paper compares simplified and finite element method (FEM) models for tower and blade in dynamic coupled analysis of floating wind turbine. A SPAR type wind turbine with catenary mooring lines is considered in numerical analysis. Floating body equation is derived using boundary element method (BEM) and convolution. Equations for mooring line, tower and blade are formulated with theories of catenary, elastic beam and aerodynamic rotating beam, respectively and FEM is applied in the formulation. By combining the equations, coupled solutions are calculated. Tower or blade may be assumed rigid or lumped body for simplicity in modeling. By comparing floating body motions, mooring line tensions and tower stresses with the simple model and original FEM model, the effect of including or neglecting elastic, rotating and aerodynamic behavior of tower and blade is discussed.

• International Journal of Ocean System Engineering
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• v.1 no.2
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• pp.76-88
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• 2011

The present study deals with the hydroelastic vibration analysis of structures in contact with fluid via coupled fluid-structure interaction (FSI) embedded with a finite element method (FEM) such that a structure displacement formulation is coupled with a fluid pressure-displacement formulation. For the preliminary study and validation of FEM based coupled FSI analysis, hydroelastic vibration characteristics of a rectangular plate in contact with fluid are first compared with the elastic vibration in terms of boundary condition and mode frequency. Numerical results from coupled FSI analysis have been shown to be rational and accurate, compared to energy method based theoretical solutions and experimental results. The effect of free surface on the vibration mode is numerically studied by changing the submerged depth of a rectangular plate. As a practical application, the hull structural vibration of 4,000 twenty-foot equivalent units (TEU) container ship is considered. Hydroelastic results of the ship hull structure are compared with those obtained from the elastic condition.

• Computers and Concrete
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• v.4 no.2
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• pp.83-100
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• 2007

Applying a direct formulation for the enrichment of the displacement field an extended finite element (XFEM) scheme for modeling of cohesive crack growth is developed. Only elements cut by the crack is enriched and the scheme fits within the framework of standard FEM code. The scheme is implemented for the 3-node constant strain triangle (CST) and the 6-node linear strain triangle (LST). Modeling of standard concrete test cases such as fracture in the notched three point beam bending test (TPBT) and in the four point shear beam test (FPSB) illustrates the performance. The XFEM results show good agreement with results obtained by applying standard interface elements in FEM and with experimental results. In conjunction with criteria for crack growth local versus nonlocal computation of the crack growth direction is discussed.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 1999.03b
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• pp.26-29
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• 1999

The sectional forming analysis program for analyzing the hydroforming processes of axisymmetric sheet parts was tleveloped. The rigid-viscoplastic FEM formulation based on membrane theory was derived, wh~cta simi~ltaneously solve force equilibrium as well as non-penetration condition. Hill's non-quadratic normal anisotropic yield theory(1979) was used for material behaviour. For describing the liquid pressure iaction, the flexible tool concept was introduced. Isotropic hardening law was also assumed. To verify the \,alidity of the formulation, the stepped cup forming process as well as the hydrostatic bulging test were \imnlated. Simulation results agreed well with Finckenstein and experimental ones.

• Transactions of Materials Processing
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• v.4 no.3
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• pp.222-232
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• 1995

The planar anisotripic FEM analysis for predicting earing profiles and draw-in amounts in the deep-drawing process is introduced. An implicit, incremental, updated Lagrangian formulation with a rigid-viscoplastic constitutive equation is employed. Contact and friction are considered through the mesh-based unit vector and normal contact pressure. The consistent full set of governing relations, which is comprising euilbrium and geometric constraint equations, is appropriately linearized. Barlat's strain-rate potential is employed, whose in-plane anisotropic properties are taken into account with anisotropic coefficients and potential parameters. The linear triangular membrane elements are used for depicting the formed sheet. In the numerical simulations of deep drawing processes of a flat-top cylindrical cup for 2090-T3 aluminum alloy sheet show good agreement with experiments, although some discrepancies were observed in the directional trend of cup height and thickness strains.

• Transactions of Materials Processing
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• v.6 no.4
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• pp.279-290
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• 1997

The sectional forming analysis of stamping pocesses for aluminum alloy sheet metals was investigated. For the modeling of the anomalous behavior of aluminum alloy sheet. the Barlat's strain rate potential and Hill's 1990 non-quadratic yield theory with an isotropic hardening rule were employed. The rigid-viscoplastic FEM formulation which solves equilibrium equation for plane-strain stage with mesh-normal geometric constraints was derived. A new method to determine the Barlat's anisotropic coefficients was also suggested. To verify the validity of the formulation, the stretch and draw forming processes of a square cup were simulated.

• Proceedings of the KIEE Conference
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• 1998.07a
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• pp.250-253
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• 1998

This paper has proposed a method to analyze a 30 KVA superconducting generator using 3-dimensional FEM program. 3 kinds of 3D formulation methods are employed such as scalar potential in core region, reduced scalar potential in air region and T-${\omega}$ formulation in stator coil region. As results of the simulation, various parameters of the generator have been analyzed like air gap flux density, induced voltage, inductance, etc.

• Progress in Superconductivity and Cryogenics
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• v.21 no.3
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• pp.32-37
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• 2019

In various types of large-scale electrical applications, the number of coil turns in such machines is usually large. Electromagnetic simulation of large-scale superconducting coils (tens to hundreds of turns) is indispensable in the design process of superconducting electrical equipment. However, due to the large scale of the coil and the large aspect ratio of super-conducting material layer in HTS coated conductor, it is usually difficult or even unable to perform 3-D transient electromagnetic simulation. This paper introduces an effective 3-D electromagnetic simulation method for large-scale HTS coated conductor coil based on T-A formulation. The simulation and experimental results show that the 3-D model based on the T-A formulation using homogeneous strategy is more accurate than the traditional 2-D models. The memory usage is not sensitive to the number of turns and this model will be even more superior as the number of turns becomes larger.

• Progress in Superconductivity and Cryogenics
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• v.15 no.1
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• pp.29-34
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• 2013

AMR (Active Magnetic Regenerative) refrigerators require the large variation of the magnetic field and a HTS magnet can be used. The amount of AC loss is very important considering the overall efficiency of the AMR refrigerator. However, it is very hard to estimate the precise loss of the HTS magnet because the magnetic field distribution around the conductor itself depends on the coil configuration and the neighboring HTS wires interact each other through the distorted magnetic field by the screening current Therefore, the AC loss of HTS magnet should be calculated using the whole configuration of the HTS magnet with superconducting characteristic. This paper describes the AC loss of the HTS magnet by an appropriate FEM approach, which uses the non-linear characteristic of HTS conductor. The analysis model is based on the 2-D FEM model, called as 'magnetic field formulation and edge-element model', for whole coil configuration in cylindrical coordinates. The effects of transport current and stacked conductors on the AC loss are investigated considering the field-dependent critical current. The PDE model of 'Comsol multiphysics' is used for the FEM analysis with properly implemented equations for axisymmetric model.