Research and Development Institute of Midas IT

Gyeonggi Do, South Korea

Research and Development Institute of Midas IT

Gyeonggi Do, South Korea

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Won S.G.,Pusan National University | Won S.G.,Research and Development Institute of Midas IT | Bae S.H.,Pusan National University | Cho J.R.,Pusan National University | And 3 more authors.
Finite Elements in Analysis and Design | Year: 2013

The numerical implementation of Mead and Markus's two sets of differential equations of motion governing the damped forced vibration of three-constrained-layer sandwich beam requires C2-basis functions or the mixed formulation. To resolve this problem, a damped beam element for three-layered symmetric straight damped sandwich structures is derived according to the virtual work principle, in which both the virtual kinetic and strain energies are expressed in terms of the lateral displacement and the transverse shear strain of a core layer. Because the forced vibration equations of three-constrained-layer damped beam are equipped with three pairs of boundary conditions, the rotation of the mid-surface which is directly derived from the lateral displacement is added for the damped beam element to have three degrees of freedom per node. The shape functions are analytically derived using the compatibility relation between the lateral displacement and the transverse shear strain. The validity of the proposed beam element is verified through the benchmark experiments, and furthermore the DOF-efficiency is justified through the comparison with Nastran 3-D solid element. © 2013 Elsevier B.V.


Bae S.H.,Pusan National University | Cho J.R.,Pusan National University | Cho J.R.,Research and Development Institute of Midas IT | Bae S.R.,Agency for Defense Development | Jeong W.B.,Pusan National University
Computer Methods in Applied Mechanics and Engineering | Year: 2014

A discrete convolutional Hilbert transform (DCHT) with the consistent imaginary initial conditions, together with the development of 2-node 8-DOF damped beam element, are presented for the reliable DOF-efficient time-domain analysis of five-layered viscoelastic sandwich beam. Motivated by the fact that the longitudinal displacements of three metallic layers can be replaced with the transverse shear strains of two viscoelastic core layers, a DOF-efficient damped beam element with the nodal DOFs composed of the deflection and rotation of beam and shear strains of two viscoelastic core layers is derived according to the virtual work principle and the compatibility relation. The standard Hilbert transform using Fourier and inverse Fourier transform of impulse signals produces the totally different results from the analytically derived ones near the end of time period, and the non-conjugate complex eigen values in a state-space formulation cause the unbounded growth in the time response of the damped structural dynamic system when a standard time integration scheme is used. To resolve these numerical problems, the imaginary external force is obtained by dividing the real external force into a finite number of rectangular impulses and by superposing Hilbert transforms of each rectangular impulse. And the time response of the damped sandwich beam subject to arbitrary external force is obtained by the convolution of time response to unit impulse. Meanwhile, the consistent imaginary initial conditions which can provide the bounded damped time response are numerically derived by splitting each decoupled complex second-order differential equation in the mode superposition approach into real and imaginary ones and by solving general solutions of each two split equations in the space-state formulation. The proposed method is validated through the numerical experiments composed of analytic and five-layered damped sandwich beam examples. © 2013 Elsevier B.V.


Cho J.R.,Pusan National University | Cho J.R.,Research and Development Institute of Midas IT | Lee J.H.,Pusan National University
Finite Elements in Analysis and Design | Year: 2012

A generalized multi-objective optimization method making use of genetic algorithm (GA) is introduced, in order to simultaneously improve the riding comfort and the durability of run-flat tire by optimally tailoring the shape and stiffness of the sidewall insert rubber. The sensitivity analysis invoking the CPU time-consuming finite element analyses is replaced with the genetic evolution and the fitness of each genome in the population is evaluated by utilizing the response surfaces of objective functions approximated by ANN. It is confirmed through the numerical experiment that a number of Pareto solutions of the shape and stiffness of the sidewall insert rubber for different combinations of weighting factors can be successfully obtained. As well, the reliability of the Pareto solutions has been justified from the comparison with the direct finite element analysis. © 2011 Elsevier B.V. All rights reserved.


Cho J.R.,Pusan National University | Cho J.R.,Research and Development Institute of Midas IT | Jee Y.B.,Narin Soft | Kim W.J.,Research and Development Institute of Midas IT | And 2 more authors.
Composites Part B: Engineering | Year: 2013

High pressure rubber hose is in the lamination structure composed of pure rubbers and braided fabric composite layers to have the sufficient strength against the excessive radial expansion and the large deformation, in which the braided fabric layer is woven with wrap and fill tows inclined to each other with the predefined helix angle in the complex periodic pattern. The consideration of detailed geometry of braided fabric layer in the numerical analysis leads to a huge number of finite elements so that the braided fabric layer has been traditionally simplified as an isotropic cylindrical one with the homogeneous isotropic material properties of braid spun tread. However, this simple model leads to the numerical prediction and design with the questionable reliability. In this context, this paper addresses the development of an in-house module, which is able to be interfaced with commercial FEM code, for the reliable large deformation analysis of the reinforced rubber hose with the element number at the level of the traditional simple model. The in-house module is able to not only automatically generate 3-D unit cell (or RVE) model of the braided fabric layer but evaluate the homogenized orthotropic material properties by automatically performing a serious of unit cell finite element analyses based on the superposition method. The validity of the in-house module and the reliability of the homogenization method are verified through the illustrative numerical experiments. © 2013 Elsevier Ltd. All rights reserved.


Cho J.R.,Pusan National University | Cho J.R.,Research and Development Institute of Midas IT | Lee H.W.,POSCO | Yoo W.S.,Pusan National University
Computer Methods in Applied Mechanics and Engineering | Year: 2013

A rotation-free mixed natural element approximation of Reissner-Mindlin plate for the locking-free numerical analysis of plate-like thin elastic structures is presented, motivated by the rotation-free approximation for plate- and shell-like elastic structures and the high smoothness of Laplace interpolation functions used in natural element method. The mid-surface deflection and the rotation of shear are directly approximated using Laplace interpolation functions, while the Voronoi polygon-wise constant curvatures and bending moments are indirectly computed by area-averaging the boundary integrals of deflection derivatives and rotation of shear. The present approximation of the deflection and rotation of shear of discretized Reissner-Mindlin plate bending problem is formulated according to the modified mixed Hu-Washizu principle. Through the numerical results, it is verified that the rotation-free mixed natural element approximation of only the deflection and rotation of shear successfully prevents shear locking in the numerical analysis of plate-like thin elastic structures. © 2012 Elsevier B.V.


Cho J.R.,Pusan National University | Cho J.R.,Research and Development Institute of Midas IT | Lee H.W.,Pusan National University | Jeong W.B.,Pusan National University
International Journal of Solids and Structures | Year: 2013

The rolling resistance (RR) and the temperature distribution of 3-D periodic patterned tire, which are induced by the hysteretic loss of viscoelastic rubber compounds, are numerically predicted using the 3-D full patterned tire model. A 3-D periodic patterned tire model is constructed by copying 1-sector mesh in the circumferential direction. Using the 3-D static tire contact analysis, the strain cycles during one revolution are approximated with the strains at Gaussian points of the elements which are sector-wise repeated within the same circular ring of elements, by neglecting the tire rolling effect. The strain amplitude during one revolution of tire is determined by taking the principal value of the half-amplitudes of each strain components in the multi-axial state of strain. The hysteretic loss during one revolution is predicted in terms of the loss modulus of rubber compound and the maximum principal value of the half-amplitudes of six strain components. The temperature dependence of the loss modulus of rubbers is interpolated using the rational 4-parameter fit, and the temperature-nonlinear hysteretic loss and temperature distribution are solved by a staggered iterative computation scheme. Through the numerical experiments, the validity of the proposed prediction method is examined from the comparison with the experiment and the rolling resistance and temperature distribution of 3-D periodic patterned tire model are compared with those of the main-grooved simple tire model. As well, the dependence of the rolling resistance and temperature on the tire tread pattern is numerically investigated. © 2012 Elsevier Ltd. All rights reserved.


Park S.-W.,Pusan National University | Cho J.-R.,Research and Development Institute of Midas IT
Structural Engineering and Mechanics | Year: 2012

An adaptive modeling and simulation technique is introduced for the effective and reliable fluid-structure interaction analysis using MSC/Dytran for large-scale complex pressurized liquid containment. The proposed method is composed of a series of the global rigid sloshing analysis and the locally detailed fluid-structure analysis. The critical time at which the system exhibits the severe liquid sloshing response is sought through the former analysis, while the fluid-structure interaction in the local region of interest at the critical time is analyzed by the latter analysis. Differing from the global coarse model, the local fine model considers not only the complex geometry and flexibility of structure but the effect of internal pressure. The locally detailed FSI problem is solved in terms of multi-material volume fractions and the flow and pressure fields obtained by the global analysis at the critical time are specified as the initial conditions. An in-house program for mapping the global analysis results onto the fine-scale local FSI model is developed. The validity and effectiveness of the proposed method are verified through an illustrative numerical experiment.


Cho J.R.,Pusan National University | Cho J.R.,Research and Development Institute of Midas IT | Lee D.Y.,Pusan National University | Yoo W.S.,Pusan National University | Lim O.K.,Pusan National University
International Journal of Advanced Manufacturing Technology | Year: 2013

The bolt-flange fitting and detaching processes are numerically investigated by the updated Lagrangian elastoplastic finite element analysis. The elastoplastic behavior of the flange is modeled by the power-law plastic model with the isotropic strain hardening, while assuming the bolt to be rigid by virtue of the big difference in the material stiffness between bolt and flange. Through the parametric numerical analyses of the bolt-flange fitting and detaching processes with respect to the shape of the bolt cross-section, the characteristics of the bolt fitting and fastening forces are investigated. The validity of the simplified 2-D axisymmetric finite element model is examined through the comparison with the numerical results obtained by 3-D full finite element model. As well, the effects of the bolt petal number on these forces are investigated, and the experiment is performed to verify the numerical simulation. © 2012 Springer-Verlag London Limited.


Cho J.R.,Pusan National University | Cho J.R.,Research and Development Institute of Midas IT | Choi J.H.,Pusan National University | Kim Y.S.,Pusan National University
Tribology International | Year: 2011

In this paper, a numerical technique for predicting the wear amount of automobile tire is presented. A power function wear model derived based on the laboratory testing of rubber abrasion is adopted to correlate the wear rate of tread rubber blocks with the frictional energy dissipation, and the driving and loading conditions of the tire in the outdoor wear test are extracted from the virtual driving simulation using ADAMS. The tire frictional energy rates produced in each driving mode are computed by the frictional dynamic rolling analysis of 3D patterned tire model. Numerical results are also given to illustrate the theoretical work. © 2011 Elsevier Ltd. All rights reserved.


Jeon S.H.,Pusan National University | Cho Y.U.,Pusan National University | Seo M.W.,Pusan National University | Cho J.R.,Pusan National University | And 3 more authors.
Ocean Engineering | Year: 2013

The station keeping and the rotational oscillation control are important to secure the dynamic stability of spar-type floating offshore wind turbine subject to irregular wind and wave excitations. Those are usually evaluated in terms of rigid body dynamic response of floating substructure which supports whole offshore wind turbine. In this context, this paper addresses the numerical investigation of dynamic response of a spar-type hollow cylindrical floating substructure moored by three catenary cables to irregular wave excitation. The upper part of wind turbine above wind tower is simplified as a lumped mass and the incompressible irregular potential wave flow is generated according to the Pierson-Moskowitz spectrum. The wave-floating substructure and wave-mooring cable interactions are simulated by coupling BEM and FEM in the staggered iterative manner. Through the numerical experiments, the time- and frequency-responses of a rigid spar-type hollow cylindrical floating substructure and the tension of mooring cables are investigated with respect to the total length and the connection position of mooring cables. © 2013 Elsevier Ltd.

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