• Proceedings of the KSR Conference
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• 2000.11a
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• pp.358-365
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• 2000

For the general case of loading conditions and boundary conditions, it is very difficult to obtain closed form solutions for buckling loads and natural frequencies of thin-walled structures because its behaviour is very complex due to the coupling effect of bending and torsional behaviour. In consequence, most of previous finite element formulations are introduce approximate displacement fields to use shape functions as Hermitian polynomials, and so on. The Purpose of this study is to presents a consistent derivation of exact dynamic stiffness matrices of thin-walled straight beams, to be used ill tile free vibration analysis, in which almost types of boundary conditions are exist An exact dynamic element stiffness matrix is established from governing equations for a uniform beam element of nonsymmetric thin-walled cross section. This numerical technique is accomplished via a generalized linear eigenvalue problem by introducing 14 displacement parameters and a system of linear algebraic equations with complex matrices. The natural frequency is evaluated for the thin-walled straight beam structure, and the results are compared with analytic solutions in order to verify the accuracy of this study.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 1999.03b
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• pp.80-83
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• 1999

Rigid Plasticity Finite Element Analysis is developed for the shapes of dead metal zone and the curving velocity distribution in the eccentric square dies extrusion. The shape of dead metal zone is defined as the boundary surface with the maximum friction constant between the deformable zone and the rigid zone. The curving phenomenon in the eccentric square dies is caused by the eccentricity of square dies. The deviated velocity is changed with the distance form the center of cross-section of the workpiece. The results show that the curving of products and the shapes of the dead metal zone are determined by Rigid Plasticity Finite Element Analysis and that the curvature of the extruded products increases with the eccentricity.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 1999.03b
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• pp.35-38
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• 1999

Tube bending is an important factor of the hydroforming processes. The tube must be bent to the approximate centerline of the finished part prior to hydroforming to enable the tube to be placed in the die cavity. This paper presents the simulation results in prebending process by a rotary bending machne and a bend die that is used to form an automotive part a tie bar, Prebending simulation is carried out to obtain the shape change of cross section and thinning in bending process. To avoid occurring wrinkle in compressive zone during bending process a wiper die included,. A parametric study is carried out to obtain the effect of the forming parameters such as a bend radius and tube thickness

• Journal of The Korean Astronomical Society
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• v.8 no.1
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• pp.3-9
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• 1975

Densities of the three constituent spheroids of the same eccentricity as our earlier model of the Galaxy are assumed to be given by an analytical form of $_{{\rho}i}$(r)=$k_ie^{-m_ir^u{_i}}$, where $k_i,\;m_i$, and ${\alpha}i$ are obtained by comparing with the results of the previous model. Using three values of $_{{\rho}i}$(r) the galactic rotation curve, mass of each spheroid and the whole Galaxy are calculated, and the three dimensional density distribution in the Galaxy is also obtained. The calculated rotation curve of the model Galaxy is in good agreement with the observed curve, and the shape of the cross section of the model Galaxy given by the computed density is very similar to the inferred shape of the spiral galaxies.

• Smart Structures and Systems
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• v.13 no.4
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• pp.637-657
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• 2014

This paper presents a dynamic analysis of three-dimensional beams. Structures made of functionally graded materials are considered. Several higher-order as well as classical theories are derived by means of a compact notation for the a-priori expansion order of the displacement field over the beam cross-section. The governing differential equations and boundary conditions are obtained in a condensed nuclear form that does not depend on the kinematic hypotheses. The problem is, then, exactly solved in space by means of a Navier-type solution, whereas time integration is performed by means of Newmark's solution scheme. Slender and short simply supported beams are investigated. Results are validated towards three-dimensional FEM results obtained via the commercial software ANSYS. Numerical investigations show that good accuracy can be obtained through the proposed formulation provided that the appropriate expansion order is considered.

• Structural Engineering and Mechanics
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• v.65 no.4
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• pp.389-400
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• 2018

An exact solution for the title problem was obtained in closed-form fashion considering general boundary conditions. The expressions of moment, shear and shear coefficient (or shear factor) of cross section under the effect of arbitrary temperature distribution were first derived. In view of these relationships, the differential equations of Timoshenko beam under the effect of temperature were obtained and solved. Second, the characteristic equations of Timoshenko beam carrying several spring-mass systems under the effect of temperature were derived based on the continuity and force equilibrium conditions at attaching points. Then, the correctness of proposed method was demonstrated by a Timoshenko laboratory beam and several finite element models. Finally, the influence law of different temperature distribution modes and parameters of spring-mass system on the modal characteristics of Timoshenko beam had been studied, respectively.

• Journal of the Korean Electrochemical Society
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• v.9 no.4
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• pp.151-157
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• 2006

A two-dimensional numerical model to study the performance of anode-supported flat-tube solid oxide fuel cell (SOFC) far the cross section of the cell in the flow direction of the fuel and air flows is developed. In this model a mass and charge balance, Maxwell-Stefan equation as well as the momentum equation by using, Darcy's law are applied in differential form. The finite element method using FEMLAB commercial software is used for meshing, discritization and solving the system of coupled differential equations. The current density distribution and fuel consumption as well as water production are analyzed. Experimental data is used to verify a predicted voltage-current density and power density versus current density to judge on the model accuracy.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2011.10a
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• pp.572-577
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• 2011

A disc spring consists of a conical disc. A load-displacement formula was newly developed in the form of energy method to consider both rigid and friction. The cross section of the disc spring has identical slope angles at the bottom of conical. To solve such a problem, an energy method calculation is proposed. To achieve the goal of this study, the proposed calculation is extended to a disc spring with friction. A firm basis background study based on Almen's work is presented in developing a new numerical approach to predict the available formulation for a disc spring with friction.

• Journal of the Korean Society of Hazard Mitigation
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• v.9 no.2
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• pp.11-15
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• 2009

This paper is concerned with the elastic buckling of thin-walled arches that are subjected to uniform bending. Nonlinear strain-displacement relations with the initial curvature are substituted into the second variation of the total potential energy to obtain the energy equation including initial curvature effects. The approximation for initial curvature effects that the bending normal strain distribution is linear across the cross section is applied consistently in the derivation process. The closed form solution is obtained for flexural-torsional buckling of arches under uniform bending and, it is compared with the previous theoretical results.

• Steel and Composite Structures
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• v.2 no.6
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• pp.461-474
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• 2002

This paper presents the experimental and theoretical results of SUS 304 stainless tubes with different diameter-to-thickness ratio (D/t ratio) subjected to pure bending creep. Pure bending creep occurs when a circular tube is bent to a desired moment and held at that moment for a period of time. It was found that the magnitudes of the creep curvature and ovalization of tube cross-section increase faster with a higher hold moment than that with a lower one. Due to continuously increasing curvature, the circular tubes eventually buckle. Finally, a theoretical form was proposed in this study so that it can be used to describe the relationship between the creep curvature and time. Theoretical simulations are compared with the experimental test data, showing that good agreement between the experimental and theoretical results has been achieved.