• Structural Engineering and Mechanics
• /
• v.44 no.1
• /
• pp.109-125
• /
• 2012

Post-buckling behavior of Timoshenko beams subjected to uniform temperature rising with temperature dependent physical properties are studied in this paper by using the total Lagrangian Timoshenko beam element approximation. The beam is clamped at both ends. In the case of beams with immovable ends, temperature rise causes compressible forces end therefore buckling and post-buckling phenomena occurs. It is known that post-buckling problems are geometrically nonlinear problems. Also, the material properties (Young's modulus, coefficient of thermal expansion, yield stress) are temperature dependent: That is the coefficients of the governing equations are not constant in this study. This situation suggests the physical nonlinearity of the problem. Hence, the considered problem is both geometrically and physically nonlinear. The considered highly non-linear problem is solved considering full geometric non-linearity by using incremental displacement-based finite element method in conjunction with Newton-Raphson iteration method. The beams considered in numerical examples are made of Austenitic Stainless Steel (316). The convergence studies are made. In this study, the difference between temperature dependent and independent physical properties are investigated in detail in post-buckling case. The relationships between deflections, thermal post-buckling configuration, critical buckling temperature, maximum stresses of the beams and temperature rising are illustrated in detail in post-buckling case.

• Transactions of the Korean Society for Noise and Vibration Engineering
• /
• v.15 no.7 s.100
• /
• pp.836-842
• /
• 2005

Nonlinear dynamic characteristics of active piezolaminated plates are investigated with respect to the thermopiezoelastic behaviors. For largely deformed structures with small strain, the incremental total Lagrangian formulation is presented based on the virtual work principles. A multi-field layer-wise finite shell element is proposed for assuring high accuracy and non-linearity of displacement, electric and thermal fields. For dynamic consideration of thermopiezoelastic snap-through phenomena, the implicit Newmark's scheme with the Newton-Raphson iteration is implemented for the transient response of various piezolaminated models with symmetric or eccentric active layers. The bifurcate thermal buckling of symmetric structural models is first investigated and the characteristics of piezoelectric active responses are studied for finding snap-through piezoelectric potentials and the load-path tracking map. The thermoelastic stable and unstable postbuckling, thermopiezoelastic snap-through phenomena with several attractors are proved using the nonlinear time responses for various initial conditions and damping loss factors. Present results show that thermopiezoelastic snap-through phenomena can result in the difficulty of buckling and postbuckling control of intelligent structures.

• Transactions of Materials Processing
• /
• v.12 no.8
• /
• pp.710-717
• /
• 2003

The implicit, finite element analysis program for analyzing the springback in the warm forming process of aluminum alloy sheets was developed. For the description of planar anisotropy in warm forming temperatures, Barlat's yield function is employed, and the power law type constitutive equation is used in terms of working temperatures for the depiction of work hardening in high temperatures. Also, Jetture's 4-node shell elements are introduced for reflecting the mechanical behavior of aluminum alloy sheet and the non-steady heat balance equations are solved for considering heat gain and loss during the forming process. For the springback evaluation, Newton-Raphson iteration method is introduced for overcoming the geometric nonlinearlity problem. In order to verify the validity of the FEM program developed, the stretching bending and springback processes are simulated. Though springback analysis results are slightly bigger than experimental ones, they have the same trend of the decreasing springback as the forming temperature increases.

• Journal of Electrical Engineering and Technology
• /
• v.8 no.3
• /
• pp.411-420
• /
• 2013

Recently, Korean system operating conditions have gradually approached an upper limit. When a contingency occurs, the power system may have no solutions. Different from the cases of bad initial guesses or the solutions are too close to the solvability boundary in which numerical methods can be applied, for unsolvable cases, the only way to restore solvability would be structure modifications. In this paper, a new approach for corrective and preventive control to such cases is proposed in two steps: (i) finding any solution regardless its feasibility; (ii) for the infeasible solution, make it feasible with additional modifications at load buses having Distributed Energy Resources. The test case built based on the peak load profile of 2008 by KEPCO including 1336 buses is analyzed. Since reactive power compensation is optimized to restore solvability, all demands are met, therefore no blackouts happen. The proposed method was integrated in the LP program designed by power21 Corporation.

• Proceedings of the KIEE Conference
• /
• 2015.07a
• /
• pp.286-287
• /
• 2015

Currently, Studies on improving the reliability of power supply is becoming an important issue because of the increase in demand of the electric power system. Therefore necessity of automation in distribution system is increasing day by day. However, a measured voltage data from FRTU of distribution automation system is incorrect because of installation space limits. Therefore there is a need of system analysis method by considering the characteristics of the distribution system. For a distribution system, applying the power flow method of transmission system has some problems, as distribution is radial system and it has unbalanced load. Therefore power flow by considering the characteristics of the distribution system have been studied. Existing power flow analysis of the distribution system has different methods like direct analysis method, backward/forward sweep method, modified method of newton raphson etc. In this paper, an improved power flow analysis method based on backward/forward sweep method is proposed in order to efficiently operate the distribution automation system. The proposed method of power flow has been verified through the result of case study.

• Advances in Computational Design
• /
• v.2 no.3
• /
• pp.165-194
• /
• 2017

The present work proposes the thermo mechanically induced statistics of nonlinear transverse central deflection of elastically supported functionally graded (FG) plate subjected to static loadings with random system properties. The FG plate is supported on two parameters Pasternak foundation with Winkler cubic nonlinearity. The random system properties such as material properties of FG material, external loading and foundation parameters are assumed as uncorrelated random variables. The material properties are assumed as non-uniform temperature distribution with temperature dependent (TD) material properties. The basic formulation for static is based on higher order shear deformation theory (HSDT) with von-Karman nonlinear strain kinematics through Newton-Raphson method. A second order perturbation technique (SOPT) and direct Monte Carlo simulation (MCS) are used to compute the nonlinear governing equation. The effects of load parameters, plate thickness ratios, aspect ratios, volume fraction, exponent, foundation parameters, and boundary conditions with random system properties are examined through parametric studies. The results of present approaches are compared with those results available in the literature and by employing direct Monte Carlo simulation (MCS).

• Transactions of the Korean Society of Mechanical Engineers
• /
• v.18 no.10
• /
• pp.2640-2652
• /
• 1994

The stiffness of 6-node isotropic element is stiffer than that of 8-node isotropic element of same configuration. This phenomenon was called 'Relative Stiffness Stiffening Phenomenon'. In this paper, an equation of sampling point modification which correct this phenomenon was derived for the composite plate, as well as an equation for an isotropic plate. The relative stiffness stiffening phenomena of an isotropic plate element could be corrected by modifying Gauss sampling points in the numerical integration of stiffness matrix. This technique could also be successfully applied to the static analyses of composite plate modeled by the 3-dimensional 16-node elements. We predicted theoretical errors of stiffness versus the number of layers that result from the reduction of numerical integration order. These errors coincide very well with the actual errors of stiffness. Therefore, we can choose full integration of reduced integration based upon the permissible error criterion and the number of layers by using the thoretically predicted error.

• Transactions of the Korean Society of Mechanical Engineers A
• /
• v.21 no.12
• /
• pp.2146-2155
• /
• 1997

This paper presents the Wire Parallel Mechanism for robot pose measurement which can be used to robot calibration. It is constructed with six parallel links using wire. The position and orientation of the end effector of a robot are calculated from the wire length that measured by the encoder. The unique solution is obtained from a Newton-Raphson method and geometric configuration of the mechanism, also the method to estimate a measuring space is presented. Through the simulations, it is verified that the proposed mechanism can measure a robot pose, and has a large measuring space. In conclusion, it can be used effectively in a robot pose measurement with little cost and effort.

• Tribology and Lubricants
• /
• v.30 no.2
• /
• pp.77-85
• /
• 2014

This study set out to predict the load capacity and rotordynamic coefficients of tilting-pad journal bearings, taking the pivot stiffness into account. The analysis uses rocker-back (cylindrical) and ball in socket (spherical) pivot models, both of which are based on Hertzian contact stress theory. The models ascertain the non-linear elastic deformation of the pivots according to the applied load, pivot geometry, and material properties. At present, the Reynolds equation for an isothermal, isoviscous, and incompressible fluid is used to calculate the film pressure by using the finite-element method, after which the Newton-Raphson method is used to simultaneously find the journal center location, pad angles, and pivot deflections. The bearing analysis, excluding the pivot models, is validated using predictions those are readily available in the literature. As the rotor speed increases, the predicted journal eccentricity and damping coefficients decrease, but the stiffness coefficients increase, as expected. Most importantly, the implementation of the pivot models increases the journal eccentricity but significantly decreases the stiffness and damping coefficients of the tilting-pad journal bearings.

• Transactions of the Korean Society of Mechanical Engineers
• /
• v.10 no.5
• /
• pp.593-600
• /
• 1986

In direct contact power transmission from primary driver to a secondary follower system, one of the important problems is the vibration transmission. In some applications the reduction of vibration level at the follower as low as possible is utmost important. The magnetically coupled power transmission system is often used for this purpose. In this paper, we report the results of a study on the nonlinear torsional vibration transmission characteristics of the rotating system with face-type magnet coupling. The equation of motion is solved analytically up to 3rd harmonics. The frictional force of the sliding bearing which is used to support the follower shaft is considered as the damping term. Numerical calculations are carried out by the Newton-Raphson method, and the calculated results are compared with the experiment for face-type magnet coupling. The experimental result shows that the reasonant frequency of the magnet coupling is very low and is in good agreement with the theoretical result when the average damping constant per unit area of the sliding bearing is 0.5kg*f*sec/cm$^{3}$.