• Proceedings of the Korea Concrete Institute Conference
• /
• 2000.10b
• /
• pp.1145-1150
• /
• 2000

Concrete behaves as ductile material at high temperature. The existing stress-strain relationship is not valid at high temperature condition. Thus, stress-strain curve of concrete at high temperature is re-established by modifying Saenz's suggestion in this study. A constitutive model of concrete subjected to elevated temperature is also suggested. The model consists of three components; free thermal stain, mechanical strain and thermal creep strain. As the temperature increase, the thermal creep becomes more critical to the failure of concrete. The thermal creep strain of concrete is derived from the modified power-law relation for the steady state creep. The proposed equation for thermal creep employs a Dorn's temperature compensated time theorem

• Steel and Composite Structures
• /
• v.18 no.3
• /
• pp.693-709
• /
• 2015

In this article, nonlinear free vibration behaviour of functionally graded spherical panel is analysed. A nonlinear mathematical model is developed based on higher order shear deformation theory for shallow shell by taking Green-Lagrange type of nonlinear kinematics. The material properties of functionally graded material are assumed to be varying continuously in transverse direction and evaluated using Voigt micromechanical model in conjunction with power-law distribution. The governing equation of the shell panel is obtained using Hamilton's principle and discretised with the help of nonlinear finite element method. The desired responses are evaluated through a direct iterative method. The present model has been validated by comparing the frequency ratio (nonlinear frequency to linear frequency) with those available published literatures. Finally, the effect of geometrical parameters (curvature ratio, thickness ratio, aspect ratio and support condition), power law indices and amplitude of vibration on the frequency ratios of spherical panel have been discussed through numerical experimentations.

• Steel and Composite Structures
• /
• v.26 no.5
• /
• pp.649-662
• /
• 2018

In this study, based on the three-dimensional theory of elasticity, free vibration characteristics of sandwich sectorial plates with multiwalled carbon nanotube-(MWCNT)-reinforced composite core are considered. Modified Halpin-Tsai equation is used to evaluate the Young's modulus of the MWCNT/epoxy composite samples by the incorporation of an orientation as well as an exponential shape factor in the equation. The exponential shape factor modifies the Halpin-Tsai equation from expressing a straight line to a nonlinear one in the MWCNTs wt% range considered. In this paper, free vibration of thick functionally graded sandwich annular sectorial plates with simply supported radial edges and different circular edge conditions including simply supported-clamped, clamped-clamped, and free-clamped is investigated. A semi-analytical approach composed of two-dimensional differential quadrature method and series solution are adopted to solve the equations of motion. The material properties change continuously through the core thickness of the plate, which can vary according to a power-law, exponentially, or any other formulations in this direction. This study serves as a benchmark for assessing the validity of numerical methods or two-dimensional theories used to analysis of laminated sectorial plates.

• Tribology and Lubricants
• /
• v.14 no.3
• /
• pp.39-45
• /
• 1998

Reynolds equation, which describes behavior of fluid film in journal bearings, basically satisfies mass conservation. But, boundary conditions usually used with this equation, e.g. half Sommerfeld or Reynolds boundary conditions, cannot fulfill this natural law of conservation. In the case of connecting rod bearing, where applied load is dynamic and its magnitude is relatively large, such unrealistic boundary conditions have serious influence on calculation results, especially on lubricant flow rate or power disspation which are important parameters in thermal analysis. In this paper, mass-conserving boundary condition was applied in the finite element analysis of connecting rod bearings. Lubricant flow rate and power dissipation rate were calculated together with journal center locus, minimum film thickness and maxmium film pressure. These computation results were compared with those of the case of Reynolds boundary condition. Balance between inlet and outlet flow rate was well achieved in the case of mass-conserving boundary condition.

• Proceedings of the KSR Conference
• /
• 2010.06a
• /
• pp.36-40
• /
• 2010

In recent society, the electricity is so essential for the human lives. Lots of modern people take many cultural benefits owing to the development of the power systems, the cell phone, the electrical appliances, and etc. However, the problems related to the electromagnetic field generate as the side effects. Examples are the fault in the electric machinery due to the electromagnetic coupling, the fault in the communication devices due to the electromagnetic field around the power line equipments, and the effect upon the human beings due to the electromagnetic field, and etc. In this paper, we induce the vector equation about the magnetic field based on Biot-Savart law. We calculate the magnetic field at the surface of the high speed train with this induced equation and the current in the high speed railroad catenary wire. Finally, we calculate the magnetic field in the high speed train considering the material property like the permeability, the conductivity, and so on.

• Journal of Power System Engineering
• /
• v.9 no.4
• /
• pp.175-180
• /
• 2005

Incorrections between model and plant are parameter, system order uncertainties and modeling error due to disturbance like friction. Therefore to achieve a good tracking performance, adaptive discrete time sliding mode tracking controller is used under time-varying desired position. Based on the diophantine equation, a new discrete time sliding function is defined and utilized for the control law. Robustness is increased by using both a recursive least-square method and a sliding function-based nonlinear feedback. The effectiveness of the proposed control algorithm is proved by the results of simulation and experiment.

• Journal of Power System Engineering
• /
• v.3 no.3
• /
• pp.14-21
• /
• 1999

The wave nature of heat conduction has been developed in situations involving extreme thermal gradients, very short times, or temperatures near absolute zero. Under the excitation of a periodic surface heating in a finite medium, the hyperbolic and parabolic heat conduction equations and the damped wave equations in heat flux are presented for comparative analysis by using the Green's function with the integral transform technique. The Kummer transformation is also utilized to accelerate the rate of convergence of these solutions. On the other hand, the temperature distributions are obtained through integration of the energy conservation law with respect to time. For hyperbolic heat conduction, the heat flux distribution does not exist throughout all the region in a finite medium within the range of very short times(${\xi}<{\eta}_l$). It is shown that due to the thermal relaxation time, the hyperbolic heat conduction equation has thermal wave characteristics as the damped wave equation has wave nature.

• Journal of Power System Engineering
• /
• v.14 no.6
• /
• pp.35-40
• /
• 2010

This article deals with the numerical analysis results of stiffness of diaphragm spring used in the clutch of a manual transmission. In order to investigate the relationship of the force and displacement in a diaphragm spring, we have established a numerical model of diaphragm spring using a well-known analytic model of Belleville spring and a cantilever beam model for the finger part of diaphragm spring. Using the stress and strain relations of Belleville spring and cantilever beam, we propose the analytic equation of motion of diaphragm spring for the use of a clutch automated actuator in an automated manual transmission. The proposed analytic model represents the typical dynamic characteristics of diaphragm spring along with the release bearing travel. And it is characterized in a closed-form equation, therefore it can be used for the further study of development of actuator and control law of clutch automating mechanism.

• Transactions of the Korean Society of Mechanical Engineers A
• /
• v.26 no.5
• /
• pp.795-802
• /
• 2002

For assessing significance of a defect in a component operating at high (creeping) temperatures, accurate estimation of fracture mechanics parameter, $C^{*}$-integral, is essential. Although the J estimation equation in the GE/EPRl handbook can be used to estimate the $C^{*}$-integral when the creep -deformation behavior can be characterized by the power law creep, such power law creep behavior is a very poor approximation for typical creep behaviors of most materials. Accordingly there can be a significant error in the $C^{*}$-integral. To overcome problems associated with GE/EPRl approach, the reference stress approach has been proposed, but the results can be sometimes unduly conservative. In this paper, a new method to estimate the $C^{*}$-integral for deflective components is proposed. This method improves the accuracy of the reference stress approach significantly. The proposed calculations are then validated against elastic -creep finite element (FE) analyses for four different cracked geometries following various creep -deformation constitutive laws. Comparison of the FE $C^{*}$-integral values with those calculated from the proposed method shows good agreements.greements.

• Explosives and Blasting
• /
• v.8 no.1
• /
• pp.3-16
• /
• 1990

The cautious blasting works had been used with emulsion explosion electric M/S delay caps. Drill depth was from 3m to 6m with Crawler Drill $\varphi{70mm}$ on the calcalious sand stone(sort-moderate-semi hard Rock). The total numbers of feet blast were 88. Scale distance were induces 15.52-60.32. It was applied to propagation Law in blasting vibration as follows. Propagtion Law in Blasting Vibration $V=K(\frac{D}{W^b})^n$ where V : Peak partical velocity(cm/sec) D : Distance between explosion and recording sites (m) W : Maximum Charge per delay-period of eighit milliseconds or more(Kg) K : Ground transmission constant, empirically determind on th Rocks, Explosive and drilling pattern ets. b : Charge exponents n : Reduced exponents Where the quantity $D/W^b$ is known as the Scale distance. Above equation is worked by the U.S Bureau of Mines to determine peak particle velocity. The propagation Law can be catagrorized in three graups. Cabic root Scaling charge per delay Square root Scaling of charge per delay Site-specific Scaling of charge per delay Charge and reduction exponents carried out by multiple regressional analysis. It's divided into under loom and over loom distance because the frequency is verified by the distance from blast site. Empirical equation of cautious blasting vibration is as follows. Over 30m----under l00m----- $V=41(D/3\sqrt{W})^{-1.41}$ -----A Over l00m-----$V= 121(D/3\sqrt{W})^{-1.66}$-----B K value on the above equation has to be more specified for furthur understang about the effect of explosives, Rock strength. And Drilling pattern on the vibration levels, it is necessary to carry out more tests.