• Computers and Concrete
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• v.11 no.3
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• pp.201-222
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• 2013

A comprehensive simulation model for the transport process of fully coupled moisture and multi-species in non-saturated concrete structures is proposed. The governing equations of moisture and ion diffusion are formulated based on Fick's law and the Nernst-Planck equation, respectively. The governing equations are modified by explicitly including the coupling terms corresponding to the coupled mechanisms. The ionic interaction-induced electrostatic potential is described by electroneutrality condition. The model takes into account the two-way coupled effect of moisture diffusion and ion transport in concrete. The coupling parameters are evaluated based on the available experimental data and incorporated in the governing equations. Differing from previous researches, the material parameters related to moisture diffusion and ion transport in concrete are considered not to be constant numbers and characterized by the material models that account for the concrete mix design parameters and age of concrete. Then, the material models are included in the numerical analysis and the governing equations are solved by using finite element method. The numerical results obtained from the present model agree very well with available test data. Thus, the model can predict satisfactorily the ingress of deicing salts into non-saturated concrete.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.21 no.3
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• pp.341-349
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• 1997

The characteristics of defect correction method are discussed in a sample heat conduction problem showing the numerical solution of the error correction equation can predict the error of the numerical solution of the original governing equation. A way of using defect correction method combined with the existing algorithm for the incompressible fluid flow, is proposed and subsequently tested for the driven square cavity problem. The error correction equations for the continuity equation and the momentum equations are considered to estimate the errors of the numerical solutions of the original governing equations. With this new approach, better velocity and pressure fields can be obtained by correcting the original numerical solutions using the estimated errors. These calculated errors also can be used to estimate the orders of magnitude of the errors of the original numerical solutions.

• Transactions of the Korean Society of Mechanical Engineers
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• v.15 no.2
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• pp.396-403
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• 1991

A solution is presented for the computation of the elastic-creep stresses in a hollow cylinder subjected to nonaxisymmetric temperature distribution. The creep problem is treated by the Maxwell creep model. Laplace transformation is used for reformation of the governing equation of elastic problem and Hooke's law in a function of .gamma. , .theta. , and creep constant. The governing equation is set up using the Airy stress function which leads to the biharmonic equation. The solution is obtained by using Fourer series method and Laplace inverse method used to obtain the stress components which include the variation of time. This solution shows excellent agreement with Lamkin's and Boley & Weiner's solution. The viscoelastic stresses are also obtained for the fuel rob tube subjecting nonaxisymmetric thermal load.

• Tribology and Lubricants
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• v.27 no.2
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• pp.77-87
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• 2011

In this study, using the governing equation for thermohydrodyamic lubrication involving the homogeneous mixture of incompressible fluid derived by based on the principle of continuum mechanics, it is discussed the effects of water within turbine oil on the performance of high speed journal bearing of a steam turbine shipping engine. The governing equation is the general equation being able to be applied on the mixture of Newtonian fluid and non-Newtonian fluid. Here, the fluid viscosity index, n of power-law non-Newtonian fluid is supposed to be 1 for the application of the journal bearing in a steam turbine shipping engine lubricated with the mixture of two Newtonian fluid, for example, water within turbine oil. The results related with the bearing performance are showed.

• Structural Engineering and Mechanics
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• v.23 no.6
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• pp.599-613
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• 2006

A method for the dynamical analysis of FE discretized uncertain linear and nonlinear structures is presented. This method is based on the moment equation approach, for which the differential equations governing the response first and second-order statistical moments must be solved. It is shown that they require the cross-moments between the response and the random variables characterizing the structural uncertainties, whose governing equations determine an infinite hierarchy. As a consequence, a closure scheme must be applied even if the structure is linear. In this sense the proposed approach is approximated even for the linear system. For nonlinear systems the closure schemes are also necessary in order to treat the nonlinearities. The complete set of equations obtained by this procedure is shown to be linear if the structure is linear. The application of this procedure to some simple examples has shown its high level of accuracy, if compared with other classical approaches, such as the perturbation method, even for low levels of closures.

• Journal of Ocean Engineering and Technology
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• v.5 no.1
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• pp.55-63
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• 1991

This study is to predict accurately the wave induced current accuring by the radiation stress which acts as the driving force around Nearshore structure. For the wave induced current, the depth integrated and time averaged governing equation of an unsteady nonlinear form is derived from the continuity and momentum equation of an incompressible fluid. Numerical solutions are obtained by a finite difference method for the governing equation. In the vicinity of a structure, computed flow patterns show good agreement with the hydraulic experimental data. The numerical results obtained by neglecting the convective term show a large change of alongshore and offshore current.

• Journal of KSNVE
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• v.2 no.3
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• pp.203-211
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• 1992

The main purpose of this paper is to present both the natural frequencies and the first critical loads of tapered columns. The ordinary differential equation governing the free vibration for tapered columns under compressive axial force is derived. Three kinds of cross sectional shape are considered in the governing equation. The Runge-Kutta method and determinant search method are used to perform the integration of the differential equation and to determine the natural frequencies, respectively. Additionally, the bisection method is used to determine the critical loads. In numerical examples, the effects of compressive axial force on the natural frequencies of tapered columns are investigated varying the end conditions. The first critical loads of tapered columns are determined on the basis of dynamic concepts. The first critical loads of tapered columns are determined on the basis of dynamic concept. The effects of cross sectional shapes are shown and some typical mode shapes are also presented.

• Proceedings of the SAREK Conference
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• 2008.06a
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• pp.603-608
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• 2008

A simple equation to find a optimum speed of desiccant rotor is presented in this theoretical study. Usually the determination of optimum speed of desiccant rotor requires tedious and lengthy procedures by solving governing differential equations with many complicated parameters. The determining equation of optimal rotating speed is derivated from governing differential equations with three linearization assumptions, which simplify temperature profile linear along the desiccant rotor depth, psychrometric chart within a proper range, and relative humidity-sorption capacity relation. This study shows that the dominant parameters of optimal rotating speed of desiccant rotor are NTU, flow velocity, desiccant rotor depth, and temperature different between dehumidification and regeneration. The comparison shows the good agreement between complicated calculation results and simple theoretical equation prediction.

• Computational Structural Engineering
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• v.7 no.2
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• pp.131-138
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• 1994

Derivatives of eigenvalues and eigenvectors for statistical properties is presented. Dynamic response of random system including uncertainties for the design variable is calculated with the first order perturbation method to original governing equation. In optimal design methods, there is fundamental requirement for design gradients. A method for calculating the sensitivity coefficients is developed using the governing equation and first order perturbed equation.

• Computational Structural Engineering
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• v.7 no.3
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• pp.115-122
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• 1994

Design sensitivity analysis of the second order perturbed eigenproblems for random structural system is presented. Dynamic response of random system including uncertainties for the design variable is calculated with the first order and second order perturbation method to original governing equation. In optimal design methods, there is fundamental requirement for design gradients. A method for calculating the sensitivity coefficients is developed using the direct differentiation method for the governing equation and first order and second order perturbed equation.