• Korean Chemical Engineering Research
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• 제53권1호
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• pp.91-102
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• 2015

Analytical solutions for the forced convection heat transfer of viscoelastic fluids obeying the Giesekus model are obtained in a concentric annulus under laminar flow for both thermal and hydrodynamic fully developed conditions. Boundary conditions are assumed to be (a) constant fluxes at the walls and (b) constant temperature at the walls. Temperature profiles and Nusselt numbers are derived from dimensionless energy equation. Subsequently, effects of elasticity, mobility parameter and viscous dissipation are discussed. Results show that by increasing elasticity, Nusselt number increases. However, this trend is reversed for constant wall temperature when viscous dissipation is weak. By increasing viscous dissipation, the Nusselt number decreases for the constant flux and increases for the constant wall temperature. For the wall cooling case, when the viscous dissipation exceeds a critical value, the generated heat overcomes the heat which is removed at the walls, and fluid heats up longitudinally.

• Advances in concrete construction
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• 제1권4호
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• pp.305-318
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• 2013

Engineering properties such as compressive strength, splitting tensile strength, modulus of rupture, modulus of elasticity and Poisson's ratio of geopolymer concrete (GPC) and steel fibre reinforced geopolymer concrete (SFRGPC) have been obtained from standard tests and compared. A total of 15 specimens were tested for determining each property. The grade of concrete used was M 40. The percentages of steel fibres considered include 0.25%, 0.5%, 0.75% and 1%. In general, the addition of fibres improved the mechanical properties of both GPC and SFRGPC. However the increase was found to be nominal in the case of compressive strength (8.51%), significant in the case of splitting tensile strength (61.63%), modulus of rupture (24%), modulus of elasticity (64.92%) and Poisson's ratio (50%) at 1% volume fraction of fibres. An attempt was made to obtain the relation between the various engineering properties with the percentage of fibres added.

• 한국농공학회논문집
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• 제46권6호
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• pp.13-19
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• 2004

This study was performed to evaluate permeable properties of eco-concrete using soil, natural coarse aggregate, soil compound and polypropylene fiber. The fIexural strength, ultrasonic pulse velocity and dynamic modulus of elasticity were increased with increasing the content of coarse aggregate, soil compound and polypropylene fiber. The flexural strength, ultrasonic pulse velocity and dynamic modulus of elasticity were 259 MPa, 3,527 m/s and 275 ${\times}$ 102 MPa at the curing age of 28 days, respectively. The coefficient of permeability was decreased with increasing the content of coarse aggregate and soil compound, but it was increased with increasing the content of polypropylene fiber. Accordingly, this concrete can be used for farm road.

• Structural Engineering and Mechanics
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• 제39권4호
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• pp.449-463
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• 2011

A free vibration analysis is made of a moderately-thick toroidal shell based on a shear deformation (Timoshenko-Mindlin) shell theory. This work represents an extension of earlier work by the authors which was based on a thin (Kirchoff-Love) shell theory. The analysis uses a modal approach in the circumferential direction, and numerical results are found using the differential quadrature method (DQM). The analysis is first developed for a shell of revolution of arbitrary meridian, and then specialized to a complete circular toroidal shell. A second analysis, based on the three-dimensional theory of elasticity, is presented to cover thick shells. The shear deformation theory is validated by comparing calculated results with previously published results for fifteen cases, found using thin shell theory, moderately-thick shell theory, and the theory of elasticity. Consistent agreement is observed in the comparison of different results. New frequency results are then given for moderately-thick and thick toroidal shells, considered to be completely free. The results indicate the usefulness of the shear deformation theory in determining natural frequencies for toroidal shells.

• 통합자연과학논문집
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• 제1권2호
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• pp.127-132
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• 2008

This project follows the heterogeneous agent market segmented model of Landon-Lane and Occhino (2007) with using Korean data, M1 and GDP deflator from 1882:I to 2007:II. This paper estimates parameters with Monte Carlo Markov Chain. The fraction of traders, ${\lambda}$, in Korea is 15.64%. The quarterly preferences discount factor's, ${\beta}$, posterior mean is 0.9922. The posterior mean of the inverse of the elasticity of the labor supply to the real wage, ${\varphi}$, is 0.0316. The elasticity of the labor supply to the real wage has a very large value. By Hansen (1985) and Christiano and Eichenbaum (1992) and Cooley and Hansen (1989), models having large elasticity of the aggregate labor supply better match macroeconomic data.

• 대한교통학회지
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• 제7권2호
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• pp.17-27
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• 1989

A nonlinear programming model for evaluating public transit fare system is proposed. The model finds transit fare level and the structure that maximizes gross fare-box revenue subject to constraints on minimum ridership and the form of the fare equations. It is assumed that the demand for transit is a function of fare and its own-fare elasticity. It is assumed that the demand for transit is a function of fare and its own-fare elasticity. It is also assumed that the conditions including fare of the other modes are unchanged ; i.e., partial equilibrium. Empirical study has been performed for the case of Seoul subway system. This study includes an analysis of fare structure ; flat system and distance-based fare system. Sensitivity and comperative static analysis for elasticity has been also demonstrated.

• Advances in aircraft and spacecraft science
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• 제6권1호
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• pp.1-18
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• 2019

This present article represents the study of the forced vibration of nanobeam of a single-walled carbon nanotube (SWCNTs) surrounded by a polymer matrix. The modeling was done according to the Euler-Bernoulli beam model and with the application of the non-local continuum or elasticity theory. Particulars cases of the local elasticity theory have also been studied for comparison. This model takes into account the different effects of the interaction of the Winkler's type elastic medium with the nanobeam of carbon nanotubes. Then, a study of the influence of the amplitude distribution and the frequency was made by variation of some parameters such as (scale effect ($e_0{^a}$), the dimensional ratio or aspect ratio (L/d), also, bound to the mode number (N) and the effect of the stiffness of elastic medium ($K_w$). The results obtained indicate the dependence of the variation of the amplitude and the frequency with the different parameters of the model, besides they prove the local effect of the stresses.

• Advances in nano research
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• 제14권3호
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• pp.285-294
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• 2023

The dynamic and sensing performances of nanomechanical resonators with their different boundary conditions are studied based on surface elasticity-based modeling and simulation. Specifically, the effect of surface stress is included in Euler-Bernoulli beam model for different boundary conditions. It is shown that the surface effect on the intrinsic elastic property of nanowire is independent of boundary conditions, while these boundary conditions affect the frequency behavior of nanowire resonator. The detection sensitivity of nanowire resonator is remarkably found to depend on the boundary conditions such that double-clamping boundary condition results in the higher mass sensitivity of the resonator in comparison with simple-support or cantilever boundary condition. Furthermore, we show that the frequency shift of nanowire resonator due to mass adsorption is determined by its length, whereas the frequency shift is almost independent of its thickness. This study enables a design principle providing an insight into how the dynamic and sensing performances of nanomechanical resonator is determined and tuned.

• Korea-Australia Rheology Journal
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• 제11권3호
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• pp.247-253
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• 1999

The growth of a spherical vapor bubble contained in a large body of upper convected Maxwell fluid is theoretically analyzed under the devolatilization condition of polymer by using a Galerkin FEM in the Lagrangian frame. Using the finite element technique, a fully explicit numerical scheme is developed both for the calculation of pressure distribution and for the tracking of bubble surface. Oscillatory behavior in bubble radius is observed during growth and the oscillatory behavior is found to be due to the interaction of mass transfer resistance and elasticity. It is found that the elasticity of fluid accelerates the growth and removal of volatile component. It is also found that the bubble growth in the devolatilization of polymers is affected by both mass transfer resistance and viscoelasticity of fluids.

• Structural Engineering and Mechanics
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• 제26권5호
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• pp.591-615
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• 2007

An improvement is introduced to solve the plane problems of linear elasticity by reciprocal theorem for orthotropic materials. This method gives an integral equation with complex kernels which will be solved numerically. An artificial boundary is defined to eliminate the singularities and also an algorithm is introduced to calculate multi-valued complex functions which belonged to the kernels of the integral equation. The chosen sample problem is a plate, having a circular or elliptical hole, stretched by the forces parallel to one of the principal directions of the material. Results are compatible with the solutions given by Lekhnitskii for an infinite plane. Five different orthotropic materials are considered. Stress distributions have been calculated inside and on the boundary. There is no boundary layer effect. For comparison, some sample problems are also solved by finite element method and to check the accuracy of the presented method, two sample problems are also solved for infinite plate.