• Journal of the KSME
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• v.16 no.1
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• pp.49-53
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• 1976

Groundwater flow in a two-layer aquifer is studied theoretically and experimentally. Nonlinear differential equations are independently linearized for the upper and the lower layer, and approximate solutions are obtained. Fine sands and coarse sands are used in experiments. For steady flow, theoretical solutions agrees excellently with experimental results For unsteady flow, however, agreement is not so good, because the experimental conditions do not match with theoretical assumptions.

• Kyungpook Mathematical Journal
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• v.59 no.1
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• pp.191-202
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• 2019

The aim of this paper is to develop a monotone iterative technique by introducing upper and lower solutions to Riemann-Liouville fractional differential equations with deviating arguments and integral boundary conditions. As an application of this technique, existence and uniqueness results are obtained.

• Steel and Composite Structures
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• v.17 no.4
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• pp.535-548
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• 2014

In this paper, the exact closed-form solutions for torsional analysis of heterogeneous magnetostrictive circular cylinder are derived. The cylinder is subjected to the action of a magnetic field produced by a constant longitudinal current density. It is also acted upon by a particular kind of shearing stress at its upper base. The rigidity of the cylinder is graded through its axial direction from one material at the lower base to another material at the upper base. The distributions of circumferential displacement and shear stresses are presented through the radial and axial directions of the cylinder. The influence of the magnetostrictive parameter is discussed. The effects of additional parameters are investigated.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.20 no.1
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• pp.328-335
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• 1996

The one-dimensional flame analysis was carried out to understand the combustion phenomena in porous media. The downstream as well as upstream solution corresponding to upper and lower solutions could be obtained. While upper flame temperature gets higher, lower flame temperature gets lower, as the flame approaches the central part of the combustor. The reason why upstream flame and downstream flame exist at the same flow condition is that the regions where net heat recirculation is identical exist in upstream and downstream of the combustor. In order for the downstream flame to be stabilized, more heats needed to be recirculated towards upstream because of larger radiation loss of downstream flame.

• 한국전산유체공학회:학술대회논문집
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• 2000.05a
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• pp.113-119
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• 2000

Two-dimensional steady flow of two immiscible, compressible fluids are considered when the temperature of each layer is constant. Both upper and lower fluids are bounded by two horizontal rigid boundaries with symmetric obstruction of compact support at the tourer boundary. By using asymptotic method, we derive the forced K-dV equation governing interfacial wave. Various solutions and numerical results are presented.

• Communications of the Korean Mathematical Society
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• v.22 no.1
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• pp.53-64
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• 2007

In this paper, we apply the generalized quasilinearization technique to a forced Duffing equation with three-point mixed nonlinear nonlocal boundary conditions and obtain sequences of upper and lower solutions converging monotonically and quadratically to the unique solution of the problem.

• Journal of the Korean Society for Industrial and Applied Mathematics
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• v.19 no.1
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• pp.57-68
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• 2015

When a straight channel formed by two parallel porous plates, through which two immiscible liquids occupying different heights are flowing a secondary motion is set up. The motion is caused by moving the upper plate with a uniform velocity about an axis perpendicular to the plates. The solutions are exact solutions. Here we discuss the effect of suction parameter and the position of interface on the flow phenomena in case of Couette flow. The velocity distributions for the primary and secondary flows have been discussed and presented graphically. The skin-friction amplitude at the upper and lower plates has been discussed for various physical parameters.

• Journal of the Korean Geotechnical Society
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• v.23 no.4
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• pp.185-197
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• 2007

Limit analysis of upper and lower bound solutions has been well developed to provide the stability numbers for shallow tunnels in cohesive soil ($c_u$ material), cohesive-frictional soil (c'-$\phi$' material) and cohesionless soil ($\phi$'material). However, an extension of these methods to relatively deep circular tunnels in the cohesionless soil has been explored rarely to date. For this reason, the closed-form analytical solutions including lower bound solution based on the stress discontinuity concept and upper bound solution based on the kinematically admissible failure mechanism were proposed for assessing tunnel collapse load in this study. Consequently, the tunnel collapse load from those solutions was compared with both the finite element analysis and the previous analytical bound solutions and shown to be in good agreement with the FE results, in particular with the FE soil elements located on the horizontal tunnel axis.

• Advances in aircraft and spacecraft science
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• v.6 no.1
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• pp.19-30
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• 2019

Two- and three-dimensional turbulent airflows in a 9-degrees-bent channel are studied numerically. The inner surfaces of upper and lower walls are parallel to each other upstream and downstream of the bend section. The free stream is supersonic, whereas the flow at the channel exit is either supersonic or subsonic depending on the given backpressure. Solutions of the Reynolds-averaged Navier-Stokes equations are obtained with a finite-volume solver ANSYS CFX. The solutions reveal instability of formed shock waves and a flow hysteresis in considerable bands of the free-stream Mach number at zero and negative angles of attack. The instability is caused by an interaction of shocks with the expansion flow formed over the convex bend of lower wall.

• Journal of the Korean Operations Research and Management Science Society
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• v.20 no.1
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• pp.1-10
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• 1995

The purpose of this paper is to develop a method of the sensitivity analysis that can be applied to a non-tree solution of the minimum cost flow problem. First, we introduce two types of sensitivity analysis. A sensitivity analysis of Type 1a is the well known method applicable to a tree solution. However this method can not be applied to a non-tree solution. So we propose a sensitivity analysis of Type 2 that keeps solutions of upper bounds at upper bounds, those of lower bounds at lower bounds, and those of intermediate values at intermediate values. For the cost coefficient we present a method that the sensitivity analysis of Type 2 is solved by finding the shortest path. Besides we also show that the results of Type 2 and Type 1 are the same in a spanning tree solution. For the right-hand side constant or the capacity, the sensitivity analysis of Type 2 is solved by a simple calculation using arcs with intermediate values.