• Journal of Ship and Ocean Technology
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• v.8 no.2
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• pp.61-69
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• 2004

Unsteady nonlinear wave motions on the free surface over a plane beach of constant slope are numerically simulated using a finite difference method in rectangular grid system. Two-dimensional Navier-Stokes equations and the continuity equation are used for the computations. Irregular leg lengths and stars are employed near the boundaries of body and free surface to satisfy the boundary conditions. Also, the free surface which consists of markers or segments is determined every time step with the satisfaction of kinematic and dynamic free surface conditions. Moreover, marker-density method is also adopted to allow plunging jets impinging on the free surface. The second-order Stokes wave theory is employed for the generation of waves on the inflow boundary. For the simulation of wave breaking phenomena, the computations are carried out with the plane beach of constant slope in surf zone. The results are compared with other existing experimental results. Agreement between the experimental data and the computation results is good.

• Journal of Advanced Marine Engineering and Technology
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• v.23 no.3
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• pp.379-388
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• 1999

Au upper bound elemental technique(UBET) program has been developed to analyze forging load die-cavity filling and optimum kinematically admissible velocity fields for flashless forging. The simulation for flashless forgings are applied plane-strain and axisymmetric closed-die forging with rib-web type cavity. The kinematically admissible velocity fields for inverse triangular and inverse trapezoidal elements are used to analyze flashless forging,. Experiments have been carried out with pure plasticine billets at room temperature. Theoretical predictions of the forging load in plane-strain and axisymmetric forging are in good agreement with experimental results.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.27 no.3
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• pp.302-310
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• 2003

Experiments were conducted to show the characteristics of the flow on unventilated parallel plane jets. Measurements of mean velocity components and turbulent intensities were carried out with a particle image velocimetry to investigate the flow field generated by the air issued from two identical plane parallel nozzles and mixed with the ambient air. The measurements range of these experiments were Reynolds number of 5300 based on the nozzle width and the cases of nozzle-to-nozzle distance were four times. six times and eight times the width of the nozzle. Results show that a recirculation zone with a sub-atmospheric static pressure was bounded by the inner shear layers of the individual jets and the nozzles plate. The positions. where maximum value of mean turbulent intensities and mean turbulent kinetic energy show, were at the same position with the merging point. The spread of jets in the merging region increases more rapidly than that of Jets in the converging and the combined region. As nozzle-to-nozzle distances were increased. it was shown that merging and combined lengths were shorter.

• Advances in nano research
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• v.7 no.5
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• pp.311-324
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• 2019

The present study aims to evaluate the nonlinear and post-buckling behaviors of orthotropic graphene sheets exposed to end-shortening strain by implementing a semi-Galerkin technique, as a new approach. The nano-sheets are regarded to be on elastic foundations and different out-of-plane boundary conditions are considered for graphene sheets. In addition, nonlocal elasticity theory is employed to achieve the post-buckling behavior related to the nano-sheets. In the present study, first, out-of-plane deflection function is considered as the only displacement field in the proposed technique, which is hypothesized by an appropriate deflected form. Then, the exact nonlocal stress function is calculated through a complete solution of the von-Karman compatibility equation. In the next step, Galerkin's method is used to solve the unknown parameters considered in the proposed technique. In addition, three different scenarios, which are significantly different with respect to concept, are used to satisfy the natural in-plane boundary conditions and completely attain the stress function. Finally, the post-buckling behavior of thin graphene sheets are evaluated for all three different scenarios, and the impacts of boundary conditions, polymer substrate, and nonlocal parameter are examined in each scenario.

• Journal of the Korean Society for Heat Treatment
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• v.37 no.2
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• pp.66-72
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• 2024

To investigate the effect of deformation condition on microstructure and texture formation behaviors of AZ91 magnesium alloy with three kinds of initial texure during high-temperature deformation, plane strain compression tests were carried out at high-temperature deformation conditions - temperature of 673 K~723 K, strain rate of 5 × 10^-3s^-1, up to a strain of -1.0. To clarify the texture formation behavior and crystal orientaion distribution, X-ray diffraction and EBSD measurement were conducted on mid-plane section of the specimens after electroltytic polishing. As a result of this study, it is found that the main component and the accumulation of pole density vary depending on initial texture and deformation caondition, and the formation and development basal texture components ({0001} <$10\bar{1}0$>) were observed regardless of the initial texure in all case of specimens.

• Proceedings of the KSME Conference
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• 2002.08a
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• pp.823-826
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• 2002

Experiments were conducted to show the characteristics of the flow on unventilated parallel plane jets. Measurements of mean velocity components and turbulent intensities were carried out with a particle image velocimetry. The measurements range of these experiments was Reynolds number of 5300 based on the nozzle width and the cases of nozzle-to-nozzle distance were 4, 6, 8, and 10 times the width of the nozzle. Results show that a recirculation zone with a sub-atmospheric static pressure was bounded by the inner shear layers of the individual jets and the nozzles plate. The positions, where maximum value of mean turbulent intensities and mean turbulent kinetic energy show, were at the same position with the merging point. The spread of jets in the merging region increases more rapidly than that of jets in the converging and the combined region. As nozzle-to-nozzle distances were increased, it was shown that merging and combined lengths were shorter.

• Proceedings of the KSR Conference
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• 2009.05a
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• pp.912-918
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• 2009

In this paper, we carried out a comparative analysis of partial discharge(PD) patterns caused by deterioration of cast-resin and oil insulation systems. Various electrode systems were fabricated such as needle-needle, needle-plane and plane-plane to simulate defects that may exist in the insulation system of transformers. A low-noise amplifier which has a gain of 40 dB and a frequency bandwidth of 500 kHz $\sim$ 30 MHz (-3 dB) was designed to detect small PD signals. From the analysis of acquired PD signals, we could find that a unique PD pattern is formed according to types of defect. These data will be applied usefully to diagnose insulation condition of transformers.

• 한국전산유체공학회:학술대회논문집
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• 2004.03a
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• pp.119-125
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• 2004

Unsteady nonlinear wave motions on the free surface over a plane beach of constant slope are numerically simulated using a finite difference method in rectangular grid system. Two-dimensional Navier-Stokes equations and the continuity equation are used for the computations. Irregular leg lengths and stars are employed near the boundaries of body and free surface to satisfy the boundary conditions. Also, the free surface which consists of markers or segments is determined every time step with the satisfaction of kinematic and dynamic free surface conditions. Moreover, marker-density method is also adopted to allow plunging jets impinging on the free surface. The second-order Stokes wave theory and solitary wave theory are employed for the generation of waves on the inflow boundary. For the simulation of wave breaking phenomena, the computations are carried out with the plane beach of constant slope in surf zone. The results are compared with each other. The marker-density method is better then the hybrid method. Also they are compared with other existing experimental results. The Agreement between the experimental data and the computation results is good.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.20 no.4
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• pp.417-425
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• 2007

The differential quadrature method(DQM) is applied to computation of eigenvalues of the equations of motion governing the free out-of-plane vibration for circular curved beams including the effects of rotatory inertia and transverse shearing deformation. Fundamental frequencies are calculated for the members with clamped-clamped end conditions and various opening angles. The results are compared with exact solutions or numerical solutions by other methods for cases in which they are available. The DQM provides good accuracy even when only a limited number of grid points is used.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2002.11b
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• pp.190-197
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• 2002

A new design methodology is presented for the multi-degree-of-freedom vibration absorber for an elastically suspended rigid body with planes of symmetry in general motion. Unlike the common single degree-of-freedom vibration absorber, the presented methodology makes use of both linear and rotational properties of the absorber. It is suggested that an absorber is designed separately for the in-plane and out-of-plane vibration modes and thereby combined the two cases for a six-degree-of-freedom absorber. The nine possible design methods are suggested for the six-degree-of-freedom absorber when an elastically suspended rigid body has one, two, or three planes of symmetry.