• Journal of Korean Society of Coastal and Ocean Engineers
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• v.21 no.2
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• pp.91-107
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• 2009

In order to compute linear wave transformation over a single step bottom, both variational approximation and eigenfunction expansion method are used. Both numerical results are in good agreement for reflection and transmission coefficients, surface displacement respectively. However x velocity profiles at the boundary of step are seen to be different to each other even though x velocity matching condition is used.

• Transactions of the Korean Society of Mechanical Engineers
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• v.17 no.10
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• pp.2437-2445
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• 1993

In this work, a new method is presented for generating the manipulator path which significantly reduces residual vibration under the torque constraints. The desired path is optimally designed so that the required movement can be achieved with minimum residual vibration. From the previous research works, the dynamic model had been established including both the link and the joint flexibilities. The performance index is selected to minimize the maximum amplitude of residual vibration. The path to be designed is developed by a combined Fourier series and polynomial function to satisfy both the convergence and boundary condition matching problems. The concept of correlation coefficients is used to select the minimum number of design variables, i.e. Fourier coefficients, the only ones which have a considerable effect on the reduction of residual vibration. A two-link Manipulator is used to evaluate this method. Results show that residual vibration can be drastically reduced by selecting an appropriate manipulator path to both of unlimited and torque-limited cases.

• Journal of the Society of Naval Architects of Korea
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• v.30 no.1
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• pp.45-64
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• 1993

This paper dealt with the application of a numerical method developed by the authors using the matching method proposed in the previous paper on "The Nonlinear motions of cylinders(I)[16]", and Cauchy's theorem to the problems associated with hydrodynamic forces acting on a heaving cylinders translating in a calm water and also motions of cylinders in waves. In spectral method. body boundary condition in submerged case is satisfied exactly but one in floating case is not satisfied exactly. In the numerical code developed here, the boundary condition at the free-surface and body surface is satisfied exactly at its instaneous position. It is of interest to note that the present scheme could be applied to a free-surface-piercing body without experiencing a difficulty in the numerical convergence. The computed results are compared with other results([6], [12]).

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.19 no.6
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• pp.640-646
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• 2008

Design procedure of corrugated horn antenna for the mm-wave frequency range is presented, and hybrid condition in horn is calculated. In this paper, corrugate profiles of horn which satisfy both transition to balanced hybrid condition and fabrication possibility under the mm-wave short wavelength are obtained. Electromagnetic fields inside horn and corrugation are derived by the cylindrical mode theory. Propagation characteristics in the horn are calculated by the mode impedance matching method with boundary conditions, and radiation fields are obtained by the Kirchhoff-Hyugen principle to the horn aperture fields. A mm-wave corrugated horn antenna which operates on $85{\sim}115GHz$ is fabricated by electric forming method. Measurements show that VSWR is under 1.3:1 over whole band and the half power beamwidth on radiation pattern 9.2, 9.16 and 9.02 degree on 85, 100 and 110 GHz are agree well with theoretical calculation.

• Bulletin of the Society of Naval Architects of Korea
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• v.26 no.3
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• pp.41-50
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• 1989

A basic formulation of the panel method, which is based on the potential field formulation, is reviewed for the case of two-dimensional hydrofoil problems. Numerical procedures to improve the computational efficiency of the panel method are suggested. By investigating local behavior of the flow around the trailing edge, a wedge type Kutta condition is formulated. By subdividing the trailing edge panels, where dipole strengths of the subdivided panels follow the local behavior of the potential values of the flow outside a wedge, the circulation around a hydrofoil is calculated accurately with a relatively small number of panels. The subdividing technique to improve the accuracy of the numerical Kutta condition is proved to be efficient. A local behavior of the flow around the leading edge is also investigated. By matching the flow around the leading edge with that around a parabola, a very accurate velocity distribution is obtained with relatively small number of panels. An accurate prediction of the stagnation point and the pressure distribution near the leading edge may contribute to improve the accuracy of cavity predictions and boundary layer calculations around hydrofoils.

• The Journal of Information Technology
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• v.4 no.3
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• pp.77-86
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• 2001

In this paper, Electromagnetic scattering problem by a resistive strip grating with 2 dielectric layers on a ground plane according as resistivity of resistive strip, relative permittivity and thickness of dielectric layers, and incident angles of a electric wave is analyzed by applying the PMM (Point Matching Method) known as a numerical procedure. The scattered electromagnetic fields are expanded in a series of floquet mode functions. The boundary conditions are applied to obtain the unknown field coefficients and the resistive boundary condition is used for the relationship between the tangential electric field and the electric current density on the strip. According as the relative permittivity and the thickness of layers are increased, the values of the geometrically normalized reflected power have a high value and the values of strip width are moved toward a high value going from left to right. When the resistivity of this paper has a value of zero, the numerical results of the geometrically normalized reflected power show in good agreement with those by the PMM of existing paper. Then, the most energys of the sharp variation point in minimum values of the geometrically normalized reflected power are scattered in direction of the other angles except incident angle.

• Journal of Ocean Engineering and Technology
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• v.16 no.3
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• pp.19-27
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• 2002

The motion of a floating OWC chamber in waves is studied taking account of fluctuating air pressure in the air chamber. An atmospheric pressure drop occurs across the upper opening of the chamber which causes not only hydrodynamic but also pneumatic added mass and damping forces to the floating chamber. A velocity potential in the water due to the free surface oscillating pressure patch is added to the conventional radiation-diffraction potential problem. the potential problem inside the chamber is formulated by making use of the Green integral equation associated with the Rankine Green function wile the outer problem with the Kelvin Green function. The two integral equations are solved simultaneously by making use of a matching boundary condition at the lower opening of the chamber to the outer water region. The chamber motion in the frequency domain is calculated for various values of parameters related to the atmospheric pressure drop. The present methods can also be sued for the analysis of air-cushion vehicle motion as well as for the design of a floating OWC wave energy absorber.

• Proceedings of the Korea Committee for Ocean Resources and Engineering Conference
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• 2002.05a
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• pp.191-197
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• 2002

The motion of a floating OWC chamber in waves is studied taking account of fluctuating.air pressure in the air chamber. An atmospheric pressure drop occurs across the upper opening of the chamber which causes not only hydrodynamic but also pneumatic added mass and damping forces to the floating chamber. A velocity potential in the water due to the free surface oscillating pressure patch is added to the conventional radiation-diffraction potential problem. The potential problem inside the chamber is formulated by making use of the Green integral equation associated with the Rankine Green function while the outer problem with the Kelvin Green function. The two integral equations are solved simultaneously by making use of a matching boundary condition at the lower opening of the chamber to the outer water region. The chamber motion in the frequency domain is calculated for various values of parameters related to the atmospheric pressure drop. The present methods can also be used for the analysis of air-cushion vehicle motion as well as for the design oj a floating owe wave energy absorber.

• The Transactions of the Korean Institute of Electrical Engineers C
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• v.48 no.6
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• pp.489-493
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• 1999

In this paper, an analysis of microstrip-slotline transition is performed using a 3D vector Finite Element Method(FEM). Artificial anistropic absorber technique is employed to implement an matching boundary condition in FEM. On the base of the analysis, power divider/combiner is designed. The structure of the power combiner already developed are Branch-line coupler, Rat-race coupler, Wilkinson coupler, Lange coupler, etc. Which are all planar, If the frequency goes up, the coupling efficiency of these planar couplers is decreased on account of skin loss. Especially, in millimeter-wave band, the efficiency of more than two ways combiner is radically reduced, so that application in power amplifier circuit is almost impossible, Microstrip-slotline transition structure is a power combining technique integrated into wave-guide, so that the loss is small and the efficiency is high. Theoretically, we can mount several transistors into the power-combiner. This makes it possible to develop a high power amplifier. The numerically calculated performances of the device that is, we believe, the best are compared to the experimental results in Ka-Band(26.5GHz-40GHz).

• Journal of the Korea Institute of Military Science and Technology
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• v.13 no.6
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• pp.998-1005
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• 2010

Rifling force has a torsion impulse effect on the gun tube and thus generates undesirable vibration of the gun tube about its bore axis, putting additional stress on the projectile. High rifling force at the muzzle of the gun tube may adversely influence the trajectory of the projectile. And, the service life of rifled gun barrels is known to depend on the rifling force. Rifling force along the path of the projectile in the longitudinal direction of the gun tube can be described with projectile mass, projectile velocity, gas pressure curve and rifling angle. Under the same conditions, the character of the rifling of the gun barrel decisively influences the rifling force curve. To reduce the above mentioned harmful effect, locally distinct maximum of rifling force has to be avoided and maximum rifling force needs to be minimized. The best way to minimize the maximum rifling force is to design a rifling angle function so that the rifling force curve has a near trapezoidal shape. In this paper a new approach to make the optimal rifling force curve is described. The rifling angle determining the rifling force is developed by combined Fourier series and polynomial function to satisfy both the convergence and boundary condition matching problems.