• Journal of the Korean Society for Marine Environment & Energy
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• v.13 no.1
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• pp.47-52
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• 2010

The wave energy absorption efficiency and the first-order and the time-mean second-order wave loads of a three-dimensional bottom-mounted oscillating water column (OWC) chamber structure are studied. The potential problem is solved by making use of a hybrid Green integral equation associated with the finite-waterdepth free-surface Green function outside a twin chamber and the Rankine Green function inside taking account of the fluctuating air pressure inside the chamber. Numerical results of the primary wave energy converting efficiency and the oscillating and steady wave loads of a three-dimensional bottom-mounted OWC pilot plant have been presented.

• Korean Journal of Fisheries and Aquatic Sciences
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• v.31 no.2
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• pp.202-209
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• 1998

A three-dimensional numerical method based on the Green's integral equation is developed to predict the motion response and drift force in waves for the ocean monitoring facilities. In this method, we use source and doublet distribution, and triangular and rectangular eliments. To eliminate the irregular frequency phenomenon, the method of improved integral equation is applied and the time-mean drift force is calculated by the method of direct pressure integration over the body surface. To conform the validity of the present numerical method, some calculations for the floating sphere are performed and it is shown that the present method provides sufficiently reliable results. As a calculation example for the real facilities, the motion response and the drift force of the vertical cylinder type ocean monitoring buoy with 2.6 m diameter and 3,77 m draft are calculated and discussed. The obtained results of motion response can be used to determine the shape and dimension of the buoy to reduce the motion response, and other data such as the effect of motion reduction due to a damper can be predictable through these motion calculations. Also, the calculation results of drift force can be used in the design procedure of mooring system to predict the maximum wave load acting on the mooring system. The present method has, in principle, no restriction in the application to the arbitrary shape facilities. So, this method can be a robust tool for the design, installation, and operation of various kinds of the floating-type ocean monitoring facilities.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.7 no.2
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• pp.156-162
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• 1995

A numerical method for a 2-D oil boom model considering the flexibility of skirt has been developed The neater is assumed rigid and the skirt is tensioned membrane having a point mass at its end The fluid motion is potential. The kinematic condition which demands the continuity of the displacement is imposed at the joint between the floater and the skirt. The dynamic condition for the point mass is imposed at the bottom end of the skirt. The numerical method is based on the Green's function method in the frame of linear potential theory. It finds it's solution simultaneously from the total system of three equations, integral equation, the equation of motion of the floater and the equilibrium equation of the deformation of the skirt. Integral equation is derived by applying the Green's theorem to radiation potential and Green's function. Proper descretization of those three equations leads to the system of a linear algebraic equation. Due to the flexibility of skirt the motion of floater can be diminished in some range of wave frequency and furthermore the mechanism of resonance of the oil boom can be changed. The motion responses of various oil booms have been compared varying the length of the skirt and the point mass. The numerical method has been validated indirectly from the good correspondence between the motion responses of the flexible skirt model and the rigid skirt model in low frequency limit.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.26 no.11B
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• pp.1600-1606
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• 2001

Resonant frequency in rectangular microstrip patch antenna on anisotropic substrates with airgap and superstrate are analyzed. Dyadic Green function is derived for selected anisotropic material by constitutive relation. From these results, integral equations of electric fields are formulated using Fourier transform in space region. The electric field integral equations are discretized into the matrix form by applying Galerkin\`s moment method. Sinusoidal functions are selected as basis functions because they resemble in the actual standing wave on the patch. To verify the validity of numerical result, we compare our result with existing one and get a good agreement between them. From the numerical results, the resonant frequency in the variation of air gap, patch length and anisotropy ratio are presented and analysed.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.38 no.9
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• pp.29-39
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• 2001

Dielectric cover effect of rectangular microstrip patch antenna on uniaxial substrates with airgap are studied. First, we derive Dyadic Green function for selected anisotropic material by constitutive relation and then formulate integral equations of electric fields using Fourier transform in space region. Using Galerkin's moment method, we discretize the electric field integral equations into the matrix form and select sinusoidal functions as basis functions. We verify the validity of numerical results and compare the results with existing ones in showing a good agreement between them. When the dielectric cover thickness is varied, the resonant frequencies and input impedances in the variation of air gap, patch length and thickness and permittivity of superstrate are presented and analyzed.

• Journal of IKEEE
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• v.5 no.1 s.8
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• pp.91-99
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• 2001

Spectral domain of resonant frequency rectangular microstrip patch antenna on anisotropic substrates and superstrate with airgap are analyzed. First, we derive dyadic Green function for selected anisotropic material by constitutive relation and then formulate integral equations of electric fields using Fourier transform in space region. Using Galerkin's moment method, we discretize the electric field integral equations Into the matrix form and select sinusoidal functions as basis functions. We verify the validity of numerical results and compare the results with existing ones in showing a good agreement between them. The resonant frequencies in the variation of air gap, patch length and permittivity of superstrate anisotrpy ratio of anisotrpic superstrate are presented and analyzed.

• Journal of the Earthquake Engineering Society of Korea
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• v.1 no.4
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• pp.59-68
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• 1997

In analysis of underground structures, the effects of artificial boundary conditions are considered as one of the major reasons for differences from experimental results. These phenomena can be overcome by using the boundary elements which satisfy the multi-layered half space conditions. The fundamental solutions of multi-layered half-space for boundary element method is formulated satisfying the transmission and reflection of waves at each layer interface and radiation conditions at bottom layer. The governing equations can be obtained from the displacements at each layer which are expressed in terms of harmonic functions. All types of waves can be included using the complete response from semi-infinite integrals with respect to horizontal wavenumbers using expansion of Fourier series and Hankel transformation. Two dimensional Green's functions are derived from cylindrical Navier equations and potentials performing infinite integration in y-direction. In this case, it is effective to transform into two dimensional problem using semi-analytical integration and sinusoidal Bessel function. Some verifications are given to show the accuracy and efficiency of the developed method, and numerical examples to demonstrate the dynamic behavior of underground with various properties.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.30 no.4
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• pp.10-17
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• 2002

A study on the dynamic ground effect on three-dimensional wings is done using an indirect boundary element method(unsteady panel method). An integral equation is obtained by applying Green's theorem on all surfaces of the fluid domain. Constant strength dipole and source panels arc distributed on a wing's surface. The wake sheet is represented by constant strength dipoles. At each time step, a row of wake panels is assumed to be convected from the trailing edge of the wing. The tip vortex behind wings in dynamic ground effect moves outward. The amplitudes of the aerodynamic coefficients for the wings in dynamic ground effect are augmented much more comparing to the case in static ground effect.

• Transactions of the Korean Society of Mechanical Engineers
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• v.9 no.1
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• pp.31-39
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• 1985

Using the tensor elastic Green functions an exact integral equation is formulated for two anisotropic precipitates embedded in an infinite anisotropic matrix; the matrix is subjected to an applied strain field or the precipitates undergo a stress-free transformation strain. This equation is reduced to an infinite system of algebraic equations by expanding the strains in Taylor series about the two points within each precipitate, and an approximation of the strain distributions within the two spherical precipitates is obtained by truncating the higher order terms. Since the present method requires no symmetry conditio between the two shperical precipitates, it is possible to obtain the strain distribution within the precipitates when the elastic constants and/or the sizes of the precipitates are different each other. The strains are expanded about arbitrary points, giving more accurate distributions of the strains than those presented elsewhere. The present method can be directly estended to the case of more than two spherical precipitates.

• Journal of the Korean Society for Marine Environment & Energy
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• v.10 no.3
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• pp.173-180
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• 2007

Oscillating wave amplitude in a bottom-mounted OWC chamber designed for wave energy converter is investigated by applying characteristic wave conditions in Korean coastal water. The effects of shape parameters of OWC chamber in a view of wave energy absorbing capability are analyzed. Both experimental and numerical approaches are adopted and their results are compared to optimize the shape parameters which can result in a maximum power production under given wave distribution. The experiment was carried out in a wave flume under 2-D assumption of OWC chamber. The numerical scheme employed a hybrid Green integral equation which adopts the Rankine Green function inside chamber to take account of fluctuating air pressure, while it uses the Kelvin Green function in outer domain. Air duct diameter, chamber width, and submerged depths of front skirt and back wall of chamber changes the magnitude and peak frequency of wave absorption significantly.