• 한국방재학회:학술대회논문집
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• 2008.02a
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• pp.241-244
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• 2008

The decomposition of incident and reflected wave on the two-dimensional experimental flume is very important to elucidate the phenomena between waves and coastal structure such as submerged breakwater or rubble-mound breakwater. In generally, two or three point methods are widely used to decompose waves. Even though three point method gives more accurate result, it requires more wave gauge to install than two point method. Sometimes, this causes economic or measurement problems. In this study, therefore, the applicability of two point method was investigated by using Eigenfunction expansion method.

• Journal of Korea Water Resources Association
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• v.35 no.6
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• pp.677-684
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• 2002

In this study, a finite element model is employed to simulate the diffraction of waves caused by a change of water depths. The model is firstly applied to the estimation of reflection coefficients of monochromatic waves over a sinusoidally varying topography. Predicted coefficients are compared with those of the eigenfunction expansion method and laboratory measurements. A good agreement is observed. The model is then used to investigate effects of heights of bottom topography and number of ripples on variation of reflection coefficients of monocromatic water waves.

• Wind and Structures
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• v.29 no.1
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• pp.33-41
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• 2019

The interaction of head waves with an infinite row of identical, equally spaced, rectangular breakwaters is investigated in the presence of uneven bottom topography. Using linear water wave theory and matched eigenfunction expansion method, the boundary value problem is transformed into a system of linear algebraic equations which are numerically solved to know the velocity potentials completely. Utilizing this method, reflected and transmitted wave energy are computed for different physical parameters along with the wave field in the vicinity of breakwaters. It is observed that the wave field becomes more complicated when the incoming wavelength becomes smaller than the channel width. A critical ratio of the gap width to the channel width, corresponding to the inflection point of the transmitted energy variation, is identified for which 1/3 of the total energy is transmitted. Similarly, depending on the incident wavelength, there is a critical breakwater width for which a minimum energy is transmitted. Further, the accuracy of the computed results is verified by using the derived energy relation.

• Korean Chemical Engineering Research
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• v.57 no.5
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• pp.652-665
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• 2019

Analytical solutions of the reactant concentration inside porous spherical catalytic particles were obtained from unsteady reaction-diffusion equation by applying eigenfunction expansion method. Various surface concentrations as exponentially decaying or oscillating function were considered as boundary conditions to solve the unsteady partial differential equation as a function of radial distance and time. Dirac delta function was also used for the instantaneous injection of the reactant as the surface boundary condition to calculate average reactant concentration inside the particles as a function of time by Laplace transform. Besides spherical morphology, other geometries of particles, such as cylinder or slab, were considered to obtain the solution of the reaction-diffusion equation, and the results were compared with the solution in spherical coordinate. The concentration inside the particles based on calculation was compared with the bulk concentration of the reactant molecules measured by photocatalytic decomposition as a function of time.

• Journal of Ocean Engineering and Technology
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• v.35 no.3
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• pp.216-228
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• 2021

In the present study, the performance of a floating oscillating water column (OWC) device has been studied in regular waves. The OWC model has the shape of a hollow cylinder. The linear potential theory is assumed, and a matched eigenfunction expansion method(MEEM) is applied for solving the diffraction and radiation problems. The radiation problem involves the radiation of waves by the heaving motion of a floating OWC device and the oscillating pressure in the air chamber. The characteristics of the exciting forces, hydrodynamic forces, flow rate, air pressure in the chamber, and heave motion response are investigated with various system parameters, such as the inner radius, draft of an OWC, and turbine constant. The efficiency of a floating OWC device is estimated in connection with the extracted wave power and capture width. Specifically, the piston-mode resonance in an internal fluid region plays an important role in the performance of a floating OWC device, along with the heave motion resonance. The developed prediction tool will help determine the various design parameters affecting the performance of a floating OWC device in waves.

• Journal of the Korean Society of Marine Environment & Safety
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• v.18 no.3
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• pp.199-205
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• 2012

In this study, wave transformation by damping due to the permeable bed of finite depth is investigated. The relationship between wave damping rate and relative water depth are presented. The damping rate is used in the eigenfunction expansion method to calculate the wave dissipation over the permeable bed. For a permeable shoal, the eigenfunction expansion model result is compared with that of the integral equation method to show good agreement. The model is also used to examine the wave reflection over the permeable planar slope of various frequency. It has been found that in general relatively short waves are more influenced by the permeability of the permeable seabed than relatively long waves unless the water depth is so large that the influence of permeable bed on surface water waves disappears.

• Journal of Ocean Engineering and Technology
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• v.21 no.4
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• pp.1-7
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• 2007

Based on the eigenfunction expansion method, the wave-absorbing performance of a square or circular pile breakwater was investigated. Flow separation resulting from sudden contraction and expansion is generated and is the main cause of significant energy loss. Therefore, evaluation of an exact energy loss coefficient is critical to enhancing the reliability of the mathematical model. To obtain the energy loss coefficient, 2-dimensional turbulent flow is analyzed using the FLUENT commercial code, and the energy loss coefficient can be obtained from the pressure difference between upstream and downstream. It was found that energy loss coefficient of circular pile is 20% that of a square pile. To validate the fitting equation for the energy loss coefficient, comparison between the analytical results and the experimental results (Kakuno and Liu, 1993) was made for square and circular piles with good agreement. The array of square piles also provides better wave-absorbing efficiency than the circular piles, and the optimal porosity value is near P=0.1.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 1998.04a
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• pp.536-541
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• 1998

Cylindrical chamber silencers with an extended inlet and outlet are widely used to reduce the propagated noise in ducts in many application fields. In this study, an acoustic analysis is carried out for concentric extended pipes inserted into a simple expansion chambers An algebraic equation is derived by using the eigenfunction expansion and orthogonality principle. Using this analytical method, transmission losses are predicted for several configurations of the concentric extended systems.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.31 no.6
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• pp.395-402
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• 2019

In order to increse the stability of old caissons, the design and the construction are performed by installation of new caissons on the back of or on the front of old caissons. In this study, we use the eigenfunction expasnion method to analyze the characteristics of wave forces when new circular caissons are installed on the back of old caissons. The comparison of numerical results between eigenfunction expansion method and ANSYS AQWA is made and the wave force acting on each circular caisson is calculated by considering the wave-structure interaction effect.

• Proceedings of the Korea Committee for Ocean Resources and Engineering Conference
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• 2004.05a
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• pp.241-248
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• 2004

In general, the salient features if the floating breakwater have excellent regulation of sea-water keeping the marine a1ways clean, up and dorm free movement with the incoming and outgoing tides, capable of being installed without considering the geological condition of sea-bed at any water depth, This study discusses the three dimensional wave transformation of the floating breakwater moored by catenary. Numerical method is based at the Green function method and eigenfunction expansion method. The validity of the present is confirmed by comparing it with the result of Ijima et a1.(1975) fer tensile maxed floating breakwater. According to the numerical results, drift and width of the floating breakwater affect at the wave transformation greatly, and incident wave of long period is well transmitted to the rear of the floating breakwater.