• Proceedings of the Korea Water Resources Association Conference
• /
• 2022.05a
• /
• pp.205-205
• /
• 2022

본 연구에서는 심해 선형파 조건에서 수중 투과성 방파제 주변의 유속장에 대해 nonhomogeneous Riemann-Hilbert problem을 이용한 해석해 및 수치해를 도출하고, 이를 반사계수와 투과계수를 산정하는 데에 활용한다. 여러 개의 얇은 투과성 판이 일렬로 배열되어 수중에 고정되어있고 규칙파가 작용하는 경우, Riemann-Hilbert problem을 정의할 수 있다. 본 연구에서는 얇은 판으로 이루어진 수중 방파제에 대한 homogeneous Riemann-Hilbert problem을 푸는 것을 넘어, 투과성 판으로 이루어진 수중 방파제에 대해 nonhomogeneous Riemann-Hilbert problem을 정의하고, 이에 대해 무한경계조건과 판 근처에서의 유속장 경계조건을 이용해 해석해를 유도하였다. 투과성 방파제의 경우 permeable boundary를 가지므로 제시한 상황은 기하학적 비선형성을 지닌다. 이에 대해 투수성을 기초로 미소 매개변수를 정의하고, 섭동법(perturbation method)을 이용해 유속장에 대한 leading order solution과 first order solution을 도출하였다. Leading order solution은 Evans (1970) 등의 선행연구에서 제시한 해와의 비교를 통해 그 타당성을 검증하였고, First order solution을 이용해 반사계수와 투과계수를 산정하여 방파제의 투수성이 유속장에 미치는 영향을 고려하였다. 아울러 수치해를 도출하여 해석해의 결과와 비교 및 분석하였다. 본 연구에서 제시한 해석해는 방파제에 가해지는 힘을 산정하는 등 다양한 방향으로 활용 가능하며, 향후 수치해나 실험값을 비교, 검증하기 위한 기초 자료로써 활용될 수 있다.

• Journal of Korean Society of Coastal and Ocean Engineers
• /
• v.30 no.4
• /
• pp.180-190
• /
• 2018

The preliminary study was carried out to utilize the rolling porous pendulum plate as a hybrid system combining blocking and extracting of wave energy. The Galerkin method suggested by Porter and Evans (1995) was used to solve the diffraction and radiation problems to obtain reflection and transmission coefficient, roll displacement, extracted power. The Galerkin method provides better convergence than the matched eigenfunction expansion method (MEEM), which improves the accuracy of the analytical solution even if the CPU time is shorter. The porous plate can not be said to be more effective than the impermeable plate in terms of wave energy extraction and wave blocking, but it has the advantage of reducing the wave load and exchanging seawater.

• Journal of the Korea Academia-Industrial cooperation Society
• /
• v.19 no.3
• /
• pp.699-706
• /
• 2018

The permeation properties of plasma polymer membranes were studied for permanent gases such as He, $H_2$, $O_2$, $N_2$, $CH_4$ and condensable vapors such as $CO_2$, $C_2H_4$, $C_3H_8$. The plasma polymers were prepared by the discharge of microwave or radiofrequency(RF) wave. Hexamethyldisiloxane (HMDS) vapor was used as a monomer for plasma polymerization. In HMDS plasma-polymerized membranes prepared under microwave discharge, the permeability coefficient was dependent of the kinetic molecular diameter of the permeate gases. Additionally the membranes showed higher $O_2/N_2$ permselectivity compared to the plasma polymers from radiofrequency discharge. On the contrary, in the HMDS plasma-polymerized membranes prepared under radiofrequency discharge, the permeability coefficient was dependent of the critical temperature of the permeant gases. The membranes showed high selectivities of $C_2H_4$ and $C_3H_8$ over $N_2$. The permeability coefficient of plasma polymerized membranes prepared under microwave discharge was dependent of the molecular diameter of permeant gases because of high crosslinking density of the membrane. However, the crosslinking density of the plasma polymerized membranes prepared under RF discharge was lower because the energy density of RF wave is weaker than that of microwave. Hence, the permeability of RF plasma polymerized membranes became dependent of the critical temperature rather than molecular diameter of the gases.

• Journal of Korean Society of Coastal and Ocean Engineers
• /
• v.19 no.6
• /
• pp.586-595
• /
• 2007

The analytic solution of wave scattering of monochromatic waves on a pile breakwater by an eigenfunction expansion method is extended to the case of directional irregular waves. The scattering wave spectrum and the force spectrum can be expressed from the reflection coefficient, transmission coefficient and the wave forces obtained from changing frequencies and incident angles in monochromatic waves. By numerical integration of 2-dimensional spectrum which is function of frequencies and incident angles, the representative values for the scattered waves and wave forces are obtained and the dependence of the transmission coefficients and wave forces on the directional distribution function, the principal wave direction, the submergence depth, and porosity is analyzed.

• 한국방재학회:학술대회논문집
• /
• 2010.02a
• /
• pp.108.1-108.1
• /
• 2010

본 연구에서는 수리모형실험을 통하여 규칙파를 적용한 수중방파제의 반사특성을 조사하였다. 수중방파제의 형상을 직사각형(${\theta}=90^{\circ}$), 사다리꼴(I)(${\theta}=75^{\circ}$), 사다리꼴(II)(${\theta}=60^{\circ}$), 삼각형(${\theta}=30.96^{\circ}$)으로 설정하여, 각각의 형상들에 대하여 주기, 입사파고, 배열을 변화시켜 얻은 실험결과를 토대로 투과율을 계산하였다.

• Journal of Korea Water Resources Association
• /
• v.37 no.9
• /
• pp.729-736
• /
• 2004

Analysis of reflection of random waves propagating over rectangular submerged non-porous breakwaters was performed by using the eigenfunction expansion method. In this study, random waves were generated by superposition of several monochromatioc waves. Reflection coefficients were calculated by summing each numerical results of regular waves. Predicted results from the eigenfunction expansion method were in a good agreement with the results of laboratory measurements. Reflection coefficients of random waves were also resonated at the Bragg reflection condition.

• Journal of Korean Society of Coastal and Ocean Engineers
• /
• v.15 no.2
• /
• pp.116-126
• /
• 2003

In this study, a method that leads to make a simple decision on important parameters in analysis of wave field in permeable rubble-mound, block-mound breakwater, such as penetration velocity of incident waves and resistance coefficient, is introduced. A model that could analyze wave field of permeable breakwater in harbor, by applying these methods and arbitrary transmission coefficient boundary condition to a time-dependent mild-slope equation, was introduced. The verification of the model was done by carrying out 2-D physical model test on permeable breakwater, measuring the change in water surface elevation, comparing the computation result with time series, and comparing the result gained from the 3-D physical model test on permeable block-mound breakwater in an field harbor with the computation result in terms of regional wave height ratio in a harbor.

• 한국방재학회:학술대회논문집
• /
• 2009.02b
• /
• pp.126-126
• /
• 2009

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
• /
• 1994.10a
• /
• pp.306-311
• /
• 1994

본 연구에서는 축대칭 형태의 음향문제를 해석할 수 있는 경계요소 프로그램을 개발하여 소음기의 투과손실(transmission loss)의 계산에 적용하였다. 우선 단순팽창관 소음기에 대해서는 경계요소법에 의해 투과손실을 구한 후 평면파이론 및 실험으로 구한 값과 비교 평가하였다. 또한, 평면파이론을 적용할 수 없는 경우로서 흡음재를 부착한 팽창관 소음기에 대해서는 경계요소법으로 구한 투과손실을 실험결과와 비교 고찰하였다.

• Journal of Korean Society of Coastal and Ocean Engineers
• /
• v.20 no.5
• /
• pp.439-451
• /
• 2008

Based on reflected and transmitted waves by a single step bottom, a new model of scatterer method is constructed which can be used to calculate wave transformation over a multi-step topography. The approximate results are tested by comparison with the more accurate results obtained from EFEM presented by Kirby and Dalrymple(1983). In the case of plane-wave approximation, solutions of the scatterer method and the EFEM are the same. Results obtained by the scatterer method with non-propagating modes are much better, in terms of phase for the calculated reflection and transmission coefficients, than those by plane-wave approximation. As the effect of non-propagating modes decreases, solutions of the scatterer method become closer to those of the EFEM.