• Proceedings of the Korean Society of Coastal and Ocean Engineers Conference
• /
• 1991.07a
• /
• pp.11-17
• /
• 1991

현재 사용중인 대부분의 항만부진동 예측을 위한 수치모형은 Lee(1969), Chen and Mei(1974)의 경우와 같이 Helmholtz 방정식을 사용하고 있으나 여기에는 경계면에서의 에너지 흡수 및 해저면 마찰에 의한 에너지 감쇠가 제외되었다. 그러나, 항내 파랑응답 문제에서는 경계면에서의 흡수와 해저면 마찰에 의한 에너지 감쇠가 중요한 역할을 하는 것으로 보고되고 있다(Ganaba et al., 1982).(중략)

• Proceedings of the Korea Committee for Ocean Resources and Engineering Conference
• /
• 2003.10a
• /
• pp.187-191
• /
• 2003

The motion and time-mean drift force of a 2-D floating BBDB in waves are studied with and without taking account of fluctuating air pressure in the air chamber. It has been found numerically that the drift for a of the BBDB is in the reverse direction of propagation of the incident waves over specific frequency ranges as found by McCormick through his experiment work. The drift force is calculated by Pinkster's near-field method. Since Maruo's formula method for the drift force is always positive, Maruo's formula is only approximate and should be replaced by the correct near-field method.

• Journal of the Computational Structural Engineering Institute of Korea
• /
• v.20 no.3
• /
• pp.303-309
• /
• 2007

For the propagation of elastic waves in unbounded domains, absorbing boundary conditions at the fictitious numerical boundaries have been proposed. In this paper we focus on both first and second order paraxial boundary conditions(PBCs) in the framework of variational approximations which are based on paraxial approximations of the scalar and elastic wave equations. We propose a penalty function method for the treatment of PBCs and apply these into finite element analysis. The numerical verification of the efficiency is carried out through comparing PBCs with Lysmer-Kuhlemeyer's boundary conditions.

• Journal of the Korean Society for Marine Environment & Energy
• /
• v.3 no.2
• /
• pp.49-59
• /
• 2000

Wave distribution in Jangjeon Harbour is numerically simulated for an optimum design of the harbour facilities. A deep-water design wave is estimated based on stochastic extreme wave analysis of wind data in the vicinity of the harbour, and it is applied to the boundary condition at open sea. Boussinesq wave theory that includes effects of frequency dispersion and nonlinearity is employed for the wave simulation. The porosity and sponge layer are adapted at beach to depict partial reflection and complete absorption of waves, respectively. The design wave for breakwater is computed in global domain with coarse grids and the wave distribution inside of wharf is simulated in local domain with fine grids.

• Transactions of the Korean Society of Mechanical Engineers A
• /
• v.40 no.6
• /
• pp.557-563
• /
• 2016

The energy absorption efficiency of a wave power generation system is calculated as the ratio of the wave power to the power of the system. Because absorption efficiency depends on the dynamic behavior of the wave power generation system, a dynamic analysis of the wave power generation system is required to estimate the energy absorption efficiency of the system. In this study, a dynamic analysis of the wave power generation system under wave loads is performed to estimate the energy absorption efficiency. RecurDyn is employed to carry out the dynamic analysis of the system, and the Morison equation is used for the wave load model. According to the results, the lower the wave height and the shorter the period, the higher is the absorption efficiency of the system.

• Proceedings of the Optical Society of Korea Conference
• /
• 2002.07a
• /
• pp.244-245
• /
• 2002

1 picosecond 보다 짧은 펄스길이를 갖는 초단파길이 레이저 펄스 (Ultrashort laser pulse, USLP)를 이용한 물질의 절제 (ablation)는 여타 nanosecond 영역의 레이저 절제와 많은 차이를 보인다(1). USLP는 순간 파워가 매우 높기 때문에 직접적으로 물질의 원자를 분리시켜 자유전자를 형성한다 이들 자유전자는 일반 선형흡수체 (linear absorbing chromophore)보다 흡수계수가 몇 십 배로 높아 대부분의 펄스 에너지가 표면 100-200 m 이내의 극히 작은 지역에 밀집되게 된다. (중략)

• Journal of the Earthquake Engineering Society of Korea
• /
• v.3 no.1
• /
• pp.123-132
• /
• 1999

One of the major difficulties in the seismic analysis of a dam-reservoir system is the treatment of the energy radiation in the upstream direction of the reservoir. In the paper, a new transmitting boundary is presented that can model properly the radiation of energy in the far field direction of a semi-infinite reservoir with constant depth. In the newly developed method, effects of surface wave motion are taken into accounted and the reservoir-foundation interaction is approximately accounted for with an absorbing boundary condition. If a dam has vertical upstream face and the infinitely long reservoir maintains constant depth, then the proposed transmitting boundary can be directly coupled with the model of dam body. In present study, the dam body is assumed to behave elastically and modeled by finite element method. Seismic responses of a dam model are investigated using the newly developed transmitting boundary.

• Geophysics and Geophysical Exploration
• /
• v.15 no.3
• /
• pp.121-128
• /
• 2012

Absorbing boundary conditions are used to mitigate undesired reflections that can arise at the model's truncation boundaries. We apply a complex frequency shifted perfectly matched layer (CFS-PML) to elastic wave modeling in the frequency domain. Modeling results show that the performance of our implementation is superior to other absorbing boundaries. We consider the coefficients of CFS-PML to be optimal when the kinetic energy becomes to the minimum, and propose the modified CFS-PML that has the CFS-PML coefficient ${\alpha}_{max}$ defined as a function of frequency. Results with CFS-PML and modified CFS-PML are significantly improved compared with those of the classical PML technique suffering from large spurious reflections at grazing incidence.

• KSBB Journal
• /
• v.6 no.1
• /
• pp.99-103
• /
• 1991

The optimum conditions and rates of absorption of isobutylene in aqueous para-toluene sulfonic acid(PTSA) were studied experimentally in a stirred reactor. The effects of acid concentration(30-70 wt%), acid loading (0.3-5), mixing intensity(400-1000 rpm), and temperature ($20-80^{\circ}C$) on the absorption conditions were examined. The absorption rate of isobutylene was first order in isobutylene and variable order in PTSA concentrations. The apparent energy of activation was found to be 13 Kcal/mole.

• Journal of the Korean Institute of Navigation
• /
• v.14 no.4
• /
• pp.41-52
• /
• 1990

Due to the constantly varying sea-state with which any wave energy conversion device must contend in order to extract energy efficiently , the ability to control the device's position relative to the incident waves is critical in achieving the creation of a truly functional and economical wave energy device. In this paper, the authors will propose methodology based on the theory of a variable structure system to utilize a three dimensional source distribution as a model to estimate anticipated surge, sway and yaw of a wave energy conversion device relative to varying angles and characteristics of incident waves and there from derive a feedback to a sliding mode controller which would reposition the device so as to maximize its ability to extract energy from waves in constantly varying ocean conditions.