• 대한원격탐사학회:학술대회논문집
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• 대한원격탐사학회 2006년도 Proceedings of ISRS 2006 PORSEC Volume I
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• pp.364-367
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• 2006

Nonlinear internal waves (NLIWs) are usually generated by nonlinear process on linear internal waves (IW). Near HengChun Ridge that links Taiwan and Luzon Islands, we found that there are linear internal waves following NLIW and they travel westward at different speed, about 1.5 m/s for IW and 2.9 m/s for NLIW. This phenomenon was observed on site with ship radar and echo sounders, and later verified with thermistor chain. West of Luzon Strait, the separation of NLIW are 5 km or more, while linear internal waves are lines of wave crests at nearly equal distance that is only a few hundred meters apart. The current hypothesis is that most of the energy of internal tide forms a beam that propagates upward from the eastern shoulder of ocean ridge and later interacts with sea surface and thermocline. The interaction with thermocline generates linear internal wave that propagate along the pycnocline at about 1.5 m/s. The interaction with sea surface scatters internal wave energy downward, ensonifies the water column and generates large nonlinear waves that propagate westward at 2.9 m/s as mode 1 in a waveguide.

• 대한수학회보
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• 제54권4호
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• pp.1457-1470
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• 2017

In this paper, we consider the stabilization of the viscoelastic wave equation with variable coefficients in a bounded domain with smooth boundary, subject to linear dissipative internal feedback with a delay. Our stabilization result is mainly based on the use of the Riemannian geometry methods and Lyapunov functional techniques.

• 한국해양공학회:학술대회논문집
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• 한국해양공학회 2001년도 춘계학술대회 논문집
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• pp.172-179
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• 2001

A numelical model has been developed for the permeable coastal structures to simulate hydraulic characteristics on the permeable slopes, which interact with internal flow field of the structures. The model includes hydraulics in the porous medium. Numerical model was calibrated using hydraulic model experiments performed in 2-D wave flume in the Institute of Orean Hydraulics in PKNU. Good agreement were obtained with the model which employed inertia resistance term than with the conventional model, PBREAK.

• 한국해양공학회지
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• 제16권5호
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• pp.34-40
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• 2002

A numerical model has been developed for the permeable coastal structures to simulate hydraulic characteristics on the permeable slopes, which interact with internal four field the structures. The model includes hydraulics in the porous medium. Numerical model was calibrated using hydraulic model experiments performed in 2-D wave flume in the Institute of Ocean Hydraulics in PKNU. Better aggrements were obtained with the model which employed inertia resistance term than with the conventional model, PBREAK.

• International Journal of Naval Architecture and Ocean Engineering
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• 제9권1호
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• pp.25-34
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• 2017

The concentric dual-buoy Wave Energy Converter (WEC), which consists of external buoy (hallow-cylinder) with toroidal appendage and cylindrical internal buoy within the moon-pool is suggested in this research and its performance in various wave conditions is studied. The Linear Electric Generator (LEG), consisting of a permanent magnet and coils, is used as a direct Power Take-Off (PTO) system. To maximize the electrical energy extracted from the PTO system, the relative heave motions between the dual buoys must be highly amplified by the multiple resonance phenomena of dual-buoy and internal-fluid motions. The high-performance range can be widened by distributing those natural frequencies with respect to the peak frequency of the wave spectrum. The performance of the newly developed dual-buoy WEC was measured throughout the systematic 1:5.95-model test in regular and irregular waves conducted in a wave tank at Seoul National University. The model-test results are also validated by an independently developed numerical method.

• 한국해양공학회지
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• 제16권3호
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• pp.34-39
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• 2002

본 논문에서는 수면파(Surface wave)와 수중파 (Internal wave)간의 동적 상관관계에 관하여 수행된 연구결과를 정리하였다. 표면파의 비선형 문제는 파의 경사매개변수를 2차원으로 가정하여 해석하였으며, Cauchy 문제는 불균일 조류상의 균일 수면중력파에 대하여 해석하였다. 또한, 파의 경사, 주기의 범위(Frequency range) 그리고 자유표면하의 조류의 분포들간의 조화에 대한 연구가 수행되었으며 해류 및 이동파와 연계되어 수중파의 최전 후방에 형성될 수 있는 정적 파형 (Steady wave pattern)이 수면파형에 포함되었다.

• Journal of Korean Medical Science
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• 제33권53호
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• pp.322.1-322.14
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• 2018

Background: Osteoprotegerin (OPG) plays protective roles against the development of vascular calcification (VC) which greatly contributes to the increased cardiovascular events in patients with chronic kidney disease (CKD). The present study aimed to find the non-traditional, kidney-related cardiovascular risk factors correlated to serum OPG and the effect of serum OPG on the arterial stiffness measured by brachial ankle pulse wave velocity (baPWV) in patients with the pre-dialysis CKD. Methods: We cross-sectionally analyzed the data from the patients in whom baPWV and the serum OPG were measured at the time of enrollment in a prospective pre-dialysis CKD cohort study in Korea. Results: Along with traditional cardiovascular risk factors such as age, diabetes mellitus, pulse pressure, and baPWV, non-traditional, kidney-related factors such as albuminuria, plasma level of hemoglobin, total $CO_2$ content, alkaline phosphatase, and corrected calcium were independent variables for serum OPG in multivariate linear regression. Reciprocally, the serum OPG was positively associated with baPWV in multivariate linear regression. The baPWV in the 3rd and 4th quartile groups of serum OPG were higher than that in the 1st quartile group after adjustments by age, sex and other significant factors for baPWV in linear mixed model. Conclusion: Non-traditional, kidney-related cardiovascular risk factors in addition to traditional cardiovascular risk factors were related to serum level of OPG in CKD. Serum OPG level was significantly related to baPWV. Our study suggests that kidney-related factors involved in CKD-specific pathways for VC play a role in the increased secretion of OPG into circulation in patients with CKD.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 1994년도 춘계학술대회 논문집
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• pp.21-24
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• 1994

A piezoelectric actuator. which is composed of a piezoelectrically driven stator and a rotor, Is made and the characteristics are investigated experimentally is a new ultrasonic actuator which transforms rotary motion to linear one is proposed and proved to work successfully. If an ultrasonic wave is excited to propagate in the stator, particles on the internal surface move elliptically. Since the internal surface is machined as an internal thread and an external thread(rotor) is put into the stator. the external thread is rotated through the friction force and moved in the axial direction. The traveling wave is excited by a piezoelectric element bonded to the stator. This idea is firstly proposed by S. Ueha, et al. in 1987. However, efficiency of their actuator is less than 3%. In this study, in order to improve characteristics of this type actuator, we used various pitches and number of the screw thread, and materials of rotor, and we obtained good charcteristics.

• 한국해양공학회지
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• 제35권3호
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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.

• 대한토목학회논문집
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• 제32권6B호
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• pp.379-385
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• 2012

최근의 컴퓨터 연산 성능의 향상과 전산유체역학 분야의 이론적 발전은 완전한 Navier-Stokes 방정식을 이용한 파랑의 수치모의를 가능하게 하였다. 본 연구에서는 질량원천함수를 이용한 내부조파 기법을 레블셋 유한요소법과 결합하였다. 수치모형은 먼저 2차원 파랑 조파와 전파에 적용되었다. 다음에 같은 문제의 3차원 파랑 모의에 적용되었다. 컴퓨터 자원의 효율적 활용과 연산속도 향상을 위하여 3차원 문제에는 병렬 계산 알고리즘이 고안되어 적용되었다. 수치모의에 의한 계산 결과를 이론적인 값과 비교하였으며, 잘 일치함을 확인할 수 있었다.