• 한국해양공학회지
• /
• 제20권2호
• /
• pp.22-28
• /
• 2006

The motion and wave drift forces of floating BBDB (backward-bent duct buoy) wave energy absorbers in regular waves are calculated, taking account of the oscillating surface-pressure due to the pressure drop in the air chamber above the oscillating water column, within the scope of the linear wave theory. A series of model tests has been conducted in order to order to verify the motion and time mean wave drift force reponses in regular waves at the ocean engineering basin, MOERI/KORDI. The pneumatic damping through an orifice-type duct for the BBDB wave energy device are deducted from experimental research. Numerical simulation for motion and drift force responses of the BBDB wave energy device, considering pneumatic damping coefficients, has been carried out, and the results are compared with those of model tests.

• 대한기계학회논문집
• /
• 제18권3호
• /
• pp.612-623
• /
• 1994

Shock-wave focusing from a two-dimensional parabolic reflector was simulated using an explicit finite volume upwind TVD scheme. Computations were performed for three different incident shock speeds of $M_s$ = 1.1, 1.2 and 1.3, corresponding to the relatively weak, intermediate, and strong shock waves, respectively. Numerical solutions nicely resolved all the waves evolving through the focusing process. As the incident shock strength increase, a transition was observed in the shock-fronts geometry that was caused by the change in the reflection type of converging shock fronts on the axis of symmetry, from regular-type to Mach-type reflection. The computed maximum on-axis pressure amplification and the trajectories of three-wave intersections showed good agreement with experimental results. The strong nonlinear effect near the focal region which determines the shock-fronts geometries at and behind the focus and at the same time confines the pressure amplification at the focus was clearly revealed from the present numerical simulation.

• 대한전기학회논문지:전기기기및에너지변환시스템부문B
• /
• 제55권6호
• /
• pp.314-324
• /
• 2006

In recent years, having the advantages of being small, low in cost and high in efficiency, Half-wave resonant type, (having only one output diode), is used in ZVS Half-Bridge DC/DC converter. This paper presents the operation mode by multi-resonant factors in the Half-wave type multi-resonant converter with direct Buck chopper circuit operated in discontinuous current mode. To study the characteristics of a multi-resonant operation in steady-state, the characteristic impedances in each mode and safe operation-region(S.O.R) are reported. Computer simulation and experimental data are also riven to verify the theoretical results.

• 한국해양공학회지
• /
• 제19권3호
• /
• pp.25-30
• /
• 2005

To predict rolling performance for a barge-type FPSO, the evaluation of correct nonlinear roll damping is critical. The square section of FPSO causes a considerable viscous damping effect. Free roll decay tests were carried out to estimate nonlinear roll damping for a barge-type FPSO, under three different conditions. The roll motion RAO was deduced from model tests in the wave condition of the wideband spectrum. In numerical calculation, the quadratic damping was considered as equivalent linear damping, using the results of free roll decay test. Tested roll performance in the JONSWAP wave spectrum was compared with numerical results. These two results shaw good agreement, in spite of the proximity of peak wave period and roll natural period.

• 한국항해항만학회지
• /
• 제27권1호
• /
• pp.71-74
• /
• 2003

Sheet형 전파흡수체를 제조하고 그들의 전자파 흡수 특성을 조사하였다. 제조된 ferrite 흡수체의 흡수특성은 2.4~3.2GHz의 주파수범위에서 입자크기의 감소에 따라 개선되었다.

• Structural Engineering and Mechanics
• /
• 제6권3호
• /
• pp.347-362
• /
• 1998

In this study an improved design method for the traditional A-type(or V-type) offshore template platform system was proposed to mitigate the vibration induced by the marine environmental loadings and the strong ground motions of earthquakes. A newly developed material model was combined into the structural system and then a nonlinear dynamic analysis in the time domain was carried out. The analysis was focused on the displacement and rotation induced by the input wave forces and ground motions, and the mitigation effect for these responses was evaluated when the viscoelastic damping devices were applied. The wave forces exerted on the offshore structures are based on Stokes fifth-order wave theory and Morison equation for small body. A step by step integration method was modified and used in the nonlinear analysis. It was found that the new design approach enhanced with viscoelastic dampers was efficient on the vibration mitigation for the structural system subjected to both the wave motion and the strong ground motion.

• 한국분말야금학회:학술대회논문집
• /
• 한국분말야금학회 2006년도 Extended Abstracts of 2006 POWDER METALLURGY World Congress Part2
• /
• pp.1179-1180
• /
• 2006

Y-type barium ferrite ($Ba_2Me_2Fe_{12}O_{22};$ Me=Zn, Co, Cu) expected as an electromagnetic wave absorber were prepared by the glass-ceramic method. The glasses with composition of $0.1ZnO{\cdot}0.9(xB_2O_3{\cdot}yBaO{\cdot}(1-x-y)Fe_2O_3)$ were prepared. Single-phase powders of Y type barium ferrite were obtained with the composition $0.1ZnO{\cdot}0.9(0.2B_2O_3{\cdot}0.5BaO{\cdot}0.3Fe_2O_3)$. The shape of Y-type crystals depended strongly on the heating temperature and changed from a plate-like hexagon to a complex polyhedron with increasing heating temperature. Correlation was recognized between saturation magnetization and crystal shape. Electromagnetic wave absorption characteristics was affected by the saturation magnetization and crystal shape.

• 한국해안·해양공학회논문집
• /
• 제29권6호
• /
• pp.286-304
• /
• 2017

본 연구에서는 어항 등과 같은 소규모 항에서 적용 가능한 격자블록결속에 의한 신형식의 원형유공케이슨을 제안하고, 이러한 방파제의 수리특성을 수치적으로 검토하였다. 본 연구에서 적용한 수치해석 코드는 최근들어 다양한 분야에서 공학적 문제해결을 위해 그 사용예가 급증하고 있는 공중사용허가서(오픈소스 기반) 라이선스 기반의 OpenFOAM(Open Field Operation and Manipulation)에 조파모듈, 투과층 해석모듈, 및 반사파 제어기능 등을 추가한 OLAFOAM을 적용하였다. 본 연구는 먼저, 1) 규칙파 하 3차원슬리트케이슨 방파제에서 파의 파압변동에 대해 기존의 실험 결과와 비교 검토하고, 2) 불규칙파를 조파하여 목표한 파의 재현과 주파수스펙트럼을 비교 검토하여 OLAFOAM의 타당성을 검증하였다. 이로부터 슬리트케이슨과 유사한 원형유공케이슨이 설치된 일정수심의 3차원수치파동수조에 불규칙파를 조파하여 유수실 폭과 유의파고 및 유의주기의 변화에 따른 원형유공케이슨 방파제에서 월파량, 반사율, 파압분포 및 그들의 상호연관성을 면밀히 검토 분석하였다. 이로부터 파압분포는 불투과연직벽체에 대한 Goda 식의 결과보다 매우 작은 결과를 나타내었으며, 반사율은 기존의 슬리트케이슨에서 반사율의 변동범위 내에 존재하는 것을 알 수 있었다.

• 한국산학기술학회논문지
• /
• 제21권2호
• /
• pp.19-24
• /
• 2020

화석 연료의 고갈로 인해 신재생 에너지에 관한 관심이 증가하고 있다. 특히, 예측가능성이 높고 이용 가능한 양이 풍부한 파력에너지 (Wave Power Energy)에 관한 연구가 활발히 진행되고 있다. 본 연구에 사용된 동축 가속형 파력 발전장치 (Coaxial Accelerator Type Wave Power Generator)는 양방향 선형 운동을 회전력으로 변환함으로써 발전 효율을 향상시킬 수 있도록 설계되었다. 본 연구에서는 해양공학수조에서 파를 생성 한 후, 파주기 및 파고에 따른 케이스 실험을 수행하였다. 실험 연구의 결과는 주파수 응답과 관련된 이론적인 방법을 통해 검증하였으며, 전반적인 경향이 일치하는 것을 확인하였다. 본 연구의 결과는 제작 전 설계 단계에서 파력 발전기의 전력을 예측하고 파력에너지의 효율을 개선하기 위한 매개 변수를 연구하는데 유용할 것으로 예상된다. 또한 제조업체는 본 연구의 결과를 통해 파력 발전기의 파력 에너지 효율을 예측하여 시행착오방지를 통해 개발 시간과 비용을 절감할 수 있을 것으로 기대할 수 있다.

• Journal of Biosystems Engineering
• /
• 제37권2호
• /
• pp.113-121
• /
• 2012

Purpose: Particle separation in solution is one of important process in a unit operation as well as in an extract preparation for biosensors. Contrary to centrifuge-type of mesh-type filter, using an ultrasonic standing wave make the filtering process continuous and free from maintenance. It is needed to investigate the characteristics of particle movement in the ultrasonic standing wave field. Methods: Through the computer simulation the effects of major design and driving parameters on the alignment characteristics of particles were investigated, and a cylindrical chamber with up-stream flow type was devised using two circular-shape PZTs on both sides of the chamber, one for transmitting ultrasonic wave and the other for just reflecting it. Then, the system performance was experimentally investigated as well. Results: The speed of a particle to reach pressure-node plane increased as the acoustic pressure and size of particle increased. The maximum allowable up-stream flow rate could be calculated as well. As expected, exact numbers of pressure-node planes were well formed at specific locations according to the wavelength of ultrasonic wave. As the driving frequency of PZT got close to its resonance frequency, the bands of particles were observed clearer, which meant the particles were trapped into narrower space. Higher excitation voltages to the PZT produced a greater acoustic force with which to trap particles in the pressure-node planes, so that the particles gathered could move upwards without disturbing their alignments even at a higher inlet flow rate. Conclusions: This research showed the feasibility of particle separation in solution in the continuous way by an ultrasonic standing wave. Further study is needed to develop a device to collect or harvest those separated particles.