• 한국신재생에너지학회:학술대회논문집
• /
• 2009.11a
• /
• pp.594-599
• /
• 2009

Recent developments such as concern over global warming, depletion of fossil fuels and increase in energy demands by the increasing world population has eventually lead to mass production of electricity using renewable sources. Apart from wind and solar, ocean holds tremendous amount of untapped energy in forms such as geothermal vents, tides and waves. The current study looks at generating power using waves and the focus is on the primary energy conversion (first stage conversion) of incoming waves for different models. Observation of flow characteristics and the velocity in the augmentation channel as well as the front guide nozzle are presented in the paper. A numerical wave tank was used to simulate the waves and after obtaining the desired wave properties; the augmentation channel plus the front guide nozzle and rear chamber were integrated to the numerical wave tank. The waves in the numerical wave tank were generated by a piston type wave maker which was located at the wave tank inlet. The inlet which was modeled as a plate wall moved sinusoidally with the general function, x=asin$\omega$t The augmentation channel consisted of a front nozzle, rear nozzle and an internal fluid region representing the turbine housing. The analysis was performed using the commercial CFD code ANSYS-CFX.

• Proceedings of the Korea Committee for Ocean Resources and Engineering Conference
• /
• 2006.11a
• /
• pp.465-468
• /
• 2006

The wave power absorbing performance of a bottom-mounted oscillating water column (OWC) chamber structure is studied. The potential problem inside the chamber is solved by making use of the Green integral equation associated with the Rankine Green function while the outer problem with the Kelvin Green function taking account of fluctuating air pressure in the air chamber. The absorbed wave power, wave elevation inside the chamber, reflection coefficient and wave loads are calculated for various values of a parameter related to the fluctuating air pressure. The present methods can also be used for the design of a OWC breakwater which can absorb and reflect the incoming wave energy at the same time.

• Journal of The Korean Society of Agricultural Engineers
• /
• v.58 no.4
• /
• pp.47-55
• /
• 2016

This study is on the stability re-evaluation of armor stones in saemangum seadike according to recently increased sea-level and frequent high wave incoming and the results are in the following. The field inspection of armor stones in the seadike revealed that damages of armor stones have been caused by higher waves than designed waves and that the reconstruction of armor stones and concrete grouting method have been used as the reinforcement work. The result of numerical simulation of wave channel conducted to estimate the safety weight of armor stones influenced by flows revealed that the safety weight of armor stones in the seadike No.4 was estimated as 5.47 tons by using the Isbash method, which is about 122 % more than 4.49 tons estimated by using Van der Meer method. Therefore, in designing armor stones which can be influenced by high waves such as the case of Saemangum seadike, it is necessary to apply the safety weight method of armor stones, based on the Isbash method, which produced the significant figures among the safety weight methods using flows as well as the safety weight method using high waves based on the Hudson method.

• International Journal of Aeronautical and Space Sciences
• /
• v.3 no.1
• /
• pp.74-85
• /
• 2002

The numerical experiment has been conducted to investigate the unsteady shock wave reflecting phenomena. The cell-vertex finite-volume, Roe's upwind flux difference splitting method with unstructured grid is implemented to solve unsteady Euler equations. The $4^{th}$-order Runge-Kutta method is applied for time integration. A linear reconstruction of the flux vector using the least-square method is applied to obtain the $2^{nd}$-order accuracy for the spatial derivatives. For a better resolution of the shock wave and slipline, the dynamic grid adaptation technique is adopted. The new concept of grid adaptation technique, which is much simpler than that of conventional techniques, is introduced for the current study. Three error indicators (divergence and curl of velocity, and gradient of density) are used for the grid adaptation procedure. Considering the quality of the solution and the numerical efficiency, the grid adaptation procedure was updated up to $2^{nd}$ level at every 20 time steps. For the convenience of comparison with other experimental and analytical results, the case of interaction between the straight incoming shock wave and a sharp wedge is simulated for various flow conditions. The numerical results show good agreement with other experimental and analytical results, in the shock wave reflecting structure, slipline, and the trajectory of the triple points. Some critical cases show disagreement with the analytical results, but these cases also have been proven to show hysteresis phenomena.

• Journal of Power System Engineering
• /
• v.17 no.5
• /
• pp.38-43
• /
• 2013

In order to design a wave energy generating system, a 6-DOF analysis technique is applied to CFD analysis on of a floating body and the behavior is interpreted according to the nature of the incoming waves. A spring constant is adopted to control the motion of multi floating bodies and to calculate the total average power absorption. Three cases of different wavelengths namely 20D, 30D and 40D have been modeled to analyze the total average power absorption. The average power absorption not only varies with the position of the floating body but also varies with wavelength. From the results obtained, it is concluded that the maximum total average power absorption is 9W approximately in wavelength 30D and the minimum total average power absorption is 4.3W approximately in wavelength 40D.

• Journal of Ocean Engineering and Technology
• /
• v.33 no.3
• /
• pp.229-235
• /
• 2019

In this study, a two-dimensional oscillating foil with forward speed in a propagating wave flow field was considered. The time-mean power to maintain the heaving and pitching motions of the foil was analyzed using the perturbation theory in an ideal fluid. The power, which was a non-linear quantity of the second-order, was expressed in terms of the quadratic transfer functions related to the mutual product of the heaving and pitching motions and incoming vertical flow. The effects of the pivot point and phase difference among the disturbances were studied. The negative power, which indicates energy extraction from the fluid, is shown as an example calculation.

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

• Transactions of the Korean Society of Mechanical Engineers
• /
• v.19 no.9
• /
• pp.2283-2296
• /
• 1995

Experiments of normal shock wave/turbulent boundary layer interaction were conducted in a supersonic diffuser. The flow Mach number just upstream of the normal shock wave was in the range of 1.10 to 1.70 and Reynolds number based upon the turbulent boundary layer thickness was varied in the range of 2.2*10$^{[-994]}$ -4.4*10$^{[-994]}$ . The wall pressures in streamwise and spanwise directions were measured for two test cases, in which the turbulent boundary layer thickness incoming into the supersonic diffuser was changed. The results show that the interactions of normal shock wave with turbulent boundary layer in the supersonic diffuser can be divided into three patterns, i.e., transonic interaction, weak interaction and strong interaction, depending on Mach number. The weak interactions generate the post-shock expansion which its strength is strong as the Mach number increases and the strong interactions form the pseudo-shock waves. From the spanwise measurements of wall pressure, it is known that if the flow Mach number is low, the interacting flow fields essentially appear two-dimensional, but they have an apparent 3-dimensionality for the higher Mach numbers.

• Proceedings of the KIEE Conference
• /
• 2004.11c
• /
• pp.574-576
• /
• 2004

The directivity of the sound pressure increases the sensitivity of the incoming sound from specific directions. The directivity measurement of the sound pressure is usually done in an anechoic room using a sloping motor. In this paper a replaceable anechoic chamber was designed for the acoustic directivity pattern measurement. Electrical equipments were interfaced with a PC for experiment automatic control. Some comparative results are shown in the result.

• Proceedings of the Korean Society of Coastal and Ocean Engineers Conference
• /
• 1996.10a
• /
• pp.137-139
• /
• 1996

It is known that under storm waves, beach will respond by eroding material from the beach Ace and the formation of longshore bar(s) in the vicinity of breaking point. This breakpoint bar is believed to have the effect of slowing down beach erosion by dissipating incoming wave energy and retarding offshore sediment transport. Recently, artificial bin are being proposed as beach protective measures based on this reasoning. (omitted)