• Journal of Korean Society of Coastal and Ocean Engineers
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• v.29 no.6
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• pp.305-314
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• 2017

Ocean wave energy harvesting is still too expensive despite developing a variety of wave energy converter (WEC) devices. For the cost-effective wave energy harvesting, it can be an effective measure to use existing breakwaters or newly installed breakwaters for both wave control and energy harvesting purposes. In this study, we investigated the functionality of both breakwater and wave-power generator for the oscillating water column (OWC)-type wave energy converter (WEC) installed in a pneumatic floating breakwater, which was originally developed as a floating breakwater. In order to verify the performance of the breakwater as a WEC, the air flow velocity from air-chamber to WEC has to be evaluated properly. Therefore, air flow velocity, wave transformation and motion of floating structure was numerically implemented based on BEM from linear velocity potential theory without considering the compressibility of air within the chamber. Air pressure, meanwhile, was assumed to be fluctuated by the motions of structure and the water level change within air-chamber. The validity of the obtained values can be determined by comparing the previous results from the numerical analysis for different shapes. Based on numerical model results, wave transformation characteristics around OWC system mounted on the fixed and floating breakwaters, and motions of the structure with air flow velocities are investigated. In summary, all numerical results are almost identical to the previous research considering air compressibility. Therefore, it can be concluded that this analysis not considering air compressibility in the air chamber is more efficient and practical method.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2012.05a
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• pp.405-406
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• 2012

• Journal of the Korean Society for Precision Engineering
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• v.18 no.9
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• pp.11-17
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• 2001

• Journal of the Korean Society of Propulsion Engineers
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• v.23 no.3
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• pp.104-111
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• 2019

A separate type rotary engine consisting of a compressor and an expander is under development. The engine motoring, compressor pressure, and fuel combustion have been tested with the initial prototype for operability checks of the mechanism. This paper describes an engine cycle analysis method designed specifically for this new-concept engine. The unique operational mechanism of the engine and the thermodynamic properties of each step of air intake, compression, filling of combustion chamber, combustion, expansion and exhaust were analyzed. The cycle efficiencies of this engine according to various engine design parameters as well as the cooling effect of compressed air between the compressor and expander can be easily calculated with this method; further, some case studies are presented in this paper.

• Proceedings of the Korean Society for Agricultural Machinery Conference
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• 1999.07a
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• pp.104-111
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• 1999

증기압축식 열펌프시스템은 그림 1에 나타난 바와 같이 증발기에서의 흡열과 응축기의 방열을 냉난방에 이용할 수 있으며, 공기를 열원으로 할 때는 공기 중 저밀도의 에너지를 고밀도의 에너지로 전환하여 이용할 수 있으며 지중 온도의 연중변화가 적은 점을 이용하여 지열을 열원으로 할 때는 공기를 열원으로 할 경우에 필요한 제상 장치(defrost cycle)가 필요 없게 되고, 압축기 부하도 줄어들게 되어 열펌프 수명이 길어지게 되며 경제성을 확보할 수 있을 것으로 기대된다. (중략)

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2009.11a
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• pp.378-381
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• 2009

A rotating stall, an instable phenomenon of compressor, brings about reducing the pressure rise, the efficiency of compressor and a mechanical demage. In order to improve instability and extend operating range, it was performed that a stability enhancement experiment applying air injection method at the 4-stage low-speed axial compressor. The coanda nozzle was used to inject air in axial direction at rotor tip and 8 injectors were set up at regular interval at the upstream of 1st stage rotor. At 80% speed, injectors were worked before rotating stall happened. As injecting the 5.4% air of mode inception flow rate, the stability of compressor operation enhanced about 4%.

• Journal of Korea Water Resources Association
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• v.53 no.4
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• pp.303-312
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• 2020

An underground deep tunnel system is a facility in form of a reverse siphon for an under flood defense structure. In this study, the 'Shinwol rainwater storage and drainage system', which is under construction for the first time in South Korea, in order to confirm the effects of undular bore and pressurized air on the hydraulic stability of the facility in various flood scenarios a hydraulic model experiment was performed. As a result of this study, it was analyzed that the undular bore generated downstream pushed the pressurized air collected in the facility while moving upstream, and the pressure inside the pipe increased at this time. It was analyzed that the pressure during the passage of the undular bore was greater than the sum of the static pressure and dynamic pressure at the time and overflow occurred when the cross-sectional size of the pressurized air was more than 40% of the cross sectional area of the tunnel. It is determined that this is correlated with the volume of pressurized air collected in the facility, and it is determined that it is necessary to study the relationship between velocity of undular bore and the volume of pressurized air in the future.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.29 no.1B
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• pp.83-90
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• 2009

This study describes the characteristics of distribution of lift-force acting under pier deck through physical experiment. The shape of peak wave pressure was sharp when compressed air existed but was not sharp without that. Values of lift-force was different between edge point and center point in the same block. Distribution of lift-force was expressed differently owing to dimensionless of deck length (l/L), wave steepness (H/L), clearance height per wave height (D/H). The dimensionless factor of D/H affected on the lift-force the clearance between still water surface and decks. This decided the maximum of lift-force. In the case of the same values of D/H, the lift-force are changed by the wave steepness (H/L). Because (D/H) become smaller as the wave steepness (H/L) is increased the height of decks must be decided with the condition which don't have the clearance with $D_{max}$ for the stable design of deck of pier. Effect of reducing lift force was greater in the on-shore than the off-shore according to compressed air existence. This researches points out that design of deck should retain compressed air in order to reduce wave lift force.

• Proceedings of the Korea Concrete Institute Conference
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• 1994.10a
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• pp.187-193
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• 1994

일반 콘크리트 (설계강도 $\sigma_{28}=210 kg/\textrm{cm}^2$)에 산업폐기물인 Fly Ash를 혼합하고 기포재 (Air Entrainment Agent) 첨가에 따른 Fly Ash-Concrete의 물성 변화를 시험하였다. Fly Ash-Concrete의 slump를 6, 8, 10cm로 고정시킨후, 각각의 slump 반죽상태에다 기포재, Neopor-400을 25,000cc/$\textrm{m}^3$, 50,000cc/$\textrm{m}^3$, 75,000cc/$\textrm{m}^3$으로 증가시켰다. 이때 기포재 증가에 따른 공기량 변화와 압축강도 $(\sigma_7 과 \sigma_{28})$ 를 측정하였다. 또한 기포재를 첨가한후, 60분과 90분까지 방치하고, 60분후와 90분후의 공기량과 압축강도 $(\sigma_7 과 \sigma_{28})$ 변화를 측정하였다. 시험결과에 의하면, 기포재가 첨가되는 시간에서부터 60분, 90분 동안 방치하면 공기량은 감소된다. 동시에 압축강도는 점진적으로 증가된다. KSF 5405가 요구하는 slump값이 90분 이내에 $12\pm0.5$의 범위에 들어 가기 위해서는 기포재는 50,000cc/$\textrm{m}^3$-75,000cc/$\textrm{m}^3$만큼 첨가되어야 한다. 이때의 7일 압축강도가 170-200kg/$\textrm{cm}^2$이고 28일 압축강도는 215-290kg/$\textrm{cm}^2$이다. 이 값은 설계강도 $\sigma$28=210kg/$\textrm{cm}^2$ 보다 최고 약 40%까지 증가율을 보여 주었다.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.36 no.11
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• pp.1063-1071
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• 2008

A piezoceramic unimoph actuator can produce a relatively larger actuation force and actuation displacement when a proper compressive load is applied during operation, because the compressive stress causes material nonlinear behavior in the piezoceramic layer and triggers mechanical buckling. In this paper, we examined effects of the actuator under compression on the flapping angle and aerodynamic force generation capability. Effects of wing shape and passive wing rotation angle on the aerodynamic force production were also investigated. The average vertical force acquired by a 2D CFD simulation for an artificial wing showed a good agreement with the measured one by the experiment.