• Progress in Superconductivity and Cryogenics
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• v.15 no.3
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• pp.35-39
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• 2013

In this paper, we present test results of developed 100 W class linear compressor for Stirling-type pulse tube refrigerator. The fabricated linear compressor has dual-opposed configuration, free piston and moving magnet type linear motor. Power transfer, efficiency and required pressure waveform are predicted with designed and measured specifications. In experiments, room temperature test with flow impedance is conducted to evaluate performance of developed linear compressor. Flow impedance is loaded to compressor with metering valve for flow resistance, inertance tube for flow inertance and buffer volumes for flow compliance. Several operating parameters such as input voltage, current, piston displacement and pressure wave are measured for various operating frequency and fixed input current level. Behaviors of dynamics and performance of linear compressor as varying flow impedance are discussed with measured experimental results. The developed linear compressor shows 124 W of input power, 86 % of motor efficiency and 60 % of compressor efficiency at its resonant operating condition.

• International Journal of Aeronautical and Space Sciences
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• v.16 no.3
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• pp.339-346
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• 2015

Aerodynamic flow control phenomena were investigated with a low-current DC surface discharge plasma actuator. The plasma actuator was found to operate in three different discharge modes with similar discharge currents of about 1 mA or less. Stable continuous DC discharge without audible noise was obtained at higher ballast resistances and lower discharge currents. However, even with continuous DC power input, a low-frequency self-pulsed discharge was obtained at lower ballast resistances, and a high-frequency self-pulsed discharge was obtained at higher set-point currents and higher ballast resistances, both with audible noise. The Schlieren image reveals that the low-frequency self-pulsed mode produces a synthetic jet-like flow implying that a gas heating effect plays a role, even though the discharge current is small. The high-frequency self-pulsed mode produces pulsed jets in a tangent direction, and the continuous DC mode produces a steady straight pressure wave. Particle image velocimetry (PIV) images reveal that the induced flow field by the low-frequency self-pulsed mode has flow propagating in the radial direction and centered between the electrodes. The high-frequency self-pulsed mode and continuous DC mode produce flow from the anode to the cathode. The perturbed region downstream of the cathode is larger in the high-frequency self-pulsed mode with similar maximum speeds.

• Ocean Systems Engineering
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• v.6 no.2
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• pp.161-189
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• 2016

This paper provides a practical stochastic method by which the maximum equilibrium scour depth around a vertical pile exposed to random waves plus a current on mild slopes can be derived. The approach is based on assuming the waves to be a stationary narrow-band random process, adopting the Battjes and Groenendijk (2000) wave height distribution for mild slopes including the effect of breaking waves, and using the empirical formulas for the scour depth on the horizontal seabed by Sumer and Fredsøe (2002). The present approach is valid for wave-dominant flow conditions. Results for random waves alone and random wave plus currents have been presented and discussed by varying the seabed slope and water depth. An approximate method is also proposed, and comparisons are made with the present stochastic method. For random waves alone it appears that the approximate method can replace the stochastic method, whereas the stochastic method is required for random waves plus currents. Tentative approaches to related random wave-induced scour cases on mild slopes are also suggested.

• Ocean Systems Engineering
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• v.7 no.3
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• pp.275-298
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• 2017

This paper provides a practical stochastic method by which the maximum equilibrium scour depth below a pipeline exposed to random waves plus a current on mild slopes can be derived. The approach is based on assuming the waves to be a stationary narrow-band random process, adopting the Battjes and Groenendijk (2000) wave height distribution for mild slopes including the effect of breaking waves, and using the empirical formulas for the scour depth on the horizontal seabed by Sumer and Fredsøe (1996). The present approach is valid for wave-dominant flow conditions. Results for random waves alone and random wave plus currents have been presented and discussed by varying the seabed slope and water depth. An approximate method is also proposed, and comparisons are made with the present stochastic method. For random waves alone it appears that the approximate method can replace the stochastic method, whereas the stochastic method is required for random waves plus currents. Tentative approaches to related random wave-induced scour cases for random waves alone are also suggested.

• Journal of Navigation and Port Research
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• v.34 no.6
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• pp.441-445
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• 2010

The ouput power of wave energy system in buoy is determined according to the inner diameter of oscillating water column and flow resistance. The increase of adhered shellfish inside the water column leads to decrease the inner diameter of wave energy converter. Influx loss of seawater reduces the efficiency of output power in the wave generation system. In this paper, the test result of AFS characteristic is described for preventing the deposition with shellfish and etc. The current of anode is controlled by buck converter, and the control algorithm developed for AFS in buoy. The experimental results is shown excellent preventing capapbility of AFS in buoy.

• Journal of the Society of Naval Architects of Korea
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• v.44 no.2 s.152
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• pp.148-153
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• 2007

Two typical impact loadings, shock wave and gas bubble pulse, due to UNDEX(UNDerwater EXplosion), should be considered together for the closest response analysis of structure subjected to UNDEX to a reality. Since these two impact loadings have different response time bands, however, their response characteristics of structure are different from each other. It is impossible to consider these effectively under the current computational environment and the mathematical model has not yet been developed. Whereas Hicks model approximates the fluid-structure interaction due to gas bubble pulse as virtual mass effect, treating the flow by the response of gas bubble after shock wave as incompressible ideal fluid contrary to the compressible flow due to shock wave, Geers-Hunter model could make the closest response analysis of structure under UNDEX to a real one as a mathematical model considering the fluid-structure interaction due to shock wave and gas bubble pulse together using acoustic wave theory and DAA(Doubly Asymptotic Approximation). In this study, the application and effectiveness of integrated dynamic response analysis of submerged structure was examined with the analysis of the shock wave and gas bubble pulse together.

• Proceedings of the Korean Society of Fisheries Technology Conference
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• 2009.05a
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• pp.71-74
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• 2009

• Journal of the Korean Society of Environmental Restoration Technology
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• v.2 no.3
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• pp.1-9
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• 1999

This paper described the results of the characteristics of the near-bottom flow and field analysis of the tidal flats sediment. It was the aim of this paper to grasp current flow of tidal flat's environment and influence factor for environmental change forecast of tidal flats. Field measurement of water velocity, water elevation, bed materials test, and temperature distribution of tidal flat were conducted. Thereafter, current flow, turbidity and temperature distribution of tidal flat sediment have been discussed. The field research results showed that the fluctuating velocity near the seabed before and after its appearance at low tide was strongly affected by the wind wave. The resuspension of the sea-bottom sediment took place with great intensity before and after the appearance of the seabed at low tide. Both the sea water level and the weather condition were a significant influential factors. Such as, temperature and turbidity just on the surface and the shallow layer of seabed sediments were varied largely with time and weather conditions, but that its deeper layers was almost constant. Temperature on the seabed sediments was strongly influenced by irradiance and water depth. The temperature variation of the tidal flat and the variation characteristics of the current flow and turbidity depend greatly on the inhabiting environment of the tidal flat benthic organism.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.1 no.1
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• pp.8-14
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• 1989

A mathematical model for computing the bed friction of combined wave-current flow has been developed based on the Prandtl's mixing length theory. Using various approximate expressions, solutions are obtained explicitly. The computational results are compared and found in reasonable agreements with the data of field measurements.

• Bulletin of the Korean Space Science Society
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• 2009.10a
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• pp.44.1-44.1
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• 2009

Identification of wave characteristics during current disruption events in the near-Earth geomagnetic tail region (~ 10 RE) is important to understand the substorm onset mechanism. In this paper, linear stability analysis in the ion-cyclotron grequency range, considering temperature anisotropy and cross-field flow is presented. It is found that the ion-cyclotron drift waves propagating in a quasi-perpendicular direction with respect to the ambient magnetic field are characterized by low frequencies ($\omega$ < $0.5{\Omega}ci$), while quasi-parallel waves have frequencies close to the ion-cyclotron frequency ($\omega{\sim}{\Omega}ci$). This finding is consistent with the observation by THEMIS spacecraft of a current disruption event in which a similar high- and low-frequency band structure is also present [A. T. Y. Lui, et al., J. Geophys. Res. 113, A00C06 (2008)]. It is also found that the quasi-perpendicular mode is excited by the ion cross-field flow.