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1
Verification of drag-reduction capabilities of stiff compliant coatings in air flow at moderate speeds

Andrey V. Boiko,Victor M. Kulik,Ho-Hwan Chun,이인원 대한조선학회 2011 International Journal of Naval Architecture and Oc Vol.3 No.4
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  KCI
Skin frictional drag reduction efficiency of “stiff” compliant coating was investigated in a wind tunnel experiment. Flat plate compliant coating inserts were installed in a wind tunnel and the measurements of skin frictional drag and velocity field were carried out. The compliant coatings with varying viscoelastic properties had been prepared using different composition. In order to optimize the coating thickness, the most important design parameter, the dynamic viscoelastic properties had been determined experimentally. The aging of the materials (variation of their properties) during half a year was documented as well. A design procedure proposed by Kulik et al. (2008) was applied to get an optimal value for the coating thickness. Along with the drag measurement using the strain balance, velocity and pressure were measured for different coatings. The compliant coatings with the thickness h = 7mm achieved 4~5% drag reduction within a velocity range 30~40 m/s. The drag reduction mechanism of the attenuation of turbulence velocity fluctuations due to the compliant coating was demonstrated. It is envisioned that larger drag reduction effect is obtainable at higher flow velocities for high speed trains and subsonic aircrafts.
2
Verification of drag-reduction capabilities of stiff compliant coatings in air flow at moderate speeds

Boiko, Andrey V.,Kulik, Victor M.,Chun, Ho-Hwan,Lee, In-Won The Society of Naval Architects of Korea 2011 International Journal of Naval Architecture and Oc Vol.3 No.4
- 원문보기
Skin frictional drag reduction efficiency of "stiff" compliant coating was investigated in a wind tunnel experiment. Flat plate compliant coating inserts were installed in a wind tunnel and the measurements of skin frictional drag and velocity field were carried out. The compliant coatings with varying viscoelastic properties had been prepared using different composition. In order to optimize the coating thickness, the most important design parameter, the dynamic viscoelastic properties had been determined experimentally. The aging of the materials (variation of their properties) during half a year was documented as well. A design procedure proposed by Kulik et al. (2008) was applied to get an optimal value for the coating thickness. Along with the drag measurement using the strain balance, velocity and pressure were measured for different coatings. The compliant coatings with the thickness h = 7mm achieved 4~5% drag reduction within a velocity range 30~40 m/s. The drag reduction mechanism of the attenuation of turbulence velocity fluctuations due to the compliant coating was demonstrated. It is envisioned that larger drag reduction effect is obtainable at higher flow velocities for high speed trains and subsonic aircrafts.
3
Development of Compact Femtosecond Yb:KYW Oscillators: Simulation and Experiment

김광훈,Juhee Yang,Elena Sall,Sergey Chizhov,Andrey Kulik,이대식,강욱,Vladimir Yashin 한국물리학회 2012 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.61 No.3
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Numerical simulations and laboratory experiments are conducted for the development of a compact femtosecond diode-pumped Yb:KYW oscillator. For optimizing the oscillator as a seeding source for a regenerative amplifier, we simulated the output power as a function of the transmission of the output coupler, the incident pump power, and the amplification axis of the gain medium by using laser cavity analysis and design (LASCAD) software. Numerical and experimental results show good agreement for both Np- and Nm-polarization for Ng- and Np-cut crystals. The experimental results show that the Nm-polarization oscillator’s average power exceeds 1.2 W at the central wavelength of 1035 nm with a pulse duration 111 fs, which is suitable for the combined gain spectrum of a dual-crystal amplifier.