• 한국전산유체공학회:학술대회논문집
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• 2008.03a
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• pp.297-301
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• 2008

The flight vehicles have cavities such as wheel wells and bomb bays. The flow around a cavity is characterized as unsteady flow because of the formation and dissipation of vortices due to the interaction between the freestream shear layer and cavity internal flow, the generation of shock and expansion waves. Resonance phenomena can damage the structures around the cavity and negatively affect aerodynamic performance and stability. The flow field is observed to oscillate in the "shear layer mode" with low aspect ratio. In the present study, numerical analysis was performed for cavity flows by the unsteady compressible three dimensional Reynolds-Averaged Navier-Stokes (RANS) equations with Wilcox's $\kappa$-$\omega$ turbulence model. The flow field is observed to oscillate in the shear layer mode" with large aspect ratio. Based on the SPL(Sound Pressure Level) analysis of the pressure variation at the cavity trailing edge, the dominant frequency was analyzed and compared with the results of Rossiter's formul. The aero-acoustic wave analyzed with CPD(Correlation of Pressure Distribution).

• 한국전산유체공학회:학술대회논문집
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• 2008.10a
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• pp.297-301
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• 2008

The flight vehicles have cavities such as wheel wells and bomb bays. The flow around a cavity is characterized as unsteady flow because of the formation and dissipation of vortices due to the interaction between the freestream shear layer and cavity internal flow, the generation of shock and expansion waves. Resonance phenomena can damage the structures around the cavity and negatively affect aerodynamic performance and stability. The flow field is observed to oscillate in the "shear layer mode" with low aspect ratio. In the present study, numerical analysis was performed for cavity flows by the unsteady compressible three dimensional Reynolds-Averaged Navier-Stokes (RANS) equations with Wilcox's ${\kappa}-{\varepsilon}$ turbulence model. The flow field is observed to oscillate in the "shear layer mode" with large aspect ratio. Based on the SPL(Sound Pressure Level) analysis of the pressure variation at the cavity trailing edge, the dominant frequency was analyzed and compared with the results of Rossiter's formul. The aero-acoustic wave analyzed with CPD(Correlation of Pressure Distribution).

• Transactions of the Korean Society of Mechanical Engineers B
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• v.27 no.6
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• pp.701-713
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• 2003

The BEM is a highly efficient method in the sense of economical computation. However, boundary integration is not easy for the complex geometry and moving surface, e.g. a rotating blade. Thus, Kirchhoff surface is designed in an effort to overcome the difficulty resulting from complex boundary conditions. A Kirchhoff surface is a fictitious surface which envelopes acoustic sources of main concern. Acoustic sources may be distributed on each Kirchhoff surface element according to their acoustic characteristics. In this study, an axial fan is assumed to have unsteady loading noise as a dominant source. Dipole sources can be modeled to solve the FW-H equation. Acoustic field is then computed by determining Kirchhoff surface on which near-field is implemented, to analyze the effect of Kirchhoff surface on it. The optimal shape and the location of Kirchhoff surface are discussed by comparing with experimental data acquired in an anechoic chamber.

• Bulletin of the Korean Mathematical Society
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• v.57 no.3
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• pp.649-660
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• 2020

This paper proves a new regularity criterion for solutions to the Cauchy problem of the 3D Boussinesq equations via one directional derivative of the horizontal component of the velocity field (i.e., (∂_iu₁; ∂_ju₂; 0) where i, j ∈ {1, 2, 3}) in the framework of the anisotropic Lebesgue spaces. More precisely, for 0 < T < ∞, if $$\large{\normalsize\displaystyle\smashmargin{2}{\int\nolimits_o}^T}({\HUGE\left\|{\small{\parallel}{\partial}_iu_1(t){\parallel}_{L^{\alpha}_{x_i}}}\right\|}{\small^{\gamma}_{L^{\beta}_{x_{\hat{i}}x_{\bar{i}}}}+}{\HUGE\left\|{\small{\parallel}{\partial}_iu_2(t){\parallel}_{L^{\alpha}_{x_j}}}\right\|}{\small^{\gamma}_{L^{\beta}_{x_{\hat{i}}x_{\bar{i}}}}})dt<{{\infty}},$$ where ${\frac{2}{{\gamma}}}+{\frac{1}{{\alpha}}}+{\frac{2}{{\beta}}}=m{\in}[1,{\frac{3}{2}})$ and ${\frac{3}{m}}{\leq}{\alpha}{\leq}{\beta}<{\frac{1}{m-1}}$, then the corresponding solution (u, θ) to the 3D Boussinesq equations is regular on [0, T]. Here, (i, ${\hat{i}}$, ${\tilde{i}}$) and (j, ${\hat{j}}$, ${\tilde{j}}$) belong to the permutation group on the set 𝕊₃ := {1, 2, 3}. This result reveals that the horizontal component of the velocity field plays a dominant role in regularity theory of the Boussinesq equations.

• Korean Journal of Materials Research
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• v.28 no.7
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• pp.398-404
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• 2018

Fatigue crack growth retardation of 304 L stainless steel is studied using a neutron diffraction method. Three orthogonal strain components(crack growth, crack opening, and through-thickness direction) are measured in the vicinity of the crack tip along the crack propagation direction. The residual strain profiles (1) at the mid-thickness and (2) at the 1.5 mm away from the mid-thickness of the compact tension(CT) specimen are compared. Residual lattice strains at the 1.5 mm location are slightly higher than at the mid-thickness. The CT specimen is deformed in situ under applied loads, thereby providing evolution of the internal stress fields around the crack tip. A tensile overload results in an increased magnitude of the compressive residual stress field. In the crack growth retardation, it is found that the stresses are dispersed in the crack-wake region, where the highest compressive residual stresses are measured. Our neutron diffraction mapping results reveal that the dominant mechanism is by interrupting the transfer of stress concentration at the crack tip.

• Proceedings of the Korean Society of Plant Pathology Conference
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• 2003.10a
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• pp.107.2-108
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• 2003

Viral disease symptoms were investigated in the field grown Longiflorum hybrid cultivars, and the damages caused by infection with Lily mottle virus (LMoV) and Cucumber mosaic virus (CMV) were assessed by comparing growth of plants produced from seeds of Longiflorum hybrid cultivar both infected by artificial inoculation and free from infection with theses viruses. Dominant symptom caused by spotaneous infection with LMoV and CMV in the field was mottle combined with chlorotic stripe on leaves. LMoV developed brownish necrotic lesion on floral leaves. The incidence of viral disease by mixed infection with LMoV, CMV or Lily symptomless virus (LSV) in the filed grown Longiflorum hybrid cultivar, cultivated for more than 6 years, was 80 to 84 percent. In comparison with virus-free plants, plants doubly infected with CMV and LMoV by artificial inoculation decreased stem length by 14 percent and fresh weight by 38 percent. In conclusion, flower quality and the stem length of Longiflorum hybrid cultivar were affected by LMoV and CMV infection.

• The Transactions of the Korean Institute of Electrical Engineers B
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• v.51 no.8
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• pp.425-433
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• 2002

This research investigates the electromechanical characteristics of a sing1e-phase squirrel cage induction motor due to broken rotor bars and rotor eccentricity. Numerical analysis is performed by solving the nonlinear time-stepping finite element equation coupled with the magnetic field equation, circuit equation and mechanical equation of motion. It shows that the asymmetry of magnetic flux due to the broken rotor bars and rotor eccentricity introduce a change in the stator current, torque, speed, magnetic force and vibration of a rotor at the same time. However, even in the existence of rotor eccentricity, 3 broken rotor bar introduces a dominant change in the magnetic force and rotor displacement, i.e., beating phenomenon in time domain and sideband frequencies in frequency spectra, respectively.

• Proceedings of the Korean Biophysical Society Conference
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• 2003.06a
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• pp.76-76
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• 2003

We report here the results on N-acetyl-N'-methylamide of 4-fluoroproline (Ac-Flp-NHMe) calculated using the ab initio molecular orbital method with the self-consistent reaction field (SCRF) theory at the HF level with the 6-31+G(d) basis set to investigate the stereoelectronic effects on the conformational preference of proline depending on the cis/trans peptide bonds and down/up puckerings along the backbone torsion angle $\square$ in the gas phase, chloroform, and water. In the gas phase, all potential energy surfaces for Ac-Flp-NHMe are quite similar to those of Ac-Pro-NHMe, except that up-puckered conformations are more stabilized than down-puckered ones. In chloroform and water, polyproline structures become dominant, whose populations are larger than those of Ac-Pro-NHMe. In chloroform and water, the populations of polyproline II (i.e., tF conformations) are quite similar to each other, but those of polyproline I (i.e., cF conformations) are larger by 5％ in water than in chloroform. In particular, all cis populations for Ac-Flp-NHMe in the gas phase, chloroform, and water are decreased than those of Ac-Pro-NHMe.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2007.11a
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• pp.167-168
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• 2007

$CdIn_2S_4$ (110) films were grown on semi-insulating GaAs (100) by a hot wall epitaxy method. Using photocurrent (PC) measurement, the PC spectra in the temperature range of 30 and 10 K appeared as three peaks in the short wavelength region. It was found that three peaks, A-, B-, and C-excitons, correspond to the intrinsic transition from the valence band states of ${\Gamma}_4(z),\;{\Gamma}_5(x),\;and\;{\Gamma}_5(y)$ to the exciton below the conduction band state of ${\Gamma}_1(s)$, respectively. The 0.122 eV crystal field splitting and the 0.017 eV spin orbit splitting were obtained. Thus, the temperature dependence of the optical band gap obtained from the PC measurement was well described by $E_g$(T)=2.7116eV - $(7.65{\times}10^{-4}\;eV/K)T^2$/(425+T). But, the behavior of the PC was different from that generally observed in other semiconductors. The PC intensities decreased with decreasing temperature. This phenomenon had ever been reported at a PC experiment on the bulk crystals grown by the Bridgman method. From the relation of log $J_{ph}$ vs 1/T, where $J_{ph}$ is the PC density, two dominant levels were observed, one at high temperatures and the other at low temperatures. Consequently, the trapping centers due to native defects in the $CdIn_2S_4$ film were suggested to be the causes of the decrease in the PC signal with decreasing temperature.

• KOREAN JOURNAL OF CROP SCIENCE
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• v.26 no.4
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• pp.287-292
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• 1981

The field studies were carried out in paddy field over a four year period in order to find out the effects of butachlor, nitrofen, oxadiazon or CG 102, benthiocarb-S, and bentazon applied successively to the same paddy field for four years on weed succession and rice yields under different fertilized conditions including compost, chemical fertilizer and straw application. Total dry weight of weeds was steadily increased yearly over 4 year period regardless of fertilized conditions, and significantly higher increase of weed dry weight was observed on non-fertilized and compost plots. The most dominant weed species was Scirpus hotarui, and Potamogeton distinctus, Eleocharis kuroguwai and Cyperus serotinus were predominated on compost plot, E. kuroguwai and E. aclularis on non-fertilized plot, E. kuroguwai, C. serotinus, and Monochoria vaginalis on chemical fertifizer plot, and C. serotinus on straw plot. When the same herbicides were used continuously on the same plots, weed control effect was decreased and thus weed population was greatly increased particularly on butachlor and nitrofen treated plots. P. distinctus, E. kuroguwai, and C. serotinus were predominated on butachlor treated plot, P. distinctus and C. serotinus on nitrofen treated plot, C. serotinus on benthiocarb-S treated plot, C. serotinus and P. distinctus on oxadiazon or CG 102 treated plot and P. distinctus on bentazon treated plot. Annual weeds were slightly increased by repeated annual application of oxadiazon or CG 102 and benthiocarb-S, whereas perennial weeds were predominated by successive application of butachlor, nitrofen. and bentazon for 4 years. Yield reduction of rice became prominent by successive application of same herbicides. particularly butachlor and nitrafen. This results suggested that successive annual application of same herbicides should be limited and herbicide combination or herbicide rotation should be applied to control the remaining weed species.