• Journal of Power System Engineering
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• v.17 no.6
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• pp.95-101
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• 2013

A stereo PIV measurements in a circulating water channel has been performed to investigate the skin friction reduction mechanism of the outer-layer vertical blades first devised by Hutchins. In a recent PIV measurement study, considerable skin friction reduction was achieved as much as 2.73%~7.95% by outer-layer vertical blades array. In the present study, the influence of vertical blades array upon the characteristics of the turbulent coherent structures was analyzed by proper orthogonal decomposition method. It is observed that the vortical structures are cut and deformed by blades array and also the turbulent intensity and the Reynolds stress were weakened by the blades. These phenomena strongly associate the skin-friction drag reduction mechanism in the turbulent boundary layer flow.

• International Journal of Naval Architecture and Ocean Engineering
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• v.6 no.1
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• pp.151-161
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• 2014

In this study, an experimental investigation has been made of the applicability of outer-layer vertical blades to real ship model. After first devised by Hutchins and Choi (2003), the outer-layer vertical blades demonstrated its effectiveness in reducing total drag of flat plate (Park et al., 2011) with maximum drag reduction of 9.6%. With a view to assessing the effect in the flow around a ship, the arrays of outer-layer vertical blades have been installed onto the side bottom and flat bottom of a 300k KVLCC model. A series of towing tank test has been carried out to investigate resistance (CTM) reduction efficiency and improvement of stern wake distribution with varying geometric parameters of the blades array. The installation of vertical blades led to the CTM reduction of 2.15~2.76% near the service speed. The nominal wake fraction was affected marginally by the blades array and the axial velocity distribution tended to be more uniform by the blades array.

• 한국정보디스플레이학회:학술대회논문집
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• 2008.10a
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• pp.344-347
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• 2008

We fabricated the outer type-dynamic microlens array using a surface-stabilized ferroelectric liquid crystal, UV curable polymer and the stacked liquid crystalline polymer. The outer type-microlens array has a lower driving voltage and fast switching property. It is applicable to a variety of optical systems.

• Journal of The Korean Astronomical Society
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• v.40 no.4
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• pp.133-135
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• 2007

A survey project of TRAO with the fifteen beam array receiver system is presented. A multibeam array receiver system has been purchased from FCRAO, and is being installed on TRAO 14m telescope. The target region of the survey is from ${\iota}=120^{\circ}{\sim}137^{\circ},\;b=-1^{\circ}{\sim}+ 1^{\circ}$, and velocity resolution would be 1 km/sec after smoothing from the original resolution of $0.64km\;s^{-1}$ in the transition of J = 1-0 of $^{13}CO$. The survey region is a part of the $^{12}CO$ Outer Galaxy Survey(OGS), and would be an extension of the Bell Laboratories $^{13}CO$ Galactic Plane Survey. By combining with the existing $^{12}CO$ database of the Outer Galaxy Survey, we will derive physical properties of identified molecular clouds and will conduct and statistical analysis of the Outer Galalxy molecular clouds. Reduction process and analysis methods will be introduced.

• Proceedings of the Korea Electromagnetic Engineering Society Conference
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• 2002.11a
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• pp.250-254
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• 2002

In this paper, we design an optimized planar array structure with triangular lattice for side-lobe reduction using a genetic algorithm. A constraint optimization is implemented by optimally removing some outer array elements far from the array center. It is shown that only the proper array shape without optimizing the magnitudes and phases of each array antenna can give low side-lobe level with a slight main beam broadening.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.26 no.2
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• pp.203-209
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• 2016

According to the wear detection history for the steam generator tubes in the nuclear power plant, the outer tubes inside the steam generator have more problems on the flow-induced vibration than inner tubes. Many researchers and engineers have used a specified added mass coefficient for a given tube array during the design stage of the steam generator even though the coefficient is not constant for entire tube in cylindrical shell. The aim of this study is to find out the distribution of added mass coefficients for each tube along the radial location. When numbers of tubes inside a cylindrical shell are increased, values of added mass coefficients are also increased. Added mass coefficients at outer tubes are less than those of inner tubes and they are decreased with increasing the gap between the outermost tube and the cylindrical shell. It also turns out when the gap between the outermost tube and the cylindrical shell approaches infinite value, the added mass coefficient converges to an asymptotic value of given tube array in a free fluid field.

• Journal of the Korean Institute of Telematics and Electronics A
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• v.31A no.5
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• pp.85-93
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• 1994

We have studied the effect of channel and/or spacing chirpings on the near field and near field intensity patterns, modal gains and radiation angles of 6 supermodes in the index-guided laser arrays with 6 channels, on the basis of the coupled mode theory. The spacings between channels can be indenpendent parameters for control of the radiation angle. It is found that an asymmetrically v channel-chirped array has both a smaller radiation angle and better supermode discrimination characteristics than a uniform array. Comparing two approaches for enhancing modal stability in point of supermode discrimination characteristics, approach I which increases the coupling cofficient between the outer-most waveguides at each end of an otherwise uniform array, has superior discrimination characteristics to the approach II which increases the propagation constant for the end elements with the same coupling between neighbor elements. Approach III which has a narrower spacing between the outer-most waveguides at one end and a wider channel width of the outer-most waveguide at another end, gets a narrower radiation angle than the approach I and good supermode discrimination characteristics by applying optimized gain profiles.

• 대한공업교육학회지
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• v.33 no.2
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• pp.273-286
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• 2008

Underwater acoustic sensor array can detect acoustic signal in underwater and the sensor array can be mounted in each left, right or front side of the UUV(Unmanned Underwater Vehicle). The sensor array could be conformal array and effected turbulent boundary layer flow noise. Therefore, in this paper numerical simulations were performed to know the how the outer flow noise affect the hydrophone which embedded in the elastomer. Corcos wall pressure model was used as turbulent boundary layer flow noise and this model was applied to the frequency density function. Characteristics of transfer function according the kx wave number were simulated and design parameters were thickness of elastomer, density, and modulus of elasticity. Based on the simulation results when increasing the thickness of elastomer noise reduction was increased. This results can be applied to the design of conformal array of UUV.

• Proceedings of the KSME Conference
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• 2007.05b
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• pp.3473-3478
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• 2007

A dual side cooling annular fuel having internal and external coolant channels has many advantages basically due to low fuel temperature and high DNBR margin, which can make a significant increase of core power density possible. So recently a 12x12 square annular fuel array was proposed for the fuel assembly to be reloaded without structural interference with operating reactors of OPR-1000s. Even through the inherent potential of the annular fuel on the high power density, it may be seriously eroded in the case of a severe unbalanced mass flux split to the internal and external channels in standpoint of DNB. Mass flux split is determined pressure drop characteristics between inner and outer channels. The spacer grids binding fuel array influence greatly the pressure drop in outer channels and the mass flux split. As an important factor of DNB behavior, the enthalpy differences at both channel exits were evaluated using the mass flux splits.

• Transactions of the Korean Society of Machine Tool Engineers
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• v.15 no.4
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• pp.69-73
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• 2006

This paper present the optimal cleaning condition of the out-hull preprocessing robot by Taguchi method in design of experiments. A $L_8(2^4)$ orthogonal array is adopted to study the effect of adjustment parameters. The adjustment parameters consist of robot speed, motor torque, motor speed and tool angle. And the quality feature is selected as surface roughness of sheet metal. Taguchi analysis is performed in order to evaluate the effect of adjustment parameters of the quality feature of cleaning process by $Minitab^{(R)}$.