• Journal of Ocean Engineering and Technology
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• v.21 no.3 s.76
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• pp.40-45
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• 2007

This study was performed to investigate the effect of various propeller tunnel shapes on the propulsion performance of a fishing boat. The propeller tunnel reduces the problem resulting from the open propeller accidentally catching the waste net and cable on the sea, as well as increasing the cruising speed. For 3 different tunnel geometries, the model test is conducted in the circular water channel, and the potential based panel method was applied to analyze the hydrodynamic characteristics of propeller. Also, both results are compared with each other to represent the difference between results of the model scale test and the potential theory. It is expected that these results could be referenced in the design of the propeller tunnel in consideration of the hydrodynamic interaction between the propeller and the tunnel.

• The Journal of the Acoustical Society of Korea
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• v.14 no.3
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• pp.114-121
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• 1995

Outdoor experimental study is presented the insertion loss caused by barrier considering discontinuous ground condition. Measurements ware made in 1/3 octave band over the frequency range 315 Hz~3150 Hz with the various geometry of the source, receiver and barriers. The frequency range of the interference pattern depends on the phase difference between path from the edge of barrier to receiver, and hence on the acoustical properties of the ground on the receiver side of the barrier. The insertion loss by barrier, in addition to diffraction, is shown to be dependent on the ground characteristic.

• 한국전산유체공학회:학술대회논문집
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• 2001.05a
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• pp.30-37
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• 2001

A Numerical simulation for the propulsion of axisymmetric body by contractive and dilative motion is carried out. The present analysis shows that a propulsive force can be obtained in highly viscous fluid by a contractive and dilative motion of axisymmetric body. An axisymmetric analysis code is developed with unstructured grid system for the simulation of complicated motion and geometry. The developed code is validated by comparing with the results of stokes approximation with the problem of uniform flow past a sphere in low Reynolds number($R_n=1$). The validated code is applied to the simulation of contractive and dilative motion of body. The simulation is extended to the analysis of waving surface with projecting part for finding out the difference of hydrodynamic performance according to the variation of waving surface configuration. The present study will be the basic research for the development of the propulsor of an axisymmetric micro-hydro-machine.

• Geomechanics and Engineering
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• v.8 no.6
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• pp.783-799
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• 2015

In this study, effect of horizontal in situ stress on failure mechanism around underground openings excavated in isotropic, elastic rock zones is investigated. For estimating the plastic zone occurrence, an induced stress influence area approach (Bray Equations) was modified to define critical stress ratio according to the Mohr-Coulomb failure criterion. Results obtained from modified calculations were compared with results of some other analytical solutions for plastic zone thickness estimation and the numerical modelling (finite difference method software, FLAC2D) study. Plastic zone and its geometry around tunnels were analyzed for different in situ stress conditions. The modified equations gave similar results with those obtained from the other approaches. However, safer results were calculated using the modified equations for high in situ stress conditions and excessive ratio of horizontal to vertical in situ stresses. As the outcome of this study, the modified equations are suggested to use for estimating the plastic zone occurrence and its thickness around the tunnels with circular cross-section.

• International Journal of Aeronautical and Space Sciences
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• v.7 no.2
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• pp.155-174
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• 2006

Parabolized stability equations for compressible flows in general curvilinear coordinate system are derived to deal with a broad range of transition prediction problems on complex geometry. A highly accurate finite difference PSE code has been developed using an implicit marching procedure. Compressible and incompressible flat plate flow stability under two-dimensional and three¬dimensional disturbances has been investigated to test the present code. Results of the present computation are found to be in good agreement with the multiple scale analysis and DNS data. Stability calculation results by the present PSE code for compressible boundary layer at Mach numbers ranging from 0.02 to 1.5 are also presented and are again seen to be as accurate as the spectral method.

• 한국연소학회:학술대회논문집
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• 2000.05a
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• pp.26-34
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• 2000

Geometry change of burner nozzle has influence on fuel atomizing and combustion characteristics. NOx reduction technologies can be divided into two method; Before combustion method(NOx treatment of fuel) and After combustion method(NOx treatment of flue gas). In this study, experiments are carried out using difference nozzle and combustion condition change to reduce NOx in heavy oil fired thermal utility boiler. These methods have advantage like easy application and low installation cost. By this method NOx can be reduced by 18% and maintain CO emission level.

• Korean Journal of Human Ecology
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• v.17 no.1
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• pp.35-43
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• 2008

The purpose of this study is to develop evaluation tools for young children's mathematical ability based on the content standards of NCTM and to verify the suitability of the tools. The tools consist of 5 sub-tests with 90 items, including number and operation, algebra, geometry, measurement, data analysis and probability. The tool analysis was examined with 300 three-to five-years-old children and 31 math education professionals. The results of this research are as follows : First, in order of age the passing rate increased. The gap between high and low score group reveals a statistically meaningful difference. Second, the internal consistency reliability coefficient, Cronbach ${\alpha}$, is .96. Test-retest reliability is around .90. The concurrent validity correlation between this tools and Choi Hye-Jin's test(2003) is .85. The analysis of the content validity was proved appropriately by math education professionals.

• Bulletin of the Korean Mathematical Society
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• v.36 no.1
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• pp.63-78
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• 1999

Let $\mu$(x) be an increasing function on the real line with finite moments of all oeders. We show that for any linear operator T on the space of polynomials and any interger n $\geq$ 0, there is a constant $\gamma n(T)\geq0$, independent of p(x), such that $\parallel T_p\parallel\leq\gamma n(T)\parallel P\parallel$, for any polynomial p(x) of degree $\leq$ n, where We find a formular for the best possible value $\Gamma_n(T)\;of\;\gamma n(T)$ and estimations for $\Gamma_n(T)$. We also give several illustrating examples when T is a differentiation or a difference operator and $d\mu$(x) is an orthogonalizing measure for classical or discrete orthogonal polynomials.

• International Journal of Air-Conditioning and Refrigeration
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• v.9 no.1
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• pp.11-19
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• 2001

To establish optimum cycle of the inverter-driven heat pump with a variation of frequency, the bypass orifice, which was a short tube haying a bypass hole in the middle, was designed and tested. Flow characteristics of the bypass orifice were measured as a function of orifice geometry and operating conditions. Flow trends with respect to frequency were compared with those of short tube orifices and capillary tubes. Generally, the bypass orifice showed the best flow trends among them. and it would enhance the seasonal energy efficiency ratio of an inverter heat pump system, Based on experimental data, a semi-empirical flow model was developed to predict mass flow rate through bypass orifices. The maximum difference between measured data and model`s prediction was within $\pm$5%.

• Korean Journal of Computational Design and Engineering
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• v.9 no.3
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• pp.253-259
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• 2004

A numerical investigation was performed to determine the effect of airfoil on the optimum flap height using NACA0015 Wells turbine. The five double flaps which have 0.5% difference were selected. A Navier-Stokes code, CFX-TASCflow, was used to calculate the flow field of the Wells turbine. The basic feature of the Wells turbine is that even though the cyclic airflow produces oscillating axial forces on the airfoil blades, the tangential force on the rotor is always in the same direction. Geometry used to define the three dimension numerical grid is based upon that of an experimental test rig. This paper tries In optimized disign the double flap of Wells turbine with the numerical analysis.