• Journal of the Korean Society of Marine Environment & Safety
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• v.17 no.1
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• pp.75-82
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• 2011

Marine current energy is one of the most interesting renewable and clean energy resources that have been less exploited. Especially, Korea has worldwide outstanding tidal current energy resources and it is highly required to develop tidal in-stream energy conversion system in coastal area. The objective of study is to investigate harnessing techniques of tidal current energy and to design the a 100 kW horizontal axis tidal turbine using blade element momentum theory with Prandtl's tip loss factor for optimal design procedures. In addition, Influence of Prandtl's tip loss factor at local blade positions as a function of tip speed ratio was studied, and the analysed results showed that power coefficient of designed rotor blade using NACA 63812 was 0.49 at rated tip speed ratio.

• The KSFM Journal of Fluid Machinery
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• v.18 no.5
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• pp.5-12
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• 2015

This paper presents a numerical investigation of the effect of the dihedral stator on the loss in a transonic axial compressor. Four stator geometries with different stacking line variables are tested in the flow simulations over the whole operating range. It is found that a large shroud loss at the rotor outlet and the subsequent shroud corner separation in the stator passage occur at low mass flow rate. The hub dihedral stator and bowed blade generate unexpected hub-corner-separation, thereby causing a large total pressure loss over the entire operating range. However, the corresponding blockage forces the high momentum flow near the hub to divert toward the upper part of the passage suppressing the negative axial velocity region. The dihedral stator increases deflection angle and secondary vorticity near the endwall where the dihedral is applied. As a result, the endwall loss which is related to the endwall relative velocity decreases.

• The Bulletin of The Korean Astronomical Society
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• v.35 no.2
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• pp.76.2-76.2
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• 2010

We present the final results of our study on the mass-loss rate of donor stars in cataclysmic variables (CVs). Observed donors are oversized in comparison with those of isolated single stars of the same mass, which is thought to be a consequence of the mass loss. Using the empirical mass-radius relation of CVs and the homologous approximation for changes in effective temperature T2, orbital period P, and luminosity of the donor with the stellar radius, we find the semi-empirical mass-loss rate M2dot of CVs as a function of P. The derived M2dot is at ~10-9.5-10-10 $M\odot$/yr and depends weakly on P when P > 90 min, while it declines very rapidly towards the minimum period when P < 90 min. The semi-empirical M2dot is significantly different from, and has a less-pronounced turnaround behavior with P than suggested by previous numerical models. The semi-empirical P-M2dot relation is consistent with the angular momentum loss due to gravitational wave emission, and strongly suggests that CV secondaries with 0.075 $M\odot$ < M2 < 0.2 $M\odot$ are less than 2 Gyrs old. When applied to selected eclipsing CVs, our semi-empirical mass-loss rates are in good agreement with the accretion rates derived from the effective temperatures T1 of white dwarfs. Based on the semi-empirical M2dot, SDSS 1501 and 1433 systems that were previously identified as post-bounce CVs have yet to reach the minimal period.

• Transactions of the Korean Society of Mechanical Engineers
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• v.17 no.8
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• pp.2110-2121
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• 1993

A numerical investigation has been carried out for the flow characteristics after exchange of some filters from the original layer to the new low pressure loss layer with equal filtering efficiency. The solution domain includes upper plenum, filter layer, clean space, access panels, and lower plenum. The concept of the distributed pressure resistance was applied to describe the momentum loss in filter layer and access panels. The evolution of the flow field is simulated using the low Reynolds number k-.epsilon. over bar turbulent model and SIMPLE algorithm based on the finite volume method. As a result, after the exchange of filter layer the power requirement can be reduced by 8-9 percent. The results also demonstrate that the perpendicularity of the flow near access panels may become worse at new filter layer than origianl filter layer. But the situation can be recovered by adjusting the jopening ratio of access panels.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.23 no.10
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• pp.1274-1284
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• 1999

The Regulatory Guide 1.82 recommends an analysis of hydraulic performance for sump of ECCS (Emergency Core Cooing System) when LOCA(Loss of Coolant Accident) occurs in a nuclear power plant. The present study deals with 3-dimensional, unsteady, turbulent and two-phase flow simulation to examine the behavior of mixture of reactor coolant and debris near the floor of containment building in conjunction with appropriate assumptions. The dispersed solid model has been adjusted to the interfacial momentum transfer between reactor coolant and debris. According to the results, the counterclockwiserecirculation zone had been formed in the region between sump and connection aisle about 376 second after LOCA occurs. The debris thickness accumulated on a sump screen periodically increases or decreases up to 2000 second, afterwards its peak decreases.

• Journal of Ocean Engineering and Technology
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• v.22 no.3
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• pp.1-7
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• 2008

In this study, a mathematical model for flaw with silt protector is proposed that adds a second-order energy loss term in the momentum equation. The three-dimensional numerical model was developed based on mathematical models and verified through comparison with flume test results. Loss coefficients were evaluated through the flume tests and applied to the numerical model. It was found through the investigation of various example cases that the downstream flow pattern was affected mainly by penetration of the silt curtain, not by the approach velocity, and also that the blocking effect of velocity was increased by the increase in mesh density of the silt curtain, below a certain mesh density. The blocking effect did not increase further above a certain mesh density.

• Nuclear Engineering and Technology
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• v.47 no.4
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• pp.416-423
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• 2015

It had been disputed how to apply wall drag to the dispersed phase in the framework of the conventional two-fluid model for two-phase flows. Recently, Kim et al. [1] introduced the volume-averaged momentum equation based on the equation of a solid/fluid particle motion. They showed theoretically that for dispersed two-phase flows, the overall two-phase pressure drop by wall friction must be apportioned to each phase, in proportion to each phase fraction. In this study, the validity of the proposed wall drag model is demonstrated though one-dimensional (1D) simulations. In addition, it is shown that the existing form loss model incorrectly predicts the motion of the dispersed phase. A new form loss model is proposed to overcome that problem. The newly proposed form loss model is tested in the region covering the lower plenum and the core in a nuclear power plant. As a result, it is shown that the new models can correctly predict the relative velocity of the dispersed phase to the surrounding fluid velocity in the core with spacer grids.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.1 no.2
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• pp.107-115
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• 1989

The swirl flame was investigated experimentally by measuring the temperature distribution, and the combustion gas concentrations. The flame structure of the swirl flame was influenced not by the swirl vane angle but by the swirler position. Due to the momentum loss as the swirler position was moved downward under the nozzle exit, the flame length was increased. Meanwhile the temperature and $CO_2$-concentrations were decreased.

• International Journal of Fluid Machinery and Systems
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• v.8 no.4
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• pp.221-229
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• 2015

For efficient design process of regenerative blower, the present study provides new generalized pressure and leakage flow loss models, which can be used in the performance analysis method of regenerative blower. The present performance analysis on designed blower is made by incorporating momentum exchange theory between impellers and side channel with mean line analysis method, and its pressure loss and leakage flow models are generalized from the related fluid mechanics correlations which can be expressed in terms of blower design variables. The present performance analysis method is applied to four existing models for verifying its prediction accuracy, and the prediction and the test results agreed well within a few percentage of relative error. Furthermore, the present performance analysis method is also applied in developing a new blower used for fuel cell application, and the newly designed blower is manufactured and tested through chamber-type test facility. The performance prediction by the present method agreed well with the test result and also with the CFD simulation results. From the comparison results, the present performance analysis method is shown to be suitable for the actual design practice of regenerative blower.

• The KSFM Journal of Fluid Machinery
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• v.16 no.2
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• pp.15-20
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• 2013

An aero-acoustic performance analysis method of regenerative blower is developed as one of the FANDAS codes. The aerodynamic performance of regenerative blower is predicted by using momentum exchange theory coupled with pressure loss and leakage flow models. Based on the performance prediction results, the noise level and spectrum of regenerative blower are predicted by discrete frequency and broadband noise models. The combination of the performance and the noise prediction methods gives aero-acoustic performance map and noise spectrum analysis results, which are well-agreed with the actual measurement results within a few percent relative error.