• Journal of Digital Convergence
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• v.11 no.8
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• pp.199-204
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• 2013

Computational fluid dynamics (CFD) is used to reduce number of experiments. The CFD tools are widely used for engine design and flow pattern analysis to reduce experiments. In this study the performance of a PEMFC single cell was analyzed by using STAR-CD, product of CD-ADAPCO. The effect of cell design and flow pattern on the performance of a PEMFC was analyzed with the 3-D simulation. As a result the performance of rectangular cell was the higher than that of square cell, while the flow direction scarcely affected on the performance of a PEMFC. Also the current density according to different excess ratio of air flow rate was compared and analyzed. The difference between maximum and minimum current density of flip-flow was lower than that of co-flow.

• Journal of IKEEE
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• v.20 no.3
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• pp.322-325
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• 2016

This paper proposed Enhanced Segmentized Clear Channel Assesment(ESCCA) for the IEEE 802.15.4 networks. This method divides original CCA into two groups to check precise channel status and perform additional CCA to increase throughput performance. Through the proposed method, the device can access the channel more often, so the transmission efficiency of the IEEE 802.15.4 network improves. To confirm the feasibility and usability of the proposed method, computer simulation has been performed. In the simulation, a star topology with one coordinator and a lot of devices is considered and the traffic flows are all one way, with the communication directed to the coordinator. Simulation results_ show the proposed method is improving maximum 10 kbps of throughput and decreasing maximum 15 of the average number of total CCA than IEEE 802.15.4 CCA method.

• Journal of Energy Engineering
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• v.27 no.2
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• pp.32-48
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• 2018

Monitoring of energy use should be a priority in order to efficiently manage building energy use. Energy use in buildings can be managed by dividing them into energy sources, uses, and ZONE. By energy source, electricity, gas, fuel, and district heating are supplied to run the building's facilities. The purpose can be divided into five main applications, including cooling, heating, lighting, hot water and ventilation, but not many elevators and electric heaters that are difficult to include in the five applications are classified. ZONE Star refers to the comparison or separate management of areas for which the purpose of the building is similar or different. In addition, energy efficiency management requires control of the temperature, humidity, and people who will be measuring energy in the building, and the recent problem of fine dust should directly affect the ventilation of the building.

• Transactions on Electrical and Electronic Materials
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• v.15 no.6
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• pp.305-308
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• 2014

Organosilyl-modified and star-shaped poly (${\varepsilon}$-caprolactone) (m-PCL) was prepared, and added to polymethylsilsesquioxane (PMSSQ), to make composites. The end groups of m-PCL are chemically similar to PMSSQ, and m-PCL mixed well with PMSSQ in the composite. Porous PMSSQ film was made by further calcination of the composite film at elevated temperature. m-PCL-templated PMSSQ and the as-prepared porous PMSSQ were structurally, optically, and thermally characterized in thin films. The chemical binding of m-PCL and PMSSQ effectively suppressed the phase separation of PMSSQ and m-PCL during the curing process. After calcination at elevated temperature, there remained many pores in the PMSSQ matrix. The refractive indices of the resulting porous PMSSQ thin films decreased with increase of the film porosities, depending on the initial m-PCL loadings.

• Journal of Power Electronics
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• v.9 no.6
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• pp.874-883
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• 2009

This paper deals with an integrated voltage and frequency (VF) controller for isolated asynchronous generators (IAG) driven by a constant power pico-hydro uncontrolled turbine feeding three-phase four-wire loads. The proposed VF controller is used to control the frequency and voltage of an IAG with load leveling. Such a VF controller is also known as an integrated electronic load controller (IELC) which is realized using an isolated star/polygon transformer with a voltage source converter (VSC) and a battery at its DC bus. The proposed generating system with a VFC is modeled and simulated in MATLAB along with Simulink and Simpower system (SPS) toolboxes. The simulated results are presented to demonstrate the performance of an isolated asynchronous generator feeding three-phase four-wire loads with neutral current compensation.

• 한국전산유체공학회:학술대회논문집
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• 2005.10a
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• pp.67-74
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• 2005

Fluid flow and heat transfer in rectangular duct system are measured and computed by commercial software of Star-CD for comparison between them. Three rectangular systems are investigated in this study. Those are a rectangular duct with 90 degree bended elbow, a rectangular duct with two branchs, and a circular cylinder in a rectangular duct. But heat transfer is studied only for last system. These investigations show us that the numerical solutions predict satisfactorily design factors (K-factor for the elbowed duct, distributions of flow rates into each branch from a duct, and Nusselt number around circular cylinder) even though there are some disagreements in velocity profiles and turbulent kinetic energy.

• Journal of Mechanical Science and Technology
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• v.16 no.3
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• pp.376-385
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• 2002

Spray impingement and fuel film formation models with cavitation have been developed and incorporated into the computational fluid dynamics code, STAR-CD. The spray/wall interaction process was modeled by considering the effects of surface temperature conditions and fuel film formation. The behavior of fuel droplets after impingement was divided into rebound, spread and splash using the Weber number and parameter K(equation omitted). The spray impingement model accounts for mass conservation, energy conservation, and heat transfer to the impinging droplets. The fuel film formation model was developed by integrating the continuity, momentum, and energy equations along the direction of fuel film thickness. Zero dimensional cavitation model was adopted in order to consider the cavitation phenomena and to give reasonable initial conditions for spray injection. Numerical simulations of spray tip penetration, spray impingement patterns, and the mass of film-state fuel matched well with the experimental data. The spray impingement and fuel film formation models have been applied to study spray/wall impingement in high-speed direct injection diesel engines.

• The Bulletin of The Korean Astronomical Society
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• v.43 no.1
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• pp.55.2-55.2
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• 2018

Neutron stars (NS) are rapidly spinning compact objects. Their rotation energy is released by particles, electromagnetic waves, and even gravitational waves. The source of the energy is of course the rotation, so by studying the rotational properties of neutron stars, we can gain some insights into matter under extreme conditions. In particular, it is known that the braking index n is sensitive to the moment of inertia and/or NS winds. The neutron star PSR B0540-69 exhibits interesting timing behavior; previous measurements of the braking index for this pulsar may suggest a change in time. In order to see if the change is real, We investigate the timing properties of B0540-69 using recent ~1000-days Swift satellite data.

• Journal of Mechanical Science and Technology
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• v.15 no.3
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• pp.357-365
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• 2001

The aim of this paper is to perform the experiment and the numerical simulation for investigating the heat transfer in a regenerator system with ceramic honeycomb and to suggest a useful correlation for optimization of the regenerator system. For achieving this, the effects of some parameters were investigated, e. g., switching time, cell size and length of honeycomb on the mean temperature efficiency. The measured temperatures by R-type thermocouples were compared with the predictions by means of the commercial package, STAR-CD. A useful correlation for thermal efficiency was newly proposed as a function of the normalized switching time, defined in terms of switching time, cell size and length of honeycomb. The results showed that the thermal efficiency is above 90% and the normalized heat exchange rate is higher than 80% when the normalized switching time is less than 1000.

• Proceedings of the KSME Conference
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• 2000.04b
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• pp.919-924
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• 2000

Spray impingement model and fuel film formation model were developed and incorporated into the computational fluid dynamics code, STAR-CD. The spray/wall interaction process were modelled by considering the change of behaviour with surface temperature condition and fuel film formation. We divided behaviour of fuel droplets after impingement into stick, rebound and splash using Weber number and parameter K. Spray impingement model accounts for mass conservation, energy conservation and heat transfer to the impinging droplets. A fuel film formation model was developed by Integrating the continuity, the Navier-Stokes and the energy equations along the direction of fuel film thickness. The validation of the model was conducted using diesel spray experimental data and gasoline spray impingement experiment. In all cases, the prediction compared reasonably well with experimental results. Spray impingement model and fuel film formation model have been applied to a direct injection diesel engine combustion chamber.