Daejeon, South Korea
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Kim H.,Kookmin University | Jin J.Y.,Korea Advanced Institute of Science and Technology | Jang C.,Korea Intellectual Property Office | Yoo H.J.,Geosystem Research Corporation | Hwang D.H.,Kookmin University
Journal of Coastal Research | Year: 2014

Long-term shoreline position of Haeundae Beach has been quite stable notwithstanding seasonal oscillatory movement. Bathymetry around Haeundae Beach was surveyed on 7 August 2007 and 12 November 2007 by using an echo-sounder, while wave, tide, and tidal current were measured between the two survey days, so that bathymetric change at Haeundae Beach was obtained from the two surveys. According to the surveys the east part of the beach was eroded, and the west part of the beach was accreted. Measured waves from SSE, SE, ESE, E during the period were stronger than measured waves from S, SSW, SW, WSW. A numerical model system CST3D was adopted to reproduce the bathymetric change at Haeundae Beach during the period. Two representative wave settings are chosen for the period as a minimum number to represent the time-series of wave record, based on equivalent sediment flux concept contained in the CERC formula. Wave field, wave-induced force field, wave-induced current field, sediment transport field, and bathymetric change are computed from individual modules, SWAN, WIF, FLOW, SED in CST3D, respectively. Computed bathymetric change agrees reasonably well with measured one. It is believed that selection of two representative wave settings is useful for simulation of seasonal bathymetric change for fairly straight morphology like Haeundae. CST3D is thought to effectively describe overall seasonal sediment transport pattern and consequent bathymetric change at Haeundae Beach. © 2014 Coastal Education and Research Foundation.

Kim H.,Kookmin University | Jin J.Y.,Korea Advanced Institute of Science and Technology | Hwang D.H.,Kookmin University | Jang C.,Korea Intellectual Property Office | Ryu H.-S.,Seil Engineering
Journal of Vibroengineering | Year: 2014

Strong wave-induced currents frequently develop at Haeundae Beach, Korea. Rip currents at the beach have threatened safety of swimmers in water. Near-shore currents at Haeundae Beach during a high wave time were measured on 4 June 2008 by using drogues equipped with GPS. The current field during measurement period showed westward flow along shoreline. Major driving force of the measured currents is thought to be the wave-induced force, and the tide-induced force was the second important driving force at the time. The wave-induced current field at the time is quantitatively described by using a numerical modelling system CST3D which adopts rearrangement of driving wave-induced forces, and the PESM for computation of advection terms. The computed wave-induced current field agrees reasonably well with the drogue measurements. The numerical model predicts development of rip current around the beach centre for S wave case, the result of which could be used for warning of possible rip current development at the site. © JVE INTERNATIONAL LTD. JOURNAL OF VIBROENGINEERING 2014.

Kim S.-K.,Korea Atomic Energy Research Institute | Choi J.,Korea Intellectual Property Office | Park S.,Chungnam National University | Song O.,Chungnam National University
JVC/Journal of Vibration and Control | Year: 2015

A first-order shear deformation plate theory model of laminated composite plates subjected to a combined electromagnetic and thermal field is developed. The coupled equations of motion are based on the electromagnetic equations (Faraday, Ampere, Ohm, and Lorentz equations) and thermal equations which are involved in constitutive equations. In order to determine the implications of a number of geometrical and physical features of the model, one special case free vibration of a composite plate immersed in a transversal magnetic field is investigated. Special coupling characteristics between the magnetic, elastic and thermal fields are described in this paper. In addition, the free vibration responses of finite composite rectangular plates immersed in a transversal magnetic field are investigated. The vibration response characteristics of a composite plate are exploited in connection with the magnetic field intensity, thermal load, and electric conductivity of fibrous composite materials. Some pertinent conclusions, which highlight the various effects induced by the electromagnetic-thermo-elastic couplings, are outlined. © The Author(s) 2013.

Lee S.,Korea Institute of Machinery and Materials | Ahn K.Y.,Korea Institute of Machinery and Materials | Lee Y.D.,Korea Institute of Machinery and Materials | Han J.,Chungnam National University | And 2 more authors.
Journal of Fuel Cell Science and Technology | Year: 2012

A catalytic combustor is a device to burn off fuel by surface combustion that is used for the combustion of anode off-gas of molten carbonate fuel cells by employing the catalytic combustor. Purified exhaust gas can be recirculated into the cathode channel for CO 2 supply to improve thermal efficiency. The design of a catalytic combustor depends on many parameters, but flow uniformity is particularly important during the emergency shut-down of a fuel cell stack. Before the temperature control of a catalytic combustor is activated, the catalytic combustor should burn off more than two times the rated amount of the fuel flow rate. Under overload conditions, assurance of flow uniformity at the inlet of the catalytic combustor can reduce damage to the catalytic burner that can be caused by a local hot zone. In this study, flow uniformity of the catalytic combustor was investigated in two steps: a preliminary step with a model combustor and a main analysis step with a practical 250 kW catalytic combustor. Models of the 0.5 and 5 kW class combustors were used in the preliminary step. In the preliminary step the model combustors were used to determine supporting matters for flow uniformity. The inlet direction of the mixing chamber below the catalytic combustor was also examined in the preliminary step. In the main analysis step the flow uniformity of the scale-up combustor was examined with selected supporting matter and inlet direction into the mixing chamber. Geometric and operating parameters were investigated. In particular, the flow rate under off-design operating conditions was examined. © 2012 American Society of Mechanical Engineers.

Kim D.,Korea Research Institute of Standards and Science | Kim K.,Korea Intellectual Property Office | Park S.H.,Samsung | Jang S.,Samsung
Measurement Science and Technology | Year: 2014

An ultra high-precision 3-DOF air-bearing stage is developed and calibrated in this study. The stage was developed for the transportation of a glass or wafer with x and y following errors in the nanometer regime. To apply the proposed stage to display or semiconductor fabrication equipment, x and y straightness errors should be at the sub-micron level and the x-y orthogonality error should be in the region of several arcseconds with strokes of several hundreds of mm. Our system was designed to move a 400 mm stroke on the x axis and a 700 mm stroke on the y axis. To do this, 1000 mm and 550 mm bar-type mirrors were adopted for real time Δx and Δy laser measurements and feedback control. In this system, with the laser wavelength variation and instability being kept to a minimum through environmental control, the straightness and orthogonality become purely dependent upon the surface shape of the bar mirrors. Compensation for the distortion of the bar mirrors is accomplished using a self-calibration method. The successful application of the method nearly eliminated the straightness and orthogonality errors of the stage, allowing their specifications to be fully satisfied. As a result, the straightness and orthogonality errors of the stage were successfully decreased from 4.4 μm to 0.8 μm and from 0.04° to 2.48 arcsec, respectively. © 2014 IOP Publishing Ltd.

Han J.-H.,Korea University | Park S.-W.,Korea Intellectual Property Office
Optik | Year: 2013

The thermal effect on wavelength detuning of the uncooled packaged complex (loss)-coupled distributed feedback (DFB) edge emitting 1.55-μm laser has been investigated for wide temperature range of -40 °C to 85 °C. The InGaAsP/InP laser diode incorporates a thin 1% compressively strained multiple quantum well (MQW) structure as well as an automatically buried InAsP buried layer in the grating region to simplify the steps of the epitaxial growth during the fabrication processes. As an experimental result, it has been found that the wavelength detuning between the gain medium (Fabry-Perot cavity) and the Bragg grating (for distributed feedback) should be optimized around -10 nm at the room temperature to accommodate their differently shifting center wavelengths for temperature changes where the gain profile changes faster than DFB wavelength for predicting a single mode operation in a wide temperature range. Based on the measured optical characteristics (threshold current, slope efficiency) of the fabricated diode laser, the characteristic temperature was estimated to be approximately 46 K and the slope efficiency ratio between room and high temperatures was around 70%. © 2011 Elsevier GmbH. All rights reserved.

Seon K.-I.,Korea Astronomy and Space Science Institute | Seon K.-I.,Korean University of Science and Technology | Edelstein J.,University of California at Berkeley | Korpela E.,University of California at Berkeley | And 7 more authors.
Astrophysical Journal, Supplement Series | Year: 2011

We present the general properties of the far-ultraviolet (FUV; 1370-1710 Å) continuum background over most of the sky, obtained with the Spectroscopy of Plasma Evolution from Astrophysical Radiation (SPEAR) instrument (also known as FIMS), flown aboard the STSAT-1 satellite mission. We find that the diffuse FUV continuum intensity is well correlated with N HI, 100 μm, and Hα intensities but anti-correlated with soft X-ray intensity. The correlation of the diffuse background with the direct stellar flux is weaker than the correlation with other parameters. The continuum spectra are relatively flat. However, a weak softening of the FUV spectra toward some sight lines, mostly at high Galactic latitudes, is found not only in direct stellar but also in diffuse background spectra. The diffuse background is relatively softer than the direct stellar spectrum. We also find that the diffuse FUV background averaged over the sky has a bit softer spectrum compared to direct stellar radiation. A map of the ratio of 1370-1520 to 1560-1710 band intensity shows that the sky is divided into roughly two parts. However, this map shows a lot of patchy structures on small scales. The spatial variation of the hardness ratio seems to be largely determined by the longitudinal distribution of OB-type stars in the Galactic plane. A correlation of the hardness ratio with the FUV intensity is found at high intensities but an anti-correlation is found at low intensities. We also find evidence that the FUV intensity distribution is log-normal in nature. © 2011. The American Astronomical Society. All rights reserved.

Park T.,Korea Intellectual Property Office | Kim T.,University of Michigan
IEEE Transactions on Power Electronics | Year: 2013

This paper presents a novel power conversion topology for systems, which include a boost and bidirectional converters to control the power flows between sources, batteries, and ultracapacitors. The proposed system (multimode single-leg power converter) substitutes the boost converter and bidirectional converter with a multifunctional bidirectional converter and has cost effectiveness and fault tolerance, preserving the same energy conversion functionalities of the conventional energy conversion system. To verify the performance of the proposed system, its operations are categorized and explained to four different modes. Then, each mode of the proposed system is simulated and implemented experimentally using a prototype test bed. The results present that the proposed conversion system is feasible and applicable for a wide range of applications including alternative/renewable power systems and electric vehicles (EVs). © 1986-2012 IEEE.

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