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Mokpo, South Korea

Mokpo National Maritime University is a national university located in Mokpo, South Korea. Wikipedia.

Choi H.-J.,Mokpo Maritime University
International Journal of Multimedia and Ubiquitous Engineering | Year: 2013

A CGH (Computer-Generated Hologram) is produced by calculating the interference pattern between the object wave and the reference wave. Thus it has been developed to get some ideal characteristics of CGH that are not possible in reality or to test the characteristics of a hologram. To generate a CGH with the hologram resolution of (M×N) for a 3D object having K light source, basically (N×N×K) calculational iterations are necessary. This paper proposes an algorithm that increases the speed of generating a digital hologram using a depth different temporal filtering (DDTF) of a depth video sequence. The proposed algorithm is a technique that performs CGH operation with only calculation the different depth values between the depth video frames. The experimental results showed that the proposed algorithm increased operation speed by 65% over the technique using the conventional CGH equation. & 2013 SERSC. Source

Lee K.-W.,Mokpo Maritime University | Park S.,Samsung | Jeong S.,Samsung
IEEE Transactions on Power Electronics | Year: 2015

The sinusoidal-wave and square-wave driving modes have been commonly used in permanent-magnet synchronous motor (PMSM) drives for household refrigerator compressors. In general, the sinusoidal-wave drive performs better in some aspects such as torque ripples, a starting performance, and a flux-weakening capability than the square-wave drive. The square-wave drive, however, has the advantage of higher efficiency at low-output-power conditions because of its relatively lower switching loss than the sinusoidal-wave drive. To selectively utilize the benefits of both driving modes, a seamless transition control between the two driving modes is proposed in this paper. Considering that the overall control structure of the sensorless PMSM drive is quite different according to the driving mode, initialization strategies, necessary for a smooth transition, for the pulse-width modulator of the inverter, speed and current controller, and sensorless position/speed estimator are presented. With the proposed method, a dual-mode operation of the sensorless PMSM drive can be achieved without stopping the compressor. The dynamic performance of the proposed transition scheme is tested using simulations and verified by experiments. Experimental result shows that the efficiency of a refrigerator increases up to 2 [%] using the dual-mode operation in comparison with the sinusoidal-wave only drive. © 1986-2012 IEEE. Source

The urea-SCR catalyst system has the advantages of high NOx conversion efficiency and a wide range of operating conditions. The key factors for successful implementation of urea-SCR technology are good mixing of urea (ammonia) and gas to reduce ammonia slip. Urea mixer components are required to facilitate evaporation and mixing, because it is difficult to evaporate urea in the liquid state; the distance to the mixer is the most critical factor affecting mixer performance. In this study, to determine the optimal distance from the injector to the mixer for urea injection, we used laser diagnostics and a high speed camera to analyze the spray characteristics of a urea injector and to determine the distribution of urea solution droplets in a transparent manifold. The spray angle with a certain value (α) was measured, the injection quantity was about 9.4208 g/s, the SMD was approximately 65 μm, and then the position Bd was the optimal location for installation of mixer. In addition, we calculated the droplet uniformity index (DUI) from the acquired images using digital image processing to clarify the distribution of the sprayed droplets. Analysis of the quantitative characteristics and spatial distribution of the droplets revealed that addition of mixers resulted in more uniform distribution of the urea solution in the exhaust pipe and improved the performance of the urea-SCR catalyst system. A grid-channel plate-type mixer was optimal for maintaining a high the DUI which increased 32% than the case without a mixer, and the NOx conversion efficiency which was 85-90%. © 2013 Elsevier Ltd. All rights reserved. Source

Kim S.-H.,Mokpo Maritime University | Das M.P.,Australian National University
Modern Physics Letters B | Year: 2012

We developed a new method of an earthquake-resistant design to support conventional aseismic system using acoustic metamaterials. The device is an attenuator of a seismic wave that reduces the amplitude of the wave exponentially. Constructing a cylindrical shell-type waveguide composed of many Helmholtz resonators that creates a stop-band for the seismic frequency range, we convert the seismic wave into an attenuated one without touching the building that we want to protect. It is a mechanical way to convert the seismic energy into sound and heat. © 2012 World Scientific Publishing Company. Source

Lee K.-W.,Mokpo Maritime University
2014 IEEE Energy Conversion Congress and Exposition, ECCE 2014 | Year: 2014

A single-phase diode rectifier fed inverter with a small dc-link capacitor has found widespread use in permanent magnet synchronous motor (PMSM) drives for appliances because of its cost effectiveness in comparison with the conventional power factor correction (PFC) circuit-based inverter. In this application, the d-q axes currents supplied to the PMSM are controlled to have ripples with a frequency that is usually two times that of the ac mains voltage, and this results in periodic magnetic saturation at the stator of the PMSM. In this paper, a back electromotive-force (back-EMF) estimator for the high-speed sensorless control of a PMSM operating under periodic magnetic saturation conditions is proposed. The transfer function of the back-EMF estimator is analyzed to examine the effect of the stator inductance variations due to the periodic magnetic saturation on the accuracy of the estimated rotor position, and a simple compensation method for the estimated position errors caused by the periodic magnetic saturation is proposed on the basis of the analysis. The effectiveness of the proposed method is experimentally verified with a PMSM drive for a vacuum cleaner centrifugal fan, whose maximum operating speed reaches 30, 000 r/min. © 2014 IEEE. Source

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