• Journal of the Korean Society for Precision Engineering
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• v.33 no.9
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• pp.707-714
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• 2016

This paper describes analysis results of vibration characteristics and modal test for a small-scale quad-rotor drone. The rotor arm has a slender body with a propeller and motor at its tip. Rotor system generates excitation for an unbalanced mass. Therefore, the drone platform is involved in the possibility of resonance. For advance identification of the possibility of resonance, confirmation of eigen-mode being closest to the propeller operation range is necessary. Material properties of CFRP tubes used for the rotor arm were acquired by finding the natural frequency based on Rayleigh method. A simplified quad-rotor FE model consisting of rotor arm assembly with tip mass was built to perform numerical analysis, and a free-free boundary condition was applied to provide flight status. Modal tests for the actual platform with impact hammer instrument were performed to verify analysis results. Separation margin from hazardous eigen-mode was checked on the propeller operation range.

• Journal of Fisheries and Marine Sciences Education
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• v.18 no.1
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• pp.11-18
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• 2006

Man has always striven to create a thermally comfortable environment. This is reflected in building traditions around the world - from ancient history to present day. Today, creating a thermally comfortable environment is still one of the most important parameters to be considered when designing buildings. It is defined in the ISO 7730 standard as being "That condition of mind which expresses satisfaction with the thermal environment". A definition most people can agree on, but also a definition is not easily converted into physical parameters. Thermal comfort is a matter of many physical parameters, and not just one, as for example the air temperature that is set by air-conditioner. The most important matter Today's common offices and homes are only depending on air-conditioning as a cooling system during the summer. This kind of system tends to be focused on the person who controls it and those who are around the air-conditioner while thermal-comfort is neglected. Futhermore, the people's body conditions are not considered during each time that beginning, middle, last of the air-conditioning which causing displeasure of the residents more and more. This kind of operating system is set for a long time may causes unbalanced air condition and man's psychologic displeasure goes to increase.

• Journal of the Korean Geotechnical Society
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• v.27 no.7
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• pp.35-45
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• 2011

Cost effective design and construction are necessary to establish the design concept of tunnel lining. Loosening load acting on the concrete lining is compared with Terzaghi tunnel theory and numerical analysis. It is analyzed under the condition of weathered rock and soil with varying in-situ stress ratio ($K_0$). Based on the result, loosening load calculated by Tcrzaghi tunnel theory is much greater than numerical analysis results. And the load calculated in weathered soil is lager than weathered rock condition. As in-situ stress ratio increases, the stress acting on the tunnel lining decreases in Terzaghi theory rapidly, whereas there is little effect in numerical analysis.

• Journal of the Korean Institute of Intelligent Systems
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• v.16 no.6
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• pp.691-697
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• 2006

Induction motors are critical components in industrial process. So there are many research in the condition based maintenance, online monitoring system, and fault detection. This paper presents a scheme on the detection and diagnosis of the three-phase squirrel induction motor under unbalanced voltage, broken rotor bar, and a combination of these two faults. Actually one fault happen in operation, it influence other component in motor or cause another faults. Accordingly it is useful to diagnose and detect a combination fault in induction motor as well as each fault. The proposed fault detection and diagnosis algorithm is based on the stator currents from the squirrel induction motor and simulated with the aid of Matlab Simulink.

• Korean Journal of Cognitive Science
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• v.20 no.1
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• pp.51-77
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• 2009

Using a modified Posner's cue-target paradigm, we investigated whether negative cues attract more attention than neutral cues in anxious people. Previous studies used commonly an unbalanced proportion of valid and invalid trials(75% vs. 25% respectively). But in the present study, an equivalent proportion of valid and invalids trials was used for measuring detection speed of cues without participant's expectancy caused by the unbalanced proportion. Emotional words(Experiment 1) and facial expressions(Experiment 2) were used as cues for target locations. The result of Experiment 1 and 2 showed that threatening cues facilitated target detection in valid trials and interfered with it in invalid trials in anxious participants and a, reverse response patterns were found in non-anxious participants. This indicates that threatening cues attract more attention to the cued location in anxious people and in contrast, non-anxious people avoid threatening stimuli. In Experiment 3, we investigated the difference of validity effect across anxiety levels. The results showed that anxious participants gave less attention to cued location when the cues were non-informative whereas non-anxious participants gave more attention to cued locations in the same condition. We discussed two kinds of cognitive bias caused by anxiety levels: attentional bias and proportion related bias.

• Journal of Korean Port Research
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• v.13 no.1
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• pp.155-166
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• 1999

The construction of the coastal structures and reclamation work causes the circulation reduced in the semi-closed inner water area and the unbalanced sediment budget of beach results in an alteration of beach topography. Among the various fluid motions in the nearshore zone water particle motion due to wave and wave-induced currents are the most responsible for sediment movement. Therefore it is needed to predict the effect of the environmental change because of development and so the prediction of wave transformation dose. The purpose of this study is to introduce the relation between waves wave-induced currents and sediment movement. In this study we will show numerical method using energy conservation equation involving reflection diffraction and reflection and the surfzone energy dissipation term due to wave breaking is included in the basic equation. For the wave-induced current the momentum equation was combined with radiation stresses lateral mixing and friction Various information is required in the prediction of wave-induced current depending on the prediction tool. We can predict changes in wave-induced current from the distribution of wave especially near the wave breaking zone. To evaluate these quantities we have to know the local condition of waves mean sea level and so on. The results from the wave field and wave-induced current field deformation models are used as input data of the sediment transport and bottom change model. Numerical model were established by a finite difference method then were applied to the development plan of the eastern Pusan coastal zone Yeonhwa-ri and Daebyun fishing port. We represented the result with 2-D graphics and made comparison between before and after development.

• KOREAN JOURNAL OF CROP SCIENCE
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• v.48
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• pp.58-64
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• 2003

To enjoy a healthy life, it is important to have a well-balanced diet. However, in today's society, there is an increase in the consumption of preprocessed foods and frequency of eating out. Also the western diet, which is becoming move popular worldwide, contains relatively high levels of protein and fat, and a low amount of fiber, Furthermore, the increased availability of favorite foods has created a condition were the individual diet is less variable. With these conditions, it is difficult to maintain a diet that is nutritionally balanced. With these unbalanced diets, which are difficult to change, there has been an increase in adult disease and health problems, such as colon and breast cancer, It is speculated that metabolites for carcinogens are produced from diet components and that intestinal bacteria contribute to the production of these metabolites. Therefore, it is necessary to evaluate the relationships between health, diet, and intestinal microflora. Soybean oligosaccharide is composed of water-soluble saccharides that have been extracted from soybean whey, a by-product from the production of soy protein. This is mainly a mixture of mono-, di-, tri-, and tetrasac-charides, with the principle components being the oligosaccharide raffinose and stachyose. When consumed by humans, the oligosaccharides cannot be digested in the human duodenal and small intestinal mucosa, and these are selectively utilized by beneficial bifidobacteria in intestines. The results of acute and subacute toxicity tests, soy-bean oligosaccharides were nonpoisonous. Soybean oligosaccharides promote the growth of indigenous bifido-bacteria in the colon which by their antagonistic effects, suppress the activity of putrefactive bacteria. Also, they reduce toxic metabolites, detrimental enzymes and plasma lipid, and increase in the frequency of bowel evacuation and fecal quantities. Consequently, soybean oligosaccharides as functional foods components have potential roles in the prevention and medical treatment of chronic adult diseases. The study of processing property and physiological function of soybean oligosacchavides and development of high oligosaccharide variety allow the creation of new and exciting foodstuffs that aye functional healthy.

• Journal of Advanced Marine Engineering and Technology
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• v.35 no.8
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• pp.1117-1123
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• 2011

Ungrounded power systems are adopted onboard vessels which enable more stabilized power supply even in case of electric leakage to hull. If earthing faults happen at these systems, they make grounding impedances of power lines unbalanced each other on the three phases, resulting in high voltages to hull which can bring more possibilities of electric shocks and electric fires. This study focuses on how to configure a calculation module for transferring a grounded condition by lowered insulation resistance into a vector diagram of the voltages to hull. By using the module, the loci of neutral points were acquired to analyze how voltages to hull are affected by earthing faults and the distributed capacitances between power lines and hull. The suggested module was simulated and compared to the measured values from a test power system in good results.

• Journal of Power Electronics
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• v.14 no.2
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• pp.271-281
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• 2014

Fluctuating wind conditions necessitate the use of a variable speed wind turbine (VSWT) with a AC/DC/AC converter scheme in order to harvest the maximum power from the wind and to decouple the synchronous generator voltage and frequency from the grid voltage and frequency. In this paper, a combination of a three phase diode bridge rectifier (DBR) and a modified topology of the diode clamped multilevel inverter (DCMLI) has been considered as an AC/DC/AC converter. A control strategy has been proposed for the DCMLI to achieve the objective of grid interface of a wind power system together with local load compensation. A novel fixed frequency current control method is proposed for the DCMLI based on the level shifted multi carrier PWM for achieving the required control objectives with equal and uniform switching frequency operation for better control and thermal management with the modified DCMLI. The condition of the controller gain is derived to ensure the operation of the DCMLI at the fixed frequency of the carrier. The converter current injected into the distribution grid is controlled in accordance with the wind power availability. In addition, load compensation is performed as an added facility in order to free the source currents being fed from the grid of harmonic distortion, unbalance and a low power factor even though the load may be unbalanced, non-linear and of a poor power factor. The results are validated using PSCAD/EMTDC simulation studies.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.56 no.1
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• pp.1-7
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• 2007

Generally, an electric railroad feeding system has many problems due to the different characteristics in contrast with a load of general three-phase AC electric power system. One of them is harmonics problem caused by the switching device existing in the feeding system, and moreover, the time-varying dynamic loads of rail way is inherently another cause to increase this harmonics problem. In Korea power systems, the electric railroad feeding system is directly supplied from the substation of KEPCO. Therefore, if voltages fluctuation or unbalanced voltages are created by the voltage and current distortion or voltage drop during operation, it affects directly the source of supply. The trainloads of electric railway system have non-periodic but iterative harmonic characteristics as operating condition, because the electric characteristic of the electric railroad feeding system is changed by physical conditions of the each trainload. According to the traditional study, the estimation of harmonics has been performed by deterministic way using the steady state data at the specific time. This method is easy to analyze harmonics, but it has limits in some cases which needs an assessment of dynamic load and reliability. Therefore, this paper proposes the probabilistic estimation method, moments matching method(MW) in order to overcome the drawback of deterministic method. In this paper, distributions for each harmonics are convolved to obtain the moments and cumulants of TDD(Total Demand Distortion), and this can be generalized for any number of trains. For the case study, the electric railway system of LAT(Intra Airport Transit) in Incheon International Airport is modeled using PSCAD/EMTDC dynamic simulator. The raw data of harmonics for the moments matching method is acquired from simulation of the LAT model.