• Transactions of the Korean Society of Mechanical Engineers A
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• v.34 no.2
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• pp.153-160
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• 2010

A magnetocardiogram (MCG) is a recording of the biomagnetic signals generated by cardiac electrical activity. Biomagnetic instruments are based on superconducting quantum interference devices (SQUIDs). A liquid cryogenic Dewar flask was used to maintain the superconductors in a superconducting state at a very low temperature (4 K). In this study, the temperature distribution characteristics of the liquid helium in the Dewar flask was investigated. The Dewar flask used in this study has a 30 L liquid helium capacity with a hold time of 5 d. The Dewar flask has two thermal shields rated at 150 and 40 K. The temperatures measured at the end of the thermal shield and calculated from the computer model were compared. This study attempted to minimize the heat transfer rate of the cryogenic Dewar flask using an optimization method about the geometric variable to find the characteristics for the design geometric variables in terms of the stress distribution of the Dewar flask. For thermal and optimization analysis of the structure, the finite element method code ANSYS 10 was used. The computer model used for the cryogenic Dewar flask was useful to predict the temperature distribution for the area less affected by the thermal radiation.

• Journal of Korea Water Resources Association
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• v.37 no.12
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• pp.1019-1032
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• 2004

Flood frequency estimate is an essential index for determining the scale of small and middle hydraulic structure. However, this flood quantity could not be estimated directly for practical design purpose due to the lack of available flood data, and indirect method like design rainfall-runoff method have been used for the estimation of design flood. To give the good explain for design flood estimates, regional flood frequency analysis was performed by flood index method in this study. First, annual maximum series were constructed by using the collected data which covers from Japanese imperialism period to 1999. Wakeby distribution recommended by WMO(1989) was used for regional flood frequency analysis and L-moment method by Hosking (1990) was used for parameter estimation. For the homogeneity of region, the discordance and heterogeneity test by Hosking and Wallis(1993) was carried for 4 major watersheds in Korea. Physical independent variable correlated with index flood was watershed area. The relationship between specific discharge and watershed area showed a type of power function, i.e. the specific discharge decreases as watershed area increases. So flood quantity according to watershed area and return period was presented for each watershed(Han rivet, Nakdong river, Geum river and Youngsan/Seomjin river) by using this relation type. This result was also compared with the result of point frequency analysis and its regionalization. It was shown that the dam construction couldn't largely affect the variation of peak flood. The property of this study was also examined by comparison with previous studies.

• FLOWER RESEARCH JOURNAL
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• v.19 no.1
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• pp.68-76
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• 2011

This study was conducted to investigate customer taste related to satisfaction of a baby's first birthday party and re-visit of venues. General characteristics of customers were similar in male and female or the married and the unmarried. Mainstream age of respondents was from in their 20's to 30's. Among them, the number of university graduates were the largest in education level. Theoretical model was composed with seven significant variables of design style and composition and design harmony and color sense for flower decoration, accessibility, facility, service and price, satisfaction, and intention of re-visit based on the result of analysis on these factors. Exploratory factor analysis was performed using SPSS 14.0K. Structural equation modeling(SEM) for simultaneous measure of path coefficient in all casualty of study model, measurement model of AMOS 7.0 for evaluation of validity, and reliability and factor analysis method using technical statistics, frequency analysis, and Cronbach's Alpha for data analysis were used. The result of hypothesis verification showed that design style and composition was the most significant item in satisfaction of parameter and it was followed by design harmony and color sense. While service and price had positive effect on satisfaction, accessibility and facility had no relation to it. It means that the most crucial variable was a flower decoration in planning and representation of the celebration of baby's first birthday. In conclusion, the finding of this study suggests that the effective utilization of these variables will contribute to the enhancement of satisfaction affecting improvement service and price or intention of re-visit.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.33 no.6
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• pp.607-613
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• 2009

In this paper, we made a simple paper feeding system which is one of MTS (media transport system) and controllers. The plant has a flexible paper and two driving rollers and two driven rollers. The control system has two conventional PID controllers. Skew angle and feeding speed of MTS deteriorate the quality of feeding system. In order to control a feeding speed and skew of feeding paper, we control rotational velocity of two driving rollers. Therefore, this controller has two inputs and two outputs as MIMO (multi-input and multi-output) system. The control inputs were the feeding speed and the skew displacement of the paper. The control outputs were the rotational velocity to each driving roller. To find appropriate PID gains of two controllers, we proposed an optimization technique. We assume the system variables and performance of a whole system as follows. PID gains of two controllers for skew and feeding speed are system variables. System performance is both skew and feeding speed. We simulates to making mathematical correlation using global Kriging interpolation. To find appropriate value of system variables, optimization method is simulation in sequence as following method. First, the optimization solver simulates with DOE (design of experiment) tables to find correlation equation of both system variable and performances. Then, the solver guesses the appropriate values and simulates if the system variables are appropriate or not. If the result of validation doesn't satisfy the convergence and iteration tolerance, the solver makes a new Kriging models and iterates this sequence until satisfy the tolerances.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.21 no.3
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• pp.35-43
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• 2007

In this paper, the inductive power collector using electromagnetic induction for vehicle such as the PRT(Personal Rapid Transit) system is suggested and son ideas for power collector design to improve tile power transfer performance are presented. And also, the analysis of the inductive power transfer system in conjunction with series resonant converter operating variable high frequency is shown. Of particular interest is the sensitivity of the complete system to variations in operational frequency and parameters. In inductive power transfer system electrical power is transferred from a primary winding in the form of a coil or tract to one or more isolated pick-up coils that my relative to the primary. The ability to transmit power without contact enables high reliability and easy maintenance that allows inductive power transfer system to be implemented in hostile environments. This technology has found application in many fields such as electric vehicles, PRT(Personal Rapid Transit) etc. But, low output power is generated due to a loosely coupled characteristic of the large air-gap. Therefore, we will show you various characteristic of inductive power transfer system as double layer construction of secondary winding, which was divided in half to increase both output current and output voltage, a model of power collector and parallel winding structure, a model of concentration/ decentralization winding and the effects of parameter and operational frequency variation.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.48 no.2
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• pp.89-97
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• 2020

In this study, a numerical analysis was performed on 26 inch single and coaxial propeller using the ANSYS Fluent 19.0 Solver to analyse the effect of the distance between coaxial propellers as one of the design parameter. The Moving Reference Frame (MRF) method was used for single propeller, while the sliding mesh method was used for a coaxial propeller to analyse the flow field varying with azimuth angle. The thrust and power are decreased as the upper and lower propeller approaching each other. As H/D is increased, interference between the propellers is decreased. According to the flow field variable contour of the coaxial propeller, it appears that the change in aerodynamic performance is due to the loading effect and the tip vortex wake effect.

• Journal of the Korea Society of Computer and Information
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• v.17 no.5
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• pp.71-80
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• 2012

In this paper, applications that require low-speed data rate on personal area network to operate the Land Warrior system is proposed. These applications can refer to WSN(wireless sensor network) technology. However, this technology is not suitable to support various data transmission rate. A suitable CSMA/CA algorithm for Land Warrior System in order to solve these existing system problems is proposed. The proposed algorithm is designed to be variable CSMA/CA algorithm parameter, depending on data rate. For the evaluation of Land Warrior system model and CSMA/CA algorithm, we used Castalia. As a result of the simulation, it is found that the proposed system model can not only relieve loads of data processing, but also probability of collision was decreased.

• Journal of the Institute of Electronics Engineers of Korea SP
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• v.44 no.1
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• pp.64-69
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• 2007

This paper designs an interpolator for a high speed ultra wide bandwidth (UWB). The UWB wireless technology will play a key role in short-range wireless connectivity supporting very high bit rates availability, low power consumption, and location capabilities. Because the UWB needs high operating speed, a cubic interpolator based on variable parameters for the UWB needs to be operated at a high speed. In order to improve an operating speed, the modified cubic interpolator is based on both a parallel processing and a pipelining in the existing interpolator simultaneously. Experimental results show that a maximum operating speed and period of the proposed interpolator using Stratix II EP2S60F1020C3 is 102.42MHz and 9.764ns, respectively. Compared to the conventional interpolator, the designed cubic parameter interpolator has been improved more than about 190%.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.40 no.4
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• pp.364-374
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• 2012

The purpose of this study is to perform the reliability-corrected development cost estimation of the launch vehicle at the conceptual design phase. In order to estimate the launch vehicle development cost, the estimation method based on the independent variable such as the rocket performance and dry mass has been mainly implemented up to now. This approach has made the approximate cost estimation possible, however, the cost variation according to the reliability requirement could not be reflected. In this paper, the cost estimation methodology that introduces the reliability factor in addition to the performance and mass in the TRANSCOST model is presented in order to improve the limitation of current cost estimation method. The development cost of KSLV(Korea Space Launch Vehicle)-II is estimated on the basis of this newly implemented concept with reliability as an added parameter.

• Journal of the Institute of Electronics Engineers of Korea SC
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• v.44 no.4 s.316
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• pp.21-26
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• 2007

Output voltage waves of a DC/AC inverter system are likely to be distorted if variable loads e.g. motors or rectifiers exist in the output terminal. This paper designs a disturbance observer-based PI-controller for a single-phase inverter system that is robust against load changes. In this Paper, we regard the output voltage changes due to various loads as disturbances of the control system. Then we design a disturbance observer for estimation of the disturbances caused by the load current and any other error sources (such as parameter uncertainties and model mismatches etc.). In order to test the performance of the proposed control law, simulation studies are carried out for a single-phase inverter system using SimPowerSystem of Matlab Simuink. Compared to a simple PI-control, the disturbance observer-based controller shows enhanced performance in transient responses for step load changes.