• Design & Manufacturing
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• v.13 no.4
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• pp.17-22
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• 2019

Currently, studies on weight reduction and fuel efficiency increase are the most important topics in the automotive industry and many studies are under way. Among them, weight reduction is the best way to raise fuel efficiency and solve environmental pollution and resource depletion. Materials such as aluminum, magnesium and carbon curing materials can be found in lightweight materials. Among these, research on improvement of bonding technology and manufacturing method of materials and improvement of material properties through study of ultrahigh strength steel sheet is expected to be the biggest part of material weight reduction. As the strength of the ultra hight strength steel sheet increases during forming, it is difficult to obtain the dimensional accuracy as the elastic restoring force increases compared to the hardness or high strength steel sheet. It is known that the spring back phenomenon is affected by various factors depending on the raw material and processing process. We have conducted analytical evaluations and studies to analyze the springback that occurs according to the cross-sectional shape of the ultra high tensile steel sheet.

• Journal of the Korean Society for Nondestructive Testing
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• v.30 no.4
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• pp.324-329
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• 2010

Fuel rods using in nuclear power plants consist of uranium dioxide pellets enclosed in zirconium alloy(zircaloy) tubes. It is vitally important for the pellet surface to remain free from pits, cracks and chipping defects after it is loaded into the tubes to prevent local hot spots during reactor operation. This paper investigates the feasibility study for detecting surface flaws of pellets contained within nuclear fuel rod through X-ray tomography simulation. Reconstructed images used by parallel and fan-beam filtered back projection method were presented and confirmed the accessibility between simulation data and MPS(missing pellet surface) image data.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.3 no.2
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• pp.93-98
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• 1993

In the ternary system of $CaF_2-CaO-P_2O_5$. Apatite$(Ca_{10}(PO_4)_6F_2)$ single crystal having a congruent point was grown by FZ process. The atmospheric condition was kept by oxygen blowing. Adjusting the growth parameters of rotation rate, growth rate and gas amount, we tried to find the optimum growth condition. By partly substituting Ca as Co element, the absorption of infrared is increased and the color effect was observed. Using the Laue back reflection, XRD and FTIR analysis, the characterization of the crystal was carried out.

• Journal of international Conference on Electrical Machines and Systems
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• v.2 no.2
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• pp.159-164
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• 2013

Difficulty of torque measurements in high-speed permanent magnet (HSPM) motors has necessitated the development of improved torque calculations. Hence, this paper presents an analytical torque calculation of a high speed permanent magnet (HSPM) motor based on the power factor angle. On the basis of analytical magnetic field solutions, the equations for circuit parameters such as back-emf and synchronous inductance are derived analytically. All analytical results are validated extensively by non-linear finite element (FE) calculations and measurements. The internal angle (${\delta}$) between the back-emf and the phase current is calculated according to the rotor speed by using analytical circuit parameters and the measured power factor because this angle is not measured but estimated in case of sensorless drive of the HSPM motor, significantly affecting torque calculation. Finally, the validity of the torque analysis method proposed in this paper is confirmed, by showing that the torque calculated on the basis of the internal angle is in better agreement with the measurements.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.58 no.10
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• pp.1930-1935
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• 2009

This paper deals with the torque ripple reduction of permanent magnet synchronous motor using harmonic current injection. Torque ripple of electric motor reduces system stability and performances, therefore efforts to reduce torque ripple are exerted in the design process. Torque ripple can be reduced by appropriate pole/slot combination, skew of rotor or stator, design of magnetic circuit, etc. In addition, torque ripple can be also reduced by input voltage and current, and many researches have been conducted to reduce torque ripple for six-step drive. Torque ripple reduction for current vector controlled permanent magnet synchronous motor also have been conducted and verified by investigating back emf wave form. Torque ripple reduction in this paper started from getting torque profile according to input current and electrical angle calculated by FEA, then instantaneous currents at each electrical angles for constant torque are calculated and applied to experiments. Therefore, 0% of torque ripple can be obtained theoretically with harmonic current injection. In order to maximize the effect of torque ripple reduction, a BLDC motor having high harmonic component of back emf is chosen. With sinusoidal current drive, over 100% of torque ripple is obtained initially, then 0.5 % of torque ripple is obtained by FEA using harmonic current injection. The effect is verified by experiment and the presented method can be effectively applicable to Electric Power Steering(EPS).

• Journal of the Korean Society of Clothing and Textiles
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• v.31 no.4 s.163
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• pp.531-539
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• 2007

The purpose of this article was to determine how the current auto mechanic's coverall restricts movements, to develop prototype coverall, and finally, to improve working efficiency. To investigate the problem and complaint of current coveralls, 35 mechanics were interviewed. Video captured method was used to analyze the representative movement. Based on the previous investigation, the prototype coverall was developed. Pleats and band were inserted on each side of the back, under the armhole, and the back waist area for flexibility. To analyze the mobility of current and prototype coveralls objectively, range-of-motion of selected movements was measured by Leighton flexometer and goniometer. Also, wearer acceptability scale was tested to investigate subjective preference of current and prototype coveralls. As subjects, 10 auto mechanics were participated. Order of testing was randomized. ANOBA and LSD were used for statistical analysis. As a results, prototype coverall was significantly different from current coverall at all test movements. Also, prototype coverall was significantly different from current coverall at 13 scales among 23 subjective scales. The results identified that prototype coverall design improved auto mechanic's body movement and subjective acceptability.

• Journal of Information Processing Systems
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• v.13 no.4
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• pp.703-715
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• 2017

Mammogram images are sensitive in nature and even a minor change in the environment affects the quality of the images. Due to the lack of expert radiologists, it is difficult to interpret the mammogram images. In this paper an algorithm is proposed for a computer-aided diagnosis system, which is based on the wavelet based adaptive sigmoid function. The cascade feed-forward back propagation technique has been used for training and testing purposes. Due to the poor contrast in digital mammogram images it is difficult to process the images directly. Thus, the images were first processed using the wavelet based adaptive sigmoid function and then the suspicious regions were selected to extract the features. A combination of texture features and gray-level co-occurrence matrix features were extracted and used for training and testing purposes. The system was trained with 150 images, while a total 100 mammogram images were used for testing. A classification accuracy of more than 95% was obtained with our proposed method.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.57 no.4
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• pp.729-734
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• 2008

Vibroarthrographic(VAG) signals, emitted by human knee joints, are non-stationary and multi-component in nature and time-frequency distributions(TFD) provide powerful means to analyze such signals. The objective of this paper is to classify VAG signals, generated during joint movement, into two groups(normal and patient group) using the characteristic parameters extracted by time-frequency transform, and to evaluate the classification accuracy. Noise within TFD was reduced by singular value decomposition and back-propagation neural network(BPNN) was used for classifying VAG signals. The characteristic parameters consist of the energy parameter, energy spread parameter, frequency parameter, frequency spread parameter by Wigner-Ville distribution and the amplitude of frequency distribution, the mean and the median frequency by fast Fourier transform. Totally 1408 segments(normal 1031, patient 377) were used for training and evaluating BPNN. As a result, the average value of the classification accuracy was 92.3(standard deviation ${\pm}0.9$)%. The proposed method was independent of clinical information, and showed good potential for non-invasive diagnosis and monitoring of joint disorders such as osteoarthritis and chondromalacia patella.

• Korean Journal of Applied Biomechanics
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• v.14 no.3
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• pp.49-65
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• 2004

The purpose of this study is development of posture evaluation and Range of Motion(ROM) system by using digital vision analysis method. The results of this study are as follows. First, Scoliosis evaluation through this research measurement system represent 3mm error in 7 cervical point and deepest lumbar point, 0.7mm error in other point. This mean this research measurement system have a reliability for scoliosis evaluation. Second, for spine line evaluation on high fat subject, we need reconstrection spine line after measurement for fat thickness in 7 cervical point and deepest lumbar point. Third, In pedioscope error test, it present 0.01848cm in X axis and 0.01757cm in Y axis. This results mean pedioscope have a reliability foot evaluation. Forth, Posture evaluation and Range of Motion measurement system by using digital vision analysis method can fast measure in range of motion and foot evaluation and posture. therefore we can expect this system application in young people posture clinic center and hospital and so on.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.25 no.12
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• pp.2062-2069
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• 2001

It has been established that a crack has an important effect on the dynamic behavior of a structure. This effect depends mainly on the location and depth of the crack. To identify the location and depth of a crack in a structure, a method is presented in this paper which uses synthetic artificial intelligent technique, that is, Adaptive-Network-based Fuzzy Inference System(ANFIS) solved via hybrid learning algorithm(the back-propagation gradient descent and the least-squares method) are used to learn the input(the location and depth of a crack)-output(the structural eigenfrequencies) relation of the structural system. With this ANFIS and a continuous evolutionary algorithm(CEA), it is possible to formulate the inverse problem. CEAs based on genetic algorithms work efficiently for continuous search space optimization problems like a parameter identification problem. With this ANFIS, CEAs are used to identify the crack location and depth minimizing the difference from the measured frequencies. We have tried this new idea on a simple beam structure and the results are promising.