• Transactions of the Korean Society for Noise and Vibration Engineering
• /
• v.15 no.9 s.102
• /
• pp.1009-1015
• /
• 2005

Fluid-elastic instability and turbulence excitation for an under developing steam generator are investigated numerically. The stability ratio and the amplitude of turbulence excitation are obtained by using the $PIAT^{(R)}$ (program for integrity assessment of steam generator tube) code from the information on the thermal-hydraulic data of the steam generator. The aspect ratio, the ratio between the height of U-tube from the upper most tube support Plate (h) and the width of two vertical portion of U-tube (w), is defined for geometric parameter study. Several aspect ratios with relocation of tube support plates are adopted to study the effects on the mode shapes and characteristics of flow-induced vibration. When the aspect ratio exceeds value of 1, most of the mode shapes at low frequency are generated at the top of U-tube. It makes very high value of the stability ratio and the amplitude of turbulent excitation as well. We can consider that the local mode shape at the upper side of U-tube will develop the wear phenomena between the tube and the anti-nitration bars such as vortical, horizontal, and diagonal strips. It turns out that the aspect ratio reveals very important parameter for the design stage of the steam generator. The appropriate value of the aspect ratio should be specified and applied.

• Journal of the Korean Society of Clothing and Textiles
• /
• v.36 no.12
• /
• pp.1247-1256
• /
• 2012

The paper details the development of a Korean style loungewear based on traditional Korean hanbok clothing. For this, we surveyed and collected data from 3,500 adults over 20 years of age. The questions were on their preferences of hanbok for both traditional and contemporary styles as well as loungewear. The survey showed that preferences for hanbok were high for both traditional and contemporary styles. The survey also suggests how a successful mass-produced Korean style loungewear should be designed to increase its popularity. It should feature comfortably simplified silhouettes, a selection of contemporary colors from Korean symbolic colors, modernized Korean textile surface designs, and easy-to-maintain healthy fabric. Based on these results, the development direction of Korean style loungewear was set and various loungewear samples were produced. Another group of survey participants were asked to try on samples and their preferences were surveyed. At the conclusion, a version that was most preferred among the participants was obtained. We suggest one-piece style and two-piece style designs with silhouettes based on the characteristics of traditional Korean costumes. The preferred fabric for loungewear was natural and soft cotton. We suggest the necessity and effectiveness of loungewear made with environment-friendly hanji-fabric. The main colors for loungewear were selected based on survey: blue, red, white, and saekdong (color stripes). We made color combinations with the main colors then applied the textile surface designs. The traditional Korean patterns of Hangeul (Korean letters), taegeuk (yin-yang), geometric figures, and samjogo (three-legged crow) were also chosen, and then loungewear using the textile designs was developed. The results have been shown on the "Han Style Fashion Show" by Jeonju City and exhibited in the "Seoul Living Design Fair" and the "International Art & Craft Trend Fair" in COEX, Seoul.

• Journal of the Korean Society for Aeronautical & Space Sciences
• /
• v.41 no.12
• /
• pp.931-939
• /
• 2013

In this paper, we try to find the lifting-line method which is applicable to the conceptual design of aircraft wings, and analyze the accuracy and coverage of the method. Two methods that are extended from the lifting-line theory of Prandtl are selected. One of the methods is Weissinger's method which imposes the velocity boundary condition at the control points located at the quarter chord, and the other is Phillips's method which combines the three-dimensional vortex lifting law. Calculations are performed for an elliptic wing, a swept back wing, and a tapered unswept wing with dihedral angle and geometric twist. The aerodynamic data of the potential flow such as spanwise distributions of circulation and downwash, lift and induced drag are obtained through calculations, and these data are compared with theoretical results and wind tunnel test data. As a result, Weissinger's method showed good accuracy and reliability regardless of wing shapes, but Phillips's method revealed inaccurate results for a swept back wing.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
• /
• v.8 no.5
• /
• pp.516-524
• /
• 1997

The propagation properties of various pulse signal types(square pulse, Gaussian pulse, trapezoid pulse, RF pulse) on coupled microstrip lines are investigated. Numerical integration technique which has its accuracy and is easily simulated, is used to obtain the time domain response of pulse signals. Frequency-dependent characteristics of coupled microstrip line is obtained using Jansen's approximate equation. The propagation properties of pulse signal on coupled microstrip lines is analyzed regarding to its geometric structure (relative permittivity ${varepsilon}_r$ substrate height h, strip width w of the microstrip line) and pulse width ${\tau}$ of signal pulse. The simulation results show that space between two lines is very significant parameter in pulse distortion in comparison of any other parameters. The results of this paper are compatible to the trade-off determination of relative permittivity, substrate height, strip width and pulse width of signal pulse when a design of MIC and MMIC is necessary.

• Structural Engineering and Mechanics
• /
• v.58 no.5
• /
• pp.757-781
• /
• 2016

The results of diagnostics and analysis of an industrial hall located on the premises of a thermal power plant severely damaged by fire are presented in the paper. The comprehensive failure-related diagnostics, non-destructive and destructive tests of steel and concrete materials, geodetic surveying of selected structural members, numerical modelling, static analysis and reliability assessment were focused on two basic goals: The determination of the current technical condition of the load bearing structure and the assessment of its post fire resistance as well as assessing the degree of damage and subsequent design of reconstruction measures and arrangements which would enable the safe and reliable use of the building. The current mechanical properties of the steel material obtained from the tests and measured geometric characteristics of the structural members with imperfections were employed in finite element models to study the post-fire behaviour of the structure. In order to compare the behaviour of the numerically modelled steel roof truss, subjected to the effects of fire, with the real post-fire response of the damaged structure theoretically obtained resistance, critical temperature and the time at which the structure no longer meets the required reliability criteria under its given loading are compared with real values. A very good agreement between the simulated results and real characteristics of the structure after the fire was observed.

• Journal of the Computational Structural Engineering Institute of Korea
• /
• v.24 no.2
• /
• pp.177-184
• /
• 2011

In this paper the nonlinear analysis that include time-dependent characteristics of materials and geometric nonlinearity of elements for the cable-stayed PSC bridges is presented. Analysis models for finite element method were developed based on the flexibility based fiber beam-column model originally proposed by Spacone et al.(1996). The developed analysis model implemented in general purpose object-oriented finite element analysis program named HFC(Cho 2009). The performance of proposed analysis models is evaluated by comparing with the former results of the design data. The deflection of time dependent analysis is larger than time ignored analysis on construction sequences, and the bridge is destructed at a smaller deflection than the time ignored analysis on failure behavior.

• Proceedings of the Korean Vacuum Society Conference
• /
• 2011.08a
• /
• pp.392-392
• /
• 2011

Carbon nanotubes (CNT) emitter has widely become an attractive mechanism that draws growing interests for cold cathode field emission.$^{1,2}$ CNT yarns have demonstrated its potential as excellent field emitters.$^3$ Extensive simulations were carried out in designing a CNT yarn-based cathode assembly. The focal spot size dependence on the anode surface of the geometric parameters such as axial distance of the electrostatic focus lens from the cathode and the applied bias voltages at the cathode, grid mesh and electrostatic focus lens were studied. The detailed computer simulations using Opera 3D electromagnetic software$^4$ had revealed that a remarkable size of focal spot under a focusing lens triode type set-up design was achieved. The result of this optimization simulation would then be applied for the construction of the CNT yarn based micro-focus x-ray tube with its field emission characteristics evaluated.

• Education of Primary School Mathematics
• /
• v.5 no.2
• /
• pp.121-142
• /
• 2001

The goal of the National Assessment of Educational Achievement(NAEA) 2001 was to affirm the accountability of school education, to scientifically manage and elevate the quality of education at the national level, and to articulate the final design of the NAEA. It was implemented on June 28th of the year 2001. The assessment frame for NAEA includes the achievement standards, the assessment standards, the instruction for the item development, and the grading policy for mathematics subject. Most of items are multiple-choice types, but the performance-based items should be at least thirty percent of the total items, also 30% in case of mathematics. Approximately 1% of students among entire population of the Grades 6 were randomly selected. Therefore, the finally sampled examines were 8023 at Grade 6. The result of the analysis of the NAEA revealed that Grade 6 students was labelled as ‘average’ level in general (Number and Operation: average, Geometric figures: average, Patterns and Functions: excellent, Measurements: average, Letters and Expressions: average, Probability and Statistics: average). The most characteristic finding was that except for Grade 6(its average is 69.92), most secondary students obtained low test scores and its average of each grade is below 50 out of 100. Especially, the scores on the performance-based items were by and large very low. This finding implies that Korean students are not familiar with the kind of test items which requires expression of ideas and feelings and they are rather familiar with the multiple-choice items. Another interesting finding was that the students in small towns and remote areas showed significantly low scores in all four skills compared with Seoul, metropolitan cities and medium and small cities. This may be attributed from the fact that the remote areas do not have equal learning environment with regard to social and cultural experience, supply of various teaching materials, extracurricular lessons which are directly related to teaching and learning. These findings may be utilized as a reliable resource fur improving curriculum and teaching and learning in Mathematics.

• Journal of KIISE:Computing Practices and Letters
• /
• v.12 no.1
• /
• pp.56-65
• /
• 2006

Recently the study on service robots has been proliferated in many fields, and there are active developments for indoor services such as supporting for elderly people. It is important for robot to recognize objects and situations appropriately for effective and accurate service. Conventional object recognition methods have been based on the pre-defined geometric models, but they have limitations in indoor environments with uncertain situation such as the target objects are occluded by other ones. In this paper we propose a Bayesian network model to reason the probability of target objects for effective detection. We model the relationships between objects by activities, which are applied to non-static environments more flexibly. Overall structure is constructed by combining common-cause structures which are the units making relationship between objects, and it makes design process more efficient. We test the performance of two Bayesian networks for verifying the proposed Bayesian network model through experiments, resulting in accuracy of $86.5\%$ and $89.6\%$ respectively.

• Journal of Drive and Control
• /
• v.11 no.4
• /
• pp.15-24
• /
• 2014

It is difficult to analytically derive a volumetric displacement formula for a gerotor hydraulic motor due to the complexity of the geometric shape of its gear lobes. This work proposes an analytical method for the volumetric displacement, a relatively easy method based upon two physical concepts: conservation between hydraulic energy and mechanical shaft energy, and torque equilibrium for the rotor's motion. The first research using these concepts was conducted on inner and outer rotors rotating with respect to each rotor axis. This work represents the second report conducted on an inner rotor revolving as a planetary motion on the stationary outer rotor. The formula equations regarding the volumetric displacement and flow rate are derived, and the proposed formula about the volumetric displacement is proven to be the same as another analytical displacement formula: the so-called vane length method. From the formula, volumetric displacement is calculated for an example geometry of the gear lobes. The resultant displacement is confirmed to be the same as the value calculated from the chamber volume method. The proposed analytical formula can be utilized in the analysis and design of gerotor hydraulic motors. Because it is based on torque equilibrium, this formula can provide a better understanding of torque performance, such as torque ripple, in designing a gerotor type motor.