• Journal of computational fluids engineering
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• v.13 no.1
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• pp.57-62
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• 2008

Laminar flows over a cube and a cuboid (cube extended in the streamwise direction) are numerically investigated for the Reynolds numbers between 50 and 350. First, vortical structures behind a cube and lift characteristics are scrutinized in order to understand the variation in vortex shedding characteristics with respect to the Reynolds number. As the Reynolds number increases, the flow over a cube experiences the steady planar-symmetric, unsteady planar-symmetric, and unsteady asymmetric flows. Similar to the sphere wake, the planar-symmetric flow over a cube can be divided into two different regimes: single-frequency regime and multiple-frequency regime. The former has a single frequency due to regular shedding of vortices with the same strength in time, while the latter has multiple frequency components due to temporal variation in the strength of shed vortices. Second, the effect of the length-to-height ratio of the cuboid on the flow characteristics is investigated for the Reynolds number of 270, at which planar-symmetric vortex shedding takes place behind a cube. With the ratio smaller than one, the flow over the cuboid becomes unsteady asymmetric flow, whereas it becomes steady flow for the ratios greater than one. With increasing the ratio, the drag coefficient first decreases and then increases. This feature is related to the flow reattachment on the side faces of the cuboid.

• Journal of the Korean Society of Manufacturing Technology Engineers
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• v.23 no.3
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• pp.223-229
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• 2014

In this paper, the natural frequency and damping ratio are analyzed with the acceleration signal of an Euler-Bernoulli beam using the impact hammer test. The results are presented according to crack depth and position using the recursive least squares method. The results are compared and investigated with FEM analysis of CATIA. Both methods agree well with each other regarding the natural mode characteristics. The captured acceleration can be used for the calculation of the natural frequency and damping ratio using time series methods that are based on the measured acceleration. Using these data, a recursive time series model with the acceleration signal was configured and the behaviors of the natural frequency and damping ratio were investigated and analyzed. Finally, the results can be used for the prediction of crack position and depth under different crack conditions for an Euler-Bernoulli beam.

• The Journal of the Korea Contents Association
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• v.15 no.4
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• pp.97-103
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• 2015

This paper empirically investigated the factors that may affect art forgery, using 5,130 authentication request data drawn from Korean Art Appraisal Board (KAAB) during 2003 and 2012. Living status of artists and trade frequency of artworks of the artists were considered as explanatory variables that may affect authentication requests and forgery ratio. We found that artists' death has significantly positive impacts on both authentication requests and forgery ratio, while trade frequency of artworks of the artists has the impact only on authentication requests. These results imply that art forgery may have multidimensional characteristics.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.17 no.9
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• pp.862-873
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• 2007

Energy dissipation devices can be considered as an alternative for the seismic performance enhancement of existing structures based on the strengthened seismic design code. In this study, seismic response mitigation effects of friction dampers are investigated through the shaking table test of a full scale 3 story building structure. Frist, the bilinear force-displacement relationship of a structure-brace-friction damper system and the effect of brace-friction damper on the increase of frequency and damping ratio are identified. Second, frequency, displacement, and torque dependent characteristics of the friction damper are investigated by using harmonic load excitation tests. Finally, the shaking table tests are performed for a full scale 3 story steel frame. System identification results using random signal excitation indicated that brace-friction damper increased structural damping ratio and frequency, and El Centro earthquake test showed that brace-friction damper reduced the peak displacement and acceleration significantly. In particular, it was observed that the damping effect due to friction damper becomed obvious when the structure was excited by more intensive load causing frequent slippage of the friction dampers.

• Journal of the Korean Society of Food Science and Nutrition
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• v.23 no.1
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• pp.55-61
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• 1994

The study was designed to investigate the relationship between dietary intakes and the obesity of 400 students who were the third grade in middle school in some areas of Seoul. The survey conducted from March 3 to 13 , 1993. The results obtained were summarized as follows :The average height and weight of surveyed subject were similar to that of standard ( the third grade students in middle school in Seoul, 1991) . Compared to the standard weight/height ratio, subject who belonged to overweight and obese group were 16.4% of male students, 16.1% of female students respectively. Female subjects showed higher ratio than male subjects in skipping meals, frequency of snack per day and concern about a dieting . In case of subjects who belonged to weight /height ratio was high, their speed of dining was fast and they have more concern about a dieting. Compared to the amount of the nutritional intakes of RDA, calcium intakes of male and female subjects were deficient. Especially iron intakes of female subjects were deficient. In takes of Calorie (p<0.01) protein(p<0.05) and fat 9p<0.01) of obese group were higher those of non-obese group. Obese group showed good appetite and overeating also . Correlation analysis showed that obese group seemed to the closely associated with relative body weight of parents, family income, frequency of meals per day, frequency of meals per day, frequency of snack per day, speed of dining and overeating .

• Journal of the Korea Institute of Military Science and Technology
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• v.16 no.1
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• pp.40-47
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• 2013

By virtue of Rec. ITU-R P.1546 and geography information system, interference analysis for the fixed wireless system and radar has been presented based upon the frequency-distance rules with minimum coupling loss, and a comprehensive methodology for assessing interoperability between systems was examined in terms of received signal, protection ratio, frequency dependent rejection. Also to find the antenna gain from a discrimination angle, a useful S-I plane was introduced based on signal and interference vectors derived from the real map with geographic information. To show some computational results, geography information on the map was taken for the given area, and field strength and path profile were illustrated for the radar and fixed wireless system operating at 2.7 GHz, for convenience. In addition the interference effect of receiver was also checked as a function of radar beam direction including protection ratio and frequency dependent rejection. The developed interference analysis can be actually applied to evaluate interoperability for wireless systems in the VHF and UHF bands.

• Journal of Power Electronics
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• v.14 no.3
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• pp.531-540
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• 2014

A novel carrier-based PWM (CBPWM) strategy of a three-level NPC converter is proposed in this paper. The novel strategy can eliminate the low-frequency neutral point (NP) voltage oscillation under the entire modulation index and full power factor. The basic principle of the novel strategy is introduced. The internal modulation wave relationship between the novel CBPWM strategy and traditional SPWM strategy is also studied. All 64 modulation wave solutions of the CBPWM strategy are derived. Furthermore, the proposed CBPWM strategy is compared with traditional SPWM strategy regarding the output phase voltage THD characteristics, DC voltage utilization ratio, and device switching losses. Comparison results show that the proposed strategy does not cause NP voltage oscillation. As a result, no low-frequency harmonics occur on output line-to-line voltage and phase current. The novel strategy also has higher DC voltage utilization ratio (15.47% higher than that of SPWM strategy), whereas it causes larger device switching losses (4/3 times of SPWM strategy). The effectiveness of the proposed modulation strategy is verified by simulation and experiment results.

• Journal of the Korean GEO-environmental Society
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• v.12 no.1
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• pp.81-87
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• 2011

The characteristics of vertical to horizontal ratio of response spectrum from 20 recent earthquakes were analysed. Response spectrum of 260 horizontal and 130 vertical ground motions were normalized by peak ground acceleration at each resonance frequency from 0.1 to 50Hz. It has been identified that the ratio of vertical to horizontal response spectrum has strong dependancy on epicentral distance and resonance frequency. The ratio of vertical to horizontal response spectrum for the 0-50km epicentral distance group are larger than 2/3 values, which is a standard engineering rule-of-thumb V/H=2/3, at resonance frequency above 7-8Hz. All the 3 groups such as 50-100, 100-150- and 150-200km epicentral distance have shown larger values of vertical to horizontal ratio than 2/3 at resonance frequency above 15Hz and also are larger than 2/3 at resonance frequency below 8-10Hz. Even though there are differences in specific resonance frequency values which depend on the epicentral distance group, we should be careful of seismic design of vertical component of the structures winch are located within the range of about 200km distance. form the potentially seismic causative faults.

• Journal of Mechanical Science and Technology
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• v.17 no.10
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• pp.1533-1542
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• 2003

In the present study, the characteristics of pressure oscillation and heat transfer performance in an oscillating capillary tube heat pipe were experimentally investigated with respect to the heat flux, the charging ratio of working fluid, and the inclination angle to the horizontal orientation. The experimental results showed that the frequency of pressure oscillation was between 0.1 Hz and 1.5 Hz at the charging ratio of 40 vol.%. The saturation pressure of working fluid in the oscillating capillary tube heat pipe increased as the heat flux was increased. Also, as the charging ratio of working fluid was increased, the amplitude of pressure oscillation increased. When the pressure waves were symmetric sinusoidal waves at the charging ratios of 40 vol.% and 60 vol.%, the heat transfer performance was improved. At the charging ratios of 20 vol.% and 80 vol.%, the waveforms of pressure oscillation were more complicated, and the heat transfer performance reduced. At the charging ratio of 40. vol.%, the heat transfer performance of the OCHP was at the best when the inclination angle was 90$^{\circ}$ the pressure wave was a sinusoidal waveform, the pressure difference was at the least, the oscillation amplitude was at the least, and the frequency of pressure oscillation was the highest.

• The Journal of Internal Korean Medicine
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• v.28 no.4
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• pp.769-778
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• 2007

Background & Object : Postprandial epigastric fullness is one of common symptoms in functional dyspepsia, but its pathophysiological mechanism has still been unknown. In this study, its association between postprandial epigastric fullness and pyloric valve disturbance was studied through analysis of bowel sounds and electrogastrography. Methods : Bowel sounds and electrogastrography were recorded together for fasting 15 min and postprandial 40 min. Parameters of bowel soundincluding motility index, sound to sound interval, standard deviation of sound to sound interval, sounds per minute, % of bowel sound, sound length, intensity, dominant frequency of sounds, and postprandial / fasting ratio of dominant frequency of sounds were analyzed with a specialized program. By electrogastrography, regularity of slow waves and power ratio were obtained. Results : Significances of bowel sounds appeared in motility index (p=0.046), dominant frequency of fasting (p=0.048), postprandial (p=0.003), and the ratio of postprandial/fasting (p=0.000); those of EGG parameters were shown in postprandial regularity of slow waves (p=0.006) and power ratio (p=0.011). Conclusion : Pyloric valve disturbance was a cause of postprandial epigastric fullness in patients with functional dyspepsia. Analysis of bowel sound might be useful in diagnosing its existence.