• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.18 no.2
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• pp.75-82
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• 2004

Zero Voltage Transition Pulse Width Modulation (ZVT-PWM) converter with active snubber circuit was proposed on this paper. The converter that has been proposed snubber circuit can be operated at the condition of light load range, and this converter is turned on and off near by Zero Voltage Switching (ZVS) or Zero Current Switching (ZCS). If the stress of voltage and current are not occurred at the main switch and main diode, we subjected the allowed level of voltage and current on the auxiliary switch and auxiliary diodes. By proposed 750[W], 80[KHz] PWM boost converter to apply soft switching on the power of total output, the loss of main switch to compare with hard switching was reduced about 27[％], and the loss of total circuit was reduced about 36[％]. The total efficiency was increased about 6[％] to compare with general converter.

• Tunnel and Underground Space
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• v.21 no.2
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• pp.109-116
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• 2011

In this study, we estimated the dynamic tensile strength and strain rate from Brazilian tensile test using Split Hopkinson Pressure Bar (SHPB) system. A pulse shaping technique, which controls the shape of the impactinduce incident waves, was used for achieving the dynamic stress equilibrium and constant strain rate before fracture of rock samples. Three kinds of rock type, Inada granite, Kimachi sandstone and Tage tuff were prepared as 50mm in diameter and 26 mm in thickness. The high-speed videography system was used to observe the fracture processes of the rock samples. As the results of the tests, the ratio of dynamic tensile strength and static tensile strength was 11.9 for Inada granite, 8.5 for Kimachi sandstone and 9.2 for Tage tuff.

• Journal of Environmental Science International
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• v.21 no.12
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• pp.1487-1494
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• 2012

This study has been carried out to verify curative effect of lavender and lawn, a green space composition factor. Thus, the physiological index value of blood pressure, heart rate and salivary amylase were measured with object of 16 women in their 20~30s for stress relaxation effect at lavender garden and lawn square, and impression assessment upon SD method as for psychological value was performed in this study. And a survey was conducted on necessity and reason of urban green space with object of 345 men and women urban workers. As a result of variance analysis between groups and multi test of Turkey upon object place, the blood pressure was lowered the same at lavender garden and lawn square, and especially, high blood pressure was greatly lowered to 30 mmHG at lavender garden. On the other hand, low blood pressure group showed the tendency of a little increasing at the same places. And for the pulse, there was difference between high blood pressure group and normal group at the same places. To conclude, at lavender garden and lawn square the blood pressure was made to be lowered when it's high, and when it's low, the effect of returning to sound status, the function of increasing, was verified. In case of impression assessment upon SD method, the lawn square was assessed as resting place and lavender garden diversional place. And over 90% of urban workers responded to the green space's necessity and curative effect, diversion and resting place were adopted for the reason in high-ranking items. As above the green space pattern that urban workers require and curative effect of lavender garden and lawn square were verified. Therefore, the functional green space plan is required, which curative effect, diversion and resting place are considered, for the future green space plan design.

• Tunnel and Underground Space
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• v.8 no.3
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• pp.184-193
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• 1998

In order to dispose radioactive wastes safely, it is needed to understand the mechanical, thermal, fluid behavior of rockmass and physico-chemical interactions between rockmass and water. Also, the knowledge about mechanical and hydraulic properties of rocks is required to predict and to model many conditions of geological structure, underground in-situ stress, folding, hot water interaction, intrusion of magma, plate tectonics etc. This study is based on researches about rock mechanics issues associated with a waste disposal in deep rockmass. This paper includes the mechanical and hydraulic behavior of rocks in varying temperature conditions, thermo-hydro-mechanical coupling analysis in rock mass and deformation behavior of discontinuous rocks. The mechanical properties were measured with Interaken rock mechanics testing systems and hydraulic properties were measured with transient pulse permeability measuring systems. In all results, rock properties were sensitive to temperature variation.

• Earthquakes and Structures
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• v.18 no.1
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• pp.73-82
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• 2020

With the coal mining depth increasing, both stress and gas pressure rapidly enhance, causing coal and gas outburst risk to become more complex and severe. The conventional method for prediction of coal and gas outburst adopts one prediction index and corresponding critical value to forecast and cannot reflect all the factors impacting coal and gas outburst, thus it is characteristic of false and missing forecasts and poor accuracy. For the reason, based on analyses of both the prediction indicators and the factors impacting coal and gas outburst at the test site, this work carefully selected 6 prediction indicators such as the index of gas desorption from drill cuttings Δh₂, the amount of drill cuttings S, gas content W, the gas initial diffusion velocity index ΔP, the intensity of electromagnetic radiation E and its number of pulse N, constructed the Bayes discriminant analysis (BDA) index system, studied the BDA-based multi-index comprehensive model for forecast of coal and gas outburst risk, and used the established discriminant model to conduct coal and gas outburst prediction. Results showed that the BDA - based multi-index comprehensive model for prediction of coal and gas outburst has an 100% of prediction accuracy, without wrong and omitted predictions, can also accurately forecast the outburst risk even for the low indicators outburst. The prediction method set up by this study has a broad application prospect in the prediction of coal and gas outburst risk.

• Journal of Biomedical Engineering Research
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• v.23 no.6
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• pp.437-449
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• 2002

Coronary arteries are subjected to very different flow conditions compared to other arteries in systemic blood circulation. We Performed a computational fluid dynamic research to investigate influence of such flow conditions in coronary arteries on development and progress of atherosclerosis in the same. The results showed big differences in the flow field of the coronary artery compared to the abdominal and femoral arteries. The coronary artery showed higher wall shear stresses due to the small vessel diameter. On the other hand, it showed only one vortex distal to the stenosis throat during a whole pulse cycle. However. several vortices were observed in the abdominal and femoral arteries in both proximal and distal sides of the stenosis throat The wall shear stresses and extent of recirculation area were increased with impedance phase angle increasing toward more negative values. Therefore, cardiac contraction and the negative impedance phase angle as large as -110。 may induce a flow field that accelerates atherosclerosis.

• Journal of Biomedical Engineering Research
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• v.29 no.5
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• pp.371-375
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• 2008

In blood pressure measurement, the oscillometric method detects and analyzes the pulse pressure oscillation while deflating the cuff around the arm. For its principle, one has to inflate cuff pressure above the subject's systolic pressure and deflate below the diastolic pressure. Most of the commercialized devices inflate until the fixed target pressure and deflate until the fixed completion pressure because there is no way to know the systolic and diastolic pressure before measurement. Too high target pressure makes stress to the subject and too low target pressure makes big error or long measurement time because of re-inflation. There are similar problems for inadequate completion pressure. In this study, we suggest new algorithm to set proper target and completion pressure for each subject by analyzing pressure waveform while inflating period. We compared our proposed method and auscultation method to see the errors of estimation. The differences between the two measurements were -4.02$\pm$4.80mmHg, -10.50$\pm$10.57mmHg and -0.78$\pm$5.l7mmHg for mean arterial pressure, systolic pressure and diastolic pressure respectively. Consequently, we could set the target pressure by 30 mmHg higher than our estimation and we could stop at 20mmHg lower than our estimated diastolic pressure. Using this method, we could reduce the measurement time.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.20 no.10
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• pp.82-93
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• 2006

In this paper, filters are designed to reduce transients overvoltage in inverter fed high-voltage large-capacity induction motor drive system. Design issues for a LCR filter at the inverter output terminals to reduce the dv/dt of the inverter output pulse and a RC filter at the induction motor input terminals to match the characteristic impedance between cable and induction motor are examined in detail. These filters are modeled to be suitable to high-voltage large-capacity induction motor. The performance of the filter is evaluated through simulation using EMTP(ElectroMagnetic Transients Program). We presented filters that used high voltage large-capacity induction Motor on the basis of this. Effect of the filter is analyzed for variation of the cable length. Characteristics of filters are analyzed to reduce harmonic in voltage waveform of induction motor input terminal. The switching surge voltage became the major cause to occur the insulation failure by serious voltage stress in the stator winding of induction motor. Filter for to mitigate transients overvoltage presents a required component in drive system of high-voltage large-capacity induction motor. Also, proposed filters are proved through simulation using EMTP.

• Magazine of the Korean Society of Agricultural Engineers
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• v.38 no.6
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• pp.83-95
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• 1996

The normal cement concrete is widely used material to build the construction recently, but it has a fault to increase the dead load on account of its unit weight is large compared with strength. So, main purpose of this study was to establish the physical and mechanical properties of lightweight concrete using expanded polystyrene bead on fine aggregate and natural gravel, expanded clay and pumice stone on coarse aggregate. The test rusults of this study are summarized as follows; 1. The water-cement ratio of concrete using pumice stone was larger than that of the concrete using natural gravel and expanded clay. 2. The unit weights of concrete using pumice stone and expanded caly were shown less than 1,000g/$m^3$. 3. The compressive strengths of all types were shown less than 60kg/$cm^2$, tensile and bending strengths were shown less than l3kg/$cm^2$ and 3lkg/$cm^2$$^2$, respectively. 4. The pulse velocity of concrete was shown similar with using natural gravel and pumice stone, and shown the lowest using pumice stone. 5. The dynamic modulus of elasticity of concrete was shown considerably smaller, and shown the lowest using pumice stone. 6. The static modulus of elasticity of concrete using expanded clay and pumice stone were shown considerably smaller, and shown 22% ~29% as compared with the dynamic modulus of elasticity. 7. The stress-strain curves of concrete were shown similar, generally. And the curves were repeated at short intervals increase and decreased irregularly.

• Journal of IKEEE
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• v.19 no.2
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• pp.265-270
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• 2015

In this paper, we proposed a dual-directional SCR (silicon-controlled rectifier) based ESD (electrostatic discharge) protection circuit. In comparison with conventional SCR, this ESD protection circuit can provide an effective protection against ESD pulses in the two opposite directions, so the ESD protection circuit can be discharged in two opposite direction. The proposed circuit has a higher holding voltage characteristic than conventional SCR. These characteristic enable to have latch-up immunity under normal operating conditions as well as superior full chip ESD protection. it was analyzed to figure out electrical characteristics in term of individual design parameters. They are investigated by using the Synopsys TCAD simulator. In the simulation results, it has trigger voltage of 6.5V and holding voltage increased with different design parameters. The holding voltage of the proposed circuit changes from 2.1V to 6.3V and the proposed circuit has symmetrical I-V characteristic for positive and negative ESD pulse.