• 한국전산유체공학회:학술대회논문집
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• 2008.03a
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• pp.297-301
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• 2008

The flight vehicles have cavities such as wheel wells and bomb bays. The flow around a cavity is characterized as unsteady flow because of the formation and dissipation of vortices due to the interaction between the freestream shear layer and cavity internal flow, the generation of shock and expansion waves. Resonance phenomena can damage the structures around the cavity and negatively affect aerodynamic performance and stability. The flow field is observed to oscillate in the "shear layer mode" with low aspect ratio. In the present study, numerical analysis was performed for cavity flows by the unsteady compressible three dimensional Reynolds-Averaged Navier-Stokes (RANS) equations with Wilcox's $\kappa$-$\omega$ turbulence model. The flow field is observed to oscillate in the shear layer mode" with large aspect ratio. Based on the SPL(Sound Pressure Level) analysis of the pressure variation at the cavity trailing edge, the dominant frequency was analyzed and compared with the results of Rossiter's formul. The aero-acoustic wave analyzed with CPD(Correlation of Pressure Distribution).

• 한국전산유체공학회:학술대회논문집
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• 2008.10a
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• pp.297-301
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• 2008

The flight vehicles have cavities such as wheel wells and bomb bays. The flow around a cavity is characterized as unsteady flow because of the formation and dissipation of vortices due to the interaction between the freestream shear layer and cavity internal flow, the generation of shock and expansion waves. Resonance phenomena can damage the structures around the cavity and negatively affect aerodynamic performance and stability. The flow field is observed to oscillate in the "shear layer mode" with low aspect ratio. In the present study, numerical analysis was performed for cavity flows by the unsteady compressible three dimensional Reynolds-Averaged Navier-Stokes (RANS) equations with Wilcox's ${\kappa}-{\varepsilon}$ turbulence model. The flow field is observed to oscillate in the "shear layer mode" with large aspect ratio. Based on the SPL(Sound Pressure Level) analysis of the pressure variation at the cavity trailing edge, the dominant frequency was analyzed and compared with the results of Rossiter's formul. The aero-acoustic wave analyzed with CPD(Correlation of Pressure Distribution).

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.19 no.2
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• pp.111-118
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• 2020

Recently, bioenergy research using microalgae, one of the most promising biofuel sources, has attracted much attention. Cell disruption, which can be classified as physical or chemical, is essential to extract functional ingredients from microalgae. In this study, we investigated the cell disruption efficiency of Chlorella sp. using low-frequency non-focused ultrasound (LFNFU). This is a continuously physical method that is superior to chemical methods with respect to environmental friendliness and low processing cost. A flat panel photobioreactor was employed to cultivate Chlorella sp. and its growth curve was fitted both with Logistic and Gompertz models. The temporal change in cell reduction by cell disruption using LFNFU was fitted with a Logistic model. The experimental conditions that were investigated were the initial concentration of microalgal cells, relative amplitude of output ultrasound waves, processing volume of microalgal cells, and initial pH value. The optimal conditions for the most efficient cell disruption were determined through the various tests.

• Journal of the Korean Institute of Telematics and Electronics S
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• v.35S no.8
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• pp.39-46
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• 1998

One of the main techniques for diagnosing heart disease is by examining the electrocardiogram(ECG). Many studies on detecting the QRS complex, P, and T waves have been performed because meaningful information is contained in these parameters. However, the earlier detection techniques can not effectively extract those parameters from the ECG that is severely contaminated by noise source. In this paper, we performed the extracting parameters from and recovering the ECG signal using wavelets transform that has recently been applying to various fields.

• Economic and Environmental Geology
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• v.16 no.1
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• pp.51-61
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• 1983

By using local earthquake data, the Korean crust model and travel-time tables were determined. The upper crustal earthquakes (Hongsung event and Ssanggyesa event) were considered as auxiliary information, and the lower crustal earthquakes (Uljin event and Pohang event) played an important role in determining model parameters. The possible existence of Low Velocity Layer (LVL) in the upper mantle was suggested by discrepancy in the arrival times of Sariwon earthquake which occurred below Moho discontinuity. Computer program for the determination of the model parameters was developed in order to screened out the optimum parameters by comparing the travel times of observed data with theoretical ones. We found that the discontinuities of Conrad, Moho, and upper and lower boundaries of LVL have their depth of 15, 32, 55 and 75 Km, respectively. The velocities of P-and S-wave in the layers between those discontinities were found to be (1) 5.98, 3.40 Km/sec (2) 6.38, 3.79 Km/sec (3) 7.95, 4.58 Km/sec (4) unknown (5) 8.73, 5.05 Km/sec, respectively from the top layer. Travel-time tables were also computed for the inter-local earthquakes which have their direct wave paths above the LVL.

• Journal of Advanced Marine Engineering and Technology
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• v.23 no.3
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• pp.346-351
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• 1999

This paper is a research for removing the hunting which came about during the parallel running of the alternators which four-pole six-phase have the converter with twelve diodes to rectify all the waves. Druing the parallel running the hunting came about under the period of 0.2-0.3{sec} not when it's load was the resistance but the capacity at the rpm band 1575[rpm] 1690[rpm] This hunting in our judgement was not come about from the general hunting causes which have been already known to but the special example. And so we checked that the hunting came about or not as per the changes of the rpm exciting current load current and converter and converter output voltage and the following facts were revealed. -The hunting occured during the constant voltage charging where r. p. m band is from 1575[rpm] to 1690[rpm] - The hunting did not came about during the constant power charging in which there was the large difference between the converter output voltage and the battery voltage. -The hunting did not came about in the low rpm band. We could see from the above facts that the existence of the hunting inducing point at the con-stant voltage charging band was the direct cause of the hunting. After trying every possible means to remove the hunting inducing point we could know that the modification of the synchronous generator is suitable for he purpos in view of the small engine room.

• Journal of Advanced Marine Engineering and Technology
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• v.23 no.3
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• pp.352-359
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• 1999

This paper is a research for removing the alternators hunting which came about during the par-allel running. The four-pole six-phase alternator is equipped with the converter made out of twelve diodes to rectify all the waves. The hunting came about during the battery charging due to the hunting inducing point existed in r. p. m band 1575[rpm-1690[rpm] To remove the hunting inducing point We modified the four-pole six-phase alternator into the four-pole twevel-phase and increased the short-circuit ratio by decreasing the field coil pitch and increasing the field coil turns. But this method has two defects the first the alternator structure becomes complicating and the second the second the alternator equipped with the converter used in general purpose lately such as the car alternator can not be run in parallel wlthout modifying. To remove the defects the equalizing line was connected between the same phase of the alterna-tor to flow the synchronizing current which syncronize the phases of generator electromotive forces by which the alternator can be run in parallel without reference to the hunting inducing point and without modifying.

• Biomedical Science Letters
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• v.18 no.4
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• pp.428-434
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• 2012

Epilepsy is a chronic neurological disease showing a symptom of repeated seizures without any other physical disorders. Among the diagnostic examination for epilepsy, the electroencephalogram (EEG) has been known as an important test. This study aimed to investigate the EEG with photic stimulation in the pediatric epilepsy patients. They underwent digital sleep and waking EEGs or waking EEGs with photic stimulation. Epilepsy type, seizure history, and season of occurring seizure were analyzed. Epilepsy patients showed more response during the period of photic-on and eye close at the frequency of 10~20 Hz during the EEG activation procedure. Photoparoxysmal response (PPR) was shown in 206 patients out of total 1,551 epilepsy patients. PPR was appeared more frequently during summer and winter seasons, and especially in the patients who had a history of seizure. During the PPR, EEG pattern showed spike (77.18%), theta (9.71%), and spike + theta (13.11%). On the other hand, beta and theta waves were not significantly changed by photic stimulation. However, alpha wave was decreased and delta wave was increased by photic stimulation (P<0.05). These changes may be due to temporarily altered electrophysiological function of the epileptic patient's brain by the photic stimulation. There was no difference in the EEG pattern between the left and right side in the brain. In conclusion, condition of photic-on with closed eyes and frequency of 10~20 Hz during the procedure of EEG activation could be appropriate for obtaining a definite photoparoxysmal response in the electroencephalogram of the pediatric epilepsy patients.

• Bulletin of the Korean Chemical Society
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• v.23 no.3
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• pp.395-399
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• 2002

The voltammetric behavior of spontaneously adsorbing Mo layers on Pt(111) and Pt(100) electrodes has been studied to estimate the number of electrons involved in the electrochemical processes of spontaneously adsorbed Mo and the number of the bloc ked Pt sites for hydrogen adsorption. On Pt(111) and Pt(100) surfaces, the spontaneously adsorbed Mo layers showed redox peaks at 0.10 V and 0.15 V, respectively, and continuous current-potential waves in the conventional hydrogen region. Since the potential range of the Mo redox processes on both surfaces overlapped partially with the potential range of hydrogen adsorption, the variation in the ratio of the total charge of Mo and H ($Q_H$ +$Q_{MO}$) to the hydrogen charge of clean Pt electrode ($Q_H^0$) was analyzed. From the analysis, six electrons were estimated to be involved in the electrochemical processes of the spontaneously adsorbed Mo, and four Pt sites for hydrogen adsorption were calculated to be blocked by one adsorbed Mo atom. Based on these figures and the pH dependence of the Mo redox processes, we have proposed an electrochemical equation for the spontaneously adsorbed Mo. This electrochemical equation led us to conclude that the saturation coverage of the spontaneously adsorbed Mo is 0.25. The coverage of Mo less than 0.25, however, could not be determined voltammetrically due to the convolution of the charges of Mo and H.

• Transactions of the Korean Society of Automotive Engineers
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• v.22 no.3
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• pp.136-142
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• 2014

Distinct features in heart rate signals during the driver's wake and sleep states could provide an initiative for the development of a safe driving systems such as drowsiness detecting sensor in a smart wheel. We measured ECG from health subjects ($23.5{\pm}2.5$ in age) during the wake and drowsiness states. The proposed method is able to detect R waves and R-R interval calculation in the ECG even when the signal includes in abnormal signals. Heart rate variability(HRV) was investigated for the time domain and frequency domains. The STD HR(0.029), NN50(0.044) and VLF power(0.0018) of the RR interval series of the subjects were significantly different from those of the control group (p < 0.05). In conclusion, there are changes in heart rate from wake to drowsiness that are potentially to be detected. The results in our study could be useful for the development of drowsiness detection sensors for effective real-time monitoring.