• Journal of the Korean Society for Precision Engineering
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• v.22 no.3 s.168
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• pp.154-161
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• 2005

In this study, the leaflet motion of a mechanical heart valve and the characteristics of two-dimensional transient blood flow in an elastic blood vessel have been numerically investigated by using fluid-structure interaction method. Here, blood has been assumed as a Newtonian, incompressible fluid. Pressure profiles have been used as boundary conditions at the ventricle and the aorta. As a result, closing motion of the leaflet is faster than opening one. While opening angles of leaflet grow up, vortex is detected at the sinus and backward of the leaflets. When the leaflet is fully closed, vortex is detected at the ventricle and at that moment maximum displacement of the elastic blood vessel is observed in the vicinity of the sinus region. Maximum displacement is caused in association with the blood flow that is oriented toward the elastic blood vessel.

• Proceedings of the Korean Nuclear Society Conference
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• 1997.05a
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• pp.551-556
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• 1997

A present study addresses a loss-of-RHR event as an initiating event under specific low power or shutdown conditions. Two typical plant configurations, cold leg opening case with water-filled steam generators and pressurizer opening case with emptied steam generators, were evaluated using the RELAP5/ MOD3.2 code. The calculation was compared with the experiment conducted at ROSA-IV/LSTF in Japan. As a result, the code was capable of simulating the system transient behavior following the event. Especially, thermal hydraulic transport processes including non-condensable gas behavior were reasonably predicted with an appropriate time step and CPU time. However, there were some code deficiencies such as too large system mass errors and severe flow oscillations in core region.

• The KSFM Journal of Fluid Machinery
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• v.7 no.3 s.24
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• pp.23-31
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• 2004

An experimental study on the performance and instability development characteristics of a centrifugal compressor equipped with an adjustable inlet guide vane has been performed with varying guide vane angles. The test was conducted at the design speed of 20,800 rpm for 6 guide vane angles : $-30^{\circ},\;-20^{\circ},\;10^{\circ},\;0^{\circ},\;10^{\circ},\;20^{\circ},\;30^{\circ}$. Unsteady pressures were measured using high-frequency pressure transducers at the inducer to investigate the instability phenomena such as rotating stall and surge inside the compressor. From the unsteady measurements, it is found that the transient process from rotating stall to surge was mainly affected by inlet guide vane angles. The results of the present study can be applied to the instability control of the centrifugal compressors using a adjustable inlet guide vane.

• Journal of Chest Surgery
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• v.18 no.2
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• pp.279-282
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• 1985

Occipital alopecia after Open Heart Surgery under the Cardiopulmonary bypass is an uncommon minor complication. We had experienced Occipital alopecia in 6 cases after Open Heart Surgery. The cause of the alopecia was transient circulatory disturbance due to pressure effect of the patient`s head and intraoperative hypotension. The prodromal symptoms of the alopecia were erythema, itching, and watery discharge, but some patients showed non-specific symptoms. The common site of the alopecia was right occipital region and the size was 2-4 cm in diameter. The regrowth of the hair was completed at postoperative 3 to 5 months without specific treatment except conservative treatment. Fortunately the postoperative alopecia is a self-limiting condition, and spontaneous regrowth of hair is the rule without other complications.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.15 no.9
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• pp.775-784
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• 1990

In this paper, a new window model for designing FIR digital filter is suggested. For the suggested model, two parameters are established and their effects to the characteristics of filter are analyzed. As a result, one of these parameters improves the characteristics of the transient region but degenerates those of peak sidelobe a little bit, and the other contrasts the characteristics with the former. These effects of parameters give selectivity to design window. Therefore the new suggested window model gives flexibility to filter design and its improved characteristics is comfirmed by simulation.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.62 no.9
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• pp.1234-1239
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• 2013

This paper provides a technical review of speed control using variable gain PI algorithm for BLDC(Brushless DC) motor. Usually the PI control is used in many motor applications, but a general PI control has problems of overshooting and disturbance for response. By the change of PI gain in motor control operation, these problems can be solved. To find the optimized PI gains for BLDC motor control, many control methods have been proposed. In this paper, the control algorithm with a variable PI gain is applied to improve overshooting response in transient region and rapid load disturbance rejection. Fixed gain and variable gain PI controls are compared. The validity of the propose method is verified by experiment.

• 한국신재생에너지학회:학술대회논문집
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• 2009.06a
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• pp.247-250
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• 2009

Sodium heat pipe for high-temperature solar thermal application was manufactured and tested for transient and steady-state operations. Total length of the heat pipe was 650 mm and the outer diameter was 12.7 mm. Thermal performance was compared experimentally for two different cooling methods of the forced and the natural convection cooling in the heat pipe condenser. During the experiment, the maximum temperature was about 1300K, and different cooling methods were applied to the condenser region to charge the operating temperature. The effective thermal conductivity and the thermal resistance were investigated as a function of heat flux, heat transport length, and operating temperature.

• Journal of Korean Neurosurgical Society
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• v.41 no.5
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• pp.327-329
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• 2007

A 44-year-old woman presented with recurrent, transient episodes of left-side hemiparesis. She had received a radiation dose of 6120 cGy to her cervical region for parotid gland carcinoma 13 years previously. Cerebral angiography revealed a long, irregular tight stenosis involving the right extracranial internal carotid artery [ICA] and common carotid artery [CCA], measuring approximately 90% at the most severe narrowing according to North American Symptomatic Carotid Endarterectomy Trial criteria. Endovascular stent placement resulted in restoration of the carotid lumen to about 80% of its original diameter. She showed no further ischemic events during the follow-up period of 48 months. Our clinical and angiographic findings suggest that carotid stenting is considered a safe and effective treatment option in patients with radiation-induced carotid stenosis.

• The Transactions of the Korean Institute of Electrical Engineers
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• v.36 no.10
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• pp.695-702
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• 1987

Nowadays as the power systems have been more complicated and have grown to ultra high voltage, it requires a accurate and high speed relaying scheme to improve the reliability and stability of power systems for a harmonious power supplying. For this purpose voltage and current have to be measured at the location of the protective device and the short circuit impedance must be determined. This paper presents the application methods and some results of digital distance relaying scheme which is based upon the theouy of real-time symmetrical components. Usually the symmetrical component have been used to solve the transient systems as well as the steady state systems under unbalanced systems. But, real-time symmetrical component frequently have not been applied to on-line control region of the large power system. We have tried to apply this method to deal with the various type of faults on artificial transmission line. And experimental results demonstrate the validity of the proposed techniques. Therefore, this study is expected that it is contributed to improve the reliability of power supplying, searching for the fault location rapidly and exactly in power system.

• Journal of Institute of Control, Robotics and Systems
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• v.16 no.4
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• pp.313-318
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• 2010

This paper deals with the relationship between zeros and step response of the second and third order LTI (Linear Time Invariant) SISO (Single-Input and Single-Output) systems with complex poles. Although it has been known that the maximum number of local extrema is less than the number of zeros in the system with only real poles[8], some cases with complex poles are shown in this paper to have many local extrema. This paper proposes monotone nondecreasing conditions and describes the relationship between the transient response and the number of local extrema in step response with each region of zeros.