• Transactions of the Korean Society of Mechanical Engineers B
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• v.40 no.4
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• pp.221-226
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• 2016

Since arterial disease in the upper extremity is less common than that in the lower extremity, experimental and numerical investigations related to upper extremity have been rarely performed. We created a three-dimensional model of the arteries, larger than approximately 1 mm, in a Korean adult's left hand (from brachial to digital arteries), from 3T magnetic resonance imaging (MRI) data. For the first time, a three-dimensional computational fluid dynamic method was employed to investigate blood flow velocity, blood pressure variation, and wall shear stress (WSS) on this complicated artery system. Investigations were done on physiological blood flows near the branches of radial and deep palmar arch arteries, and ulnar and superficial palmar arch arteries. The flow is assumed to be laminar and the fluid is assumed to be Newtonian, with density and viscosity properties of plasma.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.38 no.9
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• pp.789-795
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• 2014

In this study, the distribution characteristics of diffusers with various shapes that are installed in an open-type thermal storage system are numerically investigated. Four diffusers are designed to distribute a working fluid evenly through the holes on bifurcated pipes. Three-dimensional steady simulations of incompressible laminar flow are conducted using commercial software (ANSYS-FLUENT). The simulation results show that both the bidirectional header-type diffuser and the H-type diffuser distribute the working fluid evenly whereas both the unidirectional and the bidirectional diffusers distribute the working fluid unevenly. The results also show that the H-type diffuser requires a higher head of pump than the bidirectional header-type diffuser. Therefore, the bidirectional header-type diffuser is recommended for use because it enables even distribution of the working fluid and requires a low head of pump.

• Proceedings of the Korea Water Resources Association Conference
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• 2007.05a
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• pp.921-925
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• 2007

하천의 유량자료는 수위, 우량 등과 함께 수문 해석을 위해 매우 중요하다. 유량자료는 수자원을 정확하게 파악하기 위해 가장 중요한 자료이기 때문에 측정을 위해 많은 노력을 기울이고 있다. 그러나 유량측정은 다른 수문관측과는 달리 변동성이 크고 오차의 범위가 커서 실제 활용에 많은 한계가 있는 것도 사실이다. 유량은 유속계를 이용하여 현장에서 인력으로 직접 측정되기 때문에 현장의 측정조건, 측정하는 사람의 기술적 숙련도 등에 따라 크게 변화할 수 있는 요소를 가지고 있다. 또한 유량자료는 대부분의 경우 연속적인 자료획득이 곤란하기 때문에 수위-유량관계를 이용하여 연속측정된 수위를 유량으로 환산한다. 이와 같은 수위-유량관계는 현장의 조건이 변화하지 않는다는 가정하에서 이루어지는 것이므로 실제 현장에서 발생하는 변화를 고려할 수 없는 한계가 있다. 본 연구에서 유량 모니터링 대상인 서낙동강은 정체수역으로서 하천의 상류와 하류에 대저수문과 녹산수문이 위치해 있고, 두 수문의 개방시 일정시간 동안의 연속적이고 정확한 유량변화의 측정을 필요로 한다. 서낙동강은 녹산수문에서 바다와의 수위차를 고려하여 수문을 개방하기 때문에 대저수문과 녹산수문의 개방 시기 및 시간이 매 순간 유동적이다. 본 연구에서는 서낙동강의 수질 및 수량 관리를 위하여 수문운영에 따른 유량변화를 측정하고자 하였으며, 전술한 바와 같은 한계를 극복하기 위해 유량측정장비는 최첨단 장비인 ADCP를 활용하였다. ADCP(Accoustic Doppler Current Profiler)는 최근에 하천유량측정을 위해 활용되고 있는 장비로서 음파의 도플러 효과를 이용하여 하천을 횡단하면서 단시간에 유속과 유량을 측정한다. 국내의 경우 1990년대 후반부터 도입된 ADCP는 유량측정 기법과 현장 적용상의 문제가 일정부분 검토되고 있다. 본 연구에서는 기존의 유속계를 이용해서 측정한 유량값과 비교하여 ADCP에 의한 결과를 검증하고, 수문운영에 따른 비정상 유량변화를 모니터링하고자 하였다.

• Water for future
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• v.27 no.1
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• pp.79-88
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• 1994

This study was conducted to analyse groundwater flow in the Bugok hot spring area using the MODFLOW model which can simulate three dimensional groundwater flow both in confined and unconfined aquifers. Based on this study the following conclusions were obtained: 1) The hydraulic conductivity and the specific storage of the aquifer were 0.0135 m/day and 0.020, respectively, and the model-predicted groundwater elevation agreed well with the observed one. 2) Simulation results showed that the groundwater level declines at the end of the one-year simulation period when the annual recharge rate is small and the annual pumping rate high, which is the worst combination. Except that combination, the groundwater level does not decline at the end of one-year simulation period indication the pumping rates used were allowable. 3) The safe yield depends upon the magnitudes of the recharge and pumping rates. The pumping rate should not produce excess decline of groundwater level around April when the water level is the lowest in a year.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.38 no.8
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• pp.747-757
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• 2010

The ice accreted on the airfoil is one of the critical drivers that causes the degradation of aerodynamic performance as well as aircraft accidents. Hence, an efficient numerical code to predict the accreted ice shape is crucial for the successful design of de-icing and anti-icing devices. To this end, a numerical code has been developed for the prediction of glaze ice accretion shape on 2D airfoil. Constant Source-Doublet method is used for the purpose of computational efficiency and heat transfer in the icing process is accounted for by Messinger model. The computational results are thoroughly compared against available experiments and other computation codes such as LEWICE and TRAJICE. The direction and thickness of ice horn are shown to yield similar results compared to the experiments and other codes. In addition, the effects of various parameters - temperature, free-stream velocity, liquid water contents, and droplet diameter - on the ice shape are systematically analyzed through parametric studies.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.43 no.11
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• pp.963-970
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• 2015

In this study, the pressurization characteristics of the small piezoelectric hydraulic pump for a brake system has been analyzed through modeling the full hydraulic pump components; the pump chamber, check valve, pump load, pump drive controller etc. To analyze the pressurization characteristics, the process of charging pressure in the chamber with stacked-layer piezoelectric actuator were firstly modeled. Secondly, the flow coefficient of the check valve in terms of valve opening has been calculated after computational fluid dynamics analysis, such as the pressure distribution around check valve and the flow rate, was conducted. Also the pump driving controller, which controls the input voltage to the actuator, was designed to make the load pressure follow the input pressure command. The simulation results find that it takes about 0.03ms to reach the operating load pressure required for the braking system. The simulation result was also verified through comparison to the result of the pump performance test.

• Journal of Biomedical Engineering Research
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• v.23 no.4
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• pp.295-300
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• 2002

Localized hypoxia, due to the diminished $O_2$supply, is reported to cause necrosis of the arterial cell and to significantly decrease resistances to physiologic distending pressures. In the present study, in order to understand the mechanism of localized hypoxia which might result in the rupture of the aneurysm. $O_2$ transport phenomena across intraluminal thrombus in axisymmetric aneurysms under steady laminar flow condition were numerically analyzed using the Fick's law and the analogy with the fluid-solid heat transfer. For computational models, varying the thickness of intraluminal thrombus, numerical results showed that for the axisymmetric aneurysm with intraluminal thrombus. $O_2$ concentration became minimal at the aneurysm wall. With increased thickness of the intraluminal thrombus in the aneurysm. regions of low $O_2$ concentration were widely distributed near the aneurysm wall, which resulted in the possibility of localized hypoxia. The present study verifis that intraluminal thrombus influences $O_2$ transport to the aneurysm wall. depending on its size and structure.

• Journal of Korean Academy of Oral and Maxillofacial Radiology
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• v.29 no.1
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• pp.203-208
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• 1999

Purpose: This study was to investigate the age and sex differences of the fractal dimension of the normal parotid glands in the digitized CT images. Materials and methods: The six groups. which were composed of 42 men and women from 20 s. 40' sand 60' s and over were picked. Each group contained seven people of the same sex. The normal parotid CT images were digitized. and their fractal dimensions were calculated using Scion Image PC program. Results: The mean of fractal dimensions in males was 1.7292(±0.0588) and 1.6329(±0.0425) in females. The mean of fractal dimensions was 1.7617. in young males 1.7328 in middle males, and 1.6933 in old males. The mean of fractal dimensions was 1.6318. in young females 1.6365 in middle females. and 1.6303 in old females. There was no statistical difference in fractal dimension between left and right parotid gland of the same subject(P>0.05). Fractal dimensions in male were decreased in older group(P<0.05) and larger than female in same age group(P<0.05). But fractal dimensions in female had a tendency to decrease in older group but no statistical difference between ages(P>0.05). Conclusions: The fractal dimension of parotid glands in the digitized CT images will be useful to evaluate the age and sex differences.

• Journal of the Korean Society of Propulsion Engineers
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• v.7 no.3
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• pp.15-21
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• 2003

This experimental study describes the propagation characteristics of the impulse noise emitted from the exit of a perforated pipe attached to the open end of a simple shock tube facility. The pressure amplitudes and directivities of the impulse wave propagating outside from the exit of pipe with several different configurations are measured and analyzed for the range of the incident weak shock wave Mach number between 1.02 and 1.2. In the experiments. the impulse waves are visualized by a Schlieren optical system for the purpose of understanding their propagation characteristics. The results obtained show that for the near sound field the impulse noise strongly propagates toward the pipe axis, but for the far sound field the impulse noise uniformly propagates toward the omnidirections, indicating that the directivity pattern is almost same regardless of the pipe type. For this non-directivity in the far sound field, it is shown that the perforated pipe has little performance to suppress the impulse noise.

• Journal of the Korean Society of Propulsion Engineers
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• v.21 no.4
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• pp.1-11
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• 2017

TPTF (Turbopump Real Propellant Test Facility) at Naro Space Center has used alcohol burner system to simulate the gas flow of gas generator of liquid rocket engine. During the test at TPTF, the temperature and pressure at turbine inlet were smoothly increased while those of the gas generator of engine were constant. Present research developed a simulation code for the burner and the piping system and applied to the system. The calculation results were in good agreement with the test, and confirmed quantitatively that the non-steadiness is due to the heat transfer of the pipe. While the insulation of the pipe is ineffective, the length has a large impact on the turbine inlet condition. The present research clarified the empirically estimation of test condition, and can be applied to determination of the following test conditions.