• 대한기계학회:학술대회논문집
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• 대한기계학회 2001년도 춘계학술대회논문집E
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• pp.576-581
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• 2001

When a liquid is supplied through a nozzle onto a relatively nonwetting inclined solid surface, a narrow rivulet forms. This work provides novel physical insights into the following phenomena in the rivulet flow that have not been well understood to date. Firstly, the fundamental mechanism behind the transition of a linear rivulet to a droplet flow is investigated. The experiments show that the droplet flow emerges due to the necking of a liquid thread near the nozzle. Based on the observation, it is argued that when the retraction velocity of a liquid thread exceeds its axial velocity, the bifurcation of the liquid thread occurs, and this argument is experimentally verified. Secondly, a discussion on the curved motion of a meandering rivulet is given. This study proposes the contact angle hysteresis as a primary origin of the centripetal force that enables the rivulet's curved motion A simple scaling analysis based on this assumption predicts a radius of curvature which agrees with the experimental observation.

• 설비공학논문집
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• 제13권10호
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• pp.1042-1048
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• 2001

When a liquid is supplied through a nozzle onto a relatively non-wetting inclined solid surface, a narrow rivulet forms. This work provides novel physical insights into the following phenomena in the rivulet flow that have not been well understood to date. Firstly, the fundamental mechanism behind the transition of a linear rivulet to a droplet flow is investigated. The experiments show that the droplet flow emerges due to the necking of a liquid thread near the nozzle. Based on the observation, it is argued that when the axial velocity of a liquid is slower than the retraction velocity of its thread, the bifurcation of the liquid thread occurs, and this argument is experimentally verified. Secondly, a discussion on the curled motion of a meandering rivulet is given. This study proposes the contact angle hysteresis as a primary origin of the centripetal force that enables the rivulet\`s curved motion. A simple scaling analysis based on this assumption predicts a radius of curvature which agrees with the experimental observation.

• 대한의용생체공학회:의공학회지
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• 제21권3호
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• pp.261-271
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• 2000

벽면운동(wall motion)과 임피던스 페이즈앵글(impedance phase angle; 압력파와 유랑파 기아의 위상차)을 고려하여 맥동유동하에 있는 복부대동맥 분기관모델에서 2차원 전산유체해석을 수행하였다. 해석결과 분기광 근처에서응 전단응력의 크기가 매우 급격한 변화를 보임을 관찰하였고 벽면운동은 전단응력의 진폭을 감소시키는 효과를 가져왔다. 임피던스 페이즈 앵글이 음의 값을 향해 갈수록 시간 평균된 벽면 전단응력(mean wall shear stress)의 값은 감소하였으나 진폭(amplitude of wall shear stress)은 오히려 증가하였다. 페이즈앵글의 영향은 평균 벽면전단응력이 영에 근접하는 외벽(outer wall or lateral wall)의 바같쪽으로 휘어지는 부분(curvature site)에서 상대적으로 크게 나타났는데 $-90^{\circ}$ 페이즈앵글(혈류파가 혈압파를 1/4주기 앞서는 경우)일 경우에 $0^{\circ}$의 경우에 비해 평균은 $50\%$정도 감소하였고 진폭은 $15\%$정도의 상승를 나타내었다. 그러므로 고혈압 환자와 같이 큰 음의 페이즈앵글을 갖는 경우, 벽면전단응력의 평균은 낮아지고 시간에 따라 변화량(진폭)은 증가하므로 low and oscillatory wall shear stress 이론에 의하면 동맥경화에 더 민감하게 된다. 비뉴턴유체로 모델링한 경우에는 뉴턴유체의 경우에 비해 벽면전단응력의 평균값이 증가하므로서 동맥경화에 덜 민감하게 된다.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2008년도 춘계학술대회논문집
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• pp.385-388
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• 2008

The objective of this paper is simulating blood flow through the branched and stenotic tube numerically. SC-Tetra, which is one of the commercial code using FVM method, was utilized for this analysis. The flow is assumed as an incompressible laminar flow with the additional condition of non-Newtonian fluid. As the constitutive equation for the fluid viscosity, the following models were solved with governing equations ; Cross Model, Modified Cross Model, Carreau Model and Carreau-Yasuda Model. Final goal was achieved to get analytic data about shear stress, at specific points, changing the geometry with various factors like the bifurcation angle, diameter of the branches, the ratio of stenosis, and etc. The material property of blood was referred from the related papers. Furthermore, to verify results they were compared with those of the published papers. There were some discrepancies based on the different solver and the different data post-processing method. However, many parameters like the location of low shear stress, which arised from bifurcation or stenosis, and the tendency of various factors were found to be very similar.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2001년도 추계학술대회논문집 II
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• pp.799-804
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• 2001

Nonlinear normal mode (NNM) vibration, in a nonlinear dual mass Hamiltonian system, which has 6th order homogeneous polynomial as a nonlinear term, is studied in this paper. The existence, bifurcation, and the orbital stability of periodic motions are to be studied in the phase space. In order to find the analytic expression of the invariant curves in the Poincare Map, which is a mapping of a phase trajectory onto 2 dimensional surface in 4 dimensional phase space, Whittaker's Adelphic Integral, instead of the direct integration of the equations of motion or the Birkhotf-Gustavson (B-G) canonical transformation, is derived for small value of energy. It is revealed that the integral of motion by Adelphic Integral is essentially consistent with the one obtained from the B-G transformation method. The resulting expression of the invariant curves can be used for analyzing the behavior of NNM vibration in the Poincare Map.

• 전자공학회논문지
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• 제53권3호
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• pp.151-159
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• 2016

본 연구의 목적은 가돌리늄 조영제를 사용한 Head & Neck MR Angio검사에 있어서 매개변수인 FA(Flip Angle)이 MR신호에 미치는 영향에 대해서 알아보고자 하였으며, 이에 따른 FA의 적정 값을 제시하는 것이다. 실험은 FA증가에 따른 MR팬텀실험과 임상실험으로 진행하였고, 이에 대한 정량적 분석이 이루어졌다. 실험결과 팬텀실험에서의 조영증강 반응시작 지점인 RSP(Reaction Starting Point)는 FA증가에 따라 300~400 mmol 사이에서 반응하였고, 최대 신호강도인 MPSI(Max Peak Signal Intensity)는 2,086, 3,705, 5,109, 6,194, 7.096, 7,192 [a.u]를 기록하였다. MPSI가 형성되는 몰농도 지점인 MPP(Max Peak Point)는 FA에 증가에 따라 40, 50, 50, 40, 50, 40 mmol에서 보였으며, MPSI의 증가율인 IRMPSI(Increase Rate of MPSI)는 77.6%, 37.9%, 21.2%, 14.6%, 1.4%임을 확인하였다. 임상실험에서의 평가기준인 SICB(Signal Intensity of Carotid artery Bifurcation)는 FA증가에 따라 각 평균값 2392.5, 4165.2, 4270, 3502.2, 3263.7, 3119.6 [a.u]를 기록하였고, 아티팩트 발생율인 ORA(Occurence Rate of Artifact)는 0, 0, 20, 40, 50, 70%로 점차 증가하였다. 본 연구를 통하여 FA의 증가는 혈관 내 가돌리늄과 결합한 H1스핀의 신호강도와 아티팩트에 영향을 미친다는 사실을 확인하였고, 이는 실제 임상에서의 CE(Contrast Enhanced)-Head&Neck MR Angio검사에 있어서 본 연구의 데이터를 활용한다면 진단학적으로 효율적인 MR Angiography 영상을 구현할 수 있을 것으로 사료된다.

• 대한자기공명의과학회:학술대회논문집
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• 대한자기공명의과학회 2001년도 제6차 학술대회 초록집
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• pp.136-136
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• 2001

Purpose： Subclavian steal refers to the retrograde flow of blood in a vertebral artery that supplies t ipsilateral shoulder and arm caused by proximal subclavian artery stenosis or occlusion. T purpose of this exhibit is to demonstrate MR findings of subclavian steal on contrast-enhanc 3D (CE 3DMRA) and 2D TOF MR angiography. Method： Four patients(men 3 and women 1, age： 28-78years) with subclavian steal obtained both CE 3DMRA and digital subtraction angiography(DSA) including subclavian arterie Sequential imaging was undertaken during first pass after double dose of Gd-DTPA (0 mM/kg) Injected by a power injector. Coronal source images were obtained with coronal D-fast low angle shot sequence(TR/TE/flip angle=3.8/l.3/35, acquisition time= 10sec/one measurement). Precontrast imaging was subtracted from enhanced images and maximu intensity projection was done. 2D time-of-flight MR angiography(2D TOF) of the carot bifurcation was added in all cases with post-saturation. All studies were review retrospectively.

• 대한기계학회논문집B
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• 제36권2호
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• pp.153-159
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• 2012

협착이 발생된 관상동맥의 치료를 위해 외과적인 수술방법으로는 이식우회로술이 많이 사용된다. 이식우회로술 시술 시 개존율 향상을 위해서는 최적의 혈관 문합 시술에 대한 연구가 필요하다. 본 연구의 목적은 Y-grafting bypass 와 T-grafting bypass 시술의 효과와 분지각도 및 문합각도 변화에 따른 문합효과를 분석하였다. 이를 위해 기하학적 형상을 최적화하고 각각의 기하학적 형상에 대해 혈류역학적 특성을 비교분석하였다. 이식혈관의 분지각도와 문합각도가 각각 $30^{\circ}$와 $15^{\circ}$일 경우에 LAD 와 LCX 쪽 모두 혈류량이 고르게 분배됨을 확인하였다.

• International Journal of Air-Conditioning and Refrigeration
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• 제10권3호
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• pp.147-152
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• 2002

When a liquid is supplied through a nozzle onto a relatively non-wetting inclined solid surface, a narrow rivulet forms. There exist several regimes of rivulet flow depending on various flow conditions. In this paper, the fundamental mechanism behind the transition of a linear rivulet to a droplet flow is investigated. The experiments show that the droplet flow emerges due to the necking of a liquid thread near the nozzle. Based on the observation, it is argued that when the retraction velocity of a liquid thread exceeds its axial velocity, the bifurcation of the liquid thread occurs, and this argument is experimentally verified.

• 대한물리치료과학회지
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• 제6권4호
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• pp.153-165
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• 1999

The transcranial Doppler(TCD) is a technique for measuring blood flow velocity of intracranial and extarcranial arteries. This examination based on Doppler effect which was first formulated in 1842 by the Austrian physicist Christian Doppler. In 1982, Rune Aaslid first maked 2MHz pulsed probe and recording intracranial vessels with transcranially. There are six criteria utilized in gaining positive identification of the intracranial vessels. The six criteria are as follows l)acoustical windows 2)depth of sample volume 3)direction of flow 4)spatial relationship of ACA and MCA bifurcation 5)mean velocity and 6)response common carotid artery compression and/or oscillation test. The affected factors for TCD examination are angle of insonation, posture of subject, age, gender, hematocrit, metabolic factors, and cardiac output. Clinical application of TCD are detection of stenosis, occlusion, emboli, thrombsis in intracranial and extracranial arteries and evaluation of cerebral arterovenous malformation, collateral capacity in the circle of Willis, ischemia cerebrovascular disease, stroke patient and vertebrobasilar system.