• Korea-Australia Rheology Journal
• /
• 제21권3호
• /
• pp.161-173
• /
• 2009

This study analyzes especially drag and lift models recently developed for fluid-solid, fluid-fluid or liquid-liquid two-phase flows to understand their applicability on the computational fluid dynamics, CFD modeling of pulsatile blood flow. Virtual mass effect and the effect of red blood cells, RBCs aggregation on CFD modeling of blood flow are also shortly reviewed to recognize future tendencies in this field. Recent studies on two-phase flows are found as very useful to develop more powerful drag-lift models that reflect the effects of blood cell's shape, deformation, concentration, and aggregation.

• Advances in concrete construction
• /
• 제13권5호
• /
• pp.361-365
• /
• 2022

The objective of this study is to simulate the two-phase flow in pipes with various two-fluid models and determinate the shear stress. A hyperbolic shear deformation theory is used for modelling of the pipe. Two-fluid models are solved by using the conservative shock capturing method. Energy relations are used for deriving the motion equations. When the initial conditions of problem satisfied the Kelvin Helmholtz instability conditions, the free-pressure two-fluid model could accurately predict discontinuities in the solution field. A numerical solution is applied for computing the shear stress. The two-pressure two-fluid model produces more numerical diffusion compared to the free-pressure two-fluid and single-pressure two-fluid models. Results show that with increasing the two-phase percent, the shear stress is reduced.

• 대한수학회지
• /
• 제48권4호
• /
• pp.669-689
• /
• 2011

The notion of quasi-Einstein manifolds arose during the study of exact solutions of the Einstein field equations as well as during considerations of quasi-umbilical hypersurfaces. For instance, the Robertson-Walker spacetimes are quasi-Einstein manifolds. The object of the present paper is to study Lorentzian quasi-Einstein manifolds. Some basic geometric properties of such a manifold are obtained. The applications of Lorentzian quasi-Einstein manifolds to the general relativity and cosmology are investigated. Theories of gravitational collapse and models of Supernova explosions [5] are based on a relativistic fluid model for the star. In the theories of galaxy formation, relativistic fluid models have been used in order to describe the evolution of perturbations of the baryon and radiation components of the cosmic medium [32]. Theories of the structure and stability of neutron stars assume that the medium can be treated as a relativistic perfectly conducting magneto fluid. Theories of relativistic stars (which would be models for supermassive stars) are also based on relativistic fluid models. The problem of accretion onto a neutron star or a black hole is usually set in the framework of relativistic fluid models. Among others it is shown that a quasi-Einstein spacetime represents perfect fluid spacetime model in cosmology and consequently such a spacetime determines the final phase in the evolution of the universe. Finally the existence of such manifolds is ensured by several examples constructed from various well known geometric structures.

• 자원환경지질
• /
• 제55권2호
• /
• pp.183-195
• /
• 2022

열수 금광상은 단층대 내에서 일어나는 열수 유체의 폭발적 흐름의 증거이며, 그로 인해 만들어지는 맥의 구조 및 조직은 열수유체 재분배 기작을 반영한다. 본 리뷰 논문에서는 열수 금광상의 형성을 야기하는 지각 내 유체 순환의 기작으로서 석션 펌프와 단층 밸브 모델을 소개하고 단층역학적인 측면에서 검토한다. 석션 펌프와 단층 밸브 모델은 (1) 지구조 응력의 누적과 유체압의 증가, (2) 지진성 단층파열에 따른 지구조 응력의 해소와 유체압의 감소가 주기적으로 발생됨에 따라 단층을 통해 불균질하게 발생하는 유체의 이동 및 맥의 형성 기작이다. 두 기작들이 작동하는 지질학적 환경과 응력 조건은 서로 상이하며, 결과적으로 형성된 맥의 구조 및 조직적 특성은 서로 공통점과 차이점을 가진다. 석션 펌프와 단층 밸브 모델은 향후 한국의 열수 금광상의 구조적 성인을 정교하게 해석하고 추가적인 탐사의 효율성을 제고하는데 유용하게 활용될 수 있을 것으로 판단된다.

• Geomechanics and Engineering
• /
• 제5권2호
• /
• pp.165-185
• /
• 2013

In the present study, the numerical and experimental investigations were performed on the backfill- exterior wall-fluid interaction systems in case of empty and full tanks. For this, firstly, the non-linear three dimensional (3D) finite element models were developed considering both backfill-wall and fluid-wall interactions, and modal analyses for these systems were carried out in order to acquire modal frequencies and mode shapes by means of ANSYS finite element structural analysis program. Secondly, a series of field tests were fulfilled to define their modal characteristics and to compare the results from proposed approximation in the selected structures. Finally, comparing the theoretical predictions from the finite element models to results from experimental measurements, a close agreement was found between theory and experiment. Thus, it can be easily stated that experimental verifications provide strong support for the finite element models and the proposed procedures themselves are the meritorious approximations to the real problem, and this makes the models appealing for use in further investigations.

• 한국전산유체공학회지
• /
• 제14권2호
• /
• pp.46-51
• /
• 2009

The slip effect from the molecular interaction between fluid particles and solid surface atoms plays a key role in microscale fluid transport and heat transfer since the relative importance of surface forces increases as the size of the system decreases to the microscale. There exist two models to describe the slip effect: the Maxwell slip model in which the slip correction is made on the basis of the degree of shear stress near the wall surface and the Langmuir slip model based on a theory of adsorption of gases on solids. In this study, as the first step towards developing a general purpose numerical code of the compressible Navier-Stokes equations for computational simulations of microscale fluid flow and heat transfer, two slip models are implemented into a finite element numerical code of a simplified equation. In addition, a pressure-driven gas flow in a microchannel is investigated by the numerical code in order to validate numerical results.

• 설비공학논문집
• /
• 제15권12호
• /
• pp.1095-1102
• /
• 2003

Flow characteristics of turbulent steady fluid flow past a cylinder in rectangular duct are measured by 5 W laser doppler velocity meter. The fluid flow is also computed by commercial software of STAR-CD for comparison between the measurement and computation. The turbulent models applied in the computations are standard K-epsilon model, RNG K-epsilon model and Chen K-epsilon model. Acurracy of standard K-epsilon model is a little bit better than acurracies of other models even though those models have almost the same order of error compared to measured data. The computations predict satisfactorily the measured velocity profiles at middle section of the circular cylinder before the fluid flow diverges. However, there are some disagreements between them at down stream from the circular cylinder.

• 한국지진공학회논문집
• /
• 제22권7호
• /
• pp.401-409
• /
• 2018

Performance-based seismic evaluation is usually done by considering simplified models for the liquid storage tanks therefore, it is important to validate those simplified models before conducting such evaluation. The purpose of this study is to compare the seismic response results of the FSI (fluid-structure interaction) model and the simplified models for the cylindrical liquid storage tanks and to verify the applicability of the simplified models for estimating failure probability. Seismic analyses were carried out for two types of storage tanks with different aspect ratios (H/D) of 0.45 and 0.86. FSI model represents detailed 3D fluid-structure interaction model and simplified models are modeled as cantilever mass-spring model, frame type mass-spring model and shell type mass-spring model, considering impulsive and convective components. Seismic analyses were performed with modal analysis followed by time history analysis. Analysis results from all the models were verified by comparing with the results calculated by the code and literature. The results from simplified models show good agreement with the ones from detailed FSI model and calculated results from code and literature, confirming that all three types of simplified models are very valid for conducting failure probability analysis of the cylindrical liquid storage tanks.

• 조명전기설비학회논문지
• /
• 제18권5호
• /
• pp.35-41
• /
• 2004

본 연구에서 사용된 방전 기체는 오염물의 제거 및 박막 표면 정제 등의 연구 분야에 응용되고 있는 질소 가스를 사용하였으며, 1차원 동심구 모델의 개발로 인하여, 접지 면적을 넓게 함에 따라 경방향으로의 플라즈마 분포가 중심축의 분포와 동일하다는 1차원적 가정이 적절하지 못하다는 Barnes 모델을 보완할 수 있었다. 일정한 인가 전압하에서는 입체각($\omega$)의 증가에 따라 질소 플라즈마를 구성하는 각 입자의 수밀도 분포, 전계 및 포텐셜이 감소함을 볼 수 있었다. 그러나 면적비가 증가하면서 구동 전극에서의 각 입자들의 움직임은 상대적으로 높은 전계로부터 더욱 활발하게 형성됨에 따라 직렬 연결된 블로킹 콘덴서에서 발생하는 자기 바이어스 전압은 증가하는 것을 알 수 있었다.

• 한국전산유체공학회:학술대회논문집
• /
• 한국전산유체공학회 2003년도 The Fifth Asian Computational Fluid Dynamics Conference
• /
• pp.147-149
• /
• 2003

Using computational fluid dynamics with the fluid-structure interaction, structural effects of intra-luminal thrombus were determined in thrombosed axisymmetric abdominal aorta aneurysm (AAA) models under pulsatile flow. Four different models, varying dilatations of the aneurysm and Young's moduli of intra-luminal thrombus, were defmed. Compared with unthrombosed AAA models, both von Mises stress and radial displacements in the aneurysm wall significantly decreased. Stiffer intra-luminal thrombus reduced von Mises stress in the aneUtysm wall. The present study supported that intra-luminal thrombus might reduce wall stress in the aneurysm.