• Journal of Mechanical Science and Technology
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• v.15 no.5
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• pp.613-622
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• 2001

Interaction of blood flow and leaflet behavior in a bileaflet mechanical heart valve was investigated using computational analysis. Blood flows of a Newtonian fluid and a non-Newtonian fluid with Carreau model were modeled as pulsatile, laminar, and incompressible. A finite volume computational fluid dynamics code and a finite element structure dynamics code were used concurrently to solve the flow and structure equations, respectively, where the two equations were strongly coupled. Physiologic ventricular and aortic pressure waveforms were used as flow boundary conditions. Flow fields, leaflet behaviors, and shear stresses with time were obtained for Newtonian and non-Newtonian fluid cases. At the fully opened phase three jets through the leaflets were found and large vortices were present in the sinus area. At the very final stage of the closing phase, the angular velocity of the leaflet was enormously large. Large shear stress was found on leaflet tips and in the orifice region between two leaflets at the final stage of closing phase. This method using fluid-structure interaction turned out to be a useful tool to analyze the different designs of existing and future bileaflet valves.

• 제어로봇시스템학회:학술대회논문집
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• 1997.10a
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• pp.1754-1757
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• 1997

Three-dimensional optimum design of coat-hanger die is performed using power-law and Carreau models. It is found that the three-dimensional optimum design algorithm shows good convergence with the non-Newtonian fludis. the nore realistic optimum design is accomplished by employing Carreau model with the three-dimensional design method. The effect of vixcosity modles is investigated by comparing the optimum manifold profiles and flow rate distributions of power-law and Carreau modles. Through the accurated viscosity representation of Carreau model, the effect of total flow rate on the optimum manifold profile is investigated.

• Journal of the Korean Society for Industrial and Applied Mathematics
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• v.16 no.3
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• pp.169-180
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• 2012

The steady hydromagnetic flow of an electrically conducting non-Newtonian fluid due to the rotation of an infinite disk is studied with heat transfer with the inclusion of the ion slip as well as Ohmic heating. The governing nonlinear momentum equations and energy equations are solved using the finite difference method. The numerical results indicate the important effect of the ion slip and the non-Newtonian fluid characteristics on the velocity and temperature distributions.

• 한국전산유체공학회:학술대회논문집
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• 2008.03a
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• pp.177-180
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• 2008

The objective of this study is to get simulation data about pulsatile flow of a non-Newtonian fluid through a bifurcated tube. All the process was based on CFD method, with a commercial FVM code, SC/Tetra ver. 6.0 for solving, and with CATIA R16 for generating geometries. To define a non-Newtonian fluid, the following viscous models are used; the Powell-Eyring model, the modified Powell-Eyring model, the Cross model, the modified Cross model, the Carreau model, the Carreau-Yasuda model and the modified Power Law model. The flow calculation data using each model were compared with the other data of a existing paper. Finally, the Carreau model was recognized to give the best result with the SC/Tetra code, and the succeeding simulations are made with the model. For the pulsating flow condition, the sine wave type velocity profile is given as the inlet boundary condition. To investigate the effect of geometries and mesh, the pre-test is carried out with various curvature conditions of the bifurcated corner, and then with various mesh conditions. The final process is to calculate flow variables such as the wall shear stress (WSS) and the wall shear stress gradient (WSSG). To validate all the result, the simulation is compared with the existing data of the other papers. Generally speaking, there is a noticeable difference in the maximum and minimum value of WSS. It is not sure that the values in each data are on the exactly same location. However, the overall trend is similar. The next study needs to investigate the same situation by experimental method. Furthermore, if the flow is simulated with more pulsatile conditions, more data of flow field through a bifurcated tube could be achieved.

• 한국전산유체공학회:학술대회논문집
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• 2008.10a
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• pp.177-180
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• 2008

The objective of this study is to get simulation data about pulsatile flow of a non-Newtonian fluid through a bifurcated tube. All the process was based on CFD method, with a commercial FVM code, SC/Tetra ver. 6.0 for solving, and with CATIA R16 for generating geometries. To define a non-Newtonian fluid, the following viscous models are used; the Powell-Eyring model, the modified Powell-Eyring model, the Cross model, the modified Cross model, the Carreau model, the Carreau-Yasuda model and the modified Power Law model. The flow calculation data using each model were compared with the other data of a existing paper. Finally, the Carreau model was recognized to give the best result with the SC/Tetra code, and the succeeding simulations are made with the model. For the pulsating flow condition, the sine wave type velocity profile is given as the inlet boundary condition. To investigate the effect of geometries and mesh, the pre-test is carried out with various curvature conditions of the bifurcated corner, and then with various mesh conditions. The final process is to calculate flow variables such as the wall shear stress (WSS) and the wall shear stress gradient (WSSG). To validate all the result, the simulation is compared with the existing data of the other papers. Generally speaking, there is a noticeable difference in the maximum and minimum value of WSS. It is not sure that the values in each data are on the exactly same location. However, the overall trend is similar. The next study needs to investigate the same situation by experimental method. Furthermore, if the flow is simulated with more pulsatile conditions, more data of flow field through a bifurcated tube could be achieved.

• Journal of computational fluids engineering
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• v.22 no.1
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• pp.95-102
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• 2017

Debris flow is a composition of solid objects of various sizes, suspension and water, which occurs frequently as the results of landslide following heavy rainfall. This often causes extensive damage in the form of socio-economic losses and casualties as witnessed during the incident around Mt. Umyeon, Seoul in 2011. There have been numerous investigation to mitigate the impacts from debris flow; however, the estimation as preparedness measure has not been successful due to nonlinear and multiphase characteristics of phenomena both in material and process inherent in the debris flow. This study presents a numerical approach to simulate the debris flow using open source code of computational fluid dynamics, OpenFOAM with non-Newtonian viscosity model for three phase material modeling. In order to validate the proposed numerical method, the quantitative evaluations were made by comparisons with experimental results and qualitative analysis for the dispersion characteristics was carried for the case of debris flow in the actual incident from Mt. Umyeon.

• Proceedings of the Korea Water Resources Association Conference
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• 2015.05a
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• pp.339-339
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• 2015

우리나라는 매년 하절기에 급격한 강우로 인해 홍수의 발생빈도가 급격히 높아지고 있다. 이러한 홍수 발생으로 인한 재산 인명의 피해는 연평균 약 2조억원에 달하고 있다. 이러한 홍수 피해를 방지하기 위해 다양한 연구를 하고 있으며 본 연구에서는 홍수 흐름의 정확한 예측을 통해 홍수 피해 저감을 목표로 하고 있다. 기존의 연구에서는 홍수 흐름 예측을 하는데 있어 부정류 상태로 흐르는 홍수량에 따른 범람의 위치와 범위를 산정하는 것에 중점을 두었다. 그러나 홍수의 흐름은 물에 토사가 섞여 흐르는 혼합체의 흐름이기 때문에 홍수위 모의하는데 있어 물성치도 고려되어야 한다. 이러한 물성치 변화에 따라 홍수 흐름도 영향을 받을 것이라 생각하여 본 연구를 수행하였다. 본 연구에서 Non-Newtonian 특성을 고려하기 위해 Non-Newtonian 흐름과 일반적인 홍수 모의가 가능한 수치모형을 사용하였다. 사전 연구로 일반 사행수로 형태를 구성하고 사행수로에서의 흐름 물질을 달리하여 흐름 모의를 수행하였다. 흐름물질은 크게 물과 토석류로 나뉘고 토석류는 항복응력과 점성 등을 달리하였다. 또한 다양한 유량으로 흐름 모의를 하여 흐름 범람 시의 특징도 비교해 볼 수 있었다. 모의 결과 사행수로에서 흐름의 차이를 볼 수 있었으며 다양한 형태로 결과를 분석해 보았다. 흐름의 속도와 수심을 다양한 흐름 단면으로 비교하였고 범람되는 지역의 범위와 위치도 비교해 볼 수 있었다. 이러한 흐름 특성은 사행수로에서 곡률이 있는 부분에서 확실하게 확인할 수 있었으며, 홍수 흐름을 모의할 때 Non-Newtonian 특성과 같이 흐름에 영향을 미칠 수 있는 다른 특성에 대해도 고려해야 한다는 연구 가능성을 제시할 수 있었다.

• The KSFM Journal of Fluid Machinery
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• v.17 no.6
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• pp.29-37
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• 2014

Non-Newtonian fluid mechanics takes charge of an important role in the oil industries. Especially in the oil well drilling process, the drilling fluid such as mud keeps the drill bit cool and clean during drilling, with suspending drill cuttings and lubricating a drill bit. The purpose of this study is to examine the effect of fluid mud rheological properties to predict different characteristics of non-Newtonian fluid in the mud mixing tank on offshore drilling platforms. In this paper, ANSYS fluent package was used for the simulation to solve the hydrodynamic force and to evaluate mud mixing time. Prediction of the power consumption and the pumping effectiveness has been presented with different operating fluid models as Newtonian and non-Newtonian fluid. The comparison between Newtonain mud model and non-Newtonian mud model is confirmed by the CFD simulation method of drilling mud mixing tank. The results present useful information for the design of the drilling mud mixing tanks and provide some guidance on the use of CFD tool for such non-Newtonian fluid flow.

• 한국전산유체공학회:학술대회논문집
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• 2008.03a
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• pp.181-185
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• 2008

In this study, we attempted to quantify the relative importance of assumptions regarding blood rheology. Three patient-specific carotid bifurcation geometries and time-varying flow rates were obtained using magnetic resonance imaging. For each subject, CFD simulations were carried out assuming two different non-Newtonian rheology models Carreau and Ballyk models) and rescaled Newtonian viscosities based on characteristic shear rates to account for the shear-thinning property of blood. The sensitivity of WSS and oscillatory shear index (OSI) were contextualized with respect to the reproducibility of the reconstructed geometry and to assumptions regarding the inlet boundary conditions. We conclude that the assumption of Newtonian fluid is reasonable for studies aimed at quantifying the distribution of WSS-based extrema in an image-based CFD model of carotid bifurcation.

• 한국전산유체공학회:학술대회논문집
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• 2008.10a
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• pp.181-185
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• 2008

In this study, we attempted to quantify the relative importance of assumptions regarding blood rheology. Three patient-specific carotid bifurcation geometries and time-varying flow rates were obtained using magnetic resonance imaging. For each subject, CFD simulations were carried out assuming two different non-Newtonian rheology models (Carreau and Ballyk models) and rescaled Newtonian viscosities based on characteristic shear rates to account for the shear-thinning property of blood. The sensitivity of WSS and oscillatory shear index (OSI) were contextualized with respect to the reproducibility of the reconstructed geometry and to assumptions regarding the inlet boundary conditions. We conclude that the assumption of Newtonian fluid is reasonable for studies aimed at quantifying the distribution of WSS-based extrema in an image-based CFD model of carotid bifurcation.