An experimental evaluation of pre-yield and post-yield rheological models of magnetic field dependent smart materials

N. Mohammadi,M. J. Mahjoob,B. Kaffashi,S. Malakooti 대한기계학회 2010 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.24 No.9

The rheological behavior of field-dependent smart fluids in both the pre-yield and post-yield regimes is investigated. Typical viscoelastic and viscoplastic models are employed to model the fluids behavior. Viscoelastic models are used widely in the pre-yield regime. Viscoplastic models are also used extensively in both the pre-yield and post-yield regimes. Two smart fluids including a ferromagnetic nanoparticle fluid and an MR fluid are examined here. Using an MCR300 rheometer, the rheological properties of the fluids in both oscillation and rotational mode are measured. In the oscillation mode, the storage and loss moduli versus frequency are measured. In the rotational mode, shear stress, shear rate, viscosity and torque are measured. In the frequency domain, the pre-yield behavior of the ferromagnetic nano-particle fluid is modeled by Kelvin-Voigt solid model. Also, the three-parameter fluid model is used to model the pre-yield behavior of the MR fluid. Two viscoplastic models including Bingham-plastic and Herschel-Bulkley models are selected to model the rheological behavior of fluids in the time domain. Which model is more appropriate depends on the external magnetic field and the shear rate. Both models are used here to model the fluids’ behavior. The models properly predict the results observed in the experiments.

Two-fluid non-Newtonian models for blood flow in catheterized arteries - A comparative study

D. S. Sankar,Usik Lee 대한기계학회 2009 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.23 No.9

Steady flow of blood through catheterized arteries is studied by assuming the blood as a two-fluid model with the suspension of all the erythrocytes in the core region as a non-Newtonian fluid and the plasma in the peripheral layer as a Newtonian fluid. The non-Newtonian fluid in the core region of the artery is modeled as (i) Casson fluid and (ii) Herschel-Bulkley fluid. The expressions for the shear stress, velocity, flow rate, wall shear stress and flow resistance, obtained by Sankar and Lee (2008a, 2008b) for the two-fluid Casson model and two-fluid Herschel-Bulkley model are used to get the data for comparison. It is noticed that the plug flow velocity, velocity distribution and flow rate for the two-fluid H-B model are considerably higher than that of the two-fluid Casson model for a given set of values of the parameters. Further, it is found that the resistance to flow is significantly lower for the two-fluid H-B model than that of the two-fluid Casson model. Thus, the two-fluid H-B model is more useful than the two-fluid Casson model to analyze the blood flow through catheterized arteries.

Two-Fluid Model을 이용한 교통신호제어시스템 개선에 따른 거시적 교통류 변화 분석

정영제,김영찬,김대호 대한교통학회 2009 대한교통학회지 Vol.27 No.1

The operational effect of traffic signal control improvement was evaluated using the Two-Fluid Model. The parameters engaged in the Two-Fluid Model becomes good indicators to measure the quality of traffic flow due to the improvement of traffic signal operation. A series of experiment were conduced for the 31 signalized intersections in Uijeongbu City. To estimate the parameters in the Two-Fluid Model, the trajectory informations of individual vehicles were collected using the CORSIM and Run Time Extension. The test results showed 35 percent decrease of average minimum trip time per unit distance. One of the parameters in the Two-Fluid Model is a measure of the resistance of the network to the degraded operation with the increased demand. The test result showed 28 percent decrease of this parameter. In spite of the simulation results of the arterial flow, it was concluded that the Two-Fluid Model is useful tool to evaluate the improvement of the traffic signal control system from the macroscopic aspect. 도로교통망의 시스템변화에 대한 효과분석의 일환으로 1979년 Herman이 제시한 Two-Fluid Model을 적용하여 거시적인 교통류 변화특성을 분석하였으며, 이를 통해 도로시설의 운영개선 효과를 정량적으로 확인하였다. 본 연구에서는 일반국도 3호선 의정부 전체 구간의 약 8km, 총 31개 신호교차로를 분석 대상으로 하며, TSIS CORSIM 및 Run Time Extension을 이용한 미시적 시뮬레이션 분석으로 현황 및 개선 대안에 대한 개별차량의 주행정보를 추출하였다. Two-Fluid Model의 파라메타 산출결과 현황 대비 신호제어시스템 개선 시 네트워크의 서비스 질을 의미하는 단위거리 당 평균최소통행시간(Tm)은 약 35% 감소하였으며, 네트워크 수요증가에 대한 저항성을 의미하는 파라메타 은 약 28%의 향상된 결과를 나타내었다. 국도 축을 대상으로 하는 시뮬레이션 기반의 자료 수집으로 인해 제한된 연구결과이나 Two-Fluid Model이 신호 최적화 및 연동형 반감응제어의 적용 등 신호제어시스템 개선에 대한 우수한 거시적 효과평가 지표로 활용되어 질수 있음을 확인하였다.

Two-fluid Model 파라미터를 활용한 강우에 따른 도시부 네트워크 운영성 및 위험도 변화 분석

이재현,모대상,김선호,이청원 대한토목학회 2020 대한토목학회논문집 Vol.40 No.2

The Two-fluid Model, proposed by Herman and Prigogine in 1979, is a macroscopic model for describing network operability in urban networks. Since the Two-fluid Model parameters change according to the traffic flow characteristics, it is necessary to identify the cause of flow change when analyzing the operability using the parameters. This study compared the crash risk according to rainfall using the Two-fluid Model parameters, and explained that the driving behavior affects the operability of the urban network. The results of the parameters estimation showed poor network operation under rainfall condition. The factors of drivers’ crash risk perception model were calculated, and driving behavior was analyzed due to crash risk according to rainfall. In both the morning and evening, drivers tended to slow down their speeds to reduce the crash risk, because the risk on rainy days could be high when the speed was the same as on a sunny days. However, the crash risk was still higher on rainy days than sunny. In the future, it is necessary to analyze therelationship between the network operation and the crash risk in various networks and to improve both. 1979년 Herman과 Prigogine에 의해 제안된 Two-fluid Model은 도시부 네트워크의 운영성을 설명하는 거시적인 모형으로서 네트워크 내 정지차량 비율과 평균 주행속도의 관계에 기초하고 있다. 이러한 Two-fluid Model의 파라미터는 교통류 특성에 따라 변화하므로 파라미터를 통한 운영성 분석 시 교통류 상태 변화를 규명하는 단계가 수반되어야 한다. 이에 본 연구는 Two-fluid Model의 파라미터를 활용하여 강우에 따른 교통사고 위험도를 비교하였고, 이로 인한 주행 행태가 도시부 네트워크의 운영성에 영향을 미침을 확인하였다. 먼저 Two-fluid Model 파라미터 추정결과, 맑은 날 대비 비가 온 날의 네트워크 운영성이 저하된 것으로 나타났다. 이후 운전자의 교통사고 위험인지 모형 계수를 산출하고 강우 여부에 따른 교통사고 위험도와 그에 따른 주행 행태 변화를 분석하였다. 오전·오후 시간대 모두 운전자는 맑은 날과 동일한 속도를 유지하였을 때 비가 온 날의 교통사고 위험도가 높을 수 있기 때문에, 위험도를 낮추기 위해 주행속도를 감속하는 경향을 보였다. 그러나 맑은 날 보다 비가 온 날의 위험도는 여전히 높은 것으로 파악되었다. 향후에는 도시부 교통망의 거시적 운영성과 사고 위험도 간의 관계를 보다 다양한 네트워크에서 분석하고 동시에 개선할 수 있는 방안을 연구해볼 필요가 있겠다.

Two-Fluid 모형 파라미터 정산의 새로운 접근방안

권영범,이재현,김선호,이청원 대한토목학회 2019 대한토목학회논문집 Vol.39 No.1

The two-fluid model proposed by Herman and Prigogine is useful for analyzing macroscopic traffic flow in a network. The two-fluidmodel is used for analyzing a network through the relationship between the ratio of stopped vehicles and the average moving speed of the network, and the two-fluid model has also been applied in the urban transportation network where many signalized or unsignalized intersections existed. In general, the average travel speed and moving speed of a network decrease, and the ratio of stopped vehicles and low speed vehicles in network increase as the traffic demand increases. This study proposed the two-fluid model considering congested and uncongested traffic situations. The critical velocity and the weight factor for congested situation are calibrated by minimizing theroot mean square error (RMSE). The critical speed of the Seoul network was about 34 kph, and the weight factor of the congestion onthe network was about 0.61. In the proposed model, R2 increased from 0.78 to 0.99 when compared to the existing model, suggestingthat the proposed model can be applied in evaluating network performances or traffic signal operations. Herman과 Prigogine에 의해 제안된 Two-fluid Model은 네트워크에서 거시교통류를 분석하는데 유용하다. Two-fluid Model은 정지차량 비율과 네트워크 평균속도의 관계를 통해 네트워크를 분석하는 것으로, 주로 신호 혹은 비신호교차로가 다수 존재하는 도시부 교통망에 적용되어 왔다. 일반적으로 네트워크의 교통수요가 증가함에 따라 네트워크 내 평균주행속도와 평균통행속도 모두 감소하며, 네트워크 내 정지차량의 비율과 정체로 인한 저속차량의 비율도 증가한다. 본 연구는 정체상황을 고려한 Two-fluid Model을 제안하였다. 정체상황을 구분하는 임계속도와 정체상황이 네트워크에 미치는 가중치는 평균 제곱근 편차(RMSE)를 최소화하도록 값을 정산하여 적용하였다. 서울시 네트워크의 임계속도는 약 34 kph로 나타났으며, 정체상황이 네트워크에 미치는 영향의 가중치는 약 0.61로 나타났다. 본 연구에서 제안한 Model은 기존 Model에 비하여 R2가 0.78에서 0.99로 크게 증가하였으며, 파라미터의 값은 큰 차이를 보이지 않았다. 이는 제안한 Model이 네트워크 및 신호운영 평가에 사용될 가능성이 있음을 의미한다

Probabilistic evaluation of multi-fluid-phase carbon dioxide storage capacities of saline formations in the Pohang Basin, Korea using three-dimensional geologic modeling and grid-based Monte Carlo simulation

Park, Jai-Yong,Lee, Sungho,Kihm, Jung-Hwi,Kim, Jun-Mo,Lee, Yong Il Elsevier 2018 International journal of greenhouse gas control Vol.79 No.-

<P><B>Abstract</B></P> <P>A series of probabilistic evaluation is performed sequentially using three-dimensional geologic modeling and grid-based Monte Carlo simulation as a linked methodology to estimate multi-fluid-phase (i.e., individual gas-, liquid-, supercritical-, and whole fluid-phase) carbon dioxide (CO<SUB>2</SUB>) storage capacities of the target clastic saline formations in the Pohang Basin, Korea. The Pohang Basin is subdivided into the six geologic formations including the two clastic saline formations, which are the sandstone-dominant Fluvial Conglomerate and Sandstone (FCSS) and Shallow Marine Sandstone (SMSS) in ascending order. The results of the three-dimensional geologic modeling show that the six geologic formations are distributed very complicatedly both onshore and offshore with irregular depths and thicknesses, and they are partly dissected and offset by the eight major faults. The two clastic saline formations FCSS and SMSS are deep and thick at the three prospective areas such as Areas 1, 2, and 3 in the modeling domain. The results of the grid-based Monte Carlo simulation show the following three main contents. First, in the two clastic saline formations SMSS and FCSS, CO<SUB>2</SUB> exists as gas, liquid, and supercritical phases with the corresponding distinctive density ranges depending on the pressure and temperature with depth. Second, the theoretical multi-fluid-phase CO<SUB>2</SUB> storage capacities of the SMSS and FCSS all show asymmetric normal distributions. On the other hand, the effective multi-fluid-phase CO<SUB>2</SUB> storage capacities of the saline formations all show log-normal distributions, and their values are much lower than the values of the theoretical multi-fluid-phase CO<SUB>2</SUB> storage capacities. The mean theoretical fluid-phase CO<SUB>2</SUB> storage capacities of the SMSS and FCSS are equal to 2,511.60 Mton and 1,370.91 Mton, respectively. The mean effective fluid-phase CO<SUB>2</SUB> storage capacities of the SMSS and FCSS are equal to 64.19 Mton and 35.32 Mton, respectively. Third, in the SMSS, the grid-wise (elemental) median theoretical and effective multi-fluid-phase CO<SUB>2</SUB> storage capacities are probabilistically higher at Area 1 (mainly as supercritical and liquid phases), intermediate at Area 2 (mainly as liquid and gas phases), and lower at Area 3 (mainly as a gas phase). However, in the FCSS, the grid-wise median theoretical and effective multi-fluid-phase CO<SUB>2</SUB> storage capacities are probabilistically higher at Area 2 (mainly as supercritical and liquid phases), intermediate at Area 1 (mainly as a supercritical phase), and lower at Area 3 (mainly as a gas phase). Finally, four key criteria (parameters) for selecting or ranking the optimal CO<SUB>2</SUB> storage locations are decided by summarizing and analyzing the results of the three-dimensional geologic modeling and grid-based Monte Carlo simulation. On the basis of the four key criteria (parameters), the overall suitability ranks of Areas 1, 2, and 3 for geologic CO<SUB>2</SUB> storage are determined to be the first, second, and third, respectively.</P> <P><B>Highlights</B></P> <P> <UL> <LI> A series of three-dimensional geologic modeling and grid-based Monte Carlo simulation as a linked methodology is presented to evaluate the multi-fluid-phase CO<SUB>2</SUB> storage capacities of the two saline formations in the Pohang Basin. </LI> <LI> The saline formations are distributed very complicatedly with irregular depths and thicknesses and are partly dissected and offset by eight major faults. </LI> <LI> In the saline formations, CO<SUB>2</SUB> exists as gas, liquid, and supercritical phases with the distinctive density ranges depending on the pressure and temperature with depth. </LI> <LI> The theoretical and effective gas-, liquid-, supercritical-, and fluid-phase CO<SUB>2</SUB> storage capacities of the saline formations are evaluated probabilistically and spatially. </LI> <LI>

비선형거동과 구조물유체상호작용을 고려한 취수탑 내진모델의 보수성평가

이계희 ( Gye-hee Lee ),이명규 ( Myoung-kyu Lee ),홍관영 ( Kwan-young Hong ) 한국구조물진단유지관리공학회 2020 한국구조물진단유지관리공학회 논문집 Vol.24 No.6

본 연구에서는 물로 둘러싸인 철근콘크리트 취수탑에 대한 비선형내진해석을 수행하였다. 구조물 주변의 유체를 고려하기 위하여부가질량 및 CEL을 이용한 유체구조물 상호작용 모델을 구성하였다. 이 때 부가질량모델은 음해법을 사용하였고 유체구조물 상호작용 모델은 양해법을 사용하였다. 입력운동은 동일한 인공지진을 재현주기에 따라 500년, 1000년, 2400년에 해당하도록 크기를 조절하였다. 유체를 고려한 모델의 보수성을 평가하기 위하여 유체를 고려하지 않은 모델을 구성하여 참조해로 삼았다. 콘크리트와 철근의 재료모델은 항복후의 비선형 거동을 고려할 수 있도록 선정하였고 ABAQUS를 이용하여 해석을 수행하였다. 해석결과 얻어진 구조물의 가속도응답스펙트럼을 비교한 결과 주변 유체의 영향은 구조물의 기본 진동수에 해당하는 첨두의 진동수와 첨두값의 크기를 감소시키는 것으로 나타났다. 하지만 부가 질량 모델에서는 고차 진동수에 해당하는 첨두값에는 영향을 미치지 못하였다. 유체의 영향을 고려한 단면모멘트는 부가질량모델의 경우 참조모델의 응답에 비하여 크게 증가하였다. 특히 선형거동이 지배적인 작은 크기의 지진응답에 대해서 이러한 증폭이 크게 발생하였다. 유체구조물 상호작용 모델의 경우 낮은 진동수성분을 가진 단면모멘트는 참조모델의 응답에 비하여 증폭이 발생하나, 높은 진동수 성분을 단면 모멘트는 증폭이 발생하지 않았다. 이러한 결과를 종합하여 볼 때 부가질량모델의 보수성이 유체구조물상호작용 모델이 비해 큰 것으로 평가되었다. In this study, series of nonlinear seismic analysis were performed on a reinforced concrete intake tower surrounded by water. To consider the fluid effect around the structure, analysis models were composed using an added mass and CEL approach. At this time, the implicit method was used for the added mass model, and the explicit method was used for the fluid structure interaction model. The input motions were scaled to correspond to 500, 1000, and 2400 years return period of the same artificial earthquake. To estimate the counteractivity of the fluid coupled model, models without fluid effect were constructed and used as a reference. The material models of concrete and reinforcement were selected to consider the nonlinear behavior after yielding, and analysis were performed by ABAQUS. As results, in the acceleration response spectrum of the structure, it was found that the influence of the surrounding fluid reducing the peak frequency and magnitude corresponding to the fundamental frequency of the structure. However, the added mass model did not affect the peak value corresponding to the higher mode. The sectional moments were increased significantly in the case of the added mass model than those of the reference model. Especially, this amplification occurred largely for a small-sized earthquake response in which linear behavior is dominant. In the fluid structure interaction model, the sectional moment with a low frequency component amplifies compared to that of the reference model, but the sectional moment with a high requency component was not amplified. Based in these results, it was evaluated that the counteractivity of the additive mass model was greater than that of the fluid structure interaction model.

Fluid-structure interaction system predicting both internal pore pressure and outside hydrodynamic pressure

Hadzalic, Emina,Ibrahimbegovic, Adnan,Dolarevic, Samir Techno-Press 2018 Coupled systems mechanics Vol.7 No.6

In this paper, we present a numerical model for fluid-structure interaction between structure built of porous media and acoustic fluid, which provides both pore pressure inside porous media and hydrodynamic pressures and hydrodynamic forces exerted on the upstream face of the structure in an unified manner and simplifies fluid-structure interaction problems. The first original feature of the proposed model concerns the structure built of saturated porous medium whose response is obtained with coupled discrete beam lattice model, which is based on Voronoi cell representation with cohesive links as linear elastic Timoshenko beam finite elements. The motion of the pore fluid is governed by Darcy's law, and the coupling between the solid phase and the pore fluid is introduced in the model through Biot's porous media theory. The pore pressure field is discretized with CST (Constant Strain Triangle) finite elements, which coincide with Delaunay triangles. By exploiting Hammer quadrature rule for numerical integration on CST elements, and duality property between Voronoi diagram and Delaunay triangulation, the numerical implementation of the coupling results with an additional pore pressure degree of freedom placed at each node of a Timoshenko beam finite element. The second original point of the model concerns the motion of the outside fluid which is modeled with mixed displacement/pressure based formulation. The chosen finite element representations of the structure response and the outside fluid motion ensures for the structure and fluid finite elements to be connected directly at the common nodes at the fluid-structure interface, because they share both the displacement and the pressure degrees of freedom. Numerical simulations presented in this paper show an excellent agreement between the numerically obtained results and the analytical solutions.

GPS 자료를 활용한 도시부 도로교통망 내 교통사고 위험 인지 계수 분석 및 정지판단속도에 따른 민감도 분석

모대상,이재현,정종우,이청원 대한교통학회 2020 대한교통학회지 Vol.38 No.2

Two-fluid Model, which describes traffic flow in urban road network macroscopically, was mainly used for operational analysis of network. Recently, the studies on driver’s behavior and safety using Two-fluid Model were conducted. Especially, the estimation of the crash risk perception factors was analytically suggested based on the model. Accordingly, this study aimed to validate from the real data that the safety of urban road network could be macroscopically analyzed with the crash risk perception factors. The factors were estimated from digital tachograph data of taxis in Jongno, Seoul and Gangnam, Seoul, and the estimates showed that Gangnam with more average lanes had higher crash probability and Gangnam with less intersections had lower crash severity than Jongno. The results were consistent with the results from the previous studies with other methodologies. Meanwhile, stop speed threshold, which is introduced to accommodate the error in GPS data like digital tachograph, affects the estimation of Two-fluid Model parameters. The crash risk perception factors were also expected to vary with the stop speed threshold, and sensitivity analysis was therefore conducted. As a result, the factors increased with stop speed threshold increasing. In addition, the two factors fluctuated similarly, which implies the existence of the consistent relationship between them. This study estimated the crash risk perception factors of individual regions from taxi digital tachograph data, and verified the possibility of the macroscopic safety analysis in urban road network. The macroscopic studies on the crash risk in urban road network are anticipated in the future based on this study. 도시부 도로망의 교통류를 거시적으로 설명하는 Two-fluid Model은 주로 도로망의 운영성 분석에 활용되었다. 근래에는 Two-fluid Model을 활용한 운전자의 주행 행태와 안전성 관련 연구가 진행되었으며, 특히 해당 모형을 통해 교통사고 위험 인지 계수를 추정할 수 있음이 해석적으로 제시되었다. 이에 본 연구는 교통사고 위험 인지 계수를 활용한 도시부 도로망의 거시적인 안전성 분석이 가능함을 실증 데이터를 통해 확인하고자 하였다. 서울시 종로 지역과 강남 지역의 택시 디지털운행기록계 데이터를 활용하여 교통사고 위험 인지 계수를 추정한 결과, 종로보다 평균 차로 수가 많은 강남에서 교통사고 발생확률이 높았고, 종로보다 교차로 밀도가 낮은 강남에서 교통사고 심각도가 낮았다. 이러한 결과가 타 방법론을 활용한 기존 연구와 일관됨이 확인되었다. 한편, 디지털운행기록계와 같은 GPS 데이터의 오차를 수용하기 위해 도입되는 정지판단속도는 Two-fluid Model 파라미터 추정치에 영향을 준다. 따라서 교통사고 위험 인지 계수들도 정지판단속도에 영향을 받을 것으로 예상되어 민감도 분석을 수행하였다. 그 결과, 정지판단속도가 높아질수록 교통사고 위험 인지 계수들이 증가하는 것으로 나타났다. 또한 두 계수는 유사하게 변동하였으며, 이를 통해 두 계수 사이에 일정한 관계가 존재할 것으로 판단되었다. 본 연구는 택시 디지털운행기록계 데이터로부터 개별 지역의 교통사고 위험 인지 계수를 추정하고, 이를 통해 도시부 도로망의 거시적인 안전성 분석이 가능함을 확인하였다. 본 연구를 기초로 향후 도시부 도로망의 교통사고 위험도에 관한 거시적인 연구가 가능할 것으로 기대된다.

Remedy for ill-posedness and mass conservation error of 1D incompressible two-fluid model with artificial viscosities

김병재,이승욱,김경두 한국원자력학회 2022 Nuclear Engineering and Technology Vol.54 No.11

The two-fluid model is widely used to describe two-phase flows in complex systems such as nuclear reactors. Although the two-phase flow was successfully simulated, the standard two-fluid model suffers from an ill-posed nature. There are several remedies for the ill-posedness of the one-dimensional (1D) two-fluid model; among those, artificial viscosity is the focus of this study. Some previous works added artificial diffusion terms to both mass and momentum equations to render the two-fluid model wellposed and demonstrated that this method provided a numerically converging model. However, they did not consider mass conservation, which is crucial for analyzing a closed reactor system. In fact, the total mass is not conserved in the previous models. This study improves the artificial viscosity model such that the 1D incompressible two-fluid model is well-posed, and the total mass is conserved. The water faucet and Kelvin-Helmholtz instability flows were simulated to test the effect of the proposed artificial viscosity model. The results indicate that the proposed artificial viscosity model effectively remedies the ill-posedness of the two-fluid model while maintaining a negligible total mass error.