• 한국기계가공학회지
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• 제3권1호
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• pp.84-89
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• 2004

This study is a basic one for application of ER Fluid to fluid power systems. By mixing silicone oil with zeolite particles, four kinds of ER fluids were made, in which the weight ratio of zeolite particles are different. We examined how the Yield shear stress and Bingham characteristics of the ER fluids are effected by varying electric field intensity. We designed and constructed a disk type power transmission clutch in which ER fluid fills and this ER fluid transmits the power of drive shaft to the driven shaft. With this equipment, the revolution transmission ratio from the chive shaft to the driven shaft by varying electric field density of the ER fluid was examined.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2000년도 춘계학술대회논문집
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• pp.1298-1302
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• 2000

Electrorheological(HER) and magnetorheologica(MR) fluids have a unique ability to increase the dynamic yield stress of the fluid substantially when electric or magnetic field is applied. ER and MR fluid-based dampers are typically analyzed using Bingham-plastic shear flow analysis under Quasi-steady fully developed flow conditions. An alternative perspective, supported by measurements reported in the literature, is to allow for post-yield shear thinning and shear thickening. To model these, the constant post-yield plastic viscosity in Bingham model can be replaced with a power-law model dependent on shear strain rate that is known as the Herschel-Bulkley fluid model. The objective of this paper is to predict the damping forces analytically in a typical ER bypass damper for variable electric field, or yield stress using Herschel-Bulkley analysis.

• 한국유체기계학회 논문집
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• 제4권4호
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• pp.37-42
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• 2001

In the present study, flow characteristics of turbulent oscillatory flow in an oscillator connected to square-sectional $180^{\circ}$ curved duct are investigated experimentally. In order to investigate wall shear stress and pressure distributions, the experimental studies for air flows we conducted in a square-sectional $180^{\circ}$ curved duct by using the LDV system with the data acquisitions and the processing system. The wall shear stress at bend angle of the $150^{\circ}$ and pressure distribution of the inlet (${\phi}=0^{\circ}$) to the outlet (${\phi}=180^{\circ}$) by $10^{\circ}$ intervals of the duct are measured. The results obtained from the experiment are summarized as follows : wall shear stress values in the inner wall we larger than those in an outer wall, except for the phase angle (${\omega}t/{\pi}/6$) of 3, because of the intensity of secondary flow. The pressure distributions are the largest in accelerating and decelerating regions at the bend angle(${\phi}$) of $90^{\circ}$ and pressure difference of inner and outer walls is the largest before and after the ${\phi}=90^{\circ}$.

• 한국공작기계학회논문집
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• 제16권2호
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• pp.100-105
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• 2007

Electro-rheological(ER) fluid and valve are fabricated and evaluated experimentally in its durability to utilize the hydraulic control systems for long term operation. The two-ports ER valve used in the experiment consist of twelve parallel multi-layer electrodes and provide a restriction to the passage of ER fluid because of the viscous pressure drop and a component induced by the electric field. The durability test of ER valve are performed by measuring the surface roughness of electrodes with variation of an electric field strength and test time(1000 or 1800min.). Also, the shear stress and shear rate are measured to evaluate the durability of ER fluid as function of time. After durability test, ER shear stress increases approximately proportional to the shear rate with applied electric field intensity, In the ER valve, the center line average height roughness(Ra) of copper electrode increases about 1.56 times and ten-point median height roughness(Rz) increases about 2.2 times after the durability test. An understanding of these durability is essential to predicting the service life of ER fluid and valves.

• 한국기계가공학회지
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• 제2권3호
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• pp.48-55
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• 2003

This study investigates the effect of temperature and electric field strength on the Bingham characteristics of Electro-Rheological(ER) fluids which change their Yield shear stress and viscosity by temperature and electric field strength. It is found that under constant temperature the Yield sheal stress and viscosity of ER fluids proportionally increase with the applied electric field strength, and under constant applied electric field strength the Yield shear stress and viscosity of ER fluids decrease with the increasing temperature. These results are considered to be applied to the fluid and pneumatic power industry.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2005년도 춘계학술대회논문집
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• pp.350-355
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• 2005

This paper presents a new approach for hysteresis modeling of a magnetorheological (MR) fluid. The field-dependent hysteresis of MR fluid is investigated using the Preisach model. The commercial MR Product (MRF-132LD, Lord Corporation) is employed. Its field-dependent shear stress is then obtained using a rheometer (MCR 300, Physica). In order to show the applicability of the Preisach model to the MR fluid, two significant Properties; the minor loop property and the wiping-out property are experimentally examined. Subsequently, the Preisach model for the MR fluid is identified using experimental first order descending (FOD) curves in discrete manner. The effectiveness of the identified hysteresis model is verified in the time domain by comparing the predicted field-dependent shear stress with the measured one. In addition, the hysteresis model proposed in this work is compared to Bingham model.

• 한국소음진동공학회논문집
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• 제16권1호
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• pp.3-11
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• 2006

This paper presents a new approach for hysteresis modeling of a magnetorheological (MR) fluid. The field-dependent hysteresis of MR fluid is investigated using the Preisach model. The commercial MR product (MRF-132LD, Lord Corporation) is employed. Its field-dependent shear stress is then obtained using a rheometer (MCR 300, Physica). In order to show the applicability of the Preisach model to the MR fluid, two significant properties; the minor loop property and the wiping-out. property are experimentally examined. Subsequently, the Preisach model for the MR fluid is identified using experimental first order descending (FOD) curves in discrete manner. The effectiveness of the identified hysteresis model is verified in the time domain by comparing the predicted field-dependent shear stress with the measured one. In addition, the hysteresis model proposed in this work is compared to Bingham model.

• KSTLE International Journal
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• 제2권1호
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• pp.71-74
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• 2001

The electrorheological(ER) performance of a chitosan sebaciate suspension in silicone oil was investigated by varying the electric fields, volume fractions of particles, and shear rates, respectively. The chitosan sebacicate susepnsion showed a typical ER response caused by the polarizability of an amide polar group and shear yield stress due to the formation of multiple chains upon application of an electric field. The shear stress for the suspension exhibited a linear dependence on the volume fraction of particles and an electric field power of 1.88. On the basis of the results, the newly synthesized chitosan sebacicate suspension was found to be an anhydrous ER fluid.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2000년도 춘계 학술대회논문집
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• pp.27-32
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• 2000

In this study, the three-dimensional blood flow within the sac of KTAH(Korean artificial heart) is simulated using fluid-structure interaction model. The numerical method employed in this study is the finite element commercial package ADINA. The thrombus formation is one of the most critical problems in KTAH. High fluid shear stress or stagnated flow are believed to be the main causes of these disastrous phenomenon. We solved the fluid-structure interaction between the 3D blood flow in the sac and the surrounding sac material. The sac material is assumed as linear elastic material and the blood as incompressible viscous fluid. Numerical solutions show that high shear stress region and stagnated flow are found near the upper part of the sac and near the comer of the outlet during diastole stage.

• Journal of Korean Neurosurgical Society
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• 제61권6호
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• pp.689-699
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• 2018

Objective : The goal of this study was to compare several parameters, including wall shear stress (WSS) and flow pattern, between unruptured and ruptured anterior communicating artery (ACoA) aneurysms using patient-specific aneurysm geometry. Methods : In total, 18 unruptured and 24 ruptured aneurysms were analyzed using computational fluid dynamics (CFD) models. Minimal, average, and maximal wall shear stress were calculated based on CFD simulations. Aneurysm height, ostium diameter, aspect ratio, and area of aneurysm were measured. Aneurysms were classified according to flow complexity (simple or complex) and inflow jet (concentrated or diffused). Statistical analyses were performed to ascertain differences between the aneurysm groups. Results : Average wall shear stress of the ruptured group was greater than that of the unruptured group (9.42% for aneurysm and 10.38% for ostium). The average area of ruptured aneurysms was 31.22% larger than unruptured aneurysms. Simple flow was observed in 14 of 18 (78%) unruptured aneurysms, while all ruptured aneurysms had complex flow (p<0.001). Ruptured aneurysms were more likely to have a concentrated inflow jet (63%), while unruptured aneurysms predominantly had a diffused inflow jet (83%, p=0.004). Conclusion : Ruptured aneurysms tended to have a larger geometric size and greater WSS compared to unruptured aneurysms, but the difference was not statistically significant. Flow complexity and inflow jet were significantly different between unruptured and ruptured ACoA aneurysms.