• Smart Structures and Systems
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• v.16 no.5
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• pp.961-980
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• 2015

Magnetorheological (MR) fluids are capable of changing their rheological properties under the application of external fields. When MR fluids operate in the so-called squeeze mode, in which displacement levels are limited to a few millimetres but there are large forces, they have many potential applications in vibration isolation. This paper presents an experimental and a numerical investigation of the performance of an MR fluid under tensile and compressive loads and oscillatory squeeze-flow. The performance of the fluid was found to depend dramatically on the strain direction. The shape of the stress-strain hysteresis loops was affected by the strength of the applied field, particularly when the fluid was under tensile loading. In addition, the yield force of the fluid under the oscillatory squeeze-flow mode changed almost linearly with the applied electric or magnetic field. Finally, in order to shed further light on the mechanism of the MR fluid under squeeze operation, computational fluid dynamics analyses of non-Newtonian fluid behaviour using the Bingham-plastic model were carried out. The results confirmed superior fluid performance under compressive inputs.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.16 no.7 s.112
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• pp.754-761
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• 2006

This paper presents the dynamic characteristics of MR impact damper for vehicle collision system. Various types of mechanism have been proposed to reduce force transmitted to the vehicle chassis and finally to protect occupants from injury. In the case of head-on collision, the bumper makes main role of isolation material for collision attenuation. In this study, the proposed bumper system consists of MR impact damper and structures. The MR impact damper utilizes MR fluid which has reversible properties with applied magnetic field. The MR fluid operates under flow mode. The bellows is used for generation of fluid flow. A mathematical model of the MR impact damper is derived incorporating with Bingham model of the MR fluid. Field dependent damping force is investigated with time and frequency domain. The MR impact damper is then incorporated with vehicle crash system. The governing equation of motion of vehicle model is formulated considering occupant model. Dynamic characteristics of vehicle collision system investigated with computer simulation.

• Computers and Concrete
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• v.2 no.2
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• pp.97-110
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• 2005

Rheological behaviour of fresh concrete is an important factor in controlling concrete quality. It is recognized that the measurement of the slump is not a sufficient test method to adequately characterize the rheology of fresh concrete. To further understand the slump measurement and its relationship to the rheological properties, an elasto-viscoplastic, 2-D axisymmetric finite element (FE) model is developed. The FE model employs the Bingham material model to simulate the flow of a slump test. An experimental program is carried out using the Slump Rate Machine (SLRM_II) to evaluate the finite element simulation results. The simulated slump-versus-time curves are found to be in good agreement with the measured data. A sensitivity study is performed to evaluate the effects of yield stress, plastic viscosity and cone withdrawal rate on the measured flow curve using the FE model. The results demonstrate that the computed yield stress compares well with reported experimental data. The flow behaviour is shown to be influenced by the yield stress, plastic viscosity and the cone withdrawal rate. Further, it is found that the value of the apparent plastic viscosity is different from the true viscosity, with the difference depending on the cone withdrawal rate. It is also confirmed that the value of the final slump is most influenced by the yield stress.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.25 no.12
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• pp.1684-1691
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• 2001

Electrorheological fluids(ERFs) show a rapid and reversible increase in apparent viscosity by applied electric field. It is called the electrorheological effect (ER effect). The reason for ER effect is the induction of an electric dipole in each particle, leading to the formation of clusters in the direction of the field, which resist fluid flow. Generally, the behavior of ER fluids has been modeled on those of Bingham fluids. But there are some differences between Bingham fluids and ER fluids. The visualization of ER fliuds are presented and ER effects by the forming, growing and breaking of clusters are discussed. In the low shear rate area, the pressure drop is measured by a pressure sensor and the formation of ER particles is visualized by video camera. The reason for the nonlinear behavior of ER fluids at low shear rate is explained through results of visualization. As result, the behavior of ER fluids is nonlinear at low shear rate with overshoot area because it is different to from the clusters according to the strength of electric field. The gap of electrodes becomes narrow because of the cluster layer occurrence near to electrodes in any conditions.

• Korean Journal of Fisheries and Aquatic Sciences
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• v.28 no.4
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• pp.397-400
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• 1995

Effects of rheological parameters, such as shear rate, temperature, concerntration, salts on the apparent viscosity of chitosan(deacetylation degree: $84\%$, Mw: 267,000) dissolved in acetate buffer(pH 4.5) were investigated. Rheologiral properties of chitosan solution from cuticle of red snow crab (Chinonecetes japonicus) are as follows. $0.5\%$ chitosan in 0.1M acetate buffer (pH 4.5) solution showed Bingham flow having hysteresis loop. It's flow equation was $\sigma=0.757+19.6_\gamma(r^2=0.99)$. The viscosity of chitosan solution is exponentially increased with its concentration, and showed Arrhenius dependence with respect to the temperature $(10^{\circ}C-40^{\circ}C).$ When various salts were added to chitosan solution, the viscosity decreased as the concentration of counterion increased. But the type ot counterions itself does not have any significant effects on the viscosity.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2007.11a
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• pp.265-266
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• 2007

• Geotechnical Engineering
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• v.13 no.5
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• pp.125-132
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• 1997

It is observed that debris mitred with a wide range of soil particles and water moves downwards like viscous fluid soon after a landslide has triggered. An Assumption can be made from the field observation that the debris flow behaves as a kind of non(non-Newtoniron) Newtonian fluid which has non linear viscosity. In this study, a series of viscosity tests are carried out to measure rheological properties of debris by using a viscometer with semples taken from a landslide site. It is proved that debris flows behave as Bingham plastic mod el of non-Newtonian fluid. This model can be used predict the movement of debris flows.

• The Korean Journal of Rheology
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• v.10 no.1
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• pp.31-37
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• 1998

전기장이 인가되고 있는 유로를 유동하는 전기유변유체의 기본성질을 파악하기 위 한 실험 및 해석적 연구를 수행하여 빙햄유체로서의 유효성에 대해 알아보고 전기장과 유로 면 형상 및 진동유동으로 인한 영향에 대해 조사함으로써 ER밸브 및 ER대퍼로의 응용과 관련한 감쇄력 제어에 대해 검토하였다. 첫 번째 실험은 ER밸브의 높이가 2mm인 적극면이 평탄한것과 요철로 된 것을 사용하여 압력손실을 압력변환기로 측정함으로써 전기장 및 유 로형상에 대한 영향을 알아보았다. 압력손실 및 전단응력이 전기자세기와 함수관계를 가짐 을 알수 있었고 전기장세기와 유속의 변화시 손실계수에 의한 ER효과의 상이함이 확인되었 으며 레이놀즈수가 커지면 항복전단응력의 영향은 나타나지 않았다. 두 번째 실험은 실린더 를 정현파로 진동시켜 ER밸브에서 감쇠력제어가 가능한가를 알아보고 빙햄유체모델로 설계 된 ER댐퍼의 모델과 비교하였다. ER배르와 ER댐퍼의 수학적 모델을 시뮬레이션한 결과는 약간 벗어남이 보이기는 하나 실험결과와 일치하요 있다. 이것은 ER유체를 단순히 빙행유 체로 취급할수없으나 거시적으로는 빙햄유체로 취급할수 있음을 시사한다.

• Journal of the Korean Society for Precision Engineering
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• v.11 no.4
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• pp.148-157
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• 1994

A multi-cylindrical hydraulic valve incorporating with an electro-rheological(ER) fluid is developed in this study. Field-dependent Bingham properties of the ER fluid are exploited to devise the valve system which features fast system response as well as simple mechanism. The fast response is accrued from almost instant response characteristics of the ER fluid itself, and the mechanism configuration is simplified since no nechanically moving parts are required. The material properties of the ER fluids to be utilized for modeling of the proposed valve system are firstly tested with a couette-type electroviscometer. The design and manufacturing processes are then undertaken on the basis of model parameters. The performance characteristics of the valve system are evaluated in terms of pressure variations with respect to the intensity of employed electric fields and flow rates.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 1998.04a
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• pp.608-613
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• 1998

Damping characteristics of ER dampers and flow rates inside ER valve with two different valve types were analyzed and compared with test results. Fluid flow inside ER valves was modeled by Bingham plastic model and Hagen-Poiseulli flow, while the equations of motion of total ER damper system were modeled by flow and hydraulic force balance. A general straight valve case was compared with a bended valve case which is newly tested for a possible improvement of ER damping force. As expected, the bended ER valve generates higher damping force and lower flow rates than the conventional straight ER valve due to additional flow restriction at the bended section. Analytical models of ER valve and ER damper generally predict reasonable performance characteristics of tested results. Therefore, developed analysis can be used for designing new ER dampers and simulation of ER semi-active suspension system as well.