• The Korean Journal of Rheology
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• v.11 no.2
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• pp.105-111
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• 1999

Dampers have been used to dissipate energy in mechanical systems. There are several types of dampers such as passive, active, and semi-active damper. Semi-active dampers have higher performance than passive ones and require less power to operate than active ones. Their damping characteristics can be changed properly for varying conditions. In this paper, we investigated the semi-active damper using Magneto-Rheological fluid. Magneto-Rheological fluid, which is one of controllable fluids, changes its damping and rheological characteristics from Newtonian fluid to Bingham fluid as the magnetic field is applied. It has several advantages such as high yield strength, low viscosity, robustness to impurities and wide temperature range of stability. If we designe a semi-active damper by using this material, we can not only design a simply structured damper but also expect rapid response. In this study, we propose several types of semi-active dampers which are designed and manufactured using Magneto-Rheological fluid and some problems encountered during their applications.

• Polymer(Korea)
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• v.34 no.6
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• pp.534-539
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• 2010

Polystyrene (PS)/multi-walled carbon nanotube (MWCNT) nanocomposites were prepared via latex technology and the effect of nanotube length on rheological properties were investigated. Monodisperse PS particle was synthesized by the emulsifier-free emulsion polymerization and two types of MWCNTs were used after surface modification to improve dispersion state and to remove impurities. Final nanocomposites were prepared by the freeze-drying process after dispersing the PS particles and the surface-modified MWCNTs in a ultrasonic bath. The effects of MWCNT content and nanotube length on rheological properties were evaluated by imposing the small-amplitude oscillatory shear flow. The PS/MWCNT nanocomposites showed that rheological properties were enhanced as the amount and length of MWCNT increased. It is speculated that the rheological characteristics of nanocomposites change from liquid-like to solid-like as the MWCNT amount increases, and the critical concentration to achieve network structure decreases as the nanotube length increases.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2001.05a
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• pp.109-114
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• 2001

This paper presents field-dependent dynamic characteristics of a shock damper featuring an electro-rheological(ER) damper. A cylindrical type of the shock damper is designed and manufactured on the basis of the field-dependent Bingham model. The damping force is then measured with respect to the piston velocity at various electric fields. The measured damping force is incorporated with the 1DOF shock system to analyze the shock isolation performance.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.15 no.3 s.96
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• pp.354-363
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• 2005

Squeeze film dampers (SFDs) have been commonly used to effectively enhance the dynamic behavior of the rotating shaft supported by rolling element bearings. However, due to the recent trends of high operating speed, high load capacity and light weight in rotating machinery, it is becoming increasingly important to change the dynamic characteristics of rotating machines in operation so that the excessive vibrations, which may occurparticularly when passing through critical speeds or unstable regions, can be avoided. Semi-active type SFDs using magneto-rheological fluid (MR fluid), which responds to an applied magnetic field with a change in rheological behavior, are introduced in order to find its applications to rotating machinery as an effective device attenuating unbalance responses. In this paper, a semi-active SFD using MR fluid is designed, tested, and identified to investigate the capability of changing its dynamic properties such as damping and stiffness.In order to apply the MR-SFD to the vibration attenuation of a rotor, a systematic approach for determining the damper's optimal location is investigated, and also, a control algorithm that could improve the unbalance response characteristics of a flexible rotor is proposed and its control performance is validated with a numerical example.

• Transactions of the Korean Society of Automotive Engineers
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• v.1 no.1
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• pp.90-100
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• 1993

This paper presents some inherent characteristics of a semi-active variable damper featuring electro-rheological (ER) fluid. The damping force of the damper can be selectively adjusted or controlled by employing electric field to the ER fluid domain. This is possible owing to the pressure drop across the piston occured by field-dependent variable yield stress of the ER fluid. This is fundamentally different than the performance of a conventional adjustable viscous damper. To demonstrate the effectiveness and superiority over the conventional one, the proposed damper is incorporated with a suspension system. A quarter car model with the suspension system is formulated and represented by a state equation. By choosing numerical values based on realistic package size, power requirements and suitable ER properties, the performance characteristics of the suspension system are obtained and evaluated in both frequency and time domains. The effects of constant electric field and on-off controlled electric field which relates to the damping force are also examined.

• Journal of Advanced Marine Engineering and Technology
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• v.28 no.3
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• pp.434-440
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• 2004

The electro-rheological fluids for semi-active suspension system are a class of colloidal dispersion which exhibit large reversible changes in their rheological behavior when they are subjected to external electrical fields. This paper presents Bingham properties of ER fluids subjected to temperature variations. In addition, an appropriate size of the ER damper for a passenger car is proposed to investigate the effects of Bingham characteristics on the damping performance. The filed-dependent damping forces are evaluated according to the temperature variation and sedimentation ratio.

• Transactions of the Korean Society of Machine Tool Engineers
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• v.14 no.5
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• pp.49-54
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• 2005

An experimental Investigation was performed to study the characteristics of Electro-Rheological fluid flow in a horizontal rectangular tube with or without D.C electric field control. First, the microscopic behavior of the ER suspension structure between rectangular tube brass electrodes for the stationary ER nut(i and flow of the ER fluid was investigated by flow visualization. The flow of the ER fluid between fluid rectangular tube was solved experimental using the constitutive equation for a Bingham fluid. ER fluid is made silicon oil mixed with $0.2wt\%$ starch having hydrous particles. Velocity distributions of the ER fluids were obtained by particle image velocimetry measuring those of the clusters using an image processing technique.

• Proceedings of the Korean Society of Machine Tool Engineers Conference
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• 1999.05a
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• pp.216-221
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• 1999

Electrorheological fluids (ERF) are suspensions which show an abrupt increase in rheological properties under electric fields. The rheological response is very rapid and reversible when the electric field is imposed and/or removed. Therefore, there are many practical applications using the ERF. The purpose of the present study is to examine the flow characteristics of ERF. First, the microscopic behavior of the ER suspension structure between two fixed parallel-plate brass electrodes applied dc high voltage for the stationary and flow of the ERF was investigated by flow visualization. The electrical and rheological properties of zeolite based ERF were reported.

• Proceedings of the Korean Institute of Building Construction Conference
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• 2022.11a
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• pp.249-250
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• 2022

In this study, two types of chitosan-catechol polymers (a-CP and b-CP) were synthesized and mixed with polyvinyl alcohol (PVA) and sodium tetraborate decahydrate (Na₂B4O₇·10H₂O) to form hydrogels. The characteristics of these polymers were tuned by varying the pH during their syntheses, and their structures were characterized using nuclear magnetic resonance spectroscopy and ultraviolet-visible spectroscopy. Rheological and self-healing properties of hydrogels were evaluated. As a result, the viscoelastic modulus was improved due to the increased functional group content, and the self-healing property was excellent regardless of the functional group content.

• 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.