• Tribology and Lubricants
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• 제27권4호
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• pp.213-217
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• 2011

In this study, friction characteristics using elastomeric actuator with Magneto-rheological (MR) materials are identified. Typically, Magneto-rheological materials are divided into two groups by MR fluid in fluid state and MR elastomer in solid state like rubber. The stiffness characteristics of Magneto-rheological material can be changed as magnetic field is applied. MR fluid has been applied to various industry fields such as to brake, clutch, damper, engine mount and etc. However, MR fluid has been used under the sealed condition to prevent leaking issues. In order to overcome these problems, MR elastomer that has same property as MR fluid has been developed and studied. MR elastomer mainly consists of polymer material such as natural rubber or silicon rubber with particles that can be polarized with magnetic field. And it is called as a smart material since its stiffness and damping characteristics can be changed. In this study, MR elastomer is produced and pin-on-disc tests are carried out to identify the friction characteristics of the material. Several test conditions are applied to evaluate the feasibility to use as a smart actuator in the field of vibration control.

• 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.

• 제어로봇시스템학회:학술대회논문집
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• 제어로봇시스템학회 2004년도 ICCAS
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• pp.296-300
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• 2004

A new MR cylinder with built-in valves using MR fluid (MR valve) is proposed for fluid power control systems. The MR or Magneto-Rheololgical fluid is a newly developed functional fluid whose obvious viscosity is controlled by the applied magnetic field intensity. The MR cylinder is composed of cylinder with small clearance and piston with electromagnet. The differential pressure is controlled by the applied magnetic field intensity. It has the characteristics of simple, compact and reliable structure. The size of MR cylinder and piston has ${\varphi}$60mm${\times}$259mm and ${\varphi}$58mm${\times}$136.5mm in face size respectively and 0.8mm in gap length. Through experiments on the static characteristics, it is found that the differential pressure is controlled by the applied magnetic field intensity under little influence of the flow rate, which corresponds to a pressure control valve. Effectiveness of the MR cylinder is demonstrated through the position control of one link MR manipulator.

• Kyungpook Mathematical Journal
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• 제47권4호
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• pp.455-471
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• 2007

The magnetohydrodynamic axisymmetric instability of a streaming gas jet surrounded by bounded fluid with non-uniform field has been developed. The problem is formulated, solved and the boundary conditions are applied across the interfaces. The eigenvalue relation is derived and discussed analytically and the results are confirmed numerically. Some reported works are recovered as limiting cases from the present general results. The streaming has a destabilizing effect for all short and long wavelengths. The capillary force is stabilizing for short wavelengths but it is destabilizing for long wavelengths. The axial magnetic fields interior the gas and fluid media are stabilizing. The transverse field is destabilizing for all wavelengths. The radii ratio of the gas and fluid cylinders plays an important role for stabilizing the model and made it more realistic one than the full liquid jet or/and the ordinary hollow jet. The numerical analysis clarify the stable and unstable domains based on different values of the various parameters of the problem.

• 한국생산제조학회지
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• 제21권5호
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• pp.761-766
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• 2012

Abrasive fluid jet polishing processes have been used for the polishing of optical surfaces with complex shapes. However, unstable and unpredictable polishing spots can be generated due to the fundamental property of an abrasive fluid jet that it begins to lose its coherence as the jet exits a nozzle. To solve such problems, MR fluid jet polishing has been suggested using a mixture of abrasives and MR fluid whose flow properties can be readily changed according to imposed magnetic field intensity. The MR fluid jet can be stabilized by imposed magnetic fields, thus it can remain collimated and coherent before it impinges upon the workpiece surface. In this study, MR fluid jet polishing characteristics of fused silica glass were investigated according to injection time and magnetic field intensity variations. Material removal rates and 3D profiles of the generated polishing spots were investigated. From the results, it can be confirmed that the developed MR fluid polishing system can be applied for stable and predictable precise polishing of optical parts.

• 한국전산구조공학회:학술대회논문집
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• 한국전산구조공학회 1999년도 가을 학술발표회 논문집
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• pp.257-266
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• 1999

This paper presents a method of seismic analysis for a cylindrical liquid storage structure on/in horizontally layered half.space considering the effects of the interior fluid and exterior soil medium in the frequency domain. To capture the essence of fluid-structure-soil interaction effects effectively, a mixed finite element with two-field (u, p) approximation is employed to model the compressive inviscid fluid, while the structure and soil medium are presented by the 3-D axisymmetric finite elements and dynamic infinite elements. The present FE-based method can be applied to the system with complex geometry of fluid region as well as with inhomogeneous near-field soil medium, since it can directly model both the fluid and the soil. For the purpose of verification, dominant peak frequencies in transfer functions for horizontal motions of cylindrical fluid storage tanks with rigid massless foundation on a homogeneous viscoelastic half.space are compared with those by two different added mass approaches for the fluid motion. The comparison indicates that the Present FE-based methodology gives accurate solution for the fluid-structure-soil interaction problem. Finally, as a demonstration of versatility of the present study, a seismic analysis for a real-scale LNG storage tank embedded in layered half.space is carried out, and its member forces along the height of the structure are compared with those by an added mass approach developed by the present writers.

• Tribology and Lubricants
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• 제31권2호
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• pp.62-68
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• 2015

A magnetorheological (MR) fluid is a smart material whose rheological behavior can be controlled by varying the parameters of the applied magnetic field. Because the damping force and shear force of an MR fluid can be controlled using a magnetic field, it is widely employed in many industrial applications, such as in vehicle vibration control, powertrains, high-precision grinding processes, valves, and seals. However, the characteristics of friction caused by iron particles inside the MR fluid need to be understood and improved so that it can be used in practical applications. Surface process technologies such as polytetrafluoroethylene (PTFE) coatings and diamond-like carbon (DLC) coatings are widely used to improve the surface friction properties. This study examines the friction characteristics of an MR fluid with different surface process technologies such as PTFE coatings and DLC coatings, by using a reciprocating friction tester. The coefficients of friction are in the following descending order: MR fluid without any coating, MR fluid with a DLC coating, and MR fluid with a PTFE coating. Scanning electron microscopy is used to observe the worn surfaces before and after the experiment. In addition, energy dispersive X-ray spectroscopy is used to analyze the chemical composition of the worn surface. Through a comparison of the results, the friction characteristics of the MR fluid based on the different coating technologies are analyzed.

• 터널과지하공간
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• 제31권6호
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• pp.385-399
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• 2021

인간의 활동에 의해 발생하는 유발지진 중 유체의 주입뿐만 아니라 유체의 생산 또한 원인으로 알려져 있다. 본 기술보고에서는 유체를 생산할 때 저류층 내부의 공극압 감소로 인해 지진이 유발되는 메커니즘을 정리하였다. 유체 생산으로 인해 유발지진이 발생한 사례들 중 네덜란드 흐로닝언(Groningen) 가스전, 프랑스 라크(Lacq) 가스전 그리고 멕시코 세로 프리에토(Cerro Prieto) 지열 발전소를 소개하고 각 사례에 대한 기존 연구들을 정리하였다. 유체 생산 필드에서의 유체 생산량과 지반침하, 그리고 기존 단층의 유무가 유발지진과 큰 상관성을 보이는 것을 확인하였다. 따라서, 석유나 가스 생산 필드 그리고 지열 발전소 개발을 위해 저류층에서 유발지진의 발생 가능성을 내재하고 있는 단층 유무에 대한 정확한 탐사와 생산 중에 나타나는 지반침하를 실시간으로 모니터링하며 생산량을 조절하는 것이 중요하다.

• 한국전산유체공학회지
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• 제9권2호
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• pp.43-51
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• 2004

Interaction between fluid flow and thermal radiation has received considerable attention due to its numerous applications in engineering field. In this case the thermofluid properties of radiating fluid vary with the variation of temperature field caused by absorption and emission of radiant heat. To analyze the radiation heat transfer in radiating fluid, the simultaneous solution of the radiative transfer equation (RTE) and the fluid dynamics equations is required. This means that the numerical procedure used for the RTE must be computationally efficient to permit its inclusion in the other submodels, and must be compatible with the other transport equations. The finite volume method (FVM) and the discrete ordinates method (DOM) are usually employed to simulate radiation problems in generalized coordinates. These two representative methods are examined and compared, especially in view of the numerical integration of the radiation intensity over solid angle. The FVM shows better accuracy than the DOM owing to less constraints of the selection of control angle.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2004년도 춘계 학술대회논문집
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• pp.62-70
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• 2004

Interaction between fluid flow and thermal radiation has received considerable attention due to its numerous applications in engineering field. In this case the thermofluid properties of radiating fluid vary with the variation of temperature field caused by absorption and emission of radiant heat. To analyze the radiation heat transfer in radiating fluid, the simultaneous solution of the radiative transfer equation (RTE) and the fluid dynamics equations is required. This means that the numerical procedure used for the RTE must be computationally efficient to permit its inclusion in the other submodels, and must be compatible with the other transport equations. The finite volume method (FVM) and the discrete ordinates method (DOM) are usually employed to simulate radiation problems in generalized coordinates. These two representative methods are examined and compared, especially in view of the numerical integration of the radiation intensity over solid angle. The FVM shows better accuracy than the DOM owing to less constraints of the selection of control angle.