• 한국윤활학회:학술대회논문집
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• 한국윤활학회 1997년도 제25회 춘계학술대회
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• pp.151-166
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• 1997

ER clutch is a device using ER fluid, so called "intelligent material" and is a controlled system with electric field strength. Current problem of this device is that the temperature of ER fluid increases when ER clutch is operating and affects the performance of ER clutch. This study was undertaken to estimate this performance variation due to temperature increase of ER fluid. Analytic power transmission relationships and the temperature increase model using the rheological model of ER fluid were developed and the dynamic model of proposed ER clutch system was constructed, also. With this relationships, effects of changing geometric, kinetic parameters of ER clutch and ER fluid properties were described and performance variations due to temperature increases of ER fluid were estimated. In conclusion, compared with neglecting temperature increase effects, a performance of ER clutch was very differential. Therefore, to achieve uniform performance of ER clutch, we have to improve thermal stability of ER fluid with a view point of material development and design carefully ER clutch considering temperature increase effects with a view point of mechanical design skill.ign skill.

• 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.

• Clinical and Experimental Reproductive Medicine
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• 제27권2호
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• pp.151-157
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• 2000

Objective: The purpose of this study was to evaluate the effect of polycystic ovarian follicular fluid on sperm motility in human in vitro fertilization (IVF). Methods: From May, 1998 to July, 1999, 55 patients who complained of infertility were involved in this study. We obtained ovarian follicular fluids from the patients by ultrasono-guided aspiration. Subjects were divided into two groups. 20 patients who had polycystic ovarian disease were belong to study group, and 25 patients who had normal ovarian follicular fluid were belong to control group. The follicular fluid dilution was done with Ham's fluid as 10%, 20%, 50%, 100%. The sperm motility was analyzed by CASA at 6hr and 12hr after incubation in follicular fluids. Results: The levels of average path velocity (VAP) in all concentration fluid didn't show significant difference between study and control group. The other parameters including curvilinear velocity (VCL), amplitude of lateral head displacement (ALH), and linerity (LIN) were didn't show any significant difference between both groups. Conclusion: PCOD fluid had seemed to have an adverse effect on the sperm biological function. But, this study showed that PCOD fluid had no different effect on sperm motility with normal follicular fluid.

• 한국해양공학회지
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• 제15권2호
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• pp.135-140
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• 2001

A simply supported pipe conveying fluid and a moving mass upon it constitute a vibrational system. The equation of motion is derived by using Lagrange's equation. The influence of the velocity and the inertia force of a moving mass and the velocities of fluid flow in the pipe have been studied on the dynamic behavior of a simply supported pipe by numerical method. The velocities of fluid low are considered within its critical values of the simply supported pipe without a moving mass upon it. Their coupling effects on the transverse vibration of a simply supported pipe are inspected too. as the velocity of a moving mass increases, the deflection of midspan of a simply supported pipe conveying fluid is increased and the frequency of transverse vibration of the pipe is not varied. Increasing of the velocity of fluid flow makes the frequency of transverse vibration of the simply supported pipe conveying fluid decrease and the deflection of midspan of the pipe increase. The deflection of the simply supported pipe conveying fluid is increased by a coupling of the moving mass and the velocities of a moving mass and fluid flow.

• 한국전산유체공학회지
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• 제14권2호
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• pp.9-18
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• 2009

The cargo containment system (CCS) for ships carrying cryogenic fluid consists of at least two levels of barriers and insulation layers. It is because, even though there is a small amount of leak through the primary barrier, the liquid tight secondary barrier blocks further leakage of the cryogenic fluid. However, once the secondary barrier is damaged, it is highly possible that the leaked cryogenic fluid flows through the flat joint made of glass wool and reaches the inner hull of the ship. The primary objective of the present study is to investigate the influence of the damage extent in the secondary barrier on the amount of leaked cryogenic fluid reaching the inner hull and the temperature distribution there. Simulation results using a computational fluid dynamics tool were compared with the experimental data for the leaked cryogenic fluid flow and evaporation in the secondary insulation layer. The experimental and computational results suggest that, unless there is a massive leak, the cryogenic fluid mostly evaporates in the insulation layer and does not reach the inner hull in the state of liquid.

• 한국해안해양공학회지
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• 제8권1호
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• pp.114-122
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• 1996

간척지 매립에 있어서 최근에는 토사를 해저에서 준설하여 파이프라인을 통해 유송시켜 매립시키는 방법이 많이 쓰여지고 있다. 이러한 경우 토사와 혼합된 유체는 slurry fluid의 성질을 지닌다. slurry fluid는 점성도가 독특한 양상을 보이기 때문에 준설토 유송의 관련수치 산정에는 slurry flow 특성을 반영한 관마찰계수 산정식을 사용해야 한다. 준설토를 함유한 slurry fluid는 주로 함유된 입자의 크기에 따라 Newtonian fluid 또는 non-Newtonian fluid 특성을 갖는데, 본 연구에서는 각 특성조건별로 관마찰계수 산정식을 지수함수 형태로 제시하였으며, 이를 이용하여 준설토 유송을 위한 용량산정에 있어 펌프동력 뿐만 아니라 관경 및 유량에 대하여도 양해법 형태의 산정식을 개발하였다.

• Structural Engineering and Mechanics
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• 제59권1호
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• pp.153-186
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• 2016

This paper addresses temperature-dependent nonlinear vibration and instability of embedded functionally graded (FG) pipes conveying viscous fluid-nanoparticle mixture. The surrounding elastic medium is modeled by temperature-dependent orthotropic Pasternak medium. Reddy third-order shear deformation theory (RSDT) of cylindrical shells are developed using the strain-displacement relations of Donnell theory. The well known Navier-Stokes equation is used for obtaining the applied force of fluid to pipe. Based on energy method and Hamilton's principal, the governing equations are derived. Generalized differential quadrature method (GDQM) is applied for obtaining the frequency and critical fluid velocity of system. The effects of different parameters such as mode numbers, nonlinearity, fluid velocity, volume percent of nanoparticle in fluid, gradient index, elastic medium, boundary condition and temperature gradient are discussed. Numerical results indicate that with increasing the stiffness of elastic medium and decreasing volume percent of nanoparticle in fluid, the frequency and critical fluid velocity increase. The presented results indicate that the material in-homogeneity has a significant influence on the vibration and instability behaviors of the FG pipes and should therefore be considered in its optimum design. In addition, fluid velocity leads to divergence and flutter instabilities.

• 설비공학논문집
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• 제26권8호
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• pp.351-356
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• 2014

Typical trouble patterns in solar thermal systems include working fluid leakage and freezing other than breakdown of pump. A fluid sensor for measuring electric resistance of fluid was developed and installed at the top of the collector piping in order to check the fault of solar system. Working fluid level in the pipe was determined by measuring electric resistance from a fluid sensor. On the base of this, it was confirmed that the fluid sensor diagnoses leakage of fluid. Electric resistance of propylene glycol aqueous solution was measured in the range of $0{\sim}70^{\circ}C$ and 0~40% of concentration. The response surface analysis was performed by using a central composite design, and the regression equation was derived from the relationship between electric resistance, temperature, and concentration. Through the experiment in a real solar system, we can estimate a concentration of working fluid when a pump is not operating and predict a possibility of freezing. Finally, an effective algorithm for trouble shooting was proposed to operate and maintain the solar system.

• Geomechanics and Engineering
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• 제33권5호
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• pp.519-528
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• 2023

In this paper, we present the results of an experimental study on the effect of polymer support fluid on shaft resistance of offshore bored piles. A series of pullout tests were performed on bored piles installed under various boundary conditions considering different types of grounds and support fluids, and a range of support fluid exposure times. Contrary to previous studies concerning onshore bored piles, a time dependent effect of polymer fluid on shaft resistance was observed in all ground types. The adverse effect of polymer support fluid on the shaft resistance, however, was considerably less than bentonite support fluid for a given exposure time. No significant reduction in shaft resistance was evident when limiting the exposure time of the polymer support fluid to the side wall of the borehole within 2-3 hours. The degree to which the polymer fluid affects shaft resistance seemed to vary with the ground type. A proper consideration should be given to the time dependent effect of polymer fluid on shaft resistance of bored piles installed in offshore construction environment to limit its adverse effect on the pile performance. The practical implications of the findings are discussed.