• Title, Summary, Keyword: fluid damping

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Development of FAMD Code to Calculate the Fluid Added Mass and Damping of Arbitrary Structures Submerged in Confined Viscous Fluid

  • Koo, Gyeong-Hoi;Lee, Jae-Han
    • Journal of Mechanical Science and Technology
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    • v.17 no.3
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    • pp.457-466
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    • 2003
  • In this paper, the numerical finite element formulations were derived for the linearized Navier-Stokes' equations with assumptions of two-dimensional incompressible, homogeneous viscous fluid field, and small oscillation and the FAMD (Fluid Added Mass and Damping) code was developed for practical applications calculating the fluid added mass and damping. In formulations, a fluid domain is discretized with C$\^$0/-type quadratic quadrilateral elements containing eight nodes using a mixed interpolation method, i.e., the interpolation function for the velocity variable is approximated by a quadratic function based on all eight nodal points and the interpolation function for the pressure variable is approximated by a linear function based on the four nodal points at vertices. Using the developed code, the various characteristics of the fluid added mass and damping are investigated for the concentric cylindrical shell and the actual hexagon arrays of the liquid metal reactor cores.

Performance of Squeeze Film Damper Using Magneto-Rheological Fluid (MR유체를 이용한 스퀴즈필름 댐퍼의 응답특성)

  • 안영공;양보석;신동춘;김동조
    • Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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    • pp.67-70
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    • 2002
  • This paper presents the property of the Squeeze Film Damper (SFD) using Magneto-Rheological fluid (MR fluid). The damping property of a SFD for a flexible rotor system varied according to vibration mode. MR fluid is known as a functional fluid with controllable apparent viscosity of the fluid by applied magnetic field strength. When the MR fluid is applied in the SFD, the SFD using MR fluid can effectively reduce vibrations of the flexible rotor in a wide range of rotating speed by control of the applied magnetic field strength. To investigate in detail the SFD using MR fluid, the SFD to support one mass was constructed and its performance was experimentally investigated in the present study. The damping property of the SFD using MR fluid has viscous damping by Newtonian fluid, but not Coulomb friction by Bingham fluid. Therefore, The system damped by the SFD can be considered as a linear system.

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Damping Effects of a Flexible Structure Interacting with Surrounding Acoustic Fluid (주변 음장과 연동하는 탄성 구조체의 감쇠 효과)

  • Lee, Moon-Seok;Park, Youn-Sik;Park, Young-Jin
    • Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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    • pp.101-105
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    • 2008
  • A flexible structure submerged in acoustic fluid is affected by its surrounding fluid. In transient response of a submerged structure, the coupled effect between structures and surrounding fluid emerges as damping and added mass at early and late time, respectively. Therefore, the characteristics of submerged structure such as natural frequencies and damping coefficients are changed by its surrounding fluid. In this paper, the analytic modal equation of a spherical shell surrounded by water and air is dealt with. Through the example, the damping coefficients and natural frequencies of flexible structures are studied for various external acoustic fluid and structures.

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An Experiment Study of Semi-Active Damper Using Magnetic fluid (자성유체를 이용한 반능동식 댐퍼에 관한 실험적 연구)

  • Hwang, Seung-Sik
    • The KSFM Journal of Fluid Machinery
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    • v.7 no.4
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    • pp.24-31
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    • 2004
  • The aim of this study is to provide fundamental information for the development of Semi-Active Damper Using Magnetic fluid. To achieve the aim, the damping effect of magnetic fluid is investigated by experiments that the diameter of inner circular bar and the input amplitude were varied in the magnetic field generated by the permanent magnet and the electromagnet coil. From the study, the following conclusive remarks can be made. As the diameter of inner circular bar and input amplitude increase, the damping effect is improved. This is explained by the fact that as the contact area between inner circular bar and magnetic fluid increases, the increase of friction lowers kinematic energy. If the magnetic field is generated, the damping effect is improved. This is explained the assumption that as the intensity of magnetic fluid particle increases, there is virtual mass phenomenon.

Bingham Properties and Damping Force Control of an ER Fluid under Squeeze Mode (압착모드하에서 ER유체의 빙햄특성 및 댐핑력 제어)

  • 홍성룡;최승복
    • Journal of the Korean Society for Precision Engineering
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    • v.19 no.11
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    • pp.37-45
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    • 2002
  • This paper presents the field-dependent Bingham characteristics and damping force control of an electro-rheological (ER) fluid under squeeze mode operation. The squeeze force of the ER fluid due to the imposed electric field is analyzed and an appropriate size of the disk-type electrode is devised. On the basis of the theoretical model of the ER fluid under squeeze mode operation, the yield stress and response speed of the ER fluid are distilled from the time responses of squeeze force to the step electric potentials. Measured squeeze forces under various excitation conditions are compared with the predicted ones from Bingham model and time constant obtained at the transient response test. In addition, the controllability of the field-dependent damping force of the ER fluid under squeeze mode is experimentally demonstrated by implementing simple PID controller.

Finite Element Analysis for Evaluation of Viscous and Eccentricity Effects on Fluid Added Mass and Damping (유체 부가질량 및 감쇠 결정시 점성 및 편심 영향에 대한 유한요소해석)

  • 구경회;이재한
    • Journal of the Earthquake Engineering Society of Korea
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    • v.7 no.2
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    • pp.21-27
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    • 2003
  • In general, simple fluid added mass method is used for the seismic and vibration analysis of the immersed structure to consider the fluid-structure interaction effect. Actually, the structural response of the immersed structure can be affected by both the fluid added mass and damping caused by the fluid viscosity. These variables appeared as a consistent matrix form with the coupling terms. In this paper, finite element formula for the inviscid fluid case and viscous fluid case are derived from the linearized Navier Stoke's equations. Using the finite element program developed in this paper, the analyses of fluid added mass and damping for the hexagon core structure of the liquid metal reactor are carried out to investigate the effect of fluid viscosity with variation of the fluid gap and Reynolds number. From the analysis results, it is verified that the viscosity significantly affects the fluid added mass and damping as the fluid gap size decrease. From the analysis results of eccentricity effect on the fluid added mass and damping of the concentric cylinders, the fluid added mass increase as the eccentricity increases, however the fluid damping increases only when the eccentricity is very severe.

Damping Effects of a Flexible Structure Interacting with Surrounding Acoustic Fluid (주변 음장과 연동하는 탄성 구조체의 감쇠 효과)

  • Lee, Moon-Seok;Park, Youn-Sik;Park, Young-Jin
    • Transactions of the Korean Society for Noise and Vibration Engineering
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    • v.18 no.7
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    • pp.718-724
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    • 2008
  • A flexible structure submerged in acoustic fluid is affected by its surrounding fluid. In this case, the coupling effects between structures and surrounding fluid have an effect on the submerged structure as external force and change impedance of acoustic domain. Therefore, the coupling effects by its surrounding fluid complicatedly change the characteristics of a submerged structure such as natural frequencies and damping coefficients. In this paper, using the analytic modal equation of a spherical shell surrounded by water and air, the complex changes of damping coefficients and natural frequencies of submerged structures are studied for various external acoustic fluid and structures.

Numerical Analysis of Damping Effect of Liquid Film on Material in High Speed Liquid Droplet Impingement

  • Sasaki, Hirotoshi;Ochiai, Naoya;Iga, Yuka
    • International Journal of Fluid Machinery and Systems
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    • v.9 no.1
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    • pp.57-65
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    • 2016
  • By high speed Liquid Droplet Impingement (LDI) on material, fluid systems are seriously damaged, therefore, it is important for the solution of the erosion problem of fluid systems to consider the effect of material in LDI. In this study, by using an in-house fluid/material two-way coupled method which considers reflection and transmission of pressure, stress and velocity on the fluid/material interface, high-speed LDI on wet/dry material surface is simulated. As a result, in the case of LDI on wet surface, maximum equivalent stress are less than those of dry surface due to damping effect of liquid film. Empirical formula of the damping effect function is formulated with the fluid factors of LDI, which are impingement velocity, droplet diameter and thickness of liquid film on material surface.

Radiation Problem Involving Two-layer Fluid in Frequency-Domain Numerical Wave Tank Using Artificial Damping Scheme (주파수 영역에서 인공감쇠기법을 활용한 복층 유체의 수치조파수조 방사 문제)

  • Min, Eun-Hong;Koo, Weoncheol
    • Journal of Ocean Engineering and Technology
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    • v.31 no.1
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    • pp.1-7
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    • 2017
  • There are two wave modes induced by an oscillating body on the free surface of a two-layer fluid: the barotropic and baroclinic modes. To investigate the generated waves composed of two modes, a radiation problem involving a heaving rectangular body was solved in a numerical wave tank. A new artificial damping zone scheme was developed and applied in the frequency-domain analysis. The performance of this damping scheme was compared with given radiation boundary conditions for various conditions. The added mass and radiation damping coefficients for the heaving rectangular body were also calculated for various fluid-density ratios.

Characteristics of Directional Squeeze Film Damper Using ER Fluid (ER유체를 이용한 이방성 스퀴즈필름 댐퍼의 특성)

  • 안영공;양보석;삼하신
    • Journal of KSNVE
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    • v.11 no.2
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    • pp.301-306
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    • 2001
  • Electro-Rheological (ER) fluid is applied to a controllable squeeze film damper (SFD) for stabilizing a flexibly supported rotor system. ER fluid is a class of functional fluid whose yield stress varies according to the applied electric field strength, which is observed as viscosity variation of the fluid. In applying ER fluid to a SFD, a pair of rings of the damper can be used as electrodes. When the electrodes are divided into a horizontal pair and a vertical one, the SFD can produce damping force in each direction independently. A prototype of the directionally controllable SFD was constructed and its performance was experimentally and numerically investigated in the present work.

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