• Title/Summary/Keyword: Fluid-elastic vibration

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Frequency and critical fluid velocity analysis of pipes reinforced with FG-CNTs conveying internal flows

  • Ghaitani, M.;Majidian, A.
    • Wind and Structures
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    • v.24 no.3
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    • pp.267-285
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    • 2017
  • This paper addresses vibration and instability of embedded functionally graded (FG)-carbon nanotubes (CNTs)-reinforced pipes conveying viscous fluid. The surrounding elastic medium is modeled by temperature-dependent orthotropic Pasternak medium. Flugge shell model is applied for mathematical modeling of structure. Based on energy method and Hamilton's principal, the motion equations are derived. Differential quadrature method (GDQM) is applied for obtaining the frequency and critical fluid velocity of system. The effects of different parameters such as volume percent of CNTs, elastic medium, boundary condition and geometrical parameters are discussed.

Dynamic Stability of a Vertical Cantilevered Pipe Conveying Fluid with Additional Spring Supports (부가 스프링 지지를 갖고 유동유체에 의한 외팔 수직 파이프의 동적 안정성)

  • Ryu, Bong-Jo;Jung, Seoung-Ho;Lee, Jong-Won
    • Transactions of the Korean Society for Noise and Vibration Engineering
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    • v.12 no.12
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    • pp.979-985
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    • 2002
  • The paper presents the dynamic stability of a vertical cantilevered pipe conveying fluid and haying translational linear spring supports. Real pipe systems may have some elastic hanger supports or other mechanical attached parts. which can be regarded as attached spring supports. Governing equations are derived by energy expressions, and numerical technique using Galerkin's method is applied to the equations of small motion of the pipe. Effects of spring supports on the dynamic stability of a vortical cantilevered pipe conveying fluid are fully investigated for various locations and spring constants of elastic supports.

Flow-induced Vibration of the CE-type Steam Generator Tube (CE형 원전 증기발생기 전열관의 유동유발진동 해석)

  • Ryu, Ki-Wahn;Park, Chi-Yong
    • Proceedings of the KSME Conference
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    • 2001.06d
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    • pp.828-833
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    • 2001
  • In this study, an analysis tool to assess the susceptibility of steam generator tubes due to the flow-induced vibration was developed. The fluid-elastic instability analysis of the U-tube bundle for CE-type steam generator was accomplished. The effective mass distribution along the U-tube was obtained to calculate the natural frequency and dynamic mode shape. Finally, stability ratios for selected tubes are obtained.

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Natural Vibration Analysis for Stiffened Plate of Ship Tank Side in Contact with Water Using Assumed Mode Method (진동파형가정방법을 이용한 선박 탱크 측면 접수 보강판의 고유진동해석)

  • Kim, Byung-Hee;Cho, Dae-Seung
    • Journal of the Society of Naval Architects of Korea
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    • v.42 no.4 s.142
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    • pp.396-401
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    • 2005
  • In this study, the assumed mode method using characteristic polynomials of Timoshenko beam is applied to the free vibration analysis for the stiffened plate of ship tank side in contact with water. The hydro-elastic effect of the fluid-structure interaction is considered by fluid velocity potential, derived from boundary conditions for fluid and structure, and utilized in the calculation of added mass matrix using assumed modes. To verify the validity and effectiveness of the presented method, free vibration analysis for the stiffened plates in contact with finite and infinite fluids have been carried out and its results were compared with those obtained by a general purpose FEA software.

A study on vibration characteristics and tuning of smart cantilevered beams featuring an electo-rheological fulid

  • Park, S.B.;Cheong, C.C.;Suh, M.S.
    • Journal of the Korean Society for Precision Engineering
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    • v.10 no.1
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    • pp.134-141
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    • 1993
  • Electro-Rheological(ER) fluids undergo a phase-change when subjected to an external electic field, and this phase-change typically manifests itself as a many-order-of-magnitude change in the rheological behavior. This phenomenon permits the global stiffness and energy- dissipation properties of the beam structures to be tuned in order to synthesize the desired vibration characteristics. This paper reports on a proof-of-concept experimental investigation focussed on evaluation the vibration properties of hollow cantilevered beams filled with an ER fluid. and consequently deriving an empirical model for predicting field-dependent vibration characteristics. A hydrous-based ER fluid consisting of corn starch and silicone oil is employed. The beams are considered to be uniform viscoelastic materials and modelled as a viscously-damped harmonic oscillator. Natural frequency, damping ratio and elastic modulus are evaluated with respect to the electric field and compared among three different beams: two types of different volume fraction of ER fluid and one type of different particle concentration of ER fluid by weight. Transient and forced vibration responses are examined in time domain to demonstrate the validity of the proposed empirical model and to evaluate the feasibility of using the ERfluid as an actuator in a closed-loop control system.

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Hydroelastic vibration analysis of wetted thin-walled structures by coupled FE-BE-Procedure

  • Rohr, Udo;Moller, Peter
    • Structural Engineering and Mechanics
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    • v.12 no.1
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    • pp.101-118
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    • 2001
  • The reliable prediction of elastic vibrations of wetted complex structures, as ships, tanks, offshore structures, propulsion components etc. represent a theoretical and numerical demanding task due to fluid-structure interaction. The paper presented is addressed to the vibration analysis by a combined FE-BE-procedure based on the added mass concept utilizing a direct boundary integral formulation of the potential fluid problem in interior and exterior domains. The discretization is realized by boundary element collocation method using conventional as well as infinite boundary element formulation with analytical integration scheme. Particular attention is devoted to modelling of interior problems with both several separate or communicating fluid domains as well as thin-walled structures wetted on both sides. To deal with this specific kind of interaction problems so-called "virtual" boundary elements in areas of cut outs are placed to satisfy the kinematical conditions in partial connected fluid domains existing in realistic tank systems. Numerical results of various theoretical and practical examples demonstrate the performance of the BE-methodology presented.

Damping due to Radiation Loss for Axial Vibration of the Pipe in a Fluid-filled Borehole (유체로 채워진 보어홀 속의 파이프 종진동에 있어서 방사손실에 의한 감쇠)

  • 이현엽;류황진
    • Journal of KSNVE
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    • v.7 no.4
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    • pp.631-636
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    • 1997
  • A method to estimate the radiatio power to the surrounding formation due to axial vibration of the pipe in a fluid-filled borehole has been developed, by using the propagation modes of stress wave in an infinitely-long and uniform drilling borehole surrounded by a radially-infinite homogeneous formation. Also, the equivalent damping coefficient for the axial vibration of the pipe has been derived. As an example, results for a real drilling borehole has been presented. The analysis of the elastic motion of the infinite formation which has cylidrical cavity is simplified with the geometric axisymmetry and the low-frequency assumption so that the analytic solution is obtained.

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Performance Evaluation of Cascade Considering Fluid/Structure Coupling Deformation (유체/구조 연계 변형효과를 고려한 케스케이드의 성능평가)

  • Oh, Se-Won;Kim, Dong-Hyun;Kim, Yu-Sung;Park, Oung
    • Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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    • 2007.05a
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    • pp.275-282
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    • 2007
  • In this study, a fluid-structure interaction (FSI) analysis system has been developed in order to evaluate the turbine cascade performance with blade structural deformation effect. Relative movement of the rotor with respect to stator is reflected by modeling independent two computational domains. To consider the deformed position of rotor airfoil, dynamic moving grid method is applied. Reynolds-averaged Navier-Stokes equations with one equation Spalart-Allmaras and two-equation SST $k-{\varepsilon}$ turbulence models are solved to predict unsteady fluid dynamic loads. A fully implicit time marching scheme based on the Newmark direct integration method with high artificial damping is used to compute the fluid-structure interaction problem. Cascade performance evaluations for different elastic axis positions are presented and compared each other. It is importantly shown that the predicted aerodynamic performance considering structural deformation effect of blade can show some deviations compared to the data generally computed from rigid blade configurations and the position of elastic axis also tend to give sensitive effect.

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EFFECTS OF SUPPORT STRUCTURE CHANGES ON FLOW-INDUCED VIBRATION CHARACTERISTICS OF STEAM GENERATOR TUBES

  • Ryu, Ki-Wahn;Park, Chi-Yong;Rhee, Hui-Nam
    • Nuclear Engineering and Technology
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    • v.42 no.1
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    • pp.97-108
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    • 2010
  • Fluid-elastic instability and turbulence-induced vibration of steam generator U-tubes of a nuclear power plant are studied numerically to investigate the effect of design changes of support structures in the upper region of the tubes. Two steam generator models, Model A and Model B, are considered in this study. The main design features of both models are identical except for the conditions of vertical and horizontal support bars. The location and number of vertical and horizontal support bars at the middle of the U-bend region in Model A differs from that of Model B. The stability ratio and the amplitude of turbulence-induced vibration are calculated by a computer program based on the ASME code. The mode shape with a large modal displacement at the upper region of the U-tube is the key parameter related to the fretting wear between the tube and its support structures, such as vertical, horizontal, and diagonal support bars. Therefore, the location and the number of vertical and horizontal support bars have a great influence on the fretting wear mechanism. The variation in the stability ratios for each vibrational mode is compared with respect to Model A and Model B. Even though both models satisfy the design criteria, Model A shows substantial improvements over Model B, particularly in terms of having greater amplitude margins in the turbulence-excited vibration (especially at the inner region of the tube bundle) and better stability ratios for the fluid-elastic instability.

Vibration Characteristics of Rotating Disks with Aerodynamic Effect (I) - Theoretical Analysis - (공기 유동 효과를 고려한 회전 디스크의 진동 특성 (I) - 이론적 해석 -)

  • Lee, Seung-Yop;Lim, Hyo-Suk
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.32 no.2
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    • pp.127-134
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    • 2008
  • The aerodynamically excited vibration and natural frequency of rotating disks are analytically studied in this paper. The theoretical analysis uses a fluid-structure model where the aerodynamic effects are represented in terms of elastic, lift and drag forces. The explicit expressions on natural frequencies of the air coupled disk are obtained as functions of the aerodynamic coefficients. for the three cases where the disk rotates in three different cases (in vacuum, in open air without enclosure, and close to rigid wall). The theoretical results give that the natural frequencies of rotating disks in air are smaller than those in vacuum, because the effect of the added fluid mass decreases the frequencies. This paper also proposes an analytical method to predict the flutter speed of a rotating disk.