Bending-Torsional Flutter of a Slender Web in a Cross Flow

2017 ◽  
Author(s):  
Keiichi Hiroaki ◽  
Nobuhito Kawai ◽  
Masahiro Watanabe
Keyword(s):  
Cross Flow ◽  
The Finite Element Method ◽  
Wind Tunnel Experiments ◽  
Fluid Force ◽  
Coupled Mode ◽  
Flutter Analysis ◽  
Unsteady Fluid ◽  
Work Done ◽  
The Web ◽  
Local Work

This paper presents a flutter analysis of a slender web in a cross air flow. In the flutter analysis, a Doublet-point method (DPM) [1] based on an unsteady lifting surface theory is used to calculate the unsteady fluid force acting on the sheet surface. The equation of motion of the web with tension is derived by using the finite element method (FEM). Flutter velocity, frequency and mode are examined through the root locus of the flutter determinant of the system with changing flow velocity of air. In this study, these flutter characteristics derived by flutter analysis are compared with wind-tunnel experiments. The influence of tension of the web on flutter velocity, frequency and mode is clarified. As tension of the web becomes higher, the flutter velocity and corresponding frequency increase. In any tension, coupled mode flutter of bending and torsional modes occurs. Then, local work done by the fluid force around the upstream end of the web is positive. On the other hand, near the downstream end of the web, the local work is negative.

scholarly journals Three dimensional flutter analysis and wind-tunnel experiments of slender webs in cross flow

2017 ◽  
Vol 83 (852) ◽  
pp. 17-00025-17-00025 ◽  
Author(s):  
Keiichi HIROAKI ◽  
Nobuhito KAWAI ◽  
Masahiro WATANABE
Keyword(s):  
Wind Tunnel ◽  
Three Dimensional ◽  
Cross Flow ◽  
Wind Tunnel Experiments ◽  
Flutter Analysis

Streamwise Fluidelastic Forces in Tube Arrays Subjected to Two-Phase Flows

2014 ◽  
Author(s):  
Stephen Olala ◽  
Njuki W. Mureithi ◽  
Teguewinde Sawadogo ◽  
Michel J. Pettigrew
Keyword(s):  
Flow Direction ◽  
Cross Flow ◽  
Force Coefficient ◽  
Two Phase ◽  
Fluid Force ◽  
Phase Measurements ◽  
Force Coefficients ◽  
Void Fractions ◽  
Drag And Lift ◽  
Unsteady Fluid

Detailed unsteady fluid force and phase measurements for a single tube oscillating purely in the streamwise direction in a rotated triangular tube array subjected to air-water two-phase cross-flow have been conducted in this study for homogeneous void fractions between 0% and 90%. Additionally the streamwise steady forces were measured in two-phase flow at a Reynolds number (based on the pitch velocity), Re = 7.2 × 104. The results are compared to those previously obtained for transverse direction oscillations. The measurement results show that the magnitude of the force coefficients for both directions (drag and lift) is comparable both in trend and quantitatively. However, the phase in the drag direction is negative while that for the lift is positive. The range of variation of the phase is also significantly smaller for the drag direction. Noting that negative phase corresponds to positive damping and vice versa, this observation confirms previous findings of lack of instability in the drag direction for a single flexible tube in a rotated triangular tube array. The drag steady fluid force coefficients were found to increase with dimensionless displacement in the flow direction for the entire range of void fractions considered. The derivative of the measured steady fluid force coefficient, which is an important factor in fluidelastic instability study using the quasi-steady model, was found to remain positive in the drag direction. The effect of void fraction on the unsteady fluid force coefficient and other dynamic parameters such as hydrodynamic mass and damping are also discussed.

Self-Excited Vibration of a Plate Supported by Air Pressure in a Floating Conveying Machine

2017 ◽  
Author(s):  
Masakazu Takeda ◽  
Masahiro Watanabe
Keyword(s):  
Air Pressure ◽  
The Self ◽  
Plate Motion ◽  
Bottom Surface ◽  
Fluid Force ◽  
Gap Flow ◽  
Excited Vibration ◽  
Unsteady Fluid ◽  
The Stability ◽  
Work Done

This paper presents experiments and an analysis on self-excited vibration of a plate supported by air pressure in a floating conveying machine. In this study, the instability conditions are examined by theoretical analysis in consideration of the effect of compressibility of air in a chamber. The system’s characteristic equation is derived from the plate motion coupled with equations of the gap flow between the plate and the chamber surface. The vibration characteristics and the instability conditions of the self-excited vibration are examined through experiments. The stability of the plate is affected by an air flow rate, a mass of the plate, a spring stiffness of the plate. We clarified those influences on the instability conditions of the self-excited vibration. The unsteady fluid force acting on the plate (bottom surface) is investigated by measuring the unsteady pressure. The local work done by the unsteady fluid force is also clarified. Lastly, the instability mechanism and important parameters of the self-excited vibration are discussed based on the theoretical model and experimental results.

Aeroelastic Stability of Wide Webs and Narrow Ribbons

2007 ◽  
Author(s):  
Rahul A. Bidkar ◽  
Arvind Raman ◽  
Anil K. Bajaj
Keyword(s):  
Fluid Flow ◽  
Critical Role ◽  
Cross Flow ◽  
Aeroelastic Stability ◽  
Lattice Method ◽  
Flutter Instability ◽  
Divergence Instability ◽  
Applied Tension ◽  
Unsteady Fluid ◽  
The Web

Uni-axially tensioned wide webs and narrow ribbons commonly used in the paper-handling, textile, sheet-metal, and plastics industries are known to undergo large amplitude vibrations characterized as aeroelastic flutter. The aeroelastic stability of stationary wide webs and narrow ribbons coupled with fluid flow across the free edges of the web or ribbon is investigated in this article. The web or ribbon is modeled as a uni-axially tensioned Kirchhoff plate with vanishingly small bending stiffness. The 3D unsteady fluid flow surrounding the web or ribbon is evaluated numerically by using the vortex-lattice method. Wide webs are mainly found to exhibit the divergence instability. For some values of the applied tension, the clustered web modes exhibit frequency curve veering accompanied by a weak flutter instability before the occurrence of the divergence instability. The applied tension plays a critical role in deciding the type of instability in narrow ribbons. In cross flow, depending on the applied tension, narrow ribbons undergo flutter instability or divergence instability or the simultaneous onset of both instabilities.

Flutter Analysis and Experiments of a Rectangular Sheet Supported by a Wire

2015 ◽  
Author(s):  
Keiichi Hiroaki ◽  
Masahiro Watanabe ◽  
Ryosuke Morita
Keyword(s):  
Boundary Condition ◽  
Flow Velocity ◽  
Axial Flow ◽  
Wave Mode ◽  
Dominant Mode ◽  
Fluid Force ◽  
Sheet Surface ◽  
Flutter Analysis ◽  
The Wire ◽  
Local Work

This paper deals with a flutter analysis of a rectangular sheet supported by a wire in axial flow. In the flutter analysis, Doublet-point method based on the unsteady lifting surface theory is used to calculate the unsteady fluid force acting on the sheet surface. The equation of motion of the sheet supported the wire with tension is derived by using the finite element method. The flutter velocity and mode of the sheet are examined through the root locus of the flutter determinant of the system with changing the flow velocity. In this study, experiments are conducted and compared with the analytical results. The flutter velocity, its mode, and the local work by the fluid force acting on the sheet surface with changing tension of wire are determined. Moreover, the effects of boundary condition on flutter characteristic are determined. As the tension of the wire becomes higher, the flutter velocity and its frequency increase. Traveling-wave mode flutter occurs to the sheet when the flow velocity becomes higher. In the case of lower tension of the wire, the amplitude of the flutter mode at the upstream end is large. The local work done by the fluid force around the center of the sheet is positive, and that near the downstream end of the sheet is negative. Moreover, local work on the sheet surface and flutter mode for different boundary condition depend on dominant mode contribute to flutter mode.

scholarly journals High Sensitivity Plasmonic Sensor Based on Fano Resonance with Inverted U-Shaped Resonator

Sensors ◽  
2021 ◽  
Vol 21 (4) ◽  
pp. 1164
Author(s):  
Gongli Xiao ◽  
Yanping Xu ◽  
Hongyan Yang ◽  
Zetao Ou ◽  
Jianyun Chen ◽  
...  
Keyword(s):  
Fano Resonance ◽  
Figure Of Merit ◽  
High Sensitivity ◽  
Refractive Index Sensor ◽  
Multimode Interference ◽  
Geometrical Parameters ◽  
The Finite Element Method ◽  
Plasmonic Sensor ◽  
Coupled Mode ◽  
Plasmonic Nanosensor

Herein, we propose a tunable plasmonic sensor with Fano resonators in an inverted U-shaped resonator. By manipulating the sharp asymmetric Fano resonance peaks, a high-sensitivity refractive index sensor can be realized. Using the multimode interference coupled-mode theory and the finite element method, we numerically simulate the influences of geometrical parameters on the plasmonic sensor. Optimizing the structure parameters, we can achieve a high plasmonic sensor with the maximum sensitivity for 840 nm/RIUand figure of merit for 3.9 × 105. The research results provide a reliable theoretical basis for designing high sensitivity to the next generation plasmonic nanosensor.

Time Domain Models for Damping-Controlled Fluidelastic Instability Forces in Tubes With Loose Supports

2010 ◽  
Vol 132 (4) ◽  
Author(s):  
Marwan Hassan ◽  
Achraf Hossen
Keyword(s):  
Time Domain ◽  
Cross Flow ◽  
Work Rate ◽  
Interaction Parameters ◽  
Similar Response ◽  
Fluid Force ◽  
Support Interaction ◽  
Fluidelastic Instability ◽  
The Impact ◽  
Normal Work

This paper presents simulations of a loosely supported cantilever tube subjected to turbulence and fluidelastic instability forces. Several time domain fluid force models are presented to simulate the damping-controlled fluidelastic instability mechanism in tube arrays. These models include a negative damping model based on the Connors equation, fluid force coefficient-based models (Chen, 1983, “Instability Mechanisms and Stability Criteria of a Group of Cylinders Subjected to Cross-Flow. Part 1: Theory,” Trans. ASME, J. Vib., Acoust., Stress, Reliab. Des., 105, pp. 51–58; Tanaka and Takahara, 1981, “Fluid Elastic Vibration of Tube Array in Cross Flow,” J. Sound Vib., 77, pp. 19–37), and two semi-analytical models (Price and Païdoussis, 1984, “An Improved Mathematical Model for the Stability of Cylinder Rows Subjected to Cross-Flow,” J. Sound Vib., 97(4), pp. 615–640; Lever and Weaver, 1982, “A Theoretical Model for the Fluidelastic Instability in Heat Exchanger Tube Bundles,” ASME J. Pressure Vessel Technol., 104, pp. 104–147). Time domain modeling and implementation challenges for each of these theories were discussed. For each model, the flow velocity and the support clearance were varied. Special attention was paid to the tube/support interaction parameters that affect wear, such as impact forces and normal work rate. As the prediction of the linear threshold varies depending on the model utilized, the nonlinear response also differs. The investigated models exhibit similar response characteristics for the lift response. The greatest differences were seen in the prediction of the drag response, the impact force level, and the normal work rate. Simulation results show that the Connors-based model consistently underestimates the response and the tube/support interaction parameters for the loose support case.

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