Torsional Instability of an Elastic Flat Plate due to Hydrodynamic Loads

2014 ◽  
Vol 30 (6) ◽  
pp. 643-650 ◽  
Author(s):  
M. Armandei ◽  
A. C. Fernandes
Keyword(s):  
Free Vibration ◽  
Flat Plate ◽  
Critical Velocity ◽  
Least Square ◽  
Water Current ◽  
Hydrodynamic Loads ◽  
Identification Technique ◽  
Torsional Instability ◽  
Base Range ◽  
Flutter Derivatives

AbstractThe present work studies the torsional instability of an elastic structure due to hydrodynamic loads into the water current. The structure applied here is a rectangular flat plate with an elastic axis in its mid-chord length. The elasticity in the structure is provided by torsion spring. The flat plate has only one degree of freedom which is rotation in pure yaw about its axis. Through the free vibration experiments, it is observed that as the current speed exceeds a critical velocity, the flat plate becomes unstable. Two different chord lengths are tested and the instability occurs for a chord base range of Reynolds number, 0.75 × 105 < Rec < 1.5 × 105. As a result of the instability, the flat plate begins to yaw about the elastic axis. The hydrodynamic moment acting on the flat plate is modeled by means of the flutter derivatives. As an identification technique to extract flutter derivatives, a curve fitting scheme called General Least-Square (GLS) theory is applied on the results of the free vibration experiments. The results confirm that the structure becomes dynamically unstable due to the hydrodynamic moment applied on it beyond the critical velocity. The super-critical Hopf bifurcation is also discussed in the light of the analysis.

Flutter Derivatives of the Kao-Pin Hsi Cable-Supported Bridge

2016 ◽  
Vol 821 ◽  
pp. 172-179
Author(s):  
Andrija Buljac ◽  
Stanislav Pospíšil ◽  
Hrvoje Kozmar ◽  
Sergej Kuznetsov ◽  
Radomil Král
Keyword(s):  
Flat Plate ◽  
Bridge Deck ◽  
Engineering Structures ◽  
Long Span ◽  
Vibration Technique ◽  
Centre Of Excellence ◽  
Double Degree ◽  
Torsional Instability ◽  
Large Width ◽  
Flutter Derivatives

Long-span cable-supported bridges, characterized with low natural frequencies and mechanical damping, are very sensitive to wind effects. Therefore, investigation of the aeroelastic behaviour of bridges is particularly important when designing these complex engineering structures. The focus is on evaluation of dimensionless aeroelastic coefficients, i.e. flutter derivatives, which are considered as indicators of the aeroelastic stability of bridges. A comprehensive experimental study on dynamic wind-induced behaviour of the Kao-Pin Hsi Bridge in Taiwan is carried out in the Climatic Wind Tunnel of the Centre of Excellence Telč (CET), Czech Republic. The bridge-deck section is tested at a multipurpose experimental setup originally developed in the CET. Flutter derivatives are obtained by the means of the free-vibration technique for the double-degree-of-freedom (DDOF) system. The results are compared to those of a thin flat plate with large width to height ratio, which previously proved to be stable with respect to the flutter phenomenon. While the torsional instability is observed for the Kao-Pin Hsi bridge-deck section, the flat plate proves to be aeroelastically stable.

Stability Analysis of a Yawing Flat Plate Into the Water Current

2012 ◽  
Author(s):  
Mohammadmehdi Armandei ◽  
Antonio Carlos Fernandes
Keyword(s):  
Stability Analysis ◽  
Flat Plate ◽  
Least Square Method ◽  
Least Square ◽  
Water Current ◽  
Torsion Spring ◽  
Flutter Derivative ◽  
Liapunov Stable ◽  
The Stability ◽  
Derivatives Of

The present study deals with the stability analysis of an oscillating flat plate into the water current. The flat plate, which is attached to a torsion spring and located vertically in the water current, has only 1 DOF that is yawing motion. The experiments have shown that as the current velocity exceeds a special threshold, the flat plate becomes unstable and begins to oscillate. This oscillation can be utilized to extract energy. A free vibration experimental technique is used in this study. The experimental results are analyzed using the flutter derivative theory, in which the flutter derivatives of the motion are extracted using GLS (General Least-Square) method. The results confirm that the flat plate becomes dynamically unstable. Also, there is a Liapunov stable fixed point on the origin at the phase portrait of the yawing motion.

Experimental Identification Technique of Nonlinear Beams in Time Domain

1997 ◽  
Author(s):  
Kimihio Yasuda ◽  
Keisuke Kamiya
Keyword(s):  
Time Domain ◽  
Harmonic Balance ◽  
Least Square Method ◽  
Least Square ◽  
Governing Equations ◽  
Experimental Identification ◽  
Initial Values ◽  
Nonlinear Beams ◽  
Identification Technique ◽  
The Time Domain

Abstract In previous papers the authors proposed a new experimental identification technique applicable to elastic structures. The proposed technique is based on the principle of harmonic balance, and can be classified as the frequency domain technique. The technique requires the excitation force to be periodic. This is in some cases a restriction. So another technique free from this restriction is of use. In this paper, as a first step for developing such techniques, a technique applicable to beams is proposed. The proposed technique can be classified as the time domain one. Two variations of the technique are proposed, depending on what methods are used for estimating the parameters of the governing equations. The first method is based on the usual least square method. The second is based on solving a minimization problem with constraints. The latter usually yields better results. But in this method, an iteration procedure is used, which requires initial values for the parameters. To determine the initial values, the first method can be used. So both methods are useful. Finally the applicability of the proposed technique is confirmed by numerical simulation and experiments.

MICROCONTROLLER-BASED FOR SYSTEM IDENTIFICATION TOOLS USING LEAST SQUARE METHOD FOR RC CIRCUITS

2015 ◽  
Vol 77 (28) ◽  
Author(s):  
Ang Jia Yi ◽  
M. S. Abdul Majid ◽  
Azuwir M. N. ◽  
S. Yaacob
Keyword(s):  
Mathematical Model ◽  
System Identification ◽  
Least Square Method ◽  
Least Square ◽  
Real Time System ◽  
System Identification Method ◽  
Identification Method ◽  
Verification Methods ◽  
Identification Technique ◽  
Rc Circuit

System identification is one of the method to construct a plant mathematical model from experimental data. This method has been widely applied in the automatic control, aviation, spaceflight medicine, society economics and other fields more. With the rapid growth of the science and technology, the system identification technique has increasingly grown in various applications. Since most of the system identification devices are off-line base, this means that the system identification can only be done after collecting the data and process through a computer devices. This paper will show how to process system identification method with real-time system. This method required a microcontroller as the medium to perform. That’s why the system identification method will be programmed into a microcontroller, based on Least Square Method. Later, the system will be tested on a RC circuit to see the effect of the signal and the mathematical model obtained. The data will undergo the system identification toolbox for process using ARX and ARMAX model. On the other hand, the data will also be collected using the microcontroller created for analysis purpose. To ensure the validity of the model some verification methods are performed. Results show that the Least Square Method using Microcontroller base has the capability to work as a system identification tools.

Experimental Identification of the Constitutive Model of Viscoelastic Non-Standard Materials

2016 ◽  
Author(s):  
Stefano Amadori ◽  
Giuseppe Catania
Keyword(s):  
Rational Function ◽  
Measurement Data ◽  
Viscoelastic Behavior ◽  
Functionally Graded ◽  
Least Square ◽  
Material Behavior ◽  
Graded Materials ◽  
Identification Technique ◽  
Conventional Material ◽  
Generalized Kelvin Model

There is an increasing interest towards the use of non-conventional material such as Functionally Graded Materials (FGM) for aerospace and automotive mechanical applications. Classical material models, e.g. Kelvin or Zener, can show some limitations in describing the viscoelastic behavior of these materials. A numerical and experimental approach to identify the optimal model order and the parameters of the constitutive material relationship in the frequency domain is proposed. The constitutive equation is modeled by means of a generalized Kelvin model and expressed in the form of a rational function. To describe the complex material behavior, high order polynomials are needed for the rational function and the problem of finding the function coefficients can be ill-conditioned. Different approaches for the rational function parameters identification are compared. A least square error identification technique adopting Forsythe orthogonal polynomials is proposed. The selected procedure is first applied on numerically estimated measurements with noise, and then on real measurement data obtained by forced vibration testing of Polytetrafluoroethylene specimens.

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