Parameter Estimation of a Fluttering Aeroelastic System in the Transitional Reynolds Number Regime

2010 ◽  
Author(s):  
Mohammad Khalil ◽  
Abhijit Sarkar ◽  
Dominique Poirel
Keyword(s):  
Reynolds Number ◽  
Parameter Estimation ◽  
Wind Tunnel ◽  
Van Der Pol Oscillator ◽  
Limit Cycle Oscillation ◽  
Parameter Estimates ◽  
Stable Limit ◽  
Van Der Pol ◽  
Aeroelastic System ◽  
Rigid Wing

We report the parameter estimation results of a self-sustaining aeroelastic oscillator. The system is composed of a rigid wing that is elastically mounted on a rig, which in turn is fixed in a wind tunnel. For certain flow conditions, in particular dictated by the Reynolds number in the transitional regime, the wing extracts energy from the flow leading to a stable limit cycle oscillation. The basic physical mechanism at the origin of the oscillations is laminar boundary layer separation, which leads to negative aerodynamic damping. An empirical model of the aeroelastic system is proposed in the form of a generalized Duffing-van der Pol oscillator, whereby the linear and nonlinear aeroelastic terms are unknowns to be estimated. The model (input) noise process accounting for the amplitude modulation observed from experiments will also be estimated. We apply a Bayesian inference based batch data assimilation method in tackling this strongly nonlinear and non-Gaussian model. In particular, Markov Chain Monte Carlo sampling technique is used to generate samples from the joint distribution of the unknown parameters given noisy measurement data. The extended Kalman filter is utilized to obtain the conditional distribution of the model state given the noisy measurements. The parameter estimates for a third order generalized Duffing-van der Pol oscillator are obtained and marginal and joint probability density functions for the parameters will be presented for both a numerical model and a rigid wing that is elastically mounted on a rig in a wind tunnel.

Developing a Reduced-Order Model to Understand Non-Synchronous Vibration (NSV) in Turbomachinery

2012 ◽  
Author(s):  
Stephen T. Clark ◽  
Robert E. Kielb ◽  
Kenneth C. Hall
Keyword(s):  
Stable Limit Cycle ◽  
Forced Response ◽  
Van Der Pol Oscillator ◽  
Future Research ◽  
Limit Cycle Oscillation ◽  
Preliminary Design ◽  
Stable Limit ◽  
Van Der Pol ◽  
Reduced Order ◽  
Van Der Pol Model

This paper demonstrates the potential of using a multi-degree-of-freedom, traditional van der Pol oscillator to model Non-Synchronous Vibration (NSV) in turbomachinery. It is shown that the two main characteristics of NSV are captured by the reduced-order, van der Pol model. First, a stable limit cycle oscillation (LCO) is maintained for various conditions. Second, the lock-in phenomenon typical of NSV is captured for various fluid-structure frequency ratios. The results also show the maximum amplitude of the LCO occurs at an off-resonant condition, i.e., when the natural shedding frequency of the aerodynamic instability is not coincident with the natural modal frequency of the structure. This conclusion is especially relevant in preliminary design in industry because it suggests that design engineers cannot treat NSV as a normal Campbell-diagram crossing as they would for preliminary design for forced response; it is possible that by redesigning the blade, the response amplitude of the blade may actually be higher. The goal of future research will be to identify values and significance of the coupling parameters used in the van der Pol model, to match these coefficients with confirmed instances of experimental NSV, and to develop a preliminary design tool that engineers can use to better design turbomachinery for NSV. Proper Orthogonal Decomposition (POD) CFD techniques and coefficient tuning from experimental instances of NSV have been considered to identify the unknown coupling coefficients in the van der Pol model. Both the modeling of experimental NSV and preliminary design development will occur in future research.

Extending a Van der Pol Based Reduced-Order Model for Fluid-Structure Interaction Applied to Non-Synchronous Vibrations in Turbomachinery

2021 ◽  
Author(s):  
Richard Hollenbach ◽  
Robert Kielb ◽  
Kenneth Hall
Keyword(s):  
Fluid Structure Interaction ◽  
Reduced Order Model ◽  
Van Der Pol Oscillator ◽  
Previous Model ◽  
Stable Limit ◽  
Order Model ◽  
Van Der Pol ◽  
Fluid Structure ◽  
Reduced Order ◽  
Structure Interaction

Abstract This paper expands upon a multi-degree-of-freedom, Van der Pol oscillator used to model buffet and Nonsynchronous Vibrations (NSV) in turbines. Two degrees-of-freedom are used, a fluid tracking variable incorporating a Van der Pol oscillator and a classic spring, mass, damper mounted cylinder variable; thus, this model is one of fluid-structure interaction. This model has been previously shown to exhibit the two main aspects of NSV. The first is the lock-in or entrainment phenomenon of the fluid shedding frequency jumping onto the natural frequency of the oscillator, while the second is a stable limit cycle oscillation (LCO) once the transient solution disappears. Improvements are made to the previous model to better understand this aeroelastic phenomenon. First, an error minimizing technique through a system identification method is used to tune the coefficients in the Reduced Order Model (ROM) to improve the accuracy in comparison to experimental data. Secondly, a cubic stiffness term is added to the fluid equation; this term is often seen in the Duffing Oscillator equation, which allows this ROM to capture the experimental behavior more accurately, seen in previous literature. The finalized model captures the experimental cylinder data found in literature much better than the previous model. These improvements also open the door for future models, such as that of a pitching airfoil or a turbomachinery blade, to create a preliminary design tool for studying NSV in turbomachinery.

Bonhoeffer-van der Pol Oscillator Model of the Sino-Atrial Node: A Possible Mechanism of Heart Rate Regulation

1994 ◽  
Vol 33 (01) ◽  
pp. 116-119 ◽  
Author(s):  
S. Sato ◽  
S. Doi ◽  
T. Nomura
Keyword(s):  
Heart Rate ◽  
Stable Limit Cycle ◽  
Nonlinear Dynamic System ◽  
Van Der Pol Oscillator ◽  
Transition Curve ◽  
Stable Limit ◽  
Van Der Pol ◽  
Rate Regulation ◽  
Dynamic System Theory ◽  
Heart Rate Regulation

Abstract:A Bonhoeffer-van der Pol equation with a stable limit cycle is proposed as a model of the pacemaker in the sino-atrial node to exptain heart rate regulation. Standard tools, such as the phase transition curve in nonlinear dynamic system theory, are used to analyze the model and results are compared with other studies on experiments with dogs.

Limit-Cycle Oscillation Suppression of Bioinspired Ornithopter: Wind Tunnel Testing

2011 ◽  
Author(s):  
Jun-Seong Lee ◽  
Dong-Kyu Lee ◽  
Juho Lee ◽  
Jae-Hung Han
Keyword(s):  
Wind Tunnel ◽  
Limit Cycle ◽  
Fiber Composite ◽  
Elevation Angle ◽  
Stable Limit Cycle ◽  
Limit Cycle Oscillation ◽  
Stable Limit ◽  
Wing Motion ◽  
Cycle Oscillation ◽  
Trim Flight

This study experimentally shows that an oscillatory behavior observed in a trim flight of an ornithopter has a stable limit-cycle oscillation (LCO) characteristics and that the magnitude of the LCO in body pitch dynamics can be suppressed by active tail motion. A free flight of the tested ornithopter is emulated in the wind tunnel using a specially devised tether that provides the minimal mechanical interference to the flight of ornithopter. Due to the symmetric wing motion in forward trim flight, the longitudinal flight dynamics is more focused than the lateral one. The non-contact type sensors are used to measure the time histories of the flight state variables such as wing and tail motions, body pitch angle, and altitude. The tail motion for the pitch LCO reduction is achieved by two actuators: 1) Servo motor for the rigid-body motion of the tail elevation angle, and 2) Macro-Fiber Composite strain actuator for the elastic deformation of the tail camber. The performances of the LCO suppressions are compared in the root-mean-square-error sense and the harmonically activated in-phase tail motion linked to wing motion is observed to effectively reduce the pitch LCO.

scholarly journals MODELING AND CHARACTERIZATION OF OSCILLATOR CIRCUITS BY VAN DER POL MODEL USING PARAMETER ESTIMATION

2012 ◽  
Vol 21 (05) ◽  
pp. 1250043 ◽  
Author(s):  
IULIA DUMITRESCU ◽  
SMAIL BACHIR ◽  
DAVID CORDEAU ◽  
JEAN-MARIE PAILLOT ◽  
MIHAI IORDACHE
Keyword(s):  
Parameter Estimation ◽  
Optimal Parameter ◽  
Estimation Method ◽  
Van Der Pol Oscillator ◽  
Space Representation ◽  
Model Parameters ◽  
Identification Algorithm ◽  
Van Der Pol ◽  
Oscillator Circuit

In this paper, we present a new method for the modeling and characterization of oscillator circuit with a Van Der Pol (VDP) model using parameter identification. We also discussed and investigated the problem of estimation in nonlinear system based on time domain data. The approach is based on an appropriate state space representation of Van der Pol oscillator that allows an optimal parameter estimation. Using sampled output voltage signal, model parameters are obtained by an iterative identification algorithm based on Output Error method. Normalization issues are fixed by an appropriate transformation allowing a quickly global minimum search. Finally, the proposed estimation method is tested and validated using simulation data from a 1 GHz oscillator circuit in GaAs technology.

Analysis and Preliminary Design of a Sailboat with Self-Trimming Wing Sail

1983 ◽  
Vol 20 (04) ◽  
pp. 370-376
Author(s):  
B. G. Newman ◽  
G. I. Fekete
Keyword(s):  
Reynolds Number ◽  
Wind Tunnel ◽  
Preliminary Design ◽  
Static And Dynamic Stability ◽  
Flap Deflection ◽  
The Stability ◽  
Lift And Drag ◽  
Existing Data ◽  
Good Agreement ◽  
Rigid Wing

A theoretical analysis has been made of the static and dynamic stability of a self-trimming rigid wing sail for use on a sailboat without sheets or halyards. The effects of camber or flap deflection and the position of the trimming plane are considered. A satisfactory design incorporates an uncambered main wing of medium aspect ratio and a trimming tail plane. Wind tunnel tests on a model of this design confirmed the stability of the sail and indicated adequate damping. The measured lift and drag coefficients were in good agreement with existing data at a similar Reynolds number.

scholarly journals Design of a New Chaotic System Based on Van Der Pol Oscillator and Its Encryption Application

Mathematics ◽  
2019 ◽  
Vol 7 (8) ◽  
pp. 743 ◽  
Author(s):  
Jianbin He ◽  
Jianping Cai
Keyword(s):  
Control Method ◽  
Variable Parameter ◽  
Stable Limit Cycle ◽  
Simple Algorithm ◽  
Van Der Pol Oscillator ◽  
Stable Limit ◽  
Van Der Pol ◽  
Dynamical Characteristics ◽  
New Chaotic System ◽  
Exclusive Or

The Van der Pol oscillator is investigated by the parameter control method. This method only needs to control one parameter of the Van der Pol oscillator by a simple periodic function; then, the Van der Pol oscillator can behave chaotically from the stable limit cycle. Based on the new Van der Pol oscillator with variable parameter (VdPVP), some dynamical characteristics are discussed by numerical simulations, such as the Lyapunov exponents and bifurcation diagrams. The numerical results show that there exists a positive Lyapunov exponent in the VdPVP. Therefore, an encryption algorithm is designed by the pseudo-random sequences generated from the VdPVP. This simple algorithm consists of chaos scrambling and chaos XOR (exclusive-or) operation, and the statistical analyses show that it has good security and encryption effectiveness. Finally, the feasibility and validity are verified by simulation experiments of image encryption.

A note on state and parameter estimation in a van der Pol oscillator

Automatica ◽  
2010 ◽  
Vol 46 (10) ◽  
pp. 1735-1738 ◽  
Author(s):  
Gildas Besançon ◽  
Alina Voda ◽  
Guillaume Jouffroy
Keyword(s):  
Parameter Estimation ◽  
Van Der Pol Oscillator ◽  
Van Der Pol

EXTENDING A VAN DER POL BASED REDUCED-ORDER MODEL FOR FLUID-STRUCTURE INTERACTION APPLIED TO NON-SYNCHRONOUS VIBRATIONS IN TURBOMACHINERY

2021 ◽  
pp. 1-14
Author(s):  
Richard Hollenbach ◽  
Robert Kielb ◽  
Kenneth Hall
Keyword(s):  
Fluid Structure Interaction ◽  
Reduced Order Model ◽  
Van Der Pol Oscillator ◽  
Previous Model ◽  
Stable Limit ◽  
Order Model ◽  
Van Der Pol ◽  
Fluid Structure ◽  
Reduced Order ◽  
Structure Interaction

Abstract This paper expands upon a multi-degree-of-freedom, Van der Pol oscillator used to model buffet and Nonsynchronous Vibrations (NSV) in turbines. Two degrees-of-freedom are used, a fluid tracking variable incorporating a Van der Pol oscillator and a classic spring, mass, damper mounted cylinder variable; thus, this model is one of fluid-structure interaction. This model has been previously shown to exhibit the two main aspects of NSV. The first is the lock-in or entrainment phenomenon of the fluid shedding frequency jumping onto the natural frequency of the oscillator, while the second is a stable limit cycle oscillation (LCO) once the transient solution disappears. Improvements are made to the previous model to better understand this aeroelastic phenomenon. First, an error minimizing technique through a system identification method is used to tune the coefficients in the Reduced Order Model (ROM) to improve the accuracy in comparison to experimental data. Secondly, a cubic stiffness term is added to the fluid equation; this term is often seen in the Duffing Oscillator equation, which allows this ROM to capture the experimental behavior more accurately, seen in previous literature. The finalized model captures the experimental cylinder data found in literature much better than the previous model. These improvements also open the door for future models, such as that of a pitching airfoil or a turbomachinery blade, to create a preliminary design tool for studying NSV in turbomachinery.

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