References of "Dimitriadis, Grigorios"
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See detailBifurcation analysis of aircraft with structural nonlinearity and freeplay using numerical continuation
Dimitriadis, Grigorios ULg

in Journal of Aircraft (2008), 45(3), 893-905

In recent years the aeroelastic research community has carried out substantial work on the characterization and prediction of nonlinear aeroelastic phenomena. Of particular interest is the calculation of ... [more ▼]

In recent years the aeroelastic research community has carried out substantial work on the characterization and prediction of nonlinear aeroelastic phenomena. Of particular interest is the calculation of Limit Cycle Oscillations (LCO), which cannot be accomplished using traditional linear methods. In this paper, the prediction of the bifurcation and post-bifurcation behavior of nonlinear subsonic aircraft is carried out using Numerical Continuation. The analysis does not make use of continuation packages such as AUTO or MatCont. Two different continuation techniques are detailed, specifically adapted for realistic aeroelastic models. The approaches are demonstrated on model of a simple pitch plunge airfoil with cubic stiffness and an aeroelastic model of a transport aircraft with two different types of nonlinearity in the control surface. It is shown that one of the techniques yields highly accurate predictions for LCO amplitudes and periods while the second method trades off some accuracy for computational efficiency. [less ▲]

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See detailDiagnosis of Process Faults in Chemical Systems Using a Local Partial Least Squares Approach
Kruger, Uwe; Dimitriadis, Grigorios ULg

in AIChE Journal (2008), 54(10), 2581-2596

This article discusses the application of partial least squares (PLS) for monitoring complex chemical systems. In relation to existing work, this article proposes the integration of the statistical local ... [more ▼]

This article discusses the application of partial least squares (PLS) for monitoring complex chemical systems. In relation to existing work, this article proposes the integration of the statistical local approach into the PLS framework to monitor changes in the underlying model rather than analyzing the recorded input/output data directly. As discussed in the literature, monitoring changes in model parameters addresses the problems of nonstationary behavior and presents an analogy to model-based approaches. The benefits of the proposed technique are that (i) a detailed mechanistic plant model is not required, (ii) nonstationary process behavior does not produce false alarms, (iii) parameter changes can be non-Gaussian, (iv) Gaussian monitoring statistics can be established to simplify the monitoring task, and (v) fault magnitude and signatures can be estimated. This is demonstrated by a simulation example and the analysis of recorded data from two chemical processes. [less ▲]

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See detailNovel Instrumentation for the Measurement of the Unsteady Pressure Distribution around a Wing Undergoing Stall Flutter Oscillations
Li, Jing; Dimitriadis, Grigorios ULg; Gu, Fengshu et al

in Autumn Conference of the Institute of Acoustics 2007: Advances in Noise and Vibration Engineering (2007, October)

In this work, a wind tunnel model of a wing undergoing stall flutter oscillations is studied. It is a rectangular wing with pitch and plunge degrees of freedom and low pitch stiffness. The objective of ... [more ▼]

In this work, a wind tunnel model of a wing undergoing stall flutter oscillations is studied. It is a rectangular wing with pitch and plunge degrees of freedom and low pitch stiffness. The objective of this study is to promote the understanding of the stall flutter phenomenon by measuring the unsteady pressure distribution around the wing as well as the wing displacement, during unforced motion in two degrees of freedom. Both steady and unsteady pressures must be measured with sufficient accuracy during two types of tests. In the static tests the wing is to be clamped in position and not allowed to move and the steady pressures are to be measured around the centre-span section at different angles of attack. Thus the stall angle of attack can be identified and the stall mechanism characterized. In the dynamic tests the wing will be allowed to move and the unsteady pressures will be measured and recorded during a number of cycles of the oscillation, at a number of free stream airspeeds. [less ▲]

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See detailApproximate Numerical Continuation for Aeroelastic Systems Undergoing Aperiodic Limit Cycle Oscillations
Dimitriadis, Grigorios ULg

in Proceedings of the 2007 International Forum on Aeroelasticity and Structural Dynamics (2007, June)

This paper presents a modified numerical continuation approach for predicting the bifurcation behaviour of aeroelastic systems undergoing aperiodic limit cycles oscillations. Such oscillations can occur ... [more ▼]

This paper presents a modified numerical continuation approach for predicting the bifurcation behaviour of aeroelastic systems undergoing aperiodic limit cycles oscillations. Such oscillations can occur due to a number of nonlinear functions. Here, backlash nonlinearity in the aileron stiffness for a Generic Transport Aircraft is considered. It is shown that classical numerical continuation will fail due to the aperiodic nature of the limit cycles and the inability to perform period scaling and phase fixing. An alternative, approximate numerical continuation method is proposed, based on longer numerical integration sequences and a heuristic method for determining the period of the limit cycle oscillations. The approach is applied successfully to a simulated aeroelastic model of the Generic Transport Aircraft with backlash. [less ▲]

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See detailExperimental Study of Stall-Induced LCOs of Free Vibrating Wing
Li, Jing; Dimitriadis, Grigorios ULg

in Proceedings of the 2007 International Forum on Aeroelasticity and Structural Dynamics (2007, June)

Stall flutter is a limit cycle oscillation phenomenon occurring when all or part of the flow over a wing separates and re-attaches periodically. This paper reports on experimental investigations carried ... [more ▼]

Stall flutter is a limit cycle oscillation phenomenon occurring when all or part of the flow over a wing separates and re-attaches periodically. This paper reports on experimental investigations carried out on the subsonic stall flutter of a pitch plunge wing wind tunnel model. The object of the experiments was to investigate the aeroelastic effects of the nonlinearity introduced by boundary layer growth and flow separation and the ensuing stall-induced flutter, on a freely vibrating aeroelastic system. The motion of the wing and the pressure distribution around its surface were measured at various conditions. Three types of motion were observed, sometimes at the same wind tunnel airspeed; decay to equilibrium, symmetric limit cycle oscillations (LCO) and asymmetric LCOs. The aerodynamic mechanisms that give rise to these LCOs are described and analyzed. The effect of torsional wing stiffness on the stall flutter response of the wing is also investigated. Finally, repeating the experiments in a smaller wind tunnel showed that wind tunnel blockage has a significant effect on stall flutter. [less ▲]

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See detailLinear and Non-Linear Transonic Flow Behaviour of the Goland+ wing
Vio, Gareth Arthur; Dimitriadis, Grigorios ULg; Cooper, Jonathan Edward et al

in Proceedings of the 2007 International Forum on Aeroelasticity and Structural Dynamics (2007, June)

This paper is part of a study investigating the prediction of the aeroelastic behavior of aircraft subjected to transonic aerodynamic forces. The main objective of the work is the creation of Reduced ... [more ▼]

This paper is part of a study investigating the prediction of the aeroelastic behavior of aircraft subjected to transonic aerodynamic forces. The main objective of the work is the creation of Reduced Order Models from coupled Computational Fluid Dynamic and Finite Element calculations. The novelty of the approach lies in the identification of different types of Reduced Order Model in different flight regimes. Linear modal models are used in the Mach range range where the full CFD/CSD system is linear and nonlinear modal models in the transonic flight regime where the CFD/CSD system undergoes Limit Cycle Oscillations. Static solutions of the CFD/CSD system are used in order to determine the extent of the nonlinear Mach number range. The model treated in this work is a three-dimensional wing in a transonic flowfield. [less ▲]

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See detailAdaptive Aeroelastic Structures for Improved Aircraft Performance
Cooper, J. E.; Hodigere-Siddaramaiah, V.; Vio, G. A. et al

in Spencer Jr; Tomizuka, M.; Yun, C. B. (Eds.) et al World Forum on Smart Materials and Smart Structures Technology (2007, May)

There is a growing interest in the development of adaptive aeroelastic structures to allow aeroelastic deflections to be used in a beneficial manner. Part of the 3AS research programme was devoted towards ... [more ▼]

There is a growing interest in the development of adaptive aeroelastic structures to allow aeroelastic deflections to be used in a beneficial manner. Part of the 3AS research programme was devoted towards investigating the use of changes in the internal aerospace structure in order to control the static aeroelastic behaviour. Such an approach is desirable and arguably advantageous compared to other possible concepts. [less ▲]

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See detailDrag Minimisation Using Adaptive Aeroelastic Structures
Hodigere-Siddaramaiah, Vijaya; Cooper, Jonathan E; Vio, Gareth A. et al

in Proceedings of the 48th AIAA/ASME/ASCE/AHS/ASC Structures, Structural Dynamics, and Materials Conference (2007, April)

This paper describes the latest developments in a research program investigating the development of “adaptive internal structures” to enable adaptive aeroelastic control of aerospace structures. Through ... [more ▼]

This paper describes the latest developments in a research program investigating the development of “adaptive internal structures” to enable adaptive aeroelastic control of aerospace structures. Through controlled changes of the second moment of area, orientation or position of the spars, it is possible to control the bending and torsional stiffness characteristics of aircraft wings or tail surfaces. The aeroelastic behaviour can then be controlled as desired. A number of different adaptive internal structure concepts (rotating, moving and split spars) are compared here using a simple rectangular wing structure in order to determine which are the most effective for achieving minimum drag at different points in a representative flight envelope. A genetic algorithm approach is employed to determine the optimal spar orientation for rotating spars concept. It is shown that it is feasible to adjust the structure and trim characteristics of such wing structures in order to achieve minimum drag at all conditions. [less ▲]

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See detailFlight-Regime Dependent Reduced Order Models of CFD/FE aeroelastic systems in transonic flow
Dimitriadis, Grigorios ULg; Vio, Gareth Arthur; Cooper, Jonathan Edward

in Proceedings of the 48th AIAA/ASME/ASCE/AHS/ASC Structures, Structural Dynamics, and Materials Conference (2007, April)

This paper is part of a study investigating the prediction of the aeroelastic behavior of aircraft subjected to transonic aerodynamic forces. The main objective of the work is the creation of Reduced ... [more ▼]

This paper is part of a study investigating the prediction of the aeroelastic behavior of aircraft subjected to transonic aerodynamic forces. The main objective of the work is the creation of Reduced Order Models from coupled Computational Fluid Dynamic and Finite Element calculations. The novelty of the approach lies in the identification of different types of Reduced Order Model in different flight regimes. Linear modal models are used in the Mach range range where the full CFD/FE system is linear and nonlinear modal models in the transonic flight regime where the CFD/FE system undergoes Limit Cycle Oscillations. Static solutions of the CFD/FE system are used in order to determine the extent of the nonlinear Mach number range. The model treated in this work is a three-dimensional wing in a transonic flowfield. [less ▲]

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See detailImproved Implementation of the Harmonic Balance Method
Vio, Gareth Arthur; Dimitriadis, Grigorios ULg; Cooper, Jonathan Edward

in Proceedings of the 48th AIAA/ASME/ASCE/AHS/ASC Structures, Structural Dynamics, and Materials Conference (2007, April)

Harmonic Balance (HB) methods have been applied to non-linear aeroelastic problems since the 1980s. As the computational power available to researchers has increased, so has the order of calculated HB ... [more ▼]

Harmonic Balance (HB) methods have been applied to non-linear aeroelastic problems since the 1980s. As the computational power available to researchers has increased, so has the order of calculated HB solutions. However, the computational cost of a HB solution increases with the square of the order. Additionally, the traditional Newton-Raphson, Broyden, Toeplitz Jacobian and other techniques used for the solution of the non-linear algebraic problem at the heart of the HB methodology rely on a good initial guess for the unknown coefficients. If there are many such coefficients the probability that a good guess will be available is very low and the HB scheme may well fail. In this paper a search procedure using Genetic Algorithms (GA) is introduced to evaluate the coefficients of a harmonic balance solution. It is shown that the GA can provide high quality initial guesses for the HB coefficients. The method is applied to an aeroelastic galloping-type problem. [less ▲]

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See detailA Class of Methods for the Analysis of Blade Tip Timing Data from Bladed Assemblies Undergoing Simultaneous Resonances—Part II: Experimental Validation
Gallego-Garrido, Jon; Dimitriadis, Grigorios ULg; Carrington, Ian B. et al

in International Journal of Rotating Machinery (2007), 2007

Blade tip timing is a technique for the measurement of vibrations in rotating bladed assemblies. In Part I of this work a class of methods for the analysis of blade tip timing data from bladed assemblies ... [more ▼]

Blade tip timing is a technique for the measurement of vibrations in rotating bladed assemblies. In Part I of this work a class of methods for the analysis of blade tip timing data from bladed assemblies undergoing two simultaneous synchronous resonances was developed. The approaches were demonstrated using data from a mathematical simulation of tip timing data. In Part II the methods are validated on an experimental test rig. First, the construction and characteristics of the rig will be discussed. Then, the performance of the analysis techniques when applied to data from the rig will be compared and analysed. It is shown that accurate frequency estimates are obtained by all the methods for both single and double resonances. Furthermore, the recovered frequencies are used to calculate the amplitudes of the blade tip responses. The presence of mistuning in the bladed assembly does not affect the performance of the new techniques. [less ▲]

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See detailA Class of Methods for the Analysis of Blade Tip Timing Data from Bladed Assemblies Undergoing Simultaneous Resonances—Part I: Theoretical Development
Gallego-Garrido, Jon; Dimitriadis, Grigorios ULg; Wright, Jan Robert

in International Journal of Rotating Machinery (2007), 2007

Blade tip timing is a technique for the measurement of vibrations in rotating bladed assemblies. Although the fundamentals of the technique are simple, the analysis of data obtained in the presence of ... [more ▼]

Blade tip timing is a technique for the measurement of vibrations in rotating bladed assemblies. Although the fundamentals of the technique are simple, the analysis of data obtained in the presence of simultaneously occurring synchronous resonances is problematic. A class of autoregressive-based methods for the analysis of blade tip timing data from assemblies undergoing two simultaneous resonances has been developed. It includes approaches that assume both sinusoidal and general blade tip responses. The methods can handle both synchronous and asynchronous resonances. An exhaustive evaluation of the approaches was performed on simulated data in order to determine their accuracy and sensitivity. One of the techniques was found to perform best on asynchronous resonances and one on synchronous resonances. Both methods yielded very accurate vibration frequency estimates under all conditions of interest. [less ▲]

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See detailNon-Linear Identification in Modal Space Using a Genetic Algorithm Approach for Model Selection
Platten, Michael F; Wright, Jan Robert; Worden, Keith et al

in International Journal of Applied Mathematics & Mechanics (2007), 3(1), 72-89

The Non-Linear Resonant Decay Method is an approach for the identification of non-linear systems with large numbers of degrees of freedom. The identified non-linear model is expressed in linear modal ... [more ▼]

The Non-Linear Resonant Decay Method is an approach for the identification of non-linear systems with large numbers of degrees of freedom. The identified non-linear model is expressed in linear modal space and comprises the modal model of the underlying linear system with additional terms representing the non-linear behaviour. Potentially, a large number of these non-linear terms will exist but not all of them will be significant. The problem of deciding which and how many terms are required for an accurate identification has previously been addressed using the Forward Selection and Backward Elimination techniques. In this paper, a Genetic Algorithm optimisation is proposed as an alternative to those methods. A simulated lumped parameter non-linear dynamic system is used to demonstrate the proposed optimisation. The use of separate data sets for the identification and validation of the modal model is also investigated. It is found that the Genetic Algorithm approach yields significantly better results than the Backward Elimination and Forward Selection algorithms in many cases. [less ▲]

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See detailAeroelastic system identification using transonic CFD data for a wing/store configuration
Vio, Gareth Arthur; Dimitriadis, Grigorios ULg; Cooper, Jonathan E. et al

in Aerospace Science and Technology (2007), 11(2-3), 146-154

This paper is part of a study investigating the prediction of the aeroelastic behaviour of aircraft subjected to non-linear aerodynamic forces. The main objective of the work is the characterization of ... [more ▼]

This paper is part of a study investigating the prediction of the aeroelastic behaviour of aircraft subjected to non-linear aerodynamic forces. The main objective of the work is the characterization of the dynamic response of aeroelastic models resulting from coupled Computational Fluid Dynamic and Finite Element calculations. Of interest here is the identification of the flight condition at which the response bifurcates to limited or divergent amplitude self-sustained oscillations without carrying out a comprehensive set of full, computationally expensive, time-marching calculations. The model treated in this work is a three-dimensional wing in a transonic flowfield. Short datasets of pre-bifurcation behaviour are analysed to determine the system’s stability and degree of non-linearity. It is found that the calculated responses on the run-up to a transonic Limit Cycle Oscillation show little or no evidence of non-linearity. The non-linearity appears abruptly at the bifurcation flight condition. The variation of the local Mach number over the wing’s surface in the steady-state case is used to demonstrate that the non-linearity is due to a shock wave that can move along the surface. At Mach numbers where this is not possible the system behaves in a linear manner and its stability can be analysed using linear methods. [less ▲]

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See detailNon-linear aeroelastic prediction for aircraft applications
Henshaw, M.J. de C.; Badcock, Ken J.; Vio, G. A. et al

in Progress in Aerospace Sciences (2007), 434(4-6), 65-137

Current industrial practice for the prediction and analysis of flutter relies heavily on linear methods and this has led to overly conservative design and envelope restrictions for aircraft. Although the ... [more ▼]

Current industrial practice for the prediction and analysis of flutter relies heavily on linear methods and this has led to overly conservative design and envelope restrictions for aircraft. Although the methods have served the industry well, it is clear that for a number of reasons the inclusion of non-linearity in the mathematical and computational aeroelastic prediction tools is highly desirable. The increase in available and affordable computational resources, together with major advances in algorithms, mean that non-linear aeroelastic tools are now viable within the aircraft design and qualification environment. The Partnership for Unsteady Methods in Aerodynamics (PUMA) Defence and Aerospace Research Partnership (DARP) was sponsored in 2002 to conduct research into non-linear aeroelastic prediction methods and an academic, industry, and government consortium collaborated to address the following objectives: (1) To develop useable methodologies to model and predict non-linear aeroelastic behaviour of complete aircraft. (2) To evaluate the methodologies on real aircraft problems. (3) To investigate the effect of non-linearities on aeroelastic behaviour and to determine which have the greatest effect on the flutter qualification process. These aims have been very effectively met during the course of the programme and the research outputs include: (a) New methods available to industry for use in the flutter prediction process, together with the appropriate coaching of industry engineers. (b) Interesting results in both linear and non-linear aeroelastics, with comprehensive comparison of methods and approaches for challenging problems. (c) Additional embryonic techniques that, with further research, will further improve aeroelastics capability. This paper describes the methods that have been developed and how they are deployable within the industrial environment. We present a thorough review of the PUMA aeroelastics programme together with a comprehensive review of the relevant research in this domain. This is set within the context of a generic industrial process and the requirements of UK and US aeroelastic qualification. A range of test cases, from simple small DOF cases to full aircraft, have been used to evaluate and validate the non-linear methods developed and to make comparison with the linear methods in everyday use. These have focused mainly on aerodynamic non-linearity, although some results for structural non-linearity are also presented. The challenges associated with time domain (coupled computational fluid dynamics–computational structural model (CFD–CSM)) methods have been addressed through the development of grid movement, fluid–structure coupling, and control surface movement technologies. Conclusions regarding the accuracy and computational cost of these are presented. The computational cost of time-domain methods, despite substantial improvements in efficiency, remains high. However, significant advances have been made in reduced order methods, that allow non-linear behaviour to be modelled, but at a cost comparable with that of the regular linear methods. Of particular note is a method based on Hopf bifurcation that has reached an appropriate maturity for deployment on real aircraft configurations, though only limited results are presented herein. Results are also presented for dynamically linearised CFD approaches that hold out the possibility of non-linear results at a fraction of the cost of time coupled CFD–CSM methods. Local linearisation approaches (higher order harmonic balance and continuation method) are also presented; these have the advantage that no prior assumption of the nature of the aeroelastic instability is required, but currently these methods are limited to low DOF problems and it is thought that these will not reach a level of maturity appropriate to real aircraft problems for some years to come. Nevertheless, guidance on the most likely approaches has been derived and this forms the basis for ongoing research. It is important to recognise that the aeroelastic design and qualification requires a variety of methods applicable at different stages of the process. The methods reported herein are mapped to the process, so that their applicability and complementarity may be understood. Overall, the programme has provided a suite of methods that allow realistic consideration of non-linearity in the aeroelastic design and qualification of aircraft. Deployment of these methods is underway in the industrial environment, but full realisation of the benefit of these approaches will require appropriate engagement with the standards community so that safety standards may take proper account of the inclusion of non-linearity. [less ▲]

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See detailBifurcation analysis and limit cycle oscillation amplitude prediction methods applied to the aeroelastic galloping problem
Vio, Gareth Arthur; Dimitriadis, Grigorios ULg; Cooper, Jonathan E

in Journal of Fluids & Structures (2007), 23(7),

A global stability and bifurcation analysis of the transverse galloping of a square section beam in a normal steady flow has been implemented. The model is an ordinary differential equation with ... [more ▼]

A global stability and bifurcation analysis of the transverse galloping of a square section beam in a normal steady flow has been implemented. The model is an ordinary differential equation with polynomial damping nonlinearity. Six methods are used to predict bifurcation, the amplitudes and periods of the ensuing Limit Cycle Oscillations: (i) Cell mapping, {ii} Harmonic Balance, (iii) Higher Order Harmonic Balance,(iv) Centre Manifold linearization, (v) Normal Form and (vi) Numerical Continuation. The resulting stability predictions are compared with each other and with results obtained from numerical integration. The advantages and disadvantages of each technique are discussed. It is shown that, despite the simplicity of the system, only two of the methods succeed in predicting its full response spectrum. These are Higher Order Harmonic Balance and Numerical Continuation. [less ▲]

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See detailDemonstrating the identification of nonlinear vibrating systems to undergraduate students
Dimitriadis, Grigorios ULg; Vio, Gareth Arthur

in International Journal of Mechanical Engineering Education (2007), 35(4), 336-360

The identification of nonlinear dynamic systems is increasingly becoming a necessary part of vibration testing and there is significant research effort devoted to it. However, as the current methodologies ... [more ▼]

The identification of nonlinear dynamic systems is increasingly becoming a necessary part of vibration testing and there is significant research effort devoted to it. However, as the current methodologies are still not suitable for the identification of general nonlinear systems the subject is very rarely introduced to undergraduate students. In this paper, recent progress in developing an expert approach to nonlinear system identification is used in order to demonstrate the subject within the context of an undergraduate course or as an introductory tool for postgraduate students. The demonstration is based around a software package of an Expert System designed to apply systematically a wide range of identification approaches to the system under investigation. It is shown that the software can be used to demonstrate the need for nonlinear system identification, the complexity of the procedure, the possibility of failure and the good chances of success when enough physical information about the system is available. [less ▲]

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See detailNonlinearity Characterization for Nonlinear Dynamic System Identification Using an Expert Approach
Dimitriadis, Grigorios ULg; Vio, Gareth Arthur

in Proceedings of the 2006 International Conference on Noise and Vibration Engineering (2006, September)

The identification of nonlinear dynamic systems can be rendered significantly more parsimonious if the nonlinearity present in the system is known. While there are many successful non-parametric nonlinear ... [more ▼]

The identification of nonlinear dynamic systems can be rendered significantly more parsimonious if the nonlinearity present in the system is known. While there are many successful non-parametric nonlinear system identification methods, the resulting models do not describe the nonlinearity in physical terms and are difficult to obtain due to the large number of candidate terms that must be examined. In this paper an expert approach towards the characterization of nonlinearities in a dynamic system is presented. The methodology is based on simulations of dynamic systems with a variety of commonly occurring nonlinear functions. The responses of such systems to various types of excitation are analysed and rules are developed as to what nonlinearity is likely to be present in a system given the dynamic characteristics of measured responses. [less ▲]

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See detailAn experimental investigation of the subsonic stall flutter
Li, Jing; Andrinopoulos, Nikolaos; Dimitriadis, Grigorios ULg

in Proceedings of the 2006 International Conference on Noise and Vibration Engineering (2006, September)

This paper reports on experimental investigations of the subsonic stall flutter of a wing in a wind tunnel. Stall flutter (also know as Dynamic Stall) is a LCO phenomenon occurring when all or part of the ... [more ▼]

This paper reports on experimental investigations of the subsonic stall flutter of a wing in a wind tunnel. Stall flutter (also know as Dynamic Stall) is a LCO phenomenon occurring when all or part of the flow over a wing separates and re-attaches at least once during a full oscillation period. In order to investigate the aeroelastic effects of the nonlinearity introduced by the boundary layer growth and flow separation and the ensuing stall-induced LCO, a wind tunnel model of a wing undergoing stall flutter is designed, built and tested. The model is a rectangular wing with constant cross-section free to move in the pitch and plunge directions, restrained by torsional and linear springs respectively. The motion of the wing is measured using laser displacement probes. Two types of stall flutter are observed and measured: 1. Non-symmetric stall flutter, where the flow separates over one side of the wing only, and 2. Symmetric stall flutter, where the flow separates over both sides of the wing (deep stall). The bifurcation behaviour of the wing is very complex and both types of LCO can be observed during a single response history. [less ▲]

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See detailIdentification of Structural Free-play Non-linearities using the Non-Linear Resonant Decay Method
Yang, Z.; Dimitriadis, Grigorios ULg; Vio, Gareth A. et al

in Proceedings of the 2006 International Conference on Noise and Vibration Engineering (2006, September)

Structural non-linearities are becoming of increasing importance in determining the performance of a range of vibrating mechanical structures. As a consequence, the identification of systems with non ... [more ▼]

Structural non-linearities are becoming of increasing importance in determining the performance of a range of vibrating mechanical structures. As a consequence, the identification of systems with non-linearities is starting to become a necessary part of vibration testing procedures. NL-RDM (Non-Linear Resonant Decay Method) is an approach for the identification of non-linear multi-degree of freedom systems in modal space on a mode by mode basis, using an appropriated sine excitation to isolate modes or groups of modes. However, the application of NL-RDM to a multi-degree of freedom system with a discontinuous free-play non-linearity has not been attempted yet, except to treat it using high order polynomial terms. The difficulty of using NL-RDM when seeking a discontinuous free-play model lies in the choice of the so-called underlying linear model to be used in uncoupling the linear equations. In this paper, a simulated two degree of freedom lumped parameter system with a free-play non-linearity [less ▲]

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