Marco Prandina - Academia.edu (original) (raw)

Papers by Marco Prandina

List of Acronyms DOF Degree of freedom. DSM Dynamic stiffness matrix. FEM Finite element model. F... more List of Acronyms DOF Degree of freedom. DSM Dynamic stiffness matrix. FEM Finite element model. FFT Fast Fourier transform. FRF Frequency response function. MDOF Multiple degree-of-freedom.

An energy-based method is proposed to identify damping parameters from time histories of response... more An energy-based method is proposed to identify damping parameters from time histories of responses to sets of single-frequency harmonic excitation. The method is intended to be practically applicable to real structures and is able to identify the value of viscous damping, Coulomb friction and eventually other forms of non-linear damping models in aeroelastic systems. The inputs required are simply the accelerometer signals and the forces applied. It will be shown that if the system is undergoing Limit Cycle Oscillations, no external force is required for the identification process.

This dissertation reports a study on the identification of damping in multiple degree-of-freedom ... more This dissertation reports a study on the identification of damping in multiple degree-of-freedom systems with particular attention to the spatial location of the sources of energy dissipation. The main focus is in developing practical tools which can be used in real problems to obtain valuable information about the amplitude, the location and the way energy is dissipated in a structure. The physical phenomena involved in the energy dissipation of real vibrating structures are various. All these mechanisms have been studied separately with success by several authors, but there is still considerable doubt on how the damping behaviour should be represented in a suitable manner for engineering applications. Despite viscous damping being widely utilised in software and applications, it is a mathematical approximation of reality and therefore has to be used with an awareness of this limitation. The initial research focuses on the analysis of the existing damping models and identification ...

Journal of Physics: Conference Series, 2009

Page 1. Damping identification in multiple degree-of-freedom systems using an energy balance appr... more Page 1. Damping identification in multiple degree-of-freedom systems using an energy balance approach This article has been downloaded from IOPscience. Please scroll down to see the full text article. 2009 J. Phys.: Conf. Ser. 181 012006 ...

ABSTRACT The problem of flutter suppression in aeroelasticity may be treated using eigenvalue ass... more ABSTRACT The problem of flutter suppression in aeroelasticity may be treated using eigenvalue assignment. The conventional approach to active vibration control requires not only the structural mass, damping and stiffness terms, but also aeroelastic damping and stiffness contributions. This requirement becomes unnecessary when using the receptance method which depends only upon vibration measurements. In the cases considered in this paper it requires wind-tunnel ‘wind on’ measurement of frequency response functions. The set-up includes a two degree-of-freedom pitch-plunge aerofoil, which allows for adjustment of the open-loop eigenvalues and extrapolation of the closed-loop eigenvalues with wind speed enabling the prediction of flutter velocities. One of the advantages of using the receptance method is that in principle the controller can be continuously corrected using in-flight measurements with consequent improvements to aircraft manoeuvrability and possibly survivability in the event of damage to the aircraft. The paper describes the first experimental study of flutter suppression carried out in the Liverpool low-speed wind-tunnel including physical tests and simulated application of the receptance method using test data. Actuation of a flap is achieved by two piezo-stacks in a ‘V’ configuration and the vibration response is measured using ICP accelerometers mounted externally to the wind-tunnel. The purpose of the research is to demonstrate the delayed onset of flutter by increasing the flight envelope of stable air speeds. Preliminary experimental results are presented.

ABSTRACT This paper presents the application of the receptance method to nonlinear systems for ac... more ABSTRACT This paper presents the application of the receptance method to nonlinear systems for active vibration control. The method, previously established for linear systems, is extended to a class of single-degree-of-freedom nonlinear systems that can be characterised using describing functions. A significant advantage of the receptance method is that there is no requirement to know the system parameters such as mass, damping and stiffness terms, typically obtained using finite element methods. The method is particularly advantageous for nonlinear systems, since there is no requirement for nonlinear identification. A linear state feedback controller is applied to an example of a single-degree-of-freedom Duffing oscillator, to assign the peak resonance to a prescribed value using the established Sherman–Morrison receptance method. It is then demonstrated that an iterative form of the Sherman–Morrison receptance method is required for the accurate assignment of this peak resonance, in order to account for changes in the open-loop receptance. Both harmonic balance and Volterra series representations are investigated to approximate the receptance in the complex domain, and their advantages and disadvantages are discussed in a numerical example.

In every vibrating structure a portion of the energy input by external forces is always dissipate... more In every vibrating structure a portion of the energy input by external forces is always dissipated by damping mechanisms. Despite being often oversimplified in engineering design, there are many cases where accurate modelling of damping forces is extremely important. In this paper an energy-based method is proposed to identify damping parameters from time histories of responses to sets of single-frequency harmonic excitation. The method is intended to be practically applicable to real structures and is able to identify the spatial location and value of viscous damping, Coulomb friction and eventually other forms of nonlinear damping models in multiple degree-offreedom systems. The inputs required are the accelerometer signals in several degrees of freedom of the structure and the forces applied for a certain number of tests. There is no need to know or to evaluate the mass and stiffness matrices. Spatial incompleteness is investigated and modal incompleteness does not affect the met...

Journal of Sound and Vibration, Jun 1, 2009

Journal of Sound and Vibration, 2009

A study is carried out into the philosophy and performance of different approaches for the determ... more A study is carried out into the philosophy and performance of different approaches for the determination of linear viscous damping in elasto-mechanical systems. The methods studied include a closed-form solution, identification methods based on inverting the matrix of receptances, energy expressions developed from single-frequency excitation and responses as well as first-order perturbation methods. The work is concentrated particularly upon modal truncation and how this affects the distribution of matrix terms and the ability of the identified damping (together with known mass and stiffness terms) to reproduce the complex eigenvalues and eigenvectors of the full-order system. A simulated example is used to illustrate various points covered in the theoretical discussion of the methods considered. r

Progress in Aerospace Sciences, 2011

In this paper the use of eigenvalue stability analysis of very large dimension aeroelastic numeri... more In this paper the use of eigenvalue stability analysis of very large dimension aeroelastic numerical models arising from the exploitation of computational fluid dynamics is reviewed. A formulation based on a block reduction of the system Jacobian proves powerful to allow various numerical algorithms to be exploited, including frequency domain solvers, reconstruction of a term describing the fluidstructure interaction from the sparse data which incurs the main computational cost, and sampling to place the expensive samples where they are most needed. The stability formulation also allows nondeterministic analysis to be carried out very efficiently through the use of an approximate Newton solver. Finally, the system eigenvectors are exploited to produce nonlinear and parameterised reduced order models for computing limit cycle responses. The performance of the methods is illustrated with results from a number of academic and large dimension aircraft test cases.

Journal of Physics: Conference Series, 2009

Journal of Sound and Vibration, Jun 1, 2009

Journal of Sound and Vibration, 2009

Progress in Aerospace Sciences, 2011

Journal of Physics: Conference Series, 2009