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## Publications

Publications (139)

In this paper, mode veering, crossing and lock-in phenomena are experimentally analyzed and characterized. Their occurrence is generally found, under different conditions, when there is a parameter variation in the system that produces a change in its behaviour. It often happens that, when the natural frequencies of two modes approach each other, t...

In this work we present the results of a field trial with a FBG sensor array system for the real time monitoring of railway traffic and for the structural health monitoring of both the railway track and train wheels. The test campaigns are performed on the on the 2nd line of Milan metropolitan underground, employing more than 50 FBG sensors along 1...

When there is a parameter varying in a system, so that one natural frequency approaches another one, the phenomenon of veering is generally found and highly coupled modes are the emerging characteristic of this dynamic behavior. It is far more difficult to find systems that instead of a veering present crossing between modes, and the crossing pheno...

The phenomena of mode veering, crossing and lock-in are experimentally analyzed in this paper. Their occurrence is generally found, under different conditions, when there is a parameter varying in the system, producing a change in its behavior. It often happens that, when the natural frequencies of two modes approach each other, they can cross, vee...

It is well known that experimentally obtained mode shapes can be smoothed by using a linear combination of mode shapes from a finite element (FE) model. This is known from the theory of structural modification (SM) and from the system equivalent reduction expansion process (SEREP). Using this approach the set of FE mode shapes to be included in th...

The actual capability of monitoring mechanical systems is based on new generation of sensors, modeling and algorithms for the detection of properties, operating conditions and/or failures of the monitored system. The present paper, on the basis of several projects in progress at the University La Sapienza, Rome, illustrates the combination of new s...

In this work we present the results of a field trial with a FBG sensor array system for the real time monitoring of railway traffic and for the structural health monitoring of both the railway track and train wheels. The test campaigns are performed on the on the 2nd line of Milan metropolitan underground, employing more than 50 FBG sensors along 1...

The phenomenon of mode veering is analyzed in this paper. Veering occurs when there is a varying parameter in the system: it produces a change in the systems and it often happens that, when the frequencies approach each other, instead of crossing they veer, and the mode shapes swap from one branch to the other. The problem is presented for a genera...

In this paper a new technique is presented to estimate the rotational degrees of freedom of a flexural structure, using only a limited number of sensors that measure the translational DoFs of the system. A set of flexural mode shapes in a limited number of nodes is obtained by modal testing, while a different set of approximated mode is calculated...

Why it is difficult to solve a vibroacoustic problem; what are the hidden pitfalls that one is called to overcome; are there methods or techniques suggested in other fields of physics that can help to formulate an efficient vibroacoustic prediction model? The authors provide personal answers to these questions and suggest also a classification of t...

The method of structural dynamic optimization is applied here to two real-life structures, a small two-cylinder, air-cooled
gasoline engine and a high speed machine tool. The aim of the first application is the reduction of the kinematic vibration
transmission path composed of a piston-connecting rod, a crankshaft and an engine block, while the goa...

Vibration and acoustic requirements are becoming increasingly important in the design of mechanical structures, but they are
not usually of primary concern in the design process. So the need to vary the structural behaviour to solve noise and vibration
problems often occurs at the prototype stage, giving rise to the so-called structural modificatio...

In the context of mid- and high-frequency problems in acoustics and vibrations, the modelling of complex systems generates several difficulties, partially related to the large number of degrees of freedom in the discretised model. That makes the problem computationally heavy and very sensitive also to uncertainties in the data. For this reason, in...

. When a finger moves to scan the surface of an object, it activates the receptors located under the skin allowing the brain to identify objects and information about their properties. The information concerning the object surface is represented by the vibrations induced by the friction between the skin and the rubbed object in contact. The vibrati...

One of the most challenging field in structural dynamics is related to high frequency vibrations. These problems are born in vibration-acoustic analysis, with special interest in automotive or aerospace industry, where the capability of prediction of the noise response of the vehicle and the enhancement of its vibro-acosutic performance has a strat...

When a finger moves to scan the surface of an object, the sliding contact generates vibrations that propagate in the finger skin and transmit the information about the object characteristics to mechanoreceptors. Mechanoreceptors convert vibrations into electric impulses sent to the brain. In this context, by appropriate experiments, a frequency ana...

Despite over a century of research on brake squeal noise, an effective solution for squeal suppression is still under investigation, even if the physics behind squeal is nowadays quite well understood. In fact, there is agreement in the scientific community that squeal is mainly caused by an unstable coupling between modes of the brake rotor with m...

This paper presents a review of recent investigations on brake squeal noise carried out on simplified experimental rigs. The common theme of these works is that of approaching the study of squeal noise on experimental set-ups that are much simpler than commercial disc brakes, providing the possibility of repeatable measurements of squeal occurrence...

The complex envelope vectorization (CEV) is a recent method that has been successfully applied to structural and internal acoustic problems. Unlike other methods proposed in the last two decades to solve high frequency problems, CEV is not an energy method, although it shares with all the other techniques a variable transformation of the field vari...

The complex envelope vectorization (CEV) is a numerical procedure that can be used for the fast solution of any high frequency problem. CEV has been successfully applied to structural and internal acoustic problems. As most of other methods developed as alternative to the Statistical Energy Analysis, CEV uses a variable transformation but, unlike m...

This paper presents a synopsis of recent investigations on brake squeal noise carried out on simplified experimental rigs. The common theme of the these works is that of approaching the study of squeal noise on experimental set-ups that are much simpler than commercial disc brakes providing the possibility of repeatable measurements of squeal occur...

In this paper a mathematical model based on a multi-scale asymptotic technique for the dynamic description of honeycomb structures
is presented. The technique is used to evaluate an equivalent orthotropic model of the honeycomb. The derivation is based
on an asymptotic analysis for periodic structures developed by Bensoussan, Lions and Papanicolaou...

“Brake squeal” groups a large set of high-frequency sound emissions from brake systems. They are generated during the braking phase and are characterized by a harmonic spectrum. The onset of squeal is due to an unstable behaviour occurring in linear conditions during the braking phase, and a general approach used by several authors to determine the...

The complex envelope displacement analysis (CEDA) is a procedure to solve high frequency vibration and vibro-acoustic problems, providing the envelope of the physical solution. CEDA is based on a variable transformation mapping the high frequency oscillations into signals of low frequency content and has been successfully applied to one-dimensional...

This paper on brake squeal instability presents a reduced order model of a laboratory brake considered in a previous paper, and presents a description of the squeal mechanism occurring during experiments.The model uses the modal parameters of the laboratory brake components, the disc and the caliper, when they are not in contact between them. Succe...

At present, Statistical Energy Analysis (SEA) is the most acknowledged tool for the solution of high-frequency problems.However, a reliable solution can be obtained by SEA only if particular conditions are satisfied. In other words, the basic hypotheses would define the range of applicability of this method.Two important parameters, coupling loss f...

Brake squeal" groups a large set of high frequency sound emissions from brake systems, generated during the braking phase and characterized by a harmonic spectrum. The generation of squeal is due to an unstable behaviour of the system during the braking phase. Many researchers associate the squeal phenomena to the coalescence of two eigenfrequencie...

This paper on brake squeal instability presents a reduced order model of a laboratory brake considered in a previous paper, and presents a description of the squeal mechanism occurring during experiments.
The model uses the modal parameters of the laboratory brake components, the disc and the caliper, when they are not in contact between them. Succ...

The complex envelope vectorization (CEV) is an alternative technique to SEA and other recent energy methods developed to study high frequency problems. Notwithstanding the large efforts devoted to this topic for many years, there is not yet an appropriate technique to tackle it efficiently. In the framework of an Italian research project "Novel met...

Statistical Energy Analysis (SEA) is the most acknowledged technique to solve high frequency problems. However, SEA can be able to provide reliable results only if particular conditions are satisfied. Thus, some basic hypotheses define the range of applicability of the method. The coefficients of the SEA equations depend on the coupling loss factor...

In this paper an experimental analysis on the energy transmission in vibrating structures is considered. The Statistical Energy Analysis (SEA) is, at present, the most acknowledged theory for the solution of high frequency vibroacoustic problems. The coefficients of the SEA equations depend on the coupling loss factor (CLF), the internal loss facto...

Substructures coupling is still an important tool in several applications of modal analysis, especially structural modification and structures assembling. The subject is particularly relevant in virtual prototyping of complex systems and responds to actual industrial needs. This paper analyzes the possibility of assembling together different substr...

The complex envelope displacement vectorization (CEDV) is a promising procedure to solve high frequency vibration and vibroacoustic linear problems, alternative to energy methods. The method consists in a variable transformation that maps the high frequency response variable into an envelope variable characterized by a low wavenumber spectrum. In t...

Rotational degrees of freedom are basic to solve substructuring and structural modification problems. While they are included in finite element models, the common experimental tests do not provide these quantities, because of the difficulty of their measurement. In this paper, the possibility of using low-cost PZT transducers to estimate rotational...

Plane wave interference and space averages play a significant role in the derivation of some vibration conductivity equations that are becoming more and more popular in modelling vibroacoustic problems. Particularly, the thermal approach and the modified vibration conductivity equations are here considered with the aim of establishing similarities...

A method for evaluating the energy flow confidence level in vibrating systems with randomly perturbed parameters is presented. The energy flow is predicted in terms of the mobilities of resonant subsystems or by the solution of the velocity wave field for non-resonant subsystems. The statistical moments of the energy flow are calculated by a pertur...

The complex envelope displacement analysis (CEDA) is a procedure used to analyze high frequency problems. As other methods developed in the last decade to circumvent shortcomings typical of Statistical Energy Analysis, CEDA is capable of providing the envelope of the physical solution by solving an appropriate differential equation whose solution i...

In this paper an experimental analysis on the energy transmission of vibrating structures is developed. Most of the traditional numerical techniques such as FEM and BEM fail when one tries to solve high-frequency dynamic problems. The statistical Energy Analysis (SEA) is, at present, the most acknowledged theory for the solution of high frequency v...

Substructures coupling is still an important tool in several applications of modal analysis, especially structural modification and structures assembling. The subject is particularly relevant in virtual prototyping of complex systems and responds to actual industrial needs. This paper analyzes the possibility of assembling together different substr...

The complex envelope displacement analysis (CEDA) is a procedure to solve high frequency vibration and vibroacoustic problems, providing the envelope of the physical solution. CEDA, based originally on a variable transformation that maps the high frequency oscillations into a quasi-static displacement field, has been successfully applied to one-dim...

In this paper an experimental analysis of the energy transmission in vibrating structures is considered. The classical discretization techniques (FEM, BEM) fail when one tries to solve high-frequency dynamic problems. At present, SEA is the most acknowledged theory for providing such kind of solution, giving information on the stored mechanical ene...

Rotational degrees of freedom are fundamental to perform substructure coupling whenever moment transmission at joints is involved. While they are included in finite element models, the common experimental tests do not provide these quantities, because of the difficulty of their measurement. Therefore, when it is necessary to couple two structures t...

Since SEA was originally proposed at the beginning of the sixty's, any new model for the analysis of high frequency vibroacoustic problem uses an appropriate variable transformation leading to new sets of governing equations for the structural-acoustic problem that are expected to be computationally more convenient than the original set of equation...

The basic hypotheses of Statistical Energy Analysis (SEA) define the range of applicability of this method. In this paper these hypotheses involving the SEA parameters (coupling loss factor, damping loss factor, modal density and modal overlap) are mathematically translated. Mechanical systems with different SEA parameters have dissimilar trends at...

Rotational degrees of freedom are basic to solve substructuring and structural modification problems. While they are included in finite element models, the common experimental tests do not provide these quantities, because of the difficulty of their measurement. In this paper, the possibility of using low cost PZT transducers to estimate rotational...

Complex envelope displacement analysis seems to be a promising approach to analyze high-frequency structural problems and is expected to be useful to study structural-acoustic coupled problems. However, in the original derivation of the method it was shown the presence of a troublesome spurious solution consisting of a high wavenumber component tha...

Predicting the effect of distributed structural modifications, such as rib or plate stiffeners, on structures for which a theoretical model is not available, is not practically considered in the technical literature: this is due to the objective difficulty of coupling continuous modifications with an original structure known through its frequency r...

Predicting the effect of distributed modifications is not a simple problem, especially when the original structure is known only experimentally by its translational FRF matrix. In fact, when coupling structures together, a complete FRF matrix, including both translational and rotational degrees of freedom must be determined. While in principle rota...

Plane waves' interference and space averages play a significant role in the derivation of some vibration conductivity equations that are becoming more and more popular in modeling vibroacoustic problems. Particularly the thermal approach and the modified heat conductivity equations are here considered with the aim of establishing similarities and/o...

Rotational degrees of freedom are basic to solve substructuring and structural modification problems. While they are included in finite element models, the common experimental tests do not provide these quantities, because of the difficulty of their measurement. In this paper, the possibility of using low cost PZT transducers to estimate rotational...

A new approach to wave analysis for general vibroacoustic applications is presented. The central idea is to provide an alternative way to solve the equation of stationary waves. In this new method, the natural variable of the problem, which is the pressure or displacement, is replaced with a complex envelope. This leads to a new governing equation....

Statistical energy analysis provides a statistical estimate of the vibroacoustic response of a structure or machine at a low computational cost. However, a number of interesting approaches have been proposed in the past 20 years that are simpler and provide better results. The vibrational conductivity approach, envelope models, and wave intensity a...

It is becoming a general feeling that the model of a particular member of a population is not always appropriate to describe the vibrational behaviour of the whole set of similar structures. In fact, uncertainties on the boundary conditions, joints' and physical parameters affect the response of each member of the population, leading to different d...

A new model to analyze high frequency vibrations is presented. Instead of using the physical oscillating displacement, the problem is described in terms of a complex envelope, generated by an appropriate use of the Hilbert transform. The model can be put in the category of those methods that try to describe some representative characteristic of the...

The estimate of mass properties from the massline characteristic of experimental FRFs has attracted the attention of the modal analysis community during the last decade. The problem is typically non-linear and, in the technical literature, iterative and direct methods were proposed for its solution. In this paper a direct procedure is developed. Th...

The indirect identification of forces from the measured response is an ill-conditioned problem and its solution is generally very case dependent. Moreover most of the proposed identification techniques yield amplitude and point of application of forces only when these forces are applied in points where the response is measured. Forces at unmeasured...

The aim of this paper is to review the main techniques used to provide a significant solution to high frequency vibrations and/or structural-acoustic coupling. The characteristics of the different approaches are illustrated, focusing similarities and differences among them. A detailed description of the complex envelope displacement analysis is the...

In the present paper an approach in the frequency-wavenumber domain able to determine a set of concentrated forces acting on a structure through response measurements is presented. The method allows the identification of both locations and intensities of the applied forces even when they are applied in points not amenable of measurements. The sensi...

High frequency structural and acoustic problems require prohibitive computational efforts. The tendency, nowadays, is to find a solution in statistical terms (SEA) through an average of the field variables on the space domain. A limitation of SEA is the loss of any local information. In contrast with SEA, a power flow method [1] can describe a tren...

A potential alternative to Statistical Energy Analysis that is gaining increasing interest in recent years is the “thermal” energy flow approach. Its advantage is represented by the possibility of modelling the spatial distribution of energy density at high frequencies, thus yielding a more effective estimate of the system behaviour than the averag...

In the rational fraction polynomial method [1] the identification of modal parameters is obtained through a direct linear least-square optimization technique but a particular form of fitting error is minimized. An iterative algorithm has been recently developed which uses the true fitting error [2]. In this paper a statistical analysis is developed...

The eigen characteristics of a dynamical system offer a vector sub-space suitable for performing canonical transformations on the system of equations of the structural dynamics problems being considered. While the concept is mathematically fully developed for both damped and undamped systems, practitioners — at all levels — tend to indiscriminately...