Chiara Grappasonni

• PhD
• Aerospace Engineer at Agenzia Spaziale Italiana

HERMES Pathfinder is an in-orbit demonstration consisting of a constellation of six 3U cubesats hosting simple but innovative X-ray/gamma-ray detectors for the monitoring of cosmic high-energy transients. HERMES-PF, funded by ASI and by the EC Horizon 2020 grant, is scheduled for launch in Q1 2025. An identical X-ray/gamma-ray detector is hosted by...

Among solar system objects, comets coming from the Oort Cloud are an elusive population, intrinsically rare and difficult to detect. Nonetheless, as the more pristine objects we can observe, they encapsulate critical cues on the formation of planetary systems and are the focus of many scientific investigations and science missions. The Legacy Surve...

Among solar system objects, comets coming from the Oort Cloud are an elusive population, intrinsically rare and difficult to detect. Nonetheless, as the more pristine objects we can observe, they encapsulate critical cues on the formation of planetary systems and are the focus of many scientific investigations and science missions. The Legacy Surve...

HERMES (High Energy Rapid Modular Ensemble of Satellites) Pathfinder is a space-borne mission based on a constellation of six nano-satellites flying in a low-Earth orbit (LEO). The 3U CubeSats, to be launched in early 2025, host miniaturized instruments with a hybrid Silicon Drift Detector/GAGG:Ce scintillator photodetector system, sensitive to X-r...

The objective of this paper is to demonstrate that the addition of properly-tuned nonlinearities to a nonlinear system can increase the range over which a specific resonance responds linearly. Specifically, we seek to enforce two important properties of linear systems, namely the force-displacement proportionality and the invariance of resonance fr...

The objective of the present paper is to develop a two-step methodology integrating system identification and numerical continuation for the experimental extraction of nonlinear normal modes (NNMs) under broadband forcing. The first step processes acquired input and output data to derive an experimental state-space model of the structure. The secon...

The objective of the present study is to explore the connection between the nonlinear normal modes of an undamped and unforced nonlinear system and the isolated resonance curves that may appear in the damped response of the forced system. To this end, an energy balancing technique is used to predict the amplitude of the harmonic forcing that is nec...

The objective of the present paper is to develop a rigorous identification methodology of nonlinear normal modes (NNMs) of engineering structures. This is achieved by processing experimental measurements collected under broadband forcing. The use of such a type of forcing signal allows to excite multiple NNMs simultaneously and, in turn, to save te...

Engineering structures are designed to be lighter and more flexible, hence reducing the extent of application of linear dynamic models. Concurrently, vibration mitigation is required for enhancing the performance, comfort or safety in real-life applications. Passive linear vibration absorbers are purpose-built, often designed using Den Hartog’s equ...

The current trend of developing more slender structures is increasing the importance of nonlinearities in engineering design, which, in turn, gives rise to complicated dynamical phenomena. In this study, we evidence the somewhat paradoxical result that adding purposefully nonlinearity to an already nonlinear structure renders the behavior more line...

The objective of the paper is to obtain the frequency response curves of nonlinear mechanical systems from broadband testing. The proposed approach consists in coupling an identification method with a continuation method. Specifically, the frequency-domain nonlinear subspace identification (FNSI) method is first used to derive an experimental model...

The objective of the present study is to explore the connection between the nonlinear normal modes of an undamped and unforced nonlinear system and the isolated resonance curves that may appear in the damped response of the forced system. To this end, an energy balance technique is used to predict the amplitude of the harmonic forcing that is neces...

Isolated resonance curves are separate from the main nonlinear forced-response branch, so they can easily be missed by a continuation algorithm and the resonant response might be underpredicted. The present work explores the connection between these isolated resonances and the nonlinear normal modes of the system and adapts an energy balance criter...

Although they are generally modelled as linear systems, aircraft structures are known to be prone to nonlinear phenomena. A specific challenge encountered with fighter aircraft, besides aeroelastic nonlinearity, is the modelling of the wing-to-payload mounting interfaces. For large amplitudes of vibration, friction and gaps may be triggered in thes...

The objective of the present paper is to develop a two-step methodology integrating system identification and numerical continuation for the experimental extraction of nonlinear normal modes (NNMs) under broadband forcing. The first step processes acquired input and output data to derive an experimental state-space model of the structure. The secon...

This paper describes the development and commissioning tests of the new Clarkson University/Center for Evaluation of Clean Energy Technology Blade Test Facility. The facility is a result of the collaboration between the New York State Energy Research and Development Authority and Intertek, and is supported by national and international partners. Th...

Load characterization for wind turbines has been a major area of study with growing interest due to the upcoming extremely long and flexible turbine blades and towers. it is perhaps the most important task posed to a structural dynamics engineer in the wind energy generation field. What is currently requested by the engineering community are valida...

The objective of this paper is the definition and verification of an iterative procedure for the detailed monitoring of the dynamic response of a structural system based on the experimental modal model of the system on ground and a limited number of measurements in the operating condition. The method is formulated starting from a linear model, but...

The aim of the paper is to develop a new nonlinear tuned vibration absorber (NLTVA) capable of mitigating the vibrations of nonlinear systems which are known to exhibit frequency-energy-dependent oscillations. A nonlinear generalization of Den Hartog's equal-peak method is proposed to ensure equal peaks in the nonlinear frequency response for a lar...

The capability to reproduce and predict with high accuracy the behaviour of a real system is a fundamental task of numerical models. In nonlinear structural dynamics, additional parameters compared to classical linear modelling, which include the nonlinear coefficient and the mathematical form of the nonlinearity, need to be identified to bring the...

In this paper an approach that uses the modal signature of an Unmanned Aerial Vehicle (UAV) extracted directly from the operative conditions for the validation of a finite element model is proposed. Different operational conditions of the Clarkson University Golden Eagle UAV are considered, ranging from laboratory components and UAV assembly to on-...

The modal parameters of an aircraft structure are currently estimated from ground vibration tests (GVT). These tests are carried out on ground in order to estimate the frequency response functions first and then the modal parameters. Such estimates require one or more shakers to excite the structure together with simultaneous measurements of both t...

The development of a fiber Bragg grating (FBG) based distributed strain sensor system for real time structural health monitoring of a wind turbine rotor and its validation under a laboratory scale test setup is discussed in this paper. A 1 kW, 1.6 m diameter rotor, horizontal axis wind turbine with three instrumented blades is used in this study. T...

In the framework of the HC-AG19 Garteur Action Group, novel methodologies and procedures are proposed and analyzed to improve finite element models of helicopters through in-flight dynamic data. Thus, the development of methods allowing accurate modal parameter estimation is essential to provide reliable reference data to the model updating process...

Operational modal analysis differs from traditional experimental modal analysis in that it only requires information of the output responses and the modal parameters (in terms of natural frequencies damping ratios and mode shapes) are estimated under the assumption of white noise excitation. It presents several advantages including the availability...

The firing test of the first stage of the solid rocket motor P80 of the Vega launcher was run successfully in December 2007 at the Guyanese Space Center in Kourou, French Guiana. This research activity demonstrates the capability of the developed operational-modal-analysis methods to identify the dynamic properties of the solid rocket motor, workin...

A novel approach to monitor the dynamic response of a structure in operating condition is presented as a further application of operational modal analysis. Taking advantage of extensive experimental measurements on ground, the suggested methodology reconstructs the operating full-field dynamic response in absence of an updated numerical model using...

In the framework of the operational modal analysis (OMA), several approaches have been developed for estimating the modal parameters, i.e., natural frequencies, damping ratios, and mode shapes. In this paper, two methods for the estimate of the modal parameters from ambient responses are proposed. The first one estimates the modal parameters direct...

The objective of this paper is the definition and verification of an iterative procedure for the detailed monitoring of the dynamic response of a structural system based on the experimental modal model of the system on ground and a limited number of measurements in the operating condition. The method is formulated starting from a linear model, but...

In the present work are presented both experimental and numerical simulation results obtained with an open-loop control law applied to an individual blade control system that incorporates a mechanism for blade active impedance adaptation at the root, the active pitch link or "smart spring". It is demonstrated that the active pitch link provides par...

With the goal of developing system performance integrity monitoring tools for wind turbines the dynamic analysis of a small horizontal-axis wind turbine subjected to changes in the inertial and aerodynamic properties are investigated. The identification of the three- blade turbine modal properties, i.e. natural frequencies, damping ratios, and mode...

This paper is focused on an assessment of the state-of-the-art of operational modal analysis (OMA) methodologies in estimating modal parameters from output responses on helicopter structures. For this purpose, a ground vibration test was performed on a real helicopter airframe. In the following stages, several OMA techniques were applied to the mea...

In this paper the identification of the dynamic properties of a rotating helicopter blade has been performed using data recorded during whirl tower tests. A new methodology has been developed in order to extend the applicability of the operational modal analysis to systems characterized by harmonic component excitations blended with white noise spe...

The development of an identification procedure of the dynamic properties of a composite horizontal axis wind turbine blade using data recorded during its operative working conditions is reported in this article. The operational modal analysis method based on the properties of the Hilbert Transform applied to response signals, represented in the fre...

The operational modal analysis, OMA, allows estimating the dynamic properties of a structure, natural frequencies, damping ratios, and mode shapes, without measuring the input forces. According to the main hypothesis concerning the input excitation, i.e., stochastic with frequency independent spectra (at least in the frequency band of interest), it...

The Operational Modal Analysis (OMA) could be used for the identification of the dynamics of aerospace vehicles, in terms of natural frequencies, damping ratios and mode shapes, during flight tests, using only the output responses due to the aerodynamic envinronment. The loading acting on the flying helicopter is composed by the contributions of bo...

Environmental tests are widely used to qualify structures for space missions, because the benchmark test facilities allow the replication of the loading conditions acting on a system during the different phases of the mission. In this paper, an Output-Only-based tech-nique is proposed to estimate the full modal parameters, in the frame of the envir...

The Operational Modal Analysis, OMA, allows the estimation of the dynamic properties of a structure, i.e., natural frequencies, damping ratios, and mode shapes, without measuring the input forces. One of the main advantages of this approach consists in the capability of identifying the system modal parameters in its operative conditions. According...