169,831 research outputs found
Dynamic Identification of a Solid Rocket Motor From Firing Test Using Operational Modal Analysis
No full textThe main objective of this paper is the identification of the dynamic properties of a solid rocket motor using data recorded during a firing test, characterized by a mass variation due to the burning propeller. The dynamic identification of the motor is provided by applying Operational Modal Analysis (OMA) methodologies able to estimate the modal parameters of the structure undergoing its operative conditions. The sensitivity of the OMA approaches to deal with structures characterized by time-dependent parameters is evaluated through a numerical simulation. Moreover, a comparison between the estimates from different state-of-the-art approaches in OMA (operating in both time and frequency domain) are provided. The capabilities of the OMA methods to track the changes in the natural frequencies, damping ratios and mode shapes of the first stage of the Vega lunch vehicle will be investigated in order to asses the overall efficiency of such approaches. Copyright © 2011 by G. Coppotelli, C. Grappasonni, C. Di Trapani
On the effects of structural modifications in the large wind turbine dynamics
No full textIn this paper a numerical procedure for the investigation of the dynamic behavior of large wind turbines is developed. The aeroelastic modeling is capable to take into account the dynamic environment in which the wind turbines operate by considering the effects of the atmospheric boundary layer and the weight load of the rotating blades. The aerodynamic loads are simulated by the 2D quasi-steady aerodynamic formulation, derived from Greengberg's theory, whereas the structural dynamics of the flexible wind-turbine blade, undergoing significant elastic displacements, has been described by a nonlinear flap-lag-torsion slender-beam differential model. The loading condition and the kinematic effects are described for different configurations of the rotor using a tapered and twisted blade representative of commercial installations. Then, blade structural modifications, represented by structural weakening, are introduced to investigate the effects of local delamination (damages) of the composite compound on the dynamic response of the system giving then useful information concerning the fatigue life of the system. Sensitivity analyses have been performed varying the spanwise location and the magnitude of the reduction of stiffness. Moreover, the effects of a blade mounting error in the pitch angle have been investigated highlighting the critical loading arising from an aerodynamically unbalanced rotor. Copyright © 2011 by L. Balis Crema, G. Coppotelli, C. Grappasonni
A modal approach for dynamic response monitoring from experimental data
No full textpeer reviewedThe 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 it can be applied to weakly non-linear system, because of the iterative nature of the algorithm. It does not require the definition of a numerical model, but an experimental representation in the modal coordinates, achievable with a preliminary modal survey with an arbitrary large amount of experimental points. The proposed method is presented as well as its implementation and several numerical test cases in order to validate its formulation. Experimental analyses are performed on a uniform beam and on a full-scale aeronautical composite component with promising results
Dynamic Identification of a Solid Rocket Motor From Firing Test Using Operational Modal Analysis
No full textThe 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. This research activity demonstrates the capability of the developed operational modal analysis methods to identify the dynamic properties of the solid rocket motor, working under its actual operative conditions, by using response data only recorded during the firing test. The main objective was first to prove the applicability and then to evaluate the overall efficiency of different state-of-the-art approaches in operational modal analysis to track changes in the natural frequencies, damping ratios and mode shapes of the first stage of the VEGA launch vehicle undergoing significant mass variation due to the burning propeller. Additionally, a sensitivity of the considered approaches to deal with structures characterized by time-dependent parameters was numerically carried out
Output-Only Analyses in Environmental Testing
No full textEnvironmental 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 environmental test-ing, to increase the accuracy of the dynamic identification and to reduce the overall time and cost associated to the qualification process. The Output-Only Modal Analysis approach, de-noted as Hilbert Transform Method by the authors, will be applied for the estimate of the "bi-ased" Frequency Response Functions, FRFs, whereas the evaluation of the modal masses asso-ciated to each mode will be carried out by the application of various mass perturbation methods available in literature. The robustness of these approaches will be assessed through environ-mental tests carried out on spacecraft structures, such as a robotic arm intended for space appli-cations and a tank prototype of the Vega launcher. The accuracy of the proposed method will be finally evaluated by comparing the FRF estimates, obtained with the Output-Only approach, with the ones gained using the standard input/output technique. Copyright © (2011) by International Operational Modal Analysis Conference (IOMAC) All rights reserved
Operational Modal Analysis of a Helicopter UAV from Flight Tests
No full textThe 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 both the white noise excitation and the aerodynamic harmonics acting at discrete operational fre-quencies equal to the multiple of the fundamental angular velocity of the rotor. As a result, the system could not be considered excited by a pure white noise input and then the OMA methodologies could not be theoretically applied to the output responses to estimate the dynamical behavior of the helicopter. In this paper an approach is developed to cope with this problem. First, a method based on the statistical index, called Entropy, is introduced to identify such op-erational frequencies by means of a statistical characterization of the responses of the structure due to deterministic input superimposed to stochastic noise. Then, the effects of the removal of the previous identified harmonic contributions from the Frequency Response Functions (FRF) gained, in turn, by applying the procedure known in literature as Hilbert Transform Method, HTM, will be evaluated. In order to assess the overall accuracy in the modal parameter esti-mates, an experimental investigation, carried out on a helicopter UAV flying at different condi-tions, i.e. in- And out-of-ground effect hovering and forward flight at several advance ratios, will be presented. Copyright © (2011) by International Operational Modal Analysis Conference (IOMAC) All rights reserved
Vaccine hesitancy, a public health problem
No full textThe phenomenon of "vaccine hesitancy" has only been studied for a few years, and this attitude is becoming a serious threat that can frustrate the efforts of recent years that have led to the achievement of relevant scientific advances to human health. The paper analyzes the possible causes, the scope of the phenomenon and its consequences, trying to identify the most effective actions to resolve this trend
COVID-19: Il difficile equiliobrio tra infodemia, fake news e corretta informazione
No full textIl web sebbene abbia allargato la platea del mondo dell’informazione allo stesso tempo ha ridotto i controlli sulla
qualità e la veridicità delle news, una vera e propria “infodemia”.
Una corretta informazione, o al contrario false notizie, possono influenzare i comportamenti quotidiani con ripercussioni sulle condizioni di salute future, ancora di più oggi in relazione all’attuale pandemia. L’obiettivo della nostra indagine è stato quello di dimostrare come una corretta informazione, o al contrario le false notizie, possono
influenzare i comportamenti quotidiani con ripercussione sugli atteggiamenti da adottare in tempi di pandemia.
Ai fini dell’indagine è stato somministrato un questionario ad un campione di 872 persone, strutturato in sei sezioni, riguardanti le fonti di informazione relative alla pandemia attuale, modalità di trasmissione e comportamenti
utili per tenere lontana l’infezione, gli stati d’animo durante i periodi di “chiusura”, la fiducia nel vaccino. Il questionario, distribuito online, è stato costruito utilizzando la piattaforma Google forms ed era composto di 33 items,
molti dei quali proposti dalla Survey questionnaire del WHO sul tema “Health information on COVID-19” ed è stato
distribuito online.
I dati delle risposte sono stati elaborati e analizzati statisticamente mediante test del χ2, per p<0.05.
Nello specifico è stato possibile affermare, con un valore di significatività p<0,05, che il livello di istruzione degli
intervistati non ha influenzato la risposta data alla domanda relativa alla conoscenza di una serie di affermazioni
generali riguardanti il COVID-19, né la conoscenza di quelli che sono i suoi principali sintomi. Il livello di istruzione
e l’età non sono inoltre correlati alla conoscenza delle modalità con cui prevenire la malattia in questione. Il grado
di istruzione risulta invece essere correlato (p<0.05) alle risposte date alla domanda relativa alle modalità con cui
si diffonde il COVID-19, ed influenza sia la propensione ad informarsi e sia a fare il vaccino appena possibile. L’età,
infine, non influenza il parere espresso in merito ai comportamenti messi in atto per non ammalarsi di COVID-19
con un valore di χ2 = 166.69 (χ2 = 36.42, α = 0.05, ν = 24).
Risulta fondamentale ed urgente, dunque, una regolazione dei principali mass-media, in attesa di precise norme
legislative, che filtrino l’enorme massa di cattive informazioni che mai come in questa pandemia hanno diffuso e
diffondono notizie che allontanano il comune cittadino dalla verità scientifica, ritardando la lotta al nemico invisibile che continua a mietere un elevato numero di vittime
Daily intake of macro and trace elements in the diet. 4. Sodium, potassium, calcium, and magnesium
No full textTo complete the picture of the daily dietary intake of minerals, sodium, potassium, calcium and magnesium have now been considered. The study has been carried out in the Italian Marches Region after carefully evaluating the food consumption habits of the population. The foodstuffs comprising the 70 diets examined were collected in institutional canteens and private homes immediately prior to meals. The food was sampled ready for consumption as it had thus undergone the various preparation and cooking procedures, during which considerable changes in mineral content occur. In comparison with the various food consumption standards, the amount of sodium found appears excessively high (4.8 g/d) whereas that of magnesium is insufficient (0.24 g/d). A high sodium intake, and more recently a high Na/K ratio, have been associated with hypertension. Also a lack of magnesium and a high Ca/Mg ratio have repeatedly been associated with hypertension risk. The data to emerge from our study: a high sodium intake, an insufficiency of magnesium, and thus high Na/K and Ca/Mg ratios, would appear likely to enhance cardiovascular disease risk. Even though not all Authors agree on the existence of such correlations, a more correct diet as regards mineral intake is undoubtedly something to encourage
Knowledge and consumption of psychoactive substances in middle-school, high-school and university students.
No full textTo complete their investigations on aspects of problems concerning youth (alchohol, smoking, etc.), the Authors examined the knowledge and motivations which lead young people to using psychotropic substances, and the possible risks deriving from such use. The research was carried out by means of a quaestionnaire distributed to a sample of 1833 students from the University of Camerino and from the middle and high schools of certain towns in The Marche (Camerino, San Severino, Tolentino and Jesi). Analysis of the data showed that a relatively high degree of their families (47.5%) frequently take drugs, above all (around 18%) for insomnia and depression. Of the population sample, 22.5% take drugs not prescribed by a doctor and 5.8% of these together with alcoholic drinks. Of the students interviewed, 13.7% said they had direct experience with psychotropic drugs; this is presumably an underestimate in view of the high percentage of young people addicted to drugs (53.5%), of whom approximately 20% were attending their schools. In addition, the authors emphasize the inadequate knowldege of the concept of "addiction" whereby young people are led to understimating the consequences of consuming modest doses of cation, in particular in view of the ever increasing use by young people of new types of drugs such as ecstasy, etc
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