1,720,963 research outputs found
Analisi dinamica dei transitori nelle fasi di innesto di cinematismi con rapporto di trasmissione variabile
No full textIn questo lavoro viene analizzata la dinamica dei transitori nelle fasi di innesto di frizioni con legge di attrito coulombiano che interconnettono cinematismi con rapporto di trasmissione variabile. Le soluzioni di tipo analitico basate sulla conservazione del momento angolare cadono in difetto nel caso in cui le coppie
esterne non siano trascurabili o i tempi di innesto non siano brevi. L'algoritmo proposto, si basa sul monitoraggio dell'errore fra la velocità angolare dell'organo motore e di quello condotto, quando questo diventa minore di una tolleranza imposta viene affettuata automaticamente la transizione passando da un sistema a due gradi di libertà ad un sistema ad un grado di libertà. Si presenta un'applicazione
significativa, relativamente all'innesto del membro cedente di un quadrilatero articolato ad un carico esterno. L'attuatore risulta costituito da un motore a corrente continua
High velocity impacts against cables: nonlinear investigation of the safety conditions
No full textThis paper analyses the high velocity impact against a cable in order to define the lirnits of the impacting particle velocity to avoid the sudden cut of the cable.
The mathematical model is based on the characteristic method in order to describe the nonlinear 3D dynarnics of the cable (large deformations). The impacting object is considered as a point mass. The global system, cable impacting mass, is described trough a quasi-linear system of hyperbolic partial differential equation with boundary condition of inertial type (the particle motion). The impact is assumed perfectly anelastic and the cable longitudinal
constitutive stress-strain relationship follows the Young's law. The solution algorithm is developed on the characteristic piane trough a discrete grid of characteristic curves solved by a trial-and-error procedure. The investigations were accomplished by multiple simulations, varying the impact velocity in order to define the relation velocity-peak stress in the cable cross section. As a principal result, a parabolic relationship exists between the impact velocity and the cab le stress, in particular we can state that there exists a range of velocities where the cable stress is very sensible to the impact velocity, below of such range the influence is sensibly lower. All allows to define the range of safety conditions
Diagnostica della rigidezza di membri flessibili in macchine operatrici a regime periodico
No full textE' stato studiato e realizzato un sistema diagnostico per monitorare la rigidezza di membri flessibili in meccanismi a regime periodico. Il sistema si basa sul fatto che l'accoppiamento in frequenza tra armoniche superiori della velocità angolare del movente e frequenza propria del membro flessibile fa aumentare le ampiezze delle stesse armoniche oltre una soglia di ripetibilità. Le indagini sperimentali sono state condotte su due meccanismi appositamente progettati e realizzati
Progettazione e realizzazione di una galleria del vento subsonica per la caratterizzazione aerodinamica di tele da seccheria
No full textA general approach to load and crack monitoring in planar mechanisms
No full textA diagnostic system for monitoring the resistant load and the stiffness af flexible links in factory machines is presented. It is based an the harmanics amplitudes measurement af the angular velacity af the input link. The theoretical analysis af the dynamic behaviour af
mechanism with flexible links, highlights the possibility to realize such monitoring system with only one tachometer applied to the input link. Experimental tests show a good agreement with theoretical predictions
A low cost RC-heli UAV for mapping applications
No full textIn the last years UAV (Unmanned Aerial Vehicle) systems are become very actractive for various commercial, industrial, public, scientific and military operations. The tasks include pipeline inspection, dam surveillance, photogrammetric survey, infrastructure maintenance, inspection of flooded areas, fire fighting, terrain monitoring, volcano observations and so on. The impressive flying capabilities provided by UAVs require a well trained pilot to be fully and effectively exploited; moreover the flight range of the piloted helicopter is limited to the line-of-sight or the skill of the pilot to detect and follow the orientation of the helicopter. Such issues have motivated the research and the design for autonomous system guidance which could both stabilize and also guide the helicopter precisely along a reference path. The constant growth of research programs and the technological progress in the field of navigation systems, as denoted by the production of more and more performing GPS/INS integrated units, allowed a strong cost reduction and payload miniaturization, making the design of low cost UAV platforms more feasible and actractive.
In this paper we present the preliminary results of the low-cost autonomous model helicopter we developed for mobile mapping applications. Assessment of system perfomance is based on the measurements achieved by surveying a set of targets well distributed on a calibration field. The development of this aerial mapping system has been also based on the results derived from a flight simulation software implemented for determining the best setup for the servos
Effetto della permeabilità sullo strato limite turbolento
No full textSi valuta, sia sperimentalmente che numericamente, l'effetto della permeabilità di una parete piana sull'altezza dello strato limite in regime turbolento. L'analisi sperimentale è stata effettuata utilizzando una galleria a vento, opportunamente costruita, nella quale si misura la velocità con un tubo di Pitot montato su un servomanipolatore a tre assi. Dal rilievo del profilo di velocità in corrispondenza delle parete permeabile, si valuta l'altezza dello strato limite. L'analisi numerica è stata condotta sviluppando un modello per la soluzione non stazionaria delle equazioni di NavierStokes; l'effetto della permeabilità di parete è stato modellizzato imponendo un flusso pulsante ortogonale alla lastra piana. Dopo avere verificato la compatibilità dei risultati sperimentali e numerici, si è evidenziato che la permeabilità, nelle condizioni considerate, aumenta con fattore
superiore a due, l'altezza dello strato limite turbolento
Aerodynamic charcaterization of dryer fabrics in a wind tunnel
No full textThis paper presents a simpliffed procedure and an experimental
apparatus for aerodynamic charaaerization of dryer fabrics running
on paper machines, with particular reference to the determination of
the boundary /ayer parameters.
lnstead of measuring airflow inside the boundary layer direaly on the
dryer fabric running in the paper machine, reduced dimension specimens
of dryer fabric were studied in the test chamber of a wind tunnel,
with signipcant advantages both for time and experimental costs. The
results obtained applying this procedure to various types of dryer fabrics
are shown. /t was remarked in particular that permeability is the parameter
which most greatly influences both boundary layer thickness and
the air carried by the dryer fabric
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
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