1,720,983 research outputs found
On the computation of degrees-of-freedom: a didactic perspective
No full textSome didactic issues associated with the computation of degrees-of-freedom (d.o.f) are herein discussed. In particular, the paper reports different definitions and methodologies of computation of this important parameter It is also proposed an analytical approach to the d.o.f computation of planar figures subjected to unilateral constraints. Mechanisms with variable kinematic structure are included in the present analysis. Some ambiguities in the d.o.f definition are pointed out
An investigation on fatigue failure of turbine blades of aircraft engines by high cicles fatigue tests
No full textSull'enumerazione di meccanismi a vite
No full textEnumeration of mechanisms is classical field in kinematics. In this investigation it is addressed the
problem of enumeration of screw mechanisms. It has been proposed a new method of enumeration of these mechanism
class and somewhat new kinematic chains have been discovered. The method based on some noteworthy
relations deduced by R. Kraus, makes use of the polynomial characteristic isomorphism test adapted for labeled
graphs
Multibody model for the biomechanical analysis of the upper limb
No full textIn this paper a multibody model of the upper limb is presented. The limb is
modelled as a three dimensional 7 degrees-of-freedom system, linked to the shoulder which
has been considered as frame. The upper limb model is made up of four links corresponding
to the most important body segments: the humerus, the ulna, the radius and the hand,
considered as a single rigid body. Particular attention has been paid to the modelling of
joints in order to mimic all the possible arm and forearm movements (including pronosupination)
The model also includes 24 muscles. The mathematical model used to describe the
muscles is those proposed by Zajac in 1989, modified by the authors. The kinematic analysis
has been performed including an ergonomics index to take into account about posture and
joint physical limits. Moreover an energy optimization criteria has been included in order to
find muscular activation coefficients. The proposed model has been used to perform an
inverse dynamics analysis of automotive steering operation in order to assess the muscular
activity and the spatial attitude of each link
A Multibody Dynamic Model of a Cardan Joint with Experimental Validation
No full textThis investigation deals with the mechanical efficiency of Cardan joints. The model
includes also the effects due to manufacturing and mounting errors and the influence of rotation
speed and angular configuration of the Cardan joint on the efficiency. The joint has been
modeled as an RCCC spatial linkage and the full dynamic analysis has been performed. The
equations of motion have been deduced by means both of dual vectors algebra and of classic
multibody approach. The results have been compared with experimental ones
Formulazioni della dinamica dei sistemi multibody
No full textUn settore classico della cinematica e dinamica dei sistemi multibody concerne le formulazioni e le metodologie
di soluzione delle equazioni della dinamica al fine di simulare in maniera efficiente ed affidabile classi sempre
più ampie di sistemi meccanici. L’unità di ricerca di Roma Tor Vergata ha proposto e sperimentato numericamente
alcune formulazioni dinamich
Kinematic and dynamic analysis of a Sit-Ski for smproving the vibrational comfort
No full textThis paper reports both procedures for the kinematic design and the results of dynamic analyses of
three models of sit-ski in order to evaluate their vibrational comfort. The model described in the
US Patent US 6,019,380 has been assumed as a reference in the following kinematic and dynamic
analyses of the new models proposed. The two main features to be considered while designing a
sit-ski are the manoeuvrability and the range of vision of the driver. These two features appear to
be important considering that the sit-ski is generally used by disabled people (e.g. paraplegic). Thus
the kinematic design phase should account for the fulfillment of these requirements. On the basis
of these, three new models have been proposed and herein named: Flex, modified Flex and eightbar
linkage (Smarrini 2003). Once the kinematic synthesis and analysis have been completed the
dynamic performance of each model is investigated. For this purpose two kinds of slope profiles are
simulated in order to reproduce the stresses which may likely occur during a downhill race. In particular
the position and the acceleration of the seat have been monitored during the simulations.
This is important in order to test the range of vision and handling requirements. The seat acceleration
is also important to evaluate the vibrational comfort of the sit-ski according to the British
standard BS 6841 (Griffin 1990). The dynamic simulation is first executed by means of the
multibody dynamics code NumDyn3D, then the vibrational comfort analysis is performed using
in-house developed software (Vita 2001, Valentini and Vita 2003)
Applicazioni di tecniche di simulazione multibody nella progettazione industriale
No full textQuesto lavoro intende riassumere alcune delle attività di ricerca svolte presso il Dipartimento di Ingegneria
Meccanica dell’Università di Tor Vergata che hanno avuto come oggetto l’impiego di metodologie di modellazione CADmultibody
per la progettazione in applicazioni industriali. La rassegna dei vari casi di studio analizzati vuole essere di
esempio su come i settori applicativi che possono beneficiare di tali tecniche sono molteplici e le tipologie di investigazione
sono molto ampie
Mechanical Efficiency Analysis of a Cardan Joint
No full textThis investigation concerns with the mechanical efficiency of
Cardan joints. The model includes also the effects due to manu-
facturing and mounting errors and the influence of rotation speed
on the efficiency. The joint has been modeled as an RCCC spa-
tial linkage and the full dynamic analysis performed by means of
dual vectors algebra
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