1,721,007 research outputs found
Rattle detection in gearing systems by noise and vibration measurements
No full textRattle noise in a gear train is defined as an undesirable noise that occurs due to the impact between the gear
teeth. This work aim to apply methodologies for detecting rattle noise in powertrain transmissions through
the processing of microphone and acceleration signals. An experimental campaign was conducted on an
off-road vehicle within a truck that was capable of reproducing the real operational conditions. Two kind of
operational conditions were investigated: the constant velocities and the time instants of changing gears. The
campaign employed experienced operators to identify scenarios with and without rattling. Consequently, rattle
indices were applied to the experimental measurements of acoustic pressure and acceleration. The results
allowed for the identification of rattle noise conditions, especially if applied to vibration data. Furthermore,
the effectiveness of a modified configuration has been tested, both with subjective evaluations and, thus, with
the rattle indices
EMA and OMA techniques for vibro-acoustically coupled systems: the example of a helicopter cabin
No full textNoise and vibration levels in vibro-acoustical systems are strictly related, meaning
that a good knowledge of the structural dynamics is a useful tool for their reduction.
Through an intensive testing campaign on a EC-135 helicopter cabin, a few guidelines are given
in order to properly capture the coupled vibro-acoustical behaviour of systems. In particular,
four experimental modal analyses have been performed on the cabin, a pure acoustical modal
analysis of the enclosure, an experimental modal analysis of the internal and external surface
and an operational modal analysis of the external surface. The results presented highlight that a
direct acoustical excitation is preferred also for the external part in controlled laboratory conditions
and an acoustical reference would be more efficient for operational modal analyses
Influence of Design and Operational Parameters on the Dynamic Behaviour of Gear Pumps.
No full textThis work concerns external gear pumps for automotive applications, which operate at high
speed and low pressure and presents a sensitivity analysis about the influence of design and
operational parameters on the pump dynamic behaviour. In previous work, a non-linear
lumped-parameter kineto-elastodynamic model was developed, with the aim of including all
the important effects, as well as to get a rather simple model. Two main sources of noise and
vibration can be considered: pressure variation and gear meshing. The model has been
validated by comparison with experimental vibration data, in a wide range of operational
conditions and for different gear designs and several profile errors. This paper is focused on
the analysis of the influence of the main design and operational parameters on the pump
dynamic behaviour. In particular, the effect of operational pressure and speed, the influence of
the clearance in the journal bearing and between tooth tip and pump case, and the effect of the
dimension of the relief grooves in the bushes will be thoroughly discussed in the paper.
Finally, the model could be a very useful and powerful tool in order to evaluate design
improvements for noise and vibration reduction
Using P-U probes for the experimental vibro-acoustical modal analysis of a helicopter
No full textVibration reduction is an extremely important task to avoid fatigue and comfort problems; for this reason, the helicopter designer should make the spaced peaks of the input force spectrum coincide with the valleys of the structural frequency response functions. Experimental modal analysis is used for such a purpose. In order to provide the necessary insights, wide testing campaigns are very often carried out. The aim of the paper is to show the usefulness of the Microflown technology in this field, instead of classical methods such as accelerometers and scanning laser vibrometers. In particular an experimental vibro-acoustical modal analysis of an helicopter EC-135 is presented. The system has been excited by means of a low frequency loudspeaker located inside the cabin, and a 4x4 Microflown array has been used to measure pressures and particle velocities simultaneously. The results shown in this paper highlight the effectiveness of the Microflown technology in this context: in fact, with just one measurement, one gets the needed data allowing to carry out both a modal analysis and an acoustic intensity calculation for noise sources identification
EMA and OMA techniques for vibroacustically coupled systems: the example of a helicopter cabin
No full textNoise and vibration levels in vibro-acoustical systems are strictly related, meaning that a good knowledge of the structural dynamics is a useful tool for their reduction.
Through an intensive testing campaign on a EC-135 helicopter cabin, a few guidelines are given in order to properly capture the coupled vibro-acoustical behaviour of systems. In particular, four experimental modal analyses have been performed on the cabin, a pure acoustical modal analysis of the enclosure, an experimental modal analysis of the internal and external surface and an operational modal analysis of the external surface. The results presented highlight that a direct acoustical excitation is preferred also for the external part in controlled laboratory conditions and an acoustical reference would be more efficient for operational modal analyses
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe 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
A Model for the Elastodynamic Analysis of the Geared Timing System of a Motorbike Engine.
No full textThis work deals with the elastodynamic model of the geared valvetrain of a four-cylinder “L” engine of a Ducati racing motorbike. The model, which is an evolution of the author’s research, is obtained as a combination of lumped parameter and finite element parts. The model is able to inspect the dynamic behaviour of both the geartrain and the cam-valve mechanisms. The paper mainly describes the model validation process that is based on several experimental tests and it is achieved by means of different steps. The information obtained from the validation stages have been finally employed for the tuning of the combined lumped/finite element model of the geared timing system. The experimental procedures are also illustrated, together with some details on the signal treatments. The comparison between simulations an experiments shows that the effectiveness of the model is satisfactorily assessed, thus permitting the use of the model as a tool for the design optimisation of the motorbike timing system. The results obtained for the competitive motorbike engine can also be utilized for common production engines, where conformity to vibration and noise standards must be fulfilled
- …
