This PhD thesis concerns the development and assessment
of innovative methodologies for simulating and improving the
dynamic behaviour of mechanical components. In particular, two
correlated issues are addressed herein: hybrid FE/LP gear pump
modelling as a tool for foreseeing and optimising vibration
behaviour in operational conditions; a new methodology for
vibration reduction by applying damping patches in appropriate
positions.
In the field of positive displacement pump modelling,
external gear pumps were analysed with the aim of developing
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advanced methodologies which accurately predict of the dynamic
behaviour of these components. Indeed, the first part of this thesis
(PART A) is about external gear pumps for steering systems; the
research activity concerning gear pumps was carried out in
collaboration with the Dept. of Engineering at the University of
Ferrara in co-operation with TRW Automotive Italia S.p.A –
Divisione Automotive Pumps (Ostellato, Ferrara, Italy). This
research pertains to the creation of a hybrid model, obtained
through the integration of a nonlinear elastodynamic model with
lumped parameters in relation to moving bodies, and an FE pump
model. The model referred to bodies in motion takes into account
the most important phenomena involved in pump operations,
such as time-varying oil pressure distribution on gears, timevarying
meshing stiffness, tooth profile errors, the possibility of
tooth contact, bush displacement and hydrodynamic journal
bearing reactions. Coupling the FE with the various parts which
make up the pump, as well as coupling the lumped-parameter
model and the FE model required the development of specific
advanced techniques; thus several problems related to the
combination of the different models employed in order to form a
single hybrid LP/FE model were studied and resolved. Using
particular techniques based on comparisons between simulations
and experimental results concerning acceleration, forces and
moments, the model was experimentally validated.
Although this hybrid model is an excellent tool for improving
the dynamic behaviour of gear pumps and for optimising the early
stages of prototype design, some problems can still remain related
to unwanted vibrations into precise frequency ranges. Thus, once
the first part of the research was completed, it was decided to
delve into the problem of structural optimisation. In particular, a
methodology for surface damping treatment was created and
applied. Indeed, the second part of the research activity (PART B)
was about the optimisation of mechanical components and
systems through the application of high damping material
components known as patches; this research activity is being
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carried out by the Dept. of Mechanical Engineering (laboratoire
vibrations acoustique) at the INSA institute (Institute National
des Sciences Appliquées) in Lyon (France) where I spent thirteen
months between the second and third year of my doctoral studies.
Such treatment can be applied to existing structures and provides
high damping capability over wide temperature and frequency
ranges. In many practical plate and machinery casing structures,
it is difficult to treat the whole surface with constrained layer
viscoelastic material, due to reduced areas or inaccessible parts.
Furthermore, it may indeed be desirable to selectively apply one
or more damping patches to control certain resonances. Patch
damping design is an efficient and cost effective concept for
solving noise and vibration problems. As a result of these
considerations, the research was focused on finding a general
methodology, based on a purely energetic approach, to reduce the
unwanted amplitude vibration level in mechanical components
through the application of appropriate elements characterized by
high damping properties. The methodology was enforced using IDEAS
v7! software which makes it possible to address modelling
in terms of energy distribution within a structure. Advanced
methodologies were developed to reduce the vibration amplitude
in components such as plate and bracket by applying patches.
Specifically, potential energy estimations will precisely and
accurately define the exact locations on the surface of the
components which should be covered by the patches. As a result,
these studies enable a reduction in vibration amplitude, in
reference both to a single component and/or a complex system. In
addition, this methodology makes it possible to improve the
vibratory behaviour of a component in certain frequency ranges
while reducing, at the same time, the effect of dangerous
resonances, acting specifically on the location, extent and
quantity of the patches to be applied on the surface of the base
component.
During this thesis, different fields were contemporarily
studied: definition and identification of structural modification
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methods, theoretical aspects of material damping characteristics,
vibrational propagation methods and applicative aspects relating
to the implementation of models for the vibratory optimisation of
mechanical components.
This thesis was developed within the LVA research and
technology transfer laboratories at the INSA institute (Lyon,
France) and InterMech (Division Acoustic and Vibrations – LAV);
and was carried out with the contribution of the Emilia Romagna
Region – Assessorato Attività Produttive, Sviluppo Economico,
Piano telematico, PRRIITT misura 3.4 azione A