ADVANCED NUMERICAL METHODS FOR THE DYNAMIC OPTIMISATION OF MECHANICAL COMPONENTS

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 ! ! "#! 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 ! ! "! 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 ! ! "#! 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.