Giovanni Pallini

Design and testing of a pulley and cable actuator for large ball valves

The objective of this work is the development of an innovative actuator for Velan ABV S.p.A., which is mainly used for control and special on/off applications where high efficiency and linear behaviors are desirable specifications. The main performances of the proposed actuator, which has been protected by a patent, have been compared with a conventional scotch yoke one, using both the simulation results and the experimental data. In order to measure the efficiency and the dynamical response of the actuators, the authors have designed a hydraulic test rig, configured to fulfill different testing procedures. In this way, it is possible to perform both static tests to identify actuator efficiency and dynamic hardware-in-the-loop tests in which an assigned load or valve impedance function is simulated to verify the response of the tested object in realistic operating conditions. Finally, the proposed test rig has been successfully used to perform reliability and fatigue tests in which the actuator is stressed with realistic and repetitive loads. Moreover, the integrated development of both innovative actuator and testing devices is explained introducing interesting concepts whose applications are normally limited to robotics (e.g. impedance and force control) or vehicular technology (e.g. smart suspensions and suppression of vibrations).

Prediction of wheel and rail profile wear on complex railway networks

The modelling and the reduction of wear due to wheel-rail contact represents a crucial issue in railway applications, mainly correlated to safety, maintenance interventions and definition of strategies aimed at wheel profile optimization. A model for evaluating wheel and rail profile evolution due to wear developed for complex railway networks is presented in this paper. The model layout is composed of two mutually interacting but separate parts: a vehicle model (composed of multibody model and global contact model) for the dynamical simulations and a unit for wear computation (composed of the local contact model, the wear evaluation procedure and the profile update strategy). In order to achieve general significant accuracy results in reasonable computational effort, a suitable statistical approach for the railway track description is used, aimed at studying complex railway lines: in fact, the exhaustive analysis of vehicle dynamics and wear evolution on all the railway network is too expensive in terms of computational time for each practical purpose. The wear model has been validated in collaboration with Trenitalia S.P.A and Rete Ferroviaria Italiana (RFI), which have provided technical documentation and experimental data relative to some tests performed on a environment exhibiting serious problems in terms of wear: the vehicle ALn 501 Minuetto operated on the Aosta-Pre Saint Didier Italian line.

Effect of Structural Dynamics on the Shaft Line Rotor Response in Turbomachines

The accurate model of the complicated dynamic phenomena characterizing rotors and support structure represents a critical issue in the rotor dynamic field. A correct prediction of the whole system behavior is fundamental to identify safe operating conditions and to avoid instability operating range that may lead to erroneous project solutions or possible unwanted consequences for the plant. Although a generic rotating machinery is mainly composed by four components (rotors, bearings, stator and supporting structure), many research activities are often more focused on the single components rather than on the whole system. The importance of a combined analysis of rotors and elastic supporting structures arises with the continuous development of turbomachinery applications, in particular in the Oil and Gas field where a wide variety of solutions, such as off-shore installations or modularized turbo-compression and turbo-generator trains, requires a more complete analysis not only limited to the rotor-bearing system. Complex elastic systems such as rotating machinery supporting structures and steel foundations might, in some situations, strongly dominate the entire shaft line rotor dynamic response (mode shapes, resonance frequencies and unbalance response). They give birth to transfer functions which will introduce coupling phenomena between machines bearings, becoming enablers of a new shaft line dynamic. Since FEM theory offers a number of different solutions to represent the rotor and the rotating machine support system (beam models, solid models, transfer function, etc.), in this paper a great emphasis is given to the results of an experimental campaign done on a centrifugal compressor as validation of the new rotor dynamic approach.

Development and Validation of a Model to Describe the Bearings Interaction in Rotating Machines Due to Elastic Supporting Structures

This work focuses on the effects of the flexible supporting structures and on the bearing interaction caused by their elastic deflection on the whole rotor-substructures system [1]. More particularly, a careful theoretical and experimental analysis is performed to understand how the supporting structures influence the rotors behaviour [2, 3] through the actions of the machine bearings. To this end, this study considers a model of the whole rotating machine [4], taking into account the coupling of the dynamic behaviour of the different system components. The whole FEM model has been implemented in the ANSYS [5] simulation environment. The main goal of this research, is to offer an optimal balance between efficiency and accuracy allowing the modelling of the real physical complex system and simultaneously the reduction of calculation times. The whole analysis has been developed and validated in cooperation with General Electric S.p.A. which provided the technical and experimental data related to some tests recently performed in Massa-Carrara (Italy) on a benchmark turbocompressor machine.

Development and Preliminary Validation of a New Strategy to Model the Interaction Between Rotating Machines and Elastic Supporting Structure

The accurate modelling of the complicated dynamic phenomena characterizing rotors and support structures represents a critical issue in rotor dynamics field. A correct prediction of the whole system behavior is fundamental to identify safe operating conditions and to avoid instabilities that may lead to erroneous project solutions or possible unwanted consequences for the plant. Although a generic rotating machine is mainly composed by four components (rotors, bearings, stators and supporting structures), many research activities are often more focused on single components rather than on the whole system. The importance of a combined analysis of rotors and elastic supporting structures arises with the continuous development of turbo machinery applications, in particular in the Oil and Gas field where a wide variety of structurally optimized solutions with reduced weight on off-shore installations or modularized turbo-compression and turbo-generator trains, requires a more complete analysis not only limited to the rotor-bearing system. Complex elastic systems, in some cases, strongly affect the entire shaft line rotor dynamic response such as mode shapes, resonance frequencies, unbalance response and critical speeds. The aim of the study is a development of a new efficient methodology based on FEM approach to model the complete rotating machinery systems (rotors, bearings, stators and supporting structures), by means of appropriate transfer functions matrix. Taking advantage from the matrix of transfer functions H(ω) obtained through PSD analysis, the baseplate dynamic behavior can be timely and CPU efficiently computed, avoiding computationally expensive harmonic sweeps. The appropriate usage of undocumented ANSYS command ‘TFUN’ has been pursued in order to extract the required components of the transfer functions matrix at the bearing location. With such a solution the full dynamic interaction between the system components was accurately accounted. The outcome of the new methodology was successfully tested in a real field issue where evidences of structure to rotor interaction emerged at the proximity probe measurement during machine start-up.

An hydraulic test rig for the testing of quarter turn valve actuation systems

In this work, some preliminary design results concerning the development of a rig for the fast prototyping and the testing of the actuation system of large quarter turn valves for power plants are shown. In particular, friction forces generated on sealing and bushings by the internal pressurized fluid influence opening and closing torques of large valves. In order to test a valve actuation system, the proposed rig is able to simulate the resisting torque and more generally the mechanical impedance of pressurized quarter turn valve. The proposed actuation of the rig is hydraulic. This work aims to discuss different design solutions and suggest the choice of a testing rig with particular attention to robustness and stability troubles respect to disturbances, limited bandwidth and interaction with partially unknown tested system.