Design of an actuation system for a variable pitch axial fan

none3H.Giberti; F.Resta; L.PratoGiberti, Hermes; F., Resta; L., Prat

A mechanical approach to the design of independent modal space control for vibration suppression

Many systems have, by their nature, a small damping and therefore they are potentially subjected to dangerous vibration phenomena. The aim of active vibration control is to contain this phenomenon, improve the dynamic performance of the system, and increase its fatigue strength. A way to reach this goal is to increase the system damping, preferably without changing its natural frequencies and vibration modes. In the past decades this has been achieved by developing the well-known independent modal space control (IMSC) technique. The paper describes a new approach to the synthesis of a modal controller to suppress vibrations in structures. It turns from the traditional formulation of the problem and it demonstrates how the performance of the controller can be evaluated through the analysis of the modal damping matrix of the controlled system. The ability to easily manage this information allows us to synthesize an efficient modal controller. Furthermore, it enables us to easily evaluate the stability of the control, the effects of spillover, and the consequent effectiveness in reducing vibration. Theoretical aspects are supported by experimental applications on a large flexible system.</jats:p

On Independent Modal Control Of A Vibrating Systems

Of the multitude of available control techniques, modal control is a favourite amongst structural dynamicists because of its representation in modal coordinates. The term modal control is used to describe a wide variety of control techniques which find their origin in a description of the system through the main coordinates, defined by the modes of vibration of the system. This approach stems from the consideration that the response of a mechanical system to a disturbance is the sum of the independent responses of its vibrational modes. This motivates the desire to design a control that does not alter these mode shapes, but allows to change the natural frequency and the damping of each mode. In active vibration control the purpose is to increase the damping of modes interested in the vibratory phenomenon. The paper shows how stability, spillover effects, system controllability and sensors and actuators position are all linked to the analysis of the controlled system damping matrix and to the possibility that the forces introduced by the control is non-dissipative. Theoretical aspects are supported by numerical simulations.</jats:p

Forced and free motion aeroelastic tests on a new concept dynamometric section model of the Messina suspension bridge

The work presents a new original experimental rig to investigate more deeply the aerodynamic behaviour of long span suspension bridges. Set-up and model are designed to grant an accurate study on main aeroelastic phenomena, relevant in bridge engineering. More in details, experimental set-up and a 1:60 scale sectional model of Messina bridge deck are presented. The complete rig, composed by dynamometric model, suspension set and experimental set-up, is designed in order to execute both forced and free motion tests, by changing the average position in terms angle of attack and yaw angle and to investigate on flutter derivatives and vortex induced vibrations