Active Control in Mechanical Engineering

Proceedings of the MV2 Convention on Active Control in Mechanical Engineering, Lyon, France, 22-23 October 1997.

Louis Jezequel, Louis Jezequel

• Editore: CRC Press
• Anno: 2021
• ISBN:
  9781000446678
• Edizione: 1
• Argomento: Technology & Engineering
• Categoria: Civil Engineering

The introduction of active control in structural dynamics has led to a number of developments over wide-ranging industrial domains. This work investigates this area and examines a number of topics including: smart materials and structures; new strategies of active control and its applications.

1 Smart materials and structures

New damping technologies for vibration control

G. R. Tomlinson

Department of Mechanical Engineering, University of Sheffield, UK

Abstract

Vibration damping is traditionally carried out using either viscoelastic materials or fluid type dampers. Recent advances in the use of smart materials and structures has led to new concepts for active vibration control, often using a hybrid solution of passive and active techniques. However, the overlap between the materials scientists and dynamacists is revealing new opportunities for introducing new forms of damping treatment, particularly for complex geometry’s where conformality is important. This paper gives as introduction to some of these new damping technologies and reveals exciting prospects for the future.

1. Introduction

Damping is usually employed as a means of limiting vibration levels in resonant situations or controlling the stability of structures resulting in lower noise levels, lower dynamic stress levels, and hence improved life cycle behaviour. It is a physical process which dissipates energy through conversion of mechanical work into heat. In engineering structures it is present in several forms: hysteresis in materials, friction via the tribological action of two rubbing surfaces, viscous friction in fluids, electromagnetic effects in, for example, magnetic bearings, acoustic damping. In aerospace, automotive, and maritime applications adding damping is usually the only method of controlling unwanted vibration and in the case of retro-fitting, it is usually the most cost effective solution as a re-design is often prohibitive.

However, the understanding and modelling of damping has improved to the extent that damping is now designed into many structures. Adding damping always increases the mass and modifies the stiffness of a structure. In some cases, such as the acoustic tiles on submarines, this is not so important; in the case of aero engines, where specific fuel consumption is a major factor, the effect of added mass is a constraining factor. Other important aspects which influence the choice of damping materials/mechanisms are temperature and frequency as in the case of viscoelastic materials which are highly temperature and frequency dependent and in such cases one may have to resort to external friction mechanisms [1]. Viscoelastic passive damping treatments are now widely established and the use of such materials in slightly more novel ways, for example, “potting” techniques [2], internal damping treatments for gas turbine blades [3] and damped composite structures [4] has been reported.

Impact damping offers potential where temperature is a problem as temperature insensitive materials can be used [5,6]. The size of the granular/particles employed in impact dampers can be very small (<200μm) and can result in fluidisation phenomenon from powder effects which may provide useful damping characteristics [7].

Coatings are widely used in, for example, thermal barrier coatings. Their use as damping mechanisms has not been widely investigated although some attempt at recognising their potential has been studied [8].

Metal-matrix composites may offer a method of enhancing the damping properties of metals and the use of aluminium alloys reinforced with silicon carbide has shown some promise [9].

Active damping methods usually employ an actuator, sensor and a feedback controller to suppress undesirable vibratio...