Active Control of Machinery Noise in a Marine Environment - Lessons Learned5

A research programme to investigate the feasibility of using active control systems to control the radiated noise of a naval platform due to the on-board machinery was first setup in the late 1970s at the Defence Evaluation and Research Agency. The programme covers the development of control algorithms, development of the hardware for the controller, a trial on a naval platform, analysis of the trial results and the development of several actuators for different transmission paths. This paper presents the experience and lessons learned from the programme. The programme demonstrated that active control of tonals associated with a machine on board a naval platform is feasible. The key to success is a clear understanding of the interactions between all the possible transmission paths from the noise source. This applies to both passive and active controls. The major obstacles to wider application of active control techniques are a lack of suitable off-the-shelf actuators and their costs. INTRODUCTION Quietness is one of the essential requirements for successfid operations of a naval platform. Nowadays, there are a number of drivers pushing for a lower radiated noise signature. The advances in the passive sonar performance over the last decade allow acoustic noise detection at lower levels and frequency. To increase the detection range of any hostility requires on board sensors not to be blinded by the ship’s own noise. There are always inevitable noise and ‘@BritishCrown Copyright 1997/DERA Publishedwith the permission of the Controllerof HerBritannicMajesty’sStationaryOEice vibration generated by the prime mover and auxiliary machinery on board a ship. The conventional treatment is by means of isolation using compliant elements between the machines and their supporting or neighboring structures. The progress in the passive isolation techniques in the past decades means that they are approaching their practical limits. Particularly at low frequency where the treatments become bulky or the compliant elements can not be softened fin-ther without compromising the stability of the machines in all operating conditions. This is where active control technique becomes a practical solution to compliment passive treatments. DERA foresaw the limitation of passive controls and initiated a research programme in active control back in the late 1970s. The research programme went through a number of phases. It included the development of control algorithms; laboratory validation, fi.dl scale trials and actuators development. Valuable experience and lessons were gained from numerous experiments carried out on a floating test platform and from a trial conducted on a small diesel engine on board a naval platform. This paper reflects the experience and lessons learned by the author from his involvement in the active noise control research prograrnme at the Defence and Evaluation Research Agency.