Reception Plate Method for Structure-Borne Sound Sources

There are not presently available practical methods of characterising vibro-acoustic sources, which excite supporting and surrounding structures into vibration through the supports and other contacts. The context of the proposal concerns the prediction and control of noise due to machine vibrations being transmitted to a receiving structure, subsequently propagating and re-radiating from the structure as noise. By practical, is meant laboratory methods which yield source data in reduced form, which can be transformed into a prediction of the structure-borne power in the installed condition. Whilst generally, airborne sources have been successfully incorporated into prediction models by reference to airborne sound power, it has not yet been possible to incorporate structure-borne sources on a similar basis. There are two main challenges in seeking a structure-borne source characterisation. First, a source characterisation requires consideration of both the vibration activity and the structural dynamics at the contacts with supporting and surrounding structures. Secondly, the vibration transmission process is complicated and a full description requires a large data set and is experimentally and computationally intensive. However, design engineers, test-house managers and consultants require laboratory-based measurement systems which will yield single values of source strength and the conventional view is that these practical requirements conflict with the requirements for a physical and accurate source characterisation. The core of this investigation is to address this conflict by developing and appraising a novel reception plate method of structure-borne sound source characterisation. The machine under test is attached to a high-mobility plate, from which the source activity is obtained indirectly in the form of the velocity of the free source (i.e. as if the machine had been freely suspended). The machine then is attached to a low-mobility plate to indirectly obtain the blocked force (i.e. as if the machine had been attached to an inert structure). From these two quantities, the source mobility is obtained without direct measurement.The fundamental advantage of this method is that the time consuming and complicated process of directly acquiring the source activity and dynamics for each contact, and for each component of excitation, is replaced with an indirect method which only requires measurement of the response velocity of simple attached plates.

The work will have impact on manufacturers and suppliers of mechanical components (motors, fans, pumps, etc.), which are installed in buildings, domestic appliances and vehicles. They will be provided with a practical test method, which will allow estimates of the potential noisiness of their products when installed. This will provide an essential tool for low noise product design. The benefits are increased competitiveness through improved design, noise being an increasingly important factor in EC, US and Japanese markets. Of immediate relevance, are the recent developments of micro-CHP units, for the generation of domestic heat and electricity. The Baxi Group of the UK is presently in the process of going to market, ahead of other European manufacturers. These units are over 90% efficient but pose greater vibro-acoustic problems than conventional boiler systems. The research outlined in this grant application will synchronise with the R&D of Baxi and provide invaluable collaborative knowledge transfer throughout the life of the project and beyond (see letter of support). In terms of social benefits, the adverse effects of noisy products and installations are clear. The proposed research is expected to make a positive contribution to minimising such problems in the medium and long term, since structure-borne sound is a widespread problem, currently with little in the way of technical support. There is significant potential for the research to impact upon progress in Standardization. The Acoustics Research Unit has a proven record of research cooperation and dissemination to International Standards working groups in noise control. Professor Gibbs is a member of CEN group WG7 (Structure-borne Sound), which is composed of scientists, technical managers of national acoustic test facilities, and manufacturers, in France, Germany, Switzerland, Belgium, Sweden, Portugal and the UK. WG7 has been in existence since 2004 and convenes twice-yearly. During this period, six Doctorates were completed, three of which were registered at Liverpool University, in collaboration with Fachhochschule Stuttgart-Hochschule fur Technik. The present application will provide research that is core to the activities of European and International Standardization groups. Existing collaborative activity, involving share of measurement test facilities, between Liverpool and Germany, France and Switzerland, will continue and develop in this programme (see letters of support). The two Project Students appointed will draw substantial benefit from: Skills accrued from developing measurement methods and analytical/numerical models in vibro-acoustics; Working as part of an active research unit and with researchers in well-founded laboratories in Europe; Working with an industrial collaborator in the UK that is presently at the forefront in the development of a new generation of micro-CHP systems for domestic use. The results of the work will be disseminated by the normal process of reporting at national and international conferences and by publications in appropriate refereed journals in acoustics and noise and vibration control (e.g. Journal of Sound and Vibration, Journal of the Acoustical Society of America). During the life of the collaborative working groups, described above, special sessions were organised at international conferences, which provided forums for discussion of the collaborative research. Previous examples are: the International Congress on Sound and Vibration (ICSV), St Petersburg 2004; Lisbon 2005; Vienna 2006; Korea 2008; Krakow 2009. In addition, as part of the EU COST project, Dr Hopkins is able to disseminate to a European network of researchers working on the acoustics of timber-frame buildings.