On In-situ Methodologies for the Characterisation and Simulation of Vibro-Acoustic Assemblies

A drive towards leaner engineering has seen the use of physical prototypes become a limiting factor in the development of new products. Consequently, alternative prototyping methods are of interest. With their ability to reduce cost, accelerate time to market, and optimize products to higher levels of performance and reliability, virtual methods offer an attractive alternative. Methods for virtual prototyping with respect to visual design and engineering (i.e CAD and CAE) are particularly well developed. Unfortunately, the same cannot be said in the realm of acoustics. Although numerical methods, such as finite and boundary element analysis, are able to predict, with some accuracy, the passive properties of simple assembly components, they currently lack the ability to accurately model more complex vibro-acoustic components, for example vibration sources and their associated vibratory mechanisms. Consequently, the adoption of any virtual acoustic prototyping (VAP) methodology will require some element of experimental work. As such, this Thesis concerns the development and implementation of experimental methods for the independent characterisation of assembly components, with particular emphasis on in-situ approaches. The methods discussed in this work will focus on the determination of active and passive sub-structure properties that may be recombined virtually within a dynamic sub-structuring framework so as to construct a VAP. A well constructed VAP will allow for an engineer to `listen' to a product without it having to physically exist. With the growing importance of product sound quality, this offers a considerable advantage, particularly in the early stages of product development.<br/>
\n\t\t
\n<br/>Work begins by developing an in-situ method for the independent characterisation of resilient coupling elements. The approach holds a number of advantages over current methods as it may be applied to arbitrary structures and over a wide frequency range. In order to provide a flexible and workable method that may be used in a practical scenario three experimental extensions are provided. These extensions concern; the finite difference approximation for rotational degrees of freedom, the round trip identity for remote measurement positions, and generalised transmissibility for the use of operationally determinable quantities. Experimental studies show that the proposed method, and its extensions, are capable of determining the independent passive properties of coupling elements from a range of different assembly types with good accuracy. <br/>
\n\t\t
\n<br/>The in-situ characterisation approach goes on to form the basis of a novel in-situ decoupling procedure which is shown to accurately determine the independent free interface frequency response functions (FRFs) of resiliently coupled source and receiver sub-structures. The decoupling procedure provides a convenient alternative to the free suspension of a sub-structure whilst providing a number of potential benefits, for example, characterisation whilst under representative mounting conditions. The approach is validated experimentally and used to decouple both single and multi-contact resonant assemblies with great success. <br/>
\n\t\t
\n<br/>The in-situ blocked force approach is re-introduced to the reader as a method for independently characterising the active component of a source sub-structure. Methods for assessing uncertainties involved are also discussed. The blocked force method is subsequently extended so as to allow for an estimate of uncertainties to be made. The concept of error propagation is investigated and an experimental study presented. This study is aimed at providing an example of the in-situ blocked forces application, whilst validating the proposed measure of uncertainty. <br/>
\n\t\t
\n<br/>The Thesis concludes with an experimental case study utilizing the methods proposed throughout. This case study concerns the construction of a VAP whereby an electric pump is resiliently coupled to a cavity backed plate. It is shown that, together, the proposed methods allow for the construction of a VAP capable of predicting, with reasonable accuracy, the operational pressure and velocity response of an assembly.