Stochastic transfer operator methods for modelling the vibroacoustic properties of newly emerging transport structures

The rapid growth of computing power during the last 50 years has given rise to a whole simulation industry serving the needs of the manufacturers looking to design products in an optimal manner, without the time and costs associated with building a series of physical prototypes. Design and construction decisions are increasingly made by means of virtual prototyping as part of Computer Aided Engineering (CAE), and efficient simulation tools in all areas of engineering are sought after. Noise and vibration are particularly important performance aspects in the design of many mechanical systems. High noise and vibration levels can be damaging to structures and to their users (potentially causing hearing loss, for example). Developing computational techniques to improve our understanding of the vibration and acoustics of complex built-up structures can enhance performance, speed up the design cycle and ultimately result in safer and less noisy products.

Methodologies have long been sought after for modelling large-scale complex structures such as aircraft, trains and cars. The sheer size of these structures makes building full-scale physical prototypes expensive, and often infeasible. It also poses problems for simulation methods and limits many CAE products to low frequencies, where computational run times are relatively low and uncertainties have little influence on the vibrational behaviour. Uncertainties arising during the manufacturing process (for example, in material properties or physical dimensions) can lead to large variations in the levels of noise and vibration of a structure at high frequencies, and so mechanical engineers have turned to statistical methods to instead predict averages of these noise and vibration levels. Unfortunately, these statistical methods are based on a set of assumptions that are hard to control and generally only fulfilled for more traditional structural designs. They are not fulfilled for the large curved and moulded components used today. Therefore the CAE tools available at present for simulating mid- and high- frequency noise and vibration do not meet the needs of engineers in the transport sector.

As a result of the 2008 climate change act in the UK and similar initiatives around the globe, transport industries are undergoing a period of great change. Alternative fuel sources and lightweight materials are two of the major areas of development. An increasing number of hybrid and electric powered vehicles are appearing on the market and the use of lightweight and composite materials is increasing across the sector. Engineers were already in need of new and more versatile simulation methods at mid-to-high frequencies, but the increasing popularity of lightweight materials and electric power sources has compounded this situation for three main reasons:
- only estimates of the material properties for newly manufactured lightweight and composite materials are available introducing considerable uncertainty into the model;
- lightweight and composite materials typically emit noise at higher frequencies than more traditional steel or aluminium based structures;
- sources of noise and vibration (eg. electric motors, air resistance etc.) will mostly be at high frequencies.

In this proposal, random (or stochastic) transfer operator methods will be developed for modelling mid-to-high frequency structural vibrations in large complex structures. These methods will have the advantages of the current statistical approaches in terms of being able to model uncertainties in the structural design and materials, but crucially will be applicable to a far wider range of structures, including large moulded components and novel lightweight materials. The approach to be developed therefore has the potential to provide a black-box design tool for mechanical engineers looking to develop the next generation of green and lightweight transport structures.

I will conduct basic scientific research which has industrial relevance. The success of the proposed research programme will have direct and measurable benefits for the industrial partners. The longer term benefits of the work have the potential to spread out more widely to manufacturers in the transport sector and to society at large. The nature of this impact is explained below:

1. Direct impact.

1.1. An extension of Far UK's use of virtual prototyping to include vibro-acoustic analysis: The work packages are strongly related to modelling novel lightweight structures and materials, such as those developed by Far. The research programme has been discussed in detail with company director Lyndon Sanders, who is keen to provide case studies for testing and verification in order to extend Far UK's use of virtual prototyping to include vibro-acoustic analysis. Mid- and high-frequency analysis will be particularly beneficial for Far's automotive subsidiary Axon Automotive, leading to a faster, lower cost and improved product development cycle.

1.2. A software development opportunity for PACSYS: As a vibroacoustic analysis software specialist, PACSYS Ltd. will have first-hand experience of the newly developed methodology giving them a unique opportunity to expand their business and open up new markets. The project has been discussed with senior consultant Dr Patrick Macey and his initial plan is to compare the approach with PACSYS VibroAcoustics for frequencies at the top end of its capability, before developing a commercial software package based on the methods developed during this project.

2. Longer term and indirect impact.

2.1 Strengthening UK competitiveness: As well as making a direct contribution to the business areas of two research focused UK SMEs, the availability of both academic and commercial codes for the newly developed methodology will help it mature into a design tool that is used across the transport sector. The size and scale of the structures to be designed (trains, aircraft, ships etc.) means that full physical prototypes are usually unfeasible. Hence, equipping UK engineers with tools that allow them to design their products more quickly in a manner that optimises their performance will increase their global competitiveness. This is particularly important in the face of the current economic climate with strong competition from around the globe.

2.2 Ensuring UK leadership in Engineering: The planned dissemination and outreach activities will ensure that awareness of the project is spread to the widest possible audience, both nationally and internationally. This will enhance the UK's reputation as a world leader in engineering and indirectly generate business for UK entities.

2.3 Benefits for quality of life and public health: Providing engineers with the tools to efficiently design green and efficient transport structures will also benefit society at large. A more efficient and optimal design process will lead to lower development costs and a better end product. The result for society will be more comfortable and less noisy travel at potentially lower prices as cost savings are passed on to consumers. In addition, the ability to design more efficient vehicles more quickly with a reduced time to market means that greener and more efficient transport options will be in use earlier and in greater numbers. As a result, there are huge potential benefits for the environment in terms of reduced air pollution and C02 emissions helping the UK meet the targets set out in the 2008 climate change act, and improving quality of life in general.