Mid- and High-Frequency Vibroacoustics of Built-up Structures -- A Wave Approach

Noise and vibration are important performance aspects in many mechanical systems. High noise and vibration levels can be detrimental to structures (e.g. causing damage) and to the human operators (e.g. causing fatigue or injury). Thus, it is important to be able to understand how structures vibrate and emit noise, i.e., their vibroacoustic behavior. Traditionally, engineers would try to describe the vibroacoustics using analytical methods. However, these are only possible for very simple structures. Structures that engineers confront in the aerospace, railway or maritime sectors are often made of composite panels that are connected together using complicated structural joints. The analysis of the vibroacoustics of such complex built-up structures cannot be performed analytically.

Over the years, researchers have developed numerical techniques to solve this problem. Element-based methods (such as the finite element method) are well-developed and well-established methods with many commercial/in-house codes that can be used. However, aerospace, railway and maritime structures are relatively large. For example, a typical railway car can be modelled using the finite element method up to 500 Hz. Above this frequency, the size of the finite element model becomes too large, impractical and the associated computational cost becomes prohibitive. However, the audio frequency range is 20 Hz-20 kHz. At high frequency (above 10 kHz), the railway car can be modelled using energy-based methods such as the statistical energy analysis method. Energy-based statistical methods are valuable, but less well-established than element-based methods. The railway car example points to a frequency gap, indeed a mid-frequency gap, where neither element-based nor energy-based methods can be used.

I am proposing to use wave methods to bridge the mid-frequency gap and to further strengthen energy methods. Waves provide a unifying, intuitive approach to vibroacoustics. The computational cost of a wave model is substantially small (especially when compared to a full finite element model), and the wave properties of structures can be obtained by post processing the finite element model of a small segment of an arbitrarily large structure.

Thus, the goal of this programme is to develop a wave-based toolbox for modelling the vibroacoustics complex built-up structures. Industrial examples from the aerospace, railway and maritime sectors will be used to demonstrate the efficiency and effectiveness of the developed methods.

In this research programme, I will conduct basic scientific research which has industrial relevance. All the developed methodologies will be demonstrated through industrial examples to illustrate their suitability for real-life problems. Thus, the expected impacts of this programme include:

1. Lowering lead time - The development and industrial application of novel numerical modelling schemes will allow the construction of enhanced virtual prototypes of aerospace, railway and maritime industries. The results of this research programme are particularly relevant to these industries, where full-sized physical prototypes are not possible. Current numerical methods can be computationally prohibitive. Thus, time-efficient modelling approaches will certainly contribute to lower lead times.

2. Lowering costs - The application of time-efficient numerical tools in the various structural design stages allows concurrent optimization of the structures, subsystems and components while considering multifunctional design. More cost-effective manufacturing and construction schemes can be strived for, simulating various modifications on virtual numerical models. Furthermore, design changes due to problem detection in the original design can be shifted towards earlier design phases, consequently reducing the engineering and production costs.

3. Strengthening UK competitiveness - This programme will also strengthen the UK's manufacturing sector. This is important in the face of the fierce global competition and the current economic climate. Providing the UK engineers with tools that allows to (a) design their products and simulate their behavior in a time-efficient manner and (b) optimize their products' performance will increase their competitiveness on a global scale.

4. Ensuring UK leadership in engineering - The dissemination activities that will accompany this research programme will ensure the visibility of the UK academia at the EU and international levels. This will maintain and increase the UK's leading position in engineering and will indirectly generate business for UK entities (companies, industries, consultancy firms, etc.).

5. Creating new skills - The impact of this programme on people will be two folds: the programme will provide the best platform for me to grow and solidify my research career, leading to a readership position and securing my status as a leading international expert in structural dynamics and vibroacoustics. Furthermore, the University of Southampton has committed a PhD studentship in support of this programme and this PhD student will gain important knowledge and experience which will increase his/her future employability. Being trained in the application of the state-of-the-art methodologies, the graduate PhD student will act as another dissemination channel, transferring the project results into the industry/academia.