Concurrent topology and sizing optimisation for multifunctional structural design

The need for resource efficient transport is increasing as environmental concerns are growing ever more important. One of the most important vehicle properties when it comes to fuel consumption is the mass of the vehicle, with heavier vehicles requiring more energy and therefore more fuel to operate. A key strategy when designing more efficient vehicles for transport is thus to make the vehicles as light as possible. During operation, different vehicles are have to fulfill a number of different requirements, such as protecting passengers and cargo from the elements, being safe in case of an accident and maintaining a comfortable sound level for the passengers. These requirements are often conflicting, especially in a lightweight context. It is well known that stiff and lightweight structures tend to vibrate more when exposed to dynamic loads, severely degrading the acoustic performance. The aim of this doctoral thesis is to investigate design methodologies that can be used to design lightweight components with good structural and acoustic properties at an early stage of the design process, where the design freedom is large. Key is the fact that response to both static and dynamic loading is taken into account simultaneously instead of sequentially, this is to prevent the emergence of design solutions with very good structural performance, but whose poor dynamic behaviour requires mass-intensive sub-systems to be added at a later stage. The investigated methodology is based on using topology optimization to minimize the mass of a structure subject to constraints on the response to static and dynamic loads. An initial study extends the use Topology Optimization of Binary Structures (TOBS) method to problems with vibration constraints. The TOBS method is later extended to allow for the concurrent optimization of the core topology and face sheet thickness of a sandwich structure. This new sandwich optimization method is then used to minimize the mass of a sandwich beam subjected to a static load. Finally, the concurrent sandwich optimization is used to minimize the mass of a sandwich beam subjected to simultaneous static and harmonic loads, at both single frequencies and in frequency bands. The results show that the new concurrent sandwich optimization method offer significant improvements over optimizing the core topology with fixed face sheet thickness, resulting in a mass reduction of up to 22\%. The mass of the resulting structure is also shown to be very