Design of novel, additively manufactured cellular lattice supported composite structures using topology optimisation

Upscaling the production of wind energy capacity is of great importance domestically and globally due to three significant factors. Firstly, pollution from greenhouse gases and other emissions as a result of burning fossil fuels for energy contributes to global warming. These effects cause increased instability of the climate, resulting in more natural disasters as well as ecosystem collapse. Secondly, over-dependence on fossil fuel for energy causes insecurity and tensions between and within nations. Thirdly, increasing the installed capacity of wind energy is an economic benefit. Wind energy is highly cost efficient for producing energy and the investment in the wind industry drives economic growth due to job creation in manufacturing, construction, and operation and maintenance. The development of new technology and energy storage networks also helps to lower costs of wind and other forms of renewable energy.

One of the largest barriers to faster production of wind energy capacity is the cost and lead time of manufacturing wind turbine rotor blades. The growing scale of wind blades means that the main costs of manufacturing which are associated with materials, labour, and tooling, are a limiting factor. It is proposed that manufacturing a mould which acts as the internal structure of the blade would target each of these sources of cost through enabling automation and reduced material use by removing the need for expensive steel-backed composite moulds.

Additive manufacturing (AM) is an enabling technology which is crucial for producing large scale structures in future. It's main function for wind blade production is more efficient use of material and division of labour. AM enables the use of topology optimisation (TO) for the design of large structures. TO provides a means to design structures for specific performance needs. AM allows for the creation of these structures that have been customized, making the two technologies an ideal match for producing structures that are designed to meet specific needs. The combination of TO and AM leads to the creation of structures that are highly efficient with minimal waste and maximum speed in production.

There are two main challenges associated with using topology optimisation in wind blade design. Firstly, the aeroelastic response of the blade is an important factor in the structural design, as it can improve the blade's ability to capture energy from the wind and alleviate loads by optimising the stiffness and tuning the natural frequencies. Topology optimisation is not readily compatible with aeroelastic solvers and there is limited research combining aeroelastic design with topology optimisation due to this difficulty. Secondly, composite laminates are critical component of large wind turbine blades, due to the size of the bending moment arms. Topology optimisation of orthotropic laminates and multiple materials is limited in its ability to design large scale, manufacturable structures, given the computationally intensive process.

A design methodology is proposed, which leverages the strengths of topology optimisation and additive manufacturing to achieve optimised composite laminate configurations as well as repeated unit cell graded lattice architectures for wind turbine blades. The method involves a multi-stage topology optimisation process; In the first stage, a composite laminate structure is designed based on an idealised topology optimisation solution; In the second stage, the results from the first stage are frozen and utilised to design a 3D printed repeated unit cell architecture which supports the composite laminates and allows for improved manufacturability. The goal of this process is to combine conventional knowledge of structural requirements for efficient use of composite laminate configurations, while also enabling the inclusion of additive manufacturing to support and improve performance, weight and manufacturing cost.

There are seven principal groups of beneficiaries for our new EPSRC Centre for Doctoral Training in Composites Science, Engineering, and Manufacturing.

1. Collaborating companies and organisations, who will gain privileged access to the unique concentration of research training and skills available within the CDT, through active participation in doctoral research projects. In the Centre we will explore innovative ideas, in conjunction with industrial partners, international partners, and other associated groups (CLF, Catapults). Showcase events, such as our annual conference, will offer opportunities to a much broader spectrum of potentially collaborating companies and other organisations. The supporting companies will benefit from cross-sector learning opportunities and

- specific innovations within their sponsored project that make a significant impact on the company;
- increased collaboration with academia;
- the development of blue-skies and long-term research at a lowered risk.

2. Early-stage investors, who will gain access to commercial opportunities that have been validated through proof-of-concept, through our NCC-led technology pull-through programme.

3. Academics within Bristol, across a diverse range of disciplines, and at other universities associated with Bristol through the Manufacturing Hub, will benefit from collaborative research and exploitation opportunities in our CDT. International visits made possible by the Centre will undoubtedly lead to a wider spectrum of research training and exploitation collaborations.

4. Research students will establish their reputations as part of the CDT. Training and experiences within the Centre will increase their awareness of wider and contextually important issues, such as IP identification, commercialisation opportunities, and engagement with the public.

5. Students at the partner universities (SFI - Limerick) and other institutions, who will benefit from the collaborative training environment through the technologically relevant feedback from commercial stakeholder organisations.

6. The University of Bristol will enhance their international profile in composites. In addition to the immediate gains such as high quality academic publications and conference presentations during the course of the Centre, the University gains from the collaboration with industry that will continue long after the participants graduate. This is shown by the

a) Follow-on research activities in related areas.
b) Willingness of past graduates to:

i) Act as advocates for the CDT through our alumni association;
ii) Participate in the Advisory Board of our proposed CDT;
iii) Act as mentors to current doctoral students.

7. Citizens of the UK. We have identified key fields in composites science, engineering and manufacturing technology which are of current strategic importance to the country and will demonstrate the route by which these fields will impact our lives. Our current CDTs have shown considerable impact on industry (e.g. Rolls Royce). Our proposed centre will continue to give this benefit. We have built activities into the CDT programme to develop wider competences of the students in:

a) Communication - presentations, videos, journal paper, workshops;
b) Exploitation - business plans and exploitation routes for research;
c) Public Understanding - science ambassador, schools events, website.