Doctoral training, at the core of MSCA-ITN programmes, aims to train engineers with high quality technical and transferable skills. The main driver for the InDEStruct project was the distinct lack of well-trained scientists in the area of multi-disciplinary optimisation of engineering systems that involve thermal and mechanical loading caused by vibration excitation, aerothermal flow and their combined effect on structural damage.

Industry 4.0 is about digital transformation of companies and the use of IoT (internet of things) in a wide range of applications. One concept that fully exploits this in the area of mechanical design and manufacture is the idea of a digital twin. A digital twin is a virtual representation of a physical system. It serves as a real-time digital surrogate, providing an indication of the system’s performance. Data is sent to the digital model from the physical product with the digital model then able to provide performance measures in order to optimize the product. This increases company productivity, as it can reduce or replace expensive and time-consuming physical testing of many candidate designs.

A digital twin is necessarily a multi-disciplinary concept, where well-trained scientists integrate technology that may arise from technical fields that could pose competing design constraints to provide indicators of engineering performance. InDEStruct provided such a platform for showcasing that this non-trivial challenge can be solved in an elegant and efficient manner. The InDEStruct project also identified some of the challenges that naturally arise in a multi-disciplinary environment.

Vestas aircoil A/S, a member of the InDEStruct consortium, designs and manufactures heat exchangers for marine and locomotive engines. A digital twin can provide warning concerning the  health of the cooler, such that the risk of a train breaking down inside a tunnel can be minimized, thereby also contributing to human well-being. Such a digital twin required fundamental multi-disciplinary understanding of systems produced by the InDEStruct project. One study focussed on how vibrations and stress response will influence the life of the materials used for coolers. In this case one of the production methods of tomorrow: added metal manufacturing. To predict the vibration characteristics an efficient and accurate design tool was developed in a parallel study. Both these studies were then complemented by the experimental study of efficient modal analysis of tube and fin structures, used in heat exchangers, and incorporating the cooler response to vibration and identify response changes, which can be an indicator of failure. Vibrations alongside corrosion is the primary reason for charge air cooler failures. The final study focussed on heat exchanger optimisation, combining all material and dynamic aspects which included a vibration model/constraint with aerothermal modelling.


In the context of a multi-disciplinary optimisation of systems, the four Early Stage Researchers(ESRs) have developed tools and methods to improve the design of a heat exchanger for the company Vestas aircoil A/S. The four fellows have performed analyses and laboratory experiments from the perspective of their individual project aims, which are focussed on one specific technical aspect. In addition, ESR1 draws together these pieces of technical information within an integrated design framework. This case serves as a generic design process highlighting the challenges and benefit of a multi-disciplinary approach. ESR1 completed an automated parametric design of a helical tube and its fluid flow analysis (CFD). This resulted in a study of a charge air cooler optimization problem, which included constraints on pressure, size, weight, heat dissipation and the newly developed dynamic model from ESR2. ESR2 developed computationally efficient models of modal vibration of heat exchanger components; directly related to in-situ experimental modal and wave analysis of heat exchanger components and their assembly conducted by ESR3 to estimate the dynamic properties of these structures. ESR4 performed a fatigue evaluation of additively manufactured 316L stainless steel, with attention to crack propagation and build direction in a 3D printer. Stainless steel being the material of choice for said heat exchanger. The work of ESR4 was tied together with the work of ESR2 in the calculation of the fatigue life of an exemplar structure.

These results have shown the benefit of a multi-disciplinary approach to optimization and design development. All these tools and outcomes have been formally documented, in addition to transfer to the company and in use there within the design and validation teams as part of the industrial practice. It has provided valuable input to the direction that the company will take in future projects and the challenges are on the agenda for the R&D department in the years to come. In addition, the original research and outcomes arising from this study have commenced in generating peer reviewed research publications and these will continue to be generated after the project end.

Summarising the main results so far, the design process is driven by geometry generation, calculation of heat transfer & flow, structural analysis, vibration and fatigue testing; the ESR team worked towards an integration of these for the benefit of the lifetime of heat exchanger products. The lesson learnt is that there is a tendency for technical specialists to “work in isolation” until brought together by the design constraints. This highlights the industrial need to have specialist technology roles integrated within design teams. Also realised is that communication within design teams is very important and specialist design integration roles would have to facilitate that.


ESR1 focused on the development of novel multi-disciplinary design optimisation methods which are, in essence, the glue holding a digital twin based design and monitoring process together. Automation of geometry generation and the multi-disciplinary analysis of heat exchangers, bringing together the lessons learned from the other ESRs on fatigue and dynamic response prediction, will enable more efficient and robust heat exchangers to be designed in a shorter period. The tools developed within this framework will allow a more formalized method to explore the design space, using advanced search routines such as genetic algorithms, in order to achieve a feasible design within a fixed computational budget.

The work of ESRs 2 and 3 provided knowledge about the dynamic characteristics of heat exchangers. This can allow for more accurate estimation of vibrational properties of these structures during their design and in operation. A hierarchical design philosophy relying on simple but approximate models at early stages, followed by more elaborate but computationally expensive models seems to be the way forward within a typical design cycle. These multi-fidelity models would improve the durability of these components by ensuring critical frequencies of the engine operation are avoided, given fixed computational resources.

Variations in the process parameters during the additive manufacture of stainless steel components have been found to affect defect spatial and size distributions. This has been linked to the control of the relative effects of initiation, growth and coalescence processes in determining fatigue lifetimes by ESR4.  Future steps include the assessment of feature size effects on microstructure and defect distributions in additively manufactured (AM) structures to feed into the structural design assessment and optimisation of more complex designs with wide variations in feature size.

Surrogate models provide an interesting and inexpensive way of providing information on the performance of an engineering system on which optimal designs could be searched. The framework developed by ESR1 could be used for a single or multiple objectives as well as multiple domains of physics (e.g., heat transfer, flow calculations, stress analysis, vibration and fatigue prediction), some of them potentially posing conflicting requirements. A combination of work from ESR2 and ESR4 has provided a method to feed vibration calculations of a structure (theoretically obtained or experimentally measured) to fatigue calculations, thus achieving integration of structural dynamics and material behaviour. The knowledge generated by the application and development of experimental methods to test industrial components under ambient excitation by ESR3 should also be applicable to other industries. It has potential use for continuous condition monitoring and aid in the topics of digital twin and modal tracking for structural changes.


This collaborative doctoral training programme provides a model for the development of technology leaders, enabling them to apply scientific methods from academia to interdisciplinary industrial design. The project is driven by the need for more efficient & lower emission engine systems. Heat exchangers in engines has been identified as a key enabling technology for low-emission power systems that is vital to the EU economy and is of great societal concern. Development of high-performance heat exchangers is a complex engineering challenge requiring academic contributions at the forefront of engineering science. Having identified charge air cooling as a key enabling technology for low-emission power systems, here we propose an integrated approach to doctoral training in the area of engineering design leading to four doctorates covering diverse aspects of their mechanical engineering: structural vibration, stress & thermal analysis, additive manufacturing (AM), multifunctional metamaterials, fatigue & materials development. The programme provides mobility, industrial experience and academic foundations in an integrated manner that will uniquely equip our future technology leaders to contribute to high-value innovation within EU industry.


  • Doctoral training of 4 Early Stage Researchers (ESRs) leading to the degree of PhD from the University of Southampton.
  • 18 months at the University of Southampton campus (including secondments in the UK) 18 months at Vestas aircoil (Vestas) industrial facilities, (which also includes industrial secondments).
  • Joint industrial & academic supervision of ESRs with a multidisciplinary & inter-sectoral supervisory board.
  • A training program built upon the central theme of Engineering Design, providing a coherent structure for integration/ application of distinct engineering approaches, highlighting the interdisciplinary nature of industrial research & development.
  • Science-based taught modules laying a broad and rigorous scientific foundation.
  • Transferable skills training focussed on business innovation, project management, dissemination, intellectual property through workshops, specific courses and participation modellied on the lines of Southampton’s unique nationally-funded Centres for Doctoral Training (CDTs).
  • Individual research projects for each ESR addressing questions with technical depth & scope for originality at the forefront of engineering research that, taken together, form a fundamental basis for integrated design of advanced heat transfer systems.


ESR 1: Development of a system for automatically varying geometry & performing an aerothermal analysis; Optimisation of novel additively manufactured cellular/periodic structures for aerothermal performance.

Academic supervisors: Dr. David Toal within the Computational Engineering research group and Dr. Edward Richardson within the Aerodynamics & Flight Mechanics research group at the Faculty of Engineering and the Environment, University of Southampton.

ESR 2: Develop predictive capability to assess the performance of materials & structures for vibration response. Address the inverse problem of designing internal architecture of metamaterials & external shapes of structural components for the industrial case study of charge air coolers.

Academic supervisors: Professor Atul Bhaskar within the Computational Engineering research group and Dr Maryam Ghandchi-Tehrani at the Institute of Sound and Vibration Research (ISVR) at the Faculty of Engineering and the Environment, University of Southampton.

ESR 3: Techniques especially suited to response measurement for materials with mesoscopic structure will be employed. The results will inform modelling activities of ESR2. To understand damping in built up structures & additively manufactured materials.

Academic supervisors: Dr Neil Ferguson and Professor Atul Bhaskar in the Faculty of Engineering and the Environment are the academic supervisors, from the Institute of Sound and Vibration Research (ISVR) and the Computational Engineering research group respectively, University of Southampton.

ESR 4: The goal of this PhD project is to characterise & understand (and so predict) the fatigue behaviour of AM & typical joint microstructures, this will: 1. Establish the effect of complex loading & thermal cycles on fatigue lifetimes. 2. Evaluate the evolution of AM microstructures experiencing these thermal (service) cycles. 3. Confirm the appropriate materials constitutive models & fatigue laws to be used in lifing. 4. Assess how fouling & the service environment together with AM defect distributions affect fatigue initiation & crack growth behavior & the concomitant effects on fatigue lifing .

Academic supervisor: Professor Philippa Reed and Dr Andrew Hamilton, both within the Engineering Materials research group at the Faculty of Engineering and the Environment, are the academic supervisors, University of Southampton.

Additive manufacturing & evaluation of multifunctional materials & structures for heat exchanger applications: Identifying a major area of design improvements enabled by advances in AM, the strength of the new manufacturing process will be suitably exploited in creating macroscopic structures & architectured materials for multifunctional use. In particular, novel lattice topologies for heat & fluid flow paths will be used by ESR3 for vibration suppression. Assessment of the performance of a class of multifunctional materials & structures will be carried out computationally & experimentally, thus informing the design process.

The four researchers will collaboratively work on a host of engineering problems covering design & optimisation, structural & vibration analysis, Additive manufacturing & elastic/acoustic meta-materials, thermal analysis and materials characterisation. The activities are outlined below.

Computational modelling of heat exchanger components/assemblies for stress analysis/vibration prediction: A hierarchy of modelling techniques will be used ranging from highly simplified descriptions of the heat exchanger structures, that capture the underlying structural dynamics in an approximate but computationally efficient manner, to computationally intensive high-fidelity methods. ESR2 will do stress analysis & vibration prediction as both involve FEM of the heat exchanger structure.

Vibration measurement/damping characterisation in charge heat exchanger components/structures: To complement studying vibration of the heat exchanger structure, ESR3 will carry out experimental vibration characterisation of components, their variability, uncertainty, and subsequent behaviour of the built-up structures. ESR3 will work closely with ESR2 (modelling). Damping in material, supports, joints & fastenings in the built-up structure will be characterised to enable accurate modelling.

Material characterisation under fatigue environments for heat exchangers: ESR4 will evaluate the fatigue performance of relevant materials under the typical loading & thermal cycles produced by the service environment.  This will include the development of appropriate constitutive materials models & fatigue lifing approaches to work with ESR2 on fatigue lifing of the structures in the design optimisation process. The effects of additive manufacturing processes on subsequent materials properties in the metamaterials structures will be a particular focus with ESR3.

Aerothermal & thermomechanical analysis: Aerothermal (ESR1) & thermo-mechanical analyses (ESR2) are critical in assessing the performance, in terms of pressure losses, cooling & life of any heat exchanger system. An automated aerothermal & thermo-mechanical analysis process will be developed from which the above performance metrics can be assessed with relative ease for novel cellular heat exchanger topologies and to develop new optimisation approaches, e.g. multi-fidelity analysis which will reduce the cost of any subsequent design process. The cellular nature of the novel AM heat exchangers proposed here with high curvature and secondary flow effects also offers considerable scope for ESR1 to explore the fundamental fluid & heat transfer aspects of such systems.