Stochastic nonlinear aeroelastic models subject to unsteady loads

The accurate and efficient estimation of aircraft loads is an important problem in the aerospace industry. The extreme values of these loads are typically the key parameters used for sizing the aircraft's structure and, therefore, have a significant influence on the performance of an aircraft. Inaccurate estimations of these loads will lead to poor design choices, most typically a conservative structure design that is overweight, increasing energy consumption, toxic emissions, and noise pollution.

This research will develop tools for the efficient identification of uncertainties and nonlinearities in aircraft structural components and investigate how they affect aircraft loads. Only nonlinearities and uncertainties in the joints will be considered in this project, but the developed framework can be used for other sources of nonlinearities and uncertainties, such as aerodynamics and flight control systems. Developing such a framework is crucial in order to overcome the predominant practice whereby aircraft designs are restricted to a deterministic and linear regime, despite rapidly increasing demands to consider unavoidable uncertainties and nonlinearities from technological, economic and safety considerations.

In this project, a detailed and sophisticated numerical model of an aircraft structure will be used to explicitly identify the possible range of variations in the dynamic response due to geometric and material uncertainties and nonlinearities of a wing-store joint. These data will then be used to identify the parameters of reduced-order models (ROMs). ROMs are extremely useful for computational efficiency, and are used to efficiently predict extreme unsteady loads. The validated reduced-order structural model will be incorporated into the aeroelastic model and will allow the designer to include the effects of nonlinearities and uncertainties in the process of load calculations. The goal is to move away from the conventional safety-factor-based approach and explore the wide horizon of stochastic nonlinear aeroelastic analysis.

This project will be carried out in partnership with Airbus, which will provide the data necessary to undertake the research. Since it has been observed that multiple sources of nonlinearities and uncertainties affect aircraft performance, the study aims to investigate the following questions: 1- How can detailed numerical models be used in the identification of sources of nonlinearities and uncertainties? 2- How can the structural model updating tools (the tools that will be used to validate the numerical model based on experimental data or detailed finite element predictions) be used to obtain ROMs that are capable of including the nonlinear and uncertain effects estimated by detailed numerical models? 3- How can these validated ROMs be used to efficiently investigate the effects of uncertainties and nonlinearities in aircraft load predictions (important parameters that have significant impact on aircraft performance)?
The aforementioned questions will be answered by considering an important source of nonlinearities and uncertainties in the aircraft structure, i.e. structural joints.

This research is aligned with the EPSRC's priority area of engineering design and will contribute to the development of the UK as a more productive nation. Success in this project will enable the use of more accurate and cost-effective aeroelastic models in the process of aircraft design. The new tools developed in this project are likely to lead to significantly more accurate procedures for unsteady aircraft load calculations, playing an important role throughout much of the design of an aircraft, impacting on performance.


The new techniques developed in this research will have a direct impact on the project partner, Airbus, who will benefit from the stochastic nonlinear aeroelastic tools. They will also contribute to the project by allocating the time of various Airbus experts. The tools that will be developed in this project will be implemented into the 'Airbus Management of Uncertainty for Loads Evaluations' software to demonstrate how the presence of nonlinearities and uncertainties will affect aircraft loads. This will be carried out through industrial secondments of project team members, regular quarterly meetings with two-way exchanges of information between the university researchers and Airbus experts involved in the project and presentations at the UQ&M workshops at Airbus (held every six months). Airbus engineers will also benefit from the findings of the project through gaining an improved insight into nonlinear and uncertainty modelling, not currently considered in aeroelastic analysis.

In addition to Airbus, other aerospace industrial organisations such as DLR and Embraer are deemed to be potential beneficiaries of the work. These companies are very active in characterising the sources of uncertainty in aircraft and including them in the design process. This project will consider both the nonlinearity and uncertainty effects on the aircraft design and therefore they can benefit from nonlinear modelling and analysis that will be carried out in this project.

Understanding of nonlinearity and uncertainty effects is also beneficial to any sector which designs and manufactures performance-critical, safe and efficient structures operating in a dynamic environment. This is because the tools to be developed in the project will be based on a general finite element framework and therefore can be readily integrated into other codes. This project will potentially impact industries working on structural health monitoring of rotary machines and civil structures. The damage detection in structural health monitoring requires reliable models and in most of the cases the damage causes non-linear behaviour of the structure. For example, blade cracking in gas turbines causes non-linear behaviour due to opening and closing of cracks in the structure. Potential companies which might benefit from this project could include: Arup, Agusta, Rolls- Royce, Jaguar-Landrover, and BAE system.

In addition to the above, the research will also have an immediate impact on the researchers and engineers working closely on the project, as training of the researchers will be a huge asset to potential employers. Successful application of simultaneous modelling of nonlinear and uncertain effects in dynamic and aeroelastic structures through case studies will inspire the next generation of UK engineers to develop scientific interest in this area. In the long run, this will keep the UK engineering community ahead of global competition.