Aircraft Structural Stress Based Indicators For Loads Optimisation
Lead Research Organisation:
Queen's University Belfast
Department Name: Sch Mechanical and Aerospace Engineering
Abstract
The fundamental stages within the aerospace structural design process are loads development and stressing/sizing. The first deals with the development of possible load cases that an aircraft may encounter in service, whereas the latter is responsible for the detailed design of the structural components required to carry the aforementioned loads. Due to the large number of load cases (potentially millions when each time step in the dynamic manoeuvres is considered) a resource intensive down-selection procedure is typically implemented to reduce the number of cases to a few hundred or thousand.
The high-level aim of this new project is to develop a methodology for discovering how aircraft dynamic manoeuvres are reflected in the required performance on individual elements of the whole aircraft structure, and discover the sensitivity of those requirements to design changes.
The tasks required to accomplish this are:
- Capture the changes in distributed loading for a given change in loads design.
- Develop a strategy for identifying the structural stressing indicators that are most effective for providing the cost function to drive the optimisation of the given loads design opportunity.
- Develop the corresponding realistic structural performance envelopes for more complex structural elements, especially those requiring >3 characteristic loads. Ideally this should be scalable to the 20-40 load cases required to capture the complete wing / fuselage / HTP behaviour.
- Develop and evaluate new methods for the computation of sensitivities in the context of large numbers of complex loading states, design variables and constraints, and thereby arrive at a recommended approach for optimising loads design opportunities based upon structural stress based indicators.
The high-level aim of this new project is to develop a methodology for discovering how aircraft dynamic manoeuvres are reflected in the required performance on individual elements of the whole aircraft structure, and discover the sensitivity of those requirements to design changes.
The tasks required to accomplish this are:
- Capture the changes in distributed loading for a given change in loads design.
- Develop a strategy for identifying the structural stressing indicators that are most effective for providing the cost function to drive the optimisation of the given loads design opportunity.
- Develop the corresponding realistic structural performance envelopes for more complex structural elements, especially those requiring >3 characteristic loads. Ideally this should be scalable to the 20-40 load cases required to capture the complete wing / fuselage / HTP behaviour.
- Develop and evaluate new methods for the computation of sensitivities in the context of large numbers of complex loading states, design variables and constraints, and thereby arrive at a recommended approach for optimising loads design opportunities based upon structural stress based indicators.
Studentship Projects
| Project Reference | Relationship | Related To | Start | End | Student Name |
|---|---|---|---|---|---|
| EP/N509334/1 | 01/10/2015 | 30/09/2020 | |||
| 1649938 | Studentship | EP/N509334/1 | 01/12/2015 | 30/11/2019 | Sriharsha Sheshanarayana |
| Description | The fundamental stages within the aerospace structural design are loads development and stressing/sizing. The first deals with the development of all possible load cases that an aircraft may encounter in service, whereas the latter is responsible for the detailed design of the structural components required to carry the loads mentioned above. Based on maturity, the design process is classified into three stages, namely - conceptual design, preliminary design and detailed design. Of these, the preliminary design is a significant milestone and is typically the most resource-intensive. It interfaces the load development and stress/sizing stages together to identify with high accuracy, the critical loads driving the design and optimise the aircraft structure. Due to a large number of load cases and structural design variables(potentially millions), a resource-intensive down-selection procedure is implemented to reduce the size of the optimisation problem. This process relies heavily on engineering judgement based on previous experience. As a result, it is often difficult to solve the large optimisation problem of optimising loads and structure simultaneously. The PhD proposes an alternative approach to improve the interface between loads calculation and stress analysis in the preliminary design process. The work develops on the novel concepts of characteristic loads and performance envelopes to deliver on four key area - 1. Load case and constraint down-selection - The performance envelope built for structural components (such as a stiffened panel or a wing rib section) is used to quickly down-select critical load cases and constraints thereby reducing the magnitude of the optimisation problem. 2. Computing gradients of structural constraints to load cases - An alternative approach to calculating the expensive gradients required for optimisation is established. The gradients are computed using performance envelopes. 3. Building robust "performance envelopes" - Performance envelope is a novel concept that describes the load-bearing capacity of the structure. Building more robust envelopes are explored. 4. Improving "characteristic loads" - the characteristic loads are the basis vectors spanning the column space of the loads acting on the aircraft structure. Millions of load cases can be expressed as a linear combination of ~30 characteristic loads identified using Singular Value Decomposition (SVD) |
| Exploitation Route | The next step is to use these sensitivities computed from performance envelopes in gradient based optimisation of an aircraft structure. This would validate the accuracy of the approach in an industrial context and benchmarked with the current industry practice. Furthermore, this step forms the foundation to develop strategies for constructing performance envelopes of more complex structural elements which is again one of the objectives of this PhD. The XRF1 fast RF tool which is being developed can be used by other researchers (in fields such as aerodynamics or in preliminary design) as a black-box tool to quickly compute critical failure and constraints to large number of load cases and structures quickly and economically. |
| Sectors | Aerospace, Defence and Marine,Transport |
| URL | https://doi.org/10.2514/6.2018-1655 |