Modeling bird strikes using CEL approach
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Bird strikes cost the aviation industry tens of millions of dollars annually in aircraft damage. Moreover, it can be a serious life-threatening event eg. US Airways Flight 1549 ditched into Hudson River as a result of engine failure on both the jet engines due to multiple bird strikes on January 15, 2009, in New York, USA.
Increasing the ability of the aircraft to resist bird strike-induced damage is one part of an overall approach to mitigating this expense. Bird strike validation of aircraft components is an important step in the process of flight certification and validation.
Experimental bird strike testing is part of the certification process for certain aircraft component designs. If a subset of the tests can be replaced with computational simulations, the cost of the prototype testing can be reduced.
Further, bird strike resistance considerations can be included in the design process, thus increasing the probability that certification tests will be successful. With the increased use of composites in the aerospace industry, it is highly important to understand how composite structures fare against impact because of bird strikes.
Finite element simulation technology has matured to a greater extent to aid in virtually testing bird strike scenarios thereby giving a detailed insight into the event during the preliminary design phase. This could go a long way to meeting the design standards required for aircraft safety.
This blog aims at showcasing the capability of?ABAQUS Unified FEA product suite?from?Dassault Systemes?for easy and convenient modeling of bird strikes using a coupled Eulerian-Lagrangian approach (CEL) on a simple fuselage model. The model used here is purely for the demonstration of the capability.
Finite Element Modelling
ABAQUS offers great convenience in modeling bird strikes using specialized techniques such as CEL (Coupled Eulerian-Lagrangian) approach available in ABAQUS/Explicit.
The great advantage of CEL analyses is that most of the problems associated with extensive birds’ mesh distortion are eliminated, as the Eulerian description allows finite elements to be fixed in space and the material to flow through these elements. Birds can be modeled using a linear Us-Up EOS (Equation of State) material model.
?On the other hand, the impacted structures are discretized by traditional Lagrange finite element formulation. The impacting forces are transferred to the Lagrangian structure through general contact in ABAQUS/Explicit. ABAQUS also offers composite ply definition through ABAQUS/CAE GUI which allows users to define any complex ply lay-up definition with great ease.
Modeling of failure and damage in the composite part can be achieved by a progressive failure and damage model. This model uses Hashin’s failure initiation criterion and accounts for four modes of failure including matrix tension and compression & fiber tension and compression.
The damage and failure of composites can be modeled elaborately to include damage initiation, damage evolution which models stiffness degradation, and finally removal of the element from analysis upon complete loss of stiffness.
To demonstrate this, a simple nose cone model is taken and meshed with conventional shell elements. Composite lay-ups are then defined within ABAQUS and material properties are defined with Hashin’s damage model. Bird is represented as an ellipsoid with fluid properties. The volume fraction tool in ABAQUS is used to compute and retrieve the volume occupied by Ellipsoid within the Eulerian mesh. The relative velocity between the bird and the aircraft is given as the initial velocity of the bird. The analysis is run for the fraction of a second to capture the impact.
Results
ABAQUS/Viewer can be used to post-process the analysis results of the damage caused by the composite structure, with ply-level failure as well as animation of the bird strike event itself.
Finally, by providing an accurate simulation capability, ABAQUS/Explicit allows bird strike loading to be included in the design process. Shown below is bird strike animation and damage to the composite structure.
Conclusion
A bird strike event on an aircraft composite structure can be successfully simulated with ABAQUS/Explicit using CEL approach. With its strong composite damage and failure modelling capabilities and general contact algorithms, ABAQUS/Explicit is an ideal tool for such highly dynamic, nonlinear applications. While the present application focuses on composite materials, ABAQUS/Explicit also allows for the simulation of metallic structures with failure models.
References
Sr. Director, Airworthiness & Deputy Director General at Civil Aviation Authority of Israel
3 年Simulation of bird strike effects on structure can be acceptable if validated by tests (at least validating that the tested scenario is a critical one). But the US 1549 event was caused by bird ingestion - any thoughts on simulating this?
Senior Structures Expert at EASA
3 年Validation please….
Associate Manager, R&D Technology Consulting
3 年Very interesting read and an impressive FE model! How are the contact conditions between "bird" and fuselage defined? Thanks for sharing!
Scientist || MRINA || Council Member at Royal Institution of Naval Architects || Naval Architect || Mechanical Engineer || FSI Analyst || Pyrgotelis Zoitos Prize Awardee
3 年Good work
Staff Engineer
3 年Interesting but I prefer the SPH approach. Less complex, all lagrangian, easy to post process. EulerIan you need to model the interaction between the EulerIan mesh and lag mesh and the eulerian cage should move with the bird to avoid a huge eulerian mesh. But I know that abaqus is great in modeling coupled eulerian lag cases.