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Electromagnetic compatibility and aircraft safety
Streamlining safety design and certification with the digital twin
Aircraft technology is changing rapidly. Electrical and electronic devices are replacing mechanical systems in almost every area of aviation. But the increase in electrification brings with it an increasingly complex and more severe electromagnetic environment.
More external and internal radiating sources are present than ever before. These include higher power levels of wanted and unwanted emissions; extensive use of materials with reduced shielding effectiveness; and electronic devices replacing mechanical and hydraulic flight controls.
High-intensity radiated fields (HIRF) and indirect effect of lightning (IEL) have the potential to be catastrophic for aircraft. For example, electrical and electronic devices that perform safe¬ty-critical functions may be damaged by lightning strike or radiation, as well as by general electromagnetic compatibility (EMC) issues.
Engineers need to implement robust, efficient processes for high-fidelity EMC analysis to deal with IEL and HIRF, and ensure that aircraft achieve certification and guarantee passenger safety.
Use of a digital twin is enabling aeronautical manufacturers to identify and address potential electromagnetic issues early in the design process, before physical prototypes are built, and therefore reduce expensive and time-consuming testing.
Lightning effects and radiation
When a lightning flash strikes an aircraft, the conduction of the electrical currents can have direct effects, such as the deformation of metallic components or melting of cables, and indirect effects.
Indirect effects of lightning (IEL) refer to electromagnetic interference in electrical or electronic equipment, in particular equipment that belongs to systems or subsystems that perform critical safety functions.
To obtain IEL certification, aircraft designers must be able to show that the aircraft equipment is able to withstand the potential impact from IEL. Specifically, that the equip-ment transient design levels (ETDLs) exceed the maximum of the actual transient levels (ATLs) by a safety margin established in the certification plan agreed with certification authorities.
High-intensity radiated field (HIRF) effects and regulations
External electromagnetic radio frequency (RF) fields can penetrate an aircraft structure through specific points of entry (such as apertures, gaskets, materials with low-shielding effectiveness) and may couple with a cable harness or directly interfere with equipment.
To gain HIRF certification, aircraft designers must demonstrate HIRF immunity – that the aircraft systems and equipment (and, in particular, safety-critical equipment) are able to correctly perform their functions in the presence of any electromagnetic environment generated from external RF sources such as radio, television or radar emitters.
Challenges in creating an accurate model
Certification authorities have recognized numerical analysis (simulation) as an option to support IEL and HIRF compliance. However, there are significant challenges in modelling the highly complex electromagnetic environment of an aircraft. These include:
- Wide frequency range of analysis Simulations must be performed on a wide frequency range – from direct current (DC) to 10MHz for IEL and from 10KHz to 18/40GHz for HIRF. Therefore, several physical regimes must be managed from simply conductive (DC), skin-effect, resonance regime, to high-frequency scattering. This requires a multi-method approach – full-wave, asymptotic and power balance modeling tools. At low frequencies, common low-frequency breakdown and ill-condi¬tioning problems must be addressed. At high frequencies, where the platform is electri¬cally large, the huge number of mesh elements requires efficient computation methods to reduce random access memory (RAM) usage and overall computational time.
- High level of accuracy required Resistance and admittance values, especially at very low frequencies, can be of the order of a fraction of ohm. So, for the simulation to be effective, it must create an extremely accurate high-fidelity model.
- Wide range of physical observables to be computed Methods are required for computing observables such as bundle currents, electric field levels and Voc(t) and Isc(t) transients at equipment pins.
Using Simcenter to create a high-quality digital twin
The team at IDS, a strategic partner of Siemens Digital Industries Software, is using Simcenter to meet the complex challenges of aircraft electromagnetic (EM) modeling and simulation.
Specific capabilities of the Simcenter enable the team to economically perform analyses and find solutions, allowing the aircraft engineers to investigate and check different system configurations from the earliest design stages forward.
Integrated CAD and meshing tools for high-fidelity modeling
Meshed models are directly derived from detailed CAD models, minimizing the need for simplifying electromagnetic analysis. Thus, using the Simcenter, multiscale meshes composed of millions of elements can be generated and managed rapidly and efficiently.
The fundamental technology of Simcenter applied to this use case is based on boundary elements (the method of moments) and hence only requires surface meshes. This substantially reduces mesh sizes compared to other methods like the finite element method (FEM).
Seamless interface to electrical CAD tools
Using Simcenter, the team is able to automatically import cable harness models from electrical CAD tools such as Capital™ software, Siemens’ harness engineering software.
This includes harness architecture and 3D routing, bundle composition, cables cross-sections, cable jackets and braids, junctions, loading terminations and much more. They are then translated into models suitable for hybrid 3D electromagnetic MTLN simulation.
Multiple modeling formulations for aeronautical materials
Typical aeronautical materials (metallic, composite, engineered) are managed with modeling formula¬tions such as impedance boundary condition (IBC), thin sheet and neighbourhood impedance boundary condition (NIBC).
Complexity is reduced by basing them on equivalent parameters such as shielding effectiveness for penetration problems, or surface impedance or transfer impedance for scattering/induced current problems.
Component modeling based on equivalent representations
Where detailed electrical and geometrical information is not yet available in the early stages of development (because of supplier proprietary data or because of a preliminary development phase when only the requirements of the components have been decided), components can be modeled based on the defined requirements and equivalent representations.
Mathematical formulations based on state-of-the-art algorithms
Complex mathematical formulations are required to eliminate low-frequency breakdown, carry out high-fidelity modeling and accurately represent the skin-effect while maintaining low-numerical complexity models.
With Simcenter teams can employ a wide spectrum of state-of-the-art algorithms, including S-PEEC, to extend the standard method of moments to very low frequencies (from MHz down to DC), and an adaptive frequency sampling algorithm which reduces the number of frequencies to be evaluated.
Safety design and certification with the digital twin
Use of a high-fidelity digital twin is helping aircraft engineers gain a thorough understanding of the new electromagnetic environment of aircraft, and develop effective solutions to potential HIRF and IEL issues before physical prototypes are built. This reduces expensive and time-consuming testing and helps to make aircraft design and certification faster and more efficient.
In addition, the digital twin enables engineers to front-load the design of critical components in the product development lifecycle. This facilitates the adoption of new, state-of-the-art electrical and electronic technologies, in turn helping to secure more sustainable solutions for air travel and maintain flight safety.
"The digital twin enables engineers to front-load the design of critical components in the product development lifecycle. This facilitates the adoption of new, state-of-the-art electrical and electronic technologies."