ALEEN modeling (an E-MIND CAE Tool Module)

Accurate modeling of “Almost Equipotential Electrical Networks (ALEEN)” of com­posite aircrafts

The Problem

The metallic bodies of “standard” aircrafts are commonly used as conductive electrical pathways for the return of direct and alternating currents, faults currents, lightning currents and also other functions related to voltage differentials, electrostatic charge draining, electromagnetic shielding etc.

Such a procedure is not applicable on aircrafts made of composite materials because of their low conductivity. A dedicated conductive electrical pathway, named “Almost Equipotential Network (ALEEN)” or “Current Return Network (CRN)” has therefore to be integrated into the aircraft body. Such networks can be practically realized in several different ways, mainly exploiting both structural metallic parts of the aircraft (beams, seats rails, etc.) and also dedicated paths, but anyway they can never be an ideal ground and worse performance than those currently obtained on metal aircraft may be expected.

Accurate electrical/electromagnetic characterization of ALEEN structure is therefore important:

  • to be able to correctly design electrical systems such as EWIS, reducing risks and saving mass
  • to estimate how the ALEEN configuration works with respect to other required functions (e.g. faults currents, lightning currents, electromagnetic shielding, etc.)
  • to optimize the ALEEN configuration itself without needing expensive (and sometime practically unfeasible) repeated bread boarding.

ALEEN modeling in E-MIND

The E-MIND electromagnetic CAE Tool (http://www.idscorporation.com/images/aeronautical/homepage/BRO_AERO_EMIND.pdf ) has been updated with a new modeling procedure dedicated to ALEEN networks modeling. The Tool is able:

  • to input aircraft and ALEEN geometries and material properties from CAD (e.g. CATIA)
  • to evaluate the equivalent impedance matrix at ALEEN terminals in the frequency range DC-MHz’s, also considering the EWIS and the electromagnetic interaction with aircraft body
  • to visualize induced current and voltage distribution on the aircraft/ALEEN.

Simulation methods having special “low-frequency stability” and “high-fidelity modeling” features have been developed and validated:

  • S-PEEC (Surface-Partial Element Equivalent Circuit)
  • MR/MoM (Multi-Resolution /Method of Moment)

The Aleen model was developed in the framework of Genial project cofunded by CleanSky J.U.

The implementing team of Genial was made of Ingegneria Dei Sistemi S.p.A. and the University of L’Aquila.

They interfaced with Safran Engineering Services

CAD input , cleaning and meshing

Mechanical CAD models (e.g. CATIA, STEP, IGESS…) can be input. User friendly tools are available for model cleaning and meshing

Low - Frequency Stability

Algorithms for the numerical solution of Electric Field Integral Equation having excellent “low-frequency stability”, no matter the complexity of the model (also strongly multi-scale), have been developed and validated. It is worth noting that this is a pre-requisite to have the possibility to perform “high-fidelity modeling”.

High - Fidelity Modeling

“Low-frequency stability” and “multi-scale capability” of the computational algorithms allow for well-conditioned models and therefore also allow performing “high-fidelity modeling”. In practice this means that no “a-priori simplifications” of the geometry (which moreover are scarcely manageable to obtain accurate results in wide band analyses) are required to reduce the condition number. DC resistance, skin-effect, inductive and capacitive effects are correctly considered

Electrical properties

Material properties (e.g. conductivity, surface impedance…) can be assigned to each different part of the model. An embedded “Material Library” is available to permanently store the features of different types of materials. Models for contact and bonding resistences are available.

Selection of materials properties in the E-MIND Material Library

Validated

The Tool has been validated by comparing simulation results with data measured by SAFRAN-Labinal on an ALEEN mock-up.

ALEEN mock-up. R-L vs. frequency: comparison between simulations and measurements

 

 

 

Download the ALEEN Modeling white paper in pdf format