Overview
ARROW project aims at developing a numerical methodology and an SW tool to model indirect effects of lightning on cable-harness configurations installed aboard aircrafts made of composite materials and equipped with a “current return network” (ALEEN, ALmost Equipotential Electrical Network). The Tool shall be able to:
- input geometry and material properties of the aircraft and of ALEEN from CAD (CATIA);
- input harness “space allocation” areas from CAD and input cable-harness representation from SGO WP Leader DB
- define lightning entry/exit points and waveforms, model the electromagnetic interactions between lightning and aircraft/ALEEN and evaluate E and H near-field induced on sampling points into the “harness space allocation areas”
- interface the MTLN (Multiconductor Transmission Lines Network) based code named CRIPTE by providing it the equivalent Vs and Is distributed generators, from proper elaboration of the E and H fields
- run CRIPTE to evaluate Voc (Open Circuit voltages) and Isc (Short Circuit currents) at equipment terminals.
For any critical situation with respect to the EM compatibility to lightning threat the Tool will be able to allow modifications of the harness (different routing, improved shielding…) and to effectively repeat Voc and Isc evaluation until a safe configuration is found. A 3D full-wave solver based on PEEC method (Partial Element Equivalent Circuit) for the modelling of the lightning-aircraft interactions and the evaluation of E and H, well-conditioned for the involved low-frequency range (from DC to some MHz), will be delivered. The computational modules will be integrated, together with pre-processing and post-processing modules, into an SW CAE tool named “ALEEN-L Modelling Tool” providing user-friendly working procedures, projects management, data storing and data navigation. A general “client-server” HW configuration will be allowed. The procedure will be validated against experimental data measured on an SGO WP Leader mock-up.
Funding
Results
Executive Summary:
New generation aircraft make large use of composite materials (such as carbon fibre) because of their advantage in terms of weight and structural strength.
However, composite materials are generally less conductive than metals that replaced; therefore they cannot assure the necessary electrical conductivity to work as current return pathway as it happened with aircraft metallic bodies.
Therefore, the potential damage of Lightning (in terms of direct and indirect effects) on modern aircraft is very high.
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)” therefore has 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 sometimes practically unfeasible) repeated bread boarding.
The ARROW project aims at developing a numerical methodology and a CAE tool – named ALEEN-L – suited to model user defined cable-harness configurations installed aboard an aircraft made of composite and conductive materials, equipped with an Almost Equipotential Electrical Network.
In particular the Tool was suited to evaluate the Voc(t) and Isc(t) waveforms (Voc=Open Circuit voltage; Isc=Short Circuit current) at equipment loads, induced by lightning strikes on the aircraft, in order to allow the verification of their compatibility with the design and qualification values.
Simulation methods (based on S-PEEC: Surface-Partial Element Equivalent Circuit formulation for 3d analysis and CRIPTE for cable analysis) with special “low-frequency stability” and “high-fidelity modelling” features have been customized and validated for these kinds of applications.
Furthermore, an advanced Field-to-Transmission Line coupling procedure was developed to take into account the effects of common mode impedance for low conductivity current return paths.