Final Report Summary - GENIAL (optimizinG Electrical Network In AirpLane composite structures)
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:
1. To be able to correctly design electrical systems such as EWIS, reducing risks and saving mass
2. To estimate how the ALEEN configuration works with respect to other required functions (e.g. faults currents, lightning currents, electromagnetic shielding, etc.)
3. To optimize the ALEEN configuration itself without needing expensive (and sometime practically unfeasible) repeated bread boarding.
In the framework of GENIAL project a tool dedicated to ALEEN networks modelling has been developed. The Tool is able:
a) To input aircraft and ALEEN geometries and material properties from CAD (e.g. CATIA)
b) To evaluate the equivalent impedance matrix at ALEEN terminals in the frequency range DC-hundreds of kHz’s, also considering the EWIS and the electromagnetic interaction with aircraft body
c) To visualize induced current and potential distribution on the aircraft/ALEEN.
Simulation methods having special “low-frequency stability” and “high-fidelity modeling” features (mainly based on S-PEEC: Surface-Partial Element Equivalent Circuit formulation) have been customized and validated for this kind of applications.
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.
Project Context and Objectives:
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 in composite aircrafts because their bodies don’t assure the necessary conductivity, and a dedicated conductive electrical pathway (currently named “current return network”, hereafter referred as ALEEN, ALmost Equipotential Electrical Network) has to be integrated into the aircraft body.
Such networks can be practically realized in several different ways and can therefore have several features, e.g.:
a. It can be a network of interconnected longitudinal and lateral paths extending for the whole aircraft fuselage. Parallel and non-parallel paths can occur.
b. The paths may be made of wires, strips or also extruded metal sheets. Copper, aluminium and other types of conductive metals can be used.
c. The paths shall be fastened to the structure of the aircraft.
d. In case part of the aircraft structure is made of metal (e.g. structural beams, cages, rails to fix passengers seats, or also a whole sub-part of the aircraft like the nose) the current return network may be intentionally connected to such structures, which for this reason, become part of the return network.
e. The different parts of the network can be connected together by electrical joints (rivets, bolts and other connecting strategies).
Apart the implementation details it is obvious that not only the network can never be an ideal ground but also that worse performance than those currently obtained on metal aircraft may be expected. Therefore it is of interest to evaluate the effects the network has on connected electrical systems such as EWIS and more in general to estimate how it works with respect to each required function (e.g. return of direct and alternating currents, faults currents, lightning currents…).
GENIAL project aims at developing a numerical methodology and a CAE (Computer Aided Engineering) tool suited to model the current return networks installed aboard aircrafts also having parts made in composite materials. The tool is able:
• To input aircraft and ALEEN geometries and material properties from CAD;
• To evaluate the equivalent impedance matrix of ALEEN in the frequency range DC-hundreds of kHz’s, also considering the EWIS and the electromagnetic interaction with aircraft body;
• To interface the above mentioned impedance matrix with an electrical database of EWIS, in order to allow correct evaluation of the impedance between any two interconnection points of EWIS;
• To visualize induced current and potential distribution on the aircraft/ALEEN.
Main S&T results
The electromagnetic modelling and simulation of ALEEN structures can be considered a very challenging task. It involves structures geometrically large constituted by a lot of small parts (i.e. a strongly multi-scaled problem), in a frequency range including several electrical/electromagnetic phenomena (resistive, skin effect, capacitive and inductive coupling, full-wave electromagnetic coupling).
In the frequency range of interest (DC – hundreds of kHz) classical numerical methods of analysis usually suffer by the well-known low frequency breakdown phenomena and are not able to correctly model such kind of complex configurations. Geometrical simplifications are usually carried out by expert modellers in order to possibly reduce numerical problems. Apart the complex “over-work” which is required, it is well known that this is only applicable at the expense of the possibility of correctly evaluate the whole set of electrical/electromagnetic phenomena of interest in the whole frequency range.
For this reason, a mathematical formulation and some special improvements aimed to alleviate these problems and to avoid the need of recurring to complex and dangerous simplifications of the structure model– the PEEC method – has been chosen. The PEEC method is commonly applied to the analysis of interconnecting and packaging systems, usually very limited by a geometrical point of view.
In the framework of the Genial project, the method has been applied to geometrically large structures. In particular, a surface formulation of the PEEC method (named S-PEEC) has been specialized to the analysis of ALEEN structures. Respect to the classical PEEC formulations, where the internal volumes of all the conductors have to be discretised and inserted in the electromagnetic model, by exploiting the surface equivalence principle, only the external surface of conductors are discretized and included in the electromagnetic model. This allows the use of triangular patches and a realistic model of the structure (high fidelity modelling).
The numerical model has been validated with respect to measurements carried out on a very complex mock-up resembling almost all the situations can occur on a real aircraft (at authors knowledge the most complex and representative mock-up never implemented for this application field), and the obtained results show the stability and the accuracy (m range) of developed code in the frequency range of interest.
From another point of view it is worth noting that a complete CAE (Computer Aided Engineering) environment (i.e. a framework) usable in industrial applications (i.e. not only valuable from an academic point of view) for the analysis of ALEEN structures has been created. It can be used both in the project and in the verification stages of the design/production of such structures, promoting also the development of innovative configurations or solutions.
The numerical method developed in the Genial project can be improved, both in terms of modelling capabilities and computational requirements, imagining an extension of the framework application to other electrical/electromagnetic phenomena interesting ALEEN structures, like for example lightning. An application on a large real aircraft is thought to be mandatory in order to check on the field the performance/applicability of the whole CAE procedure in the frame of an industrial workflow. The applicability on other large complex structures like ships, cars etc could also be verified.
A relevant impact is expected from the now available CAE procedure in terms of analysis and design capabilities for this kind of new and particularly complex problem. Such expectation is obviously based on the up to day available validation results and on the reaction of people coming from the european aeronautical technical/scientific environment which have been met during the dissemination activities, but it is also further strengthened by the consideration that no similar proved capabilities seem to be appeared in the open technical literature, all over the world.
As far as dissemination concern, a number of actions were implemented.
A project public website was set up and kept updated during the project implementation.
With regard to the production of scientific papers two contributions have been presented at international conferences
1) G. Antonini, M. Bandinelli, A. Mori, M. Bercigli, D. Romano, “Surface PEEC formulation for optimizing electrical network in airplane composite structures”, in Proc. of EMCEurope 2012, Roma, September 2012.
2) M. Bandinelli, A. Mori, M. Bercigli, D. Romano, G. Antonini, “A Surface PEEC Formulation for the Analysis of Electrical Networks in Airplanes”, in Proc. of 2013 IEEE International Symposium on EMC, Denver 2013.
Another contribution will be submitted for publication on IEEE Transactions on Electromagnetic Compatibility.
The final workshop of the project was held in Blagnac – France – at the TECHNOFAN Auditorium Louis Blériot on 24th September 2013. The workshop lasted from 2 to 6 pm, with the objective to present the work done in the framework of the GENIAL project and the results obtained, as well as to do some brainstorming for future expansions. All the partners described in details their contribution to the development of the GENIAL. Interesting comments were received from the audience.
In the frame of the GENIAL project a public website has been developed. It can be reached at the following address: http://genialproject.univaq.it/
During the project, some dissemination activities have been carried out and others are foreseen following the project closure.
The dissemination activity consisted in: issuing papers, joining conferences and workshops, as well as holding presentations and setting up a public website, as documented in the tables below.
List of Websites: