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Oxford Instrument’s test coil |
Cobham Technical Services has delivered new modelling tools that dramatically extend the accuracy and speed of multi-physics finite element simulation used to develop superconducting magnets. The new tools exploit advanced finite element meshing algorithms and other facilities to boost simulation accuracy while simultaneously halving simulation times. These advances are helping a world leader in superconducting magnet systems for equipment such as NMR scanners with a highly automated means of developing and optimising designs.
The advanced finite element meshing algorithms and other tools were developed as part of the company's role in the UK's IMPDAHMA project. IMPDAHMA (Integrated Modelling Package for Designing Advanced HTS Materials Applications) - partially funded by the UK government's Technology Strategy Board - was led by superconducting magnet supplier Oxford Instruments whose aim was to obtain an integrated design and modelling environment.
Three organisations collaborated in IMPDAHMA: Oxford Instruments NanoScience, Cobham Technical Services and The Institute of Cryogenics at Southampton University. As well as leading the project, Oxford Instruments was responsible for manufacturing and testing sample magnets that included high temperature superconductor (HTS) materials and measuring material properties of composites. Southampton’s role was to obtain very precise measurements of the constituent materials at cryogenic temperatures – a crucial element to getting accurate simulation results – and also to validate the environment against Oxford Instruments’ tests. Cobham’s task was to develop its existing low temperature superconductor (LTS) simulation tools to include both LTS and HTS materials, while improving performance and accuracy.
The tools provide a direct link from the advanced superconducting magnet design and material know-how represented in Oxford Instruments' Magnet Design Database to the superconducting 'quench' solver in Cobham Technical Services' multi-physics Opera tool chain for the modelling, simulation, analysis and optimisation of electromagnetic related equipment.
Understanding the quenching process - a rapid, highly non-linear and potentially dangerous change of state from superconducting to resistive mode - is critical for this design area because superconducting magnets operate close to their critical current for reasons of performance and cost. Accurate quench simulation depends on a complete specification of the wires, coils, materials and protection circuits used in the magnetic system.
Cobham Technical Services' work during the project has resulted in three major new capabilities for Oxford Instruments. The most fundamental advance is in the finite element meshing algorithms that divide a 3D computer design model of a magnet down into smaller connected elements to allow numerical solution. Models can now be meshed using a 'mosaic' mixture of prism, hexahedral and pyramidal element shapes (as well as the tetrahedral elements that were available previously), to enhance the accuracy of the simulation solution. This mosaic meshing also improves the speed of the subsequent coupled multi-physics transient thermal and eddy current simulations. Assembling the non-linear thermal equations at each time step is much more efficient, and eddy current skin effect in conducting formers can be captured with fewer elements. The transient thermal and electromagnetic simulations were also configured so that they can run in parallel on different processors to further improve speed of execution.
Cobham Technical Services also greatly enhanced the capability of Opera’s electrical circuit modelling, including a brand new graphical interface, which describes the power, drive and protection circuitry that is essential to superconducting magnet operation (and current dissipation when a magnet goes into quench). And the company provided a direct link to Oxford Instruments' materials database, which represents the complex non-linear properties of superconducting materials. A new materials database structure that will be integrated into a future version of Opera was developed to hold the wealth of materials information created in the project. However, this database is also extendable to hold materials data for many other electromagnetic design applications.
The new Integrated Modelling Environment that has resulted from the IMPDAHMA work has been validated by The Institute of Cryogenics. Oxford Instruments conducted tests on two high-field NMR (nuclear magnetic resonance) systems used for validation. A 20 Tesla magnet with LTS coils was used initially, and an LTS magnet with additional HTS coil inserts (potentially capable of achieving a field of up to 25 Tesla) was used as new software tools and materials data became available. The tests showed very encouraging agreement between the real-world measurements and calculated values.
Dr Ziad Melhem, IMPDAHMA Project Manager at Oxford Instruments said, “The IMPDAHMA work is helping to accelerate the exploitation of HTS materials in innovative magnet applications. As HTS materials properties and manufacturing processes continue to be improved, there will be scope for even higher magnetic fields.”
"Our quench solver has been one of the leading tools for superconducting magnet design for some years, and this work has allowed us to take several major steps forward," says Chris Riley of Cobham Technical Services. "The intellectual property that has come out of this collaboration with these world leading organisations is now being incorporated into new versions of the commercial Opera simulator."
The new version of the Opera package that will incorporate most of these new resources will be released before the end of 2010.
