Non-conforming interfaces allow the usage of non-matching, interacting grids connected by an interface. In the following explanation the Nitsche method [^1] is presented, because it more robust in practical applications [^2]. For a detailed deriviation look into [^1] and [^2].
Consequently, non-conforming interfaces allow to use different meshes in the same simulation, as shown in the above figure. Both domains, \Omega_1 and \Omega_2 exist of different grids and are connected by the non-conform interface \Gamma_I. This is especially interesting if different materials are taken into account while a coupled simulation is performed. Furthermore, they are used for simulate rotating structures (for more details look into Features -> Rotating Interfaces) [^3].
For defining a non-conform interface first the surfaces, that are part of the interface, have to be defined
<domain geometryType="plane"> <surfRegionList> <surfRegion name="innerR" /> <surfRegion name="outerR" /> </surfRegionList> </domain>
In a second step the actual interface has to be established
<domain geometryType="plane"> <surfRegionList> <surfRegion name="innerR" /> <surfRegion name="outerR" /> </surfRegionList> <ncInterfaceList> <ncInterface name="ncR" masterSide="outerR" slaveSide="innerR"/> <ncInterfaceList> </domain>
Those two steps establish the interface of the domain. Now, we have to establish the formulation of the interface
<pdeList> <acoustic formulation="acouPressure"> <ncInterfaceList> <ncInterface name="ncR" nitscheFactor="100" formulation="Nitsche"/> </ncInterfaceList> </acoustic> </pdeList>
The nitscheFactor is only avaiable for non-conforming interfaces type Nitsche and defines the weighting of the coupling of the two domains \Omega_1 and \Omega_2. This factor has no major impact in the range of 20 - 100 [^2]. A rather high value correlates with a strong coupling, with from a physical point of few is good, but makes the interface numerically instable. On the other hand, a low nitscheFactor is numerically more stable, but can make the coupling unphysical.
(TODO mortar NC interface)
[^1]: M. Kaltenbacher. Numerical Simulation of Mechatronic Sensors and Actuators: Finite Elements for Computational Multiphysics. Springer Berlin Heidelberg, 2015. ISBN 978-3-642-40169-5. URL: https://www.springer.com/de/book/9783642401695. [^2]: Andreas Hüppe, Jens Grabinger, Manfred Kaltenbacher, Aaron Reppenhagen, Gerhard Dutzler, and Wolfram Kühnel. A non-conforming finite element method for computational aeroacoustics in rotating systems. In 20th AIAA/CEAS Aeroacoustics Conference, 2739. 2014. [^3]: Stefan Schoder, Clemens Junger, and Manfred Kaltenbacher. Computational aeroacoustics of the eaa benchmark case of an axial fan. Acta Acustica, 4(5):22, 2020.