3.8 Movement

This section defines the movement of the mesh. Currently only static non-conformal interfaces are supported.

3.8.1 Non-conformal meshes

Non-conformal meshes are defined using ZONES and INTERFACES. Each zone is a domain as defined in the GEOMETRY section. For a mesh to be non-conformal it must consist of at least two zones with different domain tags. These two zones can then be split by an interface where every interface is defined by two composite entities, we use LEFT and RIGHT notation to distinguish between these. Each zone must contain either the left or the right interface edge. Zones can contain multiple edges across different interfaces but must not contain both edges for the same interface. These left and right interface edges have to be geometrically identical but topologically disconnected i.e. occupy the same space physically but consist of independent geometry objects.

Non-conformal interfaces are defined enclosed in the NEKTAR tag. An example showing two non-conformal interfaces on a single mesh is below:

2    <ZONES> 
3        <FIXED ID="0" DOMAIN="D[0]" /> 
4        <FIXED ID="1" DOMAIN="D[1]" /> 
5        <FIXED ID="2" DOMAIN="D[2]" /> 
6    </ZONES> 
8        <INTERFACE NAME="First"> 
9            <LEFT  ID="0" BOUNDARY="C[0]" /> 
10            <RIGHT ID="1" BOUNDARY="C[1]"  /> 
11        </INTERFACE> 
12        <INTERFACE NAME="Second"> 
13            <LEFT  ID="1" BOUNDARY="C[2]" /> 
14            <RIGHT ID="2" BOUNDARY="C[3]"  /> 
15        </INTERFACE> 
16    </INTERFACES> 

Zones must have a type specified, at the moment only ‘FIXED’ interfaces are supported however in the future there are plans to implement rotating, sliding, and prescribed motion using the ALE method. It is important for the zone IDs to correspond with the relevant interface IDs present on the zone, that is if there is an interface with ID 0 there must also be a zone with ID 0 too. Zone IDs must be unique but interfaces can have the same ID, e.g. in the example above zone ID 1 has two interfaces attached to it. The inclusion of an "INTERFACE NAME="..." allows for specifying a name, which is used for the debug output when the verbose flag ‘-v’ is specified. This is for user reference to ensure the non-conformal interfaces are set up correctly, and shows zone/interface IDs, number of elements in each zone and interface, and connections between each zone/interface. An example debug output for the above XML is shown below:

Movement Info: 
       Num zones: 3 
       - 0 Fixed: 8  Quadrilaterals 
       - 1 Fixed: 24 Quadrilaterals 
       - 2 Fixed: 4  Quadrilaterals 
       Num interfaces: 2 
       - "First":  0 (4 Segments) <-> 1 (6 Segments) 
       - "Second": 1 (6 Segments) <-> 2 (2 Segments)