Number of nodes on a surface?

[DrBwts]

I have a flat square surface (Surf-2) that is 80 x 120 elements (all tet) & I run the following code,

mySurf = mdb.models['Model-1'].rootAssembly.surfaces['Surf-2']

surfNodes = []
surfNodesLabels = []
nodeInfo = open('LoadSurfaceNodes.txt','w')
for i, eNode in enumerate(mySurf.nodes):
    surfNodes.append(eNode.coordinates)
    surfNodesLabels.append(eNode.label)
    outStr = str(eNode.label) + ',' + str(eNode.coordinates[0]) + ',' + str(eNode.coordinates[1]) + ',' + str(eNode.coordinates[2]) + '\n'
    print outStr
    nodeInfo.write(outStr)
nodeInfo.close()

print len(surfNodesLabels), i

To my surprise I get a list of 38801 nodes!!

This backed up by there being 38801 entries in the file 'LoadSurfaceNodes.txt'

So why is this? I was expecting 81 x 121 = 9801 which isn't even a factor of 38801. Where have all these extra nodes come from?

 

[DrBwts]

OK so here's a ponderer for y'all..

First a simple model created with a hex mesh..

Second a close up of a tet mesh on the same geometry with the same seeding...

I then create a surface on the shown face.

If I run the script in the OP then for the hex mesh I get 9801 nodes under the surface (81x121=9801)

If I run the script in the OP then for the tet mesh I get 388801 nodes under the surface!! and yet as can be seen there are actually no more nodes on that surface than the hex model.

I am genuinely perplexed by this, I have included the models as attachments.

Hex mesh..

http://files.engineering.com/getfil...-8fe6-2a639f4a65bd&file=SimpleSurface_hex.cae

http://files.engineering.com/getfil...-8b63-59ace5d561e2&file=SimpleSurface_hex.jnl

Tet mesh..

http://files.engineering.com/getfil...-b30f-b29f40aa1761&file=SimpleSurface_tet.cae

http://files.engineering.com/getfil...-9d79-62ca2669ccc9&file=SimpleSurface_tet.jnl

 

[DrBwts]

OK solution found, I was using quadratic tets not linear!