# Contact Modelling with Cyclic Symmetry for Turbine Blade Shroud Contacts

Hello,

I’m trying to model a Turbine Blade Shroud contact using the flying face approach. This approach works fine in ABAQUS but I’m struggeling to realize it in CCX. The approach is as follows:

1. Mesh the blade model using C3D10

2. Copy the nodes from the shroud PS contact face to the shroud SS contact face (copy and shift it by one pitch, i.e. by 2*PI/N_blades)

3. Create a surface mesh using M3D6 based on the copied nodes to crease the “flying face” with the resulting element set ELE_SET_FLYING_FACE

4.) Create surfaces using *SURFACE
> Surface CYCLIC_SECONDARY at the shroud PS contact face
> Surface CYCLIC_FF_PRIMARY at the flying face SS (with direction SPOS into the direction of the volume mesh)
> Surface CONTACT_PRIMARY at the shroud SS contact face
> Surface CONTACT_FF_SECONDARY at the flying face SS (with direction SPOS into the direction of the volume mesh)

5.) Define a *MEMBRANE SECTION using a small ‘dummy’ membrane thickness
*SURFACE SECTION, ELSET=ELE_SET_FLYING_FACE
*MEMBRANE SECTION, ELSET= ELE_SET_FLYING_FACE, MATERIAL=BLADE_MATERIAL
1.0E-4

6.) Define the *CONTACT PAIR for the shroud contact
*CONTACT PAIR, TYPE=SURFACE TO SURFACE, INTERACTION=SHROUD_CONTACT, ADJUST=0.0
CONTACT_FF_SECONDARY, CONTACT_PRIMARY
*SURFACE INTERACTION, NAME=SHROUD_CONTACT
*SURFACE BEHAVIOR, PRESSURE-OVERCLOSURE=HARD
*FRICTION
0.5

7.) Define the cyclic symmetry constraints
*TIE, CYCLIC SYMMETRY, NAME=CYCLIC_SYMMETRY_DEFINITION
CYCLIC_SLAVE, CYCLIC_FF_MASTER
*CYCLIC SYMMETRY MODEL, N=52
0.0, 0.0, 0.0, 1.0, 0.0, 0.0

My questions are:

is the flying face approach basically possible in CCX or is there a limitation, e.g. by having two types of constraints on the flying face (contact and cyclic symmetry; ABAQUS accepts this if you have a proper definition of the PRIMARY and SECONDARY surfaces in *CONTACT PAIR and *TIE, but ANSYS for example stops with an ‘overconstraining’ error)

If it is basically possible to use the flying face approach - is ist possible to use it together with the menbrane elements? I’m a little puzzled on this because in the CCX manual there is the statement “This option is used to tie two surfaces. It can only be used with 3-dimensional elements (no plane stress, plane strain, axisymmetric, beam or shell elements).” where the *TIE command is described. Is the exclusion in the brackets also relevant for membrane elements like M3D6? To my understanding, membrane elements are 3D elements …

Is anyone aware of an existing example for a CCX input deck with such a flying face contact & cyclic symmetry definition?

Many thanks and all the best

Christian

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If you have a model in Abaqus then why won’t you try modifying the Abaqus input file to work in CalculiX ? The syntax is very similar and in most cases, just a few modifications are needed as long as features supported by CalculiX are used.

Sorry, not sure how a Turbine Blade Shroud works but looking at your drawing , wouldn’t my picture be an equivalent system?. I would avoid Contact and Cyclic at the same place.

Hello Calc_em,

I tried it but it ended up with a lot of warnings and stoped in the statoc step with convergence issues directly in the 1st increment. So a one-to-one use of the abaqus input deck is not working … unfortunately.

All the best
Christian

Hi Disla,

yes, this modelling approach works and yields the e.g. the same natural frequencies in a perturbation frequency analysis. But it requires more work in the model preparation. So from the modelling effort point of view, having a proper flying face approach in CCX (as in ABQ) would be awesome.

All the best
Christian

Maybe at least part of the Abaqus input file could be reused. Or you could fix that non-convergence without too much effort. Here’s a guide that can help you if you decide to stay with this approach: A Guide to Modifying Abaqus Input Files for Use in CalculiX

Hi Calc_em,

Thanks for your reply. I’m aware of the subtile differences between abaqus and ccx input file commands. So far I didn’t get the flying face approach running in ccx, so my fear ist that using membrane elements M3D6 in combination with cyclic symmetry ties and surface-2-surface contact and 3d continuum elements like C3D10 ist simply mit working in ccx (as e.g. in ansys and in contrast to abaqus).
Changing the model to a split volume model ist pain since the model is created in an automatized analysis process … Unfortunately.

All the best
Christian

Hi Christian,

have you found a solution to this problem? I am also interested in this topic.

How about moving just the shroud contact face a little bit in circumferential direction, as to avoid the issue pointed out by Disla? Blade and disk would not have to be modified. I would guess that the results should still be acceptable, even if the model of the shroud differed from the real part in the above mentioned way.

It’s been over 15 years since I’ve done this work but I do recall that what Oliver is saying is close to the right answer. We did this stuff in ANSYS, and we would push the tip shroud contact face in slightly, extrude off elements that would be the contact face and make the cyclic boundary cut at the base of that small extrusion.

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