IPP Annual Report 2007 - Max-Planck-Institut für Plasmaphysik ...

eing created quite detailed in one piece with contact interfaces
only at places where such ones are also in reality. The
ADINA GM is expected to be the most accurate and fastest.
However, the modelling is not finally finished, the central
support structure including the interfaces to the coil still
have to be completed before an extended test and benchmarking
phase can start. The model is now expected to be
fully operational in the second half of 2008. The ANSYS GM
as the main FE-tool was created in the last years with first
priority with the help of the Efremov Institute. The development
activities, i.e. continuous updating and improvement
of the model, are still ongoing at IPP; however, the contract
with Efremov Institute was closed. Both versions of this GM,
the half module model with boundary conditions representing
the stellarator symmetry (so-called 36° model) as well as
the full module model (so-called 72° model including also
the cryolegs) with cyclic boundary conditions are the workhorses
which are heavily used for all kind of magnet system
analyses. The 72-degree model is applied for analysing
effects which are not in accordance with the stellarator symmetry
like the presence of cryolegs and the dead weight.
However, the module model requires enormous resources.
One run takes typically one week for full load history which
includes bolt preload, dead weight, cool-down, EM force
application, and optionally the effect of winding pack (WP)
embedding. The presence of the cryolegs and the deadweight
result in 5-20 % asymmetry in the displacements
and support forces between neighbouring 36-degree semimodules.
In addition, the rigid body toroidal movement of
the Magnet system is induced by the central structure deformation
and corresponding tilting of the cryolegs. The
ABAQUS GM emerged from a simplified model used for
predicting magnet system deformations during different
assembly steps – the results had to be considered for assembly
procedures and tools. Starting from this basic model it took
relatively small effort by LTC comp. to create a 36° version
of GM in 2006 and a 72° version until the end of 2007. The
model is now installed at the IPP Greifswald and first structure
analysis confirmation runs have been started. The model
benchmarking with ANSYS GM shows good agreement
of the main results. Minor discrepancies are still under
checking and verifications in both GMs. ABAQUS will also
be used for special tasks for which this program is better
suited (e.g. for strength limit analyses which requires elastoplastic
material properties and option of large deformations).The
main GM applications are calculation of main
stresses, deformations and forces/moments in the main
structural elements occurring during different modes of
operation such as bolt tightening already at room temperature,
applying dead weight, cooling to cryogenic temperatures,
and applying the electromagnetic forces. Also the
influences of the winding pack embedding pre-stresses,
different friction factors at the gliding elements, tolerance
Wendelstein 7-X
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deviations, NSE and PSE gap variations, etc., can be simulated.
The GM is also used for prediction of handling deformations
during assembly. A further application of the GM
was the definition of positions for the mechanical instrumentation
of the structure.
Figure 13: Over-spreading of non-planar coils to install oversized lateral
support block for weld shrink compensation; deformation in mm.
The original study of the Magnet system behaviour and optimization
of the parameters was performed for four main
plasma scenarios with maximum current in different coils,
corresponding to an on-axis field of 3 T. Preliminary analysis
of the remaining 5 operational scenarios reveals that due to the
high nonlinearity of the system some of the supports might
be loaded to the limits already at plasma axis fields somewhat
below the maximal design value of 3 T, therefore the
operation limits in particular for these additional scenarios