Page 383 - Fundamentals of Magnetic Thermonuclear Reactor Design

Mechanics of Magnetic Fusion Reactors Chapter | 12 361

FIGURE 12.10 Finite-element models of the KSTAR tokamak CS. (A) A global model show-
ing current-carrying winding and load-bearing structures and (B) a local model showing conductor
axially aligned and offset.
The effectiveness of the global-local modelling as a design optimisation tool
is proved by the ITER TFC example (Fig. 12.11). The design process included
the calculation of coil displacements, case and intercoil structure stresses, and
loads accommodated by flange fasteners (Fig. 12.12). Calculations were made
for all modes of operation, and the results were used to evaluate the structural
integrity and life-time of the TFC case (Fig. 12.13) and fasteners under static
and cyclic loadings.
A stress analysis of joints that exhibit non-linear behaviour is a difficult task to
be performed in the design process. The way we accomplished that is with an in-
troduction of a refined model into a global one. For example, one can use a refined
model of the lower, most loaded part of a coil case for a stress analysis of TFC po-
loidal shear keys (Fig. 12.14). The model covers a small part of the case with four
keys, key ways, inserts between the keys and the case. The global model covers
the whole of the case. At the first stage of the design process, the keys of the same
length (the width of the TFC case) are loaded non-uniformly, with the key clos-
est to the wedging subjected to the highest stresses. As a result, excessive contact
stresses develop in the keyway. One can equalise the stresses, reduce maximum
stress and thereby optimise the design by selecting appropriate key lengths.