  An important question for the outlook of stellarator reactors is their
robustness against pressure driven modes, and the underlying mechanism behind
experimentally observed soft $\beta$ limits. Towards building a robust answer
to these questions, simulation studies are presented using a recently derived
reduced nonlinear MHD model. First, the initial model implementation is
extended to capture fluid compression by including the influence of parallel
flows. Linear benchmarks of a (2, 1) tearing mode in W7-AS geometry, and
interchange modes in a finite $\beta$, net-zero current carrying stellarator
with low magnetic shear are then used to demonstrate the modeling capabilities.
Finally, a validation study is conducted on experimental reconstructions of
finite $\beta$ W7-AS discharges. In agreement with past experimental analysis,
it is shown that (i) the MHD activity is resistive, (ii) a soft $\beta$ limit
is observed, when the plasma resistivity approaches the estimated experimental
value, and (iii) low $n$ MHD activity is observed at intermediate $\beta$
values, particularly a nonlinearly dominant (2, 1) mode. The MHD activity is
mild, explaining the soft $\beta$ limit, because the plasma volume remains
separated into distinct sub-volumes in which field lines are ergodically
confined. For the assumed transport parameters, the enhanced perpendicular
transport along stochastic magnetic field lines can be overcome with the
experimental heating power. The limitations in the current modeling are
described, alongside an outlook for characterising soft $\beta$ limits in more
detail in future work.
