Analysing the mechanical and thermal stresses within a steam turbine
casing is no trivial matter, especially when prototyping is out of the
question. Fortunately, the design can be optimised very quickly by moving
the model between CAD and CAE environments - but you need a good
interface and an accurate analytical tool to make it worthwhile, as
Siemens Power found out
When the engineering, manufacturing and service groups of Parsons Power
Generation Systems became part of Siemens Power Generation, the company’s
core business turned from the manufacture of complete turbine power
generators to designing upgraded individual turbines and servicing parts
- a new direction that required a new design philosophy. Richard
Goodfellow, a principal design engineer at Siemens Power picks up the
story.
“Whereas our previous contracts required in-depth finite element analysis
and we used Ansys multiphysics software, we do not always have the time
or need to achieve such detailed analysis. Lead times for refurbishment
of turbine plant are very short and in this competitive market a
reduction in time really does give us a competitive edge. We needed a
tool that would enable us to produce quick analyses of models created in
Pro/Engineer.”
Physical prototypes in this sector are cost prohibitive, so there is
really only one shot at design and there is no margin for error. With a
relationship going back nine years or so with Ansys, the logical step was
to see what the company could offer; that’s when the Siemens Power team
first became aware of DesignSpace.
Firstly, it has a good interface with Pro/Engineer, so the CAD models can
be imported into the DesignSpace environment without the problems
sometimes experienced when transferring an image from one package to
another. Secondly, the product has the accuracy required to conduct
stress and thermal analyses of the turbine casings. “DesignSpace makes
applying boundary conditions to the model very easy,” says Mr Goodfellow.
“Loads and pressures can be applied without worrying about the underlying
details. Simply point at the area of interest, apply the load and you get
a quick and accurate answer.”
The process begins with a 2D CAD drawing that is converted into a 3D
model of the turbine casing within Pro/Engineer. This model is
subsequently transported to DesignSpace, where the analyses of what is,
in effect, a steam pressure vessel operating at 535oC and 130bar, are
carried out. Once these are completed and the necessary changes made in
the Pro/Engineer environment, the CAD model is again imported into
DesignSpace for verification. This iterative process ensures that the
optimum design is finally achieved. According to Mr Goodfellow, this
would have taken “weeks” to complete before installing DesignSpace; now
it’s all done in a matter of days.