- [Instructor] The CAD geometry in SolidWorks
is the definitive representation of the component.
However, when we create the FE analysis,
we need additional definition of both geometry
and coordinate systems to be able to apply loads
and boundary conditions.
This video gives an overview of how and why
we want to manipulate the CAD geometry further.
I've opened the SolidWorks model of the con rod,
we can see the geometry in its as delivered state,
coming from the CAD.
When we review this geometry to see how applicable
it is going to be for the FEA workflow,
we can break it down into three task areas,
loading, boundary conditions, and meshing.
We'll go and look at the little end.
The loading is going to be applied
at the little end shown here.
We're going to have the two load cases,
one in tension, and one in compression.
The loading is going to be applied as
a pressure distribution on the inside of the bearing face
of the little end.
We're going to use conventional engineering principles
and apply the tensile bearing load as a cosine
distribution over 180 degree arc.
The compressive bearing load will be applied
as a constant pressure over 120 degree arc.
At the moment, there's no way to delimit
either the tensile or compressive loading distributions.
There's no geometry available to handle those loadings,
so we need to split the original SolidWorks
CAD geometry, ready to accept this form of loading.
This is a fairly common task in FE analysis,
and in some cases, there are many loading scenarios.
We can have a requirement for a lot of regions
to be imprinted into the CAD geometry.
We also need to define a local coordinate system
to be able to apply the bearing load.
Again, this is not something needed in the CAD definition,
it is an FEA specific requirement.
One of the things you need to consider
is how you're going to manage the FEA friendly variant
of the CAD model as I call it.
It may exist only within the analysis discipline,
or you may check it in and control it
within the overall CAD management system.
Let's look at the big end.
The constraints are going to be applied
at the big end shown here.
In an actual project analysis, we would probably
replace these constraints with equivalent,
opposing reaction forces.
A minimum constraint set, or inertia relief method
would be used to stabilize the model.
There are two reasons for doing this in a real project.
The first reason is that reactions will be created
at opposing bearing faces, dependent whether we have
compressive or tensile load cases.
We have to choose a different constraint boundary condition
for each load case.
This implies that we would need two analyses,
one for each loading condition.
The second reason is that the presence of the constraint
in the big end here will give very harsh
and unrealistic local stress condition.
Stress distribution in the big end can't be used
to assess the strength of the component.
For the con rod analysis in this course,
we're going to simplify the reaction system
by fixing the con rod to ground at the big end
in both load cases.
We accept that this means we have to ignore
the stresses around the big end,
it does however mean that we don't have to
apply any further geometry manipulation,
we can run just one analysis.
Let's look at the standard view.
Finally, we want to be able to guide the mesh,
so that the elements are small and well shaped
in regions of high stress.
Simple geometry regions with brick-like shapes
are the easiest to mesh.
Splitting the solid geometry up,
or imprinting curves on surface is a very
powerful technique to help create this kind
of brick-like geometry.
And in our case, we're going to limit this mesh control
to putting split lines running longitudinally
along the con rod.
So we've seen how the SolidWorks geometry
needs to be manipulated to allow an effective workflow
to take place.