- [Instructor] So we're going to run through
a summary of the course,
and the course is all about advanced methods.
So we've looked at four different advanced techniques.
Just summarizing them, we used planar symmetry
to simplify a model.
We applied the three, two, one method
to constrain a model.
We used geometry suppression to help control FEA mesh
when we run into difficulty with awkward geometry features.
We used plane strain analysis.
Basic motivation there is fast, efficient detail analysis.
So as we run through them,
planar symmetry is a very efficient technique.
We take our full lug model here.
What we require for any model, such as the log model,
think of any geometric features,
got to have symmetry of the geometry,
which we have in this particular case,
symmetry of the loading,
and if we have axial loading here, again, that's symmetric,
and symmetric constraints.
So again, something like the conrod we see here
is a perfect example for that.
So if we put half symmetry in, this is showing the plane
we're going to apply the half symmetry,
and there's the model.
We've chopped it in half, it's symmetric about that
cut plane through the center there.
And essentially it's like a square law or a power law.
If half the model, number of elements,
number of degrees of freedom,
just a quarter of the resource.
So in terms of runtime, the storage required,
it's about a quarter.
And that's often worth trying to grab
if we got a feature like that.
Quarter symmetry.
Again, there's the quarter symmetry plane
chopping now vertically through the center of that conrod.
And there's the resulting structure.
That gives us a huge boost of 1/16th the resource,
1/16th the runtime, roughly.
So if you spot a structure
which exhibits this plane of symmetry,
follows the rules of symmetric geometry
and loading constraints, it's a really powerful technique.
The three, two, one method.
There we're talking about free-floating models.
We've got something like the conrod.
We really don't want to constrain this.
So we want to avoid the constraints.
If we constraint a ground
at either the little end of the big end,
then we really ruin the stress concentration around there.
The opposite end is fine, but the end we're grounding out
has very poor stress quality.
So free-floating models, we improve the realism of stresses
throughout the model.
It also allows components to be analyzed in isolation.
I don't need to model an assembly here,
worry about contacts, I can just break this out.
As long as I can build up those loads
and boundary conditions, and it's really having confidence
in your boundary conditions and getting good load balance,
then we're in business.
It also allows multiple load cases
we don't have to reanalyze.
So again, here's the conrod.
We've got the tensile load case, the compressive load case.
They are simply load cases in one analysis,
rather than having to run two separate analyses
each time we want to apply
an independent type of constraint.
It's a very powerful technique there.
The downside is that it needs careful setup.
We got to apply that cut face,
carefully follow the three, two, one recipe,
and load balance is vital.
Otherwise you're just going to rip your model apart.
But those last two bullet points,
they're not insurmountable.
Little practice, little bit of care,
then we can use this technique.
Again, very, very powerful technique.
Geometry suppression.
Sometimes we have geometric features
which we want to bypass.
For example, we saw in the conrod's sliver-type features,
and there's one example there.
Now it's not physically realizable.
You can't machine that kind of component.
But it's there in the CAD model, the CAD geometry.
And somewhere between the design definition
and the actual product that comes out of the shop floor,
that feature will just be removed in practice.
So we want to simplify the geometry in that particular case,
remove the filets.
So we saw a technique to do that,
and now we have the filets gone,
and that allows us to put good quality elements
into that region, where we have the end
of the conrod meeting the shaft of the conrod.
But it's a bit of a judgment call.
We avoid the inaccurate high stresses
which the sliver feature would produce,
but the issue is is the feature
still sufficiently representative?
So do we go with either the top picture
or the bottom picture?
There are some issues with both.
We could say if we defeature completely,
I can't really get stress concentrations
accurate in that region,
but if that's not an area of concern
with stress concentrations
then I wouldn't have to worry about that.
And finally, plain strain analysis.
A very efficient technique.
We saw the lug, which was set up there,
and we could take a 2D slice of that 3D solid lug.
So there's our 2D slice.
Now mathematically, it's assumed that the stressors
are constant throughout the depth.
So mathematically we can visualize it
as a structure like that.
So the only thing we have to make sure
is that the load per unit length
matches the real, 3D lug, which is two inches length,
and then whatever load distribution we put on,
it's the same load per unit length.
So that's fairly easy to set up.
But mathematically we're applying this object here
with infinite depth in it.
Now the 2D elements, the huge payback
is they allow very, very fine mesh,
and we saw evidence of that.
The run is blisteringly fast
when you set up these 2D elements.
Allows us to really swamp the model.
In the root radius that we're interested in here,
in this particular object,
we can really saturate that with lots of elements
and get a very high quality stress distribution
coming out there.
Restrictions are it is for deep components.
If it's a thin component already,
the basics of plane strain are that it wants a solid,
stocky structure with some depth to it,
so we have to pick the right kind of components
to actually idealize using this type of approach.
Also, we want to avoid stress variation through the depth,
and if it's small, that's okay.
We talked about doing a correlation
between the 3D lug and the 2D version.
There we focused on that thing
called the stress concentration factor,
and that's what we were trying to match
between the 3D lug and the 2D slice.
Because the 3D lug, if you remember,
we saw some stress variations around the bolt hole,
and that was influencing the stressors
that flowed across the shoulder, but that's okay.
We can calibrate that, we can work with that.
So again, very powerful, very useful technique.
As I mentioned earlier, we do need to make sure
to get an equivalent load distribution.
So the load per unit length needs to match in both models.
But with those catered for, again,
very, very powerful, very, very quick method.
So in conclusion, there's a very useful range
of techniques we've got here.
So there are four techniques.
They're not always applicable.
You're going to find there's a particular component,
great, that's going to have planar symmetry applicable to it,
or maybe we can say we can use plane strain.
Or sometimes in an analysis, what I will do
is actually use several of these techniques
in combination, not just one FEA model,
but a couple of different models.
So for example, I may have one model
which looks at the overall 3D geometry,
looks at the overall 3D results,
then I might take a slice through,
like the plain strain through that lug.
And say I really want to focus in on the root radius,
and it's the sub-model or a separate model
which is really identifying
the stress concentrations in there.
So again, not just one FEA model per project.
We can use a range of FEA models
to build up our understanding of that particular project.
These are all great tools to have in your toolbox.
And I really recommend you start
to kind of build up this toolbox, build up this experience.
A range of different type of techniques.
And you can really never have too many tools,
and there are many more to explore.
So again, watch out for this space.
We'll be talking about other very, very useful techniques
in other videos to come.
So again, thanks very much indeed for watching the video.
I hope you have fun with these techniques.
Looking forward to seeing you on more courses.