- [Instructor] In this video, you'll learn how to create
a lump mass element representation
and connect to the structure using a set of rigid links,
and also show the advantages and disadvantages
of the method.
So, let's go to File, Open.
If you're using SolidWorks version 2018 or later,
then you can open the SolidWorks file directly.
Alternatively, if you're using a SolidWorks version
prior to 2018, you need to open the Parasolid file.
That Parasolid file is version independent.
So, I'm going to open the SolidWorks file.
Now the model is similar to the previous train model
in that we have a payload representation,
which is shown here by this part.
Let's go to the Simulation tab.
Click on New Study, and create a new study.
That's from this choose Frequency.
We're going to name this as Loaded Tray.
Right mouse click on Solidbody One,
Apply/Edit Material.
Going to use the default Alloy Steel.
Just click Apply and then click Close.
For the payload region, we want to do something
a little different.
Right mouse click, Apply/Edit Material.
You can use Alloy Steel but this time we're going to copy.
Then, we're going to take it down into the custom library.
Custom Materials.
There's a category here called Plastic.
So, we're going to paste into that
that new copy of the Alloy Steel.
But, I'm going to modify this.
So, I'm going to rename it as Smeared Material.
As it's a copy and it's in a custom library,
then I can edit it.
I'm going to assume an equivalent distributed stiffness
of one E to the five psi,
so it acts like a much softer material.
It's some kind of box or container.
It's obviously not as stiff as a block of steel.
It's a lot more flexible than that.
Now, we also assume a target master same as before
of two pounds.
I've worked out previously that, with the volume I have,
the density needs to be set to not quite
one pound per cubic inches.
I can click Apply and Close.
If I right mouse click on the study,
I can check mass properties.
I've got my weight of the trays before,
five point seven eight pounds.
The weight of my payload is, again, two pounds.
But this time it's represented as a part.
Notice the part is bonded into the rest of the structure
with a glued contact or bonded contact.
I'm going to set up constraints
to simulate the bolts in the support region.
This is exactly the same as we did before.
So, right mouse click on Fixtures.
Choose Roller and Slider,
and then I choose the advanced option
On Cylindrical Faces.
Again as before, I can pick the radial direction
to be constrained.
I can pick the actual direction to be constrained,
which just leaves the circumferential direction free,
essentially to spin.
I'm going to go ahead and pick the faces for the bolts,
but I'll cut to the chase in the video
so that we don't waste time.
The first bolt, second, third,
fourth, fifth, and sixth bolt.
So, they all look good, so check okay.
Right mouse click on Mesh and select Create Mesh.
I'm going to set this a little coarser
because of the presence of that box.
So check okay.
So, deliberately try to force a relatively coarse mesh
in the box here.
There's no point in wasting computing time
on trying to calculate the response of
a simple block like this.
Now right mouse click on the study
and choose Properties.
Again, we want to set this to 10 modes.
Click okay.
Now we can click on Run This Study.
Now let's quickly review the mode shapes.
In version 2018, we can use the double-headed arrows
in the legend here.
But again, prior to version 2018, we have to click
through the results here.
So again, for commonality,
as before I'm going to use this method.
So that's our first mode.
Second mode, third mode, (mouse clicking)
fourth mode, fifth mode, (mouse clicking)
sixth mode, seven, (mouse clicking)
eight, nine, (mouse clicking)
10.
Now those modes becoming different
from the previous analysis.
In particular notice the block is actually picking up
its own local modes within mode 10.
Whereas, within mode one, it was acting fairly rigidly.
Now, we want to copy this study and rename it.
Let's name this as tray dash lumped mass.
Check okay.
Now again, our results are irrelevant.
So, let's go and delete those. (mouse clicking)
Now, if I open up the two components and I look at
the component which is the payload,
what I can do here is I can create or treat it
as a remote mass.
Which means it's going to put a lump mass
at its center of gravity.
So I click on that saying that's my target object.
Now it wants a surface to connect into.
Now, the problem amount is that the object itself
is obscuring that view.
So, what I need to do is close that out.
Now, if I go across the model,
I know which component I want to deal with, which part.
So, I can basically hide that part.
Now I come back to this part and say I want to treat
that as a remote mass.
Remembers the part, Boss-Extrude12.
Now, I can pick the surface I want to connect down into.
So, this will be a series of links down toward
the nodes that are going to be generated
on this particular surface.
Click okay.
Now I just have representation of the center of gravity,
and that lump mass will now be connected
into the base there.
So, I can come to my remote mass,
say Show the CG.
That's the center of gravity on that particular mass.
So, now we go ahead and create a mesh.
(mouse clicking)
We can't see the elements, which are connecting
the mass element to the base in here.
But, there's a series of links connecting that mass element
at that CG there to all of the nodes
on the surface down in here.
So, let's run the study.
You notice the run was a lot quicker than previously
because we're not wasting any time analyzing the elements
within that solid box.
The first mode is 191 Hertz
compared to the 163 Hertz previously.
So, the stiff connection to the mass
has increased the overall stiffness.
If fact, it assumes the payload is infinitely rigid
in its connection to the tray.
So, let's compare the two results side by side
from the two studies.
Go to Window, Viewport, two views vertically.
Now at the moment we're looking
at the lump mass result here.
So, I set up a isometric view.
In the other window,
let's go for the tray without a mass,
and choose the isometric view.
Load in results.
For this result, let's clean it up.
Go to Chart Options, switch off the legend,
and choose Discrete.
For the other view here, choose the one with the lump mass.
Again, show these results.
Again, modify the chart.
No legend, and we'll set Discrete.
So, we can compare the first mode for each.
You see where the payload has a suddenly richer structure,
as in the case here.
You got 167 Hertz.
So, we've added mass, but we haven't added stiffness.
So, that's driven the frequency down.
On this side though, we've used a lump mass representation.
So, we have the same mass but the stiffness has been
significantly increased.
So, this little region in here has become very stiff.
You can see that there's a kind of a pattern
of very stiff response to structure underneath
this particular surface in here.
Imagine a series of rigid lakes
coming down from the center of gravity here
down to that surface.
And that's basically what's happened there.
So, let's save this model off.
File, Save As.
We're going to call it tray two end, and click Save.
We do want to copy the results.
We'd be looking for results which are CWR extensions.
Again, that's going to be loaded tray and tray lump mass,
with a prefix of tray two, again.
So, the conclusion in this video,
we've seen how to set up a lump mass idealization.
We have viewed its advantages,
which is it's quick and easy to set up,
easy to connect to a base,
and it reduces the element count
so the run becomes much quicker.
But the disadvantages, it does stiffen up
the backing structure here.
If that's what we want, if we have a very rigid component,
then that's appropriate.
If not, then it will over-stiffen it,
and it's better to use a softer representation,
as we've seen here.