- [Narrator] In this video,
I'm gonna look at the general principles behind
base motion in dynamic response,
and then look at the particular requirements
of SOLIDWORKS simulation.
So looking at base motion in dynamic response,
loading is applied through a set of base points.
It represents a base excitation,
and examples would be
a building subject to an earthquake,
a structure with a transmitted blast,
or maybe a naval ship with a shock loading
coming through a deck.
The components sitting on the deck would see a base motion.
In SOLIDWORKS we can only have enforced motion
to describe base motion.
So a displacement velocity, or an acceleration through time,
or a cross frequency.
It's not possible to apply a force through time,
for example.
The base motion can be applied to either
transient or frequency response.
Now the implementation in SOLIDWORKS simulation
has two approaches.
The first one is uniform base excitation,
and that means that every constrained node,
or noded to fixture, is flagged for use in base motion.
Now an arbitrary excitation direction
can be chosen by any convenient geometric edge.
For every degree of freedom within a node,
those degrees of freedom which are going to be excited
can be defined by selecting components
in the excitation direction x, y, or zed.
There is a limitation in that
only constrained types using a rectangular coordinate system
in their definition, can be used to define
uniform base excitation.
Now the old turn to method within SOLIDWORKS
is selected base excitation.
This is similar, but now one constraint set or fixture
can be selected from the set of
maybe two or three instances of fixture.
Again, the nodes within in the fixture definition
are flagged for use as base excitation nodes.
All the other constraints or fixtures are ignored.
The global coordinate system, or model coordinate system,
is the only one that can be used
for this form of base excitation.
However, we can choose any components
of that global coordinate system.
So we can select x, y, and zed,
or just x, for example.
Now the relationship between the constraint, or the fixture
and the enforced motion is a little bit abstract.
So I thought I'd try and explain that with a diagram.
So here's a node, which is being constrained,
and this particular arbitrary constraint
is translational x, y, and zed,
and then rotational Ry in some fixture definition.
So if we choose base motion as our loading input,
we point it towards this fixture set,
which includes this node,
then these constraints, or these fixtures, are flagged.
That means they're going to be used for base motion.
And as I described, this is the particular constraints
that we find at that particular node.
Now I'm assuming this node is going to be reused,
and the enforced motion, or base motion,
is going to be an acceleration in zed
at that node, and all the other nodes
which would be in this fixture.
So that means the node is being reused to define
the enforced motion direction.
The constrained directions are completely ignored,
and the enforced motion definition is separate from that.
Now I think the principle of base motion
is fairly straightforward.
The particular implementation in SOLIDWORKS
Guinness, a new templementation,
but it's a little bit of an abstraction,
so it needs thinking about quite carefully.