Simplifying Assemblies for Simulation
You can simplify complex assemblies in several ways while seeking Simulation
results if applicable. When the computational resources do not permit
for simulation on the exact model, you can consider the following simplification
options when working with assemblies
or multi-bodies.
Keep in mind that the most accurate results
are obtained by including all bodies in the assembly and using an optimal
mesh size. Simplify assemblies only if you are confident that the simplification
does not alter the problem you are trying to solve significantly.
Use this option when you are interested only
in the results for a portion of the assembly and you can estimate the
effect of the excluded bodies by applying features on the rest of the
bodies.
For example, consider the case when you exert
a force shown below to hold the suitcase. If
no other external forces are applied to the suitcase, then you can model
the handle alone as shown. The objective of such a study could be to determine
the optimal material and dimensions of the handle so that it does not
fail.
If you are interested in the results on the
suitcase body instead of the handle, you can remove the handle and apply
the loads or restraints to the imprint of the handle on the suitcase body.
An imprint is the common contact area that a body shares with another.
Note: In
general, it is better to exclude the bodies farther away from the component
you are interested in than excluding those that are nearer. it is recommended
to include the bodies that are close to important bodies unless you are
confident that you can apply the proper effect.
You can replace the bodies that you are not
interested in by treating them as remote
loads, restraints, and masses.
For certain models, it may be difficult to
replace a body using remote loads, restraints or masses. As an example,
in the figure below, even though you may not be interested in the results
for body 2, you do not replace it.
You can exclude or replace a body with its
effect if the following conditions are satisfied:
The body itself is
not of interest.
Its effect on the
rest of the bodies can be modeled correctly.
When you want to include the contact interactions
between parts but save analysis time, you can treat certain components
in the assembly as rigid. You can treat a body as rigid when it is much
stiffer than its surrounding components or when the body is far away from
the region of interest and the assembly is large. Treating components
as rigid bodies leads to better approximation in the results than excluding
them. For more details, see, Treat a Body
as Rigid. The program meshes the outer boundary of a rigid body with
shell elements to reduce simulation time.
By using connectors for modeling springs,
pins, bolts, bearings, spot welds, edge welds, links, and rigid connections,
you can reduce the number of elements in the mesh and save analysis time.
For example, you can model shock absorbers in automotive suspensions using
spring connectors instead of modeling the actual geometry. For details,
see Connectors.
Surface geometries and sheet metal bodies
mesh with shell elements and structural members mesh with one-dimensional
beam elements. For more details, see Mesh types. Using them
in the assembly wherever applicable can save analysis time by reducing
the degrees of freedom. For example, you can consider replacing thin solid
bodies with sheet metal bodies or surface geometries. For details, see
Shell
Modeling.
You
can simplify the assembly for meshing. In the Simulation study tree, right-click
Mesh and select Simplify
Model for Meshing. The
Simplify utility determines an internal calculation of insignificant volume
based on the size of the model. Supported features are listed in the task
pane. You can suppress them and perform analysis on the simplified assembly.
Oversimplifying a model can
produce erroneous results by altering the stress values significantly.
You must not suppress features that produce high stresses in important
bodies.
You can initially mesh the assembly with
a Coarse Mesh
Density, run the study, and obtain approximate results. As the
next step, you can define another Simulation study and include only those
components that you are interested in. For the second step, you can find
out the contact forces that develop on the outer boundaries of the smaller
model from the initial study and apply them to the study defined with
the finer mesh.