- 1 - SolidWorks Simulation 14 June 2011 Sam Ettinger, HMC 2012 Objectives By completing this tutorial, you will learn to conduct finite-element analysis (FEA) tests on SolidWorks models using the Simulation add-on. Introduction Finite-element analysis (FEA) is useful in predicting a model’s response to various influences such as forces, torques, periodic excitations, and heat. FEA is used to analyze large or complicated models where analytical solutions are not possible. FEA software breaks the model into thousands of small tetrahedral elements and solves numerically for each one individually. Some of the leading commercial FEA tools include COMSOL, Ansys, and SolidWorks Simulation. This tutorial covers SolidWorks Simulation because it is a comfortable environment for those who already know 3D modeling with SolidWorks. SolidWorks Simulation is primarily applicable to mechanical and thermal models. COMSOL specializes in multiphysics problems involving interaction between mechanical, thermal, and electrical behavior. Ansys also addresses mechanical and thermal simulations and has advanced capabilities required in certain fields.
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SolidWorks Simulation 14 June 2011
Sam Ettinger, HMC 2012
Objectives
By completing this tutorial, you will learn to conduct finite-element analysis (FEA) tests on
SolidWorks models using the Simulation add-on.
Introduction
Finite-element analysis (FEA) is useful in predicting a model’s response to various influences
such as forces, torques, periodic excitations, and heat. FEA is used to analyze large or
complicated models where analytical solutions are not possible. FEA software breaks the model
into thousands of small tetrahedral elements and solves numerically for each one individually.
Some of the leading commercial FEA tools include COMSOL, Ansys, and SolidWorks
Simulation. This tutorial covers SolidWorks Simulation because it is a comfortable environment
for those who already know 3D modeling with SolidWorks. SolidWorks Simulation is primarily
applicable to mechanical and thermal models. COMSOL specializes in multiphysics problems
involving interaction between mechanical, thermal, and electrical behavior. Ansys also addresses
mechanical and thermal simulations and has advanced capabilities required in certain fields.
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This tutorial will cover three of the simulation studies available in SolidWorks Simulation:
Static analysis, for identifying stresses caused by static loading
Frequency analysis, for identifying resonant frequencies and associated mode shapes
Thermal analysis, for identifying heat flow through a model
Mastering these three gives you the tools and experience necessary to make use of any of the
remaining simulation studies. We will use the same model, a wine glass, for each study.
Before you begin
On two occasions I have been asked, “Pray, Mr. Babbage, if you put into
the machine wrong figures, will the right answers come out?”...I am not
able rightly to apprehend the kind of confusion of ideas that could provoke
such a question.
- Charles Babbage, Passages from the Life of a Philosopher, 1864
Since the very beginning of computing, users have been plagued by bad outputs as a
result of bad inputs. FEA is particularly prone to such problems, generating pretty
pictures that often have no bearing on reality. As a general rule, if you don’t know
what to expect, the results you get are probably incorrect and certainly unusable.
Some common reasons for error include making invalid assumptions, setting incorrect
boundary conditions, setting incorrect material properties, and general numerical
errors. As an example, let’s consider the stress analysis of a typical model. One can
assume a linear stress-strain relationship before the yield strength of the material is
reached. The model produces incorrect results as stress or strain increase to the point
of nonlinearity on the stress-strain curve.
Setting appropriate boundary conditions can be more difficult than one might first
expect, and it is easy to overlook boundaries (such as the initial temperature of an
object). This can result in nonsensical default values being used for the simulation.
Obtaining accurate physical parameters for your materials can also be difficult,
especially if you are using nonstandard or unusual materials.
FEA inherently discretizes the object being studied. The number of elements used
presents a tradeoff between runtime and accuracy.
Before you trust your FEA results, you should plan for a significant validation process.
If possible, the best place to begin the validation process is with a simple model that
can be solved analytically. Check that the FEA simulation produces comparable
results. For example, before looking at bending in an array of bolted-together I-beams,
compare the FEA results for bending in a single I-beam to analytical results. Be sure
you are using the appropriate material parameters. Another important model validation
technique is to compare the FEA results to an actual physical prototype using simple
stimulus, such as an impulse. Beware of making claims about the FEA model results
that you cannot independently support with other analysis or measurement.
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Getting the model, defining the material
SolidWorks is, first and foremost, a 3-D modeling tool. Look in the tutorials folder for a
SolidWorks model named “glass.SLDPRT”. When you open it, it should show a wine glass, as
in Figure 1. This is the model we are going to study in this tutorial. Save a copy to your Charlie
account.
If you wish to practice your modeling, part of a technical drawing of this wine glass is included
in Appendix A. Units are in millimeters. This should be enough information to draw your own.
Figure 1. The wine glass model.
To use the model of the glass in Simulation, we must specify the material that the model is made
of. Can you guess what material we want the model to be? That’s right, glass! You can specify a
material in the Feature Manager design tree on the left-side panel. There should be an icon
named “Material <not specified>,” as in Figure 2. Right-click this and choose “Edit material” to
be brought to the Materials window, shown in Figure 3. Glass is found in the folder SolidWorks
Materials > Other Non-metals. Click “Glass,” then click “Apply” and “Close.” Your model
should change from opaque grey to transparent grey, as in Figure 4.
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Figure 2. How to change a model's material.
Figure 3. Materials window.
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Figure 4. The glass, now shown as glass.
Opening Simulation for the first time
By default, SolidWorks Simulation does not open when SolidWorks does. We can change this by
going to Tools > Add-Ins, shown in Figure 5.
Figure 5. How to start Simulation.
The Add-Ins window, replicated in Figure 6, pops up. Check the box to the left of “SolidWorks
Simulation” to enable Simulation in this instance of SolidWorks. If you want Simulation to be
enabled every time you start SolidWorks, check the box to the right of “SolidWorks Simulation”
as well. If this is your first time using Simulation, you may be asked to agree to an end-user
license agreement.
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Figure 6. The add-ins window.
If all goes right, there should be a new tab named “Simulation” in the upper-left, next to
“Features,” “Sketch,” “Evaluate” and the like. Now we can begin our first study!
Static analysis
As mentioned above, static analysis computes the effects of static loading on a model. It can
display stresses, strains, displacement, and the factor of safety at each segment of a model. In
Simulation, one has to specify the location and magnitude of each load, as well as to specify
where and how the model is supported. Identifying where stresses are highest/lowest quickly
shows the designer where a model can be improved by adding support or by removing excess
material.
We are going to investigate what happens when a 5 kg load is placed on the lip of a glass set
upright on a table. Let’s assume that placing the glass on a table can be best approximated by a
perfectly fixed support on the entire bottom face of the wine glass base. Furthermore, let’s
assume the 5 kg load is best approximated by a 50 N force pushing against the lip of the glass
with uniform distribution. In models of large objects, it is often advisable to include gravity in
the simulation, but that is not necessary for our 10-cm-tall wine glass.
To create a static study, click the Simulation tab in the upper-left. There should be a button
labeled “Study Advisor.” Click the arrow just beneath it and choose “New Study,” as in Figure 7.
Here you can see all the types of studies available in Simulation. Click “Static,” name the study
something memorable, and click the green check mark.
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Figure 7. Starting a new study.
Below the normal display pane on the left, a static study pane should open. We can use this or
the Simulation tab along the top of the screen to specify our fixtures and loads.
To set up the fixtures on the model, either right-click “Fixtures” in the static study pane or click
the arrow beneath “Fixtures Advisor” in the Simulation tab. Choose “Fixed Geometry” as the
fixture type for this study. This is shown in Figure 8. You can also have supports such as pins,
rollers, or hinges, if your model requires it. For now, though, the fixed geometry suffices. When
you click “Fixed Geometry,” the Fixture pane opens on the left. Select the bottom face of the
base of the glass and press the green check mark. You can select multiple faces at a time, if you
wish, but for this example only one face is fixed.
Figure 8. Adding a fixture.
To specify our 50 N load, right-click “External Loads” in the static study pane or click the arrow
beneath “External Loads Advisor” in the Simulation tab. As you can see, there are lots of
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possible options for loading, but we just care about the simplest one, “Force.” Click that to be
taken to the Force/Torque pane. Click the lip of the glass (you may have to zoom in a ways to
make sure you are selecting the whole face, not just one edge) to select it as the face being
loaded. Rather than having the load normal to the lip, let’s specify the load as directly down (as it
would be in reality). To do this: in the Force/Torque pane, change the direction of the force from
“Normal” to “Selected direction,” then choose the Top Plane in the design tree just to the right of
the Force/Torque pane. The design tree and the lip of the glass are shown in Figure 9. By default,
the design tree is condensed to just show the name of the part; click the boxed + to the left in
order to expand it.
Figure 9. Selecting a face and a direction to apply force.
The design tree is the tree in the upper-left corner of the figure.
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In the Force section of the Force/Torque pane, we have to specify the magnitude and direction of
our load. Click the button marked “Normal to Plane” and specify 50 N as the force. We want the
force aimed down, so check “Reverse direction” as well. These are shown in Figure 10. Finally,
click the green check mark.
Figure 10. Specifying force and direction in the Force/Torque pane.
With the forces and fixtures specified, we can run a finite element analysis now! SolidWorks
needs to break the model into small tetrahedral units, which together are called a mesh. Smaller
meshes (as in meshes with smaller individual units) produce more precise results but require
additional computing time. Large meshes run quickly but may produce wildly inaccurate results,
especially around sharp edges. It is common to use a mesh with varying element sizes: smaller
units around the areas of interest in a model, such as potential failure points, and larger units
where precise results are less valuable.
In the static study pane, right-click “Mesh” and choose “Create Mesh.” Accept the default mesh
size and check OK. This will create a uniformly sized mesh over your entire model, which
should look something like Figure 11. If you ever need a non-uniform mesh, you can do so by
right-clicking “Mesh” and choosing “Apply Mesh Control” instead.
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Figure 11. Meshed glass.
Begin the static study by clicking “Run” in the Simulation tab. You will see that even this simple
problem consumes significant memory and time. If all goes well, a folder named “Results” will
appear in the static study pane. Right-click the folder and choose “Define Stress Plot,” then
accept the default settings that appear. This will show you the von Mises stresses from the 50 N
load by coloring the mesh. You should see the greatest stress occurring at the joint between the
stem and the bowl, shown in Figure 12. Is this reasonable?
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Figure 12. Stress plot close-up.
To see the interior of the bowl better, we can slice the model in half. While looking at the stress
results, click “Plot Tools” in the Simulation tab and open “Section Clipping.” Set it to cut along
the front plane and check OK. Figure 13 shows an elegant cutaway view and an easy way of
observing the interior of the model!
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Figure 13. Stress plot cutaway.
Create a new result plot to show displacement. Right-click “Results” again and choose “Define
Displacement Plot.” In the settings pane that appears, set “Deformed Shape” to True Scale and
check OK. By default the displacement is measured in URES (“resultant displacement”—U is
commonly used to abbreviate displacement), which is a simple measure of displacement
magnitude. Measuring displacement along the X, Y, or Z axes is also an option here, though we
will stick with URES, like in Figure 14.
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Figure 14. Displacement plot.
The actual displacement caused by the 50 N load is very small, on the order of microns, and will
not be visible on this model. To make deformations visible, we need to change the displacement
settings. Right-click the actual Displacement plot in the results folder of the static study pane and
choose “Edit Definition.” Set the Deformed Shape to “Automatic.” This plot tool greatly
exaggerates the displacements, multiplying them by a factor of 5000 or so, so that they are
visible. Now we see the bowl squashed, the stem shortened, and the connection between stem
and bowl beginning to cave as in Figure 15. Again, the view can be improved by going into Plot
Tools and setting up Section Clipping, as in Figure 16.
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Figure 15. Exaggerated displacement.
Figure 16. Exaggerated displacement, cutaway.
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What to turn in
A screenshot of your model, showing the cutaway stress plot of the model.
A screenshot of your model, showing the deformation plot, with displacement
exaggerated.
Frequency analysis
Frequency analysis is done to models to identify resonant frequencies and mode shapes. The
wine glass is a good model to run frequency testing on because at least one of its resonant
frequencies yields a mode shape that can shatter the bowl while leaving the stem intact. This is a
great party trick, assuming your party includes a powerful speaker and a tone generator:
http://youtu.be/17tqXgvCN0E. We are going to find that resonant frequency using finite-element
modeling.
Create a new study by clicking the arrow under “Study Advisor” and selecting “New Study.”
This time, choose the “Frequency” option and rename the study to something relevant.
A frequency analysis pane will appear on the left side of the screen. This is very similar to the
static pane from before; it lets you add fixtures (which are obligatory) and external loads (which
are optional). Add the same fixtures from the static study; do not add any external loads. This is
all that is necessary to begin the frequency analysis!
Run the analysis just as in the static study. When it finishes, right click “Results” in the
frequency study pane. The results of the study that we care about most are the mode shapes, so
click “Define Mode Shape/Displacement Plot.” A new pane, shown in Figure 17, should open to