SolidWorks Simulation14 June 2011 Sam Ettinger, HMC 2012
ObjectivesBy completing this tutorial, you will learn to conduct finite-element analysis (FEA) tests on SolidWorks models using the Simulation add-on.
IntroductionFinite-element analysis (FEA) is useful in predicting a models 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. -1-
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 beginOn 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 dont 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, lets 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.
Getting the model, defining the materialSolidWorks 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? Thats 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 , 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.
Figure 2. How to change a model's material.
Figure 3. Materials window.
Figure 4. The glass, now shown as glass.
Opening Simulation for the first timeBy 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. -5-
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 analysisAs 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. Lets 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, lets 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.
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 -7-
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, lets 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.
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