SOLIDWORKS Simulation makes it easy to determine whether a structure satisfies its design criteria for a particular set of loading conditions. As many users can attest, having only one loading condition is rarely the case. When offering a product to the general population, the designer must consider different loading scenarios due to differences in environmental loads and in human physiology, as well as user error, to name just a few.
Consider the ladder pictured to the left.
SOLIDWORKS Simulation comes with diverse sets of loading conditions and is able to handle live loads (e.g. a person on the ladder) and dead loads (e.g. the weight of the ladder itself). It would be very time consuming to manually consider not just each case, but every combination of the loading cases. You could try to duplicate studies, but the clutter would soon become unmanageable. You could try to reuse the same study and change the values of the forces, but you would lose the history of what the previous values were, as well as being generally tedious.
Thankfully, SOLIDWORKS Simulation has a way to handle load cases. The Load Case Manager from within SOLIDWORKS is designed to make assigning these different types of loads and, more importantly, combining these loads easy. In this article, we will explore what it takes to assign load cases for the ladder pictured above.
Note: this article will apply to any major version of SOLIDWORKS greater than 2014. SOLIDWORKS 2015 was the first year that Load Cases were implemented.
You can download the simplified ladder model here to follow along if you wish (SOLIDWORKS 2015+). The ladder is simplified because the focus for this article is load cases rather than the intricacies of meshing, different types of bodies etc. that would arise should we use a geometrically accurate ladder.
Step 1: The Plan
The first step is to lay out what the challenge is and what we are looking to analyze. Let’s lay out the situation: This particular ladder is designed to hold two users on it at the same time (not the best idea in real life for safety reasons other than the structural integrity of the ladder, but we are only considering the structural safety of the ladder in this exercise). The users may be carrying tools.
For the ladder resting against a wall at 15 degrees, find the magnitude of the maximum Von Mises stress for the following cases:
- Resting on a wall; no live load
- Live Load 1 only
- Live Load 2 only
- Both Live Load 1 and 2
- [2 × Load 1] + [1 × Load 2]; (heavy user 1, normal user 2)
- [1 × Load 1] + [2 × Load 2]; (heavy user 2, normal user 1)
- [2 × Load 1] + [2 × Load 2]; (both heavy users)
Assume the ladder is made from Aluminum 1060 Alloy.
As you can see, there is much work to do, but thanks to load cases, we only have to define the study once, and the load case manager will take care of the rest.
NOTE: If you have a study already defined and want to get to the load case manager, skip to Step 8.
Step 2: Open the File
Open LADDER.SLDPRT and verify that the Simulation Add-In is turned on.
The simulation add-in can be accessed from either from Tools > Add-ins, or from the SOLIDWORKS Add-Ins tab on the ribbon.
Step 3: Create a New Static Study
There are plenty of ways to do this, but I like accessing it from the Simulation Tab. Make sure that “Use 2D Simplification” is unchecked.
Step 4: Apply the Material as Aluminum 1060 Alloy
If you haven’t already, make sure the material is set. I am using aluminum 1060 alloy here, but you can set it to whatever linear material you desire (practically any metal, for example).
Step 5: Apply Fixtures
In order for the static simulation to run properly, we must ensure that our model is properly fixtured. I used the following:
Specify the two bottom faces as Fixed Geometry. This will represent the feet of the ladder that is firmly planted on the ground.
On the top of the ladder, specify the two vertical faces as Roller/Slider Fixtures. This represents that while the ladder can’t go through our imaginary wall, it can slide along the wall.
Step 6: Apply Loads
This where the bulk of the setup occurs.
There are three main loads to consider: The weight of user 1 (Live Load 1), the weight of user 2 (live load 2) and the weight of the ladder (dead load). It is important that these loads are defined in separate features from each other. This is what is going to allow the Load Case Manager to toggle the consideration of the loads when it runs.
Live Load 1:
Right click the “External Loads” Node in the simulation tree and click “Force.” For its location, pick the second rung from the top. Change the radio button from “Normal” to “Selected Direction” and for the direction, click the Top plane
In this example, the ladder is already oriented 15 degrees with respect to the coordinate system.
Enable the “Normal to Plane” Direction button and hit “Reverse Direction” if necessary, to make sure the force is pointing down. For this, I put 1,000N.
Remember, it may be tempting to include the other rung in the blue selection box as well, but we must keep them separate for the reasons mentioned above. With Face<1> as the only item, click OK. It might be a good idea to rename the item in the tree, too. I named it “LIVE LOAD 1” to make it easier to distinguish when we get into the load case manager. You can do this by clicking on the line item and pressing F2.
Live Load 2:
Make another force with the same parameters as Live Load 1, but with the second rung from the bottom as the selected face. Type, magnitude and direction of the force are identical.
Dead Load:
Right click on the “External Loads” node and select “Gravity.” Usually it will fill out standard parameters by itself, but make sure that the selected reference is the Top Plane, direction reversed with a magnitude of 9.81 m2. I renamed this to “DEAD LOAD.”
Step 7: Mesh the Model
Of course, the penultimate step to running a study is meshing the model. I will use basic mesh settings to make the computation quick for this demonstration. Right click on the Mesh node and select “Create Mesh…”
Here, I specify a draft quality mesh with the standard coarseness settings.
Step 8: Open Up the Load Case Manager
This is where the fun begins! Normally, we would run our study. But instead, we divert to the Load Case Manager!
You can find the load case manager by right clicking the top of the study tree and finding “Load Case Manager” in the drop-down list.
Overview of the Load Case Manager
When you activate the Load Case Manager, a screen similar to this will appear with a table. The columns represent the different elements of your study (forces, fixtures etc.). Some of you may even draw parallels to the Configure Feature functionality found in SOLIDWORKS, which is very similar. It’s practically defining configurations of your study to have SOLIDWORKS run all at once!
Step 1: Add the Primary Load Cases
Looking at the rows, and you will see there are a couple sections: Primary Load Cases, Load Case Combinations and Track Results.
Let’s look at the first one, Primary Load Cases. The idea is to have each one of our three loads to have its own line, so that SOLIDWORKS can combine them. This is why it was important to separate the live loads earlier.
Click where it says, “Click here to add Primary Load Cases.” Then click inside one of the cells of a force to un-suppress it. Repeat for each of the load conditions. If you are following along, the table should look like this:
You’ll notice that this is the setup for three of the seven load cases.
Step 2: Define the Secondary Load Case Combinations
To get the other four cases, click where it says, “Add a load case combination.”
The idea here is that we can now use the load cases like variables and make equations for whatever we want. Click in the white space to pick the cases or see mathematical functions to put in the equation.
You can see that the window above has the two normal users condition that we described in step 1.
Hit OK and add the other equations! The table should now look like this:
Step 3: Add a Sensor for Tracking Results
With all the cases added, we can hit run if we wish. But before that, I will add a sensor to make it simple to see what the maximum Von Mises stress is for every case. Click “Add a sensor to track a result” then click “add sensor.”
The following image describes how I set the sensor up:
The only thing I changed from the standard settings was the units (I prefer my stress units to be in MPa).
Step 4: Run the Study
Finally, hit run and reap the benefits of your set up! It may take some time to complete based on model complexity, meshing, solver in use and the number of load cases.
Step 5: Consider the Results
After some time, SOLIDWORKS will bring you one tab over into the Results View. Here you can see a tabularized view of all the results:
As you can see in the first column (Stress1) it lists all of the maximum Von Mises values for all of the Load Cases we were interested in. Hopefully, this tutorial helps you save some time when running an analysis with multiple load cases.
Hopefully, this tutorial helps you save some time when running an analysis with multiple load cases.
Learn more about SOLIDWORKS in the whitepaper Designers Greatly Benefit from Simulation-Driven Product Development.