How do I complete a transient thermal FEA study in SOLIDWORKS Simulation Professional? Every study in SOLIDWORKS Simulation follows the same 6 general steps. You can read more about these steps here: Six Steps To Your Simulation Study. Thermal studies are no different.
If you have found this blog, chances are you have already read my other blog that covers how to perform a steady-state thermal analysis. If you have not, I would suggest reading it first here.
As a refresher, thermal analysis in SOLIDWORKS Simulation Professional allows for simulation of all 3 modes of heat transfer as either steady-state or time dependent. As an example, think of a piece of metal in a furnace. A steady state solution would tell us how hot the metal would get eventually. A transient study would give us information about the temperature of the metal at specific time intervals along the way and could tell us how long it takes to heat the metal to steady state. A transient solution is appropriate when asking questions like: How long does it take? What is the temperature at time X? What if we vary heat sources/sinks with time?
So, starting the study is done the same as all the other study types:
Once the study is created, I’ll first go into the study properties to toggle the transient option to activate time dependency.
Note that once time dependency has been activated, the “Total Time” and “Time Increment” fields become editable.
- “Total Time”- Refers to how long you want the solver to simulate the system. In this case, I want to know if the chip will reach steady state after 2 minutes (120 seconds) of active heating.
- “Time Increment”- Refers to how often the solver will calculate steps to the final time. The lower the increment, the higher fidelity the results. However, with more time increments, both the solution time and results files will increase.
Time incrementation in transient studies is crucial. I don’t want to take too few steps or I may miss crucial parts of the calculation. I don’t want to take too many steps either or the solution will take a longer time to solve. My recommendation is to start with 10-20 steps in an initial simulation, check the results and refine from there.
Now that the transient solution has been activated, the rest of the setup is nearly identical to the previous blog. There are just a couple extra bells and whistles to consider for time dependent calculations.
First, I enter an initial temperature. Because the study is time dependent, the starting temperature is a crucial input. Note that I have selected the part BODIES for the initial temperature, not the faces. In an assembly, make sure that the actual PARTS are selected from the tree.
Before I run transient thermal simulations, I like to set up sensors to help with post processing the results. For those of you unfamiliar with sensors, they are a SOLIDWORKS functionality that can be used for easy extraction of data. Almost anything in SOLIDWORKS that carries a numerical value with it can be measured or probed with a sensor, including simulation data. (For more on sensors, see the blog by my colleague Alex here.)
Sensors can be found by default under the “Evaluate” tab in the command manager.
I want a sensor that monitors the maximum temperature of the heated chip throughout the transient simulation. The setup to accomplish that appears below.
Note that I have again selected the BODY for the chip, not the face(s). Also, it is crucial to select “Transient” for the step criterion. This will ensure that we are requesting the maximum temperature of that part at every step, not just the maximum throughout all steps.
Sensors are an incredibly powerful tool in SOLIDWORKS for post-processing results. Many times, they can even be created after the simulation has completed, so give it a shot and see what kinds of sensors you can make!
After completing the setup identical to the previous blog, the analysis is ready to run! Before I do, one more note of interest. Due to the time dependency, almost all boundary conditions in transient thermal analysis can be varied throughout the course of the simulation. The heat load applied is shown below:
The heat source is applied as constant, but it could be changed with time, temperature or even have a virtual thermostat applied to it!
After running the results, an animation can be created showing the assembly heating up as time progresses.
An important note when post-processing transient results is to always pay attention to what time-step you are looking at. This information is readily available from the small black text in the graphics area.
To change the current plot step, simply right click the active plot and go to “Edit Definition.” From there, it’s possible to select either individual plot steps or use the button that looks like a replay icon to plot maximums or minimums.
Lastly, I’ll leverage the sensor I created by simply hovering over it in the SOLIDWORKS feature tree. To open a graph I can manipulate more or save, I can simply right click the sensor and select “Graph.”
From the sensor graph, it is apparent that the system has reached its thermal steady state in about a minute. From here I can leverage this information to inform design decisions.
I hope this blog has enlightened you on the basics of transient thermal analysis in SOLIDWORKS Simulation Professional. This blog has an accompanying video under the same title. Check out the Computer Aided Technology video page for more information and subscribe.
Matthew Sherak, CSWE
Simulation Product Specialist, Application Engineer
Computer Aided Technology, Inc.