Discussion Closed This discussion was created more than 6 months ago and has been closed. To start a new discussion with a link back to this one, click here.
Unknown expression in Random Vibration example model
Posted Nov 6, 2025, 6:40 a.m. EST Modeling Tools & Definitions, Studies & Solvers, Structural Mechanics Version 6.1 1 Reply
Please login with a confirmed email address before reporting spam
I'm trying to replicate one of COMSOL's example models, called "Random Vibration Test of a Motherboard". I'm following this example to learn how to apply this study in another simple mode. The the motherboard example there is an expression that I have been unable to identify its origin or definition.
In Component1>Definitions>Variables1 there are three variables called a_absX, a_absY and a_absZ, they are defined by an average function aveop1() and an expression solid.a_abs_rvX, solid.a_abs_rvY and solid.a_abs_rvZ. Where each is described as an Acceleration in each direction.
I have been unable to find/identify where solid.a_absX(YZ) is defined. If I use it in my own model, when I try to evaluate the 'Global Evaluation Sweep' that contains this variable as rvib1.psd(a_absZ) I get an error saying thet solid.a_abs_rvZ is an undefined variable.
Could someone please explain where/how the solid.a_abs_rvZ(XY) expression is defined? Best regards.
Please login with a confirmed email address before reporting spam
This is for reference, in case someone has the same problem. Short answer is, solid.a_abs_rv2 is an internal comsol variable (Absolute acceleration magnitude squared). It appears after solving the reduced order model, as part of the random vibration analysis. Long answer, if you have LiveLink for Matlab you can follow these steps for getting a better view of these internal variables:
- Save the model as .m file
- Open matlab with LiveLink and run the model
- run mphnavigator
- Select from the menu Search and look for the variable name.
This is a useful tool to get a overview of relevant variables in your model.
