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Iron losses over simulation time
Posted 14.04.2025, 02:46 GMT-4 Electromagnetics, Results & Visualization Version 6.3 2 Replies
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Hello everyone, I'd like to analyze the transient behavior of iron losses in order to determine the duration of the settling process. Coming from an ANSYS Maxwell background, I'm still getting used to COMSOL. I'm currently modeling a motor similar to the one shown in the following example: https://www.comsol.com/model/analyzing-electric-motor-and-generator-designs-97091
My first study is a stationary analysis that provides me with the magnetic flux density and torque values. This is followed by a "Time to Frequency Losses" study using the "Rotating Machinery, Magnetic" physics interface. From this, I obtain the parameter rmm.Qh, which represents the volumetric loss density in W/m³. By integrating this quantity and multiplying by the length, I calculate the total iron losses in watts. The file is in the attachment.
Am I correct in assuming that this value represents an average over all computed time steps? When I look at the dataset from the "Time to Frequency Losses" study and export the rmm.Qh value, I only see X, Y, rmm.Qh (see attachment). Which leads me to conclude that rmm.Qh is only a one-dimensional vector. This leads me to believe that the iron losses calculated in this study are not time-dependent—is that correct?
That brings me to my question, how do I plot the iron losses over the simulation time?
Another question that comes to mind: when calculating losses using the Steinmetz equation, are the results already based on a steady-state condition? In other words, do I even need to consider the transient behavior or settling time in that case?
Best regards
Attachments:
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Hi Tobias,
Steinmetz and many other analytical loss models as well as specific loss data supplied by magnetic steel manufacturers, specify iron loss as a function of flux density and frequency. To this end the Time to Frequency Losses Study performs a forward FFT from the time domain to the frequency domain to compute the losses. Your observation is correct, the computed rmm.Qh is the space distributed loss, time-averaged over the period specified as input to the Time to Frequency Losses Study. This means that iron losses cannot be observed as a function of time when computed this way. It is however possible to inspect the iron losses for each of the harmonics.
A pre-requisite to the Time to Frequency Losses Study is a steady-state time-dependent solution. That is when all oscillations are periodically repeating and any transients has vanished, and which is perhaps what you mean by "settling process"? The iron losses are computed as a result of the time-dependent solution, and is not suitable as a probe for steady-state operation. For this, inspection of losses in materials with non-zero conductivity e.g. magnets in your model, is a good indicator. Here the instantaneous loss is computed as time advances. With this you should be able to determine when time-dependent simulation has stabilized and hence what portion of the solution can be used as input to the Time to Frequency Losses Study.
If you have any further questions please do not hesitate to contact COMSOL Support.
Best regards Lars Ottar
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Dear Mr. Ottar, thank you very much for your detailed response. It has greatly clarified my understanding of how the Time to Frequency Losses Study is progressing.
I particularly appreciate your approach to addressing the losses in the model related to the magnets. I am eager to give this method a try!
Once again, thank you for your reply.
Best regards