Impedance Magnitude Offset Error 回答済み

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Laura Morrison

Hi there,

I am trying to model a piezoelectric disc located inside a piezoelectric ring and separated with a layer of epoxy. I have created two axisymmetric models which are exactly the same apart from where the loads are added. In the first model, the disc has loads added to the top and bottom faces whereas the other model has loads added to the top and bottom faces of the ring. I have double-checked all model settings including area-scaling and material properties, and I can't find any discrepancies apart from load location (i.e. either loads on the disc or on the ring).

When I take the impedance magnitude of the modelled results from the flex history file for each model and plot them against results I have from lab measurements, the ring loaded model agrees well to the measurements however the disc loaded model appears to have a large offset in terms of its impedance magnitude compared to the measurements (shown in the graph), the frequency of the resonances are a little offset from the measured result as well but I am more concerned about the magnitude offset at the moment.

I am looking for some advice as to what I could be doing wrong with the model since both models have all settings the same apart from where the loads have been added. 

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    Chloe Allison

    Hi Laura,

    Could you please share both of the model files via your preferred cloud file sharing service so we can take a look at the code to make sure everything is set up correctly.

    Best Regards,

    Chloe

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    Laura Morrison

    Hi Chloe,

     

    Yes I can do that. What email address will I send the sharing link to?

     

    Thanks

    Laura

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    Chloe Allison

    Laura,

    You can share the link here or send it to

    Thanks,

    Chloe

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    Chloe Allison

    Hi Laura,

    When it comes to amplitude differences in impedance it is usually due to area scaling being different between the models which is indeed the case here, the area scaling in your ring model is 2 but it is 6 in your disc model.

    Here is a bit about area scaling from our documentation to guide you: 

    Area scaling is the scale factor for electrode area. It is used to account for the z-dimension in 2D plane strain models and symmetry planes in 2D and 3D models. For example, if only half of an electrode's area is included within the model due to the assumption of a symmetry plane, area scaling should be increased by a factor of 2. For 2D axisymmetric problems is should be 2ς since axisymmetric models evaluate a 1 radian sector of the physical problem.

    Best Regards,

    Chloe

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    Laura Morrison
    Hi Chloe,
     
    Thank you for your reply. I was away on holiday last week and I forgot that just before I left I changed the area scaling for the disc electrode to 6. This was just a test to see what effect it would have on the impedance magnitude issue I was experiencing. For the graph that I uploaded above, these results have area scaling set to 2 for both the disc and the ring electrodes, so this can't be the problem. 
     
    Sorry about that, I totally forgot to change the value back to 2 before I shared it with you. Do you have any other ideas as to what it could be?
     
    Many thanks,
    Laura
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