An inquiry regarding an error in saving the sweep

amoraamora Member Posts: 6

Hello all,

I have some questions regarding a file that I am using:


(1) I am trying to run parametric sweeps on different parameters but I got the same error for different parameters. The results weren't saved after the end of the parametric sweep. I have a attached a screenshot of the error. I got this error 4 times for different parameters, usually the problem is with the value before the last value in the range as seen in the photo. How to fix this error and have the result saved?

(2) Also, I have a question regarding the size of the FDTD region, I read it should be at least λ/2 or more. Is λ the maximum operating wavelength or the central one?

(3) Last question please, the run finishes before the auto shutoff condition is satisfied. I increased the simulation time a lot and I got the same result, does it mean that it is safe to finish before the realization of the auto shutoff condition as long as I get the same result? Thanks,

Thanks

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Best Answer

  • greg_baethgegreg_baethge Posts: 120Ansys Employee
    Accepted Answer

    Hi @amora,

    Thanks for posting your question on this forum. I will try and address them:

    (1) I am trying to run parametric sweeps on different parameters but I got the same error for different parameters. The results weren't saved after the end of the parametric sweep. I have a attached a screenshot of the error. I got this error 4 times for different parameters, usually the problem is with the value before the last value in the range as seen in the photo. How to fix this error and have the result saved?

    The error indicates no results have been defined in the parameter sweep. Typically, you can select a result from a monitor, for example:

    Here, we selected the transmission (T) from the monitor "T600nm".

    (2) Also, I have a question regarding the size of the FDTD region, I read it should be at least λ/2 or more. Is λ the maximum operating wavelength or the central one?

    This will depend on the boundary conditions used in the simulation. With periodic or Bloch boundaries, the width in the direction of periodicity defines the period of the structure. With PML, we usually consider the PML boundaries should be at least half of the maximum wavelength away from the scattering object to avoid the PML affecting the evanescent fields at the surface of the objects.

    (3) Last question please, the run finishes before the auto shutoff condition is satisfied. I increased the simulation time a lot and I got the same result, does it mean that it is safe to finish before the realization of the auto shutoff condition as long as I get the same result? Thanks,

    FDTD is a time domain method, so we use a Fourier transform to get the fields in frequency/wavelength domain from the time domain ones. The auto shutoff monitors the fraction of energy left in the simulation region to make sure the fields have decayed enough by the end of the simulation. We use a threshold value (auto shutoff min, default value set to 1e-5). When the auto shutoff reached this threshold, we stop the simulation as we consider the fields have decayed enough. If the fields haven't decayed enough, the Fourier transform will show some artifact.

    You can check the auto shutoff in the log file of the simulation:

    0.00800595% complete. Max time remaining: 17 secs. Auto Shutoff: 1
    1.36368% complete. Max time remaining: 12 secs. Auto Shutoff: 0.000347292
    2.73003% complete. Max time remaining: 12 secs. Auto Shutoff: 5.7468e-05
    5.46272% complete. Max time remaining: 12 secs. Auto Shutoff: 1.47312e-05
    100% complete. Max time remaining: 0 mins, 0 secs. Auto Shutoff: 8.76773e-06
    Early termination of simulation, the autoshutoff criteria are satisfied.
    

    as well as from the simulation itself as the auto shutoff can be plotted vs simulation time or wall clock time:

    In this example, the simulation ended under 600fs, while the simulation time (maximum time allowed for the fields to propagate) was set to 1000fs.

    If the simulation reached the auto shutoff min, the simulation status will be 2:

    To get back to your question, you need to make sure the auto shutoff min is reached.

    I hope this will help.

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