{"id":230896,"date":"2022-08-10T17:10:09","date_gmt":"2022-08-10T17:10:09","guid":{"rendered":"\/forum\/forums\/topic\/fdtd-consistently-diverging\/"},"modified":"2023-07-17T17:59:15","modified_gmt":"2023-07-17T17:59:15","slug":"fdtd-consistently-diverging","status":"closed","type":"topic","link":"https:\/\/innovationspace.ansys.com\/forum\/forums\/topic\/fdtd-consistently-diverging\/","title":{"rendered":"FDTD Consistently Diverging"},"content":{"rendered":"

Hi,<\/p>\n

I am simulating a periodic structure with a unit cell consisting of a single dielectric resonator and a single substrate. The excitation source is a normal incident plane wave. I would like the simulation to reach autoshutoff level = 1e-7, but each time it reaches to around 1e-6, it will suddenly start to diverge (this usually takes around 30,000 to 35,000 fs).<\/p>\n

I have tried many different things to resolve this problem. I have decreased dt stability to 0.5, I have changed the meshing several times to adjust the aspect ratio, I have changed the number of PML layers; the simulation continues to diverge. I am using a single value of n and k for all wavelengths, for all materials in the simulation, so material fit shouldn’t be the cause of the instability (as far as I know).<\/p>\n

My override mesh around my dielectric resonator is 5nm in x,y and z. I am using custom non-uniform global mesh, with maximum mesh cell size of 50nm for x,y and z. Grading is allowed in x,y and z. The PML behind my plane wave source is just over 1 wavelength away from it (in the normal direction i.e. z), and the top of my resonator is at least 2 wavelengths away from the closest PML layer. I’m using 24 layers of normal PML. k is set to 0 for all materials, which is reasonable given their properties at this wavelength. dt stability = 0.5. Periodic boundary condition with symmetric\/anti-symmetric BC applied as appropriate.<\/p>\n

I’m not sure what else to try. I need my simulation to reach at least 1e-7 (preferably lower) in order to get publication-quality transmission spectra. Please let me know if you need more information about my simulation in order to help diagnose the cause of the divergence.<\/p>\n

Thank you in advance.<\/p>\n","protected":false},"template":"","class_list":["post-230896","topic","type-topic","status-closed","hentry","topic-tag-divergence","topic-tag-divergence-issues","topic-tag-fdtd","topic-tag-LumericalFDTD-1","topic-tag-photonics"],"aioseo_notices":[],"aioseo_head":"\n\t\t\n\t\n\t\n\t\n\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t