Discussion Forum

-

Hi

what do you have as time stepping, is it automatic ? or strict, or intermediate ?.

For pluses or periodic shapes you should NOT use automatic as this is tailored for diffusion or asymptotically trend solutions

--
Good luck
Ivar

It looks like you may not have updated your plot after running the simulation with the 1e-10 time steps.

I am having the same problem, and dont know what could possibly be the reason, ive definately redrawn and tried different settings for the 1D plot.

can you attach the model file .. i want to have a try at it ?

Thanks,

and if you could also tell me why my source is oscilating so irregulaly, I would be very greatfull!

Hi

there are several points I can comment:

Trick for the geometry rectangle, in V4 you can add a or several "Layers" and apply it on all boundaries, this reduces the 4 rectangles into a single rectangle call, far less to click and to take care of

Gold, your epslion seems strange, you need at least an "j" or "i" for the imaginary part, then check your sign convention, there are two around COMSOL uses the "-" one

Then check your doc if all these physics solve for sigma = 0, often its better to give al little conduction to air 1S/m or so, and gold is definitively not "0" for sigma

Your time solver, if you check the log file you see that COMSOl solves several steps, then it gets to the time to extract your demanded valaue = "out" then it solves a step again etc, but towards the end it has made a large step and your results out are all interpolations froma few solver steps hence strange behaviour.
You should use a more restricted solver stepping, in the Time Stepping tab of the Transielnt solver node change "free" to intermediate or strickt (Steps taken by the solver:)

And take some tome to read and re-read the doc, its worth it ;)

--
Good luck
Ivar

Hi,
thanks for the hints, the layers trick is handy.
and I clearly screwed up my metal.

now do I understand the time stepping settings correctly in, that if I use the strict it will use strickt discrete timesteps and not as is now the case interpolate between vast time regions?


Ive been (re).reading many tutorials, but most I feel focus on very specific tasks while I am often still trying to figure out where top and bottom is. If you have any specific suggestions they would be welcome:)

kr

Hi

I agree it took me also quite some time to get used to the COMSOL approach, hadnt done physics in this way for several years, but gently the puzzle settles and yo get the full image. But it takes some exercices and hours reading (and rereading, I run through all the new doc at least once per year)

--
Good luck
Ivar

anyway it would appear your tips helped, it seems to be working now, so its very much appreciated :)

I am running a thermomechanical elasto-plastic model with the a focus on residual stress from a transient thermal cycle. I am having a similar "jaggedness" in the spatial domain when extracting stress distributions. The smoothness improves when I increase the number of elements (quadratic) along the line that I'm extracting data from, but even at high density, there is still oscillation in regions of fairly constant values, which is worse in a region of high gradient. I could always make a point graph to hide it, but I'd rather know why it does what it does.

I can't seem to upload a screenshot. Keep getting a "file extension error" message.

Hi

you are probably getting some numerical oscillations. Thee can come from many resons, the plot smoothing functions (try to turn the plot to wireframe and turn off smoothing (main plot node settings). Then as you did increase the mesh density. You could also try increasing the shape function order. But there are also some cases that create singularitie, such as sharp corners, particularly in EM, but also Solid ...

There is also a good chapter in the doc on the numercal oscillations and the dissusion factors used, in certain physics, it's worth to take a look.

In RF one should not forget that you need at least 5-10 mesh elements per wavelength in each material, and do not forget that the index of refraction can be rather high in some materials, hence the wavelength accordingly shorter, hence this requires a denser mesh (its NOT ONLY the wavelength in vacuum that counts ;)

--
Good luck
Ivar

Thanks for the response. I'll look into it.

Hello all,

I am getting sharp peaks instaed of smooth curves .I followed some of your suggestions ,but i coudnt get the desired result.Could you please look into my model.It will be very helpfull for me .Thank you.