Discussion Forum

Hi

I do not really understand what you are missing, if you have a boundary heat flux condition and you write
P0[W/m^2]*sin(omega[1/s]*t) with a time dependent solver and omega some frequency value then you should see your system being influenced by the sinus excitation.

But do not forget that a time series solver is a transient type analysis, normally for a few periods, if you are interested in the steady state sinus exciatiaion response you should rather consider the frequency domain solvers (harmonic developments of the equations, see the Equation view

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Good luck
Ivar

Thank you Mr. Ivar

Actually I understand that the problem was with unit. I have considered omega a constant and comsol understand time,t in sec. But inside Sin function t should be [1/s], and that solves problem. Now it is working fine.

Kind Regards

Arka

Hi

It's always useful to check the units, as "t" is in seconds you can either write omega[1]*t[1/s] or omega[1/s]*t to get a unitless call for sinus(), but do not forget an orange unit "error" is a warning, COMSOl calculate anyhow, while red is an error and COMSOL will flag it and halt

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Good luck
Ivar

Hello Sir,

I have another query. Regarding the temperature profile? Since I am irradiating the boundary using a sin wave. So, I am assuming that the temperature profile at the irradiated boundary should behave a similar nature like a wave. But I am getting temperature curve at a point on the boundary straight lines. It is not following a sin nature. I am using time step of 0.1 for time marching procedure. But I think the temperature profile is not taking all the time steps it is skipping certain points. It is showing irregular straight lines like it has skipped few points. I am not sure what is the problem.

Thanking You

Arka

Hi

indeed it looks like the time stepping is being too coarse, the thing is that by default COMSOL assumes a diffusion type model decay, so when you have a periodic BC you must tweak a little the time stepping settings.

Use rather an intermediate or a strict time stepping (and not the default automatic for periodic BC conditions) then be sure you define enough time steps per periode, 5 as absolute mnimum 10 or more is better (it all depends on the time you ant to wait for the solution ...

Thne you can also consider a gen-alpha, in case of converging issues

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Good luck
Ivar

Dear Arka;
I have the same problem as you. I want to define a SIN Temperature for the comsol but i can not define it very well. Would you please help me and tell me that how did you define a Time dependant heat for the software?

Best Regards

Hi,

I have a similar problem. I have to set my convective heat flux depending how much time as passed.
For example;
Time (s) 0-500 set h=10
Time 501-1000 set h=20
Time 1001-1500 set h=35
Time 1501-2000 set h=15

How do I covert this into a IF statement to insert into the "Convective heat flux" field ?

Thanks,

Hi

Make a piecewise function, say pw1, and call it then pw1(t). See attachment.

Lasse

Thank you,
I have done the piecewise function, but how are you plotting that graph with h as a function of t?
When I plot the graph I don't get any labels at all.

Thank you,

Hi

Make a piecewise function, say pw1, and call it then pw1(t). See attachment.

Lasse

The function set-up window (my attachment) asks for the units of the argument and the function. You must fill in them properly.

Ok, I got it now, thanks for all the help.