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Can I define time step?

Posted Sep 19, 2011, 2:16 a.m. EDT Version 4.1 3 Replies

JiYoung Park
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Hi,

Can I define time step?

For example

0<t<1 : time step = 0.001

1<t<5 : time step = 1

5<t<6 : time step = 0.001

Best regards.
3 Replies Last Post Sep 19, 2011, 9:27 a.m. EDT
Ivar KJELBERG COMSOL Multiphysics(r) fan, retired, former "Senior Expert" at CSEM SA (CH)
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Posted: 1 decade ago Sep 19, 2011, 5:38 a.m. EDT
Hi

check the "definition - function tab" and fiddle a little with the formulas, it shoudl work out nicely

--
Good luck
Ivar
Hi check the "definition - function tab" and fiddle a little with the formulas, it shoudl work out nicely -- Good luck Ivar
JiYoung Park
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Posted: 1 decade ago Sep 19, 2011, 6:55 a.m. EDT
Dear, Ivar

I defined the analytic function in definition for "ttt"

0.001*(0<t<1)+1*(1<t<5)+0.001*(5<t<6)



0<t<1 : time step = 0.001

1<t<5 : time step = 1

5<t<6 : time step = 0.001

and then typed ttt in generalized alpha transient solver manual time step field.

But i got expression error message.

Can you help?

Best regards, Ji young park
Dear, Ivar I defined the analytic function in definition for "ttt" 0.001*(0
Ivar KJELBERG COMSOL Multiphysics(r) fan, retired, former "Senior Expert" at CSEM SA (CH)
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Posted: 1 decade ago Sep 19, 2011, 9:27 a.m. EDT
Hi

you can also use "t" and not "ttt" if I understand you right

I would rather write the operator as

f(t) = 0.001+(1-0.001)*(0<t)*(t<5)

you have fewer tests, or with an if(,,) (see the doc)

and then when you call "f(t)" you write "f(t[1/s])" to get a unitless "t" value expressed in seconds (or whatever unit you prefere.

I'm not fully sure the "0<t<1" double boolean is correctly parsed in COMSOL ?

--
Good luck
Ivar
Hi you can also use "t" and not "ttt" if I understand you right I would rather write the operator as f(t) = 0.001+(1-0.001)*(0

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