Discussion ClosedThis discussion was created more than 6 months ago and has been closed. To start a new discussion with a link back to this one,click here.
rectangular input
Posted 2009年7月20日 GMT+2 21:581 Reply
Please login with a confirmed email address before reporting spam
I would like to add a concentration only for a predetermined time, i.e. rectangular input instead of step input. How should I type this in the COMSOL as a expression? Will it take anything like this?
C0*( u(t)-u(t-2))
C0*( u(t)-u(t-2))
1 Reply
Last Post 2009年7月21日 GMT+2 00:25
Please login with a confirmed email address before reporting spam
Posted:
2 decades ago
Hi
why u(t) ? what do you mean by that ?
u for me has a default dimension of [m] in COMSOL, check carefully your dimensions.
But you could use a C0*(t>0.5)*(t<1), this would make a step function between 0.5 and 1.
Now, do not forget that this step function does not have any defined derivative at the discontinuities, so your solver will probably not manage to pass the steps !
The are the Heaviside functions (fldc1hs, flc2hs, flsmhs, flsmsign ...) to make smooter steps with contiuous derivatives, they work mostly better, see the doc .
By the there was another discussion about steps functions about a month ago
Good luck
Ivar
why u(t) ? what do you mean by that ?
u for me has a default dimension of [m] in COMSOL, check carefully your dimensions.
But you could use a C0*(t>0.5)*(t<1), this would make a step function between 0.5 and 1.
Now, do not forget that this step function does not have any defined derivative at the discontinuities, so your solver will probably not manage to pass the steps !
The are the Heaviside functions (fldc1hs, flc2hs, flsmhs, flsmsign ...) to make smooter steps with contiuous derivatives, they work mostly better, see the doc .
By the there was another discussion about steps functions about a month ago
Good luck
Ivar