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how to define ramp force

nagamalleswara rao alluri

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hai all,


i want, how to define ramp force with in a fixed time(means with in 6 seconds).

if any one knows please help me, it's very helpful to my project.







Nagamalli


4 Replies Last Post 11.04.2010, 12:57 GMT-4
Ivar KJELBERG COMSOL Multiphysics(r) fan, retired, former "Senior Expert" at CSEM SA (CH)

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Posted: 1 decade ago 07.04.2010, 13:09 GMT-4
Hi

if you define a boandyry load such as Fx=DF*t then you have a ramping force, with scale "DF[N/s]", if you want it to stop after 6 seconds a Fx=DF*t*(t<=6) will do, but then you have some nice spikes that might give you some solver convergence issues, to be tested out, try to set a small time intervalle around the abrupt stop.

Better you can smoothen with a heaviside function search the doc for "flc1h" or a combination of cos or sin functions (to ensure a couple of continuous derivatives), this often helps for the solver convergence

Have fun Comsoling
Ivar
Hi if you define a boandyry load such as Fx=DF*t then you have a ramping force, with scale "DF[N/s]", if you want it to stop after 6 seconds a Fx=DF*t*(t

nagamalleswara rao alluri

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Posted: 1 decade ago 08.04.2010, 13:35 GMT-4


Thanks for the response Ivar

Actually i am applying ramp force 1MN to 30MN with in 6 seconds.

is it possible to give the force with this function Fx=DF*t*(t<=6)

what i am saying is what is the meaning of DF*t* , i couldn't understand.

if possible, could explain clearly.........t is time

and DF means is it a function(like F=ma)?





Nagamalli
Thanks for the response Ivar Actually i am applying ramp force 1MN to 30MN with in 6 seconds. is it possible to give the force with this function Fx=DF*t*(t

Ivar KJELBERG COMSOL Multiphysics(r) fan, retired, former "Senior Expert" at CSEM SA (CH)

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Posted: 1 decade ago 09.04.2010, 01:23 GMT-4
Hi

Wellif I understand you correctyl youre force expression is something like

F[MN] = 1[MN]+(30-1)[MN]/(6[s])*t

with this formula you must stp your simulation after 6 seconds, because your force will continue to ramp.

Make a "function" out of this an use the plot functionality to check its shape and values.

If your simulation is to last > 6 sec, but you want to saturate at 30[MN] I would write:

F[MN] = 1[MN]+(30-1)[MN]*min(t/6,1)

does this help ?

HAve fun Comsoling
Ivar
Hi Wellif I understand you correctyl youre force expression is something like F[MN] = 1[MN]+(30-1)[MN]/(6[s])*t with this formula you must stp your simulation after 6 seconds, because your force will continue to ramp. Make a "function" out of this an use the plot functionality to check its shape and values. If your simulation is to last > 6 sec, but you want to saturate at 30[MN] I would write: F[MN] = 1[MN]+(30-1)[MN]*min(t/6,1) does this help ? HAve fun Comsoling Ivar

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Posted: 1 decade ago 11.04.2010, 12:57 GMT-4

Thanks Ivar.

this should be useful my project.





Nagamalli
Thanks Ivar. this should be useful my project. Nagamalli

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